tsaile dam modification project unearthing a safer dam€¦ · tsaile dam modification project...
TRANSCRIPT
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TSAILE DAM MODIFICATION PROJECT
Unearthing a Safer Dam
TSAILE DAM MODIFICATION PROJECT
Unearthing a Safer Dam
Bureau of Indian Affairs
Navajo Regional Safety of Dams Program
Stephen G. Brown, PE
Kleinfelder
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AcknowledgementsAcknowledgements
C. Scott Goss – BIA Chief Safety of Dams
Pearl Chamberlin – BIA Regional Officer
Chuck Nixon – BIA Regional Engineer
Rod Eisenbraun, PE
Charlie Larson, PE
Brad Piede, PE
Russ Grant, PE
Paul Kluvers, PE – Akana
Alan Heiman, PE - Akana
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Tsaile Dam, Navajo Reservation, AZTsaile Dam, Navajo Reservation, AZ
Constructed 1964
Height = 52 feet (maximum section)
Crest Length = 1,950 feet
Crest El. 7037.3 feet
Reservoir Capacity = 5,500 acre-feet
24” Dia. CMP Outlet Conduit Capacity = 40 cfs
Emergency Spillway Passes the PMF
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Existing Plan & TopoExisting Plan & Topo
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Canyon de Chelly – Navajo Culture
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Anasazi Ruins in Canyon de ChellyAnasazi Ruins in Canyon de Chelly
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Town of Chinle
Residents in the Canyon
Tourists in the Canyon
PAR= 450
Downstream - ConsequencesDownstream - Consequences
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Potential Failure ModesPotential Failure Modes
Static
– Seepage through embankment
– Seepage into/out of outlet conduit
– Seepage along outside of conduit
– Collapse of outlet conduit (CMP)
Seismic
– Liquefaction of alluvium in foundation
– Transverse cracking of embankment
Hydrologic
– Erosion of the embankment along the left side of the spillway
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Rocks in the outlet
conduit
Rocks in the outlet
conduit
Sediment in the toe
drain
Sediment in the toe
drain
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Rehab Design GoalsRehab Design Goals
Resolve the Deficiencies to Address PFMs
– Fix the outlet works by remove and replace
– Fix the foundation alluvium by remove dam and replace
Quantity of embankment is not large; limits the construction
cost
Control costs by planning construction in one season
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Downstream Embankment ShiftDownstream Embankment Shift
Downstream Limits – Wetlands & Cultural Features
Remnant of Dam to Serve as Cofferdam
Full Excavation Enables Foundation Treatment
Exposing Middle Rock Bench Provides Location for Outlet
Conduit in Rock Trench
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KEY ELEMENTSKEY ELEMENTS
Construct ‘New’ Dam from Bottom Up
– Existing Dam Removal
– Foundation Preparation
– Filter-compatible Internal Drainage System
– Zoned Embankment with Central Core
– Concrete Outlet Tower
– Concrete-Encased Outlet Conduit
– Durable Riprap
– Improved and Safer Alignment for BIA Road 8077
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EXISTING DAM REMOVALEXISTING DAM REMOVAL
Excavate the Existing Dam
Re-use Exc. Material to Construct the New Dam
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EXISTING DAM REMOVALEXISTING DAM REMOVAL
Segregate and Stockpile Excavated Material
Needed to Re-Use All of it – Available Borrow is Lesser
Quality!
