JPH0213608A - Improving method of weak ground - Google Patents

Abstract

PURPOSE:To form an improved ground to which forced precipitation or sinking of solidified material does not occur and which is light and superior in improvement effect and to improve execution efficiency and economical efficiency, by adding foaming particles and solidifying material to a weak ground and stirring and mixing them. CONSTITUTION:A pluverulent body or slurry which is arranged by mixing in advance foaming body particles of an independent bubble body type of which specific gravity is less than 0.5 and diameter of a particle is less than 2mm such as resin foaming body and solidifying material such as cement is supplied to a mixing/treating machine through a transmitting pipe. And it is discharged from the churning blade or the trencher part of the mixing machine to a soil to be improved, and immediately churning and mixing are done. In order to make weight decrease of the improved soil more distinctly, a foaming agent such as aluminum powder is used jointly. Further, in order to prevent floating of foaming body particles in the improved ground and to reinforce the improved ground, it is desirable to make use of a fiber material.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for improving soft ground.

(Prior art) Conventionally, as a method for improving soft ground, cement-based, lime-based, etc. solidifying materials are supplied to the soft ground either as a powder or in the form of a slurry by adding water, and the material is stirred and mixed.
Many construction methods are used to strengthen the ground. However, since the density of the solidifying agent is quite large compared to the density of soil particles, the weight of the improved soil tends to increase when using the assimilated material in powder form compared to before improvement. There is almost no difference when using . Therefore, unless the entire thickness of the soft ground is improved, consolidation settlement of the improved ground is unavoidable.Furthermore, if a structure is built on top of this, it will cause heaving to the surrounding ground, unevenness, etc. There were long-term negative effects.

In addition, solidification of dredged sludge using a solidification agent has been carried out many times, but in the case of sludge with a high water content of 300% or more, the solidified solidified material sinks.
This phenomenon is often observed, and there is a problem in that the surface of the solidified body is covered with separated water of the sludge or the sludge itself, and the purpose of the solidification treatment cannot be fully achieved.

Furthermore, when using solidifying material slurry for improvement, there is a limit to the ability of the pump to pump the solidifying material slurry from the slurry conditioning plant to the construction machine, so the water/solidified phase ratio of the solidifying material slurry must be adjusted depending on the conveyance distance. was increased in the range of '06 to '15 to lower the viscosity and suppress the conveying pressure from increasing. However, increasing the water/solidified phase ratio by adding extra water has the disadvantage that the improvement effect compared to using the same amount of solidified material is reduced.

(Problems to be Solved by the Invention) The purpose of the present invention is to eliminate the shortcomings of conventional techniques in the improvement method of soft ground. The purpose of this invention is to provide a method for improving soft ground with excellent performance.

(Means for Solving the Problems) The method for improving soft ground of the present invention is characterized by adding at least foam particles and a solidification material to soft ground and stirring and mixing to form improved ground. .

The essential feature of the foam particles of the present invention is that they are lightweight, and closed cell type foam particles with a specific gravity of 0.5 or less are preferably used. Specific examples of foams include resin foams made of polyolefin resins such as polystyrene resins, polyethylene, and polypropylene, synthetic resins such as polyurethane resins, polyvinyl chloride resins, and Evoquin resins, perlite, shirasu balloons, and metals. These include inorganic hollow bodies such as balloons, and include not only foamed beads formed by foaming beads, but also crushed foams such as new or recycled foam boards and foam blocks.

In addition, the particle size of the foam particles is not particularly limited as long as it does not cause problems in each construction process such as transportation, stirring and mixing (although it may not be possible to prevent it from floating in the improved ground). However, in order to ensure uniform dispersion, the particle size is preferably 2 mm or less.

Furthermore, the amount of foam particles to be added to soft soil is such that the ratio of the density of improved soil to virgin soil (improved soil/primitive soil) is 1. Although it is preferable to adjust it to OO or less, excessive addition of foam particles reduces the strength characteristics and workability of the improved soil. Therefore, the effective amount of the foam particles to be added is appropriately determined in consideration of the weight reduction, strength characteristics, workability, etc. of the improved soil so as to obtain the desired improvement effect.

The assimilation material may be any conventionally known assimilation material (such as cement, lime, gypsum, or a hydraulic composition made by adding fine aggregate, admixtures, etc. to these materials, or an asphalt composition). There are things etc.

Conventional methods can be used to add foam particles and assimilation material to soft ground and mix them with stirring. Preferably used is a method in which the mixture is supplied through a pipe to a mixing machine, discharged from a stirring blade of the mixing machine or from a part of a trencher into the soil to be improved, and stirred and mixed at the same time as the discharge.

When using a slurry of foam particles and solidifying material that is mixed and adjusted in advance, it is desirable that the water/solidified phase ratio be 0.05 or less. Lowering the water/solidified phase ratio prevents separation of foam particles and increases the improvement over the use of the same amount of solidified material.

Conventionally, setting the water/solidified phase ratio to 0.5 or less increased the conveying pressure, making construction difficult. However, by incorporating foam particles, the viscosity of the slurry can be reduced, making it possible to reduce the increase in the conveying pressure with the pump. Can be suppressed. In addition, the amount of foam particles preferably used in this case is 40 to 60 vol of the entire slurry.
1%, and this range provides excellent improvement effects and workability.

