STRENGTH TEST METHOD FOR ANCHOR INSTALLED UNDERWATER AND FLOATING BODY

A simplified structure allows inspection of the installation strength of an anchor installed underwater. A method includes applying, to an anchor, a lifting force from above a floating body floating on a water surface to submerge the floating body into water, and setting a volume of submergence by which the floating body is submerged to a value to produce a lifting force corresponding to a predetermined installation strength and determining whether the anchor is immovable. The volume of submergence by which the floating body is submerged to produce the lifting force corresponding to the predetermined installation strength is calculated based on the buoyancy acting on the floating body.

BACKGROUND OF INVENTION

Field of the Invention

The present invention relates to a strength test method for an anchor installed underwater for testing whether an anchor for various mooring targets, such as floating photovoltaic power systems, aquaculture cages, floating piers, and water sports facilities, has an intended tensile strength.

Background Art

A method for inspecting the installation state of an anchor is described in Patent Literature 1.

This inspection method includes lifting a rod of an installed anchor with a hollow hydraulic jack and determining whether a load indicated by a hydraulic gauge reaches an intended resistance against pulling. The hydraulic jack is included in a lifting structure placed at the water bottom under a floating platform.

The method uses large equipment for inspection, including the lifting structure placed at the water bottom, in addition to the floating platform, and further a holder for the hollow hydraulic jack in the lifting structure.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

One or more aspects of the present invention are directed to a simplified structure for inspecting an anchor.

Solution to Problem

A strength test method for an anchor installed underwater includes applying, to an anchor installed underwater, a lifting force from above a floating body floating on a water surface to submerge the floating body into water, and setting a volume of submergence by which the floating body is submerged to a value to produce a lifting force corresponding to a predetermined installation strength and determining whether the anchor is immovable.

The volume by which the floating body is submerged to produce the lifting force corresponding to the predetermined installation strength is calculated based on the buoyancy acting on the floating body.

In the structure, the anchor is pulled from above the floating body to submerge a portion of the floating body exposed above the water surface into the water and to apply the lifting force corresponding to the predetermined installation strength to the anchor. When the anchor remains installed, the anchor is determined to have the installation strength. When the anchor fails to remain installed, the anchor is determined to lack the strength. The anchor lacking the strength is pulled up, thus readily moving the floating body and revealing insufficient installation of the anchor.

Advantageous Effects

The method according to the above aspect of the present invention enables the inspection with a simple operation of pulling the installed anchor from above the floating body to submerge the floating body by a predetermined volume into the water. The structure simply includes at least the floating body and a device for determining the volume by which the floating body is submerged.

DETAILED DESCRIPTION

FIG. 1is a diagram describing a strength test method for an anchor installed underwater. The test method includes applying, to an anchor11installed underwater by embedding or driving, a lifting force or a vertically upward force from above a floating body13floating on a water surface12to submerge the floating body13into the water. The amount or the volume of submergence is set to a value to produce a lifting force corresponding to an intended installation strength. The method then determines whether the anchor11is immovable. When immovable, the anchor11passes the test. When moved in the pulling direction, the anchor11fails the test.

The test method uses the floating body13. The floating body13floats on the water. More specifically, the floating body13has a bottom surface submerged in the water and an upper portion including the upper surface exposed above the water surface. When the predetermined pulling force described above is applied to the anchor11from above, the floating body13with buoyancy does not entirely become submerged in the water.

FIG. 2is a perspective view of an example of the floating body13. The floating body13is a thick polystyrene board that is square in a plan view. The floating body13includes a polystyrene floating board31and a hard protective metal plate32on the upper surface of the floating board31. The floating board31is solid and includes thick polystyrene boards combined together.

The floating body13includes gauges33to indicate the depth or the volume by which the floating body13is submerged in the water. The gauges33indicating the depth of submergence can be simpler.

The gauges33shown inFIG. 2are scale plates34including scale marks indicating the length (height) of the floating body13in the vertical direction, or more specifically, in the thickness direction. The scale plates34may be fixed at appropriate positions or, for example, at the four corners. The scale plates34at such positions are easily viewable and can protect the corners of the floating body13when formed from a hard material.

Referring now toFIG. 3, the volume by which the floating body13is submerged to produce a lifting force corresponding to an intended installation strength will now be described.

The buoyancy acting on the floating body13is ρVg (N), where g (m/s2) is a gravitational acceleration, ρ (kg/m3) is the density of water, and V (m3) is the volume of a portion of the floating body13submerged below the water surface12.

