Odin completed construction of a cement-bentonite cutoff wall in Altus, Oklahoma. The project was executed to strengthen failing dike embankments at Lake Altus by installation of cement-bentonite slurry walls at the Lugert and East B Dikes. The project included installation of approximately 390,000 vertical square feet (7,270 lateral feet) of cement-bentonite cutoff wall to a maximum depth of 76 feet; excavation and placement of rockfill material; work pad grading including excavation, transport, and backfill; piezometer modifications; and gravel surface installation.

To address the water needs of the neighboring community, the project was performed on a 24-hour, six day per week schedule to complete the project by June to allow sufficient water volume within Lake Altus for irrigation during the summer months. 

The project support area had low bearing soils that required improvement to safely set up the batch plant. A design analysis performed by Tensar demonstrated to the BOR that NX850 Geogrid with 10 inches of OkDOT Type A aggregate would be adequate to support traffic and the batch plant.

Prior to constructing the cement-bentonite cutoff wall, the cutoff wall alignment was established, and support areas constructed, including clearing, grubbing, and surface improvements. Upon mobilization of personnel andequipment, rockfill material located on each dike embankment was removed and the work pad surface prepared to provide a stable working platform for the specialty long-reach excavator. Two crews, utilizing one long-reach excavator (PC-1250), worked a 24-hour, six day per week schedule to expedite completion of the project. The excavation was supported by a centralized slurry mixing plant, mixing pond, QC lab, and a backfill mixing crew. Permeability of the hardened slurry was required to be less than or equal to 2×10-6 centimeters per second at 28 days. Unconfined compressive strength (UCS) was required to be a minimum of 50 pounds per square inch at 28 days and a maximum of 75 pounds per square inch at 56 days.

The slurry trench was keyed approximately five feet into the shale bedrock. Excavation of the trench continued until the operator and/or trench hand identified shale in the spoils being excavated. Upon identification of shale, on-site BOR Quality Assurance personnel would be notified and asked to confirm the top of the shale had been reached. A sounding was then performed to document the agreed elevation for top of key and excavation would continue until bottom of key elevation was reached. Shale was excavated using a standard ripper bucket.

Where granite bedrock was present, the wall was terminated at the granite surface without damage to the granite formation during trench excavation. When the trench excavation was within 100 feet of the design granite interception point, we replaced the standard ripper bucket with a smooth bucket. The buckets were switched so that the granite surface would not be damaged by the rippers during excavation. Identification of the granite surface was the responsibility of the operator since no material could be brought to the surface for examination by QA personnel. After the operator reached the granite surface, he would scrape the top with the smooth bucket to remove debris and provide a positive termination for the CB slurry.

As the cutoff wall was excavated, approximately 56,000 cubic yards of spoils were placed on the exposed dike surface for drying. Spoil material was dried and mixed into the existing soils to be graded to design criteria and covered with rip rap rockfill to strengthen and improve the embankment. Rip rap consisted of D50 size granite, roughly six-inch rock, of which 25,000 cubic yards was placed. Following restoration of the levee slopes, crews then installed a new levee road as part of the final cap. The levee road was constructed of six inches of OkDOT Type A road base made from granite. Paired embankment measuring points were installed every 500 linear feet for future monitoring of the dike.

Work was conducted to comply with Oklahoma Pollution Discharge Elimination System Stormwater Construction General Permit OKR10. A SWPPP was developed for the site and the site was regularly inspected for compliance. BMPs installed to manage the stormwater runoff from the site included wire-backed silt fence and straw wattles.