基于CPTU的宁波黏性土不排水抗剪强度确定研究

Determination of Undrained Shear Strength of Clayey Soil in Ningbo Based on CPTU

黏性土的不排水抗剪强度是黏性土的重要力学指标,对于地铁车站的设计是非常重要的。由于获得无扰动试样的困难或成本限制,现代原位测试技术已广泛用于不排水抗剪强度的评价之中。以宁波地铁车站为工程背景,采用多功能孔压静力触探技术(CPTU)对黏性土进行土层测试和评价。介绍了CPTU测试技术的基本原理;根据十字板剪切强度反演孔压圆锥系数(NΔu),提出了不排水抗剪强度与超静孔压的关系,并探讨了孔压圆锥系数与孔压参数比的关系;将基于CPTU测试技术的不排水抗剪强度与室内测试结果进行对比。结果表明,采用CPTU测试技术能有效地评价黏性土的不排水抗剪强度;基于十字板剪切试验的不排水抗剪强度与基于CPTU测试技术的超静孔压有着较好的相关性;孔压圆锥系数与孔压参数比有着较好的对应关系。

The undrained shear strength is an important physical property of clayey soils and is also very valuable to the design of subway. According to the difficulty and cost constraint of obtaining the undisturbed samples of high quality,a modern in-situ test was commonly applied to evaluate the undrained shear strength. In the case study of Ningbo Subway,the piezocone penetration test（ CPTU） was used to test and evaluate the clayey soil. Firstly,the basic operation principles of piezocone penetration test were introduced. Secondly,according to the pore pressure cone coefficient（ NΔu） obtained from the inversion of field vane shear test,the relationship between undrained shear strength and excess pore pressure was analyzed,and the relationship between the pore pressure cone coefficient and pore pressure parameter ratio was also discussed. Moreover,the results of undrained shear strength based on the piezocone penetration test were contrasted with the results obtained from laboratory test. It is shown that piezocone penetration test can be used for effective evaluation of undrained shear strength of clayey soil; the undrained shear strength obtained from field vane shear test has a good relevance with the excess pore pressure obtained from piezocone penetration test; and the pore pressure cone coefficient and pore pressure parameter ratio have some corresponding relation with each other.