Pile Design and Construction Practice, Fifth edition

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7.9 The design of pile capping beams and connecting ground beams Structural design of piles and pile groups 393 Pile capping beams have the function of distributing the load from walls or closely spaced columns onto rows of piles. For heavy wall loading in conjunction with transverse bending moments the piles are placed in transverse rows surmounted by a wide capping beam (Figure 7.14a). The piles may be placed in a staggered row for walls carrying a compressive loading with little or no transverse bending moments (Figure 7.14b). A lightly loaded wall can be supported by a single row of piles beneath the centre-line provided that the beam capping the piles is restrained by tying it to transverse capping beams carrying cross walls in the structure. Attention should be given to providing adequate restraint to transverse movement and bending where ground beams are supported by minipiles. A design method was proposed by the Building Research Establishment (7.9) which allows the bending moments and shearing forces in a beam to be reduced if the beam can be shown to be acting compositely with the brick wall built upon it. The method may be applied to the design of pile capping beams for house foundations, and is applicable to walls having a height of not less than 0.6 of the span of the beam. The walls must not have door or window openings near to the supports, as this would interfere with the arching action of the brickwork. The bending moment produced by a uniformly distributed load on a freely supported beam is WL/8. With full composite action between beam and wall, this moment may be reduced to a minimum of WL/100 for light loading, where W is the total distributed load on the brickwork (including self weight) and L is the span of the beam. A property of composite action is that the compression in the arch within the brickwork is directed radially towards the nearest firm supports; therefore, shearing reinforcement of the beam is theoretically unnecessary if the loaded lengths at the supports can be shown to be not greater than the depth of the beam. However, the BRE recommended that all beams designed for bending moments of greater than WL/60 should be designed to resist the shearing forces produced by the full dead and imposed loading. (a) (b) Figure 7.14 Arrangement of piles in capping beams (a) Heavy wall loading with transverse bending moments (b) Light wall loading with little or no transverse bending.
394 Structural design of piles and pile groups It is recommended that the depth of the beam should be between L/15 and L/20. However, with a heavily loaded wall only a small degree of composite action is allowed and it may be necessary to use a beam deeper than L/15. When considerable composite action is present, i.e. when the bending moment is less than WL/40, the reinforcement should be calculated for a beam having a depth equal to L/15 even if a deeper beam is to be provided for other reasons. This is to ensure that there is sufficient steel in the beam to act as a tie across the springing of the arch within the brickwork. When designing pile capping beams by limit-state principles it is seldom necessary to consider the serviceability limit-state. However, an examination of the limit-state of cracking is necessary if the beam is to be exposed to soil or groundwater which can be expected to be corrosive. The limit-state of deflection should be checked if the beam is to support a wall faced with a material such as mosaic tiles, which are particularly susceptible to cracking due to small movements. The BRE design method assumed that the ground floor slab is carried by the soil and is not connected to the capping beam. If a suspended floor slab is provided the capping beam must be designed by conventional methods. A disadvantage of the BRE design is that it can inhibit house owners from removing large areas of load-bearing walls in the course of making improvements such as the addition of rear conservatories. There is a danger that the house owner may not be aware of the basis of the design of the ground beams when proceeding with these and similar structural alterations. It is a good practice to provide a suspended ground floor slab in cases where piles are provided to restrain a structure from lifting due to a swelling soil. A ground floor slab cast directly onto a swelling soil will lift and will, in turn, cause the lifting of internal partitions, with the consequent distortion of any floors carried by them, and the cracking of plaster finishes. Uplift pressures due to soil swelling against the underside of a pile capping beam must be considered. In clay soils where mature trees or hedges have been removed the clay may swell up to 100 mm over a long period of years. Swelling of pyritic mudstones and shales can occur due to the growth of gypsum crystals within the laminations of these rocks. Gypsum growth can be caused by chemical and microbiological changes consequent on changed environmental conditions (7.10) . Swelling pressures, if the upward movement of the soils is resisted by a reinforced concrete capping beam, can be of a magnitude which will cause the piles to fail as tension members, or which will lift the piles out of the soil. It is essential to insert a layer of compressible material such as Clayboard or special low density polystyrene or to provide a void between the soil and underside of the capping beam to reduce the uplift forces transferred to the piles (Figure 7.15). Load/deflection tests should be made on specimens of the compressible material to ensure that the amount of compression required by the predicted degree of soil swelling does not generate a pressure on the ground beam that is sufficient to cause structural failure of the beams or piles, or lifting of the building. There have been a number of cases of failure and cracking of piles, ground beams, and superstructures to low-rise buildings constructed on swelling clays in recent years. These have been caused mainly by deficiencies in design such as inadequate tension reinforcement and lack of proper provision for uplift on ground beams. The latter should be of generous depth to provide for differential uplift forces caused by local tension failure in piles in unpredictable conditions of soil swelling. Horizontal swelling forces can also impose loads on pile capping beams due to the restraint provided by the beam to the expansion of the mass of the soil. To avoid excessive
