I S : 2 9 1 1 ( P a r t 1/ 1 /S e c 4) 4) - 1 9 8 4 ( R e a f f i r m e d 2 00 00 2) 2)
E d i t i o n 1 .1 .1 (1987-10)
In I n d i a n S t a n d a r d CODE CODE OF P RACTIC RACTICE E FOR DE SIGN AND CONSTRUCTION CONSTRUCTIO N OF P ILE F OUN DATION DATION P AR AR T 1 S e c t io io n 4
CONCR ETE P ILE S
B o r e d P r e c a st s t Co C o n c r e t e P i le le s
(Incorp Incorp ora tin g Amen Amen dm ent No. 1)
U DC 624 .154.34 [ 691.327 ] : 006.76
© BIS 2003 B U R E AU
O F
I N D I AN
S T AN D AR D S
MANAK BHAVAN , 9 B A H A D U R S H A H ZAFAR MARG N E W D E L H I 110002
P r i ce Gr o u p 7
I S : 2 9 1 1 ( P a r t 1/ 1 /S e c 4 ) - 1 9 8 4
In I n d i a n S t a n d a r d CODE COD E OF PRACTIC PRACTICE E F OR DESI D ESI GN AND CONSTRUCTION CONSTRUCTIO N OF P ILE F OUNDATION OUNDATION P AR AR T 1 S e ct c t io ion 4
CONCR ETE P ILE S
B o r e d P r e c a st s t Co C o n c r e t e P i le le s
Foundation Engineering Sectional Committee, BDC 43 Ch a ir m a n
R ep r es en t i n g
B RI G O MBIR S INGH M em ber s
En gineer-ingineer-in-Chief Chief’’s Br an ch, Army H eadqua rt ers
C OL K. P. ANAND ( A lt ern a t e t o B r ig ig O m bi bi r S in in g h ) S H RI B. ANJIAH
Andhra Pradesh Engineering Research Laboratories, Government of Andhra Pradesh, Hyderabad D R R. K. B HANDARI Central Building Research Institute (CSIR), Roorkee S H RI C HANDRA P RAKASH ( A lt ern a te ) S H RI A. K. C HATTERJEE Gammon India Ltd, Bombay S H RI A. C. R OY ( A lt ern a t e ) C H I E F E NGINEER Calcutt Calcutt a P ort Tru st, Calcut Calcut ta S H RI S . G U H A ( A lt ern a t e ) S H RI M. G. D ANDAVATE The Concret e Assoc Associat ion ion of In dia, Bombay S H RI N. C. D UGGAL ( A lt ern a t e ) S H RI R. K. D AS G UPTA Simplex Concrete Piles (I) Pvt Ltd, Calcutta S H RI H . G U H A B ISWAS ( A lt ern a t e ) S H RI A. G. D ASTIDAR In personal capacity ( 5, Hungerford Court, 121 H u n ger for d S t r eet, eet , C a lcu t ta ) S H RI V. C. D ESHPANDE The P ressu re P illi illing ng Co (I) (I) Pvt Ltd, Bombay D IRECTOR (C S M R S ) C e n t r a l S oil & M a t e r i a l R e s e a r ch S t a t i on , N e w D el el h i D E P U T Y D IRECTOR (CSMRS) ( A lt ern a t e ) S H RI A. H. D IVANJI Asia Foundation and Construction Pvt Ltd, Bombay S H RI A. N. J ANGLE ( A lt ern a te ) S H RI A. G HOSHAL Stup Consulta Consulta nts Ltd, Bombay Bombay Continu ed on page 2 ) ( Continu
© BIS 2003 B U R E A U O F I N D I A N S T AN AN D A R D S This publication is protected under the In I n d ia n Cop yr igh ig h t A ct (XIV of 1957) and repr oduction duction in whole whole or or in pa rt by any mea ns except except with written permission of of th e publisher sh all be deemed to be an infringement of copyright copyright u nder th e said Act. Act.
I S : 2 9 1 1 ( P a r t 1/ 1 /S e c 4) 4) - 1 9 8 4 ( Contin Contin ued from page 1 ) M em ber s
R epres ep res en t in g
D R J AGDISH N ARAIN Indian Geotechnical Society, New Delhi P RO F S WAMI S ARAN ( A lt ern a t e ) AI N S H RI ASHOK K UMAR J AIN G. S. J ain & Assoc Associat iat es, Roork Roork ee AI N ( A lt ern S H RI VIJAY K UMAR J AIN er n a t e ) S H RI N . J AGANNATH Steel Authority of India, New Delhi S H RI A. K. M ITRA ( A lt ern a te ) J OINT D IRECTOR (D ESIGNS ) N a t i on a l B u i l d i n g s O r g a n i s a t i on , N e w D e l h i S H RI S U N I L B E RY ( A lt ern a te ) J OINT D IRECTOR R ESEARCH Minist ry of Railwa ys (GE)-I, GE)-I, RDSO J OINT D IRECTOR R ESEARCH (B & S ), (RDSO) ( A lt ern a t e ) D R R. K. KATTI Indian Inst itut e of Tec Techn ology, logy, Bombay Bombay S H RI S. R. K ULKARNI M. N. Dast Dast ur & Co Pvt Ltd , Calcut Calcut ta S H RI S . R OY ( A lt ern a t e ) S H RI A. P. M ATHUR Centr al Wareh ousing Corporat Corporat ion, ion, New Delhi S H RI V. B. M ATHUR McKenzies Limited, Bombay S H RI S . M U K H E R J E E In personal Capacity ( E 10 4A , S im la H ou se, N epea ep ean n S ea R oad oa d , B om ba y ) S H RI T. K. D. M U N S I En gineers gineers India Limited, New Delhi Delhi S H RI M. I YENGAR ( A lt ern a t e ) S H RI B. K. P ANTHAKY The Hindu sta n Cons Cons tru ction ction Co Ltd, Bomba Bomba y H RI ADGE S V. M. M ( A lt ern a t e ) S H RI M. R. P U N J A Cemindia Co Ltd, Bomba Bomba y S ENIOR E N G I N E E R ( A l t ern a t e ) S H RI N. E . V. V. RAGHVAN The Braithwaite Burn & Jessop Construction Co Ltd, Calcutta D R V. V. S. R AO Nagadi Consulta Consulta nts Pvt Ltd, New Delhi Delhi P RO F G OPAL R ANJAN Un iversity of Roorkee, Roorkee, Roork Roork ee S H RI AR J U N R IJHSINGHANI Cement Corporat Corporat ion ion of India, New Delhi S H RI O. P. S RIVASTAVA ( A lt ern a te ) D R A. S ARGUNAN College of Engineering, Guindy, Madras S H RI S . B OMMINATHAN ( A lt ern er n a t e ) S H RI N . S IVAGURU Ministry of Shipping and Tran sport sport S H RI K. B. S ARKAR ( A lt ern a t e ) S UPERINTENDING E N G I N E E R Centr al Pu blic blic Works Works Depar tm ent , New Delhi Delhi ESIGNS (D ) E XECUTIVE E NGINEER (D ESIGNS ) V ( A l tern te rn a t e ) ARADARAJ AN D R A. VARADARAJ Indian Inst itut e of Techn Techn ology, logy, New Delhi Delhi D R R. K ANIRAJ ( A lt ern a te ) S H RI G. R AMAN , D i r e ct or G e n e r a l , I S I ( E x-off x-o ff ici o M em ber ) Director (Civ En gg) S ecretary cretary
K. M. M ATHUR Sen ior ior Depu ty Director (Civ (Civ Engg) Contin ued on page 29 ) ( Contin
2
I S : 2911 (P a r t 1/S e c 4) - 1984
In d ian S tan d ard CODE OF P RACTICE FOR DE SIGN AND CONSTRUCTION OF P ILE F OUN DATION P AR T 1 S e c t io n 4
CONCR ETE P ILE S
B o r e d P r e c a st Co n c r e t e P i le s 0.
