JP5559622B2 - Liquefaction countermeasure ground and liquefaction countermeasure ground creation method - Google Patents

Description

  The present invention relates to a liquefaction countermeasure ground created by applying a liquefaction countermeasure to a ground including a base layer and a liquefied layer located on an upper layer of the base layer, and a method for creating the same.

  As a liquefaction countermeasure ground in which a liquefaction countermeasure is applied to a ground composed of a base layer and a liquefied layer located above the base layer, there is a method of solidifying the entire liquefied layer with cement or the like. The entire liquefied layer is solidified by injecting solidified milk such as cement into the ground and mixing the solidified milk with the liquefied layer to create a ground improvement body. The whole liquefied layer is solidified. When creating a ground improvement body, a deep mixing method or a chemical injection method is used. Among these, the deep mixing process method includes a mechanical stirring method in which stirring is performed using a heavy machine for stirring, and a high pressure jet stirring method in which solidified milk is jetted at high pressure in the ground to perform stirring. Moreover, a chemical | medical solution injection construction method prevents liquefaction by providing an adhesive force component to the ground by substituting the groundwater in the ground with a chemical solution and solidifying it.

  However, the method of solidifying the entire liquefied layer has problems such as requiring a large amount of solidifying material and prolonging the construction period. Moreover, there is a concept of partial solidification for efficiently improving a part of the ground in contrast to the entire surface improvement for improving the entire liquefied layer. In this partial solidification, there is a construction method in which a ground improvement body is formed on a part of the liquefaction countermeasure ground or a chemical solution is injected. In these methods, only a part of the ground is solidified, so that the amount of solidified material used can be reduced and the construction period can be shortened.

  Conventionally, the following are known as liquefaction countermeasures in which a part of the liquefaction countermeasure ground is solidified by a deep mixing treatment method. For example, a ground improvement body made by mixing and stirring solidified milk with the ground is arranged in a planar grid, and a grid-like ground improvement body is created to suppress the shear deformation of the ground during an earthquake, and the movement of groundwater and soil There is a construction method to prevent liquefaction by suppressing, and there are many construction results. Also known are construction methods and grid spacing calculation methods in this case (see, for example, Patent Document 1 and Patent Document 2). Furthermore, a construction method is also known in which not only a lattice-like ground improvement body is created alone but also used in combination with a pile foundation structure (for example, see Patent Document 3).

  Moreover, as a chemical | medical solution injection | pouring method, there exist some which inject | pour a chemical | medical solution partially only to the injection | pouring area | region effective in liquefaction suppression, such as performing chemical | medical solution injection | pouring only to the peripheral part of a foundation pile (for example, patent document 4, 5). By setting such an injection region, the amount of the chemical used is suppressed as compared with the entire surface injection.

  Furthermore, although it is different from countermeasures for liquefaction, there is also known a ground improvement method by partial solidification for the purpose of preventing an increase in horizontal resistance force and lateral flow of the structure (see, for example, Patent Documents 6 to 8). ). In these ground improvement methods, the pile head is fixed with steel, etc., or a plurality of horizontal solidification boards are created at intervals in the pile head or ground, and integrated with the vertical pile type improvement body. Is. Thus, the rigidity with respect to the shear deformation of a pile type improved body is raised by integrating a pile head and a horizontal solidification board with a pile type improved body.

JP 2000-265455 A JP 2008-50787 A JP 2001-342637 A JP 2008-208631 A JP 2007-217979 A JP 2003-247227 A JP 2001-20275 A JP-A-8-134485

  In creating the liquefaction countermeasure ground, the method of solidifying the entire liquefied layer is the most reliable method for liquefaction countermeasures. However, since the entire liquefied layer is solidified, there is a problem that a large amount of solidified milk is required. In addition, when the construction is performed, slime equal to or less than the amount of the solidified milk to be injected into the ground is discharged to the ground, so that there is a problem that it takes time to process and transport the discharged slime.

  On the other hand, in the construction method in which a ground improvement body is created in a part of the liquefaction countermeasure ground disclosed in Patent Documents 1 to 5 or a chemical solution is injected, the amount of solidified milk or medicine used can be suppressed. Furthermore, since the amount of solidified milk used is reduced, the amount of slime to be discharged is also reduced, and the labor required for processing and transporting the slime can be reduced.

