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Editor Work2018 Vol. 26, No. 2
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2018, 26(2): 279-285.
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A huge high-speed landslide occurred in Wenjiagou of Qingping township, Mianzhu city, during the 5.12 Wenchuan earthquake. By systematical analysis of the geologic conditions and the landslide movement characteristics, the initiation breaking and instability occurring model is proposed regarding the effects of earthquake and landslide ground vibration. Then, the processes of rock mass movement is classified as four stages which include ejecting, flying and scraping, collision and direction altering, stopping and accumulating stages. Considering the earthquake and landslide ground shaking forces, the total force direction is 285° and approximately equals to the landslide initiation direction. Furthermore, the average velocity and time corresponding with the movement mass in each stage are calculated. The average velocity is 115.64 m·s-1, 69.38 m·s-1, 41.6 m·s-1, 20.8 m·s-1 and the respective sub-total time is 11.8 s, 8.6 s, 24.0 s, 48.1 s for the ejecting to stopping and accumulating stages, respectively. The total time of the landslide movement is 92.5 s, almost same as more than 1 minute estimated by the survival inhabitants. The results show that the main reason that cause Wenjiagou landslide to move with high speed is the effect of ejecting and flying, which transfer the gravitational potential energy to kinetic energy completely.
A huge high-speed landslide occurred in Wenjiagou of Qingping township, Mianzhu city, during the 5.12 Wenchuan earthquake. By systematical analysis of the geologic conditions and the landslide movement characteristics, the initiation breaking and instability occurring model is proposed regarding the effects of earthquake and landslide ground vibration. Then, the processes of rock mass movement is classified as four stages which include ejecting, flying and scraping, collision and direction altering, stopping and accumulating stages. Considering the earthquake and landslide ground shaking forces, the total force direction is 285° and approximately equals to the landslide initiation direction. Furthermore, the average velocity and time corresponding with the movement mass in each stage are calculated. The average velocity is 115.64 m·s-1, 69.38 m·s-1, 41.6 m·s-1, 20.8 m·s-1 and the respective sub-total time is 11.8 s, 8.6 s, 24.0 s, 48.1 s for the ejecting to stopping and accumulating stages, respectively. The total time of the landslide movement is 92.5 s, almost same as more than 1 minute estimated by the survival inhabitants. The results show that the main reason that cause Wenjiagou landslide to move with high speed is the effect of ejecting and flying, which transfer the gravitational potential energy to kinetic energy completely.
2018, 26(2): 286-295.
The paper uses the data from articles on debris flow risk in CNKI database during 1988-2017, analyzes the changes in the number of papers published per year and main publishing journals, and identifies the core authors, main research institutions and high-frequent keywords based on CiteSpace Ⅲ. So it analyzes the development of this field in recent 30 years. The results show that:(1)Debris flow risk is an inter-discipline that is related to disaster science, geography and geology. The amount of the papers on debris flow risk of China from 1988 to 2017 shows a fluctuating trend, however, the proportion of the papers published in high impact factor journals and highly cited papers are relatively small.(2)The core authors and core institutions are mostly located in southwestern China and occupy a large proportion of the number of the articles, which is directly related to the frequent happens of debris flows there.(3)Hazard research is the core theme in the early stage of the risk research, and develops into the risk discipline since 2000. At that time, the research themes and the technical methods became diversified. After 2008, the discipline appears to be stagnated. However, the large debris flows induced by Wenchuan earthquake on May 12, 2008 might provide new research cases in the future for the debris flow risk study. This finding will be helpful to understand the history, present situation and the hot spots of the debris flow risk in China.
The paper uses the data from articles on debris flow risk in CNKI database during 1988-2017, analyzes the changes in the number of papers published per year and main publishing journals, and identifies the core authors, main research institutions and high-frequent keywords based on CiteSpace Ⅲ. So it analyzes the development of this field in recent 30 years. The results show that:(1)Debris flow risk is an inter-discipline that is related to disaster science, geography and geology. The amount of the papers on debris flow risk of China from 1988 to 2017 shows a fluctuating trend, however, the proportion of the papers published in high impact factor journals and highly cited papers are relatively small.(2)The core authors and core institutions are mostly located in southwestern China and occupy a large proportion of the number of the articles, which is directly related to the frequent happens of debris flows there.(3)Hazard research is the core theme in the early stage of the risk research, and develops into the risk discipline since 2000. At that time, the research themes and the technical methods became diversified. After 2008, the discipline appears to be stagnated. However, the large debris flows induced by Wenchuan earthquake on May 12, 2008 might provide new research cases in the future for the debris flow risk study. This finding will be helpful to understand the history, present situation and the hot spots of the debris flow risk in China.
2018, 26(2): 296-308.
Desiccation cracking is a common phenomenon in clay soils, which have an important influence on the properties of soils, leading to all kinds of engineering and environmental problems. Therefore, studying the soils cracking phenomenon, finding out its mechanical mechanism and build theoretical model is of great importance. This paper introduces the mechanical mechanism and related theoretical models of soil cracking by collecting relevant data, analyzing the characteristics of each model, and introducing its classification based on the theoretical basis of the models. In general, the following main conclusions are obtained. Researchers think that the mechanism of the crack haven't been unified. The mainstream view thinks that cracks are a form of damage of soil. Tension stress and tensile strength are the two key mechanical indexes, but it can't explain all the cracking phenomenon. In general, the theoretical models related to soil cracking can be divided into four categories. (1)Based on the theory of fracture mechanics, representatives are the linear elastic fracture mechanics model, elastic-plastic fracture mechanics model and the finite element model based on linear elastic fracture mechanics. (2)Based on the theory of tension stress failure, representatives are the linear elastic model, the shear failure model, elastic mechanics model and the cohesive crack model. (3)Water content-volume change model based on the process of shrinkage deformation of soil. (4)The analysis of stress path model on the basis of the soil consolidation theory. On this basis, the shortcomings and applicable conditions of each model are evaluated. Finally, this paper also puts forward the key directions of the studies about the issues. They include soil microstructure change and micromechanics analysis during the process of evaporation, the migration process, distribution and occurrence of pore water in the process of evaporation, research on soil shrinkage, research on tensile strength of soil, prediction model about fracture width, depth and growth geometry characteristics of crack soil.
Desiccation cracking is a common phenomenon in clay soils, which have an important influence on the properties of soils, leading to all kinds of engineering and environmental problems. Therefore, studying the soils cracking phenomenon, finding out its mechanical mechanism and build theoretical model is of great importance. This paper introduces the mechanical mechanism and related theoretical models of soil cracking by collecting relevant data, analyzing the characteristics of each model, and introducing its classification based on the theoretical basis of the models. In general, the following main conclusions are obtained. Researchers think that the mechanism of the crack haven't been unified. The mainstream view thinks that cracks are a form of damage of soil. Tension stress and tensile strength are the two key mechanical indexes, but it can't explain all the cracking phenomenon. In general, the theoretical models related to soil cracking can be divided into four categories. (1)Based on the theory of fracture mechanics, representatives are the linear elastic fracture mechanics model, elastic-plastic fracture mechanics model and the finite element model based on linear elastic fracture mechanics. (2)Based on the theory of tension stress failure, representatives are the linear elastic model, the shear failure model, elastic mechanics model and the cohesive crack model. (3)Water content-volume change model based on the process of shrinkage deformation of soil. (4)The analysis of stress path model on the basis of the soil consolidation theory. On this basis, the shortcomings and applicable conditions of each model are evaluated. Finally, this paper also puts forward the key directions of the studies about the issues. They include soil microstructure change and micromechanics analysis during the process of evaporation, the migration process, distribution and occurrence of pore water in the process of evaporation, research on soil shrinkage, research on tensile strength of soil, prediction model about fracture width, depth and growth geometry characteristics of crack soil.
2018, 26(2): 309-318.
The slide surface of Daguangbao landslide is developed in the interlayer fault zone where the fragmentation degree of rock mass is increased from the upper to the lower with a belt of mud at the bottom. 18 groups of medium-sized direct shear tests were carried out for the samples collected from Daguangbao interlayer fault zone. 42 groups of unconsolidated direct shear tests were carried for the samples collected from mud belt and mylonite belt by controlling the moisture content. The results show that the shear characteristics of the rock mass in interlayer fault zone are related to the degree of fragmentation. Characteristics of strain softening of rock mass with lower degree of fragmentation is more obvious while the shear strength of rock mass with higher degree of fragmentation is worse. The shear strength and the friction angle of mylonite are mostly greater than the soil in the mud belt and the shear characteristics of mylonite is less affected by the ground water than the mud. The shear strength and cohesive strength of the soil in the mud belt are decreased rapidly with the increase of moisture content. The internal friction angle has a negative exponential relation with the moisture content. The shear strength of the soil in mud belt can be greatly reduced with the intrusion of groundwater caused by the rock mass dilatancy during the earthquake. The results of this study are important for understanding the position of the slip surface. It is also important for understanding the influence of the increase of moisture percentage and the further fragmentation on the shear strength of the rock mass in the fault zone.
