JP5532325B2 - Construction method of underground wall - Google Patents

Description

  The present invention relates to a method for constructing an underground wall provided for the purpose of reducing stress on underground structures such as open tunnels during an earthquake and for reducing vibration and noise propagating through the ground.

  Conventionally, underground seismic isolation walls for the purpose of reducing stress during underground tunnels and other underground structures, along railway lines, and factories that operate large presses, etc. In general, underground vibration barriers designed to reduce vibrations and noise propagating through the ground are continuously installed in the extending direction in contact with underground structures. If there is, it can be constructed at the same time when the underground structure is constructed. For example, Patent Document 1 proposes a ground displacement absorbing method in which polymer-improved soil is cast as an underground wall such as an underground seismic isolation wall or an underground vibration isolation wall.

  On the other hand, Non-Patent Document 1, for example, discloses an underground seismic isolation wall for an underground structure such as an open-cut tunnel that is not continuously installed in the extending direction of the underground structure. In this nonpatent literature 1, the vertical cylinder-shaped polymer improvement soil is intermittently arrange | positioned in the ground along the underground structure.

JP 2006-112182 A

Tsuyoshi Murono, Masaru Tateyama, Fumi Kiryu, Shosuke Kobayashi, “Reinforcement of existing excavated tunnels with polymer seismic isolation walls”, Foundation work, 2007.3, P69-71

However, the conventional underground wall has the following problems.
That is, in the construction method for placing the polymer improved soil as disclosed in Patent Document 1, the polymer seismic isolation material is greatly compressed and deformed due to the influence of normal earth pressure and the like. Therefore, the wall thickness of the predetermined underground seismic isolation wall set at the time of construction cannot maintain the initial wall thickness for a long period of time, and there was a concern that the isolation wall might be crushed in some cases. The change in wall thickness reduces the displacement absorption performance of the polymer-isolated wall, so that the ground displacement absorbing effect of the underground seismic isolation wall is not fully demonstrated, and the stress reduction effect of the underground structure during the earthquake decreases. There was a problem.

As a countermeasure, Non-Patent Document 1 is considered in which the underground seismic isolation wall is intermittently arranged so as to avoid the continuous arrangement along underground structures such as open tunnels. However, in the seismic isolation walls that are not arranged continuously, the surrounding ground and the structure are connected by soil, so that the seismic isolation effect of sufficiently absorbing the original displacement is significantly reduced. there were.
Moreover, since the polymer material is dissolved in water in the ground where the groundwater level exists, there is a problem that the construction is not easy.

  The present invention has been made in view of the above-described problems, and can sufficiently resist long-term stability against earth pressure acting on the underground wall, and can construct the underground wall by an easy construction method. An object of the present invention is to provide a method for constructing underground walls.

In order to achieve the above object, in the underground wall construction method according to the present invention, a step of excavating an underground space in which the underground wall is installed into the ground, and 300 to 1200 kg / m ³ of the underground space. adjusted bentonite material so that the bentonite effective dry density, or those packed in the bag body material of a mixture of bentonite and aggregate, possess a filling underground space, a material packaged in a bag Is characterized in that it is adjusted to have an effective dry density of bentonite commensurate with the earth pressure at the depth position of the filling portion of the underground space .

In the present invention, when a clay-based material in a natural dry state is put into a bag body having a predetermined volume and then the bag body is filled between the ground and hollow, the bentonite in the material absorbs groundwater and starts to absorb water. And the bentonite absorbs water by adjusting the blending of the material of bentonite or the material of the mixture of bentonite and aggregate so that the bentonite effective dry density is 300 to 1200 kg / m ³ in advance. In the state of the bentonite effective dry density, it is filled between the above-mentioned underground cavities, whereby underground walls such as underground seismic isolation walls and underground vibration-proof walls can be easily constructed.
And, since the underground wall is composed of a bentonite material having water-swelling property, or a clay-based material composed of a mixture of bentonite and aggregate, the material absorbs and swells against the earth pressure due to the water-swelling property of the material, It can have a reaction force that can resist the normal earth pressure received from the ground around the material, the wall width of the underground wall is kept constant, long-term stability can be secured, and stability of material density change is excellent There are advantages.

