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    Teori KapasitasDukung Tanah

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    Defnisi-defnisiThe bearing capacity is the limiting pressurethat the footing can support.

    Foundation : Structure transmits loads to theunderlying ground (soil). Footing: Slab element that transmit load fromsuperstructure to ground

    Embedment depth, D f : The depth belowthe ground surface where the base of the footingrests.

    Bearing pressure(q) : The normal stressimpose by the footing on the supporting ground.(weight of superstructure + self weight of

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    3

    Defnisi-defnisi

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    Bearing Capacityailure

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    Transcosna !rain

    "le#ator Canada ($ct.%&' % % )

    West side of foundation sank 24-ft

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    Kegagalan KapasitasDukung

    a) !eneral Shear ailure* eruntuhan geserumum, Tipe keruntuhanyang paling umum; terjadiumumnya pada tanah yang

    kuat dan atuan b) -ocal Shear ailure

    * eruntuhan geser lo al, Kondisi antara keruntuhan

    umum dan keruntuhantum ukan

    c) /unching Shear ailure* eruntuhan gesertumbu an, terjadi pada

    pasir sangat lepas danlempung lunak

    !

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    "earing #apa$ity %ailure

    &

    eneral shear failure

    !ocal shear failure

    "unching shearfailure

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    Bearing Capacity ailurein Sand

    '

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    a) !eneral Shear ailureb) -ocal Shear ailurec) /unching Shear ailure

    1(

    )oad *s Displa$ement +a,ter esi$. +1'!3/

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    Komentar mengenaikeruntuhan geser

    "iasanya hanya perlu menganalisis keruntuhankapasitas umum

    Keruntuhan geser lokal dan 0pun$hing iasanyadapat diantisipasi pada analisis penurunansettlement

    Keruntuhan ,ondasi dangkal umumnya merupakan

    kegagalan penurunan settlement ; namun Keruntuhan kapasistas dukung harus dianalisismeskipun dalam prakteknya keruntuhan gesertidak le ih dominan dari kegagalan ataukeruntuhan aki at penurunan

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    erkem angan Teori

    Kapasitas Dukung Tanah plikasi dari metoda keseim angan atas a alnyadiusulkan oleh randtl pada analisis tum ukan pada suatumassa tipis logam

    7etoda dari randtl8s di adopsi oleh Ter9aghi untuk analisisKapasitas dukung ,ondasi dangkal:

    esi$. dan e erapa ilmuan lain memperdalam Teori asli

    Ter9aghi8s dan menam ahkan e erapa ,aktor-,aktor untukanalisis ,ondasi dangkal yang le ih lengkap:

    nalisis ,ondasi dangkal aik kapasitas dukung maupunpenurunan le ih dilengkapi dengan metoda numerik e:g:% analisys

    12

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    sumsi-asumsi 7etoda Ter9aghi

    1: Kedalaman ,ondasi adalah kurang atausama dengan le arnya:

    2: Tidak terjadi slip antara dasar ,ondasidengan tanahnya dasar ,ondasi kasar

    3: Tanah di a ah ,ondasi homogen dansemi infnite

    4: 7ohr-#oulom model erlaku padatanah

    5: Keruntuhan geser umum adalah modekeruntuhan yang menentukan +Tapi

    ukan satu-satunya mode keruntuhan/

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    ssumptions ,or Ter9aghi8s7ethod6: "elum terjadi konsolidasi pada tanah

    !: %ondasi relati, sangat rigid kakudi andingkan tanahnya

    &: Tanah diatas dasar ,ondasi tidak memilikikekuatan gesar; hanya se agai e anmerata sur$harge load terhadap e anguling o*erturning load

    ': "e an yang ekerja adalah e an tekan danekerja *ertikal pada $entroid ,ondasinya

    1(: Tidak ada e an momen yang ekerja 14

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    %ailure

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    %ailure

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    %ailure

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    =in$e Ter9aghi neglected the shear strength ofsoils between the ground surface and a depth D ,the shear sur,a$e stops at this depth and the o*erlyingsoil has een repla$ed ith the sur$harge pressure 9D :This approa$h is $onser*ati*e> and is part o, thereason ,or limiting the method to relati*ely shallo,oundations (D < B).

    Ter9aghi de*eloped his theory ,or $ontinuous,oundations +i:e:> those ith a #ery large !#B ratio ).

    This is the simplest $ase e$ause it is a t o-dimensional pro lem .

    ?e then e@tended it to sAuare and round ,oundationsy adding empiri$al $oeB$ients o tained ,rom model

    tests and produ$ed the ,ollo ing earing $apa$ity,ormulasC

    1&

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    or s0uare foundations:

    or continuousfoundations:

    or circular foundations BN N N cq q zDcult ++= 3.03.1

    BN N N cq q zDcult ++= 5.0

    N B N N cq q zDcult ++= 4.03.1

    1'

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    2(

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    "e$ause o, the shape o, the ,ailure sur,a$e> the#alues of c and only need to represent thesoil between the bottom of the footing anda depth B below the bottom . The soils

    et een the ground sur,a$e and a depth D aretreated simply as o*er urden .

