JP2019199692A - Ground improvement structure and excavating method - Google Patents

Abstract

To provide a ground improvement structure and like capable of reducing bending moment and shearing force created in an artificial impermeable layer.SOLUTION: A ground improvement structure comprises: an earth retaining wall 3 at both sides of an excavated place in the ground 2; an artificial impermeable layer 4 formed through improving the ground 2 between the earth retaining walls 3; an intermediate pile arranged between the earth retaining walls 3 and supporting a strut 7 between the earth retaining walls 3, of which a lower part is buried in the artificial impermeable layer 4. As a lower end of the intermediate pile 5 is placed at a deeper position than the artificial impermeable layer 4, the artificial impermeable layer 4 is anchored in the lower ground 2 with the part of the intermediate pile 5 deeper than the artificial impermeable layer 4 to create resistance force in the artificial impermeable layer 4 against uplifting pressure "a" of subterranean water on the artificial impermeable layer 4.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a ground improvement structure and a ground excavation method.

  The excavation of the ground is performed when the underground structure is constructed. At that time, if there is an impermeable layer at an appropriate depth, build a retaining wall that reaches the impervious layer, and then excavate the ground inside the retaining wall with hanging beams and upsets. In addition to resisting earth pressure from the outside ground, the Yamadome wall also functions as a water barrier for blocking groundwater.

  On the other hand, when there is no impermeable layer at an appropriate depth, an artificial impermeable layer (hereinafter referred to as an artificial impermeable layer) may be formed by improving the ground inside the mountain retaining wall (for example, Patent Document 1). ~ 6).

  The thickness of the artificial impermeable layer shall be able to withstand the bending moment and shear force generated in the artificial impermeable layer due to the groundwater uplift pressure. The artificial impermeable layer is provided between the retaining walls, and also functions as an underground beam that prevents deformation of the retaining walls.

JP-A-11-209998 Japanese Patent Laid-Open No. 11-247174 JP 2003-171949 A Japanese Patent Laid-Open No. 2001-182088 JP 2004-27722 A JP-A-2015-229822

  When the separation (span) of the retaining wall becomes large, there is a problem of cost increase of the artificial impermeable layer by ground improvement. In other words, the stress level of the artificial impermeable layer is calculated as a uniform beam that is applied to a simple beam with the fulcrum on both sides as the fulcrum. If the span (distance between fulcrum) of the dome wall increases, The maximum value of the bending moment and shear force generated by the pressure increases. Therefore, it is necessary to increase the thickness and strength of the artificial impermeable layer, and there is a case where a method different from the artificial impermeable layer by ground improvement must be adopted from the viewpoint of cost and construction period.

  The present invention has been made in view of the above problems, and an object thereof is to provide a ground improvement structure or the like that can reduce a bending moment and a shearing force generated in an artificial impermeable layer.

  According to a first aspect of the present invention for solving the aforementioned problems, there are a retaining wall on both sides of a ground excavation site, an artificial impermeable layer formed by improving the ground between the retaining walls, and the retaining wall. An intermediate pile provided between the walls and having a lower portion embedded in the artificial impermeable layer for supporting a cut beam with the mountain retaining wall, and the intermediate pile includes the artificial pile The ground improvement structure is characterized in that a fulcrum formation mechanism is provided to give resistance to the groundwater lifting pressure applied to the impermeable layer to the artificial impermeable layer at the position of the intermediate pile.

  In the present invention, using an intermediate pile for supporting the beam, the artificial impermeable layer is given resistance to the artificial impermeable layer between the retaining walls, and the artificial impermeable layer is supported against the underground water lifting pressure. A new fulcrum can be formed. As a result, the distance between the fulcrums of the artificial impermeable layer is reduced, and the bending moment and shear force generated in the artificial impermeable layer due to the groundwater uplift pressure can be reduced.

