foundation design: shallow and deep foundation
TRANSCRIPT
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Dr. Ir. Pintor Tua Simatupang, MT.Sekretaris Jenderal
FOUNDATION DESIGN:Shallow and Deep Foundation
HIMPUNAN AHLI TEKNIK TANAH INDONESIA(HATTI)
HATTI Mengajar
17 Juli 2021
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Materi Bahasan
1. Pengumpulan Data2. Teknik Fondasi3. Desain Fondasi Dangkal4. Desain Fondasi Dalam5. Verifikasi Desain
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1. PENGUMPULAN DATA
1.1 Informasi untuk Desain– Deskripsi proyek– Penyelidikan tanah di lapangan– Uji laboratorium
1.2 Klasifikasi Tanah1.3 Desain Muka Air1.4 Parameter desain
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● Soil boring - SPT (Standard Penetration Test) N-SPT & Undisturbed sampling (UDS)
●Mechanical CPT (Cone Penetration Test) /Sondir qc, friction ratio > jenis tanah
● Pengukuran muka air tanah (Piezometer)● Pressuremeter test● Vane Shear test (Su soft clay)
Penyelidikan Tanah di Lapangan
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Lokasi dan Frekuensi Penyelidikan Tanah
31.0036.95
R1 R3R2
38.20 38.2031.00
R4R4
43.20
R5R3
38.20 36.95
R2R5
38.20
R1
66
32
26
3016
8088
36
2927
50
3334
45
912
32
546260
3933
50
1826
21
90
8610106
BT-1
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Uji Laboratorium
– Index propertiesSieve analysis, berat jenis, specific gravity, water content, Atterberg limit (PL & LL)
– Kuat geser tanah (Su, c, φ) – Parameter konsolidasi untuk tanah kohesif
(pc, e0, Cc, Cr)
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Contoh Hasil Test Laboratorium
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Contoh variasi parameter tanah
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1.2 Klasifikasi Tanah
• Berdasarkan pengamatan visual saat boring test• Berdasarkan tes laboratorium Sieve analysis
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1.2 Klasifikasi Tanah Atterberg limit
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Klasifikasi tanah berdasarkan CPT
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1.3 Desain Muka Air
-5
-11
-18
-34
-28
-42
-48
-57
-75
Silty Clay N= 11
Sand-Silt N= 34
Sand N= 45
Clay-Silt N= 30
Clay-Silt N= 42
Sand N= 49
Clay-Silt N= 34
Clay-Silt N= 37
Sand N= 47
-9.5 m
Sand N= 40
1 1a
Silty Clay N= 23 1b
2
3
5
6
7
Ground Surface El. -1.1 m
2a
2b
2c
3a
3b
4
L-total
L-efektif
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1.4 Parameter desain- Kuat geser- Sifat deformasi (elastik, konsolidasi)- Dll
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Kuat geser tanah (shear strength)
• Undrained shear strength (Su) UUtriaxial, unconfined compression test(Lab test), atau korelasi dari N-SPT,Qc sondir, pressuremeter
• Drained strength (c’, phi’) diperolehdari triaxial CU tests
• Korelasi empirik dari sifat fisik tanah
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UU Triaxial Test Result
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Korelasi kuat geser tanah (Su) dengan N-SPT
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CU Triaxial Test Result
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Korelasi PI & φ’
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Consolidation Test
Consolidation parameter:PcCcCrCvCc’ = Cc / (1 + e0)Cr’ = Cr / (1 + e0)
C
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Korelasi empirik parameter konsolidasi
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SUMMARY
• Soil profile yang mewakili• Parameter desain didasarkan pada hasil
laboratorium, rumus empirik dan judgement • Bandingkan dengan pengalaman lampau
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2. Teknik Fondasi
2.1 Syarat Umum2.2 Beban ke fondasi2.3 Pemilihan tipe fondasi
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2. Teknik Fondasi
2.1 Syarat Umum:–Batas kapasitas/kekuatanKapasitas strukturKekuatan tanah (bearing capacity)
–Batas deformasiTotal settlementDifferential settlement
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2. Teknik Fondasi2.2 Beban-beban pada Fondasi
– Beban struktur atasBeban mati (DL)Beban hidup (LL)Beban anginBeban gempaBeban-beban lain
– Beban dalam tanahtekanan tanahtekanan air tanahgaya gempaBerat sendiri fondasi
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2. Teknik Fondasi
2.3 Pemilihan Tipe Fondasi– Tipe fondasi:Fondasi dangkalFondasi dalam
o Fondasi tiang pancango Fondasi tiang bor
Fondasi lain (raft foundation)
– Faktor-faktor yang mempengaruhi pemilihantipe fondasi:Tipe struktur atasKondisi tanahPelaksanaan konstruksiPertimbangan waktu dan ekonomi
