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NEC Civil Engineering practice questions

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Question 1Civil Engineering

In a reinforced concrete beam designed to BS 8110, which parameter primarily determines the lever arm used in the flexural design of a singly reinforced section?

  1. The span-to-effective-depth ratio of the beam
  2. The characteristic strength of the shear reinforcement
  3. The diameter of the tension reinforcement bars
  4. The ratio of the design moment to the concrete section capacity Correct answer.

Explanation

The lever arm in a singly reinforced section depends on the normalized moment ratio, which expresses the applied design moment relative to the concrete section's moment capacity. This ratio fixes the depth of the stress block and therefore the lever arm between the concrete compression and steel tension resultants. Bar diameter and shear reinforcement strength do not enter this calculation directly.

Question 2Civil Engineering

A soil sample has a moisture content of 20%, a bulk density of 1.9 Mg/m3, and a specific gravity of solids of 2.65. What is the approximate dry density?

  1. 1.58 Mg/m3 Correct answer.
  2. 1.90 Mg/m3
  3. 2.28 Mg/m3
  4. 1.72 Mg/m3

Explanation

Dry density equals bulk density divided by (1 + moisture content as a decimal). Here 1.9 / 1.20 gives approximately 1.58 Mg/m3. Specific gravity is not needed for this calculation and is a distractor.

Question 3Civil Engineering

According to Eurocode 1, which combination factor applies when assessing the characteristic value of a variable action acting alone as the leading action?

  1. 0.0
  2. 1.35
  3. 1.5
  4. 1.0 Correct answer.

Explanation

When a variable action is the leading action in a characteristic combination, its combination factor is taken as 1.0. Accompanying variable actions use their respective psi factors below 1.0. The values 1.5 and 1.35 are partial factors for ultimate limit state design, not combination factors.

Question 4Civil Engineering

A simply supported steel beam spans 6 m and carries a uniformly distributed characteristic load of 20 kN/m including self-weight. Using a partial factor of 1.5 for the variable portion treated as fully variable, what is the approximate maximum design bending moment?

  1. 180 kNm
  2. 67.5 kNm
  3. 135 kNm Correct answer.
  4. 90 kNm

Explanation

Design load equals 20 times 1.5, giving 30 kN/m. For a simply supported span the maximum moment is wL squared over 8, so 30 times 36 divided by 8 equals 135 kNm. The other values come from omitting the factor or misapplying the formula.

Question 5Civil Engineering

In a triaxial compression test on a saturated normally consolidated clay, the effective stress path typically shows which behaviour?

  1. The stress path moves away from the critical state line with volume increase
  2. The stress path remains vertical because pore pressure stays constant
  3. The stress path follows the total stress path exactly because drainage is prevented
  4. The stress path moves toward the critical state line with volume decrease Correct answer.

Explanation

A normally consolidated clay contracts during drained shear, and its effective stress path approaches the critical state line from the wet side. Dilation and volume increase are characteristic of heavily overconsolidated clays. The effective stress path differs from the total stress path whenever pore pressures change.

Question 6Civil Engineering

Which structural form is most appropriate for carrying vertical loads over a large clear span in a reinforced concrete building where headroom beneath is critical?

  1. A post-tensioned band beam
  2. A ribbed slab with downstand ribs
  3. A deep transfer beam with corbels
  4. A flat plate slab on columns Correct answer.

Explanation

A flat plate slab provides a continuous soffit with minimal structural depth, preserving headroom while spanning between columns. Deep transfer beams and downstand ribs reduce available headroom. Post-tensioning can improve efficiency but a band beam still projects below the slab.

Question 7Civil Engineering

In limit-equilibrium analysis of a slope using the method of slices, what is the primary purpose of the interslice force assumption?

  1. To make the factor of safety determinate by fixing the distribution of internal forces Correct answer.
  2. To eliminate the need for a failure surface
  3. To account for seepage forces within each slice
  4. To convert the analysis from effective to total stress

Explanation

The method of slices is statically indeterminate because interslice forces are unknown. Different methods assume a distribution of these forces to obtain a determinate solution and hence a factor of safety. The failure surface must still be defined, and seepage is handled separately through pore pressures.

