软土地区地铁车站主体基坑开挖扰动测试及对附属基坑影响分析

Excavation disturbance test of Metro station in soft ground and influence analysis on the auxiliary excavation pit

软土地区城市轨道交通建设中,地铁车站主体和附属基坑常分期施工,但时间间隔多在半年以内。由于软土的结构性和流变性,车站主体基坑先期施工扰动导致土体性能指标下降且难以恢复至详勘时的原状土状态,势必对后期施工的附属基坑造成影响。对附属基坑范围土体进行室内试验及原位试验,结合主体基坑实测监测数据分析了基坑变形特性、坑外土体扰动变形机理及扰动前后物理力学指标变化,并根据土体参数的详勘初值、试验扰动值对附属基坑进行计算分析。结果表明:坑外地表沉降与扰动土体固结压缩变形有关,埋深在坑底附近及以上的坑外土体力学指标受主体基坑施工扰动影响大,黏聚力最大下降约5.8%,内摩擦角最大下降约11.4%,压缩模量最大下降约10.8%;根据扰动度指标判定,①、②层土体受中等扰动,③、④层土体受轻微扰动;受土体扰动影响,附属基坑最大深层水平位移及坑外地表最大沉降预计增大约10%。

In the construction of urban rail transit in soft soil area,the excavation of the subway station and the auxiliary facility are often constructed in phases,but the time interval is mostly within half a year.Due to the structural and rheological properties of soft soil,the construction disturbance during the station excavation will weaken the soil and will be difficult to restore to the original state,which is bound to affect the auxiliary excavation in the later construction phase.Indoor test and in-situ test were carried out on the soil samples taken from the auxiliary excavation pit,and the deformation characteristics of the excavation,the disturbance deformation mechanism of the soil outside the pit and the changes of physical and mechanical parameters and after disturbance were analyzed based on the monitoring data during the station excavation.The auxiliary facility excavation was analyzed using the original values and disturbed values of the soil parameters.The results show that the surface settlement of the pit is related to the consolidation compression deformation of the disturbed soil,and the mechanical index of the soil outside the pit and buried near the pit bottom is greatly affected by the station excavation disturbance,and the maximum cohesion decreases by about 5.8%,the maximum decrease in internal friction angle is about 11.4%,and the maximum decrease in compression modulus is about 10.8%.According to the disturbance index,the soil of layer No.1 and No.2 is moderately disturbed,and the soil of layer No.3 and No.4 is slightly disturbed.Affected by soil disturbance,the maximum horizontal displacement during the auxiliary excavation and the maximum settlement of the surface of the pit are expected to increase by about 10%.