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 Assessing Historic Sewers: Case Study of the Assessment of the High and Low Level Interceptors in Toronto Mark E. Andrews P.Eng.2 ABSTRACT The importance and need for the inspection and condition assessment of large diameter sanitary sewers is becoming more and more apparent. High frequency Sonar technology, in conjunction with conventional CCTV, is proving to be a particularly effective diagnostic tool in assessing the condition of the wetted perimeter of these generally full-flowing types of sewers. This paper presents a case study involving the use of advanced technology in the assessment of the High Level and Low Level Interceptors in downtown Toronto. These two sewers, which are critical for the integrity of the Toronto collection system, are of particular interest since they are large (up to 2600 mm diameter), mostly constructed of triple ring brick, and were completed in 1910. Portions of the Low Level were constructed using new and then relatively unproven reinforced, precast concrete technology. The sewers were found to be in good condition and their inspection provides a unique opportunity to critique modern technology in the assessment of the durability of 90-year-old workmanship. Keywords: trunk sewers, sanitation history, sewer maintenance, Sonar 1.0 INTRODUCTION “It is a realization of not so much the present needs of a city as her future requirements that leads to the undertaking of most civic improvements”(Engineering Record, 1911). So begins a 1911 article about the construction of Toronto’s “new” main drainage works. Little could the author, or the designers for that matter, imagine that ninety years later computers and highly sophisticated electronic equipment would be used to assess the current condition of those works. Advanced CCTV equipment combined with Sonar technology was used in 1996 and 1997 to inspect and assess the structural integrity of 14 km of the now historic High Level and Low Level Interceptor Sewers through the central core of Toronto. The majority of the sections inspected were installed in tunnel and represented plain concrete, reinforced concrete and brick lined construction. The results of the assessment show the sewers to be in fine condition. The sewers are in such good condition in fact, that it makes this author wonder what sort of technology will be used to inspect them at the end of the next century. |
