Method for preventing differential settlement due to liquefaction in existing houses

Abstract

This invention provides a steel pipe and a method for installing it that suppress differential settlement of existing residential buildings due to soil liquefaction. [Solution] Steel pipes are driven into the ground within the site of an existing house, in accordance with the surrounding environment, such as adjacent houses, buildings, and structures.

Description

Technical Field

[0001] The present invention relates to a method for preventing differential settlement due to liquefaction of existing houses.

Background Art

[0002] When an earthquake of seismic intensity 5 or higher occurs, existing detached houses built on soft sandy ground below the groundwater level are damaged by liquefaction, and differential settlement occurs such that the building tilts diagonally.

[0003] Regarding the damage to existing houses caused by this differential settlement, there is a problem that repairs cannot proceed because the repair costs are too high.

[0004] Also, even when anti-settlement support piles are driven to reach stable ground or column piles are driven during new construction, if there is a layer of sand containing a large amount of water that causes liquefaction up to the stable ground, large cavities will occur in the building foundation part of the house due to liquefaction, and thus the repair construction cost also becomes a problem.

[0005] The foundation structure of the structure in Patent Document 1 is described to have an effect of preventing immediate settlement of the structure because it has a supporting force due to buoyancy even when the ground liquefies and the supporting force of the foundation is lost.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

[0007] However, the differential settlement prevention method and structure due to liquefaction described in Patent Document 1 support the house with a floating body, which still carries a high risk of large cavities forming beneath the house's foundation. Furthermore, if the tremendous energy of liquefaction causes stress to concentrate on only a part of the floating body, there is a risk that part of the floating body will break, inducing differential settlement. In addition, the construction costs are large and expensive, making it difficult to use. [Problems that the invention aims to solve]

[0008] It is said that when a house tilts due to differential settlement caused by liquefaction, it becomes uncomfortable and difficult to live in the house when the tilt exceeds 5 / 1000.

[0009] Furthermore, post-earthquake investigations have revealed that many of these structures tilt by about 10 / 1000, necessitating extensive repairs. A common repair method for this purpose is called underpinning, which involves digging a tunnel beneath the foundation, using jacks to press in and connect short steel pipes, and then setting up more than 20 jacks under the building's foundation to jack up the entire structure until it is level.

[0009] Furthermore, if liquefaction causes voids to form beneath the foundation, water and sludge-like soil containing a large amount of moisture can accumulate in those areas. This is extremely unsanitary and can lead to problems such as a decrease in bearing capacity. Therefore, the development of appropriate and effective technologies is urgently needed for existing detached houses. [Means for solving the problem] To solve the above problems, the inventor devised the following means: The inventor focused on the fact that when he investigated detached houses that had liquefied and subsided due to the Great East Japan Earthquake and the Noto Peninsula Earthquake, he noticed that almost all of them were tilting toward the neighboring houses due to the subsidence.

[0010] This phenomenon is thought to have been caused by the influence of underground stress from a house built on the adjacent property. Focusing on this, the mechanism is that underground stress is distributed downwards from the foundation at an angle of approximately 30 degrees and spreads out in a trapezoidal shape.

[0011] When neighboring houses are close together, the loads of the neighboring houses and structures overlap, creating stress concentration points. This increases the underground stress at the boundary. Furthermore, if there is a liquefaction layer (a layer of sand containing a lot of water) beneath the topsoil, it becomes muddy during liquefaction and loses its bearing capacity. Therefore, the boundary with the neighboring property, where the underground stress is high, has less bearing capacity compared to other areas, and the property tends to tilt towards that point.

[0012] The inventor discovered that by installing a structure in the ground at the boundary of an existing house site that suppresses or blocks the propagation of stress, the propagation of stress to the adjacent area is suppressed, thereby reducing the effects of liquefaction and decreasing the likelihood of the area tilting. As a result, the first invention is a liquefaction countermeasure for existing houses, in which steel pipes are laid in a continuous wall-like manner within the site, in line with the direction of surrounding houses and structures, to prevent differential settlement caused by liquefaction during earthquakes.

[0013] The second invention involves a system in which the density of the interconnected steel pipes is adjusted according to the weight and distance of surrounding houses and structures.

[0014] The third invention is designed so that when the continuous wall-shaped steel pipe intersects with sewer pipes, rainwater pipes, water pipes, lighting pipes, or tree roots, the effectiveness is not diminished even if a gap is left in the ground when the pipe is installed.

[0015] The fourth invention is designed so that the effect is realized when these interconnected steel pipes reach the non-liquefiable layer at the very bottom of the residential ground. [Effects of the Invention]

[0016] In the present invention, by laying steel pipes in a continuous wall pattern on the site of an existing house, in accordance with the direction of surrounding houses and structures, it becomes possible to suppress differential settlement of buildings due to liquefaction caused by earthquakes.

Embodiments for Carrying out the Invention

[0017] The present invention will be described below with reference to the drawings. First, regarding FIG. 1, this figure is a cross-sectional view in which steel pipes are driven on a sandy layer with a high groundwater level near the boundary with an adjacent site, showing a state where continuous-wall-shaped steel pipes are driven within the site or beneath the block wall that is the boundary with the adjacent site.

[0018] Even in the case of an existing house, when a house is constructed later on adjacent land, by providing it beneath the block wall before laying the block wall, the advantage of reducing the occurrence of differential settlement due to liquefaction in both houses can also be enjoyed.

