【発明の詳細な説明】[Detailed description of the invention]
〔産業上の利用分野〕
本発明は、海底の軟弱地盤上に防波堤を構築す
る方法に関する。
〔従来の技術〕
我が国における防波堤は、比較的強固な地盤上
に石を敷き並べたマウンドの上に砂を中詰したコ
ンクリート函からなるケーソンを設置する混成式
防波堤が一般的である。
この混成式防波堤はケーソンを滑り出させよう
とする波力に対しては、ケーソン底面とマウンド
の摩擦力で抵抗し、ケーソンを転倒させようとす
る波力モーメントに対してはケーソン部の重量に
よるモーメントで抵抗するものである。
この為、前記混成式防波堤は重力式防波堤と呼
ばれているが、防波堤が安定する為には必然的に
大きな重量が必要となり、これを支えるマウンド
及び基礎地盤もそれに応じた支持力を有すること
が必要になる。従つて、岩盤あるいは砂地盤のよ
うに地盤の支持力強度が充分な場合は前記混成式
防波堤の施工は問題が少ないが、粘土質地盤等の
軟弱地盤の場合、支持力強度が不足するので、円
弧滑り等の破壊が生じることがあり、事前の支持
強合を増す方策が採られている。
この地盤改良工法には代表的なものとして床
堀・置換工法、深層混合処理工法、サンドコンパ
クシヨンパイル工法等がある。
〔発明が解決しようとする問題点〕
前記深層混合処理工法は、石灰やセメントのよ
うな安定剤を軟弱地盤中に注入混合し、これらの
化学的合結作用を利用して軟弱粘土性土を強化す
る方法である。前記サンドコンパクシヨン工法は
軟弱地盤中に振動あるいは衝撃荷重を用いて砂を
注入し、直径の大きい圧縮された砂杭（サンドパ
イル）を造成して地盤の強化を図る方法である。
前記混成式防波堤を建設する場合は、前記床
堀・置換工法、深層混合処理工法やサンドコンパ
クシヨンパイル工法が多く採用されているが、両
者とも第１０図に示すように軟弱地盤１０の深層
部１１までの地盤改良を行い、その上にマウンド
１１を築成し、ケーソン１３を載置するようにな
つているので、建設期間が長くかかる他、建設工
費も非常に高額となる等の問題点があつた。
本発明はこのような事情に鑑みてなされたもの
で、軟弱地盤に防波堤を建設する場合において、
軟弱地盤の持つ粘着力を有効に利用し、建設期間
が短くてしかも建設工費の安い軟弱地盤に防波堤
を構築する方法を提供することを目的とする。
〔問題点を解決するための手段〕
前記目的に沿う本発明に係る軟弱地盤に防波堤
を構築する方法は、下部の接地板部と該接地板部
に一体的に連接された防波板部とからなる鉄筋コ
ンクリート製薄板構造の防波堤を予め製作し、設
置しようとする軟弱地盤上まで該防波堤を運搬し
て、該軟弱地盤上に直置きし、該軟弱地盤と前記
接地板部とを付着させて防波堤を構築するように
して構成されている。
ここに、前記防波板部は前記接地板部の中央部
に立設されているもの、２組の防波板部が前記接
地板部の前後に平行に立設されているもの、前記
地接板部の底には凸部が形成されているもの、前
記接地板部の底には透水性膜材が貼着されている
ものあるいは前記接地板部の底には楔部が形成さ
れているもの、いずれにおいては本発明は適用さ
れるものである。
〔作用〕
本発明においては、使用する防波堤は、下部の
接地板部と該接地板部に一体的に連接された防波
板部とからなる鉄筋コンクリート製薄板構造とな
つているので、全体的に軽量化される。従つて、
軟弱地盤上においても圧密沈下が少なく、円弧滑
り等が生じ難い。
そして、この防波堤を設置しようとする軟弱地
盤上まで該防波堤を運搬してその場に直置きして
いるので、軟弱地盤と前記防波堤の接地板部とを
付着し、これによつて該防波堤を軟弱地盤に固定
保持できる。
〔実施例〕
続いて、添付した図面を参照しつつ本発明を具
体化した実施例につき説明し、本発明の理解に供
する。
ここに、第１図は本発明の第１の実施例を適用
した軟弱地盤着底式防波堤の側面図、第２図は本
発明の第２の実施例を適用した軟弱地盤着底式防
波堤の側断面図、第３図は本発明の第３の実施例
を適用した軟弱地盤着底式防波堤の側断面図、第
４図は本発明の第４の実施例を適用した軟弱地盤
着底式防波堤の側断面図、第５図は本発明の第５
の実施例を適用した軟弱地盤着底式防波堤の側断
面図、第６図は本発明の第６の実施例を適用した
軟弱地盤着底式防波堤の側断面図、第７図は本発
明の第７の実施例を適用した軟弱地盤着底式防波
堤の側断面図、第８図は本発明の第８の実施例を
適用した軟弱地盤着底式防波堤の側断面図であ
る。
第１図に示すように本発明の第１の実施例に係
る軟弱地盤への防波堤構築方法に使用する軟弱地
盤着底式防波堤１５は、鉄筋コンクリート製であ
つて、下部の接地板部１６と該接地板部１６に立
設される防波板部１７とを有して構成され、全体
が軽量に形成されている。
そして、その全体の長さは前記接地板部１６の
1.5倍程度となつている（以下の、実施例におい
ても同じ）が、この長さは波高、水深等によつて
変わるのであるから本発明はこの数字に限定され
るものではない。
使用にあつては、軟弱地盤１８上の複数の前記
軟弱地盤着底式防波堤１５を連接して配設する
が、接地板部１６の接地面積は広くしかも全体重
量も軽いので単位面積当たりの荷重も小さいの
で、軟弱地盤１８が沈下しにくい。
そして、この接地板部１６の底の広い部分が軟
弱地盤１８に付着状態で接していて、しかも接地
板部１６の面積は広く更には全体重量も軽いの
で、図に矢印で示すように波の力を受けた場合、
図の破線で示すように転倒しようとするが接地板
部１６の底が軟弱地盤１８に粘着しているので転
倒に対して抵抗力が働く。
次に、第２図に示す本発明の第２の実施例に係
る軟弱地盤への防波堤構築方法に使用する軟弱地
盤着底式防波堤１９について説明すると、該軟弱
地盤着底式防波堤１９においては接地板部２０の
上部の前後に防波板部２１，２２が取付られてい
る。なお、同一の構成要素については同一の番号
を付してその詳しい説明を省略する。
これによつて使用材料が増して全体の重量は増
すが、該防波板部２１，２２の端部近傍を板２３
によつて連結することによつて内部に函体を形成
させて浮力を発生させることができ、大型起重機
等を用いずに曳航据付が可能となり、据付後は適
当個所に設けられた栓を抜いて内部に水を入れる
ことになる。
第３図に示す本発明の第３の実施例に係る軟弱
地盤への防波堤構築方法に使用する軟弱地盤着底
式防波堤２４について説明すると、一方の防波板
部２５には円形あるいは角形の開口部２６が形成
されており、これによつて内部に水が流入し、波
の持つエネルギーを消費させることが可能であ
る。このように適当に開口部２６を形成させたも
のであつても曳航時にはこれを塞ぐことによつて
浮力を利用することが可能となる。
第４図に本発明の第４の実施例に係る軟弱地盤
への防波堤構築方法に使用する軟弱地盤着底式防
波堤２７を示すが、図に示すように両側部の防波
板部２８，２９が接地板部３０の両端部に設けら
れている。これによつて図の矢印によつて示すよ
うに波の鉛直向きの力はなくなる。
しかも、大きな浮力が得られるので水深の浅い
海底においても据付が可能となる。
次に、第５図に本発明の第５の実施例に係る軟
弱地盤への防波堤構築方法に使用する軟弱地盤着
底式防波堤３１を示すが、図に示すように下部の
接地板部３２の底の両側に凸状物３３，３４が形
成されている。このように形成することによつて
底面の付着抵抗を向上させることができる他、凸
状部による受働土圧によつて滑動に抵抗すること
ができる。
第６図に本発明の第６の実施例に係る軟弱地盤
