JP7075280B2 - Ground improvement structure and excavation method - Google Patents

Description

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

The ground is excavated when constructing the underground structure. At that time, if there is an impermeable layer at an appropriate depth, after constructing a mountain retaining wall that reaches the impermeable layer, excavate the ground inside the mountain retaining wall while hanging a girder and abdomen. In addition to resisting earth pressure from the outside ground, the mountain retaining wall also functions as an impermeable wall that impedes groundwater.

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

The thickness of the artificial impermeable layer shall be able to withstand the bending moment and shearing force generated in the artificial impermeable layer due to the lifting pressure of groundwater. The artificial impermeable layer is provided between the mountain retaining walls and also functions as an underground beam to prevent deformation of the mountain retaining walls.

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

If the separation (span) of the mountain retaining wall becomes large, there is a problem that the construction period and cost required for the artificial impermeable layer increase. That is, the stress level of the artificial impermeable layer is obtained as if a uniform lifting pressure is applied to the simple beam with the fulcrum walls on both sides as fulcrums, and when the span of the fulcrum walls (distance between fulcrums) increases, the stress level is lifted. The maximum value of bending moment and shear force generated by pressure increases. Therefore, it becomes necessary to increase the thickness and strength of the artificial impermeable layer, and in some cases, it is necessary to adopt a method different from the artificial impermeable layer by improving the ground in terms of construction period and cost.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a ground improvement structure or the like that can suppress the construction period and cost required for the artificial impermeable layer.

The first invention for solving the above-mentioned problems is a ground improvement structure having an artificial impermeable layer formed by improving the ground with a solidifying material, and the artificial impermeable layer is groundwater at a plurality of fulcrums. The fulcrum is the mountain retaining walls on both sides of the artificial impermeable layer, the artificial impermeable layer is provided between the mountain retaining walls, and the upper surface of the artificial impermeable layer is It is a horizontal plane, and the lower surface of the artificial impermeable layer is formed in a convex shape upward due to the difference between the height in the intermediate portion between the fulcrums and the height at the position of the fulcrum. It is a structure.

In the present invention, by forming the lower surface of the artificial impermeable layer in a convex shape as described above, depending on the distribution of the shearing force and bending moment generated in the artificial impermeable layer due to the lifting pressure of groundwater, or artificial impermeable water. The shape of the artificial impermeable layer can be optimized to reduce the amount of improved soil so that the layer can effectively resist the pumping pressure of groundwater, and the construction period and cost can be reduced.

It is desirable that the artificial impermeable layer has a different thickness at the intermediate portion between the fulcrums and a thickness at the position of the fulcrum.
In the present invention, the convex shape of the lower surface of the artificial impermeable layer allows the thickness of the artificial impermeable layer to be optimized according to the distribution of the shear force and bending moment generated in the artificial impermeable layer due to the lifting pressure of groundwater.

For example, the artificial impermeable layer has a thickness in the middle portion between the fulcrums being smaller than the thickness at the position of the fulcrum.
When the lifting pressure of groundwater is uniformly applied to the artificial impermeable layer, the shearing force generated in the artificial impermeable layer by the lifting pressure increases on the fulcrum side, and the bending moment increases in the middle portion between the fulcrums. If the ground improvement thickness required for the maximum shear force is greater than the ground improvement thickness required for the maximum bending moment, the artificial impermeable layer in the middle between the fulcrums as described above. By making the thickness of the fulcrum smaller than the thickness at the position of the fulcrum, the thickness of the artificial impermeable layer can be optimized for the distribution of the above-mentioned shearing force and bending moment.

Alternatively, the artificial impermeable layer may have a thickness in the intermediate portion between the fulcrums larger than the thickness at the position of the fulcrum.
In some cases, such as when the lifting pressure of groundwater is small or the strength of the improved soil is high, the shape of the artificial impermeable layer can be determined mainly by the bending moment generated by the lifting pressure of groundwater. In this case, by making the thickness of the artificial impermeable layer in the intermediate portion between the fulcrums larger than the thickness at the position of the fulcrum, the thickness of the artificial impermeable layer can be optimized for the distribution of the bending moment.

