Suction foundation, and installation method of suction foundation on ground

Abstract

To reduce the occurrence of seepage failure of the ground.SOLUTION: A suction foundation 100 comprises: a foundation body 10 having a ceiling wall 11 and side peripheral walls 12 extending downward from the ceiling wall 11 and penetrating the underwater ground G; a first drainage portion 21 provided in the foundation body 10 to drain water from a space inside the foundation body 10 and above the ground G; and a second drainage portion 22 provided in the foundation body 10 to drain water from the ground G located inside the foundation body 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed herein relates to a suction foundation and a ground installation method for a suction foundation. [Background technology]

[0002] Suction foundations that are installed on underwater ground have been known for some time. For example, Patent Document 1 discloses a suction foundation that includes a foundation body having a ceiling portion and a peripheral wall portion that extends downward from the ceiling wall. The peripheral wall portion penetrates into the waterbed ground, so that the foundation body is supported by the ground. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-140880 Summary of the Invention [Problem to be solved by the invention]

[0004] In the suction foundation described above, the water inside the foundation body is forcibly drained, generating a water pressure difference (suction pressure) between the inside and outside of the foundation body, and the penetration force caused by the suction pressure is used to penetrate the foundation body into the ground. However, the suction pressure also exerts negative pressure on the water bottom ground inside the foundation body, causing upward seepage flow in the water bottom ground. This upward seepage flow may cause the water bottom ground to be destroyed (seepage failure).

[0005] The technology disclosed herein has been made in consideration of the above points, and its purpose is to reduce the occurrence of seepage failure of the ground. [Means for solving the problem]

[0006] The suction foundation disclosed herein comprises a foundation body having a ceiling wall and side peripheral walls extending downward from the ceiling wall and penetrating into the underwater ground, a first drainage section provided in the foundation body to drain water from the space inside the foundation body and above the ground, and a second drainage section provided in the foundation body to drain water from the ground located inside the foundation body.

[0007] The suction foundation disclosed herein comprises a foundation body having a ceiling wall and side walls extending downward from the ceiling wall and penetrating into the submerged ground, and a drainage section provided on the foundation body for discharging water from inside the foundation body, the drainage section including an inlet opening inside the foundation body and above the lower end of the side walls for drawing in water, and when the inlet opening of the drainage section is inserted into the ground located inside the foundation body, the drainage section discharges water from the ground located inside the foundation body.

[0008] The method of installing a suction foundation on underwater ground disclosed herein is a method of installing a suction foundation comprising a foundation body having a ceiling wall and side walls extending downward from the ceiling wall and penetrating into the underwater ground, and comprises the steps of submerging the foundation body in the water, draining water from the space inside the foundation body and above the ground to penetrate the foundation body into the ground, and draining water from within the ground located inside the foundation body.

[0009] The ground installation method for a suction foundation disclosed herein is a method for installing a suction foundation on underwater ground, the method comprising: submerging the foundation body in the water; discharging water from inside the foundation body through an inlet of a drainage section provided in the foundation body; penetrating the foundation body into the ground; and penetrating the inlet into the ground located inside the foundation body; and discharging water from the ground located inside the foundation body through the inlet of the drainage section. [Effects of the Invention]

[0010] According to the suction foundation and the ground installation method for the suction foundation, the occurrence of seepage failure of the ground can be reduced. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic diagram of a suction foundation in place. [Figure 2] FIG. 2 is a schematic enlarged view of a suction foundation. [Figure 3] FIG. 3 is a diagram illustrating a schematic hardware configuration of the control device. [Figure 4] FIG. 4 is a block diagram showing the configuration of a control system of the processor. [Figure 5] FIG. 5 is an explanatory diagram showing the suction foundation before the penetration process. [Figure 6] FIG. 6 is an explanatory view showing a state in which the foundation main body has reached the ground in the penetration step. [Figure 7] FIG. 7 is an explanatory diagram illustrating the depth position of a predetermined element of a suction foundation in water. [Figure 8] FIG. 8 is a graph showing the relationship between the pressure inside the foundation body, seawater pressure, and depth in this embodiment and a comparative example. [Figure 9] FIG. 9 is a graph showing the relationship between the pressure inside the foundation body, seawater pressure, and depth in this embodiment and the comparative example when the limit suction pressure acts in the comparative example. [Figure 10] FIG. 10 is a schematic diagram showing a suction foundation according to a modified example. [Figure 11] FIG. 11 is a graph showing the relationship between the pressure inside the foundation body and seawater pressure and depth. DETAILED DESCRIPTION OF THE INVENTION

[0012] Exemplary embodiments will now be described in detail with reference to the accompanying drawings.

[0013] Fig. 1 is a schematic diagram of a suction foundation 100 installed on ground G. The suction foundation 100 is a foundation for installing a structure on or underwater, and is sunk into underwater ground G. In the example of Fig. 1, the suction foundation 100 is a foundation for installing a wind turbine 9 offshore.

[0014] The suction foundation 100 includes a foundation body 10, a first drainage section 21 provided in the foundation body 10 and configured to drain water from the space inside the foundation body 10 and above the ground G, and a second drainage section 22 provided in the foundation body 10 and configured to drain water from the ground G located inside the foundation body 10. The first drainage section 21 drains water from the space inside the foundation body 10 and above the ground G, causing the foundation body 10 to penetrate into the ground G. Furthermore, while the foundation body 10 is penetrated into the ground G, the second drainage section 22 drains water from the ground G located inside the foundation body 10, thereby lowering the hydraulic gradient of the ground G inside the foundation body 10. In other words, the suction foundation 100 uses the first drainage section 21 to drain water from the space inside the foundation body 10 and above the ground G, and uses the second drainage section 22 to drain water from the ground G located inside the foundation body 10, thereby lowering the hydraulic gradient of the ground G located inside the foundation body 10.

[0015] The foundation body 10 is formed in the shape of a container with a closed upper end and an open lower end. The foundation body 10 has a ceiling wall 11 and peripheral side walls 12 that extend downward from the ceiling wall 11 and penetrate into the underwater ground G. The ceiling wall 11 and peripheral side walls 12 are formed, for example, from steel plates.

[0016] The ceiling wall 11 is formed in a roughly disk-like shape that extends horizontally. A support pillar 13 is arranged on the ceiling wall 11. The support pillar 13 is arranged at the center of the ceiling wall 11 and extends upward from the ceiling wall 11. When the foundation body 10 is sunk in the ground G, the upper end of the support pillar 13 is located above the water surface. The wind turbine 9 is installed on the support pillar 13.

