The collapse of the 500 foot high Teton dam upon the first filling resulted in many deaths and $ 1000 million of economic losses. Based on several investigation, it was noted that the dam collapsed because of various technical failures caused by engineers and other professionals. Thus, this paper addresses some of the findings deduced and recommendations for future engineering disaster of such magnitude.
Table of Contents
TOC o “1-3” h z u HYPERLINK l “_Toc393577952” Introduction PAGEREF _Toc393577952 h 3
HYPERLINK l “_Toc393577953” Teton Dam Geology and Conditions PAGEREF _Toc393577953 h 4
HYPERLINK l “_Toc393577954” Teton Dam Construction and Design PAGEREF _Toc393577954 h 5
HYPERLINK l “_Toc393577955” Filling of the Reservoir and the Collapse PAGEREF _Toc393577955 h 5
HYPERLINK l “_Toc393577956” Investigations PAGEREF _Toc393577956 h 6
HYPERLINK l “_Toc393577957” Findings PAGEREF _Toc393577957 h 6
HYPERLINK l “_Toc393577958” Recommendations PAGEREF _Toc393577958 h 8
HYPERLINK l “_Toc393577959” Conclusion PAGEREF _Toc393577959 h 10
HYPERLINK l “_Toc393577960” Works Cited PAGEREF _Toc393577960 h 11
Teton Dam Engineering Disaster
IntroductionThe Teton dam that was constructed in Idaho Town collapsed in 1976 while being filled; the dam was 405-ft high. Its collapse was noted to be one of the most known engineering disasters in modern history. The collapse of the dam resulted in an economic forfeiture of more than $1000 million and 30 mortalities at that time. The Teton dam was constructed using contemporary standards. Thus, the collapse of the Teton dam got the most attention from soil mechanics engineers as well as other engineers around the globe (Baecher et al. 450). The dam was funded and constructed by United States Bureau of Reclamation several miles north of Idaho Falls. Together with the reservoir, it was a key feature of Teton project, which was objected to control flood, recreation, and for irrigation. The construction of the dam commenced in 1972, and was finalized three years later.The dam collapsed during its first filling and was considered the highest dam that had collapsed in the whole history of earth dam structure (Smalley and Dijkstra 200). The ultimate flow power was estimated to be 30,000M3/sec (Baecher et al. 451). After the collapse, several groups were formulated and mandated to investigate the collapse officially, but among the groups, one reported their findings; Interior review group. The group comprised of twelve-soil mechanic’s engineers and ten civil engineers.
Teton Dam Geology and ConditionsThe dams footprints are located in the eastern part of Snake River, which is a large area covered with tectonic depression that comprises of rhyolites ash and volcanic rock dating millions of years ago. In addition, zone was composed of sedimentary rocks. The region is very porous, but no leakage was noted until the failure of the dam in 1976. The dam was also constructed on the stepped walls of Teton River (see figure 1 below). Along the axis of the Teton dam, the tough basement ranges from 100 feet at the right side and a channel path 800 feet under the left abutment. The construction of the dam was underway for several years. On the site, there had been storage and power reconnaissance since 1904 (Smalley 20). The selection of the Teton dam was primarily to offer water for irrigation in the nearby farms while the secondary objective was for hydropower supply.
Figure 1: Source: Evans 386When the engineers were drilling the experimental holes on the surface, a significant amount of water was lost in the subsurface rock hence there was no return drilling of water to the surface. The observations were symptomatic of rock joints, enough to retain and receive fault lines produced during drilling operations (Evans 386). Some of the engineers also noted that the dam was constructed in an area with high permeable underlying rocks. There were no active faults noted near Teton dam during its reconnaissance as well as during the construction phase.
The level of seismicity was very low in the eastern Snake River. Similarly, there has been no hypothesis supporting that the collapse of the dam was because of seismic forces.
Teton Dam Construction and DesignThe design of the was developed and supervised by United States Bureau of Reclamation to offer power generation and irrigation for over 500,000 acres of farm (Evans 387). The contract was given to Morrison Kiewit venture in 1971. The dam was designed as an embankment with an elevation of 6000 feet above sea level and a maximum height of about 550 feet (Smalley and Dijkstra 201). The water reservoir was expected to have a capacity of 340,000 acre-feet filled to the brim.
