JP6216091B1 - Modified ground, modifying agent used therefor, and ground modifying method - Google Patents

Abstract

The present invention provides a modified ground which is inexpensive, has a low environmental load, and has a high ability to reduce liquefaction, and a modifier used therefor. A modified ground reduces liquefaction. The modified ground 10 includes a target soil 11 and a modifier 12 added thereto. The target soil 11 is mainly composed of soil particles 13 to be modified. The modifier 12 is mainly composed of waste paper fibers 14 and is added to the target soil 11. Waste paper fibers 14 which are the main components of the modifier 12 added to the target soil 11 are intricately entangled between the soil particles 13. Thereby, when the pressure of the pore water 15 existing between the earth and sand particles 13 is increased, the excess pore water pressure is released through the waste paper fiber 14. As a result, liquefaction due to accumulation of excess pore water pressure is suppressed. [Selection] Figure 1

Description

  The present invention relates to a modified ground for reducing liquefaction of the ground, a modifying agent used therefor, and a ground modifying method.

  Due to the frequent occurrence of earthquakes throughout the country, liquefaction of the ground has become a major problem. In particular, in the Tohoku-Pacific Ocean Earthquake, liquefaction occurred frequently not only in the Tohoku region near the epicenter, but also in the coastal areas of the Kanto region such as Chiba Prefecture. For this reason, liquefaction of the ground has become a major social problem as a disaster caused by earthquakes. The ground where liquefaction is likely to occur is mainly said to be a layer in which the gaps between the particles constituting the earth and sand are filled with groundwater, and the particles of earth and sand having a uniform particle size are loosely packed. When strong vibrations such as earthquakes occur in such ground, the pore water pressure between the sediment particles increases. And if this water pressure exceeds the meshing force by the frictional force between sand particles, it will be in the state where sand particles floated in groundwater, and solid ground will liquefy.

  Thus, for example, an SCP (Sand Compaction Pile) method is known as a liquefaction countermeasure by ground reform (see Patent Document 1). In this SCP method, a casing is driven into the ground, and sand piles are press-fitted while supplying sand into the casing. Thereby, the density of the ground increases and the shear strength can be increased.

  However, conventional methods such as the SCP method have a problem that it is difficult to shorten the construction period without requiring a complicated process. Also, methods other than the SCP method have a problem that the load on the environment is large because, for example, drugs and materials with poor biodegradability are used.

JP 2014-109179 A

Accordingly, an object of the present invention is to provide a modified ground having a low cost, a low environmental load, and a high ability to reduce liquefaction, and a modifier used therefor.
Another object of the present invention is to provide a ground reforming method that is inexpensive, has a low environmental burden, and has a high ability to reduce liquefaction without incurring complicated processes.

  The modified ground and the modifying agent of the present embodiment contain waste paper fibers as a main component. The used paper fibers constituting the modifier are fine fibers, each of which is very fine and has the property of expanding when it absorbs water. The modifier contains linear or lump waste paper fibers derived from waste paper fibers. By adding a modifier mainly composed of waste paper fibers to the target soil, linear waste paper fibers are entangled in a complicated manner between particles constituting the soil. Moreover, the lump-like waste paper fiber exists in the form which adheres to the particle | grains and linear waste paper fiber which comprise soil. As a result, the modifier is stretched in a complex manner between the particles constituting the soil, and the particles and fibers form a complex microstructure.

  When vibration is applied to the soil due to an earthquake or the like, the soil contracts due to negative dilatancy. At this time, the pore water existing between the particles constituting the soil increases in pressure as the volume contracts, and excessive pore water pressure is generated. As the volume shrinkage due to vibration continues, the excess pore water pressure gradually accumulates between the particles. The soil that has lost the shear strength due to the increase of the excess pore water pressure causes liquefaction due to the excess pore water pressure. On the other hand, waste paper fibers exist between the particles constituting the soil by adding the modifier of the present embodiment. As a result, fine voids are formed between the particles constituting the soil, and the excess pore water pressure generated as the volume contracts is released through the waste paper fibers. As a result, in the modified soil, the peak value of the pore water pressure between particles constituting the soil is greatly reduced. Thus, the waste paper fiber contained in the modifier can effectively reduce liquefaction by suppressing the increase in pore water pressure.

