Study On Model Test Of Composite Foundation With Surcharge Preloading Of Deep Soft Soil Under Closed Cement Soil Fender File

Deep soft soil foundation treatment is a hot research topic in civil engineering.Due to the problems of thick soft soil cover,poor structural stability and low bearing capacity of deep soft ground,it is often difficult for various traditional treatment and construction methods to achieve the desired results.In recent years,with the continuous development of foundation treatment technique,the treatment of soft soil foundation gradually expands from a single technique to a combination of two or more techniques.And the method of joint treatment can combine the advantages of each individual technique and achieve better reinforcement effect.This paper combined the closed cement soil enclosure pile with the technology of vacuum combined with surcharge preloading,and through theoretical reinforcement analysis,indoor tests,model tests and numerical simulation to explore the reinforcement features of deep soft foundation dealt with by this joint treatment and the bearing characteristics of the composite foundation formed after work,the main research content and results are as follows:(1)A series of geotechnical experiments were carried out on the collected soft soil to determine the physical properties of the soil.This paper analyzed the basic principles and reaction process that how ordinary silicate cement improves the original soil.Through designing the ratio of cement soil,determining the growth trend of unconfined compression strength of the soil,and providing a theoretical basis for the subsequent model test.(2)Under the condition of deep soft composite foundation of closed cement soil enclosure pile,carry out the model test of vacuum combined with surcharge preloading.Formulate one-time loading and grading head loading methods,set up a control group of traditional vacuum combined with surcharge preloading,and explore the reinforcement effect of the combined scheme and the traditional scheme.In the model experiment,the distribution of vacuum degree,the degree of pressure water pressure vanishing,the moisture content and the consolidation settlement inside the drain board in each group of operating conditions are discussed.The results showed that the reinforcement effect of the joint treatment was significantly better than that of the traditional scheme,in which the average degree of consolidation of the two groups was 8% higher than that of the traditional scheme of the control group.The joint treatment can improve the consolidation efficiency of the deep soft ground,which in turn shortens the processing period.(3)Using FLAC3 D numerical simulation software to establish a computational model of the composite foundation formed after joint treatment operation.According to the role of cement soil retaining piles under load in the composite foundation,the composite foundation is divided into “enclosure type” and “bearing type”.Analyze the deformation characteristics of soil core and soil inside and outside the continuous wall of “enclosure type” compositefoundation under the loads at all levels.The deformation of the composite foundation under the load is mainly concentrated in the horizontal range of 0 to 5m outside the soil core,continuous wall and wall and the depth of 0 to 6m below the ground.explore the comprehensive application of the “enclosure type” composite foundation according to the simulation results.(4)Determine the ultimate bearing capacity of “bearing type” composite foundation according to its P-S curve and the load share ratio.Verify the “bearing type” composite foundation through the theoretical analysis.Determine the safety factor empirical values of each bearing item by comparing the results of the approximate calculation method with the numerical simulation results.