冻融循环下砂岩动力特性及其破坏规律

Sandstones dynamic mechanical properties and failure characteristics under freeze-thaw cycles

冻融作用下岩石的动态力学特性研究对揭示岩石冻融损伤机理及寒区岩体工程冻融灾害防控具有很重要的意义,通过选取5组砂岩试样,按照-30～20℃的温度范围开展0、20、40、60和80次的冻融循环,并利用霍普金森压杆装置对冻融循环后的试样开展冲击气压为0.45 MPa的动态力学试验,从动态应力-应变曲线、动态强度、峰值应变和破坏形式等方面对冻融循环下砂岩的动力性特性和破坏规律进行研究。结果表明：砂岩的动力学性能随冻融次数的增加而降低,其主要的力学指标如动态弹性模量、动态强度及峰值应变均有所劣化;砂岩内部损伤随冻融次数的增加而累积,但累积速度不均匀,当冻融次数为40时,速度变缓,这一现象在砂岩饱水质量、孔隙度、强度和峰值应变曲线上都有体现;砂岩的破坏程度随冻融循环次数的增加而增加,当循环次数为0～40时,其破坏形式与未冻融时类似,以轴向的拉伸破坏为主;当循环次数为60和80时,试样碎块呈均匀细小化分布。

Dynamic properties study on rock under freeze-thaw cycles is meaningful for revealing the rock damage mechanism under freeze-thaw and preventing the freezing-thawing disaster of geotechnical engineering in cold regions. The freeze-thaw cycles experiments of 0, 20, 40, 60 and 80 times during -30 ℃ to 20 ℃ by five groups sandstone samples were made, and then, the SPHB was used to test the dynamic mechanical properties of sandstone samples under the constant impact load which is 0.45 MPa, the sandstones dynamic mechanical properties and failure characteristics were studied from the dynamic stress strain curves, dynamic strength, peak strain and failure modes. The results show that, as the freeze-thaw cycle increasing, the sandstones dynamic mechanical property decreases, the main mechanical indices, such as dynamic elasticity modulus, dynamic strength and peak strain, are degradation. The inner damage grows with the increasing of the freeze-thaw cycles times, but the growth rate is uneven, the growth rate slow down at 40 times freeze-thaw cycles and this phenomenon also reflects in indices, such as saturated mass, porosity, strength and peak strain. The damage degree of sandstone samples also increases with the increase of the freeze-thaw cycles times, and which is similar to none freeze-thaw, the dynamic damage mode is main tensile fracture by axial direction at 0-40 times cycles, and the fragments of samples are even and tiny at 60 and 80 times cycles.