Daniel Aubram

Vibro-Injection Pile Installation in Sand: Part II—Numerical and Experimental Investigation

In Part 1 of this series of papers a macroscopic two-equation (two-field) reduced model for the mechanics of the multi-material flow associated with vibro-injection pile installation in saturated sand was derived. Here we employ this model to develop a so-called multi-material arbitrary Lagrangian-Eulerian (MMALE) method. MMALE avoids the disadvantages of the classical approaches in computational continuum mechanics concerning large deformations and evolving material interfaces. The numerical implementation of this method will be outlined, and then the experimental investigations will be presented that have been carried out in order to validate the computational model. Among these investigations, small-scale model tests in chambers with observing window have been designed step-by-step to reveal penetration and vibro-injection pile installation phenomena.

Vibro-Injection Pile Installation in Sand: Part I—Interpretation as Multi-material Flow

The installation of vibro-injection piles into saturated sand has a significant impact on the surrounding soil and neighboring buildings. It is generally characterized by a multi-material flow with large material deformations, non-stationary and new material interfaces, and by the interaction of the grain skeleton and the pore water. Part 1 in this series of papers is concerned with the mathematical and physical modeling of the multi-material flow associated with vibro-injection pile installation. This model is the backbone of a new multi-material arbitrary Lagrangian-Eulerian (MMALE) numerical method presented in Part 2.

Contribution to the Non-Lagrangian Formulation of Geotechnical and Geomechanical Processes

Numerical simulations of geomechanical and geotechnical processes, such as vibro-injection pile installation, require suitable algorithms and sufficiently realistic models. These models have to account for large deformations, the evolution of material interfaces including free surfaces and contact interfaces, for granular material behavior in different flow regimes as well as for the interaction of the different materials and phases. Although the traditional Lagrangian formulation is well-suited to handling complex material behavior and maintaining material interfaces, it generally cannot represent large deformation, shear and vorticity. This is because in Lagrangian numerical methods the storage points (nodes resp. material points) move with the local material velocity, which may cause mesh tangling resp. clustering of points. The present contribution addresses the development of models for geotechnical and geomechanical processes by utilizing Eulerian and Arbitrary Lagrangian-Eulerian (ALE) formulations. Such non-Lagrangian viewpoints introduce additional difficulties which are discussed in detail. In particular, we investigate how to track interfaces and to model interaction of different materials with respect to an arbitrarily moving control volume, and how to validate non-Lagrangian numerical models by small-scale experimental tests.

Theory and Numerical Modeling of Geomechanical Multi-material Flow

Multi-material flow describes a situation where several distinct materials separated by sharp material interfaces undergo large deformations. The research presented in this paper addresses a particular class of multi-material flow situations encountered in geomechanics and geotechnical engineering which is characterized by a complex coupled behavior of saturated granular material as well as by a hierarchy of distinct spatial scales. Examples include geotechnical installation processes, liquefaction-induced soil failure, and debris flow. The most attractive numerical approaches to solve such problems use variants of arbitrary Lagrangian–Eulerian descriptions allowing interfaces and free surfaces to flow through the computational mesh. Mesh elements cut by interfaces (multi-material elements) necessarily arise which contain a heterogeneous mixture of two or more materials. The heterogeneous mixture is represented as an effective single-phase material using mixture theory. The paper outlines the specific three-scale mixture theory developed by the authors and the MMALE numerical method to model and simulate geomechanical multi-material flow. In contrast to traditional flow models which consider the motion of multiple single-phase materials or single multi-phase mixture, the present research succeeds in incorporating both the coupled behavior of saturated granular material and its interaction with other (pure) materials.

Numerical Investigation of the Frequency Influence on Soil Characteristics During Vibratory Driving of Tubular Piles

In offshore geotechnics, tubular piles are commonly used as the foundation system. Such piles are installed using vibratory or impact driving. The choice of the proper loading configuration plays an important role in the driving performance, especially in reaching the desired penetration depth. Numerical evaluation of such processes involves handling large material deformation, making it hard for the classical numerical methods to reach a reliable result after significant deformation. In addition, in case of the dynamic cyclic loading, the soil exhibits complex behavior which emphasizes the role of a suitable soil constitutive equation. In this study, a numerical model is developed and utilized to evaluate the effects of the frequency in the vibratory installation of tubular piles on the neighboring soil. The numerical model employs the robust Multi-Material Arbitrary Lagrangian-Eulerian (MMALE) method in conjunction with an advanced material model formulation based on the hypoplasticity concept, and is validated against an experiment done at TU Berlin. Subsequently, a parametric study is performed by applying six different frequencies between 12 and 30 Hz to the dynamic load. The resulting penetration depth, void ratio and the lateral stress distribution in the soil are compared and evaluated. It is concluded that an optimum frequency must be determined to reach the maximum penetration depth by using the same load magnitudes.

Lagrange-Euler Formulierungen in der Bodenmechanik

Bodenmechanische und geotechnische Problemstellungen werden haufig durch grose Materialverformungen und andere damit einhergehende Phanomene gekennzeichnet. Bei deren Modellierung stosen die klassische Bodenmechanik und die traditionelle Finite Elemente Methode basierend auf der Lagrange Formulierung an ihre Grenzen. In dem Beitrag werden die kontinuumsmechanischen Grundlagen einer verallgemeinerten Lagrange-Euler Formulierung vorgestellt. Anschliesend werden ihre unterschiedlichen Auspragungen im Rahmen der numerischen Umsetzung anhand von Anwendungsbeispielen diskutiert sowie das Potential dieser Simulationsmethoden in der Bodenmechanik und Geotechnik aufgezeigt.