[0017] The side peripheral wall 12 is formed in a substantially cylindrical shape extending in the vertical direction. The upper end of the side peripheral wall 12 is connected to the periphery of the ceiling wall 11. The ceiling wall 11 and the side peripheral wall 12 define an internal space 15 of the foundation body 10. When the side peripheral wall 12 penetrates into the ground G, the foundation body 10 further defines an upper space 15a. In other words, the upper space 15a is a space defined by the ceiling wall 11, the side peripheral wall 12, and the ground G. The upper space 15a is a part of the internal space 15.

[0018] The foundation body 10 is installed, i.e., sunk, into the ground G by penetrating the side peripheral walls 12 into the ground G. In the suction foundation 100 installed in the ground G, a frictional force acts on the side peripheral walls 12. As a result, the suction foundation 100 is firmly fixed to the ground G.

[0019] The first drainage section 21 includes a drainage hole 41 provided in the foundation body 10 , a first water supply pipe 31 , a first valve 32 , and a first drainage pump 33 .

[0020] The drain hole 41 is formed through the ceiling wall 11. The first water supply pipe 31 is provided in the ceiling wall 11 and extends upward. The drain hole 41 is connected to the first water supply pipe 31. In other words, the first water supply pipe 31 communicates with the internal space 15 via the drain hole 41. The first valve 32 is provided at an upper part of the first water supply pipe 31 (specifically, at a part above the water surface). The first valve 32 switches the first water supply pipe 31 between open and closed states.

[0021] The first drainage pump 33 is connected to the first water supply pipe 31. When the first drainage pump 33 is operated, water inside the foundation body 10 is discharged to the outside of the foundation body 10 through the drainage holes 41 and the first water supply pipe 31. Draining water through the first drainage section 21 promotes penetration of the foundation body 10 into the ground G. Specifically, by forcibly discharging the water inside the foundation body 10, a pressure difference occurs between the inside and outside of the foundation body 10. A penetration force due to the suction pressure acts on the foundation body 10, and the side peripheral wall 12 penetrates further into the ground G.

[0022] The second drainage section 22 includes a drainage pipe 42 provided in the foundation body 10, a second water supply pipe 34, a second valve 35, and a second drainage pump 36.

[0023] Fig. 2 is a schematic enlarged view of the suction foundation 100. Note that the wind turbine 9 is not shown in Fig. 2. The drain pipe 42 is inserted into the through-hole 11a in the ceiling wall 11. The through-hole 11a is formed through the center of the ceiling wall 11. The drain pipe 42 is disposed in the center of the ceiling wall 11 and extends upward.

[0024] The second drainage section 22 includes an inlet 22a that penetrates into the ground G and sucks water from the ground G. The inlet 22a of the second drainage section 22 is located above the lower end 19 of the side peripheral wall 12. Specifically, the tip 42a of the drainage pipe 42 opens into the internal space 15 of the foundation main body 10, and the base end 42b of the drainage pipe 42 opens to the outside of the foundation main body 10. The tip 42a penetrates into the ground G. The tip 42a is located above the lower end 19 of the side peripheral wall 12. A filter (not shown) is attached to the drainage pipe 42 to prevent materials such as soil and sand that make up the ground G from entering the drainage pipe 42.

[0025] The second water supply pipe 34 is provided at the base end 42b of the drain pipe 42 and extends upward. The second water supply pipe 34 is connected to the drain pipe 42. In other words, the second water supply pipe 34 is in communication with the internal space 15 via the drain pipe 42. The second valve 35 is provided at the upper part of the second water supply pipe 34 (specifically, above the water surface). The second valve 35 switches the second water supply pipe 34 between open and closed states.

[0026] The second drainage pump 36 is connected to the second water supply pipe 34. When the second drainage pump 36 is operated, water in the ground G located inside the foundation body 10 is discharged to the outside of the foundation body 10 via the drainage pipe 42 and the second water supply pipe 34. After the first drainage unit 21 discharges water from the space inside the foundation body 10 and above the ground G, the water is discharged via the second drainage unit 22, thereby lowering the hydraulic gradient of the ground G located inside the foundation body 10. Specifically, the second drainage unit 22 lowers the hydraulic gradient in the surface layer Ga of the ground G. The hydraulic gradient refers to the difference in water pressure per unit depth of the ground G. The surface layer Ga of the ground G refers to the area near the surface, including the surface of the ground G. The surface layer Ga is located above the lower end 19 of the side peripheral wall 12.

[0027] The suction foundation 100 further includes a first water pressure sensor 51 , a second water pressure sensor 52 , and a third water pressure sensor 53 .

[0028] The first water pressure sensor 51 detects the pore water pressure of the ground G located inside the foundation body 10. The first water pressure sensor 51 is located at the tip 42a of the drain pipe 42. The first water pressure sensor 51 is attached to the outer surface of the drain pipe 42.

[0029] The second water pressure sensor 52 detects the water pressure inside the foundation body 10 and in the upper space 15a above the ground G. The second water pressure sensor 52 is attached inside the foundation body 10 and to the lower surface of the ceiling wall 11.

[0030] The third water pressure sensor 53 detects the water pressure outside the foundation body 10. The third water pressure sensor 53 is attached to the top surface of the ceiling wall 11 outside the foundation body 10.

[0031] The suction foundation 100 further includes a control device 60. The control device 60 is electrically connected to the first water pressure sensor 51, the second water pressure sensor 52, and the third water pressure sensor 53, and receives measured values ​​from each of the first water pressure sensor 51, the second water pressure sensor 52, and the third water pressure sensor 53. The control device 60 is electrically connected to the first drainage pump 33 and the second drainage pump 36, and sends control signals to each of the first drainage pump 33 and the second drainage pump 36. The control device 60 controls the flow rate of the first drainage unit 21 and the flow rate of the second drainage unit 22. Specifically, the control device 60 controls the rotation speed of the first drainage pump 33 and the rotation speed of the second drainage pump 36.

[0032] The control device 60 calculates the hydraulic gradient of the ground G located inside the foundation body 10 based on the measurement values ​​detected by the first water pressure sensor 51 and the second water pressure sensor 52, and controls the flow rate of the second drainage section 22 so that the calculated hydraulic gradient does not exceed a predetermined threshold. The threshold is the so-called critical hydraulic gradient, which is calculated in advance. If the hydraulic gradient exceeds the threshold, there is a risk of seepage failure of the ground G. The threshold may be a value that takes into account a safety factor for the critical hydraulic gradient.

[0033] The control device 60 may further calculate a suction pressure based on the measurement value detected by the second water pressure sensor 52 and the measurement value detected by the third water pressure sensor 53, and control the flow rate of the first drainage section 21 so that the calculated suction pressure falls within a predetermined allowable range. The allowable range is a pressure range that is necessary for penetration of the foundation body 10 and does not cause seepage failure of the ground G. The allowable range is calculated in advance.