Further, in the present invention, a material having a different bentonite effective dry density can be placed for each bag body, and by appropriately setting the volume of the bag body and the material to be loaded into the bag body in advance, It is possible to easily construct the underground wall by filling the space between the ground with a composition that gives an effective dry density of bentonite according to the depth. Therefore, the material adjustment work after filling the underground space with the material becomes unnecessary, and an effective underground wall corresponding to the earth pressure can be provided.

Moreover, in the underground wall construction method according to the present invention, it is preferable to use granular bentonite having a particle density of about 1500 to 2000 kg / m ³ as the bentonite material.
By using such bentonite material as a material to be loaded into the bag, it is possible to obtain a material having a predetermined bentonite effective dry density.

Moreover, in the underground wall construction method according to the present invention, the bag body is preferably made of a net-like member.
In the present invention, when the clay-based material in the bag body absorbs groundwater and expands, the bentonite gel oozes out from the mesh of the bag body and adheres to the bentonite gel leaked from the other bag body. It is possible to construct an underground wall in which a plurality of single bags filled in are integrated.

Further, in the construction method of underground walls according to the present invention, the bag is able to penetrate the water, it is preferable and a member that does not leak bentonite and aggregates.
In the present invention, the groundwater permeates into the bag body, and the clay-based material having the water-absorbing swelling property is expanded. At this time, the bag body is a member that does not leak bentonite and aggregate, and since the expanded material itself does not leak out of the bag body, the bag body can be expanded at an expansion rate corresponding to the material loaded inside, Can be improved and the reliability of the design can be improved.

According to the underground wall construction method of the present invention, the clay-based material constituting the underground wall has water-absorbing swell, can resist normal earth pressure received from the surrounding ground, and the wall width of the underground wall can be reduced. Since it can be kept constant, long-term stability can be secured.
Moreover, the underground wall can be constructed by an easy construction method in which a material corresponding to a predetermined bentonite effective dry density is filled between the hollows excavated efficiently.

It is the side view which showed an example of the construction method of the underground vibration proof wall by the 1st Embodiment of this invention. It is a figure which shows the relationship between a bentonite dry density and swelling pressure. It is a figure which shows the triaxial test result of the mixture by a bentonite mixing | blending. It is a figure which shows the bentonite repetitive nonlinear characteristic (stress-strain relationship) calculated | required with the dynamic triaxial compression test apparatus. (A), (b) is a figure which shows the construction method of an underground vibration barrier. It is a figure which shows the construction method of the underground vibration barrier following FIG.5 (b). It is a perspective view which shows the bag body which bags a clay type material. It is a figure which shows the state of the material in a bag body, Comprising: (a) is a figure before expansion | swelling, (b) is a figure after expansion | swelling. (A)-(c) is a figure which shows the construction method of the underground vibration barrier by 2nd Embodiment. It is a side view which shows the installation state of the underground vibration proof wall by a 1st modification. It is a side view which shows the installation state of the underground vibration proof wall by a 2nd modification. It is a side view which shows the installation state of the underground vibration barrier by a 3rd modification. It is a side view which shows the installation state of the underground vibration proof wall by a 4th modification. It is a figure which shows the analysis result by dynamic simulation, Comprising: It is a figure which shows the relationship between the shear wave velocity ratio of a ground, and a shear force reduction rate.

  Hereinafter, the construction method of the underground wall by embodiment of this 1st invention is demonstrated based on drawing.

As shown in FIG. 1, the underground wall construction method according to the first embodiment is based on an existing underground structure 1 (vibration generation source) that forms a subway frame. This is for constructing an underground vibration barrier 3 (underground wall) as a structure for suppressing ground vibration propagation over a predetermined width close to the building 2 side.
Here, the underground structure 1 is a reinforced concrete structure such as a box culvert constructed by an open-cut tunnel or the like, and is embedded in the ground G in a predetermined direction (direction toward the paper surface shown in FIG. 1). It is built to extend. In the ground G, vibrations generated from a train traveling in the underground structure 1 propagate from the underground structure 1 toward the surroundings.

The underground vibration-proof wall 3 is made of a clay-based material having water absorption and swelling properties, has a predetermined wall width D (see FIG. 1), and is close to the side surface 1a of the underground structure 1 on the existing building 2 side. It is arranged in the surrounding ground G and has a wall-like structure that continues in the extending direction of the underground structure 1.
The underground vibration-proof wall 3 is not limited to being provided over the entire length of the underground structure 1 to be extended, and may be provided partially in the extending direction.

