鄂西北页岩饱水软化微观机制与力学特性研究

Softening micro-mechanism and mechanical properties of water-saturated shale in Northwestern Hubei

针对鄂西北页岩隧道施工中存在的地下水加剧软岩隧道大变形问题,进行页岩饱水软化的微观机制与力学特性研究。通过开展X射线衍射、自然吸水试验和SEM电镜扫描,探索不同饱水时间条件下页岩吸水率和微观结构的变化;进而通过开展单轴压缩试验,分析页岩强度和变形参数随其饱水时间的演化规律。试验结果显示,页岩吸水率随着饱水时间的增加呈对数规律增长,页岩饱水后峰值抗压强度和弹性模量均随着饱水时间的增加呈负对数规律降低;页岩力学性质在饱水20 d内变化迅速,50 d后趋于稳定。同时,随着饱水时间的增加,页岩中绿泥石和白云母矿物遇水产生膨胀,使片层状结构分散剥离出细小矿物颗粒,并产生大量松散多孔的絮状物;由于水化作用的影响,页岩原有的致密层状结构变得松散破碎,矿物颗粒之间的胶结逐步破坏,孔隙、裂隙增多,宏观上表现为页岩强度降低,抵抗变形能力减弱,破裂面更为密集,且贯通性增强。

To resolve the problem of large deformation of tunnel in shale caused by groundwater during construction in Northwestem Hubei, softening microscopic mechanisms and mechanical properties of water-saturated shale were investigated. At different water-saturated times, the water absorption and microstructure characteristics of shale were examined using X-ray diffraction, natural water absorption experiments and scanning electron microscope （SEM）. Then evolution laws of strength and deformation parameters under different water-saturated times were analyzed by uniaxial compression tests. Experimental results show that, with the increase of saturation time, the water absorption of shale increased logarithmically, but the peak compressive strength and elastic modulus of shale decreased logarithmically. It is found that mechanical properties of shale changed rapidly within 20 days until stabilized after 50 days. As the chlorite and muscovite minerals in shale expand with the water, with increasing saturation time, the fine mineral particles were gradually stripped from the dispersed the lamellar structure. As a result, a large number of loose, porous flocs were produced. Due to the effect of hydration, the compact layer microstructure of shale became loose, and cementation among mineral particles was destroyed gradually, resulting in the growth of pores and cracks. Finally, the strength of shale and the ability to resist deformation were decreased, and the fracture surface became dense and interconnected.