JP5916432B2 - Consolidation ground improvement method - Google Patents

Description

  The present invention relates to a consolidation ground improvement method for viscous ground such as clay clay.

Cohesive clay generated by dredging works has a lot of silt and clay, and its hydraulic conductivity is 10 ^-4 to 10 ^-8 cm / sec, which is very small compared to sand. For this reason, in clay soil disposal sites, after covering the soil on the clay soil ground, vertical drains are placed to promote consolidation settlement by embankment before use as land.

  Patent document 1 discloses the manufacturing method of the fiber mixed soil which disperse | distributes a fibrous substance uniformly. In other words, the fibrous material is dispersed in the earth and sand to give adhesive strength, and when this fiber mixed soil is used on the slope of embankment, erosion of the surface layer part due to wind and rain etc. is prevented, and the whole ground It is possible to obtain a reinforcing effect such as preventing slippage, and to prevent the entanglement of the stirring blade of the mixer when mixing the fibrous material in a lump form, so that sufficient mixing can be performed smoothly. Is disclosed.

  Patent Document 2 discloses a mixing method of earth and sand and fiber material in which earth and sand and reinforcing fiber material are uniformly mixed to form a fiber mixed soil. That is, by using a fiber mixed soil reinforced with a mixture of reinforcing fiber materials, it is possible to stably build an embankment structure having a steep slope that is impossible with ordinary earth and sand in a short construction period. It is disclosed that it is possible.

Japanese Patent Laid-Open No. 08-337776 JP 05-112941 A

  As described above, there is the following problem in the case where the vertical drain is placed and consolidated after the covering soil is constructed on the clay soil.

  (1) Since clay soil has low shear strength, it may not be possible to secure the stability (supporting force) of the ground when covering the soil, and geotextile may be used as an auxiliary method to spread over the ground.・ There is a problem of cost.

  (2) After covering the soil, it is indispensable to place a drain to promote settlement during embankment. When the thickness of the disposed clay soil is about 3-5m, the drain unit length There is a problem that the installation cost per 1 meter is high.

  Patent Documents 1 and 2 disclose a method for producing a fiber-mixed soil in which fibrous substances are uniformly dispersed in the earth and sand. However, the method is to reinforce the fiber-mixed soil itself, and after constructing a cover soil on the clay soil ground. However, it does not solve the above-mentioned problem when a vertical drain is placed and consolidation is performed.

  In view of the problems of the prior art as described above, the present invention improves the stability of the ground when disposing clay soil with a small hydraulic conductivity, etc., or eliminates the need for a conventional drain placement, Alternatively, an object is to provide a consolidation ground improvement method that can be reduced.

In order to achieve the above-mentioned object, the consolidation ground improvement method according to the present embodiment uses 20 to 40 short fiber materials having water permeability to viscous soil having a water permeability coefficient in the range of 10 ⁻⁴ to 10 ⁻⁸ cm / sec. By mixing uniformly at a mixing amount of%, a short fiber mixed soil having a water permeability coefficient larger than that of cohesive soil is produced, and a consolidation treatment is performed on the ground on which the short fiber mixed soil is placed. However, the said mixing amount is based on following Formula .
Mixing amount (%) = dry weight of the short fiber material × 100 / (dry weight of the clay soil + dry weight of the short fiber material)

According to this consolidation ground improvement method, water-permeable short fiber material is uniformly mixed with viscous soil such as clay-viscous soil with a water permeability coefficient in the range of 10 ^-4 to 10 ^-8 cm / sec. Since the shear strength of the short fiber mixed soil increases due to the effect of increasing the shear strength by the short fiber material and the effect of decreasing the water content ratio due to water absorption, the stability of the ground can be improved. In addition, since the short fiber mixed soil has a larger water permeability coefficient than the viscous soil, the compacting time can be shortened in the consolidation process performed after the short fiber mixed soil is placed in a disposal site, for example. It is possible to eliminate or reduce the number of drains that need to be placed. As a result, the cost for drain improvement can be eliminated or reduced.
Another consolidation ground improvement method according to the present embodiment is that uniform permeability of short fiber material with water permeability is evenly mixed at a mixing amount of 20 to 40% on viscous soil having a water permeability coefficient in the range of 10 ⁻⁴ to 10 ⁻⁸ cm / sec. By mixing with the soil, a short fiber mixed soil having a hydraulic conductivity larger than that of the viscous soil is produced, and the consolidation method by the drain method alone or in combination with the load method and the drain method in the ground where the short fiber mixed soil is placed It is characterized by performing . However, the said mixing amount is based on following Formula .
Mixing amount (%) = dry weight of the short fiber material × 100 / (dry weight of the clay soil + dry weight of the short fiber material)

