Site Engineering Guide

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Site Engineering Guide INSTRUMENT & ACESSORIES CARE Updated: 07/01/13 Andrew Burgess B.Sc Hons www.ajb-settingout.co.

1 Site Engineering Guide INSTRUMENT & ACESSORIES CARE Updated: 07/01/13 Andrew Burgess B.Sc Hons This resource is protected by United Kingdom and International copyright laws and may not be used, other than for non-profit, educational purposes, without the express permission of Andrew Burgess.

2 INTRODUCTION INSTRUMENT & ACESSORIES CARE Most site engineers will know of the importance of looking after the surveying instruments e.g. Total Station and Automatic Level; however may over look the importance of the tripod, prisms and staffs employed in accurately measuring and setting out. All the equipment used must be maintained regularly otherwise the careful and precise field work you undertake will be erased by the use of inaccurate and imprecise equipment and accessories. AFTER WORKING IN WET WEATHER When working in wet weather conditions you should ensure that the instrument cases are properly closed, this is not to suggest that this is the only time that this should be done, as instrument cases should be kept closed at all times to prevent the ingress of dirt and dust which may cause damage to the instrument. Figure 1 below shows the steps required to maintain an instrument after use in rainfall. 1. Remove the instrument from its box and place on a level and safe surface on top of a paper towel or cloth to absorb the run off. 2. Using a paper towel or soft cloth carefully wipe down the body of the instrument to remove the bulk of the water, not forgetting to wipe in between the telescope and Tribrach 3. Do not use a paper towel, soft cloth or anything else to touch the optics on the instrument, use only the cloth supplied with the instrument in its case or alternatively allow drying naturally. 4. Wipe clean the instrument case and leave open to allow the inside of the case to dry out along with the instrument. 5. Check to ensure that the instrument case contains a silica gel pouch to absorb any moisture that may still be present with the case or instrument when packing up and returning the equipment to storage after completing the drying process. If no pouch is available, attempt to source one. Figure 1: How to maintain an instrument after use in wet weather A J Burgess 2012 Page 2 of 15

3 TRIPODS Tip NEVER put an instrument cased away when wet, always dry instruments out thoroughly before packing away. Ensure a silica gel sachet(s) is included in the case to absorb any remaining moisture while in storage. Alternatively rice may be used as an absorbing agent when no silica gel is available. Maintenance of your tripods will ensure the accuracy of the total station or indeed any other surveying instrument. Unmaintained tripods have the potential for movement after an instrument has been set up on station and levelled, the issue can be aggravated if using a robotic tripod due to the increase in weight and the servo-driven starting and stopping of the instrument causes torque. Selection It is important to select the right tripod for the instrument see table 1 below to determine which type of tripod should be used with what instrument. Tripod Type/Construction Material Instrument L/Duty H/Duty Fibreglass Timber Aluminium* Aluminium Automatic Level Rotating Laser Level Grade Laser Single or Dual Prism Station/Target Total Station Robotic Total Station * Some light weight aluminium tripod feature a reduced head size and are only suitable for lasers or automatic levels where you do not require flexibility to centre over a point. Table 1: Tripod Selection Storage Tripods should be stored ideal laid flat on a shelf however this is usually impractical on site and so should be stored in either an upright position with the feet touching the floor or alternatively if the tripod has the protective cap for the head and only if it is fitted be stored with it head touching the floor. Under no circumstances should you allow any materials or plant to be stored on top of your tripods. When starting any surveying or setting out operation and removing the tripod from storage you should inspect your tripods for any obvious signs of damage. After working in wet weather, if possible and practical open up the tripod as you would normally do to set up an instrument and allow drying before completely closing up and packing away. They can hold a surprising amount of water within their construction. A J Burgess 2012 Page 3 of 15

left. 2. Extend all the legs of the tripod and lock, keeping the tripod vertical, raise one leg at a time horizontal and release, the ideal stiffness is when the leg gently drops to the ground.

