JP2008019562A - Construction method of countermeasure against liquefaction under breakwater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a construction method of countermeasures against liquefaction under a breakwater caused by chemical grouting which enables construction to be inexpensively performed in a short period of time, and can effectively prevent the occurrence of a liquefaction phenomenon. <P>SOLUTION: A rubble-mound 11 is created on a sandy soil layer 10 on the bottom of the sea. The breakwater is constituted by installing a concrete dam body 12 on the rubble-mound 11. Under the breakwater, a horizontal soil-improving layer A like a board with a desired thickness is created in a section ranging from the top surface of a sandy soil layer 10 immediately below the dam body 12 to a desired depth. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a breakwater that prevents the breakwater function from being impaired by reducing the breakwater subsidence or collapse due to liquefaction of the ground under the breakwater built on the sandy ground of the seabed. It relates to the following liquefaction countermeasure method.

  In general, breakwaters such as jetties and offshore dikes are constructed on the ground so as to secure a supporting force that does not cause sliding and overturning against external forces such as waves.

  Conventionally, the sandy ground under and supporting the breakwater is a replacement sandy soil in which the original ground made of clay soil is replaced with sand, or the ground is against a wave or other external force. In some cases, it is sandy soil having a supporting force that does not cause sliding or falling.

  However, even in sandy ground that has sufficient support for external forces such as waves, it is assumed that the support will be lost due to the liquefaction phenomenon at the time of the earthquake and the breakwater will sink. When a liquefaction phenomenon occurs due to an earthquake, a volume change occurs in the sandy soil layer, and the dam body is expected to sink, tilt, or in some cases collapse.

  If the levee body sinks or tilts more than a certain level, the wave blocking function is impaired, the amount of overtopping to the inside of the port increases, and the calmness within the port cannot be ensured. In addition, when a tsunami comes after an earthquake, the amount of overtopping of the tsunami increases, and there is a problem that the function to stop flooding damage to the land on the back is impaired.

  Conventionally, as a countermeasure for liquefaction when building a breakwater on such sandy ground, there is a sand compaction pile method (for example, Patent Documents 1 and 2). As shown in FIG. 21, before construction of the breakwater, an improved ground 2 is created in the sandy soil layer 1 below the ground so that liquefaction can be prevented by a ground improvement method such as creation of a sand compaction pile. This is a method in which a rubble mound 3 is created on top of which a concrete dam body 4 made of concrete caisson or cast-in-place concrete is installed.

  Further, as a countermeasure against liquefaction for the existing breakwater, there is a raising method as shown in FIG. This is to raise the height just above the levee body 4 from the static water surface to the required height, and build the raised portion 5 on the dam body 4 with cast-in-place concrete to ensure stability against sliding and falling of the dam body. In order to do so, it is widened as necessary to ensure weight.

Furthermore, in order to ensure stability against the sliding and falling of the levee body as well as the widening of the levee body, a required amount of stone of about 1 to 70 kg / piece is put inside the breakwater port to create the backfilling stone portion 6.
JP-A-8-27759 JP 7-207653 A

  In the conventional construction of the new breakwater described above, the method of applying ground improvement by creating a sand compaction pile in the sandy soil layer under the breakwater increases the construction cost, because the ground improvement range is wide, There is a problem that the construction period becomes longer.

  Moreover, the raising method for the existing breakwater cannot prevent liquefaction of the sandy soil layer itself, and when the liquefaction phenomenon occurs, the levee body undergoes considerable subsidence, and the breakwater normal is not straight. There is a risk that the function as a breakwater cannot be fully achieved.

  In addition, as the expected height of the tsunami increases, it is necessary to increase the dam body width by a considerable amount in order to prevent sliding and falling over the wave force. Similarly, in order to ensure stability against sliding, the amount of lining stones inside the port must be increased, and when raising the height, the cost increases accordingly, and the sand under the breakwater There is a problem that the weight applied to the soil layer increases, which may cause settlement.