  In the consolidation ground improvement method, the short fiber material is preferably a vegetable fiber having a water-permeable conduit. As such a short fiber material, for example, straw, wood chip, peat moss and the like can be used.

  The short fiber material preferably has a fiber length of 2 mm or more and 10 cm or less. When the fiber length of the short fiber material is 2 mm or more, the consolidation coefficient Cv of the short fiber mixed soil increases, and the shortening of the consolidation time is further improved. When the fiber length is 10 cm or less, the dispersibility of the short fiber material in the viscous soil is good.

  According to the consolidation ground improvement method of the present invention, when disposing clay soil with a small hydraulic conductivity, the stability of the ground is improved at the disposal site, etc. Or less.

It is a flowchart for demonstrating the process of the ground consolidation improvement construction method by this embodiment. It is a figure which shows typically an example of the preparation system of the short fiber mixed soil by mixing the clay and short fiber material in this embodiment. It is a figure which shows the result of having implemented the standard consolidation test about the mixed soil which mixed the peat moss for gardening used as a short fiber material in Example 1 with the viscous soil, and is a graph which shows the relationship between an average consolidation pressure and a hydraulic conductivity. It is a graph which shows the relationship between an average consolidation pressure and a consolidation coefficient similarly to FIG. It is a graph which shows the relationship between the short fiber mixing amount in mixed soil (modified soil) of Example 1, and time until it becomes 80% of pressure density (U = 80%). It is a graph which shows the relationship between the consolidation pressure and gap ratio which were obtained by implementing a standard consolidation test about the mixed soil (modified soil) which mixed the short fiber material which changed fiber length in Example 2 with marine clay. . It is a graph which shows the relationship between an average consolidation pressure and a hydraulic conductivity similarly to FIG. It is a graph which shows the relationship between an average consolidation pressure and a consolidation coefficient similarly to FIG.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a flowchart for explaining the steps of the ground consolidation improvement method according to the present embodiment.

  As shown in FIG. 1, the ground consolidation improvement method according to the present embodiment performs dredging work in harbors, rivers, canals, etc. (S01), transports the dredged soil, and uniformly mixes it with a large amount of short fiber materials. (S02) A short fiber mixed soil is prepared (S03). This short fiber mixed soil is placed in a disposal site (S04), and a consolidation process is performed by a load-loading method or the like performed by embankment on the soil (S05).

  Next, the process of producing the short fiber mixed soil by mixing the clay and the short fiber material will be described with reference to FIG. FIG. 2 is a diagram schematically showing an example of a short fiber mixed soil production system by mixing clay and short fiber materials in the present embodiment.

  As shown in FIG. 2, the dredged material 11 generated by dredging work is transported by the transport ship SP, and transferred to the storage unit ST through the screen SC by the backhoe BC. Moreover, the short fiber material 12 is moved to the storage part ST by the additive automatic supply device SY. These mixtures are dropped from the storage unit ST and sent to the paddle mixer MX by the belt conveyor VC. The paddle mixer MX mixes the clay 11 and the short fiber material 12 while rotating the two shafts with the paddles, and sends them to the discharge port.

