Design of deep foundations on bored piles

Abstract

The paper describes the design of pile foundation on the site of the Elektrenai power plant, Lithuania. The foundation is aimed to support equipment of the power plant consisting of the gas turbine, the steam turbine and the generator. Besides high loads, the equipment had a strong dynamic impact on the foundation due to its working conditions and vibration. The pilling solution was adopted due to different reasons: i) the capacity of the soil to support great stresses over it; ii) the special requirements of the main equipment about settlements, movements and stresses. Pilling foundation was evaluated through immediate settlement analysis, which was carried out employing four most widely used methods. It included analysis of the soil data from cone and dynamic penetration tests, boreholes and laboratory tests. Soil properties were estimated from site investigation and soil exploration program according to Lithuanian standards. Pile settlement analysis showed that settlement value was 14 mm (pile toe settlement), and settlement value of elastic deformation of pile from vertical compressive loads was 3 mm. For such structure, foundation settlement should not be more than 16 mm (i.e., no more than 2 % of pile diameter). It was estimated that for pile of diameter 800 mm, pile length of 24 m was sufficient to endure overall loads.