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2023, 50(3): 1-11.
doi: 10.16030/j.cnki.issn.1000-3665.202211048
Abstract:
Tight sandstone gas is an important unconventional natural gas resource. Mineral characteristics of the tight sandstone not only affect the occurrence of gas, but also have a significant impact on the hydraulic fracturing effectiveness. The potential influence of tight sandstone mineral compositions and microscopic morphology on gas reservoir during hydraulic fracturing was seldom examined. In this study, five tight sandstone gas wells in the Sulige gasfield located in the Ordos Basin were drilled. The core samples of the 8th formation of the lower member of the Permian Shihezi Group (He 8) were collected. The mineral characteristics, microstructure and pore feature of the tight sandstone are systematically analyzed by using XRF, XRD, casting thin section, SEM and EDS technologies and the potential effects of the above factors on hydraulic fracturing are discussed. The results show that the tight sandstone is mainly composed of lithic sandstone and lithic quartz sandstone. The density of the tight sandstone ranges from 2.44 to 2.56 g/cm3, the porosity from 7.7% to 12.6%, and the permeability from 0.16 to 1.42 mD. The mineral compositions are mainly quartz and clay minerals (16.5%−47.4%), and feldspar and carbonate are absent. Kaolinite, illite and chlorite are the main clay minerals. Kaolinite is widely developed, filling the intergranular pores and surface in the forms of “booklets” and worm-like. The intergranular pores, intragranular solution voids, intergranular and intragranular fractures occur in the tight sandstone, which provide basic reservoir space for natural gas. The results of mineral analysis and fracturing fluid-tight sandstone interactions reveal that the stability of clay minerals, especially kaolinite and illite, are crucial for hydraulic fracturing in the Sulige gasfield. It is necessary to understand the mineral compositions and formation water of the tight reservoir and select the appropriate clay stabilizer to optimize hydraulic fracturing.
Tight sandstone gas is an important unconventional natural gas resource. Mineral characteristics of the tight sandstone not only affect the occurrence of gas, but also have a significant impact on the hydraulic fracturing effectiveness. The potential influence of tight sandstone mineral compositions and microscopic morphology on gas reservoir during hydraulic fracturing was seldom examined. In this study, five tight sandstone gas wells in the Sulige gasfield located in the Ordos Basin were drilled. The core samples of the 8th formation of the lower member of the Permian Shihezi Group (He 8) were collected. The mineral characteristics, microstructure and pore feature of the tight sandstone are systematically analyzed by using XRF, XRD, casting thin section, SEM and EDS technologies and the potential effects of the above factors on hydraulic fracturing are discussed. The results show that the tight sandstone is mainly composed of lithic sandstone and lithic quartz sandstone. The density of the tight sandstone ranges from 2.44 to 2.56 g/cm3, the porosity from 7.7% to 12.6%, and the permeability from 0.16 to 1.42 mD. The mineral compositions are mainly quartz and clay minerals (16.5%−47.4%), and feldspar and carbonate are absent. Kaolinite, illite and chlorite are the main clay minerals. Kaolinite is widely developed, filling the intergranular pores and surface in the forms of “booklets” and worm-like. The intergranular pores, intragranular solution voids, intergranular and intragranular fractures occur in the tight sandstone, which provide basic reservoir space for natural gas. The results of mineral analysis and fracturing fluid-tight sandstone interactions reveal that the stability of clay minerals, especially kaolinite and illite, are crucial for hydraulic fracturing in the Sulige gasfield. It is necessary to understand the mineral compositions and formation water of the tight reservoir and select the appropriate clay stabilizer to optimize hydraulic fracturing.
2023, 50(3): 12-22.
doi: 10.16030/j.cnki.issn.1000-3665.202208008
Abstract:
There are abundant phreatic water in loess tablelands in the Loess Plateau of northwest China. The vertical infiltration of atmospheric precipitation is the main source of the recharge, but the spatial channels of water occurrence and migration in loess are still ambiguous. Based on the geomorphology, strata structure and other hydrogeological conditions, groundwater utilization condition and related experimental data of the Dongzhiyuan and Weibei loess tablelands, combined with scanning electron microscope image processing and statistical analysis, the pore characteristics and the migration processes of water in the loess phreatic and aeration zones are discussed and zoned. Pores are considered to be the main space channel for the occurrence and migration of loess groundwater, and the minimum equivalent pore size of seepage is about 12 μm. The vertical structural combination of the loess aeration zone composed of the Malan loess with developed pores in the upper part is conducive to the infiltration of atmospheric precipitation, and the water migration in the pores of the aeration zone is very weak and slow, but is relatively continuous and uniform. The aeration zone can be divided into four zones for loess: the climate impact zone, storage regulation zone, slow runoff zone and capillary receiving zone. Except for the upper climate impact zone, the other three zones are in a basically dynamic equilibrium state of water transport. The research results can provide important references for comprehensively and systematically understanding the characteristics of water transport in the aeration zone of loess tablelands.
There are abundant phreatic water in loess tablelands in the Loess Plateau of northwest China. The vertical infiltration of atmospheric precipitation is the main source of the recharge, but the spatial channels of water occurrence and migration in loess are still ambiguous. Based on the geomorphology, strata structure and other hydrogeological conditions, groundwater utilization condition and related experimental data of the Dongzhiyuan and Weibei loess tablelands, combined with scanning electron microscope image processing and statistical analysis, the pore characteristics and the migration processes of water in the loess phreatic and aeration zones are discussed and zoned. Pores are considered to be the main space channel for the occurrence and migration of loess groundwater, and the minimum equivalent pore size of seepage is about 12 μm. The vertical structural combination of the loess aeration zone composed of the Malan loess with developed pores in the upper part is conducive to the infiltration of atmospheric precipitation, and the water migration in the pores of the aeration zone is very weak and slow, but is relatively continuous and uniform. The aeration zone can be divided into four zones for loess: the climate impact zone, storage regulation zone, slow runoff zone and capillary receiving zone. Except for the upper climate impact zone, the other three zones are in a basically dynamic equilibrium state of water transport. The research results can provide important references for comprehensively and systematically understanding the characteristics of water transport in the aeration zone of loess tablelands.
2023, 50(3): 23-33.
doi: 10.16030/j.cnki.issn.1000-3665.202208004
Abstract:
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 0.25. 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.
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 0.25. 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.
2023, 50(3): 34-43.
doi: 10.16030/j.cnki.issn.1000-3665.202206021
Abstract:
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 and exploration sites, human activities 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.
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 and exploration sites, human activities 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.
