坭洲水道桥圆形地连墙支护体系监测与分析

对虎门二桥坭洲水道桥直径90 m、深29 m东锚碇工程进行了监测,实测得到开挖过程中地连墙墙后土压力、墙体径向位移、竖向弯矩等。同时,设计并实施了地连墙槽段接缝的单元体试验,探讨了圆形地连墙环向刚度折减系数的取值方法,并结合轴对称弹性地基梁法对监测数据进行了对比分析。计算与实测分析结果表明,圆形地连墙支护体系墙体最大位移值为开挖深度的0.018%,远小于工程预警值,说明其可有效控制基坑变形;施工过程中土体开挖及内衬施工对地连墙应力影响最大,是相应深度地连墙应力达到峰值的主要原因,其影响范围为上下两倍当层开挖深度;圆形地连墙墙后土体具有空间效应,实测土压力值小于主动土压力理论计算值;由计算对比可知,考虑环向效应及环向刚度折减的弹性地基梁法可较好地反映圆形地连墙支护体系的受力变形特性。

Monitoring and Analysis on the Retaining System of Circular Diaphragm Wall for Nizhou Waterway Bridge

The monitoring outcome of Nizhou Waterway Bridge anchorage excavation, 90 m in diameter and 29 m in depth, in the Humen 2^nd bridge project was presented herein, including earth pressure developed behind the wall, radial deflection, vertical moment and so on. In addition, a series of experiment on joints between diaphragm wall panels was implemented to study the reduction coefficient of circumferential stiffness of panels. The coefficient was applied in an axisymmetric BEF method in order to compare its result to the measurement. It is indicated by the comparison that the maximum measured displacement of the wall is 0.018% of the excavation depth, which is less than the criteria. It proves that the circular diaphragm wall is an efficient retaining structure to reduce excavation displacement; each layer of soil excavation and liner construction are the main factors influencing the wall stresses, and the influenced range is approximately two times of the depth of current excavated layer; the earth pressure behind the wall is smaller than theoretical active earth pressure, indicating that the soil did not reach the active limit state; the BEF method, taking into account the hoop effect and the circumferential stiffness reduction, can reasonably capture stresses and displacements in circular diaphragm walls.