への防波堤構築方法に使用する軟弱地盤着底式防
波堤３５を示すが、図に示すように下部の接地板
部３６の周辺にスカート部３７が取付られてお
り、滑動に対する抵抗力は前記軟弱地盤着底式防
波堤３１と同様であるが、この軟弱地盤着底式防
波堤３５においては接地板部３６の周辺部におけ
る洗堀を防止する効果がある。
第７図に本発明の第７の実施例に係る軟弱地盤
への防波堤構築方法に使用する軟弱地盤着底式防
波堤３８を示すが、図に示すように接地板部１６
の下部には透水性膜材３９が貼付けられている。
粘着力は地盤の表層強度によつて決まるが、表層
強度は圧密が進行すると共に大きくなるので、前
記透水性膜材３９を貼付けることによつて圧密を
促進させることができる。なお、該透水性膜材は
透水性わえ圧密によつて排水される水が逃げ易
く、圧密促進に優れ地盤の安定性に効果がある。
第８図に本発明の第８の実施例に係る軟弱地盤
への防波堤構築方法に使用する軟弱地盤着底式防
波堤４０が示されているが、図に示すように接地
板部４１の下部が楔状となつている。
前記の如く第１〜第４及び第７の発明の実施例
に係る軟弱地盤着底式防波堤１５，１９，２４，
２７，３８においては、接地板部の底が平面であ
るので、据付時に着地と同時に滑り出す現象があ
り、これを防止するのに前記の如く接地板部４１
を楔形とするのが好ましい。
〔実施例〕
本発明に係る軟弱地盤着底式防波堤の作用効果
を確認するため、第９図に示すような軟弱地盤着
底式防波堤４２を用意し、水平張力を作用させて
最大水平抵抗力、移動量等の測定を行つた。
前記軟弱地盤着底式防波堤４２は接地板部４３
（12B×0.75H×12.5Lm）の中央に防波板部を構
成する直立壁４４（6.45Hm）を設け、これを保
持する為にバツトレス４５，４６が左右対象に
3.8ｍ間隔で設けられている。そして、接地板部
４３には左右夫々６ケ所づつ鋼杭建込も用の孔４
７，４８を設けた。
下部の軟弱地盤４９は土の比上Gs2.65、水中重
量ρt1.65t／m3、含水比ω40〜60％、組成は砂分10
〜25％、シルト分50〜65％、粘土分20〜35％であ
つた。
なお、前記軟弱地盤４９は〜の４種類あつ
て〜は鉛直載荷重が異なる試験であつて、
は前記孔４７，４８に鋼杭５０，５１を使用した
ものであり、その結果を第１表に示す。
[Industrial Application Field] The present invention relates to a method of constructing a breakwater on soft ground on the seabed. [Prior Art] Breakwaters in Japan are generally hybrid breakwaters in which a caisson consisting of a concrete box filled with sand is installed on a mound of stones laid out on relatively strong ground. This hybrid breakwater resists the wave force that tends to cause the caisson to slide out, using the frictional force between the bottom of the caisson and the mound, and resists the wave force moment that attempts to overturn the caisson due to the weight of the caisson. It resists by moment. For this reason, the above-mentioned hybrid breakwater is called a gravity breakwater, but in order for the breakwater to be stable, it inevitably requires a large amount of weight, and the mound and foundation ground that support it must also have a corresponding supporting capacity. is required. Therefore, if the ground has sufficient bearing capacity, such as rock or sand, there are few problems in constructing the hybrid breakwater, but in the case of soft ground, such as clayey ground, the bearing capacity is insufficient. Fractures such as arcuate sliding may occur, so measures are being taken to increase support reinforcement in advance. Typical examples of this ground improvement method include the floor trench/replacement method, deep mixing method, and sand compaction pile method. [Problems to be solved by the invention] The above-mentioned deep mixing method injects and mixes stabilizers such as lime and cement into soft ground, and uses their chemical binding action to stabilize soft clay soil. This is a way to strengthen it. The sand compaction method is a method in which sand is injected into soft ground using vibration or impact loading to create compressed sand piles with a large diameter to strengthen the ground. When constructing the above-mentioned hybrid breakwater, the above-mentioned floor trench/replacement method, deep mixed treatment method, and sand compaction pile method are often adopted, but all of these methods are used in the deep part of the soft ground 10 as shown in Fig. 10. Since the ground is improved up to Mound 11, Mound 11 is built on top of it, and Caisson 13 is placed on top of it, the construction period is long and the construction costs are extremely high. It was hot. The present invention was made in view of these circumstances, and when constructing a breakwater on soft ground,
