| Immersed tunnel has weadly used throughout the world, with its advantage of low buried depth, good waterproofness, great foundation flexibility, and so on. Espercailly, with the economy development of coastal areas, immersed tunnel has more and more applications in cross-river and cross-sea engineering. Segmental joints are equal to construction joints of immersed tunnel elements, and they can avoid element’s cracking caused by concrete shrinkage and creep, as well as thermal stresses. Shear keys as important components of segmental joint play an important role in water stiffness of segmental joints, however, they have not only no unified design standards but design deficiencies. This paper takes advantage of the national science and technology support project ―Research and demonstration of Hong Kong-Zhuhai-Macao bridge cluster project construction key technology‖ to research the mechanism and structural properties of segmental joints, under effects of differential settlements. The main work is as fellows:(1)Basing on field surveies, design and research data in domestic and overseas, the main influence factors of shear keys were analyzed, at the same time, typical working conditions of shear keys under the influence of differential settlements were clarified. The e-logp and improved Janbu tangent modulus method were adopted to estimate foundation stiffnesses and settlements of the immersed tunnel, which provided a guide for model tests.(2)ANSYS software was adopted to build 3-D numerical models of segmental shear keys, which had considered nonlinear characteristics of shear key rubber mat, contacting effects of segmental joints, as well as contacting effects between segments and soil. Through analyzing the characteristics of joint stress, sensitive areas of segmental joints were determined. Besides, longtitudinal and transverse distribution rules of shearing force on segmental joints were obtained by integrating node stresses of shear keys. What’s more, shearing force distribution along the length of segmental joint shear key and segmental joint shear ratios on shear keys could be obtained.(3)On the basis of foundation settlement test platform, through technical renovation and upgrading, a model test system with funcitons of model pouring, docking, settlement controlling, loading and testing was built and 1:4.69 large scale settlement model tests of segmental shear keys were carried out. In order to ensure model test safety and its smooth going, assembling shear key scheme and similarity material design were adopted. Controlling jacks at the bottom of experimental platform could simulate working conditions of longitudinal bending, longitudinal twisting and vertical shearing under effects of longditudinal and transverse differential settlements.(4)Corresponding connections between physical model tests and project entity could be built thorough the relationship between contraction scale numerical simulations and full scale numerical simulations, and the model test results could be backstep to project entity depending on this. According to the results of the stress vector in numerical simulation and destruction features in model tests, mechanisms and destruction laws of shear keys on segmental joints were proclaimed. Moreover, according to the mechanical characteristics of segmental joint shear keys, structural measures that could decrease localized stress on shear keys were put forward.(5)Using the method of 3-D numerical simulation analysis, the influence of heights, extended lengths of segmental joint shear keys, and wall thickness on segmental joint shear ratio was got. Futher more, through comparing analysis of basement stress and shear key stresses in centrifugal model tests and two-dimensional numerical simulations, from the whole interaction system of tunnel segments and soil, the relationship between shear key stresses and wall structure stiffnesses was studied. Finally, the design principle that shear key size should be proportional to the immersed tunnel wall stiffness was proposed.(6)Basing on Winker beam on elastic foundation theory, joint shear simplified formulas of longitudinal bending and vertical shearing working conditions were deduced. Furthermore, taking advantage of the shear ratio result, shear simplified formulas of each shear keys were acquired.(7)By means of theoretical calculation and experiments, ultimate shearing forces on shear keys under normal use limit state and bearing capacity limit state were obtained. According to the regression formula between differential settlement and shear key shearing forces, the allowing differential settlement value when shear keys were in serviceability limit state was Determined. Besides, on the basis of the regression formula between differential backfilling on top of cover and shear key shearing forces, the dredging standard on top of cover when shear keys were in serviceability limit state was confirmed. |
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