CHAPTER 15 - DEEP FOUNDATION I - PILE FOUNDATION

Oct 13, 2026

Chapter 15 introduces deep foundation design with a focus on pile foundations. It explains when shallow foundations are unsuitable due to weak or swelling near-surface soils, requiring transfer of structural loads to deeper firm strata. The chapter describes piles as long slender columns (driven, bored, or cast-in-situ) subjected to vertical and lateral forces, and distinguishes drilled piers from small-diameter bored piles. It then classifies piles by length-to-diameter ratio, orientation, composition (timber, concrete, steel), and by method of installation (driven vs cast-in-situ).

LanguageEnglish

CategoryGeneral

FormatPDF

Pages94

Reading Time33 min

AccessFree to download

15.1 Introduction

15.2 Classification of Piles

15.3 Types of Piles According to the Method of Installation

# CHAPTER 15 DEEP FOUNDATION I:PILE FOUNDATION ## 15.1 INTRODUCTION Shallow foundations are normally used where the soil close to the ground surface and up to thezone of significant stress possesses sufficient bearing strength to carry the superstructure loadwithout causing distress to the superstructure due to settlement.However,where the top soil iseither loose or soft or of a swelling type the load from the structure has to be transferred to deeperfirm strata. The structural loads may be transferred to deeper firm strata by means of piles.Piles are longslender columns either driven,bored or cast-in-situ.Driven piles are made of a variety of materialssuch as concrete,steel,timber etc.,whereas cast-in-situ piles are concrete piles.They may besubjected to vertical or lateral loads or a combination of vertical and lateral loads.If the diameter ofa bored-cast-in-situ pile is greater than about 0.75m,it is sometimes called a drilled pier,drilledcaisson or drilled shaft.The distinction made between a small diameter bored cast-in-situ pile (lessthan 0.75m)and a larger one is just for the sake of design considerations.The design of drilledpiers is dealt with in Chapter 17.This chapter is concerned with driven piles and small diameterbored cast-in-situ piles only. ## 15.2 CLASSIFICATION OF PILES Piles may be classified as long or short in accordance with the Lld ratio of the pile(whereL=length,d=diameter of pile).A short pile behaves as a rigid body and rotates as a unit underlateral loads.The load transferred to the tip of the pile bears a significant proportion of the totalvertical load on the top.In the case of a long pile,the length beyond a particular depth loses itssignificance under lateral loads,but when subjected to vertical load,the frictional load on the sidesof the pile bears a significant part to the total load. Copyright @Marcel Dekker,Inc.All rights reserved Piles may further be classified as vertical piles or inclined piles.Vertical piles are normallyused to carry mainly vertical loads and very little lateral load.When piles are inclined at an angleto the vertical,they are called batter piles or raker piles.Batter piles are quite effective for takinglateral loads,but when used in groups,they also can take vertical loads.The behavior of verticaland batter piles subjected to lateral loads is dealt with in Chapter 16. Types of Piles According to Their Composition Piles may be classified according to their composition as 1.Timber Piles, 2.Concrete Piles, 3.Steel Piles. Timber Piles:Timber piles are made of tree trunks with the branches trimmed off.Such piles shallbe of sound quality and free of defects.The length of the pile may be 15m or more.If greaterlengths are required,they may be spliced.The diameter of the piles at the butt end may vary from30 to 40 cm.The diameter at the tip end should not be less than 15 cm. Piles entirely submerged in water last long without decay provided marine borers are notpresent.When a pile is subjected to alternate wetting and drying the useful life is relatively shortunless treated with a wood preservative,usually creosote at 250 kg per m³for piles in fresh waterand 350 kg/m³in sea water. After being driven to final depth,all pile heads,treated or untreated,should be sawed squareto sound undamaged wood to receive the pile cap.But before concrete for the pile cap is poured,thehead of the treated piles should be protected by a zinc coat,lead paint or by wrapping the pile headswith fabric upon which hot pitch is applied. Driving of timber piles usually results in the crushing of the fibers on the head (or brooming)which can be somewhat controlled by using a driving cap,or ring around the butt. The usual maximum design load per pile does not exceed 250 kN.Timber piles are usuallyless expensive in places where timber is plentiful. Concrete Piles.Concrete piles are either precast or cast-in-situ piles.Precast concrete pilesare cast and cured in a casting yard

FAQs

When are pile foundations required instead of shallow foundations?

Pile foundations are required when near-surface soil lacks sufficient bearing strength or is loose, soft, or of a swelling type, so loads must be transferred to deeper firm strata.

How are piles classified by length-to-diameter ratio?

Piles are classified as long or short based on the L/d ratio. Short piles behave as rigid bodies under lateral loads, while long piles transfer significant vertical load through side friction under vertical loading.

What are the main composition types of piles discussed?

The chapter classifies piles by composition into timber piles, concrete piles (precast or cast-in-situ), and steel piles (H-shaped or pipe piles).

What installation methods are used to define pile types?

According to installation method, piles are grouped into driven piles, cast-in-situ piles, and driven plus cast-in-situ piles.

Oct 13, 2026

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