Field evaluation of vegetation growth in geocell-reinforced unpaved shoulders

Unpaved shoulders have been commonly used in rural areas due to the consideration of economy and low traffic demand. Unpaved shoulders are often vegetated and have relatively low load carrying capacities. To accommodate temporary heavy truck loads and/or agriculture vehicle loads, geosynthetics, such as geogrid and geocell, have been used as reinforcement to stabilize unpaved shoulders. While the geosynthetic increases the load carrying capacity of the shoulder, it may negatively influence the vegetation that is planted on the shoulder. To investigate the effect of geosynthetic reinforcement on vegetation, outdoor field vegetation tests were conducted in this study. The primary method was to compare the growth of vegetation, mainly perennial ryegrass and tall fescue, on different mixes of surface layers at the same thickness with and without geosynthetic reinforcement. Geocell reinforcement was used in this study. Different base course and topsoil combinations were investigated including: (1) 200-mm thick topsoil; (2) 200-mm thick soil-aggregate mixture (50% aggregate); (3) 50-mm thick topsoil over 150-mm thick soil-aggregate mixture (50% aggregate), and (4) 50-mm thick aggregate over 150-mm thick soil-aggregate mixture (50% aggregate). Each test section was 1.5 m long and 1.5 m wide. During the test, soil moisture content, soil temperature, and precipitation were measured. To evaluate the vegetation growth, grass blade length and population density were recorded periodically. The effect of geocell inclusion on the vegetation was evaluated by comparing the geocell-reinforced sections with the unreinforced sections.