2023, 50(3): 44-53.
doi: 10.16030/j.cnki.issn.1000-3665.202208065
Abstract:
Knowledge of the recharge from surface water to groundwater is the basement of the scientific understanding of water cycle and the sustainable management of groundwater resources. Meanwhile, the layered heterogeneity is the main structural feature of riverbed sediments (i.e., the lithologic difference between riverbed sediments and the underlying aquifer) and the main factor that controlling the recharge from surface water to groundwater. To reveal the influence mechanism of layered structure of pore media on the recharge from surface water to groundwater, a conceptual model of surface water and groundwater interaction is established based on the field test results of Henan reaches of the Yellow River, and the process of the recharge from surface water to groundwater interaction is described using flow path as the object. The results show that the exchange flux of surface water and groundwater is mainly affected by hydraulic conductivity of riverbed sediments, and the change of the thickness of riverbed sediments has little effect on the exchange flux between surface water and groundwater. That is, the increase of the ratio of the thickness of the sediments to that of the underlying aquifer (HS/H) from 0 to 0.125 leads to the interaction flux decreased by 72%, indicating that the existence of the low permeability layer is the main reason that decreases the interaction flux between surface water and groundwater. The change of the permeability and the thickness of riverbed sediments has obviously changed the flow path from surface water to groundwater and the travel time. Specifically, the increase in KU/KL leads to a lager penetration depth of groundwater flow and lager travel times. The sensitivity of exchange flux between surface water and groundwater and groundwater travel time to the hydraulic conductivity of riverbed sediments increases with the decreasing hydraulic conductivity. At the same time, the groundwater travel time is more sensitive to the change of the thickness of the low permeability riverbed sediments, and the sensitivity increases with the increasing thickness. The research results can provide reference for groundwater resource management and sustainable development.
Knowledge of the recharge from surface water to groundwater is the basement of the scientific understanding of water cycle and the sustainable management of groundwater resources. Meanwhile, the layered heterogeneity is the main structural feature of riverbed sediments (i.e., the lithologic difference between riverbed sediments and the underlying aquifer) and the main factor that controlling the recharge from surface water to groundwater. To reveal the influence mechanism of layered structure of pore media on the recharge from surface water to groundwater, a conceptual model of surface water and groundwater interaction is established based on the field test results of Henan reaches of the Yellow River, and the process of the recharge from surface water to groundwater interaction is described using flow path as the object. The results show that the exchange flux of surface water and groundwater is mainly affected by hydraulic conductivity of riverbed sediments, and the change of the thickness of riverbed sediments has little effect on the exchange flux between surface water and groundwater. That is, the increase of the ratio of the thickness of the sediments to that of the underlying aquifer (HS/H) from 0 to 0.125 leads to the interaction flux decreased by 72%, indicating that the existence of the low permeability layer is the main reason that decreases the interaction flux between surface water and groundwater. The change of the permeability and the thickness of riverbed sediments has obviously changed the flow path from surface water to groundwater and the travel time. Specifically, the increase in KU/KL leads to a lager penetration depth of groundwater flow and lager travel times. The sensitivity of exchange flux between surface water and groundwater and groundwater travel time to the hydraulic conductivity of riverbed sediments increases with the decreasing hydraulic conductivity. At the same time, the groundwater travel time is more sensitive to the change of the thickness of the low permeability riverbed sediments, and the sensitivity increases with the increasing thickness. The research results can provide reference for groundwater resource management and sustainable development.
2023, 50(3): 54-64.
doi: 10.16030/j.cnki.issn.1000-3665.202208084
Abstract:
As one of the important ecosystem service functions, water conservation function is of great significance to the ecosystem and water safety in the Zhangjiakou and Chengde districts. Based on the integrated valuation of ecosystem services and tradeoffs (InVEST) model, this study quantitatively evaluates the water conservation function and analyses its driving factors of the Zhang-Cheng district from 2001 to 2020 using high-quality remote sensing data and other reanalysis products, in order to improve the problems of insufficient consideration of topography and soil permeability, as well as the inadequate analyses of data spatial heterogeneity in previous studies. The results show that the spatial distribution of the water conservation function in the Zhang-Cheng district from 2001 to 2020 was characterized by high values in the Baxia areas and low values in the Bashang areas. Despite some differences, the spatial distribution of the water conservation function in each year had some similarities to some extent. In terms of the trend, the water conservation depth in these 20 years showed a fluctuating downward trend with an average rate of −0.08 mm/a. Combined with the Sen+Mann-Kendall analysis, the trend of the water conservation function in this area was mainly classified as "No trend", "Slight increase" and "Slight decrease", accounting for nearly 98% of the total area. The results of correlation analysis show that precipitation had a strongly significantly positive correlation with water conservation function, temperature had a significantly negative correlation with water conservation function in some areas, and the correlation between vegetation and water conservation function was complex. In the Zhang-Cheng district in 2020, the woodland had the strongest water conservation function, and the water conservation depth reached 28.64 mm. On the other hand, the grassland water conservation function had the greatest contribution in the total amount, and the water conservation reached 1.12×109 m3. During these 20 years, the water conservation of the farmland had the most obvious decrease, with a rate of −6.49×106 m3/a. The spatio-temporal change characteristics of water conservation function in the Zhang-Cheng district in these 20 years were mainly controlled by precipitation and vegetated land use. This study provides an important decision-making basis for ecological construction and water resources management in the Zhangcheng district.
As one of the important ecosystem service functions, water conservation function is of great significance to the ecosystem and water safety in the Zhangjiakou and Chengde districts. Based on the integrated valuation of ecosystem services and tradeoffs (InVEST) model, this study quantitatively evaluates the water conservation function and analyses its driving factors of the Zhang-Cheng district from 2001 to 2020 using high-quality remote sensing data and other reanalysis products, in order to improve the problems of insufficient consideration of topography and soil permeability, as well as the inadequate analyses of data spatial heterogeneity in previous studies. The results show that the spatial distribution of the water conservation function in the Zhang-Cheng district from 2001 to 2020 was characterized by high values in the Baxia areas and low values in the Bashang areas. Despite some differences, the spatial distribution of the water conservation function in each year had some similarities to some extent. In terms of the trend, the water conservation depth in these 20 years showed a fluctuating downward trend with an average rate of −0.08 mm/a. Combined with the Sen+Mann-Kendall analysis, the trend of the water conservation function in this area was mainly classified as "No trend", "Slight increase" and "Slight decrease", accounting for nearly 98% of the total area. The results of correlation analysis show that precipitation had a strongly significantly positive correlation with water conservation function, temperature had a significantly negative correlation with water conservation function in some areas, and the correlation between vegetation and water conservation function was complex. In the Zhang-Cheng district in 2020, the woodland had the strongest water conservation function, and the water conservation depth reached 28.64 mm. On the other hand, the grassland water conservation function had the greatest contribution in the total amount, and the water conservation reached 1.12×109 m3. During these 20 years, the water conservation of the farmland had the most obvious decrease, with a rate of −6.49×106 m3/a. The spatio-temporal change characteristics of water conservation function in the Zhang-Cheng district in these 20 years were mainly controlled by precipitation and vegetated land use. This study provides an important decision-making basis for ecological construction and water resources management in the Zhangcheng district.
