JP7452877B2 - Linear structures and construction methods for linear structures - Google Patents

Description

The present invention relates to a linear structure on soft ground whose upper surface is used as a road or railway, and a method of constructing the linear structure.

A linear structure on soft ground whose upper surface is used as a road or railway consists of an embankment located below the road or railway, and a foundation structure located below the embankment.

In Japan, the construction of new roads on soft ground is carried out based on the Japan Road Association's guidelines for "road earthwork countermeasures against soft ground" (Non-Patent Document 1).

In the countermeasure construction method according to the above guidelines, the strength of the foundation structure is increased by mixing cement/lime-based additives with the surface soil of the soft ground and solidifying the ground using a chemical reaction. There are some that are constructed using a surface layer mixing treatment method (for example, see pages 298-302 of Non-Patent Document 1).

The said foundation structure by said surface layer mixing treatment method is generally formed in the shape of a thick plate with a required improvement depth (for example, see illustration 6-86 on p. 300 of Non-Patent Document 1). . The above-mentioned surface layer mixing method has the characteristic that it is easy to ensure necessary trafficability depending on the construction machine used (for example, p. 191 of Non-Patent Document 1).

On the other hand, some of the basic structures are made of lattice-like ground improvement bodies (for example, see Patent Document 1).

Patent No. 3853099

“Road earthworks - Guidelines for soft ground countermeasures (2012 edition)”, Japan Road Association, August 2012, p.187, p.191, p.202, p.298-302

When constructing the foundation structure using the surface mixing method, it is conceivable to make the ground improvement depth as shallow as possible in order to shorten the construction period and reduce construction costs. If the ground improvement depth is shallow, for example, the depth below the ground surface is about 4 m or less, there will be a problem of subsidence for linear structures on soft ground, so it is necessary to reduce the maximum subsidence and relative subsidence. There is.

The present invention reduces the maximum amount of settlement and the amount of relative settlement when the ground improvement depth below the ground surface is made shallow in a linear structure whose upper surface is used as a road or railway and which causes settlement on soft ground. The purpose is to

When constructing a new road, etc. on soft ground, the guidelines of the Japan Road Association (Non-Patent Document 1) and the prior art such as Patent Document 1 both consider reinforcement with only the local ground before embankment. There is.

The reason for this is that since high-quality soil is used for embankments, it is usually not considered to improve the embankments made of high-quality soil, and when improving the embankments, a step is created at the end of the embankment. Possible reasons include that it is difficult to press (pressure and shape), and that it is difficult to construct the embankment slope.

Based on many years of experience in designing improved ground, as well as numerous construction results and their evaluation results, the inventor of the present application aims to reduce the maximum amount of settlement and relative amount of settlement while making the depth of ground improvement below the ground surface as shallow as possible. We have conducted intensive studies on the structure of linear structures on soft ground that can be used for construction. As a result, they came up with the idea of performing ground improvement on embankments above the ground surface, and completed the present invention.

The linear structure according to the first aspect of the present invention is a linear structure whose upper surface is used as a road or a railway and which sinks on soft ground. The linear structure consists of a foundation structure below the ground surface and an embankment structure above the foundation structure. The foundation structure is a foundation ground improvement body obtained by improving the surface layer of the soft ground. The foundation ground improvement body includes a lattice-like ground improvement body whose depth below the ground surface is 4 m or less . The embankment structure is an embankment ground improvement body in which the embankment itself, which is good quality soil, is mixed and stirred with a solidification material to improve the ground of the embankment, which is good quality soil.

According to the linear structure according to the first aspect of the present invention, in the linear structure where subsidence occurs on soft ground, the foundation structure below the ground surface is a foundation ground improvement body containing a lattice-like ground improvement body. This is an embankment ground improvement system in which the embankment structure above the ground surface is made of high-quality soil. In addition to the ground improvement at the site, the embankment area was also ground improved, so the rigidity of the earthworks and embankment area was increased as a single unit. Moreover, the soil improvement of the field site includes a grid-like soil improvement body. Therefore, it is possible to disperse the stress transmitted to the subsurface soil, thereby reducing the amount of subsidence.

Furthermore, since the depth of the foundation ground improvement body below the ground surface is 4 m or less, it is possible to shorten the construction period and suppress construction costs while reducing the amount of subsidence.

