Reseach On Long-term Bearing Characteristic Of Caisson Subjected To Lateral Load

The subject is sponsored by the 4th sub-project "Deepwater Foundation Bearing Behavior under Complex Environment Evolution and Long-Term Performance Design"(2013CB036304)of the National Key Basic Research and Development Program(973 Program)"large-span bridges Whole Life Basic Research disaster control and the performance design"(2013CB036300).The calculating theories and methods for bearing behavior of caisson and creep behavior of soft soil were explored.The bearing behavior and calculation of caisson in soft soil was analyzed by the research methods combined with the model tests,insitu test,numerical calculation and theoretical analysis.The paper mainly focused on the following:The global model and semi-model tests of rectangular caisson,spilt anchorage caisson and bucket caisson subjected to long-term lateral load were carried out.The law of deformation of caisson model subjected to long-term lateral load and soil resistance with time were mainly analyzed,and the long-term bearing behavior of rectangular caisson and spilt anchorage caisson was discussed.The particle image velocimetry(PIV)technique model had been introduced to measure soil displacement with time.The test results showed that the PIV testing technology could reflect the long-term deformation trend of the model caisson,and lateral displacement-time curve were close to resluts measured by the conventional test method.The insitu long-term lateral loading tests of in Wangdong River Highway Bridge and group rooted caisson in Maanshan Yangtze River Highway Bridge were carried out.The load-displacement curves of the rooted caisson and the rooted caisson group were obtained.In the case of constant lateral loading,the long-term lateral displacement of rooted caisson and rooted caisson group were also tested.The lateral displacement distribution with depth of rooted caisson,group rooted caisson and soil aound rooted caisson at different time were analyzed.The results showed that long-term deformation of rooted caisson in soft soil area could not be ignored.The basic mechanical properties test,triaxial consolidated undrained shear tests and triaxial consolidated undrained creep test of remolded saturated clay and silty clay under different confining pressures were carried out.The basic mechanical characteristic parameters and the shear strength of soil samples under diff-erent confining pressure were determined.The deformation characteristics of two kinds of soil were summarized by analyzing the axial strain and axial creep rate variation with time.The parameters of one-dimensional Merchant rheological model and Burgers rheological model for the triaxial consolidated undrained shear creep test results of two kinds of soil was identificated by the nonlinear fitting function of Origin software.Based on the test results,the parameters of one-dimensional Mersi empirical rheological function and power function considering stress-strain relation by hyperbolic function as the same as Mesri function was obtained.The calculated results by four rheological models were analyzed with tested results.The one-dimensional Burgers rheological model could be extended to three-dimensional rheological model by transforming parameters of soil.Using regression analysis,the parameters of three-dimensional rheological model were determined.The parameters of three-dimensional Burgers rheological model of FLAC3D was validated by the triaxial rheological test results.The caisson-soil interaction was established according to the load balance relationship.By discreting caisson along the depth direction and establishing control equations of caisson-soil unit,the semi-analytical solution of deformation and internal forces of caisson could be obtained by the matrix transfer method.Based on the results of triaxial creep test,the attenuation law of the soil secant modulus Eso was described by the rheological parameters.Based on the relationship between the elastic modulus and the secant modulus E50,the rheological properties of the soil were deduced,and the attenuation expression of the reaction modulus of the foundation was obtained.The long-term lateral deformation of the caisson model was calculated according to the boundary conditions and loading conditions of the model test.The weighted average value of soil reaction modulus with time was used in calculation.The results show that the calculated results are in good agreement with the test results.In addition,the triaxial creep test results of undisturbed mucky silty clay are used to describe the decay law of the reaction modulus of the soil foundation by the parameters of rheological parameters.The long-term lateral deformation of the rooted caisson of Wangdong Yangtze Highway Bridge in the field test was calculated by using this algorithm,and the variation law of the rooted caisson with the time was consistent with calculated results.Based on the calculation theory of long-term horizontal load-bearing capacity of caisson proposed in this paper,the long-term lateral deformation of circular caisson was calculated and its deformation characteristics were predicted for the whole process of Qiongzhou Strait Bridge,which could be referred by engineering safety and maintenance.Finally,the research work of this dissertation had been summarized,and some suggeastion had been proposed for further research about the mechanics of caisson subjected to the long-term loading.