Sardinia 2005, Tenth International Waste Management and Landfill Symposium S. Margherita di Pula, Cagliari, Italy; 3 - 7 October 2005 FRAMEW ORK FOR THE ESTI MATI ON OF MSW UNI T W EI GHT PROFI LE by D. ZEKKOS, J. BRAY, E. KAVAZANJIAN, Jr. , N. MATASOVIC, E. RATHJE, M. RIEMER, & K. STOKOE II Univ. of California at Berkeley, Arizona State Univ., GeoSyntec Consultants, & Univ. of Texas at Austin Sponsored by the U.S. National Science Foundation
Significant Uncertainty in Current MSW Unit Weight Estimates Augello et al. 1998
MSW Unit Weight Is Important • Large range of MSW unit weight, e.g. 5 - 15 kN/m 3” – Differ by factor of 3! • Liner interface strength 0.45 depends on overburden 5% damping 0.4 stress 0.35 0.3 PSA, g's 0.25 • Landfill capacity estimates 0.2 depend on MSW unit weight 0.15 0.1 0.05 • Seismic performance 0 depends on MSW unit 0.01 0.1 1 10 Period, sec weight profile Rock mot ion MSW surface- Kavazanjian et al. 1995 MSW surface- const ant unit weight
Methods to Evaluate MSW Unit Weight 1. Landfill Records and Post-Placement Surveys 2. Unit Weight Measured from Conventional Geotechnical Sampling 3. In-Situ Large-Scale Test Pits or Large-Diameter Boreholes (mimics sand cone density tests with calibrated gravel)
In-Situ Large-Diameter Borehole Method 1. Auger and collect waste 2. Weigh waste collected over interval (W waste ) W γ = waste waste V waste Developed by Kavazanjian and Matasovic for OII Landfill 3. Place tremie pipe in borehole 4. Fill with gravel of known unit weight (V waste )
Large Scatter in Reliable MSW Unit Weight Data Total unit weight, kN/ m 3 0 5 10 15 20 25 0 1 2 3 4 20 5 6 Depth, m Kavazanjian et al. (1995) 7 8 9 40 10 11 60 (1) Santo Tirso, Portugal (Gom es et al. 2002); (2) OI I , California, USA (Matasovic and Kavazanjian, 1998); (3) Azusa, California, USA (Kavazanjian et al, 1996); (4) Tri-Cities, California, USA (this study); (5) no nam e older landfill (Oweis and Khera, 1998); (6) no nam e younger landfill (Oweis and Khera, 1998); (7) Hong Kong, China (Cowland et al. 1993); (8) Central Mayne landfill, USA (Richardson and Reynolds, 1991); (9) 11 Canadian landfills (Landva & Clark, 1986); (10) Valdem ingom ez, Spain (Pereira et al. 2002); (11) Cherry I sland landfill, Delaware, USA (Geosyntec, 2003); Data from reliable in-situ large-scale methods available in Zekkos et al. (2005) Berkeley Geotechnical report
Characteristic MSW Unit Weight Profile Exists 0 10 20 30 0 10 20 30 0 10 20 30 0 0 0 10 10 10 20 20 20 Depth, m 30 30 30 40 40 40 50 50 50 OII Tri-Cities Azusa 60 60 60 0 10 20 30 0 10 20 30 0 10 20 30 0 0 0 Depth, m 10 10 10 20 20 20 "Younger" Cherry Island "older" 30 30 30 Geosyntec (2003), Matasovic and Kavazanjian (1998), Kavazanjian et al (1996), Oweis and Khera (1998), Zekkos et al (2005) • Need landfill-specific data • Model can be developed to capture change with depth
15.0 Total unit weight, kN/ m 3 Compaction Level (& waste composition) Determines Initial MSW W=4.5kgr, h=80 cm,t=7.5cm 10.0 W=4.5kgr, h=40 cm, t=7.5 cm Unit Weight W=5.4kgr, h=80 cm, t=5 cm W=1 0kgr, h=80 cm, t=5 cm W=1 0kgr, h=80 cm, t=7.5 cm 5.0 0.00 0.20 0.40 0.60 0.80 3 Unit w eight, kN / m Total energy per target volum e of 12 17 22 m aterial (Joule/ cm 3 ) 0 (Tri-Cities Landfill data) Mean effective stress, kPa 200 Confining Stress Determines Variation 400 of MSW Unit Weight 600 with Depth 800 Kavazanjian 1999
Hyperbolic Relationship 0 100 Unit weight , kN / m 3 Normal stress, kPa Model calibration against 10 11 12 13 200 field & lab 0 Energy to MSW (com paction L and/ or confinem ent) 10 300 3 Looser specimen, γ i =10.3 kN/m 20 3 400 Denser specimen, γ i =12.9 kN/m H 30 9 10 11 12 13 14 15 16 3 Unit weight, kN/m 40 50 z γ = γ + i α + β ⋅ z 60 70 Depending on initial unit weight, increase in depth produces large or small increase in unit weight
Characteristic MSW Unit Weight Profiles Tot al unit weight , kN/ m 3 0 5 10 15 20 0 10 increasing compact ion effort and soil cover 20 Depth, m 30 low compact ion effort and soil t ypical cover 40 high OII landfill 50 Azusa landfill "Older" landfill in New Jersey 60
RECOMMENDATIONS FOR PRACTICE (A) Design based on a comprehensive investigation Step 1: Measure MSW unit weight near surface using test pits Step 2: Measure MSW unit weight at greater depths using large-diameter boreholes Step 3: Develop MSW unit weight profile using hyperbolic model
(B) Estimates based on a limited investigation • Step 1: Estimate MSW unit weight near the surface using test pits, landfill records, or published values ( γ i ~ 13 kN/m 4 ) • Step 2: Use design charts to estimate α and β parameters ( β = 0.4 m 3 /kN and α = 3 m 4 /kN ) z γ = γ + i α + β ⋅ z 16 DESIGN CHART 1: ESTIMATION OF β - PARAMETER DESIGN CHART 2: ESTIMATION OF α - PARAMETER 1.2 Field data range 14 Increased compaction 3 Near surface unit weight, γ i , kN / m 1.0 effort & soil cover (lab) 12 3 / kN 0.8 β - parameter, m 10 0.6 n o ) Field data i t b c a a l p ( Tri-Cities Laboratory data m r 8 e o v 0.4 OII A3-1L c o c d e l i Azusa A3-3L s o a s e & A3-7L "Older" r c 6 t n 0.2 r o I A3-8L "Younger" f f e A3-12L Cherry Island 4 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0 2 4 6 8 10 12 3 / kN 4 / kN β - parameter, m α - parameter, m
(C) Design of a new landfill Use MSW unit weight profiles for low, typical, or high compaction effort and soil cover Tot al unit weight , kN/ m 3 0 5 10 15 20 0 10 increasing compact ion effort and soil cover 20 Depth, m 30 low compact ion effort and soil t ypical cover 40 high OII landfill 50 Azusa landfill "Older" landfill in New Jersey 60
z γ = γ + Conclusions i α + β ⋅ z • Comprehensive MSW unit weight database has been developed • A characteristic MSW unit weight profile exists for each landfill • A hyperbolic model can capture the dependence of MSW unit weight on its composition, compaction effort, and confining stress • The developed model was calibrated with reliable in-situ landfill unit weight data as well as large-scale laboratory data. • Landfill-specific data are important for establishing the near surface (initial) unit weight of MSW • Hyperbolic model can extend near surface data to greater depths
Thank you Additional information available at the Geoengineer website at: http://www.geoengineer.org
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