JP6327440B2 - Underground seismic isolation wall structure and underground seismic isolation wall material design method - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underground seismic isolation wall structure that constitutes a ground displacement absorption isolation structure for reducing stress on underground structures such as open tunnels during an earthquake, and a method for designing an underground isolation wall material It is.

  2. Description of the Related Art Conventionally, a ground displacement absorbing base isolation structure is known for reducing stress on underground structures such as open tunnels during an earthquake (see, for example, Patent Document 1 or 2). FIG. 4 is a schematic perspective view of the ground displacement absorbing base isolation structure of Patent Document 1. As shown in FIG. 4, when the underground seismic isolation wall 3 is provided along the underground structure 2 embedded in the surrounding ground 1, it is sufficient for the earth pressure acting on the underground seismic isolation wall 3. While it is a material that can withstand long-term stability, it is desirable that the material has low rigidity in order to exhibit the seismic isolation effect. Is required.

  The above-mentioned Patent Document 1 has been made in view of the above-described problems, and can secure the long-term stability of the underground seismic isolation wall and reduce stress on underground structures such as an open tunnel during an earthquake. A ground displacement absorbing seismic isolation structure that can be used is realized by the following measures (1) to (4).

(1) As shown in FIG. 4, a continuous wall-shaped seismic isolation layer 3 (underground wall or underground seismic isolation wall) made of a water-absorbing and swelling clay-based material between the surrounding ground 1 and the structure 2 Is installed.
(2) As a clay-based material constituting the underground wall, a mixture of bentonite and water, or a mixture of bentonite and aggregate (soil material such as gravel or artificial material that is difficult to change for a long time such as glass beads) and water is used. .
(3) The region filled with a material composed of a mixture of bentonite and water in the clay-based material constituting the underground wall is characterized by having a bentonite dry density value in a range of 300 to 1200 kg / m ^3. .
(4) In a material composed of a mixture of bentonite, aggregate and water, which is a clay-based material constituting the underground wall, an area filled with bentonite and water (bentonite and water filling the area excluding the aggregate area) In the range of 300 to 1200 kg / m ³ in terms of bentonite dry density.

  On the other hand, the underground wall construction method disclosed in Patent Document 2 is not limited to a material containing 100% bentonite, but a bentonite material adjusted to have a predetermined bentonite effective dry density, or a mixture of bentonite and aggregate. A process of filling a bag with a material filled with a bag. However, the specific method of how to design the side soil pressure received from the surrounding ground was not clear.

  By the way, said patent document 1 uses the water-absorbing expansive clay (for example, bentonite) which exhibits the swelling pressure (water absorption expansion pressure) which can oppose earth pressure, although it is a continuous underground wall, There was a feature in maintaining the structural form. On the other hand, in order to improve the seismic isolation effect, it is desirable to use a material having a smaller shear rigidity (in other characteristics, a low transverse wave velocity Vs) as the underground wall material.

For example, according to Non-Patent Document 1, as shown in FIG. 5, the smaller the ratio (Vs ratio) of the shear wave velocity Vs of the underground wall (base isolation wall) material to the shear wave velocity of the surrounding ground is, Since the reduction rate (after / before) of the shear force of (structure) is reduced, the seismic isolation effect is large. However, according to a study by one of the inventors of the present invention, for example, when the shear wave velocity Vs of the surrounding ground is 100 m / s, a bentonite material having a shear wave velocity Vs of 20 m / s as shown in the graph of FIG. although it is possible to make, as shown in FIG. 7, therefore the inflation pressure of the bentonite material dry density [rho _d is less than 0.03 MPa, becomes smaller than the lateral pressure applied from the surrounding ground, finding that the resulting It has been. Therefore, the device of the material replaced with the stability maintenance of the underground wall by a water absorption expansion pressure was desired.

JP 2012-031662 A JP 2012-031663 A

Zhang Zhiyue, Fukutake Yasuyoshi et al., “Examination of seismic isolation wall structure of underground structure using bentonite (Part 2: Consideration of seismic isolation effect by FEM analysis)”, Japan Society of Civil Engineers 65th Annual Lecture, Heisei September 22

  The present invention has been made in view of the above, and provides an underground seismic isolation wall structure and a design method for an underground isolation wall material that can sufficiently resist lateral earth pressure received from surrounding ground. With the goal.

  In order to solve the above-mentioned problems and achieve the object, the underground seismic isolation wall structure according to the present invention is a continuous wall-like structure provided between the surrounding ground and the structure and made of a material containing bentonite. The lateral earth pressure caused by the surrounding ground acting on the underground seismic isolation wall is set using a lateral earth pressure coefficient that is a ratio to the vertical earth pressure. It is characterized by being made of the material having a water absorption expansion pressure balanced to the lateral earth pressure or a water absorption expansion pressure equal to or higher than the set side earth pressure.

  Further, in the above-described underground seismic isolation wall structure according to the present invention, in the above-described invention, the material constituting the underground isolation wall is a mixed material composed of bentonite and aggregate, and the weight of the mixed material and The mixed material in which the underwater weight is heavier than the weight of the material containing 100% bentonite and the underwater weight, respectively, and the earth pressure of the underground seismic isolation wall is balanced with the earth pressure of the surrounding ground, or It is characterized by being made of the mixed material in which the earth pressure of the underground seismic isolation wall is 0.5 times or more of the earth pressure of the surrounding ground.

