JP7219897B2 - SOIL IMPROVEMENT SOIL MANUFACTURING METHOD AND SOIL IMPROVEMENT METHOD - Google Patents

Description

The present invention relates to a method for producing soil improvement soil in which nanofibers are mixed with a cementitious material and a method for soil improvement, and more particularly, to improve the dispersibility of the constituent materials to be mixed, making it more effective and efficient. The present invention relates to a method for producing ground improvement soil that can improve ground in a field and a ground improvement method using this soil improvement soil.

A soil improvement method is known in which a cement-based material or a chemical solution is mixed and injected into a target ground to improve soft ground or the like. A method for soil improvement by mixing cementitious materials and nanofibers has also been proposed (see Patent Document 1). Improvement of soil strength (uniaxial compressive strength) is expected by soil improvement by mixing nanofibers.

In ground improvement work, in order to ensure the required strength of the ground within a predetermined curing period, the ground improvement soil is mixed with cement in an amount necessary to develop the required strength. In ground improvement soil, if the constituent materials are evenly distributed, higher strength can be obtained, but in reality, the degree of distribution of the constituent materials varies. Therefore, considering the dispersibility of the constituent materials, a certain amount of cement is added in excess. In other words, in order to ensure the required strength of the ground, the current situation is that more than the required amount of cement is used. If the ground strength of the ground improvement soil after hardening becomes excessive due to the use of more than the necessary amount of cement, another problem arises in that excavation of the improved ground becomes difficult.

Therefore, there is room for improvement in improving the ground improvement effect and efficiently performing the ground improvement. Therefore, the inventors of the present application focused on nanofibers as a material to be mixed with ground improvement soil, and conducted various studies and analyses, resulting in the creation of the present invention.

JP 2015-1043 A

The object of the present invention is to improve the dispersibility of the constituent materials to be mixed, and manufacture ground improvement soil in which nanofibers are mixed with cementitious materials that can improve ground more effectively and efficiently. It is to provide a ground improvement method using a method and this ground improvement soil.

In order to achieve the above object, the method for producing soil improvement soil of the present invention mixes soil, water, cement, and nanofibers, and within a predetermined curing period after the completion of mixing, the uniaxial compressive strength is set. In a method for producing soil improvement soil for producing soil improvement soil that expresses ground strength equal to or higher than a reference value, using a plurality of test samples of the soil improvement soil, the material age is one axis of the test sample when the curing period has elapsed Compressive strength variation data is grasped in advance, and at least the mixing ratio of cement in the ground improvement soil is determined based on the grasped variation data and the reference value.

The ground improvement method of the present invention is characterized by performing ground improvement on the target ground using the soil improvement soil produced by the method for producing the soil improvement soil described above.

According to the manufacturing method of the soil improvement soil of the present invention, the variation data of the unconfined compressive strength of a plurality of test samples of the soil improvement soil grasped in advance during the curing period is used. By adding nanofibers as a constituent material to be mixed, the dispersibility of each constituent material is improved, so by using this variation data and the standard value of ground strength, it is possible to determine the appropriate cement mixing ratio that is neither too much nor too little. can be determined. Therefore, by using ground improvement soil with a cement mixture ratio determined in this way, it is possible to use more than the necessary amount of cement for ground improvement construction that secures the standard value of ground strength within a predetermined curing period. can be implemented without That is, it becomes possible to perform ground improvement more effectively and efficiently.

It is explanatory drawing which illustrates the process which is manufacturing soil improvement soil, and the test sample of soil improvement soil. FIG. 4 is a graph diagram schematically illustrating variation data of uniaxial compressive strength of test samples. FIG. 4 is a graph diagram schematically illustrating variation data of unconfined compressive strength of test samples in which only the blending ratio of cement is changed. It is explanatory drawing which illustrates the object ground which is performing ground improvement. FIG. 4 is a graph illustrating the relationship (experimental data) between compressive stress and compressive strain at 28 days of material age of test samples. Fig. 3 is a histogram showing variation in unconfined compressive strength of test samples at 28 days of age; FIG. 7 is a histogram normalizing the data of the test sample (specification 1) of FIG. 6 by standard deviation. FIG. 7 is a histogram normalizing the data of the test sample (specification 2) of FIG. 6 by standard deviation.