  As a clay-based material constituting the underground vibration barrier 3, a mixture of bentonite and water (hereinafter referred to as “first mixture”) or a mixture of bentonite, aggregate and water (hereinafter referred to as “second mixture”). Is used. Here, the aggregate in the second mixture may be a soil material such as sand or gravel, or an artificial material that is unlikely to deteriorate for a long time, such as glass beads.

In the case of the first mixture, by adjusting the density of this bentonite, a predetermined swelling pressure can be exhibited, so that a reaction force against earth pressure acting at all times can be ensured.
On the other hand, in the case of the second mixture, by adjusting the bentonite effective dry density (in the case of a material in which bentonite and aggregate are mixed, the value indicating the density of the bentonite portion satisfying the aggregate gap as a dry density) Since a predetermined swelling pressure can be exhibited, a reaction force against earth pressure acting at all times can be ensured.

Then, the material constituting the ground proof isolating wall 3, a region which is filled with bentonite and water is in the range of 300~1200kg / m ³ with a value of bentonite effective dry density.
In this density range, as shown in FIG. 2, the water absorption swelling pressure is 0.03 to 0.3 MPa. Therefore, assuming that the underwater mass of the ground G is about 1 g / cm ³ and the lateral earth pressure is 1 times the earth covering pressure, it can withstand earth pressure up to a depth of 30 m. That is, it is possible to construct the material by adjusting the density of the material according to the depth at which the underground vibration-proof wall 3 is installed, and the vibration-proof effect can be enhanced by using a material having as little rigidity as possible.
FIG. 2 is described in Non-Patent Document 2 (“Study on measurement method of swelling pressure of compacted bentonite sample”, 40th Geotechnical Research Conference, July 2005, page 2574). Note that “effective bentonite dry density” in Non-Patent Document 2 is the same as “bentonite effective dry density”.
In addition, in the case of the material which does not contain aggregate, it is bentonite dry density since it is only bentonite density, but here, it is unified and used as “bentonite effective dry density”.

Furthermore, the clay-based material used for the underground vibration barrier 3 is preferably a soft material having a low shear rigidity as described above, which can suppress the dynamic deformation of the ground G due to an earthquake and can propagate through the ground. It is possible to reduce vibration waves.
Here, the shear stiffness of bentonite has different characteristics depending on the bentonite effective dry density. This is because when the ratio of the aggregate volume to the material is 50% or less, the aggregate particles do not form a particle structure in which the aggregate particles contact each other and transmit stress to each other. This is because bentonite gel (a mixture of bentonite and water) is interposed therebetween, so that the shear characteristics of the material are mainly determined by the characteristics of the bentonite gel. Therefore, by adjusting the bentonite effective dry density, the shear rigidity of the material of the underground vibration barrier 3 can be made smaller than the surrounding ground G, and the front of the underground vibration barrier 3 (underground structure in FIG. 1). Absorbs ground vibration transmitted from the object 1 side), reduces transmission of vibration to the back of the underground vibration barrier 3 (the existing building 2 side in FIG. 1), and absorbs dynamic deformation of the ground G The effect can be expected.

FIG. 3 shows an example of a triaxial compression test result of the clay-based material of the underground vibration barrier wall 3, and the one containing bentonite has rigidity compared to the result of Toyoura sand conducted under restrained pressure. It is getting smaller.
Moreover, the nonlinear characteristic shown in FIG. 4 has shown the stress-strain relationship calculated | required with the dynamic triaxial compression test apparatus in the material of the bentonite mixing | blending 3 ((rho) d = 0.7Mg / m < ³ >) shown in FIG. Hysteresis is drawn during earthquakes (during repeated shearing), so it is suitable as a damping material (damper material) due to energy absorption. This damping effect can be increased by mixing sand into bentonite.

Next, the construction method of the underground vibration-proof wall 3 and the operation of the built underground vibration-proof wall 3 will be described with reference to the drawings.
That is, as shown in FIGS. 5 (a) and 5 (b), in the construction of the underground vibration barrier 3, the underground space (filling portion K) to be installed is excavated in the ground G, and FIG. ), As shown in (b), the bentonite material or the bentonite / aggregate mixture material adjusted to have a predetermined bentonite effective dry density with respect to the excavated filling portion K is put into the bag body 5. The stuffed product is placed in the filling part K and filled. At this time, the bentonite effective dry density is adjusted so as to match the earth pressure at the depth position of the filling portion K.