4 Maintenance Should be carried out anywhere between weekly and monthly depending on usage and as you deem suitable. 1. Check the tips on the tripod feet, are any missing or lose or in need of replacement as shown in figure 2 left. 2. Extend all the legs of the tripod and lock, keeping the tripod vertical, raise one leg at a time horizontal and release, the ideal stiffness is when the leg gently drops to the ground. Adjust the hinges as required. 3. Visually inspect the dowels at the top of the leg where it inserts into the hinge to ensure that it is not damaged and is securely attached, as shown in figure 3 left. 4. The clamps used to tighten the sliding legs should be lubricated and if they require an excessive amount of tightening to secure then they most likely need adjustment and or replacement parts, as shown in figure 4 left. 5. Wipe clean the legs with a soft cloth to remove any dust before applying a sparing amount of lubrication to the sliding parts. Stickiness when extending or retracting the legs can be caused by damage to the paint finish or the presence of foreign materials e.g. concrete splatters on the legs. If this is the cause then it would mean that the legs require refinishing or alternatively a through clean. 6. Finally inspect the tripod head surface; it should be smooth, test by running your fingers over the head to feel for any irregularities in the surface as shown in figure 5 left. If there are any then you ve not been using the protective cap supplied by most manufacturers and the irregularity in the heads surface may cause difficulty when attempting to level an instrument. Figures 2-5 (Left: Top Down): Tripod checks. PRISM POLES Prism pole which is inclusive of all types e.g. detail poles and mini prism poles are surveying instruments in themselves and should not be used for any other purpose than taking measurements, e.g. digging or as a hatchet to remove vegetation obstructing clear lines of sight. When used in wet or muddy conditions they should be wiped clean, and then allowed to dry out completely. Light oil lubrication should be applied to the prism point and thread and to the brass adjustable tip on which the prism is mounted. No lubrication should be applied to the sliding section of the pole at all. A J Burgess 2012 Page 4 of 15

Maintenance There are several methods of checking the accuracy of the circular vial bubble; some survey accessory manufacturers have produced wall mounted jigs for calibrating poles, another produces

5 They should be regularly checked for accuracy of the circular vial bubble, which is heavily relied upon when taking any measurements. Checking the accuracy of the prism pole is yet another method of ensuring accurate setting out and measuring and is in no means a substitute for poor field procedure. Maintenance There are several methods of checking the accuracy of the circular vial bubble; some survey accessory manufacturers have produced wall mounted jigs for calibrating poles, another produces a clamp called steady-rest which when used in conjunction with a tripod can convert your prism pole into a stable prism station. Below the method utilising a steady-rest and a plumb bob and door frame are described. Using a Plumb bob Required Equipment: Pin/Tack, Pencil, Plumb Bob*, Prism Pole, additional Prism Pole Point and Hex keys 1. Find a suitable door frame, with a hard surface on the threshold that can be marked using a pencil, using a push pin; suspend a plumb bob from the pin as pictured in figure 6 left. 2. When the plumb bob has settled down, mark the point on the floor, leaving you with two points on a true plumb line. *Alternatively you could use a laser plumb bob as used by drywall fixers for wall head track 3. Using an additional point, from another pole, screw the point onto the top of the pole, locate the bottom point on your mark, extend the pole as required and locate the top mark with the top point and lock off as pictured in figure 7 right. The circular vial bubble if in adjustment will be centred correctly, if not you need to adjust. 4. Using a suitable size hex hey, adjust the three grub screws at the underside of the circular vial bubble to centre the bubble within circle, making small adjustments to each grub screw to avoid over compensating. Figure 8 below shows prism pole adjustment in progress. 5. Once completed, turn the prism 180 o to ensure that the bubble is true and remains within the circle Figures 6 &7(Left): Preparing to check a Prism Bubble A J Burgess 2012 Page 5 of 15

Figure 8: Prism Pole adjustment in Process Identifying if any adjustment is required, adjusting and checking Using a Steady-rest Required Equipment: Tripod, Steady-rest, Prism Pole and Hex keys TAPES

6 Figure 8: Prism Pole adjustment in Process Identifying if any adjustment is required, adjusting and checking Using a Steady-rest Required Equipment: Tripod, Steady-rest, Prism Pole and Hex keys TAPES 1. Set up a tripod on a smooth hard surface and attached to steady-rest to the 5/8 th clamp 2. Clip the prism pole into the steady-rest and adjust the pole/holder/tripod assembly until the circular vial bubble is centred. 3. Rotate the prism pole 180 o and check the circular vial bubble. The bubble should remain centred, if not adjustment is required 4. To adjust the bubble vial, using a suitable size hex key adjust the three grub screws on the underside of the circular vial bubble, adjusting out half the error. Be careful to adjust all three screws equally to ensure you don t run out of thread and make small adjustments to avoid over compensating. 5. To check the adjustment, repeat step 2 on until the bubble remain in the circle when turned 180 o Tape measures are again easily over looked and an engineer will most likely use a tape measure of some description whether it is a 5m pocket tape or 30m tape daily in their duties. Tape measures of Class II or better should be used for setting out; tapes are marked with roman numerals inside an oval as shown below in figure 9, typically located at the start of the tape. For accurate measurement use a class I tape, class I tapes typically have a blank end, with the zero mark starting some mm inside from the hook/loop of the tape. Class II tapes have zero starting at the hook/loop. II I Figure 9: Tape Classification Markings A J Burgess 2012 Page 6 of 15

Tapes that are unclassified or manufactured from fabric or fibreglass should not be used for accurate work but instead for approximate works such as marking out excavation.

