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2023
Vol. 31,
No. 5
Previous Issue
2023,
31(5):
1495-1506.
Abstract
10328KB
Haizi Mountain in the center of Daocheng's Quaternary ice cap is widely distributed with glacial moraine of different grain magnitudes. The site, covered with various loosed sediments underlying by granite as medium coarse grained biotite granodiorite,is to be used according to the planning and construction of China's Large High Altitude Air Shower Observatory(LHAASO). This paper describes and analyses five locations with granite gravels of moraine ridge and two locations with alluvial proluvial materials of terrace at the site. The statistical results of 106 huge gravels show that the moraine gravels of major percentages are 0.5~2.5 m in diameter,and have 2.5~7.5 m2 in area and 5 m3 in volume to a certain extent. Two gravel samples of gravelly soil and fine debris soil of alluvial proluvium have the median particle size D50=2 mm and 0.7mm,the non-uniform coefficient Cu=5.40 and 2.42,the curvature coefficient Cc=0.60 and 0.95, respectively. Both are poorly graded soil,i.e. homogeneous soil. These moraines and alluvial proluvial deposits with different genetic structures and magnitudes have different important values for site planning and utilization,and have certain influence on the stability of excavation pit wall. Afterwards,the results in this paper were adopted for planning and designing of LHAASO.
Haizi Mountain in the center of Daocheng's Quaternary ice cap is widely distributed with glacial moraine of different grain magnitudes. The site, covered with various loosed sediments underlying by granite as medium coarse grained biotite granodiorite,is to be used according to the planning and construction of China's Large High Altitude Air Shower Observatory(LHAASO). This paper describes and analyses five locations with granite gravels of moraine ridge and two locations with alluvial proluvial materials of terrace at the site. The statistical results of 106 huge gravels show that the moraine gravels of major percentages are 0.5~2.5 m in diameter,and have 2.5~7.5 m2 in area and 5 m3 in volume to a certain extent. Two gravel samples of gravelly soil and fine debris soil of alluvial proluvium have the median particle size D50=2 mm and 0.7mm,the non-uniform coefficient Cu=5.40 and 2.42,the curvature coefficient Cc=0.60 and 0.95, respectively. Both are poorly graded soil,i.e. homogeneous soil. These moraines and alluvial proluvial deposits with different genetic structures and magnitudes have different important values for site planning and utilization,and have certain influence on the stability of excavation pit wall. Afterwards,the results in this paper were adopted for planning and designing of LHAASO.
2023,
31(5):
1507-1515.
Characterizing the mechanical properties of loess while considering the influence of freeze-thaw cycling is of great importance in geotechnical designs at Loess Plateau in China. Several key influencing factors are studied in a collective manner. They include the number of freeze-thaw cycles, the sand content, the salt content and the water content. In this paper,we carry out the unconfined compression tests,and obtain the uniaxial compressive strength of loess. At the same time,we also measure the shear wave velocity and the compression wave velocity of loess specimens subjected to different freeze-thaw cycles. The following are found: (1)the shear wave velocity and compression wave velocity decrease with an increase of freeze-thaw cycles. The reduction is more pronounced in loess samples with lower sand content. (2)The velocity of loess with high salt content decreases after the first freeze-thaw cycle,and it becomes less significant with further increase of the freeze-thaw cycles. (3)With the increase of freeze-thaw cycles and water content,the failure forms of soil samples change from brittle failure to plastic failure. (4)Based on the test results,we propose an empirical correlation between the wave velocity and the uniaxial compressive strength of loess. The research provides a new insight into evaluation of strength deterioration of loess under freeze-thaw cycle.
Characterizing the mechanical properties of loess while considering the influence of freeze-thaw cycling is of great importance in geotechnical designs at Loess Plateau in China. Several key influencing factors are studied in a collective manner. They include the number of freeze-thaw cycles, the sand content, the salt content and the water content. In this paper,we carry out the unconfined compression tests,and obtain the uniaxial compressive strength of loess. At the same time,we also measure the shear wave velocity and the compression wave velocity of loess specimens subjected to different freeze-thaw cycles. The following are found: (1)the shear wave velocity and compression wave velocity decrease with an increase of freeze-thaw cycles. The reduction is more pronounced in loess samples with lower sand content. (2)The velocity of loess with high salt content decreases after the first freeze-thaw cycle,and it becomes less significant with further increase of the freeze-thaw cycles. (3)With the increase of freeze-thaw cycles and water content,the failure forms of soil samples change from brittle failure to plastic failure. (4)Based on the test results,we propose an empirical correlation between the wave velocity and the uniaxial compressive strength of loess. The research provides a new insight into evaluation of strength deterioration of loess under freeze-thaw cycle.
2023,
31(5):
1516-1527.
The stratum structure combination of loess and red clay is common in Heifangtai area. Loess and red clay have penetration differences. Under continuous irrigation conditions,the red clay layer will have a water stagnation effect,which can cause layer softening and eventually induce landslides. In this paper,indoor geotechnical tests,NMR and particle fractionation tests were carried out respectively to study the unsaturated infiltration situation and pore change law at the interface between loess and red clay. The analysis of the test results show the following findings. (1)During the infiltration process,the peak value of the water-filled pore volume distribution map keeps moving to the right. The radius of the water-filled pore increases and the distribution range gradually becomes wider. Compared with pure loess,the maximum peak value in the water-filled pore volume distribution curve of the loess-red clay composite sample migrates more slowly to the right and has a narrower distribution range. The red clay layer is rich in water after the end of infiltration. (2)Under the same flow conditions,the higher the initial water content of the loess-red clay composite sample,the slower the peak value in the water-filled pore volume distribution curve shifts to the right,the smaller the change of the corresponding water-filled pore radius,and the water entering the medium and large. The fewer the pores,the less obvious the water stagnation effect at the interface. Under the condition of the same initial water content,the larger the flow rate,the faster the peak value in the water-filled pore volume distribution curve shifts to the right,and the corresponding water-filled pore radius is larger. The more water enters the medium and large pores,and the more obvious the phenomenon of water stagnation at the interface. (3)Particle migration occurs during the humidification process of the loess and red clay composite samples,which leads to changes in the contact mode between particles and the pore structure. The final sample contains more fine particles at the bottom and more coarse particles at the interface.
The stratum structure combination of loess and red clay is common in Heifangtai area. Loess and red clay have penetration differences. Under continuous irrigation conditions,the red clay layer will have a water stagnation effect,which can cause layer softening and eventually induce landslides. In this paper,indoor geotechnical tests,NMR and particle fractionation tests were carried out respectively to study the unsaturated infiltration situation and pore change law at the interface between loess and red clay. The analysis of the test results show the following findings. (1)During the infiltration process,the peak value of the water-filled pore volume distribution map keeps moving to the right. The radius of the water-filled pore increases and the distribution range gradually becomes wider. Compared with pure loess,the maximum peak value in the water-filled pore volume distribution curve of the loess-red clay composite sample migrates more slowly to the right and has a narrower distribution range. The red clay layer is rich in water after the end of infiltration. (2)Under the same flow conditions,the higher the initial water content of the loess-red clay composite sample,the slower the peak value in the water-filled pore volume distribution curve shifts to the right,the smaller the change of the corresponding water-filled pore radius,and the water entering the medium and large. The fewer the pores,the less obvious the water stagnation effect at the interface. Under the condition of the same initial water content,the larger the flow rate,the faster the peak value in the water-filled pore volume distribution curve shifts to the right,and the corresponding water-filled pore radius is larger. The more water enters the medium and large pores,and the more obvious the phenomenon of water stagnation at the interface. (3)Particle migration occurs during the humidification process of the loess and red clay composite samples,which leads to changes in the contact mode between particles and the pore structure. The final sample contains more fine particles at the bottom and more coarse particles at the interface.
2023,
31(5):
1528-1534.
The thixotropy of soft clay is of great significance for engineering design and construction. In order to analyze the thixotropy of soft clay in Tianjin area,this paper studies the influence of water content,mineral powder content and pH value on the strength and thixotropic strength ratio of the cross plate based on the orthogonal experiment. The test results show that water content,mineral powder content and pH value are the primary and secondary factors affecting the thixotropic strength ratio of Tianjin soft clay. The thixotropic strength ratio of soft clay increases exponentially with the increase of water content, decreases almost linearly with the increase of mineral powder content, and increases with the increase of pH value. But the increasing range gradually decreases. Alkaline is more conducive to the recovery of soft clay strength than acidic environment. By means of regression analysis,a prediction formula for the thixotropic strength ratio of Tianjin soft clay is established. The formula includes water content,mineral powder content and pH value,and predicts the thixotropic strength. The prediction results are better. The research results can provide theoretical reference for engineering practice.
