JP2008101379A - Supporting structure and construction method for structure foundation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a foundation uneven settlement hard to occur when liquefaction occurs in the ground below the foundation, and to suppress the foundation settlement while preventing inclination of the foundation even if its settlement is just about to occur, when suppressing the settlement of the foundation by utilizing buoyancy (water pressure). <P>SOLUTION: This supporting structure of the foundation 3 is composed of: sheet piles 4 inserted into the liquefied ground 1 to surround the foundation 3 of a structure 2 while being adjacent to the foundation 3 and being continuous in the peripheral direction of the foundation 3; and a light-weight material 6 provided or put in/into a region being deeper than a bottom face of the foundation 3 and surrounded by the sheet piles 4 to let the buoyancy or water pressure received by the light-weight material 6 from the underground water, act on the bottom face of the foundation 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a support structure and a construction method for a structure foundation that suppresses settlement of the foundation when liquefaction occurs in the ground under the foundation that supports a structure such as a pier or a building.

  When the foundation of the structure is placed on a liquefied ground such as a sandy ground as shown in FIG. 6- (a), the sandy ground or the like has a high supporting force statically because it does not easily cause consolidation settlement. During an earthquake, the groundwater level rises as shown in (b) due to the increase in pore water pressure, and the ground rapidly loses its bearing capacity. As the water pressure to the ground rises due to the rise in the groundwater level, buoyancy acts on the sand (soil) particles, so that the strength of the sand is lowered and the ground bearing capacity is lowered, resulting in the foundation sinking.

  As countermeasures against liquefaction in such sandy grounds, ground resistance is reduced by compacting the ground (sand compaction pile method, etc.), and by adding and mixing stabilizers in the ground. There are a method for increasing the force (such as deep mixing method) and a method for increasing the effective stress (such as deep well method) by changing the saturated region to the unsaturated region by lowering the groundwater level.

  In addition, there is a method (such as a continuous underground wall method) that constrains the ground from the surroundings by partitioning the ground with walls and suppresses the shear deformation of the ground when liquefaction occurs. There are no effective measures to prepare for the occurrence of the problem.

  Since sand particles settle in the liquefied sandy ground and the groundwater rises, the water pressure from the groundwater that rises pushes up the bottom surface of the foundation or generates buoyancy in the foundation. As a result, the foundation may cause subsidence.

  In order to solve this problem, there is a method in which a resin foam block is installed under the bottom surface of the foundation so as to suppress uneven settlement of the foundation (structure) using buoyancy (see Patent Document 1).

JP-A-6-287965 (Claim 1, paragraphs 0008, 0019 to 0023, FIG. 1)

  In the method of Patent Document 1, in order to ensure the integrity of the steel sheet pile and the foundation, the foundation is joined in an engaged state with the upper end of the steel sheet pile (Claim 1), but the foundation is the upper end of the steel sheet pile. Since the steel sheet pile does not surround the entire foundation, it is difficult to maintain the integrity of the foundation and the steel sheet pile when the foundation tilts and tries to cause uneven settlement. it is conceivable that. Since the steel sheet pile surrounds the resin foam block and the ground below it, it can behave integrally with these (paragraph 0018), but the steel sheet pile faces when the foundation is inclined. This is because the displacement of the foundation cannot be constrained by the surface.

  As long as the steel sheet pile cannot constrain the inclination of the foundation, the uneven settlement of the foundation must be prevented by the buoyancy (hydraulic pressure) by the resin foam block and the frictional force that is the resistance against the settlement of the steel sheet pile. However, since the force acting on the foundation from the resin foam block is only the upward water pressure at the bottom surface of the resin foam block, there is a lack of certainty in ensuring stability against the inclination of the foundation.

  Even after the foundation or the steel sheet pile is once inclined, the foundation has no room for receiving a restriction that restricts the inclination from the steel sheet pile, so that the inclination cannot be corrected.

  In the present invention, in the case of using the buoyancy (hydraulic pressure) to suppress foundation subsidence, the subsidence is difficult to occur, and when the subsidence is about to occur, the foundation subsidence is prevented while preventing inclination. The foundation support structure and construction method that can be suppressed are proposed.

