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Toolbox talk · 10 min · Excavation & Trenching

Soil Classification: One Look, One Test

Hazards: Cave-in from a soil type called too high · Fissured or previously disturbed ground read as intact · Layered ground classified on its best layer · Soil weakened by rain, seepage or vibration

Why it matters

Every slope and every shoring table starts from the soil type. Call it one grade too high and the trench looks compliant while the wall is not. CPWR's May 2024 Data Bulletin: 1926.652(a) is the most-cited trenching standard, 34.5% of trenching citations from 2011 to 2023; 39 workers died in trench or excavation work in 2022, up from 15 in 2021.

MIFACE report 17MI127 (2019): a 2017 collapse in a 7- to 8-foot trench, dry coarse sand and gravel, one wall cut nearly vertical against a driveway. Nobody classified the soil; the operator said afterward that the dirt was packed like concrete and he was watching for cracks. The wall came in with the asphalt — one worker buried and killed.

Key points

  • One look and one test, by the competent person. Appendix A (c)(1)-(2): every deposit is classified Stable Rock, Type A, B or C by the competent person, on at least one visual and at least one manual analysis. Eyeballing the face is half a classification.
  • The visual analysis, (d)(1). Particle size. Clumps when dug (cohesive) or breaks apart (granular)? Tension cracks or spalling. Layers dipping toward the trench. Water or seepage. Vibration. Previously disturbed ground.
  • The manual analysis, (d)(2). On a fresh clump of spoil. Roll a moist sample into a 1/8-inch thread: if a 2-inch length holds on one end, it is cohesive. Thumb penetration — Type A takes very great effort, Type C goes in several inches and molds under light finger pressure.
  • Hard and dry is not Type A. Gravel, sand and loamy sand are Type C under (b), however solid they feel. Granular soil has no cohesive strength.
  • Type A is easy to lose. Fissured, vibration from traffic or pile driving, previously disturbed, or layers dipping into the cut at 4H:1V or steeper — any one alone knocks it out.
  • Layered ground takes its weakest layer — (c)(4). Good clay over wet sand is a wet-sand trench.
  • Anything changes, it gets reclassified. Appendix A (c)(5). Rain, seepage, a compactor at the edge, new spoil — call the competent person back.
  • Don't know? It's Type C. Cut 1 1/2 to 1, 34 degrees — 1926.652(b)(1)(i) allows that slope with no analysis at all. Guessing upward is the one move nobody gets.

Do / Don't

Do

  • Ask the soil type, and which test said so.
  • Test fresh spoil in front of the crew.
  • Speak up if the face weeps or cracks.

Don't

  • Read "it feels solid" as Type A.
  • Reuse last week's classification on this trench.
  • Classify from the top of the bank without touching the soil.

Quick site check

  • Today's soil type, who called it, and was there a manual test?
  • Grab a clump of spoil: does it roll into a 1/8-inch thread, or crumble?
  • Walk the face: cracks, spalling, seepage, layers dipping in? Anything changed since the call?
  • Does the slope or the box match that type?
Discussion — ask the crew
  1. Today's ground: what type did the competent person call it, and which test told them that?
  2. Who here has rolled a soil thread or done a thumb penetration test? Want to try one at the spoil pile?
  3. It rained hard two nights ago. Does yesterday's classification still hold, and who decides?
  4. We are digging next to an old backfilled service trench. What does 'previously disturbed' mean for our slope?
Refs: 29 CFR 1926 Subpart P App. A — Soil Classification · 29 CFR 1926.650(b) — Competent person · 29 CFR 1926.652 — Protective systems · CPWR — Data Bulletin, Trenching Injuries and Enforcement (May 2024) · MIFACE Report 17MI127 — Laborer Died in Trench Wall Collapse (MSU, 2019)Sign-in sheet included in the printed version

Frequently asked questions

The competent person. Appendix A (c)(1) requires each soil and rock deposit to be classified by a competent person as Stable Rock, Type A, Type B or Type C. 1926.650(b) defines that person as someone capable of identifying the hazards and authorized to correct them promptly.

At least two: the classification must be based on the results of at least one visual and at least one manual analysis, per Appendix A (c)(2). One look is not a classification.

No. Gravel, sand and loamy sand are granular soils and fall under Type C in Appendix A (b), no matter how firm they feel when dry. Granular soil has no cohesive strength; only cohesive soil with an unconfined compressive strength of 1.5 tsf or more can be Type A.

The system is classified by its weakest layer, per Appendix A (c)(4). A layer may be classified individually only where a more stable layer lies under a less stable one.

Whenever the properties, factors or conditions affecting the classification change in any way — rain, seepage, new vibration, disturbance. A competent person evaluates the change and reclassifies as necessary, per Appendix A (c)(5).

Then nobody goes in on a sloped wall cut steeper than 1 1/2 horizontal to 1 vertical, 34 degrees. 1926.652(b)(1)(i) allows that slope with no further soil analysis. It is the Type C slope, and it is the honest answer to 'we do not know yet.'

Sources & references

Content checked against these sources — last reviewed August 28, 2026.

Results are estimates for planning purposes and do not replace a competent person's evaluation or an engineer's design. Follow the OSHA standards that apply to your work and your employer's written program.

By — Editorial team of SteelToeTools.com (published by LSEA SAS) Updated