The thixotropy of soft clay is of great significance for engineering design and construction. In order to analyze the thixotropy of soft clay in Tianjin area,this paper studies the influence of water content,mineral powder content and pH value on the strength and thixotropic strength ratio of the cross plate based on the orthogonal experiment. The test results show that water content,mineral powder content and pH value are the primary and secondary factors affecting the thixotropic strength ratio of Tianjin soft clay. The thixotropic strength ratio of soft clay increases exponentially with the increase of water content, decreases almost linearly with the increase of mineral powder content, and increases with the increase of pH value. But the increasing range gradually decreases. Alkaline is more conducive to the recovery of soft clay strength than acidic environment. By means of regression analysis,a prediction formula for the thixotropic strength ratio of Tianjin soft clay is established. The formula includes water content,mineral powder content and pH value,and predicts the thixotropic strength. The prediction results are better. The research results can provide theoretical reference for engineering practice.
2023,
31(5):
1535-1542.
This paper aims to explore the influence of physical and mechanical properties of expansive soil on swelling deformation. Based on principal component analysis(PCA),the paper studied the correlation between the swelling deformation of expansive soil and its physical and mechanical properties,and established the discrimination formula of swelling deformation with main physical indexes as parameters. It completed the above work through a large number of field geotechnical investigation and indoor test of an expansive soil project in Ankang,Shaanxi Province. The results show that the physical and mechanical indexes affecting the swelling deformation of expansive soil can be divided into the four types of factors. The first type of factors reflects the environment including water content,saturation,liquid index and water content ratio. The second type reflects soil structure characteristics including density,dry density and void ratio. The third reflects structural strength characteristics of soil mass including compressibility and internal friction angle. The fourth reflects soil composition including plasticity index and cohesion. Moisture content is the key index affecting the expansion deformation of expansive soil. The prediction model can provide a reference for the judgment of expansive deformation of expansive soil.
This paper aims to explore the influence of physical and mechanical properties of expansive soil on swelling deformation. Based on principal component analysis(PCA),the paper studied the correlation between the swelling deformation of expansive soil and its physical and mechanical properties,and established the discrimination formula of swelling deformation with main physical indexes as parameters. It completed the above work through a large number of field geotechnical investigation and indoor test of an expansive soil project in Ankang,Shaanxi Province. The results show that the physical and mechanical indexes affecting the swelling deformation of expansive soil can be divided into the four types of factors. The first type of factors reflects the environment including water content,saturation,liquid index and water content ratio. The second type reflects soil structure characteristics including density,dry density and void ratio. The third reflects structural strength characteristics of soil mass including compressibility and internal friction angle. The fourth reflects soil composition including plasticity index and cohesion. Moisture content is the key index affecting the expansion deformation of expansive soil. The prediction model can provide a reference for the judgment of expansive deformation of expansive soil.
2023,
31(5):
1543-1551.
Expansive soil is a special clay with remarkable shrink-swell,many cracks,and repeated deformation. It is very sensitive to the change of the external environment,which causes deformation and stability to gradually become the main subject of engineering construction in expansive soil area. This paper summarizes and analyzes the existing expansion models. It is based on the regularity that the swelling deformation of expansive soil increases with the increase of initial dry density and decreases with the increase of initial water content and vertical pressure. It proposes a loading expansion model under multi-factor coupling. In this model,the influence of initial dry density is reflected by degree of compaction. When controlled as a single factor variable,there is a linear relationship between the swelling rate and the degree of compaction,and a logarithmic relationship with the initial moisture content and vertical pressure. The loading expansion test results of strong expansive soil in Handan,medium expansive soil in Nanyang and weak expansive soil in Ninghuai are verified. All the fitting results are better. The engineering application of the model is discussed,including the estimation of the treatment thickness in expansive soil area,and the design and calculation of the lining thickness of the expansive soil slope.
Expansive soil is a special clay with remarkable shrink-swell,many cracks,and repeated deformation. It is very sensitive to the change of the external environment,which causes deformation and stability to gradually become the main subject of engineering construction in expansive soil area. This paper summarizes and analyzes the existing expansion models. It is based on the regularity that the swelling deformation of expansive soil increases with the increase of initial dry density and decreases with the increase of initial water content and vertical pressure. It proposes a loading expansion model under multi-factor coupling. In this model,the influence of initial dry density is reflected by degree of compaction. When controlled as a single factor variable,there is a linear relationship between the swelling rate and the degree of compaction,and a logarithmic relationship with the initial moisture content and vertical pressure. The loading expansion test results of strong expansive soil in Handan,medium expansive soil in Nanyang and weak expansive soil in Ninghuai are verified. All the fitting results are better. The engineering application of the model is discussed,including the estimation of the treatment thickness in expansive soil area,and the design and calculation of the lining thickness of the expansive soil slope.
2023,
31(5):
1552-1562.
Determining the dynamic shear modulus and damping ratio of coral sand is prerequisite for analysing the stability of islands under dynamic loadings. Therefore,this paper presents a study on how the confining pressure,relative compactness and saturation affect the dynamic shear modulus and damping ratio of the coral sand in South China Sea. It uses the resonant column and bender element tests. The results show the follows. (1)The maximum dynamic shear modulus G0 of saturated coral sand sample is positively correlated to the confining pressure and the relative compactness,and are decreases sensitively to the relative compactness with the increase of the confining pressure. (2)The dynamic shear modulus ratios of the unsaturated coral sand are slightly higher than those of the saturated samples,while its damping ratios are slightly lower than those of the saturated samples. (3)The coral sand samples show the maximum G0 and the minimum damping ratio at the saturation of about 10%. (4)The predicted G0 by the empirical functions based on the relative compactness and the void ratio of siliceous sand are higher and lower respectively than the results obtained in the tests. Thus,the empirical formula of G0 as a function of confining pressure is modified according to the tests. This study contributes sample values of the dynamic shear modulus and damping ratio for the stability analysis of coral sand sites on the reef islands in South China Sea.
Determining the dynamic shear modulus and damping ratio of coral sand is prerequisite for analysing the stability of islands under dynamic loadings. Therefore,this paper presents a study on how the confining pressure,relative compactness and saturation affect the dynamic shear modulus and damping ratio of the coral sand in South China Sea. It uses the resonant column and bender element tests. The results show the follows. (1)The maximum dynamic shear modulus G0 of saturated coral sand sample is positively correlated to the confining pressure and the relative compactness,and are decreases sensitively to the relative compactness with the increase of the confining pressure. (2)The dynamic shear modulus ratios of the unsaturated coral sand are slightly higher than those of the saturated samples,while its damping ratios are slightly lower than those of the saturated samples. (3)The coral sand samples show the maximum G0 and the minimum damping ratio at the saturation of about 10%. (4)The predicted G0 by the empirical functions based on the relative compactness and the void ratio of siliceous sand are higher and lower respectively than the results obtained in the tests. Thus,the empirical formula of G0 as a function of confining pressure is modified according to the tests. This study contributes sample values of the dynamic shear modulus and damping ratio for the stability analysis of coral sand sites on the reef islands in South China Sea.
2023,
31(5):
1563-1572.
The tensile strength characteristic of hydrate-bearing soil is important for evaluating the stability of hydrate-bearing layer during hydrate exploitation. Adopting the clayey silt as host sediment,the hydrate-bearing soils were synthesized by using tetrahydrofuran(THF)instead of methane. Meanwhile,the tension tests were performed in controlled temperature environment. The results show that when hydrate saturation,dry density and content of fine grain have significant influences on the tension strength. As hydrate saturation increases,the tension strength exhibits an increase tendency with exponential function. The influences of dry density and fine grain content are related with the hydrate saturation. At the low hydrate saturation,the increase in dry density and fine grain content can improve the tensile strength. At the high hydrate saturation,the tensile strength lowers with the increasing dry density and fine grain content. In addition,the acoustic wave for hydrate-bearing soil is measured. The relationship between tensile strength and acoustic wave characteristic is analyzed,which is useful for estimating the tensile strength of hydrate-bearing soil in the future.
The tensile strength characteristic of hydrate-bearing soil is important for evaluating the stability of hydrate-bearing layer during hydrate exploitation. Adopting the clayey silt as host sediment,the hydrate-bearing soils were synthesized by using tetrahydrofuran(THF)instead of methane. Meanwhile,the tension tests were performed in controlled temperature environment. The results show that when hydrate saturation,dry density and content of fine grain have significant influences on the tension strength. As hydrate saturation increases,the tension strength exhibits an increase tendency with exponential function. The influences of dry density and fine grain content are related with the hydrate saturation. At the low hydrate saturation,the increase in dry density and fine grain content can improve the tensile strength. At the high hydrate saturation,the tensile strength lowers with the increasing dry density and fine grain content. In addition,the acoustic wave for hydrate-bearing soil is measured. The relationship between tensile strength and acoustic wave characteristic is analyzed,which is useful for estimating the tensile strength of hydrate-bearing soil in the future.
