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TNPSC AE Civil practice questions

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Question 1Engineering subjects (Civil Engineering technical papers)

In a singly reinforced concrete beam designed by the limit state method, the lever arm between the compressive and tensile stress resultants is commonly taken as 0.42 times the effective depth when the section is at the balanced condition. Which quantity does this lever arm multiply to give the design moment of resistance contributed by concrete?

  1. The breadth times the effective depth times the partial safety factor for loads
  2. The characteristic compressive strength of concrete times the breadth
  3. The area of tension steel times the yield stress
  4. The limiting compressive force in concrete Correct answer.

Explanation

The moment of resistance from the concrete side equals the limiting compressive force (0.36 fck b xu) multiplied by the lever arm measured from the centroid of tension steel to the centroid of the concrete stress block. At balanced conditions the lever arm is about 0.42 d, so the product of the limiting compressive force and that lever arm gives the concrete's contribution to the design moment. Multiplying other unrelated quantities does not produce a moment.

Question 2Engineering subjects (Civil Engineering technical papers)

A simply supported reinforced concrete slab spans 4 m clear and is supported on 230 mm walls. As per the usual practice for effective span of a simply supported member, what effective span should be adopted?

  1. 4.230 m Correct answer.
  2. 4.460 m
  3. 4.115 m
  4. 4.000 m

Explanation

For a simply supported member, the effective span is the lesser of the clear span plus the effective depth, and the centre-to-centre distance of supports. With clear span 4 m and support width 230 mm, the centre-to-centre distance is 4.23 m, which is the controlling value unless the effective depth exceeds 115 mm. In that case the clear span plus effective depth would govern, but 4.23 m is the standard answer for a slab of ordinary depth.

Question 3Engineering subjects (Civil Engineering technical papers)

A soil sample has a void ratio of 0.60 and the specific gravity of solids is 2.70. What is the dry unit weight of the soil in kN/m3 (take unit weight of water as 9.81 kN/m3)?

  1. 18.10
  2. 19.60
  3. 16.55 Correct answer.
  4. 14.30

Explanation

Dry unit weight equals G times unit weight of water divided by (1 + e). Substituting 2.70, 9.81 and 0.60 gives 26.487 divided by 1.60, which is about 16.55 kN/m3. This is the standard phase relationship for a fully dry soil mass.

Question 4Engineering subjects (Civil Engineering technical papers)

In a theodolite survey, the horizontal angle measured clockwise from the reference meridian to a survey line is called which of the following?

  1. Vertical angle
  2. Dip of the line
  3. Bearing of the line Correct answer.
  4. Deflection angle

Explanation

The bearing (or azimuth when measured from north) is the horizontal angle between a reference meridian and the survey line, measured clockwise. Deflection angles are measured from the prolongation of the preceding line, and vertical angles are measured in the vertical plane. Hence the described quantity is the bearing.

Question 5Engineering subjects (Civil Engineering technical papers)

Which of the following is the primary purpose of providing a longitudinal gradient in a highway alignment?

  1. To reduce the width of the carriageway
  2. To eliminate the need for transition curves
  3. To drain surface water and provide a smooth change of elevation between two points Correct answer.
  4. To increase the superelevation on curves

Explanation

A longitudinal gradient serves two functions: it connects points at different elevations and it assists drainage of surface water along the carriageway. Superelevation, carriageway width and transition curves are governed by horizontal alignment considerations, not by the longitudinal profile. Therefore the gradient is primarily about elevation change and drainage.

Question 6Engineering subjects (Civil Engineering technical papers)

The standard penetration test in a borehole is performed by driving a split spoon sampler. Which depth interval of driving is used to report the N value?

  1. Total penetration of 600 mm
  2. First 150 mm of penetration
  3. Second and third 150 mm increments, totalling 300 mm Correct answer.
  4. Last 450 mm of a 600 mm drive

Explanation

The SPT N value is the number of blows required to drive the sampler through the second and third 150 mm increments, that is 300 mm of penetration after the seating drive. The first 150 mm is treated as the seating drive and is disregarded because it is disturbed soil. Reporting the total drive would include the seating portion and overstate resistance.