A method for constructing a linear structure according to a second aspect of the present invention is a method for constructing a linear structure whose upper surface is used as a road or railway and which causes subsidence on soft ground. The linear structure consists of a foundation structure below the ground surface and an embankment structure above the foundation structure. The foundation structure is a foundation ground improvement body obtained by improving the surface layer of the soft ground. The foundation ground improvement body includes a lattice-like ground improvement body whose depth below the ground surface is 4 m or less . The embankment structure is an embankment ground improvement body in which the embankment itself, which is good quality soil, is mixed and stirred with a solidification material to improve the ground of the embankment, which is good quality soil. In the construction method, the surface layer of the soft ground is dug up by plowing with a backhoe, and a part of the excavated soil and a solidification material are mixed and stirred with a backhoe to improve the ground, and the foundation soil improvement body is improved. a step of constructing all or a part of the foundation ground improvement body, and a step of placing a large amount of embankment on all or part of the constructed foundation ground improvement body so as to overhang from the widthwise end of the embankment ground improvement body; The method includes a step of improving the ground by mixing and stirring the embankment and solidification material using a backhoe , and constructing the embankment ground improvement body. The step of constructing the embankment ground improvement body includes a step of forming a ground improvement body including an end ground improvement part whose ends in the width direction are approximately vertical, and a step of forming the ground improvement body including an end ground improvement part whose end part in the width direction is approximately vertical, and a step in which the initial strength of the end ground improvement part is developed. Thereafter, the method includes a step of excavating and shaping the end ground improvement portion to form an embankment slope.

According to the method for constructing a linear structure according to the second aspect of the present invention, the soil is dug into the surface layer of the soft ground by plowing with a backhoe, and a part of the dug soil and the solidification material are mixed and stirred with the backhoe. The process of constructing all or part of the basic ground improvement body including the lattice-shaped ground improvement body, and adding the width of the embankment ground improvement body on all or part of the constructed foundation ground improvement body . It consists of the process of laying a large amount of embankment so that it overhangs from the end of the direction, and the process of improving the ground by mixing and agitating the embankment, which is high quality soil, and solidification material with a backhoe , and constructing an embankment ground improvement body. With this construction method, in addition to improving the ground at the site, the embankment area is also improved, making the ground work and the embankment part more rigid. Moreover, the soil improvement of the field site includes a grid-like soil improvement body. Therefore, it is possible to disperse the stress transmitted to the subsurface soil, thereby reducing the amount of subsidence. Furthermore, since the depth of the foundation soil improvement body below the ground surface is 4 m or less, soil and solidification material can be mixed and stirred using a backhoe to improve the ground, reducing the amount of subsidence and reducing construction time. It is possible to shorten the time and control construction costs.

In addition, a large amount of embankment is applied so as to protrude from the widthwise end of the embankment base improvement body, and the process of constructing the embankment base improvement body is such that the widthwise end of the embankment base improvement body becomes approximately vertical. a step of forming a ground improvement body including a ground improvement section; and a step of excavating and shaping the end ground improvement section to form an embankment slope after the end ground improvement section has developed initial strength. . Therefore, it is possible to eliminate insufficient rolling pressure when constructing an embankment ground improvement body. Moreover, construction of the embankment slope of the embankment ground improvement body can be performed reliably, and since the embankment slope is strengthened, slope collapse can be suppressed.

According to the linear structure and the construction method for the linear structure described above, in a linear structure on soft ground whose upper surface is used as a road or railway, the ground improvement depth below the ground surface is made shallow. In this case, the maximum amount of settlement and the relative amount of settlement can be reduced.

FIG. 1 is a vertical cross-sectional view showing a linear structure of a first example according to an embodiment of the present invention, and a bottom view of the linear structure. They are a longitudinal cross-sectional view showing a linear structure of a second example according to an embodiment of the present invention, and a bottom view of the linear structure. They are a vertical sectional view showing a linear structure of a third example according to an embodiment of the present invention, and a bottom view of the linear structure. They are a longitudinal sectional view showing a linear structure of a fourth example according to an embodiment of the present invention, and a bottom view of the linear structure. FIG. 2 is an explanatory diagram showing a first step in a method for constructing a linear structure according to an embodiment of the present invention. It is an explanatory view showing the 2nd process in the construction method. It is an explanatory view showing the 3rd process in the construction method. It is an explanatory view showing the 4th process in the construction method. It is an explanatory view showing the 5th process in the construction method. It is an explanatory view showing the 6th process in the construction method. They are a longitudinal cross-sectional view showing a linear structure of a first comparative example, and a bottom view of the linear structure. They are a longitudinal sectional view showing a linear structure of a second comparative example and a bottom view of the linear structure. They are a longitudinal sectional view showing a linear structure of a third comparative example and a bottom view of the linear structure. They are a longitudinal sectional view showing a linear structure of a fourth comparative example and a bottom view of the linear structure.

