Question No. 46
Should joints of concrete kerbs be in line with the joints in concrete carriageway?
Answer: In normal practice, joints are provided in road kerbs to cater for concrete expansion and contraction. However, the location of joints in kerbs is not arbitrary and they should match with joints in concrete carriageway. Otherwise, it is very likely that cracks may form in concrete kerbs at location of pavement joints (Ministry of Transport (1955)).
Question No. 47
In case mud waves occur during reclamation, what are the possible solutions to rectify the situation?
- Option 1 – Complete Removal of All Disturbed Mud: To remove all disturbed mud once mud waves occur is the fastest way to treat the problem. After that, filling material is used for replacing the disturbed mud. However, this option is a rather expensive option because it involves dredging of all disturbed mud and replacement of large amount of fill.
- Option 2 – Accelerated consolidation of Disturbed Mud: This option involves placement of surcharging loads on top of mud waves, together with installation of band drains to accelerate the consolidation of disturbed mud. This method suffers from the drawback that sufficient long time is required for the consolidation process of mud.
- Option 3 – Partial Removal of Disturbed Mud: This option is a combination of the first two options in which the top weak layer of mud is removed while the lower mud is treated with surcharging with band drain installation.
Note: Mud waves refer to excessive displacement of mud due to successive slip failure during reclamation.
Question No. 48
For compaction of free-draining sands or gravels, what is the optimum moisture content to achieve maximum density?
Answer: The compaction curve of sandy materials is totally different from that of clayey materials. For sands or gravels, there are two situations of maximum density, namely the completely dry condition and the complete water saturation. For moisture content of sands and gravels between these two states, the dry density obtained is lower than that obtained in the above-mentioned states. The presence of capillary forces account for the difficulty of compaction sand at water contents between virtually dry and saturated state. They are formed in partially filled water void between soil particles and perform as elastic ties cementing soil particles together. Reference is made to Lars Forssblad (1981).
The compaction curve for clay is suitable for the majority of soil types except sands and gravels because a small amount of clay in soils is sufficient to make the soils impermeable.
Question No. 49
What is the world’s largest concrete dam?
Answer: The Grand Coulee Dam is said to be the largest concrete dam. Currently the world's largest concrete dam is the Itaipu Dam, an accomplishment of two neighboring countries, Brazil and Paraguay in South America.
Though it is not finished yet, the Three Gorges (or Sandapong) Dam on the Yangtze River in China will take over as the largest upon its completion, which is slated for 2009.
Question No. 50
What are the main reasons for conducting pull-out tests for soil nails?
Answer: There are mainly four reasons for this test:
- To check and verify the bond strength between soil and grout adopted during the design of soil nails. This is the main objective of conducting soil nail pull-out test.
- To determine the bond strength between soil and grout for future design purpose. However, if this target is to be achieved, the test nails should be loaded to determine the ultimate soil/grout bond with a upper limit of 80% of ultimate tensile strength of steel bars.
- To check if there is any slippage or creep occurrence.
- To check the elastic and plastic deformations of test nails. This is observed during the repeated loading and unloading cycles of soil nails.
Note: Pull-out tests are carried out by applying specified forces in an attempt to pull out the constructed soil nails.
Question No. 51
In Hiley’s formula for driven piles i.e. R = E/(s + 0.5c), why is a coefficient of 0.5 applied for the term elastic deformation of piles and soil?
Answer: Hiley’s formula is based on the principle of energy conservation in which the energy brought about by hammers during the action of hitting are transferred to piles in ground. When the hammer force and displacement is plotted, the energy absorbed by piles is the area under the curve. Since the curve of elastic component is linear with a positive slope, the area i.e. energy should be the area of triangle (0.5 × R × c) where ‘R’ is reaction force and ‘c’ is elastic compression due to helmet, piles and soil system. For settlement, it is of horizontal line in force-displacement diagram and hence the energy transferred to pile-soil system is (R × s).