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3. Fondasi Dangkal
2.1 Jenis fondasi dangkal2.2 Kedalaman minimum2.3 Daya dukung (bearing capacity)2.4 Settlement2.5 Lateral resistance
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3. Fondasi Dangkal
• Beban relatif kecil• Tanah relatif baik• Step desain:
- Induced loads- Soil profile- Allowable bearing - Settlement
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3.1 Jenis Fondasi Dangkal
Spread footing
Strap footing
Combined footing
Mat foundation
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3.2 Minimum Depth of Footing
H & B ≥ 60-80 cm
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3.3 Daya Dukung (Bearing Capacity)
(Das and Sivakugan, 2019)
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3.3 Daya Dukung (Bearing Capacity)
)(10 21 B
DccBNq f
wwult +=
• Untuk pasir Meyerhof (1976)
• Peck, Hanson and Thornburn(1974) for Settlement = 25 mm
Net bearing capacity on sand (Peck, Hanson and Thornburn, 1974)
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Rumus Meyerhof (pasir)
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Bearing Capacity (Clay)
Nccqu .=
3==
FKqq ult
all
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3.4 Settlement
MBp
o... 1µµρ =
• D’Appolonia et al. (1970)
Pasir
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Settlement untuk Pasir
MBp
o... 1µµρ =• D’Appolonia et al. (1970)
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Settlement for Clay
• Immediate Settlement
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Consolidation Settlement
• p0 + Δp < Pc
0
0log.'.p
ppHCr ∆+=δ
• Overconsolidated Clay, p0 + Δp < Pc
• p0 < Pc < p0 + Δp
c
c
pppHCc
ppHCr ∆+
+= 0
0
log.'.log.'.δ
• Overconsolidated Clay, p0 < Pc < p0 + Δp
0
0log.'.p
ppHCc ∆+=δ
• Normally Consolidatedf Clay, p0 = Pc
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Under a circular footing Under a squared footing
Under a continuous footing
Vertical Stress Under Footing (∆p)
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Lateral Resistance
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Hal-hal Lain
Efek likuifaksi (loose sand). Efek settlement pada tanah urugan Pemadatan subgrade soil secara baik
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4. Fondasi Dalam4.1 Jenis fondasi dalam4.2 Fondasi Tiang
- Tiang pancang- Tiang bor
4.3 Daya dukung aksial- Single Pile- Pile Group
4.4 Daya dukung lateral- Single Pile- Pile Group
4.5 Settlement
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4.1 Jenis Fondasi Dalam
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4.2 Fondasi Tiang
Jenis yang biasa digunakan:- Fondasi bored pile - Fondasi tiang pancang dengan hammer- Fondasi tiang pancang tekan hidrolis- Minipiles- Franki pile
Daya Dukung TiangQtekan = [Qshaft + Qbearing] / FKQtarik = [Qshaft/FK] + Wpile
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Karakteristik Fondasi Tiang
Cara pelaksanaan Faktor pelaksanaan untuk desain Analisa dan desain disesuaikan dengan
pelaksanaan
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Pengaruh Pemancangan Tiang
Pemancangan mendesak tanah ke samping dan ke bawah
Tegangan air pori naik Pemancangan memadatkan tanah pasir lepas Pemancangan merusak tanah pasir padat Pengaruh pemancangan pada pasir Kishida-Meyerhoff
Ø2 = (Ø1+400)/2Ø1 = Ø pasir sebelum dipancangØ2 = Ø pasir sesudah pemancangan
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Pengaruh alat pancang
Berat hammer disesuaikan dengan berat tiang Tegangan tekan dan tegangan tarik dalam tiang Getaran pada tanah Polusi suara Energi pancang yang baik adalah hammer yang
berat dengan tinggi jatuh kecil Hammer yang ringan dengan tinggi jatuh besar
menyebabkan “efek cambuk” pada tiang
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Pelaksanaan tiang bor
Berpengaruh terhadap cara pelaksanaan dengan casing atau tidak dengan bentonite/polimer atau tidak cor beton dalam air atau tidak
Pengeboran menyebabkan “stress release” “stress release” pada dinding lubang menyebabkan
longsoran “stress release” pada dasar lubang menyebabkan
“heaving” Pada MAT tinggi dapat terjadi “boiling” dasar
lubang
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Mencegah longsoran di lubar bor
Longsoran dinding lubang bor menyebabkan:o diameter lubang lebih besaro permukaan dinding tidak haluso menambah tahanan friksi tiango menambah volume beton tiang bor
Longsoran pada pasir hanya dapat dicegah dengan “casing”
Longsoran pada tanah kohesif dapat dicegah dengan “bentonite” atau “polymer”
Longsoran tanah / lumpur di dasar lubang terisi air tidak bisa 100% dibersihkan.
