Tunnel face ground loss(TFGL)emerging in shield tunnelling can trigger ground movement and impose threats to surrounding structures.However,the impact of cutterhead vibration on TFGL in sandy soils with varying degree...Tunnel face ground loss(TFGL)emerging in shield tunnelling can trigger ground movement and impose threats to surrounding structures.However,the impact of cutterhead vibration on TFGL in sandy soils with varying degrees of saturation has been largely unexplored.To fill this gap,an innovative numerical model based on computational fluid dynamics-discrete element method(CFD-DEM)and adhesive rolling resistance linear contact algorithm is established for the simulation of TFGL.Meanwhile,algorithms are proposed to account for the effects of cutterhead vibration and support pressure.Results from the validated model reveal that the TFGL can be exacerbated by seepage and opening enlargement,but mitigated by apparent cohesion.The cutterhead vibration can merely exacerbate the relatively small TFGL,which implies the unjamming effect of the particle at the opening.The balanced support pressure(BSP)required for TFGL prevention rises remarkably with the increases in opening ratio,vibration amplitude,and frequency.The maximum BSP in unsaturated sandy ground reaches up to 0.18γD,which is significantly less than that of 1.62γD observed in saturated sandy ground.The tangential and radial intervals with the largest TFGL are located within the ranges of 82.5°-97.5°,and 0.3D≤r_(loss)≤0.45D,respectively.The increase in support pressure can alter the time-dependent development of TFGL from linear to stepwise,leading to convergence.The support pressure required for convergence is increased by cutterhead vibration and seepage,but decreased by apparent cohesion.Lastly,the prospects of the numerical study on TFGL under cutterhead vibration are also discussed.展开更多
Due to space constraints in urban areas,metro tunnels are typically constructed in pairs,with a small clearance.The interaction between twin tunnels leads to a significantly more complex ground deformation and stress ...Due to space constraints in urban areas,metro tunnels are typically constructed in pairs,with a small clearance.The interaction between twin tunnels leads to a significantly more complex ground deformation and stress distribution than that observed in a single tunnel scenario,particularly if the tunnels are excavated in sequence.A series of physical model tests were conducted to investigate soil deformation and stress disturbances caused by the excavation of twin tunnels.The test results indicate that the interaction between the twin tunnels was observed.Due to the soil arching effect,the excavation of Tunnel 2 increases the soil stress acting on Tunnel 1.An analytical method was proposed to determine soil stress considering the soil arching effect and the interaction between twin tunnels.The method categorized the relative locations between twin tunnels into non-influenced,partially influenced,and fully influenced scenarios.For non-influenced and fully influenced scenarios,the soil stresses above twin tunnels were calculated based on a symmetric major principal stress trace.For the partially influenced scenario,however,the soil arch above Tunnel 2 was asymmetric due to the interaction,and the stress distribution was obtained based on a new asymmetric major principal stress trace.The soil stress on Tunnel 1 was influenced by the load transferred from Tunnel 2 and calculated based on the force equilibrium.A comparison of the analytical and test results indicates that the proposed method effectively predicts the soil stress in the cover layer above twin tunnels excavated sequentially,considering the interaction and soil arching effects.展开更多
基金the National Natural Science Foundation of China(Grant Nos.52178385 and 52020105002)the Natural Science Foundation of Guangdong Province,China(Grant No.2024B1515040017)for their financial support.
文摘Tunnel face ground loss(TFGL)emerging in shield tunnelling can trigger ground movement and impose threats to surrounding structures.However,the impact of cutterhead vibration on TFGL in sandy soils with varying degrees of saturation has been largely unexplored.To fill this gap,an innovative numerical model based on computational fluid dynamics-discrete element method(CFD-DEM)and adhesive rolling resistance linear contact algorithm is established for the simulation of TFGL.Meanwhile,algorithms are proposed to account for the effects of cutterhead vibration and support pressure.Results from the validated model reveal that the TFGL can be exacerbated by seepage and opening enlargement,but mitigated by apparent cohesion.The cutterhead vibration can merely exacerbate the relatively small TFGL,which implies the unjamming effect of the particle at the opening.The balanced support pressure(BSP)required for TFGL prevention rises remarkably with the increases in opening ratio,vibration amplitude,and frequency.The maximum BSP in unsaturated sandy ground reaches up to 0.18γD,which is significantly less than that of 1.62γD observed in saturated sandy ground.The tangential and radial intervals with the largest TFGL are located within the ranges of 82.5°-97.5°,and 0.3D≤r_(loss)≤0.45D,respectively.The increase in support pressure can alter the time-dependent development of TFGL from linear to stepwise,leading to convergence.The support pressure required for convergence is increased by cutterhead vibration and seepage,but decreased by apparent cohesion.Lastly,the prospects of the numerical study on TFGL under cutterhead vibration are also discussed.
基金supported by the National Natural Science Foundation of China(Grant No.52308463)the Shanghai Rising-Star Program(Grant No.23YF1449100)the Fundamental Research Funds for the Central Universities(Grant No.2023-2-ZD08).
文摘Due to space constraints in urban areas,metro tunnels are typically constructed in pairs,with a small clearance.The interaction between twin tunnels leads to a significantly more complex ground deformation and stress distribution than that observed in a single tunnel scenario,particularly if the tunnels are excavated in sequence.A series of physical model tests were conducted to investigate soil deformation and stress disturbances caused by the excavation of twin tunnels.The test results indicate that the interaction between the twin tunnels was observed.Due to the soil arching effect,the excavation of Tunnel 2 increases the soil stress acting on Tunnel 1.An analytical method was proposed to determine soil stress considering the soil arching effect and the interaction between twin tunnels.The method categorized the relative locations between twin tunnels into non-influenced,partially influenced,and fully influenced scenarios.For non-influenced and fully influenced scenarios,the soil stresses above twin tunnels were calculated based on a symmetric major principal stress trace.For the partially influenced scenario,however,the soil arch above Tunnel 2 was asymmetric due to the interaction,and the stress distribution was obtained based on a new asymmetric major principal stress trace.The soil stress on Tunnel 1 was influenced by the load transferred from Tunnel 2 and calculated based on the force equilibrium.A comparison of the analytical and test results indicates that the proposed method effectively predicts the soil stress in the cover layer above twin tunnels excavated sequentially,considering the interaction and soil arching effects.
