7

th

International Conference on Environmental Science and Technology

Ermoupolis, Syros island, Greece – Sept. 2001

RISK ANALYSIS OF LANDFILL DESIGN RESPONSE

TO SEISMIC LOADING

Telemachus C. KOLIOPOULOS

1

, Adamantios SKORDILIS

2

1

University of Strathclyde, Department of Civil Engineering, Centre for Environmental

Management Research, Glasgow G4 ONG, Scotland, UK,

[e-mail],

2

Department of Environmental Studies, University of Aegean,

17 Karadoni Str., 81 100 Mytilene, Greece, [e-mail].

ABSTRACT

This paper presents the involved risk of landfill design response to seismic loading. As case
studies of the seismic impact zones to horizontal acceleration are selected the zones which exist
in Greece according to the Greek Antiseismic Regulations (GAR). Comparisons and risk
analysis and useful conclusions of the involved environmental hazard of landfill movement are
made of the examining case studies.


1.

INTRODUCTION

Sanitary landfill remains an attractive disposal route for municipal solid waste, as it is more
economical method than other alternative waste disposal systems (ie incineration method). The
landfill biodegradation processes are complex, including many factors that control the
progression of the waste mass to final stage (Fleming, 1996; Kollias, 1993; Koliopoulos et al.
1998, 1999; Skordilis, 1993; Tchobanoglous et al. 1993). The landfill gas and leachate
generation is an inevitable result of the solid waste biodegradation in landfills and their study is
necessary for future efficient designs, controlling air and groundwater pollution (Fleming 1996;
Koliopoulos 1997, 2000; Skordilis, 1993; Kollias, 1993; Tchobanoglous et al. 1993).

Landfilling technologies have been strongly developed in the last decade. Large sanitary
landfills are preferred because these provide better opportunities for potential hazard control and
an increasing potential for energy recovery. Efficiently managed sustainable landfill sites can
generate considerable volumes of methane gas (CH

4

), which can be exploited by landfill gas

recovery installations to produce electricity. According to the EU waste management strategy
separate collections will influence rates, yields and global amounts of landfill gas. The
increasing of the SWM recycling rates will influence the waste management systems; waste
composition streams; costs and emissions from waste treatment and disposal activities.
However, a plethoric flow and use of resources characterise our society in an unsustainable way.
Waste management is the discipline that is concerned with resources once society no longer
requires them. A successful sustainable development requires a continuous change and
harmonization to the life cycle of our society, bearing in mind its current-future necessities
(Koliopoulos, 1999c). Therefore, the problem is transferred to the dilemma on how can we
manage our waste better.

In spite of the progress achieved in the recent years in waste management, there is an important
parameter that has received little attention; this is the landfill response to seismic loading and its
environmental impact assessment relating to the migration of landfill emissions. This paper
assess the involved risk of different seismic impact zones and disposed waste compositions in
Greece. It presents the involved risk of the expected landfill movements based on common used
landfill design characteristics and the particular examining seismic accelerations. The resistance
acceleration factor N and seismic accelerations are presented for the examining seismic impact

202

zones. Indicative, twelve Greek sites have been selected to be analysed so as to make useful
conclusions.


2. SEISMIC LOADING

The usual limit equilibrium methods in geotechnical engineering, like the general wedge
method or Bishop one, are commonly used for the stability of landfills (Oweis, 1993; NAVFAC
DM-7.3, 1982). The waste may be treated as an engineering material and characterized by
cohesion and friction. The DM-7 wedge method (NAVFAC DM-7.3, 1982) is used in this paper
and it is illustrated in Figure 1 for a given slope of a landfill.

Figure 1: Stability analysis with the wedge method.

The definition of terms in figure 1 is given below.

Pw is the resultant force due to pore water pressure on potential sliding surface,

P

•

is the resultant horizontal force for an active or central wedge along potential sliding surface

•••••

,

203

P

•

is the resultant horizontal force for a passive wedge along potential sliding surface EZH,

W is the total weight of soil and water in wedge above potential sliding surface,

R is the result of normal and tangential forces on potential sliding surface,

c is the cohesion of layer along potential sliding surface,

•

is the friction angle of layer along potential sliding surface,

L is the length of potential sliding surface across wedge,

h

w

is the depth below phreatic surface at wedge boundary

and

•

w

is the unit weight of water.

The effect of earthquake loading changes the value of P

•

and P

•

and their value is given by the

following formula:

(1)

WA

P

P

a

a

+

=

'

(2)

WA

P

P

−

=

β

β

'

where

A is the seismic acceleration (in g's)
W is the weight of the wedge associated

Moreover, considering a square acceleration pulse of duration t, the acceleration and velocity
diagrams of an assumed rigid block are presented in Figure 2 according to Nemark (Nemark,
1965). At the bottom of the block NW is the force resisting motion. W
is the weight of the block and N is the resistance acceleration factor in g's.

However, the net velocity diagram is shown as hatched zone in Figure 2. The area of the
diagram is the displacement experienced by the rigid block. Hence,

)

)(

2

/

(

o

t

t

V

u

−

=

or

)

/

/

)(

2

/

(

Ag

V

Ng

V

V

u

−

=

or

u

(5)

)

/

1

)(

2

/

(

2

A

N

gN

V

−

=

where,

u is the displacement
N is the resistance acceleration factor (in g's) required to produce a factor of safety of 1.0
V is the maximum seismic velocity of the earthquake motion
A is the seismic acceleration (in g's)

204

Figure 2: Acceleration and displacement relationships with Nemark method.

