I am off tomorrow to help an NJ surveyor set control points in streets to monitor a slope failure from the recent storm that wiped out two dwellings and is threatening more. A second parallel street appears to be moving so whether this is for further monitoring or just damage assessment is uncertain. I understand it to be Mag nails on centerlines near and far side of damage area, both streets. This surveyor has surveyed some of the lots in the area so eventually that may tie into the assessment of movement.
He was unable to tell me what routes to the site or his office would be available tomorrow. He did ask me to bring some specific equipment.
Any experience out there on such work?
Paul in PA
Set control in stable ground. In my opinion, nothing stays exactly where it is placed. I feel using a GOOD total station can be used to obtain XYZ movement simultaneously. Set reflective control points on guide rails, trees, conc walls. (a little contact cement rubbed into the surface first and let dry helps reflective sheet stick better) with aid of some screws, etc., then resect yourself in. Setups are usually within several thousandth's. If you have to set control in slope to monitor, I would use at least 3' long rebar in concrete. Be consistent with the way you do everything(i.e holding the prism). Weather plays an important part in movement. After a rain, you may find that your monitoring points might rise depending where they are located in the slide. Get a weather monitor to input temp/pressure.
Control in stable ground is big. Then you will want some control a little further away to verify the control you will use to monitor movement. The first step when we perform structural deformation surveys on dams and levees is to check the control that will be used to monitor the SDM's.
20 Control Points Today
That is a lot of sets, plus two sets to 2 found Mags from prior surveys in the area, plus 4 front corner pins. Tomorrow we find out what else they want located, especially at the bottom of the debris field. There is at least 3 feet of dirt on the lower road, plus a septic tank. Under the debris are prior surveyed rear corners and some prior control points. I hope they try to recover the cars under the one hose. It appears they will demolish 2 houses tomorrow. A small cottage sits on it's front foundation wall and the brand new rear deck stairs are holding up the back of the house, the basement is gone and about 8 feet of dirt below the basement. I forgot to take my camera. These are typical lakeside cottages on a hillside above the lake. Some of the hillside made it across the beach to the lake damaging a vacant bar.
While setting a traverse control tie check point (mag nail in a tree root), the other surveyor stirred up ground wasps. He took 12 hits, I took six. First I got out the "Sting Eaze" applicator (10"% benzocaine), getting little relief I broke a vial of 20% benzocaine. The other surveyor started with baking soda (6 stings on the back of his neck) and a serving of benedryl and then broke out a vial of 20% benzcaine. Two weeks ago he took about a 1/2 dozen stings after digging out a pipe. I had my new "Sting Eaze" and we resupplied the vials on the way back to the office. Probably the most dangerous critters in the woods. I just took two benedryls.
Paul in PA
I would also reccommend trying to site on objects that are away from the project area that you can get a good angle measurement on, like a church tower or water tower or electrical transmission tower. It would tell you if any of your control is moving.