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Piles a

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Piles a

  1. 1. 4th Year Civil FOUNDATION ENGINEERING DEEP FOUNDATIONSApril 5, 2012 Deep Foundations 1
  2. 2. ‫‪DEEP FOUNDATIONS‬‬ ‫:‪TYPES OF DEEP FOUNDATIONS‬‬ ‫‪1- PILES‬‬ ‫الخوازيق‬ ‫‪2- CAISSONS‬‬ ‫القيسونات‬ ‫أساسات خلوية تنفذ بالتغويص والحفر‬ ‫‪3- PIERS‬‬ ‫الدعائم‬ ‫أساسات الكبارى وهى خوازيق ذات قطر كبير أو قواعد ذات حجم كبير يجفف داخلها‬ ‫‪4- PILLARS‬‬ ‫البار السكندرانى‬‫2102 ,5 ‪April‬‬ ‫‪Deep Foundations‬‬ ‫2‬
  3. 3. PILE FOUNDATIONS Piles are stiff members used to transmit surface loads to the bearing strata. ‫الخوازيق هى عناصر إنشائية جاسئة تنقل الحمل من سطح الرض إلى‬ .‫طبقة الرتكاز‬ Piles are classified to two categories according to the method of load transfer: :‫تنقسم الخوازيق من حيث طريقة نقلها للحمل إلى‬ 1- End Bearing Piles: ‫خوازيق ارتكاز‬ Tip point carries most of the load. ‫تنقل معظم الحمل عن طريق نقطة الرتكاز‬ 2- Friction Piles: ‫خوازيق احتكاك‬ Side friction carries most of the load. .‫تنقل معظم الحمل عن طريق الحتكاك السطحى مع التربة‬April 5, 2012 Deep Foundations 3
  4. 4. Pile Applications Very Large Concentrated Large Distributed Weight Weight Low Weight Soft toFirm Clay Dense SandApril 5, 2012 Strong Rock Deep Foundations 4
  5. 5. Piles are used in:1- Upper soil is weak, compressible, or could not support the surface loads.2- The loads are tension, horizontal, or inclined.3- Problematic soils; Swelling soils giving tension on the pile. Collapsing soils, adding down-drag forces on the pile.4- Scour under bridge piers. :‫تستخدم الخوازيق فى الحالت التالية‬ .‫1- عندما تكون التربة السطحية ضعيفة أو انضغاطية أو ل تستطيع تحمل الحمال السطيحة‬ .‫2- عندما تكون الحمال الناتجة عن المنشأ شد أو أفقية أو مائلة‬ .(‫3- عندما تكون التربة انتفاشية )تعطى شد على الخازوق( أو انهيارية )تعطى ضغط على الخازوق‬ .‫4- فى حالة النحر أسفل قواعد الكبارى‬April 5, 2012 Deep Foundations 5
  6. 6. Types of Pile Materials ‫أنواع المواد المستخدمة كخوازيق‬ Timber Steel Concrete Pre-cast Steel H Concrete Composite PipeTimber Steel Concrete ‫خشب‬ ‫حديد‬ ‫خرسانة مسلحة‬April 5, 2012 Deep Foundations 6
  7. 7. Timber Piles – ‫الخوازيق الخشبية‬ - Relatively inexpensive - ً ‫رخيصة نسبي‬ ‫ا‬ - Usually limited to short lengths. .‫- تقتصر غالب ً على الطوال الصغيرة‬ ‫ا‬ - Low capacity. .‫- قدرة تحمل منخفضة للحمال‬ - Advantages: Easy handling. Non-corrosive material. If permanently submerged then fairly resistant to decay. .‫- المميزات: سهولة النقل – ل تصدأ – يمكن دهانها لتلشى تآكلها مع الزمن‬ - Disadvantages: May require treatment to prevent decay, insects, and borers from damaging pile. Easily damaged during hard driving and inconvenient to splice. ‫- العيوب: تحتاج معالجة لتجنب التآكل – سهلة الكسر عن الدق – صعوبة نسبي ً فى‬ ‫ا‬ ‫الوصل‬April 5, 2012 Deep Foundations 7
