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Application of sand-well load immersion test to deep loess collapsibility evaluation
PAN Dengli, HU Xiangyang, ZHAO Cheng, YAN Gengsheng, SHAO Shengjun
 doi: 10.16030/j.cnki.issn.1000-3665.202206006
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Because of the inaccuracy of laboratory test results of self-weight collapsibility of deep collapsible loess and the lack of in-situ test methods for testing loess foundation collapsibility, a new field test method, the sand-well load immersion test method, is proposed based on the existing sand-well immersion test. The core is that after the loess under the sand well has settled stably under the action of test pressure, the collapsible loess under the bottom of the sand well and around the sand well can be quickly saturated due to the strong permeability of sand and gravel in the well, therefore the collapsibility of the loess under the bottom of the sand well and the self-weight collapsibility of the loess around the sand well can be measured. Through two sets of sand-well load immersion tests, the collapsible deformation of different depth strata under different pressure and immersion conditions is tested, and the sand-well load immersion test and the large test pit immersion test adjacent to the site are compared and analyzed. The results show that the judgment results of the sand-well load immersion test are consistent with the test pit immersion test, indicating that the sand-well load immersion test is feasible. In addition, the sand-well load immersion test has the advantages of short cycle, low cost, low site condition requirements, small water consumption, etc. The sand-well load immersion test is suitable for the study of collapsibility of deep loess. The results are of a certain reference significance for the collapsibility evaluation of loess engineering in the loess area (especially deep loess).
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A study of the resonance characteristics of a staggered rock slope under the tri-dimension earthquake wave
LIN Juncen, YAN Songhong, SUN Weiyu, OU Erfeng
 doi: 10.16030/j.cnki.issn.1000-3665.202206038
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The resonance induced by an earthquake often causes more serious damage to the slope and directly affects its seismic performance. To study the resonance characteristics of a staggered rock slope, a 3D numerical model of the slope is established by using the finite element software ANSYS, and the effect of staggered space on the natural frequency of the slope is analyzed. The resonance response laws of different locations on the slope surface and the effect of the earthquake frequency on the stress of the slope are discussed by the harmonic response analysis. The results show that (1) the larger the slope slip distance is, the smaller the fundamental frequency is, and the resonance phenomena may occur under different staggered distances. The horizontal resonance displacement of the slope surface is larger than the vertical one. The front slope has a larger peak displacement and lower resonant frequency compared with those of the back slope. (2) Both the low and high-order natural frequencies can be excited to cause resonance, but the displacement of the high-order resonance is relatively small. The horizontal displacement peak of the front slope and back slope is in the order: top > middle > foot, while that of the side slope is in the order: middle > top > foot. Under high-frequency loading, the dynamic response of the slope at the lower part may be greater than that at the upper part. (3) The shear failure of the slope toe is the main damage in slope resonance. The location of the maximum shear and tensile stress is related to the range of loading frequency. The front slope is more prone to damage. Ground motions with low frequency have a greater influence on the front slope, while high frequency ground motions have the opposite effect. The results can be used as reference to determine the key reinforcement position of a staggered slope in the seismic fortification.
A study of the critical groundwater level related to soil consolidation characteristics of land subsidence in Cangzhou
WANG Yunlong, CHEN Ye, GUO Haipeng, MENG Jing, WANG Haigang, ZANG Xisheng, ZHU Juyan
 doi: 10.16030/j.cnki.issn.1000-3665.202208040
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Land subsidence has become a serious issue in Cangzhou for a long time. In order to make reasonable use of groundwater resources, it is necessary to establish a warning groundwater level under the premise of controlling the development of land subsidence. How to quantitatively determine the critical gorundwater level (CWL) for comprehensive control of land subsidence? In allusion to this scientific problem, this paper takes the soil samples of three typical settlement areas in Cangzhou as the research object, and analyzes the formation consolidation characteristics. By correlating the stratum thickness, we improve the method of calculating the CWL with the previous consolidation pressure. Based on the monitoring data of land subsidence and groundwater level in Cangzhou for many years, the comprehensive quantitative evaluation of the CWL in Cangzhou are carried out. The results are show that the soil within a depth ranging from 0 to 150 m in Cangzhou is normally consolidated or under-consolidated, and the soil below the depth of 150 m is generally over-consolidated. The inelastic water release deformation is an important factor affecting the change of land subsidence rate in this area. Using the improved method, the CWL in Cangzhou, Suning and Dongguang is 66.8 m, 67.2 m and 67.8 m, respectively. Based on the data of the cumulative land subsidence and groundwater level change in the urban of Cangzhou, we obtain the exponential function relationship between the cumulative land subsidence and groundwater level. The subsidence rate is taken as the index, and the critical groundwater level in Cangzhou ranges from 65 to 70 m. On the basis of verifying the consistency of the calculation results of the two methods, we determined 65 m as the critical groundwater level for the prevention and control measures of land subsidence in Cangzhou. The results provide a reliable basis for the local government to formulate a reasonable groundwater exploitation plan.
Stochastic modeling of in-situ sandstone-type uranium leaching in response to uncertain and heterogeneous hydraulic conductivity
CHEN Mengdi, JIANG Zhenjiao, HUO Chenchen
 doi: 10.16030/j.cnki.issn.1000-3665.202112039
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Hydraulic conductivity in sandstone-type uranium-bearing formations is of high heterogeneity. However, restricted by the means of test and analysis, it is difficult to accurately describe the heterogeneous coefficient of permeability, which results in the deviation in the prediction of in-situ leaching uranium mining process and limits the fine control of in-situ leaching uranium mining process. To solve this problem, a random characterization method of heterogeneous parameter distribution of an ore bed is proposed in this paper. On this basis, water salt coupling numerical random simulation is carried out to reveal the internal migration process and influence range of leaching agent reservoir caused by pumping and injection of multiple wells under the conditions of different spatial distribution of coefficient of permeability. The application results in a uranium deposit in Inner Mongolia show that the coefficient of permeability increases along the direction of regional groundwater flow, which is conducive to the evacuation of the injected leaching agent. On the contrary, the leaching agent is prone to the aggregation effect. After identifying and verifying the boundary conditions of the model with groundwater level monitoring data, the diffusion rate of the solution is 210 m2/d under the assumption of homogeneity, and the diffusion area of the 20-year mining cycle is 1.53 km2. Considering the heterogeneity of the ore bed and the uncertainty of parameters, the expansion rate of the leaching agent area is predicted to be 191−228 m2/d, and the diffusion area of the leaching agent is 1.47−1.74 km2. Compared with the assumption of homogenization, the uncertainty of the diffusion rate and diffusion area of the leaching agent is 17.62% and 17.65%. Considering the heterogeneity and uncertainty of coefficient of permeability, the prediction results of leaching agent migration and transformation behavior are more representative, which provides a more reliable reference for the design of in-situ leaching uranium mining scheme and the development of sandstone type uranium resources.
Identification and time series monitoring of hidden dangers of geological hazards in the typical loess hilly regions
YIN Yuling, XU Suning, WANG Jun, HU Ke
 doi: 10.16030/j.cnki.issn.1000-3665.202211004
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The geomorphology of southern Ningxia is dominated by loess hills, with gullies and well-developed small landslides in the area, making surface deformation monitoring difficult. To explore the identification method of geological hazards in this typical geomorphological area, Jingyuan district in the city of Guyuan in Ningxia is taken as the study area, and the SBAS-InSAR technology is applied to process a total of 11 periods of ascending L-band ALOS-2 data collected from July 2016 to May 2021 to obtain the deformation rate results of the Jingyuan district. Combined with high-resolution optical images, a comprehensive analysis is carried out according to factors such as the deformation rate, deformation scale, slope, and disaster-bearing body. A total of 27 suspected hidden dangers are identified. After field verification, 22 of them show obvious signs of deformation and have clear hazard-bearing bodies. The time-series deformation analysis of the typical hidden danger points shows that these areas have continuous and significant surface deformation during the monitoring period, and the maximum subsidence rate reaches 91.5286 mm/a. The results show that the combined L-band SAR and high-definition optical image data and the application of the integrated remote sensing identification method are highly accurate and are of high applicability in the area. The results in this study can provide a method reference for comprehensive remote sensing identification of landslide hazards in loess hilly areas.
Experimental research on the injectable xanthan gum gel intercepting barrier of simulated Cr(VI) contaminated aquifer
ZHANG Li, ZHAO Yongsheng
 doi: 10.16030/j.cnki.issn.1000-3665.202112043
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Due to the unreasonable discharge of industrial waste, a large amount of heavy metal pollutant Cr(VI) enters the underground environment, which seriously threatens human health and ecological environment. The high mobility of Cr(VI) in groundwater environment makes it difficult to repair. A green, economic and effective interception method is urgently needed to improve the ability of groundwater Cr(VI) pollution control. In this paper, sodium metabisulfite is selected as a reducing agent, and Cr3+ generated from Cr(VI) in groundwater is used as an xanthan gum crosslinking agent to form a gel blocking barrier. The influences of various components on gel time and viscosity changes and the blocking effect of gel barrier on aquifer are studied. The results indicate that (1) in the system with Cr(VI) concentration up to 200 mg/L, xanthan gum solution with 0.4% mass concentration can form gel with certain mechanical strength within 1.5 h. (2) The gel has salt resistance and is suitable for common aquifers. Na+ and K+ of 2.5−5 g/L can promote the gel. (3) The injected gel blocking barrier can significantly reduce the coefficient of permeability of medium sand media to 1×10−7 cm/s, which can meet the demand of groundwater blocking. Injection-type gel barriers are formed without the introduction of harmful substances. After the interception, injection-type gel barriers can be naturally degraded by biological action without long-term changes under the aquifer hydraulic conditions. This study provides a theoretical basis for the construction of gel barrier in chromium contaminated groundwater.
