I was living in Saigon working at Tan Sun Nhut airport. I was as happy as a flea on a fat, furry dog. Saigon was a great town.
Then they sent me to Nha Trang because there was a problem. Nha Trang was about halfway up the coast between Saigon and Da Nang. To call it a “problem” was an understatement.
They were building a parking apron at the Nha Trang airport. It was 150 meters wide by 300 meters long (to the best of my memory). After they put down and compacted their base rock and added a seal coat (a coat of heavy oil) they had a rain and discovered it didn’t drain. They sent me to fix it.
The American engineering staff had disappeared. The OICC (Officer in Charge of Construction) didn’t have a clue as to what had caused the problem. Finally, the Vietnamese surveyor told me the crown of the parking apron had been lowered two meters to save base rock. The job had been completed a month ahead of schedule but the apron was flat. Two meters of crown was the entire slope in the design. They told me to fix it. It seemed impossible. How the frack do you drain a flat apron?
My first idea was to scarify the surface and blend in some base rock to give it some sort of a crown, even if not all the designer intended.
That was objected to by everyone. I think there was an embarrassment quotient involved such as completion reports and payments. Some people were stressed out.
“You will fix what is there,” I was told.
I had no idea how to do it until I started talking to the paving superintendent. This guy, it turned out, was super-competent. We were supposed to put a 10 Cm (4 inch) layer of asphalt (also called black top or tarmac) down as the final surface of the apron. The superintendent explained how he could vary the layer depth so maybe, if we could find existing swales, we could increase improve on them.
Base rock can never be laid completely flat, even if that were the design. That’s why they put in a large crown to drain it, so uneven areas of the base won’t matter. It was worth a shot so I painted dots on the parking apron in 5 meter intervals, the width of the paving machine (12 ft.) apart. Each dot had a letter and number. That gave us nearly 2000 points. We shot elevations on them. Then I made a contour map with a one Cm interval.
Now some people are gifted at one thing and some at another. I must confess that, as a lifetime engineer and surveyor, directions confuse me. I cannot get off the Bangkok subway and go up the reversing escalators without getting totally disoriented.
Ah, but contour maps are another thing. The making of those things was one of the gifts bestowed on me. When I went through surveying school, I did the maps for the entire class of 12.
So I did a contour map of the apron and found a few windows. The cross-sections and the contour map showed up swales and high spots. Following the instructions of the paving superintendent, on each point on the apron we painted the thickness of pavement needed accentuate the tiny slope. We worked closely together during the paving.
The test came at the first rain after completion. Except for a “bird bath” or two, it drained.
We didn’t say a word; we just looked at each other. No one would ever know the miracle we had performed. We had drained a flat parking apron.