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Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.

इंटरनेट मानक

“!ान $ एक न' भारत का +नम-ण”Satyanarayan Gangaram Pitroda

“Invent a New India Using Knowledge”

“प0रा1 को छोड न' 5 तरफ”Jawaharlal Nehru

“Step Out From the Old to the New”

“जान1 का अ+धकार, जी1 का अ+धकार”Mazdoor Kisan Shakti Sangathan

“The Right to Information, The Right to Live”

“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता है”Bhartṛhari—Nītiśatakam

“Knowledge is such a treasure which cannot be stolen”

“Invent a New India Using Knowledge”

है”ह”ह

IS 9759 (1981): Guidelines for dewatering duringconstruction [CED 43: Soil and Foundation Engineering]

IS: 9759 -1981

Indian Standard

Reaffirmed 2008

GUIDELINES FORDEWATERING DURING CONSTRUCTION

(First Reprint AUGUST 1997)

UDC 624.152.61 (026)

© Copyright 1981

BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

Gr 8 December 1981

IS: 9759.1981

Indian StandardGUIDELINES FOR

DEWATERING DURING CONSTRUCTION

Foundation Engmeermg Sectional Committee, BDC 43

ChairmanPROF DINESH ~10HAN

RefJ,.ese"lin~

Central Building Research Institute (CSIR),Roorkee

(CSIR),InstituteCentral Boddrog ResearchRocrkee

Calcutta Port Trust. Calcutta

The Concrete ASSoCIatIon of India, Bombay

Public Works Department, C han dig a r hAdnurustration

Central Warehousing Corporation, New DelhiMachenzres Limited, BombayEngineers India Limned, New Delhi

MembersDR R K. BHANDARI

CHIEF ENGINEFR

SHRt S GtiHA (Alterndte)SHRt M. G. DANDAVATE

SHRl N C. DUOQAL (Allernat!)SHRl A G DMTIDAR

SHRI A. P J\.IATHURSHRl V. B. MATHURSHRT T K D MUNlII

SHRI M IYENGAR (Alternate)

In personal capacity (5 Hungerford Road, 121Huneaford Street, Calcutta)

SaRI V. C. DFSHPANDE The Pressure Prlmg Co (I) Pvt Ltd, BombayDIRECTOR (CSMRS) Central Water & Power Oomrmssion, New Deihl

DEPUTY DIRECTOR (CSMRS) (Alternate)SHRI A H DIVANTI Asia Foundations and Construction Co Pvt Ltd.

Bombay:-'HRI A. N JANGLE (Allt"NlQlt')

DR R. K. DAS GVPTA Simplex Concrete Piles (India) Pvt Ltd. CalcuttaADDITIONAL CHI£P ENGINEER (.4lternak)

DR JAGDISH NARAI"l Indian Oeotechmc Society, New DelhiPROF SWAMI SARAN (Alternate)

SHRT G. S.JAlN G. S. Jam &. Associates, RocrkeeSHRI AmOK KTJM~RJAIN (Alternate)

JOINT DIRECTOR (Dt National Burldmgs Organisation, New DelhiSHlU SU""IL B~RY (Alternate)

JOINT DIRECTOR RESEARCH (51\..1) Ministry of Railways (RDSO)]OlNT DZRECTOR RESEARCH (B&5) (Alternate)

DR R K. KATTt Indian l nsnrute of Te-chnology, BombaySHRI S. R KllLKARNI M. N Dastur & Co Pvt Ltd, Calcutta

SHRI S Roy (Alternate)SHRIO. P. MALHOTRA

(Contmued on page 2)

\Cl Copyrrght 1981

fjUKEAU Ot INDIAN STANDARDS

This publication is protected under the IndIan CopYright Act (XIV of 1957) andrecrodccnon In whole or III part by any means except With wrnten perrmsston of thepublisher shall be deemed to be an mrnngement of copYright under the said Act

IS : 9759.1981

(Contmued from page J)

RepreJtnlmgThe Hmdustan Construction Company Limited,

Bombay

Cerrundra Co Ltd, Bombay

The Braithwaite Burn & Jessop Construction CoLtd, Calcutta

Vliavariag ar Steel Plant (SAll. New De/tilUnrc ersny of Roorkee, RoorkeeGammon India Limited, Bombay

Engmeer-m-Chref?s Branch, Army Headquarters,New Delhi

MembersSHRl B. K PANTHAKY

DR S. P ';HRIVASTAVA

UR R KAPlTR (Aflemate)BIlIG OMBIN. SINGH

SHRI V. M. MADGE (Aturnatt)

SIIRI M. R PuN] .....SHRI S. MUKHERJEE (AlJulIQJe)

SHRI N. E. V RAGHVA"'l

Bokarn Steel Plant (Steel Autborary of India),Bokaro

DR V V. S Reo Nagadr Consultants Pvt Ltd, New DeihlSHRI ARJUN RIJHSINGIIANI Cement Corporation of India, New Delhi

SHRJ 0 S SRI vASTAVA {Altanal",}DR A SARGUNAN College of Engmeenng, GUlOdy

SHRI S BOOMI"'4'ATHAN (Atlernnlf)SURI K. R. SAnNA Pubhc works Department, Government of Andhra

Pradesh, HyderabadUnited Technical Consultants Pvt Ltd, New Delhi

5HFll A A R"'JuPROF (.OPAL kANJAN

SHRT T N. StlDDA RAO

Smll S A. REDDI (Allcrnatr)SHRI Y V NARA'>TMHA RAO

J...l"'J H K HIIlTT<\NI (Alternale)SURI N SIVAliURU Muustrv or Shipping and Transport, New Delhi

'sHRI n \' ~11l.K'" {A/ter,ralf')SUPER1NTENDI~(. b N GIN r; r R Ce-ntral Pubhl- WOrks Department, New Dt"lhl

(UE.!>IG"'SlEXEClJTIVF ENC.JNHR (DFSIGNS) V (Alternate)

I;jHRI M D TAMBE"'AR Bombay Port Trust, BombayDR i\ \ ARAOARAJA!>l Indian Ineutuce of Technology, New Deihl

DR R KANIRAJ (Altanale)~HRI G RAMA.... Director General, B1S (E~-offiClo Ml'mber)

Director {en' Engg)

Secretary

SHRT K. M. MATHUR

Deputy Director (en' Engg), DIS

Miscellaneous Foundauon Subcomnuttee , BDC 43 : 6

ConvenerSHR( SHiTALA SHARAN Pubhc Works Department. Luckncw

MembtrfSHRI E. T ANTIA

SliRI N C. DtJGGAL (Alternate)CHIllY hNrlNEER (Ro...os)

The Concrete ASSOCiation of India, Bombay

Mmrstry of Transport and Shipping (Roads Wm.rr),New Delhi

(Continued onpage 36)

2

AMENDMENT NO.1 MARCH 1989TO

IS : 9759 • 1981 GUIDELINES FOR DEWATERINGDURING CONSTRUCTION

( Pag' 6, claus, 4.3.1.5, ,nformlll table) - Substitute 'k X 10-' ' for, k '.

( Page 12, clause 6.3.4.5 ) - Substitute' V' fOT ' V ' appearing forvacuum at pump intake.

'N ~ 'N'(Page 27, claus, 11-1.10 ) - Substitute N; fOT Nf appearing at

two places.

( Page 30, Table Z, col 3 ) - Substitute the followmg for the valueof' Q' m lines I, 2 and 4 respectively:

kD.a) -t- (H - h. )

kxb) -2L (H' - he' )

c) ( O'J3 + 0'21 H ~he ) ff (H' -ho')

[Pag' 30, Table 2, Notes (i) and (II) ] - Substitute' H - ho' fOT, H - he' appearing at two places.

( Page 31, Table 3, col 3, ltn« 2) - Substitute the following for thevalue of f Q ':

• (0 J3 +O'2J H ~ he ) ~ (HS _ ho' ) ,

( Page 31, Table 3, Nole) - Substitute the fullowing for the valueof' h':

'he + (H - hel f: ~ ,( Page 32, Table 4, last Itne ) - Substitute' ho 'foT ' he ' appearing at

two places.

( Page 32, Table 5, col 3 ) - Substitute' W. 'for' kD, "

J

( Page 33, Tnbl« 6, col 3 ) - Substitute the following value of 'Qw'agamst ' Gravity':

• h[(H-S)' - /'] [I (03+ IOrW) . \·8S].I. ( R/rw ) + H 11. H

(Pag. 33, Tabl. 6, col 3 ) - Substitute the following against thevalue of' Qwp':

2nkD ( H - hw ) G'. ( Rlrw )

(Pag. 33, Tabl« 6, NOll) - Substitute the following for the valueoff G '0

Dw (I + 7) .J rw n WIDzw-- COl 1t -2-

(HOC.3 )

2

Pnnt,ed at Ne_ Indul PrlDtlft' Pr.... K.burJa. Indj.

