Study Of Mechanical Properties Of Weathered Granite And Bearing Failure Mechanism Of Large OWT Monopile Foundation

In recent years,China has enjoyed rapid economic growth,problems such as energy shortage and environmental pollution caused by traditional fossil energy have attracted attention,and the development and utilization of green renewable energy has become a top priority to which energy has been an important influencing factor.To promote green development and the harmonious coexistence of human and nature,and to take the turn from high speed to high quality in economic development,offshore wind power generation has come into view with its unique advantages.Today,offshore wind power in China is mostly found in Jiangsu,Zhejiang,Fujian and other areas along the southeast coast,where the offshore seabed rock foundation is of different weathering degrees and complex geological conditions.The pile foundation of the offshore wind turbine is long under complex marine loading,and can easily break in daily operation,affecting normal function.However,the model and state of failure in the single pile foundation of large-scale offshore wind turbine remain unclear under complex offshore geological conditions and load.In this paper,focusing on the weathered rock foundation seabed in the coastal area of Pingtan Country,Fuzhou City,Fujian Province,the breaking mechanism of weathered granite in the seabed and failure of the load-bearing foundation of the large single-pile offshore wind turbine are analyzed with laboratory test,numerical simulation and other methods.The main work and achievements are as follows:(1)Laboratory test of element rock mass after sampling on project site(triaxial compression test).The tests produce physical-mechanical properties and strength parameters of the rock samples.By loading pre-strain triaxial test,special mechanical properties of offshore rock materials under complex loading are studied,and the causes of disaster and failure process explored.It is concluded that almost no plastic strain occurs at the low strain stage(no more than 75%of the peak strain),and the change of rock properties and internal structure is small.This is expected to provide important and accurate parameter support and reference for the engineering design,construction and safety analysis of large diameter single pile.(2)A 3D finite element numerical model is built by the way of finite element numerical simulation to analyze the failure model of load-bearing foundation of the pile with different diameter and soil properties under single-direction horizontal load.The load-displacement response and failure mode under single-direction vertical load and moment load are also studied,and the p-y curve at different depths under single-direction horizontal load extracted.Based on the built 3D finite element numerical model,the combined load is applied onto the pile head to simulate the multi-load effect on the wind turbine foundation.With the obtained failure envelope under combined load,under the effect of different combinations of complex load,select one direction each to apply the displacement that meets the failure criterion and study the development and failure model of soil around pile foundation under different loading conditions,thus determining the failure state and model of bearing failure of large pile foundation.