VAiONT DAM CASE STUDY
Christopher R. Silver
Overview
The Vaiont Dam is located in the Northeastern Alps near Belluno,Italy along the Vaiont River Gorge. The Vaiont Dam separates the Vaiont Reservoir from the Paive River Valley, with Monte Toc along the southern border of the reservoir. In 1963 the Vaiont Dam was flooded over by more than 30 million cubic meters of water. The flood was caused by a massive landslide down Monte Toc into the Vaiont Reservoir. Prior to the 1963 landslide, as shown in Figure 2(top), the mountain slope along the southern edge of the reservoir was created by a prehistoric landslide. However, The 1963 disaster was attributed to the mismanagement of the reservoir construction and filling process. The immense number of investigations into the Monte Toc slope failure make it one of the most intensively studied in history. The purpose of this case study is to analyze data from previous investigations of the slope failure in order to provide further explanation of the method of failure.
There is a large amount of speculation about the subsurface conditions of Vaiont dam location as it relates to the failure. A cross-section of the known subsurface is shown in Figure 2. Important features to note are the large amount limestone layers that can be dissolved by water and maintain aquifers as well as the marine clay layer embedded between various limestone and shale layer. Furthermore, the presence of faults near the reservoir site pose a potential threat to the project. Further site issues include:
Although the dam incorporated some of the newest technical expertise, it was been built without due process of geological reports and possible tectonic movements. Shortly after completion, there were small landslides and earthquakes.
There was also evidence of creep which continued to increase until the final failure in October of 1963.
Since the catastrophic failure, a wide range of analysis has been completed on the cause of the failure. The triggering mechanisms of the slide have been the subject of numerous engineering research and reporting. Varying on which of the main causes is considered to be primary, a wide variety of conclusions have been made as to the cause of the slide. Some of the primary causes considered include:
Based on the information and data collected it can be determined that the main cause of failure is highly questionable; however, it is clear that a combination of mismanagement, tectonic activity, and geologic setting lead to the eventual slope failure. The geologic setting of the Vaiont reservoir was not properly analyzed prior to construction. the presence of previous landslides confined aquifers, faults, and bedding planes made the site a high risk location for a reservoir. The extensive tectonic activity around the site location also provided for an unstable slope of Monte Toc and could have played a role in the rapid creep of slope into the reservoir basin. Furthermore, the mismanagement of the government agencies in monitoring the creep of the slope face and providing a proper level of safety assisted in the eventual over-topping of the dam. Overall the failure of the Mote Toc slope face was an unfortunate catastrophe, but has led to extensive research into the effects of various geologic features on slope stability in an effort to prevent similar failures.
There is a large amount of speculation about the subsurface conditions of Vaiont dam location as it relates to the failure. A cross-section of the known subsurface is shown in Figure 2. Important features to note are the large amount limestone layers that can be dissolved by water and maintain aquifers as well as the marine clay layer embedded between various limestone and shale layer. Furthermore, the presence of faults near the reservoir site pose a potential threat to the project. Further site issues include:
- the river had undercut its banks
- the limestone and clay-stone rocks made up the walls of the canyon and were inter-bedded with soft clay which followed the slope of the canyon wall
- layers of limestone contained solution caverns that became only more saturated
Although the dam incorporated some of the newest technical expertise, it was been built without due process of geological reports and possible tectonic movements. Shortly after completion, there were small landslides and earthquakes.
There was also evidence of creep which continued to increase until the final failure in October of 1963.
Since the catastrophic failure, a wide range of analysis has been completed on the cause of the failure. The triggering mechanisms of the slide have been the subject of numerous engineering research and reporting. Varying on which of the main causes is considered to be primary, a wide variety of conclusions have been made as to the cause of the slide. Some of the primary causes considered include:
- presence of clay along the failure surface.
- presence of the ancient landslide.
- poor subsurface conditions
- tectonic activity in the area.
- presence of a limestone caverns below the failure surface
Based on the information and data collected it can be determined that the main cause of failure is highly questionable; however, it is clear that a combination of mismanagement, tectonic activity, and geologic setting lead to the eventual slope failure. The geologic setting of the Vaiont reservoir was not properly analyzed prior to construction. the presence of previous landslides confined aquifers, faults, and bedding planes made the site a high risk location for a reservoir. The extensive tectonic activity around the site location also provided for an unstable slope of Monte Toc and could have played a role in the rapid creep of slope into the reservoir basin. Furthermore, the mismanagement of the government agencies in monitoring the creep of the slope face and providing a proper level of safety assisted in the eventual over-topping of the dam. Overall the failure of the Mote Toc slope face was an unfortunate catastrophe, but has led to extensive research into the effects of various geologic features on slope stability in an effort to prevent similar failures.