Study On The Characteristics Of Site Soil Based On Mesoscopic Model

Henan is located in the Central Plains.As the birthplace of Chinese culture and the political and cultural center,Henan successively has regimes of Xia,Shang,Eastern Zhou,Eastern Han,Northern Wei,Sui,Tang,Five Dynasties,Northern Song and numerous historical sites.The climate features of the central plains are windy in spring,rainy in summer,long sunshine in autumn,and cold and snowy in winter.The distinct climate features of four seasons cause the site to be in a changing environment.Under the influence of the changing environment of the outside world,the diseases of the earthen site occur continuously and show nonlinear development and evolution.Compared with brick and stone sites,the intensity of earthen sites is lower and the environment is complex.However,the research on the protection of earthen sites has always been the tough and key issue in the field of heritage protection.Therefore,the comprehensive analysis of the deformation mechanism and degradation mechanism of the earthen sites is the primary task at present.Because of the characteristics of the earthen sites of non-renewable,limited sampling,different historical periods,complex composition and deterioration,it is difficult to study the earthen sites.In this dissertation,through the methods of outdoor investigation,indoor test,theoretical analysis and numerical simulation,the macro and micro analysis of some earthen sites in the Central Plains region is carried out.What's more,based on the contact model of micro structure,the degradation of earthen sites is discussed systematically.The main research contents are as follows:(1)According to the standard of soil test method,the basic mechanical properties of the site soil were tested.The three sites of Xinzhengmen,Caiguo and Weihui were tested.In the experiment,the macro mechanical properties of site soil samples with different water content,different initial void ratio and different stress conditions were studied.The basic physical properties,chemical elements,basic mechanical properties and stress-strain relationship under different confining pressures were tested and analyzed.(2)Using the electron microscope to observe the microstructure and particle shape distribution and taking the gray level image threshold as the medium,which are different from the ordinary two-dimensional level of the soil porosity solution,this dissertation used the three-dimensional level to more accurately solve the soil porosity and the particle proportion under the micro scale,discussed the generation and algorithm of soil particles.Taking the area between different soil particles as the control parameter and considering the interface transition zone,a multi-phase soil meso model including particles and cement was established.Meanwhile,considering the influence of the particle diameter on the interface transition zone,the element without thickness was introduced,and the finite element calculation mode different from the discrete element was adopted.(3)Taking the degradation of site soil as the research object,using the commercial finite element software ABAQUS,the coupling state of multi stress field is better superposed,and the micro damage law with micro mechanism is obtained.Through the numerical model,and therefore,the stress-strain relationship is obtained,and the macroscopic phenomenon of the site is further analyzed;Based on the microscomic structural evolution of numerical simulation,the research idea of microscomic structural mechanical properties of site soil is established,and the relationship between the formation of macro site soil sample cracks and meso structural damage is also discussed.In order to verify the reliability and stability of the simulation,the plane strain microscomic soil sample model is established.Through the numerical results obtained,the influence of the micro structure characteristics on the macro mechanical parameters of soil samples is explored.By comparing the numerical simulation with the actual test,the development process of the stress and strain of soil particles under the condition of plane strain is studied.The whole mesh number is reduced and the calculation efficiency is improved by using the segmented mesh drawing process.The numerical results directly reflect the whole process from crack initiation to macro crack formation,and provide a new perspective for the mechanical properties of the site soil and the subsequent restoration of cultural relics.Based on the micro structure contact model and macro phenomenon of the particle material the earthen sites,considering the influence of degradation damage on the stability and degradation of the site soil,this dissertation takes SEM image as the medium and threshold as the means to obtain the soil structure data at the micro scale.On this basis,the finite element software is used to simulate the meso scale data,which solves the problem that the indoor test can‘t show the process of soil damage and degradation.This dissertation provides a theoretical guidance for the restoration of earthen sites,and also provides new ideas for the study of material degradation damage.