JP7616604B2 - Installation Method - Google Patents

Description

The present disclosure relates to a method for installing an object (e.g., a sensor or cable) on the bottom of an ocean or lake.

In recent years, efforts have been made to develop cable-type seafloor observation networks for the purpose of monitoring earthquakes and tsunamis. Non-Patent Document 1 discloses a sensor system consisting of an inclinometer that monitors changes in the tilt of the earth's crust, an optical fiber strain gauge that monitors horizontal deformation of the seafloor, and a pressure gauge that monitors vertical seafloor movement over the long term.

Eiichiro Araki and 4 others, "Pilot seafloor boreholetilt observation in the Nankai Trough seismogenic zone: development for future array network for slow slip events", JpGU-AGU, Joint meeting 2020, [Retrieved May 31, 2021], Internet <URL: https://confit.atlas.jp/guide/event-img/jpgu2020/SCG57-07/public/pdf?type=in>

The above-mentioned non-patent document 1 describes how a borehole (diameter 104 mm, depth 8.6 m) was formed on the seabed, and then an inclinometer was installed in the borehole, followed by a process of filling the borehole with sand, and then installing the inclinometer under the seabed. Since the task of filling a borehole on the seabed with a sufficient amount of sand is not necessarily easy to carry out, there was room for improvement in terms of work efficiency. The above-mentioned non-patent document 1 also describes that data obtained in the first six months after the installation of the inclinometer showed sawtooth noise and relatively large drift. When the inclinometer is installed by filling sand, it may take six months to a year for the inclinometer to be stably fixed in the environment under the seabed, and there was room for improvement in this regard as well.

The present disclosure provides an installation method that can efficiently perform underwater work to install an object (e.g., a sensor or cable) on the seabed or lakebed, and can secure the object in place within a relatively short period of time after installation.

The installation method according to the present disclosure includes the following steps.
(A) A step of transporting a container containing a hydraulic composition to the vicinity of the bottom surface of at least one of the sea and a lake.
(B) A step of injecting the hydraulic composition in the container through a hose into the recess provided in the bottom surface.
(C) A step of placing an object to be installed in the recess so that at least a portion of the object is embedded in the hydraulic composition filled in the recess.

The object to be installed in the recess by the above installation method is, for example, a sensor, a cable, or a stake. According to the above installation method, in step (A), a container containing a hydraulic composition is transported to the vicinity of the bottom surface, and then in step (B), the hydraulic composition is injected into the recess from that position via a hose. Therefore, these steps can be efficiently performed using, for example, a submersible vehicle. Specifically, in step (A), the container can be transported by the submersible vehicle, and the injection work in step (B) can be performed using a manipulator equipped in the submersible vehicle. The work in step (C) can also be performed by the manipulator of the submersible vehicle.

According to the above installation method, by placing an object in the recess after it has been filled with the hydraulic composition, the hydraulic composition can be filled without any gaps between the inner surface of the recess and the surface of the object, and the hydraulic composition then hardens, allowing the object to be stably fixed in place within a relatively short period of time after installation.

The recess may be a depression or groove that is originally formed in the bottom surface of the sea or lake, or may be an artificially created recess (e.g., a borehole or groove) for the purpose of installing an object. In the latter case, the installation method of the present disclosure further includes a step of forming a recess in the bottom surface prior to step (A), and in step (A), the container may be transported to the vicinity of the recess.

The water depth of the bottom surface to which the installation method according to the present disclosure is applied is, for example, 30 to 7000 m. Since it is difficult for divers to work in areas with a depth of 30 m or more, it is more efficient to use a submersible vehicle to carry out the work, as described above. The upper limit of the water depth is, for example, the depth that a submersible vehicle can reach.

The hydraulic composition contains at least a hydraulic component, a set retarder, and a separation inhibitor, and the amount of the set retarder in the hydraulic composition is preferably 1.3 to 30 parts by mass when the amount of the hydraulic component in the hydraulic composition is 100 parts by mass. By having the amount of the set retarder in this range, an appropriate pot life can be ensured, and the hydraulic composition will set in a relatively short period of time after being injected into the recess.

