Development of design guidelines for composite-geogrid reinforced unpaved pavements

Abstract

It is well-known that the inclusion of composite geogrids (CGGs) into the pavement structure assists to maximise the benefits of geosynthetic-reinforcement in flexible pavements. However, the use of CGGs in practice is limited in Queensland, Australia regardless of its potential benefits, mainly due to the absence of rational design guidelines. Therefore, this study was conducted to develop guidelines to design unpaved granular pavements/working platforms constructed with local pavement materials and reinforced with CGGs at the base-subgrade interface. Firstly, six laboratory-scale pavement model tests were conducted varying the granular base thickness as 200, 300 and 400 mm, and with and without the CGG reinforcement at the interface of the subgrade-base layer. In all these tests, a 500 mm thick subgrade was prepared to achieve a CBR value of 2.5%, and then the granular layer was compacted on top of the subgrade to achieve 91% of its maximum dry density, in a steel box with length, width and height of 1 m, 1 m and 1.2 m respectively. The pavement models were subjected to repeated loading (up to 150, 000 cycles) at the centre using a 200 mm diameter plate to simulate the maximum tyre pressure of 550 kPa. By following a step-by-step procedure, design guidelines were developed based on the rut depths of both the reinforced and unreinforced pavement models obtained after 5000 load cycles and every 25,000 load cycles up to 150,000. Both economic and environmental benefits can be obtained by adopting the proposed guidelines.