JP2008095352A - Small-scale building provided with countermeasures against liquefaction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide countermeasures against liquefaction capable of reducing the number of basic factors for liquefaction in a combined manner to increase the efficiency of the countermeasures against liquefaction, keeping the effect of the countermeasures continuously for a long time, and allowing workers to take the similar countermeasures additionally as required. <P>SOLUTION: This small-scale building provided with the countermeasures against liquefaction is provided with the building, an impervious wall arranged along edges of the building below the building, and a water draining device. The impervious wall reaches a viscous soil layer positioned below the building. The water draining device drains underground water from the soil layer positioned between the building and the viscous soil layer positioned below the building to a predetermined position. A water-level gauge for measuring a level of underground water in the soil layer positioned between the building and the viscous soil layer positioned below the building may be provided in the soil layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a small-scale building that has been liquefied. More specifically, the present invention relates to a small-scale building capable of preventing the occurrence of liquefaction by taking measures against liquefaction on the ground where a sandy soil layer having a thickness of 6 m or less exists on the surface layer. About.

  Loose sandy soil layers are liable to be liquefied by earthquakes, which can result in complete loss of bearing capacity or reduced apparent stiffness. Therefore, when a building is built on the ground where a loose sandy soil layer is distributed on the surface layer, if the foundation of the building is placed directly on the loose sandy soil layer, the settlement of the building is caused by liquefaction. And will be inclined. Even when a pile foundation that supports a building with a pile that reaches deep ground is used, the horizontal resistance of the pile lowers due to the liquefaction of the surface ground, resulting in a large displacement in the building. May occur.

As such, in saturated sand ground, liquefaction may occur due to the occurrence of liquefaction in the event of an earthquake, so it is necessary to evaluate the occurrence of liquefaction by an appropriate method and prevent its occurrence. is there. According to the Architectural Foundation Design Guidelines of the Architectural Institute of Japan, the main predisposing factors for liquefaction are as follows.
1. The soil layer is saturated (corresponding to the soil layer below the groundwater level).
2. The soil layer is generally distributed at a shallow position of about 20m from the ground surface (applicable to alluvium).
3. The fine particle content in the particle size composition is 35% or less.
4). In landfill or embankment, soil with a clay content (soil particles with a particle size of 0.005 mm or less) of 10% or less or a plasticity index of 15% or less.

Existing liquefaction measures are carried out for the purpose of reducing or eliminating the possibility of liquefaction of the target soil layer by reducing or eliminating the above predisposing factors.
Japanese Patent Laid-Open No. 7-158045 Japanese Patent Laid-Open No. 2001-262591 discloses a barrier for impervious and impermeable water from the ground surface to a desired depth, and tightens the ground by degassing the upper part of the ground surrounded by the barrier. It is disclosed to solidify and solidify the ground.

  In Patent Document 2, a water blocking wall is constructed so as to surround and seal the liquefied layer, and in the liquefied layer surrounded by the water blocking wall, the pore water pressure is reduced when the earthquake occurs. Activating the device is disclosed.

  These conventional liquefaction countermeasures are intended to improve the ground that is liable to liquefy so that liquefaction is unlikely to occur, and to prevent liquefaction when an earthquake occurs. It is accompanied by. For this reason, small-scale buildings have drawbacks in their workability and economy.

  In addition, since many conventional liquefaction countermeasures are implemented individually for the target building, high-pressure groundwater generated by liquefaction occurs in adjacent areas where countermeasures are not implemented. May flow into the direct ground board with a slight time delay, and the ground may become liquefied or close to the situation as in the adjacent land.

  The present invention is intended to solve the conventional problems, and by taking into consideration the workability of liquefaction countermeasures in small-scale buildings, small-scale buildings with liquefaction countermeasures that can be constructed using a small construction machine The purpose is to provide goods.

  In addition, the present invention improves the efficiency of liquefaction countermeasures by reducing the predisposition to liquefaction not only in a single but also in combination, and can maintain the effects of the countermeasures and add the same countermeasures as needed. The purpose is to provide a small-scale building with liquefaction countermeasures that can be constructed.

  In view of the above problems, the present invention provides a countermeasure for liquefaction suitable for a small-scale building. The small-scale building according to the present invention is arranged along the edge of a building and the lower part of the building. And the drainage device reaches the viscous soil layer located below the building, and the drainage device is connected to the building and the viscous soil layer located below the building. It is characterized by draining groundwater from a soil layer located between them to a predetermined position.

