Rock strength parameters from classification and testing - Geotechnical Investigation and Design Tables - page 66

Table 6.2 Typical refusal levels of drilling rigs in south east queensland.

Property Typical material

Drill rig Weight of rig V - Bit refusal TC - Bit refusal RR - Bit refusal

Jacro 105 3.15 t Very stiff to hard XW sandstone N/A

clays DCP 8-10 DCP Refusal ( 20) = = ∼

Gemco HP7/ 6 t XW sandstone/ XW sandstone/DW

Jacro 200 phyllite Phyllite SPT * 200-700 =

SPT * 60-80 =

Jacro 500 12 t DW phyllite DW metasiltstone

SPT * 200-700 SPT * 300-500 = =

•

SPT * = Inferred N - value:

- V - Bit is hardened steel.
-

TC bit is a tungsten carbide.

•

RR Rock roller.

6.3 Parameters from drilling rig used
•

This table uses the material strength implications from the refusal levels to provide
an on site indicator of the likely bearing capacity - a first assessment only.

•

This must be used with other tests and observations.

•

The intent throughout this text is to bracket the likely values in different ways, as
any one method on its own may be misleading.

Table 6.3 Rock parameters from drilling rig.

Property Allowable bearing capacity (kPa)

RR - Bit
refusal

Drill rig Weight of rig V- Bit refusal TC - Bit refusal

Jacro 105 3.15 t 300 500 N/A

Gemco HP7/Jacro200 6 t 450 750 1500

Jacro 500 12 t 600 1000 2000

Hard clay: C u 250 kPa
XW phyllite

DW mudstone
XW greywacke

DW sandstone
DW tuff

Typical material

•

Weight and size of drilling rig has different strength implications.

•

Drilling Supervisor should ensure the driller uses different drill bits (T.C./V-Bit)
as this is useful information.