IS : 9759· 1981

Indian StandardGUIDELINES FOR

DEWATERING DURING CONSTRUCTION

o. FOR E W 0 R D

0.1 This Indian Standard was adopted by the Indian Standards Institutionon 27 February 1981, after t he draft fina lized by the Foundation EngineeringSectional Committee had bee n approved hy the CIVU Engineering DivisionCouncil

0.2 The problem ofdewater mg d urmg co nvtructron 1S met wrth in most of thecivil r-ngmrcrmg constructions The concerned technical committee has,rhr-rcfore, felt thdt some guidehncs for dewarermg at least for the mostcommon cases could be formulated. An attempt has, therefore, been madeIn thi .. standard to givr- some guide line .. for dcwatermg for normal construc-,tton works other than rrve r valley projects (that is, the earth dams, etc, forwhich reference may be made to IS· 5050-1963*). In construction ofpower­houses in boulderjgrave l reaches, the dewatering conditions are entirelydifferent and arc not covered In rhrs standard

0.3 In the Iorrnulanon of this standard, considerable assistance has beenrendered by thr- Central Building Research Institute, Roorkee , which hasfurnished the vanous data included in the standard

0.4 For the purpose of deciding whether a particular requirement of thisstandard is comphed with, the final value, observed or calculated, expressingthe result of a test or analysts, shall be rounded off In accordance WIthIS . 2·1960t. The number of significant place' retained III the rounded offvalue should be the same as that of the specified value in th ts standar-d.

I. SCOPE

1.1 T'his standard provides J. aiude lme for dc v.. a termg durmg constructionof'foundaoon and excavanon.

2. TERMINOLOGY

2.0 1'01 th, purpo,e of this vrnnd.u d, the followrng defimuons shall apply.

2.1 Anode Povit rvely chat-gr-d electrode.

*Code of practice for design, construe.non and maintenance of relief wells,[Rules for rounding off nuun ucal values (revmd)

3

IS : 9759. 1981

2.2 Cathode - Ncganvely charged electrode.

2.3 Discharge Line -- Steel, alu miruum or plasuc conduits to conductflows from pump.

2.4 Electro-Osmosis -- Electrical drainage method for dewatering

2.5 Equipotential Line - Line in flow regron at a ll point" on wlur-h Llu­total head IS the same.

2.6 Flow, Artesian -- Flow through a perVIOUS stratum bounded above­and below by Impervious layers

2.7 now, Gravity - Flow undcr gravity through pervious ,011

2.8 Flow Line -- Path followed by a particle of water through a saturatedsoil mass

2.9 now Net -- Graphical representation ofAow through soils comprisingflow lines and equipotential hnes

2.10 now Net, Plan - - Flow net which represents the plan view of theseepagC' pattern.

2.11 Flow Net, Sectional-- Flow net which represents the sectional viewof the seepage pattern

2.12 Head Discharge - Head at which water is discharged from pump.

2.13 Head, Total DynaJDic - Sum total of operatmg vacuum at thepump intake, discharge head and discharge fricnon losses

2.14 Head Loss, Entrance - Head loss caused due to entrance of waterthrough weJJ screen

2.15 Head Loss, Friction - Hvdrauhc head loss m pipe' due to fr-iction.

2'.16 Head Loss, Total Sum total of screen entrance head Ioss, frictionhead losses due to flow through well screen and riser pipe and the velocityhead loss.

2.17 Head Loss, Velocity - Equals v2 j2g , where "z 15 the velocuv of flowthrough the rrscr pipe, and 'g' is the acceleranon due to gravny.

2.18 Line Source - RIver or stream adjacent to well system

2.19 Operating VacuulD -- Vacuum created at the welipoint pumpshrmted by the atrnoapher-rc pressure

7.20 Piezometric Level- - Hydraulic head level ccmprrsmg total head(sum of pressure head, datum head and velocuy head for flow through soils)

2.21 Pipe. Header - The pipe which collects water from the rrser pipeand leads on to the pump.

4

IS : 9759 - I!IU

7.22 Pipe, Riser - Small diameter vertical pipes connected to the well­point.

7.23 Radius of lnfluence - Radrus of the circle beyond which the wellhas no significant influence on the original ground water level or piezometricsurface.

7.24 WeD, Fully Penetrating -- Well which penetrates to the full depthof pervious stratum

7.25 WeD, Partially Penetrating - Wen which does not penetrate to thefull depth of the pervIOus stratum

7.26 Wellpoint - Small well screen made with self-jetting tips.

7.'1:7 Wellpoint SystelD - A system consisting of wellpoints around anexcavation, attached to a common header pipe, and connected to a wellpointpump.

3. GENERAL

3.1 Dewatering is the operation of lowering of ground water level. It isresorted to when excavations are made below natural ground water table,and is usually a temporary measure. Dewatering is also done to relieve thebottom of an excavation of artesian pressure.

3.7 A properly designed. installed and operated dewatering system can servethe following purposes:

a) Lowering the water table and intercepting seepage, which wouldotherwise emerge from the slope or bottom of the excavation.

b) Increasing the stability of the excavated sbopes.c) Preventing Joss of material from beneath the slopes or bottom of

the excavation.

d) Reducing lateral loads or sheeting and bracing.e) Preventing rupture or heaving of the bottom of an excavation.

f) Providing a suitable working surface at the bottom ofthe excavation.

4. RE~UIREMENTS FOR A DEWATERING PROJECT

4.1 DUnensions of the Excavation - The SIzeand depth of the proposedexcavation should be known

4.2 Required Lowering of Water Table - The allowable ground watertable or uplift pressure during construction should be ascertained.

4.3 Geological and Soil Condition

4.3.1 SubsurjQJ:e InvestigatiDn

5

IS , 9759 -1981

4.3.1.1 Use - A thorough subsurface investigation should be made byboring or jetting tests in the immediate vicmiry of the site, to ascertain thecharacteristics of the soil adjacent to and beneath the excavation. Soiltype and characteristics (see 6.3.1) Significantly affect the choice and designof a dewatering system.

4.3.1.2 Spating of bonngs - IS : 1892-1979· may be followed in thisrespect. The number and spacing of bore holes will depend upon theextent of the site and the nature. of structures coming on it. For a compactbuilding site covering an area of about 0·4 hectare, one bore hole in eachcorner and one in the centre should be adequate. For smaller and lessimportant buildings even one bore hole in the centre will suffice, Forvery large areas covering industrral and residential colonies, the geologicalnature of the terrain will help m deciding the number of bore holes. Conepenetration tests may be performed a t every 100 m by dividing the areain a grid pattern and the number of bore holes decided by examining thevariation m the penetration curves

4.3.1.3 Important boring obsewatwRS -- The thickness of various strataand stratifications, if any, should be noted. Layers of clay or any otherimpervious material should be carefully recorded.

4.3.1.4 Water table and substratum pressure - The position of watertable and substratum pressure should be reliably determined.

NOTE - It IS preferable to collect records, If available, of the positron of water tableand hydrostatic pressure With the season of the year or river stage. Alternatively, ifume perrruts, the water table of hydrostatic pressure should be observed over a periodof time, SInce It WJU frequently vary With the season of the year and WIth the stage ofan adjacent river.

4.3.1.5 Permeability of pervious stratum -- Permeability of the perviousstrata to be dewatered should be determined by field pumping test. Arough idea about the permeability of different SOlIs can be had from thefollowing table:

Type ofSand

Very fine sand

Fine sand

Fine to medium sand

Medium sand

Med tum to coarse sand

Gravel and coarse sand

CoejJi£ltnt of Permeability, (k) cmlsec

I to 50

51 to 200

201 to 500

501 to I 000

I 001 to I 500

I 501 to 3000

NOTE 1 - For large excavations and excavations underlain by deep strata of sand,the permeability should be ascertained [or the full depth.

·Code of practice for sub-surface mvesngatron for foundabons (first rerwn).

6

IS : 9759. 1981

NOTE 2 -In case the 'pumping test' IS not conducted at the site, the fol1owinl applOXi­mate formuJa for determining the coefticient of permeability for fairly uniform sandsin loose state With uniforrmry coefficient not greater than 2 may be wed.

k = C1 DI10

where

k = coefficient of permeabrliry 10 em/s,C. = a constant, varying between 100 and 150; andDto = effective gram size in em.

4.4 Source or Seepage404.1 NaJu" of Source - The nature of the source of seepage should be

properly determined. The source of seepage depends to a great extent onthe geological features of the area and adjacent streams Or bodies of water,If the wells are not close to a river or canal, and the only seepage is fromthe formation being dewatered, the source may be assumed circular. Streamsclose to the wells may act as line sources of seepage, depending on thedistance of the wells from the effecnve source of seepage (see 4.43).

