Drilling Slurry Page 53 in the Manual Introduction Used when an excavation encounters soil that may cave Must have the proper characteristics (density, viscosity, pH, and sand … … during the drilling and concrete operations Options for Drilling Fluids Water (with Engineers approval only) Mineral Slurries- Bentonite is the most common type Polymer Slurries (currently not allowed by the SCDOT) Principles of Slurry Operation When slurry is properly utilized, it keeps the shaft stable by exerting pressure on the walls of …

1 Drilling Slurry Page 53 in the Manual Introduction Used when an excavation encounters soil that may cave Must have the proper characteristics (density, viscosity, pH, and sand content) during the drilling and concrete operations Options for Drilling Fluids Water (with Engineers approval only) Mineral Slurries - Bentonite is the most common type Polymer Slurries (currently not allowed by the SCDOT) Principles of Slurry Operation When slurry is properly utilized, it keeps the shaft stable by exerting pressure on the walls of the excavation. It provides lubricant that reduces the soil resistance when casing is installed. Drilling tools do not wear as quickly when slurry is used. Principals of Slurry Operation Mineral slurries have unit weights that are slightly higher than the unit weight of the mixing water (>62.4). As drilling progresses and the slurry picks up more soil (clay, sand, and silt), the unit weight and viscosity of the slurry increase. Principals of Slurry Operation A positive head must be maintained at all times (a minimum of 4 feet above the highest piezometric head). Slurry Method of Construction Slurry Drilling Rebar Cage Placement Tremie Concrete Placement & Slurry Displacement Inspector’s Responsibilities Monitoring the Contractor’s slurry testing - Test slurry properties prior to concreting to verify the slurry is within specifications Verify complete hydration of the minerals and stabilized viscosity Verify that a positive head is maintained at all times (minimum of 4 ft above the highest piezometric head) Slurry Suspension When soils with significant amounts of granular material (sands or silts) are being excavated, the slurry may thicken quickly. This is not desirable because: - The slurry becomes incapable of suspending additional particles, which causes particles to settle in the bottom of the shaft. - The slurry becomes too viscous to be displaced by the rising fluid concrete and contaminates the concrete. Mixing and Handling Slurry tanks of adequate capacity will be required for slurry circulation, storage, and treatment. Contaminated mineral slurry is pumped to a desanding unit. Mixing and Handling (cont.) Sampling Slurry sample obtained by using a “thief” Multiple samples should be taken to ensure the slurry has stabilized after the drilling process is complete …

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