Design of unpaved forest roads - stress-strain response of a reinforced soil under triaxial conditions

Often, the design and construction of unpaved forest roads makes use of locally available soils. The road cross section consists of a base layer formed by locally available soil, good-quality aggregate or a mixture of these materials. To decrease the quantity of good-quality aggregates required for building such layer, using locally sourced soils is favoured. Including layers of geosynthetic reinforcements will contribute to reducing the quantities of granular material forming the base layer and/or increase its mechanical properties. This paper studied the influence of single pocket geocells on the mechanical response of a locally sourced soil (well-graded sand with gravel) close to an unpaved forest road (Aveiro, Portugal). The geocells were 3D printed, to define a reinforcement geometry adjusted to the soil characteristics, namely in terms of particle size distribution. The mechanical response of the composite material was characterised using triaxial tests. This allowed assessing its stress-strain response and any changes relatively to the unreinforced soil. The strength parameters of the composite material were estimated using equations from the literature. The study demonstrates that the inclusion of single pocket geocells enhanced the mechanical properties of the soil. These geocells increased the soil’s peak friction angle and provided additional confining stresses.