Direct traversing through inclined openings (Fig. 2)

Again, the method of connecting surface and underground surveys is similar to the method asemployed in the case of level adit except with a little difference owing to the inclined route of traverseprovided as entrance to the mine. The main difference lies in marking the position of survey stations.In case of moderate inclination of the shaft it may be possible to mark the survey stations in the roof.When the shaft is steeply inclined it is desirable to provide permanent stations to facilitate the work.

Fig. 2: Correlation by direct traversing

To accomplish such work, a closed traverse is required to be run form surface control point to theunderground base. In such a traverse, where stations are separated by short distances, centeringerror poses major threat to accuracy of the traverse. For instance, in a length of 10 m, a centeringerror of 3mm of the target gives rise to an error of 1 minute in the angle.

dα = 3 mm____ x 206225 ” (1 radian = 206265)10000 mm

= 3 x 20.6265 = 61,88 “ (=1’)

Correlation by plumbing wires in the vertical shafts

In the majority of the cases, correlation has to be carried out in one or two vertical shafts and thisrequires the suspension of plumb lines in the shaft or shafts. As this is common to a number ofmethods of correlation the problems of suspending the plumb lines are discussed in the beginning.

Plumb Wire: Piano wire is often used for shaft standard. Other type of wire used successfully wasa galvanized steel, wire, 1/8” dia, having breaking strength of 1 ton and a weight of 18 lb per 100yds.

The breaking strength of a wire limits the weight of the plumb bob which can be hung on it, while anincrease in the diameter of a wire increases its resistance to the air current and therefore possibility ofdeflection from the vertical. In correlation, where wires have to be observed through a theodolite, thediameter of the wire is an important factor since; the thicker the wire is the more difficult does itbecomes to make accurate pointings to it. Although plumb wires are loaded usually well towardsbreaking point, they are still affected by air currents in the shaft. The magnitude of the deflection tendsto vary as the square of the depth and therefore a wire would be deflected 25 times more at a depthof 500 m then at 100 m. The plumb wire itself offers the greatest resistance to air currents which isdirectly proportional to the diameter of wire. It is impossible to determine the probable amount ofdeflection in advance but a wire will only hang perfectly vertical with a plumb bob of infinite weight. Asfor the weight of plumb bob, a well known principle is that the amount of deflection at the base of aplumb wire is inversely proportional to the weight of the plumb-bob.

It is a common practice to immerse the plumb bob in a drum or bucket containing liquid. Heavy oilmay be used for this purpose. But the use of highly viscous liquid is very doubtful and this practiceshould be avoided. It is also a common that when two plumb wires are suspended in a shaft,

agreement in the width of plumb plane between at surface and in the underground is a satisfactorytest for verticality.

Hence each shaft plumbing must be considered entirely on its merits and if any doubt exists,experiments should be carried out to try and establish before hand the validity of the methods which isproposed to be used.Hanging wires : It is desirable that the wires used in plumbing the shaft should be fine as well asstrong to support the plumb bob so that a minimum surface is presented to outside influences, thewire is wound on a small drum fitted with a brake to hold it in any desired position. The plumb wire islowered down the shaft with small plummet weighting 3 to 5 kg attached to it. When it reaches thebottom the small plummet is replaced by a larger one which may be of the weight up to 30 kgdepending upon the breaking strength of the wire. The large plumb bob may then be immersed in adrum of water or oil to dampen the oscillation of the wire. It is essential that the wire should hangfreely in the shaft which may be determined by letting a cut-ring on the wire to pass from surface tothe shaft bottom. To observe whether the plumb wire is at rest, it should be bisected by the cross-hairs of the telescope, the wire illuminated by a lamp held behind it with a piece of white paper heldbetween the lamp and wire.

Plumb bobs are normally made of lead which has a high density and unaffected by magneticattractions. They should be symmetrical in order to aid verticality of the wire and they may be fittedwith vanes to dampen the twisting of the plumb bob when immersed in water or oil.

The various methods of correlation using plumb wires and the method adopted will depend on theavailable shaft entry into the mine.

a. Correlation by two shafts (Fig. 3)

One plumb wire is suspended in each of the two shafts. The wires at the surface connected bytraverse with the surface triangulation and the length and bearing of the line joining them arecalculated.

Fig. 3: Correlation by two shafts

An underground traverse is then carried out between the two plumb wires using an assumed bearing.The length of the line between the plumb wires can be calculated and also the bearing of this line withreference to assumed bearing. The difference between the assumed bearing of the line joining thetwo wires and the correct bearing (from the surface coordinates) gives the correction to be applied toeach underground bearing. After applying correction for bearing, coordinates of all the points arerecalculated. Any convenient line in the traverse may then be used as a base line for all subsequentsurveys.

b. Correlation by one shaft

This should be avoided if possible, particularly in deep shafts as the shaft perimeter limits the lengthof the base line (i.e. distance between two plumb wires). This method needs an extreme care in fixingthe position of the rest of the wires.