[0034] 3 is a diagram showing a schematic hardware configuration of the control device 60. The control device 60 has a processor 61, a storage device 62, and a memory 63.

[0035] The processor 61 controls the entire control device 60. The processor 61 performs various types of arithmetic processing. For example, the processor 61 is formed of a processor such as a CPU (Central Processing Unit). The processor 61 may also be formed of an MCU (Micro Controller Unit), an MPU (Micro Processor Unit), an FPGA (Field Programmable Gate Array), a PLC (Programmable Logic Controller), a system LSI, or the like.

[0036] The memory 62 stores various programs and various data executed by the processor 61. The memory 62 is formed of a non-volatile memory, a hard disk drive (HDD), a solid state drive (SSD), etc. The various programs cause the control device 60 to realize various functions. The memory 62 stores the threshold value of the hydraulic gradient, the allowable range of the suction pressure, etc.

[0037] The memory 63 temporarily stores data, etc. For example, the memory 63 is formed of a volatile memory. The measured values ​​from each of the first water pressure sensor 51, the second water pressure sensor 52, and the third water pressure sensor 53 are saved in the storage device 62 or the memory 63.

[0038] The processor 61 calculates the hydraulic gradient of the ground G based on the measurements of the first water pressure sensor 51 and the second water pressure sensor 52, and controls the flow rate of the second drainage section 22 so that the hydraulic gradient does not exceed a threshold. The processor 61 may further calculate the suction pressure based on the measurements of the second water pressure sensor 52 and the third water pressure sensor 53, and control the flow rate of the first drainage section 21 so that the suction pressure is within an allowable range.

[0039] 4 is a block diagram showing the configuration of the control system of the processor 61. The processor 61 realizes various functions by reading a program from the storage device 62 into the memory 63 and expanding the program. In detail, the processor 61 functions as a calculator 64 that calculates the hydraulic gradient and suction pressure, and a command device 65 that commands the first drainage section 21 and the second drainage section 22 to control the flow rates of the first drainage section 21 and the second drainage section 22.

[0040] The calculator 64 acquires measurements from each of the first water pressure sensor 51 and the second water pressure sensor 52, and calculates the hydraulic gradient of the ground G based on the measurements from the first water pressure sensor 51 and the second water pressure sensor 52.

[0041] For example, the calculator 64 sends a measurement command to the first water pressure sensor 51 and the second water pressure sensor 52 for each measurement period. The measurement command is a command to cause the first water pressure sensor 51 and the second water pressure sensor 52 to measure the physical quantities corresponding to them, respectively. Furthermore, the calculator 64 sends a transmission command to the first water pressure sensor 51 and the second water pressure sensor 52 for each transmission period. The transmission command is a command to cause each of the first water pressure sensor 51 and the second water pressure sensor 52 to transmit measured values ​​to the control device 60. The calculator 64 receives measured values ​​from each of the first water pressure sensor 51 and the second water pressure sensor 52 and stores the measured values ​​in the storage device 62 or the memory 63. The calculator 64 calculates the hydraulic gradient of the ground G based on the received measured values.

[0042] The calculator 64 may further acquire measurement values ​​from each of the second water pressure sensor 52 and the third water pressure sensor 53, and calculate the suction pressure based on the measurement values ​​of the second water pressure sensor 52 and the third water pressure sensor 53.

[0043] For example, the calculator 64 receives measurement values ​​from the second water pressure sensor 52 and the third water pressure sensor 53 in the same manner as it receives measurement values ​​from the first water pressure sensor 51 and the second water pressure sensor 52, and stores the measurement values ​​in the storage device 62 or memory 63. The calculator 64 calculates the suction pressure based on the received measurement values.

[0044] The command device 65 controls the flow rate of the second drainage section 22 so that the hydraulic gradient calculated by the calculator 64 does not exceed a predetermined threshold. For example, the command device 65 compares the hydraulic gradient obtained from the calculator 64 with a threshold read from the storage device 62 or the memory 63, and sends a command signal to the second drainage pump 36 so that the hydraulic gradient does not exceed the threshold. The command signal is a signal corresponding to the rotation speed of the second drainage pump 36. The command device 65 increases the flow rate of the second drainage section 22 by increasing the rotation speed of the second drainage pump 36, and decreases the rotation speed of the second drainage pump 36 to decrease the flow rate of the second drainage section 22.

[0045] When the calculator 64 calculates the suction pressure, the command device 65 may further control the flow rate of the first drainage section 21 so that the suction pressure calculated by the calculator 64 falls within a predetermined allowable range. For example, the command device 65 compares the suction pressure acquired from the calculator 64 with the allowable range read from the storage device 62 or the memory 63, and sends a command signal to the first drainage pump 33 so that the suction pressure falls within the allowable range. The command signal is a signal corresponding to the rotation speed of the first drainage pump 33. The command device 65 increases the flow rate of the first drainage section 21 by increasing the rotation speed of the first drainage pump 33, and decreases the rotation speed of the first drainage pump 33 to decrease the flow rate of the first drainage section 21.

[0046] Next, a method for installing the suction foundation 100 in the ground G will be described. Fig. 5 is an explanatory diagram showing the suction foundation 100 before the penetration step. Fig. 6 is an explanatory diagram showing the state in which the foundation main body 10 has reached the ground G in the penetration step.

[0047] First, as shown in Figure 5, the foundation body 10 without the wind turbine 9 installed is towed to the installation site. Then, the foundation body 10 is submerged in water and penetration of the foundation body 10 into the ground G begins. More specifically, the foundation body 10 sinks to the seabed due to its own weight and ballast load. As shown in Figure 6, the lower end 19 of the side peripheral wall 12 penetrates to a certain extent into the ground G due to the own weight and ballast load of the foundation body 10.

[0048] Next, water is drained from the space inside the foundation body 10 and above the ground G, penetrating the foundation body 10 into the ground G. Specifically, by operating the first drainage pump 33, water in the internal space 15 of the foundation body 10 is forcibly drained to the outside of the foundation body 10 through the drainage holes 41 and the first water supply pipe 31. This forced drainage generates a pressure difference between the inside and outside of the foundation body 10. A penetration force due to suction pressure acts on the foundation body 10, and the side peripheral wall 12 further penetrates into the ground G. At this time, the control device 60 may calculate the suction pressure based on the measurements from the third water pressure sensor 53 and the second water pressure sensor 52, and control the flow rate of the first drainage pump 33 so that the calculated suction pressure falls within a predetermined allowable range. In this way, the foundation body 10 is penetrated into the ground G, as shown in FIG. 2 . Note that, when penetrating the foundation body 10 into the ground G, the second drainage pump 36 may also be operated in addition to the first drainage pump 33. At this time, the control device 60 may control the flow rate of the second drainage pump 36 in addition to the flow rate of the first drainage pump 33 so that the suction pressure falls within an allowable range.