Spatial variability of free porosity in the groundwater level fluctuation zone in the Baoding Plain area
XU Buyun, YANG Huifeng, BAI Hua, SONG Bo, MENG Ruifang
 doi: 10.16030/j.cnki.issn.1000-3665.202208004
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Scientific determination of geological parameters of the groundwater level fluctuation zone is an important step for water resources evaluation and management. In the past 40 years, over-exploitation of groundwater in the Baoding Plain led to a serious deficit of aquifers, thus forming a huge deep vadose zone. After the South-to-North Water Diversion Project was put into operation, with the progress of ecological water supplement of rivers and lakes and groundwater limited-over-exploitation, the groundwater levels in some areas of the Baoding Plain stopped falling and rose. The quantitative relationship between the amount of water supplement and the change of groundwater levels has become an important scientific issue in the management of over-exploitation of groundwater. However, under the condition of groundwater level recovery, the calculation results will be deviated if the specific yield parameter of water release process is still used. Therefore, the free porosity parameter study of groundwater level recovery process is the key to solve this problem. Based on 67 engineering geological boreholes in the Baoding Plain, the comprehensive free porosity during groundwater level recovery is determined according to the lithologic characteristic parameters of the groundwater level fluctuation zone. The semi-variogram model is selected by the trend analysis and cross validation, and the spatial unknown points are interpolated by the Ordinary Kriging interpolation. The results show that (1) the best semi-variogram model of the comprehensive free porosity in the groundwater level fluctuation zone of the Baoding Plain is the 1 order index model. The spatial autocorrelation of the data is obvious, which is mainly affected by structural factors such as spatial location of the groundwater level fluctuation zone and stratigraphic type. (2) The comprehensive free porosity distribution shows that the southwest and northwest are the high value areas, and the extreme value can reach 0.245. The parameter gradually decreases to the central and eastern regions, and the minimum value is 0.02. (3) Compared with the value of the conventional specific yield, the value of the free porosity increases by about 0.03 in the north and south regions, which is about 1.2 times that of the conventional specific yield. In the central region, it is reduced by about 0.06, which is about half that of the conventional specific yield value. The research results are of important research value and great significance for ecological water supplement and water resources regulation in the benefited regions of the South-to-North Water Diversion Project.
Emergency rapid assessment of landslides induced by the Luding Ms 6.8 earthquake in Sichuan of China
LIU Jiamei, WANG Tao, DU Jianjun, CHEN Kun, HUANG Jianhang, WANG Haojie, RUAN Quanquan, FENG Fei
 doi: 10.16030/j.cnki.issn.1000-3665.202209057
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Seismic landslides can seriously aggravate the losses of earthquake disasters. Therefore, it is of great significance to assessment the distribution of earthquake induced landslides for emergency relief. In this paper, based on the 30 m resolution DEM and regional geologic data with a scale of 1:500,000, emergency rapid assessment of earthquake induced landslides is carried out using the Newmark cumulative displacement model. The results show that the earthquake induced landslides are relatively serious in this earthquake. The high hazard zones of the coseismic landslides are about 45 km2, which is mainly distributed on the two banks of the nearly east-west tributaries on the west bank of the Dadu River and the west of the Xianshui River fault, especially along the Yanzigou, Mozigou, Hailuogou, Feishuigou and Dagou gullies and the Shiyue and Tianwan Rivers, posing a great threat to the lives of residents and tourists. The rivers and Roads in these tributaries are at high risk of being blocked by landslides. The Lengqi, Xinglong, Moxi and Detuo Towns in Luding County and Tianwan, Caoke, Xinmin, Xianfengn, Xiluo and Caojiao Towns in Shimian County are at high risk of landslides. The Provincial Roads S434 and S211 along the Dadu River near the epicenter are more likely to be blocked by landslides. The predicted earthquake landslide hazrad in the Gongga Snow Mountain area is medium, but it is necessary to pay attention to risks of long range and high position landslide disaster (chain), such as ice avalanche and rock avalanche. Comparison between the distribution of induced landslides in zones with intensity VIII and IX obtained from post-earthquake emergency investigation and remote sensing interpretation shows that the obtained displacements can well reflect the macro distribution of coseismic landslide along the tributaries on the west bank of the Dadu River, but cannot be exerted effectively around the edge of the Moxi platform and the banks of the Dadu River, which can be enhanced through the improvement of large scale of geologic maps and high quality topography data. The results can provide reference for valuable timely reference information on post-earthquake reconstruction planning and long-time activity of post-earthquake geohazard and risk recognition of landslide disaster chains.
Analytical solution of formation temperature distribution under dynamic heat load of borehole heat exchangers
LI Jiashu, DAI Chuanshan, LEI Haiyan, MA Fei
 doi: 10.16030/j.cnki.issn.1000-3665.202205040
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The borehole heat exchanger (BHE) is a key component using shallow geothermal energy in ground source heat pump systems (GSHPS), and reasonable pipe spacing design has a great impact on the heat transfer performance and economy of the GSHPs. In most of real applications, the thermal disturbance radius of the maximum heat load per unit length (that is, the most unfavorable case) is often used as the design basis, and this makes it difficult to achieve the technical and economic optimization of the ground source heat pump system. This paper proposes a simple but more practical mathematical method to obtain the thermal disturbance radius of the borehole heat exchanger. The method first derives an analytical solution of the formation temperature distribution around the borehole under the boundary condition of periodic heat flow. On this basis, the actual dynamic building heating and cooling load is approximately expanded into a finite of sine and cosine periodic functions with the Fourier series. By superimposing the analytical solution corresponding to each periodic function obtained by Fourier series expansion of the original dynamic load, the variation of formation temperature distribution under the actual dynamic heating and cooling load conditions can be obtained.
A study of bearing capacity of the Jurassic moderately-weathered mudstone foundation
CHEN Jibin, LI Xuemei
 doi: 10.16030/j.cnki.issn.1000-3665.202207002
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The Jurassic moderately-weathered mudstone in the Chengdu area is a typical red bed soft rock. Engineering practice shows that the standard recommended value of bearing capacity of the Jurassic moderately-weathered mudstone foundation in the Chengdu area is low, which leads to conservative foundation selection of high-rise and super high-rise buildings in this area, resulting in large project cost and long target construction period. However, there is no method to maximize the bearing capacity of the Jurassic moderately-weathered mudstone foundation. In this study, the foundation project of a super high-rise building in Chengdu is taken as an example, and 9 groups of deep well adit rock foundation load tests and 17 hole rock foundation side pressure tests are carried out, respectively, for the Jurassic moderately-weathered mudstone foundation to analyze the bearing capacity of the mudstone foundation and the appropriate value of bearing capacity characteristic. The correlation equation between the characteristic value of foundation bearing capacity and the characteristic parameters of rock mass obtained by ultrasonic logging test is established. The research results show that in the Jurassic moderately-weathered mudstone area, the characteristic value (fak) of the foundation bearing capacity obtained from the plate load test and the side pressure test of the rock foundation are similar and are 2−2.5 times larger than the maximum value recommended by the regional code DB51/T5026-2001. The diameter of the bearing plate of the plate load test and the test depth of the side pressure test have no significant impact on the bearing capacity of the moderately-weathered mudstone foundation. Comprehensive analyses of parameters indicate that fak has power and exponential increasing relationship with wave velocity of rock mass and integrity index of rock mass, respectively. The research results are of important reference value for the bearing capacity of the Jurassic moderately-weathered mudstone foundation.
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Visualization experimental investigation into the dissolution processes in rough fracture under gravity conditions
ZHANG Ziyi, HU Ran, LIAO Zhen, CHEN Yifeng
 doi: 10.16030/j.cnki.issn.1000-3665.202204044
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Dissolution of rock fractures is common in natural processes and engineering practices, in which gravity plays an important role. Visual observation technology is a key means to study the mechanism of dissolution in rough fractures. However, the traditional visualization technologies have some problems, such as difficult to reproduce the rough wall of fractures and difficult to observe the dissolution process in real time. In this work, a flow-visualization system for dissolution processes in rough fractures is developed, on which flow-through experiments are conducted on four flow rates (0.05, 0.1, 0.3, and 1 mL/min) for vertical and horizontal fractures, and the gravity effect is evaluated on dissolution patterns and dissolution morphologies, which are characterized by fractal dimension and other morphological parameters. The pore volumes at Breakthrough (PVBT) are calculated for each Pe number. The experimental results show that the gravity effect significantly influences the dissolution patterns for the Peclet number Pe≤62.1. The dissolution morphologies exhibit buoyancy-dominated patterns and channeling patterns for vertical fractures, and the gravity effect will induce a single and concentrated channel. For horizontal fractures, the dissolution forms dissolution channels with relatively uniform aperture evolution and large width, which are classical wormhole patterns. When the Peclet number is large (Pe=207), dissolution in both the vertical and horizontal fractures develops into uniform dissolution. The experimental results also confirm that the dissolution in vertical fractures is more likely to develop channels through the inlet to the outlet to accelerate the breakthrough; Pe=20.7 is the optimal injection condition, which means that the amount of injected liquid is the minimum when breakthrough takes place in vertical fractures. Under this condition, the pore volumes at breakthrough (PVBT) in vertical fractures are only 1/4 of the horizontal fractures. The results in this paper are of great significance to engineering practice such as CO2 geological storage, indicating that the effect of gravity on the dissolution process should be greatly taken into account.
Research on the scale effects of solute transport in a bended karst conduit
ZHAO Xiaoer, WANG Zhengyi, WU Guizhi, LI Qi
 doi: 10.16030/j.cnki.issn.1000-3665.202203050
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Research on the scale effect of solute transport in karst conduits is very important for the correct interpretation of breakthrough curves (BTCs), but the scale effect of solute transport in a bended conduit has not been examined. In this paper, a karst conduit and a pool developed within the conduit are generalized into the transparent hose and cubic pool, respectively. Based on the previously established pool-pipe system, the bended pipes with different lengths are arranged downstream of the pool, and the tracer experiments are conducted to study the effect of the transport scale on the BTCs in conduits. We use the transient storage model to simulate the experimental curves. The results show that with the increasing pipe length downstream the pool, the peak concentration gradually decreases slowly, the rising slope of the BTCs does not change significantly, and the BTC tails gradually shorten, indicating that the longer transport distance exerts a larger effect on solute transport than the conduit bend. The CSK, tre and td are well negatively correlated with the length of the pipe system (R2>0.96). When the length of the pipe system with the symmetrical or asymmetrical pool increases to 154.5 m and 164.3 m, respectively, the CSK is close to zero, and the BTC is nearly symmetrical. The D, As and α have a good negative correlation with the length of the pipe system. When the length of the pipe system with the symmetrical or asymmetrical pool increases to 159.9 m and 178.1 m, respectively, the As is close to zero. Then, the solute retention caused by the pool basically disappears. The results have certain indications for the interpretation of the BTCs in field karst conduits.