2023,
31(5):
1573-1587.
In this study,the quartz mica schist was taken as the tested object. The uniaxial compression test was used to explore the influence of loading direction on the characteristic strength and energy evolution of this brittle schistose rock under dry and water-bearing conditions. Combined with the characteristics of micro fabric and macro failure mode,the mechanism of mechanical anisotropic behavior of schist was revealed. Results show the following. (1)During the loading process,the energy evolution curves of rocks have a good corresponding relationship with the deformation damage changes. Based on this,the characteristic strengths of rocks can be determined quickly and accurately. (2)The characteristic strengths of schist in both dry and water-bearing states always follow α=90°>α=0°>α=30°. At α=30°,the schist has a more sensitive response to water with respect to the characteristic strength. Water enhances the strength anisotropy of schist to a certain extent. (3)At α=90°,the energy storage and dissipation of schist are always higher than those at α=0° and 30°.The tendency of rock burst of schist with α=30° is stronger than that with α=90°.The damage of rock has a relatively rapid development at α=30°. (4)The flaky minerals and micro-cracks in schist provide the material basis for water effects such as lubrication,softening and water wedge.The dominant water action varies with the loading direction. (5)The quartz mica schist has the microscopic characteristics of orientation arrangement of flake minerals and the interlayered distribution of soft and hard layers. This typical structure determines the effect of loading direction on the mechanism of cracks generation and propagation,and essentially controls the anisotropy of strength and energy of the rock.
In this study,the quartz mica schist was taken as the tested object. The uniaxial compression test was used to explore the influence of loading direction on the characteristic strength and energy evolution of this brittle schistose rock under dry and water-bearing conditions. Combined with the characteristics of micro fabric and macro failure mode,the mechanism of mechanical anisotropic behavior of schist was revealed. Results show the following. (1)During the loading process,the energy evolution curves of rocks have a good corresponding relationship with the deformation damage changes. Based on this,the characteristic strengths of rocks can be determined quickly and accurately. (2)The characteristic strengths of schist in both dry and water-bearing states always follow α=90°>α=0°>α=30°. At α=30°,the schist has a more sensitive response to water with respect to the characteristic strength. Water enhances the strength anisotropy of schist to a certain extent. (3)At α=90°,the energy storage and dissipation of schist are always higher than those at α=0° and 30°.The tendency of rock burst of schist with α=30° is stronger than that with α=90°.The damage of rock has a relatively rapid development at α=30°. (4)The flaky minerals and micro-cracks in schist provide the material basis for water effects such as lubrication,softening and water wedge.The dominant water action varies with the loading direction. (5)The quartz mica schist has the microscopic characteristics of orientation arrangement of flake minerals and the interlayered distribution of soft and hard layers. This typical structure determines the effect of loading direction on the mechanism of cracks generation and propagation,and essentially controls the anisotropy of strength and energy of the rock.
2023,
31(5):
1588-1596.
Carbonaceous rock formation frequently appears as the main rock layer or interlayer in the stratigraphic units of different ages in Guangxi Province. Due to its easy weathering, cracking, disintegrating, softening, and the environmental sensitivity of engineering properties, it has brought many complex problems to the highway construction in Guangxi Province. Multiple research methods were adopted to investigate the geochemical characteristics and influence factors of disintegration for carbonaceous rocks. They include existing geological survey data collection, field geological survey and sampling tests. Researches on the distribution and assemblage characteristics of carbonaceous rocks, mineral composition and geochemical characteristics of organic matter were carried out. Meanwhile, influence factors of disintegration for carbonaceous rock and corresponding engineering measures were discussed. The research showes that carbonaceous rocks are distributed from Neoproterozoic to Paleogene in Guangxi Province. 24 major stratigraphic units containing carbonaceous rocks were identified. Its basic material composition is mainly composed of clay minerals, quartz and carbonate minerals. And the organic matter content of carbonaceous rocks in Guangxi Province is high, which belongs to the carbonaceous rocks of middle-high level source rocks. The illite and illite-smectite mixed-layer mineral in clay minerals, high content of organic matter and sulfide are the main material factors for the disintegration of carbonaceous rocks under natural exposure. Tectonic activity, water swelling and thermal dehydration of clay minerals, oxidation and decomposition reactions of organic matter and reducing minerals, and natural factors are the four main reasons for the disintegration of carbonaceous rock slopes. Related research findings can provide important references for the design, construction, prevention and treatment of slope engineering, tunnel engineering and subgrade engineering in carbonaceous rock areas.
Carbonaceous rock formation frequently appears as the main rock layer or interlayer in the stratigraphic units of different ages in Guangxi Province. Due to its easy weathering, cracking, disintegrating, softening, and the environmental sensitivity of engineering properties, it has brought many complex problems to the highway construction in Guangxi Province. Multiple research methods were adopted to investigate the geochemical characteristics and influence factors of disintegration for carbonaceous rocks. They include existing geological survey data collection, field geological survey and sampling tests. Researches on the distribution and assemblage characteristics of carbonaceous rocks, mineral composition and geochemical characteristics of organic matter were carried out. Meanwhile, influence factors of disintegration for carbonaceous rock and corresponding engineering measures were discussed. The research showes that carbonaceous rocks are distributed from Neoproterozoic to Paleogene in Guangxi Province. 24 major stratigraphic units containing carbonaceous rocks were identified. Its basic material composition is mainly composed of clay minerals, quartz and carbonate minerals. And the organic matter content of carbonaceous rocks in Guangxi Province is high, which belongs to the carbonaceous rocks of middle-high level source rocks. The illite and illite-smectite mixed-layer mineral in clay minerals, high content of organic matter and sulfide are the main material factors for the disintegration of carbonaceous rocks under natural exposure. Tectonic activity, water swelling and thermal dehydration of clay minerals, oxidation and decomposition reactions of organic matter and reducing minerals, and natural factors are the four main reasons for the disintegration of carbonaceous rock slopes. Related research findings can provide important references for the design, construction, prevention and treatment of slope engineering, tunnel engineering and subgrade engineering in carbonaceous rock areas.
2023,
31(5):
1597-1604.
Red sandstone is widely distributed in southern China. Due to the low strength,poor cementation and swelling clay minerals,red sandstone is prone to disintegrate under the influence of water,which can easily induce a variety of geological disasters. The static and disturbed disintegration tests are conducted on the slightly swelling red sandstone collected form Zhuzhou area of Hunan Province. The effects of dry temperature,external disturbance,test block mass and drying-wetting cycle on the disintegration characteristic are explored using evaluating indexes,including slake durability index,standard basis entropy,disintegration ratio and fractal dimension. The results show that,under the static disintegration mode,the drying temperature of 60 ℃is more favorable to disintegrate for red sandstone than those of 105 ℃ and 30 ℃. However,under the disturbed disintegration mode,the effect of drying temperature on the disintegration of red sandstone is almost negligible. Furthermore,in the case of constant temperature and test block mass,the external disturbance has a significant effect on the disintegration properties of red sandstone. Then,the test block mass has the influence on the disintegration behaviors of red sandstone.The faster disintegration rate occurs with the larger test block mass. In addition,the influence of drying-wetting cycle on the disintegration of red sandstone is very significant. The disintegration breakage of red sandstone gradually increases with the increasing cycle numbers.
Red sandstone is widely distributed in southern China. Due to the low strength,poor cementation and swelling clay minerals,red sandstone is prone to disintegrate under the influence of water,which can easily induce a variety of geological disasters. The static and disturbed disintegration tests are conducted on the slightly swelling red sandstone collected form Zhuzhou area of Hunan Province. The effects of dry temperature,external disturbance,test block mass and drying-wetting cycle on the disintegration characteristic are explored using evaluating indexes,including slake durability index,standard basis entropy,disintegration ratio and fractal dimension. The results show that,under the static disintegration mode,the drying temperature of 60 ℃is more favorable to disintegrate for red sandstone than those of 105 ℃ and 30 ℃. However,under the disturbed disintegration mode,the effect of drying temperature on the disintegration of red sandstone is almost negligible. Furthermore,in the case of constant temperature and test block mass,the external disturbance has a significant effect on the disintegration properties of red sandstone. Then,the test block mass has the influence on the disintegration behaviors of red sandstone.The faster disintegration rate occurs with the larger test block mass. In addition,the influence of drying-wetting cycle on the disintegration of red sandstone is very significant. The disintegration breakage of red sandstone gradually increases with the increasing cycle numbers.
