2013 Vol. 21, No. 4

论文
In the 21 century, many higher-speed, larger-scale, deeper buried rock engineering constructions are developed with the development of national economy in China. Therefore, there are two new challenging issues for the researchers of engineering geology. Whether do the rock structures still control the behavior of the rock mass when the engineering construction is buried 2500m below ground surface? an example is the water convey tunnel in Jinpin II power station. How do we predict the long-term stability of important rock engineering constructions? This paper examines and discusses the two issues. Some useful data are provided for the designer and researcher of deep rock underground engineering as references. In the 21 century, many higher-speed, larger-scale, deeper buried rock engineering constructions are developed with the development of national economy in China. Therefore, there are two new challenging issues for the researchers of engineering geology. Whether do the rock structures still control the behavior of the rock mass when the engineering construction is buried 2500m below ground surface? an example is the water convey tunnel in Jinpin II power station. How do we predict the long-term stability of important rock engineering constructions? This paper examines and discusses the two issues. Some useful data are provided for the designer and researcher of deep rock underground engineering as references.
This paper chooses the genetic type, engineering properties, space distribution, and engineering site environment of soft soil as the second level evaluation factors and their corresponding 16 individual factors as the first level evaluation factors. It then uses the method of fuzzy mathematics to build a multilevel fuzzy synthetic evaluation model especially applicable to the engineering geology of the soft soil in Tianjin Binhai New Area. This model is used to zone the shallow layer affected by light building foundations of ordinary road, yard, and single storey workshop. The results show that the soft soil engineering conditions gradually become poorer from west to east. Particularly the blast-fill site is the most unfavorable engineering site in the area. This paper chooses the genetic type, engineering properties, space distribution, and engineering site environment of soft soil as the second level evaluation factors and their corresponding 16 individual factors as the first level evaluation factors. It then uses the method of fuzzy mathematics to build a multilevel fuzzy synthetic evaluation model especially applicable to the engineering geology of the soft soil in Tianjin Binhai New Area. This model is used to zone the shallow layer affected by light building foundations of ordinary road, yard, and single storey workshop. The results show that the soft soil engineering conditions gradually become poorer from west to east. Particularly the blast-fill site is the most unfavorable engineering site in the area.
This paper is based on the first-stage in-situ test results of the Line 1 and Line 2 in Ningbo rail transit system. The tests include static cone penetration, standard penetration test, standard penetration test, and vane shear test. Accordingly, the foundation bearing capacities of the typical soils in Ningbo region are estimated and predicted with empirical formula. Then, the distributions and numerical characteristics of the predicted results are presented on basis of the K-S inspection method. Based on above analysis results, the recommended foundation bearing capacities of the typical soils are proposed after their comparisons with the empirical foundation bearing capacities of the typical soils in Ningbo area. The research findings can provide scientific references to determine the value of the bearing capacity of the geotechnical investigation and design in Ningbo area. This paper is based on the first-stage in-situ test results of the Line 1 and Line 2 in Ningbo rail transit system. The tests include static cone penetration, standard penetration test, standard penetration test, and vane shear test. Accordingly, the foundation bearing capacities of the typical soils in Ningbo region are estimated and predicted with empirical formula. Then, the distributions and numerical characteristics of the predicted results are presented on basis of the K-S inspection method. Based on above analysis results, the recommended foundation bearing capacities of the typical soils are proposed after their comparisons with the empirical foundation bearing capacities of the typical soils in Ningbo area. The research findings can provide scientific references to determine the value of the bearing capacity of the geotechnical investigation and design in Ningbo area.
Development of new coastal economic zones is a great movement for economical construction in China. In order to reduce the risk of geological environment problems and to construct the newly-developed area rationally, this paper proposes a technological system that can be adapted for risk assessment of geological environment of newly-developed areas along shoreline at Caofeidian district. Based on the geological safety assessment and geological-environmental suitable assessment system, the follow factors are considered: basic geological condition, the level of importance of the function land and general plan of newly-developed area, and finally adopt composite index assessment model to finish the geological environment assessment for residential land and public facilities land. The results indicate that:(1)the lowest risk areas make up 7.269% of all the areas. They are suit for residential land and public facilities and have little geological environmental problems.(2)the lower risk areas make up about 77.178%.In general, the geological environment suitability in these areas is good. Part of them should take some engineering measures before construction.(3)the higher risk areas make up 14.487%.There are serious geological environmental problems in these areas. These areas need special measures to deal with the poor geological conditions.(4)the highest risk areas make up 1.066%.These areas are not suit for construction and we recommend them to be used as ecological reservation land. The assessment results provide important geosciences evidence for the planning and construction of Caofeidian newly-developed areas. Development of new coastal economic zones is a great movement for economical construction in China. In order to reduce the risk of geological environment problems and to construct the newly-developed area rationally, this paper proposes a technological system that can be adapted for risk assessment of geological environment of newly-developed areas along shoreline at Caofeidian district. Based on the geological safety assessment and geological-environmental suitable assessment system, the follow factors are considered: basic geological condition, the level of importance of the function land and general plan of newly-developed area, and finally adopt composite index assessment model to finish the geological environment assessment for residential land and public facilities land. The results indicate that:(1)the lowest risk areas make up 7.269% of all the areas. They are suit for residential land and public facilities and have little geological environmental problems.(2)the lower risk areas make up about 77.178%.In general, the geological environment suitability in these areas is good. Part of them should take some engineering measures before construction.(3)the higher risk areas make up 14.487%.There are serious geological environmental problems in these areas. These areas need special measures to deal with the poor geological conditions.(4)the highest risk areas make up 1.066%.These areas are not suit for construction and we recommend them to be used as ecological reservation land. The assessment results provide important geosciences evidence for the planning and construction of Caofeidian newly-developed areas.