Embodiments according to the present invention will be described below based on the drawings.

The upper surface of a linear structure on soft ground according to an embodiment of the present invention described below is used as a road. The horizontal direction perpendicular to the direction in which the road extends (direction of movement of vehicles on the road, see arrow F in the figure) is referred to as the "width direction" (see arrow B in the figure).

<Linear structure>
The longitudinal cross-sectional view and bottom view of the linear structure A in FIGS. 1 to 4 are the first to fourth examples according to the embodiment of the present invention. The linear structure A of the first embodiment in FIG. 1 and the second embodiment in FIG. 2 is an example in which the width W of the road R is 7 m. A linear structure A shows an example in which the width W of the road R is 14 m.

As shown in FIGS. 1 to 4, the linear structure A on the soft ground S consists of a foundation structure 1 below the ground surface GL and an embankment structure 2 above the foundation structure 1.

The foundation structure 1 is a foundation ground improvement body 3 in which the surface layer of the soft ground S is improved. The foundation ground improvement body 3 includes a lattice-like ground improvement body 4 whose depth below the ground surface GL is H1. The depth H1 is 4 m or less. The dimensions of the grid-like ground improvement body 4 in the direction F in which the road R extends are, for example, L1 = 8 to 12 m, L2 = 6 to 8 m, and L3 = 2 to 4 m.

The foundation ground improvement body 3 in the first embodiment shown in FIG. 1 and the third embodiment shown in FIG. 3 consists of a horizontal plate-shaped ground improvement body and a lattice-shaped ground improvement body 4 located below it. The foundation ground improvement body 3 in the second embodiment shown in FIG. 2 and the fourth embodiment shown in FIG. 4 does not have a horizontal plate-like ground improvement body, but only consists of a lattice-shaped ground improvement body 4.

The embankment structure 2 is an embankment ground improvement body 5 obtained by improving the ground of embankment. A road R consisting of asphalt a, an upper roadbed b, and a lower roadbed c is laid on the embankment ground improvement body 5.

<Construction method for linear structures>
An example of a method for constructing a linear structure A according to an embodiment of the present invention will be described with reference to explanatory diagrams in FIGS. 5 to 10. 5 to 10 show an example of a method for constructing the linear structure A in FIG. 1.

(1st step)
As shown in FIG. 5, the soil in the primary improvement section GI1 is dug into a desired shape by plowing with a backhoe 9.

(Second process)
Next, as shown in Fig. 6, ground improvement is carried out by adding and stirring a part of the soil of the primary improvement area GI1 that has been plowed out and a solidifying agent such as a cement-based solidifying agent using a backhoe 9. 10, level the top of the primary improvement section GI1 after ground improvement.

(3rd step)
Next, as shown in FIG. 7, the top end of the leveled primary improvement section GI1 is rolled by rollers 11, and backfilled with the soil plowed out by backhoe 9. The primary improvement section GI1 corresponds to the lattice-like ground improvement body 4 that is a part of the basic soil improvement body 3. When constructing the linear structure A in FIG. 2 instead of the linear structure A in FIG.

(4th step)
Next, as shown in FIG. 8, the embankment 6 is carried in by the dump truck 12 onto the primary improvement section GI1 corresponding to the grid-like ground improvement body 4 in FIG. A large amount of embankment 6 is placed so as to overhang from the end E in the width direction B of the embankment ground improvement body 5.

(5th step)
Next, as shown in FIG. 9, the ground is improved by adding and stirring the embankment 6 and a solidifying material such as a cement-based solidifying material using a backhoe 9, thereby forming a secondary improved portion GI2. At this time, the secondary improvement part GI2 is formed so as to include the end ground improvement part 7 in which the end part E in the width direction B is substantially vertical.

(6th step)
Next, as shown in FIG. 10, the bulldozer 10 levels the top of the secondary improvement section GI2 after ground improvement, and the roller 11 rolls the top of the leveled secondary improvement section GI2. In fact, the area where the road R is laid on the upper surface of the secondary improvement section GI2 is finished so that it is at the level of the lower surface of the lower roadbed c.

After the end ground improvement portion 7 has developed its initial strength, the end ground improvement portion 7 is excavated and shaped by a backhoe 9 to form an embankment slope SL. The initial strength development of the end ground improvement section 7 is determined based on the elapsed time after the ground improvement and the site conditions (surface hardness, etc.).

