Excavating rock or soil is an important aspect of a civil engineering project. This chapter briefly discusses excavation methods. Excavation techniques or rock excavation methods differ from soil excavation. The excavation methods can be classified according to their purpose, that is, whether the excavation is for foundations, slopes or underground openings.


The methods of excavation in the broad sense can be divided into three types: excavation, tearing and sandblasting. In addition, the assessment of gravel capacity is also an important aspect of the excavation. Even the most resistant rocks, such as limestones and sandstones, when tightly joined or set, are removed by heavy scarifiers at least to the point of erosion and alleviation of surface tension. Sedimentary rocks tend to break easily. The cleanability of metamorphic rocks, such as gneiss, quartzites, schists and shales, depends on their degree of lamination and on the mica content. It is often not possible to break up igneous rocks, unless they are thinly laminated as in some volcanic lava flows. Tearing is relatively easier in open excavations. In confined areas or in a narrow pit, however, the rock itself often requires sandblasting due to the confinement effect and the difficulties of using a ripper in a confined space. The capacity of the gravel can also be evaluated using the study of seismic refraction and knowing the seismic velocities.
Excavations and trenches are special cases of confined spaces. (A trench is a narrow excavation less than 5 m wide and deeper than its width. A trench is an opening or depression carved into the surface of the earth). They create the following potential dangers:

Burial of workers in case of collapse of the excavation walls.

Accumulation of flammable or toxic vapors during excavation.

Lack of oxygen in the air in the excavation that has been created.

It falls in and around the excavation site.

Unintentional contact with public services such as electrical cables or gas pipelines.

Groundwater accumulation and drainage system.


Being crushed by falling equipment, possibly caused by vibrations in the area.

Excavation and trench operations should be managed with the confined space entry policy. In particular, the management system should include atmospheric tests for flammable and / or toxic vapors or oxygen deficiency in a trench or excavation.

As part of the excavation authorization process, the following checklist questions need to be considered:

What kind of soil will be found? Is most of the excavation work done in ‘B’ or ‘C’ type soils (these terms are explained in OSHA standards)?

Is there a safe exit from the trenches?

What are the soil moisture conditions?

Has the soil been previously disturbed?

How big and deep will the excavation be?

How long will the excavations be open?

What range of weather conditions can be expected while working?

What kind of equipment will be used and where will it be placed?

How close will the excavations be to existing structures and improvements?

How much and what kind of traffic enters or passes near the excavation site?

Will the digging operation create shocks and vibrations, such as explosions or pile drivers?

Are there other sources of shock or vibration nearby?

If shoring is needed, what types and sizes?

Are earth fault circuit breakers used whenever portable electrical equipment is in operation on site?

Are procedures in place to ensure that workers do not go under loads moved by lifting or digging equipment or within reach of booms and buckets?

Are ground obstacles, such as trees and rocks, that could create a hazard during excavation removed or properly secured?

Before any excavation, the purpose of the work and relevant safety issues should be reviewed with all workers involved in the project; your comments and feedback should be solicited. The review should include a determination of soil conditions, traffic flow and the location of underground services, and other hazards associated with an excavation operation.

If there are pipelines in the excavation area, call systems must be used, as described in Chapter 7: Transportation, before starting work. If the utility company and / or landowner cannot respond to the underground installation request within 24 hours (or longer if required by state or local law), the excavation work can continue. However, all precautions should be followed to detect pipes and other underground equipment in the area. The same precautions apply to underground electrical cables.

Overhead cables are also a safety concern. They can be hit by heavy equipment, such as backhoe or tracked arms and buckets.

Obstacles, such as carelessly excavated tools, equipment, or materials, should always be properly stored to avoid tripping, slipping or falling.

Walkways or bridges with handrails should be installed when employees or equipment are expected to pass through excavations or trenches. If walkways are used and are more than 1m high, handrails are required.

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