JPH0559060B2 - - Google Patents

Description

[Detailed description of the invention]

"Field of Application of the Invention" The present invention relates to a backfill injection material used in shield construction methods and the like. "Prior Art" In general, it is preferable that backfilling injection materials have low cost, good workability and injection characteristics, and exhibit strength early after injection. That is, as shown in FIG. 3, it is necessary to have a necessary pot life and to have good strength development thereafter. In particular, as shown in Figure 1, recent shield construction methods often employ a simultaneous injection method in which backfill material is injected in real time into tail voids that occur simultaneously with excavation. Therefore, it is necessary that the strength development property after injection is good. In addition, in the case of the shield method, since it is a one-sided push underground, the delivery of materials and machinery is limited to one place, and the excavation cross section is limited, so injection machines etc. are installed at the face. As shown in Figure 2, it is difficult to bring in the material, so it is usually mixed in an onshore plant and then transported by a pump to the face and injected into the tail void.As a result, backfill injection has the ability to be pumped over long distances. material is required. By the way, the applicant has previously proposed a backfill grout consisting of cement, water glass, and bentonite as one of the additives, which produces a fluid gel without caking and can reduce bleeding. Developed soft grout (Japanese Unexamined Patent Publication 1973-
Publication No. 41314). ``Problems to be Solved by the Invention'' However, the conventional grout described above is currently a waste of coal ash called flyash, which is discharged from thermal power plants, where the disposal site is becoming a problem as industrial waste, and the amount of grout emissions is increasing. Moreover, since it uses cement, the hydration reaction is quick (pot life is about 2-3 hours).
When it is pumped over long distances as a backfilling material, it has the disadvantage that it cannot be kept in the pumping pipe for a long time. ``Means for Solving the Problems'' In order to meet the above-mentioned demands as a backfill injection material, this invention aims to solve the problem of disposing of industrial waste, which is currently a problem, and to use coal ash, which is available at a low price, as the main material. By adding water and an adhesive such as slaked lime and fine clay mineral powder to this and kneading it, we can create an inexpensive backfilling material with good strength development that retains thixotropic properties and can be pumped over long distances. This is a proposal. ``Example'' To explain the present invention below, the backfill injection material of the present invention uses coal ash as a main ingredient, and slaked lime, clay mineral fine powder, and water are added and kneaded to form a slurry that can be pumped over long distances. Water glass is added and mixed to maintain thixotropic (plastic gel) properties. Coal ash, slaked lime, and water glass, which are the main materials used in the present invention, react as follows. That is, coal ash has latent self-hardening properties, and when slaked lime is added to it, a pozzolanic reaction occurs. However, this reaction is extremely slow, and it takes several tens of days or more to obtain the consolidation strength required as a backfilling material, making it unsuitable for practical use. However, adding water glass to this has the effect of accelerating the pozzolan reaction. On the other hand, when slaked lime and water glass are mixed, a gelation reaction occurs rapidly, causing gelation in a short time.
Appears thixotropically. Furthermore, the slurry of the backfilling material of the present invention has a long pot life and is therefore very suitable for long-distance pumping. On the other hand, cement causes the same reaction as slaked lime, but although it has higher consolidation strength than slaked lime, it has inferior gelling ability, and the pot life of the slurry is short, making it difficult to pump over long distances. Therefore, it has been excluded from the present invention. However, similar to the pozzolanic reaction of coal ash, water slag with a long pot life can be used in combination. In addition, any clay mineral can be used as long as it functions as an aggregate that prevents material separation of the mixed slurry of coal ash, slaked lime, and water and enables long-distance pumping without causing breathing. Bentonite, which is a montmorinite clay mineral that has excellent properties as a clay mineral and is easy to obtain, is particularly preferred. The above-mentioned thixotropic property refers to Japanese Patent Application No. 152229/1983 filed earlier by the present inventors and
−135292 (refers to grout that is self-supporting in a static state, but has the property of easily flowing when pressurized (injected));
This property is produced by mixing water glass into a slurry of coal ash, the above-mentioned slaked lime, fine clay mineral powder, and water and gelling the mixture. The construction of the backfill material of the present invention is basically to pump liquid A and liquid B separately and to combine both liquids A and B in front of the grout hole. , B can also be mixed and pumped. Next, various experiments were conducted by mixing water glass (hereinafter referred to as B liquid) to a slurry made by kneading coal ash, slaked lime, and bentonite with water (hereinafter referred to as A liquid), and the results shown in Figures 4 to 6 were obtained. Ta. Figure 4 shows the relationship between the rate of addition of slaked lime and the amount of bentonite added to the breathing rate in liquid A. The higher the rate of addition of slaked lime and the amount of bentonite, the more difficult it is for breathing to occur, and the lower the breathing rate is overall. I understand. It was also found that this liquid A did not solidify for about 20 hours or more and was highly fluid. Therefore, from these results, it was found that liquid A has extremely excellent long-distance pumping properties. Figure 5 shows the relationship between gel time and unconfined compressive strength as a function of the amount of slaked lime added by mixing fluid B with fluid A. The gel time becomes shorter as the amount of slaked lime increases, and the unconfined compressive strength increases accordingly. I found out. Furthermore, FIG. 6 shows the relationship between the change in unconfined compressive strength over time after gelation, and it was found that although a rapid increase in strength was observed in the initial stage, the increase thereafter was gradual. Such a large increase in initial strength can be expected to have a sufficient effect in suppressing the large displacement of the ground at the initial stage of stress release during excavation of a shield or the like. Furthermore, Figure 7 shows the relationship between coal ash concentration and unconfined compressive strength.As is clear from this figure, as the coal ash concentration increases, the strength increases significantly, especially when Ca(OH) ₂ /water This becomes noticeable when the ratio exceeds 0.1. It has been found that when this ratio is less than 0.1, there is no increase in final strength, so expectations for solidification strength are low. In general, the backfilling material should have a soil strength of 5 kg/cm ² or less, and the lower the water permeability coefficient of the material, the better. However, since the backfilling material of this invention is mainly composed of water glass siloxane gel The permeability function was extremely small, with a value of about 10 ^-6 cm/s. Example When materials A and B having the compositions shown in the table below were mixed using a pipe mixer and filled into a predetermined mold, the uniaxial compressive strength for the material age shown in FIG. 8 was obtained. As a result, it was found that the strength developed early in all cases, and the strength increased as the amount of coal ash increased.