FORE WORD
0.1 This Indian Standard (Part 1/Set 4) was adopted by the Indian Sta nda rds Inst itut ion on 27 F ebrua ry 1984, after t he dr aft finalized by the Foundation Engineering Sectional Committee had been approved by the Civil E ngin eer ing Division Coun cil. 0.2 Piles find application in foundation to transfer loads from a structure to competent subsurface strata having adequate load-bearing capacity. The load transfer mechanism from a pile to the surrounding ground is complicated and could not yet be fully determined, although application of piled foundations is in practice over many decades. Broadly, piles transfer axial loads either substa nt ially by friction along its sh aft a nd/or substa nt ially by the end bearing. Piles are used where either of the above load transfer mechanism is possible, depending upon the subsoil stratification at a particular site. Construction of pile foundations requires a careful ch oice of piling syst em , depen ding u pon t h e su bsoil con ditions, th e loa d characteristics of a structure and the limitations of total settlement, differen tial sett lemen t an d a ny other special requiremen t of a pr oject. The installation of piles demands careful control on position, alignmen t a nd dept h a nd involve specialized skill a nd experience. 0.3 This stan dar d (Pa rt 1) was origina lly published in 1964 an d included provisions regarding driven cast in-situ piles, precast concrete piles, bored ( cast in-situ ) and under-reamed piles, including load testing. Subsequently portions pertaining to under-reamed pile foundations were deleted and which are now covered in IS : 2911 (Part 3). At that time it was decided that the provisions regarding other types of piles should also be published separ at ely for t he ea se of reference an d to ta ke into account the recent developments in this field. Consequently IS : 2911 (Pa rt 1)-1964* ha s been r evised in various sections. So fa r t he following sections have been formulated. *Code of practice for design and construction of pile foundation: Part 1 Load bearing concret e piles.
3
I S : 2911 (P a r t 1/S e c 4) - 1984 Section 1 Driven cast in-situ concret e piles Section 2 Bor ed cast in-situ piles Section 3 Dr iven precast concrete piles Section 4 Bored precast concret e piles 0.3.1 This section covers the bored precast concrete piles which have now come in to use in r ecent tim es. 0.4 Bored precast concrete pile is a pile constructed in a casting yard and subsequently lowered into pre-bored holes and the space grouted. These piles find wide applications where safety against chemical aggressive subsoil and the ground water condition is needed. Such protection is possible with bored precast concret e piles, beca use t hese are made using vibrated dense, matured concrete, with low water cement ra tio an d a re n ot su bjected t o driving str esses. These a re a lso useful where artesian conditions exist or where local obstructions are encoun ter ed a bove th e foun ding level or su bsoil wat er flow exists. They also offer facility for applying protective coating on the pile surfaces. The provision in respect of segmental piles with properly designed join t s a r e u n der con sid er a t ion of t h e Com m it t ee a n d it s pr ovision s will be covered a t a la ter sta ge. 0.5 The Sectional Committee responsible for the preparation of standard, while formulating this standard, gave due consideration to th e availa ble experience in th is coun tr y in pile cons tr uction a nd a lso th e limita tions regar ding the availability of piling plan t an d equipment . 0.5.1 The information furnished by the various construction agencies and specialist firms doing piling work in this country and technical discussions thereon considerably assisted the committee in form ula t ion of th is code. 0.6 This edition 1.1 incorporates Amendment No. 1 (October 1987). Side bar indicates modification of the text as the result of incorporat ion of the a men dmen t. 0.7 For the purpose of deciding whether a particular requirement of th is sta nd ar d is comp lied with , t he fina l valu e, observed or calcula ted, expressing th e res ult of a tes t, sh a ll be roun ded off in a ccorda nce with IS : 2-1960*. The nu mber of significan t places ret ain ed in t he r oun ded off value should be the same as that of the specified value in this standard. *Rules for round ing off nu mer ical valu es ( revised ).
4
I S : 2911 (P a r t 1/S e c 4) - 1984 1. SCOP E 1.1 This standard (Part 1/Sec 4) covers the design and construction of loa d bear ing bored pr eca st concret e pile which t ra nsm it th e load of th e stru ctur e to the str at a where resista nce is adequate. N OT E — This standa rd is based on a ssumpt ion t ha t str ength of grout fill up in the space shall be at least equivalent to that of surrounding soil and the skin friction developed on th e pile shall be determ ined by probative test.
2. TER MINOLOGY 2.0 For the purpose of this standard, the following definitions shall apply. 2 .1 Al lo w a b l e L o a d — The load wh ich ma y be applied to a pile after taking into account its ultimate load capacity, pile spacing, overall bearing capacity of the ground below the pile, the allowable sett lement , negat ive skin friction a nd t he loa ding condit ions in cluding re vers a l of loa ds, et c. 2.2 B a t t e r P i le (R a k e r P i l e ) — The pile which is insta lled at an an gle to th e vertica l. 2.3 B e a r i n g P i le — A pile form ed in t he groun d for tr an smitt ing the load of a structure to the soil by the resistance developed at its tip and/or along its surface. It may be formed either vertically or at an inclina tion (Bat ter Pile) an d m ay be required to ta ke u plift. If th e pile support t he load prima rily by resista nce developed a t th e pile point or base it is r eferr ed t o as ‘E nd Bear ing P ile’, if pr ima rily by friction a lon g its su rfa ce t h en a s ‘F riction P ile’. 2.4 B or e d P r e c a s t P ile — A pile cons tr ucted in rein forced concret e in a cast ing yar d a nd subsequent ly lowered into prebored h oles a nd space grouted. 2 .5 C u t -o ff L e v e l - It is th e level wher e t he inst alled pile is cut-off to support th e pile caps or beam s or a ny oth er st ru ctu ra l components a t th at level. 2.6 F a c t or o f S a fe t y — The r at io of th e ultima te load capa city of a pile, to th e sa fe loa d of a pile. 2.7 S a fe L oa d — The load derived by ap plying a factor of sa fety on t he ultima te load ca pacity of th e pile or a s determ ined in th e loa d test . 2.8 U lt i m a t e L oa d C a p a c it y — The ma ximu m load wh ich a pile or pile sh a ft ca n car ry before fa ilur e of groun d (when th e soil fa ils by shea r as evidence from t he loa d sett lemen t cur ves) or failur e of pile m at eria ls. 2.9 Wo r k i n g Lo a d — The load a ssigned to a pile a ccordin g to design. 5
I S : 2911 (P a r t 1/S e c 4) - 1984 3 . N E C E S S A R Y I N F O R M AT I O N 3.1 For t he sa tisfactory design an d const ru ct ion of bored pr eca st piles, the following information is necessary: a) Site investigat ion dat a as laid down in IS : 1892-1979*, and oth er relevan t Codes. Sections of tr ial borin g, su pplemen ted, wher ever appr opriat e, by penetra tion test s, should incorporat e da ta /informa tion su fficient ly below t he an ticipa ted level of t he pile t ip; th e boring below the pile tip should generally be not less than 10 m un less bed rock or firm str a ta ha s been encoun ter ed earlier. The nature of the soil both around and beneath the proposed pile should be indicat ed on th e basis of appropriat e test s of strength , comp ressibility, etc. Groun d-wa ter levels a nd condit ions (such as a rt esian cond itions ) sh ould be indicat ed. Results of chem ical t est s to ascertain the sulphate and chloride content and/or any other deleterious chemical content of soil and/or ground water should be indicated, particularly in areas where large piling work is envisaged or wh ere su ch inform at ion is not gener a lly available. b) In cas e of bridge foun da tions, da ta on high flood level, ma xim um scouring depth, normal water level during working season, etc, should be provided. In the case of marine construction, high and low tide level, flow of water and other necessary information, as listed in IS : 4651 (P a r t 1)-1974† sh ou ld be provided. c) In ca se rock is en coun t ered, a dequa te description of rock t o convey its physical conditions as well as its strength characteristics sh ould be indica ted. d) Genera l pla n a nd cross section of th e str uctur e showing type of structural frame, including basement, if any, in relation to the pr oposed pile-ca p t op t r a vels should be provided. e) The genera l layout of th e stru ctu re sh owing estima ted loads, vert ical a nd horizont al, momen ts an d t orque at th e t op of pile caps, but excluding the mass of the piles and caps should be provided. Th e top levels of finish ed pile ca ps sh a ll be clear ly indicat ed. f) All tra nsient loads due to seismic and wind conditions an d loa d due to under wa ter should be indicat ed separa tely. g) Sufficient inform at ion of str uctur es existing near by and th e experience of piles in the area close to the proposed site and boring report thereof for assessing the founding level of piles should be provided. *Code of pra ctice for s ubsu rface invest igations for foun dat ions ( fi rst rev is ion ). †Code of pra ctice for plan ning an d design of port s an d ha rbours: Par t 1 Site investigation ( fi rst revis ion ).
