Possibilities abound in visitor center sinkage
EDITOR’S NOTE — This article is based solely on engineering professionals discussing possibilities of what could have failed at the Cajun Coast Welcome Center before the building subsided into the marsh June 14 in Morgan City. Both the engineers interviewed and The Daily Review are only presenting questions and possibilities concerning the structure and are not presenting conclusive findings in any way.
In the wake of the foundation failure of the new Cajun Coast Visitor’s Center in Morgan City, many questions and conjectures have been raised as to what caused the building to sink several feet into the scenic swamp it was constructed upon.
Two civil engineering professors from the University of Louisiana at Lafayette say at this point, the structural failure raises more questions than anyone is able to answer, but offers questions investigators would want to study to solve the mystery.
Dr. Kenneth McManis of the University of Louisiana at Lafayette College of Engineering, Department of Civil Engineering, said the most likely reason the approximately $3.8 million structure failed was “because of a (load) bearing capacity failure of some sort … possibly where a pile will push down and there is a rolling of soil around the sides.”
But even that type of failure, if it is the actual cause, raises questions.
“It could be lots of things,” he said. “It depends on soil strata supporting the pile and what you have on the end bearing. But this will be looked at thoroughly by everyone involved. There will also be third parties called in to do the analysis.”
Even though questions were raised locally as to the types of piles used in the construction and their possibly leading to a failure, McManis said it did not matter whether the pile material was concrete or wood as long as they were able to bear the load.
“As long as pile ratings were not exceeded, it just transfers the weight to the soil,” he said, adding soil studies in the area would also be crucial to determining the reason for the failure.
ULL adjunct and Forensic Engineer Sonny Launey said when soil GeoTech professionals make recommendations, they usually build in a safety factor of two, meaning they suggest foundations that can actually take twice the load they will need to support the structure.
They also prefer for piles to reach down to the geologic Pleistocene level in south Louisiana.
The geologic layer was laid down by the Appalachians eroding down Mississippi. Launey said over time, 30 to 40 feet of “muck” built on top of it in the region, but the layer offers a solid foundation in marshy areas.
“If piles hit Pleistocene, construction is easy money, but if you are above it, pile can slip down some,” Launey theorized. “Geotechs want to go down until they hit a solid foundation.”
He said he did not see that the load on the piles was that great, even with the large chimney at the front of the building, as it was built atop concrete beams.
Launey said another factor could have been sheer in the pile spacing, meaning the building could have not been properly attached to the foundation.
“If it failed over 4 or 5 hours, that is fast, but sometimes, the reasons are not as obvious,” Launey said. “Most times (the failure) is the result of the foundation or connections to the foundation failing. On construction side, the question arises as to whether or not the contractor followed the plans or if the owner and contractor made changes the designer did not know about or approve.
“It could be a combination of several things.”
Another factor McManis said would be considered is the load transfer from the roof to the foundation. McManis said there was a possibility the load flow was too heavy over a pile, but a pile test would be needed to determine if this was a contributing factor.
He said to begin discovering the reason for the failure, experts would also have to discover where the problem began in the structure.
“It looks like it failed along the fireplace,” he said. “That is a big (heavy) load right there. That may be the greatest load and it raises the question of whether it was accounted for. I don’t know … but it may have needed more support where that particular area was or a structural system to distribute the load. It looks like the building has the same geometry throughout for the pile plans, but I would not necessarily blame the fireplace (until more investigation is completed).”
McManis said there could be extensive variation in the geology of the area, even over short distances, possibly leading professionals to believe it was safe to place the building where they did.
There was one thing the ULL engineer was sure of — the building lost support.
But beyond that, he said the structure was offering only questions at this point.
“Soil report and description of failure would be the starting point,” Launey said. “Investigators would also need a description of what initially failed — a pile, couple piles, a line of piles, if it was the piling.”
He said another possible factor was the spacing and depth of the piles.
Launey said if real long, massive piles are used, not as many are needed. But if shorter piles are utilized, they have to be placed closer together.
After reading plans of the site, he said the piles are spaced 15 feet, 10 inches by 12 feet, 3 inches apart in a grid pattern.
McManis also said the soil could possibly have played a major role in the structural failure.
“The spacing would not give you heartburn … because it depends on the soil,” he said. “You go to one soil grouping and it may be perfect, timber or concrete, but in another soil, it could be way under-designed and fail. Offhand, I don’t like saying it was too little without knowing the soil composition.”
Launey also took a look at the fireplace location at the front of the building and agreed with McManis that the load could have contributed to the failure.
“The fireplace may be something to be investigated further,” he said. “If we were looking at that, we would look at loads, how they were distributed over pilings and what the soil guy recommended and what was actually done during construction.”
To repair the building, Launey said contractors can come in and put in additional piles by punching through the building or using augur piles to drill in and start jacking from that on one end and work inward toward the rest of the structure.
He added the process could be very expensive.