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Soil Survey Manual - Table 3-14

Rupture resistance classes for blocklike specimens

Classes Test Description
Moderately dry and very dry Slightly dry and wetter Air dried, submerged Operation Stress Applieda
Loose Loose Not applicable Specimen not obtainable  
Soft Very friable Uncemented Fails under very slight force applied slowly between thumb and forefinger < 8N
Slightly hard Friable Extremely weakly cemented Fails under slight force applied slowly between thumb and forefinger 8-20N
Moderately hard Firm Very weakly cemented Fails under moderate force applied slowly between thumb and forefinger 20-40N
Hard Very firm Weakly cemented Fails under strong force applied slowly between thumb and forefinger (80 N about maximum force that can be applied). 40-80N
Very hard Extremely firm Moderately cemented Cannot be failed between thumb and forefinger but can be between both hands or by placing on a nonresilient surface and applying gentle force underfoot. 80-160N
Extremely hard Slightly rigid Strongly cemented Cannot be failed in hands but can be underfoot by full body weight (ca 800 N) applied slowly. 160-800N
Rigid Rigid Very strongly cemented Cannot be failed underfoot by full body weight but can be by <3 J blow. 800N-3J
Very rigid Very rigid Indurated Cannot be failed by blow of <3 J. >3 J

a. Both force (newtons; N) and energy (joules; J) are employed. The number of newtons is 10 times the kilograms of force. One joule is the energy delivered by dropping a 1 kg weight 10 cm.