Geoscience Reference
In-Depth Information
General design aspects
This chapter considers the design methodology of structures using geotextile-
encapsulated sand elements. First a description of the principles of geosystems is given,
then 2.2 describes the design process for these geosystems. The safety philosophy is
then examined (2.3), with the importance of identifying potential failure mechanisms
being crucial to the design process emphasized in 2.3.3. Finally, 2.4 details the different
material aspects of geotextile containers.
2.1 BASIC PRINCIPLES OF GEOTEXTILE-
ENCAPSULATED SAND ELEMENTS
Sand is commonly used in hydraulic structures. The main reasons being that sand is
one of the cheapest building materials available, can be obtained in large quantities,
is easy to process and is reusable. Sand is also mechanically stable, volumetrically sta-
ble, and has predictable engineering properties. The drawback with sand, however, is
that it lacks cohesion and erodes easily under the influence of current and waves; and
when dumped under water, it tends to migrate even at gentle slopes. To build a sand
structure in water, it is normally necessary to contain it by creating a fore-bank (for
a quay structure) or a containment dyke. These containment structures are normally
composed of gravel, mine stone, slag or armour stone. These coarse materials are also
able to fulfil an additional function - protection of the sand from erosion by currents
and waves. Filter layers are often required to prevent the sand from eroding through
the pores of the larger-sized, granular material.
Working with stone-like materials can be expensive. Geotextile-encapsulated
sand elements are an attractive alternative since local materials can be used and (less)
armour stone needs to be extracted and transported, which presents (depending on
local prices) a possibility to reduce cost. In addition, a relatively steep, erosion resist-
ant slope can be constructed in water using these elements that are comparable with
armour stone. Both the production of these geosystems and the construction of the
structure in water are relatively straightforward. If required for temporary purposes
only, the structure may also be easily removed.
One disadvantage of geotextile-encapsulated sand elements is that they are sus-
ceptible to damage during installation. Damage may occur due to poor installation