2023, 50(3): 65-75.
doi: 10.16030/j.cnki.issn.1000-3665.202104015
Abstract:
Mine inflow threats mine safety production underground, and may trigger a decline in the groundwater level in the mine area, causing irreversible successional degradation of surface vegetation. In view of the key problems such as inaccurate generalization of boundary conditions and unreliable selection of hydrogeological parameters when constructing numerical models of water inflow, this study aims to accurately predict mine water inflow, ensure the safe mining of coal seams, and provide theoretical and data support for the protection of desert vegetation in the study area. The natural boundary is selected as the perimeter of the research area, and the model is repeatedly revised on the basis of fully collecting and analyzing the data of drilling, geophysical prospecting, pumping test, groundwater long-term monitering, and the scope of the mine goaf and its water inflow, and thus a more realistic three-dimensional unstable flow numerical model of groundwater is constructed. In addition, the model simulation and identification are carried out according to the expansion process of the mine goaf and its water inflow and groundwater monitoring data, which demonstrates the rationality and reliability of the model. The established numerical model is used to predict the mine inflow and submersible level depth drop under coal seam mining conditions, and then the influence of diving level decline on desert vegetation is analyzed based on the relationship between diving depth and desert vegetation. The results show that the predicted water inflow in the mine is 3.08×104 m3/d, resulting in a decrease of 2.08−2.35 m in the diving level in the mine area, which will lead to the deterioration or even partial withering of the representative vegetation sand willow and poplar in the mine area, showing a succession trend from mesophytic vegetation type to xerophytic vegetation. The results can provide more accurate water inflow prediction in the study area, scientific and effective measures for the protection of desert vegetation in mining areas, and reliable treatment ideas for the construction of similar numerical models of groundwater flow.
Mine inflow threats mine safety production underground, and may trigger a decline in the groundwater level in the mine area, causing irreversible successional degradation of surface vegetation. In view of the key problems such as inaccurate generalization of boundary conditions and unreliable selection of hydrogeological parameters when constructing numerical models of water inflow, this study aims to accurately predict mine water inflow, ensure the safe mining of coal seams, and provide theoretical and data support for the protection of desert vegetation in the study area. The natural boundary is selected as the perimeter of the research area, and the model is repeatedly revised on the basis of fully collecting and analyzing the data of drilling, geophysical prospecting, pumping test, groundwater long-term monitering, and the scope of the mine goaf and its water inflow, and thus a more realistic three-dimensional unstable flow numerical model of groundwater is constructed. In addition, the model simulation and identification are carried out according to the expansion process of the mine goaf and its water inflow and groundwater monitoring data, which demonstrates the rationality and reliability of the model. The established numerical model is used to predict the mine inflow and submersible level depth drop under coal seam mining conditions, and then the influence of diving level decline on desert vegetation is analyzed based on the relationship between diving depth and desert vegetation. The results show that the predicted water inflow in the mine is 3.08×104 m3/d, resulting in a decrease of 2.08−2.35 m in the diving level in the mine area, which will lead to the deterioration or even partial withering of the representative vegetation sand willow and poplar in the mine area, showing a succession trend from mesophytic vegetation type to xerophytic vegetation. The results can provide more accurate water inflow prediction in the study area, scientific and effective measures for the protection of desert vegetation in mining areas, and reliable treatment ideas for the construction of similar numerical models of groundwater flow.
2023, 50(3): 76-84.
doi: 10.16030/j.cnki.issn.1000-3665.202211007
Abstract:
Embedded piles act as an optimization structure compared with the traditional stabilizing pile. The determination of the thrust on the loading section is based mainly on the model test and numerical simulation, and there is a lack of in-depth theoretical analysis. For the bedrock-talus landslide reinforced by embedded piles, according to the potential overtop-sliding failure mode, the slide surface can be divided into top and bottom sections by the position of pile top, and the horizontal resultant force of the top section can be obtained by integration, which is the so-called thrust of the embedded section. Similarly, the force on the bottom section of the overtop-sliding surface can also be obtained. Based on the limit equilibrium theory, the force analysis of the sliding mass enclosed by the bottom sliding surface and the load section of the pile can be carried out, and the thrust on the loaded section can also be obtained. Example analyses show that the thrust of the embedded section and the loaded section obtained by the theoretical method are very consistent with the results of FLAC3D, the resultant force of the loading section decreases nonlinearly with the increase of the ratio, while the resultant force of the embedded section presents an opposite trend. With the increase of the embedded ratio from 0 to 0.67, the thrust ratio of embedded section and loading section increases slowly from 0 to 0.3−0.5. With the increase of embedded ratio from 0.67 to 0.8, the ratio increases sharply to 1.47−2.12. Generally, the thrust of embedded section is less than that of loaded section. The theoretical research of the thrust of the embedded pile is of great practical significance for the optimization of the pile internal force and the determination of the pile embedded depth, which will promote the further application of this structure.
Embedded piles act as an optimization structure compared with the traditional stabilizing pile. The determination of the thrust on the loading section is based mainly on the model test and numerical simulation, and there is a lack of in-depth theoretical analysis. For the bedrock-talus landslide reinforced by embedded piles, according to the potential overtop-sliding failure mode, the slide surface can be divided into top and bottom sections by the position of pile top, and the horizontal resultant force of the top section can be obtained by integration, which is the so-called thrust of the embedded section. Similarly, the force on the bottom section of the overtop-sliding surface can also be obtained. Based on the limit equilibrium theory, the force analysis of the sliding mass enclosed by the bottom sliding surface and the load section of the pile can be carried out, and the thrust on the loaded section can also be obtained. Example analyses show that the thrust of the embedded section and the loaded section obtained by the theoretical method are very consistent with the results of FLAC3D, the resultant force of the loading section decreases nonlinearly with the increase of the ratio, while the resultant force of the embedded section presents an opposite trend. With the increase of the embedded ratio from 0 to 0.67, the thrust ratio of embedded section and loading section increases slowly from 0 to 0.3−0.5. With the increase of embedded ratio from 0.67 to 0.8, the ratio increases sharply to 1.47−2.12. Generally, the thrust of embedded section is less than that of loaded section. The theoretical research of the thrust of the embedded pile is of great practical significance for the optimization of the pile internal force and the determination of the pile embedded depth, which will promote the further application of this structure.
2023, 50(3): 85-92.
doi: 10.16030/j.cnki.issn.1000-3665.202208017
Abstract:
In order to accurately predict the effect of crack on the rockmass compression mechanical property such as strength and stiffness, a more reasonable compression damage model for the cracked rockmass is needed to be established. On basis of the relevant experimental data and mechanical behavior of the cracked rockmass under uniaxial compression, some deficiencies in the existing compression damage models for the rockmass with intermittent cracks are analyzed in detail. Three improvements are made to improve the existing methods, e.g., the crack deformation parameter is not taken as a constant, the negative first stress intensity factor KI produced by the normal stress on the crack face is considered, and KI produced by the effective shear stress on the crack face is considered. A revised uniaxial compression damage model for rockmass considering the crack deformation parameter is proposed and the validity of the proposed model is verified with the experimental data. The results show that the prediction of the rockmass elastic modulus and damage under uniaxial compression with the proposed model are more accurate than those obtained with the existing models. Especially, when the crack dip angel is 0°, the rockmass elastic modulus obtained with the proposed model is 4.306 MPa, which is nearly equal to its tested value 4.310 MPa. The proposed model can perfectly describe the rockmass mechanical behavior under uniaxial compression, which also indicates that it is very necessary to consider the effect of the crack deformation parameter on the rockmass uniaxial compression mechanical property. This study can provide references for accurately predicting the rockmass mechanical behavior under uniaxial compression.
