Tuesday, October 5, 2010


The bentonitic mudstone underlying most of the Quarry Visitor Center has played havoc with the building for half a century. While a great deal of design and work has gone into assuring that this will not be a problem for the new building, there is still the problem of fixing the damage already done.

 One of the most serious involves the series of vertical I-beams that will form the south wall of the redone QVC. The heaving of the bentonite pushed the beams upwards various amounts.

 One of the most instructive examples involves the two beams at the east end of the building. Here one can see the once horizontal beam sloping upwards. The horizontal and vertical beams are still attached ---- one is not sliding past the other. What has happened is that the beam on the right has been pushed upwards 8 inches! The red line marks horizontal and the original position of the beam.

Although this is the most extreme example, all of the 10 beams have moved upwards or downwards various distances. The problem is how to get the bases of all these beams at the same level, then installing larger and deeper footers for each, in order to provide stability for the new building.

First a baseline level is determined. The bases of all beams will be adjusted to that level. As we’ve seen in previous posts, a steel frame box is temporarily attached to the beam. Then the existing footer is excavated and removed. Now comes the cool part.

How can one adjust the height of a 50-foot tall steel I-beam that is part of the steel skeleton of a building? The Mat Jack is a thick rubberized pad that can be inflated with a compressor. The one used at dinosaur can be inflated up to 11 inches in thickness and lift a weight of up to 70 tons.

The flattened mat is placed under wooden blocks at the ends of the steel frame boxes and then slowly inflated. By monitoring the base of the beam relative to the established baseline, it can be finely adjusted until it lines up with that baseline.

 At that point the steel frame box is blocked up with wood, the mat deflated, and the process repeated on the other side of the steel frame box.

Once both sides are blocked up, the beam can be attached to the new reinforced concrete footers that are themselves attached to the 70 foot deep micropilings. Now the I-beam should be solidly anchored.

This process is repeated for each of the 10 I-beams on the south side of the building. This is a slow process, taking many weeks, but it is remarkable to watch the fine adjustments made with the Mat Jack as it lifts and supports the weight of the building. Victoria’s Secret must be green with envy.

Once completed, the building will be the most stable it has been since it was built in 1957. If it isn’t, well we can all blame this guy -----

Photos: NPS

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