隧道石膏质围岩强度特性试验研究

Strength Behavior of Tunnel's Gypsiferous Surrounding Rock

以宜昌—巴东高速公路凉水井隧道出露的石膏质围岩为研究对象,开展了不同含水率、不同干湿循环下的石膏质岩单轴压缩试验,探讨其强度软化特性。利用微观电镜扫描石膏质岩遇水及干湿循环后微观结构,分析其强度劣化机理。结果表明:石膏质岩强度较低,属于软岩,强度及变形指标随含水率变化十分敏感,遇水软化特性显著,试样的抗压强度、弹性模量、变形模量都随着含水率的增大而降低,并与含水率呈现良好的函数关系,泊松比随着含水率的增大而近似呈现增大的趋势;干湿循环作用对石膏质岩力学性质劣化明显,抗压强度、弹性模量、变形模量随着干湿循环次数的增加而不断降低,并与干湿循环次数呈现良好的对数关系,泊松比随着干湿循环次数的增加而增大,但增幅有限;微观电镜图片显示水对石膏质岩结构破坏特征显著。石膏质岩的不良特性将对隧道建设产生不利影响,隧道施工中注意采取相应的防治措施。

In this article, gypsiferous surrounding rock exposed in Liangshuijing tunnel area of the Yichang-Badong expressway is taken as the research object by uniaxial compression test and scanning electron microscope test to explore the softening behavior and strength degradation mechanism of gypsum rock under different moisture contents and drying and wetting cycles. The research results indicate that the gypsum rock＇ s strength and deformation index are very sensitive to moisture content. It is soft rock with low compressive strength and has obvious softening char- acteristic in water, The mechanical parameters including uniaxial compressive strength, elastic modulus, and de- formation modulus reduce with the increase of moisture content in rock, displaying a good function relationship; whereas Poisson＇ s ratio approximately increases with the increase of moisture content. The drying and wetting cy- cles have an obvious effect on the degradation of gypsum rock＇ s mechanical properties. The uniaxial compressive strength, elastic modulus, and deformation modulus reduce with the increased times of drying and wetting cycles, showing a good logarithmic relationship ; while Poisson＇ s ratio increases slightly with the increased times of drying and wetting cycles. The microscanning images show that water is obviously destructive to the structure of gypsum rock. Corresponding prevention and control measures should be taken during the tunnel construction to prevent the adverse effects of bad characteristics of gypsum rock.