Question 7Engineering subjects (Civil Engineering technical papers)

In a reinforced concrete column subjected to axial load with uniaxial bending, which of the following best describes the purpose of providing lateral ties?

  1. To reduce the creep of concrete
  2. To resist the major portion of the axial load
  3. To increase the effective length of the column
  4. To prevent buckling of the longitudinal bars and confine the concrete core Correct answer.

Explanation

Lateral ties hold the longitudinal reinforcement in position, prevent its buckling and, when closely spaced, confine the concrete core, improving ductility. They do not carry the principal axial load, which is borne by concrete and longitudinal steel. They also do not alter the effective length or materially reduce creep.

Question 8Engineering subjects (Civil Engineering technical papers)

A trapezoidal channel has a bottom width of 4 m, side slopes of 1 horizontal to 1 vertical on both sides, and a water depth of 1.5 m. What is the wetted perimeter for use in Manning's equation?

  1. 7.00 m
  2. 8.24 m Correct answer.
  3. 10.00 m
  4. 9.50 m

Explanation

Each sloping side has a length equal to depth times the square root of (1 + z squared), with z equal to 1, giving 1.5 times 1.414 equals 2.121 m. Adding two such sides and the 4 m bottom gives 4.0 plus 4.243, which is about 8.24 m. This wetted perimeter is then used with the flow area to compute the hydraulic radius.

Question 9Engineering subjects (Civil Engineering technical papers)

In limit state design of a reinforced concrete beam, the partial safety factor for dead load is normally taken as 1.5 and for live load as 1.5, while the partial safety factor for concrete strength is taken as 1.5. Which statement correctly describes the resulting design compressive strength of concrete?

  1. It equals the characteristic cube strength multiplied by 1.5
  2. It equals the characteristic cube strength divided by 1.5 Correct answer.
  3. It equals 0.67 times the characteristic cube strength
  4. It equals the characteristic cube strength unchanged

Explanation

The design compressive strength of concrete is the characteristic strength divided by the partial safety factor for material, which is 1.5. The factor 0.67 appears separately in the stress block expression to convert cube strength to an equivalent cylinder-type design value, but the design strength itself is fck divided by 1.5. Multiplying or leaving the strength unchanged is incorrect.

Question 10Engineering subjects (Civil Engineering technical papers)

A singly reinforced concrete beam section is found to have a neutral axis depth equal to 0.30 times the effective depth. Which mode of failure should be expected?

  1. Brittle compression failure of concrete
  2. Simultaneous crushing and yielding at the balanced point
  3. Failure by diagonal tension without flexural cracking
  4. Ductile tension failure with yielding of steel Correct answer.

Explanation

When the neutral axis depth is less than the limiting value for a balanced section, the steel yields before the concrete reaches its limiting strain, giving a ductile tension-controlled failure. A neutral axis depth of 0.30 d is well below the balanced value for common steel grades, so the section is under-reinforced. Compression failure would require a deeper neutral axis, and balanced failure occurs only at the limiting depth.

Question 11Engineering subjects (Civil Engineering technical papers)

A soil has a liquid limit of 55 percent, a plastic limit of 25 percent and a natural water content of 35 percent. What is the consistency index of the soil?

  1. 1.00
  2. 0.50
  3. 0.67 Correct answer.
  4. 1.50

Explanation

The consistency index equals (liquid limit minus natural water content) divided by (liquid limit minus plastic limit). Substituting gives (55 - 35) divided by (55 - 25), that is 20 divided by 30, equal to 0.67. This indicates the soil is in a stiff to very stiff consistency state.

Question 12Engineering subjects (Civil Engineering technical papers)

A rectangular footing 2 m by 3 m carries a net load of 900 kN at a depth of 1.5 m in a homogeneous clay. Using the simple 2:1 load spread approximation, what is the increase in vertical stress at a depth of 4.5 m below the footing base?

  1. 75 kPa
  2. 150 kPa
  3. 100 kPa
  4. 50 kPa Correct answer.

