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Dam Deformation SurveyingAs Currently Practiced by Terrasurv, Under Contract to

the Pittsburgh District of the US Army Corps of Engineers

US Army Corps of Engineers

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∗ Owns and Operates 609 dams

∗ 19,000 km of inland waterways

∗ 212 Navigation Locks

∗ World’s Largest Public Works Agency

∗ 8 Divisions in the US

∗ 41 Districts in US, Asia, Europe

∗ Civil Works District in US are by Drainage Basin

Civil Works in the United States

US Army Corps of Engineers

Pittsburgh District∗ Allegheny, Monongahela &

Ohio Rivers – 328 miles of navigable waterways

∗ 16 flood control reservoirs

∗ 8 concrete gravity dams

∗ 8 earth-rockfill dams

∗ 23 navigation locks

∗ 26,000 mi2 (67,200 km2) of drainage area

∗ Known as the “Headwaters District”

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Monitoring Requirements

∗ Annually for reservoirs

∗ Semi-Annually or less for navigation locks

∗ More frequent observations for “problem” structures

∗ Survey Specifications and Accuracy requirements can be found in USACE Engineer Manual EM 1110-2-1009 “Structural Deformation Surveying”

∗ http://140.194.76.129/publications/eng-manuals/em1110-2-

1009/toc.htm

Deformation Survey Data Flow

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Navigation Structure Pre-Analysis

∗ Monongahela River L/D #2 at Braddock, PA, built in 1905

∗ New gated dam and new abutment added in 2004

∗ Two lock chambers-110’ X 720’ (33.5 m X 219.5 m) and 56’ X 360’ (17.1 m X 109.8 m)

∗ Land wall 2500’ (762 m) long

∗ River wall 1900’ (579 m) long

∗ Middle wall 1050’ (320 m) long

L/D #2 Monongahela River

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Monuments (X) and Pedestals (X)

Monitoring pins

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Conventional Network

Results–pins with error ellipses >3 mm

HOLDING 3 PEDESTALS M7, M8, M9

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Results–pins with error ellipses >3 mm

HOLDING 3 PEDESTALS & 6 MONS ON BEDROCK MONOLITHS

Results–pins with error ellipses >3 mm

Add constraint on left bank abutment-remaining points are 4 mm

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Summary

∗ It was necessary to add constraints beyond the reference pedestals located off structure

∗ A “primary” network is created to validate the on structure points which are subsequently constrained

∗ GPS can be used for distant parts of the network, as the GPS is more accurate over longer lines, while the total station is more accurate over short lines

Redundant Measurements

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∗ 100 km upstream from Pittsburgh

∗ Two lock chambers

∗ Land wall, Middle Wall, River wall monitored

∗ Gated Dam-piers also monitored

∗ Gate monoliths typically founded on bedrock

∗ Other monoliths typically built on pilings

∗ Monongahela: Native American word meaning “FALLING BANKS” or “WHERE BANKS CAVE IN”

Maxwell Locks and Dam

Maxwell Locks and Dam

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Alignment and Settlement

∗ Typically done every two years

∗ Settlement done by precise differential levels

∗ Alignment done by micrometer prior to 2005∗ Measured displacement for each point from reference line

∗ Only determined movement perpendicular to force∗ Landward/riverward for monoliths located parallel to flow∗ Upstream/downstream for dam piers

∗ affected by heat waves, centering errors, personal bias, etc

∗ High accuracy robotic total station used since 2005∗ Redundant data adjusted by least squares

∗ Coordinates used to compute offsets

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∗ Important to have stable reference points

∗ Survey pedestals located off structure (3)

∗ Gate monoliths are presumed stable, but must be checked in adjustment

∗ Coordinates referenced to Continuously Operating Reference Stations (CORS)

Reference Points

Reference Network-Assumed Stable

checked by adjustment

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Monitored Points

∗ Pins with punch marks in each monolith

∗ Use stakeout prism to minimize setup errors and setup time

∗ Each point shot from at least 2 different setups

∗ Design accuracy=3 mm

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Maxwell Locks and Dam

∗ Distances corrected for atmospheric delay

∗ Distances and vertical angles reduced to mark-to-mark values

∗ Observation weighting is important to obtain homogenous results and realistic error estimates

∗ Networks adjusted using Geolab-least squares adjustment program

∗ Offsets from reference lines computed using adjusted coordinates after LSA using custom software

Data Reductions

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-0,004

-0,002

0,000

0,002

0,004

0,006

0,008

0,010

0,012

0,014

M3 R20 R21 R22 R23 R24 R25 R26 R27 R28 R29 R30 R31 R32 R33 R34 R35 R36 R37 R38 R39 R40 R41 M4

m

e

t

e

r

s

Pin

River Wall

Y2000-1

Y2000-2

Y2000-3

Y2000-4

Y2001-1

Y2001-2

Y2002-1

Y2002-2

Y2003-1

Y2003-2

Y2004

Y2007

Y2009

Y2011

-0,010

-0,008

-0,006

-0,004

-0,002

0,000

0,002

0,004

0,006

0,008

0,010

R42 R43 R44 R45 R46 R47 R48 R49 R50 R51 R52 R53 R54 R55 R56 R57 R58 R59 R60 R61 R61A

m

e

t

e

r

s

pin

Lower River Wall

Y2000

Y2002

Y2004

Y2007

Y2009

Y2011

∗ 3 mm error bars show estimated accuracy

∗ Apparent movement at R61

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-0,040

-0,035

-0,030

-0,025

-0,020

-0,015

-0,010

-0,005

0,000

0,005

0,010

0,015

Feet

Settlement Results-Year 2000 base

Settlement Surveys

∗ Use same points as alignment surveys∗ Closed loops∗ Trimble Dini 12∗ 2 and 3 m Invar rods∗ Kukkimaki collimation test at start of each day∗ Verification of reference point(s)∗ Now tied to North American Vertical Datum of 1988∗ Each project has 1 or more points in National Spatial Reference System

(NSRS)∗ Required after Katrina disaster in New Orleans∗ achieved on all 16 reservoirs, Ohio River (6 locks), and Monongahela Rivers (9

locks)∗ Allegheny River in progress (8 locks)

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∗ Earth and Rock fill dam

∗ 25 m height

∗ 3.0 km length

∗ Width at base: 244 m

∗ Volume of earth: 2.5 million m3

M J Kirwan Dam

Alignment & Settlement Network

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∗ Prior to 2005, done optically∗ Very difficult due to distance

∗ EDM used from picnic area on right bank upstream of dam

∗ 2005-2007: combination of GPS and EDM as mentioned above

∗ 2007-present: GPS only∗ 2 base units, 3 roving units

∗ Static methods, 20 minutes minimum, usually 30+

Alignment Survey

-0,020

-0,010

0,000

0,010

0,020

0,030

0,040

M1 A1 A2 A3 A4 A5 A6 A7 A8 A9 M2 A10 A11 A12

m

e

t

e

r

s

2006 offset

2008 offset

2009 offset

2010 offset

2011 offset

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Conduit

Kirwan Conduit

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Settlement surveys-Outflow tunnels

Conduit Settlement

1.43 meters

settlement

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Conemaugh River Dam

Conemaugh River Dam

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2008 readings taken during record

high water event

∗ Contact: hamilton@terrasurv.com

∗ Telephone: 1+412-341-5620

Questions?