Thursday, July 20, 2006

Karst - sinkholes and solution activity, naturally

Greetings.

I was looking through the computer files that I have amassed in various geological subject matter, and trenchless subject matter as well, determining how best to add to the blog. I happened to stumble across a number of photos dealing with karst.

Karst is a generic term describing the phenomena of limestone and dolomite rock dissolution over time to form sinkholes and caverns. The name 'karst' is from the former Yugoslav Karst Plateau region, an area loaded with sinkholes and caves. Karst occurs in the United States as well.

Several states are noted for the size and number of caves that they possess. New Mexico is one, with Carlsbad Caverns and Lechuguilla Cave, both within Carlsbad Caverns National Park. This is a wonderful park, and having been there, I can relate to you one fact that I know about the National Park Service, and the effort that they expend in preserving this national treasure. To make the cave accessible to all, including the disabled, they installed an asphalt walkway system. Later on, finding out that the asphalt oils were damaging the natural habitat of the cave, they decided to remove the asphalt and replace it with concrete sidewalks. Concrete is largely composed of limestone, so it was the only choice to not affect the sensitive natural habitat of a limestone cave.

Two states that vie for the title of "Most Caves" are Tennessee and Missouri. Missouri actually has billboards which read, "Missouri - The Cave State", though Tennessee has the greater number of caves. I've been in caves in both states, but now work in Missouri where I get to see a whole lot more with a clearer understanding as a geologist.

Karst topography, or the landscape produced by the terrain of caves and sinkholes, can be an engineering nightmare! Additional loads placed upon roofs of caves by highways and the vehicles that travel over them can cause collapse, and that's a BAD thing, especially when a car or truck might end up nose down in the bottom of a cavity. Part of my job as an engineering geologist is to characterize such features so that they don't affect civil engineered construction works.

Here's a photo of a sinkhole discovered during excavations for highway foundations on state Route 21 in Jefferson County, Missouri, to illustrate my point.


To effectively make this 'safe', you have to dig down into the 'throat' of the sinkhole, clean it out, and fill up the entire sink with concrete in successive 'lifts', until a firm foundation is established, one that will stand up to compaction. Then, you can fill it up the rest of the way with gravel or soil, compact it, and you're on your way again, building a highway right over it.

This is assuming, of course, that you haven't altered the natural drainage path of the groundwater, haven't affected airflow in a natural cave (important for bats and other cave critters, some endangered), or created a low spot in the landscape and filled up the only outlet from a 'bathtub'-type sinkhole. Then, you're talking about flooding, which is a whole new set of problems that you've just CREATED.

Engineering geology is a subset of the science that requires ethics - you have to think about how you affect others with what you do. Otherwise you may create more problems than you solve.

Until next time,

Trenchless Geologist

Tuesday, July 11, 2006

More Trenchless Thoughts - Part IV

One important note to those seeking to install or remediate utility product pipe is that all construction professionals should, where it's applicable, PAY the appropriate licensing fees to those people who have developed and patented a technology. It's the same thing as computer software. Somebody's BRAIN was used to develop a method, someone who is using the method should pay for using the method. If you install Windows XP on a computer, You pay a licensing fee to Microsoft when you buy the software.

The same thinking applies to trenchless methods. Until the pipe bursting patent licensed by British Gas expired last year, people were paying a charge, measured per foot and per inch of upgrade, to British Gas through the licensing authority, Advantica, Inc. The same thing is done for other methods, such as the Tenbusch Insertion Method, and the ArrowBore method. Copying the thinking behind a method can only get you into trouble. Substantial money has normally been spent in the development of such methods, it is only right for the patent holder or their licensing agency to be compensated for the privilege of using the method. Otherwise, the money spent in the development of the method is never regained.

Intellectual property rights. Respect them.

Until next time,

Trenchless Geologist