海洋土与钢桩界面剪切强度的大型直剪试验研究

海洋工程中现行的桩-土界面剪切强度设计方法一般有两种:(1)根据工程经验与规范进行判断;(2)根据土层地质勘查报告中的土体强度参数进行判断。对于海洋桩基而言,合理地确定土-结构物界面的剪切强度尤为重要。界面剪切强度将直接影响桩基承载力的大小,过高或过低地估算桩基承载力都可能会造成严重工程事故发生。为了研究沉桩过程中桩-土界面特性,通过自制大型直剪仪对不同粒径的土样进行了直剪试验分析,提出"抗剪糙度"概念,研究了砂土的内摩擦角、相对密度和抗剪糙度三者之间的关系和黏土的抗剪糙度与不排水强度间的关系。研究表明,土与钢板界面的抗剪糙度并非常数,砂土抗剪糙度的变化规律性较强,而软黏土的抗剪糙度受固结程度、扰动程度、土体强度等因素影响而呈现较大变化。最后,对"抗剪糙度"在实际工程中的运用提出了一定的建议。

Large-scale direct shear tests on shear strength of interface between marine soil and steel piles

There are two methods to decide the interfacial shear strength of pile-soil in ocean engineering design nowadays. One is taking the advices of engineering experience and codes, the other is calculation using the strength parameters of soils derived from geological exploration. As for the pile foundation in ocean, it is very important to reasonably estimate the interfacial shear strength of soil-structure, which will make a great difference to the pile bearing capacity. Both overestimation and underestimation of the pile bearing capacity may lead to severe engineering accidents. To study the characteristics of interface between piles and soils during pile driving, a large-scale direct shear apparatus is developed to perform the direct shear tests on soil samples with varied particle diameters. The shear-resistant coarseness between the soils and the surface of structures is introduced, and the relationships among internal friction angle, relative density and shear-resistant coarseness of sand samples are studied as well as the relationships between the shear-resistant coarseness and the undrained shear strength of cohesive soil samples. According to the results of the tests, the shear-resistant coarseness is variable, and the shear-resistant coarseness of sand changes more regularly while that of soft clay changes more greatly owing to the influences of consolidation, disturbance and strength of soils. Moreover, some advices are offered to the application of shear-resistant coarseness in practical engineering.