Site Investigation - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 362

The most common drilling and core diameters in metric and American sizes are given
in Table 13.1. The smallest core diameter for exploration drillings should not be less
than 60 mm.
Immediately after placing the cores in storage boxes they should be photographed and
mapped. Only if time does not allow, should the cores be mapped after transportation
to the storage location. In the latter case, a comparison with the photographs of the
cores indicates whether the cores have altered.

Table 13.1 Diameters frequently used for core drillings (Comdrill Drilling Equipment GmbH)

Metric size American

size

Drilling
diameter
[mm]

Core diameter [mm]
Single tube
core barrels

Double tube
core barrels

Wire line
core barrels

36 - 36 22 22 -

- EX 37.5 22 22 -

46 - 46 32 32 -

- AX 47.8 29 29 26.9

56 - 56 42 42 -

- BX 59.7 41 41 36.3

66 - 66 52 38 - 52 -

- NX 76.2 54 54 47.5

76 - 76 62 48 - 62 -

86 - 86 72 58 - 72 -

- HX 95.8 - - 63.4

116 - 116 102 86 - 96 -

- PX 122.3 - - 84.8

131 - 131 117 101 - 110 -

146 SX 146 132 116 - 123 102

176 - 176 155 140 132

As an example, Fig. 13.8 shows the mapping of a 3 m long drill core (Wittke 1990).
The mapped core may be documented by a photograph or illustrated by a drawing.
The designation of the core drilling (CD8) and the drilling depth are found to the left.
The characterization of the core is subdivided into the core's degree of disintegration
and a description of the drilled rock. The degree of disintegration of the core may be
described by the total length of encountered core pieces, referred to as “core recov-
ery”, and the individual lengths of core pieces. The minimum length of considered core
pieces as a subjective measure here is selected as 5 cm. The core recovery in relation to
the core's total length as a percentage is denoted as the “total core recovery” R (ISRM
1978e). In the example illustrated in Fig. 13.8, R yields 72 %.