SuperPile 2017 Online Proceedings, (DFI)
Pile Supported Load Transfer Platform Supports Wastewater Treatment Plant Over Soft Clay
Matthew Page, P.E.
In 2015, the Town of Newmarket, New Hampshire undertook a $14 million upgrade to the existing Wastewater Treatment Plant (WTTP) that included a new aeration tank, two clarifier tanks, and control building. The facility is located close to the bank of the Lamprey River, a portion of the Great Bay Estuary. The site consists of fill, underlain by marine clay, glacial till, and sloping bedrock. The bid required a contractor-designed ground improvement system that would enhance lateral resistance of the marine clay and provide foundation support of the new below-grade structures. The winning contractor presented a cost effective approach that met all the design requirements. The approach included a stone and geogrid load transfer platform (LTP) constructed on top of small diameter, concrete-filled, steel pipe piles. Design of the pile/LTP system accounted for static and earthquake-induced vertical and horizontal loading of the proposed structures, as well as addressing consolidation settlement. The final configuration consisted of 7-inch diameter, ¾-inch wall pipe piles driven on a 5 to 6 foot rectangular grid. Four layers of crushed stone and three layers of biaxial geogrid made up the LTP. Steel plates were cast into the pile tops to enhance load transfer from the LTP into the piles. Performance of the system was established using load tests that evaluated settlement induced under a 2000 psf load. Load test results show that the system should deflect on the order of ¼ to ½ inch under maximum loading conditions and that the differential settlement should be less than 1/8 -inch between a point directly above a pile and the midpoint between piles. Given the massive nature of the tank and building mat foundations, actual differential settlements beneath individual foundations is expected to be even less. This presentation will highlight the factors responsible for the cost-effectiveness of this system.
|article #2672; publication #1031 (SP-2017)|