FOUNDATION ENGINEERING
Pile Foundation
Luthfi Hasan
Geotechnical expert
Reg : 1.2.500.2.31.09.03.02978
Hadir
maksimal
Kuliah &
SKS
aktif
SUCCESS
Reg : 1.2.500.2.31.09.03.02978
Proporsi penilaian
35 % UTS
Penilaian 50 % UAS
15 % kehadiran ≥ 10 kali
p Mengetahui dasar fondasi dalam
Target p Mampu mendesain fondasi dalam
pencapaian (pile foundation)
Reg : 1.2.500.2.31.09.03.02978
FOUNDATION ENGINEERING
(pile foundation)
Contents
Part one :
p Pengertian Geotechnical Project
p Penentuan fondasi dangkal & dalam
p Jenis Pile foundations
p Mekanisme transfer beban pada pile foundations
p Pengertian kapasitas fondasi (pile capacity)
p Pile capacity di tanah non kohesif (sand)
(end bearing & friction)
Reg : 1.2.500.2.31.09.03.02978
FOUNDATION ENGINEERING
(pile foundation)
Contents
Part two :
p Pile capacity di tanah kohesif (clay)
(end bearing & friction)
p Pile capacity berdasarkan data CPT dan SPT
p Pemancangan (pile driving)
p Uji beban (pile load test)
p Group piles
p Penurunan (settlement of group piles)
p Bored piles
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Main References
p Das, B.M. (2002). Principles of
Geotechnical Engineering, 5th edition,
Brooks/Cole Thomson Learning
p Das, B.M. (2004). Principles of Foundation
Engineering, 5th edition, Brooks/Cole
Thomson Learning
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Part One
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Typical Geotechnical Project
Geo-Laboratory Design Office
soil properties
~ for testing ~ for design & analysis
construction site Reg : 1.2.500.2.31.09.03.02978
Shallow & Deep
Foundations
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FOUNDATION
load
Foundation
Soil
Condition
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Shallow Foundations
~ for transferring building loads to underlying ground
~ mostly for firm soils or light loads
firm
ground
bed rock
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Deep Foundations
~ for transferring building loads to underlying ground
~ mostly for weak soils or heavy loads
P
I
L
weak soil E
bed rock Reg : 1.2.500.2.31.09.03.02978
Perbedaan F. Dangkal & F. Dalam
F. Dangkal F. Dalam
D/B Kecil Besar
Sampai
Di dalam
Keruntuhan permukaan
tanah
tanah
Dipancang/
Instalasi Digali
dibor
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Analisis jenis fondasi
Beban
Besar Kecil
Dalam
Fondasi F. Dalam
Lapis tanah stabil
Dalam F. Dangkal
Dangkal
F. Dalam Fondasi
F. Dangkal Dangkal
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Shallow Foundations
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Pile Foundations
p Piles are relatively long and slender members used to
transmit foundation loads through soil strata of low
bearing capacity to deeper soil or rock having a higher
bearing capacity.
p Pile resistance is comprised of
n end bearing
n shaft friction
p For many piles only one of these components is
important. This is the basis of a simple classification
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Use of pile foundations
When one or more upper soil layers are highly
compressible and too weak to support the load
transmitted by the superstructure. Piles are used to
transmit the load to underlying bedrock or a
stronger soil layer
When bedrock is not encountered at a reasonable depth
below the ground surface, piles are used to transmit the
structural load to the soil gradually. The resistance to the
applied structural load is derived mainly from the
frictional resistance developed at the soil-pile interface
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Use of pile foundations
When subjected to horizontal forces, pile
foundation resist by bending , while still
supporting the vertical load transmitted by the
superstructure
The foundations of some structures, such as
transmission towers, offshore platforms and basement
mats below the water table, are subjected to uplifting
forces. Piles are sometimes used for these foundations
to resist the uplifting force
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Use of pile foundations
Bridge abutments and piers are usually are
usually constructed over pile foundations to
avoid the loss of bearing capacity that a
shallow foundation might suffer because of
soil erosion at the ground surface
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Deep Foundations
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Pile foundation
Tall buildings need
piles down to the
rock bed to transfer
the loads directly to
the solid part in the
earth to avoid
uneven settlement
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Jembatan Suramadu
Sisi Surabaya Sisi Madura
Total panjang jembatan 5438m
Cable Stayed 818m
Causeway Approach Approach Causeway
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PONDASI CABLE STAYED BRIDGE
20 m 15 m
100 m 100 m
56 Tiang
Diameter 2.4 m
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Sutong Bridge - China
1088m
60m
Pondasi:
Panjang = 130m
Diameter = 3.2m - 60m pertama
2.8m - sisanya
Jumlah = 131 tiang Reg : 1.2.500.2.31.09.03.02978
Piled Foundations
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Pile
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Jembatan Cikubang
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Jembatan Suramadu
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Ciujung
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Type of Pile Foundations
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Types of Piles