  Further, a small-scale building according to the present invention comprises a building, a foundation disposed along the edge of the building below the building, a water shielding wall disposed below the foundation along the foundation, and a drainage device. The impermeable wall reaches the viscous soil layer located below the building, and the drainage device is located at a predetermined position from the soil layer located between the building and the viscous soil layer located below the building. You may make it drain a groundwater.

  The impermeable wall is formed of a material having poor water permeability.

  Furthermore, the small-scale building according to the present invention is provided with a water level meter for measuring the groundwater level of the soil layer in the soil layer located between the building and the viscous soil layer located below the building. It may be.

  The impermeable wall may be provided with the function of the foundation of the building.

  The water level gauge can drain the groundwater by activating the drainage device when measuring that the groundwater has exceeded a predetermined water level.

  The impermeable wall may be formed by ground improvement.

  You may make it form a water-impervious wall by arrange | positioning steel sheet piles continuously without a gap.

  The soil layer located between the building and the viscous soil layer located below the building is a sandy soil layer with a thickness of about 6 m.

  In addition, the liquefaction prevention method for a small-scale building according to the present invention is based on a foundation disposed along the edge of the building below the building and reaches the viscous soil layer located below the building. A water-impervious wall is formed, and groundwater is drained from a soil layer having a thickness of about 6 m located between the building and the viscous soil layer located below the building to a predetermined position.

  In addition, the soil layer located between the building and the viscous soil layer located below the building is equipped with a water level meter for measuring the groundwater level of the soil layer, and the water level meter exceeds the predetermined water level. The drainage device may be activated when it is measured.

  According to the present invention, it is possible to perform construction using a small construction machine by considering the workability of liquefaction measures in small-scale buildings, and also reduce the predisposition to liquefaction not only in a single way but also in a composite manner. By doing so, the efficiency of countermeasures against liquefaction can be increased, and further, the effects of the countermeasures can be maintained and the same countermeasures can be additionally applied at any time.

  Hereinafter, along with the attached drawings, a small-scale building to which liquefaction measures according to the present invention are applied will be described.

[Outline of small building]
FIGS. 1 to 3 show a small-scale building having a basic structure necessary for liquefaction countermeasures for the sake of clarity of explanation.

  FIG. 1 is a small view comprising a foundation 14, a building 10 built on the foundation 14, a water blocking wall 12 continuously installed along the foundation 14 directly below the foundation, and a drainage device 20. 1 is a partial cross-sectional side view of a scale building 1. FIG.

  The building 10 is a small-scale building, and is built on the sandy soil layer 19-1 of the sandy soil layer 19 through the foundation 14. The thickness (depth) of the sandy soil layer 19 is about 6 m. Below the sandy soil layer 19, there is a viscous soil layer 28 that does not liquefy.

  As will be described in detail later, the water-impervious wall 12 is formed of a non-permeable material, for example, a plurality of columns (columnar bodies) 12a formed by a soil cement column method adjacent to each other in the vertical direction to form a foundation 14. It is installed continuously along the base 14 and passes through the sandy soil layer 19-1 from just below the foundation 14 to reach the viscous soil layer 28.

  FIG. 2 is a plan view showing the impermeable wall 12 by omitting the building 1 and the foundation 14 from the small-scale building 1 shown in FIG. Moreover, the figure seen from the cross section AA in FIG. 2 respond | corresponds to sectional drawing of the part of the impermeable wall 12 of FIG. As shown in FIG. 2, the foundation 14 is arranged along the edge of the building 1 (omitted from FIG. 2), and the water-impervious wall 12 includes a plurality of columns 12 a, and these columns are the foundation 14. Are arranged closely in parallel with each other without any gaps, and generally form a “B” shape and surround the sandy soil layer 19-1.

  FIG. 3 is a front view of the small-scale building 1 of FIG. As shown in the figure, the building 10 is built on a foundation 14, and the foundation 14 is disposed on a water shielding wall 12. As described with reference to FIG. 2, the water shielding wall 12 includes a plurality of columns 12 a, and the plurality of columns 12 a are arranged closely or overlapped so that there is no gap between the columns. Thereby, the impermeable wall 12 prevents the groundwater from moving from the sandy soil layer 19-2 located outside the sandy soil layer 19-1 surrounded by the impermeable wall 12.

