JPH0361872B2 - - Google Patents
Info
- Publication number
- JPH0361872B2 JPH0361872B2 JP60114195A JP11419585A JPH0361872B2 JP H0361872 B2 JPH0361872 B2 JP H0361872B2 JP 60114195 A JP60114195 A JP 60114195A JP 11419585 A JP11419585 A JP 11419585A JP H0361872 B2 JPH0361872 B2 JP H0361872B2
- Authority
- JP
- Japan
- Prior art keywords
- liquefaction
- submarine
- submarine pipeline
- pipeline
- trench
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000010276 construction Methods 0.000 claims description 17
- 239000000463 material Substances 0.000 claims description 12
- 238000005452 bending Methods 0.000 description 17
- 230000002265 prevention Effects 0.000 description 13
- 238000006073 displacement reaction Methods 0.000 description 10
- 238000010586 diagram Methods 0.000 description 7
- 239000004576 sand Substances 0.000 description 6
- 238000007796 conventional method Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000009412 basement excavation Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 239000012530 fluid Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000011435 rock Substances 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
- 239000004575 stone Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/20—Hydro energy
Landscapes
- Underground Structures, Protecting, Testing And Restoring Foundations (AREA)
Description
〔産業上の利用分野〕
この発明は海底地盤に埋設された海底パイプラ
インの液状化対策工法に関するものである。
〔従来の技術〕
海底地盤に海底パイプラインが埋設される場
合、海底パイプラインは海底面下２〜３ｍの位置
に設置され、砂にて埋め戻される例が多い。この
埋め戻された砂は、有効上載圧が小さい、ゆるく
堆積しているなどの理由から地震時に液状化する
可能性が非常に大きい。砂が液状化すると、砂地
盤は、水と飽和砂の中間の比重（1.0〜2.0）の流
体と同様の挙動を示し、海底パイプラインに浮力
を与える。この液状化時の浮力により、海底パイ
プラインの浮上量と曲げ応力はかなり大きなもの
となることがわかつた。
このように、海底地盤に無対策で海底パイプラ
インが埋設され、海底パイプラインの埋め戻し地
盤が部分的に液状化した場合を第６図で示す。ま
た、これを解析のためモデル化したものを第７図
に示している（参考文献−南、清宮、土田：液状
化が海底パイプラインの応力度に及ぼす影響、港
湾技研資料、No.441、1983.5）。図中、γsは液状化
した砂の単位重量、γuはパイプラインの単位重量
を示す。第８図は下記の表１に示す諸元を有する
海底パイプラインを対象として電算機による数値
解析を行つた結果を海底パイプラインの変位・曲
げモーメントの分布を示す。図中、△は液状化区
間、Ｈは海底パイプラインの埋設深さ、γuは海底
パイプラインの単位重量を示し、Ｈ＝３ｍ、γu＝
1.7ｇ／cm3のときの海底パイプラインの変位・曲
げモーメントの分布である。
[Industrial Application Field] The present invention relates to a liquefaction countermeasure construction method for submarine pipelines buried in submarine soil. [Prior Art] When a submarine pipeline is buried in the seabed, it is often installed 2 to 3 meters below the seabed and backfilled with sand. This backfilled sand has a very high possibility of liquefaction during an earthquake because the effective overburden pressure is small and it is loosely deposited. When the sand liquefies, the sandy ground behaves like a fluid with a specific gravity between water and saturated sand (1.0-2.0), providing buoyancy to submarine pipelines. It was found that the floating height and bending stress of submarine pipelines are considerably large due to this buoyant force during liquefaction. FIG. 6 shows a case where an undersea pipeline is buried in the undersea ground without any countermeasures, and the backfilling ground for the undersea pipeline partially liquefies. In addition, a model for analysis of this is shown in Figure 7 (References: Minami, Kiyomiya, Tsuchida: Effect of liquefaction on the stress level of submarine pipelines, Port and Harbor Engineering Research Materials, No. 441, 1983.5). In the figure, γ s represents the unit weight of liquefied sand, and γ u represents the unit weight of the pipeline. FIG. 8 shows the distribution of displacement and bending moment of the submarine pipeline, which is the result of computer numerical analysis of the submarine pipeline having the specifications shown in Table 1 below. In the figure, △ indicates the liquefaction section, H indicates the buried depth of the submarine pipeline, and γ u indicates the unit weight of the submarine pipeline, H = 3 m, γ u =
This is the distribution of displacement and bending moment of the submarine pipeline at 1.7g/ cm3 .
