Civil Engineering Job Interview Questions and Answers - Part 01

Civil Engineering Technical Job Interview Questions and Answers for Freshers and Experienced:

Question No. 01
What is civil engineering?
Answer: Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings.
Civil engineering is arguably the oldest engineering discipline. It deals with the built environment and can be dated to the first time someone placed a roof over his/her head or laid a tree trunk across a river to make it easier to get across.

Question No. 02
What does civil engineering do?
Answer: They do many interesting things. Their job has to do a lot with design and construction. They can tell you what works and what will not for all sorts of situations.
There is a lot of mathematics involved along with many other disciplines. They have to have a good solid understanding of how the environment works and how nature interacts with manmade. They are probably best known for designing bridges, interstates, skyscrapers, canals, and so forth.

Question No. 03
What is the difference between shear and tensile strength?
Answer: Tensile Strength for a Bolt is determined by applying a Force along it long axis. Shear Strength for a Bolt is determined by applying a Force across its diameter, as it would be loaded in a lug joint.

Question No. 04
What are the materials used in building a gravity dam?
Answer: There are many gravity dams constructed of compacted earth. High dams are generally concrete. All dams require a spillway to be safe. The spillway must be armoured.

Question No. 05
What does civil status mean?
Answer: Civil means like, when you do not get on with someone, but only talk when you have to. Alternatively, when you do talk you do not argue. Alternatively, if you are with someone who is of your both friends and family, you do not ruin it for them.

Question No. 06
What are the functions of a column in a building?
Answer: A column is used to support the weight of the roof and/or the upper floors. Now days, many columns are used for decorative purposes. A column along with load bearing beams can support a lot of weight.

Question No. 07
What is the function of packing materials in the joint of concrete pipes in pipe jacking?
Answer: Packing materials are about 10 mm to 20 mm thick and are normally made of plywood, fibreboard or other materials. In case packing materials are absent in pipe joints for pipe jacking, then any deflection in the joints reduces the contact area of the concrete and it leads to spalling of joints due to high stresses induced. With the insertion of packing material inside the pipe joints, the allowable deflection without damaging the joint during the pipe jacking process can be increased.

Question No. 08
For drained reclamation, what is the significance of smear zone induced by installation of band drains?
Answer: During installation of band drains, smear zones are created in which zones of soil surrounding the band drains are disturbed. The compressibility of surrounding soils is increased and it results in the reduction of their permeability. In fact, the surrounding soils are remoulded during the installation process and the effectiveness of band drains is reduced. In essence, for the reduced permeability of soils around band drains, it takes longer time to complete the consolidation process.

Question No. 09
What are the causes of building collapse?
Answer: The Passage of time is one reason. Buildings also collapse due to weak foundations. Earthquakes, hurricanes and other natural disasters can also damage the structure of the buildings and cause it to collapse. Bombings or demolition of buildings is also other reasons.

Question No. 10
In selecting screw pumps in polder scheme projects, what are the factors that affect the design capacity of screw pumps?
Answer: The commonly used angles of inclination for screw pumps are 30°, 35° and 38°. For screw pumps of relatively high lifting head, like over 6.5 m, angle of inclination of 38° is normally used. However, for relatively lower head and high discharge requirement, angle of inclination of 30° shall be selected. In general, for a given capacity and lifting head, the screw pump diameter is smaller and its length is longer for a screw pump of 30° inclination when compared with a screw pump of 38° inclination.

To increase the discharge capacity of screw pumps, a larger number of flights should be selected. In fact, screw pumps with 2 flights are more economical that that with 3 flights in terms of efficiency and manufacturing cost. Moreover, the discharge capacity is also determined by the screw pump diameter and sizes of 300 mm to 5000 mm are available in current market.

Question No. 11
What is the load transfer mechanism for paving blocks in pedestrian footway?
Answer: In Hong Kong, footway is normally designed with paving slabs/interlocking blocks instead of concrete because the extensive use of concrete in pavement is boring. Moreover, poor appearance will result in concrete pavement due to frequently trench openings for utility work. In addition, owing to the prolonged setting and curing time of concrete, the use of concrete pavement inevitably generates disturbance to the general public.
The pedestrian loads are taken up through the following ways:
  1. Load carrying capacity of paving slabs/interlocking blocks are derived from their individual strength;
  2. Pedestrian loads are also supported by interlocking forces provided by friction transfer through the sand in vertical joints (K. K. Tang & Robert P. Cooper (1986).

