assessment of historic piezometer …€¢ pool vs. piezometer correlation plots • can be used to...
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Suzanne Hess-Brittelle P.G., USACE, Risk Management Center Amy Ebnet, P.G., USACE, Seattle District, NWD-W Risk Cadre 14 September 2017
ASSESSMENT OF HISTORIC PIEZOMETER DATA, ABIQUIU DAM AND RESERVOIR, RIO CHAMA, NEW MEXICO
“ The views, opinions and findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other official documentation.”
PRESENTATION OVERVIEW
• Project Overview • Construction History • Sources of Data • Geology • Post Construction Seepage • Post Construction Seepage Reduction Measures • Project Instrumentation & Piezometers • P-13 example • Conclusions
Abiquiu Dam & Reservoir
• Rio Chama; tributary of the Rio Grande • 35 river miles upstream Española, New Mexico • Construction from 1958-1963
ABIQUIU DAM - PROJECT OVERVIEW
• 340 ft high rolled earthfill dam with impermeable core, chimney drain, and blanket drain • Controlled outlet works • Uncontrolled rock-cut spillway • Hydropower facility (County of Los Alamos) • Authorized for flood control and sediment retention
Designed as a ‘dry dam’
ABIQUIU DAM - PROJECT OVERVIEW
SOURCES OF DATA • District Files, ERDC Library, National Archives • Instrumentation Data
• Periodic Inspection Reports • WinIDP Database (back to 1980 only…)
Trinidad Dam & Lake
• Abiquiu Dam located SE-corner of Chama Basin
• Chama Basin transition from Rio Grande Rift to Colorado Plateau
• Thick sequences of Permian and Triassic age sedimentary rock
• sandstones, conglomerates, and mudstones; interbedded and moderately fractured
Abiquiu Dam
(After Kelly and others, 2013)
Set 1 Set 2 Set 3
REGIONAL TECTONIC SETTING
9
• Note undulose nature of contact between Arroyo del Agua and Shinarump as well as interbeds within the Poleo • Note moderately fractured nature of rock; fractures are near vertical • Salitral (upper mudstone) essentially acts as an aquiclude between the Poleo (upper sandstone) and the Shinarump/Arroyo del Agua interbedded sandstone and mudstones
Poleo
Salitral Shinarump
Arroyo del Agua
Upper Sandstone
Upper Mudstone Middle Sandstone
Middle Mudstone Lower Sandstone
Lower Mudstone
TYPICAL STRATIGRAPHY AT
ABIQUIU DAM
Photo of downstream left abutment; taken during the 2008-2009 Bank Stabilization
Upper Aquifer
Lower Aquifer
Significant Scour &
Fill Contacts
(paleochannels)
ORIGINAL FOUNDATION GROUTING Exceptional losses of drilling fluids noted during initial drilling and testing along both abutments
Designers acknowledged highly permeable zones in rock and recommended a single-row grout curtain
• Single line grout curtain • Primary holes spaced 40 ft in stream bed and 20 ft in abutments • Grout mix varied from 0.6:1 to 4:1 by volume
Abiquiu Historic Pool Elevations Top of Dam
Conduit Invert
Sediment trap pools
Began storing SJC pool as temp deviation
Began storing authorized SJC pool
Pool of Record
HISTORIC SEEPAGE
Seepage has been a problem since water first
impounded
6200
1970 – Pool El. 6105 ft
2 cfs
HISTORIC & CURRENT OBSERVED SEEPAGE
Seepage Observed During 1987 Record Pool
Seepage Currently Observed at Left Abutment Groin
ADDITIONAL GROUTING – 1966 GROUT CURTAIN
• Grouted left abutment from Sta. 0+00G to 5+00G • Re-grouted Sta. 4+30A to 9+50A through embankment,
on left abutment • Report of fluid losses in the impervious core
Reported fluid losses from drilling and grouting
ADDITIONAL GROUTING – 1978-80 GROUT CURTAIN
Reported fluid losses during drilling
• Extended grout curtain on left abutment (5+00G to 10+00G) • Extended grout curtain on right abutment (0+00S to 10+00S) • Re-grouted Sta. 14+70 to 19+79 through embankment, on right abutment
