高填方地基强夯处理的颗粒流模拟及其横观各向同性性质

Particle flow simulations of the compaction of filling materials in highly filled foundation with analyses of the transverse isotropy

山区机场高填方地基一般采用强夯施工填筑而成,其填料通常为土石混合料。其中碎石料往往由爆破开采得到,其形状不规则,而土料的加入使其密实特性与纯碎石料又有所不同。针对高填方地基的上述特点,该文对长条形碎石颗粒采用颗粒流软件PFC3D进行土石混合料地基的强夯模拟。为研究颗粒形状和细粒含量对强夯效果的影响,同时建立了椭球形颗粒模型和球形颗粒模型作为对比模型。首先研究了强夯冲击荷载作用下的重锤响应及地基内部动应力的分布和变化规律,并给出了强夯过程中的夯沉量和孔隙比的变化,采用孔隙比变化量表征强夯效果。其次对强夯前后地基土取样进行不同大主应力方向的三轴剪切实验模拟,对比强夯前后土体性质,并统计了三维组构参数来研究强夯后土体的横观各向同性性质。结果表明:长条形颗粒的土石混合料强夯密实效果最显著;长条形碎石地基经强夯后呈现明显的横观各向同性性质,竖直方向较水平方向模量及峰值强度明显要大,而采用球形颗粒时土体保持各向同性。该文可对进一步研究强夯下高填方填料的横观各向同性本构模型提供有益的参考。

Compaction is widely used in the construction of highly filled foundations with the filling material composed of a mixture of broken rock and soil. The roekfill usually comes from explosion and, thus, has irregular shapes. In addition, with the soil, the response of the broken rock-soil mixture during compaction differs from that of pure rockfill. This study simulates the compaction of highly filled foundations filled with broken rock-soil mixtures using the particle flow software PFC3D with the particles assumed to be elongated. Two other with pure rockfill with and without elongated rockfill particles were used to investigate the influence of particle shape and fine soil grains. The tamper response and the dynamic stress distribution in the soil were carefully studied and verified by field tests. The void ratio and the settling ratio predictions by the three models and the void ratio reduction are used to evaluate the models. Then, samples taken from foundations and triaxial tests are simulated with different orientation angles of the major principal stress to compare the soil properties before and after compaction. Finally, a static model is used to analyze the three-dimensional mesoscopic fabric to study the transverse isotropy of the soils after compaction. The results indicate that the broken rock-soil mixture with elongated roekfill particles is the best among the three models and that the soil behavior with elongated rockfill particles is cross-anisotropic after compaction with a larger modulus and higher peak strength in the vertical direction than in the horizontal direction. The soil simulations with spherical particles show that soil remains isotropic after compaction.