32 research outputs found
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A study into the behaviour of the formation level of an excavation under different unloading patterns in soft deposits
The construction of basements in urban areas is often associated with the possible damage to existing structures and services. The varying construction processes inevitably lead to different stress unloading patterns and therefore the dissipation of these excess pore-water pressures may lead to non-standard deformation profiles. The three main types of basement construction processes are layered excavation (LE), basin excavation (BE) and island excavation (IE). The effect of the various unloading patterns has been investigated by a three dimensional (3D) effective stress analysis method using the developed computer program 3DBCPE4.0. An excavation of length 50 m, width 50 m and depth 9 m in a certain homogenous and isotropic saturated soft soil was modelled. This included a diaphragm wall of 800-mm thickness embedded 18 m deep into the soft soil. The different excavation deformation profiles under different excavation patterns were related to the different unloading process, the exposure time of excavation face and the dissipation of negative excess pore-water pressures. The most favourable process for controlling the horizontal deformation of a retaining wall or the heave deformation of the formation level is suggested. The ground water potentials within the formation level are also presented
Modélisation numérique par rétro-analyse du comportement des parois moulées butonnées
La construction du terminus Ouest de la ligne D du métro de Lyon a été réalisée en tranchée couverte à l’abri de parois moulées butonnées dans un horizon de colluvions limoneuses de caractéristiques médiocres. Une étude hydrogéologique préliminaire ayant mis en évidence le risque de rehaussement de la nappe dû à sa coupure partielle par les parois moulées, le soutènement a été dimensionné avec une fiche réduite. Cette configuration présentant un risque de soulèvement du fond de fouille ou de butée insuffisante devant la fiche, la paroi a été instrumentée et suivie tout au long des travaux. Les résultats de ces observations sont analysés. Cette analyse confirme l’incidence marquée des forces d’écoulement liées à l’exhaure sur le comportement mécanique de la paroi et montre également un comportement dissymétrique de la fouille dû au déroulement des travaux. De telles interactions sont difficilement prises en compte dans les approches traditionnelles et ces résultats ont été confrontés par rétro-analyse à des simulations numériques en différences finies où l’effet de l’écoulement est explicitement pris en compte. Cette confrontation a enfin été complétée par une étude paramétrique
Discussion. Passive and active earth pressures in the presence of groundwater flow
First published by Thomas Telford Ltd. and available at http://www.geotechnique-ice.com/
Experimental Study on a Three-Dimensional Passive Earth Pressure Coefficient in Cohesionless Soil
Estimation of the passive earth pressure is a crucial aspect in several geotechnical design problems. Several authors presented two-dimensional models for its evaluation while three-dimensional (3D) approaches have received less attention. It has been recognized that in many geotechnical systems, such as anchor blocks or plates or everywhere the width of the load area is limited if compared to its height, the three-dimensional passive earth pressure is quite different from the two-dimensional one and, due to side effects, is generally larger. This paper is concerned with an experimental and numerical study of 3D passive earth pressure encountered by a rigid plate of limited width in a cohesionless soil. The obtained results allowed the evaluation of a three-dimensional passive earth pressure coefficient which is not only dependent on the soil friction angle, as it occurs in a 2D formulation, but also on the ratio of the width to the height of the load area