  And since the used paper fiber which comprises the main component of a modifier originates in used paper as the name suggests, it is very cheap. At the same time, the waste paper fiber is highly biodegradable because it is formed from a natural material such as pulp. On the other hand, although the modifier is highly biodegradable, the target soil containing the modifier is gradually viscous even if the drying and wetting are repeated in the target soil containing the modifier, and the weathering accompanying this progresses. Earthing. As a result, the modified target soil turns into clay with the passage of time and changes to soil highly resistant to liquefaction. Therefore, the ability to reduce liquefaction can be increased while being inexpensive and reducing the burden on the environment.

The schematic diagram which shows the object soil and modifier which comprise the improvement ground by one Embodiment The figure which shows the photograph of the external appearance of the modifier used for the modification | reformation ground by one Embodiment. Schematic which shows distribution of the length of the waste paper fiber which comprises the modifier used for the modified ground by one Embodiment Schematic which shows distribution of the width | variety of the used paper fiber which comprises the modifier used for the modified ground by one Embodiment The schematic diagram which shows the object soil and modifier which comprise the improvement ground by one Embodiment The schematic diagram which shows the modifier and pore water which exist between the particle | grains of the target soil which comprises the modified ground by one Embodiment The schematic diagram which shows the experimental apparatus for verifying the effect of the modifier by one Embodiment Schematic showing changes in vibration acceleration over time by experimental equipment Schematic showing time-dependent changes in excess pore water pressure in an experimental example and a comparative example using a modifier according to an embodiment when the thickness of the sample is 6 cm. Schematic diagram showing the change over time of excess pore water pressure in an experimental example and a comparative example using a modifier according to an embodiment when the thickness of the sample is 9 cm. Schematic diagram showing the change over time in excess pore water pressure in an experimental example and a comparative example using a modifier according to an embodiment when the thickness of the document is 12 cm Schematic showing the effect of addition ratio of modifier according to one embodiment on the change over time of excess pore water pressure Schematic which shows the influence which the addition ratio of the modifier by one Embodiment has on the change of subsidence amount

Hereinafter, an embodiment will be described with reference to the drawings.
As shown in FIG. 1, the modified ground 10 according to an embodiment includes target soil 11 and a modifier 12. The target soil 11 is a general soil mainly composed of sand particles 13 to be modified. The target soil 11 may include particles of various particle sizes such as gravel, stone, rock, clay, in addition to the sediment particles 13 as the main component. The target soil 11 can be arbitrarily used as long as it can cause liquefaction due to an earthquake or the like.

  The modifier 12 is mainly composed of waste paper fibers 14 and is added to the target soil 11 to be modified. The modifier 12 is mainly composed of linear and lump waste paper fibers 14. The modifier 12 is added at least 3% to 10% or more with respect to the target soil 11 by mass ratio. On the other hand, the addition ratio of the modifier 12 increases the consumption of the modifier 12 as it increases, so it is preferable to set it in consideration of cost effectiveness. The used paper used as the raw material of the used paper fiber 14 is obtained, for example, by collecting the paper consumed by the home or business entity for the purpose of recycling or the like. The recovered used paper is crushed after removing impurities other than paper components. The used paper fiber 14 used for the modifier 12 is a fine fiber-like material remaining in a crusher or the like when the used paper is crushed, and has an appearance similar to dust as shown in FIG.

  The size of the used paper fiber 14 contained in the modifier 12 is measured by image analysis software based on the SEM image. Thereby, the length of the used paper fiber 14 contained in the modifier 12 has a distribution as shown in FIG. In the case of this embodiment, the length of the used paper fiber 14 is mainly about 30 μm to 1350 μm. Among these, the modifier 12 of this embodiment contains the most waste paper fiber 14 whose length becomes 150 micrometers-269 micrometers. Moreover, the width | variety of the used paper fiber 14 contained in the modifier 12 has distribution as shown in FIG. In the case of this embodiment, the width of the waste paper fiber 14 is mainly about 5 μm to 100 μm. Among these, the modifier 12 of this embodiment contains the most waste paper fiber 14 whose width | variety is 15 micrometers-24 micrometers. Most of the used paper fibers 14 included in the modifier 12 are linear fibers having a large aspect ratio, and partly include aggregated fibers formed by aggregating linear fibers. In addition, the modifier 12 should just contain the used paper fiber 14 as a main component, and may contain not only the used paper fiber 14 but the other fiber derived from a new paper etc., for example.

