Large-scale direct shear tests on soil-rock aggregate mixture under complicated environment based on orthogonal design

In order to study the strength characteristics of soil-rock aggregate mixture under complex environment more systematically and comprehensively, a series of lab large-scale direct shear tests are conducted through Geotest direct shear apparatus based on the orthogonal experimental design. These tests take into account variable factors such as water content, soaking time, wetting/drying cycles, stone content, rock property and soil property, etc. Then the degree of influence of these factors on the shear strength of soil-rock aggregate mixture is determined, which can provide a new way for this kind of multi-factor and multi-level researches. The test results indicate that the shear strength of soil-rock aggregate mixture is caused by mutual embedding, mesh and friction of aggregated rock. The rock content is the single primary factor for influencing the strength property of rock-soil aggregate mixture. With the increase of the rock content in the test specimen, the internal friction angle increases linearly. In 3 kinds of varied water effect situations, the water content has the most significant impact on the strength of soil-rock aggregate mixture. It also has high influence on the shape of shear stress-shear displacement curve. In contrast, the soaking time and wetting/drying cycles are less important for the shear strength of rock-soil aggregate mixture, and the shear strength will not continue to weaken when the specimen is soaked for more than 48 hours or under 4 wetting/drying cycles. The shear strength of the specimen is obviously affected by the rock property when its rock content is not less than 55%.