GATE 2018

(1)

GATE 2018

Civil Engineering

Date of Test 11-02-2018 : Shift -2

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GENERAL APTITUDE

Q.1 Q.1Q.1

Q.1Q.1 A three-member committee has to be formed from a group of 9 people. How many such distinct committees can be formed?

(a) 27 (b) 72

(c) 81 (d) 84

Ans.

Ans.Ans.

Ans.Ans. (d)(d)(d)(d)(d)

9

C3 = = × × =

×

9! 9 8 7 6! 3! 6 84

Q.2 Q.2Q.2

Q.2Q.2 “His face _________ with joy when the solution of the puzzle was ________ to him.”

The words that best fill the blanks in the above sentence are

(a) shone, shown (b) shone, shone

(c) shown, shone (d) shown, shown

Ans.

Ans.Ans.

Ans.Ans. (a)(a)(a)(a)(a)

Shone - It is past - participle and past form of shine.

Shown - To show means to reveal and point out something.

Q.3 Q.3Q.3

Q.3Q.3 For non-negative integers, a, b, c, what would be the value of a + b + c if log a + log b + log c = 0?

(a) 3 (b) 1

(c) 0 (d) –1

Ans.

Ans.Ans.

As a, b, c are non-negative integers and given log a + log b + log c = 0 log(a × b × c) = log 1

⇒ a × b × c = 1

Which can be possible for simple values.

a = b = c = 1 Hence a + b + c = 1 + 1 + 1 = 3 Alternate Method:

Alternate Method:Alternate Method:

Given,

log a + log b + log c = 0

As we know log 1 = 0, so each one of them can be zero if a = b = c = 1 log 1 + log 1 + log 1 = 0

By putting a = b = 1 equation satisfies a + b + c = 1 + 1 + 1 = 3

(3)

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GATE 2018 : Civil Engineering 11-02-2018 | Shift-2

Q.4 Q.4Q.4

Q.4Q.4 “Although it does contain some pioneering ideas, one would hardly characterize the work as _________.”

The word that best fills the blank in the above sentence is

(a) innovative (b) simple

(c) dull (d) boring

Ans.

Ans.Ans.

Innovative is similar to poineer.

Q.5 Q.5Q.5

Q.5Q.5 ²

times

...

n

a a a_{+ + + + =}a a b^and _times... ²

m

b b b_{+ + + + =}b ab , where a, b, n and m are natural

numbers. What is the value of (^{m m m} ⁺ ⁺ⁿ^times^{+ +}^... ^{m n n n})( ^{+ + + +}^m^times^... ⁿ)^?

(a) 2a²b² (b) a⁴b⁴

(c) ab(a + b) (d) a² + b²

Ans.

Ans.Ans.

Ans.Ans. (b)(b)(b)(b)(b)

+ + + +

times

...

n

a a a a =na = a²b

⇒ n = ab ...(i)

+ + + +

times

...

m

b b b b =mb = b²a

⇒ m = ab ...(ii)

So, + + + × + + +

times times

[ ... ] [ ... ]

n m

m m m n n n

i.e., mn × mn = (mn)² from (i) and (ii) mn = a²b²

So, result, (mn)²= (a²b²) = a⁴b⁴

Q.6 Q.6Q.6

Q.6Q.6 In manufacturing industries, loss is usually taken to be proportional to the square of the deviation from a target. If the loss is Rs. 4900 for a deviation of 7 units, what would be the loss in Rupees for a deviation of 4 units from the target?

(a) 400 (b) 1200

(c) 1600 (d) 2800

Ans.

Ans.Ans.

Ans.Ans. (c)(c)(c)(c)(c)

Loss = kd² For duration of 7 units 4900 = k (7)² ⇒ k = 100

Loss = kd² For duration of 4 units

=k (4)² ⇒ 16k = 1600

(4)

Q.7 Q.7Q.7

Q.7Q.7 Each of the letters in the figure below represents a unique integer from 1 to 9. The letters are positioned in the figure such that each of (A+B+C), (C+D+E), (E+F+G) and (G+H+K) is equal to 13. Which integer does E represent?

