Material for constructing improved pile, method for manufacturing the same, and method for improving ground

Abstract

To provide a ground improvement method capable of taking measures against liquefaction including a huge earthquake motion while applying a density increasing method at an improvement rate of 20% or less which does not make construction difficult, and to provide an improved pile construction material applied to the ground improvement method and a method of manufacturing the improved pile construction material.SOLUTION: The material 300,400 for creating an improved pile is a material for creating an improved pile having a hydraulic conductivity with an excessive pore water pressure ratio of the improved ground being less than 1.0 under a condition that an FL value, which is calculated based on an improved N value obtained by improving an N value of an original ground and is a liquefaction resistivity with respect to earthquake motion of a predetermined scale, of the improved ground is less than 1.0.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a material for constructing improved piles, a method for producing the same, and a method for improving ground. [Background technology]

[0002] Among the various ground improvement methods carried out on the original ground for various purposes, methods used as countermeasures against liquefaction during earthquakes include density increase methods and excess pore water pressure dissipation methods. Density increase methods include the Sand Compaction Pile (SCP) method, which compacts the ground by compressing sand into the ground to create sand piles, and the Vibroflotation method, which compacts the ground by forcibly vibrating the sandy ground and inserting and sinking crushed stone, etc. On the other hand, one example of an excess pore water pressure dissipation method is the DEPP (Dissipation Excess Pore Water Pressure) method. The DEPP method involves installing synthetic resin drains (artificial materials) vertically at specified intervals in the sandy ground, allowing excess pore water generated during an earthquake to flow into the drains and suppressing the rise in excess pore water pressure. Generally, a specific ground improvement method is selected, and the selected ground improvement method is carried out on the original ground.

[0003] Incidentally, one of the above-mentioned density increase methods is the TS-improver method invented by the present applicant, which is disclosed in Patent Document 1. This density increase method applies repeated shear strain to the surrounding ground by vibrating a vibrating flot that has penetrated the original ground and pressing in a filler material, thereby compacting the ground. Because this method can achieve ground improvement with low vibration and noise, it is suitable for application in areas with harsh construction environments, such as urban areas. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-41434 Summary of the Invention [Problem to be solved by the invention]

[0005] Previous density-increasing methods, including the TS-improver method disclosed in Patent Document 1, increase the liquefaction resistance by increasing the N-value of the original ground. Because the liquefaction resistance required to resist a large earthquake is high, the N-value required after improvement (post-improvement N-value) also becomes high, making it necessary to narrow the pitch of the improvement piles. However, when performing construction at a high improvement rate of over 20%, it can become difficult to install the improvement piles. The SCP method described above is said to have a limit of about 25% improvement rate.

[0006] In recent years, there has been a tendency to consider even the most extreme earthquake motions when designing. When trying to prevent liquefaction in the event of such extreme earthquake motions, the required liquefaction strength naturally becomes high, and even if ground improvement is carried out at the maximum improvement rate of the density increase method (for example, the above-mentioned 25%), it may not reach the required level.

[0007] Another issue with compaction in the density-increasing method is that the SCP method described above dynamically vibrates the vibrating rod in the vertical direction, which makes it easy for material particles to break down and makes it difficult to secure voids, so the permeability of the improved ground cannot be expected to be high.

[0008] On the other hand, the above-mentioned excess pore water pressure dissipation method is a method that specializes in drainage functions, in which artificial materials are embedded in the original ground at specified intervals (for example, 1.5 m intervals) and excess pore water pressure generated during an earthquake is quickly dissipated through the artificial materials. Therefore, since it does not have the effect of compacting the original ground between the artificial materials, it does not increase liquefaction strength, and does not give the ground stickiness, so it is unclear whether it is effective enough as a countermeasure against even large earthquake motions.

[0009] The present invention aims to provide a ground improvement method that can take measures against liquefaction, even in the event of a large earthquake, while applying a density increase method with an improvement rate of 20% or less, which is not difficult to implement, and to provide materials for construction of improved piles that can be applied to this ground improvement method, and a method for manufacturing the materials. [Means for solving the problem]

[0010] In order to achieve the above object, one aspect of the improved pile construction material according to the present invention is: This is a material for improving pile construction that is applied in a density increase method in which an improved pile is created by compressing the ground around the improved pile to create an improved ground with increased density. The improved piles are constructed to have a permeability coefficient such that the excess pore water pressure ratio of the improved ground is below 1.0 under conditions where the FL value, which is the liquefaction resistance against earthquake motion of a predetermined magnitude and is calculated based on the improved N value obtained by improving the N value of the original ground, is below 1.0.

[0011] According to this aspect, with regard to the improved pile construction material to be applied to the density increase method, although the FL method, which is originally a liquefaction determination method, determines that an FL value (liquefaction resistance rate) of 1.0 or more will not liquefy, it is acceptable for the FL value to be below 1.0 even when based on the improved N value obtained by improving the N value of the original ground using the density increase method, and under these conditions, when the excess pore water pressure ratio of the improved ground is determined, the improved pile construction material can be used to create improved piles with a permeability coefficient such that the excess pore water pressure ratio is below 1.0, making it possible to create improved ground that will not liquefy or has an extremely low possibility of liquefaction using the excess pore water pressure dissipation method. In other words, the improved pile construction material of this embodiment is a material that can be applied to a ground improvement method that combines the density increase method and the excess pore water pressure dissipation method, and is a material that, using the N value after improvement using the density increase method, has an excess pore water pressure ratio in the excess pore water pressure dissipation method that is below 1.0.This ground improvement method, which combines different construction methods, is a novel method that has not been seen before, and the improved pile construction material of this embodiment that is applied to this method can also be said to be a novel material. In the ground improvement method to which this type of improved pile construction material is applied, it is acceptable for areas to occur where the FL value is below 1.0, so in the density increase method that is carried out in advance, the improvement rate can be set to 20% or less, for example, around 15%.

[0012] Here, "density increase methods" include the above-mentioned TS-improver method and other common SCP and vibroflotation methods, but the TS-improver method is particularly suitable because it can achieve ground improvement with low vibration and noise. Furthermore, "earthquake motion of a specified magnitude" includes Level 1 (L1) earthquake motion and Level 2 (L2) earthquake motion, and Level 2 earthquake motion includes Type I earthquake motion at the plate boundary and Type II earthquake motion directly beneath the plate.

