| In underground works such as underground coal gasification,nuclear waste treatment,and high temperature rock mass geothermal exploitation,the rocks are in relatively high temperature environments.The mechanical properties of rock are very different at high temperature and room temperature and have important influence on the stability of relevant underground engineering rock masses.In this paper,typical sedimentary rocks(sandstones),metamorphicrocks(marbles),and igneous rocks(granites)are selected.Using autonomously designed heating methods,the mechanical properties of rocks under high temperature conditions are studied.The conclusions are as follows:(1)The experimental methods of rock characteristics under real-time high temperature are initially established.The high temperature furnace and high temperature rock fixture of uniaxial compression,tensile,shear are self-designed.And temperature calibration is done.(2)Revealing the mechanical properties of sandstone under high temperature.Within 400°C,under real-time high temperature and after high temperature,the uniaxial compressive strength of sandstone decreases slowly with the increase of temperature,and the maximum reduction is quite,all less than 9%.After 400°C,with the increase of temperature,the uniaxial compressive strength of sandstone increases rapidly under real-time high temperature conditions,but the sandstone after high temperature has generally declined in strength.With the increase of temperature,the elastic modulus of sandstone gradually decreases under both conditions,and the sandstone decline under real-time high temperature is less than another.Under real-time high temperature conditions,with the increase of temperature,the tensile strength of sandstone tends to decrease.It decreases by nearly 50% at 200°C and reaches 81.27% at 800°C.At 200°C,the shear strength of sandstone decreased by 23.47% compared with that at room temperature.From 200°C to 800°C,with the increase of temperature,the shear strength of sandstone increased sharply.It increase was 9.02% at 200°C,and the increase was 87.82% at 800°C.(2)Revealing the mechanical properties of marble under high temperature.Within 400 ℃,under real-time high temperature and after high temperature,the uniaxial compressive strength of marble are gradually decreased with the increasing of temperature,and the descent range of after high temperature is bigger.Under real-time high temperature conditions,the uniaxial compressive strength of marble is greater at 400°C than at 600°C.After high temperature,the compressive strength of marble is greater at 600°C than at 400°C,but it is lower than the uniaxial compressive strength at room temperature.Under real-time high temperature conditions,the uniaxial compressive strength of marble is greater at 800°C than at 600°C.After high temperature,the compressive strength of marble is less at 800°C than at 600°C.With the increase of temperature,the elastic modulus of marble under both conditions decreases gradually.At 600°C,the drop under real-time temperature is greater than that after temperature,to 800°C,the decrease is significant.With the increase of temperature,the tensile strength of marble under the real-time high temperature conditions tends to decrease.At 200°C,the marble shear strength increases by 234.55% compared with that at room temperature.From 200°C to 600°C,with the increase of temperature,the shear strength of marble under real-time high temperature conditions decreases.Comparing with 600°C at 800°C,the increase rate is 141%.And the temperature point measured in the experiment increases compared with room temperature.(3)Revealing the mechanical properties of granite under high temperature.Under the effect of real-time high temperature and after high temperature,the change trends of the compressive strength and elastic modulus of granite are consistent,and both show a downward trend.With the increase of temperature,the tensile strength of granite under real-time high temperature conditions tends to decrease.At 200°C,the shear strength of granite increases by 81.18% compared with that at room temperature.From 200 to 800°C,with the increase of temperature,the shear strength of granite decreases at high temperature.(5)Revealing the Damage and failure mechanism of rock under the coupling effect of temperature and pressure.Under real-time high temperature,from room temperature to 400°C,the reason for the slight decrease of the strength of experimental sandstone is the increase of porosity.the sandstone undergoes a sintering reaction after 400°C,and the fine crystal grains gradually increase.On the one hand,the contact area between the crystals is increased,and on the other hand,the friction between the particles is increased and the strength is strengthened.Under real-time high temperature conditions,from room temperature to 600°C,the reason for the decrease of the strength of experimental marble is the increase of porosity.the strength of the experimental marble is increased from 600°C to 800°C.On the one hand,the ductility of the marble increases and the flowability increases.On the other hand,due to the mixture of calcium oxide and magnesium oxide,the decomposition of dolomite,for marbles with after temperatures,the internal porosity increases and the overall strength decreases with increasing temperature.After the high-temperature action of sandstone,the internal porosity increases,and the overall strength decreases.The reason that the tensile strength of three kinds of rocks under the of real-time high temperature and the compressive strength of the three kinds of rock after the high temperature shows a downward trend is that the porosity of the rock is increasing. |
