Mektan 2 Kuliah 7

8/11/2019 Mektan 2 Kuliah 7

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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.jpg


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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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Mektan 2 Kuliah 7

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