JP2012241499A - Ground for fighting subsidence due to shaking by travelable inclination, and method for creating the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground for fighting subsidence due to shaking by a travelable inclination, which can effectively suppress such subsidence in the peripheral area of a non-liquefied layer structure and the surrounding ground thereof while suppressing the consumption of solidification material milk; and a method for creating the same.SOLUTION: A plurality of pile type improving bodies 1 are installed in a non-liquefied layer S12 of a ground S1 for fighting ground surface subsidence. The plurality of pile type improving bodies 1 are arranged in a zigzag shape, or at a vertex of a square. The pile type improving bodies 1 are adjusted to have a BL ratio of 0.2-0.4. Thus the arrangement of the plurality of pile type improving bodies 1 is the arrangement for suppressing ground surface subsidence to prevent ground surface subsidence of the ground S1 for fighting ground surface subsidence.

Description

  The present invention relates to a subsidence subsidence ground created by applying a subsidence subsidence measure to a ground having a non-liquefied layer structure peripheral region in the vicinity of an underground structure below a groundwater level and the like, and a construction method thereof.

  In the liquefied layer where the groundwater level is high and saturated, liquefaction occurs when the ground is repeatedly deformed during an earthquake, resulting in increased water pressure and loss of shear resistance in the ground. On the other hand, in the case of loose sand ground with low groundwater level and shallower than the groundwater level, although water exists in the gap between the ground, it is in an unsaturated state. Is difficult to rise. If the water pressure does not increase, the earth pressure acts as an effective stress, so that the shear resistance of the ground is maintained, so that the liquefaction phenomenon does not occur. Therefore, the sand ground at a position shallower than the groundwater level is a non-liquefied layer.

  In such a non-liquefied layer, liquefaction does not occur, but in subsurface structures and areas surrounding buildings (hereinafter referred to as “non-liquefied layer structure peripheral areas”), the occurrence of shaking subsidence is a problem. It has become. The causes of subsidence in the area around the non-liquefied layer structure are mainly divided into two main categories. One is the volumetric shrinkage of the ground due to repeated shear forces generated by the earthquake, and the other is slip settlement due to the relative horizontal displacement between the ground and the underground structure. The phenomenon of shaking subsidence has been confirmed around the structure, and is a subsidence phenomenon caused by a combination of the above two causes.

  The generation mechanism of rock subsidence is clearly different from land subsidence due to liquefaction. For this reason, as countermeasures against sag subsidence, the shear rigidity of the ground is increased so as not to cause volume shrinkage due to accumulated strain during an earthquake, and the response difference between the ground and the adjacent structure is eliminated to suppress relative horizontal displacement. It is considered necessary to improve the peripheral region of the non-liquefied layer structure (see Non-Patent Document 1).

  Although there is no specific technology specifically disclosed as an improved form of the area around the non-liquefied layer structure below the groundwater level (hereinafter also referred to as the “target area for improvement”), for example, if the mechanism of the occurrence of subsidence is taken into account There is a method of creating an improved body by solidifying the entire target area with a solidifying material such as cement. The main reason for the rock subsidence is that the initial stiffness before the earthquake decreases due to repeated loads that are repeatedly subjected to loading and unloading after the earthquake, and the ground softens, resulting in a large amount of ground deformation. It is thought that the rearrangement of particles is likely to occur. Also, as the amount of deformation of the ground increases, the relative horizontal displacement between the structure and the ground increases, and the amount of settlement increases further as the soil slides into the gap formed between the structure and the ground. . Therefore, by improving the entire surface of the ground and increasing the initial rigidity, the amount of decrease in the rigidity of the ground after receiving a repeated load can be reduced, and settlement can be suppressed.

  However, the method of solidifying the entire improved region has problems such as requiring a large amount of solidification material and prolonging the construction period. It is also conceivable to perform partial solidification that efficiently improves a part of the improved region in contrast to the entire surface improvement that improves the entire improved region. In this partial solidification, there is a method of creating a ground improvement body in a part of the improved region. In this construction method, only a part of the ground is solidified, so the amount of solidification material used can be reduced and the construction period can be shortened.

  When creating a ground improvement body, a deep mixing method or a chemical injection method is used. Of these methods, the chemical solution injection method is generally a method of replacing soil water with a chemical solution, and therefore it is not appropriate to apply the method to an improvement target region that is shallower than the groundwater level. Therefore, when creating a ground improvement body, it is possible to use a deep layer processing method.

