JP6217292B2 - Construction method and foundation structure of foundation structure of expansive ground - Google Patents

Description

  The present invention relates to a construction method and a foundation structure for a foundation structure provided above an inflatable ground.

  Conventionally, a structure built on the inflatable ground with a gap to prevent the foundation from being pushed up due to the expansion of the ground is formed between the bottom surface of the foundation and the top surface of the inflatable ground. As support, the foundation structure of the expansible ground disclosed in Patent Documents 1 and 2 has been proposed.

  The basic structure of the expansive ground disclosed in Patent Document 1 is a concrete structure in which a frozen ice layer having a thickness corresponding to the predicted amount of expansion of the ground is formed on the upper surface of the expansive ground and the frozen ice layer is used as a support member. By constructing a structure foundation supported by piles, then thawing the frozen ice layer and discharging the melted water to form a void between the lower surface of the structure foundation and the upper surface of the ground It is.

  The foundation structure of the expansive ground disclosed in Patent Document 2 is supported by the pile portion connected to the upper end portion, the pile portion disposed in the expansive ground with the upper end portion protruding from the ground surface of the expansible ground And a concrete foundation portion disposed so as to form a space between the ground surface of the expansive ground and supporting the uncured concrete foundation portion in which the cast concrete does not reach a predetermined strength. The support member is disposed in the space and is interposed between the concrete foundation and the expandable ground. When the expandable ground expands to fill the space, the support member expands from the ground surface. It is deformed under the power.

Japanese Patent Laid-Open No. 10-280379 JP 2008-174936 A

  However, the foundation structure of the expansive ground disclosed in Patent Document 1 is such that when the concrete is placed, the frozen ice layer is used as a support member, and until the foundation concrete expresses a predetermined strength, It is necessary to maintain the frozen ice layer so that it does not melt, and it requires many complicated facilities such as weirs, pipes and refrigerators used for draining the frozen ice layer after freezing and after thawing. .

  For this reason, the foundation structure of the expandable ground disclosed in Patent Document 1 forms a large frozen ice layer in order to place foundation concrete in a vast range, particularly when constructing a large-scale structure foundation. In addition, since it is necessary to thaw after maintaining the frozen state for a long period of time, there has been a problem that the freezing and thawing costs of the frozen ice layer and the equipment cost are remarkably increased.

  In addition, the basic structure of the expandable ground disclosed in Patent Document 1 requires freezing, thawing, drainage treatment, etc. of the frozen ice layer, and installation, removal of many complicated equipment for these treatments, Since maintenance is required, not only the construction cost required for these treatments increases, but also the work time required for these treatments increases and the entire construction period is prolonged. It was.

  In the foundation structure of the expansive ground disclosed in Patent Document 2, when the supporting member interposed between the concrete base portion and the expansive ground is buckled and deformed, the expansion force from the ground surface is applied to the concrete base portion. In order to prevent the concrete foundation from being deformed and the pull-out resistance of the pile from being lowered due to the concrete foundation being lifted, the support member must be attached after the concrete foundation is cured. Thinning out.

That is, the foundation structure of the inflatable ground disclosed in Patent Document 2 is to reinforce the concrete foundation and reduce the expansion force transmitted to the concrete foundation by thinning the support member after the concrete foundation is cured. While preventing a deformation | transformation of a concrete foundation part, it prevents that a concrete foundation part is lifted and prevents the fall of the supporting force by a pile.
However, since it is necessary to perform a thinning operation of the support member, a work period and construction cost for the work are also required, and further improvement has been desired.

  Therefore, the present invention has been devised in view of the above-mentioned problems, and its object is to reinforce the foundation part or to form between the ground surface of the expandable ground and the lower surface of the foundation part. An object of the present invention is to provide a construction method and a foundation structure for a foundation structure that can reduce the construction cost and shorten the construction period without requiring removal of the water softening member from the predetermined space.

  The construction method of the foundation structure according to the first invention is a construction method of the foundation structure provided above the inflatable ground, and the foundation portion is placed above the inflatable ground until the foundation portion exhibits a predetermined strength. A first step of supporting by a water softening member that is spaced apart and not wetted; and a second step of reducing the strength of the water softening member by wetting the water softening member after the foundation has developed a predetermined strength. And a process.