  The structure foundation support structure according to the first aspect of the present invention is inserted into the liquefied ground so as to surround the foundation of the structure, adjacent to each other, and the sheet pile continuous in the circumferential direction of the foundation, A light-weight material that is installed or filled in an area surrounded by the sheet pile deeper than the bottom surface, and that the light-weight material receives buoyancy received from groundwater, or water pressure is applied to the bottom surface of the foundation. To do. Liquefied ground mainly refers to sandy ground or ground containing sandy soil.

  The sheet pile wall, which is adjacent to the sheet pile so as to surround the foundation of the structure, is in contact with the side of the foundation (surface), and the integrity of the foundation and the sheet pile wall is Strengthens and behaves as a single unit, and therefore has the effect of restraining the foundation from its surroundings against its inclination. This effect is exhibited in two horizontal directions by the sheet pile surrounding the foundation. As long as the sheet pile wall is maintained in the vertical state (the state at the time of construction), for example, even if the foundation tries to incline, the sheet pile wall works to prevent the inclination and keep the foundation bottom level, so the foundation is not settled. Possesses high stability against

  As shown in FIG. 1- (b), earth pressure and water pressure act on the sheet pile wall from the outer periphery to the inner periphery of the region surrounded by the sheet pile wall. When groundwater exists also on the inner periphery of the sheet pile wall, the water pressure acts from the inner periphery toward the outer periphery, but the pressure acting from the outer periphery is large due to the earth pressure. Since the water pressure and earth pressure from the outer periphery of the sheet pile wall act on the entire surface of the sheet pile wall surrounding the foundation, the entire sheet pile wall that circulates is stable against inclination and horizontal movement. Since the sheet pile wall surrounds the foundation and contacts the side surface of the foundation with the surface, the pressure applied to the sheet pile wall also acts on the side surface of the foundation, so that the stability of the foundation inclination and horizontal movement is also ensured.

  For example, when the groundwater level is above the bottom of the foundation, upward water pressure acts on the bottom of the foundation as shown in (a), and buoyancy acts on lightweight materials. Supports the foundation with the ground below the sheet pile wall. The buoyancy acting on the lightweight material varies depending on the level of the groundwater level. As shown in (a), if the groundwater level is equal to or higher than the upper end level of the lightweight material, a constant buoyancy acts on the lightweight material. When the groundwater level is below the level of the upper end of the lightweight material, the buoyancy for the volume of the lightweight material immersed in the groundwater acts and can fluctuate.

  As shown in Fig.1- (a), if the distance from the groundwater level to the bottom of the foundation is L, the distance from the groundwater level to the bottom of the lightweight material is H, and the area of the bottom of the foundation and the lightweight material is A, The sum of the acting water pressures P1w is ρgLA, the buoyancy PF acting on the lightweight material is ρg (HL) A, and the force of ρgLA + ρg (HL) A = ρgHA is acting on the bottom of the foundation.

  When an earthquake occurs and the liquefied ground under the lightweight material and around the sheet pile wall liquefies and the groundwater level rises as shown in (b), if there is no lightweight material under the foundation, The ground that supports the ground loses its support ability and the foundation tries to sink. On the other hand, in Claim 1, since the light weight material exists under the foundation, the buoyancy of the light weight material and the water pressure on the bottom surface of the foundation maintain the state of supporting the foundation, and therefore the settlement of the foundation is restrained. . In addition, since the water pressure P1W acting on the bottom of the foundation increases (P1W> P1w) as L increases as the groundwater level rises, the foundation receives higher bearing capacity from the groundwater after the rise than before the rise of the groundwater level. It will be.

  By receiving a high bearing capacity after the foundation rises before the groundwater level rises, the stability of the foundation due to groundwater increases after the liquefaction of the supporting ground, and the foundation is less prone to subsidence due to liquefaction. For this reason, even if the ground loses the supporting force, the settlement of the foundation is suppressed or prevented. Even if the foundation is about to sink temporarily, the sheet pile wall that moves around the foundation and moves together with the foundation restrains the inclination of the foundation and tries to keep the foundation bottom horizontal. , The uneven settlement of the foundation is prevented.

  Since the water pressure which the bottom face of a foundation receives by the rise of a groundwater level or the water pressure which the bottom face of a lightweight material rises, in order to earn the water pressure which a foundation and a lightweight material receive, from a top to a sheet pile as described in Claim 2 An inclination from the inner peripheral side to the outer peripheral side of the region surrounded by the sheet pile may be given to the lower end. A region partitioned by the sheet pile wall surrounding the foundation is formed in a truncated pyramid shape by giving the sheet pile wall an inclination from the inner peripheral side to the outer peripheral side from the upper end to the lower end.

