SPECIAL NOTICE
B -- Review and Analysis Services of Issue Evaluation Studies of Hungry Horse Dam. Independent review of seismotectonic studies and risk analysis as part of a Consultant Review Board (CRB) for Hungry Horse Dam.
- Notice Date
- 7/12/2004
- Notice Type
- Special Notice
- Contracting Office
- BUREAU OF RECLAMATION PO BOX 25007, D-7810 DENVER CO 80225
- ZIP Code
- 80225
- Solicitation Number
- DOI-SNOTE-040712-001
- Archive Date
- 7/12/2005
- Description
- Notice of Intent 1. GENERAL: The Bureau of Reclamation (Reclamation) has a requirement for Review and Analysis Services to participate as part of a Consulting Review Board (CRB), and to provide review services to Reclamation for Hungry Horse Dam, Hungry Horse Project, Montana. As part of the CRB, the contractor shall provide an independent review of the seismotectonic studies and analysis and risk analysis activities performed by Reclamation as part of an Issue Evaluation (IE) for the dam. 2. BACKGROUND: 2.1 Hungry Horse Dam is a large concrete gravity arch structure, completed in 1953, on the South Fork of the Flathead River in northwestern Montana. The dam is over 560 feet high with a crest length of about 2100 feet. The spillway consists of an inclined shaft connecting to a horizontal tunnel through the right abutment, controlled by a ring gate on the morning-glory spillway inlet structure. The outlet works consist of three pipes through the right side of the dam. The powerplant at the toe of the dam contains four turbines, each supplied by a separate penstock constructed through the central portion of the dam. 2.2 The foundation rock is Precambrian dolomite, originally referred to as the Siyeh Limestone (it is now considered part of the Helena Formation, a unit within the middle Proterozoic Belt Supergroup). The "limestone" at the site contains siliceous, argillaceous, and dolomitic material which makes it hard and insoluble. The bedding dips about 25 to 30 degrees into the right abutment and slightly upstream. The bedding planes are planar and continuous, although their surfaces contain ripples and other irregularities that increase the roughness. Slippage and shearing along some of the bedding planes as the result of the regional folding and tilting is evident from the mapping and explorations. These shears were termed "bedding plane slips" (BPS) on the geologic maps. The character of these discontinuities is variable; in some places filled with up to a few inches of clay, in other places filled with crushed and sheared rock, and in other places exhibiting rock to rock contact. The original designers considered these to be "minor features in the foundation and abutment rock with the exception of one zone containing gouge and clay from 1/16 to 4 inches in thickness". This exception was termed the "Lift Seam". Since the mapped descriptions seem rather similar for other bedding plane slips, it is not completely clear why this one was singled out, other than perhaps it was exposed in the dam-foundation footprint and was closest to the dam-foundation contact. A series of six fault zones oriented roughly upstream-downstream cross the left dam foundation contact between the extreme left end of the dam and the river channel. Cutoff shafts were excavated along the three largest zones near the upstream and downstream face of the dam, and then backfilled with concrete. A trench was also excavated and backfilled with concrete along the entire dam-foundation contact. The Lift Seam extended from Block 8 to Block 13 on the left abutment, and from 11 to 19 feet below the foundation rock surface between Fault Zone No. 3 and Fault Zone No. 4. 2.3 Special treatment was performed for the "Lift Seam". This consisted of drilling holes on 5-foot centers across the Lift Seam. Water and air was injected into these holes at pressures less than 30 lb/in2, and vented to adjacent holes. The washing continued until the vented effluent was clean, and then the seam was grouted from the lower holes continuing to the higher holes, after a thick grout return was noted exiting from holes upslope from the injection point. After performing this procedure under Block 13, a 36-inch-diameter Calyx hole was drilled to verify the effectiveness of the method. It was noted that about half of the seam had been washed free of clay and grouted. A similar procedure was used under Block 12, but upon drilling of another Calyx hole, it was noted, "Grout was found all around the perimeter of the hole, but in laminations with thin layers and lenses of a light tan clay. The reddish-brown clay had apparently been washed out and replaced by grout." After trying several additional methods for washing and grouting the seam, the only method that appeared to dislodge additional tan clay material was using a side jet with high pressure (250 lb/in2) water. This method was continued up to Fault Zone No. 3 (Block 8), where the excavation was deep enough to remove the Lift Seam. Additional Calyx holes, drilled to check the effectiveness of this method, indicated about 70 to 80 percent of the clay had been replaced by grout. 