Pavement structure for suppressing frost heave and construction method for pavement structure

Abstract

To provide a pavement structure for suppressing frost heave.SOLUTION: A pavement structure 2 comprises a crushed stone layer 6 laid above a roadbed 4, a surface layer 8 laid above the crushed stone layer 6, and a water absorptive sheet 10 placed at a boundary between the crushed stone layer 6 and the surface layer 8 or in the crushed stone layer 6.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pavement structure that suppresses frost heave, and a method for constructing a pavement structure that suppresses frost heave. [Background technology]

[0002] Pavement structures such as roads, parking lots, and airport runways generally include a crushed stone layer laid above a roadbed and a top layer laid above the crushed stone layer.

[0003] In pavement structures built in cold regions, ice lenses can form inside the pavement structure when cold air penetrates the ground. These ice lenses grow gradually as moisture moves from the unfrozen parts. When the ice lenses reach a certain size, frost heave occurs, causing the surface of the pavement structure to rise, resulting in the problem of cracks in the pavement structure.

[0004] Therefore, various methods have been implemented to suppress frost heave, such as a replacement method in which materials that are less susceptible to frost heave are replaced, and a blocking method in which a water-impermeable layer is installed to prevent precipitation and groundwater from being replenished into the ground (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-247119 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, the snowmelt period in cold regions has been shortened due to the effects of global warming, and as a result, a large amount of meltwater flows into pavement structures in a short period of time. As a result, the moisture content in pavement structures increases rapidly during the snowmelt period, making frost heaving more likely to occur, and more effective methods of suppressing frost heaving are desired.

[0007] An object of the present invention is to provide a pavement structure that suppresses frost heave and a method for constructing a pavement structure that suppresses frost heave. [Means for solving the problem]

[0008] According to the present invention, there is provided the following pavement structure that solves the above problems. "A pavement structure that suppresses frost heave, A crushed stone layer laid above the roadbed; A surface layer laid above the crushed stone layer; The present invention provides a pavement structure comprising: a water-absorbent sheet disposed at the interface between the crushed stone layer and the surface layer or within the crushed stone layer.

[0009] Preferably, the water-absorbent sheet is installed on the upper part of the crushed stone layer. The crushed stone layer includes a lower roadbed laid on the upper surface of the roadbed and an upper roadbed laid on the upper surface of the lower roadbed, and the water-absorbent sheet is preferably installed at the boundary between the upper roadbed and the surface layer or in the upper roadbed. It is preferable that the water-absorbent sheet is installed on the upper part of the upper roadbed.

[0010] The water-absorbent sheet can be installed at a position deeper than the penetration depth of the asphalt emulsion spread on the upper surface of the crushed stone layer.

[0011] The absorbent sheet is preferably a water-absorbent reinforced sheet in which absorbent fibers are woven in a predetermined direction, and the water absorbed by the fibers is preferably guided in the predetermined direction. The absorbent sheet is preferably a water-absorbent reinforced sheet in which absorbent fibers are woven in a geotextile in a predetermined direction, and the water absorbed by the fibers is preferably guided in the predetermined direction.

[0012] In addition, according to the present invention, there is provided the following method for constructing a pavement structure, which solves the above problems. "A method for constructing a pavement structure that suppresses frost heave, laying a layer of crushed stone above the roadbed; A step of placing a water-absorbent sheet on the upper surface of the crushed stone layer or in the crushed stone layer; and laying a surface course over said crushed stone layer."

[0013] Preferably, the absorbent sheet is installed on the upper part of the crushed stone layer. As the crushed stone layer, a lower roadbed is laid on the upper surface of the roadbed, and an upper roadbed is laid on the upper surface of the lower roadbed, and the absorbent sheet is installed on the upper surface of the upper roadbed or in the upper roadbed. It is preferable to install the absorbent sheet on the upper part of the upper roadbed.

[0014] The water-absorbent sheet can be installed at a position deeper than the penetration depth of the asphalt emulsion spread on the upper surface of the crushed stone layer.