2023,
31(5):
1605-1614.
The uniaxial tensile strength(UTS) of saturated rocks is not easy to obtain because of the difficulty in specimen preparation and test execution. To estimate the saturated rocks' UTS and analyze the water effects on its accuracy,we conducted a series of uniaxial compression and direct tension tests of two hard rocks,coupled with acoustic emission(AE)monitoring. Based on the Griffith theory and Hoek-Brown(H-B)criterion,crack initiation stress determined by crack volumetric strain curve was utilized to evaluate the UTS and H-B strength parameter mi. The accuracy of estimation of these two parameters was analyzed by the spectrum characteristics of AE waveforms. Results show that,the method of crack initiation stress based on Griffith criterion is reliable to estimate the saturated hard rocks' UTS. The estimated values of dry hard rocks' UTS are smaller than those of experimental values. In comparison,the estimated saturated rocks' UTS is closer to the experimental value. This is mainly because the ductility and creep of hard rocks tend to increase after saturation,and more micro-tensile failures occur inside the rocks. The increase in mi of saturated hard rocks is related to the growing micro-tensile failures. Moreover,the mi can be used to describe the degree of the water-weakening effect. The estimation of rock UTS andmi based on Griffith's theory and crack initiation stress can be applied in the early design of rock mass engineering practice.
The uniaxial tensile strength(UTS) of saturated rocks is not easy to obtain because of the difficulty in specimen preparation and test execution. To estimate the saturated rocks' UTS and analyze the water effects on its accuracy,we conducted a series of uniaxial compression and direct tension tests of two hard rocks,coupled with acoustic emission(AE)monitoring. Based on the Griffith theory and Hoek-Brown(H-B)criterion,crack initiation stress determined by crack volumetric strain curve was utilized to evaluate the UTS and H-B strength parameter mi. The accuracy of estimation of these two parameters was analyzed by the spectrum characteristics of AE waveforms. Results show that,the method of crack initiation stress based on Griffith criterion is reliable to estimate the saturated hard rocks' UTS. The estimated values of dry hard rocks' UTS are smaller than those of experimental values. In comparison,the estimated saturated rocks' UTS is closer to the experimental value. This is mainly because the ductility and creep of hard rocks tend to increase after saturation,and more micro-tensile failures occur inside the rocks. The increase in mi of saturated hard rocks is related to the growing micro-tensile failures. Moreover,the mi can be used to describe the degree of the water-weakening effect. The estimation of rock UTS andmi based on Griffith's theory and crack initiation stress can be applied in the early design of rock mass engineering practice.
2023,
31(5):
1615-1627.
Since the impoundment to the elevation 175 m above sea level in the Three Gorges reservoir area, the carbonate karst bank slopes of the Wuxia area have been deteriorating strongly under the periodic water level fluctuations, and a large number of geological disasters have been new-born or developed rapidly. This paper aims to study the law of strength weakening of carbonate bank slopes under cyclical water level fluctuations. It conducted researches from the physical structure, chemical properties, and mechanical properties of the rock(or rockmass). Six most representative reservoir banks in Wuxia area were selected, where in-situ rock rebound strength test, in-situ point loading test and indoor wet-dry cycle test, rock mineral composition analysis, rock apparent fissures scanning test were carried out. Through these tests, the strength weakening data of carbonate rocks(or rockmass) under the condition of fluctuating water were obtained. The results of in-situ rock rebound strength test show that the strength weakening rate of in-situ rockmass is 0.3% to 25.9% per year. The results of indoor dry-wet cycle test show that after 50 dry-wet cycles, the strength weakening rate of rock is 16.4% to 23.9%, and the deformation modulus weakening rate is 17.1% to 24.9%. The results of mineral composition analysis show that the dissolution loss of CaO is 0.5% to 5.6% after 100 cycles. Through the scanning results of rock apparent fissures, new signs of deformation were found on the rock surface, the water erosion marks were aggravated, the solution pores were enlarged and the cracks were extended. Based on the dry-wet cycle test data, the rock strength weakening function is established, and the exponential function weakening calculation model at each point is deduced. Then such functions can be used to predict the numerical relationship between rock strengths, deformation modulus and water level cycle times. Taking the Quzitan dangerous rock as an example, the catastrophic effect of rock strength weakening is discussed. The work methods and the data obtained from the research can provide data and technical supports for the prevention and control of the bank slope deterioration zone in the Three Gorges Reservoir area.
Since the impoundment to the elevation 175 m above sea level in the Three Gorges reservoir area, the carbonate karst bank slopes of the Wuxia area have been deteriorating strongly under the periodic water level fluctuations, and a large number of geological disasters have been new-born or developed rapidly. This paper aims to study the law of strength weakening of carbonate bank slopes under cyclical water level fluctuations. It conducted researches from the physical structure, chemical properties, and mechanical properties of the rock(or rockmass). Six most representative reservoir banks in Wuxia area were selected, where in-situ rock rebound strength test, in-situ point loading test and indoor wet-dry cycle test, rock mineral composition analysis, rock apparent fissures scanning test were carried out. Through these tests, the strength weakening data of carbonate rocks(or rockmass) under the condition of fluctuating water were obtained. The results of in-situ rock rebound strength test show that the strength weakening rate of in-situ rockmass is 0.3% to 25.9% per year. The results of indoor dry-wet cycle test show that after 50 dry-wet cycles, the strength weakening rate of rock is 16.4% to 23.9%, and the deformation modulus weakening rate is 17.1% to 24.9%. The results of mineral composition analysis show that the dissolution loss of CaO is 0.5% to 5.6% after 100 cycles. Through the scanning results of rock apparent fissures, new signs of deformation were found on the rock surface, the water erosion marks were aggravated, the solution pores were enlarged and the cracks were extended. Based on the dry-wet cycle test data, the rock strength weakening function is established, and the exponential function weakening calculation model at each point is deduced. Then such functions can be used to predict the numerical relationship between rock strengths, deformation modulus and water level cycle times. Taking the Quzitan dangerous rock as an example, the catastrophic effect of rock strength weakening is discussed. The work methods and the data obtained from the research can provide data and technical supports for the prevention and control of the bank slope deterioration zone in the Three Gorges Reservoir area.
2023,
31(5):
1628-1636.
This paper is based on the geological hazard monitoring, the early warning work, the monitoring data analysis and the information system construction examples of geological hazards in Three Gorges Reservoir area. It focuses on the concept and connotation of geological hazard monitoring data analysis, and the development trend of geological hazard monitoring data analysis. The main findings are as follows. (1)The definition of geological hazard monitoring data analysis is put forward. It is the comprehensive analysis of geological hazard monitoring data and related achievements and data according to the purposes, contents and methods of geological hazard monitoring. (2)In the face of multi-source, heterogeneous, real-time, massive geological hazard monitoring data, the development of intelligent geological hazard monitoring data analysis system is the key to solve the problem. The system can integrate the geological hazards monitoring big data, the various analytical techniques, methods and application service systems as well as the workflow of monitoring data analysis.
This paper is based on the geological hazard monitoring, the early warning work, the monitoring data analysis and the information system construction examples of geological hazards in Three Gorges Reservoir area. It focuses on the concept and connotation of geological hazard monitoring data analysis, and the development trend of geological hazard monitoring data analysis. The main findings are as follows. (1)The definition of geological hazard monitoring data analysis is put forward. It is the comprehensive analysis of geological hazard monitoring data and related achievements and data according to the purposes, contents and methods of geological hazard monitoring. (2)In the face of multi-source, heterogeneous, real-time, massive geological hazard monitoring data, the development of intelligent geological hazard monitoring data analysis system is the key to solve the problem. The system can integrate the geological hazards monitoring big data, the various analytical techniques, methods and application service systems as well as the workflow of monitoring data analysis.
2023,
31(5):
1637-1647.