Equation (5) is for a single pulse on a horizontal surface. When the ground motion reverses
direction, the block will move in the opposite direction by the same amount if N and A are the
same. If there is the block at a slope sliding surface, movements will be downhill and each time
N is exceeded, the block will move farther (Nemark, 1965).


3. RISK ANALYSIS IN GREECE

Risk is a combination of the probability, or frequency, of occurrence of a defined hazard and the
magnitude of the consequences of the occurrence. Hazard is a property or situation that in
particular circumstances could lead to harm. Risk assessment is an analysis of the potential for
adverse health effects (Koliopoulos, 2000).

The seismological risk investigation of a site necessitates the evaluation of fault reactivation
possibility and the parameters of the expected ground motion. The relative estimations are based
on the particular local seismicity, geological conditions and historical data. However, the
following should be taken into account in a tectonic, structural study: Image study for the
localization of large-scale neotectonic structures; geological mapping of the broader area;
tectonic-structural mapping; morphotectonic analysis; fault studies and geophysical prospecting
for the localization of buried structures (Lekkas, E., 1999).

In this paper, a risk analysis examines twelve characteristic Greek sites, presenting the relative
seismic displacements and landfill emissions risk. An indicative examining landfill design
situation is applied to the Greek case studies, as it is presented in figure 3. In table 1, are
presented the four seismic impact zones, which exist in Greece and their relative seismic
accelerations according to the Greek antiseismic regulations (GAR, 2000). Moreover, in table 1
are presented the particular disposed putrescible (%) waste fractions for the examining case
studies. The disposed putrescible (%) waste fraction is taken into account as representative
biodegradation factor of each site and consequently as representative landfill emissions' risk
factor.

205

The landfill design response analysis to seismic loading is presented below based on the given

data of figure 3 and table 1.

For the refuse:

φ = 30

o

,

γ = 50 pcf (80 kN/m

3

)

For the clay: c = 600 psf (28.7 kPa),

γ = 110 pcf (17.6 kN/m

3

)

b = 91 m, h = 1.8 m, landfill thickness H = 30 m

Figure 3: Examining landfill design situation.

Below is determined the resistance acceleration factor N for the landfill design situation
described in figure 3, applying the DM-7 wedge method (NAVFAC DM-7.3, 1982).

W

1

= 65.45 tn

W

2

= 14.5 tn

W

3

= 430 tn

P

α1

= 65.45 N + 41.85

P

α2

= 14.5 N + 10.9

P

α3

= 430 N - 90

P

β1

= 4.6 - N

Σ

P

α

=

Σ

P

β

=> 510.95 N - 41.85 = 0 => N = 0.08 g

However, the expected displacements of the four seismic impact zones are calculated based on

the above and taking an indicative maximum seismic velocity 33 cm/s. Hence, for the seismic

impact zones I, II, III, IV the expected movements are presented below applying equation 5.

For the seismic impact zone I, for A = 0.12 g, it yields u = 2.7 cm.

For the seismic impact zone II, for A = 0.16 g, it yields u = 4 cm.

For the seismic impact zone III, for A = 0.24 g, it yields u = 5.4 cm.

For the seismic impact zone IV, for A = 0.36 g, it yields u = 6.3 cm.

The calculated displacements of the examining case studies are presented in table 1.

206

Table 1. Seismic accelerations, disposed putrescible (%) waste fractions and displacements at

characteristic Greek sites.

Site/Parameter Seismic

Impact
Zone
Source: [2]

Seismic

Acceleration

Source: [2]

Disposed
Putrescible
(%)
Source: [3,14]

Displacements

(cm) with

seismic velocity

33 cm/s

Athens

II

0.16 g

56

4

Thessaloniki

II

0.16 g

52

4

Patras

III

0.24 g

53.1

5.4

Iraklion

III

0.24 g

52.5

5.4

Larissa

III

0.24 g

52

5.4

Chania

III

0.24 g

55.2

5.4

Xanthi

II

0.16 g

61.2

4

Komotini

II

0.16 g

67.1

4

Rhodes

III

0.24 g

41.6

5.4

Kos

III

0.24 g

37.3

5.4

Naxos

I

0.12 g

48.3

2.7

Zakinthos

IV

0.36 g

-

6.3

In table 1, is not presented the disposed putrtescible (%) waste fraction of Zakinthos site, due to

the fact that there was not any report to be referenced. Moreover, based on the above, in figure 4

are presented the included seismic risk and landfill emissions' risk of the examining Greek sites.

Figure 4: Risks of hazard for the examining Greek sites.

207

4. CONCLUDING REMARKS

The wedge method applied for the landfill design response to seismic loading. A risk analysis

was taken place for twelve Greek sites calculating the resistance acceleration factor N and

estimating their expected displacements for a given maximum seismic velocity. High risk exists

for the case studies where there is high putrescible-biodegradable disposed waste fraction and

high site seismisity.

The allowable seismic movement(s) in landfill design is not yet regulated and is a matter of

engineering judgement. A limit of 15 cm has been used in practice to avoid tearing of

geomembrane but actual limits must be site specific. Optimum safety conditions in public works

of high environmental risk should be of first priority following the right antiseismic design. The

right determination of material properties, slope stability analysis and ground motion evaluation

are necessary for an effective earthquake-proof design.

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th

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th

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208

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th

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