Excavation safety should be of the utmost importance to people who work in the excavation industry. As experts in ore field we know how potentially dangerous and devastating a trench line or excavation collapse could be. In fact excavation work has a 112% higher fatality rate than general construction. This is why trenching & shoring standards must be met for all excavations deeper than 5 ft this is actually a required by law and depending on your location the standard may be 4 ft. Check with local and state regulations.
It is important to classify your soils before entering any excavation deeper than 4 ft. Classification of soils can only be done by soils engineer or on site certified “Competent Persons”. Soils classification is based on site conditions and soil composition. The three ways of soil classification on site are:
- Thumb penetration test
- Plasticity test
- Pocket penetrometer
There are a four types of soil classifications with the following subsets
Type A-25 Soils
Cohesive soils with an unconfined, comprehensive strength of 1.5 “Pocket Penetrometer” ton per square foot (tsf) or greater. Examples of cohesive soils are: clay, silty clay, sandy clay, clay loam and sandy clay loam. Cemented soils such as caliche and hardpan are also considered type A “stable rock”.
However, no soil is type A if:
- The soil is fissured
- The soil is subject to vibration from traffic, pile driving, or similar effects
- The soil has been previously disturbed
- the soil is part of a sloped, layered system where the layers dip into the excavation on a slope of four horizontal to one vertical (4H:1V) or greater
- The material is subject to other factors that would require it to be classified as a less stable material
Type B-45 Soil
- Cohesive soil with an unconfined compressive strength greater than 0.5 tsf but less than 1.5 tsf
- Granular cohesionless soils including: angular gravel (similar to crushed rock), silt, silt loam, sandy loam and, in some cases silty clay loam and sandy clay loam.
- Previously disturbed soils except those which would otherwise be classed as type C soils.
- Soil that meets the unconfined compressive strength or cementation requirements for type A but is fissured or subject to variation
- Dry rock that is not stable
- Material that is part of the sloped, layered system where the layers dip into the excavation on a slope less steep than four horizontal to one vertical “4 to 1”, but only if the material would otherwise be classified as type B
Type C-60 Soil
- Moist, cohesive soil or a moist dense granular soil which does not fit into type A or B classifications, and is not flowing or submerged.
- This material can be cut with near vertical sidewalls and will stand unsupported long enough to allow the vertical shores to be properly installed.
- The competent persons must monitor the excavation for signs of deterioration of soils as indicated by, but not limited to, freely seeping water of flowing soils entering the excavation around or below the sheeting
- An alternate design for less stable type C soils will be required where there is evidence of deterioration
Type C-80 Soil
- Cohesive soil with an unconfined compressive strength of 0.5 tsf or less
- Granular soils including gravel, sand, and loamy sand.
- Submerged soils or soils from which water is freely seeping.
- Submerged rock that is not stable
- Material in a sloped, layered system where the layers dip into the excavation or a slope 4 to 1 or steeper
If no certified “Competent Persons” is on site all soils must be treated as class c soils. For more information, review the current OSHA Standards.