JP7307689B2 - Method for producing high-strength solidified soil - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing high-strength solidified soil by mixing a solidifying agent into cohesive soil.

Conventionally, as a technique for effectively utilizing cohesive soil such as dredged soil and soft cohesive soil, solidified soil mixed with a solidifying material such as cement is known. The unconfined compressive strength of general solidified soil ranges from 0.1 MPa to 2-3 MPa at most. In recent years, with the aim of further expanding the effective use of dredged soil, techniques for obtaining solidified soil with higher strength have been proposed. For example, as in Patent Document 1, a cake is built and reused as a backfill material or roadbed material, and as in Patent Document 2, the dehydrated cake is re-compacted at the age of weak material to increase strength and increase the size. A method of blocking is included.

Patent No. 2764645 JP-A-2002-146763

Hiroshi Shinsha, Ayumu Matsumoto, Kyohei Nagao, Yutaka Komori, "Experiment of producing high-strength solidified soil block using dredged clay as raw material", Journal of Japan Society of Civil Engineers, Ser. C (Geosphere Engineering), Vol.75, No.1, 62-75 , 2019

The directions for increasing the strength of the above technology are to increase the amount of solidifying agent added and to reduce the amount of kneading water, that is, to lower the W/C (water solidifying agent ratio). Dredged soil, which is the base material, generally has a high moisture content, and requires a dehydration process to lower the W/C. Specifically, there is a method of forcibly consolidating and draining the dredged soil after adding and mixing the solidifying material with a high-pressure filter press. However, it is well known that the dredged soil has low permeability, and the consolidation drainage process requires a very large compaction pressure and a long period of consolidation time.

On the other hand, a method has also been proposed in which the water content of the dredged soil is sufficiently reduced by sun drying or the like, and then a solidifying material is mixed (see Non-Patent Document 1). However, if the dredged soil has a low moisture content, it loses its fluidity and exhibits plasticity, and there is concern that the workability with the solidifying material will be significantly reduced and strength development will be hindered. Also, it is very difficult to control the water content of the dredged soil because the sun drying depends on natural phenomena.

SUMMARY OF THE INVENTION In view of the problems of the prior art as described above, it is an object of the present invention to provide a method for producing high-strength solidified soil that can realize practical workability and low cost in the production of high-strength solidified soil. do.

A method for producing high-strength solidified soil for achieving the above object is a method for producing solidified soil by mixing a solidifying material with cohesive soil,
a step of adjusting the cohesive soil to a predetermined water content ratio and dehydrating the cohesive soil with the adjusted water content ratio by adding quicklime, and estimating the water content ratio after dehydration;
determining the addition amount of the solidifying material based on the estimated water content after dehydration and the target strength;
a step of adjusting the cohesive soil to be treated to the predetermined water content ratio when producing the solidified soil;
a step of adding and mixing the solidification material in the determined addition amount to the cohesive soil after adjusting the water content;
adding quicklime to the mixed solidified soil, mixing and chemically dehydrating;
A high-strength solidified soil is produced by setting the target strength to a high strength.

According to this method for producing high-strength solidified soil, first, the cohesive soil having a high water content and the solidifying material are mixed, so that the workability during kneading is high and the solidifying material can be uniformly mixed, so that the quality of the solidified soil is improved. improves. By adding quicklime as a dehydrating agent after mixing cohesive soil and solidifying material, the water content ratio of the cohesive soil can be greatly reduced, and by dehydrating the surplus water during the hydration reaction, solidification can be achieved with a small amount of solidifying material added. Higher strength of treated soil can be realized. Since chemical dehydration is performed by adding and mixing quicklime, it is possible to control the amount of dehydration, and since special manufacturing equipment such as a high-pressure dehydrator is not required, manufacturing costs can be reduced. realizable. In addition to the hydration reaction of the hardening material, the porazon reaction of quicklime can be expected to increase the strength in the long term. In addition, it is expected that the solidification expansion of the quicklime will offset the solidification shrinkage of the solidification material, and the reduction of drying shrinkage cracks can be achieved.

It is preferable to set and adjust the predetermined water content to a high water content in the method for producing high-strength solidified soil. For example, by increasing the water content of the cohesive soil to 1.1 to 1.5 times the liquid limit of the cohesive soil, the cohesive soil and solidifying material are uniformly mixed while maintaining necessary and sufficient fluidity. can be done.

