How to Construct Raft FOUNDATION & When to use Mat Foundation in Building -Step by Step Procedures

Raft foundation is used in building construction when soil has low bearing capacity, the structure carries heavy loads, or there is a risk of uneven settlement. It distributes the building’s weight evenly over a large area, making it ideal for weak soils, waterlogged areas, basements, and expansive soils. Raft foundations are also cost-effective compared to deep foundations like piles in certain conditions.

How to Construct a Raft Foundation – Step by Step Guide

A raft foundation (also known as a mat foundation) is a large, continuous slab that supports an entire structure, distributing the load evenly across the ground. This type of foundation is ideal for weak or expansive soils and helps prevent differential settlement.

Step-by-Step Procedure to Construct a Raft Foundation

Site Preparation & Excavation

Clear the site of debris and vegetation.

Excavate to the required depth based on structural design.

Ensure proper leveling and compact the soil for stability.

Soil Compaction & Anti-Termite Treatment

Compact the excavated area to prevent future settlement.

Apply anti-termite treatment to protect the foundation.

Blinding & Formwork Installation

Lay a blinding concrete layer (usually 50-100mm thick) to provide a smooth working surface.

Set up formwork (shuttering) to define the foundation edges.

Reinforcement Placement (Steel Bars)

Install reinforcement steel bars (BRC mesh or rebar) as per structural drawings.

Use spacers and cover blocks to maintain correct concrete cover.

Plumbing & Electrical Conduits (if applicable)

Lay any underground pipes or conduits before concrete pouring.

Concrete Pouring & Compaction

Pour high-quality concrete mix (typically M25 or M30 grade).

Use vibrators to eliminate air pockets and ensure uniform strength.

Curing & Strength Development

Cover the concrete with wet hessian or polythene sheets to prevent moisture loss.

Cure for at least 7-14 days to achieve the required strength.

Removing Formwork & Surface Finishing

Carefully remove formwork after the concrete has gained sufficient strength.

Conduct quality control tests such as slump and compressive strength tests.

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