A B C

D

E F G

H K

(a) 1 (b) 4

(c) 6 (d) 7

Ans.

Ans.Ans.

A + B + C = C + D + E = E + F + G = G + H + K = 13 If we add all, we will get = 4 × 13 = 52

But sum of all natural number 1 to 9 = 45 = ^{9 10}^× 2

A + B + C + C + D + E + E + F + G + G + H + K = 52 ...(i) A + B + C + D + E + F + G + H + K = 45 ...(ii) Substraction eq. (ii) from (i)

Hence, C + E + G = 7 ...(iii)

Also, C + D + E = 13 ...(iv)

Substraction eq. (iii) from (iv) D – G = 6

E = 4 Alternative Method

Alternative MethodAlternative Method Alternative MethodAlternative Method

By checking other equations

( )

(1,3,9)ABC ( ) (1,8,4)CDE ( )

(2,4,7)EFG ( ) (2,5,6)GHK

13 13 13 13

Q.8 Q.8Q.8

Q.8Q.8 The annual average rainfall in a tropical city is 1000 mm. On a particular rainy day (24-hour period), the cumulative rainfall experienced by the city is shown in the graph.

Over the 24-hour period. 50% of the rainfall falling on a rooftop, which had an obstruction- free area of 50 m², was harvested into a tank. What is the total volume of water collected in the tank in liters?

(5)

0 3 6 9 12 15 18 21 24

400 350 300 250 200 150 100 50

Cumulative rainfall (mm)

Hours

(a) 25,000 (b) 18,750

(c) 7,500 (d) 3,125

Ans.

Ans.Ans.

Cumulative rainfall = 300 mm 50% of rainfall = × 50 =

300 150 mm

100 Area = 50 m²

⇒ Volume stored in tank = 150 × 10^–3 × 50 m³

or = 7500 l

Q.9 Q.9Q.9

Q.9Q.9 Given that logP logQ logR

y₋z ⁼ z₋x ⁼ x₋y = 10 for x _≠ y _≠z, what is the value of the product PQR?

(a) 0 (b) 1

(c) xyz (d) 10^xyz

Ans.

Ans.Ans.

logP = 10(y – z) logQ = 10(z – x) logR = 10(x – y) logP + logQ + logR = 0

log(PQR) = log 1 PQR = 1

Q.10 Q.10Q.10

Q.10Q.10 A faulty wall clock is known to gain 15 minutes every 24 hours. It is synchronized to the correct time at 9 AM on 11^th July. What will be the correct time to the nearest minute when the clock shows 2 PM on 15^th July of the same year?

(6)

(a) 12:45 PM (b) 12:58 PM

(c) 1:00 PM (d) 2:00 PM

Ans.

Ans.Ans.

9 Am of 11 July of 2 PM on 15^th July = 101 hours

⎛ + ⎞

⎜ ⎟

⎝ ⎠

24 15

60 hours of incorrect clock = 24 hours of correct clock

⎛ + ⎞

⎜ ⎟

⎝ ⎠

24 15

60 hours of IC = 24 hours of correct clock 1 hour of IC = ⁹⁶

97 hours of correct clock 101 hour of IC = ⁹⁶_×101

97 hours of correct clock

= 99.958 hours of correct clock

= 99 hours + 0.95876 × 60 minutes of correct clock

= 99 hours + 57.525 minutes

= 99 hours and approx 58 minutes So, correct time will be

2 PM, 11^th july + (99 hours and 58 minutes) = 12 : 58 PM on 15^th July

(7)

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(8)

CIVIL ENGINEERING

Q.1 Q.1Q.1

Q.1Q.1 As per IS 456 : 2000, the minimum percentage of tension reinforcement (up to two decimal places) required in reinforced-concrete beams of rectangular cross-section (considering effective depth in the calculation of area) using Fe500 grade steel is ___________.

Ans.

Ans.Ans.

