Examination papers on Introductory Geotechnics

8/11/2019 Examination papers on Introductory Geotechnics

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EXAMINATIONS OF SEMESTER I 2007/2008

j

FACULTY OF: TECHNO LOGY

CODE AND NAME OF COURSE: CIV 310 - G eote chn ics I

DATE AND TIME: Decem ber 13, 2007 09: 00 Hrs DURATIO N: 3 l/2Ho urs

EXAM INERS: INTERNAL,: Mr. Maxwell Jackson EXTERNAL:

INSTRUCTIONS TO CANDIDATES:

This paper has 4 pages and 5 questions

ANSWER ALL QUESTIONS_________________________________________________________________

*

Q U E S T I O N : 1

i.( a ) A n em ba nk m ent c on sists o f clay .Ells for whi ch C := 25 IcN/ tri1 and


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*De termine the allow able bearing capac ity, assuming a factor o f safety o f 3 for short- term- *

condition. Neglect geometric factors.


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(iii) Explain the terms total pressure, pore wa ter pressure and effective pressure

as app lied to a saturate d soil and sho w how these pressures .are related to one

anoth er. What is the influence of pore water pressure on the shear strengtho f soil.-

A soil failed under a major principal stress o f262 KN /m2 with a corresponding minor

pr incipal str ess o f 115 K N /m 2. If the m inor pr incipa l s tress fo r the same so il ha d be en

250 KN /m2, determine graphically the value o f the major principal stress at failure if:

t'i) t p = 0 (ii) C = 0

An undisturbed.soil, sample, 38mm in cp and 76mm in length, sheared in a triaxial test

under an additional axial load o f 2.75 K N with a vertical deformation o f 6.5mm. The

failure plane was inclined at 50 to the horizontal and the cell pressure was 240KN/m2.

(i) Draw the M ohr circle diagram representing the above stress condition.

(ii.) Determ ine Coulo m bs equation tor the shear strength of the soil, interms o f total stress.

List the main assumptions in Terzaghis T h e o r y of Consolidation.

A laboratory' conso lidation test on a cou ple o f clay, 20m m thick, drained top and

bott om gave the fo llowing resu lts:

Pressure ( KN/m2) Vo id ratio

50 0.71


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THE UNIVERSITY OF GUYANA

EXAMINATIONS OF SEMESTER I 2004

"ACULTY OF: TECHNO LOGY

:ODE AND NAME OF COURSE: C IV 310 - Ge otech nics I

M T E AND TIME: December 20, 2004 13: 00 Hrs DURATION: 3 l/4Ho urs

EXAMINERS: INTERNA L: Mr. Maxw ell Jackson EXTERNAL:

NSTRUCTION S TO CANDIDATES:

'his paper has 3 pages and 5 questions

vNSWER .ALL QUESTIONS

5 u e s t i o n ,A

i 8


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QUESTION: 2

2.(a) An embankment consists of clay fi l l for which C = 25 kN/ m2 and ^ = 2 5

consolidation undrained tests with pore pressure measurem ents), ihe average bulk

Or" / P . 7 ,of the fill is 1.9Mglm*. Estimate the she ar strength o f the m aterial on a horizontal pi;

po in t 20 m belo w the su rface o f th e em bankm ent, if the pore pre ss ure at th is po in t is

by a pie zom ete r to be 180 kN!m2.


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-QUESTION: 4 ;

4.[a') A "clay dep osit has a u nit w eight o f 100 lbs / f t and an unconfirmed compressive

strength o f 20 0 l b s / f t 1 . De term ine the dep th at w hich the horizontal soil pressu re is zero.

. : . (2 Marks)

\

4.(b) Given the retaining wall footing'shown, Figl, determine the factor of safety in bearing' ,

capacitv. The load due to wall has the following properties Ov =3000 lbs /f t Qn =1000

* " 0 Nlbs! ft e= 0.75 ft. the wall is founde d on a silty sand with c = 0, p - 2 8 . Th e m oist density

above water table 120 lbs/ f t 3, the saturated density below water table is 125 IhjjJ f t3. s

fo;

Q U E S T I O N : 5 ' ^ ' i

5.(a) A clay layer 15 ft thick underlies a 5 ft sand layer. Assume the initial void ratio of the

clay is 0.9; the c om pression index is 0.20.tbe wate r-table is.ar the top of the clay layer. A 10

ft by 10 ft footing with a pressure of 1000 lbs! f t 1 is founded 3 ft below the ground.