  In the construction method of the foundation structure according to the second invention, in the first invention, in the second step, the water-absorbing softening member is moistened before the water-absorbing softening member is loaded with pressure due to expansion of the expandable ground. The strength of the water absorption softening member is reduced.

  A construction method for a foundation structure according to a third invention is characterized in that, in the first invention or the second invention, the water-absorbing softening member is a void tube in which cardboard is formed in a substantially cylindrical shape.

  A foundation structure according to a fourth aspect of the present invention is a foundation structure provided above the expansible ground, and is provided between the foundation portion spaced apart above the expansible ground and the foundation portion and the expansible ground. The water-absorbing / softening member is provided.

  According to a fifth aspect of the present invention, there is provided the foundation structure according to the fourth aspect, wherein the water-absorbing softening member supports the foundation portion by separating the foundation portion above the inflatable ground in a state before the foundation portion exhibits a predetermined strength. In addition, it is characterized in that the strength is lowered by wetting in a state after the base portion exhibits a predetermined strength.

  According to the present invention, until the foundation portion exhibits a predetermined strength, the water absorption softening member can be used as a support to sufficiently support the foundation portion, and the foundation portion is cured to exhibit a predetermined strength. After that, the compressive load due to the expansion of the expansive ground can not be transmitted as a reaction force to the lower surface of the foundation part or can be significantly reduced, so that the reinforcement of the foundation part, the ground surface of the expansive ground and the lower surface of the foundation part The expansion of the expansible ground can be absorbed in the predetermined space without the need to remove the water absorbing and softening member from the predetermined space formed between the two.

  Therefore, there is no need to reinforce the foundation or to remove the water softening member from a predetermined space formed between the ground surface of the inflatable ground and the lower surface of the foundation. The construction cost of the foundation structure to be provided can be reduced, and the construction period can be shortened.

It is a perspective view which shows the basic structure to which this invention is applied. It is a top view which shows the basic structure to which this invention is applied. It is a perspective view which shows the water absorption softening member of the basic structure to which this invention is applied. It is a front view which shows the state which excavated the natural ground with the construction method of the foundation structure to which this invention is applied. It is a front view which shows the state which stood the pile by the construction method of the foundation structure to which this invention is applied. It is a front view which shows the state which assembled the formwork with the construction method of the foundation structure to which this invention is applied. It is a front view which shows the state supported with the water absorption softening member until the foundation part developed predetermined intensity | strength by the construction method of the foundation structure to which this invention is applied. It is a front view which shows the state which disassembled the formwork, after the foundation part expressed predetermined intensity | strength by the construction method of the foundation structure to which this invention is applied. It is a front view which shows the state which moistened the water absorption softening member, after the foundation part expressed predetermined intensity | strength by the construction method of the foundation structure to which this invention is applied. It is a front view which shows the state which wetted the water absorption softening member before the pressure by expansion | swelling of an expansible ground was loaded by the construction method of the foundation structure to which this invention was applied, and reduced the intensity | strength. It is a front view which shows the state which built the foundation structure above the expansible ground with the construction method of the foundation structure to which this invention is applied. (A) is a water absorption softening member in a dry state, (b) is a water absorption softening member in a partially wetted state, and (c) is a front view showing a water absorption softening member in a fully wetted state. is there. It is a graph which shows the relationship between the compressive load in a void pipe, and a wet state. It is a graph which shows the relationship between the compressive load in a void pipe | tube, and the wetting time. (A) is a front view which shows the state which supported the base part with the water absorption softening member, (b) transmits the pressure by expansion | swelling of an expansible ground by wetting a water absorption softening member and reducing an intensity | strength. It is a front view which shows the state reduced.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for implementing a basic structure 1 to which the present invention is applied will be described in detail with reference to the drawings.

  As shown in FIG. 1, the foundation structure 1 to which the present invention is applied is provided above the expansible ground 5, and is provided with a base portion 2 that is spaced apart above the ground surface 5 a of the expansible ground 5. The water absorption softening member 3 provided between the lower surface 2a of the base part 2 and the ground surface 5a of the expansible ground 5 is provided.

