Curving Concrete Pipe: What a Relief

Project Background Located in the northeast corner of Cleveland (OH), Cleveland Water Pollution Control (WPC) achieved its largest project to date by designing, and constructing 5,200' of 48' sanitary relief sewer along a curved residential street (Marcella Rd.), and a heavily travelled local business corridor (East 185th St.). Despite some obstacles during the nearly $15 Million construction project, the relief sewer was a major step to mitigate area basement flooding while minimizing construction impacts to residents and businesses. This presentation will highlight the advantages, disadvantages, design considerations relative to curved microtunneling, and lessons learned. Project Objectives After decades of basement flooding complaints from property owners, modeling of the sewers confirmed capacity and high I/I issues within the Area sewer flow monitoring and modeling preceded the project design. While the service area is comprised of separate storm and sanitary sewers, high amounts of I/I exist within the common trench sanitary and storm system. Since I/I elimination impacts greatly vary on their impact to an existing system, a relief sewer was proposed. Fortunately, NEORSD had previously stubbed an appropriately sized pipe for this area that we could tie into. The relief sewer was designed to remove over 48 MGD (74 cfs) from the sanitary system during the design 5-year storm. Benefits of Presentation Microtunneling no longer is considered a new construction method. However, installing pipe along curved microtunnel alignments is a newer industry capability. This unique approach allowed the sewer alignment to follow the natural curve of the roadway. A more typical open-cut method would require a significant number of manholes due to multiple changes in direction, plus the costs associated with full depth roadway replacement, and sewer lateral replacement. This presentation will highlight current microtunneling methods and capabilities, construction area needed for launch shafts, receiving shafts, spoils processing equipment, and storage. Additional useful design information will be provided such as the importance of a thorough geotechnical report, and budgeting for unforeseen conditions. This presentation will highlight practical reasons to pursue microtunneling as an option, as well as cost comparisons to a typical open-cut installation. On East 185th Street specifically, open-cut construction would have exposed an old 72' brick storm sewer, and undermining the bedding/soils was not a risk the City was willing to take. The project also included acquisition of a small easement to accommodate microtunnel radius limitations. While land acquisition is not part of the City's typical design approach, the easement was easily acquired as the property owner got compensated without any disruption on their property. Proactive planning allowed for the necessary time for the City to obtain the required easement appraisals, and time to negotiate the acquisition before bidding and construction. Microtunneling was also a very attractive method for the City since East 185th Street is a heavily trafficked corridor with businesses, street parking, and walking traffic. Status Project construction occurred from August 2019 to November 2020. The microtunnel portion accounted for approximately 8 months of the 15 month project. As the COVID-19 pandemic emerged, the contractor was initially delayed, however once the proper safety procedures were setup, time was easily regained with the tunneling crews working night shifts. Since the night shifts were specifically for the tunneling process, worker safety due to visibility was not an issue. The tunneling equipment did have to be located in a suitable area due to the noise created, and the contractor obtained a waiver to vary from the City's noise ordinance. The microtunneling progress averaged around 34 feet per day (or shift) of progress with the tunnel. 4 months of post-construction monitoring was completed from mid-April through mid-August to compare the model's predictions to actual flows, and to demonstrate the need for additional sewer upsizing in the upstream area. The flow data did indicate that the sidestreets east of E. 185th need additional capacity. This was evident from the monitoring data as the main along E. 185th had capacity while the sidestreets were surcharged during an event near to, but less than a typical 1-year storm. Learning Outcomes - Microtunneling can reduce risk where open-cut construction would expose aging, expensive, or fragile utilities. - Budget time and money for unforeseen obstacles such as boulders and utility relocation. - Avoid or move overhead utilities before the project. Launch/receiving shafts for the manholes need to be accessed with large equipment/cranes, coordinate with utilities to mitigate construction delays. - Attendees will gain knowledge of what is possible with microtunneling, when to use or avoid microtunneling, and how to plan and budget for a microtunneling project. Conclusion This was a very important project for the City of Cleveland as the area has a long history of reported basement flooding, and action toward reducing the frequency of these events needed to be taken. The City was open to the bold approach of installing the sewer along a curved alignment via microtunnel to maintain vehicle, and pedestrian access, knowing the costs could be slightly higher than the open-cut method. The community was also very accepting of the approach, as though multiple community meetings we indicated the construction will help relieve future water-in-basement events with minimal disturbance. Home and business owners lying within the zone-of-influence of the tunnel had further confidence since the contractor offered to video inspect their basements before and after the project in addition to multiple ground points which were surveyed weekly to insure the tunneling was a safe method.