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Roger Weller, geology instructor
by Joanna Larranaga
Geological Importance in Civil Engineering:
The collapse of the St. Francis Dam
At a time like this, I envy the dead.
It was the night of March 12, 1928 in the city of Los Angeles when a rushing flood reaching 70 miles per hour took approximately 600 lives. This vicious flood carried in its way debris and huge concrete boulders, adding equipment, livestock and people on its 24 mile long path. This flood was a result of the St. Francis dam. Its purpose was to act as the new water reservoir for the Los Angeles area. How was this disaster the worse manmade catastrophic event of the 20th century? First we must understand the purpose the dam was to play. Then, I will analytically make obvious geological factors such as: materials, conditions of the foundation and location that played the major reasons in the devastating disaster in 1928.
It was years earlier that Los Angeles was a small ranch town with arid, desert- like climate. The Los Angeles River was the main water source supplying all that lived there generously. However, with new discoveries in oil and professional advances, Los Angeles quickly became the most desirable place to live. It did not take the Los Angeles River long to prove an inadequate source to the growing population. As people came the water table decreased. The city of Los Angeles demanded another water reservoir and the St. Francis dam was soon to be hypothesized.
The Santa Clarita valley in the Los Angeles area was deemed the perfect location for the dam. The valley was abundant in space providing hundreds of acres for construction. Also, the elements of the valley were most favorable for the new reservoir, because of the durable materials that made up the majority of the valley. William Mulholland, the Chief Executive Engineer, was in awestruck in the concentrations of concrete, conglomerate and laterite that he was surrounded by. So amused, he overlooked the presence of weak material, like schist and its quantity. He also disregarded the conditions of the material he was awed about and he started construction immediately.
The designing and construction went underway in 1922 and was achieved in 1926. The St. Francis Dam was a curved, concrete, gravity dam. The dam fulfilled its purpose for the city of Los Angeles and the efficiency of the dam was praised. However, to say all was great would be a terrible statement. The dam spiked concerns as it frequently leaked from different areas of the dam. On the day of March 12, 1928, the dam keepers notified Mulholland about a forceful, colored leak. The dam keepers were already cautious and worried of the damís durability, and they were amendment that Mulholland came to witness it himself.
Mulholland arrived later that day. He and a geologist inspected the leak together. The leak was located on the west abutment of the St. Francis Dam. It had a clay-like feel to it and the color was tinted red. Because dams were susceptible to leaks, Mulholland cleared the leak as normality for the dam. However, the geologist advised Mulholland that it was not normal for leaks to have a clay-like texture and to have a tint of red either. The geologist was right and on that same day, only a few hours after inspection, the dam failed. blogs.ei.columbia.org
The dam keeper and family were the
first ones to suffer the wrath of the flood. The flood wave reached a height of
140 ft. The center of the dam was all that remained. The geological factors
that were ignored since the beginning of construction could not be ignored any
longer. The materials of the dam and the location of the dam were thoroughly
examined and pronounced the cause of the collapse. For the remainder of this
paper I will emphasize the geological factors that could have prevented the
heartbreaking event entirely.
To begin with, the concrete and conglomerate that was used entirely on the St. Francis dam, was in bad condition. The concrete and conglomerate were badly fractured and could not maximize its potential and instead presented weak results. The water the dam was built to store permeated through the numerous fractures and dissolved most of the conglomerate. Furthermore, the fractures in the concrete pulled away from each other enough to unbalance the entire dam and caused uplift. The condition of the concrete is just the first factor mentioned and certainly not the last to be considered.
Another material that affected the efficiency of the St. Francis dam was laterite, which was used for the foundation. Laterite is a material whose main components are rock and soil. Mulholland thought using laterite was a great idea, because like concrete and conglomerate, it was known for its durability. What Mulholland failed to accomplish when using this material, was to research deeper in the nature of laterite under immense weight and water. Water has the tendency so dissolve rock over time and that is just what it did to the laterite. The water dissolved the entire rock component and left behind the soil characteristic. All in one word, the lack of attention to laterite, caused the laterite to be stripped, and then it completely softened the foundation of the St. Francis dam.
