JP2019199693A - Ground improvement structure and excavation method - Google Patents

Abstract

To provide a ground improvement structure and the like which can suppress work period and cost required for an artificial impermeable layer.SOLUTION: A ground improvement structure includes: earth retaining walls 3 at both sides of an excavation position in a ground 2; and an artificial impermeable layer 4 formed by improving the ground 2 between the earth retaining walls 3 using a solidification material. An upper face of the artificial impermeable layer 4 is a horizontal surface formed in a horizontal direction. A lower face of the artificial impermeable layer 4 includes an upwardly protruding shape. A thickness of the artificial impermeable layer 4 at an intermediate portion between the earth retaining walls 3 is smaller than a thickness at a position of the earth retaining walls 3.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 increases, there is a problem that the construction period and cost for the artificial impermeable layer increase. 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 becomes 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 construction period and cost.

  This invention is made | formed in view of said problem, and it aims at providing the ground improvement structure etc. which can suppress the construction period and cost concerning an artificial impermeable layer.

  A first invention for solving the above-described problem is a ground improvement structure having an artificial impermeable layer formed by improving the ground with a solidified material, wherein the artificial impermeable layer includes groundwater at a plurality of fulcrums. The at least one of the upper surface and the lower surface of the artificial impermeable layer is supported upward or downward depending on a difference in height between the fulcrum and the height at the fulcrum position. It is a ground improvement structure characterized by being formed in a convex shape.

  In the present invention, the upper and lower surfaces of the artificial impermeable layer are formed in a convex shape as described above, depending on the distribution of shear force and bending moment generated in the artificial impermeable layer due to the groundwater uplift pressure, or artificial impermeable layer. The shape of the artificial impermeable layer can be optimized to reduce the amount of improved soil so that the permeable layer can effectively resist the groundwater pumping pressure, thereby reducing the construction period and cost.

The artificial impermeable layer preferably has a thickness at an intermediate portion between the fulcrums and a thickness at the position of the fulcrum.
In the present invention, the thickness of the artificial impermeable layer can be optimized according to the distribution of shear force and bending moment generated in the artificial impermeable layer by the groundwater uplift pressure by the convex shape of the upper or lower surface of the artificial impermeable layer. .

For example, the artificial impermeable layer has a thickness at an intermediate portion between the fulcrums smaller than a thickness at the position of the fulcrum.
When the groundwater lift pressure is uniformly applied to the artificial impermeable layer, the shear force generated in the artificial impermeable layer by the lift pressure increases on the fulcrum side, and the bending moment increases at the intermediate portion between the fulcrums. If the ground improvement thickness required for the maximum value of the shearing force is larger than the ground improvement thickness required for the maximum value of the bending moment, as described above, the artificial impermeable layer in the middle part between the fulcrums The thickness of the artificial impermeable layer can be optimized with respect to the distribution of the shearing force and the bending moment described above by making the thickness of the substrate smaller than the thickness at the position of the fulcrum.

Alternatively, the artificial impermeable layer may have a thickness at an intermediate portion between the fulcrums larger than a thickness at the position of the fulcrum.
There are cases where the shape of the artificial impermeable layer can be determined mainly by the bending moment generated by the groundwater lifting pressure, such as when the groundwater lifting pressure is low or the strength of the improved soil is high. In this case, by making the thickness of the artificial impermeable layer in the middle part between the fulcrums larger than the thickness at the position of the fulcrum, the thickness of the artificial impermeable layer can be optimized with respect to the bending moment distribution.

It is also desirable that the upper surface and the lower surface of the artificial impermeable layer have a shape that protrudes downward, and the height at the intermediate portion between the fulcrums is lower than the height at the position of the fulcrum.
Thus, by forming the artificial impermeable layer into an arch shape that protrudes downward, it is possible to resist the uplift pressure of the groundwater by the axial compressive force of the artificial impermeable layer. Thus, the artificial impermeable layer can effectively resist the groundwater uplift pressure, and the thickness and strength of the artificial impermeable layer can be suppressed.

At least one of the upper surface and the lower surface of the artificial impermeable layer has an inclined surface inclined with respect to the horizontal direction, and the inclined surface is formed in a step shape by a plurality of step portions.
In the present invention, since the artificial impermeable layer is formed by ground improvement, when the upper surface and the lower surface of the artificial impermeable layer are inclined to have a convex shape, the inclined surface can be stepped.