[0013] Another aspect of the improved pile construction material according to the present invention is: The permeability coefficient is 1.0 × 10 -3 m / s to 1.0×10 -2 It is characterized by being a crusher run whose particle size has been adjusted to be in the range of m / s.

[0014] According to this embodiment, the water permeability coefficient is 1.0 × 10 -3 m / s to 1.0×10 -2 This is crusher run, which has been particle-sized to be in the range of m / s, and is a highly permeable material that can be expected to have a sufficient pore water pressure dissipation effect.

[0015] Another aspect of the improved pile construction material according to the present invention is: It is characterized by being a hard artificial material or a spherical, bead-like material.

[0016] According to this aspect, the use of hard artificial materials or spherical, bead-like materials, i.e., materials that are difficult to crush, effectively prevents crushing (particle crushing) of the improved pile construction material (fill material) when the Vibroflot is inserted into the original ground in the density increase method, preventing the improved pile construction material from becoming finer and reducing its permeability, and ensuring the required voids. Furthermore, when the TS-improver method is applied to the density increase method, the Vibroflot vibrates horizontally within the original ground, making it less likely for the fill material to be crushed compared to methods such as the SCP method, which vibrates vertically. From this perspective, the TS-improver method is also preferable.

[0017] Here, examples of hard artificial materials include steel slag, etc. Furthermore, examples of spherical, bead-like materials include granulated and solidified coal ash (fly ash) (Hi Beads (registered trademark)).

[0018] In addition, one aspect of the method for producing an improved pile construction material according to the present invention is to A method for producing the improved pile construction material, which is the highly permeable material, The particle size adjustment is characterized in that when the gravel compaction pile method, which is the density increasing method using the crusher run, is applied, the fine particles in the crusher run are adjusted or cut within the range of the performance graph in the particle size accumulation curve, and the range in the performance graph with fewer fine particles is made into the high permeability range, and the product is manufactured so that it is included in this high permeability range.

[0019] According to this embodiment, when the gravel compaction pile method is applied, the fine particles of the crusher run are adjusted or cut within the range of the performance graph in the particle size accumulation curve, making the range with fewer fine particles in the performance graph the high permeability range, and by manufacturing the material so that it falls within this high permeability range, it is possible to produce a highly permeable material for improved pile construction.

[0020] Further, one aspect of the ground improvement method according to the present invention is to a penetration step of penetrating a vibro-tool, which is equipped with a vibro-flot that generates horizontal vibrations and a silo-tube to which the improved pile construction material is supplied, into the ground to a predetermined depth while generating horizontal vibrations; a withdrawal and filling process in which the vibro-tool is withdrawn upward by a predetermined withdrawal length, and the improved pile construction material is filled into a cavity created by this withdrawal via the silo tube to create a filled body; a returning step of returning the vibro-tool downward by a predetermined returning length that is shorter than the pulling length, thereby forming an expanded diameter body in which the diameter of the packing body is expanded, The method is characterized in that an improved pile of a predetermined diameter is created by repeating the extraction and filling process and the return process, and the predetermined diameter of the improved pile is changed by changing either or both of the predetermined extraction length and the predetermined return length.

[0021] According to this aspect, the TS-improver method is applied, and a cavity formed by withdrawing a vibro-tool from a predetermined depth in the ground upward is filled with the improved pile construction material of the present invention to create a filled body, and the filled body is expanded laterally to create an expanded body. This process is repeated to gradually expand the diameter of the expanded body to create an improved pile, thereby making it possible to create an improved pile with a desired improved diameter. Furthermore, because this is a so-called bottom-feed improvement method, it is easy to control the amount of improved pile construction material input, which allows for the creation of improved piles with a highly accurate finished shape. Furthermore, since the pile construction material is supplied into the ground while applying horizontal vibrations to the ground, and the expanded body is created by expanding the filler body laterally, the vibration direction and the expansion body construction direction (expansion direction) are aligned, making this an improvement method with high construction efficiency. Furthermore, ground improvement can be performed with a suspended vibro tool using a mobile crane or similar device, without the need for special machinery such as a three-point pile driving base machine. Furthermore, by compacting the piles made from the pile construction material under the weight of the horizontally vibrating vibro tool, it is possible to both increase the density of the ground and dissipate pore water pressure.

[0022] Furthermore, because Vibroflot creates improved piles by generating horizontal vibrations underground, it is possible to keep both noise and vibration levels low, unlike the SCP method, which uses a vibrator mounted on the top of the casing pipe, making it an improvement method with excellent environmental adaptability.

[0023] In the returning step, the vibro-tool is returned downward by a return length that is shorter than the withdrawal length of the vibro-tool in the withdrawing and filling step, thereby expanding the diameter of the packed body and creating an expanded-diameter body. By repeating the creation of the packed body (supplying of material for improved pile construction), the expansion of the packed body, and the resulting expansion of the expanded-diameter body around the packed body, the diameter of the expanded-diameter body can be gradually expanded.

[0024] In this return process, the vibro tool is released from its hanging state, and when the weight of the vibro tool is applied to the packed body that has already been filled inside the expanded diameter body, the packed body is compacted while expanding in diameter, and the vibro tool is returned downward. By horizontally vibrating the vibro tool during this return process, a predetermined return length can be ensured, and an expanded diameter body of the predetermined diameter can be created. In other words, the improved pile of the predetermined diameter that is finally created is created by gradually expanding the expanded diameter body, the diameter of which is controlled each time.

[0025] For example, if the length of the filler body to be initially created is set to 1 m (therefore, the predetermined withdrawal length is set to 1 m), and the vibro-tool is returned, for example, by 80 cm (the predetermined return length is set to 80 cm), the volume of the vibro-tool 80 cm contributes to the expansion of the filler body, creating an expansion body. The diameter of the expansion body at this time can be accurately calculated. Thereafter, similarly, the vibro-tool is withdrawn, for example, by 1 m, the cavity formed by this withdrawal is filled with improved pile construction material, and then the vibro-tool is returned, for example, by 80 cm, and the diameter of the expansion body created each time is accurately calculated. Note that the degree of expansion of the expansion body may vary depending on the hardness of the ground and the type of improved pile construction material. In other words, there may be a discrepancy between the diameter of the expansion body calculated by calculation and the diameter of the expansion body actually created. Therefore, it is preferable to carry out a test construction in the construction area using the improved pile construction material to be used in the actual construction work, and to confirm the extent to which the expansion of the expansion body will be achieved by one set of extraction and filling processes and return processes.

