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Fondasi II
Luthfi Hasan
Deep foundation
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Prospek Teknik Sipil
! Bidang Pembangunan Infrastruktur
" Konsultan
" Kontraktor
! Bidang Pemerintahan
" Departemen/Dinas P.U
" Departemen ESDM
" Dinas Tata Kota" Bapenas, Bapeda
" Dinas Ketenagakerjaan
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! Bidang Industri Enerji & Pertambangan
" Manajer & CEO
" Quality Auditor
"
Quality Assurace Manager" Pertamina, PLN, freeport, Pupuk Kaltim
! Bidang Pendidikan
" Pengajar
" Peneliti
! Bidang lainnya
" Perbankan
" Asuransi
Prospek Teknik Sipil
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Yang harus disiapkan
! Penguasaan materi Teknik Sipil
!
Kemampuan digital/komputer
! Kemampuan bahasa Inggris minimal pasif
!
Soft skill/organisasi
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Bidang Teknik Sipil
! Struktur
! Geoteknik
! Transportasi
! Sumber Daya Air
! Manajemen Konstruksi
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SUCCESS
maksimal
SKS
HadirKuliah &
aktif
Penguasaan materi
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Proporsi penilaian
Penilaian
35 % UTS
50 % UAS
15 % kehadiran ! 10 kali
Target
pencapaian
!
Mengetahui dasar fondasi dalam
!
Mampu mendesain fondasi dalam
( pile foundation)
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FOUNDATION ENGINEERING
(pile foundation)
Contents
! Pengertian Geotechnical Project
! Penentuan fondasi dangkal & dalam
! Jenis Pile foundations
! Mekanisme transfer beban pada pile foundations
! Pengertian kapasitas fondasi ( pile capacity )
!
Pile capacity di tanah non kohesif (sand )(end bearing & friction)
! Pile capacity di tanah kohesif (clay )
(end bearing & friction)
Part one :
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FOUNDATION ENGINEERING
(pile foundation)
Contents
! Pile capacity berdasarkan data CPT dan SPT
!
Pemancangan ( pile driving)! Uji beban ( pile load test )
! Pile groups
! Penurunan (settlement of pile groups)
! Bored piles
Part two :
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Main References
! Das, B.M. (2002). Principles ofGeotechnical Engineering, 5th edition,
Brooks/Cole Thomson Learning
! Das, B.M. (2004). Principles of FoundationEngineering, 5th edition, Brooks/Cole
Thomson Learning
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Part One
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Typical Geotechnical Project
construction site
Geo-Laboratory
~ for testing
Design Office
~ for design & analysissoil properties
Soil
mechanics
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Shallow & DeepFoundations
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FOUNDATION
load
Soil
Condition
Foundation
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Shallow Foundations
bed rock
firmground
~ for transferring building loads to underlying ground
~ mostly for firm soils or light loads
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Deep Foundations
bed rock
weak soil
P
I
L
E
~ for transferring building loads to underlying ground
~ mostly for weak soils or heavy loads
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Perbedaan F. Dangkal & F. Dalam
F. Dangkal F. Dalam
D/B Kecil Besar
KeruntuhanSampai
permukaan
tanah
Di dalam
tanah
Instalasi DigaliDipancang/
dibor
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Analisis jenis fondasi
B e b a n
Besar Kecil
L a p i s t a
n a h s t a b i l
D a l a m
D a n g k a l
FondasiDalam
FondasiDangkal
F. DalamF. Dangkal
F. Dalam
F. Dangkal
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Pile Foundations
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! Piles are relatively long and slender members used totransmit foundation loads through soil strata of low
bearing capacity to deeper soil or rock having a higher
bearing capacity.
! Pile resistance is comprised of
" end bearing
"
shaft friction
! For many piles only one of these components is
important. This is the basis of a simple classification
Pile Foundations
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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 astronger 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
Use of pile foundations
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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 basementmats 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 areusually 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 needpiles down to the
rock bed to transferthe loads directly tothe solid part in theearth to avoiduneven settlement
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Jembatan Suramadu
Total panjang jembatan 5438m
Cable Stayed 818mApproach CausewayApproachCauseway
Sisi Surabaya Sisi Madura
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PONDASI CABLE STAYED BRIDGE
56 Tiang
100 m
15 m
100 m
20 m
Diameter 2.4 m
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Sutong Bridge - China
1088m
60m
Pondasi:
Panjang = 130m
Diameter = 3.2m - 60m pertama
2.8m - sisanyaJumlah = 131 tiang
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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 SteelPipe
Timber Steel H Pre-castConcrete
Composite
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Steel piles!
Discription" Usual length 15-60 m
" Usual load 300-1200 kN
!
Advantages" Easy to handle with respect to cut off and extension to the
desired length
" Can stand high driving stress
" Can penetrate hard layers
" High load-carrying capacity
!
