A grillage foundation is a type of foundation that is commonly used for heavy structural columns, piers, and scaffolds where the load is expected to be dispersed over a large area. This type of foundation consists of one or more tiers of beams, which can be made of either steel or timber, placed at right angles to each other. These beams are then superimposed on a concrete layer, which further helps to disperse the load over a wider area.
One of the main advantages of using a grillage foundation is that it enables the avoidance of deep excavations. This can be particularly beneficial in situations where the ground is difficult to excavate or where there are concerns about disturbing the soil structure. Additionally, using a grillage foundation can limit the depth of the foundation to between 1 meter and 1.5 meters. This can be a significant advantage in situations where it is not possible or practical to excavate deeper foundations.
Types of Grillage Foundations
The steel grillage foundation and timber grillage foundation are two types of foundations commonly used in construction. The steel grillage foundation consists of a network of steel beams that are laid out in a grid pattern and then embedded into the ground. This type of foundation is typically used in situations where the soil is not stable enough to support the weight of a building on its own. The steel beams help to distribute the weight of the building evenly across a larger area, providing greater stability and reducing the risk of settlement.
On the other hand, the timber grillage foundation is a type of foundation that consists of a series of wooden beams that are laid out in a grid pattern and then embedded into the ground. This type of foundation is typically used in situations where the soil is stable and able to support the weight of the building. The wooden beams help to distribute the weight of the building evenly across a larger area, providing greater stability and reducing the risk of settlement. Timber grillage foundations are commonly used in the construction of residential buildings, as they are cost-effective and relatively easy to install.
1. Steel Grillage Foundation
The steel grillage foundation is a type of foundation consisting of steel beams arranged in single or double tiers, which are then enclosed in concrete. The grillage beams in each tier are held in place by 25 mm-diameter pipe separators and 20 mm spacer bars. The spacing between the beams is arranged in a way that allows for the placement and compression of concrete between them.
Steel grillage foundation
It is important to maintain a minimum clearance of 8 cm between the two beams in the foundation. Additionally, the distance between the beams’ flanges should not exceed 1.5 to 2 times the flange width, with a maximum spacing of 30 cm.
To protect the steel beams from corrosion, a minimum concrete cover of 10 cm should be maintained on the outside edges of the external beams, as well as above the upper flange of the top tier. Moreover, the concrete cover under the lower beam should not be less than 15 cm.
2. Timber Grillage Foundation
Timber grillage foundation is a suitable option for construction sites with soft and water-logged soil. It can effectively support the building walls at an economical cost. This type of foundation replaces the concrete block that is typically placed below the wall footing. By limiting the soil weight to 5.5 tonne/sq.mt, a wood platform is used instead of the concrete block.
The wood platform consists of two layers of boards, one running longitudinally and the other across the wall. These boards are typically 8 to 10 cm thick and extend 45 to 60 cm beyond the footing foundation on each side. The thickness of the boards at the bottom levels ranges from 5 cm to 10 cm depending on the loads and site conditions. To divide the two layers of planks, rectangular portions of timber are spaced no more than 38 cm center to center, with a depth of 0.75 times the width.
Construction of Grillage Foundation
Grillage foundation construction involves several steps to ensure its stability and durability. The first step is to create a framework that will hold the grillage in place. This framework needs to be strong enough to support the weight of the foundation.
Next, formwork is prepared using edging boards. These boards are arranged in rectangular troughs with a height of 1-1.5 ft and a width equal to the minimum wall thickness of the building. Concrete is then poured into the formwork to create a concrete pad with a thickness of 450 mm to 600 mm.
Once the concrete pad is in place, the grillage sections, which can be made of timber or steel, are placed on top with sufficient cover on all sides. Another layer of concrete is poured over the grillage to reach the desired depth. It is important to maintain a minimum cover of 10 mm at the top grillage to prevent corrosion of the steel beams.
Overall, the process of constructing a grillage foundation involves careful planning and attention to detail at each stage to ensure that the foundation is solid and able to support the weight of the building.
Placing of Grillage Foundation
Advantages of Grillage Foundation
Grillage foundation is a type of foundation that is faster to install and cast compared to conventional foundations. This type of foundation is capable of handling heavy loads over a larger area. It is commonly used in the construction of significant structures such as column piers and scaffolds. One advantage of using grillage foundation is that it avoids the need for deep excavations in soft soils. Additionally, the depth of the foundation can be limited to 1-1.5 m, making it a more practical option for certain projects. Overall, grillage foundation is a reliable and efficient solution for projects that require a sturdy foundation.
FAQs
What is a grillage foundation?
A grillage foundation is a type of foundation that is designed to distribute the load of a structure over a wide area. It typically consists of one or more tiers of beams, which can be made of either steel or timber. These beams are placed at right angles to each other and are superimposed on a concrete layer. The purpose of this arrangement is to disperse the load of the structure evenly over a large surface area, thereby reducing the stress on the underlying soil.
Grillage foundations are commonly used in construction projects where the soil is weak or unstable. By spreading the load over a wider area, they help to prevent the foundation from sinking or settling unevenly. Additionally, they can be used to support structures that require a larger foundation than what would be possible with a traditional footing.
The beams used in a grillage foundation are typically spaced at regular intervals, and the size and spacing of the beams can be adjusted to suit the specific requirements of the project. The concrete layer that supports the beams is usually reinforced with steel bars to provide additional strength and durability.
Overall, the grillage foundation is a reliable and effective method of supporting structures in a wide range of soil conditions. By distributing the load of the structure over a large area, it helps to ensure that the foundation remains stable and secure for many years to come.
What are the types of grillage foundation?
It appears that you have repeated the same information twice. However, I can provide additional details on the two major types of grillage foundation:
- Steel grillage foundation: This type of foundation is made of steel beams that are arranged in a grid pattern to distribute the load of a structure over a wider area. Steel grillage foundations are often used for larger and heavier structures such as commercial buildings, bridges, and industrial facilities.
- Timber grillage foundation: This type of foundation is made of wooden beams that are also arranged in a grid pattern. Timber grillage foundations are typically used for smaller structures such as residential buildings, sheds, and cabins. They are often more economical than steel grillage foundations and are suitable for lighter loads.
Both steel and timber grillage foundations provide a stable and level base for a structure by distributing its weight evenly over a larger area. The choice of which type of foundation to use depends on factors such as the size and weight of the structure, the soil conditions at the site, and the budget for the project.
What are the advantages of grillage foundation?
Grillage foundation is preferred over conventional foundation due to several advantages. One of the major benefits of grillage foundation is that it requires less time for installation and casting compared to conventional foundation. This can result in faster project completion times, saving both time and money.
Another advantage of grillage foundation is its ability to transfer heavy loads over a larger area. This is particularly useful for constructing significant structures such as column piers and scaffolds. The load distribution capability of grillage foundation makes it a reliable option for such projects.
Furthermore, grillage foundation is an excellent solution for areas with soft soils. It eliminates the need for deep excavations, and the foundation’s depth can be limited to 1-1.5 m. This feature saves significant time and resources that would otherwise be spent on extensive excavation work.
In summary, the advantages of grillage foundation over conventional foundation include reduced installation and casting time, the ability to transfer heavy loads over a larger area, suitability for constructing significant structures, and avoidance of deep excavations in soft soils. These benefits make grillage foundation an attractive option for many construction projects.