Guidelines for Safe Excavation Works

Shoring

Timber has historically been used for shoring. Recently they are used to carry metal-edged hydraulic jacks to the gym. They are economical and light weight, can be put on and dismantled and have an extended life. They are actually much safer than wood to use.

Installation

Shores should be established from the surface as far as possible; That is, the vertical edges should be placed from the surface and the first horizontal brace should be installed just below the surface from above. The operator must move down into the trench with the help of a ladder that is sufficiently tongue to install the next lower brace or trench jack, thus, the trench is made safe for him to descend down to install additional horizontal braces. Trench jacks or horizontal braces should never be used as ladders to move in or out of the trench because they are not designed to carry vertical loads.

Removal

When shoring is planned to be removed, the possible collapse of the trench sides should be estimated. The newly installed utility line will then be secured in the normal course with a loose or compact filler before being removed from shore. If the gap is likely to be removed from the edge, it can be filled to the bottom of the horizontal brace. This is a safe way for the worker to move down the ladder and remove this brace, after which additional trench space can be filled up to the next horizontal brace or screw jack.

If the trench is to remain after removing the trenching, the latter should not be removed until all work within the trench is completed and the newly installed utility line is secured or covered. A worker can then use a ladder to descend the horizontal trench jack and remove it. The remaining horizontal jack must be removed as he climbs the ladder. Removing shoring is a dangerous task. A worker should never be allowed to engage in this work.

Loose Site Material

Landslides are the most serious safety problem associated with deep highway cuts. This can happen at any time during the work or after completion. Disadvantages include injury to life or body, more often after heavy rains when the soil shrinks and becomes heavier than water. All loose stones, projecting knots or earth should be removed from the trenches. Excavated sides of the trench should be adequately protected.

Minimum Check and Clear Edge of Trench

There is a tendency to dump only the excavated material at the edge of the trench where excavation is done manually. The material may slide back into the trench or apply additional load on the shoring, it is recommended to provide a clear berm of width not less than one third of the final depth of the excavation. In areas where this width of the berm is not possible, less berm width less than 1 m should be provided. It is always better to provide enough toe boards to prevent ‘roll back’ in the trench.

Plant and Machinery

Excavation can be done manually or with the help of equipment depending on the amount of work and the condition of the site. The risk of accidents in mechanical excavation is high due to the speed of excavation and dumping of the material. The following safeguards are recommended.

1. Excavator equipment must be parked at a distance not less than the depth of the trench, or at least 6 meters away from the excavated sides for trenches more than 6 meters deep.
2. With the use of power shovels, the sides of the trenches become unstable and thus hazardous to persons working nearby. These conditions should be observed and suitably improved.
3. Vehicles should not be allowed near the pit. Care should be taken to locate the roads leading to the pit. When manually loading, the vehicle should not be moved even near the pit wall. The use of spot logs will reduce the risk of accidents where the vehicle is reversed for loading.
4. Appropriate tools should be provided to the workers. Maximum rigidity is the primary requirement for cutting edges and striking faces of tools. Ignoring the importance of providing the right equipment for the job is perhaps the most serious risk for workers.
5. Workers using the tool must avoid the danger posed by the sudden movement of material that may throw them off balance. They should be given enough space to avoid mistake by means of others working nearby.

Access and Escape

• Workers should be able to run faster in the event of any accident during the excavation. It is recommended that a ladder be provided for each length of 15 m or fraction thereof in case of hazardous work, and 30 m of length or fraction thereof in the case of relatively less hazardous work. Often the roads become slippery due to deposition of mud, sand or gravel. It should be avoided. In addition, the pathways must be sufficiently strong so that they can be used. Similarly, the gangway should be of better construction. The planks used should be strong, placed parallel to the length of the gangway and fastened together against displacement. They should be thick and have cleats for safe walking. The gangway should be kept clean from excavation material and other obstructions.

Other Precautions

1. Many accidents occur due to falling into uncontrolled trenches. Such accidents are more common during the rainy season. Fences, guards or barricades should be installed to prevent individuals or livestock from falling.
2. At night, all public side walks and walkways should be adequately illuminated, and warning lights should be installed at appropriate sites to ensure the safety of pedestrians and vehicular traffic.
3. They become unstable sideways during the monsoon, they should be hung in wet weather.
4. During excavation, the excavated sides should have provisions for steps or gradual slopes to ensure the safety of men and machines in the area.
5. It is possible that harmful gases and fumes are present in a ditch. Ventilation systems should be used to reduce concentrations of gaseous matter.
6. Workers normally take their lunch in the shade near their work sites. If shade is not available, they sit in the shade or under the ditch. This practice should be stopped. When digging near or under the foundation of the building, the latter must be supported by shoring, bracing or underpinning as long as the trench remains open.
7. Vibrations caused by the operation of machinery at sites adjacent to excavated pits can cause walls to collapse until they are properly braided. In addition, accelerated sand is a hazardous phenomenon requiring the use of continuous static. Moist sand is non-stationary and may require bracing for proper support

Responsibility of Supervisor

Safety Check

Experienced and qualified supervisors should be put in charge of the excavation work. They should understand the details of their responsibilities and all safety rules. A supervisor must have authority to enforce all safety regulations on site, prevent the use of faulty safety equipment, rigging of equipment and materials, and to remove any worker from the job for which he is not qualified is. The supervisor should inform the workers about the work plan before the start of work and inform them of the potential hazards. The excavation work should be inspected by a qualified engineer once a week and after every heavy rain or storm. Site defects and corrective action should be reported immediately if defects, damage or danger are found. It should pay special attention during the excavation of water pipelines, electric wires below the surface or underground structures. Supervisors should ensure that all workers working under them are provided with safety equipment and protective equipment, and they use it.

Record Keeping

The certificate and report obtained by a contractor in respect of any test, inspection or any equipment, excavation, shores, artwork etc. should be kept at the concerned construction site. These certificates and reports should be readily available for inspection by senior officers and other concerned officials.

Read more – Safe Construction for Piles & Deep Foundations