Workshop on Engineered Barrier Performance slides by Robert C by gegeshandong

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									 Differential Settlement and its Importance on
     the Performance of Cover Systems at
     Radiological Waste Disposal Facilities

   Robert C. Bachus, John F. Beech, and Leslie M. Griffin
                       Geosyntec Consultants
                          Kennesaw GA
                          Kennesaw,



  Workshop on Engineered Barrier Performance Related to Low-Level
Radioactive Waste, Decommissioning, and Uranium Mill Tailings Facilities

                             Rockville,
                             R k ill MD
                             4 August 2010
                          p
                   Workshop
 Engineered Barrier Performance Related to Low-
 Level Radioactive Waste, Decommissioning, and
         U i          Tailings F iliti
         Uranium Mill T ili    Facilities

                   Session 3
 Experience with Monitoring Devices and Systems
         Used to Measure Performance

                   Presentation
     ff        S
  Differential Settlement and its Importance on the
Performance of Cover Systems at Radiological Waste
                   Disposal Facilities
                      p
 Differential Settlement and its Importance on the
 Performance o Co e Syste s at Radiological
   e o a ce of Cover Systems            ad o og ca
              Waste Disposal Facilities

  Engineered C
• E i              Systems
           d Cover S t
   – Components
   – Soils and Geosynthetic Material Characteristics
• Differential Settlement
   – Settlement Mechanisms
            p
   – DOE-specific Issues
• Monitoring Devices and Systems
   – Types of Devices and Systems
   – Experience
• Recommendations for DOE Facilities
   – Monitoring and Reporting
     Rehabilitation
   – R h bilit ti
Final Cover at the Fernald OSDF




                          Note: Soil
                          components
                          comprise
                          > 12 feet
   Soil and Geosynthetic Materials
          Low Permeability Soil Components

• Performance Expectations
  – Hydraulic barrier
  – Support vegetation
  – Radiological barrier
• Reality
  –   P      ti       ft      t ll d during        t ti
      Properties are often controlled d i construction
  –   Clays crack in extension at small strain
  –   Desiccation cracking is de facto reality in clay
  –   Cover systems compress (not extend) upon settlement
  –   Fine-grained soil erodes relatively easily
  –   Soils (and wastes) are compressible
        Waste Compressibility
                                p
• Mechanisms of waste compression that can lead
  to total and differential settlement
  – Mechanical Compression – compression of soil and
    waste due to loadingg
  – Raveling – Internal erosion of soil due to water and/or
    migration of soil due to large voids
    Physico chemical
  – Physico-chemical Changes – degradation of waste
    and subsequent mass loss
  – Biomechanical Changes – biological decomposition of
     as e
    waste
• Waste (and surrounding soil) compression leads
  to total and differential settlement
Waste Settlement and Differential Settlement
              (admittedly worst case)


  – Settlement is not uniform because waste may
    not be uniform
               ,
  – Therefore, localized subsidence and
    differential settlement can occur
Waste may not be uniform
Often Includes (Temporarily) Stiff Inclusions
        DOE Related
        DOE-Related Issues
• Extreme conditions as shown on previous
  slides may be just that…extreme
        p
  examples
  – Old facilities
  – Uncontrolled trench disposal practices
  – Compromised covers and raveling conditions
           y
• Can likely be controlled at new facilities
  – Monitored waste placement
  – Waste placement plans
 Concept of Stress Redistribution
       Average Stress
            g                               Actual Stress




     SOFT            HARD                     SOFT            HARD


Mother Nature does not like abrupt changes in material properties
and will redistribute stress in direct response to materials stiffness
Cracks due to Differential Settlement
 Waste Compressibility for DOE
• Mechanisms of waste compression that
  can lead to total and differential settlement
                    p              y
  – Mechanical compression – likely for DOE
  – Raveling – problematic for old DOE facilities
       y                  g             y
  – Physico-chemical changes – not likely
  – Biomechanical changes – not likely
                    ,   y
• For DOE facilities, may have different
  concerns and mechanisms when
  considering old versus new facilities
       Performance Aspects of Cover System Components