4.4.2 Radius ofInJlueru:e (R)4.4.2.1 DefinitIOn - The radius of influence, R, is defined as the radius

of the circle beyond which the well has no significant influence on theoriginal ground water level or piezometric surface.

4.4.2.2 Determination of R byfield test- The radius of influence, R,should be estimated from field pumping test, by determining the drawdowncurve by means of piezometers.

Non - The radius of influence increases with mcreased drawdown and WIth pumpingtime. The magnitude of these effects IS difficult to estimate numencaUy; therefore,the radius ofmfluence should beestimated conservatively.

4.4.2.3 Approximate formula for R - The following empirical relation­ship' may be used for estimating R:

R = C' (H-k,,)v'J;where

R = radius of influence in ill,

C' = a constant=Q·g (for gravity flows),H = depth of natural water table in metres,"_ = head at the weIJ in me tres, andk = coefficient of permeability in 10-0 cm/s.

4.43 Wells Adjacent to River4.43.1 Lin« source - If the wells are close to a river, the source 0

seepage may be considered as the river, provided the distance L from thewells to the river is less than R/2.

f.5 Chemiea1 Properties or Gr01llld Water405.1 Corrosion and Inaustation - Metallic well screens are susceptible to

.Based on Sichordt's equation.

7

IS I 9759 - 1981

attaclt by certain chemicals present in ground water causing corrosion andincrustation ofwell screens. Presence ofchemicals like carbonates, hydrogensulphide, sulphur dioxide, iron sulphide, iron sulphate, organic acids anddissolved oxygen should be tested by chemical analyses.

4.5.2 Minimizing Corrosion - Corrosion may be minimized by usingmetals in well screen which are resistant to corrosion, such as bronze.stainless steel, brass, gaJvanized iron, etc. Wood or plastics WhICh are notsubject to corrosion are preferable.

4.52.1 Limits of corrodmg material in ground waler - The principal indi­cators of corrosion by ground water are low pH, presence of dissolvedoxygen, hydrogen sulphide, total dissolved solids In excess of I 000 ppm,carbon dioxide in excess of 50 ppm, and chloride content greater than500 ppm The principal indicators of incrustating ground water are totalhardness greater than 330 ppm, total alkalimty greater than 300 ppm,iron content greater than 72 ppm, and pH greater than 8·0.

U.3 Minimizing Innwtation - For mmirmzing incrustation, the followingm.ethods can be adopted:

a) WellpointsjwelIs should be installed so that water can enter thewell with the least resistance possible,

b) Entrance velocity in the well should be kept low,

c) Water from any welI should not be pumped more than necessary, and

d) Wells can be cleaned before the incrustation becomes excessive.

5. CHOICE OF DEWATERING SYSTEM

5.1 SoIl Type - The subsurface investigations and their interpretationsshould provide the information needed to establish the kind of dewateringsystem that is required for an individual project. Table I provides a generalguidance in this regard.

5.2 Pu-tide Size Di.tributiOJl - The particle size distribution of thesoil inftuences the choice of a particular method· in a dewatering project.The range of soil types over which the various processes are applicablecan be obtained from the classification given in Fig. I. To use these curve"the particle size distribution of the soil should be obtained by sieving testsand the grading curve should be plotted on the chart. The system appli­cable to the particular soil type can then be chosen easily.

s, ANALYSIS AND DESIGN OF A DEWATERING SYSTEM

&.1 DHiga Reqairemeat. - Design of a dewatering system requiresdetermination of the number, size, spacing and penetration of the well­points or welIs and the rate at which water must be removed from thepervious strata in order to achieve the required ground water lowering.

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50

IS , 9759. 1981

6.2 DillCharge Formulae6.2.1 Use -- The fundamental relationship between discharge from wells

or wellpcints and the corresponding drawdown produced in the perviousstrata is of primary importance. The appropriate formulae should beused in the design calculations, for a particular field situation. Sincethe wells are closely spaced in a wellpoint system, the line of wells is takenas a slot for computation purposes.

6.2.2 Flow from Lme Source I<> Slot - The discharge and drawdown rela­tionships are given m Tables 2 tc 4. The line source and the slot areconsidered to be of infinite length.

6.2.3 Correction for Finite 1.Lngth ofSlot - Since a slot IS actually composedofa finite number ofwells only, corrections are apphed to the head reductioncomputed for the slot. The head reduction at the wells can be obtainedfrom Table 5.

6.2." Flow from Circular Source to Single Well- The dIScharge and draw­down relationships are given m Table 6.

6.2.5 Flow from Line Source to Single Well - The dunharge and drawdownrelationships are given in Table 7.

6.s E••ential Steps in Designing a Wellpoint/Well System6.3.1 Subsoil Properties - An accurate determination of the subsoil

profile and the permeability characteristics of the soil should be madeas mentioned m 4.3.1. The value ofk, the coefficient of'permeabiluy of thewater bearing stratum, should be determined for use in the design inaccordance with 4.3.1.5.

6.s.2 Distance of Wellpomtsl Wells from Source of Seepage - Depending onthe geological condition, the value of R or L should be ascertained accord­ing to clause 4.4. In this regard, the following considerations should betaken care of.

a) If the actual radius of influence is large compared with the radiusof the well, only an approximate estimation of R may suffice,SInce the discharge is not much sensitive to the value of R

b) An accurate estimation of L should be made for a particular de­watt"ring system, since the discharge is inversely proportional tothe value of L.

6.3.3 Effective Well Radius6.s.s.1 Wells installed without filter - Half the outside diameter of the

well screen should be taken as effective well radius.6.3.3.2 Wells mstalled with sand or gravel filter - Half the outside

diameter of the filter should be taken as effective well radius.NOTIf, - Where a well screen has been installed WIthout a filter but a natural filter

aroWld the screen is developed by surgmg. the extent of the developed filter becomesindefinite. In such a case, a conservative assumpuon of half the outside diameter ofthe aereeo should Ix taken as the effecnve well radius

10

IS : 9759 - I'ln

2-01·5io0'5

-:v-I2

V4 /

/6

I8

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a

o

o

o·

0­

WID

y

FIG. 2 FACTOR r VERSUS RATIO WJD

0-15aas 0'10

b/H

~<,

~ f..-

o

0·5

8 10o 2 4 6

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2

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1·2 1-5

0-8

3a Factor k1

NOTE ~ 2 I is = distance between slots

3b Factor kl

(I ~ width of slots)

FIG_ 3 COMPUTATION OF FACTORS k, AND k,

II

IS : 9759. 1981

63.4 Discharge Computations63.4.1 Since the wellpoints are closely spaced, they can be considered

as creating a continuous slot. Their spacing is so determined that thehead along the line of wellpoints is essentially the same as would exist ata slot. The following procedure should be followed in this respect.

63.4.2 If H is the head corresponding to the natural water tableand h. is the head at the slot, then the head reduction (N-h.) at a slotrequired to produce the desired residual head 'hD ' should be computedfrom equations given in Tables 2 to 5, read with FIg 2 and 3.

6.3.43 Assuming that ".="D, and that (11.-11",), the head difference(h.. being the head at the well) is small (assumed as 0001 H), the well­point spacmg can then be computed from the followmg equations:

a) For artesian case:

hD-h.. = _a_ In _a_N -hD 21TL 21Trw

whereL distance of wellpoints from line source,a spacing of wellpoints, andr.. radius of w-Ilpoints,

b) For gravity case:h2

D-h2 a a

...-i"'--;-;;"'''' = - InH2_h2D 21TL 21TTw

NOTE 1- For computation of welipomt spacing method of 'flow-net') as gIVen In

Appendix B be followed.NOTE 2 - In lieu of detailed computations, the approximate apacmg of wellpomt

required to produce a gIven groundwater lowering m various SOIls can be esumatedfrom the nomographs shown In Fig. 4 and 5. However, these ncmographs should beusedwith cautron, since they are based on empmcal data and are for average conditions.

63.4.4 Mter the wellpoint spacing and the head h.. at the wc lipointhave been computed, the flow Q.. per wellpomt can be computed fromthe equation given in Table 5.

63.4.5 The' above value of IIw should be equal to or greater thanthe value of h.. computed from the following equation. The total headloss in a wellpomt connection should be estimated afresh:

h.. = M-V+H, +H..in which M = distance from base of pervious stratum,

v = vacuum at punlp intake,He = average head loss in header pipe up to pump intake,

vnd IIw --'- total head loss ill each wellpoint and swing conne-ctionhead loss due to screen entrance (H,) +friction loss due to flow through the well screen (H,) +friction loss due to flow in the riser pipe (H,) +velocity head loss (N.).

12

IS : 9759 - 1981

NOTE- The top of the wellpomt screen sf culd l e set sligl tly b!LW (h.-H~) LO

ensure mat the wcllpomr J~ submerged; OWUWISf" excessive arr n ay enrr r t}-( dewatenngsystem and reduce its efficiency.

