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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。
Undrained shear strength is an important mechanical property parameter of soil. In the stability analysis of geotechnical engineering construction period, it is necessary to use the undrained shear strength value. At present, the determination of undrained shear strength mainly indoor test and cross plate shear test. However, the former is greatly affected by soil disturbance, and the latter is a small value of the shear strength of sliding surfaces of soil. When the bottom of pit is raised, the result is not accurate enough. This paper first summarizes the domestic and international CPTU-based Su determination method. In a typical soft foundation excavation project, the pore pressure static penetration test is conducted. According to the relationship between the undrained test value and the cone tip resistance, the value of the cone coefficient is inverted. Based on the inverted conic coefficients, the undrained shear strength predicted by CPTU is applied to the uplift analysis of foundation pit. The results are compared with the calculated results based on the indoor test data and the strength of the cross plate. The results show that the soft clay based on CPTU Undrained shear strength index calculation results are reasonable, in line with engineering practice, it is worth promoting in engineering design.