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Editor Work2017 Vol. 25, No. 5
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2017, 25(5): 1165-1181.
Abstract
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An increase in the number of rock slope instability case that was characterized with "toppling" movement was found in the practice of engineering geology in west China in the past decade. The significance of the potential threats caused by toppling failure has arguably moved abreast of that induced by the conventional slope movement type commonly known as "sliding", and thus it has become a more pronounced challenge faced by engineering geologists and geotechnical engineers. The critical issue in the study of toppling failure is that the current analytical and/or empirical models are primarily based on the hypothetical slide of rock slopes without considering other forms of movement. The paper analyzes the deformation and failure process of toppling movement in light of the field data obtained from a large number of engineering projects. The study of toppling movement presented here constructed engineering geology models to depict the deformation at various stages and divided the movement into the types of toppling-falling, toppling-slipping, toppling-cracking, and toppling-loosening, which provides systematic qualitative descriptions and quantitative thresholds for the characteristics of each movement type. The study aims at unifying the understanding of geological significance, static and dynamic mechanics, and slope stability analysis to provide means of evaluating the stability of rock slopes prone to toppling failure. The slope stability evaluating criteria are primarily based on deformation process compare to the previous criteria utilizing strength to assess the stability of slope subject to sliding movement.
An increase in the number of rock slope instability case that was characterized with "toppling" movement was found in the practice of engineering geology in west China in the past decade. The significance of the potential threats caused by toppling failure has arguably moved abreast of that induced by the conventional slope movement type commonly known as "sliding", and thus it has become a more pronounced challenge faced by engineering geologists and geotechnical engineers. The critical issue in the study of toppling failure is that the current analytical and/or empirical models are primarily based on the hypothetical slide of rock slopes without considering other forms of movement. The paper analyzes the deformation and failure process of toppling movement in light of the field data obtained from a large number of engineering projects. The study of toppling movement presented here constructed engineering geology models to depict the deformation at various stages and divided the movement into the types of toppling-falling, toppling-slipping, toppling-cracking, and toppling-loosening, which provides systematic qualitative descriptions and quantitative thresholds for the characteristics of each movement type. The study aims at unifying the understanding of geological significance, static and dynamic mechanics, and slope stability analysis to provide means of evaluating the stability of rock slopes prone to toppling failure. The slope stability evaluating criteria are primarily based on deformation process compare to the previous criteria utilizing strength to assess the stability of slope subject to sliding movement.
2017, 25(5): 1182-1189.
Landslide dams are natural dams formed by collapse, landslide, debris flow, etc. Landslide dams are different from man-made dams for its lack of sufficient consolidation, leading to loose dam structure and highly non-homogeneous materials. Large water head caused by rising of water level could trigger seepage deformation of soil and influence landslide dam stability, which may lead to dam breach and catastrophic damage. Due to the presence of large diameter particles in landslide dams, the conventional penetration test device is difficult to meet the requirements. A large diameter infiltration device with the diameter of 60cm was developed. The paper reports the experimental study on the seepage characteristics of landslide dam material. It was observed that piping and soil flow are the two seepage failure modes of landslide dams. The landslide dams with coarse grain in majority are prone to piping failure, and the dams with fine grain in majority and gap-graded materials are prone to soil flow failure. The experiments showed the permeability coefficient reduces with the increase of the dry density and is influenced by the amount of fine particles. Using the nonuniformity coefficient or the curvature coefficient independently is not suitable for evaluating the permeability coefficient change. A discriminant formula for the seepage failure and a critical hydraulic gradient equation for piping are provided based on the experimental data.
Landslide dams are natural dams formed by collapse, landslide, debris flow, etc. Landslide dams are different from man-made dams for its lack of sufficient consolidation, leading to loose dam structure and highly non-homogeneous materials. Large water head caused by rising of water level could trigger seepage deformation of soil and influence landslide dam stability, which may lead to dam breach and catastrophic damage. Due to the presence of large diameter particles in landslide dams, the conventional penetration test device is difficult to meet the requirements. A large diameter infiltration device with the diameter of 60cm was developed. The paper reports the experimental study on the seepage characteristics of landslide dam material. It was observed that piping and soil flow are the two seepage failure modes of landslide dams. The landslide dams with coarse grain in majority are prone to piping failure, and the dams with fine grain in majority and gap-graded materials are prone to soil flow failure. The experiments showed the permeability coefficient reduces with the increase of the dry density and is influenced by the amount of fine particles. Using the nonuniformity coefficient or the curvature coefficient independently is not suitable for evaluating the permeability coefficient change. A discriminant formula for the seepage failure and a critical hydraulic gradient equation for piping are provided based on the experimental data.
2017, 25(5): 1190-1204.
The accuracy is the most important in stability analysis of a landslide. Both the sliding plane and the slope surface are three dimensional, resulting in great spatial variation of thicknesses of the sliding body. The analysis of slope stability is usually carried out by calculating the factors of safety along the"representative longitudinal profile" of the central axis or nearby profile. Because the calculation uses a unit width, the results can only represent the local stability of the slope within small widths on both sides of the selected profile in most cases, but not the stability of the entire landslide. Therefore a multi-profile joint forces method is proposed to assess the stability of a landslide. To reduce the man-power and cost for multi-profile exploration of a landslide, the sliding surfaces are classified into two categories:simple slip surface and complex slip surface. For a simple slip surface, it is required to have a minimum of two profiles with a total of 2 to 4 boreholes. The multiple longitudinal profiles required for calculation are then delineated through drawing the auxiliary cross sections by using several curve functions of the slip surface. The multi-profile joint forces method is based on parallelogram law for addition of forces. Each profile is first divided into slices. The shear forces and resistance forces of each slice are then converted to horizontal and vertical components on each slice of a profile. The horizontal and vertical resulting forces along each profile are determined by adding the horizontal and vertical shear forces and resistance forces on all slices, respectively. The resulting joint sliding force and resistance forces on all profiles are used to calculate the sliding and resistance forces of the entire landslide. Their ratio(resistance force vs.sliding force)-the safety factor of the landslide are calculated at the end. Two case studies of landslides, one with a simple slip surface and another with a complex slip surface, are used to validate the method.
The accuracy is the most important in stability analysis of a landslide. Both the sliding plane and the slope surface are three dimensional, resulting in great spatial variation of thicknesses of the sliding body. The analysis of slope stability is usually carried out by calculating the factors of safety along the"representative longitudinal profile" of the central axis or nearby profile. Because the calculation uses a unit width, the results can only represent the local stability of the slope within small widths on both sides of the selected profile in most cases, but not the stability of the entire landslide. Therefore a multi-profile joint forces method is proposed to assess the stability of a landslide. To reduce the man-power and cost for multi-profile exploration of a landslide, the sliding surfaces are classified into two categories:simple slip surface and complex slip surface. For a simple slip surface, it is required to have a minimum of two profiles with a total of 2 to 4 boreholes. The multiple longitudinal profiles required for calculation are then delineated through drawing the auxiliary cross sections by using several curve functions of the slip surface. The multi-profile joint forces method is based on parallelogram law for addition of forces. Each profile is first divided into slices. The shear forces and resistance forces of each slice are then converted to horizontal and vertical components on each slice of a profile. The horizontal and vertical resulting forces along each profile are determined by adding the horizontal and vertical shear forces and resistance forces on all slices, respectively. The resulting joint sliding force and resistance forces on all profiles are used to calculate the sliding and resistance forces of the entire landslide. Their ratio(resistance force vs.sliding force)-the safety factor of the landslide are calculated at the end. Two case studies of landslides, one with a simple slip surface and another with a complex slip surface, are used to validate the method.
