Soil Testing
A competent person must conduct visual and manual soil tests before anyone enters an excavation.
Soil Classification
Visual and manual tests are a critical part of determining the type of protective system that will be used.
Soil and Stability
Some soils are more stable than others. The type of soil is one of the factors that determine the chance that an excavation will cave in. There are three basic soil types that you may encounter:
- Type A - very stable. Clay is an example.
- Type B - less stable than type A soil. The soil will crack or fissure. Crushed rock, silt, and soils that contain an equal mixture of sand and silt are examples.
- Type C - the least stable soil. Particles do not stick together. Gravel and sand are examples.
Soil has other qualities that affect its stability. These include granularity, saturation, cohesiveness, and unconfined compressive strength.
- Granularity refers to the size of the soil grains; the larger the grains, the less stable the soil.
- Saturation means how much water soil will absorb.
- Cohesiveness means how well soil holds together; clay is a cohesive soil.
- Unconfined compressive strength is determined by a test that shows how much pressure it takes to collapse a soil sample. For example, type A soil must have an unconfined compressive strength of at least 1.5 tons per square foot.
Knowledge Check Choose the best answer for the question.
1-7. Which of the following soil types is least stable?
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