Rock foundations

Strength Symbol Point load index Extrapolated SPT value Allowable bearing is (50) (MPa) (No)∗60 capacity

Extremely low EL <0.03 60-150 500 kPa to Very low VL 0.03 – 0.1 1.5 MPa Low L 0.1-0.3

Medium M 0.3-1.0 100-350 1 to 5 MPa High H 1.0-3.0 250-600

Very high VH 3.0-10 >500 >5 MPa Extremely high EH >10

and in the drive only – but this is insufficient data.