研制了一台适用于多种工况下的大尺寸可视直剪试验仪器，可开展不同土工合成材料与土体作用的直剪试验。该仪器改进了加载方式与反力系统，实现了直剪试验正面可视及自动化采集试验数据，并可测量土工物在土中的应变，为探索筋土界面特性与筋土受力机制以及筋土位移分析提供了新的可能。使用新研制的试验装置开展了以砾类粗粒土为填料的土工格栅直剪试验，试验结果表明：加筋土较素土的界面内聚力增加，内摩擦角降低；格栅应变总体随着剪切位移的增加而增大，格栅横肋与土体的嵌阻力快速增大造成格栅应变增长较快，但直剪作用使格栅产生的最大应变值远小于格栅的屈服应变值。素粗粒土直剪界面厚度小于格栅加筋土的界面厚度，在筋土直剪界面处粗粒土主要以平移运动为主，同时部分中小颗粒存在平转位移模式。

A large size visual direct shear testing apparatus is developed to carry out direct shear tests of geosynthetics and soil under various conditions. The loading modes and reaction system of the apparatus are improved to explore the interface properties and loading transfer mechanism of reinforcement soil. The front visualization of the shear box and automated data acquisition system are achieved to measure the strain of geotextile material. Direct shear tests are conducted on geogrid and coarse-grained soil by using the newly developed apparatus. The results show that the interfacial cohesion of reinforced soil increases, but its internal friction angle decreases compared with plain soil. The geogrid strain increases with the increase of shear displacement. Moreover, the rapid increase of embedded resistance between the geogrid transverse rib and the soil is caused by the rapid increase of the geogrid strain. However, the maximum strain of the geogrid generated by direct shear is far less than the yield strain of the geogrid. The direct shear interface thickness of plain coarse soil is less than that of the reinforced soil. The movement of coarse grained soil particles is mainly translational on the reinforced soil around the direct shear interface, and meanwhile some small particles are in the horizontal rotational movement mode.