济南某临山筏板基坑粉细砂层等施工难点控制

Deep Excavation Techniques in Silty Fine Sand Soil for a Raft Foundation at Hillside in Jinan City

某基坑为筏板基础大开挖,位于济南市药山西北侧山边,具有基坑规模大、支护分项多、水位降深大、工期紧等特征。支护和降水施工中遇到并解决了粉细砂层、厚层杂填土、部分支护桩底遇硬质岩、筏板基础施工与疏干井降水冲突等多个难题。提出了基坑底地层“凹槽滞水机理”理论,总结了桩间高压旋喷桩截水帷幕容易渗漏的原因,并给出了处理建议。施工时善用降水管井钻孔的勘察数据,锚索施工优选采用跟管工艺,支护排桩灵活使用旋挖与长螺旋钻孔桩工艺,彻底解决了降水和筏板施工的冲突。基坑服役良好,与坑内筏板基础和其他结构配合良好,可为类似基坑的设计和施工提供参考。

This deep excavation for a raft foundation is located at the northwest side of Yaoshan Mountain in Jinan City.The excavation included many components,which possesses the characteristics of large scale,deep dewatering depth,and short construction duration,etc.During the support of excavation and dewatering period,several construction difficulties were encountered and were resolved successfully.These challenges included excavation difficulties in the several soil strata,such as,silty fine sandy layers,the thick-bedded miscellaneous soil and the hard rock at the bottom of some cast-in-situ concrete piles;the conflict between the constructed raft foundation and dewatering well points,etc.For the first time,the concept of perched groundwater in depressed soil layer is proposed in this study.This paper summarizes potential factors that might results in groundwater leakage in the waterproof cut-off wall formed by jet grout method.And the solutions to the groundwater leakage are suggested.It is very beneficial for making use of the exploration data from the dewatering well points.The ground anchors with casing pipe were used with satisfactory results.The rotary drilling and the long all-flight bored technics were used flexibility in the soldier pile construction.During the construction of the raft foundation,a new dewatering device for the submersible pump left-in-place was invented,which can solve the contradiction between the dewatering devices for the foundation pit and the completed raft foundation.By utilizing this new method,the raft foundation and other structure were installed satisfactory.