Question No. 52
In designing sewer pipes, why are vitrified clay pipes commonly used for pipe size less than 600 mm while precast concrete pipes with PVC lining is used for pipe size exceeding 600 mm?
Answer: The market price of vitrified clay pipes is generally less than that of precast concrete pipes with PVC lining. Therefore, for small size of pipes (pipe diameter less than 600 mm) it is more economical to use vitrified clay pipes. However, vitrified clay pipes do suffer from the problem of brittleness and its effect is even severe for larger size of pipes. Moreover, it is rather time consuming to deliver clay pipes products because the majority of them are manufactured in Europe. Hence, for larger size of sewer pipes (diameter more than 600 mm) it is customary to use precast concrete pipes with PVC lining.
Question No. 53
What is rigging?
Answer: In sailing, the ropes used to move the sails around so the boat will move in the right direction when the wind blows.
Question No. 54
What are the considerations in selecting marine plants and land plants for installation of band drains?
Answer: For installation of band drains by marine plants, it must have sufficient water depth to accommodate the marine plants in the first place. However, due to the effect of tides and waves, the establishment of the position for installation of band drains and the subsequent installation works may be affected. In addition, the establishment cost of marine plants is higher than that of land plants.
For installation of band drains by land plants, difficulty may be encountered during the installation of band drains through the reclaimed layer e.g. C&D material. Land plants may take longer construction time due to the above-mentioned difficulty. Sometimes when the supply of public fill is increased suddenly, it may be preferable to place these fill immediately into position and in this situation the installation of band drains (originally installed by marine plants) is delayed so that the construction of band drains is changed to using land plants.
Question No. 55
What is the distance between railway tracks?
In U.S, its 4 feet and 8.5 inches
In India, its 5 feet 6 inches
Question No. 56
Why are most marine piles circular in cross section?
Answer: For marine piles, there are several options available for selection, namely H-piles, circular pipes and box piles. However, only circular piles and box piles are suitable for marine application because of the following two reasons suggested by G. M. Cornfield (1968):
- Circular piles and box piles possess high column buckling strength. For marine structures like jetties, piles are well above seabed level and therefore the column buckling effect is significant when compared with other structures. Therefore, it is essential to use pile sections which have relatively high buckling strength in piers.
- Circular piles and box piles display high energy absorbing capability. For marine structures like dolphins and fenders, which require substantial amount of berthing energy to be absorbed, these piles sections are inevitably good choices. In marine structures, it appears that circular sections prevail over the box sections. The main reason is that the range of section available for selection of circular piles is more than that of box piles.
Question No. 57
What is the purpose of the gap in the road on this bridge?
Answer: Purpose of the gap in the road is to allow the road to expand and contract with temperature changes without causing damage or deformation to the road.
Question No. 58
What is the mechanism of cavitation in pipes and drains?
Answer: Cavitation refers to the formation of air bubbles in fluid in low-pressure condition which is lower than the saturation pressure. It is a potentially damaging condition in which the fluid in pipes or sewers is at high velocities. By Bernoulli’s Equation, at high flow velocities, the pressure head of fluid is reduced accordingly. As the fluid pressure is less than saturation pressure, dissolved gases are released from the fluid and these air bubbles will suddenly collapse when the flow enters into a region of higher pressure. This produces a high dynamic pressure which causes damage to the pipelines due to its high frequency.
Question No. 59
What is the importance of geo-textiles and sand in reclamation works?
Answer: For geo-textiles used in reclamation, they serve mainly the following two purposes:
- They separate reclamation fill from marine mud;
- They may act as reinforcement to enhance the stability of reclamation. However, the reinforcement function is still under heated debate because its performance as reinforcement depends on several factors like the directional strength of woven geo-textiles and damage effect by installation of vertical band drains.
- It spreads the load of future public dump on top of it;
- It acts as drainage path for dissipation of excess pore water pressure for band drain installation.
