北京第五广场基坑支护设计与监测

Design and monitoring of supporting for Beijing No.5 Square foundation pit

介绍了与相邻地下室(基坑)距离较近的北京第五广场(24 m深)北侧、南侧基坑支护设计。通过成功利用北侧相邻基坑的桩锚支护作为新建基坑排桩支护的背拉结构体系,对有限土体土压力进行分析,解决了北侧基坑支护难题,大大节省了工程造价。通过采用桩加多排大倾角、有限长度的预应力锚杆支护体系,保证了基坑南侧锚杆不伸入相邻拟建建筑物基底,避免了因相邻建筑物基坑开挖造成基坑支护体系的失效。从基坑开挖到回填的10个月,对桩项位移、桩身钢筋应力及锚杆拉力进行了持续监测,建立了有效的基坑变形预警系统,指导在基坑维护中采取积极有效的措施,保证该基坑经受住了北侧桩后消防水管意外漏水和台风暴雨等突发事件的考验。

The design of supporting for north and south pits of Beijing No.5 Square(24 m in depth) very near the surrounding substructure(foundation pit) was presented.Through the successful use of the the pile-anchor supporting for nearby foundation pit as the pile supporting structure for the new foundation pit,as well as study on the finite earth pressure,the difficult problem of pit supporting was solved and engineering expenses were saved.By using supporting system of piles plus many rows of large angle anchors,finite length pre-force anchors,the anchors of the south pit were made sure not go into the foundation soil under nearby building.At the same time,it avoided pit supporting system to be unstable because of excavation of adjacent buildings. For about 10 months from excavation of the pit to the filling,the displacement of the pile top,the stress of pile reinforcing bars and the anchor dragging force were monitored.An effective forecasting system for displacement of foundation pits was made so as to take effective measures in pit maintenance and to ensure the safety of the foundation pit after unexpected water leakage from fire water pipes and typhoon rainstorms.