泸定大渡河桥冰碛土的结构及现场剪切试验研究

泸定大渡河桥康定岸分布巨厚层冰碛土，为研究土的抗剪强度特性，在不同位置和深度进行了6组现场剪切试验，基于地质勘察和试验结果分析土的结构特征、剪切强度和变形特性及其与土的结构的关系。研究表明:冰碛土的颗粒以粗粒、巨粒粒组为主，骨架颗粒呈悬浮状，混杂、无序堆积，骨架间充填杂基，形成骨架悬浮密实结构。根据颗粒组成和骨架风化程度，划分为骨架悬浮密实结构、软化骨架悬浮密实结构、砂砾土富集结构、大块石包绕结构等4种细观结构类型。冰碛土剪切破坏主要有剪切破碎带、包绕块石边界、锯齿状剪切和切穿软化骨架等4种模式，剪切荷载作用下线弹性变形阶段明显，剪切刚度大，初始屈服历时短。颗粒骨架和杂基形成的悬浮密实结构，是冰碛土强度与变形特性的内在控制因素，剪切荷载作用下骨架颗粒与具有一定胶结的基质间相互作用，剪切破坏时表现为基质的压碎与骨架的变位。骨架颗粒强度、大骨架颗粒分布、基质胶结程度的不同，对冰碛土强度和变形特性都构成一定的影响。土的抗剪强度、剪切刚度和剪胀性随骨架强度和基质胶结程度的提高而增大，而延性随之变差。

Soil structure and in-site shear test of moraine soil near the Xingkang Bridge over the Daduhe River in Luding

A thick layer of moraine sediments exists on the Kangding bank near the Xingkang Bridge over the Daduhe River in Luding along the Ya′an-Kangding Expressway. In order to study the shear strength characteristics of the moraine soils, six groups of field shear tests were carried out at different locations and depths. Based on the geological survey and test results, the structural characteristics, shear strength and deformation characteristics of the marine soils and their relationship with soil structure were analyzed. The results show that the grain size of the moraine soil is mainly composed of coarse grain and huge granular group. Soil skeleton particles are suspended, mixed, disorderly accumulated and filled with matrix between the skeleton, forming a skeleton suspended compact structure. According to the composition of particles and weathering degree of skeleton, four types of mesoscopic structure can be divided, such as the suspended skeleton dense structure, weathered suspended skeleton dense structure, lenticular sand-gravel enrichment structure and boulder enveloped structure. There are four main shear failure modes of moraine soil: shear fracture zone, enclosing boulder boundary, serrated shear and cutting through weathering framework. Under the shear load, the linear elastic deformation stage with large shear stiffness is obvious, and the yield stage is short. The suspension compaction structure formed by grain skeleton and matrix is the internal controlling factor of strength and deformation characteristics of the marine soil. Under the shear loading, the skeleton particles interact with the cemented matrix, when shear failure occurs, the matrix is crushed and the skeleton is dislocated. The strength and deformation characteristics of the marine soils are affected by the strength of skeleton particles, the distribution of large skeleton particles and the degree of matrix cementation. The shear strength, shear stiffness and dilatancy of the marine soils increase with the increasing skeleton strength and matrix cementation, while the ductility decreases.