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Page 1: HOMEWORK 2 - courses.ce.metu.edu.trcourses.ce.metu.edu.tr/.../2017/12/CE363_FALL_2017_HW2_Solutions.pdfHomework solutions will be posted to the course website on December 26, 2017,

CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

1

HOMEWORK 2

Homework 2 is due on December 26, 2017, Tuesday at 16:59.

CE363 Homeworks are to be submitted to the β€œCE363 Homework box” in Soil

Mechanics Lab.

Soil Mechanics lab door is locked every day at 17:00 and homeworks cannot be

submitted under the door.

Homework solutions will be posted to the course website on December 26, 2017,

Tuesday at 17:00.

Unless otherwise stated, use Ξ³water = 10 kN/m3

Question 1 (a:15%, b:10%)

A very wide granular embankment that is 2-m-thick, having unit weight of 20 kN/m3, is placed

over the ground surface of a soft (normally consolidated) clay deposit that is 3-m thick. Below the

clay layer, there is impervious rock, and water table is at the ground surface of soft clay. Saturated

unit weight of clay is 18 kN/m3, it is fully saturated and its initial average moisture content is 23%,

Gs=2.67, compression index is 0.35 and coefficient of consolidation is 6 m2/year.

a) Plot time versus consolidation settlement of clay layer until average degree of

consolidation is 95%. Note that horizontal axis should be time (in months), and vertical

axis should be settlement (vertical axis should increase in downward direction).

b) After the fill is placed, at the time when the ground surface settlement is measured as 15

cm,

- what is the average degree of consolidation of the clay layer?

- what is the degree of consolidation at 2 m depth below the top of the clay?

- what is the total pore water pressure and excess pore water pressure at 2 m depth below

the top of clay?

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CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

2

EMBANKMENT

IMPERVIOUS ROCK

N.C SOFT CLAY

2 m

3 m

π›₯𝜎 = 20 π‘˜π‘ π‘š3⁄ βˆ— 2 π‘š = 40 π‘˜π‘ƒπ‘Ž (𝑑𝑒𝑒 π‘‘π‘œ π‘£π‘’π‘Ÿπ‘¦ 𝑀𝑖𝑑𝑒 π‘’π‘šπ‘π‘Žπ‘›π‘˜π‘šπ‘’π‘›π‘‘)

𝜎0β€² = 1.5 π‘š βˆ— (18 π‘˜π‘ π‘š3⁄ βˆ’ 10 π‘˜π‘ π‘š3⁄ ) = 12 π‘˜π‘ƒπ‘Ž (π‘–π‘›π‘–π‘‘π‘–π‘Žπ‘™π‘™π‘¦ π‘Žπ‘‘ π‘‘β„Žπ‘’ π‘šπ‘–π‘‘ βˆ’ π‘‘π‘’π‘π‘‘β„Ž π‘œπ‘“ π‘π‘™π‘Žπ‘¦ π‘™π‘Žπ‘¦π‘’π‘Ÿ)

πœŽπ‘“β€² = 12 π‘˜π‘ƒπ‘Ž + 40 π‘˜π‘ƒπ‘Ž = 52 π‘˜π‘ƒπ‘Ž (π‘“π‘–π‘›π‘Žπ‘™ π‘ π‘‘π‘Ÿπ‘’π‘ π‘  π‘Žπ‘‘ π‘‘β„Žπ‘’ π‘šπ‘–π‘‘ βˆ’ π‘‘π‘’π‘π‘‘β„Ž π‘œπ‘“ π‘π‘™π‘Žπ‘¦ π‘™π‘Žπ‘¦π‘’π‘Ÿ)

Since 𝑀 βˆ— 𝐺𝑠 = π‘†π‘Ÿ βˆ— 𝑒,

𝑒0 = 𝑀0 βˆ— 𝐺𝑠 = 23% βˆ— 2.67 = 0.614 (π‘†π‘Ÿ = 1, 𝑓𝑒𝑙𝑙𝑦 π‘ π‘Žπ‘‘π‘’π‘Ÿπ‘Žπ‘‘π‘’π‘‘)

