结构性砂土静力触探试验离散元分析

Distinct element analysis of cone penetration tests in structured sand ground

为研究结构性砂土静力触探的宏微观力学特性,在10 g重力场中生成一个净砂地基;将一个考虑胶结厚度的微观胶结接触模型引入到净砂地基中以生成结构性砂土地基;用一定速率移动探杆以模拟结构性砂土中的静力触探过程,其中,探杆由4面刚性墙组成。结果表明,随着贯入深度的增加,锥尖贯入阻力逐渐增大,增长速度逐渐减慢,在达到临界深度后贯入阻力在某一定值附近波动;锥尖部位有明显的力链集中现象,力链的集中程度和范围会随着贯入深度的增加而逐渐提高和扩大;静力触探过程中,探杆两侧的土体经历了明显的加载和卸载过程,且土体主应力方向发生偏转;离探杆越远,主应力偏转速度越慢,最终偏转角越小;不同深度处平均纯转动率(APR)的变化趋势基本相同,而APR最大值会随着土体深度而逐渐增加;探杆的贯入会使土颗粒间胶结发生破坏,胶结的破坏形式主要有拉剪破坏和压剪破坏两种,而拉剪破坏数目要比压剪破坏数目多。

To study macro and micro mechanical properties of cone penetration tests in structured sand, a pure sand ground was prepared firstly under 10 g condition. Then, a bond contact model considering bond thickness was implemented into the pure sand ground to prepare the structured sand ground. A penetrometer composed of four sides of rigid walls was moving downward to simulate cone penetration tests in structured sand ground. The results showed that with the increase of penetration depth, the tip resistance increased gradually but the growth rate slowed down step by step. When the tip reached the critical depth, the tip resistance began fluctuating around a certain value. The contact force chain around the tip is very concentrated. With the increasing penetration depth, the concentrative degree of contact force chain increased gradually and the concentration range of contact force chain expanded gradually. In the process of penetration, the soil around the penetrometer underwent a significant loading and unloading process, and the principal stress direction took rotation. The farther away from the penetrometer, the slower rotation speed of the principal stress, and the smaller the final rotation angle. The averaged pure rotation rate（APR） at different depths changed in a qualitatively identical way, but the APR maximum values increased gradually with the depth of soil. The cone penetration breaks the bond between the soil particles. There are two main kinds of bond failure modes, tension-shear breakage and compression-shear breakage, and the number of tensile-shear breakage is much more than that of compression-shear breakage.