JP6873823B2 - How to check the effect of the foundation structure for measures against expansive ground - Google Patents

Description

The present invention relates to a method for confirming the effect of a foundation structure for measures against expansive ground in which a structure such as a building is constructed on expansive ground.

For example, in dry and semi-arid areas such as Southeast Asia, Africa, and the Middle East, expanded soil containing expansive clay minerals such as montmorillonite accumulates, expanding due to inundation and water absorption during the rainy season, and draining and drying during the dry season. There is a wide range of expanding soil (ground that exhibits expansiveness) that contracts.

When a structure such as a house or a factory is constructed on such expanded soil, uneven uplift and uneven settlement occur in the structure due to ground deformation due to expansion and contraction of the expanded soil in the rainy season and the dry season. Many damages such as cracks in the walls and floor slabs of structures occur.

For this reason, conventionally, the following three methods are used alone or in combination to take measures against expanded soil before constructing the structure.

First, after replacing all the expansive ground below the structure with good quality soil, the structure is constructed directly in the form of foundation support. Alternatively, after all the expansive ground is solidified with cement or lime, the structure is directly constructed in the form of foundation support.

Secondly, piles are driven up to the support layer of good quality ground that does not show expandability, and these piles resist the levitation force during expansion of the ground so that harmful deformation of the structure does not occur. (See, for example, Patent Document 1).

Thirdly, a jig is laid on the ground surface to allow the soil on the ground surface that has risen when the ground expands to penetrate (accommodate) into the voids and buffer the expansion force so that it does not act directly on the structure. , The structure is constructed directly on this jig in the form of foundation support.

However, in the above-mentioned first measures against expanded soil, all of the stratum is replaced with high-quality soil, or cement and lime are agitated and mixed for solidification treatment. Therefore, the construction period increases as the thickness of the expansive stratum increases. Will be prolonged and the cost will increase. For example, when constructing a large-scale factory on a flat surface, if it becomes necessary to treat a stratum exhibiting an expandability of 3 m or more, the construction period becomes very long and an enormous cost is required.

Further, in the above-mentioned second countermeasure against expanded soil, by supporting the entire structure with piles, it is possible to effectively prevent the structure from rising and falling due to expansion and contraction of the expanded soil. Since it is a large-scale measure, the construction period and cost will increase significantly compared to the direct foundation type that does not rely on piles. For this reason, it becomes virtually impossible to apply it to structures such as small and medium-sized buildings.

Furthermore, in the above-mentioned third countermeasure against expanded soil, the special jig is expensive, and the special jig cannot be easily obtained depending on the site or region where the structure is constructed, especially in developing countries. , In many cases it is not applicable. In addition, it is difficult to apply the special jig to a large-scale factory on a flat surface because it requires a lot of labor and labor to install it on the entire surface.

On the other hand, the applicant of the present application spreads gravel or the like on the inflatable ground and forms a groove (recess) in the inflatable ground to fill the gravel or the like to form a buffer layer / expansion suppressing layer. We have already filed a patent application for the basic structure for measures against expansive ground. According to this foundation structure for expansive ground countermeasures, it is possible to take countermeasures against expanded soil of the structure at a lower cost than in the past.

Japanese Unexamined Patent Publication No. 2008-174936

On the other hand, it can be confirmed that the above-mentioned foundation structure for expansive ground countermeasures by the applicant of the present application can take countermeasures against expanded soil of the structure at a lower cost than the conventional one, and is highly reliable countermeasures against expanded soil. However, in order to adopt it at the realization site, it is necessary to establish a method for confirming the effect, in other words, a method for construction management.

In view of the above circumstances, the present invention can confirm the effect of the foundation structure for expansive ground countermeasures on a trial basis, and can confirm the effect of the foundation structure for expansive ground countermeasures in order to realize highly reliable countermeasures. The purpose is to provide.

To achieve the above object, the present invention provides the following means.

