Research On Settlement Characteristics And Calculation Of Immersed Tube Tunnel With Soft Foundation And High Siltation

For the settlement characteristics and calculation of immersed tube tunnel with softfoundation and high siltation, there is no mature experience for reference. Foundationsettlement method and parameter selection of it has great significance for tunnel design andconstruction. In this paper, a set of effective method of parameter selection for settlementcalculation is deduced through combination of field test and indoor model test method.Settlement calculation method of immersed tube tunnel foundation with the constructionprocess is established. The springback recompression settlement characteristics of immersedtunnel natural foundation is revealed though centrifugal test of qualitative analysis andquantitative calculation of subsidence. The sensitivity influence of geotechnical parametersvariability, construction deviation and back silting quantity on settlement is analyzedcombined with the Monte Carlo probabilistic finite element method (fem). The mechanicalmode of the elastic foundation beam under the condition of uneven soil layer is established.Calculation method of settlement control for immersed tube tunnel settlement is deduced. Itprovides the important support to immersed tube tunnel for the design optimization of basecase and the improvement of construction technology.1. Small scale centrifuge model testing program of simulating the whole constructionprocess is come up based on analysis of field test data and model similarity theory andseepage consolidation theory. The centrifuge acceleration in centrifugal model test isdetermined combination with the engineering practice and the centrifugal force fieldcharacteristics. Choose special organic glass for immersed tube material. The similaritybearing conditions for the model and the prototype are realized through to the part geometrycorrection. The testing components of high sensitivity and high precision are set on the model.The results revealed the changes regularity of spring-back recompression deformation and thestress distribution of the basement. The mechanism of cushion layer function is clear-cut. Italso provides the soil sample conditions for mini-probe cone penetration test and indoorroutine test.2. Foundation parameters decide the accuracy of settlement calculation. To obtain theaccurate calculation parameters and reduce the error in the process of sample collection andpreparation, this paper based on the comparative analysis of cone penetration test with2cm2 and15cm2probe. The regression formula between the data of cone penetration test and thelocalized parameters is established as a bridge to result of CPTU test with2cm2probe. And itprovides experience for the research of cone penetration test to determine the parameters ofthe special stratum soil under the bottom of the sea. That is used to determine the calculationparameters for late.3. The model of finite element calculation and a model of simplified calculation forsettlement are established with the considering of the whole construction process such as theexcavation trench, laid bedding, intro the tunnel tube, tube top back silting and the excavationof channel. The settlement characteristic of natural foundation is revealed. The interactionmechanism between backfill, immersed tube and the foundation is clear-cut. The extents thathave larger change of foundation stiffness are determined.4. Combined with the analysis method of traditional finite element and Monte Carlotheory, the sensitivity influence of geotechnical parameters variability, construction deviationand back silting quantity on settlement is analyzed by the sensitivity analysis method basedon the Spearman rank correlation coefficient. The influence factors with larger sensitivity aredetermined. The most unfavorable conditions combination and distribution form for thesettlement are obtained. That provides a reference for construction control.5. The mechanical mode of the elastic foundation beam under the condition of unevensoil layer is established combining with the theory of beam on elastic foundation. Theequation of displacement curve along the tunnel longitudinal and the section shear of a tunnellocation are calculated. Immersed tube tunnel settlement control standard is deduced. Itprovides the conditions for the design optimization of base case and the improvementmeasures of construction technology.