  In claim 2, as shown in FIG. 4, the sheet pile wall is inclined outward from the center of the foundation from above to below, so that the water pressure and earth pressure acting perpendicularly to the outer peripheral surface of the sheet pile wall Since it has a downward component toward the circumferential side, the sheet pile wall and the foundation are pressed down, and the effect of restraining the foundation from rising during normal times and earthquakes is produced. This effect is maintained even when the groundwater level rises. The pressing effect of the sheet pile wall by water pressure can be obtained if the inclination angle of the sheet pile relative to the vertical plane is secured to about 10 degrees.

  On the other hand, in the case of claim 2, since the area A of the bottom surface of the light weight material increases in a quadratic function as the distance H increases, the buoyancy acting on the light weight material also increases due to an increase in the groundwater level. It is assumed that the buoyancy exceeds the load of the structure and the foundation is lifted. When such a situation is assumed, an inner sheet pile opposite to the sheet pile is inserted on the inner peripheral side of the sheet pile as described in claim 3, and a lightweight material is disposed in a region surrounded by the inner sheet pile. By doing so, it becomes possible to avoid lifting of the foundation. In this case, the area under the bottom of the foundation surrounded by the sheet pile wall is a double wall of the sheet pile wall and the inner sheet pile wall. The inner sheet pile is inserted vertically.

  In claim 3, as shown in FIG. 4, the sheet pile wall surrounds the foundation, and the inner sheet pile wall surrounds the lightweight material below the bottom surface of the foundation, thereby increasing the groundwater level while keeping the outer sheet pile wall inclined. Regardless of this, since the area A of the bottom surface of the lightweight material can be made constant, an increase in buoyancy acting on the lightweight material can be suppressed. The buoyancy acting on the lightweight material is proportional to (HL) because the bottom surface area A of the lightweight material is constant, but L increases when the groundwater level rises. Disappear.

  As mentioned above, the sheet pile circulates around the foundation and the integrity of the sheet pile wall and the foundation is ensured, so that the foundation retains stability against inclination, but the stability against the inclination of the foundation by the sheet pile wall is more In order to raise, the area | region under the bottom face of a foundation surrounded by the sheet pile as described in Claim 4 may be divided into a some area | region by a partition wall. In this case, a lightweight material is arrange | positioned for every divided area | region. A sheet pile is used for the partition wall.

  By dividing the area under the bottom of the foundation into multiple areas, each divided area is constrained by a partition wall, so the stability of the lightweight material for each divided area is obtained, and the weight under the bottom of the foundation is reduced. The stability of the whole material is also improved. In claim 3, the area below the bottom of the foundation is divided into an area surrounded by the inner sheet pile wall and an area outside the area. In claim 4, the area below the bottom of the foundation is divided into a plurality of areas. Similarly to the item 3, it may be divided into an inner region and an outer region.

  According to a fifth aspect of the present invention, in any one of the first to third aspects, the water stoppage between the adjacent sheet piles is ensured, and groundwater is excluded from the region surrounded by the sheet piles. To do. In this case, the lightweight material is in close contact with the bottom surface of the foundation and the inner peripheral surface of the sheet pile, and fills the area surrounded by the sheet pile without any gaps. The formation of a gap between the sheet pile wall and the lightweight material as shown in FIG. 1 may occur when the lightweight material is a molded product of foam. It is obtained by using a material in a particle state, such as a mixed material to which a solidifying material is added.

  In the case of FIG. 1, the groundwater has entered the region surrounded by the sheet pile wall, so that the water pressure due to the groundwater acts upward on the bottom surface of the foundation. In this way, water-stopping between adjacent sheet piles is ensured, and the lightweight material adheres to the bottom surface of the foundation and the inner peripheral surface of the sheet pile, so that groundwater does not enter the area surrounded by the sheet pile wall, so that the lightweight material itself has buoyancy. Does not act, and upward water pressure acts on the bottom surface of the lightweight material.

