Chapter 11- South Fork Dam Flashcards
- In the 19th century what was the safe width-to-height ratio for the design of modern masonry dams
The design of modern masonry dams had a ratio for its width to height 3:4
The worst dam disaster in the United States occurred on 31st May 1889 when the South Fork Dam suddenly burst following a period of unprecedented rain. What purpose was the dam originally built for and how were certain features of the dam’s construction modified when completed in 1853 and 27 years later, and what did these modifications do that dangerously compromised the dam’s structural integrity
the dam was built to bring a reliable source of water for Pennsylvania canal
* Modifactions where made to the bridge:
1. outlet pipes were removed
2. The dam lowered by 2ft
3. A trestle bridge was built across the spillway to allow the road to continue
4. a screen was placed in front of the trestle to prevent the loss of fish when the water overtoppled
5. Reduced the width of the spillway
all these modifactions reduced the capacity of the spillway to almost 1/3 of the intended design
- During the night of 2 December 1959, following five days of heavy rainfall, the dam suddenly cracked like and egg and burst, releasing 13 billion gallons of water. On finding that the design of the dam was entirely satisfactory what did the investigators find out about the foundations that pointed to the one of the embankments (the left) as the weak link
concrete starting cracking near the centre of the dam so it was thought that the abutment had shifted
* The design of the dam was checked and was fine
* Blocks of concrete were still found attached to each other and to pieces of bedrock therefore the joint had not failured. Joint failure was not the cause
* The fault was due to the weakness under the left embankment, this is what caused the collapse
What information, known one month before the collapse, prompted the engineer who succeeded Dargeou to write to Coyne suggesting an inspection of the dam
photo survey of the dam had revealed changes at 28 separate locations in the shape of the dam and in its foundations from its originally built dimensions
- And to close the example questions on this case study what was the root cause to the Malpasset Dam collapse
the root cause of the dam collapse was due to a thin clay-fillled seam in the rock adjacent to the left bank of the dam and had acted as a lubricant and caused the foundations to shift slightly. This displacement had cracked the dam.
