11R28. Soil Retaining Structures: Development of Models for Structural Analysis. - KJ Bakker (Delft Univ of Tech, Rijkswaterstaat, Utrecht, Netherlands). Balkema Publ, Rotterdam, Netherlands. 2000. 228 pp. ISBN 90-5809-321-2. $75.00.
Reviewed by SK Ghaswala (1/B Edena, 97 M Karve Rd, Bombay, Maharashtra 400020, India).
The study of the development of models for structural analysis, particularly for soil-retaining structures, has not been undertaken vigorously. The author has filled this lacuna by discussing in detail the model design methodology, tools for analysis, and the merits of models in the first three short chapters.
In order to test a feasible structure for its limit-state condition, models are used. The time when a structure was built and then verified by a loading test—that is a predefined overloading of the prototype—has now passed. Therefore, modern structural analysis now relies on models, and here the emphasis is on finite element techniques. The main feature of this technique is that it is general enough to produce failure mechanisms that have not been included as such in the model, but are incorporated on a deeper level by using general field of deformations. These and other various facets of design methodology are explained in these three chapters.
The approach in this study is quite practical as it deals with the development and validation of models for structural analysis preferably with prototype measurements. This approach is considered for three different types of soil-retaining structures, which in fact forms the main thesis of this text. These are block revetments, flexible retaining walls, and bored tunnels. However, before proceeding towards model analysis of the three structures, the author has rightly presented a chapter on soil mechanics and groundwater, flow as a crossover between that part that is related to methodology and the part that is related to technology. This crossover covers the main principles of soil mechanics dealing with continuity of particles, groundwater and stresses arising thereon, where soil is analyzed using continuum mechanics. Some aspects of numerical modeling of elasto-plastic soil using the Mohr-Coulomb failure criterion are also discussed.
Revetments or block mattresses are used to protect soil against erosion caused by shipping activity in canals or by wind action on river or sea dikes. A model for the evaluation of sliding stability of a cover layer for an embankment loaded by waves was developed and analyzed, and valuable conclusions were reached.
A flexible retaining wall is a driven sheet of wooden, steel, or concrete pile or plate with flexibility to interact with the deformation of the soil and to bear the loading of the retained soil. Such piles are used to stabilize the embankments of canals or to form a deep excavation on a quay wall. If a rigid plastic soil behavior is assumed, then the design of flexible retaining walls becomes highly statically indeterminate. These aspects are treated here in fair detail.
In a typical delta country like the Netherlands dominated by natural and artificial waterways, tunnels are traditionally used instead of bridges. As such, the last section covers the lining of bored tunnels in soft soil. In contrast to flexible structures such as sheet pile walls, the derivation of stresses in a tunnel lining is relatively insensitive to soil plasticity. However, the elastic parameters of the soil have a substantial influence on the stress level in the structure. Here the author gives a brief overview of the monitoring of the tunnel lining behavior of the 1350 meter long immersed Second Heinenoord Tunnel opened in the Netherlands in September 1999.
What has emerged from these studies is that finite element methods, when used for model analysis of soil-retaining structures, have distinct advantages over analytical methods because they include complex features such as nonlinear material behavior, consolidation, and creep.
The book has a fairly good set of references at the end. There are two appendices, one covering equations of equilibrium for a ring, and the other on the evaluations of ultimate limit state for a tunnel lining. It is a pity that there is no Index. On the whole, Soil Retaining Structures: Development of Models for Structural Analysis is a specialized mathematical treatise on the development and use of models for soil-retaining structures. It should be useful to engineers, designers, and builders connected with construction of canals, dikes, submerged tunnels, irrigation works, and the like.