[0026] The horizontal vibration generated by the Vibroflot is preferably a high-frequency vibration of about 30 Hz. Applying such high-frequency horizontal vibration to the ground generally increases vibration energy, which improves the compaction efficiency of the improved pile construction material filled into the ground. Furthermore, the high-frequency vibration suppresses the propagation of vibration, further reducing the impact on the surrounding environment.

[0027] Furthermore, by changing either or both of the withdrawal length and return length of the vibro-tool, it is possible to change as desired the diameter of the expanded body created each time by repeated withdrawal and return of the vibro-tool, as well as the predetermined diameter of the improved pile that is finally created. According to the ground improvement method of this aspect, it is possible to create improved piles over a wide range, for example, from 800 mm to 1500 mm in diameter, and large diameters, for example, 1000 mm or more. In addition, when an eccentric motor or the like is built into the vibroflot to vibrate it horizontally, the current value of this eccentric motor (the load value on the eccentric motor) increases with the strength of the ground. Taking advantage of this, the current value of the eccentric motor during construction can be read and the ground properties can be determined based on the current value. A method can also be applied in which the diameter of the improved pile is changed depending on the ground properties based on the current value. For example, if a predetermined current value is not reached when the vibroflot is penetrated, the target ground is determined to be soft, and the vibroflot tool is penetrated again at the same location to create an improved pile with a diameter larger than the initially set diameter. On the other hand, if a predetermined current value or more is reached when the vibroflot tool is penetrated, the target ground is determined to be solid, and construction is stopped at that position, and the improved pile is created with a diameter smaller than the initially set diameter. In this way, by determining the actual ground conditions using, for example, the current value and appropriately changing the diameter of the improvement piles depending on the ground conditions, rational and economical ground improvement can be achieved that is appropriate for the target ground.

[0028] In this specification, "expansion" refers to the general expansion of the cross-sectional area of ​​a filling body or an expansion body constructed in the ground, such as the expansion of the diameter of a pile with a circular cross section, or the expansion of the area of ​​a rectangular cross section or a track-shaped cross section with curved corners. The "predetermined diameter" of an improved pile refers to the diameter or radius of the improved pile set in the design, and is, for example, the diameter required to achieve a predetermined improvement rate.

[0029] In another aspect of the ground improvement method according to the present invention, A guide tube is provided at the tip of the silo tube to supply the improved pile construction material to the ground, The lower end surface of the guide tube is a tapered surface that is inclined upward from the outer periphery toward the inside, and / or The guide tube is characterized in that its diameter gradually increases from the middle to the lower end.

[0030] According to this embodiment, the guide tube, which is provided at the tip of the silo tube and supplies the improved pile construction material to the ground, has a tapered lower end surface that slopes upward from the outer periphery toward the inside, which reduces the resistance of the guide tube when penetrating (pushing in) the improved pile construction material filled in during the return process to compact it, allowing the silo tube to penetrate smoothly, thereby preventing the original ground (soil and sand at the original location) from mixing with the improved pile construction material. Furthermore, the guide tube gradually expands in diameter from the middle to the bottom end, which can reduce deformation (degree of collapse) of the hole wall and increase the stability of the hole wall.

[0031] In another aspect of the ground improvement method according to the present invention, A guide tube is provided at the tip of the silo tube to supply the improved pile construction material to the ground, The guide tube is characterized in that a flow straightening groove extending along the longitudinal direction or substantially the longitudinal direction of the vibro-tool is provided on the outer peripheral surface thereof.

[0032] According to this aspect, the guide tube, which is provided at the tip of the silo tube and supplies the improved pile construction material to the ground, has a straightening groove on its outer surface that extends along the longitudinal direction or approximately the longitudinal direction of the vibro tool.Therefore, when the internal pressure at the tip of the guide tube is increased while the drawing-out and filling process and the return process are being carried out, there is a risk that the hole wall will collapse if a sudden release of pressure occurs.However, the straightening groove on the outer surface of the guide tube gently releases the pressure, making it less likely that a sudden release of pressure will occur, and preventing the hole wall from collapsing. [Effects of the Invention]

[0033] According to the improved pile construction material, its manufacturing method, and ground improvement method of the present invention, it is possible to provide a ground improvement method that can take measures against liquefaction, including even large earthquake motions, while applying a density increase method with an improvement rate of 20% or less, which does not make construction difficult, as well as an improved pile construction material that can be applied to this ground improvement method and its manufacturing method. [Brief explanation of the drawings]