The slide surface of Daguangbao landslide is developed in the interlayer fault zone where the fragmentation degree of rock mass is increased from the upper to the lower with a belt of mud at the bottom. 18 groups of medium-sized direct shear tests were carried out for the samples collected from Daguangbao interlayer fault zone. 42 groups of unconsolidated direct shear tests were carried for the samples collected from mud belt and mylonite belt by controlling the moisture content. The results show that the shear characteristics of the rock mass in interlayer fault zone are related to the degree of fragmentation. Characteristics of strain softening of rock mass with lower degree of fragmentation is more obvious while the shear strength of rock mass with higher degree of fragmentation is worse. The shear strength and the friction angle of mylonite are mostly greater than the soil in the mud belt and the shear characteristics of mylonite is less affected by the ground water than the mud. The shear strength and cohesive strength of the soil in the mud belt are decreased rapidly with the increase of moisture content. The internal friction angle has a negative exponential relation with the moisture content. The shear strength of the soil in mud belt can be greatly reduced with the intrusion of groundwater caused by the rock mass dilatancy during the earthquake. The results of this study are important for understanding the position of the slip surface. It is also important for understanding the influence of the increase of moisture percentage and the further fragmentation on the shear strength of the rock mass in the fault zone.
2018, 26(2): 319-324.
The movement of the flowslide is complex due to the centrifugal force and centripetal force of curved topography. However, it was not fully considered in the past. Based on the LS_RAPID model, this paper puts forward a new method to calculate centrifugal force and centripetal force of flowslide mass due to surface topography. The control equations of the LS_RAPID are revised to a new model which considers the influence of surface topography, which is named as LSD_T(Landslide Dynamic_Terrain) model. This new model is used to simulate a typical flowslide-Dagou landslide in Tianshui city. The simulation result is compared with that of LS_RAPID model using the same parameters. Results show that the surface topography's effect on the movement of sliding mass is not obvious in the LS_RAPID model. The sliding mass rushes out of the channel at the corner, which is not conform to the actual movement of the flowslide. However, the LSD_T model can reflect the influence of the centripetal force from curve topography better. The sliding mass moves along the channel. The trajectory is basically consistent with the actual accumulation process.
The movement of the flowslide is complex due to the centrifugal force and centripetal force of curved topography. However, it was not fully considered in the past. Based on the LS_RAPID model, this paper puts forward a new method to calculate centrifugal force and centripetal force of flowslide mass due to surface topography. The control equations of the LS_RAPID are revised to a new model which considers the influence of surface topography, which is named as LSD_T(Landslide Dynamic_Terrain) model. This new model is used to simulate a typical flowslide-Dagou landslide in Tianshui city. The simulation result is compared with that of LS_RAPID model using the same parameters. Results show that the surface topography's effect on the movement of sliding mass is not obvious in the LS_RAPID model. The sliding mass rushes out of the channel at the corner, which is not conform to the actual movement of the flowslide. However, the LSD_T model can reflect the influence of the centripetal force from curve topography better. The sliding mass moves along the channel. The trajectory is basically consistent with the actual accumulation process.
RESEARCH ON DEVELOPMENT AND DISTRIBUTION RULES OF LARGE-SCALE LANDSLIDES IN BAILONGJIANG RIVER BASIN
2018, 26(2): 325-333.
After filed investigation and interpretation of remote-sensing images, 259 large-scale landslides have been obtained, and general distribution situation of large-scale landslides has been learnt. Then, the distribution of these large-scale landslides is investigated statistically using GIS techniques to determine the correlations between the occurrence of large-scale landslides and the distance from the fault, elevation and rock group type. The main results are summarized as follows:(1)The large-scale landslides show the feature of zonal distribution along the fault and linear distribution along the rivers. (2)More than 90% of the large-scale landslides are distributed within the range of 5.0 km from the fault, and the farther from the fault, the lower number of large-scale landslides. At the same time, the large-scale landslides are mainly distributed in the zones closely related with the crossing, staggering and transforming section of the fault. (3)The large-scale landslides have corresponding relationship with the elevation and micro-landform. Most large-scale landslides occur in river valley and canyon section below the elevation of 1200 to 2600 m(upstream is 2200 to 2600 m, midstream is 1600 to 2200 m, downstream is 1200 to 1600 m), particularly in the upper segment of canyon section. (4)The soft and hard stratified rock group in the basin is most favorable for the development of large-scale landslides. More than 93% of the large-scale landslides are associated with phyllite and slate metamorphic rocks.(5)The main sliding directions are the NE and W. But it shows the same characteristics as the strike of the fault, namely SE and NW oriented in Liangshui, Wudu to Lazikou, Zhouqu.(6)The sliding distances of the large-scale landslides are related to the volume of the landslide. As the landslide volume increases, the friction coefficient of the large-scale landslides decreases exponentially. Some large-scale landslides show strong debris flow characteristics.
After filed investigation and interpretation of remote-sensing images, 259 large-scale landslides have been obtained, and general distribution situation of large-scale landslides has been learnt. Then, the distribution of these large-scale landslides is investigated statistically using GIS techniques to determine the correlations between the occurrence of large-scale landslides and the distance from the fault, elevation and rock group type. The main results are summarized as follows:(1)The large-scale landslides show the feature of zonal distribution along the fault and linear distribution along the rivers. (2)More than 90% of the large-scale landslides are distributed within the range of 5.0 km from the fault, and the farther from the fault, the lower number of large-scale landslides. At the same time, the large-scale landslides are mainly distributed in the zones closely related with the crossing, staggering and transforming section of the fault. (3)The large-scale landslides have corresponding relationship with the elevation and micro-landform. Most large-scale landslides occur in river valley and canyon section below the elevation of 1200 to 2600 m(upstream is 2200 to 2600 m, midstream is 1600 to 2200 m, downstream is 1200 to 1600 m), particularly in the upper segment of canyon section. (4)The soft and hard stratified rock group in the basin is most favorable for the development of large-scale landslides. More than 93% of the large-scale landslides are associated with phyllite and slate metamorphic rocks.(5)The main sliding directions are the NE and W. But it shows the same characteristics as the strike of the fault, namely SE and NW oriented in Liangshui, Wudu to Lazikou, Zhouqu.(6)The sliding distances of the large-scale landslides are related to the volume of the landslide. As the landslide volume increases, the friction coefficient of the large-scale landslides decreases exponentially. Some large-scale landslides show strong debris flow characteristics.
2018, 26(2): 334-339.
The key to debris flow initiation is rain erosion and infiltration. With the controllable intensity artificial rainfall experiment, debris flow alluvium of Zhangye City, Gansu Province was chosen as media to study rainfall erosion-resistant on the 100 mm·h-1 heavy rain conditions. And debris flow alluvium was sprayed on surface with SH agents. The results of this study are as follows. The untreated soil surfaces were eroded obviously and formed several erosion gullies and it had a large number of erosion particles in bottom. However, soil treated with SH agent had significantly rainfall erosion-resistant. The protective layer formed by SH agent connecting soil particles had strong adhesion. There were no obvious trances and only a few erosion particles existed. Moreover, rainfall erosion-resistant first was strengthened then stabilized with increasing SH amounts."Mosaic structure" layer formed on silt and sand soil were more stable than that of "floating structure" layer formed on gravely soil. The rainfall erosion-resistant was effected by SH agent amounts and soil types. Considering of aspects of cost and rainfall erosion-resistant etc., the findings suggest that a SH agent amount of 1.0 kg·m-2 would be ideal for silt and sand soil, but need aptly to increase SH agent amounts for gravely soil.
The key to debris flow initiation is rain erosion and infiltration. With the controllable intensity artificial rainfall experiment, debris flow alluvium of Zhangye City, Gansu Province was chosen as media to study rainfall erosion-resistant on the 100 mm·h-1 heavy rain conditions. And debris flow alluvium was sprayed on surface with SH agents. The results of this study are as follows. The untreated soil surfaces were eroded obviously and formed several erosion gullies and it had a large number of erosion particles in bottom. However, soil treated with SH agent had significantly rainfall erosion-resistant. The protective layer formed by SH agent connecting soil particles had strong adhesion. There were no obvious trances and only a few erosion particles existed. Moreover, rainfall erosion-resistant first was strengthened then stabilized with increasing SH amounts."Mosaic structure" layer formed on silt and sand soil were more stable than that of "floating structure" layer formed on gravely soil. The rainfall erosion-resistant was effected by SH agent amounts and soil types. Considering of aspects of cost and rainfall erosion-resistant etc., the findings suggest that a SH agent amount of 1.0 kg·m-2 would be ideal for silt and sand soil, but need aptly to increase SH agent amounts for gravely soil.
2018, 26(2): 348-355.
