Hydraulic and earth engineering – Drainage or irrigation – Porous or apertured pipe – flume – or tileway
Patent
1996-11-19
1999-11-09
Graysay, Tamara L.
Hydraulic and earth engineering
Drainage or irrigation
Porous or apertured pipe, flume, or tileway
405 36, 405 15, 405129, E02D 1720, E02D 300, E02B 1100
Patent
active
059801557
DESCRIPTION:
BRIEF SUMMARY
The invention relates to geosynthetics, also known as and sometimes referred to as geotextiles, for use in the construction industry.
Geosynthetics are typically referred to by their principle function for any particular application and since there are essentially five principle functions there are five types of geosynthetics. These are filtration, separation, membrane, drainage and reinforcement geosynthetics.
Geosynthetics that are used for filtration typically prevent soils from migrating into drainage aqueducts or pipes while maintaining water flow through the system.
Geosynthetics that are used for separation prevent material, for example road based material, from penetrating into underlying material such as soft subgrade thus maintaining the design, thickness and integrity of a roadway.
Geomembranes are used in waste disposal and act as barriers to the passage of leakage out of or water into a waste disposal site.
Geosynthetics that are used for drainage allow water to drain from or through soils of low permeability, for example, they can be used for the dissipation of pore water pressures at the base of embankments.
Geosynthetics that are used for reinforcement add tensile strength to a soil mixture and thereby produce a more competent structural material. Reinforcement enables stable embankments to be constructed over very soft foundations and permits the construction of steep slopes and retaining walls.
The invention is in one aspect primarily, but not exclusively, concerned with drainage and reinforcement geosynthetics and therefore these types will be described in greater detail hereinafter.
Reinforcement geosynthetics can consist of high strength fibres set within a polymer matrix or encased within a polymer skin. The fibres provide the tensile properties for the material while the matrix or skin provides the geometrical shape and protects the fibres from damage. The matrix can be made from highly stable and durable polymers and the fibres can be engineered during manufacture to provide the required properties in terms of tensile strength and extension. Alternatively, the reinforcement geosynthetic can be made from a single material; ideally a high density polyethylene. In addition, the geosynthetic can be formed into specific geometric shapes which optimise the bond characteristics between the geosynthetic and the adjacent soil. Manufacturers determine the nature of a reinforcement geosynthetic such as its tensile strength, extension, structure, durability, temperature tolerance and cost. The complex interplay of these characteristics tends generally to define the type of reinforcement material to be used. However, in general, the tensile stiffness and strength of reinforcement geosynthetics is very important since deformation of reinforced soil is determined by stiffness and strength. Basically there are four main requirements for reinforcement geosynthetics;
A reinforcement geosynthetic must have sufficient strength to support the force required to achieve equilibrium in the soil. Moreover, it must have sufficient stiffness so that a required force can be mobilised at a tensile strain which is compatible with the allowable deformation in the soil. The geosynthetic must bond sufficiently with surrounding soil in order to transmit the required forces. This latter characteristic is less important for wide width reinforcement materials than for geostrips or geobars, mainly because the former have a much larger surface area over which to bond with the soil than the latter.
Finally, the geosynthetic must be durable. This means that time and environmental conditions must be considered. A distinction has to be drawn between a relatively short term application, for example reinforcing an embankment over soft soil, and a longer term application where creep becomes a significant consideration in assessing load carrying capacity. (Creep being an increase in extension of material under a constantly applied load). In practice, creep problems do not appear to be significant if high strength durable polymer
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Eng Kjell
Jones Colin John
Graysay Tamara L.
Lagman Frederick L.
University of Newcastle Upon Tyne
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