Hereinafter, the method for producing soil improvement soil and the method for soil improvement of the present invention will be described based on the embodiments shown in the drawings.

As exemplified in FIG. 1, in the present invention, soil 2, water 3, cement 4, and nanofibers 5 are blended in a predetermined ratio and mixed using a mixing device 8 to produce ground improvement soil 1. . Using this mixing device 8, various test samples 6 (6a, 6b, 6c) of the ground improvement soil 1, which will be described later, can also be produced. The means for mixing the constituent materials of the ground improvement soil 1 is not particularly limited, and a device other than the exemplified mixing device 8 can also be used. In addition, the ground improvement soil 1 can be appropriately mixed with other materials (admixture such as AE water reducing material) as necessary.

The type of the soil 2 is not particularly limited, and various known soils such as the soil at the construction site of ground improvement can be used. The type of cement 4 is not particularly limited, and various known cements such as Portland cement can be used.

The nanofiber 5 is, for example, a material obtained by subdividing cellulose such as trees and flowers into nano-levels through mechanical treatment, chemical treatment, or a combination thereof. The nanofibers 5 are used, for example, as a powder or a gel by mixing with water.

Typical specifications of the nanofibers 5 are about several nanometers in fiber length and several nanometers to several tens of micrometers in fiber width. The fiber width varies to some extent. Materials for the nanofibers 5 include, for example, wood pulp, bamboo pulp, softwood pulp, and the like. Not only the cellulose nanofibers 5 made of such plant-derived raw materials, but also nanofibers 5 made of animal-derived raw materials such as crustaceans can be used. The nanofibers 5 have various specifications, and various known nanofibers 5 can be used.

The nanofibers 5 are a bulky material, and when mixed, they reduce the fluidity of the soil improvement soil 1. Therefore, the blending ratio in the soil improvement soil 1 cannot be made too large from the viewpoint of handling. Therefore, the mixing ratio in the ground improvement soil 1 is, for example, about 0.1 wt % to 5.0 wt % in dry weight ratio of soil particles with respect to the soil particles constituting the ground improvement soil 1 .

The ground improvement soil 1 hardens by promoting cement hydration reaction after the completion of mixing of its constituent materials, and develops ground strength (uniaxial compressive strength qu) equal to or higher than the reference value C within a predetermined curing period T. do. Since this reference value C is set in advance, the cement 4 is blended into the ground improvement soil 1 in an amount that can secure the ground strength equal to or higher than this reference value C.

However, due to the degree of dispersion in the soil improvement soil 1 of each constituent material to be mixed, variations occur in the developed ground strength, and if the dispersion is poor, sufficient ground strength cannot be obtained. In particular, it is difficult to evenly disperse powdered cement 4 . Therefore, it is necessary to determine the mixing ratio of the cement 4 so as to more reliably obtain a ground strength equal to or greater than the reference value C within the curing period T, taking into consideration the dispersibility of the constituent materials to be mixed.

As a result of various examinations and analyses, the inventors of the present application have found that mixing the nanofibers 5 makes it easier to more uniformly disperse the constituent materials in the ground improvement soil 1 . Therefore, in order to determine the mixing ratio of the cement 4 in the ground improvement soil 1, a plurality of test samples 6 of the ground improvement soil 1 are used to acquire the variation data Q of the uniaxial compressive strength qu of the test samples 6. . The unconfined compressive strength qu is measured according to JIS A1216. The variation data Q is obtained when a predetermined curing period T has elapsed after the completion of mixing, and the number of test samples 6 is preferably 10 or more, more preferably 20 or more.