[0034] [Figure 1] 1(a) and 1(b) are both schematic diagrams of an example of an improved pile construction material according to an embodiment. [Figure 2] This is a diagram showing a particle size accumulation curve that explains the particle size adjustment method in the production method for improved pile construction material, which is a highly permeable material. [Figure 3] FIG. 1 is a diagram comparing particle size accumulation curves before and after improvement. [Figure 4] 1 is a diagram showing an example of a ground improvement device applied to a ground improvement method according to an embodiment. FIG. [Figure 5] 5 is a view taken in the direction of the arrow V in FIG. 4, showing an example of a vibro unit as viewed from below in the direction of penetration into the ground. [Figure 6] FIG. 2 is a perspective view of an example of a vibro unit as viewed obliquely from below. [Figure 7] FIG. 10 is a longitudinal cross-sectional view showing another example of the guide tube. [Figure 8] FIG. 10 is a longitudinal cross-sectional view showing yet another example of a guide tube. [Figure 9] FIG. 10 is a view showing another example of a vibro unit including yet another example of a guide tube, viewed from below in the direction of ground penetration. [Figure 10] FIG. 2 is a process diagram illustrating an example of a ground improvement method according to an embodiment. [Figure 11] FIG. 10 is a vertical cross-sectional view of an example of an improved pile constructed. [Figure 12] FIG. 1 is a diagram showing an example of the construction arrangement of improved piles in an embodiment. [Figure 13] This figure shows the results of ground surveys before and after improvement using the density increase method. [Figure 14]This figure shows the results of liquefaction assessment of ground after remodeling using the density increase method. [Figure 15] FIG. 1 is a diagram showing the design flow for a pore water pressure dissipation evaluation method. [Figure 16A] This figure shows the specifications and acceleration waveform of level 1 earthquake motion applied to dynamic analysis in the pore water pressure dissipation evaluation method. [Figure 16B] This figure shows the specifications and acceleration waveform of level 2 earthquake motion applied to dynamic analysis in the pore water pressure dissipation evaluation method. [Figure 17] This figure shows material conditions and cases considered in the pore water pressure dissipation evaluation method. [Figure 18] FIG. 1 is a diagram showing a ground model applied to dynamic analysis in a pore water pressure dissipation evaluation method. [Figure 19] FIG. 10 is a diagram showing the evaluation results regarding the maximum excess pore water pressure ratio. [Figure 20A] This figure shows the relationship between the average maximum excess pore water pressure ratio and drain spacing when the permeability coefficient is 1.0 × 10-2. [Figure 20B] This figure shows the relationship between the average maximum excess pore water pressure ratio and drain spacing when the hydraulic conductivity is 1.0 × 10-3. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention relates to a method for improving a pile construction material, a method for manufacturing the same, and a method for improving ground, and the like.

[0036] [Improved pile construction material and manufacturing method thereof, and ground improvement method according to the embodiment] An example of an improved pile construction material, a method for producing the same, and a ground improvement method according to an embodiment will be described with reference to Figures 1 to 20. Figures 1(a) and 1(b) are both schematic diagrams of an example of an improved pile construction material according to an embodiment. Figure 2 is a diagram showing a particle size accumulation curve that explains a particle size adjustment method in a method for producing an improved pile construction material, which is a highly permeable material. Figure 3 is a diagram comparing the particle size accumulation curves before and after improvement.

[0037] The improved pile construction material 300 shown in FIG. 1(a) has a permeability coefficient of 1.0×10 -3 m / s to 1.0×10 -2 This is a highly permeable material made of crusher run 302, which has been sized to be in the range of m / s.

[0038] Here, a method for producing the improved pile construction material 300, which is a highly permeable material, will be described with reference to FIGS.

[0039] As shown in Figure 3, when the case where crushed stone (C-40) was used for improvement was taken as an example, the permeability coefficient was 3.7179 × 10 -6 The value of (m / s) was obtained. The permeability coefficient estimated from the initial grain size distribution of this crushed stone (Kroger's formula) is 1.80 × 10 -2 (m / s), and comparing the two, the permeability is four orders of magnitude lower.

[0040] Figure 3 shows that the particle size accumulation curve for the pile core after improvement using the density increase method shifts to the left (in the direction of finer particle size) in the Z2 direction. This is thought to be due to a variety of factors, including the crushing of the fill material used for the improved pile construction during improvement, or the infiltration of surrounding sand. However, the aforementioned decrease in permeability and change in particle size of the improved pile construction material can also occur with density increase methods such as the conventional SCP method and GCP (Gravel Compaction Pile) method, which use crushed stone as the improved pile construction material, as well as the TS-improver method.

[0041] The ground improvement method according to the embodiment uses the TS-improver method as a density-increasing method, applying the improved pile construction material 300 shown in Figure 1(a) and the like, to increase the N-value of the original ground to a post-improvement N-value. When the FL method, a liquefaction assessment method using the post-improvement N-value, is implemented, an FL value (liquefaction resistance) of 1.0 or more is determined to be non-liquefiable, but it is acceptable for the FL value of some or all of the improved ground to be below 1.0. Under these conditions, when the excess pore water pressure ratio of the improved ground is assessed, an improved pile construction material capable of creating improved piles with a permeability coefficient such that the excess pore water pressure ratio is below 1.0 is manufactured and applied to the ground improvement method.

[0042] The decrease in permeability of improved piles is due to the fact that the particle size becomes finer as a result of improvement, which reduces the gaps between the particles.In addition, the crushed stone (C-40) used as material for improving pile construction is crushed stone with a particle size of 0mm to 40mm, and contains a large amount of fine particles.

[0043] Therefore, as shown in Figure 2, a manufacturing method is used to adjust or cut the fine particles of ordinary crushed stone (C-40), thereby reducing the fine particles in the Z1 direction, and an improved pile construction material 300 is produced that includes crusher run 302, a highly permeable material.

[0044] In Figure 2, the range of crushed stone (highly permeable material) with adjusted fine grain content is indicated by the diagonal line. In Figure 2, the dotted line range on the left and right represents the range of the improved pile construction material (filling material) in the GCP method. The dashed line and the double-dashed line respectively represent the permeability coefficient (Kroger method) K = 1.0 x 10 of the pile core when improved using highly permeable material. -3 m / s, 1.0×10 -2 This is an estimate of the curve corresponding to m / s.

[0045] When applying the GCP method, if a highly permeable material is used for improved pile construction, and the grain size change of the improved pile construction material after improvement using the TS-improver method is on the order of the dotted and dashed lines in the grain size accumulation curve, then it is estimated that the permeability of the improved pile core will be maintained at a sufficiently high level, and a sufficient pore water pressure dissipation effect can be expected.

[0046] Here, adjusting or cutting out the fine particles can cause problems such as insufficient compaction of the ground between the improved piles. However, as shown in Figure 2, it is estimated that as long as the particle size of the material used to create the improved piles in the GCP method is within the range of actual results, a sufficient density increase effect can be achieved even when a highly permeable material is used.

[0047] While the improved pile construction material 300 shown in Figure 1(a) is a highly permeable material, the improved pile construction material 400 shown in Figure 1(b) is a hard artificial material or a spherical, bead-like material, and therefore is a material that is difficult to crush.

[0048] Examples of hard artificial materials include steel slag, etc. Examples of spherical, bead-like materials include Hi Beads (registered trademark), which are made by granulating and solidifying coal ash (fly ash). Hi Beads 402 are hard artificial materials that are spherical and bead-like, and therefore are less susceptible to particle crushing and can maintain high water permeability, making them preferable.