  The bag 5 shown in FIG. 7 is preferably a member that is permeable to water and does not allow bentonite and aggregate to leak out, that is, a material that does not easily allow expanded bentonite to pass through. For example, commercially available polypropylene fiber flat yarn plain weave It is possible to use sandbags. With this commercially available sandbag, bentonite particles hardly leak from the inside of the bag.

  Specifically, when a clay-based material in a natural dry state is put into a bag body 5 having a predetermined volume, and then the bag body 5 is placed (or charged) in a filling portion K, bentonite in the material absorbs groundwater. Then start to absorb water. Then, by adjusting the composition of the material in the bag body 5 so as to have a predetermined bentonite effective dry density in advance, the bentonite absorbs water and is filled in the filling portion K in the state of the target bentonite effective dry density. Thus, the underground vibration barrier 3 can be easily constructed.

Here, for example, a case where a material having an effective dry density of bentonite of 500 kg / m ³ will be described.
In the bag body 5 having a volume of 100 L, when the aggregate 4a is put into the bag body 5L, the volume of the region other than the aggregate 4a is 50L as shown in FIG. Here, the bulk density of general commercially available bentonite powder 4b in a naturally dried state is approximately 1000 kg / m ³ (1000 g / L). Therefore, bentonite powder 4b corresponding to a dry weight of 250 kg can be put in the bag body 5. In this state, a space equivalent to about 25 L is left in the volume of the bag body 5. Then, as shown in FIG. 8B, when the bagged material is placed in a groove-shaped filling portion K excavated underground (see FIG. 5), the groundwater is absorbed and bentonite is absorbed and expanded. At this time, when the water absorption and expansion completely occur and the bentonite gel 4c (a composite material of bentonite and water) reaches 50 L, the bag body 5 does not expand further. That is, the area excluding the aggregate area is filled with bentonite gel 4c, and the bentonite effective dry density is equivalent to 500 kg / m ³ .
Thus, by changing the blending conditions of the material and the filling conditions of the bag body 5, a groove-like underground space excavated underground with a material whose bentonite effective dry density is in the range of 300 to 1200 kg / m ³ ( Filling part K) can be filled.

As described above, the bulk density of the bentonite powder is about 1000 kg / m ³ (1000 g / L) in the clay-based material, but 1200 kg / m ³ (1200 g / L) when preliminarily compacted. This can be used.

The clay-based material may be granular bentonite having a particle density of about 1500 to 2000 kg / m ³ as the bentonite material.
In other words, a part of granular bentonite (crushed raw ore or pellet-like material) with a particle density of about 1500 to 2000 kg / m ³ can be used to obtain a material having a predetermined bentonite effective dry density. It is.

  In addition, since the material to be packed in the bag body 5 is adjusted to have the bentonite effective dry density corresponding to the earth pressure at the depth position of the filling portion of the filling portion K, the bentonite effective dry density varies depending on the bag body 5. The material can be put in, and by setting the volume of the bag body 5 and the material to be loaded in the bag body 5 in advance, the bentonite effective dry density according to the depth of the underground vibration barrier 3 is obtained. The underground vibration-proof wall 3 can be easily constructed by filling the filling portion K by blending. Therefore, the material adjustment work after filling the material into the filling portion K becomes unnecessary, and the effective underground vibration barrier 3 corresponding to the earth pressure can be provided.

  Furthermore, since the bag body 5 is a member through which only water permeates, the ground water penetrates into the bag body 5 and the clay-based material having the water absorption swelling property is expanded. Since the material does not leak out of the bag body 5, the bag body 5 can be inflated at an expansion rate corresponding to the material loaded therein, the design becomes easy, and the design reliability can be increased.

  In the construction method described above, the underground vibration barrier 3 is composed of a bentonite material having water absorption swellability, or a clay-based material made of a mixture of bentonite and aggregate, and the earth pressure is less than the water absorption swellability of the material. Because it repels and expands, it can have a reaction force that can resist the normal earth pressure received from the surrounding ground G of the material, and the wall width of the underground anti-vibration wall 3 is kept constant, ensuring long-term stability In addition, there is an advantage that the stability of the material density change is excellent.