The present disclosure provides an installation method that allows efficient underwater work to be performed to install an object on the ocean or lake bottom, and that allows the object to be fixed in place in a relatively short period of time after installation.

FIG. 1 is a cross-sectional view showing a schematic diagram of an inclinometer installed under the seabed. FIG. 2 is a cross-sectional view showing a schematic state after a borehole is formed on the seabed. Figure 3 is a photograph showing the process of inserting the tip of the hose into the borehole by operating the manipulator of the submersible. FIG. 4 is a cross-sectional view showing a schematic state after a predetermined amount of hydraulic composition has been filled into the borehole. FIG. 5 is a photograph showing the placement of the assembly in the borehole using a winch system. FIG. 6 is a cross-sectional view showing a schematic state in which the assembly including the inclinometer has reached the bottom of the borehole. FIG. 7 is a photograph showing the state in which sand in a sandbag is being poured into a borehole in the installation method according to the comparative example. 8(a) and 8(b) are graphs showing measurement data of the inclinometers installed by the methods according to the embodiment and the comparative example, respectively.

Below, an embodiment of the present disclosure will be described with reference to the drawings. The present invention is not limited to the following embodiment. Here, an example will be described in which a borehole is formed in the seabed and an inclinometer is installed in the borehole.

<Installation method>
The installation method of this embodiment includes the following steps, and through these steps, an inclinometer 1 (target object) is installed under the seabed as shown in Figure 1. A cable (not shown) for transmitting measurement data is connected to the inclinometer 1.
(1) A step of forming a borehole BH (a recess) in the seabed surface SF.
(2) A step of transporting the container containing the hydraulic composition to the vicinity of the borehole BH by a submersible vehicle.
(3) A step of injecting a hydraulic composition in a container disposed near the borehole BH into the borehole BH via a hose.
(4) A step of placing the inclinometer 1 in the borehole BH so that the inclinometer 1 is buried in the hydraulic composition 10.
(5) A step of filling sand 20 into section S2 in the borehole BH above section S1 filled with the hydraulic composition.
As shown in Fig. 1, the inclinometer 1, together with a weight 2 and a centralizer 3, constitutes an assembly 5. In this embodiment, the assembly 5 is embedded in the borehole BH by the hardened hydraulic composition.

[Step (1)]
FIG. 2 is a cross-sectional view showing a state after the borehole BH is formed in the seabed surface SF. The borehole BH can be formed using a seabed drilling device. For example, a BMS (boring machine system, manufactured by Cellula Robotics) can be used as such a device. The seabed drilling device is transported by ship to a position where the inclinometer 1 is installed, and then the device is lowered to the seabed. The device is operated on the seabed to form the borehole BH. The water depth of the seabed surface SF is, for example, 30 m or more, and may be 40 m or more or 50 m or more. It is difficult for divers to work in areas with a water depth of 30 m or more. On the other hand, the upper limit of the water depth of the seabed surface SF is the operating depth of the seabed drilling device or the depth that a submersible can reach. These depths may be, for example, 7000 m, 6500 m, or 6000 m.

The diameter of the borehole BH may be set according to the size of the inclinometer 1, and may be, for example, 100 to 500 mm, 150 to 400 mm, or 180 to 300 mm. The depth of the borehole BH (the distance from the seabed surface SF to the bottom of the borehole BH) may be, for example, 5 to 30 m, 8 to 25 m, or 12 to 23 m.

[Step (2)]
The container containing the hydraulic composition is transported to the vicinity of the borehole BH by a submersible. "Very close" here means a distance that allows the operation of transferring the hydraulic composition to the borehole BH by a hose in step (3). This distance depends on the length of the hose, the movable range of the manipulator equipped in the submersible, or the capacity of the pump for discharging the hydraulic composition. The submersible may be a manned submersible, an ROV (Remotely Operated Vehicle), or an AUV (Autonomous Underwater Vehicle).