Moreover, the water content ratio after the dehydration can be determined by the following equation.
w＝( _w0-0.77d )/(1+1.32d)
However, w: water content ratio after dehydration, _w0 : water content ratio before dehydration, d: quicklime addition rate quicklime addition rate d = amount of quicklime added/dry weight of cohesive soil

Further, in the step of determining the amount of the solidifying material to be added, it is preferable to conduct a blending test with a plurality of formulations using the amount of the solidifying material to be added as a variable, and to determine the amount of the solidifying material to be added based on the test results. Further, it is preferable that the blending test is carried out using a plurality of blends with the addition amount of the quicklime as a variable, and the addition amount of the quicklime is determined based on the test results.

Also, the compounding test includes a uniaxial compressive strength test and/or a flow test. Further, it is preferable to set the upper limit of the amount of quicklime to be added based on the mixing plan or the amount of water (surplus water) that does not contribute to the hydration reaction of the solidifying material according to the above formula.

Further, it is preferable to set the execution timing of the step of adding and mixing the quicklime based on the solidification start time of the solidifying material.

According to the method for producing high-strength solidified soil of the present invention, practical workability and low cost can be realized in the production of high-strength solidified soil.

4 is a flow chart for explaining each step of the method for producing high-strength solidified soil according to the present embodiment. Table (a) showing the basic information of the materials used in this experiment, Table (b) showing the initial water content ratio of the dredged soil in FIG. 2 (a), When the dredged soil in FIG. Tables (c) and (d) showing the water content after dehydration calculated from the formula (1). It is a table|surface which shows the compounding data and experimental result of this experiment example. FIG. 4 is a graph showing the relationship between the water-cement ratio (W/C) and the unconfined compressive strength (material age: 28 days) in the experimental example of FIG. 3. FIG.

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated using drawing. FIG. 1 is a flow chart for explaining each step of the method for producing high-strength solidified soil according to this embodiment.

In the method for producing high-strength solidified soil according to the present embodiment, after kneading cohesive soil and cement as a solidifying agent in a state in which necessary and sufficient fluidity is maintained, quicklime is added and mixed as a dehydrating agent. By chemically dehydrating the soil, we realized practical workability and cost reduction in the production of high-strength solidified soil. In this embodiment, high-strength solidified soil refers to solidified soil having a uniaxial compressive strength of at least 9.8 MPa. The set strength (9.8 Mpa) is the strength required for use as a semi-hard stone, and is the non-deteriorating strength required for exposure to seawater.

Each step S01 to S10 of the method for producing high-strength solidified soil according to this embodiment will be described with reference to FIG. First, the cohesive soil is adjusted to a predetermined moisture content in accordance with the moisture content of the cohesive soil during field dredging (S01).

The predetermined water content ratio of cohesive soil is set and adjusted as follows.
・Investigate the natural water content and liquid limit of cohesive soil collected by dredging, etc., in advance.
・Adjust the water content of the cohesive soil collected by dredging, etc. at the site to 1.1 to 1.5 times the liquid limit wL.

By setting the water content ratio of the cohesive soil to a high value as described above, it is possible to secure and maintain necessary and sufficient fluidity during kneading of the cohesive soil and the solidifying material.

Next, the water content ratio reduction effect of quicklime when dehydrating the cohesive soil with the water content ratio adjusted by adding quicklime, that is, the water content ratio after dehydration is estimated (S02).

Quicklime not only has the effect of reducing the apparent water content by digestion and water absorption, but also has the effect of chemically reducing the water content. The water content ratio after dehydration when quicklime is added to the cohesive soil with the above water content ratio and dewatered is estimated by calculation using the following formula (1). In addition, the formula (1) is a formula for the effect of reducing the water content ratio by quicklime described in "Stabilization method for soft ground using lime" (Japan Lime Association).
w＝( _w0-0.77d )/(1+1.32d) (1)
However, w: water content ratio after dehydration, _w0 : water content ratio before dehydration, d: quicklime addition rate quicklime addition rate d = amount of quicklime added/dry weight of cohesive soil

For example, adding quicklime (d=5%) to cohesive soil (ρ=2.686g/cm ³ , wL=75.9%, w ₀ =100%) gives w=90.2% from equation (1), which is about 10% of water content ratio reduction effect is obtained. By chemically dehydrating with quicklime in this manner, the amount of dehydration can be controlled.

Next, assuming that the amount of water corresponding to the water content after dehydration is used for the hydration reaction due to the addition of cement, the amount of cement to be added that satisfies the target uniaxial compressive strength was tentatively determined, and the determined amount of addition was used. For reference, a blending test is carried out with several types of blending using the amount of cement added as a variable and the amount of quicklime added as a variable (S03). Based on the test results, the amount of cement to be added and the amount of quicklime to be added are determined (S04).

