Research Of Soil Behavior With The Sinking Of Large Cassion

The sinking of large caisson causes the variation of soil stress state,which leads to the change of the mechanical property of soil.The way to evaluate the influences on soil from the sinking of caisson has important theoretical value and engineering guiding significance for ensuring the safety of construction and the protection of environmental.The research,based on water intake engineering construction of Dagang,in Zhenjiang,is performed by laboratory test,in-situ monitoring test,and numerical analysis to study the stress path,small strain characteristic and deformation pattern of soil from the sinking of caisson.The main research contents and results are as follows:（1）In-situ monitoring on the construction field of the sinking caisson shows that the time span of each time of caisson sinking is relatively short comparing to the long period of construction so that the sinking of caisson can be considered as undrained process.The sinking of caisson is a process of deviation rectifying,with a maximum inclination angle of 1.1o.In the process of caisson sinking,soil move towards inside of the caisson.Soil at the depth higher than 5m is more susceptible to the effect of construction.The maximum lateral displacement is about 150mm,which divides by sinking depth is 0.39%,within the scope of small strain.（2）A numerical method based on CEL method is introduced and verified aiming to solve the difficulty of the coupling of penetration and excavation simultaneously.Based on this method,subjects of stress path and deformation pattern of soil in the construction of large caisson are studied.Numerical results indicate that,the stress path pattern of soil out of shaft wall in the process of sinking of large caisson is following the paths of unloading-loading-unloading,while the soil inside shaft wall is only following the unloading path.When soil inside shaft wall is excavating,soil out of shaft wall heaves,and move away if the depth higher than caisson’s cutting shoe,but move towards caisson if depth lower than caisson’s cutting shoe.The effect of caisson’s sinking on soil’s deformation is opposite to that of excavation.（3）Small strain characteristic of soil under the stress path caused by sinking of large caisson is studied by using GDS stress path triaxial apparatus equipped with hall-effect displacement sensor and bend element device.Empirical formula of the relationship between maximum shear modulus G_max and effective mean principal stress p?as well as void ratio e is established based on experimental data.In addition,the reduction of shear modulus of soil loaded under different stress paths is analyzed.Results indicate that the rate of reduction is very high in the scope of small strain.Deflection angle of stress path has considerable influences on initial shear modulus,thus the results of bend element test after sample is consolidated under K₀ path are usually different from initial shear modulus in modulus reduction curve.（4）Numerical method to analyze caisson sinking process with the consideration of small strain characteristic is improved in utilizing Abaqus’subroutine VUMAT.FEM results present a small stress concussion phenomenon,better settlement curves of soil,and closer results of lateral displacement to monitoring result.A prediction line was proposed to predict surface settlements of caisson sinking under representative geological conditions in Zhenjiang.