Maik Schenke

Simulation of Soils Under Rapid Cyclic Loading Conditions

The stability of structures strongly relies upon the strength and stiffness of the foundation soil underneath. If fluid-saturated or nearly saturated soils are subjected to rapid cyclic loading conditions, for instance, during earthquakes, the intergranular frictional forces might be dramatically reduced. Subsequently, the load-bearing capacity decreases or even vanishes, if the soil grains loose contact to each other. This phenomena is often referred to as soil liquefaction. Drawing our attention to fluid-saturated granular materials with heterogeneous microstructures, the modelling is carried out within a continuum-mechanical framework by exploiting the macroscopic Theory of Porous Media (TPM) together with thermodynamically consistent constitutive equations. In this regard, the present contribution proceeds from a fully saturated soil, composed of an elasto-plastic solid skeleton and a materially incompressible pore fluid. The governing material parameters of the solid skeleton have been identified for the research-unit sand. The underlying equations are used to simulate soils under rapid cyclic loading conditions. In this regard, the semi-infinite domain is split into a near field, which usually the domain of interest, and a far field, which extents the simulated domain towards infinity. In order to avoid wave reflections at the near-field boundaries an energy-absorbing layer is introduced. Finally, several simulations are carried out. Firstly, a parametric study of the particular far-field treatment is performed and, secondly, soil liquefaction is simulated, where the underlying initial-boundary-value problem is inspired by practically relevant scenarios.

Simulation of Cyclic Loading Conditions Within Fluid-Saturated Granular Media

In civil engineering, the installation of a reliable foundation is essential for the stability of the emerging structure. Already during the foundation process, a comprehensive survey of the mutual interactions between the preliminary established construction pit and the surrounding soil is indispensable, especially, when building in an existing context. In this regard, drawing our attention to the construction site at the Potsdamer Platz in Berlin, which resides within a nearly fully saturated soil and in the immediate vicinity of existing structures, measurements have revealed significant displacements of the retaining walls during the vibratory installation of the foundation piles via a so-called vibro-injection procedure. Herein, due to the gradual plastic strain accumulation and the small pore-fluid permeability of the granular assembly, the rapid cyclic loading conditions gave rise to a gradual pore-pressure build-up, which degraded the load-bearing capacity of the surrounding soil.

Towards the Holistic Simulation of Geotechnical Foundation Processes Using Vibro-Injection Piles

In civil engineering, the installation of a reliable foundation is essential for the stability of the emerging structure. Thus, already during the foundation process, a comprehensive survey of the mutual interactions between the preliminary established construction pit and the surrounding soil is indispensable, especially when building in the existing context. Addressing the simulation of geotechnical foundation processes using vibro-injection piles, complex initial-boundary-value problems are necessary. In particular, the numerical model is composed of several mutual interacting parts, such as retaining walls, anchors and vibro-injection piles, all interacting with the surrounding soil. Additionally, a fine mesh is required in order to adequately resolve local effects such as shear bands. However, when such complex simulations are inevitable, explicit time-integration schemes are advantageous over implicit schemes. In this regard, the present contribution addresses the development and application of a numerical soil model based on the Theory of Porous Media, which is suitable for simulations exploiting the explicit time-integration schemes of Abaqus/Explicit. The underlying numerical soil model is investigated in terms of accuracy and parallel efficiency.

On the Analysis of Porous Media Dynamics Using a Dune-PANDAS Interface

The increasing complexity of numerical models and the requirement for more computational power is covered by multi-processor and multi-core hardware architectures. In order to exploit the capabilities of these machines, parallel algorithms are necessary. Therefore, the following article will describe first attempts in parallelizing the finite-element code PANDAS through an interface to the parallel software framework Dune. In this regard, this connection will overcome the computational limits of the sequential finite-element code PANDAS by introducing its material definitions to the Dune framework, in particular, to the external Dune module Dune-PDELab. As a first example, the propagation of a two-dimensional elastic shear-wave through a fluid-saturated soil will be analyzed in a non-parallel environment.