Sunday, May 6, 2001 10:47 AM
How do the builders of coaster know EXACTLY where to pour the footers? If they are even off my an inch, the support wont line up. So how do they accomplish this? A protractor and directions? lol
SROS at SFNE, the #1 steelie
Sunday, May 6, 2001 11:07 AM
It all starts off with careful design of the entire coaster so that the exact location that the footers need to be at is known. Then careful surveying is used to position the footers exactly where they are needed. Good surveying can place footers accurately to within 1/4" over a coaster which is actually less variation in location than what will occur from the expansion and contraction of the coaster with temperature.
There is usually more error in the pouring of the concrete and the positioning of the anchor bolts than in the actual surveying. Anchor bolts are often installed in sleeves which allow them to be adjusted slightly until they are grouted. Small vertical adjustments are also taken care of by grout under the baseplates. If necessary, baseplate holes can also be adjusted, but at that point, the project engineer isn't happy.
Lots of fancy laser equipment is used in modern surveying, but for most practical purposes it just makes the work faster and more economical rather than more accurate.
A job like the channel tunnel is a real surveying challenge. Tunneling from both directions the tunnels had to meet to within a few inches after miles of cutting through the earth.