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Excavations
1293 Airport Road
Beaver, WV 25813
Phone: (304) 253-8674
Fax: (304) 253-7758
E-mail: [email protected]
Vincent J. Giblin, General President
This material was produced under grant number 46C5-HT16 from the Occupational
Safety and Health Administration, U.S. Department of Labor. It does not
necessarily reflect the views or policies of the U.S. Department of Labor, nor does
mention of trade names, commercial products, or organizations imply
endorsement by the U.S. Government.
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program
Excavation
An excavation is a man-made cut, cavity, trench or depression in the earth surface that is formed by earth removal
Operating Engineers National Hazmat Program
Soil Mechanics
Tension Cracks - Usually form at a horizontal distance of 0.5 to 0.75 times the depth of the trench.
Sliding - Sliding or sluffing may occur as a result of tension cracks
Toppling - Occurs when the trench’s vertical face shears along the tension crack line and topples into the excavation
Operating Engineers National Hazmat Program
Soil Mechanics
Subsidence and Bulging - An unsupported excavation can create an unbalanced stress in the soil, which in turn, causes subsidence at the surface and bulging of the vertical face of the trench. If uncorrected this can cause face failure and entrapment of workers in the trench.
Operating Engineers National Hazmat Program
Soil Mechanics
Heaving and Bulging - Caused by downward pressure created by the weight of adjoining soil. This pressure causes a bulge in the bottom of the cut
Boiling - Upward water flow into the bottom of the excavation
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program
Unit Weight of Soils
Operating Engineers National Hazmat Program
Determination of Soil Type
Stable Rock Type A Soil Type B Soil Type C Soil Layered Strata
Operating Engineers National Hazmat Program
Stable Rock
Stable rock is a natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed.
Usually identified by a rock name such as granite or sandstone.
Operating Engineers National Hazmat Program
Type A Soil
Cohesive soils with an unconfined compressive strength of 1.5 tons per square foot (tsf) or greater
Clay, Silty Clay, Sandy Clay, Clay Loam No Soil is Type A if it is fissured, is
subject to vibration, has been previously disturbed, or has seeping water
Operating Engineers National Hazmat Program
Type A Slope
Operating Engineers National Hazmat Program
Type A Single Bench
Operating Engineers National Hazmat Program
Type A Multiple Bench
Operating Engineers National Hazmat Program
Type B Soil
Cohesive Soil with an unconfined compressive strength of 0.5 (tsf) or greater
Angular Gravel Silt Loam Previously disturbed soils
Operating Engineers National Hazmat Program
Type B Soil
Soils that meet the Type A Strength requirements but are fissured
Dry unstable rock Layered Systems
Operating Engineers National Hazmat Program
Type B Slope
Operating Engineers National Hazmat Program
Type B Single Bench
Operating Engineers National Hazmat Program
Type B Multiple Bench
Operating Engineers National Hazmat Program
Type B Slope with a Shield
Operating Engineers National Hazmat Program
Type C Soil
Cohesive with an unconfined compressive strength of 0.5 tsf
Granular Soils (Gravel, Sand, Submerged Soil)
Submerged Rock Soil from which water is freely seeping
Operating Engineers National Hazmat Program
Type C Slope
Operating Engineers National Hazmat Program
Layered Strata (Soil)
When soil types are in layers, the soil must be classified on the basis of the weakest soil layer
Each layer must be classified individually if a more stable layer is below a less stable layer
Operating Engineers National Hazmat Program
Type A over type B
Operating Engineers National Hazmat Program
Type A over Type C
Operating Engineers National Hazmat Program
Type B over Type A
Operating Engineers National Hazmat Program
Type B over Type C
Operating Engineers National Hazmat Program
Type C over Type A
Operating Engineers National Hazmat Program
Type C over Type B
Operating Engineers National Hazmat Program
Test Equipment and Methods for Testing Soil
Pocket Pentrometer Shearvane (torvane) Thumb Penetration Test Dry Strength Test Plasticity Test Visual test
Operating Engineers National Hazmat Program
Pocket Pentrometer
Pocket Pentrometer. Direct reading spring operated instrument used to determine the unconfined compressive strength of saturated cohesive soils.
Pentrometers have error rates of +/- 20% to 40%
Operating Engineers National Hazmat Program
Shearvane (Torvane)
Used to determine the unconfined compressive strength of soil by pressing the blades of the vane into a level section of undisturbed soil, and the torsion knob is slowly turned until soil failure occurs.
Operating Engineers National Hazmat Program
Thumb Penetration Test
Procedure involves an attempt to press the thumb firmly into the soil in question.
If the thumb makes an indentation with great difficulty, it is probably Type A
If the thumb penetrates no deeper than the thumbnail, it is probably Type B
If the thumb penetrates the full length of the thumb, probably Type C
Operating Engineers National Hazmat Program
Dry Strength Test
Dry soil that crumbles freely or with moderate pressure into individual grains is granular.
Dry soil that falls into clumps that the break into smaller clumps (and the smaller clumps can be broken only with difficulty) is probably clay with a combination of gravel, sand or silt
Operating Engineers National Hazmat Program
Dry Strength Test
If the soil breaks into clumps that do not break into smaller clumps, the soil is considered unfissured unless there is visual indication of fissuring
Operating Engineers National Hazmat Program
Plasticity or Wet Thread Test
The test is done by molding a moist sample into a ball, then rolling it into a thin thread 1/8” in diameter by 2” long. The sample is held at one end, if the sample doesn’t break it is considered cohesive
Operating Engineers National Hazmat Program
Visual Test
An evaluation of the whole excavation site by the competent person
Done Daily and after any change in conditions (rain, snow, underground obstruction, etc.)
Inspect the soil being removed from t he excavation. Verify that original soil type determination was correct
Operating Engineers National Hazmat Program
Visual Test
Check for crack-line openings Look for existing utilities that indicate the
soil had been previously disturbed Look at the open side of the excavation for
layered soil types Look for signs of bulging, boiling, or sluffing Check spoil distance from the edge of the
excavation
Operating Engineers National Hazmat Program
Visual Test
Check spoil distance from the edge of the excavation
Inspect heavy equipment distance Vibration Traffic control Barricades (Fall Protection) Access / Egress from the excavation
Operating Engineers National Hazmat Program
Trench Boxes
This material was produced under grant number 46C5-HT16 from the Occupational
Safety and Health Administration, U.S. Department of Labor. It does not
necessarily reflect the views or policies of the U.S. Department of Labor, nor does
mention of trade names, commercial products, or organizations imply
endorsement by the U.S. Government.
ENDThis publication was made possible by
grant numbers 5 U45 ES06182-13 AND 5 U45 ES09763-13 from the National Institute of Environmental Health Sciences (NIEHS), NIH. Its
contents are solely the responsibility of the authors and do not necessarily represent the official views of the
NIEHS, NIH.
