DAM INVESTIGATION, ANALYSIS AND DESIGN

R. CRAIG FINDLAY, PH.D., P.E., G.E.

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Findlay Engineering, Inc. (FEI) conducts various numerical analyses for water resource clients.  As tools to efficiently conduct those analyses, FEI has a number of state of the art computer analysis programs available which results in savings of time and money to the client.   FEI uses the following software (please note that FEI does not sell software):

PROGRAM

DESCRIPTION

PURPOSE

SLOPE/W GeoStudio 2007 (Geo-Slope Int’l)

CAD interface limit equilibrium analysis

Slope stability analysis, both circular and non-circular

SEEP/W GeoStudio 2007    (Geo-Slope Int’l)

CAD interface FEM analysis of seepage

Two dimensional seepage analysis, both steady state and transient.

SIGMA/W GeoStudio 2007  (Geo-Slope Int’l)

FEM analysis of stresses and deformations

Analysis of stress, deformation and soil-structure interaction

QUAKE/W GeoStudio 2007  (Geo-Slope Int’l)

FEM analysis of seismic response and pore pressure development

Analysis of dynamic response of earth structures to seismic loading (time history analysis)

TEMP/W GeoStudio 2007  (Geo-Slope Int’l)

FEM analysis of thermal dynamics in soils and foundations

Analysis of ground temperature changes and foundation insulating behavior

CLARA-W  (O.Hungr Geotechnical Research,lnc.) Slope Stability Analysis in 3D Analysis of three dimensional slope stability problems of earth structures and natural slopes 
UTEXAS 4 (Shinoak Software) Two and Three Step limit equilibrium analysis Analysis of  rapid drawdown and pseudo-static slope stability of embankments

SAP2000NL V11.0 (CSI)

Three dimensional FEM analysis of structures

Static and seismic (response spectra or time history) stress analyses of structures such as arch dams, gravity dams and radial gates.

QUAD4M (UCB)

Two dimensional seismic response FEM analysis

Dam liquefaction potential and deformation analysis

SHAKE91

One dimensional finite difference dynamic response

Flat ground liquefaction potential and deformation analysis

MODFLOW/EM (USGS)

CAD type  three dimensional finite difference seepage model

Construction dewatering, relief well drawdown, three dimensional seepage in irregular situations.

SP5 (UCB)

Generates hyperbolic stress-strain properties from triaxial compression CID and UU test data.

Strength, stress-strain and bulk modulus parameters for input into SIGMA/W

SPECEQ/UQ (UCB)

Generates Response Spectra

Derive period of maximum spectral acceleration for input of into QUAD4M (along with actual time histories)

STABL5 and 6

Limit equilibrium analysis

Slope Stability

FEIDAM

Spread sheet gravity dam analysis developed by FEI

Computation of base pressures, overturning, cracked base and and sliding of two and three dimensional gravity dam sections and blocks

CSLIDE (ACOE)

Corps of Engineers gravity dam analysis

2D Sliding Stability

3DSAD (ACOE)

Corps of Engineers Gravity Dam analysis

3D Gravity Section Analysis

COM642

Pile lateral load analysis

Lateral pile load capacity

WEAP (FHWA) Pile wave equation analysis Pile drivability and capacity
AUTOCAD LT 2006 CAD drawing/analysis program For drafting figures, conducting areas analyses
HEC-RAS Water surface profile and flow analysis For determining tailwater rating curve under various flows for dam stability analyses

Below is a summary of representative analyses conducted by Dr. Findlay:

 

Post-Earthquake Analysis of a Semi-Hydraulic Fill Embankment, Sinclair Dam, Georgia Power Company Between 2003 through 2007, Dr. Findlay conducted a detailed seismic analysis of the 90 foot high West Embankment of Sinclair Dam, located on the Oconee River, near Milledgeville, Georgia, and assisted in addressing follow-on questions and analyses requested by the FERC. The dam has lower upstream core sections consisting of semi-hydraulic fill, and exhibited in old construction photographs (circa 1920s) and as determined by low SPT “N” values measured in test borings. The FERC has requested several dam owners in the southeast to re-evaluate the seismic stability of their semi-hydraulic fill dams, based on potentially loose conditions that could exist and the proximity of some of the dams to the 1886 Charleston, S.C earthquake epicenter. Georgia Power retained Dr. Findlay to conduct the seismic assessment. The assessment included assessing liquefaction potential based on SPT “N”-values, assessment of post-earthquake residual strength, and post-earthquake and seismic deformation analysis. The post-earthquake analysis was conducted using the program UTEXAS4, which required extensive review and assessment of drained and undrained triaxial test data to develop strength parameters for the two-step Lowe and Karafiath type undrained strength approach incorporated into the program. The analysis indicated adequate seismic stability. Deformation was computed using the Makdisi-Seed approach, and indicated that seismic deformation under the maximum credible earthquake would be tolerable. The analyses have been accepted by the FERC in 2007, and no rehabilitation of the West Embankment has been required.

Cross Channel Analysis of Ambursen-Type Slab and Buttress Dam, Aziscohos Project, FPL Energy Maine Hydro LLC – In 2004, Dr. Findlay conducted a 3D finite element stress analysis of the internally arched buttress dam section of Aziscohos Dam, located on Magallowag River near Wilson Mills, Maine. Response spectra were developed for the analysis in the three orthogonal directions. Five bays of the dam were modeled (the deepest bays) using the program SAP2000NL, and seismic loading was applied in the cross channel, channel parallel and vertical directions. Seismic loading at normal full reservoir level, both with and without ice loading, was considered. The dam was found to be structurally adequate.