Question 8Civil Engineering

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

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

Explanation

The liquid limit is determined using the Casagrande cup apparatus, which measures the water content at which a grooved soil pat closes over a specified number of blows. The Proctor test gives compaction characteristics, the vane shear test gives undrained strength, and the constant head test gives permeability.

Question 9Civil Engineering

A rectangular channel 3 m wide carries a discharge of 6 m3/s at a normal depth of 1.0 m. What is the Froude number, and what is the flow regime?

  1. Approximately 1.15, supercritical
  2. Approximately 0.65, subcritical Correct answer.
  3. Approximately 0.65, supercritical
  4. Approximately 1.53, supercritical

Explanation

Velocity equals discharge divided by area, so 6 / 3 equals 2 m/s. Hydraulic depth is area divided by top width, giving 3 / 3 equal to 1 m. The Froude number is 2 divided by the square root of 9.81 times 1, about 0.64, which is below 1 and therefore subcritical.

Question 10Civil Engineering

In a gravity dam, which load combination generally governs stability against overturning at the ultimate limit state?

  1. Dry reservoir with full uplift
  2. Normal operating water level with uplift and earthquake Correct answer.
  3. Flood level with uplift and no earthquake
  4. Construction stage with no water

Explanation

Stability of a gravity dam is usually governed by the normal retained water level combined with uplift and seismic loading, as this produces the largest overturning moments. Dry conditions reduce the driving moment, and construction stages typically have lower loads. Flood levels are checked, but seismic combinations often control.

Question 11Civil Engineering

Which property of fresh concrete is most directly assessed by the slump test?

  1. Compressive strength at 28 days
  2. Consistence or workability Correct answer.
  3. Air content
  4. Setting time

Explanation

The slump test measures consistence, a practical indicator of workability of fresh concrete. It does not measure strength, air content, or setting time, which require separate tests. Slump is used to check that a mix is suitable for placing and compaction.

Question 12Civil Engineering

A short reinforced concrete column is subjected to a factored axial load and a small moment. Which design check is essential in addition to the axial capacity check?

  1. Shear friction at the column base
  2. Fire resistance of the column
  3. Biaxial bending interaction using a column design chart Correct answer.
  4. Deflection of the slab above

Explanation

Columns carrying axial load with moment must be checked against the interaction between axial force and bending, often using design charts or interaction diagrams. The moment may be uniaxial or biaxial depending on the frame. Shear friction, slab deflection, and fire resistance are separate checks.

Question 13Civil Engineering

Which instrument is most suitable for measuring the vertical settlement of a structure to millimetre precision over several years?

  1. A hand-held tape measure
  2. Precise levelling with a digital level and invar staff Correct answer.
  3. A total station with a single prism
  4. A piezometer

Explanation

Precise levelling using a digital level and invar staff provides the accuracy and repeatability needed for long-term settlement monitoring. A tape measure is imprecise, a single-prism total station is less accurate for vertical movement, and a piezometer measures pore water pressure.

Question 14Civil Engineering

In a direct shear test on a dense sand, the peak shear stress is reached at a small horizontal displacement. What best explains the subsequent drop to a residual value?

  1. Pore pressure increases to the point of liquefaction
  2. The sample becomes saturated during shearing
  3. Dilation is overcome and particles reorient, reducing interlocking Correct answer.
  4. The normal stress decreases during the test

Explanation

Dense sands dilate during shearing, and the peak strength reflects interlocking and dilation. As displacement continues, particles reorient and dilation is exhausted, so strength falls to a residual value. Liquefaction and normal stress changes are not the cause here.

Question 15Civil Engineering

Which of the following best describes the purpose of a geotextile in a reinforced soil retaining wall?

  1. To act as a waterproof membrane
  2. To carry the vertical load of the facing units
  3. To provide tensile reinforcement and drainage within the fill Correct answer.
  4. To replace the need for granular fill

Explanation

Geotextiles in reinforced soil walls act as tensile reinforcement, resisting pull-out and improving stability, and they can also provide drainage. They do not carry the vertical facing load, act as an impermeable membrane, or eliminate the need for suitable fill.