                                                                                                  Support Vegetation
                                            YER
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                        PRO      NCH                                                             Drainage
                            (24 I

  GEOCOMPOSITE
 DRAINAGE LAYER                          D

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                                                                                         1
                                                                                         0
                                                                                             /
                                                                                                 Low Permeability
                                                                                                 Soil and Geomembrane
                                        RIER
                                    BAR
                              SOIL        ICK)
PE GEOMEMBRANE                     NCH TH
                             (18 I
    (40 MIL THICK)                                                                               Isolation
                                                  ER/
                                          IL  COV      K)
                                     E SO         THIC
                                DIAT         NCH                                                 R i f       t
                                                                                                 Reinforcement
                            RME        (12 I
                       INTE       FILL                 1
                           TURAL               4 to 20
                                                                                                 (optional)
                        UC
                     STR

      Example
USEPA Subtitle D
Final Cover System                                                                                                 20
 Properties and Measurements
                   p
• How to Assess Properties
  – Laboratory tests
  – Performance monitoring and back calculation
  – Monitored large test fill
• Candidate Field Monitoring Concepts/Devices
  –   Visual inspection
  –   Aerial survey
  –   Settlement plates
  –   Buried settlement plates
  –   Hydraulic sensors
  –   Instrumented geotextiles
Large Scale
Large-Scale Testing of Waste




                                     1500
                                                 NORMAL STRESS = 1980 psf
                                                 NORMAL STRESS = 1970 psf
                                     1000        NORMAL STRESS = 1930 psf
                                                 NORMAL STRESS = 1890 psf




                SHEAR STRESS (psf)
                                      500



                                       0



                                     -500



                                     -1000



                                     -1500
                                            -4        -3        -2          -1          0       1   2   3   4

                                                                                 SHEAR STRAIN (%)


                                     CYCLIC SIMPLE SHEAR TEST RESULTS FOR WASTE SAMPLE
                    p          y
           Waste Compressibility
(mechanical… but with time can be physico-chemical and biological)


                             Primary Compression (Cc, Cr)

                                           Cr
                                                            Maximum Preconsolidation
                                      V
         n                                                       Stress = p’c
                                                     Cc


                     v
                                                     log n

                             Secondary Compression (C)

                                                                Initial
                                                                  &
                                 v                            Primary
                                                                            Secondary
                                                    C

                                                 Log Time
           Monitoring Devices
• Visual inspection
  – Probably best for DOE
                                     p
  – Evidence of erosion and “bowl shapes”
• Aerial survey
  – Excellent, except for resolution
  – Provides general assessment
• Settlement plates and surface monitoring points
  – Best, low-cost solution
  – Need to be where there is movement!
Riser Pipe and Surface Settlement
              Plate
              Pl
         Monitoring Devices
• Buried settlement plates
  – Can help assess variations with depth
  – Help assess effects of age
• Hydraulic sensors
  – Good for automated monitoring
  – Good for “profiling”
• Instrumented geotextiles
  – May be helpful in long-term study
  – Potential for automated profiling
 Instrumented Test Fill - MSW
• Vertical and Lateral Expansion of South Shelby
  Landfill, Memphis, TN

• New Waste Placement
  Causes Considerable
  Settlements of Old
  (Unlined) Waste


• Analogous to DOE
  placement of thick cover
  over existing waste
3D View of Test Fill

              30-foot platform

              20-foot
              20 foot platform

              10-foot platform
View of Test Fill
 Settlement Profiler Schematic


                               Test
                               T t Fill
Water Reservoir




                  Measurements Taken Every 1 foot
 Settlement Hub
     Settlement Profiler System
              Constant - Head Liquid Reservoir

                                          Liquid- filled Tubing




                                                                                            Test Fill
                                                                                                                     ha   hb



                                                                                                         a
                                                                                                                h

                                                                                                          b
Settlement Calculation
   Settlement = h = hb-ha

    But,
    But we know from the pressure transducer that:                          Electrical Pressure Transducer

        ub-ua = whb-wha

              = w(hb-ha)
                                                                  Transducer Position Before Fill Placement (Output = ua = haw)
              = w (h)