  As shown in Fig.2- (a), if the distance from the groundwater level to the bottom of the foundation is L, the distance from the groundwater level to the bottom of the lightweight material is H, and the area of the foundation bottom and the lightweight material bottom is A, the bottom of the lightweight material The water pressure P2w of ρgH acts on, and the sum becomes ρgHA. This force is equal to the force acting on the base bottom surface in the case of FIG. When an earthquake occurs and the groundwater level rises as shown in (b), the water pressure P2W acting on the bottom of the foundation increases (P2W> P2w) as H increases, so the foundation is before the groundwater level rises. Higher support from groundwater after rising.

  In this case as well, the foundation receives higher bearing capacity after the groundwater level rises than before, and the stability of the foundation increases after liquefaction occurs in the bearing ground. Is suppressed or prevented. Even if the foundation is about to sink temporarily, the sheet pile wall tries to keep the bottom of the foundation horizontal, so that the foundation is prevented from sinking.

  In both cases of FIG. 1 (Claim 1) and FIG. 2 (Claim 5), when the ground loses its supporting force mainly due to liquefaction and the foundation is about to sink, The buoyancy from the lightweight material and the upward water pressure work to suppress or prevent the settlement of the foundation, and the buoyancy and water pressure compensate for the decrease in ground support capacity, so the foundation will not rise due to buoyancy and water pressure. .

  Lightweight materials include foamed polystyrene and other foamable materials, as well as lightweight mortar and other materials with a specific gravity smaller than water. These materials include single-use materials and solidified materials that are cement-based materials. It may be used in a state. The solidifying material is added, for example, when a lightweight material is present as particles and it is difficult to maintain a solid state in which the particles are aggregated. When the light weight material includes a solidified material, the light weight material can be filled under the bottom surface of the foundation without any gap, and therefore, it is mainly used in the case of FIG. A lightweight material including a solidifying material may be used in combination with a lightweight material made of a molded product. When a solidifying material is included, there is also an advantage that the strength of the lightweight material is increased by the solidifying action of the lightweight material.

  Specifically, the water stoppage between adjacent sheet piles in claim 5 is ensured by ground improvement in advance at least at the location where the sheet pile is inserted, as described in claim 6. The ground improvement material such as solidification material is added to the original ground where the sheet pile is inserted, and the sheet pile is inserted while stirring and mixing, so that the gap between adjacent sheet piles as the ground solidifies Therefore, the water stoppage between the adjacent sheet piles is easily secured, and the state is easily maintained continuously.

  In claim 6, since the ground is improved with respect to the original ground, the ground can be solidified after being loosened once regardless of the geology. Even when the ground exists, there is an advantage that the sheet pile insertion work and the water stoppage between the sheet piles are ensured.

  In the case of claim 3 in which the inner sheet pile is inserted on the inner peripheral side of the sheet pile, ground improvement may be applied to the insertion position of the inner sheet pile, and the area under the bottom surface of the foundation is divided by the partition wall. In the case of claim 4, the ground may be improved at the insertion location of the partition wall.

  FIG. 1 and FIG. 2 also show a situation where the depth of the bottom surface of the lightweight material is aligned with the depth of the tip of the sheet pile. Actually, since it is necessary to secure the depth of the sheet pile into the ground, the depth of the sheet pile tip is larger than the depth of the bottom surface of the lightweight material, but the depth of both is substantially equal.

  As mentioned above, earth pressure and water pressure act on the sheet pile wall continuous in the circumferential direction of the foundation from the outer periphery to the inner periphery, and water pressure acts from the inner periphery to the outer periphery, but the pressure acting from the outer periphery is Since there is earth pressure, the section deeper than the foundation bottom of the sheet pile wall tends to bend toward the inner periphery. As a result, as shown in FIG. 1, even when there is a gap between the periphery of the lightweight material and the inner peripheral surface of the sheet pile wall, the sheet pile wall fills the gap and tries to adhere to the lightweight material. Since the earth pressure is larger in the downward direction, the earth pressure acting on the sheet pile trying to adhere to the lightweight material can have a vertically upward component, so the lightweight material receives an upward force and tries to adhere to the bottom surface of the foundation. To do.

  When the length of the sheet pile is about several times the thickness of the resin foam block corresponding to the lightweight material of the present invention as in Patent Document 1, and the resin foam block is located in the section above the sheet pile, Since it is considered that the deformation of the sheet foam has little influence on the resin foam block, the deformation of the sheet pile caused by earth pressure cannot be expected to push the resin foam block upward. On the other hand, when the depth of the bottom surface of the lightweight material is aligned with the depth of the sheet pile tip, it is easy to receive a force toward the inner periphery due to the deformation that occurs in the sheet pile, so the effect that the lightweight material adheres to the bottom surface of the foundation is obtained. It is done.

