武汉某地下室预应力锚杆施工遇微承压水结构抗浮解决方案

Anti-floating solution of micro-confined water during construction of pre-stressed anchor rod in a basement in Wuhan

武汉某高层住宅小区为2层地下室,高层主楼抗压采用钻孔灌注桩形式,2层地下室底板抗浮采用预应力锚杆形式。在锚杆1、2号成孔施工作业出现了微承压水涌出现象,经过测算,承压水头位于地下室底板面以上0.5m左右,承压水量中等。现场已采取抽水等紧急措施,经过监测虽然对基坑安全没有影响,但持续涌出的承压水不但让原设计采用的预应力锚杆抗浮方案难以实施,而且对已经开挖出来的地下室持力层有不利影响。各方对微承压水的产生原因进行了分析,并从技术可行性、造价、工期等角度详尽分析了基坑降水、锚杆钢护筒、泄水降压、回填土打小直径灌注桩4个地下室抗浮解决方案,最终决定采用先回填土再用长螺旋钻机打小直径灌注桩的抗浮方案。结合理论计算及现场试桩结果情况,该方案切实可行。对类似基坑施工中遇微承压水问题有很好的借鉴意义。

A high-rise residential district in Wuhan contains 2-storey basement,the foundation of the high-rise main building is in the form of bored piles,and the anti-floating of the 2-storey basement foundation is in the form of pre-stressed anchors.The phenomenon of micro-confined water gushing occurred in the drilling operation of No.1 and No.2 anchors.According to the calculation,the confined water head is located about 0.5 m above the basement floor surface,and the confined water quantity is moderate.On-site emergency measures such as pumping have been taken.Although the monitoring has no impact on the safety of the foundation pit,the continuous gushing of confined water not only makes it difficult to implement the anti-floating scheme of the pre-stressed anchor used in the original design,and has the disadvantageous influence to the basement bearing stratum which has already excavated.The causes of micro-confined water are analyzed,from the view of technical feasibility,cost and construction period,the anti-floating solutions of 4 basements,such as foundation pit dewatering,anchor steel tube,dewatering and pressure reducing,backfilling soil driving small diameter cast-in-place pile,are analyzed in detail.Finally,the anti-floating scheme of filling soil first and then driving small-diameter cast-in-place pile with long auger was adopted.According to the analysis of the field situation and the calculation results,the scheme is feasible.This paper can be used for reference to the problem of micro-confined water in foundation pit construction.