Jobsite Journal – Drilling with Poly-Bore

Recently, our Atlantic Supply store in Largo, Florida provided a local drilled shaft contractor with their first order of Poly-Bore for a large project in Southwest Florida.  Poly-Bore, manufactured by Baroid Industrial Drilling Products (IDP), is a PHPA-type polymer used in the drilled shaft and HDD industries.  The primary advantage of using Poly-Bore over a bentonite/mineral drilling fluid is Poly-Bore’s ability to quickly drop out the suspended drill cuttings.

Typical bentonite based drilling fluids are designed to suspend the cuttings while the fluid is at rest, (otherwise known as “gel strength”), which can be problematic in drilled shaft applications.  Drilled shafts require a minimal amount of suspended sand so it will not co-mingle with the concrete as it is poured into the shaft.

The contractor was assisted on the jobsite by Doug Keller, a senior field engineer with Baroid IDP, and Mitch Davis, who works for Atlantic Supply’s Largo office in outside sales and technical services.  When a contractor is starting a project and using Poly-Bore for the first time, the FDOT will usually require a manufacturers representative to assist the contractor with product mixing and disposal procedures.

Mr. Keller, who lives in Florida, assists various Atlantic Supply customers on projects such as drilled shaft, HDD, and water well installations.  The services provided by Baroid IDP’s field engineers are free of charge for Baroid users and it is a very valuable asset.

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When a drilled shaft project begins there are many factors for the contractor to consider such as equipment, labor, materials, on-site inspectors, traffic safety, etc.  The challenge with drilled shaft drilling fluids is the contractor must maintain four fluid parameters in order to be allowed to pour concrete and finish the shaft.  These parameters are pH, viscosity, density, and sand content, and they can vary from state to state and can be different depending on if a bentonite or polymer fluid is being used.  Another advantage of Poly-Bore is that it can be reused, provided that it meets the four parameters prior to reuse.  The used fluid may be reconditioned by adding more Poly-Bore, Soda Ash (for pH increase), water, mixing through a centrifugal pump, etc.

These parameters are tested before, during, and after drilling is completed and they can change during the drilling process based on the chemistry of the soil and ground water in which the shaft is placed.  Also, as opposed to other types of drilling where a contractor can use practically any polymer additive they need based on the ground conditions, a drilled shaft contractor may only used pre-approved products.  Since there are considerations for how the concrete shaft bonds with the surrounding soil, polymer additives are usually prohibited.  If the contractor cannot keep the borehole stable with the fluids they are allowed to use, they may be required to install a temporary steel casing to stabilize the borehole.

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The contractor was well prepared with mixing tanks and hoppers, a centrifugal mixing pump, and soda ash.  Since the contractor had previous experience with bentonite and polymer additives, the initial set up and mixing went as planned.  The first shaft measured four-feet wide and 22-feet deep and the ground conditions were mostly fine to medium sand with some light clay.  The ground was saturated with water due to recent heavy rains and a nearby fresh-water lake.

The Poly-Bore worked as advertised and they completed drilling the first shaft ahead of schedule.  After the hole was drilled, the contractor was pleased to see that the sand content of the fluid was nearly zero and the other testing parameters were well within tolerance.

If you would like more information on Poly-Bore or would like to find out how Atlantic Supply can help you with your drilling fluids program, please contact your local Atlantic Supply store.

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