  However, in the construction method for creating the grid-like ground improvement body disclosed in Patent Documents 1 to 3, the wall body is constructed by continuously building the ground improvement body by wrapping it. For this reason, the problem that the loss of the solidification material milk still remains. Further, in the method of performing chemical solution injection disclosed in Patent Documents 4 and 5, the injected chemical solution is generally more expensive than the solidified milk, and the management of the injection range of the chemical solution may be difficult. There are difficulties in terms of warranty.

  Then, the subject of this invention is providing the liquefaction countermeasure ground which can suppress the consumption of solidification material milk, and its preparation method, when taking the countermeasure against the liquefaction of the ground.

A liquefaction countermeasure ground according to the present invention that has solved the above-mentioned problems is a liquefaction countermeasure ground in which a liquefaction countermeasure is applied to a ground including a base layer and a liquefaction layer formed on an upper layer of the base layer. A plurality of pile-type improvement bodies are placed from the liquefaction layer to the depth reaching the base layer, and a plurality of columnar reinforcement bodies are formed between the pile-type improvement bodies adjacent in the lateral direction. Each of the reinforcing bodies formed between the improved bodies connects adjacent pile type improved bodies, and a plurality of reinforcing bodies are spaced apart in the depth direction between adjacent pile type improved bodies. A plurality of reinforcing bodies, comprising an upper layer reinforcing body disposed in the uppermost layer and a lower layer reinforcing body disposed in the lowermost layer, the thickness between the upper layer reinforcing body in the liquefied layer and the ground surface And the thickness between the lower layer reinforcement and the base layer is the thickness of the liquefied layer in the depth direction. The thickness in the depth direction between the upper layer reinforcing body and the lower layer reinforcing body in the liquefied layer is 30% or less of the thickness in the depth direction of the liquefied layer. The distance is set .

Further, the liquefaction countermeasure ground according to the present invention is a liquefaction countermeasure ground in which a liquefaction countermeasure is applied to the ground including a base layer and a liquefaction layer formed on an upper layer of the base layer, and the liquefaction layer in the ground A plurality of pile-type improvement bodies are placed from the depth to the base layer, and a reinforcement body is formed between adjacent pile-type improvement bodies. It is connected and formed between the adjacent pile-type improvements in the depth direction, and is formed as a plurality, and as a plurality of reinforcements, the upper layer reinforcement is arranged in the uppermost layer, and the lower layer is arranged in the lowermost layer. The thickness of the liquefied layer between the upper layer reinforcing body and the ground surface and the thickness between the lower layer reinforcing body and the base layer are respectively thicknesses in the depth direction of the liquefied layer. 20% to 40% of the distance between the upper layer reinforcing body and the lower layer reinforcing body in the liquefied layer, The thickness of the depth direction between, characterized in that it is set to 30% or less of the distance in the depth direction of the liquid layer thickness.

In the liquefaction countermeasure ground according to the present invention, a pile-type improved body is placed in the liquefied layer, and a reinforcing body is formed between the pile-type improved bodies. By forming the pile-type improved body reinforcing body, it is possible to suppress the consumption of the solidified milk for forming the pile-type improved body and the reinforcing body, compared with the case where the entire liquefied layer is solidified. . Moreover, since the reinforcing body is formed without wrapping all pile-type improved bodies in the depth direction as in the wall-like arrangement, the loss of the solidified milk can be reduced. Furthermore, when forming pile-type improved bodies and reinforcements, it is not necessary to use chemicals used in chemical injection methods, so countermeasures for ground liquefaction are taken while eliminating the need for management as in the case of chemical injection. be able to. In addition, the pile-type improved bodies can be efficiently reinforced by forming a plurality of reinforcing bodies spaced apart in the depth direction between adjacent pile-type improved bodies, thereby forming a reinforcing body. Therefore, it is possible to further suppress the injection amount of the solidifying material milk. Further, the thickness between the upper layer reinforcing body and the ground surface in the liquefied layer and the thickness between the lower layer reinforcing body and the base layer are 20% to 40% of the thickness in the depth direction of the liquefied layer, respectively. The thickness in the depth direction between the upper layer reinforcing body and the lower layer reinforcing body in the liquefied layer is set to a distance of 30% or less of the thickness in the depth direction of the liquefied layer. Thereby, the liquefaction suppression effect can be made high.