6
I S : 2911 (P a r t 1/S e c 4) - 1984 4 . E Q U I P M E N T A N D AC C E S S O R I E S 4.1 The equipment and accessories will depend on the type of bored precast piles chosen in a job and would be selected giving due consideration to the subsoil strata, ground-water conditions, type and founding material and the required penetration therein wherever applicable. 4.2 Among the commonly used plants, tools and accessories, there exist a large variety; suitability of which depends on the subsoil conditions, ma nn er of opera t ion, et c. Boring operations are generally done by any appropriate method with or without temporary casing. Boring may be carried out using mu d st abilisation if required. 4.3 H a n d l in g E q u i p m e n t fo r L ow e r in g — H a n d lin g e q u ip m e n t such a s cra ne, derricks, movable gant ry, ma y be used for h an dling an d lowering of the precast piles in the bore. The choice of equipment will depend upon length, ma ss, an d oth er pra ctical requiremen ts. 4.4 G r o u t in g P la n t — The m ixing of th e grout can be car ried out in any suitable high speed collidal mixer. For grouting a suitable grout pump with st irring/agita ting arr an gement ma y be used. 5. DESIGN CONSIDE RATION 5.1 G e n e r a l — Pile foun da tions sh all be designed in such a way th at the load from the structure it supports, can be transmitted to the soil with out cau sing any soil failure a nd without cau sing such set tlement differential or total under permanent transient loading as may result in str uctur al da ma ge and/or functiona l distr ess. The pile sha ft sh ould have adequate structural capacity to withstand all loads (vertical, axial or otherwise) and moments which are to be transmitted to the subsoil and shall be designed according to IS : 456-1978*. The shaft of bored p recast piles m ay be of circular or octa gona l sha pe, an d m a y be of solid section or with a central hollow core. The limiting size of the pile will depend m ainly on a vaila ble ha ndling equipment a nd t he m ass of th e pile sha ft t o be ha ndled. 5.2 Ad j a c e n t S t r u c t u r e s 5.2.1 When working near existing structures care shall be taken to avoid any damage to such structures. In the case of bored pile care shall be taken to avoid effect due to loss of ground; when boring is car ried out using mu d, the st a bility of th e bore pa rt icular ly adjacent t o loa ded foun da tions sh a ll be exa min ed. 5.2.2 In case of deep excavations adjacent to piles, proper shoring or other suitable ar ra ngement sha ll be done to gua rd a gainst the lat eral moveme nt of soil st ra tu m or r eleasing th e confinin g soil st ress. *Code of practice for plain an d r einforced concret e ( th ird revision ).
7
I S : 2911 (P a r t 1/S e c 4) - 1984 5.3 S o il R e s is t a n c e — The bear ing ca pacity of a pile is dependent on t he properties of the soil in which it is embedded. Axial load from a pile is norma lly tra nsm itted to th e soil th rough sk in friction a long th e sha ft a nd end bear ing at its tip. A horizont a l load on a vertical pile is t ra nsm itted to th e subsoil prima rily by horizont al su bgra de rea ction genera ted in th e upper pa rt of th e sha ft . A single pile is n orm a lly designed t o ca rr y loa d along its axis. Tra nsver se load bear ing cap acity of a single pile depends on the soil reaction developed and the structural capacity of the shaft un der bending. In case th e horizont a l loads a re of higher ma gnitude, it is essent ial to investigat e th e phen om enon u sing principles of horizont al subsoil rea ction ad optin g appr opr iat e values for h orizont al m odulu s of th e soil. Alter na tively piles ma y be insta lled in ra ke. 5.3.1 The ultimate load capacity of a pile may be estimated using a suitable static formula. However, it should preferably be determined by an initial load test [ see IS : 2911 (Pa rt 4)-1984]*. The cross sectional area for the purpose of the calculation shall be the concrete section excluding the grout where chemical aggression is likely to inhibit set tin g of cemen t. The s ett lemen t of pile obta ined a t s a fe load /work ing load from loa d test resu lts on a single pile sha ll not be direct ly used in forecast ing th e sett lemen t of str uctur e [ see IS : 8009 (P a rt 2)-1980† ]. The average settlement may be assessed. It would be more appropriat e to assess t he a vera ge sett lemen t on th e basis of subsoil dat a a nd loading details of the structure as a whole using the principles of soil mechanics. 5.3.1.1 S tatic form ula — By using stat ic form ula, the estima ted value of ultimate load capacity of a typical pile is obtained, the accuracy being dependent on the reliability of the formula and the reliability of th e ava ilable soil pr oper ties for va rious str a ta . The soil pr opert ies to be adopted in such formula may be assigned from the results of labora tory test s an d field test s like sta nda rd penet ra tion t ests ( see IS : 2131-1981‡ ). Results of cone p enet ra t ion t est s m ay a lso be ut ilized where n ecessar y corr elat ion with soil result s dat a h as been est ablished [ see IS : 4968 (P a rt 1)-1976§ ], IS : 4968 (P a rt 2)-1976§, IS : 4968 (Pa rt 3)-1976§. Two sepa ra t e sta t ic form ula comm only ap plica ble for cohe sive an d coh esion less soil respe ct ively ar e indicat ed in Appen dix A *Code of practice for design and construction pile foundations: Part 4 Load test on piles ( fi rst revis ion ). †Code of practice for calculation of settlement of foundations: Part 2 De ep foun dat ions subjected to symm etrical sta tic vertical loading. ‡Method for st an dar d penet ra tion t est for soils ( fi rst rev is ion ). §Method for subs ur face soun ding for s oils: Pa rt I Dyna mic meth od using 50 mm cone without bent onite slur ry ( fir st rev isi on ). Pa rt II Dynam ic meth od using cone an d bentonite slur ry ( fi rs t revis ion ). Par t III Sta tic cone penetra tion t est ( fi rs t rev is ion ).
8
I S : 2911 (P a r t 1/S e c 4) - 1984 to serve only as a guide. Other alternative formula may also be applicable, depending on the subsoil characteristics and method of inst a llat ion of piles. 5.4 N e ga t i v e Sk i n F r i c t io n o r D r a g d o w n F o r c e — W h en a s oil stra tu m t hr ough which a pile sha ft h as penetra ted into an underlying ha rd st ra tu m, compr esses as a result of either it being un consolidated or it being un der a newly placed fill or as a resu lt of rem oulding of the pile, a dr a gdown force is gener a ted a long th e pile sha ft u p to a point in depth where t he su rr oun ding soil does not m ove downwar d r ela tive to th e pile sha ft. N OT E — Est imat ion of th is dragdown force is still un der resea rch stu dies and considerations, although a few empirical approaches are in use for the same. The concept is constantly under revision and, therefore, no definite proposal is embodied in this standard.
