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**Session 17 – 18 PILE FOUNDATIONS**

Course : S0484/Foundation Engineering Year : 2007 Version : 1/0 Session 17 – 18 PILE FOUNDATIONS

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PILE FOUNDATIONS Topic: Types of pile foundation Point bearing capacity of single pile Friction bearing capacity of single pile Allowable bearing capacity of single pile

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INTRODUCTION

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**TYPES OF PILE FOUNDATION**

STEEL PILE

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**TYPES OF PILE FOUNDATION**

CONCRETE PILE

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**TYPES OF PILE FOUNDATION**

CONCRETE PILE

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**TYPES OF PILE FOUNDATION**

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**TYPES OF PILE FOUNDATION**

WOODEN PILE

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**TYPES OF PILE FOUNDATION**

COMPOSITE PILE COMBINATION OF: STEEL AND CONCRETE WOODEN AND CONCRETE ETC

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**PILE CATEGORIES END BEARING PILES**

Classification of pile with respect to load transmission and functional behaviour: END BEARING PILES These piles transfer their load on to a firm stratum located at a considerable depth below the base of the structure and they derive most of their carrying capacity from the penetration resistance of the soil at the toe of the pile FRICTION PILES Carrying capacity is derived mainly from the adhesion or friction of the soil in contact with the shaft of the pile COMPACTION PILES These piles transmit most of their load to the soil through skin friction. This process of driving such piles close to each other in groups greatly reduces the porosity and compressibility of the soil within and around the groups.

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PILE CATEGORIES END BEARING PILE

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PILE CATEGORIES FRICTION PILE

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PILE CATEGORIES Classification of pile with respect to effect on the soil Driven Pile Driven piles are considered to be displacement piles. In the process of driving the pile into the ground, soil is moved radially as the pile shaft enters the ground. There may also be a component of movement of the soil in the vertical direction.

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**Classification of pile with respect to effect on the soil Bored Pile **

PILE CATEGORIES Classification of pile with respect to effect on the soil Bored Pile Bored piles(Replacement piles) are generally considered to be non-displacement piles a void is formed by boring or excavation before piles is produced. There are three non-displacement methods: bored cast- in - place piles, particularly pre-formed piles and grout or concrete intruded piles.

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PILE CATEGORIES

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**DETERMINATION OF PILE LENGTH**

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**BEARING CAPACITY OF PILE**

Two components of pile bearing capacity: Point bearing capacity (QP) Friction bearing capacity (QS)

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**BEARING CAPACITY OF PILE**

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**POINT BEARING CAPACITY**

For Shallow Foundation - TERZAGHI SQUARE FOUNDATION qu = 1,3.c.Nc + q.Nq + 0,4..B.N CIRCULAR FOUNDATION qu = 1,3.c.Nc + q.Nq + 0,3..B.N - GENERAL EQUATION Deep Foundation Where D is pile diameter, the 3rd part of equation is neglected due to its small contribution qu = qP = c.Nc* + q.Nq* + .D.N* qu = qP = c.Nc* + q’.Nq* ; QP = Ap .qp = Ap (c.Nc* + q’.Nq*) Nc* & Nq* : bearing capacity factor by Meyerhoff, Vesic and Janbu Ap : section area of pile

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**POINT BEARING CAPACITY MEYERHOFF**

PILE FOUNDATION AT UNIFORM SAND LAYER (c = 0) QP = Ap .qP = Ap.q’.Nq* Ap.ql ql = 50 . Nq* . tan (kN/m2) Base on the value of N-SPT : qP = 40NL/D 400N (kN/m2) Where: N = the average value of N-SPT near the pile point (about 10D above and 4D below the pile point)

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**POINT BEARING CAPACITY MEYERHOFF**

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**POINT BEARING CAPACITY MEYERHOF**

PILE FOUNDATION AT MULTIPLE SAND LAYER (c = 0) QP = Ap .qP Where: ql(l) : point bearing at loose sand layer (use loose sand parameter) ql(d) : point bearing at dense sand layer (use dense sand parameter) Lb = depth of penetration pile on dense sand layer ql(l) = ql(d) = 50 . Nq* . tan (kN/m2)