[0049] Next, water is drained from the ground G located inside the foundation body 10. Specifically, as the foundation body 10 penetrates the ground G, the tip 42a of the drain pipe 42 and the first water pressure sensor 51 also penetrate into the ground G with some delay. At this time, the control device 60 calculates the hydraulic gradient of the ground G (more specifically, the hydraulic gradient of the surface layer Ga of the ground G) based on the measured values ​​from the first water pressure sensor 51 and the second water pressure sensor 52, and controls the flow rate of the second drainage pump 36 so that the calculated hydraulic gradient does not exceed a threshold value. For example, the control device 60 operates the second drainage pump 36 before the hydraulic gradient reaches the threshold value, thereby draining water from the ground G to the outside of the foundation body 10 via the drain pipe 42 and the second water supply pipe 34, lowering the hydraulic gradient and thereby reducing the occurrence of seepage failure of the ground G. When the second drainage pump 36 is operated, the control device 60 controls the flow rate of the first drainage pump 33 so that the suction pressure falls within an allowable range.

[0050] After the installation of the suction foundation 100 is completed, the wind turbine 9 is installed on the foundation body 10. More specifically, the wind turbine 9 is installed on the support 13.

[0051] Next, a method for removing the suction foundation 100 will be described. A service period is set for the suction foundation 100. After the service period has elapsed, the suction foundation 100 is removed. The suction foundation 100 is removed, for example, after the wind turbine 9 has been removed from the foundation main body 10.

[0052] In the suction foundation 100, water is supplied to the internal space 15 of the foundation body 10 by operating a water supply pump (not shown). The pressure of the water supply acts between the ceiling wall 11 and the ground G, and a force acts on the foundation body 10 in a direction that causes it to float up. This promotes the floating of the foundation body 10 from the ground G. The suction foundation 100 can be removed without vibration or noise.

[0053] Next, a description will be given of an example of a method for calculating the suction pressure and hydraulic gradient by the control device 60. Fig. 7 is an explanatory diagram illustrating the depth position of a predetermined element of the suction foundation 100 in water.

[0054] In Figure 7, the depth of the third water pressure sensor 53 and the depth of the second water pressure sensor 52 are approximately the same value Z1, the depth of the surface of the ground G is Z2, the depth of the first water pressure sensor 51 and the depth of the tip 42a of the drain pipe 42 are approximately the same value Z3, and the depth of the lower end 19 of the side peripheral wall 12 is Z4. The difference between depth Z1 and depth Z2 is h, the difference between depth Z2 and depth Z3 is α, and the difference between depth Z2 and depth Z4 is δ.

[0055] The pressure inside the foundation body 10 at a given depth z is P i(z), and the pressure of seawater outside the foundation body 10 at a predetermined depth z (hereinafter referred to as seawater pressure) is P0(z). Hereinafter, for convenience, depth Z1 will be used as the reference. That is, depth Z1 is set to 0, depth Z2 is set to h, depth Z3 is set to h+α, and depth Z4 is set to h+δ. The measurement value of the third water pressure sensor 53 is expressed as P0(0) when z=Z1=0 for seawater pressure P0(z). The measurement value of the second water pressure sensor 52 is expressed as the pressure P i (z) P when z=Z1=0 i The measurement value of the first water pressure sensor 51 is expressed as the pressure P i (z) P when z=Z3=h+α i It is expressed as (h+α).

[0056] First, the suction pressure is calculated. S is the difference between the measured value P0(0) of the third water pressure sensor 53 and the measured value P i (0) is subtracted from the suction pressure P S =P0(0)-P i (0).

[0057] Next, the hydraulic gradient is calculated in the surface layer Ga of the ground G. The surface layer Ga of the ground G is defined as the region from the surface of the ground G to the first water pressure sensor 51 and the suction port 22a. The density of seawater is defined as ρ.

[0058] The hydraulic gradient i is expressed by the following equation (1):

[0059]

number

[0060] Here, assuming that the water pressure in the ground G changes linearly, with ε = α and z = h, the hydraulic gradient i in the surface layer Ga of the ground G is expressed by the following equation (2).

[0061]

number

[0062] Next, an example of the pressure distribution during drainage in the foundation body 10 controlled by the control device 60 will be described. i 8 is a graph showing the relationship between depth z and seawater pressure P0(z) and depth z. Depths Z1, Z2, Z3, and Z4 on the vertical axis of FIG. 8 correspond to the depths Z1, Z2, Z3, and Z4 in FIG.

[0063] In FIG. 8, the solid line L1 indicates the pressure P i The dotted line L0 is a graph of the seawater pressure P0(z). The dashed line L2 is a graph of the pressure P i 8 is a graph of (z). In the comparative example, a suction foundation is used that does not have the second drainage section 22 of the present invention. In other words, in the comparative example, drainage within the foundation body is performed only through the first drainage section 21 of the present invention. Note that in FIG. 8, for convenience, the pressure of the solid line L1 and the pressure of the two-dot chain line L2 are drawn to be the same as the pressure of the dotted line L0 at depth Z4, but in reality, the pressure of the solid line L1 and the pressure of the two-dot chain line L2 become the same as the pressure of the dotted line L0 at a sufficiently deep position.

[0064] In FIG. 9, the solid line L3 indicates the limit suction pressure P sc When the pressure P i The dashed double-dashed line L4 indicates the limit suction pressure P sc As a comparative example, the pressure P inside the foundation body is generated i (z) is a graph of the limit suction pressure P sc is the suction pressure at which seepage failure of the ground occurs, and is calculated in advance based on the balance of forces. In the graph of the dashed dotted line L5, the hydraulic gradient of the ground corresponds to the critical hydraulic gradient as a threshold value. In other words, the slope of the graph between depth Z2 and depth Z4 corresponds to the critical hydraulic gradient.

[0065] As shown in Figure 8, the pressure of the solid line L1 is smaller than the pressure of the two-dot chain line L2. The reason for this is that in the suction foundation corresponding to the solid line L1, water is drained not only from the first drain section 21 but also from the second drain section 22, while in the suction foundation corresponding to the two-dot chain line L2, there is no second drain section 22 and water is drained only from the first drain section 21.

[0066] In the solid line L1, the rate of increase in pressure with respect to depth from depth Z2 to depth Z3 is smaller than the rate of increase in pressure with respect to depth from depth Z3 to depth Z4. This is because the second drainage section 22 is draining water from the ground G at depth Z3.