  Furthermore, the some reinforcement body formed spaced apart in the depth direction can be made into the aspect by which the volume is formed large as it approaches the ground surface.

  In this way, as the plurality of reinforcing bodies approach the ground surface, that is, the volume is formed large at a depth where shear deformation acting on the ground is large, the effect of suppressing liquefaction is further enhanced. Can do.

  In addition, the plurality of pile-type improved bodies may be arranged in the corners of a square or a regular triangle as viewed in plan, or arranged in a staggered manner as viewed in plan.

  Thus, the arrangement positions of the plurality of pile-type improved bodies can be arranged at the corners of a square or equilateral triangle when viewed in plan, respectively, or can be arranged in a staggered pattern when viewed in plan.

  According to the liquefaction countermeasure ground and its creation method according to the present invention, the consumption of the solidified milk can be suppressed when the ground liquefaction countermeasure is taken.

It is a sectional side view of the liquefaction countermeasure ground which concerns on 1st Embodiment. It is a top view of the liquefaction countermeasure ground. It is process drawing which shows the creation process of the liquefaction countermeasure ground. It is a top view of the other example of a liquefaction countermeasure ground. It is a top view of the further another example of the liquefaction countermeasure ground. It is a figure of the model of the side cross section of the liquefaction countermeasure ground used for analysis, (a) is a state which does not provide a reinforcement improvement body, (b) is a figure which shows the state which provided the reinforcement improvement body. (A)-(c) is a graph which shows the shear distortion inhibitory effect. It is a graph which shows an example of the result of the repeated loading test of sandy soil. It is a sectional side view of the liquefaction countermeasure ground which concerns on 2nd Embodiment. It is a top view of the further another example of the liquefaction countermeasure ground. It is a top view of the further another example of the liquefaction countermeasure ground.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each embodiment, portions having the same function are denoted by the same reference numerals, and redundant description may be omitted.

  FIG. 1 is a side sectional view of a liquefaction countermeasure ground according to a first embodiment of the present invention, and FIG. 2 is a plan view thereof. As shown in FIGS. 1 and 2, the liquefaction countermeasure ground S1 according to the present embodiment includes a base layer S11, and the liquefaction layer S12 is located above the base layer S11. The base layer S11 also serves as a support layer for the structure, and is a solid ground that hardly liquefies even when an earthquake occurs. The liquefied layer S12 is made of sandy soil or the like, and is a ground where liquefaction is likely to occur when an earthquake occurs.

  In the liquefied layer S12, a plurality of pile-type improved bodies 1 are placed. The pile-type improved body 1 reaches the base layer S11 in the lower layer beyond the liquefied layer S12. The pile-type improved body 1 is preferably rooted in the base layer S11, but the depth of rooting is not a problem. Further, as shown in FIG. 2, four of the plurality of pile-type improved bodies 1 are arranged at positions that become square corners in plan view. In this way, a plurality of pile-type improvement bodies 1 are placed in a state where the four adjacent ones are arranged at positions that form square corners in plan view.

  Between the adjacent pile type improvement bodies 1 in the plurality of pile type improvement bodies 1 in the liquefied layer S12, a reinforcement improvement body 2 that is a reinforcement body of the present invention is formed. As shown in FIG. 1, a plurality of reinforcing improvement bodies 2 are formed apart from each other in the height direction between adjacent pile improvement bodies 1. In this embodiment, five reinforcement improvement bodies 2 between adjacent pile type improvement bodies 1 are formed.

  The diameter when the pile-type improved body 1 is viewed in plan is, for example, φ2.2 m. Moreover, the distance between adjacent pile type improved bodies 1 is 1 m, for example. Furthermore, the diameter when the reinforcing body 2 is viewed in plan is, for example, φ1.8 m. Moreover, the reinforcement improvement body 2 is arrange | positioned in the center position of the shortest line segment which connects the pile center in the adjacent pile type improvement body 1. FIG. For this reason, as shown in FIG. 2, the reinforcement improvement body 2 has connected adjacent pile type improvement bodies 1 mutually.

