The Giroud-Han methodology is a recognised engineering design method used to determine the required thickness of aggregate layers for unpaved roads and working platforms constructed over weak subgrades. Developed by Jean-Pierre Giroud and Jie Han, the methodology is widely used across civil engineering, infrastructure, renewable energy and construction projects where temporary or permanent trafficked surfaces are required.
The method was developed as an advancement of earlier unpaved road design approaches, incorporating the mechanical benefits of geogrid reinforcement within aggregate layers. Unlike purely empirical methods, the Giroud-Han approach combines theoretical modelling, laboratory testing and full-scale trafficking data to assess how aggregate platforms behave under repeated wheel loading.
At its core, the methodology evaluates how traffic loads are distributed through the aggregate layer and transferred into the underlying subgrade. Weak soils are more susceptible to deformation and rutting under repeated loading, particularly during construction activities involving heavy plant and vehicle movements. The methodology uses subgrade strength, typically represented by California Bearing Ratio (CBR), together with traffic loading and allowable rut depth to calculate the aggregate thickness required to achieve acceptable performance.
Where geogrid reinforcement is incorporated, the methodology also considers how the geogrid improves aggregate confinement and load distribution. By restricting lateral movement within the aggregate layer, the geogrid increases stability and reduces stress transfer to the subgrade. This can allow a reduction in aggregate thickness while maintaining the required trafficking performance.
The Giroud-Han methodology is commonly applied to haul roads, temporary access roads, crane pads, working platforms, renewable energy developments and rail infrastructure projects. Its widespread adoption reflects the increasing need for more efficient and sustainable construction practices, particularly where reducing aggregate usage, vehicle movements and embodied carbon are important project objectives.
The methodology should always be applied using accurate site investigation data and appropriate engineering judgement. Factors such as drainage conditions, aggregate quality, trafficking frequency and construction methods can all influence performance and should be considered during design.
Within Geoworks IQ, the Giroud-Han methodology forms the basis of the geogrid design calculations used for haul roads and working platforms. The platform enables users to compare reinforced and unreinforced aggregate build-ups while assessing material quantities, carbon impacts and project efficiencies. The use of geogrids and geotextiles within these applications aligns with wider geosynthetic design principles described within BS 8661:2019, which provides guidance for the specification of geotextiles for separation and filtration functions in civil engineering applications.
