基于大型直剪试验的强风化粗粒料剪胀特性试验研究

剪胀性是岩土材料的重要特性之一，为研究不同工况条件下粗粒料室内大型直剪试验中的剪胀特性，采用新型室内大型直剪仪对3组不同含水率、4组不同剪切速率、5组不同含砾率等3种不同影响因素的试样进行了室内大型直剪试验，分析了剪切时试样的垂直位移与水平剪切位移及垂直应力的关系。试验结果表明：在保持其他影响因素相同条件下，垂直应力的增加导致相同水平剪切位移对应的剪缩量增加；试样的最大剪缩量随着含水率的增加有一定程度的增大，而随着剪切速率的增加而减小；含砾率低于30%试样的最大剪缩量较含砾超过于30%试样的剪缩量大很多，最大剪缩量差别为3倍。当试样含砾率小于50%时，由于试样中富含细颗粒的影响，使得应力-应变曲线具有应变软化属性以及剪胀性趋于一固定值。峰值强度前的应力比-位移增量关系采用非线性的二次项拟合比线性关系的拟合度更好，认为Matsuoka提出的二维剪胀公式不适用于粗粒料，将其修正成二次多项式并给出试验中的经验参数μ的取值区间。

Dilatant behavior of intensely weathered coarse-grained soils in large-scale direct shear tests

Shear dilatancy is one of the most common phenomena of geological materials. A series of experiments were conducted in a newly manufactured large-scale direct shear apparatus to study the dilatant behavior of intensely weathered coarse-grained soils, including that 3 groups of various moisture contents, 4 groups of various shearing rates and 5 groups of various gravel contents samples were tested, respectively. Dependence of vertical and horizontal displacements on the applied normal stress was analyzed. The results show that when other controlling conditions are fixed, the shear shrinkage increases with the applied normal stress. The maximum shrinkage increases with the increase of moisture content or the decrease of shearing rate; and the shrinkage of samples with gravel content less than 30% is significantly larger than that with higher gravel content. Our results suggested that for those samples with gravel content less than 50%, the effect of fine content became significant, so that the samples show a strain-softening behavior; and the dilation tends to a fixed value. It is shown that the two-dimensional dilation formulation proposed by Matsuoka is not applicable to the coarse-grained materials. Instead of the formulation, a quadratic polynomial can be adopted to represent the relationship between the stress ratio and the strain increment at the peak strength, the value range of experience parameters μ in this formula is given.