More on Soil Classification

A previous article discussed the difference between the effect that previously disturbed soil has on soil stability, and the effect that water has on soil stability according to the OSHA Excavation Standard (Subpart P). Specifically, we pointed out that water will cause any soil to be classified as a Type C, however previously disturbed simply means the soil cannot be classified as a Type A. Meaning, a previously disturbed soil could potentially be classified as a Type B. There is no comparison at all to the effects that those two site conditions have on soil classification. (See previous article for clarification)

This article is going to focus on why that matters. Why shouldn’t we just classify every excavation as a Type C soil and forget this nonsense of trying to rate the stability of soil?

The answer to this question is not complicated. Here are some reasons.

1. The only reason we are classifying soil is to satisfy the requirement in 1926.652 a(1) which says we must have an adequate protective system. Determining the stability of the soil is a key aspect of that process. If we say we have the worst-case soil stability, then we are automatically limiting ourselves only to those protective systems which are designed to handle the worst-case soils. This makes protective system selection and installation much more difficult. Making things more difficult unnecessarily does not make things safer. I could make the case that it could make things less safe. Note: I have seen jobsites where the organization had a worse-case Type C mandate, but the soil was sloped to a Type A. But I’m sure they felt better because in a safety manual somewhere it is written that all soils on the jobsite are Type C. This infringes on ultimate absurdity.

2. Competent soil classification is not difficult. But I believe that is what drives the “worst-case scenario” mentality. Subpart P was written for the competent person to understand and implement. This competent person is not expected to be a soils engineer. The authors of subpart intended for the competent person to attend training sessions that would explain soils, protective systems, and the requirements of the standard and to implement those safe practices on the excavation site. It is doable.

3. Most jobs don’t have the room to slope to Type C correctly. When using a shield, automatically calling it Type C could mean having to use a heavier steel shield when a lighter aluminum shield would’ve worked just fine. And using shoring systems for worst-case Type C are quite limiting, and often isn’t practicable because the workers are not familiar with how to use these worse-case products such as waler systems or excavation braces.

So, the main takeaway here is that the decision to go with worse-case scenario soil classification is many times not well-thought out and implementation lacks honesty and guidance. We follow the established standards, or we don’t. But there needs to be a direct relationship between what the pre-determined safety procedures are and what happens in the field.

Final thought. In those areas where there is a high-water table or for example the soil is sandy, and the classification will automatically be a Type C, I understand the position to make sure all excavations in those areas are classified as a Type C. That is not the point that I’m making in this article. I’m referring to those areas where the soil could easily be classified as Type B but there are safety policy or manual limitations. Here’s a quote that I’ve heard many times; “We classify all of our jobs as Type C, so we bench everything.”

If you understand sloping and benching, you understand the irony.

Thanks for reading this. For more information on this and other excavation safety topics please visit www.trenchandexcavationsafety.com