F-6.1 Following aspects should also be considered while planning for land/building development in hilly areas:
a) The hillside with less than slope are in general stable. Therefore, building sites (temporary or permanent) should in general be located on hillside with not more than slope. In areas where most of the land is above slope, spatial regulations should control construction activity on slopes above , provided that appropriate technology is used.
b) The maximum height of the building shall be fixed.
c) Flat land is normally not available in hilly regions. The houses are required to be constructed on partially sloping land made available by cut and fill. It shall be therefore necessary to protect the houses by building retaining walls/breast walls to avoid landslides occurring at time of earthquakes or heavy rains (see F-7.4).
d) Cut slopes with height less than 5 m or two to three storey heights of residential buildings are in general stable. For higher cut slopes, special investigation should be carried out and details of protection works should be worked out and implemented.
e) Site development in hilly regions consumes about 30 to 40 per cent of total cost of building complex, therefore the following investigations shall be done to obtain the following geotechnical parametres depending upon the size and complexity of the building project:
- Type of soil rock, weathered or intact,
dip of bedding planes, drainage conditions, shear planes, material between the joints, tension cracks, type of plantation, verticality of trunks of the trees, etc.
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Cliff sides and spur faces need to be protected with appropriate technology including wire netting and/or blowing of RCC along the walls.
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Thickness of overburden, nature of soil strata, details of soil matrix, etc.
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Estimation of shear parameters of the in situ soil mass, which will govern the failure.
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Drainage pattern of the area and permeability tests to observe the drainage conditions.
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Specific slip zones in the area, if any.
f) Provisions for landslide hazard mitigation, seismic micro zonation and mitigation of liquefaction hazard should be integrated.