In order to accurately predict the effect of crack on the rockmass compression mechanical property such as strength and stiffness, a more reasonable compression damage model for the cracked rockmass is needed to be established. On basis of the relevant experimental data and mechanical behavior of the cracked rockmass under uniaxial compression, some deficiencies in the existing compression damage models for the rockmass with intermittent cracks are analyzed in detail. Three improvements are made to improve the existing methods, e.g., the crack deformation parameter is not taken as a constant, the negative first stress intensity factor KI produced by the normal stress on the crack face is considered, and KI produced by the effective shear stress on the crack face is considered. A revised uniaxial compression damage model for rockmass considering the crack deformation parameter is proposed and the validity of the proposed model is verified with the experimental data. The results show that the prediction of the rockmass elastic modulus and damage under uniaxial compression with the proposed model are more accurate than those obtained with the existing models. Especially, when the crack dip angel is 0°, the rockmass elastic modulus obtained with the proposed model is 4.306 MPa, which is nearly equal to its tested value 4.310 MPa. The proposed model can perfectly describe the rockmass mechanical behavior under uniaxial compression, which also indicates that it is very necessary to consider the effect of the crack deformation parameter on the rockmass uniaxial compression mechanical property. This study can provide references for accurately predicting the rockmass mechanical behavior under uniaxial compression.
2023, 50(3): 93-103.
doi: 10.16030/j.cnki.issn.1000-3665.202201042
Abstract:
The coefficient of permeability is an important index to evaluate the migration and diffusion of heavy metal polluted liquid in remodeled loess. At present, the existing studies have shown that there is a certain correlation among the pH value, the value of electrical conductivity, ion content and saturated coefficient of permeability of the polluted liquid, but the geochemical reaction mechanism during the infiltration process has not been clarified. Therefore, the Qp loess in the Bailuyuan area of Xi’an is collected, and the Cu2+ solution is selected as the infiltration solution to carry out the saturated infiltration test of the reshaped loess, and the geochemical inversion model based on the Netpath software is established. The results show that the saturated coefficient of permeability decreases significantly from the first day during the test, and has a larger decrease compared with the deionized test group, with a range of 5.57×10−5 cm/s. The ion source analysis proves that the geochemical reaction occurs, including mineral dissolution, precipitation and cation exchange. The geochemical inversion simulation results show that the presence of Cu2+ aggravates the mineral dissolution and produces a large amount of Ca2+, which promotes the leftward shift of the carbonate mineral dissolution balance, starting from the first day continual calcite and dolomite precipitation, and the precipitation amounts are 1.912 mmol and 0.958 mmol, respectively, which blocked the seepage pores and reduced the coefficient of permeability of the soil. The results are helpful in understanding the change of the saturated the permeability coefficient of the remodeled loess during the intrusion of heavy metal ions, and are of important theoretical significance for further clarifying the geochemical mechanism affecting the change of the permeability coefficient.
The coefficient of permeability is an important index to evaluate the migration and diffusion of heavy metal polluted liquid in remodeled loess. At present, the existing studies have shown that there is a certain correlation among the pH value, the value of electrical conductivity, ion content and saturated coefficient of permeability of the polluted liquid, but the geochemical reaction mechanism during the infiltration process has not been clarified. Therefore, the Qp loess in the Bailuyuan area of Xi’an is collected, and the Cu2+ solution is selected as the infiltration solution to carry out the saturated infiltration test of the reshaped loess, and the geochemical inversion model based on the Netpath software is established. The results show that the saturated coefficient of permeability decreases significantly from the first day during the test, and has a larger decrease compared with the deionized test group, with a range of 5.57×10−5 cm/s. The ion source analysis proves that the geochemical reaction occurs, including mineral dissolution, precipitation and cation exchange. The geochemical inversion simulation results show that the presence of Cu2+ aggravates the mineral dissolution and produces a large amount of Ca2+, which promotes the leftward shift of the carbonate mineral dissolution balance, starting from the first day continual calcite and dolomite precipitation, and the precipitation amounts are 1.912 mmol and 0.958 mmol, respectively, which blocked the seepage pores and reduced the coefficient of permeability of the soil. The results are helpful in understanding the change of the saturated the permeability coefficient of the remodeled loess during the intrusion of heavy metal ions, and are of important theoretical significance for further clarifying the geochemical mechanism affecting the change of the permeability coefficient.
2023, 50(3): 104-114.
doi: 10.16030/j.cnki.issn.1000-3665.202202049
Abstract:
The Shuitoushang landslide in Ershe in Qijiagou Village of Xinchang Town in Tongjiang County is a typical red-bed terrace landslide in eastern Sichuan. There are few studies on the seepage analyses of such landslides in this area, but similar slopes are widely distributed in the area. In this paper, on the basis of a large number of field investigations, surveys and data collection of disaster sites, the satellite remote sensing, UAV aerial photography, airborne LiDAR, indoor tests and other technical means are comprehensively used to analysis the landslide. Based on the mathematical model of Fredlund & Xing soil-water characteristic curve, the SEEP/W module in Geo-Studio is used to conduct the seepage analysis, and the analysis results at different time stages are coupled with the SLOPE/W module. Then the dynamic relationship between the stability coefficient, rainfall and time is obtained, revealing the deformation process and formation mechanism of the landslide. The results show that: (1) the continuous rainfall causes the groundwater level to rise and the slope stability to decrease, eventually leading to the overall instability and failure of the Shuitoushang landslide. (2) The deformation process of the landslide and the characteristics of groundwater exposure are basically consistent with the results calculated by Geo-Studio, indicating that the results based on Fredlund & Xing model can provide more accurate simulation results in similar areas. (3) Reclamation of terraced fields (paddy fields) will reduce slope stability. The results can provide theoretical support for hidden danger investigation and active prevention of similar landslide disasters in mountainous areas of Sichuan, and provide a reference for disaster prevention and mitigation.
