Geosynthetics October/November 2020 - 8

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PUNCTURE AFTER NDT

TIME BETWEEN TRIAL WELDS

Q: I would like your opinion on the fate
of punctures in the air channel leftover
from nondestructive air channel tests
(NDTs), specifically in regard to sealing the
air channels to prevent leachate or water
ingress. We are particularly concerned with
this situation on a landfill cover should liquid
freeze and expand in the air channel.

Q: Is there a standard or guideline for how
much time between trial welds during the
course of a day is acceptable? We are working
with an older CQA plan that states no more
than four hours, which is shorter than the
normal five hours the installer was expecting
and that I've normally seen in other CQA plans.

A: I hope this email finds you well. Thank you
for your Techline question in regard to repair
of NDT testing punctures.

A: In regard to a specific time between trial
welds, we usually see it at five or six rather
than four hours. This guidance can be found
in the following two references:

Yes, is the answer. The puncture(s) in the air
channel leftover from the NDT needle and
unsealed end(s) need attention after the test.
I have seen the following written into plans
and specifications:

Daniel, D. E., and Koerner, R. M. (2006).
Waste containment facilities: Guidance for
construction, quality assurance and quality
control of liner and cover systems, 2nd ed., ASCE
Press, New York.

1.	 Extrusion bead over needle hole and hot
air weld (Leister) shut the far end after
air release

Daniel, D. E., and Koerner, R. M. (1993). "Quality
assurance and quality control for waste
containment facilities," US EPA Technical
Guidance Document, EPA/600/R-93/182,
Washington, DC, Office of R & D, Cooperative
Agreement No. CR-815546-01-0.

2.	 Patch area of NDT to isolate air channel
from intrusion
3.	 Cutoff end where NDT occurred and
seam perimeter (i.e., linear low-density
polyethylene [LLDPE] cover to highdensity polyethylene [HDPE] liner) with
an extrusion weld or solid wedge with
"T" seams
In all cases the air channel is isolated to
prevent liquid from entering it. Confirmation
of these events is in the construction quality
assurance (CQA) record as verification. Today,
expert systems are even requiring photo
documentation of the events surrounding
this isolation.

8

Both documents state that trial welds are
tested on-site two times a day: Once to start
the day and then after the lunch break. Sure
would hate to do trial welds for a second time
in the morning an hour before lunch and
then knock off. That stated, the site-specific
CQA plan rules one behavior, and you need to
follow it to the letter if you intend to get paid.

Geosynthetics | October November 2020

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Geosynthetics October/November 2020

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