site investigation and geotechnical evaluation

KING FAHD UNIVERSITY OF PETROLEUM & MINERALS College of Engineering Sciences and Applied Engineering Civil and Environmental Engineering Department Master of Science in Geotechnical Engineering

CE558 ENVIRONMENTAL GEOTECHNICS: TERM PROJECT: LANDFILL SETTLEMENT ANALYSIS Revision No. Status Date

Rev.0 Term Project 30th April 2016

PREPARED FOR DR. HABIB UR REHMAN KFUPM – DHAHRAN

Revision History

Rev.0

30th April, 2016

Term Project

Hamzah M. Al-Hashemi g201552950

Revision No.

Date

Description

Prepared By

Landfill Settlement Analysis.

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ACKNOWLEDGMENT

I would like to pass my profound thankfulness to my term project advisor, Dr. Habib Ur Rehman. I have comprehended plentiful thingummies since I became Dr. Habib’s student. He exerts exceedingly abundant time guiding me how to compose a paper, how to scout about literature and how to compile data. My thankfulness should be extended to include but not limited to; Dr. Alaa Kourdey, Dr. Ahmed Dalqamouni, Dr. I. Thusyanthan, ACES and KFUPM staff for their support.

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TABLE OF CONTENTS 1.0 INTRODUCTION ..................................................................................................................... 3 2.0 OBJECTIVE AND PROBLEM DESCRIPTION ........................................................................ 3 3.0 METHODOLOGY AND LITERATURE REVIEW .................................................................... 4 3.1 SOIL MECHANICS-BASED SETTLEMENT APPROACHES ................................................................ 4 3.1.1 (Sowers 1975) ............................................................................................................... 4 3.1.2 (Bjarngard and Edgers 1990) ........................................................................................... 5 3.1.3 (Hossain and Gabr 2005) ................................................................................................ 6 3.2 EMPIRICALLY-BASED SETTLEMENT APPROACHES ..................................................................... 7 3.2.1 (Gibson and Lo 1961) Rheological Model......................................................................... 7 3.2.2 (Yen and Scanlon 1975) Logarithmic Function .................................................................. 7 3.2.3 (Edil, Ranguette, and Wuellner 1990) Power Creep Model ................................................. 8 3.2.4 (Coumoulus and Koryalos 1997) Attenuation Equation ...................................................... 8 3.2.5 (Park and Lee 1997) First-Order Kinetics.......................................................................... 9 3.2.6 (Ling et al. 1998) Hyperbolic Function ............................................................................. 9 3.2.7 (Marques 2001) Rheological Model ............................................................................... 10 3.2.8 (Hettiarachchi, Meegoda, and Hettiaratchi 2009) First-Order Reaction Kinetics .................. 11 3.3 FEM/FEA BASED SETTLEMENT APPROACH ............................................................................ 12 3.3.1 About RS2 (Phase2) Software ....................................................................................... 12 3.3.2 Model Geometry and Properties .................................................................................... 13 4.0 SUBSURFACE PROFILE ....................................................................................................... 30 5.0 RESULTS AND DISCUSSIONS .............................................................................................. 31 6.0 CONCLUSION ....................................................................................................................... 34 LIST OF REFERENCES ............................................................................................................... 35

List of Tables Table 1: Subsurface Profile Properties ............................................................................................... 30 Table 2: Comparison of Different Settlement Approaches .................................................................... 33

