Study On The Mechanical Properties Of The Weak Layer Zone And Its Influence On The Dynamic Stability Of High And Steep Rock Slope

The instability of high and steep rock slopes is the main geological environment problem in engineering construction in Qinling-Bashan mountains.Because of the action of strong tectonic activities,the folds,faults,and joints develop,making the geological structure of the slope very complex,and the rock mass of the slope has a weak layer zone formed by various discontinuous structural planes.It’s closely related to slope stability.Along with the rapid development of society’s economy,human activities such as engineering construction,road construction,and mining have aggravated the instability and damage of high and steep rock slope in the area.Among them,blasting in mining engineering and various vibrations continuously generated in the mining will affect the stability of high and steep rock slopes.Therefore,it is important theoretically to carry out research on the mechanical properties of weak layer zone,the dynamic response law of high and steep rock slopes containing weak layer zone under the action of vibration,and their deformation and failure characteristics and stability.In this paper,the "8·12" landslide in Shanyang was taken as an example.The field investigation,laboratory test,shaking table test,numerical simulation and theoretical analysis,etc.were conducted to study the mechanical properties of argillaceous interlayer and the argillaceous interlayer-siliceous slate samples in the weak zone,and explore the attenuation law of strength parameters under the action of vibration,and carry out physical and numerical simulation research on dynamic response law,deformation and failure characteristics of high and steep rock slope,as well as the dynamic stability of the slope is analyzed to provide theoretical support for the instability prediction of this kind of slope.The main research contents and results are as follows:(1)Through the triaxial shear test of argillaceous interlayer and argillaceous interlayer siliceous slate samples respectively to comparing and analyzing the static characteristics of them.It is found that the strength characteristics of argillaceous interlayer-siliceous slate samples are significantly reduced due to the existence of contact surface.The strength parameter cohesion of under static action is 43%-59% smaller than that of argillaceous interlayer,and the internal friction angle is about 20%-25% smaller than that of argillaceous interlayer sample.The water content and confining pressure have significant effects on the stress-strain relationship and failure strength of the argillaceous interlayer and the argillaceous interlayer-siliceous slate samples in the weak zone.In addition,the failure strength of both samples increases with the increase of confining pressure and decreases with the increase of water content.(2)Through the dynamic strength test and dynamic deformation characteristic test,the dynamic elastic modulus of the two samples first decreases and then gradually stabilizes with the increase of strain,the damping ratio increases with the increase of axial strain,and the strength parameters of argillaceous interlayer samples and argillaceous interlayer-siliceous slate samples will deteriorate under the action of vibration.After 100 times of vibration under dynamic action,the dynamic strength parameter cohesion of argillaceous interlayer sample decreases by 17%,while that of argillaceous interlayer-siliceous slate sample decreases by 6%;The internal friction angle of the two samples also attenuated by about 25%.Based on the dynamic strength test,the deterioration mathematical model of mechanical strength parameters of argillaceous interlayer and argillaceous interlayer-siliceous slate samples is constructed.It is found that the influence of dynamic action on argillaceous interlayer is much greater than that of argillaceous interlayer-siliceous slate samples.(3)Based on the rock and soil parameters obtained from the laboratory test,a shaking table model test is designed for the high and steep rock slope with weak layer to explore the dynamic response characteristics and instability failure mode of the slope.The test results show that the dynamic response characteristics of slope have obvious elevation and surface amplification effect,and there is also significant amplification effect at the argillaceous interlayer.The more significant the dynamic response characteristics are,the more obvious the strength attenuation is,and the greater the promotion effect on the instability and failure of the slope is.The PGA amplification coefficient of different monitoring points decreases with the increase of the amplitude from 0.05 g to 0.15 g.In addition,the failure characteristics of the slope are also obtained.The slope is subjected to repeated tension and shear stress under the continuous vibration,the tensile crack appears at the back edge of the slope is further expanded,and the sliding face is transfixion,shear cracks begin to appear on the left side of the slope,and shear failure occurs gradually at the locked section of the slope,while dissolution cracks on the left side gradually close and the slope fails.The failure mode of the slope is tensile-shear-horizontal slip.(4)Based on the laboratory test data and shaking table model test results,the numerical simulation of Shanyang "8.12" landslide prototype under different dynamic parameters is carried out by using FLAC3 D software,and the deformation and failure evolution process of the slope under continuous vibration is reproduced.The results show that the dynamic response characteristics of the slope under the action of vibration waves with different dynamic parameters are consistent with the results obtained from shaking table model test,with obvious elevation effect and surface effect.In addition,it is also found that the weak interlayer weakens the propagation of vibration waves,has damping effect in the slope,and inhibits the elevation effect and surface effect of the slope to a certain extent.It is found that the change of dynamic parameters has different influence on the dynamic response at different positions of the slope.When the dynamic load amplitude increases from 0.05 g to 0.25 g,the PGA amplification factor at different positions decreases by 13%-44%;When the dynamic load frequency increases from 5Hz to 25 Hz,the PGA amplification factor at different positions decreases by about 70%-80%.(5)According to the deformation and failure mode of the slope obtained from the model test,the stress analysis of the slope is carried out from the two angles of the free surface direction of the front edge and the dissolution crack direction of the left side of the slope,and the variation law of the dynamic stability of the slope is studied.Based on the ultimate balance theory,the Mohr-Coulomb strength criterion,and the definition of the coefficient of stability,an algorithm model of dynamic stability coefficient of rock slope considering the strength deterioration and damage of rock and soil mass is established from a three-dimensional point of view.The time history curve of slope stability coefficient change under dynamic action can be obtained by dynamic calculation,which can provide theoretical support for slope instability prediction.