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PEC EPE Civil practice questions

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Question 1Civil Engineering

A simply supported reinforced concrete beam spans 6 m and carries a uniformly distributed factored load of 20 kN/m. What is the maximum factored bending moment at midspan?

  1. 60 kN·m
  2. 90 kN·m Correct answer.
  3. 180 kN·m
  4. 120 kN·m

Explanation

For a simply supported beam with a uniformly distributed load, the maximum moment is wL²/8. Substituting gives 20 × 6² / 8 = 20 × 36 / 8 = 90 kN·m at midspan.

Question 2Civil Engineering

In limit-state design of a reinforced concrete beam, which parameter most directly controls whether the section is classified as under-reinforced?

  1. The clear cover to the tension reinforcement
  2. The characteristic cube strength of the concrete alone
  3. The area of tension steel relative to the balanced steel ratio Correct answer.
  4. The span-to-effective-depth ratio

Explanation

A section is under-reinforced when the tension steel area is below the balanced value, so the steel yields before the concrete crushes. This ductile behaviour depends on the ratio of provided steel to the balanced steel ratio.

Question 3Civil Engineering

A soil sample has a natural water content of 20%, a specific gravity of solids of 2.65, and a void ratio of 0.60. What is its degree of saturation?

  1. 100%
  2. 88% Correct answer.
  3. 53%
  4. 73%

Explanation

Degree of saturation is S = w·Gs/e. Substituting gives 0.20 × 2.65 / 0.60 = 0.53 / 0.60 ≈ 0.88, or about 88%.

Question 4Civil Engineering

Which standard test is used to determine the liquid limit of a fine-grained soil?

  1. Vane shear test
  2. Standard Proctor test
  3. Constant head permeability test
  4. Casagrande cup method Correct answer.

Explanation

The liquid limit is the water content at which soil closes a standard groove after a specified number of blows in the Casagrande cup. It is an Atterberg limits test defining the boundary between plastic and liquid states.

Question 5Civil Engineering

In open-channel flow, the Froude number is used to classify the flow regime. A Froude number of 0.6 indicates which condition?

  1. Critical flow
  2. Supercritical flow
  3. Subcritical flow Correct answer.
  4. Uniform flow

Explanation

The Froude number compares inertial to gravitational forces. Values below 1 indicate subcritical (tranquil) flow, where disturbances can travel upstream; values above 1 indicate supercritical flow.

Question 6Civil Engineering

In a structural steel tension member, which failure mode is checked by limiting the net area rather than the gross area?

  1. Yielding of the gross section
  2. Shear lag at the connection
  3. Fracture of the net section at bolt holes Correct answer.
  4. Local buckling of the plate

Explanation

Fracture is checked on the net section because bolt holes reduce the effective resisting area and stress concentrates there. Yielding, by contrast, is checked on the gross area because it is a ductile, section-wide phenomenon.

Question 7Civil Engineering

Which of the following is the primary purpose of a slump test on fresh concrete?

  1. To measure the compressive strength of hardened concrete
  2. To assess the workability or consistency of the mix Correct answer.
  3. To determine the air content of the mix
  4. To estimate the setting time of the cement

Explanation

The slump test is a simple field measure of the consistency and workability of fresh concrete. It indicates how easily the mix flows and can be placed, not its hardened strength.

Question 8Civil Engineering

In surveying, a level is set up and a backsight of 1.50 m is taken on a benchmark of reduced level 100.00 m. What is the height of the instrument?

  1. 103.00 m
  2. 98.50 m
  3. 101.50 m Correct answer.
  4. 100.00 m

Explanation

The height of the instrument equals the benchmark reduced level plus the backsight reading. Adding 100.00 m and 1.50 m gives 101.50 m.

Question 9Civil Engineering

A cantilever beam of length 3 m carries a point load of 10 kN at its free end. What is the magnitude of the fixed-end moment?