Concrete Steel Timber Steel H Pre-cast Composite
Pipe Concrete
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Steel piles
p Discription
n Usual length 15-60 m
n Usual load 300-1200 kN
p Advantages
n Easy to handle with respect to cut off and extension to the
desired length
n Can stand high driving stress
n Can penetrate hard layers
n High load-carrying capacity
p Disadvantages
n Relatively costly
n High level of noise during driving
n Subject to corrosion
n H-piles may be damaged or deflected during driving through
hard layers
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Concrete piles
p Precast piles
n Using ordinary reinforcement
n Prestressed : using high-strength steel
prestressing cable
p Cast-in-situ piles
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Concrete piles
p Discription
n Usual length 10-15m (press : 10-45m)
n Usual load 300-3000 kN (press : 7500-8500 kN)
p Advantages
n Can be subjected to hard driving
n Corrosion resistant
n Can be easily combined with a concrete superstructure
n High load-carrying capacity
p Disadvantages
n Difficult to achieve proper cutoff
n Difficult to transport
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Steps in Rational Pile Selection
p Adequate Subsurface Investigation
p Soil Profile Development
p Appropriate Lab/Field Testing
p Selection of Soil Design Parameters
p Static Analysis
p Applied Experience
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Load Magnitude
Typical range of
Deep foundation Typical length
nominal (ultimate)
type (feet)
resistance (kips)
Timber pile 75 – 200 20 – 40
Concrete pile 200 – 2,000 20 – 150
Steel H-pile 200 – 1,000 20 – 160
Pipe pile 175 – 2,500 20 – 100
Drilled shaft 750 – 10,000 20 – 160
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What is a Driven Pile?
A Driven Pile is a deep
foundation that is constructed
by driving a concrete, steel or
timber pile to support the
anticipated loads in competent
subsurface material.
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Driven Low Displacement Piles
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Driven High Displacement Piles
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Drilled Shafts (bored piles)
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Driven & Bored Pile
Jenis Keunggulan Kekurangan
Kualitas terjamin
Dynamic pile capacity
Driven pile
Pelaksanaan singkat Vibrasi saat driving
(Precast pile)
Displacement pile
Human error kecil
Kualitas perlu ketelitian
Bored pile Tanpa vibrasi Non dynamic pile capacity
(cast insitu) Non displacement pile Pelaksanaan cukup lama
Human error relatif besar
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Type of piles based on installation
p Non displacement pile (bored pile)
p Displacement pile ( driven pile)
p Extra displacement pile ( franki ple)
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Pile capacity
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Ultimate Bearing Capacity -
Static Formula Method (Qu = Qp + Qs)
Qu = Ultimate Bearing Capacity
Qs = fAs
f = Unit Frictional
Embedded Resistance
=D
Length AS = Shaft Area
qP = Unit Bearing
Capacity
AP = Area of Point
QP = qPAP
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Qu
ΔL1 QS1 Layer 1
ΔL2 QS2 Layer 2
ΔL3 QS3 Layer 3
Qu = ΣQs+Qp
ΔL4 Layer 4
QS4
Qp
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End Bearing or Friction?
END BEARING FRICTION
LOAD LOAD
SANDS SANDS
SANDS
L L
L
O O
O
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A A
A
D D
D
SOFT CLAYS
CLAYS
CLAYS
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ROCK SAND
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Method of Support
End Bearing Side Friction Combined
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Mekanisme trasfer beban
p Tahanan friksi (gesekan permukaan) termobilisasi penuh
jika telah terjadi displacement sebesar :
● 5-10 mm (0,2-0,3 inch)……………..B.M. Das
● 0,30 – 1% lebar/diameter tiang …..Tomlinson
p Tahanan ujung termobilisasi penuh jika telah terjadi
displacement sebesar
● 10-25% lebar/diameter tiang ……….B.M. Das
● 10-20% lebar/diameter tiang ……….Tomlinson
Reg : 1.2.500.2.31.09.03.02978
Ultimate Bearing Capacity -
Static Formula Method
Qu = Ultimate Bearing Capacity
Qu = Qp + Qs
Qs = fAs
f = Unit Frictional
Embedded Resistance
=D
Length AS = Shaft Area
qP = Unit Bearing
Capacity
AP = Area of Point
QP = qPAP
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End Bearing Piles
PILES SOFT SOIL
ROCK
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Friction Piles
PILES SOFT SOIL
Strength
increases
with depth
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Mekanisme keruntuhan
Terzaghi Meyerhof Vesic Skempton
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Luthfi Hasan (1998)
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Arching at Pile Tip
Ground Surface
Arching Action D
f
Zone of
Shear & PO = αγDf γDf
Volume
Decrease
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Loads applied to Piles
M
V
p Combinations of vertical, horizontal and moment
H
loading may be applied at the soil surface from
the overlying structure
p For the majority of foundations the loads applied
to the piles are primarily vertical
p For piles in jetties, foundations for bridge piers,
tall chimneys, and offshore piled foundations the
lateral resistance is an important consideration
p The analysis of piles subjected to lateral and
moment loading is more complex than simple
vertical loading because of the soil-structure
interaction.