  Incidentally, the water-absorbing softening member 3 means a member that has a predetermined strength when not wetted, and has a property of softening and reducing strength when wetted. A typical example is a void tube. it can. In FIG. 1, a part of the plurality of water-absorbing / softening members 3 is omitted, but for example, the plurality of water-absorbing / softening members 3 can be arranged in an arrangement as shown in FIG. 2.

  As shown in FIGS. 1 and 2, the foundation structure 1 to which the present invention is applied is such that the foundation portion 2 is formed by curing a time-curable material such as concrete, and the ground surface of the expandable ground 5. The hardened base portion 2 is supported by the piles 8 such as a plurality of steel pipe piles above the expandable ground 5 in a state where the space S is formed between the piles 5a.

  The expansive ground 5 is a ground in which steelmaking slag is reclaimed, and free lime remaining in the steelmaking slag comes into contact with water such as groundwater and rainwater, so that free lime causes a hydration reaction and expands in volume. The ground itself filled with steelmaking slag will expand and rise.

  The pile 8 is provided on the ground drilled up to the support layer, and is erected in a state where the lower end of the support layer is reached by the sand 6 and supported by the hard ground. The pile 8 is made by reducing the frictional resistance of the outer peripheral surface by using a bitumen material or the like coated on the outer peripheral surface.

  In the pile 8, when the expandable ground 5 is expanded to the side, the pressure due to the expansion of the expandable ground 5 is applied to the outer peripheral surface. However, the pile 8 can be expanded by reducing the frictional resistance of the outer peripheral surface. It is possible to prevent the ground 5 from being caught, and even when the expandable ground 5 is further expanded upward, it is prevented from floating upward from the ground surface 5a of the expandable ground 5 Will be able to do.

  The foundation 2 is mainly provided as a foundation of a structure constructed above the expansible ground 5, and cures a time-curable material such as concrete with the upper end of the pile 8 embedded. By this, it will be spaced apart from the ground surface 5a above the expansible ground 5, and will be supported by the pile 8.

  Since the foundation portion 2 does not exhibit sufficient strength during the curing period until the time-curable material such as concrete is cured, the lower surface 2a of the foundation portion 2 and the ground surface 5a of the expansible ground 5 In the meantime, a predetermined number of water-absorbing softening members 3 are used as concrete support.

  The water-absorbing softening member 3 used here is a state in which the base portion 2 is separated from the ground surface 5a and supported above the expansible ground 5 in a state before the base portion 2 exhibits a predetermined strength. In the state after the base portion 2 has developed a predetermined strength, a material whose strength in the compression direction or the like is reduced by wetting with groundwater or the like is selected.

  As shown in FIG. 3, the water absorption softening member 3 is most preferably a void tube 30 in which cardboard is formed in a substantially cylindrical shape so as to have a predetermined length. However, the water softening member 3 is not limited to this, and any material and shape may be used. For example, a cardboard formed in a substantially box shape may be used.

  As shown in FIG. 3A, the void tube 30 has an outer diameter of 300 mm and a substantially circular cross section. The void tube 30 is not limited to this, and may have any outer diameter such as an outer diameter of 200 mm, or may have any cross-sectional shape. Furthermore, as shown in FIG. 3B, the void tube 30 may be provided with a notch 30a on the outer periphery.

  As shown in FIGS. 1 and 4, the construction method of the foundation structure 1 to which the present invention is applied is provided with the foundation structure 1 to which the present invention is applied above the expansible ground 5 provided by excavation. .

  The construction method of the foundation structure 1 to which the present invention is applied includes a first step of supporting the foundation portion 2 with a water absorbing and softening member 3 in a state in which the foundation portion 2 is not wetted until the foundation portion 2 exhibits a predetermined strength, and the foundation portion 2 is predetermined. A second step of reducing the strength of the water-absorbing softening member 3 by wetting the water-absorbing softening member 3.

