动三轴CT条件下粗粒土填料的力学特性与细观力学性能分析

Mechanical Properties and Meso Mechanical Performance Evaluation of Coarse-grained Soil Fillers Based on Dynamic Triaxial CT Test

在多重环境因素长期作用下,粗粒土路基填料的动力特性会发生改变,目前对不同荷载频率、压实度及含水率下粗粒土填料的长期稳定性能尚缺乏统一认识。为了研究以上因素作用下粗粒土填料长期动力特性,采用大型动静三轴仪器开展粗粒土填料的三轴试验,同时运用工业CT对三轴试验前后2个阶段的试样进行断层扫描,分析不同荷载频率、压实度及含水率对粗粒土填料动力特征与损伤演化的影响规律。研究结果表明:循环荷载达到1 000次之前,为粗粒土填料颗粒之间的挤密阶段,以颗粒间的挤密压缩为主,横向膨胀为辅,颗粒间压缩挤密引起的密度增加量远大于试样横向膨胀变形引起的密度减小量;当循环荷载增加到1 000次以后,试样横向变形引起的密度减小量迅速增大,而由颗粒间压缩挤密引起的密度增加量减缓,并在之后阶段表现出稳定状态,试样从应变软化型向应变硬化型转变;荷载频率越高,试样表现出的回弹模量越大;高频率作用下应力-应变滞回圈曲线近似为线性,试样在高频率下其泊松比有所下降,材料的动能损耗降低;随着三轴试验的进行,横剖面局部颗粒受挤压程度增加,最终状态下扫描层内的CT值存在差异性,试样颗粒在循环荷载作用下存在挤密、错动、融合的现象。

The dynamic characteristics of coarse-grained soil subgrade fillers change under long-term multiple environmental factors. At present, there is a lack of clear understanding on the long-term stability of coarse-grained soil fillers under different loading frequencies, compaction degrees, and moisture content. To study the long-term dynamic characteristics of subgrade-based coarse-grained fillers under these conditions, a large-scale static and dynamic triaxial equipment was used to conduct triaxial tests of coarse-grained soil. Simultaneously, industrial CT triaxial tests were performed before and after the two stages of the specimen tomography. The dynamic characteristics and damage evolution of coarse graded embankment were analyzed under different loading frequencies, compaction degrees, and water cuts. Results indicate that, before the cyclic load is amplified by a factor of 1 000, the compaction of soil particles between the coarse stages, compaction to main compression between particles, and lateral expansion via supplementary stages, the increase in the density caused by the compressive compaction between the particles is much larger than the decrease in the density caused by the expansive deformation of the sample. When the cyclic load increases to 1 000 times, the decrease in the density caused by the transverse deformation of the specimen increases rapidly, the increase in density due to inter-particle compression slows down and reaches a steady state at a later stage. The specimen changes from strain softening to strain hardening. The higher the load frequency, the greater the modulus of resilience of the specimen is; the stress-strain hysteresis curve remains approximately linear under high frequency, indicating a decrease in the Poisson’s ratio of the sample material at high frequency and reduction of the kinetic energy loss of the material. After the triaxial tests, the cross sections of the local particles are squeezed to increase the degree, the CT values and damage variable in the scanning layer are different in the final state, and the particles of the specimens demonstrate compaction, dislocation, and fusion under the action of cyclic loading.