TEXTILES.ORG
By Ian D. Peggs
At the Geosynthetics-2007 conference earlier this year in Washington, I had dinner with a geomembrane manufacturer colleague and he asked me, “How should we respond to a customer’s question: ‘Is your geomembrane compatible with my chemical solution of A, B, C, at XY°C?’ and then says he is going to order material in three days?”
I answered, of course, that if you cannot be sure, it would be wise to advise a chemical-resistance test. He agreed that, theoretically, that would be the correct answer. But, in practice, there is no time to do this. Any answer other than a convincing “Yes” will result in losing that project to another manufacturer.
This could almost be a “company-on-the-line” decision! My colleague and his company have been fortunate so far, but other parties have not. Who should decide which geomembrane material should be selected, or which grade of material should be used—the geomembrane manufacturer, the liner fabricator, the design engineer, the owner, the general contractor, the installer, or the CQA firm?
And if one of these parties makes a recommendation, should it be checked and confirmed by any other?
The chemical resistance question led to the consideration of decisions/requests made, or not made, in other projects that generated similar theory/practice conflicts.
Consider the following events.
The wrong solution
A studded HDPE concrete protection liner was proposed for the walls of mine solvent extraction mixer/settlers with loose HDPE liner on the floor. The two were joined on the floor a few feet away from the wall. The copper process solution consisted of aromatic hydrocarbons with sulfuric acid at a temperature of about 55°C.
The liner manufacturers strongly recommended that a chemical resistance test be performed in the multi-component solution. The engineer declined to do the $10,000 max test, insisting that HDPE had been successfully used in such solutions before.
We later found that those solutions were in fact not the same and were at much lower temperatures. The mixer/settlers were built and the liners failed (Photo 1). The floor HDPE swelled and buckled. The wall liners blistered as stud/liner junctions cracked. Extrusion welds between loose sheet and studded sheet peeled and cracked. And ultimately cracks occurred along the tops of wrinkles.
Who was blamed? The liner installer, of course, because the welds were not properly made and were not strong enough.
So is it a welding problem? Or a design materials selection problem? It’s a good thing, this time, that the liner manufacturer did not quickly say “Yes” to the chemical compatibility question and instead suggested a chemical resistance test.
Who let thewastewater out?
In a similar wastewater treatment pond situation, the material manufacturer did say “Yes,” the liner material would be resistant to the process solution. The liner failed. The owner faulted the general contractor, the liner installer, and the liner manufacturer, but not the design engineer.
Surely the design engineer, being the one who knows the most about the operating conditions of the facility, has ultimate responsibility for the material selection independent of commitments by others. Certainly the design engineer should seek expert advice, including expert review of his/her decision, but it is the engineer’s ultimate responsibility. The engineer stamps the drawings and the project specifications.
Taking the wrong steps
As per the design, HDPE steps were welded to HDPE strips that were tack welded to the HDPE geomembrane liner on long steep slopes of an irrigation pond in a cold region. The pond started filling in the fall until it was full in the spring. Ice formed on the surface of the water and around the strips. As water continued to enter the pond, the floating ice lifted the strips, then the tack welds, and after some end/edge tack weld separation, at regions of increased bonding holes, were made in the liner (Photo 2).
The liner installer was faulted for not making adequately strong welds that would not separate from the liner. The owner/engineer declined to pay the general contractor, who was then forced out of business. In fact, the installer had tried to make “poor” tack welds that would peel off the liner without damage under ice action, but that would still have adequate shear strength to hold people walking up and down the steps—an admirable theoretical target but practically impossible to achieve consistently.
Steps on a steep slope liner are also an admirable target and can work well in warm environments. But where ice can form on the water, and ice cornices break off the crest and slide down the liner, they are, in practice, a recipe for disaster, as shown. Litigation placed all responsibility on the owner/engineer.
The pond that swalloweda million dollars—the installer
Now, turning the tables on installers, a general contractor and facility owner, knowing nothing about liners, handed over the design and installation of an irrigation pond HDPE liner to a local installer, supposedly an “approved” installer of one of the big manufacturers at the time. The general contractor was assured that the QC program of the manufacturer would be followed.
