Discrete Element Numerical Simulation Study on the Stability of Subway Shield Tunnel Excavation Faces in Sandy Pebble Stratum
In order to study the collapse and instability modes of sandy pebble stratum,a three-dimensional numerical model of granular flow is established to analyze the stability of tunnel excavation faces.Firstly,the sandy pebble stratum is divided into four conditions ranging from loose to dense,and the parameters are calibrated accordingly.Then,the influence of burial depth ratio and internal friction angle on the failure modes of tunnel excavation faces and the limit support pressure is analyzed.Finally,the instability modes of tunnel excavation face in the sandy pebble stratum are studied,and the height of collapse arches in the sandy pebble stratum is modified based on the numerical simulation results.The research results indicate the following:(1)The larger the internal friction angle,the more significant the influence of burial depth ratio on the support pressure.Under different burial depth ratios,the limit support pressure decreases with an increase in the internal friction angle.Moreover,the larger the burial depth ratio,the more significant the influence of the internal friction angle on the support pressure.(2)As the internal friction angle increases,the failure zone gradually decreases.Under the same internal friction angle,a larger burial depth ratio results in a larger range of the failure zone.(3)When the burial depth ratio exceeds 1.0,most layers can form arches,and the shape of the failure zone is a combination of ellipsoids and rotated paraboloids.(4)In shallow burial depth conditions,collapse arches cannot form.The error between the modified formula and the simulation results is below 15%,indicating that the modified formula has a certain applicability.
subwaysandy pebble stratumexcavation surfacesupport pressurefailure zoneheight of collapse arch
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