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List of Figures Figure 1: FE Model Mesh ................................................................................................................ 13 Figure 2: FE Model Initial Stage (Natural Ground) .............................................................................. 13 Figure 3: FEM Project Settings ......................................................................................................... 14 Figure 4: FEM Stages Definition....................................................................................................... 14 Figure 5: FEM GWT Properties ........................................................................................................ 15 Figure 6: FEM Water Head Application ............................................................................................. 15 Figure 7: FEM Material Properties .................................................................................................... 16 Figure 8: FEM Material Properties .................................................................................................... 16 Figure 9: FEM Material Properties .................................................................................................... 17 Figure 10: FEM Hydraulic Properties ................................................................................................ 17 Figure 11: FEM Hydraulic Properties ................................................................................................ 18 Figure 12: FEM Hydraulic Properties ................................................................................................ 18 Figure 13: FEM Mesh Setup ............................................................................................................. 19 Figure 14: FEM Assign Material ....................................................................................................... 19 Figure 15: FEM Geometry ............................................................................................................... 20 Figure 16: FEM Geometry ............................................................................................................... 20 Figure 17: FEM Geometry ............................................................................................................... 21 Figure 18: FEM Geometry ............................................................................................................... 21 Figure 19: FEM Project Summary ..................................................................................................... 22 Figure 20: FEM General Settings ...................................................................................................... 22 Figure 21: FEM Field Stress ............................................................................................................. 23 Figure 22: FEM Mesh Quality .......................................................................................................... 23 Figure 23: FEM GMA SAND Properties............................................................................................ 24 Figure 24: FEM Gray Till Clay (Long-Term) Properties ...................................................................... 25 Figure 25: FEM Brown Till Clay (Long-Term) Properties .................................................................... 26 Figure 26: FEM CCL (Long-Term) Properties .................................................................................... 27 Figure 27: FEM Waste (Long-Term) Properties .................................................................................. 28 Figure 28: FEM Cover Properties ...................................................................................................... 29 Figure 29: FEM Settlement Results after 1000 Years ........................................................................... 31 Figure 30: FEM Settlement Flow after 1000 Years .............................................................................. 31 Figure 31: FEM Settlement Results along Stages ................................................................................ 32 Figure 32: Comparison of Different Settlement Approaches ................................................................. 33

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1.0

INTRODUCTION In General, Landfills (waste dump areas) endure from a major post-closure settlement that

takes place over a prolonged period of time. A huge differential settlement may deteriorate structures, foundations, and other related facilities that constructed atop of a landfill. In addition, it may lead to shattering of the geomembrane and wastage of the cover system in the landfills. The refuse (waste) materials show diversified engineering properties that diverge over positions and time within the landfill. Hence, with the conjunction of that the landfills behavior is not fully understood; recognize a conventional soil mechanics approach less appealing to predict the settlement. Instead, empirical and semi-empirical approaches of estimating the landfill settlement are commonly used side by side with field observations. (Ling et al. 1998)

2.0

OBJECTIVE AND PROBLEM DESCRIPTION As declared before, the deformation (Settlement) of a landfill will behave in a different way

than conventional earth structures due to heterogeneous material exist in the landfills (e.g. different type of waste, liners, covers, layers, etc), the deformation behavior and interaction effects for each of these materials. Comprehensive modeling (physical and numerical) of a landfill settlement will lead to a more realistic analysis that can enhance the meager knowledge about the landfill deformation and hence to prevent any expected hazards/risks could be resulted from such deformation. Data of an existing landfill is collected and employed in landfill settlement modeling. The analysis is launched by utilizing site-specific parameters and/or default parameters provided in the literature. Upon the analysis accomplishment; outcomes is presented and discussed for further application. The existing landfill is called OSDF; on-site disposal facility, and located in Fernald, Ohio, USA. OSDF consists of 8 cells, with a total area of each cell of 6.5 acres (26,305.0 sq. m). The impacted (waste) material placed in the OSDF consists of on-site contaminated soil (85 %), fly ash, Rev.0-Term Project

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demolition debris, municipal solid wastes (MSW), and lime sludge. Comprehensive design and analysis of OSDF were reported and produced by GeoSyntec Consultants (GeoSyntec 1997), and consists of required volume calculation, static and seismic slope stability analysis, settlement analysis, leachate management (generation, collection, detection and transmissions systems), final cover system, surface water management, support facility, borrow areas, waste management, and monitoring wells design. Good to mention that; well-established research on the seismic behavior of MSW landfill is conducted by (Thusyanthan, Madabhushi, and Singh 2006).

3.0

METHODOLOGY AND LITERATURE REVIEW The settlement of the ground is the sum of four parts; immediate/elastic settlement,

distortion settlement, consolidation settlement, and secondary compression settlement. Distortion settlement is evolved from lateral movements of the soil due to changes in vertical effective stresses, this mainly happened when a massive loading is applied over a small area which resulting in a lateral deformation. The value of distortion settlement is much smaller than consolidation settlement and is generally ignored. (Conduto 1999) Different settlement approaches either soil mechanics based or empirically based are well produced by (Pauzi et al. 2010) as shown below:

3.1

Soil Mechanics-Based Settlement Approaches

3.1.1

(Sowers 1975) He used the basic soil mechanics-based model of consolidation to estimate the settlement of

MSW. The long-term compression associated with creep and biodegradation phenomena is expressed in terms of the secondary compression index Cα in which a decrease in the void ratio during the secondary compression is related to the time elapsed between the initial time (t 1) and the final time (t2). The model can be expressed as in Eq. (1).