The method for confirming the effect of the foundation structure for expansive ground countermeasures of the present invention is a method for confirming the effect of the foundation structure for expansive ground countermeasures constructed by laying granules on the surface of the ground exhibiting expandability. A test piece is produced by laminating a glass bead layer made of glass beads imitating the granules on expanded soil obtained from the ground exhibiting expandability, and the test piece is restrained on the side of the test piece. Is immersed in water, and a loading pressure is gradually applied to the test body from above to obtain a loading pressure at which the height of the test body becomes the same as the initial height before loading, and the loading pressure is defined as an expansion pressure. It is characterized by doing.

The method for confirming the effect of the foundation structure for expansive ground countermeasures of the present invention is a foundation structure for expansive ground countermeasures constructed by forming a recess on the surface of the ground exhibiting expandability and filling the recess with a granular material. This is a method for confirming the effect of the above, in which a test piece is manufactured so as to sandwich a glass bead layer made of glass beads imitating the granules with expanded soil obtained from the ground showing expansiveness, and the side of the test piece. The test piece is immersed in water in a restrained state, and a load pressure is gradually applied to the test piece from above to obtain a load pressure at which the height of the test piece becomes the same as the initial height before loading. , The loading pressure is an expansion pressure.

According to the method for confirming the effect of the foundation structure for expansive ground countermeasures of the present invention, the effect of the foundation structure for expansive ground countermeasures can be confirmed on a trial basis, and highly reliable expansive ground countermeasures can be realized. It will be possible.

It is a figure which shows the foundation structure for expansion ground measures which concerns on 1st Embodiment of this invention. It is a figure which shows the method of measuring the expansion pressure by the collected expansion soil in the effect confirmation method of the foundation structure for expansion ground measures which concerns on 1st Embodiment of this invention. It is a figure which shows the effect confirmation method of the foundation structure for expansion ground measures which concerns on 1st Embodiment of this invention. Using the method for confirming the effect of the foundation structure for expansive ground countermeasures according to the first embodiment of the present invention, the effect due to the difference in the granularity and the replacement height of the foundation structure for expansive ground countermeasures according to the first embodiment is confirmed. It is a figure which shows the result of this. It is a figure which shows the foundation structure for expansion ground measures which concerns on 2nd Embodiment of this invention. It is a figure which shows the method of manufacturing the test body used in the effect confirmation method of the foundation structure for expansion ground measures which concerns on 2nd Embodiment of this invention. It is a figure which shows the effect confirmation method of the foundation structure for expansion ground measures which concerns on 2nd Embodiment of this invention. Using the method for confirming the effect of the foundation structure for expansive ground countermeasures according to the second embodiment of the present invention, the effect due to the difference in granules and groove width of the foundation structure for expansive ground countermeasures according to the second embodiment was confirmed. It is a figure which shows the result.

Hereinafter, a method for confirming the effect of the foundation structure for expansive ground countermeasures according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 4.

Here, in this embodiment, a building is constructed on expanded soil (ground showing expansiveness) containing expansive clay minerals such as montmorillonite, which is widely present in arid and semi-arid areas such as Southeast Asia, Africa, and the Middle East. It relates to the structure of the foundation for expansive ground countermeasures for constructing such structures, and particularly to the method of confirming the effect of the foundation structure for expansive ground countermeasures.

Further, in the present embodiment, as shown in FIG. 1, the surface of the expansive ground 1 is replaced with crushed stone (granular body) 2a such as limestone to form a buffer layer 2 (and an expansion suppressing layer 3 such as a concrete layer). The present invention relates to a method for confirming the effect of a foundation structure A for measures against expansive ground, which is formed and reduces the influence of the expansive ground 1 on a floor slab or the like.

In the inflatable ground countermeasure foundation structure A of the present embodiment, the inflatable ground 1 expands, and the expansion pressure can be absorbed and reduced by the buffer layer 2 (and the expansion suppression layer 3), and the foundation structure A can absorb and reduce the expansion pressure. It is possible to prevent the expansion pressure from acting on the supported superstructure.