2nd invention has the process (a) which improves the ground with a solidification material and provides an artificial impermeable layer, and the process (b) which excavates the ground above the artificial impermeable layer, The artificial impermeable layer is supported at a plurality of fulcrums against groundwater lifting pressure, and at least one of the upper and lower surfaces of the artificial impermeable layer has a height at an intermediate portion between the fulcrums and the position of the fulcrum. The excavation method is characterized by being formed in a convex shape upward or downward depending on the difference in height.
The second invention is an excavation method for excavating the ground by forming the ground improvement structure of the first invention.

  By this invention, the ground improvement structure etc. which can hold down the construction period and cost concerning an artificial impermeable layer can be provided.

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 which shows the inclined surface 41. FIG. The figure which shows the groundwater lift pressure A, the bending moment M and the shearing force S of the artificial impermeable layer 4, and required ground improvement thickness. The figure which shows the artificial impermeable layer 4a. The figure which shows the artificial impermeable layer 4b. The figure which shows the box culvert 10. FIG. The figure which shows the artificial impermeable layer 4c. The figure which shows the axial pressure N of the lifting pressure A of the groundwater and the artificial impermeable layer 4c. 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 1a. The figure which shows the fulcrum of artificial impermeable layer 4 '. An example in which the arrangement of the intermediate piles 5, 5 'is different. The figure which shows the ground improvement structure using the ground anchor. 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 of FIG. 1 is an artificial impermeable layer, this is mentioned later.

(2. Construction method of pump chamber 1)
2 and 3 are diagrams showing a construction method of the pump chamber 1. 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 is 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.

  After constructing the mountain retaining wall 3, 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 at a depth that hits 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 are substantially at the same depth.

  Adhesive force is generated between the artificial impermeable layer 4 and the mountain retaining wall 3, and this adhesive force gives the artificial impermeable layer 4 resistance to the groundwater uplift pressure. That is, the artificial impermeable layer 4 is supported against the groundwater uplift pressure with the position of the mountain retaining wall 3 as a fulcrum.

  Although the upper surface of the artificial impermeable layer 4 is a horizontal plane formed in the horizontal direction, the lower surface of the artificial impermeable layer 4 has a height at an intermediate portion between the mountain retaining walls 3 and a height at the position of the mountain retaining wall 3. It is convex upward due to the difference. Therefore, the thickness of the artificial impermeable layer 4 (ground improvement thickness) is different between the intermediate portion between the mountain retaining walls 3 and the position of the mountain retaining wall 3, and the thickness at the intermediate portion is at the position of the mountain retaining wall 3. It is smaller than the thickness.

  On the lower surface of the artificial impermeable layer 4, inclined surfaces 41 are provided at both ends on the mountain retaining wall 3 side, and a horizontal surface 42 is provided at an intermediate portion between the mountain retaining walls 3. The inclined surface 41 is linearly inclined so as to become higher as it goes to the intermediate portion side between the mountain retaining walls 3. The horizontal surface 42 connects the upper ends of the inclined surfaces 41.

  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 and improving. In these methods, since the ground is improved while changing the construction depth in stages, the inclined surface 41 of the artificial impermeable layer 4 is actually composed of a plurality of step portions 411 as shown in FIG.

  After the artificial impermeable layer 4 is formed in this way, the ground 2 above the artificial impermeable layer 4 between the mountain retaining walls 3 is excavated to the flooring position as shown in FIG. When excavating the ground 2, a cut beam (not shown) is bridged between the retaining walls 3 as necessary.

  Thereafter, the pump chamber 1 is constructed as shown in FIG. In the present embodiment, the beam and the mountain retaining wall 3 are 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. 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.

  The shape of the artificial impermeable layer 4 described above was determined so as to optimize the thickness of the artificial impermeable layer 4 according to the bending moment and shear force distribution generated in the artificial impermeable layer 4 due to the groundwater uplift pressure. Thus, the amount of improved soil of the artificial impermeable layer 4 can be reduced, and the construction period and cost can be suppressed.

