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 SAAX, 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 SAAX 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 SAAX manual.
For those planning to install SAAX, 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 SAAX manual.
1. Use the right size conduit for your installation conditions
For most installations, a 60 mm (2.375") outside diameter PVC pipe with 49 mm inside diameter (1.939") can be used for horizontal installations. This corresponds to a 2" schedule 80 trade dimension PVC pipe. If the live loading exceeds those seen for highway and rail traffic (Railway E80 load), you will need to check that the PVC pipe selected can withstand the live loads. Similarly, if the depth of burial exceeds 40 m, you will need to ensure that the PVC pipe can withstand the earth loads. A discussion on the calculation of the PVC pipe deflection can be found in Sample Calculations for Pipe Deflection in Horizontal Installations.
2. Secure the SAAX inside the casing
Either end of the SAAX may be used as the reference end in horizontal installations. The SAAX should be secured at one end of the conduit, but never at both. There should be at least 25 mm (1”) of room at the unsecured end. These measures prevent rotation, and allow for some expansion and contraction of both the SAAX and PVC.
3. Ensure that water cannot freeze within the conduit
If water has somehow entered the conduit after installation of the SAAX, 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 SAAX which can lead to damage to the instrument. Consult local guidelines for antifreeze before installation.
4. Ensure a portion of the SAAX is in stable ground, or use survey techniques to obtain global settlement values
If both ends of the SAAX are inside the settlement zone, then the SAAX will only return relative settlement along its length. Use a survey marker placed at the reference end of the SAAX in order to determine the global settlement values. In order to get proper corrections, ensure the marker is associated with a known location along the sensorized portion of the SAAX.
5. Be aware that SAAX can be damaged by lightning
When an SAAX has a long cable, energy from a nearby lightning strike can induce electromagnetic forces along the SAAX cable. Use a Measurand SAA Surge Protection Device (SAASPD) near the top of the SAAX with long cables to protect it from these surges. An SAA232 or SAA232-5 at the logger station provides some protection for the logger. Using an SAASPD will minimize the chances of destruction by nearby lightning strikes. For more information, see ShapeArray™ Lightening Protection.
6. Ensure SAAX is connected directly to the power source
When logging with Campbell Scientific data loggers via a Measurand SAA232 or SAA232-5 interface, we recommend that you power the SAAX directly from a 12 V power source, such as a battery, without going through the data logger. The current being drawn by the SAAX can overwhelm the logger's ability to provide power under some circumstances. This can lead to bad readings being recorded by the logger as the SAAX 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.