  Next, the creation method of the liquefaction countermeasure ground which concerns on this embodiment is demonstrated. FIG. 3 is a process diagram schematically showing a creation process of the liquefaction countermeasure ground according to the present embodiment. When creating a liquefaction-preventing ground, first, a pile-type improved body 1 that penetrates the liquefied layer S12 and reaches the base layer S11 is formed. Create. Hereinafter, the procedure will be described.

  When creating the liquefaction countermeasure ground S1, the pile-type improved body 1 is created. The pile-type improved body 1 can be formed by, for example, a deep mixing treatment method, and here is formed by a so-called high-pressure jet stirring method. In the high-pressure jet agitation method, an injection nozzle is inserted at a position where the pile-type improved body 1 is formed, and the solidified milk is injected at a high pressure from the side of the injection nozzle and is gradually pulled up while rotating the injection nozzle.

  In this way, the mixture of the cylindrical solidified material milk and the ground is formed at the position where the pile-type improved body 1 is formed by pulling up the spray nozzle to the ground surface position of the liquefaction countermeasure ground S1. The pile-type improved body 1 is created by solidifying the solidified milk in the mixture. If the several pile type improvement body 1 is created by the same procedure, the reinforcement improvement body 2 will be formed between adjacent pile type improvement bodies 1 mutually. In the formation of the reinforcement body 2 as well, the deep mixing treatment method, here, the high-pressure jet stirring method can be used as in the case where the pile type improvement body 1 is formed.

  When building the reinforcement improvement body 2, as shown to Fig.3 (a), the injection rod 10 is inserted in the intermediate position of adjacent pile type improvement bodies 1 mutually. The insertion position of the injection rod 10 at this time is the center position of the line segment connecting the respective pile centers between the adjacent pile-type improved bodies 1 or the vicinity thereof. The injection port for the solidified milk is formed. At this time, the injection rod 10 is inserted so that the position of the injection port in the injection rod 10 is a depth position where the reinforcement improving body 2 is formed. When the injection rod 10 is inserted, the solidified material milk is injected at a high pressure from the side of the injection rod 10 and is gradually pulled up while the injection rod 10 is rotated, as in the case where the pile-type improved body 1 is formed.

  Then, when the injection rod 10 is pulled up by the thickness of the reinforcing improvement body 2, the injection of the solidified milk from the injection port of the injection rod 10 is temporarily stopped. Next, the injection rod 10 is pulled up to a position where the reinforcement improvement body 2 above is formed. For this reason, since the unimproved portion remains at a predetermined interval in the depth direction between the reinforcing improved bodies 2, the consumption of the solidified milk can be reduced accordingly.

  Thereafter, as shown in FIG. 3 (b), the solidified milk is injected from the side of the injection rod 10 at a high pressure again from the position where the next reinforcing and improving body 2 is formed, and gradually while rotating the injection rod 10. I will raise it. In this way, the upper reinforcement body 2 can be formed sequentially.

  Further, as shown in FIG. 3C, the injection rod 10 is further moved upward to inject the solidified milk from the side of the injection rod 10 at a high pressure, and gradually while rotating the injection rod 10. I will raise it. Moreover, high-pressure injection of solidified material milk is performed between the other pile type improved bodies 1 shown in FIG. 1 by the same procedure. Further, the upper ground surface of the reinforcement improvement body 2 is separately subjected to reinforcement processing. For this reinforcing treatment, it is preferable to use a cement stabilization treatment or the like. Thereafter, the solidified material milk sprayed from the spray nozzle is solidified, whereby the pile-type improved body 1 and the reinforcing improved body 2 are formed, and the liquefaction countermeasure ground S1 is created.

  When an earthquake occurs, the liquefied layer S12 made of sandy ground is subjected to seismic force, and the excess pore water pressure rises, resulting in liquefaction. In order to prevent liquefaction in the liquefied layer S12, it is roughly classified into a method for suppressing shear deformation and a method for preventing an increase in excess pore water pressure. In order to suppress the excessive pore water pressure, it is conceivable to solidify the sandy ground and to replace the pore water with a chemical solution. However, these methods require a large amount of solidifying material and chemical solution.

