Study On Dynamic Response And Disaster Mechanism Of Rock Slope With Weak Interlayer Under Blasting

Geological disasters such as slope damage and instability caused by blasting mining have attracted great attention from engineering and academic circles.This paper relies on the geological disaster investigation project of coal mining area in Lingshi County,Shanxi Province.In the history of the county,blasting technology had been used for coal mining for a long time,resulting in large-area subsidence of the ground in the coal mining area,cracks or pull grooves in the slope body and so on.Therefore,based on the phenomenon of slope geological disasters caused by blasting in the study area,the purpose of this paper is to study the slope dynamic response and disaster mechanism under the action of coal mining.The main research contents,research methods and conclusions are as follows.(1)Field geological hazard investigation was carried out in the study area,field drilling was carried out and the natural occurrence of rock and soil layers on the damaged slope was obtained.The distribution status and distribution law of slope cracks and pull-out grooves were counted,and the geological characteristics such as joint development and weathering degree of sandstone and mudstone were clarified.The comprehensive analysis shows that the slope is a geological body with sandstone and mudstone intercalated and controlled by three groups of structural planes.It is in a state of continuous deformation under the action of long-term blasting and natural forces.(2)In order to explore the mechanical evolution process of blasting damaged slope,the indoor experimental study on the dynamic and static mechanical characteristic parameters of rock was carried out.The rock density test and rock ore test were carried out on the obtained rock core,and the lithology naming and physical property indexes are achieved.The static mechanical properties of sandstone under uniaxial and triaxial stress are obtained,and the shear strength indexes in the scope of Mohr Coulomb and Drucker Prager criterion are calculated.The static tensile strength index of sandstone is obtained.The laboratory dynamic tests of sandstone were carried out,and the dynamic mechanical characteristics and energy response characteristics under different vibration frequencies and periods are obtained.The energy variation law of sandstone under cyclic loading and unloading stress is analyzed,and the relationship between sandstone dissipated energy and vibration frequency and confining pressure is analyzed;The difference and evolution law between different definitions of dynamic elastic modulus are discussed,and the regression relationship between dynamic elastic modulus and cumulative dissipated energy and cumulative residual strain is analyzed.The Hopkinson bar test(SHPB)was carried out to obtain the dynamic characteristics of sandstone and mudstone at medium and low strain rate,and the viscoelastic damage constitutive relationship of sandstone is established.An observation method for determining the characteristic value of sandstone strength is proposed,which is based on Hooke’s law.The method can determine the compaction stress,initiation stress and damage stress of sandstone.(3)On the basis of fully understanding the geological disaster phenomenon in the study area,and in order to further explore the response mechanism of velocity and acceleration of slope under blasting,the field blasting physical test model is constructed based on the similarity theory.The slope model with weak interlayer is constructed on its concrete base,and detonators and explosives are placed in the vertical and horizontal blasting holes to produce blasting effect.The velocity response at the top of the slope is obtained by the blasting vibration monitor.The frequency spectrum analysis results show that the vibration produced by the physical model test device is typical blasting seismic wave.The acceleration response in the slope body is obtained from the acceleration sensor set in the slope body.Its elevation change law confirms the "amplification effect" at the top of the slope,the "damping effect" and "energy absorption effect" of the weak interlayer.Its vector analysis also reveals the triggering downward trend of the blasting seismic wave on the slope.Based on the analysis of blasting physical model test results,a simplified mechanical analysis model of slope with weak interlayer is established.(4)In order to comprehensively study the dynamic response and damage mechanism of slope under blasting seismic wave,the numerical test model of slope composed of sandstone,mudstone and coal seam is constructed based on Abaqus finite element software.Combined with the previous indoor test results and relevant data,the physical and mechanical parameters of rock stratum and coal seam are set,the Mohr Coulomb elastic-plastic constitutive relationship is selected,the corresponding boundary conditions of mechanics and acceleration are set,and the blasting seismic wave action is applied,so as to realize the multiple blasting mining and removal process of coal seam,and truly simulate the mining process and blasting seismic wave propagation process.(5)According to the Abaqus numerical simulation test results,the nephogram and vectorgram of acceleration field,displacement field,velocity field,Mises stress field and strain field on the slope surface and inside show the regularity of changing with the blasting mining position.The acceleration,displacement and velocity increase coefficients are introduced to evaluate the strong "mutation effect" on the surface of weak intercalated mudstone,and the maximum values are 7.08,2.99 and 1.22 respectively.The stress triaxiality index is used to evaluate the comprehensive stress state of the slope under the action of blasting seismic wave.The complex stress state obtained from the stress triaxiality analysis at the weak interlayer is very consistent with the seismic damage phenomenon of the slope with weak interlayer in natural earthquake,and the area with large stress triaxiality value is the stress concentration area,which corresponds to the crack and areas of pull grooves,etc.The nephogram of plastic strain(PE)and equivalent plastic strain(PEEQ)can reflect the area and degree of plastic strain or damage of materials.Compared with hard sandstone,weak mudstone interlayer is more prone to damage.The changes of total kinetic energy and total plastic dissipation energy are analyzed,and the law that the plastic dissipation energy of slope increases gradually and nolinearly with the increase of mining times is obtained.Expansion and connection of equivalent plastic strain region caused by multiple simulated mining can reasonably explain the cumulative damage and disaster mechanism of slope caused by long-term blasting seismic wave.Combined with the numerical simulation test results,the energy response analysis is carried out,and the results show that the numerical test results are reliable.In a word,the numerical simulation test results more comprehensively explain the dynamic response and disaster causing mechanism of the slope under the action of blasting seismic wave,and play a key role in the interpretation of "trigger sliding mechanism" and "damage causing mechanism" of the slope under the action of blasting seismic wave.