Our engineering team at Measurand spends a lot of time improving and revising our software and manuals and providing what we hope is outstanding support for our products. For SAAF, and for many other geotechnical instruments, installation details are key to success of monitoring programs.
The following is a short list of installation concerns that will greatly increase the success of incorporating SAAF into your monitoring program. These items frequently arise as causes when we hear from customers about issues with data, or that we see in some installation photos. All of the information in the list can be obtained in the SAAF manual.
For those planning to install SAAF, we hope this list will provide a good synopsis of some common installation and pre-installation planning faults that can be avoided. It should be used in conjunction with the information presented in the SAAF manual.
1. Ensure conduit with the correct inside diameter (ID) is being used
Use 27 mm ID PVC for all vertical or convergence installations. Such conduit is available either as electrical conduit (mainly in North America), or as fluid tubing in many other countries. Contact Measurand for assistance in locating the correct conduit.
For more information, refer to the following documentation:
2. Ensure the SAAF is not twisted when un-reeling
When installing in a vertical conduit, as a first choice, use the SAA+PVC
method. Pull the SAAF into PVC, check that the X-marks at two ends of the ShapeArray point the same way, then install PVC with ShapeArray inside into the borehole, maintaining at least 3.5 m radius of curvature.
If that is not possible, grout the conduit into a borehole ensuring it is straight. Then unreel from top of reel into borehole, allowing SAAF to rotate freely about its long axis.
Keep the path of the SAAF short and do not bend joints more than 45 degrees. Whenever the SAAF is inserted into a conduit, allow it to rotate freely about its long axis. Anything else can result in twist.
3. The reel dots are not aligned after installation
The dots on the SAAF show that it is properly stored on the reel. They are NOT the same as X-marks, which show the bearing of the SAAF after unreeling. When unreeling, the SAAF should be allowed to rotate freely about its long axis. It will naturally rotate a bit during this operation, and should be allowed to do so. The rotation will result in the reel marks pointing at different bearings. All the X-marks (at a minimum, there is an X-mark at the near and far end of each ShapeArray) should end up pointing to the same bearing. The dots should not! When an SAAF is reeled back up on its reel, it should be arranged to go back on the same way it came off, with the reel dots all facing out when the process is done. This should not require any forcing.
4. The azimuth of the X-mark on an SAAF should only be changed in software
Install the SAAF into its conduit with its X-mark at an arbitrary azimuth. Refer to the Pulling the ShapeArray into the PVC Conduit section of the SAAF manual for more information. Then, use the Measurand protractor, provided with each SAAF, to sight its azimuth offset. Follow the SAA X-Mark Protractor guide for detailed instructions. Enter this azimuth offset into the software. Do not lift the SAAF to adjust the alignment of the instrument. Any lifting and turning is likely to introduce twist!
5. Install SAAF flush with or below the ground surface
Whenever possible, SAAF and any conduit should be finished off below ground level. Use a utility vault to provide room and reduce coupling between ground movements, such as frost heaves, and the SAAF installation. Any projections above ground level can become sources of rotation for the SAAF within its conduit. If you must have some of the SAAF or its PEX project above ground level, use a well head in such a way that subsequent movements of the well head cannot move the SAAF or PEX. Consider and prepare for the effects of frost and settlement!
For more information, refer to the following documentation:
6. Ensure the borehole is deep enough to accommodate the entire length of the SAAF
Many problems arise from an SAAF or its PEX projecting above ground level. Consider over-drilling if that is possible. It is always possible to hang the SAA+PVC assembly in the hole and fill any excess space beneath the SAAF conduit with grout.
7. Secure the SAAF at the cable end
Use the Measurand SAA Install Kit with two screws to secure the SAAF to the conduit. If left unsecured, the SAAF can rotate within its conduit, which can produce data that looks like deformation, but is simply rotation. The erroneous-data problem increases with slant of the SAAF away from vertical. It is possible to correct most rotations using the anti-rotation algorithm in software, but it is better to minimize it mechanically first.
Although it is possible to use saw cuts and clamps to fasten an SAAF at the top of the conduit, our testing has shown that a Measurand Install Kit with two set screws will prevent rotation and maintain axial compression better than saw cuts and clamps.
8. Be aware that blasting can rotate an SAAF
When blasting is expected, ensure that the SAAF is secured really well. That means an SAA Install Kit and two or more screws tightened thoroughly. Be careful not to strip the tapped holes by over-tightening the screws.
9. Ensure conduit remains straight in the borehole
It is important that the conduit be grouted in straight if the SAAF is to be installed after grouting the conduit. There are several methods outlined in the SAAF manual. One of the most common mistakes in attempting to maintain straightness is to put a weight on the top of the conduit and allow it to float up against the weight during curing of the grout. This causes the conduit to push up against the weight creating s-curves in the conduit.
10. Properly plan installations where the conduit will be installed on the side of inclinometer casing
27 mm ID PVC conduit may be taped to inclinometer casing using due care. Use shims between the conduit and the casing to take up the space created by the conduit couplings. Do not place the top of the conduit so that subsequent manual inclinometer readings require moving the conduit in any way. Observe the precautions about avoiding waviness of the conduit due to conduit floating in grout. See the ShapeArray Conduit: How Stiff?
section of the ShapeArray Conduit Considerations
section of the SAAF manual for more information. The tape will not hold it straight if a weight is placed on top to keep the conduit down.
11. Ensure conduit is free of water before pushing an SAAF into it
Pushing an SAAF into a tight conduit that has water in it can raise the water pressure beyond the rated pressure-proofing of the SAAF and cause a leak in the SAAF coverings. Remove the water first using a tremmie pump or compressed air.
You can make a pump by putting a constriction at the far end of a small (e.g. 3/8” ID) tube. The constriction can be a hole in a piece of tape. Insert the tube to the bottom, wait for it to fill, pull the tube out rapidly and empty it.
To clear water with compressed air, insert a tube to the bottom and blast the water out. If some water remains in the bottom, insert the SAAF very slowly near the bottom. Please observe all safety precautions when using compressed air.
12. Ensure that water cannot freeze within the conduit
If water has somehow entered the conduit after installation of the SAAF, steps must be taken to ensure that the water does not freeze. Water freezing within the conduit can cause pressures that greatly exceed the tolerances of the SAAF which can lead to damage to the instrument. Consult local guidelines for antifreeze before installation.
13. Ensure PVC cement appropriate to the installation environment's temperature is used
In cold weather, use cold-rated PVC cement to connect pieces of conduit.
For more information refer to the following documentation:
14. Be aware that SAAF can be damaged by lightning
Use a Measurand SAA Surge Protection Device (SAASPD) near the cable end of the SAAF, which may be far from the logger station. An SAA232 or SAA232-5 at the logger station provides some protection for the logger, but not much for the SAAF. Lightning protection should be close to the SAAF. Use an SAASPD to minimize the chances of destruction by nearby lightning strikes. For more information, see ShapeArray Lightening Protection.
15. Ensure SAAF is connected directly to the power source
We recommend that you power the SAAF directly from a 12 V power source, such as a battery, without going through the data logger. The current being drawn by the SAAF can overwhelm the logger's ability to provide power. This can lead to bad readings being recorded by the logger as the SAAF is not receiving appropriate power. We recommend connecting the red and black wires from the SAA232 or SAA232-5 directly to the power source instead of a logger's 12 V and G terminals.