  In this respect, in the liquefaction countermeasure ground S1 created by the above procedure, the reinforcement improvement body 2 is formed between the adjacent pile improvement bodies 1, and the pile improvement body 1 is connected by the reinforcement improvement body 2. Therefore, the adjacent pile improvement bodies 1 can be integrated. Therefore, since the rigidity against the shear deformation at the time of the earthquake can be significantly increased, the shear deformation can be suitably prevented, and the liquefaction of the liquefied layer S12 at the time of the earthquake is not required without requiring a large amount of solidifying material or chemical solution. Can be prevented. Furthermore, the formation of the reinforcing improvement body 2 can block the transmission of excess pore water pressure from the liquefied layer S12.

  Moreover, by forming the reinforcement improvement body 2 between adjacent pile type improvement bodies 1, while being able to perform reliable construction, even when the width | variety of adjacent pile type improvement bodies 1 is wide, it adjoins. The pile type improved bodies 1 can be easily integrated.

  Further, the pile-type improved body 1 and the reinforcing improved body 2 are formed while repeatedly performing the injection of the solidified milk and the extraction of the injection rod 10 by the high-pressure injection stirring method. For this reason, the improvement range can be partially adjusted. Moreover, since the reinforcement improvement body 2 can be formed by partial injection, the improvement rate can be reduced as compared with the case where the entire improvement is performed, and the consumption of the solidified material can be reduced. Furthermore, by partially injecting the solidified milk, it is possible to suppress the generation of slime and contribute to the suppression of the generation of construction waste.

  Moreover, about arrangement | positioning of the pile type improvement body 1 and the reinforcement improvement body 2, as shown in FIG. 2, forms other than the form arrange | positioned in the center of the shortest line segment which connects the pile center of the adjacent pile type improvement body 1 and You can also For example, as shown in FIG. 4, the reinforcement improvement body 2 may be formed at the centroid (center position) of the four pile type improvement bodies 1 arranged as square corners in plan view. it can. Or it is set as the aspect which forms the reinforcement improvement body 2 in the center position of the three pile-type improvement bodies 1 among the many pile-type improvement bodies 1 arrange | positioned in zigzag in plan view as shown in FIG. Although not shown in the drawing, it can be arranged to be the corners of a regular triangle. Furthermore, it can also be formed by combining the modes shown in FIGS. 2, 4, and 5.

  Next, the present inventors performed the following earthquake response analysis about the arrangement | positioning conditions of the reinforcement improvement body 2. FIG. In the analysis, as shown in FIG. 6A, a ground model assuming a liquefied layer S12 and a base layer S11 was used. In this ground model, the example which arrange | positions the three pile type improved bodies 1 used as the distance L between piles with respect to liquefaction layer S12 and base layer S11 was assumed. Moreover, as shown in FIG.6 (b), the example which arrange | positions the two reinforcement | strengthening improvement bodies 2A and 2B to the unimproved part in the ground between piles in liquefied layer S12 was assumed. Among these, the upper layer reinforcement improvement body 2A was arrange | positioned in the uppermost layer of several reinforcement improvement bodies, and the lower layer reinforcement improvement body 2B was arrange | positioned in the lowest layer of several reinforcement improvement bodies.

  Here, the thickness in the depth direction in the upper layer region from the ground surface to the upper layer reinforcement body 2A is defined as the upper layer thickness h1, and the thickness in the depth direction in the middle layer region between the upper layer reinforcement body 2A and the lower layer reinforcement body 2B. Is the middle layer thickness h2. Moreover, it is set as the thickness lower layer thickness h3 of the depth direction of the lower layer area | region between the lower layer reinforcement improvement body 2B and base layer S11. Using this ground model, the shear deformation suppression effect in the pile-type improved body 3 was determined. The liquefied layer S12 has a liquefied layer thickness H.

In order to evaluate the shear deformation suppressing effect, the respective shear strain ratios γ _max / γ _{max (unreinforced)} in the upper layer region, the middle layer region, and the lower layer region were determined. Here, γ _max is a shear strain value generated in the ground between piles when a reinforced improvement body is added to the pile type improvement body, and γ _{max (unreinforced)} is a pile in the case of only the pile type improvement body. This is the shear strain value generated in the interstitial ground. Therefore, the shear strain ratio is a reduction rate of the shear strain at the time of an earthquake that is suppressed when the reinforcing body enters the ground between piles improved. The lower the shear strain ratio γ _max / γ _{max (unreinforced)} , the higher the shear deformation suppressing effect, which means that the occurrence of shear deformation is suppressed.

