Weisbach Triangle :

Weisbach Triangle :

When transferring ground level azimuth U/G by suspensions 

of two wires down a shaft. It is difficult to set up the 

theodolite exactly in line with them. In addition one wire 

being nearer obscures. The wire beyond leading to an 

inaccurate bisection. In weisbach method the theodolite is 

set up slightly out of line forming a small triangle with the two 

wires. This triangle is known as weisbach triangle & the 

azimuth of the line joining the two wires is found by solution 

of the triangle of formed. .α is obtained form the triangle W1 

TW1 by the sine rule 

 α sin β

sin α= ----------------- e = c.sinα

b

In a weisbach triangle W2 TW1 called the weisbach angle β & the ratio c/b must be very small for 

which the theodolite station (T) should be very near to the wire (W1). If the weisbach angle is less 

than 25 minutes. There is no necessary of measuring sides. The angle should be measured very 

accurately to avoid any error.

Purpose of correlation survey : The various purposes of correlation of surface and U/G.

1. To determine with high degree of accuracy the relative positions of the U/G roadway & 

faces may be correctly laid down on the working plan.

2. To fix the boundary of the mine for limiting the extent of U/G working.

3. To fix the positions of railways, road and important building or structures on mine plans.

4. To mark the river, lake, tank, pond etc. on mine plans so as to take adequate precautions 

against inundati

5. To select suitable site for proposed pits drifts or boreholes to connect with U/G working.

Explain correlation survey. Define different method of U/G survey. What should be 

accuracy.

Correlation survey : Correlation in surveying is the method of surveying by which the surface 

survey are U/G survey are connected to the same base.

Different methods : The method employed for correlation surveys are controlled to a large extent 

by the conditions at the mine the different methods are

1. Direct traversing when working are reached by adits or drifts.

2. Shaft plumbing methods when access is by means of vertical shaft.

(a) One wire in each of two shafts.

(b) Two or more wires in a single shaft by

(i) Coplaining or exact alignment method.

(ii) Approximate alignment or method of weisbach triangles.

(iii) Methods of weis quadrilateral.

3. Optical method or direct transference of azimuth sown a shaft by a transit theodolite.

4. Magnetic methods.

(a) By tabular compass.

(b) By magnetic theodolite.

5. Gyro-theodolite method.

Accuracy : The permissible angular error for correlation 18 + 2 minutes or arc. Therefore the 

accuracy in correlation survey should not exceed the maximum permissible angular error.

Explain triangulation survey. Describe principle involved in triangulation survey. What are 

the points to be fixing the position for triangulation station.

Triangulation survey : The process of measuring the angle of a series of indercounted angles by a 

no of st mark on the surface on the earth is called triangulation survey.

Principle : On the surface, where the country is comparatively open, the survey is performed by 

triangulation. It is based on the trigonometric proposition that if only one side and all side are three 

angles of a triangle be known then the remaining sides can be calculated by the sine-rule. 

Suitable triangulation station from the vertices of a series of mutually connected triangles of the 

triangulation system. In this system on side called the base line and all the angles are very 

carefully measured and the length of all other lines in the system are then computed and all the 

angles being known. The direction of each line relative to some standard direction may be 

determined. The position of each triangulation station with reference to a predetermined point in 

the area surveyed can be computed.

Fixing Triangulation station :

1. All available surface plans of the area should be made for fixing probably positions of 

triangulation station.

2. The station points each triangle are inter visible & the height available ground should be 

inter visible.

3. They should be well conditioned triangle.

4. All station should be easily accessible.

5. The base line should be located on flat ground so that well shaped triangles can be formed 

in connecting the end of station of the base to the main triangulation system.

6. They are so located that the cost of clearing obstruction from the line of sight is minimum.

7. they should be useful detail surveys important surface features such as shafts, inclines 

bunkers, important building etc. should be located near the triangulation station.

8. They should be fixed on firm ground avoiding sand or loose earth and two stations should 

not be use one triangle.

9. When angle or U/G obstructs the line between the two stations, stations may be raised by 

erecting wooden scaffold so as to clear the greater part of the obstruction avoided and the 

remainder cleared at small cost.