It is also desirable that the lower surface is formed in an arc shape that is convex upward.
Further, inclined surfaces are provided at both ends of the lower surface on the fulcrum side, a horizontal plane is provided at the intermediate portion of the lower surface, and the inclined surface is inclined so as to become higher toward the intermediate portion side. It is also desirable to connect the upper ends of the inclined surfaces to each other.

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 stepped manner by a plurality of step portions.
In the present invention, since the artificial impermeable layer is formed by ground improvement, when the upper surface or the lower surface of the artificial impermeable layer is inclined to be convex, the inclined surface can be made stepped.

The second invention includes a step (a) of improving the ground with a solidifying material to provide an artificial impermeable layer, and a step (b) of excavating the ground above the artificial impermeable layer. The artificial impermeable layer is supported by the lifting pressure of groundwater at a plurality of fulcrums, and the fulcrum is a mountain retaining wall on both sides of the artificial impermeable layer, and the artificial impermeable layer is formed between the mountain retaining walls. The upper surface of the artificial impermeable layer is a horizontal plane, and the lower surface of the artificial impermeable layer is convex upward due to the difference between the height in the intermediate portion between the fulcrums and the height at the position of the fulcrum. It is an excavation method characterized by being formed in.
The second invention is an excavation method for excavating the ground by forming the ground improvement structure of the first invention.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a ground improvement structure or the like that can suppress the construction period and cost required for the artificial impermeable layer.

The figure which shows the pump chamber 1. The figure which shows the construction method of a pump chamber 1. The figure which shows the construction method of a pump chamber 1. The figure which shows the inclined surface 41. The figure which shows the pumping pressure A of the groundwater, the bending moment M and the shearing force S of the artificial impermeable layer 4, and the necessary 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. The figure which shows the artificial impermeable layer 4c. The figure which shows the pumping pressure A of the groundwater and the axial compressive force N of the artificial impermeable layer 4c. The figure which shows the construction method of the pump chamber 1a. The figure which shows the construction method of the pump chamber 1a. The figure which shows the construction method of the pump chamber 1a. The figure which shows the fulcrum of the artificial impermeable layer 4'. An example in which the arrangement of the intermediate piles 5 and 5'is different. The figure which shows the ground improvement structure using the ground anchor 8. The figure which shows the construction method of the pump chamber 1b. The figure which shows the construction method of the pump chamber 1b. The figure which shows 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 by utilizing the ground improvement structure according to the 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 an intake port and an intake channel, and is supplied to the turbine chamber of the power plant by a circulating water pump.

The pump chamber 1 is an underground structure constructed on the ground 2, and has a box-shaped skeleton composed of a bottom slab 11 and a side wall 12 formed of concrete. A concrete diversion wall 13 is provided in the middle portion between the side walls 12.

Reference numeral 4 in FIG. 1 is an artificial impermeable layer, which will be described later.

(2. Construction method of pump chamber 1)
2 and 3 are diagrams showing a method of constructing the pump chamber 1. In the present 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 thereof will also be described below.

That is, in the present embodiment, when constructing the pump chamber 1, the mountain retaining wall 3 is first constructed on the ground 2 as shown in FIG. 2 (a).

The mountain retaining wall 3 is provided on both sides of the excavated part of the ground 2 (the place where the pump chamber 1 is constructed). The mountain retaining wall 3 resists the earth pressure from the outer ground 2 and also functions as a water blocking wall for blocking 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, or the like can be used.

After the mountain retaining wall 3 is constructed, the ground 2 is improved between the mountain retaining walls 3 as shown in FIG. 2 (b) to form an artificial impermeable layer 4. As a result, a 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 at substantially the same depth.

