This study investigates the influence of the elastic modulus(E)of the composite strata on the trough width coefficient(i).It is hypothesized that,in composite strata,the relationship between the trough width coefficie...This study investigates the influence of the elastic modulus(E)of the composite strata on the trough width coefficient(i).It is hypothesized that,in composite strata,the relationship between the trough width coefficient(i)and the stratum thickness(H)follows a piecewise linear trend.Specifically,within strata of identical elastic modulus(E),i exhibits a linear correlation with H,while variations in E affect the slope of this correlation.Building upon the non-iterative analytical method(NIAM)for evaluating tunnel excavation responses in composite strata,this study proposes two novel approaches:the crucial point method(CPM)and the standard curve method(SCM).These methods incorporate the elastic modulus into the estimation of i.The values of i obtained via NIAM and refined through CPM and SCM are validated against field data using the parameter K.The results are consistent with existing research findings,thereby confirming the reliability of the proposed methodology.Furthermore,the study investigates the relationship between tunnel depth(h0)and tunnel radius(R),and explores the interactions among the layer number of stratum(n),elastic modulus(E),and layer thickness(H).A reduction coefficient(η)is introduced to improve the model's accuracy.The proposed approach is applied to nine tunnel engineering cases,and comparisons with measured data demonstrate its accuracy and practical applicability.展开更多
Due to the large differences in physico-mechanical pro perties of composite strata,jamming,head sinking and other serious consequences occur frequently during tunnel boring machine(TBM)excavation.To analyse the stabil...Due to the large differences in physico-mechanical pro perties of composite strata,jamming,head sinking and other serious consequences occur frequently during tunnel boring machine(TBM)excavation.To analyse the stability of surrounding rocks in composite strata under the disturbance of TBM excavation,a geomechanical model test was carried out based on the Lanzhou water supply project.The evolution patterns and distribution characteristics of the strain,stress,and tunnel deformation and fracturing were analysed.The results showed that during TBM excavation in the horizontal composite formations(with upper soft and lower hard layers and with upper hard and lower soft layers),a significant difference in response to the surrounding rocks can be observed.As the strength ratio of the surrounding rocks decreases,the ratio of the maximum strain of the hard rock mass to that of the relatively soft rock mass gradually decreases.The radial stress of the relatively soft rock mass is smaller than that of the hard rock mass in both types of composite strata,indicating that the weak rock mass in the composite formation results in the difference in the mechanical behaviours of the surrounding rocks.The displacement field of the surrounding rocks obtained by the digital speckle correlation method(DSCM)and the macro-fracture morphology after tunnel excavation visually reflected the deformation difference of the composite rock mass.Finally,some suggestions and measures were provided for TBM excavation in composite strata,such as advance geological forecasting and effective monitoring of weak rock masses.展开更多
The construction of coal mines often encounters deep composite soft rock roadways,which is characterized by significant deformation and poor stability.To deeply study the failure mechanism and large deformation challe...The construction of coal mines often encounters deep composite soft rock roadways,which is characterized by significant deformation and poor stability.To deeply study the failure mechanism and large deformation challenges of a composite strata roadway in deep and soft rock masses,a numerical model of 3DEC tetrahedral blocks was established based on the method of rock quality designation(RQD).The results showed that original support cannot prevent asymmetric failure and large deformation due to the adverse geological environment and unsuitable support design.According to the failure characteristics,a coupling support of“NPR bolt/cable+mesh+shotcrete+steel pipe”was proposed to control the stability of the surrounding rock.The excellent mechanical properties of large deformation(approximately 400 mm)and high constant resistance force(bolt with 180 k N;cable with 350 k N)were evaluated by the tensile tests.The numerical results showed that the maximum deformation was minimized to 243 mm,and the bearing capacity of the surrounding rock of the roadway was enhanced.The field test results showed that the maximum deformation of the surrounding rock was 210 mm,and the forces of the NPR bolt and cable were stable at approximately 180 k N and 350 k N,respectively.This demonstrated the effectiveness of the coupling support with the NPR bolt and cable,which could be a guiding significance for the safety control of large deformation and failure in deep composite soft rock roadways.展开更多