Chittenden Dam Slope, Gravity and Seismic Stability Analyses - Central Vermont Public Service - In 2006, Dr. Findlay updated stability analyses on selected interpretive cross sections of Chittenden Dam. The dam is located in central Vermont, about eight miles northwest of the city of Rutland at the head of East Creek. The analyses included consideration of the west (main) embankment cross section, an east embankment cross section, and a concrete spillway section founded over a portion of the embankment dam. The cases of normal full pool loading, flood loading, normal plus seismic, and rapid drawdown were analyzed. The embankment slope stability analyses were conducted using the program SLOPE/W, licensed by FEI from GEOSLOPE International, Calgary Alberta, Canada. The analysis was completed using the Spencer Method. Analyses of the concrete gravity ogee spillway were made using the two-dimensional gravity analysis method, and the normal, PMF and post-earthquake loading cases were considered. The tailwater elevation at the spillway is an important consideration with regard to assessing uplift under the concrete gravity spillway. No previous analysis of the PMF tailwater elevation has been made for the project. For this analysis, a simple HECRAS model of the spillway discharge using the inline spillway feature of HECRAS. Three cross sections upstream of the spillway were developed to model the reservoir and three cross sections downstream of the dam were developed to model tailwater conditions. The upstream boundary condition of the model was a constant head elevation of the reservoir, and the downstream boundary condition (900 feet downstream of the spillway) was critical flow depth. The steady state model used downstream cross sections developed from interpretation of USGS topographic mapping, and the available near-dam project topography. The analyses found the structures were adequately stable under all considered loading conditions.

Upper and Middle Dam Remedial Measures, Androscoggin River Drainage, FPL Energy-Maine Hydro LLC – From 2005 through 2008, Dr. Findlay was responsible for the geotechnical aspects of the remediation of the embankments for Upper and Middle Dams located in the Western Mountains of Maine. This work was under review of the Federal Energy Regulatory Commission (FERC). The dams are owned and operated by FPL Energy and regulated by the FERC. The embankments were constructed in the early 1900’s and in recent years were identified to have seepage, artesian pressure and slope stability problems that the FERC had directed the owner to remediate. The FERC had also directed the owner to assess if the embankments had any seismic stability/liquefaction issues. Dr. Findlay planned an extensive geotechnical investigations conducted by Findlay Engineering, Inc. to assess subsurface conditions for planning the remediations. Engineering evaluation included assessment of existing slope stability, seismic and liquefaction stability, and design analyses of several potential remedial approaches. The subsurface investigations determined that sections of the embankments are founded on pervious alluvial soils underlain by relatively impervious, dense glacial till. The pervious alluvial soils were assessed to be responsible for the artesian conditions identified at the toe of the embankments in at least one locations. To remediate the embankments, it was planned to install a 500 foot long sheet pile cutoff wall at one embankment, and a downstream filter berm at the other. The sheet pile approach was used where the alluvial layer was at a low elevation, to avoid the need to have a prolonged drawdown of the storage reservoir retained by the embankment or expensive dewatering measures which would otherwise been needed for other remediation approaches which would have required excavation of the downstream toe or slope. At other locations where the alluvial soils are at a higher elevation and would only be a problem with regard to embankment stability during extreme flood scenarios, a filter berm will be constructed. At present, the sheet pile cutoff has been completed, and design of the other remedial measures is underway.

Slope and Seismic Stability Analyses, Lake Robinson Dam, Lake Robinson Nuclear Station, Progress Energy - In 2007, Dr Findlay conducted slope and seismic stability assessments of the embankment dam retaining Lake Robinson, which is adjacent to Robinson Nuclear Plant near Hartsville, S.C. The earth dam about 4,300 feet long and up to 50 feet in height. The dam and power plant are owned and operated by Progress Energy of Raleigh, NC. The analyses were prepared as required by the Nuclear Regulatory Commission (NRC) for inclusion in the plant’s Facility Description and Safety Report on file with the NRC. The potential for foundation liquefaction needed to be assessed and embankment deformation was to be assessed using a Newmark approach. The original analysis details could not be found, and the analysis was required to be redone. Dr. Findlay reviewed available subsurface investigation information, soil profiles, geology reports and construction specifications to develop properties for use in the analyses and to characterize the appropriate seismicity of the project locations. The slope and seismic stability analysis was conducted using the Programs SEEP/W and SLOPE/W, which were developed by GeoSlope International, of Calgary, Alberta, Canada. Since phreatic surface conditions at the embankments are not known by the analyst, a finite element seepage analysis using SEEP/W was conducted to define the steady state phreatic surface through the embankment, based on assumed hydraulic conductivity values. The results of the seepage analysis were then imported into the slope stability analysis program (SLOPE/W), and slope stability analyses, using the Spencer Method were conducted. The analyses found the embankment had adequate stability under all considered loading cases, that foundation liquefaction was not anticipated under the regional seismicity (as indicated by standard penetration test results), and that embankment deformation would be minimal under the operating basis earthquake.

Silver Lake and Sugar Hill Dams, Central Vermont Public Service – In 2006, Dr. Findlay served as an owner’s representative for review of a field investigation and stability assessment for the two dams which are owned and operated by Central Vermont Public Service. The analyses and field work were conducted by another consultant retained by the owner. The field investigation encountered relatively loose, saturated soils under the upstream slope of one of the dams, triggering a more detailed assessment of liquefaction and potential seismic deformation under a maximum credible seismic event. Dr. Findlay reviewed and commented on the analyses performed by the other consultant and participated in discussions between the owner and the Federal Energy Regulatory Commission as a technical expert.