[0049] It is thought that particle crushing of the material used to make the improved piles occurs when the vibrating flotation penetrates during compaction, and it is speculated that the decrease in permeability of the improved piles is due to the reduction in voids caused by particle crushing during the improvement process.

[0050] Therefore, by applying the improved pile construction material 400 made of a material that is difficult to crush, particle crushing that occurs during improvement can be suppressed, and by ensuring a certain amount of void space between the particles, it is possible to achieve both the compaction effect of the density increase method and the pore water pressure dissipation effect of the pore water pressure dissipation method.

[0051] Next, an example of a ground improvement method according to an embodiment will be described with reference to Figures 4 to 11. Here, Figure 4 is a diagram showing an example of a ground improvement device applied to the ground improvement method according to the embodiment. Figure 5 is a view taken in the direction of arrow V in Figure 4, showing an example of a vibro unit as viewed from below in the direction of ground penetration. Figure 6 is a perspective view of an example of a vibro unit as viewed from below in an oblique direction. Figures 7 and 8 are both vertical cross-sectional views showing other examples of guide tubes. Figure 9 is a view of another example of a vibro unit including yet another example of a guide tube as viewed from below in the direction of ground penetration. Furthermore, Figure 10 is a process diagram explaining an example of a ground improvement method according to the embodiment, and Figure 11 is a vertical cross-sectional view of an example of a constructed improved pile.

[0052] The illustrated ground improvement method is a method of constructing improved piles by applying the improved pile construction materials 300, 400 shown in FIG. 1 and the TS-improver method as a density increasing method.

[0053] As shown in Figure 4, a ground improvement device 100 applied to the ground improvement method includes a vibro unit 80 and a crawler crane 90 (an example of heavy machinery) with the vibro unit 80 and a bucket 85 suspended by a wire W1. The vibro unit 80 includes a silo tube 10 with a hopper 17 at its upper end, and a vibro tool 20 attached to the lower end of the silo tube 10. In Figure 4, the ground penetration direction is indicated by Z0. The original ground G to be improved has a high groundwater level, contains a sandy layer, and is highly susceptible to liquefaction.

[0054] 6, the vibro unit 80 has a silo tube 10 made of a casing pipe and a vibro tool 20 attached to the lower end of the silo tube 10, and the vibro tool 20 has a vibro flot 30 with a built-in eccentric motor (not shown) that generates horizontal vibrations, and a silo tube 40 that is attached to the vibro flot 30 and communicates with the silo tube 10. A guide tube 50 is provided at the tip of the vibro tool 20 in the ground penetration direction, and a tip fin 55 is provided on the guide tube 50, protruding from the tip of the guide tube 50 in the ground penetration direction.

[0055] The horizontal vibrations generated by the vibrating flot 30 are preferably high-frequency vibrations, for example, about 30 Hz. Applying such high-frequency horizontal vibrations to the ground generally increases vibration energy, thereby improving the compaction efficiency of the improved pile construction material filled into the ground. Furthermore, the high-frequency vibrations suppress vibration propagation, further reducing the impact on the surrounding environment. Furthermore, the current value (load value on the eccentric motor) of the eccentric motor (not shown) built into the vibrating flot 30 increases in response to the strength of the ground G. By utilizing this, the current value of the eccentric motor during construction can be read and the ground conditions can be determined based on the current value. This current value determination also makes it possible to apply a method of changing the diameter of the improved piles depending on the ground conditions.

[0056] In the above embodiment, for example, if the current value does not reach a predetermined value when the vibro unit 80 is penetrated into the original ground G, the target ground is determined to be soft, and the vibro unit 80 is penetrated again at the same location, allowing the improvement piles to be constructed with a diameter larger than the initially set predetermined diameter. On the other hand, if the current value reaches a predetermined value or more when the vibro unit 80 is penetrated into the original ground G, the target ground is determined to be solid, and construction is stopped at that position, allowing the improvement piles to be constructed with a diameter smaller than the initially set predetermined diameter. In this way, rational and economical ground improvement tailored to the target ground can be achieved by determining the actual ground properties using, for example, the current value and appropriately changing the diameter of the improvement piles depending on the ground properties.

[0057] By using a high-frequency (and therefore high-output) eccentric motor, it is possible to increase the vibration energy and compact the filler material filled into the ground with high efficiency. Also, compared to conventional SCP methods, which apply low-frequency vertical vibrations to the ground, this method applies high-frequency horizontal vibrations to the ground while improving the ground, thereby minimizing the impact on the surrounding environment of the improved area.

[0058] Furthermore, the ground improvement device 100 has a configuration in which the vibro unit 80 is suspended from the crawler crane 90, and therefore does not require special machinery such as a three-point pile driving base machine as a component, as is the case with ground improvement devices used in the SCP method, etc. Therefore, it is possible to carry out ground improvement work using general-purpose heavy machinery 90, which makes it possible to reduce construction costs.

[0059] At the tip of the vibro-tool 20 in the ground penetration direction is provided a guide tube 50 having a hollow interior with a larger cross-section than the cross-sectional area of ​​the hollow interior at the tip of the silo-tube 40. More specifically, as shown in Fig. 5, the planar shape of the silo-tube 40 and the vibroflot 30, which are arranged side by side, (or the cross-sectional shape perpendicular to the ground penetration direction) is track-shaped, while the guide tube 50 has two arc-shaped regions 50a, 50b corresponding to the silo-tube 40 and the vibroflot 30. One arc-shaped region 50a has a cross-sectional area A1 that is approximately the same as the hollow interior of the silo-tube 40, and the other arc-shaped region 50b has a cross-sectional area A2 that is a portion of the vibroflot 30, and the guide tube 50 has a cross-sectional area A3 that is the sum of both regions.

[0060] 6, in the vibro unit 80, a water jet supply pipe 65 is attached from the outer peripheral surface of the silo tube 10, via the outer peripheral surface of the vibro tool 20, to the outer peripheral surface of the guide tube 50. A water jet is supplied to an upper end 65b of the water jet supply pipe 65 from a water jet supply mechanism (not shown) located on the ground, and the water jet is supplied to the ground G via a lower end 65a of the water jet supply pipe 65. The vibro unit 80 shown in the figure is equipped with a pair (two) of water jet supply pipes 65 at opposing positions on its outer peripheral surface.

