Experimental Study On Mechanical Properties And Constitutive Model Parameters Of Artificially Frozen Jurassic Sandstone

With the continuous progress of China's socialism and the continuous acceleration of economic construction,our demand for coal energy is also increasing,and the coal resources in the central and eastern regions of China are also exhausting.Therefore,the state has proposed a strategy for the development of the western region and re-enactment.The strategic layout of energy in the new situation.Different from the central and eastern mining areas,the mine construction in the western part of China mostly passes through the thick-water Cretaceous and Jurassic deep-buried coal-bearing water-rich strata,which are mostly constructed by freezing method,but the rock formation of this series has a late diagenesis time and poor cementation.The shear strength is low and it is easy to weather,and it is easy to soften and disintegrate when it meets water,which brings many difficulties for the construction of western mines.However,the experimental research and related theoretical analysis of the physical and mechanical properties of weakly cemented rocks such as Jurassic and Cretaceous are not comprehensive enough at home and abroad.Therefore,the experimental study on the mechanical properties and strength criteria of artificially frozen Jurassic sandstone is important for the construction of western mines.This paper is based on the construction of the Balasu mine in Yulin City,Shaanxi Province,this paper takes the Jurassic Zhiluo Formation rock as the research object,and uses the electronically controlled servo hydraulic rock triaxial apparatus,nuclear magnetic resonance instrument and electron microscope scanning to explore the physical and mechanical properties of the Jurassic sandstone under low temperature conditions,and further studied the damage constitutive model of Jurassic sandstone.The specific work and results are as follows.Through the single-and tri-axial compression tests of sandstones at different temperatures in the Jurassic,the stress-strain curves of the whole process of rock compression deformation are obtained.Under the same confining pressure,the compressive strength of Jurassic sandstones is frozen.The temperature decreases and increases continuously,but as the freezing temperature decreases,the increase in compressive strength decreases continuously,and the quadratic curve rises.The relationship is:P(28)-.01198T~2(10)18.564.In addition,as the temperature decreases,the strain value of the rock compaction stage also decreases,but the elastic modulus of the elastic compression stage continues to increase;under the same temperature conditions,as the confining pressure increases,The compressive strength of rock is also increasing,and it has a clear linear relationship.The linear parameters will be different when the temperature is different.Similarly,as the confining pressure increases,the strain value of the rock compaction stage decreases,and the elastic modulus of the elastic compression stage increases continuously.The nuclear magnetic resonance technique is used to determine the porosity of rock.The porosity of rock decreases with the decrease of temperature,but the decrease of porosity decreases with the decrease of temperature.The frozen porosity and temperature of rock also become The relationship of quadratic linear relationship is:y)82(-0.0355T~2-.08812T(10).46187.And there is a significant similarity with the change law of rock compressive strength with temperature.It is found that the compressive strength of rock increases exponentially with the increase of frozen porosity.Based on the Coulomb's failure criterion,the mechanical parameters of the rock are obtained.It is found that the internal friction angle of the sandstone in the Jurassic system increases continuously with the decrease of temperature,but with the further decrease of temperature,the increase tends to be gentle.And the rock cohesion also increases with the decrease of temperature,but gradually becomes stable and even decreases a little.Finally,the rock damage softening model based on Weibull distribution is deduced.The model can well reflect the whole process of compression deformation of Jurassic rocks under complex stress state,especially the post-peak softening of rock.By considering the extreme value of the stress-strain curve in the process of compression deformation and combining the strain softening after the rock peak,the model parameters F and m are solved by numerical analysis.The analysis shows that with the decrease of temperature,the parameter m value is overall.The trend is decreasing,while the F value is generally increasing.