3. NECESSARY Load Pile The load assigned to a pile according to design. 

INFORMATION

3.1 For the satisfactory design and construction of bored cast in situ and bored compacted under-reamed piles and pile foundation, the information on the following aspects is necessary: 4 Site investigation data as- laid down in IS : 1892-1979* or any other relevant Indian Standard. Sections of trial, borings, supplemented wherever appropriate by penetration tests, should incorporate data/information sufficiently on soil condition below the anticipated level of pile tip. The nature of the subsoil both around and beneath the proposed pile should be indicated on the basis of appropriate tests of strength, compressibility, etc. Ground-water levels and conditions (such as artesian conditions) should be indicated. Results of chemical tests to ascertain the sulphate and the chloride content and groundwater should be indicated particularly in areas where large scale piling is envisaged or where such information is not generally available. b) A qualitative indication of the degree of expansiveness of soil is given in Appendix A. The free swell test will be carried out according to IS: 2720 (Part-XL)-1977t. 4 In case of bridge foundations, data on high flood level, maximum scouring depth, normal water level during working season, etc. *Code of practice for subsurface investigations for foundations (jirst revision). tMethod of test for soils, Part XL Determination of free swell index of soils. 6

IS: 2911 (Part III) - 1980 In case of marine construction, necessary information as listed in IS: 4651 (Part I)-1974* should be provided.

4

In case rock is encountered, adequate description of the rock to convey its physical conditions as well as its strength characteristics should be indicated. In case of weathered rock, adequate physical description and its expected physical behaviour on boring should be indicated.

4 f1

‘General plan and cross section of the building showing type of structural frame, including basement, if any, in relation to the proposed pile cap top levels. The general layout of vertical and horizontal, caps, but excluding the levels of finished pile caps the structure moments and weight of the shall be clearly showing estimated loads, torque at the top of pile piles and caps. The top indicated.

&I) It

is preferable to have the dead load, equipment and live loads separately indicated. Loads and moments for wind and earthquake should also be .separately indicated. Sufficient information about structures existing nearby should be provided.

4

33 As far as possible, all information in 3.1 shall be made available to the agency responsible for the design and/or construction of piles and/or foundation work. 3.3 The design details .of pile foundation shall indicate the information necessary for setting out the layout of each pile within a cap, cut-off levels, finished cap levels, orientation of cap in the foundation plan and the safe capacity of each type of piles, etc. 3.4 Due note shall be taken of the experience of under-reamed and other piles in the area close to the proposed site and any soil strata report thereof. 4. MATERrALS

Cl cement :Sg;z%1976t,

-The cement used shall conform to the requirements of IS: 455-1976$, IS: 8041-1978$, IS : 6909-19731) or IS:1489-

‘*Code of practice.for plauning and design of ports and ha&ours, P+rt I Site inv&igation
(j#Cf6&k). fSpcc+a~on +Speuficat~on ~Specification K5+xification QSpcciEcation for for for for for ordinary and low heat Portkyd cement (Turk rcvirb) . Portland and a&q cement (f&d &.&VI). rapid hardening Portland cement. supuaulphatcd cement. Portland pozzolana cement (scoondr&&n). .

7

IS : 2911 (Part III) - 1980 4.2 Steel - Reinforcement steel shall conform to IS : 432 (Part I)-1966* or IS: 1139-1966t or IS : 1786-1979$ or IS : 226-19755. The stresses allowed in steel should conform to IS : 456-197811. 4.2.1 For under-reamed bored compaction piles, the reinforcement cage shall be prepared by welding the hoop bars to withstand.the stresses during compaction process. 4.3 Concrete 4.3.1 Materials and methods of manufacture for cement concrete shall in general be in accordance with the method of concreting under the conditions of pile installation. 4.3.2 Consistency of concrete for cast in situ piles shall be suitable to the method of installation of piles. Concrete shall be so designed or chosen as to have homogeneous mix having a flowable ‘character consistent with the method of concreting under the given conditions of pile installation. In achieving these results, minor deviations in the mix proportions used in structural concrete may be necessary. 4.3.3 Slump of concrete shall range between 100 mm to 150 mm for concreting in water-free unlined boreholes. For concreting by tremie, a slump of 150 mm to 200 mm shall be used. 4.3.4 1,n case of tremie concreting for piles of smaller diameter and depth of up to 10 m, the minimum cement content should be 350 kg/m* of For piles of large diameter and/or deeper piles, the minimum concrete. cement content should be 400 kg/m* of concrete. For design purpose, the strength of concrete mix may be taken equivalent to Ml5 and M20, respectively, for concrete with cement content of 350 kg/m* and 400 kg/m*. Where concrete of higher strength is needed, richer concrete mix with higher cement content may be designed. In case of piles subsequently exposed to free water or in case of piles where concreting is done under water or drilling mud using methods other than the tremie, 10 percent extra cement over that required for the design grade of concrete at the specified slump shall be used subject to the minimum quantities -of cement specified above. 4.3.5 For the concrete, water and aggregates specifications laid down in IS: 456-197811 shall be followed in general. Natural rounded shingle of appropriate size may also be used as coarse aggregate. Tt helps to give high slump with less water cement ratio. For tremie concreting aggregates having nominal size more than 20 mm should not be used.
*Specification for mild steel and medium tensile steel bars and hard drawn steel wire for concrete reinforcement, Part I Mild steel + medjum tensile se bys (Iccond rev&m). Specification for hot rolled mild steel, tm(AA)tensde :teel and hqh yield strength steel d a ormed bars for concrete reinforcemen $Specification for cold worked high strengthdeibrmed &xl bars for concrete reinf&cement (se& r&n). @pecification for structural steel (standard quality) _fuc r&.&n). Code of practice for plain and reinforced concrete ( y. raGaIr).

8

IS : 2911 (Part III) - 1980 4.3.6 The concrete for piles in aggressive surroundings due to presence of sulphates, etc, should have a concrete mix of appropriate type of cement in suitable proportion.
4.3.6.1 If the concentration of sulphates (measured as SOs) exceeds one percent in soil or 2 500 parts per million (ppm] in water a mix using For soils 400 kg/m3 of sulphate resisting Portland cement should be used. with 0.5 to 1 percent of sulphates or ground water with 1 200 to 2 500 ppm, For the mix should have 330 kg/m3 of sulphate resisting Portland cement. concentrations lesser than above concrete mix with 330 kg/m3 ordinary In place Portland cement or 310 kg/m3 sulphate resisting should be used. of ordinary Portland cement, pozzolana cement/blast furnace slag cement may be used. 4.3.6.2 Concentration of sulphates ppm in water may be inconsequential. up to O-2 percent in soil and 300

4.3.7 For bored compaction piles rapid hardening cement (see 4.1) shall not be used. To facilitate construction, admixtures for retarding the setting of concrete may be used. 5. DESIGN

CONSIDERATIONS

foundations shall be designed in 5.1 General - Under-reamed pile such a way that the load from the structure they support, can be transmitted to the soil without causing any soil failure and without causing such settlement, differential or total, under permanent transient loading as may The pile shaft result in structural damage and/or functional distress, should have ‘adequate structural capacity to withstand all loads (vertical, axial or otherwise) and moments which are to be transmitted to the subsoil. 5.1.1 In deep deposits of expansive soils the minimum length of piles, irrespective of any other considerations, shall be 3.5 m below ground level. If the expansive,soil deposits are of shallow depth and overlying non-expansive soil strata of good bearing or rock, piles of smaller length can also be provided. In recently filled up grounds or other strata or poor bearing, the piles should pass through them and rest in good bearing strata. 5.1.2 The diameter of under-reamed bulbs may vary from 2 to 3 times stem diameter depending upon the feasibility of construction and design requirements. In bored cast in Titusunder-reamed piles the bulb diameter shall normally be 2.5 times, and in under-reamed compaction piles two times.