Question No. 12
What is the meaning of soil reinforcement?
Answer: Soil reinforcement is the act of improving soil strength to enable it support or carry more load.
Two common examples are:
  1. Mixing a soil amendment such as lime into weak clayey soil and re-compacting to improve soil-bearing capacity (often done under the road base in highway construction)
  2.  Installing plastic or composite webbing layers (called geo-grid material) alternating with compacted soil to produce a stronger sloped soil structure (often done on steep roadway embankments to improve strength and stability)

Question No. 13
If the construction of concrete carriageway is carried out in summer, can expansion joints be omitted?
Answer: If the construction of concrete carriageway is carried out in summer, expansion joints may not be necessary as suggested by Arthur Wignall, Peter S. Kendrick and Roy Ancil. Expansion of concrete carriageway is mainly due to seasonal changes with an increase in temperature from that during construction to the ambient temperature (i.e. the temperature in summer). However, if the construction of concrete carriageway takes place in summer, the concrete carriageway will undergo contraction in the following winter, thus the space available in contraction joints can accommodate the future expansion in the next summer.

Question No. 14
Why are steel tubular marine piles often driven open-ended?
Answer: In marine structures where piles are constantly subject to significant lateral and uplift forces induced by berthing operation and wave action, it is necessary to drive the piles to much greater depth. To avoid premature refusal so that insufficient soil cover may develop which is incapable of providing the required lateral and uplift resistance, tubular piles are normally driven open-ended so that they are driving to greater depths than piles with closed ends.

Question No. 15
What is the difference between engineering stress and true stress?
Answer: In biology, Stress is something that disrupts homeostasis of an organism. In engineering, Stress is an external force that pushes, pulls, twists, or otherwise puts force on something.
Engineering stress assumes that the area a force is acting upon remains constant, true stress takes into account the reduction in area caused by the force.

Question No. 16
Why are high and narrow beams not desirable in concrete piers?
Answer: Based on past experience in other countries (Carl A. Thoresen (1988)), high and narrow beams after several years of construction showed signs of serious deterioration at the bottom of the beams. However, the deterioration of pier slabs was not significant when compared with that of the deep beams. The main reason to account for this is due to the close proximity of the deep beams to the sea level. To avoid these problems, either beamless slab or wide with shallow beams are normally designed.

Question No. 17
Why does the pressure increase under soil?
Answer: Soil pressure increases with depth due to the overburden or self-weight of the soil and due to loads imposed upon the soil.
For example, the pressure variation below the depth of soil is linear and the relation is given by pressure = unit wt × depth.
As depth increases, there will be a linear increase in the soil pressure.

Question No. 18
Geotechnical Instrumentation is frequently employed for monitoring the condition of reclamation. Sometimes two piezometers are installed inside the same borehole. What is the reason behind this?
Answer: For standpipes, they normally contain one plastic tube between its intention is to measure water level only. However, for piezometers, they are used for measuring pore water pressure in a certain depth below ground. For instance, if there are two clayey layers below ground at different depths, a multiple piezometer including two separate piezometers may be sunk at the same borehole to determine the pore water pressure at these layers respectively. This arrangement has the advantage that it saves the cost of installation of separate boreholes for several piezometers. However, the installation of multiple piezometers within the same borehole is affected by occurrence of leakage along the pipes as suggested by Marius Tremblay (1989).

Question No. 19
What do you mean by honeycomb in concrete?
Answer: Some people call it an air pocket in the concrete or a void.

Question No. 20
In the construction of pump troughs for accommodation of screw pumps, what is the construction method to ensure close contact between the screw pumps and the pump trough?
Answer: In the construction of screw pump troughs, trapezoidal-shaped troughs are usually formed by using normal formwork. In order to enhance close contact between screw pumps and troughs, upon lifting the screw pumps into the troughs screeding works is carried out. Screw pumps are set to rotate and screeds are placed between the gap of screw pumps’ blade and trapezoidal-shaped troughs during the rotating action of screw pumps. After the screed sets, it serves to prevent leakage of water during the pumping operation of screw pumps.

Question No. 21
How did street originate in the plumbing term street ell?
Answer: A "street ell" may have gotten its name because it describes a 90 fitting particularly useful in tight, street ditches. When installing water pipes under a street, or from a water service, again under the street, into a home or business, this street ell allows one to change pipe direction with one less fitting, and in less space, than with a standard ell.

Question No. 22
In General Specification for Civil Engineering Works (1992 Edition), it specifies the temperature requirements for bituminous material during and after mixing. What is the reason behind this?
Answer: Temperature is one of the factors that govern the compaction of bituminous material and the air void content is found to decrease with an increase in compaction temperature. This phenomenon is explained by the viscosity-temperature relations: the higher is the viscosity of binders, the greater is the resistance to compaction. Therefore, in normal contract for bituminous laying, the temperature requirements for bituminous material during and after mixing are specified.

Question No. 23
What is diversion tunnel in a dam?
Answer: When a dam is to be built, a diversion tunnel is usually bored through solid rock next to the dam site to bypass the dam construction site. The dam is built while the river flows through the diversion tunnel.

