Accurate transfer of surface alignment down a vertical shaft using two plumbwires can be achieved by
- ARise and fall method
- BCollimation method
- CBowditch’s method
- DWeisbach triangle methodCorrect
Solution
Concept
Weisbach triangle method
Step-by-step solution
1. Two plumb wires are hung down the shaft to carry a line (azimuth) from the surface to the underground workings. 2. The Weisbach triangle method uses small triangles formed at the top and bottom to compute the underground azimuth.
Explanation
The Weisbach triangle (or Weiss quadrilateral) method is used to correlate the surface and underground surveys through a shaft.
Why the other options are wrong
Rise and fall and collimation are levelling reduction methods. Bowditch's rule adjusts a closed traverse.
Shortcut
Shaft + two plumb lines → Weisbach triangle.
Common mistake
Choosing Bowditch's method.
Correct answer: D) Weisbach triangle method