Given, 𝐢𝑐 = 0.35 & the soil is normally consolidated,

𝑆𝑐 =𝐢𝑐

1 + 𝑒0βˆ— 𝐻 βˆ— log (

πœŽπ‘“β€²

𝜎0β€²) =

0.35

1 + 0.614βˆ— 3 βˆ— log (

52

12) = 0.414 π‘š = 41.4 π‘π‘š

a) Consolidation settlement vs time graph is asked. Given,

𝑐𝑣 = 6 π‘š2 π‘¦π‘’π‘Žπ‘Ÿβ„ = 0.5 π‘š2/π‘šπ‘œπ‘›π‘‘β„Ž

𝑇𝑣 =𝑐𝑣 βˆ— 𝑑

𝐻2, π‘€β„Žπ‘’π‘Ÿπ‘’ 𝐻 (π‘œπ‘Ÿ 𝑑, 𝐷) = 3 π‘š (𝑠𝑖𝑛𝑐𝑒 π‘‘β„Žπ‘’ π‘™π‘Žπ‘¦π‘’π‘Ÿ 𝑖𝑠 β„Žπ‘Žπ‘™π‘“ π‘π‘™π‘œπ‘ π‘’π‘‘. )

𝑇𝑣 π‘π‘Žπ‘› 𝑏𝑒 π‘Ÿπ‘’π‘™π‘Žπ‘‘π‘’π‘‘ π‘€π‘–π‘‘β„Ž π‘Žπ‘£π‘’π‘Ÿπ‘Žπ‘”π‘’ π‘‘π‘’π‘”π‘Ÿπ‘’π‘’ π‘œπ‘“ π‘π‘œπ‘›π‘ π‘œπ‘™π‘–π‘‘π‘Žπ‘‘π‘–π‘œπ‘› π‘€π‘–π‘‘β„Ž π‘“π‘œπ‘™π‘™π‘œπ‘€π‘–π‘›π‘” π‘“π‘œπ‘Ÿπ‘šπ‘’π‘™π‘Žπ‘ :

π‘“π‘œπ‘Ÿ π‘ˆ < 60 % β†’ 𝑇𝑣 =πœ‹

4βˆ— π‘ˆ2

π‘“π‘œπ‘Ÿ π‘ˆ > 60% β†’ 𝑇𝑣 = βˆ’0.933 βˆ— log(1 βˆ’ π‘ˆ) βˆ’ 0.085

𝐻𝑒𝑛𝑐𝑒, 𝑑 β†’ 𝑇𝑣 β†’ π‘ˆ β†’ 𝑆

πΉπ‘œπ‘Ÿ π‘–π‘›π‘ π‘‘π‘Žπ‘›π‘π‘’,

𝐴𝑑 𝑑 = 3 π‘šπ‘œπ‘›π‘‘β„Žπ‘ , 𝑇𝑣 =0.5 π‘š2 π‘šπ‘œπ‘›π‘‘β„Žβ„ βˆ— 3 π‘šπ‘œπ‘›π‘‘β„Žπ‘ 

9 π‘š2= 0.167

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CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

3

π‘ˆ = √4 βˆ— 𝑇𝑣

πœ‹= √

4 βˆ— 0.167

3.14= 0.461 = 46.1 % (π‘ˆ < 60%)

𝑆 = 41.4 π‘π‘š βˆ— 46.1 % = 19.1 π‘π‘š

𝐴𝑑 𝑑 = 12 π‘šπ‘œπ‘›π‘‘β„Žπ‘ , 𝑇𝑣 =0.5 π‘š2 π‘šπ‘œπ‘›π‘‘β„Žβ„ βˆ— 12 π‘šπ‘œπ‘›π‘‘β„Žπ‘ 

9 π‘š2= 0.667

π‘ˆ = 1 βˆ’ 10βˆ’(𝑇𝑣+0.085)/0.933 = 1 βˆ’ 10βˆ’0.667+0.085

0.933 = 0.844 = 84.4 % (π‘ˆ > 60%)

𝑆 = 41.4 π‘π‘š βˆ— 84.4 % = 34.9 π‘π‘š

Similarly,

t (months) Tv U Settlement (cm)

0 0.000 0.000 0.0

0.1 0.006 0.084 3.5

0.5 0.028 0.188 7.8

1 0.056 0.266 11.0

2 0.111 0.376 15.6

3 0.167 0.461 19.1

4 0.222 0.532 22.0

5 0.278 0.595 24.6

6 0.333 0.644 26.7

7 0.389 0.689 28.6

8 0.444 0.729 30.2

9 0.500 0.764 31.6

10 0.556 0.794 32.9

11 0.611 0.821 34.0

12 0.667 0.844 34.9

13 0.722 0.864 35.8

14 0.778 0.881 36.5

15 0.833 0.896 37.1

16 0.889 0.910 37.7

17 0.944 0.921 38.2

18 1.000 0.931 38.6

19 1.056 0.940 38.9

20 1.111 0.948 39.3

20.3 1.129 0.950 39.4

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CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

