2.4 Layers, reclassification and the competent person's authority
A soil classification is not a permanent property of a jobsite. It is a judgment about a deposit under the conditions of that moment, and Appendix A says so twice: layered ground takes its weakest layer, and any change in the properties, factors or conditions affecting the classification has to be evaluated and the deposit reclassified as necessary. In MIFACE 15MI117 a foreman arrived at a wet trench, saw the wall about to go and shouted; one worker got out and the other did not. Conditions had changed, and the classification had not.
1 Layered systems: the weakest layer rule
Appendix A (c)(4): "In a layered system, the system shall be classified in accordance with its weakest layer. However, each layer may be classified individually where a more stable layer lies under a less stable layer."
Read the exception carefully, because it is the opposite of what people assume. You may classify layers individually only when the stronger material is underneath. Strong over weak — the common case, a clay cap over sand or wet silt — gets the weak layer's class for the whole system.
| Profile | Class of the system | Why |
|---|---|---|
| 4 ft firm clay over 4 ft wet sand | Type C | Weakest layer governs; wet sand is granular and possibly seeping |
| 3 ft loose fill over 6 ft stiff clay | Layers may be classified individually | The more stable layer lies under the less stable one |
| Any profile with layers dipping into the cut at 4H:1V or steeper | Type C | Appendix A (b) Type C (v) |
| Layers dipping into the cut less steeply than 4H:1V, material otherwise Type B | Type B | Appendix A (b) Type B (vi) |
| Micaceous seams or weakened planes in rock or shale | Treated as layered | Included in the Appendix A definition of layered system |
Figure B-1.4 of Appendix B handles the sloping configurations for layered soils, and its logic follows the same principle: the combinations allowed depend on which material sits where. Where layered ground does not fit the figure, you are on one of the other routes in 1926.652(b) — tabulated data or an engineer.
2 Reclassification: the rule that keeps the class honest
Appendix A (c)(5): "If, after classifying a deposit, the properties, factors, or conditions affecting its classification change in any way, the changes shall be evaluated by a competent person. The deposit shall be reclassified as necessary to reflect the changed circumstances."
"In any way" is broad on purpose. Here is what actually changes on a jobsite between Monday and Wednesday:
- Water. Rain, a broken service, a rising table. Submerged soil or soil from which water is freely seeping is Type C, and the thumb penetration paragraph says outright that wetting influences require the classification to be changed.
- Vibration. A plate compactor working the backfill next door, a pile rig arriving, the street reopening to trucks. Vibration disqualifies Type A.
- Disturbance. Re-opening your own trench, or excavating into last week's backfill.
- Time and exposure. Faces dry, crack, ravel and lose the apparent cohesion that was holding them.
- Loads. A spoil pile that grew, a box of fittings, a truck parked at the lip. These are surcharges under Appendix B (c)(3)(iii) and force the actual slope below the maximum allowable.
3 What 15MI117 shows about "wet, but not too bad"
MIFACE report 15MI117 describes a winter 2015 collapse in a residential subdivision with a known high water table. The trench was 6 ft 4 in deep, 7 feet wide at the top and 4 feet at the base. Groundwater stood roughly 18 inches below the top of the trench and 5 feet above the base. The base had a 1½-foot seam of wet sand, and about 5 feet of wet clay above it.
The excavator operator noticed the moisture and asked the decedent whether he wanted to use the trench box that was already on site. The offer was declined. A surviving coworker described the ground as "wet, but not too bad." The foreman — the competent person — arrived, saw the impending failure and shouted for the men to get out. One made it. The pipe layer, a man in his forties, was struck by the collapsing wall and died.
Three lessons sit in that report, and all three are classification lessons. Wet sand under wet clay is a layered system taking its weakest layer. A known high water table is a condition affecting classification that was known before the dig. And the decision about a protective system is not the entrant's to decline — it belongs to the employer through the competent person.
4 The competent person's authority, in practice
1926.650(b) defines the role as capability plus authorization to take prompt corrective measures. Subpart P then hands that person a specific list of decisions. Knowing the list is how you know whether your site actually has one.
| Decision | Paragraph |
|---|---|
| Classify each soil and rock deposit | App. A (c)(1) |
| Evaluate changes and reclassify | App. A (c)(5) |
| Examine the ground for the under-5-foot exception | 652(a)(1)(ii) |
| Reduce the actual slope for surcharge loads and for signs of distress | App. B (c)(3)(ii)-(iii) |
| Inspect daily, through the shift, and after every rainstorm | 651(k)(1) |
| Remove exposed employees when evidence of a hazard is found | 651(k)(2) |
| Monitor water removal equipment and operations | 651(h)(2) |
| Inspect after runoff from heavy rain, with (h)(1) and (h)(2) compliance | 651(h)(3) |
| Examine damaged protective system material and judge continued use | 652(d)(3) |
| Design a structural ramp for employees (equipment ramps need structural design qualification) | 651(c)(1)(i) |
Ten decisions, and every one of them can require stopping production. That is why the authorization half of the definition is not a formality. A competent person who has to phone the office for permission to pull a crew out of a trench does not meet 1926.650(b).
5 A shift-change handover that works
- 1State the class and the evidence: "Type C — granular, sand and gravel, thread would not form."
- 2State the disqualifiers in play: "previously disturbed on the driveway side, traffic vibration all day."
- 3State the system and its basis: "1½:1 both sides above 4 feet, box below — box chart is in the truck."
- 4State what changed since the last inspection: "rain overnight, seepage at the north seam, spoil moved back 3 feet."
- 5State what is being watched: "the seam, and the pump — running since 6 a.m."
- 6Name who is authorized to stop work on this shift.
Six sentences. The daily inspection record is the natural home for them, and the point of writing them down is that the next competent person starts from a classification and its evidence rather than from an inherited habit.
6 Where Part 3 picks up
You now have a class, supported by two analyses, and a rule that forces you to revisit it whenever conditions move. Part 3 spends that class: Table B-1 turns it into an angle, Figure B-1 into a configuration, and the shoring and shield chapters into what to do when there is no room for either.
- A layered system takes its weakest layer; individual classification is allowed only where the more stable layer lies underneath.
- Layers dipping into the excavation at 4H:1V or steeper make the material Type C.
- Appendix A (c)(5) requires reclassification whenever the properties, factors or conditions change in any way — water, vibration, disturbance, exposure, new loads.
- Wetting influences after the classification force it to change; a known high water table is a condition to settle before digging.
- The protective system decision is not the entrant's to decline — it belongs to the employer through the competent person.
- Subpart P assigns the competent person about ten specific decisions, most of which can require stopping work; without that authority, 1926.650(b) is not met.
Free educational content — not OSHA-authorized training, no certificate or card issued. Follow your employer's program and the standards cited.