Question No. 60
Why is the statue of liberty made of copper?
Answer: Copper is a very durable material when exposed to weather and is soft enough that it can be easily molded to curved shapes such as those in the Statue of Liberty. It is also traditionally used in buildings for complex roofs, so there would have been trades people available trained to use it.
Other metals that can be molded are lead but it does not have the attractive verdigris color, and gold much is more expensive
Question No. 61
Why is shallow bedrock condition unfavourable for open berth piers?
Answer: The most severe load on piers generally is the horizontal load due to berthing of large vessels. Since the widths of open berth piers are relatively small so that they provides a short lever arm to counteract the moment induced by berthing loads. Moreover, the dead load of open berth piers are normally quite light and therefore the resisting moment provided by the dead load of pier structures may not be sufficient to counteract the moment generated by berthing loads.
To aid in providing adequate resistance to the overturning moment by the berthing load, the soil resistance above bedrock contributes to stabilizing moment. For commonly adopted marine piling type, i.e. driven steel tubular piles with reinforced concrete infill, driven piles can at most be founded on top of rock-head surface. In case the rock-head level is shallow, then the little soil cover may result in insufficient lateral resistance to the berthing load.
Question No. 62
Where is the world’s longest elevator and how long is it?
Answer: Gold mines in South Africa go a few kilometers below the surface. The world’s deepest mine now is the Mponeng, is a gold mine in South Africa's North West Province. It extends over 4 kilometres below the surface, and is considered to be one of the most substantial gold mines in the world. The lift itself descends 3037 m to a point 1200 m below sea level.
Question No. 63
Should dolphins be designed in a rigid manner, i.e. resting on several raking piles?
Answer: In designing dolphins, they are normally supported on a system of three to four raking piles. This in essence is a rigid structure and exhibits little flexibility e.g. movement against impact and berthing loads by vessels. In fact, this kind of design may not be desirable in terms of maintenance because the dolphins are readily susceptible to damage by high berthing vessels. To rectify this situation, some energy absorption devices like rubber/plastic fenders have to be installed to reduce the impact load deriving from its own deflection. On the other hand, by designing dolphins as flexible structures capable for allowing slight deflection, it helps to reduce the large forces generated during berthing of vessels. In this connection, one way of designing dolphins as flexible structures is by provision of a single pile only.
Note: For a rigid structure, it takes up external loads without undergoing excessive deformations.
Question No. 64
Who built the sears tower?
Answer: While he did not build the structure (he died in l959), there is some evidence the idea was suggested under a different name (Illinois Building) by Frank Lloyd Wright, one of the few true skyscrapers in which he had a role. The original design for the Illinois Building would have topped off at 5,280 Feet! The Swears tower is a quarter of this at most, but there are similarities.
Question No. 65
What is the strongest bridge for a school contest?
Answer: If you are making a spaghetti bridge, bunch it all together in a triangular prism or a big brick and just fill the gaps with Paste.
Question No. 66
Why are intermediate jacks designed in some pipe jacking projects?
Answer: When the process of pipe jacking stops, building up of resistance is very fast in some soil. For instance, increase in jacking force of 20%-40% is required for a stoppage of pipe jacking for just several hours. Hence, it is recommended that pipe jacking should be carried out in a continuous operation.
For a long pipeline, the frictional forces established between the jacking pipes and soil is high. Sometimes, such resisting forces may be so high that they can hardly be overcome by the jacks in jacking pits. Moreover, even if the jacks can overcome the high frictional forces induced during jacking, high loads are experienced in jacking pipes during driving. Jacking pipe’s material e.g. concrete may not have sufficient strength to resist these stresses and hence pipe strength is another factor that governs the need for consideration of using intermediate jacks.
Question No. 67
What is the best type of wood glue?
Question No. 68
What is the purpose of adding cooling pipes or even using cold water for concrete in concreting operation?
