Dynamic Response And Failure Mechanism Of Anchorage System In Energy Dissipation Shed

As an important part of the combined energy dissipation shed,bolt is an important guarantee for the normal use of the combined energy dissipation shed.The response of anchor under dynamic action affects the stability of the whole shed-tunnel structure.in order to meet the requirements of maintaining good performance of the shed-tunnel structure under various possible dynamic actions,it is very important to explore the response characteristics of anchor under dynamic action.it has important theoretical significance and engineering application value to carry out the research on the dynamic response characteristics of anchor quality.However,due to the complexity and diversity of the anchor system,the response of the anchor rod under dynamic action is still in the exploratory stage.based on the national natural fund project(no 51408484),the dynamic response and failure mechanism of the anchor rod under different rockfall shapes,different rockfall masses and different rockfall heights are studied by means of model test,numerical simulation and theoretical method,which provides a certain reference for the improvement of the anchor system.The main research results are as follows:(1)The model test results show that under the action of spherical rockfall,the strain of anchor rod is the largest,the cube is the second,the cuboid is bigger and the cylinder is the smallest.If the falling height of rockfall and the falling quality of rockfall are bigger,the strain produced by anchor rod is bigger,and the increasing trend of strain is more obvious with the increasing of height.The further away from the rockfall impact position,the smaller the strain,and the bigger the opposite;Due to the reflection of stress wave at the end of anchor rod,the strain reduction of No.2 measuring point relative to No.1 measuring point is greater than that of No.3 measuring point relative to No.2 measuring point;Under the same excitation,the bigger the strain of anchor rod is,the smaller the strain is.it is suggested that the larger the cross-sectional area of anchor rod is,the stronger the overall strength of surrounding rock(such as grouting cement slurry when the surrounding rock is broken)is also a favorable engineering measure.(2)Through spectrum analysis,the excitation signal of rockfall impact anchor system is composed of low frequency signal and high frequency signal,the low frequency signal frequency band is 0 ~ 500 Hz,the high frequency signal frequency band is 4500 ~ 5000 Hz;The impact signal is mainly composed of a peak impact signal,which decreases rapidly after the peak value,and is relatively small compared with other peak values,and the larger the impact excitation,the larger the gap between the peak value and the peak value.The larger the excitation load,the larger the amplitude and power of the spectrum,and the larger the rockfall height,the larger the variation of the amplitude and power of the spectrum.(3)Through that correlation analysis of the impact signal,it is known that the function value of the correlation function has a positive correlation with the magnitude of the load excitation,and when the abscissa is zero,the correlation function reach the maximum value,and when the abscissa deviates from the zero point,the function value of the correlation function rapidly decrease to zero,so the dynamic response time of the anchor rod is relatively short,and periodic vibration is difficult to form;Wavelet analysis shows that when rockfall impacts the tunnel structure,the energy of anchor impact signal is mainly concentrated in low frequency band,accounting for 81.89 % of the total energy.the impact energy of high frequency band only accounts for 0.06 % of the total impact energy,and the energy of other frequency bands accounts for 18.05 %.it is suggested that the impact effect of low frequency band should be considered in anchor design,and the energy impact of high frequency band signal can be ignored.(4)The numerical simulation results show that,due to the extremely short process time of rockfall impacting the roof of the shed,the internal resistance of the anchor material is limited by the external surrounding rock at the same time,and the displacement and velocity of the measuring point firstly increase rapidly and then decrease gradually with the passage of time,and finally become zero,and the time of displacement and velocity increase is far less than the time of decrease;The energy produced by anchor rod is mainly internal energy and kinetic energy in the process of rockfall impact,and the two energy are transformed into each other in the process of rockfall impact on the roof of shed hole until the energy disappears;The kinetic energy,the internal energy and the total energy of the anchor rod are positively correlated with the rockfall height,and the increase of the internal energy,the kinetic energy and the total energy increases with the increase of the rockfall height;Compared with the concrete anchor body,under the same working condition,when the anchor body is mudstone,the equivalent stress,stress and strain of the anchor rod are smaller,and the displacement and velocity of the anchor rod are larger.The maximum equivalent stress,displacement,velocity and stress of anchor rod when bearing is set are smaller than when bearing is not set,which indicates that setting bearing on shed-hole structure can reduce dynamic response of anchor rod and enhance impact resistance of shed-hole structure.(5)In this paper,the failure mechanism of anchor rod is to analyze the load transfer path of anchor system,and then use the basic principles of material mechanics,theoretical mechanics and steel structure to determine the failure form of anchor rod:(1)type I shear failure(2)type ii shear failure(3)tensile failure,and finally get the failure situation and failure load of anchor rod.