WATER PUMPING EQUIPMENT and DEWATERING SYSTEM€¦ · · 2015-01-13WATER PUMPING EQUIPMENT and...

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

2 water pump and dewatering system

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

3

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


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)


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.


Types of Piezometer

• Standpipe

• Pneumatic

• Vibrating wire – Multi level

– Vented


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)


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


• To remove water from undesirable location to another locations

• To dry up construction site

• To provide water when and where needed

• Facilitate grouting process

10

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


example of pumping system

11

Waste-water Plant

12

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


Mining

13

Face & stage dewatering

Shaft bottom drainage

Main drainage station

Nuisance liquid/slurry handling

Recovery of water

Recovery of slurry

Active dewatering

Open cast drainage


Industry

14

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 process water

Handling of bottom ash


Construction

15

Flood defense & clean-up

Active dewatering

Seawater drainage

Temporary by-pass pumping

Tunnelling drainage

Manhole clean-up & drainage

Stand-by pumps

Work site drainage


• Dewatering cofferdams

• Removing water from pits, tunnels and other excavations

• Lowering the water table for excavations

• Furnishing water for jetting

16

Construction pumps frequently perform under severe conditions:


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


Types of Pumping Equipment

18

• CENTRIFUGAL PUMPS

Principle: kinetic to potential

energy conversion

centrifuge

reciprocating

• DISPLACEMENT PUMPS

• Reciprocating

• Diaphragm


Rotary Displacement Pumps


Reciprocating Pumps

20

inflow

outflow

single acting

inflow

outflow outflow

double acting


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


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

22

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


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

23

3960

)gpm(Q)ft(TDHWHP

4569

min)/l(Q)m(TDHWHP

e

)gpm(Q)ft(TDHBHP

3960

BHP

WHPe


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

25

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)

26

V = velocity (fps)

g = gravity acceleration (fps) 32.2 fps @ sea level

h = height of fall (feet)

gh2V g2

Vh

2


Submersible Pumps


Installation of Submersible Pumping System


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

30

h = 2.31 p or p = 0.433 h

h = difference in elevation (head), ft

p = pressure at, psi


Pressure loss in piping system

31

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


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.


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)


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


Head Loss

35

Friction of water per 100 ft of plastic pipes


Head Loss


Head Loss

37

Friction of water per 100 ft or 100 m of steel pipes


Head Loss

38

Friction of water per 100 ft or 100 m of steel pipes


Head Loss

39

Friction of water per 100 ft or 100 m of hose


Head Loss

40

Friction of water per 100 ft or 100 m of hose


Piping Accessories


Valves

42

Diaphragm Valves

Gate Valves

Check Valves

Globe Valves


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

43

Equivalent length of steel pipe of fittings and valves (ft)


44

Capacity of M rate Self Priming Centrifugal Pumps


45

Capacity of M rate Self Priming Centrifugal Pumps


WELL-POINT SYSTEM

46

depressed water area

depressed water table

original water table


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


WELL-POINT SYSTEM

w

o

w

rR

hHBKQ

ln

2

48

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



Multistage Well-point System

49


Depressed

water table


Multistage Well-point System

50

raiser

raiser

raiser

header

spacing

2 – 5 ft


Well-point Dewatering System

51

Main Pump

Raiser pipes Header pipes


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


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)


DEEP WELLS

54

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.


SURFACE PUMPING METHODS

55

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


Terima Kasih

57

Reference:

CONSTRUCTION DEWATERING

New Methods and Applications, 2nd Ed.

J. Patrick Powers

WATER PUMPING EQUIPMENT and DEWATERING SYSTEM€¦ · · 2015-01-13WATER PUMPING EQUIPMENT and...

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