Performance of Multi-axial Geogrid-Stabilized Unpaved Shoulders Under Cyclic Loading

Low-volume roadways usually have unpaved aggregate shoulders for vehicles to stop during an emergency. To provide a good condition for vegetation, turf soil can be mixed with aggregate. However, the use of turf soil unavoidably results in the reduction of the load carrying capacity of the unpaved shoulders. To improve the performance of aggregate-turf shoulders, geogrid can be included to stabilize the base materials. In this study, four test sections of 0.15 m thick aggregate or aggregate-turf bases over subgrade with CBRs of 3% were constructed in a geotechnical box (2.2 m long x 2 m wide x 2 m high) to investigate their performance. The base courses of these test sections included one non-stabilized aggregate base, one non-stabilized aggregate-turf base, one geogrid-stabilized aggregate base, and one geogrid-stabilized aggregate-turf base. A cyclic load with a magnitude of 40-kN was applied on the surfaces of these test sections through a circular plate (0.305 m in diameter). Earth pressure cells and/or displacement transducers were installed at varying locations away from the loading plate to measure the vertical stresses, permanent deformations, and resilient deformations. The results show that the existence of geogrids reduced vertical stresses and permanent deformations but increased resilient deformations. The geogrid stabilized section with the aggregate-turf base outperformed that with the non-stabilized aggregate base.