    Therefore,                                                    T    d     Position Aft     Placement (O t t = ub = hbw)
                                                                  Transducer P iti After Fill Pl      t (Output
          h = (ub-ua)/w
                        Cross Section
           Longitudinal Cross-Section

                                                                                30’
                                    Test Fill Soil                       20’
                                                                   10’




          Existing Waste




            Foundation Soils (thickness ~1000 ft)


           Bedrock
                                                     Settlement Profile Pipe

                                                     Surface Settlement Plate

                                                     Deep Settlement Plate
(Not to Scale)
                         Surface Settlement Plate

                        60
Height (feet)




                        40
                                        End of Construction

                        20


                         0
                              0   20   40      60       80    100   120   140
   tlement (feet x 10




                        -20
               t)




                        -40
Sett




                        -60
                                               Time (days)
                  Surface Settlement Plates
                                    Days
                                    D
                      0   25   50    75    100   125            150
                  0

                  1                                     Fill
                                                       Height
                  2
                                                       ~ 11 feet
            ft)




                  3
Settlement (f




                  4
                                                       ~22 feet
                  5
S




                  6                                    ~ 31 feet

                  7

                  8
                  Settlement Profile with Depth

                                                       Days
                        0          20        40   60          80   100   120   140
                  0.0


                  0.5
                                                                                     Deep
                  10
                  1.0
 ettlement (ft)




                                                                                     Medium

                  1.5
Se




                  2.0
                              Test Fill

                            Existing Waste                                           Shallow
                  2.5
                                                                                     Surface

                  3.0
Settlement Profiler Results
                                              445

                                              440

                                                                                                       8-Dec-00
            Fill Elevation (ft)
                                              435
                                                                                                       28-Nov-00
                                              430                                                      17-Nov-00
                                                                                                       27-Oct-00
                                              425                                                      23-Oct-00
                                                                                                       19-Oct-00
                                              420

                                              415
                                                    0   100   200    300     400     500   600   700
                                                               Distance along Pipe (ft)


                                               7
   Relative Elevation of Profiler Pipe (ft)




                                               6
                                               5
                                                                                                       19-Oct-00
                                r




                                               4
                                                                                                       23-Oct-00
                                               3
                                                                                                       27-Oct-00
                                               2
                                                                                                       17-Nov-00
                                               1
                                                                                                       28-Nov-00
                                               0                                                       8-Dec-00
                                              -1 0      100   200    300     400     500   600   700
         ve




                                              -2
                                              -3
                                                               Distance along Pipe (ft)
            Settlement Profiler Results

                          7
            vation (ft)




                          5
Relative Elev




                          3


                          1


                               0   100                       200           300         400      500        600          700
                          -1
                                                                                        Distance from Eastern Hub (ft)
                                          elative Elevation (ft)




                                                                    5
                                                                    4
                                                                    3
                                                                    2
                                                                    1
                                                                    0
                                                                   -1190         195          200          205            210
                                         Re




                                                                   -2
                                                                   -3
                                                                                       Distance from Eastern Hub (ft)
    Implications to DOE Sites
• In the absence of raveling and the
  introduction of water, differential
                            j problem
  settlement is NOT a major p
• Most of the settlement is due to application
  of load
• Time-dependent settlements are small and
           y
  relatively uniform
• Monitoring requirements are relatively
      p
  simple
Liner System and Cover System
          (example for Subtitle D MSW)
                                                              LANDFILL GAS WELL
                                              INTERMEDIATE    (TO FLARE OR TURBINE)
 PIPELINE TO                     ACTIVE       COVER
 LEACHATE                        AREA
                                                                 FINAL COVER SYSTEM
 STORAGE TANK
 OR TREATMENT PLANT




                                                        DAILY COVER

                      LEACHATE REMOVAL PUMP
                                                  LINER SYSTEM
            SUMP                                  (COMPOSITE LINER OVERLAIN BY
                                                  LEACHATE COLLECTION SYSTEM)
Leachate Generation Rates
                             400




       L EACHATE FLOW RATE
                             350

                             300


                    W
                             250

                             200

                             150                                    MSW LANDFILL
                                                                     (PENNSYLVANIA)
                             100
                                                                 Rainfall = 39 inches/years
                               0
                              50

