3 reasons why dam owners should prioritize adequate instrumentation and data
November 08, 2022
When you reduce assumptions, you can more comfortably manage risk. A geotechnical engineer talks about the importance of accurate performance data.
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Dam safety projects are fascinating for a geotechnical engineer. Each site brings its own history and quirks. These projects provide interesting puzzles for us to solve, so we can understand what’s happening at each site and then work with our clients to help them manage their assets and associated risks.
After a decade of professional experience working on these types of projects, I’d like to stress two vital components: quality instrumentation and reliable data. Geotechnical engineers use instrumentation to observe and assess conditions—like groundwater levels or soil deformation—to evaluate the performance of dams and identify any safety issues. We rely upon instruments like weirs, piezometers, inclinometers, and strain gauges to understand how a dam is performing. Do you have adequate instrumentation on your site, and are you maintaining it so that you have quality data?
Here’s why I’m asking: dam owners and operators want to reduce operational and commercial risk as much as possible.
Access to proper instrumentation and good quality data will reduce the risks to your asset and help keep the public safe.
The risks I’m referring to are related to the overall performance and functionality of the structure. Instruments are used to flag conditions that will tell us if the performance is changing or deteriorating. Injury, loss of life, environmental damages, or structural damages are all potential outcomes of a dam safety emergency or failure. Public safety and preservation of the environment are paramount, as well as the avoidance of loss of electricity generation or storage capacity in the case of hydro-electric or tailing dams, respectively.
Instrumentation data can help better manage those risks. Let’s look closer at three of the benefits of prioritizing instrumentation and maintaining data collection.
1. Minimize the number of assumptions
For geotechnical engineers, it can be challenging to understand how a structure is performing if we don’t have information about what’s happening inside. When working on dam safety related assessments, it’s necessary to compare observations from the field with the theoretical performance of a dam to assess whether the dam meets safety guidelines. When engineers don’t have that data, they need to make assumptions. You introduce uncertainty each time you assume something.
For example, the phreatic surface is critical to the geotechnical stability of an earth-embankment dam. Piezometers, when installed in key areas, can provide an accurate picture of the phreatic surface, which is used in the stability assessment. The use of instrumentation increases the confidence of engineers (and clients) that an assessment is accurate, whether the results are favorable or unfavorable. In this example, if there are no piezometers available to measure water pressure, a theoretical phreatic surface will be assumed. In the worst-case scenario, this could result in an assessment that the factor of safety meets the minimum requirements when in fact the phreatic surface is much less favorable. While no owner ever wants to learn that the dam does not meet safety guidelines, it’s preferable to learn this before a failure occurs so that the problem can be fixed.
In this example, the piezometers at the crest and mid-slope of an embankment dam provide critical information regarding two possible scenarios. Is the phreatic surface located along the yellow dotted line or the blue one? The only way to be certain is to measure.
Fewer assumptions mean you can have more confidence that your assessment matches the actual conditions. Limiting assumptions reduces uncertainty and facilitates the management of risk when you can be confident in understanding the conditions that need to be managed.
2. Create a more complete picture
A lack of information can really affect management of risk. More information leads to increased confidence because when you know what’s driving the behavior and performance of your dam, then you can better manage your risk.
It’s not possible to eliminate risk. The goal should be to get your risk to a point where it’s managed and you’re comfortable with it.
Functional instrumentation provides valuable information and creates a fuller picture. It reminds me of those connect-the-dots drawings that I used to do as a child. Imagine starting one of these drawings of a teddy bear with only eight equally spaced-out dots. Then compare it to a drawing of the same bear but with 20 dots placed in strategic locations. Those 20 dots will present a much clearer visual for you to sketch out, compared to eight dots spread out across a page. Tools like updated topographic surveys, piezometers, and weirs can help engineers see these “dots.”
It’s not possible to eliminate risk. The goal should be to get your risk to a point where it’s managed and you’re comfortable with it.
If you can only see a small number of “dots” on a dam project, or if those “dots” are not at meaningful locations, you may not fully understand the problem. And when there are fewer “dots,” engineers need to make more conservative assumptions about the input parameters used in their analyses. If engineers don’t have confidence in those parameters, we must assume the conservative case. As those assumptions accumulate, the conservativism snowballs, which may lead to an inaccurate assessment of a structure. An extreme example would be an assessment indicating that a dam is unstable—even if it’s been performing satisfactorily for many years and is clearly stable. This scenario is frustrating for both engineers and owners of dams. This tells you that you need more information.
By “connecting the dots,” instrumentation can also be thought of as a way to compare the theoretical and the reality.
I’d like to also emphasize that the installation of instruments needs careful consideration and planning—you don’t want to inadvertently introduce defects in the dam itself.
3. Work with accurate and reliable measurements
For dam safety programs, it’s important to work with accurate and reliable measurements. Over time it is expected that instruments may fail. If instruments stop working because of a lack of maintenance, they’ll likely produce unusual readings. Geotechnical engineers are then forced to ask: “Does this measurement indicate a real problem? Or is this a false alarm and a result of the instrument not working? Can I trust this measurement?”
Without instrumentation, you can’t be certain about the performance structure. Proper instrumentation will reduce uncertainty and increase confidence.
In the end, the maintenance is worth it. For example, piezometers are used for measuring porewater pressures in the ground, and they’re relatively inexpensive. In addition to installing instruments, it is critically important that the owner has the means to collect and record measurements. If no one is collecting measurements, then the information can’t help anyone. By maintaining your instrumentation, introducing redundancy, and collecting measurements regularly, your geotechnical team will be able to recognize issues and react before those issues turn into serious problems.
As you can see, it’s vital to practice proper documentation, record-keeping, and maintenance.
The latest generation of geotechnical instrumentation allows for simpler installation (wireless data mesh transmission—without all the wires), cloud computing (real time data is accessible anytime), and more advanced data analysis software. By taking advantage of these new technologies, you don’t have to send staff to a site to collect data. The interpretation of the data can be fully automated and presented quickly in a meaningful manner, which allows engineers and owners to make decisions more promptly.
Improved risk management
Engineers have a responsibility to keep the public safe while helping owners protect their asset from commercial and financial damages. Access to proper instrumentation and reliable data will help us work together to manage the many facets of risk that are applicable to all dam owners.
I love immersing myself in unique puzzles on dam projects, and I can’t wait for the next opportunity to connect the dots.