  1. 30 kN·m Correct answer.
  2. 10 kN·m
  3. 90 kN·m
  4. 15 kN·m

Explanation

For a cantilever with an end point load, the fixed-end moment equals the load times the cantilever length. Multiplying 10 kN by 3 m gives 30 kN·m.

Question 10Civil Engineering

A reinforced concrete beam has a balanced steel ratio of 0.020 and a provided steel ratio of 0.012. How should the section be classified?

  1. Over-reinforced
  2. Balanced
  3. Compression-controlled
  4. Under-reinforced Correct answer.

Explanation

When the provided steel ratio is less than the balanced ratio, the tension steel yields before the concrete crushes, producing a ductile under-reinforced section. Here 0.012 is well below 0.020.

Question 11Civil Engineering

A clay layer has a coefficient of consolidation of 2.0 m²/year and a drainage path length of 2 m under double drainage. Using the approximate relation T50 ≈ 0.197, what is the time for 50% consolidation?

  1. 0.39 years Correct answer.
  2. 0.79 years
  3. 1.58 years
  4. 0.20 years

Explanation

The time factor is T = cv·t/H², so t = T·H²/cv. With H = 2 m, T = 0.197, and cv = 2.0, this gives 0.197 × 4 / 2.0 ≈ 0.39 years.

Question 12Civil Engineering

A retaining wall retains dry sand with a unit weight of 18 kN/m³ and an angle of internal friction of 30°. Using Rankine theory, what is the active earth pressure coefficient?

  1. 0.50
  2. 1.00
  3. 0.33 Correct answer.
  4. 3.00

Explanation

Rankine's active earth pressure coefficient is Ka = (1 − sin φ)/(1 + sin φ). For φ = 30°, sin φ = 0.5, giving Ka = 0.5/1.5 = 0.33.

Question 13Civil Engineering

In a pipe network analysis using the Hardy Cross method, what is the fundamental correction applied to each loop?

  1. A pressure correction that balances velocities at each node
  2. A roughness correction that balances friction factors
  3. A flow correction that balances head losses around the loop Correct answer.
  4. A temperature correction that balances density changes

Explanation

Hardy Cross iteratively adjusts assumed pipe flows so that the algebraic sum of head losses around each closed loop equals zero. The correction is derived from the loop head-loss imbalance divided by the sum of derivatives of head loss with respect to flow.

Question 14Civil Engineering

A trapezoidal channel has a bottom width of 4 m, side slopes of 1:1 (H:V), and a flow depth of 2 m. What is the wetted perimeter?

  1. 9.66 m Correct answer.
  2. 8.00 m
  3. 6.66 m
  4. 10.00 m

Explanation

Each sloping side has a length equal to the depth times the square root of (1 + z²), where z = 1, giving 2 × √2 ≈ 2.83 m. The wetted perimeter is the bottom width 4 m plus two sides, 4 + 2(2.83) ≈ 9.66 m.

Question 15Civil Engineering

Which of the following best describes the function of shear connectors in a composite steel-concrete beam?

  1. To provide lateral bracing against wind loading
  2. To resist longitudinal shear and ensure composite action between the slab and steel beam Correct answer.
  3. To control the deflection of the steel section under its own weight
  4. To transfer vertical loads directly to the foundations

Explanation

Shear connectors transfer horizontal shear between the concrete slab and the steel beam, enabling them to act as a single composite section. This increases stiffness and flexural capacity compared with the bare steel beam.

Question 16Civil Engineering

A standard penetration test records an N-value of 30 at a depth of 10 m in clean sand. Which statement best reflects the engineering interpretation of this result?

  1. The sand is very loose and prone to liquefaction
  2. The sand has a medium-dense to dense relative density Correct answer.
  3. The sand has negligible bearing capacity
  4. The sand is a highly plastic clay

Explanation

An uncorrected N-value of about 30 in clean sand typically indicates a medium-dense to dense condition with reasonable bearing capacity. Relative density correlations place this well above loose states.