2017, 25(5): 1205-1212.
Secondary toppling failure is one of typical instabilities of steep stratified rock slopes. The limit equilibrium analysis method is the main method to analyze the toppling failure of rock slopes. Analysis of secondary toppling failure of counter-tilt jointed rock slopes has an important bearing on engineering practice, especially for mountain area of southwest China where there are many slope engineering. Based on the analysis method of limit equilibrium proposed by Goodman and Bray, a geomechanical model of the secondary toppling of counter-tilt jointed rock slope under the action from rear soil pressure are developed, The related analysis method is proposed. This model takes into account the factors such as groundwater pressure, joint connectivity, and rock cohesion. A formulation is derived for calculating the pushing force of each rock formation. The comprehensive safety coefficient is given. The stability of secondary toppling of counter-tilt jointed rock slope can be easily analyzed using a Matlab program, which provides a theoretical basis for the design and reinforce of this type of slope. An example is introduced. It analyses the influence of groundwater pressure, joint connectivity as well as rock cohesion on the pushing force of each rock formation and comprehensive safety coefficient. Compared with the block toppling failure of rock slopes, for secondary toppling failure of counter-tilt jointed rock slopes, from top to bottom, the rock formation above destruction surface is divided into three parts:the slip zone, the toppling area and the stabilization zone. The groundwater pressure, joint connectivity and the rock cohesion of the underlying fractured rock have obvious influence on the failure form and stability safety coefficient of each rock formation, especially in the lower part of the slope and the foot part of the slope. The minimum stability factor of each rock formation is concentrated in the upper part of the slope.
Secondary toppling failure is one of typical instabilities of steep stratified rock slopes. The limit equilibrium analysis method is the main method to analyze the toppling failure of rock slopes. Analysis of secondary toppling failure of counter-tilt jointed rock slopes has an important bearing on engineering practice, especially for mountain area of southwest China where there are many slope engineering. Based on the analysis method of limit equilibrium proposed by Goodman and Bray, a geomechanical model of the secondary toppling of counter-tilt jointed rock slope under the action from rear soil pressure are developed, The related analysis method is proposed. This model takes into account the factors such as groundwater pressure, joint connectivity, and rock cohesion. A formulation is derived for calculating the pushing force of each rock formation. The comprehensive safety coefficient is given. The stability of secondary toppling of counter-tilt jointed rock slope can be easily analyzed using a Matlab program, which provides a theoretical basis for the design and reinforce of this type of slope. An example is introduced. It analyses the influence of groundwater pressure, joint connectivity as well as rock cohesion on the pushing force of each rock formation and comprehensive safety coefficient. Compared with the block toppling failure of rock slopes, for secondary toppling failure of counter-tilt jointed rock slopes, from top to bottom, the rock formation above destruction surface is divided into three parts:the slip zone, the toppling area and the stabilization zone. The groundwater pressure, joint connectivity and the rock cohesion of the underlying fractured rock have obvious influence on the failure form and stability safety coefficient of each rock formation, especially in the lower part of the slope and the foot part of the slope. The minimum stability factor of each rock formation is concentrated in the upper part of the slope.
2017, 25(5): 1213-1219.
This paper uses the combining method of ANP and fuzzy cluster analysis in karstic collapse. It considers the factors such as mining activities, groundwater movement, karst development and cladding features. It is based on a great deal of practice. It further uses ANP to make a comprehensive analysis towards the influencing degree among various factors and adopts the method of Fuzzy clustering analysis to do clustering in dangerous areas. It is successfully applied to the prediction of karst collapse in Pb-Zn mining area in Gudan. The results indicate that carrying out mining activities is the mainest factors resulting in karst collapse. Other factors have effects on it as well. The study area can be divided into high risk area and low risk area. The results are in line with the empirical value and the measured value, which indicates that this method is reasonable and feasible, and provides a new method and thinking for the evaluation and prediction for dangerous area of karst.
This paper uses the combining method of ANP and fuzzy cluster analysis in karstic collapse. It considers the factors such as mining activities, groundwater movement, karst development and cladding features. It is based on a great deal of practice. It further uses ANP to make a comprehensive analysis towards the influencing degree among various factors and adopts the method of Fuzzy clustering analysis to do clustering in dangerous areas. It is successfully applied to the prediction of karst collapse in Pb-Zn mining area in Gudan. The results indicate that carrying out mining activities is the mainest factors resulting in karst collapse. Other factors have effects on it as well. The study area can be divided into high risk area and low risk area. The results are in line with the empirical value and the measured value, which indicates that this method is reasonable and feasible, and provides a new method and thinking for the evaluation and prediction for dangerous area of karst.
STABILITY OF UNSTABLE ROCK IN NEARLY-HORIZONTAL SANDSTONE-MUDSTONE STRATUM DUE TO ENLARGED ROCK-CELL
2017, 25(5): 1220-1229.
The retreated rock-cell is a key factor of change in stability of unstable rocks in nearly-horizontal sandstone-mudstone in the part of Chongqing of the Three Gorges Reservoir. Based on parallel retreating rock-cell theory, this paper proposes the mechanical mechanism of shear failure and tension failure under retreating mudstone-cell, and stability calculation method for three kinds of unstable rocks in consideration of retreating rock-cell parameters. Pursuant to stability calculation outcome of Taibai unstable rocks in Wanzhou District, Chongqing, it is concluded as follows using the method proposed in this paper. Unstable sliding rock W12, unstable toppling rock W22 and unstable dropping rock W4 are stable. Unstable toppling rock W59 is sub-stable. Unstable dropping rock W16 is almost stable. They are identical with the field monitoring data from 2008 to 2013. Against unstable sliding rock W12, this paper discusses and concludes that the minimum principal stress decreases linearly over time. With the continuously decreased minimum principal stress, the shear failure firstly occurs to mudstone. Then the mudstone is broken with tension. The angle of rupture of mudstone unceasingly decreases with the decreased minimum principal stress. With enlarged rock-cell, stability coefficient decreases in concave curve. So enlarged rock-cell is the root cause of unstable rock failure. It exists one critical rock-cell depth. Unstable rock would break under this critical rock-cell depth. It can forecast the failure time of unstable rock.
The retreated rock-cell is a key factor of change in stability of unstable rocks in nearly-horizontal sandstone-mudstone in the part of Chongqing of the Three Gorges Reservoir. Based on parallel retreating rock-cell theory, this paper proposes the mechanical mechanism of shear failure and tension failure under retreating mudstone-cell, and stability calculation method for three kinds of unstable rocks in consideration of retreating rock-cell parameters. Pursuant to stability calculation outcome of Taibai unstable rocks in Wanzhou District, Chongqing, it is concluded as follows using the method proposed in this paper. Unstable sliding rock W12, unstable toppling rock W22 and unstable dropping rock W4 are stable. Unstable toppling rock W59 is sub-stable. Unstable dropping rock W16 is almost stable. They are identical with the field monitoring data from 2008 to 2013. Against unstable sliding rock W12, this paper discusses and concludes that the minimum principal stress decreases linearly over time. With the continuously decreased minimum principal stress, the shear failure firstly occurs to mudstone. Then the mudstone is broken with tension. The angle of rupture of mudstone unceasingly decreases with the decreased minimum principal stress. With enlarged rock-cell, stability coefficient decreases in concave curve. So enlarged rock-cell is the root cause of unstable rock failure. It exists one critical rock-cell depth. Unstable rock would break under this critical rock-cell depth. It can forecast the failure time of unstable rock.