Calculate the se ttlem ent of the layer using the three layers shown. Take the avera ge stresses

in the layers as the stresses at the m idpoints shown, in F.ig2 (Use th e ^ .l m etho d j (10 Marks)

5.(b) If the clay has a coefficient of consolidation of 0.3 f t 1 / day . De termine the t ime when

50% of the total se ttlemen t.will occur.(2 Marks)


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T H E U N I V E R S I T Y O F G U Y A N A> \ .

EXAMINATIONS OF S E M E S T E R I 2005

:ULTY OF: TECHNOLOGY

DE AND NAM E OF COURSE: C IV 31.0 - G eo tech nic s I

TE AND TIME: December 15, 2005 13: 00 Mrs DURATION: 3 l/2H ours

AMINERS: INTERNAL: Mr. Maxwell Jackson EXTERNAL:

>TRUCTIONS TO CANDIDATES:

,s paper has 3 pages and 5 questions

ISWER ALL QU ESTIONS

U F S T IO N : 1

!> A- retain ing, w a ll l ia s a ve rt ic a l back and. is Sir hiU.ll TllC SOll IS & S'AIlcVy \0iiITV Ot WUlt

light 17.17 kN ! nv '. It shows a cohesion of 13 kN , nr and (j) = 20 Ne glect any effect of

ill friction and the upper surface of the fill is horizontal. Determine the thrust on the wall.


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QUESTION: 2

2.(a) An em bankm ent consists of clay fill for which C = 25 kN/ m2 and


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Original ground surface

Sltj

6Dry xmii

n Gs~z.m

T2 Ground water table ei

$

r* -'isjkr- ------ ------------ Sand

5ft11 0xa s

1C

Soft, noTHially cofi:>oitciated clayGs 2 7 2e 0.9

R Liiqutci limit 42%

Sand \

Fig 10-10

estion 4:

ne inch thick clay specimen was subjected to a conventional con solidation test. W hen the

ctive pressure on the soil spec ime n was in crease d from 2000 lb/ft2 to 4000 lb/ft2, the void

) decre ased from 0.75 to 0.62. Also the time for 50% conso lidation was de term ined to be

m. What is the coefficient of permeability, k. of the clay for the loading range? 10 m ark s

stion 5:

:he retaining w all shown, recom men d a base width B to provide a sliding safety factor o f

or slightly above). Assume that the base is rough and the friction angle between concrete

;and can be tak en as 30. /cone. = 1-50 lb /ft3

determine the overturning and resisting'mo m ent. Check the resulting factor o f satety


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' i O '

y t > / v / *1

' 1

___> G E O T E C H N I C S CSV .310

A soil normally consolidated clay layer 25m thickness has a natural

:or.tent of 55%; saturated unit w eight o f 17.2kiv/m , n pa nicle specific gravity ofi liquid limit o f 65%. A foundation load will cause a vertical s tress increase o f

Estim ate the settlem ent o f the found ation if the ground w ater table is at thet h e c l a y .

A c lay layer 15 ft thick u nde rlies a 5 ft sand layer. A ssum e the iuitial void

clay is 0.90 and the comp ression index is 0.20. A foundation1load 1000 p sf isft below the ground. Unit weight sand - 100 pc f. Unit weight c lay - 420 p c fnine the net pressu re increas e at the base of the foundation.ate die settlem ent o f the clay layer, 1 -

. (i) Exp lain the C onsolidation T heo ry bv Terzaghi.

y layer in Qu estion 2. has a C v o f 0.3ft /d ay D etcc nithi Total SctTlejjieiU-wilhaoGuc_ mine the time when 50%

1C [he reaso ns to r a site investig ation.

Inc (a) Norm ally consolidatedb) O ver conso li date d and O C R

c) Geop hysical invest igation

L A .L Q

%


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S r

Q III /.,VI

( , I' v i I I- > UI vu s | t I \ ' IIIu"' J 1.

J / j , / I yl- sle d is lAjridctl To a wcmihl ol 7 >N and pu lled nu o ss ii be ac h i Ii

' o takes a horiz onta l lnn :e/of, I l l m pull the sled Whui me the slicn yth pa ram eter s o

' 'fieach snnd?( I Points)

2.'A layer ofsancl ,1m thick rvci ies a stratum (if saturated clay of unknown depth,

water table is at 21^ below gjouiid level.

