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Design of Lateral Drainage System in Landfill - Design Calculator

 

Problem Statement
The ultimate transmissivity of a geocomposite drainage layer is calculated by two methods:

The first method is based on the McEnroes equations. From the McEnroes equations, the required permeability of a drainage media is calculated. Iteration procedure is used to find the required permeability such that the liquid thickness is equal to the thickness of the liquid collection layer. This permeability multiplied by the thickness of the liquid collection layer result in the required transmissivity. The ultimate geocomposite transmissivity can then be calculated by incorporating the total serviceability factor (product of safety factor and reduction factors).

The McEnroe equation requires the input of an impingement rate (qh), a drainage media permeability (k) and a liner slope (b). This information is used here to find the liquid thickness on the liner.

The McEnroes solutions are for three cases.

  1. Case 1 is for a saw-tooth bottom, with the liquid mound overtopping the peak. (R > 1/4)
  2. Case 2 has the liquid mound starting at the peak of the saw-tooth. (R = 1/4)
  3. Case 3 has the mound starting below the peak of the tooth. (R > 1/4)
McEnroe Equation

The second method is based on Giroud's equation. The geocomposite's ultimate transmissivity is calculated directly.

Giroud's equation, with great simplicity, produces a very close solution as compared to McEnroe's equations.

Giroud Equation

Note: Giroud's equation is based on a factor of safety applied to maximum liquid thickness to ensure unconfined flow.

Required Data

Symbol Name Dimensions
S The liner slope, S = tan b %
qh Impingement rate Length / Time
L Length of slope measure horizontally Length
tLCL Thickness of the Liquid Collection Layer for geocomposite. Length

FSd Overall factor of safety for drainage
RFin Intrusion Reduction Factor
RFcr Creep Reduction Factor
RFcc Chemical Clogging Reduction Factor
RFbc Biological Clogging Reduction Factor

 

Input Values
Note: If you do not wish to perform calculations for 3 cases, please leave default data as is.

Case 1 Case 2 Case 3
S % % %
qh cm/s cm/s cm/s
L m m m
tLCL cm cm cm
Factor Case 1 Case 2 Case 3
Leachate Collection and Removal Leachate Detection Systems
RFin [1]
1.0 - 1.2 1.0 - 1.2
RFcr [2] Calculate RFCR

RFcc [3]
1.5 - 2.0 1.1 - 1.5
RFbc [3]
1.1 - 1.3 1.1 - 1.3
FS [4]
2.0 - 10.0 2.0 - 10.0
Note: The reduction factor values given correspond to the case where the seating time exceeds 100 hours and the boundary conditions due to adjacent materials are simulated in the hydraulic transmissivity test.


[1] Intrusion reduction factor from 100 hour to design life. Giroud et. al (2000)
[2] Creep reduction factor from 100 hour to design life (for instance, 30 years). RFCR is determined from 10,000 hour compressive creep test, extrapolated to design life, GRI-GC8 (2001). RFCR is product and normal load specific.
[3] GRI-GC8
[4] FS value = 2-3. Giroud, et. al (2000)
    FS value > 10 for filtration and drainage. Koerner (2001)
[5] Note: The calculated transmissivity is corresponding to the case where the seating time is 100 hours and the boundary conditions due to adjacent materials are simulated in the hydraulic transmissivity test.

 
References

"GRI-GC8, Determination of the Allowable Flow Rate of a Drainage Geocomposite". Geosynthetics Research Institute, 2001.

"Designing with Geosynthetics". R.M. Koerner, Prentice Hall Publishing Co., Englewood Cliffs, NJ, 1998.

"Hydraulic Design of Geosynthetic and Granular Liquid Collection Layers". J. P. Giroud, J. G. Zornberg and A. Zhao, Geosynthetics International, Vol. 7, Nos 4-5.

"Lateral Drainage Design update - part 2". G. N. Richardson, J.P. Giroud and A. Zhao, Geotechnical Fabrics Report, March, 2002

"Maximum Saturated depth over Landfill Liners". B. McEnroe, Journal of Environmental Engineering (Vol. 19, No. 2, March/April, 1993).

Copyright 2001 Advanced Geotech Systems.  All rights reserved.