[0015] The absorbent sheet is preferably a water-absorbent reinforced sheet in which absorbent fibers are woven in a predetermined direction, and the water absorbed by the fibers is preferably guided in the predetermined direction. The absorbent sheet is preferably a water-absorbent reinforced sheet in which absorbent fibers are woven in a geotextile in a predetermined direction, and the water absorbed by the fibers is preferably guided in the predetermined direction. Effect of the Invention

[0016] According to the present invention, moisture that accumulates below the surface layer is absorbed by the absorbent sheet, suppressing an increase in the moisture content below the surface layer, thereby suppressing the formation or growth of ice lenses and suppressing frost heaving. [Brief description of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view showing an example of a pavement structure according to the present invention (an example in which an absorbent sheet is installed at the boundary between the crushed stone layer and the surface layer). [Diagram 2] 4 is a cross-sectional view showing another example of a pavement structure according to the present invention (an example in which an absorbent sheet is installed in a crushed stone layer). [Diagram 3] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, preferred embodiments of the pavement structure of the present invention will be described with reference to the drawings.

[0019] (Pavement Structure 2) As shown in FIGS. 1 and 2, the pavement structure 2 comprises a crushed stone layer 6 laid above a roadbed 4, a surface layer 8 laid above the crushed stone layer 6, and a water-absorbent sheet 10.

[0020] (Crush layer 6) The crushed stone layer 6 shown in FIG. 1 includes a lower roadbed 6a laid on the upper surface of the roadbed 4 and an upper roadbed 6b laid on the upper surface of the lower roadbed 6a. The material of the lower roadbed 6a may be crushed run, crushed run steel slag, recycled crushed run, cut gravel, mountain gravel, sand, etc. The material of the upper roadbed 6b may be size-adjusted crushed stone, size-adjusted steel slag, recycled size-adjusted crushed stone, hydraulic size-adjusted steel slag, etc. Although not shown, asphalt emulsion is sprayed on the upper surface of the crushed stone layer 6 (the upper surface of the upper roadbed 6b in the illustrated embodiment). The crushed stone layer 6 may be a single layer instead of a two-layer structure having the lower roadbed 6a and the upper roadbed 6b.

[0021] (Surface layer 8) The surface layer 8 may be composed of an asphalt layer or a concrete layer. FIG. 1 and FIG. 2 show an example in which the surface layer 8 is an asphalt layer. The illustrated surface layer 8 has a base layer 8a laid on the upper surface of the upper roadbed 6b, and a surface layer 8b laid on the upper surface of the base layer 8a. However, the surface layer 8 may be a single layer, not a two-layer structure having the base layer 8a and the surface layer 8b.

[0022] Both the base layer 8a and the surface layer 8b of the surface layer 8 may be composed of an asphalt mixture. The aggregate grain size of the base layer 8a may be different from that of the surface layer 8b. The asphalt mixture constituting the base layer 8a and the surface layer 8b may be a room temperature asphalt mixture, but it is preferable to use a heated asphalt mixture, which is more durable than a room temperature asphalt mixture. Although not shown, an asphalt emulsion is sprayed on the upper surface of the base layer 8a.

[0023] (Water-absorbent sheet 10) The absorbent sheet 10 may be placed at the boundary between the crushed stone layer 6 and the surface layer 8 (see FIG. 1), or may be placed in the crushed stone layer 6 (see FIG. 2). When the absorbent sheet 10 is placed in the crushed stone layer 6 as shown in FIG. 2, it is preferable that the absorbent sheet 10 is placed in the upper part of the crushed stone layer 6 (above the vertical middle part of the crushed stone layer 6).

[0024] When the crushed stone layer 6 includes a lower subgrade 6a and an upper subgrade 6b as in the illustrated embodiment, the water-absorbent sheet 10 may be placed at the boundary between the upper subgrade 6b and the surface layer 8 (see FIG. 1), or placed in the upper subgrade 6b (see FIG. 2). When the water-absorbent sheet 10 is placed in the upper subgrade 6b, it is preferable that the water-absorbent sheet 10 is placed in the upper portion of the upper subgrade 6b (above the vertical middle portion of the upper subgrade 6b).

