2015 Vol. 37 No. 10
2015, 37(10): 1745-1750.
DOI: 10.11779/CJGE201510001
Abstract：
The main problem for deep-water sheet-pile wharf is how to deal with the earth pressures acting on the front wall, which dramatically increase with the excavation depth. The design idea of the barrier-pile structure is as follows: a row of barrier piles are constructed in front of the traditional sheep-pile wharf, and part of the earth pressures acting on the front wall are shared owing to their barrio effects so as to reach the condition for building large deep-water sheet-pile wharf. Using the developed analysis software for soil-structure interaction based on ABAQUS, the NHRI double-yield face elastoplastic constitutive model is employed to simulate stress-strain relation of soils. The constitutive model based on contact mechanics is used to simulate soil-wharf interaction. The mechanism and effect of barrier piles are studied, the distribution rules of earth pressures at the two sides of the front wall of the sheet-pile wharf with barrier piles are discussed as well as its deformation and distribution of bending moment. By comparing with the sheet-pile wharf with single anchorage, the deep-water sheet-pile wharf with barrier piles is validated.
The main problem for deep-water sheet-pile wharf is how to deal with the earth pressures acting on the front wall, which dramatically increase with the excavation depth. The design idea of the barrier-pile structure is as follows: a row of barrier piles are constructed in front of the traditional sheep-pile wharf, and part of the earth pressures acting on the front wall are shared owing to their barrio effects so as to reach the condition for building large deep-water sheet-pile wharf. Using the developed analysis software for soil-structure interaction based on ABAQUS, the NHRI double-yield face elastoplastic constitutive model is employed to simulate stress-strain relation of soils. The constitutive model based on contact mechanics is used to simulate soil-wharf interaction. The mechanism and effect of barrier piles are studied, the distribution rules of earth pressures at the two sides of the front wall of the sheet-pile wharf with barrier piles are discussed as well as its deformation and distribution of bending moment. By comparing with the sheet-pile wharf with single anchorage, the deep-water sheet-pile wharf with barrier piles is validated.
Abstract：
The semi-analytic method is adopted to analyze the influence of ground vibration due to train moving on viaduct supported by group piles to explore ways of reducing ground vibration. The semi-analytic numerical models include train-rail model, viaduct model and group pile model. The train is simulated by a multiple-mass spring-damping model. The America power spectrum is used to model the rail irregularities. The rail is modeled by Eular beam and the wheel-rail contact Hertzian non-linear formula is used. The wheel-rail force is solved by modal analysis method. The railway viaduct is modeled by elastically supported beam, and the impedance of group piles is analyzed by transfer coefficient matrix and interaction factors. The bridge pier-ground interaction force is solved by dynamic equilibrium equations and the ground vibration on half space is solved by Green function. The influence of the parameters of group piles on ground vibration is discussed. The results show that the rail irregularities have a great influence on pier force. The ground vibration greater than 6 Hz is influenced by the rail irregularities while the vibration less than 6 Hz is little affected. The ground vibration can be mitigated by combined bridge span and train speed. When the train speed is less than 260 km/h, the influence of pile diameter on ground vibration is limited; while it is greater than 260 km/h, increasing pile diameter can reduce the ground vibration. Increasing the pile spacing has two advantages of keeping away from the vibration increasing area and reducing the ground vibration as the increase of train speed. The increasing area of ground vibration can be reduced by the rational design of pile length.
The semi-analytic method is adopted to analyze the influence of ground vibration due to train moving on viaduct supported by group piles to explore ways of reducing ground vibration. The semi-analytic numerical models include train-rail model, viaduct model and group pile model. The train is simulated by a multiple-mass spring-damping model. The America power spectrum is used to model the rail irregularities. The rail is modeled by Eular beam and the wheel-rail contact Hertzian non-linear formula is used. The wheel-rail force is solved by modal analysis method. The railway viaduct is modeled by elastically supported beam, and the impedance of group piles is analyzed by transfer coefficient matrix and interaction factors. The bridge pier-ground interaction force is solved by dynamic equilibrium equations and the ground vibration on half space is solved by Green function. The influence of the parameters of group piles on ground vibration is discussed. The results show that the rail irregularities have a great influence on pier force. The ground vibration greater than 6 Hz is influenced by the rail irregularities while the vibration less than 6 Hz is little affected. The ground vibration can be mitigated by combined bridge span and train speed. When the train speed is less than 260 km/h, the influence of pile diameter on ground vibration is limited; while it is greater than 260 km/h, increasing pile diameter can reduce the ground vibration. Increasing the pile spacing has two advantages of keeping away from the vibration increasing area and reducing the ground vibration as the increase of train speed. The increasing area of ground vibration can be reduced by the rational design of pile length.
Abstract：
A number of creep-induced rock bursts suggest that this type of rock burst belongs to hidden disasters featuring spontaneity and time delay. Lacking knowledge of its mechanism leads to challenging rock burst prevention and control, posing a severe threat to deep mining safety of extra-thick coal seam. Creep-induced rock burst is closely related to unstable creep. By establishing a creep model and a three-dimensional creep equation, it is found that high ground stress and extra-thick coal seam provide favorable conditions for its formation. The breaking process of roadway surrounding rock due to unstable creep is studied, and it is found that unstable creep activates rock burst and reduces resistance through strength corrosion and stress relief, thus inducing rock burst in weak areas of roadway by the impact of external static stress. An estimation formula for assessing possibility of creep-induced rock bursts is proposed. Based on the mechanism of creep-induced rock bursts, some specific measures of prevention and control are put forward: optimization of roadway layout, strengthening of active support, optimization of pressure relief parameters and long-term stress monitoring.
