Inverse Analysis in Road Geotechnics
Inverse Analysis in Road Geotechnics

Author: Carlo Rabaiotti

Publisher: vdf Hochschulverlag AG

Published: 2011

Total Pages: 243

ISBN-13: 3728132748

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This research work had the aim of developing a procedure for back-calculating accurate and precise parameter values, describing the mechanical behaviour of the materials built in an existing road structure. After reviewing the existing testing techniques, a new device was designed and assembled at the IGT, Institute for Geotechnical Engineering (ETH Zürich) for measuring the three dimensional deflection bowl under a standard axle load (SAL). Particular attention was paid for obtaining precise and accurate significant measurements for inverse analysis. Three field tests on different locations and road structures were carried out: a flexible pavement type built in a concrete pit (indoor facility) at the EPFL (Ecole Polytechnique Federale de Lausanne), a semirigid type in Hinwil (Switzerland) and a flexible type in Bellinzona (Hinwil). The tests results show that the measured road displacements under a SAL, for relatively low temperatures, are generally reversible and time independent. Laboratory tests (uniaxial compression) were carried out on cores obtained from field samples.The strain measurements of the loaded samples were carried out with strain gages, and validated against devices with different technology (LVDT). The analysis of the test results showed that the materials have different bulk and deviatoric stress-strain behaviour. A new thermodynamical framework for non linear viscoelasticity (hyperviscoelasticity) was developed. Experimentally validated hyperviscoelastic and hyperelastic constitutive laws were adopted respectively for describing the mechanical behaviour of asphalt and cement stabilized mixtures. The inverse analysis of the field tests results was carried out with two different optimization algorithms (Levenberg Marquardt and Mesh Adaptative Direct Search), the FE program ABAQUS, and the developed user defined models. The results demonstrate the accuracy and precision of the parameter values obtained with the proposed inverse analysis procedure, demonstrating a potential for application of the developed technique for non destructing testing of real road structures.

Static effects and aspects of feasibility and design of drainages in tunnelling
Static effects and aspects of feasibility and design of drainages in tunnelling

Author: Sara Zingg

Publisher: vdf Hochschulverlag AG

Published: 2017-02-21

Total Pages: 228

ISBN-13: 3728138193

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This PhD thesis investigates the effectiveness of drainage measures with respect to two particularly important problems associated with tunnelling through water-bearing, weak ground: the stability of the tunnel face and the stability and deformation of grouting bodies. Water is an adverse factor with respect to the stability and deformation of underground structures due to the pore water pressure and the seepage forces associated with seepage flow towards the tunnel. Drainage boreholes reduce the pore water pressure and the seepage forces in the vicinity of the cavity. Furthermore, loss of pore water pressure increases the effective stresses and thus the shearing resistance of the ground („consolidation“), which is favourable in terms the deformation occurring during and after tunnelling. The goal of the PhD thesis is to elaborate a more detailed understanding of the interrelationships between drainage measures and the stability of the tunnel face and grouting bodies. The main objectives of the investigations relating to the tunnel face are: 1. analysis of face stability through limit equilibrium computations taking account of the numerically determined seepage flow conditions prevailing in the ground after the implementation of drainage measures; 2. systematic investigation of tunnel face stability considering several different drainage layouts and working out designnomograms; 3. consideration of a series of aspects limiting pore pressure relief and thus the effectiveness of drainage measures and their impact on face stability. The main objectives of the investigations with regard to grouting bodies are: 1. a study of the stabilizing effect of the virtual case of ideal drainage on tunnel support and plastification in grouted fault zones in plane strain conditions; 2. a comparison with the stabilizing effect of real drainage layouts, i.e. when considering pore pressure relief due to specific drainage borehole arrangements; 3. application of the drainage measure both before and after the injection works. In summary, the contribution of this PhD thesis is the detailed investigation of the static effects of drainage measures during tunnelling in water-bearing ground with respect to the stability of the tunnel face and the grouting body as well as the supply of design aids capable of providing a quick assessment of face stability when considering a number of advance drainage schemes.