上記のような従来のアースアンカを用いて海底
パイプラインの浮上を防止する工法では、液状化
対策としては効果的であるが、アンカ３の岩盤Ｒ
への打込みが海中で施されることから施工費が割
高になるという問題点があつた。
また、従来の錘を適切な場所に設置して浮上を
防止する工法では錘５を砂地盤Ｓ中に埋設するこ
とが海中で施工されることから施工費が割高とな
ると共に錘５の沈下が海底パイプライン１の悪影
響を及ぼすという問題点があつた。
更に、海底地盤に設けられ、海底パイプライン
が設置されたトレンチの全長を液状化しない材料
で埋め戻す工法ではトレンチの全長を液状化しな
い材料で埋め戻すことから材料費がかなり高くな
るという問題点があつた。
この発明は、かかる問題点を解決するためにな
されたもので、海底パイプラインの海底地盤への
埋設に際し、安価に液状化対策を行い、海底パイ
プラインの浮上を防止できるようにした海底パイ
プラインの液状化対策工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〕
この発明に係る海底パイプラインの液状化対策
工法は、海底地盤の海底パイプラインが埋設され
る位置に掘削によりトレンチを設け、トレンチの
底部に海底パイプラインを設置し、該トレンチに
液状化しない材料で埋め戻した液状化防止区域と
液状化の可動性がある材料で埋め戻した液状化許
容区域とを交互に施工し、液状化防止区域が海底
パイプラインに働く浮力に抗するように構成した
ものである。
〔作用〕
海底パイプラインが設置された海底地盤が液状
化して海底パイプラインに浮力が働いたとして
も、海底地盤のトレンチに施された液状化防止区
域が海底パイプラインの浮力に対する引抜抵抗を
有し、海底パイプラインが長くなつても液状化防
止区域によつて最大浮上量と最大曲げ応力の浮上
が許容される所定値内におされられ、海底パイプ
ラインの浮上が防止される。
〔実施例〕
第１図はこの発明の工法の一実施例を示す斜視
図で、第１図ａは液状化防止区域を示し、第１図
ｂは液状化防止区域と液状化許容区域を示してい
る。第２図はこの発明の工法により施工された海
底パイプラインを示す断面図、第３図は第２図の
−線断面図、第４図は第２図の−線断面
図、第５図はこの発明の工法により施工された海
底パイプラインにおける液状化許容区域が液状化
した場合の海底パイプラインの変位・曲げモーメ
ントの分布を示す説明図である。
図において１０は砂地状の海底地盤である。ま
ず、海底地盤１０の海底パイプライン１が埋設さ
れる位置に断面逆三角形状で深さＤが4.2ｍ、幅
Ｗが18ｍのトレンチ１１が所要長掘削される。次
に、トレンチ１１の底部に海底パイプライン１が
設置される。更に、海底パイプライン１が設置さ
れたトレンチ１１に砕石などの液状化しない材料
が埋め戻して施工される約18ｍの長さL1の液状
化防止区域１２と砂などの液状化の可能性がある
材料で埋め戻して施工される約78ｍの長さL2の
液状化許容区域１３とを交互に施工して行う。液
状化防止区域１２は液状化時に安定するよう下部
が拡がる幅広に形成されている。なお、液状化許
容区域１３の長さL2は第８図及び第９図ａ，ｂ
のグラフを用いて最大浮上量が50cm、最大曲げ応
力が1500Kg／cm2以内に収まるように決めたもので
ある。
次に上記のように構成されたこの本発明の工法
により施された海底パイプライン１における液状
化許容区域１３が液状化した場合の海底パイプラ
イン１の変位・曲げモーメントの分布と、無対策
で海底地盤が海底地盤が液状化した場合の海底パ
イプラインの変位・曲げモーメント分布とを第８
図と第５図のグラフをもとに比較すると、無対策
の場合には海底パイプライン１の長さが長くなる
とその変位と曲げモーメントの値が次第に大きく
なるが、この発明の工法による場合には海底パイ
プライン１の長さが長くなつても液状化した液状
化許容区域１３における海底パイプライン１の変
位と曲げモーメントは低い値で所定値より大きく
なることはないことがわかる。なお、第５図にお
いてL1は液状化許容区域、L2は液状化防止区域、
ruは海底パイプラインの単位重量、rsは液状化し
た砂の単位重量を示し、海底パイプライン１の埋
設深さＨが4.2ｍで、ru＝1.7ｇ／cm3のときの海底
パイプライン１の変位・曲げモーメントの分布で
ある。
また、この発明の工法により施工された海底パ
イプライン１と無対策の海底パイプライン１との
最大浮上量と最大曲げ応力の比較を下記の表で
示すが、この表から、この発明の工法では最大
浮上量が無対策では350cm以上であるのに対し40
cmであり、液状化対策に非常に効果的であること
がわかる。
The conventional method of preventing submarine pipelines from surfacing using earth anchors as described above is effective as a countermeasure against liquefaction, but the rock R of anchor 3
There was a problem in that the construction cost was relatively high because the driving was done underwater. In addition, in the conventional method of installing weights in appropriate locations to prevent floating, the weights 5 are buried in the sandy ground S, which means that the construction is carried out underwater, which results in relatively high construction costs and prevents the weights 5 from sinking. There was a problem with the negative impact of submarine pipeline 1. Furthermore, the method of backfilling the entire length of a trench in the seabed with a submarine pipeline installed with a material that does not liquefy has the problem that the material cost is considerably high because the entire length of the trench is backfilled with a material that does not liquefy. It was hot. This invention was made to solve this problem, and is an undersea pipeline that takes measures against liquefaction at low cost and