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Pile Design and Construction Practi
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Pile Design and Construction Practi
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Contents Preface to fifth edition i
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7.3 Designing piles to resist drivi
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Preface to fifth edition Piling rig
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Preface to fifth edition xi Pearson
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Chapter 1 General principles and pr
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(a) Backfill Bulb of pressure Appli
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are allowed to be used by Eurocode
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application of different load facto
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Load transfer The contractor’s gu
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(7) Jacked-down steel tube with clo
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Types of pile 13 needed to avoid cr
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(a) (b) Precast concrete Head of ti
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Table 2.2 Modification factor K 2 b
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4d d 10 mm M.S. plate sleeve tarred
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Table 2.3 Working loads and maximum
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Cement content �300 kg/m3 �325
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Types of pile 25 Table 2.5 BS 8004
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(a) (b) (c) (d) Cast iron or cast s
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Sheathing Bottom boards Figure 2.9
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Misplaced bearers Lifting holes Cra
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Section Bayonet plug Plan Locking p
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Existing foundation Precast pile ca
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Types of pile 37 Where very long le
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Types of pile 39 rotate during driv
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Types of pile 41 Because of their r
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(a) (b) Types of pile 43 Figure 2.2
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(a) (b) Welds Welds Types of pile 4
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(a) M.S. plate shoe Welds (b) 2.2.6
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Types of pile 49 brittle fracture r
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(a) (b) (c) Hammer Driving tube Con
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Types of pile 53 all cast-in-place
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Figure 2.28 The TaperTube pile.
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(a) (b) Figure 2.29 (a) The ScrewSo
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Types of pile 59 The simplest form
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Types of pile 61 Transverse reinfor
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Types of pile 63 completion the res
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Types of pile 65 permanently in the
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Types of pile 67 (3) Construction o
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Types of pile 69 can withstand fair
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Chapter 3 Piling equipment and meth
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Piling equipment and methods 73 A r
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Maximum height 26.32 m Usable leade
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Figure 3.4 Liebherr LRH 400 48 m lo
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Piling equipment and methods 79 the
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Piling frame Single-acting hammer S
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Guides for engaging leaders Steam o
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Table 3.1 Characteristics of some s
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Table 3.2 Characteristics of some h
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Piling equipment and methods 89 Tab
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Table 3.4 Characteristics of some d
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Figure 3.16 Driving a pile casing w
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Table 3.5 Continued Piling equipmen
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Soil resistance to driving (MN) 25
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Figure 3.19 Noise-abatement tower u
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Dolly M.S. plate Plastics Hardwood
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Standard elbow bend Detachable scre
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Figure 3.24 Discharging concrete in
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Piling equipment and methods 107 Fi
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Table 3.6 Continued Piling equipmen
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Figure 3.30 Top-hinged under-reamin
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Rotary table Hydraulic motor Water
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Piling equipment and methods 121 sl
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Pile head Pile base 2 holes ∅ 4 m
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Piling equipment and methods 125 Ca
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Piling equipment and methods 127 sm
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Piling equipment and methods 131 Th
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Piling equipment and methods 133 th
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Piling equipment and methods 135 Pi
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Piling equipment and methods 137 ve
