软土地区大覆土明挖隧道沉降变形规律研究

Settlement Deformation Regularity of Large Covering Soil Open Excavation Tunnel in Soft Soil Area

针对软土地基大覆土明挖隧道的工程特点,考虑深基坑开挖卸荷导致下卧土层压缩特性较大变化以及软弱地基加固对隧道沉降产生整体影响等诸多因素,采用二维有限元计算,对有无地基处理情况下,隧道修建和覆土回填对隧道沉降的影响规律进行分析,研究结果表明:基础桩的施加使得结构沉降减小了约90%。在软土地区,在原有软弱地基上修建隧道,若不进行地基处理,会引起较大沉降和不均匀沉降,造成结构受力偏大甚至产生裂缝危害结构安全。而在这种软弱地基中,因基础桩与底板相互接触,同时基础桩底部插入了中风化花岗岩层,故隧道所受力可通过基础桩直接传递到持力层,大大减小了软弱土层的压缩,从而保证结构安全。

For the engineering characteristics of large covering soil open excavation tunnel in soft soil foundation,and considering many factors such as a large change of solum compression features caused by unloading of deep foundation pit excavation,and the overall impact of soft foundation reinforcement on the tunnel settlement. By adopting the method of two-dimensional finite element calculation,we analyze the influence law of tunnel construction and overlying soil backfill on tunnel settlement with or without foundation treatment. The results show that the structure settlement is reduced by 90% with the increasing foundation pile. In soft soil area,the tunnel is built on the existing soft foundation,it will cause a larger and uneven settlement without foundation treatment,and then a bigger structure stress or even cracks endanger the safety of structure will be caused. In the soft foundation,the overlying load of tunnel can be directly transferred to the bearing layer on the basis of the mutual contact between foundation pile and bottom board as well as the bottom of foundation pile is inserted into moderately weathered granitic layer,which can greatly reduce the compression of soft soil layer,so as to ensure the safety of structure.