Gravity Analysis of H. Neely Henry Dam, Alabama Power Company - In 2004, Dr. Findlay conducted a gravity analysis of the spillway, powerhouse and two bulkhead section of the H. Neely Henry Project, located on the Coosa River near Ohatchee, Alabama. The spillway and powerhouse had sloped bases, complicating the uplift computations. The loading cases of normal full reservoir, post-earthquake and inflow design flood (IDF) were considered. For the IDF (PMF) case, nappe pressures were estimated on the crest by the method proposed by Brand (1999). The bulkheads were assessed as 2D slices, and the powerhouse and spillway were assessed as 3D blocks. The effects of inoperative drains in the downstream apron were also investigated in sensitivity computations. The dam was found to be stable for all modeled loading cases.

Seismic Analysis of Arch and Gravity Dams, Avista CorporationIn 2002, Dr. Findlay performed a detailed finite element analysis of the Long Lake Dams, located on the Spokane River in eastern Washington State.  The development includes  gravity intake and spillway sections, and a separate arch dam.  The gravity sections are up to about 160 in height, and the arch section is about 108 feet high.  Two 2-D cross sections of the gravity portions of the dam were modeled. In addition, a 3-D model of the arch dam was developed.  The Computer program SAP2000 NL, licensed from Computers and Structures, Inc. of Berkeley, CA was used.  A response spectra approach was used for seismic analyses.  For the gravity structures, a post-earthquake analysis using the conventional gravity approach was used.  The analysis included conducting a seismic characterization of the site to develop an appropriate peak ground acceleration and response spectra based on the seismic history of the region, factoring in a recent swarm of small events that recently occurred in relative close proximity to the dam site.  

Finite Element Analysis of Arch Dam, Southern California Edison CompanyIn 2001, Dr. Findlay performed a detailed finite element analysis of Southern California Edison Company’s 50 foot high Rush Meadows Dam, located on the eastern side of the Sierra Nevada Mountains of California, in an area of relatively high seismicity.  Work included field reconnaissance to define and verify structure geometry. The dam is unique in that the upper right end of the dam is free standing (see the photo below). The Model SAP2000 NL was used. The normal full pool, PMF and seismic cases were analyzed. Response spectra and time history approaches were used for seismic case analysis.

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Rush Meadows Arch Dam

Hydraulic Fill Dam Seismic Stability Analysis, Beaver River, Niagara Mohawk Power Corporation - Dr. Findlay is a consultant to Orion Power NY (and formerly Niagara Mohawk Power Corporation) regarding seismic stability issues and assessment of the need for and approaches to remediation of Diversion Dam. The dam is an 80-foot high hydraulic fill structure, which is part of the Beaver River Project, located in New York State. Work is currently ongoing and has included a major field investigation program using energy calibrated standard penetration testing on both the upstream (barge) and downstream slopes of the dam. The field investigation was conducted in the summer of 1998 to assess the relative density of a construction cofferdam observed on the upstream side of the dam in old 1924 construction photographs. The borings were also conducted using carefully controlled methods, in accordance with the published recommendations of Seed and others. The drilling procedure including prevention of the development of unbalanced hydrostatic head on the sample zone during drilling rod removal. The controlled drilling methods facilitated measurement of standard penetration test blow count values which were improved over those from previous field investigations made at the site. The field work is the subject of a paper that Dr. Findlay co-authored to be presented at the 1999 USCOLD Annual Lecture in Atlanta. Dr. Findlay performed static finite element analysis (SIGMA/W), dynamic response finite element (QUAD4M), and liquefaction triggering analyses, and integrated seismic deformation analyses to determine the possible need for remedial measures to improve seismic stability. The work is being conducted under close review of the FERC. Rehabilitation of the dam is currently under design, and should be completed in 2002.

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Big Creek Dam 4 During Construction in 1913

Gravity Dam Analyses in Follow Up to Part 12 Inspection, Oswego Falls Project, Oswego River, New York, Niagara Mohawk Power Corporation - Dr. Findlay conducted the first FERC Part-12 Inspection of the Oswego Falls Project (FERC No.5984-NY). which is operated by Niagara Mohawk Power Corporation (NMPC). The project is located in Fulton, New York at Lock O-2 of the Oswego Canal (Oswego River) about 12.3 miles upstream of the mouth of the river at Lake Ontario. The Oswego Canal is part of the New York State Barge Canal System operated by the New York State Canal Corporation (NYSCC), a division of the New York State Turnpike Authority (NYSTA). NMPC operates the hydroelectric aspects of the project in cooperation with NYSTA, who is responsible for facilitating navigation on the river. The portions of the project owned by NMPC include forebay walls and powerhouses. Portions of the project owned by NYSTA include the west bulkhead and the spillways. The spillways include a main and side overflow spillway, and a gated spillway section. The First FERC Independent Consultant Part 12 Inspection Report of the Project recommended reanalysis of the structural stability of the Main, Side and Gated Spillway because no analyses of the stability of the current configuration of these structures were available for review.

NMPC retained Dr. Findlay to conduct the analyses. Two and three dimensional gravity analyses for base stresses, cracked base analysis, uplift and sliding were conducted using gravity analysis spreadsheet programs developed by Dr. Findlay. Analysis of the spillway structures also considered stability against sliding on an assumed failure plane within the relatively weaker Grimsby sandstone which underlies the spillways, including review of boring logs from a previous investigation to assess if a continuous mud seam might exist at shallow depth. No shallow mud seam appears to be indicated by the boring logs. The Army Corps of Engineers Program CSLIDE was used to check stability with respect to possible sliding on a deep failure plane within the horizontally bedded rock foundation. The results of the analyses indicated that the Side, Main and Gated spillway structures have adequate stability to resist the loading conditions stipulated in the FERC Guidelines, assuming a PMF flow of 142,000 cubic feet per second. The PMF case was found to result in a tolerable cracked base condition for the PMF case of the Main and Side spillways. The structures were found to be stable assuming a friction angle of 27 degrees and a cohesion of 10 pounds per square inch.