The method of confirming the effect of the foundation structure A for expanding ground countermeasures of the present embodiment for confirming the effect of such measures against expansive ground simulates the actual expanded soil collected from the expansive ground 1 and crushed stone (granular body). This is a laboratory test method using the glass beads, and is for grasping the influence on the floor and the foundation from the expansion amount and expansion pressure obtained by the test.

Specifically, in the method for confirming the effect of the foundation structure A for measures against inflatable ground of the present embodiment, first, the expansion characteristics (expansion amount and expansion pressure) of the inflatable ground 1 are determined by ASTM D4546-96 (Standard Test Methods for). Obtained according to One-Dimensional Swell or Settlement Potential of Cohesive Soils, Method A).

In this expansion characteristic acquisition step of the expansive ground, a test piece having a predetermined size, for example, a diameter of 5 cm and a height of 2 cm is cut out from a sample collected from the actual expansive ground 1 (a sample collected without disturbance). The test piece used in the subsequent process is also cut out in the same manner.

As shown in FIG. 2A, the test body 4 is set in a metal cylindrical container 5 that can be restrained sideways, and the container 5 is installed in a container-shaped cell 6. Then, a loading means 7 provided with, for example, a loading plate, a piston, etc. is installed on the upper part of the test body 4 in the container 5, and the test body 4 is subjected to a very small load (for example, about 5 kPa) P1 by the loading means 7. Load.

As shown in FIG. 2B, while maintaining the state in which the load P1 does not change, water W is put into the cell 6 and the test body 4 is immersed in the water W together with the container 5, and the test body 4 of the expanded soil 1 is subjected to. It promotes expansion and at the same time reads the displacement of the displacement measurement point of the loading means 7. As a result, the amount of expansion (Free Swell) (%) at extremely low pressure is obtained.

As shown in FIG. 2C, the loads P1, P2, P3 ... Are gradually increased by the loading means 7. At this time, the test piece 4 of the expanded soil contracts due to consolidation, and the height decreases. The loading pressure is gradually applied until the height of the test body 4 becomes lower than the initial height, the loading pressure at which the height of the test body 4 becomes the same as the initial height is obtained, and this loading pressure is used as the expansion pressure (Swelling Pressure). ).

Next, as shown in FIG. 3A, another test piece 4 is set in a metal cylindrical container 5 that can be restrained sideways, and glass beads simulating crushed stone (granular body) 2a. 8a is placed in the container 5, and the glass bead layer 8 is laminated on the test body 4. Then, a loading means 7 is installed above the glass bead layer 8 in the container 5, and a very small load (for example, about 5 kPa) P1 is loaded on the glass bead layer 8 and the test body 4 by the loading means 7.

As shown in FIG. 3 (b), while maintaining the state in which the load P1 does not change, water W is put into the cell 6 and the glass bead layer 8 and the test body 4 are immersed in the water W together with the container 5, and the expanded soil 1 The expansion of the test body 4 is promoted, and at the same time, the displacement of the displacement measurement point of the loading means 7 is read. As a result, the amount of expansion (Free Swell) (%) at extremely low pressure is obtained.

As shown in FIG. 3C, the loads P1, P2, P3 ... Are gradually increased by the loading means 7. At this time, the test piece 4 of the expanded soil and the glass bead layer 8 shrink due to consolidation, and the height decreases. The loading pressure is gradually applied until the height of the specimen (test specimen) 9 composed of the specimen 4 and the glass bead layer 8 becomes lower than the initial height, and the height of the specimen 9 becomes the same as the initial height. The loading pressure is obtained, and this loading pressure is defined as the expanding pressure (Swelling Pressure).

Further, in order to confirm the effect of the size of the crushed stone 2a and the effect of the thickness of the buffer layer 2, the above loading test is carried out with the diameter of the glass beads 8a and the thickness of the glass beads layer 8 as parameters. In the present embodiment, for example, glass beads 8a having a diameter of 1 mm, 2 mm, and 3 mm (3 levels) are used, and the thickness of the glass bead layer 8 is changed to 10 mm, 20 mm, and 30 mm (3 levels), and the above loading is repeated. Perform the test and determine the loading pressure (expansion pressure) in each test case.

