RiverRenew Lightweight Fill

Lightweight Pipe Backfill

Alexandria, Virginia

The Job

This lightweight pipe backfill is part of the City of Alexandria’s RiverRenew project, its largest in history. The project includes installation of new interceptors, and a large CSO/conveyance tunnel.

The Challenge

A pile-supported, concrete-encased interceptor needed to be backfilled. Due to the pile support capacity, the maximum allowable density of the backfill was 90lb/cuft.

The Solution

To bring the average backfill density to 90lb/cuft, CJGeo proposed filling between the SOE & concrete encasement with 30lb/cuft CJFill-High Permeability (HP). CJFill-HP has very high permeability, so reduces buoyancy when saturated when compared to other lightweight fill materials. CJGeo successfully filled between the concrete encasement and SOE with 145CY of CJFill-HP. The placements was done in a single, 6′ deep lift in less than an hour.

To facilitate the fast placement speed, CJGeo used a mobile batch plant to generate the CJFill-High Permeability cellular grout onsite. Onsite generation blends dry, bulk cement onsite with water, using custom batch plants which also make generate the preformed foam on site. The cement slurry is around 110lb/cuft, and the preformed foam is around 2.5lb/cuft. CJGeo’s batch plants utilize colloidal mixing, which ensures the highest quality cement paste, and therefore the highest quality finished product possible.

The use of very low density material then allowed the client to backfill on top of the structure with normal unit weight material while maintaining the average 90lb/cuft density through the full depth of the fill column.

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