  The sheet pile wall is in close contact with the lightweight material, and the lightweight material is in close contact with the bottom surface of the foundation, so that the earth pressure received by the sheet pile wall is used as a force to support the foundation, as with the upward water pressure and buoyancy described above. Therefore, the effect of suppressing the settlement of the foundation accompanying the liquefaction of the ground is improved.

  The structure foundation support structure according to any one of claims 1 to 6 is constructed not only newly but also by refurbishing an existing structure foundation. In a new case, as described in claim 7, a step of inserting a sheet pile continuously in the circumferential direction of the foundation while adjoining the liquefied ground so as to surround the foundation of the structure to be constructed. Discharging the earth and sand up to the bottom surface of the foundation in the area surrounded by the sheet pile, and the area surrounded by the sheet pile deeper than the bottom surface of the foundation is subjected to buoyancy or water pressure received from groundwater on the foundation It completes with the construction method of the structure foundation including the process of installing or filling the light weight material made to act on the bottom face of this, and the process of constructing | assembling the said foundation on the said light weight material.

  The sheet pile is inserted adjacent to the ground so as to surround the foundation of the structure, and light material is installed or filled deeper than the bottom of the foundation. The sinking of the foundation can be suppressed by the hydraulic pressure acting upward and the buoyancy of the lightweight material. In particular, the sheet pile wall made of sheet piles is in contact with the side surface of the foundation by the surface, restrains the foundation from the surroundings with respect to the inclination, and exhibits the effect of preventing the inclination, so the stability against the uneven settlement of the foundation is high.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  1 is inserted in the liquefied ground 1 so as to surround the foundation 3 of the structure 2, and is surrounded by a sheet pile 4 continuous in the circumferential direction of the foundation 3 and a sheet pile 4 deeper than the bottom surface of the foundation 3. An example of a support structure for a structure foundation that includes a lightweight material 6 that is installed or filled in a region and that causes the buoyancy that the lightweight material 6 receives from groundwater to act on the bottom surface of the foundation 3 is shown. FIG. 1- (a) shows the state during normal times as described above, and FIG. 1 (b) shows the state during and after the earthquake. The sheet pile 4 constitutes the sheet pile wall 5 by being continuous in the circumferential direction of the foundation 3.

  In FIG. 1, the depth of the bottom surface of the lightweight material 6 is substantially aligned with the depth of the tip of the sheet pile 4, but the depth of the tip of the sheet pile 4 may be larger than the depth of the bottom surface of the lightweight material 6. The drawing also shows a case where the structure 2 is a bridge pier, but the object of the structure 2 is not limited, and the structure 2 includes civil engineering and building structures in general. The pier supports the bridge girder as the superstructure.

  For the lightweight material 6, foamed polystyrene, foamed polypropylene or other foamed material, foamed beads as the raw material, or lightweight mortar are used. In principle, molded products of foam and lightweight mortar are used as a single unit, and foam beads are used in the state of solidified material or solidified material and raw ground soil added and mixed, but molded products and foam beads are used in combination. Sometimes it is done.

  The specific gravity of the foam is in the range of about 0.01 to 0.1, and the specific gravity of the light weight mortar is in the range of about 0.5 to 0.8. Although the specific gravity of the mixed soil composed of the expanded polystyrene beads and the solidifying material is larger than the specific gravity of the foam, it varies depending on the blending of the solidifying material and can be reduced. The mixed soil has good fillability in the gap and has the advantage of increasing the strength of the lightweight material 6, and is suitable for use when groundwater is excluded from the area surrounded by the sheet pile wall 5 as shown in FIG.

  In FIG. 1, the groundwater level is located above the bottom surface of the foundation 3, and there are voids between the upper surface of the lightweight material 6 in the solid state and the bottom surface of the foundation 3, and between the side surface of the lightweight material 6 and the sheet pile wall 5. The case where the groundwater has entered the area surrounded by the sheet pile wall 5 is shown. FIG. 1- (a) shows a state before the occurrence of the earthquake. In this state, the water pressure acts directly upward on the bottom surface of the foundation 3, and the buoyancy acting on the lightweight material 6 also acts. The buoyancy prevents the subsidence of the foundation 3 along with the supporting ground.