’ 5.1.3 For piles up to 30 cm diameter, the spacing of bulbs should not For piles of diameter greater than exceed 1.5 times the diameter of bulb. 30 cm spacing can be reduced to I.25 times the stem diameter.
5.1.4 The top-most bulb should be at a minimum depth of 2 times the In expansive soils it should also not be less than l-75 m bulb diameter. The minimum clearance below the underside of pile below ground level. 9

IS : 2911 (Part III) - 1980 cap embedded in the ground and the bulb should be a minimum the bulb diameter. 5.1.5 Under-reamed without ensuring their by drilling mud. The should not exceed two 1.5 times

piles with more than two bulbs are not advisable feasibility in strata needing stabilization of boreholes number of bulbs in case of bored compaction piles in such strata. needing consisting stabilization of harmful pile

5.1.6 The minimum diameter of stem for borehole by drilling mud should be 25 cm. 5.1.7 The constituents, minimum diameter of stem for strata such as sulphates, should be 30 cm.

5.1.8 For guidance typical details of bored cast in silu under-reamed foundations are shown in Fig. 1.

5.1.9 For batter piles, a batter of 30” for piles in dry ground conditions and 15” with horizontal for water or drilling mud filled holes should generally not be exceeded. The under-reamed compaction piles are normally constructed up to a batter of 15”. pile 5.2 Design of Piles - The load carrying capacity of under-reamed depends mainly on the pile dimensions and soii strata. Axial load on a pile is transmitted by point bearing at the toe and the projected area of the bulb(s) and skin friction along the pile stem. Depending upon the nature of soil and pile geometry, in addition to the skin friction on stem, friction can develop on the soil cylinder between the extreme bulbs. In under-reamed compaction piles, the mechanism of load transfer remains the same but soil properties improved by compaction process are considered. In uplift load, point bearing component at toe is absent but unlike other straight shaft piles, point bearing on an anular projection of the bulb is present. Lateral load and moment are sustained by horizontal soil reaction developed along the pile length, which depends on several factors. The design of piles shall be such that it has an adequate factor of safety: a) as a structural member to transmit the imposed loads, and b) against failure of strata due to reaching ultimate strength. Further it should ensure that the desired limit of settlement is not exceeded. 5.2.1 Pile as a Struc@al Member - The pile should have adequate strength to sustain the design loads. The pile cross-section should be checked for combined effect of vertical loads (compressive and uplift) and/or lateral loads and moments. The stem should be designed as a short column considerating both concrete and steel (see 5.2.2) by the limit state method or working stress method. In case of latter, the permissible increase in (see IS : 875-1964* and stresses shall be taken for wind and seismic loads. IS : 1893-1975t.)
*Code of practice for structural safety of buildings: Loading standards (rev&j). tcriteria for earthquake resistant design of structures (third revision).

10

IS : 2911(Part III) - 1980

BORING LEV<L FOR MAKING

SECOND/LAST BULB 7

:

--Id-t
COVER 75 TO

100 30°-45”Approx,Du=NonnallyZ?5D 1B !hCTION OFMULTIUNDER-REAMED Px~x

9,=45” Approx,& 1A %kTION OF ~%NOLE UNDER-REAMED PILE

All dimensions millimctres in

Fm. 1

TYPICAL DETAILSOF BOREDCAST in situ UNDER-REAMED PILE FOUNDATIONS

5.2.2 Reinfwcemmt in Piles - The provision of reinforcement will depend on nature and magnitude of loads, nature of strata and method of installation. It should be adequate for vertical load, lateral load and moments, acting individually or in combination. It may be curtailed at appropriate depth subject to provision given in 5.2.2.1 and 5.2.2.2. 5.2.2.1 The minimum area of longitudinal reinforcement in stem should be 0.4 percent of mild steel (or equivalent deformed steel). Rein11

IS : 2911 (Part lII) - 1980
forcement is to be provided in the full length irrespective of any other considerations and is further subject to the condition that a minimum number of three lo-mm diameter mild steel or three 8*mm diameter high The transverse reinforcement as strength steel bars shall be provided. circular stirrups shall not be less than 6-mm diameter mild steel bars at a spacing of not more than the stem diameter or 30 cm whichever is less. In under-reamed compaction piles, a minimum number of four, 12-mm diameter mild steel or four IO-mm diameter high strength steel bars shall be provided. For piles of lengths exceeding 5 m and or 37.5 cm diameter, a minimum number of six 12-mm diameter bars of mild or high strength steel shall be provided. For piles exceeding 40 cm dia, a minimum number of six 12-mm diameter mild or high strength steel bars shall be provided. The circular stirrups for piles of lengths exceeding 5 m and diameter exceeding 37.5 cm shall be of 8 mm diameter bars. 5.2.2.2 For piles subjected to uplift loads, adequate reinforcement shall be provided to take full uplift which shall not be curtailed at any stage. 5.2.2.3 For piles up to 30 cm diameter, equivalent amount of steel placed centrally if concreting is done by tremie, may be provided. reinforcement etc, it may be

5.2.2.4 The minimum clear cover over the longitudinal shall be 40 mm. In aggressive environment of sulphates, increased to 75 mm.

5.2.3 Safe Load - Safe load on a pile can be determined from (a) calculating tiltimate load from soil properties and applying suitable factor of safety, (b) load test on pile as provided in IS : 2911 (Part IV)-1979*, and (c) safe load tables. 5.2.3.1 Safe loadfrom ultimate load capacity - The ultimate load capacity The soil properties required of a pile can be calculated from soil properties. are strength parameters, cohesion, angle of internal friction and soil density. If these properties are not available directly from laboratory and field tests, they may be indirectly obtained from in situ penetration test data [IS : 4968 (Part II)-19767 and IS : 6403-1971$]. The success of the approach essentially depends how realistically the soil properties are determined or deduced. a) Clayey soils For clayey soils the ultimate load carrying pile may be worked out from tpe following QU= where ~4, (cm”) A,.JV,C,+A,.JV,.C’,+C,‘.A,’ capacity of an under-reamed expressions: + .c.C,.A,

Qu (kg)

=

=

ultimate bearing capacity of pile; cross-sectional area of pile stem at toe level;

*Code of practice for design and construction of pile foundations: Part IV Load test on piles. tMethod for subsurface sounding’for soils: Part III Static cone penetration test (_/irst

rtiion)

$Code of practice for determination of allowable bearing pressure on shallow foundations. 12

.

IS : 2911 (Part III) - 1980 bearing capacity factor, usually taken as 9; C, (kgf/cmt) z cohesion of the soil around toe; A, (cm2) = 7r/4 (D2U-D2) where D,(cm) and D (cm) are the under-reamed and stem diameter, respectively; C’, (kgf/cm2) = average cohesion of soil around the under-reamed bulbs; reduction factor (usually taken 0.5 for clays) ; ;a (kgf/cm2) z average cohesion of the soil along the pile stem; A, (cm2) = surface area of the stem; and A’, (cm2) = surface area of the cylinder circumscribing the underreamed bulbs.

Jve

The above expression holds for the usual spacing of under-reamed spaced at not more than one-and-a-half times their diameter.
NOTE 1 components. NOTE 2 NOTE 3 If the pile is with one bulb only the third term will not occur. For calculating uplift load first term will not occur in formula.

bulbs

The first two terms in formula are for bearing and the last two for friction

b) Sandy soils For sandy soils the following expression be used: Qu= A,.(&.D.X..NX+ X.dJV,,)+A, (~.D,.n.h..hQ+h.Nq

+-&.n.D.X.K tan S x (d:+df--di) where A, (cm2) A, (cma)

r=n x d,. r=l

; (kglcms) .NAand IV, dr (cm) d+ (cm) K S dl (cm) d,, (cm)

= rr/4.D2, where D (cm) is stem diameter; where D, (cm) is the under-reamed = n/4(Dz-Da) bulb diameter; ?= number of under-reamed bulbs; = average unit weight of soil (submerged unit weight in strata below water table); = bearing capacity factors depending upon the angle of internal friction; depth of the centre of different under-reamed bulbs = below ground level ; = total depth of pile below ground level; = earth pressure coefficient (usually taken 1.75 for sandy soils) ; = angle of wall friction (may be taken equal to the angle of internal friction 4) ; = depth of the centre of first under-reamed bulb; and = depth of the centre of the last under-reamed bulb.

