To Dig or Not to Dig: Process to eliminate open cut sewer rehabilitation in Mature Neighbourhoods

摘要

Over the last decade, the City of Edmonton has conducted a program to repair, rehabilitate andrenew existing sewers within older neighborhoods. This paper describes the City of Edmonton’s experiencein reducing the length and number of repairs that use excavating and replacing the pipe (open cut repair).The City of Edmonton’s Great Neighbourhood Program is a collaborative effort amongst TransportationServices, Community Services, Drainage Services and other utilities that strives to make neighbourhoodsgreat places to live in a sustainable manner.The renewal process starts with the prioritization of neighbourhoods based on infrastructure sustainabilityand other benefits and costs.Once the neighbourhoods have been defined and ranked, Drainage Design and Construction begins therenewal procedure. To be cost effective, neighbourhood renewal begins with the deepest utilities, that is, thestorm and sanitary collection systems.Drainage Neighbourhood Renewal begins with cleaning the sewers to the extent that when a CCTV camera ispassed through the pipes all defects around the perimeter of the pipe are visible. Next the structural andservice conditions are assessed using the City of Edmonton’s Standard Condition Rating Systems. During theCCTV inspection, the type and severity of all defects are recorded. The number of “spot” defects and both thestart and end of “extended” defects are recorded. All the sewers within the neighbourhood are inspected. .Forquality control, the designer verifies both the quality of the video and the quality of the defect coding.The next step is the design, in this phase, the designer identifies the alternatives for addressing the defects. Bycomparing the alternatives in terms of benefits and costs (value), risk and affordability over the Life Cycle ofthe assets, the best action is selected. Alternatives include the “do-nothing” or “maintenance only” option.If the nature of the defects or the likelihood and magnitude of risks requires intervention, the City uses anumber of methods to rehabilitate pipelines and manholes. If the method selected is open cut, and because ofit there will be the appearance of destruction and a high amount of disturbance to the public and businesses,a detailed review process will be applied to attempt to eliminate the open cut repair and replace it with atrenchless method such as tunneling, pipe bursting, pilot tube micro-tunneling (PTMT or guided-bore), curedin-place (CIPP) pipe lining, slip lining, or lateral lining. We will discuss the procedure the City uses toeliminate the open cut; in addition, we will highlight the issues, constraints, and compromises the City has toaccount for to eliminate the open cut.