On the role of constitutive behaviour in the response of squeezing ground to tunnelling
On the role of constitutive behaviour in the response of squeezing ground to tunnelling

Author: Weijie Dong

Publisher: vdf Hochschulverlag AG

Published: 2017-08-14

Total Pages: 205

ISBN-13: 3728138606

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Squeezing conditions in tunnelling are characterized by the occurrence of large deformations of the opening or high rock pressure that may overstress the lining. Squeezing is associated with poor quality rock. Tunnelling in squeezing ground involves great uncertainties. It is therefore very important to gain a better understanding of the underlying mechanisms. Triaxial testing is the main source of information in order to understand the mechanical features of squeezing ground. Despite the complexity of the squeezing mechanism and the behaviour observed under relatively simple loading conditions, most of previous research work and engineering design practice considers the ground as a linearly elastic, perfectly plastic material obeying the Mohr-Coulomb yield criterion. While the MC model is capable of predicting the final strength and post-failure volumetric behaviour of the squeezing rock, it cannot map some potentially important pre-failure features or the occasionally observed contractant plastic deformation. In addition, the MC model usually leads to an overestimation of the strength under undrained conditions, which is unsafe for tunnel design. The present thesis mainly addresses the influence of constitutive modelling on predictions about the response of squeezing ground to tunnelling in order to provide some general guidelines for basic engineering analysis. This objective is achieved by investigating the behaviour of squeezing rocks theoretically and experimentally, using samples from several tunnel projects, including the Gotthard base tunnel and the planned Gibraltar strait tunnel.

River dyke failure modeling under transient water conditions
River dyke failure modeling under transient water conditions

Author: Wilmer Ferney Morales Peñuela

Publisher: vdf Hochschulverlag AG

Published: 2015-11-26

Total Pages: 436

ISBN-13: 3728136301

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Knowledge of the performance of river dykes during flooding is necessary when designing governmental assistance plans aimed to reduce both casualties and material damage. This is especially relevant when floods have increased in their frequency during the last decades, together with the resulting material damage and life costs. Most of previous attempts for analyzing dyke breaching during flooding have neglected to consider the soil mechanics component and the influence of infiltration and saturation changes on the failure mechanisms developed in the river dyke. This research project aimed to fill that gap in knowledge by analyzing, in a comprehensive manner, the effect of transient water conditions, represented by successive flood cycles, on the seepage conditions and subsequent breaching of dykes. Therefore, three key sub-projects were carried out: • the analysis of the results from an overflow field test, • the physical modeling of small-scaled models under an enhanced gravity field, • the numerical modeling of the flow response and the resulting stability of both the air- and water-side slopes. The results from the numerical simulations matched accurately with the results obtained with the centrifuge modeling, including the prediction of local instabilities during the flood cycles for those dykes that did not include a toe filter.

Centrifuge modelling of ground improvement for double porosity clay
Centrifuge modelling of ground improvement for double porosity clay

Author: Emma Jane Pooley

Publisher: vdf Hochschulverlag AG

Published: 2015-11-10

Total Pages: 270

ISBN-13: 3728136514

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Double porosity soil is characterised by a soil continuum containing two distinct porosities. Typically, this consists of macro-grains (lumps) of soil that have an internal porosity defined as the intragranular porosity. The spaces between lumps are identified as intergranular voids that give rise to the intergranular porosity. Human activities such as land reclamation or mining can give rise to large areas of land with subsoil that exhibits double porosity. The need to build in, or on, these areas is increasing, due to demand for land for industrial usage, infrastructure, and residence. However, the engineering properties of such soils are challenging, and often difficult to predict due to their inhomogeneity and a lack of information about the initial or current parameters. Double porosity mining waste landfills in Northern Bohemia in the Czech Republic were studied in this project. There, decades of open-cast mining of brown coal have left vast areas of land affected by the waste overburden that has been removed and dumped in old mining pits. Redevelopment of areas affected by mining sometimes requires construction on old overburden waste spoil heaps, which consist primarily of lumps of overconsolidated clay and are therefore characterised by a double porosity soil structure. The loading response on these clayfills entails large absolute and relative deformations, which means that ground improvement is normally needed before construction begins, to ensure that both stability and service limit state requirements are met. The primary aim of this research was a comparison, through physical modelling, of ground improvement techniques on double porosity clay landfills. A secondary objective was to contribute to the understanding of the material behaviour governing response to loading and other processes on double porosity soil.

Prediction and Simulation Methods for Geohazard Mitigation
Prediction and Simulation Methods for Geohazard Mitigation

Author: Fusao Oka

Publisher: CRC Press

Published: 2009-05-07

Total Pages: 628

ISBN-13: 0203871049

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The last decades have shown a remarkable increase in the number of heavy rains, typhoons and earthquakes. These natural phenomena are the main causes for geohazards. As a result the mitigation of geohazards has become a major research topic in geotechnical engineering, and in recent years simulation-based predictions and monitoring tools have been