| The engineering rock mass is usually in a state of three-way compression.The tunneling of underground mines and underground energy drilling and mining construction can be regarded as excavation and unloading,which will unload the compressive stress in one direction to zero,resulting in redistribution of the in-situ stress,making the direction of the compressive stress redistributed.The stress gradually transforms into tensile stress,and finally produces obvious tensile deformation in the radial direction.At this time,the engineering rock mass is subjected to the dual action of compressive stress and tensile stress,that is,it is in a state of compressive-tension coupling.In addition,underground engineering is often adversely affected by high temperatures and groundwater.Therefore,it is particularly important to carry out experimental research on the influence of temperature and water content on the mechanical properties of rock in the compression-tension coupling state,to grasp the influence of temperature and water,and to propose safe and reliable prevention and control measures.In this paper,the red sandstone type I sample is taken as the research object,and the mechanical properties of red sandstone at different temperatures and different water contents in the compression-tension coupling are explored from the macroscopic and microscopic perspectives.The main contents and results of this paper are as follows:(1)Based on MTS815 rock mechanical test system,combined with the compression tensile stress conversion device developed by the research group,the "I" type red sandstone sample is taken as the research object to study the mechanical properties of red sandstone under different temperature and water content under the compression tensile coupling state.(2)In the compression-tension coupling experiment,the fracture of the I-type red sandstone specimen occurred in the middle of the specimen under,and the full stress-strain curve is a smooth and complete upward convex curve,which can be divided into three stages.That is,the elastic stage,the yield stage and the failure stage,in which the yield point occurs when the tensile stress is about 7MPa,and the failure stage is instantaneous fracture,which is manifested as obvious brittle failure.(3)Due to the softening effect of water on rock,the tensile strength of red sandstone decreases gradually with the increase of water content,and the reduction range also increases gradually.The axial limit strain increases continuously with the increase of water content,and the elastic modulus shows a downward trend.This shows that the increase of water content will reduce the brittleness and enhance the plasticity of red sandstone.(4)There are obvious differences in the performance of red sandstone after treatment at different temperatures.The mechanical properties of red sandstone are slightly strengthened after treatment at200 °C,and the mechanical properties are deteriorated after treatment at500 °C and 800 °C.There is a good corresponding relationship,the elastic modulus shows a decreasing trend with the increase of temperature,while the axial ultimate strain shows a change trend of increasingdecreasing-increasing again.(5)The existence of water weakens the cohesion between the mineral grains contained in red sandstone.Under the action of confining pressure,pore water pressure will also be generated to shear the mineral grains,resulting in internal damage.(6)On the one hand,the high temperature causes the internal moisture of the sample to lose,resulting in a continuous decrease in the quality of the sample,and on the other hand,the mineral particles expand due to the heat.When the temperature is low,moderate expansion squeezes the original fracture to enhance its mechanical properties.After the temperature rises,the red sandstone will undergo excessive expansion,grain melting,and further water loss,which will lead to changes in microstructure and deterioration of mechanical properties. |
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