Question 17Civil Engineering

A simply supported beam of span 8 m carries a uniformly distributed load of 15 kN/m. What is the maximum shear force at the supports?

  1. 30 kN
  2. 120 kN
  3. 240 kN
  4. 60 kN Correct answer.

Explanation

For a simply supported beam under a uniformly distributed load, the maximum shear at each support equals wL/2. Substituting gives 15 × 8 / 2 = 60 kN.

Question 18Civil Engineering

In a concrete mix design, reducing the water-cement ratio while maintaining adequate workability generally produces which effect?

  1. Higher compressive strength and lower permeability Correct answer.
  2. Lower compressive strength and higher permeability
  3. Higher compressive strength and higher permeability
  4. No change in strength but increased shrinkage

Explanation

A lower water-cement ratio reduces porosity in the hardened paste, which increases compressive strength and reduces permeability. Workability is maintained by using admixtures rather than extra water.

Question 19Civil Engineering

A soil has a liquid limit of 45% and a plastic limit of 25%. What is its plasticity index, and how is it interpreted?

  1. 20%, indicating moderate plasticity Correct answer.
  2. 70%, indicating high plasticity
  3. 25%, indicating the water content at the liquid limit
  4. 45%, indicating the water content at the plastic limit

Explanation

The plasticity index is the liquid limit minus the plastic limit, 45% − 25% = 20%. This value indicates a moderate range of water content over which the soil remains plastic.

Question 20Civil Engineering

A rectangular reinforced concrete column is subjected to a factored axial load and a small factored moment. Which design approach is most appropriate?

  1. Design using the balanced steel ratio regardless of load eccentricity
  2. Design only for the moment as if no axial load existed
  3. Design as a purely axially loaded column ignoring the moment
  4. Design for combined axial load and bending using an interaction diagram Correct answer.

Explanation

Columns carrying both axial load and moment must be proportioned using an axial load–moment interaction diagram. This ensures the section capacity envelope encloses the factored load combination.

Question 21Civil Engineering

In a water distribution system, a pump delivers water against a static head of 30 m and friction losses of 12 m at the design flow. What is the total head the pump must develop?

  1. 360 m
  2. 30 m
  3. 42 m Correct answer.
  4. 18 m

Explanation

The total pump head equals the static head plus the system head losses at the design flow. Adding 30 m and 12 m gives 42 m.

Question 22Civil Engineering

A reinforced concrete beam section has a neutral axis depth that remains small relative to its effective depth under factored load. Which statement best explains the resulting behaviour?

  1. The tension steel yields first, producing a ductile failure Correct answer.
  2. The section behaves as a compression-controlled member
  3. The concrete crushes first, producing a brittle failure
  4. The section fails by shear before flexure

Explanation

A shallow neutral axis means the tension steel reaches its yield strain while the concrete compression strain is still below its ultimate value. The steel yields first, giving the ductile, tension-controlled response designers prefer.

Question 23Civil Engineering

A normally consolidated clay layer undergoes primary consolidation under an applied load. Which change occurs to the effective stress and void ratio as consolidation progresses?

  1. Effective stress and void ratio both increase
  2. Effective stress increases while void ratio decreases Correct answer.
  3. Effective stress decreases while void ratio increases
  4. Effective stress and void ratio both decrease

Explanation

As excess pore pressure dissipates, the load is transferred to the soil skeleton, increasing effective stress. The soil compresses, so its void ratio decreases until primary consolidation is complete.

Question 24Civil Engineering

A cantilever retaining wall is being checked for overturning. Which factor of safety formulation is consistent with limit-state design principles?

  1. The ratio of overturning moment to resisting moment must exceed a specified minimum
  2. The sum of resisting and overturning moments must equal zero
  3. The ratio of resisting moment to overturning moment must exceed a specified minimum Correct answer.
  4. The overturning moment must be less than the base width

Explanation

Overturning stability compares the stabilizing moment about the toe with the overturning moment. The resisting-to-overturning ratio must meet or exceed the required minimum factor.