Disadvantages" Relatively costly
" High level of noise during driving
" Subject to corrosion
" H-piles may be damaged or deflected during driving throughhard layers
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Concrete piles
! Precast piles
" Using ordinary reinforcement
" Prestressed : using high-strength steelprestressing cable
! Cast-in-situ piles
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Concrete piles
!
Discription" Usual length 10-15m (press : 10-45m)
" Usual load 300-3000 kN (press : 7500-8500 kN)
!
Advantages
" Can be subjected to hard driving" Corrosion resistant
" Can be easily combined with a concrete superstructure
" High load-carrying capacity
!
Disadvantages
" Difficult to achieve proper cutoff
" Difficult to transport
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Steps in Rational Pile Selection
! Adequate Subsurface Investigation
! Soil Profile Development
! Appropriate Lab/Field Testing
! Selection of Soil Design Parameters
! Static Analysis
! Applied Experience
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Deep foundationtype
Typical range ofnominal (ultimate)resistance (kips)
Typical length(feet)
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
Load Magnitude
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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.
What is a Driven Pile?
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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
Driven pile(Precast pile)
Kualitas terjamin
Dynamic pile capacity
Pelaksanaan singkat
Displacement pile
Human error kecil
Vibrasi saat driving
Bored pile(cast insitu)
Tanpa vibrasiNon displacement pile
Kualitas perlu ketelitian
Non dynamic pile capacityPelaksanaan cukup lama
Human error relatif besar
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Type of piles based on installation
! Non displacement pile (bored pile)
! Displacement pile ( driven pile)
! Extra displacement pile ( franki ple)
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Pile capacity
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Embedded
Length= D
Qu = Ultimate Bearing Capacity
Qs = fAs
f = Unit FrictionalResistance
AS = Shaft Area
qP = Unit Bearing
Capacity
AP = Area of Point
QP = qPAP
Ultimate Bearing Capacity -
Static Formula Method (Qu = Qp + Qs)
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Qu = Qs+Qp
Layer 4
Layer 3
Layer 2
Layer 1L1 QS1
Qp
L2 QS2
L3 QS3
L4
QS4
Qu
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The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted.Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.
The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted.Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.
END BEARINGLOAD
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D
SANDS
SOFTCLAYS
ROCK
LOA
LOAD
L O A D
SANDS
CLAYS
FRICTION
L O A D
SANDS
CLAYS
SAND
End Bearing or Friction?
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End Bearing Side Friction Combined
Method of Support
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Mekanisme trasfer beban
! 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
! Tahanan ujung termobilisasi penuh jika telah terjadidisplacement sebesar
! 10-25% lebar/diameter tiang ……….B.M. Das
! 10-20% lebar/diameter tiang ……….Tomlinson
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Ultimate Bearing Capacity -
Static Formula Method
Embedded
Length= D
Qu = Ultimate Bearing Capacity
Qs = fAs
f = Unit FrictionalResistance
AS = Shaft Area
qP = Unit Bearing
Capacity
AP = Area of Point
QP = qPAP
Qu = Qp + Qs
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End Bearing Piles
ROCK
SOFT SOILPILES
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Friction Piles
SOFT SOILPILES
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 TipGround Surface
Arching Action
B
Df
$DfPO = %$Df
Zone of
Shear &VolumeDecrease
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! Combinations of vertical, horizontal and momentloading may be applied at the soil surface fromthe overlying structure
! For the majority of foundations the loads appliedto the piles are primarily vertical
! For piles in jetties, foundations for bridge piers,tall chimneys, and offshore piled foundations thelateral resistance is an important consideration
! The analysis of piles subjected to lateral andmoment loading is more complex than simplevertical loading because of the soil-structureinteraction.
Loads applied to Piles
V
M
H
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Estimation of Pile Capacity
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Tahapan desain
! Mengusahakan data tanah melalui soil investigation,berupa :
- Cone Penetration Test (CPT = Sondir)
- Standard Penetration Test (SPT)
- Boring (pengambilan sampel tanah)
!
Melakukan survei tentang kedalaman fondasi tiang padabangunan sekitarnya
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Tahapan desain (lanjutan)
!
Melakukan estimasi kapasitas fondasi tiang tunggalmenggunakan static formula, berdasarkan data:
- Cone Penetration Test (CPT)
- Standard Penetration Test (SPT)
- Hasil uji laboratorium
- Korelasi dari berbagai data diatas
!
Melakukan estimasi kelompok tiang berdasarkan hasilestimasi tiang tunggal dan beban kolom yang harus
ditahan
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Tahapan desain (lanjutan)
! Melaksanakan pile driving dengan menggunakandynamic formula berdasarkan estimasi nilai static
formula. Menentukan kapasitas tiang yang digunakan
! Melaksanakan pile load test bagi fondasi tiang yang
meragukan.