[0067] On the other hand, for the two-dot chain line L2, the rate of increase in pressure with respect to depth from depth Z2 to depth Z4 is constant. In other words, for the two-dot chain line L2, the slope of the pressure with respect to depth from depth Z2 to depth Z4 is constant. The reason for this is that there is no second drainage section 22, and water in the ground G cannot be drained.

[0068] As shown in Figure 9, the gradient of pressure with respect to depth from depth Z2 to depth Z3 (corresponding to the hydraulic gradient) on solid line L3 is smaller than the gradient of pressure with respect to depth from depth Z2 to depth Z3 (corresponding to the critical hydraulic gradient) on dashed-dotted line L5. In other words, on solid line L3, the hydraulic gradient in the surface layer Ga of ground G from depth Z2 to depth Z3 is smaller than the critical hydraulic gradient. This reduces the occurrence of seepage failure in the surface layer Ga of ground G.

[0069] Here, since the confining pressure of the surface layer Ga of the ground G is small, seepage failure is likely to occur in the surface layer Ga of the ground G and is likely to become the starting point of seepage failure. Therefore, by reducing the hydraulic gradient in the surface layer Ga of the ground G, where seepage failure is likely to occur and is likely to become the starting point of seepage failure, the occurrence of seepage failure in the ground G can be reduced.

[0070] The gradient of pressure with respect to depth from depth Z3 to depth Z4 (corresponding to the hydraulic gradient) on solid line L3 is greater than the gradient of pressure with respect to depth from depth Z3 to depth Z4 (corresponding to the critical hydraulic gradient) on dashed-dotted line L5. In other words, the hydraulic gradient on solid line L3 in the region deeper than the surface layer Ga of ground G from depth Z3 to depth Z4 is greater than the critical hydraulic gradient. Thus, although the hydraulic gradient in the region deeper than the surface layer Ga of ground G increases, if no seepage failure of the surface layer Ga of ground G occurs, the region deeper than the surface layer Ga of ground G is subjected to a large confining pressure due to the surface layer Ga, and the critical hydraulic gradient in the region deeper than the surface layer Ga increases. Therefore, even if the hydraulic gradient in the region deeper than the surface layer Ga of ground G is greater than the critical hydraulic gradient in that region before the foundation body 10 penetrated the ground G, the occurrence of seepage failure of the ground G can be reduced.

[0071] The suction foundation 100 described above is equipped with the first drainage section 21 and the second drainage section 22, and therefore the first drainage section 21 drains water from the space inside the foundation body 10 and above the ground G, and the second drainage section 22 drains water from the ground G located inside the foundation body 10, thereby lowering the hydraulic gradient of the ground G located inside the foundation body 10. This reduces the occurrence of seepage failure of the ground G.

[0072] Furthermore, when the first drainage section 21 drains water from the space inside the foundation body 10 and above the ground G and the foundation body 10 penetrates the ground G, the second drainage section 22 drains water from the ground G located inside the foundation body 10. This reduces the hydraulic gradient of the ground G and reduces the occurrence of seepage failure of the ground G.

[0073] In addition, the suction port 22a of the second drainage section 22 is located above the lower end 19 of the side peripheral wall 12. This reduces the hydraulic gradient in the surface layer Ga of the ground G, further reducing the occurrence of seepage failure of the ground G.

[0074] Here, because the confining pressure of the surface layer Ga of the ground G is small, the surface layer Ga of the ground G is prone to seepage failure and is also prone to become the starting point of seepage failure. Furthermore, even if the hydraulic gradient in the area deeper than the surface layer Ga of the ground G is large, if seepage failure of the surface layer Ga of the ground G does not occur, the area deeper than the surface layer Ga of the ground G will be subjected to a large confining pressure due to the surface layer Ga, and the critical hydraulic gradient of the area deeper than the surface layer Ga will increase. Therefore, by reducing the hydraulic gradient in the surface layer Ga of the ground G, the occurrence of seepage failure of the ground G can be reduced.

[0075] Furthermore, the tip 42a of the drain pipe 42 is located above the lower end 19 of the side peripheral wall 12. This reduces the hydraulic gradient in the surface layer Ga of the ground G, further reducing the occurrence of seepage failure of the ground G.

[0076] In addition, since the first water pressure sensor 51 and the second water pressure sensor 52 are provided, the hydraulic gradient of the ground G can be easily calculated using the measurement values ​​of the first water pressure sensor 51 and the second water pressure sensor 52.

[0077] Furthermore, since the first water pressure sensor 51 is located at the tip 42a of the drain pipe 42, the first water pressure sensor 51 has good responsiveness to the drainage from the drain pipe 42. This improves the responsiveness of the calculation of the hydraulic gradient.

[0078] Furthermore, since the second water pressure sensor 52 detects the water pressure inside the foundation body 10 and in the space above the ground G, the second water pressure sensor 52 can also be used to calculate the suction pressure.

[0079] Furthermore, since the control device 60 is provided, the hydraulic gradient of the ground G can be adjusted according to the situation when the suction foundation 100 penetrates the ground G. This makes it possible to further reduce the occurrence of seepage failure of the ground G.

[0080] According to the above-described ground installation method for the suction foundation 100, water is discharged from the space inside the foundation body 10 and above the ground G, and water is discharged from the ground G located inside the foundation body 10, thereby lowering the hydraulic gradient of the ground G located inside the foundation body 10. This reduces the occurrence of seepage failure of the ground G.

[0081] <<Variation>> 10 is a schematic diagram showing a modified suction foundation 200. Fig. 10 also explains the submerged depth positions of certain elements of the suction foundation 200, and corresponds to Fig. 5.

[0082] The suction foundation 200 according to the modified example differs from the suction foundation 100 in that it does not have the first drainage section 21. The following description will focus on the configuration of the suction foundation 200 that differs from the suction foundation 100. Note that in the suction foundation 200, the same reference numerals as those in the suction foundation 100 have the same configuration as the suction foundation 100, and therefore their description will be omitted.

[0083] The suction foundation 200 comprises a foundation body 10 and a drainage section 22. The foundation body 10 has a ceiling wall 11 and side peripheral walls 12 that extend downward from the ceiling wall 11 and penetrate into the ground G underwater.

[0084] Drainage section 22 is provided in foundation body 10 and drains water from inside foundation body 10. Drainage section 22 includes suction port 22a that opens inside foundation body 10 and above lower end 19 of side peripheral wall 12 and draws in water. When suction port 22a of drainage section 22 penetrates into the ground G located inside foundation body 10, drainage section 22 drains water from inside the ground G located inside foundation body 10. This generates a pressure difference (suction pressure) between the inside and outside of foundation body 10, and generates a downward seepage flow in the ground G located above suction port 22a, thereby compacting the ground G.