A number of creep-induced rock bursts suggest that this type of rock burst belongs to hidden disasters featuring spontaneity and time delay. Lacking knowledge of its mechanism leads to challenging rock burst prevention and control, posing a severe threat to deep mining safety of extra-thick coal seam. Creep-induced rock burst is closely related to unstable creep. By establishing a creep model and a three-dimensional creep equation, it is found that high ground stress and extra-thick coal seam provide favorable conditions for its formation. The breaking process of roadway surrounding rock due to unstable creep is studied, and it is found that unstable creep activates rock burst and reduces resistance through strength corrosion and stress relief, thus inducing rock burst in weak areas of roadway by the impact of external static stress. An estimation formula for assessing possibility of creep-induced rock bursts is proposed. Based on the mechanism of creep-induced rock bursts, some specific measures of prevention and control are put forward: optimization of roadway layout, strengthening of active support, optimization of pressure relief parameters and long-term stress monitoring.
Abstract：
According to the thick hard conditions of separated stratum space under overlying high-position magmatic rocks in working surface, the evolution rules and morphological characteristics of separated stratum space under the main key strata are studied by similar material simulation test. The horizon evolution and horizontal scaling law of separated stratum space and the migration law of overlying strata and the main key strata are analyzed. Through theoretical analysis, the formation mechanism and conditions of separated stratum space are revealed. A method to determine the evolution characteristics of separated strata space is put forward, and the analysis model and prediction method of the maximum separated stratum space at the bottom of main key strata are proposed. Researches show that the instability migration of combined strata forms a "crescent moon" shaped separated stratum space which intermittently jumps up to the bottom of the magmatic rocks. When the separated stratum space densely exists at the bottom of the magmatic rocks, and is gradually transformed from the " crescent " form into the “straight line " one, the burst migration of magmatic rocks contributes to the closure of separated strata. The separated stratum space lies at the bottom of the inferior key stratum and the main key stratum dynamically developes and closes from bottom to top. There is a positive correlation between the layer heights together with the development scope and the advancing distance. The “multi-trapezium” method can be used to determine its evolution process. The migration of overlying strata experiences five-state subsidence of the inferior key stratum, development migration to the bottom of main key stratum, migration of the magmatic rocks and the overall stability. The subsidence form of the overlying strata is successively presented as shapes of “V”, “√” and “U”. The migration of magmatic rocks can also be divided into five steps which are named lower support, extension of the bottom separated stratum space, rupture of the follow-up, instability migration and stable closing of separated stratum space. The overlying strata structure of the maximum separated stratum space and the elastic foundation beam model are established, and the forecast formula for its area and volume is derived so as to provide theoretical basis for the safety mining under high magmatic rocks.
According to the thick hard conditions of separated stratum space under overlying high-position magmatic rocks in working surface, the evolution rules and morphological characteristics of separated stratum space under the main key strata are studied by similar material simulation test. The horizon evolution and horizontal scaling law of separated stratum space and the migration law of overlying strata and the main key strata are analyzed. Through theoretical analysis, the formation mechanism and conditions of separated stratum space are revealed. A method to determine the evolution characteristics of separated strata space is put forward, and the analysis model and prediction method of the maximum separated stratum space at the bottom of main key strata are proposed. Researches show that the instability migration of combined strata forms a "crescent moon" shaped separated stratum space which intermittently jumps up to the bottom of the magmatic rocks. When the separated stratum space densely exists at the bottom of the magmatic rocks, and is gradually transformed from the " crescent " form into the “straight line " one, the burst migration of magmatic rocks contributes to the closure of separated strata. The separated stratum space lies at the bottom of the inferior key stratum and the main key stratum dynamically developes and closes from bottom to top. There is a positive correlation between the layer heights together with the development scope and the advancing distance. The “multi-trapezium” method can be used to determine its evolution process. The migration of overlying strata experiences five-state subsidence of the inferior key stratum, development migration to the bottom of main key stratum, migration of the magmatic rocks and the overall stability. The subsidence form of the overlying strata is successively presented as shapes of “V”, “√” and “U”. The migration of magmatic rocks can also be divided into five steps which are named lower support, extension of the bottom separated stratum space, rupture of the follow-up, instability migration and stable closing of separated stratum space. The overlying strata structure of the maximum separated stratum space and the elastic foundation beam model are established, and the forecast formula for its area and volume is derived so as to provide theoretical basis for the safety mining under high magmatic rocks.
Abstract：
The existing researches indicate that the mechanical properties of rockfill materials are significantly affected by the particle crushing. In order to reproduce the fundamental features of particle breakage, the changes of the particle size distribution (PSD) have to be described in mathematical form, i.e., to track the evolution of the PSD. This is difficult for the triaxial test processes due to the measurability limit of particle breakage. The single particle strength of the rockfill is measured and the crushing sample is sieved. The results show that the strengths of particles obey the Weibull statistics, and that the fractal distribution is found for PSD of crushed aggregates. Based on those findings, the changes of PSD can be described during the triaxial test process, the breakage of the triaxial tests is simulated, and the results reveal that the breakage process well agrees with the experimental data.
The existing researches indicate that the mechanical properties of rockfill materials are significantly affected by the particle crushing. In order to reproduce the fundamental features of particle breakage, the changes of the particle size distribution (PSD) have to be described in mathematical form, i.e., to track the evolution of the PSD. This is difficult for the triaxial test processes due to the measurability limit of particle breakage. The single particle strength of the rockfill is measured and the crushing sample is sieved. The results show that the strengths of particles obey the Weibull statistics, and that the fractal distribution is found for PSD of crushed aggregates. Based on those findings, the changes of PSD can be described during the triaxial test process, the breakage of the triaxial tests is simulated, and the results reveal that the breakage process well agrees with the experimental data.
