Excavation works
Introduction
In activities related to earth moving and infrastructure works (sewers, utilities, etc.), excavation works represent a high percentage of serious or mortal accidents, being one of the main causes of burial caused by collapses, subsidence and landslides.
Definitions:
Earth Moving:The set of works effected on the ground to suitably modify its surface, prepare it for construction work and adapt it to its definitive shape. It comprises both the extraction and addition of earth.
Excavation Work: the extraction of earth carried out in localised areas of ground.
Trench and Pit: We define a trench as a long, narrow excavation and a pit as a vertical or inclined excavation in which the dimension of depth predominates over the other two, both of which are effected in the ground using manual or mechanical means and which also fulfil the following characteristics: Width/Diameter ≤ 2 m, Depth ≤ 7 m, water table lower than the depth or lowering, not including rocky ground or soft or expansive ground.
Excavation: Open-cast excavation performed by manual and/or mechanical means whose entire perimeter remains below ground level. Ground that requires the use of explosives and sludge are excluded from this definition. When the width/diameter of the excavation ≤ 2 m, we shall have a trench or pit.
Slope: The inverse of the inclination of the ground.
The most important hazards when carrying out excavation work are:
- Personnel falling onto the same level.
- Personnel falling into the excavation.
- Materials, earth or rocks coming loose and falling.
- The ground or adjacent buildings collapsing.
- Becoming trapped.
- Flooding.
- Blows caused by objects or tools.
- Vehicles colliding.
- Machinery overturning.
- Being run over or hit by vehicles.
- Noise.
- Other hazards resulting from interfering with other buried utility conduits (electricity, gas, water, etc.).
Basic measures for any type of excavation
- Have prior knowledge of the physical and mechanical characteristics of the ground (stratification, fissures, etc.).
- Scrupulously follow Works Management instructions.
- If necessary, be in possession of a prior Geological and/or Geotechnical Study to determine the most suitable method for protecting the inside of excavations.
- If the case of not using shuttering and deciding to make slopes, we must know:
- - The seismic degree of the place where the cut is to be made.
- - The ground plans and cross-sections of the provisional cuts of the project.
- - The type, situation, depth and dimensions of nearby foundations and roadways that are at a distance equal to or less than twice the depth of the provisional cut.
- - The assessment of the compression stress transmitted to the ground by nearby foundations on the same level or at a greater depth.
- - The water table level.
- - The ground’s permeability and friability in water.
- - Its degree of desiccation.
- - Its apparent specific weight.
- - The simple compression strength of unaltered samples.
- - The characteristics of ground cuts backed by experience in the place where the works are situated.
- If the obligation to carry out the geotechnical study does not exist, either because the works lack a project or for any other reason, and this study is in fact not conducted, the most favourable measures from the point of view of prevention are to be taken based on professional appraisal.
- Be in possession of the information from public bodies and utility companies that allows the locating of water, gas, telephone, sewage and electricity conduits so as to determine the most appropriate excavation method and means of protection.
- Foresee the static and dynamic overloads on the ground that may result from the proximity of buildings, machinery, stock yards and roads or streets.
- Foresee the shoring and props needed, taking into account the proximity of adjacent buildings, machinery, stock yards and roads or streets.
- Always bear in mind that subsidence or landslides may occur, even in rocky ground.
- Check daily the excavation (regardless of the type: trench, pit or excavation), slope and support systems; especially if:
- - There are prolonged interruptions to work
- - Situations of freezing and thawing, rain, etc., occur
- If any unforeseen anomaly occurs when excavating, interrupt work and inform the Works Supervisor.
- The presence of a Preventive Resource figure when there is a serious risk of burial or subsidence.