It is noted that the run-out and deposition processes of rockslide-avalanche can be greatly affected by the width of the depositing zone. However, there are limited studies regarding the influence of the width of the depositing zone on the run-out and deposition processes of rockslide-avalanche in literature. In this study, a model test system with an easily adjustable width of the depositing zone is designed and used for a series of model tests. During the tests, the images and data of the run-out process and deposition behaviors, with different widths of depositing zone, are collected and used for deriving the velocity and deposition behaviors of the granular flow. Further, numerical simulations are undertaken to reveal the underlying mechanisms of the run-out and deposition behaviors. On the basis of the obtained results, the following conclusions are drawn. The divergence of the sliding materials on its inclined sliding path tends to increase with the sliding distance. The sliding velocity of the materials in the depositing zone decreases with the width of the depositing zone, the sliding direction of the materials changes in the depositing zone and this change becomes more distinct with the increase of the width of the depositing zone. The increase of the width of the depositing zone tends to lead to the decrease of the length of the granular flow deposition in the depositing zone while the increase of the width of the granular flow deposition. The area of the granular flow deposition decreases first and then increases with the width of the depositing zone. Numerical simulations indicate that collision is the main type of energy transfers among the sliding martials while friction is the main type of energy consumption. With the increase of the width of the depositing zone, the frequency of collisions decreases and the sliding materials tends to move towards two sides. The energy consumption induced by friction could lead to the increase of the width of the granular flow deposition while the decrease of the deposition length.
It is noted that the run-out and deposition processes of rockslide-avalanche can be greatly affected by the width of the depositing zone. However, there are limited studies regarding the influence of the width of the depositing zone on the run-out and deposition processes of rockslide-avalanche in literature. In this study, a model test system with an easily adjustable width of the depositing zone is designed and used for a series of model tests. During the tests, the images and data of the run-out process and deposition behaviors, with different widths of depositing zone, are collected and used for deriving the velocity and deposition behaviors of the granular flow. Further, numerical simulations are undertaken to reveal the underlying mechanisms of the run-out and deposition behaviors. On the basis of the obtained results, the following conclusions are drawn. The divergence of the sliding materials on its inclined sliding path tends to increase with the sliding distance. The sliding velocity of the materials in the depositing zone decreases with the width of the depositing zone, the sliding direction of the materials changes in the depositing zone and this change becomes more distinct with the increase of the width of the depositing zone. The increase of the width of the depositing zone tends to lead to the decrease of the length of the granular flow deposition in the depositing zone while the increase of the width of the granular flow deposition. The area of the granular flow deposition decreases first and then increases with the width of the depositing zone. Numerical simulations indicate that collision is the main type of energy transfers among the sliding martials while friction is the main type of energy consumption. With the increase of the width of the depositing zone, the frequency of collisions decreases and the sliding materials tends to move towards two sides. The energy consumption induced by friction could lead to the increase of the width of the granular flow deposition while the decrease of the deposition length.
2023,
31(5):
1648-1654.
Collapse is one of the most common and serious geological disasters in the Loess Plateau of China. In this paper, the seismic wave velocity characteristics of the potential slope failure internal structure of Lishi loess are analysed in detail using the in-situ seismic wave testing through field drilling test. The results show that the seismic wave velocity in the vertical direction increases with the depth, while the seismic wave velocity in the horizontal direction gradually increases from slope surface to interior of the slope. Numerical simulation results indicate that the potential slope failure generates outward deformation due to the unloading rebound. The deformation increment is related to distance to the slope surface, the closer the distance, the greater the deformation increment. The decrease of density is an important reason for the difference of wave velocity in the potential failure. The study shows that the variation pattern of seismic wave velocity can reflect the internal structure characteristics of the potential slope failure, and thus can be a method in research on prevention and control of loess collapses.
Collapse is one of the most common and serious geological disasters in the Loess Plateau of China. In this paper, the seismic wave velocity characteristics of the potential slope failure internal structure of Lishi loess are analysed in detail using the in-situ seismic wave testing through field drilling test. The results show that the seismic wave velocity in the vertical direction increases with the depth, while the seismic wave velocity in the horizontal direction gradually increases from slope surface to interior of the slope. Numerical simulation results indicate that the potential slope failure generates outward deformation due to the unloading rebound. The deformation increment is related to distance to the slope surface, the closer the distance, the greater the deformation increment. The decrease of density is an important reason for the difference of wave velocity in the potential failure. The study shows that the variation pattern of seismic wave velocity can reflect the internal structure characteristics of the potential slope failure, and thus can be a method in research on prevention and control of loess collapses.
2023,
31(5):
1655-1667.
Ground fissure is a kind of geological disaster and caused by linear fracture in surface rock and soil. The formation and development of tectonic ground fissures are closely related to the movement characteristics of active faults. The existing reports of tectonic ground fissures are mostly related to fault creep-slip movement, but the ground fissures formed by fault stick-slip(earthquake) are generally divided into seismic surface rupture zones. The main focus is on the investigation of their distribution characteristics. Research on the rupture characteristics and genetic mechanism of a single ground fissure is rare. In this paper, the ground fissure formed in Huangcaoping section of Batang fault is taken as the research object. The shallow-medium-deep geometric structure of ground fissures and their formation mechanisms have been revealed through field geological surveys, unmanned aerial vehicle surveying and mapping, field trenching, and geophysical prospecting. Batang fault forms a valley landform in Huangcaoping segment. The ground fissure in the valley shows a linear geomorphic scarp S1 with a height of 0.26±0.03 m. The geological trench across the valley revealed 18 ground fissures densely developed under and on both sides of the steep slope. Based on the situation of ground fissures penetrating into the overlying strata, three active periods can be roughly divided, which may represent three seismic events since the Holocene on Batang Fault. Part of the ground fissure penetrated to the surface and connected with scarp S1, which may be caused by Batang M 7\begin{document}$ {\raise0.7ex\hbox{1} \!\mathord{\left/ {\vphantom {1 2}}\right.} \!\lower0.7ex\hbox{2}}$\end{document} \begin{document}$ {\raise0.7ex\hbox{1} \!\mathord{\left/ {\vphantom {1 2}}\right.} \!\lower0.7ex\hbox{2}}$\end{document}
2023,
31(5):
1668-1679.
After it enters deep mining, the metal mine will face the complex geological conditions of "three highs and one disturbance". The disturbance of ore body mining can easily induce water inrush disasters. In this paper, the systematic hazard identification and risk assessment of water inrush were carried out on the basis of the hydrogeological structure investigation of the Maoping lead-zinc mine in Northeast Yunnan Province. The control measures of water inrush hazard sources were determined in the deep mining process. According to the geological, tectonic and hydrogeological conditions of the Maoping lead-zinc mine, two types of hydrogeological structures were classified, namely, the strongly water-rich aquifer lateral filling water-steep dip type on the west flank of the Shimenkan anticline and the medium Karst aquifer roof-floor filling water-gentle type on the east flank of the Shimenkan anticline. From the three aspects of tectonic development, aquifer/aquiclude and mining disturbance, a detailed analysis of the hazard identification and risk assessment of water inrush in deep mining of the Maoping lead-zinc mine was conducted. An analytic hierarchy process evaluation model was established to obtain the evaluation map of water inrush risk in the main mining level. The five area types of safe, relatively safe, transitional, relatively dangerous and dangerous area were divided. The evaluation results show that the drainage center of the inverted triangular cone of the mine is the area with less risk of water inrush, i.e., the safe area. The Permian Qixia and Maokou Formation Karst fissure strong water-rich aquifer in the north is the area with the greatest risk of water inrush in the deep mining, i.e., the dangerous area. The zoning maps of the 490 m and 310 m levels show that the dangerous area and the relatively dangerous area are striped in a north-east and north-west direction, which is consistent with the development direction of the main hydraulic conductivity structures. This research provides a scientific basis for the establishment of a five-in-one integrated water control key technology system of "exploration, prevention, blocking, dredging and monitoring" in the deep mining of metal mines.
After it enters deep mining, the metal mine will face the complex geological conditions of "three highs and one disturbance". The disturbance of ore body mining can easily induce water inrush disasters. In this paper, the systematic hazard identification and risk assessment of water inrush were carried out on the basis of the hydrogeological structure investigation of the Maoping lead-zinc mine in Northeast Yunnan Province. The control measures of water inrush hazard sources were determined in the deep mining process. According to the geological, tectonic and hydrogeological conditions of the Maoping lead-zinc mine, two types of hydrogeological structures were classified, namely, the strongly water-rich aquifer lateral filling water-steep dip type on the west flank of the Shimenkan anticline and the medium Karst aquifer roof-floor filling water-gentle type on the east flank of the Shimenkan anticline. From the three aspects of tectonic development, aquifer/aquiclude and mining disturbance, a detailed analysis of the hazard identification and risk assessment of water inrush in deep mining of the Maoping lead-zinc mine was conducted. An analytic hierarchy process evaluation model was established to obtain the evaluation map of water inrush risk in the main mining level. The five area types of safe, relatively safe, transitional, relatively dangerous and dangerous area were divided. The evaluation results show that the drainage center of the inverted triangular cone of the mine is the area with less risk of water inrush, i.e., the safe area. The Permian Qixia and Maokou Formation Karst fissure strong water-rich aquifer in the north is the area with the greatest risk of water inrush in the deep mining, i.e., the dangerous area. The zoning maps of the 490 m and 310 m levels show that the dangerous area and the relatively dangerous area are striped in a north-east and north-west direction, which is consistent with the development direction of the main hydraulic conductivity structures. This research provides a scientific basis for the establishment of a five-in-one integrated water control key technology system of "exploration, prevention, blocking, dredging and monitoring" in the deep mining of metal mines.