Ans.Ans. (0.17)(0.17)(0.17)(0.17)(0.17)

Minimum percentage of steel (for Fe500)

= ⁸⁵% ⁸⁵ % 0.17%

y 500

f ⁼ ⁼

Q.2 Q.2Q.2

Q.2Q.2 A probability distribution with right skew is shown in the figure.

f( )x

x

The correct statement for the probability distribution is (a) Mean is equal to mode

(b) Mean is greater than median but less than mode (c) Mean is greater than median and mode

(d) Mode is greater than median Ans.

Ans.Ans.

f( )x

t₀ t_L t_mean = t_e t_p x mode

mean

t_L<t_mean = Curve is skew to right.

mode < mean

i.e., mean > median and mode

Mean is greater than the mode and the median. This is common for a distribution that is skewed to the right [i.e., bunched up toward the left and a ‘tail’ stretching toward the right].

(9)

Q.3 Q.3Q.3

Q.3Q.3 For a given discharge in an open channel, there are two depths which have the same specific energy. These two depths are known as

(a) alternate depths (b) critical depths

(c) normal depths (d) sequent depths

Ans.

Ans.Ans.

Depth with same specific energy are called Alternate depths of flow. It represents a subcritical depth of flow (Y₂) and a supercriitical depth of flow (Y₁).

Y₂

Y₁

Specific energy (E)E Depth

Q.4 Q.4Q.4

Q.4Q.4 Peak Hour Factor (PHF) is used to represent the proportion of peak sub-hourly traffic flow within the peak hour. If 15-minute sub-hours are considered, the theoretically possible range of PHF will be

(a) 0 to 1.0 (b) 0.25 to 0.75

(c) 0.25 to 1.0 (d) 0.5 to 1.0

Ans.

Ans.Ans.

0.25 ≤ PHF₁₅≤ 1

Q.5 Q.5Q.5

Q.5Q.5 The solution of the equation dy 0 d ^{+ =}y

x x passing through the point (1, 1) is

(a) x (b) x²

(c) x^–1 (d) x^–2

Ans.

Ans.Ans.

dy y dx ⁺

x = 0

dy xd

x = –y dy

y ⁼

−dx x 1dy

∫y ⁼ ∫⁻_x¹^d^x

lny = –lnx + c

when y = 1, x = 1

c = 0

⇒ y = ¹

x = x^–1

(10)

Q.6 Q.6Q.6

Q.6Q.6 A vertical load of 10 kN acts on a hinge located at a distance of L/4 from the roller support Q of a beam of length L (see figure).

10 kN

P Q

3 /4L L/4

The vertical reaction at support Q is

(a) 0.0 kN (b) 2.5 kN

(c) 7.5 kN (d) 10.0 kN

Ans.

Ans.Ans.

10 kN A

R_Q

P Hinge Q

3 4L/ L/4

Bending moment about hinge point A = 0 (consider the right hand side of A) R_Q×

4 L = 0

R_Q= 0 kN

Q.7 Q.7Q.7

Q.7Q.7 Which one of the following statements is NOT correct?

(a) When the water content of soil lies between its liquid limit and plastic limit, the soil is said to be in plastic state.

(b) Boussinesq’s theory is used for the analysis of stratified soil.

(c) The inclination of stable slope in cohesive soil can be greater than its angle of internal friction.

(d) For saturated dense fine sand, after applying overburden correction, if the Standard Penetration Test value exceeds 15, dilatancy correction is to be applied.

Ans.

Ans.Ans.

Boussinesq’s assumed soil as isotropic hence not applicable for stratified soil.

Q.8 Q.8Q.8

Q.8Q.8 A reinforced-concrete slab with effective depth of 80 mm is simply supported at two opposite ends on 230 mm thick masonry walls. The centre-to-centre distance between the walls is 3.3 m. As per IS 456 : 2000, the effective span of the slab (in m, up to two decimal places) is ___________.

(11)

Ans.

Ans.Ans.

