徐州粉土三轴压缩特性及二维离散元数值模拟

Experimental and 2D DEM simulation on the triaxial compression characteristics of Xuzhou silt

摘要

【目的】徐州粉土分布广泛，为了解其三轴压缩特性，给工程建设提供参数依据，【方法】对取自徐州地铁一号线的粉土，进行常规三轴压缩试验，不断施加轴向压力直到土体破坏，将整个试验过程看作是外加荷载对土体的做功过程。在此基础上，采取数值模拟方法，对徐州粉土的三轴试验过程进行模拟。【结果】结果显示：粉土峰值强度、残余强度和变形模量均随围压增大而增大；不同围压下均表现为剪切破坏，低围压下橡皮膜扭曲更明显。各类裂纹均逐渐增加，试样微裂纹在应力达到峰值时开始激增，剪裂纹占比逐渐增加；加载初期，荷载做功几乎完全转化为应变能，整个过程中应变能先增大后减小，摩擦能和阻尼能则一直增大至模型破坏；应变能、摩擦能与阻尼能之和约占边界能的60%,且随轴向应变增速变化与粉土应力-应变曲线关系密切。【结论】结果表明：数值模拟结果与室内试验结果很好吻合；剪切裂纹主导了粉土的最终破坏；根据能量变化将粉土三轴压缩过程破坏模式划分为峰值前的孔隙压密、弹性变形和塑性变形三个阶段，及峰值后的加速破坏和强度剩余两个阶段。然而随着围压的增大，峰后加速破坏和强度剩余阶段可能会消失。

Abstract

[Objective] Silt from Xuzhou is widely dispersed. In order to comprehend its triaxial compression characteristics and offer a parameter foundation for engineering buildings, [Methods] the silt from Xuzhou Metro Line 1 was subjected to the standard triaxial compression test, in which the axial pressure was applied constantly until the soil was destroyed. The entire test procedure can be thought of as the applied load on the soil's work process. On this premise, the numerical simulation approach is applied to simulate the triaxial test process of Xuzhou silt. [Results] The results show that: With the increase of confining pressure, the peak strength and residual strength of silt increase linearly, and the deformation modulus shows a positive correlation trend; it shows shear failure under different confining pressures, and the rubber membrane distortion is more obvious under low confining pressure. All kinds of cracks gradually increase, the microcracks of the sample begin to increase sharply when the stress reaches the peak value, and the proportion of shear cracks gradually increases; at the initial stage of loading, the load work is almost completely converted into strain energy; during the whole process, the strain energy increases first and then decreases, while the friction energy and damping energy increase until the model is destroyed; the sum of strain energy, friction energy, and damping energy accounts for about 60% of the boundary energy, and the change with the axial strain growth rate is closely related to the stress-strain curve of silt. [Conclusion] The numerical simulation results are in excellent agreement with the laboratory test result. Shear cracks dominate the final failure of silt. According to the energy change, the failure mechanism of the triaxial compression process of silt is separated into three stages: pore compaction, elastic deformation, and plastic deformation before the peak value, and two stages: accelerated failure and strength residual after the peak value. However, with the increase of confining pressure, the post-peak accelerated failure and strength residual stage may disappear.

关键词

粉土 / 三轴压缩 / 离散元方法 / 微裂纹演化 / 能量演化 / 破坏阶段 / 数值模拟 / 影响因素

Key words

silt / triaxial compression / discrete element approach / microcrack evolution / energy evolution / failure stages / numerical simulation / influencing factors

基金资助

国家重点研发计划(2022YFC3003301)