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The model of dynamic loading of rockbolts |
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The model of dynamic loading of rockbolts
Author: A. Nierobisz
The article uses the results of tests carried out in the framework of the Targeted Project of the State
Committee for Scientifi c Research (KBN) entitled “Rockbolting systems for roadway workings threatened
with tremors” (registr. No 6T122003C/06233)for verifi cation of a rockbolt dynamic loading model. This
model assumes that a tremor or rockburst can be considered as a hit of conventional weight on a rockbolt
bar, which on one side is ended with a washer and nut, and on the other side is fi xed at the hole bottom
(Fig. 1). Omitting the longitudinal vibrations of the rockbolt bar accompanying the hit and its mass we
can assume that the rockbolt bar supports a conventional rock block with mass m1, which is hit by mass
m2 > m1 with kinetic energy Ek. Assuming a plastic model of collision of masses m1 and m2, the kinetic and
potential energy, which the system of masses m1 and m2 possesses after plastic collision, was calculated.
The total impact energy Eu defi ned by the relation (5) was compared with the rockbolt work Wk, which
quantitatively is equal to the fi gure fi eld under the curve determined by the function F(p), showing the
displacement of the rockbolt (relation 6) (Fig. 2). For the verifi cation of theoretical assumptions of the
model, a physical model with mass m1 was created, consisting of mass m1 that was loading a rockbolt
which was grouted into a test cylinder (simulating the rock mass). On the mass m1 one has dropped from
a suitable height the impact mass m2, observing the rockbolt behaviour and measuring by means of apparatus
the rockbolt loading and its displacement (Fig. 6, 7). The obtained results were collected in Table 1
and their statistical analysis was carried out according to the following procedures:
1. The absolute difference between the impact energy Eu and rockbolt work Wk for each test was
calculated. When the difference exceeded 5%, the result was rejected.
2. It has been checked if the number of results determined when using the method mentioned above
is suffi cient.
3. With the aid of a test of difference rank signs the hypothesis was checked assuming that the
theoretically calculated impact energy Eu is not essentially different from the measured rockbolt
work Wk.
As a result of the analysis the random sample of results which met the assumed signifi cance criteria
was selected. Afterwards by help of the test of difference rank signs it has been indicated that there is no
reason to reject the hypothesis that the total impact energy Eu calculated by means of theoretical relations
is not essentially different from the rockbolt work Wk calculated from measurement results.
Keywords: safety, mining, rockbursts, roofbolting |
2011