With the national-wide mines shutdown, a great amount of mine slots are abandoned, which become one main media for the formation of geological hazards. At the center of Daxingyu Mine, there are eight mine lots close to the county of Jixian. Their total area is 207.8 ha. The existing man-made highly incised slopes lead to frequent geological hazards, and seriously influence the routine living environment of the residents in those areas. This paper takes the Daxingyu Mine of Jixian as the example, and investigates in detail for the damage modes and hazard factors, possible hazard protection and integrated environment management solutions for the highly incisive slopes formed with dolomite rocks in the Jixian mine area. Based on the investigation, there are four types of hazard modes including slope debris flow, collapse, bedding slip cracks, and slip bending. They mainly result from the change of slope shape with the man-made digging. With the multiple influence of internal and external factors, the formation of bedding landslide can be triggered, which finally leads to the series of geological hazards. The proper hazard protection solutions include top cutting, bottom filling, anchor reinforcement, slope protection. The integrated environment remediation should employ platform tree planting, hole planting, vine climbing and spray seeding greening methods. In addition, the targeted mine slot is located within the urban planning scope close to a critical traffic junction. So the environment landscape design should also need to be considered seriously. Thus the solutions of slope cutting and local anchor reinforcement can be selected for the hazard remediation, which will highly rely on the integrated environment management measures. In addition, the arbor and bushes can be planted on the created platform with the slope-cutting, which results in a very good comprehensive treatment measure.
With the national-wide mines shutdown, a great amount of mine slots are abandoned, which become one main media for the formation of geological hazards. At the center of Daxingyu Mine, there are eight mine lots close to the county of Jixian. Their total area is 207.8 ha. The existing man-made highly incised slopes lead to frequent geological hazards, and seriously influence the routine living environment of the residents in those areas. This paper takes the Daxingyu Mine of Jixian as the example, and investigates in detail for the damage modes and hazard factors, possible hazard protection and integrated environment management solutions for the highly incisive slopes formed with dolomite rocks in the Jixian mine area. Based on the investigation, there are four types of hazard modes including slope debris flow, collapse, bedding slip cracks, and slip bending. They mainly result from the change of slope shape with the man-made digging. With the multiple influence of internal and external factors, the formation of bedding landslide can be triggered, which finally leads to the series of geological hazards. The proper hazard protection solutions include top cutting, bottom filling, anchor reinforcement, slope protection. The integrated environment remediation should employ platform tree planting, hole planting, vine climbing and spray seeding greening methods. In addition, the targeted mine slot is located within the urban planning scope close to a critical traffic junction. So the environment landscape design should also need to be considered seriously. Thus the solutions of slope cutting and local anchor reinforcement can be selected for the hazard remediation, which will highly rely on the integrated environment management measures. In addition, the arbor and bushes can be planted on the created platform with the slope-cutting, which results in a very good comprehensive treatment measure.
FULL SECTION MONITORING OF LAND SUBSIDENCE BOREHOLE USING DISTRIBUTED FIBER OPTIC SENSING TECHNIQUES
2018, 26(2): 356-364.
This paper introduces a full section monitoring of land subsidence borehole using distributed fiber optic sensing(DFOS)techniques, which can obtain data on multi-fields and multi-parameters and provide delicate monitoring of land subsidence. The concept of full section monitoring of borehole using DFOS is firstly introduced. The key techniques on the application of this method include the selections of cables and sensors, the backfill materials, the coupling of cables and soils and the installation of cables and sensors in boreholes. A system frame of the full section monitoring of borehole with DFOS is built. Finally, the whole process of full section monitoring with DFOS and its features are illustrated with a case in Shengze Town, Suzhou.
This paper introduces a full section monitoring of land subsidence borehole using distributed fiber optic sensing(DFOS)techniques, which can obtain data on multi-fields and multi-parameters and provide delicate monitoring of land subsidence. The concept of full section monitoring of borehole using DFOS is firstly introduced. The key techniques on the application of this method include the selections of cables and sensors, the backfill materials, the coupling of cables and soils and the installation of cables and sensors in boreholes. A system frame of the full section monitoring of borehole with DFOS is built. Finally, the whole process of full section monitoring with DFOS and its features are illustrated with a case in Shengze Town, Suzhou.
2018, 26(2): 365-373.
This paper simulates and evaluates the influence of groundwater exploitation on land subsidence in Cangzhou area, and provides decision basis for municipal planning and groundwater resources management. On the basis of Biot's consolidation theory, it establishes a three-dimensional full coupling mathematic model of groundwater exploitation and land subsidence in Cangzhou. On the basis of the identification and verification of the model, it simulates the trend of land subsidence under the superposition of current situation of groundwater exploitation from December 31, 2010 to December 31, 2025. It partitions the land subsidence according to the rate of land subsidence. The results show that the maximum cumulative land subsidence in Cangzhou area is 466.82 mm, and the minimum cumulative land subsidence is 241.54 mm. Most areas are four or five warning areas. Only Suning County is the three warning area.
This paper simulates and evaluates the influence of groundwater exploitation on land subsidence in Cangzhou area, and provides decision basis for municipal planning and groundwater resources management. On the basis of Biot's consolidation theory, it establishes a three-dimensional full coupling mathematic model of groundwater exploitation and land subsidence in Cangzhou. On the basis of the identification and verification of the model, it simulates the trend of land subsidence under the superposition of current situation of groundwater exploitation from December 31, 2010 to December 31, 2025. It partitions the land subsidence according to the rate of land subsidence. The results show that the maximum cumulative land subsidence in Cangzhou area is 466.82 mm, and the minimum cumulative land subsidence is 241.54 mm. Most areas are four or five warning areas. Only Suning County is the three warning area.
2018, 26(2): 374-383.
The argument about the cause of geological disaster(natural or man-made) induced by excavation unloading during the construction period is raised. A case study of the landslide occurred on the slope of an expressway in north China is conducted. The slope is a dip slope composed of the weak interbedded mica schist. Through the engineering geological survey and data analysis, it is concluded that the multiple weak interlayers which constitute the slope body and the strong precipitation encountered during the construction are the main natural reasons that affect the slope stability. Insufficient understanding of the complex geological conditions, and inadequate prevention and control measures during the investigation, design and construction process are the main man-made reasons. The weights of six parameters including natural and human factors are calculated using Analytic Hierarchy Process(AHP), Multi-factor interaction matrix method and Delphi method, and then the responsibility is divided. The results of this study are expected to provide some references for the selection factors of similar engineering and the division of responsibilities.
The argument about the cause of geological disaster(natural or man-made) induced by excavation unloading during the construction period is raised. A case study of the landslide occurred on the slope of an expressway in north China is conducted. The slope is a dip slope composed of the weak interbedded mica schist. Through the engineering geological survey and data analysis, it is concluded that the multiple weak interlayers which constitute the slope body and the strong precipitation encountered during the construction are the main natural reasons that affect the slope stability. Insufficient understanding of the complex geological conditions, and inadequate prevention and control measures during the investigation, design and construction process are the main man-made reasons. The weights of six parameters including natural and human factors are calculated using Analytic Hierarchy Process(AHP), Multi-factor interaction matrix method and Delphi method, and then the responsibility is divided. The results of this study are expected to provide some references for the selection factors of similar engineering and the division of responsibilities.
2018, 26(2): 391-399.
The Qinhuai East River, in Nanjing city, is designed to pass through the section of Tongjiashan hill, where the Huangmaqing group of Tertiary (T2h) will be excavated for the new river. The excavated stratum is mainly composed of sandstone, cemented by mud and iron. The maximum height of the future slope will arrive at 70 m. Results of the field investigation and drilling holes show that the rock mass near the ground surface has intense cracks and low integrity, but the rock mass at the deep location has good integrity and few cracks. The cracks are closed with the favorable cementation strength. The wet and dry cycle tests are carried out for the rock cores. When the samples are tested for the five times of wet and dry cycles, a majority of the samples are cracked and disintegrated. But when the samples are immersed under the natural conditions, after twenty cycles, the samples are continuative and not cracked. This phenomenon can be explained that the small cracks in the rocks, where the water is not easy to enter under natural condition but enter easily in the vacuum, are very developed. When the water enters the small cracks, the cements are softened and the small cracks open, water swelling. The deterioration of the rocks due to water are caused by the double mechanisms. The mineral composition analysis is taken by the XRD apparatus. The results indicate that the more clay minerals in the rocks are the important causation due to softening of the rock, which result in the weak expansion. After the cycles of dry and wet tests, the wave velocity, unconfined compression strength and elastic modulus decrease obviously. The physical and mechanical characteristics are sensitive to the water. With the cycle numbers increase, under the compressive stresses condition, the pore compaction and elastic deformation process of the rock gradually disappear. After excavation of the high slope for the Qinhuai East River at the section of Tongjiashan hill, the effect of water on the stability should be considered adequately.
