| With the increase of the number of immersed tunnel construction and the use time,the settlement problem of immersed tunnel foundation is gradually prominent,especially under the condition of offshore large siltation,the settlement of immersed tunnel foundation needs more attention.In addition,for segmental immersed tunnel,there are few practical projects to retain the longitudinal prestress for floating and sinking,so it is a matter of the utmost engineering importance to judge the influence of the degree of prestress tension on the foundation settlement from the quantitative point of view.Relying on the immersed tunnel project of Hong Kong-Zhuhai-Macao Bridge,this paper takes E18 pipe section which is located in the natural foundation section and the upper part with large siltation as the prototype,and uses the means of model test and numerical simulation to study the settlement law of immersed tunnel foundation and the distribution law of basement stress under different siltation degree and different prestress tension degree.The main contents and conclusions are as follows:First of all,this paper summarizes the research status of foundation settlement and foundation stress of immersed tunnel,determines the research contents,and selects the research methods.After determining the prototype of the model test and its related parameters,according to the similarity theory,determine the similarity relationship,simplify the model test,select the model material,determine the loading mode,determine the measurement system,set the test conditions,and then complete the formulation of the model test scheme.In the next place,after completing the preparatory work of customizing model soil box,calibrating tunnel model,preparing foundation model and calibrating measuring equipment,the model test was carried out according to the test scheme.The results of model test show that:no matter what degree of back siltation,the maximum settlement of pipe section decreases about0.47×10-4m every time the prestress increases by 20%;no matter what degree of back siltation,the maximum differential settlement of adjacent section is about 0.7‰when the prestress is not set,and the maximum differential settlement of adjacent section is about 0.17‰when the back siltation reaches 100%and the prestress tension reaches 80%,it is about 25%of that without prestress.After that,taking the model test as the object,the finite element software was used to select the constitutive model,establish the geometric model,determine the material parameters,divide the model mesh,and define the calculation section.The results of numerical simulation show that the maximum settlement of pipe section decreases by about 0.45×10-4m every time the prestress increases by 20%;no matter what degree of siltation,the maximum differential settlement of adjacent sections is about 0.5‰when the prestress is not set,and the maximum differential settlement is about 0.15‰when the prestress is 80%,which is about 30%when the prestress is not set.In the end,the achievements of the model test and the results of the numerical simulation is compared,and it is discovered that the foundation settlement laws of the two are relatively consistent,and the differential settlement and the distribution of foundation stress are basically consistent.The outcomes of the model test and the numerical simulation both show that:with the increase of the degree of prestressing,the foundation settlement and differential settlement decrease in varying degrees,which shows that the prestressing can inhibit the foundation settlement and differential settlement;the greater the back siltation,the greater the base stress,and the increase value of the base stress of each segment of the pipe section is basically the same;when the back siltation is the same,with the increase of the degree of prestress tension,the difference of the base stress between each segment of the pipe section gradually decreases,which indicates that the application of prestress has a homogenizing effect on the base stress. |
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