[0025] In the illustrated example, the water-absorbent sheet 10 is installed substantially horizontally, but the water-absorbent sheet 10 may be installed inclined with respect to the horizontal plane. In addition, the water-absorbent sheet 10 may be installed in a folded state so as to have locally inclined or vertical portions.

[0026] The water-absorbent sheet 10 is preferably placed at a position deeper than the penetration depth of the asphalt emulsion spread on the upper surface of the crushed stone layer 6 (at a position not reached by the asphalt emulsion). This makes it possible to prevent a decrease in the water-absorbing function of the water-absorbent sheet 10 due to the asphalt emulsion soaking into the water-absorbent sheet 10.

[0027] The absorbent sheet 10 may be a woven or nonwoven fabric made of synthetic resin. As shown in Fig. 3, the illustrated absorbent sheet 10 has absorbent fibers 10a woven in a predetermined direction (the direction indicated by the arrow X in Fig. 3), and the fibers 10a guide the water absorbed in the predetermined direction (X direction). It is preferable that the fibers 10a have hydrophilicity in addition to absorbency.

[0028] Examples of materials for the fibers 10a of the water-absorbent sheet 10 include nylon, polyester, polyolefin, cellulose ester, etc. As shown in Fig. 3, the fibers 10a form a plurality of lines extending in the X direction at intervals in the direction indicated by the arrow Y in Fig. 3 (the vertical direction in Fig. 3, which is a direction perpendicular to the X direction). Each of the plurality of lines formed by the fibers 10a (a single line) is composed of a large number of fibers 10a. Moreover, the plurality of lines formed by the fibers 10a are parallel to one another.

[0029] The water-absorbent sheet 10 may be a water-absorbent reinforcing sheet in which absorbent fibers 10a are woven into a main portion 10b formed as a geotextile. This allows the water-absorbent sheet 10 placed on the pavement structure 2 to not only absorb and discharge groundwater and infiltration water (infiltration water that infiltrates into the pavement structure 2 from the surface and sides of the pavement structure 2) in the pavement structure 2, but also to reinforce the pavement structure 2. Examples of materials that can be used for the main portion 10b include polyolefins such as polypropylene and polyethylene, and polyester.

[0030] In the water-absorbent sheet 10, water is absorbed into the gaps between the fibers 10a forming a single line by capillary action, and the absorbed water is guided in a predetermined direction (X direction) into the gaps between the fibers 10a. The water-absorbent sheet 10 may also be configured such that one or more recesses (not shown) extending in the longitudinal direction (X direction) of the fibers 10a are formed in each of the fibers 10a, so that water is absorbed into the recesses of the fibers 10a by capillary action and the water is transported in the predetermined direction (X direction) via the recesses of the fibers 10a.

[0031] In the water-absorbent sheet 10, the fibers 10a absorb water by capillary action, and therefore, not only can the water-absorbent sheet 10 absorb moisture from the upper part thereof, but also can draw up moisture from the lower part thereof against gravity.

[0032] The illustrated absorbent sheet 10 has drainage sections 10c at both ends in the Y-axis direction that drain the water absorbed by the fibers 10a. Since the drainage sections 10c are connected to the outside of the pavement structure 2, the water absorbed by the absorbent sheet 10 is drained to the outside of the pavement structure 2 from the drainage sections 10c.

[0033] Alternatively, if a suitable drainage means such as a drainage ditch (not shown) is provided inside the pavement structure 2, the drainage portion 10c of the water-absorbent sheet 10 may be connected to the drainage means. In this case, the water absorbed by the water-absorbent sheet 10 is discharged to the outside of the pavement structure 2 through the drainage means.

[0034] In addition, drainage portions may be provided in parts of the absorbent sheet 10 other than both ends in the Y-axis direction by connecting the parts other than the ends of the absorbent sheet 10 to the outside of the pavement structure 2 or to drainage means, etc.