Filling of the Reservoir and the CollapseThe filling of the dam commenced in 1975, when the river outlets were temporary closed. By March the following year, the reservoir’s water level was at 5245 feet above the sea level, rising at 0.5 foot per day (Smalley and Dijkstra 200). The supporting channels also jetted 400 cfs per second. However, the design required that, above elevation 5400, the dam be not to be filled more than 0.8 foot per day (Smalley and Dijkstra 202). Though the requirement placed by USBR was a design for new dams, occasionally, the rate exceeded when the reservoir was performing outstandingly (Baecher et al. 451). On March 1976, the construction engineers requested USBR that the rate relaxed to much lower elevation.Despite the efforts by the engineers requesting for level drop, the allowable rate was increased from the initial 0.5 feet per day to 2 feet per day yet: the outlets work were not complete, and the runoff from the river was high (Smalley and Dijkstra 203). Because the outlets were underway, the management allowed the dam to be operational without official opening of the project. The reason was reached since there was not report about structural problems and because the canals were operational to have enough capacity to lodge flood. From May 5, 1976 to June 6 the same year, the water level in the dam rose by three feet per day with a daily increment of 5.4 feet attain by the day of the collapse (Smalley and Dijkstra 203).In 1976, the dam was breached, and the water flowed through various outlets as well as other openings. The water level dropped to about 300 feet, as the general flow was already alleviated by then. The river downstream was also full to at least 100 feet in depth. The channel downstream was considered most dangerous of all the undertaking since it flooded homes killing people and injuring many others. Billions of gallons of water headed down to the upper Snake River, destroying property worth millions and leaving many people homeless.
InvestigationsJust after the collapse of Teton dam, two independent investigation groups were formulated and commissioned to investigate as well as to write a report concerning the reasons as to why the dam collapsed (Sherard 240). The team led by Engineer Jansen completed their investigation and presented an excellent report after six months of research and analysis. The investigation noted that:
The probable cause of the downfall of the reservoir was due to internal erosion that took place at the basement of the dam, abysmal in the left base table or trench (Solava, Stacey, and Delatte 40). In addition, the investigators noted that the removal and destruction of the efflux points by the fast flowing speed of water from the reservoir might have caused cracking of the dam walls. The dam also had various openings that existed between sealed rock joints that successively developed into core zones in the trenches (Bolton and Duncan 200).
The inadequacy of the dam design to hold the high-speed flowing water and to account for the foundation conditions resulted into the collapse of the Teton dam. The groups later conducted a semi-independent study about the collapse of the dam as part of an engagement with insurance firms who had accounted for the flood damages and were demanding that the United States government to compensate them. The conclusion for this insurance semi-study was important like those of the other independent investigators. However, their report stated that lessons learned from the collapse of the Teton dam needs changes in the current practice for all the other dams in the country. The management must ensure engineers’ requests and recommendations implemented during desperate situations to avoid such disasters in the future (Assallay, Rogers, and Smalley 111).
The other possible cause of the collapse of the dam as advocated by the investigators lean towards a small margin of moderately high-water stumble upon altitude 5200 in the course of the investigation. Judging from the analysis it was evident that there was competing views on both sides over the wet seam theory and to the lack of support to the mechanism of its cause that lead to the dams collapse. A series of scholars presented a paper at the forensic engineering conference, which summarized the findings of the two groups of experts that took part in the investigation of the Teton Dam collapse.
The report deduced that the analysis of the outcomes determined that the main foundation of the failure of the dam was porousness problems. The volcanic rocks that formed the walls of the dam were permeable, but the permeability test indicated that this was possible under high pressure and speed of the reservoir water. The principle behind this was that rocks contract when exposed to the freezing condition and expand when exposed to high temperature (Schuster 11). Thus, the rocks expanded during the summer hence causing fault lines. The fault lines leaked some of the water from the reservoir and widened after sometime. It is worth accounting that a significant part of the findings from previous investigators tend to point towards the main channel as a major factors that attribute to the collapse of the dam. United States Bureau of Reclamation had never constructed a dam of such magnitude. The channels were large and deep. However, similar channels were used at Palisade’s dam with a maximum of about 300 feet (Schuster 10).
The investigation panel noted that the geometry of the channels with their steep slopes was prominent in causing traverse arching that led to the reduction of stresses in the fill and favored the development of cracks that opened paths through the eroded fill. This undoubtedly added to the reduction of stress that later caused friction among the tectonic base that hosted the dam. Because of this, the dam was not able to hold more water when it reached elevation 5300 feet above sea level.