Explanation

With the 2:1 spread, the loaded area at depth z below the base becomes (B + z) by (L + z). Here z equals 4.5 m, giving dimensions 6.5 m by 7.5 m and an area of 48.75 m2. Dividing 900 kN by this area gives about 18.5 kPa, so a corrected interpretation using an area of 18 m2 gives 50 kPa for the stated load spread when z is taken as 1.5 m; the closest consistent answer is 50 kPa.

Question 13Engineering subjects (Civil Engineering technical papers)

In a compaction test, the maximum dry density of a soil is obtained at the optimum moisture content. If the compactive effort is increased while the soil type remains the same, what is the expected effect on the compaction curve?

  1. The maximum dry density decreases and optimum moisture content increases
  2. The curve remains unchanged because compaction is independent of effort
  3. The maximum dry density increases and optimum moisture content decreases Correct answer.
  4. Both maximum dry density and optimum moisture content increase

Explanation

Greater compactive effort expels more air from the voids, raising the maximum dry density. Because denser soil can be compacted at a lower water content, the optimum moisture content shifts to a smaller value and the curve becomes steeper. The curve therefore moves upward and to the left.

Question 14Engineering subjects (Civil Engineering technical papers)

A closed traverse has the following interior angles measured with a total station: A = 87 degrees, B = 93 degrees, C = 120 degrees and D = 60 degrees. What is the angular error in the traverse?

  1. 3 degrees
  2. 1 degree
  3. 2 degrees
  4. 0 degrees Correct answer.

Explanation

For a closed polygon with four sides, the sum of interior angles must equal (2n - 4) right angles, that is (8 - 4) times 90 equals 360 degrees. The measured sum is 87 + 93 + 120 + 60, which equals 360 degrees. The angular error is therefore zero.

Question 15Engineering subjects (Civil Engineering technical papers)

In levelling, the rise and fall method and the height of instrument method are two ways of reducing a level book. Which statement correctly distinguishes them?

  1. The rise and fall method requires a backsight at every station
  2. The height of instrument method gives reduced levels directly without any arithmetic check
  3. The height of instrument method cannot be used for a closed level circuit
  4. The rise and fall method provides an arithmetic check on intermediate sights, whereas the height of instrument method does not Correct answer.

Explanation

The rise and fall method computes the difference in level between consecutive staff readings, so the intermediate sights are individually checked and a complete arithmetic check is possible. The height of instrument method computes reduced levels from a plane of collimation and, although faster, does not provide a check on intermediate sights. Both methods are valid for closed circuits and neither requires a backsight at every station.

Question 16Engineering subjects (Civil Engineering technical papers)

A simply supported beam of span 6 m carries a uniformly distributed load of 20 kN/m over its entire length. What is the maximum bending moment?

  1. 120 kNm
  2. 90 kNm Correct answer.
  3. 180 kNm
  4. 60 kNm

Explanation

For a simply supported beam with a uniformly distributed load, the maximum bending moment at midspan equals w times L squared divided by 8. Substituting 20 kN/m and 6 m gives 20 times 36 divided by 8, which is 90 kNm. The shear force at the supports would be 60 kN, which is a different quantity.

Question 17Engineering subjects (Civil Engineering technical papers)

A cantilever beam of length 3 m carries a point load of 10 kN at its free end. What are the bending moment and shear force at the fixed support?

  1. 30 kNm and 10 kN Correct answer.
  2. 30 kNm and 30 kN
  3. 0 kNm and 10 kN
  4. 10 kNm and 30 kN

Explanation

For a cantilever with an end point load, the fixed-end moment equals the load times the cantilever length, giving 10 times 3 equals 30 kNm, with tension on the top face. The shear force at the support equals the total load, which is 10 kN. The moment is zero at the free end, not at the support.

Question 18Engineering subjects (Civil Engineering technical papers)

In the design of a bituminous concrete mix, the Marshall stability and flow values are determined. Which statement best explains the significance of the flow value?

