The performance of the Dharan-Dhankuta Road, east Nepal, in the context of the Fookes et al. (1985) mountain model: a tribute to the late Professor PG Fookes

The mountain model developed by Fookes et al. (Eng Geol 21:1–152, 1985) comprised four terrain zones applicable to the Himalayan foothills in which the 50 km-long road from Dharan to Dhankuta was designed and constructed between 1974 and 1982. Forty years on, performance assessment of the completed road shows that the model has proven successful in allowing landslide and fluvial hazards and problematic ground conditions to be anticipated and hence accommodated in route selection and engineering design. Persistent slope failure and resultant road damage have occurred at two locations only, both in the vicinity of major thrust faults, and both in response to exceptional rainfall and earthquakes. Nevertheless, a total of 1.5 km of the road length in valley floor terrain has been repeatedly destroyed by river scour or blocked by debris at tributary fan crossings. The potential for these fluvial hazards was recognised in the mountain model, but considerations of cost and construction expediency prevailed over engineering geological advice. Despite these outcomes, less than 3% of the alignment suffers from recurrent damage, and it is concluded that the road has performed well in comparison to some others in Nepal. The use of models such as that developed by Fookes et al. (1985) provides a valuable means for assessing the potential geohazards and ground engineering problems posed by different route and design options.