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Equation 1

Where ΔH: settlement due to primary and secondary consolidation. H: initial thickness of the layer. Cc*: primary compression ratio. σ0: existing overburden pressure acting at midlevel of the layer. Δσ: increment of overburden pressure acting at midlevel of the layer from the construction of an additional layer. Cα: secondary compression index. t1: time for completion of initial compression. t2: ending time period for which long term settlement of layer is desired. The values of compression indices Cc* and Cα for MSW are reported to range from 0.163 to 0.205 and 0.015 to 0.350, respectively. 3.1.2

(Bjarngard and Edgers 1990) They subdivided the secondary compression into two sub-phases, through the adjustment of

two straight lines, and introduced the intermediate coefficient of secondary compression (Cα1) and a final coefficient of secondary compression (Cα2). The settlement model can be expressed as in Eq. (2).

Equation 2

Where

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Cα1: intermediate secondary compression ratio. Cα2: long–term/final secondary compression ratio. t2: time for intermediate secondary compression. t3: time for total period of time considered in modeling. Typical parameter values are reported to be Cc* =0.205, Cα1=0.035; Cα2=0.215; t1=1 to 25 days; and t2=200 days. 3.1.3

(Hossain and Gabr 2005)

They modeled long-term settlement with three terms as given in Eq. (3).

Equation 3

Where Cα1: compression index, which is a function of stress level and degree of decomposition (~0.03). t1: time for completion of initial compression (~10-15 days). t2: time duration for which compression is to be evaluated (~100 to 2,000 days). Cβ: biodegradation index (~0.19). t3: time for completion of biological compression (~3,500 days). Cαf: creep index. t4: time for the creep at the end of biological degradation. The mechanical compression under applied stress and/or the pressure due to self-weight were not included. As biodegradation occurs, the organic solid mass is converted to gas and the void ratio increases with a subsequent increase in waste settlement. The model developed was based on the results of experimental program. The degree of decomposition was characterized from gas generation rates and the cellulose plus hemicelluloses to lignin ratio. The time factor t1, t2, t3 and t4 for compressibility were determined from the gas production curve and utilized for model development.

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3.2

Empirically-Based Settlement Approaches

3.2.1

(Gibson and Lo 1961) Rheological Model

They proposed a model that is applicable to peaty soils. This model is used by (Edil, Ranguette, and Wuellner 1990) to predict long-term total settlement of MSW. The model uses an analogy that represents primary compression and secondary compression in which a compression of a spring expresses immediate compression and a combination of piston and spring expresses the slow deformation. The model can be expressed as in Eq. (4).

Equation 4

Where Δσ: compressive stress depending upon waste height, density, and external loading. a: primary compressibility parameter (=1.0 x 10-4 to 8.0 x 10-5 /kPa). b: secondary compressibility parameter (=2.0 x 10-3 to 1.6 x 10-2 /kPa). λ/b: rate of secondary compression (=1.4 x 10-4 to 9.0 x 10-4 /day). t: time since load application. (El-Fadel et al. 1999) 3.2.2

(Yen and Scanlon 1975) Logarithmic Function

The logarithmic function is expressed as in Eq. (5).

Equation 5

Where Hf: initial height of the landfill. α: fitting parameter (=0.00095Hf +0.00969). β: fitting parameter (=0.00035Hf +0.00501). t: time since beginning of filling. Rev.0-Term Project

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tc: construction period. 3.2.3

(Edil, Ranguette, and Wuellner 1990) Power Creep Model

The power creep model is a simple relation for time-dependent deformation under constant stress and expressed as following in Eq. (6)

Equation 6

Where M’: reference compressibility (=1.6 x 10-5 to 5.8 x 10-5 /kPa). N’: rate of compression (=0.50–0.67). t: time since load application. tr: reference time is typically introduced to make time dimensionless, usually taken as 1 day (El-Fadel et al. 1999). The parameter M’ is site specific and N’ is the rate of compression, which varies with respect to age and placement conditions of the waste. However, the variability of N’ is less than that of M’ (Edil, Ranguette, and Wuellner 1990). 3.2.4

(Coumoulus and Koryalos 1997) Attenuation Equation

They proposed an attenuation equation, which was based on the proposition that landfill settlements can be approximated by a straight line, as a function of the logarithm of time. The main advantage of this model is that data from different points on the landfill with different characteristics can be grouped and compared. The model can be expressed as in Eq. (7).

