Hydraulic fill
Encyclopedia
A hydraulic fill is an embankment or other fill in which the materials are deposited in place by a flowing stream of water, with the deposition being selective. Gravity, coupled with velocity control, is used to effect the selected deposition of the material.
Where borrow pit
s containing suitable material are accessible at an elevation such that the earth can be sluice
d to the fill after being washed from the bank by high-pressure nozzles, hydraulic fill is likely to be the most economic method of construction. Even when the source material lacks sufficient elevation, it can be elevated to the sluice by a dredge pump. In the construction of a hydraulic fill dam
, the edges of the dam are defined by low embankments or dykes which are built upward as the fill progresses. The sluices are carried parallel to and just inside these dykes. The sluices discharge their water-earth mixture at intervals, the water fanning out and flowing towards the central pool which is maintained at the desired level by discharge control. While flowing from the sluices, coarse material is deposited first and then finer material is deposited (fine material has a slower terminal velocity thus takes longer to settle, see Stoke's Law) as the flow velocity is reduced towards the center of the dam. This fine material forms an impervious core to the dam. The water flow must be well controlled at all times, otherwise the central section may be bridged by tongues of coarse material which would facilitate seepage through the dam later.
Hydraulic fill dams can be dangerous in areas of seismic activity due to the high susceptibility of the uncompacted, cohesionless soils in them to earthquake liquefaction. In these situations, a dam build of compacted soil may be a better choice. The Lower San Fernando Dam http://cgpr.ce.vt.edu/Photo_album_for_geotech/Earthquake%20hazards/LSF%20dam/LSF%20dam%20-%20Main.html is an example of a hydraulic fill dam that failed during an earthquake.
The Fort Peck Dam
is an example of a hydraulic fill dam that failed during construction where the hydraulic filling process may have contributed to the failure.
Hydraulic fill is also a term used in hard rock mining and describes the placement of finely ground mining wastes into underground stope
s in a slurry by boreholes and pipes to stabilise the voids.
Where borrow pit
Borrow pit
A borrow pit, also known as a sand box, is a term used in construction and civil engineering. It describes an area where material has been dug for use at another location. Borrow pits can be found close to many major construction projects...
s containing suitable material are accessible at an elevation such that the earth can be sluice
Sluice
A sluice is a water channel that is controlled at its head by a gate . For example, a millrace is a sluice that channels water toward a water mill...
d to the fill after being washed from the bank by high-pressure nozzles, hydraulic fill is likely to be the most economic method of construction. Even when the source material lacks sufficient elevation, it can be elevated to the sluice by a dredge pump. In the construction of a hydraulic fill dam
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
, the edges of the dam are defined by low embankments or dykes which are built upward as the fill progresses. The sluices are carried parallel to and just inside these dykes. The sluices discharge their water-earth mixture at intervals, the water fanning out and flowing towards the central pool which is maintained at the desired level by discharge control. While flowing from the sluices, coarse material is deposited first and then finer material is deposited (fine material has a slower terminal velocity thus takes longer to settle, see Stoke's Law) as the flow velocity is reduced towards the center of the dam. This fine material forms an impervious core to the dam. The water flow must be well controlled at all times, otherwise the central section may be bridged by tongues of coarse material which would facilitate seepage through the dam later.
Hydraulic fill dams can be dangerous in areas of seismic activity due to the high susceptibility of the uncompacted, cohesionless soils in them to earthquake liquefaction. In these situations, a dam build of compacted soil may be a better choice. The Lower San Fernando Dam http://cgpr.ce.vt.edu/Photo_album_for_geotech/Earthquake%20hazards/LSF%20dam/LSF%20dam%20-%20Main.html is an example of a hydraulic fill dam that failed during an earthquake.
The Fort Peck Dam
Fort Peck Dam
The Fort Peck Dam is the highest of six major dams along the Missouri River, located in northeast Montana in the United States, near Glasgow, and adjacent to the community of Fort Peck...
is an example of a hydraulic fill dam that failed during construction where the hydraulic filling process may have contributed to the failure.
Hydraulic fill is also a term used in hard rock mining and describes the placement of finely ground mining wastes into underground stope
Stoping (mining method)
Stoping is the removal of the wanted ore from an underground mine leaving behind an open space known as a stope. Stoping is used when the country rock is sufficiently strong not to cave into the stope, although in most cases artificial support is also provided...
s in a slurry by boreholes and pipes to stabilise the voids.