At 7:49a.m. April 14th 2010,a Ms 7.1 earthquake occurred in Yushu county, Qinghai province, China. The Yushu earthquake not only resulted in destruction of lots of buildings and plenty of casualty, but also brought lots of geo-hazards such as debris flows, rock falls, landslides and ground cracks. So it evidently changed the distribution regularity and development characteristics of the geohazards at the region. Based on field investigations and statistics, the distribution regularity and development characteristics of the geohazards before and after the earthquake are analyzed. The results show that the geohazards scatter in the area and take place from May to July every year. The main types of the geohazards were debris flows and unstable slopes, as well as the main small scale of geohazards before the Yushu earthquake; After the earthquake, the numbers of geohazards increased obviously, and the distribution of geohazards concentrated in the areas where the main faults cross the Valley of Baqu river, the mountain areas of northern Jiegu town and southern of Zhaqu river, and the geohazards distribute sporadically in the areas where far away from the main faults or macroscopic epicenter. The geohazards are controlled evidently not only by the main faults, but also by the shape, altitude and gradient of slopes. The geohazards mainly distributed in the area of within 2km away from north of the main faults, and on the bulgy shape slopes, altitude of 3800~4000m, and the gradient of 25~40,focused on the gradient of 30~35.The geohazards induced by the ground cracks in the mountains develop distinctly, and the numbers of large and middle scales of geohazards increase clearly, so that the harm of geohazards increase greatly. Especially, the geohazards took place more frequently in rain season, which accelerates the development of geohazards in freezing and thawing periods. At 7:49a.m. April 14th 2010,a Ms 7.1 earthquake occurred in Yushu county, Qinghai province, China. The Yushu earthquake not only resulted in destruction of lots of buildings and plenty of casualty, but also brought lots of geo-hazards such as debris flows, rock falls, landslides and ground cracks. So it evidently changed the distribution regularity and development characteristics of the geohazards at the region. Based on field investigations and statistics, the distribution regularity and development characteristics of the geohazards before and after the earthquake are analyzed. The results show that the geohazards scatter in the area and take place from May to July every year. The main types of the geohazards were debris flows and unstable slopes, as well as the main small scale of geohazards before the Yushu earthquake; After the earthquake, the numbers of geohazards increased obviously, and the distribution of geohazards concentrated in the areas where the main faults cross the Valley of Baqu river, the mountain areas of northern Jiegu town and southern of Zhaqu river, and the geohazards distribute sporadically in the areas where far away from the main faults or macroscopic epicenter. The geohazards are controlled evidently not only by the main faults, but also by the shape, altitude and gradient of slopes. The geohazards mainly distributed in the area of within 2km away from north of the main faults, and on the bulgy shape slopes, altitude of 3800~4000m, and the gradient of 25~40,focused on the gradient of 30~35.The geohazards induced by the ground cracks in the mountains develop distinctly, and the numbers of large and middle scales of geohazards increase clearly, so that the harm of geohazards increase greatly. Especially, the geohazards took place more frequently in rain season, which accelerates the development of geohazards in freezing and thawing periods.
Frost heave has caused serious damage to railway roadbeds in seasonal frozen regions. Therefore, frost heave prevention is the basic principle of roadbed design in seasonal frozen regions. It is a rigorous task because of the strict demand of the deformation in high-speed railway. The heat transport equation and two-dimensional finite element method are employed to simulate the maximum frozen depth in the coming 50 years. The simulation consider the warming environment temperature in the conditions of different depths, shapes, filling materials, and construction seasons. It studies the roadbed temperature field of different parts in high-speed railway. Based on the numerical simulation, appropriate depth, shape, filling material and construction season are proposed for exchange filling material roadbed design. The relationship between the railroad and the railway thermal stability is analyzed as well. Frost heave has caused serious damage to railway roadbeds in seasonal frozen regions. Therefore, frost heave prevention is the basic principle of roadbed design in seasonal frozen regions. It is a rigorous task because of the strict demand of the deformation in high-speed railway. The heat transport equation and two-dimensional finite element method are employed to simulate the maximum frozen depth in the coming 50 years. The simulation consider the warming environment temperature in the conditions of different depths, shapes, filling materials, and construction seasons. It studies the roadbed temperature field of different parts in high-speed railway. Based on the numerical simulation, appropriate depth, shape, filling material and construction season are proposed for exchange filling material roadbed design. The relationship between the railroad and the railway thermal stability is analyzed as well.
After the Wenchuan earthquake, debris flows in quake-hit area have the characteristics of smaller critical rainfall, greater scale and higher risk. Considering the effect of rainfall and earthquake, grey correlation method has been used to analyse the weights of scale, valley area, gully length, basin elevation difference, cutting density, unstable groove proportion, average annual rainfall and seismic intensity of 72 debris flow valleys in Beichuan. Thus a hazard assessment model of debris flow in quake-hit area has been established to evaluate this 72 debris flow valleys. And research results show the following: the weights of average annual rainfall and seismic intensity are greater than the other factors; the evaluation results based on the model raised in this essay are roughly consistent with those given by Liu Xilin. But the risk value improves relatively, and the risk of seven debris flow valleys among those improves a grade. After the Wenchuan earthquake, debris flows in quake-hit area have the characteristics of smaller critical rainfall, greater scale and higher risk. Considering the effect of rainfall and earthquake, grey correlation method has been used to analyse the weights of scale, valley area, gully length, basin elevation difference, cutting density, unstable groove proportion, average annual rainfall and seismic intensity of 72 debris flow valleys in Beichuan. Thus a hazard assessment model of debris flow in quake-hit area has been established to evaluate this 72 debris flow valleys. And research results show the following: the weights of average annual rainfall and seismic intensity are greater than the other factors; the evaluation results based on the model raised in this essay are roughly consistent with those given by Liu Xilin. But the risk value improves relatively, and the risk of seven debris flow valleys among those improves a grade.