  That is, when the groundwater lifting pressure A is uniformly applied to the artificial impermeable layer 4 as shown in FIG. 5A, the artificial impermeable layer 4 is supported with the position of the mountain retaining wall 3 as a fulcrum (see ▽ in the figure). FIG. 5B shows an outline of the bending moment M (t · m / m) and the shearing force S (t / m) generated in the artificial impermeable layer 4 when a simple beam is used. The shear force S is an absolute value.

Fig. 5 (c) shows the ground improvement thickness h1 (m) required for the bending moment M and the ground improvement thickness h2 (m) required for the shear force S. It can be calculated by the following formulas (1) and (2). In equations (1) and (2), b (m) is the unit length in the depth direction of the improved soil (corresponding to the normal direction of the paper surface in FIG. 5A), for example, b = 1. Also, σ (tf / m ² ) and τ (tf / m ² ) are the allowable compressive stress level and the allowable shear stress level of the improved soil, respectively.
h1 = (6 · M / (σ · b)) ^0.5 (1)
h2 = S / (τ · b) (2)

  As shown in FIGS. 5 (b) and 5 (c), when a uniform lifting pressure A is applied to the artificial impermeable layer 4, the shear force S generated in the artificial impermeable layer 4 increases at the position of the mountain retaining wall 3. The bending moment M increases at an intermediate portion between the mountain retaining walls 3. In this example, the ground improvement thickness h2 required for the maximum value of the shear force S is larger than the ground improvement thickness h1 required for the maximum value of the bending moment.

  The shape of the lower surface of the artificial impermeable layer 4 of the present embodiment is the ground required for the ground improvement thickness h1 and the shear force S required for the bending moment M, as shown by the solid line B in FIG. As a result of satisfying all of the improved thickness h2 and reducing the amount of improved soil as much as possible, the artificial impermeable layer 4 is formed thick at the position of the mountain retaining wall 3 as described above, and the space between the mountain retaining walls 3 is increased. The artificial impermeable layer 4 is convex upward so that it is formed thinner in the middle part.

  Thereby, as shown in the chain line C of FIG. 5C, the ground improvement thickness is made constant according to the maximum value of the required ground improvement thickness (the lower surface of the artificial impermeable layer 4 is horizontal), Improved soil volume can be reduced by about 30%.

  In addition, it can replace with the artificial impermeable layer 4 of this embodiment, and can also use the artificial impermeable layer of the shape which reversed the said artificial impermeable layer 4 up and down, and this is the example of FIG. 6, 7 mentioned later. But the same is true. For example, in the present embodiment, the ground improvement thickness shown by the solid line B can also be realized by turning the artificial impermeable layer 4 upside down so that the lower surface is a horizontal surface and the upper surface is convex downward.

  As described above, according to the present embodiment, the artificial impermeable layer 4 has a convex shape, and the artificial impermeable layer 4 has an artificially impermeable layer according to the distribution of the shearing force S and the bending moment M generated in the artificial impermeable layer 4 by the groundwater lift pressure A. The thickness of the water permeable layer 4 can be optimized, the amount of improved soil can be reduced, and the construction period and cost can be suppressed.

  That is, when the groundwater lifting pressure A is uniformly applied to the artificial impermeable layer 4, the shear force S generated in the artificial impermeable layer 4 by the lifting pressure A increases at the position of the mountain retaining wall 3, and the bending moment M is the mountain. It becomes large at the intermediate part between the retaining walls 3. When the ground improvement thickness h2 required for the maximum value of the shearing force S is larger than the ground improvement thickness h1 required for the maximum value of the bending moment M, an artificial part in the intermediate portion between the retaining walls 3 is used. By making the thickness of the impermeable layer 4 smaller than the thickness at the position of the mountain retaining wall 3, the thickness of the artificial impermeable layer 4 can be optimized with respect to the distribution of the shearing force S and the bending moment M described above.

  In this embodiment, since the end of the artificial impermeable layer 4 on the side of the retaining wall 3 is thickened to withstand the shearing force S, the artificial impermeable layer 4 behaves integrally with the retaining wall 3 and functions as a substantial fulcrum. The range of the water permeable layer 4 expands inward, and the effect of reducing the maximum value of the bending moment M generated in the artificial water-impermeable layer 4 by reducing the substantial distance between fulcrums can be expected. Therefore, it is also possible to make the thickness of the artificial impermeable layer 4 in the intermediate part between the mountain retaining walls 3 smaller.