2023,
31(5):
1680-1688.
The failure of anti-dip slopes can induce serious geological disasters, so it is of great significance to study the stability and failure modes of anti-dip rock slopes with soft and hard interbed. This paper is based on numerical simulation method and uses discrete element software UDEC. Firstly, this paper takes into account the influence of the slope angle, rock inclination angle, slope height, total thickness of adjacent soft and hard rock layers, thickness ratio of hard and soft rock layers, ratio of mechanical parameter number of hard and soft rock layers, and the mechanical parameters of structural plane. Then based on orthogonal experimental design method, this paper designs 32 sets of orthogonal tests to simulate the stability of the slope and possible failure modes by the strength reduction method. The sensitivity analysis is conducted from two aspects of slope safety factor and displacement. It is found that the slope angle and rock inclination angle have a great impact on the safety factor, and the mechanical parameters of structural plane and slope height have a great impact on the slope displacement. Then the failure modes of anti-dip rock slope with soft and hard interbed are summarized and divided into three types: bending-dumping, collapse-sliding and block-dumping failures.The characteristics of each failure modes are analysed in detail.
The failure of anti-dip slopes can induce serious geological disasters, so it is of great significance to study the stability and failure modes of anti-dip rock slopes with soft and hard interbed. This paper is based on numerical simulation method and uses discrete element software UDEC. Firstly, this paper takes into account the influence of the slope angle, rock inclination angle, slope height, total thickness of adjacent soft and hard rock layers, thickness ratio of hard and soft rock layers, ratio of mechanical parameter number of hard and soft rock layers, and the mechanical parameters of structural plane. Then based on orthogonal experimental design method, this paper designs 32 sets of orthogonal tests to simulate the stability of the slope and possible failure modes by the strength reduction method. The sensitivity analysis is conducted from two aspects of slope safety factor and displacement. It is found that the slope angle and rock inclination angle have a great impact on the safety factor, and the mechanical parameters of structural plane and slope height have a great impact on the slope displacement. Then the failure modes of anti-dip rock slope with soft and hard interbed are summarized and divided into three types: bending-dumping, collapse-sliding and block-dumping failures.The characteristics of each failure modes are analysed in detail.
2023,
31(5):
1689-1695.
Fuzzy clustering techniques are often used in the study of three-dimensional data sets,such as orientation data. Other methods are used in finding groups within directional data. But traditional methods usually meet difficulties when dealing with some complicated data sets. In this paper,a new DifFUZZY clustering method proposed by Ornella Cominetti and Anastasios Matzavinos for the complex data sets,is firstly applied to cluster the orientation data. The results show the follows. (1)DifFUZZY is a new simple and powerful method to realize the 3D-simulation of joint sets,which can automatically separate directional data into distinct clusters and get the dominated value of orientation data. (2)DifFUZZY does not require any advanced information about the orientation data,and it just randomly selects the initial values as the dominated orientation and then according to its own algorithm finally decide which points belong to a cluster and the finally dominated orientation values of the clusters. The suggested method makes it possible to analyse the local stability of rock slope quickly. (3)DifFUZZY can self-acting return the cluster number and on the principle of the membership value it can automatically decide the point lies in which cluster or not.
Fuzzy clustering techniques are often used in the study of three-dimensional data sets,such as orientation data. Other methods are used in finding groups within directional data. But traditional methods usually meet difficulties when dealing with some complicated data sets. In this paper,a new DifFUZZY clustering method proposed by Ornella Cominetti and Anastasios Matzavinos for the complex data sets,is firstly applied to cluster the orientation data. The results show the follows. (1)DifFUZZY is a new simple and powerful method to realize the 3D-simulation of joint sets,which can automatically separate directional data into distinct clusters and get the dominated value of orientation data. (2)DifFUZZY does not require any advanced information about the orientation data,and it just randomly selects the initial values as the dominated orientation and then according to its own algorithm finally decide which points belong to a cluster and the finally dominated orientation values of the clusters. The suggested method makes it possible to analyse the local stability of rock slope quickly. (3)DifFUZZY can self-acting return the cluster number and on the principle of the membership value it can automatically decide the point lies in which cluster or not.
2023,
31(5):
1696-1710.
One basic principle of the 'equilibrium mining' theory is the space conservation-based mining damage invariant equation. This paper analogically analyzes the damage patterns between caving and fractured zones in a long-wall coal mining goaf. Specifically,the paper derives linear(caving zone) and logarithmic(fractured zone) functional expressions to capture the vertical expansion and void distribution characteristics of the above two-zones in abandoned Jiahe colliery. On this basis,a multi-stage conceptual model is then proposed to describe the evolution processes of the vertical expansion and void distribution characteristics of the two-zone. After the required void characteristic parameters of the two-zone are obtained,the paper roughly calculates the void/water-storage volume under the hypothesis of inverted trapezoidal shape of the two-zone structure. Accordingly,the potential of the mine water-based low enthalpy geothermal fluid formed in abandoned and thereafter flooded Jiahe coal mine is evaluated using the volume method. The results indicate that the estimated water storage capacity contained in a typical long-wall mining goaf in abandoned Jiahe mine is 3.4~3.8×105 m3. The overlying rock lithology affects the bulking factor and void ratio vertical distribution in the caving and fractured two-zones,and thereby the water volume and geothermal potential of the order of 10%. Moreover,the void-water stored in mining gobs is about two orders of magnitude larger than that in the shafts and tunnels for abandoned coal mines,which need to have more attention in future study. Finally,the total estimated water storage capacity of the abandoned Jiahe colliery is about 2.2×107 m3,corresponding to a static geothermal potential of approximately 127 GWh(~4.6×105 GJ),which may provide guideline for further exploration and exploitation.
One basic principle of the 'equilibrium mining' theory is the space conservation-based mining damage invariant equation. This paper analogically analyzes the damage patterns between caving and fractured zones in a long-wall coal mining goaf. Specifically,the paper derives linear(caving zone) and logarithmic(fractured zone) functional expressions to capture the vertical expansion and void distribution characteristics of the above two-zones in abandoned Jiahe colliery. On this basis,a multi-stage conceptual model is then proposed to describe the evolution processes of the vertical expansion and void distribution characteristics of the two-zone. After the required void characteristic parameters of the two-zone are obtained,the paper roughly calculates the void/water-storage volume under the hypothesis of inverted trapezoidal shape of the two-zone structure. Accordingly,the potential of the mine water-based low enthalpy geothermal fluid formed in abandoned and thereafter flooded Jiahe coal mine is evaluated using the volume method. The results indicate that the estimated water storage capacity contained in a typical long-wall mining goaf in abandoned Jiahe mine is 3.4~3.8×105 m3. The overlying rock lithology affects the bulking factor and void ratio vertical distribution in the caving and fractured two-zones,and thereby the water volume and geothermal potential of the order of 10%. Moreover,the void-water stored in mining gobs is about two orders of magnitude larger than that in the shafts and tunnels for abandoned coal mines,which need to have more attention in future study. Finally,the total estimated water storage capacity of the abandoned Jiahe colliery is about 2.2×107 m3,corresponding to a static geothermal potential of approximately 127 GWh(~4.6×105 GJ),which may provide guideline for further exploration and exploitation.
2023,
31(5):
1711-1718.
The fluorescence photoelectric monitoring is an important method for monitoring groundwater seepage. The value of distortion coefficient is the key to single-hole fluorescence photoelectric monitoring. This paper aims to systematically study the distortion coefficient with different seepage conditions. It designs a test apparatus of seepage monitoring system to monitor the groundwater seepage. First, the mathematical expression of the distortion coefficient for the fluorescence photoelectric method is derived on the basis of the single-hole dilution model. According to homemade photoelectric monitoring device, a test apparatus of seepage monitoring system is then designed to monitor the groundwater seepage. Finally, the variation law of distortion coefficient is studied with different permeability velocity values, single-hole aperture and opening rate. The experimental results show that the distortion coefficient increases with the aquifer and opening rate, but decreases with the aperture of single-hole. What's more, the importance of the influencing factor follows the regulation of the aquifer > the single-hole aperture > the opening rate. The above research results provide a useful reference for the engineering application of single-hole fluorescence photoelectric method in monitoring groundwater seepage.
