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Geomembrane Puncture Protection, Geotextile Selection - Design Calculator

 

Problem Statement

There are many circumstances where geomembranes are placed on or beneath soils containing relatively large-sized stones. For example, poorly prepared soil subgrade with stones protruding from the surface, and cases where crushed-stoned drainage layers are to be placed above the geomembrane.

In all of these situations, a nonwoven needle-punched geotextile can provide significant puncture protection to the geomembrane. The issue of determining the required mass per unit area of the geotextile becomes critical.

The method presented herein (Koerner, 1998) focuses on the protection of 1.5 mm thick HDPE geomembranes. The method uses the design by function approach.

where:

FS factor of safety against geomembrane puncture
Pact actual pressure due to the landfill contents or surface impoundment
Pallow allowable pressure using different types of geotextiles and site specific conditions.

pallow is determined by the following equation:

where:

Symbol Name Unit
Pallow allowable pressure kPa
M geotextile mass per unit area g/m2
H height of the protrusion above the subgrade m
MFS modification factor for protrusion shape -
MFPD modification factor for packing density -
MFA modification factor for arching in solids -
RFCR reduction factor for long-term creep -
RFCBD reduction factor for long-term chemical/biological degradation -


Modification Factors and Reduction Factors for Geomembrane Protection Design
Using Nonwoven Needle-Punched Geotextile


MFS   MFPD   MFA  
Angular: 1.0 Isolated 1.0 Hydrostatic 1.0
Subrounded: 0.5 Dense, 38 mm 0.83 Geostatic, shallow 0.75
Rounded: 0.25 Dense, 25 mm 0.67 Geostatic, mod. 0.50
    Dense, 12mm 0.50 Geostatic, deep 0.25



RFCBD

RFCR

38 25 12
Mild leachate 1.1 Geomembrane alone N/R N/R N/R
Moderate leachate 1.3 270 N/R N/R >1.5
Harsh leachate 1.5 550 N/R 1.5 1.3
1100 1.3 1.2 1.1
>1100 1.2 1.1 1.0

N/R = Not Recommended

 

Input Values

FS Safety Factor against Puncture (>= 3 is recommended)
d Depth of material on top of geomembrane (m)
Unit weight of material on top of geomembrane (kN/m3)
H Protrusion height (m)

Modification and Reduction Factors
MFS
MFPD
MFA
RFCR
RFCBD

 
References

Wilson-Fahmy, R.F., Narejo, D. and Koerner, R.M. (1996), "Puncture Protection of Geomembranes Part I: Theory", Geosynthetics International, Vol. 3, No. 5, pp. 605-628.

Narejo, D. and Koerner, R.M. and Wilson-Fahmy, R.F., (1996), "Puncture Protection of Geomembranes Part II: Experimental", Geosynthetics International, Vol. 3, No. 5, pp. 629-653.

Koerner, R.M., Wilson-Fahmy, R.F. and Narejo, D. (1996), "Puncture Protection of Geomembranes Part III: Examples", Geosynthetics International, Vol. 3, No. 5 pp. 655-675.

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

Copyright 2001 Advanced Geotech Systems.  All rights reserved.