(i.) D eterm ine the To tal, P oie am. infe ctiv e ires sure s to a de pth o f 7m A ssum e no

capillary rise in the sand. Void ratios: for smtd 0.45, clay 0,90. Specific gravities: s

2.65 a nd clay 2.70.Unit weight o f wa ter: 9.81 kN /m 3. .(ii)Consider an OCR. of 5; determine the preconsolidation pressure at 7rn .

(4 Points)

3, The 10 10 ft area shown is loaded with n uniform pr essu re of 100 0'psf. D eten

hd stress increase at point A, which is 10 ft below the surface at the location shov,(2 Points)

in 10

j(k-rv &/. ,,pv u- ->,

K/

i

-


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1Quizz#3 Answer all Questions

G4V 3 1 Q

A* sa nd f iU;4m-lthicic 13placed o v e r th e e x is ti n g g ro un d s u r g e s o f a n o r m a l l y * 'consd|idated clay 2m.tfti.ck. fb e clay properties are: liquid limit 42%,and sp,gravity 2772, unit weight =17,,S l^/m*and k 2.2 xlQ^m/s? -XllOwater table

is located at 1.5m and the moist or saturated unit weight ofthg fill is !?.SKN/m?.

Determine (a) the settlement o f the clay layer, (b) the time for 50%

ponsolidation(5marks)I (

A test was carried out at a depth of 6m below ground level in clay soil has determined the horizontal total stress to he U.Q kN/ra2' Tbs water table lies 1.4rabelow ground level. Assume the clay to be folly rafiiTStwi Witfe unit weight of20.SkNVm^. Determine the coefficient of earth pressure at the depth of thetest. (2 m arks)

A compacted fill is to be constructed with a total volume o f 10,000 cubic metexxThe fill is to be ajmpacteci toa & y unit weight of i f j j 9 ^ / m ran2f a

Minimum water content of 1Q%.'SqUin the borrow area has a dry density of

and average water content o f 8%. How many PH^iP>Rjstep o f feftljPW

materials must be excavated and how njanyHiters must be hauled in? fS.marks)

ff-pr,surface"oft&efilleq iB ialent to 1

magnitude and point o f application afthe thrust on the wall per metre run.(i) if the fill is well drained, ......

(ii) if the fill i? water logged after a storm (asum.e the saturated densities of thet wo strata 1.9 and 2.0 Mg/m* nMjpectiyejy^Smarks)

ground water level is at a depth of 4m.

Determine a value for the safe bearing capacity of the fpundatipm(2marks)

Jl'


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/V\ A

'//


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Q u i22#3 Af l swsr a l l Quest ions

C4V310

' /h sand 1511'4m. thick is placed qv er th e g risting ground surfece o f a normallycon solidate d clay 2m. thick Th e clay pro pertie s are: liquid limit 42% , e,, **9.92

- l

.


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(;In | l'


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inal Test A nsw er All Q uestions:

'"Nl

(1): A build ing foundation 3m by 3m will impose 1500 kN total loading onto the

surface o f a thick stratum ,of normally consolidated (beneath ce ntre) ciay soil.Determine the foundation!settlement due to primary consolidation in the clay, using

Layers that are lrn; 1m; 2m and 2m thick respectively, from foundation load downward. For simplification, use a soil unit weight of 17.5 kN/m'1constant with depth, an

in-place void ratio of 1.2D. and a compression index equal to 0,38 for each, layer.

Assu me Bo ussin esq conditions; apply.

------- (2'Dmarks)

(2): (a)yCompute the ultimate load that an eccentrically loaded squ are footing of width

2.4 m w ith eccentricity (e) of 0.4m can sustain ifj '=1 8k N /m J; and c - 10kN /m2 and

(Z^56;..and surch arge intensity at the base of the looting o f 10 kN/m 2.

< i T;;'l (lOmarks)[(b) A continuous footing'is founded 3ft below the ground surface in=nous ciay. Determine the ultimate and allowable bearing-capacities. :125pcf

C-1^00psf; and < j > - 0. Assume F.S= ;3.0 (5 m arks)

))A cut is to excava ted in a soil which has a cohesio n .of 96kN /m", a unit weight

N7m3 and an gle o f inte rnal fric tio n of 10". T he de sign requ ires a slope

x (P) o f 60. What is the maxim um depth that can be excava ted and still.

" ma intain a factor o f safety of 1.5 with respect to'the height ofxlje slope. UseTajsfcaugjability ch an s. ^ (5marks)

(b) ^Determine the factor of safety for a slope of 40 and 30m high in an areavvli^re a uniform clay exists, using c=96kN/m2; y- I 7kN / m 3 a nd A

-"ro cktstratum exists 45m below the ground surface. Use Taylor stability charts.

