Tunnel Business Magazine

AUG 2018

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TUNNELINGONLINE.COM F E A T U R E S T O RY 2 4 TBM: TUNNEL BUSINESS MAGAZINE // AUGUST 2018 T he Louisv o area, like many cities across the country, is experiencing the effects of an ag- ing sewer system that is unable to handle the surrounding area's cur- rent volume of sewage and storm water. Older combined sewer overflow sys- tems (CSOs) are designed to handle storm water, domestic sewage and industrial wastewater. In heavy rain events, the volume of storm water exceeds the ca- pacity of the treatment plant leading to overflows that pollute nearby streams and rivers and causing harmful water pollution and increased incidents of sewage backups. The Louisville and Jefferson County opolitan Sewer District in Ken- tucky created Project Waterway Im- prov ehabilitate the sewer system and improve local wa- ter quality to ensure compliance with the federal Clean Water Act. The $850 million project, which will span more than five years, includes a series of sew- er overflow reduction projects designed to improve water quality in the Louis- v o area. The Portland CSO Basin is one of the many projects within Project and more specifically, within the Innovative Overflow Abatement Program (IOAP.) The first part of the project, which must be in place by 2020, included the installation of multiple basins to retain a mixture of rainwater and sewage during heavy rain events that would gradually be released for treatment rather than overflowing the system and polluting waterways. Construct ion in the Round The Portland CSO project includes a circular storage basin that will provide 6.7 million gallons of combined sew- age and storm water storage beneath historic Lannan Park in Louisville. The Portland CSO Basin has a drainage area of 850 acres with 61 overflows and 167 mgd per typical year. The new storage basin is expected to reduce the number of overflow occurrences by 86%. Construction of the new storage basin required a circular excavation r y different types of temporary support of excavation systems were considered, and ultimately a concrete diaphragm wall shaft was selected. on was contracted by general contr ers to install a 42-in. thick, 246-ft diameter, circu- lar concrete diaphragm wall to act as a temporary support of excavation (SOE) shaft as part of the first phase of the oject. on worked with Dugan and ers and the Owner's Engineer to de- velop a Value Engineering (VE) alternate that effectively reduced the diameter of the shaft to 239-ft, and incorporated the diaphragm wall into the perma- nent structure, effectively utilizing the weight and strength of the diaphragm wall to simplify the planned construc- tion of the permanent structure. The VE alternate also included the installation of tension micropiles to resist uplift loads on the permanent bottom slab of the basin. Acceptance of the VE proposal al- lowed the general contractor to offer the owner cost savings and a streamlined construction sequence. Subterreanean Basin Blues A unique structure, the Portland CSO basin is one of the largest diameter dia- phragm wall shafts constructed in the United States. The support of excavation is provided solely by the circular wall acting as a compression ring. Verticality of the panels is extremely important to maintain the integrity and water tight- ness of the structure. Construction began in fall 2017 on the diaphragm wall and the process wasn't without its challenges. The Lannan Park site was located on an old bottle land- fill with a lot of trash and debris in the upper 16 ft of fill. The soils in this zone presented unforeseen challenges with significant slurry loss while excavating PORTLAND CSO BASIN: BUILDING WHAT LIES BENEATH

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