龙门吊移动荷载对地铁车站深基坑变形的影响

青岛地铁苗岭路站是在土岩组合地层下开挖的狭长型换乘车站,深基坑两侧既有建筑物众多且临近基坑,施工中采用龙门吊运输材料。为探究龙门吊移动荷载作用下基坑围护结构和土体的空间变形规律,建立三维有限元数值模型,对比分析了加载前后基坑围护桩侧移变形和坑外地表沉降,并探讨了起吊物与边跨的距离对基坑变形的影响。结果表明:龙门吊移动荷载作用下基坑产生明显的动态响应;围护桩桩体侧移变形比竖向变形响应明显且沿深度有所不同,嵌岩点处侧移响应最明显,土岩交界面处响应最小;受基坑阴角效应的影响,动载作用下角隅处土体沉降变形保持不变,坑外土体最大变形位置由距坑边2 m处转移至基坑边;起吊物的移动在基坑边产生明显的变形动态响应区域,随着起吊物远离边跨,桩周土体的沉降量逐渐减小,动态响应区域向远离坑角方向增大;加强冠梁连接、适当增大阴角处桩间距或减少锚杆施作可以保证基坑的稳定性,经济有效。

Spatial impact of the heavy loadings of the portal crane on the deep founda-tion pits of the subway stations

The given paper is aimed at making an investigation of the spatial deformation features of the soil and the retaining structure at the foundation pit under the moving loading of the portal crane. As is known,Miaoling Road Station of Qingdao Metro is a narrow but long transit station built on the soil-rock integrated stratum. The said station can be taken as a transit station with the semi-sine load taken to represent the cyclic loading and the dynamic numerical model built up via the 3-D finite element method(3D-FEM). With the multiple surrounding buildings up the surface ground near the foundation pit,it is necessary to choose the portal crane to move the construction materials.For such a purpose,a comparison has to be done between the numerical results and measured data to confirm the validity of the above mentioned 3D-FEM model. On the other hand,it is also necessary to compare particularly to work out the vertical and lateral displacement data of the retaining piles pre-&-pro the dynamic loading and the surface settlement under the same building conditions. Besides,it is also necessary to analyze the effect of the distance of the lifting objects carefully against the side span over the dynamic response of the foundation pit. And,so,the results of the above calculation and measurement indicate that the moving loading of the portal crane should have a significant impact on the foundation pit. Literally speaking,the lateral displacement response of the piles proves more influential than the vertical displacement response. For instance,the lateral displacement response of the piles varies along the depth,with the most significant dynamic response given oriented at the rocksocketed part of piles with the least pronouncedly at the soil-rock interface. And,so,being affected by the concave corner response,the soil settlement at the corner of the foundation pits tends to stay constant under the pressure of the dynamic loading and the serious deformed position at the ground surface from 2 m away from side-to-side of the pit. What is more,the movement of the lifting objects is also likely to cause obvious partly deformed dynamic response. With the lifting objects moving away from the side span,the soil around the piles may tend to shrink gradually whilst the dynamic response area would like to be getting farther away from the corner of the pit. And,needless to say,in such a situation,there exists a great practical need to strengthen the crown beam and extend the pile spacing so as to decrease the number of bolts at the concave corner effectively so as to guarantee the stability of the foundation pit.