  Further, in the above-described invention, another underground seismic isolation wall structure according to the present invention calculates the wet weight and the underwater weight of the mixed material using a preset bentonite blending ratio, and the underwater weight is calculated in the depth direction. It is obtained from the mixed material designed based on the degree of approach between the vertical earth pressure and the vertical earth pressure of the surrounding ground. And

  In addition, in the above-described invention, another underground seismic isolation wall structure according to the present invention uses an aggregate having a high particle density as the aggregate to be mixed with bentonite, and is made of the material constituting the underground seismic isolation wall. It is characterized by an increased weight in water.

  In addition, in the above-described invention, another underground seismic isolation wall structure according to the present invention is the relationship between the aggregate mixing ratio of the mixed material and the aggregate mixing ratio acquired in advance according to the bentonite density and the shear wave velocity. It is characterized by the aggregate mixing ratio designed based on the above.

  Moreover, the design method of the underground seismic isolation wall material according to the present invention is the material for a continuous wall-shaped underground seismic isolation wall provided between the surrounding ground and the structure and made of a material containing bentonite. The lateral earth pressure due to the surrounding ground acting on the underground seismic isolation wall is determined using a lateral earth pressure coefficient that is a ratio to the vertical earth pressure. The material having a water absorption expansion pressure that is set and balanced to the set side earth pressure or a water absorption expansion pressure that is equal to or higher than the set side earth pressure is used as a material constituting the underground seismic isolation wall. It is characterized by that.

  Further, in the above-described invention, the design method of the underground seismic isolation wall material according to the present invention is the above-described invention, wherein the material constituting the underground seismic isolation wall is a mixed material composed of bentonite and aggregate, and the mixed material The mixed material in which the soil covering pressure of the underground seismic isolation wall is balanced with the soil covering pressure of the surrounding ground. Alternatively, the mixed material in which the earth covering pressure of the underground seismic isolation wall is 0.5 times or more of the earth covering pressure of the surrounding ground is used as a material constituting the underground seismic isolation wall, To do.

  In addition, in the above-described invention, the design method of another underground seismic isolation wall material according to the present invention calculates the wet weight and underwater weight of the mixed material using a preset bentonite blending ratio, and calculates the underwater weight. A value integrated in the depth direction is obtained as the vertical earth pressure of the material constituting the underground seismic isolation wall, and the mixed material is designed based on the degree of approach between the vertical earth pressure and the vertical earth pressure of the surrounding ground. It is characterized by that.

  In addition, in the above-described invention, the design method for another underground seismic isolation wall material according to the present invention uses an aggregate having a high particle density as the aggregate to be mixed with bentonite, and configures the underground isolation wall. It is characterized by increasing the weight of the material to be washed in water.

  Moreover, the design method of the other underground seismic isolation wall material according to the present invention, in the above-described invention, the relationship between the aggregate mixing rate and the shear wave velocity is acquired in advance according to the bentonite density, and the acquired Based on the relationship, the composition ratio of the mixed material is designed.

  According to the underground seismic isolation wall structure according to the present invention, it is a structure of a continuous wall-shaped underground seismic isolation wall that is provided between the surrounding ground and the structure and made of a material containing bentonite, The lateral earth pressure due to the surrounding ground acting on the underground seismic isolation wall is set using a lateral earth pressure coefficient that is a ratio to the vertical earth pressure, and the water absorption expansion pressure balanced with the set side earth pressure Alternatively, since it is made of the material having a water absorption expansion pressure equal to or higher than the set side earth pressure, it is possible to provide an underground seismic isolation wall structure that can sufficiently resist the side earth pressure received from the surrounding ground. There is an effect.

  Further, according to another underground seismic isolation wall structure according to the present invention, the material constituting the underground isolation wall is a mixed material composed of bentonite and aggregate, and the weight of the mixed material and the weight in water are reduced. The mixed material in which the soil covering pressure of the underground seismic isolation wall is balanced with the soil covering pressure of the surrounding ground, or the weight of the material containing 100% bentonite is heavier than its own weight and underwater weight. Since the earth wall pressure of the earthquake wall is 0.5 times or more of the earth ground pressure of the surrounding ground, if the aggregate particle density is larger than the bentonite particle density, the effective bentonite dry density is There is an effect that it can be made smaller. Moreover, the weight of the material in water can be increased, and a material in which the shear wave velocity does not increase so much can be produced.

  Further, according to another underground seismic isolation wall structure according to the present invention, the wet weight and the underwater weight of the mixed material are calculated using a preset bentonite blending ratio, and the underwater weight is integrated in the depth direction. Since the value is obtained as the vertical earth pressure of the material constituting the underground seismic isolation wall, and is composed of the mixed material designed based on the degree of approach between the vertical earth pressure and the vertical earth pressure of the surrounding ground, such a material The underground seismic isolation wall structure constructed by adopting the effect of being able to sufficiently resist the earth pressure when the side pressure coefficient is larger than that received from the surrounding ground.

  Moreover, according to another underground seismic isolation wall structure according to the present invention, an aggregate having a high particle density is used as the aggregate to be mixed with bentonite, and the weight of the material constituting the underground isolation wall is reduced underwater Since it is increased, the effective bentonite dry density can be further reduced. As a result, it is possible to provide an underground seismic isolation wall structure having lower rigidity (softness) than a material containing 100% bentonite.

