JPS6213449B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reinforcing seabed foundation for excavating a shaft using an artificial island.

Conventional undersea coal mining has been limited to operations several kilometers offshore from land or islands due to limitations in underground ventilation. The purpose of this invention is to sink one or more concrete-structured caissons having steel pipes for constructing vertical shafts into the seabed offshore, in order to further develop the seabed coal mining currently in operation to the seabed offshore and to develop new offshore seabed coalfields. However, unlike the case of excavating a shaft on land, the artificial island is constructed using conventional technology, and in addition, it has to be stable against waves and the artificial island's own weight. We will prevent the sinking of the artificial island, prevent the condensation of sludge on the bottom of the artificial island, and prevent water from flowing out when excavating the gap between the artificial island's bottom and the seabed and the shaft beneath the seabed. Therefore, the intention is to construct an artificial island with reinforced undersea foundations and construct a shaft for the development of new seabed mining coal.

In order to achieve the purpose of this invention, the number of vertical shafts to be constructed within an artificial island should be changed from one inlet shaft to one exhaust shaft to a plurality of inlet and exhaust shafts (in the present invention, inlet and exhaust shafts are constructed separately). The upper caisson 2 and the lower caisson 1 each have steel pipes for shaft construction, which are the outer frame of the shaft that divides the outer frame of the artificial island made of concrete into upper and lower halves. Manufactured with

Next, the manufactured lower caisson 1 is floated to the surface, towed to the artificial island installation site off the coast, and then sunk to the seabed. A well is drilled into the seabed subsurface to the required depth by an offshore drilling vessel 10 equipped with a drilling device through a guide pipe placed on the outside of the steel pipe (lower part) 4 for constructing a shaft on an artificial island (including the inside of the lower caisson 1). While excavating, a steel pipe pile 5 is buried in the excavated well.

Cement is injected into the annular gap 13 between the inner circumferential wall of the excavated well and the outer circumferential wall of the buried steel pipe pile 5 and the gap between the lower caisson bottom 11 that has landed on the seabed surface and is allowed to solidify.

After the cement sets, the buried steel pipe pile 5
The gun is applied from the inside of the seabed through the setting cement part 14 to soft spots in the seabed subsoil (including cracks 16 in the seabed subsoil, gaps 17 between the bottom of the lower caisson and the bottom of the seabed, and hollow parts under the bottom of the lower caisson). Gun perflation hole 1 due to perflation
5 is penetrated, and cement is injected into the soft parts of the seabed sub-soil through said seabed base 15 and allowed to solidify.

Through the above process, the method of strengthening the seabed foundation for excavating a shaft using an artificial island can prevent the artificial island from sinking due to its own weight, and prevent water from flowing out from weak spots in the seabed foundation when excavating the shaft. It becomes possible.

To explain this invention according to the drawings, Fig. 1 is a drawing showing an artificial island with reinforced undersea foundations constructed and preparations for excavating a shaft completed, with necessary incidental equipment omitted. Figure 2 shows the steel pipe for shaft construction (lower part) 4, which will be the outer frame of the shaft manufactured at an onshore facility.
FIG. 2 is a floating view of the lower caisson 1 with the caisson attached thereto. FIG. 3 shows that after the above-mentioned 1 is towed to the artificial island installation location, seawater is injected into the caisson, it is sunk to the seabed, and the steel pipe pile 5 is pulled from the board of the offshore drilling vessel 10 through the guide pipe placed inside the above-mentioned 1. It is a diagram showing one well being excavated to the required depth below the seabed in order to bury it underground. FIG. 4 shows a state in which gravel or crushed stone 7 is being poured into the lower caisson 1 from the sea by a transport ship in order to stabilize the lower caisson 1 by gravity after completion of excavation and burying of the steel pipe pile 5 by the offshore drilling ship 10. be. FIG. 5 is a floating view of the upper caisson 2 to which the shaft construction steel pipe <upper part> 3, which will be the outer frame of the shaft manufactured at an onshore facility, is attached. After that, it is towed to above the lower caisson 1 installed on the seabed, and then the above 2 is stacked on top of the above 1 to construct the outer frame of the artificial island.