  In the first step, first, as shown in FIG. 5, a pile is applied to the expansive ground 5 in which steelmaking slag or the like is buried in a state where a bitumen material or the like is applied to the outer peripheral surface of the pile 8 such as a plurality of steel pipe piles. 8 is erected, and the upper end portion of the pile 8 is provided so as to protrude upward from the ground surface 5a of the expansible ground 5. At this time, the expandable ground 5 is provided with leveled concrete or the like on the ground surface 5a to form the flat surface portion 40 in order to make the ground surface 5a substantially flat as necessary.

  In the first step, as shown in FIG. 6, next, a plurality of water softening members 3 that are not moistened are placed side by side on the ground surface 5a of the expandable ground 5 to cure a time-curable material such as concrete. The mold 20 for assembling is assembled so as to contact the upper end surface 3a of the water absorption softening member 3. At this time, the mold frame 20 is supported by the plurality of water-absorbing softening members 3 in a state of being spaced apart from the ground surface 5a of the expandable ground 5 by a space between the ground surface 5a of the expandable ground 5. S is formed.

  In the first step, next, as shown in FIG. 7, a time-curable material such as concrete is poured into the inside of the mold 20 assembled so as to be in contact with the upper end surface 3 a of the water absorption softening member 3, Until the base part 2 develops a predetermined strength, the base part 2 is supported by the water absorption softening member 3 inside the mold 20. At this time, the temporally curable material such as concrete is cured by passing through a predetermined curing period in a state where the upper end portion of the pile 8 is embedded therein, and exhibits a predetermined strength and is a self-supporting base portion 2. It becomes.

  In the second step, first, as shown in FIG. 8, the base portion 2 develops a predetermined strength and is self-supporting, and the lower surface 2 a of the base portion 2 is not required to be supported by the water absorption softening member 3. The foundation portion 2 is supported by the pile 8 in a state where the space S is formed between the ground surface 5a of the expansive ground 5 and the ground surface 5a. In addition, after the base part 2 expresses predetermined intensity | strength, the side surface of the formwork 20 may be disassembled at arbitrary timings.

  In the second step, next, as shown in FIG. 9, ground water, rainwater, or the like flows into the space S, and the water storage part 7 in which the ground water or the like is stored is provided in the space S. The water absorption softening member 3 installed side by side on the ground surface 5a of 5 is wetted with groundwater or the like. Further, in the second step, when the inflow of groundwater or the like into the space S is insufficient, such as when the altitude of the expandable ground 5 is higher than the groundwater level, water is artificially supplied to the space S with a hose or the like. Thereby, the water absorption softening member 3 can also be moistened.

  Next, in the second step, as shown in FIG. 10, the water absorbing / softening member 3 is wetted over a predetermined time, thereby reducing the strength of the water absorbing / softening member 3 in the compression direction and the like. At this time, even if the water absorption softening member 3 is a case where the ground surface 5a is raised by the expansion of the expandable ground 5 and the raised surface 5b is formed, the pressure due to the expansion of the expandable ground 5 is increased from the raised surface 5b. Before being loaded, the strength in the compression direction or the like can be reduced.

  In the second step, finally, as shown in FIG. 11, the earth retaining block 41 is disposed so as to surround the space S, and the foundation portion 2 is buried by, for example, backfilling the backfilling soil 42. The base structure 1 to which the present invention is applied is constructed above the above. At this time, the foundation portion 2 prevents the backfilling soil 42 and the like from flowing into the space S by the earth retaining block 41, and the raised surface 5 b due to the expansion of the expandable ground 5 is accommodated in the space S. The pressure due to the expansion of the expandable ground 5 cannot be transmitted to the lower surface 2a or can be reduced.

  In the first step, the construction method of the foundation structure 1 to which the present invention is applied assumes that the entire surface L of the water absorbing and softening member 3 is not wetted on the ground surface 5a of the expansible ground 5 as shown in FIG. It is installed in a dry state. Furthermore, the construction method of the foundation structure 1 to which the present invention is applied includes a predetermined immersion length L1 in a state where a part of the water-absorbing softening member 3 is wetted in the second step, as shown in FIG. A predetermined dry length L2 in a dried state is formed. In addition, the construction method of the foundation structure 1 to which the present invention is applied is such that, in the second step, as shown in FIG. 12 (c), the entire water-absorbing / softening member 3 is wetted so that the immersion length L1 extends over the entire length L. It may be formed.