4

b) π‘Šβ„Žπ‘’π‘› 𝑆 = 15 π‘π‘š, π‘ˆ =15 π‘π‘š

41.4 π‘π‘š= 36.2 % π’‚π’—π’†π’“π’‚π’ˆπ’† π’…π’†π’ˆπ’“π’†π’† 𝒐𝒇 π’„π’π’π’”π’π’π’Šπ’…π’‚π’•π’Šπ’π’

𝑇𝑣 = πœ‹

4βˆ— (36.2 %)2 = 0.103

π·π‘’π‘π‘‘β„Ž π‘“π‘Ÿπ‘œπ‘š π‘‘π‘œπ‘ π‘œπ‘“ π‘‘β„Žπ‘’ π‘π‘™π‘Žπ‘¦ = 2 π‘š, π‘€π‘Žπ‘₯π‘–π‘šπ‘’π‘š π‘‘π‘Ÿπ‘Žπ‘–π‘›π‘Žπ‘”π‘’ π‘‘π‘–π‘ π‘‘π‘Žπ‘›π‘π‘’ = 3 π‘š

π‘ˆπ‘§ = 0.14 , π’…π’†π’ˆπ’“π’†π’† 𝒐𝒇 π’„π’π’π’”π’π’π’Šπ’…π’‚π’•π’Šπ’π’ π‘Žπ‘‘ 2 π‘š π‘‘π‘’π‘π‘‘β„Ž π‘π‘’π‘™π‘œπ‘€ π‘‘β„Žπ‘’ π‘‘π‘œπ‘ π‘œπ‘“ π‘‘β„Žπ‘’ π‘π‘™π‘Žπ‘¦

0

5

10

15

20

25

30

35

40

45

0 2 4 6 8 10 12 14 16 18 20 22

Set

tlem

ent

(cm

)

Time (months)

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CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

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π‘ˆπ‘§ =𝑒𝑖𝑒 βˆ’ 𝑒𝑒

𝑒𝑖𝑒, π‘€β„Žπ‘’π‘Ÿπ‘’ 𝑒𝑖𝑒 = π‘–π‘›π‘–π‘‘π‘–π‘Žπ‘™ 𝑒π‘₯𝑐𝑒𝑠𝑠 π‘π‘œπ‘Ÿπ‘’ π‘π‘Ÿπ‘’π‘ π‘ π‘’π‘Ÿπ‘’, 𝑒𝑒 = 𝑒π‘₯𝑐𝑒𝑠𝑠 π‘π‘œπ‘Ÿπ‘’ π‘π‘Ÿπ‘’π‘ π‘ π‘’π‘Ÿπ‘’

𝑒𝑖𝑒 = π›₯𝜎 = 40 π‘˜π‘ƒπ‘Ž

πΉπ‘œπ‘Ÿ π‘ˆπ‘§ = 0.14 = 40 βˆ’ 𝑒𝑒

40,

𝑒𝑒 = 34.4 π‘˜π‘ƒπ‘Ž, 𝑒π‘₯𝑐𝑒𝑠𝑠 π‘π‘œπ‘Ÿπ‘’ π‘π‘Ÿπ‘’π‘ π‘ π‘’π‘Ÿπ‘’ π‘Žπ‘‘ 2 π‘š π‘‘π‘’π‘π‘‘β„Ž π‘π‘’π‘™π‘œπ‘€ π‘‘β„Žπ‘’ π‘‘π‘œπ‘ π‘œπ‘“ π‘‘β„Žπ‘’ π‘π‘™π‘Žπ‘¦

π΅π‘’π‘“π‘œπ‘Ÿπ‘’ π‘’π‘šπ‘π‘Žπ‘›π‘˜π‘šπ‘’π‘›π‘‘ π‘π‘œπ‘›π‘ π‘‘π‘Ÿπ‘’π‘π‘‘π‘–π‘œπ‘›, 𝑒0 = 2 π‘š βˆ— 10 π‘˜π‘ π‘š3⁄ = 20 π‘˜π‘ƒπ‘Ž

