软弱地层半逆作深基坑支撑轴力变化规律

Regularity of Supporting Axial Forces of Deep Foundation Pit with Semi-top-down Method in Soft Ground

结合软土地区某地铁深基坑工程,通过对半逆作深基坑的横纵剖面支撑轴力值随土体开挖变化数据规律的分析,阐明了在软弱地层条件下,半逆作法深基坑支撑轴力的变化特征。结果表明:支撑轴力大小及其变化形式与支撑空间位置、施工工况、支撑形式、挖土时机及开挖速度等因素密切相关;缩短第二道钢支撑及基坑垫层浇筑时的无支撑暴露时间可有效减小最大支撑轴力值;逆作下二层板框架下土体开挖引起基坑某一剖面整体支撑轴力重分布;因第一道钢筋混凝土支撑刚度较大,其对深基坑稳定具有重要作用。

In project of a typical silt-based pit of subway station with semi-top-down method, the retaining struc- tures of steel supports, reinforced concrete support and frame structure of subbasement with diaphragm wall are mainly applied. This paper is based on monitoring result of axial forces of the strut. The change laws of inner-support axial- force characteristics caused by excavation are investigated. Then the variation features of axial force of strut in weak strata environments were illustrated. According to the analysis of on-site monitoring data, it could be obtained that the value and change of inner-support axial-force is closely related to space position, construction steps, supporting form and excavation speed etc. ; the maximum value of support axial-force can effectively decrease with the reduction of ex- posing time of the soil of the second steel support and concrete pouring; the deep excavation under frame structure of subbasement causes redistribution of the support axial-force at whole profile; the reinforced concrete support with large-stiffness of the first layer plays an important role in stability of deep excavation. This work is significant to the study of foundation pit with semi-top-down method in soft ground.