Following are the few methods commonly employed:

(i) Co-planarity or exact alignment (Fig. 4)

In co-planing, the object is to set the theodolite in the line of the plumb-plane so that its azimuth canbe transferred to a reference line by angular observations. As both wires have to be seen through thetelescope, even when it is exactly in line with them, it is necessary to set up close to the nearest wire,usually about 3 m away. At this distance the diverging rays of light from the far wire are not obscuredand both wires can be observed by simply changing focus. No difficulty is experienced in identifyingthe wires, as the nearest one will always appear to be the thicker.

Fig. 4: Exact alignment method of correlation

Before co-planing begins, the instrument can be plumbed and the lateral shift measured from theplumbed mark at right angles to the plumb-plane. This is particularly easy if optical plumbingarrangement is incorporated in the instrument itself. Many surveyors, however, prefer to estimate theamount of movement required to effect an alignment and proceed on the basis of trial and error, andthe final fractional movement has usually to be made on this basis, even with the former method.

The alignment is not always easily accomplished and much patience and manipulative skill arerequired, as a single alignment may take from a few minutes to half an hour. It should be noted thatwith modern inverting telescopes the actual shift is always in a direction opposite to that apparentthrough the telescope, and it is unwise to try and observe the wires while the shift is being made.

(ii) The Weisbach Method

This method involves setting of two stations one at surface close to the wires suspended in the shaftand another at underground close to the wires in such a way that Weisbach triangle is formed as

shown in Fig.5. The instrument is set at Ws, the station at surface and Wg, the station atunderground. The corresponding angles as required for transferring the bearing from surface line ABto underground line XY, are measured using the theodolite. The distances which are required forcalculations as shown in figure 6 are measured with the metallic tape.

Fig. 5: Correlation surveys by forming Weisbach triangle

Fig. 6: Calculation for transfer of bearing of line AB at surface to XY in underground

ORIENTATION SURVEY WITH LASER-EYEPIECE AND NADIR PLUMMET

Shaft plumbing with wires and heavy plumb bob is still the most frequently used method. Objectionsto the use of such mechanical method are associated with the impossibility of attaining undisturbed

conditions. The use of lasers for shaft plumbing has been investigated. Experimental results haveshown that a standard deviation of 0.14” in setting the laser vertical achievable. In conventionalmethod the wire is suspended from top of the shaft to transfer the co-ordinates from surface toground. With increase in depth this may lead to incorrect correlation.

Thus lasers are used which are very precise even at large depths. Laser beam is sent to the shaftbottom for 4 different positions of plummet at 900 apart. The use of laser plummet has furtherimproved the accuracy. When GLO2 Laser eyepiece is attached to the Nadir plummet a laser beam isshot down in the shaft in a vertical line. A Nadir plummet (Fig. 7) is an instrument which can be usedfor precise plumbing. It consists of two pendulum compensators acting at right angles to each other,which automatically defines two vertical planes, the intersection of which is the plumb line.

Fig. 7: Nadir Plummet

A laser Eyepiece is attached to the telescope of a Nadir plummet. The laser instrument (called laserintensity regulator) is connected to the Laser eye piece by means of a cable. Laser is generated in thelaser instrument and is passed to the nadir plummet through a glass fiber cable and laser eye piece.The laser beam enters the nadir plummet horizontally and is diverted vertically downwards with thehelp of a penta prism (Fig. 8). The nadir plummet is leveled with the help of a circular level and fineleveling is taken care by a compensator fitted in the nadir plummet. The laser beam which is receivedat pit bottom as a red circular spot may not be exactly vertical below the surface point. This problem issolved by rotating the beam by rotating the telescope of the Nadir plummet about its vertical axis infour (x2) perpendicular directions. Four positions of the laser spot will be obtained at the pit bottom ona white painted metallic sheet. Joining the diagonals (Fig. 9 & Fig.10) will give the exact position of apoint vertically below the surface point.

Figure 11 shows the picture of correlation survey being carried out through Nadir Plummet and lasereye piece in a shaft mine at a depth of 500m.

Fig. 8: Schematic diagram representing correlation survey using laser eye piece and nadir-plummet

Fig. 9: Laser beam received at the bottom

Fig. 10: Laser beams received at the underground on a plate

Fig. 8: Schematic diagram representing correlation survey using laser eye piece and nadir-plummet

Fig. 9: Laser beam received at the bottom

Fig. 10: Laser beams received at the underground on a plate

Fig. 8: Schematic diagram representing correlation survey using laser eye piece and nadir-plummet

Fig. 9: Laser beam received at the bottom

Fig. 10: Laser beams received at the underground on a plate