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Void Filling


Russellville, KY: Pressure Grouting Mud River Flood Retarding Structure #12

dam-void-filling-mud-river-ky

The project was performed for the USDA-NRCS under the American Resource Recovery and Reinvestment Act (ARRA) to mitigate seepage through the dam foundation and preclude potential future failure of the flood-control structure. The foundation contains karstic "Haney" limestone formations, which resulted in the development of a large sinkhole within the embankment and several major interconnected water-conduits/voids in the foundation near the right abutment area.

Six (6) exploratory borings were initially installed using Split Spoon Sampling and Rock Coring methods to assess the condition of the embankment and delineate the location of the Haney Limestone formation.

Pre-grouting of the sinkhole and major void locations were performed prior to the installation of the grout curtain. The sinkhole and void locations were thoroughly cleaned and prepped for grouting. Dental concrete work was performed and the features were grouted under low pressure with low mobility.

Grout borings were installed in two phases:

  • Drill through the overburden material and set a 3.5" PVC casing into the bedrock layer.
  • Drill through the underlying rock to the specified elevation.

Grout borings were installed at a 30-degree angle (from vertical) to maximize the likelihood of intercepting high-angle fractures and joints. Casing was installed through the overburden using appropriate casing-advance methods and was grouted in place. Borings were drilled with a rotary drill rig utilizing a destructive bit with water-only flush to approximately 50-feet below ground surface. This drilling method produces a smooth walled hole to facilitate pressure testing and grouting operations.

Water pressure tests were conducted in 10-foot ascending stages to assess the permeability of the rock. Water passed through Geo-Con's "Accugrout" header system containing high-precision pressure and flow control valves, mag-flow meter and electronic pressure transducer, with on-board displays prior to delivery to the test stage. The test stage interval was isolated using a water packer apparatus that consisted of two straddle-style pneumatic packers separated by perforated pipe. Borings were water tested with single pressure three-minute tests in 20-foot ascending stages. Water flow rates and total takes were recorded and used to generate total Lugeon values for each stage.

Grouting of the bedrock progressed in 10-foot ascending stages. Geo-Con established a grouting program that included progressive grout viscosity adjustment and flow rate limitations in response to real-time assessment of grouting parameters. The goal of the program was to achieve efficient refusal/closure of fractures while maintaining a limited grouting reach in each boring. Grout passed through the "accugrout" header system prior to delivery to the target grout stage. Stages were isolated with a grout packer apparatus that consisted of a single pneumatic packer attached to the bottom of an aluminum grout pipe. Difficult or high-take stages were addressed with a Medium Mobility Grout containing Portland cement, bentonite and fly ash. Grout flow rates, apparent Lugeon, pressure, and total gallons of grout pumped were recorded and used to generate grouting reports for each stage. Geo-Con also performed access road improvements and the installation of a stream crossing, site clearing, and installation of E&S and Pollution controls.



 

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