Bowey, Alan William
Predictions of soil behaviour using finite element analysis.
PhD thesis, University of Glasgow.
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Measured data from five geotechnical structures have been back analysed to determine, in each case, the set of material parameters that will permit a reasonable match to the observed pre-failure foundation response. Back analyses have been performed using simple constitutive soil models (Tresca, Mohr-Coulomb and modified Cam clay) as implemented in the finite element analysis package CRISP90. Trial loading data are available from:
1. The rapid loading to failure of a soft clay soft foundation through a rigid reinforced concrete slab.
2. The loading to failure of a soft clay foundation via the rapid construction of a trial embankment.
3. The long-term behaviour of a soft clay foundation loaded via a stable trial embankment.
4. The behaviour of two long span, flexible culverts under (granular) backfill and imposed loads.
From comparison of the computed and observed responses conclusions have been drawn which have implications for the general application of finite element analysis to geotechnical problems; parameter selection or numerical analyses; and the essential requirements of the soil model for predicting soil behaviour.
In chapters 3, 4 and 5 the main concern of analyses was to reproduce the observed settlements, lateral displacements and excess pore water pressures induced within the soft clay foundations. Analyses primarily concentrated on the use of the modified Cam clay soil model. Particularly in chapter 3, the ability of modified Cam clay to predict the essential elements of the foundation behaviour was reasonable. However, in chapters 4 and 5 predictions of lateral displacements and excess pore water pressures were poor. More accurate estimates of the observed lateral displacements and excess pore water pressures were obtained using empirical methods (hand calculations). The reason for the different quality of lateral displacement and excess pore water pressure predictions is thought, mainly, to be due to incomplete saturation of the soft clay at the trial embankment test site. The influence of incomplete saturation is thought to initially force a drained foundation response, which in the short term will give rise to smaller lateral displacements and excess pore water pressures than those predicted from fully undrained analyses. In the long term, further improvement of embankment lateral displacements and excess pore water pressures may be achieved through considerations of viscosity
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