For example, the lower end of the intermediate pile is at a position deeper than the artificial impermeable layer, and the fulcrum formation mechanism is a portion deeper than the artificial impermeable layer of the intermediate pile. Alternatively, the fulcrum formation mechanism may be a ground anchor connected to the intermediate pile and having a lower end fixed to the ground deeper than the artificial impermeable layer.
As a fulcrum formation mechanism, a portion of the intermediate pile that functions as an anchor can be a part deeper than the artificial impermeable layer, or a ground anchor fixed at a position deeper than the artificial impermeable layer. It is possible to anchor to the ground of the ground to provide resistance against the groundwater uplift pressure, and to prevent the artificial impermeable layer from floating and to form a fulcrum in the artificial impermeable layer. In the former case, since the intermediate pile itself has a fulcrum formation mechanism, the construction is simple, and in the latter case, a high resistance can be given by the tension of the ground anchor. In any case, the configuration other than the fulcrum forming mechanism is the same as the conventional one, and it is possible to suppress the increase in cost by making a minor change.

Moreover, the concrete provided in the circumference | surroundings of the said intermediate pile above the said artificial impermeable layer may be sufficient as the said fulcrum formation mechanism.
Thereby, it becomes possible to form a fulcrum in an artificial impermeable layer like the above by giving concrete load from the upper part to an artificial impermeable layer via an intermediate pile. In this case, since a fulcrum formation mechanism can be provided in the ground part, construction is also easy.

The second invention includes a step (a) of providing a mountain retaining wall on both sides of a ground excavation site, an intermediate pile between the mountain retaining wall and an artificial impermeable layer, and excavating the ground between the mountain retaining walls; A step (b) of installing a beam between the mountain retaining wall and the intermediate pile, and a lower portion of the intermediate pile is embedded in the artificial impermeable layer, The excavation method is characterized in that a fulcrum formation mechanism is provided for providing the artificial impervious layer with resistance to groundwater lifting pressure applied to the artificial impermeable layer at the position of the intermediate pile.
The second invention is an excavation method for excavating the ground by forming the ground improvement structure of the first invention.

The fulcrum formation mechanism is, for example, concrete provided around the intermediate pile above the artificial impermeable layer, and the concrete is constructed in order from the top in the step (b).
Thereby, it becomes possible to form a fulcrum in an artificial impermeable layer by giving concrete load from the upper part to an artificial impermeable layer via an intermediate pile. In addition, since the fulcrum formation mechanism can be provided on the ground part, construction is easy, and it is possible to prevent the extension of the construction period for construction of the underground structure by constructing the concrete using the reverse winding method and using it as the main structure of the underground structure .

  According to the present invention, it is possible to provide a ground improvement structure or the like that can reduce the bending moment and shear force generated in the artificial impermeable layer.

The figure which shows the pump chamber. The figure shown about the construction method of the pump chamber. The figure shown about the construction method of the pump chamber. The figure shown about the construction method of the pump chamber. The figure which shows the fulcrum of the artificial impermeable layer. The figure which shows the beam material 9. FIG. The figure which shows the box culvert 10. FIG. The figure shown about the construction method of the pump chamber 1a. The figure shown about the construction method of the pump chamber 1a. The figure shown about the construction method of the pump chamber 1b. The figure shown about the construction method of the pump chamber 1b. The figure shown about the construction method of the pump chamber 1b.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
(1. Pump room 1)
FIG. 1 is a diagram showing a pump chamber 1 constructed using a ground improvement structure according to an embodiment of the present invention.

  The pump chamber 1 is used for using seawater as cooling water in a thermal power plant, a nuclear power plant, or the like. Seawater is guided to the pump chamber 1 through the intake port and intake channel, and is supplied to the turbine chamber of the power plant by the circulating water pump.

  The pump chamber 1 is an underground structure constructed on the ground 2, and has a box-shaped casing made up of a bottom plate 11 and side walls 12 made of concrete. A diversion wall 13 made of concrete is provided in an intermediate portion between the side walls 12.

  In addition, although the code | symbol 4, 5, and 6 of FIG. 1 are an artificial impermeable layer, a part of intermediate | middle pile, and the fixing | fixed part of an intermediate | middle pile, these are mentioned later.

(2. Construction method of pump chamber 1)
2-4 is a figure shown about the construction method of the pump chamber 1. FIG. In this embodiment, the ground improvement structure is formed prior to the construction of the pump chamber 1 and then the ground 2 is excavated. The excavation method will be described below.

  That is, in this embodiment, when constructing the pump chamber 1, first, the mountain retaining wall 3 and the intermediate pile 5 are constructed on the ground 2 as shown in FIG.

