PONDASI DANGKAL MEKANIKA TANAH II YULVI ZAIKA Powerpoint Templates

SYARAT- SYARAT PEMILIHAN PONDASI KEDALAMAN TANAH KERAS BEBAN YANG DITAHAN BIAYA YANG TERSEDIA PENGARUH-PENGARUH LAIN

PONDASI TELAPAK Lapisan Tanah Keras

Combined footing If P2/P1 < 1/2, use strap combined footing property line 2 footings close to each other P1 close to property line and P2 > P1 property line P1 P2 If 1/2 < P2/P1 < 1 use trapezoidal footing property line P1 P2

BENTUK PONDASI TELAPAK

PONDASI TELAPAK MENERUS/ LAJUR

PONDASI RAKIT

PONDASI RAKIT

PONDASI RAKIT

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: Stabilitas, aman terhadap keruntuhan geser deformasi harus lebih kecil dari yang diizinkan. Lapisan Tanah Keras Df B

METODA PELAKSANAAN

KERUNTUHAN PADA PONDASI DANGKAL PADA TANAH PASIR PADAT DAN LEMPUNG KAKU B

MODEL KERUNTUHAN GESER Beban/luas Penurunan qu qu1 Permukaan runtuh (a) (b) (c) 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%

MODEL KERUNTUHAN BERDASARKAN RELATIF DENSITY

Terzaghi Assumptions Df ≤ B c = 0 above ( F.L ). 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.  = 

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.

PROSES TERJADINYA KERUNTUHAN

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

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 f-1)} qu A B J Pp W  f B=2b Zona aktif Zona pasif Zona geser radial

PERSAMAAN DAYA DUKUNG TERZAGHI UNTUK PONDASI LAJUR/ MENERUS Nq = Nc = = e

TEORI DAYA DUKUNG TERZAGHI (1943) Pondasi lajur Pondasi bujursangkar Pondasi lingkaran Untuk keruntuhan geser lokal: c’ = 2/3 c dan f’ = 2/3f qu q=gDf B Df 45-f/2 a A C D E F H G J I

GRAFIK FAKTOR DAYA DUKUNG Local shear failure General shear failure

PERBANDINGAN BIDANG RUNTUH

RUMUS UMUM DAYA DUKUNG PONDASI MEYERHOF (1963) Fcs , Fqs , Fs = faktor bentuk Fcd , Fqd , Fd = faktor kedalaman Fci , Fqi , Fi = faktor inklinasi

FAKTOR PENGARUH MEYERHOF F. BENTUK F. KEDALAMAN F. INKLINASI b Q T R

DISTRIBUSI TEGANGAN TANAH AKIBAT TEG. VERTIKAL DAN MOMEN P M

Tegangan kontak akibat beban vertikal dan momen P M B R e e < B/6 qmax qmin e > B/6 qmax qmin e = B/6 qmax qmin

P e e = B/6 qmax qmin e < B/6 qmax qmin e > B/6 qmax qmin

Pondasi Lajur e B B-2e

Stabilitas Daya Dukung Tegangan kontak : tegangan akibat beban Menentukan eksentrisitas DPT C