Abstract：
The penetration processes of a typical silica powder in saturated porous media composed of quartz sands are studied by column seepage tests. The tests consider 6 kinds of particle sizes (i.e., 10, 15, 20, 25, 33, 47 μm), 3 particle concentrations (i.e., 0.2, 0.5, 0.8 mg/mL), 3 flow velocities (i.e., 0.087, 0.173, 0.260 cm/s), and different flow directions (i.e., downward, horizontal, upward), etc. According to the test results, the physical mechanisms of suspended particle migration such as hydrodynamics, dispersion and deposition are discussed. The studies show that for the same seepage velocity, the peak concentrations of penetration process decrease generally with the increase of particles size. On the other hand, the effect of hydrodynamic processes on particle transport is increased obviously with the increase of flow velocity while the effect of particle size is degenerated correspondingly. Besides, there exists a critical injected concentration, and beyond this value the relative concentration in the effluent begins to decrease, which is related to the logging of pores of porous media due to a large number of deposited particles.
The penetration processes of a typical silica powder in saturated porous media composed of quartz sands are studied by column seepage tests. The tests consider 6 kinds of particle sizes (i.e., 10, 15, 20, 25, 33, 47 μm), 3 particle concentrations (i.e., 0.2, 0.5, 0.8 mg/mL), 3 flow velocities (i.e., 0.087, 0.173, 0.260 cm/s), and different flow directions (i.e., downward, horizontal, upward), etc. According to the test results, the physical mechanisms of suspended particle migration such as hydrodynamics, dispersion and deposition are discussed. The studies show that for the same seepage velocity, the peak concentrations of penetration process decrease generally with the increase of particles size. On the other hand, the effect of hydrodynamic processes on particle transport is increased obviously with the increase of flow velocity while the effect of particle size is degenerated correspondingly. Besides, there exists a critical injected concentration, and beyond this value the relative concentration in the effluent begins to decrease, which is related to the logging of pores of porous media due to a large number of deposited particles.
Abstract：
Owing to the prestress loss particularity of the anchor cables in foundation pits, field tests are conducted. The distribution of shear stress on anchorage body is tested in the load tensioned process, and the prestress loss laws under different tensile loads and cyclic loads are analyzed. Through the numerical model of a project example, the prestress change laws of anchor cables in pit excavation process are considered, and the displacement and bending moment of supporting piles are compared between measures of a single tension and tension by steps. The results indicate that the debond slip in the front section of anchorage body is an important factor in prestress loss in tensioned locking process, and that the loss rate of prestress will be reduced under more cyclic tensile times and lower tensile force. For the supporting piles with multi-row anchor cables, the prestress of anchor cables in the upper row will be reduced by the tension of anchor cable in the lower row, and the anchor cable prestress shows a tendency of fluctuating increase throughout the excavation process. Through the control measures of tension by steps, the prestress loss of anchor cables is significantly reduced in the tensioned locking and excavation process, meanwhile, the force and deformation of supporting piles are more reasonable in excavation process. Such control measures can provide a reference for the construction of similar projects.
Owing to the prestress loss particularity of the anchor cables in foundation pits, field tests are conducted. The distribution of shear stress on anchorage body is tested in the load tensioned process, and the prestress loss laws under different tensile loads and cyclic loads are analyzed. Through the numerical model of a project example, the prestress change laws of anchor cables in pit excavation process are considered, and the displacement and bending moment of supporting piles are compared between measures of a single tension and tension by steps. The results indicate that the debond slip in the front section of anchorage body is an important factor in prestress loss in tensioned locking process, and that the loss rate of prestress will be reduced under more cyclic tensile times and lower tensile force. For the supporting piles with multi-row anchor cables, the prestress of anchor cables in the upper row will be reduced by the tension of anchor cable in the lower row, and the anchor cable prestress shows a tendency of fluctuating increase throughout the excavation process. Through the control measures of tension by steps, the prestress loss of anchor cables is significantly reduced in the tensioned locking and excavation process, meanwhile, the force and deformation of supporting piles are more reasonable in excavation process. Such control measures can provide a reference for the construction of similar projects.
Abstract：
To scientifically reveal the characteristics of the setting and long-term performance of PS-(C+F) slurry which is applied in the anchoring conservation of earthen sites, the slurry with the optimum mix ratio (0.39) is studied by means of aging strength, aging moisture, aging wave velocity and shrinkage tests, and its durability is investigated by using the temperature-humidity cycling, frozen-thaw cycling, water stabilizing, soundness and alkali resistivity tests. The test results indicate that the aging strength can firmly meet the requirements of the anchoring craft, and that the elastic-fragile mechanical performance of the slurry is compatible to the earthen sites on the appearance, density, void ratio and strength. Furthermore, the very low shrinkage guarantees the interfacial mechanical property. Besides them, the consolidation has a strong durability to resist the arid and semi-arid climate in Northwest China. However, the slurry is not suitable for the earthen sites with high-content sodium sulphate. In conclusion, with strong compatibility and durability, the PS-F slurry with mix ratio of (C∶F=1, PS∶( C+F) =0.39) can satisfy the need of the anchoring conservation of earthen sites in Northwest China.
To scientifically reveal the characteristics of the setting and long-term performance of PS-(C+F) slurry which is applied in the anchoring conservation of earthen sites, the slurry with the optimum mix ratio (0.39) is studied by means of aging strength, aging moisture, aging wave velocity and shrinkage tests, and its durability is investigated by using the temperature-humidity cycling, frozen-thaw cycling, water stabilizing, soundness and alkali resistivity tests. The test results indicate that the aging strength can firmly meet the requirements of the anchoring craft, and that the elastic-fragile mechanical performance of the slurry is compatible to the earthen sites on the appearance, density, void ratio and strength. Furthermore, the very low shrinkage guarantees the interfacial mechanical property. Besides them, the consolidation has a strong durability to resist the arid and semi-arid climate in Northwest China. However, the slurry is not suitable for the earthen sites with high-content sodium sulphate. In conclusion, with strong compatibility and durability, the PS-F slurry with mix ratio of (C∶F=1, PS∶( C+F) =0.39) can satisfy the need of the anchoring conservation of earthen sites in Northwest China.