Question 25Civil Engineering

A steel beam is laterally unsupported over part of its span. Which phenomenon is the governing design concern in that unsupported region?

  1. Fatigue cracking at midspan
  2. Local flange buckling only
  3. Lateral-torsional buckling Correct answer.
  4. Block shear rupture at the supports

Explanation

When the compression flange is not laterally restrained, the beam can buckle sideways and twist, a mode known as lateral-torsional buckling. It reduces the available flexural capacity below the full plastic moment.

Question 26Civil Engineering

A concrete cube test gives a characteristic strength of 30 MPa at 28 days. Which statistical interpretation does the characteristic strength represent under standard concrete design practice?

  1. The strength exceeded by 95% of test results Correct answer.
  2. The strength below which no test result is permitted to fall
  3. The strength at which the mix may be rejected outright
  4. The average strength of all cubes tested

Explanation

Characteristic strength is defined statistically as the value below which a specified small proportion of test results is expected to fall, conventionally 5%. The target mean strength is set higher than the characteristic value to satisfy this criterion. It is not a minimum acceptance floor for individual cubes, nor the average.

Question 27Civil Engineering

In a simply supported rectangular RC beam, the main tension reinforcement is placed near the bottom face. Which statement correctly describes why cover to that reinforcement is specified?

  1. It reduces the self-weight of the beam
  2. It protects the steel from corrosion and provides fire resistance Correct answer.
  3. It increases the modular ratio of the section
  4. It improves the shear capacity of the section

Explanation

Nominal cover provides a durable alkaline environment around the steel, delaying carbonation and chloride ingress, and gives a thermal barrier for fire resistance. Cover also ensures bond and anchorage, but its primary design purpose is durability and fire. It does not enhance shear strength or alter self-weight meaningfully.

Question 28Civil Engineering

A soil sample has a void ratio of 0.65 and a specific gravity of solids of 2.65. What is the saturated unit weight of the soil, taking the unit weight of water as 9.81 kN/m³?

  1. 18.2 kN/m³
  2. 21.5 kN/m³
  3. 20.4 kN/m³
  4. 19.6 kN/m³ Correct answer.

Explanation

For a saturated soil, the saturated unit weight equals (Gs + e) times the unit weight of water divided by (1 + e). Substituting gives (2.65 + 0.65) x 9.81 / 1.65 = 3.30 x 9.81 / 1.65, which is approximately 19.6 kN/m³. This follows directly from the phase relationships of a fully saturated two-phase model.

Question 29Civil Engineering

A rectangular channel carries a discharge per unit width of 3 m²/s. What is the critical depth, taking g as 9.81 m/s²?

  1. 1.45 m
  2. 0.97 m Correct answer.
  3. 2.10 m
  4. 0.72 m

Explanation

Critical depth in a rectangular channel is obtained from the cube root of q squared divided by g. Here q²/g equals 9/9.81, about 0.917, and its cube root is approximately 0.97 m. At this depth the Froude number equals unity and specific energy is minimum.

Question 30Civil Engineering

A soil element is subjected to a major principal stress of 200 kPa and a minor principal stress of 100 kPa, with zero pore pressure. What is the maximum shear stress on any plane through the element?

  1. 50 kPa Correct answer.
  2. 150 kPa
  3. 200 kPa
  4. 100 kPa

Explanation

Maximum shear stress equals half the difference between the major and minor principal stresses. With 200 kPa and 100 kPa, the difference is 100 kPa and half of that is 50 kPa. This corresponds to the radius of the Mohr circle.

Question 31Civil Engineering

Which structural idealisation is appropriate when analysing a continuous beam for gravity load effects using approximate coefficients in a typical building code?

  1. Modelling the beam as a pin-jointed truss
  2. Ignoring the pattern loading entirely
  3. Treating all supports as fixed against rotation
  4. Assuming the beam is prismatic and members are of similar stiffness Correct answer.

