Numerical simulations of stone column installation

Canadian Geotechnical Journal (Impact Factor: 0.81). 09/2010; 47(10):1127-1138.

ABSTRACT This paper describes the results of numerical simulations investigating the installation effects of stone columns in a natural soft clay. The geometry of the problem is simplified to axial symmetry, considering the installation of one column only. Stone column installation is modelled as an undrained expansion of a cylindrical cavity. The excess pore pressures generated in this process are subsequently assumed to dissipate towards the permeable column. The process is simulated using a finite element code that allows for large displacements. The properties of the soft clay correspond to Bothkennar clay, modelled using S-CLAY1 and S-CLAY1S, which are Cam clay-type models that account for anisotropy and destructuration. Stone column installation alters the surrounding soil. The expansion of the cavity generates excess pore pressures, increases the horizontal stresses of the soil, and most importantly modifies the soil structure. The numerical simulations performed allow quantitative assessment of the post-installation value of the lateral earth pressure coefficient and the changes in soil structure caused by column installation. These effects and their influence on stone column design are discussed.Cet article décrit les résultats de simulations numériques visant à investiguer les effets de l'installation de colonnes ballastées dans de l'argile molle naturelle. La géométrie du problème est simplifiée sous forme de symétrie axiale, en considérant l'installation d'une seule colonne. L'installation de la colonne ballastée est modélisée en tant qu'une expansion non-drainée d'une cavité cylindrique, ainsi la pression interstitielle excessive générée est dissipée vers la colonne perméable. Le processus est simulé à l'aide d'un code par éléments finis qui permet les grands déplacements. Les propriétés de l'argile molle correspondent à l'argile Bothkennar, qui est modélisée avec S-CLAY1 et S-CLAY1S, qui eux sont des modèles de type Cam-clay considérant l'anisotropie et la déstructuration. L'installation des colonnes ballastées altère le sol environnant. L'expansion de la cavité génère des pressions interstitielles excessives, augmente les contraintes horizontales sur le sol, et modifie de façon importante la structure du sol. Les simulations numériques effectuées ont permis d'évaluer la valeur du coefficient de pression latérale des terres post-installations ainsi que les variations dans la structure du sol causées par l'installation des colonnes. Ces effets et leur influence sur la conception des colonnes ballastées sont discutés.

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    ABSTRACT: Although finite element packages facilitating coupled consolidation analyses are increasingly in use, many practitioners still favour linear uncoupled analysis out of familiarity with the use of coefficients of consolidation. However, coefficients of consolidation measured by any single means tend to exhibit significant variation, with mean results from different laboratory and field tests also varying widely, leaving uncertainty over the correct values to apply to field problems. In this paper, a finite difference approach is used to back-calculate operational coefficients of consolidation from pore pressure measurements pertinent to a pile group driven in clay–silt. The research shows that this method is capable of successfully capturing the process of pore pressure dissipation, and that the operational coefficient of consolidation around the pile group is higher than that derived from piezocone dissipation tests in the same material.
    Geotechnical and Geological Engineering 31(1).


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