  In view of the conventional problems as described above, the present invention can be applied in a short period of time at low cost regardless of whether it is applied to any existing or new breakwater, and the settlement of the levee body due to liquefaction phenomenon It was made for the purpose of providing a liquefaction countermeasure method under a breakwater that can effectively prevent the dam.

  The feature of the invention described in claim 1 for solving the conventional problems as described above and achieving the intended purpose is that a rubble mound is formed on a sandy soil layer on the seabed, and concrete is formed on the rubble mound. A liquefaction countermeasure construction method under a breakwater constructed by installing a dam body made of a chemical solution for ground improvement or a portion extending from the surface of the sandy soil layer directly under the dam body to a desired depth By injecting a cement-based solidifying material, a horizontal ground improvement layer having a disk shape with a desired thickness that does not cause a liquefaction phenomenon is created.

  A feature of the invention described in claim 2 is that, in addition to the structure of claim 1, the chemical solution uses a water glass-based, special silica-based or polymer-based chemical solution for ground improvement.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect, the breakwater is a newly installed breakwater, and the sandy ground that is under the breakwater before the rubble mound is formed has the plate shape. It is to create a horizontal ground improvement layer.

  According to a fourth aspect of the present invention, in addition to the configuration of the first or second aspect, the breakwater is an existing breakwater, and the ground is formed in a sandy soil layer under the existing breakwater. The purpose is to create an improved layer.

  The invention according to claim 5 is characterized in that, in addition to the structure of claims 1 to 3 or 4 above, a horizontal ground improvement layer having the plate shape is formed immediately below the bank body, and both front and rear edges of the bank body A pair of impermeable or hardly permeable underground walls is created in the sandy soil layer slightly below the outer side along the part.

  A feature of the invention described in claim 6 is that, in addition to the structure of claim 5, the pair of impermeable or hardly permeable underground walls are provided in the sandy soil layer with a chemical solution for ground improvement or It is to create by injecting cement-based solidifying material.

  According to a seventh aspect of the present invention, in addition to the structure of the fifth aspect, the pair of impermeable or hardly permeable underground walls are formed by placing a sheet pile in the sandy soil layer. It is to create.

  In the present invention, a rubble mound is formed on a sandy soil layer on the seabed, and a desired dam is formed from the surface of the sandy ground directly under the breakwater of the breakwater constructed by installing a concrete dam on the rubble mound. If a horizontal ground improvement layer with a desired thickness that does not cause liquefaction phenomenon is created by injecting a chemical solution or cement-based solidifying material for soil improvement into the depth part, The liquefaction phenomenon occurs in the sandy soil layer that is not ground improved under the horizontal ground improvement layer, but the liquefaction phenomenon does not occur in the horizontal ground improvement layer in the shape of a plate directly under the bank.

  The amount of subsidence that occurs when the liquefaction phenomenon occurs in the ground where the liquefaction phenomenon occurs, that is, the structure on the liquefiable ground, is proportional to the thickness of the liquefiable ground under the structure. Therefore, by creating a horizontal ground improvement layer that does not cause liquefaction in the sandy soil layer, which is the liquefiable ground directly under the dam body, as described above, the thickness of the liquefiable ground is increased accordingly. Therefore, the amount of subsidence at the time of occurrence of liquefaction due to the earthquake will decrease corresponding to the thickness of the horizontal ground improvement layer.

  Therefore, by calculating the ratio of the thickness of the horizontal ground improvement layer in the form of a plate to the sandy soil layer so that the subsidence caused by liquefaction is less than the allowable subsidence amount of the breakwater, the necessary thickness is calculated. By creating the horizontal ground improvement layer, it is possible to maintain the necessary functions of the breakwater even in the event of an earthquake.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a cross section of a breakwater according to the first embodiment in which countermeasures against liquefaction have been taken according to the present invention and the ground below it. In the figure, reference numeral 10 indicates a sandy soil layer when the original ground under the breakwater is sandy soil, and 11 indicates a rubble for foundations having a weight of about 10 to 200 kg / piece thereon. The created rubble mound 12 is a dam body made of concrete caisson or cast-in-place concrete placed on the rubble mound 11.