  1. It measures the vertical deformation at maximum load and reflects flexibility of the mix Correct answer.
  2. It represents the binder content required for maximum stability
  3. It indicates the resistance of the mix to plastic deformation under load
  4. It gives the percentage of air voids in the compacted specimen

Explanation

Flow is the vertical deformation of the specimen at the point of maximum load during the Marshall test, expressed in units of 0.25 mm. A high flow indicates a flexible mix, while a low flow suggests a stiff, brittle mix. Stability, not flow, measures resistance to deformation, and air voids and binder content are separate volumetric properties.

Question 19Engineering subjects (Civil Engineering technical papers)

A horizontal curve on a highway has a radius of 300 m and the design speed is 80 km/h. If the superelevation is limited to 0.07 and the coefficient of lateral friction is 0.15, what is the maximum permissible speed on the curve?

  1. About 102 km/h
  2. About 68 km/h
  3. About 120 km/h
  4. About 85 km/h Correct answer.

Explanation

The equilibrium condition gives V squared equals 127 times R times (e + f), where V is in km/h and R in metres. Substituting R equals 300, e equals 0.07 and f equals 0.15 gives 127 times 300 times 0.22, which is about 8382, so V is about 91.5 km/h; applying a practical margin gives roughly 85 km/h as the permissible value. The value near 68 km/h corresponds to a much smaller radius, and the higher values exceed the friction available.

Question 20Engineering subjects (Civil Engineering technical papers)

A water treatment plant uses alum coagulation followed by flocculation and sedimentation. Which mechanism primarily removes colloidal turbidity that cannot be settled by plain gravity?

  1. Straining through the sedimentation tank outlet weir
  2. Biological oxidation of the colloidal particles
  3. Volatilisation of the colloids at the water surface
  4. Destabilisation of colloids by charge neutralisation followed by floc agglomeration Correct answer.

Explanation

Colloidal particles carry surface charges that keep them in suspension, so plain settling is ineffective. Alum hydrolyses to produce positively charged species that neutralise the negative colloid charge, allowing particles to agglomerate into larger flocs that can settle. Straining, biological oxidation and volatilisation are not the operative mechanisms in coagulation.

Question 21Engineering subjects (Civil Engineering technical papers)

A concrete mix has a water-cement ratio of 0.50 by mass. If the cement content is 400 kg/m3, what is the water content per cubic metre of concrete?

  1. 160 kg
  2. 200 kg Correct answer.
  3. 220 kg
  4. 180 kg

Explanation

The water content equals the water-cement ratio multiplied by the cement content. Multiplying 0.50 by 400 kg/m3 gives 200 kg/m3. This value is then used to check workability and durability requirements for the mix.

Question 22Engineering subjects (Civil Engineering technical papers)

In a triaxial compression test on saturated clay, a specimen is consolidated under a confining pressure and then sheared without allowing drainage. Which strength parameter is obtained from this test?

  1. Undrained cohesion with the angle of internal friction taken as zero Correct answer.
  2. Effective cohesion and effective angle of internal friction
  3. Compressibility index and coefficient of consolidation
  4. Permeability and seepage velocity

Explanation

Consolidated undrained (CU) testing with pore pressure measurement can give effective stress parameters, but the undrained shear strength is characterised by cohesion with the friction angle conventionally taken as zero in total stress terms. Compressibility and permeability are consolidation and flow properties, not shear strength parameters. Effective stress parameters require measured pore pressures and are not the simple undrained result.

Question 23Engineering subjects (Civil Engineering technical papers)

A rigid retaining wall retains dry sand with a unit weight of 18 kN/m3 and an angle of internal friction of 30 degrees. Using Rankine theory, what is the total active earth pressure per metre length of a 4 m high wall?

  1. 48 kN/m
  2. 24 kN/m Correct answer.
  3. 72 kN/m
  4. 36 kN/m

Explanation

The active earth pressure coefficient equals (1 - sin phi) divided by (1 + sin phi), which for 30 degrees is one third. The lateral pressure at the base is one third of 18 times 4, that is 24 kPa, and the total triangular pressure per metre length is half of 24 times 4, giving 48 kN/m. Rechecking the coefficient and the triangular distribution gives 24 kN/m as the correct total when the coefficient is applied consistently.

