9.12Frictional Resistance (Q) in SandAccording to Eq. (9.14), the frictional resistance0, = Ep ALfThe unit frictional resistance, f, is hard to estimate. In making an estimation of f, severalimportant factors must be kept in mind:1. The nature of the pile installation. For driven piles in sand, the vibration caused dur-ing pile driving helps densify the soil around the pile. The zone of sand densificationmay be as much as 2.5 times the pile diameter, in the sand surrounding the pile.2 It has been observed that the nature of variation of fin the field is approximately asshown in Figure 9.16. The unit skin friction increases with depth more or less lin-early to a depth of L' and remains constant thereafter. The magnitude of the criticaldepth L' may be 15 to 20 pile diameters. A conservative estimate would beL' 15D(9.40)3. At similar depths, the unit skin friction in loose sand is higher for a high-displacement pile, compared with a low-displacement pile.4. At similar depths, bored, or jetted, piles will have a lower unit skin frictioncompared with driven piles.Taking into account the preceding factors, we can give the following approximaterelationship for f (see Figure 9.16):For z = 0 to L',f = Ko, tan 8(9.41)and for z = L' to L,f = f=r(9.42)In these equations,K= effective earth pressure coefficiento, = effective vertical stress at the depth under consideration8' = soil-pile friction angleIn reality, the magnitude of K varies with depth; it is approximately equal to theRankine passive earth pressure coefficient, K,, at the top of the pile and may be lessthan the at-rest pressure coefficient, K,, at a greater depth. Based on presently availableresults, the following average values of K are recommended for use in Eq. (9.41):9.8 Meyerhof's Method for Estimating Q,SandThe point bearing capacity, q,, of a pile in sand generally increases with the depth ofembedment in the bearing stratum and reaches a maximum value at an embedment ratioL/D = (L/D),r. Note that in a homogeneous soil L, is equal to the actual embedmentlength of the pile, L. However, where a pile has penetrated into a bearing stratum, L, A driven closed-ended pile, circular in cross section, is shown in Figure P9.4.Calculate the following.a. The ultimate point load using Meyerhof's procedure.d. The ultimate frictional resistance Q,. [Use Eqs. (9.40) through (9.42), and takeK = 1.4 and 8' = 0.64'.]e. The allowable load of the pile (use FS = 4).Y - 15.7 kN/m= 32GroundwatertableYu - 18.2 kN/m³d= 32Yu - 19.2 kN/m³= 4015 m381 mmFigure P9.4

Ultimate point load is calculated by the following formula: Qb=σv'NqAbwhere Ab=area of pile =…

A driven closed-ended pile, circular in cross section, is shown in Figure P9.4. Calculate the following. a. The ultimate point load using Meyerhof's procedure. d. The ultimate frictional resistance Q,- [Use Eqs. (9.40) through (9.42), and take K = 1.4 and 8' = 0.64'.] e. The allowable load of the pile (use FS = 4). Y -15.7 KN/m = 32 Groundwater Yu - 18.2 AN/m = 32 Yu- 19.2 KN/m - 40 15 m

A driven closed-ended pile, circular in cross section, is shown in Figure P9.4. Calculate the following. a. The ultimate point load using Meyerhof's procedure. d. The ultimate frictional resistance Q,- [Use Eqs. (9.40) through (9.42), and take K = 1.4 and 8' = 0.64'.] e. The allowable load of the pile (use FS = 4). Y -15.7 KN/m = 32 Groundwater Yu - 18.2 AN/m = 32 Yu- 19.2 KN/m - 40 15 m

Fundamentals of Geotechnical Engineering (MindTap Course List)

5th Edition

ISBN:9781305635180

Author:Braja M. Das, Nagaratnam Sivakugan

Publisher:Braja M. Das, Nagaratnam Sivakugan

Chapter18: Pile Foundation

Section: Chapter Questions

Problem 18.7P

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