[0061] By supplying a water jet from the water jet supply pipe 65 to the outer periphery of the guide tube 50, even if a hard layer with an N value of about 20 or more exists in the ground G to be improved, the vibro unit 80 can be reliably penetrated (sinks) into the ground by both its own weight and the crushing force of the water jet.

[0062] 6, in the vibro unit 80, an air jet supply pipe 67 is attached from the outer peripheral surface of the silo tube 10, via the outer peripheral surface of the vibro tool 20, via the outer peripheral surface of the guide tube 50, and to the inner surface of the guide tube 50. An air jet is supplied to the upper end of the air jet supply pipe 67 from an air jet supply mechanism (not shown) located on the ground, and the air jet is supplied to the inner tip region of the guide tube 50 via the lower end 67a of the air jet supply pipe 67. The vibro unit 80 shown in the figure is equipped with one air jet supply pipe 67 on its outer peripheral surface.

[0063] By supplying an air jet from the lower end 67a of the air jet supply pipe 67 into the inside of the guide tube 50, it is possible to quickly supply the improved pile construction material inside the silo tube 10 into the ground and to prevent soil and sand from flowing back from the tip of the guide tube 50 into the vibro tool 20.

[0064] Here, other examples of guide tubes will be described with reference to Figures 7 to 9. Guide tube 50A shown in Figure 7 differs from guide tube 50 in that its lower end surface is a tapered surface 51 that slopes upward from the outer periphery toward the inside.

[0065] Because the lower end surface of the guide tube 50A is a tapered surface 51 that slopes upward from the outer periphery toward the inside, the resistance of the guide tube 50A when penetrating (pushing in) and compacting the improved pile construction material filled in during the return process described below can be reduced, allowing the silo tube 40 to penetrate smoothly, which in turn prevents the original ground (soil and sand at the original site) from mixing with the improved pile construction material 300, 400.

[0066] On the other hand, a guide tube 50B shown in FIG. 8 differs from the guide tube 50 in that it has an expanded diameter portion 52 whose diameter gradually expands from the middle toward the bottom end.

[0067] The guide tube 50B has the expanding diameter portion 52 that gradually expands in diameter from the middle to the bottom end, thereby reducing deformation (degree of collapse) of the hole wall and increasing the stability of the hole wall.

[0068] On the other hand, the guide tube 50C shown in Figure 9 differs from the guide tube 50 in that the outer surface 53 of the guide tube 50C is provided with multiple straightening grooves 54 extending along the longitudinal direction or approximately the longitudinal direction of the vibro tool 20.

[0069] Because the guide tube 50C has multiple straightening grooves 54 on its outer surface 53, there is a risk that the hole wall will collapse if a sudden pressure release occurs during the drawing-out filling process and the return process while the internal pressure at the tip of the guide tube 50C is increased.However, the straightening grooves 54 on the outer surface 53 of the guide tube 50C gently release the pressure, making it less likely that a sudden pressure release will occur and preventing the hole wall from collapsing.

[0070] Although not shown, a control panel is mounted in the operator's seat of the heavy equipment 90, and various controls, such as drive control of the Vibroflot 30 and the water jet mechanism and air jet mechanism, are executed on this control panel. The control panel includes a central processing unit (CPU), random access memory (RAM), read-only memory (ROM), hard disk drive (HDD), and non-volatile RAM (NVRAM), which are connected via a system bus for data communication. The ROM stores various programs and data used by the programs. The RAM serves as a storage area for loading programs stored in the ROM and as a work area for the loaded programs. The CPU performs various functions by processing the programs loaded into the RAM. For example, the supply of water jets and air jets is controlled based on the optimal water jet supply amount and air jet supply amount for each depth, which are determined in advance through test construction.

[0071] Figure 10 is a process diagram explaining the ground improvement method according to the embodiment, and is a series of process diagrams proceeding from the left to the right of Figure 10. That is, the process up to constructing improved piles in the ground G directly below the same ground surface location is shown in order from the left diagram (process (A)) to the right diagram (process (G)). Note that in processes (B) to (G) in Figure 10, the crawler crane is not shown, and only the state in which the vibro unit 80 is suspended by the wire W1 is shown.

[0072] The ground G to be improved, shown in Figure 10, has a layered structure of multiple layers with different ground properties, consisting of, from the surface, sandy layer G1, sandy layer G2 (both layers are of the same quality, but are formally described as separate layers due to the groundwater level between them), silt layer G3, sandy layer G4, and gravel layer G5. The groundwater level is located around the boundary between the homogeneous sandy layers G1 and G2. The distance from the surface to the midpoint of the gravel layer G5 is set to a predetermined depth h (see step (B)), which will be the ground improvement depth.

[0073] As shown in step (A) of Figure 10, pre-boring is performed using a leading drilling machine 200 while rotating the auger in the X1 direction to the lower end of the sandy layer G2 (pre-boring step), and then, as shown in step (B), the leading drilling machine 200 is retracted, and the vibro unit 80 is lowered via a wire W1 using a crawler crane 90 (see Figure 1), and the vibro tool 20 at its tip is inserted into the ground G.

[0074] Then, as necessary, a water jet is discharged into the ground G from the tip of the water jet supply pipe 65, and an air jet is discharged from the air jet supply pipe 67 into the guide tube 50, while the vibro unit 80 is caused to sink into the ground G in the X1 direction under its own weight, and the vibro unit 80 is penetrated to a predetermined depth h (penetration process).

[0075] After the vibro unit 80 has penetrated to a predetermined depth, as shown in step (C), improved pile construction material 400 (or improved pile construction material 300) is loaded into the hopper 17 using a bucket 85, and the improved pile construction material 300 is stored inside the silo tube 10. Then, as shown in step (D), the vibro unit 80 is pulled out in the X2 direction upward by a predetermined pulling length h1, and the improved pile construction material 400 is filled into the cavity created below the vibro tool 20 by this pulling out via the silo tube 40 and further via the guide tube 50.

