Answered: Civil Engineering Surveying Levels

Setting up an automatic level

a.    Extend fully the tripod legs and fix the automatic level on the tripod head.

b.   Move the instrument to a suitable location free of obstruction and disturbances. Spread the tripod legs evenly apart and maintain the tripod head nearly level.

c.    Plant all the tripod legs firmly into the ground by applying your full weight on each foot peg

d.   Carry out coarse levelling by adjusting the lengths of the tripod legs so as to partially centre the bubble in the circle.

e.    Carry out fine levelling by adjusting the levelling screws so as to centre the bubble into the circle. Use the left thumb rule to adjust the levelling screws.

f.    After centring the bubble, turn the instrument about 90 degrees and ensure the bubble remains centred. If the bubble does not remain at the centre of the circle, readjust the screws and recheck the level again.

g.   Aim and measure

How to determine and record levels using an automatic level

a.       After setting up the instrument, identify a benchmark and take the first staff reading at the bench mark.

b.      Record the first reading as a backsight.

c.       With the instrument at the same position, take subsequent staff readings and record them as intermediate sights.

d.      Where there is need to change the instrument position, record the last reading before changing the position as a foresight.

e.       Finish the level run on a benchmark or a known datum point.

f.       Determine the reduced ground levels of the required points using either the height of collimation method or the rise and fall method.

Accuracy of the automatic level

The automatic level takes highly accurate levels because it has an internal compensator mechanism which automatically adjusts the line of sight to eliminate any errors.

 Setting up a laser level

a.       Plant the tripod on a stable ground at a convenient location.

b.      Mount the laser level on the tripod head.

c.       Turn on the laser level

d.      Give it some time to self-level. If it is a manual laser level, ensure the bubble vials show level by adjusting the screws near the vial.

e.       Identify a point on the ground at your desired elevation

f.       Attach a laser receiver to a staff and position the staff on your identified point

g.      Move the laser receiver up and down by sliding it on the staff. The receiver will beep when it intercepts the laser beam and at that point you have found level.

h.      Tighten the receiver at that point

i.        The bottom of the staff is your desired ground height.

How to determine and record levels using a laser level

a.       After setting up the laser level and receiver, record the staff reading as the initial reading.

b.      Move to other points and record the staff readings when the receiver intercepts the laser beam.

c.       Subtract the initial staff reading from these other staff readings to get positive or negative differences.

d.      A positive difference indicates a low spot and a negative difference indicates a high spot.

Accuracy of a laser level

     Just like the automatic level machine, laser levels have enhanced accuracy by way of self-levelling that continuously keeps the laser beam on level. Also, the fact that laser levels can be used over long distances without necessarily changings instrument positions further enhances accuracy.

Question 2

a.       Mark two positions (A and B) thirty meters apart on a reasonably level terrain as shown in the figure above.

b.      Set the automatic level exactly midway (at point C) between points A and B.

c.       Take and record the staff readings at both points A and B.

d.      Assign A to be zero and derive B as (A-B). Assume the staff reading of A was 1.523 and that of B was 1.502, then the elevation of A is assigned zero and B = (1.523-1.502). Hence B = 0.021

e.       Move the automatic level about 3m from point A (point D) and take and record the staff reading at point A. To get the staff reading you should expect at point B, subtract the elevation of B from the staff reading of A. For example, assume your reading at point A is 1.257m, then the expected staff reading at point B should be

B = 1.257 - 0.021 = 1.236

f.       Take and record the staff reading at point B and compare it to the expected reading.

g.      If the two readings are not equal, then there is an error that requires to be corrected by moving the instruments crosshairs up or down until the expected staff reading is recorded.

h.      Repeat the procedure to ensure the adjustment worked.