Dynamic Mechanical Properties Of Sandstone With Different Ice Saturation At Sub-zero Temperature

In cold regions,different ice saturation has a great impact on the changes of mechanical properties of sandstone,especially when subjected to dynamic disturbance.Therefore,understanding the variation law of dynamic mechanical properties of sandstone under different ice saturation is of great significance to engineering practice.To study the mechanical properties of sandstones,especially the variation law of mechanical properties such as dynamic peak strength and elastic modulus,SHPB impact experiments are carried out to deeply analyze the mechanical properties of a variety of sandstones with varying ice saturation.The main research contents and conclusions of this paper are as follows:（1）Using nuclear magnetic resonance technology to accurately measure the different ice saturation of sandstone,and conduct SHPB dynamic compression test to analyze the dynamic mechanical properties of sandstone with different ice saturation at low temperature;The experimental results show that the dynamic mechanical strength of sandstone increases with the temperature decreasing from 0℃to-20℃;When the temperature decreasing from-20℃to-30℃,the dynamic mechanical strength of sandstone reaches the peak;When the temperature drops to-30℃,the dynamic mechanical strength of sandstone decreases.（2）For dry and fully saturated sandstone,the mechanical strength increases first and then decreases as the temperature decreases from normal temperature to-40℃,and the downward trend is obvious at-40℃;For unsaturated sandstone,the mechanical strength increases with the decrease of temperature,and the lower the saturation is,the more obvious the enhancement effect is;（3）It can be seen from the variation diagram of dynamic elastic modulus and strength damage factor that different sandstones are greatly affected by different ice saturation.Among them,low porosity sandstones are less affected by temperature and higher by different ice content,while high porosity sandstones are affected by both temperature and ice content.（4）Dynamic impact tests with different strain rates(range 110～190s^-1)were carried out on dry and saturated sandstone at low temperature and normal temperature to study the effect of strain rate on the mechanical strength of sandstone at different temperatures;The results show that sub-zero temperature can improve the dynamic compressive strength and elastic modulus of sandstone.Furthermore,the strength increases with the increase of strain rate.The strain rate dependency of saturated unfrozen samples is the highest,followed by saturated frozen samples,dry unfrozen samples,and dry frozen samples.（5）The change mechanism of mechanical properties of sandstones with different ice saturation under dynamic loading is discussed,and the difference is explained.The change of dynamic strength of sandstone with different ice saturation is affected by many factors.In the temperature range such as normal temperature or 0℃,the effect of low temperature on sandstone is still very small.Therefore,in this temperature range,the change of sandstone strength is still controlled by internal free water,and its weakening by water is the main reason for its strength change;When the ambient temperature drops further,the dynamic peak strength and dynamic elastic modulus of sandstone are increasing,which is mainly due to the joint influence of the shrinkage and compaction of mineral particles,the support and bonding effect of porous ice and so on;However,when the temperature decreases further,the sandstone mineral particles will deform greatly.The intergranular cracking of mineral particles caused by the uncoordinated deformation of mineral particles and the huge frost heaving force generated in the sandstone under hydrothermal migration are the main reasons for the internal damage of sandstone.