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4.3 Daya Dukung Aksial
1. Single Pile- Tahanan geser selimut- Tahanan ujung
2. Pile Group
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Daya Dukung Aksial Tiang Tunggal
Rumus umum daya dukung aksial fondasi dalam:
Qult = Qs + Qp
Qs = Tahanan Geser Selimut TiangQp = Tahanan Ujung Tiang
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Qu = Qp + Qs
SFQQ u
all =
Daya Dukung Umum
FS = 2.5
Qs
Qp
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Daya dukung izin ??
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Tahanan Geser Selimut (Qs)
1. Tanah KohesifTiang PancangTiang Bor
2. Tanah PasirTiang PancangTiang Bor
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1. Tahanan Geser Selimut TiangTanah Kohesif
Tahanan geser selimut tiang yang merupakan kon-tribusi dari kohesi tanah adalah:
Qs = qs. Li. p (qs = α. cu)Dimana,qs = unit gesekan kulitα = Koefisien adhesi antara tanah dan tiangcu = Undrained cohesionLi = Panjang lapisan tanahp = keliling tiang
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Faktor Adhesi (α) pada Tanah Kohesifuntuk “Tiang Pancang”
1. API Metode, 1986
2. API Metode, 2000
𝛼𝛼 = 0.5 Ψ−0.5 untuk Ψ ≤ 1.0
𝛼𝛼 = 0.5 Ψ−0.25 untuk Ψ > 1.0Ψ = ⁄𝑐𝑐𝑢𝑢 𝜎𝜎
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Faktor Adhesi (α) pada Tanah Kohesifuntuk “Tiang Pancang”
3. Tomlinson, 2001 :
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Faktor Adhesi (α) pada Tanah Kohesifuntuk “Tiang Bor”
1. Reese and O’Neill, 1988
α = 0.55
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Batasan Tahanan Selimutpada Tanah Kohesif untuk “Tiang Bor”
Tahanan gesekan kulit tiang bor pada tanah kohesif perludibatasi sebagaimana dinyatakan oleh Tomlinson (2001),
𝑞𝑞𝑠𝑠 = 𝛼𝛼 𝑐𝑐𝑢𝑢 ≤ 𝑞𝑞𝑠𝑠(𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖) = 1.0 ⁄kg cm2
= 100 kN/m2
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2. Tahanan Geser Selimut Tianguntuk tanah pasiran
Tahanan geser selimut tiang yang merupakankontribusi dari sudut geser dalam (φ) adalah:
Qs = qs.Li.pDimana,qs = tahanan geser selimut per satuan luasLi = Tebal lapisan tanahp = keliling tiang
𝑞𝑞𝑠𝑠 = 𝐾𝐾𝜎𝜎 tan 𝛿𝛿
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Tahanan Geser Selimut “Tiang Pancang”untuk Tanah Berpasir
𝑞𝑞𝑠𝑠 = 𝐾𝐾𝜎𝜎 tan 𝛿𝛿
K adalah tekanan tanah lateral
K = 0.8 (untuk tiang pipa ujung terbuka)
K = 1.0 (untuk full displacement)
σ adalah tegangan efektif overburden
δ = gesekan tiang dengan tanah
API, 2000
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Meyerhof (1976) dengan menggunakan nilai N-SPT
Tahanan Geser Selimut “Tiang Pancang”untuk Tanah Berpasir
𝑞𝑞𝑠𝑠 = 0.1 𝑁𝑁 ⁄𝑡𝑡 𝑚𝑚2 untuk displacement kecil𝑞𝑞𝑠𝑠 = 0.2 𝑁𝑁 ⁄𝑡𝑡 𝑚𝑚2 untuk displacement besar
Displacement kecil atau besar merupakan usaha peman-cangan tiang. Displacement besar dapat diartikan sebagaipemancangan dengan menggunakan hammer. Kalaudisplacement kecil dapat diartikan bahwa usaha peman-cangan kecil seperti pemancangan dengan menggunakanmetode push-in atau jacking.