NOTE I- ‘?Yhefirst two terms in the formula are for bearing component and the .<. ‘as;= $W fnction cpmpone$. - For uphft bearing on tip, Ap will not occur.

13

IS : 2911 (Part RI) - 1980
NOTE 3 - NA will be as specified in 1S : 6403-1971* and Jv, will be taken from Fi .2. This factor, apart from the angle of internal friction 4 depends upon the meth o! of installation of pile and the component containing this factor will generally be over estimated (up to about twice) in bored piles. c)

Soil strutu having both cohesionandfriction In soil strata having both cohesion and friction or in layered strata having two types of soil, the beari.ng capacity may be estimated using both the formula. However, in such cases the load tests will be a better guide. d) Comjaction piles in sandy strata For bored compaction piles in sandy strata, the formula in 5.2.3.1(b) shall be applicable but the modified value of C$ will be used as given below: where $= angle of internal friction of virgin soil. The values of NA, .N, and 6 are taken corresponding to The value of the earth pressure coefficient K will be 3.

4l

e) Piles resting on rock For piles resting on rock, the bearing component will be obtained by multiplying the safe bearing capacity of rock with bearing area of pile stem plus the bearing provided by the bulb portion. f) Factors of safety To obtain safe load in compression and uplift from ultimate load capacity generally the factors of safety will be 2.5 and 3, respectively. But in case of bored compaction piles with bulb diameter twice the shaft diameter, the factor of.safety in compression should be taken 2.25. 553.2 Safe 1oadJiom pile load tests- The safe load on pile(s) in compression uplift and lateral can be determined by carrying out load test on piles in accordance with IS : 2911 (Part IV)-1979t. In sizable work (more than two hundred piles) where detailed information about the strata and the guidance of past experience is not available, there should be a minimum of two pile load tests before finalizing the safe load on piles.
NOTE - It is unlikely that two simihu pile load testa ‘ve the same loaddetlection W viour. Also, ground conditions, position of water taT le, moisture content in soil and desiccation of top strata, can affect the load tests conducted at different tima of the ye. These factors should be kept in view while deciding the safe load.

5.2.3.3 In the absence of actual tests and detailed investigations, the safe load on under-reamed piles of bulb diameter 2-5 times the stem diameter may be taken as given in Appendix B. *Code of praeticc for determination of allowable bearing presure on &allow foundations.
t&de pile% of practice for dcaign and construction of pile foundations: Part IV Load test on

14

Is : 2911 (Part III) - 1980

20

25

30

35
fi

*u

IDJ

ANGLE OF INTERNAL FRlCTlON

FIG. 2

BEARING CAPACITY FACTOR Na 15

IS : 2911 (Part III) - 1980 5.2.3.4 The lesser of the two safe loads obtained from 5.2.3.1 and 5.2.3.3 should be used in designs. Higher values can be used if established by initial load tests.

4

other than 5.!235, the total increase over safe load including those of 593.5 exceed 50 percent.

5.2.3.5 Permissible increase over safe load on biles Overloading- When a pile designed for a certain safe load is found to fall just short of the required load carried by it, an overload of up to 10 percent of the safe load on pile may be allowed on each pile. The total overloading on group should not be more than 10 percent of the safe load on group, nor more than 40 percent of the safe load on single pile. b) Tramient loading - The maximum permissible increase over the safe load of a pile as arising out of wind loading is 25 percent. In case of loads and moments arising out of earthquake effects the increase over the safe load on a pile may be limited to the provisions contained in IS : 1893-1975*. For seismic loads, under-reamed piles shall be treated as point bearing piles. The seismic and wind forces will not be considered to act simultaneously. For transient loading arising out of superimposed loads, no increase generally may be allowed. For broken wire conditions in transmission line tower foundations, permissible increase will be as provided in IS : 4091-19797. NOTE If any increasein load on a pile has already been permitted for reasons

shall not

5.2.4 Jvegative Skin Friction or Drag Down Force-When a soil stratum through which a pile shaft has penetrated into an underlying hard stratum, compresses as a result of either it being unconsolidated or it being under a newly placed fill or as a result of remoulding during driving of the pile, a drag-down force is generated into the pile shaft up to a point in depth where the surrounding soil does not move downward relative to the pile shaft.
of this drag-down force is still under investigation, although a NOTE -Estimation few empirical approaches are in use. The concept is constantly. under revision and, therefore, no definite proposal is embodied in this standard. (Recognition of the existence of such a phenomenon shall be made and suitable reduction shall be made to the allowable load where appropriate. There is no evidence to show that the use of drilling fluids for the construction of piles afkcts the skin friction.)

5.2.5 LatGral Load on P&s - A pile may be subjected to transverse force from a number of causes, such as wind, earthquake, water current, earth pressures, effect of moving vehicles or ships, plant and equipment, etc. The lateral load carrying capacity of a single pile depends not only on the horizontal subgrade modulus of the surrounding soil but also on the structural strength of the pile shaft against bending consequent upon application of a lateral load. While &msidering lateral load on piles, effect of other
*Criteria for eartlqttake resistant design of atructurca (tied rmision). tCode of practice for design and construction of foundations for transmission line towers urd poles (jrfi r&).

16

I!3 : 2911 (Part III) - 1980 existent loads including the axial load on the pile should be taken into consideration for checking the structural capacity of the shaft. Piles under the action of lateral load and moment can be analysed by the modulus of subgrade reaction approaches. Due to the presence of bulbs, under-reamed piles tend to behave more as rigid piles and the analysis can be done on rigid pole basis. Normally reinforced long single bulb piles which are not rigid may be analysed after the generalized solutions of Matlock and Reese for sandy soils and Broms for clayey soils. For lateral loads with or without axial loads, up to those given in the Table 1 of Appendix B, no analysis may be necessary, if external moment is not acting. In the absence of actual in situ test values from prototype pile load test, the modulus of subgrade reaction values may be taken from the Table 2 given in Appendix C.
NOTE - It may be kept in view that modulus of subgrade reaction is a criti$Lf;o;er in the above analysis, yet there is no precise method for determining it. it will be realistic to ascertain the adequacy of design by field tests.

2

5.2.6 Batter Piles (Raker Piles) - Raker piles are normally provided where vertical piles cannot resist the required applied horizontal forces. In the preliminary design the load on raker ~pileis 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 given to 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 moments due to their own weight or external forces from other causes. Raker piles embedded in 8l.l or consolidating deposits may become laterally loaded owing to the settlement of the surrounding soil. 55.7 Sfiacing of Piles 55.7.1 Spacing of piles shall be considered in relation to the nature ground, the types of piles and the manner in which the piles transfer the load to the ground.

of

52.7.2 Generally the centre to centre spacing for bored cast in situ under-reamed piles in a group should be two times the bulb diameter (20,). It shall not be less than l-5 D,,. For under-grade beams the maximum spacing of piles should generally not exceed 3 m. In under-reamed compaction piles, generally the spacing should not be less than l-5 D,, If the. adjacent piles are of different diameter, an average value of bulb diameter should be taken for spacing. 5.2.8 Grouping and Layout 528.1 For bored case in situ under-reamed piles at usual spacing of 2 D,, the group capacity will be equal to the safe load of individual For piles at a spacing pile multiplied by the number of piles in the group. of l-5 D, the,safe load assigned per pile in a group should be reduced by 10 percent. 17

IS : 2911 (Part III) - 1980 In under-reamed compaction piles, at the usual spacing of 1.5 D.,, the capacity will be equal to the safe load on individual pile multiplied by the number of piles in the group.
group Nom - In under-reamed compaction piles, the capacity of the group may be more than given in 5.2.&l on account of the compaction effect.

