Ce-443.pdf

Date: 24/01/2016

L-4/T -2/CE

BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY, L-4/T-2 Sub:

DHAKA

B. Sc. Engineering Examinations 2013-2014

CE 443

(Earth Retaining Structures)

Full Marks: 140

Time: 3 Hours

The figures in the margin indicate full marks. USE SEP ARA TE SCRIPTS FOR EACH SECTION SECTION -A There are FOUR questions in this Section. Answer any THREE. Assume reasonable missing value/values. 1. (a) List examples of structures for which the foundations

are to be designed with

(5~)

considerations of lateral loads. (b) Determine the factor of safety against bearing capacity failure for the retaining wall shown in Fig. 1. Calculated loads on the base per meter of wall are: Vertical-450 kN,

(10)

Horizontal-250 kN. Use Hansen's method.

(Table containing Hansen's bearing capacity factors is provided). (c) A concrete caisson foundation is to be constructed for a bridge pier (Fig. 2). Analyze

(8)

to determine the wall thickness for the caisson to be self sinking.

(8)

2. (a) Mention the advantages and disadvantages of different types of caissons. (b) State situations for which analysis for deep stability of a retaining wall is required.

(5~)

Also briefly state the procedure for such analysis. (c) A braced excavation, 18 m x 21 m in plan and 10m in depth, is planned to be made in a soft to medium stiff clay (qu = 60 kPa) for construction of a basement. It is considered that the bracing system will consist of steel sheet piles along with I-sections as wales and struts. The struts will be placed at three levels from the ground surface (at 2m, 5m and 8m depths) and will be horizontally 3m apart from each other. Analyze and comment on'

(10)

the possibility for failure by bottom heaving.

3. (a) Discuss,

with sketches,

different

types of braced

cofferdams

considering

the

(8~)

arrangement of components. (b) Analyze the retaining wall shown in Fig. 3 and comment on its stability against failure

(10)

by sliding. (c) Discuss the considerations

for selecting soil parameters

in the design of braced

(5)

excavation in stiff fissured clays. Contd

P/2

=2=

CE 443 4. (a) Discuss the different types ofloads that are to be considered in the design of caissons.

(6)

(b) Discuss factors that govern the magnitude of lateral earth pressure on a rigid retaining

(8)

wall. (c) A long trench, 7 m deep and 5 m wide, is to be made in sand for construction of a tunnel segment. If struts are placed as shown in Fig. 4, determine the force on strut B.

(9~)

Consider 2 m center to center spacing of the struts in plan.

SECTION -B There are FOUR questions in this Section. Answer any THREE.

5. (a) What are the benefits of construction dewatering? What techniques are available?

(9)

Point out how soil permeability affects the selection of method. (b) Discuss the desirable properties and role of slurry in slurry trench wall construction,

(9)

Comment on the loss of slurry during construction.

(5~)

(c) Show pressure diagrams for designing braced excavations in sand and clay.

6. (a) Briefly compare the different methods available for the analysis of laterally loaded piles. Comment on the suitability of these methods. (b) List advantages of steel sheet piles. Comment on the use of different sections of such

(9)

piles.

(3x2=6)

(c) Write short notes on: (i) Use of factor of safety in sheet pile design (ii) Effect of wall movement on lateral earth pressure. 7. (a) Determine the required length of cantilever sheet pile

III

cohesive soil (Fig. 5)

(15)

retaining cohesive backfill. Consider short term loading. ,)

cLAY .~ ... I

;./', b

so::t. ..- ---_ ..

,,~ ,_.,

~v.. =

-::::1

g

'1/ 3l" KN "r'"\ j-. .. -

. .--

~"~-

90

"

,

Kfo.-

Contd

P/3

=3=

CE 443 ~

Contd ... Q. No.,W

(b) Using Broms' method, determine the factor of safety against bearing failure for a 24 inch dia 30 ft. long free standing pile subjected to a horizontal load of 10 kips, 2 ft. above ground level. Also determine the horizontal deflection of the pile. Consider the ground water table to be at G.L. Soil properties are: Unit weight

= 112 pcf, Angle of

internal friction = 30°, nh = 12 ton/ft3. Pile properties are : Yield Moment = 300 kip-ft, E = 3.2

X

06 psi.

