冻融循环对绿砂岩动态抗压性能影响的试验研究

Experimental Study on the Effect of Freeze-Thaw Cycles on the Dynamic Characteristics of Green Sandstone

  • 摘要: 冻融循环对岩石材料的性能有着至关重要的影响. 为研究冻融循环对绿砂岩物理及动态抗压强度特性的影响,对冻融0、25、50、75、100次的绿砂岩开展了应变率范围为55.98~151.84 s−1的动态压缩试验. 研究发现,随冻融循环次数增加,质量、纵波波速减小,孔隙率以及饱和吸水率增大. 50次冻融循环后绿砂岩内部损伤严重,饱和吸水率增速逐渐降低,穿晶裂纹及裂纹簇增多. 冻融次数对动态抗压强度起劣化作用,应变率对动态抗压强度起强化作用,两者影响机制相反,而冻融次数和应变率增加均会提高砂岩的破碎程度. 综合纵波波速和孔隙率建立冻融损伤因子,给出了考虑冻融损伤、应变率的动态抗压强度经验方程. 基于纵波波速、孔隙率分别建立的强度衰减模型均能够很好地反映动态抗压强度的劣化规律;动态抗压强度均随纵波波速变化量、孔隙率变化量增加而减小.

     

    Abstract: Freeze-thaw cycles have a crucial impact on the properties of rock materials. In order to study the effect of freeze-thaw cycles on the physical and dynamic compressive strength characteristics of green sandstone, a dynamic uniaxial compression test was conducted on freeze-thaw cycled green sandstone of 0, 25, 50, 75, and 100 cycles under 55.98 ~151.84 s−1 impact. It is found that with the increase of freeze-thaw cycles, the mass and P-wave velocity decreased, while the porosity and saturated water absorption increased. Green sandstone with over 50 freeze-thaw cycles had severe internal damage, and the saturation water absorption rate increase of green sandstone gradually decreased, and the number of crystal-piercing cracks and crack clusters increased. The number of freeze-thaw cycles and the strain rate had opposite effects on the dynamic compressive strength, while both the number of freeze-thaw cycles and the increase in strain rate increased the degree of sandstone fragmentation. The freeze-thaw damage factor was established by combining the longitudinal wave velocity and porosity and the dynamic compressive strength empirical equation, taking the freeze-thaw damage and the strain rate into account, was obtained. The strength attenuation models built on the P-wave velocity and porosity can reflect the degradation law of the dynamic compressive strength. The dynamic compressive strength decreases with the increase of the P-wave velocity and porosity.

     

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