Trailer suction hopper dredgers are vessels which remove material off the seabed through hydraulic suction by using pumps. During the dredging operation, a mixture of soil and water is transported through suction pipe to storage hoppers. Significant turbulence inside the hoppers keeps the dredged mixture in suspension and this should be minimized to enhance the material to settle swiftly prior to the process of overflowing. Trailer suction hopper dredgers are mounted with draghead or dragarm pumps which increases the dredging depth and trims down the occurrence of cavitation as suggested by John B. Herbioh (1992). This machine is limited to dredging relatively low-strength material. Moreover, they cannot be deployed in very shallow waters and instead grab dredgers should be used. However, its dredging capacity is higher than that of grab dredger and it can be mobilized in relatively deep-water region.

Trailer suction hopper dredgers are renowned for their mobility, versatility and capability to operate in unfavorable sea conditions.

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.

To illustrate the different approaches adopted for reclamation in deep water and shallow water region, the following example is used:

In deepwater region, consider the seabed level is –8.5mPD. After laying of geotextiles and 1.5m thick sand blanket, the top level of sand blanket is about –7mPD. Split barges are deployed for dumping public fill to –2.5mPD. Afterwards, end dipping of public fill by trucks will be carried out up to +2.5mPD which is the designed reclamation level. Between level –2.5mPD and +2.5mPD, it is too shallow for split barges to enter the water, thus the method of end dipping is used instead.

For shallow water region, the seabed level is taken as –5.5mPD in this example. With the laying of geotextiles and 1.5m sand blanket into position, the top level of sand blanket is about –4mPD. In this case, split barges are also used for reclamation work between the level –4mPD and –2.5mPD. After that, if end dipping is used for reclamation work above –2.5mPD, then in considering the relative thin layer of fill above seabed (1.5m sand blanket + 1.5m sand blanket), it stands a high chance that mud wave would occur in seabed. Therefore, half-loaded derrick barges are employed for reclamation up to level 0mPD. With a thicker layer of public fill now, end dipping can then be used for reclamation between 0mPD and +2.5mPD.

This above reclamation sequence is just an example to demonstrate the different considerations for reclamation in deep water and shallow water region.

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.

Timber fenders:
They are low in strength and are subject to rotting and marine borer attack. Moreover, they have low energy absorption capacity and the berthing reaction depends on the point of contact. The contact pressure between fender and vessels are high. They are considered to be environmentally unfriendly because they consume tropical hardwoods in their production.

Plastic fenders:
Their strength is similar to that of timber fenders but they have relatively high abrasive resistance. They are resistant to chemical and biological attack. Their energy absorption capacities are moderate and the berthing reactions are also dependent on the point of contact. The reaction is lower when compared with timber fenders for a given energy absorption. They are considered to be environmental friendly because they are manufactured from recycled material.

Rubber fenders:
They possess high abrasive resistance and are also resistant to most biological and chemical attacks. They have moderate to high energy absorption capacity and the energy absorption performance is independent of the point of contact. Similar to plastic fenders, they are also environmental friendly products.

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.

In many pier structures the connection of fenders 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.

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 weight chain is used to sustain the weight of face and frontal panel. Shear chain help protect the fender from damage while the fender is in shear deformation and they are orientated at 20 – 30° to the horizontal. Tension chain serves to guard the fender against damage when the fender is under compression.

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.