Trench-bank definition and shoring in clay

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

July 7, 1976

MEMORANDUM TO: ROBERT B. HANNA, AREA DIRECTOR MILWAUKEE

Subject: Specific Trenching Requirements

This is in response to your letter of inquiry dated May 18, 1976, concerning the above stated subject matter.

29 CFR 1926.652(a) addresses "banks" in the manner stated under the section on definitions which is: "a mass of soil rising above a digging level". This area was addressed to take into consideration trenches passing close to a side of a hill or a vertical face that would have a direct bearing on the sides of the trench being excavated.

Table P-1, as referenced in 29 CFR 1926.652(a), has a note which states: "clays, silts, loans, or non-homogeneous soils require shoring and bracing". The composition and characteristics of clay have so many variables, along with water content, that it makes it impossible to safely predict the action that this solid will take in any given circumstance. Therefore, the shoring and bracing requirements as stated in the table must be adhered to. As far as sloping to the angle of repose, this would require an evaluation of the conditions found in each and every case. Constant examination of the conditions of the conditions of the solid as exposed in the trenching operations, the final depth of the trench as well as the length of time that the trench will be open are some of the pertinent factors to be considered by a competent person in the making of the final determination.
Barry J. White
Associate Assistant Secretary
for Regional Programs