Question No. 01
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. 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. 02
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):
(i) They provide strength to the sides of road pavements and avoid lateral displacement of carriage way due to traffic loads.
(ii) In terms of road safety, they serve as a separation line between footway and carriageway and aid car drivers in driving safely.
(iii) They act as a vertical barrier to guide the surface runoff collected in road pavements to the gullies.
Question No. 03
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. 04
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. 05
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 diggling action with 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 06
What are the advantages and disadvantages of lead products in construction?
Answer: Disadvantages: Lead 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. 07
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. 08
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:
(i) They induce additional head loss to the sewer system which is undesirable in hydraulic performance;
(ii) U-shaped siphons create sediment accumulation problem and previous experience showed that inverted siphons were easily blocked due to siltation;
(iii) Maintenance of invert siphons is difficult due to its inaccessibility.
Question No. 09
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. 10
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:
(i) 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.
(ii) Since the foundation of rubber dams is comparatively lighter than that of steel-gate dams, it saves both construction cost and time.
(iii) Rubber dams can be designed with longer spans without piers while steel-gate dams require intermediate piers for long spans.