Next, the action of reducing the liquefaction of the modified ground 10 having the above configuration will be described.
The used paper fibers 14 constituting the modifier 12 are fine fibers, and each of the fibers is very fine and has a property of expanding when it absorbs water. By adding the modifier 12 having the waste paper fiber 14 as a main component to the target soil 11, as shown in FIG. 1 and FIG. Is tangled like a spider web. Moreover, the very fine lump-like waste paper fiber 14 exists in the form which adhere | attaches to the particle | grains 13 and the linear waste paper fiber 14 which comprise the object soil 11. FIG. Thus, the modifier 12 is stretched in a complicated manner between the particles 13 constituting the target soil 11, and the particles 13 and the used paper fibers 14 form a complicated fine structure as shown in FIG.

  In general, when vibration is applied to soil due to an earthquake or the like, the soil repeatedly undergoes undrained shear. By repeating such non-draining shear, the soil causes volume contraction due to negative dilatancy. At this time, the pressure of the pore water existing between the particles of the earth and sand constituting the soil increases as the volume contracts. The increase in the pressure of the pore water generates an excessive pore water pressure, so-called excessive pore water pressure. Then, as the volume shrinkage due to vibration continues, the excess pore water pressure gradually accumulates among the particles constituting the soil. When the excess pore water pressure increases in this way, the soil loses shear strength and the soil liquefies due to the excess pore water pressure.

  On the other hand, in the case of this embodiment, by adding the modifier 12 to the target soil 11, there is used paper fiber 14 between the sand particles 13 constituting the target soil 11 as shown in FIG. 6. . Thereby, a fine space is formed between the particles 13 constituting the target soil 11. At this time, the pressure of the interstitial water 15 existing between the particles 13 constituting the target soil 11 increases as the volume of the target soil 11 contracts. In the case of this embodiment, the excess pore water pressure, which is the pressure of the pore water 15, is released through the waste paper fibers 14 intertwined with the particles 13. As a result, in the modified ground 10 that has been modified, the peak value of the pore water pressure between the particles 13 constituting the target soil 11 is greatly reduced. In this way, the waste paper fibers 14 contained in the modifier 12 suppress the increase in the pore water pressure between the particles 13, thereby effectively reducing liquefaction.

  Moreover, the used paper fiber 14 which comprises the main component of the modifier 12 originates in used paper as the name says, and is very cheap. At the same time, the used paper fiber 14 is formed from a natural material such as pulp, and thus has high biodegradability. On the other hand, although the modifier 12 is highly biodegradable, drying and wetting are repeated in the target soil 11 containing the modifier 12, and when the weathering accompanying this progresses, the target soil 11 containing the modifier 12 becomes Gradually becomes clayey. That is, when water supply and drying are repeated with respect to the used paper fiber 14 constituting the modifier 12, the used paper fiber 14 causes a decrease in strength due to weathering, but the resistance to shearing does not significantly decrease due to the viscous soil. . Further, the used paper fiber 14 constituting the modifier 12 has an increased adhesive force due to repeated drying and wetting. That is, the mixture of the target soil 11 and the modifier 12 containing water forms a fine structure in which the particles 13 and the waste paper fibers 14 constituting the target soil 11 are intertwined in a complicated manner. This fine structure is not destroyed by repeated drying and wetting, and the used paper fibers 14 are fixed to the particles while being modified. That is, the target soil 11 including the modifier 12 tends to become clayey soil over time due to the waste paper fibers 14 included in the modifier 12. As a result, the modified target soil 11 changes to soil highly resistant to liquefaction over time.

Hereinafter, examples will be described in detail.
(Experimental conditions)
In order to verify the effect of adding the modifier 12, an experiment was conducted under the following conditions. The experimental conditions will be described in detail. In the example, the modifier 12 was mixed with Toyoura standard sand that simulates the target soil 11 as a sample, and a vibration experiment was performed. Toyoura sand is a natural silica sand that does not contain organic substances, and is used in various experiments and inspections related to sand as sand defined in the Japanese Standard (JIS). Since the particles that make up Toyoura sand are not crushed artificially, they approximate the shape that exists in nature. The particle size distribution of this Toyoura sand is classified as sand (S) in the “technical classification method of ground material” defined in the standard JGS0051 by the Geotechnical Society. The particle size distribution of this Toyoura sand is very likely to cause liquefaction.
The waste paper fiber 14 used as the modifier 12 has the same properties as described above, and a description thereof will be omitted.

