p dangkal1
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mekanika tanahTRANSCRIPT
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SILABUS MATA KULIAH
PONDASI DANGKAL- MODEL KERUNTUHAN
- DAYA DUKUNG BATAS
- DAYA DUKUNG (TERZAGHI, MEYERHORF, VESIC,HANSEN)
* BEBAN SENTRIS DAN EXSENTRIS
- PENGARUH MUKA AIR TANAH
- DAYA DUKUNG AKIBAT TANAH BERLAPIS
- DAYA DUKUNG BERDASARKAN DATA SONDIR DAN SPT
- PENURUNAN ELASTIS (SEGERA) DAN KONSOLIDASI
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PONDISIASI DALAM- JENIS PONDASI DALAM
- MEKANISME KERUNTUHAN
- DAYA DUKUNG UJUNG DAN FRIKSI TIANG TGL
# DATA LABORATORIUM
# DATA SPT DAN SONDIR
- EFISIENSI TIANG
- DAYA DUKUNG TIANG KELOMPOK
- PENURUNAN TIANG (TUNGGAL DAN KELOMPOK)
- UJI PEMBEBANAN
- DAYA DUKUNG AKIBAT PEMANCANGAN
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TURAP- TURAP KANTILEVER PADA TANAH PASIR
- TURAP KANTILEVER PADA TANAH LEMPUNG
- TURAP BERANGKUR PADA TANAH PASIR
- TURAP BERANGKUR PADA TANAH LEMPUNG
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SYARAT- SYARAT PEMILIHAN PONDASI
1. KEDALAMAN TANAH KERAS
2. BEBAN YANG DITAHAN
3. BIAYA YANG TERSEDIA
4. PENGARUH-PENGARUH LAIN
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SHALLOW FOUNDATIONS
YULVI ZAIKA, DR ENG
KDK GOETEKNIK
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PONDASI TELAPAK
Lapisan Tanah Keras
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Combined footing
2 footings close
to each other
P1 close to property
line and P2 > P1
property line
P1 P2
If P2/P1 < 1/2, use strap combined footing
property line
If 1/2 < P2/P1 < 1
use trapezoidal footing
property line
P1 P2
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BENTUK PONDASI TELAPAK
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PONDASI RAKIT
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PONDASI RAKIT
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PONDASI RAKIT
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SYARAT PONDASI DANGKAL
Kedalaman tanah pondasi kurang atau sama dengan lebarnya atau kedalaman (Terzaghi, 1943).
Teori lain, kedalaman pondasi dangkal 3-4 kali lebar pondasi.
Pondasi setempat harus memenuhi syarat-syarat:
1. Stabilitas, aman terhadap keruntuhan geser
2. deformasi harus lebih kecil dari yang diizinkan.
Lapisan Tanah Keras
Df
B
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METODA PELAKSANAAN
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KERUNTUHAN PADA PONDASI DANGKALPADA TANAH PASIR PADAT DAN LEMPUNG KAKU
B
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MODEL KERUNTUHAN GESER
keruntuhan umum geser pasir padat Dr>67%
lempung kaku NSPT >12
Koruntuhan lokal pasir atau
pasir kelempungan kurang padat (medium)
30%<Dr<67%
Keruntuhan penetrasi Pasir lepas
Dr< 30%
Beban/luas
Penurunan
qu
Beban/luas
Penurunan
qu1
qu
Beban/luas
Penurunan
qu1
qu qu
Permukaan runtuh
Permukaan runtuh
Permukaan runtuh
(a)
(b)
(c)
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MODEL KERUNTUHAN BERDASARKAN RELATIF DENSITY
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DAYA DUKUNG BATAS
Daya dukung batas (qu= q ultimate)
Pada pondasi dangkal yang letaknya dekat permukaan tanah (Df/B kecil) qu terjadi pada:
- penurunan = 4 - 10 % B (keruntuhan geser umum)
- penurunan = 15 -25 % B (keruntuhan geser lokal)
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Terzaghi Assumptions
1. Soil under footing is homogeneous and isotropic 2. Soil surface is horizontally 3. The base of footing is rough, to prevent the shear displacement. 4 The foot is shallow foundation, i.e. the depth of foundation is less than
the width of foot… Df ≤ B
3. Shear strength above the level of the base of footing is negligible.
c = 0 above ( F.L ). 4. Consider only the surcharge which produced as uniform pressure q = DF at foundation level. 5. The load on foundation is vertical and uniform. 6. The foot is long strip footing (pondasi lajur, B/L 0). 7. =
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Shear failure happened on many stages
I) Stage I: The soil in the elastic case and behave as the part of foundation it still that, and by increasing the load performed the region I which called active zone.
II) Stage II: At this stage the foundation load effect on the active zone and neighboring soil so perform the region which called arc of logarithmic spiral zone.
III) Stage III: By increasing the load performed the third part curve in which part the soil became in the passive case it make to resist the failure.
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PROSES TERJADINYA KERUNTUHAN
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Three components produced to resist the failure of soil.
I) (Pp)γ = Component produced by the weight of shear zone II,
III.
II)(Pp)c = Component produced by the cohesive stress.
III) (Pp)q = Component produced by the surcharge q.
Pp = (Pp)γ + (Pp)c + (Pp)q
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DASAR PENURUNAN RUMUS TERZAGHI
Kesetimbangan Gaya qu(2b)= -W+ 2Pp+f sin f W=(1/2)2bg btan =a b2gtanf f=c DC= c. b/cosf Pp=(1/2)g (b tan f)2 Kg + c (b tan f)Kc +q(b tan f) Kq qu =c{tan (f Kc +1)} +q(tan f Kq) + g B/2{(1/2) tan (f Kg. tan -1)}f
qu
A C
DPp
Pp
W
a aff
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PERSAMAAN DAYA DUKUNG TERZAGHIUNTUK PONDASI LAJUR/ MENERUS
1
2u c qq cN qN BN
245cos2 2
2
a
Nq =
a= e
cot1qNNc =
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TEORI DAYA DUKUNG TERZAGHI (1943)
Daya dukung:
Pondasi lajur
Pondasi bujursangkar
Pondasi lingkaran
Untuk keruntuhan geser lokal:
c’ = 2/3 c dan f’ = 2/3 f
qu
q=gDf
B
Df
45-f/2 45-f/2 45-f/2 45-f/2a aA C
D
EF
H G
J I
1
2u c qq cN qN BN
1.3 0.4u c qq cN qN BN
1.3 0.3u c qq cN qN BN
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GRAFIK FAKTOR DAYA DUKUNG
General shear failureLocal shear failure
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Contoh soal 1
KEDALAMAN SPT LAB
0-1 6 c=25 kN/m2 = 20f 0 =17g kN/m3
1-2 12 c=20 kN/m2 = 30f 0 =17.5g kN/m3
2-3 25 c=15 kN/m2 = 35f 0 =18g kN/m3
3-4 40
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CONTOH SOAL 2
KEDALAMAN SONDIR Qc (kg/cm2)
PARAMETER
0 0
1 12 c=20 kN/m2 = 15f 0 =16.5g kN/m3
1.5 75 c=15 kN/m2 = 25f 0 =17g kN/m3
2 150 c=10 kN/m2 = 35f 0 =19.3g kN/m3
2.5 120 c=15 kN/m2 = 30f 0 =18g kN/m3
3 180