Equation 7

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Y: vertical strain rate (expressed in percent/month or percent/year). C’α: coefficient of secondary compression (~0.02 to 0.25). t: time elapsed in month or year. tc*: filling time usually assumed as 1 month. It must be noted, however, that the accuracy of Y depends on the accuracy of C’α. 3.2.5

(Park and Lee 1997) First-Order Kinetics

They proposed a settlement model that considers time-dependent biodegradation of waste. The settlement rate is assumed to be the amount of subsidence that is directly proportional to the amount of solids solubilized. Solubilization of organic materials is generally expressed using firstorder kinetics. However, the determination of the kinetic coefficients or the hydrolysis constants as well as their variation with environmental conditions is difficult. The settlement model can be expressed as in Eq. (8).

Equation 8

Where K: first order decomposition strain rate constant/time (=2.37 to 1.35/year). εtot_dec = total amount of compression that will occur due to decomposition of biodegradable waste (=7.2–6.1%). The summation of both the terms gives the total compressive strain. 3.2.6

(Ling et al. 1998) Hyperbolic Function

They proposed the following hyperbolic equation to compute settlement at a given time if the ultimate settlement of the landfill is known as shown in Eq. (9).

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Equation 9

Where ρ0: initial rate of settlement (=0.001 m/day). Sult=ultimate settlement. t: time since load application. 3.2.7

(Marques 2001) Rheological Model

He developed a composite rheological model to account for primary and secondary compression mechanisms, governed by rheological parameters that also accounts for waste degradation. The primary compression formulation is introduced as an “immediate compression,” which is independent of time, based on the observation that the respective process is linear for curves of void ratio as a function of the logarithm of the applied stress. The model is represented by Eq. (10).

Equation 10

Where b: coefficient of secondary mechanical compression. c: secondary mechanical compression rate. Edg: total compression due to waste degradation. d: secondary biological compression rate. t’: time elapsed since loading application. t”: time elapsed since waste disposal.

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3.2.8

(Hettiarachchi, Meegoda, and Hettiaratchi 2009) First-Order Reaction Kinetics

They also developed a settlement model assuming that the settlement due to biodegradation follows the first-order reaction kinetics. The total settlement is expressed as a combined process of mechanical compression or (ΔH)m and biodegradation-induced settlement or (ΔH)b. The model is expressed as in Eq. (11).

Equation 11

Where C*: compressibility parameter (0.174–0.205). fsj: initial solids fraction for each waste group (0.15–0.35). ρw=density of water. Gsj: specific gravity of jth group of waste solids (1–3). λj =first-order kinetic constant for the jth group (0–0.001/day).

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3.3

FEM/FEA Based Settlement Approach

3.3.1

About RS2 (Phase2) Software

RS2 (Phase2 - v. 9.0) is a powerful 2D finite element program for soil and rock applications (RS2 = Rock and Soil 2-dimensional analysis program). RS2 can be used for a wide range of engineering projects and includes excavation design, slope stability, groundwater seepage, probabilistic analysis, consolidation, and dynamic analysis capabilities. Complex, multi-stage models can be easily created and quickly analyzed - tunnels in weak or jointed rock, underground powerhouse caverns, open pit mines and slopes, embankments, MSE stabilized earth structures, and much more. Progressive failure, support interaction and a variety of other problems can be addressed. RS2 offers a wide range of support modeling options. Liner elements can be applied in the modeling of shotcrete, concrete, steel set systems, retaining walls, piles, multi-layer composite liners, geotextiles, and more. Liner design tools include support capacity plots, which allow you to determine the safety factor of reinforced liners. Bolt types include end anchored, fully bonded, cable bolts, split sets, and grouted tiebacks. One of the major features of RS2 is finite element slope stability analysis using the shear strength reduction method. This option is fully automated and can be used with either MohrCoulomb or Hoek-Brown strength parameters. Slope models can be imported or exported between Slide and RS2 allowing easy comparison of limit equilibrium and finite element results. RS2 includes steady-state, finite element groundwater seepage analysis built right into the program. There is no need to use a separate groundwater program. Pore pressure is determined as well as flow and gradient, based on user defined hydraulic boundary conditions and material conductivity. Pore pressure results are automatically incorporated into the stress analysis. Material models for rock and soil include Mohr-Coulomb, Generalized Hoek-Brown and Cam-Clay. Powerful new analysis features for modeling jointed rock allow you to automatically generate discrete joint or fracture networks according to a variety of statistical models. With new Rev.0-Term Project

