基坑底部土体裙边加固模型试验与数值模拟研究

为研究基坑底部土体裙边加固对基坑变形和内力的影响,分别对未进行坑底加固和采用坑底裙边加固2种工况进行模型试验。在填土过程中预先浇筑加固土体,实现坑底土体加固。在基坑开挖过程中对地表沉降、冠梁侧向位移、桩身弯矩以及桩后土压力进行监测。用有限元软件Abaqus对模型试验进行拓展,将基坑变形的计算结果进行极差分析。研究表明,对坑底土体采用裙边加固,可以有效地减小支护结构的侧向位移;坑顶地表沉降虽有减小,但效果不明显;桩身弯矩略小于未进行坑底加固的工况;土体开挖,桩随着坑底下某一点发生转动,造成桩上半部分土压力减小,桩底处土压力增大;裙边加固尺寸中深度相较于宽度对基坑的变形影响更大;土体加固深度与宽度超过一定范围,控制基坑变形的效果有所提高但不明显,加固深度宜取0.3～0.4倍的开挖深度,宽度宜取0.35～0.45倍的开挖深度。

A model test and numerical study of skirt border reinforcement in the bottom of the excauation

In order to study the effect of skirt soil reinforcement on the deformation and stress of foundation pit, model tests were carried out for cases without bottom reinforcement and skirt reinforcement respectively. To realize the reinforcement of bottom soil, the method of reinforcing soil by pre-pouring in the process of filling was adopted. The ground subsidence,the lateral displacement of top beam,the bending moment of piles and the earth pressure are measured during excavation. Extensive FE parametric studies indicate that the skirt reinforcement can effectively reduce the lateral displacement of the supporting structure. Although surrounding settlements decreased, the effect is less obvious. The bending moment of the pile is slightly less than that of the pile without reinforcement. With the excavation, the earth pressure in the upper part of the pile decreases and pressure at the bottom increases as the pile rotates at a certain point under the pit. The depth of skirt reinforcement has greater influence on the deformation of foundation pit than the width of reinforcement. When the depth and width of soil reinforcement exceed a certain range, the effect of controlling the deformation of foundation pit is marginaly improved. The reinforcement depth should be 0.3~`0.4 times of the excavation depth and the width should be 0.35~0.45 times of the excavation depth.