When excavating or digging a trench the type of soil impacts the safety measures required.
Categories:
(1) stable dry rock
(2) type A soil
(3) type B soil
(4) type C soil
Features of type A soil - all of the following:
(1) cohesive soil
(2) unconfined compressive strength >= 1.5 ton per square foot (144 kPa)
(3) free of the following:
(3a) fissures
(3b) being previously disturbed
(3c) subject to vibration from heavy traffic, pile driving, etc
(3d) any other factor making it less stable
Features of type B soil - any of the following:
(1) cohesive soil with unconfined compressive strength 0.5 to 1.49 ton per square foot (48 to 144 kPa)
(2) granular cohesionless soils (angular gravel, silt, silt loam, sandy loam, etc)
(2) previously disturbed soil not type C
(3) type A soil with other defects (fissuring, vibration)
(4) dry rock that is not stable
Features of type C soil - any of the following:
(1) cohesive soil with unconfined compressive strength < 0.5 ton per square foot (< 44 kPa)
(2) granular soil (gravel, sand, loamy sand)
(3) submerged soil or soil freely seeping water
(4) submerged rock that is not stable