Construction projects in arid(semi-arid) coarse saline soil area in the west of China have resulted in the finding of a salt cementation layer(commonly known as salt layer).It has great significance for engineering project. It exists near-surface ground. So far the it has still not been detailed enough. In order to study of the cementation layer formation process, a field test was designed in Dunhuang area within the Hexi corridor. The test site is a gravel sand strata which is interposed with a number of thin sand layer. An exploratory well with 7.5m depth(deeper than annual change depth) was excavated in this site. The data of salt content, moisture content and ground temperature of the section were observed in 171 days in winter. From this test, it observed the process of salt migrated and accumulated to the near-surface ground, as well as measured the migration of water and salt by the geothermal gradient, which impact over the annual changes depth. It is found that as long as there is some geothermal gradient and the appropriate moisture content, the salt content of the cemented layer would continue to increase. Engineering concerned with the engineering properties of the formation in the near-surface(within 5.0m depth) remains uncertain. Construction projects in arid(semi-arid) coarse saline soil area in the west of China have resulted in the finding of a salt cementation layer(commonly known as salt layer).It has great significance for engineering project. It exists near-surface ground. So far the it has still not been detailed enough. In order to study of the cementation layer formation process, a field test was designed in Dunhuang area within the Hexi corridor. The test site is a gravel sand strata which is interposed with a number of thin sand layer. An exploratory well with 7.5m depth(deeper than annual change depth) was excavated in this site. The data of salt content, moisture content and ground temperature of the section were observed in 171 days in winter. From this test, it observed the process of salt migrated and accumulated to the near-surface ground, as well as measured the migration of water and salt by the geothermal gradient, which impact over the annual changes depth. It is found that as long as there is some geothermal gradient and the appropriate moisture content, the salt content of the cemented layer would continue to increase. Engineering concerned with the engineering properties of the formation in the near-surface(within 5.0m depth) remains uncertain.
Fiber reinforcement is a new concept of soil improvement technique. The discrete fibers are evenly incorporated into the soil mass, which aims at improving the mechanical properties of soil. Based on the achievements at home and abroad for the past 20 years in this field, this paper presents the research progress of fiber reinforcement materials, the engineering properties of fiber reinforced soil and reinforcement mechanisms. Generally, there are two categories of fiber reinforcement materials that can be used, i.e.artificial synthetic fibers and natural fibers. On the engineering properties of fiber reinforced soil, the fiber reinforcement is effective in improving soil shear strength, compressive strength, tensile strength, bearing capacity and cracking resistance, increasing the fracture toughness and permeability of soil, reducing the swelling and shrinkage potential of expansive soil. For the fiber reinforcement mechanism, it is believed that the fiber reinforcement benefit is dominated by the interfacial mechanical interactions between fiber/soil, namely the interfacial bonding and friction force. Finally, the current research limitations in this field are discussed, and some new directions and research topics are proposed for the future work. They are development of specialized apparatus and technologies for fiber/soil mixing, development of more specialized fiber products and lower fiber costs, large-scale model tests and field tests, study on interfacial mechanical interactions between fiber reinforcement and soil, study on failure mechanisms and damage effects of fiber reinforced soil, study on mechanical model and calculation theory of fiber reinforced soil, as well as study on dynamical characteristics of fiber reinforced soil. Fiber reinforcement is a new concept of soil improvement technique. The discrete fibers are evenly incorporated into the soil mass, which aims at improving the mechanical properties of soil. Based on the achievements at home and abroad for the past 20 years in this field, this paper presents the research progress of fiber reinforcement materials, the engineering properties of fiber reinforced soil and reinforcement mechanisms. Generally, there are two categories of fiber reinforcement materials that can be used, i.e.artificial synthetic fibers and natural fibers. On the engineering properties of fiber reinforced soil, the fiber reinforcement is effective in improving soil shear strength, compressive strength, tensile strength, bearing capacity and cracking resistance, increasing the fracture toughness and permeability of soil, reducing the swelling and shrinkage potential of expansive soil. For the fiber reinforcement mechanism, it is believed that the fiber reinforcement benefit is dominated by the interfacial mechanical interactions between fiber/soil, namely the interfacial bonding and friction force. Finally, the current research limitations in this field are discussed, and some new directions and research topics are proposed for the future work. They are development of specialized apparatus and technologies for fiber/soil mixing, development of more specialized fiber products and lower fiber costs, large-scale model tests and field tests, study on interfacial mechanical interactions between fiber reinforcement and soil, study on failure mechanisms and damage effects of fiber reinforced soil, study on mechanical model and calculation theory of fiber reinforced soil, as well as study on dynamical characteristics of fiber reinforced soil.
The integrity coefficient of rock mass presents general quality and strength of rock mass. It is an important input parameter in many analysis of rock mass behavior such as in rating of rock mass integrity and quality and rock mass classification. However, there are divergences in relevant codes on how to determinate and apply the integrity coefficient. This paper discusses the contributing factors on determination of integrity coefficient. It then suggests that the elastic wave velocity of intact rock and rock mass for calculation of integrity coefficient be measured in the similar weathered rocks with the same geophysical method. Otherwise, the measured value has to be corrected. The openness and filling conditions of discontinuities should be carefully considered when the integrity coefficient is estimated with the volumetric joint number. In rock mass classification and estimation of rock burst, the term ratio of rock mass strength to ground stress has different geological implications. The rock mass strength has relation with integrity coefficient of rock mass. The integrity coefficient of rock mass presents general quality and strength of rock mass. It is an important input parameter in many analysis of rock mass behavior such as in rating of rock mass integrity and quality and rock mass classification. However, there are divergences in relevant codes on how to determinate and apply the integrity coefficient. This paper discusses the contributing factors on determination of integrity coefficient. It then suggests that the elastic wave velocity of intact rock and rock mass for calculation of integrity coefficient be measured in the similar weathered rocks with the same geophysical method. Otherwise, the measured value has to be corrected. The openness and filling conditions of discontinuities should be carefully considered when the integrity coefficient is estimated with the volumetric joint number. In rock mass classification and estimation of rock burst, the term ratio of rock mass strength to ground stress has different geological implications. The rock mass strength has relation with integrity coefficient of rock mass.
Red clay is a special soil that is formed from the carbonate rocks by weathering under the hot and humid environment. Its pores are large and can have high water contents. It has the character of strong two layer structure. The upper layer clay has the rigid and hard plastic condition and high bearing capacity. The lower layer clay is soft plastic, has flowing plastic condition and weak bearing capacity. The soft red clay needs treatment. This paper uses the soil-cement mixing method to treat the soft red clay. With the variation of the environment and conditions continuously, the red clay is polluted in large areas. And, the existence of the organic matter affects the strength of the foundation. But the test results show that reasonable application of the additives can improve the properties of cement red clay that has been polluted by organic matter. The test results include shear strength, compression coefficient and unconfined compressive strength of cemented clays and take into account the quantity of additives. Red clay is a special soil that is formed from the carbonate rocks by weathering under the hot and humid environment. Its pores are large and can have high water contents. It has the character of strong two layer structure. The upper layer clay has the rigid and hard plastic condition and high bearing capacity. The lower layer clay is soft plastic, has flowing plastic condition and weak bearing capacity. The soft red clay needs treatment. This paper uses the soil-cement mixing method to treat the soft red clay. With the variation of the environment and conditions continuously, the red clay is polluted in large areas. And, the existence of the organic matter affects the strength of the foundation. But the test results show that reasonable application of the additives can improve the properties of cement red clay that has been polluted by organic matter. The test results include shear strength, compression coefficient and unconfined compressive strength of cemented clays and take into account the quantity of additives.
