Sample Questions
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Geosynthetic Materials and Compacted Clay Liners
GT-1 Geotextiles are usually joined in the field by:
A.Overlapping
B.Sewing
C.Heat bonding
D.All of the above
E.None of the above
GT-2 When installed on a slope, a geotextile should always be:
A.lapped with the downstream edge over the upstream edge
B.placed adjacent to each other with no overlap
C.overlapped six inches and sewn
D.be constructed so that no joints ever occur
GM-1 The primary reason extrusion fillet welding of polyolefin geomembranes requires surface grinding of the sheets is:
A.for convenience of the welders
B.the edges are usually too thick
C.for added material strength
D.to remove surface oxidation
GM-2 Why are trial test strips important in the installation of a geomembrane?
A.to satisfy regulations requirements
B.to test the seamer’s abilities
C.to verify that the equipment is working properly and the workmanship is acceptable
D.to generate friction with the liner contractor
GCL-1 Adjacent rolls of GCLs are jointed by what method?
A.sewing
B.stapling
C.mechanical connection
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D.welding
E.overlapping
GCL-2 When a GCL has a nonwoven needle punched geotextile on one surface and a woven slit film geotextile on the other surface:
A.placement of which surface is up does not matter
B.the nonwoven geotextile side should always be up
C.the woven geotextile side should always be up
D.the site-specific plans must provide guidance
CCL-1 The zero air voids curve is also known as:
A.maximum density curve
B.100% saturation curve
C.100% relative compaction curve
D.95% relative compaction curve
CCL-2 Fines are defined as:
A.fraction of soil passing through the opening of a 100 sieve (150 mm)
B.fraction of soil passing though the openings of No. 200 sieve (75 mm)
C.loamy fraction of a soil
D.clay fraction of a soil
RE: Liner questions
I am designing a surface impoundment with interior side slopes of 1.5H:1V. This impoundment requires (per regulations) a geosynthetic clay liner (Bentomat DN or equivalent), 40-mil HDPE secondary liner, and 60-mil HDPE primary liner. A leak-detection system has been requested.
The pit is small (approximately 500ft x 200ft) without much travel distance for fluids should a leak occur. To avoid too many liners on a steep slope, I would like to use two textured HDPE liners as both the primary and the secondary without adding a fourth layer in for the leak-detection system.
I have the following questions:
(Melissa | Missouri)
Reply: Tough questions … 34 degrees is at, or slightly higher than, the best of geosynthetic interfaces (e.g., nonwoven to textured, internal to GCLs, etc.). So you are flirting with disaster to begin with.
It is much worse with a GM-to-GM even when they are textured. In fact, even more so, since the shear plane must ride up on the asperities. What remaining transmissivity there is depends on the normal pressure applied.
Clearly ASTM D is the appropriate test to use and will also allow one to get a glimpse of how the asperities behave.
Lastly, it very much depends on how the texturing has been manufactured. I suspect that blown film will indeed be different from structured with regard to shear strength and transmissivity.
Melissa, you need to do some lab testing to quantify my commentary.
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