water pumping equipment and dewatering...
TRANSCRIPT
WATER PUMPING EQUIPMENT and DEWATERING SYSTEM
TSP-308 MPK Ferdinand Fassa
Lecture 11
dewatering
• The purpose is to remove water from an excavation without
causing instability in either the side slopes or the bottom
– Improve excavating and hauling
– Increase stability of excavated slopes
– Reduce lateral loads on bracing
– Prevent rupture of the bottom of the excavation
• Dewatering methods:
– open pumping
– pre-drainage
– cutoff and exclusion
– ground freezing (freezewall)
– combination
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Factors affecting the selection of dewatering method
• Nature of soil
• Groundwater hydrology
• Size and depth of excavation
• Proposed method of excavation and ground support
• Proximity of existing structures; type and depth of foundations
• Design and function for structure being built
• Schedule
• Nature of any contamination at the site
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water pump and dewatering system
side effects of dewatering
• Settlement of adjacent area
• Temporary reduction in yield of water supply wells in adjacent area
• Long-term damage to water supply aquifer due to salt water infiltration
• Aerobic organism attack to timber structure below water table
• Lower water table harms vegetation
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principle of fluid flow • D’arcy’s law of flow:
Q = K.A.h/L
Q = quantity of water flow
K = permeability of medium (soil)
A = cross sectional area
h/L = friction loss in distance L (hydraulic gradient)
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Piezometer Applications • Monitoring dewatering schemes for excavations and underground
openings.
• Monitoring ground improvement techniques such as vertical drains, sand drains, and dynamic compaction.
• Monitoring pore pressures to determine safe rates of fill or excavation.
• Investigating the stability of natural and cut slopes.
• Monitoring the performance of earthfill dams and embankments.
• Monitoring seepage and ground water movement in embankments.
• Monitoring pore pressures to check containment systems at landfills and tailings dams.
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Types of Piezometer
• Standpipe
• Pneumatic
• Vibrating wire – Multi level
– Vented
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terminologies of dewatering
• Aquifer zone of soil or rock through which groundwater moves
• Confined aquifer permeable zone between two aquicludes
• Aquicludes layers of clay or rock that is essentially impervious to water flow
• Transmissibility (T) the easiness of water moves through a unit width of aquifer
T = K.B (gpd/ft or m2/day)
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Range of Permeability of Natural Soil
Description Permeability (µ/sec)
Openwork gravel GP 10,000 or higher
Uniform gravel GP 2,000 – 10,000
Well graded gravel GW 500 – 3,000
Uniform sand SP 50 – 2,000
Well graded sand SW 10 – 1,000
Silty sand SM 10 – 50
Clayey sand SC 1 – 10
Silt ML 0.5 – 1.0
Clay CL 0.1 – 0.0001
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• To remove water from undesirable location to another locations
• To dry up construction site
• To provide water when and where needed
• Facilitate grouting process
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The main function is to move liquid material from one
(undesirable) location to another (desirable) locations
Water pumps are important pieces of equipment for wet construction, such as rivers, swamps, and when raining
Benefits and Applications of Water
Pumps in Construction Projects
Water pumps
water pump and dewatering system
example of pumping system
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Waste-water Plant
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Storage of wastewater
Sewage pump station
Homogenisation sludge storage
Intake lift station
Equalisation tank
Biological treat- ment process
Recirculation of digested slurry
Pumping return- activated sludge
Application of Pumping System
water pump and dewatering system
Mining
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Face & stage dewatering
Shaft bottom drainage
Main drainage station
Nuisance liquid/slurry handling
Recovery of water
Recovery of slurry
Active dewatering
Open cast drainage
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Industry
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Mixing of drilling mud
Mixing in quenching tank
Raw water intake
Waste water pump station
Coal pile run-off sump
White water handling
Handling of mill scale pro- cess water
Handling of bottom ash
water pump and dewatering system
Construction
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Flood defense & clean-up
Active dewatering
Seawater drainage
Temporary by-pass pumping
Tunnelling drainage
Manhole clean-up & drainage
Stand-by pumps
Work site drainage
water pump and dewatering system
• Dewatering cofferdams
• Removing water from pits, tunnels and other excavations
• Lowering the water table for excavations
• Furnishing water for jetting
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Construction pumps frequently perform under severe conditions:
water pump and dewatering system
Factors affecting the selection of Pumping Types
• Capability and capacity of pumping system • Types and amount of attachments (fitting, pipes, valves, etc.)