The Shuitoushang landslide in Ershe in Qijiagou Village of Xinchang Town in Tongjiang County is a typical red-bed terrace landslide in eastern Sichuan. There are few studies on the seepage analyses of such landslides in this area, but similar slopes are widely distributed in the area. In this paper, on the basis of a large number of field investigations, surveys and data collection of disaster sites, the satellite remote sensing, UAV aerial photography, airborne LiDAR, indoor tests and other technical means are comprehensively used to analysis the landslide. Based on the mathematical model of Fredlund & Xing soil-water characteristic curve, the SEEP/W module in Geo-Studio is used to conduct the seepage analysis, and the analysis results at different time stages are coupled with the SLOPE/W module. Then the dynamic relationship between the stability coefficient, rainfall and time is obtained, revealing the deformation process and formation mechanism of the landslide. The results show that: (1) the continuous rainfall causes the groundwater level to rise and the slope stability to decrease, eventually leading to the overall instability and failure of the Shuitoushang landslide. (2) The deformation process of the landslide and the characteristics of groundwater exposure are basically consistent with the results calculated by Geo-Studio, indicating that the results based on Fredlund & Xing model can provide more accurate simulation results in similar areas. (3) Reclamation of terraced fields (paddy fields) will reduce slope stability. The results can provide theoretical support for hidden danger investigation and active prevention of similar landslide disasters in mountainous areas of Sichuan, and provide a reference for disaster prevention and mitigation.
Influence mechanism of vegetation infiltration effect on shallow landslides of granite residual soil
2023, 50(3): 115-124.
doi: 10.16030/j.cnki.issn.1000-3665.202205054
Abstract:
The landslides induced by typhoons and rainstorms in Southern China are often shallow, fluidized and clustered. A large number of investigations have shown that vegetation infiltration has a significant impact on the formation of granite residual soil landslides. However, most of the current studies have focused on the effect of vegetation roots on soil infiltration. The influence mechanism of vegetation infiltration enhancement effect on shallow landslides has not been revealed. Therefore, the mass landslide disaster on September 9, 2019 in Longchuan County in Guangdong is taken as an example, and a large number of landslide site investigations are made to identify the geological environment conditions and vegetation development in the landslide area and analyze the infiltration effect of vegetation on shallow landslides. The “double-ring method” is used to measure infiltration rate of different vegetation types, and to analyze the infiltration process and infiltration law of different vegetation types. A typical landslide profile is selected to establish a geological model, and the Geo-Studio software is used to simulate the seepage law of shallow landslide and the stress-strain characteristics of the soil under heavy rainfall conditions (250 mm/d). Finally, combined with the simulation results and field investigations, the infiltration effects of vegetation and their response mechanisms to shallow landslides under heavy rainfall are analyzed. The results show that vegetation can effectively enhance the permeability of soil, and the order of permeability is coniferous forest land, shrub forest land and bare land. Under the influence of vegetation infiltration effect, rainwater infiltration to the bottom of the root-soil composite layer will cause water stagnation, the shallow soil tends to be saturated rapidly, the pore water pressure and seepage force in the soil increase instantaneously, the soil is saturated with water, the residual soil softens, and the weight of the slope increases, which eventually leads to the overall instability of the slope. The research results explain the formation mechanism of granite residual soil landslide in high vegetation covered area under heavy rainfall in Southern China, and provide scientific basis for early warning and prediction of such disasters, which are of great significance.
The landslides induced by typhoons and rainstorms in Southern China are often shallow, fluidized and clustered. A large number of investigations have shown that vegetation infiltration has a significant impact on the formation of granite residual soil landslides. However, most of the current studies have focused on the effect of vegetation roots on soil infiltration. The influence mechanism of vegetation infiltration enhancement effect on shallow landslides has not been revealed. Therefore, the mass landslide disaster on September 9, 2019 in Longchuan County in Guangdong is taken as an example, and a large number of landslide site investigations are made to identify the geological environment conditions and vegetation development in the landslide area and analyze the infiltration effect of vegetation on shallow landslides. The “double-ring method” is used to measure infiltration rate of different vegetation types, and to analyze the infiltration process and infiltration law of different vegetation types. A typical landslide profile is selected to establish a geological model, and the Geo-Studio software is used to simulate the seepage law of shallow landslide and the stress-strain characteristics of the soil under heavy rainfall conditions (250 mm/d). Finally, combined with the simulation results and field investigations, the infiltration effects of vegetation and their response mechanisms to shallow landslides under heavy rainfall are analyzed. The results show that vegetation can effectively enhance the permeability of soil, and the order of permeability is coniferous forest land, shrub forest land and bare land. Under the influence of vegetation infiltration effect, rainwater infiltration to the bottom of the root-soil composite layer will cause water stagnation, the shallow soil tends to be saturated rapidly, the pore water pressure and seepage force in the soil increase instantaneously, the soil is saturated with water, the residual soil softens, and the weight of the slope increases, which eventually leads to the overall instability of the slope. The research results explain the formation mechanism of granite residual soil landslide in high vegetation covered area under heavy rainfall in Southern China, and provide scientific basis for early warning and prediction of such disasters, which are of great significance.
2023, 50(3): 125-137.
doi: 10.16030/j.cnki.issn.1000-3665.202206041
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 Maojian 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 0.82, 0.88, 0.90 and 0.91, indicating that the SOM-I-SVM model can effectively improve the accuracy of landslide susceptibility prediction.
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 Maojian 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 0.82, 0.88, 0.90 and 0.91, indicating that the SOM-I-SVM model can effectively improve the accuracy of landslide susceptibility prediction.
2023, 50(3): 138-148.
doi: 10.16030/j.cnki.issn.1000-3665.202210038
Abstract:
The active characteristics and genetic mechanism of coupled ground fissures mainly induced by fault activities and pumping are studied, and the Songzhuang Town in Tongzhou District of Beijing is taken as the research archetype. The damage of surface planes and stratigraphic profiles caused by ground fissure activities are clarified through field investigation, and the variation characteristics of the displacement field and stress field of the strata caused by different dislocation amounts and groundwater level drop are revealed. The response processes of the model stratum under the two conditions of fault misalignment and groundwater extraction are simulated and studied respectively by using the finite difference method. Finally, the relationship between this type of ground fissure and the main inducing factors is discussed. The results show that (1) the ground fissure is characterized by three-dimensional activities, which causes the vertical tension of the shallow stratum and wall to be 0.3−1.2 cm, and the vertical dislocation of the deep stratum gradually increases with the burial depth. (2) Stress changes caused by fracture activities are concentrated in the ground fissure development area and lead to significant vertical displacements in the hanging wall, the stratum located in the ground fissure area has large shear and traction deformation, and the vertical displacement difference between the two sides is the largest. The gradual increase of fault dislocations causes the hidden fractures to extend upward, and cause secondary cracks on the shallow surface of the hanging wall, resulting in the overall distribution of ground fissures with a certain width. (3) The vertical extension and horizontal expansion of ground fissures are aggravated by the lowering of groundwater levels, and the surface on both sides of the crack produces continuous settlement response, making the center of the subsidence funnel become a concentrated development area of ground fissures, with the maximum settlement of 10.2 cm in the model stratum at the fissure in its central area, and the settlement range of about 38 m in the hanging wall and about 16 m in the foot wall. (4) This type of ground fissures is obviously controlled by faults, but the increased activity in this period is mainly due to groundwater over-exploitation. This work will be of great theoretical and practical significance to understand ground fissure mechanism, establish quantitative relationship between formation and fault with groundwater, and prevent and reduce disasters.