  8. 8. Steel Piles – ‫الخوازيق الحديدية‬ - Advantages: high axial working capacity. Wide variety of sizes. Easy on-site modifications. Fairly easy to drive, minimal soil displacement, good penetration through hard materials (with shoe). ‫- المميزات: قدرة تحمل عاليه – مقاسات وقطاعات مختلفة – يمكن‬ ‫تعديلها فى الموقع – سهولة نسبية فى الدق – يمكن دقها فى طبقات‬ .‫التربة القوية باستخدام كعب‬ - Disadvantages: high cost, difficulty in delivery, relatively higher corrosion, noisy driving. ‫- العيوب: غالية الثمن – صعوبة فى النقل – تحتاج لمعالجات لمنع‬ .‫الصدأ – مزعجة فى عملية الدق‬April 5, 2012 Deep Foundations 8
  9. 9. Concrete Piles – ‫الخوازيق‬ ‫الخرسانية‬ - Advantages: High capacity, relatively inexpensive, usually durable and corrosion resistant in many environments (not marine). ‫المميزات: قدرة تحمل عالية – رخيصة نسبي ً – تقاوم العوامل‬ ‫ا‬ - .‫البيئية )عدوانية التربة أو المياه الجوفية( إل فى البحر‬ - Disadvantages: Handling, splicing, and transportation difficulties (for precast piles). Soil caving in cast insitu piles. ‫العيوب: النقل والوصل فى الخوازيق سابقة الصب – يمكن‬ - .‫حدوث اختناق فى قطاع الخازوق أثناء الصب‬April 5, 2012 Deep Foundations 9
  10. 10. End Bearing Piles – ‫خوازيق الرتكاز‬April 5, 2012 Deep Foundations 10
  11. 11. End bearing piles: Pile Load, P Transmit most of their loads to the load bearing layer (dense sand or rock). Most of the pile capacity inferred from the end bearing point. Side Friction ‫ينقل الجزء الكبر من الحمل عن‬ ‫طريق نقطة الرتكاز وهى‬ ‫الخوازيق التى ترتكز على الرمل‬ .‫الكثيف أو الصخر‬ End Bearing PbaseApril 5, 2012 Deep Foundations 11
  12. 12. Friction Piles – ‫خوازيق الحتكاك‬April 5, 2012 Deep Foundations 12
  13. 13. Friction Piles: Transmit most of their Pile Load, P load through the layers through which the piles pass, i.e., mostly through the surface friction with the surrounding soils. ‫ ينقل معظم الحمل عن طريق الحتكاك‬Side Friction ‫السطحى مثل الخوازيق المنفذة‬ .‫فى التربة الطينية الصرفة‬ End Bearing base PApril 5, 2012 Deep Foundations 13
  14. 14. PILE CAPACITY 1- Bearing capacity of piles from soil parameters: Static Formula Method (Qu = Qb + Qs) Qu = Ultimate Bearing Capacity Qs = fAs f = Unit Frictional Resistance Embedded AS = Shaft Area (Pile surface area) Length =D qb = Unit Bearing Capacity Ab = Area of Pile BaseApril 5, 2012 Qb = qbAb Deep Foundations 14
  15. 15. Base Resistance Qb = Ab [cbNc + Pob(Nq-1) + 0.5γBNγ + Pob] minus weight of pile, Wp but Wp ≈ Ab.Pob and as L >> B, 0.5γBNγ << Wp Qb and for φ > 0, Nq - 1 ≈ Nq Qb = Ab [cbNc + Pob Nq]April 5, 2012 Deep Foundations 15
  16. 16. Shaft Resistance Due to cohesion or friction or both As Cohesive component : Qsc = As . caFrictional component : Qsf = As .KHC Pob tan δ Pob KHC.Pob Qs = Qsc + Qsf = As [ca + KHC Pob tan δ ]April 5, 2012 Deep Foundations 16
  17. 17. Total Pile Resistance Qu = Qb + QsQu = Ab [cb Nc+Pob Nq] + As [ca + KHC Pob tan δ ]April 5, 2012 Deep Foundations 17
  18. 18. Piles in Sand Qu = Ab [cbNc+ PobNq] + As [ca + KHC Pob tan δ] Qu = Ab [ Pob Nq ] + As [ KHC Pob tan δ ] Qu = Ab Pob Nq + As KHc Pob tan δ δ = 20o for Steel = ¾ φ for Concrete = ¾ φ for TimberApril 5, 2012 Deep Foundations 18
