2.2 The visual analysis: reading the site and the face

1 What the visual analysis is for

Appendix A (d)(1) states the purpose: visual analysis is conducted to determine qualitative information about the excavation site in general, the soil adjacent to the excavation, the soil forming the sides of the open excavation, and the soil taken as samples from excavated material.

Four subjects, then: the site, the ground next to the hole, the walls, and the spoil. And (d)(3) sets the standard of care — the visual and manual analyses "shall be designed and conducted to provide sufficient quantitative and qualitative information as may be necessary to identify properly the properties, factors, and conditions affecting the classification."

2 The seven observations

Three of the seven — (iv), (v) and (vii) — cannot be answered by looking at the wall at all. Previously disturbed soil is a records-and-history question. Layer dip is geometry read across the whole face. Vibration is a question about the street, the plant next door and your own compactor.

3 Previously disturbed soil: the invisible disqualifier

Appendix A gives no definition of "previously disturbed," and it does not need one: any ground that has been excavated and put back is disturbed. Backfill is not the same material it was, however long ago it went in and however well it was compacted.

Where to look for it, in rough order of how often it catches crews:

• The old utility trench you are paralleling or crossing. Utility corridors are layers of other people's backfill.
• Any dig inside a graded subdivision, a parking lot subgrade or an engineered fill.
• The second pass. The moment you re-open your own trench, the soil in it is disturbed.
• Trees, stumps and old foundations removed and the void filled.
• Anything near a structure: the excavation for the footing was backfilled against the wall.

The visual clue is a change in color, texture or particle mix that runs vertically rather than horizontally — a seam of different material where an old trench wall used to be. If you can see the outline of somebody else's excavation in your face, that side is disturbed.

4 Reading layers and their dip

Appendix A (d)(1)(v) asks you to identify a layered system and estimate whether the layers slope toward the excavation, and how steeply. That matters because the dip angle changes the class outright: layers dipping into the cut at 4H:1V or steeper put the material in Type C; less steeply than 4H:1V, and Type B (vi) may apply if the material would otherwise be Type B.

4H:1V is a shallow angle — 14 degrees, one unit down for four along. It looks nearly flat on a trench face. Interpreting it needs the whole face, not a patch: sight along the seam from one end of the open cut to the other and see whether it rises or falls toward you.

5 A five-minute route around the excavation

1. 1
   Start at the spoil: particle sizes, does it clump, is there a seam of different material in the pile?
2. 2
   Walk the full length of each open face: cracks, spalling, ravelling, seams and their dip, any change in color or texture.
3. 3
   Look at the ground surface 10 to 15 feet back from each edge: tension cracks parallel to the trench, subsidence, old pavement patches marking a buried trench.
4. 4
   Look for water: standing water, damp bands on the face, seepage at a seam, the bottom going soft.
5. 5
   Stand still and feel the ground: traffic on the street, a compactor, a pile driver, your own excavator tracking past.
6. 6
   Write down the class and the two analyses that support it, on the daily inspection record, with your name.

The last step is the one that turns an opinion into a classification. The standard does not prescribe a form, and OSHA does not require a specific record here — but a class with no name attached is not a decision anybody can inherit at shift change.

6 What the visual analysis cannot tell you

It cannot give you strength. Type A and Type B are separated by unconfined compressive strength — 1.5 tsf — and no amount of looking produces that number. That is why (c)(2) requires a manual analysis as well, and why "we looked at it and it's good clay" is half a classification at best.

It also cannot tell you what is behind the face. The failure surface of a cave-in develops in the soil behind the wall you are looking at, which is why the signs in Appendix B — subsidence at the edge, tension cracks back from the lip — matter as much as the face itself. Chapter 2.3 puts hands on the soil.