π‘‡π‘œπ‘‘π‘Žπ‘™ π‘π‘œπ‘Ÿπ‘’ π‘€π‘Žπ‘‘π‘’π‘Ÿ π‘π‘Ÿπ‘’π‘ π‘ π‘’π‘Ÿπ‘’ π‘€β„Žπ‘’π‘› 𝑆 = 15 π‘π‘š , 𝑒𝑓 = 20 π‘˜π‘ƒπ‘Ž + 34.4 π‘˜π‘ƒπ‘Ž = 54.4 π‘˜π‘ƒπ‘Ž

Question 2 (a: 14%; b: 5 %)

Following results are obtained in a series of CU triaxial tests performed on saturated samples of

Ankara clay.

a) Calculate the effective stress-based modified shear strength parameters, intercept a' and

slope angle ' , by filling up the following table and plotting the modified Mohr-Coulomb

failure envelopes on the chart provided below.

Test Number 1 2

Confining Pressure

(kPa) 40 80

Deviatoric Stress

(kPa) 120 170

Pore water pressure

at failure (kPa) 15 25

'3,f (kPa) 25 55

'1,f (kPa) 145 225

'1,f+'3,f)/2 (kPa) 85 140

'1,f-'3,f)/2 (kPa) 60 85

From the figure above: a' = 21.4 kPa & ' = 24.4o

sin(πœ™β€²) = tan(𝛼′) β†’ sin(πœ™β€²) = tan(24.4) β†’ πœ™β€² = 27Β°

𝑐′ =π‘Žβ€²

cos(πœ™β€²)=

21.4

cos(27)= 24 π‘˜π‘ƒπ‘Ž

y = 0.4545x + 21.364

0

50

100

150

200

250

0 50 100 150 200 250

(1'-

3')

/2

(1'+3')/2

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CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

6

b) Vane shear test is used to determine the undrained shear strength of the same clay in Part

(a). If the clay is known to have a sensitivity ratio of 3 and undrained shear strength of

cu=35 kPa, estimate the peak and the residual torques. The shear vane used in the test has

a diameter of 75 mm and length of 150 mm.

)62

(32 DLD

cT u

π‘‡π‘π‘’π‘Žπ‘˜ = πœ‹ βˆ— 35 βˆ— ((0.0752π‘₯0.15

2) + (

0.0753

6)) = 54.1 𝑁. π‘š

𝑆𝑒𝑛𝑠𝑖𝑑𝑖𝑣𝑖𝑑𝑦 π‘Ÿπ‘Žπ‘‘π‘–π‘œ = π‘‡π‘π‘’π‘Žπ‘˜

π‘‡π‘Ÿπ‘’π‘ π‘–π‘‘π‘’π‘Žπ‘™= 3 β†’ π‘‡π‘Ÿπ‘’π‘ π‘–π‘‘π‘’π‘Žπ‘™ = 18.0 𝑁. π‘š

Question 3 (4%)

A silty clay specimen was placed in a triaxial cell and sheared as part of an unconfined

compression test. If it is sheared at deviator stress of 50 kN/m2,

Draw the Mohr circle corresponding to failure state. Estimate the followings:

i. Confining stress, Οƒ3………0………. ...kPa........

ii. Major principal stress, Οƒ1……50…………. .kPa..........

iii. Unconfined compressive strength, qu………50………. .kPa.

iv. Undrained shear strength, cu……25…………. ..kPa.........

0

10

20

30

40

50

60

0 10 20 30 40 50 60

t(k

Pa)

(kPa)

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CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

7

Question 4 (a: 7%, b: 3%)

The one dimensional consolidation test data for a soil sample is given below:

Effective stress (kPa) 25 50 100 150 200 250 300

void ratio 0.96 0.93 0.89 0.84 0.78 0.71 0.65

The pre-consolidation pressure of the soil sample is πŸπŸπŸ“ π’Œπ‘·π’‚ and initial void ratio is given as

eo=0.98.

a) Determine the coefficient of volume of compressibility, compression index, and reload

(recompression) index assuming that the initial effective stress on the sample is 155 kPa

and the final effective stress will be 245 kPa.

