粗粒土剪切强度是重要的力学指标,传统上颗粒材料剪切强度使用摩尔-库伦准则表示,然而该准则并未考虑颗粒破碎的影响。采用理论与试验相结合的探究方法,通过考虑高竖向应力作用下的粗粒土剪切,发现剪切破坏面上会发生颗粒破碎现象,提出了粗粒土剪切强度的幂函数表达。首先假设颗粒剪切面符合分形分布,同时剪切强度全部来源于颗粒间的摩擦力,推导出了粗粒土剪切强度的分形理论。然后利用全自动高压直剪仪对钙质砂、生石膏、硬质硅藻土三种材料进行高压直剪试验,探究初始孔隙比及竖向应力对于剪切特性的影响,结果表明:初始孔隙比对剪切强度及竖向位移基本无影响,而随着竖向应力的增大,剪切强度及竖向位移均增大,剪切强度与竖向应力为幂函数关系;对试验后得到的碎屑进行筛分后获取分维,代入至剪切强度的分形理论公式中,剪切强度的预测结果与试验结果符合良好。
The shear strength of coarse-grained soil is a critical mechanical parameter. Traditionally, the shear strength of granular materials has been described using the Mohr-Coulomb criterion. However, this classical approach does not account for the influence of particle breakage, which can significantly affect the mechanical behavior of such materials. A combined theoretical and experimental approach was employed to investigate the shear behavior of coarse-grained soil under high vertical stress. It was observed that particle breakage occurs on the shear failure plane. Based on these findings, a power-law function was proposed to describe the shear strength of coarse-grained soil. Assuming that the particle shear surface conforms to the fractal distribution, and the shear strength is all derived from the friction between the particles, the fractal theory based on the shear strength of coarse-grained soil is derived. Then, the automatic high-pressure direct shear instrument was used to carry out high-pressure direct shear tests on three materials: calcareous sand, gypsum and hard diatomaceous earth. The effects of the initial porosity ratio and vertical stress on the shear characteristics were investigated, and the results showed that the initial porosity ratio did not affect the shear strength and vertical displacement, but with the increase of vertical stress, the shear strength and vertical displacement increased. The shear strength is related to the vertical stress by a power function. The debris collected after the test was sieved to obtain the fractal dimension. This value was then substituted into the fractal shear strength formula. The predicted shear strength showed good agreement with the test results, verifying the validity of the fractal shear strength theory for coarse-grained soils.
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