GRILLAGE FOUNDATIONS.

A grillage foundation is a special type of isolated footing, generally provided for heavily loaded steel stanchions, specially in those locations where bearing capacity of soil is poor. The depth of foundation is limited from 1 m lo 1.5 m. The load of the column or stanchion is distributed or spread to a very large area by means of layers or tiers of joists, each tier being placed at right angles to the next tier. Grillage foundations are of two types:

1. Steel grillage foundation Steel grillage foundation is constructed of steel beams, structurally known as rolled steel joists(RSJ.), provided in two or more tiers. In the case of double tier grillage(which is commonly provided), the top tier of grillage beams is laid at right angles to the bottom tier. The joists or beams of each tier are held in position by 20 mm diameter spacer bars wtth 25 mm diameter pipe separators. Fig. 3.10 shows the plan and section of such a foundation. The grillage beams are embedded in concrete....
 
2. Timber grillage foundation. Timber grillage foundation is provided for heavily loaded timber column or masonry wall. The foundation uses timber planks and timber beams in the place of steel joists. This foundation is specially useful in water logged areas where the bearing power of the soil is very low, and where the steel beams may get corroded due to subsoil water. The loading on the soil is limited to 50 to 60 kN/m2. No concrete is embedded between the timber joists. However, the bottom concrete (provided in steel grillage...