基于位错理论的饱和土渗流特性CPTU评价研究

Evaluation of coefficient of permeability of saturated soils based on CPTU dislocation theory

孔压静力触探(CPTU)测试数据通常用于土层划分和岩土工程设计参数评价。国际上CPTU测试技术的最新进展之一在于采用测得的锥尖阻力、侧壁摩阻力和孔隙水压力快速、连续地获得饱和土的渗透系数,以避免孔压消散试验费时的缺点。首先简要回顾了基于CPTU测试资料确定饱和土渗透系数的的研究成果,并进行了分析与改进,提出了基于位错理论和圆柱面径向流模型的水平向渗透系数预测新方法。选取典型场地进行了CPTU测试,并在黏性土场地采用薄壁取土器获得无扰动的原状试样,进行室内水平向渗透试验,在无黏性土场地进行现场钻孔抽水试验。以室内渗透试验和现场抽水试验的结果为参考,对3种基于CPTU连续评价饱和土渗透系数的方法进行了对比分析。研究表明,位错理论适用于评价饱和土的原位渗透系数,然而准确性与所采用的渗流模型有关。对国际标准CPTU探头,孔压过滤环位于锥肩(u2)位置时,采用圆柱面的径向流模型能够获得最为准确的水平向渗透系数预测结果,采用球面流或半球面流模型时趋于低估土层的渗透性。

The parameters obtained from measurements during piezocone penetration tests （CPTU） are commonly used for soil profiling and geostratigraphy as well as the assessment of geotechnical design. Since a dissipation test often takes significant time, efforts have been made to continuously evaluate the coefficient of permeability of saturated soils using the measured cone tip resistance, sleeve fiction and pore water pressure. In this study, the researches on evaluation of the coefficient of permeability of saturated soils are briefly reviewed and analyzed. Two novel methods based on the dislocation theory and the cylindrical flow model to estimate in-situ horizontal permeability are suggested. Piezocone penetration tests are conducted at typical sites. Horizontal permeability tests in laboratory on undisturbed samples of cohesive soils from high-quality thin-wall samplers and field pumping tests in borehole on cohesionless soils are also performed. A total of five methods are used to estimate the coefficient of permeability of soils, and the results are compared with those from laboratory and field tests. It is concluded that the values of coefficient of permeability evaluated from the proposed methods are more representative of the laboratory and field values than those evaluated using the available alternative methods. The dislocation theory can be used to estimate the coefficient of permeability of soils, but the accuracy depends on the flow model in porous media. For a standard cone with pore pressure element located at the shoulder of cone penetrometer （u2 position）, the radial flow normal to a cylindrical surface can support the best prediction of in-situ permeability.