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Emergency rapid assessment of landslides induced by the Luding Ms 6.8 earthquake in Sichuan of China
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doi: 10.16030/j.cnki.issn.1000-3665.202209057
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2023, 50(1): 1-2.
doi: 10.16030/j.cnki.issn.1000-3665.202209031
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2023, 50(1): 3-12.
doi: 10.16030/j.cnki.issn.1000-3665.202112011
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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.
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.
2023, 50(1): 13-20.
doi: 10.16030/j.cnki.issn.1000-3665.202204007
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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.
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.
2023, 50(1): 21-31.
doi: 10.16030/j.cnki.issn.1000-3665.202201025
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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.
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.
2023, 50(1): 32-40.
doi: 10.16030/j.cnki.issn.1000-3665.202110013
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.
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.
2023, 50(1): 41-50.
doi: 10.16030/j.cnki.issn.1000-3665.202201036
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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.
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.
2023, 50(1): 51-59.
doi: 10.16030/j.cnki.issn.1000-3665.202111055
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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.
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.
2023, 50(1): 60-68.
doi: 10.16030/j.cnki.issn.1000-3665.202205038
Abstract:
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.
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.
2023, 50(1): 69-77.
doi: 10.16030/j.cnki.issn.1000-3665.202112040
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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.
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.
2023, 50(1): 78-86.
doi: 10.16030/j.cnki.issn.1000-3665.202205027
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.
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.
2023, 50(1): 87-93.
doi: 10.16030/j.cnki.issn.1000-3665.202110048
Abstract:
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.
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.
2023, 50(1): 94-103.
doi: 10.16030/j.cnki.issn.1000-3665.202202042
Abstract:
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.
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.
2023, 50(1): 104-112.
doi: 10.16030/j.cnki.issn.1000-3665.202204014
Abstract:
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.
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.
2023, 50(1): 113-121.
doi: 10.16030/j.cnki.issn.1000-3665.202204054
Abstract:
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.
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.
2023, 50(1): 122-131.
doi: 10.16030/j.cnki.issn.1000-3665.202203034
Abstract:
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.
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.
2023, 50(1): 132-143.
doi: 10.16030/j.cnki.issn.1000-3665.202205041
Abstract:
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.
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.
2023, 50(1): 144-151.
doi: 10.16030/j.cnki.issn.1000-3665.202205004
Abstract:
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.
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.
2023, 50(1): 152-157.
doi: 10.16030/j.cnki.issn.1000-3665.202201050
Abstract:
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.
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.
2023, 50(1): 158-167.
doi: 10.16030/j.cnki.issn.1000-3665.202205017
Abstract:
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.
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.
2023, 50(1): 168-178.
doi: 10.16030/j.cnki.issn.1000-3665.202202050
Abstract:
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.
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.
2023, 50(1): 179-188.
doi: 10.16030/j.cnki.issn.1000-3665.202111076
Abstract:
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.
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.
2023, 50(1): 189-196.
doi: 10.16030/j.cnki.issn.1000-3665.202202028
Abstract:
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.
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.
2023, 50(1): 197-206.
doi: 10.16030/j.cnki.issn.1000-3665.202111005
Abstract:
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.
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.
Supervisor: China Geological Survey
Sponsor: China Institute of Geo-Environment Monitoring
Chief Editor: Li WenPeng
Editor&Publication: Editorial Office of Hydrogeology & Engineering Geology
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010-60850956 (宗老师)
010-60850960 (张老师)
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