JP5822201B2 - Basic structure of the structure - Google Patents

Description

  The present invention relates to a foundation of a structure, and more particularly to a foundation structure suitable for application to a medium to low-rise building constructed on a liquefied ground.

Direct foundations are often adopted as the basic structure of medium- and low-rise buildings where the number of ground floors is about several floors and the number of basement floors is about one floor. The building 1 is constructed on the liquefied ground 2 (the ground on which the soft liquefied layer 2b such as the sand layer is deposited on the stable non-liquefied layer 2a), and the foundation bottom slab 1a is formed on the liquefied layer 2b. When the liquefied layer 2b directly under the building 1 is liquefied due to an earthquake, the ground supporting force for the foundation bottom slab 1a disappears and the liquefied layer 2b directly under the building as indicated by the broken arrow. However, there is a concern that the bottom of the water blocking wall 3 may flow around and the entire building 1 may sink significantly or may cause significant uneven settlement.
The water blocking wall 3 is temporarily provided at the time of construction and is left as it is after the construction. However, this type of water blocking wall 3 of this type is a liquefaction of the liquefied ground 2 and as a result thereof. It does not have a function for preventing or suppressing the settlement of the building 1.

It is also common to adopt a pile foundation as shown in FIG. 6 instead of the direct foundation. This supports the building 1 by the support pile 4 provided so as to reach the non-liquefaction layer 2a. According to this, even if liquefaction occurs, the support pile 4 can prevent the building 1 from sinking. is there.
However, the pile foundation is more costly than the direct foundation, and even if it can prevent the settlement of the building 1 itself due to liquefaction, if the surrounding ground sinks greatly, it will cause a significant unevenness with it and the earthquake It may hinder later service, and in that respect, it is not necessarily perfect.

  In any case, when constructing various structures on the liquefied ground, it is necessary to take sufficient measures to prevent liquefaction in advance. For this purpose, various construction methods and structures as shown in Patent Documents 1 to 4 are proposed. Has been.

Japanese Patent Laid-Open No. 9-95954 Japanese Unexamined Patent Publication No. 2007-191984 JP 2000-136541 A JP 2004-92049 A

However, all of the conventional liquefaction prevention methods shown in Patent Documents 1 to 4 require large-scale construction and inevitably require a considerable cost, so that they have not been widely spread.
From the above, the actual situation is that an optimum structure is required as a foundation of a structure for liquefaction countermeasures that can be constructed relatively easily and at a low cost, in particular, a structure for middle- and low-rise buildings.

ことを特徴とする。 In view of the above circumstances, the invention described in claim 1 is a basic structure applied to a structure constructed on a liquefied ground in which a liquefied layer is present on an upper layer of a non-liquefied layer, and is underground of the structure. A drainage zone provided with a water blocking wall that reaches the non-liquefied layer around the outer wall and surrounding the liquefied layer immediately below the structure by the water blocking wall and the base bottom plate of the structure. A vertical drain communicating with the water permeable layer between the underground outer wall and the water blocking wall of the structure, and providing a water permeable layer between the foundation bottom plate of the structure and the liquefied layer immediately below the bottom slab the provided, Ri Na and drainable constructed from drainage zone excess pore water generated in the drainage zone by liquefaction of the liquid layer to the surface through the water permeable layer and the vertical drain, permeability of the vertical drain k _2, vertical The value of cross-sectional area A _wV lanes need wastewater [Delta] V w by ground subsidence amount D _s after _{liquefaction,} the required flow rate q _w1, subsidence time Delta] t, the lower end depth H of the vertical drain, when possible wastewater q _w2 by vertical drain , Determined to satisfy the following formula

It is characterized by that.

  The invention according to claim 2 is the basic structure of the structure according to claim 1, wherein a vertical drain leading to the water permeable layer is installed in the drainage zone.

  According to the basic structure of the present invention, although the liquefied ground itself cannot be completely prevented, the amount of settlement can be controlled while allowing the structure constructed there to be settled, and thus the entire building. It is possible to effectively prevent the occurrence of large subsidence or significant uneven subsidence, resulting in large unevenness with the surrounding ground, thus preventing sufficient liquefaction damage such as the inability to use the building. It can be greatly reduced.