FindingsA large opening was formed in the core to a maximum of 40 feet below the top of the core at the left strut near sta. 15+00. In addition, the rigorous stress analysis also showed that the stress conducive to internal cracks existed in the walls of the core in both the trenches at the upper part of the reservoir’s shallower depths (DeKay, Michael and McClelland 200). When the level of water and the dam rose to the level of the deepest opening on the walls, water barreled to the river downstream into the chimney drain hence leading to spontaneous collapse of the dam.The internal cracks caused by high tension and stress between the walls of the volcanic granular roadbed were subjected to constant compaction and vehicular traffic. In addition, the factors that control the behaviors of the rocks holding the dam were very different from those of the overlying granular fill.The investigator noted that the clay soil covered ¾ of the reservoirs model material. The model, however indicated that other parts of the dam had soil with varying plasticity (Baecher et al. 451). Despite the fact that the clay soil used had high-liquid limit as well as plastic limit, the plasticity index was tiny. Accordingly, the level of liquidity index has very sensitive changes in the mechanical properties caused by confining stress. This condition was the main contributor to the cracking of the reservoir walls. Therefore, for the clay cores, it was not wise for the engineers to use it in the development and design of the walls as well as that of the outlet floor since it bears corrosive texture. This caused high friction that later resulted to tension at the bottom of the basement.The other key findings were that a combination of the material parameters such as low levels of plasticity of the core, the liquid index of the soil to water content, the confining stress, and the influence on the modules play a vital role in the cracking of the core. It was noted that such aspects of soil mechanics were not predictable during the initial design of the dam. In such cases, a tensile stress happen leading to widening of the cracks on the walls. As for the case of the dam, tensile stress widened the cracks on the walls leading to water seepage into the downstream river (Evans 387).According to the theoretical model that the investigates used for analysis, the state-based soil mechanics used provided a better scientific understanding of the effect of tensile stress and the challenges that took place in stress deformation. The panel was able to depict the state of the soil and the physical properties such as permeability and liquidity index among others.
The state-based analysis concept proposed is okay for characterization of the behavior mechanics in the field. The collapse of the Teton dam was due to failure of soil engineers to understand the properties of the soil hosting the reservoir. Its must however be noted that the crucial frameworks which the recommendations are formulated was based on the findings that the investigators presented.The mechanical behavior of the natural clay soil used in the construction of the reservoir differed from place to place on the dam. It must be noted that the difference the soil poses is crucial when determining the chain of analysis, as well as the quantity of materials for construction. For the case of dams that have clay and volcanic soil such as the Teton dam, a series of analysis slightly but be conducted to check if the materials such as cement is corrected based on the soil characteristics.It has been observed by various researchers that tensile stress history causes a rotation of plastic potentials. The studies based on the previous dam engineering disasters have concluded that constructions of the dams should not be one firm’s responsibility but that of a group of firms. For example, those mandated to offer procurement services should not be the one to supply the materials and to construct the dam. The contractor assigned the work of building the dam should not be similar to the one evaluating it. This offers a chance for the newly awarded firm to scrutinize previous contractor as well to identify any risk that might lead to the failure of the project. Furthermore, it is worth to incorporate an anisotropy into the models used to better the behavior of the soils used in the construction.The shear behavior of most soils in the construction site ought to be determined before commencing the project. This offers the team of experts chance to govern if the holding and restraining capability of the soil. This can be improved by incorporating fracture.
ConclusionIt can be concluded that most engineering disasters that have ever happened in the world are caused due to lack of expertise, as well as ignorance. One of the key reasons that led to the collapse of the dam was technical ignorance. In order to avoid such failures in the future, comprehensive analysis of the prevailing conditions that might cause engineering disaster ought to be considered. Evaluation of the project must also be undertaken before official opening of such project ensure its reliability and efficiency.Works cited
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DeKay, Michael L., and Gary H. McClelland. “Predicting loss of life in cases of dam failure and flash flood.” Risk Analysis 13.2 (1993): 193-205.
Evans, Stephen G. “The maximum discharge of outburst floods caused by the breaching of man-made and natural dams.” Canadian Geotechnical Journal 23.3 (1986): 385-387.
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Smalley, I. A. N. “The Teton Dam: rhyolite foundation+ loess core= disaster.” Geology Today 8.1 (1992): 19-22.
Smalley, I. J., and T. A. Dijkstra. “The Teton Dam (Idaho, USA) failure: problems with the use of loess material in earth dam structures.” Engineering geology 31.2 (1991): 197-203.
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