Reading Comprehension and Critical Thinking When Exploring Key Concepts of Soil Classification in Appendix A of Subpart P

You may have seen evidence of how a lapse in reading comprehension and critical thinking occurs involving Subpart P and soil classification.

First, for the context of this article, this is how I define the two:

Reading comprehension means “Understanding what it says”.

Critical thinking means “How does it work?”, or “How do things fit together?”, or perhaps “How did I arrive at my conclusion?”

By the way, this is not a tutorial of how to classify soil. For that you could attend a good excavation safety competent person class or perhaps read chapter 4 of the book “Trench and Excavation safety by the Book”.?It is available at www.trenchandexcavationsafety.com

Let’s get right to the point. The first sentence of Appendix A provides the foundation for how the framers of Subpart P approach soil classification. It says:

“This appendix describes a method of classifying soil and rock deposits based on site and environmental conditions and on the structure and composition of the earth deposits.”

Let’s stop here for a moment to make an observation. The words “based on” and what follows are extremely important. That sentence is very clear about what soil classification is based on. It says that the soil is to be classified based on the type of soil we are excavating, as well as what site conditions might be influencing the stability on the soil.

Further, when reading through the entire appendix A, we find that paragraphs (b) Definitions, (c) Requirements, and (d) Acceptable visual and manual tests each contribute to help us discover those two important variables as well as how they are combined to come up with a Type A, B, or C. To reiterate, those two variables would be (1) the kind of soil(s) and (2) the site condition(s) that might be affecting that soil.

Observation number 1 – Have you ever heard someone say “You have to do one visual test and one manual test to classify soil”?

That statement is made off-the-cuff many times, but it is technically inaccurate. And at the risk of being nit-picky, let’s look at several reasons why it would be incorrect according to appendix A of subpart P.

First though, in fairness to many whom I’ve heard make that statement over the years, I’m quite sure they really do know what the standard says and how to classify soil, they are just repeating something they have heard without the benefit of thinking it through. So I do not mean to be critical of those who know what soil classification is all about.?

The first reason why the statement would be inaccurate is that one must do as many manual tests as it takes to figure out what type of soil is being excavated, since that variable is one of the key factors which soil classification is based on.

Likewise, one must also do as many visual tests as it takes to discover all of the site conditions that may have an influence on the soil.

Case in point: Suppose someone literally thinks “I only have to do one manual test” and so, since they are excavating moist or wet soil, they only conduct the plasticity test as proscribed in paragraph (d). And, let’s say after conducting the plasticity test they discover they are working in clay. Knowing that the soil is moist clay would be incomplete information. The fact that they are working in clay is not nearly enough. A follow-up test should be either the “thumb penetration” test or to use an instrument such as a pocket penetrometer to get an estimate of the unconfined compressive strength of the cohesive soil. In this case they needed to do no less than two manual tests to satisfy what soil classification is based on in the first sentence.

In another scenario let’s say we were working in layered soil. This could require several tests to determine the soil type(s) in each layer.

As for visual testing, there are seven visual tests. The first two visual tests are there to give us an idea of the type of soil we are working in by observing how the excavated soil falls out of the bucket.?The last five visual tests each address a particular site condition. So if I were to pursue the assumption that I only have to do ONE visual test, which ONE of the seven would I do? You see, one test shows where to look for fissures, the next test listed shows where to look for previously disturbed soil, the next for layers and also for layers that might be sloping toward my excavation, the next for water, and the last test is checking for sources of vibration. Which one should I do if I only have to do ONE?

Again, I should do as many visual tests as I need to, in order to get a complete understanding of the site conditions, and not overlook anything that might affect the soil stability.

So, where did we ever get the idea that all we have to do is one visual and one manual test? It might come from the 2nd requirement in paragraph (c) of appendix A that is titled “Basis of classification” where it states “The classification of the deposits shall be made based on the results of at least one visual and at least one manual analysis”. Note that it clearly states one “analysis” not one “test”. Those are two different things.

The next sentence after that explains further; “Such analyses shall be conducted by a competent person using tests described in paragraph (d) or in other recognized methods . . . “.

Using reading comprehension skills and logic, we can deduce that what we need to do “ONE” of is an analysis. One visual and one manual analysis. It does not say how many tests have to be done. And based on the first sentence in appendix A, the logical conclusion would be to do as many manual tests and as many visual tests as it takes to say you have done a visual and a manual analysis and therefore could come to an understanding of what the soil is made of and have identified all of the site conditions that contribute to its stability.

So, if someone ever tells you that you have to one visual and one manual test, just asked them “Which one? There are seven visual tests and five manual tests. Which one of them should I do?”

Again, in consideration to most of those who make the statement that we need to do one visual and one manual test, they really do understand soil classification but while thinking “analysis” they are using the word “test”.

Observation number 2 – Another reading comprehension failure that I find in the industry on this subject involves the very first of the requirements in paragraph (c) which states

“Classification of soil and rock deposits. Each soil and rock deposit shall be classified by a competent person as Stable Rock, Type A, Type B, or Type C in accordance with the definitions set forth in paragraph (b) of this appendix”.

The point we make here is that in the definition of each of the referenced classifications (Types A, B, C) is each of the variables that were mentioned in the first sentence of appendix A. In other words, in the definition of Type A there is a list of the soils that could potentially be classified as Type A, as well as a list of site conditions that will keep that particular soil from being classified as Type A.

In the definition of Type B there is a list of soils that qualify as a Type B. Included in the list are soils that failed to qualify as a Type A because they were either previously disturbed, subject to vibrations, or were fissured soils.

Then, in the definition of Type C soil there is a list of the soils that are not stable enough to be a Type B soil. They list clay soils with an unconfined compressive strength of 0.5 tsf or less, gravel, sand, and loamy sand. The Type C definition also includes two site conditions; one is 4:1 sloped layered systems, the other is submerged soils or soil from which water is freely seeping.

In spite of the clarity in which these definitions are written, quite often a safety professional can be heard making a statement such as “Well, everything we dig has been previously disturbed, so that automatically makes it Type C”.

The words “previously disturbed” do not show up in the definition of Type C soil. They only appear in the definition of Type A and Type B soil. It states that Type A cannot be previously disturbed but Type B can. The only two site conditions listed in Type C involve having a sloped layer system and/or water issues. In other words, it takes much more than being “previously disturbed” to make a Type A or B soil be classified as a Type C.

If that isn’t enough, the federal register (page 45939) states

“This definition (of Type B) is very similar to proposed paragraph (b)(13), except that the agency has added specific examples to this definition to assist the user, as discussed, and has clarified that most disturbed soils are Type B.” ?

A similar thing occurs when someone excavating silt soil puts it in the Type C category although appendix A doesn’t do that. According to the definition of Type B soils, silt and angular gravel are granular soils that qualify as a Type B.

Evidently, the fact that silt will break up into a fine powder when crushed with hand pressure makes some people suspicious and they instinctively want to classify it as a less stable soil like Type C.

There are other misunderstandings that I’ve heard from people regarding appendix A because of a failure to read with comprehension and to think critically about the issue. So I challenge the reader to carefully examine their approach to soil classification against what is plainly written in appendix A.

Now many in the industry want to classify all soils as a Type C because it’s the “worse-case scenario”. The only problem with that is it means we are limited to Type C soil protective system options. If the soil is better than a Type C, then we have unnecessarily made things more difficult. Making things harder do not make them safer. I would argue that making things unnecessarily harder makes them less safe because we are limiting our protective system options.

And here I leave you with one final question.

“What is the one site condition that affects soil stability that is not mentioned anywhere in appendix A?”

That’s your reward for reading this far.

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