Abstract：
The conventional borehole stability prediction methods are characterized by a large amount of calculation, complex operation and limited applicability, which can seriously affect real time application of the technology. Through intensive studies on the quantitative relationships between acoustic velocity, seismic data and borehole stability parameters, the direct seismic inversion model for pore pressure, in-situ stress and rock strength is established. Based on the nonlinear characteristics of the inversion model as well as the geological statistics features of borehole stability parameters, pore pressure, in-situ stress and rock strength of the formation to be drilled can be predicted by employing the stochastic inversion method so as to further forecast borehole stability. In actual drilling, the real-time geological logging data and layered statistical mode of borehole stability parameters can be used to predict borehole stability of the formation ahead of bit while drilling. The practical application of the proposed method in Yuanba Gas Field of Northeast Sichuan shows that the proposed method possesses strong ability of prediction while drilling and its comprehensive performance is significantly improved compared with the conventional methods.
The conventional borehole stability prediction methods are characterized by a large amount of calculation, complex operation and limited applicability, which can seriously affect real time application of the technology. Through intensive studies on the quantitative relationships between acoustic velocity, seismic data and borehole stability parameters, the direct seismic inversion model for pore pressure, in-situ stress and rock strength is established. Based on the nonlinear characteristics of the inversion model as well as the geological statistics features of borehole stability parameters, pore pressure, in-situ stress and rock strength of the formation to be drilled can be predicted by employing the stochastic inversion method so as to further forecast borehole stability. In actual drilling, the real-time geological logging data and layered statistical mode of borehole stability parameters can be used to predict borehole stability of the formation ahead of bit while drilling. The practical application of the proposed method in Yuanba Gas Field of Northeast Sichuan shows that the proposed method possesses strong ability of prediction while drilling and its comprehensive performance is significantly improved compared with the conventional methods.
Abstract：
Based on the reinforcement project of k70 embankment along Kunming-Bangkok Expressway, the bearing characteristics of prestressed sheet pile wall in embankment stabilization are studied through a series of in-situ tests. The history of pile displacement, earth pressure, bending moment and prestress of cables are measured and used to illustrate the bearing characteristics and behaviors of the structure. The measured results show that the prestressed sheet pile wall significantly increases the stability of the embankment, and that the structural displacement increases linearly with the height of embankment at the beginning of backfill and then slows down with the construction of cables. The pile flexure rather than pile rotation becomes increasingly prevalent with the increasing height of filling embankment. The distribution of earth pressures exerting against the pile is triangular and that on the face of plate is parabolic. The earth pressures against the pile are systematically larger than those of plate at the same depth, which results from arching effects. The maximum value of earth pressures of the pile is close to the thrust, while the maximum value of the plate is close to the active earth pressure. Analysis of the piles using the simple elastic analysis gives that the bending moments and displacements are close to the measured ones. The test results also indicate that the percentage of loss for cables is about 10% in the short term and 12%~15% in the long term.
Based on the reinforcement project of k70 embankment along Kunming-Bangkok Expressway, the bearing characteristics of prestressed sheet pile wall in embankment stabilization are studied through a series of in-situ tests. The history of pile displacement, earth pressure, bending moment and prestress of cables are measured and used to illustrate the bearing characteristics and behaviors of the structure. The measured results show that the prestressed sheet pile wall significantly increases the stability of the embankment, and that the structural displacement increases linearly with the height of embankment at the beginning of backfill and then slows down with the construction of cables. The pile flexure rather than pile rotation becomes increasingly prevalent with the increasing height of filling embankment. The distribution of earth pressures exerting against the pile is triangular and that on the face of plate is parabolic. The earth pressures against the pile are systematically larger than those of plate at the same depth, which results from arching effects. The maximum value of earth pressures of the pile is close to the thrust, while the maximum value of the plate is close to the active earth pressure. Analysis of the piles using the simple elastic analysis gives that the bending moments and displacements are close to the measured ones. The test results also indicate that the percentage of loss for cables is about 10% in the short term and 12%~15% in the long term.
Abstract：
Using the elastoplastic and damage constitutive methods for concrete respectively, a 3-D FEM model for segment joints of shield tunnel is established to simulate the process of bending failure under positive and negative loads. By comparing the simulated results with the experimental data, at the initial stage, the deformation curve is almost coincident with the FEM using the elastoplastic and damage constitutive methods, and both of them show a good agreement with the test results. With the increasing load, the results using the damage constitutive method are closer to the experimental values, and it can simulate the dropping process of structural bearing capacity better. Through the convergence analysis of FEM, the rationality of mesh generation is proved, and the grid sizes of similar element models are suggested. Finally, based on the simulated results, some evaluation indices for health assessment of segment joints are proposed.
Using the elastoplastic and damage constitutive methods for concrete respectively, a 3-D FEM model for segment joints of shield tunnel is established to simulate the process of bending failure under positive and negative loads. By comparing the simulated results with the experimental data, at the initial stage, the deformation curve is almost coincident with the FEM using the elastoplastic and damage constitutive methods, and both of them show a good agreement with the test results. With the increasing load, the results using the damage constitutive method are closer to the experimental values, and it can simulate the dropping process of structural bearing capacity better. Through the convergence analysis of FEM, the rationality of mesh generation is proved, and the grid sizes of similar element models are suggested. Finally, based on the simulated results, some evaluation indices for health assessment of segment joints are proposed.
