This document discusses numerical modeling of landfill cover systems. It includes: - Background on field monitoring studies that evaluated the performance of cover system elements. - Discussion of how climate change may impact cover system performance over long time periods based on previous modeling studies. - Description of using the Hydrus model to simulate water flow through unsaturated soil layers of a landfill cover. - Results from Hydrus simulations showing changes in volumetric water content and pressure head over time at different depths within a single soil layer cover system. - Setup of a multi-layer cover system model in Hydrus with different soil types and evaluation of outputs like volumetric water content, pressure head, and

1. Associate prof.
IIT Guwahati
154104040
M.Tech
1

2. Associate prof.
IIT Guwahati
P.hd Scholar
IIT guwahati
2

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4.  to separate waste from environment
 to maximize runoff
 to give suitable surface for
• vegetation
• aesthetic view.
 Landfill Cover ?
 design criteria ?
Design conditions ?
4

5.  Percolation
 harmful leachate
 migration of contaminants
 pollution of the groundwater
 blowing of litter or dust
 emission of landfill gas
 potential for fire hazard
5

6. Field monitoring of Cover System
Mellies &
Gurtung
(2004)
Field tests in
large
lysimeter
 Drainage geo-composite and the Ca-
GCL proved to be performance
effective elements within cover system.
Melchoir et
al.
(2010)
Large-scale
lysimeter
(Tensiometers
, neutron
probes and
TDR Sensors)
 Evapotranspiration can be increased
significantly by planting bushes
 limited the potential leakage through
barrier layers.
Mellies &
Schweizer
(2011)
Large-scale
lysimeter
(FDR probes;
Delta
Devices)
 K of CCL or GCL may increase
substantially, if there is no long-lasting
protection against desiccation (thick
soil cover or a GM)
6

7. Cover System under climate change
Chang et
al.
(1999)
HELP
 Until 100 years the infiltration flux for
cover design was negligible even
under doubling of the precipitation
 Considering degradation after 100
years, the infiltration flux significantly
increased to the design criteria.
Khire et
al.
(2000)
UNSAT-H
 Simulations indicated that thickness
and hydraulic properties of the surface
layer significantly affect the WB of
capillary barriers.
7

8. Numerical Modeling Considering
Different Climatic Conditions
Chang et
al.
(1999)
Water balance
method
 Until 100 years the infiltration flux for
cover design was negligible even
under doubling of the precipitation
 Considering degradation after 100
years, the infiltration flux significantly
increased to the design criteria.
Khire et
al.
(1997)
HELP and
UNSAT-H
 Captured seasonal variations in
overland flow, evapotranspiration, soil
water storage, and percolation.
 Percolation is slightly over predicted
by HELP and under predicted by
UNSAT-H.
Luellen &
Brydges
(2005)
HELP Model
and Leakage
Equations
 Observed uncertainties about the
effects of degradation mechanisms on
long-term cap performance.
8

9. Reason consequences effect on cover
Energy from sun
Absorption
Reflection
Tilt of earth
Orbital shape of earth
Green house gases
Volcanic eruption
Earth’s rotation
feedback
Change in rainfall
Flood
Heat waves
Drought
Change in marine
Temperature
Desiccation
Unwanted plant
Erosion
Permeability
Freeze/thaw
9

10. Numerical Modelling in Hydrus (2D/3D)
Data Input
Simulation
Data Output
10

11. SWCC Model by van Genuchten (1980)
𝛉 𝛙 = 𝛉 𝐫 +
𝛉 𝐬 − 𝛉 𝐫
𝟏 + 𝛂𝛙 𝐧 𝐦
⟹ 𝐒 𝐞 =
𝛉 𝛙 − 𝛉 𝐫
𝛉 𝐬 − 𝛉 𝐫
= 𝟏 + 𝛂𝛙 𝐧 −𝐦
Where
𝑺 𝒆 is the effective water saturation 𝟎 < 𝐒 𝐞 < 𝟏 𝐟𝐨𝐫 𝛙 < 𝟎 𝐚𝐧𝐝 𝐒 𝐞 = 𝟏 𝐟𝐨𝐫 𝛙 = 𝟎 ,
𝜽 𝝍 is volumetric water content corresponding to the suction, 𝝍 on the SWCC Model
𝜽 𝒔 is the saturated volumetric water content,
𝜽 𝒓is the residual volumetric water content,
𝛂 =
𝟎.𝟕𝟖
𝛙 𝐛
𝟏.𝟐𝟔
for 𝟏 < 𝝍 𝒃 < 𝟏𝟎𝟎 where 𝝍 𝒃 = air entry suction in kPa and 𝛂 > 𝟎,
n is related to pore size distribution of soil and 𝒏 > 𝟏
and m 𝒎 = 𝟏 −
𝟏
𝒏
is related to overall symmetry of the curve
Useful SWCC Model
11

