Road Repair -- work day two

It's the formerly busy intersection of Garfield Street and Golf Course Road in Midland, Texas, currently closed to traffic. City Engineer Rene Franks was kind enough to explain what happened in terms elementary enough that even I could understand.

There's good news, and there's bad news. First, the good news. The old pipe will be dug up in the intersection and replaced with new plastic pipe with a 50 year life expectancy. And the bad news? The intersection will probably be closed until after Thanksgiving. OK, we got that out of the way.

Ms. Franks provided a little history. There are some natural low spots in the area that have always accumulated rain water --maybe they were buffalo wallows. The city made these temporary reservoirs into parks, and drainage pipes were put under the streets so that the water could be pumped out of the parks.

But these 35 year old pipes developed problems in two ways.

The drainage pipes were coated with zinc which should prevent corrosion. However, a rock might enter the system and bounce along the bottom, nicking the zinc all along the way. Once the zinc was nicked, corrosion could occur. First a pin hole would develop, and the pressure of the draining water would create a jet of water which would eat away at the surrounding soil. The hole gets bigger, and water creates a cavern.

The other way, and the one which caused the most damage in this intersection, was a size mismatch in the drainage pipes. There's a water line crossing the spot where the drainage pipe was supposed to have been. And the original installers attempted to solve this problem by using a smaller diameter drain pipe in that spot to avoid having to move the water pipe. The smaller drain pipe was connected to the bigger drain pipe with an adapter. Eventually the adapter gave way, and a major soil erosion problem developed under the street producing a big cavern. But amazingly, a layer of caliche above the leak became so compacted that it formed a hard ceiling which prevented the street from collapsing into the cavern.

Ultimately, a small hole appeared at the surface, and that started this whole ball rolling.

P.S. The same thing happened a year ago at an intersection a mile West of this one. And there are drain pipe connections with the same type adapter all over the city.

Comments

[kabus]

thank you