Dynamic Mechanical Properties Of Low Temperature Damaged Sandstone Under Different Water Content

Many large open-pit coal mines in China are located in the western alpine regions such as Xinjiang.Under the action of low temperature freezing,the internal microstructure and macroscopic mechanical properties of the rock mass with waterbearing damage on the slope will change significantly.In the process of open-pit mining,it also bears the dynamic load such as blasting impact,which leads to geological disasters such as landslides.Therefore,it is of great practical significance to study the low temperature dynamic mechanical properties of damaged sandstone under different moisture contents for ensuring the slope stability and safe and efficient mining of openpit coal mines in alpine regions.In this thesis,The Real-time Low Temperature Split Hopkinson Pressure Bar(LT-SHPB)test system was used to carry out dynamic compression tests on frozen sandstone with different moisture contents.Combined with Scanning Electron Microscopy(SEM)technology and energy dissipation theory,the dynamic mechanical properties,dynamic failure characteristics and energy dissipation law of frozen sandstone were systematically studied.Finally,based on the experimental results,the damage statistical constitutive model of sandstone under initial damagedynamic and static load was established,and its rationality was verified.The main research results are as follows.(1)The uniaxial compression tests of sandstone with different damage values were carried out.It is found that with the increase of damage value,the peak stress and elastic modulus of sandstone decrease significantly,and the peak strain increases.The failure mode changes from tensile failure to shear failure,and the number of broken fragments increases gradually.(2)The real-time low temperature dynamic compression test of sandstone with different moisture contents and damage value was carried out.It is found that the dynamic peak stress and elastic modulus of frozen sandstone decrease significantly with the increase of damage value under different moisture content,and the dynamic peak strain increases significantly.The rock sample size decreases significantly and the average particle size decreases after failure.With the increase of impact velocity,the dynamic peak stress,elastic modulus and peak strain increase gradually,and the fracture morphology changes from block like powder particles,and the average particle size decreases.(3)Based on the energy dissipation theory,it is found that with the increase of damage value,the incident energy and reflection energy of frozen sandstone are basically unchanged,the transmission energy decreases,the dissipation energy increases,the reflection energy ratio is basically unchanged,the transmission energy ratio decreases,and the dissipation energy ratio increases;with the increase of impact velocity,the incident energy,reflection energy,transmission energy and dissipation energy increase,but the reflection energy ratio and dissipation energy ratio increase,and the transmission energy ratio decreases.(4)The microscopic failure characteristics of sandstone were observed by the Scanning Electron Microscope.The failure mode of frozen sandstone is mainly brittle failure,but with the increase of damage value,the internal ductile fracture characteristics will appear.(5)The damage statistical constitutive model of sandstone under dynamic and static load is established.The theoretical calculation results of stress-strain curve are in good agreement with the experimental results,which verifies the correctness of the constitutive model.The research results of this thesis can provide a theoretical basis for the prevention and control of slope rock mass instability in the process of open-pit coal mining in cold regions,and also have guiding significance for the construction of rock engineering in cold regions.There are 60 figures,11 tables and 101 references.