POLES,~

o GRAVEL

.c \fERY FINE GRAVEL

---0 MEDIUM SANO

__ a COARSE SAND:l,l

VERY FINE-"! --GR"El •• -

:: tMEOIUM ----oFtNE SAND

GAND

J -

,-

7

•9

10

COARSESAND

, -

5

B ­g

10

15

- 6-

]Q

15

2\

5-

20

GROUND WAlERLOWERING ~O 3m~­

60

50

20

25FIN[ SAND

FL. 4 WELLPOINT SPACING FOR UNIFORMCLEAN SANDS AND GRAVELS

6.3.5 Design of Filters - The requirements tor filter material shall beas Wider:

Character ofFilter A/aterials

Uniform grain size disrr-ibuzicn (U~3 to 4)

Wen graded to poorly graded (non-uniform);subrounded grains

Wen graded to poorly graded [non-uniform};angular particles

RatIO R.o5 to 10

12 to 5B

9 to 30

Ratio R15

12 to 40

6 to 18

I~

IS : 9759. 1981

D.. of filter materialD•• ofmaterial to be protected

D 15 of filter materialD15 ufmaterial to be protected

Nora - Pipmg Pretention - The phenomenon of piping may be prevented at seepageaiD: in an excavanon by provrdmg artrficral devices such as drams and filters. Mostdramege systems make use of porous filter aggregates to collect the water and conductit to outlets, often with the aid of perforated or slotted pIpes Proper filter design isImportant for prevention of prpmg

If a filter layer satisfies the cntena, it is virtually Impossible for pIpmg to occur, evenunder extremely large hvdrauhc gradients Adequate specrficauons and careful con­structions are requrred, If the works, as they are constructed, are to be completely safefrom piping troubles.

GROUND WATERlOWERING x D'lm

SPACING OF WEll POINTS x 0·3mr---------"'---------, POLES.----..,

__ -o COARSE--- SAND

11{__,I:) GRAVEL--5 _-<> VERY FINEj.O_.... GRAVEL

- GRAVEL

---- - -<) MEDIUM

SAND

2

1,

10

15

VERY FINEGRAVEL

»>: 5

6050

'0

302 2

2520 1

3

15 2,

'.::~~

__5

10 -- 5... --8 <, ...~ ---6 --6 ... ... 7 10

5 8, 10 9 '510 COARSE

3 '5 SANDFINESAND IS2

MEDIUMSAND

FIG. 5 WELLPOINT SPACING FOR STRATIFIED

CLEAN SANDS AND GRAVELS

6.3.6 Design and Selecuoa of Well Screens -- The followmg criteria maybe observed in designmg and selecting well screens or wellpoints:

Slot width < D,. (filter or aquifer sand)Hole diameter or width < D•• (filter or aquifer sand)

14

IS : 9759. 1981

NOTE - Where silty sods ale to be drained, the welJpoJDt should be provided witha graded medium to coarse sand filter designed In accordance with the filter criteriaset forth in 6.35.

6.3.7 Horse Power if Pump- The following formula shall be used todetermine the required 'horse power' of the pump to be selected for thedewarermg system:

HTotal discharge in gpm XTotal dynamic head

orse power=. .3960 X Efficiency of the pump and engine

where total dynamic head = operating vacuum at the pumpintake +discharge friction Iosses,

6.3.8 Layout Scheme - A layout scheme should be chosen for the weillwel1point system, depending on the size and shape of the excavation. Thechoice can be made of the following two systems:

a) Progressive syskm - This system is used for trench work. Theheader should be laid out along the SIdes of the excavation, andpumping should be continuously in progress in one length a.further points are jetted ahead of the pumped down section andpulled out from the completed and backfilled lengths. Fornarrow excavations it ]5 often sufficient to have the header onone side only. For wide excavatIOn'S or in soils containing bandsof relatively impervious materials, the header should be placedon both sides of the trench.

b) Ring system - The header main in this system surrounds the exca­vation completely. ThIS is suitable for rectangular excavations.

6.3.9 Collector Lanes

6.3.9.1 Hydraulic head losses - The wellpoints, riser pipes, headerpipes and pumps should be of adequate sizes for the flow being handled,so that the hydraulic head losses in the wellpoint and collector systemsare kept minimum, Head losses to be considere d are those due to velocityand friction, and enlargements, tees. elbows, valves and other discontinuitiesin the line. For estimating losses due to irrcgularuics in the- line, the usualformulae on hydraulics can be used.

6.3.9.2 Header pipes- Header pipes commonly consist of relativelylight weight steel or plastic pipes. Headers for wellpoints contain inletsfor wellpoint connections at short intervals. Headers are normally ofsizes varying from 15 to 30 cm of diameters.

6.3.9.3 Non-return valves - The connection of collector lines to theheader pipes should be through non-return valves.

6.3.10 We/lpoint Pumps

15

18 I 9759. 1981

6.3.10.1 Selection of pumpsa) Vacuum pumps - Cenmfuga! pumps are used for pumping through

the collector pIpes in a wellpoint system. Thc selected pumps shouldhave sufficient air handling capacuy, and they should be able to producea high-vacuum. A wcllpoint pump consisting of a self-primmg centrifugalpump with attached vacuum pump proves to be adequate. IL develops6 to 7 5 m of vacuum An assumption of 6 m of Vacuum may h~ safelymade in the design. Consideration should, however, b- given for positivepressure head.

b) Jet-tdllctor pumps-If the depth of water table lowering is large(greater than 4 5 m) but the rate of pumpage for each wellpoint is rela­tively small (less than 10 to 15 gpm), installation of a single stage wellpointsystem at the top of the excavation or water table, with attached jet-eductorpump may prove to be advantageous than a multi-stage wellpomt system.A jet-eductor wellpoint system can lower the water table by 15 to 30 m.

6.3.10.:Z Location and spacing if pumps - The locanon and spacing ofwelijloint pumps depend on the length of header pipe, discharge rate,and point ofdi,cnarge. Ifa long collector line (say 150-300 m) is pumpedby a single pump, the pump should be located at the centre of the lineto obtain a maximum vacuum m the lin-. In short lines and where theflow 15 small, the pump can be located wherever convenient.

6.3.10.3 Pump inlaMa) The intake of the pump should be set as low as practicable and

it should not be more than 45 to 55 m above the bottom of the excavation.b) If the discharge is large, the pump intake should be set at the

same elevation as the collector lines.6.:J.IO.4 Selection of power U'lit - In s<"lecting the power unit to be

used for drivmg the pumps, consideration should b ~ given to the initialcost of th- unit) and the cost of op-ration, tncludtng maintenance andfuel.

6.3.10.5 Slandby equipments - Standby umrs should bo kept readyfor immediate use in case of any emergency.

6.3.11 Discharge Lines6.3.11.1 DIscharge lines can consut of steel, aluminium or plastic

pipes.6.3.11.:Z Tue pipes should b> of proper size to conduct the flow with

relatively small head loss.6.3.11.3 Ditches C3n bo dug to conduct the flow away from the sue.

However, such duches shall be kept Well back from the top of the excava­tion to prevent saturating the upp~r parts of the stope.

6.3.12 Wellpointing in Deep Excauauons - Multi-stage wellpoints,6.3.U.I Genera! - The limitations in the drawdown to 4 5 to 6 m

by a si.'1~I~ w ~llp:Jint necessitates successive stages of wellpoints to be

16

IS , 9759 - 1981

installeo u" deeper cxc watton below standing water level is required. Thereis no :lmit to the depth of drawdown In this way, but the overall widthof excavation at top level becomes very large.

6.3.12.2 Position ~ header pipes - The lowest header of multistagesystem should be located not more than about 45 m above subgrade toensure that proper drawdown of the ground water level can be achievedwith the vacuum available in the line.

6.3.123 Observations - Observations should be made immediatelyprior to and while pumping the upper stage, for discharge and groundwater lowering. Comparison should then be made with the computedvalues to check the adequacy of the lower stage pnor to its installation.

63.13 DeepBored Welts63.13.1 General - Large diameter deep wells can be used effectively

where the depth of excavation below the water table is large (more thanabout 10 m), or where artesian pressure in a deep aquifer beneath anexcavation must be reduced. Deep wells are suitable where the excavationpenetrates or is underlain by sand or coarser granular SOllS. Whereadequate submergence is available and the required rate of pumping islarge, deep bored wells may be preferable to wellpoints.

6.3.13.2 Design - The procedure for designing a system of deep wellsis similar to that for wellpoints. Clauses 6.3.1 to 6.3.7 can be referredto ill this regard.

6.3.133 Sizes of welt and welt screens ~ The wells should be largeenough for the pump required and to keep the head losses low. The wellscreen should be of sufficient length to admit the flow with small headloss Deep wells normally have diameters of 15 to 45 em with screensof 6 to 22·5 m length.