Lastly, the material schist is left to explain. Schist is the weaker material compared to concrete and conglomerate. In fact, Mulholland never planned on schist to act as a building factor for the dam. It was just there and Mulholland certainly did not think it was any good in spending time mentioning it. The trouble with schist was the scattered appearance of it. It was weak, and had a sheet-like appearance. As the concrete was moving and the laterite was dissolving the schist made it easy for the rocks to budge, with a near glide motion. The schist was the cherry on top that pushed the dam in a violent and sudden downfall.
The materials were the most important factors in the construction of the St. Francis dam and as demonstrated above, the materials were faulty from the beginning. More attention and knowledge of the materials could have avoided the disaster enormously. But to say the materials were the only reason, would not be justified. There is one last geological factor worth mentioning and is the most crucial one yet.
A fact that was later revealed was one in which the dam was built on an ancient landslide. In order for a landslide to occur, four conditions must be met. To state them quickly it is:
1) The slope must be steepened.
2) Weight must be added to the slope.
3) The slope must be lubricated.
4) A sudden and violent shaking of the ground will take place.
When construction started 1924 no one had any idea that the ground beneath them had collapsed before. So they went fourth, and created all the conditions for another landslide. The slope of the ground was steepened to shape the curve for the gravity dam. Tons of weight of building material pushed the surface of the ground down. The water the dam was storing not only permeated through the concrete, but down into the ground as well. Lastly, with the last slide of concrete the dam furiously collapsed and never was to be rebuilt.
They placed the cause of the failure on the western hillside. "The west end," the commission stated, "was founded upon a reddish conglomerate which, even when dry, was of decidedly inferior strength and which, when wet, became so soft that most of it lost almost all rock characteristics." The softening of the "reddish conglomerate" undermined the west side. "The rush of water released by failure of the west end caused a heavy scour against the easterly canyon wall ... and caused the failure of that part of the structure." There then "quickly followed ... the collapse of large sections of the dam." 
It turns out the materials and location was crucial for the damís structure. Yes, the majority of the foundation was used with durable materials, but it was the conditions of the materials that eventually brought the dam violently down. To restate the geological factors briefly: the fractured concrete, the perilous nature of laterite, and the fatal, unstable ground were the lead causes of the collapse. The The St. Francis dam proved geology was not handled correctly and innocent people paid the ultimate price.
After the reveal of the ancient landslide the only place the dam could go was down. It was unfortunate that this horrendous catastrophe had to happen to reveal the importance of geological knowledge. Since then, Geologists now work side by side with Civil Engineers on dam sites. The geologists advise best locations and materials. In conclusion, geology plays a crucial and vital role when designing and developing civil infrastructures.
1. Wilson, L. (2004). The rise of the golden city: Los Angeles in the twentieth century. Journal of Urban History, 30(2), 275-288.
2. ABET. (2011). Criteria for accrediting engineering technology programs, 2012 Ė 2013. Retrieved from http://www.abet.org/DisplayTemplates/DocsHandbook.aspx?id=1808
3. Public Broadcasting Service. (2001). New perspectives on the West: William Mulholland. Retrieved from http://www.pbs.org/weta/thewest/people/i_r/mulholland.htm
4.Outland, C. F. (1977). Man-made disaster: The story of St. Francis Dam. (Rev. ed.) Western Lands and Water Series III. Glendale, CA: Arthur H. Clark Company.
5. Rogers, J. D. (2006). Lessons learned from the St. Francis Dan failure. Geo-Strata, 6(2), 14-17.
6. Jackson, D. C. & Hundley, N., Jr. (2004). Privilege and responsibility: William Mulholland and the St. Francis Dam disaster. California History, 82(3), 8-47; 72ff.
7. Noted forensic geologist unravels the disaster. (1998). Retrieved from http://www.csun.edu/~fl1222/stfran.html