[Table] It goes without saying that the backfilling material of the present invention can be used in a wide range of applications, including shield construction methods, other backfilling materials, and injection materials for cavity filling.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal side view showing the state of simultaneous injection construction in the shield method, Fig. 2 is a partial longitudinal side view of the main part, Fig. 3 is a diagram showing the strength characteristics required for backfill injection material, Fig. 4 is a diagram showing the results of a breathing test of the backfill material of the present invention, Fig. 5 is a diagram showing the experimental results of gel time and unconfined compressive strength, and Fig. 6 is a diagram showing the change in unconfined compressive strength over time. FIG. 7 is a diagram showing the experimental results, FIG. 7 is a diagram showing the relationship between coal ash concentration and strength, and FIG. 8 is a diagram showing the strength characteristics of the injection material shown in Examples.

Claims (1)

[Claims] 1. A slurry made of coal ash as a main material, slaked lime, clay minerals, and water added and kneaded to form a slurry that can be pumped over long distances, and water glass added and mixed to form a thixotropic slurry. A backfilling material characterized by 2 Water glass is added to 1 slurry of 0.1 to 0.8 by weight of coal ash, 0.1 to 0.4 of slaked lime, and 0.05 to 0.4 of bentonite in a weight ratio of 1 to 1 of water.
The backfilling material according to claim 1, characterized in that it is made by mixing 0.05 to 0.4.