12. Concept of Water Balance
𝐈𝐧𝐟𝐥𝐨𝐰 = 𝑶𝒖𝒕𝒇𝒍𝒐𝒘 + 𝑪𝒉𝒂𝒏𝒈𝒆 𝒊𝒏 𝑺𝒕𝒐𝒓𝒂𝒈𝒆
𝐏𝐄𝐑𝐂 = 𝐏 − (𝐑 + 𝐄𝐓 + ∆𝐖𝐬𝐨𝐢𝐥 + 𝐋)
Percolation starts if S > Sc
S = soil water storage
Sc =soil water storage capacity
12

13. Flow of Water in Porous Soil Media
Saturated Soil Media
Darcy, 1856
13

14. Flow of Water in Porous Soil Media
Unsaturated Soil Media
Richard’s , 1931
14

15. Properties RS BB SS RB
Specific Gravity (G) 2.63 2.88 2.68 2.70
Hygroscopic Water Content (%) 5.45 11.67 2.54 7.32
GrainSize
Distribution(%)
Gravel ( > 4.75 mm) 0.16 NA NA 0.12
Coarse sand (2.00 mm – 4.75 mm) 22.00 NA 20 15.4
Medium sand (0.425 mm – 2.00
mm)
33.64 NA 42 23.53
Fine sand (0.075 mm – 0.425 mm) 28.04 4.4 38 20.85
Silt (0.002 mm – 0.075 mm) 9.83 38.77 NA 18.51
Clay ( < 0.002mm) 6.49 56.83 NA 21.59
Liquid limit (%) 40.50 295 NA 115
Plastic limit (%) 22.60 40 NA 27
Shrinkage limit (%) 20.77 10.5 NA 17
Plasticity Index (%) 17.9 255 NA 88
Classification ML CH SP ML
Specific Surface Area (m2/gm) 55 348 NA 142
Optimum Moisture Content (%) 17 38 19 23
Maximum Dry Density (g/cm3) 1.73 1.26 1.77 1.6
Saturated Hydraulic Conductivity (m/s)
2.9E-
8
2.3E-
12
4.23E-
6
2.7E-
9
Linear Shrinkage (%) 1.83 3.22 NA 2.25
Free Swell Index (%) 10 686 NA 212
Organic Content (%) 0.48 0.22 NA 0.40
Cation Exchange Capacity (meq/100gm) 10 48 NA 21
Basic Characterization of the Materials Used in the Study
1E-4 1E-3 0.01 0.1 1 10
0
20
40
60
80
100
120
%Finer
Grain size (mm)
RS; RB; BB; SS
5 10 15 20 25 30 35 40 45
1.2
1.3
1.4
1.5
1.6
1.7
1.8
Drydensity(g/cc)
Water content (%)
RS; RB; BB; SS
15

16. 0
10
20
30
0 500 1000 1500 2000 2500 3000 3500 4000
Radiation(MJ/m2day)
solar radiation
15
20
25
30
35
40
0 500 1000 1500 2000 2500 3000 3500
Temp
temperature
0
0.2
0.4
0.6
0.8
0 500 1000 1500 2000 2500 3000 3500
Evaporation(cm/day)
Evaporation
0
5
10
15
20
25
30
0 500 1000 1500 2000 2500 3000 3500
precipitaion(cm/day)
Time (day)
precipitation
16

17. Layer → Homo
Dimension
Thickness (m) 1.150
Length (m) 1.5
Width (m) 0.5
Material RS
% of Sand 83.7
% of Silt 9.8
% of Clay 6.5
PredictedvGenuchten’sParameters
0.04
0.4
0.17047
n 1.3077
0.250
I 0.5
0.4
0.4
0.17047
0.250
0.305
N
U
M
E
R
I
C
A
L
M
O
D
E
L
l
I
N
G 17

18. 18

19. 0
200
400
600
800
1000
1200
0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
Depth(mm)
Water content
1000 days
2000 days
3000 days
1000 WHC
2000 WHC
3000 WHC
0
200
400
600
800
1000
1200
-10000-8000-6000-4000-20000
Depth(mm)
pressure (cm of head)
1000
days DC
2000
days DC
3000
days DC
1000
days
WHC
2000
days
WHC
19