(8~)

8. (a) Detennine the required length of anchored sheet pile shown in Fig. 6, embedded in sandy soil. Determine the force in tie-rod. Note that the back fill supports a surcharge

(18)

load of 15 kPa to a large distance.

1'-.----- ...--,..---.

-.------F;--K.~1~ev--=-------...-.

----t-=-t-. -~-t--t--..1--.+--.. j

r.------ ..- .......,..-......,..-.. 1---"-"'-'"

:2 --

j

-'--l'

----....

~_...~~~~_~

--I

.____

~:::

1YV

.... -. -. -----:-:. ... - ..----

\(, KtY~'3

:SlJk;"».::

...=0_._ ..

1"2.-

__

._..... _. ..

..,"

~----~4 ~.-'"-----..

t5std:; . \9-\j1J/ ~---'!

-"--"-45 ';3-i-°-'-' -:--.~ .._._ --.I

!----~--:._-._._.-.-

.._-~._._..•__

;.

<5~..

_~

J~

r-.--...-.~.._-cc_-~~t:~ol<~-~c_---l -j

.

-..- ..-.-~._.._.--.----_.- ----.

--'

-'--"-(---3-"---'-'--

--J ~~

T2-'

fl<j.

b

(b) If the water table in front of the wall (Fig. 6) drops by 2 m, while that in the' backfill material remains unchanged,

what will be the effect on the problem? Elaborate the

procedure how you will consider this in your analysis.

m_1 I-

0.4

2 m ~ = 30° y= 18 kN 1m3

~ = 12° c = 40 kPa

5 m ys", = 18 kN 1m3 ~

2m

2 I~

~6

~

1--

---...-1--1 4m

m

T

7 m River Bed

Silty clay ISm

~=15°,

qu

12 m

3m

= 60

kPa

Fine sand ~ = 250

12 m

Semi-circle

OAm

_I ISm 3m

-c-

A

lIO

=20(J c = 15 kPa Y,a! = 18 kN 1m'

"I

1m

Sand

<j>

Sm

-.,-_ ..-~..

FigA) .'- .-.••.. ..

--'"

B

_r

2m

r~---"'---"oi

c = 80 kPa Ysa! = 20 kN 1m'

2m ~

2m 2m

Excavation Bottom

~ =30° Y = 16 k

..

,~ ()

Shape, depth, inclination, ground and base factors for use in either the Hansen (1970) or Vesic (1973) bearing-capacity equations. Factors apply to either method unless subscripted with (H) or (V). Use primed factors when cP = 0

,

:~

{30

B

S,

=0.2'-

S,

= 1 + N,'L

L Nq B

S,

Sq

d~

=

d,

= 1 + OAk

=

1

+-

L

tan cP

= 0.5 - 0.5 ~ I -

., t,(H)

OAk

dq

=

1

+ 2 tan

= 1 - O.4'~

L

dy

k

k

= =-

B

=

=

{]O g,

1- i

iq -

(Hansen

--q

Nq -1

for - ~ I B-

.(

0.5H)5

V

1-

+ A/c.

1 - 1470

9q(H)

=

9y(HI

= (1 - 0.5 tan (3)5

(lq(V)

=

{lyIV\

= (1 - tan {3)2

cot cP

iq(V)

=

H V + A/c. cot cP

(1 -

)m

7]0

I. Do not use 51 in combination with ii' 2. Can use 5, in combination with d" gh and bt•

11

b~ = 1470

.U't

7]0

D

- 17

=

and Vesic)

D tan - I - for - > 1 (rad) B B

3. For LIB ~ 2 use tP" ForLIB > 2 use I/Jps = UI/J" For rP ~ 34~ use rPP' =
= - 2 sin {3for cP = 0

Base factors (tilted base)