  In addition, as shown in FIG. 1, the small-scale building 1 is provided with a drainage device 20. The drainage device 20 may be any device as long as it drains groundwater. In this embodiment, the drainage device 20 includes a pump 22, a strainer 26, and a pipe 24 connecting them. The strainer 26 is embedded at a predetermined location in the sandy soil layer 19-1. When the pump 22 is driven, the groundwater in the sandy soil layer 19-1 can be pumped through the strainer 26, and the groundwater can be drained to an arbitrary position in the sandy soil layer 19-1. Further, a groundwater level gauge 50 (or a pore water pressure gauge) is provided at a predetermined depth in the sandy soil layer 19-1. The groundwater level gauge 50 is connected to the control device 52 via the wiring 54. The control device 52 is electrically connected to the pump 22 of the drainage device 20, and the groundwater level gauge is set according to the setting. Based on the signal from 50, the drive or stop of the pump 22 of the drainage device 20 can be controlled. The control device 52 may be provided with a display device (not shown) that displays the groundwater level indicated by the groundwater level gauge 50, and is provided with a lamp that displays the ON / OFF state of the pump 22 in the control device. Also good.

[Overview of liquefaction measures]
In order to prevent liquefaction, first, before making the foundation 14 of the building 10 in FIG. 1, as shown in FIG. 2, a plurality of columns 12a are arranged adjacent to each other without a gap as shown in FIG. 12 is formed. The impermeable wall 12 also passes through the sandy soil layer 19 from just below the foundation 14 to reach the viscous soil layer 28. With such a configuration, the sandy soil layer 19-1 located below the building 10 is surrounded by the impermeable wall 12 and the viscous soil layer 28, and the sandy soil layer 19-1 is surrounded around the building 10. It can be separated from a sandy soil layer 19-2. Then, a foundation 14 is formed thereon along the impermeable wall 12, and the building 10 is built on the foundation. In addition, the strainer 26 of the drainage device 20 is embedded in an appropriate position in the sandy soil layer 19-1 and the pump 22 is installed outside the building 10 at an appropriate time before the building 10 is built.

  Next, the pump 22 is actuated to draw and drain the groundwater from the sandy soil layer 19-1 surrounded by the impermeable wall 12. As shown in FIG. 1, when the groundwater level in the sandy soil layer 19-1 is at the position of the groundwater level line 16 as shown in FIG. Since the layer 16a of the sandy soil layer 19-1 positioned is in an unsaturated state, liquefaction does not occur. In this way, when the groundwater is drained, the soil layer above the groundwater becomes unsaturated, and liquefaction does not occur. Therefore, the inside of the sandy soil layer 19-1 surrounded by the impermeable wall 12 and the viscous soil layer 28. However, if the difference between the groundwater level in the sandy soil layer 19-2 adjacent to the periphery of the building 10 and the groundwater level in the sandy soil layer 19-1 becomes too large, The adjacent sandy soil layer 19-2 may pass through the impermeable wall 12 and may cause a problem that groundwater easily penetrates into the sandy soil layer 19-1. On the other hand, as will be described in detail later, for the layer 16b of the sandy soil layer 19-1, the vertical effective stress corresponding to the variation in the groundwater level of the sandy soil layer 19-1 located above the groundwater level is reduced. An increase is expected, which increases the resistance to liquefaction of the layer 16b of the sandy soil layer 19-1 located below the groundwater level and reduces its risk. When the water level is determined in consideration of the advantage of enhancement, it can be seen that the effect is sufficiently exhibited as a countermeasure for liquefaction. Therefore, for example, in this embodiment, the groundwater is drained to the position of the groundwater level line 16 as shown in FIG. The method for setting the groundwater level line will be described later.

  Thereafter, with the passage of time, the groundwater in the sandy soil layer 19-2 oozes out from the impermeable wall 12 to the sandy soil layer 19-1, and the groundwater level in the sandy soil layer 19-1 gradually increases. May end up. If the groundwater level rises in such a way, it becomes inadequate as a countermeasure against liquefaction. Therefore, for example, as shown in FIG. 1, when the groundwater level line 16 rises to the groundwater level line 17, the pump 22 can be activated to discharge the increased groundwater level. The setting can be performed by the control device 52. When the setting is performed, when the groundwater level exceeds the groundwater level line 17, a signal indicating that is sent from the groundwater level gauge 50 to the control device 52, and the control is performed. The device 52 activates the pump 22 and starts draining groundwater. Thereafter, the pump 22 is stopped when the groundwater is reduced to the original groundwater level line 16.

  Thus, if the drainage device 20 is provided, the effect of the liquefaction countermeasure can be maintained.