When the pond was filled, well, it wouldn’t fill (the leak rate became higher than the fill rate), and many whales formed. When emptied, 109 leaks were found in 15% of the area of the liner, including a destructive sample patch that had been welded only 75% around the edge (Photo 3).
This was an unbelievably bad installation. Fortunately for the installer, the contractor/owner just needed the facility fixed, properly, as soon as possible, so did not sue for the $1.3 million it cost him to properly design and reline the facility.
This was clearly a situation where a saving of $15,000 by going with the local installer did not pay off!
The pond that swalloweda million dollars—the manufacturer
The tables are now turned on the manufacturer of replacement liner (fPP) in the same project. The new project specifications went so far as to define the PP resin that was required for the geomembrane. During communications with the manufacturer regarding the resin and the critical test data required, the owner’s representative was assured there would be no problem in meeting all specifications.
The contractor/owner required that a plant audit be done for CQA purposes. The first thing noticed during the audit was that the specified resin was not being used! From a comparison of resin specification sheets, it appeared to the CQA auditor that the new resin would not meet the critical multiaxial burst strength specification. The manufacturer assured the auditor that it would.
The finished geomembrane was on its way to site (overseas) before samples, after repeated requests, were provided for testing. The geomembrane failed the multiaxial burst strength test by a large margin. Rather than accept the deficient material “in the interests of time,” the manufacturer was required to replace the material. It is unfortunate how many times nonconforming material is used because of project time constraints.
Conformance testing: Before or after shipping?
Along the same lines, a textured HDPE geomembrane was delivered to an overseas site. Conformance testing was not performed before shipping but when it arrived on site. It did not meet the stress cracking resistance (SCR) specification and met the standard oxidative induction time (OIT) specification by only one minute (101 min). However, sharp CQA eyes noted that the OIT test had been performed at 180°C rather than the required 200°C, thereby generating a longer OIT. Clearly a test at 200°C, giving a shorter time, would not have met project specifications.
Discussions by all parties determined that the non-conforming OIT would not detrimentally affect the performance of the material in its buried application. However, the low SCRremained grounds for rejection of the material—no compromise was made “in the interests of time.” The manufacturer was required to replace the material and did so without complaint.
This time conformance testing was done before the replacement material was shipped!
Liner-leak survey: Before or after covering?
Finally, there was the wise installer who was required to perform an electrical leak-location survey on the installed liner but with no stipulation of before or after the cover soil was placed on the liner by an earthwork contractor doing his first geomembrane liner project.
The decorative pond was in a park on top of a landfill. Clearly it was in the interest of the installer to find all leaks before the potentially geomembrane-challenged soil mover had access to the liner. Just as clearly, it was in the owner’s interest to find all leaks in the finished liner as-covered, because most damage (~74%) is done during the covering process. The installer selected the former. Four small leaks were found at pipe penetrations and were satisfactorily repaired.
A few days later the site was revisited, just at the right time, after soil had been placed on the liner and before filling with water. The soil was probably from the landfill. It contained many fragments of glass as large as 3-4 in. It is highly probable, almost certain, that there would now be many holes in this liner. The installer made a wise choice of when to do the survey. The project engineer was not specific enough in the project specifications as to when to perform the survey.
In all of these cases, theory is one thing but practice can be quite different.
Searching theory forthe practical answer
So, where does that leave us?
My colleague says, “Yes” when he is comfortable; but bites the bullet and says, “I can’t be sure. We need to do a chemical resistance test” when he is not sure, and loses the order—but he minimizes the risks to his company.
But, as noted, there are many in similar positions at other companies, and all may not have the same standards and expertise. Thus, the owner/engineer may get the answer he wants, but not the liner performance.
Which is more important? I know. But will it, and will this technical note, make any difference? In theory I would like to think so, but in practice it probably will not.
Theory and practice? Mostly they walk side by side but definitely not hand in hand.
And when they don’t, be prepared for a few sideswipes and have your checkbook ready.
Caveat emptor certainly. But caveat venditor is just as important!