冻融循环后红砂岩静动态劈裂拉伸性能对比分析

Comparative analysis of static and dynamic split tensile properties of red sandstone after freeze-thaw cycles

研究冻融循环作用后岩石的劈裂拉伸性能对分析寒区岩体稳定性具有重要的参考价值,以寒区典型的红砂岩为研究对象,对红砂岩开展了0、5、10、15、20次冻融循环试验,研究了冻融循环次数对红砂岩纵波波速、干密度和孔隙率的影响规律,采用岩石试验机和ø50 mm分离式Hopkinson压杆实验系统,进行了不同冻融循环次数后红砂岩试样的静、动态力学性能试验,分析了冻融循环次数对红砂岩静、动态强度、变形和破坏形态的影响,基于纵波波速的变化定义了红砂岩的冻融损伤度。研究结果表明:随着循环次数的增加,红砂岩内部裂隙不断扩展,矿物颗粒之间黏结力逐渐减弱,试件的纵波波速和干密度逐渐减小,而孔隙率和损伤度逐渐增大;红砂岩的静、动态劈裂拉伸强度随冻融次数的增加逐渐下降,而达到峰值应力所需的时间逐渐增加,20次冻融循环后,红砂岩试件的静、动态劈裂强度分别降低了41.88%和21.93%。相同冻融循环次数条件下,红砂岩试件的动态劈裂强度比静态劈裂强度提高了2.0~3.5倍。静态劈裂条件下,红砂岩试件呈中心劈裂破坏模式,与静态相比,试件的动态破碎形态在加载两端出现明显的压碎区域,且区域面积随循环次数的增加不断增大,破碎区的碎块尺寸逐渐减小。红砂岩内部的损伤度随循环次数的增加呈对数增大。

It's of great value to study on splitting tensile properties of rock after freeze-thaw cycles of rock mass in cold regions.The typical red sandstone in cold region was selected for testing,the freeze-thaw(F-T)cycle experiments with different numbers(0,5,10,15,and 20 times)were performed on red sandstone specimens,and the effects of F-T cycle number on the P-wave velocity,dry density,and porosity of red sandstone were studied in detail.In addition,both the static and dynamic mechanical properties of red sandstone specimens after different F-T cycles were tested by using rock testing machine andø50 mm split Hopkinson bar system,and the influence of F-T cycle number on the static and dynamic strength,deformation,and failure mode of red sandstone was systematically analyzed.F-T damage degree of red sandstone was defined based on the variation in P-wave velocity.Results show that with the increase of F-T number,the internal cracks of red sandstone continuously expand,bonding between mineral particles gradually decreases.Both the P-wave velocity and dry density of specimens gradually decrease,while the porosity and damage degree gradually increase.The static and dynamic splitting tensile strengths of red sandstone specimens gradually decrease with the increase of F-T number,while the time needed to reach the peak stress gradually increases.After 20 F-T cycles,the static and dynamic splitting strengths of red sandstone specimens decreased by 41.88%and 21.93%,respectively.Under the same F-T cycle number,the dynamic splitting strength of red sandstone specimens is increased by 2~3.5 times compared to the specimen under static loading.Under the static splitting condition,the red sandstone specimen exhibits the central splitting failure mode.However,an obvious crushed region at both ends of specimens was observed under dynamic loading.Additionally,with the increase of F-T number,the crushed area increases gradually,while the size of fragments gradually decreases.The damage degree of red sandstone increases logarithmically with the increase of F-T number.