• Height of pumping
• Reliability of pumping system and equipment • Easiness of operation (including number of operators) • Easiness of maintenance and repair • Economic values
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Types of Pumping Equipment
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• CENTRIFUGAL PUMPS
Principle: kinetic to potential
energy conversion
centrifuge
reciprocating
• DISPLACEMENT PUMPS
• Reciprocating
• Diaphragm
water pump and dewatering system
Rotary Displacement Pumps
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Reciprocating Pumps
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inflow
outflow
single acting
inflow
outflow outflow
double acting
water pump and dewatering system
Reciprocating Pumps
Advantage Disadvantage
Able to deliver constant
rate at various elevation
Valves are potential to
damage, especially for
pumping water with
abrasive material
Efficient (small head loss) Potential damage for
pumping at high head
Self priming Bulky and heavy
High speed and large
capacity
Unsteady flow
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Pumping Capacity
c = loss of efficiency due to slippage (0.95 – 0.97)
d = diameter of cylinder (inch)
l = length of stroke (inch)
n = number of strokes / minute (x 2 for double acting)
N = number cylinders in a single pump (N = 2 for duplex)
Nnld
cQ
924
2
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Pumping Power
W = energy to move water (ft-lbs/minute)
w = weight of 1 gallon of water/liquid (lbs)
Q = pump capacity (gpm)
h = total head (including loss) (ft)
e = pumping efficiency (%)
e000,33
hQw
000,33
WP
Reciprocating Pumps
water pump and dewatering system
Pumping Power
• Water horse power (WHP) is the power required to accomplish pump a volume of water over a total dynamic head (TDH)
• Break horse power (BHP) is the amount of power that must be applied to the pump.
• Efficiency is the ratio of WHP over BHP
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3960
)gpm(Q)ft(TDHWHP
4569
min)/l(Q)m(TDHWHP
e
)gpm(Q)ft(TDHBHP
3960
BHP
WHPe
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Diaphragm Pumps
• Good for pumping dirty water or water that contains soil particles
• Good for pumping in large capacity
• Pumping capacity • two-inch, single : 2,000 gpm
• three-inch, single: 3,000 gpm
• four-inch, single : 6,000 gpm
• four-inch, double : 9,000 gpm
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Centrifugal Pumps • Rotation element (impeller) produces a velocity that causes
liquid to discharge against considerable pressure.
• Kinetic energy (velocity) is converted to potential energy (height)
• Pumping efficiency up to 75%
• Self-priming
• Submersible pump
• Multi-stages pump (for suction and discharge)
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V = velocity (fps)
g = gravity acceleration (fps) 32.2 fps @ sea level
h = height of fall (feet)
gh2V g2
Vh
2
water pump and dewatering system
Submersible Pumps
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Installation of Submersible Pumping System
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Pressure Loss in Piping System • Water flow inside piping system will loose its pressure (flow energy) due to:
Friction against pipe surface
Dimension and Geometric of pipe
Difference in elevation (head)
• Tables for Pump capacity
Equivalent length of pipe for various fittings & valves
Friction loss per 100 ft of steel pipes
Friction loss per 100 ft of hose
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h = 2.31 p or p = 0.433 h
h = difference in elevation (head), ft
p = pressure at, psi
water pump and dewatering system
Pressure loss in piping system
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tota
l st
ati
c h
ead
stati
c d
ischarg
e h
ead
tota
l
sucti
on
lift
C L impeller
C L discharge
Static suction lift is the vertical distance from the pump impeller to the surface of the liquid pumped.
Suction capability is limited by
atmospheric pressure. Maximum
practical suction lift is 25 ft.
Decreasing suction lift will increase the
volume that can be pumped.
Static discharge head is the vertical distance from the pump impeller to the point of discharge
Total static head
is the static
suction lift plus
the static
discharge head
water pump and dewatering system
Effect of Altitude and Temperature
• Above 3,000 ft there is a definite effect on pump performance. A self-priming pump will lose about one foot of priming ability for every 1,000 ft of elevation.
• At an elevation of 7,000 ft, a self-priming pump will only develop 18 ft of suction lift.
• As the temperature of water increases suction lift will decrease. At sea level practical suction lift is:
0oF = 25.0 ft.
100oF = 15.5 ft.