[0085] Specifically, the drainage section 22 has a configuration similar to the second drainage section 22 of the suction foundation 100 described above. The drainage section 22 has a drainage pipe 42. The drainage pipe 42 includes a tip 42a located inside the foundation body 10 and above the lower end 19 of the side peripheral wall 12. When the tip 42a of the drainage pipe 42 penetrates the ground G located inside the foundation body 10, the drainage section 22 drains water from the ground G located inside the foundation body 10, creating a pressure difference between the inside and outside of the foundation body 10 and generating a downward seepage flow in the surface layer Ga of the ground G, thereby compacting the surface layer Ga of the ground G. In the suction foundation 200 related to the modified example, water is drained only from the drainage section 22, thereby creating a hydraulic gradient even though the hydraulic gradient is only due to hydrostatic pressure.

[0086] The control device 60 calculates the hydraulic gradient of the ground G and controls the flow rate of the drainage section 22 so that the calculated hydraulic gradient does not exceed a predetermined threshold. Specifically, the control device 60 is electrically connected to the second drainage pump 36 and controls the rotation speed (flow rate) of the second drainage pump 36.

[0087] The control device 60 may further calculate the suction pressure and control the flow rate of the drainage section 22 so that the calculated suction pressure falls within a predetermined allowable range. Specifically, the control device 60 controls the rotation speed (flow rate) of the second drainage pump 36.

[0088] Next, a method for installing the suction foundation 200 in the ground G will be described. First, the foundation body 10 is submerged in water. Then, water from inside the foundation body 10 is discharged through the suction port 22a of the drainage section 22 provided on the foundation body 10, the foundation body 10 is penetrated into the ground G, and the suction port 22a is penetrated into the ground G located inside the foundation body 10. Then, water is discharged from the ground G located inside the foundation body 10 through the suction port 22a of the drainage section 22.

[0089] Specifically, the foundation body 10 penetrates into the ground G only by draining water from the drainage section 22. Furthermore, the drainage pipe 42 also penetrates into the ground G after a delay. At this time, the control device 60 controls the flow rate of the drainage section 22 so that the suction pressure does not exceed a threshold value. This allows the suction foundation 200 to penetrate into the ground G while compacting the surface layer Ga of the ground G and suppressing the occurrence of seepage failure of the ground G.

[0090] Next, an example of the pressure distribution during drainage in the foundation body 10 controlled by the control device 60 will be described. i 11 is a graph showing the relationship between depth z and seawater pressure P0(z) and depth z. The depths Z1, Z2, Z3, and Z4 on the vertical axis of FIG. 11 correspond to the depths Z1, Z2, Z3, and Z4 in FIG. 10. FIG. 11 corresponds to FIG. 8.

[0091] In FIG. 11, the solid line L6 indicates the pressure P i The dotted line L0 is a graph of seawater pressure P0(z). Note that in Figure 11, for convenience, the pressure of the solid line L6 is drawn to be the same as the pressure of the dotted line L0 at depth Z4, but in reality, the pressure of the solid line L6 will be the same as the pressure of the dotted line L0 at a sufficiently deep position.

[0092] 11, in the solid line L6, the pressure from depth Z2 to depth Z3 gradually decreases from depth Z2 to depth Z3. On the other hand, the pressure from depth Z3 to depth Z4 gradually increases from depth Z3 to depth Z4. In other words, a downward seepage flow occurs in the ground G (surface layer Ga) between depth Z2 and depth Z3, which allows the surface layer Ga of the ground G to be compacted and reduces the occurrence of seepage failure in the surface layer Ga of the ground G.

[0093] In other words, the hydraulic gradient in the surface layer Ga of the ground G between depths Z2 and Z3 on the solid line L7 is a negative value according to equation (2). Therefore, the hydraulic gradient is smaller than the critical hydraulic gradient (see dashed line L5 in Figure 9). This reduces the occurrence of seepage failure in the surface layer Ga of the ground G.

[0094] According to the suction foundation 200 described above, when the suction port 22a of the drainage section 22 penetrates the ground G located inside the foundation body 10, the drainage section 22 discharges water from the ground G located inside the foundation body 10, generating a pressure difference between the inside and outside of the foundation body 10 and generating a downward seepage flow in the ground G above the suction port 22a. The downward seepage flow can compact the ground G above the suction port 22a. This reduces the occurrence of seepage failure in the ground G.

[0095] According to the above-described ground installation method for the suction foundation 200, the suction port 22a of the drainage section 22 penetrates the ground G located inside the foundation body 10, and water is discharged from the ground G located inside the foundation body 10 through the suction port 22a, which generates a pressure difference between the inside and outside of the foundation body 10 and generates a downward seepage flow in the ground G located above the suction port 22a, thereby compacting the ground G. This reduces the occurrence of seepage failure in the ground G.

[0096] The description of the other configurations, actions, and effects will be omitted, but the description of the suction foundation 100 can be used to describe the suction foundation 200.

[0097] Other Embodiments As described above, the above embodiment has been described as an example of the technology disclosed in this application. However, the technology of the present disclosure is not limited to this and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. Furthermore, the components described in the above embodiment can be combined to create new embodiments. Furthermore, the components described in the accompanying drawings and detailed description may include not only components essential for solving the problem, but also components that are not essential for solving the problem in order to exemplify the technology. Therefore, the fact that these non-essential components are described in the accompanying drawings or detailed description should not be interpreted as immediately determining that these non-essential components are essential.

[0098] For example, the shape of the foundation body 10 is not limited to a substantially cylindrical shape. The foundation body 10 can be formed into any shape as long as it has a ceiling wall, peripheral side walls, and an open bottom. For example, the foundation body 10 may be formed into a rectangular tube shape with a cross section that is substantially square or pentagonal. Furthermore, the foundation body 10 may be formed into a dome shape with a curved ceiling wall.

[0099] The material of the foundation body 10 is not limited to steel plate, but may be any material, for example, concrete.

[0100] The structure installed on the suction foundation 100 is not limited to the wind turbine 9. The structure may be a wind observation tower, a caisson, or the like. The foundation body 10 does not necessarily need to be provided with the support columns 13.

[0101] The first drainage section 21 has drainage holes 41, but may have drainage pipes instead of the drainage holes 41, and the drainage pipes are provided, for example, in the ceiling wall 11 or the side peripheral wall 12. The number of first drainage sections 21 may be multiple.

[0102] The second drainage section 22 has a drainage pipe 42, but may have a drainage hole instead of the drainage pipe 42, and the drainage hole is provided, for example, in the side peripheral wall 12 and connected to the second water supply pipe 34. The number of second drainage sections 22 may be multiple.

