Long Term Performance of a Reinforced Base Layer on a Gravel Road

On a local gravel road at Leppävirta, Central Finland (about 62° 27' N, 28° E), test pavements were constructed in the fall of 1996 to strengthen a gravel road, suffering from thaw damage. The improvement methods studied were bitumen stabilization in situ of the base layer, and a macadam overlay reinforced with a steel net. In the primary monitoring in 1997–98 it was fond that the improvement of the surface modulus was significantly higher at the reinforced pavement than a non-reinforced one. The estimated material modulus of the reinforced macadam layer (200mm thick) during thaw was 300–500 MPa. According to the FWD measurements in the spring of 2005, the back-calculated, equivalent material modulus of the reinforced layer during thaw had decreased to about a half of the value estimated after construction. The modulus in summer state was not observed to have significantly changed. In the test pit excavated across the road down to the reinforcement, and the leveling of the reinforcement it could be observed a bending (rutting) of the reinforcement. The estimated rut depth was 25 – 85 mm, and it was increasing with decreasing minimum thaw modulus of the gravel pavement. The rutting of the pavement was relatively low. Thus, it seems obvious that the reinforcement should be treated, not only applying as stiffening of the overlay, but also as an anchoring element, preventing the horizontal and shear stresses below.