Gravity Dam Analysis, Tuxedo Hydro Project, Green River, North Carolina, Duke Power Company - Dr. Findlay conducted the North Carolina Utilities Commission 5-Year Safety Inspection of Duke Power's Tuxedo Hydro Project. The Inspection is similar in scope to a FERC Part 12 Inspection. The project includes a 254-foot-long, 130-foot-high single-arch concrete dam with an intake that serves as a thrust block on the left abutment of the arch dam. The intake was previously analyzed and shown to be satisfactory to resist the normal reservoir and seismic (0.10g) cases. Previous analyses indicated that the structure might fail at a reservoir level of 2018.1 feet; however, those analyses did not consider the reaction of the arch dam which presses the intake into the abutment, mobilizing a significant amount of side friction to resist sliding and overturn. To assess the stabilizing effects of this side friction, FEI conducted a gravity analysis (sliding, overturning and base friction computations, including consideration of the effects of a cracked base) which included consideration of side friction imposed by the arch dam on the intake. That analysis found that the intake has an adequate factor of safety, if side friction is considered, to resist floods up to at least the zero freeboard flood.

Rock Creek Dam (Drum), Seismic Rehabilitation Feasibility Study, Rock Creek, California, Pacific Gas & Electric Company - Dr. Findlay was the lead geotechnical engineer for a feasibility study to rehabilitate a 1,020-foot-long, 35-foot-high multiple arch dam for Pacific Gas & Electric Company. The dam was determined to be deficient to resist cross-channel seismic loading by the California State Department of Safety of Dams (DSOD). Work included development of a number of different feasible remediation alternatives, including an option of fill between the buttresses utilizing an earth reinforcement approach to support the buttresses during seismic shaking while minimizing the potential for differential seismic loading of the buttresses from the fill.

Lake Blackshear Dam, Dam Breach Repair, Flint River, Georgia, Crisp County Power Commission - During July 1994, Tropical Storm Alberto released torrential rains which caused overtopping of the 3,400-foot-long north embankment of Lake Blackshear Dam, causing a breach about 650 feet in length. Dr. Findlay was retained by the Crisp County Power Commission to provide geotechnical engineering services to investigate subsurface conditions, design a repair of the breached section, and assess the integrity of the intact portion of the northern embankment. The subsurface investigation program consisting of 15 borings. Because the dam is founded on alluvial sands which are loose at some locations, liquefaction analysis was conducted using the approach developed by Seed, et al. A 2-dimensional transient finite element seepage model was used to assess the cause of boils observed during the flood at locations of the dam that remained intact. As a result of the investigation, a cutoff wall consisting of a cement-bentonite slurry was constructed using slurry trench methods along the axis of the entire northern embankment. The cutoff was determined to be necessary to remediate potential seepage damage to the intact portions of the dam and to mitigate the potential for future piping through the alluvial sands below the breached section. The project included close coordination with the Federal Energy Regulatory Commission and the Federal Emergency Management Agency. The geotechnical aspects of the project were the subject of papers presented by Dr. Findlay at Waterpower '95 in San Francisco in July 1995, the Association of State Dam Safety Officials Annual Convention in Atlanta in September 1995, and the Maine Section of ASCE in March 1996.

Drawdown Effects on Bank Stability - A confidential client was interested in determining how the nominal 2-foot-daily drawdown at one of their reservoirs might safely be interpreted to mitigate reservoir bank stability. For example, if a one-foot rise followed by a three-foot draft in 24 hours could be interpreted as a "net" 2-foot-daily drawdown, some optimization of reservoir operation could be realized, provided such operation did not exacerbate bank erosion. Reservoir fluctuations can impact bank stability if the groundwater does not immediately equilibrate with reservoir level changes. In other words, the greater the lag time of groundwater response, the greater impact on slope stability of the reservoir banks. As a result, the study planned and conducted by Dr. Findlay included field samples and testing, laboratory testing, and groundwater modeling of the response of the water table in the reservoir banks to various reservoir fluctuation scenarios at three selected critical sites. Field work included in situ permeability testing. The USGS groundwater flow model MODFLOW was used to assess groundwater response to fluctuations. The resulting groundwater information was then used to analyze impacts on slope stability. Slope stability analysis was completed using the program STABRD (developed at the University of California at Berkeley) to compute the effects of the groundwater lag on slope stability. Preliminary results of the study indicate the "net" interpretation will have no significant impact on bank stability up to incremental level changes of 4 feet.

Pontook Hydroelectric Project, New Hydroelectric Development, Androscoggin River, New Hampshire, Combustion Engineering - Dr. Findlay was the lead geotechnical engineer for development of a new hydroelectric project under contract to Combustion Engineering. The project included geotechnical investigation, design, and construction consultation for a new 11.4 MW hydroelectric facility on the Androscoggin River in mountainous northern New Hampshire. Included was design and construction of a 6,000-foot unlined canal in glacial till to transport water to a new powerhouse. The canal construction involved full cut sections up to 70 feet in depth, as well as hill side embankment sections up to 30 feet in height. Excavation for the canal and the powerhouse involved deep well depressurization of artesian layers within the till to mitigate excavation instability. Unlined canal design included assessment of ability of the glacial till to self-armor to limit channel erosion. A 700-foot-long timber crib dam with a shear key to increase sliding stability was constructed across the Androscoggin River, downstream of the canal intake, to raise river levels sufficiently for power production. The project was selected by the Consulting Engineers of Maine to receive the "Award for Engineering Excellence" in January of 1988 and was the subject of a technical paper authored by Dr. Findlay for the 1988 Second International Conference on Case Histories in Geotechnical Engineering, sponsored by the University of Missouri Rolla, St. Louis, Missouri.