  Moreover, in this embodiment, since the artificial impermeable layer 4 is formed by ground improvement, the inclined surface 41 can be made into the step shape comprised by the several step part 411. FIG.

  However, the present invention is not limited to this. For example, the shape of the artificial water-impermeable layer 4 satisfies both the ground improvement thickness h1 required for the bending moment M and the ground improvement thickness h2 required for the shear force S, and the amount of improved soil is minimized. What is necessary is just to define and it is not restricted to what was shown by the said embodiment.

  For example, by setting the ground improvement thickness as shown by the broken line B ′ in FIG. 5 (c), the lower surface of the artificial impermeable layer 4a is formed into a substantially arc-shaped curved surface that protrudes upward as shown in FIG. Is also possible. Also in this case, the inclined surface 43 is provided on the lower surface of the artificial impermeable layer 4a, and the inclined surface 43 is also formed in a step shape by a plurality of step portions as in the example of FIG.

  Further, there are cases where the shape of the artificial impermeable layer can be determined mainly by the bending moment M, such as when the groundwater lifting pressure A is low or the strength of the improved soil is high. In the case of considering only the bending moment M, as shown in FIG. 7, the lower surface of the artificial impermeable layer 4b is formed into a substantially arcuate curved surface that protrudes downward, and the artificial imperfection at the intermediate portion between the mountain retaining walls 3 is formed. The thickness of the water permeable layer 4 b may be larger than the thickness at the position of the mountain retaining wall 3. The inclined surface 44 on the lower surface of the artificial water-impermeable layer 4b is formed in a step shape by a plurality of step portions as in the example of FIG.

  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.

  Furthermore, 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. 8 has a bottom plate 110, a side wall 120, a middle wall (or column) 130, and a top plate 140. FIG. 8 shows an example of the double box culvert 10, but the present invention can be similarly applied to a quadruple box culvert or a single box culvert without the 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.

  In this embodiment, the mountain retaining wall 3 extends in the depth direction (corresponding to the normal direction of the paper surface in FIG. 2A), and the cross-sectional shapes of the artificial impermeable layers 4, 4a, 4b are also constant in the depth direction. However, for example, the mountain retaining wall 3 may be formed in a cylindrical shape. In this case, the cross section in each direction of the plane may be the cross sectional shape of the artificial impermeable layers 4, 4 a, 4 b described above. For example, in the case of the artificial impermeable layer 4b shown in FIG. 7, if the mountain retaining wall 3 is cylindrical, the lower surface thereof is formed in a lens shape so that the cross-section in each direction of the plane has a shape as shown in FIG.

  Hereinafter, another example of the present invention will be described as second and third embodiments. The second and third embodiments will mainly describe different configurations from the first embodiment, and the same configurations will be denoted by the same reference numerals in the drawings and the like, and description thereof will be omitted.

[Second Embodiment]
In the second embodiment, as shown in FIG. 9, the upper and lower surfaces of the artificial impermeable layer 4c are substantially arc-shaped curved surfaces that protrude downward, and the mountain retaining walls 3 on the upper and lower surfaces of the artificial impermeable layer 4c. The height at the intermediate portion between the two is lower than the height at the position of the mountain retaining wall 3. The upper and lower inclined surfaces 45 and 46 of the artificial impermeable layer 4c are formed in a step shape by a plurality of step portions as in the example of FIG. FIG. 9 shows a state where the ground 2 between the mountain retaining walls 3 is excavated to the flooring position. In this embodiment, the ground 2 is interposed between the artificial impermeable layer 4c and the flooring position.

  In the present embodiment, the artificial impermeable layer 4c is thereby formed into a substantially arcuate arch that protrudes downward, and the shape of the artificial impermeable layer 4c is optimized so as to effectively resist the groundwater uplift pressure. .

  That is, in this embodiment, as shown in FIG. 10A, the arch-shaped artificial impermeable layer 4 c resists the groundwater lift pressure A by the axial compression force N and transmits the force to the mountain retaining wall 3. Thereby, high proof stress can be given to the artificial impermeable layer 4c, and the thickness and intensity | strength of the artificial impermeable layer 4c can be suppressed.

