Is it laid out correctly? Does it look right? These are fundamental questions that all field engineers should ask themselves after establishing any points in the field. This article provides some helpful hints experienced surveyors and layout persons have suggested on what they looked for when they were performing layout, and what they continue to look for as they walk the jobsite now. As can be expected, most of their suggestions are common-sense approaches to reviewing the work.
Step Back, Look At It and Question It
After laying something out, walk 50 or more feet away from the layout and look it over. Eyeball things for proper alignment, grade, etc. Does it look like you visualized it? Do the distances look right? Do the columns line up? Are they supposed to?
Has a common-sense approach to layout been used? Could a different approach be taken? Were there violations of standard practices?
Watch for too much control in a small area. Several lines or stakes within a few feet of each other is confusing. Look for improper markings on stakes; in haste, someone may have marked a stake as being offset 5 feet when it is actually 10 feet.
Re-measure if Necessary
Come in from a different direction to check critical points. This is a method that must be used frequently, especially when coordinates are being used as the basis of the layout system. The only way to discover some mistakes is to do it differently. If you performed the layout using steps A-B-C, do not check by using steps A-B-C or even steps C-B-A! Use steps D-E-F as quick check and steps X-Y-Z for an extreme check. In other words, checking from a different direction and by a completely different and independent method is what is required.
Cross-check measured distances. Measure diagonals if possible. Use the 3/4/5 method to check 90-degree angles. When measuring angles, use the Close-the-Horizon method of summing the angles to check their total.
Check dimensions of work already in place. Check old work to see if it meets the tolerances established. Check new work to see if you are obtaining the same results. Any deviation indicates a problem in procedures or instrumentation.
Calibrate it First
New equipment should always go through a calibration check. Calibration should be performed for transits and theodolites, levels, site levels, rods and especially chains. Theodolites should be checked for proper internal geometric relationships. Levels should be pegged to confirm that a horizontal line of sight exists.
Only after each new piece of equipment has been personally checked, should it be used for layout work.
Get Another Opinion
If the points are very critical and the outcome of the project depends on the points being absolutely correct, it may be necessary to ask someone else to perform the check such as another crew or even an outside consultant. If others do come in, they should check using independent methods and their own equipment.
If you don’t have the luxury of another crew, or money to spend on an outside consultant, ask the most experienced person on the jobsite to review your methods and procedures. Your work will be looked at from a different perspective and detailed questions will be asked. A second opinion is always helpful.
If problems in layout are encountered, don’t forget to check the project control. Are the project control points disturbed? Has heavy equipment been working next to the control points? Measure angles and distances at the control points to confirm their location. Re-calculate the coordinates for the control points and compare them to the original calculations. Re-measure angles and distances from the primary control points to secondary control points. Any deviation from the original work should be thoroughly investigated and analyzed.
One of the fundamental mistakes new surveyors make is they don’t understand that tolerances vary for the different types of work on the jobsite. Rough staking of the site work might only need to be within a foot, and measuring them to the same tolerance as anchor bolts is a waste of time and money. If tolerances aren’t understood, ask several others on the site with experience. Use their judgment and yours to determine if the layout is acceptable.
Don’t try to achieve the impossible. Sometimes the tolerances found in the specifications are unreasonable. After all, architects don’t build buildings. Review with others who have been field engineers and with your local equipment dealer to see if it is physically possible to achieve the stated tolerance. It may not be possible. If so, have the superintendent discuss the issue with the architect and owner to educate them about what is achievable.
Consult with Subcontractors
Sometimes an excellent source for checking work is to talk to subcontractors. See if their needs are being met by your layout. They have to make their work fit around the work of others and are sometimes the first to find out if things aren’t fitting properly. They may not have said anything earlier since they are able to force things to fit, but in reality, their work would proceed better if the layout was exactly correct. Ask them. They may see something you haven’t thought about.
Speak up at jobsite meetings when the schedule is reviewed. A major source of error in surveying layout doesn’t come from the quality of measurements; rather, it comes from a lack of planning the surveyor’s time. When surveyors are supposed to be in two or three places at one time, something will suffer. Ultimately, it may be the accuracy of the work. With a little better planning of the surveryor’s time on the jobsite, adequate time should be allotted to each layout activity. If it isn’t, justify your time requirements and speak up!
These comments are just the tip of the iceberg related to common-sense checks of construction layout. Perhaps if you, the readers, are helpful and submit your own methods of checking layout, a “Part 2” article can be written. Contact me by E-mail at firstname.lastname@example.org to submit your methods of checking layout work.