Redistribution of hydrogen and oxygen isotopes in groundwater flow systems: from altitude effect to depth effect
HAN Pengfei, WANG Xusheng, JIANG Xiaowei, WAN Li
 doi: 10.16030/j.cnki.issn.1000-3665.202211053
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The hydrogen and oxygen isotopes in precipitation have the altitude effect, and they participate in the groundwater circulation after the infiltration of precipitation. How does the altitude effect of hydrogen and oxygen isotopes in precipitation transform to the depth effect of hydrogen and oxygen isotopes in groundwater under the influence of groundwater flow systems? The existing research lacks quantification for this problem. In this study, the steady-state groundwater flow theoretical models represented by unidirectional inclined basin and bimodal wavy basin are constructed. The MODFLOW and MT3DMS programs are used to simulate the two-dimensional groundwater flow field in the profile and the convection-dispersion process of heavy isotope molecules to obtain the spatial distribution of D and 18O values in groundwater and discuss the mechanism of altitude effect of the hydrogen and oxygen isotopes transforming to depth effect in the groundwater flow systems. The results indicate that in the monoclinal basin, the altitude effect of D and 18O content in precipitation in the recharge area is transformed to the depth effect of δD and δ18O values in groundwater through the regional groundwater flow system which exponentially decreases with the increasing water table depth in the drainage area. In the bimodal wavy basin, when the permeability of the aquifer is relatively larger than the infiltration intensity (K0/w=1000), only one regional groundwater flow system develops, and the distribution of δD and δ18O presents a S-shaped curve with the increasing water table depth in the discharge area of regional groundwater. When the permeability of the aquifer is relatively smaller than the infiltration intensity (K0/w=250), multiple local groundwater flow systems develop in the bimodal wavy basin. The δD and δ18O indicate an S-shaped curve with the increasing water table depth in the discharge area of regional groundwater, while in the discharge area of local groundwater, they show a monotonic attenuation trend with the increasing water table depth. This study theoretically advances the understanding of the influence mechanism of groundwater flow systems on solute transport, and reveals the indicative role of hydrogen and oxygen isotopes in groundwater flow systems.
A study of the multi-tiered risk assessment method of site groundwater contamination considering transport-induced risk
ZHANG Xingzhou, YIN Leyi, CHEN Jian, ZHOU Xiaoxiao, YANG Lihu, WU Jichun, XIE Yueqing
 doi: 10.16030/j.cnki.issn.1000-3665.202209006
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Contaminants in groundwater can spread downstream, causing risks to receptors along the path. The risk assessment of our current site groundwater contamination focuses mainly on human health risks. It rarely considers integrated risks of groundwater contamination, particularly neglecting risks to recepters at downstream locations. This study constructs a new index system and a tiered risk assessment approach for site groundwater contamination based on the “source-pathway-receptor” model considering risks to downstream receptors. For the construction of the index system, the source, pathway and receptor of site groundwater contamination are considered. For the risk assessment approach, a multi-tiered risk assessment are determined according to site groundwater contamination status. Based on the hypothetical case study of a chromium-contaminated site, four scenarios of groundwater contamination states are set. The spatio-temporal changes of groundwater contamination plumes are calculated by using the Wexler solute transport model, and risk assessment is carried out for different states of the groundwater contamination. The results show that in the two cases where the site groundwater contamination plumes have not reached the site boundary, the risk scores of the site groundwater are 4 and 6.4 points, respectively. The risk of the site groundwater at the two contamination states is low and medium, respectively. In the two cases where the site groundwater contamination plumes have arrived or exceeded the site boundary, the risk scores of the site groundwater are 7.0 and 8.8 points, respectively. The corresponding risk at the two contamination states is medium and high, respectively. It can be seen that this new method can comprehensively assess the potential level of harm of groundwater contamination to both human health and ecological environment, and therefore can provide technical support for the management of contaminated sites.
A study of the increase in subsurface freshwater on coral islands by slope seepage control: experiment and modeling
LI Yinghao, HAN Dongmei, CAO Tianzheng, SONG Xianfang, CAI Dizhu
 doi: 10.16030/j.cnki.issn.1000-3665.202204006
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Fresh groundwater lenses are important resources for local inhabitants and ecosystems in coral islands. In view of the complexity of the coral islands, it is necessary to seek the measures of low-cost, effective and less impact on the stability and the ecosystem to increase freshwater reserves. Based on the sandbox experiments and numerical simulation, this study proposes an engineering measure to increase freshwater reserves by laying impermeable materials on the slope of an island. The effects of the measure on fresh groundwater lenses formation and different factors on increasing freshwater reserves in slope seepage prevention are evaluated. The practical feasibility of this measure is also discussed in case of the Yongxing Island. The results show that the slope seepage control increases the freshwater reserves by changing the groundwater flow field to increase the freshwater head, and then the stabilization time of the freshwater lens is also increased. After laying impermeable materials on slope of the sandbox (with the length, width and height of 50 cm, 5 cm and 35 cm, respectively), the maximum thickness of freshwater lens increases from 13.7 cm to 24.9 cm, the freshwater reserves increases from 561.8 cm3 to 1592.3 cm3, and stabilization time increases from 120 min to 150 min, respectively. The increased freshwater reserves develop with the increasing rainfall intensity and slope impermeable depth, and also extend with the decreasing permeability of coral sand and impermeable materials. The Yongxing Island is taken as an example, and laying impermeable materials with a depth of 2 m on the slope will increase the freshwater reserves from 3.4×106 m3 to 4.4×106 m3 in the next 30 years, increasing the original reserve by 1/4. This study can provide theoretical support and practical guidance for sustainable groundwater management and water resources security in island areas of China.
An experimental study of the stress-strain relationship of different excavation paths for soft soil K0 consolidation
RUAN Yongfen, PAN Jiqiang, QIAO Wenjian, YAN Ming, GUO Yuhang
 doi: 10.16030/j.cnki.issn.1000-3665.202206007
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In the process of foundation pit excavation, the soil mass in different parts shows dynamic destruction characteristics due to diverse unloading mechanics. In order to study the complex unloading stress path in the foundation excavation, the TSZ-1S stress control triaxial compression apparatus is used to carry out the loading and unloading tests of the lacustrine sedimentary peat soil under the conditions of consolidation undrained and K0 consolidation, respectively, and the test scheme is formulated according to different unloading conditions such as lateral, axial and axial lateral meantime unloading, so as to simulate the stress-strain curves of soil under different unloading paths in the foundation excavation, and the variation laws of strength and initial tangent modulus under unloading shear failure. The test results show that the stress-strain characteristics of soil are closely related to the stress path, and the stress-strain curves under each path are approximately hyperbolic. The strength of unloading shear failure is significantly lower than that of loading failure. The study of initial tangent modulus Ei under different unloading paths shows that Ei is greatly affected by lateral unloading, Ei increases after unloading, and axial unloading has little effect on it. The stress-strain curves are normalized, and the normalization equation of peat soil considering different normalization factors is constructed. Based on this equation, the peat soil under different stress paths is normalized, and the results are verified. The results of this work can provide reference for the study of deformation parameters and constitutive relations of foundation pits on peat soil sites under different unloading paths.
Study on the spatial vriability of hydraulic conductivity of underground reservoir in Fuping section of Shichuan River
WANG Jiling, ZHOU Weibo, SUN Lili, WANG Yimeng
 doi: 10.16030/j.cnki.issn.1000-3665.202206021
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The study on the spatial variability of hydraulic conductivity is the basis for artificial recharge of groundwater reservoir. In order to study the spatial variability of the hydraulic conductivity of underground reservoirs in Fuping section of Shichuan River, Box-Cox transform and Johnson transform were introduced to preprocess the field double-loop percolation test and exploration hole data. Traditional statistical methods and geostatistical methods were applied to analyze the hydraulic conductivity of the reservoir area with the variation function as a tool. The results show that the hydraulic conductivity of the reservoir area varies from 0.02 m/d to 6.44 m/d and obeys both logarithmic normal distribution and Box-Cox transformation normal distribution, the spatial correlation of the hydraulic conductivity is medium, and the best fitting model is Gaussian model. The Kriging interpolation results based on the optimal model show that the hydraulic conductivity as a whole is larger in the northwest and smaller in the southeast. The hydraulic conductivity is the largest near Meijiaping Township and Nanshe Township, ranging from 2.84 m/d to 6.44 m/d, with small spatial variation scale. It varies significantly near Mizi Township and Zhuangli Township, with large spatial variation scale. It is the smallest in the south of Dongshangguan Township, all less than 0.2 m/d, with small variation scale. The spatial variation is influenced by the combination of topography, geomorphology, distribution of stratigraphic lithology, hydro-meteorological conditions, distribution of test sites, manual sand extraction, mechanical crushing and other factors. The location of recharge should be chosen in Meijiaping town and other locations with large hydraulic conductivity, small spatial variation scale and low influence by human disturbance. The research results can provide theoretical references for the construction of underground reservoirs.
Effect of injection time and hydrostatic pressure on chloride migration in a porous geothermal reservoir
ZHAO Li, HUANG Shangzheng, ZHANG Qing, LU Yucan, JIN Yi, WANG Xinyi, XING Mingfei
 doi: 10.16030/j.cnki.issn.1000-3665.202206026
Abstract(54) HTML(72) PDF (3505KB)(98)
Abstract:
Few studies have focused on the effects of injection time and hydrostatic pressure on the solute transport in porous geothermal reservoirs to date. The chloride displacement experiments were individually carried out at 35 °C at the injection time of 1 h, 2 h, 3 h, 4 h and 5 h individually through the simulated columns packed with the thermal reservoir fine sand. Column experiments were performed at 35 °C at hydrostatic pressure of 0, 6 and 9 MPa individually. By using the one-dimensional CDE model in the CXTFIT 2.1 software, the migration law of Cl and its influencing factors in the studied matrix were examined. The results show that the Cl breakthrough curves under different injection time and hydrostatic pressure are symmetrically distributed, and they can all be well described by the CDE model. Thus, the solute dispersion can conform to the Fick’s law in the simulated low-temperature pore geothermal water. The breakthrough curve and transport parameters of Cl are highly correlated with the injection time due to the variations of the total amount of solute mass injected, concentration differences and molecular diffusion ability in the studied geothermal water. In addition, the value of D increases from 25.22 cm2/h at 0 MPa to 36.13 cm2/h at 9 MPa, combining with the increasing molecular diffusion coefficient, dispersion coefficient and dispersivity with hydrostatic pressure. Hence, the solute hydrodynamic dispersion in the simulated sandy column are enhanced with the increasing hydrostatic pressure. The results are of great significance to enrich the theory of solute transport in groundwater.
