Effects of time-dependent deformation（TDD） on a tunnel constructed using the micro-tunneling technique in Queenston shale（QS） are investigated employing the finite element method. The TDD and strength parameters o...Effects of time-dependent deformation（TDD） on a tunnel constructed using the micro-tunneling technique in Queenston shale（QS） are investigated employing the finite element method. The TDD and strength parameters of the QS were measured from tests conducted on QS specimens soaked in water and lubricant fluids（LFs） used in micro-tunneling such as bentonite and polymer solutions. The numerical model was verified using the results of TDD tests performed on QS samples, field measurements of some documented projects, and the closed-form solutions to circular tunnels in swelling rock. The verified model was then employed to conduct a parametric study considering important micro-tunneling design parameters, such as depth and diameter of the tunnel, in situ stress ratio（K;）, and the time lapse prior to replacing LFs with permanent cement grout around the tunnel. It was revealed that the time lapse plays a vital role in controlling deformations and associated stresses developed in the tunnel lining.The critical case of a pipe or tunnel in which the maximum tensile stress develops at its springline occurs when it is constructed at shallow depths in the QS layer. The results of the parametric study were used to suggest recommendations for the construction of tunnels in QS employing micro-tunneling.展开更多
From an analysis of the relationships of grouting coefficients under the conditions of grouting reducing subsidence, it is concluded that the reducing subsidence rate is in direct proportion to the grouting-recovery r...From an analysis of the relationships of grouting coefficients under the conditions of grouting reducing subsidence, it is concluded that the reducing subsidence rate is in direct proportion to the grouting-recovery ratio, and its proportional coefficient depends on the coefficient of reducing subsidence and collapsing coefficient.The coefficient for reducing subsidence volume φ=ΔV/V_(ash) is related to overburden lithology.The coefficient for reducing subsidence volume φ is always larger than 1.This improves the reducing subsidence rate,the grouting-recovery ratio, and the coefficient for reducing subsidence volume, which can maximize the control of surface subsidence.展开更多
A new experiment was made on the developing of bed separations and mining subsidence from Tangshan T2192 working face by equivalent materials simulation.The overburden deformation and the developing of bed separations...A new experiment was made on the developing of bed separations and mining subsidence from Tangshan T2192 working face by equivalent materials simulation.The overburden deformation and the developing of bed separations with working face advanc- ing was simulated by a new model.The results show that the maximum value of bed separations moved forward gradually along with the working face advancing;the maxi- mum value of bed separations is 0.31～0.50 times of mining thickness.The key strata have a great influence upon surface subsidence during the overburden movement process.The mechanics parameters of new experiment are fitted with results in fields perfectly.展开更多
Focused upon the dynamic changing regularity and tendency of overburden movement and bed separation developing during the strip mining and stoping under rail- ways were simulated by ANSYS model.The results show that m...Focused upon the dynamic changing regularity and tendency of overburden movement and bed separation developing during the strip mining and stoping under rail- ways were simulated by ANSYS model.The results show that movement and rheology developing of key strata is one of the main reasons to cause surface subsidence and to further induce deformation of surface railways.It provids a basis for taking efficient meas- ures to control the deformation of surface railways.展开更多
In order to found an applicable equation of consolidation for gassy muddy clay, an effective stress formula of gas-charged nearly-saturated soils was introduced. And then, a consolidation equation was derived. Subsequ...In order to found an applicable equation of consolidation for gassy muddy clay, an effective stress formula of gas-charged nearly-saturated soils was introduced. And then, a consolidation equation was derived. Subsequently, supposing soils were under tangential loading, the expressions of pore water pressure were presented. The analytic solution of pore water pressure was attempted to be validated by the measured values in a real embankment. The parameters in the expressions of pore water pressure were gotten by the method of trial. The result shows that the consolidation model is rational and the analytic solution of pore water pressure is correct. The following conclusions can be made: 1) the influence of bubbles on the compressibility of pore fluid should be considered; 2) the effective stress would be influenced by bubbles, and the consolidation would depend on the compressibility of soil skeleton: the softer the soils are, the more distinct the influence of bubbles is; for normal clay, the influence of bubbles on the effective stress may be commonly neglected.展开更多