2017, 25(5): 1230-1237.
Ili valley of Xinjiang in large areas are covered with loess. Loess landslides occur frequently in this region. Its number accounts for 80% of all landslides in Xinjiang province. The loss caused by loess landslide is remarkable. Compared with other typical loess landslides in western China, loess landslides in Ili valley are characterized by complex slope structures and rainfall-induced unsaturated seepage instabilities. Case study of the unsaturated seepage failure mechanism for Gallente landslide is presented in this study. Slope structure model for Gallente landslide is firstly established. Based on unsaturated seepage theory, the two-dimensional unsaturated seepage field in the slope is simulated and analyzed. Then the seepage failure process and mechanism induced by rainfall are examined. The coupling seepage-stability computing method is used to analyze the destabilizing process of slope structure induced by unsaturated seepage. The unsaturated seepage failure mechanism of large-scale loess landslide in Ili valley is eventually revealed.
Ili valley of Xinjiang in large areas are covered with loess. Loess landslides occur frequently in this region. Its number accounts for 80% of all landslides in Xinjiang province. The loss caused by loess landslide is remarkable. Compared with other typical loess landslides in western China, loess landslides in Ili valley are characterized by complex slope structures and rainfall-induced unsaturated seepage instabilities. Case study of the unsaturated seepage failure mechanism for Gallente landslide is presented in this study. Slope structure model for Gallente landslide is firstly established. Based on unsaturated seepage theory, the two-dimensional unsaturated seepage field in the slope is simulated and analyzed. Then the seepage failure process and mechanism induced by rainfall are examined. The coupling seepage-stability computing method is used to analyze the destabilizing process of slope structure induced by unsaturated seepage. The unsaturated seepage failure mechanism of large-scale loess landslide in Ili valley is eventually revealed.
2017, 25(5): 1238-1244.
The maximum acceleration can also be used to evaluate the stability of slopes. It has been found that the correlation between the safety factor and the acceleration is more significant when cohesion has smaller weight in shear strength of the soil. In this paper, the correlation between the critical slip surfaces of acceleration and safety factor are further investigated. Results show that for slopes with the slope angle α ≥ 45°, the critical slip surface of acceleration is close to that of safety factor when ξ < 0.1. For reinforced slopes, smaller safety factors are located near the end of the reinforcement when the reinforcement is short. While the location will not change when the reinforcement is long enough. However, the bigger accelerations are always located near the end of the reinforcement, the mechanism of which need further investigation.
The maximum acceleration can also be used to evaluate the stability of slopes. It has been found that the correlation between the safety factor and the acceleration is more significant when cohesion has smaller weight in shear strength of the soil. In this paper, the correlation between the critical slip surfaces of acceleration and safety factor are further investigated. Results show that for slopes with the slope angle α ≥ 45°, the critical slip surface of acceleration is close to that of safety factor when ξ < 0.1. For reinforced slopes, smaller safety factors are located near the end of the reinforcement when the reinforcement is short. While the location will not change when the reinforcement is long enough. However, the bigger accelerations are always located near the end of the reinforcement, the mechanism of which need further investigation.
2017, 25(5): 1245-1251.
This paper aims to provide a scientific decision and basis of disaster prevention and reduction for the line determination and safe construction and operation of road engineering in Sichuan-Tibet traffic corridor. By field survey and remote sensing interpretation on the landslides and avalanches along the proposed railway and highway of Sichuan-Tibet, we find out that the spatial distribution characteristics and potential hazard conditions of the hazards. Further, we systematically analyze and summarize the possible hazard ways of the hazards in the corridor in detail, combined with the existing research results of hazard characteristics and their hazard ways along the old Sichuan-Tibet roads. The research results show that there are totally 488 hazards in Kangding to Linzhi section of the corridor. They include 262 landslides and 226 collapses(including sand-sliding slope).148 hazards have potential hazards and threats on the proposed railway. They include 89 landslides and 59 collapses. The ways of the hazards on the road engineering are mainly summarized as follows.(1) Landslide and avalanches threaten tunnel and its import and export.(2) Landslide and avalanches advance, bury and destroy road engineering.(3) Landslide and avalanches threaten the safety of stations.(4) Landslide and avalanches block rivers and flooding road engineering.(5) Landslide and avalanches destroy road engineering by converting into hazard chains, such as debris flows and floods.(6) Avalanches and sand-sliding slopes impact, disturb and bury road engineering.
This paper aims to provide a scientific decision and basis of disaster prevention and reduction for the line determination and safe construction and operation of road engineering in Sichuan-Tibet traffic corridor. By field survey and remote sensing interpretation on the landslides and avalanches along the proposed railway and highway of Sichuan-Tibet, we find out that the spatial distribution characteristics and potential hazard conditions of the hazards. Further, we systematically analyze and summarize the possible hazard ways of the hazards in the corridor in detail, combined with the existing research results of hazard characteristics and their hazard ways along the old Sichuan-Tibet roads. The research results show that there are totally 488 hazards in Kangding to Linzhi section of the corridor. They include 262 landslides and 226 collapses(including sand-sliding slope).148 hazards have potential hazards and threats on the proposed railway. They include 89 landslides and 59 collapses. The ways of the hazards on the road engineering are mainly summarized as follows.(1) Landslide and avalanches threaten tunnel and its import and export.(2) Landslide and avalanches advance, bury and destroy road engineering.(3) Landslide and avalanches threaten the safety of stations.(4) Landslide and avalanches block rivers and flooding road engineering.(5) Landslide and avalanches destroy road engineering by converting into hazard chains, such as debris flows and floods.(6) Avalanches and sand-sliding slopes impact, disturb and bury road engineering.
2017, 25(5): 1252-1263.
The loess is loose, and contains numerous large pores and vertical joints inside, which provides channels for the rapid infiltration of rainfall. The shallow loess landslides have caused significant casualties and economic losses. In order to effectively reduce the social and economic impact of landslides induced by rainfall, it is of great realistic significance to carry out the laboratory experimental study on rainfall-induced landslides. The purpose of this paper is to study the effects of different rainfall pattern and different slope structure on the deformation and failure process of loess slope. Three groups of indoor physical model experiments are designed and conducted. They include loess slope with continuous heavy rainfall, loess slope containing a vertical joint with continuous heavy rainfall, and loess slope with intermittent heavy rainfall. Three kinds of sensors including volume moisture sensors, matric suction sensors and pore water pressure sensors are buried to record the internal changes in each loess slope. Analyzing the changing readings of sensors and experimental phenomenon, and comparing the experimental procedures and results under the different experimental conditions disclose the deformation and failure law of shallow loess landslide under rainfall condition. The failure mode and triggering mechanism of this kind of landslides are summarized. The experimental results show that, in the early stage of the experiments, the matric suction of the loess decreased gradually and maintained stable in the end, therefore the strength reduced, with the continuous increases of volume moisture. In the later stage, the upper loess of the slope reached the saturation stage, excess pore water pressure generated by the slope deformation and poor drainage of the loess decreased the effective stress and the strength of the loess, and as a result, the strength reached the minimum, which resulted in landslides. And meanwhile, the influence of slope structure on slope stability is greater than that of rainfall pattern.