A study of influencing factors of spatio-temporal evapotranspiration variation across the Yellow River Basin under the Budyko framework
WANG Yaqin, YANG Wei, XING Bo, LUO Yi
 doi: 10.16030/j.cnki.issn.1000-3665.202205066
Abstract(116) HTML(116) PDF (5963KB)(30)
Abstract:
Evapotranspiration is an important part of water cycle, and the study of evapotranspiration is conducive to understanding the spatio-temporal variation of regional water resources. The Yellow River Basin (YRB) is located in an arid and semi-arid region, and water resources are sparse and uneven in spatio-temporal distribution, and the water issues are prominent. Analyzing the response of evapotranspiration to the changing environment in the YRB and revealing the hydrologic and water resources effects of climate change, vegetation seasonality and phenological variations are of great theoretical and practical significance for the sustainable development and planning and management of regional water resources. Based on the MARS non-parametric model, this paper analyzes the correlation between the water-energy coupling control parameter ϖ and environmental variables under the Budyko framework by using GIMMS3g NDVI datasets, meteorological data, soil data, land use/cover data and topographic and geomorphic data of 30 sub-basins in the YRB. The influence mechanism of changing environmental variables on evapotranspiration is discussed. The results show that (1) the spatial variation of the water balance relationship is significantly correlated with the water-energy coupling seasonality, the spatial variability of geomorphology, and the precipitation seasonality (average storm depth and coefficient of variation of precipitation). (2) On the inter-annual scale, a) the water and energy synchronicity is the most important climate seasonality that affects the inter-annual water balance: as water and energy synchronicity increases, the evapotranspiration ratio decreases and runoff yield increases; b) the more concentrated the precipitation, the higher the annual variation and the more obvious the seasonal precipitation, suggesting the smaller the evapotranspiration ratio; c) vegetation seasonality is an important factor affecting the catchment water balance: the stronger the vegetation growth and the longer the growing season, suggesting the larger the evapotranspiration ratio and the smaller the runoff yield coefficient. (3) There is a strong auto-correlation among environmental variables, which co-evolve and act on evapotranspiration.
Water-rock /soil interaction reflected by the chemical characteristics of groundwater of Jichang landslide in Guizhou Province
LIU Jianqiang, XU Qiang, ZHENG Guang, CHENG Da, WANG Zhuo, JIANG Jinjing
 doi: 10.16030/j.cnki.issn.1000-3665.202203077
Abstract(97) HTML(92) PDF (6489KB)(23)
Abstract:
The water-rock/soil interaction of a landslide is a complex physical and chemical synthesis, which seriously affects the stability of the slope.Research on the water-rock/soil interaction of a landslide on the occurrence of geological disasters is relatively weak. This article takes the Jichang landslide as the research object, analyzes the characteristics of the mineral composition and chemical composition of the rock and soil in the landslide area, combines the compositional changes of bedrock fissure water and atmospheric precipitation in the area, and uses the principal component analysis method to study the water-rock of the Jichang landslide The process of action and the influence of water and rock evolution on the stability of landslides are analyzed. The results show that: (1) The weathering process of basalt in the sliding body is a water-(rock) interaction coupled by mechanical crushing-mineral alteration, occurring on three scales of “micro-micro-macro”, (2) selection The first three factors, (accounting for 49.365%, 27.135%, and 15.092% of the total variance, respectively) analyze the chemical characteristics of groundwater. The main factor reflects the control effect of the dissolution of basalt primary minerals on the chemical composition of the groundwater, and the main factor reflects the groundwater. The main factor of the evaporation and the precipitation of minerals in which the solubility changes with pH, the main factor reflects the ion exchange between groundwater and rock (soil), and the main participating ions are sum. (3) Water-rock interaction products are mainly clay minerals such as illite, smectite, and chlorite, which increase the content of clay minerals in the structural plane of the rock mass, deteriorate and damage the rock mass, which is important for the formation of slip zones and the disintegration of landslides. influences. The results of principal component analysis of groundwater can reflect the main process of interaction between landslide groundwater and rock and soil.
Landslide susceptibility assessment based on the SOM-I-SVM model
JIA Yufei, WEI Wenhao, CHEN Wen, YANG Qingzhuo, SHENG Yifan, XU Guangli
 doi: 10.16030/j.cnki.issn.1000-3665.202206041
Abstract(103) HTML(109) PDF (8965KB)(24)
Abstract:
When using machine learning models for landslide susceptibility evaluation, the non-landslide sample points are usually selected randomly outside the landslide influence area, leading to a certain error. To improve the accuracy of landslide susceptibility evaluation, this paper couples the self-organizing map (SOM) neural network, information (I) model, and support vector machine (SVM) model, and proposes a SOM-I-SVM model-based method of landslide susceptibility evaluation, comparing with K-means clustering to verify the reliability of this model. The Maoyou District of the city of Shiyan is taken as an example, and seven factors of the distance from water system, slope, rainfall, distance from structure, relative height difference, distance from road, stratigraphic lithology are selected by correlation and importance analyses of environmental factors to establish a landslide susceptibility evaluation system. Based on these, the graded information values of each factor are calculated and used as input variables for landslide susceptibility evaluation. The SOM neural network and K-means clustering are used to select non-landslide samples, and the sample data set is substituted into the I-SVM model to predict landslide susceptibility. The prediction accuracies of the four models, SVM, I-SVM, KMeans-I-SVM and SOM-I-SVM, are compared, and the area under the ROC curve (AUC values) are 0.819, 0.882, 0.901 and 0.917, indicating that the SOM-I-SVM model can effectively improve the accuracy of landslide susceptibility prediction.
A study of the tunnel collapse mechanism based on the BP neural network inversion analysis
CHEN Hang, ZHANG Beibei, KUANG Huajiang, XIAO Lina
 doi: 10.16030/j.cnki.issn.1000-3665.202208066
Abstract(104) HTML(132) PDF (4639KB)(121)
Abstract:
Tunnels in karst areas are prone to collapse during construction. There are many analyses on the mechanism of tunnel collapse in mechanical aspects, but the mechanism of tunnel collapse in karst weak fracture zones and other strata were seldom examined, which makes the progress of tunnel engineering more difficult and risky. In order to ensure the safety, economy and feasibility of tunnel construction, it is necessary to master the mechanism of collapse in the tunnel construction. Relying on a tunnel project in a karst broken stratum in Guizhou, where the collapse phenomenon occurred during the excavation process, the monitoring data of the tunnel are examined, and the construction principle of the BP neural network is used to invert the stratum parameters of the tunnel. The inversion soil mechanical parameters are input into different construction models constructed by using the Flac3D finite element software, and the collapse failure mechanism and risk of typical sections are judged and analyzed. The results show that the stratum inversion parameters obtained by the BP neural network have certain reliability and can accurately reproduce the actual failure of the tunnel collapse. The construction method has a great influence on the stability of the tunnel excavation, and for the tunnel with the surrounding rock grade V , the three-step seven-step method and the single-side wall pilot pit method are safer for construction, and the tunnel collapse has no relationship with the simultaneous excavation of the tunnel in both directions. The predicted value of the tunnel vault displacement obtained by the inversion is 2.3 cm, and the predicted value of the surface displacement is 1.2 cm. The deviation from the monitoring data is about 13%, and the error is small. The research results are of important guiding significance for the construction of tunnels and highways in weak and broken strata in karst areas.
Characteristics of geological hazards and it’s mitigations of the Ms6.8 earthquake in Luding County, Sichuan Province
TIE Yongbo, ZHANG Xianzheng, LU Jiayan, LIANG Jingtao, WANG Donghui, MA Zhigang, LI Zongliang, LU Tuo, SHI Shengwei, LIU Minsheng, BA Renji, HE Longjiang, ZHANG Xinke, GAN Wei, CHEN Kai, GAO Yanchao, BAI Yongjian, GONG Lingfeng, ZENG Xiaowen, XU Wei
 doi: 10.16030/j.cnki.issn.1000-3665.202209029
Abstract(148) HTML(106) PDF (5917KB)(130)
Abstract:
On 5th September, 2022, the Ms 6.8 earthquake in Luding County, Sichuan Province induced large numbers of geological hazards. To deeply understands the evolution, distribution, and characteristics of geological hazards caused by the earthquake, we got the distribution of geological hazards by the field investigation and remote sensing interpretation. Then we analyzed the conditions for hazard control and the countermeasures for hazard prevention and reduction. The results show that as of 22:00 on September 14, 2022, the earthquake has induced 565 geological hazards with threat objects in Luding County and Shimian County (including 331 collapses and 234 landslides), and there were 81 existing geological hazards became more deformed. The types of geological hazards induced by the earthquake are mainly medium and small mass high-level collapses, which are mainly concentrated in the areas with Seismic intensity zone ofⅨ near the epicenter. These areas include Moxi Town, Detuo Township, both banks of Dadu River between Detuo Township and Dewei town in Luding County, Caoke Township and wanggangping Township in Shimian County. According to the experience of the Wenchuan earthquake, the debris flow will be active in the next five years, and its characteristics of high frequency and viscous debris flow should be considered in the design of debris flow prevention and control engineering. Under the rainfall condition, the landslide deposition remaining on the slopes of Dadu River banks in the section of Detuo Township Dewei town can be easily transformed into debris flow. It is suggested that the transformation forms of the two hazards’ types should be fully considered in the design of prevention and control projects. The study can provide a reference for earthquake geological hazard prevention and post hazard reconstruction planning in the earthquake area.
Status and prospects of studies on anti-slide shaft technology
WANG Wenpei, YIN Yueping, WANG Lichao, SHEN Yaqi, SHI Pengqing, LI Ruidong, HE Qing, CHEN Liang, YIN Baoguo
 doi: 10.16030/j.cnki.issn.1000-3665.202206028
Abstract(206) HTML(242) PDF (3303KB)(308)
Abstract:
On one hand, anti-slide shaft technology can overcome the problems of blocking the seepage and drainage path in the slope by traditional anti-slide piles. On the other hand, it can reduce the excavation quantities when the vertical drainage and anti slide structures are separately constructed. Besides, it can fully provide the hydration-heat dissipation surface to ensure the overall structure quality. It has been an important technology in modern landslide prevention engineering, and the novel one of geological disaster, hydrogeology and underground engineering in recent years. Due to the anti-slide shaft technology involving hydrodynamic mechanics and solid mechanics, as well as hydrodynamic model, structural model, engineering geological model, etc and the problems restricted the promoted application, such as the lack of mature theoretical system, the relatively complex of this spatial structural combination, and the difficulty of the construction technology, it is necessary to carry out targeted current status summary research. Based on consulting a large number of relevant documents, patents and practical engineering applications at home and abroad, firstly, through summarizing the characteristics and classification of anti-slide shaft structure (anti-liquefaction pile, hollow anti-slide shaft, box anti-slide shaft, etc), it has been found that, its main forms are mostly are pile-type or tie-type, forming a 3-D structure system with the combination characteristics of seepage, collection, drainage and anti-slide. This kind of seepage-collection-drainage structures usually include water permeable holes, radiant seepage holes and drainage pipes. Secondly, through the demonstration of typical application examples, it shows that although the anti-slide shafts have the advantage of significant improvement on the stability, there is still a large optimization space from its extensive use and diversification. Thus, this paper puts forward that the current complex construction process, unclear mechanical properties and drainage characteristics, imperfect stability calculation theory, plane layout optimization method to be improved in anti-slide shaft technology are important scientific issues and research trend that need to be paid attention to in this field in the future. The solution of these scientific problems is not only beneficial to improving the mechanical and drainage theory, but also beneficial to improving the overall application level of anti-slide shaft technology.
