Introduction of Grillage Foundation
Grillage foundations are used to transfer heavy structural loads on soils with weak or low bearing capacity.
The grillage foundation is very useful for industrial building as a shallow foundation. The footing has more than two layers of steel or timber beams. This beam is used to spread the load of the structure on the ground.
This is usually done by grillage foundation design to transfer the heavy structural load to the bearing capacity of poor soil.
What Is Grillage Foundation?
The grillage foundation helps to distribute the heavy structural load over a wide area. This foundation does not require deep excavation. because the design of the grillage foundation provides the necessary support for the transmission of the load, the depth of the grillage foundation can usually be from 1 m to 1.5 m.
Beams in two or more layers at right angles are provided to distribute the heavy load of the structure over a large area in the grillage foundation.
Steel, precast concrete or wood materials can usually be used as the grillage beams of this type of foundation. Such foundations can be made at low cost if the wood is used as the material. But wood used as a grillage beam must have the right quality and strength.
It is advantageous when rolled steel sections are used in grillage foundation. The use of rolled steel becomes an ideal design factor for permanent conditions for grillage foundations.
Use of Grillage Foundation
Grillage foundation is used in the complex area as follows;
- Grillage foundation is used in areas where hard rock soil is not available, and mat foundation is not possible.
- Grillage foundation does not require deep excavations. So it is cost-effective.
- Heavy structure loads can be safely transferred through the use of a grillage foundation.
- The grillage foundation is used in the main project as follows. Electrical Transmission line project, Telephone tower foundation.
Types of Grillage Foundation
Here, the information of two types of grillage foundation is as follows.
- Timber Grillage Foundation
- Steel Grillage Foundation
1. Timber Grillage Foundation
- Timber grillage foundations are used to support structural walls economically. Timber Grillage foundation is used as the foundation of structural walls in case of high waterlogging or low bearing capacity.
- This type of timber grillage foundation uses timber beams and timber planks instead of steel beams.
- The load of the building structure can be safely transferred to the ground by timber grillage foundation by reducing the load to 5.5 t / sq m. In construction, concrete loads are placed under the wall instead of concrete blocks to increase the ground load-bearing.
- Timber Beam used in timber platform for Timber Grillage foundation is usually 80 mm to 100 mm thick. Timber beams are laid in layers as required in these platforms.
- The thickness of the timber beam in the bottom layer for the timber grillage foundation is kept from 50 mm to 100 mm, depending on the position of the site and the load on the walls.
- In timber grillage foundation, the timber beam is placed according to the position at the right angles.
2. Steel Grillage Foundation
- Steel beams are used as Grillage beams in steel grillage foundations, which is provided in single or double layers in the foundation at a right angle.
- In a grillage foundation, the lower face of the grillage beam is arranged in such a way that it is 10cm longer than the beam in the upper layer. The depth of the grillage beam in concrete is kept at least 15 cm.
- In grillage foundations, shuttering is done so that the steel beams are properly covered on the bottom and side.
- So that the grillage protects the steel from groundwater by concrete in the foundation.
- Thus, the cover provided in steel can prevent steel from corrosion due to groundwater.
- During concreting, the concrete can be properly compacted by a vibrator machine.
Features of Grillage Foundation
- The strength of the grillage foundation is higher than other foundations. A minimum of approximately 800 mm (8 cm) is allowed between the grillage beams to obtain the appropriate strength in the grillage foundation. The concrete can be poured easily and compacted properly.
- The heavyweight of the house safely contributes to an even distribution on the ground through the Grillage foundation.
- In this type of foundation, the depth of concrete is kept at least 150mm (15cm) to protect the lower level steel beam against corrosion.
- No more space is required to transfer the heavy load of the building to the ground.
- This type of Grillage foundation can be used very effectively in poor soil and waterlogged area.
Installation of the Grillage Foundation
The following steps are filled in for the method of installing the Grillage Foundation.
- First, we excavate the soil for depth according to the basic design. This type of Grillage foundation is usually a shallow type of foundation. The minimum depth for grillage foundation is 90 cm.
- After excavation, compaction is done by levelling the surface of the excavation. Grillage is PCC in 15 cm thickness on compacted soil for the foundation.
- The first layer of grillage beam is then placed with a 100mm cover from the prepared concrete surface. The number, size and distance of the beams are then placed according to the design of the grillage foundations.
- The formwork is shuttered in such a way that it gets proper cover from the grillage beam.
- Then, concrete is prepared in a concrete mixer according to the design ratio. Concrete prepared in this way is poured into the formwork.
- Adequate Compaction of Concrete is required during Concrete in grillage foundation.
- Curing is done for seven consecutive days after concrete.
Advantages of Grillage Foundation
Grillage foundations are mostly used in place of poured concrete for a large area. The grillage foundation saves a lot of time due to the simple process of installation.
2. Costs Reduce
Labour costs for grillage foundation are reduced.
3. Multipurpose foundation solution
The grillage foundation can be designed according to different construction requirements. Grillage foundation is therefore suitable for various applications of construction.
4. Load bearing capacity
Grillage foundation is suitable for the foundation in construction in areas where soil load-bearing is low, and soil is waterlogging.
5. Load transfer
Heavy load for building construction can be easily transferred to the ground due to the grillage beam in the grillage foundation.
Disadvantages of Grillage Foundation
Some of the disadvantages of Grillage Foundation are classified as follows.
- This type of foundation is unable to withstand extreme uplift pressure during natural conditions.
- Piles need to be inserted in greater depth according to the design for this foundation.
- Grillage foundations require skilled labour during the installation of the steel beam.
- Cranes are used for heavy materials such as beams for grillage foundation so that they can be safely installed in the foundation.
- It is difficult to install and align steel beams for grillage foundation.