Liquefaction Resistance And Evaluation Method Of Geosynthetic-Encased Stone Columns Composite Foundation Under Strong Earthquakes

With the further development of the major strategic concept of"the Belt and Road initiative",the countries along the belt and road are facing a great demand for port construction.However,the countries along the belt and road are mostly in areas with frequent earthquakes,and the situation of earthquake prevention and disaster reduction in cities along the border is extremely severe.Soil liquefaction is one of the main causes of earthquake damage to port engineering buildings,the reinforcement of liquefaction sites is the key issues facing port engineering directly in earthquake prevention and disaster reduction.Geosynthetic-encased stone column is widely used in soft soil reinforcement,especially in port engineering,because of its advantages of good reinforcement effect,low cost and convenient construction.Scholars at home and abroad have carried out a lot of research work on the application of geosynthetic-encased stone column,but at present there are few studies about the application of geosynthetic-encased stone column in liquefiable sites,many problems still to be solved urgently:The understanding of liquefaction law of geosynthetic-encased stone column composite foundation is not thorough enough,the influencing factors of liquefaction resistance of geosynthetic-encased stone column composite foundation are not clear enough,and the evaluation method of liquefaction resistance effect still needs to be developed.In view of this,on the basis of existing research on liquefaction resistance of geosynthetic-encased stone column,the liquefaction resistance of geosynthetic-encased stone column composite foundation under strong earthquake is studied by means of numerical simulation and model test.The main work is summarized as follows:Firstly,a shaking table test on liquefaction resistance of stone column and geosynthetic-encased stone column were carried out in horizontal liquefiable sites.The dynamic response and liquefaction development law of saturated sand,stone column composite foundations and geosynthetic-encased stone column composite under earthquake were obtained.Difference of seismic response of saturated sand foundation,stone column composite foundation and geosynthetic-encased stone column composite foundation were analyzed emphatically.Then,based on the finite element numerical simulation method,a three-dimensional finite element model of geosynthetic-encased stone column composite foundation in liquefaction site is established,and the correctness of the numerical model is verified by shaking table test results.Based on the model,an one-way variation analysis method is used to comparative analysis the effects of pile diameter d,stiffness J of geosynthetic and shear modulus ratio of column to soil G_r on liquefaction resistance of geosynthetic-encased stone column composite foundation by selecting the design parameters which are of great importance in the engineering application of geosynthetic-encased stone column.Finally,based on the cyclic stress ratio method,the concept of seismic shear stress reduction of geosynthetic-encased stone column on soil around column is introduced,by comparing the distribution of shear stress reduction coefficient ratio of reinforced composite foundation,a simplified method for evaluating the liquefaction resistance effect of geosynthetic-encased stone column composite foundation is proposed,which is verified by numerical simulation results.