Abstract：
Thaw and frozen heave are both the important factors for the stability of surrounding rock in cold region tunnels. A theoretical model is estublished to study the stress distribution when the surrounding rocks melt in seasonal cold region tunnels. The model is based on the condition that frost heave occurs firstly in the surrounding rocks, and the deflation in volume and the compression progress of thawing surrounding rocks under load when the frozen surrounding rocks melt are considered. When the frozen surrounding rocks melt and the volume reduces, the surrounding rocks outside the thawing range move to the tunnel, the thawing surrounding rocks are compressed and deformation occurs. After the balance is reached, other frozen surrounding rocks also enter the thawing range. They will also melt and the surrounding rocks outside them also move to the tunnel. The melting surrounding rocks are compressed again and the new balance is reached at last. The phenomenon is repeated, until the entire system is stable. In order to simplify the analysis, it is assumed that all progress is completed one time and the deflation in volume when the frozen surrounding rocks melt is approximately equal to the frost heave. The lining and thawing surrounding rocks are regarded as a composite retaining structure. Its deformation is regarded as the compression process of thawing surrounding rocks. The results of the example show that when the frozen surrounding rocks thaw, the maximum principal stress in lining will reduce and the stress in thawing range will also decrease distinctly. The stress in the surrounding rocks without thaw increases due to the change of geometrical sizes. In addition, the influence law of the linear strain of frost heave, geostress and thawing radius is analyzed. The proposed model can well reflect the actual situation in the field. It may provide a certain reference for the thawing study of surrounding rocks in cold region tunnels and well guide the design of cold region tunnels.
Thaw and frozen heave are both the important factors for the stability of surrounding rock in cold region tunnels. A theoretical model is estublished to study the stress distribution when the surrounding rocks melt in seasonal cold region tunnels. The model is based on the condition that frost heave occurs firstly in the surrounding rocks, and the deflation in volume and the compression progress of thawing surrounding rocks under load when the frozen surrounding rocks melt are considered. When the frozen surrounding rocks melt and the volume reduces, the surrounding rocks outside the thawing range move to the tunnel, the thawing surrounding rocks are compressed and deformation occurs. After the balance is reached, other frozen surrounding rocks also enter the thawing range. They will also melt and the surrounding rocks outside them also move to the tunnel. The melting surrounding rocks are compressed again and the new balance is reached at last. The phenomenon is repeated, until the entire system is stable. In order to simplify the analysis, it is assumed that all progress is completed one time and the deflation in volume when the frozen surrounding rocks melt is approximately equal to the frost heave. The lining and thawing surrounding rocks are regarded as a composite retaining structure. Its deformation is regarded as the compression process of thawing surrounding rocks. The results of the example show that when the frozen surrounding rocks thaw, the maximum principal stress in lining will reduce and the stress in thawing range will also decrease distinctly. The stress in the surrounding rocks without thaw increases due to the change of geometrical sizes. In addition, the influence law of the linear strain of frost heave, geostress and thawing radius is analyzed. The proposed model can well reflect the actual situation in the field. It may provide a certain reference for the thawing study of surrounding rocks in cold region tunnels and well guide the design of cold region tunnels.
Abstract：
A solution of face collapse failure under earthquakes is obtained in the realm of plasticity theory with the help of the calculus of variations. A simplicity face collapse failure model is introduced. Based on the Hoek-Brown failure criterion and the upper bound theorem, an exact function of face failure curves under earthquakes is presented. The extreme collapse curves derived by the Euler-Lagrange equation are solved in a nonlinear PDF. And then the exact extreme curves of face collapse failure are got when B=0.5. It is shown that the most remote distances (zmax ) are consistent with the numerical results, but the area of collapse zone is too large. Also, a sensitivity analysis to some direction angles () of the face detachment and several face pressures () is presented. The resulting expressions are so simple and rational to show the characteristics of face collapse failure, and can be used to make comparisons of the empirical and numerical analyses.
A solution of face collapse failure under earthquakes is obtained in the realm of plasticity theory with the help of the calculus of variations. A simplicity face collapse failure model is introduced. Based on the Hoek-Brown failure criterion and the upper bound theorem, an exact function of face failure curves under earthquakes is presented. The extreme collapse curves derived by the Euler-Lagrange equation are solved in a nonlinear PDF. And then the exact extreme curves of face collapse failure are got when B=0.5. It is shown that the most remote distances (zmax ) are consistent with the numerical results, but the area of collapse zone is too large. Also, a sensitivity analysis to some direction angles (
Abstract：
Soil-bentonite (SB) slurry walls are widely used in controlling migration of the contaminants in groundwater. Adding two types of phosphate to lead contaminated SB backfills may be advantageous to maintain the deflocculated structure of the bentonite in backfill, which is beneficial to enhance contaminant retarding ability of the backfill. A series of sedimentation and scanning electron microscope (SEM) tests are conducted to investigate changes in sedimentation behavior of SB backfills with various lead concentrations and phosphate contents/types, and the relevant mechanism is given. The results reveal that lead results in flocculation of the SB backfill and a 36% increase in the sediment volume. A certain amount of phosphate makes sedimentation curve of the contaminated backfill change from flocculation sedimentation type to accumulation sedimentation type, and the sediment volume of the backfill decreases significantly. Addition of phosphate enhances dispersity of the SB backfill due to steric stabilization of the phosphate and increased negative charge of the clay particle surfaces. The soil particles present a paralleled arrangement. Sodium hexametaphosphate has higher dispersibility compared with sodium pyrophosphate, because the backfills amended with sodium hexametaphosphate have smaller sediment volume. Optimum content of the phosphate is 0.1%, 0.5% and 2% while lead concentration in the backfill ranges in 0~0.1, 1~2, 6 mmol, respectively. The results obtained in this study may provide a meaningful guidance for improving dispersity of contaminated SB backfills.
Soil-bentonite (SB) slurry walls are widely used in controlling migration of the contaminants in groundwater. Adding two types of phosphate to lead contaminated SB backfills may be advantageous to maintain the deflocculated structure of the bentonite in backfill, which is beneficial to enhance contaminant retarding ability of the backfill. A series of sedimentation and scanning electron microscope (SEM) tests are conducted to investigate changes in sedimentation behavior of SB backfills with various lead concentrations and phosphate contents/types, and the relevant mechanism is given. The results reveal that lead results in flocculation of the SB backfill and a 36% increase in the sediment volume. A certain amount of phosphate makes sedimentation curve of the contaminated backfill change from flocculation sedimentation type to accumulation sedimentation type, and the sediment volume of the backfill decreases significantly. Addition of phosphate enhances dispersity of the SB backfill due to steric stabilization of the phosphate and increased negative charge of the clay particle surfaces. The soil particles present a paralleled arrangement. Sodium hexametaphosphate has higher dispersibility compared with sodium pyrophosphate, because the backfills amended with sodium hexametaphosphate have smaller sediment volume. Optimum content of the phosphate is 0.1%, 0.5% and 2% while lead concentration in the backfill ranges in 0~0.1, 1~2, 6 mmol, respectively. The results obtained in this study may provide a meaningful guidance for improving dispersity of contaminated SB backfills.