In order to make full use of the waste slag and stone, the rock-filled embankment has taken one kind of ideal embankment form in highway in mountain area. To ensure the stability, it is urgent to study this material. This paper studies the effect of grain composition and roughness to the specimen property. It is based on the large scale triaxial test with the samples from Ya-Lu highway. It examines the grain roughness effect with DEM to fit the properties of graded gravel material under the large scale triaxial test. The paper introduces the principle of the fitting of the sample grain shape and roughness and presents the generation process of the graded gravel rock with numerical samples in details. According to the numerical process and results, the samples with clumps can simulate the Skeleton-pore structure of the gravel realistically. The distribution of the contact force is very reasonable and uniform before loading. Mosaic texture between clumps can tremendously improve the strength of the numerical sample. Deformation process reflects the irregular intergranular bite and sliding characteristics. Sample strength and grain roughness(namely the D4 value) also have a linear proportional relationship. Sample initial coordinate number is one of the decisive factors for the friction angle. The law of coordinate number of the sample with clumps varying with the axial strain development reappears the microscopic mechanical properties of the elastic deformation for the granular material. In order to make full use of the waste slag and stone, the rock-filled embankment has taken one kind of ideal embankment form in highway in mountain area. To ensure the stability, it is urgent to study this material. This paper studies the effect of grain composition and roughness to the specimen property. It is based on the large scale triaxial test with the samples from Ya-Lu highway. It examines the grain roughness effect with DEM to fit the properties of graded gravel material under the large scale triaxial test. The paper introduces the principle of the fitting of the sample grain shape and roughness and presents the generation process of the graded gravel rock with numerical samples in details. According to the numerical process and results, the samples with clumps can simulate the Skeleton-pore structure of the gravel realistically. The distribution of the contact force is very reasonable and uniform before loading. Mosaic texture between clumps can tremendously improve the strength of the numerical sample. Deformation process reflects the irregular intergranular bite and sliding characteristics. Sample strength and grain roughness(namely the D4 value) also have a linear proportional relationship. Sample initial coordinate number is one of the decisive factors for the friction angle. The law of coordinate number of the sample with clumps varying with the axial strain development reappears the microscopic mechanical properties of the elastic deformation for the granular material.
Aiming at the material composition and mechanical properties of the debris landslide, the theory that unload-load response ratio is taken as the evaluation parameter of landslide stability is put forward in the framework of system dynamics. Comparing and analyzing parameters of the unload-load response ratio and the load-unload response ratio, it is found that the unload-load response ratio parameters have more theoretical significance and practical application value in slope stability evaluation and engineering practice than the load-unload response ratio parameter. The unload-load response ratio parameter is determined and its feasibility is analyzed. Then, the model of unload-load response ratio, based on displacement acceleration and monthly rainfall, is established. As an example, the Xintan typical debris landslide is analyzed and calculated. The results show that the steady state reflected by the timing curve of the unload-load response ratio is consistent with the actual status. When Y' Y'- and Y'0,the overall unstability of landslide would appear. That shows it is available to use the unload-load response ratio to forecast landslide's deformation stage and as a criterion of landslide instability. Aiming at the material composition and mechanical properties of the debris landslide, the theory that unload-load response ratio is taken as the evaluation parameter of landslide stability is put forward in the framework of system dynamics. Comparing and analyzing parameters of the unload-load response ratio and the load-unload response ratio, it is found that the unload-load response ratio parameters have more theoretical significance and practical application value in slope stability evaluation and engineering practice than the load-unload response ratio parameter. The unload-load response ratio parameter is determined and its feasibility is analyzed. Then, the model of unload-load response ratio, based on displacement acceleration and monthly rainfall, is established. As an example, the Xintan typical debris landslide is analyzed and calculated. The results show that the steady state reflected by the timing curve of the unload-load response ratio is consistent with the actual status. When Y' Y'- and Y'0,the overall unstability of landslide would appear. That shows it is available to use the unload-load response ratio to forecast landslide's deformation stage and as a criterion of landslide instability.
Large number of engineering practice shows that there are thick sand layers in the foundation along the middle and lower reaches of the Yangtze River, China. The sand layers are good bearing stratum for pile foundations. In the area, the sands are at shallow depths, have big thicknesses, and include silt and silt clay. As the depth increases, the sands become dense. The experimental results of the driven piles indicate that the status of the density of sands has great influence on the construction of the performed piles. The pile-driving operation is easier in the loose or slightly dense sands than in the medium or very dense sands. In this paper, large scale static load tests are carried out for three piles of a power station. The characteristics of the pile settlement with load variation are studied. The axial force and side resistance of the piles are calculated at the same time. The designed diameter of the three piles is 800mm, and their length is 47.2m. The grade of the concrete is C35.Nine soil layers are passed through by the pile body. The results of static loading tests indicate that the relation of the load(Q) and settlement(s) is nonlinear. The Q-s curves can be divided into three stages including the elastic, elastic-plastic and overall damage. The frictional resistance of the sands under 15m depth is much bigger than the silt clay or the muddy soil. The results indicate that the bearing capacities of the piles are all more than 4800kN.It will be provided as reference for future design and research. Large number of engineering practice shows that there are thick sand layers in the foundation along the middle and lower reaches of the Yangtze River, China. The sand layers are good bearing stratum for pile foundations. In the area, the sands are at shallow depths, have big thicknesses, and include silt and silt clay. As the depth increases, the sands become dense. The experimental results of the driven piles indicate that the status of the density of sands has great influence on the construction of the performed piles. The pile-driving operation is easier in the loose or slightly dense sands than in the medium or very dense sands. In this paper, large scale static load tests are carried out for three piles of a power station. The characteristics of the pile settlement with load variation are studied. The axial force and side resistance of the piles are calculated at the same time. The designed diameter of the three piles is 800mm, and their length is 47.2m. The grade of the concrete is C35.Nine soil layers are passed through by the pile body. The results of static loading tests indicate that the relation of the load(Q) and settlement(s) is nonlinear. The Q-s curves can be divided into three stages including the elastic, elastic-plastic and overall damage. The frictional resistance of the sands under 15m depth is much bigger than the silt clay or the muddy soil. The results indicate that the bearing capacities of the piles are all more than 4800kN.It will be provided as reference for future design and research.