In this case, the ground improvement thickness t (m) required for the artificial impermeable layer 4c can be expressed by the following equation (3). In Equation (3), σ (tf / m ² ) is the degree of compressive allowable stress of the improved soil. N (t / m) is the axial compression force.
t = N / σ (3)

Here, the axial compression force N can be expressed by the following equation (4).
N = w · R (4)

In formula (4), w (t / m ² ) is the value of the groundwater lift pressure A. R (m) is the arch radius and can be expressed by the following equation (5) using the span L (m) and the rise h (m) of the artificial impermeable layer 4c (see FIG. 10B). .
R = L ² / (8 · h) + h / 2 (5)

  Thus, in this embodiment, the arch-shaped artificial impermeable layer 4c resists the groundwater lift pressure A by its axial compressive force N, thereby providing the artificial impermeable layer 4c with high proof stress and artificial impermeable water. The thickness and strength of the layer 4c can be suppressed. The thickness of the artificial impermeable layer 4c is determined so that it can withstand the axial compressive force N and can be transmitted to the mountain retaining wall 3. However, in the present embodiment, the entire thickness of the artificial impermeable layer 4c can be reduced. Compared to the embodiment, the amount of improved soil can be reduced. Also in this embodiment, the lower end of the artificial impermeable layer 4c and the lower end of the mountain retaining wall 3 are at substantially the same depth. However, as a result of making the artificial impermeable layer 4c thinner, the root depth of the mountain retaining wall 3 becomes smaller and the construction period And cost can be reduced.

  In addition, after satisfy | filling said ground improvement thickness t, the thickness of the artificial impermeable layer 4c in the position of the mountain retaining wall 3 is made larger than the intermediate part between the mountain retaining walls 3 similarly to 1st Embodiment. It is also possible. Also in the case of FIG. 7 described above, in the case where the groundwater lift pressure increases and cracks occur on the upper surface, an arch-like resistance mechanism that resists the lift pressure is generated by the axial compression force as in this embodiment. it is conceivable that.

[Third Embodiment]
The third embodiment is an example in which the bending moment and shear force generated in the artificial impermeable layer are reduced by using the intermediate pile for supporting the cut beam to reduce the construction period and cost for the artificial impermeable layer.

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

  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 the cut beam. In this embodiment, the intermediate pile 5 is provided at the center of the span of the mountain retaining wall 3. 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.

  After the mountain retaining wall 3 and the intermediate pile 5 are thus constructed, the ground 2 is improved between the mountain retaining walls 3 as shown in FIG. 11 (b) to form an artificial impermeable layer 4 '. Thereby, the ground improvement structure including the artificial impermeable layer 4 'is formed.

  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 as described above. The lower part of the intermediate pile 5 is buried in the artificial impermeable layer 4 '. In particular, in the present embodiment, the lower portion of the intermediate pile 5 penetrates the artificial impermeable layer 4 ′ and the lower end thereof is at a deeper position than the artificial impermeable layer 4 ′.

  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 beam 7 are repeated as shown in FIGS. 12 (a) and 12 (b). One end of the cut beam 7 is erected and connected to the mountain retaining wall 3 through 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. 13 (a), the pump chamber 1a is constructed as shown in FIG. 13 (b). During the construction of the pump chamber 1a, the intermediate pile 5 and the beam 7 are removed at an appropriate time. For example, the beam 7 is removed in order from the bottom as the bottom plate 11 and the side wall 12 of the pump chamber 1a are constructed from the bottom, and 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 the present embodiment, the lower end of the intermediate pile 5 is deeper than the artificial impermeable layer 4 ′, and the artificial impermeable layer 4 ′ is anchored to the lower ground 2 by a portion deeper than the artificial impermeable layer 4 ′ of the intermediate pile 5. Then, resistance against the groundwater lifting pressure is applied to the artificial impermeable layer 4 ′ at the position of the intermediate pile 5 to prevent the artificial impermeable layer 4 ′ from being lifted.

  Accordingly, as shown in FIG. 14, a fulcrum (indicated by ▽ in the figure) for supporting the artificial impermeable layer 4 ′ with respect to the groundwater lifting pressure A is added to the position of the mountain retaining wall 3 and the position of the intermediate pile 5. Can be 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 pressure A, the distance between the fulcrums becomes 1/2 of the conventional distance. Therefore, 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, respectively, of the prior art.