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

The upper surface of the artificial impermeable layer 4 is a horizontal plane formed in the horizontal direction, but the lower surface of the artificial impermeable layer 4 is the height at the intermediate portion between the mountain retaining walls 3 and the 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) differs between the intermediate portion between the mountain retaining walls 3 and the position of the retaining wall 3, and the thickness at the intermediate portion is at the position of the 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 horizontal planes 42 are provided at the intermediate portion between the mountain retaining walls 3. The inclined surface 41 inclines linearly so as to become higher toward the intermediate portion side between the mountain retaining walls 3. The horizontal plane 42 connects the upper ends of the inclined surfaces 41 to each other.

The method for forming the artificial impermeable layer 4 (improvement method for the ground 2) is not particularly limited, and for example, a known injection mixing stirring method, mechanical mixing stirring method, chemical solution injection method, or the like is used, and the ground 2 is made of a solidifying material such as cement milk. The artificial impermeable layer 4 can be formed by solidifying and improving. Since the ground is improved while the construction depth is changed stepwise in these construction methods, 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 forming the artificial impermeable layer 4 in this way, as shown in FIG. 3A, the ground 2 above the artificial impermeable layer 4 between the mountain retaining walls 3 is excavated to the flooring position. When excavating the ground 2, a girder (not shown) is laid between the mountain retaining walls 3 as needed.

After that, the pump chamber 1 is constructed as shown in FIG. 3 (b). In the present embodiment, the girder 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. Further, in the present embodiment, the flooring position at the time of excavation (corresponding to the lower surface position of the bottom slab 11 of the pump chamber 1) is set to 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 slab 11 of the pump chamber 1 and the artificial impermeable layer 4. 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, but the position of the outer surface of the pump chamber 1 may be inside.

The shape of the artificial impermeable layer 4 described above is defined so as to optimize the thickness of the artificial impermeable layer 4 according to the distribution of the bending moment and the shearing force generated in the artificial impermeable layer 4 due to the lifting pressure of the groundwater. As a result, the amount of improved soil in the artificial impermeable layer 4 can be reduced, and the construction period and cost can be suppressed.

That is, when the lifting pressure A of the groundwater 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 shear force S (t / m) generated in the artificial impermeable layer 4 when the simple beam is formed. The shear force S shows an absolute value.

FIG. 5C 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, and h1 and h2 are shown respectively. It can be calculated by the following equations (1) and (2). In the formulas (1) and (2), b (m) is a unit length in the depth direction of the improved soil (corresponding to the paper normal direction as shown in FIG. 5A), and for example, b = 1. In addition, σ (tf / m ² ) and τ (tf / m ² ) are the allowable compressive stress and the allowable shear stress 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 shearing force S generated in the artificial impermeable layer 4 increases at the position of the retaining wall 3. , The bending moment M becomes large in the middle portion between the mountain retaining walls 3. Further, 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.

As shown by the solid line B in FIG. 5C, 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 required for the bending moment M and the shearing force S. As a result of considering that all of the improved thickness h2 is satisfied and the amount of improved soil is reduced as much as possible, the artificial impermeable layer 4 is formed thickly at the position of the mountain retaining wall 3 as described above, and the artificial impermeable layer 4 is formed thickly between the mountain retaining walls 3. The artificial impermeable layer 4 is formed in a convex shape upward so that the artificial impermeable layer 4 is formed thinner than that in the intermediate portion.

As a result, as compared with the case where the ground improvement thickness is made constant according to the maximum value of the required ground improvement thickness as shown by the chain line C in FIG. 5 (c) (the lower surface of the artificial impermeable layer 4 is horizontal). The amount of improved soil can be reduced by about 30%.

Instead of the artificial impermeable layer 4 of the present embodiment, it is also possible to use an artificial impermeable layer having an inverted shape of the artificial impermeable layer 4, which is an example of FIGS. 6 and 7 described later. But the same is true. For example, in the present embodiment, the ground improvement thickness shown in the solid line B can be realized by turning the artificial impermeable layer 4 upside down so that the lower surface is horizontal and the upper surface is convex downward.

As described above, according to the present embodiment, due to the convex shape of the artificial impermeable layer 4, artificial immobility is performed according to the distribution of the shear force S and the bending moment M generated in the artificial impermeable layer 4 due to the lifting pressure A of the groundwater. The thickness of the permeable layer 4 can be optimized, the amount of improved soil and the like can be reduced, and the construction period and cost can be suppressed.