Question 16Civil Engineering

A cantilever retaining wall retains 4 m of soil with a unit weight of 18 kN/m3 and an active earth pressure coefficient of 0.33. What is the approximate total active thrust per metre length?

  1. 47.5 kN/m Correct answer.
  2. 95.0 kN/m
  3. 190.0 kN/m
  4. 23.8 kN/m

Explanation

Active pressure at the base equals Ka times unit weight times height, giving 0.33 times 18 times 4, about 23.8 kPa. The total thrust is half the base pressure times height, so 0.5 times 23.8 times 4 equals about 47.5 kN/m. Omitting the triangular distribution gives the doubled value.

Question 17Civil Engineering

In structural steel design, what does the classification of a cross-section as Class 1 (plastic) indicate?

  1. It can form a plastic hinge with rotation capacity without local buckling Correct answer.
  2. It can reach yield but not develop a plastic hinge
  3. It is suitable only for compression members
  4. It buckles locally before reaching yield

Explanation

Class 1 sections can develop a full plastic moment and possess sufficient rotation capacity for plastic analysis without local buckling. Class 2 sections reach the plastic moment but have limited rotation capacity, and Class 3 sections reach yield only. Class 4 sections buckle locally before yield.

Question 18Civil Engineering

Which phenomenon causes a reduction in the effective stress of a saturated loose sand deposit under cyclic loading, potentially leading to liquefaction?

  1. Increase in soil unit weight
  2. Increase in total vertical stress
  3. Generation of excess pore water pressure Correct answer.
  4. Reduction in groundwater level

Explanation

Cyclic loading on loose saturated sand tends to generate excess pore water pressure because the soil skeleton contracts while drainage is restricted. This reduces effective stress and can bring it to zero, causing liquefaction. Lowering groundwater or increasing total stress does not cause this effect.

Question 19Civil Engineering

In a water distribution network, which method is used to determine pipe flows when the network contains loops?

  1. Thiessen polygon method
  2. Manning equation alone
  3. Hardy Cross method Correct answer.
  4. Rational method

Explanation

The Hardy Cross method iteratively balances heads around loops in a pipe network until continuity and energy conditions are satisfied. The Manning equation describes flow in a single pipe, the rational method estimates runoff, and Thiessen polygons estimate areal rainfall.

Question 20Civil Engineering

Which type of foundation is most suitable for a tall building on soft clay where shallow spread footings would settle excessively?

  1. Raft foundation bearing directly on the soft clay
  2. Piled foundation transferring load to a deeper firm stratum Correct answer.
  3. Strip footing at shallow depth
  4. Pad footing on the soft clay

Explanation

Piles transfer loads through the soft clay to a deeper competent stratum or develop capacity through skin friction, reducing settlement. Shallow strip, pad, and raft foundations bear on the soft clay and would suffer excessive settlement. A raft may help distribute load but does not solve weak bearing strata as effectively as piles.

Question 21Civil Engineering

What is the primary function of shear studs welded to the top flange of a steel beam in a composite floor?

  1. To transfer longitudinal shear between the steel beam and concrete slab Correct answer.
  2. To provide fire protection to the beam
  3. To stiffen the beam against lateral-torsional buckling
  4. To resist vertical uplift from wind

Explanation

Shear studs provide the longitudinal shear connection that allows the steel beam and concrete slab to act compositely. They are not primarily for uplift, fire protection, or lateral-torsional restraint. Composite action increases flexural stiffness and strength.

Question 22Civil Engineering

A concrete mix has a target mean strength of 40 MPa and a standard deviation of 5 MPa. If the characteristic strength is defined at 5% failure, what approximate target mean strength margin above characteristic is needed?

  1. 0 MPa
  2. 5 MPa
  3. 2.5 MPa
  4. 8 MPa Correct answer.

Explanation

For a 5% failure probability the margin is about 1.64 standard deviations. Multiplying 1.64 by 5 MPa gives approximately 8 MPa above the characteristic strength. Using one standard deviation or half of it underestimates the required margin.

Question 23Civil Engineering

Which of the following is the main reason for providing a camber in a long-span prestressed concrete beam?