This paper presents a detailed investigation and analysis anatomy for the Lutingxi No. W24 typical slope. The paper compares this slope with other slopes available in the literature and puts forward a type of failure mode of plate slope. The paper confirms that this type slope can occur in the nearly horizontal sandstone intercalated with shale strata, in the upper mainly horizontal hard-harder limestone strata, and in the lower mainly horizontal soft sand mudstone rock strata. This papers analyzes the formation mechanism of this type slope from the perspective of geological evolution. The progress can be divided into three phases: ① Unload rebound phase; ② Extended phase of pressing-crack Surface from bottom to up; ③ the Phase of sliding surface though. The paper briefly analyzes the factors of affecting the stability of slope, and focuses on analysis of the effects of groundwater conditions for the stability of such type slopes. Based on limit equilibrium theory, the paper uses different methods to calculate the starting head water of such slopes, and analyzes the stability of such slopes under rainfall conditions. According to the typical slope of No. W24,the paper loads the starting water head to simulate the whole process of such type slopes form accumulating deformation to the overall instability by discrete element numerical simulation technology. At last, through the study of failure mechanism and stability of such type slopes, the paper proposes targeted measures for such type slopes. This paper presents a detailed investigation and analysis anatomy for the Lutingxi No. W24 typical slope. The paper compares this slope with other slopes available in the literature and puts forward a type of failure mode of plate slope. The paper confirms that this type slope can occur in the nearly horizontal sandstone intercalated with shale strata, in the upper mainly horizontal hard-harder limestone strata, and in the lower mainly horizontal soft sand mudstone rock strata. This papers analyzes the formation mechanism of this type slope from the perspective of geological evolution. The progress can be divided into three phases: ① Unload rebound phase; ② Extended phase of pressing-crack Surface from bottom to up; ③ the Phase of sliding surface though. The paper briefly analyzes the factors of affecting the stability of slope, and focuses on analysis of the effects of groundwater conditions for the stability of such type slopes. Based on limit equilibrium theory, the paper uses different methods to calculate the starting head water of such slopes, and analyzes the stability of such slopes under rainfall conditions. According to the typical slope of No. W24,the paper loads the starting water head to simulate the whole process of such type slopes form accumulating deformation to the overall instability by discrete element numerical simulation technology. At last, through the study of failure mechanism and stability of such type slopes, the paper proposes targeted measures for such type slopes.
This paper examines the expansive soil shear strength improved with weathered sand by indoor direct shear test. It studies the modified expansive soil shear strength parameters and the the relationship of the normal stress and the shear stress under different vertical loads, different sand proportions and different moisture contents. The two key factors that affect the direct shear test results is the vertical load and shear rate test. Existing norms of the shear rate is clearly defined, but the vertical load only a recommended value. The expansive soils were mixed with 10%, 20%, 30%, 40%, 50% of the weathered sand, respectively and matched with 6%, 8%, 10%, 12%, 14%water contents. They were loaded under the level I(12.5~50kPa),level Ⅱ(62.5~100kPa),or level Ⅲ(100~400kPa) of vertical loads for the shear test. The test results give the following findings. Vertical load has a high impact on the improved expansive soil shear strength parameters. When the vertical load is reduced, the angle of the soil internal friction gradually increases but its cohesion gradually decreases. At all the levels under the vertical load and the moisture content in the same condition, the cohesive force gradually decreases with the increase of the mixed sand ratio, and the angle of internal friction initially increases and then decreases. In the same sand proportion, the cohesive force and angle of internal friction first increase and then decrease as the moisture content increases. The research results provide a test basis for using weathered sand to improve expansive soil for highway roadbed filler. This paper examines the expansive soil shear strength improved with weathered sand by indoor direct shear test. It studies the modified expansive soil shear strength parameters and the the relationship of the normal stress and the shear stress under different vertical loads, different sand proportions and different moisture contents. The two key factors that affect the direct shear test results is the vertical load and shear rate test. Existing norms of the shear rate is clearly defined, but the vertical load only a recommended value. The expansive soils were mixed with 10%, 20%, 30%, 40%, 50% of the weathered sand, respectively and matched with 6%, 8%, 10%, 12%, 14%water contents. They were loaded under the level I(12.5~50kPa),level Ⅱ(62.5~100kPa),or level Ⅲ(100~400kPa) of vertical loads for the shear test. The test results give the following findings. Vertical load has a high impact on the improved expansive soil shear strength parameters. When the vertical load is reduced, the angle of the soil internal friction gradually increases but its cohesion gradually decreases. At all the levels under the vertical load and the moisture content in the same condition, the cohesive force gradually decreases with the increase of the mixed sand ratio, and the angle of internal friction initially increases and then decreases. In the same sand proportion, the cohesive force and angle of internal friction first increase and then decrease as the moisture content increases. The research results provide a test basis for using weathered sand to improve expansive soil for highway roadbed filler.
Debris or mud flow caused by the landside is one of complicated geologic hazards in mountain area, which is usually related to geology, lithology, the mechanical characteristics of the rock and soil, rainfall, groundwater, and land usage condition. The analysis of immanent relationships between landslide and mud flow can not only afford a reference for the analysis of landslide failure mechanism, but also be used as the basis of evaluation of mud flow triggered by landslides. In this paper, the depth integral is applied two two-dimensional mathematical model of mud flow. The model is based on the principle of conservation of mass and viscous Newtonian fluid Navier-Stovkes equation. Then, this equation is numerically computed by using the finite difference method. The relational expression between streams tilt angle and the width of affected range of mud flow is obtained from statistics. It is applied to analyzing the possibility of mud flow induced by landslides which once failed under the similar geological conditions. Combining with GIS,the model can also be used to predict impacted range of mud flow by using risk map to show the zones that may be affected by the mud flow. Debris or mud flow caused by the landside is one of complicated geologic hazards in mountain area, which is usually related to geology, lithology, the mechanical characteristics of the rock and soil, rainfall, groundwater, and land usage condition. The analysis of immanent relationships between landslide and mud flow can not only afford a reference for the analysis of landslide failure mechanism, but also be used as the basis of evaluation of mud flow triggered by landslides. In this paper, the depth integral is applied two two-dimensional mathematical model of mud flow. The model is based on the principle of conservation of mass and viscous Newtonian fluid Navier-Stovkes equation. Then, this equation is numerically computed by using the finite difference method. The relational expression between streams tilt angle and the width of affected range of mud flow is obtained from statistics. It is applied to analyzing the possibility of mud flow induced by landslides which once failed under the similar geological conditions. Combining with GIS,the model can also be used to predict impacted range of mud flow by using risk map to show the zones that may be affected by the mud flow.