5.2.8.2 In non-expansive soils, when the cap of the pile group is cast directly on reasonably firm stratum it may additionally contribute towards the bearing capacity of the group. 5.2.8.3 The settlement of pile groups depends upon soil and pile characteristics, spacing, group size method of installation and magnitude . and nature of loading. In clays sometimes long term settlements can become important while in sands almost all the settlements will be over quickly. A group of free standing piles is likely to settle more than a single pile but this increase may be marginal if the safe load on the piles is according to 5.2.3 and 5.2.8.1.
NOTE 1 - The settlement, in case of piles in sand, are generally computed from empirical relations. A suggested relationship for estimating settlements of free standing under-reamed pile groups in sands is:

where Ss = settlement of group in St = settlement of single pile B = distance between outer D = pile stem diameter in

cm, in cm; piles are under the same safe load per pile, piles centre in cm, and cm.

In clays the immediate settlements are computed using theory of elasticity and the long term settlements by consolidation theory. For the later, the pile group is considered as a footing at the centres of the lowermost bulbs. It may be noted that computed settlements, by the above approaches particularly piles in clay, are very large as compared to actually occurring in practice. for

Nom 2 -For the groups with caps resting on ground settlements are comparable with an isolated pile. NOTE 3 - In the case of under-reamed compaction piles with cap resting on ground, which is very often the case, the settlements of groups may be even less than the settlement of an isolated pile.

5.2.8.4 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 that a high order of differential settlement may result depending on the type of subsoil supporting the piles. 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 pile cap may be loaded to a level higher than that of a pile in a group in order to achieve reduced differential settlement between two adjacent pile caps supported on differential number of piles. 18

IS : 2911 (Part III) - 1980 5.2.8.5 In load bearing walls, piles should generally be provided under all wall junctions to avoid point loads on beams. Positions of intermediate piles are then decided by keeping door openings fall in between two piles as far as possible. 5.3 Grade Beams 5.3.1 The grade beams supporting the walls shall be designed taking due account of arching effect due to masonry above beam. The beam with masonry due to composite action behaves as a deep beam. For the design of beams, a maximum bending moment of ~1~150, where w is uniformly distributed load per metre run (worked out by considering a maximum height of two storeys in structures with load bearing walls and one storey in framed structures) and 1 is the effective span in metres, will be taken if the beams are supported during construction till the masonry above it gains strength. The value of bending moment shall be increased to w12/30 if the beams are not supported. For considering composite action the minimum height of wall shall be 0.6 times the beam span. The brick strength should not be less than 30 kgf/cm2. For concentrated loads and other loads which come directly over the beam, full bending moment should be considered. 5.3.2 The minimum overall depth of grade beams shall be 150 mm. The reinforcement at bottom should be kept continuous in all the beams and an equal amount may be provided at top to a distance of quarter span both ways from the pile centres. The longitudinal reinforcement both at bottom and top should not be less than three bars of 10 mm diameter mild steel (or equivalent deformed steel). Stirrups of 6-mm diameter bars should be at a 300 mm spacing which should be reduced to 100 mm at the door openings near the wall edge up to a distance, of three times the depth of beam. No shear connectors are necessary in wall. 5.3.3 In expansive soil, the grade beams shall be kept a minimum of 80 mm clear off the ground. In other soils, the beams may rest on ground over a levelling concrete course of about 80 mm (see Fig. 3). In this case, part load may be considered to be borne by the ground and it may be accounted for in the design of piles. However, the beams should be designed as per clause 5.3.1. 5.3.4 In case of exterior beams over piles in expansive soils, a ledge projection of 75 mm thickness and extending 80 mm into ground (see Fig. 3) shall be provided on outer side of beam. 5.4 Design of Pile Cap -Pile caps are generally designed considering pile reaction as either concentrated loads or distributed loads. The depth of pile cap should be adequate for the shear for diagonal tension and it should also provide for necessary anchorage of reinforcement both for the column and the piles. 19

IS : 2911 (Part III) - 1980 5.4.1 The pile caps may be designed by assuming that the load from column or pedestal is dispersed at 45” from the top of the cap up to the middepth 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.
5.4.2 When pile reactions are considered as point loads, the critical section for shear in diagonal tension is taken at a distance equal to half the depth of cap from the face of the column or pedestal. For bending moment and shear for bond, the critical section is taken at the face of the column or pedestal. In computing the external shear or the critical section the entire reaction of any pile of diameter D whose centre is located at D/2 or more outside the section shall be assumed as producing shear on the section; the reaction from any pile whose centre is located at D/2 or more inside the section shall be assumed as producing no shear on the section. For intermediate positions of the pile centre, the portion of the pile reaction to be assumed as producing shear on the section shall be based on straight line interpolation between full value at D/2 outside the section and zero value inside the section. 5.4.3 The cap may also be designed as a solid slab carrying concentrated loads from piles. A square/rectangular pile cap can be divided in four triangular/trapezoidal areas by drawing diagonal lines at 45” from the corners. When the pile is cut by the line, the load on this pile is shared equally between the adjacent areas. The reaction of piles under an area will be taken towards producing shear. The bending moment are assumed to act from the centre of piles under an area at the face of the nearest pedestal or column. 5.4.4 Full dimension of the cap shall be taken as width to analyse the section for bending and shear in respective direction. Method of analysis and allowable stresses may be according to.%: 456-1978*. 5.4.5 The clear overhang of the pile cap beyond the outer most pile in the group shall normally be 100 to 150 mm, depending upon the pile size. 5.4.6 The cap is generally cast over a 75 mm thick levelling course of concrete. The clear cover for main reinforcement in the cap slab shall be not less than 75 mm. 5.4.7 The pile should pro_jcct 40 mm into the cap concrete.

6. EQUrPMENT

AND ACCESSORIES

6.1 The selection of equipment and accessories will depend upon the type of under-reamed piles, site conditions and nature of strata. Also it will depend on economic considerations and availability of manually or po\ver operated equipment.
*Code of practice for plain and reinforced concrete (f&d rc&&n). 21

IS : 2911 (Part III) - 1980 6.2 A typical Appendix D. list of equipment for manual construction is given in

6.3 Bore holes may be made by earth augers. In case of manual boring, an auger boring guide shall be used to keep the bores vertical or to the desired inclination and in position. After the bore is made to the required depth, enlarging of the base shall be carried out by means of an under-reaming tool. 6.4 In ground with high water table having unstable pile bores, boring and under-reaming may be carried out using a suitable drilling mud. General guidelines for bentonite drilling mud are given in Appendix E. In normally met soil strata, drilling mud can be poured from top while boring and underreaming can be done by normal spiral earth auger and under-reamer. The level of drilling mud should always be about one metre above water table or the level at which caving in occurs. In case of very unstable strata with excessive caving in, continuous circulation of drilling mud using suitable pumping equipment and tripod, etc, alongwith modified auger and underreamer may be used. 6.5 Sometimes permeable strata overlying a rim clayey stratum may be cased and normal boring and under-reaming operation may be carried out in clayey stratum. 6.6 To avoid irregular shape and widening of bore hole in very loose strata at top, a casing pipe of suitable length may be used temporarily during boring and concreting. 6.7 For improved control over the inclination of batter piles, a tripod hoist with fixed pully should be used for lowering in of under-reaming tools. 6.8 For placing the concrete in bore holes full of drilling mud or subsoil water, tremie pipe of not less than 150 mm diameter with flap valve at the bottom should be used. 6.9 For batter under-reamed piles, the reinforcement cage should be placed If concreting is not guiding it by a chute or any other suitable method. done by tremie, it should be done by chute. 6.10 In guiding vertical suitable under-reamed compaction piles, suitable devices should be used for the movement of drop weight and specified core assembly for its driving. For operating the drop weights of adequate capacity, winch with hoisting attachment should be used.

