Geoscience Reference
In-Depth Information
for innovative contracts) and the design of a structure using these geosystems. Since
the design (type of geotextile, and type and size of elements and their geometrical
layout) is governed to a significant extent by the choice of materials to be used and
the corresponding construction method, a successful design requires close interac-
tion between the designer, supplier of geotextiles and the installation contractor.
The design of geotextile-encapsulated sand elements is characterised by an itera-
tive process (as is usual in design processes), where various solutions are sought that
comply with the functional and performance requirements. This manual assumes
that the designer has already gone through the initial phase of the design process;
the initiation and the exploration phase, and has opted for a design using these geo-
systems. The design process begins with the chosen type of geotextile-encapsulated
sand elements (which has normally been chosen on the basis of design data, e.g.
water depth, dimensions of structure, hydraulic loading, etc). Figure 2.1 illustrates
this design process.
Based on the functional requirements and the local conditions (specifically the
hydraulic and geotechnical conditions), the key dimensions of the overall structure are
established, such as the characteristic cross-section, longitudinal profile, crest height
and the slope. Further, the construction procedure is taken into account and this
should include an inventory of the available fill material.
Next, the specific dimensions and component configuration of the structure can
be determined using, for instance, applications and practical examples given in the
literature [46 and 47]. The size (weight and dimensions) of the geotextile-encapsulated
sand elements and their number, can then be determined.
When the overall size and dimensions of the structure are known the potential
failure mechanisms can be established and the interrelationship between these failure
mechanisms may be drawn up in the form of a fault tree (see 2.3.3).
The next step is to assess the hydraulic stability of the elements - the impact of
waves and/or currents. In many cases the geotechnical stability of the elements must
also be assessed, e.g. when they are used as bank protection. This stability assessment
must account for both the construction and the operational phases. The construction
phase is often dominant. If the elements do not fulfil the stability requirements dur-
ing construction, then a different size (weight/dimension) must be chosen. This does
have an impact on the number of elements to be used and possibly on the method of
construction.
If the elements fulfil the various stability requirements, the minimum tensile
strength and strain capacity needed for these elements can then be determined. This
minimum tensile strength also applies to the required strength capacity of any seams
(often the weakest part in these elements). From this, the required tensile strength and
strain capacity for the geotextile can be established, followed by the choice of mate-
rial for the geotextile. Finally, the chosen geotextile is checked for durability and for
“blocking” and “clogging” resistance (see Appendix A).
In principle, this general approach applies to all the geotextile-encapsulated
sand elements considered in this manual, where the calculations for determining the
strength of the geotextile are related to specific, proven, methods of construction.
Chapters 3 to 6 cover the general design procedure for each of the various types of
these geosystems.
