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.
Installation of SAAV Extend Base Array
The initial SAAV Extend base array is installed using the standard SAAV with Springbox installation method. It is not required to record the fiberglass extension cut length as this can be read off the scale on the side of the extension tube.
As an initial step, it’s important to plan the casing and ShapeArray lengths to obtain a minimum casing stickup of between 1 m to 1.5 m. You should allow for SAAV cyclical installation compression of approximately 0.8% into an 85 mm casing and 0.5% into a 70 mm casing.
To begin, measure the depth from the bottom of the casing to the top lip to get the total casing length (TCL). Measure the casing stickup amount from the ground surface to the top lip of the casing and subtract this value from the TCL to get the “In Ground Casing Length”. Multiply the In Ground Casing Length by the cyclical compression factor (1.008 or 1.005, depending on the casing size) and add 0.5 m. Round this amount up to the nearest 0.5 m. This is the SAAV Extend “sensorized length.” The added 0.5 m will ensure that the connector is accessible above ground and allow room for a casing repair coupling when it is time to do a dam lift, adding more SAAV Extend segments.
Sensorized length = (TCL - casing stickup amount) * 1.008 (for a 85 mm casing) + 0.5
Sensorized length = (TCL - casing stickup amount) * 1.005 (for a 70 mm casing) + 0.5
NOTE: When ordering an SAAV Extend for a new borehole, the sensorized length will be based on your planned “In Ground Casing Length,” measured from bottom of casing to ground surface. Install the casing to the planned depth with a minimum 0.5 m stickup. Allow the grout to set. Verify the measurements before installing.
Plan to add more casing after the SAAV Extend base array is inserted and pumped to make up a full 1 m to 1.5 m stickup. To add casing you will need a casing repair kit, as per the casing manufacturer's recommendations.
NOTE If casing is too shallow for the purchased SAAV Extend the casing 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 opportunity to shorten this. Conversely, if the casing is too deep a Silent Segment assembly can be added to the bottom of the SAAV Extend.