Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to marine structures, and
moxe particularly, to a method of constructing a marine
structure and an improved caisson.
Generally, marine structures for a breakwater,
revetment, quay and the like are constructed by fabri-
cating a bo-ttom-covered caisson on land, towing it on
water to a selected site, and submerging it to rest on
seabed. Since the caisson has a bottom cover, the entire
area of seabed on which the caisson is placed must be
properly leveled. Such a leveIing operation is quite
difficult and inefficient because of submarine operations
and the finished accuracy is very low. Particularly at
sites having a great depth of water, where there is a
strong tid~, and in muddy water, ground leveling opera-
tions are very difficult and inhibit the overall construc-
tion process.
Another construction method uses a caisson
without a bottom cover. ~ottomless caissons are economic
since their area of contact with seabed is small so that
the area of seabed required to be leveled is less than
that required for bottom-covered caissons. Even in the
case of bottomless caissons, an area of the seabed must
be leveled where it is irregular.
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Under these circumstances, it was proposed to use
provisional supports as shown in Fig. 6 and as disclosed
in Japanese Patent Application Kokai No. 57-15727, for
example. In this method, a limited area of seabed a on
which provisional supports c are to rest is horiæontally
leveled with little treatment on the outside seabed area.
A caisson d is placed on the provisional supports c on the
leveled area and then filled with concrete at the bottom.
This method can reduce the area of seabed to be leveled, but
has several disadvantages. Where the depth of water is
large, it is not necessarily easy to accutately rest the
caisson d on the provisional supports c. The provisional
supports c are fabricated, transported, and submerged
separately from the caisson d, adding to the cost of construc-
tion. Since only two provisional supports are placed longitu-
I s c~s~d
dinal of the caisson, a great reaction rcsults in the provi-
B sional supports when waves act on them immediately after
placement. It is, therefore, required that the provisional
supports be of great strength and the ground reaction be
sufficient.
In addition to caissons having a rectangular cross
section, caissons having a side wall consisting of a plurality
of interconnected arcuate shells as shown in Fig. 5 are known
in the art. Such aFcuate shell walls reduce the stress or
bending moment exerted by external and internal forces due
to their arch effect, considerably reducing the wall thick-
ness or the material required with an economic benefit. In
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installing such an arcuate shell caisson on seabed using pro-
visional supports as described above, calculation must be
made on the assumption that the width of the caisson is an
internal width s' rather than an external width s as shown
in Fig. 5. This is disadvantageous in view of stability
calculation because of increased ground reaction, and thus
uneconomlc.
The present invention provides a method of con-
structing a marine structure in which a caisson may be
steadily installed on a m;n;m~l leveled area without the
need for accurate placement of provisional supports on
seabed.
The present invention also provides a method of
construction a marine structure without the need for fabri-
~ating and transporting provisional supports separately
from a caisson body.
The present invention further provides an improved
arcuate shell type caisson whose external width is an
effective width in structural calculation.
The present invention again provides an improved
arched shell type caisson which requires m;n;m; zed ground
reaction when it is subjected to waves immediately after
placement on seabed.
According to a first aspect of the present inven-
-tion, there is provided a method of constructing a marine
structure, comprising the steps oE placing on the seabed
a hollow caisson
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which is open at the top and bottom and has a pair of longi-
tudinal side walls each consisting of at least one, and
preferably, a plurality of curved shells, a pair of straight
and lateral side walls connecting said longitudinal side
walls and a footing extending outwardly from the bottom
edge of each longitudinal side wall; and introducing a
fillin~ into an interior cavity defined by the seabed and
the hollow caisson. Preferably concrete is firs-t intro-
duced into the interior cavity of the caisson to form a
lower concrete layer in staking relation to the seabed,
and ano-ther filling material, for example, sand and earth,
stone, silt and cement, and industrial wastes is then in-
troduced into the interior cavity above the concrete layer.
According to a second aspect of the present inven-
tion, there is provided a box-like caisson for use in con-
structing a marine structure, comprising a first pair of
open top and bottom sides, a second pair of opposite
longitudinal side walls each consisting of at least one,
and preferably a plurality of curved shells, a thixd pair
of opposite straight transverse side walls, and a pair of
footings extending longitudinally and outwardly from the
bottom edge of the longitudinal side walls.