As the short fiber material 12, for example, those derived from plants such as straw, wood chips, peat moss, and the like can be used, and these are fibers having a water-permeable conduit inside, and the fiber length is 10 cm. Hereinafter, it is preferably 2 mm or more. The short fiber material 12 has an in-plane water permeability coefficient (water permeability coefficient of water passing through the cross section of the short fiber material) that is larger than the hydraulic conductivity of clayey clay in the range of 10 ⁻⁴ to 10 ⁻⁸ cm / sec. However, it is preferable that the in-plane permeability coefficient is 100 times or more than that of the clay.

  Regarding the in-plane hydraulic conductivity, for example, in the case of a drain placed in the ground, even if the drain has a hollow core material inside, it is called the hydraulic conductivity, and after the drain is placed in the ground, the vertical hydraulic conductivity However, here, since the directionality of the pipe line in the short fiber material is not asked, it is called in-plane hydraulic conductivity.

  As described above, the clay 11 and the short fiber material 12 are uniformly mixed to produce the short fiber mixed soil 13. This short fiber mixed soil 13 is driven into the disposal site by the clam shell CS by operation of the crane CR. In addition, it is preferable to install the preparation system of the short fiber mixed soil of FIG. 2 near the disposal site.

  According to this embodiment, the embedding is performed on the modified soil (short fiber mixed soil) ground placed in the disposal site, and the consolidation process by the load-loading method is performed. By mixing a large number of short fiber materials whose internal hydraulic conductivity is larger than that of clayey soil, the hydraulic conductivity is more than 10 times larger than that of clayey soil. A compact consolidation process can be performed. For this reason, the consolidation process by the drain method is unnecessary, and the cost for the drain placement is not incurred.

  When the disposal site as described above is used as land later, the period until the land can be used can be shortened, the efficiency can be improved, and more economically than before. Furthermore, straw, wood chips and the like that can be used as short fiber materials are often used as waste, leading to effective use of waste.

  In addition, by mixing a large number of short fiber materials in clay soil, the shear strength of the short fiber material increases due to the effect of increasing the shear strength by the short fiber material and the effect of decreasing the water content by water absorption. The stability of the ground can be improved. For this reason, a conventional auxiliary method such as geotextile, which is necessary for securing the stability (supporting force) of the ground, becomes unnecessary.

  Further, the pressure density can be controlled by changing the mixing amount of the short fiber material to be mixed, and the same effect as changing the drain pitch in the drain method can be obtained. In addition, it is possible to improve the ground having a constant strength in a large amount, and in this case, since a solidifying material is not used, it is an economical ground improvement method.

  The consolidation method is a ground improvement method based on the principle that the water in the ground flows between the soil particles and is drained to increase the density. Up to now, drain methods such as vertical drain method and horizontal drain method have been developed as a method of promoting drainage, but in this embodiment, short fiber material that is permeable to soft clay soil By mixing these, consolidation characteristics equivalent to those of the conventional drain method can be obtained.

Next, under the following conditions, a drain is placed on the viscous ground and the consolidation treatment is performed, and the modified ground prepared by mixing the short fiber material as described above is subjected to the consolidation treatment by the loading method. Compare the consolidation time of both cases.
Conditions: Sink down to layer thickness H = 5m and average pressure density U = 80%.

(1) Consolidation time when drain material (converted diameter 5cm) is placed in a square layout of 0.6m (calculated by Barron's approximate solution)
Average consolidation coefficient = 10cm ² / day → U = 80% time t ₈₀ = 174 days

(2) Consolidation time for modified soil 30 (see Example 1 below) (calculated by Terzaghi theory)
Average consolidation factor = 250cm ² / day → U = 80% time t ₈₀ = 142 days

  As described above, it can be seen that the ground can be improved in substantially the same consolidation time under both conditions. Therefore, according to the present embodiment, it is possible to provide a ground improvement method capable of realizing a compaction characteristic equivalent to that in the case of drain placement by a load-loading method.

  Next, Examples 1 and 2 of a short fiber mixed soil obtained by mixing clay clay (marine clay) and a short fiber material will be described. In addition, this invention is not limited to a present Example.

