Use Retaining Structures Reinforced Soil Structures Reinforced soil

Use of Earth Retaining Structures in
Manila Harbour Centre

Earth-retaining
structures are structures designed to retain soil, rock or other materials from
bulk lateral movement or erosion. The purpose of retaining walls is to provide
lateral support or reinforcements to an unstable soil mass. Retaining walls are
also used to maintain the difference in elevation of the ground surface.

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A
retaining wall must be designed to support the lateral load or pressure of the
earth behind it and any other applied loads, and prevent water build-up which
will increase the lateral pressure as well as reduce the wall’s bearing
capacity and resistance to sliding. (Elkink, 2010). According to Brooks and
Nielsen (2013), there are three primary concerns for the design of a retaining
wall: 1.) It must have an acceptable Factor of Safety against overturning and
sliding, 2.) The allowable soil bearing pressure is not exceeded, and 3.) The
stresses within the components are within the code allowable limits to
adequately resist imposed vertical and lateral loads.

 

Alternative Earth
Retaining Structures

Reinforced Soil Structures

Reinforced
soil structures have been widely used as an alternative design to traditional
reinforced concrete retaining walls for supporting earth fills. (Bourdeau et
al., 2001). Due to its flexibility and mechanically redundant structures,
reinforced soil walls are adequate for foundation soil conditions that may
experience settlements in the long run. Reinforced soil retaining walls also
referred to as MSE walls. Mechanically Stabilized Earth (MSE) is a term
applicable to any type of reinforced soil structures. (Bourdeau et al., 2001).
Reinforcing elements of MSE varies but includes steel and geosynthetics.
Geosynthetics as a reinforcing element includes geotextiles and geogrids.

·        
Geotextiles

Geotextiles
consist of synthetic fibers which are made into flexible, porous fabrics by
weaving machines or are matted together in a random manner. Geotextiles are
porous and highly permeably to liquid flow across their manufactured planes.
Also, geotextiles conduct fluids within their plane.

·        
Geogrids

Geogrids
are plastic meshes formed into a very open, grid-like configuration. Geogrids
are generally manufactured by extruding holes from a large plain polymer sheet.
Geogrids also are permeable to flow across their plane but unlike geotextiles,
they do not conduct fluids along their plane.

 

Quay Walls

Quay
walls are earth retaining structures that separates the land from the water,
for the mooring or tying-up of ships/vessels, and for loading and unloading of
goods and passengers. The walls are equipped with bollards and fenders, and are
used for the handling of goods by cranes and other equipment moving alongside
the ship. (Richwien, 2008). Quay walls are designed to resist overturning,
sliding, and tilting when subjected to seismic forces, although some horizontal
wall movement is tolerated.

            Quay
walls constructed from steel sheet-pile cells are commonly used type of earth
retaining structure in designing ports and harbors. These walls are commonly
constructed where the depth of the water does not exceed about 15.0 m, and the
bottom conditions are suitable to support this type of structure. Steel-pile
cells are constructed from flat web steel sheet piles and are usually filled
with granular soil or rubble. When fill is placed inside the cell, the sheet
piling acts in tension. The pile-fill system forms a gravity-type structure
able to resist lateral and vertical loads and forces. (Tsinker, 1997). Aside from
continuous quay walls, free-standing sheet-pile cells are also used in port and
harbor engineering. These types of structures are basically used as foundations
for heavy cargo handling equipment.

            According
to Maas (2011), constructing a durable and sustainable structure throughout its
whole lifecycle is becoming more important. The durability of a quay wall means
it must be able to withstand all the increasing loads of ships, cranes, weather
and surroundings. An alternative design for quay walls may include the use
composites like Fiber Reinforced Polymers (FRP).

            Fiber
reinforced polymer (FRP) composites have been increasingly used in civil
engineering applications due to their high-strength, high-stiffness fibers,
lightweight, environmentally resistant matrices, and high energy efficiency.
(Davalos & Qiao, 2013). FRP composites consist of a polymer resin matrix
reinforced by glass or carbon fibers. The strength and stiffness of a composite
component are determined primarily by the type, orientation, quantity and
location of the fibers within the part. The choice of resin must be adjusted to
the structure, temperature, environmental conditions, and the production
method. FRP composites can be used to strengthen concrete marine structures,
such as piers and quay walls, to reinforce concrete canals, and as ground
anchors.