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Naval Engineering Facilities Command{
Qs = 0.2 x (N SPT) x Li x p (ton)
Tahanan Geser Selimut “Tiang Pancang”untuk Tanah Berpasir
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Tahanan Geser Selimut “Tiang Bor”untuk Tanah Berpasir
𝑞𝑞𝑠𝑠 = 0.32 𝑁𝑁 ⁄t m2 untuk 𝑁𝑁𝑆𝑆𝑆𝑆𝑆𝑆 < 53
𝑞𝑞𝑠𝑠 =𝑁𝑁 − 53
450+ 1.6 ⁄t ft2 untuk 53 < 𝑁𝑁𝑆𝑆𝑆𝑆𝑆𝑆 ≤ 100
Catatan: ⁄1 t ft2=10.764 ⁄t m2
Reese and Wright, 1977
Naval Engineering Facilities Command{
Qs = 0.1 x (N SPT) x Li x p (ton)
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Batasan Tahanan Selimutpada Tanah Pasir untuk “Tiang Bor”
Nilai batas gesekan kulittiang bor (Reese danWright, 1977)
𝑞𝑞𝑠𝑠 = 1.6 𝑡𝑡𝑡𝑡𝑡𝑡𝑢𝑢𝑢𝑢𝑡𝑡𝑢𝑢𝑢𝑢 𝑁𝑁𝑆𝑆𝑆𝑆𝑆𝑆 < 53
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Tahanan Ujung (Qp)
1. Tanah LempungTiang PancangTiang Bor
2. Tanah PasirTiang PancangTiang Bor
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Daya Dukung Ujung untuk Tanah Kohesif cu
Tiang Pancang dan Tiang Bor:
Qp = qp x Ap
qp = 9 x cu
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Daya Dukung Ujung untuk Tanah Pasiran φ
Tiang Pancang :Qp = qp x Ap
Nilai N – SPT Desainadalah:
Ndesain = ½ (N1 +N2)
𝑞𝑞𝑝𝑝 = 40 𝑁𝑁 ⁄𝑡𝑡 𝑚𝑚2 < 1600 ⁄t m2
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Daya Dukung Ujung untuk Tanah Pasiran
Tiang Bor
=7 N (t/m2)
=400 (t/m2)
𝑞𝑞𝑝𝑝 = 7 N ⁄t m2dimana 𝑞𝑞𝑝𝑝(𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑠𝑠) ≤ 400 ⁄t m2
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Summary
τ
qp
Clay Sand
Pancang PancangTiang Bor Tiang Bor
α c α c
Untuk pancangAPI, 2001
Untuk Tiang BorReese and O’Neill, 1988
0.2 N < 2 tsf 0.1 N < 1 tsf
9 c40 N
< 1600 t/m2
N=(N1+N2)/2
7 N (t/m2) < 400 (t/m2)
Pult = 2πr Σ ∆l τ + πr2 qp
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Pile Group
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Pile Group
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Keuntungan Kelompok tiang
Tiang tunggal tidak memadai Deviasi pada instalasi tiang Timbulnya eksentrisitas menambah momen Satu tiang gagal, dibantu tiang lain
(prinsip redudancy) Pemadatan ke arah lateral pada pemancangan
(terutama sandy soil)
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Pengaruh Pada Kelompok Tiang
Bearing capacity
Settlement
Pile Group < Single Pile
Pile Group > Single Pile
Zona Tegangan
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Aksi Tiang Tunggal dan Kelompok
(Tomlinson, 1977)
Lensa
Prilaku kelompok tiang sangat berbeda
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Efisiensi
Daya dukung bataskelompok tiang
Daya dukung batastiang tunggal
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Efisiensi bergantung pada:
Jumlah tiang, panjang, diameter, pengaturan tiang, dan jarak
Modus transfer beban Prosedur instalasi (pancang atau bor) Urutan instalasi Jangka waktu setelah pemancangan Interaksi pile cap dan ground
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Efisiensi Pile Group
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Efisiensi Pile Group
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PersamaanConverse-Labarre
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Efisiensi Pile Group
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Untuk perhitungan dengan effisiensi, kapasitas dukung pile group dihitung dengan cara sebagai berikut,
