In a win-win scenario for safe disposal of dredged harbor sediment and the need for additional fill material for closure and capping of a wastewater pond, planners and contractors turned to ALLU-brand equipment to perform insitu mass stabilization.
The overall project, funded by the U.S. EPA’s Great Lakes Restoration Initiative and managed by the U.S. Army Corps of Engineers, included plans to dredge 120,000 cu. yd. (91,746 cu m) of sediment from the Ashtabula Harbor in Ohio. Plans called for placing this dredged treated sediment into an existing wastewater settling pond near the Harbor. This suited the pond owner’s needs to provide additional fill material to create and support a crowned cap during closure of the pond.
The Ohio EPA-approved closure plan for the 9-acre pond included de-watering of the existing contents in order to physically support the additional material being placed within the pond’s embankments. Decanting and de-watering operations were complicated by the effects of Hurricane Sandy, which inundated the pond in October 2012.
The project managers turned to in situ mass stabilization of the existing pond contents to provide geo-technical properties needed to support the additional material. Insitu mass stabilization involves mixing a binding agent into approximately 200,000 cu. yd. (15,291 cu m) of pond sediment. The insitu mixing devices being used are two ALLU Power Mixers (PM).
An ALLU PM is an attachment to an excavator resembling a rototiller on a stem. Powered by the excavator’s hydraulic system, each PM has two rotating mixing drums that quickly and thoroughly mix binding agents into the pond contents ranging in depths of 5 to 20 ft. (1.5 to 6 m). The binding agents are injected pneumatically directly to the area being mixed by a nozzle located between the drums.
The geotechnical performance standards for the mass stabilization of the pond contents include attaining an unconfined compressive strength of 1,000 to 1,500 psf and an unconsolidated shear strength goal of 1,250 psf. These strengths are being achieved with 10 to 20 percent addition of binding agent, percentage addition varied according to the consistency of material being treated. The cost of binders may be 50 percent or more of the cost of a mass stabilization project. The high mixing shear of PMs make the most efficient use of binders and increase production rates.
In some areas of the pond, previously excavated material is being mixed with binder by using an ALLU screener/crusher. This attachment resembles an open-bottomed excavator bucket. Rows of drums within the attachment size-reduce and screen material scooped into the attachment as the material passes through. Perfect for mixing binding agent into piled material.
“ALLU power mixers and screener/crushers continue to prove to be convenient and versatile tools for contractors involved in geotechnical and environmental projects. The mixing efficiencies of our equipment make the best use of valuable resources such as binders and improve production rates for our contractor clients. We’re proud that our equipment is being used in a project that contributes to the environmental improvement and economic vitality of the Harbor while lowering the closure costs of the pond,” said Chuck Wilk, ALLU’s manager of mass stabilization and remediation applications.