FIG. 2 shows the variation data Q of soil improvement soil 1 produced by mixing each constituent material (soil 2, water 3, cement 4, nanofiber 5) at a predetermined mixing ratio (that is, the same mixed batch Variation data of ground improvement soil 1) is described. In addition, the variation data Q ₀ of the improved soil (hereinafter referred to as the conventional improved soil) when only the nanofiber 5 is removed from the ground improvement soil 1 (that is, the variation data of the conventional improved soil of the same mixed batch ) are also indicated by dashed lines. In FIG. ₂ , the mean values of the uniaxial compressive strength for the variation data Q and _Q0 are indicated by M and M0, respectively. The curing period T is set to an appropriate length, for example, about 28 days.

Based on the variation data Q of the unconfined compressive strength qu of the plurality of test samples 6 grasped in advance and the reference value C of the ground strength, the mixture ratio of at least the cement 4 in the ground improvement soil 1 is determined. As exemplified in Fig. 2, there are variations in the unconfined compressive strength qu in both the ground improvement soil 1 and the conventional improvement soil, but most of the test samples 6 did not develop a ground strength greater than the reference value C within the curing period T. ing. Comparing the variation data Q and Q0, the ground improvement soil ₁ has smaller variation in the unconfined compressive strength qu than the conventionally improved soil. Also, the average value M of the unconfined compressive strength qu of the soil improvement soil 1 is higher than the average value M ₀ of the conventional improvement soil (M>M ₀ ).

That is, the nanofibers 5 mixed in the ground improvement soil 1 have the effect of dispersing the mixed constituent materials more uniformly and improving the ground strength. Therefore, by comparing the variation data Q and the reference value C, the blending ratio of the cement 4 that can secure the reference value C within the predetermined curing period T is determined by considering the variation of the constituent materials. Determine the minimum amount.

Specifically, with respect to the blending ratio of the cement 4 in the test sample 6 from which the variation data Q illustrated in FIG. The correlation between the increase/decrease amount of the cement 4 and the unconfined compressive strength qu after a predetermined curing period T is utilized. Then, using this correlation, the amount of cement 4 that can be reduced with respect to the mixture ratio (mixture amount) of cement 4 in this test sample 6 is calculated.

The smaller the degree of dispersion of the unconfined compressive strength qu in the variation data Q, the smaller the probability that the ground strength of the reference value C cannot be secured. no longer needed. Accordingly, the amount of cement 4 that can be reduced increases. Also, the higher the average value M of the unconfined compressive strength qu in the variation data Q is than the reference value C, the easier it is to reduce the amount of cement 4 .

Then, the mixture ratio calculated by subtracting the calculated reduction amount of cement 4 from the mixture amount of cement 4 of test sample 6 is adopted as the mixture ratio of cement 4 in soil improvement soil 1 . The mixing ratio of the other constituent materials (soil 2, water 3, nanofibers 5) of the soil improvement soil 1 can be the mixing ratio of this test sample 6, or can be adjusted appropriately within the allowable range.

In order to determine the blending ratio of cement 4 in ground improvement soil 1, it is also possible to use multiple types of test samples 6a, 6b, and 6c in which only the blending ratio of cement 4 is substantially different. can. In this case, as illustrated in FIG. 3, variation data Qa, Qb, and Qc of respective test samples 6a, 6b, and 6c are acquired. The mixing ratio of the cement 4 is gradually increased in the order of the test samples 6a, 6b, and 6c.

As a result of this comparison, among the test samples 6a, 6b, and 6c, the uniaxial compressive strength qu of the reference value C or more is developed at a predetermined probability (preset allowable probability) or more when the curing period T has elapsed, and The test sample 6 with the smallest mixing ratio (mixing amount) of the cement 4 is selected. This predetermined probability is for example 85%, more preferably 90%. In this embodiment, a test sample 6a (variation data Qa) is selected. Then, the blending ratio of cement 4 in the selected test sample 6a may be adopted as the blending ratio of cement 4 in the ground improvement soil 1. In this method, the blending ratio of all the constituent materials (soil 2, water 3, cement 4, nanofiber 5) in the selected test sample 6a may be adopted in the soil improvement soil 1, and within the allowable range as appropriate It can also be adjusted.

