JP2889464B2 - Stabilization method for backfill soil - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underground structure in which a ground is excavated or excavated to bury underground pipes such as water and sewage, electricity, gas and the like and an underground structure (hereinafter referred to as an underground structure). After constructing or laying the soil, in the construction where the earth and sand are buried around it, in order to stabilize the buried soil around the underground structure, spray or inject a consolidation chemical solution into it, The present invention relates to a method for stabilizing backfill soil for strengthening and reducing water permeability. 2. Description of the Related Art Conventional stabilization methods for backfill soil include a method of digging or excavating the ground to build (or lay) an underground structure underground, and then using a sandy soil such as mountain sand as much as possible. In many cases, it is densely tamped and backfilled, and cement,
A method of backfilling after adding a solidifying material such as lime has been proposed. [0003] The above-mentioned conventional stabilization of backfill soil around an underground structure has the following problems. [0004] In the conventional method of backfilling permeable sandy soil itself such as mountain sand, which is the most common, the voids around the underground structure to be backfilled are very narrow and localized, and general Unlike the case where a large landfill area with expansion like an embankment is ensured, it is difficult to mechanically roll it with heavy equipment or the like, and it is not possible to expect sufficiently compacted backfill. [0005] For this reason, there is a problem that ground subsidence occurs due to vibration of a running vehicle such as an automobile, an earthquake, or the like, and a cavity is formed below a road surface or the road surface collapses. [0006] In particular, in the case of tap water and sewerage, the connecting portion of the laid pipe is damaged due to the depression of the road surface and the like, and water leakage or infiltration of groundwater occurs. The problem is that subsidence occurs. (B) On the other hand, the method of adding a small amount of solidification material to backfill soil (sandy soil) can increase the solidification strength to some extent, but the solidification material is powder and is uniformly stirred. It is very difficult to mix, and there is a problem that water permeability cannot be reduced. As described above, the conventional method for stabilizing backfill soil includes many problems. To solve such problems, reduction in compaction strength and water permeability are required. It is desired to develop an improved stabilization method. According to the present invention, as a chemical liquid for solidifying backfill soil, finely divided calcium hydroxide having an average particle size of about 8 μm or less, which is insoluble in water and poured into water, is applied to 1 m of the chemical liquid. By adding water glass to a suspension containing 2.5 to 25 kg per ³ , an osmotic chemical solution that dissolves most of the calcium hydroxide is sprayed or injected into the backfill soil and consolidated. It proposes a stabilization method for the backfilled soil. The solubility of calcium hydroxide in water is 20 ° C.
0.165 g / 100 g of water, which is a poorly soluble alkali that is only slightly soluble in water.However, in the presence of a water glass component, it dissolves in an amount sufficient for practical use, and water glass with a gel time according to the amount added. Is gelled. This calcium hydroxide has a small change in gel time even if the amount of calcium hydroxide is slightly varied, the gel time can be easily adjusted (gel time: 3 to 150 minutes), the workability is very excellent, and the gel ability is excellent. It is very excellent as a solidifying agent for backfill soil, such that even a small amount of hardening agent can be solidified. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of stabilizing backfill soil according to the present invention is intended to solve the problem that conventional suspension-type (non-permeable) chemicals cannot be used as a flash-setting type using only cement components. Auxiliary as a chemical accelerator (not used alone)
Fine powder containing calcium hydroxide as a component
It has been found that the powder has a unique reaction with water glass, and has been completed by using a chemical solution that sufficiently satisfies the performance as a permeable chemical solution. That is, calcium hydroxide has a solubility in water of 0.165 g / 100 g of water at 20 ° C., and it is well known that calcium hydroxide is a sparingly soluble alkali which is very slightly soluble in water. It has been found that a practically sufficient amount dissolves in the presence. The amount by which the calcium hydroxide fine powder of the present invention dissolves in the presence of water glass is affected by the fineness, the type of water glass, the contact time with water glass, the mixing method, and the like. Among them, the influence of the fineness is particularly large. According to the embodiment, the amount of calcium hydroxide that is dissolved (50% or more) is about 25 per m ³ of the chemical solution.
