Study On Seismic Failure Mechanism Of Raw Soil Block Wall

As one of the traditional buildings with a long history in the world,the raw earth building has the advantages of easy to obtain materials,low cost,easy construction,low energy consumption,no pollution and so on.It is widely distributed in villages and towns in Xinjiang.However,due to the defects of raw earth materials,the wall strength is low,and the seismic performance is poor.It belongs to the most serious structural form in previous earthquakes.At present,there is no clear seismic design method for raw soil structure,and its seismic fortification mainly depends on structural measures.Therefore,it is of great significance to study the failure mechanism of raw soil wall under seismic action,and put forward reasonable evaluation index and failure criterion of raw soil structure performance degradation under seismic action,so as to establish the design method of raw soil structure,carry out seismic damage assessment and reinforcement.In this paper,experimental research,numerical simulation and theoretical research are combined to study the failure mechanism of raw soil block wall.The main research work and conclusions are as follows(1)In order to study the seismic performance of three typical types of wall in raw soil building,including solid wall,wall with window opening and wall with door opening,and reveal the whole process of the three types of wall from intact to collapse failure under earthquake action,four low cycle reciprocating horizontal loading tests of raw soil block walls were carried out.The results show that: 1)the failure mode of raw soil block wall is mainly shear deformation,and its failure phenomenon is similar to that of brick masonry structure,and the cracks basically extend along the mortar joint.The failure process can be divided into four stages: elastic stage,elastic-plastic stage,failure stage and collapse stage.2)In the failure process of the three types of walls,the test phenomena are different.The X-type main inclined cracks are formed on the surface of the wall;The results show that the test phenomenon of the wall limb on both sides of the door and window opening is basically the same.The asymmetric X-shaped main inclined cracks are formed on both sides of the window opening in the wall with the window opening,and the X-shaped main cracks are formed on both sides of the wall with the door opening in the failure process.(2)In order to study the influence of vertical stress,height width ratio,height thickness ratio and other factors on the seismic performance and failure process of the wall,and comprehensively reveal the seismic failure mechanism of the raw soil block wall,this paper uses ABAQUS finite element software to carry out the extended parameter full-scale model analysis.The results show that: 1)with the increase of height to thickness ratio,the failure mode of the wall gradually changes from shear failure to shear /crushing failure,and the smaller the height to thickness ratio is,the greater the bearing capacity of the wall is,but the height to thickness ratio has little effect on the deformation capacity of the wall,and the time of specimens entering each stage is basically the same;2)When the vertical compressive stress is between0.1MPa and 0.2MPa,its influence on the failure mode of the wall is not obvious,but the larger the value of the vertical compressive stress is,the higher the bearing capacity and deformation capacity of the wall will increase,and the later the specimen enters each stage;3)With the increase of shear span ratio,the failure mode of the wall changes from shear failure to shear / cable-stayed failure;The larger the shear span ratio is,the smaller the bearing capacity of the wall is,but it has little influence on the deformation capacity of the wall,and the later the wall enters the elastic-plastic stage.(3)In order to determine the reasonable evaluation index and failure criterion of the performance degradation of the raw soil structure,the quantitative value of the seismic performance index in each stage of the failure process of the raw soil wall under the earthquake action is proposed based on the results of the low cycle horizontal loading test,the finite element simulation,and the literature on the raw soil wall.Based on the existing seismic damage model,a modified model combining stiffness and deformation is proposed The combination parameters of the damage evaluation expression and the division range of each damage level are determined,and the effectiveness of the improved model is verified.