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DEEP SOIL MIXING
CASE HISTORIES |
OUTER HARBOR
Buffalo, New York
 Remedial Construction Services, L.P. (RECON) was contracted by Honeywell International to use its soil mixing and jet grouting technologies to assist with the remedial action and redevelopment of the Outer Harbor in Buffalo, New York.
Phase 1, Soil Mixing
The initial phase of the project was the in-situ chemical oxidation to stabilize the nitrobenzene-impacted soil. RECON installed 155 columns using the Single Auger Mixing (SAM) technique. The 8-foot diameter columns were overlapped to ensure the entire 5,400 cubic yards of impacted soil was treated. Oxidizing agent (Potassium Permanganate) was introduced at a rate of approximately 600 pounds per column and was mixed with the impacted soil between 8.0 and 22.0 feet below ground surface for 20 minutes.
RECON used its own RH190 Delmag crawler-mounted hydraulic drill rig to advance, rotate and withdraw the mixing tool. The drill rig has a top drive rotary head capable of transferring 190,000 foot-pounds of torque to the mixing tool. The RH190 is capable of producing a crowd force of 73,000 pounds and an extraction force of 92,000 pounds. It’s equipped with a cab-mounted, real-time monitoring system that allows the driller to control the soil mixing operation by monitoring the tool rotation speed, tool penetration, and agent/grout placement.
Phase 2, Jet Grouting
Phase 2 included injecting additional Potassium Permanganate to treat “hot spot” areas identified after verification sampling. RECON used our jet-grouting rig to deliver the reagent because the chemically oxidized area was impassible and the jet-grouting rig provided angular drilling.
RECON’s jet grouting rig includes a hydraulic drill equipped with the capability of injecting reagent. This procedure influenced a 14-foot diameter zone around the drill stem. RECON’s high-pressure pump delivered reagent at a rate of 40 gpm at a pressure of over 6,500 psi. The jet grout pump delivered the reagent solution from an agitated holding tank, through a hose to a swivel on top of the mixing tool shaft. The swivel allows the reagent mix to flow through the shaft and exit through ports on the mixing tool while the tool is rotating. The flow rate was monitored at the pump with a flow meter to ensure placement of the prescribed reagent dose.
Phase 3, Soil Stabilization and Final Treatment
TCLP levels of nitrobenzene were lowered to a maximum of 35.4 ppm as a result of Phase 1 and 2 treatment events. Treatability studies were performed, by RECON, to determine the percentage of cement required to stabilize the fluidized material. Additionally, it was decided to mix 4% granular activated carbon (GAC) to absorb the majority of the remaining nitrobenzene. Adding the GAC reduced the nitrobenzene levels by 98%.
After the treatability studies were presented to and accepted by the agencies, RECON re-mobilized the Delmag Soil Mixing rig to perform cement-GAC stabilization of the fluidized area as final treatment.
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SIMS BAYOU
Houston, Texas
 Sims Bayou is a major stormwater conveyance feature that comes under the auspices of the U.S. Army Corps of Engineers (USACE). When a deep failure plane – caused by the presence of low-strength soils combined with a seasonal upward hydraulic gradient – developed along a stretch of the bayou’s 20-foot high embankment, the USACE selected the single-fluid jet grouting technique to stabilize the slope.
Jet grouting is a replacement mixing technology that uses a high-pressure jet of grout to erode and mix the soils in-situ, creating a blended soil/grout matrix with improved engineering properties.
Jet Grouting Program
The intent of the jet-grouting program was to intercept the active failure plane and prevent further soil movement into the bayou. Deleterious material was excavated and the area was backfilled to construct a stable working platform. Jet grouting was accomplished using Remedial Construction Services, L.P. (RECON’s) state-of-the-art equipment, including an automated grout batch plant, high-pressure pump, and hydraulic drill equipped with a single-fluid jet grout drill string. RECON installed 120,30-inch diameter jet grout columns to a depth of 32 feet, creating a stabilized zone of soil approximately 100 feet long and 10 feet wide. The project was successfully completed within the 240-day schedule.
Quality Control and Quality Assurance
Prior to production work, six test columns were installed within the area of the permanent system. After being allowed to cure, all six columns were excavated and visually inspected to verify that the required column diameter could be achieved in the highly plastic Gulf Coast clays. One unconfined compressive strength (UCS) test was performed for every 10 production columns to ensure that the specified minimum UCS of 250 psi in 28 days had been achieved.
Site Restoration
In addition to the jet-grouting program, RECON performed the following items of work at the site:
- Installation of silt barriers to protect Sims Bayou during construction,
- Installation of a cellular concrete mattress from the base of the jet-grouted section to below the water line to prevent erosion of the slope into the bayou.
- Installation of relief wells and drainage structures, and
- Restoration of the slope to its pre-failure condition, including turfing and tree planting.
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CLOSURE OF REFINERY SLUDGE CONSOLIDATION CELL SWMU SI-19, CELL 3
Port Arthur, Texas
Remedial Construction Services, L.P. (RECON) was contracted by MOTIVA Enterprises LLC to solidify sludge in Cell 3 Refinery Sludge Consolidation Impoundment at the Motiva Enterprises Port Arthur Manufacturing Complex in Port Arthur, Texas. The primary goals of the solidification project were to in-situ stabilize the sludge; cover the area with a minimum one-foot imported clay cap without excessive bulking of material; and avoid excessive use of expensive reagents.
Scope of Work
 Work consisted of:
- Demolition and decontamination of weir structures and piping,
- Removal of standing water,
- Stabilization of sludge to depth of 10 feet (65,000 cubic yards),
- Excavation and replacement of impacted soil with clean fill (1,400 cubic yards),
- Regrading sludge surface,
- Placement of soil cover,
- Installation cover grading and drainage,
- Placement of cover seeding and Restoration of perimeter road.
Scope Changes
In addition to the primary scope of work, RECON stabilized approximately 40,000 cubic yards more sludge than originally anticipated largely because the sludge extended to depths ranging between 10 and 18-feet deep. 
In an effort to minimize the amount of reagent used and cost to the client, (especially since the depth of sludge requiring treatment exceeded the target depth), RECON proposed the addition of a clayey soil to be blended with the sludge and fly ash reagent. The fly ash had high-available lime content capable of reducing the moisture content in sludge.
RECON proposed unit price deductions to the contract amount in the event that less imported soil and fly ash reagent would be needed to achieve the same project goals. Our revised stabilization approach enabled us to use 7,500 tons of fly ash and 36,000 cubic yards of clay fill material – in spite of the additional quantity of sludge. As a result, RECON saved MOTIVA over $250,000, which was deducted from the original contract amount.
Despite stabilizing an additional 40,000 cubic yards of sludge, only one month was added to the construction schedule.
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RECON saved our client over $250,000 as a result of an efficient and effective stabilization approach. | |
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