4.1. Geonets are used specifically for their in-plane drainage capability. Give the reasons they
are not used for the following:
(a) Separation
(b) Reinforcement
(c) Filtration
(d) Containment (moisture barrier)
4.2. When using geonets for drainage functions, what keeps the adjacent soil from getting in
their apertures and blocking flow?
4.3. If a geotextile is placed adjacent to a geonet, what function(s) does the geotextile provide?
How does the combination of geotextile and geonet accommodate flow?
4.4. All of the geonets described in this chapter are made of polyethylene. Could they be
made from other polymers? Why do you suppose they are made from polyethylene?
4.5. It is noted in this chapter that the aperture size varies from product to product. What effect
does aperture size have on flow and intrusion?
4.6. In the typical extruded biplanar geonets, the vertical axes of the intersecting ribs are not
quite perpendicular to one another. What implications does this have for the compressive
load-carrying capacity of the geonet?
4.7. For the foamed extruded geonets shown in Figure 4.2, answer the following questions:
(a) What are the foamed pores within the ribs filled with?
(b) What are the long-term implications of this?
(c) How would Fick's law (of diffusion) enter into this discussion?
4.8. For triplanar geonets, the flow rate is significantly higher than for biplanar geonets.
(a) Where in a typical landfill configuration can these geonets best be used?
(b) Why is knowledge of the slope direction critical to know?
(c) Why is the flow in the cross-machine direction not particularly important?
4.9. The shear strength between a geotextile and a geonet can be quite low and troublesome
when used in side-slope design. Describe two methods by which the geotextile can be attached
to the geonet to avoid the potential problem. Include the advantages and disadvantages
of each method.
4.10. The flow-rate reductions between Figures 4.7 and 4.8 as tabulated in Table 4.1 are up to
40% for 500 kPa normal stress. Beyond this stress level the reductions are lower. Why are
they lower at the higher stress levels?
4.11. Regarding the placement and use of a compacted clay liner over a geotextile bonded onto
a geonet:
(a) What are the implications of using a lighter-weight geotextile for the results shown in
Figure 4.8?
(b) What would happen if a woven monofilament geotextile of ~6% open area were
used?
(c) What would happen if a nonwoven heat bonded geotextile were used?
4.12. Discuss the difference between extrusion and intrusion for a geotextile covering a geonet
that has a clay liner placed above it.
4.13. The ultimate flow rate of a geonet being considered for the primary leachate collection
system on a landfill side slope is 7.3 X 10-4m2/s. Using the maximum values in Table 4.2,
what is the allowable flow rate?