January 2016
|
World Coal
|
25
Naj Aziz, Jan Nemcik and Ali Mirzaghorbanali, University of Wollongong,
Australia,
discuss shear strength properties of cable bolts.
C
able bolt usage in
Australian coal mines is
on the increase, because it
is mostly used as a
secondary support to supplement the
primary support system for strata
reinforcement. Several factors have
contributed to the increase in cable bolt
usage in mines. The most prominent of
these are a better understanding of the
principals of rock mechanics and strata
control, as well as better management of
difficult ground conditions. As a
consequence, the reliance on short
encapsulation pull testing (SEPT) of
cable bolts cannot be considered by
itself as an adequate means of providing
realistic answers to the credibility of
installation in given ground conditions.
The unwinding/unscrewing of the
cable bolts from their anchorage
medium, as well as shear behaviour
across the stratified formation, both
represent important challenges that
must be addressed. A number of papers
have been reported on studies
examining the load transfer and
unscrewing characteristics of cable bolts
and there have been significant
variations in the design to include both
plain and indented cable bolts of
different sizes and combinations.
1,2,3
The increased variations in cable bolt
configurations and designs have also
generated deep interest in shear failure
of tendons. In-situ studies in cable bolt
shear are difficult to conduct, but can be
carried out in laboratory-simulated
conditions. Goris
et al.
carried out shear
testing of cable bolts using pairs of
0.025 m
3
concrete blocks made from fine
sand-concrete mix, with an average
28 days compressive strength of
69 MPa.
4
The concrete mixture was
poured into steel moulds that contained
