Effect of embedment depth and stress anisotropy on expansion and contraction of cylindrical cavities

Hany El Naggar, M. Hesham El Naggar

In the proceedings of: GEO2010 Calgary: 63rd Canadian Geotechnical Conference & 6th Canadian Permafrost Conference

Session: T1-B

ABSTRACT: The semi-analytical solutions for expansion and contraction of cylindrical cavities in elasto-plastic dilatant soils developed by Yu and Houlsby (1991, 1995) were applied to a wide spectrum of applications from interpretations of pressuremeter tests in sand and the end bearing pressure of deep foundations to horizontal directional drilling (HDD). The main assumptions of these solutions are: 1) infinite medium; and 2) isotropic stress field everywhere (i.e., the coefficient of lateral earth pressure, Ko =1). For HDD applications, these assumptions are not justified for most installations, and the effect of any deviation from these assumptions needs to be evaluated. This paper investigates the effect of the free surface, the stress gradient, and the in-situ stress anisotropy (i.e. Ko¹1) on the displacements during expansion and contraction phases of cavities embedded in dilatant sands. A finite element model was built using the software Plaxis. The finite element was first verified for the case of infinite medium and isotropic stress field. The verified model was then used to examine the effects of the different influencing parameters of the HDD installation.

RÉSUMÉ: The semi-analytical solutions for expansion and contraction of cylindrical cavities in elasto-plastic dilatant soils developed by Yu and Houlsby (1991, 1995) were applied to a wide spectrum of applications from interpretations of pressuremeter tests in sand and the end bearing pressure of deep foundations to horizontal directional drilling (HDD). The main assumptions of these solutions are: 1) infinite medium; and 2) isotropic stress field everywhere (i.e., the coefficient of lateral earth pressure, Ko =1). For HDD applications, these assumptions are not justified for most installations, and the effect of any deviation from these assumptions needs to be evaluated. This paper investigates the effect of the free surface, the stress gradient, and the in-situ stress anisotropy (i.e. Ko¹ 1) on the displacements during expansion and contraction phases of cavities embedded in dilatant sands. A finite element model was built using the software Plaxis. The finite element was first verified for the case of infinite medium and isotropic stress field. The verified model was then used to examine the effects of the different influencing parameters of the HDD installation. 1 INTRODUCTION

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