Then, the expansion amount (Free Swell) at extremely low pressure when the diameter of the glass bead 8a is changed and the thickness of the glass bead layer 8 are changed, and the expansion pressure (Swelling Pressure) obtained in the loading test. Ask for a relationship. This relationship makes it possible to quantify and confirm the effect of the foundation structure A for expanding ground countermeasures of the present embodiment. In other words, it becomes possible to determine the specifications of the foundation structure A for expanding ground countermeasures based on the test results.

Here, 18 test specimens 4 are prepared from the expanded soil sample collected from the expansive ground 1, 9 of them are in a state without countermeasures, and the remaining 9 are in a countermeasure work (for expansive ground countermeasures of the present embodiment). The result of acquiring the expansion characteristics of the state of the foundation structure A) and confirming the effect of the countermeasure work will be described.

FIG. 4 shows the test results.
In this figure, the vertical axis represents the amount of expansion obtained by the test, and the horizontal axis represents the expansion pressure. Further, one plot is a set of results obtained from one test piece 4, and the filled marks indicate the expansion characteristics when there is no countermeasure work, and the white marks indicate the expansion characteristics when there is a countermeasure work.

First, while the expansion characteristics of the expansive ground 1 used are about 2.5 to 4% in terms of expansion amount and about 55 to 125 kPa in terms of expansion pressure, glass beads 8 are used to simulate an upper replacement type countermeasure work. The values obtained by the test method (method for confirming the effect of the foundation structure for expansive ground countermeasures of the present embodiment) are an expansion amount of 0 to 2.5% and an expansion pressure of 10 to 75 kPa. It was proved that it could be confirmed.

From FIG. 4A, the influence of the glass bead diameter on the countermeasure effect can be confirmed.
That is, the larger the diameter of the glass beads, the smaller the expansion coefficient and the expansion pressure were obtained, and it was demonstrated that the larger the diameter of the crushed stone (granular body), the more effective it was.

FIG. 4B shows the result of comparing the same data by the thickness of the glass beads.
From this figure, it was confirmed that even if the glass bead thickness was different from 10 mm, 20 mm, and 30 mm, no significant difference was obtained in the expansion characteristics, and it was confirmed that the effect was not increased even if the buffer layer 2 was thickened. It was. That is, it can be said that the buffer layer 8 is effective if it has a thickness several times the particle size.

As described above, using the method for confirming the effect of the foundation structure for expanding ground countermeasures of the present embodiment, expansion at extremely low pressure when the diameter of the glass beads 8a is changed and when the thickness of the glass bead layer 8 is changed. By determining the relationship between the amount (Free Swell) and the expansion pressure (Swelling Pressure) obtained in the loading test, the effect of the foundation structure A for expanding ground countermeasures can be quantified and confirmed, and the test results can be used. Based on this, it was demonstrated that the specifications of the foundation structure A for measures against expansive ground can be determined.

Therefore, according to the method for confirming the effect of the foundation structure for expansive ground countermeasures of the present embodiment, the effect of the upper replacement type expansive ground countermeasure can be confirmed on a trial basis, and a highly reliable expansive ground countermeasure can be obtained. It will be possible to realize.

Next, with reference to FIGS. 5 to 8, a method for confirming the effect of the foundation structure for expansive ground countermeasures according to the second embodiment of the present invention will be described.

Here, in the present embodiment, as shown in FIG. 5, a groove (recess) 10 is provided in the expansive ground 1, and the groove is filled with crushed stone (granular body) 2a such as limestone to provide a buffer layer 2 (a buffer layer 2 (recess). The present invention relates to a method of forming an expansion suppressing layer 3) such as a concrete layer and confirming the effect of a foundation structure B for expanding expansion ground measures that reduces the influence of the expanding ground 1 on a floor slab or the like.

