User Manual

32 Utility AirSpade Technical Applications Bulletin
Appendix B: Soil Characteristics
SOIL CLASSIFICATIONS
The effectiveness of airspading largely depends upon
the type of soil present. Although hundreds of soil
types exist, the Occupational Health & Safety
Administration (OSHA) classifies soils into four
categories (in decreasing order of strength):
l
Stable Rock
l
Cohesive Soil Type A
l
Cohesive Soil Type B
l
Cohesive Soil Type C
Relative strengths of the four soil classifications are
measured using the metric Unconfined Compression
Strength, expressed in tons per square foot. Data on
these soils are contained within the three tables to
the right.
STABLE ROCK
Unconfined Compressive Strength by Rock Type
Rock Type
Unconfined Compressive Strength (tons/sq ft)
Minimum Maximum
Schist 84 1,729
Sandstone 104 2,455
Shale 358 2,412
Limestone 369 3,894
Granite 505 3,383
Gneiss 882 2,620
COHESIVE SOILS
Unconfined Compressive Strength by Soil Type
OSHA
Cohesive
Soil Type
Soil Description
Unconfined
Compressive
Strength
(tons/sq ft)
A
Clay, silty clay, sandy clay, clay loam, caliche, hardpan
Some silty clay loam, sandy clay loam
≥1.5
B
Granular cohesive soils such as angular gravel, silt,
silt loam, sandy loam
0.5 - 1.5
C
Granular soils such as gravel, sand, loamy sand,
submerged soil
Soil from which water is freely seeping
≤0.5
CLAYS
Unconfined Compressive Strength by Consistency
OSHA
Unconfined Compressive Strength
(tons/sq ft)
Very Soft 0 - 0.25
Soft 0.25 - 0.5
Medium 0.5 - 1
Stiff 1 - 2
Very Stiff 2 - 4
Hard >4