Law of water-rock /soil interaction reflected by the chemical characteristics of groundwater of Jichang landslide in Guizhou Province
LIU Jianqiang, XU Qiang, ZHENG Guang, CHENG Da, WANG Zhuo, JIANG Jinjing
 doi: 10.16030/j.cnki.issn.1000-3665.202103009
Abstract(329) HTML(257) PDF (4866KB)(174)
Abstract:
The water-rock /soil interaction of a landslide is a complex physical and chemical synthesis, which seriously affects the stability of the slope.Research on the water-rock /soil interaction of a landslide on the occurrence of geological disasters is relatively weak.This article takes the Jichang landslide as the research object, analyzes the characteristics of the mineral composition and chemical composition of the rock and soil in the landslide area, combines the compositional changes of bedrock fissure water and atmospheric precipitation in the area, and uses the principal component analysis method to study the water-rock of the Jichang landslide The process of action and the influence of water and rock evolution on the stability of landslides are analyzed. The results show that: (1) The weathering process of basalt in the sliding body is a water-(rock) interaction coupled by mechanical crushing-mineral alteration, occurring on three scales of "micro-micro-macro", (2) selection The first three factors, (accounting for 49.365%, 27.135%, and 15.092% of the total variance, respectively) analyze the chemical characteristics of groundwater. The main factor reflects the control effect of the dissolution of basalt primary minerals on the chemical composition of the groundwater, and the main factor reflects the groundwater. The main factor of the evaporation and the precipitation of minerals in which the solubility changes with pH, the main factor reflects the ion exchange between groundwater and rock (soil), and the main participating ions are sum. (3) Water-rock interaction products are mainly clay minerals such as illite, smectite, and chlorite, which increase the content of clay minerals in the structural plane of the rock mass, deteriorate and damage the rock mass, which is important for the formation of slip zones and the disintegration of landslides. influences. The results of principal component analysis of groundwater can reflect the main process of interaction between landslide groundwater and rock and soil.
Display Method:
2023, 50(1).  
Abstract(108) HTML(135) PDF (355KB)(284)
Abstract:
2023, 50(1): 1-2.   doi: 10.16030/j.cnki.issn.1000-3665.202209031
Abstract(166) HTML(190) PDF (2833KB)(452)
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Interaction between groundwater and seawater in bedrock islands
ZHANG Kang, HAN Dongmei, CAO Tianzheng, SONG Xianfang, WANG Wei, CAO Yanling
2023, 50(1): 3-12.   doi: 10.16030/j.cnki.issn.1000-3665.202112011
Abstract(149) HTML(99) PDF (3773KB)(104)
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The hydrogeological settings of bedrock islands in northern China are unique. Climate change and human activities can affect the interaction between groundwater and seawater around the islands to varying degrees, but there is a lack of quantitative understanding of such hydrological processes, including seawater intrusion (SWI) and submarine groundwater discharge (SGD). In this study, we analyzed the precipitation, groundwater levels, and water quality data (2012-2016) for identifying the characteristics and controlling factors of the interaction between groundwater and seawater in bedrock islands by using mathematical statistics, spatial interpolation, and hydraulics methods. The results show that precipitation and groundwater pumping are the main factors affecting the groundwater-seawater interaction. The variations of groundwater levels lag behind the rainfall events by about 10 days. There occurred no SWI in most areas on the northeastern and southern coasts of the South Island, with relative stable marine groundwater discharge. The average SGD velocity was 0.2 m/d, and the average NO3-N flux to the sea was 81.8 mmol/(m2·d). The southeast area of the North Island has been seriously threatened by SWI, and the groundwater levels have been below sea level for a long time and falling year by year. The average SWI rate is 0.3 m/d, and the average NO3-N flux towards the land is 69.6 mmol/(m2·d). The SGD rates of the South and NorthIslands were estimated for dry season (April 2014) and wet season (September 2013), respectively. It was 3.5×104−4.5×104 m3/d for the North Island, and 0.4×104−1.1×104 m3/d for the South Island. The results can provide important reference for coastal groundwater resource management and ecological environment protection in bedrock islands.
Research on regional evapotranspiration in the Zhangcheng area based on the SEBS model
DONG Xiangwang, JIN Xiaomei, ZHANG Xucai, YIN Xiulan, JIN Aifang, LANG Jie, LUO Xufu, MA Jingxuan
2023, 50(1): 13-20.   doi: 10.16030/j.cnki.issn.1000-3665.202204007
Abstract(172) HTML(96) PDF (4285KB)(104)
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Evapotranspiration (ET) is the main process of water and energy conversion in the hydrosphere, atmosphere and biosphere. Accurately estimation of ET is of great significance in ecological environment protection. The city of Chengde and Zhangjiakou, taken as the study area, is an important barrier for the ecological security of the Beijing-Tianjin-Hebei urban areas. There have been fewer studies of actual evapotranspiration for long-term sequences in the region. In this paper, the monthly actual ET in the study area from January, 2001 to December, 2020 is simulated based on the SEBS model using MODIS and GLDAS data. The SEBS results are compared with the MOD16A2 data in trend, and the field measurements on July 2021 are also used for validation at the pixel scale. The method of Sen+MannKendall test is used to analyze the temporal and spatial trend changes, and the correlation analysis was used to discuss the influencing factors on ET change. The results show that the monthly SEBS ET has a good correlation with the mod16A2 data, and the relative error with the field measurement is less than 15%. Therefore, the reliability of the SEBS result is validated to be relatively high. The actual ET of the study area has shown a fluctuating upward trend in the past 20 years. The maximum value of ET appeared in 2013 with the value of 545 mm, and the minimum value was 348 mm in 2002; and the evapotranspiration in Chengde was significantly higher than that in Zhangjiakou; In the past 20 years, the ET of 75.41% of the study area was basically stable, 5.13% of the area increased, 1.11% of the region was significantly decreased and 18.35% of the area was slightly decreased. The temperature and vegetation change have a significant positive correlation with evapotranspiration variation. The ET of different land use types is: forest land>water>grass land>arable land>construction land>unused land.
Prediction of coal mine water inflow by different mining methods and environment impact analyses
WEI Huapeng, LUO Qibin, KANG Weidong, ZHANG Zichen
2023, 50(1): 21-31.   doi: 10.16030/j.cnki.issn.1000-3665.202201025
Abstract(99) HTML(62) PDF (3951KB)(103)
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Improper mining of coal mines can cause damage to water resources and the water environment, especially in areas with relatively fragile ecological environment. At present, the prediction of mine water inflow mainly focuses on the single working face or mining area, and enough attention has not been paid to the influence of long-term mining of coal groups in the gully on groundwater environment. The Toudaoheze gully is selected as the study area. Based on the data of groundwater exploration and coal field investigation, a 3D numerical model of groundwater unsteady flow of the whole gully is constructed. The model is identified and verified with the monitoring data of groundwater and surface water and the long-term data of mine water inflow in coal groups. Taking 9# coal mine as a typical area, the mine water inflow and its influence on water environment under the fully mechanized mining and strip filling mining methods are analyzed. The main results show that (1) under the fully mechanized mining method, the increase of mine water inflow is 0.70×104 m3/d, resulting in the reduction of groundwater overflow of 0.20×104 m3/d and causing groundwater level to drop between 0.21 and 17.92 m in the mining area and region. Under the strip filling mining method, the increase of mine water inflow is 0.11×104 m3/d, resulting in the reduction of groundwater overflow is 0.04×104 m3/d and causing groundwater level to drop between 0.01 and 0.44 m in mining area and region. (2) The water-conducting fracture zone connects with a large area of the Quaternary phreatic aquifer under the fully mechanized mining method, and mine water inflow has a great impact on water environment. If the strip filling method is carried out, the height of the water-conducting fracture zone will be greatly reduced, and the Quaternary phreatic aquifer will not be connected, and mine water inflow will have less impact on water environment. The filling mining method can be adopted when coal mining in the area has small thickness of strata above the coal seam. The results can provide a basis or reference for the formulation of mining schemes in the study area or other similar coal fields, and for scientifically handling the relationship between coal resource mining and ecological environmental protection.
An improved method for inhomogeneous space grid in the simulation of unsaturated flow
ZHU Shuairun, HE Bo, WU Lizhou, LI Shaohong, QING Yiwei
2023, 50(1): 32-40.   doi: 10.16030/j.cnki.issn.1000-3665.202110013
Abstract(99) HTML(82) PDF (3919KB)(52)
Abstract:
The Richards’ equation is widely used in the simulation of unsaturated flow and related fields. In the numerical solution process, the finite difference method can be used to carry out numerical discretization and iterative calculation. However, in order to obtain a more reliable numerical solution, the space step size of a conventional uniform grid is often small. For some unfavorable numerical conditions, such as infiltration into dry soil, iterative calculation is time-consuming and even the accuracy cannot be improved very well. Therefore, an improved method is proposed by using the Chebyshev space grid, which combines the finite difference method to numerically discretize the Richards’ equation to obtain linear equations. Then the classic Picard iterative method is used to iteratively solve the linear equations to obtain the numerical solutions of the Richards’ equations. Through two examples of unsaturated flow under unfavorable conditions for homogeneous soil and layered soil, combined with the analytical solution of the model and the software Hydrus-1D, the accuracy of the numerical solution obtained by the improved grid method and the uniform grid method is compared and examined. The results show that the proposed Chebyshev grid method can obtain higher numerical accuracy with a smaller number of nodes than the traditional uniform grid, and the computational cost is smaller. This method has a good application prospect.
