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Soil classification for Excavation

Soil classification for Excavation

Excavation is one of the most important segments of any construction activity. Due to insufficient attention to the safety aspects, it sometimes becomes a major hazard and cause of many serious accidents. Excavation is dangerous irrespective of its depth. Even small excavations may cause serious accidents.

To ensure the safety of those involved, excavation work has to be properly planned, managed, supervised and executed in order to prevent accidents. Persons involved at all stages should be aware of the hazards involved and the procedures in place to control the risks associated with this type of work.

Soil collapse is one of the primary risks to be controlled in excavation activity. Soil collapse can occur very quickly and without warning. To avoid the soil collapse the condition of soil to be checked prior to excavation.

The major causes for excavation failure are:

Sliding of Soil: Due to inadequate sloping / benching

Toppling: Due to Soil erosion at bottom, Undercutting on sides, Keeping loads / Overburden near edge of excavation.

Soil classification:

Type A Soils are cohesive soils with an unconfined compressive strength of 1.5 tons per square foot (tsf) (144 kPa) or greater. Examples of Type A cohesive soils are often: clay, silty clay, sandy clay, clay loam and, in some cases, silty clay loam and sandy clay loam

Type B Soils are cohesive soils with an unconfined compressive strength greater than 0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa). Examples of other Type B soils are: angular gravel; silt; silt loam; previously disturbed soils unless otherwise classified as Type C; soils that meet the unconfined compressive strength or cementation requirements of Type A soils but are fissured or subject to vibration; dry unstable rock.

Type C Soils are cohesive soils with an unconfined compressive strength of 0.5 tsf (48 kPa) or less. Other Type C soils include granular soils such as gravel, sand and loamy sand, submerged soil, soil from which water is freely seeping, and submerged rock that is not stable.

Slopping and benching for various classification soil as follows:

Soil / Rock type

Maximum slope (H : V)
Angle of repose (Angle with respect to
Stable Rock
Type A Soil
0.75 : 1
Type B Soil
1 : 1
Type C Soil
1.5 : 1

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