63.13.4 Use of surf",e pumps- Pumping from wells can be under­taken by surface pumps with their suction pipes installed in bored wells.However, the depth of drawdown by this method IS not much more than7 5 m. If eenrrifugal pumps are used in a deep well system, the pumpscan be located on the excavauon slopes and connected to a common headerpipe. The top of the well screen In such cases should be set below thecomputed water surface in the well.

63.13.5 Use ~ deep well pumps- For deep excavations, electricallypowered submersible pumps should be installed, w.ith a rising main to thesurface. It should be seen that there is sufficient depth of pervIOus materialbelow the level to which the water table is to be lowered, for adequatesubmergence of well screen and pump. If wells are located at the topof the excavation, interference WIth the cxcavanon and construction callbe eliminated.

63.13.6 Selection oj deep wellpumps- Turbines or submersible pumpsare used to pump large diameter (150 mm and above) wells. Properselection of pumps should be made in respect of pump capacity, from the

17

IS : 9759. 1981

variety of deep well pumps that are available. Discharge from the wellmay often be limited by the pump, and not necessarily by the availableyield of the pervious stratum. For determining the approximate maximumcapacity of deep well pumps Table 8 may be used.

NOTE - Pumps should be selected to operate at their normal fated speeds. Addi­tional capacity is available at speeds greater than normal. Thw, some mergtn of safetyalway! exists.

7. INSTALLATION AND OPERATION OF WELLPOINTS

7.1 Pressure and Quantity o£ Water for Jetting WeUpoiats - Forjetting down wcllpoints into the ground, water may be required to be ata pressure of up to 14·5 kg/emS and up to 900 litres ofwater may be requiredfor a single wellpoint.

7.2 Cisy Overlying Pervious StratulD - If a layer of clay overlies thewater bearing stratum, it is often more convenient to bore through theclay by hand auger, rather than attempting jetting through it.

7.3 Sandiug iu - The process of sanding in the points may be followedas an important safeguard against drawing fine materials from the groundwhich might clog the system or cause subsidence. 'Sanding in' shouldbe done as follows:

'After jetting down the wellpoints to the required level, the jettingwater supply should be cut down to a low velocity sufficient to keepthe hole around the poin- open. Coarse sand should then be fedaround the annular space to form a supplementary filter around thepoint and the water then cut off A rapid pouring of filter materialstends to bridge the hole, while an intermittent pouring causes heavysegregation of the filter materials, resulting in obstructions to verticaldrainage.'

VI 'Sandiug in' in Highly Permeable Gravel- There may be difficultyin sanding in a wellpoint in highly permeable gravels, because the jettingwater will be dissipated into the surrounding ground and will not reachthe surface around the riser pipe. Normally, a wellpoint does not need'sanding in' in these conditions, but If it so happens that the coarse gravelsare overlying sand with the wellpoints termmaung m the latter, the well.points must be inserted in a lined bore hole, the lining tubes being with.drawn after the filter sand is placed.

7.5 Pervious Stratulll Overlying Clay - If the pervIous stratum isimmediately underlain by clay, the wellpoints can be installed in holexpenetrating about I m into the clay and backfilled with sand, so that thewater level in the wellpoints during pumping can be maintained at 01'"

below the bottom of the pervious stratum. This procedure will reduceor eliminate seepage that would otherwise bypass the wellpoints if theywere installed only with theu- tips at the top of the clay stratum.

18

IS : 9759· 1981

7.6 Sand Drains

7.6.1 UJe~ Troubles may arrse in a dewatering scheme in the formof breaks in the drawdown curves If impervious layers of silt or clay (evenas thm as 3 mm) are met in water bearing sandy soils. These troublescan be largely overcome by installing sand drains. Holes can be jettedon the side of wellpomts away from the excavation and be filled with sand.These sand columns will provide a path down which the water can seepthrough the wellpom t5 more readily than towards the sides of the excava..non. Weeping from the side of the excavation can thus be prevented.

7.6.2 Design tf Sand Drams

7.6.2.1 Hydraulic head tosses - The drain. should be of such size,permeability and spacing as to conduct the flow to the lower sand stratumWIth small hydraulic head loss Sand or gravel filled drains are not effectivewhen installed in highly pervlOus sods, because they do not have enough.hydraulic carrying capacity to permit flow to the lower stratum withoutexcessive head loss

NOTE - For design of sand drams standard formulae be used.

7.7 Installing Header Pipes - After selecting the required header pipes,the header pipehne should be fitted with plug cocks of suitable size at therequired spacmg. laid along the line. The wellpoints can then be con,nected to the respective plug cocks through flexible connections. Theheader pipeline should be connected through valves to pumps of required.number and capacity which, in turn, should be connected to a commondischarge pipe leading to a basin or a ditch at a considerable distanceaway from the SIde.

7.8 WeUpointing in Sheet Piled Excavation, Position ofWeUpoints ~III the case of"dlpo<ntiag in sheet piled cxcsvstton, the wdlpomts shouldbe placed close to the toe of the sheet piles, to ensure lowermg the waterlevel between the sheet pile rows.

7.9 Dewatering Operation

7.9.1 Necessary Checks hefore Slarting - The dewatering operation shouldbe started only after checking up all engine parts and priming of the pumps.The whole pIpe line system should be checked against leakage. If leakagesare detected, they should be properly mended with paints and by tighteningthe joints.

7.9.2 Air-Sucking hy Wellpoints - In cases where the flow per weUpointis less than expected and the drawdown goes deeper, the wellpoints maystart sucking air. This may be indicaled by the fluctuations of the vacuumgauge fitted to the wellpoint pump, and discharge of excessive air fromthe vacuum pump outlet The air sucking can be stopped by suitablyadjusting the plug cocks to increase friction loss.

19

IS , 9759. 1981

7.9.3 Repairing Choked Wellpoints - In spite ofusing graded filter materials,a few wellpoints may get choked by finer silty particles These deadpoints can be made active by developing the shrouding material withjetting of water.

7.9.4 Protection ofPump Bast - Care should be taken to see that the pumpbases are not flooded due to the flow ofwater through the sandy soil. Thismay make the pump base quite slushy and cause tilting of the pumps.In such situations, a few wellpoints and sand drains can be installed on thebasin side of the pumps to intercept this flow.

8. INSTALLATION AND OPERATION OF DEEP WELL SYSTEMS

8.1 Installation of Deep Wells - The following points should be takennote of while installing deep wells.

8.1.1 The outer casing of the bore hole, which is sunk first, should havea diameter some 20 to 30 em larger than the inner casing. The diameterof the latter depends on the size of the submersible pumps.

8.1.2 The inner casing, which is inserted after completion of the borehole, should be provided with a perforated screen over the length wherethe dewatermg of the soil is required and it should terminate in a 3·6 Inlength of unpcrforated pipe to act as a sump to collect any fine mater-ialwhich may be drawn through the filter mesh.

8.1.3 The perforated screen may consist of ordinary well cas109 slotsor holes burned through the well and brass mesh spot - welded roundthe outside. Slots are preferable to holes, since there is less risk of blockagefrom round stones.

8.1.4 The effective screen area can be increased by welding rods longi­tudinally or spirally onto the casing to provide a clear space between themesn and tne casing.

8.1.5 If centrifugal pumps are used III a deep well system, the tops ofthe screens should be set below the computed water surface in the well.If the wells are pumped by deep well pumps, the bottoms of the wellsshould be set to provide sufficient length of submerged screen to admitthe flow without excessive head loss.

8.2 Pouring the Filter Material~ After the well casing is installed,graded filter material can be placed between it and the outer bore holecasing over the length to be dewatered. The outer casing should be.withdrawn m stages as the filter material is placed. The remaining spaceabove the screen can be backfilled with any available material. Thewater in the well should then be surged by a boring tool to promote flowback and forth through the filter, to get rid of any unwanted fines whichfaU into the sump and are cleaned out by bailer before the submersiblepump is installed.

20

IS : 9759· 1981

9. SUMP PUMPING

9.1 General- The method is essentral where wcllpointing or bored wellscannot be used because of boulders or other massive obstructions in theground, and it 1<; the only pracucal m .... thod for rock excavations. However,it has the dls3.dvant"1g~ that th- ground water flows towards the excavationwith a high head on steep alopas, and there is a risk of the coHapsc of thesides. There is also the risk in open or timbered excavation, of instabilityof the base due to upward seepage towards the pumping sump. Thecost of installing and maintaining the plant is, however, comparativelylow.

9.2 Essential Features9.2.1 The sump should be made below thc general level of thc excava­

tion. It can b- placed at one or more corners or sides.

9.2.2 The floor of the excavation should be made clear of standingwater. For this, a small ditch should be dug around the bottom of theexcavation falling towards the sump. It should be sufficiently wide tokeep the velocity low enough to prevent erosion.

Safeguards against erosion can also be taken by placing boards acrossthe dttch, or by stone or concrete paving, Open jointed pipes can alsobe lard, surrounded by graded stone or gravel filter material.