  1. To improve the bond between tendon and concrete
  2. To offset the upward deflection caused by prestress and reduce final sag Correct answer.
  3. To reduce the amount of prestressing steel required
  4. To increase the concrete compressive strength

Explanation

Prestressing induces upward deflection, and a small initial downward camber can compensate so the beam reaches a suitable profile under service loads. Camber does not change concrete strength, improve bond, or reduce the required prestressing force. It is a geometric measure to control deflection.

Question 24Civil Engineering

In hydrology, which method estimates peak runoff from a small catchment using a runoff coefficient, rainfall intensity, and catchment area?

  1. Muskingum method
  2. Penman method
  3. Unit hydrograph method
  4. Rational method Correct answer.

Explanation

The rational method uses Q equals CiA, where C is the runoff coefficient, i is rainfall intensity, and A is catchment area, to estimate peak runoff for small catchments. The unit hydrograph and Muskingum methods address runoff routing and hydrograph shape, while the Penman method estimates evapotranspiration.

Question 25Civil Engineering

A simply supported beam of span 8 m carries a point load of 50 kN at midspan. What is the maximum bending moment?

  1. 50 kNm
  2. 200 kNm
  3. 100 kNm Correct answer.
  4. 400 kNm

Explanation

For a simply supported beam with a central point load P over span L, the maximum moment is PL/4. Here 50 times 8 divided by 4 equals 100 kNm. Using PL/2 or PL/8 gives the incorrect distractors.

Question 26Civil Engineering

In reinforced concrete design, which term denotes the constant depth of the rectangular stress block used in the ultimate flexural strength calculation for a singly reinforced section?

  1. The effective depth measured from the compression face to the tension steel centroid
  2. The partial safety factor applied to the concrete compressive strength
  3. The modular ratio used to transform steel area into equivalent concrete
  4. The neutral axis depth factor derived from strain compatibility Correct answer.

Explanation

Ultimate flexural strength is computed from a simplified rectangular stress block whose depth is expressed as a fraction of the neutral axis depth, obtained from the assumed limiting concrete strain and steel yield strain. The block parameters come from strain compatibility at the ultimate limit state.

Question 27Civil Engineering

A simply supported one-way slab spans 4.0 m and carries a characteristic imposed load of 3.0 kN/m2 plus self-weight. Which action effect must be checked at the support region of the slab where torsion is restrained by monolithic beams?

  1. Punching shear around the column heads
  2. Crack width at the soffit governed by bar spacing
  3. Deflection at midspan governed by span-to-depth ratio
  4. Torsional cracking at the slab-beam junction requiring edge reinforcement Correct answer.

Explanation

Where a slab is cast monolithically into edge beams, restrained rotation induces torsional moments at the junction, and reinforcement must be detailed to control the resulting cracking. Midspan deflection and soffit crack width are serviceability checks governed by different criteria.

Question 28Civil Engineering

In a triaxial compression test on a saturated normally consolidated clay, the measured effective stress path rises with increasing axial strain while the deviator stress peaks and then falls. Which statement correctly describes the drained behaviour of this soil?

  1. The soil contracts throughout shearing and mobilises a friction angle close to the critical state value Correct answer.
  2. The soil dilates strongly and shows a peak friction angle well above the critical state value
  3. The soil exhibits brittle failure with a sharp loss of strength after peak
  4. The soil shows no volume change because it is saturated

Explanation

Normally consolidated clays contract during drained shear and mobilise strength at the critical state without a pronounced peak, because their structure has not been developed by prior loading. Dilation and brittleness are characteristic of overconsolidated or dense soils.

Question 29Civil Engineering

A gravity retaining wall is to be founded on a stiff clay. Which check most directly governs the base width required to prevent the resultant thrust from moving outside the middle third of the base?

  1. Sliding resistance along the base
  2. Settlement of the wall footing
  3. Overturning about the toe Correct answer.
  4. Bearing capacity of the foundation soil

Explanation

The middle-third rule is a check on overturning stability: if the resultant of vertical and horizontal forces falls outside the middle third, tension develops at the heel and the wall is considered unstable against rotation. Bearing pressure and sliding are separate checks.

Question 30Civil Engineering

A precast prestressed concrete beam is to be handled and lifted at two points during transport. Which design consideration most directly controls the amount of prestressing force at transfer?

