Enhancing stiffness and strength of super-absorbent-polymers-solidified excavated spoils and slurries

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Hydraulic excavators are increasingly being used for excavations needed for repair or replacement of buriedinfrastructure, such as water mains, sewers, communication cables, etc. Because of their high water content,hydraulic excavation spoils have a sludge-like consistency and can neither be disposed off as solid waste norrecycled nor reused as a backfill. The disposal problem can be addressed by adding super-absorbent polymers(SAPs) to the spoils. SAPs can absorb several hundred times their own mass in water, thereby providing"instant" solidification of the spoils and facilitating their disposal as solid waste. Provision of SAP-basedsolidification solutions to a broad range of applications, including spoils from hydraulic as well as traditionalexcavations and tunnelling, is one of the core businesses of the industry partner MetaFLO. MetaFLO's clientsare looking for ways of using SAP-solidified spoils as a backfill material for post-repair closure of excavations.Presently, SAP-solidified spoils cannot be used to backfill excavations because of lack of information on theirexpected geotechnical properties and must be transported and disposed at solid waste disposal sites. A keyobjective of the proposed project is to identify the threshold inherent water content of the spoils above whichthe use of SAPs to solidify the spoils will not result in a fill that is of sufficient stiffness and strength to permitits use as a fill or a backfill. The project will also explore mixing of natural soils with the SAP-solidified spoilsto enhance stiffness and strength of the spoils. The overarching goal of the project is to develop guidelines forthe use of SAPs, which can be used by contractors to establish the relative proportions of spoils, SAPs, andnatural soils to achieve desirable geotechnical properties of the resulting mix based on the measured inherentwater content of the spoils. A comprehensive lab testing program that uses the state-of-the-art geotechnical labtesting facilities at York is proposed in which combinations of clay slurries prepared at different watercontents, two types of SAPs, and general-purpose Portland cement as binding agent are used to ascertainAtterberg limits, stiffness, strength, compaction, and hydraulic flow properties of the resulting mixes.