The amount of hydraulic composition to be transported may be set according to the amount to be injected into the borehole BH. The container mounted on the submersible has a structure capable of withstanding water pressure. The capacity of the container is, for example, 30 to 200 L, and may be 50 to 150 L. If this value is 30 L or more, there is a tendency to reduce the number of trips between the ship storing the hydraulic composition and the seabed, while on the other hand, if this value is 200 L or less, there is a tendency for the container to be transported by a submersible of relatively compact size.

(Hydraulic Composition)
The hydraulic composition according to the present embodiment includes at least a hydraulic component, a hardening retarder, and a separation inhibitor. The hydraulic component is, for example, cement such as Portland cement (JIS R5210) and Ecocement (JIS R5214); mixed cement such as blast furnace cement (JIS R5211) and silica cement (JIS R5212); special cement such as alumina cement; gypsum, etc. The hydraulic component may be used alone or in combination of two or more.

The set retarder is a substance for adjusting the pot life of the hydraulic composition. It is preferable to use an organic compound as the set retarder, and specific examples thereof include the following materials.
・Re-emulsified resin powder of styrene-acrylic copolymer ・Re-emulsified resin powder of vinyl acetate-acrylic copolymer ・Precursor of urethane polymer of polyol-polyisocyanate ・Carboxylic acid ester with polyoxyethylene chain ・Sodium tartrate

When the amount of hydraulic components in the hydraulic composition is 100 parts by mass, the amount of the set retarder in the hydraulic composition is 1.3 to 30 parts by mass, preferably 1.4 to 28 parts by mass, and more preferably 1.6 to 26 parts by mass. This composition of the hydraulic composition is set in consideration of the peculiarities of the above-mentioned installation method, which requires work on the seabed. That is, it is desirable to ensure a pot life of at least 24 hours for on-board work, such as kneading a powdered hydraulic composition with water on a ship to prepare a paste-like hydraulic composition, and then storing it in a container. After that, assuming that the container is transported to the vicinity of the seabed deeper than the thermocline and the hydraulic composition is injected into the borehole BH at that position via a hose, it is desirable to maintain the suspension state for, for example, 1 to 20 days (more preferably 5 to 20 days) under temperature conditions near the seabed (for example, 1 to 8°C). On the other hand, in order to fix the inclinometer 1 under the seabed as soon as possible after the hydraulic composition is injected into the borehole BH, it is desirable for the hydraulic composition to harden within the borehole BH in a relatively short period of time.

When a hydraulic composition is blended with a set retarder in an amount exceeding the upper limit, good fluidity after 24 hours can be ensured. However, in this case, it tends to be difficult to harden the hydraulic composition in a relatively short period of time in the borehole BH. On the other hand, when a hydraulic composition is blended with a set retarder in an amount less than the lower limit, it tends to be difficult to ensure a pot life of 24 hours or more for on-board work after preparation.

The separation inhibitor is a component that inhibits the components contained in the hydraulic composition from separating in water. If the amount of hydraulic components in the hydraulic composition is 100 parts by mass, the amount of the separation inhibitor in the hydraulic composition is preferably 0.01 to 5 parts by mass. It is preferable to use a methylcellulose-based thickener as the separation inhibitor. Methylcellulose-based thickeners have high hydrophilicity, can highly inhibit aggregation, and have excellent non-separation properties in water.

The hydraulic composition preferably has a specific gravity of 1.2 to 3.5. With a specific gravity of 1.2 or more, the hydraulic composition injected into the borehole BH can easily replace the water in the borehole BH. On the other hand, with a specific gravity of 3.5 or less, it is easy to insert the inclinometer 1 into the hydraulic composition in the borehole BH in step (4), and the integrity of the hydraulic composition in the borehole BH tends to be maintained. The hydraulic composition may further contain aggregate. By adjusting the amount and type of aggregate, it is possible to adjust the specific gravity of the hydraulic composition to some extent. Note that a hydraulic composition containing fine aggregate as an aggregate is mortar, and a hydraulic composition containing coarse aggregate and fine aggregate as fine aggregate is concrete.

