We were setup on a lock wall this week, over a control point, with a Crain tripod, Trimble tribrach (no optical plummet), adapter, and seco mini prism. The point is adjacent to the lock chamber, which is 720' long, 56' wide, and about 30' deep. The lock was dewatered for repairs, and we were checking the wall monoliths for movement (6 mm tolerance). We were setup in the middle of the opposite wall with the S6. The tripod with prism was straddling a wire safety barrier about 3' high.
All of a sudden, a strong wind whipped up, and we took cover. When we came back out, put the gun back on, and turned to the backsight, there was no backsight. At first we thought someone took it (there are construction surveyors working there as well on a long term project). We walked over, and what happened was that it got picked up by the wind, slammed against the opposite vertical concrete wall 60' away, and crashed to the bottom of the lock chamber.
Amazingly, the tripod was UNDAMAGED. The tribrach was split, can't get the adapter out of it, but the prism is pretty much OK, just the threads sticking out of the top are beaten up.
I would have thought the tripod would be the first to break.
some pics from the project
Here are some pics I took this morning while I was there doing a follow-up survey.
Downstream gate sill with pump and gate in background:
View looking upstream in dewatered chamber. Struts are temporary support for walls during dewatering:
Downstream needle dam (bulkhead) with 20" pump on left (steel pipe) and two smaller pumps at the top.
Another view looking upstream from middle wall. Rectangular openings at base of wall are for filling the chamber
Monitoring pin with prism
Looking downstream. Tripod was on top of wall on the right, and impacted the wall on the left about 1/2 way down.
Upstream gate sill, with gates removed, needle dam in background. One thing I had to do today was shoot the top of steel beam which will be the new gate sill
Looking downstream, you can see the normal water line on the wall. The gizmo on the right is a butterfly valve for the filling conduits below
From moving in to finishing up is about two weeks total, they expedited it since there is only a single lock chamber here (second one was closed years ago, and a new chamber is U/C), and the river traffic is shut down during the repairs.
Trimax is a real man's tripod.
Some don't like the weight but it has a handle which makes it easy to carry combined with the lack of aggravation in using it. I even prefer it in a rough forest environment although I have to carry it. Weight is not the only consideration for me.
I have 5 in the truck. I took off the shoulder straps, head caps and slip out straps and stored them away so we don't have to fight that stuff when using the tripods. Also the plumb bob hooks.