  Moreover, the foundation structure of the present invention basically belongs to the category of direct foundation and is advantageous in terms of cost compared to a pile foundation. Because it is a simple structure that only has a water permeable layer and a vertical drain inside, it does not require large-scale construction to prevent the occurrence of liquefaction itself, as in various conventional liquefaction prevention methods. Because it can be easily implemented at low cost, it is a relatively small-scale building with a relatively small scale, such as an existing or newly-built detached house or ancillary equipment that was difficult to prevent sufficient liquefaction in the past. It is the best to apply to.

It is an elevation sectional view showing an embodiment of a foundation structure of the present invention. FIG. FIG. It is a figure for demonstrating the principle of this invention. It is an elevational sectional view showing a conventional general foundation structure (direct foundation). It is a sectional elevation showing a conventional general foundation structure (pile foundation).

1 to 3 show a basic structure according to an embodiment of the present invention.
This is an application example to a building 1 of a middle to low level constructed on a liquefied ground 2 in which a liquefied layer 2b exists on the upper layer of the non-liquefied layer 2a as described above. By providing the water blocking wall 3 temporarily provided around the outer wall so as to reach the non-liquefiable layer 2a, the water blocking wall 3 and the foundation bottom slab 1a which is the bottom surface of the building 1 are provided directly below the building 1. A drainage zone 5 that surrounds the liquefied layer 2b and is isolated from the surroundings is formed, and even if the liquefied layer 2b is liquefied, the lateral flow of the direct foundation board of the building 1 is prevented and the building resulting from it as in the past It is based on preventing 1 subsidence.
The above-mentioned water blocking wall 3 can adopt an appropriate structure. Usually, as shown in FIG. 4 to FIG. 5, a general structure that is provided as a temporary structure during construction and is left as it is is sufficient. However, in the present invention, the water blocking wall 3 is provided so as to reach the non-liquefied layer 2a as described above, and at least has a strength capable of preventing the lateral flow of the direct base plate during liquefaction. Construction is necessary.

  And in the foundation structure of this embodiment, when the liquefaction generate | occur | produced in addition to preventing the lateral flow of the liquefied layer 2b just under the building 1 by the drainage zone 5 formed by the water blocking wall 3 In the drainage zone 5, excess pore water is quickly drained to the ground surface to suppress an excessive increase in pore water pressure, so that the liquefied layer 2 b in the drainage zone 5 collapses or is excessively deformed. The main objective is to prevent the liquefaction damage to the building 1 by preventing the excess pore water from being ejected to the surface of the earth, the accompanying sand sand, and the floating of the building 1 due to the excess pore water pressure.

More specifically, a water permeable layer 6 is provided between the foundation bottom slab 1a of the building 1 and the liquefied layer 2b immediately below it, and the water permeable layer 6 is formed between the underground outer wall of the building 1 and the water blocking wall 3 described above. By providing the vertical drain 7 so as to communicate with the water, excess pore water generated in the drainage zone 5 due to the liquefaction of the liquefied layer 2b can be drained to the surface through the permeable layer 6 and the vertical drain 7 as shown by arrows in the figure. It is configured.
The water permeable layer 6 may be formed by laying a permeable material such as gravel all over or partly at an important point. Further, the vertical drain 7 is continuously formed over the entire circumference between the underground outer wall of the building 1 and the water blocking wall 3 as shown in FIG. 2, or many vertical drains 7 as shown in FIG. However, in any case, the vertical drain 7 is formed by filling a permeable material such as gravel like the permeable layer 6, or an appropriate drain material is installed. By doing so, it may be formed.
Furthermore, it is also preferable to provide another vertical drain 8 in the drainage zone 5 so as to communicate with the water permeable layer 6, as shown in FIGS.

  As described above, a drainage zone 5 for preventing lateral flow is formed by a water blocking wall 3 immediately below the building 1 and excess pore water can be quickly drained from the drainage zone 5 to the ground surface during liquefaction. In addition to being able to prevent lateral flow even when the liquefied layer 2b immediately below the building 1 is liquefied, it is possible to prevent subsidence, thereby controlling the excess pore water pressure in the drainage zone 5. As a result, the settlement of the building 1 can be effectively controlled and suppressed.

