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Marine Works

Why are most marine piles circular in cross section?

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):

(i) 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.

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What are the functions of slip joints in blockwork seawalls?

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 blockwork 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.

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In case a road passes through a reclaimed land and an existing land, what is the main concern regarding the design of pavements?

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.

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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?

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.

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Why can vacuum preloading be employed to accelerate the rate of consolidation?

In vacuum preloading, the drainage boundary of clay is isolated from the atmosphere by a membrane. A partial vacuum (e.g. suction of 80kPa) is applied within the membrane to reduce the water pressure so as to speed up consolidation.

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