[0076] The vibro unit 80 is withdrawn while driving the eccentric motor to vibrate the vibro tool 20 at high frequency in the horizontal direction Y1. The cavity formed by the withdrawal of the vibro tool 20 is filled with a water-permeable material to create a filling body C1. The created filling body C1 has a volume calculated by multiplying the cross-sectional area A3 of the guide tube 50 shown in FIG. 5 by the withdrawal length h1. For example, when the predetermined length h is approximately 5 to 10 meters, the withdrawal length h1 can be set to approximately 1 meter (this is the withdrawal and filling process). Note that whenever the water-permeable material in the silo tube 10 decreases by a certain amount, the improved pile construction material 400 is replenished into the silo tube 10.

[0077] After the filler C1 having a volume calculated by multiplying the cross-sectional area A3 and the withdrawal length h1 is produced, the vibro unit 80 is returned downward in the X3 direction by a predetermined return length h2, which is shorter than the withdrawal length h1, as shown in step (E). This return of the vibro unit 80 is also performed while driving the eccentric motor to vibrate the vibro tool 20 at high frequency in the horizontal Y1 direction.

[0078] The return of the vibro unit 80 is performed by self-sinking of the vibro unit 80 while vibrating the vibro tool 20 at high frequency in the horizontal direction. For example, when the extraction length h1 is set to about 1 m, the return length h2 can be set to about 50 cm to 85 cm.

[0079] By returning the vibro unit 80 downward by a return length h2 that is shorter than the withdrawal length h1, the packing C1 is pushed sideways by the weight of the vibro unit 80 and expands in diameter, creating an expanded-diameter body C2. For example, if the withdrawal length h1 is set to 1 m and the return length h2 is set to 80 cm, the expanded-diameter body C2 maintains its original height of 1 m, but expands in diameter sideways by the volume of the inserted vibro tool 20 in the upper 80 cm height region where the vibro tool 20 is pushed inside, creating a stepped expanded-diameter body C2 as shown in the example shown.

[0080] In this way, the expanding body C2 is created as the filler C1 is pushed in from above by the weight of the vibro unit 80, expanding it laterally. During this process, the vibro tool 20 pushes in the filler C1 while vibrating horizontally at high frequency, and the vibration direction of the vibro tool 20 and the creation direction (expansion direction) of the expanding body C2 are the same, resulting in an improvement method with high construction efficiency (referred to as the return process).

[0081] The above-mentioned steps (C) to (E), i.e., the preparation for filling the improved pile construction material 400, the pull-out and filling step, and the return step, are considered as one set, and this set is repeated a predetermined number of times as shown in step (F) of Fig. 10. When the pull-out and filling step and the return step are repeated, the high-frequency vibration of the vibro-tool 20 is constantly performed in the horizontal Y1 direction, and this high-frequency vibration is applied to the ground, thereby constructing the improved pile upward.

[0082] As shown in step (G), the construction of the improvement piles C5 at one location in the improvement area is completed by constructing the improvement piles C5 having a predetermined diameter φ, for example, down to the ground surface.

[0083] Here, by changing either or both of the withdrawal length and return length of the vibro unit 80, the diameter of the expanded body created each time by repeated withdrawal and return of the vibro unit 80 and the predetermined diameter of the improved pile to be created can be changed as desired. For example, even if the predetermined withdrawal length is set to 1 m, the diameter of the expanded body created will differ between construction where the predetermined return length is set to 80 cm and construction where it is set to 85 cm. Also, even if the predetermined return length is set to 80 cm, the diameter of the expanded body created will differ between construction where the predetermined withdrawal length is set to 1 m and construction where it is set to 1.5 m. Therefore, it is preferable to create an improved pile of a predetermined diameter by setting the withdrawal length and return length of the vibro tool 20 so that optimal compaction management can be performed depending on the hardness and softness of the ground.

[0084] The illustrated ground improvement method is implemented as a measure against liquefaction, and as an example shown in Figure 11, improvement piles C5 with diameters adjusted for each layer are constructed in the sandy layers G2 and G4, which are liquefiable layers, with improvement piles of larger diameter than the other layers.

[0085] [Example of evaluation verifying pore water pressure dissipation effect] Next, an example of an evaluation carried out by the present inventors to verify the pore water pressure dissipation effect will be described with reference to FIGS.

[0086] Here, we present an example of an evaluation based on ground that has been improved with an improvement rate of 15% (less than 20%) using the TS-improver method, a density increase method already explained. First, a liquefaction assessment is performed using the estimated N-value after improvement using the density increase method. Next, an evaluation is performed on the dissipation of pore water pressure for sandy layers with an FL value below 1.0. Three cases of hydraulic conductivity for the improved piles are assumed, and the value of the excess pore water pressure ratio that occurs during an earthquake is confirmed for each case. Figure 12 shows the results of construction with an improvement rate of 15%, as well as the relative locations of the boring surveys conducted before and after the improvement. Furthermore, the design method used in this study was "DEPP Method Technical Document 3: Drain Design" provided by the DEPP Method Research Group.

[0087] Figure 13 shows the results of ground surveys before and after improvement in the 15% improvement area. Figure 14 also shows the results of liquefaction assessment using the estimated N-value (Yamazaki method) after improvement. The liquefaction assessment method used here complies with the Japan Road Association's Specifications for Highway Bridges, Commentary, Vol. V, Earthquake-Resistant Design, 2017.

[0088] Figure 14 shows that the FL value is below 1.0 at the sandy soil ground (depth GL-2.30m) with an improvement rate of 15%. Therefore, an evaluation of pore water pressure dissipation will be carried out at that depth.

[0089] Figure 15 shows the design flow for this study. In this study, the improvement rate and the pitch of the improved piles have already been determined, so the excess pore water pressure (Umax / ??′ ?? ) ??ve The flow is to obtain the following.

[0090] Regarding the design earthquake motion, the specifications and acceleration waveforms of the input earthquake motion (Level 1 and Level 2) used in the dynamic analysis are shown in Figures 16A and 16B, respectively. The input earthquake motion was taken at port facilities in areas where ground improvement work had been carried out.

[0091] Here, the level 1 earthquake motion was downloaded from the website of the National Institute for Land and Infrastructure Management (Port Facilities Research Laboratory website (nilim.go.jp)).