(5inarks)

(4) (a) A 10,000 lb load acts uniform ly over 4ft*4 ft footing. Es tim ate the average?

L-'pressure distribution on a plane 5ft below the!footing base. (5 marks)

If the "above footing is founded on a sand with a soil modulus o f 200 kips

pe r square foot zmd a Pois so ns ratio of 0.4. Es timate the se tt le m ent o f the

footing. (30m ark s)

(b) A clay deposit has a unit weight of 100 lb/ftJ and an unc onf ined


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G EO TE CH NIC S 1 C IV 310

Answer all Questions \ $

v. ^S -* ^ P ~ n _ >3

Calculate the total lateral force acting against a smooth unyielding wall 3m high

that retains cohesionless soil. Assuming no lateral deformation occurs in the soil mass

and the at rest conditions applies and the water table is lm below top o f wall. Properties

o f the retaine d soil are: cp=35 y=1 8.2kN /m2 2 m ar ks r r L ^ \

2. A retaining wall supports a sand backfill. Assum ing an active lateral pressurecond ition and rising soil properties given in question 1. De term ine (a) the lateral force

pe r un it leng th o f the wal l. 5 marks Q ~ 'Sa / f 'iK V

/. /?3. A flexible foundation 4m*4m is placed on a clay layer\0mthick and exerts auniform pressure of 120kN/m2.Determine the immediate settlement at the center andcom er of the foundation. E=20M N/m2 and u=0.4 6 m ar ks ' ( }'

j t *i '

4. A clay laye r 20ft thick has sand above it and an impe rvious sha le below it; thecoefficie nt o f consolid ation is 0.4ft2/day.. A uniform s tress incre ase is applied to the soil.

Calculate the time w hen 50% o f settlement will have occurred. If the clay stratum were

40 ft instead o f ,20ft, how long w ould it take to achieve 50% of the ultimate settlemen t?

U(T)=50% T=0.197 5 m arks " T - -

|

5. A soft norm ally conso lidated clay layer is 15m thick with natural m oisture content

of 40%. The clay has a saturated unit weight of 18kN/m3, a particle specific gravity of (\

2.65, and a liquid limit of 80%. The foundation load will subject the center of the layer to */a vertical stress increase of 15kN/m. Estimate the value for the se tttem en T of the /foundation if ground \jVater level is at the surface of the clay. 7 m ark s / ^


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A sand fill 4m thick is placed over the existing ground surface o f a normally

consolidated clay 2m thick. The clay properties are: liquid limit 42%, = 0.92 andSp gravity 2.72, unit wgt. = 17.5 kN/m3 and k = 2.2 xlOy m/s. Th e water table is

located at 1,5m and the moist or saturated weight ot the fill is 19.5 kN/m3.

Determine: (a) the settlem ent of the clay layer. ,(b) the time for 50%-consolidation.

-A test was carried out at a depth of 6m below g round level in clay soil has

determined the horizontal total stress to be 120 kN/m: . The w ater table lies 1.4m

below grou nd level. Assum e the clay to be fully sa tu ra ted with un it weigh t of^eCSkN/m8 Determ ine the coefficient of earth pressure at the depth o f the test. .

A compacted fill is to be constructed v'ith a total volume of 10,000 cubic meters.

The fill is to be com pac ted to a dry unit we ight o f at lea st 20 k N/m 3, and a

minimum w ater content of 10%. Soil in the borrow are a has a dry density of 19

kN /m1 and average water content or' 8%. How many cubic meters of borrow

materials must be excavated and how many liters must be hauled in?

A retaining wall with vertical back 8m high. The de nsity o f the top 3m of fill is

1 75 M g/m ' and the angle yf shearing resistance 30 For the lower 5m the values

arc 1,85 Mg/m 3 and 35 respectively. There is a surc harge load on the horizontal

surface of the fill equivalent to 1.2 M g/m'' uniformly distributed. Find the

mag nitude and point of application o f the thrust on the wall per metre run.

(1) if the fill is well drained,

(2) if the fill is water logged after a storm (assuming the saturated densities of

the two strata 1.9 and 2.0 Mg/m 3respectively.