D

Where Af = effective footing area B' x L' (see Fig. 4-4) c. = adhesion to base = cohesion or a reduced value D = depth of footing in ground (used with B and not B') eB' eL = eccentricity of load with respect to center of footing area H = horizontal component of footing load with H ~ Vtan b V = total vertical load on footing P = slope of ground away from base with downward = ( +) b = friction angle between base and soil-usually b = tP for concrete on soil '1 = tilt angle of base from horizontal with ( + ) upward as usual case General:

for Vesic use Ny

1.00 for all cP

D

147c

cP(1 - sin cP)k

iq(H)

Sy

=

g~ =

AfcoN,

_.

i,

--. Arca

mH --

., -1tc{y)

= 1 for strip B

.il> J>

Ground factors (base on slope)

Inclination factors

. Depth. factors

Shape factors

b, = I - 14T

iy(H)

+ c.Af

.

=( (

ly(H)

=

iy(V)

=(

m

=

5

1

V

-

+

O.7H. A/co cot cP )

(",

O

(0.7-I] /450)H)5 1 - V + ArC. cot q, 1

H

V

-

+ ArC.

2 + BIL

mS = ---

1

+ BIL

2

+ LjB

m = mL = --1 + LIB

cot

4J

=

0)

(1]>0)

bq(H)

= exp (-

bY(H)

= exp

bq(Y}

=

by(v)

Nates:

)"'+1

)'

21] tan cP) (- 2.7" tan 4J)

=

(1 -

I]

tan cP)2

P + '7 ;:i 90° P-;;cP

H parallel to B

'-

H parallel to L

Note: iq, iy > 0

.~/~~~

..

~

••••••••• :z.

",;l\1@!4IM!

1

:

200

•

,

L£ 44'-' 150

L.

.I ..

~

'"0 ~ ...•.

.

~

-1If+--

CL

D-

o

120

Restrained

-'

.;'"

" 0

•.. 80 d

~ Cl

'tl

.~ 0.

40

0-

«' 00

L 10

Length.

for coheS"lonless length. After

Ultimate lateral reqistance soils related to embedment sengI

B. Sroms

10.0

yield

moment

Ultimate lateral yield moment.

20

15

12

1000

10,000

Myield/D4rKp

regislance 'for cohes.ionless After Bengl B. Brams

soiJ$

rel'al.ed

.to

i-.T-TTl-'

10

----.--' .'-----~f---- ..----I-.--- ..- l-----I--, !

Free ,..-eh.ended

_ Restrained

e c

o

L

U
6

------

L

.....

....•, Cl

~'iI

o ~ .r c Vl

4

elL'" 2"0

~

tn ~

c~ C1J'(l

-'.

Q

--_._-_ ..

Ow

Vl

'-'

-

1'5

0

C >--

E

_/-_

......-_

2

o

..-....._~--.,'''O-. '.I (:' 0 ',8

0.6~

--C-_.~ ~-o],--' t ,--~-

00

2

I,

Dim en ti 0 n Ie S 5 Fig.

6

LaiNol so il 5

.

'8

6 l. e ng th

dl.'flecfions at ground After Sengt B. Brams

10

'll. surface

tor

cohesio.nless

,.'.

-6

....

,

L-4/T-2/CE

Date: 31/01/2017

BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY, DHAKA L-4/T-2 Sub:

B. Sc. Engineering Examinations 2014-2015

CE 443

(Earth Retaining Structures)

Full Marks : 140

Time : 3 Hours

The figures in the margin indicate full marks. USE SEPARATE SCRIPTS FOR EACH SECTION _________

•

M_M

••••

__

• __

••••

_ ••

••••

_

••••••••••

-

..•.....•...••••

-

•••

_.

••••

__

•••••••••

_

SECTION -A There are FOUR questions in this Section. Answer any THREE. Assuming reasonable value of missing data, only if necessary.

1. (a) With neat sketches briefly describe different techniques available for construction

(13)

dewatering. Indicate suitability of each method. (b) Briefly describe the construction procedure for constructing diaphragm wall using slurry trench method and tremie concreting. Discuss slurry circulation

and cleaning

techniques. Present neat diagrams.