This study presents stability analyses of layered soil slopes in unsaturated conditions and uses a limit equilibrium method to determine the factor of safety involving suction stress of unsaturated soil.One-dimensiona...This study presents stability analyses of layered soil slopes in unsaturated conditions and uses a limit equilibrium method to determine the factor of safety involving suction stress of unsaturated soil.One-dimensional steady infiltration and evaporation conditions are considered in the stability analyses.An example of a two-layered slope in clay and silt is selected to verify the used method by comparing with the results of other methods.Parametric analyses are conducted to explore the influences of the matric suction on the stability of layered soil slopes.The obtained results show that larger suction stress provided in unsaturated clay dominates the stability of the layered slopes.Therefore,the location and thickness of the clay layer have significant influences on slope stability.As the water level decreases,the factor of safety reduces and then increases gradually in most cases.Infiltration/evaporation can obviously affect the stability of unsaturated layered slopes,but their influences depend on the soil property and thickness of the lower soil layer.展开更多
Current design methods for the internal stability of geosynthetic-reinforced soil(GRS)walls postulate seismic forces as inertial forces,leading to pseudo-static analyses based on active earth pressure theory,which yie...Current design methods for the internal stability of geosynthetic-reinforced soil(GRS)walls postulate seismic forces as inertial forces,leading to pseudo-static analyses based on active earth pressure theory,which yields unconservative reinforcement loads required for seismic stability.Most seismic analyses are limited to the determination of maximum reinforcement strength.This study aimed to calculate the distribution of the reinforcement load and connection strength required for each layer of the seismic GRS wall.Using the top-down procedure involves all of the possible failure surfaces for the seismic analyses of the GRS wall and then obtains the reinforcement load distribution for the limit state.The distributions are used to determine the required connection strength and to approximately assess the facing lateral deformation.For sufficient pullout resistance to be provided by each reinforcement,the maximum required tensile resistance is identical to the results based on the Mononobe-Okabe method.However,short reinforcement results in greater tensile resistances in the mid and lower layers as evinced by compound failure frequently occurring in GRS walls during an earthquake.Parametric studies involving backfill friction angle,reinforcement length,vertical seismic acceleration,and secondary reinforcement are conducted to investigate seismic impacts on the stability and lateral deformation of GRS walls.展开更多
基金Ward and Burke Microtunneling Ltd. for its excellent technical and financial support
文摘Effects of time-dependent deformation（TDD） on a tunnel constructed using the micro-tunneling technique in Queenston shale（QS） are investigated employing the finite element method. The TDD and strength parameters of the QS were measured from tests conducted on QS specimens soaked in water and lubricant fluids（LFs） used in micro-tunneling such as bentonite and polymer solutions. The numerical model was verified using the results of TDD tests performed on QS samples, field measurements of some documented projects, and the closed-form solutions to circular tunnels in swelling rock. The verified model was then employed to conduct a parametric study considering important micro-tunneling design parameters, such as depth and diameter of the tunnel, in situ stress ratio（K;）, and the time lapse prior to replacing LFs with permanent cement grout around the tunnel. It was revealed that the time lapse plays a vital role in controlling deformations and associated stresses developed in the tunnel lining.The critical case of a pipe or tunnel in which the maximum tensile stress develops at its springline occurs when it is constructed at shallow depths in the QS layer. The results of the parametric study were used to suggest recommendations for the construction of tunnels in QS employing micro-tunneling.
基金Supported by the National Natural Science Foundation of China (50174035, 50474029)
文摘From an analysis of the relationships of grouting coefficients under the conditions of grouting reducing subsidence, it is concluded that the reducing subsidence rate is in direct proportion to the grouting-recovery ratio, and its proportional coefficient depends on the coefficient of reducing subsidence and collapsing coefficient.The coefficient for reducing subsidence volume φ=ΔV/V_(ash) is related to overburden lithology.The coefficient for reducing subsidence volume φ is always larger than 1.This improves the reducing subsidence rate,the grouting-recovery ratio, and the coefficient for reducing subsidence volume, which can maximize the control of surface subsidence.
