Study On Seismic Ground Motion Effect Of Unsaturated Loess Site In Ningnan Hilly Area

The surface of the central and western regions of China is widely covered with loess of different ages and thicknesses.Affected by various factors such as topography,geological structure and human activities,it has become a frequent occurrence of geological disasters.The earthquake damage survey shows that various high-rise earthquake disasters in the loess area are closely related to the site conditions.In this paper,the influence of surface rate of water on the dynamic characteristics of loess is considered by dynamic triaxial test.The effects of surface water on ground motion response are studied by combining one-dimensional soil layer reaction analysis and numerical calculation.According to the characteristics of earthquake disasters in Xiji area of Ningxia,the loess hills are taken as the research object.The ground pulsation test and numerical calculation method are used to study the strong ground motion characteristics of the loess hilly region under strong earthquakes,revealing the earthquake disaster and strong ground motion in this area.Relationship between.The main conclusions of the paper are as follows:(1)The dynamic triaxial test of unsaturated undisturbed loess in southern Ningxia shows that with the increase of water content,the dynamic shear modulus of loess decreases and the damping ratio increases.When the water content reaches the plastic limit,the water content changes.The influence of dynamic shear modulus and damping ratio is obviously weakened;for loess with the same water content,the greater the burial depth,the larger the maximum dynamic shear modulus.(2)Seismic response analysis of soil layers in unsaturated loess sites shows that with the increase of input seismic wave intensity and water content,the ground motion peak acceleration(PGA)and response spectrum values of loess sites generally show an increasing trend;The effects of changes on the ground motion intensity and characteristics of different computational profiles vary widely.(3)On-site survey and ground microtremor test analysis found that the slope ofhilly area with intensive development of landslide damage in the study area is gentle,the thickness of loess cover is about 10-40m;the soil layer on the development side of landslide test site is thicker.The H/V spectral ratio magnification is higher than the untriggered landslide side.(4)The calculation of the 2D numerical model of the ground microtremor test site shows that the different terrain and cover layers on both sides of the hilly terrain cause different ground motion amplification effects,which is one of the factors leading to the development of unilateral landslides in the study area;The calculation results show that the ground motion amplification effect of the rolling loess hilly terrain can be approximated by the product of the ground motion amplification effect under the action of the terrain and the soil layer alone.