IMPORTANCE OF SOIL DILATANCY AND 3D EFFECTS IN BRACED EXCAVATION BPROBLEMS AND ITS APPLICATION TO STRESS-DEFORMATION ANALYSIS

在城市明挖工程中，如何预测地表沉降和计算支撑墙上的土压力是一个亟待解决的问题。然而，在目前的实用方法中，土压力的预测通常是采用传统的方法，如框架模型结合朗肯土压力理论。也没有合适的方法来预测地面沉降，通常使用经验法和/或弹性有限元法。除此之外，有限元分析通常假设平面应变条件等二维条件进行。传统的明挖施工方法没有考虑施工顺序对地表移动和土压力的影响，包括三维效应，本文旨在研究支撑开挖过程中地表移动和土压力的变化规律，为城市明挖施工提供合理、经济的方法。为此，我们进行了弹塑性有限元分析，其中适当考虑土，结构和土与结构之间的接触面的力学行为，并结合相应的模型试验。本文的主要研究内容包括：●研究支撑墙刚度和支撑刚度对支撑开挖引起的地表沉降和土压力的影响●研究开挖顺序（包括支撑的布置）对地表沉降和土压力的影响●验证一种新提出的无支撑开挖和临时挡土墙作为永久结构的一部分的开挖方法的有效性●表征隧道开挖对地表沉降和土压力的三维效应。

How to predict the surface settlements of the ground and how to evaluate the earth pressure on the braced wall are serious problems at open excavation in urban area. However, in the present practical methods, the earth pressure is usually predicted by conventional methods such as a frame model together with Rankine's earth pressure theory. There is also no appropriate method to predict the surface settlements of ground-usually empirical method and/or elastic finite element method are commonly used. In addition to this, finite element analysis is usually carried out assuming two-dimensional condition such as plane strain condition. The ground movements and earth pressure are much influenced by the construction sequence including three-dimensional effect, which are not considered in these conventional methods.This research has been carried out to investigate the ground movements and the earth pressures during braced excavation and devise proper and economic open excavation methods in urban area. For this purpose, we carried out elastoplastic finite element analyses in which the mechanical behavior of soils, structures and interface between soil and structure are properly taken into consideration, together with the corresponding model tests. Main contents of the present research can be summarized as follows :●Investigate the influence of the stiffness of wall and strut on surface settlements and earth pressure due to braced excavation●Investigate the influence of excavation sequence (including the arrangement of struts) on the surface settlements and earth pressure.●Verify the usefulness of a newly proposed exaction method, in which no strut is used in excavation and temporary retaining wall is used as a part of permanent structure.●Characterize three-dimensional effects of tunnel excavation on surface settlements and earth pressure.