[0103] The suction port 22a (tip 42a of the drain pipe 42) of the second drain section 22 is located above the lower end 19 of the side peripheral wall 12, but it may also be located below the lower end 19 of the side peripheral wall 12, or may be located at the same height as the lower end 19 of the side peripheral wall 12.

[0104] The suction foundation 100 has a first water pressure sensor 51, but instead of the first water pressure sensor 51, a flow rate sensor that measures the flow rate of the second drainage section 22 may be provided, and the pore water pressure of the ground G may be calculated by calculation from the measurement value of the flow rate sensor.

[0105] The suction foundation 100 has a second water pressure sensor 52, but instead of the second water pressure sensor 52, a flow rate sensor that measures the flow rate of the first drainage section 21 may be provided, and the water pressure inside the foundation body 10 may be calculated from the measurement value of the flow rate sensor.

[0106] The suction foundation 100 has a third water pressure sensor 53, but a depth sensor may be provided instead of the third water pressure sensor 53, and the water pressure outside the foundation body 10 may be calculated from the measurement value of the depth sensor.

[0107] The first water pressure sensor 51 is located at the tip 42a of the drain pipe 42, but may be located above the tip 42a of the drain pipe 42. The first water pressure sensor 51 is attached to the outer surface of the drain pipe 42, but may also be attached to the inner surface of the side peripheral wall 12. Alternatively, the first water pressure sensor 51 may be attached to the inner surface of the drain pipe 42.

[0108] The second water pressure sensor 52 is attached to the underside of the ceiling wall 11 , but may also be attached to the inner surface of the side peripheral wall 12 .

[0109] The third water pressure sensor 53 is attached to the upper surface of the ceiling wall 11, but may also be attached to the outer surface of the side peripheral wall 12.

[0110] The second water pressure sensor 52 detects the water pressure in the upper space 15a of the foundation body 10, but may also detect the pore water pressure in the ground G above the first water pressure sensor 51.

[0111] The control device 60 controls the flow rate of the second drainage section 22 so that the calculated hydraulic gradient does not exceed a predetermined threshold value, but it may also be configured to control the flow rate of the first drainage section 21 in addition to the second drainage section 22, that is, it may be configured to control the flow rate of at least the second drainage section 22 out of the first drainage section 21 and the second drainage section 22.

[0112] The suction foundation 100 uses a control device 60 to control the hydraulic gradient of the ground G, but the hydraulic gradient of the ground G may also be lowered by manual operation by an operator without using the control device 60.

[0113] [Aspect] The above-described embodiment is a specific example of the following aspects.

[0114] (Aspect 1) The suction foundation 100 comprises a foundation body 10 having a ceiling wall 11 and a side peripheral wall 12 extending downward from the ceiling wall 11 and penetrating into the underwater ground G, a first drainage section 21 provided in the foundation body 10 and discharging water from the space inside the foundation body 10 and above the ground G, and a second drainage section 22 provided in the foundation body 10 and discharging water from the ground G located inside the foundation body 10.

[0115] According to this configuration, the first drainage section 21 drains water from the space inside the foundation body 10 and above the ground G, and the second drainage section 22 drains water from the ground G located inside the foundation body 10, thereby lowering the hydraulic gradient of the ground G located inside the foundation body 10. This reduces the occurrence of seepage failure of the ground G.

[0116] (Aspect 2) In the suction foundation 100 described in aspect 1, when the first drainage section 21 drains water from the space inside the foundation body 10 and above the ground G and the foundation body 10 penetrates the ground G, the second drainage section 22 drains water from the ground G located inside the foundation body 10.

[0117] According to this configuration, the hydraulic gradient of the ground G can be lowered, thereby reducing the occurrence of seepage failure of the ground G.

[0118] (Aspect 3) In the suction foundation 100 described in aspect 1 or aspect 2, the second drainage section 22 includes an inlet 22a that penetrates into the ground G and sucks water from the ground G, and the inlet 22a of the second drainage section 22 is located above the lower end 19 of the side peripheral wall 12.

[0119] According to this configuration, the suction port 22a of the second drainage section 22 is located above the lower end 19 of the side peripheral wall 12. This reduces the hydraulic gradient in the surface layer Ga of the ground G, which is prone to seepage failure and is likely to become the starting point of seepage failure. Therefore, the occurrence of seepage failure in the ground G can be further reduced.

[0120] (Aspect 4) In the suction foundation 100 described in any one of aspects 1 to 3, the second drainage section 22 has a drainage pipe including a tip 42a that penetrates into the ground G, and the tip 42a of the drainage pipe 42 is located above the lower end 19 of the side peripheral wall 12.

[0121] According to this configuration, the tip 42a of the drain pipe 42 is located above the lower end 19 of the side peripheral wall 12. This reduces the hydraulic gradient in the surface layer Ga of the ground G, further reducing the occurrence of seepage failure of the ground G.

[0122] (Aspect 5) The suction foundation 100 described in any one of aspects 1 to 4 is provided with a first water pressure sensor 51 that detects the pore water pressure of the ground G located inside the foundation body 10, and a second water pressure sensor 52 that detects the water pressure inside the foundation body 10 and above the first water pressure sensor 51.

[0123] According to this configuration, since the first water pressure sensor 51 and the second water pressure sensor 52 are provided, the hydraulic gradient of the ground G can be easily calculated using the measurement values ​​of the first water pressure sensor 51 and the second water pressure sensor 52.

[0124] (Aspect 6) In the suction foundation 100 described in any one of aspects 1 to 5, the second drainage section 22 has a drainage pipe including a tip 42a that penetrates into the ground G, the tip 42a of the drainage pipe 42 is located above the lower end 19 of the side wall 12, and the first water pressure sensor 51 is located at the tip 42a of the drainage pipe 42.

[0125] According to this configuration, the first water pressure sensor 51 is located at the tip 42a of the drain pipe 42, which improves the responsiveness of the first water pressure sensor 51 to the drainage from the drain pipe 42. This improves the responsiveness of the calculation of the hydraulic gradient.

[0126] (Aspect 7) In the suction foundation 100 according to any one of the first to sixth aspects, the second water pressure sensor 52 detects the water pressure inside the foundation body 10 and in the space above the ground G.

[0127] According to this configuration, the second water pressure sensor 52 detects the water pressure inside the foundation body 10 and in the space above the ground G, and therefore the second water pressure sensor 52 can also be used to calculate the suction pressure.

[0128] (Aspect 8) The suction foundation 100 described in any one of aspects 1 to 7 further includes a control device 60 that calculates the hydraulic gradient of the ground G located inside the foundation body 10 based on the measurement value detected by the first water pressure sensor 51 and the measurement value detected by the second water pressure sensor 52, and controls the flow rate of at least the second drainage section 22 out of the first drainage section 21 and the second drainage section 22 so that the calculated hydraulic gradient does not exceed a predetermined threshold value.