The present invention will be more closely des-
cribed in conjunction with the accompanying drawings,
in which
Fig. 1 is a perspective view of one embodiment of
the caisson according to the present invention;
Fig. 2 is an elevational view of a marine structure
constructed on seabed according to the present invention;
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Fig. 3 is a vertical cross section of the marine
structure shown in Fig. 2;
Fig. ~ is a plan view of the caisson shown in Fig~ 1;
Fig. 5 is a plan view of a prior art caisson; and
Fig. 6 is an illustration of a caisson placed on a
provisional support according to a prior art method.
One preferred embodiment of the present invention will
be described.
[A] Structure
Referring to Figs. 1 - 4, a ho~low caisson 1 according
to the present invention is illustrated in the form of a box-
like caisson of concrete which is topless and bottomless or
has a first pair of open top and bottom sides. The caisson 1
has a second pair of opposed longitudinal side walls 2 each
consisting of a plurality of interconnected curved shells
such as arcuate or arched shells, and a third pair of transverse
straight side walls joining the longitudinal side walls at
their ends. The caisson 1 is usually fabricated by integrating
a plurality of arched shells into a shell side wall, and
joining two shell side walls by straight side walls into a
unit.
The above-described caisson is of a well-known configu-
ration. According ~o the present invention, the caisson 1 is
provided with an integral footing 3 at the bottom edge of each
longitudinal shell side wall 2. This footing 3 is a shelf-
like member formed integral with the caisson 1 and extends
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throughout the length of the side wall 2 and outwardly from
the bottom edge of the side wall 2 to ~orm a straight edge.
In the illustrated embodiment, the caisson 1 has in its
interior longitudinal and transverse intermediate partitions 4
e ~ e ~
which ~ro c~tcnd~d between the opposed side walls to enhance
B the strength of the caisson. The transverse partitions
connect the connections between adjacent shells in the side
walls 2 and extend parallel to the straight side walls. The
longitudinal partition connects the straight side walls and
crosses with the transverse partitions. The partitions 4
need not be provided with a footing at their bottom edge.
~B] Construction
After the caisson 1 is fabricated on land, it is
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transported to a destincd site ~ the sea. Transportation
may be carried out by various methods, for example, by attach-
ing a ceiling plate to the top of the caisson 1 to render it
buoyant, using a ship equipped with a crane by which the
caisson is suspended, or by attaching floats to the caisson
to allow it to float.
The seabed on which a marine structure is to be constructed
is leveled. More specifically, the limited linear areas of
seabed on which the footings 3 are to rest are roughly leveled~
Then, the caisson is gently submerged and rested on the
leveled seabed area~ Since the footings 3 are formed integral
with the caisson 1, the caisson 1 may be placed in a steady
manner irrespective of some irregularities in the seabed.
After placement, concrete is introduced into the interior
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cavity of the caisson 1 to form a lower concrete layer 4.
Since the concrete layer 4 fills recesses in the seabed
ground, it serves to stake the caisson to the ground, provid-
ing a substantial resistance to horizontal forces by waves
together with the caisson itself.
~ onstruction is completed by introducing a filling 5 of
sand and earth on the concrete layer 4 in the cavity of the
caisson 1. In addition to sand, examples of the filling
ma-terial 5 include stones, mixtures of silt and cement, muddy
deposits and cement, and industrial wastes.
The present invention has the following advantages.
(a) The caisson may be rested on seabed in a sufficiently
steady manner only by leveling the seabed over a narrow area
on which the footings sit, eliminating the need for leveling
the seabed over a wider area in contact with an entire bottom
surface as required in the case of bottom covered caissons.
The labor and time required for leveling operation and con-
comitant danger may be substantially reduced.
(b) The footings formed integral with the caisson lead to
a substantial reduction in work and construction period
because the two step construction of first submerging provi-
sional supports and accurately submerging and resting a caisson
body on them as in the prior art is unnecessary.
(c) The presence bf footings allows the external width B
(shown in Fig. 4) between the footing outer edges to be used
as the effective width in stability calculation. The present
invention thus allows the ground reaction to be reduced more
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than possible for the effective width in the prior art.
(d) When the caisson undergoes horizontal forces by waves
in an unsteady condition immediately after placement on sea~
bed, the footing integral with the caisson allow the ground
reaction to be reduced.
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