Abstract: To investigate the impact of gravel content on shear strength and dilatation of sand-gravel mixture, the large-scale simple shear tests of 21 simples were conducted using an advanced shear apparatus. Seven groups of sand-gravel mixture samples with gravel content ranging from 0% to 80% were prepared for shear tests under three different normal pressures (100, 200, 300 kPa). Relationships among the gravel content and shear strength, dilatation, shear contraction of sand-gravel mixture were analyzed based on the test results. It is shown that under the same normal stress, the internal friction angle and cohesion of the sand-gravel mixture initially increase then decrease as the gravel content rises. The shear strength achieves the maximum as the gravel content is located within the range of 40%-50%. Further analysis indicates that the shear strength of the sand-gravel mixture significantly depends on the void ratio of mixture. Meanwhile, the structure of sand-gravel mixture and dominant particles change as the gravel content increases. When the gravel content is below 20%, the sand-gravel mixture is dominated by fine component, and presents a typical suspended dense structure. In this case, the shear strength of sand-gravel mixture is close to that of the matrix. When the gravel content is between 20% and 50%, the sand-gravel mixture shows a skeleton-pore structure. As the gravel content increases, the skeleton is formed gradually, and biting force between particles increase, leading to the raise in the strength of the mixture. When the gravel content is above 50%, the mixture exhibits a typical dense skeleton structure. In this case, void ratio of the mixture increases, and the matrix is unable to fill the void as the gravel content increases, which results in lower shear strength.

Key words: sand-gravel mixture, simple shear test, shear strength, shear dilation, gravel content