Study on Stabilizing Mechanism of Deep Excavation in Soft Clay Groud

近年来，利用地下空间已成为一种公认的必要性，在城市地区广泛进行深挖。在这种情况下，阐明基坑的稳定机理是十分重要的。特别是在软粘土地基的情况下，其力学性能的某些方面仍有待研究。本报告的目的是为基坑横向支护系统的设计提供参考。主要研究了以下两个课题。(1)软粘土中作用于支撑墙的土压力和水压力。根据详细的现场实测结果，研究了软粘土中作用于背侧和开挖侧支撑墙的土压力和水压力的力学行为。由于墙体变形、地下水状态以及土体的变形和强度特性等因素对其力学性能的影响很大，因此本研究阐明了土体的力学性能与这些因素之间的关系。特别地，将开挖侧墙被动土压力分为两个因素，即与开挖侧墙位移有关的增量项和与开挖引起的覆盖层压力降低有关的递减项。(2)软粘土浆壕开挖稳定机理研究了软粘土浆壕开挖在正固结条件下的稳定机理。浆液沟法连续墙施工越来越多地应用于软粘土中。为了保证该方法的可靠性，弄清泥浆壕开挖的稳定机理至关重要。本研究认识到软粘土中沟壁的稳定机理有待研究。因此，通常固结的软粘土只产生轻微的沟槽位移，达到了泥浆和侧压力之间的平衡，从而允许使用连续墙采用泥浆沟槽法。少

In recent years, the utilization of underground spaces has become a recognized necessity and deep excavations have been carried out extensively in urban areas. In such cases, it is important to elucidate the stabilization mechanism of the excavation. Particularly in the case of ground consisting of a soft clay, some aspects of its mechanical behavior remain to be studied.The purpose of this report is to contribute the design of lateral supporting systems for excavation. The following two subjects were mainly studied.(1) Earth and water pressures acting on braced walls in soft clayThe mechanical behavior of earth and water pressures acting on the back-and excavation-side braced walls in soft clay was investigated based on the results of detailed field measurements. Because mechanical behavior strongly depends on such factors as wall deformation, the groundwater state, and the deformation and strength properties of the soil, this study clarifies the relationship between mechanical behavi … More or and these factors. In particular, passive earth pressure on the excavation-side wall is separated into the two factors as an incremental term related to wall displacement towards the excavation side and a decremental term related to decrease of overburden pressure due to excavation.(2) Stabilizing mechanism of slurry trench excavation in soft clayThe stabilizing mechanism of a slurry trench excavation in soft clay under normal consolidation was investigated. Diaphragm wall construction, using the slurry trench method, is increasingly being applied to soft clay. To ensure the reliability of this method, it is important to clarify the stabilizing mechanism of slurry trench excavation. In this research it was recognized that the mechanism of trench wall stability in soft clay was to be studied. Consequently, normally consolidated soft clay yeilds only a slight trench displacement which achieves a balance between slurry and lateral pressures, thus permitting use of the diaphragm wall employing the slurry trench method. Less