Ans.Ans. (3.15)(3.15)(3.15)(3.15)(3.15)

Effective depth

d = 80 mm Width of support = 230 mm c/c distance between walls = 3.30 m

Clear span of slab = 3.30 – 0.23 = 3.07 m Effective span = Minimum ( ^clear + )

c/c distance between supports

L d

•

⎧⎨•⎩

= Minimum

(3.07 + 0.08 = 3.15 m) 3.3 m

⎧•

⎨•⎩

So, L_eff= 3.15 m

Q.9 Q.9Q.9

Q.9Q.9 As per IS 10500:2012, for drinking water in the absence of alternate source of water, the permissible limits for chloride and sulphate, in mg/L, respectively are

(a) 250 and 200 (b) 1000 and 400

(c) 200 and 250 (d) 500 and 1000

Ans.

Ans.Ans.

As per IS-10500 : 2012

Permissible limit in absence of alternate source.

Chloride (as Cl^–) Sulphate as [SO₄]^–2

1000 400

Q.10 Q.10Q.10

Q.10Q.10 All the members of the planar truss (see figure), have the same properties in terms of area of cross-section (A) and modulus of elasticity (E),

P P

L

For the loads shown on the truss, the statement that correctly represents the nature of forces in the members of the truss is:

(a) There are 3 members in tension, and 2 members in compression

(b) There are 2 members in tension, 2 members in compression, and 1 zero-force member (c) There are 2 members in tension, 1 member in compression, and 2 zero-force members (d) There are 2 members in tension, and 3 zero-force Members

(12)

Ans.

Ans.Ans.

P

A P P B

V_B = 0

P C P

H_D = P D V_D = 0

H_B = P P

L

Since member BD neither elongate nor contract.

Hence, F_BD= 0

So there are 2 tension members (AB and DC) and 3 zero force members (AD, BD, BC).

Q.11 Q.11Q.11

Q.11Q.11 The initial concavity in the Load-penetration curve of a CBR test is NOT due to (a) uneven top surface (b) high impact at start of loading

(c) inclined penetration plunger (d) soft top layer of soaked soil Ans.

Ans.Ans.

Initial concavity in CBR test due to :

• Improper compaction

• Soft top layer

• Inclined plunger

Q.12 Q.12Q.12

Q.12Q.12 The graph of a function f(x) is shown in the figure.

0 1 2 3 x

3h

2h

h f()x

For f(x) to be valid probability density function, the value of h is (a) ¹

3 (b) ²

3

(c) 1 (d) 3

(13)

Ans.

Ans.Ans.

3

0

f( )d

∫ ^{x x} ^{= 1}

1 2 3

0 1 2

( ) ( ) ( )

f d ₊ f d ₊ f d

∫ ^{x x} ∫ ^{x x} ∫ ^{x x} ^{= 1}

2 3

2 2 2

h h h

+ + = 1

6h = 2 ⇒ h = ¹ 3

Q.13 Q.13Q.13

Q.13Q.13 The contact pressure and settlement distribution for a footing are shown in the figure.

The figure corresponds to a

(a) rigid footing on granular soil (b) flexible footing on granular soil (c) flexible footing on saturated clay (d) rigid footing on cohesive soil Ans.

Ans.Ans.

Rigid footing on granular soil.

Q.14 Q.14Q.14

Q.14Q.14 The clay mineral, whose structural units are held together by potassium bond is

(a) Halloysite (b) Illite

(c) Kaolinite (d) Smectite

Ans.

Ans.Ans.

Kaolinite → Hydrogen bond

Illite → Ionic Bond/Potassium Bond Montmorillonite → Water Bond

Q.15 Q.15Q.15

Q.15Q.15 A fillet weld is simultaneously subjected to factored normal and shear stresses of 120 MPa and 50 MPa, respectively. As per IS 800 : 2007. the equivalent stress (in MPa.

up to two decimal places) is

(14)

Ans.

Ans.Ans.

Ans.Ans. (147.99)(147.99)(147.99)(147.99)(147.99)

Factored normal stress, f_a = 120 MPa Factored shear stress, q = 50 MPa

According to IS-800 : 2007, clause 10.5.10.1.1 The equivalent stress, f_e= ² ₃ ²

3

u a

mw

f q f + ≤ Y

f_e= 120²+ ×3 50² =147.99

⇒ f_e ≤

3

u mw

f

y = 400

3 1.25_× = (184.75 MPa) Note :

Note :Note :

Note :Note : The above check for combination of stresses need not be done for fillet welds where the sum of normal and shear stresses does not exceed f_wd [clause 10.5.10.1.2(b)]

Hence, sum of normal and shear stresses = 120 + 50 = 170 MPa ≤ f_wd (= 184.75 MPa) So, the above check need not be done.