A study of dispersion experiment and simulation of the cohesive layered soil in the transition zone of the Jianghan Plain
LIU Yongyi, SHI Tingting, WANG Qing, LIU Tianwen, LIU Yalei, LI Mengru
2023, 50(1): 41-50.   doi: 10.16030/j.cnki.issn.1000-3665.202201036
Abstract(113) HTML(71) PDF (3671KB)(63)
Abstract:
In order to study the law of solute migration in the cohesive stratified soil in the transitional zone of the Jianghan Plain-Dabie Mountain area, the conservative anion Br is taken as a tracer agent in the isothermal adsorption experiment. One-dimensional dispersion experiment and HYDRUS-1D software simulation inversion method are used, and the adsorption parameter, migration law and migration inversion dispersion parameter of Br in the cohesive stratified soil are examined. The results indicate that (1) both the Freundlich model and Langmuir model can well fit the adsorption experiment results, along with the increase of proportion of clay particle in the soil, and the saturation adsorption amount of the soil to Br- increases. (2) Both the soil texture and structure in the stratified soil can influence the shape of the breakthrough curve, but the dispersion process in one-dimensional saturation earth pillar mainly depends on the proportion of clay particles in the water-bearing media system, and the increase of clay particles will produce resistance for solute transport. (3) The invert dispersion parameter through the HYDRUS-1D software construction model, R2 is always larger than 0.991, and the fitting effect is good. The analysis results show that no matter soil component type or layer thickness and ordering in the stratified soil, the essence to influence dispersion function is by changing the average hole flow velocity of the soil, and the dispersion coefficient becomes smaller as the average hole flow velocity is smaller. (4) The silty clay dispersion coefficient in the experiment ranges from 0.005 to 0.048 cm2/d, far less than the sand dispersion coefficient 0.524 to 7.477 cm2/d in the under part, the difference value reaches two order of magnitudes, indicating that the thick layer clay soil is a control layer and will greatly resist solute transport of groundwater. The pollutant or organic matter in the upside water-bearing stratum is very hard to penetrate this layer and migrate downward, and this layer has very good sewage removal performance. The results are of great application value for groundwater environmental protection and water quality control in the transition zone of the Jianghan Plain.
An experimental study of salt/heat transport in a fracture-matrix system based on the resistivity method
DING Rui, DENG Yaping, QIAN Jiazhong, YANG Ze, MA Lei
2023, 50(1): 51-59.   doi: 10.16030/j.cnki.issn.1000-3665.202111055
Abstract(99) HTML(63) PDF (4312KB)(107)
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In order to explore the effectiveness of salt and heat tracers in a fracture-matrix system, a fracture-matrix test model is designed. The tracer tests with different tracers are carried out. The transport process of tracer is described in the fracture-matrix with the real-time dynamic resistivity monitoring data at different measuring points, and the effectiveness of salt and heat tracers based on the resistivity method is discussed. The results show that the process of injecting three different tracers into the fracture-matrix system and the existence of fracture can be seen by the resistivity method. Under the salt-heat tracer, the difference between the volume conductivity in the fracture and the matrix is the largest, and the change rate of the volume conductivity in the fracture and the matrix decreases with the increasing depth. The fitting effect of concentration and volume conductivity is better than that of temperature and volume conductivity. These indicate that the tracer based on the resistivity method is effective in describing the positions of the fracture and matrix in the fracture-matrix system, and the salt-heat combined tracer has the best effect. The results are of certain reference for the field electrical exploration of the positions of fractures and other heterogeneous layers.
Strength characteristics and strength prediction of fluid geopolymer solidified soil
YI Fu, JIANG Shan, MU Dehui, GUAN Maocheng
2023, 50(1): 60-68.   doi: 10.16030/j.cnki.issn.1000-3665.202205038
Abstract(126) HTML(145) PDF (3880KB)(56)
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Geopolymer cementitious materials can replace cement-based cementitious materials as curing agents in engineering problems, such as backfilling of narrow fertilizer troughs, and effectively reduce pollution and energy consumption in the cement production process. There are few studies on cementitious materials. Three new green cementitious materials combined with alkali activators are used to solidify engineering slag and form fluidized geopolymer-solidified soil. The strength prediction model is established to analyze the influence of different factors on the strength. The results show that the strength of the solidified soil increases first and then decreases with the increasing modulus of the alkali activator, increases with the content of GGBS, fly ash and rice husk ash, and decreases with the increasing particle size. When the modulus of alkali activator increases to 1.2, the content of GGBS increases to 10%, the content of fly ash increases to 8%, and the content of rice husk ash increases to 11%, the strength of the solidified soil increases significantly. The average relative error of the prediction results of the strength prediction model is only 5.57%, which is relatively accurate for the solidified soil. The calculation results of the weights of each layer in the prediction model show that the curing age has the greatest impact on the strength of the solidified soil, and the particle size of rice husk ash has the minimal impact. The research results can provide theoretical support for the application of solidified soil in practical engineering.
Energy consumption in a large- scale 3D electro-osmosis-hydraulic synergism system for sludge consolidation
ZHENG Ruoxuan, SUN Xiuli, WANG Yu, JIN Xun, YU Qinjie, LIU Wenhua
2023, 50(1): 69-77.   doi: 10.16030/j.cnki.issn.1000-3665.202112040
Abstract(115) HTML(102) PDF (3544KB)(108)
Abstract:
The 3D electro-osmosis-hydraulic synergistic consolidation method is proposed based on the theory of electroosmosis and consolidation to solve the problem of the high energy consumption and large-scale simulation of practice conditions for low permeability and high-water content soils. A set of multi-functional catchment drainage systems combining the synergistic action of the cathode-catchment-intermittent pumping mode is developed. Consolidation of two types of Taihu lake sediments from the Gonghuwan wetland and Baimao Storage site are investigated using this system. Two key indicators of energy consumption per unit volume and displacement per unit volume of the 3D electro-osmosis-hydraulic synergistic consolidation system and the traditional 1D electroosmosis system are analyzed to illustrate the advantage of the 3D system. The results show that the design of water collecting well can greatly reduce the resistance near the soil cathode, intermittently improve the system current, improve the drainage efficiency and reduce the energy consumption. Intermittent pumping can intermittently reduce the system current, and maintain the continuity of system seepage by using the electric and hydraulic synergistic effect. A decrease-increase periodic decrease mode of the current for the 3D electrohydraulic seepage consolidation system is observed. The decrease rate of the current is slower than that of the 1D electro-osmotic system, especially for the soil with high organic matter content, the current in the electroosmotic process is maintained at a relatively higher level, which improves the drainage consolidation efficiency. The energy consumption per unit volume and displacement per unit volume of the 3D electro-hydraulic seepage consolidation system are about 2/3 and 1/30 that of the 1D electro-osmotic system, respectively. The 3D electro-hydraulic seepage consolidation system has remarkable energy saving effect in consolidation and drainage of soft soil with high water content. The 3D electroosmosis-hydraulic consolidation system can greatly improve the drainage consolidation efficiency, greatly reduce energy consumption and better guide the application of the proposed method to the electro-osmotic consolidation of high-water content sludge and another related field.
An empirical method for calculating the roughness coefficient of structural plane with line-plane combination
FAN Xiang, AN Honglei, BAO Han, REN Xianda, DENG Zhiying, WU Rui
2023, 50(1): 78-86.   doi: 10.16030/j.cnki.issn.1000-3665.202205027
Abstract(82) HTML(89) PDF (5492KB)(34)
Abstract:
The shear mechanical properties of structural plane are mainly determined by the surface roughness, and the roughness coefficient is the main method to characterize the roughness. At present, the research on the roughness coefficient is limited to a single dimension. Multi-angle and quantitative calculation of the roughness coefficient of structural plane can avoid the limitation of inaccurate calculation caused by single dimension analysis. Cubic granite blocks with structural plane are prepared by Brazilian splitting. High-precision 3D scanner is used to scan the prepared structural interview samples and obtain the point cloud data of the structural planes. At the same time, three-dimensional reconstruction of point cloud data is carried out by reverse software. The distribution frequency in the Z direction of the point cloud data, the relationship between the section ratio and joint roughness coefficient (JRC) values of the section line, and the relationship between the structural plane area ratio and the mean JRC values are studied. The results show that the distribution frequency in the Z direction of point cloud data can be used as a preliminary method to evaluate the roughness of structural surface. The relationships between section ratio and JRC value as well as area ratio of structural plane and mean JRC are both quadratic function. By numerical analysis, the binary function relation between the mean JRC of the structural planes and the section ratio and area ratio is established, and the empirical formula of the mean JRC of the structural plane is obtained. This study provides a "point-line-plane" idea to evaluate the roughness of discontinuities. The obtained empirical formula provides a new method for calculating the mean value of JRC of the structural plane.
Roughness coefficient of rock discontinuities based on random forest regression analyses
LI Wenbin, FENG Wenkai, HU Yunpeng, ZHOU Yongjian, CHEN Kai, LIU Yun
2023, 50(1): 87-93.   doi: 10.16030/j.cnki.issn.1000-3665.202110048
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The peak shear strength of the discontinuities can be estimated quickly by the roughness of the discontinuities. However, it is difficult to quantify the roughness of the structural surface using the single statistical parameter. In order to improve the prediction accuracy of the standard discontinuities roughness, eight statistical parameters in the aspects of undulating degree and trace length of 112 structural profile curves are collected, and the method of cross-validation of random forest regression model is used to evaluate the importance of statistical parameters. The evaluation results show that the importance of six statistical parameters, including the maximum undulation, undulation height standard deviation, mean undulating angle, undulating angle standard deviation, mean relative undulation rave and roughness profile index, accounts for 93.2%, and the regression fitting coefficient tends to be stable. Based on the importance assessment results, a random forest regression model is established. The model prediction results fitting excellence is up to 98.1%, showing the excellent prediction results. Compared with the traditional linear regression results, such as the results of the slope-based mean square root, structural function and roughness profile index, the random forest regression model has higher accuracy, smaller error and better fit. The random forest regression model is more suitable for structural roughness inversion.