Abstract：
The numerical manifold method has been successful in solving continuous and discontinuous problems in a unified way, but the precondition is to generate the physical cover and contact loops correctly. For problem domains invariant during analysis, at first, the generation process of the physical cover and contact loops is expounded, where an algorithm for searching for loops, as the core of NMM pre-processing, is emphasized. Furthermore, a new algorithm much closer to the nature of NMM for the generation of physical cover and contact loops during the crack growth is proposed based on the concept of updating physical patch loops and contact loops. In theory, it is suitable for the cases of arbitrary crack growth length, and the crack tips are allowed to stop at any point of the manifold element, which has eliminated the mesh dependence to a great degree. Finally, the robustness and correctness of the proposed method is confirmed by an example of multiple crack growth.
The numerical manifold method has been successful in solving continuous and discontinuous problems in a unified way, but the precondition is to generate the physical cover and contact loops correctly. For problem domains invariant during analysis, at first, the generation process of the physical cover and contact loops is expounded, where an algorithm for searching for loops, as the core of NMM pre-processing, is emphasized. Furthermore, a new algorithm much closer to the nature of NMM for the generation of physical cover and contact loops during the crack growth is proposed based on the concept of updating physical patch loops and contact loops. In theory, it is suitable for the cases of arbitrary crack growth length, and the crack tips are allowed to stop at any point of the manifold element, which has eliminated the mesh dependence to a great degree. Finally, the robustness and correctness of the proposed method is confirmed by an example of multiple crack growth.
Abstract：
To illustrate the evaluation laws of thermal and mechanical properties of lignin-treated silt during curing period, a series of laboratory tests including standard proctor compaction test, thermal resistivity test, unconfined compressive strength test, modulus of resilience test, mercury intrusion porosimetry and scanning electron microscopy analysis are conducted to study the relationship among thermal resistivity, strength and stiffness and lignin content, moisture content and curing time of treated silt. Moreover, the changes of microstructure of lignin-treated silt are qualitatively or quantitatively evaluated to state the relationship between thermal and mechanical properties of treated silt. The test results show that the maximum dry density of treated silt is higher than that of natural silt, but the optimum moisture content is lower than that of natural silt. The sensitivity of the dry density to changes of moisture content increases. The thermal resistivity of treated silt increases nearly with the increase of lignin content and curing time, and after 60 days of curing all the treated soils, the thermal resistivity tends to be the same. It is closely related to the density of soils and the thermal properties of soil compositions. The strength of treated silt increases with the increase of lignin content and curing time and are 6.0 times higher than natural silt for 12% lignin treated after 28 days of curing. The variation of modulus of resilience for treated silt is similar to that of the unconfined compressive strength. The optimum content of lignin for treating silt is approximately 12%. The total pore volume and average pore diameter of silt are significantly reduced, and a more stable soil structure is formed by coating, connecting particles and filling pores after treatment of lignin.
To illustrate the evaluation laws of thermal and mechanical properties of lignin-treated silt during curing period, a series of laboratory tests including standard proctor compaction test, thermal resistivity test, unconfined compressive strength test, modulus of resilience test, mercury intrusion porosimetry and scanning electron microscopy analysis are conducted to study the relationship among thermal resistivity, strength and stiffness and lignin content, moisture content and curing time of treated silt. Moreover, the changes of microstructure of lignin-treated silt are qualitatively or quantitatively evaluated to state the relationship between thermal and mechanical properties of treated silt. The test results show that the maximum dry density of treated silt is higher than that of natural silt, but the optimum moisture content is lower than that of natural silt. The sensitivity of the dry density to changes of moisture content increases. The thermal resistivity of treated silt increases nearly with the increase of lignin content and curing time, and after 60 days of curing all the treated soils, the thermal resistivity tends to be the same. It is closely related to the density of soils and the thermal properties of soil compositions. The strength of treated silt increases with the increase of lignin content and curing time and are 6.0 times higher than natural silt for 12% lignin treated after 28 days of curing. The variation of modulus of resilience for treated silt is similar to that of the unconfined compressive strength. The optimum content of lignin for treating silt is approximately 12%. The total pore volume and average pore diameter of silt are significantly reduced, and a more stable soil structure is formed by coating, connecting particles and filling pores after treatment of lignin.
Abstract：
In order to study the long-term stability of engineering rock mass under cyclic loading, various uniaxial tests are conducted on yellow sandstone under different maximum stresses and stress amplitudes using the rock mechanics test system Rockman207. The laboratory investigation results show that the fatigue failure of yellow sandstone is controlled by the axial strain, lateral strain and volumetric strain of the complete stress-strain curve. There is an initial failure in the process of fatigue tests, and the initial failure occurs at peak strength or behind peak strength of the control curve. The difference of strain rate is the essential factor of 3 stages of the axial and lateral irreversible deformation development laws, and the fatigue failure process of yellow sandstone is the accumulating process of axial and lateral irreversible deformations. The fatigue life of yellow sandstone can be predicted by using the cycles-maximum stress curve (N-S curve) under certain conditions.