2.4 Well defined foundation blocks occur in the left abutment, formed by bedding plane "slips" parallel to the abutment, intersecting with fault and shear zones and daylighting in the canyon wall downstream. Continuous high angle joint sets form release planes for the blocks. Rigid block static stability analyses of left abutment foundation blocks indicate factors of safety of around 1.5 for normal loading conditions. The analyses are based on assumed discontinuity friction angles, and foundation uplift forces calculated from the foundation pressure gages and known surface seep locations. The foundation loads were estimated from structural finite element analyses and applied to the block in an uncoupled calculation. 2.5 Reclamation has performed studies to evaluate the risk associated with Hungry Horse Dam under a variety of different loading conditions. Based on these studies, the level of risk associated with both static and seismic loading was determined to be above Reclamation guidelines. The static risk is in the range to take risk reduction action. Since there is only one static potential failure mode, sliding of the left abutment drives the risk. It should be noted that the annual failure probability is fairly low, and from a deterministic standpoint, the abutment would likely be considered to meet previously accepted stability criteria. However, the high structure, large reservoir, and significant consequences drive the risk to an area where further action is justified. The seismic risk is borderline for justification to take expedited action. This too is driven almost exclusively by the left abutment sliding potential failure mode. The majority of the risk stems from remote seismic loading (less than 10-5 exceedence probability) associated with the Branciforte earthquake record. A deterministic approach would not consider events this remote. If the Branciforte record was not considered, the risk would still be in a range justifying risk reduction actions, driven primarily by the large consequences, although it would be comfortably below the expedited action guideline. 2.6 A review of the analyses performed to identify and evaluate potential failure modes and to estimate their level of risk is now required. 3. CONTRACTOR QUALIFICATIONS: 3.1 30-years experience in hazard and decision analysis as applied to critical facilities 3.2 Must have provided probablisitic seismic hazard and ground motion analysis 3.3 Must have provided seismic source and ground motion characterization. 3.4 Must be capable of development of hazard methodologies. 3.5 Must have provided assessment of potential earthquake hazards for at least 10-existing or proposed dams and or nuclear power plants of similar size as Hungry Horse Dam or larger. 3.6 Must have participated in review boards and provided expert testimony for potential or surface faulting at proposed or existing sites. 3.7 Experience with Reclamation facilities desirable but not necessary. 3.8 Proven expert elicitation in the development of hazard methodologies and uncertainty treatment in performance assessment. 3.9 Developed multiple regional seismic hazard mapping and microzonation studies. 3.10 Documented reports on seismic source and ground motion characterization for risk analysis. 3.11 Ph.D. Geotechnical engineering 3.12 Demonstrated knowledge in the quantitative evaluation of hazard by combining statistical data and expert judgment. 3.13 Demonstrated capability to integrate the fields of earth sciences, hazard analysis and risk assessment. 3.14 Demonstrated capability must be in the form of citable publications. It is Reclamation's belief that Dr. Robert R. Youngs of Geomatrix Consultants, Inc. possesses the above experience and is the only source capable of providing Reclamation with the services required. This is not a formal solicitation. However, individuals or concerns that respond shall be able to provide proof of their capability to meet the above requirements of the review board member prior to being provided a copy of the solicitation. This notice may represent the only official notice of such a solicitation.
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- Record
- SN00619278-W 20040714/040712212409 (fbodaily.com)
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