CPD Specifier May 2015 issue September 2015 | Page 48

Outdoor Engineering

Steeply sloping
building sites
made viable with
Maccaferri
retaining walls
David Crowther, Technical
Manager of Geo-engineering
specialists Maccaferri,
explains how innovation
in retaining wall design,
materials and construction
could help relieve the UK’s
critical housing shortage
GABIONS

Although most UK housebuilding companies say that they are busier than
they have been for years, we are also told that the country is in the middle
of an acute housing shortage.

Gabions are stone filled cages of woven wire mesh, nominally 2.0 x 1.0
x 1.0m. Their mass and flexible composition means that Gabion walls
are ideal for engineered applications and can accommodate significant
differential settlement, should this be a requirement.

Reasons are many and varied, including short-term materials shortages
and the lack of skilled labour, but one which frequently finds itself at the
top of pile is the lack of good quality building land.

The un-bound stone infill also prevents the build-up of hydrostatic
pressure behind the wall and, because of these qualities, engineers
throughout the world have frequently made gabions their retaining wall,
solution-of-choice.
When used in combination with geosynthetic reinforcing geo-grid, they can
create reinforced soil structures of immense strength and durability, as in
the Maccaferri Paramesh system.

Building on green-belt sites is not an environmentally responsible option
and in October 2014, the then Communities Secretary Eric Pickles
responded to calls to relax restrictions by saying he would be tightening
the government’s new planning rules on the subject of the greenbelt.
As a consequence, house builders have been forced to find ways of
using more brown field sites as well as land that was previously felt to be
at the margins of usability - particularly steeply sloping sites that need
considerable re-profiling before being viable.

Gabions are also available in square welded wire composition for use
where engineering requirements are less onerous or where a higher
aesthetic finish is desired.

The construction material industry has responded positively to these
challenges and has provided house builders with a range of innovative
ground engineering solutions to make difficult sites economically
buildable.

GREEN TERRAMESH
Green Terramesh is a modular, steep-slope, reinforced soil system. The
integral stiffened face is designed to allow creation of a steeply sloping
vegetated-face structure.

One company at the leading edge of ground re-profiling is retaining
solutions specialists Maccaferri. The company has developed a portfolio
of retaining wall and soil reinforcement systems which allow major contour
modifications through the introduction of retaining walls and engineered
terracing.

Double twist wire mesh forms the basis of the reinforced facing unit. A
bio-degradable blanket is factory fitted behind a stiff, steel mesh face
to provide shape, prevent initial erosion and promote rapid vegetation
establishment. For higher structures, geo-grids are used to supplement
the woven mesh facing unit.

From a site sustainability perspective, the re-use of site won soils as
structural fill in these reinforced soil retaining structures virtually eliminates
the need to import and export bulk materials and reduces heavy-truck
movements to a minimum.

A wedge of topsoil behind and in contact with the blanket provides a
moisture and nutrient reservoir, essential for successful vegetation.
Green Terramesh is an ideal solution when a naturally vegetated ‘greenfaced’ steep slope is required, such as in environmentally sensitive areas.
48

Page 48.indd 1

26/08/2015 12:16:39