Burdens offers expertise, as well as choice, on the latest solutions needed to manage water effectively, especially useful given ever-changing legislation and tighter planning constraints.
Burdens holds the largest distribution stocks in the UK of geotextiles and geogrids – up to 10,000 rolls, as well as large
amounts of grass paving, and SUDS cells. The firm also offers advice to specifiers/architects/designers, particularly relevant given ever-changing legislation in water management. This gives its Burdens/WTB Geotechnics strand the ability to claim a unique position in the marketplace.
With the requirements of Future Water and similar documents calling for more technical solutions, such as permeable paving on domestic driveways, architects and specifiers are now faced with planning constraints calling for soakaways, rainwater harvesting, and stormwater attenuation. This is where WTB Geotechnics can help, providing solutions that encompass storage systems, liners, geotextiles, and flow control, all connected back to the Burdens range of civils materials, ensuring a comprehensive solution to most applications.
Its technical and design office offers guidance both to contractors, specifiers working regularly with geotechnical materi-
als. It is of particular relevance to specifiers/architects/designers who are unfamiliar with these items, but who have to offer soaka-ways, attenuation systems, or rainwater harvesting to clients.
The firm can assist specifiers in ‘joining up’ the disparate elements of a geotechnical
solution, from initial groundworks to permeable paved surfaces and flow control devices for stormwater. Using geogrids can reduce the amount of stone used by up to 50%, with a consequent reduction in vehicle movements. A stabilised layer incorporating a geogrid can increase the service life of an unpaved road by a factor of three. Some recent developments are the Triax geogridfrom Tensar (see box), Concrete Canvas, and stormwater chambers.
As land usage becomes increasingly critical, there is a requirement for higher geotechnical standards. ‘Orange marker’ geotextiles like the NW100HV are now commonplace as the initial separation layer on former industrial sites. WTB Geotechnics can offer design advice to assist low CBR, contaminated ground conditions, and sites requiring engineered solutions such as retaining walls, to make them suitable for redevelopment.
Embankment Design
Several options may be appropriate within embankment design. Erosion control covers prevent the wearing away of the upper soil layer by rain, wind/water, or foot/animal traffic. Soil stabilisation means reinforcing the subsoil and topsoil layer, where these become detached from the base soil layer and instability results due to water ingress. Soil reinforcement is used where the whole soil mass needs restraining, in particular where the base soil is to be steeper than its natural angle of repose. A retaining wall may be needed to hold a slope in place to allow the construction of buildings or roads and railways. Depending on the site design constraints, one, two or all of the above methods in combination can be used for an appropriate embankment design.
Use of biodegradable embankment stabilisation materials, such as permeable grass paving and cellular confinement systems in tree root protection, also contribute to a greener environment.
Biodegradable pre-seeded matting can often be used to achieve an attractive surface in a short time. Three-dimensional
matting or cellular confinement materials can be used where larger scale topsoil retention is required. WTB Geotechnics can offer a variety of slope and embankment design solutions, or, in conjunction with Enviromesh, retaining wall solutions.
The Triangular revolution in Geogrids
Geogrid technology has been developed over the past 30 years for stabilising construction over poor ground. By enabling the ground to bear higher loads with manageable deformations, the technology offers advantages in, cost, time, material and environmental savings. Geogrid solutions use stiff polymer grids placed at the base and sometimes also within the aggregate fill to create a mechanically-stabilised layer which provides high load-bearing capacity.
Until recently such ground stabilisation solutions employed a biaxial geogrid (with rectangular or square apertures). Since their emergence in the 1980s, a wide number of uses have been developed and proven for geogrids. Applications include highways, access roads, parking areas, capped sludge lagoons, temporary load platforms and trafficked areas in general. Benefits include reduce construction thickness, increase bearing capacity, control differential settlement and extended asset life.
After six years R&D, the revolutionary new family of geogrids known as TriAx – was launched by Tensar in 2008 (pictured). They are distinguished by their triangular apertures and near isotropic in-plane stiffness. They have been proven by testing at the BRE, Transport Research Laboratory, and the University of Nottingham to achieve significantly improved mechanical stabilisation and load bearing performance, enabling even thinner layers of fill to be used
than with the biaxial geogrids previously tested.
Aside from the cost and environmental benefits, this can allow new developments on marginal ground which previously may not have been considered cost-effective. This includes ground with variable and low load-bearing capacity such as weak clays, peat, silts and, increasingly, made ground on brownfield sites.
A case study which demonstrated a major carbon emissions saving, was at a site for a new hotel in Barnsley, Yorkshire. The TriAx geogrid enabled the efficient creation of a mechanically stabilised layer for the hotel permanent car parks and access routes, also temporary access and a safe working platform for a crawler crane. The design saved 380 mm of sub-base thickness, 27% in CO2 emissions, and reduced aggregate, transport and plant required, when compared with the traditional nonstabilised solution.
