In some cases, it is not possible to lay out the PVC on the ground and assemble it for the SAA+PVC installation. In these cases, the PVC will need to be assembled and lowered into the hole prior to inserting the ShapeArray (SAA). This installation method is susceptible to buoyancy effects and care must be taken to avoid sinuating the PVC prior to installing the ShapeArray.
Recommended reading prior to using this guide:
- Common Mistakes in ShapeArray Installations
- The Conduit section of the ShapeArray Installation manual
- ShapeArray Conduit Considerations
- SAAF - Recommended Installation Methods for Vertical to Sub-vertical Installations
Step 1 - Choose the Right Conduit
Figure 1: 27 mm ID electrical conduit, end cap, and coupler appropriate for ShapeArray installation
Step 2 - Choose the Right Adhesive
PVC couplings are attached with PVC solvent cement. In cold temperatures, it is imperative to use an appropriately rated cement. Do not use too much cement, as it can squeeze into the inner part of the conduit. Debur, clean, and use a solvent cleaner on the conduit before applying cement. Most manufacturers specify applying glue to only one surface of the joint.
Figure 2: An example of PVC solvent cement
Step 3 - Prepare the Conduit
All PVC conduit ends should be kept clean from dust, oil, and snow. Look inside the PVC pipes to ensure that no foreign objects are inside the PVC pipe. The edges of conduit over which the ShapeArray is being installed should be smoothed using a deburring tool to prevent abrasion.
Figure 3: Preparing conduit - (a) examples of deburring tools, (b) cleaning and deburring the conduit
Step 4 - Assemble the Conduit
It is easier to assemble the PVC conduit as it is lowered into the borehole. Start by gluing and taping the end cap onto the bottom most piece of PVC before inserting it into the borehole. Lower the first piece of PVC conduit then glue the next piece on and tape the joint. Due to buoyancy effects, an assistant will be needed to hold the pieces in place while working. Keep adding more conduit, gluing and taping each joint, until the required length of conduit has been assembled. Glue the bottom part of the top stack included in the SAA Install Kit to the top of the PVC conduit at this time.
Figure 4: Assembling the conduit as it is lowered into the borehole - (a) Assistant holding it in place, (b) next piece glued and taped at the joint
Step 5 - Avoid Buoyancy During Grouting
A factor which must be considered during installation is the buoyancy of the PVC conduit. Typical grout used for back-filling the PVC conduit has a density ranging between 1,200 kg/m^3 and 1,450 kg/m^3. The grout mix recommended in the Backfilling Recommendations section of the ShapeArray Installation manual has a low density similar to the density of the PVC filled with the SAAF.
It is important to weight the PVC down rather than allowing it to float up against a hard stop at the top. When the conduit is held from the top, buoyancy causes the conduit to bend and form S-curves making it difficult to insert the ShapeArray. It is recommended that the ShapeArray conduit be weighted down using chain or use the SAA+PVC Installation method to minimize buoyancy effects.
WARNING: Do not use water to weigh down the conduit unless the water is removed before inserting the ShapeArray into the PVC.
Figure 5: Inserting chain to weigh down the PVC until the grout has cured
Step 6 - Place the Reel Stand
Figure 6: Place the reel and reel stand approximately 1 m - 1.5 m from the borehole such that the ShapeArray comes off the top of the reel
Step 7 - Lower the ShapeArray Into the Casing
Step 8 - Use the SAAF Install Kit to Finish the Installation
Once the SAAF has been inserted into the pre-cased borehole, the SAAF Install Kit should be used to complete the installation. This involves adding compression to the SAAF, determining the azimuth offset, marking the X-Mark on the outside of the casing, adding the top stack, and running cabling to the data acquisition system. More detailed instructions for this process are available in the Finishing the Installation Process Using the SAAF Install Kit guide.