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).
