The interesting observation in the Poulos-Davis-Randolph PDR design methodology for piled raft, but using a simple stiffness formula, the piled raft foundation can be designed and analyzed. It is observed that an increase in pile length leads to. Poulos, E. Corpus ID:

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William Lambe Robert V. William Lambe, Soil Mechanics by T. William Lambe and Robert V. Whitman, Soil Dynamics by Robert V. Poulos and E. Prin ciples from these basis disciplines are backed by experimen: tal evidence from laboratory and field investigations and from observations on actual structures.

Judgment derived from experience and engineering economics are central to soil enginzering. The books if tis series are intended primarily for use in university courses, at both the undergraduate end graduate levels, The editors also expect that all of the books will serve as valuable reference material for practicing engineers.

Wiliam Lambe and Robert V. Published simultaneously in Coad. Many excellent text books are concerned with the more practical aspects of pile foundations, such as the factors influencing the selection of the type of pile, the techniques of installation, and practical details of construction and maintenance of piles.

No attempt has been made to duplicate this type of inform. The aims of the present book are to 1. Present a consistent theoretical approach to the predic: tion of pile deformation end load capacity 2. Present parametric solutions for a wide cange of cases, 3. Demonstrate how such solutions can be used for design purposes, 4.

Review the applicability of these approaches to practi cal problems, In any theory, a certain amount of idealization is neces sary to obtain a tractable mathematical solution; this is especially so when dealing with problems involving sol. In dealing with the deformations of pile foundations i this book, we have generally considered the soll as an elastic material, with allowances made for pilesoil sip and soil yield where appropriate.

When used in this manner, with due discretion and a measure of engineering judgment, elastc-based theory has hhad considerable success in predicting the deformation of both shallow and deep foundations.

Although other simple soll models have also been successfully used for various aspects of pile analysis For example, the theory of subgrade reaction as applied to laterally loaded piles , elastic theory provides a unified basis for the analysis of all types of foundation; it also makes possible identification of the Parameters that exercise a significant influence on pile performance. Since elastic theory allows consideration of stress transmission through a mass, it can be used to analyze the Interaction between two or more piles and, therefore, to examine the behavior of groups of piles.

The behavior of piles under vertical loads Chapters 2. The behavior of piles under lateral Toading Chapters 7 and 8 and under combined vertical and lateral loading Chapter 3, The behavior of piled rafts Chapter 10 4, Piles subjected to vertical of lateral soil movements Chapters , 5. Miscellaneous topics such as pile buckling, dynamic loading, and pile load tests Chapters 4 to 16 Although the text deals with a relatively wide range of topics, it is by no means exhaustive, Furthermore, since geotechnical analysis is advancing ata very rapid rate, there may well be cases in which the analytical techniques we describe may have been superseded by more versatile methods capable of modeling real soil behavior more realistically.

Mattes, of the Elec: tricity Commission of New South Wales, who obtained a considerable number of the elastic solutions presented, Dr. R, Booker and Dr. Brown of the University of Sydney, who provided a great deal of assistance with various aspects of the theoretical analyses, Mr.

Wiesner, who obtsined some of the solutions presented in Chapter Grateful acknowledgement is given to Professor J. Roderick, former Head of the Department of Civil Engineering, who made the facilities of the Department available to us, to C.

Peiti, B. Crook, J. Papallo who prepared many of the diagrams. Poulos EH. Effects of Pile Driving ia Clays 2. Effects of Pile Driving in Sands Ultimate Load Capacity of Single Piles 3. Use of In-Situ Tests 3. Introduction 4. Typical Solutions from Wave Equation Analysis 4. Pile Stresses 4. Reliability of Wave Equation 4.

Theoretical Methods of Analysis 5. Theoretical Solutions for Settlement and Load Distribution 5. Determination of Soil Parameters SS. Empirical Correlations 5. Analysis of Group Settlement 6. Theoretical Solutions for Freestanding Groups 6.

Subgrade-Reaction Analysis Elastic Analysis for Single Piles 8. Determination of Soit Modulus 8. Simple Statical Analysis 9. Equivalent-Bent Method 9. Analysis of Single Battered Pile Analysis of Pile Groups 9. Introduction Lateral Load Tests Modern literature on piles can be said to date from the publication of Piles and Pile Driving, edited by Wellington of the Engineering News later to become the Engineering News-Record in in whick che widely known Engineering News pile-driving formula was proposed.

Since this frst atiempt ata theoret: ical assessment of the capacity of a pie, a great volume of field experience and empirical data on the performance of pile foundations has been published.

It can be imperfect because it is inadequate: that is, parts of the structure fail or deform excessively; in the present context, the design involws too few, too-slender, or too-short piles, But it can also be imperfect because it is more than adequate too many, oolong, or too-substantial piles and therefore is an excessively costly design, Design based on empiricism alone tends to focus attention on the former, because recorded experience gerierally only distinguishes between unsatis: factory and trouble-free pecformance and rarely between economical and uneconomical design.

Only by under- standing the behavior of the engineering structure in an analytical as well as empirical sense can engineers reason- ably expect to achieve designs that are neither inadequate inor overadequate.

In other words, to obtain the full benefit of experience of actual engineering behavior, it is important o fiave a sound theoretical understanding of the problem. In reality, for complicated structures, the load: on the foundations determine their movernent, but this movement affeots the loads imposed by the struc: ture; thete is inevitably, iteration between structure and foundation.

