Excavation and Shoring Safety

Purpose

A pier pit is small, and small is exactly why crews die in them. Roughly a cubic yard of soil weighs about as much as a small car, it arrives without warning, and a worker buried to the chest cannot be pulled out by hand.

Two separate requirements govern a foundation pit and they are constantly confused. The cave-in protection trigger is depth: a protective system is required at 5 ft or deeper under 29 CFR 1926.652(a)(1), and shallower than that whenever the competent person sees indication of a potential cave-in. The other requirement has no depth trigger at all. Excavating below the base of an existing footing is prohibited under 29 CFR 1926.651(i)(2) unless a support system is in place, the excavation is in stable rock, or a registered professional engineer has determined that the excavation will not pose a hazard. A pier pit exists precisely to get under a footing, so that paragraph applies to every pit this shop digs, at any depth.

Scope

Covers excavation for pier pits, wall access trenches, drain trenches and inspection pits: soil classification, protective system selection, undermining of existing footings, egress, spoil control, atmospheric testing, and the daily inspection.

Does not cover utility clearance, which the utility locate SOP owns and which completes before any soil moves, or the pier work performed inside the pit, which the pier installation standard owns. Does not cover confined space entry into a vault, tank or manhole, and does not substitute for an engineered shoring design where the protective system manufacturer's tabulated data or the design professional requires one.

Roles and responsibilities

Procedure

Step 1: Confirm the locate is complete and the pit is staked before soil moves

Check that the one-call ticket is live, marks are present, private lines are located, and the pit outline is staked to the plan. Acceptance: ticket number, positive response and mark photos in the job file, plus stakes on the ground. Wrong looks like a crew digging inside a valid ticket that no utility actually marked; stop, because a ticket is a request and not a clearance. Hazard: everything in the utility locate SOP applies here, including the hand-dig and vacuum excavation rules inside the tolerance zone.

Step 2: Classify the soil, and record the tests that produced the classification

The competent person performs at least one visual and at least one manual analysis as required by 29 CFR 1926 Subpart P Appendix A, using thumb penetration, a pocket penetrometer, a dry strength test or a plasticity ribbon test. Acceptance: classification recorded as Type A, B or C with the specific tests and their results written beside it. Wrong looks like a classification with no test behind it, or a classification that ignores water seeping from the face. Soil from which water is freely seeping is Type C regardless of how it looks or feels, and backfill placed against a foundation is disturbed material that will never classify as Type A. The classification is a finding, not a lever: it is never adjusted upward to make a geometry work.

Step 3: Select the protective system against the classification, and do the geometry before you dig

Maximum allowable slopes in 29 CFR 1926 Subpart P Appendix B are 3/4 to 1 for Type A, which is 53 degrees, 1 to 1 for Type B at 45 degrees, and 1 1/2 to 1 for Type C at 34 degrees. Benching is not permitted in Type C at all. Acceptance: the setback is computed from the planned depth before excavation and the space is confirmed to exist on the ground. Wrong looks like discovering mid-dig that the required slope runs into the house on one side and a fence on the other. Stop; the answer is a shield or a shoring system rated for the depth, or the excavation does not happen today. Where a shield is used with sloping above it, the shield must extend at least 18 in above the point where the slope begins, per 29 CFR 1926.652(g).

Step 4: Treat undermining the footing as its own requirement with its own paper

Before the cut goes below the base of any existing footing, confirm the job file holds either a support system designed for the condition or the registered professional engineer's written determination under 29 CFR 1926.651(i)(2). Acceptance: that document is in the file and names this structure and this pit. Wrong looks like a crew relying on the 5 ft depth rule to decide whether they need anything, because this paragraph has no depth trigger and a 3 ft pit under a footing is squarely inside it. Stop and escalate to the design professional. Hazard: the exposed length of footing is itself a limit, and where the plan states one, exceeding it removes bearing from the wall you are there to support.

Step 5: Set egress, spoil and edge controls before the first entry

Provide a ladder, ramp or stair for any excavation 4 ft or deeper, positioned so lateral travel to it does not exceed 25 ft, per 29 CFR 1926.651(c)(2). Keep spoil, material and equipment at least 2 ft back from the edge under 1926.651(j)(2), or retain it. Measure the pit: where depth exceeds width and width is 15 ft or less it meets the definition of a trench and the trench-specific provisions apply, which a narrow pier pit routinely does. Acceptance: ladder in place and extending above the edge, spoil distance measured, edge clear. Wrong looks like a spoil pile at the lip because the yard is tight; move it, since that pile is surcharge load driving the very failure the protective system is rated against.

Step 6: Test the atmosphere where it could be bad, and get the water out

Test before entry in any excavation more than 4 ft deep where an oxygen deficiency or a hazardous atmosphere could reasonably be expected, per 29 CFR 1926.651(g)(1)(i), which on this trade means near a sewer lateral, a septic field, a landfill or a fuel tank. Acceptance: test results with the instrument and time recorded, or a written note that no such condition exists. Wrong looks like entering a pit that has cut a sewer lateral because it does not smell bad; hydrogen sulfide deadens the sense of smell at concentrations that can kill. Stop, ventilate, and do not re-enter on a nose test. Nobody works in accumulated water until it is removed and the competent person has re-inspected, because saturated soil no longer holds the classification it was given dry.

