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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)

Approx. Basin

Guajataca Dam

Precipitation Amount from Sept 19 - 21

>20 inches5 10 15

GUAJATACA SPILLWAY – FAILURE SEQUENCEImagery Date: 3/4/2017

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.

Thank You, • Questions• Comments• Discussion…