March 31, 2017

Geosyntec to Present at the USSD 2017 Annual Conference and Exhibition

Geosyntec staff will make a substantial technical contribution to the United States Society on Dams (USSD) 2017 Annual Conference and Exhibition in Anaheim, California on April 3-7, 2017.

Presentations will be made by Lelio Mejia, Chris Conkle, Al Preston (California), Glenn Rix, Raphael Siebenmann (Georgia), Lucas deMelo (Maryland), Jamey Rosen (Guelph), Andrew Higgins (Ontario).

The 2017 USSD Conference Theme is "It's a Small World: Managing Our Water Resources." The theme makes lighthearted reference to the Conference venue in Anaheim, just blocks away from Disneyland, and points to how the world is connected to a finite amount of water resources, especially fresh water. With so many interconnected competing interests for our limited water resources, collaboration from a diverse population is a necessity — just as the "It's a Small World" attraction at Disneyland showcases cultural diversity and international unity.

The United States Society on Dams (USSD) is dedicated to advancing the role of dam and levee systems and building the community of practice. As the United States member of the International Commission on Large Dams (ICOLD), USSD provides a forum for the exchange of knowledge and experiences and is charged with leading the profession of dam and levee engineering.

Abstracts

Construction of Borinquen Dam 1E for the Panama Canal Expansion

Lelio H. Mejia, Ph.D., P.E., G.E.
James Toose, AECOM
Jorge Fernandez, Panama Canal Authority

The recently completed Panama Canal Expansion project required construction of a 6.7-km-long channel at the Pacific entrance to the Panama Canal, to provide navigation access from the new Post-Panamax locks to the existing Gaillard Cut section of the Canal. The new channel required construction of four dams, known as Borinquen Dams 1E, 2E, 1W, and 2W. The dams retain Gatun Lake, the main waterway of the Panama Canal, approximately 11 m above the level of Miraflores Lake and 27 m above the Pacific Ocean.

The dams were designed as rockfill embankments with a central impervious core of residual soil flanked by filter and drain zones of processed sands and gravels. Design of the dams posed multiple challenges, some of which had to be addressed during construction as well, including: 1) variable foundation conditions with occasional unpredictable weak features, 2) use of residual soils derived from rock weathering as core materials, 3) a wet tropical climate with a 4-month dry season, and 4) geologic faults across the dam foundations.

The largest of the dams, Dam 1E, is 2.2 km long and up to 30 m high, and abuts against Fabiana Hill at the dam's southern end, and against the original Pedro Miguel Locks at the northern end. Construction of the dam included the following main project elements: 1) erection of a 1.3-km-long, 20-m-high, cellular sheetpile cofferdam, 2) installation of a 30-m-long, 18-m-deep, triple-row jet-grout cutoff wall, 3) construction of a 460-m-long, 18-m-deep, cement-bentonite slurry cutoff wall, 4) dewatering and excavation of the dam foundation, 5) treatment and geologic mapping of the foundation, 6) injection of a 2.4-km-long, double-row grout curtain, 7) installation of performance monitoring instrumentation, 8) placement of a 5.9-million-cubic-meter, zoned rockfill embankment, and 9) construction of a 100-m-long, 22-m-deep, secant pile wall to provide closure against the structure of the Pedro Miguel Locks.

This paper provides an overview of the construction of Dam 1E including the chronology and sequencing of the works, borrow of the embankment materials from the required channel excavations and other sources, and the key aspects of construction of the above project elements. The paper will also describe the most important design changes required during construction of the dam.

Performance of Fena Dam during the 1993 Guam Earthquake

Lelio H. Mejia, Ph.D., P.E., G.E.

The potential for softening and strength loss of cohesionless and clay-like soils during strong, long-duration earthquake shaking is a key issue in the seismic safety assessment of embankment dams located in tectonic subduction regions of the world, and in regions where the hazard from large magnitude earthquakes is significant. Limited published experience is available regarding the performance of dams underlain by fine-grained soils subjected to large earthquakes. This paper presents a case history on the observed performance of Fena Dam during the magnitude 7.8, 1993 Guam Earthquake, which was generated by subduction of the Pacific Plate under the Philippine Plate. Located on the Island of Guam, the dam is an earth and rockfill embankment founded on deep, young alluvial and lacustrine deposits. The paper describes the observed performance of the dam during the earthquake, presents analyses of the dam's seismic stability, and discusses implications of the observed behavior for practice.

Instrumentation and Information Management at Boone Dam

Rozh Ameen, Civil Engineer, P.E., PMP, Tennessee Valley Authority
Raphael Siebenmann, Civil Engineer, P.E.
Jamey Rosen, Geologist, M.Sc., P.G.
Andrew Higgins, Scientist, B.Sc.

The appearance of a large sinkhole on October 20, 2014 at Boone Dam, followed by turbid seepage observed in the tailrace a few days later, triggered emergency response actions by Tennessee Valley Authority (TVA), which included immediate lowering of the headwater level, installation of filter at the tailrace of the dam, continuous surveillance and monitoring of the project, a thorough review of historical records, an extensive subsurface exploration and instrumentation program, and the initial exploratory grouting. These programs have and will continue to generate a significant amount of data that, along with the archives of historical data, need to be reviewed and accessed, often in real time, by a broad range of stakeholders.