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**POINT BEARING CAPACITY MEYERHOF**

PILE FOUNDATION AT SATURATED CLAY LAYER (c 0) QP = Ap (c.Nc* + q’.Nq*) For saturated clay ( = 0), from the curve we get: Nq* = 0.0 Nc* = 9.0 and QP = 9 . cu . Ap

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**POINT BEARING CAPACITY VESIC**

BASE ON THEORY OF VOID/SPACE EXPANSION PARAMETER DESIGN IS EFFECTIVE CONDITION QP = Ap .qP = Ap (c.Nc* + o’.N*) WHERE: o’ = effective stress of soil at pile point Ko = soil lateral coefficient at rest = 1 – sin Nc*, N* = bearing capacity factors

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**POINT BEARING CAPACITY VESIC**

According to Vesic’s theory N* = f (Irr) where Irr = Reduced rigidity index for the soil Ir = Rigidity index Es = Modulus of elasticity of soil s = Poisson’s ratio of soil Gs = Shear modulus of soil = Average volumetric strain in the plastic zone below the pile point

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**POINT BEARING CAPACITY VESIC**

For condition of no volume change (dense sand or saturated clay): = 0 Ir = Irr For undrained conditon, = 0 The value of Ir could be estimated from laboratory tests i.e.: consolidation and triaxial Initial estimation for several type of soil as follow: Type of soil Ir Sand 70 – 150 Silt and clay (drained) 50 – 100 Clay (undrained) 100 – 200

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**POINT BEARING CAPACITY JANBU**

QP = Ap (c.Nc* + q’.Nq*)

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**POINT BEARING CAPACITY BORED PILE**

QP = . Ap . Nc . Cp Where: = correction factor = 0.8 for D ≤ 1m = 0.75 for D > 1m Ap = section area of pile cp = undrained cohesion at pile point Nc = bearing capacity factor (Nc = 9)

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**FRICTION RESISTANCE Where: p = pile perimeter**

L = incremental pile length over which p and f are taken constant f = unit friction resistance at any depth z

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**FRICTION RESISTANCE SAND**

Where: K = effective earth coefficient = Ko = 1 – sin (bored pile) = Ko to 1.4Ko (low displacement driven pile) = Ko to 1.8Ko (high displacement driven pile) v’ = effective vertical stress at the depth under consideration = soil-pile friction angle = (0.5 – 0.8)

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**FRICTION RESISTANCE CLAY**

Three of the presently accepted procedures are: method This method was proposed by Vijayvergiya and Focht (1972), based on the assumption that the displacement of soil caused by pile driving results in a passive lateral pressure at any depth. method (Tomlinson) method

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**FRICTION RESISTANCE CLAY - METHOD**

Where: v’= mean effective vertical stress for the entire embedment length cu = mean undrained shear strength ( = 0) VALID ONLY FOR ONE LAYER OF HOMOGEN CLAY

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**FRICTION RESISTANCE CLAY - METHOD**

FOR LAYERED SOIL

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**FRICTION RESISTANCE CLAY - METHOD**

For cu 50 kN/m2 = 1

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**FRICTION RESISTANCE CLAY - METHOD**

Where: v’= vertical effective stress = K.tanR R = drained friction angle of remolded clay K = earth pressure coefficient at rest = 1 – sin R (for normally consolidated clays) = (1 – sin R) . OCR (for overconsolidated clays)

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**FRICTION RESISTANCE BORED PILE**

Where: cu = mean undrained shear strength p = pile perimeter L = incremental pile length over which p is taken constant

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**ULTIMATE AND ALLOWABLE BEARING CAPACITY**

DRIVEN PILE FS= BORED PILE D < 2 m and with expanded at pile point no expanded at pile point

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EXAMPLE A pile with 50 cm diameter is penetrated into clay soil as shown in the following figure: NC clay = 18 kN/m3 cu = 30 kN/m2 R = 30o 5 m 20 m GWL OC clay (OCR = 2) = 19.6 kN/m3 cu = 100 kN/m2 R = 30o Determine: End bearing of pile Friction resistance by , , and methods Allowable bearing capacity of pile (use FS = 4)

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