The loess is loose, and contains numerous large pores and vertical joints inside, which provides channels for the rapid infiltration of rainfall. The shallow loess landslides have caused significant casualties and economic losses. In order to effectively reduce the social and economic impact of landslides induced by rainfall, it is of great realistic significance to carry out the laboratory experimental study on rainfall-induced landslides. The purpose of this paper is to study the effects of different rainfall pattern and different slope structure on the deformation and failure process of loess slope. Three groups of indoor physical model experiments are designed and conducted. They include loess slope with continuous heavy rainfall, loess slope containing a vertical joint with continuous heavy rainfall, and loess slope with intermittent heavy rainfall. Three kinds of sensors including volume moisture sensors, matric suction sensors and pore water pressure sensors are buried to record the internal changes in each loess slope. Analyzing the changing readings of sensors and experimental phenomenon, and comparing the experimental procedures and results under the different experimental conditions disclose the deformation and failure law of shallow loess landslide under rainfall condition. The failure mode and triggering mechanism of this kind of landslides are summarized. The experimental results show that, in the early stage of the experiments, the matric suction of the loess decreased gradually and maintained stable in the end, therefore the strength reduced, with the continuous increases of volume moisture. In the later stage, the upper loess of the slope reached the saturation stage, excess pore water pressure generated by the slope deformation and poor drainage of the loess decreased the effective stress and the strength of the loess, and as a result, the strength reached the minimum, which resulted in landslides. And meanwhile, the influence of slope structure on slope stability is greater than that of rainfall pattern.
2017, 25(5): 1264-1269.
The exploitation of non-ferrous metal mines has caused serious heavy metal pollution to the surrounding soil. The effect of heavy metal Zn2+ on the strength and strength damage of Guilin red clay under leaching condition is studied using the self-made heavy metal leaching pollutant device. The indoor heavy metal Zn2+ contaminated soil is prepared with consolidation undrained triaxial shear test. The results show that the strength damage behavior of heavy metal Zn2+ to Guilin red clay is obvious. The shear strength is decreased by 30.61%~56.6%on average. The stress hardening relationship is strain hardening. The damage variable D is between 0.478~0.566. The damage of Zn2+ to Guilin red clay under leaching condition is mainly due to the irreversible erosion damage of the double clay layer and the double-layer structure of red clay. The strength of Zn2+ is decreased with the increase of Zn2+ concentration. The damage variable also increases, but the difference is small. This is because red clay has a certain adsorption effect on Zn2+ during prolonged leaching process, which leads to the similar effect of cumulative damage and high concentration of the soil, even under low concentration of contaminated solution leaching.
The exploitation of non-ferrous metal mines has caused serious heavy metal pollution to the surrounding soil. The effect of heavy metal Zn2+ on the strength and strength damage of Guilin red clay under leaching condition is studied using the self-made heavy metal leaching pollutant device. The indoor heavy metal Zn2+ contaminated soil is prepared with consolidation undrained triaxial shear test. The results show that the strength damage behavior of heavy metal Zn2+ to Guilin red clay is obvious. The shear strength is decreased by 30.61%~56.6%on average. The stress hardening relationship is strain hardening. The damage variable D is between 0.478~0.566. The damage of Zn2+ to Guilin red clay under leaching condition is mainly due to the irreversible erosion damage of the double clay layer and the double-layer structure of red clay. The strength of Zn2+ is decreased with the increase of Zn2+ concentration. The damage variable also increases, but the difference is small. This is because red clay has a certain adsorption effect on Zn2+ during prolonged leaching process, which leads to the similar effect of cumulative damage and high concentration of the soil, even under low concentration of contaminated solution leaching.
2017, 25(5): 1279-1286.
This paper examines the adaptability of the uniformity coefficient method for adjusting the seepage deformation type of cohesionless coarse-grained soil. Experimental verification and other methods combining with theory analysis are adapted to test the adaptability of this method. Statistical analysis is done on experimental results of seepage deformation of 313 samples in 43 projects. The results indicate that only the third rule is suitable in the three rules of B.C Istormingna uniformity coefficient. The first and second rules are not suitable and the result of the first one is even totally opposite to the actual experimental result. So we can draw a conclusion that B.C Istormingna uniformity coefficient method is not applicable in general to adjust the deformation type of cohesionless coarse-grained soil.
This paper examines the adaptability of the uniformity coefficient method for adjusting the seepage deformation type of cohesionless coarse-grained soil. Experimental verification and other methods combining with theory analysis are adapted to test the adaptability of this method. Statistical analysis is done on experimental results of seepage deformation of 313 samples in 43 projects. The results indicate that only the third rule is suitable in the three rules of B.C Istormingna uniformity coefficient. The first and second rules are not suitable and the result of the first one is even totally opposite to the actual experimental result. So we can draw a conclusion that B.C Istormingna uniformity coefficient method is not applicable in general to adjust the deformation type of cohesionless coarse-grained soil.
2017, 25(5): 1287-1292.
The particle breakage is satisfied with the fractal model and characteristized by the fractal dimension. The particle breakage of the bottom ash from municipal solid waste incineration(MSWI) is conducted, and the fractal dimension of particle breakage is analysized statistically. The evolution of the fractal dimension of particle breakage with the failure stress and breakage energy is studied based on the data collected in the literature. The value of the fractal dimension changes with the failure stress and breakage energy, and is gone by the name of the quasi fractal dimension. The quasi fractal dimension increases with the increases in the failure stress and breakage energy, and trends to a constant value 2.60 or so. This limit value of the fractal dimension is called as the intrinsic fractal dimension. Relation of the quasi fractal dimension to the failure stress and breakage energy is proposed based on the Weibull statistics.
The particle breakage is satisfied with the fractal model and characteristized by the fractal dimension. The particle breakage of the bottom ash from municipal solid waste incineration(MSWI) is conducted, and the fractal dimension of particle breakage is analysized statistically. The evolution of the fractal dimension of particle breakage with the failure stress and breakage energy is studied based on the data collected in the literature. The value of the fractal dimension changes with the failure stress and breakage energy, and is gone by the name of the quasi fractal dimension. The quasi fractal dimension increases with the increases in the failure stress and breakage energy, and trends to a constant value 2.60 or so. This limit value of the fractal dimension is called as the intrinsic fractal dimension. Relation of the quasi fractal dimension to the failure stress and breakage energy is proposed based on the Weibull statistics.
2017, 25(5): 1293-1298.
This paper explores the mechanism of Nano-CaCO3 on the mechanical properties of Guilin red clay. Triaxial shearing test under unconsolidated-undrained conditions is carried out using TSZ-1 type triaxial tester. The influence of the amount of Nano-CaCO3 on cohesive force, internal friction angle, shear strength and stress-strain curve of remolded red clay under different dry density conditions is analyzed. The mechanism of the influence of Nano-CaCO3 on the mechanical strength of red clay is explained from the point of view of collochemistry character of red clay mineral grain. The result of the experiment shows that with the increase of Nano-CaCO3 content, the cohesion, internal friction angle and shear strength of red clay show a tendency to decrease first and then increase. The incorporation of Nano-CaCO3 to change the original dielectric charge PH value changes the adsorption balance of the original iron oxide cementation to a new calcium cemented aggregate. It changes the strength characteristics of red clay. When the initial dry density is 1.4g·cm-3, the stress-strain curve of the remolded red clay sample changes from an elastic ideal plastic strain type to a strain hardening type after adding Nano-CaCO3.
