Modeling Vacuum Cconsolidation with Finite Elements

Chapter 1 Introduction 1.1 Ground Improvement Techniques One of the first and the more important considerations in most of civil engineering projects is the selection of a suitable site for construction. A suitable site usually means, from a geotechnical point of view, one where the foundation material has sufficient strength and stiffness to carry the loads imposed without unacceptable large deformations or stability problems, or else has drainage properties suitable for the particular construction application. In practice the most suitable site is determined by social or economic requirements, rather than purely engineering considerations and in many cases the mechanical properties of the soils (strength, stiffness or hydraulic conductivity) need to be improved through different engi- neering methods called ground improvement techniques. Due to increased urbanization there is now a growing shortage of available land in many cities which leads to the search for ways to build on land previ- ously thought unsuitable. Indeed for example there are airports, sea ports or even skyscrapers that have been developed on land reclaimed from the sea. Another example of applications for which ground improvement is almost inevitably re- quired occurs in railway and highway construction. Because these transportation routes often pass through regions underlain by deposits of soft or weak soils. The mechanical properties of these softer soils often have to be improved in order to adequately support the associated earth structures and to reduce the residual set- tlements that occur during the useful life of the transport infrastructure. Those are the main reason for which many ground improvement techniques have evolved during the years. All those techniques seek to improve those soil characteristics that match the desired results of a project, such as an increase in density and shear strength to aid problems of stability, the reduction of soil compressibility, influencing permeability to reduce and control ground water flow or to increase the rate of consolidation, or to improve soil homogeneity. In ground improvement, distinction is made between methods of compaction or densification and methods of soil reinforcement through the introduction of additional material into the ground. Bergado et al. [1] classified the various ground improvement methods according to whether or not additives are used to directly 1