  The deep mixing treatment 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 injected at high pressure in the ground to perform stirring. Conventionally, the following is known as a method of solidifying a part of the ground by a deep mixing treatment method. For example, the solidified milk is mixed and agitated with the ground, and the ground improvement body is arranged in a plane lattice shape. This planar grid-like ground improvement body is formed in a wall shape when viewed from the side. This ground improvement body suppresses the shear deformation of the ground during an earthquake and suppresses the movement of groundwater and soil (for example, see 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).

JP 2000-265455 A JP 2008-50787 A JP 2001-342637 A

Makoto Ishimaru, Tadashi Kawai: Gravity field model shaking table experiment to understand the subsidence mechanism during earthquake of a rigid structure near the bottom with a fixed bottom, Geotechnical Journal, Vol.4, No.4, 369-380.

  In creating ground for countermeasures against subsidence, the method of solidifying the entire area to be improved is the most reliable method to prevent subsidence. However, since the entire solidified material milk in the improvement target region is injected to solidify the entire improvement target region, there is a problem that a large amount of solidified material 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 for creating a grid-like ground improvement body on a part of the ground disclosed in Patent Documents 1 to 3, it is possible to suppress the use amount of the solidifying material milk and the medicine. 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, since the problem that the loss of solidification material milk arises still remains, there is room for further suppression of the consumption of solidification material milk.

  On the other hand, when the whole improvement object area is solidified and the whole improvement body is created, the difference in rigidity between the structure and the whole improvement body becomes small, but the difference in rigidity between the unimproved ground and the whole improvement body is very large. It is getting bigger. For this reason, when seismic motion is input to the whole improved body in the vertical direction of the wall, the way of shaking between the whole improved body and the unimproved ground is greatly different, and the relative horizontal displacement is greatly different. Therefore, there has been a problem that there is a possibility that the settlement proceeds due to a gap between the overall improved body and the unimproved ground.

  Therefore, the problem of the present invention is to reduce the consumption of the solidified milk and to prevent the subsidence in the area around the non-liquefied layer structure and the surrounding subsidence effectively. And to provide a method for producing the same.

  The ground for subsidence subsidence according to the present invention that solves the above problems is included in the base layer and the non-liquefied layer shallower than the groundwater level in the upper layer of the base layer, and the non-liquefied layer structure around the underground structure The ground with the surrounding area is a rock subsidence countermeasure ground with a countermeasure for rock subsidence, and a plurality of pile-type improvement bodies are placed in the non-liquefaction layer, It is characterized by an arrangement that suppresses subsidence.

  In the rock subsidence countermeasure ground according to the present invention, a plurality of pile-type improvement bodies are placed in the non-liquefaction layer, and the plurality of pile-type improvement bodies are arranged to suppress the rock-in subsidence. The sunk subsidence placement is an effective way to control the squeeze subsidence, so even if it is repeatedly deformed by an earthquake, the ground subsidence can be suppressed, eliminating the need for repairs due to ground subsidence. . Therefore, it is possible to effectively suppress shaking subsidence in the non-liquefied layer structure peripheral region and the surrounding ground. In addition, since the pile type improved body is arranged to suppress the squeeze subsidence and suppress the squeeze subsidence, it is necessary to form the pile type improved body rather than solidifying the whole area around the non-liquefied layer structure. The consumption of the solidified milk can be suppressed. Therefore, it is possible to suppress the consumption of the solidified milk, and to effectively suppress the sinking and sinking in the area around the non-liquefied layer structure and the surrounding ground.

  Here, the shaking subsidence suppressing arrangement can be an aspect in which a plurality of pile-type improved bodies are arranged in a staggered manner in a plan view of the non-liquefied layer.

  In this way, when the liquefied layer is viewed in plan, the pile type improved body is placed in a staggered arrangement, and the rocking is an arrangement that is effective in suppressing land subsidence. A sinking suppression arrangement can be suitably generated.

  Moreover, the distance relationship between pile type improvement bodies can be set as the aspect by which the ratio of the span between piles and the placement pitch is 0.2-0.4.

  Thus, while the distance relationship between the pile-type improved bodies is the span B between piles / the placement pitch L = 0.2 to 0.4, while suppressing the planar improvement rate of the ground, It is possible to suitably generate the sag subsidence arrangement.

  Furthermore, the squeeze settlement suppression arrangement can be an aspect in which a plurality of pile-type improved bodies are respectively located at the vertices of a square in a plan view of the non-liquefied layer.

