Scale Modelling And Numerical Analysis Of Monopile In Marine Soft Clay Soil Under Lateral Cyclic Loads

In recent years,with the rapid development of offshore wind turbine engineering,the pile foundation(especially the large monopile foundation)became the first priority foundation in offshore wind industry with the advandages of simple structures,short construction duration.Meanwhile,a monopile foundation of an offshore wind turbine will be subjected to long-term lateral low-frequency cyclic loading,such as wind,wave and ocean current loads over the its lifetime and creates accumulated lateral deformation.When the rotation deformation of the pile foundation excels 0.5°,the wind turbine would propably operate unnormally and failed.At present,the standard design procedure for pile foundation of offshore wind turbine is the nonlinear p-y curve method which is adopted by API and DNV codes.The proposed p-y curve methods are based on field and lab tests with small diameter piles and limited cycles,and the soil conditions within tests are mostly sand and stiff clay,which makes most of these studies is not applicable for soft clay condition.Thus,how to assess and predict the lateral deformation of offshore wind turbine monopile foundation in soft clay under long-term cyclic loading is very important for engineers.To deal with this problem,this paper conducts lab and numerical model tests to investigate the behaviours of monopile pile foundation in soft saturated marine clay under lateral cyclic loading.the main work is listed as follows:(1)Developed a kind of new lateral cyclic loading equipment,which is simple and easy to design for yourself and capable to create harmonic loads woith different amptitude.(2)Conducted indoor monopile model tests under static loading and studied its stress and deformation behaviours.Then,compared the test results with the API p-y curve results.(3)By conducting the cyclic loading tests of monopile foundation,the cyclic stress and accumulated deformation behaviours of the monopile,the attenuation effect of p-y curve along the depth discussed.Also,this paper describes the failure evolution of soil foundation and porepressure generation phenomenon of the soil around the pile.(4)The three dimensional finite element model of monopile foundation was presented to study the lateral accumulated deformation of pile head,pile stress and soil stress along the depth under cyclic lateral loading.Meanwhile,the effects of loading types(one way and double way loading),loading amptitude and soil-pile contact conditions on the monopile cyclic behaviours are also investigated.