Soil Classification: BOLO FOR TYPE C
If you’re a CSI fan, you know that BOLO stands for “Be On the Look-Out for something. For example, be alert for a person or maybe a vehicle.
To simplify Type C soil, it might help to think in terms of BOLO for the soil type or the site conditions that would cause a soil to be classified as Type C.
From Appendix A the definition of Type C soil reads as follows:
Type C?means:
(i) Cohesive soil with an unconfined compressive strength of 0.5 tsf or less; or
(ii) Granular soils including gravel, sand, and loamy sand; or
(iii) Submerged soil or soil from which water is freely seeping; or
(iv) Submerged rock that is not stable; or
(v) Material in a sloped, layered system where the layers dip into the excavation on a slope of four horizontal to one vertical (4H:1V) or steeper.
Out of these five statements, two of them refer to three soils that can be labeled “Type C”. The other three statements refer to two site conditions which cause any soil to be labeled as “Type C”.
When it’s broken down, it begins to look much easier to understand. For example:
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1. Weak clay, sand, and some gravels are Type C soils.
2. Submerged soil, or water seeping into the excavation from the sides or the bottom makes it soil Type C.
3. Layers of soil that are sloped towards the open excavation on a slope of 4:1 is also considered Type C.
And that’s it folks. That is the definition of Type C. Be on the lookout for those soil types and those site conditions, and if you find any of those, the soil is Type C. If you don't find those soil types or site conditions, you can call it Type B.
What isn’t found in the definition of Type C is any mention of “previously disturbed soil”, or "fissures", or "vibrations". That is because those site conditions simply mean we cannot call that soil “Type A”. Let me say that another way. “Previously disturbed” soil is not a Type C site condition. We will cover that topic next time.
The BOLO technique for soil classification as discussed above, allows for an easy soil classification short cut. To reiterate, it goes like this:
If you have weak clay, sand, or gravel. Or, if you have water issues or there are layers on a 4:1 slope – It is Type C. Otherwise, you can call it Type B.
That’s a useful short cut.
For more information on this or other excavation safety topic I refer you to my book at www.trenchandexcavationsafety.com
See you next time. Thanks for reading this.