Study On Dynamic Response Characteristics And Instability Mechanism Of Rock Slope With Weak Intercalation

On May 12,2008,an Ms 8.0 earthquake was occurred in Wenchuan,China.There are 112 large-scale landslides?landslide area>0.5 km²?triggered by the Wenchuan earthquake.The Daguangbao?DGB?landslide with a volume of 1.1×10⁹m³was the largest one.The landslide zone is located in the bedding fault which is form of the earlier tectonic activity,it is the main reason of triggered landslide.In the mountains in the existence of weak interlayer for landslide triggering provides geological foundation,especially the Wenchuan earthquake,a large tectonic background of Longmen orogenic belt,various properties of weak interlayer are widely distributed,this is the mountain unstable provides conditions,this kind of rock slope with weak interlayer of dynamic response is key in this paper for the Wenchuan earthquake,and considers the effect of amplitude and frequency.Based on the results of shaking table test and FLAC 3D numerical simulation,a generalized model is established to analyze the dynamic uncoordinated response characteristics of soft interlayer.The main ideas are as follows:?1?According to the characteristics of mudding and mylonization in the lower part of the interlayer dislocation zone,combined with the field investigation,it is found that the interlayer dislocation zone is basically saturated with water.The dynamic triaxial test of saturated soil in the bedding fault of Daguangbao landslide is carried out.Under dynamic load,the pore pressure of C₁ C₂ increases slowly,the change of dynamic strength is smaller than that of C₃ pore pressure,and the dynamic strength obviously decrease.The static triaxial test of C₃ is carried out.The dynamic triaxial test of confining pressure and influence factor test show that the pore pressure of the static shear specimen is stable after rising to the maximum under different confining pressure,and the pore pressure of the specimen is higher at the steady state.The results of uniaxial and biaxial dynamic triaxial tests show that the pore pressure increases faster under the bidirectional vibration,and the dynamic strength of the bidirectional vibration with equal amplitude decreases by about 20%compared with that of the unidirectional vibration.?2?In the shaking table test,the acceleration magnification coefficient of the sinusoidal wave increases obviously with the elevation increasing,and the horizontal vibration is more obvious than the vertical vibration,and the acceleration magnification coefficient decreases with the increase of the amplitude of vibration.Under horizontal and vertical loads,the soil pressure of the weak layer is much larger than that of the upper and lower hard layers,and the soil pressure peak and valley values of each layer are obviously dislocated during vibration,and under the action of horizontal and vertical vibration,the soil pressure of the weak layer is much larger than that of the upper and lower layers.The displacement of the upper boundary of the weak layer is significantly larger than that of the lower boundary.The maximum displacement of the upper boundary of the vertical vibration is 6 times of that of the lower boundary,and the horizontal vibration is nearly 20 times of that of the lower boundary.?3?The effect of vibration amplitude and frequency on the dynamic response of the model is considered.Under vertical vibration,the acceleration magnification coefficient of soft layer and upper layer decreases with the increase of vibration amplitude,while the magnification factor of weak layer and upper layer increases first and then decreases with the increase of vibration amplitude under horizontal vibration.Under vertical and horizontal vibration,the soil pressure of the three layers of the model increases with the increase of the amplitude of vibration,the gap between the soil pressure of the upper and lower hard layers and the soft layer increases with the increase of the amplitude,and the displacement response increases obviously with the increase of the amplitude of vibration.Under vertical vibration,the acceleration magnification factor of weak layer increases first and then decreases with the increase of vibration frequency,and then decreases with the increase of vibration frequency,and then decreases with the increase of vibration frequency,and then increases with the increase of vibration frequency,and then increases with the increase of vibration frequency.Under the action of vertical and horizontal vibration,the soil pressure of weak layer increases with the increase of frequency,and the regularity is good.For the displacement response,the deformation shift decreases at first and then increases with the increase of the frequency under vertical action,and it is minimum at 10Hz,and increases with the increase of frequency under horizontal action.?4?Based on FLAC 3D,an expanded generalized model is established to calculate the soil pressure values of each layer of the model under the action of sinusoidal wave,seismic wave loading and hydraulic coupling calculation.Similar to the physical simulation,the soil pressure of the weak layer is much larger than that of the upper and lower hard layer under the action of vertical sine wave,and the larger model is the greater the difference between the soil pressure of the weak layer and the upper and lower hard layer.The soil pressure under horizontal vibration is mainly located at the boundary between the weak layer and the upper and lower hard layer.When the Qingping seismic wave is loaded,it is found that the amplitude of the earthquake increases and the soil pressure of the weak layer increases,and the difference between the seismic amplitude and the upper and lower hard layers increases.The hydraulic coupling calculation with weak intercalation?model 1?and homogeneous model?model 2?shows that the pore water pressure of the model with weak intercalation is obviously higher than that of homogeneous model under the same conditions.?5?The dynamic incongruent effect of weak intercalation is studied,including punch-tensioning effect,horizontal vibration shear effect and pore water pressure effect.During the earthquake,the relatively weak interlaminar staggered zone is subjected to a strong punch-tensioning effect.When the vertical impact force exceeds the pressure threshold of the crack,the pressure failure will occur.At the same time,under the strong punching action,the compressive tensile crack controlled by the Griffith criterion may be produced,and when the tension in the weak layer causes the stress concentration at the two ends of the crack,Once the crack tensile strength is reached,the fracture will cause tensile damage.Shear deformation occurs in the weak zone under horizontal vibration,forming two kinds of echelon fracture planes:tensional geese and compression-torsional faults.During the earthquake,the weak layer is subjected to strong vertical and horizontal seismic forces,and the compressive shear of the weak intercalation may cause the pore pressure to rise rapidly and the strength to drop sharply.The above three effects have great influence on the strength change of the weak intercalation and the instability of the mountain body under earthquake.Finally,the starting mechanism of Daguangbao landslide is put forward:the fault zone between saturated layers provides the geological foundation for the start of landslide.Under the action of strong earthquake,the dynamic uncoordinated deformation leads to the stress concentration in the interlayer dislocation zone,which is subjected to strong tension and compression and shear action.The pore pressure of the material in the interfault zone between strong seismic forces rises and the strength attenuates,which causes the landslide to start.Finally,the starting mode of Daguangbao landslide is put forward.