ROADS IN DIFFICULT AREAS(DESERTS,SWAMPY SOILS AND

BLACK COTTON SOILS)BY: AASTHA R. MEHTA

GUIDED BY: PROF. M.P. JAIN

DESERT AREAS• Due to blowing of wind, sand dunes are formed in deserts.• Types: 1. Longitudinal sand dunes

parallel to flow winds do not have much change in direction• 2. Transverse sand dunes perpendicular to flow

winds have a change in direction

Longitudinal Transverse

PRINCIPLES OF ROAD LOCATION IN DUNE AREAS

• Avoid sections where sand is loose and unstable.• Align road where sand is covered by vegetation.• Preference should be given to areas having coarse sands.• Avoid locating the road on the slopes of sand ridges– instead locate

them on the dunes or the inter-dunal space.

GUIDELINES FOR DESIGN• Sections with partial cut and partial fill should be avoided since they

are difficult to maintain.• Cuttings should be avoided as much as possible and high

embankments should be avoided in areas subjected to strong winds.• Stones are rare in the desert regions so specifications involving locally

available materials (though of low grade) must be included. Gravel and dhandla can be used for base course and for surface course in secondary roads.

Contd.• Sand-bitumen base courses* are ideal for deserts because they do not

need stone aggregates and water.• Built-up spray grout# and Dry bound macadam^ can be used in

deserts due to scarcity of water for water bound macadam.*Sand bitumen mix consists of sand, binder(bitumen) and filler.#This technique consists of two layer composite construction of crushed coarse aggregate with application of bituminous binder after each layer and aggregate on the top of second layer. ^Dry bound macadam refers to roadbase material in which unbound stones are compacted in a dry state .

MAINTENANCE• Preventing wind erosion on the slopes of the embankment.• Clayey soils must be used as a thin cover to foster the growth of

vegetation.• Locally available shrubs must be planted on slopes.• A thin spray of bituminous materials on slopes where plants have

grown, will faster the growth.

SWAMPY AREAS:• Areas where there is stagnation of water and soil is permanently

saturated are called “swamps” or “bogs”.• Soil is extremely soft, highly compressible and has very low strength.• Some swamps fail under their own weight.• Example- Rann of Kachchh in Gujarat.

LOCATION GUIDELINES• In most cases, it must be bypassed. If unavoidable, the road must

cross the swamp where its width is narrow and its shallow.• Proper soil surveys must be carried out to know the exact

characteristics and conditions . • The depth of water and the type of water influencing the area must

be checked.

EMBANKMENT DESIGN

BOG BLASTING VERTICAL SAND DRAIN

Contd..• Since the swampy soil is weak in strength, light weight material must

be used . Cinder* is a good solution.• Where the soil is extremely soft, it may be feasible to take the road

over trestles of reinforced cement concrete resting on deep piles.

BLACK COTTON SOILS:• Such soils exhibit changes when the water content changes and thus

the roads become wavy.• As the soil absorbs moisture, the soil loses its supporting power and

the materials in the base sink into the subgrade.

TYPE OF SURFACE • Having heavy-duty traffic of 4500 commercial vehicles per day and msa 150 as

generally found on our National Highways and taking CBR value of 2%, total crust thickness of flexible pavement works out to 830 mm which is practically an impossible preposition.

• Assuming heavy traffic intensity of 4500 commercial vehicles per day and msa 150, crust thickness of rigid pavement works out approximately 300-320 mm, which is about one third of thickness needed for flexible pavement. Therefore, it sounds reasonable to adopt cement concrete pavement in Black cotton soil areas. This type of pavement may save the engineers from day to day maintenance problems also.

SOLUTION• The most effective way of dealing with such soils is to provide a

suitable layer between the soil and the stone layer. Minimum thickness – 10 cm.• Material- gravel of low P.I. ,sand or soil stabilised with lime.• It is also found that soils can be improved by compaction at water

contents slightly above the optimum.

REFERENCES• www.john-knapton.com/roads.htm• Google images• Wikipedia• http://

nbmcw.com/articles/roads-pavements/307-practical-problems-of-highway-construction-in-black-cotton-soil-area.html• Kadiyali L.R.- Principles and practices of highway engg.