  In this way, when the liquefied layer is viewed in plan, a pile-type improvement body is preferably generated by placing a pile-type improvement body in an arrangement in which a plurality of pile-type improvement bodies are respectively located at the vertices of a square. can do.

  Moreover, it can be set as the aspect by which the ratio of the span between piles between pile type improved bodies located in the diagonal of a square, and a placement pitch is 0.2-0.4.

  Thus, by making it the span span between piles between the pile type improvement bodies located in the diagonal of a square / setting pitch L = 0.2-0.4, the planar improvement rate of the ground It is possible to suitably generate the sag subsidence arrangement while suppressing the above.

  Furthermore, the pile type improvement body can be set as the aspect constructed | assembled by the high pressure jet stirring.

  Thus, an unevenness | corrugation can be formed in the side surface of a pile type improved body by the pile type improved body being constructed | assembled by the high pressure jet stirring.

  On the other hand, the method for constructing the ground for subsidence subsidence according to the present invention, which has solved the above-mentioned problems, is included in the basement layer and the non-liquefaction layer shallower than the groundwater level in the upper layer of the basement layer. When taking measures against sunk subsidence, where the ground with the surrounding area of the liquefied layer structure is subjected to sunk subsidence measures, multiple pile-type improved bodies are placed in a non-liquefied layer as a squeeze subsidence arrangement. It is characterized by placing a formula improvement body.

  According to the rock subsidence countermeasure ground and its creation method according to the present invention, the consumption of the solidified milk is suppressed, and the rock subsidence in the region around the non-liquefied layer structure and the surrounding ground is effectively suppressed. can do.

It is a sectional side view of the rock subsidence countermeasure ground which concerns on 1st Embodiment. It is a top view of the rock subsidence settlement ground. It is an expanded sectional side view of a pile type improved body. It is process drawing which shows the creation process of the sway subsidence countermeasure ground. It is a top view which shows the positional relationship of a pile type improved body. It is a graph which shows the relationship between the settlement rate and B / L ratio in the result of a vibration experiment. It is a graph which shows the relationship between the improvement rate of a ground, and B / L ratio. It is a graph for demonstrating the maximum value of suitable B / L ratio. It is a graph for demonstrating the minimum value of suitable B / L ratio. It is a graph for demonstrating the range of suitable B / L ratio and improvement rate. It is a top view which shows the other example of the positional relationship of a pile type improved body.

  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 the ground surface settlement countermeasure ground according to the first embodiment of the present invention, and FIG. 2 is a plan view thereof. As shown in FIG. 1 and FIG. 2, the ground surface settlement countermeasure ground S1 which is a ground subsidence countermeasure ground according to the present embodiment includes a basement layer S11, and the upper layer of the basement layer S11 has a shallow groundwater level. A non-liquefaction layer S12 is present. The base layer S11 also serves as a support layer for underground structures, and is a solid ground that hardly deforms even when an earthquake occurs. Further, the non-liquefied layer S12 is made of loose sandy soil and the like, and is a ground that is liable to stagnate and sink when an earthquake occurs.

  In addition, a plurality of pile-type improved bodies 1 are placed in the non-liquefied layer structure peripheral region R in the vicinity of an important underground structure M such as a common groove formed in the non-liquefied layer S12. . The pile improvement body 1 has reached the base layer S11 in the lower layer beyond the non-liquefaction 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. In addition, as shown in FIG. 2, a plurality of pile-type improved bodies 1 are placed on the ground surface settlement countermeasure ground S1, and four of them are located at square corners in plan view. Has been placed.

  The diameter when the pile-type improved body 1 is viewed in plan is, for example, about φ1 to 5 m in the case of the high-pressure jet stirring method. In addition, the arrangement of the plurality of pile-type improved bodies 1 is a sunk subsidence suppression arrangement which is an effective arrangement for suppressing sunk subsidence that prevents ground subsidence due to subsidence subsidence of the ground subsidence countermeasure ground S1. . The shaking subsidence suppression arrangement is determined by the pile diameter (improved diameter) of the pile-type improved body 1, the span between piles, the placement pitch, and the like. Details of these will be described later.

  The pile-type improved body 1 can be formed by high-pressure jet agitation or mechanical agitation, but when formed by high-pressure agitation jet, fine irregularities are formed on the side surface of the pile-type improved body 1 as shown in FIG. Shape is added. The dashed-dotted line in FIG. 3 has shown the part which measures the improvement diameter in the pile type improvement body 1. FIG.