-Fluid losses were recorded in the core
OTHER HISTORIC SEEPAGE REDUCTION MEASURES • 1966: 12 horizontal drains installed 110 ft into fractured conglomeratic
sandstone on downstream left abutment • 1977: 12 horizontal drains installed 110 ft into fractured conglomeratic sandstone
(elev. 6075 ft) on downstream right abutment • 1978: Toe Drain Construction; modified in 1990
INSTRUMENTATION
• Piezometers • No PZs installed during original construction • Foundation & Embankment Drain
• Flumes • Along Right and Left Abutment
• Surface Settlement & Horizontal Movement Points
PIEZOMETERS
• Piezometers installed throughout history of project • 14 installed in 1966 (P-1 through P-14) • 21 installed in 1977 (P-15 through P-35) • 10 installed in 1986 (P-35 through P-40; P-43, P-45, P-48) • 8 installed in 1987 (AB-C-1 through AB-C-8) • 2 replaced in 2008 (P-14a and P-39a) • 3 installed in 2013 (P-49 through P-51)
• Downhole camera survey in 2007
• Piezometers automated in 2010
PIEZOMETER RECORDS OVER TIME
Plot taken from the 1976 PI Report Plot taken from the 1970 PI Report
• Records span 50 years and in most cases, tabulated historic records (pre-1980) were not located after exhaustive records searches
• They are shown in time history plots in Periodic Inspection (PI) reports
P-13 P-13
PIEZOMETER RECORDS OVER TIME (CONT.) • PZs read manually on a monthly
basis; and for every 5-ft increase/decrease of pool • PZs read weekly during record pool
and as pool receded
PREPARATIONS FOR 2013 PERIODIC ASSESSMENT
• Requirement to assess all historic performance data • WinIDP database was only complete to 1980
• Could not locate tabulated instrument reports • Covered 36 years of performance for a 54 year old project
• Wanted to go back as far as possible…
• Had enthusiastic intern estimate piezometer elevations from old
time history plots • Estimated water surface elevations were within +/- 2 ft
2014-2016: IES – TAKING PIEZOMETER DATA FURTHER TO ASSESS PERFORMANCE
• Updated the overall database to include more recent automated data
• Searched for PZ boring log and construction details • Drafted new sections to help assess performance of abutments
and structure • In some cases, it was obvious that the seepage reduction
measures (grouting, adits) lowered the phreatic surface • In some cases, interpretation was problematic…
• Multiple instruments has suspect readings
LT ABUTMENT LOWER AQUIFER & DRAINAGE BLANKET PERFORMANCE
6000
6050
6100
6150
6200
6250
6300
Jan-
76
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77
Jan-
78
Jan-
79
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80
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00
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13
Wat
er S
urfa
ce E
lev.
(FT
-NGV
D29)
Date
Abiquiu DamHorizontal Drainage Blanket and Lower Sandstone
Piezometers Left Abutment
P-10
P-11
P-12
P-13
AB-C-3POOL
P-7
P-28
P-29
P-30
P-31
Low
erSa
ndst
one
Drai
nage
Bl
anke
t1977 right abutment horiz. drains added
1978 Supplemental alignment grouting; possible core damage
1979 grouting in both abutments September 2010 instrument
automation goes online
1989-1990 right and left aditconstruction
1980 right and left abutment horiz. drains added
1986 embankment raised 14.8ft and spillway widened 28ft
2008 instruments cleaned
1987-1990 hydropowerplant construction
2009-2011 low flow turbine construction
• Less responsive to pool fluctuations after construction of adits • Abutment piezometers have higher water levels than the drain
• Water flow pattern is not moving into abutment, but is moving from abutments into the drain
• Significant drop across grout curtain 88 ft between P-15 and P-13 in 1987.