  The upper surface of the rubble mound 11 is covered with a covering stone 13 having a weight of about 1 t / piece except for the bottom of the dam body 12, and the solid stone 14 is stacked before and after the root portion of the dam body 12. ing.

  The liquefaction countermeasure in the present invention is a horizontal plate having a desired thickness by injecting a chemical solution for improving the ground into a portion from the surface of the sandy soil layer 10 immediately below the dam body 12 to a desired depth. This is done by creating a ground improvement layer A.

  In this horizontal ground improvement layer A, a permanent water glass type, special silica type or polymer type chemical solution is infiltrated into the sandy soil layer 10 or cement slurry is injected and mixed into the sandy soil layer 10. The horizontal ground improvement layer A has a structure in which liquefaction does not occur when an earthquake occurs.

  Next, when a breakwater is newly installed on the sandy soil layer 10, an example in which the liquefaction countermeasure of the first embodiment shown in FIG.

  FIG. 2 shows the construction flow. In the laying sand work in the construction flow, the laying sand 30 is laid on the sandy soil layer 10 where the horizontal ground improvement layer A is to be created. The laying sand 30 is laid to prevent the chemical liquid injected into the ground from flowing into the water in order to create the horizontal ground improvement layer A, and has a thickness of about 1.0 m.

  As shown in Fig. 3, the sand-laying work is conventionally used, such as using a bottom-open type earth-moving ship 31 and putting it directly by opening the bottom or using a grab bucket with a self-propelled carrier ship with a grab. It is carried out by the existing sanding method.

  After carrying out the laying sand work in this way, a chemical solution injection work for creating the horizontal ground improvement layer A is performed. This chemical injection is performed by a method similar to that used in the osmosis solidification processing method used on land, and as shown in FIG. 4, a drilling machine 41 mounted on a work table ship 40 is used. To do.

  As shown in FIG. 5, this work table ship 40 is supported on the bottom of the water by raising and lowering the support column 40a, and is fixed at an accurate position and height without being affected by tides and waves. It is preferable to use one that can perform the operation.

  Next, a procedure for injecting the chemical solution will be described.

  First, as shown in FIG. 6, drilling is performed by a drilling machine 41. This drilling is performed until the depth of the horizontal ground improvement layer A to be created is reached while discharging the earth and sand while adding the hollow cylindrical casing 42.

  After this drilling operation is completed, the casing 42 is extracted, and an outer tube 45 for injecting a chemical solution is inserted into the hole 43 after the extraction. As shown in FIG. 7A, the outer tube 45 is formed with chemical liquid discharge holes 46, 46... At predetermined intervals in the longitudinal direction, and the vertical positions of the chemical liquid discharge holes 46. Cloth sleeves 47, 47,...

  Next, a slurry-like cement bentonite 48 is injected into each cloth sleeve 47 from within 45, and the cloth sleeve 47 is inflated to be integrated with the ground on the inner surface of the drilling hole. The cement bentonite 48 is injected by using a cement bentonite injection hose 49 as shown in FIG. The cement bentonite injecting hose 49 is provided with a cement bentonite discharge hole 50 on the side surface of the lower end portion, and packers 51 and 51 made of rubber-like elastic material are fixed to the upper and lower outer surfaces thereof. By injecting and expanding water, the inner surface of the outer tube is pressed against the inner surface of the outer tube, and the gap between the upper and lower outer tube surfaces is closed, so that the cement bentonite 48 from the discharge hole 50 becomes the cement bentonite injection hole of the outer tube 45. The cloth sleeve 47 is filled through 47a.

  In this way, the cement bentonite injection operation into the fabric sleeve 47 is performed on all the fabric sleeves 47 by stepping up in order from the lower end.

  Cement bentonite 48 is injected, and after the solidification curing, a chemical solution injection operation is performed. This chemical injection operation is performed by inserting a chemical injection hose 55 into the outer tube 45 as shown in FIG. The chemical solution injection hose 55 has a chemical solution discharge hole 56 on the outer periphery of the tip end thereof, and fixed to the upper and lower outer peripheries of packers 57 and 57 similar to those described above by water injection, and this packer 57 is expanded. By closing the inner pipe gap above and below the chemical solution discharge hole 46 of the outer tube 45 and discharging the chemical solution at a high pressure from the chemical solution discharge hole 56, the chemical solution penetrates into the sandy ground from the chemical solution discharge hole 46 of the outer tube 45. The spherical chemical solution permeation part 60 is formed.

