Mechanical Properties Of Tunnel Fractured Rock Mass Under Thermodynamic Coupling

Natural rocks are not homogeneous bodies.After a long geological time,under various external loads such as mechanics and heat,defects such as faults and fissures will occur inside rocks,and these defects are the inductive factors for common geological engineering accidents.Previous scholars in the study of fractured rock mass,the author of this paper the shortage of consensus and in sichuan-tibet highway She Duo Shan deep buried tunnel rock as the prototype,from the perspective of the similarity theory,choose high strength cement mortar materials for similar materials,and in which precast single fissure cylinder standard specimen,through different angles by uniaxial compression test and conventional triaxial compression test data as the foundation,Establish PFC numerical model;The systematic simulation of thermodynamically coupled uniaxial compression and conventional triaxial loading and unloading tests was carried out to study the relationship between the failure modes of fractured rock mass and its mechanical properties under the action of temperature,and to discuss the law of fracture expansion and the influence of thermodynamically coupled on the failure modes of fractured rock mass.Finally,the influence of rock burst on fractured rock mass in tunnel under thermodynamic coupling is analyzed.The main research results of this paper are as follows:(1)The basic mechanical characteristics of rock mass with prefabricated fractures are mainly affected by the dip Angle of prefabricated fractures.Under uniaxial compression,triaxial compression and triaxial unloading confining pressure,the peak strength of rock mass with prefabricated fractures is all lower than that of intact rock samples.The peak strength increases with the increase of the dip Angle of the prefabricated crack.The presence of the prefabricated crack has the greatest influence on the peak strength of the 0° dip Angle and the lowest compressive strength.The maximum compressive strength and peak strain of axial stress-strain curve are most close to those of intact rock mass samples.(2)The basic mechanical characteristics of rock mass with prefabricated fractures are mainly affected by the dip Angle of prefabricated fractures.Under uniaxial compression,triaxial compression and triaxial unloading confining pressure,the peak strength of rock mass with prefabricated fractures is all lower than that of intact rock samples.Specifically,the peak strength increases with the increase of the dip Angle of the prefabricated crack.The presence of the prefabricated crack has the greatest influence on the peak strength of the 0° dip Angle,and its compressive strength is the lowest.When the inclination Angle is 90°,the influence is the least,and the stress-strain curve is the closest to that of the intact rock mass sample.(3)In the range of 20℃ to 80℃,the increase of temperature increases the brittleness of rock mass to some extent,which shows that the peak compressive strength decreases and the failure trend is advanced with the increase of temperature.The increase of the length of the prefabricated fracture has a certain tendency to promote the failure of the rock-like model,which reduces the compressive strength of the rock mass,and has the greatest effect on the 0° dip Angle model.The effect decreases with the increase of the dip Angle of the prefabricated fracture.(4)In triaxial compression test and triaxial unloading confining pressure test in the process,as a result of the existence of confining pressure,the uniaxial compression to the class when the rock sample produce certain influence to the formation of micro cracks,concrete manifestation is: with the increase of confining pressure,can effectively prevent the lateral deformation of rocks on the rise,the ability of the crack propagation is more concentrated on the main damage fracture trend.The increase of confining pressure within 0～15MPa increases the peak compressive strength of the model to a certain extent,but the increase range gradually decreases.Compared with triaxial compression,the post-peak brittleness of rock mass samples with the same condition tends to increase during the unloading process of confining pressure.(5)In terms of tunnel simulation,under the same conditions,the rock burst effect of the tunnel model with prefabricated cracks is better than that of the tunnel without prefabricated cracks.The lateral pressure coefficient mainly affects the position of rock burst,and the temperature mainly enhances the rock burst effect of the tunnel model.The influence of the length of prefabricated crack on the tunnel model is reflected in that the longer the crack is,the more obvious the rock burst effect will be.The initial confining pressure of the surrounding rock is the direct factor affecting the rockburst effect of the tunnel model.The larger the initial confining pressure is,the stronger the rockburst is.The effect of rock burst can be effectively reduced by slowing down the excavation speed of the tunnel chamber.