This is dependable foundation and is used in those place where the load of the structure is pretty and bearing capacity of soil comparatively poor. The grillage foundation helps in distributing the load over a wider area of subsoil. The grillage foundation helps in avoiding deep excavations as the necessary base area is provided for the load of transmission.
This type of foundation generally used for heavy structure columns piers and stanchions etc. the grillage foundation generally consist of steelI I section (R.S.J) laid in single or double larges. The second larger . The number of R.S.J.S and their distanced a part depend upon the load of the structure and the bearing capacity of the soil.
To construct a grillage foundation a trench of the required width and depth is excavated. The surface the trench is leveled and rammed. Over the rammed surface a layer of cement concrete is spread and is well compacted so as to make if impervious. R.S.J.S are of desired dimensions are laid at regular intervals. The lower flanges of the R.S.J.S are embedded in to the concrete by pouring rich cement mortar the R.S.J.S are connected together by pipes and bolts. The bolts are driven in to web of the R.S.J.S .
G.I. pipe pieces are placed between R.S.J.S and a long bolt is pass through all the holes and pipes. This will connect the R.S.J.S together there by forming a rigid mass.