The Qinhuai East River, in Nanjing city, is designed to pass through the section of Tongjiashan hill, where the Huangmaqing group of Tertiary (T2h) will be excavated for the new river. The excavated stratum is mainly composed of sandstone, cemented by mud and iron. The maximum height of the future slope will arrive at 70 m. Results of the field investigation and drilling holes show that the rock mass near the ground surface has intense cracks and low integrity, but the rock mass at the deep location has good integrity and few cracks. The cracks are closed with the favorable cementation strength. The wet and dry cycle tests are carried out for the rock cores. When the samples are tested for the five times of wet and dry cycles, a majority of the samples are cracked and disintegrated. But when the samples are immersed under the natural conditions, after twenty cycles, the samples are continuative and not cracked. This phenomenon can be explained that the small cracks in the rocks, where the water is not easy to enter under natural condition but enter easily in the vacuum, are very developed. When the water enters the small cracks, the cements are softened and the small cracks open, water swelling. The deterioration of the rocks due to water are caused by the double mechanisms. The mineral composition analysis is taken by the XRD apparatus. The results indicate that the more clay minerals in the rocks are the important causation due to softening of the rock, which result in the weak expansion. After the cycles of dry and wet tests, the wave velocity, unconfined compression strength and elastic modulus decrease obviously. The physical and mechanical characteristics are sensitive to the water. With the cycle numbers increase, under the compressive stresses condition, the pore compaction and elastic deformation process of the rock gradually disappear. After excavation of the high slope for the Qinhuai East River at the section of Tongjiashan hill, the effect of water on the stability should be considered adequately.
2018, 26(2): 400-406.
Taking compacted clay liner(CCL)as the object, thermal diffusion under the effect of temperature gradient is added to traditional convection dispersion equation. The analytical solution in a semi-infinite domain is obtained. The results show that relative concentration and flux at the base of CCL obtained from the analytical solution considering thermal diffusion are greater than those obtained from traditional convection dispersion equation. The stable flux at ST=0.5 K-1 is 2.5 times larger than that at ST=0. Thermal diffusion flux is -ASTD/v times the convection dispersion, and both increase with service time. With the increasing of time, molecular diffusion flux increases to a peak, then approaches zero. Taken the effects of temperature on migration parameters and thermal diffusion into account, temperature increase leads to the increase of relative concentration, the advance of breakdown time, and the significant increase of flux. When the temperature increases from 30℃ to 70℃, the breakdown time changes from 8.5 to 5.1 years, and the steady flux increases by 1.7 times. Pollution risk may be higher when the effect of temperature on contaminant transport is eliminated in design of CCL.
Taking compacted clay liner(CCL)as the object, thermal diffusion under the effect of temperature gradient is added to traditional convection dispersion equation. The analytical solution in a semi-infinite domain is obtained. The results show that relative concentration and flux at the base of CCL obtained from the analytical solution considering thermal diffusion are greater than those obtained from traditional convection dispersion equation. The stable flux at ST=0.5 K-1 is 2.5 times larger than that at ST=0. Thermal diffusion flux is -ASTD/v times the convection dispersion, and both increase with service time. With the increasing of time, molecular diffusion flux increases to a peak, then approaches zero. Taken the effects of temperature on migration parameters and thermal diffusion into account, temperature increase leads to the increase of relative concentration, the advance of breakdown time, and the significant increase of flux. When the temperature increases from 30℃ to 70℃, the breakdown time changes from 8.5 to 5.1 years, and the steady flux increases by 1.7 times. Pollution risk may be higher when the effect of temperature on contaminant transport is eliminated in design of CCL.
2018, 26(2): 407-415.
This paper studies the solidification mechanism and identificates the chemical reaction between SH agent and clay minerals. It carries out the X-ray diffraction test, infrared spectrum test, microscope and polarizing microscope observation, and scanning electron microscopy detection, respectively, on clay minerals(montmorillonite, kaolinite), quartz, saline soil and theirs solidifying one with SH agent. At the same time, in order to evaluate the effect of solidification, it carries out the mechanical tests and freeze-thaw test on solidified lime-saline soils and SH agent-lime-saline soils. The results show that XRD spectrum and IR spectrum of the solidified materials are generally consistent with one of original materials, and the mineral composition is not changed. The functional groups of SH agent are not combined with the clay minerals, and no new substance is generated. SH agent produces an elastic and three-dimensional network and the silk fills the pores, and the soil particles are bonded in a whole, which increases the strength and decreases pore ratio of solidifying saline soil. Meanwhile, because of SH agent wrapping soil particles, the adhesive force and hydrophobicity of soil particle are increased. The results of the mechanical tests on SH agent-lime-saline soil have proved that SH agent can improve the strength in air and water, deformation resistance, anti-permeability of saline soil. The results of freeze-thaw experiments confirm that the three-dimensional network and the silk can partly resist the expansion and contraction of soil during freezing and thawing, and weaken the structural damage of soil. Therefore, the addition of SH agent is helpful to enhance the freeze-thaw resistance of solidified soil. SH agent does not generate chemical reaction with clay minerals. The improvement on the mechanical properties of saline soil mainly depends on the physical effect between SH agent and soil particles.
This paper studies the solidification mechanism and identificates the chemical reaction between SH agent and clay minerals. It carries out the X-ray diffraction test, infrared spectrum test, microscope and polarizing microscope observation, and scanning electron microscopy detection, respectively, on clay minerals(montmorillonite, kaolinite), quartz, saline soil and theirs solidifying one with SH agent. At the same time, in order to evaluate the effect of solidification, it carries out the mechanical tests and freeze-thaw test on solidified lime-saline soils and SH agent-lime-saline soils. The results show that XRD spectrum and IR spectrum of the solidified materials are generally consistent with one of original materials, and the mineral composition is not changed. The functional groups of SH agent are not combined with the clay minerals, and no new substance is generated. SH agent produces an elastic and three-dimensional network and the silk fills the pores, and the soil particles are bonded in a whole, which increases the strength and decreases pore ratio of solidifying saline soil. Meanwhile, because of SH agent wrapping soil particles, the adhesive force and hydrophobicity of soil particle are increased. The results of the mechanical tests on SH agent-lime-saline soil have proved that SH agent can improve the strength in air and water, deformation resistance, anti-permeability of saline soil. The results of freeze-thaw experiments confirm that the three-dimensional network and the silk can partly resist the expansion and contraction of soil during freezing and thawing, and weaken the structural damage of soil. Therefore, the addition of SH agent is helpful to enhance the freeze-thaw resistance of solidified soil. SH agent does not generate chemical reaction with clay minerals. The improvement on the mechanical properties of saline soil mainly depends on the physical effect between SH agent and soil particles.
2018, 26(2): 416-421.
This paper examines the engineering properties of lime-modified red sandstone residual soil, and determines the best dosage. It takes the red sandstone residual soil in Enshi, Hubei province as a case. It prepares the modified soil samples with different lime contents, and carries out compaction, compression, unconfined compression tests. The results show that, as the lime content increases, the optimum water content of modified soil gradually increases, the maximum dry density gradually decreases, the compression modulus of modified soil decreases first and then increases, the compressive modulus increases first and then decreases. The corresponding optimum lime content is 7%. The unconfined compressive strength of the modified soil increases first and then decreases, the optimum lime content is 9%. The main reasons for above results are that the hydration, ion exchange, carbonation and crystallization of lime can enhance the bonding of sand particles, and improve the integrity of the soil, thus, improves the compression and strength characteristics of the lime-modified soil. However, too much lime can appeare as free-ash between the gap of soil particles, which can lead to deformation increase and unconfined compressive strength decrease of the lime-modified soil.
This paper examines the engineering properties of lime-modified red sandstone residual soil, and determines the best dosage. It takes the red sandstone residual soil in Enshi, Hubei province as a case. It prepares the modified soil samples with different lime contents, and carries out compaction, compression, unconfined compression tests. The results show that, as the lime content increases, the optimum water content of modified soil gradually increases, the maximum dry density gradually decreases, the compression modulus of modified soil decreases first and then increases, the compressive modulus increases first and then decreases. The corresponding optimum lime content is 7%. The unconfined compressive strength of the modified soil increases first and then decreases, the optimum lime content is 9%. The main reasons for above results are that the hydration, ion exchange, carbonation and crystallization of lime can enhance the bonding of sand particles, and improve the integrity of the soil, thus, improves the compression and strength characteristics of the lime-modified soil. However, too much lime can appeare as free-ash between the gap of soil particles, which can lead to deformation increase and unconfined compressive strength decrease of the lime-modified soil.
2018, 26(2): 422-430.
