Points to Remember for Excavation of the Foundation

Excavation is the process of creating an open face, trench, or cavity to remove soil or rock. It involves layers of procedures done at various stages of the building process. Site preparation, setting out, excavation, and safety precautions depending on the depth of excavation are all part of the excavation process for foundation construction. It can be done using tools, machinery, or explosives. Since there is an ocean of terminologies and procedures, it is necessary to know the basic yet important aspects of excavation of foundation.

Manual Excavation of Foundation

List of Contents

1. Settlement of Foundation

2. Basic Excavation Terminology

3. The Procedure For Excavating A Foundation

4. Machinery Used for Excavation

5. Points To Remember In The Excavation And Filling Of The Basement

6. Conclusion

Settlement of Foundation

One area of a building's foundation may settle at a different rate and to a different extent than another area of the foundation as a result of possible ground movements beneath it. To limit the damage to the building's superstructure, this differential settlement must be minimised as much as possible. While a rigidly framed structure with panels cannot allow the same extent of differential movement of the foundation of the structure, some structural forms can do so by allowing minor movement of the small brick units and mortar joints. On clayey soils, settlement is generally greater and more continuous over time.

Basic Excavation Terminology

1. Shoring

Shoring is the process where temporary supports are propped in the trench, which prevents the sides from collapsing during construction. It is mainly used for construction that requires up to 20-foot-deep excavation, road construction, underground utilities, etc. Residential projects built on loose soil also require shoring.

Shoring (Image by Fons Heijnsbroek via Wikimedia Commons )

2. Planking

Planking is the process of placing temporary timber supports at the sides of an excavated trench. It can be either open planking (intermittent) or closed planking. If the soil is soft or loose, closed planking is preferable, where horizontal planks are placed.

Planking (Image by Elie Malti via Wikimedia Commons )

3. Strutting

The process of strutting involves laying vertical sheets, also known as sheeting or polling boards, against the trench's two walls and securing them in place with one or more rows of struts. It can be done only if the depth of the trench does not exceed 2 meters. It is mostly done for construction that requires a deep foundation.

Strutting (Image via Wikimedia Commons )

4. Dredging

Dredging is the process of excavating materials underwater. It is usually done to reshape land and water forms, to excavate minerals, to construct dams, etc.

Dredging (Image by Ana 2016 via Wikimedia Commons )

5. Grading

Grading is done to level the base of a trench or to form a particular slope. It is done before laying the foundation, landscaping, storm water drainage, etc.

Grading (Image by NASA via Wikimedia Commons )

6. Trenching

Trenching is a narrow excavation below the earth's surface where the depth is greater than its width. The width cannot be greater than 4.6 metres.

Pipeline Trench (Image by Sabino Freitas Correa via Wikimedia Commons )

The Procedure for Excavating a Foundation

1. Small Buildings

The foundation can be excavated using manual methods and tools for construction such as pick axes, spades, crow bars, etc.

2. Loose Soil/ Deep Excavation

Shoring, planking and strutting are suitable for deep foundations or when built on soil that is unsuitable.

3. Hard Soil

If the depth of excavation is less than 1.5 metres, the sides of the trench do not require external support.

Manual Excavation Using Pickaxe (Image by Petty Officer 1st Class Brandon Shelander via Wikimedia Commons )

Machinery Used for Excavation

The use of heavy machinery comes for deep excavation, where manual excavation with a pickaxe won’t suffice. The advantage of this machinery is that it is time-saving and flexible. They can reduce the need for labour and require about 1-2 people to operate the machinery.

Tractors

Tractors are the basic form of a bulldozer, backhoe, scraper, and digger. The machine is flexible in terms of adding parts as needed.

Tractor (Images by Clément Bardot via Wikimedia Commons )

Bulldozers

They are heavy, motorised equipment with metal blades, used for pushing earth and rocks for construction and road building.

Bulldozer (Image by Matthew T Rader via Wikimedia Commons )

Backhoes

Backhoes have equipment attached to the front and back. It has a long arm and a bucket-shaped shovel to move earth.

Backhoe (Image by frankenstoen via Wikimedia Commons )

Power Shovels

Power shovel has a bucket shaped equipment used to dig and load earth or rocks. It is mainly used to relocate earth after excavation.

Power Shove

Scrapers

Scrapers are used to scrape the ground's surface as part of site preparation for construction or excavation.

Scraper (Image by Ryan G. Wilber, U.S. Navy via Wikimedia Commons )

Draglines

Draglines are heavy equipment that has a rope and bucket and can dig earth from greater depths.

Dragline (Image by Alexander Novikov via Wikimedia Commons)

Clamshell

Clamshell excavators have buckets with jaws which can be used for collecting clayey soil or water.

Clamshell (Image by Cjp24 via Wikimedia Commons )

Ripper

Rippers are tractors with an arm attached that is suitable for moving rocks instead of blasting or drilling, which can be time consuming and costly.

Ripper (Image by Ana 2016 via Wikimedia Commons )

Points to Remember in the Excavation and Filling of the Basement

1. The bottom of foundation pits should be dressed level in all directions before any concrete is put in, and they should be well watered and thoroughly rammed.

2. The surface to receive the filling should first be cleared of all the roots, vegetation, and spoil before it is thoroughly wetted.

3. Filling up to plinth level should be done in layers as the building is built, so that the earth filling is thoroughly consolidated by the trampling of the workers.

4. The basement fill should have an optimum moisture content. It should be well consolidated by ramming it into 15-cm layers using iron rammers and the butted ends of crowbars.

5. When filling reaches a finished level, the surface should be flooded with water for at least 24 hours, allowed to dry, and then rammed and consolidated in order to avoid any settlement at a later stage.

6. If necessary, protection against slides and caving should be provided.

Conclusion

Excavation is one of the first steps towards constructing a building foundation, reservoirs, and roads. There are various stages during the excavation of the foundation, which must be done very cautiously so as to get better results. At the same time, using the right kind of equipment and machinery can speed up the process and reduce the time drastically. In addition, the type of soil determines the type of excavation and the procedure used to increase stability. Thus, being aware of the important aspects of excavation can help design a cost-friendly building.

Visit the links given below, to read some of our blogs:

1. Points to Remember While Doing Flooring

2. Points to Remember for Reinforcement for Concrete

3. Points to Remember While Doing Formwork and Shuttering