基于CPTU原位测试的深基坑工程中黏性土静止土压力系数的评价研究

Determination of static earth pressure coefficient of clay in deep excavation project based on piezocone penetration test

静止土压力系数K0是岩土工程设计中的一个重要参数,对深基坑工程设计和安全可靠性有直接的影响。由于土体经历复杂的加载、卸载过程以及室内试验的限制,往往难以准确地确定K0,因此现代原位测试技术更加广泛地用于K0的评价之中。国外广泛采用了扁铲侧胀试验、旁压试验和孔压静力触探试验等对K0进行预测,并提出了一些经验公式。本文以南京金融城二期深大基坑工程为背景,采用多功能孔压静力触探(CPTU)对黏性土层进行测试和分析。首先介绍了基于CPTU预测静止土压力系数K0的方法,然后将基于CPTU测试预测的K0值与室内试验值进行对比,最后研究了南京黏性土的静止土压力系数K0与归一化锥尖阻力的相关关系。试验结果表明,采用多功能CPTU测试技术能够有效地评价黏性土的静止土压力系数,并建立了预测南京黏性土K0的公式。

The static earth pressure coefficient K0 is an important parameter in geotechnical engineering design,which affects directly on the design and safety reliability of deep excavation works.Due to the complicate loading-unloading process and the limitation of laboratory tests,K0 is often difficult to determine accurately.Therefore the modern in-situ testing techniques,such as flat dilatometer test,pressuremeter test and piezocone penetration test are widely used to determine K0,and some empirical formulas have been proposed.Based on the deep excavation project of Nanjing Financial City phase II,multi-functional piezocone penetrating test(CPTU)was used to test and analyze the K0 value of clay.The method of predicting K0 based on CPTU is introduced,and then comparing the K0 value measured by CPTU and the value obtained from indoor consolidation test,the correlation between K0 value of Nanjing clay and the normalized tip resistance is studied finally.The results show that the CPTU test technique can effectively evaluate the K0 of clay,and the new formula to estimate K0 of Nanjing clay is proposed.