To provide a method for constructing a breakwater on soft ground that effectively utilizes the adhesive force of soft ground, requires a short construction period, and is inexpensive. [Means for Solving the Problems] A method for constructing a breakwater on soft ground according to the present invention in accordance with the above-mentioned object includes: a lower ground plate portion; a breakwater portion integrally connected to the ground plate portion; A breakwater with a thin plate structure made of reinforced concrete is manufactured in advance, and the breakwater is transported to the soft ground where it is to be installed, placed directly on the soft ground, and the ground plate portion is attached to the soft ground. It is constructed to construct a breakwater. Here, the above-mentioned wave-break plate part is installed in the central part of the above-mentioned ground plate part, the case where two sets of wave-break plate parts are installed in parallel in front and behind the above-mentioned ground plate part, and the above-mentioned ground plate part. A convex portion is formed on the bottom of the ground plate portion, a water-permeable membrane material is attached to the bottom of the ground plate portion, or a wedge portion is formed on the bottom of the ground plate portion. The present invention is applicable to any of the above. [Function] In the present invention, the breakwater used has a reinforced concrete thin plate structure consisting of a lower ground plate portion and a breakwater plate portion integrally connected to the ground plate portion. Lighter. Therefore,
There is little consolidation settlement even on soft ground, and arcuate slips are less likely to occur. Since the breakwater is transported to the soft ground where it is to be installed and placed directly on the spot, the soft ground and the ground plate part of the breakwater are attached, and this allows the breakwater to be installed. Can be fixed and held on soft ground. [Examples] Next, examples embodying the present invention will be described with reference to the attached drawings to provide an understanding of the present invention. Here, FIG. 1 is a side view of a soft ground type breakwater to which the first embodiment of the present invention is applied, and FIG. 2 is a side view of a soft ground type breakwater to which the second embodiment of the present invention is applied. 3 is a side sectional view of a soft ground type breakwater to which the third embodiment of the present invention is applied, and Figure 4 is a side sectional view of a soft ground type breakwater to which the fourth embodiment of the present invention is applied. The side sectional view of the breakwater, FIG. 5, is the fifth embodiment of the present invention.