  The mountain retaining wall 3 is provided on both sides of the excavation site of the ground 2 (the construction site of the pump chamber 1). The mountain retaining wall 3 resists earth pressure from the outer ground 2 and also functions as a water shielding wall that shields groundwater. The mountain retaining wall 3 is not particularly limited, and a steel sheet pile wall, a steel pipe sheet pile wall, a soil mortar wall containing a core material, and the like can be used.

  The intermediate pile 5 (also referred to as an intermediate column) is a steel vertical material placed between the mountain retaining walls 3 and is used to support a cut beam described later. In the present embodiment, a plurality of intermediate piles 5 are provided at the center of the span of the retaining wall 3 in the extending direction of the retaining wall 3 (corresponding to the normal direction of the paper surface of FIG. 2A). As the intermediate pile 5, for example, H-shaped steel is used, and its lower end is fixed by a fixing portion 6 made of concrete or the like. A known method can be used for the construction of the intermediate pile 5.

  After constructing the mountain retaining wall 3 and the intermediate pile 5 in this way, the ground 2 is improved between the mountain retaining walls 3 as shown in FIG. 2 (b) to form the artificial impermeable layer 4. Thereby, the ground improvement structure including the artificial impermeable layer 4 is formed.

  In the present embodiment, the artificial impermeable layer 4 is formed to a depth corresponding to the bottom of the mountain retaining wall 3, and the lower end of the artificial impermeable layer 4 and the lower end of the mountain retaining wall 3 substantially coincide with each other. The lower part of the intermediate pile 5 is embedded in the artificial impermeable layer 4. In particular, in this embodiment, the lower part of the intermediate pile 5 penetrates the artificial impermeable layer 4 and the lower end thereof is at a position deeper than the artificial impermeable layer 4.

  The formation method of the artificial water-impermeable layer 4 (the improvement method of the ground 2) is not particularly limited. For example, the ground 2 can be made of a solidified material such as cement milk using a known jet mixing stirring method, mechanical mixing stirring method, chemical injection method, or the like. The artificial impermeable layer 4 can be formed by solidifying.

  After the artificial impermeable layer 4 is formed, the excavation of the ground 2 between the mountain retaining walls 3 and the installation of the cut beams 7 are repeated as shown in FIGS. 3 (a) and 3 (b). One end of the cut beam 7 is erected and connected to the mountain retaining wall 3 via the boss 70, and the other end is attached to the intermediate pile 5. Thereby, the cut beam 7 is supported between the mountain retaining wall 3 and the intermediate pile 5.

  After excavating the ground 2 between the mountain retaining walls 3 to the flooring position as shown in FIG. 4 (a), the pump chamber 1 is constructed as shown in FIG. 4 (b). When the pump chamber 1 is constructed, the intermediate pile 5 and the cut beam 7 are removed at an appropriate time. For example, the beam 7 is removed from the bottom in order as the bottom plate 11 and the side wall 12 of the pump chamber 1 are constructed in order from the bottom. After the side wall 12 is constructed to the top, the intermediate pile 5 is cut on the bottom plate 11 and removed. Then, the flow dividing wall 13 is constructed.

  In this embodiment, the mountain retaining wall 3 is also removed when the pump chamber 1 is constructed, but the mountain retaining wall 3 may be left behind. In the present embodiment, the flooring position during excavation (corresponding to the lower surface position of the bottom plate 11 of the pump chamber 1) is the upper surface of the artificial impermeable layer 4, but a higher position may be used. In that case, the ground 2 is interposed between the bottom plate 11 of the pump chamber 1 and the artificial impermeable layer 4. Moreover, although the position of the outer surface of the pump chamber 1 corresponds to the position of the inner surface of the mountain retaining wall 3, the position of the outer surface of the pump chamber 1 may be inside.

  In this embodiment, the lower end of the intermediate pile 5 is located deeper than the artificial impermeable layer 4, and the artificial impermeable layer 4 is grounded below the artificial impermeable layer 4 by a portion (fulcrum formation mechanism) deeper than the artificial impermeable layer 4 of the intermediate pile 5. The artificial impervious layer 4 is prevented from being lifted by giving a resistance force against the groundwater lifting pressure to the artificial impermeable layer 4 at the position of the intermediate pile 5.

