THE PROBLEM

Access roads and working platforms were required to carry heavy loads over fine sand subgrade soils in the development of a new wind farm. The access roads needed to support traffic from construction vehicles, as well as from the turbine delivery vehicles and cranes. At the same time, it was important that working platforms ensured safe support for the crane pads on site.

THE SOLUTION

A Tensar MSL™ (mechanically stabilised layer) incorporating TriAx® was adopted for the site access roads and working platform. Designed to cater for construction traffic operations taking into account loose, low strength formation soils.

PROJECT DESCRIPTION

The construction of 5 wind turbines (2MW) up to 100 metres in height required 2.5km of 4m wide access roads and 7,000m2 of working platforms to allow construction operations to take place.

Assessment of site conditions suggested that a formation CBR value of 3.0% would be appropriate for use in the design of the new access roads and working platforms.

The original design proposed a layer of well graded crushed stone together with a geogrid/geotextile geocomposite material. Tensar were able to rationalise the original design by using a Tensar MSL™ mechanically stablised layer incorporating a TriAx geogrid, reducing the original stone thickness by around 40% which resulted in savings in construction cost and carbon emissions. By assessing the properties of the proposed fill and underlying soil, Tensar were able to remove the requirement for a geocomposite as the geogrid alone would provide stabilisation and separation functions of the granular layer.

The traffic load for the access roads was assessed in terms of dynamic loading from the movement of stone delivery vehicles, concrete mixers and turbine component delivery and construction vehicles. A serviceability limit in terms of surface deformation was set at 40mm for the access roads.

A further check was carried out on the working platforms to ensure they could carry the target bearing pressure of 200kN/m2 anticipated during turbine installation operations

The Tensar MSL provided stabilised access roads and working areas, as well as allowing site operations to be completed in good time with the project benefiting from reduced costs in terms of both cash and carbon.