Question No. 24
What is the function of a separation membrane between concrete pavement slab and sub-base?
Answer: The separation membrane between concrete pavement slab and sub-base has the following functions:
  1. It aids in reducing the frictional forces between concrete slab and sub-base and helps to movement of concrete slab with respect to sub-base owing to changes in temperature and moisture.
  2. It prevents the loss of cement and water in immature concrete which significantly affects the strength and durability of hardened concrete.
  3. It avoids the mixing up of sub-base materials and freshly placed concrete.
Polythene sheeting, which is a waterproof material, is commonly used as separation membrane.

Question No. 25
Why was the Empire State Building made of steel?
Answer:
  • Strength - Steel is very strong
  • Flexibility - Ability to flex in the wind
  • Cost - Inexpensive and fast to build; Prefab construction
Concrete, a possible alternative, has less compressive strength than steel. The bottom support structure of the empire state building would consist of a large percentage of solid concrete simply to support the weight of the building.

Question No. 26
Why is sulphate-resisting cement not used in marine concrete?
Answer: The main components of Portland cement are tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite. In sulphate-resisting cement, it contains a low amount of tricalcium aluminate in order to avoid sulphate attack. Otherwise, tricalcium aluminate would react with sulphates to form calcium sulphoaluminate and gypsum that cause expansion and crack the concrete structure.

However, for marine concrete sulphate-resisting cement should not be used because tricalcium aluminate has high affinity for chloride ions. This is based on the possible reaction of chloride ions and tricalcium aluminate to form calcium chloroaluminate hydrate as suggested by P. Kumar Mehta (1991) and the reduction of which may increase the rate of chloride attack to the concrete marine structure and result in faster corrosion of steel reinforcement in marine structures.

Question No. 27
What black man invented the clothes dryer?
Answer: George T. Sampson

Question No. 28
Would you cause a 55 gallon drum of water to weigh more by climbing in?
Answer: A person will sink in water if he is not holding enough air in his lungs to keep him floating. Therefore, the person weighs more than the amount of water that he will displace.

Question No. 29
Is it worthwhile to carry out tests on particle density of soil particles for geotechnical design?
Answer: Particle density of soils is defined by the ratio of soil particle mass and soil particle volume. Depending on soil types, the range of variation of soil particle density varies not significantly, i.e. by 4%. Therefore, it may not be worthwhile to order laboratory tests and incur additional expenditure just to determine the particles density by recognizing that the variation of particles density is not significant.

Question No. 30
What is the withdrawal force of steel nails?
Answer: In engineering, the code allowable withdrawal force is zero, because the wood expands and contracts over time and the nail pullout force can reduce to zero.

Question No. 31
Are there any differences in the methods of compaction between clayey soil material and sandy material?
Answer: As suggested by Lars Forssblad (1981), the three main actions of compaction are static pressure, impact force and vibration. Different compactors contain one or more modes of these actions. For example, vibratory tampers perform mainly by the principle of impact while vibratory rollers work with principle of static pressure and vibration.

For sandy soils, vibration is adequate for normal compaction because the action of vibration sets the soil particles in motion and friction forces between soil particles are virtually demolished. During this vibration motion, the soil particles rearrange themselves to develop a dense state.

For normal soils, it is necessary to combine the action of vibration together with static pressure to breakdown the cohesion forces between soil particles in order to allow for better compaction. The static pressure of vibratory machines is adopted to exert a shearing force to eliminate the cohesion in clayey soils.

Question No. 32
Are kerbs necessary in road pavements?
Answer: In general, kerbs are essential in road pavements due to the following reasons (based on Arthur Wignall, Peter S. Kendrick and Roy Ancil):
  1. They provide strength to the sides of road pavements and avoid lateral displacement of carriageway due to traffic loads.
  2. In terms of road safety, they serve as a separation line between footway and carriageway and aid car drivers in driving safely.
  3. They act as a vertical barrier to guide the surface runoff collected in road pavements to the gullies.

Question No. 33
Can a wave happen in the middle of the ocean like in the movie Poseidon 2006?
Answer: Yes. Rogue waves have been known to capsize ships.

Question No. 34
In connecting fenders to pier structures, should single lock nuts or double lock nuts be used?
Answer: In many pier structures the connection offenders to piers is achieved by using single lock nuts. However, they do not perform well because some timber fenders loosen more easily when subject to vibrating loads due to berthing, wave and tidal actions. To solve this problem, double lock nuts should be adopted as they prove to function satisfactory in other structural elements which are subject to frequent vibration loads.
Note: Double lock nuts mean two nuts are adopted in a single bolt connection between fenders and marine structures.