[0035] Generally, in pavement structures, when the temperature of the surface layer rises due to solar radiation, the moisture present in the roadbed and crushed stone layer turns into water vapor and rises through the gaps in the roadbed and crushed stone layer. This water vapor is blocked by the surface layer, which has low permeability, such as the asphalt layer or concrete layer, and tends to accumulate below the surface layer (especially near the bottom surface of the surface layer) (capping effect of the surface layer).

[0036] In the pavement structure 2 of the illustrated embodiment, the water vapor rising from the roadbed 4 and crushed stone layer 6 is absorbed by the water absorbent sheet 10 and discharged to the outside, so that it is possible to suppress a local increase in moisture content below the surface layer 8. Therefore, the pavement structure 2 can suppress the formation or growth of ice lenses and suppress frost heaving. In addition, because a local increase in moisture content below the surface layer 8 is suppressed, it is also possible to suppress suction of the crushed stone layer 6.

[0037] As described above, since moisture tends to accumulate particularly near the underside of the surface layer 8, the water-absorbent sheet 10 is preferably placed in a position close to the boundary between the crushed stone layer 6 and the surface layer 8. However, from the viewpoint of suppressing a decrease in the water-absorbing function of the water-absorbent sheet 10 due to the penetration of the asphalt emulsion, it is more preferable that the water-absorbent sheet 10 be placed in a position deeper than the penetration depth of the asphalt emulsion spread on the upper surface of the crushed stone layer 6.

[0038] Next, a method for constructing the pavement structure 2 as described above will be described.

[0039] When constructing the pavement structure 2, first, a process of laying a crushed stone layer 6 above the roadbed 4 is carried out. In the illustrated embodiment, the crushed stone layer 6 includes a lower roadbed 6a and an upper roadbed 6b, so in this process, the lower roadbed 6a is laid on the upper surface of the roadbed 4, and then the upper roadbed 6b is laid on the upper surface of the lower roadbed 6a.

[0040] When laying the lower roadbed 6a on the upper surface of the roadbed 4, for example, roadbed material carried in by a dump truck is spread on the upper surface of the roadbed 4 using a leveling vehicle such as a motor grader, and then compacted by a rolling vehicle. This allows the upper surface of the lower roadbed 6a to be finished flat. Similarly, the upper roadbed 6b can be laid by spreading the roadbed material for the upper roadbed 6b carried in by a dump truck on the upper surface of the lower roadbed 6a and then compacting it.

[0041] Next, after laying the crushed stone layer 6, the water-absorbent sheet 10 is placed on the upper surface of the crushed stone layer 6 (i.e., the upper surface of the upper roadbed 6b) (see FIG. 1). Alternatively, the water-absorbent sheet 10 may be placed in the crushed stone layer 6 when laying the crushed stone layer 6. When placing the water-absorbent sheet 10 in the crushed stone layer 6, it is preferable to place the water-absorbent sheet 10 on the upper part of the crushed stone layer 6 (the upper part of the upper roadbed 6b).

[0042] The depth at which the absorbent sheet 10 is installed should be deeper than the depth at which the asphalt emulsion spread on the top surface of the crushed stone layer 6 penetrates. This makes it possible to prevent the absorbent sheet 10 from losing its absorbency due to the asphalt emulsion soaking into the absorbent sheet 10.

[0043] In the pavement structure 2 constructed in this manner, the water vapor rising from the roadbed 4 and crushed stone layer 6 is absorbed by the water absorbent sheet 10 and discharged to the outside, thereby suppressing a local increase in moisture content below the surface layer 8. Therefore, the pavement structure 2 can suppress the formation or growth of ice lenses and suppress frost heaving. In addition, because a local increase in moisture content below the surface layer 8 is suppressed, suction of the crushed stone layer 6 can also be suppressed.

[0044] In addition, in snowy regions, de-icing agents are spread on paved roads in the winter. Because these agents contain salt, the salt concentration in groundwater and seepage water can increase, causing the salt to crystallize.