  In this way, as shown in FIG. 9, the spherical chemical liquid permeation portions 60 are sequentially formed from the lower end of the outer tube 45 while overlapping each other. This series of operations is sequentially repeated over the entire area where the horizontal ground improvement layer is scheduled to be formed, thereby creating the horizontal ground improvement layer A having a desired thickness and width.

  After creating a horizontal ground improvement layer A having a desired thickness from the surface of the sandy soil layer 10, the ground sand removal work is performed. This sand removal work is due to the fact that the sand is not sufficiently improved with chemicals and its physical properties are inhomogeneous, and it is deemed inappropriate to use materials with inhomogeneous physical properties as a basis. To implement. In addition, when it is judged that the material of the ground sand and the uplifted soil near the surface layer is homogeneous and suitable for use as a foundation, it will not be removed.

  Next, as shown in FIG. 1, a rubble mound 11 is formed by a method similar to the conventional method, and a bank body 12 is installed thereon.

  Next, an example in which the present invention is applied to the liquefaction countermeasure of the first embodiment shown in FIG. 1 by injecting a chemical solution into a sandy soil layer under an existing breakwater will be described. In this example, a bending hole drilling device 70 similar to the device used in the permeation solidification processing method used on land is used.

  As shown in FIG. 10, the curved hole drilling device 70 is mounted on a work table boat 40 similar to the above-described embodiment, and is separated from the tip of the rubble mound 11 constituting the breakwater from a position required. Then, a hole is drilled in the sandy soil layer 10 below the rubble mound 11 obliquely from the bottom of the sea, and a work hole 71 for injecting a chemical solution is drilled horizontally below the dam body 12.

  In this drilling operation, as shown in FIG. 11, a sheath tube 72 is used to prevent the work hole 71 from collapsing, and a drilling rod 74 having a drilling blade 73 fixed at the tip is inserted between the sheaths 72. In addition, the sheath pipe 72 is pushed out while drilling with the drilling blade 73 in advance, and the drilling is advanced while the inner surface of the work hole 71 is covered with the sheath pipe 72.

  A gyroscope (not shown) for detecting the position and a bending sensor 75 for detecting bending in the vertical and horizontal directions are provided at the tip of the drilling rod 74, and a drilling blade 73 is fixed to the tip of the bending sensor 75. Has been. The drilling blade 73 has an inclined surface 73a for determining the traveling direction on one side of the tip, and a jet water spray nozzle 76 at the tip.

  Although not shown in the drawing, the drilling rod 74 is provided with a drilling water supply path and a drilling water return path for returning the drilling water containing the drilling earth and sand. From the drilling water supply path, high-pressure water for drilling is provided. Is drilled into the front ground by jetting drilling water from the nozzle at the tip of the drilling blade 73, and drilling water containing the excavated earth and sand is returned to the work ship through the drilling rod. It is supposed to be.

  In addition, the drilling hole is straightly advanced by advancing the drilling blade 73 while rotating the drilling rod 74, and the drilling blade 73 is inclined by moving forward with the rotation of the drilling rod 74 stopped. Curved holes are cut by the surface.

  Further, a drilling position is calculated by a computer on the ship based on information from the gyroscope and the bending sensor 75, and a desired curve is drilled.

  In this way, after forming the working hole 71 whose inner surface is covered with the sheath tube 72, the drilling rod 74 is removed leaving the drilling blade 73 at the tip in the ground.

  Next, the chemical solution injection hose 80 is inserted into the sheath tube 72 from which the drilling rod 74 has been removed. As shown in FIG. 12, the chemical solution injection hose 80 is provided with packers 82 and 82 which are expanded by injecting water at a distal end portion, and a chemical solution discharge nozzle 81 is opened between the packers 82 and 82. The chemical injection hose 80 is provided with a water injection path for injecting water into both packers under pressure and a liquid injection path for supplying the chemical liquid.

