Effect of Cone Geometry and Hammer Weight on the Penetration Resistance of Fibre-Reinforced Unpaved Road Layer

This study investigated the effects of dynamic cone penetrometer (DCP) geometry in fibre-reinforced pavement subgrades. Four DCP configurations comprising a conventional and a modified device, each equipped with a cone and a flat tip, were tested under three hammer weights. Tests were conducted on fibre-reinforced pavement models containing 12 mm strands and 40 mm discrete polypropylene fibres at contents ranging from 0– $$3.0%$$ . Three performance indices were evaluated: the dynamic cone penetration index (DCPI), ductility index (DI), and pavement structural energy ratio (PSER). Fibre reinforcement reduced DCPI and improved DI and PSER, with optimum performance observed at fibre contents of 1.8– $$2.4%$$ . The modified DCP produced lower DCPI and higher DI and PSER than the conventional device. The 8.0 kg hammer produced the highest penetration energy, whereas the 2.5 kg hammer detected layer interfaces more effectively. Discrete fibres outperformed strand fibres in terms of DI and PSER, while strand fibres produced more stable DCPI profiles. Flat-bar tips yielded higher DI and PSER but more variable DCPI than cone tips. Correlations between the California bearing ratio (CBR) and DCPI ( R² = 0.61 ) indicated that the flat-bar DCP shows promise as a low-cost field indicator for assessing fibre-reinforced pavement subgrades.