Stone Column Ground Improvement Against Liquefaction for the Preveza-Aktio Immersed Tunnel

The construction of the road fixed-link crossing between Preveza and Aktio on the north-western coast of Greece has recently been completed. The project consists of an immersed single-tube tunnel under the strait and two cut-and-cover tunnels at the ends of the immersed part. The immersed section is constructed of eight precast rectangular concrete elements placed on the sea bottom at a depth of 25 m. The site is characterized by high seismicity. Foundation soil consists of Holocene marine sediments comprising irregular layers of sands, silts and clays that extend to great depth in the central part of the strait. Along the entire tunnel alignment the silty sands and sandy silts of the top layers are classified as potentially liquefiable due to their low density. Soil improvement in the form of stone columns has been carried out below the tunnel foundation for reducing risk from liquefaction. The soil conditions and the seismic input parameters are presented and an overview of the extensive dynamic laboratory testing program conducted is given. The seismic site response analyses performed for determining the depth of ground improvement are summarized. The design of the stone columns as well as a practical method for estimating the stiffness of the composite soil are described

Lagrange-Euler Formulierungen in der Bodenmechanik

Bodenmechanische und geotechnische Problemstellungen werden häufig durch große Materialverformungen und andere damit einhergehende Phänomene gekennzeichnet. Bei deren Modellierung stoßen 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. Anschließend werden ihre unterschiedlichen Ausprägungen im Rahmen der numerischen Umsetzung anhand von Anwendungsbeispielen diskutiert sowie das Potential dieser Simulationsmethoden in der Bodenmechanik und Geotechnik aufgezeigt.DFG, 76838227, Numerische Modellierung der Herstellung von Rüttelinjektionspfähle

Geotechnical and Environmental Consideration by Planning and Construction of the Transportation Infrastructure in the Centre of Berlin

Since the mid of the nineties in the City of Berlin there have been built underground installations, i.e. railway and street tunnels as well as foundations deep embedded in the groundwater, with some extraordinary measures. The surface area of all tunnel constructions of the VZBProject (inner city traffic tunnels in Berlin) amounts to approx. 240,000 square meters. The excavation pits for the tunnel structures have depths of more than 20 meters and widths of more than 100 meters. All this projects lead in the mid nineties to the characterization of the City of Berlin as Europe`s biggest construction site. A general overview of the transportation infrastructure project will be given here. A number of technical problems had to be resolved and new strategies devised at the planning stage because of the geotechnical and hydrogeological conditions in the central area of Berlin, the environmental requirements concerning groundwater conditions, and interaction with the surrounding green area and the nearby existing buildings. Several methods of tunnelling constructions in cohesionless soils with high ground water level were applied, such as caissons, shield driven tunnels and trough-type excavations (cut-and-cover tunnels). The geotechnical and hydrogeological conditions will be presented and the planning and realization of the tunnelling construction methods will be explained in the paper. Quality assurance was an important issue of the project and included an extensive monitoring system to ensure the quality of the constructions and to control the prior design and calculations. The impact of the project on the urban life and on the environment wouldn`t be minimized without a sophisticated project and ground water management. A very extensive measurement program in the frame of the quality assurance and geotechnical observation method was performed. It consisted of tension loading tests of single piles and groups of piles as well as measurements of anchor forces, wall deformations, uplift and leak water. Some data of monitoring are presented and discussed in this case history report

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.DFG, 76838227, Numerische Modellierung der Herstellung von Rüttelinjektionspfähle

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

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.DFG, 76838227, Numerische Modellierung der Herstellung von Rüttelinjektionspfähle

Dynamic stresses in an elastic half-space

This paper deals with the problem of time-varying point loads applied onto the surface of an elastic half-space and the stresses that such loads elicit within that medium. The emphasis is on the evaluation of the isobaric contours for all six of the stress components at various frequencies of engineering interest and for a full range of Poisson’s ratios. The extensive set of pressure bulbs presented herein may be of help in predicting the severity of dynamic effects in common practical situations in engineering—or even the lack thereof

An ALE method for penetration into sand utilizing optimization-based mesh motion

The numerical simulation of penetration into sand is one of the most challenging problems in computational geomechanics. The paper presents an arbitrary Lagrangian–Eulerian (ALE) finite element method for plane and axisymmetric quasi-static penetration into sand which overcomes the problems associated with the classical approaches. An operator-split is applied which breaks up solution of the governing equations over a time step into a Lagrangian step, a mesh motion step, and a transport step. A unique feature of the ALE method is an advanced hypoplastic rate constitutive equation to realistically predict stress and density changes within the material even at large deformations. In addition, an efficient optimization-based algorithm has been implemented to smooth out the non-convexly distorted mesh regions that occur below a penetrator. Applications to shallow penetration and pile penetration are given which make use of the developments.DFG, FOR 1136, Modellierung von geotechnischen Herstellungsvorgängen mit ganzheitlicher Erfassung des Spannungs-Verformungs-Verhaltens im Boden (GeoTech

Prediction and interpretation of the performance of a deep excavation in Berlin sand

This paper describes the application of a generalized effective stress soil model, MIT‐S1, within a commercial finite element program, for simulating the performance of the support system for the 20m deep excavation of the M1 pit adjacent to the main station “Hauptbahnhof” in Berlin. The M1 pit was excavated underwater and supported by a perimeter diaphragm wall with a single row of prestressed anchors. Parameters for the soil model were based on an extensive program of laboratory tests on the local Berlin Sands. This calibration process highlights the practical difficulties in both measurements of critical state soil properties and in model parameter selection. The predictions of excavation performance are strongly affected by vertical profiles of two key state parameters, the initial earth pressure ratio, K0, and the in‐situ void ratio, e0. These are estimated from field dynamic penetration test data and geological history. The results show good agreement between computed and measured wall deflections and tie‐back forces for three instrumented sections. Much larger wall deflections were measured at a fourth section and may be due to spatial variability in sand properties that has not been considered in the current analyses. The results of this study highlight the importance of basic state parameter information for successful application of advanced soil models.National Science Foundation (U.S.) (Wester Europe program grant INT-0089508)German Academic Exchange Service (DAAD

Design and Construction of Granular Soil Columns for Ground Improvement of Very Soft Soils for Road Embankments

The first presented case history is the construction of a new federal road south of Berlin, Germany. An embankment has been designed to cross a region of very soft peat soil with underlying organic silt, sand and boulder clay, with a total length of about 140 m. Ground improvement using sand columns with a diameter of 0.6 m and a distance of 1.5 m were designed and applied to all regions with more than 2.5 m thickness of the organic soil layer. Geogrids were used in addition to the vertical sand columns to take into account the action of horizontal forces beneath the embankment. The measured settlements as well as the tensile strains in the geogrids show the significant creep behaviour of organic soils over very long periods of time. The second case history is the renewal and enlargement of a federal expressway resting on very soft organic soils. Extensive laboratory tests as well as a large scale model test in a geotechnical testing pit using in situ excavated organic silt have been done to investigate the soilcolumn interaction behaviour in more detail. The data confirm that the long term deformations of the organic soils are mainly influenced by the creep behaviour of these soils