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مدل سازی تحلیلی و عددی پی برای توربین بادی بلند در خاک های مختلف
analytical and numerical modeling of foundations for tall wind turbine in various soils
wind farm construction is increasing progressively, to cope-up with the current global energy scenario. the advantage of clean energy and sustainability helps wind turbine construction to flourish rapidly. location of wind turbines is independent of foundation soil condition but depends on the wind speeds and socio-environment issues. hence, a construction sites may not be favorable in terms of geotechnical demands. the taller wind towers facilitate the generation of high energy production, which will increase loads on the foundation, and eventually increase the dimension of the foundation. hence, the choice of a suitable foundation system is necessary for geotechnical engineer to design tall wind towers.
this study aims to analyze different foundation types e.g., raft/mat foundation, pile group foundation, and piled raft/mat foundation using analytical calculation verified with numerical models using plaxis 3d software. the foundation for steel wind turbine towers 100 m high was designed for different types of soils e.g., soft clayey soil, medium-stiff clayey soil, stiff clayey soil, and sandy soil. the design wind speed was taken from the asce 7-10 (2010) standard for occupancy category iii and iv buildings and other structures, as the illinois region falls in that category.
the parametric study was performed by varying the diameter of raft/mat, wind speed, number of piles, and soil types to evaluate the settlement in any type of foundation with load sharing proportion in piled raft/mat foundation. first, the raft/mat foundation design was carried out manually by changing the diameter of 15 m, 20 m, 25 m, 30 m, and 35 m, and changing load by considering different wind speed. then the foundation was modeled using plaxis 3d software with a raft/mat diameter of 25 m, 30 m, and 35 m only, by considering the eccentricity and factor of safety criteria. with the increase in wind speed, the differential settlement on the raft/mat foundation was found to be increased. however, the increase in diameter of raft/mat caused the reduction in differential settlement. soft clayey soil was found to be more sensitive than other soils used in the present study. for the same diameter of raft/mat, applied the same wind load, the differential settlement of foundation in soft clayey soil was found to be 6-10 times higher than the sandy soil.
the position of piles was fixed based on the spacing criteria in the pile group foundation. the number of piles used in this study were 23, 32, and 46. settlement was found to be varied with the number of piles in all soils used in this study. the lateral deflection for soft clayey soil decreased to half, when number of piles increased from 23 to 46. the differential settlement was found to be increased with the increase in wind speed in pile group foundation. raft/mat foundation settlement was found to be 4 to 6 times higher than the settlement in pile group foundation in any soils, used in this study, for a given wind speed.
the result of piled raft/mat foundation showed that the majority of the total load is shared by the piles (i.e., 60% to 94%) and remaining load is shared by the raft/mat (i.e., 6% to 40%), based on the stiffness of raft/mat and piles as well as pile-soil-pile interaction. the increase in wind speed in the wind turbines increased the differential settlement of piled raft/mat foundation in all soils. similarly, the lateral deflection also increased with the increase in wind speed in pile raft/mat foundation in all soils. the plaxis 3d analysis revealed that the differential settlement in soft clayey soil was 1.5 to 2.0 times higher than the settlement in sandy soil.
the validation of numerical modeling was carried out by the raft/mat foundation using boussinesq’s theory and calculating settlement for single pile and group pile foundation.
the current study showed that the soft clayey soil and medium-stiff clayey soil favor deep foundation, like pile group and piled raft/mat rather than shallow foundation, like raft/mat foundation. the results obtained from both analytical calculation and numerical modeling was found to be approximately matching. this study will help local construction company and geotechnical engineer to guide a proper foundation design of tall onshore wind turbine.
مدل هیدرولوژیکی-ژئوتکنیکی جفت شده برای تعیین ظرفیت باربری و نشست الاستیک پی ها
coupled hydrological-geotechnical model for determining bearing capacity and elastic settlement of foundations
this dissertation presents a coupled hydrological-geotechnical framework to investigate the performance of shallow and deep foundations under hydrological events such as heavy rainfall and drought. the variation in performance of foundation, interface between the structure and ground surface, is caused by the uncertainties associated with not only the geotechnical parameters but also the hydrological parameters that include intensity and duration of hydrological events and water table depth. the impact of such hydrological events significantly alters the performance of foundations by changing the soil strength and stiffness parameters of subsurface soil which may lead to foundation failures. such failures can cause damage to the supporting structure. therefore, to better understand the performance of geotechnical systems under different hydrological events and also to build sustainable and resilient infrastructure systems, the design of geotechnical systems should be carried out in a coupled hydrological-geotechnical manner considering the site-specific geotechnical and hydrological parameters. to this end, a numerical framework is developed based on the partially saturated soil mechanics principles and applied to a number of sites in the united states to show the impacts of hydrological events in the performance of shallow and deep foundations. in this framework, the one-dimensional richards’ equation is numerically solved to compute the spatial and temporal variation of the degree of saturation and matric suction in subsurface soil due to the site-specific rainfall, evapotranspiration, and water table depth as model boundary conditions. then, the critical settlement and bearing capacity of foundations (as critical design values) are calculated using the average degree of saturation and matric suction within the foundation influence zone. it is worth mentioning that two different design methodologies based on the probabilistic analysis and single extreme hydrological cycle are considered in the proposed framework to have a better assessment of foundation performance. the results show that the hydrological parameters have a significant impact on the performance of shallow and deep foundations, and in general, they improve the predicted foundation design values obtained from conventional methods in terms of the settlement and bearing capacity. the proposed method can be used as a decision-making tool for selecting the suitable design values of foundations in engineering practice.