In the seismic response analysis, the liquefaction layer thickness H is constant, and the upper layer thickness h1, the middle layer thickness h2, and the lower layer thickness h3 are appropriately changed, and the respective shear strain ratios γ _max / γ in the upper layer region, the middle layer region, and the lower layer region. _{max (unreinforced)} was determined. The results are shown in FIGS. 7A, 7B, and 7C for the upper layer region and the lower layer region, respectively. Moreover, from the results of the seismic response analysis, the ratio of the thickness in the depth direction of the ground between the piles (upper layer thickness h1, middle layer thickness h2, lower layer thickness h3) to the liquefaction layer thickness H is effective in suppressing liquefaction. Thus, the arrangement of the reinforcement improvement body was determined. In other words, it is reasonable for the liquefaction suppression to set the separation in the depth direction of the reinforcing improvement body at the distance determined here.

  FIG. 8 is an example of a result of a repeated loading test in which a specimen made of sand simulating a liquefied layer was given a certain strain corresponding to repeated earthquake force. Here, “RD” in FIG. 8 means relative density, and indicates what percentage of the density of the specimen is between the dense packing and the loose packing. “Σ′3” indicates the restraining pressure of the specimen when the experiment was performed. Further, “f” represents a frequency representing the number of times of loading of the load per unit time when the load is loaded on the specimen in order to reproduce the seismic force.

  As can be seen from FIG. 8, if the shear strain generated in the ground can be suppressed by about 50%, the number of repetitions of the seismic force until liquefaction increases greatly, and the margin for the repeated seismic force is greatly improved. Therefore, if the shear strain can be reduced to 50%, the risk of liquefaction can be greatly reduced. From this, the arrangement of the reinforcement bodies 2A and 2C was examined with a shear strain ratio of 50% or less as a target value.

  As shown in FIG. 7A, in the upper layer region, when the upper layer thickness h1 of the inter-pile ground is 20 to 30% of the liquefied layer thickness H, the shear strain generation ratio can be suppressed to about 50%. Moreover, as shown in FIG. 7B, in the lower layer region, when the lower layer thickness h3 of the inter-pile ground is 30 to 40% of the liquefied layer thickness H, the shear strain generation ratio can be suppressed to about 50%. it can. The difference in the ratio of the upper layer region and the lower layer region to the liquefied layer thickness H is that the upper layer region away from the base layer has a larger shear deformation, and therefore it is necessary to densely insert the reinforcement body 2 in the upper layer region. This is due to From this result, it can be seen that it is preferable to set the formation interval of the reinforcing improvement bodies 2A and 2B so that the upper layer thickness h1 and the lower layer thickness h3 are about 20 to 40% of the liquefied layer thickness H. .

In the middle layer region between the upper layer reinforcement body 2A and the lower layer reinforcement body 2B, as shown in FIG. 7C, the shear strain ratio γ _max / γ _{max (unreinforced)} as the middle layer thickness h2 decreases. Becomes smaller, and the effect of suppressing shear deformation becomes higher. Here, when the middle layer thickness h2 is 30% or less of the liquefied layer thickness H, the ratio of decreasing the shear strain ratio γ _max / γ _{max (unreinforced)} decreases, and a large increase in the shear deformation suppressing effect cannot be expected. Therefore, it is most reasonable to provide the reinforcement bodies 2A and 2B so that the middle layer region h2 is about 30% of the liquefied layer thickness H.

Next, the number of reinforcement improvement bodies formed between the pile type improvement bodies 3 will be examined. Now, the number of reinforcement improvement bodies is set to n, and the thickness of a reinforcement improvement body is set to t uniformly. In this case, the following equation (1) is established.
H = h1 + h2 + h3 + n · t (1)

Here, the intermediate layer thickness h2 is the total thickness when a plurality of intermediate layer regions are formed. At this time, if the upper layer thickness h1, the middle layer thickness h2, and the lower layer thickness h3 are all 20% of the liquefied layer thickness H, the equation (1) can be expressed by the equation (2).
H = 0.2H + 0.2H + 0.2H + n · t (2)

  Since the liquefaction layer thickness H is a predetermined value in advance depending on the liquefaction countermeasure ground, the number and thickness of the reinforcing improvement bodies are determined by determining one of them. For example, when the thickness t of the reinforcement improvement body is 0.1H, the number n of the reinforcement improvement bodies is 4. In this way, a reinforcement improvement body can be formed suitably.

