Surveying in the Outback
The Equipment That Made a DifferenceThe Greenmount section is a two-lane road, which involved the reconstruction and the realignment of a small section of the Great Eastern Highway that runs through the Greenmount suburb on the eastern fringes of Perth. The job involved difficult and demanding working conditions with many obstacles that were potentially problematic to a timely completion. One obstacle was the limitation imposed by surveying a busy stretch of highway. Along with the 20,000 vehicles, the Greenmount section required that two lanes remain open during morning peak hours (7-9 a.m.). Afternoon traffic required the same from 3-5 p.m. for outward-bound traffic. Between the hours of 9 a.m. to 3 p.m., one lane in each direction remained open to traffic.
Due to traffic safety reasons, pegs were not allowed to remain in the median lanes overnight. As such, traditional surveying methods would have required that a full survey be repeated every morning, significantly delaying the progress of the job. To overcome some of the difficulties that the standard survey method would have caused, we opted to use the TDS Ranger with TDS Survey Pro software and its DTM stakeout routine (Tripod Data Systems, Corvallis, Ore.) with Topcon robotics and GTS-711 non-robotic total stations (Topcon Positioning Systems, Pleasanton, Calif.).
In the traditional surveying method of a construction project, the surveyor does the initial survey according to surface design specifications. Once the initial grade is set, the grader comes through and makes a rough cut of the proposed surface. Then the grading work needs to be checked by the stringers (a glossary of Australian surveying terms appears at the end of this article). Once the grading is accomplished, the surveyor performs data collection on the as-con surface and generates a report. This process is usually repeated for each surface (sub-grade, sub-base, and base course).
The TDS Ranger, Survey Pro and the Topcon total station combination effectively eliminates two of the traditional steps—the use of stringers to check grade surfaces and the completion of as-cons. The instrumentation only requires that the surveyor do the sub-grade surface setout. The grade surface check and as-con are accomplished simultaneously by the instrument and surveyor and replaces the need for stringers, providing a substantial impact on the efficiency and cost of the work in progress.
The DTM model is loaded into the Ranger, which enables the surveyor to start work in front of the grader immediately, needing no pegs. On every cross section, the surveyor marks cut/fill values obtained from the Ranger with spray paint, just like stringers would measure from the string line to the surface. Then the grader trims the surface to those cut/fill marks, and the process is repeated until finished. One important difference from using stringers is that it does not require the surveyor to go over the same section of road again and again to check the as-con surface and report it accordingly. Assuming approximately 700 meters is graded daily, that checking would take a surveyor three to five hours to complete.
But by using TDS’ Survey Pro, the surveyor records the as-con surface at the same time as grading and the report is ready to be printed immediately, thus significantly reducing survey time and eliminating the need for stringers. Since this option allowed us to eliminate the need for pegging every morning and the subsequent grade check that the stringers perform, work could commence immediately each morning, and as a result we finished significantly ahead of the scheduled time.
Noticeable SavingsAs is true in many places in the world, the project deadline was reinforced by the approaching winter. We at D. Benic Surveys were able to complete the project early, a very favorable result. Even the project managers commented that the project would never have finished before winter set in had we not implemented this technology. The end result was ultimately achieved through a team effort—good surveyors and good technology.
By using the TDS Ranger and robotic total station the surveyor is freed from doing as-cons and instead can take on the work the second crew would have been doing. This effectively means a tremendous savings by being able to reduce the work required by the second crew.
A fully-equipped TDS Ranger and total station means a reduction in computing time associated with the accurate design setout. Furthermore, total setout time is reduced since only the setout of the sub-grade surface is required. Technically, Survey Pro eliminates the need for sub-grade pegging, but the sub-grade setout allows the grader driver and others to see the actual alignment and feel more comfortable that they are going in the right direction.
The workflow for the surveyor, and in particular for the grader driver, is significantly improved since there is no intermittent work stoppage to allow for stringing.
The implications are that not only is the speed at which the work progresses improved but also resources, both human and mechanical, are released for application elsewhere.
An upgrade of skills for the grader driver and of his machinery is not required. In fact, the proposed system keeps all current procedures and methods of doing things intact with the exception that the surveyor is able to eliminate the extra work normally required for as-cons while taking over the work of the stringers. This equates to savings in the order of A$4,500 (U.S.$2,250) per kilometer in survey costs alone, without considering the more efficient utilization of construction equipment and operators due to reduced field survey time.
Also, the TDS Ranger and total station is very effective in bulk earthworks. Once the design surface is loaded into the Ranger, controlling large cut and fill operations becomes much more efficient since the possibility of human error and the need for any extra computing time are eliminated. The surveyor can thus increase daily production between 40 percent and 60 percent, which ultimately translates to considerable savings in the running costs of projects.
Even the project managers commented that the project would never have finished before winter set in had we not implemented this technology.
Note: All Australian dollar to U.S. dollar conversions have been calculated at the rate of A$2=U.S.$1
Glossary to Australian surveying terms:
As-con: an as-constructed surface or as-built
Base course: the final surface upon which the asphalt is laid
Pegs: stakes; Pegging: staking; Re-pegging: replacing lost or damaged pegs
Pickup: data collecting
Stringers: workers using string line attached to survey pegs to check design surface grade
Sub-grade: a surface under the road pavement or top of embankment
Sub-base: the next course up from the sub-grade