π‘šπ‘‰ =1

1+𝑒0βˆ— (

βˆ†π‘’

βˆ†πœŽ) =

1

1+0.84βˆ— (

0.84βˆ’0.71

250βˆ’150) = 7.06 βˆ— 10βˆ’4π‘š2/π‘˜π‘ (e0 for Οƒ = 150 kPa)

πΆπ‘Ÿ =(𝑒0 βˆ’ π‘’πœŽπ‘)

log Οƒ 𝑝 βˆ’ log π‘π‘œ=

βˆ†π‘’

log πœŽπ‘/π‘π‘œ=

(0.93 βˆ’ 0.89)

log (10050

)= 0.133

The closest void ratio data for stress level of 155 kPa and 245 kPa are 150 kPa and 250 kPa in the

table given above. Therefore Cc is calculated based on these stress levels. Alternatively you may

determine void ratio values for 155 kPa and 245 kPa and calculate Cc.

0.50

0.60

0.70

0.80

0.90

1.00

10 60 110 160 210 260 310 360

e

Οƒ' (kPa)

e-Οƒ'

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CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

8

𝐢𝑐 =(π‘’πœŽπ‘ βˆ’ 𝑒)

log 𝜎 βˆ’ log πœŽπ‘=

βˆ†π‘’

log 𝜎/πœŽπ‘=

(0.84 βˆ’ 0.71)

log (250150

)= 0.586

b) Calculate the consolidation settlement of a 5 m-thick clay layer in part (a) if initial and final

effective stresses at mid-depth are πŸ“πŸŽ π’Œπ‘·π’‚ 𝒂𝒏𝒅 𝟐𝟎𝟎 π’Œπ‘·π’‚ respectively.

𝑆𝑐 =πΆπ‘Ÿ

(1 + π‘’π‘œ)βˆ— 𝐻 βˆ— log (

πœŽπ‘“

πœŽπ‘–) +

𝐢𝑐

(1 + π‘’π‘œ)βˆ— 𝐻 βˆ— log (

πœŽπ‘“

πœŽπ‘–)

𝑆𝑐 =0.133

(1 + 0.98)βˆ— 5 βˆ— log (

115

50) +

0.586

(1 + 0.98)βˆ— 5 βˆ— log (

200

115)

𝑆𝑐 = 0.121 + 0.356 = 0.477 π‘š = 47.7 π‘π‘š

Question 5 (a:4%, b:4%, c:4%)

A direct shear apparatus has πŸ”πŸ‘ π’Žπ’Ž sample diameter. Following data were recorded at failure

during the tests caried out over the samples of a clayey sand using this device.

Do not perform area correction

𝑡 (π’Œπ‘΅) 𝑻 (π’Œπ‘΅) 𝝈 (π’Œπ‘·π’‚) 𝝉 (π’Œπ‘·π’‚)

Test 1 0.15 0.15

Test 2 0.45 0.36

a) Complete the table and plot the failure envelope of the tested soil. When plotting, use an

appropriate scaling for the axes and clearly indicate the stresses defining the envelope.

Οƒ =N

A=

150 N

3117.2 π‘šπ‘š2= 0.048 π‘€π‘ƒπ‘Ž = 48 π‘˜π‘ƒπ‘Ž

Ο„ =T

A=

150 N

3117.2 π‘šπ‘š2= 0.048 π‘€π‘ƒπ‘Ž = 48 π‘˜π‘ƒπ‘Ž

Οƒ =N

A=

450 N

3117.2 π‘šπ‘š2= 0.1444 π‘€π‘ƒπ‘Ž = 144.4 π‘˜π‘ƒπ‘Ž

Ο„ =T

A=

360 N

3117.2 π‘šπ‘š2= 0.1155 π‘€π‘ƒπ‘Ž = 115.5 π‘˜π‘ƒπ‘Ž

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CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

9

𝑡 (π’Œπ‘΅) 𝑻 (π’Œπ‘΅) 𝝈 (π’Œπ‘·π’‚) 𝝉 (π’Œπ‘·π’‚)

Test 1 0.15 0.15 48 48

Test 2 0.45 0.36 144.4 115.5

b) Calculate the shear strength parameters of the clayey sand.

