黄河冲积平原地区超大型深基坑开挖现场监测分析

Monitoring analysis of super large and deep foundation pit in alluvial plain of Yellow River

介绍了黄河冲积平原地区某开挖范围为271 m×192 m,开挖深度为18.7~19.5 m,采用土钉、预应力锚索加钻孔灌注桩作为支护结构的超大型深基坑开挖现场监测实例,研究了超大型深基坑开挖过程中围护结构变形、地表沉降、锚索轴力的变化规律。研究表明:围护桩水平位移随开挖深度的增加而增大,围护桩最大水平位移随开挖深度的增加逐渐向深部发展。基坑外纵向地表沉降大致呈马鞍形分布,地表沉降最大值位于基坑中部附近,基坑角部沉降约为基坑中部沉降的33.9%,纵向沉降影响范围大于基坑开挖范围。基坑分层开挖过程中锚索轴力随开挖深度的变化而动态调整,下层锚索施工完成后,上层锚索的锚固力先减小后缓慢增长并最终趋于稳定。锚索钻孔和高压注浆施工过程中对周围已有锚索的扰动影响不容忽视。

A foundation pit with excavation zone of 271 m×192 m and excavation depth of 18.7 m^19.5 m is monitored during excavation. The foundation pit is located in the alluvial plain of the Yellow River and supported by soil nailings, bored piles and prestressed anchor cables. Based on the monitoring results, the variation of deformation of retaining structures, ground settlement and anchor cable force are analyzed. It can be concluded that the horizontal displacement and the location of the maximum horizontal displacement of retaining piles increase with the increasing excavation depth. The longitudinal ground settlement has a saddle-shaped distribution. The maximum ground settlement appears in the middle zone of excavation, and the value of pit corner settlement is about 33.9% times that of the middle zone settlement in the longitudinal direction of pit. The longitudinal surface settlement trench is wider than the pit. Moreover, the value of the anchor cable force dynamically varies with the excavation depth. The value of the upper anchor first decreases, then slowly increases, and tends to be stable after the lower anchor is completed. The influences of the anchoring effect caused by drilling bore hole of anchor and high pressure grouting can not be ignored.