prevents the undersea pipeline from surfacing when it is buried in the undersea ground. The purpose is to provide a liquefaction countermeasure construction method. [Means for Solving the Problems] The liquefaction countermeasure construction method for submarine pipelines according to the present invention is to provide a trench by excavation at the location where the submarine pipeline will be buried in the submarine ground, and to install the submarine pipeline at the bottom of the trench. A liquefaction prevention zone is constructed by backfilling the trench with non-liquefiable material and a liquefaction permissible zone is backfilling with liquefiable material. It is constructed to resist the buoyant force acting on the body. [Function] Even if the seabed ground on which the submarine pipeline is installed liquefies and buoyancy acts on the submarine pipeline, the liquefaction prevention area provided in the trench in the submarine ground will resist the pulling out of the submarine pipeline against the buoyant force. However, even if the submarine pipeline becomes long, the maximum floating height and maximum bending stress are kept within predetermined values that allow floating due to the liquefaction prevention zone, and the floating of the submarine pipeline is prevented. [Example] Fig. 1 is a perspective view showing an embodiment of the construction method of the present invention, Fig. 1a shows a liquefaction prevention area, and Fig. 1b shows a liquefaction prevention area and a liquefaction permissible area. ing. Fig. 2 is a sectional view showing a submarine pipeline constructed by the construction method of the present invention, Fig. 3 is a sectional view taken along the - line in Fig. 2, Fig. 4 is a sectional view taken along the - line in Fig. 2, and Fig. 5 is a sectional view taken along the - line in Fig. 2. FIG. 2 is an explanatory diagram showing the distribution of displacement and bending moment of a submarine pipeline constructed by the construction method of the present invention when a liquefaction permissible area of the pipeline is liquefied. In the figure, numeral 10 indicates sandy submarine ground. First, a trench 11 having an inverted triangular cross section, a depth D of 4.2 m, and a width W of 18 m is excavated to a required length in the seabed ground 10 at a position where the submarine pipeline 1 is to be buried. Next, the submarine pipeline 1 is installed at the bottom of the trench 11. Furthermore, a liquefaction prevention zone 12 with a length of approximately 18 m L1 is constructed by backfilling the trench 11 in which the submarine pipeline 1 is installed with materials that do not liquefy, such as crushed stone, and the possibility of liquefaction such as sand. This is done by alternately constructing the liquefaction permissible area 13, which is approximately 78 m long and has a length of L2 , and is constructed by backfilling with a certain material. The liquefaction prevention area 12 is formed to be wide and widen at the bottom so as to be stable in the event of liquefaction. In addition, the length L 2 of the liquefaction permissible zone 13 is shown in Figures 8 and 9 a and b.