𝑄𝑄𝑔𝑔 (𝑖𝑖𝑖𝑖𝑖𝑖𝑢𝑢) = 𝑄𝑄𝑠𝑠 (𝑖𝑖𝑖𝑖𝑖𝑖𝑢𝑢) × 𝜂𝜂 × 𝑢𝑢
Daya Dukung Pile Group
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Untuk perhitungan block failure digunakan formula berikut,
𝑄𝑄𝑔𝑔 𝑏𝑏𝑏𝑏𝑏𝑏𝑐𝑐𝑢𝑢 = 𝐿𝐿𝑔𝑔 × 𝐵𝐵𝑔𝑔 × 𝑐𝑐𝑢𝑢 × 𝑁𝑁𝑐𝑐∗ + �𝑡𝑡𝑠𝑠 × 𝑝𝑝 × 𝐻𝐻
Untuk lapisan lempung fs diganti dengan α x cu
Nilai Nc* diperoleh dari Gambar berikut.
Daya Dukung Pile Group
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4.4 Daya Dukung Lateral Tiang
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Daya Dukung Lateral Tiang
Metode Brom
Metode BromMetode p-y curve
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Daya Dukung Lateral Tiang
Lebih tepat menggunakanmetoda p-y curves: memperhitungkan interaksiantara tanah dan tiang, dapat digunakan untuklapisan tanah yang berbeda-beda, dll.
Metode p-y Curve
Computer Program :
1. COM 6242. LPILE
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Gaya lateral V pada defleksi kepala tiang y
S = slope of curveM = bending momentp = soil reaction
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Single PileFree Head Fixed Head
Top deflection 10 mmLateral 100 kN
Top deflection 10 mmLateral 226 kN
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Single Pile
Static loading
Cyclic loading
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Pile Group
Efek pile group diperoleh dengan mereduksi p-y curve berdasarkan suatu p-multiplier
Coduto, Kitch, Yeung (2016)
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Reduksi p-y curve
Reese and van Impe (2011)
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Reduksi p-y Curve Untuk Lateral Grup Pile
Faktor koreksi : 0.45
0
20
40
60
80
100
120
140
160
180
200
0 0.01 0.02 0.03 0.04 0.05 0.06
p (
kN/m
)
y (m)
Initial
Depth: 2.5 m dari kepala tiang
Sandy Clay Layer
-30
-25
-20
-15
-10
-5
0-100 -50 0 50 100 150 200 250 300
Dep
th (
m)
Gaya Lateral (kN)
Initial : H = 240 kN
Setelah Koreksi : H = 113kN
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Contoh Daya Dukung Izin Lateral Tiang Tunggal Dalam Grup
H-izin (Non seismic) = 113 kN ; Top Deflec. : 6.30 mmH-izin (Seismic) = 151 kN ; Top Deflec. : 12.0 mm
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Bending Moment
H-izin (Non seismic) = 113 kN
Bending Moment , M = 221 kN-m< M-crack = 250 kN-m (Ok)
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H-izin (Seismic) = 151 kN
Bending Moment , M = 343 kN-m> M-y = 0.9 x 315 = 283.5 kN-m (Not-Ok)
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H-izin (Seismic) = 134 kN
Bending Moment , M = 281 kN-m< M-y = 0.9 x 315 = 283.5 kN-m (Ok)
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4.5 Settlement
• Immediate Settlement• Consolidation Settlement• Total Settlement• Differential Settlement
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4.5 Settlement
• Immediate Settlement
(Das and Sivakugan, 2019)
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4.5 Settlement
• Consolidation Settlement
(Das and Sivakugan, 2019)
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4.5 Settlement
Posisi Eqivalent Footing
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4.5 Settlement
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4.5 Settlement
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Terima Kasih