The second failure of the most deadly dam in the history of the United States suddenly happened. The Dam de Sant Francesc was a gravity of concrete 205 feet high in the cannon of San Francisquito, 30 miles north of Los Angeles. It was built to store water supplied by the main source of water in the city, the Los Angeles aqueduct, which brought water from the Owens Valley, to 200 miles further north.
Shortly after the end of the 1926 dam, a moderate filtration was seen in the dam, as well as two vertical contraction cracks on the face of the dam. William Mulholland, chief engineer of the Water Works and Supply Office of Los Angeles, along with his chief engineer assistant and general director Harvey Van Norman, inspected the cracks and judged them on waiting for a specific dam.
On March 12, 1928, shortly after the reservoir reached its first capacity, the dam goalkeeper, Tony Harnischfeger, who lived in the place, saw a new leak at the western foothills of the dam. He notified Mulholland and Van Norman, who spent two hours inspecting -he decided that there was no danger and left.
The dam collapsed just before midnight. An article by the ENR, written by the publisher of the Pacific Coast, Nathan A. Bowers, stated: “ Without the slightest warning, the large structure was suddenly broken: a single piece remained standing, while the rest fell to the floor of the valley or it was devastated.A large blocks of the concrete mass, which weighed many thousands of tons, were half a kilometer or more. ”
The full water of 38,000 hectares (12 billion gallons) of water formed a wave of 140 feet high that beat the cannon for 11 miles, and then along the Santa Clara river to the west for 50 miles to the ocean, going down to 1,825 feet. Bridges, roads and line of the South Pacific Railway branch. “The number of deaths is calculated at 431, and many bodies never recovered.
Sixty -four of the victims were workers at the house of power and their families. Eighty four victims were staff in southern California Edison who lived in a temporary construction field on the riverbank.
Bowers, based in San Francisco, quickly traveled to the disaster, studied the wreck, interviewed the engineers who built the dam and other prey engineers, and telegated a 2,400 -word article at the New York Office of ENR within 36 hours after failure. He brought strong credentials to his reports, after having obtained a doctorate. In Civil Engineering of the University of Stanford, in which his thesis was entitled “Engineering Fallas in the field of water power”.
His article stated the founding of the dam: “The excavation for the Foundation spread 30 feet below the bed of current in the middle of the channel and less depths at higher elevations. Two types of rock occur at the foundation, gathering on a well-defined plane visible on the net side of the canyon. Under the bed of the stream and the left bed [east] Bank there is a geologically classified rock as a ski, but locally known as Graywacke’s Shale. The right bank over the contact plan is usually called red conglomerate. Although part of this rock was not of the best quality, however, it was accepted as the proper basis, and excavations of the base rock and buttresses became deep enough to provide what was considered a safe anchor. “”
Bowers said that the dam did not have many characteristics found in other dams. “No reintegration of foundations was made, but … in the holes at the bottom of the current they sank 20 to 30 feet deep and … the pipes of 4 in. The joints, but allow them to produce contraction cracks wherever they are closed and later those that are necessary.
Bowers described how the fundamental rock was eroded. “ On the right bank, the rock is now naked from the bed to the crest level. This part of the cross section of the barrel, now exposed, has been significantly eroded below the surface where the concrete was poured … It was at least 15 feet in some places.We are two different formations in a contact plane of this bank … Throughout the contact the fingers.
The land along a section of 40 miles from the Santa Clara valley was denied by the flood. The orchards and fertile agricultural fields were now “sections of spine wind and gravel deposits.
Some living orchard trees could save by removing waste. The efforts of repair and recovery were robust. The City Council approved a $ 1 million allocation. The city formed a plan with the chapter of that of the General Associate Contractors of America, where 1,300 workers entered the flood area with tractors, trucks, power shovels and polypastos to erase waste, recover partially buried cars and help in rescue work. AGC chose ten companies for non -profit work.
A simple device that was invaluable was the “stone boat”, a steel sled used to move large loads of waste to burn batteries. They were made of two pieces of old railway welded at the bottom as runners and went back behind the tractors.
The abnormal pressure of floodwater caused three pauses in the aqueduct for a total of 412 feet of crew made repairs and restored the aqueduct in the service 12 days after the disaster. During this time, the city was based on storage reservoirs at the lower end of the aqueduct.
Ralph Bennett, an engineer, visited the prey on the same day as Bowers, and contributed to an article in his findings. He wrote: “The schists on which this prey was found will remain very high when they remain dry and contain. But when they wet they become soft and soapy. They are completely destroyed and they can be chosen in small pieces. They climb freely where they are subjected to the flow action. Up.
Two months later, Bowers wrote a long article reviewing and extracting the findings of the six researchers, each formed by engineers and geologists. His conclusions about the causes of failure were very good. The report of the Engineering Committee of the City Council of La LA, chaired by Dr. Elwood Mead, head of the United States Claim Office, said: “ The red conglomerate cementation material consists of clay, amorphous iron and silica oxides dissolve the plaster that filled some of the fissures in the formation. Brought with the chalk in solution, the water would be clear and the plaster would be clear, wash part of the basis of the dam. “
The report of the Technical Commission of the County’s District prosecutor found that “the dam was built without a sufficiently exhaustive examination and comprehension of the foundation materials on which the dam was built; that the failure of the dam was due to the incompetent geological formations on which the dam was built; that the taken as a designed should not have been built on this site.”
Perhaps the most cursed mistake was that such a massive masonry structure was designed and built completely at home without any exterior review. Mulholland, a self -taught engineer, had run the office for more than two decades, during which he had built 19 prey. State law exempt municipalities from needing state permits for prisoners. The jury’s jury verdict stated: “The construction of this dam, without having the design and foundation conditions passed by independent engineers and geologists, and without more exhaustive and systematic methods of design, supervision and inspection, was a mistake in the engineering trial of it.” In the Coroner’s investigation, Mulholland accepted responsibility, saying: “Whether it is good or bad, do not blame anyone, you only pay attention. If there was an error in the human judgment, I was the human being, I will not try to fix it to anyone else.”
A publisher was enroused just after the tragedy stated: “The current disaster does not contain any fact or that it justifies the restriction of the construction of dams. However, the need, for an effective review of the individual judgment on foundations where there are many lives at stake, says.” ENR had promoted for the first time the supervision of all the prisoners by state officials in 1889 after the junus of Johnstown. California passed a law that establishes the state supervision of its dams in 1929.