  Moreover, according to another underground seismic isolation wall structure according to the present invention, the aggregate blending ratio of the mixed material is based on the relationship between the aggregate blending ratio and the shear wave velocity acquired in advance according to the bentonite density. Because it is the designed aggregate composition ratio, it is possible to provide an underground seismic isolation wall structure with improved reliability against the seismic isolation effect of the underground seismic isolation wall and the effect of improving the stability at all times. Play.

  Further, according to the design method of the underground seismic isolation wall material according to the present invention, the continuous wall-shaped underground seismic isolation wall provided between the surrounding ground and the structure and made of a material containing bentonite. A method for designing an underground seismic isolation wall material for designing the material, the lateral earth pressure due to the surrounding ground acting on the underground isolation wall being a lateral earth pressure coefficient that is a ratio to a vertical earth pressure. The material having a water absorption expansion pressure that is set using and balanced to the set side earth pressure, or has a water absorption expansion pressure that is equal to or higher than the set side earth pressure, is used as a material constituting the underground seismic isolation wall. Since it is used, it is possible to provide an underground seismic isolation wall that can sufficiently resist the lateral earth pressure received from the surrounding ground.

  Further, according to another underground seismic isolation wall material design method according to the present invention, the material constituting the underground isolation wall is a mixed material composed of bentonite and aggregate, and the weight of the mixed material and The mixed material in which the underwater weight is heavier than the weight of the material containing 100% bentonite and the underwater weight, respectively, and the earth pressure of the underground seismic isolation wall is balanced with the earth pressure of the surrounding ground, or Since the mixed material in which the earth pressure of the underground seismic isolation wall is 0.5 times or more than the earth pressure of the surrounding ground is used as the material constituting the underground earthquake isolation wall, the particle density of the aggregate Is larger than the particle density of bentonite, there is an effect that the effective bentonite dry density can be further reduced. Moreover, the weight of the material in water can be increased, and a material in which the shear wave velocity does not increase so much can be produced.

  Further, according to the design method for other underground seismic isolation wall material according to the present invention, the wet weight and the underwater weight of the mixed material are calculated using a preset bentonite blending ratio, and the underwater weight is calculated in the depth direction. Is obtained as the vertical earth pressure of the material constituting the underground seismic isolation wall, and the mixed material is designed based on the degree of approach between the vertical earth pressure and the vertical earth pressure of the surrounding ground. The underground seismic isolation wall structure constructed by adopting such a material has the effect that it can sufficiently resist the earth pressure when the lateral pressure coefficient is larger than that received from the surrounding ground.

  Moreover, according to the design method of the other underground seismic isolation wall material according to the present invention, an aggregate having a high particle density is used as the aggregate to be mixed with bentonite, and the material constituting the underground isolation wall is used. Since the weight in water is increased, the effective bentonite dry density can be further reduced. As a result, it is possible to provide an underground seismic isolation wall having lower rigidity (softness) than a material containing 100% bentonite.

  Moreover, according to the design method of the other underground seismic isolation wall material according to the present invention, the relationship between the aggregate mixing ratio and the shear wave velocity is acquired in advance according to the bentonite density, and based on the acquired relationship. In addition, since the composition ratio of the aggregate of the mixed material is designed, it is possible to further improve the reliability of the design method for improving the stability at all times while maintaining the seismic isolation effect of the underground seismic isolation wall. .

FIG. 1-1 is a diagram conceptually showing the distribution of lateral earth pressure in the surrounding ground. 1-2 is a figure which shows the relationship between an effective bentonite dry density and a water absorption expansion pressure. FIG. 2-1 is a cross-sectional view showing an image seen with a microscope when the aggregate is homogeneously mixed with bentonite and wetted (saturated) with water. FIG. 2-2 is a diagram illustrating the relationship between bentonite dry density and shear wave velocity. FIG. 2-3 is a diagram showing the relationship between the aggregate blending ratio and the shear wave velocity. FIG. 3A is a conceptual diagram schematically showing the weight ratio and volume ratio of the mixed material of bentonite and aggregate in FIG. 2-1. FIG. 3-2 is a graph plotting an example in which three types of density values are designed according to depth. FIG. 3-3 is a graph plotting the relationship between depth and earth pressure. FIG. 4 is a schematic perspective view showing a conventional ground displacement absorbing base isolation structure and an underground base isolation wall structure constituting the same. FIG. 5 is a diagram showing the relationship between the ratio of the shear wave velocity of the underground wall material to the shear wave velocity of the surrounding ground and the seismic isolation effect. FIG. 6 is a diagram showing the relationship between bentonite dry density and shear wave velocity. FIG. 7 is a diagram showing the relationship between bentonite dry density and expansion pressure (swelling pressure).