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Estimation of Pile Capacity
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Tahapan desain
p Mengusahakan data tanah melalui soil investigation,
berupa :
- Cone Penetration Test (CPT = Sondir)
- Standard Penetration Test (SPT)
- Boring (pengambilan sampel tanah)
p Melakukan survei tentang kedalaman fondasi tiang pada
bangunan sekitarnya
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Tahapan desain (lanjutan)
p Melakukan estimasi kapasitas fondasi tiang tunggal
menggunakan static formula, berdasarkan data:
- Cone Penetration Test (CPT)
- Standard Penetration Test (SPT)
- Hasil uji laboratorium
- Korelasi dari berbagai data diatas
p Melakukan estimasi kelompok tiang berdasarkan hasil
estimasi tiang tunggal dan beban kolom yang harus
ditahan
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Tahapan desain (lanjutan)
p Melaksanakan pile driving dengan menggunakan
dynamic formula berdasarkan estimasi nilai static
formula. Menentukan kapasitas tiang yang digunakan
p Melaksanakan pile load test bagi fondasi tiang yang
meragukan.
Reg : 1.2.500.2.31.09.03.02978
Estimasi kapasitas tiang
Q u = Q p + Qs − ( W )
Q u = A p .q p + A s .q s
A p .q p As .q s
Qall = +
SF1 SF2
Qp Tahanan ujung end bearing)
Qs Tahanan friksi (friction resistance)
qp Unit daya dukung
qs Unit tahanan friksi
SF1 Angka keamanan untuk tahananujung
SF2 Angka keamanan untuk tahanan friksi
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Menghitung tahanan ujung (end bearing)
Q p = A p .q p
Terzaghi
_
q u = 1,3.c.N c + q N q + 0,4.B.γ.N γ Square footing
_
q u = 1,3.c.N c + q N q + 0,3.B.γ.N γ Circular footing
Meyerhof
_
q u = c.N c .Fcs .Fcd + q N q .Fqs .Fqd + 0,5.B.γ.N γ .Fγs .Fγd
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Menghitung tahanan ujung (end bearing)
Deep foundation
_
General equation q p = c.N*c + q .N*q + γ.B.N*γ
N*c , N*q , N*γ Bearing capacity factors
Nilai B atau D kecil γ.B.N*γ ≈ 0
_
*
q
Sehingga : p = c.N c + q .N*q
_
* *
Q p = A p (c.N c + q .N q )
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DAYA DUKUNG AKSIAL
Qu = Qp + Qs
Qs =Σ2πr Δl (α C)
+ Σ2πr Δl (k σv tanδ)
Δl Qu
Qall =
κ σv F.S.