The excavated soil in the chamber of an earth pressure balance (EPB) shield is typically required to achieve a plastic flow state during tunneling to ensure a stable excavation face and the smooth discharge of soil. W...The excavated soil in the chamber of an earth pressure balance (EPB) shield is typically required to achieve a plastic flow state during tunneling to ensure a stable excavation face and the smooth discharge of soil. When EPB shield tunneling takes place in composite strata with gravelly sand above and moderately weathered argillaceous siltstone with high clay mineral content below, the changing sand–rock ratio on the excavation face leads to a greater risk of water spewing and clogging on the cutterhead, posing enormous challenges to soil conditioning. In the study reported here, we used foam and bentonite slurry as conditioning materials for mixed soil. A series of laboratory tests were performed on the conditioned soil with different sand–rock ratios and water contents to determine the optimal injection ratios of conditioning materials. A miniature EPB shield model test involving soil pressure balance, conditioning material injection, and tunneling control was conducted to simulate the continuous excavation process from full-face sand to full-face rock stratum. The model and field test results of thrust, torque, and soil pressure in the soil chamber and screw conveyor validate the effectiveness of the proposed soil conditioning schemes for composite strata with different sand–rock ratios. The test results indicate that the volume ratio 4:1 of foam to bentonite slurry achieves better performance of the conditioned gravelly sand at a lower total injection ratio (TIR < 10%). The bentonite slurry has a significant improvement effect on the flow plasticity of crushed moderately weathered argillaceous siltstone. The influence of bentonite slurry on the slump value of conditioned soil is greater than that of foam. Based on the optimal injection ratios of conditioning materials for full-face sand (ϕ = ∞) and full-face rock (ϕ = 0), the injection ratios for composite strata were obtained by weighted summation according to the area ratio of different strata on the tunnel face. This research provides valuable insights into soil conditioning and parameter determination methods for EPB shield tunneling in composite strata.展开更多
基金support from the National Natural Science Foundation of China(Grant No.52278387).
文摘This study investigates the influence of the elastic modulus(E)of the composite strata on the trough width coefficient(i).It is hypothesized that,in composite strata,the relationship between the trough width coefficient(i)and the stratum thickness(H)follows a piecewise linear trend.Specifically,within strata of identical elastic modulus(E),i exhibits a linear correlation with H,while variations in E affect the slope of this correlation.Building upon the non-iterative analytical method(NIAM)for evaluating tunnel excavation responses in composite strata,this study proposes two novel approaches:the crucial point method(CPM)and the standard curve method(SCM).These methods incorporate the elastic modulus into the estimation of i.The values of i obtained via NIAM and refined through CPM and SCM are validated against field data using the parameter K.The results are consistent with existing research findings,thereby confirming the reliability of the proposed methodology.Furthermore,the study investigates the relationship between tunnel depth(h0)and tunnel radius(R),and explores the interactions among the layer number of stratum(n),elastic modulus(E),and layer thickness(H).A reduction coefficient(η)is introduced to improve the model's accuracy.The proposed approach is applied to nine tunnel engineering cases,and comparisons with measured data demonstrate its accuracy and practical applicability.