[0045] In this regard, in the water-absorbent sheet 10, the water-absorbent fibers 10a absorb the groundwater and infiltrating water in the pavement structure 2 by capillary action, but do not absorb crystallized salt, so that even if the salt concentration of the groundwater and infiltrating water increases and the salt crystallizes, the fibers 10a of the water-absorbent sheet 10 are unlikely to become clogged, and the water-absorbing function of the water-absorbent sheet 10 is hardly reduced. Similarly, the water-absorbent sheet 10 also prevents fine soil particles from flowing into the fibers 10a from the roadbed 4 or crushed stone layer 6. Therefore, in the pavement structure 2, the formation or growth of ice lenses can be suppressed for a long period of time, and frost heaving can be suppressed. [Explanation of symbols]

[0046] 2: Pavement structures 4: Roadbed 6: Crushed stone layer 6a: Lower roadbed 6b: Upper roadbed 8: Surface layer 8a: Base layer 8b: Surface layer 10: Water-absorbent sheet 10a: Fiber 10b: Main part of absorbent sheet 10c: Drainage section of absorbent sheet

Claims

1. A pavement structure that suppresses frost heave, A crushed stone layer laid above the roadbed; A surface layer laid above the crushed stone layer; A pavement structure comprising an absorbent sheet placed at the boundary between the crushed stone layer and the surface layer or in the crushed stone layer.

2. 2. The pavement structure according to claim 1, wherein the water-absorbent sheet is placed on an upper portion of the crushed stone layer.

3. The crushed stone layer includes a lower roadbed laid on an upper surface of the roadbed, and an upper roadbed laid on an upper surface of the lower roadbed, 2. The pavement structure according to claim 1, wherein the water-absorbent sheet is installed at a boundary between the upper subgrade and the surface course or in the upper subgrade.

4. The pavement structure according to claim 3 , wherein the water-absorbent sheet is installed on an upper portion of the upper roadbed.

5. 2. The pavement structure according to claim 1, wherein the absorbent sheet is placed at a position deeper than the penetration depth of the asphalt emulsion spread on the upper surface of the crushed stone layer.

6. 2. The pavement structure according to claim 1, wherein the absorbent sheet has absorbent fibers woven in a predetermined direction, and the absorbent fibers guide water absorbed in the predetermined direction.

7. 2. The pavement structure according to claim 1, wherein the absorbent sheet is an absorbent reinforcement sheet in which absorbent fibers are woven into a geotextile along a predetermined direction, and the water absorbed by the fibers is guided in the predetermined direction.

8. A method for constructing a pavement structure that suppresses frost heave, comprising the steps of: laying a layer of crushed stone above the roadbed; A step of placing a water-absorbent sheet on the upper surface of the crushed stone layer or in the crushed stone layer; and laying a surface layer above said crushed stone layer.

9. The method for constructing a pavement structure according to claim 8, further comprising placing the water-absorbent sheet on an upper portion of the crushed stone layer.

10. As the crushed stone layer, a lower roadbed is laid on the upper surface of the roadbed, and an upper roadbed is laid on the upper surface of the lower roadbed; The method for constructing a pavement structure according to claim 8, further comprising placing the water-absorbent sheet on an upper surface of the upper subgrade or in the upper subgrade.

11. The method for constructing a pavement structure according to claim 10, further comprising placing the water-absorbent sheet on an upper portion of the upper subgrade.

12. 9. The method for constructing a pavement structure according to claim 8, wherein the absorbent sheet is placed at a position deeper than the penetration depth of the asphalt emulsion spread on the upper surface of the crushed stone layer.

13. 9. The method for constructing a pavement structure according to claim 8, wherein the absorbent sheet has absorbent fibers woven in a predetermined direction, and the absorbed water is guided in the predetermined direction by the fibers.

14. The method for constructing a pavement structure as described in claim 8, wherein the absorbent sheet is an absorbent reinforcement sheet in which absorbent fibers are woven into a geotextile along a predetermined direction, and water absorbed by the fibers is guided in the predetermined direction.

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