Dave Martin, P. Eng. Quantum Technical Services Ltd. St. Albert Canada, email@example.com.
Note: ECS is a registered trademark of Western Engineered Containment, and is produced exclusively for WEC by Quantum Chemical Ltd.
The ability to resist puncture failure from a protruding object in the subgrade is a critical performance parameter for a geomembrane. The ability to lay a geomembrane over imperfect subgrade, without geotextile protection can lead to significant savings in the overall cost of a project. In an effort to best simulate actual service conditions in the field this study evaluates large scale puncture resistance of Precidium ECS (ECS), a proprietary spray applied polymer, which has been sprayed onto a conductive foil backing. A substrate bed composed of a base of small diameter aggregate with specifically sized larger gravels placed intermittently on top of the base was prepared. 60 mil ECS sprayed on a foil backing was pressed over the subgrade up to a maximum pressure of 300 Kpa, which equates to 100 feet of water, following ASTM D5514. 60 mil HDPE was also tested for comparison. This study used crushed gravel with effective protrusion heights of 1.5” to 4.0”; the gravel is shown in the picture below and contained some sharp edges which would cause quite a bit of abrasion on the geomembrane as it was stretched over-top. HDPE was tested with a protective cushion of 8 oz non-woven geotextile as this is how it is generally installed in the field. The 60 mil ECS membrane was tested with and without the 8oz nonwoven as ECS is generally installed without a protective nonwoven geotextile.
The Standard Test Method for Large Scale Hydrostatic Puncture Testing of Geosynthetics (ASTM D5514) has methods for testing over rock subgrades or manufactured truncated cones of various heights. The truncated cone method has been more widely used and published results for many types of geomembranes are available. Marcotte et. al. 2009 , found that truncated cone results for HDPE closely mimicked results for stone aggregate, as the sharp edges of the aggregate don’t cause failure as much as the inability of HDPE to stretch elastically over protrusions. In this study we wanted to compare ECS and HDPE, as ECS offers much more elastic stretching potential. In truncated cone studies, HDPE gives much weaker results than ECS sprayed on foil. However we felt it was important to compare the two geomembranes under conditions which more closely relate to actual service conditions. All of the testing done in the ECS/HDPE studies was completed by a third party laboratory, Sageos/CTT Group in Montreal.
Figure 1: Example of The Subgrade Constructed for the ECS/HDPE Comparison.
Table 1 shows the results of the 60 mil ECS sprayed on foil comparison to 60 mil HDPE.
Figure 2: ECS/Foil Composite Conforming Completely to Subgrade of 3.0” Aggregate
Figure: 3 HDPE Puncture Over 2.5” Gravel Substrate
60 mil ECS clearly outperforms 60 mil HDPE in terms of resisting puncture and stretching over stones in the subgrade. As shown in Figure 1 (3.5” diameter Gravel) ECS sprayed on foil was able to elastically stretch over some very substantial stones with or without a nonwoven cushion. In this study, the limit of ECS was not found. Comparatively HDPE (accompanied by an 8 oz. nonwoven cushion) failed at a gravel height of 2.5”.
ECS is a proprietary spray applied polymer designed specifically for primary and secondary containment. ECS sprayed on a foil backing offers a unique set of properties amongst the range of geomembranes available in the marketplace such as leak detection and leak location. It is clear that ECS can be placed over larger protrusions than HDPE and will avoid puncture over less than ideal subgrade conditions. When factoring in surface preparation, the cost of a geotextile cushion, and the large financial and environmental costs caused by a geomembrane failure, ECS appears to be the most cost effective option available currently.
ECS is the result of 15 years of evolution of this type of proprietary chemistry. With its elastic behaviour and durability, combined with installation advantages of a spray applied system, ECS is a cost effective candidate for both primary and secondary containment projects. As an added advantage the application of ECS to a metallic (conductive) foil allows for inexpensive and accurate leak detection surveys of the entire containment.
Marcotte M., Denis R., and Blond E. (2009) Design Algorithm for Puncture Resistance of PVC Geomembranes for Heap Leach Pads. Proceedings of Second Middle East Geosynthetics Conference, Dubai, UAE. Nov. 2009.