Nov 6, 2018

In-focus: How damaged inclinometer casing affects monitoring strategy and what SAAV can do about it

Tyler Morency
1 year ago

A damaged inclinometer casing can pose serious challenges to the smooth execution of a geotechnical monitoring program.

Inclinometer casing can be damaged in a number of ways, from improper installation to excessive deformation. Grooved casing can spiral during installation, which can cause inclinometer wheels to slip off-track or cause the instrument to rotate, resulting in uncertainty in the expected direction of movement. While subsurface movement can bend or shear inclinometer casing after installation. This can prevent the retrieval of monitoring instrumentation, or more worrisome, depending on the amount of movement in the area, could damage the instrument and prevent any monitoring from being performed at all. Generally, areas with significant levels of subsurface movement warrant continued monitoring.

“The reason you are monitoring in the first place is that you are trying to either mitigate risk or verify the performance of a design,” Christiane Levesque, Measurand’s Senior Support Manager said. “It is unlikely you would want to stop monitoring if it is an active site.”

Inclinometers typically require the casing to remain relatively uniform to allow correct functionality. If subsurface movement has caused the casing to bend, manual inclinometers may have issues navigating through the curve or in-place inclinometers (IPIs) may get damaged or bent, depending on the gauge length. The minimum negotiable casing radius of manual inclinometers can range from 3.12 m to 1.99 m, depending on the manufacturer.

“If you have any sort of appreciable shear zone, you won’t be able to get a manual inclinometer past the shear zone,” Measurand’s chief of staff, Jeff Barrett said. “Typically, people have dummy probes that they send down first to make sure that they don’t get their instrument stuck.”

Traditionally, impassable casings are considered “sheared off” and subsequently abandoned. To continue monitoring the area, a new borehole must be drilled and a fresh inclinometer casing must be grouted in place, a costly and time-intensive task.

Retrofitting bent and damaged inclinometer casing with traditional IPI’s is typically out of the question. However, Measurand’s SAAV model ShapeArray allows the instrument to pass through tight curves. The narrow width (approximately 19 mm) and 500 mm segment lengths of the SAAV means a smaller bend radius than other inclinometer instruments.

Complex bends can pose problems for some instrumentation. SAAV (left) and inclinometer (right).

Another benefit of SAAV is that it does not require grooved casings. Thus, in situations where inclinometer casing has spiralled, and a manual or in-place inclinometer cannot be used, a SAAV can. This again saves significant cost by utilizing an existing casing.

Learn more about how SAAV can be used to retrofit damaged inclinometer casing by contacting today.

How did engineers use the observational method during the construction of a new highway interchange?

How did engineers use the observational method during the construction of a new highway interchange?

Download the Provincial Trunk Highway interchange Settlement Analysis datasheet.