That is, when the lifting pressure A of the groundwater is uniformly applied to the artificial impermeable layer 4, the shearing force S generated in the artificial impermeable layer 4 by the lifting pressure A increases at the position of the retaining wall 3, and the bending moment M is a mountain. It becomes larger in the middle part between the retaining walls 3. When 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 M, the artificial portion between the mountain retaining walls 3 is artificial. 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 for the distribution of the shearing force S and the bending moment M described above.

Further, in the present embodiment, since the end portion of the artificial impermeable layer 4 on the mountain retaining wall 3 side is thickened in order to withstand the shearing force S, the artificial imperfections that behave integrally with the mountain retaining wall 3 and function as a substantial fulcrum. It is also expected that the range of the permeable layer 4 will be expanded inward, the substantial distance between the fulcrums will be reduced, and the maximum value of the bending moment M generated in the artificial permeable layer 4 will be reduced. Therefore, it is possible to reduce the thickness of the artificial impermeable layer 4 in the intermediate portion between the mountain retaining walls 3.

Further, in the present embodiment, since the artificial impermeable layer 4 is formed by improving the ground, the inclined surface 41 can be a stepped one composed of a plurality of step portions 411.

However, the present invention is not limited to this. For example, the shape of the artificial 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 shearing force S, and the amount of improved soil is reduced as much as possible. It may be determined, and is not limited to that shown in the above 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 made into a substantially arcuate curved surface which is convex 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 stepped 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 lifting pressure A of the groundwater is small or when the strength of the improved soil is high. When 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 is convex downward, and the artificial imperfections in the intermediate portion between the mountain retaining walls 3 are formed. The thickness of the permeable layer 4b may be larger than the thickness at the position of the retaining wall 3. The inclined surface 44 on the lower surface of the artificial impermeable layer 4b is formed in a stepped manner by a plurality of stepped portions as in the example of FIG.

Further, the present embodiment has been described with reference to an example of the pump chamber 1, but the present invention is not limited to this, and the intake pit provided on the upstream side of the pump chamber 1 and the seawater discharged from the turbine chamber are discharged to the flood channel. It can also be applied to water discharge pits. Further, the diversion wall 13 may be omitted.

Further, the present embodiment can be applied to the construction of other underground structures, and can also be applied to the construction of a box culvert 10 such as a road tunnel as shown in FIG. The box culvert 10 of FIG. 8 has a bottom slab 110, a side wall 120, a middle wall (or pillar) 130, and a top slab 140. FIG. 8 shows an example of a double-unit type box culvert 10, but it can be similarly applied to a quadruple-type box culvert, a single-unit type box culvert without a middle wall 130, and the like. The method for constructing the box culvert 10 is substantially the same as described above. However, after the top plate 140 is constructed, the upper part is backfilled with backfill soil.

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

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

[Second Embodiment]
In the second embodiment, as shown in FIG. 9, the upper surface and the lower surface of the artificial impermeable layer 4c are substantially arcuate curved surfaces that are convex downward, and the mountain retaining wall 3 on the upper surface and the lower surface of the artificial impermeable layer 4c. The height in the middle part between the two is lower than the height at the position of the mountain retaining wall 3. The inclined surfaces 45 and 46 on the upper surface and the lower surface of the artificial impermeable layer 4c are formed in a stepped manner by a plurality of stepped portions as in the example of FIG. Note that FIG. 9 shows a state in which the ground 2 between the mountain retaining walls 3 is excavated to the flooring position, and in the present 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 formed in an arch shape having a substantially arc that is convex downward, and the shape of the artificial impermeable layer 4c is optimized so that it can effectively resist the lifting pressure of groundwater. ..

That is, in the present embodiment, as shown in FIG. 10A, the arch-shaped artificial impermeable layer 4c resists the lifting pressure A of the groundwater by the axial compressive force N, and the force is transmitted to the mountain retaining wall 3. This makes it possible to impart high yield strength to the artificial impermeable layer 4c and suppress the thickness and strength of the artificial impermeable layer 4c.

