Analysis of Excavation-induced Deformation with Different Soil Models
Abstract: The monitored case of deep excavation works located in the centre of Warsaw is described and back analysed as a boundary value problem with the finite element method. The excavation was carried out in over-consolidated clayey layers under the support of braced diaphragm walls. Accurate simulation of such soil-structure interaction problems requires advanced soil constitutive models – especially for the pre-failure range of small strains. On the other hand, such models should not be very complex and their material parameters should be relatively simple to obtain from laboratory and in situ surveys. By means of a case study, this paper examines several simple elasto-plastic constitutive models for the simulation of the behaviour of soil layers. The influence of such characteristics of the soil behaviour, as anisotropy and non-linearity of stiffness, is studied in the paper. The discussion concerns the problems related to the application of the models for a practical example. The comparison is focused on the obtained and measured displacements of the neighbouring building and diaphragm walls.
Determination of Soil Stiffness Parameters for Clays as a Construction Subsoil for Warsaw Underground
Analysis of soil-structure interaction demands properly determined parameters for a particular calculation method. In the case of deformation modulus determination, it is essential to take actual construction activities into consideration. It means that these moduli should correspond to stress-strain range of a particular construction. The use of numerical methods, allowing for more realistic soil-structure interaction, compatibility of displacements, as well as to account for the stiffness of the structure and the soil, may provide more realistic prediction of displacements. The article presents the methods of stiffness parameters determination including all factors that should be taken into consideration in geotechnical design. The article characterizes clays of Poznań formation, a subsoil for many structures in almost 75% area of Poland. Investigations conducted for clays in Warsaw were used as a background with the focus on an underground Metro station. Direct measurements of the unloading of the bottom of the excavation in clays were used for validation. Finite Element Method (FEM) was used to verify stiffness parameters and their determination methods. The correctness of obtained results was verified by comparison with deformation measurements of station construction and displacement measurements in the adjacent area. As a conclusion, the article shows that the type of a construction and its character should be taken into consideration in geotechnical parameter determination. The analysis with stiffness parameters determined in the small-strain range of deformations allows to obtain displacement values approximate to real ones. In the case of an underground station, large area of soil interacts with a structure, and in this case, the deformations are small, which should be taken into account in a design analysis.
ANISOTROPIC ELASTIC PARAMETERS FOR SOIL
Synopsis The concept of soil as an anisotropic elastic material is considered and the theoretical bounding values of the relevant elastic parameters are described. The bounding values of the parameters are repre-sented in three-dimensional space. Within the space any given material is represented by a point and points in certain regions represent particular types of material. The requirements for infinite bulk modulus, for uncoupled volumetric and distortional phenomena and for dilatant soil are repre-sented within the bounds of possible materials. On considere le concept du sol en tant que materiau eĺastique anisotrope et on decrit les valeurs limites theoriques des parametres d'elasticite s'y rapportant. Les valeurs limites des parametres sont repre-sentEes dans un espace a trois dimensions. A l'interieur de l'espace, tout materiau donne est represente par un point et des points dans certaines zones representent des types particuliers de materiaux. Les conditions requises pour un module de masse infinie...