ABSTRACT
CONTENTS 6.1 Introduction ....................................................................................................................... 236 6.2 Design of Pile Foundations ............................................................................................. 236
6.2.1 Selection of Pile Material for Different Construction Situations .................. 236 6.2.1.1 Timber Piles ........................................................................................... 237 6.2.1.2 Concrete Piles ........................................................................................ 237 6.2.1.3 Steel Piles ............................................................................................... 238
6.2.2 Selection of the Method of Installation ............................................................. 238 6.2.3 Design Criteria ...................................................................................................... 239
6.2.3.1 Allowable Loads ................................................................................... 239 6.2.3.2 Allowable Deflections .......................................................................... 239
6.3 Estimation of Static Pile Capacity of a Single Pile ...................................................... 239 6.3.1 Estimation of Point Capacity .............................................................................. 241
6.3.1.1 Meyerhoff’s Method............................................................................. 241 6.3.1.2 Vesic’s Method...................................................................................... 242
6.3.2 Skin-Friction Capacity of Piles............................................................................ 244 6.3.2.1 Unit Skin Friction in Sandy Soils ....................................................... 244 6.3.2.2 Skin Friction in Clayey Soils ............................................................... 244 6.3.2.3 The a Method........................................................................................ 246 6.3.2.4 The b Method........................................................................................ 246 6.3.2.5 The l Method ........................................................................................ 247
6.3.3 Pile Capacity Estimation from In Situ Tests..................................................... 247 6.3.3.1 Pile Capacity Estimation from Standard
Penetration Test Results ...................................................................... 247 6.3.3.2 Pile Capacity Estimation from Cone
Penetration Test Results ...................................................................... 248 6.4 Pile Load Transfer ............................................................................................................ 253 6.5 Time Variation of Pile Capacity (Pile Setup) ............................................................... 254
6.5.1 Reported Results from Field Studies................................................................. 256 6.6 Computation of Pile Settlement ..................................................................................... 259
6.6.1 Elastic Solution ...................................................................................................... 259 6.6.2 Computation of Pile Settlement Using Approximate Methods.................... 262
6.6.2.1 Elastic Method for End-Bearing Piles ............................................... 262 6.6.2.2 SPT-Based Method for End-Bearing Piles ........................................ 263 6.6.2.3 Elastic Shortening of Piles................................................................... 263
6.7 Pile Groups ........................................................................................................................ 265 6.7.1 Bearing Capacity of Pile Groups........................................................................ 265 Pile
6.7.3 Approximate Methods for Computation of Immediate Settlement of Pile Groups ................................................................................. 271 6.7.3.1 Vesic’s Pile Group Interaction Factor.............................................. 271 6.7.3.2 CPT-Based Method for Pile Groups................................................ 272 6.7.3.3 Load Distribution Method for Pile Groups.................................... 272
6.8 Downdrag (Negative Skin Friction) ............................................................................ 272 6.9 Load and Resistance Factor Design Criteria .............................................................. 272
6.9.1 Strength Limit States......................................................................................... 273 6.9.2 Service I Limit State .......................................................................................... 273 6.9.3 Design Criteria for Axially Loaded Piles........................................................ 274
6.10 Static Capacity of Piles on Rock ................................................................................... 277 6.10.1 Determination of Strength Properties of Rock............................................. 279
6.11 Pullout Capacity of Driven Piles.................................................................................. 279 6.12 Screw Piles ....................................................................................................................... 280
6.12.1 Atlas Screw Piles............................................................................................... 282 6.12.2 Omega Screw Pile ............................................................................................. 282 6.12.3 Application of Screw Piles .............................................................................. 282
6.13 Pile Hammers .................................................................................................................. 283 6.13.1 Impact Hammers .............................................................................................. 284
6.13.1.1 Drop Hammer .................................................................................. 284 6.13.1.2 Single Acting Air or Steam Hammers.......................................... 284 6.13.1.3 Double Acting Air or Steam Hammers........................................ 284 6.13.1.4 Differential Acting Air or Steam Hammers ................................ 285 6.13.1.5 Diesel Hammers............................................................................... 285
6.13.2 Vibratory Hammers.......................................................................................... 285 6.14 Additional Examples...................................................................................................... 286 References ................................................................................................................................... 297
A pile foundation can be employed to transfer superstructure loads to stronger soil layers deep underground. Hence, it is a viable technique for foundation construction in the presence of undesirable soil conditions near the ground surface. However, owing to the high cost involved in piling, this foundation type is only utilized after other less costly alternatives, such as (1) combined footings and (2) ground modifications, have been considered and ruled out for the particular application. On the other hand, piles may be the only possible foundation construction technique in the presence of subgrades that are prone to erosion and in offshore construction involving drilling for petroleum.