  1. The tensile stress at the top fibre at the lift points under the beam self-weight Correct answer.
  2. The anchorage zone bursting reinforcement requirement
  3. The compressive stress at the bottom fibre at midspan under service load
  4. The loss of prestress due to creep of the concrete

Explanation

At transfer, the prestress force plus self-weight produces tension at the top of the beam near the ends or lift points, and this tensile stress limits the prestress that can be applied. Service-load compression and long-term losses are checked at later stages.

Question 31Civil Engineering

A steel column in a braced frame has a pinned base and is restrained against sway at floor levels. Which parameter is required to determine the effective length for buckling about the major axis?

  1. The ratio of the column stiffness to the stiffness of the beams framing into it at each end Correct answer.
  2. The torsional constant of the section
  3. The ratio of dead load to imposed load on the column
  4. The yield strength of the steel only

Explanation

Effective length depends on the rotational and translational restraint at each end, which is quantified by the stiffness ratio of the column to the connecting beams. In a braced frame the sway is prevented, so only rotational end restraint remains to be assessed.

Question 32Civil Engineering

In a steel beam with a concrete slab on its top flange, lateral-torsional buckling is prevented within the composite stage. Which condition is essential for this benefit to be realised?

  1. The beam must be simply supported rather than continuous
  2. The steel beam must be fully encased in concrete
  3. The slab must be prestressed
  4. The shear connection must be designed to transfer the longitudinal force between the slab and the steel beam Correct answer.

Explanation

Composite action, and hence restraint of the top flange by the slab, depends on an adequate shear connection that transfers longitudinal force at the steel-concrete interface. Without it the two components act independently and the steel beam still requires lateral restraint.

Question 33Civil Engineering

A concrete mix design uses the absolute volume method. Given cement content 350 kg/m3, water content 175 kg/m3, and entrapped air 2 percent, which quantity must be determined next to compute the fine and coarse aggregate masses?

  1. The total absolute volume of aggregates, obtained by subtracting the volumes of cement, water, and air from one cubic metre Correct answer.
  2. The 28-day cube strength
  3. The fineness modulus of the fine aggregate alone
  4. The slump of the fresh mix

Explanation

The absolute volume method sums the volumes occupied by cement, water, and air and subtracts them from unit volume; the remainder is the volume available for aggregates, which is then split between fine and coarse fractions by the chosen proportions.

Question 34Civil Engineering

A sample of sand is tested in a constant-head permeameter. The coefficient of permeability measured at 20 degrees Celsius is 2.5 x 10^-4 m/s. If the same sand is tested with water at 10 degrees Celsius, which change in measured permeability is expected?

  1. It remains unchanged because permeability depends only on void ratio
  2. It increases because viscosity falls at lower temperature
  3. It increases because density of water increases at lower temperature
  4. It decreases because the viscosity of water increases at lower temperature Correct answer.

Explanation

Hydraulic conductivity is proportional to the unit weight of water divided by its viscosity. As temperature falls, viscosity rises substantially while density changes only slightly, so the measured permeability decreases.

Question 35Civil Engineering

A soil profile consists of 6 m of sand above a thick clay layer. The water table is at 3 m depth. Unit weight of sand above the water table is 17 kN/m3 and below it is 20 kN/m3. What is the vertical effective stress at 6 m depth?

  1. Approximately 122 kPa
  2. Approximately 62 kPa
  3. Approximately 92 kPa Correct answer.
  4. Approximately 152 kPa

Explanation

Total stress equals 17 x 3 plus 20 x 3, giving 111 kPa. Pore pressure at 6 m is 3 m of water times 9.81, about 29 kPa, so effective stress is approximately 111 minus 29, that is 92 kPa.

Question 36Civil Engineering

A slope in stiff fissured clay has remained stable for many years at an angle steeper than the critical state friction angle would allow. Which factor best explains this apparent stability?

  1. Apparent cohesion from interlocking and cementing between soil particles Correct answer.
  2. Negative pore pressures due to capillary action in the clay
  3. Under-estimation of the unit weight in the analysis
  4. Immediate settlement of the slope crest

Explanation

Stiff clays derive temporary strength from apparent cohesion, which arises from inter-particle bonding and negative pore pressures within the unsaturated or structured fabric. This strength is progressively lost through softening and fissure development, so long-term stability must be checked with residual or critical state parameters.