Answer: All these measures aim at reducing the placing temperature and reducing thermal cracks induced during concreting of massive pours. Since the final concreting temperature should be the ambient temperature, reducing the initial placing temperature will also lower the peak hydration temperature. Therefore, the temperature difference between the hydration peak and the ambient temperature is reduced accordingly and subsequently the thermal effect to concrete structure can be reduced by controlling the placing temperature.
Question No. 69
What are the advantages of using top-down approach in basement construction?
Answer: The advantages of top-down approach are listed below:
- The structures above ground can be carried out simultaneously with the structures below ground. This greatly reduces the time for construction.
- By using this approach, settlement can be reduced.
- Since the permanent columns and slabs can be utilized to support loadings during construction, it saves the cost of form-work.
Note: Top-down approach means construction of basement is carried out from ground level downwards.
Question No. 70
In selection of waterstop, shall engineers use plain dumb-bell type or center-bulb type?
Answer: The plain dumb-bell type is used for joint location where small movements are anticipated.
Therefore, construction joints are desirable locations of this type of waterstop. On the other hand, center-bulb type water-stop is suitable for expansion joints or locations where lateral and shear movements occur due to settlement or deflection. Reference is made to W. L. Monks (1972).
Question No. 71
Why are two gate valves required in normal practice to form a washout valve?
Answer: In fact, the situation is analogous to that of fire hydrants in which two gates valves are installed with a single fire hydrant. Washout valves are used for normal maintenance work of watermain like allowing flowing out of water during cleaning of watermain. At the junction where a tee-branch out to a washout point, a gate valve is installed to separate the two pipelines. However, this gate valve is open during normal operation while another gate valve further downstream is installed (closed during normal operation). If the downstream gate valve is not installed in position, then the pipe section of branched-out watermain will be left dry during normal operation and there is a high probability that damage to watermain and frequent leakage would occur. With the downstream gate valve installed, the segment of branched-out watermain contains water in normal operation. In case there is any leakage, it can be readily detected by using the two gate valves.
Question No. 72
What is an ice dam sock?
Answer: If you have never used a ice dam melting sock on your roof before, you will find that they provide an inexpensive method for removing roof ice dams and improving your home's heating efficiency. Roof ice dams are an annoying source of roof damage, leaks, and heat loss in the winter. The main causes are drip melt from improperly capped warm air vent pipes and poor roof insulation. Laying a ice melt sock onto the roof so it crosses the ice dam and overhangs the gutter, will melt through the snow and ice and create a channel for water to flow down into the gutters or off the roof. If done properly those ice sickles that form as the snow melts from the edges of the gutters will never appear, they too are a cause of much damage and are dangerous to life and limb.
Question No. 73
In concrete compression test, normally 150 mm × 150 mm × 150 mm concrete cube samples is used for testing. Why isn’t 100 mm × 100 mm × 100 mm concrete cube samples used in the test instead of 150 mm × 150 mm × 150 mm concrete cube samples?
Answer: Basically, the force supplied by a concrete compression machine is a definite value. For normal concrete strength application, say below 50MPa, the stress produced by a 150 mm × 150 mm × 150 mm cube is sufficient for the machine to crush the concrete sample. However, if the designed concrete strength is 100MPa, under the same force (about 2,000 kN) supplied by the machine, the stress under a 150mmx150mmx150mm cube is not sufficient to crush the concrete cube. Therefore, 150 mm × 150 mm × 150 mm concrete cubes are used instead to increase the applied stress to crush the concrete cubes.
For normal concrete strength, the cube size of 150 mm × 150 mm × 150 mm is already sufficient for the crushing strength of the machine.
Question No. 74
In pipe jacking/microtunneling, it is commonly accepted that cover depths of jacking pipes cannot be too shallow (i.e. less than 2D where D is the diameter of jacking pipes). Why?
