Aim:To determine the gradient between two stations by the principles of statia Tacheometry.
Instrument and Accesories Required:
Theodolite, Tripod Stand, Levelling Staff, Pegs, Arrows, etc.
- The theodolite is mounted on the tripod stand.
- The theodolite is centered over an arbitrarily selected station P from where the staff stations A and B can be sighted without any obstruction and the instrument is levelled using the foot screws and both the plate bubble and the altitude bubble are brought to the centre of their run.
- The theodolite is set on the face right mode and the vernier A on the face right mode and the vernier A on the horizontal circle is initially set at 0°00’00” and the staff station A is sighted.
- The central vertical cross hair is made to bisect the staff station A and the central horizontal cross hair is made tangential to 2.5 m mark on the staff station.
- The horizontal and vertical angles are recorded by reading the horizontal and vertical circles respectively.
- The stadia hair readings for the staff station A are also observed and recorded.
- The theodolite is swing to the right and the staff station B is sighted.
- The central vertical cross hair is made to bisect the staff station B and the central horizontal cross hair is made tangential to 2.5 m mark on the staff station B.
- The horizontal and vertical angle are recorded by reading the horizontal and vertical circle respectively.
- The stadia hair readings for the staff station B are also observed and recorded.
- The observations are closed on the first staff station A.
- The theodolite is then set on the face left mode and the horizontal and vertical angles and the stadia hair reading are observed for both the staff station A and B are recorded by repeating the above procedure for the initial settings of 180°00’00” on vernier A. The staff stations are sighted in the same sequence as above but by swinging the theodolite to the left.
- The average of the horizontal angles subtended by the line AB at the instrument station P and the vertical angles are found.
- The average vertical angles and the staff intercepts are substituted in the relevant expression for horizontal distance for inclined line of sight and vertically held staff and the horizontal distances of the staff stations A and B from the instrument station P are determined by the principles of stadia tacheometry.
- From the mean value of the horizontal angle APB and the horizontal distance PA and PB, the horizontal distance AB is determined by the cos rule.
- The difference in elevation between the two staff stations A and B is also determined.
- The gradient between the two staff stations A and B is determined from the difference in elevation and the horizontal distance between them.
Horizontal Circle Reading -Vernier
Average Included Angle
Vertical Circle Reading - Vernier
Average Vertical Angle
Stadia Hair Reading
PA = KSACOS2(Angle A) + C COS (Angle B)
PB = KSBCOS2(Angle A) + C COS (Angle B)
Horizontal Distance between AB can be obtained by using Cosine rule
AB2 = PA2 + PB2 – 2PA x PB Cos APB
h1= 2- PAtan (Angle A)
h2= 2- PBtan (Angle B)
Difference in elevation between A and B = h2- h1
Gradient from A to B = Vertical distance AB/ Horizontal distance AB
Result: The gradient between the two stations is determined.The gradient between the two stations A and B is 1 in ____