Question 37Civil Engineering

In a flow net for steady seepage beneath a sheet pile wall, the quantity of seepage per unit length is computed as k H Nf / Nd. What does the ratio Nf/Nd represent?

  1. The exit gradient at the toe of the wall
  2. The total head loss divided by the coefficient of permeability
  3. The number of flow channels divided by the number of equipotential drops Correct answer.
  4. The factor of safety against piping

Explanation

In a flow net, Nf is the number of flow channels and Nd the number of equipotential drops between upstream and downstream heads. Their ratio, multiplied by permeability and total head, gives the seepage discharge per unit length.

Question 38Civil Engineering

A reinforced concrete beam is designed as under-reinforced. Which condition defines this behaviour at the ultimate limit state?

  1. The concrete crushes before the steel yields
  2. Both steel and concrete reach their limiting strains simultaneously
  3. The steel yields before the concrete reaches its ultimate compressive strain Correct answer.
  4. The section remains uncracked up to failure

Explanation

An under-reinforced section is one in which the tension steel yields first, giving a ductile flexural failure with warning. Balanced sections reach both limiting strains together, and over-reinforced sections fail by concrete crushing before steel yield, which is brittle.

Question 39Civil Engineering

A short braced reinforced concrete column carries an axial load with a small eccentricity. Which design action is required in addition to checking the axial capacity?

  1. Designing the section for the applied moment using the column interaction chart Correct answer.
  2. Checking the slenderness ratio against the limiting value for a non-sway column
  3. Providing links to resist the shear from the applied moment
  4. Ensuring the reinforcement percentage does not exceed the maximum permitted

Explanation

A column with an eccentric load must be designed for combined axial force and bending, which is done using an interaction diagram relating axial load capacity to moment capacity for the chosen reinforcement. Slenderness checks determine whether second-order effects must be added, and link and percentage checks are detailing requirements.

Question 40Civil Engineering

A concrete dam is analysed for stability. Which combination of loads is normally treated as the most severe for overturning about the toe?

  1. Normal water level with uplift, self-weight, and silt load Correct answer.
  2. Normal water level with no uplift
  3. Empty reservoir with self-weight only
  4. Maximum flood level with uplift and no silt

Explanation

Overturning is driven by horizontal water and silt thrust and reduced by the stabilising moment of self-weight. Including uplift reduces the effective weight, so the normal operating condition with uplift and silt present is generally the most severe combination for the toe.

Question 41Civil Engineering

A rectangular channel of width 4 m carries a discharge of 12 m3/s at a depth of 1.2 m. Taking g as 9.81 m/s2, what is the Froude number and the flow regime?

  1. Approximately 0.73, supercritical
  2. Approximately 0.73, subcritical Correct answer.
  3. Approximately 1.37, subcritical
  4. Approximately 1.37, supercritical

Explanation

Velocity equals 12 divided by (4 x 1.2), giving 2.5 m/s. Hydraulic depth equals area divided by top width, which is 4.8/4 = 1.2 m. Froude number is 2.5 divided by the square root of (9.81 x 1.2), about 0.73, which is below unity and therefore subcritical.

Question 42Civil Engineering

A trapezoidal channel is to be designed to carry a given discharge at minimum excavation. Which geometric condition corresponds to the most efficient hydraulic section?

  1. The side slopes are vertical
  2. The hydraulic radius equals half the flow depth Correct answer.
  3. The wetted perimeter is maximised for the given area
  4. The top width equals twice the hydraulic depth

Explanation

The most efficient section minimises wetted perimeter for a given area, which maximises hydraulic radius and thus conveyance. For a trapezoid this condition is satisfied when the hydraulic radius equals half the depth.

Question 43Civil Engineering

In a pipe network solved by the Hardy Cross method, what is the iterative correction applied to each loop?