Explanation

Approximate coefficient methods assume reasonably uniform spans, prismatic members and similar stiffness so that moment redistribution follows standard patterns. They also require the loading arrangements specified in the code, including pattern loading for critical effects. Treating supports as fully fixed would contradict the idealisation.

Question 32Civil Engineering

A steel column of effective length 4 m is to be designed against buckling about its weak axis. Which parameter most directly governs the reduction in compressive resistance due to buckling?

  1. The slenderness ratio relative to the yield slenderness limit Correct answer.
  2. The yield strength of the steel alone
  3. The gross cross-sectional area alone
  4. The self-weight of the column

Explanation

Buckling resistance is governed by the member slenderness, expressed as effective length divided by radius of gyration, compared with the yield slenderness limit. This ratio determines the buckling curve and the reduction factor applied to the squash load. Area and yield strength set the squash load but not the slenderness-dependent reduction.

Question 33Civil Engineering

In a triaxial compression test on saturated normally consolidated clay, the sample is sheared slowly with drainage permitted. Which strength parameter is measured?

  1. Total cohesion only
  2. Apparent cohesion from compaction
  3. Undrained shear strength with zero friction angle
  4. Effective cohesion and effective friction angle Correct answer.

Explanation

A slow drained triaxial test allows pore pressures to dissipate, so the measured stresses are effective stresses. The Mohr circles at failure give the effective cohesion and effective friction angle. Undrained strength is obtained from tests without drainage.

Question 34Civil Engineering

A groundwater flow net for seepage beneath a sheet pile wall shows 12 equipotential drops and 4 flow channels. If the coefficient of permeability is 5 x 10⁻⁵ m/s and the total head loss is 6 m, what is the seepage quantity per metre of wall?

  1. 5.0 x 10⁻⁵ m³/s per m
  2. 1.2 x 10⁻⁴ m³/s per m
  3. 2.0 x 10⁻⁴ m³/s per m
  4. 1.0 x 10⁻⁴ m³/s per m Correct answer.

Explanation

Seepage per unit length equals permeability times head loss times the ratio of flow channels to equipotential drops. Here 5 x 10⁻⁵ x 6 x (4/12) gives 1.0 x 10⁻⁴ m³/s per metre. The ratio Nf/Nd captures the geometry of the flow net.

Question 35Civil Engineering

A concrete mix is specified with a target mean strength of 42 MPa and a standard deviation of 5 MPa. If the characteristic strength is 30 MPa, which relationship is consistent with the target mean strength formula?

  1. Target mean equals characteristic strength plus the standard deviation only
  2. Target mean equals characteristic strength divided by the standard deviation
  3. Target mean equals characteristic strength minus the standard deviation
  4. Target mean equals characteristic strength plus 1.65 times the standard deviation Correct answer.

Explanation

For the usual 5% defect allowance, the target mean strength is the characteristic strength plus 1.65 times the standard deviation. With the stated values, 30 + 1.65 x 5 is about 38 MPa, so a target of 42 MPa would be conservative. The 1.65 factor comes from the standard normal distribution.

Question 36Civil Engineering

A rigid footing rests on a homogeneous elastic half-space. According to elastic theory, at what depth below the footing does the vertical stress due to a point load fall to roughly one tenth of its value at the surface?

  1. Approximately three times the footing width
  2. Approximately twice the footing width Correct answer.
  3. Equal to the footing width
  4. Approximately five times the footing width

Explanation

Boussinesq theory shows that the vertical stress influence factor for a point load decreases rapidly with depth, and at a depth of about twice the loaded width the stress is a small fraction of the surface contact pressure. The common rule of thumb is that the significant stressed zone extends to about two to three times the footing width. This governs the depth of exploration for settlement calculations.

Question 37Civil Engineering

A simply supported beam of span 6 m carries a point load of 24 kN at midspan. What is the maximum bending moment?