    Ter9aghi8s ,ormulas are presented in terms o,e e$ti*e stresses: 1owe#er > they also may eused in a total stress analyses y su stituting c T T and D for c', ', and D If saturated undrained$onditions e@ist> e may $ondu$t a total stress

    analysis with the shear strength de ned asc T $ % u and T $ &. 2n this case , ' c $ . , ' q $*.+, and ' $ +.+.

    The Ter9aghi earing $apa$ity ,a$tors areC 21

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    ( )

    =

    >

    =

    ==

    =

    +=

    1cos2

    tan

    0tan

    1

    07.5

    )2/45(cos2

    2

    tan360/75.0

    2

    2

    p

    qc

    c

    q

    K N

    for N

    N

    for N

    ea

    a N

    #ontdE

    22

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    Fntuk ,ondasi yang menunjukkan indi asi

    eruntuhan geser lo al pada tanahnya> Ter9aghimenyarankan menggunakan rumus-rumus erikutuntuk menghitung kapasitas C

    Dari "raja m: das

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    Dari "raja m: das

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    % #TGH G% = % TI

    FS

    qq

    FS q

    q

    unet net all

    uall

    )()( =

    =

    JhereC

    Au ultimate earing $apa$ity o, shallo ,oundation

    Aall allo a le earing $apa$ity o, shallo ,oundation

    Anet+u/ net ultimate earing $apa$ity o, shallo ,oundation

    Aall net allo a le earing $apa$ity o, shallo ,oundation

    %= %a$tor o, =a,ety +%= 3/

    f

    uunet

    Dq

    qqq

    .)(

    ==

    2!

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    Lotes on Ter9aghi8s

    7ethod#atatan untuk 7etoda Ter9aghi Karena kohesi tanah sulit untuk ditentukan>maka nilai $ohesi $ yang konser*ati,se aiknya digunakan

    Kekuatan ,riksi nilai M le ih dapatdiandalkan dan tidak perlu diam il nilai yangkonser*ati, seperti nilai $

    7etoda Ter9aghi simple dan umum digunakanoleh praktisi geoteknik; tapi metoda ini elummempertim angkan anyak ,aktor: 2&

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    2'

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    3(

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    urther 3e#elopments

    =kempton +1'51/ 7eyerho, +1'53/ "rin$h ?anson +1'61/ De "eer and )adanyi+1'61/ 7eyerho, +1'63/ "rin$h ?anson +1'!(/ esi$ +1'!3> 1'!5/ 31

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    Auation:7ayerho, 7ethod ith $om ination o, ?ansen and

    esi$ ,a$torsN

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    33

    )1)tan(1.4(N N1)cot(N N

    /2)(45tane N

    q

    qc

    2tanq

    = =

    +=

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    The

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    The

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    Gther %a$tors

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    Gth % $t ? d

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    Gther %a$tors ,rom ?ansen andesi$

    3!

    O %or $ontinuous,ooting>s 1

    O %or perpendi$ularload> i 1O %or le*el ,oundation> 1O %or le*el ground>

    g 1O Leed to $ompute,a$tors

    - "earing #apa$ity %a$tor L> - Depth %a$tor d

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    !round water "4ects

    3&

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    4(

    e$ts

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    $$T26!S 72T1"CC"6T52C$5 26C-26"3 -$8326!S

    41

    $$entri$ity

    2nclination

    $$T26!S 72T1 $ne 7ay

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    $$T26!S 72T1 $ne 7ay "ccentricity Pn most instan$es> ,oundations are su je$ted to moments in

    addition to the #ertical load as sho n elo : Pn su$h $ases thedistri ution o, pressure y the ,oundation upon the soil is not uniform :

    42

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    43

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    44

    $$T26!S 72T1 $ne 7ay

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    Lote that in these eAuations> hen the e$$entri$ity e e$omes B9 ' q min is ;ero :

    %or e < B9 >q min ill e negati#e > hi$h means thattension ill de*elop: *not good===,

    "e$ause soils $an sustain *ery little tension> there ille a separation et een the ,ooting and the soil under

    it: lso note that the eccentricity tends to decrease

    the load bearing capacity o, a ,oundation: Pn su$h $ases> pla$ing ,oundation $olumn o -$enter> as

    sho n in %igure is pro a ly ad*antageous: Doing so in e e$t> produ$es a $entrally loaded

    ,oundation ith a uni,ormly distri uted pressure:45

    $$T26!S 72T1 $ne 7ay "ccentricity

    $$T26!S 72T1 $ne 7ay

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    46

    $$T26!S 72T1 $ne 7ay "ccentricity

    ti g ith T >

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    ooting with Two>way"ccentricities#onsider a ,ooting su je$t to a #ertical ultimate load ? ult and a

    moment @ as sho n in %igures a and : %or this $ase> the $omponents

    o, the moment @ a out the @ and y a@is are @ A and @ y respe$ti*ely: This$ondition is eAui*alent to a load Q pla$ed e$$entri$ally on the ,ooting

    ith A eB and y e- as sho n in %igure d:

