Structures and buildings built on soft soil require deep foundations often consisting of piles. Through the piles, loads are transferred to deeper soil layers which are capable to mobilise enough bearing capacity for the superstructure. During installation of a displacement pile, the soil around the pile gets distorted which leads to a change of stress, density and soil properties in the distorted zone. The quantification of change in soil properties, soil state and the influenced zone around the pile during installation are yet a remaining uncertainty in geotechnical engineering. This thesis examines the mechanisms that govern pile installation and subsequent loading by numerical analysis. The study focuses on jacked and impact hammer installation techniques in dry and fully saturated sand...@en

A constitutive model for granular materials which considers grain crushing effects is developed in the framework of hypoplasticity. As grain crushing occurs the behaviour of granular material can usually be significantly affected. Several empirical relations between peak strength, uniformity coefficient and stiffness of sand depending on stress level or amount of grain crushing have been derived in the past. In this paper, such relations are employed to improve a basic hypoplastic constitutive model based on the changes of stress level or grain size distribution. In the proposed modified hypoplastic model only two additional physical parameters, namely uniformity coefficient and mean grain size are incorporated. The validation of the modified model for three different sands under triaxial test response with cell pressures up to 30 MPa is presented and shows a significantly better correspondence with regard to the original basic hypoplastic model.

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In this study, installation of jacked piles in sand is simulated using Press-Replace Method (PRM) and Material Point Method (MPM) and the results are compared together. This comparison is important because a realistic and yet efficient simulation of installation of jacked piles is an appealing step towards the design and analysis of this type of displacement piles. It is shown that PRM as a method that is founded on small-strain finite element method can produce pile and soil responses that are in a promising agreement with those of MPM which is a finite-deformation analysis method.@en