A footing 3 m by 6m is to be founded it a depth of 2m in a saturate d o f unit weight

19 l


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/ ' v-

L S

8. If a 4m x 4m lies 1 ,5m below the surface of a soil h aving coh esion o f 50 kN/m*anyle of friction 30 and a unit weight of 20 k N /m '. Determ ine the net allowable

bea ring ca pac ity if FS = 3

9. A sied is loade d to a weight o f 75N and pulled acros s a beach. If it takes a

horizontal force o f 45N to pull the sled. What are the strength parameters of the

be ach sand ? i / ( \ ' *'

10. A layer o f sand 3m thick overlies a stratum o f clay o f unknown depth. The w.t. isat 2m below ground leve l. (1) Determine the Total, Pore and Effective Pressures

to a depth o f 7m. Assum e no capillary rise in the sand Void ratios: for sand 0.45

and clay 0.90. Specific gravities: sand 2.65 and clay 2.70. Unit wgt. ol wate r =9.81 kN/m 3 . (2) Consid er an OCR o f 5: determ ine the pre-cons olidatio n pressure

. at 7m. !

11. Th e 10 x 10 ft area s how n is loaded with a unifo rm pre ssu re o f lOOOpsf.

i / ' Determine the stress increase at point A, which is 10 ft below the surface at the

location shown.

< \

if \

For the same foundation and loading calculate the average stress increase al adepth o f 12 ft.

If the footing is found ed on a sand with a soil m odulu s o f 200 kips/112 and apois sons ra tio o f 0.4. Est im ate the se ttlement o f the footing.

A conce ntrated load oi 20 kN acts on the surface of an hom ogenous soil m ass oflarge extent. Find the stress intensity at depth of 10m.

(1) Dire ctly under the load. *

(2) At a horizontal distance of 5m.

i


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y .

founded 3 ft below the ground. Unit wgt. sand = 100 pcf. Unit wgt. clay = 120pcf (a) Determinfe the net pressure increa se at the base o f the foun da tion.

(b) Calculate the settlement of the clay layer.

15. (a) Explain the consolidation theory by Terzaghi.

(b) The clay layer in Qu 14 has a C, of 0.3 ft3/day De term ine the time when 50%

and 90% o f the total settlement will occur.

, ' 6. (aj State the reasons for a site investiga tion I.

* (b) Define: Norm ally consolidated, Over consolidated and OC R, Geophysicalinvestigation.

*i 17. A building fou ndation 3m x 3m will impo se 1500 kN total loading onto the surface

of a thick stratum o f normally consolidated (bene ath centre) clay soil. Determ ine

the foundation settlement due to primary consolidation in the clay, using layers

that are 1m, 1m, 2m, and 2m thick respectively, from foundation load down ward.

For simp lification, use a soil unit wgl. o f 17.5 k'N/m3 con stan t with dep th, an in-

place void ratio o f 1.20 and co mpress ion inde x equa l to 0.38 for each layer

Assume Boussinesq conditions apply.i\ f Q u . < > v t e > S %\

18. (a) Compu te tne ultimate load that an eccentrically loaded square footing o f width ^

2 4m with ecce ntricity e = 0.4m can sus tain if y = 18 k_N/m3 , and c = 10 kN /m '

and


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^ " ^ C 3 ) [ ^ I s

,2jL Ca lcula te the total lateral- for ce acting against- asm


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_2J_. Calculat e th e total latera l fo.c e acting again st asm


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Determine (a) the factor if] safety against sliding and (b) the overturning moment.

29. The fig. belo

and (b) the

and use av

ti

lera

w shows a

me for 50%

ge stress inc:

foundation. D eterm ine (a) the con solidation settlement

consolidation. Co nsider p0 at the c en tre'o f the clay layer

ease method.

A?

j

30 At a pl a n n k construction jslite subsurface sampling indicates that the w ^ u n i t w st

o 1 soil S 123 pcf. (a) determine the effective verncal1 (b) the effective vertical stress at the 12 tt deptn u tne

the water tible is deep andwate r table |i|s at the g roun d puriace.

urfacc is 6m und er the water surface. Sa nd ies itom the

lake indicate a bulk density of 2 M g/m . Determ ine them the deposit at a,depth 12m below the soil surface. Alio.'indicate

1stress at the same point. j

ion the soil sAt a lake loieat

soil deposit underlying theeffective stress

the total veil

. / >32- Com pare thl^ stress increase: 2m below the centre o f a 3m x 3m square foundation

V imp osing aj. bearing pressure o f 145 kPa. (a) W hen the B pu ssin esq : stress

distribution is assumed and|(b) 2:1 average pressure increase is assum ed.: j

! L: I! , ! i.33. (a) A retaining has a v^h ical back and is 8m high. Th e soil isja san di/lo am o f

un it wgt, 17.17 SN/rn3. II shows a cohesion o f 13 kN/m* and cp|=,2||0. 'Neglect!any effect off wall frictio|n and the upp er surface o f the fill is ho ri z o n ta l'Determine the thrust on

(b) Find the resultant thrust

ibehind tAssume

ie Will until tlsaturated unit w

the wall.

on the wall if drains are blocked' and water

ii water table is at 3m above the) bottom ofit 19.62 kN/m3.

bu ild s up

file waij.


