Sight rails are used for setting out :
- Alarge buildings
- Bbridges
- Cthe gradient of canal beds
- Dthe gradient of trench of bottom or pipe invertsCorrect
Solution
Concept
Use of sight rails and boning rods
Step-by-step solution
1. Sight rails are horizontal boards fixed on posts on either side of a trench. 2. With a travelling rod (boning rod) they fix the gradient of the trench bottom or of pipe inverts.
Explanation
Sight rails give a line parallel to the required gradient at a fixed height above the formation, so that the trench bottom or pipe invert can be dug and checked to the designed slope.
Why the other options are wrong
Large buildings and bridges are set out with theodolites and total stations. Canal bed gradients are set with levelling instruments.
Shortcut
Sight rail + boning rod = pipe trench gradient.
Common mistake
Choosing canal bed gradients.
Correct answer: D) the gradient of trench of bottom or pipe inverts