what gps field crews can learn from...

G PS for civil construction is a new technology. We have benefited from meteoric

growth in the equipment and its adoption. Many of us can clearly remember having the surveyor come out and stake the job. Things have progressed quickly and we enjoy the combination of a surveyors work and GPS accuracy to supplement it. Before GPS, jobs were built well and contractors made money.

Fast forward and we have raised the bar, not only in technology but speed as well. I always tell new GPS users to never forget how they did things before they got the new toys. With that in mind, I would now like to take a look at some of the basic survey functions in use for years that will improve your productivity.

Initial Job ReviewA critical function of a surveyor is to confirm the property boundaries and the limits of work. Usually the contrac-tor will occupy the same points used by the surveyor for the localization/calibration of the site. If the surveyor has not set perimeter control you will need to get it correctly established.

When you have set the job up, make sure you and the surveyor agree on the localization. This will save you untold issues in the future. It is not uncommon to have trouble establishing control on a job. Take your time with this step,

everything else is going to be dependant on the quality of the first step. The image shows the coordinate geometry (COGO) of a property line as well as the location of property pins/corners. Things move and change, view these with caution and proceed accordingly.

When you are happy with the job orientation of a site, it is now time to make sure everything fits.

Critical DimensionsThe best laid plans sometimes need to change. The term “critical dimensions” refer to the things that have to be that size and no different. Examples are building size, entry dimensions and retention volumes. These need to be

set up on the site first, leaving room for adjustments in the not as critical areas.

The example here shows a soccer field for a school project. The fiels has slopes that tie to the existing ground on all four sides. If there are unseen conditions found on the site, the field can be moved. Let’s say there is rock found on the west side of the field, it can be moved to the east. The critical dimension of the soccer field needs to be maintained.

The opportunity also exists to use the soccer field to help balance the dirt quantities on the site. In this instance, the field can be moved in three dimensions to accomplish this. Here is the way to go about it; perform a takeoff of the site and review the quantities. Some takeoff

What GPS Field Crews Can Learn From Surveyors

MARCO CECALA

Make sure the job is localized correctly and you are in sync with the surveyor.

continued on page 60

Displayed with permission • Machine Control Magazine • Vol. 3 No. 2 • Copyright 2013 Spatial Media • www.machinecontrolonline.com

programs may allow you to balance the site by adjusting specific areas. The site can also be moved manually and raised or lowered to make the earthwork balance.

While this may not be what a surveyor will do on every job, there is no reason you cannot. Refer to these tips;

◾ Any ideas you come up with need to be cleared through the design engineer. ◾ This is easier to do in private work than public jobs. ◾ The best takeoffs have bore logs included and entered in the takeoff software. This will let you know how you change material types as well as quantities. ◾ Never ask a question unless you know the answer. Will the job still drain? Is access affected? How much money will the owner save with the change?

With the critical dimension areas veri-fied, you need to review what is going to happen in order to fit everything required. Most jobs have non-critical areas in between the absolute ones. Green space is one good example. Many municipalities have requirements for green space in new improvements, if things are really off, you may need to confirm required percent-ages. On small, busy sites you may run out of room and have to make up green space somewhere else. There have been times where parking spaces had to be removed in order to accommodate green space requirements. In one particular instance, the parking was able to be retained; cel-lular grassed paving was used as parking as well as green space.

It seems the biggest issues with adjust-ing the job come with maintaining proper retention volumes. During excavation,

subsurface conditions can cause issues. Utilities or rock can make further work more expensive or impossible. If the site is large enough, the retention is sized accordingly and work continues. With smaller sites and infill projects, this is not always an option. Underground retentions have become a regular feature in sites. When building data for under-ground retentions on large sites, we often make ramps for scrapers to efficiently move material for the pipe installation.

In order to propose a change to a retention area, you need to know the

design volume required. Review the plans for the calculations provided by the engineer. Many software programs have commands for calculating volumes in retention ponds. It pays to know the proposed change will work before you run it up the food chain. You will not only look professional, it saves time.

