Research Of The Influences On The Underground Structure Due To Unloading

During excavation, unloading of soil will cause soil rebound within certain depth from excavation bottom, at the same time, soil rebound will affect underground structures and cause vertical upheaval deformation. Displacement of existent underground structures caused by above unloading mainly comprises two aspects: first, excavation bottom's stress field caused by unloading;second, the stiffness of underground structures. At the same time, due to the space and time effect of excavation on soil rebound, the unevenness of unloading will cause the displacement of underground structures continuously, and cause uneven curvature change along longitudinal direction. To obtain the rules of underground structures' displacement and displacement field in the excavation, this paper mainly carry out analysis of the following aspects:1. To adopt the equivalent axial stiffness continuous model, this paper carries out research on metro tunnel's longitudinal stiffness, and analyzes the effects of different parameters on equivalent longitudinal stiffness.2. From the perspective of mechanics, this paper analyzes: tunnels' additional stress due to unloading, the effects on tunnels' additional stress by different parameters;and tunnels' deformation as well as deformation characteristics under additional stress.3. Starting with the analysis of soil's displacement caused by unloading, this paper mainly analyzes effects on excavation rebound due to residual stress, unloading module, time effect, space effect and other factors, and obtains the quantitative relations between these factors and rebound;combining with unloading test, this paper analyzes the rheological properties of soft clay under unloading stress path condition, and ascertains a rational way to determine computational parameters;finally, this paper also validates the computational formula with field data from the Dongfang Road Underpass project.4. Based on the Dongfang Road Underpass project, this paper discusses construction technique of controlling unloading effects on underground structures, and with ANSYS program to stimulate construction condition and compare displacement of different conditions.