The Engineer Says: “Excavation is Safe.” Is it?

Excavation wall exposed

The engineer says the excavation is safe. What do you say?

Is an Excavation Safe Because a Soil Engineer Says It Is?

Would you work at the toe of a nine-foot vertical wall of dirt with no protective system? Hopefully your answer is 'no.' But what if you received a letter from a soils engineer who had evaluated the composition of the dirt and declared it safe? What if the engineer (his stamp on the letter) asserted that, "The near vertical cut consists of very dense glacial till which can remain stable for very long periods of time." What if he went on to say:

"We observed no evidence of loose or sloughing soil or groundwater seepage in the cut. No evidence of tension cracks or other signs of instability were observed at the top of the cut. It is our opinion that on a temporary basis (one month) the cut could be considered stable and construction of the basement could continue."

The engineer adds that the cut should be re-evaluated at the end of the month, no surcharge loads should be placed within the affected zone, and surface waters should be prevented from flowing into the cut. So if a contractor had this letter in his possession while the workers were exposed to the face of this cut, would the letter be enough to prevent an OSHA citation? In other words, can the assessment of an engineer trump OSHA requirements? That was the question that a client recently posed to me. He is located in Washington State to the response reflects their requirements (which are basically the same as the Federal rules except for the requirement of having a protective system at four-feet of depth as opposed to five for the Federal regulations). How would you respond? Think about it for a minute and then scroll down to see what I wrote. -------------------------------------------

Dear [Name Withheld]:
I reviewed the letter dated May 30, 2014 and sent by[Name Withheld], PE.
Your question was whether this letter, which asserts the stability of a 9-foot vertical wall of glacial till would satisfy OSHA inspectors and preclude the issuance of any citations. The letter indicates that these soils are 'stable' and can remain standing for long lengths of time therefore a protective system is not needed. That may be the case, however, dispensing with a protective system would violate OSHA regulations.
The Washington OSHA rules for excavations state that if the excavation is deeper than four-feet a protective system is required unless the excavation is in solid rock. Glacial till is not solid rock. The rule citation is below:
WAC 296-155-657 Requirements for protective systems.

(1) Protection of employees in excavations.

(a) Each employee in an excavation shall be protected from cave-ins by an adequate protective system designed in accordance with subsections (2) or (3) of this section except when:

(i) Excavations are made entirely in stable rock; or

(ii) Excavations are less than 4 feet (1.22m) in depth and examination of the ground by a competent person provides no indication of a potential cave-in.

The rules do allow a sloping and benching system to be designed by a registered professional engineer (per Option 4, cited below), but no provision of the OSHA code allows an engineer to dispense with the need for a protective system altogether based on a site survey. The rule citation is below:
(d) Option 4-Design by a registered professional engineer.
(i) Sloping and benching systems not utilizing Option 1 or Option 2 or Option 3 under subsection (2) of this section shall be approved by a registered professional engineer.
(ii) Designs shall be in written form and shall include at least the following:

(A) The magnitude of the slopes that were determined to be safe for the particular project;

(B) The configurations that were determined to be safe for the particular project; and

(C) The identity of the registered professional engineer approving the design.

(iii) At least one copy of the design shall be maintained at the jobsite while the slope is being constructed. After that time the design need not be at the jobsite, but a copy shall be made available to the director upon request.

In my opinion, the letter you sent does not meet the requirement for (d)(2)(A, B, and C) since it doesn't specify the exact magnitudes of the slopes (i.e., it specifies 'near vertical,' not an actual slope) and it states that for a one-month period the cut, 'could be considered stable' after which it would need to be re-evaluated. 'Could be considered stable' is not the same thing as 'stable,' and changes in the site conditions (vibration, for example) could impact the stability of this dirt wall over the one-month period.

Ultimately the final authority on whether a citation would be issued is up to the the OSHA inspector. It is possible that OSHA would grant a variance to the regulations based upon this, and similar, letters. You would have to go through OSHA's variance process for them to make this determination. That is typically not a quick process.
Jim Johnson


D2000 Safety, Inc.


Agree or disagree? Bottom line: I wouldn't let my son work next to this wall, engineer's letter or not. The consequences are simply too great. Slope the dang thing!


D2000 Safety was founded in 1992 to provide employers with Industrial Safety and Rescue training programs that meet the highest standards in the industry. Specialties included Industrial Safety and Rescue, Confined Space, Fall Protection, Excavation, Tower, Wind Turbine and High-Angle Rescue. Most of our class offerings are conducted at our clients locations; however, we do offer a number of Open-Enrollment courses. Click here to find find out more about D2000 Safety's Open-Enrollment class schedule.

Jim Johnson July 8, 2014

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