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    I f Z / I / / 0 '7 j

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    EXAMS OFFICEUSE ONLYI '1:S' 1 -- 1, 'vJ .,w,6 I

    ourse of topic No(s)niversity of the Witwatersrand, Johannesburg

    se or topic name(s)aper Number &titlest / * to be hed during monthjs) of"deete as applicable)ar of Study (Arts &Science leave blank)egree/Diplomas for whichis course is prescribedSSc (Eng) should indicate which branch)culty/ies presenting candidates

    terna examner(s) andephone extension number(s)xterna examner(s)

    ia materias required/music/drawing paper, maps,

    iagrams, tables, computer cards, etc.)

    ime Allowance

    structions to candidatesamners may wish to use this spaceindicate, interaia, the contributionade by this examnation or lest towardsyear mark, if appropriate)

    I CIVN30(_'4 _ _ 1I GEOTE.CHNICAL ENGINEERING II Ir;o;;MBER 2007 II THIRD YEAR II BSc (Eng) (Civil) II Engine(~~~~ II Dr M Theron x77126 IDr J Orowe x77120Professor G Blight I

    ~ II C~~~VN3004 I HOURS I THREE (3) I[ ANSWER ALL QUESTIONS I

    CIVN 3004GEOTECHNICAL ENGINEERING I

    November 2007

    Question 1a) Describe with the ad of suitable illustrations the draned shear behaviour of

    normaly consolidated and overconsolidated clay. [6]b) Consolidated undraned triaxia shear tests were carried out on a soil at three

    consolidation pressures. The origina dimensions of the triaxia samples were100nun diameter x 200nun heght. The fina measurements at falure wererecorded and summarised in the table beow:

    Table 1:Consolidated undraned triaxia shear test resultsTest 1 Test 2 Test 3

    Cel pressure 275.51 375.38 590.30(kPa)Pore pressure -44.99 -47.45 -55.73(kPa)Applied load (kN) 5.07 675 10.43Axia stran (%) 5.22 6.10 5.89

    i) Determne the friction angle and cohesion of the materia (in terms ofeffective stresses). [17]

    ii) Comment on the type of soil based on the results of the triaxia tests. [2][Tota 25]

    Question 2Discuss the influence of compaction on the structure, permeability, shear strength andcompressibility of a clay. [25]

    IV\ e '" - : 101 h P c \IV ) """10'" ~JI)' IU-b(.L11,'j W I , ' . .., ". 1 -

    ~

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    CIVN 3004GEOTECHNICAL ENGINEERING I

    November 2007

    Question 3.For the concrete retaning wal shown in Fig.Q3. determne:

    (a) (i) The crack depth in the clay [5](ii) The latera forces on the wal [8J(iii) The overturning moment about point "A" [4J(iv) The restraning moment about point "A" and the wal 's

    factor of safety aganst overturning. [8)

    (b) (i) The bearing stress of the wal on the soil, assumng thewal exerts a uniform bea.ring stress on the soil due toits self weght on Iy. (Ignore the effect of any momentsabout the base of the wa l on the bearing stress.)

    (2)(ii) The bearing ca.pacity of the soil using Terzhagi's

    equation and assumng foundation depth D =Om. Notethe water table leve.[6J(iii) The factor of safc.,: aganst bearing stress falure of thewal. [2]

    [Tota 35)

    Given:for Clay: "(= J 8.5 l

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    CIVN 3004GEOTECHNICAL ENGINEERINGOCTOBER 2008 . PAGE 3 of6Question 3(a)The figure below shows atypical borehole log for a site where a tower is to beconstructed. The tower is supported by four widely spaced columns, each carrying 4000kN. Determine the size of the square foundation footing for each column using theTerzaghi equation for net ultimate bearing capacity given below.

    . ,,)

    Take the cohesion at the foundation level to be 50 kN/m2, < p for the soil to be 30 and use. . " " ( 'a factor of safety of 3 in your calculations. tij .::;:.-~i t\1 . : : - - 1 1 ff R. h" (10]

    ...,::....i:,-~.":,,......

    000", l'l.L/./- 5i ' i ;. '71.001'1 '.7,Co..rOJ

    1 0 O f " )

    (b)

    S i l t y s o . n d '1' = 19 kN/I'13

    S t i f f c l o . y Y s o . t =1 8 kN/I'13 Foundo tlonL e v e l 0.t 2 . 5 1'1Is::: a ~ - r ""A ~.

    '(I ::.. 8 --- 1,gls: 2l)11 .

    \ .( ,

    "RR C o o . r s e g r o . v e l o . n d s o . n d

    The following data were obtained from acompaction test on a cement stabilized soil,having a specific gravity of2,65.

    . '". - : - .. - - '.. '.).::..'

    Water content 5 8 10 \' 13, 16, 2Q(%)Dry density 1640 1780 1850 1890 1840 1700(kg/m'') " ,V

    Plot these data and on the same axes plot the zero air voids line. Indicate on ~;~ .: ~your plot the OMC and MDD. [5] f J cWhat percentage of air voids exists in the sample at the optimum moisturecontent? [3]Give adescription of an appropriate field control test which will be useful inmonitoring the compaction. (7]

    Total [25]

    (i)(ii)(iii)

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    CIVN 3004GEOTECHNICAL ENGINEERINGOCTOBER 2008 PAGE 4of6Question 4

    a) Calculate and plot on aclear diagram thevertical effective stresses on the vertical. centreline through the foundation shown below, before the foundation is loaded.[10]

    b) Calculate and tabulate the additional vertical effective stresses imposed by thefoundation onthe samevertical line at 1mintervals down to 4,Om: [10]

    (i) Immediately after the foundation load isapplied, assuming no rise in~porepressure in the sand but no drainage inthe clays.(ii) After all excess pore pressures induced by the loading have dissipated.