5.5 S t r u c t u r a l C a p a c it y — The piles shall have necessary structura l str ength to tra nsm it th e loads imposed on it, ultima tely to th e soil. 5.5.1 Axial Capacity — Where a pile is wholely embedded in t he soil ( ha ving a undr ained shear strength not less tha n 0.1 kgf/cm 2 ) its a xial ca rr ying cap a city is not limited by its st ren gth a s a long colum n. Wher e piles ar e inst a lled thr ough very weak soils ( ha ving an u ndra ined shea r str engt h less th a n 0.1 kgf/cm 2 ) specia l consider at ions sha ll be ma de to determine whether the shaft would behave as long column or not; if necessar y suitable reductions sh all be made for its st ru ctu ra l stren gth following the normals tructural principles covering the buckling ph enomenon. When th e finished p ile projects above groun d level an d is not secured a gainst buckling by a dequa te br acing, th e effective lengt h will be governed by fixity conditions imposed on it by the structure it support s an d by the n at ur e of th e soil into which it is inst alled. The depth below t he gr oun d su rface to th e lower point of cont ra flexur e var ies with th e type of th e soil. A st ra tu m of liquid mu d should be tr ea ted a s if it was wa te r . The degr ee of fixity of th e posit ion a nd inclin a t ion of th e pile top an d t he rest ra int provided by an y bracing sh all be estima ted following accepted st ru ctu ra l principles. The perm issible str ess sha ll be r educed in a ccorda nce with similar provisions for reinforced concret e colum ns a s laid down in IS : 456-1978*. 5.5.2 L atera l L oad Capacity — A pile ma y be subjected t o tr an sverse force from a nu mber of cau ses, such as wind, ear th qua ke, wa ter cur rent , ear th pr essu re effect of moving vehicles or sh ips, plan t a nd equ ipmen t, etc. The lat era l loa d carr ying capa city of a single pile depends n ot only on t he h orizont al su bgrad e modulus of th e sur roun ding soil but also on *Code of practice for plain an d r einforced concret e ( th ird revision ).
9
I S : 2911 (P a r t 1/S e c 4) - 1984 the structural strength of the pile shaft against bending consequent upon a pplicat ion of a la t era l load . While cons idering lat era l load of piles, effect of other coexistent loads including the axial load on the pile, should be ta ken in to cons idera tion for checking th e str uctu ra l ca pa city of th e sha ft. A recom men ded met hod for t he det erm ina tion of dept h of fixity, lateral deflection and maximum bending moment required for design is given in Appendix B for fully or partially embedded piles. Oth er a ccept ed met hods, such a s th e met hod of Reese an d Mat lock for fully embedded piles ma y also be used. N OT E — Becau se of limited inform at ion on horizont al m odulus of soil, and refinemen ts in t he th eoret ical an alysis, it is suggested th at adequa cy of a design ma y be checked by a n actua l field load test .
5.5.3 R ak er Pi les — Raker piles ar e norm ally provided where vertical piles cannot resist the required applied horizontal forces. In the preliminary design the load on a raker pile is generally considered to be axial. The distribution of load between raker and vertical piles in a group may be determined by graphical or analytical methods. Where necessary, due consideration should be made for secondary bending induced as a result of the pile cap movement, particularly when the cap is rigid. Free-standing raker piles are subjected to bending moment s du e to th eir own m ass, or exter na l forces from oth er cau ses. Raker piles embedded in fill or consolidating deposits, may become lat era lly load ed owing to th e sett lement of th e sur roun ding soil. 5.6 S p a c i n g o f P i le s — The cent re-to-cent re spa cing of piles sh ould be consider ed from two as pects: a ) pr actical a spects of inst a lling th e piles, an d b) th e na tu re of th e load tr an sfer t o th e soil an d possible reduction in t he bea rin g cap acity of a group of piles t her eby. The choice of the spacing is normally made on semi-empirical approach. 5.6.1 In case of piles which a re pr edomina nt ly rest ing on h ar d str at um and deriving their capacity mainly from end bearing, the spacing will be governed by the competency of the end bearing strata. The minimu m spacing in su ch cases, sha ll be 2.5 times t he diam eter of th e pile. In case of piles rest ing on rock, th e spa cing of twice t he diam eter of th e pile may be a dopted. 5.6.2 Piles der iving th eir bear ing ca pa city ma inly from frict ion s ha ll be sufficiently apa rt to ensu re t ha t t he zones of soils from wh ich t he piles derive th eir support do not overlap to such a n extent th at th eir bear ing values are reduced. Generally the spacing in such cases shall not be less tha n t hr ee times the diam eter of th e pile. 10
I S : 2911 (P a r t 1/S e c 4) - 1984 5.6.3 The spacing should not be so close as to cause direct contact between two adjacent piles in a group, th e deviat ions at depths ar ising out of the tolerance allowed in the installation. This would mean the min imu m spa cing would, to some ext ent , depend on t he lengt h of piles installed. 5.7 P i le G r o u p i n g — In order t o determ ine the bear ing capa city of a group of piles, a n um ber of efficiency equa tions a re in u se. However, it is very difficult to establish the accuracy of these efficiency equations as th e beha viour of piles group is dependen t on m a ny comp lex factors. It is desira ble to cons ider each case sepa ra tely on its own mer it. 5.7.1 The bea rin g ca pa city of a p ile group m ay be either : a) equal t o the bea ring capa city of individual piles m ultiplied by th e nu m ber of piles in t he group , or b) it may be less. 5.7.2 In case of piles deriving their support mainly from friction and connected by a pile cap, the group may be visualized to transmit load to the soil, as if from a column of soil enclosed by the piles. The ultim at e capa city of the gr oup m a y be com pu ted following th is concept, taking into account the frictional capacity along the perimeter of the column of soil as above and the end bearing of the said column using th e accepted pr inciples of soil mecha nics. 5.7.2.1 When the cap of the pile group is cast directly on reasonably firm st ra tu m which su pport s the piles it m a y cont ribute t o th e bea ring capacity of the group. The additional capacity along with the individua l ca pa city of th e piles m ult iplied by th e nu mber of piles in t he group should n ot be more th a n th e capa city work ed out in 5.7.2 . 5.7.3 When a moment is applied on the pile group either from super structure or as a consequence of unavoidable inaccuracies of installation, the adequacy of the pile group in resisting the applied momen t should be checked. In case of a single pile su bjected to momen ts due to lateral forces or eccentric loading beams may be provided to rest ra in t he pile ca p effect ively from lat era l or r ota t iona l movement . 5.7.4 In case of structure supported on single pile/group of piles, resulting into large variation in the number of piles from column to column, it is likely, depending on the type of subsoil supporting the piles, to result in a high order of differential settlement. Such high order of differential settlement may be either catered for in the structural design or it may be suitably reduced by judicious choice of variations in the actual pile loadings. For example, a single piles cap ma y be loaded t o a level higher th a n t ha t of a pile in a group in order t o achieve redu ced differen tia l settlem ent between t wo a djacent pile cap s supp ort ed on d ifferen t nu mber of piles. 11
I S : 2911 (P a r t 1/S e c 4) - 1984 5 .8 F a c t o r o f S a f e t y a n d S a fe L o a d 5.8.1 F a ctor of sa fet y should be ju diciou sly chosen a ft er con sider ing: a ) th e r eliability of t he va lue of ultim at e load ca pa city of a pile, b) th e type of superstr uctur e an d t he t ype of loading, an d c) allowable tota l/differen t ial sett lement of t he st ru ctu re. 5.8.2 The ultimate load capacity may be obtained whenever pra cticable, from a loa d t est (initia l) [ see IS : 2911 (P a rt 4)-1984* ]. 5.8.3 When t he u ltima t e load capa city is com put ed from st at ic form ula the factor of safety would depend on the reliability of the formula depending on a particular site and locality and the reliability of the subsoil parameters employed in such computation. The minimum factor of safety on static formula shall be 2.5. The final selection of factor of safety shall take into consideration the load settlement cha ra cter istics of th e str uctur e as a whole at a given site. 5.8.4 Factors of safety for assessing safe load on piles from load test dat a should be increased in un favour able conditions where: a) sett lemen t is to be limited or u nequa l sett lement a voided as in th e case of accur a tely aligned m echiner y or a supers tr uctur e with fragile finishings, b) large impact or vibra ting loads a re expected, c) th e properties of th e soil ma y be expected to deter iora t e with time, an d d) t he live load on a st ru ctu re car ried by friction piles is a consider a ble port ion of t he t ota l load a nd a pproxima t es to th e dead load in its duration. 5.9 T r a n s ie n t L oa d i n g — The ma ximu m perm issible increase over th e sa fe loa d of a pile as a rising out of wind loa ding, is 25 per cent . In case of loads and moments arising out of earthquake effects, the increase of safeload on a single pile may be limited to the provisions contained in IS : 1893-1975†. For transient loading arising out of super imposed loa ds no increa se m ay be genera lly allowed. 5.10 O v e r l oa d i n g — When a pile in a group, designed for a cert ain safe load is found, during or after execution, to fall just short of the load required to be carried by it, an overload up to 10 percent of the pile capa city ma y be allowed on ea ch pile. The t ota l overloa ding on t he *Code of pra ctice for design a nd const ru ction of pile found at ions : Pa rt 4 Load t est on piles ( fi rst revis ion ). †Criteria for earth quake r esista nt design of stru ctur es ( th ird revision ).