  Thereby, the artificial impermeable layer 4 ′ can be thinned and the strength can be suppressed, and the construction period and cost for the artificial impermeable layer 4 ′ can be suppressed. In addition, since the position of the intermediate pile 5 becomes a new fulcrum as described above, the shape of the artificial impermeable layer 4 ′ has the same shape as the artificial impermeable layer 4 described with reference to FIG. A total of two are formed between the mountain retaining wall 3 and the intermediate pile 5.

  Thus, according to this embodiment, resistance against the groundwater uplift pressure A is given to the artificial impermeable layer 4 ′ between the mountain retaining walls 3 using the intermediate pile 5 for supporting the cut beam 7. A fulcrum that supports the artificial water-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 lifting pressure A can be reduced. Therefore, the artificial impermeable layer 4 ′ can be thinned and the strength can be reduced, and the construction period and cost for the artificial impermeable layer 4 ′ can be further reduced.

  In addition, since the intermediate pile 5 also has the purpose of preventing buckling of the beam 7, when the span of the retaining wall 3 is large, a plurality of intermediate piles 5 may be disposed between the retaining walls 3. is there. For example, when two intermediate piles 5 are arranged so that the span of the mountain retaining wall 3 is divided into three as shown in FIG. 15 (a), the bending moment and shear force generated in the artificial impermeable layer 4 ″ by the groundwater lifting pressure A Are respectively 1/9 and 1/3. The shape of the artificial impermeable layer 4 ″ in this case is the same as the artificial impermeable layer 4 described with reference to FIG. A total of three are formed between each mountain retaining wall 3 and the intermediate pile 5 and between the two intermediate piles 5.

  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 has the configuration of this embodiment as shown in FIG. 15 (b), and the other intermediate piles are the present embodiment. The lower end of the intermediate pile 5 ′ that does not function as a fulcrum and is supported by the artificial impermeable layer 4 ′ can be obtained. In this case, the shape of the artificial impermeable layer 4 ′ is the same as that of the artificial impermeable layer 4 described with reference to FIG. It will be formed.

  On the other hand, when all the intermediate piles between the mountain retaining walls 3 are normal intermediate piles 5 ', artificial impermeable water similar to that of the first embodiment is formed between the mountain retaining walls 3 as shown in FIG. 15 (c). The layer 4 may be provided. FIG. 15C is an example in which one intermediate pile 5 ′ is disposed between the mountain retaining walls 3, but the same applies when a plurality of intermediate piles 5 ′ are disposed between the mountain retaining walls 3.

  In this embodiment, in each example, the shape of the artificial impermeable layer is the same as that of the artificial impermeable layer 4 described with reference to FIG. However, instead of this, other shapes such as the artificial impermeable layers 4a, 4b described in FIGS. The shape of 4c may be provided between the mountain retaining wall 3 and the intermediate pile 5, between the intermediate pile 5 and between the mountain retaining walls 3. Also in the case where there is a normal intermediate pile 5 ′, as shown in FIGS. 15B to 15D, regardless of the intermediate pile 5 ′, between the mountain retaining wall 3 and the intermediate pile 5, between the intermediate piles 5, What is necessary is just to provide the shape of the artificial water-impermeable layer 4a, 4b, 4c somewhere between the walls 3. In the case of the arch-shaped artificial impermeable layer 4c (see FIG. 9), the lower end of the intermediate pile 5 'is supported by the ground on the artificial impermeable layer 4c as shown in FIG. 15 (d).

  Moreover, the mechanism (fulcrum formation mechanism) for forming a fulcrum is not limited to the portion of the intermediate pile 5 deeper than the artificial impermeable layer 4 ′, and a ground anchor 8 may be used as shown in FIG. 16.

  In this example, the lower part of the intermediate pile 5 does not penetrate the artificial impermeable layer 4 ′ and the lower end of the intermediate pile 5 is inside the artificial impermeable layer 4 ′. Instead, the lower end of the ground anchor 8 is fixed with concrete or the like. It is fixed to the ground 2 at a position deeper than the artificial impermeable layer 4 ′ at the portion 6 a, and the upper end of the ground anchor 8 is fixed to the top of the intermediate pile 5 and is strained.

