The Power Mutagenic Effects On Rock Mass Media Interface Of Liujiawan Landslide

The rock physics mechanics property has different nature on different space position, thus forming different wave impedance characteristics. Under strong seismic actions, stress wave forms the strong reflection, refraction effect in the interface of dielectric property difference in the propagation process, produce a great dynamic tensile stress and shear stress, which leads to the slope rock mass be destroyed and form unique instability characteristics. Thus, through the study on rock mass medium interface dynamic mutation has important significance of earthquake preparedness and disaster reduction. This paper takes 2008 "Wenchuan Earthquake" triggered Qingchuan,Liujiawan village large-scale rock landslides as the research object, combined with the related geological data to carry out theoretical research,and through the field investigation、physics and mechanics feature experiment of the rock mass in landslide area and the discrete element numerical simulation, to discuss under strong earthquake, the characteristics of dynamic stress mutations caused by stress wave penetrate different geological units in Liujiawan landslide, result in the failure mechanism of the landslide instability. In response to the forming phase:Through the field survey of Liujiawan village landslide, General speaking, Slope is dualistic structure combination which is “hard inward and soft outward”, the external geological units consist of the carbonaceous slate and sericite quartz phyllite of Hujiazai Formation of Sinian System, and the inferior geological units consist of dolomite of inferior segment of Yuanji Formation of Sinian System. Through analyzing the results of the rock physical and mechanic parameter laboratory tests, the modulus of elasticity of three kind of rock mass gradually decreases. The elasticity modulus of dolomite is 7.1 times that of the carbonaceous slate, and the elasticity modulus of the carbonaceous slate is 10.7 times that of phyllite. Laboratory experiment results show that the physical mechanics property of composition materials of the slope were obvious differences, under strong seismic actions, on the formation lithology boundary formed significant dynamic and stress abrupt change.Special geological structure combination makes transmitted stress approximately equals 0.54 times that of initial stress when stress through the dolomite and carbonaceous slate geological unit. In this case, stress wave reflected into the dolomite strata is stretching wave, formed strong dynamic and stress, dynamic shear stress on the formation lithology boundary, cause the slope damaged and slide out at high-speed along the formation lithology boundary, formed landslide.The discrete element numerical simulation of Liujiawan village landslide shows that the shear strain of the slope focused in the “Soft Rock” slate which outside the slope on the formation lithology boundary at first. Under the continuous loading of seismic dynamic,the shear strain first focused on both sides of interface, produced distortion along the formation lithology boundary and concentrate on the locked segment of slope toe, finally caused the locked segment damaged and slide out at high-speed along the formation lithology boundary. As a whole, there were elevation amplification effect on the horizontal acceleration and vertical acceleration of particle.Which takes monitoring point M6 as reference, the magnification factors of vertical acceleration of monitoring point M5- M1 were in order of 1.11、1.02、1.19、1.19、1.42 times, the horizontal acceleration magnified more apparent.The dynamic differentiation and wave impedance ratio formed by the dual structure which is “hard inward and soft outward” consisted of dolomite and slate, on interface between media are closely related, when wave impedance ratio is less than 0.8,the maximum principal stress present amplifier effect when stress wave go though interface between media; when wave impedance ratio is 0.8, there are no obvious enlarged or reduced, when stress wave go though interface between media, which can be regarded as critical condition of stress differentiation effect; when wave impedance ratio is more than 0.8, the maximum principal stress present decline effect when stress wave go though interface between media, and the larger wave impedance ratio, the more obvious decline effect, so that reflection effect is stronger of stress wave on interface between media.The failure mechanism of Liujiawan village landslide is the special formation lithology combination “soft outward and hard inward” caused seismic wave refracted,reflected and other dynamic stress effect when it gone though the geological interface, the amplifier effect of coupled topography caused the dynamic response of the slope overwhelmingly strong, and caused the landslide cut out along the weak structure surface. The deformation failure of Liujiawan village landslide can be divided into five stages: the long cumulative effect of earthquake stage- the stress mutation of the geological interface stage-the high-speed collapse sliding stage-debris flow accumulation stage-secondary collapse sliding phase.