9.2.3 Where the ground water is present in a permeable stratum over­lying a clay, and the excavation is taken down mto tile latter material,it is preferable to have the pumping sump at the base of the permeahlestratum. This procedure reduces the pumping head and avoids softeningof the day at the base of the excavation.

9.2.4 The greatest depth to which the water table may be lowered bysump method is not much more than 7,5 m below the sump, dependingupon it, type and mechanical efficiency.

9.2.5 For large depth of excavation, the pumps can be installed at aIowa level. Use can also be made of sinking pump or submersible deepwell pumps suspended by chains and progressively lowered down a timberedshaft or perforated steel tube.

9.2.6 For deep excavations, a useful procedure can be to sink the pumpingsump for the full depth of the excavation by m-ans of a umbered shaftwith spaces between the poling boards to allow the water to flow into theshaft. Gravel filter materials should be pack d behind the timbers ifexcessive fine material is washed through 'I'Ius method ensures dryworking condition for the subsequent bulk excavation, and It also providesan exploratory shaft for obtaining inform.uron on ground conditions tosupplement that found from borings.

9.2.7 Adequate standby pumping plant of a opacity at least 100 percentof the steady pumping rate should b- provided for use in emergency.

21

IS : 9759· 1981

9.2.8 Type, of pump' suitable for operating for opcn sumps arc givenin Table 9.

10. CONTROL OF SURFACE WATER10.1 General-~In laying out a dewatering system, adequate measuresshould he taken to control surface water, as otherwise floodmg of the pumpcan result in failure of the system. Uncontrolled run-off also can causeserious erosion of slopes. The measures include dikes, ditches, sumps andpumps, and mulching and seeding to minimise slope erosion.

10.2 Essential Factors for Surface Control Measures - In selectingand designing measur-es to control surface water, the following factorsshould be considered:

a) Duration of construction,b) Frequency of rainfall occurrence,c) Intensity of rainfall and the resulting run-off,d) Size of area to be protected, andc) Available sump storage.

10.3 Run-Off Measurement - - The rate of run-off, Q. can be computedfrom the following equation:

Q. = 0·278 CiA

whereC a constant, ranging From 0 to I;

rainfall rate In mm per hour;A drainage area, in sq km; andQ. peak rate of flow, in Cu tul»,

10.4 Dikes and Ditches10.4.1 A dike can be burlc around the top of the excavation to eliminate

run-off into the excavation from the surrounding area.

111.4.2 Dikes should be high enough to prevent water from overtoppingthem and of sufficie-nt seotton to withstand he ad against them. The topof the dike should be at least 30 em above the computed elevation of thesurface water to be impounded. The width of the dike should be 40 to150 em with slopes of I on 2 or 2·5.

10.4.3 Run-off retained by the dikes can be pumped off or conductedto sumps in the bottom of the excavation by pipes or line channels, andthen pumped out of the excavation.

10.4.4 Ditches should contain ample allowance for silting, freeboardand storage. Velocities of flow shall be low enough to reduce the extentof maintenance necessary to keep the ditch unobstructed.

IS : 9759 - 1981

10.4.5 Dikes can be combined with duches and located excavationslopes to control run-off and reduce slope erosion.

10.4.6 Sumps and Pumps - Tne required capacity of pumps for pumpingsurface run-off can be estimated from the following expression:

Q.n (h.-VIT

whc re

Q.l> = total pump capacity,

QR average rate of run-off,

V volume of sumps, and

T duration of rainfall.

11. SETTLEMENT OF ADJACENT GROUND SURFACE

11.1 Geaeral- The effective pressure at a point near an excavationwhere the ground water is being lowered by pumping is increased by anamount equivalent to the head of water which existed above the levelbefore dewatering. This increase in effective pressure will cause conso ... ....Iidaticn of the compressible strata with corresponding settlement of thecompressible strata with corresponding settlement at ground level. Theeffects arc severe in soft clays and peats. Loose sands under conditionof fluctuating water table also undergo appreciable settlements. Littleor no trouble need be feared in dense sands and gravels, provided theground water' low...:nng system has efficient filters to prevent loss of finesfrom the soil.

11.2 Precaution - To maintain the existing ground water conditions inshallow deposits, the water can be discharged into an 'absorption' ditchat ground level. To m-rintarn the existing head in lower pervlOus layerswater can be discharged into the injection or 'rechargmg" wells.

23

IS 9759 - 1981

APPENDIX A

(Clause 5.1, and Table I)

METHOD OF ELECTRO-OSMOSIS

A-I. ELECTRO-OSMOSIS

A-I.I Use -- Some slits, clayey silts and fine clayey silrv sands may betroublesome to dram, br-causc capillary [OTn s acting on the pore waterprevent It<; flowing Ire.ely under gravity to a filter well or sump. In suchcases successful d-amage can be achn vcd by well" or wcllpom t~ in comhi­nanon WIth flow of ek ctrn iry through the soil to the we lls The clr ctrrcaldrainage mr thod, or clcctro-osmosrs, 1<; a costly method, but under certatncircumstances, It is the only practical means of soil stabilization. ThereIS al~fl no advantage 1Il applying this method fur de watering unle-ss pern1e­ability of the SOIl to be dr amcd 15 sigmficanrly lower than 0 5 X 10-' cm/sec.

A..l.2 Electrodes - Anodes can consist of any available conductor, suchas steel P'Pv . Tall, etc Cathodes usually consist of small diameter wellsor wcllpomts, but with sufficient diameter to admit a suction pipe (usually25 mm diameter) from a pump. Anodes and cathodes should extendin depth at least 15m 0, low the bottom of the slope or excavation.

A-I.3 Spacing of Electrodes -- Cathodes can be installe d in one ormore Imc-sand "paced on 7 5 to 10.5 m ccn tt cs, WIth anodes mstallr d midwaybetween tilt" cathodes.

NOfE - The proper spacing of electrodes depends mainly on the voltage availableat the site Potennal gradients of more than 0 5 volr per (j~l between electrodes shouldnot be exceeded for long tum apphcaucr-s, because }ugh(r gradients result In excessrveenergy losses 10 tht fUI III of I t-,Itmg of the ground

A-I.4 Voltage Requirement - Applu d voJtaW" va, y between 30 and100 v lb. the IOWIT V( 'ltagt -, bcing satisfactory where the ground watercon ram -, a lllgh conccntrauon of rmnvrals

A-1.5 Power Requirem.ent - POWCl Tl qurrcd per well may range from0,] to 25 kW, for n <pr-ctive gradients of about 1·5 and 4 volts per 30 emdistance between electrodes.

A-l.6 Current Requirement - Current requirements range between15 A and 30 A The required current can be esumatcd from the followingcxpreSSlOm,. This equation is not applicable to very low clay contents:

It = 41c-25

where

I current, in A, required per gram of water expelled;t time in sec; and

24

IS : 9759. 1981

c = cia} content of soil, percent (percent by weight of soilfiner th on 0 002 rn m)

A-I.7 Collection of Water - - When a dire-ct e-lr ctric CUITent is passedbetween the electrode s, wate-r contained In the sor! will migratr- throughthe ;011 from the anode to the cathode Watn collected in the well (cathode)can then be removed by pumpmg.

NOTE- Smce the rate of discharge at a cathode IS small, mterrnittent pumping maysuffice.

A-L8 Discharge - An esurnau- of the discharg« Q, to a well can beobtained from tlu- followmg CXpn-sslons-

Q" "-- ke 'tJ a.:

where

k(J coefficient of cle ctrovmocic pcrmc abrl ity.

o .:J> 10-01 em per volt per em,

z", = gradIent In volts rex em, be tween electrodes;

z depth of soil being stabilized in em; and

a ~ effccnvc spacing of wells ill em.

Non.- For practical purposes, the value of k. can be assumed to be the same forsands, sdts or day.

APPENDIX B

(Clause 6.3,4.3, Note 1)

FLOW NET METHOD

8-1. GENERAL

8-1.1 Use -~~ A flow net can be a useful tool whcn designing dewateringsystems, especially when cornphcated boundary conduions are presentA flow net may be constructed either to represent the plan view of theseepage pattern, or a sectional view, depending OIl the requlfeIneut inthe design.

8-1.2 Flow Line - The path followed by a particle of water flowingthrough a saturated soil mass is called a 'flow line',

25

IS : 9759 - 1981

B-1.3 Eqaipot~ntial Lin~ - It rs the lme at eve ry point of wluch thetotal head 15 the same.

B-1.4 Flo... Net - A combmation of flow lines and equipotential hnes,which satisues the following charactenstics, is called a flow net:

a) Flow lines and equipotential hnes meet at right angles; and

b) Intersection of flow lines and equipotential lines forms curvilmearsquares, when the permeabihry in all directions is identical.

