Need help-EG4110 – Land & Construction Surveying
University of East London School of Architecture, Computing & Engineering
EG4110 – Land & Construction Surveying 2016-17
PRACTICAL 4 Assessment Component 1: Part 1 Control Levelling (30%)
Aim • To give experience at setting up, levelling and use of a surveyor’s automatic level. • To practice standard level observation and booking procedures • To consider the accumulation of errors
Description Field Work: Working in a group of 3: 1. Carry out a “Two Peg Test” to ensure that the equipment is working correctly: a) Determine two points which can be easily and uniquely identified 40 – 50 metres apart. b) Set up the level in a safe location, so that the distance to each point is approximately equal. c) Take readings on the staff held at each of the 2 points and calculate difference. d) Move Level to a location such that is it much nearer to one point then the other. e) Take readings on the staff held at each of the 2 points and calculate the difference. f) Compare the results obtained and determine whether the instrument is functioning properly.
2. Determine the difference in height of control points on the Docklands Campus. The location of the points will be provided. Use the industry standard method of recording and calculating your measurements, “Rise & Fall”. Calculation of the rise, fall and reduced height should be undertaken in the field during observation. a) Set up the level instrument so that you can see a staff placed on a control point (assume a height of 15.120m) and no more than 25 metres from it, then take a backsight reading to the staff. b) The staff should be moved to another point towards (change point) or possibly on one of your control points (no more than 25 metres for the instrument) and a foresight reading taken to it. c) Keeping the staff at this point, move the level instrument to a point so that it can take a backsight reading to the staff and foresight to the next point. d) Reduce your levels whilst you are observing, in the field, by determining the rise or fall between each pair of readings from an instrument position. Also calculate the height of each point.
e) Repeat this process, so that the staff should visit each of the points which are to be change points (CP) – that is a backsight and foresight are taken to the staff from different instrument positions. f) Complete the level loop by taking the final foresight to a staff on the bench mark. g) Calculate the checks on the measurement and calculations: Sum of backsights minus the sum of the foresights, sum of the rises minus the sum of the falls, and the difference between the last height and the first height should all be the same. Since you started and finished on the same point this difference should equal to zero. Any difference from the known height difference of the points is the misclosure. Assess your misclosure – if it is large the measurements should be re-observed.
• Perform the calculations of Rise, Fall, Heights and checks as outlined above. • Abstract the heights of the points required and list separately as these are the results of the task.
Prepare a report, to be included in the portfolio for component 1, on the exercise containing the following:
• A brief description of the task • Equipment used • A brief description of the procedure / method. • Discussion of the results considering: o The size of the misclosure obtained in your level loop o Sources of error in the measurement – Assess the possible size of each and their effect on the result. o How errors can be reduced or removed from the measurement process. o Prepare a set of guidelines for high precision measurement practice in view of your experiences.