7. CONSTRUCTION 7.1 Under-reamed piles may be constructed by selecting suitable installation techniques at a given site depending on subsoil strata conditions and type of under-reamed pile and number of bulbs. 22

IS : 2911 (Part III) - 1980 7.2 In construction
with the equipment given in 6, initially boring guide is fixed with its lower frame levelled for making desired angular adjustment Boring is done up to required depth and under-reaming for piles at batter. is completed. 7.2.1 In order to achieve proper under-reamed bulb, the depth of bore hole should be checked before starting under-reaming. It should also be checked during under-reaming and any extra soil at the bottom of bore hole removed by auger before reinserting the under-reaming tool.

7.2.2 The completion of desired under-reamed bulb is ascertained by (a> the vertical movement of the handle, and (6) when no further soil is cut. 7.2.3 In double or multi-under-reamed piles, boring is first completed to the depth required for the first (top) under-ream only and after completboring is extended further for the second undering the under-reaming, ream and the process is repeated.
7.3 Control of Alignment - The piles shall be installed as correctly as possible at the correct location and truly vertical (or at the specified batter). Great care shall be exercised in respect of single pile or piles in two-pile As a guide, for vertical piles a deviation of 1.5 groups under a column. percent and for raker piles a deviation of 4 percent shall not normally In special cases, a closer tolerance may be necessary. Piles be exceeded. shall not deviate more than 75 mm or one quarter the stem diameter, whichever is less (75 mm or D/ 10 whichever is more in case of piles having diameter more than 600 mm) from the designed position at the working level. In the case of single pile under a column, the positional deviation should not be more than 50 mm or one quarter of the stem diameter whichever is less (100 mm in case of piles having diameter more than 600 mm). For piles where cut-off is at substantial depths, the design should provide for the worst combination of the above tolerances in position and inclination. In case of piles deviating beyond these limits, corrective measures where necessary may be taken in the form of increasing pile size, provision of extra reinforcement in the pile, redesign of pile cap and pile ties. If the resulting eccentricity cannot be taken care of by the above measures, the piles should be replaced or supplemented by one or more additional piles.
NOTE- In case of raker piles up to a rake of 1 in 6, there may be no reduction in the capacity of the pile unless othenvise stated.

7.4 Concreting shall be done as soon as possible after completing the pile bore. The bore hole full of drilling mud should not be left unconcreted for more than 12 to 24 hours depending upon the stability of bore hole. 7.5 For placing concrete in pile bores, a funnel should be used and method of concreting should be such that the entire volume of the pile bore is filled

23

IS : 2911 (Part III) - 1980
up without the formations in the concrete. of voids and/or mixing of soil and drilling fluid

7.5.1 In empty bore holes for under-reamed piles a small quantity of concrete is poured to give about a 100 mm layer of concrete at the bottom. Reinforcement is lowered next and positioned correctly. Then concrete is poured to fill up the bore hole. Care should be taken that soil is not scrapped from sides if rodding is done for compaction. Vibrators shall not be used. 7.5.2 If the water is confined up to the bucket length portion at the toe and seepage is low, the water should be bailed out and concreting should be done as in 7.5.1. 7.5.3 In case the pile bore is stabilized with drilling mud or by maintaining water head within the bore hole, the bottom of bore hole shall be carefully cleaned by flushing it with fresh drilling mud, and pile bore will be checked for its depth immediately before concreting. Concreting shall be done by tremie method. The tremie should have a valve at its bottom and lowered with its valve closed at the start and filled The valve is then qpened to permit the flow of concrete up with concrete. which permits the upwards displacement of drilling mud. The pouring should be continuous and tremie is gradually lifted up such that the tremie pipe opening remains always in the concrete. If the final stage the quantity of concrete in tremie should be enough so that on tinal withdrawal some concrete spills over the ground.
NOTZ 1 - The concrete should be coherent, rich in cement (not less than 350 l&/m%) and of slump not less than 150 mm.
NOTE 2- The tremie pipe should always penetrate well into the concrete with an adequate margin of safety against accidental withdrawal of the pipe is surged to discharge the concrete NOTE 3 - The pile should be concreted wholly by tremie and the method ofdeposition should not be changed part way up the pile, to prevent the laitance from being entrapped within the pile. NOTE 4-

All tremie tubes should be scrupulously cleanrd before and after use.

NOTE 5 - Normally concreting of the piles should be uninterrupted. In the exceptional case of interruption of concreting, but which can be resumed within 1 or 2 hours, the tremie shall not be taken out of the concrete. Instead it shall be raised and lowered slowly, from time to time to prevent the concrete around the tremie from setting. Concreting should be resumed by introducing a little richer concrete with a slump of about 200 mm for easy displacement of the partly set concrete. If the concreting cannot be resumed before final set-up of concrete already placed, the pile so cast may be rcjectcd, or used with modifications. Nom 6 - Tn case of withdrawal of tremie out of the concrete, either a&dentally or to remove a choke in the tremie, the tremie may be re-introduced in a manner to prevent impregnation oflaitance or scum lying on the topof theconcrete already deposited in the bore.

24

Is : 2911 (Part III) - 1980 7.5.4 In inclined piles, the concreting or by tremie method. should be done through achute

7.5.5 For under-reamed bore compaction piles, the pile bore is first filled up without placing any reinforcement. Concreting is done as in 7.5.1 Soon after, the specified core assembly shall depending upon situation. be driven and extra concrete shall be poured in simultaneously to keep the level of concrete up to ground level. If hollow driving pipe is used in core assembly, the pipe-shall be withdrawn after filling it with fresh concrete which will be left behind.
NOTE - In under-reamed bored compaction piles, concreting should be uninterrupted and notes 45) and (6) under clause 7.5.3 will not apply.

7.5.6 The top of concrete in a pile shall be brought above the cut-off level to permit removal of all laitance and weak concrete before capping and to ensure good concrete at the cut-off level for proper embedment into the pile cap. 7.5.7 Where cut-off level is less than 1.5 metre below working level, concrete shall be cast to a minimum of 300 mm above cut-off level. For each additional O-3 m increase in cut off level below working level, additional coverage of 50 mm minimum shall be allowed. Higher allowance may be necessary depending on the length of the pile. When concrete is placed by tremie method, it shall be cast to the piling platform level to permit overflow of concrete for visual inspection or to a minimum of one metre above cut-off level. In the circumstance where cut-off level is below ground water, the need to maintain a pressure on the unset concrete equal to or greater than water pressure should be observed and accordingly length of extra concrete above cut-off level shall be determined. 7.5.8 Defective Pile -In case, defective piles are formed, they shall be removed or left in place whichever is convenient without affecting performance of the adjacent piles or the cap as a whole. Additional piles shall be provided to replace them as directed. 705.9 Any deviation from the designed location alignment or load capacity of any pile shall be noted and adequate measures taken well before the concreting of the pile cap and plinth beam if the deviations are beyond the permissible limit. 7.5.10 Estimation of Concrete Quantity - The extra concrete required for each bored cast in situ under-reamed bulb of 2.5 times the stem diameter may be taken equal to a stem length of 4 to 4.5 times its diameter, depending on the nature of strata and other site conditions. The volume of concrete actually placed shall be observed in the case of few piles initially cast and the average figure obtained may be used as a guide for working out the quantities of the concrete and cement for subsequent piles. 25

.

IS : 2911 (Part III) - 1980 For under-reamed compaction piles the amount of concrete used is about 1.2 times of the under-reamed cast in situ piles. is Nom - If the estimates of concrete consumption on the volumeof bore hola and not on the basis of concrete quantity actually consumed, the concrete used may be found smaller than estimated and cement tonsumption may work out to be less. 7.5.11 Recording of Pile Details records of ‘necessary information following may be recorded : A competent person at site should keep about the construction of piles. The

4 b) 4. 4 e) f1

Date and, sequence of installation of piles in a group;
Pile details -

Length, diameter of stem and bulbs, number of bulbs, type of pile, reinforcement, etc; Cut-off level and working level; Method of boring;

Ground water level; Any other information.