The active characteristics and genetic mechanism of coupled ground fissures mainly induced by fault activities and pumping are studied, and the Songzhuang Town in Tongzhou District of Beijing is taken as the research archetype. The damage of surface planes and stratigraphic profiles caused by ground fissure activities are clarified through field investigation, and the variation characteristics of the displacement field and stress field of the strata caused by different dislocation amounts and groundwater level drop are revealed. The response processes of the model stratum under the two conditions of fault misalignment and groundwater extraction are simulated and studied respectively by using the finite difference method. Finally, the relationship between this type of ground fissure and the main inducing factors is discussed. The results show that (1) the ground fissure is characterized by three-dimensional activities, which causes the vertical tension of the shallow stratum and wall to be 0.3−1.2 cm, and the vertical dislocation of the deep stratum gradually increases with the burial depth. (2) Stress changes caused by fracture activities are concentrated in the ground fissure development area and lead to significant vertical displacements in the hanging wall, the stratum located in the ground fissure area has large shear and traction deformation, and the vertical displacement difference between the two sides is the largest. The gradual increase of fault dislocations causes the hidden fractures to extend upward, and cause secondary cracks on the shallow surface of the hanging wall, resulting in the overall distribution of ground fissures with a certain width. (3) The vertical extension and horizontal expansion of ground fissures are aggravated by the lowering of groundwater levels, and the surface on both sides of the crack produces continuous settlement response, making the center of the subsidence funnel become a concentrated development area of ground fissures, with the maximum settlement of 10.2 cm in the model stratum at the fissure in its central area, and the settlement range of about 38 m in the hanging wall and about 16 m in the foot wall. (4) This type of ground fissures is obviously controlled by faults, but the increased activity in this period is mainly due to groundwater over-exploitation. This work will be of great theoretical and practical significance to understand ground fissure mechanism, establish quantitative relationship between formation and fault with groundwater, and prevent and reduce disasters.
2023, 50(3): 149-158.
doi: 10.16030/j.cnki.issn.1000-3665.202208066
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. 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 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 inversion result has certain reliability. The research results are of important guiding significance for the construction of tunnels and highways in weak and broken strata in karst areas.
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. 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 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 inversion result has certain reliability. The research results are of important guiding significance for the construction of tunnels and highways in weak and broken strata in karst areas.
2023, 50(3): 159-171.
doi: 10.16030/j.cnki.issn.1000-3665.202112022
Abstract:
Organic pollution of polycyclic aromatic hydrocarbons (PAHs) in topsoil has threatened human health and ecological environment. In order to understand the distribution and pollution characteristics of PAHs in topsoil in the Beiyun River Basin in Beijing, an investigation is carried out to examine the contents, distribution trends, spatial distribution and pollution sources of 16 optimal PAHs in topsoil of the study area by means of multivariate statistical methods including the Kriging interpolation, principal component analysis-multiple linear regression and the concentration ratio among certain components. The results are as follows (1) all 16 PAHs are detected, and most of them are high loop PAHs (4−6 rings). The total contents of PAHs in topsoil range from 10.5 to 19466.5 μg/kg, about 29.63% of the samples are polluted in the study area. (2) The PAHs contents in topsoil show a trend of higher in the middle and lower at ends in both east-west and south-north direction. In terms of spatial distribution, the PAHs contents in topsoil are higher in the northern region and the central urban area, while the PAHs contents are lower in other areas. Due to the accumulation of PAHs caused by human activities at some points, point source pollution or local pollution exist. (3)The ratio of specific PAHs components and principal component analysis indicate that the sources of 16 PAHs in the study area are mainly coal, biomass combustion and traffic combustion. Multiple linear regression shows that the contribution rates of the two are 89% and 11% respectively. The research results can provide strong support for pollution prevention and control, land quality evaluation and territorial space planning in the study area.
Organic pollution of polycyclic aromatic hydrocarbons (PAHs) in topsoil has threatened human health and ecological environment. In order to understand the distribution and pollution characteristics of PAHs in topsoil in the Beiyun River Basin in Beijing, an investigation is carried out to examine the contents, distribution trends, spatial distribution and pollution sources of 16 optimal PAHs in topsoil of the study area by means of multivariate statistical methods including the Kriging interpolation, principal component analysis-multiple linear regression and the concentration ratio among certain components. The results are as follows (1) all 16 PAHs are detected, and most of them are high loop PAHs (4−6 rings). The total contents of PAHs in topsoil range from 10.5 to 19466.5 μg/kg, about 29.63% of the samples are polluted in the study area. (2) The PAHs contents in topsoil show a trend of higher in the middle and lower at ends in both east-west and south-north direction. In terms of spatial distribution, the PAHs contents in topsoil are higher in the northern region and the central urban area, while the PAHs contents are lower in other areas. Due to the accumulation of PAHs caused by human activities at some points, point source pollution or local pollution exist. (3)The ratio of specific PAHs components and principal component analysis indicate that the sources of 16 PAHs in the study area are mainly coal, biomass combustion and traffic combustion. Multiple linear regression shows that the contribution rates of the two are 89% and 11% respectively. The research results can provide strong support for pollution prevention and control, land quality evaluation and territorial space planning in the study area.
2023, 50(3): 172-181.
doi: 10.16030/j.cnki.issn.1000-3665.202108051
Abstract:
Analyzing the temporal and spatial changes of vegetation and its correlation with soil moisture and quantitatively revealing the impact of soil moisture on vegetation growth are of certain significance for drought monitoring and ecological protection. However, previous quantitative researches on soil moisture and vegetation growth are not enough. Based on MOD13Q1 NDVI products and global land data assimilation system (GLDAS) soil moisture data, Sen + Mann Kendall trend test and correlation analysis are used to analyze the temporal and spatial variation characteristics of vegetation and the impact of land use change on vegetation growth in the Yellow River Basin from 2000 to 2020. The correlation between vegetation and soil moisture at different depths in growing season is explored. The results show that (1) the vegetation growth is characterized by “high in the south and low in the north”. Along the runoff direction of the Yellow River, the vegetation growth on the right bank of the upper reaches is significantly better than that on the left bank, and there is no significant difference in the vegetation growth on the two banks of the middle and lower reaches. The NDVI increases by 22.19% from 2000 to 2020, with the highest value of 0.435 and the lowest value of 0.356. (2) The order of NDVI value of different land use types from large to small is woodland>cultivated land>grassland>unused land. The order of NDVI value of different seasons from large to small is summer>autumn>spring>winter. (3) Most of the vegetation is in the state of improvement and stability, and a small part is in the state of degradation. The main reason for the degradation is grassland degradation, and urban expansion leads to the degradation of cultivated land and the conversion of cultivated land to construction land. (4) NDVI is positively correlated with soil moisture at different depths (0−10 cm, 10−40 cm, 40−100 cm, 100−200 cm), with the correlation coefficients of 0.535, 0.647, 0.681 and 0.619, respectively. The correlation between NDVI of different land use types and soil moisture of different depths is different. The positive correlation area between NDVI and soil moisture of cultivated land, grassland and unused land is the largest at the depth of 10−40 cm, while the positive correlation area between NDVI and soil moisture of forest land is the largest at the depth of 40−100 cm.