7 Tapes that are unclassified or manufactured from fabric or fibreglass should not be used for accurate work but instead for approximate works such as marking out excavation. Figure 10 below shows how to identify classified and unclassified tape measures. Avoid kinks and twists when taking measurements Tape measures should be wiped clean of mud and dirt before winding in Wiped dry if used in wet conditions Regularly given a light coating of oil to the mechanism and tape itself if manufactured from steel to prevent surface corrosion. Visually be inspected for loose, end hooks and kinks which will lead to inaccuracies, removing any damaged tapes from service. See Figure 10 below for a loose hook and worn tape with the loss of mm markings at the beginning of the tape measure. Regular check against a steel tape measure which is set aside purposely for the checking of tapes and not for field use. Tip When measuring NEVER rely on the end of a tape measure, the hook will invariable become loose over time, instead when measuring, always use the 100mm mark and adjust your measurements accordingly. Figure 10: Tape Measure Classification and Wearing damage. LEVELS (AUTOMATIC & LASER) - TWO PEG TEST Select two points, point A and Point B, 30 metres apart. Having selected your points, if soft ground, then drive two pegs in, otherwise for hard surfaces such as tarmac and concrete drive in two surveying nails. Set up the instrument exactly half-way between points A and B with an accuracy of 0.5m as shown in the figure 11 below. A J Burgess 2012 Page 7 of 15

8 Figure 11 Sight and record the staff reading at Point A Sight and record the staff reading at Point B Relocate the instrument to 1m beyond the back sight (Point B) as shown in figure 12 below Figure 12 Sight and record the staff reading at Point A Sight and record the staff reading at Point B Now calculate the differences between Points A and B in setup 1 and setup 2. Subtracting from the highest. The difference between the figures obtained from setup 1 and 2 is the collimation error and should be +/- 2mm. In the event of an error greater than +/-2mm, repeat the exercise to ensure the result is not from an observation error. If still out of tolerance adjust the instrument if capable and confident otherwise send away for servicing and adjustment. TIP Use the Two Peg Test Sheet found in the appendix to both record your results and act as an aide moiré. The sheet also makes a useful QA record for site records. A J Burgess 2012 Page 8 of 15

9 PRISM STATION (HALF TRAVERSE) Plate Bubble Orientate the instrument and torpedo bubble to be parallel with two Tribrach foot screws and level the bubble. Turn the instrument 90 o and level the bubble using the third foot screw. Turn back 90 o, adjust if required as before. Turn 180 o, the bubble should be central within the torpedo level if adjusted correctly. If not repeat the procedure again to determine if any errors were made during the procedure before adjusting or sending the instrument away for servicing and adjustments. Optical Plummet Mark a cross target on the surface, using pen, self adhesive retro reflective sticker or cartridge nail. Set up the instrument as you would normally. Turn the instrument 180 o whilst simultaneously observing the plummet If the point does not remain central throughout the rotation then the instrument requires servicing and adjusting. TOTAL STATION Plate Bubble Orientate the instrument and torpedo bubble to be parallel with two Tribrach foot screws and level the bubble. Turn the instrument 90 o and level the bubble using the third foot screw. Turn back 90 o, adjust if required as before. Turn 180 o, the bubble should be central within the torpedo level if adjusted correctly. If not repeat the procedure again to determine if any errors were made during the procedure before adjusting or sending the instrument away for servicing and adjustments. Optical Plummet Mark a cross target on the surface, using pen, self adhesive retro reflective sticker or cartridge nail. Set up the instrument as you would normally. Turn the instrument 180 o whilst simultaneously observing the plummet If the point does not remain central throughout the rotation then the instrument requires servicing and adjusting. A J Burgess 2012 Page 9 of 15

10 Horizontal Collimation Using the instrument as set up and correctly levelled having past the first two tests Sight a prism station located 100m distance away from the total station as shown in Figure 13, alternatively a distance fixed object e.g. a church spire flag pole, the corner of a multi-storey building and record the Horizontal Angle Reading in Face Left: angle H 1 Now repeat the sight only in Face Right: angle H 2 The difference between H 1 and H 2 should be 180 o + 00 o if the instrument is operating correctly. Figure 13: Horizontal Collimation Check Vertical Collimation Figure 14: Vertical Collimation Check Using the instrument as set up and correctly levelled having past the first three tests Sight the same prism station located a distance of 100m away from the total station as done in the horizontal collimation check or alternatively a well defined elevated object e.g. a coping, roof ridge or window sill and record the Vertical Angle Reading in Face Left: angle V 1 A J Burgess 2012 Page 10 of 15