In order to study the long-term stability of engineering rock mass under cyclic loading, various uniaxial tests are conducted on yellow sandstone under different maximum stresses and stress amplitudes using the rock mechanics test system Rockman207. The laboratory investigation results show that the fatigue failure of yellow sandstone is controlled by the axial strain, lateral strain and volumetric strain of the complete stress-strain curve. There is an initial failure in the process of fatigue tests, and the initial failure occurs at peak strength or behind peak strength of the control curve. The difference of strain rate is the essential factor of 3 stages of the axial and lateral irreversible deformation development laws, and the fatigue failure process of yellow sandstone is the accumulating process of axial and lateral irreversible deformations. The fatigue life of yellow sandstone can be predicted by using the cycles-maximum stress curve (N-S curve) under certain conditions.
Abstract：
In order to investigate the evolution of porosity and permeability of sandstone during the cyclic loading and unloading, the cyclic loading and unloading tests on sandstone are carried out by using the test system of gas permeability measurement for compact rock. The test results show that the porosity and permeability of sandstone decrease with the increasing confining pressure. The permeability and porosity curve in the process of loading does not overlap that in the unloading process. In the process of loading, the relationship among porosity, permeability and confining pressure can be well described by an exponential function, and it can be well described by a power function in the process of unloading. The permeability changes faster under low confining pressure than that under high confining pressure. The permeability changes much more largely in the first cyclic loading, and from the second cyclic loading, due to the pre-compaction, the permeability changes with the decreasing confining pressure. But in the process of unloading, the permeability gradually increases with the decreasing confining pressure in the fifth cycles, and compared to that of the first cycle, the recovery of permeability is much smaller with the increase of cycles.
In order to investigate the evolution of porosity and permeability of sandstone during the cyclic loading and unloading, the cyclic loading and unloading tests on sandstone are carried out by using the test system of gas permeability measurement for compact rock. The test results show that the porosity and permeability of sandstone decrease with the increasing confining pressure. The permeability and porosity curve in the process of loading does not overlap that in the unloading process. In the process of loading, the relationship among porosity, permeability and confining pressure can be well described by an exponential function, and it can be well described by a power function in the process of unloading. The permeability changes faster under low confining pressure than that under high confining pressure. The permeability changes much more largely in the first cyclic loading, and from the second cyclic loading, due to the pre-compaction, the permeability changes with the decreasing confining pressure. But in the process of unloading, the permeability gradually increases with the decreasing confining pressure in the fifth cycles, and compared to that of the first cycle, the recovery of permeability is much smaller with the increase of cycles.
Abstract：
By reasonably simplifying the stress wave, a simplified model for the reciprocity between the plane p-wave and the circular anchoring roadway is built. Based on a typical case, through analyzing such remarkable parameters as radial stress of deep surrounding rock, tangential stress of roadway surface, radial displacement of roadway surface and radial displacement difference between deep surrounding rock and roadway surface, the strategic locations of support are confirmed, the force mechanism of bolt is deduced, and the corresponding failure patterns and failure criteria are put forward. The results show that the side facing the stress wave and the lateral position are the strategic locations of support. It is found that: (1) The total stress of bolt on the side facing the stress wave is the superposition of static axial stress, dynamic stress of bolt vibration and subsidiary stress caused by the surrounding rock deformation under dynamic load. Under the strong impact, a single instantly destroyed destruction will occur, the surrounding rock is pressed to fracture and the loose bolts lose the reinforcement. Under the cyclic weak impact, the pressed surrounding rock is gradually damaged to fracture, and that the bolt is loose owing to being pressed and straightened repeatedly intensifies the fracture of the surrounding rock further. When the strength of the load-bearing arch is decreased to a certain value, a weak impact can induce the burst failure of roadway; and (2) The total stress of the bolt at the lateral position is the composition of the static axial stress and the subsidiary stress caused by the surrounding rock deformation under the dynamic load. The bolt here is being subjected to tension, so tensile failure will occur under the strong impact. The results of similar simulation experiments are consistent with the theoretical ones, indicating that the theoretical analysis can be a significant guidance for engineering practice.
By reasonably simplifying the stress wave, a simplified model for the reciprocity between the plane p-wave and the circular anchoring roadway is built. Based on a typical case, through analyzing such remarkable parameters as radial stress of deep surrounding rock, tangential stress of roadway surface, radial displacement of roadway surface and radial displacement difference between deep surrounding rock and roadway surface, the strategic locations of support are confirmed, the force mechanism of bolt is deduced, and the corresponding failure patterns and failure criteria are put forward. The results show that the side facing the stress wave and the lateral position are the strategic locations of support. It is found that: (1) The total stress of bolt on the side facing the stress wave is the superposition of static axial stress, dynamic stress of bolt vibration and subsidiary stress caused by the surrounding rock deformation under dynamic load. Under the strong impact, a single instantly destroyed destruction will occur, the surrounding rock is pressed to fracture and the loose bolts lose the reinforcement. Under the cyclic weak impact, the pressed surrounding rock is gradually damaged to fracture, and that the bolt is loose owing to being pressed and straightened repeatedly intensifies the fracture of the surrounding rock further. When the strength of the load-bearing arch is decreased to a certain value, a weak impact can induce the burst failure of roadway; and (2) The total stress of the bolt at the lateral position is the composition of the static axial stress and the subsidiary stress caused by the surrounding rock deformation under the dynamic load. The bolt here is being subjected to tension, so tensile failure will occur under the strong impact. The results of similar simulation experiments are consistent with the theoretical ones, indicating that the theoretical analysis can be a significant guidance for engineering practice.
Abstract：
The filtration applications of nonwoven geotextiles are usually subjected to uniaxial tensile strain, resulting in the variation of pore sizes and failure of filtration engineering. The pore-size distributions of two needle-punched nonwoven geotextiles subjected to unconfined uniaxial tensile strains are measured by using the strain-controlled dry sieving tests. The experimental results of the dry sieving tests are compared with the predictions of two analytical solutions. One is the analytical solution of equivalent opening size O95 proposed by She Wei. The other is the analytical solution of pore-size distribution proposed by Rawal et al. The experimental values of O95 of two thermally bonded nonwoven geotextiles tested by previous studies are used to confirm the validity of the two analytical solutions. By comparing the predictions of O95, the accuracy and the error of two analytical solutions are analyzed. O95 decreases approximately linearly with unconfined uniaxial tensile strains. The prediction of the variation rate by She Wei is accurate, while that by Rawal et al. is larger than the experimental rate. The prediction of the value of O95 should be done considering the results of She Wei solution and Rawal solution.