  The water-absorbing softening member 3 is a case where the void tube 30 is used, and the compression load P (kN) when yielding in the compression direction is the vertical axis and the wet state of the void tube 30 is the horizontal axis. As shown, the relationship between the compressive load P and the wet state is represented. Here, the void tube 30 having an outer diameter and a total length L of 300 mm is used as a specimen, and the immersion length L1 of the void tube 30 is changed to 50 mm, 100 mm, and 300 mm.

  In the void tube 30, the compression load P when yielding in the compression direction is 28.8 kN during drying in a state where the full length L is not wetted. Further, when the wet state is wet, the compression load P is 3.5 kN when the immersion length L1 is 50 mm, the compression load P is 3.0 kN when the immersion length L1 is 100 mm, and the immersion length L1 is 300 mm. The compression load P is 2.1 kN.

  As described above, in the void tube 30, the compression strength is about 1/14 to 1/9 compared with that at the time of drying by being wetted to have a predetermined immersion length L 1. The strength in the compression direction can be significantly reduced.

  Further, in this void tube 30, the compression load P when the immersion length L1 is 50 mm and the immersion length L1 are 8.7 kN at the time of re-drying after being wetted at a predetermined immersion length L1 and then dried again. The compression load P when the thickness is 100 mm is 9.9 kN, and the compression load P when the immersion length L1 is 300 mm is 14.6 kN.

  Thus, in this void tube 30, even when it is re-dried after being wetted so as to have a predetermined immersion length L1, it is about 1/4 to 1/2 of that at the time of initial drying. The compression strength is obtained, and particularly the strength in the compression direction can be sufficiently reduced.

  Further, when the compression load P (kN) when yielding in the compression direction is taken as the vertical axis and the wet time is taken as the horizontal axis, as shown in FIG. 14, the relationship between the compression load P of the void tube 30 and the wet time as shown in FIG. Is represented. Here, a void tube 30 having an outer diameter and a total length L of 300 mm is used as a specimen, and the result of changing the immersion length L1 of the void tube 30 to 50 mm and 100 mm is shown.

  At this time, when the immersion length L1 is 50 mm, the void tube 30 has a compression load P of 4.1 kN in a wet time of 1 hour, and when the immersion length L1 is 100 mm, the compression load P in a wet time of 1 hour. Becomes 3.2 kN. As described above, the void tube 30 has a compressive strength of about 1/9 to 1/7 as compared with the time of drying even in a short wet time of about 1 hour. The strength of can be significantly reduced in a short time.

  It has been confirmed that the above results show the same tendency in the void tubes 30 of various sizes.

  As shown in FIG. 15 (a), the construction method of the foundation structure 1 to which the present invention is applied is such that, in the first step, the lower surface 2a of the foundation portion 2 is water-absorbing softening member until the foundation portion 2 exhibits a predetermined strength. 3 is supported by the support force Q.

  As a result, the construction method of the foundation structure 1 to which the present invention is applied is the time between the lower surface 2a of the foundation part 2 and the ground surface 5a of the expansible ground 5 until the foundation part 2 develops a predetermined strength and becomes independent. In the state where the space S is formed therebetween, the base portion 2 can be sufficiently supported by the support force Q with the water absorption softening member 3 as a support.

  In the construction method of the foundation structure 1 to which the present invention is applied, for example, when a void tube 30 having an outer diameter and an overall length L of 300 mm is used as the water absorption softening member 3, the support force Q of the void tube 30 per piece is maximum. 28.8kN. Thereby, the construction method of the foundation structure 1 to which the present invention is applied has, for example, a maximum support force Q as compared with a case where a canister having a maximum support force Q of 11.9 kN is used as a support. The void tube 30 that is twice or more can be used as a support work, and the number of void tubes 30 to be installed can be significantly reduced.

  As shown in FIG. 15 (b), the construction method of the foundation structure 1 to which the present invention is applied is such that, in the second step, after the foundation portion 2 exhibits a predetermined strength, the water absorption softening member 3 is wetted to soften the water absorption. The strength of the member 3 is reduced.

