Key Factors Determining the Dimensions of a Drilling Rig

O. D. Alimov, A. S. Simonov, V. M. Zakhlebnyi

(Presented by Prof. P. M. Alabuzhev, Doctor of Technical Sciences)

In the coal industry, for drilling blast holes during the driving of capital and development mine workings, pneumatic drilling hammers and column-type electric drills are used for the most part.

Increasing the productivity of drilling operations with this equipment is possible through the following measures: first, by increasing the machine drilling speed of the blast holes, which will reduce the time spent drilling each hole; second, by reducing the time spent on auxiliary operations (setting up the machine, changing drill bits, etc.); third, by combining the drilling of several holes in time.

An increase in the machine drilling speed of blast holes, provided that the machine operates at optimal regimes, requires an increase in the power consumed and, consequently, leads to an increase in the dimensions and weight of the machine. The dimensions of the drilling machine, in turn, are limited by the dimensions of underground workings. Increasing the weight of the machine without increasing the labor intensity of servicing it is possible only by creating improved manipulators for setting up the machine at the face. Mounting drilling machines on manipulators makes it possible to reduce the time spent on auxiliary operations associated with setting up the machine for drilling each blast hole [3].

A considerable amount of time is also spent on repeatedly changing the tool when drilling a single blast hole, which likewise cannot be considered normal. Indeed, only a few years ago drills were manufactured mainly in one piece with drill bits and blades made of carbon steel. With such drills, in hard rocks it was possible to drill, without resharpening the drill or replacing it, no more than 500 mm of a blast hole.

As a result, when drilling one blast hole 1.5–2.5 m deep, it was necessary to replace several worn drills. For these reasons, each drilling machine was supplied with a set of drills 500, 1000, 1500, 2000, and 2500 mm long [2]. Accordingly, drilling machines were designed with a maximum tool-feed travel of 600–900 mm. This feed length is found in most machines produced at the present time; for example, the KTsM-4 drilling hammer has a feed travel of 900 mm; the EBK-2M column-type electric drill has a maximum spindle travel of 895 mm. When drilling a blast hole 2.5 m deep with such machines, the drilling tool must be changed 3 times.

At present, drilling is carried out mainly with drills with removable bits tipped with hard-alloy plates, whose service life is 30–50 times greater than that of bits made of carbon steels. Therefore, in rocks with a hardness up to 12–14, it is possible to drill several blast holes 2000–2500 mm deep with one bit without resharpening [2]. This determines the expediency of using drilling machines with long-

feeders, with a travel of 2200–2700 mm, which would ensure continuous drilling of a blast-hole over its entire length. Combining the drilling of several blast-holes in time, while simultaneously reducing the number of drillers and the labor intensity of their work, requires the creation of special machines and installations for group drilling.

When selecting the basic parameters of newly designed drilling machines, it is also necessary to take into account the requirements for these machines arising from the mining and geological conditions of their operation. Below we consider one of the questions posed—the question of the maximum possible overall dimensions of a drilling rig.

To select the principal dimensions of a drilling rig (the drilling machine and supporting devices), the designer must know the following information from the operating conditions of the machine:

1. The transverse dimensions of mine workings—in order to substantiate the dimensions of the devices for installing drilling machines.

2. The arrangement and depth of the blast-holes—in order to substantiate the kinematics of the manipulators, the feed stroke of the drilling machine, and its maximum possible length.

In what follows we have attempted to generalize this information, proceeding from the operating conditions of drilling machines most frequently encountered in practice.

Cross-Sections of Mine Workings

At present, in the practice of the coal industry, single-track and double-track workings for 1–3-ton mine cars have become the most widespread (Fig. 1).

Fig. 1. Typical cross-section of a single-track working.

Typical cross-sections of the most common workings are given in Table 1. The cross-sectional area of the workings ranges from 6 to 16 m².

Table 1

Typical cross-sections of workings

The practice of advanced heading crews has proved that the least time for drilling the face is achieved when several drilling hammers are installed at the face, on the basis of one hammer per \(1\text{–}2\ \text{m}^2\) of the working cross-section [1; 4; 5]; therefore devices for installing and feeding drilling hammers can be designed for 3–8 drilling hammers.

The design of the manipulators and of the feeders mounted on them must make it possible to drill faces of the following dimensions: face height from 2270 to 3000 mm, face width from 3000 to 5000 mm.