  And since the underground vibration barrier 3 is provided between the underground structure 1 and the existing building 2, the generated vibration generated from the underground structure 1 propagates in the ground G, and between the existing building 2 The vibration is almost absorbed by the underground vibration-proof wall 3 that is located, and the influence of vibration on the existing building 2 located outside the underground vibration-proof wall 3 (on the right side in FIG. 1) can be minimized. .

Moreover, construction is easy even in an environment where the groundwater level is high due to the water absorption and expansion characteristics of bentonite. Even if the groundwater level is low, if the ground G is not dry, bentonite will exhibit its water absorption swellability and keep the water retained at the time of construction, so the rigidity will not change due to drying. Even if the rank is low, the function is not lost.
Furthermore, even if a crack or some kind of damage occurs in the underground vibration barrier 3, the damage can be self-repaired under the condition that the groundwater penetrates, and the clay-based material constituting the underground vibration barrier 3 Since it is a natural inorganic mineral material, there is no alteration, the water retention state is hardly changed, and there is an effect that no maintenance is required.

When the underground structure 1 is newly constructed, the underground vibration isolation wall 3 is constructed so as to be close to the underground structure 1, but in such a case, the necessary construction around the underground structure 1 is performed. Space can be reduced. Further, even when the underground vibration barrier 3 is constructed later on the underground in the vicinity of the existing underground structure 1, it is a narrow place or a narrow site where an adjacent underground structure exists. It can also be installed outside the underground structure as a seismic isolation measure for existing structures.
Furthermore, even in the seismic reinforcement work for the underground structure 1 that does not satisfy the earthquake resistance standard, it can be effectively used for the reinforcement of the underground structure 1 that is difficult to be seismically strengthened with the existing structure.

As described above, in the underground wall construction method according to the first embodiment, the clay-based material constituting the underground vibration-damping wall 3 has water-absorbing swell, and the normal earth pressure received from the surrounding ground G Since the wall width of the underground vibration-proof wall 3 can be kept constant, long-term stability can be ensured.
Moreover, the underground vibration-proof wall 3 can be constructed | assembled by the easy construction method of filling the material equivalent to a predetermined bentonite effective dry density in the underground space (filling part K) excavated efficiently.

  Next, another embodiment of the underground wall construction method of the present invention will be described with reference to the accompanying drawings. The same reference numerals are used for members and parts that are the same as or similar to those in the first embodiment. A description of the configuration different from that of the first embodiment will be given by omitting the description.

As shown in FIG. 9, the construction method of the underground wall according to the second embodiment is based on a method of excavating in a state where the groove-like underground space (filling portion K) excavated underground is replaced with muddy water 6. It is.
That is, as shown in FIG. 9A, after excavating a predetermined filling portion K for installing the underground vibration barrier 3 with the muddy water 6, the muddy water 6 is used as shown in FIG. 9B. The filled body K filled with the clay-based material set to a predetermined composition is placed in order from the bottom, and the filled body K is filled with the filled body 5 (see FIG. 9C). .
In this case, the bag body 5 slowly settles in the muddy water 6 and settles at the bottom of the filling portion K, and eventually begins to absorb water. Therefore, since the bag body 5 is set so as to have a predetermined bentonite effective dry density, the bentonite absorbs water and becomes a target material.

  As described above, in the second embodiment, since the density of the muddy water 6 is slightly heavier than the density of the groundwater of the surrounding ground G, there is a movement that permeates the excavated ground side surface. A mud cake is formed on the thin clay layer, and a thin clay layer with low water permeability is formed. The pressure of the muddy water 6 acts on the thin clay layer to prevent the ground side from collapsing. Can be secured. As a result, since excavation is possible over a longer excavation section, a more efficient construction method can be achieved.

As mentioned above, although embodiment of the construction method of the underground wall by this invention was described, this invention is not limited to said embodiment, In the range which does not deviate from the meaning, it can change suitably.
For example, in the present embodiment, a sandbag that only permeates water is used as the bag body 5, but the present invention is not limited to such a member, and for example, a bag body made of a net-like material can be used. It is. In the case of such a net-like bag, when the clay-based material in the bag absorbs groundwater and expands, the bentonite gel oozes out from the mesh of the bag and adheres to the bentonite gel leaked from other bags Therefore, it is possible to construct an underground wall in which a plurality of single bags filled between the hollow spaces are integrated.

