Experiment Study On Freezing-thawing Damage Mechanism Of Rock Under The Condition Of Coupling Of Multiple Factors

The research of rock freezing-thawing cycles is becoming a hotspot of rock mechanics due to its cold regions engineering background. As it is the direct guidance of mining development and other engineering projects for analysis and prevention of freezing-thawing disaster in high altitude cold regions, Experiment study on freezing-thawing damage mechanism of rock under the condition of Coupling of multiple factors has important theoretical and practical significance.In the paper, sandstone as the research object. Freezing-thawing test of rock experienced loading and unloading and freezing-thawing test of rock placed in different chemical solution environments were designed and completed. Experimental mechanics and nuclear magnetic resonance test were comprehensively used to observe and analyze physical and mechanical properties and internal microstructure changes of freezing-thawing rock. And the damage mechanism of rock under the condition of Coupling of multiple factors include freezing-thawing cycles was studied based on the test results.The main results are as follows:(1) The mass, overall shape and Poisson’s ratio of rock experienced loading and unloading was no significant change after freezing-thawing cycles0-135times. Rock uniaxial compression strength decreased slightly with the increase of freezing-thawing cycles. Elastic modulus of specimen decreased with the increases of unloading point. Specimen brittle has been enhanced due to freezing-thawing cycles.(2) Chemical environment has a large influence on rock damage, the mass and tensile strength of rock placed in different chemical solution environments significantly reduced with the increase of freezing-thawing cycles. Specimens surface appeared flaking and swap blocks at different degree.(3) The porosity of yellow sandstone specimen showed a general slowly rising trend with the increase of freezing-thawing cycles. The rock internal damage modes are that small size pores were generated rapidly in the early stage and subsequent slow expansion. Rock loading and unloading operation has no marked effect to freezing-thawing damage pattern and evolution of the pore structure of specimen.(4) The porosity of red sandstone specimen showed a general linearly increasing trend with the increase of freezing-thawing cycles. The pore expansion of specimen has been significantly accelerated by Chemical solution. The rock internal damage modes are that native small pores expand rapidly to large-size pores in the early stage, subsequent new small pores were generated and expanded rapidly until the collapse of destruction of the large pores.The results show that the freezing-thawing damage mechanism of large aperture uniform porous rock is in line with hydrostatic pressure theory and the freezing-thawing damage mechanism of non-uniform small aperture porous rock is in line with osmotic pressure theory. Therefore, different pore structure of rock material is an important reason to explain the difference in the mechanisms of freezing-thawing damage.