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Über dieses Buch

Cities built on unconsolidated sediments consisting of clays, silt, peat, and sand, are particularly susceptible to subsidence. Such regions are common in delta areas, where rivers empty into the oceans, along flood plains adjacent to rivers, and in coastal marsh lands. Building cities in such areas aggravates the problem for several reasons:

1. Construction of buildings and streets adds weight to the region causing additional soil deformations.

2. Often the regions have to be drained in order to be occupied. This results in lowering of the water table and leads to hydro-compaction.

3. Often the groundwater is used as a source of water for both human consumption and industrial use.

4. Levees and dams are often built to prevent or control flooding.

Earth fissures caused by ground failure in areas of uneven or differential compaction have damaged buildings, roads and highways, railroads, flood-control structures and sewer lines. As emphasized by Barends , "in order to develop a legal framework to claims and litigation, it is essential that direct and indirect causes of land subsidence effects can be quantified with sufficient accuracy from a technical and scientific point of view."

Most existing methods and software applications treat the subsidence problem by analyzing one of the causes. This is due to the fact that the causes appear at different spatial scales. For example, over-pumping creates large scale subsidence, while building loading creates local subsidence/consolidation only.

Then, maximum permissible land subsidence (or consolidation) is a constraint in different management problems such as: groundwater management, planning of town and/or laws on building construction. It is, therefore, necessary to quantify the contribution of each cause to soil subsidence of the ground surface in cities urban area.

In this text book, we present an engineering approach based on the Biot system of equations to predict the soil settlement due to subsidence, resulting from different causes. Also we present a case study of The Bangkok Metropolitan Area (BMA).

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
In this section, the effect of land subsidence in urban area is presented on the example of the Bangkok area. In Section “The Effect of Land Subsidence in Urban Areas: The Bangkok Area”, the different aspects of land subsidence are presented for the Bangkok area. Monitoring of soil settlements, determination of the causes, legal aspects are fundamental subjects of soil subsidence in urban areas. In Section “The Scope of the Book”, a general presentation of the chapters is detailed.
David G. Zeitoun, Eliyahu Wakshal

Chapter 2. The Subsidence Phenomenon Throughout the World

Abstract
In this section, the different types of land subsidence are discussed. They are separated into natural causes and man-induced causes. The natural causes are mainly geological causes, such as formations of caves, sinkholes, and karst topography. The man-induced causes are mainly mining or fluid withdrawal (groundwater and/or oil or gas). Also, loads of buildings are an important cause of consolidation in urban areas. These causes are explained in general term, and examples of subsidence in the United States are briefly referred to.
David G. Zeitoun, Eliyahu Wakshal

Chapter 3. Mechanical Modeling of Porous Media

Abstract
In this chapter, the various mathematical models currently used for the analysis of soil deformation for each type of subsidence are presented. The various models of subsidence are presented in terms of
  • a geometrical model of the porous media is needed and a definition of representative element volume (REV);
  • the variables of the model and the governing equations for the fluid and/or the gas flow as well as the mechanical behavior of the soil skeleton;
  • the boundary conditions associated with the partial differential equations appearing in the model; and
  • the type of loadings and the way it acts on the soil matrix.
Then, the models are described for different types of subsidence commonly encountered in practice:
  • subsidence due to water withdrawal in saturated soil;
  • subsidence due to oil and gas withdrawal in non-saturated soils;
  • subsidence due to sea water encroachment;
  • subsidence appearing in fracture rocks.
David G. Zeitoun, Eliyahu Wakshal

Chapter 4. Fundamentals of the Consolidation Theory for Soils

Abstract
In this chapter, we describe the Terzaghi theory of consolidation as a way of decoupling the general Biot equations using the assumption of constant total stress. We detailed the computation of the water pressure and the soil displacement. The classical one-dimensional theory is presented with solved exercises.
We also discuss the use of the theory of consolidation for large-scale problems such as subsidence due to large-scale groundwater pumping. We review the different approaches that were used in the literature for the numerical modeling of the subsidence due to groundwater pumping. We concentrate on two main points:
1.
The mechanical behavior of the clayey soil; and
 
2.
The connection between groundwater movement and stress pressure in the soil.
 
Then, a critical review of the consolidation theory for large-scale problems is presented in terms of the principle of superposition of loadings.
Also, the three-dimensional theory is described, and we discuss the limitation of the theory in the case of internal loadings.
David G. Zeitoun, Eliyahu Wakshal

Chapter 5. Biot’s Theory of Consolidation

Abstract
In this chapter, we present the constitutive equations of the Biot model. The main difficulties of this model are the coupling of the equations and the application of the superposition principle. We present the general solution of the coupled problem resulting from the Biot model. This solution is based on a new method for decoupling the equations. This decoupling approach permits to derive a superposition principle of the loadings. Several types of loadings and boundary conditions for the water pressure and the displacement field are discussed. Analytical solutions are also derived and discussed.
Also, the problem of the computation of the different causes and their relative contribution to the total subsidence and/or settlement is analyzed in terms of two main principles of the partial differential equations, as follows:
  • the coupling/decoupling of the system of equations; and
  • the principle of superposition of loadings.
For soft clays and/or loose sand, the ratio between the maximum vertical displacements using the coupled model may be 170 times larger than the maximum vertical displacement computed with the decoupled model.
Also, for large values of the shear modulus and a standard value of the Young modulus (gravel sand), the consolidation ratio of the coupled solution and the decoupled solution are similar. This ratio deceases rapidly with the radial distance to the pumping well. However, for small values of the shear modulus, the consolidation ratio is decreasing slowly with the radial distance to the pumping well.
David G. Zeitoun, Eliyahu Wakshal

Chapter 6. The Numerical Solution of the Biot Equations

Abstract
In this chapter, first a review of the iterative methods proposed for the numerical solution of the coupled Biot equations is presented. Then, the numerical scheme based on the decoupling method of the solution of the Biot model is presented. The numerical method, called the compartmental model is similar to the finite-volume method. We describe the treatment of the different types of boundary conditions.
David G. Zeitoun, Eliyahu Wakshal

Chapter 7. General Software

Abstract
In this chapter, the interface of the software is described in general terms, and we have detailed the computation of the different types of loadings and the input data.
David G. Zeitoun, Eliyahu Wakshal

Chapter 8. A Case Study: The Bangkok Plain

Abstract
In this chapter, the implementation of the methodology is described on a modeling study of the Bangkok area. The use of historical satellite maps of the urbanization of the Bangkok area is connected with the GIS system. The building of the model data is described in detail. We analyze separately the different types of effects. The computational of the total subsidence and each component is presented. Also, the effect of pumping from a deep layer on subsidence in the upper layer is presented.
David G. Zeitoun, Eliyahu Wakshal

Chapter 9. Conclusions

Abstract
The maximum permissible land subsidence (or consolidation) is a constraint in various management problems such as: groundwater management (Ramnarong and Buapeng 1991; Brozovic et al. 2006), and the planning of town and the laws on building construction (Corwin et al. 1991). In order to develop a legal framework to litigation, it is essential that direct and indirect causes of land subsidence effects can be quantified with sufficient accuracy from a technical aspect.
David G. Zeitoun, Eliyahu Wakshal

Backmatter

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