Taming the Hill Roads—A Case Study

Abstract

Engineering of hill roads is always a daunting task, especially owing to unstable strata of the young fold Himalayan Mountains as geologically, and rocks in outer and lesser Himalayas are in formative stage and inherently very weak like highly weathered or fractured sedimentary formations such as sandrocks, siltstones, claystones. Some rocks’ formation primarily shows good in situ strength, but weathering exposure weakens its strength. Located in Seismic Zone IV, even minor tremors instigate weak rocks to behave as flowing soil mass/tend to swell and fail along bedding/structural weak planes, resulting in disastrous slope failures. To make a safe and reliable access to the remotest hilly region, hill slopes are required to be stabilized artificially by mechanical means besides stabilization by natural phenomenon and vegetative growth. Hill roads are normally constructed by part-cut and part-fill method. To construct the required formation width of highway, provisions of retaining structures in valley side are necessarily desired. Retaining structures contribute 20–30% of the total project cost in hill road construction. Parwanoo to Solan section of NH 22 is also proposed to be widened to four lanes from existing two lanes by cut-and-fill method. This paper presents a case study on design and construction of embankment on valley side using reinforced soil slope at steeper angle due to ROW constraint.