  At this time, in the construction method of the foundation structure 1 to which the present invention is applied, when the raised surface 5 b is formed by the expansion of the expandable ground 5, the compression load P due to the expansion of the expandable ground 5 is applied to the lower surface 2 a of the foundation portion 2. In the state where the reaction force V is not transmitted or significantly reduced, the void tube 30 undergoes crushing deformation while forming the crushing portion 30b with a predetermined immersion length L1.

  Thereby, the construction method of the foundation structure 1 to which the present invention is applied does not require the water-absorbing softening member 3 to be crushed and deformed, and the water-absorbing softening member 3 is removed from the space S without expanding the expansible ground 5. It can be absorbed in the space S. In addition, the construction method of the foundation structure 1 to which the present invention is applied is such that the compressive load P due to the expansion of the expansible ground 5 is not transmitted to the lower surface 2a of the foundation portion 2 as a reaction force V, or is significantly reduced. It becomes possible not to require 2 reinforcement.

  Conventionally, when a Ito can or the like is used as a supporting work, the Ito can is buckled and deformed by applying pressure due to the expansion of the inflatable ground 5, and then the inflatable ground 5 is deformed by this buckling deformation. The reaction force V that acts on the lower surface 2a of the base portion 2 from the Ito can is reduced by absorbing the pressure due to the expansion of. For this reason, in the prior art, the load substantially the same as the compression load P is directly transmitted to the lower surface 2a of the base portion 2 before the Ito can is buckled and deformed, and the reaction force V is excessive. Therefore, it was necessary to reinforce the base 2 and to remove the Ito can. For this reason, as a further improvement, there has been a demand for a construction method capable of omitting operations such as removal of the Ito can.

  The construction method of the foundation structure 1 to which the present invention is applied mainly reduces the strength of the water absorbing softening member 3 before the pressure due to the expansion of the expansible ground 5 is applied to the water absorbing softening member 3. The water absorption softening member 3 can be crushed and deformed only by the compression load P due to the expansion of the expansible ground 5. Thereby, the construction method of the foundation structure 1 to which the present invention is applied can easily crush and deform the water absorbing and softening member 3 only by the compression load P. Therefore, the compression load P due to the expansion of the expandable ground 5 is applied to the foundation portion 2. It is possible not to transmit the reaction force V as a reaction force V to the lower surface 2a or to significantly reduce it.

  The construction method of the foundation structure 1 to which the present invention is applied is, for example, when a void tube 30 having an outer diameter and a total length L of 300 mm is used as the water absorption softening member 3, and the void tube 30 is wetted and compared with the case of drying. The compression strength can be about 1/14 to 1/9. Thereby, since the construction method of the foundation structure 1 to which the present invention is applied can remarkably reduce the strength of the void pipe 30, the compressive load P due to the expansion of the expandable ground 5 is applied to the lower surface of the foundation portion 2. It is possible to prevent 2a from being transmitted as the reaction force V or to significantly reduce it.

  In the construction method of the foundation structure 1 to which the present invention is applied, for example, when a void pipe 30 having an outer diameter and a total length L of 300 mm is used as the water absorption softening member 3, inflow of groundwater or the like into the space S is insufficient. As a result, even when the void tube 30 is re-dried, the compressive strength can be about 1/4 to 1/2 as compared with the initial drying time. Thereby, since the construction method of the foundation structure 1 to which the present invention is applied can expand the void tube 30 because the strength of the void tube 30 can be sufficiently reduced even when the void tube 30 is re-dried. The compressive load P due to the expansion of the ground 5 cannot be transmitted as the reaction force V to the lower surface 2a of the base portion 2 or can be significantly reduced.

  As described above, the construction method of the foundation structure 1 to which the present invention is applied can sufficiently support the foundation portion 2 until the foundation portion 2 exhibits a predetermined strength using the water absorption softening member 3 as a support. At the same time, after the base portion 2 is cured and exhibits a predetermined strength, the compressive load P due to the expansion of the expandable ground 5 is not transmitted as the reaction force V to the lower surface 2a of the base portion 2 or is significantly reduced. Therefore, it is possible to absorb the expansion of the expansible ground 5 in the space S without requiring reinforcement of the base portion 2 or removal of the water absorption softening member 3 from the space S.

