Thursday, July 25, 2013

Florida Sinkholes and a Possible Cause

I'm not an Engineer or a soil expert, I'm a resident of a sinkhole state - Florida. What's so unique about Florida and why there are so many sinkholes here? That's something a professional geologist could explain in probably 10,000 words or less, maybe more. Here are the basics as I understand them.

1. Florida is a giant peninsular of sand, underground water, and limestone. Under the sand lies the great depth of limestone with large aquifers of drinking water interspersed around the entire state, some areas larger than others, much larger.

2. Florida, in the last 15+ years has seen extensive shifts in the underground water tables due to drought that reduces the table and hurricanes along with other more 'normal' weather that serve top raise the tables.

What does this mean in layman's terms? I'm sure there's a difficult answer but I'm going to cut through the chaff and give the simplest answer - subterranean erosion! When the water tables are up there is a constant saturation of the limestone and the pressure of limestone and water make for a stable surface tension - no collapsing of the land. When the table raises and lower too frequently erosion of the limestone will occur as the water basically washes the limestone to the bottom of the aquifer and thins the sides and top of the 'bubble' that used to be contained with water and limestone together. To better provide a more visual example of this try to remember one of those Science Channel or Modern Marvel shows that show how a train, or subway, tunnel is created by hollowing out the soil under a city or whatever. The one thing you always see them do during construction is to constantly put reinforcement up to the roof of the tunnel being created with cement and steel bars. Why? It's because when you hollow out underneath supportive soil you weaken it to the point of collapse. In a roundabout way, causing a man-made sinkhole when the roof finally collapses, which is inevitable and is guaranteed to happen! The further tunneling will cause ground vibrations that will coax the soil to loosen and collapse. True? Let me apply this to Florida's sinkhole problem then. Florida had a home building boom several decades ago when things were pretty stable, weather wise, and the ground soil was pretty stable as well with water tables at normal levels with limestone and water existing in perfect harmony. Changes to the soil went pretty much unnoticed underground due to the stable structure of the supporting matrix of liquid and solid. What I'm going to express next is based on what I've seen and heard that have brought me to my conclusion of this circumstance, strictly my opinion of what I believe to be true and worth noting for home construction and after market construction purposes.

This is what I'm seeing and hearing but nobody seems to be admitting.

1. Homes built (with or without pools) PRIOR to the last big drought seem to be at the lowest risk from the majority of sinkholes unless the house is in the proximity of new construction, either housing or business,

2. Homes built during, or after, the drought appear to be at the highest risk for sinkhole effects (with or without pools),

3. Homes built (without pools) PRIOR to last big drought that have constructed pools AFTER the end of the drought appear to have a significantly higher risk of developing a sinkhole.

What hypothesis did I end up with given these points? In my opinion, houses built when the aquifers were 'normal' appear to be at little, if any, risk of developing a sinkhole on or around their property unless heavy equipment construction has taken place within a close vicinity of that property. The reason being is that the limestone under the house has, if a bubble did indeed exist on that spot, remained stable due to the lack of a catalyst effecting the stability of the soil, thereby not disturbing the 'shell' under the house. Adding a pool after the drought in turn will disturb the tension of the under lying soil and potentially cause a collapse of the once rigid structure underground. In a given example imagine putting a 5lb weight on an egg and walking away. What happens to the egg? Nothing, because the structure is stable, What happens to the egg with the weight when you hit it with a hard object on the side? The weight will collapse in on the egg! Why? You've effected the stability and tension of the bubble(shell) and the load bearing ability of it will be destroyed. It's a simplistic example but easy to picture in ones mind. The most likely suspects that will effect this damage are the vibration, impact, and subsequent weight applied to the ground with the heavy equipment and tons of cement applied to the soil that were never there before when the ground was stable. New home construction after the drought, with or without a pool is irrelevant, is more likely to result in a later sinkhole if there is a significant underground void on that site. The aforementioned equipment and aggregate weight would be a contributing factor in the destabilization of the subterranean structure where a void existed or limestone decomposition has already occurred where the return of water counter pressure is no longer a factor in the soil stability, making a lower risk area into a higher risk home site.

One possible band-aid may be to utilize ground penetrating radar to determine if a building site is at risk for a sinkhole by ascertaining, through scientific means, the detection of a nearby void. It's not rocket science but it's better than watching your worldly possessions get swallowed into a giant hole in the ground.

As I've stated above, I've come to these conclusion while living amongst sinkholes and seeing the properties that have been effected and what's different about them from sinkhole to sinkhole. These are my opinions and I think that I'm pretty close to being on the mark with the conclusions I've made. Older homes with or without original construction pools don't seem to get hit as often as homes adding pools to older homes or new homes being built, with or without pools.

Please leave your opinions to my article as I like to hear from people that have additional contributing data.

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