σv
Qp =Ap(c Nc +q Nq)
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Bearing Capacity Factors for Deep Foundations (Meyerhof, 1976)
1000
800
600
400
200
100
80
60
40
and
20
10
8
6
4
1
0 10 20 30 40 45
S oil
friction
a ngle,
Ø
(deg)
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Tahanan ujung tiang pada tanah pasir
Tanah pasir c = 0 , sehingga : Q p = A p .q p
_ _
Q p = A p . q .N*q q = ∑ γh
Meyerhof s
Method :
Loose
L=LB
L
LB Dense
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Tahanan ujung tiang pada tanah pasir
qp akan naik sejalan dengan naiknya LB dan akan maksimum pada :
L B ⎛ L B ⎞
= ⎜ ⎟
D ⎝ D ⎠critic
Dibawah (Lb/D)cr digunakan qp
Diatas (Lb/D)cr digunakan qp = qL (limit/batas)
_
Sehingga : Q p = A p . q .N*q ≤ A p .q L
q L = 50.N*q . tan φ kN/m2
q L = 5.N*q . tan φ T/m2
q L = 1000.N*q . tan φ lb/ft2
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Cases
Case-1
Kedalaman tiang 305x305 mm adalah 12 m. Tanah pasir homogen dengan
γb=16,8 kN/m3, φ = 35o. Hitung nilai tahanan ujung tiang (Qp) dengan cara
Meyerhof
Case-2
γb=15,7 kN/m3
5m loose φ = 30o Dimensi fondasi : 309 X 309 mm2
∇
⊆ c=0
Hitunglah : Qp
γsat=18,1 kN/m3
13 m
loose φ = 30o
c=0
γsat=19,4 kN/m3
4m
dense φ = 40o
c=0
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Menghitung tahanan friksi (friction)
General : Qs = ∑ p.ΔL.f
p = perimeter (keliling tiang)
ΔL = unit panjang tiang
∑p. ΔL = luas selimut tiang
f =qs = unit tahanan friksi
f = K.σ'v . tan δ
K = Koefisien tekanan tanah
σ v = Tegangan efektif vertikal pada kedalaman yang
ditinjau, dianggap konstan setelah kedalaman 15D
(Meyerhof) atau 10D (Schmertmann)
δ = Sudut gesek permukaan (tanδ = µ)
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DAYA DUKUNG AKSIAL
Qu = Qp + Qs
Qs = Σ2πr Δl (k σ tanδ)
v
Δl Qu
Qall =
κ σv F.S.
σv
Qp =Ap(c Nc +q Nq)
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Nilai K dan δ
Nilai K :
Metoda instalasi K
Tiang pancang, displacement besar (1-2)Ko
Tiang pancang, displacement kecil (0,75-1,75)Ko
Bored pile (0,75-1)Ko
Ko = 1-sinφ
Nilai δ :
Interface δ
Baja halus (0,5-0,7) φ
Baja kasar (0,7-0,9) φ
Precast concrete (0,8-1) φ
Cast in place φ
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Menghitung tegangan effektif (σv )
σ v akan naik sejalan dengan kedalaman tiang
hingga mencapai kedalaman L = 15D (asumsi,
tergantung dari nilai φ, Cc dan Dr), selanjutnya
konstan.
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Case-3
γb=15,7 kN/m3
5m loose φ = 30o Dimensi fondasi = 400X400 mm ,
∇
⊆ c=0
K = 1-sin φ , δ = 0,6 φ
γsat=18,1 kN/m3
13 m φ = 30o Hitung tahanan friksi tiang (Qs).
loose
c=0
γsat=19,4 kN/m3
4m
dense φ = 40o
c=0
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Tahanan ujung tiang pada clay (lempung)
_
Q p = A p (c.N*c + q .N*q )
_
Tanah lempung : φ = 0 ; q N q ≈ kecil Nc = 9
Q p = A p .9.c u
cu = undrained cohesion
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Menghitung tahanan friksi (friction)
Banyak metoda diperkenalkan untuk mencari tahanan
friksi pada lempung : Metoda α, metoda λ dan metoda β
Metoda α
f = α.cu = α.Su
f = unit friksi ; α = adhesion factor ;
cu = undrained cohesion ; Su= undrained strength
α dicari dengan beberapa cara, yang banyak digunakan
adalah API (American Petroleum Institute, 1981) dan
Randolph & Murphy (1985)
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DAYA DUKUNG AKSIAL
Qu = Qp + Qs
Qs =Σ2πr Δl (α c)
Δl Qu
Qall =
F.S.
Qp =Ap.c Nc
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Faktor penentu nilai α
p Konsolidasi tanah selama pelaksanaan
p Dragdown lapisan diatasnya saat pemancangan
p Cara mendapatkan Su atau cu
p Tipe instalasi fondasi tiang
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Menentukan α
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Menentukan α
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Nilai undrained shear strength (Su) :
Clay Su (kPa) Su (kg/cm2)
Very soft 0-12 0-0,12
Soft 12-24 0,12-0,24
Medium 24-48 0,24-0,48
Stiff 48-96 0,48-0.96
Very stiff 96-192 0,96-1,92
Hard > 192 > 1,92
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Case-4
5m cu =30 kN/m2
∇ γ = 18kN/m3
⊆
5m cu =30 kN/m2
γsat = 19,2 kN/m3 Hitung :
Kapasitas tiang ijin (Qall)
Jika diamater tiang 315 mm
cu =100 kN/m2
20m dan FS = 4
γsat = 19,8 kN/m3
5m
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