Study On Physical And Mechanical Properties Of Rock After Thermal-cold Cycles

In view of the potential problems in relation to rock thermal-cold condition in underground engineering,laboratory experiments were conducted using granite and granodiorite as the samples.The change laws and the physical models are obtained of rock physical and mechanical properties with temperature and thermal-cold cycle.And the correlations among physical and mechanical properties are also anylized such as thermal conductivity – P-wave velocity,peak strain – P-wave velocity,tencile strength – thermal conductivity.At last,the distribution of temperature field in the process of rapid cooling of granodiorite in water is analyzed by numerical method.The results can provide theoretical and experimental support for the possible problems in geothermal development or tunnel fire rescue.The main contributions of this paper are as below.(1)It is the first time that systematically thermal-cold experiment for granite and granodiorite was conducted in the temperature range of 100~700 oC and in the cycle time range of 1~20.And it is also the first time that the systematic correlations of parameters such as thermal conductivity,P-wave velocity,porosity,uniaxial compressive strength and tensile strength was analyzed and the general laws in typical properties was obtained with the change in temperature and cycle time.The temperature and cycle time threshold are 450~500 oC and 3~5 times,respectively.(2)Physical and mechanical properties of granite and granodiorite change with temperature.Green-red component,yellow-blue component,porosity,the max strain in compaction stage and peak strain increase with the increase in temperature.P-wave velocity,thermal conductivity,total ringing counts,the max stress in compaction stage,peak stress,modulus of elasticity,tensile strength,and pry's coefficient decrease with the increase in temperature.(3)Physical and mechanical properties of granite and granodiorite change with thermal-cold cycle.the max strain and stress in compaction stage increase a little with the increase in thermal-cold cycle.P-wave velocity,thermal conductivity,total ringing counts,modulus of elasticity,peak stress and tensile strength decrease with the increase in thermal-cold cycle.The change laws of porosity with thermal-cold cycle are different at different temperatuers.And the decreases in P-wave velocity,thermal conductivity and tessile strength depend on temperature.(4)The relationships of stress-expansive rate in heating and rapid colling processes due to expansion or shrink were established for granite and granodirite,respectively.And the danmage mechanism was also analyzed for both twe racks.In heating process,scale damage in rock only takes place at the tempertures that exceeds 400 oC,while in rapid cooling process,rock scale damage appears at the temperature that is less than 300 oC due to the oversized shrink stress.The calculated results correspond to the experimental data well.