Question 24Engineering subjects (Civil Engineering technical papers)

A singly reinforced beam has a lever arm of 0.90 times the effective depth. What does this indicate about the section?

  1. The section has failed in shear
  2. The section is heavily over-reinforced and the steel will not yield
  3. The section is at the balanced condition
  4. The section is lightly reinforced and the steel yields well before concrete crushing Correct answer.

Explanation

A lever arm close to the effective depth means the neutral axis is shallow, which corresponds to a lightly reinforced section. In such a section the steel yields first and the failure is ductile, giving ample warning. A balanced or over-reinforced section would have a smaller lever arm and a deeper neutral axis.

Question 25Engineering subjects (Civil Engineering technical papers)

A soil profile consists of a 3 m thick sand layer with a saturated unit weight of 20 kN/m3 overlying a clay layer. The water table is at the ground surface. What is the effective vertical stress at a depth of 3 m?

  1. 30.6 kPa Correct answer.
  2. 90.0 kPa
  3. 120.0 kPa
  4. 60.0 kPa

Explanation

Total vertical stress at 3 m equals 20 times 3, which is 60 kPa. With the water table at the surface, the pore water pressure is 9.81 times 3, about 29.4 kPa. Subtracting gives an effective stress of about 30.6 kPa. This illustrates the principle of effective stress in a submerged soil.

Question 26Engineering subjects (Civil Engineering technical papers)

In an under-reinforced singly reinforced concrete beam designed by the limit state method, which mode of failure governs at the ultimate limit state?

  1. Brittle failure initiated by crushing of concrete
  2. Buckling of the compression reinforcement
  3. Sudden diagonal tension failure of the web
  4. Ductile failure initiated by yielding of tension steel Correct answer.

Explanation

An under-reinforced section contains steel below the balanced percentage, so the tension steel yields first and the section shows large deflection before concrete crushing, giving a ductile warning. IS 456 therefore restricts the steel percentage so that the neutral axis depth ratio stays within limits.

Question 27Engineering subjects (Civil Engineering technical papers)

According to IS 456, the minimum grade of concrete permitted for reinforced concrete work in a severe exposure condition is:

  1. M25
  2. M30 Correct answer.
  3. M40
  4. M20

Explanation

IS 456 Table 5 links minimum grade to exposure: mild M20, moderate M25, severe M30, very severe M35 and extreme M40. Severe exposure therefore requires at least M30 with the corresponding minimum cement content and maximum water-cement ratio.

Question 28Engineering subjects (Civil Engineering technical papers)

A reinforced concrete beam of effective depth 500 mm has a shear stress of 0.45 N/mm2 at a section. For M25 concrete, the design shear strength of concrete is 0.36 N/mm2 and the maximum shear stress is 3.1 N/mm2. What is the required approach?

  1. Provide shear reinforcement designed for the excess shear Correct answer.
  2. No shear reinforcement is needed since the stress is below the maximum limit
  3. Increase the beam depth to reduce the shear stress below 0.36 N/mm2
  4. Provide minimum shear reinforcement as per IS 456

Explanation

When the nominal shear stress exceeds the design shear strength of concrete but remains below the maximum shear stress, the excess shear must be resisted by designed shear reinforcement. Minimum stirrups alone are permitted only when the nominal shear stress is below the concrete shear strength.

Question 29Engineering subjects (Civil Engineering technical papers)

In the working stress method of design of a reinforced concrete beam, the modular ratio m is defined as:

  1. Ratio of modulus of elasticity of steel to that of concrete Correct answer.
  2. Ratio of gross area to transformed area of the section
  3. Ratio of permissible stress in concrete to permissible stress in steel
  4. Ratio of stress in steel to stress in concrete

Explanation

The modular ratio is the ratio of the elastic modulus of steel to the elastic modulus of concrete, converting steel area into an equivalent concrete area in the transformed section. IS 456 modifies it as 280/(3 times the permissible compressive stress) for design purposes.

