U.K. Case Study: Bluewater Retail and Leisure Destination Reinforced Soil Slopes to Form Steep-Sided New Lakes - Reinforced Soil Engineering: Advances in Research and Practice - page 140

Netlon 813 geotextile (formerly named Netlon 1004R), manufactured by
Naue Fasertechnik GmbH, was specified. It has independent certification from
the German Federal Waterways Authority (BAW) based on rigorous
performance testing with a range of soils including silty sand. These tests assess

Filter performance by filtering a real soil in turbulent conditions and also
examining the resultant permeability after

impregnation with soil

particles
Residual tensile strength following exposure to abrasion (16 £ 5000

revolutions of a rotating drum containing gravel and water)
Puncture resistance in a test replicating rock armor units being dropped on a
soil-supported sample

This nonwoven geotextile is manufactured by needle-punching two
separate geotextiles, one containing staple (short) fibers of polypropylene and the
other, a polyester, to create an integrated 800-g/m 2 duplex material. This efficient
double-layer arrangement provides a coarse fiber prefilter that, additionally,
interacts with the soil to achieve a degree of mechanical stabilization of soil
particles that may otherwise be prone to migration.
Despite this certified evidence of the geotextile's robustness and field exp-
erience with similar products under extremely severe test conditions (Dixon and
Osborn, 1990), the engineer was concerned about its vulnerability to damage, for
example, from accidental impact, burrowing animals, nesting birds, and long-term
exposure to ultraviolet (UV) radiation. Unlike some geogrids, there is little or no
information available on the long-term life of geotextiles fully exposed to sunlight.
The engineer, therefore, specified an outer grid wraparound face retaining a
15-cm-wide layer of 5-10-cm-sized hard durable fill as cover protection to a
geotextile wraparound local to the face of the silty sand fill (Fig. 7) .
With the specified grids it is possible to create a full-strength connection
between adjacent lengths using an HDPE bodkin (Fig. 8) . In a wraparound detail,
this bodkin provides a more positive joint than simply relying on a frictional
anchorage. Furthermore, when the higher grid length is tensioned during
installation, this helps pull the lower wraparound face tight.

3 CONSTRUCTION

3.1 Contract Award

The Enabling Works contract was let by Bluewater Construction Management
Team (BCMT) to O'Rourke Civil Engineering Limited in early 1996 following a
competitive tendering process. O'Rourke chose to use the specified geosynthetics.
They appointed a specialist subcontractor to supply and install the lining system
for Lake 1 and opted to construct the reinforced soil slopes themselves.