APPENDIX [Clause 3.1 (b)]
DEGREE

A

OF E?LPANSJ.VENESS

A-I. The degree of expansiveness and consequent damage to the structures with light loading may be qualitatively judged as shown below:
Degree of ex~ensivenm Differential free swell, percent

Low Moderate High Very high

Less than 20 20 to 35 35 to 50 Greater than 50

A-l.1 In areas of soil showing high or very high differential free swell values, conventional shallow strips footings may not be adequate. 26

IS : 2911 (Part IIX) - 1980

APPENDIX

B

(Clauses 5.2.3.3 and 5.2.5)
SAFE LOAD ON UNDER-REAMED PILES

B-l. SAFE LOAD TABLE B-l.1 The safe bearing, uplift and lateral loads for under-reamed piles given in Table 1 appiy to both medium compact (lO<N <30) sandy soils and clayey soils of medium (4<N < 8) consistency including expansive soils. The values are for piles with bulb diameter equal to two-and-a-half times the shaft diameter. The columns (3) and (4) of on Table 1 provide the minimum pile lengths for single and double under-reamed piles, respectively, in deep deposit of expansive soils. Also the length given for 375 mm diameter double underThe values given for reamed piles and more in other soils are minimum. double under-reamed piles in columns (9) and (13) are only applicable in expansive soils. The reinforcement shown is mild steel and it is adequate for loads in compression and lateral thrusts [Columns (8), (9), (16) and (17)]. For uplift [Column (12) and (13)], re q uisite amount of steel should be provided. In expansive soils, the reinforcement shown in Table 1 is adequate to take upward drag due to heaving up of the soil. The concrete considered is M 15. provided in 5.2.2. The cover requiremepts will be as

B-l.2 Safe loads for piles of lengths different from those shown in Table 1 can be obtained considering the decrease or increase as from columns 10, 11, 14 and 15 for the specific case. B-1.3 Safe loads for piles with more than two bulbs in expansive soils and more than one bulb in all other soils (including non-expansive clayey soils) can be worked out from Table 1 by adding 50 percent of the loads shown in columns (8) or (12) for each additional bulb in the values given in these columns. The additional capacity for increased length required to accommodate bulbs should be obtained from column (10) and (14). B-I.4 Values given in columns (16) and (17) for lateral be increased or decreased for change in pile lengths. Also reamed piles the values should not increase than those given For longer and/or multi-under reamed piles higher lateral adopted after establishing from field load tests. thrusts may not for multi-under in column (17). thrusts may be

B-l.5 For dense sandy (N 30) and stiff clayey (N 28) soils, the safe loads in compression and up P obtained from Table 1 may be increased by ift 25 percent. The lateral thrust values should not be increased unless the stability and strength of top soil (strata up to a depth of about three times the pile shaft diameter) is ascertained and found adequate. For piles in 27

IS: 2911(PartIII)-1980 loose(4~ N ~10) sandy and soft (2~ N <4) clayey soils, the safe loads should be taken 0.75 times the values shown in the Table. For very loose (N < 4) sandy and very soft (N Q 2) clayey soils the values obtained from the Table should be reduced by 50 percent. B-I.6 The safe loads obtained from Table 1, should be reduced by 25 percent if the pile bore holes are full of subsoil water of drilling mud during concreting. No such reduction may be done if the water is confined to the shaft portion below the bottom-most bulb. B-I.7 The safe loads in uplift and compression given by in Table 1 or obtained in accordance with B-l.2 to B-l.6 should be reduced by 15 percent for piles with bulb of twice the stem diameter. But no such reduction is required for lateral loads shown in Table 1. B-1.8 The safe loads for under-reamed compaction piles can be worked out by increasing the safe load of equivalent bored cast in situ under-reamed pile obtained from Table 1 by 1.5 times in case of medium (10~ N < 30) and 1.75 times in case of loose to very loose (N d 10) sandy soils. Depending upon the nature and initial compactness of strata, pile geometry and lay-out of piles, this increase may be up to a factor of 2 and initial load tests are suggested to arrive at final safe load values for design in case of sizable works. The values of lateral loads should not be increased by more than 1.5 times in all cases. In obtaining safe load of compaction pile the reduction for pile bore holes full of subsoil water or drilling mud during concreting should be taken 15 percent instead of 25 percent as given in B-1.6. The reduction for piles with twice the bulb diameter is to be taken 10 percent instead of 15 percent as given in B-1.7. The provision of reinforcement in under-reamed compaction piles will also be guided as stipulated in 5.2.2.1. El.9 The safe loads in Table 1, and the recommendations made to obtain safe load in different cases (B-l.2 to B-1.8) are based on extensive pile load tests. The loads thus obtained may be taken equal to two-thirds the loads corresponding to deflection of 12 mm for loads in compression and uplift. The deflections corresponding to respective safe loads will be about 6 mm and 4 mm. The deflection at safe lateral load will be about 4 mm. The values given in Table 1 will be normally on conservative side. For working out ultimate compressive and uplift loads, if defined as Gads corresponding to 25 mm deflection on load-deflection curve, the value obtained from Table 1 can be doubled.. But in case of lateral thrust twice the values in Table 1 should be considered corresponding to deflection of 12 mm only. El.10 The permissible increase over safe loads obtained from Table 1 should be taken as stipulated in 5.2.3.5 for respective conditions. Also the group capacity should be obtained in accordance with 5.2.8. 28

TABLE 1 SAFB LOAD FOR VBRTICAL BORED CAST IN SITU UNDBR-REN+fBD CLAYBY SOILS INCLUDING BLACK COlTON SOlLS Slza I DiaUnder Td meter cm
LENOTH MILD STaBL RElNFO~CXMWf

FILBswsANDYNm

COMPRBYZON
Increase 3pe;m Length t (8) t (9) 12 18 24 36 42 52.5 63 t (10) 0.9 1.15 1.4 1.8 1.9 2.15 2.4 Decreare per 3ocm Length t (11) 0.7 0.9 1.1 1.4 1.5 1.7 1.9

sA?B Loma Single underreamed

IN

UPWFT

&LtamTANoB

E”Y

“IF pile cm

Si le Double Qx&udinal un r- under- Remforcemrnt % reamed remed ,-,

R’pg-3 Single Double rwcmg under- underofdfimi reamed -d rings

Double underreamed

Incper 30 cm length

De- *crease, under underrecamed reamed 3fzn length

m (3) 3.5 3.5 3.5 3.5 3.5 3.5 3.5

m (4) 3.5 3.5 3.5 3.75 4.0 4.5 5.0

No. (5) 3 4 4 5 6 7 9

Dia mm (6) 10 10 12 12 12 ‘12 12

cm (7) 18 22 25 30 30 30 30

t
(12) 4 6 8 12 14 17.5 21

t
(13) 6 9 12 18 21 25.75 ,31.5

t
(14) 0965 0.85 1.05 1.35 1.45 160 1.80

t
(15) 0.55 0.70 0.85 l-10 1.15 1.30 1.45

t
(16) 1.0 1.5 2.0 3.0 3.4 4.0 4.5

t
(17) 1.2 1.8 2.4 3.6 4.0 4.8 54

2

(1)
20 25 30 37.5 40 45 50

(2)
50 62.5 75 94 100 112.5 125

a
12 16 24 23 35 42

IS : 2911 (Part III)

- 1980

B-l.11 For piles subjected to external moments and or larger lateral loads than those given in Table 1, the pile should be designed properly and requisite amount of steel should be provided.
NOTE -For ’ obtaining safe loads from Table 1, ‘N’ value (standard penetration test value) a weighted average should b&taken up to a depth equal to the bulb diameter below the pile toe. In case of predominantly silty soils, the guiding ‘N’ value for obtaining safe loads may be taken between the values given for sandy and clayey soils.

