基坑开挖过程中变形监测预警指标的动态确定

Deformation Monitoring and Early Warning Indicators During Foundation Pit Excavation Dynamic Determination

针对基坑开挖过程中多数城市根据经验或规范给一固定的变形监测预警指标值,提出一种确定基坑开挖过程中变形监测预警动态指标的方法。以芜湖城南过江隧道基坑工程为例,考虑地下水对土体的劣化作用和地下水渗透作用两因素,通过放大两因素对基坑稳定性的影响,采用FLAC^(3D)软件对基坑开挖过程进行模拟,动态分析不同开挖层时的基坑变形值,获得基坑达到临界失稳状态时支护结构最大水平位移和地表最大沉降量,以此作为基坑变形预警动态指标。通过对比芜湖某基坑工程开挖模拟结果、监测值及规范值,验证所提方法的正确性。结果表明:支护结构水平位移累计量和地表最大累计沉降量随开挖过程的增大而增大,实际工程中地表沉降量和支护结构水平位移的预警控制值应随开挖次数的增加而相应变化;采用本文方法可有效确定基坑开挖过程中的动态预警指标,本研究可为该工程及该地区类似基坑工程开挖过程中变形监测预警指标的确定提供参考。

In the process of foundation pit excavation,most cities give a fixed value of deformation monitoring and early warning index according to experience or specifications.A method was proposed to determine the dynamic indicators of deformation monitoring and early warning during the excavation of foundation pits.Taking the foundation pit project ofWuhu Chengnan River Crossing Tunnel as an example,the degradation of groundwater on the soil and the penetration of groundwater were mainly considered.By amplifying the influence of these two factors on the stability of the foundation pit,FLAC^(3D) software was used to simulate the excavation process of the foundation pit,and the deformation values of the foundation pit in different excavation layers were dynamically analyzed.The maximum horizontal displacement of the supporting structure and the maximum ground settlement were obtained when the foundation pit reached the critical instability state,which were used as the dynamic indexes of the foundation pit deformation early warning.The correctness of the proposed method was verified by comparing the excavation simulation results,monitoring values and specifications of a foundation pit project in Wuhu.The results show that the cumulative horizontal displacement and the maximum cumulative surface settlement increase with the increase of excavation process,and the early warning control value of the surface settlement and the horizontal displacement of the supporting structure should change with the increase of excavation times;The method can effectively determine the dynamic early warning indicators during the excavation process of the foundation pit,which can provide reference for the determination of deformation monitoring and early warning index in the process of excavation of this project and similar foundation pit projects in this area.