Statistical analysis method is used to arrange locations of measuring points reasonably. The test results of soil mechanic parameters are both accurately and economical quick. In a rare earth mine southern Jiangxi province, 6 measuring points were arranged and each measuring point had 3 test holes. Through pressuremeter test and borehole shear test, the mechanical values of pressuremeter modulus, deformation modulus, compression modulus, cohesion and internal friction angle of ion-absorbed rare earth ore body were obtained. And the spatial variability of the mechanic parameters in ore body was analyzed by classical statistics method and geology statistics method. It is found that the cohesion and the pressuremeter modulus of ore body in test block are strong variation. The variation coefficient of the cohesion is 0.48 and the variation coefficient of the pressuremeter modulus is 0.36. The internal friction angle is weak variation and its variation coefficient is 0.067. It was assumed that the test values of mechanic parameters are truth value and the acceptable error of engineering is 15%. Through classical statistics method and geology statistics method, it is shown that, in this test block, the test result can efficiently estimate the mean and the variation coefficients of ore body's cohesion and pressuremeter modulus by arrangement 5 measuring points uniformly in 45m scope.
Statistical analysis method is used to arrange locations of measuring points reasonably. The test results of soil mechanic parameters are both accurately and economical quick. In a rare earth mine southern Jiangxi province, 6 measuring points were arranged and each measuring point had 3 test holes. Through pressuremeter test and borehole shear test, the mechanical values of pressuremeter modulus, deformation modulus, compression modulus, cohesion and internal friction angle of ion-absorbed rare earth ore body were obtained. And the spatial variability of the mechanic parameters in ore body was analyzed by classical statistics method and geology statistics method. It is found that the cohesion and the pressuremeter modulus of ore body in test block are strong variation. The variation coefficient of the cohesion is 0.48 and the variation coefficient of the pressuremeter modulus is 0.36. The internal friction angle is weak variation and its variation coefficient is 0.067. It was assumed that the test values of mechanic parameters are truth value and the acceptable error of engineering is 15%. Through classical statistics method and geology statistics method, it is shown that, in this test block, the test result can efficiently estimate the mean and the variation coefficients of ore body's cohesion and pressuremeter modulus by arrangement 5 measuring points uniformly in 45m scope.
2018, 26(2): 431-437.
In order to solve the long-term stability problem of Active Heated Fiber Optic(AHFO)in distributed soil moisture monitoring, a new method is developed on the basis of carbon fiber cable(abbreviated as C-AHFO). A laboratory calibration experiment and an in-situ field test are conducted and a numerical model is built to simulate rainfall penetration. The relationship between soil moisture and temperature characteristic values is established. The laboratory experimental results show that this relationship can be expressed by a piecewise-function. When the soil moisture is less than 0.08 m3·m-3, a liner function is used. Otherwise, a logarithmic function is adopted. The 16 months' field monitoring results indicate that C-AHFO method has a good long-term stability during this period, which can provide us with effective soil moisture data with errors less than 0.033 m3·m-3. C-AHFO method also can record surface(less than 20 cm) soil moisture variation process which reflects weather and season changes. The development and application of C-AHFO provides a new method for achieving real-time and large scale ground moisture.
In order to solve the long-term stability problem of Active Heated Fiber Optic(AHFO)in distributed soil moisture monitoring, a new method is developed on the basis of carbon fiber cable(abbreviated as C-AHFO). A laboratory calibration experiment and an in-situ field test are conducted and a numerical model is built to simulate rainfall penetration. The relationship between soil moisture and temperature characteristic values is established. The laboratory experimental results show that this relationship can be expressed by a piecewise-function. When the soil moisture is less than 0.08 m3·m-3, a liner function is used. Otherwise, a logarithmic function is adopted. The 16 months' field monitoring results indicate that C-AHFO method has a good long-term stability during this period, which can provide us with effective soil moisture data with errors less than 0.033 m3·m-3. C-AHFO method also can record surface(less than 20 cm) soil moisture variation process which reflects weather and season changes. The development and application of C-AHFO provides a new method for achieving real-time and large scale ground moisture.
2018, 26(2): 438-444.
In the northern coastal area of China, the alternated phenomenon of rainy season and dry-windy weather is threatening the soil stability. It needs to improve the mechanical properties of treated soil under dry and wet cycles before utilization. The mechanical distribution of oil contaminated soil treated with lime and fly ash are studied in this manuscript. Unconfined compressive strength index is chosen. Wet and dry cycle process is simulated. Results indicate the follows. (1)The quality of treated oil contaminated soil decreased with wet-dry cycle process. It presented small fluctuations in 6 times, then decreased significantly during 7-8 times, and stabilized finally after 9 times. The maximum decrease is 4.5%. (2)The compressive strength of oil contaminated soil treated with lime and fly ash increased first and then decreased with the increasing of dry and wet cycles. It reached the maximum at 3 times. It stabilized after 7 times. The residual strength was more than 70% of initial strength. So the oil contaminated soil treated with lime and fly ash had good water stability. (3)The water stability of treated oil contaminated soil reduced with the increasing of oil contamination levels. The failure gradually tended to hardening type with wet-dry cycle. The best proportion of lime and fly-ash was 0.75. Therefore, the oil-contaminated soil can be used as roadbed fill to achieve the purpose of recycling contaminated soil.
In the northern coastal area of China, the alternated phenomenon of rainy season and dry-windy weather is threatening the soil stability. It needs to improve the mechanical properties of treated soil under dry and wet cycles before utilization. The mechanical distribution of oil contaminated soil treated with lime and fly ash are studied in this manuscript. Unconfined compressive strength index is chosen. Wet and dry cycle process is simulated. Results indicate the follows. (1)The quality of treated oil contaminated soil decreased with wet-dry cycle process. It presented small fluctuations in 6 times, then decreased significantly during 7-8 times, and stabilized finally after 9 times. The maximum decrease is 4.5%. (2)The compressive strength of oil contaminated soil treated with lime and fly ash increased first and then decreased with the increasing of dry and wet cycles. It reached the maximum at 3 times. It stabilized after 7 times. The residual strength was more than 70% of initial strength. So the oil contaminated soil treated with lime and fly ash had good water stability. (3)The water stability of treated oil contaminated soil reduced with the increasing of oil contamination levels. The failure gradually tended to hardening type with wet-dry cycle. The best proportion of lime and fly-ash was 0.75. Therefore, the oil-contaminated soil can be used as roadbed fill to achieve the purpose of recycling contaminated soil.
2018, 26(2): 445-450.
This paper examines the penetration tests on pretension high-strength concrete(PHC pile) piles with fiber Bragg grating sensing technology at a site. Two buried methods for installing the sense onto the pile are used. One method grooves on the PHC pile. The other implants in the PHC pile. The pile shaft force curves and the behaviors of base resistance are compared. It reveals that the pile shaft force of two buried methods decreases with the increasing of pretension depth. The transfer rate of the pile shaft force and the slope of curves are closed. The test result of base resistance from the method of implanting in the PHC pile is less than that of the method of grooving on the PHC pile, but the range of difference is small. The survival rate of fiber Bragg grating sensing sensors using the implanting in the PHC pile is high. Such reliable data show that the implanting method can be used in stress measurement of PHC pile.
This paper examines the penetration tests on pretension high-strength concrete(PHC pile) piles with fiber Bragg grating sensing technology at a site. Two buried methods for installing the sense onto the pile are used. One method grooves on the PHC pile. The other implants in the PHC pile. The pile shaft force curves and the behaviors of base resistance are compared. It reveals that the pile shaft force of two buried methods decreases with the increasing of pretension depth. The transfer rate of the pile shaft force and the slope of curves are closed. The test result of base resistance from the method of implanting in the PHC pile is less than that of the method of grooving on the PHC pile, but the range of difference is small. The survival rate of fiber Bragg grating sensing sensors using the implanting in the PHC pile is high. Such reliable data show that the implanting method can be used in stress measurement of PHC pile.
2018, 26(2): 451-458.
This paper studies the influence of effective confining pressure, dynamic load and silt content on liquefaction characteristics of the remolded saturated silty soil at Yellow River delta. It carries out a series of undrained dynamic triaxial tests using the constant clay content and dry density approach. These tests are conducted on specimens of size 50 mm diameter and 100 mm height. The results show that:(1)Under the condition of the silt content not less than 50%, the increase of silt content reduces the liquefaction potential of the remolded saturated silty soil. (2)The dynamic strength of the remolded saturated silty soil increases along with the effective confining pressure increasing, and it shows an approximate linear relationship with the logarithm of the initial liquefaction vibration number. (3)Compared with sandy soil, the dynamic pore pressure of silty soil is difficult to achieve the effective confining pressure. With the increase of effective confining pressure, the ratio of dynamic pore pressure to the effective confining pressure decreases. With the increase of silt content, the influence of silt content on the dynamic pore pressure decreases. The increase of silt content slows down the growth of dynamic pore pressure. (4)According to the experimental results, a dynamic pore pressure calculation model and related parameters of the remolded saturated silty soil is proposed.
