含水率对红层泥岩填料刚度劣化特性及微观结构影响研究

Effect of water content on stiffness degradation and microstructure of red mudstone fill material

为研究含水率对红层泥岩填料刚度劣化规律和微观结构的影响,开展了不同含水率下三轴不排水剪切试验、压汞试验和扫描电镜试验,基于能量守恒定律推导了填料刚度劣化与弹塑性应变能增量间的关系。结果表明:填料黏聚力随含水率增加而降低,内摩擦角则随含水率增加先增加后降低。填料结构损伤由应变能转化引起,从宏观上表现为刚度劣化。归一化刚度比值随塑性应变能增量占比增加而线性降低,随应力发展呈非线性衰减。以最优含水率为界,当试样在干侧时,填料有较好的荷载抵抗能力;湿侧填料荷载抵抗能力远低于干侧。损伤应力等值线与等含水率线构成上下界为对数曲线的状态面。填料孔隙分布在干侧为单峰形态,粒间接触较为紧密,结构稳定性好。在湿侧呈双峰结构,团聚体排列定向性程度较低。填料应在干侧压实填筑,推荐采用5%~7%作为填筑目标含水率。

A series of undrained triaxial shear tests,mercury intrusion porosimetry(MIP)tests,and scanning electron microscopy(SEM)tests were conducted on red mudstone fill material(RMF)at varying water contents to investigate its microstructure and stiffness degradation.Based on the principle of energy conservation,a relationship between the stiffness degradation of the fill material and the increment of elastoplastic strain energy was derived.The results show that the cohesion of RMF decreases with increased water content,while the internal friction angle initially increases and then decreases on the wet side.The evolution of strain energy leads to structural damage and subsequent stiffness degradation.The normalized stiffness ratio linearly decreases with the ratio of plastic strain energy to total strain energy and nonlinearly decreases with normalized shear stress.With optimal water content as the boundary,the RMF exhibits better load-bearing capacity on the dry side,while significantly lower on the wet side.The contours of damage stress and constant water content lines define a state boundary surface,whose upper and lower bounds follow logarithmic curves.The pore size distribution(PSD)of RMF on the dry side exhibits a uni-modal pattern with strong inter-aggregate contacts and good structural stability.On the wet side,however,a bi-modal structure is observed with weaker orientation of aggregates.It is recommended that the fill material be compacted on the dry side,with a target water content ranging from 5%to 7%.