This paper explores the mechanism of Nano-CaCO3 on the mechanical properties of Guilin red clay. Triaxial shearing test under unconsolidated-undrained conditions is carried out using TSZ-1 type triaxial tester. The influence of the amount of Nano-CaCO3 on cohesive force, internal friction angle, shear strength and stress-strain curve of remolded red clay under different dry density conditions is analyzed. The mechanism of the influence of Nano-CaCO3 on the mechanical strength of red clay is explained from the point of view of collochemistry character of red clay mineral grain. The result of the experiment shows that with the increase of Nano-CaCO3 content, the cohesion, internal friction angle and shear strength of red clay show a tendency to decrease first and then increase. The incorporation of Nano-CaCO3 to change the original dielectric charge PH value changes the adsorption balance of the original iron oxide cementation to a new calcium cemented aggregate. It changes the strength characteristics of red clay. When the initial dry density is 1.4g·cm-3, the stress-strain curve of the remolded red clay sample changes from an elastic ideal plastic strain type to a strain hardening type after adding Nano-CaCO3.
2017, 25(5): 1299-1306.
The particles in the saturated fine-grained soils are small. Their specific surface areas are large. The pore water and organics in the soil tends to form aggregates. This combination has important influence on the physical and mechanical properties of the soil. In this paper, the effect of multi-material structure of saturated fine-grained soil on its consolidation and evolutionary properties is discussed from the perspective of three-dimensional microstructure. The components in the soil samples are classified into four groups:pores, organics, multi-minerals and illite-dominated minerals. The structures were analyzed by synchrotron radiation μCT combined with the data constrained modelling in the consolidation process. The results show that illite-dominated minerals are hydrophilic and displaya coexistence of multiple phases in a voxel with pore, so that the water is difficult to be discharged under high pressure(1600kPa).Organics combined with illite minerals form organoclay agglomerated particles. It is not only adsorbed on the illite-dominated mineral surface, but also embedded in the mineral structure. The organics migrated in consolidation progress, which is illustrated by gradually increased volume of organics(in 40~400μm diameter).The strength of the soil between the soil particles weakened. This research utilizes qualitative and quantitative analysis to obtain evolutionary characteristics of minerals and organics. The approach presented would be applicable in studying the relationship between microstructure and macro-properties for special engineering soils.
The particles in the saturated fine-grained soils are small. Their specific surface areas are large. The pore water and organics in the soil tends to form aggregates. This combination has important influence on the physical and mechanical properties of the soil. In this paper, the effect of multi-material structure of saturated fine-grained soil on its consolidation and evolutionary properties is discussed from the perspective of three-dimensional microstructure. The components in the soil samples are classified into four groups:pores, organics, multi-minerals and illite-dominated minerals. The structures were analyzed by synchrotron radiation μCT combined with the data constrained modelling in the consolidation process. The results show that illite-dominated minerals are hydrophilic and displaya coexistence of multiple phases in a voxel with pore, so that the water is difficult to be discharged under high pressure(1600kPa).Organics combined with illite minerals form organoclay agglomerated particles. It is not only adsorbed on the illite-dominated mineral surface, but also embedded in the mineral structure. The organics migrated in consolidation progress, which is illustrated by gradually increased volume of organics(in 40~400μm diameter).The strength of the soil between the soil particles weakened. This research utilizes qualitative and quantitative analysis to obtain evolutionary characteristics of minerals and organics. The approach presented would be applicable in studying the relationship between microstructure and macro-properties for special engineering soils.
2017, 25(5): 1307-1313.
Relic soil sites are disappearing gradually due to the damage of their external environment and themselves' worse physical and mechanical properties. The collapsed and sapping at part of relic soil sites can be recovered by mixing then backfilling. The surface which was weathered away needs spray or hole grouting consolidation. In this article, we research into NaCl solute's migration, the collapse resistance ability, dry wet circulation resistance ability and freeze circulation resistance ability of relic soil sites with different dry density values. The relic soils are reinforced by penetrating the high polymer material SH in the perspective of mass loss. We discover that after penetrating SH, the ability of collapse resistance is improved greatly. The ability of dry-wet circulation resistance increases with the growth of dry density. The change of freeze circulation resistance ability is influenced by both water content and dry density. The lower dry density, the higher value of equilibrium moisture content. SH can inhibit water to migrate to the upper. At last, we explain the above experiment phenomenon reasonably.
Relic soil sites are disappearing gradually due to the damage of their external environment and themselves' worse physical and mechanical properties. The collapsed and sapping at part of relic soil sites can be recovered by mixing then backfilling. The surface which was weathered away needs spray or hole grouting consolidation. In this article, we research into NaCl solute's migration, the collapse resistance ability, dry wet circulation resistance ability and freeze circulation resistance ability of relic soil sites with different dry density values. The relic soils are reinforced by penetrating the high polymer material SH in the perspective of mass loss. We discover that after penetrating SH, the ability of collapse resistance is improved greatly. The ability of dry-wet circulation resistance increases with the growth of dry density. The change of freeze circulation resistance ability is influenced by both water content and dry density. The lower dry density, the higher value of equilibrium moisture content. SH can inhibit water to migrate to the upper. At last, we explain the above experiment phenomenon reasonably.
2017, 25(5): 1314-1321.
In the process of evaporation and drying, soil will cracks, which greatly change the nature of its engineering, triggering a variety of engineering geological disasters. In order to study the effect of interfacial roughness on soil cracking, two kinds of cracking tests are carried out, by applying Vaseline at the bottom of the container(S1) and posting sandpaper(S2) to change the interface roughness. During the experiment, the fissure development of the soil is recorded on a regular basis. The geometric characteristics of the fractures are quantitatively analyzed by digital image technology. The dynamic development process and related parameters of soil crack under different interface roughness are obtained. The results show the following aspects. (1) Soil evaporation process can be divided into three typical stages:constant rate stage, deceleration rate stage and residual stage. (2) Cracks are generally divided into three typical stages:the main fissure generation stage, the secondary fissure generation stage and the fracture growth stabilization phase. (3) The interface roughness has an important effect on the development of the fissure. For the relatively smooth interface of the base, the soil sample tends to shrink to the center as a whole, and the surface hardly produces cracks. For the rough interface, by the role of the base friction, soil surface developed criss-crossing the fissure network. The influence of interface roughness on the growth rate of fissure is different in different fissure development stages. The higher the interface roughness, the lower the surface fissure in the final stability.
In the process of evaporation and drying, soil will cracks, which greatly change the nature of its engineering, triggering a variety of engineering geological disasters. In order to study the effect of interfacial roughness on soil cracking, two kinds of cracking tests are carried out, by applying Vaseline at the bottom of the container(S1) and posting sandpaper(S2) to change the interface roughness. During the experiment, the fissure development of the soil is recorded on a regular basis. The geometric characteristics of the fractures are quantitatively analyzed by digital image technology. The dynamic development process and related parameters of soil crack under different interface roughness are obtained. The results show the following aspects. (1) Soil evaporation process can be divided into three typical stages:constant rate stage, deceleration rate stage and residual stage. (2) Cracks are generally divided into three typical stages:the main fissure generation stage, the secondary fissure generation stage and the fracture growth stabilization phase. (3) The interface roughness has an important effect on the development of the fissure. For the relatively smooth interface of the base, the soil sample tends to shrink to the center as a whole, and the surface hardly produces cracks. For the rough interface, by the role of the base friction, soil surface developed criss-crossing the fissure network. The influence of interface roughness on the growth rate of fissure is different in different fissure development stages. The higher the interface roughness, the lower the surface fissure in the final stability.
