Why did hydraulic filling fall out of favor for building embankment dams?

Hydraulic filling, a technique where materials are transported by water and deposited by draining the surplus, was a popular construction method for embankment dams in the early 20th century. However, the practice fell out of favor primarily due to significant safety concerns regarding structural stability.1

The primary reason for its decline was the vulnerability of these structures to liquefaction. Because hydraulic fill dams retain a large quantity of water within their soil structure, they are susceptible to losing strength and "slipping" when subjected to seismic shocks. This risk was highlighted by two major incidents:2
* A partial failure of the Fort Peck Dam during its construction in the late 1930s.1
* The partial collapse of the Van Norman Dam in Los Angeles during a 1971 earthquake, where the saturated hydraulic fill failed.2

Modern engineering now favors placing soils in thin, individually compacted layers to ensure maximum density and strength, rather than relying on the hydraulic deposition process.1