If an overall structural approach is to be successful, we need to know much more about a particular pile than that it can be classified as, say, a ton pile, We need to know its load-settlement behavior up 0 failure, possibly its behavior under lateral load and moment, and how its behavior is modified by adjacent piles.

This is analogous to saying that we need the complete load-deformation characteristics of beams and columns, not just their load capacities, before we can analyze complete. Most of this book is concerned with bringing the ana- lytical treatment of the losd-deformation and the failure behavior of pile foundation systems to the same level of sophistication as similar analytical treatments available for systems of structural frames.

Thus for vertical failure, the shear stress at the shaft-soil interface attains a limiting value possibly varying with depth and soil type , and for horizontal failure result ing from lateral load or moment, the normal stress at the interface attains a limiting value again, possibly varying with depth. This load can be taken as the answer if itis less than the um of the failure loads for the piles, calculated individually, Furthermore, the assumption of anything mote complicated than 4 linearly elastic material for the soil in the pile-soil contin- tuum situation would generally Jead to unduly complicated theory lacking useful generality.

That is, they have either been back- figured from field tests on piles in similar situations, or determined from laboratory tests employing stress changes similar to the average changes in the soil mass in the partic lar case. Alternatively, the elastic response can be assumed to be that of a series of unconnected springs, that is, a Winkler medium or the subgrade reaction assumption, In spite of what is said by some of the protagonists of this approach, it most Gundamentally be inferior to the elastic continuum approach of the Mindlin equations, since it ignores the very real interconnection among elements throughout the soil mass.

However, it does have the advantages of com. On the other hand, it can never take into account the important matter of interaction between adjacent pies, 1. Piles in soft clay are often driven to a stiffer stratum of sand, which may in turn overlie a different clay before encountering bedrock, Both the failure theory and the deformation theory should therefore be capable of coping with such changes in properties from layer to layer.

The modification cof the failure theory for this matter presents litle diff culty, but the modification of the deformation theory may require a number of simplifying assumptions. In complicated problems such as that of pile behavior, the engineering theory itself is often not fully rigorous, since approximations have to be made to obtain numerical answers even for the ideal situation.

Thus, there is a judge: ment to make about the extent to which a particular set of numerical answers is an accurate enough answer to the ideal problem. This judgement is largely the job of the research engineer. There is also a judgement to be made on the practical side, of the accuracy with which the idealized situation fits the real situation, This judgement is largely the job of the practicing engineer. It is important that the difference becween these judgements should be recognized and that they should never be made as one.

Foundations or deep cay OL ip, Oj. Furthermore, a high proportion of the settlement is inrecoverable, so that variations in load might produce further settlement. The single large-diameter pile and the fourpile group have similar behaviors and may even involve setilements that are more than satisfactorily small.

At the working load, the pile is carrying its full faluredoad but nevertheless succeeds in reducing the settlement well below that of the pad on its own, 2 Vertically Loaded Foundations on Clay over Gravel The cases of a surface pad footing and a pile driven to a stiff gravel base under the soft clay are illustrated in Fig 1.

Again, each foundation caries the same load and has the same factor of safety. The results of calculation ate given in Table 1. Foundations on cay over eave itis the strength of the concrete of the pile which deter- imines its diameter, rather than soil properties.

For more slender piles, the pro- portion of the load taken by the shaft can be even higher. In terms of installation method, piles may be classified as 2 Deiven piles, b Bored or castin-situ piles, c Driven and castinsitu piles a Screw pites, Detailed descrivsions of these methods and equipment used in installation may also be found in the above four references. Long-term phenomena of strength-regain in the sol, Some data is available on al the above effects, although the state of knowledge, particularly in relation to d , is gener- ally limited, 2.

Based fon the evidence from load tests to failure carried out on piles at different times after theic installation, it can be inferred that the undrained strength of a clay is initially decreased considerably because of driving, but that signif- icant regain of strength occurs with elapsed time between driving and pile testing.

Generally, it may be expected that the driving of piles into clay will initially cause some or even considerable loss in undrained strength of the clay because of remolding at constant water content.

Conceivably, there would be situations in which the consolidation was negative Le. Other than for thixotropic regain, the rate of increase of soil strength subsequent to pile driving is reluted to the rate of dissipation of excess pore pressure. Results of measurements of pore pressure at the pile face in many of these papers have revealed that the excess pore pressures may become equal to or even greater than the effective overburden stress.

However, the induced excess pore pressures decrease rapidly with distance from the pile and generally dissipate very rapidly A summary of some measurements of the variation with radial distance of the excess pore pressures around a single driven pile are given in Fig. Data presented by Aithart et al, suggests that near the pile tip, even greater pore pressures may be developed, amounting to 3 t0 4 times the insitu vertical effective stress.

The former method is based on an elastoplastic analysis, while the latter is an adaption of the theory of expansion of a cylindrical cavity in a mass for use with the measured undrained stress-strain behavior of a soil.

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## Pile foundation analysis and design

William Lambe Robert V. William Lambe, Soil Mechanics by T. William Lambe and Robert V. Whitman, Soil Dynamics by Robert V. Poulos and E. Prin ciples from these basis disciplines are backed by experimen: tal evidence from laboratory and field investigations and from observations on actual structures. Judgment derived from experience and engineering economics are central to soil enginzering.

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