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

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

W (t / m ² ) in the equation (4) is the value of the pumping pressure A of the groundwater. Further, R (m) is an 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. 10 (b)). ..
R = L ² / (8 · h) + h / 2 ... (5)

As described above, in the present embodiment, the arch-shaped artificial impermeable layer 4c resists the lifting pressure A of the groundwater by its axial compressive force N, thereby imparting a high yield strength to the artificial impermeable layer 4c and artificially impermeable. 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, but in the present embodiment, the entire artificial impermeable layer 4c can be thinned, so that it is the first. The amount of improved soil can be reduced as compared with the embodiment. Further, in this embodiment as well, 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, but as a result of thinning the artificial impermeable layer 4c, the rooting depth of the mountain retaining wall 3 becomes smaller and the construction period And costs can be reduced.

In addition, after satisfying the above-mentioned ground improvement thickness t, the thickness of the artificial impermeable layer 4c at the position of the mountain retaining wall 3 is made larger than the intermediate portion between the mountain retaining walls 3 as in the first embodiment. It is also possible. Further, also in the above-mentioned example of FIG. 7, in the case where the lifting pressure of the groundwater becomes large and cracks occur on the upper surface, an arch-shaped resistance mechanism that resists the lifting pressure is generated by the axial compressive force as in the present embodiment. it is conceivable that.

[Third Embodiment]
The third embodiment is an example in which the bending moment and the shearing force generated in the artificial impermeable layer are reduced by using the intermediate pile for supporting the girder, and the construction period and the cost required for the artificial impermeable layer are reduced.

That is, in the present embodiment, when constructing the pump chamber, first, as shown in FIG. 11A, the mountain retaining wall 3 and the intermediate pile 5 are constructed on the ground 2.

The intermediate pile 5 (also referred to as an intermediate column) is a vertical steel material to be placed between the mountain retaining walls 3 and is used to support the girder. In the present embodiment, the intermediate pile 5 is provided at the center of the span of the mountain retaining wall 3. For example, H-shaped steel is used as the intermediate pile 5, and the lower end thereof is fixed by a fixing portion 6 made of concrete or the like.

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. 11B to form an artificial impermeable layer 4'. As a result, a ground improvement structure including the artificial impermeable layer 4'is formed.

The artificial impermeable layer 4'is formed at a depth corresponding to the bottom of the mountain retaining wall 3, and the positions of the lower end of the artificial impermeable layer 4'and the lower end of the mountain retaining wall 3 are substantially the same as described above. Further, the lower portion 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 located deeper than the artificial impermeable layer 4'.

After forming the artificial impermeable layer 4', excavation of the ground 2 between the mountain retaining walls 3 and installation of the girder 7 are repeated as shown in FIGS. 12 (a) and 12 (b). One end of the girder 7 is connected to the mountain retaining wall 3 via the abdominal raised 70, and the other end is attached to the intermediate pile 5. As a result, the girder 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). When constructing the pump chamber 1a, the intermediate pile 5 and the girder 7 are removed at an appropriate time. For example, the cutting beam 7 is removed in order from the bottom according to the construction of the bottom slab 11 and the side wall 12 of the pump chamber 1a in order from the bottom, the side wall 12 is constructed to the top, and then the intermediate pile 5 is cut and removed on the bottom slab 11. Then, the diversion wall 13 is constructed.

In the present 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 anchored to the ground 2 below the artificial impermeable layer 4'by the portion deeper than the artificial impermeable layer 4'of the intermediate pile 5. Then, a resistance force against the lifting pressure of the groundwater is applied to the artificial impermeable layer 4'at the position of the intermediate pile 5 to prevent the artificial impermeable layer 4'from rising.

As a result, as shown in FIG. 14, a fulcrum (indicated by ▽ in the figure) supporting the artificial impermeable layer 4'with respect to the lifting pressure A of the groundwater is added to the position of the mountain retaining wall 3 and the position of the intermediate pile 5. Can be newly formed with.