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fajctor ol' safety in bearing

cap acity . Th e loa d clue to wall 1ms the fjjljiowuig pro pe rties Q v - 300 0 lb/ft, Qi, =

100 0 lb/f t an d e = 0.75 ..ft. Th e wall is fotfricl'ed oil a silt}] san d w ith c = 0 and

(p &. 28 T he m oist density abo ve W .T, 1.20 lb/ft3, the satur ate d density beJowW-.'ff: ;*! 125 lb /f t3.. i !

35. Giv en the re taining wall footing shown.; djeteijjiine he

' i>V odO

36 . (a):A clay layer 15 ft tiiid i uivdorlies-a:5 ft sand layer. Ajssume the initial vo id ratio

o f the c lay i s 0 .9, the compress ion i n 4 ^ & ff 2 . : The W .T. i s a t'"thetop_ o f the clay

UyW. A 10 ft x 10 ft foo ting w ith a p res su re o f . 10|LXi Ibis ii^birndecl: 3 ft be low thegrou nd. Cal the settlem ent o f the layer using; tile thre e layers sh o w i1. Take 'lie

a^;i'a;e stres ses in the layers as the stress 35

(b )jlf the clay has a coefficient o f con solidation o f 0.3 ft2/day. De term ine the time

when 50% o f the total settlement will occur.

at" the midpo

I

ib shin own.

I !i3|7. A-rectangu lar footing 4.5m long and J Onj Vide is placed at a depth o f 1.8m below

grou nd level in a deposi t.ol' f irm son, ' ; led rHiy. T h c j W T

bi-'.c.w g round it;vel. D ele ji m ne me g ro w -Uijid net u lt im ate bearing capac it ie s ioi

(a) undrained c 60 kN/m 2, ym[= 2J .8 IcNj/ip3 an d (b) draiined c = 5 kN/rn2,


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28. fo r the tig. shown beiow and considering that y = 125 lb/ft3 and (p = 30; thet friction*.angle between concrete and sand can be taken as 30. yconc = 150 lb/ft3,r Determine (a) the factor of safety against sliding and (b) the overturning moment.

2!-. The below shows a foundation. Detennine (a) the consolidation settlementand (b) the time for 50% consolidation. Consider p0 at the centre o f the clay layerand u.se average stress increase method.

30 At a planned construction site subsurface sampling ind:cates that the wet unit wgtof the soil is 123 pcf. (a) determine the effective vertical stress at the 12 ft depth if

the water table is deep and (b) the effective vertical stress at the 12 ft depth if thewater table is at the ground surface.

rO31 At a lake location the soil surfacc is 6m under the water surface. Samples from the

soil deposit underlying the lake indicate a bulk density o f 2 Mg/m3. Determine the

effective stress in the deposit at a depth 12m below the soil surface. Also indicatethe total vertical stress at the same point.

Ji

32. Compare the stress increase 2m below the centre of a 3m x 3m square foundationC imposing a bearing pressure of 145 kPa. (a) When the Boussinesq stress

distribution is assumed and (b) 2:1 average pressure increase is assumed. ,

(a) A retaining wall has a vertical back and is 8m high. The soil is a sandy loam ofunit wgt 17.17 kN/m3. It shows a cohesion of 13 kN/m2 and cp= 20. Neglectany effect of wall friction and the upper surface of the fill is horizontal.