(1 0 ~)

2. (a) Write short notes on the following:

(3x3=9)

(i) Filter skin (ii) Factor of safety in sheet pile design (iii) Stability number (b) Distinguish between computational p - y curve method and finite element method for

(5 ~)

laterally loaded piles. (c) Draw the earth pressure envelope and determine the strut loads for the braced y = 15 kN/m3, ~ == 30°, strut spacing = 4 m. Also

excavation in sandy soil. Assume:

(6)

determine the maximum moment developed in the wales.

.' fTc' i. ,,': <

~~.

\

...

" .••••••. ~.

~,

.

..

.•

I

. I

(3)

(d) List advantages of steel sheet piles.

Contd

P/2

=2=

CE 443 3. A cantilever sheet pile needs to retain 4.5 m of sandy backfill material. It is embedded in

(15+8 ~ =23 ~)

clay soil as shown in Fig. 2

(i) Determine the required depth of penetration of the sheet pile for short term loading condition. (ii) What will be the depth of penetration if drained condition is considered? Why do you need to consider drained condition?

---_. _"~'

.... ~-'. -. .. ~-'-

""""""" 't. -

.t...;.., ~.- ~, ..'

~'

--

4. (a) Determine the required length of anchored sheet pile shown in Fig. 3 embedded in sandy soil. Determine the size of mild steel tie rod and its spacing assuming fy = 400

(19)

MPa.

((sit

=:z. .

Ig-'-K-I\\f~?

S~

o~ "

-' (b) Why do you need to place the anchor block at a minimum distance from the anchored sheet pile? Show the minimum distance required in a 2 layer soil.

SECTION-B There are FOUR questions in this Section. Answer any THREE. 5. (a) List the internally stabilized earth retaining systems. Show in neat sketches the overturning and deep-seated stability problems of mechanically stabilized retaining wall.

(3+3=6)

(b) Compare between counterfort retaining wall and buttressed retaining wall. Show the

(3+2=5)

common proportions of counterfeit retaining wall in schematic diagram. Contd

P/3

=3=

CE 443 Contd ... Q. NO.5

(c) Check the stability against sliding and bearing failure for the square footing (2.3 m x 2.3 m) shown in the Fig. 4 . If the factor of safety against sliding is not sufficient what can be done? What will you do if the unit weight of the soil is not constant? (Use bearing

(12 X)

capacity factors presented in Table 1).

6. (a) Why coarse-grained soils are chosen as backfill? List the common types of retaining

(3+2=5)

wall drainage. (b) Briefly describe the general construction procedure of caissons.

(4)

(c) Determine the factor of safety against overturning and sliding failure for the retaining wall shown in Fig. 5. Unit weight of concrete, Yconc = 22.5 kN/m3. Consider the pas~ive resistance in front of the wall. Comment on the safety of the retaining wall against

(14 X)

overturning and sliding.

7. (a) List the principal components of a braced cofferdam. Draw qualitative earth pressure diagrams for design of braced cofferdams

in sand and clay (show the controlling

ordinates).

(2+3=5)

(b) Discuss briefly the phenomenon of 'earth pressure on braced cofferdams in stiff clays'.

(4)

(c) A bracing system for a 5 m wide open cut is shown in Fig. 6. Determine the forces in the struts A, B and C. The struts are spaced at 3 m center to center horizontally.

8. (a) List the uses of caissons. Compare between the Pneumatic caissons and Box caissons.

(14 X )

(2+3=5)

(b) Describe briefly the permanent design loads for designing caissons. Draw schematic diagrams of cutting edge for (i) hard stratum and (ii) soft soil.

(3+2=5)

(c) A circular caisson is shown in Fig. 7. Is the caisson self sinking? If not determine: (i) the required amount of ballast and (ii) the thickness for self sinking. Unit weight of concrete, Yconc = 22.5 kN/m3. Assume reasonable value if necessary.

(13 X)

I

Qv 620kN I" I

-+

3

y=17.0kN/m

2.7 m

t.=C4-

0.3 m

Uniform soil layer <1>=27° c=20kPa

180 kN

2.3 m x 2.3 m

5

Fig. [for Q. 7(c)

It

-.1

t.~ .. ,,~~.

..