12
I S : 2911 (P a r t 1/S e c 4) - 1984 group s hould not be more th an 10 percent of t he capa city of th e group and not more than 40 percent of the allowable load on a single pile. This is su bject to th e increa se of t he load on a ny pile not exceeding 10 percent of its ca pa city. 5.11 L ift i n g a n d H a n d l in g S t r e s s e s — Stresses induced by bending in t he cross section of a pr eca st pile dur ing liftin g an d ha ndling ma y be estimated just as for any reinforced concrete section in accordance with relevant provisions of IS : 456-1978*. The calculations with regard to moments depending on the method of support during handling will be as given below. Excessive whippiness in handling precast pile ma y gener ally be avoided by limiting t he length of pile to a ma ximu m of 50 times the least width . N u m ber of Poin ts L ocation of Poin t of S u pport from B en d in g M om en t of Pick U p and in T erm s of Length of Pile to be Allowed for for M in im u m M om en ts Des ign WL ----------On e 0.293 L 23.3 Two
0.207 L
WL ----------46.6
Three
0.145 L , th e m iddle point will be at t he cent re
WL --------95
where W = ma ss of pile in kg, and L = le n gt h i n m e t r e s.
During hoisting the pile will be suspended at one point near the head and the bending moment will be the least when it is pulled in a dist a n ce of 0.293 L , and th e value of bending m om ent will be: WL ----------23.3 5.12 R e i n fo r c e m e n t — The longitu dinal reinforcemen t sh all be provided in for the entire length preferably of high yield strength to withst an d th e han dling stresses to the extent t o meet r equirement as given in 5.11 . All the main longitudinal bars shall be of the same length. The area of the main longitudinal reinforcement of any type an d grad e sha ll not be less th an 0.4 percent of th e cross section a rea of the piles or as required to cater for handling stresses whichever is great er. The lat era l reinforcemen t sha ll be links or spirals prefera bly of not less th an 6 mm diam eter bar s. The cover of concret e over a ll th e reinforcement including bending wire should not be less than 40 mm, but wh ere th e piles ar e exposed to th e sea wat er or water ha ving oth er *Code of practice for plain an d r einforced concret e ( third revision ).
13
I S : 2911 (P a r t 1/S e c 4) - 1984 corrosive contents the cover should be no where less than 50 mm. A thin gauge sheathing pipe of approximately 40 mm diameter may be attached to the reinforcement cage, in case of solid piles, to form the cent ra l duct for pu m ping grout to th e bott om of th e bore. 5 .1 3 D e s i g n o f P i le C a p 5.13.1 The pile caps ma y be designed by assum ing th at th e load from colum n is dispersed a t 45° from t he t op of th e cap u p to the m id-dept h of the pile cap from the base of the column or pedestal. The reaction from piles may also be taken to be distributed at 45° from the edge of the pile, up to the mid-depth of the pile cap. On this basis the maximum bending moment and shear forces should be worked out at critical sections. The methods of analysis and allowable stresses sh ould be in a ccord a nce with IS : 456-1978*. 5.13.2 Pile cap shall be deep enough to allow for necessary anchorage of th e colum n a nd pile reinforcemen t. 5.13.3 The pile cap should normally be rigid enough so that the imposed loa d could be distr ibut ed on th e piles in a group equita bly. 5.13.4 In case of a large cap, where differential settlement may be imposed between piles u nder th e sam e cap, due considera tion for th e consequ ent ial momen ts sh ould be given. 5.13.5 The clear overha ng of th e pile cap beyond th e out erm ost pile in th e group sh all norma lly be 100 to 150 mm depend ing upon t he pile size. 5.13.6 The cap is genera lly cas t over a 75 mm th ick levelling cour se of concrete. The clear cover for main reinforcement in the cap slab shall not be less tha n 60 mm . 5.13.7 The pile should project 50 m m int o th e cap concret e. 5.14 The design of grade beams if used shall be as given in IS : 2911 (P a r t 3)-1980†. 6. MATER IALS 6.1 C e m e n t — The cement used sha ll conform to the requiremen ts of IS : 269-1976‡, IS : 455-1976§, IS : 8041-1978 | | , IS : 1489-1976¶, and IS : 6909-1973** as t he case may be. *Code of practice for plain an d r einforced concret e ( th ird revision ). †Code of practice for design and construction of pile foundations : Part 3 Underream ed pile founda tions ( fi rs t revis ion ). ‡Specificat ion for ordina ry a nd low h eat Portlan d cement ( th ird revision ). §Specificat ion for P ortla nd s lag cemen t ( third revision ). | | Specificat ion for r apid h ar dening P ort land cement ( fi rs t rev is ion ). ¶ Specifica t ion for P or t la n d-pozzola n a cem en t ( second revision ). **Specification for super-sulphated cement.
14
I S : 2911 (P a r t 1/S e c 4) - 1984 6.2 S t e e l — Reinforcement steel shall conform to IS : 432 (Pa rt 1)1982*, IS : 1786-1985† or IS : 226-1975‡. 6 .3 C o n c r e t e 6.3.1 Mat erials a nd met hod of ma nu factur e for cement concrete sh a ll in general be in accordance with the relevant requirements given in IS : 456-1978§. The st resses in concrete due t o workin g load a nd du ring ha ndling, pitching a nd dr iving of th e pile should not exceed th a n t hose stipulat ed in IS : 456-1978§ according to th e grade of concrete used an d ha ving due r egard t o th e age of piles a t t he t ime of ha ndling. 6.3.2 The gra de of concret e should be prefera bly not less th an M25. 6.3.3 For the concrete, water and aggregates specifications laid down in IS : 456-1978§ sha ll be followed in genera l. Nat ur al r oun ded sh ingle of appropriate size may also be used as coarse aggregate. It helps to give high slump with less water-cement ratio. For tremie concreting aggregat es ha ving nominal size more th an 20 mm should not be used. 7 . WO R K M A N S H I P 7.1 As far as possible in-situ extensions shall be avoided. The casting yard for all concrete piles should preferably be so arranged that they can be lifted directly from their beds and transported to the piling frame with a minimum of handling. The casting yard should have a well-drained surface to prevent excessive or uneven settlement due to softening dur ing ma nu fa ctu re a nd curing. 7.2 As far as practicable each longitudinal reinforcement shall be in one len gth. In ca ses wh ere joint s in r einforcing bar s can not be a voided, the joints in bars shall be staggered. The hoops and links for reinforcement sha ll fit t ight ly against longitudina l bars an d be boun d to them by welding or by tying with mild steel wire, the free ends of which should be turned into the interior of the pile. The longitudinal bars m ay be held apart by tempora ry or perman ent spreader forks not more than 1.5 m apart. The reinforcement shall be checked for tight ness a nd position im m ediat ely before concret ing. 7.3 C a s t i n g a n d C u r in g 7.3.1 The piles should be cast in a continuous operation from end to end of each pile. The concret e sh ould be t horoughly com pa cted a gainst th e form s a nd ar oun d t he r einforcement by mean s of imm ersion an d/or shu tt er vibra t ors. The fa ces of th e pile including th ose exposed at th e *Specification for mild steel and medium tensile steel bars and hard drawn steel wires for concrete r einforcement: Pa rt 1 Mild st eel and m edium t ensile steel bars ( third revision ). †Specification for high strength deformed steel bars and wires for concrete reinforcement ( th ird revision ). ‡Specificat ion for str uctur al st eel (sta nda rd qua lity) ( fi ft h revis ion ). §Code of practice for plain an d r einforced concret e ( third revision ).