In the fourth step, a large amount of embankment 6 is applied so as to protrude from the end E in the width direction B of the embankment ground improvement body 5, and in the fifth step, the end portion E in the width direction B becomes approximately vertical. A secondary improved section GI2 is formed to include the improved section 7. Therefore, insufficient rolling pressure in the secondary improvement section GI2 in the sixth step can be eliminated. Moreover, in the sixth step, after the initial strength of the end ground improvement section 7 has been developed, the end ground improvement section 7 is excavated and shaped to form the embankment slope SL. Therefore, the embankment slope SL of the embankment ground improvement body 5 can be reliably constructed, and the embankment slope SL becomes strong, so slope collapse can be suppressed.

<Road construction method>
After performing the sixth step of the method for constructing the linear structure A and rolling the secondary improved portion GI2 to develop improved strength, the material for the lower roadbed c is brought in, leveled, and rolled. Next, the material for the upper roadbed b is brought in, leveled, and compacted. Next, asphalt a material is brought in, leveled, and rolled.

<Numerical analysis>
Next, a description will be given of numerical analysis performed to confirm the effects of the present invention.

(analysis method)
A two-dimensional numerical analysis will be performed using the ground FEM (Finite Element Method) analysis software (PLAXIS) with the parameters shown in Tables 1 and 2. The evaluation items are "maximum subsidence" and "relative subsidence".

(Example and comparative example)
The examples are the first example to the fourth example. The comparative examples are the first comparative example to the fourth comparative example shown in the vertical cross-sectional views and bottom views of the linear structure A in FIGS. 11 to 14. In each of the first to fourth comparative examples, the portion above the ground surface GL corresponding to the embankment structure 2 of the example is not the embankment ground improvement body 5 but the embankment 6.

In the linear structure A of the first comparative example in FIG. 11 and the third comparative example in FIG. 13, the foundation ground improving body 3 is a thick plate-like ground improving body 8. In the linear structure A of the second comparative example in FIG. 12 and the fourth comparative example in FIG. 14, the foundation ground improvement body 3 consists of only the grid-like ground improvement body 4.

(Loading condition)
The load is the weight of the embankment ground improvement body 5 or the embankment 6 and the road R, which are located above the ground surface GL and are long-term loads.

(Relative settlement amount)
The "relative settlement amount" in Example 1 in FIG. 1, Example 2 in FIG. 2, Comparative Example 1 in FIG. 11, and Comparative Example 2 in FIG. It's the difference.

The "relative sinking amount" in Example 3 of FIG. 3, Example 4 of FIG. 4, and Example 3 of FIG. 13 is the difference between the sinking amount of point Q1 and the sinking amount of point Q2.

The "relative sinking amount" in Comparative Example 4 in FIG. 14 is the difference between the sinking amount of Q3 and the sinking amount of Q2, since the sinking amount of Q3 is larger than the sinking amount of Q1.

(Analysis result)
The analysis results are shown in Tables 1 and 2.

(Analysis results in Table 1)
From Table 1, in the first comparative example and the second comparative example in which the embankment 6 is above the ground surface GL, the foundation In the second comparative example in which the ground improvement body 3 includes only the grid-like ground improvement body 4, the maximum settlement amount is the same, but the relative settlement amount is large, and the relative settlement amount is 3.8 times.

On the other hand, the embankment ground improvement body 5 is above the ground surface GL, and the foundation ground improvement body 3 is composed of a horizontal plate-shaped ground improvement body and a lattice-shaped ground improvement body 4 located below it. In this example, the maximum settlement amount is 0.79 times and the relative settlement amount is 0.27 times as compared to the first comparative example, and the maximum settlement amount and relative settlement amount are small.

In addition, in the second embodiment, in which the embankment ground improvement body 5 is above the ground surface GL and the foundation ground improvement body 3 is composed of only the lattice-like ground improvement body 4, the maximum amount of settlement is lower than that of the first comparative example. 0.82 times, and the relative settlement amount is 0.67 times, and the maximum settlement amount and relative settlement amount are small.

(Analysis results in Table 2)
From Table 2, in the third comparative example and the fourth comparative example where the embankment 6 is above the ground surface GL, the foundation ground improvement body 3 is the thick plate-like ground improvement body 8. In the fourth comparative example in which the ground improvement body 3 consists of only the grid-like ground improvement body 4, the maximum settlement amount is 0.94 times, but the relative settlement amount is large, and the relative settlement amount is 1.59 times.