Sand <1>=30° 3 Y= 18 kN/m

,

Silty clay 4.5m

<1>= 15° c= 15kPa 3 Y$OI=17.SkN/m

I

2m

~om ~0.6m

k

>1

4m

5

~

Fig. 7'for Q. )tc) Sm

I<

>1 A

1.5m

Clay

2.5 m

3

B

Y= 18 kN/m c= 40 kPa

C

<1>=0

2.5 m 1.5 m

.

Excavation bottom

1-

G

Fig. ;Yfor Q. J(c) i j

\<

I

>\

Sm

I

If'

2.5 m

~

l' 4m

-.

0.5 m

t

t 5m

Clay cu= 40kN/m2

~

Ysat=18 kN/m

3

t

Sand

Sm

<1>=30° 3

~.

=fFig.jfor

8 Q.

Ysat=18kN/m

3

Sand <1>=32°, Y$at=19 kN/m

Jt(c)

.

s~

'

_

h::::

-

'-J

Table 1

ncaring~ca pad ty,factprs.co rith~Tc(zaglli:c~luatioitS V,ll ucsb (Nyiur:;i/t-b rd;lni\d'4 lttUc 0 {j glli:i1 {rc(i(t~hi' vtttbe!; b;l~k.~()lunplP'K,iY

. Hnd'usc,dto

~*'. "':--~.'N;~,~,i_:--.::.>~I;i¥'?~,:1m41:\-':.

4>.d

,-"'

I

_.

o

~.;",

.

,.'-:ii-' .,.,,:.~.',' -. '" :,,',

=' .',

: •. : ",.;,.

'.

Nt ....

\0,8 12;2;

o~o

5~7'1" .:LO

~i • :},!r~~~\~;;~1~,~.~ I

1.4:1

1~:6:

2525;1 300'7;2 34

12(/9:7 -52:6

C'

-'$1:8

35

.22:5

19.7

.. 36;5

36,0

'4}.4

40_~5tI8L3' i

45172.'3

I I

4826Ri3> ,50

-------

25.0 35.0

4-2';4

10004

1733"-;ig'I;0780;l

1ljt~

-/Ftsj!

}97.5

1St?

...•.•...•.•..•..••. ........,;.----"-"---'--...;...;..;->--..:.-.- .....•..•. _-'---'--.

52;0

.[

82.0. 141.0

298.0 _ S()o.o "-.''«(

I

I

I i

-!"

Ioj:

j

. I I

I

I

L-4/T -2/CE

Date: 06/08/2017

BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY, DHAKA L-4/T-2 Sub:

B. Sc. Engineering Examinations 2015-2016

CE 443 (Earth

Retaining Structures)

Full Marks: 140

Time: 3 Hours

The figures in the margin indicate full marks. USE SEP ARA TE SCRIPTS FOR EACH SECTION

SECTION-A There are FOUR questions in this Section. Answer any THREE. 1. (a) List the causes that may induce lateral load to foundations. How does lateral load

(5)

affect the bearing capacity of foundation? (b) Referring to the excavation shown in Fig. 1, show that failure by bottom heaving will

not occur if

(p.+q)B, -q.( H - ~ )- ; B,q. ~q.B,

(8)

(c) Check the stability against sliding for the square footing (2.0 m x 2.0 m) shown in the Fig. 2. What should be the minimum factor of safety against sliding? If the factor of

(lOX)

safety against sliding is not sufficient what can be done?

(4)

2. (a) Compare between cantilever retaining wall and counterfort retaining wall. (b) Show with neat sketches the ultimate limit states of external instability for gravity

(6)

retaining walls. (c) Determine the factor of safety against overturning and sliding failure for the retaining wall shown in Fig. 3. Ignore the passive resistance in front of the wall. Comment on the

(13 X)

safety against overturning and sliding. Unit weight of concrete, Yconc = 22.5 kN/m3•

3. (a) List the principal components of a braced cofferdam. Write the main functions of each

(4)

principal component. (b) Discuss briefly the phenomenon of 'earth pressure on braced cofferdams in sand'. Why does the lateral earth pressure on braced cofferdam in stiff clay change over time?

(6)

(c) A bracing system for an open cut is shown in Fig. 4. Determine the force in the struts

(13 X)

A, B and C. The struts are spaced 3 m center to centre horizontally.

