Influence of freeze-thaw cycles on dynamic compressive strength and energy distribution of soft rock specimen

冻融循环对软岩试件动态抗压强度与能量分布的影响

Cold Regions Science and Technology, Volume 153, September 2018, Pages 10-17

Qinyong Ma, Dongdong Ma, Zhaoming Yao

摘要：The effect of freeze-thaw cycles on the dynamic uniaxial compressive strength and energy distribution parameters including the specific energy absorbency rate (ES), energy reflectivity (ER) and energy transmitted rate (ET) are experimentally investigated in this research. The dynamic compression tests on two kinds of soft rock (i.e., sandy mudstone and mudstone) after different freeze-thaw cycles (i.e., 0, 3, 6, 9, 12, and 15 times) have been carried out with splitting Hopkinson pressure bar setup. In addition, the dynamic freeze-thaw damage coefficient (Kdf) and freeze-thaw damage variable (D) are defined. The experimental results show that the dynamic uniaxial compressive strength decreases logarithmically with increasing number of freeze-thaw cycles. The dynamic freeze-thaw damage coefficient (Kdf) of mudstone is larger than that of sandy mudstone at the same freeze-thaw cycles. All these energy distribution parameters are significantly influenced by the freeze-thaw cycles. There has a negative linear correlation between dynamic uniaxial compressive strength and freeze-thaw damage variable (D).

Experimental investigations on the effects of ambient freeze-thaw cycling on dynamic properties and rock pore structure deterioration of sandstone  

冻融循环环境对砂岩动态特性与孔隙结构劣化影响的实验研究

Cold Regions Science and Technology, Volume 154, October 2018, Pages 133-141

Jielin Li, Rennie B. Kaunda, Keping Zhou

摘要：The issue of rock pore structure deterioration and dynamical mechanical properties has drawn much attention in recent years in the rock engineering community. In this study, a series of 140 freeze-thaw cycling tests are conducted on sandstone samples. The sandstone pore structure after freeze-thaw cycles was detected by Nuclear Magnetic Resonance (NMR), and the dynamic load test was carried out by Split Hopkinson Pressure Bar system (SHPB). The results are: with the increase of freeze-thaw cycles, the saturated mass and porosity of sandstone increase, the dynamic peak stress of sandstone decreases; while the peak strain and total strain increase gradually, and the macroscopic damages of rocks increase. The results of T2 distribution and pore size changes are that the pore sizes of sandstones increase, especially that of micro-pores and macro-pores increase obviously after 140 freeze-thaw cycles. Under the effect of freeze-thaw cycles, the sandstone pores become connected with each other, some of the micro-pores and mini-pores are changed into meso-pores and macro-pores. The number of marco-pores increases evidently, and the largest increase is 197.23%. The rock pore structures have changed, which would lead to the change of mechanic properties. As the number of freeze-thaw cycles increases, the rock dynamical peak stress gradually decreases and the peak strain and the overall strain increase gradually.

Effect of freeze-thaw cycles on shear strength of saline soil  

冻融循环对盐渍土剪切强度的影响

Cold Regions Science and Technology, Volume 154, October 2018, Pages 42-53

Yan Han, Qing Wang, Ning Wang, Jiaqi Wang, Yuanyuan Kong

摘要：Freeze-thaw (F-T) cycle is an important external factor affecting the mechanical properties of saline soils in cold regions. In this study, the effects of F-T cycles (0, 1, 5, 10, 30, 60 and 120) and salt contents (0, 0.5, 1.0, 2.0 and 3.0%) on the shear properties of saline soil in western Jilin Province of northeastern China, including stress-strain behavior, peak undrained shear strength (τu), resilient modulus (ER), cohesion (cu) and internal friction angle (φu), were investigated by conducting unconsolidated-undrained (UU) triaxial compression tests. The results demonstrated that, when the salt content was the same, the τu, ER and cu basically showed a decreasing-steady-decreasing trend with increasing F-T cycles, and the dynamic evolutions of soil microstructure were mainly responsible for such variations. The Gouy-Chapman diffuse double layer together with matrix suction theories were employed to analyze the mechanism of the effects of salt content on the cu and φu at different freeze-thaw cycles; the thicker diffuse double layer induced by higher sodium ion contents and the decreasing matrix suction were deemed as the main reasons that led the cu to continuous reduction; the φu was believed to be successively affected by the enhanced lubrication effect and the salt crystallization process, and there was a threshold salt content (2.0%) which was influenced by the number of F-T cycles. Finally, by categorizing the different experimental combinations into relative undamaged, single-factor damaged and two-factor damaged states concerning the τu, an empirical mathematical equation of high reliability (R2 > 0.985) was established to describe the combining effects of F-T and salinity on the changes in τu.