15
I S : 2911 (P a r t 1/S e c 4) - 1984 top of pile should be dense as far as possible. Immediately on completion of the casting the top surface should be finished level without excessive trowelling. Care should be taken to ensure that vibration from adjoining works does not effect the previously placed concret e for p iles du rin g th e set tin g period. 7.3.1.1 All shuttering shall be placed on firm supports capable of with sta nding th e loads of shu tt ering, wet concrete a nd in cident al load of workm en, so th at cast piles a re st ra ight a nd free from deform at ions. The sh ut ter ing sha ll be coa ted wit h oil on t he ins ide fa ce. 7.3.2 Though from consideration of speed and economy precast concret e piles will have t o be placed wit h t he lea st possible delay a fter cast ing, it sha ll be kept in mind th at a t horough curing and ha rden ing is necessary before the piles are placed and proper schedule to take ca re of th is sha ll be decided for th e opera tions of ca stin g, st a cking a nd placing. The m ost im port a nt fa ctors effectin g th e tim e of cur ing ar e th e method of curing, weather during hardening, probable hardness of placing a nd t he m eth od of lifting a nd pit chin g. 7.3.4 Before the operation of handling the piles, the minimum periods counted from the time of casting as given in IS : 456-1978* shall be followed. 7.4 S o r t i n g a n d H a n d l in g 7.4.1 Piles sh all be stored on firm groun d free from liability to un equa l subsidence or set tlem ent un der t he m as s of th e sta ck of piles. The piles sha ll be placed on timber su pport s which a re t ru ly level an d spaced so as to avoid undue bending in the piles. The support shall be vertically one a bove the other . Spaces sha ll be left r oun d th e piles to enable th em to be lifted without difficult y. The order of st acking sh all be such t ha t the older piles can be withdrawn for placing without disturbing the newer piles. Separate stacks shall be provided for different lengths of piles. Wherever curing is needed during storage, arrangements shall be made to enable the piles to be watered if weather conditions so require. For detailed precautions with regard to curing operations re fer en ce ma y be m a de t o IS : 456-1978*. 7.4.2 Care shall be taken at all stages of transporting, lifting and handling of the piles that they are not damaged or cracked. During transportation, the piles shall be supported at the appropriate lifting holes provided for the purposes. If the piles are put down temporarily after being lifted, t hey sh all be pla ced on t res tles of blocks locat ed a t th e liftin g point s. *Code of practice for plain an d r einforced concret e ( th ird revision ).
16
I S : 2911 (P a r t 1/S e c 4) - 1984 7 .5 C o n t r o l o f P i le I n s t a ll a t i o n 7.5.1 Bored precast piles sh all be cons tr ucted by suit a ble choice of borin g and installation techniques; covering the manner of soil stabilization, th a t is, us e of ca sing a nd /or u se of dr illing mu d a n d choice of borin g tools in order to permit a satisfactory installation of a pile at a given site. Su fficient deta iled inform at ion about th e subsoil cond itions is essent ial to predeterm ine th e deta ils of th e insta llat ion technique. The bott om end of th e pile sha ll have proper ar ra ngement s for clean ing an d grout ing. 7.5.2 Con trol of Alignm en t — Piles sha ll be insta lled as accur at ely as possible according to the designs and drawings either vertically or to the specified batter. Greater care should be exercised in respect of installation of single pile or piles in two pile groups. As a guide, for vertical piles a devia tion of 1.5 per cent an d for ra ker piles a deviat ion of 4 percent sh ould n ot be norm a lly exceeded a lth ough in special cases a closer tolerance may be necessary. Piles should not deviate more tha n 75 mm or D /6 wh ich eve r is le ss (75 m m or D /10 wh ich ever is m or e in case of piles having diameter more than 600 mm) from their designed positions a t t he work ing level. In t he ca se of a single pile in a colum n t he positiona l tolera nce should not be more th an 50 mm or D /6 whichever is less (100 mm in case of piles having diameter more than 600 mm). Greater tolerance may be prescribed for piles driven over wat er a nd for ra king piles. For piles to be cut off a t a substa nt ial depth (below ground level) or height (above ground level), the design should provide for the worst combination of the above tolerance in position and inclination. In case of piles deviating beyond these limits and to such an extent that the resulting eccentricity cannot be taken care of by a r edesign of t he p ile ca p of pile ties, th e piles should be r epla ced or supplemented by one or more additional piles. In case of piles, with non-circular cross section ‘ D ’ sh ould be ta ken a s th e dimen sions of th e pile, along which the deviation is computed. In such cases the permissible deviation in each direction should be different depending upon t he dim ension of t he pile a long t ha t direction. 7.6 F l u s h i n g — The cent ra l duct/hole shall be conn ected t o a suita ble pump and water drilling fluid allowed to flow through the bottom of th e pile rem oving loose ma ter ial. 7.7 G r o u t in g — San d an d cement grout m ixed with water in a h igh speed collidal m ixer is t o be fed int o the pile with a grout pu mp of suitable capa city conn ected t o th e cent ra l duct th rough a m a nifold. A grout of sand and cement with additives as necessary, of strength not less t h a n 1 : 2 ce m en t a n d sa n d ( see also Note under 1.1 ) suitable for pumping into the annulus, may also be used. The temporary casing her e used sh all be rem oved in st a ges with th e rise of th e level of grout . After final removal of the temporary casing, the grout level shall be brought up to the t op by pour ing in additiona l grout a s r equired. 17
I S : 2911 (P a r t 1/S e c 4) - 1984 7.8 D e fe c t i v e P i le — In case, defect ive piles a re form ed, th ey sh a ll be removed or left in place whichever is convenient without affecting performance of the adjacent piles or the cap as a whole. Additional piles sha ll be provided to replace them . 7.9 Any deviation from the designed location alignment or load capa city of a ny pile shall be noted an d adequa te m easu res t a ken well before the concreting of the pile cap and plinth beam if the deviations ar e beyond th e prem issible limit. 7 .1 0 R e c o r d i n g o f D a t a 7.10.1 A competent inspector shall be present to record the necessary information during installation of piles and the data to be recorded sha ll include: a) th e sequence of inst a llat ion of piles in a group; b) th e dimensions of th e pile including t he r einforcemen t deta ils a nd ma rk of th e pile; c) the depth placed; d) cu t off level/work ing level; a n d e) an y other importa nt observation. 