  19. 19. Piles in Clay Qu = Ab [cbNc+ PobNq] + As [ca+ KHC Pob tan δ] Qu = Ab [cbNc] + As [ca] Q u = A b c bN c + As c aApril 5, 2012 Deep Foundations 19
  20. 20. Overburden Stress Pob Qu = [Ab Pob Nq] + [AsKHC Pob tan δ] Meyerhof Method : Pob = γz Vesic Method : critical depth, zc for z < zc : Pob = γz for z > zc : Pob = γzc zc/d is a function of φ after installation Suggested value = 20 dApril 5, 2012 Deep Foundations 20
  21. 21. Max Limit on End Bearing? Some suggest a limit on end bearing to match experience. Problems with that approach: more complex than that; need to consider both strength and compressibility of the soil friction angle varies with effective stress Over-consolidation causes changes in bearing capacityApril 5, 2012 Deep Foundations 21
  22. 22. Nq from the Egyptian Code Table (3): Nq Values Vs φ for Sand, Egyptian Code. o φ 25 30 35 40 Nq 15 30 75 150 Nc for Clay Nc = 9.0 for calculating the end bearing resistance of piles in clay.April 5, 2012 Deep Foundations 22
  23. 23. EXAMPLE Medium stiff clay: C = 30 kN/m2 Ca = 25 kN/m2Determine the allowable γ = 18 kN/m3 satcapacity for the concrete 12.00 mbored pile shown inFigure.Pile Diameter D = 0.50 mPile Length L = 14.0 m Dense Sand: φ = 40o 2.00 m γ sat = 19 kN/m3April 5, 2012 Nq = 150, KHC = 1.0 Deep Foundations 23
  24. 24. SOLUTION Side Friction: Qs = As [ca + K Pob tan δ ] HC qs in clay: 10.0 m qs-c = ca = 25 kN/m2 Lc = Qs-clay = ca [πDLc] 12.0 m = 25 [π*0.50*12.0] = 25 *18.85 = 471.25 kN qs in sand: qs-s = KHC Pob tan δ Ls = Critical depth 2.0 m Zc= 20 * 0.50 = 10.00 mApril 5, 2012 Deep Foundations 2 Pbo distribution
  25. 25. SOLUTIONδ = 3/4 φ = 30oQs-s = 1.0 * 80 * 0.578 = 46.24 kN/m2Qs-s = qs [πDLs] = 46.24 [π*0.50*2.0] = 145.27 kNTotal side friction:Qs = Qs-c + Qs-s = 471.25 + 145.27 = 616.52 kNEnd Bearing Resistance:qb = Pob Nq = 80 * 150 = 12000 kN/m2Qb = qb * Ab = qb * πD2 = 12000 * 0.196 = 2356.2 kNUltimate Pile Capacity = 616.52 + 2356.2 = 2973 kNApril 5, 2012 Deep Foundations 25
  26. 26. SOLUTIONUltimate Pile CapacityQult = 2973 kNAllowable Pile CapacityQall = Qult/F.S.Qall = 2973/3.0 = 991 kN = 99.10 ton Check of Concrete Capacity: Pc = fc (Ac + 1.14 * n * As) = 5000 (0.196 + 1.14 * 10 * 0.00196) = 5000 * (0.218) = 1090 kN = 109 ton > 99.10 (Qall-soil) (O.K.)April 5, 2012 Deep Foundations 26
  27. 27. Arrangement of Pile Groups The spacing between piles in a group can be assumed based on the following: 1- Driven piles need higher spacing than bored piles. 2- Friction piles need higher spacing than end bearing piles. 3- Minimum spacing (S) between piles is 2.5. 4- Maximum spacing (S) between piles is 8.0.April 5, 2012 Deep Foundations 27
  28. 28. 4 Piles 5 Piles SS S S 2 Piles 3 Piles S S 7 Piles S S 6 PilesApril 5, 2012 Deep Foundations S S 28
  29. 29. S S S S S S S 8 Piles 9 PilesApril 5, 2012 Deep Foundations 29

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