The flow value of the hydraulic composition is preferably 100 to 250 mm. When the flow value is 100 mm or more, the following effects are achieved.
- The hydraulic composition is easy to transport with a hose.
- It is easy to fill the borehole BH with hydraulic composition.
- It is easy to ensure the integrity of the inclinometer 1 and the hydraulic composition.
When inserting the inclinometer 1 into the borehole BH, even if the inclinometer 1 is moved up and down within the borehole BH to adjust its position, the hydraulic composition is prevented from being pulled, and the seawater at the top of the borehole BH or the clay on the side of the borehole BH is prevented from being drawn in.
On the other hand, if the flow value is less than 250 mm, material separation tends to be suppressed.

The number of days for hardening the hydraulic composition is preferably 3 to 28 days (more preferably 7 to 28 days). By having the number of days for hardening be 3 days or more, hardening of the hydraulic composition can be prevented before the inclinometer 1 is installed, while having the number of days for hardening be 28 days or less can prevent the inclinometer 1 from tilting due to environmental influences after the inclinometer 1 is installed. It is preferable that the Young's modulus and Poisson's ratio of the hardened hydraulic composition do not differ significantly from those of the seabed ground.

[Step (3)]
The hydraulic composition in a container arranged near the borehole BH is injected into the borehole BH through a hose. The hose is a flexible pipe. In addition to the tank, the diving vehicle is equipped with a manipulator, a pump for discharging the hydraulic composition in the tank, and a hose. From the viewpoint of preventing clogging, it is preferable to use a screw pump as the pump. The amount of hydraulic composition discharged by the pump is, for example, about 1 to 5 L/min. It is preferable to use a pressure-resistant hose as the hose. For example, the inner diameter of the hose is 38 to 55 mm, and the length is 1 to 25 m. A valve that can be opened and closed by remote control may be provided at the tip of the hose. A camera may be provided in the tank so that the remaining amount of hydraulic composition can be confirmed.

With the tip of the hose positioned at the bottom of the borehole BH, the pump is driven to fill the borehole BH with hydraulic composition. The operation of inserting the tip of the hose into the borehole BH can be performed using a manipulator. By launching the hydraulic composition from the bottom of the borehole BH, the hydraulic composition can be filled into the borehole BH while replacing the drilling mud and seawater in the borehole BH. Figure 3 is a photograph showing the operation of inserting the tip of the hose into the borehole by operating the manipulator of the submersible. Figure 4 is a cross-sectional view showing the state after a predetermined amount of hydraulic composition 10 has been filled into the borehole BH.

[Step (4)]
An assembly 5 including the inclinometer 1 is placed in the borehole BH so that the inclinometer 1 is buried in the hydraulic composition. A winch system can be used to place the assembly 5. FIG. 5 is a photograph showing the operation of placing the assembly in the borehole using the winch system. The winch system includes a tower, a pulley provided on the top of the tower, and a rope for suspending the assembly 5. By using the winch system, the assembly 5 can be lowered at a predetermined speed until the weight 2 abuts against the bottom of the borehole BH. FIG. 6 is a cross-sectional view showing a schematic state in which the assembly 5 has reached the bottom of the borehole BH.

[Step (5)]
Sand 20 is filled in section S2 above section S1 in borehole BH, which is filled with hydraulic composition 10. After step (4), sand can be poured into borehole BH. Through this step, borehole BH can be filled with hydraulic composition 10 and sand 20 (see FIG. 1).

The installation method of the above embodiment employs a process in which a container is transported to the vicinity of the borehole BH and then the hydraulic composition is injected from that position into the borehole BH via a hose, so these steps can be efficiently performed using a submersible vehicle. Specifically, in step (2), the container can be transported by the submersible vehicle, and the injection work in step (3) can be performed using a manipulator equipped in the submersible vehicle. The work of installing the winch system in step (4) can also be performed using the manipulator of the submersible vehicle.

According to the installation method of the above embodiment, the assembly 5 including the inclinometer 1 is inserted into the borehole BH after it has been filled with the hydraulic composition, so that the hydraulic composition can be filled without any gaps between the inner surface of the borehole BH and the surface of the inclinometer 1, and then the hydraulic composition hardens, allowing the inclinometer 1 to be stably fixed in the borehole BH.