This paper studies the influence of effective confining pressure, dynamic load and silt content on liquefaction characteristics of the remolded saturated silty soil at Yellow River delta. It carries out a series of undrained dynamic triaxial tests using the constant clay content and dry density approach. These tests are conducted on specimens of size 50 mm diameter and 100 mm height. The results show that:(1)Under the condition of the silt content not less than 50%, the increase of silt content reduces the liquefaction potential of the remolded saturated silty soil. (2)The dynamic strength of the remolded saturated silty soil increases along with the effective confining pressure increasing, and it shows an approximate linear relationship with the logarithm of the initial liquefaction vibration number. (3)Compared with sandy soil, the dynamic pore pressure of silty soil is difficult to achieve the effective confining pressure. With the increase of effective confining pressure, the ratio of dynamic pore pressure to the effective confining pressure decreases. With the increase of silt content, the influence of silt content on the dynamic pore pressure decreases. The increase of silt content slows down the growth of dynamic pore pressure. (4)According to the experimental results, a dynamic pore pressure calculation model and related parameters of the remolded saturated silty soil is proposed.
2018, 26(2): 459-466.
Heifangtai is one of the typical loess platforms in Gansu province. The platform surface has been largely irrigated over the past forty years. The underground water level upraised and many landslides occurred. The frequent loess landslides have seriously threatened the local development. This paper carries out the double rings infiltration tests, varying-head infiltration test for the disturbed samples and varying-head infiltration test for the remolded samples. It analyzes the characteristics among the three tests. It uses the geophysical prospecting to verify the test results. The following conclusions are made:(1)The permeability coefficient of unsaturated loess tested by the three kinds of tests are linearly decreases with the increase of dry density; (2)Under the same conditions the permeability coefficient tested by the double rings infiltration tests is the largest. The remolded samples' permeability coefficient is the minimum. The differences among the results from the three types of permeability coefficient tests decrease with the increase of dry density; (3)The permeability coefficient tested by the double rings infiltration tests is most close to the in situ loess permeability according to the high-density electrical method.
Heifangtai is one of the typical loess platforms in Gansu province. The platform surface has been largely irrigated over the past forty years. The underground water level upraised and many landslides occurred. The frequent loess landslides have seriously threatened the local development. This paper carries out the double rings infiltration tests, varying-head infiltration test for the disturbed samples and varying-head infiltration test for the remolded samples. It analyzes the characteristics among the three tests. It uses the geophysical prospecting to verify the test results. The following conclusions are made:(1)The permeability coefficient of unsaturated loess tested by the three kinds of tests are linearly decreases with the increase of dry density; (2)Under the same conditions the permeability coefficient tested by the double rings infiltration tests is the largest. The remolded samples' permeability coefficient is the minimum. The differences among the results from the three types of permeability coefficient tests decrease with the increase of dry density; (3)The permeability coefficient tested by the double rings infiltration tests is most close to the in situ loess permeability according to the high-density electrical method.
2018, 26(2): 467-474.
This paper illustrates a case study detecting roadbed quality of a highway embankment through its degree of compaction and the Benkelman Beam static deflection method. Based on field filling test, the paper examines the compaction mechanism of embankment filled with soil-rock mixtures, and the influence of different construction parameters(times of rolling, loose laying depth, grain composition, moisture content and mode of vibration) and their different combinations to compaction effect. The results indicate that:(1)As compaction effort increases, the deflection value of roadbed decreases at first and then stabilizes gradually, while the degree of compaction increases at first and then stabilizes gradually. (2)It will be a better degree of compaction for the roadbed by carrying out static pressure twice, high frequency vibration six times, 30 cm loose laying depth and sprinkling two or three times. (3)Particle breakage is one of the factors that increase the compactness of roadbed. As the coarse particles break into fine particles, which has filled the interstices and engaged for each other, the degree of compaction gradually increases. According to these test results, this paper establishes the Gaussian exponential relationship between the degree of compaction and modulus of resilience. It can provide a theoretical guidance for the highway embankment construction.
This paper illustrates a case study detecting roadbed quality of a highway embankment through its degree of compaction and the Benkelman Beam static deflection method. Based on field filling test, the paper examines the compaction mechanism of embankment filled with soil-rock mixtures, and the influence of different construction parameters(times of rolling, loose laying depth, grain composition, moisture content and mode of vibration) and their different combinations to compaction effect. The results indicate that:(1)As compaction effort increases, the deflection value of roadbed decreases at first and then stabilizes gradually, while the degree of compaction increases at first and then stabilizes gradually. (2)It will be a better degree of compaction for the roadbed by carrying out static pressure twice, high frequency vibration six times, 30 cm loose laying depth and sprinkling two or three times. (3)Particle breakage is one of the factors that increase the compactness of roadbed. As the coarse particles break into fine particles, which has filled the interstices and engaged for each other, the degree of compaction gradually increases. According to these test results, this paper establishes the Gaussian exponential relationship between the degree of compaction and modulus of resilience. It can provide a theoretical guidance for the highway embankment construction.
2018, 26(2): 475-483.
This paper studies on the variation of acoustic emission(AE)characteristics during granite failure under cyclic loading through the MTS815 rock mechanics testing system. Changes of AE parameters of granite were studied under different confining pressure, cycle times and water content. Based on the recorded AE data, the rock failure process is divided into three stages, namely, the initial stage, uniform development stage and the acceleration transition stage. The variation characteristics of RA value, damage parameter D and Kaiser Effect in each stage are studied. The results show that:(1)The RA value of the saturated rock is less than the RA value of the rock in the natural state, and the rocks of both states appear obvious high RA zone before failure. (2)The confining pressure can effectively prolong the time of the accelerating transition phase and improve the compressive strength of the rock.(3)The average value of the damage parameter D in the last cycle is increased by 0.6. (4)The limitation of the rock Kaiser effect is verified, and the rock will not be destroyed by the cumulative damage after the Felicity Effect occurs.
This paper studies on the variation of acoustic emission(AE)characteristics during granite failure under cyclic loading through the MTS815 rock mechanics testing system. Changes of AE parameters of granite were studied under different confining pressure, cycle times and water content. Based on the recorded AE data, the rock failure process is divided into three stages, namely, the initial stage, uniform development stage and the acceleration transition stage. The variation characteristics of RA value, damage parameter D and Kaiser Effect in each stage are studied. The results show that:(1)The RA value of the saturated rock is less than the RA value of the rock in the natural state, and the rocks of both states appear obvious high RA zone before failure. (2)The confining pressure can effectively prolong the time of the accelerating transition phase and improve the compressive strength of the rock.(3)The average value of the damage parameter D in the last cycle is increased by 0.6. (4)The limitation of the rock Kaiser effect is verified, and the rock will not be destroyed by the cumulative damage after the Felicity Effect occurs.
2018, 26(2): 484-493.
The stabilizing pile is widely used in the governance of the high slope. And the soil arch characters, including the soil arching type and the soil arching height, which may be affected by the sectional dimesion of the stabilizing pile, have an important role in the design of the stabilizing pile. This paper firstly adopts the numerical simulation technique to research the influence of the sectional dimesion to the soil arching characters, then this paper combines with the mechanical calculation to explain the reasons for changes of soil arching types and soil arching heights. The result shows that under the circumstance that the clear distance between piles is definite, along with the decrease of the pile sectional dimesion. The soil arching type is more likely to transfer from the end bearing arching to the friction arching. As for the end bearing arch, the soil arching height is mainly affected by the width and suffered pressure of the pile back. Along with the increase of the width of piles, the height of the soil arching increases. As for the friction arching, the soil arching height is mainly affected by the height and suffered pressure of the pile section. Along with the increase of the height of the pile section, the height of the soil arching increases accordingly.
The stabilizing pile is widely used in the governance of the high slope. And the soil arch characters, including the soil arching type and the soil arching height, which may be affected by the sectional dimesion of the stabilizing pile, have an important role in the design of the stabilizing pile. This paper firstly adopts the numerical simulation technique to research the influence of the sectional dimesion to the soil arching characters, then this paper combines with the mechanical calculation to explain the reasons for changes of soil arching types and soil arching heights. The result shows that under the circumstance that the clear distance between piles is definite, along with the decrease of the pile sectional dimesion. The soil arching type is more likely to transfer from the end bearing arching to the friction arching. As for the end bearing arch, the soil arching height is mainly affected by the width and suffered pressure of the pile back. Along with the increase of the width of piles, the height of the soil arching increases. As for the friction arching, the soil arching height is mainly affected by the height and suffered pressure of the pile section. Along with the increase of the height of the pile section, the height of the soil arching increases accordingly.
2018, 26(2): 494-503.
