PennDOT, I'm Sorry

I was involved on-and-off in the earthwork operations of a large building expansion site in Roxbury this summer. A huge trucking distribution center was expanding its existing building and putting up a new one next to it. The earthwork involved was almost a perfectly balanced cut-and-fill situation straight from a geotech textbook. The area under construction was the slope of a hill, with the bottom half being below grade and the upper half being above grade. Solution: Move top half of hill to bottom half of hill, creating level building pad.

In cutting the upper part of the hill, the contractor generated massive amounts of boulders. They can't use boulders as structural fill, so they brought a crusher onto site for a few weeks and before long, they had turned un-usable boulders into gravel they could use as retaining wall backfill. In paying a little extra to operate the crusher and transport the new gravel, they probably made out like bandits by not having to pay to truck boulders off site and then pay to truck gravel in. The eliminated the middle man (the quarry) and came out smelling like roses.

This is common practice for such a situation since it makes sense and is to the advantage of most everyone involved. However, it got me thinking...

What do they do in areas like the Lehigh Valley, where the parent bedrock is limestone? Do they re-use limestone?


*We've come to the part of this entry where Scott has succesfully built a 'stop'--a point where the reader will have to stop to wonder, "Why would the re-use of limestone be a problem, Scott? Tell us, tell us!" This is what we in the business call a captured audience.*


Limestone is a geotechnical concern because many types of limestone are dissolvable in water. You've probably seen a picture of a sinkhole. Maybe your uncle Phil lost his Audi into a sinkhole when one opened up in his driveway. They look like imploded crater holes.

Sinkholes occur where water seeps into the subsoil, ponds on a section of limestone, and essentially causes the limestone to vanish. This happens so gradually over time that often the soils will retain enough of their strength so as to make the dissolving to be practically imperceptible until failure. On the surface, the roadway or farmer's field looks normal until one morning uncle Phil can't drive to work and farmer Maurice can't harvest any corn from his field.

Limestone, therefore, would be a problem to re-use as structural fill because the life expectancy of a subgrade prepared with limestone--particularly one close to the surface or near the groundwater table--would be significantly reduced.

So, getting to the apology, eventually...

Only a measly ten miles of the entire PA section of I-80 widens to five lanes across; the other 352 miles is only four lanes. The New Jersey part of I-80, by comparison, has only ten miles of four-lane highway; the rest is six or more! New Jersey's interstates are it's pride and joy (which is helpful since seemingly half of the ground cover of the greater Newark area is interstate) and are a smooth ride almost anywhere. In Pennsylvania, I have always complained, a driver is hard pressed to find a stretch of one mile without a pothole or 100 miles without construction.

Well, PennDOT, it seems I was too quick to pass judgment. For years I have bad-mouthed you and scoffed at your inability to maintain your sorry excuse for an interstate highway system. I always assumed that your highway design engineers were a rag tag bunch of buffoons who didn't know DGA from a DCP. It turns out, you're not bad engineers, after all--you're just good businessmen and inconsiderate of your state's drivers.

You know about limestone's susceptibility to decay over time and yet that hasn't stopped you from using crushed limestone as your roadbase. You didn't see the need to spend millions of taxpayers' dollars on importing costs when you had all the subbase material you needed right in your own backyard. Instead of bringing in clean stone from another state, you simply paid your local Tom, Dick, and Harry Pennsylvanian to give you cheap processed limestone for your roads. You save millions of dollars, and instead figure you'd just spend a portion of the fortune you saved by employing Frank, Joe, and Larry road crewman to repair the roads that always go bad because they're paved on limestone subbase and limestone dissolves in water!


Engineering school prepared me to think like an engineer (innocent as a dove), but a year of working for an engineering firm has taught me to think like a businessman (wise as a serpent). Engineers design in a perfect world, and they are driven by fear of failure. This is how we get the reputation of being out of touch and unrealistic. Businessmen live and breathe in the real world and they are driven by the bottom line. This is how they get the reputation of being ruthless and sacrificial when it comes to quality.

Any good engineering solution needs to be driven by both quality and practicality. PennDOT, in my opinion, has sacrificed quality for the bottom line. They have paved their roads with a material that dissolves in water, all for the sake of a little green.