Unitec Institute of Technology Land Surveying 2 (2015) (ENGG & DE6207) Assignment No. 2 (10% of total course) “Precise Levelling Observations, Reductions & Analysis” Due Date: 20 April 2015 Introduction Precise Levelling is one of the functions a surveyor can be required to undertake as part of the process of establishing reliable height information on a project. Nearly all construction & infrastructure projects require reliable level and height information, to varying degrees of precision and accuracy. It is common for such information to be at the high end of the accuracy scale, requiring suitable techniques and instrumentation to establish reliable and accurate values. Accordingly, as with construction setout, precise levelling is an important skill to understand and learn. Correct and accurate level information is required for different purposes, some examples of which are as follows: For overall, project network control purposes. To enable setout height information to meet certain tolerance limits. Monitoring purposes as part of any post construction phase, or where such monitoring is required during specific parts of construction. As per normal surveying practice, reduced level information supplied by the surveyor must be correct. As such, it is vital that independent checks are completed as part of the observation process to ensure such reliability. In general, the main criterion is to have sufficient redundancy to ensure any gross errors are found and rectified. This is normally achieved by completing independent check observations and measurements. Assignment Details For this assignment, you will be required to complete a full set of precise levelling observations in terms of established Unitec benchmarks C2A & Y5. In addition, you are required to observe to marks C3, C4, C5 & C6, Y6A as part of the observational process, with the aim of deriving final reduced level values for these marks in terms of the LINZ 2V order level origin values provided herein. The field levelling observations will be completed in groups of 3, however every team member must complete their own precise levelling observation-run between BMs, and be involved in assisting their team members to complete theirs, by holding the levelling staff in a vertical and stable manner, and measuring and monitoring distances between change points as required. Note that this includes the completion of a separate 2-peg collimation-calibration test before the completion of each observation period. Results are to be processed and analysed on an individual basis, with individual reports submitted for assessment purposes. If you miss this initial calibration test requirement, you will need to redo all your levelling observations, so don’t forget ! Observing Specifications The following requirements apply: Use double run levelling. Use the “BF-FB Line Levelling” method of levelling. Maximum 25m for each forward/backsight distance. Sight and Crest Clearance (except on elevated PRMs). Sight Distances. Sight Imbalances. Height Misclosure of Run. ≤ 0.5m 5m ≤ D ≤ 25m I ≤ ± 0.5m ΣI ≤ ± 2.0m Δ ≤ ± 2mm x √L where D is the sight distance, I is the single set-up sight distance imbalance, L is the approximate length (in Kilometres) of the levelling run and Δ is the misclosure. A “Run” is closed when you return to (FS) the benchmark where you first started the BFFB line levelling sequence. Field observations will need to form a closed-loop in both directions between the specified benchmarks, with appropriate attention paid to minimising errors, such as collimation, equalising backsights and foresights and the like. Equipment Each group should ensure that they have the following levelling equipment: 1 x Digital Level (with at least 2 x instrument batteries) 2 x Digital Level Staves with staff bubbles (if windy: bring support poles) 1 x Tripod (sturdy) 1 x Field Bag: 2 x Change Plates (minimum); 30 m tape; Chalk The precise levelling instruments (Leica DNA03, or Trimble DiNi)) will be available for completion of this assignment, although you will need to book them through David Poyner (Unitec Survey Technician) to ensure all groups have access to the equipment to allow completion of the field work as necessary. Practical Procedure Details of the operation of the digital level to complete this practical assignment have been provided during the lectures. Practical procedure details are as follows: Each group will be allocated the same level run, which will be approximately 0.7km long. The run will connect the two existing BMs, and there are a series of five new BMs along the route to be observed. Duties of observer, booker, and staff person are to be rotated, with one complete run to be undertaken by each group member. A collimation check of the level is required, before levelling commences and immediately after the completed levelling operation. The results of these collimation checks are to be included within the final report. Change Point (CP) setting out is to be shared and should be carried out in the most effective manner. The levelling staves need to be handled with care – only extend as far as required. Caution must always be taken with regard to your own safety, pedestrian safety and when working alongside roadways. It is the responsibility of all members of the field party to ensure appropriate safety measures are in place, and due care and attention is paid to identification of hazards. Correct PPE must be worn at all times during this field assignment. Further, it is essential that the levelling staves are held vertically and in a stable manner at all times. This is necessary to avoid rework due to excessive misclosure and to provide the best chance of achieving the required accuracies. Change-plates are to be used as CPs for the staves. Plates need to be seated by (gently) stepping on the change-plate supplied to ensure a stable platform for the staff. Upon commencement of your levelling runs, initially allow the levelling instrument to adapt to the ambient temperature prior to commencing work; The observer assumes control of operations and should determine what length sight-distances will be used when setting out. Some factors to be considered are: wind, air pollutants, heat shimmer and access roads. The observer will indicate when staff personnel can remove their staves, pins, or change-plates. It is desirable to carry out observations at a consistent and even pace, at each set-up. Benchmark Information Benchmark Approx. Northing Approx. Easting Point C2A Point Y5 395135mE 394717mE 799872mN 799892mN Reduced Level (Ak MSL Datum 1946) 27.9307m 23.0241m Precise levelling data can be processed using the levelling module within the Leica Geo Office programme (version 8.3) for which Unitec has licences currently operating. These can be accessed via any of the computer labs. Figure 1 – Unitec site & levelling mark locations Report Format This assignment is to be presented using a short report structure using a conventional word processing package. The various elements to be contained within this format are as follows: Levelling methods and processes utilised. Relevant group details, observation dates, etc Reduction of data (to enable final results to be determined). Independent field checks completed and levelling closures achieved. Processing of results through appropriate software package. Presentation of final precise levelling results for the three unknown marks. Summary & conclusions Note that presentation is again important, so make the effort to submit a report of suitable quality and content. Total mark for this section of the assignment will be 10% of the total course mark. Due date for this assignment will be 20 April 2015, by 1:00pm.
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