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Timber shoring for a 13 ft trench in Type A soil: the four arrangements of OSHA Appendix C, Example 1

Tool	Trench Shoring
Source	Occupational Safety and Health Administration (2023). Safety and Health Regulations for Construction, Subpart P: Excavations. 29 CFR Part 1926, Appendix C to Subpart P, paragraph (f)(1) Example 1 and Table C-1.1, Code of Federal Regulations, 7-1-23 edition, pp. 360 and 362.
Level	Professional

Problem

A trench is dug 13 ft deep and 5 ft wide in a cohesive soil with an unconfined compressive strength of 2 tsf that is neither fissured, disturbed nor subject to vibration. Classify the soil by Appendix A, read the acceptable timber shoring arrangements from the actual-size table for mixed oak, and state what else the excavation standard requires at this depth.

Inputs to Enter

Protective system: timber shoring, Tables C-1 (actual sizes, mixed oak or equivalent, bending strength 850 psi or more)
Trench 13 ft deep, 5 ft wide at the bottom, 100 ft long; cohesive soil, unconfined compressive strength 2 tsf, no fissures, vibration, disturbance, water or dipping layers
Spoil set back 2 ft, swell factor 1.25, spoil slope 1.5 : 1; cross braces at up to 6 ft counted

Open the Trench Shoring tool (loaded with this example)

Answers

Appendix A: Type A (cohesive, 1.5 tsf or more); Table C-1.1, depth 10 to 15 ft, width up to 6 ft; heading pressure 25 × 13 + 72 = 397 lb/ft²
Arrangement 1: 4 × 4 cross braces at 6 ft horizontally and 4 ft vertically, no wales, 3 × 8 uprights at 6 ft (book the same, "skip shoring")
Arrangement 2: 4 × 6 cross braces at 8 ft, 8 × 8 wales at 4 ft vertically, 2 × 6 uprights at 4 ft (book the same)
Arrangement 3: 6 × 6 cross braces at 10 ft, 8 × 10 wales, 2 × 6 uprights at 5 ft (book the same; the table itself prints 6X5 for the brace)
Arrangement 4: 6 × 6 cross braces at 12 ft, 10 × 10 wales, 3 × 8 uprights at 6 ft (book the same)
Tool only, arrangement 1: four brace levels at 2, 4.83, 7.67 and 10.5 ft (top brace within 2 ft of the top, lowest within 2.5 ft of the bottom); 17 brace positions and 68 cross braces in 100 ft
Tool only: 240.7 yd³ in the bank; spoil windrow 7.36 ft high on a 22.08 ft base; protective system required (5 ft or more), two ladders (25 ft of lateral travel), no engineer's design required by depth (20 ft or less)

Notes

The tool's default inputs are this case; press Submit. The tool also flags that a spoil pile taller than 2 ft within 13 ft of the edge is outside the surcharge the tables allow for (Appendix C (d)(2)(ii)(A)), a condition the example does not mention. Choosing Type B or Type C under Soil Type reproduces Examples 2 and 3 of the appendix (Tables C-1.2 and C-1.3).