Civil Engineering: Dumpy Level Survey Step-by-Step Guide

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Example:

The Bench Mark value was 8.52m; however this was set too high to read through the level, so a TBM was created on the concrete at the base of the wall, which was 0.7m below the height of the BM, giving the height of TBM 1 of 7.82m.

This was then used to backsight to, which gave a reading of 0.3m, which added to the TBM gave an IH of 8.12m (TBM1 + BS = IH). A foresight was then taken on the new TBM (a black brick in the churchyard wall facing the survey area), this reading was 0.16m, which subtracted from the IH gives a value of 7.96 for TBM 2

(IH – FS = TBM2).BM= 8.52

BS = -0.7

TBM 1 = 7.82m +

BS= 0.30

IH = 8.12

FS = 0.16

TBM 2 = 7.96m

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The value of TBM 2 was 7.96m, the new backsight reading was 0.29m, giving an instrument height of 8.25m (TBM + BS = IH). A number of foresights were then taken within the survey area and these readings were then subtracted from the instrument height to give a real/reduced level.

TBM 2 = 7.96 +

BS = 0.29 IH = 8.25

(IH – FS = RL)

Fore sights (m) Reduced Level (m)

1= 2.25 6.00

2= 3.62 4.63

3= 1.92 6.33

4= 2.18 6.07

5= 3.19 5.06

6= 3.09 5.16

And finally....Some notes on taking care and use of the equipment

• The staff can be difficult to steady in high winds; you do need to keep it vertical and still. Do not use fully-extended near overhead power cables.

• Always pull out (and return) the sections one at a time, and put the staff back in its sleeve after use. Keep mud and grit off it as much as possible, as this will scratch the painted markings. After a survey, dampen the microfiber cloth supplied and wipe off each section of the staff as you close it up.

• The level head is a precision instrument, and should be handled carefully. When not in use it should always be kept in its box. If it is raining please make sure that you cover it with a bag or rain hood, or preferably unscrew the head and place it in its box. If the level head does become wet, make sure that it dries out somewhere inside/out of the rain before being returned to its box. If you don't dry it out properly, moisture may seep inside which will result in the telescope 'fogging up' and possible damage to the internal parts.

• When your survey is complete, carefully unscrew the level head and place it in its correct position within the box, close the lid and make sure the catch is secure.

• PLEASE TAKE CARE NOT TO DROP THE BOX: If the level head or box containing the level head is kicked or dropped you must report this to the Jigsaw team as soon as possible as it may require calibration or repair.

• Undo the catches on the tripod legs and carefully move there tract the legs and clamp the catches back and fasten the belt. Please ensure that the tripod does not get dented or damaged, as this may make it unusable.

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