JP2651098B2 - Excavation residual soil treatment method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating excavated soil generated in construction, civil engineering, etc., and facilitating reuse of the excavated soil.

[0002]

2. Description of the Related Art Excavated soil generated during construction, civil engineering, etc., when used as it is as backfill soil, has poor consolidation properties and may cause land subsidence. Therefore, mountain sand is used as backfill soil, or quick lime is added to the excavated soil to improve the soil quality, and the excavated soil is reused. However, in recent years, with increasing demands for environmental conservation and resource recycling, it has become difficult to collect mountain sand and to dispose of residual soil, and it is necessary to expand the reuse of excavated residual soil.

[0003] A conventional method of treating excavated remains is as follows.

[0004] The remaining soil is crushed, and about 3% of quicklime (CaO) is added thereto. The hydration reaction and the heat of reaction generated at this time reduce the water content in the soil and aggregate the soil particles to improve the soil quality.

[0005] CaO + H ₂ O → Ca (OH) ₂ +15.2 Kcal

However, this soil treatment has the following problems. a. Since calcium hydroxide (Ca (OH) ₂ ) remains in the treated soil, there is a possibility that groundwater will be alkali-polluted. b. After backfilling, it hardens and makes it difficult to drill again.

In order to alleviate such problems, it is effective to accurately measure the water content of the excavated soil to be treated and to control the amount of quicklime to be added to minimize the amount of addition. However, in practice, the properties of the soil to be treated vary greatly, making it difficult to precisely control the amount of addition.

If the amount of quicklime added is too small, there is a problem that soil adheres to the inside of the crusher and hinders the operation of the plant. Therefore, at least 2-3% of quicklime must be added. .

As described above, there is a limit to improving the soil quality of excavated soil by controlling only the amount of quicklime added, and it is not sufficient to expand the reuse of the excavated soil.

An object of the present invention is to solve the problems of alkali contamination and soil hardening after backfilling, which cannot be solved by the conventional methods, and a method of treating excavated remnant soil for expanding reuse of excavated remnant soil. It is to provide a device.

[0010]

The configuration of the present invention is as follows.

1. Add quicklime to excavated soil and dehydrate,
In the method for treating excavated surplus soil for stabilization, the carbon dioxide is further added to the surplus soil after the treatment to neutralize the alkalinity of the surplus soil, and excessive hardening is prevented to optimize the bearing capacity of the soil. Excavation residual soil treatment method.

2. A hopper for charging the quicklime treated soil, a rotary valve for sending out the quicklime treated soil from the hopper by a fixed amount, and a rotating blade that is rotated by a motor drive are incorporated therein and a carbon dioxide gas line is introduced. And a rotary valve for feeding neutralized soil from the reactor in a fixed amount.

3. A hopper for charging the quicklime treated soil, a continuous feeder for sending out the quicklime treated soil from the hopper by a fixed amount, and a screw rotating by a motor drive are incorporated therein and a carbon dioxide gas line is introduced. And a continuous feeder for feeding the neutralized soil from the reactor by a constant amount.

[0014]

The calcium hydroxide remaining in the excavated soil after the quicklime treatment is neutralized by carbon dioxide into calcium carbonate by the following reaction.

Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O The generated water evaporates and decreases due to reaction heat generated during the neutralization reaction.

Further, there is a research result that the hardened lime-treated soil hardens over time after backfilling due to the porazone reaction.

That is, the porazone reaction refers to silica (SiO ₂ ) alumina (Al ₂ O ₃ ) which is a clay component in soil.
Reacts with quicklime to form lime silicate and lime aluminate, and is a reaction that hardens the soil.

The improved excavated soil must be properly hardened after backfilling and have the necessary bearing capacity, but excessive hardening is undesirable because it makes re-excavation difficult.

Accordingly, by suppressing the above reaction by neutralizing the quicklime treated soil with carbon dioxide gas before backfilling,
Excessive curing can be prevented over time. Calcium carbonate produced by the neutralization treatment is a naturally occurring substance and is harmless. As the carbon dioxide to be added, liquefied carbon dioxide, dry ice, and carbon dioxide by-produced in a petroleum refinery or a chemical factory can be used. Further, boiler combustion exhaust gas and the like can be used by performing an appropriate dehydration treatment.

Among the processing apparatuses, in a rotary blade type batch processing apparatus, a fixed amount of treated soil to which quicklime is added is received by a hopper, and is put into a reactor through a rotary valve. A prescribed amount of carbon dioxide required for the neutralization reaction is introduced into the reactor, and the mixture is stirred by a rotating blade to bring soil and carbon dioxide into contact and react. After completion of the neutralization reaction, the neutralized soil is discharged to a receiving hopper or a belt conveyor by a rotary valve at the bottom of the reactor.

On the other hand, in a continuous processing apparatus, treated soil to which quicklime is added is received by a hopper, and is continuously supplied to a reactor by a continuous feeder. From the other end of the reactor, a specified amount of carbon dioxide required for the neutralization reaction is introduced at a constant flow rate, and is brought into contact with and react with the treated soil transferred by the screw. The neutralized treated soil is continuously discharged onto a hopper or a belt conveyor by a feeder.

The above-described reactor is a dedicated device for performing a neutralization treatment. However, carbon dioxide gas is directly introduced into a crusher usually used in a process for treating excavated soil, and the neutralization reaction is performed simultaneously with the crushing. Can also be performed. As the neutralizing agent, in addition to carbon dioxide gas or waste gas containing carbon dioxide gas, liquefied carbon dioxide or dry ice can be used. In the latter case, a specified amount is directly or vaporized and then introduced into the reactor.

[0023]

EXAMPLES Experimental Example-1 (Experiment on Alkalinity) Kanto loamy soil was used as excavated soil, and 3%
Was added and crushed and mixed.

