基坑中基于CPTU软土不排水强度确定及应用

不排水抗剪强度是土的重要力学特性参数。在岩土工程施工期稳定性分析中,需用不排水抗剪强度值。目前,不排水抗剪强度的确定主要有室内试验和十字板剪切试验。但前者受土样扰动影响大,后者十字板强度是土体各滑动面上抗剪强度的较小值,在基坑工程验算坑底隆起时,结果不够准确。本文首先总结了国内外基于CPTU的Su确定方法,在典型软土基坑工程中进行了孔压静力触探试验,根据不排水试验值与锥尖阻力的关系,反演出圆锥系数的值。基于反演的圆锥系数,把CPTU预测的不排水抗剪强度应用到基坑的隆起分析中,与基于室内试验数据和基于十字板强度的计算结果进行了比较,结果表明:基于CPTU的软粘土不排水抗剪强度指标计算结果合理,符合工程实际,值得在工程设计中推广。

Evaluation and Application of Undrained Shear Strength in Excavation from Piezocone Tests (CPTU)

The undrained shear strength is an important parameter for soil deformation calculation and strength analysis. The undrained strength is more frequently used among the currently used strength parameters in assessing the stability analysis of the structure during the construction stage. The previous methods to obtain the undrained shear strength were generally based on the laboratory test or field vane testing. The laboratory test was of time consuming and low accuracy due to disturbance from sampling, transportation and conservation, also the vane strength is smaller compared with the strength on other shear surfaces. Furthermore,these values can’t meet there quirements for calculating the basal stability analysis. This paper summarizes the methods to determine the undrained shear strength based on the piezocone tests,provides the measurements of in situ CPTU and laboratory undrained triaxial testing of soft soil excavation.Based on the cone tip and the undrained shear strength in the triaxial test,it deduced the cone factor.The deduced undrained shear strength values by CPTU,triaxial tests and field vane tests have been used to calculate the basal stability analysis. Through comparison,it is shown that the value based on CPTU is sufficiently accurate for determining basal stability analysis.Therefore,it is notably suitable for use in engineering practice.