  As a result, as shown in FIG. 5, a fulcrum (indicated by ▽ in the figure) that supports the artificial impermeable layer 4 with respect to the groundwater lifting pressure a is added at the position of the intermediate pile 5 in addition to the position of the mountain retaining wall 3. Newly formed.

  In the conventional structure, the fulcrum of the artificial impermeable layer 4 is only the position of the retaining wall 3, and the distance between the fulcrum is the separation (span) of the retaining wall 3. By newly adding a fulcrum that resists a, the distance between the fulcrums becomes 1/2 of the conventional distance. For this reason, the maximum values of the bending moment and the shearing force generated in the artificial impermeable layer 4 by the lifting pressure a are 1/4 and 1/2 of the conventional values, respectively. The length of the intermediate pile 5 and the specification of the fixed portion 6 are set so that the effect as a fulcrum is obtained. It is also possible to provide a plate (not shown) around the intermediate pile 5 at a position corresponding to the upper surface of the artificial impermeable layer 4, thereby suppressing the artificial impermeable layer 4 and preventing the artificial impermeable layer 4 from rising. is there.

  As described above, according to the present embodiment, the resistance against the groundwater uplift a is applied to the artificial impermeable layer 4 between the mountain retaining walls 3 using the intermediate pile 5 for supporting the cut beam 7. The fulcrum which supports the artificial impermeable layer 4 with respect to the lifting pressure a can be newly formed. Thereby, the distance between the fulcrums of the artificial impermeable layer 4 is reduced, and the bending moment and shear force generated in the artificial impermeable layer 4 due to the groundwater lift pressure a can be reduced.

  Therefore, the artificial impermeable layer 4 can be made thin or the strength can be suppressed, and the cost and construction period for forming the artificial impermeable layer 4 can be suppressed. For example, when the maximum value of the shear force generated in the artificial impermeable layer 4 by the groundwater lifting pressure a can be ½ of the conventional value as in this embodiment, the thickness of the artificial impermeable layer 4 is 1/2 of the conventional value. Is possible. Moreover, in this embodiment, since the position of the lower end of the mountain retaining wall 3 and the artificial impermeable layer 4 is made to correspond substantially, as a result of making the artificial impermeable layer 4 thin, the depth of the mountain retaining wall 3 can also be reduced.

  Moreover, in this embodiment, the part deeper than the artificial impermeable layer 4 of the intermediate pile 5 is used as an anchor, and thereby the artificial impermeable layer 4 is anchored to the ground 2 below to provide resistance to the groundwater lifting pressure a. Then, the artificial impermeable layer 4 is prevented from floating and a fulcrum is formed on the artificial impermeable layer 4. In this case, since the intermediate pile 5 itself has a fulcrum formation mechanism, the construction is simple. In addition, other configurations are the same as in the past, and minor changes can be made, so that an increase in cost can be suppressed.

  However, the present invention is not limited to this. For example, since the intermediate pile 5 has the purpose of preventing buckling of the cut beam 7, when the span of the retaining wall 3 is large, a plurality of intermediate piles 5 may be arranged between the retaining walls 3. . For example, when two intermediate piles 5 are arranged so that the span of the mountain retaining wall 3 is divided into three, the maximum bending moment and shear force generated in the artificial impermeable layer 4 due to the groundwater uplift pressure a are respectively 1 / 9, 1/3.

  Moreover, it is not necessary to make all the intermediate piles between the mountain retaining walls 3 function as fulcrums, and only a part may function as fulcrums. For example, when three intermediate piles are provided between the mountain retaining walls 3, only the middle intermediate pile 5 can have the configuration of the present embodiment.

  Moreover, as shown in FIG. 6, it is also possible to connect the intermediate piles 5 adjacent to each other in the extending direction of the mountain retaining wall 3 by the beam material 9, thereby further enhancing the effect as a fulcrum. For example, the beam member 9 is provided near the surface of the ground 2 between the mountain retaining walls 3 and is changed downward according to the excavation of the ground 2 and is disposed near the surface of the flooring position when the flooring is excavated. To be.

