Experimental Study On The Influence Of Loading Rates On Mechanical Properties Of T-shaped Fractured Rock Mass

The rock mass with different inclination angles,numbers,and cross patterns will cause slope landslides,cavern collapse,roof fall and other disasters under the action of external forces.Research on the mechanics and energy characteristics of fractured rock masses has practical guiding value for the safety and stability evaluation of various fractured rock mass projects.It has also become one of the current hot topics in rock mechanics.In this paper,uniaxial compression test and uniaxial cyclic loading and unloading test of T-shaped fracture specimen were carried out to reveal the influence of factors such as crack inclination and loading rate on the static and dynamic mechanics and energy characteristics of T-shaped fractured rock mass.Based on the energy dissipation method,the characteristic strength of jointed rock mass during progressive failure is studied,and a method for determining the yield strength of T-shaped fractured rock masses is proposed.The research results are as follows:(1)The static mechanical properties of the T-shaped fractured rock mass are studied,and the results show that the peak strength,elastic modulus and failure strain of the T-shaped fracture rock mass increase with the increase of the angle of the sub-fracture when the inclination angle of the main fracture is 0.The peak strength,elastic modulus and failure strain of the jointed rock mass decrease with the increase of the angle of the sub-fracture,when the inclination angle of the main fracture is 45 and 90.The increase in loading rate makes the peak strength and elastic modulus of the T-shaped cracked specimens strengthened,and the failure strain weakened.(2)When the inclination angle of the main fissure is 0,with the increase of the angle of the secondary fissures,the total energy,elastic strain energy,dissipation energy,and elastic energy ratio of the T-shaped fissure rock mass increase,while the dissipation energy ratio decreases.When the inclination angle of the main fissure is 45 and 90,with the increase of the angle of the secondary fissure,the total energy,elastic strain energy,dissipated energy,and the ratio of the dissipated energy of the cracked sample decreases,and the elastic energy ratio increase.With the increase of the loading rate,the total energy at the peak point of the fractured rock mass,the ratio of elastic energy to elastic energy increases,and the ratio of dissipated energy to dissipated energy decreases.(3)The energy dissipation coefficient is defined,the evolution law of the energy dissipation coefficient is studied,and the method for determining the yield strength of the fractured rock mass in the progressive failure process is proposed.The accuracy and rationality of the proposed energy dissipation method are verified by comparing with the traditional method,crack volume strain method.In addition,the rockburst tendency criterion about energy dissipation coefficient is established,and the rockburst probability of T-shaped fractured rock mass samples is predicted.(4)The dynamic and mechanical properties of the T-shaped fractured rock mass are studied.The results show that with the increase of loading rate,the dynamic peak strength,dynamic elastic modulus and ratio of dynamic to static peak strength increase,while the ratio of dynamic to static elastic modulus decreases.At low loading rate,the dynamic peak strength is less than the static peak strength,while the dynamic elastic modulus is greater than the static elastic modulus in the loading rate range of this paper.(5)The dynamic energy characteristics of T-shaped fracture specimens with different strain ratio,loading rate and fracture dip angle are studied.It is concluded that with the increase of strain ratio,the area of hysteresis loop increases by power function,the damping ratio decreases first and then increases,and the damping coefficient increases.With the increase of loading rate,the hysteresis area,damping ratio and damping coefficient increase.When the main fracture inclination angle of T-shaped fracture specimen is 0 and 45,the hysteretic ring area,damping ratio and damping coefficient increase with the increase of secondary fracture angle.When the main fracture inclination angle of T-shaped fracture specimen is 90,the hysteretic ring area area,damping ratio and damping coefficient decrease with the increase of secondary fracture angle.