Step 7: Inspect daily, after rain, and after anything that changes the hole

The competent person inspects before the start of each shift, as needed through the shift, and after every rainstorm or other occurrence that increases hazard, per 29 CFR 1926.651(k)(1). Acceptance: a dated, timed, signed inspection entry naming the conditions found, for every shift the pit is open. Wrong looks like a pit released on Monday and worked on Thursday on Monday's inspection; it is not released and nobody enters. Watch for tension cracks parallel to the edge, spalling off the face, water seeping where it was dry, and any bulge at the toe, and treat any of those as an immediate order everyone out.

Step 8: Control entry, work and exit while the pit is open

Only released pits are entered, only by people named on the release, and the pit is barricaded or covered whenever nobody is working it. Acceptance: barricade or cover in place at every break and at end of shift, release list current. Wrong looks like an open pier pit left beside a house overnight where a homeowner or a child can walk into it. Hazard: keep mobile equipment off the edge, use a spotter or a stop log where it must approach, and keep everyone out of the swing radius and from under a suspended bucket.

Step 9: Backfill, compact and close the excavation record

Backfill in lifts to the plan's compaction requirement, working from outside the pit, and restore grade so water runs away from the wall rather than ponding in fresh fill. Acceptance: lift thickness and compaction method logged, final grade slope checked, record closed. Wrong looks like loose fill dumped in one throw against a wall the shop just supported, which settles within a season and produces the callback. Re-do it in lifts.

The record this produces

One excavation record per pit: location and staked outline; ticket reference; soil classification with the visual and manual tests behind it; the protective system selected with its rating and its tabulated data or engineered design; the 1926.651(i) support or engineer determination for undermining; depth and width measured, with the trench determination stated; egress type and position; spoil distance; atmospheric test results or a not-applicable note; a dated and signed inspection entry per shift and after each rain; and the backfill and compaction record.

The competent person writes it. The pier crew reads the release line before entering. The office keeps it because an inspector or an insurer will ask for the daily inspection entries specifically, and a pit worked for four days with one inspection entry is the finding.

One worked pass

Pier pit at a rear bracket location, plan depth 4 ft 8 in to seat the bracket under the footing. Step 2 classified the soil: granular backfill against the foundation with water seeping from a failed downspout line at about 3 ft. Freely seeping water puts it in Type C, and that is what the record says, with the visual description and a thumb penetration result written beside it.

The footing turned out deeper than the plan assumed and the pit had to go to 5 ft 4 in. That crosses the 5 ft trigger at 1926.652(a)(1), so a protective system is now required and step 3's geometry check ran on the spot. Type C slopes at 1 1/2 to 1, so 5.33 ft of depth needs 8.0 ft of horizontal setback on each side. The pit sits against the house on one side and 4 ft from a property line fence on the other, so sloping does not fit in either direction. Benching is not permitted in Type C, so that option was never available. Reclassifying to Type B would demand 5.33 ft of setback and still not fit, which is worth printing because it removes the temptation rather than leaving it unexamined.

The crew had no shield or shoring rated for that depth on the truck. Under step 3's stop rule they stopped, nobody entered, the pit was barricaded and the competent person and supervisor were called. Shoring arrived the following morning, rated for the depth per its tabulated data, and the pit was cut vertical to grade with the shoring extending to the surface. Because there was no sloping above the system, the 18 in provision at 1926.652(g) did not apply, and the record says not applicable rather than claiming a pass on a check that was never run.

Closing figures for the record: depth 5 ft 4 in, width 3 ft, so depth exceeds width and it is a trench, and the trench provisions applied. Ladder set with lateral travel under 6 ft against the 25 ft limit. Spoil measured 3 ft back against the 2 ft minimum. Sewer lateral within 8 ft, so the atmosphere was tested before each entry with instrument and time logged. Five inspection entries over two days, one of them after an overnight rain that put standing water in the pit and delayed the morning release until it was pumped.

References

• 29 CFR 1926 Subpart P, Excavations, including 1926.651(c)(2) egress, 1926.651(g)(1)(i) atmospheric testing, 1926.651(i)(2) excavation below the base of a footing, 1926.651(j)(2) spoil placement, 1926.651(k)(1) inspections, 1926.652(a)(1) protective system trigger, and 1926.652(g) shield systems.
• 29 CFR 1926 Subpart P Appendix A, soil classification, and Appendix B, sloping and benching, including the prohibition on benching in Type C soil.
• The protective system manufacturer's tabulated data, which sets the rated depth and any limits on the system as installed.
• See related: the utility locate SOP, which completes before this procedure begins, and the pier installation standard for work performed inside the released pit.