Soil Classification: Appendix A’s Simplicity and Soil Complexity

There’s probably no part of the Excavation Standard that is more misunderstood and abused than Appendix A. In the excavation industry the reaction to the issue of soil classification ranges from competent classification to giving it passing attention or just avoiding it altogether. This is a shame as the authors of Appendix A describe a method of classifying soil stability in the simplest way. Unfortunately, Appendix A continues to be a misunderstood aspect of excavation safety.

Yes, the subject of geology and soil stability can be complicated and for obvious reasons. Our point here is that despite the enormity of the subject and its complexity, we want to make the case that Appendix A is designed to simplify what the competent person needs to know about soils so they can know for certain that a protective system is adequate. Here’s another way to say that to drive home a point. The only reason to classify soil is to make sure we are using an adequate protective system (see 1926.652 a). Without competent soil classification, adequacy of protective systems becomes guesswork.

The authors of Appendix A knew that the competent person would need a simplified way of evaluating soil stability without the benefit of a degree in geology. And an objective view of Appendix A certainly proves that point. For example, there are two variables to consider when classifying soil. One factor is the makeup of the soil (such as clay), the other is the site conditions (for example water). A good competent person class should explain those two variables in enough detail that the competent person will be able to identify both and then put that information together to come up with an A, B or C based on the definitions in Appendix A.

What is required to get there is a complete understanding of what the standard says as well as what it doesn’t say. This requires study and reading comprehension skills. It is my opinion that it is extremely helpful to have access to important ancillary documentation such as the federal register. Without which, erroneous conclusions may be reached, and also some just give up and say, “The whole world is Type C!”

What’s wrong with classifying everything as “Type C” instead of looking at the full range of soil stability ratings? Simply this. If we are truly matching our protective systems to type C soil, we are making things much harder. Making things harder as a rule does not mean we are making things safer.

Here's another point. I have looked at excavations that have been deemed to be type C many times, however in these cases a protective system for type A or type B had been used. Why wasn’t a type C protective system used? Well, a type C protective system wouldn’t work in those situations. So, what I’m advocating is a sense of intellectual and practical honesty. I’m suggesting that the protective system that is used must match how the soil stability has been evaluated.

Ideally, one day we will eventually arrive at the point where the competent person will be trained and knowledgeable and it will be the norm for soil stability to be determined competently.

To be able to classify soil and be able to explain how one arrives at a conclusion is known as critical thinking. I believe that is what the authors of Appendix A were hoping for.

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

There you’ll find Jon Preston’s Trench and Excavation Safety by the Book. It is an excavation safety reference guide and contains a copy of the federal register. The best part is that the cost of this book is only $39.00

Keep learning my friends.