Project Features:
- Single-Line Grout Curtain
- Pressure grouting of rock and weathered rock/soil overburden
- Drilling through dam embankment soil and casing
- High-speed coring through spillway structure
- Used a suite of low to high mobility balanced, stable grouts
Background:
The Pahagaco Lake and Dam was formerly used to supply water to the Glatfelter Paper Spring Grove Facility. While the lake is no longer used as a water supply, Glatfelter maintains the lake for public recreational use. High water flows in downstream toe drains prompted repairs to the dam foundation and bedrock contact soils in the embankment.
Description of Work:
The following summarizes the grout curtain parameters:
| Length: | 256 Lineal Feet |
| Number of Borings: | 76 Locations |
| Total Depth: | 42-feet Max, 37-feet Average |
| Total Overburden Drilling: | 1,380 Lineal Feet |
| Total Concrete Coring: | 121 Lineal Feet |
| Total Rock Drilling: | 1,400 Lineal Feet |
| Total Grouted Length: | Approximately 2,160 Lineal Feet (rock and 10-feet of soil immediately overlying) |
Drilling and grouting on Pahagaco dam was represented by 3 cases:
Case 1 – Drilled from existing embankment
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- Drill and case through overburden
- Drill rock
- Grout Rock
- Pull casing and grout 10-feet above bedrock
Case 2 – Drilled from existing embankment within footprint of existing spillway footing.
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- Drill and case through overburden
- Core through concrete spillway footing
- Drill rock
- Grout Rock
- Grout footing interface
- Pull Casing and grout 10-feet above bedrock
Case 3 – Drilled from existing concrete forebay slab
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- Core through concrete forebay slab
- Drill rock
- Grout Rock
Geo-Solutions subcontracted the drilling associated with the installation of the grout curtain. Grouting of the bedrock progressed in 10-foot ascending stages. Grout passed through Geo-Solutions’ custom 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. Steel casing set in overburden was extracted 10-feet and the soil/bedrock contact zone was grouted to address any potential defects or flow paths.
Project Challenges:
Narrow dam crest made coordination of drilling and grouting operations challenging. Highly erodible embankment soils necessitated careful control of drill water.
