lightweight flowable fill installation to fill a pit at a water treatment plant

Pit Fill With Lightweight Flowable Fill

Aberdeen, Maryland

The Job

An abandoned water treatment plant at a federal facility was being rehabilitated and brought back into service. As part of the project, lightweight flowable fill was needed to fill a 12′ deep tank below the building floor needed to be filled before installing a new floor and equipment.

The Challenge

The majority of the pit is below ground water level. The original foundation design used a 62PCF fill density for the pits, presuming they would only ever hold water.

The backfill material also needed to completely encase a number of new micropiles installed for machine bases.

The designer had two competing interests–given the closeness of the water table to finish floor, avoid any buoyancy of the fill material, while using the lightest possible material to avoid inducing any settlement.

The Solution

CJGeo proposed filling the pit with CJFill-UW, at 70lbs/cuft. At 70lb/cuft, there are no uplift concerns, and the material is just barely denser than water, which helps minimize the amount of anticipated settlement. To help ensure future excavatability, CJGeo used a sanded base slurry (as opposed to the usual neat mix slurry) to generate 830CY of lightweight flowable fill material. The 28 day design strength was 150psi. The average 28 day tested compressive strength was 200psi. The removability modulus of the material is 0.75, which means the material is readily excavatable.

Traditional “lightweight” flowable fill is closer to 95lb/cuft. At 150psi, 95lb/cuft material has a removability modulus of 1.18. This is above ACI’s benchmark value of 1 for ease of excavatability.

For this project the CJFill-UW was generated by adding preformed foam to ready mix truck drums. The drum blends the slurry & foam as it rotates. The blended CJFill-UW discharges via the chute directly into the placement area.

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