Trenching and Excavation Safety (Part 2)

Understanding the different types of soil

All soil is not created equal. Different soil acts differently and you therefore need to know the type of soil you are dealing with in order to know which type of protective shoring to use. Ultimately, analysis of and proper identification of soil is something that should be handled by a competent person who is properly trained.

With regards to this, OSHA states OSHA standards require that trenches be inspected daily and as conditions change by a competent person prior to worker entry to ensure elimination of excavation hazards. A competent person is an individual who is capable of identifying existing and predictable hazards or working conditions that are hazardous, unsanitary, or dangerous to employees and who is authorized to take prompt corrective measures to eliminate or control these hazards and conditions.”

 

There are three classifications of soil, classified as A, B or C:

  1. Clay, caliche or hardpan
  2. Loam, silt, sandy loam or silty loam
  3. Sand or other types of sand-like soil

 

The classification of soil, however, is not just in reference to the nature of the soil. The conditions, including humidity, water content, etc… is also to be taken into account. As temperature and humidity content change, so may the classification of the soil. What this classification is ultimately trying to determine is cohesiveness (how well it sticks together as opposed to crumbling and breaking apart). The above type classifications then are only valid for each of the soils when there is average water content. Even A type soils can became C type soils when there is little to no water content. A more technical classification, based on cohesiveness looks like this:

  1. Soils with an unconfined comprehensive strength of 1.5 tsf (tons per square foot) or greater.
  2. Soils with an unconfined comprehensive strength between 0.5 and 1.5 tsf.
  3. Soils with an unconfined comprehensive strength of 0.5 tsf (tons per square foot) or less.