1. 4th Year Civil
FOUNDATION ENGINEERING
DEEP FOUNDATIONS
April 5, 2012 Deep Foundations 1
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 السكندرانى
2102 ,5 April Deep Foundations 2
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 التربة
April 5, 2012 Deep Foundations 3
4. Pile Applications
Very Large Concentrated
Large Distributed Weight
Weight
Low
Weight
Soft to
Firm Clay
Dense Sand
April 5, 2012 Strong Rock
Deep Foundations 4
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 الكبارى
April 5, 2012 Deep Foundations 5
6. Types of Pile Materials
أنواع المواد المستخدمة كخوازيق
Timber Steel Concrete Pre-cast
Steel H Concrete Composite
Pipe
Timber Steel Concrete
خشب حديد خرسانة مسلحة
April 5, 2012 Deep Foundations 6
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
الوصل
April 5, 2012 Deep Foundations 7
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 الدق
April 5, 2012 Deep Foundations 8
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 الصب
April 5, 2012 Deep Foundations 9
10. End Bearing Piles – خوازيق الرتكاز
April 5, 2012 Deep Foundations 10
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 Pbase
April 5, 2012 Deep Foundations 11
12. Friction Piles – خوازيق الحتكاك
April 5, 2012 Deep Foundations 12
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
P
April 5, 2012 Deep Foundations 13
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 Base
April 5, 2012 Qb = qbAb Deep Foundations 14
15. Base Resistance
Qb = Ab [cbNc + P'ob(Nq-1) + 0.5γBNγ + P'ob]
minus weight of pile, Wp
but Wp ≈ Ab.P'ob
and as L >> B, 0.5γBNγ << Wp
Qb
and for φ > 0, Nq - 1 ≈ Nq
Qb = Ab [cbNc + P'ob Nq]
April 5, 2012 Deep Foundations 15
16. Shaft Resistance
Due to cohesion or friction or both As
Cohesive component : Qsc = As . ca
Frictional component : Qsf = As .KHC P'ob tan δ
P'ob
KHC.P'ob
Qs = Qsc + Qsf = As [ca + KHC P'ob tan δ ]
April 5, 2012 Deep Foundations 16
17. Total Pile Resistance
Qu = Qb + Qs
Qu = Ab [cb Nc+P'ob Nq] + As [ca + KHC P'ob tan δ ]
April 5, 2012 Deep Foundations 17
18. Piles in Sand
Qu = Ab [cbNc+ P'obNq] + As [ca + KHC P'ob tan δ]
Qu = Ab [ P'ob Nq ] + As [ KHC P'ob tan δ ]
Qu = Ab P'ob Nq + As KHc P'ob tan δ
δ = 20o for Steel
= ¾ φ for Concrete
= ¾ φ for Timber
April 5, 2012 Deep Foundations 18
19. Piles in Clay
Qu = Ab [cbNc+ P'obNq] + As [ca+ KHC P'ob tan δ]
Qu = Ab [cbNc] + As [ca]
Q u = A b c bN c + As c a
April 5, 2012 Deep Foundations 19
20. Overburden Stress P'ob
Qu = [Ab P'ob Nq] + [AsKHC P'ob tan δ]
Meyerhof Method : P'ob = γ'z
Vesic Method : critical depth, zc
for z < zc : P'ob = γ'z
for z > zc : P'ob = γ'zc
zc/d is a function of φ after installation
Suggested value = 20 d
April 5, 2012 Deep Foundations 20
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 capacity
April 5, 2012 Deep Foundations 21
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. EXAMPLE Medium stiff clay:
C = 30 kN/m2
Ca = 25 kN/m2
Determine the allowable γ = 18 kN/m3
sat
capacity for the concrete 12.00 m
bored pile shown in
Figure.
Pile Diameter D = 0.50 m
Pile Length L = 14.0 m
Dense Sand:
φ = 40o 2.00 m
γ sat = 19 kN/m3
April 5, 2012
Nq = 150, KHC = 1.0
Deep Foundations 23
24. SOLUTION
Side Friction:
Qs = As [ca + K P'ob 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 P'ob tan δ Ls =
Critical depth 2.0 m
Zc= 20 * 0.50 = 10.00 m
April 5, 2012 Deep Foundations
2 P'bo distribution
26. SOLUTION
Ultimate Pile Capacity
Qult = 2973 kN
Allowable Pile Capacity
Qall = 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. 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. 4 Piles 5 Piles
S
S
S S
2 Piles 3 Piles S
S 7 Piles
S S
6 Piles
April 5, 2012 Deep Foundations S S 28
29. S
S
S
S S S S
8 Piles 9 Piles
April 5, 2012 Deep Foundations 29