基金The National Natural Science Funds Committee(50174035)
文摘A new experiment was made on the developing of bed separations and mining subsidence from Tangshan T2192 working face by equivalent materials simulation.The overburden deformation and the developing of bed separations with working face advanc- ing was simulated by a new model.The results show that the maximum value of bed separations moved forward gradually along with the working face advancing;the maxi- mum value of bed separations is 0.31～0.50 times of mining thickness.The key strata have a great influence upon surface subsidence during the overburden movement process.The mechanics parameters of new experiment are fitted with results in fields perfectly.
基金the National Natural Science Funds Committee(50174035)
文摘Focused upon the dynamic changing regularity and tendency of overburden movement and bed separation developing during the strip mining and stoping under rail- ways were simulated by ANSYS model.The results show that movement and rheology developing of key strata is one of the main reasons to cause surface subsidence and to further induce deformation of surface railways.It provids a basis for taking efficient meas- ures to control the deformation of surface railways.
基金Projects(51278462,51378469)supported by the National Natural Science Foundation of ChinaProject(2011B81005)supported by Ningbo Science and Technology Innovation Team,ChinaProject(2013A610202)supported by Ningbo Natural Science Foundation of China
文摘In order to found an applicable equation of consolidation for gassy muddy clay, an effective stress formula of gas-charged nearly-saturated soils was introduced. And then, a consolidation equation was derived. Subsequently, supposing soils were under tangential loading, the expressions of pore water pressure were presented. The analytic solution of pore water pressure was attempted to be validated by the measured values in a real embankment. The parameters in the expressions of pore water pressure were gotten by the method of trial. The result shows that the consolidation model is rational and the analytic solution of pore water pressure is correct. The following conclusions can be made: 1) the influence of bubbles on the compressibility of pore fluid should be considered; 2) the effective stress would be influenced by bubbles, and the consolidation would depend on the compressibility of soil skeleton: the softer the soils are, the more distinct the influence of bubbles is; for normal clay, the influence of bubbles on the effective stress may be commonly neglected.
基金the National Natural Science Foundation of China(Grant Nos.52078185 and 51878248).
文摘This study presents stability analyses of layered soil slopes in unsaturated conditions and uses a limit equilibrium method to determine the factor of safety involving suction stress of unsaturated soil.One-dimensional steady infiltration and evaporation conditions are considered in the stability analyses.An example of a two-layered slope in clay and silt is selected to verify the used method by comparing with the results of other methods.Parametric analyses are conducted to explore the influences of the matric suction on the stability of layered soil slopes.The obtained results show that larger suction stress provided in unsaturated clay dominates the stability of the layered slopes.Therefore,the location and thickness of the clay layer have significant influences on slope stability.As the water level decreases,the factor of safety reduces and then increases gradually in most cases.Infiltration/evaporation can obviously affect the stability of unsaturated layered slopes,but their influences depend on the soil property and thickness of the lower soil layer.
基金This study was supported by the National Natural Science Foundation of China(Grant Nos.52078185,51878248,and 41630638).
文摘Current design methods for the internal stability of geosynthetic-reinforced soil(GRS)walls postulate seismic forces as inertial forces,leading to pseudo-static analyses based on active earth pressure theory,which yields unconservative reinforcement loads required for seismic stability.Most seismic analyses are limited to the determination of maximum reinforcement strength.This study aimed to calculate the distribution of the reinforcement load and connection strength required for each layer of the seismic GRS wall.Using the top-down procedure involves all of the possible failure surfaces for the seismic analyses of the GRS wall and then obtains the reinforcement load distribution for the limit state.The distributions are used to determine the required connection strength and to approximately assess the facing lateral deformation.For sufficient pullout resistance to be provided by each reinforcement,the maximum required tensile resistance is identical to the results based on the Mononobe-Okabe method.However,short reinforcement results in greater tensile resistances in the mid and lower layers as evinced by compound failure frequently occurring in GRS walls during an earthquake.Parametric studies involving backfill friction angle,reinforcement length,vertical seismic acceleration,and secondary reinforcement are conducted to investigate seismic impacts on the stability and lateral deformation of GRS walls.