  This chemical solution injection hose 80 is inserted to the distal end portion of the sheath tube 72, and only the sheath tube 72 is pulled out to a position where both the packers 82 and 82 protrude from the distal end of the sheath tube. Thereafter, water is poured into the packers 82 and 82, and the outer peripheral surface is pressed against the ground surface of the work hole 71. In this state, the chemical solution is discharged from the chemical solution discharge nozzle 81 at a high pressure, so that the chemical solution is injected from the ground surface between the packers 82 and 82 into the surrounding ground and penetrates into the soil gap of the surrounding ground. After the injection operation at one place is completed in this way, the inside of the packers 82 and 82 is decompressed and contracted, and the next injection operation place is pulled out together with the sheath tube 72, and the same chemical solution injection operation is sequentially repeated.

  The above-described chemical solution injection operation is sequentially repeated to form a number of work holes 71 in the planned horizontal ground improvement layer formation region with a space in the vertical and horizontal directions, and each work hole is required to have a space in the axial direction. The chemical solution injection operation is performed at several places, and the planned horizontal ground improvement is performed by overlapping the spherical chemical solution infiltration portions 60 at each chemical solution injection operation position as shown in FIG. Layer A is created.

  In the above-described chemical solution injection method, while pulling out the sheath tube, both packers are pressed against the ground surface of the work hole to inject the chemical solution. There are various conventionally used injection methods such as a method of forming a through hole for injecting a chemical solution, pressing both packers against the inner surface of the sheath tube, and injecting the chemical solution into the natural ground through the injection hole of the sheath tube. Can be used.

  Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 13 shows a cross section of the breakwater and the ground below it that have been liquefied according to this embodiment. In the figure, the same parts as those in the above-described embodiment are denoted by the same reference numerals, and redundant description thereof is omitted.

  In this example, a plate-like horizontal ground improvement layer A is created directly under the above-mentioned dam body, and a pair of underground walls B, B by ground improvement at a height reaching the bottom of the sandy soil layer 10 is formed on both sides thereof. It was created and the ground was improved with a gate-shaped cross section.

  The underground walls B and B have a higher rigidity than the surrounding sandy soil layer by mixing the sandy soil layer 10 with a cement-based fluidized solidifying material such as cement slurry to improve the ground. It is an impermeable or hardly permeable wall.

  In addition, this underground wall B uses the permeation solidification processing equipment shown in FIG. 4 described above, and permeates a permanent water glass-based, special silica-based or polymer-based chemical into the sandy soil layer 10. You may build it by.

  The greater the thickness of the underground wall, the greater the effect of suppressing shear deformation and the more the subsidence of the dam body during an earthquake is suppressed. However, considering the necessary subsidence suppression effect, economic efficiency and workability, 1 About 0.0-3.0 m is preferable.

  First, the case where construction is performed in the construction of a new breakwater will be described. After completion of the laying sand work in the first embodiment described above, a plate-like horizontal ground improvement layer A is formed by chemical injection, or at the same time. The underground walls B and B are formed by adding and mixing cement-based solidified material into the sandy ground.

  For the construction, a device similar to a ground improvement device for injecting and mixing a solidified material to a soft ground at the bottom of the water can be used. As shown in FIG. 14, this apparatus includes a rotating shaft 22 integrally provided with an auger 21 on the outer periphery in a parallel arrangement, and a plurality of stirring blades 23 project from the outer periphery of the lower end of each rotating shaft. The agitating blade 23 is provided with a solidifying material discharge nozzle (not shown) so that the solidifying material can be discharged from the nozzle through the rotating shaft 22 and the rotating shaft 22 rotates the rotating shaft 22 at the upper end. A ground improvement machine 20 having 24 is provided.

  As shown in FIG. 15A, the ground improvement machine 20 is installed so as to be vertically movable along a leader 26 standing on the deep mixing treatment ship 25, and the ground improvement machine 20 is connected to the bottom of the water from the deep mixing treatment ship 25. It can be moved up and down toward.

