Ground-borne vibration in end-bearing pile foundations : Numerical analyses and full-scale field tests

Ground-borne vibration originating from roads or railways is a growing concern in the design of buildings in urban areas. For soft cohesive soils, which are particularly susceptible to ground-borne vibration, pile foundations are often used. In shallow formations of soft soil on till and bedrock, which are conditions encountered in densely populated areas in Sweden, the piles are designed as end-bearing to transfer loads to the bedrock. The transmission of vibrations to a building is governed by the interaction between the soil and the foundation. It is therefore essential that the dynamic interaction between the foundation and the soil is taken into account when predicting vibrations in buildings at a design stage. This thesis aims to increase the understanding of ground-borne vibration transmission to end-bearing pile foundations and investigate how it can be taken into account in vibration assessment for buildings yet to be constructed. The problem is addressed through experiments and numerical simulations. A set of full-scale field tests are performed at a site with clay on till and bedrock to validate model predictions. Vibration measurements are performed in three stages of construction of a pile foundation: (1) at the free ground surface, (2) on the top of four end-bearing concrete piles and (3) on the concrete pile cap joining the piles together. Numerical models are implemented to investigate the influence of pile and soil parameters. The results are subsequently used to develop a simple approximation factor that can be used for estimating the foundation response from vibrations at the ground surface. The main scientific contributions of this work is the experimental validation of models or predicting ground-borne vibrations in an end-bearing pile foundation and an investigation of the influence of pile and soil properties on dynamic pile-soil interaction. The results show that the vertical vibration level of piles is considerably affected by the fixation of the pile tip and the relationship between the pile axial stiffness and the stiffness of the soil. It is found that, in contrast to floating piles, the vertical response of end-bearing piles subjected to an incident wave field can be significantly affected by pile-soil-pile interaction. The field tests show that, if the dynamic properties of the soil can be accurately determined, a numerical model can predict the dynamic vibration response of the pile foundation with reasonable accuracy. This provides confidence in the results obtained from numerical models, motivating their use for vibration assessment.