2017, 25(5): 1322-1327.
This paper aims to find the reason for preventing the crushing and water inrush accidents under deep buried soil-rock interface at coal mine in Eastern China. It analyses the geological environment of fractured rock mass with high water pressure under deep buried sand-sandstone interface. It uses the measured data including the height of water flowing fractured zone and simple hydrological observations data of drilling hole. It examines the development rules of the height of water flowing fractured zone during mining under deep buried soil-rock interface using principal component analysis. The results show that:ratio of the height of water flowing fractured zone and mining thickness and waterproof coal pillar fits Boxlucas1 exponential function model. The thickness of weathered zone inhibits the height of water flowing fractured zone to some extent. But for the sand-sandstone interface, as the presence of adown penetration zone, the inhibitory effect of weathered rock on the height of water flowing fractured zone increases.
This paper aims to find the reason for preventing the crushing and water inrush accidents under deep buried soil-rock interface at coal mine in Eastern China. It analyses the geological environment of fractured rock mass with high water pressure under deep buried sand-sandstone interface. It uses the measured data including the height of water flowing fractured zone and simple hydrological observations data of drilling hole. It examines the development rules of the height of water flowing fractured zone during mining under deep buried soil-rock interface using principal component analysis. The results show that:ratio of the height of water flowing fractured zone and mining thickness and waterproof coal pillar fits Boxlucas1 exponential function model. The thickness of weathered zone inhibits the height of water flowing fractured zone to some extent. But for the sand-sandstone interface, as the presence of adown penetration zone, the inhibitory effect of weathered rock on the height of water flowing fractured zone increases.
2017, 25(5): 1328-1335.
Many studies focus on the characteristics and mechanisms of the hydraulic fracturing because there are lots of factors influence the fracturing process and results. In this paper, effects of different initial hydraulic pressures on hydraulic fracturing are numerically investigated with a finite element method. It considers the heterogeneous of rocks through Weibull distribution of mechanical and strengthen parameters in a coupled seep-stress-failure model. The simulations reveal that when the initial hydraulic pressure is less than or equal to the tensile strength of the rock specimens and increases with a low growth rate, similar to the static loading method, hydraulic fractures can be initiated and propagated at a comfortable speed, which eventually forms two groups of umbrella-shaped fracture network. However, when the initial hydraulic pressure is greater than the breakdown pressure of the rock specimens, similar to the dynamic loading method, hydraulic fractures can initiated and propagated rapidly in all direction of the hole, which produces a radial fracture network. The processes and characteristics of hydraulic fractures reflect different water-rock interaction mechanisms under different loading modes. As for the reservoir fracturing improvement, the radial fracture network is the optimum result because it creates the maximum fracture surface area for migration and desorption of the shale gas.
Many studies focus on the characteristics and mechanisms of the hydraulic fracturing because there are lots of factors influence the fracturing process and results. In this paper, effects of different initial hydraulic pressures on hydraulic fracturing are numerically investigated with a finite element method. It considers the heterogeneous of rocks through Weibull distribution of mechanical and strengthen parameters in a coupled seep-stress-failure model. The simulations reveal that when the initial hydraulic pressure is less than or equal to the tensile strength of the rock specimens and increases with a low growth rate, similar to the static loading method, hydraulic fractures can be initiated and propagated at a comfortable speed, which eventually forms two groups of umbrella-shaped fracture network. However, when the initial hydraulic pressure is greater than the breakdown pressure of the rock specimens, similar to the dynamic loading method, hydraulic fractures can initiated and propagated rapidly in all direction of the hole, which produces a radial fracture network. The processes and characteristics of hydraulic fractures reflect different water-rock interaction mechanisms under different loading modes. As for the reservoir fracturing improvement, the radial fracture network is the optimum result because it creates the maximum fracture surface area for migration and desorption of the shale gas.
2017, 25(5): 1336-1343.
The compression coefficient and compression modulus are two important parameters of soil to evaluate the compressibility of soil. They are of great significance to the calculation of soil settlement. However, there are still some problems in the method of determining the compressibility index of soil in practice. Based on the definition of the compression coefficient and the compression modulus, this paper theoretically analyzed the relationship of the compression coefficient, compression modulus and the void ratio of soil. Two kinds of the calculation formula about these three parameters were also derived. Then these corresponding relations among the compression coefficient, compression modulus and the void ratio of soil were studied. This paper takes the weak swelling cohesive soil in Hefei area as the research object. The fast-consolidation tests of six sets of cohesive soil samples from Hefei with different saturation were carried out through multi-cycle loading and unloading. The problem of amending formula of deformation commonly used in the fast-consolidation test was pointed out and then the improved method was proposed. The correlation of the compression index, the number of loading and unloading and the degree of saturation were discussed. Then the exponential function was used to fit the relationship between the compression modulus and the degree of saturation. Using the probabilistic method, the fitting coefficients were obtained. The results show that the soil samples transmit from plastic state to elastic state with the increase in the time of loading and unloading cycle. With the increase of the degree of saturation, the compression modulus decrease gradually until come to stable.
The compression coefficient and compression modulus are two important parameters of soil to evaluate the compressibility of soil. They are of great significance to the calculation of soil settlement. However, there are still some problems in the method of determining the compressibility index of soil in practice. Based on the definition of the compression coefficient and the compression modulus, this paper theoretically analyzed the relationship of the compression coefficient, compression modulus and the void ratio of soil. Two kinds of the calculation formula about these three parameters were also derived. Then these corresponding relations among the compression coefficient, compression modulus and the void ratio of soil were studied. This paper takes the weak swelling cohesive soil in Hefei area as the research object. The fast-consolidation tests of six sets of cohesive soil samples from Hefei with different saturation were carried out through multi-cycle loading and unloading. The problem of amending formula of deformation commonly used in the fast-consolidation test was pointed out and then the improved method was proposed. The correlation of the compression index, the number of loading and unloading and the degree of saturation were discussed. Then the exponential function was used to fit the relationship between the compression modulus and the degree of saturation. Using the probabilistic method, the fitting coefficients were obtained. The results show that the soil samples transmit from plastic state to elastic state with the increase in the time of loading and unloading cycle. With the increase of the degree of saturation, the compression modulus decrease gradually until come to stable.
2017, 25(5): 1344-1350.
Laboratory simulation experiment is an important method for studying roadway deformation condition and mechanism. Based on the theory of solidification pressure, we built a vertical experimental model used by low strength material. This model, which initial strain energy equaled zero, simulated the solidification pressure. And this model made up for the deficiency of displacement field of horizontal solidification method. According to similarity theory, the material is desirable. In solidification process, this experimental model simulated physical and mechanical property in different depth. The simulated object was ore-body in 14-exploration line used two-sublevel mining under self-weight stress. Experiment results matched numerical simulation. Roadway deformation mechanism has been analyzed based on experiment results and numerical simulation.
Laboratory simulation experiment is an important method for studying roadway deformation condition and mechanism. Based on the theory of solidification pressure, we built a vertical experimental model used by low strength material. This model, which initial strain energy equaled zero, simulated the solidification pressure. And this model made up for the deficiency of displacement field of horizontal solidification method. According to similarity theory, the material is desirable. In solidification process, this experimental model simulated physical and mechanical property in different depth. The simulated object was ore-body in 14-exploration line used two-sublevel mining under self-weight stress. Experiment results matched numerical simulation. Roadway deformation mechanism has been analyzed based on experiment results and numerical simulation.