  Then, after inserting the ground improvement machine 20 while rotating it to the bottom of the sandy soil layer 10, it is rotated while being pulled up, and at the same time, the solidified material is discharged from the nozzle of the stirring blade 23, thereby as shown in FIG. 15 (a). A columnar body 20a in which a solidifying material is mixed into the sandy earth and sand of the sandy earth layer 10 is formed.

  In this way, the operation of injecting the solidifying material into the sandy soil layer 10 and forming the columnar body 20a with the side portions integrated with each other is repeated to form a continuous underground wall B.

  Thus, after extending a pair of underground wall B and B in order in the horizontal direction one by one in parallel arrangement | positioning, the covering sand 30 is removed as needed, and as shown in FIG. The rubble mound 11 is formed by the above, and the levee body 12 is installed thereon.

  Next, the case where the liquefaction countermeasure of 2nd Example is constructed with respect to the existing breakwater is demonstrated.

  The horizontal ground improvement layer A immediately below the dam body 12 is formed in the same manner as the construction for the existing breakwater in the first embodiment described above. The underground walls B and B are created in parallel with or before and after this.

  In this case, the underground walls B, B are formed continuously in the sandy soil layer 10 at the outer position avoiding the position of the stone 6 in the direction along the edge of the dam body 12. The underground walls B and B are created using the same ground improvement machine 20 as described in the construction at the time of construction on the new breakwater described above.

  In creating the underground wall B, first, a ground improvement machine insertion portion 27 for allowing the ground improvement machine 20 to be inserted into the sandy soil layer 10 under the rubble mound 11 as shown in FIG. Form. This ground improvement machine insertion part 27 temporarily removes a part of the foundation rubble to form a window hole on the front and back of the rubble mound, and it may be possible to remove the rubble by operating the work machine by a diver. Although not shown in the figure, it may be formed by cutting into a cylindrical shape using a cutting machine using a core cutter.

  In this way, the ground improvement machine insertion part 27 is formed to have an insertion width of one to several times of the ground improvement machine 20, and the ground improvement machine 20 is passed through the ground improvement machine insertion part 27 as shown in FIG. After inserting while rotating to the bottom of the sandy soil layer 10, the solidifying material is discharged from the nozzle of the stirring blade 23 at the same time as it is pulled up, thereby mixing the solidifying material into the sandy soil of the sandy soil layer 10. The columnar body 20a is formed.

  After the columnar body 20a is created in this manner, as shown in FIG. 16 (c), the foundation rubble is returned to the ground improvement machine insertion portion 27 to restore the rubble mound to its original state. By repeating this process, as shown in FIG. 15 (b), a plurality of column states 20a, 20a,...

  It is to be noted that the formed ground good machine insertion portion 27 is filled with backfilling sand, and the mixing of the solidified material by the ground improvement machine 20 is continued to the backfilled sand after the mixing of the solidified material into the sandy soil layer 10. In this case, the ground improvement machine insertion portion 27 is filled with the underground wall B as shown in FIG.

  In the above-described embodiment, a pair of underground walls are formed by mixing cement-based solidified material in the sandy soil of the sandy soil layer. Alternatively, the underground wall which is impermeable or hardly permeable may be formed.

  When the sheet pile is placed, the sheet pile placement portion is formed by removing the rubble of the rubble mound at the placement position, as in the above-described embodiment. When removing rubble, it may be removed one by one or by cutting using a cutting machine. Moreover, the sheet pile to use can use steel sheet piles, steel pipe sheet piles, etc. other than concrete sheet piles.