We often times need to get involved with innovative solutions on dense sites. Even though underground retention is much more expensive than a pond, it’s cheaper than losing parking or retail space. On one project, a small

The soccer field can move a bit, it still needs to be the correct dimensions.

Cecala, continued from page 64


underground storage combined with the new smaller pond has given us solution to a difficult problem. Think outside the box.

Grid LayoutBefore GPS allowed a contractor to run out to a site and start working, the surveyor would set up some initial stakes for areas of large cut and fill. Often times the surveyor would perform grid staking at a specified horizontal interval. The surveyor still needs to stake critical items and verify the contractors work. What the contractor can now do is a lower accuracy version using GPS and some paint.

I take a can of red and a can of blue upside down marking paint and tape them together at the bottom to make my cut/fill marker. Using GPS you can now follow a grid, or just make paint marks on the dirt at random distances. Red for cut and blue for fill will guide the rough grading equipment to start to job and provide just enough information as the job get closer to grade. The marks get wiped out on a regular basis; a grade checker can stay busy.

This rough marking technique is not very accurate; I use it to get within a foot or so of grade. With big cuts and fills it helps to give an operator an idea of how

to shape the initial surface and what things are going to look like later.

Points become surfacesWhen GPS became portable enough for surveyors, the software written was for them. All the normal commands that were used with a total station and a helper on a pole were now in the hands of one individual with a base and rover.

The first data collectors for GPS were able to store only points. Line work and surfaces came later. In the early days we could make a lot of points look like a surface, but were limited by file size requirements. We were sent out to stake points that pertained to the task at hand. Roads would get cross section stake out and a site would get grid or details.

With power comes responsibility. Commands meant for survey can

Not a lot of room. The building on the right and property line on the left leaves little room for adjustment.

This retention got pushed to the Northeast in order to preserve water volumes.


radically change what a job looks like quickly. The manufacturers of GPS equipment knew that a grade checker in the field would not need the horsepower of survey commands on a data collector. The mere presence of the commands could cause problems if improperly used. Specific collectors and software became the norm for GPS field crews. Some of our clients want more options and have upgraded to survey software on their rovers. It is a natural progression for those who are dedicated to learning and utilizing everything the technology has to offer.

The biggest jump in usability for GPS field crews came when surfaces could be loaded into a data collector and line work added. The transition from point stakeout to surface visualization was a reality. No longer was it required to adjust between stakes, the surface file would take care of that. The job could be built numerous times in the office before moving dirt. This increases accuracy and reduces rework.

Team EffortThe surveyor has the difficult task of staking the job and making sure everything gets done correctly. A contractor now has much of the same information at their disposal. When they work together the combined efforts increase productivity dramatically.

We build a lot of data for both surveyors and contractors. We find that when the surveyor contracts with us to build a job, it goes smoother. The reason is that the surveyor gives the file to the contractor to use for grading and layout. Surveyor’s come in for critical areas and confirmation, but a fair amount of the job can be started by the contractor. Control/localization is confirmed and

the surveyor has reviewed the data and will be able to submit intelligent requests for any problems at the start of the job saving time and energy.

When a contractor offers a model to a surveyor, it is often times viewed with hesitation. The surveyor has a responsi-bility to make sure everything is correct. It is usually easier to just do the work from scratch than to review someone else’s work. A surveyor may not find the need to build a complete surface for a job and therefore cannot even do a basic comparison to the contractor’s model.

The best way to develop a relationship in this instance is to check into the surveyor’s stakes and confirm your information is the same. If you see something different, consult with the surveyor so it can be remedied before

moving too much dirt. Everybody will benefit when issues are discovered early. When differences happen more than a few times, it becomes better for everyone to be working on the same model. Either share yours or theirs. If review is necessary, the time it takes to work out the issues on the screen and paper plans is much shorter than constant meetings in the field. If your model was the one with inconstancies, go to school on the experience. What did you do to make it not conform and most importantly what can be done to make a better one the next time. MC

Marco Cecala is the owner of Take-off Professionals in Arizona and is a nationally-known expert and teacher of CAD, automated surveying and machine guidance.

Paint cut numbers in red (and fill in blue) on the ground for rough grading.


what gps field crews can learn from...

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