  Moreover, although this embodiment demonstrated and demonstrated the example of the pump chamber 1, it does not restrict to this, The water intake pit provided in the upstream of the pump chamber 1, and the seawater discharge | released from the turbine chamber are discharged into a discharge channel It can also be applied to water discharge pits. Further, the flow dividing wall 13 may be omitted.

  Further, the present embodiment can be applied to the construction of other underground structures, and can be applied to the construction of a box culvert 10 such as a road tunnel as shown in FIG. The box culvert 10 in FIG. 7 has a bottom plate 110, a side wall 120, a middle wall (or column) 130, and a top plate 140. FIG. 7 shows an example of a double box culvert 10, but the present invention can be similarly applied to a quadruple box culvert or a single box culvert having no inner wall 130. The construction method of the box culvert 10 is substantially the same as described above. However, after the top plate 140 is constructed, the upper part thereof is backfilled with backfill.

  Hereinafter, another example of the present invention having different fulcrum forming mechanisms will be described as second and third embodiments. In the second and third embodiments, the configuration different from that of the first embodiment will be mainly described, and the description of the same configuration will be omitted by attaching the same reference numerals in the drawings and the like. In addition, the configurations described in each embodiment including the first embodiment can be used in combination with each other.

[Second Embodiment]
The second embodiment is different from the first embodiment in that a ground anchor is used as a fulcrum formation mechanism.

  That is, in the second embodiment, as shown in FIG. 8A, the mountain retaining wall 3 and the intermediate pile 5 are placed and the ground anchor 8 is installed, and the ground anchor 8 is connected to the intermediate pile 5. The ground anchor 8 is provided at a planar position corresponding to the intermediate pile 5, and the lower end thereof is fixed by a fixing portion 6a such as concrete. The construction method of the ground anchor 8 is not particularly limited, and a known construction method can be used.

  Thereafter, as shown in FIG. 8B, the artificial impermeable layer 4 is formed, and the top portion of the ground anchor 8 is fixed to the top portion of the intermediate pile 5, and then it is strained. Even in this embodiment, the lower portion of the intermediate pile 5 is embedded in the artificial impermeable layer 4, but the lower portion does not penetrate the artificial impermeable layer 4. Instead, the lower end of the ground anchor 8 is fixed to the ground 2 at a position deeper than the artificial impermeable layer 4.

  Thereafter, similarly to the first embodiment, the excavation of the ground 2 between the retaining walls 3 and the installation of the cut beams 7 are repeated, and the ground 2 inside the retaining walls 3 is floored as shown in FIG. After excavating to the attachment position, the pump chamber 1a is constructed as shown in FIG. 9 (b).

  In the present embodiment, the artificial impermeable layer 4 is anchored to the lower ground 2 by the ground anchor 8 and the intermediate pile 5, and the artificial impermeable layer 4 is subjected to the groundwater lifting pressure a as in the first embodiment. A fulcrum that gives resistance and supports the artificial impermeable layer 4 against the lifting pressure a can be newly formed at the position of the intermediate pile 5. Thereby, also in 2nd Embodiment, the effect similar to 1st Embodiment is acquired. The specification of the ground anchor 8 is set so as to obtain an effect as a fulcrum.

  Furthermore, in this embodiment, a high resistance can be given by the tension of the ground anchor 8. Further, since the configuration other than the ground anchor 8 is the same as the conventional configuration, a slight change can be made and an increase in cost can be suppressed.

[Third Embodiment]
The third embodiment differs from the first embodiment in that concrete is wound up around the intermediate pile 5 as a fulcrum formation mechanism.

  In the third embodiment, first, as shown in FIG. 10A, the mountain retaining wall 3, the intermediate pile 5, and the artificial impermeable layer 4 are constructed. The method is the same as in the first embodiment, and the lower part of the intermediate pile 5 is also embedded in the artificial impermeable layer 4, but the lower part does not penetrate the artificial impermeable layer 4, and the lower end of the intermediate pile 5 is artificial. The impermeable layer 4 is fixed by the fixing portion 6.