Example 1
In Example 1, horticultural peat moss was used as a short fiber material, and a standard consolidation test was performed on a short fiber mixed soil (modified soil) obtained by mixing this short fiber material with marine clay. In this example, the proportion of the short fiber material (peat moss) added to the marine clay was changed, and the modified soil 20 (the short fiber material mixing amount 20%) was defined by the following formula: ), Modified soil 30 (30% short fiber mix) and modified soil 40 (short fiber mix 40%). The fiber length of the short fiber material was 10 cm or less. In addition, peat is a general term for organic soil often found in Hokkaido and the like, and peat moss was obtained by washing peat, removing soil, and drying it, and cutting it to 10 cm or less.

  Example of mixing amount of modified soil 30: Dry weight of peat moss x 100 / (dry weight of marine clay + dry weight of peat moss) = 30%

Based on "Consolidation test method by stage loading of soil" (JIS A 1217: 2009) for the above-mentioned modified soil 20, modified soil 30, modified soil 40 and marine clay (without mixing short fiber material) The results of the standard consolidation test are shown in FIGS. Fig. 3 shows the average consolidation pressure and hydraulic conductivity obtained by conducting a standard consolidation test on short fiber mixed soil (modified soil) in which short fiber material (garden peat moss) is mixed with marine clay. Similarly, FIG. 4 shows the relationship between the average consolidation pressure and the consolidation coefficient. In the figure, a power of 10 (for example, 1.0 × 10 ⁻⁰⁵ ) may be expressed by using E (for example, 1.0E−05) (and so on).

The consolidation coefficient Cv is defined by the following equation, and is a soil constant that governs the consolidation speed of clay.
Cv = k × γ _w / m _V
Here, m _V: (obtained from the relationship between the compressive strain and the compaction pressure) volume compression factor
k: hydraulic conductivity γ _w : unit volume weight of water

  According to FIG. 3, it can be seen that when the mixing amount of peat moss is increased, the hydraulic conductivity k of the short fiber mixed soil greatly increases. Moreover, according to FIG. 4, when the addition amount of peat moss is increased, it is understood that the consolidation coefficient Cv of the short fiber mixed soil is greatly increased.

  Compared with the marine clay that does not mix short fibers and the modified soil 20 (mixed amount of short fiber material 20%), the modified soil 20 is better when the average consolidation pressure is smaller. It can be seen that it is about 10 times larger. Further, regarding the consolidation coefficient Cv in FIG. 4, when comparing the marine clay not mixed with short fibers and the modified soil 20 (mixing amount of short fiber material 20%), when the average consolidation pressure is small, the modified soil 20 It can be seen that is 10 times larger.

  Further, the time until the pressure density reached 80% (U = 80% time) was measured for the mixed soil (modified soil) of this example, and the relationship between the time and the amount of short fiber material mixed is shown in FIG. Shown in It can be seen that the time until the pressure density reaches 80% decreases as the amount of the short fiber material increases.

(Example 2)
Next, the same standard consolidation test was performed with the mixing amount of the short fiber material being constant (the mixing amount of the short fiber material being 30%) and the fiber length being changed to three types of 1 mm or less, 1-2 mm, and 2-5 mm. . As the short fiber material, the modified soil 30 in which the short fiber material in the peat moss was sorted by length and mixed with marine clay was used.

  The test results of this example are shown in FIGS. FIG. 6 shows the relationship between the consolidation pressure and the gap ratio obtained by conducting a standard consolidation test on mixed soil (modified soil) obtained by mixing short fiber materials having different fiber lengths with marine clay in this example. 7 shows the relationship between the average consolidation pressure and the hydraulic conductivity, and FIG. 8 also shows the relationship between the average consolidation pressure and the consolidation coefficient. Each figure also shows the result of marine clay of Example 1 (no mixing of short fiber material).