In the inflatable ground countermeasure foundation structure B of the present embodiment, the inflatable ground 1 expands, and the expansion pressure can be absorbed and reduced by the buffer layer 2 (and the expansion suppression layer 3), and the foundation structure B can absorb and reduce the expansion pressure. It is possible to prevent the expansion pressure from acting on the supported superstructure.

The method of confirming the effect of the foundation structure B for expanding ground countermeasures of the present embodiment for confirming the effect of such measures against expansive ground is the same as that of the first embodiment, using the actual expanded soil collected from the expansive ground 1 and the expanded soil. This is a laboratory test method using glass beads simulating crushed stone (granular body), and is for grasping the influence on the floor and foundation from the expansion amount and expansion pressure obtained by the test. Therefore, in the present embodiment, the same reference numerals are given to the same configurations as those in the first embodiment, and detailed description thereof will be omitted.

In the method of confirming the effect of the foundation structure B for measures against expansive ground of the present embodiment, as shown in FIG. 6, the expanded soil is put into the cylindrical forming container 11 and formed into a disk shape, and then the disk-shaped expanded soil is formed. The molded body 12 of the above is taken out from the molding container 11, and the central portion thereof is cut in a predetermined width dimension in the radial direction.

The cut portion 13 is removed to form a pair of test pieces 14 and 15 having a substantially semicircular shape in a plan view, and the test pieces 14 and 15 are returned to the molding container 11 so that a groove (recess) 16 is formed in the center.

Then, by filling the groove 16 formed between the pair of test pieces 14 and 15 with the glass beads 8a, the grooving replacement type expansive ground of the present embodiment in which the glass bead layer 8 is sandwiched between expanded soils. A test body 17 of the basic structure B for countermeasures is manufactured.

Next, as shown in FIG. 7A, the test body 17 is set in a metal cylindrical container 5 that can be laterally restrained. Then, a loading means 7 is installed on the upper part of the test body 17 in the container 5, and a very small load (for example, about 5 kPa) P1 is loaded on the test body 17 by the loading means 7.

As shown in FIG. 7B, while keeping the load P1 unchanged, water W is put into the cell 6 and the test body 17 is immersed in the water W together with the container 5, and the expanded soil of the test body 17 is expanded. At the same time, read the displacement of the displacement measurement point of the loading means 7. As a result, the amount of expansion (Free Swell) (%) at extremely low pressure is obtained.

As shown in FIG. 7C, the loads P1, P2, P3 ... Are gradually increased by the loading means 7. At this time, the test body 17 contracts due to consolidation, and the height decreases. The loading pressure is gradually applied until the height of the test body 17 becomes lower than the initial height, the loading pressure at which the height of the test body 17 becomes the same as the initial height is obtained, and this loading pressure is used as the expansion pressure (Swelling Pressure). ).

Further, in order to confirm the effect of the size of the crushed stone 2a and the effect of the thickness of the buffer layer 2, the above loading test is carried out with the diameter of the glass beads 8a and the thickness of the glass beads layer 8 as parameters. In the present embodiment, for example, glass beads 8a having a diameter of 1 mm, 2 mm, and 3 mm (3 levels) are used, and the groove width (width of the glass bead layer 8) is changed to 5 mm, 10 mm, and 15 mm (3 levels) and repeated. The above loading test is carried out, and the loading pressure (expansion pressure) in each test case is determined.

Then, the expansion amount (Free Swell) at extremely low pressure when the diameter of the glass bead 8a is changed and the groove width of the glass bead layer 8 are changed, and the expansion pressure (Swelling Pressure) obtained in the loading test. Ask for a relationship. This relationship makes it possible to quantify and confirm the effect of the foundation structure B for expanding ground countermeasures of the present embodiment. In other words, it becomes possible to determine the specifications of the foundation structure B for expanding ground countermeasures based on the test results.

Here, 23 test specimens were prepared from the expanded soil sample collected from the expansive ground 1, 14 were in the state without countermeasures, and the remaining 9 had countermeasures (foundation for expansive ground countermeasures of the present embodiment). The result of acquiring the expansion characteristics of the state of the structure B) and confirming the effect of the countermeasure work will be described.

