Dam: Failures Modes and Their Possible Solutions

Though constructed with different materials and built in different sizes, dams share the same purpose of controlling water. This structure is utilized to hold back water which creates a reservoir with a handful of purposes based on its needs. More so, the materials used to construct the dam will serve and hold certain capacities. Despite coming in various sizes and using different materials, these dams, unfortunately, will still encounter failures. Different dams along with various failure modes will be discussed. As these failure modes are presented, different solutions that could have been done to avoid these failures will be given alongside different measures that can be considered during the pre-construction phase.

One of the many ways to classify dams is through its construction materials. Rigid dams are constructed with rigid materials such as concrete, steel, and timber and include the following examples: concrete dams, steel dams, timber dams, and others (Anupoju 2018). On the other hand, non-rigid dams are constructed using materials such as rocks and soils include earthen and rockfill dams. Not only can dams be classified by their materials but they can be classified based on their structure and design. Examples with such designs may include gravity dams, arch dams, and embankment dams. Based on these characteristics, the dams will come with their own limitations on how much they can withstand. 

Based on the type of construction materials that are used for dams will also affect the shape they need to be constructed in. For instance, rigid dams typically come in a triangular shape (Anupoju 2018).  A rigid dam such as a gravity dam will come in a triangular shape because this will help resist the water pressure. The deeper the water the more pressure is exerted on the dam. Therefore, by implementing this shape on this dam, which has the purpose of using its weight to hold back the water in the reservoir, it will make the upper surface of the reservoir not feel much water pressure until at the bottom which will feel maximum pressure (USSD). In contrast, non-rigid dams come in a trapezoidal shape such as the earthen embankment dam. Typically described as a dam shaped-hill, its shape provides the support it needs for foundations that have weak soils. For instance, it provides the appropriate amount of space needed to include the layers that are desired to build this type of dam such as having a central core made of soil material with low permeability (Mishra 2018). Despite each dam having their own appropriate  preparation and calculations, there is the possibility of it failing. 

Failure is unacceptable for dams because not only it is financially costly, but people’s lives are put at risk. Despite having the goal to avoid any type of failure, unfortunately, it still may occur due to different reasons. The United States has seen numerous incidents for different size dams where lives were sadly lost. By extending our research and finding out how we can prevent this from occurring we may be able to prevent these accidents from occurring in the future. However, to start this process one must be familiar with the different failure types and look at related case scenarios, which may help us with coming up with a solution through empirical observation. The different failure modes may include overtopping, seismic failure, or foundation defects.

Overtopping is one of the many reasons why dams fail. This failure is caused by water spilling over the top of the dam, which is mainly due to inadequate spillway design, possible debris blockage of spillways, or the dam crest settling. This type of failure mode is really common given that it accounts for almost 34% of the dam failures in the United States alone (ASDSO 2013). However, there are cases where only a few inches of water spill over the top, but the dam does not breach. Typically dams that are made of weak and fractured rock would not be able to survive an overtop flow unlike a concrete dam that might have a better chance because it has more resistance (USBR 2019). An example of a most recent case where a dam failed due to overtopping was the Sanford dam. 

Edenville dam failed on May 19, 2020 in mid-Michigan due to 7 inches of rain causing it to fail due to rotational-type failure. The failure of this dam was so severe that it had the opportunity to affect and lead to the Sanford dam’s failure as well. This steady rain brought a few inches of rain, but it was still capable of bringing damage to this earth embankment dam causing it to overtop. The destruction of this dam caused the Sanford dam to overtop as well causing a flood in the Midland area of Michigan. Unfortunately, issues with the dam were detected before such that state regulators were aware the Edenville dam did not meet state flood standards as of August 2019 as well as federal regulators asking the dam’s owner to add capacity to avoid any future issues (Wilkinson and House, 2020). These demands to seek change and improvement for the dam were avoided and thus the costly failure on May 19, 2020 occurred. As a result of this failure, the Department of Environment, Great Lakes, and Energy addressed to Governor Whitmer, there is potential for more improvements in policies, procedures, funding, and regulations such that this can avoid a disastrous outcome in the future (Clark 2020).

Figure 1: Edenville Dam is ruptured due to overtopping. 

The location of a dam near seismic activity has the likelihood to cause issues as well. As much as one may try to avoid these areas, it may be near impossible to do so. Therefore, the design team must accommodate such areas and do appropriate calculations. However, it has been noted that earthfill, rockfill, and concrete gravity dams perform better in such areas (Taylor). Despite having dams that may be able to withstand a bit more than other types, accidents can still occur. Earthquakes can lead to liquefaction, overtopping, cracking that may result in internal erosion. However, given that a seismic location may be the root cause of many of these problems that were listed before, it is hard to pinpoint and sum all the failures that have occurred in the past. 

The failure of the Fujinuma Dams is a prime example of a dam failure that failed due to an earthquake with a magnitude of 9.0 that took place on March 11, 2011 at the coast of Japan. This earthquake resulted in two dams failing; the main dam encountered lateral displacement due to the seismic shaking but a large drop in the crest left the dam vulnerable to overtopping, ultimately leading to its breaching point. Furthermore, a smaller second dam, the Fujinuma Saddle Dam, was not breached, but did experience slope failure due to the earthquake (Pradel, Wartman, and Tiwari 2013). Given that this dam was constructed in 1949, there are no drawings or documents of the construction that were saved that could help engineers evaluate this failure and possible reasons why it happened. However, after the failure engineers were able to evaluate what was left and come up with their own theories as to why it failed (Harder, Kelson, Kishida, and Kayen 2011). Therefore, as a lesson learned from this dam would be that dams that were constructed many years ago need to be reevaluated to make sure they pass any safety dam precautions. More actions need to be taken either by providing more funding or urging engineers to reassess old dams in order to avoid more disastrous failures to occur.

