季节性温度变化对某深大基坑工程的影响分析

Effects of seasonal temperature change on a large excavation project

通过对软土地区某停滞深大基坑16个月监测数据的整理分析,研究了季节性温度变化对环梁支撑受力、围护结构位移及基坑周边环境的影响规律。该基坑近似呈矩形,长178 m,宽148 m,采用多道钢筋混凝土圆环支撑结合中部对撑的布置形式。监测结果表明:环梁支撑轴力随着夏季到来持续增大,进入冬季后又逐渐减小,支撑内力变化受温度升降趋势影响显著;温度降低阶段,围护桩明显向坑内移动,且桩顶水平位移增量与温度变化近似呈线性关系,降温引起的多道水平支撑体系的围护结构变形增量呈倒三角变形模式;围护结构水平位移的增加,进一步加剧了坑外土体沉降,对基坑的整体变形以及基坑周边环境造成不利的影响。另外,三维有限元分析表明,围护结构刚度对支撑的温度应力影响很大,土质条件越硬,温度对支撑轴力的影响越大。

The effects of seasonal temperature change on loads of circle beam strut, displacements of retaining structure and variation of the surroundings are investigated based on 16 months＇ monitoring data of a stagnant braced excavation in soft clay area. The excavation, 148 m wide and 178 m long, is supported by soldier piles and lagging with circle beam reinforced concrete struts. The monitoring results indicate that the loads of the circle beam with the arrival of the summer continue to increase, and decrease gradually after the winter comes. The supporting load is consistent well with the change of the seasonal temperature. At the same time, the soldier piles show apparent movement to the pit and there is approximately a linear relationship between the horizontal displacement of pile top increment and the temperature change. The temperature decrease induces the inverted triangle deformation pattern in enclosure structure with multi-level support system. The increase of horizontal displacement of the retaining structure further aggravates the soil settlement outside the foundation pit, causing adverse effects on the whole deformation of the foundation pit and the surrounding environment. In addition, three-dimensional finite element（FE） analysis is performed. The results suggest that the stiffness of retaining structure plays an important role in strut stress. The harder the soil conditions, the greater the temperature effects on the axial force.