基于CPTU确定软黏土超固结比的理论改进方法

利用孔压静力触探(piezocone penetration test,CPTU)试验结果确定超固结比(over consolidation ration,OCR)不仅能避免传统室内试验方法中土样扰动的问题,还能得到地层剖面上连续的OCR值。将静力触探锥头的挤土模式看作是球形孔的扩张,锥面上的正应力和剪应力分别假定为极限扩孔压力和锥–土接触摩擦力;基于修正剑桥模型中圆孔扩张的近似闭合解,提出了利用CPTU测试结果确定OCR的理论改进方法。分别选取轻超固结和重超固结场地的CPTU试验结果,对提出方法的可靠性进行验证。结果表明,在综合考虑锥面粗糙度以及贯入速率等因素的影响后,预测得到的OCR值较已有理论方法更接近实测结果。最后在连云港海相黏土中对该理论改进方法进行应用,计算表明该土层处于欠固结~轻超固结状态。

A modified approach to determine over consolidation ration from piezocone penetration tests in soft clays

Determination of over consolidation ration(OCR) from piezocone penetration tests(CPTU) can not only avoid the sample disturbance in laboratories but also provide the continuous profiles of OCR of soil with depth. The penetration of piezocone is taken as the ultimate internal pressure required in expanding a spherical cavity. Assuming the normal and shear stresses on the cone face to be the friction at the cone-soil interface and the ultimate expansion pressure respectively，a modified approach to determine the OCR from CPTU was proposed using the solution of a spherical cavity expansion described with the modified cam clay. Two CPTUs in lightly and heavily over-consolidated clays are selected to verify the general validity of the proposed method. Comparisons between the predicted and measured results show that the presented method is more reliable than the existing approaches because more factors such as the cone roughness and cone penetration rate are taken into account. The presented method is also applied to Lianyungang marine clay for OCR prediction，and the result shows that the layer is consolidated or lightly over consolidated.