  As shown in Fig. 1- (b), the groundwater level rises and the water pressure acting on the bottom of the foundation 3 increases, resulting in liquefaction in the ground and the ground loses bearing capacity. As a result, the settlement of the foundation 3 is suppressed, and the stability of the foundation 3 is ensured. In the state of (b), the ground supporting force that lost the increase in water pressure is compensated, and the water pressure and buoyancy continue to support the foundation 3.

  In FIG. 2, the groundwater level is located above the bottom surface of the foundation 3, the water stoppage between the adjacent sheet piles 4, 4 is ensured, the groundwater is excluded from the area surrounded by the sheet pile wall 5, and the lightweight material 6 is the foundation 3. In this case, the bottom surface of the sheet pile and the inner peripheral surface of the sheet pile 4 are in close contact with each other and the region surrounded by the sheet pile wall 5 is filled without any gap.

  FIG. 2- (a) shows the state before the occurrence of the earthquake. In this state, the water pressure does not act directly on the bottom surface of the foundation 3, but acts indirectly by acting on the bottom surface of the lightweight material 6. Buoyancy acting on the lightweight material 6 also acts on the bottom surface of the foundation 3, and this water pressure and buoyancy together with the ground prevent normal settlement of the foundation 3. There is no limitation on the means for securing the water stoppage between the sheet piles 4, 4. For example, a sealing material is connected to at least one of the adjacent sheet piles 4, 4, and the other sheet pile 4 is inserted later. It is ensured by bringing it into close contact.

  In addition, the water stoppage between the sheet piles 4 and 4 can be ensured by improving the ground at least at the place where the sheet piles 4 are inserted as shown in FIG. The ground improvement is performed, for example, by supplying the ground improvement material 9 such as a solidified material to the original ground where the sheet pile 4 is inserted, and stirring and mixing with the original ground. The improved ground closes the gap between the adjacent sheet piles 4 and 4 with solidification, and ensures the water-stopping property between the adjacent sheet piles 4 and 4.

  At the time of and after the occurrence of the earthquake, as shown in Fig. 2- (b), the groundwater level rises and the water pressure acting on the bottom surface of the foundation 3 increases, so liquefaction occurs in the ground as in Fig. 1, The subsidence of the foundation 3 due to the loss of bearing capacity of the ground does not occur, and the stability of the foundation 3 is ensured. In the state of (b), the ground supporting force that lost the increase in water pressure is compensated, and the water pressure continues to support the foundation 3.

  FIGS. 3A to 3D show examples of construction procedures when a support structure for the foundation 3 is newly constructed. In the case of new construction, as shown in (a), the sheet pile 4 is inserted (press-fit) to the target depth in the liquefied ground 1 such as sandy ground that may be liquefied in the event of an earthquake. The ground in the area surrounded by the sheet pile wall 5 is excavated and discharged. In order to ensure the water stoppage between the adjacent sheet piles 4, 4, for example, as shown in FIG. 5, before the sheet pile 4 is inserted, the ground is improved on the ground where the sheet pile 4 is inserted.

  Although the steel sheet pile (sheet pile) is mainly used for the sheet pile 4, the kind of sheet pile 4 is not ask | required. In order to allow buoyancy due to groundwater to act on the lightweight material 6 from normal times, it is appropriate that the ground is excavated to a depth where the upper surface of the lightweight material 6 is below the groundwater level.

  After discharging the earth and sand, the lightweight material 6 is installed or filled in a region deeper than the bottom surface of the foundation 3 to be constructed as shown in (b), and then split onto the upper end of the lightweight material 6 as shown in (c). Abandoned concrete 7 is constructed by placing a chestnut stone and receiving the foundation 3. Thereafter, as shown in (d), the foundation 3 is constructed on the discarded concrete 7 and the structure 2 is constructed on the foundation 3. After the foundation 3 is constructed, earth and sand are refilled on the foundation 3 as necessary.

  After that, the pier as the structure 2 is constructed on the foundation 3, and then the bridge girder is constructed on the pier.

  FIG. 4 shows a case where the sheet pile 4 is inserted from the upper end to the lower end of the sheet pile 4 with an inclination from the inner peripheral side to the outer peripheral side of the region surrounded by the sheet pile wall 5, and on the inner peripheral side of the sheet pile 4. An example of construction in the case where the inner sheet pile 8 facing the sheet pile 4 is inserted vertically and the lightweight material 6 is arranged in the area surrounded by the inner sheet pile 8 is shown.

