成都膨胀土地层大型地铁车站施工方法及力学特征研究

Construction Methods and Mechanical Characteristics of Large Metro Stations in Expansive Soil Layers in Chengdu

[目的]成都部分膨胀土地区下伏基岩为泥岩,为地下水的富集提供了良好的空间,导致膨胀土吸水膨胀,较大的膨胀力易使得该地区车站主体结构侧墙开裂。为避免此类情况发生,需对该地区车站主体结构施工过程中侧墙、中板、顶板等易受拉部位的受力特性进行深入研究。[方法]以成都地铁17号线二期东延线威灵车站主体结构工程为研究对象。介绍了车站主体结构施工工序;并采用室内试验以及数值模拟的研究方法,分析了不同施工工序下主体结构易受拉部位的应力变化特征;确定了主要影响施工工序和施工过程的最不利监测位置。[结果及结论]车站施工范围内膨胀土的自由膨胀率均在40.0%以上,最高的为48.0%,为弱膨胀土,膨胀压力随着天然含水率的增加而减小,现场土体膨胀力为42.8 kPa;威灵站主体结构施工中采用了“两端向中间合拢施工方法”,缩短了膨胀土基坑开挖后的暴露时间,成功避免了侧墙等主体结构开裂;拆除第一道和第二道支撑会使结构拉应力明显增大,为施工主要影响工序;车站主体结构中受力最不利位置为负一层侧墙距离中板7.23 m处、顶板及底板距离右侧墙4.00 m处、中板跨中位置处,最大拉应力为0.587 MPa,满足安全控制要求。

[Objective]In parts of Chengdu,the underlying bedrock in expansive soil area is mudstone,providing a conducive space for groundwater accumulation.This leads to the swelling of expansive soil upon water absorption,causing significant expansion pressure that can easily crack the sidewalls of station structures in the area.To prevent such occurrences,it is necessary to conduct in-depth research on the mechanical characteristics of tension-prone parts such as side walls,middle slabs,and top slabs during the construction of station main structure in this area.[Method]Taking the main structure Chengdu Metro Line 17 Weiling Station East Extension Line Phase II project as research object,the construction procedures of station main structure are introduced.By employing laboratory tests and numerical simulation methods,the stress variation characteristics of tension-prone areas under different construction procedures are analyzed.The most unfavorable monitoring locations for the major influencing construction processes are identified.[Result&Conclusion]The free expansion rate of expansive soil within the station construction area is over 40.0%,with a maximum of 48.0%,classifying it as weak expansive soil.The expansion pressure decreases with increasing natural moisture content,with the on-site soil expansion force measured at 42.8 kPa.The construction of Weiling Station main structure adopts a construction method of′both ends closing towards the middle′,which reduces the exposure time of the expansive soil foundation pit after excavation,successfully preventing cracks in the main structure such as the sidewalls.Removing the first and second supports significantly increases tensile stress in the structure,marking it as a major influencing construction process.The most critical stress locations in the main structure are 7.23 m from the middle slab on the sidewalls of first basement level,4.00 m from the right sidewall on both the top and bottom slabs,and the midpoint of the middle slab span,with a maximum tensile stress of 0.587 MPa,meeting safety control requirements.