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Session 17 – 18 PILE FOUNDATIONS

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

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Session 17 – 18 PILE FOUNDATIONS

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

  2. 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

  3. INTRODUCTION

  4. TYPES OF PILE FOUNDATION STEEL PILE

  5. TYPES OF PILE FOUNDATION CONCRETE PILE

  6. TYPES OF PILE FOUNDATION CONCRETE PILE

  7. TYPES OF PILE FOUNDATION

  8. TYPES OF PILE FOUNDATION WOODEN PILE

  9. TYPES OF PILE FOUNDATION • COMPOSITE PILE • COMBINATION OF: • STEEL AND CONCRETE • WOODEN AND CONCRETE • ETC

  10. PILE CATEGORIES Classification of pile with respect to load transmission and functional behaviour: • END BEARING PILES These piles transfer their load on to a firm stratumlocated 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.

  11. PILE CATEGORIES END BEARING PILE

  12. PILE CATEGORIES FRICTION PILE

  13. 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.

  14. 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.

  15. PILE CATEGORIES

  16. DETERMINATION OF PILE LENGTH

  17. BEARING CAPACITY OF PILE Two components of pile bearing capacity: • Point bearing capacity (QP) • Friction bearing capacity (QS)

  18. BEARING CAPACITY OF PILE

  19. 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

  20. POINT BEARING CAPACITYMEYERHOFF 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)

  21. POINT BEARING CAPACITYMEYERHOFF

  22. POINT BEARING CAPACITYMEYERHOF 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)

  23. POINT BEARING CAPACITYMEYERHOF 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

  24. POINT BEARING CAPACITYVESIC • 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

  25. POINT BEARING CAPACITYVESIC 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

  26. POINT BEARING CAPACITYVESIC 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:

  27. POINT BEARING CAPACITYJANBU QP = Ap (c.Nc* + q’.Nq*)

  28. POINT BEARING CAPACITYBORED 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)

  29. 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

  30. FRICTION RESISTANCESAND • 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)

  31. FRICTION RESISTANCECLAY • 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

  32. FRICTION RESISTANCECLAY -  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

  33. FRICTION RESISTANCECLAY -  METHOD FOR LAYERED SOIL

  34. FRICTION RESISTANCECLAY -  METHOD For cu 50 kN/m2   = 1

  35. FRICTION RESISTANCECLAY -  METHOD Where: v’= vertical effective stress  = K.tanR 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)

  36. FRICTION RESISTANCEBORED PILE Where: cu = mean undrained shear strength p = pile perimeter L = incremental pile length over which p is taken constant

  37. ULTIMATE AND ALLOWABLE BEARING CAPACITY DRIVEN PILE FS= 2.5 - 4 BORED PILE D < 2 m and with expanded at pile point no expanded at pile point

  38. 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 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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