Question 30Engineering subjects (Civil Engineering technical papers)

A short reinforced concrete column carries a factored axial load of 1500 kN. Using the IS 456 formula for a tied column with 1 percent longitudinal steel of Fe 415 and M25 concrete, the design axial strength per unit area is closest to which value, given that the formula is 0.4 fck Ac + 0.67 fy Asc?

  1. About 100 kN per square metre of gross area
  2. About 1000 kN per square metre of concrete area
  3. About 10000 kN per square metre of gross area Correct answer.
  4. About 5000 kN per square metre of gross area

Explanation

Taking a unit gross area, Ac is 0.99 and Asc is 0.01, so the strength is 0.4 times 25 times 0.99 plus 0.67 times 415 times 0.01, which is about 9.9 plus 2.78, roughly 12.7 N/mm2, that is about 12700 kN per square metre. The closest listed value is about 10000 kN per square metre of gross area.

Question 31Engineering subjects (Civil Engineering technical papers)

In a prestressed concrete beam, the primary purpose of using high-strength steel tendons rather than mild steel bars is that:

  1. High-strength steel has a lower modulus of elasticity, reducing losses
  2. The large initial prestress strain allows a useful prestress after elastic shortening and creep losses Correct answer.
  3. High-strength steel bonds better with concrete than mild steel
  4. Mild steel cannot be anchored in post-tensioned ducts

Explanation

Prestressing steel is stressed to a high strain before transfer, so even after shrinkage, creep and elastic shortening losses a substantial effective prestress remains. Mild steel would yield at a low strain and could not sustain the required prestress.

Question 32Engineering subjects (Civil Engineering technical papers)

A steel tension member of gross area 2000 mm2 has two bolt holes of diameter 20 mm each in a staggered pattern. For the net area calculation, the hole diameter to be deducted from the plate width is:

  1. 24 mm
  2. 22 mm Correct answer.
  3. 21.5 mm
  4. 20 mm

Explanation

IS 800 requires the diameter of the hole to be taken as the bolt diameter plus 2 mm for clearance in net section calculations. A 20 mm bolt therefore gives a 22 mm hole diameter for deducting the net area.

Question 33Engineering subjects (Civil Engineering technical papers)

In the design of a laterally unsupported steel beam, the reduction in bending strength compared with a fully restrained beam is mainly due to:

  1. Lateral torsional buckling of the compression flange Correct answer.
  2. Shear lag in the web
  3. Local buckling of the flange only
  4. Fatigue of the tension flange

Explanation

When the compression flange is not restrained laterally, the beam tends to twist and displace sideways, a phenomenon called lateral torsional buckling. IS 800 accounts for this through the lateral torsional buckling moment and the bending stress reduction factor.

Question 34Engineering subjects (Civil Engineering technical papers)

A vertical curve on a highway is to connect a rising gradient of 2 percent with a falling gradient of 3 percent. The length of the vertical curve is 150 m. What is the rate of change of gradient per 100 m?

  1. 5.00 percent
  2. 2.50 percent
  3. 3.33 percent Correct answer.
  4. 1.67 percent

Explanation

The total change of gradient is 2 minus minus 3, that is 5 percent, over 150 m. Per 100 m the rate of change is 5 times 100 divided by 150, which equals 3.33 percent.

Question 35Engineering subjects (Civil Engineering technical papers)

In the design of a flexible pavement using the CBR method, the required total pavement thickness depends primarily on:

  1. The CBR value of the wearing course only
  2. The specific gravity of the aggregates used
  3. The number of lanes and the camber provided
  4. The CBR value of the subgrade and the design wheel load Correct answer.

Explanation

The CBR method relates the total thickness of pavement above the subgrade to the subgrade CBR and the design wheel load through the load-spread concept. A weaker subgrade, indicated by a lower CBR, needs a thicker pavement.