The fluorescence photoelectric monitoring is an important method for monitoring groundwater seepage. The value of distortion coefficient is the key to single-hole fluorescence photoelectric monitoring. This paper aims to systematically study the distortion coefficient with different seepage conditions. It designs a test apparatus of seepage monitoring system to monitor the groundwater seepage. First, the mathematical expression of the distortion coefficient for the fluorescence photoelectric method is derived on the basis of the single-hole dilution model. According to homemade photoelectric monitoring device, a test apparatus of seepage monitoring system is then designed to monitor the groundwater seepage. Finally, the variation law of distortion coefficient is studied with different permeability velocity values, single-hole aperture and opening rate. The experimental results show that the distortion coefficient increases with the aquifer and opening rate, but decreases with the aperture of single-hole. What's more, the importance of the influencing factor follows the regulation of the aquifer > the single-hole aperture > the opening rate. The above research results provide a useful reference for the engineering application of single-hole fluorescence photoelectric method in monitoring groundwater seepage.
2023,
31(5):
1719-1727.
Dewatering before bulk excavation is able to cause centimeter-level wall deflection, while the commonly-used inner strut system cannot effectively limit the wall deflection at deep location. Recently, aiming at the inner cross-wall system frequently used to achieve sectionalized construction in soft soil area, some scholars proposed a deformation-control idea of making use of cross wall and optimizing its layout, which effectively restricts the dewatering-induced deformation. This paper aims to further optimize the arrangement of the cross wall to ensure the deformation control effect under the most economical conditions. It investigates the influence of cross wall height on the enclosure wall deflection incurred by dewatering before bulk excavation. Based on an actual foundation pit, a series of numerical simulations are conducted to explore the deformation characteristics of enclosure wall incurred by dewatering before bulk excavation under different pumping depths and cross wall height. On this basis, this paper proposes the optimized layout of cross wall in depth direction. Results show that the layout of cross wall in depth direction has a great influence on its deformation control effect. Specifically, the installation of cross wall within the pumping depth can significantly reduce the retaining wall deflection triggered by pumping, while the installation of cross wall below the pumping depth has a very limited effect on the control of retaining wall deformation. In order to take into account both the economy and deformation control effect, this paper recommends to set the cross wall top at 0.33-0.67Hd above the pumping depth(Hd) and set the cross wall bottom at Hd. When there are deeply-buried structures outside the pit which are sensitive to deformation, it should be better to extend the cross wall bottom downward by 1/3Hf to achieve the deformation control of deeply buried structures, where Hf is the distance between the pumping depth location to the retaining wall bottom.
Dewatering before bulk excavation is able to cause centimeter-level wall deflection, while the commonly-used inner strut system cannot effectively limit the wall deflection at deep location. Recently, aiming at the inner cross-wall system frequently used to achieve sectionalized construction in soft soil area, some scholars proposed a deformation-control idea of making use of cross wall and optimizing its layout, which effectively restricts the dewatering-induced deformation. This paper aims to further optimize the arrangement of the cross wall to ensure the deformation control effect under the most economical conditions. It investigates the influence of cross wall height on the enclosure wall deflection incurred by dewatering before bulk excavation. Based on an actual foundation pit, a series of numerical simulations are conducted to explore the deformation characteristics of enclosure wall incurred by dewatering before bulk excavation under different pumping depths and cross wall height. On this basis, this paper proposes the optimized layout of cross wall in depth direction. Results show that the layout of cross wall in depth direction has a great influence on its deformation control effect. Specifically, the installation of cross wall within the pumping depth can significantly reduce the retaining wall deflection triggered by pumping, while the installation of cross wall below the pumping depth has a very limited effect on the control of retaining wall deformation. In order to take into account both the economy and deformation control effect, this paper recommends to set the cross wall top at 0.33-0.67Hd above the pumping depth(Hd) and set the cross wall bottom at Hd. When there are deeply-buried structures outside the pit which are sensitive to deformation, it should be better to extend the cross wall bottom downward by 1/3Hf to achieve the deformation control of deeply buried structures, where Hf is the distance between the pumping depth location to the retaining wall bottom.
2023,
31(5):
1728-1737.
Because Green-Ampt model is too simplified to accurately calculate the total infiltration volume, we propose an improved Green-Ampt model which conforms to the actual infiltration law in this paper. The proposed model divides the soil profile into saturated, transitional saturated and natural saturated zones. A soil column test is performed to verify the accuracy of the proposed model and the existence of transitional zone. Three indexes are used to evaluate the accuracy of the model. They are the mean absolute error(MAE), the mean absolute relative error(MARE) and the root mean square error(RMSE). The MAE, MARE and RMSE are smaller than those of the classical Green-Ampt model. As a result, the accuracy of the proposed model is higher than that of Green-Ampt model. The proposed model is also used to analyze the stability of an unsaturated soil slope. The calculated results show that the slope angle and precipitation rainfall intensity are inversely proportional to the slope safety factor, and the former has a greater influence impact on the slope safety factor. Compared with the proposed model, the Green-Ampt model underestimates the slope safety. The improved Green-Ampt model provides references for analyzing the risk of rainfall and landslides.
Because Green-Ampt model is too simplified to accurately calculate the total infiltration volume, we propose an improved Green-Ampt model which conforms to the actual infiltration law in this paper. The proposed model divides the soil profile into saturated, transitional saturated and natural saturated zones. A soil column test is performed to verify the accuracy of the proposed model and the existence of transitional zone. Three indexes are used to evaluate the accuracy of the model. They are the mean absolute error(MAE), the mean absolute relative error(MARE) and the root mean square error(RMSE). The MAE, MARE and RMSE are smaller than those of the classical Green-Ampt model. As a result, the accuracy of the proposed model is higher than that of Green-Ampt model. The proposed model is also used to analyze the stability of an unsaturated soil slope. The calculated results show that the slope angle and precipitation rainfall intensity are inversely proportional to the slope safety factor, and the former has a greater influence impact on the slope safety factor. Compared with the proposed model, the Green-Ampt model underestimates the slope safety. The improved Green-Ampt model provides references for analyzing the risk of rainfall and landslides.
2023,
31(5):
1738-1747.
With the development and utilization of urban underground space, more and more basement excavations were located nearby an existing utility tunnel and have an important impact on the safety and waterproof performance of the utility tunnel. Based on a field case in Xiamen, a three-dimensional finite element analysis was conducted, using PLAXIS 3D with a HS-Small small-strain soil constitutive model, to investigate the effects of basement excavation on an adjacent double-compartment utility tunnel. The numerical results show that the deformation mechanism of an adjacent utility tunnel induced by excavation can be divided into three characteristic deformation modes, namely a translational-rotation zone, a relative torsion zone and a displacement constraint zone. Around the middle part of the basement excavation, the utility tunnel shifts towards the basement and rotates about its axis. Around the boundary of the basement excavation, the utility tunnel was subjected to relatively torsion. In a zone far from the basement, the utility tunnel was constrained by the surrounding soil and was relatively static. The cross-section of the utility tunnel located in the translational-rotation zone and the relative torsion zone was sheared towards the basement excavation. The roof of the utility tunnel displaces horizontally relative to the floor. Besides, the roof of the municipal compartment near the basement excavation and the lower part of the side wall far away from the basement excavation experience larger deformation. The distance between the utility tunnel and the basement has insignificant effect on the distribution of the three deformation characteristic zones. The closer the basement excavation is to the utility tunnel, the greater the deformation of the utility tunnel.
With the development and utilization of urban underground space, more and more basement excavations were located nearby an existing utility tunnel and have an important impact on the safety and waterproof performance of the utility tunnel. Based on a field case in Xiamen, a three-dimensional finite element analysis was conducted, using PLAXIS 3D with a HS-Small small-strain soil constitutive model, to investigate the effects of basement excavation on an adjacent double-compartment utility tunnel. The numerical results show that the deformation mechanism of an adjacent utility tunnel induced by excavation can be divided into three characteristic deformation modes, namely a translational-rotation zone, a relative torsion zone and a displacement constraint zone. Around the middle part of the basement excavation, the utility tunnel shifts towards the basement and rotates about its axis. Around the boundary of the basement excavation, the utility tunnel was subjected to relatively torsion. In a zone far from the basement, the utility tunnel was constrained by the surrounding soil and was relatively static. The cross-section of the utility tunnel located in the translational-rotation zone and the relative torsion zone was sheared towards the basement excavation. The roof of the utility tunnel displaces horizontally relative to the floor. Besides, the roof of the municipal compartment near the basement excavation and the lower part of the side wall far away from the basement excavation experience larger deformation. The distance between the utility tunnel and the basement has insignificant effect on the distribution of the three deformation characteristic zones. The closer the basement excavation is to the utility tunnel, the greater the deformation of the utility tunnel.