FIG. 8 shows the test results.
In this figure, the vertical axis represents the amount of expansion obtained by the test, and the horizontal axis represents the expansion pressure. Further, one plot is a set of results obtained from one test piece, and the filled marks indicate the expansion characteristics when there is no countermeasure work, and the white marks indicate the expansion characteristics when there is a countermeasure work.

First, while the expansion characteristics of the expansive ground 1 used are about 3 to 5% in terms of expansion amount and about 100 to 175 kPa in terms of expansion pressure, a test simulating a groove replacement type countermeasure work using glass beads 8 The values obtained by the method (method for confirming the effect of the foundation structure for expansive ground countermeasures in the present embodiment) are an expansion amount of 2 to 3.5% and an expansion pressure of 20 to 115 kPa, and the effect of the countermeasure work can be sufficiently confirmed. Was demonstrated.

From FIG. 8A, the influence of the glass bead diameter on the countermeasure effect could not be confirmed.

FIG. 8B shows the results when the width of the groove is changed.
From this figure, the influence of the width of the groove on the countermeasure effect is not clearly recognized. That is, it can be said that if a slight expansion can be allowed in the horizontal direction, the influence on the floor in the vertical direction can be reduced.

As described above, the amount of expansion at extremely low pressure (Free Swell) when the diameter of the glass beads 8a is changed and when the width of the groove is changed by using the method for confirming the effect of the foundation structure for expanding ground countermeasures of the present embodiment. ) And the expansion pressure (Swelling Pressure) obtained in the loading test, it was demonstrated that the effect of the foundation structure B for expanding ground countermeasures can be confirmed.

Therefore, according to the method for confirming the effect of the foundation structure for expansive ground countermeasures of the present embodiment, the effect of the grooving replacement type expansive ground countermeasure can be confirmed on a trial basis, and the highly reliable expansive ground countermeasure can be confirmed. Will be possible.

The first and second embodiments of the method for confirming the effect of the foundation structure for expanding ground countermeasures according to the present invention have been described above, but the present invention is not limited to the above embodiment and does not deviate from the gist thereof. It can be changed as appropriate within the range.

1 Expandable ground (expanded soil)
2 Buffer layer 2a Crushed stone (granular body)
3 Expansion suppression layer 4 Specimen 5 Container 6 Cell 7 Loading means 8 Glass bead layer 8a Glass beads 9 Specimen (test specimen)
10 grooves (recesses)
11 Molded container 12 Molded body 13 Cut part 14 Test piece 15 Test piece 16 Groove 17 Specimen A Foundation structure for expansive ground countermeasures B Foundation structure for expansive ground countermeasures W Water

Claims (2)

It is a method to confirm the effect of the foundation structure for expansive ground countermeasures constructed by laying granules on the surface of the expansive ground.
A test piece was produced by laminating a glass bead layer made of glass beads imitating the granules on the expanded soil obtained from the expansive ground.
The test piece is immersed in water with the side of the test piece restrained, and a loading pressure is gradually applied to the test piece from above, so that the height of the test piece is the same as the initial height before loading. A method for confirming the effect of a foundation structure for measures against expansive ground, which comprises obtaining a load pressure to be obtained and using the load pressure as an expansion pressure. It is a method of confirming the effect of the foundation structure for measures against expansive ground, which is constructed by forming a recess on the surface of the ground showing expandability and filling the recess with granules.
A test piece was produced so as to sandwich a glass bead layer made of glass beads imitating the granules with expanded soil obtained from the ground exhibiting expandability.
The test piece is immersed in water with the side of the test piece restrained, and a loading pressure is gradually applied to the test piece from above, so that the height of the test piece is the same as the initial height before loading. A method for confirming the effect of a foundation structure for measures against expansive ground, which comprises obtaining a load pressure to be obtained and using the load pressure as an expansion pressure.

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