  Next, the creation procedure of the ground surface settlement countermeasure ground according to the present embodiment will be described. FIG. 4 is a process diagram showing a process of creating a ground for subsidence. As shown in FIG. 4 (a), when constructing the ground for subsidence, first the pile type improvement that penetrates the non-liquefied layer S12 around the underground structure M and reaches the base layer S11. Build body 1 sequentially. FIG. 4A shows a state in which the creation of some of the pile-type improved bodies 1 is completed and the pile-type improved bodies 1 are created on the sides thereof.

  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, as shown in FIG. 4A, the injection rod 10 is inserted at a position where the pile type improved body 1 is formed. An injection port for the solidified milk is formed at the tip of the injection rod 10. When the injection rod 10 is inserted, as shown in FIG. 4 (b), the solidified milk is injected from the side of the injection rod 10 at a high pressure and is gradually pulled up while rotating the injection rod 10. It is effective to inject solidified material milk and compressed air from the injection rod 10. In this way, the injection rod 10 is pulled up to the top of the ground surface settlement countermeasure ground S1, and the placement of the pile-type improved body 1 is completed. Thereafter, by placing the pile-type improved body 1 at each position where the ground surface settlement suppression arrangement is provided, the ground surface settlement countermeasure ground S1 is created.

  In this way, in the ground subsidence countermeasure ground S1 created by the above procedure, a plurality of pile-type improvement bodies 1 are placed in the non-liquefaction layer S12. It is a surface settlement suppression arrangement. For this reason, since surface subsidence can be suppressed only by forming pile type improvement object 1, ground surface subsidence itself can be controlled, reducing the need for maintenance. Furthermore, since the pile-type improved body 1 is not overlapped and built in a wall shape, the average improvement rate with respect to the usage amount of the improved material can be increased. Moreover, the slime discharge process by improvement can be reduced by the several pile-type improvement body 1 being arrange | positioned by ground subsidence suppression arrangement | positioning.

  Hereinafter, the arrangement for suppressing the subsidence will be described. In the ground subsidence countermeasure ground according to the present embodiment, when an earthquake motion that causes sunk subsidence occurs, the subsidence of the ground surface between the plurality of pile improvement bodies 1 is caused by the arrangement of the plurality of pile improvement bodies 1. It is to suppress. In this embodiment, in order to suppress subsidence of the ground surface due to rock subsidence, the distance relationship of the pile-type improved body 1 is constructed with a predetermined span between piles. Here, attention is paid to the span between piles in the pile-type improved body 1.

  The present inventors conducted a model experiment for examining the relationship between the span between piles and the settlement rate of the ground surface. In the experiment, as shown in FIG. 5, a countermeasure ground model, which is a model of the ground subsidence countermeasure ground in which the pile-type improved bodies 1 are arranged in a staggered manner, was prepared. In this countermeasure ground model, as an example, the span B between the piles is adjusted under the condition that all the improved diameters D of the pile-type improved body 1 are unified, and the ratio between the span B between the piles and the placement pitch L (hereinafter, “B / L ratio ”) was adjusted, and the land surface settlement rate was measured.

  In addition, as a comparative example, a ground subsidence rate in which an improvement rate when viewed in plan in a conventional general grid improvement (hereinafter simply referred to as “improvement rate”) is 50% was also measured under the same conditions. However, in a general lattice improvement, the improvement rate may be increased to about 60%. The result is shown in FIG. In FIG. 6, the results of the examples are indicated by circles, and the results of the comparative examples are indicated by squares. Moreover, the 1st line L1 which shows the ratio of the ground surface settlement rate with respect to B / L ratio defined based on the result of the Example was calculated | required.

  As shown in FIG. 6, in the pile type improvement body 1 in an Example, the tendency for the ground surface settlement rate to become small was seen, so that B / L ratio became small. From this, it can be seen that in order to reduce the land surface settlement rate, it is required to reduce the B / L ratio. Here, in the lattice improvement as a comparative example, the B / L ratio was about 0.7, and the ground surface settlement rate in this case was about 0.4.

  Next, the relationship between the improvement rate and the B / L ratio will be described with reference to FIG. FIG. 7 is a graph showing the relationship between the improvement rate and the B / L ratio. An example of conventional lattice improvement is shown by the second line L2, and an example of the pile type improvement of the embodiment is shown by the third line L3. ing. As shown in FIG. 7, it can be seen that the B / L ratio becomes smaller when the pile improvement of the example is the same improvement rate as compared with the conventional lattice improvement. Specifically, the B / L ratio when the improvement rate in the conventional lattice-like improvement is 50% is about 0.7, while the pile type improvement of the example has an improvement rate of 50%. The B / L ratio is about 0.2.