In the conventional structure, the fulcrum of the artificial impermeable layer 4'is only at the position of the mountain retaining wall 3, and the distance between the fulcrums is separated (span) from the mountain retaining wall 3, but it is lifted to the position of the intermediate pile 5. By adding a new fulcrum that resists the pressure A, the distance between the fulcrums becomes half of the conventional one. 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 of the conventional values, respectively.

As a result, the artificial impermeable layer 4'can be thinned or its strength can be suppressed, and the construction period and cost required for the artificial impermeable layer 4'can be suppressed. As for the shape of the artificial impermeable layer 4', since the position of the intermediate pile 5 becomes a new fulcrum as described above, the shape similar to that of 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.

As described above, according to the present embodiment, the artificial impermeable layer 4'is provided with resistance to the lifting pressure A of the groundwater between the mountain retaining walls 3 by using the intermediate pile 5 for supporting the cutting beam 7. , A fulcrum that supports the artificial impermeable layer 4'with respect to the lifting pressure A can be newly formed. As a result, the distance between the fulcrums of the artificial impermeable layer 4'is reduced, and the bending moment and shearing force generated in the artificial impermeable layer 4'due to the lifting pressure A of the groundwater can be reduced. Therefore, the artificial impermeable layer 4'can be thinned or the strength can be suppressed, and the construction period and cost required for the artificial impermeable layer 4'can be further suppressed.

Since the intermediate pile 5 also has the purpose of preventing buckling of the cutting beam 7, when the span of the mountain retaining wall 3 is large, a plurality of intermediate piles 5 may be arranged between the mountain retaining walls 3. be. For example, when two intermediate piles 5 are arranged so as to divide the span of the mountain retaining wall 3 into three as shown in FIG. 15A, the bending moment and the shearing force generated in the artificial impermeable layer 4 ”by the lifting pressure A of the groundwater. The maximum values of are 1/9 and 1/3 of the conventional ones, respectively. 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. 2 (b). A total of three are formed between each retaining wall 3 and the intermediate pile 5 and between the two intermediate piles 5.

Further, it is not necessary to make all the intermediate piles between the mountain retaining walls 3 function as fulcrums, and only a part of them may function as fulcrums. For example, when three intermediate piles are provided between the mountain retaining walls 3, only the central intermediate pile 5 has the configuration of the present embodiment as shown in FIG. 15 (b), and the other intermediate piles have the present embodiment. It can be a normal intermediate pile 5'with the lower end supported by the artificial impermeable layer 4', which does not have the structure of the above and does not function as a fulcrum. In this case, the shape of the artificial impermeable layer 4'has the same shape as that of the artificial impermeable layer 4 described in FIG. 2 (b) and the like, in total of two between each mountain retaining wall 3 and the central intermediate pile 5. It will be formed.

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

In the present embodiment, in each example, the shape of the artificial impermeable layer is the shape of the artificial impermeable layer 4 described in FIG. 2 (b) or the like, between the mountain retaining wall 3 and the intermediate pile 5, and the intermediate pile 5. The space is provided in any of the mountain retaining walls 3, but instead of this, other shapes such as the artificial impermeable layers 4a and 4b described with reference to FIGS. 6, 7, 9 and the like. The shape of 4c may be provided in any of the space between the mountain retaining wall 3 and the intermediate pile 5, the intermediate pile 5, and the mountain retaining wall 3. Even when there is a normal intermediate pile 5', as shown in FIGS. 15 (b) to 15 (d), regardless of the intermediate pile 5', between the mountain retaining wall 3 and the intermediate pile 5, between the intermediate piles 5, and the mountain retaining. The shapes of the artificial impermeable layers 4a, 4b, and 4c may be provided in any of the spaces 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).

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

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', but instead, the lower end of the ground anchor 8 is fixed with concrete or the like. The portion 6a is fixed to the ground 2 at a position deeper than the artificial impermeable layer 4', and the upper end of the ground anchor 8 is fixed to the top of the intermediate pile 5 and is tensioned.