7.10.2 Typica l dat a sheet for fa cility of recordin g piling da ta a re shown in Appendix C. 7 .1 1 S t r i p p i n g P i le H e a d s 7.11.1 The concrete should be str ipped to a level such t ha t t he r ema ining concrete of a pile will project minimum 50 mm into the pile cap. The effect of this projection on the position of any reinforcement in the pile cap sh ould be consider ed in design. The p ile r einforcemen t should be left with adequate projecting length above the cut off level for proper embedment into the pile cap. Exposing such length should be done carefully to avoid shattering or otherwise damaging the rest of the pile. Any cracked or defective concrete should be cut away and ma de good with new concret e pr operly bond ed t o the old. 7.12 L e n g t h e n i n g P i le s — Where a pile is to ha ve an other length cast on to it before or during placing the longitudinal reinforcement should preferably be jointed by full penetration butt welding. The concret e a t th e top of t he origina l pile sh ould be cut down to expose n ot less th an 200 mm of th e bars. The bar s should be held accur at ely and rigidly in position during welding. Where facilities at site are insufficient to make good butt welding practicable the joint may be ma de by lappin g. The r einforcemen t a t t he h ead of t he pile will need t o be exposed for a distan ce of 40 times th e bar dia met er a nd t he n ew bars overlapped for t his dista nce. If th e bond s a re lap ped, spot welding sha ll be done. As an alt ern at ive special bolt a nd n ut joint s ma y be provided. 18
I S : 2911 (P a r t 1/S e c 4) - 1984
AP P E N D I X
A
( Clause 5.3.1.1 ) L O AD C AR R YI N G C AP AC I T Y — S T AT I C F O R M U L A A-1 . P I L E S I N G R AN U L A R S O I L S A-1.1 The ultimate bearing capacity ( Q u ) of piles in granular soils is given by th e following for m u la:
where A p = cross-sectiona l ar ea of pile toe in in cm 2 ; D = s t e m d ia m e t er i n cm ;
γ = effective un it weight
of soil at pile toe in k gf/cm 3 ;
P D = effective overbur den p ressu re a t p ile toe in k gf/cm 2 ; N r a n d N q = bearing capa city factors depen ding upon t he a ngle of int ern a l friction φ at toe;
sum ma tion for n layers in wh ich pile is ins ta lled; K = coefficient of ear th pressu re;
P Di = effective overbur den pr essu re in kg/cm 2 for the i t h layer where i var ies from l to n ;
δ = a ngle
of wall friction between pile a nd s oil, in d egrees ( m a y b e t a k e n e qu a l t o φ ); a nd
A si = sur face area of pile stem in cm 2 i n t h e i t h layer where i var ies from l to n . N OT E 1 — N r factor can be t ak en for gener al sh ear failure as per IS : 6403-1981* N OT E 2 — N q factor will depend, ap ar t from na tu re of soil on th e type of pile a nd its method of construction, for bored piles, the value of N q corresponding to angle of shearing r esistan ce φ ar e given in F ig. 1. This is based on Bereza nt seu ’s curve for D / B of 20 up to φ = 35° an d Vesic’s cur ves beyon d φ = 35°. N OT E 3 — The earth pressure coefficient K depends on t he n atu re of soil strata , type of pile and its method of construction. For bored piles in loose medium sands, K values between 1 and 2 should be used.
*Code of practice for determination of bearing capacity of shallow foundations ( fi rst revision ) .
19
I S : 2911 (P a r t 1/S e c 4) - 1984
F IG 1
B EARING C APACITY F ACTOR N q F OR B ORED P ILES
20
I S : 2911 (P a r t 1/S e c 4) - 1984 N OT E 4 — The an gle of wall friction ma y be taken equal to an gle of shea r resista nce of soil. N OT E 5 — In working out pile capa cities using sta tic form ula, for piles longer t ha n 15 to 20 pile diam eter, m aximum effective overburden at th e pile tip should corr espond to pile length equ al to 15 to 20 diamet ers.
A-2 . P I L E S I N C O H E S I V E S O I L S A-2.1 The ultimate bearing capacity of piles ( Q u ) in cohesive soil is given by t h e followin g: Q u = A p . N c. C p +
α. C . A s
where A p = cross sectiona l area of pile toe in cm 2 , N c = bear ing capa city factor usua lly ta ken as 9, C p = avera ge cohesion a t pile tip in kg/cm 2 ,
α
= r e d u ct i on fa c t or ,
C = avera ge cohesion th roughout t he length of pile in kg/cm 2 , an d A s = surface area of pile shaft in cm 2 . N OT E 1 — The following values of α ma y be tak en depen ding upon th e consisten cy of th e soils:
Con sisten cy
Soft t o very soft Medium Stiff St iff to ha rd
N Valu e
Valu e of α
<4 4 to 8 8 t o 15 > 15
0.7 0.5 0.4 0.3
N OT E 2 — (a) Stat ic form ula m ay be used as a guide only for bear ing capa city estima te. Better r elian ce may be put on load t eat on piles. (b) For workin g out safe load a m inimum factor of safety 2.5 should be used on t he ultima te bearing capacity estima ted by stat ic form ulae. N OT E 3 — α ma y be ta ken to vary from 0.5 to 0.3 depending upon t he consisten cy of the soil. Higher values of up to one may be used for softer soils, provided the soil is not sen sitive.
A-2.2 When full static penetration data is available for the entire depth, the following correlations may be used as a guide for the deter min a tion of sha ft r esista nce of a pile.
21
I S : 2911 (P a r t 1/S e c 4) - 1984 T ype of S oil
L ocal S id e Friction , f s qc -----30 qc ------
Clays and peat s where qc < 10 Cla ys
25
qc ---------10 0 qc ---------10 0
Silt y cla ys a n d silt y sa n ds Sa n ds Coar se sands a nd gravels
< f s
qc < -----10
< f s
2 qc < --------25
< f s
qc < -----25
< f s f s
2 qc < ----------
100 qc < ---------15 0
where q c = sta tic point resistan ce, an d f s = local side friction. For non-hom ogeneous soils th e ultima te point bea rin g ca pa city ma y be calculat ed u sing t he following rela tions hips: q co + q c1 ----------------------- + q c2 2 q u = -------------------------------------2 where q u = ultima te point bearing capa city, q co = avera ge sta tic cone r esista nce over a dept h of 2 d below th e bas e level of the p ile, q c1 = minimum stat ic cone r esistan ce over t he sam e 2 d below th e pile tip, q c2 = average of the minimum cone r esista nce values in the diagram over a height of 8 d above the base level of the pile, an d d = diamet er of th e pile base or t he equivalent diamet er for a non-circula r cross section . A-2.3 The correlation between standard penetration test value N a n d static point resistance q c given below may be used for working the sha ft r esista nce an d skin friction of piles. S oil T ype
Clays Silts, san dy silt s an d slight ly cohesive silt sa nd m ixtu res Clean fine to medium sa nds a nd slight ly silty sa nds Cour se san ds an d san ds with litt le gravel Sa ndy gra vels and gra vel 22
q c /N 2.0 2.0 3-4 5-6 8-10
I S : 2911 (P a r t 1/S e c 4) - 1984
AP P E N D I X
B
( Clause 5 .5 .2 ) D E T E R M I N AT I O N O F D E P T H O F F I XI T Y, L AT E R A L D E F L E C T I O N AN D M AXI M U M M O ME N T O F L AT E R AL L Y L O AD E D P I L E S B -1. D E T E R M I N AT I O N O F L AT E R AL D E F L E C T I O N AT T H E P I L E H E AD AN D D E P T H O F F I XI T Y B-1.1 The long flexible pile, fully or pa rt ially embedded, is tr eat ed a s a can tilever fixed a t s ome d epth below th e groun d level ( see F i g. 2 ).
F IG . 2
D ETERMINATION OF D E P T H F IXITY
B-1.2 Determ ine th e depth of fixity an d h ence the equivalent length of th e can tilever u sing th e plots given in F ig. 2. where E I E I T = 5 ------- a n d R = 4 ------- ( K 1 a n d K 2 are constants given in K 1 K 2 Tables 1 and 2 below, E is t h e You n g’s m odu lus of th e pile material in kg/cm 2 a n d I is th e momen t of iner tia of th e pile cross-section in cm 4 ). N OT E — Fig. 2 is valid for long flexible piles wher e th e embedded len gth L e is
23
≥ 4 R or 4 T .
