膨胀土基坑悬臂桩支护设计中土压力计算方法探讨

Calculation Method of Earth Pressure of Swelling Soil in Design of Cantilever Retaining Pile of Building Foundation Excavation

在基坑支护设计中,膨胀土压力的计算尚未有统一标准。实际工程中,膨胀土地区土压力计算往往采用抗剪强度参数折减的方法处理,导致基坑支护结构失效的情况时有发生。通过研究"成都黏土"基坑支护现状及已有的设计方法,对膨胀土基坑土压力计算方法进行改进,主要从土体抗剪强度参数确定、膨胀土压力分布和支护桩锚固段有效深度3个方面分别进行讨论。分析结果表明:在基坑设计中膨胀土体的抗剪强度指标应依据抗剪强度与含水率关系的试验结果进行确定,膨胀土压力按照三角形进行分布,锚固段有效深度宜在计算值的基础上加本地区大气影响急剧层深度。在上述分析的基础上,以时代欣城和科创中心基坑为例,采用改进方法进行设计并与原设计对比,时代欣城基坑改进后桩的锚固深度为6.4m,大于原设计计算值1.8m和采用值5.0m,科创中心基坑改进后桩的锚固深度为5.6m,大于原设计计算值3.4m,小于采用值6.0 m,改进的计算方法在实际工程支护中的应用合理、可行。

In the retaining design of building foundation excavation,no universal standard is available for the calculation method of swelling soil pressure.In practical engineering,the method of reducing shear strength parameters is often used in the calculation of soil pressure in swelling soil area,which may lead to the failure of retaining structure.Based on the study of current situation of building foundation excavations in the clay area in Chengdu and the existing design methods,the calculation method of earth pressure of swelling soil was improved,which was mainly discussed from three aspects of the determination of soil shear strength parameters,the distribution of swelling soil pressure and the effective depth of anchor retaining pile.The analysis results show that the shear strength parameters of swelling soil in foundation design should be based on the results of the tests on the relationship between the shear strength and water content.The swelling soil pressure is distributed according to triangle.The effective depth of pile anchored segment should add the sharp layer depth of atmosphere influenced on the basis of calculated value.A case study of the foundation excavations of Times Bustling City project and Science Innovation Centre project was carried out.The improved method was used in a design,which was compared with the original design.The pile anchored depth of the Times Bustling City project after foundation improvement was 6.4 m,which was greater than the original calculated value of 1.8 mand adopted value of 5.0 m,while the pile anchored depth of the Science Innovation Centre project after improvement was 5.6 m,which was greater than the original design value of 3.4 m,but less than the adopted value of 6.0 m.The improved calculation method is reasonable and feasible in practical retaining.