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Estimasi kapasitas tiang
)W(QQQ s pu !+=
ss p pu q.Aq.AQ +=
2
ss
1
p pall
SF
q.A
SF
q.AQ +=
Tahanan ujung end bearing)
Tahanan friksi (friction resistance)Unit daya dukung
Unit tahanan friksi
Angka keamanan untuk tahananujung
Angka keamanan untuk tahanan friksi
Qp
Qs
qp
qs
SF1
SF2
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Menghitung tahanan ujung (end bearing)
p p p q.AQ =
!!++= N..B.4,0 N N.c.3,1q q
_
cu q
!!++= N..B.3,0 N N.c.3,1q q
_
cu q
dsqdqsq
_
cdcscu F.F. N..B.5,0F.F. NqF.F. N.cq !!!!++=
Terzaghi
Square footing
Circular footing
Meyerhof
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Menghitung tahanan ujung (end bearing)
**q
_ *c p N.B. N. N.cq q
!!++=
Deep foundation
General equation
**q
*c N, N, N !
Bearing capacity factors
0 N.B. *
!" "Nilai B atau D kecil
*q
_ *c p N. N.cq q+=Sehingga :
) N. N.c(AQ *q
_ *c p p q+=
DAYA DUKUNG AKSIAL
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DAYA DUKUNG AKSIAL
Qu
= Qp
+ Qs
Qp
Qs ="2&r #l (% C)+ "2&r #l (k 'v tan()
. S . F Q
Q u all =
=Ap(c Nc +q Nq)
#l
'v
) 'v
Bearing Capacity Factors for Deep Foundations (Meyerhof, 1976)
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! "! #! $! %! %&
#
"
%
'
("!
#!
%!
'!
(!"!!
#!!
%!!
'!!
(!!
"!!!
) *
+
,-./ 12.34.-* )*5/67 8 9+65:
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Tahanan ujung tiang pada tanah pasir
Tanah pasir c = 0 , sehingga :
*q
_
p p N..AQ q=
Meyerhof ’s
Method :
! "= hq _
p p p q.AQ =
L=LB L
LB
Loose
Dense
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Tahanan ujung tiang pada tanah pasir
q p akan naik sejalan dengan naiknya LB dan akan maksimum pada :
critic
BB
D
L
D
L!"
#$%
&=
Dibawah (Lb/D)cr digunakan qp
Diatas (Lb/D)cr digunakan qp = qL (limit/batas)
L p*q
_
p p q.A N..AQ q !=Sehingga :
!= tan. N.50q *qL
!= tan. N.5q *qL
!= tan. N.1000q *qL
kN/m2
T/m2
lb/ft2
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Menghitung tahanan friksi (friction)
! "= f .L. pQsGeneral :
p = perimeter (keliling tiang)
#L = unit panjang tiang
*p. #L = luas selimut tiang
f =qs = unit tahanan friksi
!"= tan..K f '
v
K = Koefisien tekanan tanah
'’v = Tegangan efektif vertikal pada kedalaman yang
ditinjau, dianggap konstan setelah kedalaman 15D
(Meyerhof) atau 10D (Schmertmann)
( = Sudut gesek permukaan (tan( = µ)
DAYA DUKUNG AKSIAL
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DAYA DUKUNG AKSIAL
Qu = Qp + Qs
Qp
Qs = "2&r #l (k 'v tan()
. S . F Q
Q u all =
=Ap(c Nc +q Nq)
#l
'v
) 'v
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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-sin+
Nilai ( :
Interface (
Baja halus (0,5-0,7) +
Baja kasar (0,7-0,9) +
Precast concrete (0,8-1) +
Cast in place +
Nilai K dan (
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Menghitung tegangan effektif (' v )
'’v akan naik sejalan dengan kedalaman tiang
hingga mencapai kedalaman L’ = 15D (asumsi,
tergantung dari nilai +, Cc dan Dr), selanjutnya
konstan.
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Tahanan ujung tiang pada clay (lempung)
) N. N.c(AQ *q
_ *c p p q+=
Tanah lempung : + = 0 ; kecil Nq q
_
! 9 Nc =
u p p c.9.AQ =
cu = undrained cohesion
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Menghitung tahanan friksi (friction)
Banyak metoda diperkenalkan untuk mencari tahanan
friksi pada lempung : Metoda %, metoda , dan metoda -
Metoda % uu S.c.f !=!=
f = unit friksi ; % = adhesion factor ;
cu = undrained cohesion ; Su= undrained strength
% dicari dengan beberapa cara, yang banyak digunakan
adalah API (American Petroleum Institute, 1981) dan
Randolph & Murphy (1985)
DAYA DUKUNG AKSIAL
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DAYA DUKUNG AKSIAL
Qu = Qp + Qs
Qp
Qs ="2&r #l (% c)
. S . F Q
Q u all =
=Ap.c Nc
#l
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Faktor penentu nilai%
! Konsolidasi tanah selama pelaksanaan
!
Dragdown lapisan diatasnya saat pemancangan
! Cara mendapatkan Su atau cu
! Tipe instalasi fondasi tiang
Menentukan %
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Menentukan %
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Nilai undrained shear strength (Su) :
C l a y 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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