There is about kg. The fineness of the calcium hydroxide of the present invention is preferably as fine as possible. However, in consideration of the technical limitations at present, fine particles having an average particle diameter smaller than about 8 μm are used as a standard. In the present invention, since such fine particles are used,
Even if a very small amount of insoluble particles are present in the chemical solution, they can penetrate sandy soil. That is, even if the fine sand particles are very fine and the fine powder particles of calcium hydroxide cannot penetrate, the amount contained in the chemical solution is very small, so that the penetration of the solution portion is inhibited. There is almost no permeability and it shows the same or similar permeability as the conventional solution type. Therefore, the amount of calcium hydroxide used in the present invention is in the range of about 2.5 to 25 kg per m ³ of the chemical solution. That is, about 1 m ^{3 of} calcium hydroxide
Although it has a gelling ability even if it is 2.5 kg or less, it was excluded from the present invention because its consolidation strength was too small. On the other hand, when the amount of calcium hydroxide is about 25 kg or more per 1 m ³ , the insoluble content tends to be larger than the dissolved content. However, depending on the type of the backfill soil, if the technical range of the permeable chemical solution of the present invention can be sufficiently exhibited, the amount of calcium hydroxide slightly exceeds the above-mentioned limit. However, it can be considered as the scope of the present invention. The hardly soluble fine particle calcium hydroxide of the present invention which is introduced into water is present as a substance called Ca (OH) ₂ when introduced into water, and is specifically slaked lime and quicklime. . The same fine particles of calcium compound
Even compounds other than calcium hydroxide have water glass
Hardly melts below, or melts to some extent
Since it does not show a practical gelling ability,
Not suitable . In the present invention, as in the prior art for fine particles, it is needless to say that a dispersant, a retarder if necessary, and other additives can be used. [0025] Even if the chemical solution is outside the limited range of the present invention, if it has the same properties as the chemical solution of the present invention and can obtain sufficiently satisfactory results in terms of construction, the backfill of the present invention can be used. Can be used as a soil compaction agent. The construction method for solidifying the backfill soil of the present invention is not particularly limited, but the following two methods can be adopted. (A) When the underground structure such as a buried pipe is relatively shallow, after the pipe periphery is densely backfilled with sandy soil such as mountain sand, a chemical solution having a long gel time of about 30 minutes or more (as the solution A) Water glass, B
Liquid mixture of fine particles and calcium hydroxide suspension)
And infiltrate the backfill soil to consolidate it. Further, in the spraying method of the present invention, a chemical solution is sprayed on the ground surface of a highly permeable ground such as a sand ground outside of the backfill soil to reduce or solidify the ground. be able to. (B) When the underground structure is relatively deep, an injection pipe is buried at the same time when the sandy soil is backfilled, or after the backfill, the injection pipe is inserted to inject the chemical. In this case, although not particularly limited,
When the gel time of the chemical solution is 20-30 minutes or more, use the one-shot method (a mixture of A and B liquids as in the case of spraying). When the gel time is 20-30 minutes or less, use the 1.5-shot method (the A and B liquids). The two liquids are pumped by separate pumps and the two liquids are merged at the head of the injection pipe) to infiltrate and solidify the backfill soil and the surrounding ground. When an injection pipe is used in the above-mentioned construction method, the chemical solution of the present invention is used not only for backfilled soil (disturbed soil) but also for natural ground (undisturbed soil) as well as general ground injection. Of course, it can be penetrated. By the above construction method, the backfill soil around the underground structure is infiltrated with the chemical solution and solidified.
Permeability decreases with increasing ground strength. Therefore, it is possible to prevent vibrations and earthquakes of vehicles and the like, land subsidence due to the vibrations and the resulting collapse of cavities and road surfaces (roads), thereby preventing damage to underground structures such as buried pipes. Even if the buried pipes of water and sewage are broken, there is little water leakage and the backfill soil around the pipes is solidified, so there is little outflow of sand, and cavities and depressions are prevented. Can be. Hereinafter, the chemical solution of the present invention will be described in detail with reference to examples. The calcium hydroxide used in the experiment was a sample 1 (average particle diameter of 10.9) having different particle diameters (particle diameter distribution) shown in FIG.
μ = Brain value 10,315 cm ² / g ), sample 2 (average particle size 5.3 μm)
= Brain value 18,150cm ² / g ), Sample 3 (average particle size 2.8μ)
= Brain value 24,760cm ² / g ), water glass is JI
S3 product was used. As the backfill soil, mountain sand from Chiba Prefecture having the properties shown in Table 1 below was used. [Table 1] "Experiment-1" In order to confirm the amount of fine particles of calcium hydroxide suspended in water to dissolve in the presence of water glass, both were stirred and mixed for a certain period of time, and then filtered through a paper filter (No. In 2), solid-liquid separation was performed by suction filtration, and the amount of dissolution was measured. Further, the gel time of the filtered solution (chemical solution) was measured, and the gel time when the calcium hydroxide fine particles and water glass were constantly stirred and mixed until gelling was measured. Table 2 shows the results. [Table 2] In the column of the amount dissolved in water glass in Table 2, * indicates the result of stirring both solutions A and B for 3 seconds, and ** indicates the effect of stirring for 60 seconds. Indicates the result of stirring for 30 seconds. From the above Table 2, it is found that the compound is hardly soluble in water (0.165 g / water).