  An experimental apparatus 20 for conducting a vibration experiment repeatedly applies vibrations to a sample 23 accommodated in a container 22 using a vibration table 21 as shown in FIG. The sample 23 placed in the container 22 is provided with a polystyrene foam plate 24 that simulates a paved road surface as an impermeable layer. And in order to accelerate | stimulate liquefaction, the weight 25 which simulated the structure is installed on this foamed polystyrene board 24. FIG. In the case of the experiment of the present embodiment, the weights 25 have a plate shape of 800 g, and the four weights 25 are equally arranged above the foamed polystyrene plate 24. A water pressure sensor 26 for detecting an excess pore water pressure generated by vibration is installed on the bottom surface of the container 22. The vibration table 21 is provided with an acceleration sensor 27 for detecting the acceleration of vibration. Thereby, the water pressure sensor 26 detects the excessive pore water pressure of the sample 23 accommodated in the container 22. The acceleration sensor 27 detects acceleration applied to the sample 23.

  When conducting an experiment, first, a water pressure sensor 26 is installed at the bottom of the container 22. After the water pressure sensor 26 is installed, a predetermined amount of water is poured into the container 22. The bottom 28 of the container 22 is simulated as a rock layer that is an impermeable layer, and the groundwater layer is simulated by the injected water. After the water is injected, a sample 23 to be simulated in the target soil 11 to be a liquefied layer is accommodated. The sample 23 is prepared by mixing Toyoura sand as the target soil 11 with the waste paper fiber 14 as the modifier 12 and only Toyoura sand not containing the modifier 12 for comparison. These samples 23 are simulated by the liquefied layer, that is, the target soil 11. Further, a polystyrene foam plate 24 simulated as an impermeable layer and a weight 25 simulated by a structure are installed above the sample 23 as described above. The container 22 containing the sample 23 prepared by the above procedure is repeatedly vibrated by the experimental apparatus 20. In this experiment, the experimental apparatus 20 applies a vibration with a vibration acceleration of about 1000 gal to the container 22 including the sample 23 for one minute. The vibration acceleration applied to the sample 23 by the experimental apparatus 20 includes a change over time as shown in FIG.

(Additional effect of modifier)
Under the above experimental conditions, the effect of adding the modifier 12 was verified.
As a comparative example in which the modifier 12 is not added to the target soil 11, three types of layer thicknesses of the sample 23 simulated by the liquefied layer were prepared. Specifically, samples 23 having a layer thickness of 6 cm (Comparative Example A1), 9 cm (Comparative Example A2), and 12 cm (Comparative Example A3) were prepared. Similarly, as an example in which the modifier 12 was added to the target soil 11, three types of layer thicknesses of the sample 23 simulated by the liquefied layer were prepared. Specifically, samples 23 having a layer thickness of 6 cm (Example B1), 9 cm (Example B2), and 12 cm (Example B3) were prepared. In this case, the sample 23 contains the modifier 12 of 3% of the total mass.

  As shown in FIG. 9, in the case of Comparative Example A1, the excess pore water pressure gradually rises several seconds after the start of the experiment, and rapidly rises after about 10 seconds. Further, Comparative Example A1 shows a behavior in which the excess pore water pressure gradually decreases after reaching a peak in about 20 seconds, and the value starts to converge after about 50 seconds. Further, in the case of Comparative Example A1, after the vibration for 1 minute is finished, the excessive pore water pressure value decreases in 2 to 3 seconds and then converges to a constant value.

  On the other hand, in the case of Example B1, the excessive pore water pressure shows a behavior in which a large change does not occur despite the occurrence of the liquefaction phenomenon, and it changes at a low value. Moreover, it turns out that the maximum value of the excess pore water pressure value of Example B1 falls significantly compared with Comparative Example A1.

  As apparent from FIG. 10 in which the thickness of the sample 23 is 9 cm and FIG. 11 in which the thickness of the sample 23 is 12 cm, the excess pore water pressure between the comparative examples A1 to A3 and the examples B1 to B3 is The difference decreases as the thickness of the sample 23 increases. On the other hand, the excess pore water pressure is lower in Examples B1 to B3 than in Comparative Examples A1 to A3 regardless of the thickness of the sample 23. Thereby, it turns out that the excess pore water pressure falls in Examples B1 to B3 containing the waste paper fibers 14 as the modifier 12 compared to Comparative Examples A1 to A3 not containing the modifier 12.

  As mentioned above, it turns out that the peak value of excess pore water pressure falls in Examples B1-B3 which mixed the used paper fiber 14 as the modifier 12. As shown in FIG. That is, when the thickness of the layer of the sample 23 corresponding to the liquefied layer is 6 cm, the excess pore water pressure in Example B1 is reduced to about 0.004 to 0.28 times that in Comparative Example A1. Moreover, when the thickness of the sample 23 is 9 cm, the excess pore water pressure in Example B2 is reduced to about 0.45 to 0.64 times that in Comparative Example A2. Furthermore, when the thickness of the sample 23 is 12 cm, the excess pore water pressure in Example B3 decreases by about 0.71 to 0.75 times.