The maximum flying height was determined to be within 50cm and the maximum bending stress was within 1500Kg/ cm2 using the following graph. Next, we will discuss the distribution of displacement and bending moment of the submarine pipeline 1 when the liquefaction permissible zone 13 of the submarine pipeline 1 constructed by the construction method of the present invention constructed as described above liquefies, and the distribution of the bending moment without any countermeasures. The displacement and bending moment distribution of the submarine pipeline when the submarine ground liquefies is explained in Section 8.
A comparison based on the graph in Figure 5 and Figure 5 shows that in the case of no countermeasures, the displacement and bending moment values of the submarine pipeline 1 gradually increase as the length of the submarine pipeline 1 increases, but in the case of the construction method of this invention, It can be seen that even if the length of the submarine pipeline 1 becomes longer, the displacement and bending moment of the submarine pipeline 1 in the liquefied liquefaction permissible zone 13 are low values and do not exceed predetermined values. In addition, in Figure 5, L 1 is the liquefaction permissible area, L 2 is the liquefaction prevention area,
r u is the unit weight of the submarine pipeline, r s is the unit weight of liquefied sand, and the submarine pipe when the buried depth H of submarine pipeline 1 is 4.2 m and r u = 1.7 g/cm 3 This is the distribution of displacement and bending moment of line 1. In addition, the table below shows a comparison of the maximum floating height and maximum bending stress between the submarine pipeline 1 constructed by the construction method of this invention and the submarine pipeline 1 without countermeasures. From this table, it can be seen that the construction method of this invention The maximum floating height is 40cm compared to 350cm without measures.
cm, and it can be seen that it is very effective as a countermeasure against liquefaction.
この発明は以上説明してきたとおり、海底地盤
に掘削により設けられたトレンチの底部に海底パ
イプラインを設置した後、そのトレンチに液状化
しない材料で埋め戻した液状化防止区域と液状化
の可能性のある材料で埋め戻した液状化許容区域
とを交互に施工し、液状化防止区域が海底パイプ
ラインの浮力に対する引抜抵抗を有し、更に海底
パイプラインの最大浮上量と最大曲げ応力が海底
パイプラインが長くなつても液状化防止区域によ
つて浮上が許容される所定値内におさえられるの
で、海底パイプラインの浮上を防止でき、しかも
従来に比べて施工が容易で施工費も安価に済むと
いう効果を有する。
As explained above, this invention involves installing a submarine pipeline at the bottom of a trench created by excavation in the seabed, and then backfilling the trench with a material that does not liquefy into a liquefaction prevention area and preventing liquefaction. The liquefaction-preventing areas are constructed alternately with liquefaction-permissive areas backfilled with a certain material, and the liquefaction-preventing areas have pull-out resistance against the buoyancy of the submarine pipeline, and the maximum floating height and maximum bending stress of the submarine pipeline are Even if the line becomes long, the liquefaction prevention zone will keep the surfacing within the permissible predetermined value, making it possible to prevent submarine pipelines from surfacing.Moreover, construction is easier and cheaper than conventional methods. It has this effect.