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EXISTING DAM REMOVALEXISTING DAM REMOVAL
Internal Erosion
Hole In-Progress
In-line with CMP
Outlet Conduit
and beneath d/s
stability berm
8 to 10 feet
diameter
8 feet deep
Small amount of
water in bottom
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EXISTING DAM REMOVALEXISTING DAM REMOVALExposed in the Foundation:
– Embankment Packed Beneath Rock Overhangs
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EXISTING DAM REMOVALEXISTING DAM REMOVAL
Exposed in the Foundation:
– Rock Overhangs – More Extensive than Anticipated
– Alluvial Deposits – Present Beneath Downstream Shell
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EXISTING DAM REMOVALEXISTING DAM REMOVAL
Remove Rock Overhangs – Drill and Excavate to 1H:4V Slope
Used Rock Excavation Bid Item
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EXISTING DAM REMOVALEXISTING DAM REMOVAL
Rock Overhangs Removed
Lower, Middle, and Upper Foundation Benches
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Limited Grout Exploration Program (Foundation Seepage is
Not a PFM)
Single Line, Targeted Steeply Dipping Joints
Only two holes had substantial grout take!
FOUNDATION PREPARATIONFOUNDATION PREPARATION
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FOUNDATION PREPARATIONFOUNDATION PREPARATION
Paleo-Stream Channel in Joints
Treated 2 Joints with Dental Concrete
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FOUNDATION PREPARATIONFOUNDATION PREPARATIONClean Foundation Rock
– Shovels, Brooms, Pressurized Air Wands
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FOUNDATION PREPARATIONFOUNDATION PREPARATIONTreat a Former Stream Bed Channel with Dental Concrete
Address Shallow Seepage and ‘Steps’ in Rock
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FOUNDATION PREPARATIONFOUNDATION PREPARATION
Key Trench
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KEY TRENCHKEY TRENCH
Zone 1 Core Placed in Key Trench
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DRAINAGE SYSTEMDRAINAGE SYSTEM
Zone 1 Core, Chimney Drain and Blanket Drain
Blanket 1 ft Sand, 2 ft Gravel, 1 ft Sand – Imported
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DRAINAGE SYSTEMDRAINAGE SYSTEM
Toe Drain – Lower Foundation
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DRAINAGE SYSTEMDRAINAGE SYSTEM
Middle Foundation Blanket Drain
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ZONED EMBANKMENTZONED EMBANKMENT
Zone 1 – Clay with Silt
Zone 2 – Sandy Silt with Clay
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ZONED EMBANKMENTZONED EMBANKMENTContractor Informs Us Zone 2 Will Run Out!
Additional Material Needed to Complete Upper Portion of
Downstream Shell
Proposal - Use the Zone 2 Contaminated with Sandstone
Cobbles – Zone “2B”
Pre-spreading Operation using Dozer to Break Down Oversize
and Raking
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ZONE 2B EMBANKMENTZONE 2B EMBANKMENT
Test Fill to Demonstrate Means and Methods
Prescribed Number of Compactor Passes
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ZONED EMBANKMENTZONED EMBANKMENT
Zone 2B, Chimney, Zone 1, Zone 2
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OUTLET CONDUITOUTLET CONDUIT
DIP Encased in Concrete in Rock Trench
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Intake TowerIntake Tower
Rock 14 feet Low at Tower Location – Critical Path Task
Excavated and Placed 14 ft Concrete Pedestal Foundation
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RIP RAPRIP RAP
On-Site Borrow Sandstone Not Durable
Design Change Notice to Import Basalt
D50 = 14”
T = 2.8’
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FINDINGS DURING CONSTRUCTIONFINDINGS DURING CONSTRUCTION
Outlet Conduit CMP in Failed Condition – Severe Internal
Erosion
Overhanging Rock - Additional Rock Excavation
Foundation Grouting – No Major Issues
Intake Tower Foundation Lower than Anticipated – Build
Concrete Pedestal
Able to Use all Stockpiled Material – No Need to Open Borrow
On-Site Sandstone Riprap was Poor Quality – Import Basalt
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PROJECT SUCESSESPROJECT SUCESSES
Eliminated Static and Seismic PFMs
Close CM coordination with Contractor and BIA
Ability to adjust the work to the conditions
Maintained construction schedule
After many years of planning – A Completed Project!
New dam will serve the Navajo Nation and community for
many decades
Construction Cost $8.5M
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QUESTIONS?QUESTIONS?