The above-described procedure for determining the blending ratio of the cement 4 is based on the premise that the blending ratio of the nanofibers 5 is fixed and constant. Therefore, in order to determine the blending ratio of cement 4 in ground improvement soil 1, multiple types of test samples 6a, 6b, and 6c in which only the blending ratio of nanofibers 5 is substantially different are used as test samples 6. You can also

Also in this case, similarly to FIG. 3, the variation data Qa, Qb, Qc of the uniaxial compressive strength of the respective test samples 6a, 6b, 6c are acquired. Then, each variation data Qa, Qb, Qc and the reference value C are compared. As a result of this comparison, among the test samples 6a, 6b, and 6c, the uniaxial compressive strength qu of the reference value C or more is expressed at a predetermined probability or more when the curing period T has elapsed, and the blending ratio of the nanofibers 5 (blending Select the test sample 6 with the lowest amount). Then, the blending ratio of cement 4 and nanofiber 5 in the selected test sample 6 is adopted as the blending ratio of cement 4 and nanofiber 5 in soil improvement soil 1 .

In this method, the mixing ratio of nanofibers 5 can be minimized. The mixing ratio of other constituent materials in the selected test sample 6 can be adopted in the soil improvement soil 1 or can be adjusted appropriately within the allowable range.

As test samples 6, a plurality of types of test samples 6a _f , 6b _f , and 6c _f are used in which nanofibers 5 a , 5 b , and 5 c having respective specifications are mixed with only the specifications of the nanofibers 5 substantially different. can also In _{this case also} , _{similarly to FIG} . Compare the compressive strengths qu. As a result of this comparison, among the test samples 6a _f , 6b _f , and 6c _f , the uniaxial compressive strength qu of the reference value C or more is developed at a predetermined probability or more after the curing period T has elapsed, and the uniaxial compressive strength qu Nanofibers 5 of the same specifications as the nanofibers 5 mixed in the test sample 6 with the largest are used for the soil improvement soil 1 .

The nanofibers 5 selected in this manner are considered to have the highest effect of improving the strength of the ground, and are advantageous for reducing the blending ratio of the cement 4 in the ground improvement soil 1 . The mixing ratio of the constituent materials including the cement 4 in the ground improvement soil 1 may be determined by the method described above.

The ground improvement method of the present invention uses ground improvement soil 1 to improve the target ground 7 as illustrated in FIG. In this embodiment, using a soil improvement device 9 equipped with a stirring blade, water 3, cement 4 and nanofibers 5 are mixed with the soil 2 of the target ground 7 to produce the soil improvement soil 1 while ground improvement construction It is carried out.

Soil improvement is not limited to the method exemplified in this embodiment, and various methods using the soil improvement soil 1 can be adopted. For example, the ground improvement soil 1 previously manufactured at the construction site or a place different from the construction site can be buried in the target ground 7 for ground improvement.

As described above, the dispersibility of each constituent material of the ground improvement soil 1 can be improved by adding the nanofiber 5 as a constituent material to be mixed. Then, by manufacturing the ground improvement soil 1 using the above-described variation data Q grasped in advance, it is unnecessary to excessively consider the dispersion condition of the constituent materials, and an appropriate cement mixing ratio that is neither excessive nor deficient is determined. can do.

By using the ground improvement soil 1 that adopts the blending ratio of the cement 4 determined in this way, the ground improvement construction that secures the reference value C of the ground strength within the predetermined curing period T can be performed with more than the necessary amount of cement. 4 can be implemented. That is, according to the ground improvement method of the present invention, it becomes possible to improve the ground improvement effect more efficiently and more efficiently. In addition, in the ground improvement soil 1, the strength of the ground after a long period of time is suppressed as the amount of the cement 4 is suppressed, which contributes to the improvement of construction efficiency such as excavation of the improved ground.

The manufactured ground improvement soil 1 can be used not only for ground improvement of the target ground 7 but also for other purposes. For example, the ground improvement soil 1 can be moved to another location and used as various reinforcing materials.