For example, the unconfined compressive strength of solidified soil is highly correlated with the water-cement ratio (W/C). With the amount of quicklime added as a variable, 3 to 5 levels of mixtures are prepared for each, and the mixtures are examined according to the target unconfined compressive strength and flow value. In addition, when the amount of quicklime to be added is determined, a formulation is prepared with the amount of cement to be added as a variable.

Examples of the compounding test include a flow test based on NEXCO Test Method Test Method 313 and a uniaxial compression test based on JIS A1216:2009. Examples of target performance include a cylinder flow value of 100 to 120 mm and unconfined compressive strength qu (material age of 28 days) of 10 MPa or more. The composition is determined while checking the workability and strength immediately after kneading. In some cases, either the uniaxial compression test or the flow test may be used as the compounding test.

Next, when actually producing the solidified soil, the cohesive soil to be treated is adjusted to the predetermined moisture content set as described above (S05). At this time, by setting and adjusting the water content ratio of the cohesive soil to a high value, dehydration treatment is not required and only an easy addition of water is required.

Next, the amount of cement determined as described above is added to the cohesive soil and mixed (S06).

Next, the quicklime determined as described above is added to the mixed material in which cement is mixed with cohesive soil, and the mixture is dehydrated (S07).

In the above steps S06 and S07, the cohesive soil and cement are sufficiently mixed and stirred, then quicklime is added as a dehydrating agent, and mixed and stirred again. This is based on the idea of mixing cohesive soil and cement homogeneously in a state of high fluidity, and then dewatering surplus water that is unnecessary for the cement hydration reaction by the dehydrating effect of quicklime.

As for the period from the end of step S06 to the start of step S07, that is, the timing of adding and re-mixing the dehydrating agent, it is preferable to perform it before the initial stage of cement setting. This setting start time may be determined by referring to the concrete setting time test method (JIS 1147).

Next, the mixed material obtained as described above is placed, for example, in a mold corresponding to the required final shape (S08), cured for a required period (S09), and high-strength solidified soil is obtained. Manufacture (S10). As described above, for example, a stone-like material consisting of high-strength solidified soil for use in underwater mounds can be produced. Incidentally, when the high-strength solidified soil is produced without changing the conditions, steps S05 to S10 are repeated.

According to the method for producing high-strength solidified soil of the present embodiment, cohesive soil having a high water content and cement as a solidifying material are mixed, so workability during kneading is high and uniform mixing is possible. The quality of solidified soil is improved. By adding quicklime as a dehydrating agent after cohesive soil and cement are mixed, the water content of the cohesive soil can be greatly reduced. can achieve high strength. Since chemical dehydration is performed by adding and mixing quicklime, it is possible to control the amount of dehydration, and since special manufacturing equipment such as a high-pressure dehydrator is not required, manufacturing costs can be reduced. realizable. In addition to the hydration reaction of cement, a high strength increase can be expected in the long term due to the porazon reaction of quicklime. In addition, the solidification expansion of quicklime can be expected to offset the solidification shrinkage of cement, and the reduction of drying shrinkage cracks can be achieved.

Next, an experimental example of the present invention will be described, but the present invention is not limited to this experimental example. Figure 2 (a) shows the basic information of the materials used in this experiment, Figure 2 (b) shows the initial water content ratio of the dredged soil in Figure 2 (a), Figure 2 (c) (d) Two cases of water content after dehydration calculated from the formula (1) when the dredged soil of 2(a) is dehydrated with quicklime are shown. FIG. 3 shows the data and experimental results of each formulation in this experimental example. Fig. 4 shows the relationship between the water-cement ratio (W/C) and the unconfined compressive strength (age: 28 days) in the experimental example of Fig. 3 .

The blending cases of the experimental example in Fig. 3 are 3.0%, 5.0%, and 10.0% quicklime QL, and the water-cement ratios (W/C) are 2.32, 1.99, and 1.74, respectively, for a total of 9 blending cases. The dredged soil of Fig. 2(a) was kneaded with cement and then kneaded with quicklime, and after curing, a uniaxial compression test was performed to measure the uniaxial compressive strength on the 7th and 28th days. In each case, three specimens were tested (however, one specimen was tested with a quicklime addition rate of 5.0% and W/C = 2.32), and these measurement results are shown in Fig. 4, and their average values is shown in FIG. FIG. 4 also shows experimental results for a comparative example in which quicklime is not added.

