ABSTRACT

The chapters in this book show that a careful blend of engineering judgement and advanced principles of engineering mechanics may be used to resolve many complex geotechnical engineering problems. It is hoped that these may inspire the geotechnical engineering practice to make more extensive use of them in future.

chapter |13 pages

p in semi-saturated conditions

chapter |5 pages

7f= [ 1 + «

chapter 98|32 pages

where (1) J3 =1(siisi;) (2) .13= (3)

chapter |1 pages

of/06

chapter |39 pages

6q=M ybq y (38b)

chapter |3 pages

analysed under more practical, in-situ conditions. The properties as well as the penetration process were kept identical to the experimental set-up. However, a finer mesh was developed to establish the convergence of the results obtained from utilizing the coarse mesh for this case. It was found that the fine mesh predicted a higher value of changes in both the effective radial stress and the pore pressure close to the pile, when compared to the coarse mesh. This was attributed to the fact that the fine mesh was able to capture the response more accurately due to more elements around locations of high gradients. The final residual effective stress values were higher than that in-situ by an average of at the end of the driving and about 4.0 Cu at the end of final consolidation. This indicates an increase in the undrained shear strength of the soil around a driven pile, a beneficial factor reported by several previous inves-tigators. The entire finite deformation FE algorithm was introduced into an existing FE Fortran program called CRISP (Gunn and Britto, 1984) and is capable of analysing general problems of three-dimensional, two-dimensional plane strain or axisymmetry.

chapter |3 pages

cal structure. Several additions and modifications were needed to make the modelling possible, including sedimentation logic, viscous material behaviour and large time scales. The successful implementation of these features demonstrates the adaptability of the technique. Furthermore, subsequent simulations of the evolving geological structure were used to characterise the behaviour of the two-layer sequence and to test the applicability of a simplified analytical solution to the problem. In essence, a competent overburden produces deformations in the underlying viscous layer which are similar to the analytical predictions, but if the frictional overburden yields, the deformation of the viscous layer is modified by the translation and deformation of the overburden, and large extensional and compressional regions are formed in the overburden. The modelling has therefore prompted a better qualitative and quantitative understanding of the geological setting. Some further general comments are reserved for the concluding section of the next chapter.

chapter |3 pages

reservoirs. Even with only two joint patterns and two different regional stress states, a number of mechanisms and corresponding flow regimes have been revealed. Typically, fluctuating injection pressures, anisotropy of hydraulic conductivities (both initial and induced), and irreversible changes of stress and joint dilation are predicted. In addition, the magnitude of the injection pressures and the net effect of the injection period on the final distribution of fracture conductivity are quite different in each case. This response is qualitatively similar to some field obser-vations (for example, Shuck and Komar, 1979). Thus a very idealised model has prompted a better understanding of mechanisms that may explain the observed characteristics of fluid injection into jointed rock. Both examples fall into the data-limited category as defined by Star-field and Cundall (1988). It would be only too easy to dismiss the modelling attempts on the basis of the lack of information available; there is uncertainty concerning geometry and material behaviour in both cases. However, the implementation of an idealised numerical model which can then be used as an experiment to probe the behaviour of the system has, in both cases, led to a better understanding and a characterisation of the system response. The numerical models described here, based on the explicit finite-difference technique, have proved to be extremely valuable tools in this context.

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