Measurand's SAAV Extend allows for continuous deformation monitoring during the raising of tailings dams. It utilizes an initial SAAV Extend base array and top assembly, plus additional SAAV Extend lift extension segments to extend the casing as required.
Figure 1: Typical SAAV Extend Installation Steps
The main consideration for extending the casing is ensuring that there is sufficient casing stickup to allow access to the top assembly connection during future dam lift operations. If the required casing stickup is not maintained, manual excavation or ShapeArray reinstallation may be required. The required casing stickup can be reduced by minimizing the length of fiberglass extension used.
Determining SAAV Extend Base Array Length
Before doing the preliminary installation of the SAAV Extend base array, it is extremely important to properly determine the proper instrument length. This will ensure extending the casing and the instrument in the future, when a dam lift is performed, will go smoothly. To determine the SAAV Base Array length, you must know a few very specific details about the installation. These details are described and illustrated in the figure below.
- Total Casing Length (TCL) - the length of casing including any casing sticking up above the ground
- In-Ground Casing Length (IGCL) - the overall casing length less the casing stick up
- Instrument Stick-Up (ISU) - the distance between the uppermost joint above the ground and the ground surface (N.B. minimum instrument stick-up to should be 485 mm or 19".)
- Casing Stick-Up (CSU) - the length from the top of the casing to the ground surface
NOTE: It is very important to verify these measurements prior to ordering your SAAV Extend base array.
Figure 2. Required preliminary installation details
To properly calculate the length of the SAAV Extend base array required for the preliminary installation, take the following actions.
1. Measure the Total Casing Length (TCL), and the Casing Stick-Up (CSU).
NOTE: CSU will need to be at least 520 mm (20.5") greater than the ISU to allow for compression and a minimum length of fibreglass extension tube of 150 mm (6").
2. Determine the In-Ground Casing Length (IGCL) by subtracting the Total Casing Length (TCL) from the Casing Stick-Up (CSU): IGCL = TCL - CSU.
3. Determine the number of segments for the proposed instrument length by rounding up the result from step 2 to the nearest full segment length.
For example, if the IGCL is 20.3 m, you would need to consider a 20.5 m (41 segments) SAAV Extend with 500 mm segments or a 20.74 m (34 segments) SAAV Extend with 610 mm segments.
4. Determine the expected compression by using packing information below and the number of segments for the proposed instrument length calculated in step 3.
- SAAV Extend 500
- Packing in 70 mm inclinometer casing 1.9 mm/segment
- Packing in 85 mm inclinometer casing 3.3 mm/segment
- SAAV Extend 610
- Packing in 70 mm inclinometer casing 1.5 mm/segment
- Packing in 85 mm inclinometer casing 2.6 mm/segment
5. Subtract the expected compression from step 4 from the proposed instrument length calculated in step 3.
6. Calculate the Instrument Stick-Up (ISU) by subtracting the compressed instrument length calculated in step 5 from the In-Ground Casing Length (IGCL) calculated in step 2 (ISU = Instrumented length - IGCL).
7. Compare the result of step 6 with the minimum Instrument Stick-Up (ISU) which is 485 mm (19”). If the result is less than 485 mm (19”), add segments to the proposed instrument length to reach the minimum instrument stick up and then repeat steps 4 to 7 until ISU is equal to or greater than 485 mm (19”).
NOTE: Casing stick-up will need to be at least 520 mm (20.5") greater than the ISU to allow for compression and a minimum fibreglass extension tube length of 150 mm (6").
If the casing is too shallow for the purchased SAAV Extend, it can be extended and a berm installed to access the top of the new casing. If there is a Silent Segment assembly on the SAAV Extend far end, there would be an opportunity to remove or shorten the silent segment assembly length. Conversely, if the casing is too deep, a Silent Segment assembly can be added to the bottom of the SAAV Extend.
Once you have determined the proper length for the SAAV Extend base array, you can install it in the same manner as a regular SAAV using the Casing Cap installation hardware or the Compression Clamp installation hardware.