Slope gradient is one of indispensable internal factor during the development process of landslides. After counting and analyzing a great deal of gradients at 113 soil landslides in Goupitan reservoir area, we find that the distribution of gradients have the characteristics of the normal distribution. Using Chi-square test, we verify the gradients of landslides follow normal distribution and establish the function that reflect the relationship between gradient and probability of soil landslides. According to the relationship, we calculate the probability of landslide in different gradient ranges. We then divide the probability into three kinds. The gradients of 25.0~45.0have the maximum probability to soil landslides, which accounts for 60.47% of the total landslides. The gradients of 18.0~25.0and 45.0~51.0have the middle probability to soil landslides, which accounts for 25.46%.The gradients less than 18.0or more than 51.0have the minimum probability to soil landslides, which accounts for 14.07%.The research result inosculates preferably with the fact. The result of this paper not only provides potent gist to the construction of Goupitan reservoir area in future, but also provides a new idea to determine the weighting and index quantification in the process of assessment the landslide danger degree. Slope gradient is one of indispensable internal factor during the development process of landslides. After counting and analyzing a great deal of gradients at 113 soil landslides in Goupitan reservoir area, we find that the distribution of gradients have the characteristics of the normal distribution. Using Chi-square test, we verify the gradients of landslides follow normal distribution and establish the function that reflect the relationship between gradient and probability of soil landslides. According to the relationship, we calculate the probability of landslide in different gradient ranges. We then divide the probability into three kinds. The gradients of 25.0~45.0have the maximum probability to soil landslides, which accounts for 60.47% of the total landslides. The gradients of 18.0~25.0and 45.0~51.0have the middle probability to soil landslides, which accounts for 25.46%.The gradients less than 18.0or more than 51.0have the minimum probability to soil landslides, which accounts for 14.07%.The research result inosculates preferably with the fact. The result of this paper not only provides potent gist to the construction of Goupitan reservoir area in future, but also provides a new idea to determine the weighting and index quantification in the process of assessment the landslide danger degree.
This paper examines the effects of parameters in the generalized Hoek-Brown failure criterion on the mechanical parameters of slope rock mass using orthogonal test method. It gives a comprehensive analysis of various factors and effectively explains the limitation of single-factor method. Sensibility analysis of the criterion parameters based on the orthogonal test is done within the slope of 5# abutment in Longqiao Extra-large Bridge. It is found that the Geological Strength Index (GSI) influences the rock mass deformation parameter Em significantly, and the compressive strength ci and disturbance factor of rock mass D have greater impact on the rock mass strength parameters C、. In summary, the index GSI and ci are more sensitive to the mechanical parameters of rock mass comparing to disturbance factor of rock mass D,and then mi;There is no interaction between the criterion parameters, and they are relatively independent. This paper examines the effects of parameters in the generalized Hoek-Brown failure criterion on the mechanical parameters of slope rock mass using orthogonal test method. It gives a comprehensive analysis of various factors and effectively explains the limitation of single-factor method. Sensibility analysis of the criterion parameters based on the orthogonal test is done within the slope of 5# abutment in Longqiao Extra-large Bridge. It is found that the Geological Strength Index (GSI) influences the rock mass deformation parameter Em significantly, and the compressive strength ci and disturbance factor of rock mass D have greater impact on the rock mass strength parameters C、. In summary, the index GSI and ci are more sensitive to the mechanical parameters of rock mass comparing to disturbance factor of rock mass D,and then mi;There is no interaction between the criterion parameters, and they are relatively independent.
Huang Juewan high-steep rock slope is composed by mudstone and sandstone. The rock beddings are similar to the cookies.They have soft and hard layers with gentle dip layered structure. The high-steep slope in addition to the top of the steep cliff in thick sandstone occurred collapses. Outside the instability main slope body bottom, there are local cutting layer instability. To ensure a smooth start of the lower part of high slope and the safety of the residents, this paper uses the method of numerical simulation on the high slope of the stability evaluation. The paper selects the natural dignity and seismicity load as the two conditions for slope stability analysis. The results show that:(1)Main slope rock mass in the two kinds of working conditions is still in the stable state; but seismic loads slope stability reduced significantly influence; (2)Steep cliff and main slope near the contact zone and the ramp slope foot place obvious stress concentration phenomenon more likely to damage; (3)the potential sliding surface of slope is located in the central slope. The cut points may be located at the slope toe. Huang Juewan high-steep rock slope is composed by mudstone and sandstone. The rock beddings are similar to the cookies.They have soft and hard layers with gentle dip layered structure. The high-steep slope in addition to the top of the steep cliff in thick sandstone occurred collapses. Outside the instability main slope body bottom, there are local cutting layer instability. To ensure a smooth start of the lower part of high slope and the safety of the residents, this paper uses the method of numerical simulation on the high slope of the stability evaluation. The paper selects the natural dignity and seismicity load as the two conditions for slope stability analysis. The results show that:(1)Main slope rock mass in the two kinds of working conditions is still in the stable state; but seismic loads slope stability reduced significantly influence; (2)Steep cliff and main slope near the contact zone and the ramp slope foot place obvious stress concentration phenomenon more likely to damage; (3)the potential sliding surface of slope is located in the central slope. The cut points may be located at the slope toe.
