Research On The Mechanical Response Of The Embedded Foundation Under Horizontal Loads

Civil engineering construction witnesses a bloom with the implementing of the"Belt and Road"national strategy.Urban space utilization has gradually developed into three-dimensional,bridge construction has gradually expanded from inland to the sea,resource exploration has also shifted from land to the ocean,structures such as cross-river and cross-sea bridges emerge consecutively.Embedded foundations are adopted as the foundations of over 76%of the crossriver and cross-sea bridges because its high stability,integrity and stiffness.For example,the open anchor caisson foundations are subjected to great lateral loads during the structure operation,which result in significant stress variation response and bearing capacity problems of the soil.The dynamic interaction between the soil and offshore foundation is also very complicated when the foundation is subjected to horizontal dynamic wave loads or seismic loads,etc.Therefore,a comprehensive study on the soil stress characteristics,bearing capacity and dynamic response of embedded foundation under horizontal loading has both theoretical importance and engineering practical significance.In this study,indoor experimental test,theoretical analysis and numerical simulation are combined to investigate the static and dynamic mechanical response of embedded foundation under horizontal loading.The main research contents are summarized as follows:Self-designed lateral loading apparatus was used to demonstrate the bearing capacity performance of embedded foundation under horizontal loading.The distribution characteristics of the resistance force along the foundation side was obtained.Meanwhile,the loaddisplacement curves of embedded foundation were also depicted.Test results show that the resistance force along the foundation side distributes as parabolic form,the ultimate bearing capacity of the soil increases with the aspect ratio and upper loads of the foundation.The progressive failure mechanism was revealed by visualized semi-model test combined with Digital Image Correlation(DIC)technique.Spatial load distribution model of embedded foundation under horizontal load was established according to the test results.Based on Mindlin's basic stress solution and superposition principle,the analytical solution of non-uniform spatial distribution load induced additional stress was derived and evaluated.Parametric study results indicate that the horizontal load on the front side of the foundation accounts for the largest percentage of induced horizontal additional stress in the soil.The soil additional stress distribution law and influence scope are dependent with the aspect ratio and radius of the foundation.The soil failure envelope and evolution law of embedded foundation under vertical and horizontal loads were investigated by indoor tests together with numerical analysis.Based on the failure modes and soil displacement vector,the soil failure maneuvering field was established.The Mohr-Coulomb failure criterion and associated flow rule were adopted to derive the bearing capacity under the coupling effect of vertical and horizontal loads.The analytical results were assessed by comparing with the test results.Based on Biot's dynamic governing equation,the dynamic interaction between the foundation sidewall and soil are considered.Simplified Novak thin layer method and boundary conditions were introduced to obtain the reaction force along the foundation side and the foundation base.By the virtue of the dynamic equilibrium equation,the horizontal dynamic impedance of the embedded foundation in poroelastic medium were deduced.The accuracy of analytical solutions were verified by comparing with existing solutions.Numerical results were obtained to investigate the influence of dimensionless excitation frequency,foundation aspect ratio and relative soil stiffness on the horizontal dynamic response of the embedded foundation.The finite element model of soil-foundation dynamic interaction system was established considering the nonlinear behavior of the soil.A comprehensive study of the horizontal acceleration response under different seismic parameters and soil density were conducted.The soil-foundation interaction coefficient was introduced to demonstrate the effect of site conditions and input ground motion parameters.Results show that the soil density has significant impact on the dynamic response of structures.The relative lateral displacement of the site soil increases from linearly to exponentially with the weakening of the soil properties.