富水大断面黄土隧道开挖流固耦合效应分析

Analysis of Fluid-Solid Coupling Effect during Excavation of the Water-rich Large-section Loess Tunnel

兰州市轨道交通1号线东岗站后配线区间大断面隧道洞身黄土层含水率达到28.5%左右,饱和度达95%以上,施工中会诱发初期支护沉降变形过大、围岩长时间难于稳定等复杂问题。文章根据室内土工试验数据,建立三维有限元模型,基于流固耦合和不耦合效应,分析对比了富水大断面黄土隧道采用CRD法和双侧壁导坑法施工时的初期支护受力和变形特征、地表沉降及孔隙水压力场分布特征。结果表明:在该地层条件下,考虑流固耦合作用较不考虑流固耦合作用,地表沉降、初期支护竖向和水平位移无论是增长速率还是最终值都要大,后期无明显减小,且更接近现场实测值,但两者作用下的初期支护受力变化不大;基于流固耦合效应,采用CRD六部法在地表沉降和隧道变形控制效果方面更加有利,两种工法初期支护受力数值近似,但分布形式不同;流固耦合作用下,地下水水力梯度较大的地方主要位于隧道边墙和仰拱,施工时易发生渗漏,同时应做好拱部喷混凝土密实和回填注浆等,防止渗流场发生转移。

The water content of loess layer of the tunnel body with a large section in the rear distribution area of Donggang station of Lanzhou rail transit line 1 is about 28.5% and the saturation is over 95%, which induces large settlement of primary support and long time to get stable for the surrounding rock. Based on the data of laboratory geotechnical test, a three-dimensional finite element model was established, the mechanical and deformation characteristics of primary support, ground surface settlement and pore water pressure distribution during construction by CRD method and double side drift method were compared and analyzed based on fluid-solid coupling and uncoupling effects. The results show that the ground surface settlement, vertical and horizontal displacements and their increase rates of primary support considering the effect of fluid-solid coupling are larger than that without considering the effect of fluid-solid coupling, there is no significant decrease in the later period and they are closer to the measured values at site, while there is no big change of mechanical behavior;it is more favorable to adopt the construction method of CRD with six excavation sections to control ground surface settlement and tunnel deformation based on fluid-solid coupling effect and the force applied on primary support are approximate under the two construction methods but the distribution forms is different;under the effect of fluid-solid coupling, the places with large hydraulic gradient of groundwater are mainly located at tunnel sidewall and invert, which is prone to leakage during construction, and compaction of shotcrete at crown and backfill grouting should be carried out to prevent the seepage field from shifting.