  In the pile type improvement according to the embodiment, the ground surface settlement rate can be lower than or equivalent to the conventional grid-like improvement, but it is required to reduce the improvement rate. Since the ground surface settlement rate in the conventional lattice improvement is about 0.4, the ground surface settlement rate is required to be 0.4 or less also in the pile type improvement according to the embodiment. The B / L ratio at which the ground surface settlement rate is 0.4 is the maximum value of the B / L ratio in the pile-type improved body 1. The maximum value of the B / L ratio in the pile type improved body 1 is 0.4 as shown in FIG.

  On the other hand, the improvement rate in the conventional lattice improvement is about 60%, and the minimum value of the B / L ratio in the pile-type improvement body 1 is a numerical value corresponding to this improvement rate of 60%. For this reason, the minimum value of the B / L ratio in the pile-type improved body 1 is 0.2 or more as shown in FIG. Accordingly, the B / L ratio in the pile-type improved body 1 according to the embodiment is preferably in the range of 0.2 to 0.4, and the pile is in the range of B / L ratio = 0.2 to 0.4. By disposing the formula improvement body 1, a high settlement suppression effect can be obtained while the improvement rate is lower than that of the lattice improvement. Moreover, as shown in FIG. 10, when the B / L ratio in the pile-type improved body 1 is 0.2 to 0.4, the improvement rate is about 30% to 60%. This range X becomes a range which shows the suitable conditions for creating the pile type improved body 1.

  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, although the several pile type improvement body 1 is arrange | positioned at the vertex of a square, it can also arrange | position in a staggered manner.

  When the pile type improved body 1 is arranged at the apex of the square, as shown in FIG. 11, the inter-pile span BS is a distance between the pile type improved bodies located at the diagonal of the square. By setting the span span between piles as this distance, the pile-type improved body 1 is disposed in the range of span span BS / pile pitch L = 0.2 to 0.4, and the improvement rate is lower than that of the grid-like improvement. However, a high settlement suppression effect can be obtained.

DESCRIPTION OF SYMBOLS 1 ... Pile type improvement body 1A ... Concavity and convexity 10 ... Injection rod D ... Improvement diameter L ... Placing pitch S1 ... Ground surface settlement countermeasure ground S11 ... Base layer S12 ... Non-liquefaction layer

Claims (7)

A ground subsidence included in the non-liquefiable layer below the groundwater level in the upper layer of the basement layer and the surrounding area of the non-liquefied layer structure in the vicinity of the underground structure was subjected to a sunk subsidence measure It is a ground to prevent subsidence,
A plurality of pile-type improvements are placed in the non-liquefaction layer,
The plurality of pile-type improved bodies have a sunk subsidence suppression ground, wherein the sunk subsidence ground is provided.   2. The rock subsidence countermeasure ground according to claim 1, wherein the rock subsidence suppression arrangement is an arrangement in which the non-liquefied layer is viewed in plan and a plurality of the pile-type improved bodies are arranged in a staggered manner.   The ground subsidence countermeasure ground according to claim 2, wherein the distance relationship between the pile-type improved bodies is such that the ratio between the span between piles and the placement pitch is 0.2 to 0.4.   2. The rock subsidence subsidence ground according to claim 1, wherein the rock subsidence suppression arrangement is an arrangement in which the plurality of pile-type improved bodies are respectively located at the vertices of a square in a plan view of the non-liquefied layer.   The rock subsidence countermeasure ground according to claim 3, wherein a ratio of a span between piles and a placement pitch between pile-type improved bodies located on the diagonal of the square is 0.2 to 0.4.   The rock subsidence countermeasure ground according to any one of claims 1 to 5, wherein the pile-type improved body is constructed by high-pressure jet stirring. A ground subsidence included in the non-liquefiable layer below the groundwater level in the upper layer of the basement layer and the surrounding area of the non-liquefied layer structure in the vicinity of the underground structure was subjected to a sunk subsidence measure In taking measures against stagnation and subsidence,
A method for creating a ground for countermeasures against sunk subsidence, wherein the plurality of stake type improved bodies are placed in the non-liquefied layer as a sunk subsidence restraining arrangement.

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