António Silva Cardoso

Influence of train dynamic modelling strategy on the prediction of track–ground vibrations induced by railway traffic

This paper presents a study developed in order to identify the influence and relevance of the mechanical properties of the train in the prediction of vibrations induced by passenger railway traffic. Based on experimental data and numerical simulation, a discussion about the influence of the modelling strategy adopted for the train simulation is performed. Special emphasis is placed on the study of the influence of the unsprung and semi-sprung masses of the train on the train–track interaction mechanism. From the developed study it was found that the modelling strategy adopted for the train simulation is a key factor in the prediction of the free-field vibrations. Moreover, the accuracy of the prediction is considerably increased if the train simulation considers the unsprung and semi-sprung (bogies) masses of the train.

OVERALL STABILITY OF GEOSYNTHETIC- REINFORCED EMBANKMENTS ON SOFT SOILS

Abstract Overall stability of geosynthetic-reinforced embankments on soft soils is analysed using two different methodologies: application of a numerical model based on the finite element method; use of a limit equilibrium method. These two methodologies are described and also applied on three geosynthetic-reinforced embankments on soft soils. One of the cases is a case history constructed up to failure. Considering the analysis of the results, some conclusions are formulated on the limit equilibrium method accuracy, namely regarding the critical slip surface, overall safety factor and overturning and resisting moments.

Structural behaviour and parametric study of reinforced embankments on soft clays

Abstract Geotechnical behaviour of a reinforced embankment on soft ground is studied by a numerical model based on the finite element method. Special emphasis is given to the stress states (stress levels and pore pressures), displacements, tensile forces in the geosynthetic and overall stability, during and after construction. The influence of some parameters, namely geosynthetic stiffness and viscosity, embankment width and construction sequence, is also analysed. Several conclusions are obtained.

Vibrations inside buildings due to subway railway traffic. Experimental validation of a comprehensive prediction model

The present paper focuses on the experimental validation of a numerical approach previously proposed by the authors for the prediction of vibrations inside buildings due to railway traffic in tunnels. The numerical model is based on the concept of dynamic substructuring and is composed by three autonomous models to simulate the following main parts of the problem: i) generation of vibrations (train-track interaction); ii) propagation of vibrations (track-tunnel-ground system); iii) reception of vibrations (building coupled to the ground). The experimental validation consists in the comparison between the results predicted by the proposed numerical model and the measurements performed inside a building due to the railway traffic in a shallow tunnel located in Madrid. Apart from the brief description of the numerical model and of the case study, the main options and simplifications adopted on the numerical modeling strategy are discussed. The balance adopted between accuracy and simplicity of the numerical approach proved to be a path to follow in order to transfer knowledge to engineering practice. Finally, the comparison between numerical and experimental results allowed finding a good agreement between both, fact that ensures the ability of the proposed modeling strategy to deal with real engineering practical problems.

MODELLING PERFORMANCE OF A SLOPED REINFORCED SOIL WALL USING CREEP FUNCTION

Abstract The paper describes a rheological model based on a series of Kelvin models for analysing creep behaviour. This model is implemented in a finite element analysis to predict the behaviour of an instrumented sloped reinforced soil wall. The performance of the numerical model and the actual behaviour of the structure are compared. The analysis is carried out using both constant and variable reinforcement stiffness with respect to time. The results and the findings are discussed.

BEARING CAPACITY FAILURE OF TIED-BACK WALLS - A COMPLEX CASE OF SOIL- WALL INTERACTION

Abstract The paper presents a study of bearing capacity failures of tied-back walls induced by vertical forces applied by the anchors. A review of some failures or incidents and small scale test results as well as an attempt of numerical simulation of a “case history” are included. Subsequently, a simple numerical case study is analysed in order to identify the main features of that mode of failure and the parameters that govern the response of the system. Emphasis is put on the mobilization of the skin resistance on both wall faces. Some practical conclusions are extracted.

Natural Variability of Shear Strength in a Granite Residual Soil from Porto

The renewal imposed by the Eurocodes regarding the methodologies of safety evaluation requires a statistical analysis of the variability of ground geotechnical parameters. However, the studies published in the reviewed literature do not cover the typical materials from the northeast region of Portugal—residual soils from granite—to which a strong heterogeneity is associated. Hence, a statistical characterization of the natural variability of a granite residual soil from Porto has been made through a significant amount of experimental tests, focusing on its geomechanical properties. In order to provide a database for probabilistic analysis of problems involving this type of soils, an appropriate statistical law has been used to model its variability, which has been quantified by means of coefficients of variation and scales of fluctuation.