FIG. 6 is a side sectional view of a soft ground type breakwater to which the sixth embodiment of the present invention is applied, and FIG. 7 is a side sectional view of a soft ground type breakwater to which the sixth embodiment of the present invention is applied. FIG. 8 is a side sectional view of a soft ground type breakwater to which the seventh embodiment of the present invention is applied. FIG. 8 is a side sectional view of a soft ground type breakwater to which the eighth embodiment of the present invention is applied. As shown in FIG. 1, a soft ground type breakwater 15 used in the method of constructing a breakwater on soft ground according to the first embodiment of the present invention is made of reinforced concrete, and has a lower ground plate part 16 and a ground plate part 16. It is comprised of a ground plate part 16 and a wave-proof plate part 17 which is installed upright, and the whole is formed to be lightweight. The entire length of the ground plate portion 16 is
The length is approximately 1.5 times (the same applies to the following examples), but since this length varies depending on wave height, water depth, etc., the present invention is not limited to this number. In use, a plurality of the above-mentioned soft ground type breakwaters 15 are arranged in a connected manner on the soft ground 18, but since the contact area of the ground plate portion 16 is wide and the overall weight is light, the load per unit area is reduced. The soft ground 18 is also small, so it is difficult for the soft ground 18 to sink. The wide part of the bottom of the ground plate 16 is in contact with the soft ground 18, and the area of the ground plate 16 is large and the overall weight is light, so the waves are If you receive force,
As shown by the broken line in the figure, the robot tries to fall, but since the bottom of the ground plate portion 16 is stuck to the soft ground 18, a resistance force acts against the fall. Next, the soft ground type breakwater 19 used in the method of constructing a breakwater on soft ground according to the second embodiment of the present invention shown in FIG. 2 will be explained. Wavebreak plate parts 21 and 22 are attached to the front and back of the upper part of the main plate part 20. Note that the same components are given the same numbers and detailed explanation thereof will be omitted. This increases the amount of material used and the overall weight;
By connecting them together, a box can be formed inside and buoyancy can be generated, making it possible to install by towing without using a large hoist, and after installation, the plugs installed at appropriate locations can be removed. This will allow water to enter inside. To explain the soft ground type breakwater 24 used in the method of constructing a breakwater on soft ground according to the third embodiment of the present invention shown in FIG. 3, one breakwater plate part 25 has a circular or square opening. A section 26 is formed, which allows water to flow into the interior and consume the energy of the waves. Even if the opening 26 is appropriately formed in this manner, it is possible to utilize the buoyancy by closing the opening 26 during towing. FIG. 4 shows a soft ground type breakwater 27 used in the method of constructing a breakwater on soft ground according to the fourth embodiment of the present invention, and as shown in the figure, breakwater plate parts 28, 29 on both sides are provided at both ends of the ground plate portion 30. This eliminates the vertical force of the wave, as shown by the arrow in the figure. In addition, the large buoyancy allows installation even on shallow