20. 0.25
0.27
0.29
0.31
0.33
0.35
0.37
0.39
0 500 1000 1500 2000 2500 3000 3500
VWC
Time ( days )
Node 1
Node 2
Node 3
0.2
0.25
0.3
0.35
0.4
0 500 1000 1500 2000 2500 3000 3500
-6000
-5000
-4000
-3000
-2000
-1000
0
0 1000 2000 3000 4000
pressure(cm)
Time (days)
Node 1
Node 2
Node 3
-35000
-30000
-25000
-20000
-15000
-10000
-5000
0
0 500 1000 1500 2000 2500 3000 3500
Time (days) 20

21. Layer → PL DL BL
Dimension
Thickness (m) 0.450 0.300 0.400
Length (m) 0.3 0.3 0.3
Width (m) 0.3 0.3 0.3
Material RS SS RB
% of Sand 83.7 100 59.7
% of Silt 9.8 0 18.5
% of Clay 6.5 0 21.6
PredictedvGenuchten’sParameters
0.04 0.02 0.07
0.4 0.36 0.465
0.17047 0.83956 0.01195
n 1.3077 1.68609 1.29446
0.250 365.472 0.00173
I 0.5 0.5 0.5
0.4 0.36 0.465
0.4 0.36 0.465
0.17047 0.83956 0.01195
0.250 365.472 0.00173
0.305 0.07 0.36
Numerical Modelling
21

22. 22

23. 0
200
400
600
800
1000
1200
0 0.2 0.4 0.6
depth(mm)
VWC
50 days
150 days
265 days
0 days
0
200
400
600
800
1000
1200
-25000-20000-15000-10000-50000
pressure (cm)
50 days
150 days
265 days
0 days
23

24. 0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 100 200 300
Node 1
Node 2
Node 3
Node 4
30
32
34
36
38
40
42
0 30 60 90 120 150 180 210 240 270
PPS3(300mm) 5TM (225mm)
March April May June July August Sept. Oct. Nov.
Top: Protection Layer
5
10
15
20
25
30
35
40
1 31 61 91 121 151 181 211 241 271
PPS5(600mm)
5TM (600mm)
March April May June July August Sept. Oct. Nov.
Middle: Drainage Layer
36
38
40
42
44
46
48
1 31 61 91 121 151 181 211 241 271
PPS6(1000mm)
5TM (850mm)
March April May June July August Sept. Oct. Nov.
Bottom: Barrier Layer
24

25. -20000
-18000
-16000
-14000
-12000
-10000
-8000
-6000
-4000
-2000
0
0 50 100 150 200 250 300
Node 1
Node 2
Node 3
Node 4
5
105
205
305
405
505
605
1 31 61 91 121 151 181 211 241 271
PL (225mm)
March April May June July August Sept. Oct.
Top: Protection Layer
5
55
105
155
205
255
1 31 61 91 121 151 181 211 241 271
Time (Days)
DL(600mm)
Middle: Drainage Layer
March April May June July August Sept. Oct.
5
305
605
905
1205
1505
1 31 61 91 121 151 181 211 241 271
Suction(kPa)
Time (Days)
BL(850mm)
Bottom: Barrier Layer
March April May June July August Sept. Oct.
25

26. 26
CONCLUSIONS
 same trend as VWC increases suction decreases.
 Suction and VWC Fluctuating is lesser at the lower part. After a certain
depth effect of climate become invisible and they become constant.
 At all the nodal point suction and VWC varies between two extreme values
and corresponding suction which is input by user as material properties.
 The extreme value of VWC and suction depends upon the soil profile, its
particle arrangement and texture. That is why they differ layer to layer.
 Results of the model depend upon the fitted parameters of SWCC, initial
wetting and drying curve and hysteresis.
 During the rainfall season the permeability ,water content and percolation
tends toward the saturation value in upper zone as well as in the lower zone
of cover therefore it is in critical condition during these periods

27. 27
CONCLUSIONS
 Variation in lab cylindrical model and numerical model is may be because of
mixing, handling, not uniform initial pressure condition, leakage of water
along periphery.
 Not fully saturation in real model shows air entrapment.

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29. FUTURE SCOPES
 Numerical modelling with catastrophic rainfall events to access the worst condition in
future.
 Numerical modelling by considering the degradation phenomena.
 Numerical modelling with erosion.
 Prediction next 100 year climatic data using GCM model.
 Comparison of the results obtained in numerical studies with field monitoring.
 Probabilistic sensitivity of different evaporation method on cover design.
 Validation of the work with using another code VADOSE/W.
29

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