  Then, as shown in FIG.10 (b), excavation of the ground 2 between the mountain retaining walls 3 and concrete placement of the flow dividing wall 13 are performed. Here, the concrete of the flow dividing wall 13 is driven so that the intermediate pile 5 can be wound up using the intermediate pile 5 as a supporting member, and then the cut beam 7 is installed as shown in FIG. The beam 7 is fixed to the concrete outer surface of the flow dividing wall 13. Hereinafter, excavation of the ground 2 between the mountain retaining walls 3, placement of the concrete of the flow dividing wall 13, and installation of the beam 7 are performed in order from the top. As a result, as shown in FIG. 11B, the ground 2 between the mountain retaining walls 3 is excavated to the flooring position, and the flow dividing wall 13 is constructed by the reverse winding method.

  Thereafter, a pump chamber 1b is constructed as shown in FIG. In this embodiment, since the main branch wall 13 is constructed in advance, only the bottom plate 11 and the side wall 12 of the pump chamber 1b may be constructed here. Moreover, unlike the first embodiment, the intermediate pile 5 is left without being removed.

  In this embodiment, the intermediate pile 5 is installed at the position of the flow dividing wall 13, and the concrete of the flow dividing wall 13 located above the artificial impermeable layer 4 is driven around the intermediate pile 5 by the reverse winding method. A concrete load from above is applied to the artificial impermeable layer 4 through 5. Thereby, like the first embodiment, it is possible to give the artificial impermeable layer 4 a resistance against the groundwater lifting pressure a, and to form a fulcrum in the artificial impermeable layer 4 at the position of the intermediate pile 5, The same effect as in the first embodiment can be obtained. The weight of the concrete of the flow dividing wall 13 is set so that the effect as a fulcrum can be obtained.

  Moreover, in this embodiment, since a fulcrum formation mechanism can be provided in a ground part, construction is also easy, and concrete is constructed by the reverse winding method and used as the main branch wall 13 of the pump chamber 1b. It can also prevent the construction period from being extended. Furthermore, there is no big change in the specifications of the intermediate pile 5 and the flow dividing wall 13, and an increase in cost can be suppressed.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea disclosed in the present application, and these are naturally within the technical scope of the present invention. Understood.

DESCRIPTION OF SYMBOLS 1, 1a, 1b: Pump room 2: Ground 3: Mountain retaining wall 4: Artificial impermeable layer 5: Intermediate pile 6, 6a: Fixed part 7: Cut beam 8: Ground anchor 9: Beam material 10: Box culvert 11, 110: Bottom plate 12, 120: Side wall 13: Split wall 130: Middle wall 140: Top plate

Claims (6)

Mountain retaining walls on both sides of the excavation point of the ground,
An artificial impermeable layer formed by improving the ground between the mountain retaining walls;
An intermediate pile for supporting a beam between the mountain retaining wall, provided between the mountain retaining walls, and a lower part embedded in the artificial impermeable layer,
Have
The ground improvement, wherein the intermediate pile is provided with a fulcrum forming mechanism for giving the artificial impervious layer resistance to groundwater lifting pressure applied to the artificial impermeable layer at the position of the intermediate pile. Construction. The lower end of the intermediate pile is deeper than the artificial impermeable layer,
The ground improvement structure according to claim 1, wherein the fulcrum formation mechanism is a portion deeper than the artificial impermeable layer of the intermediate pile.   The ground improvement structure according to claim 1, wherein the fulcrum formation mechanism is a ground anchor connected to the intermediate pile and having a lower end fixed to a ground deeper than the artificial impermeable layer.   The ground improvement structure according to claim 1, wherein the fulcrum formation mechanism is concrete provided around the intermediate pile above the artificial impermeable layer. A step (a) of providing a mountain retaining wall on both sides of a ground excavation site, an intermediate pile between the mountain retaining wall and an artificial impermeable layer;
(B) performing excavation of the ground between the mountain retaining walls, and installing a beam between the mountain retaining wall and the intermediate pile;
Have
The lower part of the intermediate pile is embedded in the artificial impermeable layer,
The intermediate pile is provided with a fulcrum formation mechanism for providing the artificial impervious layer with resistance to groundwater lifting pressure applied to the artificial impervious layer at the position of the intermediate pile. . The fulcrum formation mechanism is concrete provided around the intermediate pile above the artificial impermeable layer,
The excavation method according to claim 5, wherein the concrete is constructed in order from the top in the step (b).

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