  Next, a second embodiment of the present invention will be described. FIG. 9 is a sectional side view of the liquefaction countermeasure ground according to the second embodiment. As shown in FIG. 9, the liquefaction countermeasure ground S2 according to the present embodiment includes a base layer S21 and a liquefaction layer S22, like the liquefaction countermeasure ground S1 according to the first embodiment. A plurality of pile-type improved bodies 3 are formed in the formation layer.

  Four of the plurality of pile-type improved bodies 3 are arranged at positions that become square corners in plan view, like the pile-type improved body 1 in the first embodiment shown in FIG. Moreover, four reinforcement improvement bodies 4A-4D spaced apart in the height direction are formed between the adjacent pile type improvement bodies 3.

  Among these, the 1st reinforcement improvement body 4A is formed in the form exposed to the ground surface in liquefaction layer S22. A second reinforcement improvement body 4B is formed as a lower layer of the first reinforcement improvement body 4A, and a third reinforcement improvement body 4C is formed as a lower layer of the second reinforcement improvement body 4B. Further, a fourth reinforcement improvement body 4D is formed as a lower layer of the third reinforcement improvement body 4C.

  Here, when the thickness in the depth direction of the first reinforcement improvement body 4A to the fourth reinforcement improvement body 4D is compared, the first layer thickness t1 which is the thickness of the first reinforcement improvement body 4A is the thickest. Next, the second layer thickness t2 which is the thickness of the second reinforcement improvement body 4B is increased. Subsequently, the third layer thickness t3 that is the thickness of the third reinforcement improvement body 4C is increased, and the fourth layer thickness t4 that is the thickness of the fourth reinforcement improvement body 4D is the thinnest. The other points have the same configuration as that of the first embodiment.

  Next, the effect | action of the liquefaction countermeasure ground S2 which concerns on this embodiment is demonstrated. In the liquefaction countermeasure ground S2 according to the present embodiment, the plurality of pile-type improvement bodies 3 are integrated by the reinforcement improvement bodies 4A to 4D. For this reason, there exists an effect similar to the liquefaction countermeasure ground S1 which concerns on the said 1st Embodiment. Moreover, in the liquefaction countermeasure ground S2 which concerns on this embodiment, the thickness is thinned, so that the arrangement | positioning position is deep in reinforcement improvement bodies 4A-4D.

  Generally, in the liquefied layer S22, the closer to the ground surface, the greater the amount of shear deformation in the pile type improved body 3. Further, the shear deformation amount becomes smaller as the depth becomes deeper. Thus, the 4th reinforcement improvement body 4D in the deep position where the 1st reinforcement improvement body 4A near the ground surface where the amount of shear deformation of the pile type improvement body 3 is large and the shear deformation amount of the pile type improvement body 3 is small is small. By reducing the thickness of the solidified material milk, the shear deformation of the pile-type improved body 3 is efficiently suppressed, thereby effectively preventing the liquefaction countermeasure ground S2 from being liquefied. Can do.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, in the said embodiment, the pile type improvement body 1 and the reinforcement improvement body 2 are used. Although all are formed by the high-pressure jet stirring method, it can also be formed by other deep layer processing methods such as a mechanical stirring method. Of course, other ground improvement methods can also be used.

  For example, a pile-type improved body can be created by biaxial mechanical stirring. In this case, as shown in FIG. 10, it can be set as the aspect which forms the comparatively large diameter reinforcement improvement body 2 between small diameter pile type improvement bodies 1 mutually. In such a case, the reinforcement body 2 is formed by a high-pressure jet stirring method. In this way, it can also be set as the aspect which creates the liquefaction countermeasure ground.

  On the other hand, the pile type improved body and the reinforced improved body can have an appropriate improved diameter. Here, in the high-pressure jet agitation method, it is possible to adjust the improved diameter by adjusting the specification of the jet rod, the jet pressure, and the amount of solidified milk injected. For this reason, as shown in FIG. 11, even when forming a pile-type improved body 1 having a small diameter, for example, φ2 m or less, and a reinforcing improved body 2 having a large diameter, for example, φ5 m, by a high-pressure injection stirring method using a single injection rod. Creation is possible. Of course, even when the large-diameter pile-type improvement body 1 and the small-diameter reinforcement body 2 are formed, it can be similarly formed by a high-pressure injection stirring method using a single injection rod.

