Construction Technology IV

(DQS252)
Week 5: Basement
Dewatering System
Lecturer / Team Teaching
DR. NORHAFIZAH YUSOP
Email:
norha158 @uitm.edu.my
 WELL POINT
SYSTEM

(BL)

SHALLOW / HORIZONTAL
DEEP BORED TYPES OF GROUND
WELLS DEWATERING WATER
SYSTEM CONTROL

SUMP
PUMPING
SUMP PUMPING SYSTEM
• Sump or water collection pit should be excavated below
the formation level of the excavation.
• Preferably sited in a corner position to reduce any
possible soil movement due to settlement.
• Open sump pumping is usually limited to maximum
depth of 7.50m due to the limitations of suction lifts of
pump.
• Alternative method to open sump pumping is jetted
sump.
• In this method a metal tube jetted into the ground and
the void created is filled with a sand media, a disposable
hose and strainer (Filter).
• This method is suitable for most subsoils and in
particular gravels and coarse sands when working in
open shallow excavations.
SUMP PUMPING SYSTEM
JETTED SUMP PUMPING SYSTEM
THE INSTALLATION OF SUMP PUMPING
SYSTEM
1. Before performing a sump pump installation, it is always disconnect
the pump from the power source before handling.
2. The pit must be clear from any debris and place the pump inside. A
solid bottom is required to prevent dirt from clogging the pump.
3. The pump is centered so that it will not come into contact with the
sides of the pit which might cause operational problems.
4. Pipe the sump pump discharge into the drainage system, a dry well
or a storm drain.
5. A swing type check valve on the discharge piping is install to
prevent backflow of water into the sump pump.
THE INSTALLATION OF SUMP PUMPING
SYSTEM
6. In the discharge pipe, a relief hole is drill to ensure that the
pump will not “air lock”, which would allow the pump to run
but not pump water.
7. The pump cord is secure to the discharge pipe.
8. The sump is test by running a water through it.
9. The sump pump is fill with water to the normal turn on level.
10. After the sump pump installation is completed, the
installation of a sump pump cover can be done. This will help
eliminate debris from falling on top of the pump.
ADVANTAGES & DISADVANTAGES OF
SUMP PUMPING SYSTEM
ADVANTAGES DISADVANTAGES

It is suitable for all types of ground It cannot be used for a deeper

excavation due to its limitation of
types and conditions. suction lift of pumps.
Economical to install and maintain. Inappropriate sump pumping
installation will cause a significant
ground movement.
Simplest dewatering method. The discharge of the water at the
disposal point is likely to cause
environmental problems.
Can be added or removed easily to
meet required pumping capacity.
May be removed from one sump and
used elsewhere if needed.
WELL POINT SYSTEM
• The oldest practical method of pre-drainage.
• It is best suited for relatively shallow excavations
in stratified soils (from gravel through to silty
fine sand).
• Used for lowering the water table in porous
(absorbent) soils or for intercepting seepage.
• To dewater beyond 5.0 – 6.0m depth requires a
multi stage installation.
WELL POINT SYSTEM
• Water jet into the ground a number
of small diameter wells which are
connected to a header pipe which is
attach to a vacuum pump.
• Well point system can be installed
with the header pipe acting as:
i. A ring main enclosing the area to
be excavated.
ii. A progressive line arrangement
where the header pipe is place
along side a trench or similar
excavation to the side or both
sides.
WELL POINT SYSTEM
WELL POINT SYSTEM
ADVANTAGES & DISADVANTAGES OF
WELL POINT SYSTEM
ADVANTAGES DISADVANTAGES
Can be installed along any flexible line The well point system is not suitable
or shape of excavation area. for very deep areas because it will
cause a very large sloping area.
Quick and easy to install in suitable Long pumping periods contribute to
soils. high installation & maintenance cost.
Economical for short pumping periods Difficult to install in open gravel or
of a few weeks. ground containing cobbles and
boulders.
The number of well can be reduced Pumping must be continuous and
because of its high dewatering noise of pump may be a problem in a
capacity. built up area
SHALLOW BORED WELL SYSTEM
• Similar to well point pumping, but more appropriate
when the earlier method is to be operated for a
longer period, thus running cost a less.
• Can be arrange as a multi – stage system when
depth exceed 5m.
• Used as an alternative to a multi stage well point
system installation when depth greater than 9m is
required.
• A borehole is formed by sinking a 300 – 600 mm
dia. Steel lining tube into the ground to the required
depth.
• A perforated well liner (plastic, nylon, or steel) to be
install with an electro-submersible pump to extract
water.
SHALLOW BORED WELL SYSTEM
• The annular space is fillet with suitable media such
as sand and gravel as the outer lining tube is
remove.
• Shallow wells comprise surface pumps which draw
water through suction pipes installed in bored wells
drilled by the most appropriate well drilling and or
bored piling equipment. The limiting depth to which
this method is employed is about 8 m. Because wells
are pre-bored, this method is used when hard or
variable soil conditions preclude the use of a well
point system.
• The shallow well can be used to extract large
quantities of water from a single hole.
DEEP BORED WELL SYSTEM
• Deep wells can be used to dewater pervious sand
or rock formations or to relieve artesian pressure
beneath an excavation.
• They are particularly suited for dewatering large
excavations requiring high rates of pumping,
and for dewatering deep excavations for dams,
tunnels, locks, powerhouses, and shafts.
• Excavations and shafts as deep as 300 feet can
be dewatered by pumping from deep wells with
turbine or submersible pumps.
• Can be defined as a dewatering device equipped
with its own submersible pump.
DEEP BORED WELL SYSTEM
• Deep well systems consist of one or more
individual wells.
• Deep wells can vary from 3 to over 24 in. (75 to
600 mm) in diameter, and pump from fractions
of a gallon per minute to thousands of gallons
per minutes.
• Suitable for high water-table or confined
aquifers area and will lower the water table.
• Can be installed from 20 feet (6m) to 100 of feet
(30m) deep or more in a single lift without
staging.
DEEP BORED WELL SYSTEM
DEEP BORED WELL SYSTEM
DEEP BORED WELL SYSTEM
DEEP BORED WELL SYSTEM
SUBMERSIBLE PUMP
THE INSTALLATION OF BORED WELL
• When water has to be extracted from depths greater than
8 m- shallow wells to gain a few extra meters of depth
the deep wells are such and submersible pumps installed
within them.
• The diameter will be 150 – 200 mm larger than the well
inner casing, which in turn is sized to accept the
submersible pump.
• Deep well systems use bored wells installed by cable
percussion or rotary drilling methods.
ADVANTAGES & DISADVANTAGES OF
BORED WELL SYSTEM
ADVANTAGES DISADVANTAGES
It can be installed around the edge of Difficult to install in open gravel or
an excavation and thus leave the ground containing cobbler and
construction area obstruct by boulders.
dewatering equipment.
Ability to penetrate strata impervious Pumping must be continuous and
with the jetting method of well point noise of pump may be a problem in a
systems. built up area.
Installation of up to 100 feet (30m) Suction lift is limited to about 5.25 –
deep or more in a single stage. 5.5m, if greater lowering is needed
multi stage installation is necessary.
Capable of pumping thousands of Require time for setting up and
gallons per minute per well. dismantling the machine.
Large displacement of soil may cause
soil movement.
 THANK YOU
ANY QUESTIONS?
J
Construction Technology IV
(DQS252)

