The immersed tube method for underwater crossing involves the following basic construction steps:

(i) Prefabricating long tunnel units (steel shell or concrete) in a dry-dock or shipyard
(ii) Floating and towing the units with removable bulkhead to the site
(iii) Immerse the units in a pre-dredged trench
(iv) Connect the units one by one
(v) Covering the completed tunnel with backfill

Steel immersed tunnel is sometimes adopted because of the ease of fabrication and its relative lightness. Moreover, shorter construction time is required when compared with concrete immersed tubes.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

One of the major effects of angle of approaching velocities of ships is its influence of the energy to be absorbed by the fender system. Consider several ships berth on the same pier at the same speed but with different angle of approach, though their kinetic energies are the same, the amount of energy absorbed by fender differs. The amount of energy absorbed by fender is :

where W= energy absorbed by the fender
m= mass of the ship
v=velocity of the ship
k= radius of gyration of the ship
r= distance of centre of gravity of the ship to the point of contact of the fender

Hence, when the direction of approaching velocity of a ship is normal to the fender system (i.e. phi=90 ), the amount of energy absorbed is smaller when compared with that of a ship whose velocity is tangential to the shoreline.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Landings are designed as resting place for passengers during berthing and deberthing of vessels. In general, landings are provided near mean high and mean low water levels to facilitate embarking and disembarking of passengers (BS6349: Part 2: 1988). Therefore, the level of landing steps should be different from place to place because of different mean high and mean low water levels in different locations.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

The choice between the Morison’s equation and diffraction analysis in determining the wave forces on piles depends on the ratio between the diameters of piles to wavelength. If the ratio between the diameter of piles to wavelength is less than 0.2, the Morison equation is usually
recommended. The reason behind this is that the effect of viscosity and separation is significant below this ratio. On the contrary, if the ratio between the diameter of piles to wavelength exceeds 0.2, the waves are scattered with negligible occurrence of separation. As such, diffraction analysis is adopted to calculate the wave forces on piles

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Hudson’s formula is commonly adopted in preliminary design to obtain rough initial estimate of rock size. The formula is derived from the results of regular wave tests. However, this formula does not take into account the following elements which Van der Meer formula does: wave period, damage level, permeability of structure and storm duration. Moreover, Hudson’s formula deals with the use of regular waves only.

Compared with Hudson’s formula, Van der Meer formula is more complicated and it is derived from results of a series of physical model tests. They include the consideration of wave period, storm duration, clearly-defined damage level and permeability of structure. The choice of the appropriate formula is dependent on the design purpose (i.e. preliminary design or detailed design).

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.