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Marine Works

Buttress Dams and its Classifications

What are buttress dams?
A buttress dam consists of water retaining sloping membrane or deck on the upstream which is supported by a series of buttresses at right angles to the axis of the dam. The upstream water retaining sloping membrane may be in the form of a reinforced concrete slab or a series of arches or thickened buttress heads. At the upstream end a cutoff is provides to prevent or reduce the seepage of water.

buttress dams
Buttress dams [1]

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From Sediment Dredging to Island Making

Mansoureh Hasanzadeh
Ports and Maritime Organization of Iran, Coasts and Ports Department

The challenge of maximizing dredging efficiency is still remains as a dilemma in port management and brings about unforeseen costs annually. While among many environmental and safety rules which are addressed and executed in marine waters, there’s no exact direction about dumping dredged sediments. It’s obvious that dredging operations to deepening shipping channel and increasing draft should be done temporarily. On the other hands, the dumping of picked sediment (both contaminated and clean) supposed to be done based on comprehensive technological aspects. Whereas, a cost dredging and crucial environmental consequences are worryingly high.Initial surveys reveals that the availability of information on target marine area should be as enough as its need to make big necessary data which should be drawn.
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Liquefaction Investigation On Sea Walls By Shaking Table Tests

Ghalndarzadeh A., Akbari N., Fakher A. from University of Tehran

Seismic behavior of quay walls is one of major concerns in earthquake geotechnical engineering field. Among different types of quay walls such as caisson and concrete block walls, deck and pile structures and anchored flexible walls the behavior of flexible walls looks more complicated. In the presented research, a series of shaking table tests were carried out in order to understand the seismic behavior of anchored flexible quay walls. The models were fully instrumented to monitor their behavior during shakings. Displacement of the wall, accelerations in the backfill, excess pore pressures in the soil, bending moment in the wall and tension of tie-rods were measured. By making different relative densities for the backfill and the foundation, different failure modes were observed. It is concluded that the performance of an anchored quay wall is strongly influenced by the occurrence of liquefaction.

Keywords: Anchored flexible quay wall, liquefaction, softening, failure modes
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What is immersed tube method for underwater crossings?

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

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How does the direction of approaching velocities of ships affect berthing?

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 :

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What is the design level of landings in piers?

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).

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Should the Morison equation or diffraction analysis be adopted in determining wave force on piles?

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.

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Hudson’s formula and Van der Meer formula are commonly used in the design of armour. Which one is a better choice?

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.

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What are the factors determining the stability of a single armour unit?

There are mainly three main factors which govern the stability of a armour unit, namely, gravity, intertangling and squeezing. Obviously, it is beyond doubt that the ability of the armour unit to stay in place should be closely related to gravity force.

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Should small vessels be considered in the design of fenders?

Smallest vessel should also be taken into consideration when designing fender system. In vertical orientation of fender system, the types and sizes of all vessels should be considered taking into account the tidal effect at that region. To conduct proper design of fender system, engineers must consider the height and draft of both the smallest and largest vessels to determine the point of contact on the fender. It is not uncommon that design of fender system considers only the largest vessels berthing in the pier which should be avoided as it might not function for smaller vessels berthing in dock.

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