Powerful teamwork saves lives and reconnects Allegheny County communities after the collapse of a key travel artery.
Creating Better Geohazard Solutions, Together.
Geohazard challenges created by landslides and other ground movements present significant hazards to public safety for people and property across the country, and around the globe.
Gannett Fleming, a proud sponsor of the Association of Environmental & Engineering Geologists (AEG) Annual Meeting’s Opening Session, has provided geohazards remediation and geotechnical solutions customized to meet our clients’ goals for more than four decades. Our skilled experts look forward to sharing their insights with you, our valued AEG colleagues, as we work toward creating better solutions for geohazard challenges.
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Geology as Related to Featured Dams and Cofferdams in Western Pennsylvania
Thursday, September 15, 2022 • 8:40 a.m.
Located in northwest Pennsylvania on the Allegheny River, Kinzua Dam is a combination concrete gravity and earth-rock fill dam that impounds a 26-mile-long reservoir. Siting of the dam was of paramount importance to optimize the location of the structure in the Allegheny River Valley and to reduce cost as summarized in the Geology of Pittsburgh, Pennsylvania, USA, Gray, et al. (2015). The original siting for the dam was more than a mile upstream of its present-day location.
Due to considerable depth to sound bedrock, the original design called for a rather deep excavation with cofferdam construction for a gravity dam. Geologic studies led to conforming the dam design and its foundation to a much more optimal and cost-effective location. The Kinzua Dam project completed in 1956 was cited as an outstanding example of geology in the Handbook of Geology in Civil Engineering by Leggett and Karrow (1976).
Point Marion Lock, originally built in 1926, had exceeded its design life and a new larger lock chamber was needed to improve structural reliability and passage of river cargo moved by barges. The challenge was to build a larger lock chamber on the landward side of the old existing lock chamber.
Construction of a similar project had been attempted only once before at Wheeler Lock and Dam, Ala. As with Point Marion Lock, Wheeler Lock used the landwall of the old lock as a cofferdam for the excavation for the new structure. In 1961, Wheeler Lock failed catastrophically with loss of life and shutting down of the Tennessee River. Taking lessons from this tragic cofferdam failure, the Point Marion landwall cofferdam was stabilized with nearly 500 prestressed rock anchors and was highly instrumented for movement (Greene et al., 1993). The project was successfully constructed and was recognized as an Outstanding Project by ASCE.
A Closer Look at Instrumenting Old Casagrande Piezometers with New Vibrating-Wire Sensors
Thursday, September 15, 2022 • 2:40 p.m.
Observation wells and Casagrande piezometers, or open-standpipe piezometers, are commonly installed in embankment dams for measuring water levels and pore water pressures, respectively, for the purpose of modeling the phreatic surface and flow patterns.
Manual measurements of the height of water within the well or piezometer casing are taken using a water-level indicator. For semi-automated or fully automated measurements, vibrating-wire pressure transducers (sensors) can be placed within the well or open-standpipe casing, which is a popular, cost‑effective application for increasing the value of older, existing installations.
Ideally, the manual and sensor measurements are close, and manual measurements can be used to validate the sensor reading. However, discrepancies greater than 1 foot are known to occur, and a better understanding of the causes will benefit the dam safety and instrumentation and data monitoring community.
This presentation will summarize preliminary results from initial field and lab testing conducted to compare manual vs. vibrating-wire pressure transducer measurements of observation wells and open‑standpipe piezometers.
Erodibility Studies Performed at the Don Pedro Dam Emergency Spillway
Friday, September 16, 2022 • 10:40 a.m.
Following the incident at the Oroville Dam spillway in February 2017, a focused spillway assessment was performed for the controlled and emergency spillways at Don Pedro Dam (the 9th highest dam in the United States) located in the Sierra Nevada foothills near La Grange, Calf.
The focused spillway assessment identified potential erosion concerns along the left emergency spillway training wall, which separates flow within the emergency spillway from the adjacent controlled spillway structure and channel. An erodibility study was performed in two phases:
- An initial phase for reviewing existing information and performing a geologic reconnaissance and seismic refraction survey to develop Erodibility Index Method input parameters to assess the erosion potential along the training wall foundation.
- A second phase for performing surficial cleaning of the emergency spillway channel materials along the training wall to better characterize bedrock conditions and to locate two bedrock shears that were mapped within the adjacent controlled spillway during construction.
This presentation provides an overview of the studies performed and a summary of how the results were used to inform a semi-quantitative risk assessment (SQRA) that was performed to identify key risk drivers at the site. It also serves as a lead in to the second presentation regarding use of the Block Theory Rock Erodibility Method on the right abutment of the emergency spillway.
Geohazard Projects: Leveraging Traditional Data & Technology to Develop Site Characterization, Investigation & Mitigation Plans