Brassua Hydroelectric Project, Expert Witness for Piping Failure, Rockwood, Maine - Dr.  Findlay was retained as an expert witness for the contractor during post-construction litigation of a piping failure which developed during construction. The piping developed underneath an existing concrete gravity dam founded on glacial till. Dr. Findlay thoroughly reviewed the project design and construction documentation and provided a deposition during the discovery period. The litigating parties decided to attempt mediation to settle the case. Dr. Findlay made a technical presentation for a mediation hearing on the mechanics of piping and a review of the chronology of events leading to the piping failure.

Graham Lake Dam, Graham Lake Dam Remedial Measures Project, Union River, Maine, Bangor Hydro-Electric Company - Dr. Findlay was the lead geotechnical engineer for the Graham Lake Dam Remedial Measures Project, undertaken to improve dam stability and spillway capacity. Stability analysis and liquefaction analysis indicated the dam had deficient downstream slope stability, and the upstream slope was susceptible to liquefaction. This project consisted of building a new flood control structure just downstream of an existing semi-hydraulic fill dam in Ellsworth, Maine for Bangor Hydro-Electric Company. One aspect of involvement included design of a deep well dewatering system to intercept seepage through the existing dam which served as the upstream cofferdam for the work. This design included three-dimensional groundwater flow modeling using the USGS program MODFLOW to assess the effectiveness and number of wells needed to accomplish dewatering. After installation of the wells, pumping tests were conducted and the results incorporated into the model to verify expected performance. In addition to the dewatering aspects of the project, the existing dam was founded on soft clay, making excavation for the new flood control structure a potentially risky situation. Dr. Findlay developed an innovative excavation stabilization system which consisted of a cellular-constructed granular stabilization berm which was significantly reduced costs over an originally proposed tie-back wall system. The project was completed in the spring of 1994, and was the subject of technical papers presented by Dr. Findlay at the 1993 ASCE Specialty Conference on Dam Rehabilitation in Raleigh, North Carolina, and the 1994 Association of State Dam Safety Officials (ASDSO) Annual Convention in Boston, Massachusetts, and the 1996 ASDSO Annual Convention in Seattle, Washington.

Slope Stability Analysis in Follow-Up to FERC Part 12 Dam Safety Inspections, Upper Raquette River Project, New York, Niagara Mohawk Power Corporation - Dr. Findlay is the Independent Consultant for conducting the FERC Part 12 Inspections for the Upper Raquette River Project which includes five developments and a mix of concrete gravity dams and earthfill dikes up to about 70 feet in height. The dikes were previously analyzed assuming a pseudo-static coefficient of 0.05g. Since the dikes are located in Seismic Zone 2, a pseudo-static coefficient of 0.1g is stipulated in the FERC guidelines. Dr. Findlay conducted pseudo-static slope stability analysis on the worst case dike on each of the five developments of the project using the computer program STABL5.

 

 

Slope Stability and Seepage Analysis of Vermilion Dam, Southern California Edison Company Vermilion Dam is a 165 foot high, 4,234 foot long zoned embankment dam located at about elevation 7,650 feet in the Sierra Nevada Mountains of California. The dam is founded on a complex soil foundation of glacial moraine and interbedded alluvial materials. Seepage is controlled by numerous drainage systems, some of which were originally designed under the review of Dr. Karl Terzaghi. One of the key monitoring piezometers for a section of Vermilion Dam had elevated readings that were above the phreatic surface assumed in previous slope stability analyses, bringing the minimum computed factor of safety for slope stability into question. The previous analyses used a phreatic surface model consisting of a single phreatic surface. However, the piezometers at the dam are nested in sets of three piezometers each at various depths. Threshold values for each of the piezometers had not been established, and using phreatic surface assumptions of the previous slope stability analyses would not properly account for the flownet-like distribution of phreatic conditions actually indicated by the piezometer readings. Because the foundation layer was relatively thick, it was postulated that the single phreatic surface assumption of the previous analyses was overly conservative with regard to slope stability compared to the flownet-like conditions that actually exist. Dr. Findlay used the program SEEP/W to model the seepage through and within the foundation below the dam, calibrated using the piezometer readings. The resulting seepage model was then imported into the slope stability program SLOPE/W, and slope stability analysis was conducted. The dam was found to be adequately stable even with the elevated piezometer water level observed. An additional important aspect of the finite element seepage analysis and associated slope stability analyses conducted by Dr. Findlay was that they allowed a rational approach to developing threshold piezometer readings for the several sets of nested piezometers at the dam, satisfying requirements for the Performance Monitoring Plan for the dam.

Sugar River 1 Dam, Stability Analysis, Sugar River Hydro Power Company, Sugar River, Newport, NH - Dr. Findlay analyzed the stability of this mat supported Ambursen-type slab and buttress structure founded on a pervious soil foundation.  The analyses included determination of headwater and tailwater rating curves using HEC-RAS, and determination of uplift pressures using the finite element seepage modeling program SEEP/W. The analyses required determining the worst case flood scenario with regard to sliding and base pressures, since the PMF case is not the worst case flood loading.  The normal, ice and seismic cases were also analyzed for sliding and base pressures.  The structural stability of the slab under the postulated loading was also assessed using the structural stress analysis program SAP2000..