Although the embodiments of the present disclosure have been described above in detail, the present invention is not limited to the above embodiments. For example, in the above embodiments, the object to be installed is an inclinometer, but it may be another type of sensor or another structure. For example, the installation method according to the above embodiments may be applied to the end of an optical fiber provided in an optical fiber strain gauge, or to the installation of a pile. In addition, in the above embodiments, the recess is a borehole, but the recess may be a trench. Examples of objects to be installed in the trench include various cables (e.g., optical fiber cables). In addition, a suction pump, for example, can be used to form a trench on the seabed. In the above embodiments, the object is installed under the seabed, but it may be under the lakebed.

The present disclosure will be described below based on examples and comparative examples. Note that the present invention is not limited to the following examples.

<Preparation of mortar>
To prepare the mortar (hydraulic composition), the following materials were prepared.
[Hydraulic components]
- High-early-strength Portland cement (manufactured by Ube Mitsubishi Cement Co., Ltd.)
[Fine aggregate]
・No. 5 silica sand (N50, manufactured by Nichihyogyo Co., Ltd.)
[Cure retarder]
A: Re-emulsified resin powder consisting of styrene-acrylic copolymer (LDM7400P, manufactured by Japan Coating Resin Co., Ltd.)
B: Re-emulsified resin powder consisting of vinyl acetate-acrylic copolymer (DM2072P, manufactured by Japan Coating Resin Co., Ltd.)
C: A precursor of a urethane polymer consisting of a polyol having an ethylene oxide terminal and a polyisocyanate. D: A carboxylic acid ester having a polyoxyethylene chain (AP 101F, manufactured by SKW East Asia Co., Ltd. (BASF)).
It is presumed that these hardening retarders adsorb to the cement surface, making it hydrophobic/water-repellent, thereby preventing contact with water and delaying hydration.
[Separation inhibitors]
Hydroxypropyl methylcellulose thickener (3403Q, manufactured by Shin-Etsu Chemical Co., Ltd.)
[Antifoaming agent]
A: B115F (polyol-based defoamer, manufactured by ADEKA Corporation)
B: BYK1794 (manufactured by BYK Chemie)

(Formulation Examples 1 to 13 and Reference Examples 1 to 4)
Using the above materials, mortars were prepared having the compositions shown in Tables 1 to 3. The mortars were evaluated for the following items.
[Flow value and specific gravity]
The mixed mortar was sealed at 20°C and left to stand for 24 hours, after which the flow value and specific gravity were measured. Samples that showed bleeding were re-kneaded and subjected to the test. A 50 mm diameter x 100 mm container was used to measure the flow value, and a 500 cc container was used to measure the specific gravity.
[Bleeding]
The mortar was molded into a size of 50 mm diameter x 100 mm, sealed at 20°C and allowed to stand for 24 hours, after which the thickness of the bleeding water pooled on the surface of the test specimen was measured.
[Non-separable in water]
The mixed mortar was sealed at 20°C and left to stand for 24 hours, and then poured into seawater at 5°C to measure the amount of suspended solids. The test was conducted in accordance with the method described in Annex 2 of the 1991 Draft Guideline for Design and Construction of Underwater Non-Segregation Concrete by the Japan Society of Civil Engineers.
[Curing days]
The mixed mortar was sealed at 20° C. and allowed to stand for 24 hours, and then transferred to a thermostatic chamber set at 5° C. The period from mixing to the completion of setting (JIS R5201) in an environment of 5° C. was defined as the number of hardening days.

The mortars in Reference Examples 1 and 2 did not contain any hardening retarding substances and hardened in less than one day after mixing. The mortars in Reference Examples 3 and 4 did not have sufficient hardening inhibition and hardened in two days after mixing. It is presumed that the mortars in Reference Examples 1 to 4 had already hardened by the time they arrived at the seabed in their containers, making transportation by hose difficult. Of the hardening retarding substances A to D, it was found that C had a sufficiently high hardening retarding effect even when mixed in small amounts.

