Abstract: The carbonaceous mudstone is a special soft rock that is widely distributed in Southwestern China. The carbonaceous mudstone aggregate mixtures samples are tested by a large size direct shear test device under both saturated and unsaturated conditions. The aggregate mixtures have three different carbonaceous mudstone contents: 30%, 60% and 100%. The test results indicate that, under the same vertical stress, the shear strength increases with the increase of carbonaceous mudstone contents. With the increase of carbonaceous mudstone contents, the internal friction angle decreases and the cohesion values increases. The shear stress increases with the increase of the horizontal displacement and no obvious peak values are observed. Under the saturated condition, a flatter shear stress and horizontal displacement relationship can be found.

Key words: Aggregate of Carbonaceous Mudstone Mixtures, Shear Strength Parameters, LargeSize Direct Shear Tests, Shear Stresses