Major cost of forest construction operation is spent to earthwork operations. Therefore, time studies, estimation machine productivity and earthwork operation cost would be necessary to better utilization of current resources. In this research, impact of subsurface materials as key factor in forest road construction operation was investigated in a one kilometer forest road as study area. Subsurface material of the road, constructed by a Hydraulic excavator and a bulldozer, was contained three layers in term of digging: soft (soil), medium and hard (rocky). For this purpose, time of machines work cycle elements included warm up, movement from camp to study area, extracting remained trunk if any, earthwork activity, mealtimes and regular delays were accurately recorded during 15 working days. Furthermore, relevant cut and fill subsurface material was measured precisely. The results of continues time studies showed that mean production rates vary from 34.98 m3/hr in hard layer to 331.63 m3/hr in soft layer. The results indicated that there was a direct relationship between rock share volume and delay times, therefore technical and personal delays in rocky layers were considerably more than other layers. Proportions of delays were 9% and 16% in soil and rocky layers, respectively. Also, production cost was 0.12 $/m3, 0.27 $/m3 and 1.13 $/m3 in soil, medium, and rocky layers, respectively.