The floating body13having a mass m (kg) is also under a gravitational force with a magnitude mg (N), which is balanced with the buoyancy (ρVg=mg). Thus, the volume V of the portion submerged in the water is

indicating that the floating body13is submerged in the water by m/ρ (m3).

Buoyancy is proportional to the volume of a submerged portion in the water. Thus, a volume V1(m3) by which the floating body13is to be submerged to produce a lifting force corresponding to an intended installation strength is obtained. With this volume of submergence and the dimensions of the floating body13, a depth H of submergence for the floating body13is obtained as, for example, 10 cm for producing a lifting force of 2 t (ton).

For the floating body13, a machine is used to pull the anchor11installed underwater. As indicated by the imaginary lines inFIG. 1, the anchor11is pulled by a construction machine15, such as a hydraulic excavator. The construction machine15in use has a piling attachment16attached to the distal end of the arm.

As shown inFIG. 4, the construction machine15with the piling attachment16is also used to drive or embed the anchor11. The floating body13is used as a working platform17for placing the construction machine15on the water. In other words, the floating body13used for the strength test also serves as the working platform17for installing the anchor11.

The installation strength test for the anchor11using the floating body13and the construction machine15is performed consecutively to the installation of the anchor11.

More specifically, the construction machine15is placed on the floating body13used as the working platform17, and the floating body13is towed to a site on the water under which the anchor is to be installed. At the site, the construction machine15holds the upper end of the anchor11and drives the anchor11into a water bottom18as shown inFIG. 4. This completes the installation of the anchor11.

While holding the upper end of the anchor11, the construction machine15subsequently pulls the anchor11. The anchor11driven into the water bottom18is not easily pulled out. As indicated by the solid lines inFIG. 1, the portion of the floating body13exposed above the water surface12is submerged into the water.

The volume to be submerged by pulling is set to a value for producing the predetermined lifting force described above. The volume by which the floating body13is submerged is determined with the gauges33included in the floating body13.

More specifically, the position of the water surface12before the submergence is determined with the scale plates34serving as the gauges33. For example, when a depth of submergence of 10 cm produces a lifting force of 2 t, which corresponds to the intended installation strength, a lifting force is applied to the anchor11until the floating body13is submerged 10 cm deeper from the yet submerged water surface12. The scale plates34may be checked from above the floating body13or may be checked by a diver entering the water for installing the anchor11.

Although the floating body13may be inclined by a lifting force applied to the anchor11, the scale plates34, having the scale marks at the four corners indicating the depth of submergence, allow determination of the submergence depth at each corner. This allows easy calculation of the predetermined volume of submergence.

After the depth of submergence reaches a predetermined depth, the floating body13retains the state for a predetermined duration. In other words, the floating body13retains the state of being submerged by the predetermined volume. The duration is determined as appropriate in accordance with, for example, the use of the anchor11, an intended installation strength, and an underwater environment. The duration is not excessively long and may be several to ten and several minutes, or more specifically about five minutes, to demonstrate the intended installation strength.

When the anchor11remains immovable after being pulled for the duration, the anchor11passes the test. When the anchor11is lifted, the anchor11fails the test and is reinstalled immediately. The anchor11installed improperly is lifted, allowing the diver working underwater to notice the movement. The operator operating the construction machine15also readily senses the movement, rather than with the digital numbers indicated on the machine.

As described above, the inspection includes the simple operation of pulling the anchor11from above the floating body13to submerge the floating body13in the water by a predetermined volume. The volume by which the floating body13is submerged is determined with the gauges33included in the floating body13. The operation includes simply pulling the anchor11while checking the gauges33, and is easy.

The operation uses the floating body13including the gauges33. The anchor11is pulled with the construction machine15as described above. The floating body13eliminates a fixed, dedicated machine (not shown) for pulling the anchor11. The floating body13can thus have a simpler structure, simplifying the entire equipment for the test.

In particular, the floating body13also serves as the working platform17for installing the anchor11, further simplifying the entire equipment.

The installation of the anchor11and the test on the installation strength are performed consecutively. This increases the operation efficiency, and provides higher reliability in determining the installation strength than in the inspection performed a predetermined time after the installation.

The reliability is further increased by retaining the submerged state of the floating body13for a duration in the installation strength test, after simply submerging the floating body13by the predetermined volume.

The structure described above is one example for implementing the present invention. The present invention is not limited to the structure described above and may include other structures.

The gauges33may include, rather than scale marks for indicating the depth of submergence as described above, other components including a float on the water surface12to allow determination of the depth of the actual submergence with a sense rather than with scale marks. The gauges33may also include a member that indicates the portion submerged in the water by changing its appearance.

REFERENCE SIGNS LIST