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s i h J u c l .5 + h Q c J X J l i L L

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T = / t --Sw* r___L>______ OC-

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T (wj ) n

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33/53

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34/53

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35/53

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36/53

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37/53

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38/53

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39/53

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40/53

Original ground surface

Ground wats r table

5 ft

iDry sandCs =52.68* m

5 ft

to

Sand0.5

ft

Soft, normally consolfdated clayG, 2:72&*m2

.'Uqtiidlirrift 42%

^


41/53

EXAM INATIONS OF SEMESTER I 2012

FACULT Y OF: TECHNO LOGY

CODE AND NAME OF COURSE: CIV 310 - Geotechnics I

DATE AN D TIME: December 10, 201 2 09: 00 Hrs DURATION: 3 l/4H ours

EXAMINERS; INTERNAL: Mr. Max well Jackson EXTERNA L:



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

ANSWE R ALL QU ES TIONS ____________________________________________________________________


QUESTION: 1

l.(a) A retaining wall has a vertical back and is 8m high. The soil is a sandy loam of unit

weight 17.17 kN/m \ It shows a cohesion of 13 kN/m2 and - 20 Neglec t any effect o f

wall friction and the upper surface of the fill is horizontal. Determine the thrust on the wall

both before and after the tensile crack occurs

(5 Marks)


42/53

1. A cut is to be excavated in soft clay to a depth of 9m. The material has a unit weight of

18.3 kN/m3 and cohesion of 34 kPa. A hard layer underlies the soft layer at a depth o f 12m

below the original ground surface. What is the slope angle at which failure is likely to occur?

( 5Marks)

QUESTION: 2

2.(a) A 10 ft thick fill embankment of very large extent is to be placed over a clay layer as

shown, while the ground water table is to be simultaneously lowered to 12 ft below ground

surface. The clay is saturated with a speciiic gravity of 2.69 and average water content of

30%, compression index was determined to be 0.28. Assuming the clay layer is normally

consolidated, determine settlement of the fill.

C ^ (10 Marks)

2.(b) Approximate the time required for 80% consolidation of the clay layer if Cv is 4.3 x

10 6 ft2 /sec. For 80% T = 0.567 5 marks

* - -2.. G^\

rr (JO


43/53

QUESTION: 3

3.(a) Given the height of the backfill shown, what is the height of the keyless concrete

gravity wall required to adequately resist sliding with a factor of safety of 2? Use 150 lbf/ft3

for the unit weight of concrete. Note: CAis adhesion

^wall

mudl ine

i j f p lI H pt p | l

Wm mm m t ,

, . clayey sand '

W. -.'V 105.7 lbf/ft3 : . Ca = 150 lbf/ft 2 . '

8 ft . cj) = 27

S = 15

20 f t : ' . ; '. 7 ' 4 ft *'

I M K k ) e>

(not to scale) u j -- n o

U U z b o o

15 marks

QUESTION: 4

1. 4.(a) For a warehouse with large bay spaces, the interior footings are required to

support a structural dead load plus live load of 100 kips per interior column.

Assuming square interior footings are designed in the soil profile as shown. What

is the factor o f safety of the given loading with respect to ultimate bearing

capacity? Assume the column loading is concentric.


44/53

g ro u n d | | p

surface

m

1.5 ft :

i H l t l i

^ c l a y e y s andl&iy - 103.4 lbf/ f t3

&: = 25>Xr: c 50 lb f/ ft 2 rV

6 ft

(10 Marks)

4. (b) What are the steps necessary to check the stability o f retaining structures?

(ii) Discuss the purposes of geotechnical investigations. 5 marks

T h e b e a r i n g c a p a c i t y fa c t o r s ( V e s i c , 1 9 7 1 ) ar e:


45/53

g p y ( , )

/V c = ( N - 1 ) t a n 0

JVy = 2 ( i V + 1 ) t a n *

T h e v a r i a t io n s o f / V , / V , a n d /V w i th s o i l f r ic t i o n a n g l e 0 a re s h o w n in F i g . 1 0 - 2 1 .H * t

T h e s h a p e f a c t o r s a r e a s f o l l o w s :

Fa - 1 +

V ,+

/ J

' i f

^ = 1 - 0 . 4f i r

T h e d e p t h f a c t o r s (Df


46/53

50 40 30 20

Slope angle, as (degrees)

Stability

num

ber,


47/53


FACU LTY OF: TECHNOLOG Y

CODE AND NAME OF COURSE: CIV 310 - Geotechnics 1

DATE AN D TIME: Decemb er 11, 2006 13 :00H rs DURATION: 3 1/21-

EXAMIN ERS: INTERNAL: Mr. Maxwell Jackson EXTERNAL:



ANSWER ALL. QUESTIONS and show neat: sketches and diagrams____________________________

QUESTION:: 1

1. (a) A 6m tail cantilever wall retains a soil of unit weight 19.2 kN/ in'and (j) - 30

Neglect any effect of wall friction and the upper surface of the fill is horizontal. Determine

the thrust on the wall.