βˆ…β€² = π‘Žπ‘Ÿπ‘π‘‘π‘Žπ‘› (βˆ†π‘¦

βˆ†π‘₯) = π‘Žπ‘Ÿπ‘π‘‘π‘Žπ‘› (

βˆ†π‘¦

βˆ†π‘₯) = π‘Žπ‘Ÿπ‘π‘‘π‘Žπ‘› (

115.5 βˆ’ 48

144.4 βˆ’ 48) = π‘Žπ‘Ÿπ‘π‘‘π‘Žπ‘› (

67.5

96.4)

βˆ… β‰… 35 Β°

𝜏 = 𝑐′ + πœŽβ€² βˆ— π‘‘π‘Žπ‘›βˆ…β€²

115.5 = 𝑐′ + 144.4 βˆ— π‘‘π‘Žπ‘›35

𝑐′ β‰… 14.4 π‘˜π‘ƒπ‘Ž

c) At what shear stress would this soil fail if the normal stress is πŸ–πŸ“ π’Œπ‘·π’‚.

𝜏 = 𝑐′ + πœŽβ€² βˆ— π‘‘π‘Žπ‘›βˆ…β€²

𝜏 = 14.4 + 85 βˆ— π‘‘π‘Žπ‘›35 = 73.9 π‘˜π‘ƒπ‘Ž

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140 160

Ο„

(kP

a)

Οƒ (kPa)

Page 10: HOMEWORK 2 - courses.ce.metu.edu.trcourses.ce.metu.edu.tr/.../2017/12/CE363_FALL_2017_HW2_Solutions.pdfHomework solutions will be posted to the course website on December 26, 2017,

CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

10

Question 6 (a:6%, b:4%)

During a consolidated undrained triaxial test on a saturated clay sample, failure is reached at a

principle stress difference of 385 kPa. The consolidation (all-round) pressure was 250 kPa and the

pore pressure was measured at failure as 145 kPa.

a) Plot the total and effective stress Mohr circles corresponding to the stress state at failure.

Use an appropriate scale when drawing and clearly indicate the necessary data to define

the circles.

Given

βˆ†πœŽ = 385 π‘˜π‘ƒπ‘Ž

𝜎3 = 250 π‘˜π‘ƒπ‘Ž

𝑒 = 145 π‘˜π‘ƒπ‘Ž

𝜎3 = 250 π‘˜π‘ƒπ‘Ž

𝜎1 = 𝜎3 + βˆ†πœŽ = 250 + 385 = 635 π‘˜π‘ƒπ‘Ž

𝜎´1 = 𝜎1 βˆ’ 𝑒 = 635 βˆ’ 145 = 490 π‘˜π‘ƒπ‘Ž

𝜎´3 = 𝜎3 βˆ’ 𝑒 = 250 βˆ’ 145 = 105 π‘˜π‘ƒπ‘Ž

b) If the effective angle of internal shear of this clay is known to be 30Β°, calculate the effective

cohesion parameter.

π‘ π‘–π‘›πœ™Β΄ =

𝜎´1 βˆ’ 𝜎´3

2𝜎´1 + 𝜎´3

2+

π‘Β΄π‘‘π‘Žπ‘›πœ™Β΄

𝑠𝑖𝑛30 =

490 βˆ’ 1052

490 + 1052

+𝑐´

π‘‘π‘Žπ‘›30

Solving for 𝑐´ = 50.5 π‘˜π‘ƒπ‘Ž

0

50

100

150

200

250

300

350

400

450

500

-200 -100 0 100 200 300 400 500 600 700 800 900 1000

t(k

Pa)

, ' (kPa)

TSCESC

105 kPa 250 kPa

u

635 kPa

cΒ΄=50.5 kPa

Page 11: HOMEWORK 2 - courses.ce.metu.edu.trcourses.ce.metu.edu.tr/.../2017/12/CE363_FALL_2017_HW2_Solutions.pdfHomework solutions will be posted to the course website on December 26, 2017,

CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

11

Question 7 (a:12%, b:4%, c:4%)

Consider the retaining wall shown in the figure below:

a) Using Rankine’s theory of lateral earth pressure calculate and plot the active and passive

earth pressure distributions at the back and in front of the wall respectively.

