CABLE BOLTING
Cable bolting is an established technique used extensively for reinforcement of the rock mass adjacent to surface and underground rock excavations.
REQUIRED FOR.
Cable bolting is effective rock reinforcement system developed and adopted successfully for strata control in metal ferrous mine. Techniques are required for both safety and productivity consideration in rock masses which are unstable in the required geometrical configuration. In the mining industry they enable more economical extraction of ore body through steeper slope in open pits or increased recovery rates from underground stopes.
CABLE BOLTING TECHNIQUE Bolting technique includes the reinforcing element like cables, glass fiber bolt, anchor, dowels, bolts, tendons and bonding element being cement grout or polyester resin. The installation procedures could be preand-post reinforcement, pre-and post-tensioning, grouted and un-grouted, bonded or debonded, couple and uncouple, permanent or temporary reinforcement. The philosophy behind the reinforcement scheme design is strata reinforcement, rock support, cable doweling, rock anchoring, pattern reinforcement and spot bolting. The cable bolting is a special reinforcement technique for long column or thick formation using flexible steel rope.
REINFORCEMENT ELEMENT Following mentioned
reinforcing element like:
Steel
cable
Nutcase cable bolt
Fiber
Arapree and weld grip rock bolt
glass bolt
These all have distinct properties and varied application.
STEEL
CABLES
STEPS
In metal mine or civil application, the diameter of the hole is governed by the type of drill string available and the length of hole to be drilled. For coal mining application, refer to Minicage ® form data sheet. Holes are drilled approximately 200mm shorter than the bolt length. If bolts are to be tensioned, a tail of between 200 to 500mm is required, dependent on the type of tensioning unit to be used.
STEPS
(CONT.)
Plain
cable bolts are prepared for installation by attaching a breather tube to the full length of the bolt. An excess of breather tube, approximately 2 meters, to protrude from the hole mouth. These cables can also be installed using an alternate "retreat" grouting method by withdrawing the grout tube from the hole. Approximately 1 meter of grout tube is attached to the bottom of the cable with sufficient tail provided to connect to the pump.
STEPS
(CONT.)
The cable bolt is inserted into the hole and the hole mouth sealed to eliminate loss of grout when pumping. Connect the grout tube to the pump. The air bleed (breather) tube is placed into a container of water and pumping commenced. Air bubbles will exhaust from the hole whilst pumping and be visible in the water container. When the hole is full of grout, these air bubbles will cease to flow.
STEPS
(CONT.)
After the grout has cured, the cable bolt can be tensioned, provided sufficient free length of cable is available. Note that HD P tubes are often used to provide a de-bonded section to allow tensioning.
ADVANTAGES
Because
of the flexible nature of a cable bolt it is particularly useful in the reinforcement of rock strata that is subject to significant horizontal shifting of the strata layers. The flexibility of cable bolts is also particularly adaptable for insertion in bore holes of a considerable length
shifting movement generates shear forces which can break a steel bar bolt. However, a cable bolt can withstand substantial lateral deflection due to shifting of the rock strata before it breaks. The effectiveness of a cable bolt to support a rock formation is determined to a great extent by the capacity of the cable bolt to resist pullout under the loads exerted by fractured rock strata.
PROBLEM WITH CABLE BOLT
One
of the major problems associated with the use of fully grouted cable bolts is the Lack of a reliable method to monitor the tension that develops in response to rock mass displacements. Existing gauges are mounted external to the cable itself and therefore potentially interfere with the bond strength in the measurement area. This can make the results extremely difficult to interpret.
