The Mechanism Of Seismic Instability Of Loess Slope With Fissures And Its Early Identification

The geological structure of the Loess Plateau in China is complex.The North-South seismic belt,the North-South seismic belt,and the Qinling-Qilian seismic belt are all active fault in Loess Plateau.Which are one of the regions where the seismic geological disasters are extremely developed in China,and a large number of destructive earthquakes have occurred in its history.Due to the strong collapsibility and dynamic vulnerability of the loess,these earthquakes have brought serious disaster effects,induced tens of thousands of landslides,caused a lot of road damage,bridge destruction,house collapse and secondary geological disaster,resulting in significant economic losses and casualties.Therefore,it is of great scientific significance to deeply study the dynamic response characteristics,instability mechanism and early identification of typical slopes in Loess Plateau under the action of strong earthquakes.Fissures are widely developed in the interior of loess slope,Among them,the most common slope is the one which exposed the fissures at the front edge of the top surface.In this paper,the typical fissur slopes and non-fissur slopes are taken as the research objects,the methods of on-site survey,laboratory test,large-scale shaking table are comprehensively used to study the dynamic response and instability mechanism of the slopes under strong earthquake.Furthermore,taking the co-seismic landslide induced by the Minxian-Zhangxian Ms6.6 earthquake in 2013 as the object,the early identification of the fissure slopes was carried out from remote sensing and ground signs.Finally,ArcGIS is used to analyze the spatial distribution characteristics of landslides,and the influence factors were refined to establish the spatial prediction model of the landslide.1.The natural geography,meteorology and hydrology,lithology,topography of the study area are introduced in detail,and analyze the distribution characteristics of the landslides induced by the Minxian-Zhangxian earthquake.Taking the typical loess slopes as a conceptual model,a 1:25 shaking table model test on fissur loess slopesand non-fissuresed loess slopes was carried out.the slope dynamic response characteristics of the two structures are analyzed by inputting horizontal and vertical seismic waves of different amplitudes.2.Peak acceleration method and Arias intensity method are used to analyze the response law of acceleration on the slope surface and vertical section,it is found that the horizontal and vertical seismic waves have obvious nonlinear amplification along the slope surface and the internal vertical direction,and reach the maximum value at the top of the slope.The amplification effect of horizontal seismic wave on slope is greater than vertical seismic wave under the same intensity of seismic wave.Moreover,the existence of fissures has an important influence on the propagation and response of seismic waves in slopes.3.The dynamic response between horizontal seismic wave and vertical seismic wave on two slopes is analyzed by FFT.The predominant frequency of the input seismic wave has changed significantly after it passes through the slope medium,slope will selectively enlarge middle and high frequency bands with the increase of elevation,which is more obvious on the fissure slope and the predominant frequency will shift to the low frequency direction with the increase of seismic wave,and the predominant frequency attenuation is not obvious under the action of vertical seismic wave.4.PGD and △PGD are used to divide the deformation of slopes into three stages:elastic stage,plastic deformation stage and failure stage by using three-dimensional optical measurement technology.the deformation and failure process of the fissur slope and non-fissure loess slopes under different intensities are summarized,through the macro deformation,and analyzed the failure mechanism.5.The fissure slope is identified by remote sensing and ground signs.The remote sensing targets mainly include the vegetation around the slope is in the shape of circular chairs and stepped slope.The ground signs are mainly divided into four categories and nine sub categories,including slope structure signs,topographic and geomorphic signs,lithologic signs and hydrogeological signs.It is found that the factors that contributed to the fissureed slope from large to small were the distance from the fracture zone,landform,lithology,elevation and slope degree based on thelogistic regression model,At last,the vulnerability zoning map of Seismic Landslides in the target area is drawn.