• P-13 and P-AB-C-1 erratic readings
1995 Pool Groundwater Contours - Lower Aquifer, Blanket Drain & Alluvium
1987 POR Water Levels
1995 High Pool Water Levels
HOW CAN WE LOOK AT SOME KEY INSTRUMENTS MORE CLOSELY?
• Check construction details and any modifications • Sound depth of instrument • Conduct downhole camera survey to get a visual
on instrument (scale, debris, sediment) • Conduct insitu testing (slug test, falling head
test)
• PZs sounded in Feb 2006
• Downhole camera survey conducted in Aug-Sep 2007 • Could not image PZs
completed with ¾-inch ID PVC
HOW CAN WE LOOK AT SOME KEY INSTRUMENTS MORE CLOSELY?
• P-13 has historically been difficult to interpret • Degradation of grout curtain over time? • Something else? • Can data collected even be trusted/used?
• Began taking historic data for all PZs and created correlation plots
• Intention was to use these to create PZ threshold plots too
• Time-History Plots • Typically how data is presented and can be useful
• Pool vs. Piezometer Correlation Plots • Can be used to predict future performance at higher pools
P-13
• In order to better understand plot, tried to bracket time between seepage reduction measures • 1979 left abutment
grouting • 1988-1990 adit
construction • And bracketed
estimated, manual, and automated readings
P-13
• Since 1986 • Water levels in P-13 rise to ~6200 ft
when pool is above 6210 – 6225 ft. • Drop to ~6100 when pool is below
6210 - 6225 ft. • Started before the POR.
• Possible Causes • Damaged riser in Piezometer allowing
water from upper aquifer to enter piezometer?
• Degradation of grout curtain? • Leak through Aquiclude
P-13
Manual readings
Automated readings
~Elev. 6130 ft
Conducted basic falling head test for P-13 • 5 gallon bucket, funnel and hose
• Water dropped fairly consistently • And then started coming back up
6130
Interpreted to be a break in riser pipe at approximate elevation 6130 ft
HOW EFFECTIVE WERE THE SEEPAGE REDUCTION MEASURES?
Right abutment, downstream grout curtain Left abutment,
downstream grout curtain
P-13 CONCLUSIONS • Initial construction of P-13 (1966), where the lower portion of the
instrument was left open to the fractured foundation rock, resulted in collapse of the lower 24 ft • Instrument was sleeved with ¾-inch ID PVC in 1977
• The instrument appeared to be functioning until the pool of record in 1987, at which time it was likely damaged
• Correlation plot was helpful in confirming that instrument behavior was indicative of a damaged instrument
• Insitu permeability testing was useful in gaining understanding that riser pipe is likely broken and open to the formation
• P-13 is slated for replacement per the results of the study
CONCLUSIONS 38
• For projects with challenging site conditions and variable instrument datasets, interpretation of data can be challenging • Fractured bedrock with impermeable layers that control seepage flow • Poor instrument construction practices • Multiple phases of seepage reduction measures over long project
history • Encourage the assembly of all performance data and integration
of this data with respect to the site characterization • Encourage teams to conduct comprehensive instrument
evaluations to understand what your instruments are telling you and where you may need to upgrade your monitoring system
ACKNOWLEDGEMENTS Albuquerque District: Dwayne Lillard, P.E., Geotechnical Engineer (SPD DSPM, retired) Jim McAdoo, P.G., Engineering Geologist (retired) Art Maestas, P.E., Geotechnical Engineer (now DSO) Carlos Aragon, P.E., Geotechnical Engineer Tracy Baker Aragon, P.E., Geotechnical Engineer NWD-W Cadre: Sharon Schulz, Hydraulic Engineer (Portland), Cadre Lead Lisa Scott, P.G, Geologist, Cadre PM (Seattle) Amy Ebnet, P.G., Geologist, (Seattle) Michael Gonia, P.E., Geotechnical Engineer (Seattle) Risk Management Center Gregg Batchelder Adams, P.E., Senior Advisor Andy Hill, P.E., Technical Advisor Troy O’Neal, P.E., Former Senior Advisor