hacettepe university department of mining engineering

Prepared by ERSİN DİK

HACETTEPE UNIVERSITY Department of Mining Engineering

Contents:

-Introduction -Cable Bolt Background -Bond Strenght -Grouts and Grouting -Cable Installation -Advantages of the Cablebolts -Cables For Slope Reinforcement -Conclusion

HACETTEPE UNIVERSITY Department of Mining Engineering 1/18 Prepared by Ersin DİK

Introduction

Cable Bolts are

commonly used for rock

reinforcement in areas of

strata movement.

They can be used to

supplement existing

strata reinforcement.


Cable Bolt Background

Cable Bolts have been used

extensively in underground mines

since the early 1970's.


At that time, modified cable bolts was

developed to improve the load transfer and was

introduced into both Underground and Open pit Mines.


Summary of the development of cable reinforcing systems for underground mining.

4/18 Prepared by Ersin DİK


Cable installation

There are two types of grouting

cables in upholes.

First one is the traditional

method 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).



Cable installation

Alternative methods for grouting cables in upholes.

Breather tube method Grout tube method



Cable installation

The main problem with

breather tube method is that

it is difficult to detect when the

hole is full of grout.



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.


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.



Grouts and Grouting



Grouts and Grouting

Mohr failure envelopes for the peak strength of grouts with different water/cement ratios, tested at 28 days.

11/18

Water /cement ratio of 0.35 to 0.4 are significantly

better than those with ratios in excess of 0.5.

Prepared by Ersin DİK

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.


Bond strength


Forces and displacements associated with a stressed cable grouted into a borehole in rock.



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 and

cables have proved to be

very effective in such applications.


40 m long multi-strand cables with a capacity of 200 tons each being prepared for installation in a dam excavation.


Cables for slope reinforcement


These cables were

installed to stabilise the

slopes of a dam

foundation in gneiss.


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


Conclusion:

17/18

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.

Prepared by Ersin DİK

hacettepe university department of mining engineering

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