    4!

    ti g ith T >

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    4&

    ooting with Two>way"ccentricities

    T7$>78 "CC"6T52C2T D C8S" %

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    T7$>78 CC 6T52C2T D C8S %

    4'

    4'

    T7$>78 "CC"6T52C2T D C8S" E

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    T7$>78 CC 6T52C2T D C8S E

    5(

    5(

    T7$>78 "CC"6T52C2T D C8S"

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    T7$>78 CC 6T52C2T D C8S

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    51

    T7$>78 "CC"6T52C2T D C8S"

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    T7$>78 CC 6T52C2T D C8S

    52

    52

    T7$>78 "CC"6T52C2T D C8S" F

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    T7$>78 CC 6T52C2T D C8S F

    53

    53

    TJG-J I ## LTHP#PTI R # = 4

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    TJG-J I ## LTHP#PTI R # = 4

    54

    TJG-J I ## LTHP#PTI R # = 5

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    TJG J I ## LTHP#PTI R # 5

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    55

    "A l %

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    "Aample %

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    "A l %

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    5!

    "Aample %

    "A l E

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    5&

    "Aample E

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    5'

    "Aampl

    e E

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    ootings with 2nclined-oads

    6(

    ootings with 2nclined

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    1: #ompute the in$lination ,a$tors using the eAuationsgi*en elo C

    in$lination o, load ith respe$t to *erti$al

    2: Fse the in$lination ,a$tors just $omputed to $ompute?ansen shape ,a$tors as

    61

    ootings with 2nclined-oads

    ootings with 2nclined

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    3: These are used in the ,ollo ing modif$ations o, the

    Sedited0 ?ansen earing $apa$ity eAuationC

    Fse the smaller #alue of q ult $omputed y either o,Auations:

    62

    ootings with 2nclined-oads

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    The Bearing Capacity

    of @ulti>-ayered Soils

    63

    The Bearing Capacity of -ayered

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    g p y ySoils

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    The Bearing Capacity of -ayered

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    Pn layered soil profles> the unit weight o, the soil> the angleof friction and the cohesion are not constant throughout

    the depth: The ultimate sur,a$e ,ailure may e@tend throught o or more o, the soil layers:

    Consider the case when the stronger soil is underlainby a wea er soil : P, 1 > the thi$kness o, the layer o, soil elo

    the ,ooting> is relati#ely large then the ,ailure sur,a$e ill e$ompletely lo$ated in the top soil layer> hi$h is the upperlimit ,or the ultimate earing $apa$ity:

    P, the thi$kness 1 is small $ompared to the ,oundation idth

    B> a punching shear failure will occur at the top soilstratum> ,ollo ed y a general shear ,ailure in the ottom soillayer:

    P, 1 is relati#ely deep > then the shear ,ailure ill o$$ur only

    on the top soil layer:

    65

    g p y ySoils

    The Bearing Capacity of -ayered

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    7eyerho, and ?anna +1'!&/ and 7eyerho,+1'!4/

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    The Bearing Capacity of ayeredSoils

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    6!

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    6&

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    6'

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    !(

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    !1

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    7eyerho, and

    ?annas pun$hingshear $oeB$ient K s

    !2

    The "earing #apa$ity o )ayered

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    The earing #apa$ity o, )ayered=oils

    ariation o,

    c a c 1 ith

    q 2 q 1ased on thetheory o,

    7eyerho, and?anna +1'!&/ !3

    "Aample on layered soils

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    !4

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    @ample on layered soils

    !5

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    @ample on layered soils

    !6

    ! d t

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    !round actors

    !!

    B t

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    Base actor

    %or ,ootings ith angled ,oundation ases Jhen ,ooting is le*el> 1

    !&

    5igidi

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    !'

    gty

    actors

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    Bearing Capacity from ield Tests

    &(

    Bearing Capacity from

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    Bearing Capacity fromS/T

    &1

    Bearing Capacity from

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    &2

    Bearing Capacity fromS/T

    Bearing Capacity from

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    &3

    Bearing Capacity fromS/T

    Bearing Capacity

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    Bearing Capacityusing C/T

    &4

    Bearing Capacity for ield

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    Bearing Capacity for ield-oad Tests /-T

    &5

    Bearing Capacity for ield -oad

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    g p yTests /-T

    %or

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    penetration number Pt has een suggested that the = T e standardi9ed to

    some energy ratio Er hi$h should e $omputed as

    Lote that larger *alues o, Er decrease the lo $ount Nnearly linearly> that is> Er45 gi*es N = 20 and Er90 gi*es L 1(;

    @ample o, N ,or Er45 = 2( e o tain ,or the ar itrarily$hosen Er = !(> + Er70 /C

    &!