  In the above-described embodiment, the raw ground is sandy ground, and the countermeasure for liquefaction under the breakwater built on the sandy soil layer 10 has been described. However, as shown in FIGS. In the case of the soft base ground 90 having a small supporting force (N value) made of soil, it is built on a sandy soil layer 10a composed of so-called replacement sand in which a part of the base ground is replaced with sand. As a countermeasure against liquefaction under the breakwater, construction may be performed in the same manner as described above. 18 shows a case where the embodiment shown in FIG. 1 is performed, and FIG. 19 shows a case where the embodiment is executed similarly to the embodiment shown in FIG. The same parts as those in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

Confirmation of effect Next, confirmation of the effect of the liquefaction countermeasure method of the present invention by an earthquake response analysis by the finite element method will be described. In this analysis, the structure for the analysis was modeled, the material constants for the modeling were set, and the seismic response was calculated by selecting the input ground motion (maximum amplitude, waveform). As analysis results, horizontal and vertical maximums and residual displacements are calculated.
a. Outline of numerical analysis Outline diagram of numerical analysis: FIG.
Target structure: Breakwater (width B = 15.0m)
Liquefaction target layer thickness (sandy soil layer thickness): H = about 20m Input seismic motion: Hachinohe basement incident waveform calculated from records obtained at Hachinohe Port during the 1968 Tokachi-oki earthquake. Maximum acceleration 400gal
Liquefaction countermeasure 1: Installation of horizontal ground improvement layer of the first embodiment only Liquefaction countermeasure 2: Horizontal ground improvement layer of the first embodiment and underground wall of the second embodiment in combination Horizontal ground improvement layer thickness: D = 6.5 m, 2 types of D = 3.5 m Underground wall thickness: 1 type of L = 1.5 m b. Study Cases Four cases as shown in Table 1 were used.

c. Analysis results Table 2 shows the calculation results of the subsidence amount when the bank remains.

  As described above, the method of the present invention can suppress the subsidence amount to about 0.22 and 0.40 when only the horizontal ground improvement layer is formed, compared with the case where no countermeasure work is performed, and the horizontal ground. When both the improved layer and the underground wall were constructed, the amount of subsidence could be suppressed to about 0.17.

  From this result, it was confirmed that the measures according to the present invention exerted a great effect compared to the case where only the horizontal ground improvement layer and the combination of this and the underground wall were not taken. In addition, when only the horizontal ground improvement layer is provided, it has been found that if the ratio of the horizontal ground improvement layer thickness to the sandy soil layer thickness is 20: 3.5 or more, a sufficient settlement suppression effect can be obtained.

  In addition, the case 3 using the horizontal ground improvement layer and the underground wall in combination may be lower in cost than the case 2 using only the horizontal ground improvement layer having a large thickness, and the horizontal ground improvement layer and the underground wall The effect of liquefaction countermeasures to improve the ground on the cross-sectional gate type using both and is great.

It is a longitudinal cross-sectional view which shows an example of the breakwater which applied the countermeasure against liquefaction of 1st Example of this invention, and the ground under it. It is a flowchart which shows an example which constructs 1st Example shown in FIG. 1 before construction of a new breakwater. It is sectional drawing which shows a laying sand work same as the above. It is sectional drawing which shows schematic structure of a chemical | medical solution injection work same as the above. It is sectional drawing which shows the case where the chemical | medical solution injection | pouring work same as the above is performed with a raising / lowering type work boat. It is sectional drawing which shows the drilling process in a chemical | medical solution injection | pouring work same as the above. (A) is sectional drawing which shows the outer tube insertion state in the drilling hole in the chemical | medical solution injection | pouring work same as the above, (b) is sectional drawing which shows the outer tube fixing state in the drilling hole. It is sectional drawing which shows the chemical | medical solution injection | pouring state in a chemical | medical solution injection | pouring work same as the above. It is sectional drawing which shows the chemical | medical solution penetration state in a chemical | medical solution injection | pouring work same as the above. FIG. 2 is a cross-sectional view showing an outline of a curved hole used for construction under an existing breakwater according to the first embodiment shown in FIG. It is sectional drawing which shows the drilling state by the bending drilling apparatus same as the above. It is sectional drawing which shows the chemical | medical solution injection | pouring state by a chemical | medical solution injection hose same as the above. It is a longitudinal cross-sectional view which shows an example of the breakwater which applied the countermeasure against liquefaction of 2nd Example of this invention, and the ground under it. It is a front view which shows an example of the ground improvement machine used for the liquefaction countermeasure of 2nd Example. (A) Longitudinal sectional view showing a state where the ground improvement machine of FIG. 14 is installed on a work boat and the present invention construction method is being constructed before construction of a new breakwater, (b) shows the underground wall to be created It is a cross-sectional view. (A)-(c) is schematic sectional drawing explaining the construction process in the case of constructing 2nd Example under the existing breakwater. It is sectional drawing which shows the other example of the formation method of the ground improvement machine insertion part shown to FIG. FIG. 2 is a cross-sectional view showing a case where the method of the present invention is carried out in the same manner as the embodiment shown in FIG. 1 on a breakwater built on a sandy soil layer made of replacement sand in which a part of soft ground is replaced with sand. is there. Sectional drawing which shows the case where the method of this invention is implemented similarly to the Example shown in FIG. 13 on the breakwater built on the sandy soil layer which consists of substitution sand which replaced a part of soft ground with sand. is there. It is a schematic diagram of the numerical analysis used for confirmation of the effect of the present invention. It is a longitudinal cross-sectional view which shows an example of the conventional liquefaction countermeasure under a breakwater. It is sectional drawing which shows an example of the liquefaction countermeasure with respect to the existing existing breakwater.

