Incorporation of the Influence of Hexagonal Stabilisation Geogrids into Mechanistic-Empirical Pavement Design Method

Abstract

Since their introduction to civil engineering almost 40 years ago, geogrids have become one of the standard solutions for constructing roads over soft soils. However, traditionally geogrids are used for the primary purpose of reaching a required bearing capacity of the road foundation, and they are not considered as providing benefit to the final pavement structure itself and their influence is not taken into account in the whole pavement design. In recent years, a new approach has been introduced to use geogrids to stabilise the unbound aggregate base of the whole pavement structure. Stabilisation of an aggregate layer with a suitable geogrid can improve the mechanical properties of this layer, which results in substantial increase of final pavement performance. This can be utilised either to increase pavement life or to reduce the thickness of the pavement or a combination of the two, including thickness of asphalt layers, leading to reduced construction costs. This way of incorporating geogrids can be used in pavements constructed both on weak and firm soils. This paper describes the process of developing a modification of Mechanistic-Empirical Pavement Design Method (MEPDM) which allows for incorporation of the influence of one type of stiff hexagonal geogrid on the performance of a whole pavement construction. Results of full-scale accelerated pavement tests of non-stabilised and geogrid stabilised sections are presented, as well as other tests and studies which confirm that geogrid can increase the stiffness of an unbound aggregate layer, limit deformations and retain higher stiffness for longer period of time. Based on analysis of data from these tests, a modification of MEPDM has been developed in the form of special algorithms for calculation of the factors enhancing the pavement life.