Trenching/Backfill

Trenching and backfilling go hand in hand. Typically what gets dug up will then get backfilled after the repairs or new materials are installed.

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Trenching is the excavation in which material removal forms a narrow opening in the ground. OSHA considers excavation to be a trench if it is fifteen feet wide or less at the bottom of the excavation. So generally speaking it is deeper than it is wide. A trench can also be applied to an excavation where the structure within an excavation reduces the width between the excavation wall and structure to fifteen feet or less.

 

A trench may seem simple enough, but if machinery, such as an excavator is required to dig the trench then an experienced operator is a must. There are many things to consider such as the type of trench, soil type, existing pipes or other wires under the soil and access for the equipment.

A Straight Trench is where the sides are parallel and the base is at a right angle. The Straight trench is typically used when there is limited surface area to disturb. Some examples would be near buildings or a roadway. OSHA requires protection systems such as trench boxes or shoring based on a variety of conditions that H & S company is knowledgeable in determining to eliminate risk.

If the trench requires angled sides to prevent a cave in, it is called a Slope Trench. Many factors will determine the angle of the slope such as trench depth, soil type and how long the trench needs to stay open. This type of trench is used for placing large culverts or pipes. It is also common in new construction sites because a wider path of soil is not a problem.

When the work is complete and the trench is ready to be covered up it is called Backfilling. Knowledge and skill are required to backfill the trench with the correct specifications, contract requirements and soil conditions.

Care must be taken to prevent damage to the shaft, structure, cabling, pipeline or other buried elements when backfilling. Depending on specifications, backfill is often done in ‘Lifts’. This is the process of backfilling a determined amount of material such as 18” Lift. The first Lift is compacted and repeated until the final grade is met. If the trench was for utility lines the excavation contractor will have special considerations when backfilling and compacting.

Compaction is achieved by an excavator or a compactor machine such as a ‘jumping jack’ or ‘vibrator plate’ or various attachments to the excavator equipment.