5. The roof boit that follows the principle of point anchorage is
Answers
Explanation:
In principle, the same remarks apply here as for mechanical anchors. The only difference
Hope its help.
Answer:
Coal mining contributes to the energy and chemical industries in South Africa. The total annual
production of run of mine coal in 2005 was 273 million tons of which approximately 50 per cent
was mined by underground methods (Chamber of Mines of South Africa, 2007). Of the
underground production approximately 80 per cent is mined by methods which rely on some
form of roof support.
Today, roof bolting is, by far, the most common support system used in South African collieries.
Because it is more economic than other methods; it saves material and manpower
consumption. Most important of all, roof bolting is more effective and efficient because it is an
active support method, utilising the rock to support itself by applying internal reinforcing
stresses. Furthermore, rock bolting can be satisfactorily used to meet a variety of geological
conditions and various support requirements. Roof bolts are available in many forms and the
methods to attach them to the rock mass are almost as varied. Full column single resin bolts,
full column slow-fast combination resin bolts, resin point anchors and mechanical anchors are
the most widely used support systems used in South Africa. Significant advances have been
made over the last 20 years in all elements of roof bolting. The design of roof bolt patterns has
also been improved. However, studies into the causes of falls of ground show that falls of
ground (FOG) have been the major cause of fatalities in South African collieries since 1970.
The distribution of all fatality and injury rates in South African collieries for the period 1984 to
2004 is presented in Figure 1-1. This figure indicates that although there has been a steady
reduction in the rates of both fatalities and injuries in collieries until 2001, the rate of fatalities
and injuries have increased since 2001. It is also seen in this figure that over many years the
rates of fatalities and injuries fluctuated significantly, therefore the fatality and injury rates are
not predictable. The peak in the fatality rate in 1993 in this figure was due to a methane
explosion in a colliery, which killed 53 miners.
The cause of fatalities in South African collieries for the period 1995 to 2004 is shown in Figure
1-2. This Figure indicates that for this period FOG has been the major cause of fatalities in
South African collieries, and the greatest reduction amongst all other causes for fatalities has
been achieved in the FOG since 1996