Temporary site access roads are regularly required on construction sites. Also known as temporary haul roads, they provide access for what can be heavy construction vehicles carrying materials and equipment needed to complete the project at hand.
Because these roads are required only temporarily, they tend to be constructed from a granular fill or aggregate placed on existing ground. The granular fill or aggregate acts as the road surface itself.
Temporary site access roads can be as short as a few tens of metres or long enough to extend several kilometres (for example, to allow access for the construction of wind farms).
Although an access road may only be needed for a short period—say six months—it should be designed based on the anticipated traffic load it will carry over its operational life.
An access road design assessment will take several factors into account for the site under consideration:
• Existing ground strength—normally expressed as a California Bearing Ratio (CBR) , undrained shear strength or stiffness modulus
• Anticipated traffic load—expressed as a number of vehicle visits of differing type and configuration (e.g. concrete mixers, steel delivery vehicles) from which a number of Equivalent Standard Axle Loads (ESAL’s) can be calculated*
• Granular fill grading — This refers to the quality of the aggregate used to build the road and would typically be classified using a particle size distribution curve
• Target surface deformation or rut depth — A serviceability target for the road surface after trafficking
*It’s important to recognise that before the traffic for the main construction project uses these temporary roads, vehicles delivering the granular fill to build the access road itself will need to use them too. This means the critical time for building an access road is the construction phase itself, where the vehicles delivering the granular fill are travelling at their closest point to the subgrade soils.
The temporary haul road design procedure identifies what thickness of granular fill is needed to carry the traffic load. The traffic load is based on a surface deformation target established using a method of calculation derived from empirical data.
In the UK, the granular foundation to a surfaced road is designed separately to the asphalt layer laid over it. The methods adopted can be traced back to the Transport Road Research Laboratory (TRRL) and the UK Highways Agency (Figure 1).
If you have any questions on what is geogrids. We will give the professional answers to your questions.