Analytical and Numerical Modelling of Combined Pile-Raft Foundation for Tall Wind Turbine in Various Soils

Abstract

The wind farm construction is increasing progressively based on current global energy scenario. The advantage of sustainability and clean energy helps wind turbine construction to increase rapidly. The location of wind turbines is based on the higher energy production (i.e. wind speeds) and socio-environment issues. Hence, construction sites may not be favourable in terms of geotechnical demands. The use of taller towers facilitates the generation of high power which will increase loads on the foundation. Hence, good foundation system is necessary for the designers. The aim of this study was to analyse combined pile-raft foundation (CPRF) using analytical calculation and verify the result with numerical modelling using PLAXIS 3D software. The foundation for wind turbine tower of 120 m high was designed for different types of soils, e.g. soft soil, medium-stiff soil, stiff soil, and sandy soil. The design wind speed was taken from ASCE 7-10 (2010) standard for Occupancy Category III and IV Buildings and Other Structures. The parametric study was performed to evaluate the effect of wind speed, the number of piles, and different soil types. It was found that the increase in wind speed increases the differential settlement of foundation. The result shows that majority of the total load was taken by the piles and remaining load was taken by raft based on the stiffness of both raft and pile as well as pile-soil-pile interaction. There was significant decrease in differential settlement of pile-raft foundation in stiff and sandy soil as compared to soft soil and medium-stiff soil.KeywordsCombined pile-raftNumerical modellingWind turbineLoad sharing mechanism