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

如何预测地表沉降和评价支撑墙的土压力是城市露天开挖中面临的重要问题。然而，在目前的实际方法中，土压力的预测通常采用框架模型和Rankine土压力理论等传统方法。目前还没有合适的方法来预测地表沉降，通常采用经验法和/或弹性有限元法。除此之外，通常在平面应变等二维条件下进行有限元分析。包括三维效应在内的施工顺序对地面运动和土压力的影响很大，而这些传统的方法没有考虑到这一点。本文通过对城市露天基坑支护过程中地表运动和土压力的研究，设计出合理、经济的露天开挖方法。为此，我们进行了弹塑性有限元分析，其中适当考虑了土、结构和土与结构之间的界面的力学行为，并进行了相应的模型试验。本研究的主要内容可概括为：●研究墙体和支杆刚度对支撑开挖地表沉降和土压力的影响●研究开挖顺序（包括支杆布置）对地表沉降和土压力的影响。●验证新提出的开挖方法的有效性，该方法在开挖中不使用支撑，将临时挡土墙作为永久结构的一部分。描述隧道开挖对地表沉降和土压力的三维影响。

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.