Brief Overview:
In York, Ontario, a utility project involving a three-mile-long, 42-in./30-in. diameter pre-cast concrete feeder main underwent a Subsurface Utility Engineering (SUE) investigation at 30% design completion.
The SUE findings, which cost $20,000 (0.25% of the project total), led to route adjustments and grade changes, preventing costly and risky placement beneath an 18-ft. deep sewer force main.
A University of Toronto study calculated a favorable benefit/cost ratio of approximately 3.9 for the SUE component of the project.
Full Case Study Report:
A utility project involved the construction of a three mile long, 42-in./30-in. diameter, pre-cast concrete feeder main along Major Mackenzie Drive in York, Ontario, at a projected cost of $8 million.
Funding for the SUE investigation was justified by claims in previous projects, which were caused by inaccurate utility information, as well as for the nature of the project that called for pre-cast concrete pipe.
This pipe type lead to limited flexibility, as all bends and chambers are pre- fabricated in the plant and shipped to site.
Thus, field modifications would be costly as elements would have to be re-ordered with new dimensions and configurations, resulting in extra construction costs and delays.
SUE was utilized when approximately 30% of the design was completed. At this time, a preliminary route had been selected based on known data.
The SUE investigation revealed several unmarked abundant utilities and several potential conflicts with poorly marked traffic control and electrical utilities.
The added accuracy in terms of location of existing utilities, as well as the identification of several unmarked pipes and conduits, resulted in changes in the route and the grade of the new pipe to avoid 39 these conflicts.
Namely, because of the information provided, the new pipe was not placed beneath an 18-ft. deep sewer force main, which would have been costly and risky considering the deteriorated structural condition of the force main.
The investigation included approximately 30,000 linear ft. of utility designation and five test holes, at a cost of $20,000, or about 0.25% of the project total cost.
A study by the University of Toronto calculated a benefit/cost ratio of approximately 3.9 for the SUE component of the project.