- Apply advanced soil classification methods including visual and manual tests
- Design and implement shoring and shielding systems
- Develop confined space entry permits and atmospheric monitoring programs
- Plan and execute confined space rescue procedures
Lección 1
Soil Classification Methods
The competent person must classify soil using at least one visual AND one manual test method before selecting a protective system.
Visual Tests
Particle size - Clay (finest), silt, sand, gravel (coarsest)
Cohesion - Does soil clump or crumble?
Water - Seeping water weakens soil
Cracks - Indicate drying and potential failure
Manual Tests
Thumb penetration - Pushes in easily = Type C
Pocket penetrometer - Reads unconfined compressive strength
Ribbon test - Roll soil between palms; long ribbon = clay (Type A)
Dry strength - Crumbles easily = Type C
Important rule: If ANY condition downgrades the soil, the entire excavation must be classified at the lower category. For example, if the soil tests as Type A but there is water seeping into the trench, it must be downgraded to at least Type B or C depending on conditions.
Soil Classification Types
The four soil classifications determine the required slope or protective system:
| Type | Characteristics | Allowable Slope |
|---|---|---|
| Type A | Unconfined compressive strength 1.5+ ton/ft2, cohesive, no fissures | 3/4:1 (53 degrees) |
| Type B | Unconfined compressive strength 0.5-1.5 ton/ft2, fissured, disturbed | 1:1 (45 degrees) |
| Type C | Unconfined compressive strength under 0.5 ton/ft2, granular, wet | 1.5:1 (34 degrees) |
| Layered | Solid rock, well-cemented | Vertical (90 degrees) |
Type A soil that is fissured (showing cracks) must be reclassified to Type B. Previously disturbed soil cannot be classified Type A regardless of its compressive strength.
Additional visual soil tests:
- Checking for fissures: Cracks running parallel to the excavation face indicate potential failure plane. Any fissured soil cannot be classified Type A.
- Checking for previously disturbed soil: Fill material, backfill, utility trenches, or construction debris in the excavation wall indicates previously disturbed material that cannot be Type A.
- Checking for tension cracks: Cracks opening parallel to and near the excavation edge indicate the soil is under tension and could collapse. All work must stop until the hazard is evaluated.
Water management in excavations:
Water in excavations is one of the most dangerous conditions because it both weakens soil and increases the weight of saturated material. Control measures include:
- Diverting surface water away from the excavation with berms and drainage channels
- Pumping standing water to lower the water table
- Installing well points for dewatering large excavations
- Never allowing workers in an excavation that has water present at the working level unless the water is controlled
Soil classification requires at least one visual AND one manual test. If any condition downgrades the soil, the entire excavation uses the lower classification. Water seepage always downgrades soil from its initial classification. Type A allows 3/4:1 slope; Type C requires 1.5:1. Tension cracks near the excavation edge require stopping work until evaluated.