Arrangement of Holes in the Face

The choice of the arrangement of holes in the face depends on the strength and character of the occurrence of the rock masses being intersected, on the cross-sectional dimensions of the working, and on the convenience of placing the drilling equipment. Practice has established several typical schemes for drilling faces. In general, the schemes for arranging holes in the face differ from one another in the position and angle of inclination of the so-called cut holes. These holes are intended to create an additional free surface in the rock mass (in addition to the plane of the face of the working) before the blasting of the auxiliary and breaking holes. To achieve the maximum blasting effect, cut holes are arranged differently under different mining-and-geological conditions. The arrangement of cut holes in the face is a determining factor in selecting the drilling machine and the depth of the holes.

The most common schemes for arranging cut holes are given in the appendix. As can be seen from the appendix, schemes for arranging cut holes may be divided into two main groups:

1) cuts formed by holes inclined to the plane of the face (Fig. 2),
2) straight cuts, in which the cut holes are arranged perpendicular to the plane of the face.

Cuts of the first group make it possible, under certain mining-and-geological conditions and with a relatively small amount of drilling work, to achieve effective use of the explosive force; therefore they have become widely used in practice. But arranging the holes at an angle considerably reduces the possible length of the drilling machine, the length of the tool, and consequently the depth of the holes and the advance of the face per cycle.

Cuts of the second group have recently become widely used in the practice of innovator driftmen. Straight cuts are formed by a row of holes drilled perpendicular to the plane of the face of the working. Some of these holes are not charged and are intended to increase the effect of the explosion of the charged cut holes. For this purpose the diameter of the uncharged holes or boreholes is increased to 50–90 mm. Straight cuts make it possible to increase considerably the advance of the face of the working per cycle. When drilling straight cuts, the arrangement of holes in the face is simplified, the installation of the drilling equipment is facilitated, and this leads to an increase in the utilization of the drilling equipment over time.

Fig. 2. Designation of the parameters of a vertical wedge cut and the length of the drilling installation.

When straight cuts are used, the possible length of the drilling machine does not depend on the dimensions of the cross section of the working. But the use of straight cuts requires an increase in the volume of drilling work, an increase in the number of meters of holes drilled and in their diameter. To ensure a high coefficient of utilization of holes during blasting, it is necessary to drill adjacent cut holes sufficiently parallel. As a result, in order to obtain

to obtain the greatest effect from the use of a straight cut in development work, it is necessary to use powerful and high-capacity drilling machines and improved devices for installing them. The design of the feed mechanisms and manipulators for this case must ensure the required direction of the blast-holes during drilling.

Determination of the Maximum Possible Length of a Drilling Rig in Cuts Formed by Inclined Blast-Holes

By the maximum length of a drilling machine, in what follows, we shall mean the total length of the drilling tool, the drilling machine, and the mounting devices. The maximum possible length of the machine determines the possible length of the drilling tool and the magnitude of the feed stroke.

Vertical Wedge Cut

For a vertical wedge cut (Fig. 2), the length of the cut holes and the distance between their mouths are determined by the formulas

\[ l = \frac{w}{\sin \alpha}, \tag{1} \]

\[ r = 2\sqrt{l^2 - w^2}, \tag{2} \]

where \(l\) is the length of the blast-hole, m;
\(w\) is the distance from the face plane to the end of the blast-hole along the axis of the working (blast-hole depth), m;
\(\alpha\) is the angle of inclination of the blast-hole to the face plane, degrees;
\(r\) is the distance between the mouths of the blast-holes in the horizontal plane, m.

Then the maximum length of the drilling equipment that can be installed in the working when drilling cut holes can be determined by the following formula

\[ L = \frac{b}{2\cos \alpha} - l, \tag{3} \]

where \(L\) is the maximum length of the drilling equipment, m;
\(b\) is the width of the working, m.

From formula (3) it is evident that the maximum length of the drilling equipment depends mainly on the width of the working, the angle of inclination, and the length of the cut holes.

The angle of inclination of the cut holes is taken as varying depending on the strength of the rocks.

The optimum relationships between the strength of the rock \(f\), the angle of inclination of the holes to the face \(\alpha\), the distance between two parallel holes of the cut \(S\), and the number of cut holes \(n\), established by the practice of innovators, are given in Table 2.

The maximum length of the drilling rig as a function of the width of the working and the angles of inclination of the holes of a vertical wedge cut is shown in Fig. 3.