FIG. 6 shows a steel pipe pile 5 being placed on a seabed base 1 from aboard an offshore drilling ship 10 equipped with the drilling rig shown in FIG.
2, excavation is carried out into the above 12, and the required number of steel pipe piles 5 are lowered, and the annular gap 13 between the outer periphery of the above 5 and the seabed base 12 and the gap between the lower caisson bottom 11 and the seabed surface are filled. This is a diagram in which cement is injected into the portion 17 with the injection cement 14, and the increase in frictional resistance due to condensation between the outer periphery of the steel pipe pile 5 and the seabed foundation 12 reduces the stability of the artificial island against waves and the sinking of the artificial island due to its own weight. This is intended to prevent water from flowing out from the gap 17 during excavation of the vertical shaft.

FIG. 7 shows a gunperflation hole 15 that penetrates from the inside of the steel pipe pile 5 to a soft spot in the seabed subsoil 12 by gunperflation after the setting cement portion 14 has set. FIG. 7 shows a crack 16 in the seabed subsoil which has further penetrated the set cement portion 14 and destroyed a part of the soft spot of the seabed subsoil 12 due to this gunperflation.

Gunperflation is a process in oil field development in which crude oil in an oil reservoir flows out into a buried steel casing pipe by firing bullets at necessary locations within the steel casing pipe to penetrate the steel pipe and the solidified cement part on the outer periphery of the steel pipe. It is widely used as a method to destroy parts of oil reservoirs.

The present invention aims to strengthen the seabed foundation by injecting cement into the weak spots of the seabed foundation 12 through the gunperflation hole 15, as shown in FIG. 8, instead of letting crude oil flow out through the gunperflation hole 15. It is. In other words, FIG.
This is a diagram showing a state in which cement is injected into the interior of the steel pipe pile 5 to form a set cement portion 14, and the aforementioned 14 is subsequently formed inside the steel pipe pile 5. This strengthens the seabed base 12 and also strengthens the vertical shaft. This is to prevent water from flowing out during excavation.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram illustrating the construction of an artificial island with reinforced seabed foundation for excavating a shaft, and Figures 2, 3, 4, and 5 are diagrams showing the main steps of this process. . Figures 6, 7, and 8 are diagrams showing the main steps of burying steel pipe piles in the seabed foundation and performing cement injection and gunperflation to strengthen the seabed foundation. 1...Lower caisson, 2...Upper caisson, 3
... Steel pipe for shaft construction <upper>, 4 ... Steel pipe for shaft construction <lower>, 5 ... Steel pipe pile, 7 ... Gravel or crushed stone, 10 ... Offshore drilling ship, 11 ... Lower caisson bottom, 12 ... ...Seafloor subgrade, 13...Annular gap, 14...Set cement part, 15...Gumper formation hole, 16...Crack in the seabed subsoil, 17...Gap between the bottom of the lower caisson and the seabed surface .

Claims (1)

[Scope of Claims] 1. A step of constructing an artificial island for shaft excavation by sinking one or more caissons having steel pipes for shaft construction off the coast (step a), and a step of constructing an artificial island for shaft excavation by a offshore drilling ship equipped with a drilling equipment. A step (b step) of excavating a well to a required depth in the seabed subsurface through a guide pipe placed on the outside of a steel pipe for constructing a shaft on an artificial island, and burying a steel pipe pile in the well; Step (c) of injecting and condensing cement into the annular gap between the inner circumferential wall of the pile and the outer circumferential wall of the buried steel pipe pile and the gap between the lower part of the caisson that has landed on the seabed and the seabed; After solidification, a gun perforation hole is penetrated from the inside of the buried steel pipe pile through the solidifying cement part to a soft spot in the seabed base by gun perforation, and the soft spot in the seabed base is penetrated through the perforation hole. A method for strengthening the seabed foundation for excavating a shaft using an artificial island, characterized by comprising the steps a to d described above, including a step (d step) of injecting and condensing cement.