100 g) of calcium hydroxide was found to dissolve in a very large amount in the presence of water glass, and the amount of dissolution was affected by the fineness of the calcium hydroxide and the stirring time. There was found. Further, the gel time of the solution portion excluding the particle portion is delayed with respect to the gel time in which the water glass and the calcium hydroxide fine particles are always mixed until gelation,
It can be seen that the degree is greatly affected by the fineness of the particles, and the difference is particularly large when the fineness is 10 μm (sample 1). In view of the above dissolution amount and gel time,
The fineness of the calcium hydroxide used in the present invention is preferably fine particles having an average particle size of about 8 microns or less, which is within the scope of the present invention. "Experiment-2" The following experiment was carried out in order to see the reduction of the solidification strength and water permeability when the chemical solution of the present invention was sprayed on mountain sand. A sample of the consolidation strength was prepared by dividing mountain sand into three layers in a vinyl chloride tube (mold) having an inner diameter of about 5 cm and a height of 15 cm with a closed bottom, and performing five times per layer (with a stick having a diameter of 4.8 cm). (With a tree). From the upper part of the sample, the chemical solution (mixture of A and B) of Example 2 in Table 2 was solidified by sufficiently spraying it from a mug. One day later, it was unframed, shaped to a height of 10 cm, cured for 7 days, and measured for uniaxial compressive strength to be 1.8 kgf / cm ² . The hydraulic conductivity is determined by the same method as described above.
When a consolidated product having a height of 10 cm and a height of 15 cm was prepared and measured according to JIS A1218T, it was 2.5 × 10 ^-6 cm / sec, and the permeability was significantly reduced as compared with untreated mountain sand. "Experiment-3" An experiment was conducted on the solidification strength and water permeability when the chemical solution of the present invention was poured into mountain sand. For the preparation of a sample having a compaction strength, as in Experiment 2, mountain sand was densely packed in a mold having an inner diameter of 5 cm and a height of 15 cm. For injection, the chemicals (mixtures A and B) of Example 11 in Table 2 were press-fitted from below the mold. The injection pressure at that time was about 0.5 kgf / cm ² or less. The unconfined compressive strength was measured in the same manner as in Experiment-2 and found to be 3.1 kgf / cm ² . When the coefficient of permeability was measured in the same manner as in Experiment-2, the coefficient of permeability was 6.8 × 10 ⁻⁷ cm / sec, which was significantly reduced. As shown in Experiment 2 and Experiment 3 above, by spraying or injecting a chemical solution, it is possible to strengthen the backfill soil around the underground structure, reduce the water permeability, and stabilize it. it can. As described above, according to the present invention, fine particles of calcium hydroxide are used as a hardening agent for a chemical solution used as a solidifying agent for backfill soil around an underground structure, and the presence of water glass is used. An excellent backfill soil that can protect the underground structure and stabilize the surrounding ground by consolidating the backfill soil around the underground structure with a permeable chemical solution that is largely dissolved in the chemical solution It is a consolidation method. In the method for spraying a chemical solution according to the present invention, the chemical solution is directly sprayed on the ground surface of a ground having good water permeability such as sand ground outside the backfill soil to reduce the water permeability of the ground or to consolidate the ground. In addition, the method using an injection pipe reduces the water permeability and consolidation of the ground by general ground injection for natural ground (undisturbed soil) in addition to backfill soil (disturbed soil). It can also be used as a ground stabilization method.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a particle size distribution diagram of each sample of calcium hydroxide used in an experiment of the present invention.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shigeyoshi Tomita 5-19-16 Minamisuna, Koto-ku, Tokyo (56) References JP-A-1-176262 (JP, A) JP-A-1-190786 (JP, A) JP-A-5-320644 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) E02D 3/12 101 E02D 3/12 103

Claims (1)

(57) [Claims] Insoluble calcium hydroxide having an average particle size of about 8 μm or less, which is poured into water, is added in an amount of about 2.5 to 25 kg per m ³ of a chemical solution.
By adding water glass to the suspension containing the osmotic drug solution in which most of the calcium hydroxide was dissolved,
A method for stabilizing a backfill soil, comprising scattering or pouring into the backfill soil and consolidating the same.