Dewatering
Encyclopedia
Dewatering is the removal of water
from solid material or soil by wet classification, centrifugation
, filtration
, or similar solid-liquid separation process
es, such as removal of residual liquid from a filter cake
by a filter press
as part of various industrial processes.
Construction dewatering, unwatering, or water control are common terms used to describe removal or draining groundwater or surface water from a riverbed
, construction site
, caisson
, or mine shaft, by pumping or evaporation. On a construction site, this dewatering may be implemented before subsurface excavation for foundations, shoring, or cellar space to lower the water table
. This frequently involves the use of submersible "dewatering" pump
s, centrifugal ("trash") pumps, eductors, or application of vacuum
to well points.
around the well in which there is little or no water remaining in the pore spaces of the surrounding soil. Deep wells work best in soils with a permeability of k=1x10−3m/s to 1x10−5m/s; the amount of drawdown
that a well can achieve is limited only by the size of the pump.
Deep wells can be installed in a ring around an excavation to lower the water level and maintain a safe, dry site. Several equations can be used to design deep well dewatering systems, however many of these are based on empirical data and occasionally fail. Practice and experience, along with a firm understanding of the underlying principles of dewatering, are the best tools for designing a successful system. Some dewatering situations "are so common that they can be designed almost by rule of thumb".
Deep wells
are also used for aquifer test
ing and for groundwater drainage by wells.
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
from solid material or soil by wet classification, centrifugation
Centrifugation
Centrifugation is a process that involves the use of the centrifugal force for the sedimentation of mixtures with a centrifuge, used in industry and in laboratory settings. More-dense components of the mixture migrate away from the axis of the centrifuge, while less-dense components of the mixture...
, filtration
Filtration
Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...
, or similar solid-liquid separation process
Separation process
In chemistry and chemical engineering, a separation process, or simply a separation, is any mass transfer process used to convert a mixture of substances into two or more distinct product mixtures, at least one of which is enriched in one or more of the mixture's constituents. In some cases, a...
es, such as removal of residual liquid from a filter cake
Filter cake
A filter cake is formed by the substances that are retained on a filter. The filter cake grows in the course of filtration, becomes "thicker" as particulate matter is being retained. With increasing layer thickness the flow resistance of the filter cake increases. After a certain time of use the...
by a filter press
Filter press
Filter press which describes the style of filters developed from the 19th century onwards originally for clay. The majority of today's filters are more correctly called "chamber filter press", "Membrane filter press", or "Membrane Plate Filter"...
as part of various industrial processes.
Construction dewatering, unwatering, or water control are common terms used to describe removal or draining groundwater or surface water from a riverbed
Riverbed
Riverbed may refer to:*Stream bed, the channel bottom of a stream or river or creek*Wadi, a dry riverbed that contains water only during times of heavy rain*Riverbed Technology, an American technology company...
, construction site
Construction Site
Construction Site is a television series created by The Jim Henson Company in 1999, and consists of 7 construction vehicles. The show was broadcast on ABC Kids for a while, and had a range of videos. It was originally produced for and shown on CITV starting in 1999. In 2000 it was nominated for a...
, caisson
Deep foundation
A deep foundation is a type of foundation distinguished from shallow foundations by the depth they are embedded into the ground. There are many reasons a geotechnical engineer would recommend a deep foundation over a shallow foundation, but some of the common reasons are very large design loads, a...
, or mine shaft, by pumping or evaporation. On a construction site, this dewatering may be implemented before subsurface excavation for foundations, shoring, or cellar space to lower the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
. This frequently involves the use of submersible "dewatering" pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
s, centrifugal ("trash") pumps, eductors, or application of vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
to well points.
Dewatering by deep wells
A deep well typically consists of a borehole fitted with a slotted liner and an electric submersible pump. As water is pumped from a deep well, a hydraulic gradient is formed and water flows into the well forming a cone of depressionCone of depression
A cone of depression occurs in an aquifer when groundwater is pumped from a well. In an unconfined aquifer , this is an actual depression of the water levels. In confined aquifers , the cone of depression is a reduction in the pressure head surrounding the pumped well.When a well is pumped, the...
around the well in which there is little or no water remaining in the pore spaces of the surrounding soil. Deep wells work best in soils with a permeability of k=1x10−3m/s to 1x10−5m/s; the amount of drawdown
Drawdown
Drawdown has four distinct meanings:* Drawdown , a lowering of a reservoir or a change in hydraulic head in an aquifer, typically due to pumping a well.* Drawdown , decline in the value of an investment, below its all-time high....
that a well can achieve is limited only by the size of the pump.
Deep wells can be installed in a ring around an excavation to lower the water level and maintain a safe, dry site. Several equations can be used to design deep well dewatering systems, however many of these are based on empirical data and occasionally fail. Practice and experience, along with a firm understanding of the underlying principles of dewatering, are the best tools for designing a successful system. Some dewatering situations "are so common that they can be designed almost by rule of thumb".
Deep wells
Water well
A water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a trash pump, a vertical turbine pump, a handpump or a mechanical pump...
are also used for aquifer test
Aquifer test
An aquifer test is conducted to evaluate an aquifer by "stimulating" the aquifer through constant pumping, and observing the aquifer's "response" in observation wells...
ing and for groundwater drainage by wells.