[0129] According to this configuration, since the control device 60 is provided, the hydraulic gradient of the ground G can be adjusted according to the situation when the suction foundation 100 penetrates the ground G. This makes it possible to further reduce the occurrence of seepage failure of the ground G.

[0130] (Aspect 9) The suction foundation 200 comprises a foundation body 10 having a ceiling wall 11 and side walls 12 extending downward from the ceiling wall 11 and penetrating into the underwater ground G, and a drainage section 22 provided on the foundation body 10 to discharge water from inside the foundation body 10, the drainage section 22 including an inlet 22a that opens inside the foundation body 10 and above the lower end 19 of the side walls 12 to draw in water, and when the inlet 22a of the drainage section 22 is penetrated into the ground G located inside the foundation body 10, the drainage section 22 discharges water from the ground G located inside the foundation body 10.

[0131] According to this configuration, with suction port 22a of drainage section 22 penetrated into the ground G located inside foundation body 10, drainage section 22 discharges water from the ground G located inside foundation body 10, thereby generating a pressure difference between the inside and outside of foundation body 10 and generating a downward seepage flow in the ground G above suction port 22a, thereby compacting the ground G above suction port 22a. Therefore, the occurrence of seepage failure of the ground G can be reduced.

[0132] (Aspect 10) The ground installation method for a suction foundation 100 is a method for installing a suction foundation 100, which comprises a foundation body 10 having a ceiling wall 11 and side peripheral walls 12 extending downward from the ceiling wall 11 and penetrating into the underwater ground G, on underwater ground G, and includes submerging the foundation body 10 in the water, discharging water from the space inside the foundation body 10 and above the ground G to penetrate the foundation body 10 into the ground G, and discharging water from the ground G located inside the foundation body 10.

[0133] According to this configuration, water is discharged from the space inside the foundation body 10 and above the ground G, and water is discharged from the ground G located inside the foundation body 10, so it is possible to lower the hydraulic gradient of the ground G located inside the foundation body 10. This makes it possible to reduce the occurrence of seepage failure of the ground G.

[0134] (Aspect 11) The ground installation method for the suction foundation 200 is a method for installing a suction foundation 200, which comprises a foundation body 10 having a ceiling wall 11 and side walls 12 extending downward from the ceiling wall 11 and penetrating into the underwater ground G, on underwater ground G, and includes submerging the foundation body 10 in the water, discharging water from inside the foundation body 10 through the suction port 22a of the drainage section 22 provided on the foundation body 10, penetrating the foundation body 10 into the ground G, penetrating the suction port 22a into the ground G located inside the foundation body 10, and discharging water from the ground G located inside the foundation body 10 through the suction port 22a.

[0135] According to this configuration, suction port 22a of drainage section 22 penetrates into the ground G located inside foundation body 10, and water is discharged from the ground G located inside foundation body 10 through suction port 22a, which generates a pressure difference between the inside and outside of foundation body 10 and also generates a downward seepage flow in the ground G located above suction port 22a, thereby compacting the ground G. Therefore, the occurrence of seepage failure of the ground G can be reduced. [Explanation of symbols]

[0136] 100,200 Suction base 10 Base body 11 Ceiling Wall 12 Side walls 19 Bottom end 21 1st drainage section 22 2nd drainage section 22a Intake port 42 Drain pipe 42a tip 51 First water pressure sensor 52 Second water pressure sensor 60 Control device G Ground Ga surface layer

Claims

1. a foundation body having a ceiling wall and a side peripheral wall extending downward from the ceiling wall and penetrating into the underwater ground; A first drainage section provided in the foundation body to drain water from inside the foundation body and from a space above the ground; A suction foundation comprising a second drainage section provided on the foundation body and configured to drain water from the ground located inside the foundation body.

2. The suction foundation according to claim 1, A suction foundation in which the first drainage section drains water from the space inside the foundation body and above the ground, and when the foundation body is penetrated into the ground, the second drainage section drains water from the ground located inside the foundation body.

3. The suction foundation according to claim 1, The second drainage section includes an inlet that penetrates the ground and sucks water from the ground, A suction foundation in which the suction port of the second drainage section is located above the lower end of the side peripheral wall.

4. The suction foundation according to claim 1, The second drainage section has a drainage pipe including a tip that penetrates the ground, A suction foundation in which the tip of the drain pipe is located above the lower end of the side wall.

5. The suction foundation according to claim 1, A first water pressure sensor located inside the foundation body for detecting pore water pressure of the ground; A suction foundation comprising a second water pressure sensor that detects water pressure inside the foundation body and above the first water pressure sensor.

6. The suction foundation according to claim 5, The second drainage section has a drainage pipe including a tip that penetrates the ground, The tip of the drain pipe is located above the lower end of the side peripheral wall, The first water pressure sensor is a suction foundation located at the tip of the drain pipe.

7. The suction foundation according to claim 5, The second water pressure sensor is a suction foundation that detects water pressure inside the foundation body and in the space above the ground.

8. The suction foundation according to any one of claims 5 to 7, A suction foundation further comprising a control device that calculates the hydraulic gradient of the ground located inside the foundation body based on the measurement values ​​detected by the first water pressure sensor and the measurement values ​​detected by the second water pressure sensor, and controls the flow rate of at least the second drainage section of the first drainage section and the second drainage section so that the calculated hydraulic gradient does not exceed a predetermined threshold.

9. a foundation body having a ceiling wall and a side peripheral wall extending downward from the ceiling wall and penetrating into the underwater ground; a drainage section provided on the foundation body to drain water from inside the foundation body, The drainage section includes an intake port that opens inside the foundation body and above the lower end of the side peripheral wall to draw in water, A suction foundation in which the drainage section discharges water from the ground located inside the foundation body when the suction port of the drainage section penetrates into the ground located inside the foundation body.

10. A method for installing a suction foundation on underwater ground, the method comprising: a foundation body having a ceiling wall and a side wall extending downward from the ceiling wall and penetrating into the underwater ground; Submerging the foundation body in the water; Draining water from a space inside the foundation body and above the ground to penetrate the foundation body into the ground; A ground installation method for a suction foundation, comprising draining water from the ground located inside the foundation body.

11. A method for installing a suction foundation on underwater ground, the method comprising: a foundation body having a ceiling wall and a side wall extending downward from the ceiling wall and penetrating into the underwater ground; Submerging the foundation body in the water; Discharge water from inside the foundation body through an inlet of a drainage section provided in the foundation body, penetrate the foundation body into the ground, and penetrate the inlet into the ground located inside the foundation body; A ground installation method for a suction foundation, comprising discharging water from the ground located inside the foundation body through the suction port.

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