  Since the construction method of the foundation structure 1 to which the present invention is applied does not require reinforcement of the foundation portion 2 or removal of the water absorption softening member 3 from the space S, the foundation structure 1 provided above the inflatable ground 5 The construction cost can be reduced and the construction period can be shortened.

  Since the construction method of the foundation structure 1 to which the present invention is applied is shown in FIG. 10, the water absorption softening member 3 can be easily wetted by the water storage portion 7 of the space S using groundwater or the like. Since no extra work or equipment for reducing the strength of the member 3 is required, the work cost and equipment cost for constructing the foundation structure 1 provided above the expandable ground 5 are reduced. It becomes possible.

  Since the construction method of the basic structure 1 to which the present invention is applied can significantly reduce the strength of the void tube 30 in a short wet time of about 1 hour, water is artificially supplied to the space S with a hose or the like. Even if it is a case, the intensity | strength of the water absorption softening member 3 can be reduced easily and rapidly. Thereby, the construction method of the foundation structure 1 to which the present invention is applied reduces the strength of the water absorption softening member 3 easily and quickly in the second step, and the construction cost of the foundation structure 1 provided above the expansible ground 5. As a result, the construction period can be shortened.

  As shown in FIG. 1, the basic structure 1 to which the present invention is applied remarkably changes the strength of the water-absorbing softening member 3 in the compression direction before and after the water-absorbing softening member 3 is wetted. As a result, the foundation structure 1 to which the present invention is applied not only allows the foundation portion 2 to be sufficiently supported and the space S to be formed without increasing the number of installed water-absorbing / softening members 3 before wetting. It is possible to sufficiently support the foundation portion 2 by the pile 8 by easily crushing and deforming the water absorbing and softening member 3 after being wet and sufficiently absorbing the expansion of the expansible ground 5 in the space S. It becomes. The foundation structure 1 to which the present invention is applied reduces the frictional resistance of the outer peripheral surface of the pile 8, so that even if the expandable ground 5 expands upward, the pile 8 extends from the ground surface 5 a of the expandable ground 5. It is possible to prevent the pile 8 from being lifted upward and to prevent a decrease in the supporting force in the pile 8.

  As mentioned above, although the example of embodiment of this invention was demonstrated in detail, all the embodiment mentioned above showed only the example of actualization in implementing this invention, and these are the technical aspects of this invention. The range should not be construed as limiting.

DESCRIPTION OF SYMBOLS 1: Foundation structure 2: Foundation part 2a: Lower surface 20: Formwork 3: Water absorption softening member 3a: Upper end surface 30: Void pipe 30a: Notch part 30b: Collapse part 40: Plane part 41: Retaining block 42: Backfill soil 5 : Expandable ground 5a: Ground surface 5b: Raised surface 6: Sand 7: Reservoir 8: Pile S: Space

Claims (5)

It is a construction method of the foundation structure provided above the expansible ground,
A first step of supporting the base part with a water-absorbing softening member in a state where the base part is spaced apart above the inflatable ground and is not wetted until the base part develops a predetermined strength;
And a second step of reducing the strength of the water-absorbing / softening member by wetting the water-absorbing / softening member after the base portion has developed a predetermined strength. In the second step, before the pressure due to expansion of the expandable ground is applied to the water absorbing softening member, the water absorbing softening member is wetted to reduce the strength of the water absorbing softening member. Construction method of the described basic structure. The construction method for a foundation structure according to claim 1 or 2, wherein the water-absorbing softening member is a void tube in which cardboard is formed in a substantially cylindrical shape. A basic structure provided above the expansible ground,
A foundation structure comprising: a base portion provided to be spaced apart above the expansible ground; and a water absorption softening member provided between the base portion and the expansible ground. The water-absorbing softening member is a member that supports the foundation part spaced apart above the inflatable ground in a state before the foundation part develops a predetermined strength. The foundation structure according to claim 4, wherein the strength is reduced by wetting in a state after the strength is expressed.

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