Download - Cable Bolts
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Prepared by ERSİN DİK
HACETTEPE UNIVERSITY
Department of Mining Engineering
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Contents:
-Introduction
-Cable Bolt Background
-Bond Strenght
-Grouts and Grouting
-Cable Installation
-Advantages of the Cablebolts
-Cables For Slope Reinforcement-Conclusion
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Introduction
Cable Bolts are
commonly used for rock
reinforcement in areas ofstrata movement.
They can be used to
supplement existingstrata reinforcement.
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Cable Bolt Background
Cable Bolts have been used
extensively in underground mines
since the early 1970's.
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At that time, modified cable bolts was
developed to improve the load transfer and was
introduced into both Underground and Open pitMines.
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HACETTEPE UNIVERSITYDepartment of Mining Engineering
Summary of the development of cable reinforcing systems for underground mining.
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HACETTEPE UNIVERSITYDepartment of Mining Engineering
Cable installation
There are two types of grouting
cables in upholes.
First one is the traditionalmethod of grouting. This method
will be called the ‘breather tube
method’ .( water/cement ratio ˃ 0.4)
An alternative method, called the ‘grout tube
method’ . (0.3 to 0.35 water/cement ratio).
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HACETTEPE UNIVERSITYDepartment of Mining Engineering
Cable installation
Alternative methods for grouting cables in upholes.
Breather tube method Grout tube method
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HACETTEPE UNIVERSITYDepartment of Mining Engineering
Cable installation
The main problem with
breather tube method is that
it is difficult to detect when the
hole is full of grout.
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HACETTEPE UNIVERSITYDepartment of Mining Engineering
Cable installation
• The principal advantage
of grout tube method is that it
is fair when the hole is full of grout,
• And the smaller number of
components required,
makes the method attractive when compared with the
traditional method.
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Grouts and Grouting
The question of grout quality has always been a
matter of concern in reinforcement systems for
underground construction.
One of the critical factors in this matter has
been the evolution of grout pumps capable of pumping
grouts with a low enough water/cement ratio (by
weight) to achieve adequate strengths.
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HACETTEPE UNIVERSITYDepartment of Mining Engineering
Grouts and Grouting
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HACETTEPE UNIVERSITYDepartment of Mining Engineering
Grouts and Grouting
Mohr failure envelopes for the peak strength of grouts with different water/cement ratios, tested at 28days.
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Water /cement ratio of 0.35 to 0.4 are significantly
better than those with ratios in excess of 0.5.
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Bond strength
As the cable pulls out of the grout, the grout
imprints or flutes causes radial displacement or
dilation of the interface between the grout and the
cable.
The radial dilation induces a confining
pressure.It is proportional to the stiffness of the grout
and the rock surrounding the borehole.
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Bond strength
HACETTEPE UNIVERSITYDepartment of Mining Engineering
Forces and displacements associated with a stressed cable grouted into a borehole in rock.
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HACETTEPE UNIVERSITYDepartment of Mining Engineering
Cables for slope reinforcement
Drilling machine for the installation of 40 m long reinforcing
cables in 150 mm diameter holes in a dam excavation.
Also, it may also be
necessary to reinforce
slopes and foundations andcables have proved to be
very effective in suchapplications.
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40 m long multi-strand cables with a
capacity of 200 tons each being prepared for
installation in a dam excavation.
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Cables for slope reinforcement
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These cables were
installed to stabilise the
slopes of a dam
foundation in gneiss.
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Advantages of the Cable Bolts
Cable bolts also have advantages over other rock
anchors and these include:
• More “stretch”
• More load capacity
• Higher shear strength
• The cable’s inherent flexibility
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Conclusion:
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Clearly cable bolts are generally
a more costly type of rock bolt
support and hence should only be
used where appropriate from a roof
control (safety) point of view.
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