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Chapter 4 Calculating the resistanc
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O C Settlement A Reloading Load B U
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Resistance of piles to compressive
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for spread foundations in various c
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structural actions and A2 to geotec
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Geometrical data are concerned with
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Figure 4.3 Failure surfaces for com
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Depth below ground level in m 5.6 1
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(a) (b) Peak adhesion factor a p Le
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orehole or test profile over the pe
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Effective length Shaft friction not
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4.3 Piles in coarse-grained soils 4
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Depth below ground surface (m) Resi
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Depth of penetration (m) 0 0 5 10 1
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using standard penetration tests or
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� � Resistance of piles to comp
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Safety factors generally used in th
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Depth to NAP datum (m) Cone resista
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The conditions at the interface can
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The shear modulus G in equation 4.3
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2.0 OD tubular steel pile with clos
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where Resistance of piles to compre
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eached the point of ultimate resist
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(4) Obtain the safe end-bearing loa
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Vertical force, t t-z curve Vertica
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where the bearing capacity factor:
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and RQD of the rock as shown in Tab
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Depth below ground level (m) 0 5 10
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settlement of the pile are summariz
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Rock socket reduction factor a 1.0
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Table 4.17 � and � values of we
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Influence factor, l p 2.0 1.6 1.2 0
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(a) (b) No load on pile head Residu
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a closed end into a deep deposit of
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Average shearing strength along pil
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It is assumed that the shear streng
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Depth below ground level (m) Figure
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Figure 4.45 Depth below ground leve
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Depth of h(m) Segment (m bql) � h
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For a wall thickness of 19 mm in mi
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Pile groups under compressive loadi
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24.0 m 16.0 m The comparative group
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where c � cohesion intercept of s
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Inclination factor, i c Inclination
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z/B 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
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Compressive stress 1.5 q n q n B A
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E u/c u 3000 2500 2000 1500 1000 50
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0 0 1 2 3 4 H/B 5 6 7 8 9 0 1 2 3 4
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D LB LB D 0.50 0 0.1 0.2 0.3 0.4 0.
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Initial tangent constrained modulus
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factor N for which Schmertmann sugg
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0 0 2 4 H/B 6 8 10 Influence factor
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Overall loading 100 kN/m2 (a) (b) (
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(a) (b) (c) (d) Pile groups under c
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Depth below ground level in m 5 10
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For the arrangement of the piles sh
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Soft clay Sand B/2 5 11.2 m Figure
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Unit negative skin friction at top
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Chapter 6 The design of piled found
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(a) Tie rod Wholly compression Whol
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esistance of cylindrical augered fo
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in the ground is assumed to be equa
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Section 3.3.1. Enlargements cannot
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Piles to resist uplift and lateral
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Spacer Top of hard rock Drilling pi
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where m is the modular ratio of ste
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Table 6.3 Examples of bond stress b
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Top of rock 30˚ 30˚ Figure 6.15 F
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(b) P/n & �Vm Vc 2.0 1.8 1.6 1.4
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Table 6.4 Partial resistance factor
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and adjustment, starting with a ver
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Coefficient of subgrade modulus var
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where e is the height from the grou