I S : 2911 (P a r t 1/S e c 4) - 1984 T AB LE 1
VAL UE S O F C ON ST AN T
K 1
(kg/cm 3 )
( Clause B -1 .2 ) VALUE
Loose sand Medium sa nd Dense sand Very loose sand under repea ted loading or norm ally loadin g clays T AB LE 2
Dr y
Su bm er ged
0.260 0.775 2.075
0.146 0.525 1.245
—
0.040
VAL UE S O F C ON ST AN T
K 2
( k g / c m 2)
( Clause B -1 .2 ) U NCONFINED C OMPRESSIVE S TRENGTH IN kg/cm 2
VALUE
0.2 t o 0.4 1 to 2 2 to 4 More tha n 4
7.75 48.80 97.75 195.50
B-1.3 Knowing the length of the equivalent cantilever the pile head deflection ( Y ) sha ll be com put ed u sing th e following equa tions: 3
Q ( L 1 + L F ) Y = ---------------------------------3 E I ( cm )
...for free h ea d pile
3
=
Q ( L 1 + L F ) ---------------------------------12 E I
...for fixed h ea d pile
where Q is the lat era l load in kg. B -2. D E T E R M I N AT I O N O F M AXI M U M M O M E N T I N T H E P I L E B-2.1 The fixed end moment ( M F ) of the equivalent cantilever is higher th an t he actua l ma ximum moment ( M ) of the p ile. The a ctu al ma ximu m moment is obta ined by multiplying th e fixed end m omen t of the equivalent cantilever by a reduction factor, m given in Fig. 3. The fixed end momen t of th e equivalent can tilever is given by: M F = Q ( L 1 + L f )
...for fr ee h ea d pile
Q ( L 1 + L f ) = ------------------------------2
...for fixed h ea d pile
The actua l ma ximu m m oment ( M ) = m ( M F ). 24
I S : 2911 (P a r t 1/S e c 4) - 1984
F IG . 3 D ETERMINATION OF R EDUCTION F ACTORS F OR C OMPUTATION OF M AXIMUM M OMENT IN P ILE
25
I S : 2911 (P a r t 1/S e c 4) - 1984
AP P E N D I X
C
( Clause 7 .1 0.2 ) D AT A S H E E T S Site.............................................................................................................. Title............................................................................................................. Date of enquiry........................................................................................... Da t e pilin g com m en ced.............................................................................. Act u a l or a n t icipa t ed da t e for com plet ion of pilin g wor k .......................... N u m ber of p ile.................................................. T E S T P I L E D AT A P ile:
P ile t est com m en ced......................................... P ile t es t com ple t ed ............................................
P ile t yp e:
P ile spe cifica t ion:
Sequ en ce of piling ( for Gr ou ps ):
Con cr et e:
........................................................................... (Men t ion pr opr ieta r y syst em , if an y)...............
Shape.............................................................. Size — Sh a ft...................t oe.......................... Rein for ceme n t .......No......dia for.......(dept h ) .......................................................................) Fr om centr e towards t he per iphery or from periphery towar ds the cent re
Mix r a tio 1:................: ...........by volu m e/m a ss or st r en gth a ft er ............da ys ..............kgf/cm 2 Qua nt ity of cement per m 3 : ............................. Extr a cement a dded if an y:
Det a ils of dr illin g m u d i f us ed : .................................................................. Tim e t a k en for con cre t in g: ........................................................................ Qu a n t it y of con cre t e — Act u a l: ................................................................. — Th eor et ica l: ......................................................... 26
I S : 2911 (P a r t 1/S e c 4) - 1984 Test load ing: ..................................................................................................................... Capacity of jack........................................................................................... If anchor piles used, give........................No., Length................................ Dist a n ce of tes t pile from n ea r est a n chor p ile........................................... Test pile an d an chor piles were/were n ot workin g piles. Meth od of ta king observat ions : Dia l ga u ges /En gin eer s level....................................................................... Reduced level of pile toe............................................................................. Genera l Remar ks: ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... Special difficulties encountered: ............................................................................................................. ............................................................................................................. ............................................................................................................. Results: Working load specified for the test pile............................................. Set t lem en t sp ecified for t h e t est pile................................................. Set t lem en t spe cified for t h e s t r u ctu r e............................................... Work ing loa d a ccepted for a sin gle pile as a r esu lt of t he t est ......... ............................................................................................................. ............................................................................................................. Work ing load in a group of piles a ccepted a s a resu lt of th e t est ..... ............................................................................................................. ............................................................................................................. Gen er a l descript ion of t h e st ru ct ur e to be fou nd ed on piles............. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. 27
I S : 2911 (P a r t 1/S e c 4) - 1984 Name of the constructing agency.......................................................... ................................................................................................................ N a m e of p er son con du ctin g t h e t est ...................................................... ................................................................................................................ Na m e of t h e pa rt y for wh om t he t est wa s cond u ct ed............................ ................................................................................................................ B O R E -H O L E L O G 1. Sit e of bore h ole r ela t ive to te st pile posit ion ........................................ ................................................................................................................ 2. N OT E — If no bor e hole, give best a vaila ble groun d con dit ions....................................... ............................................................................................................................................. .............................................................................................................................................
Soil S oi l D es cr ip t ion Properties
R ed u ced L evel
Soil L egen d
Depth B elow G.L.
Thickness of Strata
Position of the toe of pile to be indicted th us → Standing ground water level indicat ed thu s ∇ M E T H O D O F S I T E I N VE S T I G AT I O N Tria l pit/post-hole a uger /sh ell an d au ger boring/percussion/probing/ wash borings/mud-rotary drilling/core-drilling/shot drilling/ su bsu r fa ce s oun ding by cone s or st a n da rd sa m pler............................. ................................................................................................................ ................................................................................................................ N OT E — Gra phs, showing th e following relations, sha ll be prepar ed and a dded t o t h e r ep or t : 1 ) L oa d vs Time 2 ) S e t t le m e n t vs Load
28
I S : 2911 (P a r t 1/S e c 4) - 1984 ( Contin ued from page 2 )
P ile Foun da tions S ubcomm itt ee, BDC 43 : 5 Con ven er
S H RI M. D. TAMBEKAR
R epresen tin g
In personal capacity ( Pradeep Villa, 92 Kotnis Path, Mahim , Bombay
M em bers
S H RI C HANDRA P RAKASH
Central Building Roorkee
Research
Institute
(CSIR),
S H RI K. G. GARG ( A lt ern ate ) S H RI A. G HOSHAL
Stup Consultant s Ltd, Bombay
S H RI M. I YENGAR S H RI J . K. BAGCHI ( A lt ern ate ) S H RI P. K. J AIN
En gineers In dia Ltd, New Delhi
S H RI A. N. J ANGLE
Asia Foundations and Construction Pvt Ltd, Bombay
J OINT D IRECTOR R (GE)-II, RDS O
E S E AR C H
Un iversity of Roorkee, Roork ee
Minist ry of Railways
D Y D IRECTOR R ESEARCH (GE)III, RDSO ( A lt ern ate ) S H RI B. K. P ANTHAKY S H RI P. V. N AIK ( A lt ern ate )
Hindu sta n Constru ction Co Ltd, Bombay
S H RI M. R. P U N J A
Cemindia Co Ltd, Bombay
S H RI B. R USTOMJEE
Pile Foundations Construction Co (I) Pvt Ltd, Calcutta
S H RI S. C. B OS E ( A lt ern ate ) S UPERINTENDING (D ESIGNS )
E
N G I N E E R
Centr al Public Works Depar tm ent , New Delhi
E XECUTIVE E N G I N E E R (D ESIGNS ) V ( A ltern at e )
29
