Piles a

4th Year Civil

FOUNDATION ENGINEERING

DEEP FOUNDATIONS

April 5, 2012 Deep Foundations 1

‫‪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

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

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

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

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

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

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


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

End Bearing Piles – ‫خوازيق الرتكاز‬


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

Friction Piles – ‫خوازيق الحتكاك‬


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


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

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]

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 ]

Total Pile Resistance

Qu = Qb + Qs

Qu = Ab [cb Nc+P'ob Nq] + As [ca + KHC P'ob tan δ ]


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

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


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

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


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.

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

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

SOLUTION
δ = 3/4 φ = 30o
Qs-s = 1.0 * 80 * 0.578 = 46.24 kN/m2
Qs-s = qs [πDLs]
= 46.24 [π*0.50*2.0] = 145.27 kN
Total side friction:
Qs = Qs-c + Qs-s = 471.25 + 145.27 = 616.52 kN
End Bearing Resistance:
qb = P'ob Nq = 80 * 150 = 12000 kN/m2
Qb = qb * Ab = qb * πD2 = 12000 * 0.196
= 2356.2 kN
Ultimate Pile Capacity = 616.52 + 2356.2 = 2973 kN

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.)

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.


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

S
S

S
S S S S
8 Piles 9 Piles


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