Research On Dynamic Responses Of Underground Openings And Ground Motions Under Dynamic Load

The stress waves would propagate in the rock mass when subjected to dynamic loads such as blasting,which may cause instability or even destruction of adjacent structures.Discontinuities such as joints in natural rock masses could lead to the attenuation of the wave amplitude and slowing down of the wave propagation speed.However,there is still a lack of systematic research on the influence of stress wave propagation in joined rock mass on the dynamic responses of underground and ground structures.Therefore,the propagation and attenuation laws of blasting stress waves in joined rock mass and the characteristics of the dynamic responses of adjacent openings and ground motions were revealed and related support analysis was carried out with the method of model test and numerical simulation in this paper.The related research results have great scientific value and engineering significance for the in-depth understanding of stress wave propagation law and dynamic response characteristics of surrounding rock and structure,as well as the safety protection of underground and ground structures.The main research work of this paper are as follows:(1)The blasting model tests were carried out to analyze the effects of joints and blasting parameters on the dynamic responses of surrounding rocks and underground openings and ground motions under the action of blasting stress waves.By comparing with the model test,the applicability and effectiveness of the finite element and discrete element numerical method(AUTODYN-UDEC/3DEC)to simulate the explosion process,the blasting stress wave propagation and the dynamic response of underground opening were verified.(2)With the coupled numerical method of 2D finite element and discrete element(AUTODYN-UDEC),the dynamic response characteristics of surrounding rock and adjacent opening under different explosive properties,the explosion chamber shape and joint characteristics were analyzed,and the influence law of different soil cover thickness on the ground motions was revealed.Considering the attenuation effect of joints on stress waves,an improved formula for the peak particle velocity(PPV)of surrounding rock mass was obtained,and a general method for calculating the safety critical distance between structures in joined rock mass was proposed.In combination with blasting test and numerical simulation results,it is found that explosive properties have significant effects on the dynamic response of surrounding rock and underground opening and ground motions.The joint properties,such as joint stiffness,dip angle,crossing angle and spacing,are the main factors that affect the propagation and attenuation of stress waves.The ground motions are dependent on soil cover thickness and the number of joints between the ground and the explosion source.The main frequency of ground motion above the explosion chamber increases with increasing joint angle,but the change of charge density has no obvious effect on the main frequency.(3)With the coupled numerical method of 3D finite element and discrete element(AUTODYN-3DEC),the influence of 3D parameters such as joint strike,joint dip angle and blasting location on the dynamic responses of underground opening and the movement characteristics of sensitive blocks in tunnel wall were investigated,and the supporting effects of different supporting methods were compared and analyzed.For the parallel chamber group,the PPV of the back-blasting surface is lower than that of the front-blasting surface for the side wall of the opening close to the explosion source,regardless of the joint strike or dip angle.However,the change of strike or dip angle might result in that the PPV of the measuring points on the back-blasting surface of the chamber which is far away from the explosion source is greater than those of the chamber close to the explosion source.For the upper-lower chamber groups,the PPV of the vault presents an inverted “V” distribution along the chamber axis,and the existence of joints may cause the dynamic response of the back-blasting surface to be greater than that of the front-blasting surface.The displacement of the sensitive block is affected by PPV and the shape of the block itself.The greater the joint dip angle and the greater the cross angle caused by the change of joint strike,the greater the displacement of the sensitive block.(4)The propagation characteristics of tension-compression stress wave and compression-tension stress wave in jointed rock mass were compared by using UDEC.The influence mechanism of joint tensile strength and buried depth of rock mass on the propagation of tensile stress wave and the influence law of joint properties,the buried depth,and lateral stress coefficient on the dynamic response of underground opening under the action of tensile stress wave were revealed,and the supporting effect of the supporting parameters of underground opening was analyzed.The joint tensile strength has significant effects on stress wave propagation if it is lower than the amplitude of tensile stress wave in the shallow rock mass,where the transmission coefficient for tension-compression wave is lower than that for compression-tension wave.For joints with low tensile strength,the joint opening displacement decreases with the increase of buried depth,and the PPV on the surface of underground opening increases.The lateral stress coefficient has little effect on the dynamic response of underground opening.The installation of rock bolts with appropriate number and length and shotcreting with sufficient thickness could effectively reinforce the surrounding rock and reduce the area of disturbed zones when subjected to dynamic extension.When the supporting parameters reach the threshold value of bolt number/length and the optimal lining thickness,the influence on the disturbance area is not great.