The vinyl liner pool battle began July 9, l979 when the board voted to disallow, as of Oct. 15, 1979 the use of in-ground vinyl liner swimming pools installed below the flood level criteria of the South Florida building code. After a Miami law firm representing NSPI challenged the ban, the board agreed on Oct. 9 to allow past permits to be re-issued and to grant product approval for 60 days or more depending on how long it would take the building and zoning department's product control division to formulate testing criteria.

NSPI formed a committee of 12 vinyl liner manufacturers and builders. Ultimately, this committee, not the county, designed and funded a test which was conducted Feb. 23 ,1980 in Davie, Fla. The pool site, which is in neighboring Broward County, reportedly was selected because the owner agreed to the use of his land. NSPI reported that attempts to find a suitable location in Dade County were unsuccessful.

The NSPI committee selected Trojan Pools, a subsidiary of AM! International Ltd., to supply the pool and The Schundler Company of Metuchen New Jersey to supply the vermiculite. Trojan Pools of South Florida provided the labor. NSPI engaged Robert M. Wilcox, who was then director of marketing/sales for Trojan Pools and a 21-year veteran industry technician, to supervise the construction, installation and testing of the pool.

Wilcox said unusual dimensions--- 16 ft. by 32 ft. by 8.5 ft.--- were selected "because Dade County would only approve pool depths and we wanted the test to include all pools up to 20 ft. by 40 ft. with diving hoppers.

"I insisted on Schundler V+16 Pool Base for the pool base because it has a greater continuity in quality and particle size. Otherwise, the base, which is mixed in batches, can lose the structural and porosity capabilities necessary," he said.

The two-inch thick vermiculite mineral floor is rigid, but it acts like a sieve, holding the dirt back but letting water' through. This makes it difficult for the water table to put pressure on the pool because the water goes through the bottom.

The first step in the project was to dig a 28 ft. by 48 ft. by 10 ft. excavation into which a similar-sized plastic membrane was placed. The membrane then was filled with disturbed earth, packed, and tamped. Then, the 16 ft. by 32 ft. by 8½ ft. pool excavation was cut.

"In this way, we created a trenching system to artificially raise the hydrostatic water table," Wilcox said.

"Our aim was to simulate flood conditions, a concern because there is so much water in Florida. Another concern was that vinyl pools are not strong enough when put in highly granular, soft sugar sand. That is the type of sand in which we installed the test pool," he said.

"Some yards in Florida are naturally like the simulated conditions. I had installed pools under these conditions so I knew the pool could take it," Wilcox said.

He reported that for the test, the pool first was filled with water, then the outer membrane was filled with water to artificially create a hydrostatic water table equal to ground level.

"The force in the pool at this time was 86 tons. We then started to empty the pool while it was being subjected to the inward force of the hydrostatic water table. Then the outward force in the pool no longer equalled the inward force of the water table, and the liner floated," Wilcox said.

"We made the liner float deliberately by dropping the water level inside the pool. The liner, as the intermediate between two pressures, began to float. We wanted to test the floor and to show that the liner didn't break away from the main drain.' he said.

"After pumping all the water out of the pool, we examined the pool floor for fractures, but there were none. There was no distortion and the walls didn't deflect. They doubted we would he able to keep the pool intact, but there were no failures," Wilcox said.

The test was conducted only once, though it originally had been expected to he run three times. Wilcox said, "It was feared that water traveling behind the floor could create channels or voids, weakening the support of the floor. They thought that when we re-filled the pool with 86 tons of water, the earth would no longer support the floor.

"But we had dry run the test before the officials came and we knew this was not a problem. We broke out chunks of the floor on three sides of the diving hopper to show the full support of the earth and the absence of big voids," he said.

John Pistorino, a private consulting engineer for Dade County, confirmed that a test normally is run three times in order to take into account any types of errors or unexpected events.

"However," he said, "at any time we feel there is no need to continue testing, we will stop the test. If a test is a total failure or if, as in this case, the test is very good and all the factors we wanted to consider were addressed, it is not necessary to incur any additional cost and time."

At one point during the test, Pistorino and Tolat allowed Wilcox to release two corners of the vinyl liner to permit water to transfer from one side to the other to help equalize the pressure.

"Under natural conditions, while the water table would he rising, water in the pool probably would evaporate, creating an equalized situation. However, we were raising the water table six inches every 20 minutes as compared with a natural rise of no more than two or three inches per hour," Wilcox said.

He said this unnatural effect was keeping the vinyl liner from rising because the downward force of the water in the pool was greater than the upward force in the water table. Wilcox also pointed out that the water inside the pool exerted greater pressure than the water outside because the water table pressure was diffused by the soil while the water pressure inside the pool was at full strength.

Other witnesses to the test included Henry S. Mantell, president of AMI Inter national Ltd., parent company of Trojan Pools; Spartan Pools Corp. Technical Ad visor George Hauser, and Manhar K. Jadav, consulting engineer who has been a strong opponent of vinyl liner pools. However, after watching the test, Jadav said, "If it can withstand this most severe test, I am convinced that vinyl liner pools are a good thing to have in Dade County."

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