This paper will provide an overview of the development and implementation of the state of the art Information Management System (IMS) and Instrumentation Data Acquisition System (IDAS) to support the monitoring and construction activities. These systems include the use of web technology to consume and visualize high-frequency instrumentation data, and the use of Geographical Information Systems (GIS) technology to allow access to disparate data streams in a common geospatial context. The paper will describe how these tools are currently being used by TVA in the development of a hydrogeological model, in the monitoring of the embankment during exploratory grouting, and finally to ensure the most important objective is met, which is to cause no harm during investigation and construction activities.

Modeling of Internal Erosion in Earthen Embankment Dam

Al Preston, Ph.D, P.E
Keil Neff, Ph.D., P.E., Bureau of Reclamation
Chunling Li, Ph.D., P.E.
Lucas de Melo, Ph.D., P.E.

In 2014, a high hazard embankment dam in South East Appalachia developed a sinkhole at the toe and additional inspections revealed muddy water seeping from the riverbank into the tailrace, indicating potential internal erosion.  Consequences of dam failure included probable loss of human life and significant economic and environmental consequences.  Numerical modeling of the geotechnical and hydrotechnical components of a potential internal erosion failure was conducted to assess downstream risk due to potential dam breach and to examine potential mitigation strategies.

The Windows™ Dam Analysis Modules – Version C (WinDAM C) numerical model was used to evaluate the potential internal erosion failure and provide hydrograph input for downstream flow-routing modeling.  A bootstrapping technique was used to estimate realistic ranges of soil erodibility based on standard soil test results and using relationships from the literature.  The WinDAM C model provided predictions of the peak downstream flow rate and time of occurrence, downstream warning time, and the final size of the breach in the embankment.  The results demonstrated that maintaining the reservoir at a low pool elevation was the most effective strategy for minimizing the risk associated with internal erosional dam failure. Other mitigation strategies, such as opening the spillways at the onset of failure, were also assessed. The results of the modeling provided critical information to better assess the dam safety risk and facilitate decisions on mitigation strategy.

Seismic Deformation Analysis of Blue Ridge Dam

Glenn J. Rix, Ph.D., P.E.
Lucas de Melo, Ph.D., P.E.
Christopher L. Saucier, Ph.D., P.E., Tennessee Valley Authority
Michael A. Morrison, P.E., PMP, Tennessee Valley Authority

Blue Ridge Dam (BRD) was constructed in the 1920s on the Toccoa River near Blue Ridge, Georgia, and was subsequently purchased by the Tennessee Valley Authority (TVA) in 1939. BRD is approximately 985-ft long and 172-ft high and retains a useful storage volume of approximately 183,900 acre-feet. The dam is a semi-hydraulic fill earthen embankment constructed by placing uncompacted "dumped" fill from local, residual soil sources on the upstream and downstream faces. The dumped fill was subsequently "washed" using water cannons to mobilize the fines, creating a "sluiced fill" zone and a central "puddled core" of fine-grained material. The resulting embankment materials are transitional soils that straddle the boundary between non-plastic, coarse-grained and moderate plasticity, fine-grained soils. The dam is located in a low-to-moderate seismic hazard area near the Eastern Tennessee Seismic Zone. Because of the nature of the construction and location of BRD, TVA decided to evaluate seismic deformations of BRD. An extensive site investigation program was used to characterize the embankment soils, including the use of normalized (i.e., SHANSEP) monotonic and cyclic strength parameters and stress history profiles. PM4SAND, an advanced constitutive model available for FLAC® 7.0 (Fast Lagrangian Analysis of Continua) was calibrated using the monotonic and cyclic laboratory results and used for numerical analyses. A suite of earthquake time histories representing high- and low-frequency ground motions and two return periods (3,000 and 10,000 years) was employed in the analyses.

Stability Analysis of a Concrete‐Faced Rockfill Dam using Parametric Evaluations

Christopher Conkle, P.E., G.E.

The authors were retained by the owner of a rockfill embankment dam as part of an ongoing Dam Safety and Risk Assessment Program (DSRAP) to better understand the risks associated this dam. The dam, an approximately 500 foot long concrete‐faced rockfill embankment dam, as part of a larger complex hydroelectrc system was built the early 1900's. Due to limited information about materials within the dam, static stability analysis included an in‐depth desk study to establish typical, lower, and upper bound rockfill static and dynamic material properties based on literature data, anecdotal information from the Dam operators, historical information, and photographic evidence. A parametric static stability evaluation was performed to identify critical slip surfaces and material properties. Results of the parametric static stability analysis were used to evaluate stability in required scenarios and identify critical slip surfaces for seismic stability analysis. Seismic stability analysis involved selecting a suite of near‐field and far‐field strong ground motions scaled to a site-specifc conditional mean spectrum (CMS). The selected ground motions were then applied to a QUAD4MU model to estimate accelerations throughout the dam cross section. The QUAD4MU model material properties were parametrically varied to identify the critical set of material properties. The appropriate Dam response time history was selected based on the identified cross section in the static stability analysis and used to evaluate potential crest displacement with a Newmark sliding block approach. The authors provided typical, lower, and upper bound estimates of expected seismic displacement of the Dam crest based on combinations of material properties and ground motions identified in the parametric analysis. The analysis allowed the dam's owner to identify which unknown material properties had the largest effect on displacements and therefore warranted additional investigation.

More Information

For more information regarding the conference, visit: USSD 2017 Annual Conference and Exhibition and the conference schedule PDF.
For more information on managing water resources, contact Al Preston This email address is being protected from spambots. You need JavaScript enabled to view it..

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