Elastic analysis of soil media.

Abstract

Elastic Solutions can be used to predict stresses and displacements in loaded soil media provided the non-linear stress-strain behaviour of the soil is recognised and allowance made for it in calculating displacements. This thesis examines the methods of elastic analysis suitable for examining problems in Soil Mechanics and the determination of suitable stress-strain parameters. The use of the Finite Element method in Soil Mechanics is reviewed, and a computer program for examining linear elastic plane stress and plane strain problems is presented. The program has been used to examine a range of problems involving infinitely long excavations of rectangular cross-section in the surface of a stratum overlying a rigid base. The excavations were analysed for a uniform vertical loading in the base of the excavation and for lateral wall loads representing the effect of the release of the insitu stresses during excavation. Cases in which the lateral movement of the walls is completely restrained are also considered, and the effect of wall restraint on the vertical displacements due to the vertical base loading is shown to be small. Results obtained by the author suggest that care should be exercised in the use of the Finite Element method to analyse problems involving loaded rigid footings or the stresses behind rigid retaining walls, and that the solutions in these cases may be inaccurate. The solutions available for surface loadings on layered elastic strata are reviewed and results obtained from a Fourier Series approach are presented for a range of problems involving surface loadings on a single rigid base elastic stratum. Uniform vertical and horizontal strip loadings and rigid strip footings with vertical, horizontal and moment loadings are considered. A uniform vertical strip load on the surface of a multilayer stratum overlying a half space or rigid base is also analysed. The computer programs and full mathematical derivations for the strip loading cases are presented, and the extension of the solutions to rectangular loadings is discussed and the basic mathematical derivations outlined. The application of the Fourier Series solutions to the calculation of consolidation settlements is discussed. Work by other investigators suggests that a hyperbolic model may be suitable for approximating soil stress-strain curves and that fundamental stress-strain behaviour should be examined in tests in which the bulk stress remains constant during the application of the shear stress. Equipment designed to carry out slow drained triaxial tests in which the bulk stress is constant during the shearing phase is described, and the results of a short series of tests used to proof test the equipment are presented.