Inclinometer Casing
Function of Casing
Inclinometer casing is a special purpose, grooved pipe used in inclinometer installations. It is typically installed in boreholes, but can also be embedded in fills, cast into concrete, or attached to structures.
Inclinometer casing provides access for the inclinometer probe, allowing it to obtain subsurface measurements of tilt. Grooves inside the casing control the orientation of the probe and provide a surface from which repeatable tilt measurements can be obtained.
Inclinometer casing is typically installed in boreholes, but may also be embedded in fills, cast into concrete, or attached to structures.
Choosing Inclinometer Casing
Although all casing supplied by Gage Technique International is competitively priced, price should never be the deciding factor in choosing inclinometer casing. The cost of casing is quite small relative to the cost of mobilizing a drill rig, and very small relative to the cost of a failed installation. This page summarizes the most important factors to consider when choosing casing.
Casing Diameter
Casing is designed to deform with movement of the adjacent ground or structure. The useful life of the casing ends when continued movement of the ground pinches or shears the casing, preventing passage of the inclinometer probe. Larger diameter casing generally provides longer life.
Large diameter casing (85 mm, 3.34 inch) is suitable for landslides and long term monitoring. It is also approprate for monitoring multiple shear zones or very narrow shear zones. Large diameter casing is required when the horizontal probe is used.
Medium diameter casing (70 mm, 2.75 inch) is suitable for construction projects. It can also be used for slope stability monitoring when only a moderate degree of deformation is expected.
Small diameter casing (48 mm, 1.9 inch) is suitable for applications where small deformations are distributed over broad zones. It is generally not installed in soils.
Casing Grooves
Measurement accuracy is directly influenced by the quality of casing grooves. For this reason, both Gage Technique International and Slope Indicator cuts grooves by machine broaching. This process allows the width and chamfer of the grooves to be optimized for the wheels of the Digitilt inclinometer probe and also minimizes spiralling of the grooves.
Casing Strength
In borehole installations, the annular space around the casing is usually backfilled with grout. The grouting process can generate pressures high enough to cause the casing to col-lapse. Stage grouting is one way to avoid this problem. Strong casing is another. Both Gage Technique International and Slope Indicator starts with thick-walled pipe and then carefully controls the depth of the grooves during the broaching process to prevent weakening casing walls.
Sealable Couplings
If casing joints are not adequately sealed, grout can force its way into the casing. After the grout hardens, it will prevent the probe from reaching its intended depth. In some cases, the installation will be ruined.
Gage Technique International offers several types of couplings and casings, and all of them can be sealed easily and consistently. The newest casing features O-ring seals and our traditional casing features tight-fitting surfaces that are fused together with solvent cement.
Assembly
Inclinometer casing should be easy to assemble, even with an untrained crew. Slope Indicator QC casing, which snaps together, is the current leader in quick and easy assembly. Other types of casing are assembled with shear wires or with solvent cement.
Casing Materials
Gage Technique International only supply ABS casing. The ABS formulation is suitable for long term contact with all types of soils, grouts, and ground water. ABS plastic retains its shape and flexibility over a wider range of temperatures than PVC plastic, and ABS is much easier to handle than fiberglass casing. Aluminum casing is no longer recommended for any application.
For more information
For further information, please refer to the related document (pdf). These documents can be viewed and printed with Adobe Acrobat Reader.