  1. A correction to pipe diameter based on the Reynolds number
  2. A flow correction proportional to the sum of head losses around the loop divided by the sum of the derivatives of head loss with respect to flow Correct answer.
  3. A pressure correction equal to the average nodal demand
  4. A correction to the friction factor based on the Colebrook equation

Explanation

Hardy Cross corrects assumed loop flows by distributing the imbalance in head losses around each loop, scaled by the sum of the terms representing sensitivity of head loss to flow. The procedure is repeated until the loop head-loss imbalance becomes negligible.

Question 44Civil Engineering

A catchment of 50 hectares has a runoff coefficient of 0.4. Using the rational method with a rainfall intensity of 60 mm/h, what is the estimated peak discharge?

  1. Approximately 0.33 m3/s
  2. Approximately 12 m3/s
  3. Approximately 1.2 m3/s
  4. Approximately 3.3 m3/s Correct answer.

Explanation

The rational method gives Q equal to C i A divided by 360 when A is in hectares and i in mm/h. Substituting 0.4 x 60 x 50 / 360 gives approximately 3.3 m3/s.

Question 45Civil Engineering

Which unit hydrograph assumption states that the time base of the direct runoff hydrograph is constant for storms of a given duration?

  1. Proportionality of peak discharge to rainfall excess
  2. Uniform spatial distribution of rainfall
  3. Linearity of response
  4. Time invariance of the unit hydrograph Correct answer.

Explanation

The unit hydrograph theory assumes that a given effective rainfall produces a runoff hydrograph of fixed shape and time base regardless of when the storm occurs, which is the time-invariance assumption. Linearity and proportionality describe how the response scales with rainfall depth.

Question 46Civil Engineering

In a direct shear test on a normally consolidated clay, the sample is sheared slowly enough for full drainage. Which strength parameter is measured?

  1. The total stress cohesion intercept only
  2. The undrained shear strength
  3. The residual friction angle of the clay
  4. The effective cohesion and effective angle of internal friction Correct answer.

Explanation

Slow shearing allows pore pressures to dissipate, so the measured normal and shear stresses are effective stresses and the test yields effective strength parameters. Undrained strength requires a fast test with pore pressure measurement, and residual strength requires large displacements.

Question 47Civil Engineering

A 200 mm diameter concrete cube is tested in compression and fails at 800 kN. What is the compressive strength?

  1. 20 MPa Correct answer.
  2. 40 MPa
  3. 4 MPa
  4. 16 MPa

Explanation

The loaded area is 0.2 m x 0.2 m, equal to 0.04 m2. Dividing 800 kN by 0.04 m2 gives 20,000 kPa, which is 20 MPa.

Question 48Civil Engineering

In a standard Proctor compaction test, the dry density is plotted against moisture content and a peak curve is obtained. What does the peak represent?

  1. The moisture content at which the permeability is greatest
  2. The maximum dry density achievable for the given compactive effort and its corresponding optimum moisture content Correct answer.
  3. The moisture content at which the soil has zero air voids
  4. The moisture content at which the soil becomes fully saturated

Explanation

For a fixed compactive effort, dry density rises with moisture content up to a maximum and then falls, because water lubricates particles initially but later occupies volume that would otherwise be filled by solids. The peak defines the maximum dry density and optimum moisture content.

Question 49Civil Engineering

A soil sample has a liquid limit of 45 percent, a plastic limit of 25 percent, and a natural moisture content of 30 percent. What is the liquidity index?

  1. 1.25
  2. 0.25 Correct answer.
  3. 0.75
  4. 0.50

Explanation

The plasticity index is 45 minus 25, equal to 20 percent. The liquidity index is the natural moisture content minus the plastic limit, divided by the plasticity index, giving (30 - 25)/20, which is 0.25.

Question 50Civil Engineering

A building is to be founded on a deep deposit of soft compressible clay. Which foundation solution most directly reduces the settlement of the structure by transferring load to a deeper, stiffer stratum?

  1. A raft foundation bearing on the soft clay
  2. A piled raft combining a spread footing with piles to the deeper stratum Correct answer.
  3. A strip footing widened to reduce contact pressure
  4. A ground improvement scheme using surface compaction

Explanation

Piles extending to a stiffer stratum carry load by shaft and base resistance and reduce the load transmitted to the compressible clay, while the raft shares the load and controls differential movement. Widening a footing on soft clay increases the depth of influence and does not reduce settlement reliably.