Access routes are an integral part of all new construction sites
Providing access for staff, contractors, equipment and materials, they are essential to efficient project management and delivery. Correct construction and detailed design is essential for both short-term and long-lasting benefits – ensuring they are robust enough to withstand heavy vehicles during construction works, and allowing the area to be reinstated once a project is complete.
However, access routes – whether at site entrances or haul roads up to 5 miles long – are often required over unstable, variable or weak ground, and even peat bog.
Choosing the right reinforcements on which to build the road, to displace loads and strengthen the ground, will support on-time, on-budget and safe project delivery. Getting access routes wrong risks ground slippages and pollution, inaccessible areas and costly remedial works, and even injury, through the overturning of vehicles or plant. There is clear correlation between well designed access routes and reduced hazards or health and safety incidents.
Collecting the right information
Access route design must take a number of factors into account, including existing ground strength, expected weather conditions, vehicle weights and regularity, and the speed of operations.
A good design will identify more than just the strength required. It will also inform on the width, angles of junctions and turning spaces required, the skid resistance, stopping distances and sight distances needed, and appropriate inclines, declines or ramps.
Starting out with a CBR (California bearing ratio) test will determine the ground’s existing load-bearing capacity. This test works by replicating wheel loads and weights to measure what pressure will penetrate soils. CBRs are used to determine the thickness of materials required for any access route, whether temporary or permanent, for both vehicles and people. Conducting borehole testing may also be required, to determine if and how deep water or gases sit below the ground.
A geotechnical report will inform on the likely impact of ground conditions, such as soil strength, movement of water through the ground and depth of stone required. Where stone for cover is required, cost-effective, sustainable off-site solutions or availability of materials on site, from ‘borrow pits’, will need to be identified. Depending on the cover used, design will need incorporate a dust control plan to maintain good visibility and prevent pollution. As with design for permanent roads, the proper banked curves or slope inclines and facility for adequate drainage must all be factored into technical designs for temporary routes.
Crucially, information will be required from site teams’ project managers and civil engineers to establish the types, weights and regularity of vehicle movements across site. Basing a routes’ width, load-bearing capacity and the angles of any curves or junctions on the heaviest, lowest and least agile vehicle, or vehicles, set to access site is advised.
While collecting comprehensive information will incur costs it is a valuable investment as some geotextile products reduce the time needed to construct access routes by up to 75%, delivering immediate cost benefits.
Before access routes are then constructed, the topsoil will need to be stripped and safely stored to be reinstated for landscaping or permanent roads on completion. Since the challenge of reinstatement usually takes place within the strictest time limits or budget constraints, as a project nears completion, this will be achievable if the optimal access route has been designed.
Figure 1 – Access road formation
Identifying the right reinforcements
With a range of reinforcements available the information collected will inform which are the optimal products to use.
Where stabilization is the primary requirement, geogrids often with a geotextile layer beneath are ideal, able to displace loads or build strength using multiple layers. Where drainage is necessary, geocells offer permeability while creating a fixed, strong layer of vertical and lateral support.
Should an access route require capacity for large loads, woven geotextiles offer greater strength and load bearing, particularly over soft ground where impermeability for stones is essential. However, if permeability is required for drainage, non-woven geotextiles are optimal.
Once a solution has been chosen, regular testing, maintenance and implementation of a dust control plan will be essential to sustaining the access route’s use and success.
Carrying out sufficient testing and preparatory works is extremely important in delivering effective and efficient access routes.
For expert advice on the design and engineering of access routes, get in touch.