Figure 2: This is an outtake of what the Fujinuma Dam looked like once it failed.

Foundation defects are another cause for dam failures. There are many reasons why there could be defects in the foundation such as the following: settling in the foundation of the dam, seepage around the foundation, or uplift pressures. This category of failure accounts for 30% of all dam failures in the United States. (ASDSD 2013). Similar to overtopping, this might be the second most common reason why dams fail. There is a high number of dam failures and one of the reasons could be because of the construction or wrong calculations.  

The Malpassest dam in France was a victim of foundation issues. It failed on December 2, 1959 due to cracking that occured due to uplift pressures. Given that the dam was built in the early 1950s, the engineers and designers of the dam likely lack the amount of knowledge and case studies engineers have access to now. Therefore, not only were foundation issues a reason why this dam failed, but many additional issues were a part of it too such as geological and human error (Duffaut 2013). For instance, metamorphic rocks are not typically affected by reservoirs and are strong enough for a dam foundation, however, it was not the case for this dam foundation. Furthemore, this dam had geologic failures from the very beginning; as engineers continue to work and complete constructing this dam more issues would pile up. Unfortunately, the team never did any geological investigations when construction first started, therefore, after the failure all different types of tests were done, which then helped pinpoint the main reason for failure: uplift pressure. The pressures caused the foundation to enter a compressed state. As time went on, the dam would only sustain so much before cracks would form, resulting in the thrust block to dislodge.

            Figure 3: Current state of the Malpassest Dam after failing due to foundation defects.

Overtopping, seismic failure, and foundation defects are only a few reasons why dams may fail, but there are many other factors that can contribute to failures as well. Despite what the reason may be, one may agree that at the end of the day the goal is to avoid more dams from failing because not only are these costly mistakes, but it may result in casualties and environmental impact. One way engineers may be able to avoid further damage occurring is by using technology to analyze all current dams to ensure whether a dam is stable or not since many dams were created a while ago before higher safety measures were considered. 

Safety is the number one priority especially for dams with the potential to cause significant damage. By using advanced technology, engineers have the potential to study such issues with dams and propose ways to fix them to avoid any disasters in the future. For instance, engineers may use slope stability computer programs to look for any critical failure surfaces within a fill embankment (USSD 2007). There are many computer programs one may use based on what you are aiming to look for, but programs used to find the critical failures include SLOPE/W, UTEXAS3, Wright, or STABL (Sengupta and Upadhyay, 2009). By implementing this technology to study any critical failures, the engineers will have more knowledge of current state dams and brainstorm ideas on how they can be improved in order to avoid accidents. However, there are steps that can be taken to monitor current dams, but another way to improve dams is to implement technology during the pre-construction and construction phase.

Technology that can be implemented during the construction phase includes monitoring dams with UAVs, also known as unmanned aerial vehicles. UAVs consist of developing 3-D models used to see the progress for dam projects with the help of BIM as well. With the assistance of this, engineers have the capacity to monitor and develop the construction activities (Coetzee 2018). By collecting such data, catastrophes such as accidents or floods can be avoided. Given that the 3-D models are able to provide real-life data, engineers will have a better understanding of any possible movements or cracking a dam may experience  (He 2019). For instance, if such technology was implemented in the previous cases that were mentioned above, to some extent such accidents could have been avoided or caused less damage because engineers would have been more aware of what was going on with the structure and the potential to warn others. Luckily, technology would only be improving as time goes by and hopefully will help reduce the number of unstable dams. However, as much as new ideas are suggested to keep track of the dam’s state or use during the construction phase of dams, the main issue why dams haven’t improved is due to the lack of money set aside for these projects.

There are numerous dams that are not deemed safe and many more that one may not be aware of because of the lack of resources. The American Society of Civil Engineers have rated dams in the U.S. based on whether they were deemed safe; as of 2017, at least 90k were rated a “D.” According to them as well, this value has not decreased since their report that was conducted in 1998 (Leslie 2019). Many dams are in desperate need of getting repaired or removed, but the price tag for these actions are the driving force why many government representatives do not want to use tax dollars for them. However, this should not be the case. There should be a different team that allows such repairs to take place without the government needing to decide whether or not it does happen. According to Workman, 85% of the dams will exceed their 50 year lifespan within the next two decades, so if no progressive change is done not only are people getting put at risk but surround properties and the environment as well.

Dams are such complex and fascinating structures with various purposes. However, with such unique aspects and forms come different failures that can occur such as overtopping, seismic vulnerability, and foundation defects. Despite different solutions and actions that could have been done to avoid such failures, the area of focus needs to be done on current structures. Using case studies and technology, one may be able to see recurring patterns and brainstorm solutions to avoid accidents from occuring on our current dams. Before all else, funding needs to be increased and made the main priority in order to allow such improvements to be made or else no progress will ever be made. Dam failures have been occurring since the 1950s and are still happening up until now. There needs to be a greater urge to improve our infrastructure. If not, disasters will continue to occur as well as more money being wasted to fix such failures when improvements could have been made before.

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