As a test sample of ground improvement soil, as shown in Table 1, the only difference was that the conventional example without nanofibers and the conventional example with additional nanofibers mixed (specification A total of 30 pieces of each of the two types of 1) were produced. In Specification 1, cellulose nanofibers produced from wood pulp by the TEMPO oxidation method were used as the nanofibers. In the conventional example, powdered cement was added to Kawasaki clay (dredged soil) whose liquid limit ratio was adjusted to about 1.55 by adjusting the water content, and mixed with a soil mixer for 1 minute. Specification 1 is Kawasaki clay, in which powdered cellulose nanofibers and powdered cement are manually mixed for 5 minutes in advance, and the water content ratio is adjusted in the same way as in the conventional example to set the liquid limit ratio to about 1.55. (dredged soil) and mixed with a soil mixer for 1 minute.

For each test sample, the uniaxial compressive strength qu (compressive stress σ-compressive strain curve ε) at a material age of 28 days was obtained in accordance with JIS A 1216. The results are shown in FIG. 5, where D ₀ (solid line) and Da (broken line) indicate the data of the conventional example and specification 1, respectively.

Moreover, based on the data shown in FIG. 5, Table 2 shows the minimum value, maximum value and average value of each data such as the uniaxial compressive strength qu of 30 samples for each test sample. FIG. 6 is a histogram showing variations in the uniaxial compressive strength of each test sample, with the conventional example shown in black and the specification 1 shown in shaded graph. 7 and 8 are histograms obtained by normalizing the variations in the unconfined compressive strength of the conventional example and the specification 1 by the standard deviation, respectively.

From the results of FIGS. 5 to 8, in specification 1 (Qa), the test data of the unconfined compressive strength qu are all within the range of ± (standard deviation σ × 2), and the fluctuation compared to the conventional example (Q ₀ ) It can be seen that the coefficient CV is small and the variation in the unconfined compressive strength qu is small. Also, it can be seen that the average value M of the uniaxial compressive strength qu of the specification 1 (Qa) is larger than the average value M ₀ of the conventional example (Q ₀ ). Therefore, when producing ground improvement soil that secures the ground strength of the reference value C within a predetermined curing period T, in the specification 1 (Qa), the amount of cement compounded is higher than in the conventional example (Q ₀ ). Greater room for reduction. Along with the reduction in the amount of cement compounded, if the compounding ratio of the constituent materials in specification 1 (Qa) is adopted for the ground improvement soil, it is advantageous for suppressing the long-term ground strength.

1 ground improvement soil 2 soil 3 water 4 cement 5 (5a, 5b, 5c) nanofiber 6 (6a, 6b, 6c) test sample 7 target ground 8 mixing device 9 ground improvement device

Claims (5)

Soil, water, cement, and nanofibers are mixed, and within a predetermined curing period after the completion of mixing, ground improvement soil that develops ground strength equal to or higher than the standard value set for unconfined compressive strength is produced. In the soil manufacturing method,
Using a plurality of test samples of the ground improvement soil, the variation data of the uniaxial compressive strength of the test samples when the material age has passed the curing period is grasped in advance, and the grasped variation data and the reference value A method for producing soil improvement soil, characterized in that the blending ratio of at least cement in the soil improvement soil is determined based on. 2. The method for producing ground improvement soil according to claim 1, wherein a plurality of types of test samples are used as said test samples, in which only the blending ratio of said cement is different. 2. The method for producing ground improvement soil according to claim 1, wherein a plurality of types of test samples are used as the test samples, in which only the compounding ratio of the nanofibers is different. As the test samples, a plurality of types of test samples were used in which only the specifications of the nanofibers were different. The method for producing soil improvement soil according to claim 1, wherein nanofibers having the same specifications as nanofibers mixed in the test sample having the highest compressive strength are used in the soil improvement soil. A ground improvement method for improving the target ground using the soil improvement soil produced by the method for producing the soil improvement soil according to any one of claims 1 to 4.

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