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GEOTECHNICAL CONSTRUCTION Jet Grouting Beacon Lake Dam was built to impound the water of a small creek and create the Beacon Lake Reservoir. Since completion of the earthen dam, the Owner, Bluegreen Southwest Land, Inc., has been unable to raise the level of the lake even though they have been pumping water into the lake. The dam was constructed with a clay core within the embankment dike overlying a soil-bentonite barrier wall (slurry wall) constructed through the natural ground and keyed into bedrock to cut off seepage beneath the embankment. Previous investigations by the Engineer indicated the possibility of voids or very loose areas in the soil-bentonite barrier wall which may be allowing a significant amount of seepage underneath the dam and preventing the lake from filling.
Working closely with the Engineer, Geo-Con developed and implemented a three-phase approach to improving the integrity of the barrier wall and mitigating the seepage through the dam. Phase I consisted of performing exploratory drilling to identify soft areas, voids and potential areas of seepage in the dam core and slurry barrier wall. Geo-Con installed 130 exploratory bore holes placed every 16 feet along the alignment of the 2,000 foot-long dam embankment. A track-mounted drill rig was used which could readily maneuver to the correct position on the dam crest. Borings were drilled from the dam crest through the clay core, slurry barrier wall and into the natural key material with depth up to 90 feet. Results of the boring program indicated several potential problem areas consisting of very soft or loose soils and possibly voids within the slurry barrier wall with some extending beneath the barrier wall into the foundation key material. In addition, it was determined from the drilling that the alignment of the clay core strayed from the slurry barrier beneath a corner of the dam embankment leaving a gap in the seepage barrier of the dam.
Phase II consisted of pressure grouting the soft zones and potential voids identified in the barrier wall along a 200-foot long segment of the dam. Geo-Con performed pressure grouting with a high viscosity cement-bentonite grout to displace soil materials and fill voids near the base of the slurry barrier wall and natural key. Over 50 grout columns were placed at 4-feet on centers to ensure overlap of grout from column to column. Once the pressure grout was set, each column was jet grouted with cement-bentonite grout to reestablish a continuous barrier wall and seal the joint between the barrier wall and the clay core. A total of over 160 columns were drilled and grouted with depths typically near 90 feet deep. Grouting was completed with Geo-Con's track-mounted jet grout drill rig, high pressure jet pump and custom grout plant. Initial indications show seepage from the dam has been significantly reduced and the impoundment level is rising.
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