4. (a) What is meant by caissons? Draw schematic diagrams of open caisson and box caisson. Compare the advantages of open caissons and box caissons.

(6)

(b) Describe briefly the design loads for designing caissons.

(6)

(c) Will the caisson shown in the Fig. 5 be self sinking? If not determine (a) the required

(11 X)

amount of ballast and (b) the thickness for self sinking.

Contd

P/2

=2=

CE 443 SECTION-B There are FOUR questions in this Section. Answer any THREE questions. Assume reasonable value of missing data, only if necessary.

5. (a) Discuss importance of construction dewatering. Describe the methods of dewatering

(12~)

using well points and deep wells. Comment on pumps available for these methods. (b) What do you mean be slurry trench wall construction?

List advantages

and

(11)

disadvantages of this method.

(4x3=12)

6. (a) Write short notes on the following (answer any three): (i) Effect of wall movement on lateral earth pressure (ii) Raker bracing (iii) Design against clay bursting in excavation pit. (iv) p-y curve for analysis oflaterally loaded piles. (b) With neat sketch describe construction sequences of a braced excavation.

Also

comment on the preloading of struts and why it is recommended. (c) Discuss advantages and disadvantages of using steel sheet piles.

(5~) (6)

7. (a) A cantilever sheet pile needs to retain 3.5 m of sandy backfill material. It is embedded in sandy soil as shown in Fig. 6. Determine the required depth of penetration of the sheet pile, assuming a surcharge load of 10 kN/m2 on backfill.

(15)

(b) With neat sketches show different types of anchorage systems for anchored sheet piles. (c) How do you account for unbalanced water pressure in sheet pile design?

(5~) (3)

8. (a) Determine the required length of anchored sheet pile shown in Fig. 7 retaining sandy soil but embedded in cohesive soil. Also determine the size and spacing of mild steel tie rod.

(19)

(b) Why do you need to consider moment reduction in anchored sheet pile design? How do you account for it in design?

(4~)

-----~~ ------ --. _._--_.-.--_ -

.•..

_._~---------

B B= width of excavation q= surcharge per unit length

a

5= shear resistance along the surface 'cd' Unconfined compressive strength of soft c1ay= qu

S

Unit wt.,

Ii

y

H

I I

1

I I I.

c:

------

:

b

I

,, /

\

\ \

"

Soft clay

,

I

,

__

r

:

\

"

I

. _.. _.'_'_'._._.. --=-"-e--=- __

k

.'_"

Stiff or granular soil .l:oollo\

Bottom of excavation

_

\,

_-----~.•.

_

.

I

--------~

..==~========::::::::::::::::..~.

Uniform soil layer , y=17.0 kN/m3

3m

~=27°

-+-

c=30 kPa

0.3 m

2.0 m x 2.0 m I

I ,_., _ ,. _

Fig. 2. for Q. l(e)

r---~."---

---------~~ --- .".-.~------

------

.~.

-.1

~= 25° c= 70 kPa 3

Y= 17 kN/m

Clean sand

5.0m

1

_2.5 m

=34°

I

2m

1

1

Ysal=

3

18 kN/m

to.

6m

11~(-----_7)1 4m Fig. 3. for Q. 2(e)

7

.'\......-__

--

--- _----- ----.•...•

....,.•..•..•

5m

.2m ,. i

A Loose Sand

3m

B

3

y= 16.5 kN/m ~= 30

0

f-)

3m

I' f, ~ !

..

f', . ,

>1

\

c 2m

Fig. 4. for Q. 3(e)

----------_._-- ~------__ .•.

.

-3-

•

Sm

-->,1 T

2.5m ~

l' Sm

4m

..-

t

t

O.Sm

Clay

cu= 40 kN/m2 ~sat=18 kN/m3

Sm

~

tSm

Sand ~= 30° Ysat=17 kN/m3

.~

Fig. 5. for Q. 4(e) _

-."'----

J

. ,._

~

.•••• ~-.,-~_~_

••

~

Y.. ...J.-...~_._I~ 1./ N/. .. 3' TSiZ-t. 'l>-".~ .~._ _-

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