WEEK 6: BASEMENT
BLENDED LEARNING
Lecturer / Team Teaching
DR. NORHAFIZAH YUSOP
Email:
norha158 @uitm.edu.my
DEWATERING SYSTEM
• Dewatering is the process of removing water from
an excavation.
• Ground water can be effectively controlled by a variety of
method which have been designed either to:
▫ lowering the groundwater table before the excavation
works (Lower the water table). This method of
dewatering is often used by placing pipelines in areas
with high groundwater levels.
▫ Alternatively, excavation may be accomplished first
and the water simply pumped out of the excavation
site as work proceeds (Exclude the water from
particular area).
DEWATERING SYSTEM
• Methods for controlling groundwater may be
divided into three categories:
▫ Removal of groundwater from the site by
pumping from sumps, wells, well points, or drains.

▫ Reduction of artesian pressure beneath the

bottom of an excavation.

▫ Isolation of the excavation from the inflow

of groundwater by a sheet-pile cutoff, grout
curtain, slurry cutoff wall, or by freezing.
TYPES OF DEWATERING SYSTEM
• Temporary dewatering systems.
Dewatering and control of groundwater during construction may
be accomplished by one or a combination of methods (sump
pumping, well points, deep bored well). The applicability of
different methods depends on various types of excavations,
groundwater lowering, and soil conditions.

• Permanent drainage systems.

A method often used for permanent groundwater control consists
of relief wells installed beneath and adjacent to the
structure, with drainage blankets beneath and
surrounding the structure at locations below the water
table. The water entering the wells and drainage blanket
is carried through collector pipes to sumps, pits, or
manholes, from which it is pumped or drained.
Permanent groundwater control may include a combination of
wells, cutoffs, and vertical sand drains.
PERMANENT DEWATERING SYSTEM
THE PRINCIPAL FACTORS AFFECT THE CHOICE OF
THE DEWATERING TECHNIQUES

• The soil within which the excavation is to take

place.
• The size of the excavation (and available space).
• The depth of ground water lowering.
• The flow into the excavation.
• Propose method of excavation.
• Proximity of existing structural and their depths
and types of foundation.
• Economic considerations.
COST CONSIDERATION FOR
DEWATERING SYSTEM
• Type, size, and pumping requirements of
project.
• Type and availability of power.
• Labour requirements.
• Duration of required pumping.
 WELL POINT
SYSTEM

(BL)

SHALLOW / HORIZONTAL
DEEP BORED TYPES OF GROUND
WELLS DEWATERING WATER
SYSTEM CONTROL

SUMP
PUMPING
HORIZONTAL DEWATERING SYSTEM
• Consist of installing into the ground a 100mm dia.
PVC suction pipe (max depth 5m).
• The pipe is covered with a nylon filter sleeve to
prevent the infiltration of fine partial.
• The pipe is installed using a special machine which
excavates a narrow trench, lays pipe and backfill the
excavation in one operation at speed up to 180m/hr.
• The pipe is than connected to a single suction pump
(handle approx. 230m of pipe run).
• For distance in excess of the pumping length, and
overlap of consecutive pipe length of up to4m is
required.
HORIZONTAL DEWATERING SYSTEM
HORIZONTAL DEWATERING SYSTEM
HORIZONTAL DEWATERING SYSTEM
ADVANTAGES & DISADVANTAGES OF
HORIZONTAL DEWATERING SYSTEM
ADVANTAGES DISADVANTAGES
Eliminates the need for capital investments Need special excavator to excavate the
for headers, points, swings, punches, horizontal trench for inserting the pipe.
cranes, jet hoses, jet pumps, special fittings,
and transport equipment used in
traditional well pointing.
Reduces conventional equipment rental
cost and promotes more productive use of
on-site construction equipment and labour.
Reduces debris and site congestion caused
from jetting.

Quicker installation than conventional well

pointing, allowing installation on short
notice to accommodate tight production
schedules.
 THANK YOU
ANY QUESTIONS?
J