Dynamic Stability And Long-term Deformation Characteristics Of Gravity Breakwater On Soft Ground

Soft ground is widely distributed in the coastal areas of China.Soft soil exhibits obvious strength evolution and long term deformation with its characteristics of high natural moisture content,large compressibility,low permeability,low strength and high sensitivity under the cyclic wave and gravity load.Usually,the gravity structures are built in high bearing capacity ground,such as rock,sand,gravel or hard clay ground.It is a new subject of port and coastal engineering construction for building gravity breakwater on soft ground.Enhancement of physical and mechanical indexes of soft soil under static load,strength weakening of soft soil under cyclic loading,settlement deformation characteristics of soft soil under long term cyclic loading,stability and long-term settlement analysis of gravity breakwater on soft ground under long term cyclic loading are the key scientific and technical problems to be solved.In this paper,the above problems are studied systematically.The main research contents and results are as follows.(1)The static three axial test of soft soil strength under the action of static deviator stress,the dynamic three axial test of strength weakening of soft soil under cyclic loading and the dynamic three axial test of creep behavior of soft soil under long term cyclic loading were carried out.On this basis,the cyclic strength evolution model of soft soil considering the effect of anisotropic consolidation and the creep model of soft soil under long term cyclic loading were established,which provides a scientific basis for stability analysis and long-term deformation analysis of gravity breakwater on soft ground.(2)Based on the finite element dynamic model,the motion characteristics,the ground deformation characteristics,the bearing capacity mechanism and the failure modes of gravity breakwater on soft ground,as well as the elastic and plastic deformation of ground on the bearing capacity mechanism and the failure modes were investigated.The criterion of cumulative slippage for the dynamic anti-sliding stability analysis,the criterion of critical cumulative dip angle for the dynamic antioverturning stability analysis and the criterion of cumulative settlement for the ground bearing capacity analysis were put forward.(3)Based on the large scale finite element analysis platform ABAQUS,the cyclic strength evolution model of soft soil considering the effect of anisotropic consolidation established in this paper was implemented in ABAQUS by the secondary development,and the dynamic stability analysis model of gravity breakwater on soft ground was established considering the cyclic strength evolution of soft soil.The effects of the strength enhancement of soft soil under the action of static deviator stress and the strength weakening of soft soil under cyclic loading on the sliding stability,the overturning stability and the ground bearing capacity of gravity breakwater on soft ground were investigated by numerical calculations.(4)Based on the large scale finite element analysis platform ABAQUS,the cyclic creep model of soft soil under long term cyclic loading established in this paper was introduced into the CREEP user subroutine of ABAQUS by the secondary development,and the long-term deformation analysis mode of gravity breakwater on soft ground was established considering the creep behavior of soft soil under long term cyclic loading.The effect of cyclic creep of soft soil on the long-term deformation of gravity breakwater on soft ground was investigated by numerical calculations.(5)On the basis of the above works,the simplified dynamic model for the sliding stability and the overturning stability analysis of gravity breakwater on soft ground was proposed.Based on the criterion of allowable cumulative slippage,the criterion of critical cumulative dip angle in the design reference period and the stochastic simulation technique,the stability analysis methods for anti sliding and anti overturning of gravity breakwater in life cycle were established.The sliding stability and the overturning stability of a gravity breakwater in the life cycle were investigated using the stability analysis methods.(6)The method for the long-term deformation of gravity breakwater on soft ground considering the creep behavior of soft soil under long term cyclic loading was presented by integrating the proposed cyclic creep model of soft soil and layered summation method of ground settlement calculation.The long-term deformation of a gravity breakwater on soft ground was investigated using the method.