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64-bit and multi-core parallel processing options RS2 can solve larger and more complex models in shorter times. 3.3.2

Model Geometry and Properties

Enclosed below the details of FE model:

Figure 1: FE Model Mesh

Figure 2: FE Model Initial Stage (Natural Ground)

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Figure 3: FEM Project Settings

Figure 4: FEM Stages Definition

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Figure 5: FEM GWT Properties

Figure 6: FEM Water Head Application

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Figure 7: FEM Material Properties


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Figure 10: FEM Hydraulic Properties

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Figure 13: FEM Mesh Setup

Figure 14: FEM Assign Material

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Figure 15: FEM Geometry


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Figure 19: FEM Project Summary

Figure 20: FEM General Settings

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Figure 21: FEM Field Stress

Figure 22: FEM Mesh Quality

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Figure 23: FEM GMA SAND Properties

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Figure 24: FEM Gray Till Clay (Long-Term) Properties

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Figure 25: FEM Brown Till Clay (Long-Term) Properties

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Figure 26: FEM CCL (Long-Term) Properties

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Figure 27: FEM Waste (Long-Term) Properties

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Figure 28: FEM Cover Properties

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4.0

SUBSURFACE PROFILE

Subsurface profile as encountered and produced by (GeoSyntec 1997): Table 1: Subsurface Profile Properties

Material (Bottom to Top)

Bedrock

GMA SAND

Gray Till Clay

Brown Till Clay

CCL

Waste

Cover

Unit Weight kN/m3

-

21.2

22.8

21.2

20.42

15.3

19.8

Saturation %

-

-

100

95

90

-

-

Void ratio e0

-

-

0.38

0.29

0.43

0.75

-

Compression Index Cc

-

-

0.074

0.075

0.13

0.2

-

Recompression Index Cr

-

-

0.014

0.015

0.035

0.035

-

-

-

3.76E-07

6.45E-07

5.91E-07

5.37E-07

-

-

-

0.0013

0.0015

0.0015

0.0015

-

OCR (or Pc)

-

-

1

1.7

48 kPa

45 kPa

-

Poission’s Ratio

-

0.3

0.49

0.475

0.475

0.4

0.3

Su kPa

-

0

100

57

57

10

-

Friction Angle (short)

-

35

0

0

0

25

25

Cohesion (Short) kPa

-

0

95

60

25

10

0

Friction Angle (Long)

-

35

30

25

25

25

25

Cohesion (Long) kPa

-

0

0

0

0

0

0

Coefficient of Compression Cv (m2/sec) Secondary Compression Index Ca

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* Wherever properties are missing; they were assumed.

5.0

RESULTS AND DISCUSSIONS

Results of FEA of post-closure settlement are shown up to 1000 years are shown below:

Figure 29: FEM Settlement Results after 1000 Years

Figure 30: FEM Settlement Flow after 1000 Years

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Figure 31: FEM Settlement Results along Stages

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Table 2: Comparison of Different Settlement Approaches

Maximum Post-Closure Settlement (m)

Method

0.942

FEM

0.420

(GeoSyntec 1997)

0.480

(Sowers 1975)

0.998

(Yen and Scanlon 1975)

0.511

(Edil, Ranguette, and Wuellner 1990)

Maximum Post Closure Settlement (meters) FEM

GeoSyntec

Sowers

Yen and Scanlon

Edil, Ranguette, and Wuellner

0.998

0.942

0.420

0.480

0.511

Figure 32: Comparison of Different Settlement Approaches

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6.0

CONCLUSION Based on: FEA and conventional analysis that performed in this project, following may be

concluded:

 It was noted that the post-closure settlement of a landfill is time dependent.  FEA matched well with (Yen and Scanlon 1975) method.  Mainly (GeoSyntec 1997) differ than FEA slightly due to that the Geosynthetic material was not considered in the FE model to facilitate the analysis.  (Sowers 1975) and (Edil, Ranguette, and Wuellner 1990) results are shown well matching with (GeoSyntec 1997) results.  The nature of impacted (waste) material is close to being soil-like material and that mainly due to (85% of contaminated soil, fly ash, construction debris, and lime sludge.  However, field observations will play a key role to calibrate any of the above-listed methods, which can consider many factors same as but not limit to; gas generation, leachate generation and flow, hydrology, weather, etc.