So, weld is designed for a resultant shear stress of (f_r)

f_r = f_a²₊q² ₌ 120² ₊50² ₌130 N/mm²

So, the design stress is 130 N/mm²; however equivalent stress 147.99 MPa.

Q.16 Q.16Q.16

Q.16Q.16 A structural member subjected to compression, has both translation and rotation restrained at one end, while only translation is restrained at the other end. As per IS 456 : 2000, the effective length factor recommended for design is

(a) 0.50 (b) 0.65

(c) 0.70 (d) 0.80

Ans.

Ans.Ans.

One end is fixed Other end is pin jointed

Effective length of column (as per IS:456–2000)

= 0.80 L

Q.17 Q.17Q.17

Q.17Q.17 The intensity of irrigation for the Kharif season is 50% for an irrigation project with culturable command area of 50,000 hectares. The duty for the Kharif season is 1000 hectare cumec. Assuming transmission loss of 10%, the required discharge (in cumec, up to two decimal places) at the head of the canal is __________.

Ans.

Ans.Ans.

Ans.Ans. (27.78)(27.78)(27.78)(27.78)(27.78)

Culturable command area = 50000 ha Intensity of irrigation for kharif season = 50%

∴ Area under kharif = 25000 ha

(15)

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Duty for kharif season = 1000 ha/cumec Duty = Area

Discharge

∴ Discharge at the head of field

Q= 25000 ha

1000 ha/cumec = 25 cumec Transmission/conveyance loss = 10%

∴ η_conveyance= 90%

Discharge at the head of canal = ²⁵cumec

0.9 = 27.78 cumec

Q.18 Q.18Q.18

Q.18Q.18 In the figures. Group I represents the atmospheric temperature profiles (P, Q, R and S) and Group II represents dispersion of pollutants from a smoke stack (1, 2, 3 and 4).

In the figures of Group I, the dashed line represents the dry adiabatic lapse rate, whereas the horizontal axis represents temperature and the vertical axis represents the altitude.

Group I Group II

P

Q

R

S

1

3

4 2

Inversion over superadiabatic

Looping plume

Coning plume

Fanning plume

Fumigation Superadiabatic

Adiabatic

Inversion

The correct match is

(a) P-1, Q-2, R-3, S-4 (b) P-1, Q-2, R-4, S-3 (c) P-1, Q-4, R-3, S-2 (d) P-3, Q-1, R-2, S-4 Ans.

Ans.Ans.

(17)

Q.19 Q.19Q.19

Q.19Q.19 Probability (up to one decimal place) of consecutively picking 3 red balls without replacement from a box containing 5 red balls and 1 white ball is ________.

Ans.

Ans.Ans.

Ans.Ans. (0.5)(0.5)(0.5)(0.5)(0.5)

Probability, P ⁼ ⁵₆^{× ×}⁴₅ ³₄⁼₂¹⁼^0.5

Q.20 Q.20Q.20

Q.20Q.20 A flownet below a dam consists of 24 equipotential drops and 7 flow channels. The difference between the upstream and downstream water levels is 6 m. The Length of the flow line adjacent to the toe of the dam at exit is 1 m. The specific gravity and void ratio of the soil below the dam are 2.70 and 0.70. respectively. The factor of safety against piping is

(a) 1.67 (b) 2.5

(c) 3.4 (d) 4

Ans.

Ans.Ans.

N_f = 7 N_d = 24 H = 6 m

Critical Hydraulic Gradient i_c = ¹ ^2.7 ¹ 1

1 1 0.7

G e

− = − =

+ +

Exit Gradient (i_exit) =

6 24 1

1m 4

d

H h N

⎛ ⎞ ⎛ ⎞

⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠

Δ = = =

l l

F.O.S. = ¹ 4

1 4

c exit

= =

⎛ ⎞⎜ ⎟

⎝ ⎠ i

i

Q.21 Q.21Q.21

Q.21Q.21 As per IRC : 37-2012, in order to control subgrade rutting in flexible pavements, the parameter to be considered is

(a) horizontal tensile strain at the bottom of bituminous layer (b) vertical compressive strain on top of subgrade

(c) vertical compressive stress on top of granular layer (d) vertical deflection at the surface of the pavement Ans.

