衬砌-砂卵石地层随动塌落伞拱力学模式研究

Study on the Mechanical Model of Arch Collapse Umbrella Sand Gravel Layer Lining

针对北京地铁既有线穿越松散砂卵石、大颗粒粗砂、粉土互层交替、软硬不均复合地层区间段的典型工程特点,开展浅埋衬砌1~3倍洞径覆土的开挖破坏模型试验,建立衬砌-土相互作用的随动塌落伞拱结构力学模型,观测衬砌周边随动滑移区的压力拱特征,分析砂卵石复合地层地铁衬砌土压分布的分区.模型可较好描述滑裂区附近的局部成拱效应及分区土压折减特征,涵括衬砌-土相互作用的地层拟成拱、渐进塌沉、瞬间塌穿等破坏过程.FLAC3D模拟结果与模型破坏试验的结果吻合.通过对比天坛东门站拱顶土压的实际监测值,对该力学模式进行了初步验证,可为类似工程的过程土压荷载取值提供参考.

In response to typical engineering characteristics of existing Beijing subway traversing the loose sand and gravel,large particles of coarse sand,silt interbed,and complex uneven hardness sections,an excavation failure model experiment was carried out for shallow buried tunnel lining with tunnel overburden layer of 1-3 times of the tunnel diameter.The mechanical model of the dynamic collapse umbrella arch structure with the interaction of lining-soil structure was established,to observe the dynamic slip zone pressure arch characteris-tics surrounding the lining,and to analyze the pressure distribution partition of the sand gravel composite for-mation for metro lining earth.This model can define the local soil arching effect and area reduction characteris-tics in the vicinity of the sliding area,including the interaction of lining-soil structure formation of quasi arch, progressive collapse sink,failure experiment instant collapse wear failure process.The results of FLAC3D sim-ulation and model failure experiment were coincident.Through the actually monitored results of soil pressure value of the arch crown of the Tiantandongmen subway station,the mechanical model was preliminarily veri-fied,which can provide reference for the load values of process soil pressure of similar proj ects.