seabeds. Next, FIG. 5 shows a soft ground type breakwater 31 used in the method of constructing a breakwater on soft ground according to the fifth embodiment of the present invention. Projections 33 and 34 are formed on both sides of the bottom. By forming it in this way, it is possible to improve the adhesion resistance of the bottom surface, and also to resist sliding due to the passive earth pressure exerted by the convex portion. FIG. 6 shows a soft ground type breakwater 35 used in the method of constructing a breakwater on soft ground according to the sixth embodiment of the present invention. 37 is attached, and its resistance to sliding is similar to that of the soft ground type breakwater 31, but in this soft ground type breakwater 35, scouring in the peripheral area of the ground plate part 36 is prevented. effective. FIG. 7 shows a soft ground type breakwater 38 used in the method of constructing a breakwater on soft ground according to the seventh embodiment of the present invention.
A water-permeable membrane material 39 is pasted to the lower part of.
The adhesive force is determined by the surface layer strength of the ground, and since the surface layer strength increases as consolidation progresses, consolidation can be promoted by pasting the water permeable membrane material 39. The water-permeable membrane material is water-permeable and allows water drained during consolidation to easily escape, and is excellent in promoting consolidation and is effective in stabilizing the ground. FIG. 8 shows a soft ground type breakwater 40 used in the method of constructing a breakwater on soft ground according to the eighth embodiment of the present invention. As shown in the figure, the lower part of the ground plate part 41 is It is wedge-shaped. As described above, the soft ground type breakwaters 15, 19, 24 according to the first to fourth and seventh embodiments of the invention,
In Nos. 27 and 38, since the bottom of the ground plate portion is flat, there is a phenomenon that the ground plate portion 41 starts to slide at the same time as landing on the ground during installation.
is preferably wedge-shaped. [Example] In order to confirm the effects of the soft ground type breakwater according to the present invention, a soft ground type breakwater 42 as shown in Fig. 9 was prepared, and horizontal tension was applied to the breakwater to increase the maximum horizontal resistance. , the amount of movement, etc. were measured. The soft ground type breakwater 42 has a ground plate portion 43.
(12B x 0.75H x 12.5Lm) is provided with an upright wall 44 (6.45Hm) in the center that constitutes a breakwater plate, and to hold it, buttresses 45 and 46 are symmetrical on the left and right sides.
They are placed at 3.8m intervals. The ground plate part 43 has holes 4 for installing steel piles in 6 places on each left and right sides.
7,48 were set up. The soft ground 49 at the bottom has a soil ratio of Gs 2.65, underwater weight ρt 1.65t/m 3 , water content ω 40-60%, and a composition of sand 10.
~25%, silt content 50-65%, and clay content 20-35%. In addition, the soft ground 49 has four types of ~, and ~ is a test with different vertical loads,
In this case, steel piles 50 and 51 were used in the holes 47 and 48, and the results are shown in Table 1.