Explanation of symbols

A horizontal ground improvement layer B underground wall 10 sandy soil layer 10a sandy soil layer 11 rubble mound 12 levee body 20 ground improvement machine 20a columnar body 21 auger 22 rotary shaft 23 stirring blade 24 rotary drive machine 25 deep mixing processing ship 26 Leader 27 Ground improvement machine insertion part 30 Sediment sand 31 Self-propelled carrier ship with grab 40 Work table ship 40a Prop 41 Drilling machine 42 Casing 43 Hole 45 Outer pipe 46 Chemical solution discharge hole 47 Cloth sleeve 47a Cement bentonite injection hole 48 Cement bentonite 49 Cement bentonite Injection hose 50 Cement bentonite discharge hole 51 Packer 55 Chemical solution injection hose 56 Chemical solution discharge hole 57 Packer 60 Chemical solution penetration part 70 Curved hole drilling device 71 Work hole 72 Sheath tube 73 Hole hole 73a Inclined surface 75 Curved sensor 76 Jet water injection nozzle 80 Chemical injection hose 81 Chemical discharge nozzle 82 Packer 90 Soft ground

Claims (7)

A liquefaction countermeasure method under a breakwater constructed by creating a rubble mound on a sandy soil layer on the seabed and installing a concrete dam body on the rubble mound,
By injecting a chemical solution for improving the ground or a cement-based solidifying material into a portion from the surface of the sandy soil layer directly below the dam body to a desired depth, a plate shape having a desired thickness without causing a liquefaction phenomenon. A liquefaction countermeasure method under a breakwater, characterized by creating a horizontal ground improvement layer.   2. The liquefaction countermeasure method under a breakwater by injecting a chemical solution according to claim 1, wherein the chemical solution for ground improvement uses a water glass-based, special silica-based, or polymer-based chemical solution for ground improvement.   The countermeasure for liquefaction under a breakwater according to claim 1 or 2, wherein the breakwater is a newly installed breakwater, and the horizontal ground improvement layer having the disk shape is formed on the sandy ground that becomes the breakwater before the rubble mound is formed. Construction method.   The liquefaction countermeasure construction method under a breakwater according to claim 1 or 2, wherein the breakwater is an existing breakwater, and the plate-like horizontal ground improvement layer is formed on a sandy soil layer under the existing breakwater.   A horizontal ground improvement layer having the shape of a plate is formed immediately below the bank body, and a pair of impervious or difficult water is formed in the sandy soil layer slightly below the front and rear edges of the bank body. The liquefaction countermeasure construction method under a breakwater according to claim 1 or 2, wherein a permeable underground wall is constructed.   The pair of impervious or hardly permeable underground walls are formed by injecting a chemical solution or cement-based solidifying material for ground improvement into the sandy soil layer. Liquefaction countermeasure method.   6. The liquefaction countermeasure method under a breakwater according to claim 5, wherein the pair of impermeable or hardly permeable underground walls are formed by placing a sheet pile in the sandy soil layer.

Images