Analyzing the temporal and spatial changes of vegetation and its correlation with soil moisture and quantitatively revealing the impact of soil moisture on vegetation growth are of certain significance for drought monitoring and ecological protection. However, previous quantitative researches on soil moisture and vegetation growth are not enough. Based on MOD13Q1 NDVI products and global land data assimilation system (GLDAS) soil moisture data, Sen + Mann Kendall trend test and correlation analysis are used to analyze the temporal and spatial variation characteristics of vegetation and the impact of land use change on vegetation growth in the Yellow River Basin from 2000 to 2020. The correlation between vegetation and soil moisture at different depths in growing season is explored. The results show that (1) the vegetation growth is characterized by “high in the south and low in the north”. Along the runoff direction of the Yellow River, the vegetation growth on the right bank of the upper reaches is significantly better than that on the left bank, and there is no significant difference in the vegetation growth on the two banks of the middle and lower reaches. The NDVI increases by 22.19% from 2000 to 2020, with the highest value of 0.435 and the lowest value of 0.356. (2) The order of NDVI value of different land use types from large to small is woodland>cultivated land>grassland>unused land. The order of NDVI value of different seasons from large to small is summer>autumn>spring>winter. (3) Most of the vegetation is in the state of improvement and stability, and a small part is in the state of degradation. The main reason for the degradation is grassland degradation, and urban expansion leads to the degradation of cultivated land and the conversion of cultivated land to construction land. (4) NDVI is positively correlated with soil moisture at different depths (0−10 cm, 10−40 cm, 40−100 cm, 100−200 cm), with the correlation coefficients of 0.535, 0.647, 0.681 and 0.619, respectively. The correlation between NDVI of different land use types and soil moisture of different depths is different. The positive correlation area between NDVI and soil moisture of cultivated land, grassland and unused land is the largest at the depth of 10−40 cm, while the positive correlation area between NDVI and soil moisture of forest land is the largest at the depth of 40−100 cm.
2023, 50(3): 182-192.
doi: 10.16030/j.cnki.issn.1000-3665.202209049
Abstract:
A great mountain seismic often triggers a large number of co-seismic landslides, causing direct damage to local vegetation cover and growth. As an important indicator of landslide activity intensity, the vegetation recovery is of great significance for the activity of post-earthquake geo-hazards. However, due to the limitation of observational data, the current research on vegetation restoration process in earthquake areas is mostly on a small scale. In addition, there is insufficient understanding of the vegetation evolution mechanism in a large area and the relationship between vegetation and the activity of geological disasters. Therefore, this paper uses multi-temporal and long-time series (2000−2020) high-precision remote sensing images to study the vegetation restoration process in the Wenchuan earthquake area. By calculating vegetation recovery rates in different periods, we explore the universal law of vegetation restoration in a large range, and analyze the relationship between vegetation restoration and the change of landslide activity intensity. The results show that by 2020, 71.34% of the landslide area in the earthquake area has been better restored. The proportions of highly active, moderately active, low active and basically stable landslides are 17.6%, 12.4%, 17.7% and 52.3%, respectively. The surface recovery trend of co-seismic landslide indicates that the vegetation in the Wenchuan earthquake area is expected to recover to the pre-earthquake average level about 17 years after the earthquake. However, the process of vegetation recovery and changes in landslide activity are often subject to the combined effects of multiple factors. Although the vegetation recovery of landslide surface reflects the decline of landslide activity after the earthquake to some extent, the effects of the earthquake on landslide activity will last longer than the recovery of surface vegetation to the pre-earthquake level. Referring to the results of previous studies, this paper suggests that the post-earthquake landslide activity will last 25 years or more.The conclusion can provide reference for the assessment and prevention of post earthquake geological disasters in Wenchuan earthquake area.
A great mountain seismic often triggers a large number of co-seismic landslides, causing direct damage to local vegetation cover and growth. As an important indicator of landslide activity intensity, the vegetation recovery is of great significance for the activity of post-earthquake geo-hazards. However, due to the limitation of observational data, the current research on vegetation restoration process in earthquake areas is mostly on a small scale. In addition, there is insufficient understanding of the vegetation evolution mechanism in a large area and the relationship between vegetation and the activity of geological disasters. Therefore, this paper uses multi-temporal and long-time series (2000−2020) high-precision remote sensing images to study the vegetation restoration process in the Wenchuan earthquake area. By calculating vegetation recovery rates in different periods, we explore the universal law of vegetation restoration in a large range, and analyze the relationship between vegetation restoration and the change of landslide activity intensity. The results show that by 2020, 71.34% of the landslide area in the earthquake area has been better restored. The proportions of highly active, moderately active, low active and basically stable landslides are 17.6%, 12.4%, 17.7% and 52.3%, respectively. The surface recovery trend of co-seismic landslide indicates that the vegetation in the Wenchuan earthquake area is expected to recover to the pre-earthquake average level about 17 years after the earthquake. However, the process of vegetation recovery and changes in landslide activity are often subject to the combined effects of multiple factors. Although the vegetation recovery of landslide surface reflects the decline of landslide activity after the earthquake to some extent, the effects of the earthquake on landslide activity will last longer than the recovery of surface vegetation to the pre-earthquake level. Referring to the results of previous studies, this paper suggests that the post-earthquake landslide activity will last 25 years or more.The conclusion can provide reference for the assessment and prevention of post earthquake geological disasters in Wenchuan earthquake area.
2023, 50(3): 193-206.
doi: 10.16030/j.cnki.issn.1000-3665.202110028
Abstract:
The Sichuan Basin located in the intersection of the Tethys−Himalaya and Pacific domains is a multicycle sedimentary basin surrounded by orogenic belts. The geothermal resources are good, but with complex geological structures. Geothermal conditions and heat generation models are different in different tectonic zones in the basin, which seriously restrict the geothermal exploration, development and utilization of geothermal resources. In this paper, the distribution of geothermal resources, characteristics of geothermal fluids, heat flow and geothermal gradients in the Sichuan Basin are comprehensively analyzed by collecting the existing geothermal and petroleum exploration and development data. The geothermal reservoirs and caprocks, the burial depth and the resource conditions of different types of the basin-mountain structure areas in the Sichuan Basin are analyzed. The suggested exploration target for exploration and development are proposed in different tectonic units of the Sichuan Basin. The results show (1) the terrestrial heat flow values in the Sichuan Basin and its surrounding areas are from medium to low, and the geothermal gradient varies between 16 °C/km and 30 °C/km. The terrestrial heat source is obviously controlled by active faults and basement structure, and the hydrothermal systems are conductive and belong to the low-moderate temperature geothermal resources in the Sichuan Basin. (2) The distribution of geothermal resources in the Sichuan Basin is mainly controlled by basin structure, stratigraphic distribution and hydrologic conditions. (4) There are at least 4 karst-type geothermal reservoirs in the marine strata, and 1 − 2 glutenite-type geothermal reservoirs in clastic strata. Geothermal water is of SO4 — Ca type and is brackish. The Middle-Lower Triassic and Middle Permian carbonate rocks are considered as the best marine reservoirs, especially in the eastern and western basin. Secondly, other marine karst-type geothermal reservoirs are selected for exploration. The continental clastic rocks should be cautious because their caprocks, groundwater recharge and heat source are worse than the geothermal conditions of the marine carbonate rocks. This study may provide important guidance for further promoting geothermal exploration, exploitation and utilization in the Sichuan Basin.
