Date of Award

1985

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Abstract

A theoretical analysis of a Quasistatic Cone Penetrometer Test (QCPT) is presented in this work. A large strain, elasto-plastic formulation is developed for this purpose and is implemented into a finite element method program. The basic relations of the theory are developed in an Eulerian reference frame, subsequently transformed to a Lagrangian coordinate system, and through simple time differentiation, the necessary rate equations are derived. Both isotropic and kinematic hardening of the Ziegler type are introduced in this theory. The plasticity models implemented are the extended von Mises and the cap model by DiMaggio and Sandler. The pore water pressures are obtained through the introduction of a bulk modulus of the soil-water system. The theory is applied to the solution of a cone penetration problem in a soft cohesive soil (E = 5000 KN/m('2), s(,u) = 50 KN/m('2)). The displacement strain, stress and pore water pressure fields around the penetrating cone are thus calculated. Interesting conclusions are drawn from this analysis, the most important of which are listed below: (a) The penetration mechanism during the QCPT seems to be a localized phenomenon for soft clays; that is, the recorded response during the test is averaged over small regions, which results in more meaningful and accurate predictions of the soil properties. (b) The kinematic field obtained from the axi-symmetric penetration is different from the one obtained from the plane strain penetration problem. No slip zones appear in the axi-symmetric problem; consequently, an analysis based on this concept is inappropriate for soft cohesive soils. (c) A separation zone occurs between the shaft and the soil above the cone tip. Readings of the soil response in this area could therefore be unreliable. (d) As the penetration acquires steady state characteristics, the pore water pressures generated around the cone probe become more uniform. It can thus be concluded that the position of the pore pressure transducer is not critical.

Pages

108

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