[Setting of groundwater level line]
In general, the safety factor Fi relating to the occurrence of liquefaction is obtained by the following equation (1) for the soil layer at each depth. It is determined that there is no liquefaction for soil layers with Fi values greater than 1 ("Guidelines for Designing Building Foundations").

Fi = (τl / σ'z) / (τd / σ'z) (1)
Here, (τl / σ'z) is the liquefaction resistance ratio of the saturated soil layer (corresponding to the layer 16b of the sandy soil layer 19-1), and (τd / σ'z) is the repeated shear stress ratio. . Further, σ′z is an effective earth covering pressure (vertical effective stress) at the examination depth. If the safety factor Fi is simply shown, it is as shown in the following formula (2).

Fi = τl / τd (2)
Here, τl is the liquefaction resistance of the saturated soil layer (corresponding to the layer 16b of the sandy soil layer 19-1), and τd is the repeated shear stress.

  Before and after the lowering of the groundwater level, the liquefaction resistance ratio (τl / σ'z) of the target saturated soil layer (corresponding to the layer 16b of the sandy soil layer 19-1) does not change, but the groundwater level is, for example, the groundwater level By decreasing to the line 16, the liquefaction resistance τl is corresponding to the fact that the effective earth covering pressure σ′z at the examination depth after the decrease in the groundwater level becomes larger than σ′z before the decrease. To increase. On the other hand, the cyclic shear stress τd is generally the same magnitude before and after the groundwater level lowering without being affected by the local groundwater level lowering. As a result, it can be seen from equation (2) that the safety factor Fi against liquefaction increases.

  By calculating backward from the safety factor Fi, it is possible to obtain the groundwater level at which the sandy soil layer below the groundwater level does not liquefy.

  According to the above-described embodiment, when the pressure of groundwater becomes higher than the initial level due to liquefaction in the sandy soil layer 19-2 in the adjacent land where liquefaction countermeasures are not implemented, the sandy soil layer 19-1 Is cut off from the sandy soil layer 19-2 by the impervious impermeable wall 12, so that the sandy soil layer immediately below the building 10 from the sandy soil layer 19-2 in a short time after the occurrence of an earthquake. Groundwater does not flow toward 19-1, and the ground of the building 10 can maintain the effect of liquefaction countermeasures.

  Moreover, the impermeable wall 12 continuously installed along the outer periphery of the building 10 is hardly permeable, but in the long term, the sandy soil layer 19-1 and the sandy soil layer 19-2 adjacent thereto are formed. Since it is difficult to completely eliminate the infiltration of groundwater from the adjacent ground due to the difference in groundwater level, the groundwater level of the sandy soil layer 19-1 may gradually increase. For this reason, the drainage device 20 discharges the increased amount of groundwater, and maintains the groundwater level of the sandy soil layer 19-1 at a predetermined height, thereby managing the groundwater level to prevent liquefaction. The effect can be retained permanently.

  The groundwater level can be managed by installing a groundwater level meter 50 in the sandy soil layer 19-1 and checking whether the groundwater level of the sandy soil layer 19-1 is maintained at a predetermined level. It becomes. A pore water pressure gauge may be used in place of the groundwater level gauge.

[Other examples of small buildings]
FIG. 4 is a plan view showing a water shielding wall 42 in a small-scale building 100 according to another embodiment of the present invention. As in the embodiment shown in FIG. 2, the water-impervious wall 42 is composed of a plurality of columns 42 a, and these columns are arranged in parallel and directly below the foundation 64 along the shape of the foundation 64 without any gaps. The sandy soil layer 19 is penetrated from right under 42 to the viscous soil layer 28.

  Further, the water-impervious wall 42 includes a substantially “B” -shaped outer peripheral portion 44 disposed along a foundation 64 formed on the outer periphery, and a partition wall disposed along a portion of the foundation 64 protruding inward thereof. 46. The outer peripheral portion 44 of the impermeable wall 42 surrounds the sandy soil layer 19-1, and the sandy soil layer 19-1 is surrounded by the viscous soil layer 28 located below the sandy soil layer 19-1. Is separated from the sandy soil layer 19-2.

  Since the partition wall 46 does not need to have water shielding properties, the column may not be continuous.

