A new technology that has been recently implemented in the in practice is the use of the global positioning system (GPS) on heavy equipment such as dozers, motor graders, and excavators, private sectors are quickly jumping on board with this idea because it speeds the project delivery in cuts costs. The use of this technology is expanding quickly into other construction equipment areas such as pavers, milling machines, and boring machines because of the advantages it offers both the contractors and the owners.
Some state highway agencies have started to implement this new technology, but not without concerns regarding the accuracy on a larger scale of errors on margins in vertical control and signal variability, equipment compatibility and liability issues. The states that have utilized this GPS equipment guidance have been reluctant to develop special technical requirements to govern the GPS usage because of the developing nature of the technology.
Though, most have allowed the contractors to use the GPS technology at their discretion. This has resulted in contractors investing in a variety of equipment types and proprietary systems, which now complicates development and implementation. Some contactors have invested in GPS machine guidance technology and many are eager to begin. The benefits include accurate grading, real time decision making, improved material usage, lower operating costs, automated controls daily as-built reports, and safer operations (Fenton, 2006).
According to McAninch (2005) the need for rework is greatly reduced because, scrapers work more closely to the final grade so dozers have less work to do. There is less survey preparation work, fewer passes with the machines, fewer machines, no waiting for surveys, and no re-surveys (Fenton, 2006). Building of three-dimensional models from plans can identify problems before work begins in the field, therefor reducing the need for expensive change orders (Streett, 2006).
The technology provides for pre-construction simulations and remote viewing of the site (Fenton, 2006). Usually, contactors desire a single source for all control information, a single source for all electronic data, conducting their own quality control checks in the field, and having quality assurance checks, made by the project engineer, referenced to the same three-dimensional model that was used for construction. DOT oversight of the model building, primary control, site calibration file, and construction results is required.
In the engineering community there is very positive outlook towards the GPS machine guidance. Their experience proves that the usage of the technology saves time over staking, three-dimensional model surfaces allows field staff to quickly verify grades, plan errors are found prior to construction when building the models, model building allows the engineer to quickly check different parts of a plan at once for possible conflicts, and the contractor can move more quickly in the field when not waiting for grade check (Vonderohe, Brockman, Whited, and Zogg, 2008).
Some engineers were skeptical at first, but shortly after their experience with the technology their doubts were alleviated. They noted that surveying crew time was reduced, and that working with an experienced contractor provides an advantage (Vonderohe, Brockman, Whited, and Zogg, 2008). Contractors have adopted this technology from two primary vendors: TOPCON and Trimble. Leica is also a provider of GPS machine guidance technology, but they don’t seem to have that much presence in the field. Vendors feel very strong regarding this technology as it is their business.
Their assertions of 30% productivity increases and 30% reduction in level of effort for quality control and quality assurance are at the high ends or report from the contractor and engineering communities. Vendors estimates that 75% to 90% of problems with the usage of the technology arise from human error such as integer transportation on the data entry. These are the same kinds of mistakes that are made frequently in surveying practice, and vendors are moving away from the need for manual data entry as quickly as possible.
The removal of paper trails and the need for reverse engineering processes from the Three-dimensional-survey-design-construct-inspect work flow is expected to lead to 185% return on overall investment (Fenton, 2006). The technology is somewhere in the range between the beginning stage and the development stage. With the technology rapidly increasing for its usage, the State Highway Agency are focused to either 1)develop specifications to ensure the completed work meets the standards is the contractor’s responsibility and therefor they are free to choose the methods and techniques to achieve the end results and must live with the consequences.
Given that the public’s expectation regarding the quality of the work will be done as quickly as possible and the State Highway Agencies are in charge, the latter approach does not seem prudent since the technology is still under development. Controlling specifications need to be developed that establish accuracy limits, define quality control and assurance, and verification processes, allocate risk for errors and establish payment mechanisms. References Fenton, S. , (2006), “Design to Construction: A Digital Evolution”, presented at the HEEP Annual Meeting, September.
Retrieved from http://www. maine. gov/mdot/heep2006/program. php McAninch, Inc. , (2005) “GPS Technology” West Des Moines, IA. Retrieved from http://www. mcaninchcorp. com/ Streett, D. , (2006), “Business Advantages of Using 3D technologies”, presented at the HEEP Annual Meeting, September. Retrieved from http://www. maine. gov/mdot/heep2006/program. php Vonderohe, A. , Brockman, K. , Whited, G. , and Zogg, J. , (November 12, 2008) “DEVELOPMENT OF A SPECIFICATION FOR GPS-MACHINE-GUIDED CONSTRUCTION OF HIGHWAY SUBGRADE” Retrieved from http://jjhannon. com/NCHRP/09-0217. pdf Table 1.