  In other words, even if the water blocking wall 3 is merely provided to prevent the lateral flow, the rapid increase in the excess pore water pressure cannot be prevented. However, it is assumed that the building 1 is lifted due to excessive pore water pressure, but the drainage zone 5 is defined by the water blocking wall 3 as described above, and then the permeable layer 6 and the vertical drain 7 are formed from the inside. By promoting drainage, it is possible to control the amount of settlement of the building 1 to be the amount of settlement determined from the volume strain potential of the liquefied layer 2b and to suppress it to the same extent as the amount of settlement of the surrounding ground. Therefore, at least, it is possible to effectively prevent the occurrence of a large unevenness that impedes the service between them.

The basic principle of the present invention will be described in detail with reference to FIG.
In the design method for normal liquefaction, the state where the excess pore water pressure ratio of the ground has reached 1 is not considered as the state after this as a completely liquefied state (a state in which it has become liquid). Then, pay attention to the fact that the rigidity is restored by shear deformation after the excess pore water pressure ratio reaches 1 (hereinafter referred to as “post-liquefaction state”), and the post-liquefaction state is continued stably. Therefore, it is based on the design philosophy of maintaining and securing the supporting force for the structure.
That is, as shown in FIG. 4, when the shear force continues to act on the ground that has reached the post-liquefaction state without draining, the reversible due to the directivity is applied to the irreversible plastic volume strain (compression side). Plastic volume strain (expansion side) cannot catch up, and the ground becomes completely liquid. This state is the state that reached the destruction of the ground where the undesired subsidence of the sand and structures.
On the other hand, if the above shear force is applied while draining properly, the irreversible plastic volume strain compression side) and the reversible plastic volume strain (expansion side) are always balanced, and the post-liquefaction state continues stably. In the present invention, by maintaining such a stable post-liquefaction state, the supporting force of the structure is secured, and liquefaction damage such as settlement or inclination of the structure is reduced.

  By the way, in the present invention, in order to allow the amount of subsidence to be appropriately controlled while allowing the subsidence of the building 1 as described above, excess pore water is appropriately removed from the drainage zone 5 at and after the occurrence of liquefaction. Since it is necessary to be able to drain water, and in particular, it is necessary to appropriately install the vertical drain 7, a specific design method for that purpose will be described below.

"Estimation of wastewater due to building settlement"
The vertical drain 7 is designed to have the ability to drain pore water generated during liquefaction and ground subsidence after liquefaction to the ground surface.
For that purpose, the required amount of drainage ΔV _w based on the ground subsidence amount D _s after liquefaction is calculated by the equation (1), and the necessary flow rate q _w1 is calculated by the equation (2) based on that.
The ground subsidence amount D _s may be calculated by a known calculation method disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-9558. Further, the settlement time Δt may be about one day.

“Possible drainage of vertical drain”
On the other hand, the possible drainage amount q _w2 from the vertical drain 7 is calculated by the equation (3).
Here, the hydrodynamic gradient iv is calculated by the equation (4) from the lower end depth H of the vertical drain 7 and the heads h _w1 and h _w2 acting on the lower end and the upper end of the vertical drain 7, respectively.

And the possible drainage amount q _w2 by the vertical drain 7 determined above is

K ₂ and A _wv may be determined so as to satisfy the above.

  As described above, according to the basic structure of the present invention, it is impossible to completely prevent the liquefied ground 2 from being liquefied or the ground subsidence from occurring, but the building 1 is allowed to sink. However, the amount of subsidence can be controlled and suppressed, so that it is possible to effectively prevent the entire building 1 from subsidizing significantly or causing significant uneven subsidence and large unevenness with the surrounding ground. Therefore, it is possible to sufficiently prevent or significantly reduce the large liquefaction damage that the building 1 cannot be used.

