Grillage foundation is used for structures requiring heavy loads to be distributed over a large, shallow foundation area. It consists of steel beams arranged in two or more tiers at right angles to spread the load. This allows for transferring load to poorer soils while limiting excavation depth to 1-1.5 meters. The beams are embedded in concrete and connected together to form a rigid foundation mat that distributes structural loads across a wide subsoil area.

1. Grillage Foundation

2. Use - Grillage Foundation design is applied for heavy structural loads
from columns, piers or beams are required to transfer bearing capacity
of a soil comparatively poor.
The grillage foundation helps in distributing the load over a wider
area of the subsoil.
This foundation helps in avoiding deep excavations as the necessary
base area is provided for the load of the transmission.
The depth of foundation is limited from 1m to 1.5m.
Grillage Foundation definition – The grillage foundation
consists of two or more tiers of beams laid at right angles to
distribute the load over a large area.

3. This type of foundation is generally used for heavy structure
columns piers and stanchions. Grillage consists of steel I I
section (R.S.J) laid in single or double large.
The second larger. The number of R.S.J.S and they’re
distanced apart depend upon the load of the structure and
the bearing capacity of the soil.

4. The depth of foundation is limited from 1m to 1.5m , as its a
type of shallow foundation.
However it should not be less then 90 cm.
Steel beams are provide in two or more tiers, the top tier of
grillage beam is laid at right angles to the bottom tier.
The beam of each tier are held in position by 20 mm
diameter spacer bars or with 25 mm diameter pipe separators.

5. 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 dimension that are laid at regular intervals.
The lower flanges of the R.S.J.S are embedded into the concrete by
pouring rich cement mortar the R.S.J.S are connected together by pipes
and bolts. The bolts are driven into web of the R.S.J.S.
After levelling the base and pouring the concrete its should be checked
that compaction is done properly and formed an impervious layer of
thickness not less than 15 cm. This protect steel joist from groundwater,
which can cause corrosion.

7. 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 thereby
forming a rigid mass.

8. PRECAUTION TO BE TAKEN
The depth of footing should not be less than 90cm.
The distance between the flanges should not exceed 30cm so
that filled concrete acts monolithically with the beams. The
concrete filling should not carry any load ; its simply keeps the
beams in the position.
A minimum gap of 10cm is kept on the outer side of the external
beam, as well as the upper flanges of top tier.
The depth of concrete below lower tier should be atlest 15cm.

13. Grillage Foundations Advantages
Steel grillage foundation gives more advantages for contractors
than wooden grillage.
The speed of Installation – Contractors can save time using a
foundation of grillage.
Convenience – grillage foundation uses to avoid poured
concrete and saves time with easy installation.
Costs effective method – Contractor can reduce cost through
minimal disruption of transport infrastructure.
Versatile foundation solution – the technology suits many
different applications.

14. 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 foundation is replaced by
timber platform constructed of timber planks.

15. Timber grillage for column

16. Timber grillage for wall