Face passive failure can severely damage existing structures and underground utilities during shallow shield tunneling,especially in coastal backfill sand.In this work,a series of laboratory model tests were developed...Face passive failure can severely damage existing structures and underground utilities during shallow shield tunneling,especially in coastal backfill sand.In this work,a series of laboratory model tests were developed and conducted to investigate such failure,for tunnels located at burial depth ratios for which C/D=0.5,0.8,1,and 1.3.Support pressures,the evolution of failure processes,the failure modes,and the distribution of velocity fields were examined through model tests and numerical analyses.The support pressure in the tests first rose rapidly to the elastic limit and then gradually increased to the maximum value in all cases.The maximum support pressure decreased slightly in cases where C/D=0.8,1,and 1.3,but the rebound was insignificant where C/D=0.5.In addition,the configuration of the failure mode with C/D=0.5 showed a wedge-shaped arch,which was determined by the outcropping shear failure.The configuration of failure modes was composed of an arch and the inverted trapezoid when C/D=0.8,1,and 1.3,in which the mode was divided into lower and upper failure zones.展开更多
Stability of tunnel face is crucial,but previous studies often overlooked the effect of longitudinal tunnel inclination,leading to inaccurate stability assessments.In this study,nine groups of 1g model tests were cond...Stability of tunnel face is crucial,but previous studies often overlooked the effect of longitudinal tunnel inclination,leading to inaccurate stability assessments.In this study,nine groups of 1g model tests were conducted to study the influence of longitudinal tunnel inclination on passive limit support pressure and passive failure mode of soil in front of the tunnel face under shallow burial conditions(i.e.,cover depth ratio of 0.25,0.50 and 0.75)in a sand stratum.In addition,discrete element method(DEM)analyses at the same scale were established and calibrated against the model test results.Accordingly,the micromechanical information of soil was derived from a microscopic perspective.The results indicate that upon the passive instability of tunnel face,the soil in front of the tunnel face firstly moved approximately perpendicular to the tunnel face,and then it deflected.The instability area of soil in front of the tunnel face increased with the decrease of longitudinal inclination,when the tunnel cover depth was fixed.Furthermore,microscopic analyses indicate that the longitudinal inclination could significantly affect the soil contact orientation in front of the tunnel face.This was more likely to cause the failure zone to rotate.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.41972276)the Natural Science Foundation of Fujian Province(No.2020J06013)the“Foal Eagle Program”Youth Top-notch Talent Project of Fujian Province(No.00387088).
文摘Face passive failure can severely damage existing structures and underground utilities during shallow shield tunneling,especially in coastal backfill sand.In this work,a series of laboratory model tests were developed and conducted to investigate such failure,for tunnels located at burial depth ratios for which C/D=0.5,0.8,1,and 1.3.Support pressures,the evolution of failure processes,the failure modes,and the distribution of velocity fields were examined through model tests and numerical analyses.The support pressure in the tests first rose rapidly to the elastic limit and then gradually increased to the maximum value in all cases.The maximum support pressure decreased slightly in cases where C/D=0.8,1,and 1.3,but the rebound was insignificant where C/D=0.5.In addition,the configuration of the failure mode with C/D=0.5 showed a wedge-shaped arch,which was determined by the outcropping shear failure.The configuration of failure modes was composed of an arch and the inverted trapezoid when C/D=0.8,1,and 1.3,in which the mode was divided into lower and upper failure zones.
基金supported by the Xiaomi Young Talents Program,the Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2023A1515012159,2025A1515010029,and 2023A1515012334)the“GDAS”Project of Science and Technology Development(2022GDASZH-2022010105)the Doctoral Scientific Research Foundation of Liaoning Province(Grant No.2024010136-JH3/101).
文摘Stability of tunnel face is crucial,but previous studies often overlooked the effect of longitudinal tunnel inclination,leading to inaccurate stability assessments.In this study,nine groups of 1g model tests were conducted to study the influence of longitudinal tunnel inclination on passive limit support pressure and passive failure mode of soil in front of the tunnel face under shallow burial conditions(i.e.,cover depth ratio of 0.25,0.50 and 0.75)in a sand stratum.In addition,discrete element method(DEM)analyses at the same scale were established and calibrated against the model test results.Accordingly,the micromechanical information of soil was derived from a microscopic perspective.The results indicate that upon the passive instability of tunnel face,the soil in front of the tunnel face firstly moved approximately perpendicular to the tunnel face,and then it deflected.The instability area of soil in front of the tunnel face increased with the decrease of longitudinal inclination,when the tunnel cover depth was fixed.Furthermore,microscopic analyses indicate that the longitudinal inclination could significantly affect the soil contact orientation in front of the tunnel face.This was more likely to cause the failure zone to rotate.