Regional stability analysis has important significance for scientific and rational site selection of underground water sealed caverns. Firstly, this paper puts forward the range of regional stability study area of underground water sealed caverns, around western Pacific coastal area, according to the basic principles of underground water sealed caverns construction site selection and based on fully consideration of the distribution of large-scale Wharf and oil refinery in China. Secondly, the regional faults, formation lithology, peak acceleration of seismic and heat flow values are determined as sensitive factors of regional stability evaluation, based on the analysis of sensitive factors that influence the regional stability of underground water sealed caverns, and taking into account the available data. Then, the sensitive factors are divided into several grades according to the influence on regional stability. Finally, spatial overlay analysis to regional stability of study area is carried out. The results of study area regional stability are obtained, with the method of integrated index and using of MAPGIS.The analysis provides reference and support to location planning of latter large-scale underground water sealed caverns construction in China. Regional stability analysis has important significance for scientific and rational site selection of underground water sealed caverns. Firstly, this paper puts forward the range of regional stability study area of underground water sealed caverns, around western Pacific coastal area, according to the basic principles of underground water sealed caverns construction site selection and based on fully consideration of the distribution of large-scale Wharf and oil refinery in China. Secondly, the regional faults, formation lithology, peak acceleration of seismic and heat flow values are determined as sensitive factors of regional stability evaluation, based on the analysis of sensitive factors that influence the regional stability of underground water sealed caverns, and taking into account the available data. Then, the sensitive factors are divided into several grades according to the influence on regional stability. Finally, spatial overlay analysis to regional stability of study area is carried out. The results of study area regional stability are obtained, with the method of integrated index and using of MAPGIS.The analysis provides reference and support to location planning of latter large-scale underground water sealed caverns construction in China.
The limit equilibrium method(FEM) is used to analyze the deformation rule of loess high slope at Dong Loutian coal mine before and after excavation. The larger displacement of the loess high slope will happen after excavation. The dynamic design method is used for the important protection location according to the displacement development rule and stress concentration region in numerical analysis. The slope surface is supported by anchors and soil nails. The straight arm segment of slope is supported by steel internal bracing and slope protection piles. The simulation results show that the stress field redistributes after excavation and reinforcement and the horizontal displacement of the slope is inhibited effectively. It provides the scientific basis for dynamic design and construction of the important reinforcement region of slope. The design project can be satisfied with the design requirements of engineering safety grade. The limit equilibrium method(FEM) is used to analyze the deformation rule of loess high slope at Dong Loutian coal mine before and after excavation. The larger displacement of the loess high slope will happen after excavation. The dynamic design method is used for the important protection location according to the displacement development rule and stress concentration region in numerical analysis. The slope surface is supported by anchors and soil nails. The straight arm segment of slope is supported by steel internal bracing and slope protection piles. The simulation results show that the stress field redistributes after excavation and reinforcement and the horizontal displacement of the slope is inhibited effectively. It provides the scientific basis for dynamic design and construction of the important reinforcement region of slope. The design project can be satisfied with the design requirements of engineering safety grade.
Slope failure is one of the geological disasters frequently occurring in water resources and hydropower engineering. The evaluation on slope stability with three dimensional numerical simulation is of great significance and value for the disaster prevention and mitigation and landslide forecast. This paper mainly studies the slope stability at the right bank of Lazhai hydropower station. The station is located in Yunnan Province, China. The paper presents a systematic investigation of the site engineering geological conditions the type of rock mass structure, and the mechanism of deformation. It examines the occurrence relations between structural plane and slope and the potential induction factor of the failure of the slope in detail. Meanwhile, the stress filed, the displacement field and the distribution of the plastic zones of the original slope, the non-supporting and supporting slopes after excavation are respectively obtained with true-three-dimensional numerical simulation(FLAC3D).The mechanism of the deformation is analyzed, combining the analysis of the engineering geologic condition. The results shown the slope is in the initial stage of tension and its deformation is affected by the excavation obviously. According to the research results of the slope deformation mechanism, some corresponding reinforcement measures are taken to control the deformation of the slope. These measures mainly include the prestressed anchor cable, grid beam and suspended net shotcrete. Slope failure is one of the geological disasters frequently occurring in water resources and hydropower engineering. The evaluation on slope stability with three dimensional numerical simulation is of great significance and value for the disaster prevention and mitigation and landslide forecast. This paper mainly studies the slope stability at the right bank of Lazhai hydropower station. The station is located in Yunnan Province, China. The paper presents a systematic investigation of the site engineering geological conditions the type of rock mass structure, and the mechanism of deformation. It examines the occurrence relations between structural plane and slope and the potential induction factor of the failure of the slope in detail. Meanwhile, the stress filed, the displacement field and the distribution of the plastic zones of the original slope, the non-supporting and supporting slopes after excavation are respectively obtained with true-three-dimensional numerical simulation(FLAC3D).The mechanism of the deformation is analyzed, combining the analysis of the engineering geologic condition. The results shown the slope is in the initial stage of tension and its deformation is affected by the excavation obviously. According to the research results of the slope deformation mechanism, some corresponding reinforcement measures are taken to control the deformation of the slope. These measures mainly include the prestressed anchor cable, grid beam and suspended net shotcrete.
On the basis of the detailed analysis of the valley geological conditions as well as geostress distribution and deep fractures in the left bank of Baihetan hydropower station, the evolvement and development of the site valley are simulated by using distinct element codes UDEC with denudation method to analysis the formation mechanism of deep fractures in the left bank. Simulation results show that valley stress field distribution presents the law of a typical deep valley with three stress districts of relaxation, increase and unchanged, as well as valley bottom existing high geostress fold.Based on the deep analysis of different parts in the valley slope, different stages of the stress variation and present valley geological features, it is considered that the deep fractures are results of the tensile failure. The outcrops of the consequent dip fault zones after the eroded valley unloads make shear failure further grow. Those shear failures are formed because the local stress concentrations make rock shear failure during the valley development process at the special geological structures such as the dip direction of rocks along slope, the high regional tectonic stress, the asymmetric v-shaped valley and rapid incision of Baihetan hydropower station valley. On the basis of the detailed analysis of the valley geological conditions as well as geostress distribution and deep fractures in the left bank of Baihetan hydropower station, the evolvement and development of the site valley are simulated by using distinct element codes UDEC with denudation method to analysis the formation mechanism of deep fractures in the left bank. Simulation results show that valley stress field distribution presents the law of a typical deep valley with three stress districts of relaxation, increase and unchanged, as well as valley bottom existing high geostress fold.Based on the deep analysis of different parts in the valley slope, different stages of the stress variation and present valley geological features, it is considered that the deep fractures are results of the tensile failure. The outcrops of the consequent dip fault zones after the eroded valley unloads make shear failure further grow. Those shear failures are formed because the local stress concentrations make rock shear failure during the valley development process at the special geological structures such as the dip direction of rocks along slope, the high regional tectonic stress, the asymmetric v-shaped valley and rapid incision of Baihetan hydropower station valley.