[0092] On the other hand, for Level 2 earthquake motion, the amplitude of Level 1 earthquake motion is expanded so that the maximum acceleration is 700 gal, based on the design horizontal depth of Type II ground for Level 2 earthquake motion (Type II) shown in the "Highway Bridge Specifications and Commentary V Earthquake-Resistant Design Edition 2017, p. 69," for which kheg = 0.70.

[0093] Figure 17 shows the material conditions and the case under consideration, and Figure 18 shows the ground conditions of the model used for dynamic analysis. For the case under consideration, the permeability coefficient of the improved pile is Kd = 1.0 × 10 -2 m / s, Kd = 1.0 × 10 -3 m / s, Kd = 1.0 × 10 -4 The experiment was carried out for three cases of m / s. The permeability coefficient Ks of the original ground was calculated using the Creager method, with 20% grain size D20.

[0094] For the three cases above, the maximum excess pore water pressure ratio that occurs during an earthquake was calculated from the relationship between drain intervals (a / b) and the relationship between the time coefficient (Tl). Figure 19 shows the evaluation results of the excess pore water pressure ratio. Figures 20A and 20B also show the relationship between the average maximum excess pore water pressure ratio and drain intervals.

[0095] In the liquefaction assessment of the 15% improvement area, the FL value was less than 1.0 and liquefaction was predicted. Taking into account the dissipation of pore water pressure, the permeability coefficient of the improved pile was Kd = 1.0 × 10 -2 m / , the excess pore water pressure ratio generated during an earthquake is 0.49, and Kd = 1.0 × 10 -3 In the case of m / s, the excess pore water pressure ratio is 0.71, which is below 1.0 in both cases, so we can expect an effect of dissipating excess pore water pressure and prevent the occurrence of liquefaction.

[0096] In contrast, Kd = 1.0 × 10 -4 In the case of m / s, the chart does not apply and the excess pore water pressure ratio is assumed to be 1.0 or more.

[0097] Therefore, the permeability coefficient of the improved ground after the density increase method is 1.0 × 10 -3 m / s to 1.0×10 -2 It has been found that a permeability coefficient of about m / s is required, and it has been verified that the improved pile construction materials 300 and 400 that achieve this permeability coefficient are suitable.

[0098] The results of this verification have demonstrated that by implementing the ground improvement method according to the embodiment using the improved pile construction material according to the embodiment, it is possible to take measures against liquefaction, even up to large earthquake motions, while applying a density increase method with an improvement rate of 20% or less, which is not difficult to carry out.

[0099] It should be noted that the present invention is not limited to the configurations shown here, and other embodiments may be possible in which other components are combined with the configurations described in the above embodiments. In this regard, the present invention can be modified within the scope of the present invention, and can be appropriately determined depending on the application form. [Explanation of symbols]

[0100] 10: Silotube 11:Top edge 17: Hopper 20: Vibro Tool 25: Anti-rotation wing 30: Vibroflot 40: Silotube 5050A, 50B, 50C: Guide tube 51: Tapered surface (bottom end surface) 52: Expanded diameter part 53: Outer surface 54: Rectifying groove 55: Tip fin 56: Tapered surface 65: Water jet supply pipe 67: Air jet supply pipe 80: Vibro unit 85: Bucket 90: Crawler crane (heavy equipment) 100: Ground improvement equipment 200: Pre-drilling machine 300: Improved pile construction material (highly permeable material) 302: Crushed stone 400: Improved pile construction material (hard to crush material) 402: Hi Beads G: Original ground (ground) C, C5: Improved pile C1: Filler C2, C4: Expanded diameter body

Claims

1. This is a material for improving pile construction that is applied in a density increase method in which an improved pile is created by compressing the ground around the improved pile to create an improved ground with increased density. A material for constructing improved piles, characterized in that the improved piles have a permeability coefficient such that the excess pore water pressure ratio of the improved ground is less than 1.0 under conditions where the FL value, which is the liquefaction resistance rate against earthquake motion of a predetermined magnitude, calculated based on the improved N value obtained by improving the N value of the original ground, is less than 1.

0.

2. The permeability coefficient is 1.0 × 10 －３ m / s to 1.0×10 －２ 2. The improved pile construction material according to claim 1, characterized in that it is a graded crusher run whose grade has been adjusted to fall within the range of m / s.

3. 2. The improved pile construction material according to claim 1, characterized in that it is a hard artificial material or a spherical, bead-like material.

4. 3. A method for producing an improved pile construction material according to claim 2, comprising: This is a method for producing materials for improved pile construction, characterized in that the particle size adjustment is within the range of the performance graph in the particle size accumulation curve when the gravel compaction pile method, which is the density increase method using the crusher run, is applied, and the range in the performance graph with fewer fine particles is made into a high permeability range by adjusting or cutting the fine particles in the crusher run, and producing the material so that it is included in this high permeability range.

5. a penetration step of penetrating a vibro-tool, which comprises a vibro-flot that generates horizontal vibrations and a silo-tube to which the improved pile construction material according to claim 1 is supplied, into the ground to a predetermined depth while generating horizontal vibrations; a withdrawal and filling process in which the vibro-tool is withdrawn upward by a predetermined withdrawal length, and the improved pile construction material is filled into a cavity created by this withdrawal via the silo tube to create a filled body; a returning step of returning the vibro-tool downward by a predetermined returning length that is shorter than the pulling length, thereby forming an expanded diameter body in which the diameter of the packing body is expanded, A ground improvement method characterized by creating an improved pile of a predetermined diameter by repeating the extraction and filling process and the return process, and changing the predetermined diameter of the improved pile by changing either or both of the predetermined extraction length and the predetermined return length.

6. A guide tube is provided at the tip of the silo tube to supply the improved pile construction material to the ground, The lower end surface of the guide tube is a tapered surface that is inclined upward from the outer periphery toward the inside, and / or 6. The ground improvement method according to claim 5, wherein the diameter of the guide tube gradually increases from the middle to the lower end.

7. A guide tube is provided at the tip of the silo tube to supply the improved pile construction material to the ground, 7. The ground improvement method according to claim 5, wherein the outer peripheral surface of the guide tube is provided with flow straightening grooves extending along the longitudinal direction or substantially the longitudinal direction of the vibro-tool.

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