The Slippery Slope of Improper Sloping and Benching

I began a class by asking the question “What protective system do you use?”

A hand shot up in the back of the room. “We slope everything!”

“How much do you slope?” I asked.

After a brief pause he responded “We slope according to how much room we got.”

That got a lot of laughs but unfortunately, that is often the reality for many who depend primarily on that one type of protection from cave ins.

By law protective systems must be adequate. Adequate sloping means sloping according to soil stability, not on “how much room we got”. It means basing our slope system on the guidelines in subpart P or perhaps on an engineer’s plan. Sloping incorrectly can result in injury or death. That is a fact.

The most common option for sloping is to follow the guidelines in Appendix B of Subpart P. The problem a lot of people encounter is that there just isn’t enough room to slope properly as proscribed. So ultimately they slope less, and are taking a terrible risk.

The same applies to benching. When benching according to Appendix B of subpart P, note the following:

1. When benching in Type B soil, it must be clay soil (cohesive).

2. Benching takes the same amount of room as sloping.

3. We are not to bench Type C soil.

?Let’s look at number 2 in the above list for a minute, because this is often overlooked. When benching properly, we will not be removing less soil than sloping, but more. One person told me at the outset of a class “We slope unless we don’t have the room, then we bench”.?Later in the class he realized and admitted that they had been benching incorrectly.

Please refer to Appendix B of subpart P to see how to properly construct a safe benching system. Note that only the first bench is allowed inside of maximum allowable slope. All secondary benches are outside of maximum allowable slope.?Also note that if the benching system is based on the plans drawn up by a registered professional engineer, the design might appear different than what we find in Subpart P.

I’ve often heard “All of our soils are Type C, so we bench everything”. That’s an easy one to fix. There are no benching options in Appendix B of Subpart P for Type C soil.

Alternatives to sloping and benching have proven to be more productive. On average using a trench shield requires digging only a third of the soil compared to sloping the walls of the same excavation. Factor in the other costs associated with additional soil removal extending out from the excavation and it can amount to considerable savings.

The point really is to always use an adequate protective system. If sloping and benching is the protective system of choice, just make sure it is constructed correctly. If using a shoring system or a trench shield, make sure it is adequate as well, considering critical factors such as trench depth, width, soil type, etc. But never take chances with a less than adequate protective system of any kind. That is a slippery slope that leads to trouble.

Finally, make sure employees are trained in recognizing hazards as well as how to deal with them. This can be done in a safety class such as excavation safety competent person training, confined space entry training, or OSHA 10-hour training just to name a few. Knowledgeable and empowered employees are a key step to maintaining a safe jobsite.