浅埋顶管沉井周边土体的三维破坏形状及沉降研究

Research on Three Dimensional Soil Failure Shapes and Settlements Around Shallow Buried Pipe Jacking Caisson

为研究顶管沉井及周边土体在顶进力作用下的形变范围与大小,以加固旋喷桩作为沉井周围加固体建立ABAQUS软件计算模型,并将模拟结果与工程实例、PLAXIS 3D软件所得结果进行对比分析。同时,采用广州地区花岗岩残积土进行室内沉井模型试验,并通过试验结果对数值模拟结论进行验证,得出结论如下:1)在开挖基坑前达到设计强度的旋喷桩能有效减小基坑周边土体塌陷变形、坑底隆起。2)在施加工作顶推力下,前侧主动区首先出现贯通裂缝,竖向位移斜率增大出现明显拐点;继续增大顶推力,土体位移会急剧增大导致地表沉降严重。3)对于后背土体,在顶推力作用下,地表破裂线的切线角度从0°逐渐增大至45°+φ/2,导致破裂范围也不断扩大;达到45°+φ/2处后,继续施加顶推力会导致短轴方向破坏范围扩大的速度较长轴方向的速度更快;三维空间中被动区破坏土体在地表处产生形状为椭圆的破坏面,椭圆长轴方向为顶推轴线方向,被动破坏体呈现为牛角状椭圆楔体。

In order to study the deformation of pipe-jacking caisson and its surrounding soil under jacking force,the ABAQUS software calculation model with reinforced jet grouting pile as caisson strengthening method is established,and the simulation result is analyzed and compared with practical project and the result of PLAXIS 3D software.Meanwhile,a caisson model test is carried out with the granite residual soil of Guangzhou to verify and complement the numerical simulation results.The conclusions are as follows:(1)Jet grouting pile with designed strength before excavation can effectively reduce soil collapse around the foundation pit and pit heave.(2)When the working jacking force is applied,the penetrating crack firstly appears in the front active zone,and the vertical displacement slope increases and an obvious inflection point appears;if the jacking force continues to increase,the soil displacement will increase sharply and the surface settlement will be serious.(3)For the soil at the back,under the jacking force,the tangent angle of the surface rupture line gradually increases from 0°to 45°+φ/2,resulting in the expansion of the fracture range;When the jacking force reaches 45°+φ/2,the extension of the failure range in the short axis direction is faster than that in the long axis direction;In the three-dimensional space,the failure surface of the failure soil in the passive zone is elliptic in shape at the surface;The direction of the long axis of the ellipse is the direction of the pushing axis,and the passive failure body shows an elliptic wedge in the shape of a bull horn.