含石量对土石混合体剪切特性的影响

为了探究不同含石量对土石混合体的抗剪强度及剪胀性的影响，利用先进的大型单剪试验仪进行了21组大型单剪试验。试验设计了从0%～80%含石量共7组试验样品，在100、200、300 kPa三种不同的法向压力下进行单剪试验。基于试验结果，分析了含石量对土石混合体的抗剪强度和剪胀、剪缩特性之间的关系。试验结果表明，在相同的法向压力下，随着含石量的增加，土石混合体的内摩擦角及黏聚力总体上有先增大后减小的趋势。当土石混合体在含石量为40%～50%之间时，其抗剪强度最大。研究表明：土石混合体抗剪强度受到土石混合体孔隙比的影响，同时随着含石量的增加，土石混合体中的结构形式及主导颗粒也相应的发生变化。当含石量在0%～20%之间时，细集料在土石混合体中占主导地位，土石混合体为悬浮密实结构，此时土石混合体的抗剪强度与基质颗粒的性质相近；当含石量在20%～50%时，土石混合体为骨架孔隙结构，随着含石量的增加，土石混合体的骨架逐渐形成，颗粒之间咬合力增加，使得黏聚力及内摩擦角都有明显提高；当含石量超过50%之后，土石混合体表现为骨架密实结构，孔隙率开始上升并且细粒料开始大幅减少，细集料不能充分填充块石之间的孔隙，于是土石混合体抗剪强度开始下降。

Effect of gravel content on shear behavior of sand-gravel mixture

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.