成都地铁17号线东延伸段膨胀土胀缩变形力学特性

Swell-Shrink Deformation Mechanical Property of Expansive Soil in Chengdu Metro Line 17 East Extension Section

为了研究成都地区典型膨胀土深基坑的支护参数,采用现场调研、室内试验、数据分析和现场监控量测等方法,以成都地铁17号线二期东延伸段威灵站深基坑工程为例,开展膨胀土的自由膨胀率、无荷载膨胀率及膨胀力等胀缩变形力学特性研究。结合现场施工监控量测分析,研究了各施工步骤下基坑的支护桩水平位移、断面支撑轴力和地面竖向位移的情况。研究结果表明:(1)该地区膨胀土主要分布在地下5~10 m深度处,主要为弱膨胀土,自由膨胀率在50%以内;(2)试验土样的无荷载含水率与含水率有较大的关系,遇水后的无荷载膨胀率随着土样含水率的增加而降低;(3)随着土体含水率的增加,试验土样的膨胀力呈线性降低趋势;(4)随着基坑的开挖,支护桩的水平位移逐渐增大,其主要发生在第1道支撑和第3道支撑之间,桩体主要向基坑内侧偏移,少部分向基坑外侧偏移;(5)支撑轴力出现过大的现象,当开挖至轴力监测点ZL32-3支撑位置时,ZL32-1测点处的支撑轴力超过设计值约50 kN;(6)从地面竖向位移监测结果来看,该工程深基坑开挖支护设计总体可控。

To study the support parameters of typical expansive soil deep foundation pit in Chengdu area,taking the Weiling Station deep foundation pit engineering of Chengdu Metro Line 17 phase II east extension section as an example,the methods of field investigation,indoor test,data analysis,field monitoring and measurement are adopted to conduct mechanical property research on expansive soil swell-shrink deformation,such as the free expansion rate,no-load expansion rate and expansive force.Combined with the field construction monitoring and measurement analysis,the retaining pile horizontal displacement,the section supporting axial force and the ground vertical displacement at each construction step are studied.Research results show that:(1)the expansive soil in this area is mainly distributed at the depth of 5-10 m underground,mainly composed of weak expansive soil with the free expansion rate within 50%;(2)the no-load water content is closely related with water content for test soil sample,and the no-load expansion rate after encountering water decreases with the increase of soil sample water content;(3)with the increase of soil water content,the expansive force of test soil sample decreases linearly;(4)with the excavation of foundation pit,the retaining pile horizontal displacement increases gradually,which mainly occurs between the first support and the third support,most of the pile body shift to the inside of the foundation pit,and a small part to the outside;(5)excessive supporting axial force may occur,and when the excavation reaches the supporting position at ZL32-3 axial force monitoring point,the supporting axial force at ZL32-1 point exceeds the design value by about 50 kN;(6)according to the ground vertical displacement monitoring results,the deep foundation pit excavation and support design of the project is generally controllable.