APPENDIX (Clause 5,2.5)
MODULUS

C

OF SUBGRADE

nB

C-1. The values of the constant of modulus of horizontal subgrade reaction in sand or the modulus of subgrade reaction, K, in clay may be taken from Tables 2 and 3.
TABLE
SOIL

2

TYPICAL

VALUES r

OF m,

Tvrv.

ah XN kg/cm* h \ Submerged Dry 0.260 0.775 2076 0.146 0.526 I.245 0.041

Loose sand Medium sand . Dense sand Very loose sand under repeated loading

TABLE

3

TYPICAL

VALUES

OF X (for

prehaded

clay)

UNCONFINED coMPRFsIVE STRENGTH kg/cm8

RANGE OF ‘VALUEOPK kg,'cm'

PROBABLE vrwRo~K kg/cm

0.2 to 0.4 1 to2, 2 to4 4

7 to 42 32 to 65 65 to 130

7.73 43.79 97.73 19546

30

IS : 2911 (Partm)-1!380

APPENDIX (CZazw 6.2)

D

EQUIPMENT FOR UNDER-REAMED (MANUAL CONSTRUCTION) D-l. EQUIPMENT the following equipment

PILES

D-l.1 Normally operation : a) An auger;

will be required

in manual

b) An under-reamer; c) A boring guide ; and d) Accessories like spare extensions, etc. cutting tool, concreting funnel,

D-1.1.1 For the piles of size larger than 30 cm and for larger depths additional equipment required will be a portable tripod hoist with a manually operated winch. D-1.1.2 For piles in high ground water tamale and unstable soil condii tions, boring and under-reaming shall be carried out with bentonite slurry using suitable equipment. Tremie pipe shall be used for concreting. D-1.1.3 The additional equipment compaction pile are the following: b) Pipe or solid core. normally required for under-reamed

a) Drop weight for driving the core assembly, and

APPENDIX (Clause 6.4)
BASXC PROPERTIES El. PROPERTIES OF DRILLING

E

MUD

(BENTONITE)

E-l.1 The bentonite suspension used in bore holes is basically a clay of montmorillonite group having exchangeable sodium cations. because of thegresence of medium cations, bentonite on dispersion will break down 31

as : 2911 (Part III) - 1980 into small plate like particles having a negative charge on the surfaces and positive charge on the edges. When the dispersion is left to stand undisturbed, the particles become oriented building up a mechanical structure of its own, the mechanical structure held by electrical bonds is observable as a jelly like mass or jell material. When the jell is agitated, the weak electrical bonds are box-ken and the dispersion becomes fluid. E2. FUNCTIONS E-2.1 The action of bentonite in stabilizing the sides of bore holes is primarily due to the thixotropic property of bentonite suspensions. The thixotropic property of bentonite suspension permits the material to have the consistency of a fluid when introduced into the excavation and when undisturbed forms a jelly which when agitated becomes a fluid again. E2.2 In the case of a granular soil, the bentonite suspension penetrates into the sides under positive pressure and after a while forms a jelly. The bentonite suspension gets deposited on the sides of the hole and makes the surface impervious and imparts a plastering effect. In impervious clay, the bentonite does not penetrate into the soil, but deposits only a thin film on the surface of the hole. Under such conditions, stability is derived from the hydro-static head of the suspension. E3. SPECIFICATION piling work shall satisfy the

E-3.1 The bentonite suspension used for following requirements :

a) The liquid limit of bentonite when tested in accordance with IS: 2720 (Part V)-1965* shall be more than 300 percent and less than 450 percent. b) The’sand content of the bentonite powder shall not be greater than 7 percent.
NOTEThe purposeof limiting the sand contentis mainly to control and reduce the and tear of the pumpingequipment.

Bentonite solution should be made by mixing it with fresh water using pump for circulation. The relative density of the bentonite solution should be between 1.034 and, 1.10. The differential free swell shall be more than 546 percent.

*Methods of test for soils: Part Determinationof liquid and plastic limits (&: r&). V 32

(crmtinucd from page 2)

Pile Foundations Connener
SHRI M. D. TAMBEKAR Members SHRI K. N. DADINA

Subcommittee,

BDC 43 : 5

Representing

Bombay Port Trust, Bombay In personal capacity (P 820, Block P, flew Al$ore,
Calcutta)

DEPUTYD=CT~R RESEARCH hIini%ry of Railways (SM II) &PUTY DIRECTOR STANnARD.5 SHRIdBG:zpL II) (Al&t-W Braithwaite Bum & Jessops Construction Co Ltd, . Calcutta M. N. Dastur & Co Pvt Ltd. Calcutta SHRIS. R. KULKARNI Cementation Co Ltd, Bombaj SHRIM. R. PUNJA Metallurgical & Engineering Cons&anti (Steel Snru S. K. SANYAL Authority of India), Bhilai Engineers India Ltd, New Delhi SHR~K. SARICAR Cen~~r!~lding Research Institute (CSIR), &RI D. SHARMA
DR S. P. SHRNASTAVA

Unit$dh’echnical

Consultants (Pvt) Ltd, New

DR R. KAFVR (Alternate)

33

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AMRNDMENT NO. 1
TO

JANUARY 1983

IS : 2911( Part III) - 1980 CODE OF PRACTICE FOR DESIGN AND CONSTRUCTION OF PILE FOUNDATIONS
PART III UNDER-REAMED

PILES

(Firat Revision)
AbratiOM ( Pagt 12, chus~ 5.2.2J,.lin49 ) 197lz#‘. ( Pag# 12, foot-note r&h e # ’ mark ) [ Page 15, C~UU.W 5.2.5.1(b) 1: a) Lines3 and 4, z&8 existing matter: ’ Q~ - ~: .A. * . Delete. Substitute ‘ of’ for 6or ‘.

(Pags E~~IU~ 12, 5.2.3.1,linr 6 ) - Delete the words ‘ and IS : 6405-

of ‘&’

-

Substitute

the following Y.~~~~~

for the n

‘.~~~~f~:~~~~~jn.y.~

n

r=l

b) Line ? - Substitute ‘ y( kg/cm~ ) ’ for ‘ A( kg/u+) c) Line 10 ( Pags 14,
Fw. 2.

‘.

Sub.tit.utc ‘ NY’ fol ‘.Na ‘.

Note ) - Substitute the following for the existing note: 3
willbetakenfrom

‘N~3-~NywilIbcu’rpecifiedinIS:6103-1981*~dNcr

beyond+ !w.' =

This is based on Berexa~tseu’r curve up to 4 = !W and

Vaic'r carvea

[Pagu 14, clmus 5.2.3.1 (d), GM 7 ] - Substitute ‘ Ny ‘for ‘ MI ‘.
(Page 14, foot-note roith ‘ the existing foot-note:
l

’ mark ) -

Substitute

the following

for

* *&de of practice for determination (jJ# rwiaia ).’

of’ bearing capacity

of rhallow found&m

1

( Page 15, Fig. 2 ) - Substitute the following for the existing figure:
SO(1

20

25
ANGLE OF

30
INTERNAL

35

40
FRICTION $

bb

FM.

2

BEARINO CAPACITY FACTOR JV,,

1970r

( PW 32, &l4se E3.1, linr 4) - Substitute ‘ IS : 2720( Part V)' ‘ : 2720( Part V )-196!i* ‘. fw IS

AMENDMENT NO. 2 TO

SEPTEMBER 1984

IS:2!?ll(Part 3)-1980 CODE OF PRACTICE FOR DESIGN
AND CONSTRUCTION PART 3 OF PILE FOUNDATIONS PILES UNDER-REAMED

iFirs t Revision) Alterations --a--(Page 8, o&zuse 4.2, tine 1) - Substitute '1~:43z?(Part l)-lg82*' for '1s:4HPart l)-lg66*'. (Page 8, foot-nob with '*' mzrk) - Substitute the following for the existing foot-note: '*Specification for mild steel and medium tensile steel bars and hard dram steel bars and hard drawn steel wire.for concrete reinforcement: Part 1 Mild steel and medium tensile steel bars (thirdre~.&ion).

