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

Setting up the level

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1. Set up the tripod where you have a clear sight of the benchmark, at a similar height to but preferably higher, than the benchmark. If possible, set up in the center of the area that you intend to survey, or somewhere that you can see all of the site as well as the backsight/Bench Mark, with the top plate relatively level.

Release the catches on each leg and extend to full length, close the catches. Space the tripod legs well apart, with the level plate about chest height of the person who will be reading the levels. NB: the tripod needs to low enough for the smallest person on site to use the dumpy level!

Note: Bear in mind that if at some point you have to move the level (higher or lower, or to a new location) you will need to re-level it and retake the backsight reading (see below).

2. Place the level head on the baseplate and attach it to the central screw beneath the baseplate. With the telescope parallel to two of the foot screws, level off by adjusting the two foot screws simultaneously, turning them in opposite directions until the level bubble is central.

Then turn 90 degrees so the telescope points towards the third foot screw, and use the third screw to adjust the spirit level until the bubble is central along this axis. Check again in all directions. Now you should be perfectly level. NB: If the legs get kicked or moved by mistake, you will have to repeat the above steps.

Taking a reading

Taking the backsight (BS)

• The first measurement that you need to take is the backsight.

This will enable you to calculate the height of the instrument/level (IH) from which all other levels are calculated.

• The person with the staff should place the bottom of the staff level on the BM or TBM, keeping it as vertical as possible.

• The person at the Level rotates the telescope until the central line/cross hairs are lined up with the staff; you may need to focus the eyepiece first to see the cross hairs then the telescope focus to see the numbers on the staff; use the fine adjustment to be perfectly lined-up.

• When looking through the telescope, you take the reading where the central or stadia cross hairs meet, to the nearest centimeter. For example in the diagram to the right (above) the reading would be 1.42m.

1) The leveling bubble should be central

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2) Calculating the instrument height:

(IH) (or height of the Level) In order to calculate the height of the instrument (IH; ie the height of the Level Head telescope) you add the value of the reading you have just taken to the known value of the BM or TBM that you are using.

3) Taking Foresight (FS):

Readings and calculating reduced levels Begin taking height (level) readings of anything you want to illustrate on your site: top of slope, bottom of slope, break of slope – to illustrate changes in height and create profiles.

Mark the location of your levels on the plan, starting at 1 (see example below) or the next available number if returning to a survey, and read off each height reading and record these in a separate notebook. Make sure you write clearly and record the date, where the survey is, what the BM or TBM is and the initials of the people undertaking the survey.

Each time you will have to rotate the telescope, sight on the staff in its new location, focus and carefully take the reading, always check twice that you have read the number correctly

Once you have taken all the levels you want, you will need to calculate the actual height values, or reduced levels (RL) by subtracting each one from the instrument height (IH). This gives you the 'real' height of the ground at the base of the staff.

Continuous reading!

Read example Click here