Question

Discuss common causes and sources of drill hole misalignments in an underground mining
environment. Briefly discuss methods to measure the quality of drill holes. Add diagrams to motivate
your answe? (25 marks)

Answer 1

Causes :

a. Geology
b. An inexperienced driller
c. The elevation of the drilling bench
d. Misalignment of the drill mast from vertical or the    intended angle

Sources :

1.Collaring deviations, or the lateral displacement of a hole from its planned starting
point: this can be caused by

*the topography of the drill site,

* poor drill set-up,
and/or

* the inability of the drill to hold the boom and feed beam in a rigid position
(worn pins and bushings).

2.Alignment deviations, or inaccuracies in setting the feed on which a drill is mounted
in a planned direction: this can be caused by

(1) instabilities of the drill rig, (2) lack of
precision in positioning equipment,

(3) misaligning the feed beam,

(4) topography at
the collaring point, and/or

(5) structural geology

Hole quality measurement method :

The purpose of drill-wear monitoring is to provide a method for automatical-
ly controlling a drilling process and ensuring that acceptable holes are drilled. The
process would allow adequate time to replace the drill bit. However, in addition to
the time determination in terms of drill wear, monitoring on-line changes in quality
measurements of drilled holes can provide more useful information for controlling
the drilling process. The reason behind this is that, since unacceptable hole qualities
may be produced even before the failure point of the drill bit, an on-line hole quality
monitor might be needed to decide when to initiate an adaptive change to control the
drilling process.
A drilling force which can be measured on-line was used in an experimental
investigation by Radhakrishnan and Wu in 1981 [26] for prediction of hole surface
quality for composite materials. The lamination frequency associated with the
laminated fiber of the composite material was used to present the waviness of the
hole surface. This lamination frequency was given by the ratio of number of
laminations per inch of material to the time taken by the drill to penetrate an inch of
material. The correlation between the change in this frequency and drilling forces
was investigated.

cutting force such as the mean or peak thrust/torque did not provide a reliable
indication of changes in hole surface quality. Comparatively, the dynamic
characteristics of the drilling thrust force using the Dynamic Data System developed
by Wu in 1977 [27] showed a very strong correlation between the hole surface and
the changes in the standard deviation of the lamination-frequency content of the
drilling-thrust force.