An Excavation is a manmade cut, cavity, and trench in an earth surface that is formed by earth removal. Or we can say that excavation is the process of moving earth, rock, or other materials with tools, equipment’s or explosives. Excavation includes earthwork, trenching, wall shafts tunneling and underground, etc.
Excavation is used in constructions to create building foundations, reservoirs, and roads. Without excavation, an area of new construction cannot be safely built on the site and it is also used for geotechnical purposes. In the simplest form, we can say that excavation is any opening or depression in the earth’s surface.
Permit to work is required for all excavations and trenches more than 1.2 meters deep. Excavation is the most hazardous construction operation. There are two methods of excavation (1) Manual Excavation and (2) Mechanical Excavation.
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What is Excavation safety?
Excavation safety is most important because Excavation and trenching are among the most hazardous construction operations. Excavation safety is a complete set of safety precautions for trenching and excavation to eliminate hazards.
Excavation safety precautions:
- Detection of underground facilities using metal or cable detectors.
- Soil protection methods like stepping, slopping and shoring.
- Drawing and surface marking of underground utilities.
- Gas test inside excavation before the job.
- Excavated material shall be placed 1 meter from the edge of the excavation or remove.
- Safe entry and exit.
- Maintain proper access and egress.
- Provide safe angle access of 45o.
- Create bund walls for preventing outside water.
- Follow all standards of confined space if excavation becomes a confined space.
- Signalman shall always be present with vehicle movement.
- Hard barricade and signboard most important.
- Alternate access if excavation is near the road.
- In narrow trenches, a ladder should be extended from bottom to top and 1 meter above the ground surface.
- Avoid vehicle movement.
- Chemical waste and contamination should be safely removed.
- Good lighting/ illumination.
- Cutting shall be done from top to bottom. No undercutting of the side shall be allowed.
- Follow the work permit system and sop.
- Daily inspection is most important.
- Helmets and gum-boots should be given to all workers working inside.
In large-scale excavations for dams, huge buildings, highways, railways, etc., accidents occur mostly due to vehicles, dumpers, trucks, etc. Therefore, such vehicles must be checked for warning sirens, horns, lights, signals, reverse alarm, etc. Rules of driving should be enforced. Sufficient lighting should be provided for nightwork.
Hazards of excavation
- Building or structures collapsing due to excavation.
- The presence of underground installations, pipelines, cables, etc.
- Collapsing of excavation wall/cave-in.
- Drowning due to water seepage into the trench.
- Presence of toxic gasses and oxygen deficiency.
- Fall of person, materials, and tools.
- Improper access and egress.
- Soil vibration due to machinery/ heavy vehicles operating in the vicinity.
- Water accumulation in the excavation.
- Overhead power lines
- Falling of vehicle
- Permit violation
- Nearby structure and its conditions.
- Falling of removed soil.
Protective system for excavation:
1.Shoring protective system:
This method requires installing hydraulics, pneumatics, and timber shoring or other types of supports of the side of an excavation to prevent cave-ins and also support the face of excavation, and prevent movement of soil, underground utilities, roads, and foundations. Some systems can be installed without the workers entering the trench.
2.Shielding protective system:
Using trench boxes or other supports to prevent soil cave-ins. The shielding protective systems are probably the most commonly used protective system and it provides most effective protection from potential collapses. There are multiple types of shielding systems are available and it is used in all soil types. The shielding system includes trench boxes, steel plates, or a combination of protective systems.
The shielding system provides protection to workers but not excavation. A shielding system can be a permanent structure or can be designed to be portable type and moved along as work progress. Workers are familiar with shielding protective systems as compared to others.
3.Slopping protective system:
It involves cutting back the trench wall at an angle inclined away from the excavation. The slopping method is considered the safest method as compared to shoring and shielding. It is the most cost-effective and safest protection system but it requires adequate space around the excavation to get the required slope ratio and also the angle of slope required to depend on the soil condition.
Another advantage of a slopping system is to introduce or remove workers, materials, and equipment, or vehicles from just about any direction. A slopping protection system provides great benefits when an excavation is necessary.
4.Benching protective system:
Benching creates a series of horizontal levels on the excavation sides by cutting it vertically between the levels. Benching protective system is one of the least common types of protection system used in construction. Benching is possible for only type “A’’ and type “B”. It is not possible to apply a benching protection system in type “C” soil and this protective system is rarely used in construction.