As a result, the artificial impermeable layer 4'can be anchored to the ground 2 below it by using the ground anchor 8 and the intermediate pile 5, and the artificial impermeable layer 4'has resistance to the lifting pressure A of the groundwater as described above. A fulcrum that supports the artificial impermeable layer 4'with respect to the lifting pressure A can be newly formed at the position of the intermediate pile 5. Further, in this example, a high resistance force can be given by the tension force of the ground anchor 8.

Further, 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 is constructed as shown in FIG. 17 (b). By repeating the steps of excavation and placing concrete of the diversion wall 13 and installing the girder 7 as shown in FIG. 18 (a) in order from the top, the mountain retaining wall 3 as shown in FIG. 18 (b). The ground 2 between them may be excavated to the flooring position.

As a result, a concrete load can be applied to the artificial impermeable layer 4'from above via the intermediate pile 5, and the artificial impermeable layer 4'is given a resistance force against the lifting pressure A of the groundwater to give the position of the intermediate pile 5. A fulcrum can be formed in 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 flow diversion wall 13 is constructed in advance by the reverse winding method, only the bottom slab 11 and the side wall 12 of the pump chamber 1b are constructed here. Just do it. Further, unlike the above, the intermediate pile 5 is left without being removed.

In this example, since the fulcrum forming mechanism can be provided on the ground portion, the construction is easy, and the construction of the pump chamber 1b is started by constructing the concrete by the reverse winding method and using it as the main diversion wall 13 of the pump chamber 1b. It is also possible to prevent the extension of the construction period.

Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art can come up with various modified or modified examples within the scope of the technical idea disclosed in the present application, and these also naturally belong to the technical scope of the present invention. Understood.

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: Culvert 8: Ground anchor 10: Box culvert 11, 110: Bottom slab 12, 120: Side wall 13: Dividing wall 41, 43, 44, 45, 46: Inclined surface 42: Horizontal plane 130: Middle wall 140: Top slab 411: Step

Claims (6)

It is a ground improvement structure having an artificial impermeable layer formed by improving the ground with a solidifying material.
The artificial impermeable layer is supported by the lifting pressure of groundwater at a plurality of fulcrums.
The fulcrum is a mountain retaining wall on both sides of the artificial impermeable layer, and the artificial impermeable layer is provided between the mountain retaining walls.
The upper surface of the artificial impermeable layer is a horizontal plane.
The lower surface of the artificial impermeable layer is a ground improvement structure characterized in that it is formed in a convex shape upward due to a difference in height between the height in the intermediate portion between the fulcrums and the height at the position of the fulcrum. The ground improvement structure according to claim 1, wherein the artificial impermeable layer has a different thickness at an intermediate portion between the fulcrums and a thickness at the position of the fulcrum. The ground improvement structure according to claim 1 or 2, wherein the lower surface is formed in an arc shape that is convex upward. Inclined surfaces are provided at both ends of the lower surface on the fulcrum side.
A horizontal plane is provided in the middle portion of the lower surface, and a horizontal plane is provided.
The inclined surface is inclined so as to become higher toward the intermediate portion side.
The ground improvement structure according to claim 1 or 2, wherein the horizontal plane connects the upper ends of the inclined surfaces to each other. Any of claims 1 to 4, wherein 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 stepped manner by a plurality of step portions. Ground improvement structure described in Crab. The step (a) of improving the ground with a solidifying material to provide an artificial impermeable layer, and
The step (b) of excavating the ground above the artificial impermeable layer and
Have,
The artificial impermeable layer is supported by the lifting pressure of groundwater at a plurality of fulcrums.
The fulcrum is a mountain retaining wall on both sides of the artificial impermeable layer, and the artificial impermeable layer is provided between the mountain retaining walls.
The upper surface of the artificial impermeable layer is a horizontal plane.
An excavation method characterized in that the lower surface of the artificial impermeable layer is formed in an upward convex shape due to a difference in height at an intermediate portion between the fulcrums and a height at the position of the fulcrum.

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