πΎπ‘Žπ‘ π‘œπ‘–π‘™βˆ’1 =1 βˆ’ π‘ π‘–π‘›βˆ…β€²

1 + π‘ π‘–π‘›βˆ…β€²=

1 βˆ’ 𝑠𝑖𝑛27

1 + 𝑠𝑖𝑛27= 0.375

πΎπ‘Žπ‘ π‘œπ‘–π‘™βˆ’2 =1 βˆ’ π‘ π‘–π‘›βˆ…β€²

1 + π‘ π‘–π‘›βˆ…β€²=

1 βˆ’ 𝑠𝑖𝑛30

1 + 𝑠𝑖𝑛30= 0.333

πΎπ‘π‘ π‘œπ‘–π‘™βˆ’2 =1 + π‘ π‘–π‘›βˆ…β€²

1 βˆ’ π‘ π‘–π‘›βˆ…β€²=

1 + 𝑠𝑖𝑛30

1 βˆ’ 𝑠𝑖𝑛30= 3

Calculate the active pressure (z=depth from ground surface)

πœŽβ„Žβ€² = πœŽπ‘£

β€² βˆ— πΎπ‘Ž βˆ’ 2 βˆ— 𝑐′ βˆ— βˆšπΎπ‘Ž

πœŽβ„Žβ€² = πœŽπ‘£

β€² βˆ— 𝐾𝑝 + 2 βˆ— 𝑐′ βˆ— βˆšπΎπ‘

𝐴𝑑 𝑧 = 0 π‘š; πœŽβ„Žβ€² = 18 βˆ— 0 βˆ— 0.375 βˆ’ 2 βˆ— 10 βˆ— √0.375 = βˆ’12.25 π‘˜π‘ƒπ‘Ž

𝐴𝑑 𝑧 = 4 π‘š; πœŽβ„Žβ€² = 18 βˆ— 4 βˆ— 0.375 βˆ’ 2 βˆ— 10 βˆ— √0.375 = 14.75 π‘˜π‘ƒπ‘Ž

𝐴𝑑 𝑧 = 4 π‘š; πœŽβ„Žβ€² = 18 βˆ— 4 βˆ— 0.333 βˆ’ 2 βˆ— 0 βˆ— √0.333 = 24 π‘˜π‘ƒπ‘Ž

𝐴𝑑 𝑧 = 7π‘š; πœŽβ„Žβ€² = ((18 βˆ— 4 + (21 βˆ’ 10) βˆ— 3) βˆ— 0.333 βˆ’ 2 βˆ— 0 βˆ— √0.333 = 35 π‘˜π‘ƒπ‘Ž

4 m

3 m

Soil-1

cΒ΄=10 kPa

ϕ´=27Β°

Ξ³=18 kN/m3

Soil-2

cΒ΄=0 kPa

ϕ´=30Β°

Ξ³sat=21 kN/m3

Page 12: HOMEWORK 2 - courses.ce.metu.edu.trcourses.ce.metu.edu.tr/.../2017/12/CE363_FALL_2017_HW2_Solutions.pdfHomework solutions will be posted to the course website on December 26, 2017,

CE 363 Soil Mechanics Middle East Technical University

Homework 2 Department of Civil Engineering

12

Calculate the passive pressure (z=depth from ground surface)

𝐴𝑑 𝑧 = 0 π‘š; πœŽβ„Žβ€² = (21 βˆ’ 10) βˆ— 0 βˆ— 3 + 2 βˆ— 0 βˆ— √3 = 0 π‘˜π‘ƒπ‘Ž

𝐴𝑑 𝑧 = 3 π‘š; πœŽβ„Žβ€² = (21 βˆ’ 10) βˆ— 3 βˆ— 3 + 2 βˆ— 0 βˆ— √3 = 99 π‘˜π‘ƒπ‘Ž

4 m

3 m

12.25 kPa

14.75 kPa

24 kPa

35 kPa 30 kPa30 kPa 99 kPa

b) Calculate the depth of tension crack at the back of the wall.

πœŽβ„Žβ€² = πœŽπ‘£

β€² βˆ— πΎπ‘Ž βˆ’ 2 βˆ— 𝑐′ βˆ— βˆšπΎπ‘Ž = 0

πœŽβ„Žβ€² = 0 = 18 βˆ— 𝑧 βˆ— 0.375 βˆ’ 2 βˆ— 10 βˆ— √0.375

𝑧 =12.25

18 βˆ— 0.375= 1.81 π‘š

c) Calculate the total passive resistance in front of the wall.

Total passive resistance (including water pressure)

𝐹𝑝 = (99 βˆ— 3 βˆ—1

2) = 148.5 π‘˜π‘/π‘š

𝐹𝑀 = 30 βˆ— 3 βˆ—1

2= 45 π‘˜π‘/π‘š

Active Pressure

Distribution Passive Pressure

Distribution

Hydrostatic Pressure

Distribution

Hydrostatic Pressure

Distribution