Table 2

The graph in Fig. 3 is constructed for the conditions of drilling cut-in holes 1.5 m long, which, with a hole utilization coefficient of 0.75 and 0.85 (at \(\alpha = 65^\circ\) and \(\alpha = 70^\circ\)), provides an advance of the working per cycle of 1.0 and 1.2 m, respectively.

Fig. 3. Dependence of the length of the drilling rig on the width of the working and the angle of inclination of cut-in holes
I — \(\alpha = 55^\circ\); II — \(\alpha = 60^\circ\); III — \(\alpha = 65^\circ\);
IV — \(\alpha = 70^\circ\); V — \(\alpha = 75^\circ\).

On the basis of the graph in Fig. 3, the following conclusions may be drawn:

1. Drilling holes 1.5 m long for a wedge cut and at an angle \(\alpha = 55\text{–}65^\circ\) when driving workings less than 3–3.5 m wide is impossible, since in this case the value of \(L\) is less than 1.5 m; therefore even into a predrilled hole it is impossible to insert a drill 1.5 m long.

In these cases, in hard rocks, cut-in holes are drilled at an angle greater than \(65^\circ\), but the number of cut-in holes is increased.

1. For drilling a vertical wedge cut when driving single-track workings, it is necessary to use short-stroke feeders with a feed travel \(S_{\mathrm{p}} = 500\text{–}600\) mm and, as the drilling tool, a set of drills consisting of drills 0.5–1.0 and 1.5–1.6 m long. For double-track workings 4 m wide and more, feeders with a feed travel of up to 1.5–1.6 m may be used. Such a feed travel will make it possible to drill holes with drills 1.5–1.6 m long without using additional shorter drills (starter drills), which will reduce the time of auxiliary operations.

To eliminate misalignment and bending of the drill during collaring, long-stroke feeders must be equipped with special guiding devices (steady rests). Feeders with a feed travel of 1.5 m may be used when drilling holes for a vertical wedge cut and in single-track workings when the rock strength is less than \(f = 10\).

Horizontal wedge cut

All conclusions drawn with respect to the vertical wedge cut apply to the same extent to the horizontal wedge cut, taking into account that the role of the width here is played by the height of the working.

The length of the drilling equipment may be determined by formula (3), substituting into it the height of the working instead of its width.

Since the workings have a height of no more than 3 m, the angle of inclination of the cut holes in this case must be no less than \(65^\circ\). Consequently, in hard rocks the use of this cut is very difficult; therefore it finds its greatest application when drilling rocks with a hardness of no more than \(f = 10\).

Pyramidal cut

This cut is used in driving workings in hard, massive rocks, and also, regardless of the character of the occurrence of the rocks and their hardness, in workings of circular cross section and, in particular, when sinking mine shafts.

The greatest length of the drilling equipment can likewise be determined by formula (3), with the corresponding replacement of the width of the working by the distance between the diagonally opposite corners of the working section.

For this case, after certain transformations, we obtain the formula

\[ L = \frac{b}{1.4 \cos \alpha} - l. \tag{4} \]

Comparing formula (4) with formula (3), we see that, when a pyramidal cut is used, the length of the drilling equipment under the same conditions may be taken as 30% greater than with a wedge cut.

Side cut

The greatest length of the drilling equipment can be determined by the formula

\[ L = \frac{b}{\cos \alpha} - l. \tag{5} \]

From formula (5) we see that the length of the drilling equipment, when a side cut is used, will be twice as great (for the same conditions) as with a wedge cut.

Thus, with a working width of more than 2.5 m and an angle of inclination of the cut holes of less than \(\alpha = 55^\circ\), the possible length of the drilling equipment may be more than 2.5 m. Therefore, when a side cut is used, even in driving single-track workings in hard rocks, it is possible to use feeders with a feed stroke of more than 1.5 m.

Upper and lower cuts

The conclusions drawn for the side cut will also be valid for the upper and lower cuts.

The maximum length of the drilling equipment can likewise be determined by formula (5), replacing the working width “\(b\)” by the height “\(h\).”

Conclusions

1. For the most effective use of drilling hammers under various mining and geological conditions, the manufacturer, at the request of consumers, should produce feeders of two types: short-stroke feeders, with a feed stroke of about 600–800 mm, and long-stroke feeders, with a feed stroke of 1500–1600 mm.

2. It is advisable to eliminate the use of wedge cuts and to switch to prismatic cuts using holes of increased diameter when driving permanent mine workings driven through rocks

of medium hardness and hard. This will require designing a powerful drilling machine with automatic feed and a setup for simultaneous drilling with several drilling hammers.

