不同含水率冻融后红砂岩剪切蠕变特性

针对高海拔地区岩体在冻融作用及含水状态下的劣化特征及长期稳定性,对不同含水率红砂岩进行了冻融后核磁共振检测及剪切蠕变试验,揭示了冻融循环及含水率变化对红砂岩细观结构及蠕变特性的影响机制,据此构建合理的剪切蠕变模型。研究结果表明:在冻融作用下,饱水红砂岩呈现出由小尺寸孔隙增长向中小尺寸孔隙共同增长的趋势,而饱和红砂岩主要以中、大孔隙增长为主。在长期荷载作用下,随着含水率的增加,冻融后红砂岩的蠕变量普遍增大,而长期强度及长期折减系数显著降低,破坏前试样更易出现加速蠕变特征,破坏后试样宏观形态更为碎裂。根据红砂岩的冻融损伤及时效性损伤效应,建立了红砂岩冻融剪切蠕变模型,并对模型进行了参数优化辨识,借此验证了模型的正确性及合理性。研究结果对于冻融岩质灾害的防控和评价具有参考价值。

Shear creep characteristics of red sandstone after freeze-thaw with different water contents

According to the deterioration characteristics and long-term stability of rock mass in high altitude under the action of freeze-thaw and in water-saturated state, the nuclear magnetic resonance(NMR) technique is used to test the red sandstone samples subjected to freeze-thaw cycles under different water contents, and the shear creep experiments are conducted. Based on the experimental phenomena, the effects of freeze-thaw cycles and water content on the microstructure and creep characteristics of red sandstone are analyzed, and a reasonable creep model is proposed. The results show that the microstructure of wet red sandstone evolves from the main increase of small-size pore to the mutual increase of small-size pore and mesopore with the increasing freeze-thaw cycles, while the mesopore and macropore propagate mainly inside the saturated red sandstone. With the increase of water content, the creep strain of red sandstone generally increases, while the long-term strength and long-term reduction coefficient decrease significantly, the accelerated creep characteristics of red sandstone appear more easily before rock failure, and the macroscopic modes become more fragmented after rock failure. Considering the effects of freeze-thaw damage and time-dependent damage, a new shear creep model for red sandstone subjected to freeze-thaw cycles is established. The parameters of the model are identified by applying the 1 stOpt mathematical analysis software, and the correctness and rationality of the model are verified. The research results have reference value for the prevention and evaluation of rock disasters in cold regions.