FRAMEWORK FOR THE ESTIMATION OF

MSW UNIT WEIGHT PROFILE

Sardinia 2005, Tenth International Waste Management and Landfill Symposium

S. Margherita di Pula, Cagliari, Italy; 3 - 7 October 2005

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/m3”

– Differ by factor of 3!

• Liner interface strength depends on overburden stress

• Landfill capacity estimates depend on MSW unit weight

• Seismic performance depends on MSW unit weight profile

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.01 0.1 1 10

Period, sec

PS

A,

g's

Rock motionMSW surface-Kavazanjian et al. 1995MSW surface-constant unit weight

5% damping

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

Developed by Kavazanjian and Matasovicfor OII Landfill

waste

wastewaste V

W=γ

1. Auger and collect waste 2. Weigh waste collected over interval (Wwaste)

3. Place tremie pipe in borehole 4. Fill with gravel of known unit weight (Vwaste)

Data from reliable in-situ large-scale methods available in Zekkos et al. (2005) Berkeley Geotechnical report

0

20

40

60

0 5 10 15 20 25Total unit weight, kN/m3

Depth

, m

1

2

3

4

5

6

7

8

9

10

11

(1) Santo Tirso, Portugal (Gomes et al. 2002); (2) OII, California, USA (Matasovic and Kavazanjian, 1998); (3) Azusa, California, USA (Kavazanjian et al, 1996); (4) Tri-Cities, California, USA (this study); (5) no name older landfill (Oweis and Khera, 1998); (6) no name 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) Valdemingomez, Spain (Pereira et al. 2002); (11) Cherry Island landfill, Delaware, USA (Geosyntec, 2003);

Kavazanjian et al. (1995)

Large Scatter in Reliable MSW Unit Weight Data

Characteristic MSW Unit Weight Profile Exists

Tri-Cities

0

10

20

30

40

50

60

0 10 20 30

Dep

th, m

0

10

20

30

40

50

60

0 10 20 30

Azusa

0

10

20

30

0 10 20 30

"Younger" "older"

0

10

20

30

0 10 20 30

0

10

20

30

0 10 20 30

Dep

th, m

Cherry Island

0

10

20

30

40

50

60

0 10 20 30

OII

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

0

200

400

600

800

12 17 22Unit w eight, kN / m3

Mea

n ef

fect

ive

stre

ss, k

Pa

Kavazanjian 1999

Compaction Level (& waste composition) Determines Initial MSW Unit Weight

Confining StressDetermines Variationof MSW Unit Weight with Depth

5.0

10.0

15.0

0.00 0.20 0.40 0.60 0.80

Total energy per target volume of material (Joule/cm3)

Tota

l unit w

eig

ht,

kN

/m3

W=4.5kgr, h=80 cm,t=7.5cm

W=4.5kgr, h=40 cm, t=7.5 cm

W=5.4kgr, h=80 cm, t=5 cm

W=10kgr, h=80 cm, t=5 cm

W=10kgr, h=80 cm, t=7.5 cm

(Tri-Cities Landfill data)

Model calibration against field & lab

zz

i ⋅++=

βαγγ

Hyperbolic Relationship

9 10 11 12 13 14 15 16

400

300

200

100

0

Nor

mal

stre

ss, k

Pa

Unit weight, kN/m3

Looser specimen, γ i=10.3 kN/m3

Denser specimen, γ i=12.9 kN/m3

0

10

20

30

40

50

60

70

10 11 12 13Unit weight, kN / m3

Energ

y t

o M

SW

(co

mpact

ion

and/o

r co

nfinem

ent)

L

H

Depending on initial unit weight,increase in depth produces large or small increase in unit weight

Characteristic MSW Unit Weight Profiles

0

10

20

30

40

50

60

0 5 10 15 20

Total unit weight, kN/m3

Depth

, m

low

typical

high

OII landfill

Azusa landfill

"Older" landfill in New Jersey

compaction effort and soil cover

increasing compaction effort and soil cover

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 (γi ~ 13 kN/m4)

• Step 2: Use design charts to estimate α and β parameters (β = 0.4 m3/kN and α = 3 m4/kN )

0.0 0.2 0.4 0.6 0.8 1.0 1.24

6

8

10

12

14

16DESIGN CHART 1: ESTIMATION OF β - PARAMETER

Increa

sed c

ompa

ction

effort

& soil c

over

(lab)

Nea

r sur

face

uni

t wei

ght, γ i ,

kN /

m3

β - parameter, m3 / kN

Field data Tri-Cities OII Azusa "Older" "Younger" Cherry Island

0 2 4 6 8 10 120.0

0.2

0.4

0.6

0.8

1.0

1.2 Field data range

Laboratory data A3-1L A3-3L A3-7LA3-8LA3-12L

Increased compaction

effort & soil c

over (lab)

DESIGN CHART 2: ESTIMATION OF α - PARAMETER

β - p

aram

eter

, m3 /

kN

α - parameter, m4 / kN

zz

i ⋅++=

βαγγ

(C) Design of a new landfillUse MSW unit weight profiles for low, typical, or high

compaction effort and soil cover

0

10

20

30

40

50

60

0 5 10 15 20

Total unit weight, kN/m3

Depth

, m

low

typical

high

OII landfill

Azusa landfill

"Older" landfill in New Jersey

compaction effort and soil cover

increasing compaction effort and soil cover

Conclusions• 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

zz

i ⋅++=

βαγγ

Thank you

Additional information available at the Geoengineer website at:

http://www.geoengineer.org