    I' 2.0m _\L --------- T- -2.0m1

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --

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    CIVN 3004GEOTECHNICAL ENGINEERINGOCTOBER 2008 PAGE 5of6Question 5The following datawas obtained fromthree drained triaxial tests:

    TestNumber ConfiningStress(kPa)

    Deviator StressDifference(kPa)

    123

    10020040084 ~..'"lI '-J40 c" '-I .. .c:30 ~'-I ~20I 10

    I 010.0 5t ' . > 1.0 0.1

    Particle Diameter (mm)

    Question 2 ~{\\' 6~ ~During a consolidated undrained (cu) triaxial(te~t,~the chamber pressure is increased tc:10 psi andthe deviator stress reaches a maximum of O:psi. Pore water pressures were measured thro-ughoutthe test, and the recordedvalue at failure':;;;; =18 psi. ""~~

    a. What was the value of the A pore pressure parameter at failure (Af)? [2]b. If the soil is known to have a cohesion of 10 psi, determine the magnitude of the effective~friction angle. (Implicit determination of < P is good for full mark. Analytical solution of < P will~count for 3 bonus marks.) [6]

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    ~~/ ~During a consolidated drained (CD) triaxial test, the chamber pressure is increased to 50 psi. Then 03

    js reduced while 01 is increased at th~same rg1e.0:=>=a. If the soil tested is known to have < p =25 and s = - . Q . , determine the maximum shear stressthat the sample will be able to bear. [5]b. Draw the effective stress path that corresponds to this loading. [2]

    Question 4

    Extraction wells have been installed below elevation -21.0 m of the soil profile shown in the figure.The water table has remained constant at elevation +4.0 m due to rainfall recharge, however, thepressure head at elevation -21.0m has been reduced to 16 m. Calculate the pressure heads at depths+4.0m, -11.0m and -21.0m considering the flow regime. [8]

    . _ .1 ;( 9 . .- ' I\l Groundlevel : : J 'Pf--=-~------=~:':':'::"":"::"::"=:""----"7-t!L--------+4.0 me = l.50 /' Yt= 16.66 kN/m3 1k = 2 X 10.9 m/s ~ 1 . , '\

    lJrp}( UJr--------------,~~---:k--------..,,..-4-:f:-11.0 mC lay II e = 2.20 / Yt= 14.70 'k~m3

    k = 2 X 10.9 m/s

    Clay I

    ---------------------!---l>- -21.0 m

    0 ;

    0 ' ~ 0 ; - (f ~-[)~t)1 z: _ 1 _ C f - o ;

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    CIVN 3004GEOTECHNICAL ENGINEEIUNG I

    November 2007

    - 5 -

    CIVN 3004. GEOTECHNICAL ENGINEERlNG r

    November 20071 '

    Question 4 (cont. .... ) -\ . .['1.\\\\\1 \ \\1\ zi/ti '\

    \. .\~rt"'"\~' -~" - . /~ I~ ;

    ~ zcr "~ .. : : : : ::..0'\ '"

    Z \ ~'"~+- -~- r - r~- r~~ \ \ , ~~~+-~~ .,V 1 "' -~~- r~- - j - ~~ \ \ ' "i 'l\ ~ ~o < ' A ~

    Given:-Vertica stress [TomSquare footing> (use attached chart)Vertica stress from Circular footing> (use attached chart)Vertica Stress from Line Load> 0"2 =2QZ3 I [n(x2 +Z2)2 J

    where Q = line loadx=horiz. dist. from

    line load.z=depthn=3.14159

    '1/ ~ I

    "f

    [Tota 15]

    t,nen " " ~",' "'"4",,'

    -4

    10

    ooo

    oo

    rrZzz

    ~

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    CIVN 3004GEOTECHNICAL ENGINEERING I

    November 2007

    0.28 I L l m z '-U I n ! .f-- T- //Xn Z L q / ->- 2.0_r-- + I

    ~Vz , 11)F=-1-:-~ ---

    ~ 1.0) I ~V/ O~,= ql, ~v -~ VI JIh V3 V / A-I--"" O.~/ IlvV V )_- e--- 01l/ V //1f--. ( I ; 1/ V )/1 V-I--/ ./JI~ V /F 0.3VV ---r- r---k0W V V vV' 0 . 11/ V

    ~ ~ ~ / l. - -- -'I/- - - r - - i~ VvV f.--f-- _ e--- I 0.1~~ ~

    ~-- 'I I -+

    0.260,240.220,200,180,16

    I, 0.14

    0,120,100,00,0

    0,00,0

    0.1 10m

    Vertica Stress Uuder Corner Of Rectangular Area Carrying Uniform Pressure

    - 6-

    . CIVN 3004

    GEOTECHNICAL ENGINEERING INovember 2007

    ~:p=- - = - - , t i J0.8 ~,J -T P I -+-'0 . 7 1 - 1 . _ ' - { ~06_ ! I J05 -r I I. (1, = 1c I04 I----t--I--rt----t--t--_-+---t----+----J1i, .-1----+--1-!: ,2 _ ', Q _ r ~T -- - l - - tL ,- - I - L - L _ - - 1 - _ ~- - Jo 2

    I . .,

    3 4o 5z

    6 7 8

    Vertica Stress Under Centre Of Clrcnln- Area carrying Uniform Pressure

    - '1,

    "

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    L--hr_s 1 1 '- - - - : _ /EXAM S OFFICEUSE ONL YL_University of theWitwatersrand, Johannesburg

    Course of topic No(s)

    Course ortopic name(s)Paper Number &titleTest / * to be held during mon