Ans.Ans.

As per IRC : 37-2012

N =

4.5337 0.08 1 4.1656 10

V

− ⎡ ⎤

× ⎢⎣∈ ⎥⎦

Bituminous Surface

∈_t ∈t

Granular layer

∈v

Subgrade

N =

4.5337 8 1 1.41 10

V

− ⎡ ⎤

× ⎢⎣∈ ⎥⎦

(18)

where N = Number of cumulative standard axle

∈v= Vertical strain in the subgrade

Bituminous Surface

∈t ∈_t

Granular layer

∈v

Subgrade

Q.22 Q.22Q.22

Q.22Q.22 A culvert is designed for a flood frequency of 100 years and a useful life of 20 years.

The risk involved in the design of the culvert (in percentage, up to two decimal places) is ________.

Ans.

Ans.Ans.

Ans.Ans. (18.20)(18.20)(18.20)(18.20)(18.20)

Risk = The probability of a flood to occur at least once in n-successive years.

∴ Risk = 1 – qⁿ

= 1 – (1 – P)ⁿ

= 1 1 ¹

n

T

⎛ ⎞

−⎜⎝ − ⎟⎠ =

1 20

1 1 100

⎛ ⎞

−⎜⎝ − ⎟⎠

= 1 – (0.99)²⁰

= 0.18209 = 18.209%

Q.23 Q.23Q.23

Q.23Q.23 Dupuit’s assumptions are valid for

(a) artesian aquifer (b) confined aquifer (c) leaky aquifer (d) unconfined aquifer Ans.

Ans.Ans.

Dupuit’s theory assumptions hold that groundwater flows horizontally in an unconfined aquifer and that ground water discharge is proportional to saturated aquifer thickness.

Q.24 Q.24Q.24

Q.24Q.24 The quadratic equation 2x² – 3x + 3 = 0 is to be solved numerically starting with an initial guess as x₀ = 2. The new estimate of x after the first iteration using Newton-Raphson method is __________.

Ans.

Ans.Ans.

Ans.Ans. (1)(1)(1)(1)(1)

Given f(x) = 2x² – 3x + 3, x₀ = 2 f′(x) = 4x – 3

(19)

By Newton-Rapshon

x₁= ( )

( ) ^{( )} ( ) ^{( )}

2 0

0 0

2 2 3 2 3

2 4 2 3

f f

− +

− = −

−

′ x x

x

= ² ⁵ ¹

− =5

Q.25 Q.25Q.25

Q.25Q.25 The setting time of cement is determined using

(a) Le Chatelier apparatus (b) Briquette testing apparatus (c) Vicat apparatus (d) Casagrande’s apparatus Ans.

Ans.Ans.

Vicat apparatus is used to determine the normal consistency, IST, FST of cement.

Q.26 Q.26Q.26

Q.26Q.26 A coal containing 2% sulfur is burned completely to ash in a brick kiln at a rate of 30 kg/min. The sulfur content in the ash was found to be 6% of the initial amount of sulfur present in the coal fed to the brick kiln. The molecular weights of S, H and O are 32, 1 and 16 g/mole, respectively. The annual rate of sulfur dioxide (SO₂) emission from the kiln (in tonnes/year, up to two decimal places) is ________.

Ans.

Ans.Ans.

