DA Smith completed a 2024-25 Phase 1 drilling and instrumentation campaign at Denver Water's Gross Reservoir hydroelectric dam located near Boulder, Colorado, as part of the $464 million Gross Reservoir Expansion (dam raise) project being constructed by Kiewit-Barnard Joint Venture (KB). A series of difficult-access groundwater monitoring holes were drilled into the foundation of the dam and at downstream points beyond the dam’s footprint. Holes were completed with casing, screen, filter media, and aluminum locking monuments in accordance with engineered design. DA Smith installed Geokon vibrating wire piezometers in all monitoring holes. Additional holes were drilled and instrumented with Geokon multiple point borehole extensometers. DA Smith also installed solar panels and telemetry nodes at select holes for remote transmission of piezometer data.
Drilling required setting up on steep sections of the dam or on cliff edges along the river canyon. Tracked and frame-mounted modular drills were used. Equipment was hoisted to inaccessible hole locations by KB construction cranes.
Drilling was conducted with a state-of-the-art water hammer system capable of rapid penetration while imparting minimal disturbance to the rock mass. Air-hammer drilling was prohibited due to industry-wide concerns about foundation fracturing. Coring was conducted on a limited basis. All drilling required filtered recirculation of drilling fluids with zero discharge to site. Water hammer drilling proved successful, achieving high efficiency and stable boreholes.
DA Smith utilized Colog to complete high-resolution optical and acoustic televiewer (OBI and ABI) logging of the holes. Colog produced statistical fracture analyses from the televiewer logs.
DA Smith also re-drilled multiple historical drain holes from the dam crest to recondition the drains for dam expansion.
The project was completed successfully and on schedule in spite of inclement weather during winter months in the Rocky Mountains. DA Smith worked closely with key project stakeholders, including Kiewit-Barnard, AECOM, Black & Veatch, Colorado Division of Water Resources, and Denver Water.