2017, 25(5): 1351-1356.
Qingdao has a water rich sand in the ground comprising soil and rock strata. This paper analyses the advanced deep hole grouting and curtain grouting reinforcement technique in the soft hard formation under tunnel construction. It uses field monitoring and excavation sampling analysis for their applicability in formation combining soil and rock strata. The results show that when the advanced deep hole grouting is used in water rich sand layer in the tunnel vault, the grouting effect is difficult to control, the vaults, the nearer the sand grouting effect is more difficult to master, the more serious the tunnel leakage. Construction is easy to bulge on the formation and the tunnel seepage more. When the sand layer in the vault above by curtain grouting, monitoring results show that hole deformation and surface subsidence can be controlled within the effective range. Grouting effect and workers' technology demand are higher. For rock combined with rich water sand, soil excavation can use the loose blasting technique, which makes reinforcement strata to form part of the leaking channels.
Qingdao has a water rich sand in the ground comprising soil and rock strata. This paper analyses the advanced deep hole grouting and curtain grouting reinforcement technique in the soft hard formation under tunnel construction. It uses field monitoring and excavation sampling analysis for their applicability in formation combining soil and rock strata. The results show that when the advanced deep hole grouting is used in water rich sand layer in the tunnel vault, the grouting effect is difficult to control, the vaults, the nearer the sand grouting effect is more difficult to master, the more serious the tunnel leakage. Construction is easy to bulge on the formation and the tunnel seepage more. When the sand layer in the vault above by curtain grouting, monitoring results show that hole deformation and surface subsidence can be controlled within the effective range. Grouting effect and workers' technology demand are higher. For rock combined with rich water sand, soil excavation can use the loose blasting technique, which makes reinforcement strata to form part of the leaking channels.
2017, 25(5): 1357-1363.
This paper investigates the influence of water content on shear strength of glaciofluvial deposits in Taoping area. Unconsolidated undrained triaxial shear tests were conducted on original samples with six different water content conditions. The unsaturated strength characteristics of this special soil are discussed by combining the soil water characteristic curve. Water content has a significant effect on the shear strength of the breccia soil in Taoping deposit. When the soil is saturated, its cohesion and internal friction angle are 40.0% and 29.5%lower than that in the case of natural water content. The increase of water content causes the matrix suction of glaciofluvial deposits to decrease rapidly, and the ability to suppress the plastic sliding of soil particles is greatly reduced. The fine cracks in the soil are continuously developed and expanded, resulting in the destruction of macro-microstructure and the attenuation of shear strength. Aiming at the shallow landslides which are widespread on the slope, it is necessary to carry out dynamic monitoring of rainfall in the accumulation area, to optimize the irrigation method and to strengthen the construction of the drainage system.
This paper investigates the influence of water content on shear strength of glaciofluvial deposits in Taoping area. Unconsolidated undrained triaxial shear tests were conducted on original samples with six different water content conditions. The unsaturated strength characteristics of this special soil are discussed by combining the soil water characteristic curve. Water content has a significant effect on the shear strength of the breccia soil in Taoping deposit. When the soil is saturated, its cohesion and internal friction angle are 40.0% and 29.5%lower than that in the case of natural water content. The increase of water content causes the matrix suction of glaciofluvial deposits to decrease rapidly, and the ability to suppress the plastic sliding of soil particles is greatly reduced. The fine cracks in the soil are continuously developed and expanded, resulting in the destruction of macro-microstructure and the attenuation of shear strength. Aiming at the shallow landslides which are widespread on the slope, it is necessary to carry out dynamic monitoring of rainfall in the accumulation area, to optimize the irrigation method and to strengthen the construction of the drainage system.
2017, 25(5): 1364-1373.
The wear of the cutter in the high abrasive dense sandy stratum seriously restricts the construction efficiency. This paper aims to accurately predict the wear and the digging distance of the scraper of the large diameter slurry shield TBM.It statistically analyses the dense composite sandy stratum by counting the area ratio and the volume ratio of each stratum in the typically tunnel cross section and district. The sandy stratum distance ranges from the DK0+0 to DK1+780 of Sutong GIL Utility Tunnel Engineering. The weighted average abrasion coefficient K' and its variation for each cross section and district in the composite sandy stratum can be obtained by combining the area ratio of each stratum, the volume fraction of each stratum and the abrasion coefficient K of each stratum. The calculated weighted average abrasion coefficient K' and the corresponding tool wear model are used to predict the tool wear and the digging distance of the large diameter slurry shield TBM in the dense composite sandy stratum. The results of tool wear and life prediction are compared with those in the actual construction process of large diameter slurry shield in Nanjing Yangtze River Tunnel under similar engineering geological conditions. The results show that the weighted average abrasion coefficient K' gradually increases with the increase of the mining mileage. The maximum value is at the milestone of 1778m and the maximum value is K'max=18.36×10-3mm·km-1. The maximum wear of the cutter locates at the installation diameter D=12.07m. If the upper limit wear value is set as δ=5mm, the cutter needs to be replaced twice, with the corresponding digging distance of L1=1063m and L2=453m. The comparison with the actual wear of the slurry shield TBM in Nanjing Yangtze River Tunnel shows that the prediction results are reliable. The results of the study provides theoretical basis for the wear prediction and cutter replacement of the slurry shield TBM in the Sutong GIL Utility Tunnel Engineering and similar cross-river tunnels.
The wear of the cutter in the high abrasive dense sandy stratum seriously restricts the construction efficiency. This paper aims to accurately predict the wear and the digging distance of the scraper of the large diameter slurry shield TBM.It statistically analyses the dense composite sandy stratum by counting the area ratio and the volume ratio of each stratum in the typically tunnel cross section and district. The sandy stratum distance ranges from the DK0+0 to DK1+780 of Sutong GIL Utility Tunnel Engineering. The weighted average abrasion coefficient K' and its variation for each cross section and district in the composite sandy stratum can be obtained by combining the area ratio of each stratum, the volume fraction of each stratum and the abrasion coefficient K of each stratum. The calculated weighted average abrasion coefficient K' and the corresponding tool wear model are used to predict the tool wear and the digging distance of the large diameter slurry shield TBM in the dense composite sandy stratum. The results of tool wear and life prediction are compared with those in the actual construction process of large diameter slurry shield in Nanjing Yangtze River Tunnel under similar engineering geological conditions. The results show that the weighted average abrasion coefficient K' gradually increases with the increase of the mining mileage. The maximum value is at the milestone of 1778m and the maximum value is K'max=18.36×10-3mm·km-1. The maximum wear of the cutter locates at the installation diameter D=12.07m. If the upper limit wear value is set as δ=5mm, the cutter needs to be replaced twice, with the corresponding digging distance of L1=1063m and L2=453m. The comparison with the actual wear of the slurry shield TBM in Nanjing Yangtze River Tunnel shows that the prediction results are reliable. The results of the study provides theoretical basis for the wear prediction and cutter replacement of the slurry shield TBM in the Sutong GIL Utility Tunnel Engineering and similar cross-river tunnels.
2017, 25(5): 1374-1380.
