Method of construction of W.B.M. Road

Water bound macadam roads are constructed through the following stages as detailed below : 

1. Preparation of sub-grade - sub grade is provided by digging up the sub soil and the level of the sub - grade is decided by subtracting the total thickness of the pavement from the finished level of the road pavement . Form the finished level of the road pavement . The sub grade is throughly compacted by rollers weighing 8 tonnes by during rolling must be made up to and brought to the grade as required.  In rocky regions the sub grade are not rolled whearas in region of clay soils, a layer to natural sand moorum or gravel , is provided over sub grade and is duly-packed.
2. Preparation of sub-base - on the well compacted subgrade , spread 10 to 20 cm size boulders or broken stones , or over burnt bricks in layer of 15 cm thickness and total width of the sub base to be kept 60 cm wider then the pavement width , projecting 30 cm on each sides . The sub base should be compacted by a roller to provide an even surface 
3. Preparation of base - on the prepared sub- base or directly on sub grade, as the case may be, the specified materials of the base course is spread and proper grade, thickness and cross sections maintenaned as per design shown on the supplied drawings
4. Preparation of wearing course - this course may be laid in one or two layers according to the total designed thickness and the thickness of each layer should not exceed 10 cm . This component being very important, the following steps may be taken systematically

      (1) check the defective portions of the newly laid                   base course i.e. soling and rectify them

       (2) provided either bricks on end edging or                         earthen kerbs strong enough to prevent the new road material form spreading outward and also to       l retain water used in consolidation of the wearing   ourse .