A study of the characteristics and influence mechanism of time delayed rockburst in a TBM tunnel under the blasting disturbance
QUAN Yongwei, WANG Jun, XIONG Yongrun, YAO Zhibin, ZHANG Yu, HU Lei
2023, 50(1): 94-103.   doi: 10.16030/j.cnki.issn.1000-3665.202202042
Abstract(92) HTML(89) PDF (5404KB)(104)
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The occurrence of time delayed rockburst usually has strong randomness and will pose a great threat to construction safety. Excavation disturbance and blasting disturbance will have impact of varying degrees on the potential time delayed rockburst area. It is of great significance to carry out studies of the characteristics and mechanism of time delayed rockburst in a TBM tunnel under the blasting disturbance. Based on a TBM headrace tunnel, five time delayed rockburst occurred in K54+000—K54+700 section during demolition tunnel blasting excavation are studied by using theoretical analysis and comparative analysis method. The results show that (1) strong and medium rockburst areas are located near gentle dip faults. Short and small concealed joints and fine joints with filling are developed in surrounding rocks. The slight rockburst is far from the fault or near the normal fault. Except for the fine joints with filling, at least one steep structural plane with filling tendency and dipping in SW direction is developed. (2) The time delayed rockburst of the TBM tunnel has longer delay blasting time and longer lag working face distance, and the disturbance effect of blasting on the TBM tunnel is relatively small. (3) Blasting disturbance makes it easy for the surrounding rock instability in the potential time delayed rockburst area, which accelerates the process of time delayed rockburst. The research results can provide a useful reference for the early warning and prevention of time delayed rockburst in TBM tunnels.
An experimental study of spatial-temporal evolution of water-soil response and stability of a rainfall-induced accumulation landslide
MENG Shengyong, JIANG Xingyuan, YANG Yi, SUN Qianzheng, SHI Wenbing
2023, 50(1): 104-112.   doi: 10.16030/j.cnki.issn.1000-3665.202204014
Abstract(113) HTML(139) PDF (5244KB)(73)
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The change of soil and water mechanics caused by rainfall infiltration in loose soil is the key to affect stability. At present, most studies focus on the influence of particle size, content and other factors on slope failure. However, the research on the internal water-soil response and spatial-temporal evolution of slope stability is insufficient. Based on a field landslide case, this study explores the deformation and failure processes and mode of loose accumulation slope triggered by rainfall through the flume test, soil mechanics test, and theoretical analysis. The Van Genuchten model (VG model) is used to reconstruct the soil-water characteristic curve of the soil, and the mechanical change of soil and water in the slope and the temporal and spatial evolution of stability are mainly explored. The results show that: (1) The failure processes of the accumulation slope emerge in three stages, that is, the micro-fracture development stage, local failure stage and complete collapse stage, presenting the failure mode of “initial cracking-slope collapsing-plastic sliding”. (2) The volumetric water content and pore water pressure of slope increase rapidly during infiltration, while the matric suction between soil particles decreases or even dissipates, which promotes the development of slope failure. (3) The mechanical strength of soil decreases exponentially with the increasing volumetric water content. When the volumetric water content is 36.3%, the effective cohesion and effective internal friction angle are only 0.27 kPa and 3.39°. (4) Based on the limit equilibrium theory and the monitoring data of slope soil-water characteristics, the spatio-temporal evolution map of slope stability is constructed, which is in good agreement with the failure characteristics of the model test. The research results provide theoretical support for monitoring and early warning of accumulation slope under rainfall and disaster prevention and mitigation.
Mechanisms and stability analysis of the Jinjiling landslide in the Three Gorges Reservoir area based on Midas-GTS
TAN Yinlong, XU Wanzhong, CAO Jiaju, LUO Dan, WANG Bendong, QIAO Lijia, ZHOU Yi
2023, 50(1): 113-121.   doi: 10.16030/j.cnki.issn.1000-3665.202204054
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The Jinjiling landslide was obviously deformed after the rainstorm, and preliminary conclusions were drawn through on-site investigation, drilling, geophysical prospecting, deep displacement monitoring and horizontal displacement monitoring. On this basis, in order to further find out the genesis mechanism of the landslide, this paper interprets the existing survey and monitoring data, combines the Midas-GTS software to analyze the seepage field, displacement field, and stability calculation of the landslide under different working conditions, and comprehensively evaluates its genesis mechanism. The results indicate that (1) geophysical interpretation shows that the Jinjiling landslide is a rock-soil mixed, water-bearing landslide, and the sliding surface is located at the boundary between T2b1 marlstone and T2b2 mudstone. (2) Deep displacement monitoring data reveals that the landslide occurs in a superficial soil mass, and the position of the slip surface is consistent with the location of the slip surface obtained by geophysical exploration. (3) The horizontal displacement monitoring shows that the superficially distributed Houbang landslide and Panjialing landslide have fast deformation rates and stronger deformation. (4) The numerical simulation results show that the Jinjiling landslide is currently in a basically stable state; it is in a basically stable state when the groundwater is drained; it is in a less stable state under heavy rain conditions, which may cause overall slippage, and the Panjialing and Houbang landslides produce secondary soil slippage. (5) The topography, geological structure, stratigraphic lithology of the Jinjiling landslide provide provenance and site conditions for the formation and development of the landslide. Torrential rain and human engineering activities are the inducing factors, which further aggravate the deformation of the landslide. The research results will provide a theoretical basis for the analysis of the genetic mechanism and stability of similar landslides in the Three Gorges Reservoir area, and have important guiding significance for the later control measures.
Experimental study on prevention measures of extruded ice on highway subgrade slope in Sichuan-Tibet cold region
ZHAO Wen, LIU Yaxiong, JI Anna, GAO Wenjie, WANG Guosheng
2023, 50(1): 122-131.   doi: 10.16030/j.cnki.issn.1000-3665.202203034
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Extruded ice is a common disease in road engineering in Sichuan-Tibet cold region, which seriously threatens the safety of road construction and operation. Preventing groundwater from being exposed to the surface or the groundwater level being too high can slow down or eliminate the formation of extruded ice. Field investigation and satellite map identification show that extruded ice in Sichuan-Tibet cold region is mainly overflow type. The prevention effects on extruded ice of backfilling with gravelly coarse sand or pebbles to dredge groundwater and laying waterproof geotextiles are analyzed by indoor physical simulation experiments. The results show that extruded ice will gradually form when the frozen depth is lower than the depth of groundwater level. Backfilling seepage layer with gravelly coarse sand or pebbles can accelerate the discharge of groundwater and reduce the pore water pressure effectively. Compared with the untreated slope, the volume of extruded ice is reduced by 85.4% and 93.9% respectively, and the pore water pressure is reduced by 46.2% and 58.1% respectively. By blocking groundwater with waterproof geotextile, the volume of extruded ice is reduced by 97.5%, but the pore pressure will increase. Considering the sufficient pebble (or gravel) materials in Sichuan-Tibet alpine region, it is recommended to use permeable pebble (or gravel) as backfill layer to accelerate groundwater drainage and control extruded ice disease in subgrade slope. And waterproof geotextile is recommended to be laid on backfill layer. The research results can provide reference for the prevention of extruded ice in Sichuan-Tibet traffic roads.
Ground vibration test of the Zhengzhou-Xi’an high-speed railway and analyses of the vibration isolation trench effect
SONG Yulan, YANG Lizhong
2023, 50(1): 132-143.   doi: 10.16030/j.cnki.issn.1000-3665.202205041
Abstract(108) HTML(123) PDF (6927KB)(8)
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The dynamic load of high-speed railway train can cause environmental vibration problems. In order to study the environmental vibration effect caused on the viaduct bridge section and embankment section by high-speed train, the field test of the Zhengzhou - Xi’an high-speed railway is carried out, and the ground vibration characteristics and attenuation law of viaduct bridge section and embankment section are compared and analyzed. The test results show that the vibration response of the embankment section is greater than that of the viaduct bridge section, and the attenuation effect in the near-field area of the viaduct bridge section is higher than that in the near-field area of the embankment section. There are multiple rebound increases in the process of vibration propagation, and the ground vibration rebound of the embankment section lags behind that of the viaduct bridge section. The increase rate of secondary rebound in the viaduct bridge section and embankment section is significantly greater than that of primary rebound. The attenuation of Z vibration level with the distance conforms to the law of logarithmic attenuation. The Z vibration level attenuation formula in the loess area is obtained by fitting, and the maximum deviation appears in the rebound increasing area. The infinite element-viscoelastic coupling boundary is introduced to establish a 3D track-soil-vibration isolation trench numerical model of the embankment section. The influence of vibration isolation trench on vibration reduction and isolation of high-speed railway is analyzed. The results show that the vibration isolation effect of empty trench on the medium and high frequency (30 - 60 Hz) vibration wave is more obvious than that of low frequency (1 - 20 Hz), and it has the function of low-pass filtering. The vibration isolation effect of empty trench is better than that of filled trench, but soft materials can be filled in the trench considering the stability of trench walls. The research results can provide references for the design of high-speed railway and the evaluation and control of environmental vibration.
Connotation, layering, mapping and supporting objectives of the integrated survey of ground substrates
YIN Zhiqiang, CHEN Ziran, LI Xia, WEI Xiaofeng, SHAO Hai
2023, 50(1): 144-151.   doi: 10.16030/j.cnki.issn.1000-3665.202205004
Abstract(134) HTML(118) PDF (7023KB)(211)
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Comprehensive investigation and evaluation of ground substrate is the fundamental work to support suitable forest, grass, farming and wasteland. The guiding theory, target positioning, scientific connotation and mapping unit of comprehensive investigation of ground substrate are the focus and hotspot of current scientific issues. In this paper, based on the comprehensive survey and multi-scale mapping of ground substrate in Chengde Ecological Civilization Demonstration Area in recent years, and combined with the pilot practices of ground substrate survey in different regions, we further clarify the scientific connotation and supporting service objectives of ground substrate, establish the fourth-level classification scheme, mapping unit and naming convention, and proposed the depths range of the production layer, ecological layer and living layer of ground substrate. Finally we take two cases of afforestation and grass degeneration in the Bashang region as examples to reveal the constraining effect of ground substrate on vegetation community. All the above research results will provide a fundamental reference for understanding in-depth of the scientific significance of ground substrate and implementation of survey, monitoring, evaluation and zoning of ground substrate in China.