Mianyang Pingyang Fujun gateway has been named as national key cultural relics protection units. It was most seriously damaged ever during the Wenchuan Earthquake. The parts of the gateway were destroyed. The rocks were twisted, dislocated, broken and caved in. The stability of the gateway was significantly affected. We use the Midas GTS software to establish body 3D model, input seismic time-history curve of Wenchuan. Finally, we compare the calculate results with the damage observed at the site. It shows that the numerical simulation results are in agreement with the actual observations. So, the numerical simulation results can reflect the true destruction of the towers.
Mianyang Pingyang Fujun gateway has been named as national key cultural relics protection units. It was most seriously damaged ever during the Wenchuan Earthquake. The parts of the gateway were destroyed. The rocks were twisted, dislocated, broken and caved in. The stability of the gateway was significantly affected. We use the Midas GTS software to establish body 3D model, input seismic time-history curve of Wenchuan. Finally, we compare the calculate results with the damage observed at the site. It shows that the numerical simulation results are in agreement with the actual observations. So, the numerical simulation results can reflect the true destruction of the towers.
2017, 25(5): 1381-1388.
In the mountain valley area, epigenetic deformation of the shallow rock mass is common. Directional samples are taken at left bank of Jinping Ⅰ hydropower station dam. Thin sections are made. Direction distribution of micro fracture zones and micro cracks are analyzed by polarization microscope. Three conclusions are drawn. Firstly, micro fracture zone in thin section which is perpendicular to σ3 has no obvious directionality, but micro fracture zone in thin section which is perpendicular to σ2 or σ1 is parallel to bank surface. Secondly, micro cracks tend to occur along low index plane including cleavage plane, which accords with least energy principle. So intracrystalline cracks in calcite crystal show linear or step style. Thirdly, unloading stress induces and controls the direction of micro cracks, so micro cracks have obvious directionality.
In the mountain valley area, epigenetic deformation of the shallow rock mass is common. Directional samples are taken at left bank of Jinping Ⅰ hydropower station dam. Thin sections are made. Direction distribution of micro fracture zones and micro cracks are analyzed by polarization microscope. Three conclusions are drawn. Firstly, micro fracture zone in thin section which is perpendicular to σ3 has no obvious directionality, but micro fracture zone in thin section which is perpendicular to σ2 or σ1 is parallel to bank surface. Secondly, micro cracks tend to occur along low index plane including cleavage plane, which accords with least energy principle. So intracrystalline cracks in calcite crystal show linear or step style. Thirdly, unloading stress induces and controls the direction of micro cracks, so micro cracks have obvious directionality.
2017, 25(5): 1389-1394.
The 6th China Youth's Symposium on Engineering Geology(CYSEG)was successfully held at Chengdu University of Technology from 21th to 23th of July 2017. This is the second time for the 3rd Youth Committee of Engineering Geology in China to organize such a symposium with specific theme. There are 185 participants from domestic universities, research institutes and the industry. The theme of this symposium is "Formation mechanism and risk assessment of geohazards under complex conditions", which is the specialty of Engineering Geology discipline in Chengdu University of Technology. A total of 13 keynote speeches, 10 lectures and 3 roundtable discussions were presented. These presentations are both rich and insightful in content. This symposium is a grand event for young scholars in the field of engineering geology and related field to initiate academic discussion and in-depth exchange. It plays a positive role for promoting academic exchanges between young scholars, strengthening academic ties of geological engineering with geotechnical engineering and related disciplines, training communication and organization skills of young scholars and nurturing young talents.
The 6th China Youth's Symposium on Engineering Geology(CYSEG)was successfully held at Chengdu University of Technology from 21th to 23th of July 2017. This is the second time for the 3rd Youth Committee of Engineering Geology in China to organize such a symposium with specific theme. There are 185 participants from domestic universities, research institutes and the industry. The theme of this symposium is "Formation mechanism and risk assessment of geohazards under complex conditions", which is the specialty of Engineering Geology discipline in Chengdu University of Technology. A total of 13 keynote speeches, 10 lectures and 3 roundtable discussions were presented. These presentations are both rich and insightful in content. This symposium is a grand event for young scholars in the field of engineering geology and related field to initiate academic discussion and in-depth exchange. It plays a positive role for promoting academic exchanges between young scholars, strengthening academic ties of geological engineering with geotechnical engineering and related disciplines, training communication and organization skills of young scholars and nurturing young talents.
2017, 25(5): 1270-1278.
Revealing the fracture mechanism of tight sandstone has important guiding significance for the fracturing design of tight oil and gas reservoir and the reconstruction of fracture network. This paper carries out the conventional triaxial compression tests of tight sandstone at different confining pressures. The rock samples are obtained from the Chang-6 reservoir of Yanchang Formation of the Ordos Basin. The influence of confining pressure on the mechanical properties of rock is analyzed. The fracture process of sample is studied by acoustic emission localization technique. The characteristics of acoustic emission location events and the space-time evolution of acoustic emission signals under different confining pressures are analyzed. In addition, CT scan is performed on the sample after rupture. The internal fracture characteristics of samples are observed based on CT slice images. The conclusions include the following. (1) The space-time evolution of acoustic emission is mainly expressed in the compaction stage under different confining pressures. With the increase of confining pressure, main acoustic emission events are postponed. (2) The effect of confining pressure on accumulative count is mainly manifested in the compaction stage. The accumulative count shows a similar trend on the other stage. Under different confining pressures, the moment when accumulative count increases rapidly can be as a sign of rock fracture. (3) With the increase of confining pressure, the fractured phenomena tends to simple. The complex phenomena dominated by tensile fracture gradually change into a single shear fracture. (4) CT scanning section directly reflects the fracture configuration of the sample. The whole fracture configuration of the sample is consistent with the acoustic emission location. Based on the acoustic emission location, the crack distribution and the interaction process of the crack are further described. The fracture process of sample is studied with acoustic emission technique and CT scanning technique, which is significant for investigating rock mass failure and instability mechanism.
Revealing the fracture mechanism of tight sandstone has important guiding significance for the fracturing design of tight oil and gas reservoir and the reconstruction of fracture network. This paper carries out the conventional triaxial compression tests of tight sandstone at different confining pressures. The rock samples are obtained from the Chang-6 reservoir of Yanchang Formation of the Ordos Basin. The influence of confining pressure on the mechanical properties of rock is analyzed. The fracture process of sample is studied by acoustic emission localization technique. The characteristics of acoustic emission location events and the space-time evolution of acoustic emission signals under different confining pressures are analyzed. In addition, CT scan is performed on the sample after rupture. The internal fracture characteristics of samples are observed based on CT slice images. The conclusions include the following. (1) The space-time evolution of acoustic emission is mainly expressed in the compaction stage under different confining pressures. With the increase of confining pressure, main acoustic emission events are postponed. (2) The effect of confining pressure on accumulative count is mainly manifested in the compaction stage. The accumulative count shows a similar trend on the other stage. Under different confining pressures, the moment when accumulative count increases rapidly can be as a sign of rock fracture. (3) With the increase of confining pressure, the fractured phenomena tends to simple. The complex phenomena dominated by tensile fracture gradually change into a single shear fracture. (4) CT scanning section directly reflects the fracture configuration of the sample. The whole fracture configuration of the sample is consistent with the acoustic emission location. Based on the acoustic emission location, the crack distribution and the interaction process of the crack are further described. The fracture process of sample is studied with acoustic emission technique and CT scanning technique, which is significant for investigating rock mass failure and instability mechanism.
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