From Fig. 4, it can be seen that the smaller the W/C, the higher the unconfined compressive strength (28 days old), and there is no significant difference in the unconfined compressive strength (28 days old) between quicklime addition rates of 3.0% and 5.0%. However, it can be seen that the unconfined compressive strength (28 days old) is low at 10.0%. If the target unconfined compressive strength (material age 28 days) is set to, for example, 12 MPa, in the case of this experimental example, the target is achieved by setting W/C = 1.9 to 2.4 and the quicklime addition rate to about 3 to 7%. strength can be achieved.

Next, the upper limit of the addition rate of quicklime (dehydration agent) is examined. As can be seen from Fig. 4, when the W/C is low (≒water content ratio of the dredged soil is low), if the amount of quicklime added is large (d = 10%), the hydration reaction does not occur sufficiently and the strength decreases. Tend. On the other hand, (1) the amount of water that reaches the plastic limit of the dredged soil is not used for hydration reaction, (2) the hydration reaction of cement requires 0.6 times the amount of cement added, ( 3) Considering that the amount of water that is 0.45 times the amount of quicklime added evaporates as a reference for the formulation study, if the excess water in Fig. 3 is 0 or less, the cement hydration reaction is not sufficient, and the amount of quicklime added It is preferable to set it as the upper limit of. In the experimental example of FIG. 3, the excess water is 0 or less in the cases where the quicklime addition rate is 10.0% and the W/C is 1.99 and 1.74. The surplus water is the amount of water that does not contribute to the hydration reaction of cement, and is obtained from the amount of water after dehydration-(hydration reaction water + plastic limit water + quicklime reaction water).

Although the embodiments for carrying out the present invention have been described above, the present invention is not limited to these, and various modifications are possible within the scope of the technical idea of the present invention. For example, the high-strength solidified soil produced by the production method of the present invention can of course be used for other purposes as well as riprap that constitutes an underwater mound.

According to the present invention, practical workability and low cost can be realized in the production of high-strength solidified soil, so high-strength solidified soil can be efficiently supplied at low cost, and dredged soil and construction surplus soil can be used. etc. can be promoted.

Claims (8)

A method for producing solidified soil by mixing a solidifying material with cohesive soil,
a step of adjusting the cohesive soil to a predetermined water content ratio and dehydrating the cohesive soil with the adjusted water content ratio by adding quicklime, and estimating the water content ratio after dehydration;
determining the addition amount of the solidifying material based on the estimated water content after dehydration and the target strength;
a step of adjusting the cohesive soil to be treated to the predetermined water content ratio when producing the solidified soil;
a step of adding and mixing the solidification material in the determined addition amount to the cohesive soil after adjusting the water content;
adding quicklime to the mixed solidified soil, mixing and chemically dehydrating;
A method for producing high-strength solidified soil, wherein the target strength is set to high strength to produce high-strength solidified soil. 2. The method for producing high-strength solidified soil according to claim 1, wherein the predetermined water content is adjusted to a high water content. 3. The method for producing high-strength solidified soil according to claim 1 or 2, wherein the moisture content after dehydration is determined by the following equation.
w＝( _w0-0.77d )/(1+1.32d)
However, w: water content ratio after dehydration, _w0 : water content ratio before dehydration, d: quicklime addition rate quicklime addition rate d = amount of quicklime added/dry weight of cohesive soil 4. The method according to any one of claims 1 to 3, wherein in the step of determining the amount of the solidifying material to be added, a blending test is performed using a plurality of formulations with the amount of the solidifying material to be added as a variable, and the amount of the solidifying material to be added is determined based on the test results. A method for producing high-strength solidified soil according to any one of the above. 5. The method for producing high-strength solidified soil according to claim 4, wherein the blending test is carried out with a plurality of blends in which the amount of quicklime added is also a variable, and the amount of quicklime added is determined based on the test results. 6. The method for producing high-strength solidified soil according to claim 4 or 5, wherein said mixing test includes a uniaxial compressive strength test and/or a flow test. 4. The method for producing high-strength solidified soil according to claim 3, wherein the upper limit of the amount of quicklime added is set based on the mixing plan or the amount of water that does not contribute to the hydration reaction of the solidifying material according to the formula. 8. The method for producing high-strength solidified soil according to any one of claims 1 to 7, wherein the timing of performing the step of adding and mixing the quicklime is set based on the solidification start time of the solidifying material.

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