Question No. 35
What are the different applications of draglines, backhoes and shovels?
Answer: An excavator is defined as a power-operated digging machine and it includes different types like shovels, draglines, clamshells, backhoes, etc.
  1. A dragline possesses a long jib for digging and dumping and it is used for digging from grade line to great depths below ground. Its characteristic is that it does not possess positive digging action and lateral control of normal excavators. A dragline is normally deployed for bulk excavation.
  2. A backhoe is designed primarily for excavation below ground and it is especially employed for trench excavation works. It digs by forcing the bucket into soils and pulling it towards the machine and it possesses the positive digging action and accurate lateral control.
  3. A shovel is a machine that acts like a man’s digging action with a hand shovel and hence it is called a shovel. It digs by putting the bucket at the toe of excavation and pulling it up. Though a shovel has limited ability to dig below ground level, it is very efficient in digging above ground like digging an embankment.

Question No. 36
What are the advantages and disadvantages of lead products in construction?
Answer:
Disadvantages: Lead is very toxic; Its use can result in pollution of the ground and more importantly of water supplies. This leads to the contamination of drinking water and can cause hazards to human health as well as disrupting entire ecosystems.

Advantages: Because of its toxicity, lead is being bought less and less around the world, which of course results in the lowering of its cost. In addition, lead melts at a relatively low temperature, making it great for solder. However, recently the Chinese have shown an interest in buying mass quantities to manufacture batteries made from a base of lead so the price of this metal may soon rise.

Question No. 37
In case a road passes through a reclaimed land and an existing land, what is the main concern regarding the design of pavements?
Answer: For an existing land, it is anticipated that there will be no major settlement within the design life of pavement structures. However, for a recently reclaimed land, even with surcharging and installation of vertical drains, some settlement will still occur after the construction. If a road pavement has to be constructed connecting these two areas, special design has to be made in this transition region. In order to avoid the occurrence of differential settlement which may damage the pavement structure, a transition slab may be designed to accommodate such movement (J. S. M. Kwong (1996)).

Question No. 38
What is the application of inverted siphons? What are the disadvantages of using inverted siphons?
Answer: Inverted siphons are designed at locations in which a sewer system is blocked by underground utilities or storm-water drains. They are sometimes called depressed sewers because it is claimed that there is no actual siphon action. They connect the upstream and downstream sewers with U-shaped vertical alignment such that they are always running full.
The drawbacks of inverted siphons are:
  1. They induce additional head loss to the sewer system which is undesirable in hydraulic performance;
  2. U-shaped siphons create sediment accumulation problem and previous experience showed that inverted siphons were easily blocked due to siltation;
  3. Maintenance of invert siphons is difficult due to its inaccessibility.

Question No. 39
What are the uses of Groynes?
Answer: They prevent, or slow down erosion, and stop long shore drift. This, however, can have bad knock-on effects somewhere near.

Question No. 40
In selection of dams in drainage channels, what are the advantages of using rubber dams instead of steel-gate dams?
Answer: The advantages of rubber dams are as follows:
  1. Since rubber is flexible in nature it is capable of performing deflation even in the presence of dirt and sedimentation on the downstream side. However, for rigid steel-gate dams, it may not be possible to open when there is excessive sediment.
  2. Since the foundation of rubber dams is comparatively lighter than that of steel-gate dams, it saves both construction cost and time.
  3. Rubber dams can be designed with longer spans without piers while steel-gate dams require intermediate piers for long spans.

Question No. 41
What Tor stands for in Tor steel?
Answer: The owner’s last name

Question No. 42
What is the purpose of carrying out water absorption test for pre-cast concrete pipes?
Answer: Cement will mix with more water than is required to eventually combine during hydration of cement paste. As such, some voids will be left behind after the hydration process which affects the strength and durability of concrete. With the presence of air voids in concrete, it is vulnerable to penetration and attack by aggressive chemicals. Good quality concrete is characterized by having minimal voids left by excess water and therefore, water absorption test for pre-cast concrete pipes is adopted for checking the quality of concrete in terms of density and imperviousness.

Question No. 43
What are the advantages of building a dam on the river Nile?
Answer: It is the same as building a dam on any river. Dams are built to control flooding downstream during the wet season, generate power year round, and provide irrigation in the dry season.

Question No. 44
What are the functions of slip joints in block-work seawalls?
Answer: Slip joints are joints which are formed through a complete vertical plane from the cope level to the toe level of seawalls. These joints are designed in block-work seawalls to cater for possible differential settlements between adjacent panels of seawalls. The aggregates inside the half-round channels in slip joints allow for the vertical movements induced by differential settlement and at the same time providing aggregate interlocking forces among adjacent panels of seawalls to link the panels in one unit against the lateral earth pressure exerted on seawall.

Besides, slip joints provide a path for the relief of water pressure developed and allow the lateral movement (e.g. contraction) due to seasonal variations.

Question No. 45
Will going from a 3-tap to 6-tap increase water pressure?
Answer: No, the pressure will be the same; you will get more volume only if your pumps can handle the GPM, to increase pressure you may need a booster pump or a single pump that is rated for your needs.

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