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Single Auger Mixing technology uses a crane-mounted turntable or a self-contained hydraulic or electric drilling rig to rotate and advance a specially designed mixing tool into the soil. The mixing tool is selected based on site requirements and will usually vary from six to twelve feet in diameter. This technique is generally used for depths up to 45 feet. As the mixing tool advances, cement grout or other reagents are injected into the soil through the tool. Usually the reagents are mixed
with water to produce a grout or slurry. Although, gases such as hot air or steam can be used that are particularly useful in environmental applications. The advancement and injection rates of the mixing tool are phased to create uniform columns of treated soil. Columns can be used as individual elements, or overlapped to form walls or to treat soil masses for a variety of applications including:
Since soil mixing is an in-situ process, off gassing is reduced. If necessary, a hood can be used to cover the point of mixing and/or a vacuum can be used to draw the collected gasses through an emission treatment system. Whether the goal is to improve the bearing capacity of soft soils, provide structural support, reduce permeability, or to treat hazardous waste, soil mixing is a valuable technique within the hands of experienced contractors such as RECON. Additional information on Soli Mixing is located at www.soil-mixing.com
Soil Mixing Case Studies
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New Castle, Delaware
When soil in one area of the former Halby Chemical Company site, in New Castle, Delaware, were found to contain high concentrations of Carbon Disulfide (CS2,) Terra Constructors, an acquisition of Remedial Construction Services, L.P. (RECON), was awarded a contract to conduct a remediation test program using insitu chemical oxidation. In this process, as oxygen is brought into contact with the CS2, a chemical reaction takes place that breaks down the contaminant into carbon dioxide and sulphate salts, both harmless compounds. RECON/ Terra delivered the oxygen to the target soils in the form of an oxidant slurry, using the Single Auger Mixing (SAM) process.
Single Auger Mixing
In this technique, a specially designed, hollow-stem mixing tool with carbide cutting teeth is advanced and rotated into the soil by means of a crane-mounted turntable. Concurrently, the reagent is pumped through ports in the mixing tool and blended with the in situ soil as the mixing tool is lowered and raised through the target zone. A grid treatment pattern designed to achieve overlapping "columns" ensures uniform mass treatment.
For this project, a 60-ton crane supported the drilling platform, which was capable of producing as much as 100,000 foot-pounds of torque. Torque was transferred to the 6-foot diameter mixing tool, and "down pressure" was provided, by a specially fabricated kelly bar.
Test Program
Three areas, approximately 6 feet wide, 10 feet long and 12 feet deep, were designated for the test program. The oxidant, an adduct of soda ash and peroxide, was blended with water in a high shear mixer to produce a pumpable suspension. Heat generated during the oxidation process resulted in the formation of gases that were drawn through a thermal oxidation unit for treatment.
Soils with median CS2 concentrations of 5,000 mg/kg, ranging up to 160,000 mg/kg, were successfully treated to below the clean-up goals of 1,010-mg/kg average and 2,020-mg/kg maximum.
Production Contract
The success of the test program led to RECON/Terra being retained to treat approximately 11,000 cubic yards of contaminated soil. A solidified cap was formed by adding cement into the top four feet of soil with an excavator.
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Cartersville, Georgia
When soil in one area of Goodyear´s Cartersville facility were determined to have been contaminated with significant levels of formaldehyde, Terra Constructors, an acquisition of Remedial Construction Services, L.P. (RECON), was retained to perform soil remediation using insitu chemical oxidation. In this process, an oxidant slurry is delivered to the target soils using the Single Auger Mixing (SAM) process. As the oxidant is brought into contact with the formaldehyde, a chemical reaction takes place that breaks down the contaminant into carbon dioxide and water both harmless compounds.
Single Auger Mixing Method
The SAM technique utilizes a specially designed, hollow-stem mixing tool with carbide cutting teeth. The tool is advanced and rotated into the soil by means of a crane-mounted turntable. Concurrently, the reagent is pumped through ports in the mixing tool and blended with the in situ soil as the mixing tool is lowered and raised through the target zone. A grid treatment pattern designed to achieve overlapping "columns" ensures uniform mass treatment.
Production Work
For this project, a 60-ton crane supported the drilling platform, which was capable of producing as much as 100,000 foot-pounds of torque. Torque was transferred to the 6-foot-diameter mixing tool.
The oxidant, an adduct of sodium percarbonate, was blended with water in a high shear mixer to produce a pumpable suspension. Treatment of the 500 cubic yards of contaminated soil successfully reduced formaldehyde concentrations from as high as 42,000 mg/kg to below the specified cleanup level of 100 mg/kg.
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