Terram - a Fiberweb business

Embankment drainage with Terram drainage composites

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Courtesy of Terram - a Fiberweb business

Project
Design and construction of a new 3km runway, 45m wide with 7.5m shoulders on each side, with taxiways and turning circles, main civils contract £108m; total project cost £172m.

Terram Application
Terram 1B1 drainage composite was used extensively (some 300,000nr) in the construction of the embankment carrying the runway over the River Bollin valley. The long-term settlement of the completed runway must not exceed 100mm over 15 years.

Embankment Construction
The 24m high embankment (approx. 400m length and 350m width at the toe) was constructed over a subgrade of 4.5m alluvium; mainly silty sands with little organic material. The embankment fill material, some 1.6mn.m3, was mainly clay of variable quality.

To facilitate the rapid settlement the embankment included a multi-layer drainage system. Beneath the runway zone 200mm thick stone drainage blankets were installed at heights varying from 2m in the lower section to 3m in the upper area.

Terram 1B1 drainage composite was used in the shoulders of the embankment linking to the core stone drainage layers and also, to further speed up consolidation, between the stone drainage layers in discrete areas within the core section. In the shoulders the 2m Terram strips, supplied in 100m rolls, were installed at 2m centres vertical 10 the line of the embankment; the strips in the next layer above being placed over the free space of the lower layer. Within the core the Terram was again installed at 2m centres. This method achieved a maximum drainage path of 2m.

Terram Drainage Composite Advantages
i. Transport
160,000m' of stone drainage material weighing some 300,000 tonnes was imported via a specially converted railway link. This figure would have been increased bv some 40% without the introduction of a drainage composite. The weight of 300.000m2 of Terram 1B1 was around 300 tonnes, a weight reduction factor of 1:400.

ii Installation
The difference between the costs of constructing stone drainage blankets and installing the K ram drainage composite was extensive. Aside from material costs rolling out the drainage composite was significantly quicker than placing 200mm thick granular layers.

iii. Drainage Capacity
The transmissivity of Terram 1151 at a loading of 500kPa was evaluated and found to be acceptable; the extruded net core provides bilateral and interconnected flow paths.

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