Lundy Lake Dam, Southern California Edison - In 2003, Dr Findlay conducted a post-earthquake analysis of Lundy Lake dam, located in the eastern Sierra Mountains, near Mono Lake, California. A portion of the upstream fill of the embankment section was constructed using hydraulic fill methods.  The analysis was conducted assuming liquefaction of the hydraulic fill materials.  The program SLOPE/W was used.  The dam was found to have adequate post-earthquake resistance.

Abbott Brook Dike Seismic Stability Assessment and Rehabilitation, Aziscohos Project, FPL Energy Maine Hydro LLC – Dr Findlay conducted an assessment of post-earthquake stability and deformation analysis for this 700 foot long, 40 foot high hydraulic fill dam located in Northern Maine. The analysis was based on SPT blow counts and the methods of Seed and Idriss, recently updated as summarized by Youd and Idriss. It was determined that the downstream lower core of the structure potentially susceptible to liquefaction, and the downstream slope had minimum computed factors of safety less than would be desirable, under the maximum credible earthquake loading event. As an additional complicating factor, the foundation soils for the dam (glacial till interlayered with sand) contained artesian pressure in excess of the ground surface at the toe of the dam. As a result, rehabilitation has been proposed, consisting of toe drainage and a stability berm to improve the post-earthquake stability of the dam as well as mitigating the potential of heave at the toe of the embankment. The rehabilitation scheme is currently under review of the FERC, and final design (to be completed by Dr. Findlay) and construction is anticipated in 2009-2010.

Tioga Lake Dams, Southern California Edison - In 2003, Dr Findlay conducted a slope stability and seismic deformation analysis of the timber-faced rockfill dam at Tioga lake because of a change in the recognized MCE for this damsite.  The analysis was conducted using the program SLOPE/W.  He also conducted a finite element analysis of the single arch concrete dam at the project using the response spectra approach and the program SAP2000 V6.  The cases of normal full pool, PMF and earthquake loading were considered.  The project is located in the eastern Sierra Mountains, near Tioga Pass and Toms Place, California.  The analyses determined that the dams were adequate to resist the loading of all analyzed loading cases.

Gravity Analysis of Lay Dam, Alabama Power Company - In 2007, Dr. Findlay conducted a gravity analysis of the spillway, powerhouse and bulkhead sections of the Lay Dam, located on the Coosa River near Ohatchee, Alabama. The loading cases of normal full reservoir, post-earthquake and inflow design flood (IDF) were considered. For the IDF (PMF) case, the peak PMF elevation was about equal to the spillway design flood height and nappe pressures were considered negligible, and therefore were neglected. The bulkheads were assessed as 2D slices, and the powerhouse and spillway were assessed as 3D blocks. The dam was found to be stable for all modeled loading cases.

Seismic Analysis the Skelton Project, Florida Power & LightIn 2003, Dr. Findlay conducted a seismic stability analyses of the components of the Skelton Hydroelectric project on the Saco River in Southern Maine.  The analyses addressed the concrete gravity spillway and 70 foot high embankment.  The spillway was analyzed for post-earthquake stability with regard to sliding and potential pier cracking due to cross channel loading.  In addition, the FERC requested that sensitivity analyses be conducted by ignoring base cohesion and using the revised recommended minimum factors of safety presented in the new FERC gravity dam guidelines.  Conventional gravity analysis approaches were used for the spillway analyses.  The embankment was evaluated for liquefaction potential (triggering analysis) and post-earthquake stability.   Dr. Findlay conducted the triggering analysis using previously made standard penetration tests and the methods recommended by the recent NCEER liquefaction workshop.   The analyses determined adequate stability for all analyzed cases. From the triggering analysis, a post-earthquake strength cross section was developed.  The post-earthquake analysis was conducted using the program SLOPE/W.

Review of Embankment Stability, Instrumentation and Relief Wells, Skelton Project, Florida Power & Light Dr. Findlay assisted FPL Energy Maine Hydro LLC in the reassessment of the instrumentation and relief well system of its 75 foot high Skelton Embankment on the Saco River in Southern Maine. Throughout the history of the dam, pore pressures have been rising and in 2000, began reaching levels where remedial work appeared called for.  Since 2000, work has included a historic review of construction and maintenance records, review of historic monitoring data, slope stability analysis under elevated piezometric regimes, and heave analysis. Remediation efforts included planning and observing a program of redevelopment and/or reconstruction of the existing system of 15 relief wells and replacement of an extensive system of aging instrumentation with a centralized VW readout system. The work also included installation of two 12-inch diameter, stainless steel screened pumped filter pack relief wells to replace wells that were not functioning properly.  As a result of the work, piezometric levels have been significantly reduced.

Gravity Analyses of Feeder Dam Powerhouse, Brookfield Power, New York - In 2004, Dr. Findlay conducted a gravity analysis of the powerhouse of Feeder Dam, located on the Hudson River, near South Glens Falls, New York. The analysis considered the normal, post-earthquake, and IDF loading cases. The structure was found to have adequate stability for all considered loading cases.

Post-Earthquake Analysis, Gulf Island Dam, Florida Power & Light – Dr. Findlay conducted post-earthquake analyses of this dam for FPL Energy Maine Hydro, LCC at their Gulf Island Project located on the Androscoggin River, in Lewiston, Maine. The analysis approach included the assumption of liquefaction of suspected relatively looser zones of the embankment cross sections, assessment of appropriate post-earthquake residual strength values, and post-earthquake slope stability analysis using the program SLOPE/W. The embankment was found to be adequately stable with regarding the loading under the maximum credible earthquake.