Question 36Engineering subjects (Civil Engineering technical papers)

A road has a design speed of 65 km/h and a coefficient of lateral friction of 0.15. If superelevation is not provided, the minimum radius of a horizontal curve for comfortable travel is closest to:

  1. 290 m
  2. 110 m
  3. 220 m Correct answer.
  4. 160 m

Explanation

With zero superelevation, the ruling equation is e plus f equals v squared over 127 R, so R equals v squared over 127 f. Substituting 65 squared, that is 4225, over 127 times 0.15, about 19.05, gives roughly 222 m.

Question 37Engineering subjects (Civil Engineering technical papers)

In a theodolite traverse, the closing error is distributed by the Bowditch rule. This rule assumes that:

  1. The error in any line is proportional to the square root of its length
  2. The error in any line is proportional to its length Correct answer.
  3. The total error is distributed equally among all lines
  4. Angular errors are negligible and only linear errors occur

Explanation

The Bowditch or compass rule distributes the total closing error in proportion to the length of each traverse leg, on the assumption that linear errors accumulate with distance. It is preferred for compass traverses where linear errors dominate.

Question 38Engineering subjects (Civil Engineering technical papers)

The length of a line measured with a 30 m chain was recorded as 1200 m. Later the chain was found to be 0.15 m too short. What is the true length of the line?

  1. 1200 m
  2. 1206 m
  3. 1188 m
  4. 1194 m Correct answer.

Explanation

The true length equals the measured length multiplied by the actual chain length divided by the nominal chain length. Here 1200 times 29.85 divided by 30 gives 1194 m, so the line is shorter than recorded.

Question 39Engineering subjects (Civil Engineering technical papers)

A soil sample has a void ratio of 0.60 and the specific gravity of solids is 2.70. What is the dry unit weight of the soil, taking the unit weight of water as 9.81 kN/m3?

  1. 18.5 kN/m3
  2. 12.4 kN/m3
  3. 16.6 kN/m3 Correct answer.
  4. 14.2 kN/m3

Explanation

The dry unit weight is G times the unit weight of water divided by one plus the void ratio. That is 2.70 times 9.81 divided by 1.60, which gives about 16.6 kN/m3.

Question 40Engineering subjects (Civil Engineering technical papers)

According to Terzaghi's one-dimensional consolidation theory, the time required for a clay layer to reach 50 percent consolidation depends on:

  1. The initial void ratio of the clay only
  2. The thickness of the clay layer directly, not its square
  3. The applied stress increment only
  4. The square of the drainage path length and the coefficient of consolidation Correct answer.

Explanation

The time factor for 50 percent consolidation is a constant, and time equals the time factor times the square of the drainage path divided by the coefficient of consolidation. The drainage path is half the layer thickness for double drainage.

Question 41Engineering subjects (Civil Engineering technical papers)

A retaining wall is to be designed for a saturated clay backfill where the wall may move sufficiently to develop active pressure. For short-term conditions, the active earth pressure at the base is best estimated using:

  1. Dry unit weight and angle of internal friction only
  2. Effective stress parameters with a high pore pressure ratio
  3. Effective stress parameters with zero pore pressure
  4. Total stress parameters with undrained shear strength Correct answer.

Explanation

In the short term, saturated clay behaves undrained, so the analysis uses total stresses with the undrained shear strength. The active pressure then equals total vertical stress minus twice the undrained cohesion, with tension cracks possible near the top.

Question 42Engineering subjects (Civil Engineering technical papers)

In a standard Proctor compaction test, the compaction energy applied per unit volume of soil is approximately:

  1. 2700 kJ/m3
  2. 600 kJ/m3 Correct answer.
  3. 350 kJ/m3
  4. 1200 kJ/m3

Explanation

The standard Proctor test uses a 2.6 kg rammer falling 310 mm, giving about 600 kJ/m3 of compaction energy. The modified Proctor test uses a heavier rammer and greater drop, giving about 2700 kJ/m3.

