Environmental Engineering Reference
In-Depth Information
Stage
Type of defects
Possible cause/comment
Manufacture
Pinholes; excessive
thickness changes; poor
stress-crack resistance
Unusual now for procedures with good
quality control. Poor resin quality
Delivery
Scuffing; cut; brittle cracks;
tears; punctures
Unloading with unsuitable plant or
lifting equipment. Impact on the
geomembrane. Poorly prepared storage
areas
Placement
Scratches; cuts; holes; tears
Dragging the sheet along the ground,
trimming of panels. Rough subgrade.
Use of equipment on top of the sheet
without a protection layer. Wind
damage. Large wrinkles or folds.
Damage by lifting bars
Welding
Cuts; overheating; scoring;
poor adhesion; crimping
Careless edge trimming; welding speed
or temperatures incorrect; excessive
grinding; dirt or damp in weld area;
excessive roller pressure
Cover
placement
Tears; cuts and scratches;
holes; stress in membrane
Action of earthmoving plant;
insufficient cover during placement;
careless probing of cover depth;
contraction of sheet due to ambient
temperature reduction
Post-
installation
Holes; tearing; slits; cracks
Puncture from drainage materials;
puncture by items of deposited waste;
opening of partial depth cuts; pulling
apart of poor quality welds; downdrag
stresses caused by settling waste;
differential settlement in the base
Table 16.2.
Typical defects and possible causes (from [MCQ 99]
Another interesting aspect related to geomembrane defects is the leak density per
liner area (i.e. number of leaks per hectare or m
2
). The results of the survey
presented by McQuade and Needham [MCQ 99] indicated a large range in
frequency (from 0 to 120 holes per hectare). The average frequency for the 111 sites
surveyed was 4.2 holes per hectare, although the median of 0.7 holes per hectare
was considered more representative of the standard achievable with competent
installation and thorough quality assurance control. There were incomplete data
relating the number of holes to the presence and rigor of quality control and
assurance procedures. For sites where it was known that a thorough program of
quality assurance control was implemented, the hole frequency ranged from
0-5.7 ha
2
, with an average of 0.8 and a median of zero. McQuade and Needham