  1. 36 kN·m Correct answer.
  2. 18 kN·m
  3. 72 kN·m
  4. 144 kN·m

Explanation

For a central point load on a simply supported span, the maximum moment equals the load times the span divided by four. Here 24 x 6 / 4 gives 36 kN·m. The reactions are each 12 kN and the moment at midspan is 12 x 3.

Question 38Civil Engineering

In a reinforced concrete slab designed as one-way spanning, which reinforcement is provided perpendicular to the main bars and why?

  1. Distribution steel to control shrinkage and temperature cracking Correct answer.
  2. Compression steel to increase moment capacity
  3. Shear reinforcement to resist punching
  4. Torsion reinforcement to resist twisting of the slab

Explanation

One-way slabs carry load primarily in the span direction, but shrinkage and temperature movements occur in both directions. Distribution steel perpendicular to the main bars controls cracking and helps spread concentrated loads. It is not intended to resist torsion or punching shear.

Question 39Civil Engineering

A slope in a stiff clay is analysed using a total stress approach. Which condition best justifies using undrained shear strength parameters?

  1. Short-term construction condition where excess pore pressures persist Correct answer.
  2. Steady seepage through the slope
  3. Fully drained granular fill
  4. Long-term drained conditions after full consolidation

Explanation

In the short term, low-permeability clay does not drain appreciably, so excess pore pressures persist and total stress analysis with undrained strength is appropriate. Long-term conditions allow dissipation and require effective stress parameters. Granular fill drains freely and is analysed with effective stress.

Question 40Civil Engineering

A pump is required to deliver 20 L/s against a total head of 25 m. Taking water density as 1000 kg/m³ and pump efficiency as 70%, what is the required shaft power?

  1. 9.8 kW
  2. 7.0 kW Correct answer.
  3. 4.9 kW
  4. 14.0 kW

Explanation

Hydraulic power equals density times gravity times discharge times head, giving 1000 x 9.81 x 0.020 x 25, about 4.9 kW. Dividing by the efficiency of 0.70 gives about 7.0 kW at the shaft. The hydraulic power alone is not the motor rating.

Question 41Civil Engineering

In a water treatment plant, coagulation with alum is followed by flocculation and sedimentation. What is the primary purpose of the rapid mix stage?

  1. To allow flocs to settle under gravity
  2. To disperse coagulant rapidly and destabilise colloidal particles Correct answer.
  3. To remove dissolved organic matter by adsorption
  4. To disinfect the water before filtration

Explanation

Rapid mixing disperses the coagulant throughout the water so that it can neutralise the surface charge on colloidal particles and begin aggregation. Slow flocculation then encourages collisions to build settleable flocs. Settling and disinfection occur in later stages.

Question 42Civil Engineering

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

  1. The curve is adequate only if the coefficient of friction is ignored
  2. The curve is adequate because the required superelevation is below the limit Correct answer.
  3. The curve is adequate regardless of speed because the radius exceeds 250 m
  4. The curve is inadequate and the speed must be reduced or the radius increased

Explanation

The required lateral force ratio is v²/(gR), which with 80 km/h (22.2 m/s) and R = 300 m gives about 0.168, well below the combined limit of 0.07 + 0.15 = 0.22. The curve can therefore be negotiated with superelevation within the permitted value. The check compares the demand with the sum of superelevation and available friction.

Question 43Civil Engineering

In a flexible pavement, which layer is designed primarily to distribute the wheel load to a level that the subgrade can support without excessive deformation?

  1. The base course Correct answer.
  2. The subgrade itself
  3. The wearing course
  4. The surface course

Explanation

The base course spreads the load from the surface over a wider area, reducing the vertical stress reaching the subgrade. The surface course provides a smooth, skid-resistant riding surface and seals the pavement. The subgrade is the natural formation and is not designed to distribute load.

Question 44Civil Engineering

A concrete dam retains water to a height of 20 m. Taking the unit weight of water as 9.81 kN/m³, what is the resultant hydrostatic force per metre length of dam?