Types of excavation
Excavation by material
This type of excavation removes the top layer or exposed layer of earth from the construction site. This excavation method removes vegetation, soil, and any other decaying material that could make the land unsuitable to bear the structural load.
Usually in excavation topsoils are removed because it has high moisture content as compared with lower levels and also topsoils are compressible which means you can not build until its removed. Once the topsoil layer has been removed it loses moisture content and it is easy to work.
When more than one layer of soil needs to be removed then earth excavation is required. It is required for building foundations, bridges, drainage ditch, etc. This excavation process is relatively easy.
This excavation is useful for the rocky surfaces at the construction site. Rock excavation is used to remove the rocks and it is more complex excavation as compared to other types of excavation. It requires special excavation methods such as drilling (by hand or with heavy machinery) or blasting with explosives to remove the rock from the tough surface.
Muck excavation is used where the soil has high water content. Removal of soil and water is most necessary before construction. This excavation method is used for excessive wet soil type. Because of the high water content, the soil loses its consistency. The muck can also be spread out so that it can dry or it can be moved to another area.
Excavation by purpose
5.Cut and fill Excavation
This type of excavation is used to clear large areas before starting the construction. Cut and fill excavation is also known as stripping excavation. It involves the removal of wide and shallow layers of topsoil, rocks, and other unwanted materials. This procedure may also include grading the land.
In trench excavation, the length of the excavated area exceeds the depth. Trench excavation is typically used to bury service lines, install pipelines and sewer systems, or lay foundations. Shallow trenches of less than 6 meters or deep trenches of more than 6 meters are done using trench excavation.
A basement is an area typically below the ground level. These types of excavation can become complicated depending upon the size of the property. Excavating a basement that is either partially or fully undergrounds.
Dredging is the process of excavating and removing sediments and debris from below water level, typically from the bottom of lakes, rivers, harbors, etc, and allows boats and ships to pass easily and for other construction purposes. Basically, these types of excavations are used underwater.
FAQs For Excavation:
1. What is the chief excavation hazard?
In an Excavation, cave-ins are the chief and dangerous excavation hazard.
2. How does the excavation process work.
Before an excavation carefully examined your job site. The excavation process includes:
1. Setting corner benchmarks.
2. Surveying ground and top levels.
3. Excavation to approved depth etc.
4. Marking up the cut-off levels.
5. Marking the boundaries of the construction site.
3. What are cave-ins?
Cave-ins are the most common hazard in an excavation. A cave-in occurs when the walls of an excavation collapse. To prevent cave-ins some excavation protection systems are used such as:
4. What is the difference between the excavation and trench?
Excavation is any manmade cut, cavity, trench, or depression in the ground formed by the removal of the earth. Where a trench is a narrow excavation made below the surface of the ground. The hole describes whether it is an excavation or trench. In general, the depth of the trench is greater than its width. But the width of a trench is not greater than 15 feet.
5. When does an excavation have to be inspected?
1. Excavation inspected by a competent person.
2. At least once every day.
3. If it is more than 2-meter-deep, then inspect at the start of each shift before starting the work.
4. After any accidental fall of rock, earth, or any other equipment or materials.
5. Inspect after heavy rain and flood.
6. What measures should be taken to prevent excavation collapse?
1. Batter the sides and the ends to a safe angle.
2. Where it is not possible to batter, support the walls with timber, sheeting, or proprietary support systems.
3. Do not allow any vehicle or item of the plant near an edge of an excavation that may be likely to cause collapse.
4. Never work ahead of the support.
5. Ensure adequate protective measures are taken even in rock-cut excavations.
7. Before beginning work in an excavation what should you do?
1. Identify the soil types
2. Identify and locate overhead power lines.
3. Make sure these services are de-energized as necessary.
4. Know all of the contact numbers of these services if there is an emergency.
5. Test for hazardous gas, vapors, and dust before entering.
6. Test for oxygen levels in the space before entering etc.
8. What measures should be in place to avoid the accumulation of water in the excavation?
A plan for evacuation of personnel and equipment in case of emergency and flooding shall be developed.
9. What are the soil classification categories?
1. Stable rock
2. Type ‘A’ soil (Clay, Silty Clay, Clay Loam, Cemented Soils and Hardpan, etc).
3. Type ‘B’ soil (Granular, cohesionless soil, like crushed rock, silt, silt loam, etc).
4. Type ‘C’ soil (Granular soils, sand, or soil with free seeping water, etc).