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Neven MatasovicGeo-Logic Associates, Anaheim, Californianmatasovic@geo-logic.com; Direct: 714-465-8240

Landfill Slope StabilityCauses, Impacts, and Special Considerations

MSW & Hazardous Waste LandfillsTailings ImpoundmentsHeap Leach Pads

12 August 2015

PRESENTATION OUTLINE

1. Introduction (Facilities, Loading & Materials)2. Evaluation of Seismic Loading3. Material Characterization4. Modeling

• Pseudostatic Analysis• Site Response Analysis• Seismic Deformation• (Seismic) Liner Tension• “Advanced” Modeling

5. Take-Away and Recommendations

Matasovic 2010

State-of-the-Practice

“Ignored” Issue

State-of-the-Art

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MODERN WASTE DISPOSAL FACILITY …

LANDFILL LINERThe Eagle Mountain,Landfill, CA design fillheight is 1,200 ft !

MATERIALS, DISPOSAL PRACTICE, …

Municipal Solid Waste …Matasovic 2010

Containerized Liquid Waste

Interfaces …

Municipal Solid Waste …

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Peak Ground Acceleration = 0.2 g

Peak Ground Acceleration = 1.0 g

SEISMIC LOADING(Design Ground Motions)

Application ofGeosynthetics

Conceptual Trend of Increasing Design Ground Motion (CA)

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2014 M 6.0 South Napa Eq. – max PGA = 1.0 g!

SEISMIC PERFORMANCE CRITERIA(State and Federal Regulatory Requirements)

Maximum Calculated Permanent Seismic Displacement:

• Composite Liner: 6 - 12 in. (Seed and Bonaparte, 1992)

• Composite Cover: 12 – 36 in. (typical)

• Other (site-specific; e.g., BKK Landfill Table 7-1)

Factor of Safety (Seismic):

• FS ≥ 1.5 (California; not clear about seismic coefficient)

• FS ≥ 1.1 (typical; other concerns; e.g., soil liquefaction)

Other

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EVALUATIONS

SEISMIC HAZARD ANALYSIS

Matasovic 2010

Bedrock PHGA as High as 1.0 g!

•2,475-yr Return Period• B/C boundary/weak rock• 1-Hz SA = Spectral

Acceleration @ T = 1 sec

http://geohazards.usgs.gov/deaggint/2008/

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UCERF 3 - Uniform CaliforniaEarthquake Rupture ForecastUCERF-3 Fault Model: Fault sections are divided into an integer number of equal lengthsubsections. All subsections shown in green are connected (assumes earthquakes cannot“jump“ more than 5 km)

UCERF-3:305,709 “viable” fault ruptures (350 mega faults)

UCERF-3:1,440 logic tree branches5-second visual examination takes 350hours of supercomputer time for justone of 1,440 alternatives

The rate at which the Cucamonga fault co-ruptures(participates) with other fault sections

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Example Application: Participation Rate Map(Cucamonga Fault)

SITE

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TargetSpectrum

(Ds)Design Motion ≥ (Ds)Target

Design MotionSpectrum

EVALUATION OF DESIGN GROUND MOTIONS

Matasovic 2010

PGAPGA

PGAPGA PGAPGA

Accelerograms

Spectral Analysis ofSurface Waves (SASW)

WASTE MASS CHARACTERIZATION

Multichannel Analysisof Surface Waves(MASW)

T-Rex (University of Texas Austin; part of NEES) Only Two Geophonesare Required

Matasovic 2010

(T-Rex Weighs 30 tons!)

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Matasovic and Kavazanjian (1998)

WASTE MASS CHARACTERIZATION (CONT.)

Shear Wave Velocity Profile: Poisson’s Ratio Profile:

Matasovic 2010

Ramaiah et al. (2015) (Submitted)

WASTE MASS CHARACTERIZATION (CONT.)

Matasovic 2010

Results of statisticalanalysis of VS data forall USA data

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WASTE MASS CHARACTERIZATION (CONT.)

Matasovic 2010

Results of statisticalanalysis of VS data forall Worldwide data

Ramaiah et al. (2015) (Submitted)

≈ 0.84H: 1.0 V (friction angle ≈ 50 degrees)

WASTE MASS CHARACTERIZATION (CONT.)

Shear Strength of Waste

Matasovic 2010

≈ 0.84

1.0

50 degrees / 1.5 = ≈ 33 degrees (design)

50o

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Bucket AugerDrilling,Sampling & In-Hole DensityMeasurements

VIDEO®

MSW Unit Weight Profile

Matasovic 2010

WASTE MASS CHARACTERIZATION (CONT.)

Borehole Video Log

LAB. MEASUREMENT OF MSW PROPERTIES

The CyDSS Device Weighs 4 tons!