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and Thus from Figure 6.24 deflectio
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(a) Deflection coefficient Ay (c) D
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(a) (b) (c) Depth coefficient Z 0 1
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Horizontal load H; Bending moment =
Page 358 and 359: Methods of drawing sets of p-y curv
Page 360 and 361: Calculations to determine the ultim
Page 362 and 363: (a) (b) Pressure Soil reaction p Ps
Page 364 and 365: Z�x/R 0 1.0 2.0 3.0 4.0 5.0 M(z)
Page 366 and 367: (a) yroGc H0 Ep Gc 1/7 (b) 0 0 0.1
Page 368 and 369: (a) determining the compressive and
Page 370 and 371: A X Z B R A Resultant R R B Y C D R
Page 372 and 373: 6.8 FREEMAN, C. F., KLAJNERMAN, D.,
Page 374 and 375: Thus the load to be carried by anch
Page 376 and 377: If high-tensile steel (which has a
Page 378 and 379: sustained horizontal load which can
Page 380 and 381: Calculating the allowable horizonta
Page 382 and 383: Pile cap (Weight�2475 kN) F E D C
Page 384 and 385: The resultant of the vertical and h
Page 386 and 387: The Brinch Hansen bearing capacity
Page 388 and 389: Modulus of elasticity of pile � 2
Page 390 and 391: Chapter 7 Some aspects of the struc
Page 392 and 393: (a) (b) (c) Lifting rope Lifting po
Page 394 and 395: 7.3 Designing piles to resist drivi
Page 396 and 397: Structural design of piles and pile
Page 400 and 401: should not arise if the piles are d
Page 402 and 403: (a) (b) (c) M.S.plate cover M.S.cap
Page 404 and 405: 45˚ Structural design of piles and
Page 406 and 407: X Column Y9 Y9 Y Critical section f
Page 410 and 411: Damp-proof course Cranked vent Grou
Page 414 and 415: (a) (b) Deck of wharf Fender Rubber
Page 416 and 417: (a) (b) y y e z f A The bending mom
Page 418 and 419: Piling for marine structures 403 th
Page 420 and 421: Pipe trunkways Hose handling platfo
Page 422 and 423: Piling for marine structures 407 8.
Page 424 and 425: Piling for marine structures 409 sh
Page 426 and 427: In SI units, equation 8.8 becomes f
Page 428 and 429: The natural frequency of the member
Page 430 and 431: The empirical equation of Korzhavin
Page 432 and 433: Piling for marine structures 417 re
Page 434 and 435: Table 8.3 Minimum safety factors fo
Page 436 and 437: Piling for marine structures 421 th
Page 438 and 439: Piling for marine structures 423 sh
Page 440 and 441: 8.21 GERWICK, B. C. Construction of
Page 442 and 443: Soil resistance p in kN per m of de
Page 444 and 445: From Figures 6.29a and b the comput
Page 446 and 447: giving 9.7y � 0.26, y � 0.26
Page 448 and 449: From �7.5 to �3.0 m: no increas
Page 450 and 451: Miscellaneous piling problems 435 W
Page 452 and 453: 9.2 Piling for underpinning Miscell
Page 454 and 455: Miscellaneous piling problems 439 B
Page 456 and 457: Miscellaneous piling problems 441 T
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Miscellaneous piling problems 443 p
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Longitudinal reinforcement is provi
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Light-gauge steel lining tubes Stow
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When inspecting the geological cond
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Miscellaneous piling problems 451 f
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natural ‘freeze-back’ around th
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Miscellaneous piling problems 455 b
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Miscellaneous piling problems 457 w
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Drainage layer 8.0 m 6.0 m Fill 1.0
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p m/c u 10.5 2p 0 and the mean hori
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Bridge abutment support piles Emban
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Figure 9.23 Drilling equipment for
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Max. water level +16 m Min. water l
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2-4 m marine clay dredged out MHW R
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Miscellaneous piling problems 471 o
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Miscellaneous piling problems 473 c
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The ground temperature around the p
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9.40 URANOWSKI, D. D., DODDS, S., a
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The durability of piled foundations
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and European Standards as shown in
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martesia with some teredo, and at C
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economics, taking into account the
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Depth of borehole 1.5 B 1 in 4 B Gr
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Ground investigations, contracts an
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(a) DCP n (blows/100 mm) 40 35 30 2
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Table 11.2 Daily pile record for dr
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Paper fixed to pile by adhesive tap
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Figure 11.10 Patented arrangement f
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following expressions: (11.1) Load
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(b) Settlement of pile head in mm S
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(a) Settlement � (mm) 0 0 4 8 Gro
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experience to give reasonably relia
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Appendix Properties of materials A.
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Subdivisions of Grades A to C chalk
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544 Name index Davis, E. H. 354 Dav
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546 Name index Schaaf, S. A. 424 Sc
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548 Subject index contiguous piles
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550 Subject index Pali Radice piles
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Pile Design and Construction Practice, Fifth edition

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