2023,
31(5):
1748-1756.
Currently, cross-passages in the section of twin-tunnels have become an indispensable part, which has the functions, such as drainage, fire prevention, connecting the two tunnels, and acting as "escape passages" in tunnel accidents. To accurately grasp the development law of the temperature field during construction of tunnel cross-passages in seashore area in Xiamen using the ground freezing method, the full process monitoring and analysis of the ground freezing construction of No.2 cross-passage in Ma-ji section of Xiamen Metro Line 6 were conducted. Correspondingly, the three-dimensional finite element model was established to analyze the variation law of the temperature field in the process of freezing construction. The numerical results were compared with the measurements of some typical points. The results show that the tendency of the temperature change of each measuring point is basically the same, and the deeper the position of the point, the better the effect of freezing. In the early stage, the discrepancies of the pressures between various pressure relief holes are mainly caused by the inherent earth pressure of points at different positions. The closer to the freezing pipes the soil is, the faster the temperature drops, the higher the strength of the frozen soil. Accordingly, the freezing efficiency is enhanced after the formation of a frozen wall. The temperature field by the numerical analysis is unsymmetrical. This numerical modeling method is of convenience, good feasibility, and high reliability. It can be an approach to predict the temperature field in the process of freezing construction of similar projects.
Currently, cross-passages in the section of twin-tunnels have become an indispensable part, which has the functions, such as drainage, fire prevention, connecting the two tunnels, and acting as "escape passages" in tunnel accidents. To accurately grasp the development law of the temperature field during construction of tunnel cross-passages in seashore area in Xiamen using the ground freezing method, the full process monitoring and analysis of the ground freezing construction of No.2 cross-passage in Ma-ji section of Xiamen Metro Line 6 were conducted. Correspondingly, the three-dimensional finite element model was established to analyze the variation law of the temperature field in the process of freezing construction. The numerical results were compared with the measurements of some typical points. The results show that the tendency of the temperature change of each measuring point is basically the same, and the deeper the position of the point, the better the effect of freezing. In the early stage, the discrepancies of the pressures between various pressure relief holes are mainly caused by the inherent earth pressure of points at different positions. The closer to the freezing pipes the soil is, the faster the temperature drops, the higher the strength of the frozen soil. Accordingly, the freezing efficiency is enhanced after the formation of a frozen wall. The temperature field by the numerical analysis is unsymmetrical. This numerical modeling method is of convenience, good feasibility, and high reliability. It can be an approach to predict the temperature field in the process of freezing construction of similar projects.
2023,
31(5):
1757-1766.
Hammer efficiency is defined as the energy transfer rate, and is an important index in standard penetration test to evaluate site bearing capacity and to assess liquefaction potential. In standard procedure outside China, the energy transfer rate is usually obtained by real in-situ testing using an energy measurement equipment, and then to correct blow counts. In Chinese codes, however, the energy transferred into the rod during hammering is not considered instead that the uncorrected blow counts are used in engineering practice, which leads to blow counts of standard penetration test obtained in China can hardly be compared with others. To solve this issue, three typical testing sites in Xichang earthquake experiment site are selected to test the hammer efficiency used in the Chinese routine standard penetration test equipment and to evaluate stability of energy transferring. The analytical results indicate that the energy transfer ratio is remarkably stable that the average energy transfer ratios exceed 75%. A slight trend of energy transfer ratio increasing with depth is delineated that the incremental of the energy transfer rate stays about 10% in the depth range of 20 m. The energy transfer ratio obtained in the tests can be used to evaluate the current standard penetration test apparatus.
Hammer efficiency is defined as the energy transfer rate, and is an important index in standard penetration test to evaluate site bearing capacity and to assess liquefaction potential. In standard procedure outside China, the energy transfer rate is usually obtained by real in-situ testing using an energy measurement equipment, and then to correct blow counts. In Chinese codes, however, the energy transferred into the rod during hammering is not considered instead that the uncorrected blow counts are used in engineering practice, which leads to blow counts of standard penetration test obtained in China can hardly be compared with others. To solve this issue, three typical testing sites in Xichang earthquake experiment site are selected to test the hammer efficiency used in the Chinese routine standard penetration test equipment and to evaluate stability of energy transferring. The analytical results indicate that the energy transfer ratio is remarkably stable that the average energy transfer ratios exceed 75%. A slight trend of energy transfer ratio increasing with depth is delineated that the incremental of the energy transfer rate stays about 10% in the depth range of 20 m. The energy transfer ratio obtained in the tests can be used to evaluate the current standard penetration test apparatus.
2023,
31(5):
1767-1773.
Collapsibility is the most important factor restricting loess site construction. Loess field test is long in time and high in cost. This paper carries out the static cone peneration test in the New District in Lanzhou loess ground and the Jingyuan Yellow River high terrace loess area. It examines the taper cone tip resistance relation between frictional resistance along the depth of soil layer. It takes the original state collapsibility loess samples for indoor test. It is found that the coefficient of self-weight collapsibility measured in laboratory tests has a good linear relationship along the depth,and the relationship between the cone tip resistance and the cone side resistance. The coefficient of self-weight collapsibility measured by static penetration test is established. A method for rapidly evaluating self-weight collapsibility of loess site is put forward based on the results of static penetration test. Based on the above studies,the self-weight collapsibility of loess sites in the Jingyuan Yellow River terrace and Lanzhou New Area is evaluated,and the feasibility and accuracy of the method are verified.
Collapsibility is the most important factor restricting loess site construction. Loess field test is long in time and high in cost. This paper carries out the static cone peneration test in the New District in Lanzhou loess ground and the Jingyuan Yellow River high terrace loess area. It examines the taper cone tip resistance relation between frictional resistance along the depth of soil layer. It takes the original state collapsibility loess samples for indoor test. It is found that the coefficient of self-weight collapsibility measured in laboratory tests has a good linear relationship along the depth,and the relationship between the cone tip resistance and the cone side resistance. The coefficient of self-weight collapsibility measured by static penetration test is established. A method for rapidly evaluating self-weight collapsibility of loess site is put forward based on the results of static penetration test. Based on the above studies,the self-weight collapsibility of loess sites in the Jingyuan Yellow River terrace and Lanzhou New Area is evaluated,and the feasibility and accuracy of the method are verified.
2023,
31(5):
1774-1781.
This paper aims to study the effect of gradation on the compaction and strength characteristics of coal gangue subgrade filler. It takes the coal gangue collected from an abandoned coal mine in Xiangtan of Hunan Province as the research object. It studies the gradation effect of the compaction and strength behaviors for coal gangue subgrade filler using large vibration compaction experiment and large-scale triaxial test. Based on the gradation equation of fractal model, the limit of well gradation is captured, and the advantages of using this gradation equation for designing gradation are analyzed. Moreover, the gradation has great influence on the compaction and strength of coal gangue subgrade filler. With the increase of fine particle content, the maximum dry density and deviatoric stress first increase and then decrease, which reflects the existence of an optimal range of particle gradation for coal gangue subgrade filler. On this basis, the optimal gradation ranges of coal gangue subgrade filler is obtained. In addition, the test results show that the optimal gradation ranges of coal gangue subgrade filler obtained by large-scale triaxial test and vibration compaction experiment are basically the same. Considering the high cost of large-scale triaxial test, the vibration compaction is recomended to obtain the experiment optional gradation.
This paper aims to study the effect of gradation on the compaction and strength characteristics of coal gangue subgrade filler. It takes the coal gangue collected from an abandoned coal mine in Xiangtan of Hunan Province as the research object. It studies the gradation effect of the compaction and strength behaviors for coal gangue subgrade filler using large vibration compaction experiment and large-scale triaxial test. Based on the gradation equation of fractal model, the limit of well gradation is captured, and the advantages of using this gradation equation for designing gradation are analyzed. Moreover, the gradation has great influence on the compaction and strength of coal gangue subgrade filler. With the increase of fine particle content, the maximum dry density and deviatoric stress first increase and then decrease, which reflects the existence of an optimal range of particle gradation for coal gangue subgrade filler. On this basis, the optimal gradation ranges of coal gangue subgrade filler is obtained. In addition, the test results show that the optimal gradation ranges of coal gangue subgrade filler obtained by large-scale triaxial test and vibration compaction experiment are basically the same. Considering the high cost of large-scale triaxial test, the vibration compaction is recomended to obtain the experiment optional gradation.
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