  Furthermore, in the present embodiment, the bag body 5 loaded with the clay-based material is filled in the entire underground space of the filling portion K. For example, the bag body 5 is partially arranged in the region of the substantially lower half of the underground space, The upper half region may be filled with a slurry appropriately blended with a mixture of bentonite and water or a mixture of bentonite, aggregate and water.

In the present embodiment, the underground vibration-proof wall 3 is provided at a position close to the side surface 1a of the underground structure 1 forming the tunnel of the subway. However, the present invention is not limited to this. For example, as in Modification 1 shown in FIG. 10, the underground vibration isolation wall 3 is provided between the underground structure 1 and the existing building 2 at a position separated from the underground structure 1 by a predetermined interval. Anyway. Further, as in the second modification shown in FIG. 11, it is also possible to provide the underground anti-vibration wall 3 at a position close to the underground structure 1 side of the existing building 2 </ b> A such as a high-rise building such as a hotel or a hospital. .
Furthermore, as shown in FIGS. 12 and 13, the foundation of the elevated railway may be used as an underground structure 1A (vibration generation source). Can be targeted.

  In addition, as shown in FIG. 10, the clay-type material (bag body 5) with which the filling part K shown to FIG. 6 (a) was filled in the upper part (ground surface side) of the underground vibration barrier 3 is the filling part. A closing member 7 having a lid function may be provided so as not to bulge upward from K. The closing member 7 can be applied by, for example, filling the filling portion K from the ground surface to a predetermined depth with the bag body 5 and then placing concrete between the remaining ground-side hollows.

Further, in the present embodiment, the underground vibration prevention wall 3 of the ground vibration propagation suppressing structure is targeted as the underground wall, but the present invention is not limited to this, and the purpose is to reduce the stress on the underground structure 1. You can use the underground seismic isolation wall (underground wall). In this case, for example, the clay-based material has a rigidity that is 0.6 times or less that of the surrounding ground, so that the effect of reducing the shearing force of the underground structure 1 can be obtained, and the deformation of the ground during an earthquake can be mitigated. And can exhibit seismic isolation effects.
This is confirmed based on the analysis result (see FIG. 14) of the shear force reduction rate calculated by the dynamic simulation when the ratio of the shear wave velocity Vs of the clay-based material of the surrounding ground and the underground seismic isolation wall is different. be able to. Here, the shear force reduction rate is the value obtained by dividing the shear force generated in the underground structure with the underground isolation wall by the shear force generated in the underground structure without the underground isolation wall. is there.
In the dynamic simulation shown in FIG. 14, the wall width of the underground seismic isolation wall is set to 2 cases of 0.5 m and 1.0 m. Has been obtained. That is, it can be confirmed that it is not necessary to use a material that is significantly softer (small shear rigidity) than the surrounding ground, and it can be said that it is not difficult to design the material.

  In the above-described embodiment, the existing buildings 2 and 2A are targeted, but a new building may be used. In the case of this new building, the underground vibration barrier 3 can be constructed at an appropriate position as in the above-described embodiment simultaneously with the installation of the building.

1, 1A underground structure 2, 2A existing building 3 underground vibration barrier (underground wall)
5 Bag body 6 Mud water 7 Blocking member G Ground K Filling part (underground space)

Claims (4)

Excavating the underground space where the underground wall is installed into the ground;
A material in which a bentonite material adjusted to have an effective dry density of bentonite of 300 to 1200 kg / m ³ with respect to the underground space, or a material of a mixture of bentonite and aggregate packed in a bag, Filling with
I have a,
The underground wall construction method is characterized in that the material to be packed in the bag body is adjusted to have an effective dry density of bentonite corresponding to the earth pressure at the depth position of the filling portion of the underground space . The material, method of constructing underground walls according to claim 1, characterized in that particle density as bentonite material is present use a 1500~2000kg / ^{m 3} approximately granular bentonite. The bag is how to build underground walls according to claim 1 or 2, characterized in Rukoto such a member of the reticulated. The bag is able to penetrate the water, and a method for constructing underground walls according to any one of claims 1 to 3, bentonite and said member der Rukoto avoid leaking aggregate .

Images