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Todd N. Loar, PG, CEGSenior Geological EngineerUSACE, Risk Management CenterLakewood, CO
Dennis Zeveney, PEChief, Geotechnical BranchUSACE, Jacksonville DistrictJacksonville, FL
FAILURE, EMERGENCY RESPONSE, MITIGATION, AND ENGINEERING GEOLOGY OF GUAJATACA DAM SPILLWAY, PUERTO RICO
1
International Association of Engineering Geologists &Association of Engineering Geologists Annual MeetingSan Francisco, CASeptember, 2018
GUAJATACA DAM – LOCATION
San Juan11 mi (17km)
Approx. Basin
Ponce
Caguas
Arecibo
Mayaguez
Guayama
Aguadilla
GUAJATACA DAM – BACKGROUND
Designed & built early 1920’s Water supply Max. height: 121 ft (37m) Outlet Works tunnel in right abutment Emergency spillway in left abutment, uncontrolled semi-circular ogee weir Semi-hydraulic fill (“puddle-core”) with core wall
Deformations of the embankment and foundation during construction
Core wall
Semi-hydraulic fill
Guajataca River
Water supply canal
Spillway
OW Tunnel
(Circa 1930’s aerial photo)
(Example dam section, left abutment)
GUAJATACA DAM – PROJECT LAYOUT
Embankment Crest (mod. 1980)
ApproachChannel
Berm (mod. 1980)
IntakeTower
Outlet Portal
Control House
Stabilization Berm (added 1980)
Stabilization Buttress
(added 1980)
Outlet WorksTunnel
Water Supply Canal
Guajataca River Channel
Sleeve valve house
Water Filtration
Plant
Rip Rap Dissipation
Original spillway
Head-walloutlet
N
1970’s - USBR geotechnical investigation 1980’s - designed and constructed
modifications of the spillway and embankment due to distress relating to landslide creep.
Deformations continued
Rip rap dissipation
Rip rap dissipation
Embankment Footprint
Bridge
Crest cracking and settlement
HURRICANE MARIA – SEPTEMBER 20, 2017 Category 4 to 5 Hurricane Catastrophic wind and flooding damage:
Winds 130 to 155 mph (209 to 250 km/hr) 10 to 50 inches (25 to 127 cm) of rain Widespread loss of power, water, and communication No fuel readily available Debris blocked road access to most areas
President signs Major Disaster Declaration (FEMA-4339-DR-PR) Sept. 20 3-5 feet of water over the spillway crest (1/2 of design flows)
Erosion initiated at NW end of spillway where the flows were concentrated.
Removed rip-rap and undermined the unprotected lower left portion of the spillway chute.
N
Stabilization Buttress
(1980)
StabilizationBerm (1980)
1234
56
7
Imagery Date: 9/24/2017
N
Head-cutting of spillway foundation and lateral erosion into the stabilization buttress.
Rip-rap remnant
StabilizationBerm (1980)
Stabilization Buttress
(1980)
12
3
4
5
67
plunge pool off sab #5
Imagery Date: 11/22/2017
N
Spillway slab #5 failed as a small slide feature slumped into the scour hole.
StabilizationBerm (1980)
Stabilization Buttress
(1980)
Slump
(Image shows Jersey barriers and rock fill protection placed in scour hole)
1234
56
7
slump
failed slab #5
1) Initiation 2) ProgressionErosion
3) Continuation(Slide)
Head-walloutlet
GUAJATACA SPILLWAY – EMERGENCY ENGINEERING ASSESSMENT Immediate concerns for the integrity of the remaining spillway and the embankment:
1. Another storm or continued flows further erode the remainder of the spillway and breach the reservoir
2. Lateral erosion removes stability berm along toe and caused embankment failure
Stabilization Buttress(1980)
StabilizationBerm (1980)
GUAJATACA SPILLWAY – EMERGENCY RESPONSE Team developed an immediate plan of action implemented with significant military support:
1. Protect the exposed spillway foundation
Located Jersey barriers (locally)
Dropped barriers into scour hole with helicopters to break up the water jet and provide some protection of the spillway foundation.