  Hereinafter, embodiments of the underground seismic isolation wall structure and the design method thereof according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Example 1
First, Example 1 of the present invention will be described.
The design method of the underground seismic isolation wall material according to the first embodiment of the present invention is the above-described continuous wall-shaped underground seismic isolation wall provided between the surrounding ground and the structure and made of a material containing bentonite. A material design method for an underground seismic isolation wall material, wherein the lateral earth pressure due to the surrounding ground acting on the underground isolation wall is determined using a lateral earth pressure coefficient that is a ratio to a vertical earth pressure. The material having a water absorption expansion pressure balanced to the set side earth pressure or a water absorption expansion pressure equal to or higher than the set side earth pressure is used as a material constituting the underground seismic isolation wall. It is characterized by doing. Moreover, the underground seismic isolation wall structure of Example 1 of this invention is constructed | assembled by this method.

  FIG. 1-1 is a diagram conceptually showing the distribution of lateral earth pressure in the surrounding ground. Table 1 is a table in which the lateral earth pressure from the surrounding ground assumed in the present example is determined for each depth from the wet density and the lateral pressure coefficient K of the surrounding ground using the lateral pressure coefficient K as a parameter. The calculation conditions at this time are as follows.

(1) The material of the underground wall was 100% bentonite.
(2) The wet density (saturated state) of the surrounding ground was 2.2 g / cm ² .
(3) The lateral pressure coefficient K was assumed to be 0.25, 0.50, and 1.0.

  FIG. 1-2 is a graph illustrating the relationship between the effective bentonite dry density (the dry weight of bentonite existing in a space excluding the space occupied by aggregates in a unit volume of material) and the water absorption expansion pressure. This figure is used to obtain a regression equation. In addition, about the specific method regarding this, it can carry out using the method as described in Japanese Patent Application No. 2012-233303 for which it applied by this applicant.

For example, the water absorption expansion pressure P _swell (MPa) can be calculated by the following equation (1).

By modifying the above relational expression (1), the effective bentonite dry density ρ _dB (g / cm ³ ) can be calculated from the value of the expansion pressure by the following expression (2).

  Table 2 shows an example of the results obtained by using the above equation (2) to determine the effective bentonite dry density of the underground wall material that balances the lateral earth pressure acting from the surrounding ground.

Thus, the material design of the underground seismic isolation wall can be specifically implemented by using the relational expression between the value of the expansion pressure and the effective bentonite dry density ρ _dB (g / cm ³ ).

(Example 2)
Next, a second embodiment of the present invention will be described.
In the design method of the underground seismic isolation wall material according to the second embodiment of the present invention, the material constituting the underground isolation wall is a mixed material composed of bentonite and aggregate, and the weight of the mixed material and the weight in water are determined. The mixed material in which the soil covering pressure of the underground seismic isolation wall is balanced with the soil covering pressure of the surrounding ground, or the weight of the material containing 100% bentonite is heavier than its own weight and underwater weight. The mixed material in which the earth covering pressure of the seismic wall is 0.5 times or more the earth covering pressure of the surrounding ground is used as a material constituting the underground seismic isolation wall. Moreover, the underground seismic isolation wall structure of Example 2 of this invention is constructed | assembled by this method.

  FIG. 2-1 is a cross-sectional view showing an image seen with a microscope when the aggregate is homogeneously mixed with bentonite and wetted (saturated) with water. Assuming that the aggregate is composed of spheres having the same diameter, theoretically, the volume percentage when the hexagonal closest packing is 74%. Therefore, if the aggregate is mixed so that the volume percentage is 60% or less, the aggregate particles constituting the aggregate are not in contact with each other as shown in FIG. The bentonite gel is formed by absorbing water between the aggregate particles and the aggregate particles. Since the bentonite blending ratio is calculated by weight ratio, this condition is satisfied if the bentonite blending ratio is 40% or more if the particle densities of the bentonite particles and the aggregate particles are equal. If the aggregate particle density is larger than the bentonite particle density, more bentonite can be blended.

  If the aggregate particles are in contact with each other, the shear wave propagates through the aggregate particles. As a result, the shear wave velocity of the mixed material is larger than that of the material containing 100% bentonite. However, if the aggregate particles are not in contact with each other, the shear wave velocity travels through the 100% bentonite gel region. As a result, it is possible to make a material in which the weight of the material in water can be increased and the shear wave velocity is not so great (the density wave velocity is easily affected by the propagation velocity of the aggregate, but is less susceptible to the shear wave velocity). .

(Modification of Example 2)
Next, a modification of the second embodiment of the present invention will be described.
As described above, if the aggregate mixing ratio (= 1-bentonite mixing ratio) in the mixed material of bentonite and aggregate is 60% or less, it is exempted according to the density of the bentonite gel filling between the aggregate particles. The seismic effect can be maintained, and the density of the mixture of aggregate and bentonite increases by mixing the aggregate, and the stability at normal time increases by the self-weight effect.

  In this case, it is possible to grasp in advance at the design stage how much aggregate mixing ratio can actually maintain the seismic isolation effect, and the difference in effect due to the density of the bentonite portion filling the aggregate particles. Thus, it is desirable to increase the reliability of the design.

By the way, the seismic isolation performance of the underground seismic isolation wall depends on the shear wave velocity, and the lower the shear wave velocity, the better the seismic isolation performance. FIG. 2-2 shows the relationship between the shear wave velocity and the bentonite dry density when the underground seismic isolation wall is constructed of bentonite alone. As an example of a material having high seismic isolation performance, wet bentonite materials (saturated with water) whose values converted to dry density as shown in FIG. 2-2 are 0.4 Mg / m ³ and 0.6 Mg / m ³ Fig. 2-3 shows the result of measuring the shear wave velocity of the mixed material of aggregate and bentonite when making a mixed material in which the aggregate is mixed with the material) and increasing the aggregate blending ratio. The aggregate blending ratio is the ratio of the aggregate weight to the total weight (mixed material of aggregate and bentonite).

