landfilldesign.com - Geomembrane Puncture Protection, Geotextile Selection

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Geomembrane Puncture Protection, Geotextile Selection - Design Calculator

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
P_act	actual pressure due to the landfill contents or surface impoundment
P_allow	allowable pressure using different types of geotextiles and site specific conditions.

p_allow is determined by the following equation:

where:

Symbol	Name	Unit
P_allow	allowable pressure	kPa
M	geotextile mass per unit area	g/m2
H	height of the protrusion above the subgrade	m
MF_S	modification factor for protrusion shape	-
MF_PD	modification factor for packing density	-
MF_A	modification factor for arching in solids	-
RF_CR	reduction factor for long-term creep	-
RF_CBD	reduction factor for long-term chemical/biological degradation	-

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

MF_S		MF_PD		MF_A
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

RF_CBD		RF_CR
RF_CBD			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
MF_S
MF_PD
MF_A
RF_CR
RF_CBD

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.