Kuliah_ke_3.1_pile_foundation.pdf

8/14/2019 Kuliah_ke_3.1_pile_foundation.pdf

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Poulos, 1980, Pile foundation analysis anddesign, by J ohn Wiley & Sons Inc.

Bowles, J .E., 1997, Foundation analysisand design, fifth edition,, Mc Graw HillBook Company-Singapore.

Prakash S & Sharma HD., 1990, Pile

foundation in Engineering practice, J ohnWiley & Sons

Coduto DP., 1994, Foundation design,Prentice Hall, Inc.


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Konsep dasar daya dukung aksial pondasidalam: tahanan ujung dan tahanan friksi

Efek jenis tanah (pasir & lempung) padadaya dukung: penggunaan konseptegangan total dan konsep tegangan efektifserta pemilihan parameter kuat geser tanah

Efek metode konstruksi (driven, bored) padadaya dukung: perubahan pada parameterkuat geser tanah


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MEA LC of

PILES

Full scale

load test

ControlledStress test

Controlledstrain test

Based onsoiltest

Anlysisbased on

Soilproperties

Cohesion-less soil

End

bearing

Skin

friction

Cohesive

soils

End

bearing

Skin

friction

Rock

Analysis

based on

In situ test

SPT

End

bearing

Skin

friction

CPT

End

bearing

Skin

frction

Pressure

meter

Based onPile driving

dynamics

Pile

driving

formula

Wave

equation

Case

method


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Tiang biasanya selalu digunakan dalamgrup, tetapi untuk beban desain selalu

ditentukan oleh tiang tunggal. Beban desain mengikuti:

Beban ijin yg didapatkan dari membagibeban ultimate pada saat runtuh dengan

safety faktor

Beban terkait dengan settlement ijin daritiang


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Tiang menerima axial compression load J ika (Qv)ult adalah axial compressive load yg

bekerja pada kepala tiang maka beban

tersebut akan dibagi pada pile tip (Qp) danfrictional resistance (Qs) sehingga :

(Qv)ult = (Qp) + (Qs) - W

dimana (Qv

)ult

adalah ultmate bearing capacity

Qp adalah end bearing capacity dan

Qs adalah frictional capacity sepanjang perimeter tiang

W =berat tiang


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Qp dapat ditulis :

Qp = Ap [cNc + BN + DfNq]

dimana Ap

adalah pile end area

c adalah cohesion dr lapisan tanah

adalah unit weight tanah

Nc, N dan Nq adalah bearing capacity parameter

B adalah lebar atau diameter tiang

Df adalah kedalaman pile tip dibawah permukaan


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Qs = L pifsdimana p = perimeter tiang,fs = unit shaft friction sepanjang L dan L

panjang tiang

a = ca + n tana

n =Kv

dimana a adalah pile-soil shear strenth; ca = adhesion;n = normal stress dan a = angle of friction

L pi fsQv = Ap [cNc + BN + DfNq] +


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Untuk tiang pada clay, digunakan beban kapasitas undrainedkecuali tanahnya highly OC

J ika clay saturated maka = 0 dan a = 0

Sehingga Nq,=1,N=0 (Kulhawy et,al 1983)

Qp = Ap [cu Nc +Df] jika berat tiang diperhitungkan makaQp = Ap [cu Nc +Df] Df Ap sehingga

Qp = Ap cu Nc

Qs = pi LfsfS = caQu = Qp + Qs Qu = Apcu Nc + pi Lfs

Adhesion factor ca untukclay sands dan very siff clay diberikan padagambar atau tabel berikut


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A straight-shafted drilled pile was installed through clay till to bear on clay shale.The pile had a 20 inch (500mm) shaft diameter and was 31 ft (9.5m) long.Undrained shear strength (cu) for clay till was 9501b/ft2(45.5 kN/m2) and for clay

shale was 6576 Ib/ft2 (315 kN/m2). Estimate the allowable bearing capacity of thispile.SOLUTIONB=20 in. Df=L=31 x 12 in.Ap = (/4)B

2 =/4(20/12)2 = 2.18ft2

D f/ B = 31 x 12/20 = 18.6

From Table, for (Df/B) = 18.6, Nc = 9From Table 5.8, for B = 20/12 = 1.67ft, Nc = 7The lower of the above two N, values is 7 and will be used for these calculations.cu = 6576 Ib/ft* for the c lay shale on which the pile tip will bearp =B = x 20/12 = 5.24ftFrom Table 4.7 for drilled concrete piles forCu = 9501b/ftz, ca/cu = 0.6, Ca = 0.6 x 950 = 570 Ib/ft2 - fs= ca

Le = 31 - 5 = 26 ft (assuming that 5 ft is the depth of seasonal variation)

Qu = Ap cu Nc +pi Lfs (fs=ca)

(Qu)ult = 2.18 x 6576 x 7 + 5.24 x 26 x 570 lb(Qu)ult = 178 kips

(Qu)all= 178/3 = 59 kips (262 kN), if a factor of safety of 3 is used


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Reese & ONeill (1989)

qe = Nc su 4000 kpa

Nc

= 6[1+0,2(D/B )] 9

dimana

Nc = bearing capacity factor

D = depth of bottom of the shaftBb = diameter of shaft base

Su = undrained shear strength

jika B > 190 cm harga

qer= FrqeFr= 2.5/[120 1 Bb /(Br+ 2) ]