As shown in FIG. 2-3, in the case of 0.4 Mg / m ³ where the density of the bentonite portion is lower, the shear wave velocity does not change up to about 60% of the aggregate blending ratio, and when it exceeds 60% However, the rate of increase in shear wave velocity is slight.

On the other hand, when the density of the bentonite portion is 0.6 Mg / m ³ , the shear wave velocity does not change until the aggregate content rate is about 40%, but when it exceeds that, the shear wave velocity increases greatly. I understand that

  From this, when the underground seismic isolation wall is constructed of a mixed material in which aggregate is mixed with bentonite, the density of the bentonite portion can be designed to be 60% or less when the density of the bentonite portion is small. Since the range of the aggregate blending ratio that can maintain the seismic isolation effect becomes narrower as the density increases, it is necessary to design by obtaining experimental data in advance.

  Then, the design method of the underground seismic isolation wall material of the modification of Example 2 of this invention was made | formed in view of the above, Comprising: According to the bentonite density, the relationship between an aggregate compounding rate and a shear wave velocity is made | formed. The aggregate mixing ratio of the mixed material is designed based on the acquired relationship. Moreover, the underground seismic isolation wall structure of the modification of Example 2 of this invention is constructed | assembled by this method.

For example, when designing based on the relationship shown in FIG. 2-3, the aggregate content ratio of the mixed material may be designed to be 60% or less under the condition of 0.4 Mg / m ³ where the density of the bentonite portion is lower. it can. On the other hand, under the condition of 0.6 Mg / m ³ where the density of the bentonite portion is higher, it is desirable to design the aggregate content ratio of the mixed material to 40% or less.

  As described above, according to the modification of the second embodiment, by obtaining the shear wave velocity by changing the aggregate mixing rate and the bentonite density, the seismic isolation effect of the underground seismic isolation wall is constantly maintained. The reliability of the design method that increases the stability of the can be further increased.

(Example 3)
Next, Embodiment 3 of the present invention will be described.
In the design method of the underground seismic isolation wall material according to Example 3 of the present invention, the wet weight and the underwater weight of the mixed material were calculated using a preset bentonite mixture ratio, and the underwater weight was integrated in the depth direction. A value is obtained as a vertical earth pressure of a material constituting the underground seismic isolation wall, and the mixed material is designed based on an approach degree between the vertical earth pressure and the vertical earth pressure of the surrounding ground. It is. Moreover, the underground seismic isolation wall structure of Example 3 of this invention is constructed | assembled by this method.

  Tables 3-1 and 3-2 show the effective bentonite dry density having an expansion pressure corresponding to the lateral earth pressure coefficient K by the method of this example, and then the bentonite compounding ratio B / (B + S) as a parameter. The results of calculating the dry density, wet (saturated) density of the underground wall material, unit volume weight in water (underwater weight), and effective vertical earth pressure of the underground wall (effective earth pressure on the underground wall) were shown. Is. Here, B is the weight of bentonite per unit volume, and S is the weight of aggregate per unit volume.

As calculation conditions at this time, the following characteristic values are used.
(1) The wet density (ground density) of the surrounding ground is assumed to be 2.2 (g / cm ³ ).
(2) The lateral earth pressure balanced with the expansion pressure of bentonite is assumed to be earth pressure coefficient K = 0.5.

Table 3-1 shows the calculation results when the bentonite content is 0.7.

Table 3-2 shows the calculation results when the bentonite content is 0.6.

  In each of the above tables, the effective vertical earth pressure value of the surrounding ground is illustrated, but when the underground wall material is an aggregate mixed material, as shown below, it is balanced with the expansion pressure of bentonite. It is a material that can cope with the following soil pressure greater than the lateral soil pressure coefficient of 0.5.

Table 3-1 shows the case where the bentonite compounding ratio is 0.7, which corresponds to an earth pressure of 0.214 MPa equivalent to a ground earth pressure (vertical earth pressure) x 0.89 times at a depth of 20 m. I understand that.
Table 3-2 shows the case where the bentonite compounding ratio is 0.6, which corresponds to an earth pressure of 0.219 MPa equivalent to a ground covering earth pressure (vertical earth pressure) of 0.91 times at a depth of 20 m. I understand that.

  As shown in the above calculation example, by devising the aggregate composition, it is possible to increase the unit volume weight of the underground wall material in water, and as a result, against the deformation action due to earth pressure from the surrounding ground, The stability of the underground wall can be secured more advantageously.

  Fig. 3-1 to Fig. 3-3 show examples of soil material design for underground seismic isolation walls. In this design example, the bentonite blending ratio is set to 0.6, and the blending / density is designed so that the water absorption expansion pressure due to bentonite corresponds to a lateral pressure of 0.5 times the soil covering pressure of the surrounding ground.

  FIG. 3A schematically shows the weight ratio and volume ratio of the bentonite / aggregate mixed material shown in FIG. 2-1. According to FIG. 3-1, the formula for the blending and density of the mixed material of bentonite and aggregate is as follows.