To determine the most expedient types of machines, their number in the setup for group drilling, the arrangement of the machines at the face, and their movement relative to the face, it is necessary to carry out special studies.

Appendix

Types of cuts used in driving development workings

1. Cuts formed by blastholes inclined to the plane of the face:

a) A vertical wedge cut (Fig. 4) is used in driving mine workings in rocks of homogeneous structure with vertical arrangement of fissures. The cross section of the working is \(6\ \mathrm{m}^2\) and more. The cut blastholes form a vertical wedge in the central part of the face. The number of blastholes and the angle of their inclination depend on the hardness of the rocks;

Fig. 4.

b) A horizontal wedge cut (Fig. 5) is used in rocks of homogeneous structure with horizontal arrangement of fissures. The cross section of the working is \(4\ \mathrm{m}^2\) and more. The cut blastholes form a horizontal wedge in the central part of the face;

Fig. 5.

c) A pyramidal cut (Fig. 6) is used in dense, monolithic hard rocks, and in bedded rocks of varying hardness but with a steep dip of the beds. The cross section of the working is \(4\ \mathrm{m}^2\) and more. The cut blastholes form a four-sided pyramid in the central part of the face;

Fig. 6.

Fig. 7.

c) a side cut (Fig. 7) is used in bedded rocks with steep dip and when driving workings parallel to the contact of the rocks. The cross-section of the workings is \(4 \, m^2\) or more. The cut holes form one vertical row inclined toward the wall of the working;

d) an upper cut (Fig. 8) is used in bedded fractured rocks of medium hardness and with the dip of beds and fractures away from the face. The cross-section of the working is \(4 \, m^2\) or more. The cut holes form a row inclined toward the roof of the working.

Fig. 8.

Fig. 9.

e) a lower cut (Fig. 9) is used in bedded fractured rocks of medium hardness and with the dip of beds and fractures away from the face. The cross-section of the working is \(4 \, m^2\) or more. The cut holes form a row inclined toward the floor of the working.

1. Straight cuts in which the blast-holes are arranged perpendicular to the plane of the face:

a) the slot cut (T. Shevchenko) (Fig. 10) is used in massive rocks of medium strength. The cut consists of several blast-holes arranged along one line and charged through every other hole. When the charges are detonated, a cut is formed having the shape of a slot; the spacing between the blast-holes, depending on the strength of the rocks, is taken as 10 to 20 cm;

Fig. 10.

b) the prismatic cut (Fig. 11) is used in hard massive rocks. The cut consists of five parallel blast-holes, of which the central blast-hole is not charged and serves to facilitate the action of the charges in the other blast-holes. In order to increase the effectiveness of the cut, the diameter of the central blast-hole, or borehole, is taken as 50—70—90 mm;

Fig. 11.

c) the spiral cut (Fig. 12) is used in massive rocks of medium strength to increase the dimensions of the cut formed without increasing the number of blast-holes. In this cut, each succeeding charged blast-hole is placed at a greater distance from the uncharged blast-hole, forming a spiral;

Fig. 12.

![Figure 13]

Fig. 13.

c) a cut with a distributed charge (the Pazenko cut) (Fig. 13) is used in monolithic rocks and rocks of medium hardness. The cut is formed by means of deep blast-holes (3 m deep and more), located at the corners of the square they form, with a side of 0.5 m. Three charges of explosives are placed in each blast-hole, separated from one another by stemming. Blasting is carried out in series, beginning with the charge first from the mouth of the blast-hole;

d) a cut with a chamber charge (the Gushchevsky cut) (Fig. 14) is used when drilling monolithic rocks in order to reduce the number of cut blast-holes, and in order to make it possible to place the required quantity of explosives in one or two blast-holes, chambers are created by preliminary firing.

![Figure 14]

Fig. 14.

LITERATURE

1. Buchnev V. K. Drilling-and-blasting operations. Ugletekhizdat, 1950.

2. Bryndin A. I. and Zverev B. V. Drill bits and rods. Ugletekhizdat, 1955.

3. Zhuravlev K. I. MBI-5u manipulators for drilling mechanisms. Ugletekhizdat, 1952.

4. Ministry of the Coal Industry of the USSR. Instruction on the organization of work according to the cyclicity schedule in driving horizontal and inclined mine workings in coal and shale mines under construction. Ugletekhizdat, 1953.

5. Potapov I. A., Lurye V. E. Driving horizontal mine workings in the construction of mines in the Kizel coal basin. BTI, Ugletekhizdat, 1952.