Feb 112007
 

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It started raining Thursday night, and we’ve had a setback. Part of the rock behind the shoring wall has collapsed down below the wall, before we had a chance to get shotcrete over the excavated area.

The drilling and soil nail placement was completed on Thursday, but a nice big Pacific storm moved in. It rained for about 18 hours, and by a stroke of luck, one of the subcontractors visited the site early Friday morning and saw the collapse beginning. I came out and watched as a couple of yards of material came down and contributed to the pile. Quite a rumble. And heartbreaking to watch.

This is what it looked like this morning (Saturday), after the rain stopped. The rock on this side (the right, or south side) is very fractured, and Bob Settgast, our geotechnical engineer calls it “melange”. It breaks apart easily, and since we’ve excavated away the soil and rock around it, it’s been starting to fall apart. The shelf in the wall above this area is open to the weather, and our contractor did not put any weatherproofing (like plastic sheeting) over the exposed surface. The water rained right in, and apparently contributed to the mess. Here is the top side of the cave-in, the unprotected surface.

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Because the rock is no longer packed around the soil nails, this area of the wall is at risk of falling apart. The soil nails are not capable of holding the wall up, and this shotcrete does not contain any structural steel. So the subcontractor brought in 4×4 lumber, and put wooden shores up under the wall to help keep it up…just in case.

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By the way, this shows just how much over-excavation is happening. This whole area under the wall has to be filled in with concrete and rock!

 Posted by at 5:39 am

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