ShapeArray Fundamentals in 2023: Your questions answered

Measurand’s Mitchell Pollock and Terra Insights’ Josh Smith presented ShapeArray™ Fundamentals, a webinar that details everything you need to know about ShapeArray, the only patented geotechnical monitoring instrument of its kind.

This webinar covered: 

  • When ShapeArray is the right instrument for your project 
  • Specific ShapeArray installation methods for typical monitoring applications 
  • How to use technical specifications to select the right geotechnical sensors 
  • Real-world examples of geotechnical monitoring applications 

We’ve received several questions during the webinar that we’ve answered below: 

Q: Can you mix 250 mm and 500 mm segments in the same ShapeArray?

A: As of now, that is not an option. We need to have the same size of segments relative to one another for our math to work in these arrays. At this time, no, we cannot mix segment lengths. However, with an in-place inclinometer, you can mix segment lengths, albeit not down to 250 mm, but you could have 500 mm plus segments.

Q: Could we also connect other instrumentation like piezometers or extensometers to the same data logger that the ShapeArray is using? 

A: The answer with RSTAR Affinity is yes. RSTAR Affinity Data Logger is a five-channel node. Those channels can be customized depending on your site requirements. They can be any combination of vibrating wire, or digital (eg. ShapeArray), depending on what instruments you need to connect. Or they could be five digital channels so you could connect up to five ShapeArrays into one RSTAR Affinity Data Logger node. The answer to that question is yes using the RSTAR Affinity system. But as far as I’m aware, it is the only system you can do that with.  

Q: As a result of the Terra Insights’ acquisitions, will the telemetry solutions across SAAV be improved with GeoExplorer and NavStar? 

A: Yes, we’re constantly working together to integrate the instrumentation and make that sync up nicely. One thing we’ve done is we’ve linked the RSTAR Affinity system with the GeoExplorer system. If you are using the RSTAR Affinity Data Logger node you can link that via API into the GeoExplorer platform.  

Q: Does each sensor have the capability to monitor temperature as well as deflection? 

A: Yes. Each ShapeArray segment contains a sensor that can measure temperature. Temperature is also factored into calculations of deflection and deformation.  

Q: What’s the maximum displacement is ShapeArray able to measure? 

A: This is an interesting question that we get frequently. There isn’t a simple answer – it depends on a few variables ranging from site conditions, stratigraphy, casing choice, and sensor spacing. There are several different elements that can play into that. Speaking to one of the examples shown, specifically, this landslide in Minnesota. This array was approximately 25 to 30 m in length and had been installed in three-inch casing. It was able to survive 3 m of deformation, though that’s on the extreme end. We don’t know what the general maximum is because it is different every time. We’d need to assess what the site conditions are, what your plans for casing are, and how you plan on using the array. Ultimately, if you’d like to chat more about that later, I’m happy to discuss based on what might be possible.  

Q: Can you clarify if it is okay to use a ShapeArray longer than the length of the casing? 

A: No. For vertical installation we need the ShapeArray to fit within the length of the casing. The ShapeArray needs to be shorter than the casing. 

Q: Is an SAAScan Extend possible? 

A: Not at this time. That’s an interesting question. Right now, SAAScan is built to length and used for repeated borehole alignment verification. 

Q: If I order an SAAV and later want to add segments, is that possible? Or do I need to start fresh with an SAAV Extend? 

A; If you have an existing SAAV that you’d like to add length too, there are a couple of options. Essentially, you don’t have the option to add sensorized segments in the field, but we can assist with modifying that instrument to a different length if required. Also, we’ve been delving into the option of converting your standard SAAV ShapeArray into a SAAV Extend model through modification at our facility if that’s of interest. Happy to chat about that as well. 

Q: Is there a maximum number of extensions for SAAV Extend? 

A: There isn’t a limit to how many extensions that can be added, although there’s some caveats to discuss with adding lift extensions to an array. Each time extensions are added, the casing must also be extended. Obviously, there’s a bit of a limit to the length of these lift extensions that can be added purely based on the physicality of it. Someone would need to be on a ladder or something to install both the new extensions and casing. No, there isn’t really a limit to the length of how many extensions besides the overall length limit of ShapeArrays, which is around 200 m for vertical installations.  
One of the other considerations is the number of segments depends on the data logging system that you are planning on using. One of the limitations of using certain data logging systems is they have a limit on the number of segments they can monitor. You need to be a little cautious when selecting which data logging system to use.  

Q: What is the main difference between a time-domain reflectometer (TDR) and ShapeArray?  

A: A TDR will give you an indication that movement has occurred. Whereas a ShapeArray will give an indication of how much movement has occurred. TDR gives a very basic measurement. It’s literally going to give you a reflection at the depth the movement has happened. If you haven’t got crimps within that TDR cable, it is going to be difficult to locate that depth. ShapeArray is going to give you far more information than what a TDR would give you. Pricing-wise it is going to be more expensive, but the information that you get is going to be a lot better and likely more useful.  

Q: If the top 2 m of a borehole/drillhole freezes but the rest of the drillhole doesn’t, does that mean the ShapeArray wouldn’t work in the drillhole, or can you just have sensors where the drillhole doesn’t freeze?

A: There’s a couple of options. Freezing in the upper portion of the casing with a ShapeArray installed could cause issues for several reasons. As the water expands in the casing, that could impact the position of the array itself, and potentially damage it due to overpressure. As we know, when ice expands, it doesn’t really care what is in the way, so there’s a chance of damage to segments from the ice. One of the things we’ve seen people do in the past is to use antifreeze to keep the ice away from the top portion of the casing. Or try to remove the water from that area. We’re still trying to figure out how to best manage the ice problem. It’s a bit tricky at times. There’s a couple of custom ways we can manage—keeping water out of the area entirely if possible, or by changing the composition of that water so it isn’t able to freeze. Another option could be adding heat tracing to the upper portion of the casing if applicable.  

This transcript has been edited for clarity. Watch the webinar on-demand to explore the fundamentals of ShapeArray. 

Speak with an Expert

I’m very happy with the quality of the instrumentation and technical support from RST, as always. They worked with us from the initial stages of the project to ensure that we were fully prepared and equipped to use the RSTAR network for the first time. They delivered everything within the tight project time frame to ensure that there were no delays on site, and the submersible tilt meters looked like new even after over twelve months of being submerged in Thames water!
-Richard Lipscombe, BEng (Hons), Director & Principle Consultant - RL Geotechnical Ltd