  FIG. 6 shows that the relationship between the gap ratio e and the consolidation pressure p hardly depends on the fiber length. Further, from FIG. 7, when the fiber length of the short fiber material is 2 mm or less, the hydraulic conductivity k greatly decreases as the average consolidation stress p increases, but when the fiber length is 2 to 5 mm, the average consolidation stress p increases. However, almost no decrease in the hydraulic conductivity k is observed. Further, from FIG. 8, when the fiber length of the short fiber material is 2 mm or less, the consolidation coefficient Cv does not change much even if the average consolidation stress p increases, but when the fiber length is 2 to 5 mm, the consolidation coefficient Cv is an average. It can be seen that it increases with increasing consolidation stress p.

  As described above, the consolidation coefficient Cv increases with increasing average consolidation stress p, so mixed soil (modified soil) in which peat moss (mixing amount 30%) with a fiber length of 2 to 5 mm is mixed with marine clay. It can be said that the consolidation settlement is completed in a shorter period.

  The reason for this is that if a large number of long fibers with good water permeability are mixed in the modified soil, the long fibers are entangled with each other, and the pore water that has been drained is transferred by compaction (the drain pipe is It is considered that the consolidation coefficient Cv increases.

  As described above, the fiber length is preferably 2 mm or more, as is apparent from a comparison between the short fiber material having a fiber length of 2 to 5 mm and the short fiber material having a fiber length of 2 mm or less. Further, if the fiber length of the short fiber material is 10 cm or less, the fiber length of the short fiber material is preferably 10 cm or less because it is easy to disperse when mixed in the clay.

  As described above, the modes for carrying out the present invention have been described. However, the present invention is not limited to these, and various modifications can be made within the scope of the technical idea of the present invention. For example, in the present embodiment, the compaction processing of the short fiber mixed ground is performed by the load-loading method, and the drain placement is unnecessary, but the present invention is not limited to this, and the horizontal drain, the vertical drain, The drain construction method using sand drain or the like may be used in combination, or may be performed alone. In this case, the drain pitch can be reduced, the compaction time can be shortened, and an efficient consolidation process is possible.

Further, the present invention uniformly mixes a large number of short fiber materials having an in-plane permeability coefficient larger than that of the viscous soil into viscous soil having a permeability coefficient of 10 ⁻⁴ to 10 ⁻⁸ cm / sec. It is a consolidation ground improvement method that can be used to improve the compacted ground by making short fiber mixed soil (modified soil) whose permeability coefficient is 10 times larger than that of the viscous soil. In order to efficiently dispose of clay soil, etc., and efficiently use the land at the disposal site by placing it as reformed soil as described above in a disposal site that disposes etc. It can also be grasped as a clay soil disposal method and a ground preparation method for ground preparation. In addition, since the soil quality is improved by mixing short fiber materials, a soil quality improvement method or a modified soil production method can be used.

11 dredged soil
12 Short fiber material 13 Short fiber mixed soil

Claims (3)

By mixing the short fiber material with water permeability uniformly in a mixing amount of 20-40% to the viscous soil with a permeability of 10 ^-4 to 10 ^-8 cm / sec, the permeability is higher than that of the viscous soil. Make a short mixed fiber of short fiber,
A consolidation ground improvement method, wherein consolidation treatment is performed on the ground on which the short fiber mixed soil is placed. However, the said mixing amount is based on following Formula .
Mixing amount (%) = dry weight of the short fiber material × 100 / (dry weight of the clay soil + dry weight of the short fiber material ) By mixing the short fiber material with water permeability uniformly in a mixing amount of 20-40% to the viscous soil with a permeability of 10 ^-4 to 10 ^-8 cm / sec, the permeability is higher than that of the viscous soil. Make a short mixed fiber of short fiber,
A consolidation ground improvement method characterized by performing a consolidation treatment by a drain method alone or a combination of a loading method and a drain method on the ground on which the short fiber mixed soil is placed. However, the said mixing amount is based on following Formula .
Mixing amount (%) = dry weight of the short fiber material × 100 / (dry weight of the clay soil + dry weight of the short fiber material) The consolidated ground improvement method according to claim 1 or 2 , wherein the short fiber material is a plant fiber having a water-permeable conduit.

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