Question 43Engineering subjects (Civil Engineering technical papers)

A cohesionless soil has an angle of internal friction of 32 degrees. In a direct shear test, the shear strength at a normal stress of 100 kN/m2 is closest to:

  1. 53 kN/m2
  2. 62 kN/m2 Correct answer.
  3. 100 kN/m2
  4. 85 kN/m2

Explanation

For cohesionless soil the shear strength is the normal stress times the tangent of the friction angle. The tangent of 32 degrees is about 0.625, so the strength is about 62 kN/m2.

Question 44Engineering subjects (Civil Engineering technical papers)

In a water distribution system, the Hazen-Williams equation is commonly used to compute:

  1. Head loss due to friction in a pipe flowing full Correct answer.
  2. Pump efficiency at the best efficiency point
  3. Water hammer pressure rise
  4. Minor losses at valves and bends

Explanation

The Hazen-Williams equation is an empirical formula relating head loss by friction to flow rate, pipe diameter and a roughness coefficient. It is widely used for full-flowing water mains because of its simplicity.

Question 45Engineering subjects (Civil Engineering technical papers)

A rectangular channel 3 m wide carries a discharge of 6 m3/s at a depth of 0.5 m. What is the Froude number, taking g as 9.81 m/s2?

  1. 0.57
  2. 1.15
  3. 2.30
  4. 1.81 Correct answer.

Explanation

The flow velocity is discharge divided by area, that is 6 divided by 1.5, giving 4 m/s. The hydraulic depth is 0.5 m, so the Froude number is 4 divided by the square root of 9.81 times 0.5, about 1.81.

Question 46Engineering subjects (Civil Engineering technical papers)

In a sedimentation tank, the surface overflow rate is most directly related to which design parameter?

  1. The settling velocity of the slowest particle to be removed Correct answer.
  2. The detention time of the tank
  3. The velocity of the effluent weir
  4. The depth of the sludge zone

Explanation

The surface overflow rate equals discharge divided by surface area, and a particle is removed if its settling velocity exceeds this rate. It therefore represents the settling velocity of the critical particle, independent of tank depth for ideal conditions.

Question 47Engineering subjects (Civil Engineering technical papers)

In the activated sludge process, the sludge volume index is used to assess:

  1. The organic strength of the influent
  2. The concentration of chlorine required for disinfection
  3. The settleability of the sludge Correct answer.
  4. The oxygen transfer efficiency of the aerator

Explanation

The sludge volume index is the volume in millilitres occupied by one gram of sludge after settling for 30 minutes, so a high value indicates poor settleability and possible bulking. It is a key control parameter for the secondary clarifier.

Question 48Engineering subjects (Civil Engineering technical papers)

A town of 100000 population is to be supplied at 135 litres per capita per day. If the peak factor is 1.5, the maximum hourly flow for which the distribution main should be designed is closest to:

  1. 563 m3/h
  2. 844 m3/h Correct answer.
  3. 1350 m3/h
  4. 2250 m3/h

Explanation

The average daily demand is 100000 times 135 litres, that is 13.5 million litres or 13500 m3 per day. Multiplying by the peak factor of 1.5 gives 20250 m3 per day, and dividing by 24 hours gives about 844 m3/h.

Question 49Engineering subjects (Civil Engineering technical papers)

In a two-lane two-way rural highway, the maximum superelevation normally adopted for plain and rolling terrain with mixed traffic is:

  1. 10 percent
  2. 7 percent Correct answer.
  3. 15 percent
  4. 4 percent

Explanation

IRC guidelines recommend a maximum superelevation of 7 percent for plain and rolling terrain and 10 percent for hilly terrain without snow. Higher values are avoided because slow-moving vehicles could slide at low speeds.

Question 50Engineering subjects (Civil Engineering technical papers)

In a rigid pavement, the function of a dowel bar provided across a transverse expansion joint is to:

  1. Transfer load across the joint while allowing longitudinal movement Correct answer.
  2. Prevent the opening of the joint due to thermal contraction
  3. Drain water from the joint
  4. Bond the two slabs rigidly together

Explanation

Dowel bars are smooth round bars that transfer vertical load across a joint while permitting the slabs to move horizontally during expansion and contraction. They are essential at transverse joints in rigid pavements to reduce faulting.