Gravity Analyses of Minetto Dam Spillway - In 2004, Dr. Findlay conducted a gravity analysis of the spillway of Minetto Dam, located on the Oswego River, in Minetto, New York. The analysis considered the normal, normal plus ice, post-earthquake, and IDF loading cases. The spillway was found to have adequate stability for all considered loading cases.

CR FLOOD Modeling of Big Creek Dam 7, San Joaquin River, Southern California Edison Company - Dr. Findlay used the EPRI model CR FLOOD, licensed through Southern California Edison Co. (SCE) to analyze the potential effects of base cracking on drain efficiency during the PMF flood event for a gravity analysis of SCE's Big Creek Dam 7.  The model provided a rational basis for assessing the performance of the drains during the extreme flood event and the resulting uplift on the base of the dam.  The analysis resulted in justification for assuming little loss in drain efficiency during the PMF, and avoidance of post tension anchoring.  

Radial Gate Finite Element Stress Analyses, Skelton, Messalonskee, Flagstaff and Brassua Projects, Florida Power & Light Corporation – As part of Part 12 Inspections performed in between 2000 and 2005, Dr. Findlay performed finite element analyses of the radial gates on each of the projects to resist a trunnion friction coefficient of 0.3, in accordance with the Federal Energy Regulatory Commission's (FERC) radial gate assessment requirements.  The gate analyses were conducted using the three dimensional finite element program SAP2000, which is licensed to FEI by Computers and Structures, Inc. of Berkeley, CA.  The analysis included consideration of lifting forces such as J-seal side friction and wire lifting rope pressure on the skinplate.  The cases of static normal full pool and gate lifting during normal full pool (with trunnion friction) were analyzed. 

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Drilling on Upstream Side of Diversion Dam

Big Creek Dam 4 and Dam 5 Abutment Analysis, Big Creek, California, Southern California Edison Company -The Federal Energy Regulatory Commission was concerned with the abutment slope stability of these 50 and 75 foot high concrete arch dams supported by exfoliated granite abutments. Dr. Findlay conducted a detailed analysis of the stability of the granite abutments of Big Creek Dams 4 and 5, part of Southern California Edison's Big Creek Project located in the Sierra Nevada Mountains of California. Dr. Findlay first mapped the bedrock features of both abutments at each dam which involved access by technical climbing. The mapping identified the critical blocks of the exfoliating granite for analysis, as well as the strikes and dips of the joints defining the blocks. Joint roughness was estimated by measuring the asperities of an exposed surface of the potential sliding plane of the most critical block. The analyses were made using the sliding block approach as outlined by Hoek and Bray as well as by using a spread sheet coding of the two plane wedge (with tension crack) approach, also outlined by Hoek and Bray. The analyses found the abutments to be stable under normal gravity and seismic loading (0.15g) and PMF flooding, except on the left abutment of Dam 4, where the block was found to be marginally unstable if the tension crack was surcharged with water (such as might occur under PMF overtopping or during an extreme flood event). In addition, a lower block on the right abutment of dam 5 was found to be vulnerable if water could intrude into a vertical crack. It was recommended that the vertical and near vertical joints defining the Dam 4 left abutment block and the right abutment of Dam 5 be sealed with dry pack (a stiff cement/sand grout) to mitigate surcharging with water.

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Gated Spillway at Oswego Falls Project

Schaghticoke Project, Hoosic River, New York, Niagara Mohawk Power Corporation – Dr. Findlay was retained by Orion Power – NY (and formerly Niagara Mohawk Power Company) to serve as their liaison and peer reviewer of the geotechnical aspects for the design and replacement of the aging 1,100 foot long penstock. The penstock ruptured during the spring of 1998 under full hydrostatic load. The penstock traverses a pipe bridge across the Hoosic River, and steep slopes which have had historic slope stability problems. To complicate geotechnical issues, a confined zone of artesian pressure was identified by Niagara Mohawk under the penstock alignment, which is being considered in the review of slope stability. Work conducted by FEI included independent laboratory testing and review of significant subsurface investigations by both the designer and Niagara Mohawk, independent detailed slope stability analysis conducted with SLOPE/W, participating in weekly design review meetings, and detailed review and comment on the design criteria, drawings and specifications.

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Tuxedo Dam

Radial Gate Finite Element Stress Analyses, Oswego Falls Dam and Stark Dam, Brookfield Power New York – As part of Part 12 Inspections performed in 2002 and 2006, Dr. Findlay performed finite element analyses of the radial gates on each of the two projects to resist a trunnion friction coefficient of 0.3, in accordance with the Federal Energy Regulatory Commission's (FERC) radial gate assessment requirements.  The gate analyses were conducted using the three dimensional finite element program SAP2000, which is licensed to FEI by Computers and Structures, Inc. of Berkeley, CA.  The analysis included consideration of lifting forces such as J-seal side friction and wire lifting rope pressure on the skinplate.  The cases of static normal full pool and gate lifting during normal full pool (with trunnion friction) were analyzed. 

Dam Safety Inspection, Murphy Dam Project, Connecticut River, New Hampshire Department of Environmental Services - Water Resources Council - Dr. Findlay was the Project Manager, Lead Dam Inspector, and Lead Geotechnical Engineer for a detailed review of the condition of this 100 foot high zoned earthfill dam in northern New Hampshire. The project consisted of a review of project seismicity since two Magnitude 5 earthquakes have occurred within about 10 kilometers of the dam within the past 35 years. In addition, work included installation of monitoring piezometers, assessment of liquefaction potential, a review and update of the structural stability of the dam and spillway, review and update of the PMF, a dam break analysis and preparation of inundation mapping to be used by the State for preparation of an Emergency Action Plan, and preparation of a list and cost estimate of capital improvements anticipated to be necessary to maintain the facility into the future.