B-1.S Discharge from Flow Net - From the flow net, the dischargeper unit length perpendicular to the direction of flow can be obtained by:

q k (H-h,) ::,where

k coefficient of permeability of the sod,

N, number of flow channels, and

N, total number of equipotential drops between the full headH and the head h, at the point of oxu.

B-1.6 Piau Flow N~t - The plan flow net should be drawn with thcassumption that the flow hnes are horizontal and as such, the equipotentiallines are vertical. The analysis thus essentially requires the flow to betwo-dimensional. The slot/wells, therefore, need to be fully penetrating.CorrectIOns to be made for partially penetrating cases are mentioned inB-1.10.

B-1.7 Discharg~ frOID Plan Flow Net - The total discharge Q isobtained from plan flow net by multiplying the value of 'q' (given in B-l.S)by the thickness D of the pervious stratum, as follows:

Q = g.D

B-1.8 Spacing of Wellpoints{Wells frOID Flow - Wclb should bespaced proportionally to the flow lines

&1.9 Limitations in the UR of Plan Flow Net - As mentioned inB-l.6 j plan tow net analysis is effective for two-dimensional problems.The converging flows m the vrcmiry of partially penetratmg wellspresent a three-dimensional case for which plan flow net analysis will giveerroneous results, except when the penetration is at least 90 percentCorrection factors can, however, be applied for getting correct results fromplan flow net. This is given in B-1.10.

B-1.10 Corr~olls to be Applied to Computations from Pi.... FlowNet - Oorrected relationships between discharge Q", per well and the

26

IS : 9759 - 1981

head htIJ at the well taking into consideranon the penetration of the well,and also the fact that the system consist, of a finite group of wells and nota continuous slor. are grven below:

Q"N.l aH -h.. = - (n - 1- - In --) : for full) penetrating wells

k» N! '2 21fT"

and

n-s; ~ ~' (n:; + 0.) :for partially penetrating wellv

where a is the well spaclng; D is the depth of the pervious stratum,r.., is effective well radius, and 9a 15 called 'uplift factor'. The valuesof fJQ for various penetrations of the well screen mto the pervIOUS stratumhas been mentioned in various text books.

27

TA

lIL

EI

CO

MP

AR

AT

IVE

ST

UD

IES

OF

DE

WA

TE

lUN

GS

YS

TE

MS

(Cla

use

51)

3D

eep

bore

dfi

lter

Gra

vels

tosi

ltyD

eep

exca

vati

ona)

wel

lsW

ithel

ec-

fin.

,sa

nd

,an

dIn

thro

ug

ho

rtr

icsu

bmer

sibl

ew

ater

bear

ing

abo

ve

wat

erp

um

ps

rock

sb

ean

ng

form

auon

sb)

ScM

E:.

TK

OD

So

iLS

SU

ITA

.8L

EU

SE

SA

DV

AN

TA

GE

!N

o.F

OR

TR

Ei\

TIo

fE",

-r

(I)

(2)

(3)

(4)

(5)

Su

mp

pum

pang

Cle

angr

avel

san

dO

pen

shal

low

Sim

ples

tp

um

pm

gco

arse

sand

sex

cav

atio

ns

equ

ipm

ent

2W

dL

po

mt!oystem~

Solu

dygr

avel

sO

pen

exca

vati

ons

a)

QU

ick

and

easy

toW

ith

pu

mp

sd

ow

nto

nne

mcl

udm

gro

llin

gm

stal

lIn

suu

ablc

SO

Ih.

sand

s(w

ith

pip

etr

ench

pro

per

cont

rol

exca

vat

ion

sca

nal

sobe

used

blL

l.OI1

0mlC

alfo

rsh

ort

""In

silt

ysa

nds)

pu

mp

ing

peri

ods

ofd.

0:>

few

wee

ks

No

bu

uta

no

non

amou

ntof

draw

dow

nas

ther

eIS

for

suct

ion

pum

ping

Aw

ell

can

beco

nst

rue­

ted

tod

raw

wat

erfr

omse

ver

alla

yers

thro

ug

ho

ut

Its

dep

thc)

Wel

lsca

nbe

SIte

dcl

ear

ofw

orki

ngar

ead)

No

nors

epr

oble

mif

ma4

.nse

lect

nci

wsu

pp

lylS

avai

labl

e

DIS

AD

VA

NT

AG

ES

(6)

a)F

mes

easi

lyre

mov

edfr

omg

rou

nd

b)E

nco

ura

ges

uis

tab

ilu

vof

form

an

on

a)D

iffi

cult

toIn

stal

l111

op

engr

avel

san

dg

rou

nd

sco

nta

un

ng

cobb

les

and

boul

der<

;

b)P

um

pin

gm

ust

beco

nti

nu

ou

sau

dno

ise

o!p

um

pm

aybe

d.p

ro­

blem

,In

abu

ilt

up<i

red.

c)S

ucti

onlif

tIS

lum

ted

to4

5to

60

md)

Ifg

reat

erlo

wer

mg

IS

nee

ded

rnul

n-st

age

mst

alla

non

ISne

cess

ary

Hig

hm

stal

lan

on

cost

r;; ~ , .. :: ..

4E

lect

ro-o

smos

is(s

et'

App

endi

.xA

)

Silts

,si

ltycl

ays

and

som

epe

ats

Op

enex

cav

ano

nII

Iap

pro

pri

ate

soils

orto

spee

ddi

ssip

atio

nof

con

stru

ctio

np

ore

pres

sure

s

.\n

yap

pro

pri

ate

SOils

can

beus

edw

hen

noo

ther

wat

erlo

wer

ing

met

ho

dIS

appl

icab

le

Inst

alla

tion

san

dru

nn

ing

eons

arc

usua

llyhi

gh

'"~

5Je

ted

uct

oe

San

ds

(wit

hpr

o-a)

Dee

pex

cava

-a,

No

hm

uau

on

ona)

Imu

al

inst

alla

tion

l!'1

syst

emp

erco

ntr

ol

can

tion

s(m

spac

eac

cou

nto

fd

raw

-do

wn

fair

lyco

stly

also

be

used

inso

conf

ined

b)R

akm

gh

ole

sar

eh)

RIS

kof

floo

ding

Silty

sand

san

dth

at

mu

lu-

poss

ible

exc

ava

uo

nIf

high

san

dy

Silt)

stag

ew

ellp

om

t-pr

essu

rew

ater

mai

nm

gca

nnot

be15

rup

ture

dus

ed)

c)O

pti

mu

mo

per

atio

nb)

Usu

ally

mer

ed

Iffi

cult

toco

ntr

ol

appr

opna

teto

low

per

mea

bil

ity

soil

s

1il ~ .. .. j ...

TA

BL

E2

FLO

WT

OA

SL

OT

FR

OM

ASI

NG

LE

UN

ES

OU

RC

E(C

kzus

,6.2

.2)

PE

NE

TR

AT

ION

Ful

lyp

enet

rati

ng

slot

FL

OW

CO

ND

mO

N

Art

esia

n

Gra

vity

DIS

CH

AR

GE

FO

R\f

l.'L

.\E

kDx

Q~T-(H-h,)

kxQ

=2L

-(H

'-h

',)

R.-.

Hee

cng

inal

gro

un

dw

ater

leve

lhe

e-g

rou

nd

wat

erle

vel

atth

eus

eQ

=ft

ow

rate

Le-

drst

ance

ofth

esl

otfr

omth

eb

ne

sou

rce

Dee

dept

hof

perv

ious

stra

tum

\'-e

drs

tan

cep

erp

end

icu

lar

toth

edi

rect

ion

of

flow

.. fIl ~ , ... :I ...

'"oP

artl

aHy-

pene

trat

tn/i

tslo

tA

rtes

ian

Gra

vit

y

QtD

x(H

-h,)

-L-

'+El

l.

Q~(O

73

+0

27H

-he

)~'

:-_(

H2_"

2o)E~

e.ex

tra-

len

gth

fact

oras

des

cn-

H2£

bed

byv

arro

us

aurh

crs

Fo

'L

fH;;

'3

No

n:

-T

he

max

imu

mre

sid

ual

hea

d,

h Dd

ow

nst

ream

fro

mth

esl

ot

can

beco

mp

ute

dfr

om

the

foll

owin

gr-

XP

II:S

310n

s'

(l)

Fo

r'a

rtes

ian

'cas

e

(u)

For

'gra

vity

'cas

e

E,

(H-h

.)+

he.

hDL

+E

A

[1,

48]

"D~ho

L(H~/je)--1

I

for

L/H

;;'3

(00

)

(0'0

)

TA

BL

E3

FL

OW

TO

AS

LO

TF

RO

MT

WO

LIN

ES

OU

RC

ES

(Cla

use

6.2.