Shale gas, as one kind of unconventional gas, is an important energy supplement. The pore structure characteristic is an important index used to measure and evaluate the storage capacity and fracturing of shale reservoir. The Weiyuan marine shale(1#), Jiaoshiba marine shale(2#), Yaoqu tuff(4#) and Yaoqu continental shale(5# and 6#) are selected for tests with mercury porosimetry(MP), N2 adsorption(NA) and nuclear magnetic resonance(NMR) devices. Based on fractal theory, the relationships between fractal dimensions and pore structure are investigated with MP, NA and NMR to characterize the pore anisotropy. The results illustrate that the fractal dimensions of continental samples 5# and 6# are bigger than that of marine sample 2# in the pore range between 0.1~100 μm based on MP method. The fractal dimensions of marine sample 2# is bigger than those of continental samples 5# and 6# in the pore range of 2~200 nm based on NA method. In contrast, the max fractal dimensions(DNMR) of marine sample 2# are about equal to those of continental samples 5# and 6# in the pore range between 10 nm to 10 μm by NMR method. Especially, the fractal dimensions of Jiaoshiba marine sample 2# are biggest among all the samples using NA method. The micropores of Jiaoshiba marine shale are the most development, so the heterogeneity of pore characteristic is the strongest. Therefore, the fractal dimension can be used as an important parameter to evaluate the fracturing effect of shale reservoir and the heterogeneity of pore structure.
Shale gas, as one kind of unconventional gas, is an important energy supplement. The pore structure characteristic is an important index used to measure and evaluate the storage capacity and fracturing of shale reservoir. The Weiyuan marine shale(1#), Jiaoshiba marine shale(2#), Yaoqu tuff(4#) and Yaoqu continental shale(5# and 6#) are selected for tests with mercury porosimetry(MP), N2 adsorption(NA) and nuclear magnetic resonance(NMR) devices. Based on fractal theory, the relationships between fractal dimensions and pore structure are investigated with MP, NA and NMR to characterize the pore anisotropy. The results illustrate that the fractal dimensions of continental samples 5# and 6# are bigger than that of marine sample 2# in the pore range between 0.1~100 μm based on MP method. The fractal dimensions of marine sample 2# is bigger than those of continental samples 5# and 6# in the pore range of 2~200 nm based on NA method. In contrast, the max fractal dimensions(DNMR) of marine sample 2# are about equal to those of continental samples 5# and 6# in the pore range between 10 nm to 10 μm by NMR method. Especially, the fractal dimensions of Jiaoshiba marine sample 2# are biggest among all the samples using NA method. The micropores of Jiaoshiba marine shale are the most development, so the heterogeneity of pore characteristic is the strongest. Therefore, the fractal dimension can be used as an important parameter to evaluate the fracturing effect of shale reservoir and the heterogeneity of pore structure.
2018, 26(2): 504-509.
Characterizing pore structure of shale is the basic work for shale reservoir evaluation. Shale in this study is collected from the upper Triassic Yanchang formation in Ordos Basin. Pore structures including pores and throats, in spaces 10 μm3, 20 μm3, 30 μm3, 39 μm3, are investigated with Nano-CT(scanning accuracy is 65 nm). The numbers of pores and throats connecting with pores in different spaces are counted. Assuming pores and throats as balls and tubes, respectively, the physical models "ball-and -tube models" of pore structures are abstracted. The corresponding mathematical models of pore connectivity are founded through complex network theory. The pores and throats are respectively treated as nodes and edges. The pore connectivity network in 10 μm3 is constructed by Matlab software according to the mathematical characterizes of scale-free network. The conception of network connectivity entropy is introduced to assess the heterogeneity of pore connectivity networks. The investigation indicates that the pore connectivity networks in spaces 10 μm3, 20 μm3 and 39 μm3 are the scale free networks whose degree distribution conforms to power law distribution. The degree distribution of pore connectivity networks in spaces 10 μm3 accords with exponential distribution. The connectivity of pore and throat network decreases as the network connectivity entropy increases. The method in this study can be used to evaluate the connectivity of porous structures of shale, and assess the porous and permeable characteristics of shale gas reservoir.
Characterizing pore structure of shale is the basic work for shale reservoir evaluation. Shale in this study is collected from the upper Triassic Yanchang formation in Ordos Basin. Pore structures including pores and throats, in spaces 10 μm3, 20 μm3, 30 μm3, 39 μm3, are investigated with Nano-CT(scanning accuracy is 65 nm). The numbers of pores and throats connecting with pores in different spaces are counted. Assuming pores and throats as balls and tubes, respectively, the physical models "ball-and -tube models" of pore structures are abstracted. The corresponding mathematical models of pore connectivity are founded through complex network theory. The pores and throats are respectively treated as nodes and edges. The pore connectivity network in 10 μm3 is constructed by Matlab software according to the mathematical characterizes of scale-free network. The conception of network connectivity entropy is introduced to assess the heterogeneity of pore connectivity networks. The investigation indicates that the pore connectivity networks in spaces 10 μm3, 20 μm3 and 39 μm3 are the scale free networks whose degree distribution conforms to power law distribution. The degree distribution of pore connectivity networks in spaces 10 μm3 accords with exponential distribution. The connectivity of pore and throat network decreases as the network connectivity entropy increases. The method in this study can be used to evaluate the connectivity of porous structures of shale, and assess the porous and permeable characteristics of shale gas reservoir.
2018, 26(2): 510-519.
Shale is a kind of sedimentary rock with well-developed bedding planes. It is proved by conventional mechanical tests under static loading that bedding planes is the main influence factor on the anisotropic behavior of shale. However, as an experimental factor, strain rate is supposed to have a nonnegligible influence on the anisotropic behavior of shale as well. To investigate the effects of strain rates on the anisotropic mechanical properties of shale and the corresponding failure modes, the experiment on the shale samples with varied bedding plane angle β from 0°to 90åt the interval of 15°is conducted under strain rates of 10-4 s-1, 5×10-4 s-1, 10-3 s-1 and 10-2 s-1, respectively. The tests give the following results. (1)The anisotropic behavior of elastic modulus of shale samples becomes less obvious under high strain rates, while the Poisson's ratio of shale samples is rarely affected by strain rate. (2)The increase of compressive strength of shale samples for β=45°~60°is the most obvious one if compared with the rest shale samples. The anisotropic behavior of peak strength of shale samples is weakened by high strain rate. (3)The failure modes of shale samples are relatively less affected by bedding planes under high strain rates and the anisotropic behavior of shale samples becomes less obvious under high strain rates. In conclusion, the anisotropic behavior of shale is weakened by high strain rate. The results can provide references for a deeper understanding of the mechanical properties of shale.
Shale is a kind of sedimentary rock with well-developed bedding planes. It is proved by conventional mechanical tests under static loading that bedding planes is the main influence factor on the anisotropic behavior of shale. However, as an experimental factor, strain rate is supposed to have a nonnegligible influence on the anisotropic behavior of shale as well. To investigate the effects of strain rates on the anisotropic mechanical properties of shale and the corresponding failure modes, the experiment on the shale samples with varied bedding plane angle β from 0°to 90åt the interval of 15°is conducted under strain rates of 10-4 s-1, 5×10-4 s-1, 10-3 s-1 and 10-2 s-1, respectively. The tests give the following results. (1)The anisotropic behavior of elastic modulus of shale samples becomes less obvious under high strain rates, while the Poisson's ratio of shale samples is rarely affected by strain rate. (2)The increase of compressive strength of shale samples for β=45°~60°is the most obvious one if compared with the rest shale samples. The anisotropic behavior of peak strength of shale samples is weakened by high strain rate. (3)The failure modes of shale samples are relatively less affected by bedding planes under high strain rates and the anisotropic behavior of shale samples becomes less obvious under high strain rates. In conclusion, the anisotropic behavior of shale is weakened by high strain rate. The results can provide references for a deeper understanding of the mechanical properties of shale.
2018, 26(2): 520-527.
In order to reflect the whole process of rock deformation, the Harris function is improved. The micro-unit strength of rock is supposed to obey the improved Harris probability density distribution. The continuum damage theory is combined and the correction of damage variable is considered. As a result, statistical damage softening model of rock is established. The YSJ-01-00 rock triaxial creep testing machine is used to carry out conventional triaxial compression test of red mudstone. Sensitivity of model parameters is analyzed using test data of red mudstone. The physical meanings of the model parameters are described and the expansion process of cumulative damage is analyzed. Test data of monzonitic granite and sandstone in related literatures are used and the test data of three kinds of rock materials are verified using the model of this paper. Constraint range of initial damage coefficient is given. Finally, the rationality and applicability of the model are proved by comparing the experimental curves and theoretical curves of three kinds of rock materials.
In order to reflect the whole process of rock deformation, the Harris function is improved. The micro-unit strength of rock is supposed to obey the improved Harris probability density distribution. The continuum damage theory is combined and the correction of damage variable is considered. As a result, statistical damage softening model of rock is established. The YSJ-01-00 rock triaxial creep testing machine is used to carry out conventional triaxial compression test of red mudstone. Sensitivity of model parameters is analyzed using test data of red mudstone. The physical meanings of the model parameters are described and the expansion process of cumulative damage is analyzed. Test data of monzonitic granite and sandstone in related literatures are used and the test data of three kinds of rock materials are verified using the model of this paper. Constraint range of initial damage coefficient is given. Finally, the rationality and applicability of the model are proved by comparing the experimental curves and theoretical curves of three kinds of rock materials.
2018, 26(2): 528-539.