Quartz is a general mineral in various rocks. The size and content of quartz grains not only control the strength, hardness and abrastivity of rock, but also influence the TBM driving efficiency directly. The identification of rock thin-sections is carried out with 124 pieces of rock samples from the West Route of South-to-North Water Transfer Project in China. The distribution law of quartz contents in the rocks from different zones is obtained, based on grain-size analysis of rocks. The influence of distribution characters of quartz contentd on the classification of surrounding rock mass cut by TBM and the driving efficiency in west route of South-to-North Water Transfer Project is analyzed according to the statistic results of quartz contents in different rocks, based on the characters of TBM construction. The research results show that there are obvious differences in the quartz contents of sandstone and greywacke, siltstone and slate. The quartz contents of sandstone and greywacke, siltstone are relatively higher, 74.21% and 80.41% respectively. While the quartz content of slate is relatively lower, 9.36%.The quartz contents of sandstone and greywacke, siltstone are commonly more than 60%.Their influence on the classification of surrounding rock mass cut by TBM belongs to the serious grade. The quartz content of slate is mostly less than 30%.Its influence on the classification of surrounding rock mass cut by TBM is from the slight to the obvious grade. The higher the quartz content is,the bigger the hardness and abrastivity are,the bigger the cutter consumption is,the slower the Penetration Rate and Advance Rate of TBM are.The research results can provide references for optimizing type selection of TBM,classification of surrounding rock mass cut by TBM and prediction of construction progress in the West Route of South-to-North Water Transfer Project. Quartz is a general mineral in various rocks. The size and content of quartz grains not only control the strength, hardness and abrastivity of rock, but also influence the TBM driving efficiency directly. The identification of rock thin-sections is carried out with 124 pieces of rock samples from the West Route of South-to-North Water Transfer Project in China. The distribution law of quartz contents in the rocks from different zones is obtained, based on grain-size analysis of rocks. The influence of distribution characters of quartz contentd on the classification of surrounding rock mass cut by TBM and the driving efficiency in west route of South-to-North Water Transfer Project is analyzed according to the statistic results of quartz contents in different rocks, based on the characters of TBM construction. The research results show that there are obvious differences in the quartz contents of sandstone and greywacke, siltstone and slate. The quartz contents of sandstone and greywacke, siltstone are relatively higher, 74.21% and 80.41% respectively. While the quartz content of slate is relatively lower, 9.36%.The quartz contents of sandstone and greywacke, siltstone are commonly more than 60%.Their influence on the classification of surrounding rock mass cut by TBM belongs to the serious grade. The quartz content of slate is mostly less than 30%.Its influence on the classification of surrounding rock mass cut by TBM is from the slight to the obvious grade. The higher the quartz content is,the bigger the hardness and abrastivity are,the bigger the cutter consumption is,the slower the Penetration Rate and Advance Rate of TBM are.The research results can provide references for optimizing type selection of TBM,classification of surrounding rock mass cut by TBM and prediction of construction progress in the West Route of South-to-North Water Transfer Project.
Complicated cavities with wide distribution, multi-layers, variable thicknesses and depths as well as the complex surrounding lithology, result in difficulties on their grouting effect test. Therefore, there is no reliable testing system at present. Based on cavities grouting practice, the resistivity of the slurry stones is tested and the apparent resistivity range of 93~130 m has a great difference quantity from cavities and surrounding rocks. Cavities are tested by sounding method and electromagnetic wave CT before and after grouting, showing that: after grouting, in shallow range of 0~30m, the apparent resistivity generally is reduced and becomes relatively uniform and stable; low resistivity abnormity in deep range is mitigated with expanded uniform range; electromagnetic wave absorption coefficient increased by about 25% in 40~70m range. Core drilling indicates that, grouting slurry stone is visible in most boreholes, and 10 detecting holes' grouting volume is not more than 15% of the adjacent four holes grouting average. The above test results show that: the cavities have lower electromagnetic wave absorption coefficient, which rises after grouting; cavities above the water table have high resistivity, which come down after grouting, and cavities below the water table have totally reverse attribute. Before and after grouting the cavities have great difference on the properties, showing the grouting quality is very good and there is a good correspondence between the results of several detection methods. The result indicates that, by comparing with drilling results and detection-hole grouting data, geophysical method of overall electrical sounding detection and partial detailed electromagnetic wave CT,can effectively detect complicated cavities grouting effect. The achievement can be drawn on in other similar cavities. Complicated cavities with wide distribution, multi-layers, variable thicknesses and depths as well as the complex surrounding lithology, result in difficulties on their grouting effect test. Therefore, there is no reliable testing system at present. Based on cavities grouting practice, the resistivity of the slurry stones is tested and the apparent resistivity range of 93~130 m has a great difference quantity from cavities and surrounding rocks. Cavities are tested by sounding method and electromagnetic wave CT before and after grouting, showing that: after grouting, in shallow range of 0~30m, the apparent resistivity generally is reduced and becomes relatively uniform and stable; low resistivity abnormity in deep range is mitigated with expanded uniform range; electromagnetic wave absorption coefficient increased by about 25% in 40~70m range. Core drilling indicates that, grouting slurry stone is visible in most boreholes, and 10 detecting holes' grouting volume is not more than 15% of the adjacent four holes grouting average. The above test results show that: the cavities have lower electromagnetic wave absorption coefficient, which rises after grouting; cavities above the water table have high resistivity, which come down after grouting, and cavities below the water table have totally reverse attribute. Before and after grouting the cavities have great difference on the properties, showing the grouting quality is very good and there is a good correspondence between the results of several detection methods. The result indicates that, by comparing with drilling results and detection-hole grouting data, geophysical method of overall electrical sounding detection and partial detailed electromagnetic wave CT,can effectively detect complicated cavities grouting effect. The achievement can be drawn on in other similar cavities.