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Lake Blackshear Dam Breach

Graham Lake Dam, Dam Safety Slope Stability Analysis, Ellsworth, Maine, Bangor Hydro-Electric Company - Dr. Findlay conducted slope stability analysis of Graham Lake Dam to assess slope stability of the upstream and downstream slopes to satisfy FERC licensing compliance. The dam is a 35-foot-high semi-hydraulic fill structure founded on soft marine clay. The dam has a high hazard rating because of populated areas downstream.

Baldwin Hydroelectric Project, New Hydroelectric Development, Connecticut River, New Hampshire, Baldwin Hydro Corporation - Project manager and lead geotechnical engineer in the development and design of a 4.4 MW hydroelectric facility on the Connecticut River in Pittsburg, New Hampshire. The project includes construction of a 170-foot-wide concrete gravity dam, canal headworks, a 4,600-foot-long unlined canal requiring excavation up to 50 feet deep, a penstock intake, and 450-foot-long penstock, a powerhouse and tailrace. It was determined that construction of the powerhouse would require deep dewatering using drilled gravel packed wells to depressurize a confined aquifer to allow excavation up to 50 feet in depth. The project has not yet been constructed.

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Pontook Hydroelectric Project

Hydro-Kennebec Project, Increased Headpond Level, Kennebec River, Maine, Scott Paper Company - Dr. Findlay was the lead geotechnical engineer for assessment of several miles of shoreline which were to be impacted by raising the normal water elevation of the existing dam at Scott Paper Company's (now Kimberly Clark) Winslow, Maine paper making facility. This increase in dam height resulted in a substantial increase in the impoundment elevation, affecting the shoreline at several industrial and residential areas. Assessment was made in two phases; a preliminary phase to evaluate the impact at individual locations based on observation, and a follow-up phase which included subsurface investigation and additional assessment at critically impacted areas. The assessment resulted in delineation of areas and recommended methods for slope stabilization. Work included development of contract plans and specifications for implementation of the recommendations. Involvement included consultation and monitoring services through construction.

Spencer Hydro Project, Upgrade Feasibility Study, Niobrara River, Nebraska, Nebraska Public Power District - Dr. Findlay was part of the team selected to evaluate approaches for remediation of the Spencer Hydro Project on the Niobrara River in northeastern Nebraska. The project is owned and operated by the Nebraska Public Power District. Geotechnical engineering services provided by Dr. Findlay included evaluation of a 3,500-foot earth embankment constructed of weathered clay shale and founded on pervious alluvial sand. The results of the evaluation included recommendations for monitoring seepage, monitoring scour of the upstream dam face, and repair of sloughing to maintain slope stability. The river carries a heavy sediment load, and the reservoir is almost completely filled with alluvial material. The assessment included review of sediment sluicing options and the potential of sediment siphoning as a possible future operation alternative. The spillway structure was founded on Pierre Shale, an expansive bentonite shale, and had to be evaluated for sliding stability.  Because the rock erodes easily, the tailrace has eroded about 10 to 20 feet since the project was constructed. The reservoir and tailrace are bordered by cliffs of Pierre Shale which are undergoing continuing erosion. Assessment of remediation alternatives included consideration of impacts of remediation alternatives on continued erosion of the tailrace channel and slope stability of the adjacent cliffs.

M-5 Hydroelectric Project, Seepage Study, Messalonskee Stream, Maine - Dr. Findlay was the lead geotechnical engineer and project manager for assessment of observed embankment seepage at the downstream toe of Central Maine Power Company's M-5 dam on Messalonskee Stream in Waterville, Maine. A gauging weir consisting of a half barrel was installed to monitor any increase in flow from the seep. Subsurface investigation using soil borings was conducted to characterize embankment and foundation materials to install piezometers to identify the source and direction of the seepage. Engineering analysis concluded that a downstream toe drain should be installed to lower the phreatic surface and eliminate soil erosion that was occurring.

Keowee Hydroelectric Project, Finite Element Seepage Analysis, Keowee River, South Carolina, Duke Power Company - Dr. Findlay developed a finite element model and preliminary input parameters for seepage analysis of an 80-foot-high intake dike for the Keowee Hydroelectric Project/Oconee Nuclear Project in Oconee County, South Carolina. The dike is for the intake of the nuclear project, and is also a water retaining structure for Duke's Keowee Hydroelectric Project. Work included setting up and debugging the model so that Duke Power Company could use the model for a parametric study of the effect of varying hydraulic conductivity on seepage. The program SEEP/W (Geoslope International) was used to develop the model.

Gravity and Pseudo Dynamic Analysis in Follow-Up to FERC Part 12 Inspection, Hunters Dam, Murphys Project, Murphys, California, Utica Power Authority - Dr. Findlay conducted two and three dimensional gravity analyses on two sections of the thrust blocks of Hunters Dam, a single concrete arch dam (FERC 2019-CA). In addition, Dr. Findlay Conducted a pseudo-dynamic analysis, using the method developed by Fenves and Chopra (1986).  The pseudo-dynamic analysis included use of a static 2D finite element analysis to determine the stress distribution in the dam due to the computed pseudo-dynamic loads.  No known previous analyses of the sections existed, and the area seismicity had recently been upgraded.  The thrust blocks were found to be stable for all analyzed cases.

Other Gravity Analyses: - Lake Creek Dam Gravity Analyses in Troy, Montana; Nine Mile Dam Gravity Analyses in Spokane, Washington; Post Falls Dam Gravity Analysesin Post Falls Idaho; and Wyman Dam Gravity Analyses in Bingham Maine.-

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