Aggregate volume V _S
Volume of bentonite V _B
Volume of water V _W
Weight M _S of the aggregate
Weight M _B of bentonite
Water weight _MW
Since it is a unit volume, V = V _S + V _B + V _W = 1
Drying density of mixed material ρ _d = (M _S + M _B ) / V
Wet density of mixed material ρ _sat
Effective bentonite dry density ρ _dB
Aggregate particle density G _S
Particles of bentonite density ^{_{G B = 2.80 (g / cm}} 3)
Density of water ρ _W = M _W / V _W = 1 (g / cm ³ )
Bentonite blending ratio _{a = M B / (M B} + M S)
Then,
M _S = G _S × V _S , M _B = G _B × V _B ,
M _B = a / (1-a) × M _S , M _S = (1-a) / a × M _B
M _B = ρ _dB / [1+ (1−a) / a × ρ _dB / G _S ]
M _S = (1−a) / a × M _B
ρ _d = (M _S + M _B ) / V
= _M S + _{M B}
= (Ρ _dB × G _S ) / [a × G _S + (1−a) × ρ _dB ]
_{ρ sat = ρ d + 1-} ρ dB / [a + (1-a) × ρ dB / G S] × [(1-a) / G S -a / G B]

FIG. 3-2 is a graph plotting an example in which the following three types of density values are designed according to the depth.
(1) Effective bentonite dry density value (corresponding to dry density when designed with 100% bentonite blend) (symbol in the figure: ρ _dB )
(2) Dry density when the effective bentonite dry density is the same when mixed at a blending rate of 60% (the bentonite particle density is 2.80 (g / cm ³ ), and the aggregate particle density is 2.60. (Value in the case of using an aggregate of (g / cm ³ )) (symbol in the figure: ρ _d )
(3) Wet density when a mixed material with a blending ratio of 60% is saturated with water (symbol in the figure: ρ _sat )

FIG. 3-3 is a graph plotting the relationship between depth and earth pressure. The earth pressure showed the following four values.
(1) Side earth pressure acting from the ground (in the case of a side pressure coefficient of 0.5) (symbol in the figure: K = 0.5)
(2) Side earth pressure acting from the ground (when the side pressure coefficient is 1.0) (symbol in the figure: K = 1.0)
(3) Water absorption expansion pressure when the underground wall material is mixed at a blending rate of 60% (symbol in the figure: P _swell ). Since examples designed as _{P swell} in Figure 3-3 matches the lateral soil pressure when the lateral pressure coefficient of 0.5, the expansion and the plot of the lateral soil pressure K = 0.5 pressure _{P swell} plots Are overlapping.
(4) Effective earth cover pressure (vertical earth pressure) of underground wall material based on unit volume weight in water when mixed material is 60% (symbol in the figure: (ρ _sat −ρ _w ) · h)

The following can be seen from the plots of FIGS. 3-2 and 3-3.
(1) As shown in FIG. 3-3, the water absorption expansion pressure of the underground wall material is larger than the lateral pressure coefficient 0.5 and smaller than the lateral pressure coefficient 1.0 in the lateral earth pressure condition received from the surrounding ground. .
(2) On the other hand, when the effective earth pressure of the soil material constituting the underground wall is equivalent to a lateral pressure coefficient of 0.89 in a lateral earth pressure condition received from the ground at a depth of 20 m, the lateral pressure coefficient is 1.0. Almost equal to the lateral earth pressure.
(3) That is, the underground seismic isolation wall that is designed in this way is based on the effective earth pressure of the underground wall soil material rather than the pressure resistance performance due to the pressure based on the water absorption expansion pressure against the side pressure received from the surrounding ground. Excellent pressure resistance.

  The underground seismic isolation wall structure constructed by using such materials is effective because it can sufficiently resist the earth pressure when the lateral pressure coefficient is larger than that received from the surrounding ground. In addition, a method for designing the material constituting the underground seismic isolation wall structure as described above is also effective.

Example 4
Next, a fourth embodiment of the present invention will be described.
In the design method of the underground seismic isolation wall material according to the fourth embodiment of the present invention, an aggregate having a large particle density is used as the aggregate to be mixed with bentonite, and the underwater weight of the material constituting the underground seismic isolation wall is determined. It is characterized by being enlarged. Moreover, the underground seismic isolation wall structure of Example 4 of this invention is constructed | assembled by this method.

  The earth pressure balance shown in FIG. 3-2 can be designed to have a smaller effective bentonite dry density by employing an aggregate having a larger particle density and a heavier aggregate. As a result, an underground wall having lower rigidity (softness) than a material containing 100% bentonite can be constructed.

For example, assume the following materials as aggregates.
(A) Chromite sand: density 2.81 (g / cm ³ ). This is a crushed iron ore and is commercially available as a casting mold material.
(B) Iron particles: density 7.874 (g / cm ³ )
(C) In addition, the density of magnetite is 5.2 (g / cm ³ ) and the density of copper metal is 8.96 (g / cm ³ ). Be a candidate.