  Regarding the amount of settlement of the sample 23, in Comparative Examples A1 to A3 using only Toyoura sand, the amount of settlement increases as the thickness of the sample 23 increases. On the other hand, Examples B1 to B3 including the waste paper fibers 14 as the modifier 12 tend to converge with the change becoming smaller as the thickness of the sample 23 increases. From these results, it is clear that in Examples B1 to B3 of this embodiment, the waste paper fiber 14 exerts a great inhibitory effect against the increase in excess pore water pressure that greatly affects the expression of the liquefaction phenomenon. At the same time, it can be seen that the modifier 12 containing the waste paper fibers 14 as a main component exerts an inhibitory effect on the ground subsidence caused by liquefaction.

(Addition ratio of modifier)
Next, the influence of the addition ratio of the modifier 12 was verified.
In the example of verifying the “addition effect of the modifier”, the ratio of the modifier 12 added to the sample 23 is set to 3% by mass ratio. Here, the effect when the ratio of the modifier 12 added to the sample 23 is 6% and 9% is verified.

  As shown in FIGS. 12A to 12C, it can be seen that the modifier 12 contributes to the reduction of the excess pore water pressure regardless of the addition ratio and the thickness of the sample 23. On the other hand, it can also be seen that the influence of the addition ratio of the modifier 12 varies depending on the thickness of the sample 23.

Moreover, as shown in FIG. 13, it turns out that the amount of settlement of the sample 23 which is a liquefied layer tends to decrease as the addition ratio of the modifier 12 increases.
Thus, it can be seen that the modifier 12 contributes to a decrease in excess pore water pressure and a decrease in the amount of settlement of the liquefied layer by changing the addition ratio.

  As described above, the modified ground 10 and the modifying agent 12 according to an embodiment include the used paper fiber 14 as a main component. By adding such a modifier 12 to the target soil 11, waste paper fibers 14 exist between the earth and sand particles 13 constituting the target soil 11. As a result, fine voids are formed between the sediment particles 13 constituting the target soil 11, and excess pore water pressure generated due to volume shrinkage due to vibration is released through the waste paper fibers 14. As a result, in the modified target soil 11, the peak value of the pore water pressure between the particles 13 of the earth and sand constituting the target soil 11 is greatly reduced. Thus, the waste paper fiber 14 contained in the modifier 12 suppresses the increase in the pore water pressure, so that the liquefaction and the subsidence associated therewith can be effectively reduced.

  And the used paper fiber 14 which comprises the main component of the modifier 12 originates in used paper as the name says, and is very cheap. At the same time, the used paper fiber 14 is formed from a natural material such as pulp, and thus has high biodegradability. On the other hand, although the modifying agent 12 is highly biodegradable, drying and wetting are repeated in the target soil 11 containing the modifying agent 12, and weathering accompanying this progresses, so that the modifying soil 12 contains the modifying agent 12. 11 gradually becomes clayey. As a result, the modified target soil 11 is turned into clay with the passage of time, and changes to soil highly resistant to liquefaction. Therefore, the ability to reduce liquefaction can be increased while being inexpensive and reducing the burden on the environment.

The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.
Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments and structures. The present disclosure includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more or less, are within the scope and spirit of the present disclosure.

  In the drawing, 10 indicates a modified ground, 11 indicates a target soil, 12 indicates a modifier, 14 indicates waste paper fibers, and 16 indicates a modifier pile.

Claims (3)

A modified ground that reduces liquefaction of the ground,
Target soil mainly composed of earth and sand to be modified;
A modification having a length of 30 μm to 1350 μm, a width of 5 μm to 100 μm, mainly composed of waste paper fibers containing aggregated fibers of linear fibers and linear fibers, and added to the target soil Agent,
Improved ground. The length is from 30 μm to 1350 μm, the width is from 5 μm to 100 μm, and the main component is waste paper fibers including aggregated fibers in which linear fibers and linear fibers are aggregated, and used for the modified ground according to claim 1. Modifier. A ground improvement method for reducing ground liquefaction,
A preparation step of preparing a target soil to be modified;
A modifier having a waste paper fiber as a main component, which has a length of 30 μm to 1350 μm, a width of 5 μm to 100 μm, and includes aggregated fibers in which linear fibers and linear fibers are aggregated, in the prepared target soil. An addition step of adding
A ground improvement method including