Control For Monitoring

[sireath]

What do you mean monitor piles? What we normally do for piles is to stake out the positions for them to pile and pick up the eccentricity of the piles. During the piling phase, no one is near the rigs for safety reasons as well.

i do a mixture of ground control points and also if there are buildings near by would put reflector sheets on them to perform resections. I use at least 3 stations to get a good fix and I know of people who just uses 2 stations and I am uncomfortable with the residuals for it.

[roadhand]

sireath, post: 352402, member: 9370 wrote: .. I know of people who just uses 2 stations and I am uncomfortable with the residuals for it.

Wouldn’t a 2 point resections residuals look good, even if they are wrong?

[RADAR]

Roadhand, post: 352405, member: 61 wrote: Wouldn’t a 2 point resections residuals look good, even if they are wrong?

Not necessarily; if the distance between the 2 points was wrong, the angle and distances you measured would catch it. The direction between the 2 points would swing where ever the coordinates took it though.

Dougie

---

I hope everyone has a great day; I know I will!

[ken]

I use Carlson survce with a two point resection to targets with a tie out to a third for a check, using forward-reverse vertical. Always get great residuals. Just make sure you pick solid target locations! Some sites aren’t conducive to this method if you don’t have buildings away from construction and at good angles.

[squowse]

standing on the corner, post: 352346, member: 8561 wrote: Just got a request to monitor piles in an active construction site. The way this project is phased, there is no location where we can set ground control that will remain undisturbed throughout the duration of the required monitoring.

I am interested in what you guys are using to set control. Are you using permanent targets (reflective sheets) and resect in every day? What have you tried and later regretted?

We will be using a 2″ S7.

another option for your control would be to use Leica circular prisms on spigots mounted either horizontally or vertically. These can then be angled to face the total station. This gives more flexibility if you need to vary your position , for example to tighten up the network with multiple observation positions. It can be possible to set up over a vertical spigot as well.

I’m assuming the piles are forming a retaining wall and will lean as it is excavated on one side.

[Mike Falk]

Using two points for resection would give two solutions.
Using three points for resection would give one solution.
Using four points for resection would give one solution with a check.

[squowse]

Mike Falk, post: 352460, member: 442 wrote: Using two points for resection would give two solutions.
Using three points for resection would give one solution.
Using four points for resection would give one solution with a check.

These days most “resections” are what used to be called “freestation”. Using angles and distances so I don’t think the above (based on distance only resection) is quite true for most users.
The more the merrier when it comes to resection (freestation) observations. Our subcontractor at the moment regularly uses 6-7 retro targets for his setup.

[chris-mills]

The suggestion by Squowse is a good one.

I’ve used mini glass prisms in the same way, mounted onto angle brackets bolted to structures a 100 metres or more away from the working area and high enough not to be obscured too often. A 5/8″ bolt through the bracket base holds the prism in general alignment with the working area. With four of these you can usually be sure of seeing at least 3, which not only gives you a check but enables you to determine which one is out if they don’t agree.

Remember to calibrate the total station against the prisms first, to determine exactly what prism constant needs to be used (and to check that they are all the same).

If you need to record data while driving stick multiple targets on the upper part of the pile and label them so you know which one you are observing. in most cases there will be a pause in driving when you can recover those then in reach of the ground (stick them on backing sheets which are taped to the pile, so they can be re-used).

Gone are the days when we used to crouch under the piling gate marking a card with a pencil trace to determine the temporary compression.

[u1011919]

If you think the control may move during the duration – it may pay to setup a Network.
By running the network with multiple stations + monitoring points through Star*net you will still be able to retain relative movement.

I would do this initially in most cases and then Station setup and check as shown in pic.

Attached files

[standing-on-the-corner]

Thanks all-

Looks like we will be setting 2 temporary stations at the piles, setting 8 reflective sheet targets visible from each station, and creating a network and running everything through star-net twice a week.