Large-Diameter (457-mm/18 in.)CyDSS Apparatus:

Matasovic 2010

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Matasovic et al. (1998)

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Cyclic Loops:

CYDSS TEST RESULT INTERPRETATION(S)

Alternative Interpretation: Modulus Reduction & Damping Curves

LAB MEASUREMENT OF IN-PLANE STRENGTH

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Conventional Shear Box:• Box: 305×305 mm (12×12 in.)

• Dmax = 90 mm (3.5 in.)

• σn = 500 kPa (≈105 ft of waste)

• 1 mm/min (0.04 in./min)

• Static Only!

GEOCOMPOSITEDRAINAGE LAYER

HDPE GEOMEMBRANE(60 mil)

GEOSYNTHETICCLAY LINER (GCL)

OPERATIONS LAYER

FOUNDATION LAYERFOUNDATION LAYER

Dmax

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• Box: 1067×305 mm(42 ×12 in.)

• Dmax = 254 mm(10 in.)

• σn = 2,070 kPa(≈ 430 ft of waste)

• Static + Dynamic

Fox et al. (2006)

Large Cyclic (Dynamic) Direct Shear Device:

LAB MEASUREMENT OF IN-PLANE STRENGTH

This DS DeviceWeighs 1.4 tons!

σn = 141 kPa (30 ft of

waste)

Δ = 225 mm (9 in.)

Nye and Fox (2007)

GCL (Bentomat DN)

LAB MEASUREMENT OF IN-PLANE STRENGTH

Failed Specimen

Stress-Displacement Response (Static Test)

3.0 in. (typ.)

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0.4 in./min (ASTM)

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LAB MEASUREMENT OF IN-PLANE STRENGTH

σn = 141 kPa

Δ = ± 25 mm

f = 1 Hz

GCL (Bentomat ST)

Stress-Strain Loops (Cyclic Test):

Nye and Fox (2007)

Matasovic 2010

1.0 in.

LAB MEASUREMENT OF INTERFACE CREEP

Static Only !

Fowmes, Dixon, and Jones (2008)

Schematics of “Measuring Box” (Creep)(Sandwich Testing)

Results: synthetic MSW vs. non-wovengeotextile vs. textured HDPE vs. wood

10 ft of MSW !

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REVIEW

1. Des. Ground Motions2. Properties of MSW

• Static• Dynamic

3. Interface Properties• Static (incl. creep)• Dynamic

4. Other (Bedrock Prop., …)

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Numerical Modeling

STATE OF PRACTICE - DECOUPLED ANALYSIS

Pseudostatic Slope Stability Model: SLOPE/W (GeoSlope International, 2007)Nonlinear Site Response Model: D-MOD2000 (GeoMotions, 2007)

Site Response Model

WASTE

Matasovic 2010

aavg ≡ (kh)g ≡ HEA

ky = 0.12 g (example)

FS =

BEDROCK

ALLUVIUM

WASTE

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STATE OF PRACTICE - DECOUPLED ANALYSIS

aavg(t)β

ky = 0.12 g (example)

Sliding Block Model:(Classical Newmark Analysis)

Presentation of the Results& Seismic Stability Criteria:

Stability Criterion: 12 in.

ky = 0.12 g (example)

aavg(t)

Decoupled Analysis is conservative …Lin and Whitman [1983], Gazetas and Uddin [1994], Matasovic et al. [1997; 1998], Kramer andSmith [1997], Rathje and Bray [1999], Wartman et al. [2003; 2005], …

But does not tell us if membrane is ruptured / will gas and leachate escape…

IGNORED ISSUE - “LINER TENSION”

TENSION (TEAR ?)IN GEOMEMBRANE

Matasovic 2010

Static Component(Initial Shear Stress due toSettlement)

Seismic Component(Seismically-InducedSettlement & Shear Stress)

Stress

Static(Creep) Seismic

Strain

LINER TENSION:(Gas Escape Issue)

LANDFILL GAS

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1994 Chiquita Canyon Landfill

• Mw 6.7 Northridge Earthquake• PHGA (Bedrock) = 0.29 g• ≈12-in. Rupture in HDPE

TEAR

“LINER TENSION” – FIELD OBSERVATION

Yazdani, Campbell & Koerner (1995)

“LINER TENSION” – FIELD MEASUREMENTS

• Waste Fill Height: 2 m (7 ft)• Monitoring: 3 yrs. upon

filling; Strain Gauges:

• Measured axial strain inHDPE < 1% (@ top )

Static Component Only(Initial Shear Stress due toSettlement)

Matasovic 2010

1995 Yolo Co. Landfill

Strain Gauge

7 ft

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Matasovic 2010

“LINER TENSION” – TOOL BOX

Developed Sensor-Enabled Geotextile(GeoDetect, 2010); Canbe used in GCL perrequest

Thusyanthan et al. (2007)

Centrifuge Testing - Test Results

Matasovic 2010

TENSIONIN GEOMEMBRANE 5-25% Increase in Liner

Tension due to ShakingPGA = 0.1 – 0.3 g

7 m (23 ft)

“LINER TENSION” – CENTRIFUGE TESTING

Laminar Box (Univ. Cambridge)

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HOW TO OVERCOME THE LIMITATIONSOF LAB TESTING, FIELDINSTRUMENTATION, AND PHYSICALMODELING?