2)

PE

NE

TR

AT

lON

FL

OW

CO

ND

ITIO

ND

ISC

HA

RG

EF

OR

MU

L\E

RE

'Io

IAR

h'5

2kD

x(H

-he)

Q~

L+

rn

<.0 -

Par

nal

lyp

enet

rati

ng

slot

Art

esia

n

GC

d.V

lty

Q=

flow

toth

esl

otr

=a

fact

orw

hic

hd

epen

ds

onth

era

tio

WID

wh

ere

Q.~

(0

73

+0

27H-he)~

(H2.

_h,J

e)

W=

pen

etra

tio

nof

the

slot

un

oth

eH

Lp

elY

IOllS

stra

tum

(To

bed

eter

­n

un

edfr

omFi

g.2)

Ful

lyp

enet

rau

ng

slot

Th

efl

owIS

twrc

eth

atco

mp

ute

dfr

omT

able

2fo

rth

ere

spec

tive

case

s

NO

TE

-T

he

slot

ISn

ud

way

betw

een

the

hn

eso

urce

s

NO

TE--

At

dist

ance

sJ

from

the

slot

,II

Iexc

ess

of<i

.bou

t1

3D

the

hea

dII

incr

ease

sli

near

lyas

yin

crea

ses,

and

can

beco

mp

ute

das

follo

ws.

It-h

e-H

H-k

e)

y'r

-DL

+yD

!i: ~ • .. !

IS : 9759 - 1981

TABLE f FLOW TO TWO PARTIALLY PENETRATING SLOTS MIDWAYBETWEEN AND PARALLEL TO TWO UNE SOURCES

(Claw, 6.2 2)

FLOWCONDmON

Artesian

DISCHARGE FORMULAE

Flow from one source to the closest of the twoslots 15 obtained from equations of Table 2.

Head IhD' midway between SIOlS IS obtained fromTable 2.

REMARKS

Flow from either slot is determined from k1 and k" can be obtainedTable 2. from FIg. 3

The head '''D' midway between the slots l'i glw:n

by

[k, k, ]hD ~ h. -L- (H - h.) + 1

TABLE 5 HEAD REDUCTION FOR FINITE LENGTH OF SLOT

(CltJWIS 62.3 and 6 3.4.4)

PENETRATIONFLOW

I-lE.AD REDUCTION AT THE WELLSCONDmoN

Artesian n-s; -Q. I,,_a_ + Q.L

2.,..kD 21f TII' kD.Fully

penetraungwell 2Q.L Q. a

Gravnv H'l.-h2w = """"k(J + --;k In

21TT.

PartiallyArtesian H-h. Q. <+ + 8. )penetra llOg ~ kD

Gravity The formula for fully pcnctratmg case can be usedprovided Q. IS computed from an appropriateequation.

NOTE 1 - Q..=dJScharge per well.NOTE 2 - eo =upht factor (for detads as gIven III various text books).NOTE 3 -Il. -ehead at the well

32

TA

BL

E6

FL

OW

TO

AS

ING

LE

WE

LL

CfR

CU

LA

RS

OU

RC

E

(Cla

us,

62.4

)

NO

TE

-Fo

ra

wel

llo

cate

dat

dist

ance

Efr

omth

ece

ntr

eo

fth

eC

ircl

eof

Infl

uenc

e,th

efl

owIS

grve

nb

y'

'" '"

PE

NE

TR

AT

ION

Ful

lyp

enet

rati

on

wel

l

FL

OW

CO

ND

Ino

N

Art

esia

n

Gra

vnv

Q. Q

.

DIS

CH

AR

GE

FOR

M1.

'1...

AE

2"k

D(H

-h.)

In(R

lr.)

2"kD

(H-h

,.:

ln[(

R'-

E')

/Rr.

l

k1t(H2_h~

..)

I1I(R

lrll'

\

RE

MA

RK

S

(1)

Q."

=fl

owto

the

wel

l

(11)

h w=

hea

dat

the

wel

l(m

)R

=ra

diu

sof

infl

uenc

e(IV

)W

ell

isat

the

cent

reo

fth

eC

ircu

lar

sour

ces

Par

ual

lyp

enet

ratm

g....

.ell

Ora

vltv

Art

esia

n

Qk.[

(H-S

i'-I

'][l

03

io-,

IB

.Il

WIn.

(Rtr

l/!)

/-(

•~

-h-)

Sln

HJ

Q'P~

2k.

kD(H

-hw

)G

(in

(Rlrl

/lJ

G=

rati

oof

flow

[10m

par

ti­

ally

pen

etra

tin

gw

ell

toa

fully

pen

etra

tin

gw

ell,

COl

the

Sam

ed

raw

dow

nat

the

per

iph

ery

ofth

ew

ells

NO

TE

-G

ISgi

ven

byth

efo

llow

ing

expr

essi

on.

W(r:

-"w

iD)

G=

-1

+7

\J-

cos---

D2~

2

In

wh

ich

wID

equa

lsth

ep

enet

rati

on

ofth

ew

ell

scre

enm

toth

epe

rvio

usst

ratu

mex

pres

sed

asa

dec

imal

.

;l ~ , .. !

IS : 9759 - 1981

TABLE 7 FLOW TO A SINGLE WELL-LINE SOURCE

(Cla/ise b 2.5)

FLOWDISCHARC.L FORMULAE. REMARKS

CONDITIO-,

Artesian Q. -2.kD (H-h.) Q. = flow to the wellI. (2L/,.)

Gravity Q..1. (H'-h'.) H-h..." = drawdown at the well

III (2Llrw)

TABLE 8 CAPACITY OF DEEP WELL PUMPS

(Uau" b 3 136)

PUMP BOWl SIZE. em PRFH.RIH"I) '}.hNIMlJ\l \PPROXIMAT£ MAXIMUM

(l\bNlMUM ID OF WELL PUMP ID OF WELL, em CAPACITY 0·0036 m 3Jm

WILL ENTER)

10 115 90

11') IJ 160

I:' 20 450

20 0" 600-J

25 30 1200

30 35 1 BOO3j 40 2400

40 4", 3000

34

IS I 9759. 1981

TABLE 9 PUMPS FOR SUMP PUMPING

(Claus, 9.2.8)

SLNo.

2

3

4

6

TYPE OF

PUMP

Handliftdiaphragm

Motor-drivendiaphragm

Pneumatic sumppumps

Self-pnmmgcentrifugal

Rotaryduplacement(monopump)

Sinking pumps

OuTPUT

From 54·6 math for 3 em suction;up to 655 mlJh for 10 em sue­lion

From 983 m'/h for 7 5 em suctionup to 1 747 mSIh. for 10 emsuction

From 1 310 m3/h against 15 mhead to 2 620 IIl'/h agamst S mhead. at 7·3 kg/em"'airpressure

From 2 184 m'fh for 5 em suctionto 19656 mll/h for 20 em suc­tion

1638 m3 jh for 7 5 em pump,agamet 6 m head

From 875 m3jh for 5 em suctionto 10 920 m3/h for )5 em Suc­tion

35

SUitable for intermittent pump­109 m small quantities

Can deal with sand and silt In

limited quantities

Useful for intermittent pumpingon sues where compressed airis available, can deal withsand and silt in limitedquannues

Sand and sdt in water causeexcessive wear on impeller forlong periods of pumpmg,therefore. desirable to haveefficient filter around sumpor pump sucnon. Widelyused for steady pumpmg offairly clean water. SmallestUnits can be carried by oneman

Can deal with considerablequantities of ~1l1t and sand

Can pump against 60 m head.SUitable for working In deepshafts or other confined spaceswhere pumps must be pro..gressrvely lowered with fallingwater table. Can be verticalspmdle centruugal pump orsteam operated pulsometertype

IS I 9759. 1981

(Contin""d from Pdge 2)

Memkrs RepresenhngDsecr-r DIRECTOR Rg<:EARCH Mmmry of Railways (RDSO)

(SM II)DEPUTY Dtaecroe STANDARD (CB I) (Alternatel

DIRECTOR High\VaY~ Research Laboratory, MadrasSHRI S, MUKHERJEE Cemmdra Company Limned BombaySHRI B K. PANTHAKV Hmdustan Construction Company Lunlted,

&mbaySURf P G RAMAKRI~HNAN EngmeerIng Coustrucnon Corporation Limited,

Madras

Bombay

Government of West

Instuute. Roorkee

India

Public Work~ Department,Bengal, Calcutta.

Central Burldmg Research

Gammon

SIlRI D SHA.RMA

SIIRI AMAR SINOH (Allernat~)

SIIRIO S SRIVASTAVA Cement Corporauon of India, New DelhiSHiU S K CHATTERJEE (Alterllate)

SHR. G. B SINGH (AJlerna!/!)SHRr S A R~DlJl

SURf G R. HARIDAS (Alternate)SURI A K. SARKAR

Adhoc Panc 1for Preparation of Indian Standard Oil Guidehucs forDewatl nng Dunng Construction, BDC 43 .6/P,

Member

DR U BASU Engmeers India Ltd. New Delhi

36

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