Answer: For pipe jacking/microtunneling, the causes of large settlement are loss of face stability, failure to stabilize ground around shafts, presence of annular space around pipes and shield, drag along pipe joints, etc. The settlement mechanism of shallow depths of pipe jacking/microtunneling is the formation of a settlement trough on top of the jacking pipes. The width of the trough depends on soil properties; the larger is the cover depth of jacking pipes, the larger is the width of settlement trough. For the same soil volume loss due to pipe jacking/microtunneling, the width of settlement trough for shallow cover depth is smaller and therefore it results in a larger vertical maximum settlement.
Question No. 75
What is the force exerted by the Tacoma narrows bridge?
Answer: The force exerted to the Tacoma narrows bridge was initially the wind resistance. The wind resistance caused the whole bridge to act as a system with forced vibration with damping.
Question No. 76
What is the mechanism of protection by hot dip galvanizing?
Answer: Hot dip galvanizing protects steel/iron from corrosion by:
- It forms a metallic zinc and zinc-iron alloy coating on top of steel surface. This zinc coating reacts with moisture in atmosphere to from zinc salts which act as an insulating layer for steel/iron.
- Zinc is higher than steel/iron in the galvanic series and when these dissimilar metals with different electrical potential are in contact, the zinc anode corrodes and offers sacrificial protection to steel/iron and hence steel/iron is protected from corrosion.
Question No. 77
Comparing the rate of “Formwork exceeding 300 mm wide, horizontal or at any inclination up to and including 5° to the horizontal” with the rate of “Formwork exceeding 300 mm wide, at any inclination more than 85° up to and including 90° to the horizontal”, which one is higher?
Answer: The item “Formwork exceeding 300 mm wide, at any inclination more than 85° up to and including 90° to the horizontal” refers to formwork formed vertically and when compared with formwork erected in horizontal plane, the amount of false-work required is smaller.
The item “Formwork exceeding 300 mm wide, horizontal or at any inclination up to and including 5° to the horizontal” refers to formwork to be erected in horizontal position and in general it requires much false-work to support this type of formwork. Therefore, the rate for this item is higher than the one mentioned in the above paragraph.
Question No. 78
In pre-stressing work, if more than one wire or strand is included in the same duct, why should all wires/strands be stressed at the same time?
Answer: If wires/strands are stressed individually inside the same duct, then those stressed strand/wires will bear against those unstressed ones and trap them. Therefore, the friction of the trapped wires is high and is undesirable.
Question No. 79
What is a kip?
Answer: 1 kip = 1000 lbs
Question No. 80
What is the difference between fasteners, bolts and screws?
Answer: Fastener is a general term to describe something which is used as a restraint for holding things together or attaching to other things.
The main physical distinction between screws and bolts is that screws are entirely full of threads while bolts contain shanks without threads. However, a better interpretation of the differences between the two is that bolts are always fitted with nuts. On the contrary, screws are normally used with tapped holes.
Question No. 81
How do you measure concrete?
Answer: Cubic feet, Cubic yards, Cubic Meter
Question No. 82
What are the advantages of piers constructed monolithically with the bridge deck over usage of bearings?
Answer: Basically, piers constructed monolithically with the bridge deck are advantageous in the following ways:
- Movement of the bridge deck is achieved by the bending deformation of long and slender piers. In this way, it saves the construction cost of bearings by using monolithic construction between bridge deck and piers. Moreover, it is not necessary to spend extra effort to design for drainage details and access for bearing replacement. On the other hand, in maintenance aspect substantial cost and time savings could be obtained by using monolithic construction instead of using bearings as bridge articulation.
- Monolithic construction possesses the shortest effective Euler buckling length for piers because they are fixed supports at the interface between bridge deck and piers.
Note: Monolithic construction means that piers are connected to bridge decks without any joints and bearings.
Question No. 83
What is braced excavation all about?
Answer: Excavations are braced to prevent the cavein of surrounding unstable soil.
