It's all about dewatering

1. DEWATERING
• DEFINITION-Removal of under ground water
– 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" pumps, centrifugal ("trash") pumps,
eductors, or application of vacuum to well points.

2. DEWATERING EQUIPMENTS IN CONSTRUCTION
-The purpose of construction dewatering is to
control the surface and subsurface hydrologic
environment in such a way as to permit the
structure to be constructed “in the dry.”
-Dewatering means “the separation of water
from the soil,” or perhaps “taking the water out
of the particular construction problem
completely.”
-This leads to concepts like pre-drainage of
soil, control of ground water, and even the
improvement of physical properties of soil.

3. METHODS OF DEWATERING
• Dewatering by pumps
• Dewatering by well points
• Dewatering by vaccum wells
• Dewatering by Electro osmosis wells

4. DEWATERING BY PUMPING
• When soil is excavated below or near the water
table, pumps will usually be used to dewater the site

5. PUMPING

6. CLASSIFICATION OF PUMPS
1.DISPLACEMENT
-RECIPROCATING PUMP
-DIAPHRAGM PUMP
2.CENTRIFUGAL PUMP
3.SUBMERSIBLE PUMPS
4.JETPUMPS

7. SELECTION OF PUMPS
• Rate at which the water must be pumped
• Discharge head and suction head
• Pressure head
• The variation in water level at suction head
• The altitude of the project
• Size of the delivery pipe

8. DEWATERING BY WELL POINTS

11. DEWATERING

12. VACCUM WELLS
This type is just wellpoints that are sealed at the
surface at the well casing with bentonite or clay in
order from the pump to get better suction.
In fine-grained soils, a sand filter should be used
around the well point and the riser pipe

13. ELECTRO OSMOSIS WELLS
 This method is the process of accelerating the flow of water through a soil
by using direct current.
 Usually space wells at intervals of about 35 ft – then drive grounding rods
between the wells. Attach a negative terminal of DC voltage at each well
and the positive terminal on each grounding rod.
 A voltage of 1.5 to 4 Volts per foot between the well and ground rod is
then applied. This will increase the flow of water to the well.
 The applied voltage should not exceed 12 V/ft. The typical current
requirements are 15 – 30 Amps per well. Which is a power demand of .5 –
2.5KW per well
 Studies have proven this method to be extremely effective for increasing
water flow through fine soil(Clay).