<Example of installation method>
Using the mortar according to Mixture Example 6, an inclinometer was installed under the seabed at a depth of 1,880 m in the Nankai Trough. First, a borehole (diameter: 230 mm, depth: 19 m) was formed in the seabed (soft marine ground) using a seabed-mounted drilling system (BMS). The mortar according to Mixture Example 6 was prepared on board a ship. The mortar was placed in a container (volume: 100 L) equipped on an unmanned exploration vehicle (ROV). The unmanned exploration vehicle was equipped with a pump and a hose that, together with a tank, constitute a casting unit. A screw pump was used as the pump. Hydraulic pressure supplied from the ROV was used as the power source. The discharge rate was about 1 to 5 L/min. A pressure-resistant hose (inner diameter: 38 mm, total length: 20 m) was used as the hose. A valve that can be opened and closed remotely was provided at the tip of the hose.

After the hose was lowered to the bottom of the borehole, the valve at the tip was opened and 60 L of mortar was injected into the borehole. Using the winch system shown in the photograph in Figure 5, the assembly including the inclinometer (total length: 1.3 m) was inserted into the borehole. This resulted in embedding the assembly with a total length of 1.3 m in the mortar to a depth of 2 m. Sand was then poured into the borehole, completely filling it with mortar and sand (see Figure 1).

<Comparison example of installation method>
First, a borehole (diameter: 230 mm, depth: 19 m) was formed in the seabed (soft marine ground) using a seabed-mounted drilling system (BMS). An assembly (total length: 1.3 m) including an inclinometer was inserted into the borehole using a winch system. A number of sandbags were transported by an unmanned vehicle from the ship to the seabed near the borehole. Then, as shown in the photograph of Figure 7, the sand in the sandbags was poured into the borehole using the winch system and manipulator.

Figure 8(a) is a graph showing the measurement data of the inclinometer installed by the method of the embodiment, and Figure 8(b) is a graph showing the measurement data of the inclinometer installed by the method of the comparative example. According to the installation method of the embodiment, the stability of the observation data was high immediately after installation, and the measurement data became almost flat about 10 days after installation. In contrast, according to the installation method of the comparative example, sawtooth noise was confirmed in the measurement data immediately after installation, and it took about one year to stabilize. The inclinometers according to the embodiment and the comparative example are used to observe slow slippage. Slow slippage occurs when fluctuations of about 0.1 to several microradians (μrad) occur over a period of several days to about one month, and are observed as mountain-shaped, valley-shaped, or step-shaped fluctuations depending on the type of slippage. At the noise level of Figure 8(b), it is difficult to observe slow slippage events, but at the noise level of Figure 8(a), even small-scale slow slippage events can be observed.

1...inclinometer (object), 2...weight, 3...centralizer, SF...seabed, BH...borehole (recess), 10...hydraulic composition, 20...sand, S1...section filled with hydraulic composition, S2...section filled with sand.

Claims (7)

(A) a step of transporting a container containing a hydraulic composition to the vicinity of a bottom surface of at least one of the sea and a lake;
(B) injecting the hydraulic composition in the container through a hose into a recess provided on the bottom surface;
(C) placing an object to be installed in the recess so that at least a portion of the object is embedded in the hydraulic composition;
Including, installation methods. The installation method according to claim 1, wherein the object is at least one selected from the group consisting of a sensor, a cable, and a stake. The method further includes, prior to the step (A), forming the recess in the bottom surface,
The installation method according to claim 1 or 2, wherein in step (A), the container is transported to a position near the recess. The installation method according to any one of claims 1 to 3, wherein the water depth of the bottom surface is 30 to 7000 m. The installation method according to any one of claims 1 to 4, wherein in step (A), the container is transported by a submersible. The installation method according to any one of claims 1 to 5, in which at least one of steps (B) and (C) is performed using a manipulator provided on the submersible. The hydraulic composition includes at least a hydraulic component, a set retarder, and a separation inhibitor,
The installation method according to any one of claims 1 to 6, wherein the amount of the set retarder in the hydraulic composition is 1.3 to 30 parts by mass when the amount of the hydraulic component in the hydraulic composition is 100 parts by mass.

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