基金supported by the National Natural Science Foundation of China(Grant No.41941018)the National Program on Key Basic Research of China(973 Program)(Grant No.2014CB046902)The partial support from the Hubei Province Natural Science Foundation Innovation Group(Grant No.2018CFA013)。
文摘Due to the large differences in physico-mechanical pro perties of composite strata,jamming,head sinking and other serious consequences occur frequently during tunnel boring machine(TBM)excavation.To analyse the stability of surrounding rocks in composite strata under the disturbance of TBM excavation,a geomechanical model test was carried out based on the Lanzhou water supply project.The evolution patterns and distribution characteristics of the strain,stress,and tunnel deformation and fracturing were analysed.The results showed that during TBM excavation in the horizontal composite formations(with upper soft and lower hard layers and with upper hard and lower soft layers),a significant difference in response to the surrounding rocks can be observed.As the strength ratio of the surrounding rocks decreases,the ratio of the maximum strain of the hard rock mass to that of the relatively soft rock mass gradually decreases.The radial stress of the relatively soft rock mass is smaller than that of the hard rock mass in both types of composite strata,indicating that the weak rock mass in the composite formation results in the difference in the mechanical behaviours of the surrounding rocks.The displacement field of the surrounding rocks obtained by the digital speckle correlation method(DSCM)and the macro-fracture morphology after tunnel excavation visually reflected the deformation difference of the composite rock mass.Finally,some suggestions and measures were provided for TBM excavation in composite strata,such as advance geological forecasting and effective monitoring of weak rock masses.
基金supported by the National Natural Science Foundation of China(Grant No.51874311,52174096)。
文摘The construction of coal mines often encounters deep composite soft rock roadways,which is characterized by significant deformation and poor stability.To deeply study the failure mechanism and large deformation challenges of a composite strata roadway in deep and soft rock masses,a numerical model of 3DEC tetrahedral blocks was established based on the method of rock quality designation(RQD).The results showed that original support cannot prevent asymmetric failure and large deformation due to the adverse geological environment and unsuitable support design.According to the failure characteristics,a coupling support of“NPR bolt/cable+mesh+shotcrete+steel pipe”was proposed to control the stability of the surrounding rock.The excellent mechanical properties of large deformation(approximately 400 mm)and high constant resistance force(bolt with 180 k N;cable with 350 k N)were evaluated by the tensile tests.The numerical results showed that the maximum deformation was minimized to 243 mm,and the bearing capacity of the surrounding rock of the roadway was enhanced.The field test results showed that the maximum deformation of the surrounding rock was 210 mm,and the forces of the NPR bolt and cable were stable at approximately 180 k N and 350 k N,respectively.This demonstrated the effectiveness of the coupling support with the NPR bolt and cable,which could be a guiding significance for the safety control of large deformation and failure in deep composite soft rock roadways.
基金supported by the National Natural Science Foundation of China(Grant No.52378414)the Natural Science Basis Research Plan in Shaanxi Province of China(No.2019JLP-23).
文摘The excavated soil in the chamber of an earth pressure balance (EPB) shield is typically required to achieve a plastic flow state during tunneling to ensure a stable excavation face and the smooth discharge of soil. When EPB shield tunneling takes place in composite strata with gravelly sand above and moderately weathered argillaceous siltstone with high clay mineral content below, the changing sand–rock ratio on the excavation face leads to a greater risk of water spewing and clogging on the cutterhead, posing enormous challenges to soil conditioning. In the study reported here, we used foam and bentonite slurry as conditioning materials for mixed soil. A series of laboratory tests were performed on the conditioned soil with different sand–rock ratios and water contents to determine the optimal injection ratios of conditioning materials. A miniature EPB shield model test involving soil pressure balance, conditioning material injection, and tunneling control was conducted to simulate the continuous excavation process from full-face sand to full-face rock stratum. The model and field test results of thrust, torque, and soil pressure in the soil chamber and screw conveyor validate the effectiveness of the proposed soil conditioning schemes for composite strata with different sand–rock ratios. The test results indicate that the volume ratio 4:1 of foam to bentonite slurry achieves better performance of the conditioned gravelly sand at a lower total injection ratio (TIR < 10%). The bentonite slurry has a significant improvement effect on the flow plasticity of crushed moderately weathered argillaceous siltstone. The influence of bentonite slurry on the slump value of conditioned soil is greater than that of foam. Based on the optimal injection ratios of conditioning materials for full-face sand (ϕ = ∞) and full-face rock (ϕ = 0), the injection ratios for composite strata were obtained by weighted summation according to the area ratio of different strata on the tunnel face. This research provides valuable insights into soil conditioning and parameter determination methods for EPB shield tunneling in composite strata.