Note that, for the purpose of producing a slurry in which foam particles are uniformly dispersed, an admixture such as a surfactant may be added.

Another method of rolling, stirring and mixing foam particles and solidifying material onto soft ground is to pump the foam particles through a pipe and, in addition to discharging a slurry or powder solidifying material, into the soft ground. There is a method of discharging and stirring and mixing together with a solidifying material.

In this case, the amount of foam particles to be added can be selected relatively freely, although the number of conveying equipment is increased.

In order to reduce the weight of the improved soil more significantly, a foaming agent is used in combination. Examples of the foaming agent include powders of aluminum, magnesium, zinc, and aluminum alloys, and may be added in an effective amount depending on the purpose of soil improvement.

The foaming agent preferably used is aluminum powder, and the amount added is usually 2 wt % or less based on the solidifying material.

Furthermore, it is preferable to utilize a fibrous material in order to prevent the foam particles from floating in the improved soil and to reinforce the improved soil. Examples of fiber materials include short resin fibers, small pieces of nonwoven fabric, or small pieces of woven fabric, etc.
There is no particular limitation as long as it can be stirred and mixed, and the method of addition is also a method of spraying a predetermined amount on soft ground in advance, a method of mixing it with foam particles and a solidifying agent in advance, and using it. Any method that allows uniform stirring and mixing may be used.

(Effects of the Invention) The present invention makes it possible to improve the problem of consolidation settlement and the problem of subsidence of solidified material in ultra-soft ground with the same workability as conventional methods in the improvement method for soft ground. .

According to the present invention, as a result of mixing foam particles into the ground, soft soil replaces the foam particles, and the amount of solidifying agent added can also be reduced.

In addition, when using a slurry solidifying material, even if the water solidifying material ratio of the slurry itself is lowered, the workability will not be impaired.
It also has the effect of increasing the improvement effect when using the same amount of assimilated material.

When applied to the solidification treatment of dredged sludge, the present invention reduces the weight of the solidified material and causes it to float on top of the sludge, causing the surface of the solidified material to rise above the sludge water surface, causing the separated water of the sludge to cover the surface of the solidified material. As the surface area dries, the solidified material itself becomes stronger and exhibits a particularly remarkable effect.

Furthermore, when a mixture of foam particles and powder solidified material is transported by air, it is less likely to be clogged by moisture inside the pipe. It can also be used in solidification treatment in sludge ponds, and compared to the use of slurry in stable treatment of ultra-high water content, it does not add water, leading to improved improvement effects and a reduction in the amount of solidification material used.

The combined use of a foaming agent is effective in supplementing the weight reduction effect of improved soil when the amount of foam particles added is limited by construction ability.

In addition, the use of fiber materials randomly intertwines with the foam particles in the uncured improved ground, suppresses the lifting of the foam particles, disperses them uniformly, and has the effect of reinforcing the improved ground, thereby preventing sludge. This is especially effective when the solidified material is floating on top of sludge, such as during solidification treatment.

(Example) Polystyrene foam beads (particle size 2+n+++) were mixed into cement slurry as foam particles, the mixability was confirmed, and the mixture was further mixed with ultra-soft soil and this mixture was studied. Note that aluminum powder was used as the foaming agent.

Ultra-soft soil was prepared in a circular soil tank (φ2700.h2100), and an improved column (φ800.h2100. 17T1') was constructed.

Soft soil is prepared by adding water in advance in a soil tank and mixing thoroughly.
It has the following properties.

For this soft soil, add 200 kg/m of ordinary cement.
Slurry-like solidifying materials were prepared for the following four types with the target addition amount of ', and mixed and stirred.

(A) (B) (C) (D) Immediately after this mixing, the density of the sample was measured and the results are as follows.

From this result, the density of the improved soil using cement slurry containing foam beads is 1.274 t/m', while the density of the soft soil is 1.340 t/m'. No subduction occurs. Furthermore, by adding a foaming agent, the density of the improved soil is further reduced, which is found to be effective when used for the purpose of weight reduction.

In addition, conventional cement slurry only ((B) and (
It can be seen that in C)), the density increases due to the amount of cement added.

Furthermore, the results of the unconfined compressive strength (7 days curing) of these improved soils are as follows.

This result shows that although there is a decrease in strength due to the inclusion of foam beads, the improvement effect is improved by reducing the water-cement ratio.
It can be seen that the improvement effect is almost the same as that of conventionally used cement slurry. Although the addition of a foaming agent lowers the strength compared to adding and mixing only foamed beads, it is judged that there is no problem as long as it is used according to the purpose.

Even when mixed with ultra-soft ± (high water content) in this way,
As long as the foam particles themselves were fine particles, no significant separation was observed, and a good improved product was obtained.

Patent applicant: Nippon Hodo Co., Ltd. ,,p-5, Agent: Patent attorney Takehiko Saito Same as patent attorney Kawase Ryo 1o-18.

Claims (1)

[Scope of Claims] 1. A method for improving soft ground, which comprises adding at least foam particles and a solidifying agent to soft ground and stirring and mixing to form improved ground. 2. The method for improving soft ground according to claim 1, characterized in that a foaming agent is also added to the soft ground and mixed with stirring. 3. The method for improving soft ground according to claim 1 or 2, characterized in that a fiber material is also added to the soft ground and mixed by stirring.