GUAJATACA SPILLWAY – EMERGENCY RESPONSE Team developed an immediate plan of action to be implemented with significant military support:
1. Protect the exposed spillway foundation2. Provide hydraulic energy dissipation in the plunge pool
Preparation of temporary stilling basin
Delivery and placement of gravel filled “supersacks” placed to create a temp. weir
downstream of the Jersey barriers.
Build a temporary stilling basin with rockfill.
Temp. stilling basin
Temp. stillingbasin
rockfill
GUAJATACA SPILLWAY – EMERGENCY RESPONSE Team developed an immediate plan of action to be implemented with significant military support:
1. Protect the exposed spillway foundation2. Provide hydraulic energy dissipation in the plunge pool3. Lower the reservoir elevation
Installed pumps with generators and HDPE pipelines to bypass the spillway and supply water to the canal and river and drop the reservoir off the spillway.
Pumps
Canaldischarge
Riverdischarge
USGS Landslide Complex Extent
GuajatacaDam
Water supply canal
Guajataca River
Aguada Limestone Formation
AguadaLimestone Formation
CibaoFormation
Karsticlimestone
Calcareous claystone, marl, and argillaceous
limestone
Extensive sinkhole terrain (no defined surface drainage system)
Extensive sinkhole terrain
Translational Block Slide(Varmes 1978)
Spillway
Cibao Fm.
Aguada Fm.
Cartoon concept of geologic section across Guajataca Valley
Landslide Area Reconnaissance Level Mapping & Field Observations:
Aguada Fm. Large block of intact (?) limestone
formation due to large-scale translational movement
Aguada Fm.
Aguada Fm.
Buttress
Berm
Qc – Colluvium/Talus
Qls
Qls
Translational Landslide Complex
Translational Landslide Complex
Translational Landslide Complex
(Graben?)
Qls
Aguada Fm.Blocks
Qc – Colluvium
Qt –Talus
Qc – Colluvium/Talus
Aguada Fm.
Aguada Fm.
Aguada Fm.?
Qls
Qal – river terrace deposits
Qls
Spill
way
Qls
Qc
Guajataca River
Canal
FiltrationPlant
FiltrationPlant
Canal (concrete
lined)
Typical houses (cinder block and mortar (stucco)
Aguada Fm.
Aguada Fm.
Pre-dam topography superimposed on current aerial photo (layered in google earth pro)
Spillway cracking and deformation
Cut for approach channel
Drainage re-entrant under spillway
alignment
I-8 (creeping toward OW “pit”).
Limestone Block
Enclosed depressions in pre-dam topo
(sinkhole or grabenfeatures?)
I-7
I-8
I-4
I-5
I-6
I-1
I-3
I-2
I-14
Inset, or nested, scarps interpreted from pre-dam topo
Slide movement with displacement vector
Little slide movement
USBR Landslides (modified based on recent site observations)
GUAJATACA SPILLWAY – MITIGATION
Phase 1:• Flow-able fill placed under failed slab and around Jersey barriers• Sealing existing large cracks in slab• Install rock anchors to secure the existing slab• Protect exposed foundation under slab 4 (drains, flowable fill, anchors)• Re-establish water supply siphon
Phase 2:• Place rockfill to restore original grade of spillway and buttress• Grout the rockfill in lifts for upper 2 m.• Install back-ward erosion cutoffs at critical locations• Build a grouted rockfill stilling basins and weir to direct flows toward river channel• Grout under the existing spillway slab to fill voids• Place an over-lay of reinforced concrete over the existing slab
Grouted rockfill
GUAJATACA SPILLWAY – REMEDIAL CONSTRUCTION
Acknowledgments:Dan Blaydes, Chad Gillan, Sam Hutsell, Carlos Cepero, Carla Roig-Silva, and Rafael Rios (SAJ project development team); John Kendall and Chris Papiernik (SAJ risk assessment team); and Gregg Batchelder-Adams, Chuck Redlinger, Thomas Terry, Mike Phillips and Sal Todaro at the RMC.