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forces to move water
• A pump works against “heads” (restraining forces)
ht = hl + hf + (hv or hp) + h0
ht = total dynamic head hl = static suction lift hf = total friction head hv = velocity head @ outlet hp = pressure head @ outlet h0 = elevation difference
• hv = v2/2g (ft) v = velocity • hp = p/w (ft) p (psf) & w (pcf)
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Water friction and velocity head in 1000 ft of smooth bore hoses
Size (inch)
Head Water Flow (gpm)
50 70 100 150 200 250 375 450 600 900 1200
2 ht 5 11 19 41 68
2 hv 0.4 0.9 1.6 3.6 6.5
3 ht 0.7 1.5 2.6 5.6 9.6 15 31
3 hv 0.1 0.2 0.3 0.7 1.3 2.0 4.5
4 ht 0.6 1.3 2.3 3.5 7.4 10 18
4 hv 0.1 0.2 0.4 0.6 1.4 2.0 3.6
6 ht 0.3 0.5 1.0 1.4 2.4 5.2
8 ht 0.4 0.6 1.3 2.3
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Head Loss
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Friction of water per 100 ft of plastic pipes
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Head Loss
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Head Loss
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Friction of water per 100 ft or 100 m of steel pipes
water pump and dewatering system
Head Loss
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Friction of water per 100 ft or 100 m of steel pipes
water pump and dewatering system
Head Loss
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Friction of water per 100 ft or 100 m of hose
water pump and dewatering system
Head Loss
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Friction of water per 100 ft or 100 m of hose
water pump and dewatering system
Piping Accessories
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Valves
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Diaphragm Valves
Gate Valves
Check Valves
Globe Valves
water pump and dewatering system
Head Loss
Item
Nominal size (inch)
1 1-1/4 1-1/2 2 2-1/2 3 4 5 6 8 10 12
90o elbow 2.8 3.7 4.3 5.5 6.4 8.2 11.0 13.5 16.0 21.0 26.0 32.0
45o elbow 1.3 1.7 2.0 2.6 3.0 3.8 5.0 6.2 7.5 10.0 13.0 15.0
Tee, side outlet 5.6 7.5 9.1 12.0 13.5 17.0 22.0 27.5 33.0 43.5 55.0 66.0
Close return bend 6.3 8.4 10.2 13.0 15.0 18.5 24.0 31.0 37.0 49.0 62.0 73.0
Gate valve 0.6 0.8 0.9 1.2 1.4 1.7 2.5 3.0 3.5 4.5 5.7 6.8
Globe valve 27.0 37.0 43.0 55.0 66.0 82.0 115.0 135.0 165. 215. 280.0 335.
Check valve 10.5 13.2 15.8 21.1 26.4 31.7 42.3 52.8 63.0 81.0 105.0 125.
Foot valve 24.0 33.0 38.0 46.0 55.0 64.0 75.0 76.0 76.0 76.0 76.0 76.0
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Equivalent length of steel pipe of fittings and valves (ft)
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Capacity of M rate Self Priming Centrifugal Pumps
water pump and dewatering system
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Capacity of M rate Self Priming Centrifugal Pumps
water pump and dewatering system
WELL-POINT SYSTEM
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depressed water area
depressed water table
original water table
water pump and dewatering system
Well-point System
• Are used to lower water table to provide a water-free construction site environment
• Are used in ground material that is homogeneous such as sands and silts.
• Good to pulling water down to approximately 18’ (6m) below original water table
• Staging will allow deeper dewatering but requires more space
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WELL-POINT SYSTEM
w
o
w
rR
hHBKQ
ln
2
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Q = pumping quantity (gpm)
K = permeability (fps)
H = depth of original water table (ft)
hw = depth of depressed water table (ft)
Ro = radius of depressed area (ft)
rw = radius of riser pipes (ft)
B = thickness of confined aquifer (ft)
H hw
Ro
rw
Q
B
original water table
water pump and dewatering system
Multistage Well-point System
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original water table
Depressed
water table
water pump and dewatering system
Multistage Well-point System
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raiser
raiser
raiser
header
spacing
2 – 5 ft
water pump and dewatering system
Well-point Dewatering System
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Main Pump
Raiser pipes Header pipes
water pump and dewatering system
Well-point Dewatering System
• Things to consider
Physical layout
Adjacent areas
Soil conditions
Permeability
The amount of water to be pumped
Depth of imperviousness
Stratifications
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Other well system
• Borewell system
– Large diameter
– Water supply
• Horizontal well system
– Oil and gas industry
• Concentric Dewatering System
• Vacuum wellpoints (for fine-grained soils)
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DEEP WELLS
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Large-diameter deep wells are suitable for lowering the water table when the soil becomes more pervious with depth or the excavation penetrates or is underlain by sand or coarse granular soils.
water pump and dewatering system
SURFACE PUMPING METHODS
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Sumps and Ditches:
A perimeter ditch, inside the excavation, carries seep water to a sump.
The sump is located in the deepest part of the excavation.
Water collected in the sump is pumped away.
ditch
sump water pump and dewatering system
Exercise
• Design water pump system to discharge water from a ditch to a temporary water storage, given the following technical specifications: – Required capacity 700 gpm
– Total pipe length 320 ft
– Depth of pipe suction below water 12 ft
– Height of pump above water 9 ft
– Height of water discharge above pump 35 ft
– Piping accessories:
• 2 gate valves
• 4 90o elbows
• 1 45o elbow
• 1 check valve
• 1 foot valve
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Terima Kasih
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Reference:
CONSTRUCTION DEWATERING
New Methods and Applications, 2nd Ed.
J. Patrick Powers