(3 Marks)

1. (b) Find the resultant thrust on the wall if drains are blocked and water builds up behind


QUESTION 2


48/53

QUESTION: 2

2. (a) An embankment consists of clay fill for which C = 25 kN/m2 and = 26 (from

consolidation undrained tests with pore pressure measurements). The average bulk density

of the fill is 1.9Mg/m}. Estimate the shear strength of the material on a horizontal plane at a

point 20m below the surface of the embankment, if the pore pressure at this poinx is shown

by a piezometer to be 180kN / m2.

(3 Marks)

2. (b) A 15m high embankment is inclined at 30 to the horizontal. If ^-=15 and cohesive

strength is 15 kPa and unit weight of embankment Soil is 17.5kN I m . Find the factor of

safety.

(3 Marks)

2. (c) A 4m high road embankment has to be made out of clay with negligible internal

friction. If cohes ion is lOkPa and a hard stratum exists at 2m below the ground surface. Find

the safe inclination for the slope of the embankment.

( 3 Marks)

QUESTION: 3

3.(a) The 10x10 ft area shown (Fig3) is loaded with a uniform pressure of 1000 pounds per

square foot. Determine the stress increase at a point A, which is 10 ft below the surface at the

location shown.

(3 Marks)

3. (b) For the. same foundation and loading calculate the average stress increase at a depth of

12ft.

QUE STION: 4 ^


49/53

4. (a) An uneon fined compression test has been performed on a 35mm diameter and 75mm

long sample of clay. The axial load and the strain at failure were 12.0 and 7.5% respectively.

Compute the undrained shear strength. / / -

v m m j

~ ' ' - >

4. (b) A 949 kN column load is to be supported on a square concrete footing that will be

underlain by a clayey silt with undrained shear strength of 125 kPa and unit weight of 18.0

kN/m3 . The bottom of this footing will be 1.6m below the ground surface, and the water

table is more than 30m below the ground surface. Using a factor of safety of 3.0, compute the

required footing width, y c= 23.6 kN/m3

/ /^ \ ------- 0 0 Marks)


50/53


FACULTY OF: TECHNOLOGY

CODE AND NAME OF COURSE: CIV 310 - Geote chn ics I

DATE AND TIME: February 01, 2010 09: 00 Hrs DURATION: 3 l/2Hours

EXAMINERS: INTERNAL: Mr. Maxwell Jackson EXTERNAL: \>




i' y-

ANSWER ALL QUESTIONS NOTE: highlight each step of analysis and neatness is rewarded

QUESTION: 1

1. A planned construction site is underlain by a thick depos it of

normally consolidated clay soil. A building foundation 6 ft, square

will be located on the ground surface and carry a total loading of

180,000 lb.

Determine the foundation settlement (beneath the centre) by

analyzing the volume changes due to primary co m pression in layers

that are 2, 4, and 6ft. thick, respectively, from the foundation level

~ t w (01__


51/53

QUESTION: 2

An existing building is to be renovated. One of the existing footingsis 1.5m by 1,5m in area and 1m below the adjacent soil surface. The

structural changes for the building would require this footing to

support a loading of 2000 kN. Determine if the footing size and soil

bearing c apa city are adequate. Soil investigation indicates that the

foundation soils are (medium - dense tq dense sands. The angle of

internal friction is 34%nd the unlf weigRns l^k N /rn3" Apply a factor

. of safety of 2.5 8marks JCla ^ ^ 'V

V

QU ESTION : 3 \ w

(a) Describe the 'causes and factors that affect slope stability""" ?

(b) An area of planned construction is underlained by sandy soil where the angle of

internal friction is 35. What is the maximum safe slope angle for the soil if there is

no ground water flow? If it is assumed that groundwater flow could occur through theslope, approximately what slope angle should be considered as the allowable

maximum?

(c) Describe how you would plan and conduct a subsurface investigation for the design

of a multi storey faculty of law building at Turkeyen campus.

10 marks


52/53

QUESTION: 5

Figure 2 below shows a foundation. Determine (a) the consolidation settlement and (b)

the time for 50% consolidation. Consider p0 at the center of the clay layer and use

average stress increase method. ^ i j y

(10 marks)


53/53

Normally consolidated clay

7,= 108 lb/ft3

s*2.75w m28% >~

>' >_> Ce= 0.4Cv* 0.1 ft/day

End o f Exam

Documents

Examination papers on Introductory Geotechnics