基于孔压静力触探确定土体的渗透系数

Determination of permeability coefficient of soil based on CPTU

近年来许多研究者致力于通过孔压静力触探(CPTU)确定土体的渗透系数,但是存在偏差大,而且不能从机制上清楚地解释孔压静力触探确定土体渗透系数的原因。为了应用孔压静力触探现场快速地确定土体的渗透系数,在总结前人对孔压静力触探确定土体渗透系数方法的研究基础上,提出孔压静力触探时锥头处呈球冠形孔隙水流动的计算模型,假定锥头处初始超孔隙水压力为负指数型分布,推导出土体渗透系数的表达式,并且结合现场实测数据,将所提出的方法与已有的方法进行对比分析。研究发现:所提出的方法扩大了现有方法的应用范围;渗透系数计算结果受锥头角度的影响较大,随着锥头角度的增大而增大;针对国际上通用的60°角的标准锥头,所提出的方法计算的渗透系数大于前人的方法,而且更接近室内外试验结果。

Efforts have been made to estimate permeability coefficient of soil using cone penetration test with pore pressure measurement （CPTU） in recent years. However, there are large deviations for the current approaches. Moreover, the mechanism of permeability coefficient determined by CPTU can not be explained explicitly. In order to directly determine the permeability coefficient of soil by CPTU in the field, two assumptions are proposed： i） the flow surface area for pore water is assumed to be a spherical crown covered the tip of the cone; ii） negative exponent distribution of initial excess pore water pressure during CPTU is assumed. Based on these two assumptions and the previous approaches for evaluating the permeability coefficient of soil using CPTU, the equation to calculate the permeability coefficient of soil is derived. According to the measured data in the field, the comparison is made between the proposed approach and the existing one. The results show that the proposed modified approach extends the range of the application of existing approaches. The permeability coefficient of soil is influenced by the degree of the tip of the cone greatly, which increases with the increasing of the degree of the tip. For a cone penetrometer with 60 degrees accepted as the reference and specified in the international reference test procedure, the permeability coefficient determined by the proposed approach is larger than that of previous approaches and more close to that of lab and field tests.