Hydraulic and mechanical performance of granular sub base and geo-composite drainage layers in flexible pavements: insights from laboratory experiments and field investigations

Most of the pavements undergo failures due to poor sub surface drainage, especially in the granular sub base (GSB) layer. This study thoroughly investigates the the movement of water through GSB layer, and also through the Geocomposite Drainage Layer (GCDL), an alternative to conventional GSB. The hydraulic properties of conventional GSB and GCDL of different grades were examined through the laboratory studies. Test sections were constructed within BITS Pilani Hyderabad Campus to get the valuable insights on use of GCDL and its comparison with GSB. The results revealed a substantial improvement with the use of GCDL, indicating a 2 to 3-fold increase in permeability compared to conventional GSB. By incorporating a thin GCDL layer would result in a savings of around 2500 m³ of material per km for a 2-lane flexible pavement. Also, it was calculated and found that there is a reduction of 24MT of Carbon emission with the use of GCDL. The effectiveness of GCDL emerges as a transformative and enduring solution for subsurface drainage as the permeability ranged between 1400 and 3200 m/day which is higher than the specified value of 300 m/day, as per the Indian Roads Congress.