Simulation achievement of lab-scale formations with high geotemperature gradient
ZHANG Deqian, LEI Haiyan, DAI Chuanshan
2023, 50(1): 152-157.   doi: 10.16030/j.cnki.issn.1000-3665.202201050
Abstract(104) HTML(95) PDF (4783KB)(133)
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The heat exchange between geothermal wells and surrounding formations is important to the heat production of geothermal wells. Due to the difficulty in arranging measurement points around geothermal wells in real engineering, it is hard to verify the results of geothermal reservoir modelling, thereby verify the modelling results. Therefore, geothermal wells are only considered as source/sink in most of the previous geothermal reservoir modeling, and the coupled flow and heat transfer between the geothermal fluid and the reservoir is not considered. In contrast, lab-scale experiments are convenient to arrange the measurement points, and the experimental results can verify the coupled geothermal reservoir-wellbore numerical model. However, how to achieve the lab-scale formations with geotemperature gradients is the key issue, and there are no similar studies yet. In this paper, based on the basic principles of heat transfer, a lab-scale simulated formation with high geotemperature gradient is quickly achieved. By determining the geometric size of the simulated geothermal reservoir and caprock, selecting the filled porous media and a simulated reservoir with constant temperature, a simulated formation with high geotemperature gradient is designed. Through the layered heating and boundary dynamic thermal supplementation method, the linear temperature distribution of the simulated formation at the reservoir temperature of 60 °C, 65 °C and 70 °C, respectively, are achieved. The relative error between the numerical simulation obtained by the finite volume method and the experimental results is within the range of ±2.5%, indicating that the simulated and experimental results are in good agreement, which can provide experimental conditions for the coupled reservoir - wellbore heat transfer experiment. The simulated formation system designed and established in this paper can provide experimental conditions for the reservoir-wellbore heat transfer experiment, and then verify the developing numerical software of coupling the reservoir-wellbore flow and heat transfer.
Geochemical characteristics and formation mechanisms of the seawater-recharged geothermal systems in Yantian of Fujian, China
LIU Chunlei, LI Yasong, HONG Bingyi, CAO Shengwei, WANG Wanli, LI Jianfeng
2023, 50(1): 158-167.   doi: 10.16030/j.cnki.issn.1000-3665.202205017
Abstract(89) HTML(84) PDF (4061KB)(82)
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Seawater-recharged geothermal systems are characterized by abundant recharge, low temperature and salinization. Ascertaining the circulation recharge conditions and genetic mechanisms of geothermal water in coastal areas of southeast China is of important significance in the rational exploration, utilization and protection of geothermal resources in these areas. In this study, 14 samples of geothermal water, groundwater and seawater are collected from the Yantian geothermal field near Guanqiao Town in Fujian Province, China and the hydrochemical and isotopic characteristics are analyzed. The circulation recharge of the geothermal water and the genetic mechanisms of the geothermal resources in the geothermal field are revealed using geothermometers. The results show that hydrochemical type of the geothermal water in the Yantian geothermal field is of Cl—Na type, which is similar to that of the seawater. Total dissolved solids of geothermal water samples H01 and H02 are 2 610 mg/L and 3 090 mg/L, respectively. By contrast, the groundwater in the geothermal field is dominated by the HCO3—Na type, and the groundwater samples have TDS of less than 400 mg/L. Moreover, the geothermal water is rich in Br, which is not detected in the groundwater. These results indicate that modern seawater or ancient seawater in marine sedimentary layers is a recharge source of the geothermal water. As shown by the results of H01 and H02 calculated using the Cl mixing model, geothermal water samples H01 and H02 have seawater mixing ratios of 9.13% and 10.76%, respectively, and H01 is mixed with more groundwater after being exposed to Quaternary sediments. The comprehensive analyses show that the geothermal water in the Yantian geothermal field is primarily recharged by seawater and its chemical composition is significantly affected by seawater mixing. Furthermore, the comprehensive analyses also suggest that the deep geothermal water is mixed with groundwater or seawater twice or more times as it rises upward, thus forming shallow geothermal reservoirs with a temperature of 89 °C to 121 °C, as estimated by using the SiO2 geothermometer and the multi-mineral equilibrium method.
An analysis of the endowment characteristics and geneses of geothermal resources in the Zhangye Basin
YIN Zheng, LIU Yonggang, ZHANG Xuru, LI Yushan, FENG Jiaxing
2023, 50(1): 168-178.   doi: 10.16030/j.cnki.issn.1000-3665.202202050
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As a part of Hexi Corridor in Gansu Province, the Zhangye Basin is located in the middle reaches of the Heihe River Basin, with high topography in the southeast and low topography in the northwest. The existing exploration data show that the Zhangye basin is rich in hydrothermal geothermal resources. Based on the study of geophysical exploration, geothermal drilling, geo-temperature measurement and hydrogeochemistry, this paper analyzes the occurrence characteristics of geothermal resources and discusses the genetic mode in Zhangye Basin. The geothermal field in the Zhangye basin belongs to the sedimentary basin type of low-medium temperature. The geothermal reservoir is composed of sandstone and glutenite of Neogene Baiyanghe Formation with layered distribution. Temperature of the geothermal reservoir ranges from 47 to 82 °C calculated by using the potassium magnesium geochemical temperature standard. The caprock consists of mudstone of Neogene Shulehe Formation and Quaternary unconsolidated sediments. The geothermal water type is mainly clastic pore water. The characteristics of hydrogen and oxygen isotope indicate that the main recharge source is atmospheric precipitation in the southern Qilian Mountains. The deep faults in the northern margin of Qilian Mountains and NNW-trending basement faults in the basin are good conduits for deep circulation of the geothermal fluids. After receiving recharge, groundwater migrates along the water-conducting fault zones or rock pore fractures. Heating by the deep heat conduction, it occurs in the pores of clastic rocks and forms geothermal resources in this area. The results of hydrochemical analyses show that the geothermal water in this area belongs to continental sedimentary water containing dissolved water in rock salt formation, and the hydrochemical type is of Cl·SO4—Na. The contents of fluorine, SiO2, total dissolved solids and total hardness increase with the increasing water temperature. The tritium value of hot water in the area is generally less than 2.0 TU, indicating that the formation age is relatively early. The results of carbon-14 analysis further confirm that the formation age of the regional geothermal water is more than 20,000 years, reflecting the characteristics of a long geothermal fluid supply path and slow runoff. The research results can provide important reference for exploration and utilization of geothermal resources in the Zhangye Basin.
A study of soil thermal conductivity measurement based on the actively heated distributed temperature sensing cable
YAO Juncheng, LIU Jie, WANG Jinlu, SUN Mengya, FANG Ke, SHI Bin
2023, 50(1): 179-188.   doi: 10.16030/j.cnki.issn.1000-3665.202111076
Abstract(105) HTML(93) PDF (3989KB)(102)
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The actively heated distributed temperature sensing technology (AH-DTS) can realize distributed continuous measurement of the soil thermal conductivity in different layers through optical cables implanted in the soil. However, the accuracy and sensitivity of soil thermal conductivity measurement by AH-DTS method need to be further studied. Through designing indoor tests with the loess, the aim of this study is to compare the thermal response process and the soil thermal conductivity measured by carbon fiber heated cable (CFHC) and copper-mesh heated cable (CMHC) under different heating strategies. The numerical simulation is used to furtherly verify the influence of the optical cable structure on the thermal conductivity measurement results. The results show that the thermal response process of CFHC and CMHC can be divided into three stages: Internal heat transfer of optical cable, fiber-soil transition and stable heat transfer of soil. The difference in optical cable structure will lead to different heat transfer rates, which makes the initial time of thermal conductivity measurement of CFHC 100 s earlier than that of CMHC. The temperature rise value of CFHC is higher under the difference of optical cable size and specific heat capacity. The thermal conductivity measurement result of CFHC is more stable and accurate than CMHC under the same DTS temperature measurement accuracy. Increasing the heating power or increasing the heating time will improve the accuracy of the soil thermal conductivity measurement by CFHC and CMHC. The research results provide an important basis for further improvement and promotion of this technology.
Groundwater pollution risk evaluation of pharmaceuticals and personal care products in land application of sludge
WU Lin, SHI Guowei, LIU Yaci, LI Yasong, LI Qingsheng
2023, 50(1): 189-196.   doi: 10.16030/j.cnki.issn.1000-3665.202202028
Abstract(136) HTML(129) PDF (3370KB)(150)
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In order to further clarify the groundwater pollution risk of the pharmaceutical and personal care products (PPCPs), also known as emerging organic contaminants, in land application of sludge, groundwater pollution risks of 29 PPCPs under sand and loam soil conditions are primarily evaluated using a mathematical model. The results show that ciprofloxacin, ofloxacin, oxytetracycline, norfloxacin and caffeine have risk index values higher than 1 under sand soil conditions, indicating high groundwater pollution risks. Except caffeine, all the other 4 PPCPs with high groundwater pollution risks are antibiotics, which need to be further monitored and controlled in groundwater. Under loam soil conditions, all the 29 PPCPs show low groundwater pollution risks. Sorption is the main factor affecting the groundwater pollution risk of PPCPs. Sensitivity analyses indicate that the half-life of PPCPs in soil, organic carbon partition coefficient, soil density, organic carbon content and depth of the zone with organic matter are the key parameters affecting the model output. Uncertainty analyses show that changes in the organic carbon partition coefficient and half-life of PPCPs in soil have great impact on groundwater pollution risks. Test and verification show that PPCPs with higher groundwater pollution risk index values had higher detection rates in groundwater, indicating that the evaluation results are reliable. Further researches on degradation products of PPCPs, their safe levels in groundwater, interactions between coexisting PPCPs and medium heterogeneity effects should be strengthened in order to evaluate the groundwater pollution risk of PPCPs with reasonable accuracy.
Spatial distribution characteristics of soil thickness in the Zhenfeng-GuanlingHuajiang karst rocky desertification area in Guizhou Province
DENG Dapeng, LIU Qi, LU Yaoru, YAN Yiquan
2023, 50(1): 197-206.   doi: 10.16030/j.cnki.issn.1000-3665.202111005
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Soil thickness is closely related to the development degree of rocky desertification, and soil is the basis of ecological restoration and agricultural production in karst rocky desertification areas. In order to examine the spatial distribution law of soil thickness in typical plateau rocky desertification areas, by combining field investigation of soil thickness with geostatistic methods, this paper analyzes the spatial distribution characteristics of soil thickness and its influencing factors in the karst plateau gorge area of the Zhenfeng-Guanling Huajiang small watershed in Guizhou. The results show that the average soil thickness in the study area is only 26 cm, and the average thickness of soil is: Slope farmland > wasteland > forest land. The spatial variability of soil thickness in the study area is mainly intensity. The spatial distribution continuity of soil thickness in wasteland is better than that of forest land and slope farmland. The spatial distribution of soil thickness in forest land has obvious mutation. The soil thickness in slope farmland is characterized by point distribution, and the soil thickness near crops is large. There are significant negative correlations between soil thickness and altitude, bedrock exposure rate and slope. Serious soil erosion under natural and man-made effect is the main reason for the uneven distribution of soil thickness in the study area, and the combination of engineering measures and biological measures can be used to control rocky desertification in the study area. The results are of guiding significance for the control of rocky desertification in the study area and control of soil erosion, ecological restoration and rational agricultural production in other similar areas.