Download - Engineering Surveyor

Levelling instrumentsWhether the site engineer is measuring levels (eg for original ground levels or completed work) or providing levels(eg for blinding level for slab), the principles are similar.Using and setting-up an optical level check collimation of instrument at least weekly (two-peg test) ensure firm base and comfortable telescope height avoid traffic and other vibration where possible arrange back-sight to be approximately equal to fore-sight do not leave instrument unattended.Use of change pointsUse peg, footplate or other convenient point to: avoid sighting more than, say, 40 m cater for large changes in ground level cope with obstructions.Use of staff check that staff is undamaged ensure staff is held vertical or rocked (if no bubble is fitted) minimise use of extended staff. If extension used, check catch is fully engaged avoid sighting on bottom 0.5 m of staff (refraction is severe near ground) use inverted staff to measure soffit levels (book reading on staff as negative) having marked a given level (eg floor level) on a vertical surface (eg column face), the assistant shouldremove staff and reset staff to the mark before a check observation is made a tape is sometimes substituted for a staff (eg in a shaft).Use of TBMs check for signs of disturbance and check reduced levels regularly transfer to permanent works as soon as practicable open and close levelling runs on different TBMs whenever possible check closing error is within acceptable limits.Other levelling methods levels can be transferred by spirit level or water level a rotating laser can provide a horizontal reference plane but must be regularly checked against an opticallevel.Use of precise optical level for establishing primary control on a large or extensive construction site for time-dependent deflections, eg pile load tests for precise levelling of mechanical equipment.Use of digital levelsDigital levels use infrared or laser to take a reading from a bar-coded staff. When using digital levels: read the manufacturer’s literature follow the same working practices as with traditional optical levels to reduce traversing errors ensure that the staff is always held vertical the staff must be in a well-lit area – self-illuminating staffs are available the infrared/laser may be affected by ambient conditions, eg heat haze, air temperature changes, whichcause refraction errors.CIRIA C70941