OR/15/065 Appendix 2 - Strength, consistency and density classification terms and descriptions

Entwisle, D, Lee, K A, and Lawley, R S. 2015. User guide for ‘BGS Civils’ - a suite of engineering properties datasets. British Geological Survey Internal Report, OR/15/065.

BS5930_term	Unconfined compressive strength or SPT N-values	BS5930_field_assessment
Extremely Strong	250+ MPa	May be chipped or not with geological hammer, rock may ring when hit, may be broken or not by sledge hammer.
Very Strong	100–250 MPa	Requires many blows with a geological hammer to fracture.
Strong	50–100 MPa	Requires more than one blow of a geological hammer to fracture.
Medium Strong	25–50 MPa	Cannot be scraped or peeled with pocket knife, specimen can be fractured with one blow of a geological hammer.
Weak – Strong	5–100 MPa	Ranges from: Can be peeled with pocket knife with difficulty and shows shallow indentations with firm blows with point of geological hammer, to: requires more than one blow of a geological hammer to fracture.
Weak – Medium Strong	5–50 MPa	Ranges from: Can be peeled with pocket knife with difficulty and shows shallow indentations with firm blows with point of geological hammer. to: Cannot be scraped with pocket knife.
Weak	5–25 MPa	Can be peeled with pocket knife with difficulty, shallow indentations made by firm blow with point of geological hammer, Gravel sized lumps broken in half with heavy hand pressure.
Very Weak – Very Strong	1–250 MPa	Ranges from: Can be peeled by a pocket knife or crumbles under firm blows with point of geological hammer, to: requires many blows of a geological hammer to fracture.
Very Weak – Strong	1–100 MPa	Ranges from: Can be peeled by a pocket knife or crumbles under firm blows with point of geological hammer, to: requires more than one blow of a geological hammer to fracture.
Very Weak	1–5 MPa	Can be peeled by pocket knife. Crumbles under firm blows with geological hammer. Gravel-size lumps can be crushed between finger and thumb.
Extremely Weak	0.6–1.MPa	Can be indented by thumbnail. Gravel sized lumps crush between finger and thumb.
Hard*	0.6–1.25 MPa	Can be scratched by thumbnail. Should only be used for transported materials such as tills, otherwise classed as extremely weak rock.
Very Stiff	0.3–0.6 MPa	Thumb nail will indent. Crumbles in rolling a 3 mm thick thread and cannot be remoulded into a lump.
Stiff to Very Strong	0.15–250 MPa	Ranges from: Thumb nail will indent. Crumbles in rolling a 3 mm thick thread, but can be remoulded into a lump, to: requires many blows with a geological hammer to fracture.
Stiff – Weak	0.15–25 MPa	Ranges from: Thumb nail will indent, to: can be peeled with pocket knife with difficulty and shows shallow indentations with firm blow with point of geological hammer.
Stiff – Very Weak	0.15–5 MPa	Ranges from: Can be indented by thumb nail, to: can be peeled by pocket knife and crumbles under firm blows with geological hammer.
Stiff	0.15–0.3 MPa	Thumb nail will indent. Crumbles in rolling a 3 mm thick thread, but can be remoulded into a lump.
Firm – Stiff	0.08–0.3 MPa	Ranges from: Thumb easily makes an impression and cannot be moulded by fingers and rolls in the hand a 3 mm thick thread without breaking or crumbling, to: can be slightly indented and crumbles when rolled to a 3 mm thick thread but can be remoulded into a lump.
Firm	0.08–0.15 MPa	Thumb makes impression (easily). Cannot be moulded by fingers, rolls in the hand to a 3 mm thick thread without breaking or crumbling.
Soft – Firm	0.04–0.15 MPa	Ranges from: Finger pushed in by 10 mm and moulds with light finger pressure, to: thumb easily makes impression and rolls in the hand to a 3 mm thick thread without breaking or crumbling.
Soft	0.04–0.08 MPa	Finger pushed in by 10 mm. Moulds by light finger pressure.
Very Soft – Soft	<0.08 MPa	Ranges from: Finger pushed in by 25 mm and exudes between the fingers, to: finger pushed in by 10 mm and moulds by light finger pressure.
Very Soft	<0.04 MPa	Finger pushed in by 25 mm and exudes between the fingers.
Very Dense – Weak	50+ Blows to 25 MPa	Ranges from: Requires pick for excavation. 50 mm wooden peg hard to drive, to: can be peeled with pocket knife with difficulty and shallow indentations with firm blow with point of geological hammer.
Very Dense	50+ Blows	Requires pick for excavation. 50 mm wooden peg hard to drive in.
Dense	30–50 Blows	Requires pick for excavation. 50 mm wooden peg hard to drive in.
Medium Dense – Dense	10–50 Blows	Requires pick for excavation. 50 mm wooden peg hard to drive in.
Medium Dense	10–30 Blows	Requires pick for excavation. 50 mm wooden peg hard to drive in.
Loose – Medium Dense	4–30 Blows	Ranges from: Can be excavated with spade and 50 mm wooden peg easily driven in, to: requires pick for excavation and 50 mm wooden peg hard to drive in.
Loose	4–10 Blows	Can be excavated with spade. 50 mm wooden peg easily driven.
Very Loose	<4 Blows	Can be excavated with spade. 50 mm wooden peg easily driven.
Variable		Highly variable currently cannot be predicted.
Not Applicable		Value is not applicable as the classification is inappropriate for the LEX-RCS code (e.g strength and consistency for coarse soils or relative density for fine soils and rocks).

Italics — nominal uniaxial compressive strength but no longer used.
* Hard is no longer used and extremely weak with a rock description should be used (BSI 2015).