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LIST OF REFERENCES Bjarngard, A., and L. Edgers. 1990. ―‗Settlement of Municipal Solid Waste Landfills.‘‖ In Proc. 13th Annual Madison Waste Conf., 192–205. University of Wisconsin, Madison Wis.

Conduto, D. 1999. Geotechnical Engineering: Principles and Practices. Prenctice Hall. Coumoulus, D. G., and T. P. Koryalos. 1997. ―‗Prediction of Attenuation of Landfill Settlement Rates with Time.‘‖ In Proc 14th Int. Conf. on Soil Mechanics and Foundation Engineering, edited by ISSMFE, 1807–11. Hamburg, Germany. Edil, T. B., V. J. Ranguette, and W. W. Wuellner. 1990. ―Settlement of Municipal Refuse. In: Geotechnics of Waste Fills – Theory and Practice: ASTM STP 1070.‖ American Society of Testing and Materials, ASTM, 225–39. El-Fadel, M., S. Shazbak, E. Saliby, and J. Leckie. 1999. ―Comparative Assessment of Settlement Models for Municipal Solid Waste Landfill Applications.‖ Waste Management & Research 17 (5): 347–68. doi:10.1177/0734242X9901700504. GeoSyntec. 1997. ―Final Design: Calculation Package of On-Site Disposal Facility.‖ Fernald, Ohio. Gibson, R. E., and K. Y. Lo. 1961. ―A Theory for Soils Exhibiting Secondary Compression.‖ Acta. Polytech. Scand. 296: 1–16. Hettiarachchi, Hiroshan, Jay Meegoda, and Patrick Hettiaratchi. 2009. ―Effects of Gas and Moisture on Modeling of Bioreactor Landfill Settlement.‖ Waste Management (New York, N.Y.) 29 (3): 1018–25. doi:10.1016/j.wasman.2008.08.018. Hossain, S.M., and M.A. Gabr. 2005. ―‗Prediction of Municipal Solid Waste Landfill Settlement with Leachate Recirculation‘, Vol. 168.‖ In Proc. Geo. Frontier, 50. Austin Tex.: ASCE. Ling, Hoe I., Dov Leshchinsky, Yoshiyuki Mohri, and Toshinori Kawabata. 1998. ―Estimation of Municipal Solid Waste Landfill Settlement.‖ Journal of Geotechnical and Geoenvironmental Engineering 124 (1): 21–28. doi:10.1061/(ASCE)1090-0241(1998)124:1(21). Rev.0-Term Project

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Marques, A. C. M. 2001. ―‗Compaction and Compressibility of Municipal Solid Waste.‘‖ Sao Paulo Univ. Park, H. I., and S. R. Lee. 1997. ―‗Long-Term Settlement Behavior of Landfills with Refuse Decomposition.‘‖ Journal of Solid Waste Technology and Management 24 (4): 159–65. Pauzi, Nur Irfah Mohd, Omar Husaini, Bujang Kim Huat, and Halina Misran. 2010. ―Settlement Model of Waste Soil for Dumping Area in Malaysia.‖ EJGE, Electronic Journal of Geotechnical Engineering 15: 1917–29. Sowers, G.F. 1975. ―Settlement of Waste Disposal Fills.‖ International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 12 (4). Moscow: 57–58. doi:10.1016/01489062(75)90051-0. Thusyanthan, Indrasenan N., Gopal S. P. Madabhushi, and S. Singh. 2006. ―Centrifuge Modeling of Solid Waste Landfill Systems—Part 2: Centrifuge Testing of Model Waste.‖ Geotechnical Testing Journal 29 (3): 14314. doi:10.1520/GTJ14314. Yen, B. C., and B. S. Scanlon. 1975. ―Sanitary Landfill Settlement Rates. 7F, 2T, 8R.‖ International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 12 (10): 140. doi:10.1016/0148-9062(75)92394-3.

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