11 Now repeat the sight only in Face Right: angle V 2 There should be no difference between V 1 and V 2, if the instrument is correctly adjusted as demonstrated in figure 14. Trunnion Axis Figure 15: Trunion Axis Using the instrument as set up and correctly levelled having completed the previous checks Lay a levelling staff on the ground, relatively close to the instrument or alternatively a tape measure. Sight the prism station as previously used or alternatively a well defined elevated point or object and centre the cross hairs in Face Left. Now sight the telescope at the levelling staff or tape measure and record the reading T 1. Repeat the exercise in Face Right and record T 2. The readings T 1 and T 2 should be equal. Distance Check Figure 16: Distance Check Layout Create a base line that is 100m long, with nails/pegs at chainage 0m, 50m and 100m as shown in figure 16. Set up at Point B (Chainage 50m) and backsight Point A (Chainage 0m). Taking three horizontal distance measurements B-A and obtaining the mean distance. Do not record a slope distance as this will produce an erroneous result. Still on Point B, foresight Point C (Chainage 100m) and again taking three horizontal distance measurements B-C and calculate the mean. A J Burgess 2012 Page 11 of 15

12 Calculate the total of the two mean results obtained so far. Now relocate to Point A (Chainage 0m) and foresight Point C (Chainage 100m) again taking three horizontal distance measurements A-C and obtain the mean. Compare the mean result obtain now A-C with the total calculated from the combined total of B-A and B-C TIP Use the Total Station Test Sheet found in the appendix to both record your results and act as an aide moiré. The sheet also makes a useful QA record for site records. GENERAL TOOLS This includes all the other tools you may have collected and require as described in the tools and marking out accessories chapter. After every use if they have been used in muddy or wet conditions tools such as hammers etc should be wiped clean of mud and allowed to dry before the application of a little oil or lubrication too inhibit the formation of rust. Visually inspect the heads of hammers: - The striking face for signs damage of damage e.g. chips, cracks or mushrooming around the edges Loose or broken handles replace or repair as required Safety Tip NEVER strike any hardened steel surface with a steel claw hammer A J Burgess 2012 Page 12 of 15

13 APPENDIX Two Peg Test Sheet Total Station Check Sheet A J Burgess 2012 Page 13 of 15

14 Instrument type: Serial No: Checked By: Calibration Due: Date Checked: Weather Conditions: Point A and B to be either Pegs/Pins in soft ground or survey nails in a hard surface. Instrument to be located on same line as Points A and B Pt A Setup 1 Pt B * +/- 0.5m 15m 15m Pt A Pt B Setup 2 30m 1m Visual inspection of instrument: No damage, loose screws or water ingress Pass / Fail Rotate instrument 180 Circular bubble remains central (Self levelling laser N/A) Setup 1 Setup 2 Setup location 1 Setup location 2 Point A reading Allowable collimation error +/- 2mm Point B Reading Δ Setup 1 Δ Setup 2 Pass / Fail Δ Pt A - Pt B (Highest Lowest) If Error greater than 2mm, repeat to ensure no observation errors, before adjusting instrument Notes: Instrument has been found to be NOT* within allowable tolerances Signed: (* Delete as necessary)

15 Instrument type: Serial No: Checked By: Calibration Due: Date Checked: Weather Conditions: Plate Bubble Check Orientate the instrument and torpedo bubble to be parallel with two Tribrach foot screws and level the bubble. Turn the instrument 90 o and level the bubble using the third foot screw. Turn back 90 o, adjust if required as before. Turn 180 o, the bubble should be central within the torpedo level if in adjustment. Optical Plummet Check Level and plumb the instrument as normal over a cross or nail. Turn the instrument 180 o whilst simultaneously observing the plummet If the point remains central throughout the rotation then the instrument is in adjustment. Horizontal Collimation Check Face Left (FL): Face Right (FR): FR-FL: = 180 o + Misclosure Misclosure < 00 o = Pass Vertical Collimation Check Face Left = Face Right Misclosure < 00 o = Pass Trunnion Axis Check Face Left Staff/Tape Reading: Face Right Staff/Tape Reading: Misclosure < 00 o = Pass Pass Fail Pass Fail Pass Fail Pass Fail Pass Fail Distance Measurement Check Distance B-A Mean Distance B-C Mean Calculated total A-C Distance A-C Mean Error (Calc Total A-C Distance A-C) mm Repeat failed checks to ensure no observational or procedural errors exist. Instrument has been found to be NOT* within allowable tolerances Signed: (* Delete as necessary) Pass Fail A J Burgess 2012 Page 15 of 15

TO RECEIVE the most benefit from a

Using Surveying Equipment TO RECEIVE the most benefit from a tool, it must be used properly. In addition, it must be well maintained. In most cases, the user will need some instruction and training regarding