Factors Influencing the Geometric Design of Hills Roads Design of Hill Road
a) Rock cutting
The rock stratum slopes downward into the hill side, the rock is permitted to overhang the road forming a half tunnel. Blasting is done either from face or from one or both sides. The strata are inclined towards the hill slope, cutting is continued until the inner slope is at a safe angle to prevent slipping.
b) Precipice work
Where the time available does not allow for blasting and tunnel work, cliff galleries and cradles are restored for the negotiation of cliffs and precipices. These are suitable only for light vehicles or foot traffic and considered only for short term use and not as a permanent road way for regular traffic. It is important that the strata should dip inwards from the face in order to ensure safe attachments for the jumpers and holdfasts and to lessen the risk of rock falls.
c) Retaining walls
Retaining walls are the most important structure in hill road construction to provide adequate stability to the roadway and to the slope. Retaining walls are constructed on the valley side of the roadway and also on the cut hillside to prevent landslides towards the roadway.
d) Pavement walls
The embankment slopes are normally protected with rough stone pitching about 30cm thick in order to avoid erosion due to flow of water. If the stopping length is too long it is preferable to construct a toe wall to support the embankment and depending upon the slope available. Where the cutting slope is steep and contains loose or scour able soils, slips are likely to occur.
e) Pavement type
Because of the high intensity of rainfall generally throughout the year in the hill reigns, an important type of pavement proves more effective, though the initial cost may be high. A permeable surface such as W.B.M gets eroded by the heavy rains and regular maintenance cost comes out to be high. The bituminous pavements are therefore preferred on hill roads. Cement concrete pavements are not considered suitable because of its high initial cost and delay in construction.