Transcript
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KULIAH 7
DAYA DUKUNG TANAH
UNTUK PONDASIDANGKAL
Eko Andi Suryo, ST., MT., PhD.
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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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PONDASI TELAPAK
Lapisan Tanah Keras
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Combined footing
2 footings close
to each other
P1close 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 TELAPAK MENERUS/ LAJUR
http://www.colonialbarn.com/images/foundation_repair1.jpghttp://www.colonialbarn.com/images/foundation_repair1.jpg8/11/2019 Mektan 2 Kuliah 7
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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 ataukedalaman (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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Konsep Daya Dukung Batas Tanah
untuk Pondasi Dangkal
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KERUNTUHAN PADA PONDASI DANGKAL
PADA TANAH PASIR PADAT DAN LEMPUNG KAKU
B
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MODEL KERUNTUHAN BERDASARKAN
RELATIF DENSITY
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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 thanthe 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) = 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)+ (Pp)c + (Pp)q
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DASAR PENURUNAN RUMUS TERZAGHI
Kesetimbangan Gaya qu(2b)= -W + 2Pp + fsin
W=(1/2)2bbtan = b2 tan
f=c DC= c. b/cos Pp=(1/2)(b tan )2K+ c (b tan )Kc +q(b tan ) Kq
qu=c{tan Kc +1)} +q(tan Kq) + B/2{(1/2) tan K. tan -1)}
quA B
J
PpPp
W
ff
B=2b
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PERSAMAAN DAYA DUKUNG TERZAGHI
UNTUK PONDASI LAJUR/ MENERUS
1
2u c q
q cN qN BN
=
245cos2
2
2
a
Nq =
= e
cot1-qNNc =
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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 = 2/3
quq=Df
B
Df
45-/2 45-/2 45-/2 45-/2 A C
D
EF
H G
J I
1
2u c q
q cN qN BN
=
1.3 0.4u c qq cN qN BN
=
1.3 0.3u c q
q cN qN BN
=
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GRAFIK FAKTOR DAYA DUKUNG
General shear failure Local shear failure
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Tugas 2
Lapisan Tanah Keras
= 17kN/m3
c0
= 18kN/m3
= 38
0,5m
= 17kN/m3
C= 38 kN/m2
= 18kN/m3
= 15
Soal 1Soal 2
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