  Moreover, in the said embodiment, the reinforcement improvement body 2 and the pile type improvement body 1 are integrated so that the reinforcement improvement body 2 may bite into the pile type improvement body 1, but the reinforcement improvement body 2 is piled improvement body. The reinforcement improvement body 2 and the pile-type improvement body 1 can also be made into an integrated form by making a contact with 1. Furthermore, in the said embodiment, although the pile type improvement body 1 and the reinforcement improvement body 2 are formed and liquefaction countermeasure ground S1 is created, piles, such as a pile type improvement body 1, etc. are created beforehand. Alternatively, a liquefaction countermeasure ground can be created by forming the reinforcement improvement body 2 around it.

DESCRIPTION OF SYMBOLS 1,3 ... Pile type improvement body 2,4 ... Reinforcement improvement body 4A ... 1st reinforcement improvement body 4B ... 2nd reinforcement improvement body 4C ... 3rd reinforcement improvement body 4D ... 4th reinforcement improvement body 4X ... Upper layer reinforcement improvement body 4Y ... lower layer reinforcement body 10 ... injection rod S1, S2 ... liquefaction countermeasure ground S11, S21 ... base layer S12, S22 ... liquefaction layer

Claims (4)

A liquefaction countermeasure ground in which a liquefaction countermeasure is applied to a ground including a base layer and a liquefaction layer formed on an upper layer of the base layer,
A plurality of pile-type improvement bodies are driven from the liquefied layer to the depth reaching the base layer in the ground, and a plurality of columnar reinforcement bodies are formed between the pile-type improvement bodies adjacent in the lateral direction. Has been
Each of the reinforcing bodies formed between the pile-type improved bodies connects the adjacent pile-type improved bodies,
A plurality of the reinforcing bodies are formed apart in the depth direction between the adjacent pile type improved bodies,
As the plurality of reinforcing bodies, comprising an upper layer reinforcing body disposed in the uppermost layer, and a lower layer reinforcing body disposed in the lowermost layer,
The thickness between the upper layer reinforcing body and the ground surface in the liquefied layer and the thickness between the lower layer reinforcing body and the base layer are each 20% of the thickness in the depth direction of the liquefied layer. The distance in the depth direction between the upper layer reinforcing body and the lower layer reinforcing body in the liquefied layer is set to a distance of ˜40%, and is 30% or less of the thickness in the depth direction of the liquefied layer. Liquefaction countermeasure ground characterized by being set at a distance of. A liquefaction countermeasure ground in which a liquefaction countermeasure is applied to a ground including a base layer and a liquefaction layer formed on an upper layer of the base layer,
A plurality of pile-type improved bodies are placed from the liquefied layer in the ground to a depth reaching the base layer, and a reinforcing body is formed between adjacent pile-type improved bodies,
The reinforcing bodies are connected to each other between the pile-type improved bodies adjacent to each other, and are formed between the adjacent pile-type improved bodies apart from each other in the depth direction.
As the plurality of reinforcing bodies, comprising an upper layer reinforcing body disposed in the uppermost layer, and a lower layer reinforcing body disposed in the lowermost layer,
The thickness between the upper layer reinforcing body and the ground surface in the liquefied layer and the thickness between the lower layer reinforcing body and the base layer are each 20% of the thickness in the depth direction of the liquefied layer. The distance in the depth direction between the upper layer reinforcing body and the lower layer reinforcing body in the liquefied layer is set to a distance of ˜40%, and is 30% or less of the thickness in the depth direction of the liquefied layer. Liquefaction countermeasure ground characterized by being set at a distance of.   The liquefaction countermeasure ground according to claim 1 or 2, wherein the plurality of reinforcing bodies formed apart from each other in the depth direction have a larger volume as they approach the ground surface.   The plurality of pile-type improved bodies are arranged in corners of squares or equilateral triangles in plan view, respectively, or arranged in a staggered manner in plan views, respectively. Liquefaction countermeasure ground.

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