Milton Wastewater Treatment Plant
As part of the Milton Regional Sewer Authority’s wastewater treatment plan to add a new anaerobic process to treat high-strength wastewater and increase capacity, the construction of two 208 foot diameter by 34 foot high concrete wastewater treatment tanks were required. The tanks are located adjacent to the Susquehanna River just upstream of Lewisburg, PA.
Soils generally consist of 5 to 15 ft of very soft to soft sandy silt and very loose to loose silty sand underlain by medium dense to very dense silty sand overlying weathered limestone bedrock. Groundwater was encountered at depths of 3 to 11 ft below bottom of tank elevation. The combination of a thick loose silty sand layer and heavy tank loading of 2000 psf , keeping settlement within tolerance (total and differential settlement of 1” and ½”) resulted in the project specifications requiring an H-Pile foundation and a structural concrete slab. With the costs for the project falling outside the Authorities budget, contractors looked for economical alternatives.
Dutchland, Inc., which manufactures and installs concrete tank systems, suggested to the General Contractor an alternative system to the H-piles and structural slab consisting of Grouted Impact Pier elements supporting a conventional tank slab. The savings in the foundation system (combination slab and Geopier elements) resulted in the project coming on line and this alternative was used to build the project.
Grouted Impact Pier elements provided the capacity required at an efficient spacing to minimize the slab thickness of the tank and support the loading within the settlement tolerances required.
To optimize the slab thickness, pier spacing and load transfer platform thickness, Finite Element Analyses were performed.
Finite Element Stress Profile
The analysis resulted in a slab thickness of 12 inches, a 2 foot thick LTP and pier spacing at 7.5 feet on center to support the 2000 psf tank loading.
A total of 628 – 20-inch Grouted Impact Pier elements were installed for each tank. Pier lengths varied from approximately 15 to 24 feet and all tagged the limestone bedrock.
The use of FEA analyses helped optimize the design and allowed for funding of the project.
Milton Regional Sewer Authority - Milton, PA
Herber, Rowland & Grubic, Inc - Harrisburg, PA
Worth & Company, Inc - Pipersville, PA
Tank Supplier & Installer
Duchland, Inc - Gap, PA
Zug & Associates - Lititz, PA
Kleinfelder, Inc - Exton, PA