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“ADVANCED” ANALYSIS

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β

Fully-Coupled Analysis:(+ static + creep + gas + temp …)

“ADVANCED” ANALYSIS

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ACKNOWLEDGEMENTS

• Ed Kavazanjian (Co-PI)• Neven Matasovic (Co-PI)• Mohamed Arab

Collaborative Research: The Integrity of Geosynthetic Elements of WasteContainment Barrier Systems Subject to large Settlements or SeismicLoading, NSF Award Number CMMI-08-0800873, 2009 - 2011

• Patrick J. Fox (Co-PI)• Two MS Students• Jim Olsta (Industrial Partner)

Matasovic 2010

FULLY-COUPLED ANALYSIS – FLACTM MODEL

2-D FLACTM V 6.0 SiteResponse Model withInterface Elements

The Geosynthetic InterfaceModel does not come w/FLACTM! We adopted theSalah-Mars (1992) NestedYield Surface Model for thisapplication and coded itinto FLACTM by the meansof the FISHTM programminglanguage

The Equivalent LinearModel comes with FLACTM

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CALIBRATION OF THE FLACTM MODEL

MSW ParametersInterface Model

Shaking Table (test)

Unlined Landfill (case history)

Calibration = find “right”amount of damping and pickappropriate modeling (elementtype) options

CALIBRATION – MSW PARAMETERS

OII Landfill, Monterey Park, CA (unlined landfill) – Aerial View

Matasovic 2010

SM-2SM-1

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Matasovic 2010

CALIBRATION – MSW PARAMETERS

Quietboundary

Quietboundary

SM-1

SM-2

FLAC V6.0 Model

MSW

ROCK

ROCKROCK

ROCKROCK

MSW

MSWMSW

Shaking table testing by Yegian and Kadakal (2004)

Matasovic 2010

PGA = 0.6 g

Schematic Representation of Shaking Table Test:

CALIBRATION – INTERFACE MODEL

Shaking Table

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Arab, Kavazanjian and Matasovic (2010)

Matasovic 2010

CALIBRATION – INTERFACE MODEL

Interface Elements

Base

Rigid Block

X

Y

Salah-Mars (1992) ConstitutiveModel; adopted for Interface(s)

PGA = 0.6 g

Shaking Table Model:

MODELING - FULLY-COUPLED ANALYSIS

FLACTM Model with theInterface Elements and “best”material characterization

PGA = 0.6 g

Calculated Interface Response duringShaking (modified Salah Mars model)

30 tons 4 tons 1.4 tons

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FULLY-COUPLED ANALYSIS – SAMPLE RESULTS

Arab, Kavazanjian and Matasovic (2010)

Matasovic 2010

6 in.

PGA = 0.6 g

LINER TENSION

DISPLACEMENTS

A NOTE ON COMMERCIAL APPLICATIONS

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Numerical Model – SIGMA/WTM

(stripped-down version of FLAC)

SIGMA/WTM LINER TENSION MODEL(“stripped down” FLACTM model)

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A NOTE ON COMMERCIAL APPLICATIONS

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Results (Static) – SIGMA/W

LINER TENSION MODEL - RESULTS

HIGHLIGHTS AND TAKE-AWAY

• There are generic sets of material parametersof MSW (and of interfaces), but designground motions must be evaluated on a site-by-site basis, …

• Order of Importance: Ground MotionMaterial ParametersMethod of Analysis …

• “Liner Tension” is a GWT protection issue (gasescapes …), not a stability issue, but …

• Advanced Analysis - Acquired knowledgeallows for safe design in areas of moderate tohigh seismicity!

Matasovic 2010

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RECOMMENDATIONS

Zekkos, Matasovic &Tufenkjian (2010)

T-Rex(Stokoe)

In-Situ Test ResultInterpretation

• Require measurement of Vs and dynamicwaste properties on the important projects.

• Require interface testing during the designstage of the project.

• Pseudostatic method is O.K. for PGA ≤ 0.2 g; Performance based design for PGA ≥ 0.2 g; Charts O.K. up to 0.4 g; Nonlinear and/or 2-Dsite response models if PGA ≥ 0.4 g.

• Require proper calibration of advancednumerical models (FLAC, PLAXIS,…).

• Be open to revised liner and/or anchor trenchdesign in areas of high seismicity.

• Require that G.E. (CA and OR) or D.GE. (otherstates) signs design reports.

• Subcontract G.E. or D.GE. to review on yourbehalf.

Matasovic 2010

QUESTIONS ?

Matasovic 2010