  1. 1962 kN/m Correct answer.
  2. 981 kN/m
  3. 3924 kN/m
  4. 196 kN/m

Explanation

The hydrostatic pressure varies linearly from zero at the surface to gamma times height at the base, so the resultant force per unit length equals half of gamma times height squared. Substituting gives 0.5 x 9.81 x 400, which is 1962 kN per metre. The resultant acts at one third of the height above the base.

Question 45Civil Engineering

In surveying, a closed traverse has a total angular misclosure of 30 seconds over 6 angles. How is this misclosure corrected in practice?

  1. By adjusting only the angles measured with a total station
  2. By applying the full correction to the first angle only
  3. By distributing the correction equally among all angles Correct answer.
  4. By ignoring it if it is less than one minute

Explanation

Angular misclosure is distributed equally among the measured angles so that the adjusted angles sum to the theoretical total. This spread minimises the maximum introduced error. Ignoring the misclosure leaves the traverse internally inconsistent.

Question 46Civil Engineering

A rectangular column of 400 mm by 400 mm is reinforced with 8 bars of 20 mm diameter. What is the reinforcement ratio, expressed as a percentage of the gross area?

  1. 1.57% Correct answer.
  2. 3.14%
  3. 0.79%
  4. 2.36%

Explanation

The area of eight 20 mm bars is 8 x 314 = 2513 mm², and the gross concrete area is 400 x 400 = 160000 mm². The ratio is 2513/160000, which is about 1.57%. This falls within the usual minimum and maximum limits for longitudinal reinforcement in columns.

Question 47Civil Engineering

A steel beam is designed as simply supported and laterally restrained along its compression flange by a floor slab. Which check is most relevant to the compression flange in this condition?

  1. Fatigue of the tension flange
  2. Local buckling of the web in shear
  3. Lateral torsional buckling of the unrestrained length
  4. Yielding and local buckling of the compression flange Correct answer.

Explanation

When the compression flange is continuously restrained by the slab, lateral torsional buckling is prevented and the section can reach its plastic moment capacity. The governing checks then become yielding and local buckling of the compression flange and shear or local buckling of the web. Fatigue is a separate consideration for cyclic loading.

Question 48Civil Engineering

A soil has a natural water content of 20% and a saturated water content of 30% at the same void ratio. Which statement describes the field condition?

  1. The soil is partially saturated with air voids present Correct answer.
  2. The soil is in a quick condition
  3. The soil is fully saturated
  4. The soil is dry and above the water table

Explanation

When the natural water content is below the saturated value for the same void ratio, the voids are not completely filled with water, so the soil is partially saturated. The degree of saturation equals the ratio of natural to saturated water content, here about 0.67. Quick conditions require upward seepage, not moisture content alone.

Question 49Civil Engineering

In a sedimentation tank, the overflow rate is 30 m³/m²·day and the particle settling velocity is 40 m³/m²·day. What does this imply for the removal of these particles?

  1. Particles with settling velocity greater than the overflow rate are fully removed Correct answer.
  2. No particles are removed because the overflow rate is finite
  3. All particles of that settling velocity are removed
  4. Removal depends only on the tank depth

Explanation

In ideal sedimentation, particles whose settling velocity exceeds the overflow rate reach the bottom before the water exits and are fully removed. Particles with lower settling velocity are removed only in proportion to the ratio of velocities. Tank depth affects detention time but not the fundamental overflow rate criterion.

Question 50Civil Engineering

A reinforced concrete cantilever retaining wall is checked for sliding. Which resistance mechanism is normally relied upon in the design?

  1. Active earth pressure behind the wall
  2. Passive resistance of the soil in front of the toe plus base friction Correct answer.
  3. Overturning moment about the toe
  4. Uplift pressure beneath the base

Explanation

Sliding resistance is developed by friction between the base and the soil, together with any passive resistance mobilised in front of the toe. Passive resistance is often ignored or reduced because the soil may be disturbed. Active pressure and overturning moment are destabilising actions, not resistances.