(Page II, olause 5.2.2.1, first sentence) Substitute the following for the existing sentence:
'The tinimum area of longitudinal reinforcement (any type or grade) within the pile shaft shall be 0.4 percent of the sectional area calculated on the basis of outside area of the shaft or casing if used.'

(Page21, okuse

5.4.2 cmd 5.4.3) - Delete.

(Page 21, okzuse 5.4.7) - Substitute '50 mm' for '40 mm'.

Addenda ---word8 after

(Pags 6, ~.WW 2.18, tine 2) - Ada the folbifing the word 'Shearwithin the bracket'as 'evidenced from the load aeMeleme%kt curves'.
:
(Page 8,
0242248s

Ena

5.2) - Ada

the

f~llouing in

the

‘ana shall be designedaccording IS: to 456-1978 Code of practicefor plain snd reinforced concrete(third
lWd8h?Z). ’

in *Yes
:

24, atauss 5.2.3(c)

- Ada the f0110uing

![sse IS:29ll(Part 4).1979+.1*.

mc

43) 2

AMENDMENT

NO. 3
TO

JULY 1987

IS : 2911( Part 3 )-1980 CODE OF PRACTICE FOR
DESIGN AND CONSTRUCTION PILE FOUNDATIONS
PART 3 UNDER-REAMED ( First clause: ‘4.3.4 The minimum grade of concrete to be used for piling shall be M-20 and the minimum cement content shall be 4C0 kg/m8 in all coaditions. For piles up to 6 m deep M-15 concrete with minimum cement content 350 kg/ma without provision for under-water concreting may be used under favourable non-aggressive subsoil condition and where concrete of higher strength is not needed structurally or due to aggressive site conditions. The concrete in aggressive surroundings due to presence of sulphates, etc, shall conform to provision given in IS : 456-197811. For the concrete, water and aggregates specifications laid down in IS : 456-197811shall be followed in general. Natural rounded shingle-of appropriat? size may also be used as coarse aggregate. It helps to give high slump with less water-cement ratio. For tremie concreting aggregates having nominal size more than 20 mm should not be used.’ ( Page 9, clauses 4.3.6.1 and 4.3.6.2 ) - Substitute the following for the existing clauses: ‘4.3.6 The average compressive stress under working load should not exceed 25.percent of the specified strength at 28 days calculated on the total cross-sectional area of the pile. If in the portion of the shaft above the top under-reamed a permanent casing of adequate thickness and of suitable size is used, the allowable stress may be suitably increased.’ [ Page 14, clauses 5.2.3.1(c) and ‘5.2.3.2 see also Amendment - Substitute ‘IS : 2911 ( Part 4 )-1984t’ J or ‘IS : 2911 ( Part 4)T”6;9;, )I . ( Page 14,foot-note the existing foot-note: with ‘t’ mark ) Substitute the following for

OF

PILES

Revision )
the following for the existing

( Page 8, clause 4.3.4 ) - Substitute

‘tCodc of practice for design and construction of pile foundations: Part 4 Load test 0n piles (first revision ).’
[

Page 16, claw 5.2.3.5(b), last sentence ] - Delete.
( Pa@ 16pfoot-note with *t’ mark ) Delete,

Gr 1 1

( Page 17, clause 5.2.5, second para and Note ) following for the existing matter:

Substitute

the

‘A recommended method for the determination of depth of fixity, lateral deflection and maximum bendirg moment required for design is given in Appendix C for fully or partially embedded piles. Other accepted methods, such as the method of Reese and Matlock for fully embedded piles may also be used. Due to the presence of bulbs, underreamed piles tend to behave more as rigid piles and the analysis can be done on rigid pile basis. For lateral loads with or without axial loads, up to those given in Table 1 of Appendix C, no analysis may be necessary if external moment is not acting.
NOTE - Because of limited information on horizontal modulus of soil and refinements in the theoretical analysis, it is suggested that the adequacy of a design should be checked by an actual field load test.’

23, clause 7.3 ): a) ( Lines 7 and 11 ) - Substitute ‘sixth’for ‘quarter’. b) (Line 13)Add the following matter after the word ‘depths’: ‘( below ground level ) or high ( above ground level )‘. ( Page 26, clause A-l, column heading of informal ruble ) ‘Free swell, percent’ for ‘Rifferential free sw.ell, percent’.
( Page 30, Appendix C ) -

( Page

Substitute

Appendix

Substitute the following for the existing including Fig. 4 and 5:

‘APPENDIX ( Clause 5.2.5 )

C

DETERMINATION OF DEPTH OF FIXITY, LATERAL DEFLECTION AND MAXIMUM MOMENT OF LATERALLY LOADED PILES C-l. DETERMINATION OF LATERAL DEFLECTION PILE HEAD AND DEPTH OF FIXITY AT THE

C-l.1 The long flexible pile, fully or partially embedded, is treated as a cantilever fixed at some depth below the ground level ( see Fig. 4 ).

C-l.2 Determine the depth of fixity and hence the equivalent the cantilever using the plots given in Fig. 4. where T=5
EI KIand R=4 ‘F

length of

( Kl and Kz are constants given

2 2

in Tables 2 and 3 below, E is Young’s

modulus of the pile material in kg/cm2 and I is the moment of inertia of the pile cross-section in cm4 ).

Z-3 4 2.1 !,
I \ \

-FREE ----FIXED

HEAD HEAD

PILE PILE

Q

\

.

e

\

.

3
OL 0

1.9 ----__, FOR PILES IN SANDS AND NORMALLY LOADED CLAYS

oz

3

1.3 0

I 2

I 4 L,/R OR

6 Ll/l

8

FOR PILES PRELOADED Ia

IN CLAYS

FIG. 4 DETERMINATION OF DEPTH FIXITY NOTE- Figure 5 is valid for long flexible piles where the embedded length, L is > 4R or 4T.

TABLE 2 VALUES OFCONSTANT
TYPEOPSOIL
(-__--___L---_~

Kl( kg/cmS)
VALUE

Dry

Submerged (3) 0.146 0925 1.245 0.040

(1)
Loose sand

(2) 0.260 0.775 2.075 -

Medium sand Dense sand Very loose sand under repeated loading or normally loading clays

3

L,/R 54 1.2. I

OR

Ll/T
PILE

iOR FREE HEAD

z z e
” 9

-

FOR

PILES

IN

I

PiELOAdED AND CLAYS

CLAYS

FOR
I.0 ----NORMALLY

PILES

IN SANDS
LOADED

c

’

0.6

0

0.5

1.0

15 OR
HEAD

2.0

24

L,/R
58 FOR FIXED

Ll/T
PILE

FIG. 5 DETERMINATION REDUCTIONFACTORSFOR OF COMPUTATION MAXIMUM MOMENT IN PILE OF

TABLE 3

VALUES

OF CONSTANT K, (

Wcm’ )
VALUE

uNCOk44~N~~~MPRESWVB

kg/cm’ (1) 0.2 to O-4 1 to 2 2to4 More than 4 C-l.3 Knowing (2) 7-75 48-80 9775 195.50

deflection

the length of the equivalent cantilever the Dile head (Y) shall be computed using the following equations: Y (cm) =
Q( h + LF )" 3 El

. ..for free head pile
. . . for fixed head pile

= Q ( LI + LP I3 12 El

where Q is the lateral load in kg. C-2. DETERMINATION OF MAXIMUM MOMENT IN THE PILE C-2.1 The fixed end moment (Mp) of the equivalent cantilever is higher than the actual maximum moment (M) of the pile. The actual maximum moment is obtained by multiplying the fixed end moment of the equivalent cantilever by a reduction factor, m given in Fig. 5. The fixed end moment of the equivalent cantilever is given by: . ..for free head pile j&=8(&+ Lr)

=Q(L+Lr)
2 The actual maximum moment (M) = m
(MF).'

...for fixed hkad pile

5
Pf4nWd at Slmco Printing Press. Delhi, India _