Table 4-1 shows the blending / density design results when 2.81 (g / cm ³ ) of chromite sand is used as the aggregate. When the bentonite compounding ratio is 0.7, it has a soil covering pressure of 0.224 MPa that can counter the earth pressure equivalent to 0.933 times the earth covering earth pressure (vertical earth pressure) at a depth of 20 m, This is comparable to the bentonite content of 0.6 when the aggregate particle density is 2.60 (g / cm ³ ). Moreover, the effective bentonite dry density can be designed to be smaller. That is, the underground wall can be made of a softer material, and can sufficiently counter the ground soil pressure.

Table 4-2 shows the blending / density design results when iron particles 7.874 (g / cm ³ ) are used for the aggregate. When the bentonite compounding ratio is 0.8, it has a soil covering pressure of 0.229 MPa that can counter the earth pressure equivalent to 0.95 times the earth covering earth pressure (vertical earth pressure) at a depth of 20 m, And the effective bentonite dry density can be designed smaller. That is, it is possible to construct an underground wall that employs a softer material and can resist the ground pressure.

  As described above, according to the underground seismic isolation wall structure according to the present invention, a continuous wall-shaped underground seismic isolation wall provided between the surrounding ground and the structure and made of a material containing bentonite. The lateral earth pressure due to the surrounding ground acting on the underground seismic isolation wall is set using a lateral earth pressure coefficient that is a ratio to the vertical earth pressure, and the set side earth pressure is set. The seismic isolation wall structure that can sufficiently resist the lateral soil pressure received from the surrounding ground Can be provided.

  Further, according to another underground seismic isolation wall structure according to the present invention, the material constituting the underground isolation wall is a mixed material composed of bentonite and aggregate, and the weight of the mixed material and the weight in water are reduced. The mixed material in which the soil covering pressure of the underground seismic isolation wall is balanced with the soil covering pressure of the surrounding ground, or the weight of the material containing 100% bentonite is heavier than its own weight and underwater weight. Since the earth wall pressure of the earthquake wall is 0.5 times or more of the earth ground pressure of the surrounding ground, if the aggregate particle density is larger than the bentonite particle density, the effective bentonite dry density is It can be made smaller. Moreover, the weight of the material in water can be increased, and a material in which the shear wave velocity does not increase so much can be produced.

  Further, according to another underground seismic isolation wall structure according to the present invention, the wet weight and the underwater weight of the mixed material are calculated using a preset bentonite blending ratio, and the underwater weight is integrated in the depth direction. Since the value is obtained as the vertical earth pressure of the material constituting the underground seismic isolation wall, and is composed of the mixed material designed based on the degree of approach between the vertical earth pressure and the vertical earth pressure of the surrounding ground, such a material The seismic isolation wall structure constructed by adopting can sufficiently resist the earth pressure when the lateral pressure coefficient is larger than that received from the surrounding ground.

  Moreover, according to another underground seismic isolation wall structure according to the present invention, an aggregate having a high particle density is used as the aggregate to be mixed with bentonite, and the underwater weight of the material constituting the underground seismic isolation wall is reduced. Since it is increased, the effective bentonite dry density can be further reduced. As a result, it is possible to provide an underground seismic isolation wall structure having lower rigidity (softness) than a material containing 100% bentonite.

  Moreover, according to another underground seismic isolation wall structure according to the present invention, the aggregate blending ratio of the mixed material is based on the relationship between the aggregate blending ratio and the shear wave velocity acquired in advance according to the bentonite density. With the designed aggregate composition ratio, it is possible to provide an underground seismic isolation wall structure with higher reliability for the seismic isolation effect of the underground isolation wall and the effect of improving the stability at all times.

  Further, according to the design method of the underground seismic isolation wall material according to the present invention, the continuous wall-shaped underground seismic isolation wall provided between the surrounding ground and the structure and made of a material containing bentonite. A method for designing an underground seismic isolation wall material for designing the material, the lateral earth pressure due to the surrounding ground acting on the underground isolation wall being a lateral earth pressure coefficient that is a ratio to a vertical earth pressure. The material having a water absorption expansion pressure that is set using and balanced to the set side earth pressure, or has a water absorption expansion pressure that is equal to or higher than the set side earth pressure, is used as a material constituting the underground seismic isolation wall. Because it is used, it is possible to provide an underground seismic isolation wall that can sufficiently resist the lateral earth pressure received from the surrounding ground.

  Further, according to another underground seismic isolation wall material design method according to the present invention, the material constituting the underground isolation wall is a mixed material composed of bentonite and aggregate, and the weight of the mixed material and The mixed material in which the underwater weight is heavier than the weight of the material containing 100% bentonite and the underwater weight, respectively, and the earth pressure of the underground seismic isolation wall is balanced with the earth pressure of the surrounding ground, or Since the mixed material in which the earth pressure of the underground seismic isolation wall is 0.5 times or more than the earth pressure of the surrounding ground is used as the material constituting the underground earthquake isolation wall, the particle density of the aggregate If it is larger than the particle density of bentonite, the effective bentonite dry density can be made smaller. Moreover, the weight of the material in water can be increased, and a material in which the shear wave velocity does not increase so much can be produced.

  Further, according to the design method for other underground seismic isolation wall material according to the present invention, the wet weight and the underwater weight of the mixed material are calculated using a preset bentonite blending ratio, and the underwater weight is calculated in the depth direction. Is obtained as the vertical earth pressure of the material constituting the underground seismic isolation wall, and the mixed material is designed based on the degree of approach between the vertical earth pressure and the vertical earth pressure of the surrounding ground. The underground seismic isolation wall structure constructed by adopting such materials can sufficiently counter the earth pressure when the lateral pressure coefficient is larger than that received from the surrounding ground.