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Drained pile soil adhesion = 0 makaNq

danN dapat diabaikan sehingga

Qp = Ap [cu Nc]

cu =undrained shear strength= su ; Nc=9

Qp = Ap 9 cu

fS = v tansQs = p LfsQs = p v tans L


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Skin friction

method (effective stress)

= K tan sfS= v =K tan s v

method (total stress)

fS= cu = ca =adhesion

factor

Qs = p LfS

Qu = Qp + Qs


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A certain OC clay has a Su/ v =0.61 and drained friction angle of 220 ,

unit weight of soil 110 lb/ft3, unit weight of water 62.4lb/ft3 . GWT is at 5 ft

below the ground surface

Using beta method compute the allowable axial capacity of 50 ft long and 12

inch square prestressed concrete that will support permanent structure. The

foundation is to be built with poor control (SF=2.8)


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Classification

of structure

Acceptab

le proba-

bility of

failure

Design

Good

control

Factor

Normal

control

of Safety

Poor

control

F

Very

poor

controlMonumental

10-5 2.3 3.0 3.5 4.0

Permanent

10-4 2.0 2.5 2.8 3.4

Temporary

10-3 1.4 2.0 2.3 2.8


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Ca = 0 dan cNc =0

fS= h tan s fS= Ks v tans

Qs = p LfS =p Ks tansv Ls= 2/3

Qp = Ap [ DfNq] . v =Df

Q = Qp + Qs

Kulhawy 1983 :Qp= Ap [BN+ d(Nq-1)]

method = 0.18 + 0.65DrDr=re la t ive d e nsity sa nd

fS= v

s = sudut geser antara tiang dengan tanah


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Bearing capacity factors for piles in cohesionless soils(Coyle and Castello,1981


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Values Nq and


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Qp = Ap [ Df Nq]

Qs = p LfS =p Ks tansv L

v =Df


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Bored piled

qe= 0.6 rN604500 kpa

dimana

r= reference stress = 100 kpaN60=mean SPT N60value

qe= net unit end bearing resistanceJ ika B>120 cm maka;

qer

=4.17 (Br

/Bb

) qe

Bb

120 cm

Br= reference width = 0.3m=30cmBb = base diameter of drilled shaft


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method (Effective stress analysis)

fs= v

= K tan s

atau Reese & O neal 1989

0.25


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A closed ended 12-in. (300 mm) diameter steel pipe pile is driven into sand to 30-ft (9 m), depth.


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A closed ended 12 in. (300 mm) diameter steel pipe pile is driven into sand to 30 ft (9 m), depth.

The water table is at ground surface and sand has = 36" and unit weight () is 125 lb/ft3 (19.8

kN/m3). Estimate the pipe pile's allowable load.


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Scope untukpenyelidikan pondasi

Klassifikasi tanah Coarse-grained soil

Fine-grained soil

Organic soil

USCS


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Penyelidikan tanah untuk menetapkan luas, ketebalan,properti tanah dan batuan dan MAT lapangan

Kedalaman explorasi harusmemperhatikan vertikal stress ygdiakibatkan oleh konstruksi yg barulebih kec il10% dari stresssebelumnya pada level yg sama

Minimal satu bore-hole dilakukan sampai menembus lapisanbedrock

Lapisan bedrock ditembussampai minimal 3 m

MAT dicatat selama waktu tertentu untuk mendapatkankeseimbangan MAT


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Contoh preasumsi soil parameter dalam suatu biding penyelidikan tanah


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Penyelidikantanah danmetoda percobaan

Penyelidikan tanah

Boring method

Auger boring

Hollow-stem augerboring

Wash boring

Rotary drilling

Percussion drilling

Rock core drilling Wire-line drilling


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Penyelidikan tanah dan metodapercobaan

Test pits Hand excavated Backhoe excavated Dozer cuts

Soil sampling

Disturbed soil samples

Undisturbed soil samples

Rock coring

Pengukuran GWT/MAT dg : Open standpipe piezometers

Porous element piezometers Electric pizometers Pneumatic piezometers


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Field testing

Standard penetration test (SPT)

Dynamic cone penetration test Static cone penetration test (CPT)

Flat dilatometer test

Field vane shear test

Pressuremeter tests


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Laboratory testing untuk melakukanklassifikasi dan menyediakan parametertanah untuk desain

Tingkat variasi tanah dilapangan

Informasi tanah dari explorasi sebelumnya pada areayang sama

Karakteristik tanah

Kebutuhan struktur terhadap diffrerential settlemet

Atterberg limit

Unconfined compressive strength Parameter konsolidasi

Shear parameters


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Strength parameter

Angle of internal friction untuk tanah non kohesif Undrained shear strength Su untuk tanah kohesif

Su = Cu =v (0.1 + 0.004 PI)

Soil pile adhesion c a, sangat tergantung pada:1)Soil consistency, 2) metoda instalasi, 3) material tiang

dan 4) waktu

Elastic soil parameterSchmertmann (1970) : qc= hasil dari SCPT dan pc =preconsolidation pressure

s= c qc c = 1.5 - 4 ( pasir)

s = c pc c = 4060 (clay)

Parameterdesain


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Kuliah_ke_3.1_pile_foundation.pdf