On the other hand, the embankment ground improvement body 5 is above the ground surface GL, and the foundation ground improvement body 3 is a third implementation consisting of a horizontal plate-shaped ground improvement body and a lattice-shaped ground improvement body 4 located below it. In this example, the maximum settlement amount is 0.76 times and the relative settlement amount is 0.35 times as compared to the third comparative example, and the maximum settlement amount and relative settlement amount are small.

In addition, in the fourth embodiment, where the embankment ground improvement body 5 is above the ground surface GL and the foundation ground improvement body 3 is composed of only the lattice-like ground improvement body 4, the maximum amount of settlement is lower than that of the third comparative example. The maximum settlement amount and the relative settlement amount are small.

From the above analysis results, in addition to making the foundation structure 1 the foundation soil improvement body 3 including the lattice-like ground improvement body 4, as in the first to fourth embodiments of the present invention, When the ground improvement depth H1 below the ground surface GL is made shallow by making the upper part into the embankment ground improvement body 5 (for example, in Embodiments 1 to 4, H1 = 2 m), the maximum settlement amount and the relative settlement amount It can be seen that it is possible to significantly reduce the

In the linear structure A on soft ground S of the present invention, the foundation structure 1 below the ground surface GL is a foundation ground improvement body 3 including a lattice-like ground improvement body 4, and the embankment structure 2 above the ground surface GL is the embankment ground improvement body 5 obtained by improving the embankment 6. In addition to the ground improvement at the site, the embankment area was also ground improved, so the rigidity of the earthworks and embankment area was increased as a single unit. Moreover, the soil improvement of the field site includes a grid-like soil improvement body. Therefore, it is possible to disperse the stress transmitted to the subsurface soil, thereby reducing the amount of subsidence.

In the linear structure A on the soft ground S of the present invention, by setting the depth H1 of the foundation ground improvement body 3 below the ground surface GL to 4 m or less, the amount of subsidence can be reduced while reducing the construction period and construction cost. can be suppressed.

Although the linear structure in the description of the above embodiments has an upper surface used as a road, the linear structure of the present invention may have an upper surface used as a track.

The above description of the embodiments is all illustrative, and the present invention is not limited thereto. Various improvements and changes can be made without departing from the scope of the invention.

1 Foundation structure 2 Embankment structure 3 Foundation ground improvement body 4 Grid-like ground improvement body 4A Lower end face 5 Embankment ground improvement body 6 Embankment 7 End ground improvement part 8 Thick plate-like ground improvement body 9 Backhoe 10 Bulldozer 11 Roller 12 Dump A Linear structure B Width direction E End F Traveling direction GI1 Primary improvement section GI2 Secondary improvement section GL Ground surface R Road S Soft ground SL Embankment slope a Asphalt b Upper roadbed c Lower roadbed

Claims (2)

A linear structure whose upper surface is used as a road or railway and which is subject to subsidence on soft ground,
The linear structure consists of a foundation structure below the ground surface and an embankment structure on the foundation structure,
The foundation structure is a foundation ground improvement body in which the surface layer of the soft ground is improved,
The basic ground improvement body includes a lattice-like ground improvement body whose depth below the ground surface is 4 m or less ,
The embankment structure is an embankment ground improvement body in which the embankment, which is good quality soil, is ground-improved by mixing and stirring the embankment itself, which is good quality soil, and a solidification material.
Linear structure. A construction method for a linear structure whose upper surface is used as a road or railway and which causes subsidence on soft ground,
The linear structure consists of a foundation structure below the ground surface and an embankment structure on the foundation structure,
The foundation structure is a foundation ground improvement body in which the surface layer of the soft ground is improved,
The basic ground improvement body includes a lattice-like ground improvement body whose depth below the ground surface is 4 m or less ,
The embankment structure is an embankment ground improvement body in which the embankment, which is good quality soil, is ground-improved by mixing and stirring the embankment itself, which is good quality soil, and a solidification material ,
The surface layer of the soft ground is excavated by plowing with a backhoe, and a part of the excavated soil and a solidification material are mixed and stirred with a backhoe to improve the ground , and all or part of the basic ground improvement body is improved. The construction process and
A step of placing a large amount of embankment on all or part of the constructed foundation ground improvement body so as to overhang from the widthwise end of the embankment ground improvement body;
Improving the ground by mixing and stirring the embankment and solidification material with a backhoe , and constructing the embankment ground improvement body;
Consisting of
The step of constructing the embankment ground improvement body includes:
forming a ground improvement body including an end ground improvement part in which the width direction end part is substantially vertical;
After the initial strength of the end ground improvement section has been developed, excavating and shaping the end ground improvement section to form an embankment slope;
including,
Construction method for linear structures.

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