  Moreover, according to the design method of the other underground seismic isolation wall material according to the present invention, an aggregate having a high particle density is used as the aggregate to be mixed with bentonite, and the material constituting the underground isolation wall is used. Since the weight in water is increased, the effective bentonite dry density can be further reduced. As a result, an underground seismic isolation wall having lower rigidity (softness) than a material containing 100% bentonite can be provided.

  Moreover, according to the design method of the other underground seismic isolation wall material according to the present invention, the relationship between the aggregate mixing ratio and the shear wave velocity is acquired in advance according to the bentonite density, and based on the acquired relationship. In addition, since the mixture ratio of the aggregate of the mixed material is designed, the reliability of the design method that increases the stability at all times while maintaining the seismic isolation effect of the underground seismic isolation wall can be further increased.

  As described above, the design method of the underground seismic isolation wall structure and the underground isolation wall material according to the present invention is a ground displacement absorption immunity for reducing the stress on underground structures such as open tunnels during an earthquake. It is useful for underground seismic isolation wall structures that constitute seismic structures, and is particularly suitable for designing and constructing underground isolation walls that can sufficiently resist lateral earth pressure received from the surrounding ground.

1 Surrounding ground 2 Underground structure 3 Underground seismic isolation wall (underground wall)

Claims (8)

It is a structure of a continuous wall-shaped underground seismic isolation wall that is provided between the surrounding ground and the structure and is made of a material containing bentonite,
The lateral earth pressure due to the surrounding ground acting on the underground seismic isolation wall is set using a lateral earth pressure coefficient that is a ratio to the vertical earth pressure, and the water absorption expansion pressure balanced with the set side earth pressure or, Ri Do from the material having a hygroscopic expansion pressure on the lateral soil pressure or set,
The material constituting the underground seismic isolation wall is a mixed material composed of bentonite and aggregate, and the weight of the mixed material and the weight in water are made heavier than the weight of the material containing 100% bentonite and the weight in water, respectively. The ground covering pressure of the underground seismic isolation wall is balanced with the soil covering pressure of the surrounding ground, or the soil covering pressure of the underground seismic isolation wall is 0.5% of the soil covering pressure of the surrounding ground. An underground seismic isolation wall structure comprising the mixed material that is twice or more . Calculate the wet weight and underwater weight of the mixed material using a preset bentonite content ratio, and obtain the value obtained by integrating the underwater weight in the depth direction as the vertical earth pressure of the material constituting the underground seismic isolation wall 2. The underground seismic isolation wall structure according to claim 1 , comprising the mixed material designed based on a degree of approach between the vertical earth pressure and the vertical earth pressure of the surrounding ground. The underground license according to claim 1 or 2 , wherein an aggregate having a high particle density is used as the aggregate to be mixed with bentonite, and the weight of the material constituting the underground seismic isolation wall is increased. Seismic wall structure. Claims 1-3, characterized in that the aggregate mixture ratio of the mixed material was an aggregate mixing ratio designed based on the relationship between the previously obtained aggregate blending ratio in accordance with the bentonite density and shear wave velocity The underground seismic isolation wall structure as described in any one of. A design method for underground seismic isolation wall material, which is provided between a surrounding ground and a structure and designs the material of a continuous wall-shaped underground isolation wall composed of a material containing bentonite,
The lateral earth pressure due to the surrounding ground acting on the underground seismic isolation wall is set using a lateral earth pressure coefficient that is a ratio to the vertical earth pressure, and the water absorption expansion pressure balanced with the set side earth pressure Or, using the material having a water absorption expansion pressure equal to or higher than the set side earth pressure as a material constituting the underground seismic isolation wall ,
The material constituting the underground seismic isolation wall is a mixed material composed of bentonite and aggregate, and the weight of the mixed material and the weight in water are made heavier than the weight of the material containing 100% bentonite and the weight in water, respectively. The ground covering pressure of the underground seismic isolation wall is balanced with the soil covering pressure of the surrounding ground, or the soil covering pressure of the underground seismic isolation wall is 0.5% of the soil covering pressure of the surrounding ground. A design method for underground seismic isolation wall material, wherein the mixed material that is twice or more is used as a material constituting the underground isolation wall. Calculate the wet weight and underwater weight of the mixed material using a preset bentonite content ratio, and obtain the value obtained by integrating the underwater weight in the depth direction as the vertical earth pressure of the material constituting the underground seismic isolation wall 6. The underground seismic isolation wall material design method according to claim 5 , wherein the mixed material is designed based on an approach degree between the vertical earth pressure and the vertical earth pressure of the surrounding ground. The underground license according to claim 5 or 6 , wherein an aggregate having a high particle density is used as the aggregate to be mixed with bentonite, and the weight of the material constituting the underground seismic isolation wall is increased. How to design the wall material. The relationship between the aggregate mixing ratio and shear wave velocity previously acquired in advance according to the bentonite density, based on the acquired relationship, claim 5, characterized in that designing the aggregate mixing ratio of the mixed material method of designing underground MenShinkabe material according to any one of to 7.

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