Two dimensional numerical particle flow code(PFC2D) is an important method to study the crack propagation characteristics of cracked rock. In review of related literatures, it is analyzed and summarized as follows:the current PFC2D simulation methods are summarized in three aspects of particle contact constitutive model, microparameters calibration and simulation method of crack. According to the current research, the PFC2D simulation of crack propagation characteristics is summarized focusing on the single cracked, intermittent double cracked rock under different loading methods. On this basis, the shortcomings of the current research are pointed out as follows. The fracture toughness of PFC2D model is not in line with the actual value of rock. Simulation results of parallel-bond model and test results of rock are different. There are differences between real crack and simulation crack. Combined with the existing shortcomings in the study, the corresponding solutions are put forward and are expected to contribute to the development of PFC2D simulation methods for cracked rocks.
Two dimensional numerical particle flow code(PFC2D) is an important method to study the crack propagation characteristics of cracked rock. In review of related literatures, it is analyzed and summarized as follows:the current PFC2D simulation methods are summarized in three aspects of particle contact constitutive model, microparameters calibration and simulation method of crack. According to the current research, the PFC2D simulation of crack propagation characteristics is summarized focusing on the single cracked, intermittent double cracked rock under different loading methods. On this basis, the shortcomings of the current research are pointed out as follows. The fracture toughness of PFC2D model is not in line with the actual value of rock. Simulation results of parallel-bond model and test results of rock are different. There are differences between real crack and simulation crack. Combined with the existing shortcomings in the study, the corresponding solutions are put forward and are expected to contribute to the development of PFC2D simulation methods for cracked rocks.
2018, 26(2): 540-550.
An accurate assessment model for geothermal potential regions can help to lower the risk of the development and to reduce the investment. Based on the platforms of GIS, the promising geothermal areas are identified through the information value model according to the relationship between geothermal occurrences and their controlling factors in Tengchong county, China. Publicly available databases for this analysis include epicenters, distribution of faults, Bouguer gravity, Landsat7 Enhanced Thematic Mapper Plus(ETM+)images, the magnetic data, and digital elevation model(DEM)data. They are extracted as the b-value map, distance to faults map, distance to main grabens map, LST(land surface temperature) map, magnetic anomaly map, and distance to rivers map respectively. To ensure the model is suitable to evaluate the geothermal potential sites within the region, the method of factor analysis based on information values is applied to test the conditional independence. The results of index analysis and area ratio analysis indicate that the information value model can be applied well in the evaluation of geothermal potential regions. Four potential areas in final map, of which have not been explored or exploited, are located in Longchuan River, Nandi River and Nu River. Furthermore, the total area of unexplored geothermal potential field is 1835.6 km2, accounting for 6.72% of study area. It is expected that the study can guide further preliminary investigations performed for large areas having limited information and can lower the risk in economy.
An accurate assessment model for geothermal potential regions can help to lower the risk of the development and to reduce the investment. Based on the platforms of GIS, the promising geothermal areas are identified through the information value model according to the relationship between geothermal occurrences and their controlling factors in Tengchong county, China. Publicly available databases for this analysis include epicenters, distribution of faults, Bouguer gravity, Landsat7 Enhanced Thematic Mapper Plus(ETM+)images, the magnetic data, and digital elevation model(DEM)data. They are extracted as the b-value map, distance to faults map, distance to main grabens map, LST(land surface temperature) map, magnetic anomaly map, and distance to rivers map respectively. To ensure the model is suitable to evaluate the geothermal potential sites within the region, the method of factor analysis based on information values is applied to test the conditional independence. The results of index analysis and area ratio analysis indicate that the information value model can be applied well in the evaluation of geothermal potential regions. Four potential areas in final map, of which have not been explored or exploited, are located in Longchuan River, Nandi River and Nu River. Furthermore, the total area of unexplored geothermal potential field is 1835.6 km2, accounting for 6.72% of study area. It is expected that the study can guide further preliminary investigations performed for large areas having limited information and can lower the risk in economy.
2018, 26(2): 551-560.
As an ideal green energy, geothermal resources play an increasingly important role in the world. The geothermal resources in Beijing belongs to low-medium temperature geothermal resources, which is mainly distributed in ten geothermal fields. The focus on geothermal water concentrated development and utilization in Beijing has 40 years history. In order to grasp the development potential of geothermal resources in Beijing, this paper carries out the potential assessment of geothermal resources based on the characteristics analysis of tectonic, the types of geothermal resources and the distribution of geotemperature. Based on the geothermal energy extraction coefficient, the exploitation of geothermal water and the water level deceleration, regionalization of the geothermal resources potential in Beijing is constructed. The geothermal fields are divided into 29 evaluation units and are divided into six zones including serious overdraft area, overdraft area, balance area, low potential area, higher potential area, and highest potential area.
As an ideal green energy, geothermal resources play an increasingly important role in the world. The geothermal resources in Beijing belongs to low-medium temperature geothermal resources, which is mainly distributed in ten geothermal fields. The focus on geothermal water concentrated development and utilization in Beijing has 40 years history. In order to grasp the development potential of geothermal resources in Beijing, this paper carries out the potential assessment of geothermal resources based on the characteristics analysis of tectonic, the types of geothermal resources and the distribution of geotemperature. Based on the geothermal energy extraction coefficient, the exploitation of geothermal water and the water level deceleration, regionalization of the geothermal resources potential in Beijing is constructed. The geothermal fields are divided into 29 evaluation units and are divided into six zones including serious overdraft area, overdraft area, balance area, low potential area, higher potential area, and highest potential area.
2018, 26(2): 340-347.
Wenchuan earthquake induced a large amount of geological disasters such as landslides and collapses. Besides, the earthquake also caused a lot of the loose and broken rock mass. Those loose rock mass can produce large amounts of secondary geological disasters under the rainfall and other factors, which has great danger. Therefore, it has very important practical significance for geological disaster susceptibility evaluation of Wenchuan country. Based on GIS raster data model, this paper selects nine factors including elevation, gradient, slope direction, relief amplitude, gully density, the engineering rock group, fault, drainage and roads. It adopts the information, logistic and information-logistic coupling models for assessment of geological hazards. The results show that the coupling model is more reasonable and has higher precision. High and very high susceptibility of geological hazard areas are concentrated in the water extension area and fault concentration area. Susceptibility partition map of the calculation results is consistent with the actual situation of the study area and can play an important reference role in the geological hazard risk assessment.
Wenchuan earthquake induced a large amount of geological disasters such as landslides and collapses. Besides, the earthquake also caused a lot of the loose and broken rock mass. Those loose rock mass can produce large amounts of secondary geological disasters under the rainfall and other factors, which has great danger. Therefore, it has very important practical significance for geological disaster susceptibility evaluation of Wenchuan country. Based on GIS raster data model, this paper selects nine factors including elevation, gradient, slope direction, relief amplitude, gully density, the engineering rock group, fault, drainage and roads. It adopts the information, logistic and information-logistic coupling models for assessment of geological hazards. The results show that the coupling model is more reasonable and has higher precision. High and very high susceptibility of geological hazard areas are concentrated in the water extension area and fault concentration area. Susceptibility partition map of the calculation results is consistent with the actual situation of the study area and can play an important reference role in the geological hazard risk assessment.
2018, 26(2): 384-390.
According to the foundation pit excavation of the Lücuo station in Xiamen Subway Line 1, the similar ratio of the key parameters of the model is obtained with the respective similitude theory. Besides, the whole model is made and the monitoring system is designed. By simulating the actual excavation process and analyzing the monitoring data, the ground settlement, the deformation and stress distribution of the diaphragm are given. The results show that, the ground settlement is negatively correlated with the distance away from the diaphragm and positively correlated with the length of the diaphragm and the depth of excavation. The shapes of the curve are related to the total settlement caused by the excavation unloading, and the spatial and corner effect are obvious. The ground settlement mainly occurs in the stage of excavation. The influence of excavation on the ground settlement is gradually reduced with the excavation progress developing. The bending moment of the diaphragm is positively correlated with depth of excavation. The maximum bending moment of the diaphragm is at the excavation face of the foundation pit.
According to the foundation pit excavation of the Lücuo station in Xiamen Subway Line 1, the similar ratio of the key parameters of the model is obtained with the respective similitude theory. Besides, the whole model is made and the monitoring system is designed. By simulating the actual excavation process and analyzing the monitoring data, the ground settlement, the deformation and stress distribution of the diaphragm are given. The results show that, the ground settlement is negatively correlated with the distance away from the diaphragm and positively correlated with the length of the diaphragm and the depth of excavation. The shapes of the curve are related to the total settlement caused by the excavation unloading, and the spatial and corner effect are obvious. The ground settlement mainly occurs in the stage of excavation. The influence of excavation on the ground settlement is gradually reduced with the excavation progress developing. The bending moment of the diaphragm is positively correlated with depth of excavation. The maximum bending moment of the diaphragm is at the excavation face of the foundation pit.
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