第１図はこの発明の工法の一実施例を示すもの
で、第１図ａは液状化防止区域を示す斜視図、第
１図ｂは液状化許容区域を示す斜視図、第２図は
この発明の工法により施工された海底パイプライ
ンを示す断面図、第３図は第２図の−線断面
図、第４図は第２図の−線断面図、第５図は
この発明の工法により施工された海底パイプライ
ンにおける液状化許容区域が液状化した場合の海
底パイプラインの変位・曲げモーメントの分布を
示す説明図、第６図は海底地盤に無対策で埋設さ
れた海底パイプラインの埋め戻し地盤が部分的に
液状化した場合を示す説明図、第７図は第６図の
海底パイプラインを解析のためモデル化した説明
図、第８図は海底地盤に無対策で埋設された海底
パイプラインの変位・曲げモーメントの分布を示
す説明図、第９図ａは海底パイプラインにおける
液状区間長と最大浮上量との関係を示すグラフ、
第９図ｂは海底パイプラインにおける液状区間長
と最大曲げ応力との関係を示すグラフ、第１０図
は従来のアースアンカを用いて海底パイプライン
の浮上を防止する工法の説明図、第１１図はもう
一つの従来の錘を適切な場所に設置して浮上を防
止する工法の説明図である。
図において、１は海底パイプライン、１０は海
底地盤、１１はトレンチ、１２は液状化防止区
域、１３は液状化許容区域である。なお各図中、
同一符号は同一又は相当部分を示す。
Fig. 1 shows an embodiment of the construction method of the present invention, Fig. 1a is a perspective view showing the liquefaction prevention area, Fig. 1b is a perspective view showing the liquefaction permissible area, and Fig. 2 is a perspective view showing the liquefaction prevention area. A cross-sectional view showing a submarine pipeline constructed by the construction method of the invention, FIG. 3 is a cross-sectional view taken along the - line in FIG. 2, FIG. 4 is a cross-sectional view taken along the - line in FIG. 2, and FIG. An explanatory diagram showing the distribution of displacement and bending moment of a constructed submarine pipeline when the liquefaction permissible area of the constructed submarine pipeline liquefies. An explanatory diagram showing a case where the returned ground is partially liquefied. Figure 7 is an explanatory diagram of the submarine pipeline in Figure 6 modeled for analysis. Figure 8 is an illustration of the seabed buried in the submarine ground without any countermeasures. An explanatory diagram showing the distribution of displacement and bending moment of the pipeline, Figure 9a is a graph showing the relationship between the liquid section length and the maximum floating height in a submarine pipeline,
Figure 9b is a graph showing the relationship between liquid section length and maximum bending stress in a submarine pipeline, Figure 10 is an explanatory diagram of a method of preventing floating of a submarine pipeline using a conventional earth anchor, and Figure 11. This is an explanatory diagram of another conventional method of installing weights at appropriate locations to prevent floating. In the figure, 1 is an undersea pipeline, 10 is an undersea ground, 11 is a trench, 12 is a liquefaction prevention area, and 13 is a liquefaction permissible area. In each figure,
The same reference numerals indicate the same or equivalent parts.
Claims (1)
置に掘削によりトレンチを設け、トレンチの底部
に海底パイプラインを設置し、該トレンチに液状
化しない材料で埋め戻した液状化防止区域と液状
化の可能性がある材料で埋め戻した液状化許容区
域とを交互に施工し、液状化防止区域が海底パイ
プラインに働く浮力に抗することを特徴とする海
底パイプラインの液状化対策工法。1. A trench is excavated in the seabed at the location where the submarine pipeline will be buried, the submarine pipeline is installed at the bottom of the trench, and the trench is backfilled with a material that does not liquefy to prevent liquefaction and prevent liquefaction. A construction method for preventing liquefaction of submarine pipelines, which is characterized by constructing alternately liquefaction-permissive areas backfilled with resistant materials so that the liquefaction-preventing areas resist the buoyant force acting on the submarine pipeline.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP60114195A JPS61274191A (en) | 1985-05-29 | 1985-05-29 | Method of liquefying countermeasure construction of offshorepipeline |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP60114195A JPS61274191A (en) | 1985-05-29 | 1985-05-29 | Method of liquefying countermeasure construction of offshorepipeline |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS61274191A JPS61274191A (en) | 1986-12-04 |
| JPH0361872B2 true JPH0361872B2 (en) | 1991-09-24 |
Family
ID=14631577
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP60114195A Granted JPS61274191A (en) | 1985-05-29 | 1985-05-29 | Method of liquefying countermeasure construction of offshorepipeline |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS61274191A (en) |
-
1985
- 1985-05-29 JP JP60114195A patent/JPS61274191A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS61274191A (en) | 1986-12-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EXPY | Cancellation because of completion of term |