The filtration applications of nonwoven geotextiles are usually subjected to uniaxial tensile strain, resulting in the variation of pore sizes and failure of filtration engineering. The pore-size distributions of two needle-punched nonwoven geotextiles subjected to unconfined uniaxial tensile strains are measured by using the strain-controlled dry sieving tests. The experimental results of the dry sieving tests are compared with the predictions of two analytical solutions. One is the analytical solution of equivalent opening size O95 proposed by She Wei. The other is the analytical solution of pore-size distribution proposed by Rawal et al. The experimental values of O95 of two thermally bonded nonwoven geotextiles tested by previous studies are used to confirm the validity of the two analytical solutions. By comparing the predictions of O95, the accuracy and the error of two analytical solutions are analyzed. O95 decreases approximately linearly with unconfined uniaxial tensile strains. The prediction of the variation rate by She Wei is accurate, while that by Rawal et al. is larger than the experimental rate. The prediction of the value of O95 should be done considering the results of She Wei solution and Rawal solution.
2015, 37(10): 1917-1923.
DOI: 10.11779/CJGE201510021
Abstract：
A multi-component gas migration model is presented for determining each component flux of landfill gas. The method to determine transport parameters in unsaturated soils is also given. A soil column test is conducted to simulate the progress of gas migration in landfill final cover. The test results are compared with the theoretical ones. It shows that the multi-component gas migration model can give the flux of each component more accurately. Change in the injected gas component fraction has a significant influence on the gas distribution in soils. Amount of apparent gas permeability depends on gas pressure. Bulk diffusion is the main factor to determine the distribution of each component in soils. Changing in effective diffusion coefficient may improve the methane oxidation capacity.
A multi-component gas migration model is presented for determining each component flux of landfill gas. The method to determine transport parameters in unsaturated soils is also given. A soil column test is conducted to simulate the progress of gas migration in landfill final cover. The test results are compared with the theoretical ones. It shows that the multi-component gas migration model can give the flux of each component more accurately. Change in the injected gas component fraction has a significant influence on the gas distribution in soils. Amount of apparent gas permeability depends on gas pressure. Bulk diffusion is the main factor to determine the distribution of each component in soils. Changing in effective diffusion coefficient may improve the methane oxidation capacity.
Abstract：
The single wheel load of vehicle is simplified as a uniform circular pressure acting on the road surface, then an integral solution method for calculating the induced stresses in subsoil due to a single moving wheel load is proposed based on the theoretical solution of Eason. An integral program for the proposed integral solution is coded so as to numerically evaluate the induced dynamic stresses. The cases of elastic half-space solid subjected to single wheel load with different acting radii and moving velocities are analyzed by the program. The calculated results reveal that the effect of acting radius and moving velocity on induced stresses depends on the depth of the soil element, and the distribution curves of induced dynamic stresses can be normalized to be one group of curves. The induced dynamic stresses due to a group of wheel load are evaluated using the superposition method. The effects of stress superposition and the moving velocity are more significant for deeper soil elements in subsoil, which results in complicated stress paths.
The single wheel load of vehicle is simplified as a uniform circular pressure acting on the road surface, then an integral solution method for calculating the induced stresses in subsoil due to a single moving wheel load is proposed based on the theoretical solution of Eason. An integral program for the proposed integral solution is coded so as to numerically evaluate the induced dynamic stresses. The cases of elastic half-space solid subjected to single wheel load with different acting radii and moving velocities are analyzed by the program. The calculated results reveal that the effect of acting radius and moving velocity on induced stresses depends on the depth of the soil element, and the distribution curves of induced dynamic stresses can be normalized to be one group of curves. The induced dynamic stresses due to a group of wheel load are evaluated using the superposition method. The effects of stress superposition and the moving velocity are more significant for deeper soil elements in subsoil, which results in complicated stress paths.
2015, 37(10): 1931-1936.
DOI: 10.11779/CJGE201510023
Abstract：
A new gradation equation which can be used to describe continuous gradation is put forward. Basic properties and reflection ability for different soils of the equation are studied, and general applicability of the equation is validated. The study shows that the equation can describe three typical soil gradation curves which are hyperbola, reversed S-shaped and approximate straight line shape, and has a wide applicability of clay, silt, sand and coarse-grained soil. The shape of gradation curve is determined by parameter b, namely hyperbola or reversed S-shaped, and when m is small, the curve is similar to a straight line. The slope of the curve is mainly determined by parameter m, and increases with the increase of m. The equation has more obvious advantages and broader applicability than Swamee's. Gradation curves of artificial blasting rockfill material from six earth-rock dams at home and abroad are studied, indicating that the range of parameters is roughly -0.28<b<0.64 and 0.45<m<0.75.
A new gradation equation which can be used to describe continuous gradation is put forward. Basic properties and reflection ability for different soils of the equation are studied, and general applicability of the equation is validated. The study shows that the equation can describe three typical soil gradation curves which are hyperbola, reversed S-shaped and approximate straight line shape, and has a wide applicability of clay, silt, sand and coarse-grained soil. The shape of gradation curve is determined by parameter b, namely hyperbola or reversed S-shaped, and when m is small, the curve is similar to a straight line. The slope of the curve is mainly determined by parameter m, and increases with the increase of m. The equation has more obvious advantages and broader applicability than Swamee's. Gradation curves of artificial blasting rockfill material from six earth-rock dams at home and abroad are studied, indicating that the range of parameters is roughly -0.28<b<0.64 and 0.45<m<0.75.