Moreover, although the foundation structure of the present invention needs to be provided with the water blocking wall 3 around the underground outer wall, it basically belongs directly to the category of the foundation, and the water blocking wall 3 is also used for general temporary use. Since it is sufficient to install what is to be installed so as to reach the non-liquefied layer 2a, it is advantageous in terms of cost as compared with the case of using a pile foundation.
Of course, since the water-permeable layer 6 and the vertical drain 7 are provided inside the water blocking wall 3 in addition to the water blocking wall 3 and another vertical drain 8 is further provided as necessary, various conventional liquids can be used. Unlike the liquefaction prevention method, it does not require large-scale construction to prevent the occurrence of liquefaction itself, and therefore it can be carried out simply and at low cost. It is ideal for application to relatively small and medium-sized buildings such as existing or newly built detached houses and incidental facilities that were difficult.

In addition, in the liquefaction countermeasure construction methods shown in Patent Documents 1 and 2, it seems that drainage of excess pore water from the direct base board is possible, but these are points that prevent the occurrence of liquefaction itself. In addition to being fundamentally different from the present invention, Patent Document 1 collects excess interstitial water in a water storage tank provided around the structure, and Patent Document 2 directly covers the ground surface from a horizontal drain. Since these are only drained, they do not have elements corresponding to the water blocking wall 3 and the vertical drain 7 in the present invention, and are completely different from the basic structure of the present invention.
In addition, Patent Documents 3 and 4 disclose the vertical drain, but none disclose the water blocking wall 3, and Patent Document 3 does not relate to the foundation structure of the building. The structure is completely different from the present invention in that there are no elements corresponding to the water blocking wall 3 in the present invention and the vertical drain 7 is provided so as to penetrate the mat slab, and these are also different from the basic structure of the present invention. Needless to say, it is a completely different technology.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and appropriate design changes and applications can be made without departing from the gist of the present invention.
For example, although the said embodiment is an example at the time of applying to the foundation of the building 1 of a middle-low-rise grade, this invention is widely applied as a foundation structure of the various structures constructed | assembled not only on a middle-low-rise building but on a liquefied ground. Of course it is possible.
The geology of the liquefied ground 2 is also the structure of the water blocking wall 3 and its construction method, the material of the water permeable layer 6 and the vertical drain 7, the specifications such as the water permeability coefficient, the formation pattern, the construction method, etc. In consideration of various conditions such as the actual situation, the structure of the structure to be built, its own weight and form, etc., it is sufficient and efficient for the desired lateral flow prevention performance and excess pore water for the direct foundation board of the structure What is necessary is just to design optimally so that drainage performance is obtained.

1 Building (structure)
DESCRIPTION OF SYMBOLS 1a Foundation bottom plate 2 Liquefaction ground 2a Non-liquefaction layer 2b Liquefaction layer 3 Water blocking wall 4 Support pile 5 Drain zone 6 Permeable layer 7 Vertical drain 8 Vertical drain

Claims (2)

A basic structure applied to a structure constructed on a liquefied ground where a liquefied layer is present on the non-liquefied layer,
Providing a water blocking wall that reaches the non-liquefied layer around the underground outer wall of the structure, and surrounding the liquefied layer immediately below the structure with the water blocking wall and the foundation bottom plate of the structure Forming a more isolated drainage zone,
A water permeable layer is provided between the foundation bottom plate of the structure and the liquefied layer immediately below the bottom slab, and a vertical drain leading to the water permeable layer is provided between the underground outer wall of the structure and the water blocking wall,
Ri Na drained configured to be able to excess pore water generated in the drainage zone by liquefaction of the liquid layer from the drainage zone to the surface through the water permeable layer and the vertical drain,
Permeability of vertical drain _{k 2,} the value of the cross-sectional area _{A wV} vertical drains, requires wastewater by ground subsidence amount _{D s} after liquefaction [Delta] V _w, the required flow rate _{q w1,} subsidence time Delta] t, the vertical drain bottom depth H, If possible drainage q _w2 by vertical drain, it is determined to satisfy the following formula:

The basic structure of the structure. A basic structure of the structure according to claim 1,
A basic structure of a structure, wherein a vertical drain communicating with the water permeable layer is installed in the drainage zone.

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