[0019] Next, FIG. 2 shows the relationship between the site, the adjacent site, and the building built on the adjacent site. An adjacent house A19 is built on the east side and an adjacent house B20 is built on the north side.

[0020] FIG. 3 shows a state in which steel pipes 4 are driven in a continuous-wall shape near the boundary line 3 with the adjacent site shown in FIG. 2.

[0021] FIG. 4 shows a state in which the steel pipes 4 are driven while avoiding the buried pipes 12.

[0022] FIG. 5 shows an embodiment of the present invention, assuming clay 18 in a soil layer 16 with tires 21, sand 17 thereon, water 22 representing the groundwater level 8, concrete blocks (1) 14 and concrete blocks (2) 15 spaced apart therefrom thereon, steel pipes 10 driven in a row therebetween and inserted into the clay 18, and a weight 13 dropped for testing.

[0023] FIG. 6 is a plan view of what is shown in FIG. 5.

[0024] FIG. 7 is a cross-sectional view showing the situation of the in-ground stress range in which the housing load is dispersed into the ground. This in-ground stress is dispersed downward from the foundation at an angle of about 30 degrees in a trapezoidal shape, and a stress concentration part 31 will be formed if the distance to the housing built on the adjacent land is short.

[0025] FIG. 8 is a plan view showing the situation of the test of the embodiment of the present invention. A sand layer 7 containing a clay layer 6 and water 22 is provided in the soil layer, and concrete blocks 1 and 2 serving as substitutes for the housing are placed at intervals thereon, and a heavy weight 13 is dropped from a certain height to show a plan view of the test specimen for performing the test.

[0026] FIG. 9 represents the case where the test of the embodiment of the present invention was carried out 10 times.

[0027] From the embodiment, by driving the steel pipe 4 to the clay layer 6, it was confirmed that the settlement amount of the building 1 was lower than that of those in which the steel pipe 4 was not driven or those that did not reach the clay layer 6, and no differential settlement, which is a problem, occurred.

[0028] That is, in order to make it difficult to transmit the housing load in the direction of the adjacent house and to make it difficult to transmit the housing load from the adjacent housing to the liquefied layer, small-diameter steel pipes or the like may be driven in a sheet pile shape into the ground within the boundary of the site.

[0029] To drive this small-diameter steel pipe or the like, it can be dealt with by a small cordless impact, a wooden mallet, a boring machine, etc., so it can be constructed if there is a little space and the workability is also good.

[0030] By the test using this test specimen, Even if vibrations sufficient to cause liquefaction are applied to the base of the soil tank under the same conditions, the effect is obvious even when compared with those in which the sheet pile-shaped iron pipes driven to the viscosity layer are not laid.

[0031] Note that the present invention is not limited to the above-described embodiment and various modifications are possible. For example, the iron pipe may not be round but may be a plate shape, a square pipe, or a polygonal pipe.

Brief Description of the Drawings

[0032] [Figure 1] A cross-sectional view showing a steel pipe driven into the ground near the boundary with the adjacent property. [Figure 2] A floor plan showing the relationship between the site and the adjacent property. [Figure 3] A plan view showing steel pipes driven into the ground near the boundary with the adjacent property. [Figure 4] A plan view showing the installation of steel pipes when buried pipes are present. [Figure 5] Figure 8 shows a cross-sectional view of the A-A' section of the liquefaction experiment soil tank. [Figure 6] Plan view of the liquefaction experiment tank. [Figure 7] A cross-sectional view showing how the load of a house is distributed underground. [Figure 8] This is a plan view showing the test specimen. [Figure 9] This is an example. [Explanation of symbols]

[0033] 1. Housing 2 GL 3 Boundary lines 4 Steel pipe 5 Block wall 6. Clay layer 7 sand layer 8 Groundwater level 9. Underground stress range 10 rows of steel pipes 11. Influence of adjacent land load 12 buried pipes 13 weights 14 concrete blocks (1) 15 concrete blocks (2) 16 soil layers 17 Sand 18 clay 19 Adjacent House A 20 Adjacent House B 21 wheels 22 water 23 Specimen angle (a) 24 Specimen angle (b) 25 Specimen angle (c) 26 Specimen angle (d) 27 Specimen angle (e) 28 Specimen angle (f) 29 Specimen angle (g) 30 Specimen angle (h) 31. Stress concentration areas

Claims

1. This construction method is used to lay down liquefaction countermeasures for existing houses. A method for preventing differential settlement due to liquefaction, characterized by laying steel pipes in a continuous wall-like manner within the site, in line with the direction of surrounding houses and structures.

2. The method for preventing differential settlement due to liquefaction according to claim 1, characterized in that the density of the continuous wall-shaped steel pipes is adjusted according to the weight and distance of surrounding houses and structures.

3. The method for preventing differential settlement due to liquefaction according to claims 1 and 2, characterized in that when the aforementioned wall-shaped steel pipes intersect with sewer pipes, rainwater pipes, water pipes, lighting pipes, or tree roots, the portion in which they intersect is left open during installation.

4. The method for preventing differential settlement due to liquefaction according to claims 1 to 3, characterized in that the aforementioned wall-like steel pipes reach the non-liquefiable layer of the residential ground.

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