  The small-scale building 100 according to the present embodiment includes a drainage device 70 for draining the groundwater of the sandy soil layer 19-1, and the drainage device 70 includes a pump 72, a pipe 74, and a plurality of strainers. 76. The plurality of strainers 76 are arranged one by one in the area surrounded by the partition wall 46, and are used for efficiently discharging the groundwater in each area. However, the required quantity of the drainage device 70 and the strainer can be determined in consideration of the planar size of the building and the water permeability of the sandy soil layer 19-1. Moreover, although not shown in figure, the groundwater level meter is provided in the sandy soil layer 19-1, the groundwater level in the sandy soil layer 19-1 is monitored, and the water level of the sandy soil layer 19-1 is When the predetermined water level is exceeded, the drainage device 70 is activated to keep the water level constant.

[Other variations]
In the above embodiment, the impermeable wall 12 has been described as a plurality of columns formed by a soil cement column method installed adjacent to each other in the vertical direction. However, any material that is hardly permeable can be used. Well, for example, other steel sheet piles may be used, and by improving the ground corresponding to the water-impervious wall 12 by a method different from the soil cement column method, the portion is made impermeable. You may do it.

  In the above embodiment, the foundation 14 and the water-impervious wall 12 are provided separately. However, they may be formed as an integral foundation so that the foundation has poor water permeability.

  Further, the drainage device 20 may be any device as long as it can drain the groundwater in the sandy soil layer 19. For example, a submersible pump is disposed at the position of the strainer 26 and is connected via the pipe 24. You may make it drain ground water. The quantity and performance of the drainage device 20 are determined in consideration of the planar size of the building and the permeability of the ground located immediately below the building.

  Further, the drainage devices 20 and 70 may be driven intermittently so as to drive when exceeding a predetermined groundwater level line and stop when reaching a predetermined groundwater level line, as in the above embodiment, or Depending on the increasing amount of groundwater, it may be continuously driven so as to discharge the amount continuously and always maintain a constant groundwater level.

FIG. 1 is a partial cross-sectional side view of a small-scale building according to an embodiment of the present invention. FIG. 2 is a plan view showing a water shielding wall by omitting buildings and foundations from the small-scale building shown in FIG. FIG. 3 is a front view of the small-scale building shown in FIG. FIG. 4 is a plan view showing a water shielding wall 42 in another embodiment of the small-scale building according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,100 Small-scale building 10 Building 12, 42 Impermeable wall 14, 64 Foundation 20, 70 Drainage device 19 Sandy soil layer 28 Cohesive soil layer

Claims (12)

A building, a water shielding wall disposed along the edge of the building, and a drainage device, the water shielding wall reaching a viscous soil layer located below the building, A small-scale building in which the drainage device drains groundwater from a soil layer located between the building and the viscous soil layer located below the building to a predetermined position. A building, a foundation disposed along the edge of the building below the building, a water shielding wall disposed below the foundation along the foundation, and a drainage device, wherein the water shielding wall includes the Reaching the viscous soil layer located below the building, and the drainage device drains groundwater from the soil layer located between the building and the viscous soil layer located below the building to a predetermined position. A small building that drains. The small-scale building according to claim 1 or 2, wherein the water-impervious wall has poor permeability. 3. The small-scale building according to claim 1 or 2, further comprising: measuring the groundwater level of the soil layer in the soil layer located between the building and the viscous soil layer located below the building. A small building with a water level gauge. The small-scale building according to claim 1, wherein the water shielding wall also has a function of a foundation of the building. 5. The small-scale building according to claim 4, wherein the drainage device is activated to drain groundwater when the water level gauge measures that groundwater has exceeded a predetermined water level. The small-scale building according to claim 1 or 2, wherein the water shielding wall is formed by ground improvement. The small-scale building according to claim 1 or 2, wherein the water-impervious wall is formed by continuously arranging steel sheet piles without any gaps. 3. The small-scale building according to claim 1 or 2, wherein the soil layer located between the building and the viscous soil layer located below the building is a sandy soil layer having a thickness of about 6 m. Small building. A water-impervious wall is formed so as to reach a viscous soil layer located below the building, along a foundation disposed along the edge of the building below the building, and located below the building and the building. A liquefaction prevention method for small-scale buildings, in which groundwater is drained from a soil layer having a thickness of about 6 m located between the clay soil layer and a predetermined position. The liquefaction prevention method for a small-scale building according to claim 10, wherein the water shielding wall has poor water permeability. The method for preventing liquefaction of a small-scale building according to claim 10, further comprising: setting a groundwater level of the soil layer to the soil layer located between the building and the viscous soil layer located below the building. A method for preventing liquefaction of a small-scale building, comprising a water level meter for measuring, and starting the drainage device when the water level meter measures that groundwater has exceeded a predetermined water level.

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