【表】【table】
〔発明の効果〕〔Effect of the invention〕
本発明に係る軟弱地盤への防波堤構築方法は以
上の説明からも明らかなように、薄板構造によつ
て構成しているので、全体として重量を軽減で
き、従つて軟弱地盤の上に載置しても沈下、傾斜
等が少ない。
また、下部に接地板部が設けられ軟弱地盤に付
着力でもつて接合させているので、受ける波に対
して該軟弱地盤着底式防波堤が移動してりあるい
は傾斜したりすることがない。
更にはその建設に際しては軟弱地盤着底式防波
堤上に載置するだけで工事が完了するので、工事
期間の著しい短縮、工費の軽減を図ることができ
ることとなつた。
そして、その移動も極めて容易で、不必要な場
合は取外し、別の場合にその軟弱地盤着底式防波
堤を使用して新たな防波堤の建設ができることと
なつた。
As is clear from the above explanation, the method of constructing a breakwater on soft ground according to the present invention is constructed using a thin plate structure, so the overall weight can be reduced, and therefore it can be installed on soft ground. However, there is little subsidence or slope. Further, since the ground plate portion is provided at the lower part and is adhesively bonded to the soft ground, the soft ground type breakwater does not move or tilt due to the waves it receives. Furthermore, the construction can be completed by simply placing it on the soft ground type breakwater, which makes it possible to significantly shorten the construction period and reduce construction costs. It was also extremely easy to move, and it became possible to remove it when unnecessary and use it to construct a new breakwater in other cases.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図は本発明の第１の実施例を適用した軟弱
地盤着底式防波堤の側面図、第２図は本発明の第
２の実施例を適用した軟弱地盤着底式防波堤の側
断面図、第３図は本発明の第３の実施例を適用し
た軟弱地盤着底式防波堤の側断面図、第４図は本
発明の第４の実施例を適用した軟弱地盤着底式防
波堤の側断面図、第５図は本発明の第５の実施例
を適用した軟弱地盤着底式防波堤の側断面図、第
６図は本発明の第６の実施例を適用した軟弱地盤
着底式防波堤の側断面図、第７図は本発明の第７
の実施例を適用した軟弱地盤着底式防波堤の側断
面図、第８図は本発明の第８の実施例を適用した
軟弱地盤着底式防波堤の側断面図、第９図は本発
明の作用効果を確認する為に行つた実験状態を示
す側面図、第１０図は従来例に係る軟弱地盤に建
設した防波堤の側面図である。
〔符号の説明〕、１５，１９，２４，２７，３
１，３５，３８，４０，４２……軟弱地盤着底式
防波堤、１６，２０，３０，３２，３６，４１，
４３……接地板部、１７，２１，２２，２５，２
８，２９、……防波板部、１８，４９……軟弱地
盤、２６……開口部、３３，３４……凸状物、３
７……スカート部、３９……透水性膜材、４４…
…直立壁（防波板部）。
FIG. 1 is a side view of a soft ground type breakwater to which the first embodiment of the present invention is applied, and FIG. 2 is a side sectional view of a soft ground type breakwater to which the second embodiment of the present invention is applied. , FIG. 3 is a side sectional view of a soft ground type breakwater to which the third embodiment of the present invention is applied, and FIG. 4 is a side sectional view of a soft ground type breakwater to which the fourth embodiment of the present invention is applied. 5 is a side sectional view of a soft ground type breakwater to which the fifth embodiment of the present invention is applied, and Figure 6 is a side sectional view of a soft ground type breakwater to which the sixth embodiment of the present invention is applied. FIG. 7 is a side sectional view of the seventh embodiment of the present invention.
FIG. 8 is a side sectional view of a soft ground type breakwater to which the eighth embodiment of the present invention is applied, and FIG. 9 is a side sectional view of a soft ground type breakwater to which the eighth embodiment of the present invention is applied. FIG. 10 is a side view showing the state of an experiment conducted to confirm the operation and effect, and FIG. 10 is a side view of a conventional breakwater constructed on soft ground. [Explanation of symbols], 15, 19, 24, 27, 3
1, 35, 38, 40, 42...Soft ground type breakwater, 16, 20, 30, 32, 36, 41,
43...Ground plate section, 17, 21, 22, 25, 2
8, 29, ... Wavebreak plate part, 18, 49 ... Soft ground, 26 ... Opening, 33, 34 ... Convex object, 3
7...Skirt part, 39...Water permeable membrane material, 44...
...Upright wall (breakwater plate part).