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%.