Increasing the Soil Rotational Stiffness using Rammed Aggregate Piers for Wind Turbine Tower Foundations

Juan Pablo Rodriguez¹; Kord Joachim Wissmann¹

¹ Geopier Foundation Company

Baixar PDF doi:10.20906/CPS/CB-04-0066

Resumo

Wind turbine tower foundations must be designed to limit the angular rotation of the tower. Rammed Aggregate Piers (RAPs) are commonly used as a mean for increasing the available soil rotational stiffness by taking advantage of their higher stiffness compared to that of the matrix soil being reinforced. A composite stiffness approach using the elastic dynamic parameters of the soil and the RAP elements is used to develop a solution for increasing the foundation soil available rotational stiffness, thereby meeting the project design requirements. This article presents the technical background and procedures used for developing a solution for increasing the foundation soil rotational stiffness using Rammed Aggregate Piers for support of wind turbine tower foundations. A case history example is also presented at the end to support the technical discussion. Rammed Aggregate Piers are a ground improvement solution that have been used for more than 20 years to provide soil reinforcement solutions or foundation support in the commercial, industrial, manufacturing and power markets. This ground improvement technology is used to provide improved strength and stiffness of soft or compressible soils. An example of this system involves drilling a 0.60m to 0.90m diameter cavity, (depending on design requirements), placing thin lifts of aggregate within the cavity and vertically ramming the aggregate using a high energy beveled impact tamper. During construction, the high-frequency energy delivered by the modified hydraulic hammer, combined with the beveled shape of the tamper, not only densifies the aggregate vertically to create a stiff aggregate pier, but also forces aggregate laterally into the sidewall of the hole, resulting in a lateral stress increase in surrounding soil. The lateral stress increase reduces the compressibility of the surrounding soil and promotes positive coupling of the aggregate system element and the soil to create an improved composite, reinforced soil zone. The RAPs construction procedure may us

Palavras-chave: Rotational Stiffness; Rammed Aggregate Piers; Wind Turbine Tower Foundations; Ground Improvement; Soil Reinforcement; Settlement