Ans.Ans. (592.88)(592.88)(592.88)(592.88)(592.88)

Coal burned in one year = 30 × 24 × 60 × 365

= 1.5768 × 10⁷ kg

Sulfur content = ² 1.5768 10⁷ 10 ⁶ 100

× × × − = 315.36 tonnes/year

Sulfur content in ash = ⁶ ^315.36

100× = 18.92 tonnes/year Sulfur converted to SO₂= 315.36 – 18.92 = 296.44 tonnes/year

S + O₂→ SO₂

1 mole of S is present in 1 mole of SO₂ 32 gm of S is present in 64 gm of SO₂

∴ Rate of SO₂ emission = 64× =

296.44 592.88 tonnes /year 32

Q.27 Q.27Q.27

Q.27Q.27 A flocculation tank contains 1800 m³ of water, which is mixed using paddles at an average velocity gradient G of 100/s. The water temperature and the corresponding dynamic viscosity are 30°C and 0.798 × 10^–3 Ns/m², respectively. The theoretical power required to achieve the stated value of G (in kW, up to two decimal places) is ________.

(20)

Ans.

Ans.Ans.

Ans.Ans. (14.36)(14.36)(14.36)(14.36)(14.36)

Power required

P =μVG²

= 0.798 × 10^–3 Ns/m² × 1800 m³ × (1005)²

= 14364 Nm/s or Watt

= 14.364 kW

= 14.36 kW

Q.28 Q.28Q.28

Q.28Q.28 A prismatic propped cantilever beam of span L and plastic moment capacity M, is subjected to a concentrated load at its mid-span. If the collapse load of the beam is

p, M

α L the value of α is _________.

Ans.

Ans.Ans.

Ans.Ans. (6)(6)(6)(6)(6)

P

l/2 l/2

P_u= 6M_p

l So, α = 6

Q.29 Q.29Q.29

Q.29Q.29 A prismatic beam P-Q-R of flexural rigidity EI = 1 × 10⁴ kNm² is subjected to a moment of 180 kNm at Q as shown in the figure.

180 kNm

Q R

P

5 m 4 m

The rotation at Q (in rad, up to two decimal places) is _________.

Ans.

Ans.Ans.

Ans.Ans. (0.01)(0.01)(0.01)(0.01)(0.01)

180 kNm

Q R

P θP = 0 θR = 0

5 m 4 m

K_Q=K_QP + K_QR

= ⁴ ⁴

5 4

E E

I + I = 1.8 EI

θ_Q= ¹⁸⁰ ₄ ^{0.01 rad} 1.8 10

Q Q

M

K ⁼ _× ⁼

(21)

Alternate solution Alternate solutionAlternate solution Alternate solutionAlternate solution

M_QP= fQP ² ^[2 Q P^]

M ₊ E^I _{θ + θ}

l {M_fQP = 0, θ_P = 0}

= 4 104

5 ^Q 8000 ^Q

× × θ = θ

M_QR= _fQR ²E [2 _Q _R] M ₊ ^I _{θ + θ}

l {M_fQR = 0, θ_R = 0}

= 2 104

[2 ] 10000

4 ^Q Q

× θ =

ΣMQ= 0

⇒ M_QP + M_QR + 180 = 0

⇒ 18000⋅ θQ= –180

⇒ θ_Q= 0.01 radian (anticlockwise)

Q.30 Q.30Q.30

Q.30Q.30 The matrix

2 4

4 2

⎛ − ⎞

⎜ ⎟

⎝ − ⎠ has

(a) real eigenvalues and eigenvectors

(b) real eigenvalues but complex eigenvectors (c) complex eigenvalues but real eigenvectors (d) complex eigenvalues and eigenvectors Ans.

Ans.Ans.

A =

2 4

4 2

⎡ − ⎤

⎢ − ⎥

⎣ ⎦

|A – λI| = 0

2 4

4 2

− λ −

− − λ = 0 –4 – 2λ + 2λ + λ² + 16 = 0 λ² + 12 = 0

λ = _±2 3i (Complex eigen values)

(1) λ = 2 3i

Consider (A – λI)X = 0

1 2

2 2 3 4

4 2 2 3

⎡ − − ⎤⎡ ⎤

⎢ − − ⎥ ⎢ ⎥

⎢ ⎥ ⎣ ⎦

⎣ ⎦

i x

i x = ⁰

0

⎡ ⎤⎢ ⎥

⎣ ⎦ 2 2 3₋ i x1 = 4x₂

1

4

x = ²

2−2 3 x

i