Study On Settlement Of Floating Cement-soil Piles Composite Foundation

Thick soft soil is widely distributed in the coastal area of southeast China.How to obtain a kind of effective method to reinforce soft ground has become an increasingly significant problem today.Cement soil mixing method is a common method for soft ground treatment,but when the soft soil layer is too thick,piles would not completely penetrated the soft soil,and there will still exist a deep soft soil layer.Piles can be called floating piles at this time.At present the studies on floating cement-soil piles composite foundation are few in number,settlement calculation methods on it have also not been unified yet.Therefore,to explore strengthening mechanism and bearing characters of floating cement-soil piles composite foundation may provide references for foundation treatment design and construction.The research on settlement of floating cement-soil piles composite foundation is based on an engineering example at coastal region of eastern Fujian.Model tests and finite element analysis are performed to explore strengthening mechanism and bearing character of floating cement-soil piles composite foundation.The main works and conclusions are given as follows:(1)Through analyzing projects of cement-soil piles composite foundation in the research area,the ratio of the bearing capacity to the characteristic bearing capacity,which is defined as safety reserve index--"K",is got.The statistical results show that the value of the safety reserve of this region is about 2.8,and it also comfirmed by the engineering example based on.(2)In order to analyze settlement characteristics of floating cement-soil piles composite foundation,model tests were carried out.The settlement of the composite foundation,the stress of the piles and the soil stress were monitored during these tests.The experimental results show that there is a reasonable range of the length of floating piles,and settlement of the models is obviously reduced when the length of piles are in the reasonable range.Besides,stress ratio is increased with the increasement of the length of floating piles.(3)Finite element models based on model tests are built in Plaxis 3D.The FEA results agree well with the conclusion of the model tests.By comparing the testing data with the FEA results,a more suitable soil constitutive model is selected.(4)On the base of chapter 2 and 3,a finite element model of the engineering practice in the research area is built to discuss settlement of composite foundation with different floating pile lengths,pile spacing and loadings.The FEA results show that there is a reasonable range of the length of floating piles and pile spacing,within which the reduction of the settlement is most significant.