                              0

                                        ACTIVE        COVER    CELL CLOSED
                                        FILLING

                                      RAINFALL
                                   ONTO ACTIVE AREA
LEACHATE
TRANSFER
PIPE


                                                   LEACHATE
                                                  GENERATION




                                                                   LINER SYSTEM
     SUMP                              LEACHATE PUMPED
                                       FROM SUMP                                              15
Generalized MSW Leachate
Generation Rates – Rainfall Factor

  1000 – 2000 gpad
  (30 to 60% of rainfall)
 300 – 600 gpad
 (10 to 20% of rainfall)

 100 – 200 gpad
 (3 to 6% of rainfall)

 20 – 40 gpad
 (0.6 to 1.2% of rainfall)

10 – 20 gpad
(0.3 to 0.6% of rainfall)
Influence of Time after Closure on
     Leachate G
     L                ti Rate
         h t Generation R t

                       HW LANDFILLS
           Recommendations
• Monitor Performance of Existing Facilities
  – Seems that “data” includes visual assessment
            q
  – Limited quantitative data
  – Summary report of problems may exist
     • Visual reports
       Settlement plates
     • S ttl     t l t
     • Leachate generation rate
• Report Findings
  – Identify forum for presentation of monitoring results
  – Report performance of rehabilitation measures
    Design Challenges and Solutions

Issue – Differential Settlements
•   Differential settlements along liner resulting from waste variability and local
      ft h d          t (e.g., collapsing void...the “ t d refrigerator”) may
    soft or hard spots (         ll   i     id th “rusted f i       t ”)
    impair the liquid containment capability of the leachate collection system
    and/or cause localized settlements that result in the ponding of liquids or
    excessive liner system strain.

Solution
•   Assess actual site conditions to avoid “worst case” analyses. Incorporate
    high stiffness g
      g                y                                    y
                   geosynthetic reinforcement in the liner system or subbase
    and/or construct a foundation “buffer layer” between liner system and
    existing waste. Also, ground improvement techniques (e.g., deep dynamic
    compaction) can be used to minimize near-surface heterogeneities.
•   Analytical procedures are available to select appropriate reinforcement
    properties (e.g., strength, stiffness) or minimum thickness buffer layer.
Design Challenges and Solutions
 “Rusted Refrigerator” Scenario


      SURFACE BEFORE SETTLEMENT

      SURFACE AFTER SETTLEMENT




                                     WASTE



            ZONE OF INFLUENCE




             LOCALIZED COLLAPSE OR
           SETTLEMENT WITHIN WASTE

                                  SLOPE AREA
                                 “SLOPE AREA”
Design Challenges and Solutions
      Compressible Void
                       LOCALIZED LOW SPOT

                           LINER SYSTEM
                       AFTER SETTLEMENT
                                               FUTURE WASTE
                     COMPACTED CLAY

             LOCALIZED LOW SPOT




                                               EXISTING WASTE

   COLLAPSIBLE VOID/HIGHLY
      COMPRESSIBLE ZONE*

   * DIFFERENTIAL SETTLEMENT MAY ALSO RESULT
     FROM HETEROGENEOUS NATURE OF WASTE
Design Challenges and Solutions
  Geosynthetic Reinforcement

    LINER SYSTEM


        GEOGRID
  REINFORCEMENT
         LAYERS




                          VOID
        ZONE OF
      INFLUENCE
                         SOFT AND/OR
                   COMPRESSIBLE/COLLAPSABLE
                             ZONE
                                       EXISTING WASTE
Design Challenges and Solutions
D i Ch ll            d S l ti
          Buffer Soil


   LINER SYSTEM




   ENGINEERED FILL
   FOUNDATION LAYER



  LIMITS OF DIFFERENTIAL
    SETTLEMENT EFFECTS
                   VOID    WASTE
Design Challenges and Solutions
  Deep Dynamic Compaction
            EXISTING WASTE
            SURFACE               WASTE SYSTEM AFTER
                                        SURFACE AFTER
                                  DEEP DYNAMIC
                                  COMPACTION




                        EXISTING WASTE

								
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