The Sichuan Basin located in the intersection of the Tethys−Himalaya and Pacific domains is a multicycle sedimentary basin surrounded by orogenic belts. The geothermal resources are good, but with complex geological structures. Geothermal conditions and heat generation models are different in different tectonic zones in the basin, which seriously restrict the geothermal exploration, development and utilization of geothermal resources. In this paper, the distribution of geothermal resources, characteristics of geothermal fluids, heat flow and geothermal gradients in the Sichuan Basin are comprehensively analyzed by collecting the existing geothermal and petroleum exploration and development data. The geothermal reservoirs and caprocks, the burial depth and the resource conditions of different types of the basin-mountain structure areas in the Sichuan Basin are analyzed. The suggested exploration target for exploration and development are proposed in different tectonic units of the Sichuan Basin. The results show (1) the terrestrial heat flow values in the Sichuan Basin and its surrounding areas are from medium to low, and the geothermal gradient varies between 16 °C/km and 30 °C/km. The terrestrial heat source is obviously controlled by active faults and basement structure, and the hydrothermal systems are conductive and belong to the low-moderate temperature geothermal resources in the Sichuan Basin. (2) The distribution of geothermal resources in the Sichuan Basin is mainly controlled by basin structure, stratigraphic distribution and hydrologic conditions. (4) There are at least 4 karst-type geothermal reservoirs in the marine strata, and 1 − 2 glutenite-type geothermal reservoirs in clastic strata. Geothermal water is of SO4 — Ca type and is brackish. The Middle-Lower Triassic and Middle Permian carbonate rocks are considered as the best marine reservoirs, especially in the eastern and western basin. Secondly, other marine karst-type geothermal reservoirs are selected for exploration. The continental clastic rocks should be cautious because their caprocks, groundwater recharge and heat source are worse than the geothermal conditions of the marine carbonate rocks. This study may provide important guidance for further promoting geothermal exploration, exploitation and utilization in the Sichuan Basin.
2023, 50(3): 207-216.
doi: 10.16030/j.cnki.issn.1000-3665.202208003
Abstract:
Xietongmen County is located in the alpine mountain area of the Qinghai-Tibet Plateau, where the Kaga hot spring occurs. Geothermal energy is expected to be developed to solve the local heating problem, but research on the genesis and reserves of geothermal energy has not been carried out. By analyzing the geological structure and geothermal activity law of the survey area, and carrying out detailed geological survey, audio frequency magnetotelluric sounding and soil radon measurement near the Kaga hot spring, this paper discusses the genesis and thermal reservoir characteristics of ths Kaga hot spring by comprehensively using geological and geophysical exploration data. The research results show that (1) the audio frequency magnetotelluric and soil radon measurement results clearly reveal the extension and superposition relationship of the deep NE, NW and SN trending faults in the area, indicating that the area has a good permeable channel and thermal storage space. (2) The heat source in the study area is composed of the middle and shallow Eocene Oligocene magmatic rock decay exothermic heat source and the deep high-temperature magmatic melting heat source. The fracture zone is not only a deep thermal reservoir, but also a channel for the upwelling of deep hot water. The alluvial proluvial and other accumulative layers in the upper part of the Quaternary system are good caprocks of geothermal water, while the unconsolidated sediments in the lower part of the Quaternary system and some bedrock weathering crusts constitute shallow geothermal reservoirs in the area. These indicate that the geothermal application potential in this area is large, but it should be noted that, according to the three-dimensional display of audio frequency magnetotelluric sounding results, it is found that the deep S1 and S2 abnormal areas are connected at the shallow part, and the surface hot spring vent is just above its connecting channel, so the impact of the water volume of this hot spring vent needs to be evaluated when drilling water nearby. Finally, combined with the geothermal characteristics and electrical characteristics of geothermal water in this area, the “geophysical geothermal geology” model of the survey area is constructed, providing reference and guidance for the exploration and development of geothermal resources in other regions of Tibet.
Xietongmen County is located in the alpine mountain area of the Qinghai-Tibet Plateau, where the Kaga hot spring occurs. Geothermal energy is expected to be developed to solve the local heating problem, but research on the genesis and reserves of geothermal energy has not been carried out. By analyzing the geological structure and geothermal activity law of the survey area, and carrying out detailed geological survey, audio frequency magnetotelluric sounding and soil radon measurement near the Kaga hot spring, this paper discusses the genesis and thermal reservoir characteristics of ths Kaga hot spring by comprehensively using geological and geophysical exploration data. The research results show that (1) the audio frequency magnetotelluric and soil radon measurement results clearly reveal the extension and superposition relationship of the deep NE, NW and SN trending faults in the area, indicating that the area has a good permeable channel and thermal storage space. (2) The heat source in the study area is composed of the middle and shallow Eocene Oligocene magmatic rock decay exothermic heat source and the deep high-temperature magmatic melting heat source. The fracture zone is not only a deep thermal reservoir, but also a channel for the upwelling of deep hot water. The alluvial proluvial and other accumulative layers in the upper part of the Quaternary system are good caprocks of geothermal water, while the unconsolidated sediments in the lower part of the Quaternary system and some bedrock weathering crusts constitute shallow geothermal reservoirs in the area. These indicate that the geothermal application potential in this area is large, but it should be noted that, according to the three-dimensional display of audio frequency magnetotelluric sounding results, it is found that the deep S1 and S2 abnormal areas are connected at the shallow part, and the surface hot spring vent is just above its connecting channel, so the impact of the water volume of this hot spring vent needs to be evaluated when drilling water nearby. Finally, combined with the geothermal characteristics and electrical characteristics of geothermal water in this area, the “geophysical geothermal geology” model of the survey area is constructed, providing reference and guidance for the exploration and development of geothermal resources in other regions of Tibet.
Supervisor: China Geological Survey
Sponsor: China Institute of Geo-Environment Monitoring
Chief Editor: Li WenPeng
Editor&Publication: Editorial Office of Hydrogeology & Engineering Geology
Telephone:
010-60850926 (汪老师)
010-60850953 (刘老师)
010-60850956 (宗老师)
010-60850960 (张老师)
010-60850986 (王老师)
Email: swdzgcdz@vip.163.com
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