Question No. 84
In the design of pipe jacking, what particular areas on pipe joints should engineers take care of?
Answer: Since in pipe jacking, the jacked pipes could hardly be jacked in the designed level and alignment and some deviation from the original one is commonly acceptable provided that the deviation are within the tolerance of the Contract. However, in order to avoid damage made to the pipe joints due to over-stressing, it is necessary to estimate the stress concentrations resulting from these angular deflections.
Note: Pipe jacking is a trenchless method in which pipes are jacked underground from jacking pits and receiving pits.
Question No. 85
In the design of service reservoirs, how are reservoir floors designed to prevent leakage of water due to seasonal and shrinkage movements?
Answer: There are in general two main approaches in designing floors of service reservoirs:
- In the first method, movement joints are designed in each panel of reservoir floors so that they can expand and contract freely. Each panel is completely isolated from one another and a sliding layer is placed beneath them to aid in sliding.
- The second method, on the contrary, does not make provision to free movement. Due to seasonal and shrinkage movements, cracks are designed to occur in the reservoir floors such that very tiny cracks are spread over the floor and these cracks are too small to initiate corrosion or leakage. However, in this case, the amount of reinforcement used is much larger than the first approach.
Question No. 86
In erection of false-work, for a rectangular panel inside a false-work should it be braced along the two diagonals?
Answer: When a rectangular panel is subject to an eccentric load or a lateral load, it tends to deform into a parallelogram with one diagonal shortening and the other elongating. Theoretically, it is sufficient to brace along one of the diagonals (the one in tension). If one diagonal is only allowed to brace inside the rectangular panel, it should be not braced in the diagonal in compression because under severe lateral loading the diagonal may buckle leading to failure of structure.
However, in actual situation lateral loads may come from both sides of the panel and hence it should be braced in both diagonals.
Question No. 87
What are the applications of modulus of elasticity?
Answer: As the term implies, "Modulus of Elasticity relates to the elasticity or "flexibility" of a material. The value of modulus of elasticity is very much significant relating to deflection of certain materials used in the construction industry. Take for example the general E value of mild carbon steel is about 200 GPA compared to about 70 GPA for aluminium. This simply translate that aluminium is 3 times flexible than steel.
Question No. 88
What are the functions of different components of paint?
Answer: For normal paint application, there are mainly three main components of paint, namely primer, undercoat and finishing coat.
- Primer: This is the first layer of a typical painting system and it is used to inhabit corrosion and provide a good bond for subsequent coats.
- Undercoat: This component acts as a barrier to corrosion agents and even out irregularities of bonding surface. It also serves to hide the underlying background and prevent the details and colour of the area of application to affect the designed colour and finishing details of paint.
- Finishing coat: This is the final layer of a typical painting system and it protects the underlying layers from the effect of adverse weather conditions (e.g. sunlight) and to provide the designed properties of paint like colour, impermeability, wearing resistance, etc.
Question No. 89
Why is the span length ratio of end span/approach span to its neighboring inner spans usually about 0.75?
Answer: From aesthetic point of view, an odd number of spans with a decrease in length in the direction of abutment is desirable. Moreover, spans of equal length are found to be boring. However, the arrangement of irregular span lengths is not recommended because it gives a feeling of uneasiness.
From structural point of view, for a multi-span bridge with equal span length, the sagging moment at the mid-span of the end span/approach span is largest. In order to reduce this moment, the span length of end span/approach span is designed to be 0.75 of inner spans. However, this ratio should not be less than 0.40 because of the effect of uplifting at the end span/approach span support.
Note: End span refers to the last span in a continuous bridge while approach span refers to the first span of a bridge.
Question No. 90
What is the tallest man made structure in the world?
Answer: The tallest artificial structure is Burj Khalifa, a skyscraper in Dubai that reached 829.8 m (2,722 ft) in height on January 17, 2009. By April 7, 2008 it had been built higher than the KVLY-TV mast in North Dakota, USA.