  In FIG. 4, among the water pressure and earth pressure acting on the sheet pile wall 5 from the outer peripheral side, the vertically downward component works to hold down the sheet pile wall 5 downward, so that the water pressure and light weight acting on the bottom surface of the foundation 3 due to the rise of the groundwater level. Even if the buoyancy acting on the material 6 increases, the effect of restraining the lifting of the foundation 3 can be obtained.

  In FIG. 4, when the inner sheet pile 8 does not exist below the bottom surface of the foundation 3, the entire lightweight material 6 has a truncated pyramid shape, and the volume of the lightweight material 6 increases compared to when the sheet pile wall 5 does not tilt. The buoyancy acting on 6 increases. Therefore, as shown in the figure, since the lightweight material 6 is surrounded by the inner sheet pile 8 vertically inserted below the bottom surface of the foundation 3, the increase in buoyancy acting on the lightweight material 6 is eliminated. Lifting of the foundation 3 due to an increase in buoyancy is prevented.

(A) is a vertical cross-sectional view showing the normal state of the support structure when groundwater enters the area surrounded by the sheet pile wall, (b) is a vertical cross-sectional view showing the state at the time of the earthquake is there. (A) is a longitudinal sectional view showing a normal state of the support structure when groundwater does not enter the region surrounded by the sheet pile wall, and (b) is a longitudinal sectional view showing a state during an earthquake. . (A)-(d) is the longitudinal cross-sectional view which showed the example of the construction procedure in the case of constructing | supporting the support structure of this invention newly. It is the longitudinal cross-sectional view which showed the construction example at the time of attaching an inclination to a sheet pile, inserting an inner sheet pile vertically on the inner peripheral side of a sheet pile, and arrange | positioning a lightweight material in the area | region enclosed by the inner sheet pile. It is the longitudinal cross-sectional view which showed the example of construction when the ground of the location where a sheet pile is inserted is improved beforehand. (A) is the longitudinal cross-sectional view which showed the mode of normal time of the conventional structure where the foundation is directly supported on the liquefied ground, (b) is the longitudinal cross-sectional view which showed the mode at the time of an earthquake.

Explanation of symbols

1 ……… Ground 2 ……… Structure 3 ……… Basic 4 ……… Sheet 5 ……… Sheet wall 6 ……… Lightweight material 7 ……… Discarded concrete 8 ……… Inner sheet pile 9 ……… Ground Improvement material

Claims (7)

  It is inserted in the liquefied ground so as to surround the foundation of the structure, and is installed or filled in a sheet pile that is continuous in the circumferential direction of the foundation and deeper than the bottom of the foundation and surrounded by the sheet pile. A structure foundation support structure, wherein a buoyancy or water pressure received from groundwater is applied to the bottom surface of the foundation.   The support structure for a structure foundation according to claim 1, wherein the sheet pile is inclined from the upper end to the lower end, and is inclined from the inner periphery side to the outer periphery side of the region surrounded by the sheet pile.   The inner sheet pile which opposes the said sheet pile is inserted in the inner peripheral side of the said sheet pile, The lightweight material is arrange | positioned in the area | region enclosed by this inner sheet pile, The Claim 1 or Claim 2 characterized by the above-mentioned. Support structure of the foundation of the structure.   The support structure for a structure foundation according to any one of claims 1 to 3, wherein a region under the bottom surface of the foundation surrounded by the sheet pile is divided into a plurality of regions by a partition wall. .   The structure foundation support according to any one of claims 1 to 3, wherein water-stopping between the sheet piles adjacent to each other is ensured, and groundwater is excluded from a region surrounded by the sheet piles. Construction.   6. The structure foundation support structure according to claim 5, wherein at least the ground where the sheet pile is inserted is previously improved. In the liquefied ground, adjacent to surround the foundation of the structure to be constructed, inserting the sheet pile continuously in the circumferential direction of the foundation, and the area of the foundation surrounded by the sheet pile A step of discharging the earth and sand to the bottom surface, and a step of installing or filling a lightweight material that causes buoyancy received from groundwater or water pressure to act on the bottom surface of the foundation in a region surrounded by the sheet pile deeper than the bottom surface of the foundation And a step of constructing the foundation on the lightweight material.

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