Table 1 shows the alkalinity and water content of the soil before and after the quick lime treatment.

[0025]

[Table 1]

Moisture: The soil sample was left at room temperature for 100 hours and dried to reduce the amount of drying. Carbon dioxide was added to the quicklime-treated soil for neutralization.

The alkalinity of the soil after the neutralization treatment is as shown in Table 2.

[0028]

[Table 2]

Neutralization treatment (1): In the case where 1 mol of carbon dioxide gas is added to 1 mol of added quick lime, carbonate is generated by the following neutralization reaction.

Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O After the reaction, it shows weak alkalinity. Neutralization treatment (2): In a case where carbon dioxide gas is excessively added at a ratio of 3 moles per mole of added quick lime, the neutralization reaction further proceeds, and the quick lime reacts with the carbon dioxide gas to form hydrogen carbonate.

After the reaction, Ca (OH) ₂ + 2CO ₂ → Ca (HCO ₃ ) ₂ is almost neutral.

As described above, in the neutralization treatment operation, by controlling the amount of carbon dioxide gas added, the reaction can be stopped at an appropriate stage and the alkalinity of the reclaimed soil can be adjusted. Experimental Example-2 (Experiment on Hardening of Soil) As an experimental sample, excavated residual soil to which about 3% of quicklime was added, and soil neutralized by further adding carbon dioxide to the treated residual soil were prepared. (Vaporize dry ice,
As a method for measuring the degree of soil hardening, a "subgrade bearing capacity ratio (CBR) test" (Japanese Industrial Standard JIS-A-1211) was performed for each sample.

Table 3 shows the experimental results.

After the co-specimen was prepared by the prescribed method, a curing period of 6 days in air and 4 days of water immersion was set, and then CBR was performed.
The value was measured.

[0035]

[Table 3]

The No. 1 sample was a soil sample to which about 2.8% of quicklime was added and which was not neutralized with carbon dioxide gas.
The value was as high as 50.4, indicating that the degree of cure was too high.

The sample of No. 2 was subjected to a neutralization treatment with carbon dioxide, and the degree of neutralization was calculated by adding the theoretical amount of carbon dioxide to the reaction of Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O. Equivalent to

In this case, the CBR value decreased, indicating that the degree of curing was considerably reduced.

The sample of No. 3 corresponds to the case where 1.5 times the theoretical amount of carbon dioxide was added, and the CBR value was further reduced, and the degree of hardening was further reduced.

In general, the appropriate CBR value is 3 to 20, but the CBR value can be controlled to an appropriate range by the carbon dioxide neutralization treatment.

The CBR value of mountain sand generally used as backfill soil is about 10 to 20, and the neutralized excavated soil shows the same CBR value as mountain sand.

FIG. 1 shows a batch-type processing apparatus using rotating blades. Reference numeral 1 designates a quicklime-treated soil, which is put into a hopper 2 and sent out via a rotary valve 3 in fixed amounts. The sent quicklime-treated soil 1 is sent into a reactor 4 in which a rotating blade 4a driven by a motor is incorporated. Carbon dioxide gas is introduced into the reactor 4 via a carbon dioxide gas line 5. As a result, the quicklime-treated soil 1 is uniformly reacted with carbon dioxide by stirring by the rotating blades 4a and neutralized. The neutralized soil thus neutralized is sent out by a rotary valve 6 to a neutralized soil receiving hopper 7 by a fixed amount. In the figure, reference numeral 8 denotes an exhaust line. FIG. 2 shows a continuous processing apparatus. In the case of this apparatus, the quicklime treated soil in the hopper 2 is fed from a continuous feeder 9 into a continuous reactor 10 incorporating a screw 11 driven by a motor.
While being agitated by the screw 11 and proceeding while being stirred, it is neutralized by reacting with the carbon dioxide introduced into the reactor 10 via the carbon dioxide gas line 5. The neutralized treated soil is sent out from the continuous feeder 12 to the neutralized treated soil receiving hopper 7.

[0043]

According to the present invention, the excavated surplus soil subjected to quick lime treatment is further neutralized with carbon dioxide gas to prevent alkaline contamination of groundwater upon reuse of the surplus soil and excessive hardening of the soil after backfilling. . As a result, the reuse of excavated surplus soil can be expanded, and the impact on the environment caused by collection of mountain sand and disposal of surplus soil can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a batch type processing apparatus embodying the present invention.

FIG. 2 is an explanatory diagram of a continuous processing apparatus embodying the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Quicklime treated soil 2 Hopper 3 Rotary valve 4 Rotary reactor 4a Rotor blade 5 Carbon dioxide gas line 6 Rotary valve 7 Neutralized soil receiving hopper 8 Exhaust line 9 Continuous feeder 10 Continuous reactor 11 Screw 12 Continuous feeder

Claims (3)

(57) [Claims] 1. A method for treating excavated remnant soil in which quicklime is added to the excavated remnant soil to perform dehydration and stabilization treatment, wherein carbon dioxide gas is further added to the treated remnant soil to neutralize the alkalinity of the remnant soil. A method for treating excavated soil, characterized by preventing hardening and optimizing soil bearing capacity. 2. A hopper for charging the quicklime treated soil, a rotary valve for feeding the quicklime treated soil from the hopper by a fixed amount, and a rotating blade which is rotated by a motor drive is built therein and a carbon dioxide gas line is built therein. And a rotary valve for feeding neutralized soil from the reactor in a fixed quantity. 3. A hopper for charging the quicklime-treated soil, a continuous feeder for feeding the quicklime-treated soil from the hopper by a fixed amount, and a screw that is rotated by a motor drive is incorporated therein and a carbon dioxide gas line is introduced. And a continuous feeder for feeding the neutralized soil from the reactor in a fixed amount.