逆作法基坑支护结构三维m法及工程应用

逆作法技术广泛应用于软土地区敏感环境下的深大基坑工程施工。虽然基于连续介质力学的三维实体有限元方法已逐渐被用于分析评估深开挖对周围环境的影响,工程实用中支护结构的内力变形分析仍采用基于梁–土弹簧体系的弹性抗力法,而传统的支护结构弹性抗力法不能考虑逆作法基坑复杂施工因素的影响。以杭州某逆作法深大基坑工程为案例,结合现场实测数据,通过PLAXIS平面有限元分析与弹性抗力法反分析,得到逆作法深大基坑中盆边留土、坑底工程桩作用和蠕变影响的杭州软黏土等效水平基床比例系数m的拟合公式,提出了考虑逆作法复杂施工因素影响的基坑三维梁系有限元分析方法。研究表明,该方法的计算结果比现有方法更合理;对于深厚软黏土逆作法基坑工程,土体蠕变对基坑变形影响显著。

Three-dimensional m method for retaining structures and its application for top-down construction of excavations

The top-down method is widely used in construction of deep and large foundation pits under sensitive environment in soft soil areas. Although the three-dimensional finite element method based on the continuum mechanics has been gradually used to analyze and evaluate the impact of deep excavation on the surrounding environment, the elastic resistance method based on the beam-soil spring system is still used to analyze the internal force and deformation of retaining structures in engineering practice, while the traditional elastic resistance method cannot consider the influence of complex construction factors of foundation pits by the top-down construction method. Based on a deep and large foundation pit project with top-down method in Hangzhou, combined with the field measured data, the fitting formula for the equivalent horizontal resistance coefficient m is obtained through PLAXIS analysis of plane finite element and back analysis of elastic resistance method. The formula can consider the effect of the earth berm, the working pile close to the retaining wall and the creep of soft clay. A 3D finite element method for beam-spring system considering these complex factors due to top-down construction is proposed. It is shown that the calculated results of this method are more reasonable than those of the existing methods. For the deep soft clay foundation pits with top-down construction method, the creep of soils has a significant effect on the deformation of the retaining walls.