  As a result, the artificial impermeable layer 4 ′ can be anchored to the ground 2 below by using the ground anchor 8 and the intermediate pile 5, and the resistance to the groundwater lifting pressure A is applied to the artificial impermeable layer 4 ′ as described above. And a fulcrum supporting the artificial impermeable layer 4 ′ with respect to the lifting pressure A can be newly formed at the position of the intermediate pile 5. In this example, a high resistance can be given by the tension of the ground anchor 8.

  Furthermore, after constructing the mountain retaining wall 3, the intermediate pile 5 and the artificial impermeable layer 4 ′ as shown in FIG. 17 (a), the ground 2 between the mountain retaining walls 3 as shown in FIG. 17 (b). By excavating and placing the concrete of the flow dividing wall 13 and installing the beam 7 as shown in FIG. 18 (a), the mountain retaining wall 3 as shown in FIG. 18 (b) is repeated in order from the top. The ground 2 may be excavated to the flooring position.

  Thereby, the concrete load from above can be given to the artificial impermeable layer 4 ′ through the intermediate pile 5, and the resistance of the artificial water impermeable layer 4 ′ to the groundwater lifting pressure A is given to the position of the intermediate pile 5. Thus, a fulcrum can be formed on the artificial impermeable layer 4 ′. In this example, the lower end of the intermediate pile 5 is fixed in the artificial impermeable layer 4 ′ by the fixing portion 6.

  The pump chamber is then constructed as shown in FIG. 19, but in this example, since the main branch wall 13 is constructed in advance by the reverse winding method, only the bottom plate 11 and the side wall 12 of the pump chamber 1b are constructed here. That's fine. Also, unlike the above, the intermediate pile 5 is left without being removed.

  In this example, since a fulcrum formation mechanism can be provided on the ground part, the construction is easy, and the construction of the pump chamber 1b is performed by constructing the concrete by the reverse winding method and using it as the main branch wall 13 of the pump chamber 1b. Extension of the work period can also be prevented.

  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 chamber 2: Ground 3: Mountain retaining wall 4, 4 ', 4 ", 4a, 4b, 4c: Artificial impermeable layer 5: Intermediate pile 6, 6a: Fixed part 7: Cut beam 8: Ground anchor 10: Box culvert 11, 110: Bottom plate 12, 120: Side wall 13: Dividing wall 41, 43, 44, 45, 46: Inclined surface 42: Horizontal surface 130: Middle wall 140: Top plate 411: Stepped portion

Claims (7)

A ground improvement structure having an artificial impermeable layer formed by improving the ground with a solidifying material,
The artificial impermeable layer is supported against groundwater lifting pressure at a plurality of fulcrums,
At least one of the upper surface and the lower surface of the artificial impermeable layer is formed in a convex shape upward or downward due to a difference in height at an intermediate portion between the fulcrums and at a position of the fulcrum. Improved ground structure.   The ground improvement structure according to claim 1, wherein the artificial impermeable layer has a thickness at an intermediate portion between the fulcrums and a thickness at the position of the fulcrum.   The ground improvement structure according to claim 2, wherein the artificial impermeable layer has a thickness at an intermediate portion between the fulcrums smaller than a thickness at the position of the fulcrum.   The ground improvement structure according to claim 2, wherein the artificial impermeable layer has a thickness at an intermediate portion between the fulcrums larger than a thickness at the position of the fulcrum.   The upper surface and the lower surface of the artificial impermeable layer have a shape that protrudes downward, and a height at an intermediate portion between the fulcrums is lower than a height at the position of the fulcrum. Item 1. The ground improvement structure according to item 1.   The at least one of an upper surface and a lower surface of the artificial impermeable layer has an inclined surface inclined with respect to a horizontal direction, and the inclined surface is formed in a step shape by a plurality of step portions. The ground improvement structure according to claim 5. (A) providing an artificial impermeable layer by improving the ground with a solidifying material;
A step (b) of excavating the ground above the artificial impermeable layer;
Have
The artificial impermeable layer is supported against groundwater lifting pressure at a plurality of fulcrums,
At least one of the upper surface and the lower surface of the artificial impermeable layer is formed in a convex shape upward or downward due to a difference in height at an intermediate portion between the fulcrums and at a position of the fulcrum. And drilling method.

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