JPH1181293A - Soft ground improving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively utilize industrial wastes and to reduce the execution cost by erecting coal ash columns in the soft viscous ground, covering the ground surface with a waterpermeable material, applying a load to it, draining the moisture in the viscous soil through the coal ash columns, hardening the coal ash columns, and forming the composite ground of the viscous soil and coal ash. SOLUTION: The coal ash generated at a thermal power plant is placed into the viscous soil of the soft viscous ground 1 to be improved by the sand drain method. Coal ash columns 2 are erected to reach the water-permeable layer 3 in the viscous soil, the ground surface is covered with a water-permeable material 4 such as sand mats, then a load 5 is applied by banking. According to this execution, the water in the soft viscous ground 1 is discharged to the ground surface through the coal ash columns 2, the load 5 is applied to the viscous ground 1, consolidation strengthening proceeds, and the ground 1 is improved. Industrial wastes are effectively utilized, and the execution cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention mainly relates to a method for improving the soft and viscous ground by placing a pillar of coal ash, applying a load to the entire ground, and utilizing the water permeability of the coal ash. Evacuate the moisture in the clayey soil of the ground to the surface,
The present invention relates to a method for improving soft ground, which effectively uses coal ash such as fly ash generated mainly from a thermal power plant to form a composite ground of viscous ground and coal ash utilizing the self-hardening property of coal ash.

[0002]

2. Description of the Related Art Conventionally, in order to improve a soft clay ground, a pillar of sandpile such as sand is poured into the soft ground, and a load is applied to the entire ground to thereby improve the soft ground. The sand drain method, which allows moisture to escape to the surface, is widely used.In this sand drain method, a large amount of good sand with relatively high permeability is used for the columns of the sand pile, and the cost of the sand used is low. Will occupy a large part of the construction cost for soft ground improvement.

On the other hand, the amount of coal ash generated at thermal power plants in the world in recent years has reached 500 million tons, but a large amount of coal ash is generated even in Japan, which is less dependent on thermal power generation than other countries. Approximately 60% of the coal ash is used as cement, construction and agricultural materials, but the remaining 40% is stored in power plants. Is to be buried, but there is a limit in the processing, and since these coal ash are industrial wastes, there is a problem that the processing is very expensive.

[0004] Accordingly, there is a demand for an effective utilization method of coal ash generated in large quantities in the above-mentioned thermal power plants.
As described above, the use as a cement material or as a material for construction or agriculture was not possible using coal ash alone, and the amount of use was limited.

[0005]

SUMMARY OF THE INVENTION As described above, the present invention uses coal ash generated in a thermal power plant as a pillar for improving soft, viscous ground by utilizing its permeability and self-hardening. To use and effectively use industrial waste coal ash,
An economical method for improving soft ground that can reduce the construction cost is provided.

[0006]

SUMMARY OF THE INVENTION The present invention comprises a method for improving a soft ground in which a pillar of coal ash is erected in a soft viscous ground, and the ground surface is covered with a water-permeable material before loading. According to the present invention, a pillar of coal ash is erected on a soft clay ground, the surface of the coal ash is covered with a permeable material, loading is performed, and the pillars of coal ash are used to load the clay ash into the clay ground. The method comprises a method of improving soft ground, which drains water and hardens coal ash columns to form a composite ground of cohesive soil and coal ash columns.

Further, the method for improving soft ground according to the present invention comprises:
As the above-mentioned coal ash, using fly ash and using clinker ash mixed with fly ash, using the above-mentioned coal ash as a slurry with water, and further packing the coal ash in a bag To use.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the method for improving soft ground according to the present invention will be described below with reference to the drawings.
FIG. 4 is a side sectional view showing a construction example when the ground improvement is performed by applying the above-described improvement method. In this case, as described above, in the viscous soil of the soft viscous ground 1 to be improved, A plurality of pillars 2 of coal ash are erected at a predetermined pitch by pouring the coal ash using a sand lane method generally used in the related art.

When such a pillar 2 of coal columns is erected, the casing is penetrated into the ground with a vibro hammer, coal ash is charged into the casing, and only the casing is pulled out. By charging the coal ash as a slurry mixed with water or by pre-packing the bag with the coal ash, it is easy to put the coal ash into the casing.

Next, as shown in FIG. 1, a pillar 2 of coal ash is erected in the viscous soil of the soft viscous ground 1 so as to reach the permeable layer 3, and the surface of the ground is permeable by a sand mat or the like. Material 4
Then, loading 5 by embankment or the like is performed. By performing such construction, water in the viscous soil 1 of the viscous ground 1 is drained upward through the pillars 2 of coal ash, so that the water in the soft viscous ground 1 is discharged to the surface of the ground and the load 5 Accordingly, a load is applied to the viscous ground 1 to strengthen the consolidation, thereby improving the ground.

Next, as the coal ash used above,
Generally, fly ash and clinker ash are roughly classified, but fly ash is mostly composed of fine particles of silt or less, so it seems to be naturally limited to use as a material for pillar 2 of coal ash. However, as a result of a series of investigations and experiments, the present inventors have found that the following characteristics are obtained.

That is, fine particles below the silt are certainly shown in FIG.
As shown in the particle size distribution diagram of fly ash, the fine ash is 80% occupied, but the fine particles are non-plastic soil, which is completely different from ordinary clayey soil. As a result, the water permeability is quite high, and when evaluated by the consolidation coefficient, it is 10 ³
It has been confirmed that it reaches 10 ⁴ times.

On the other hand, it has been pointed out that fly ash is a non-plastic material and therefore has a low liquefaction strength. However, as shown in FIG. Since a hardening action occurs, the above-mentioned disadvantages can be covered. Here, it should be noted that fly ash does not show a decrease in the water permeability due to the hardening effect over time, as shown in the relationship diagram between the consolidation time and the water permeability in FIG.

Next, in order to examine the applicability of the fly ash used as the coal ash as a drain material, a ground made of clay and fly ash is formed in an earth tank, and the ground made of clay and fly ash is formed. conducted a series of compaction experiments against the consolidation degree U an example of the experimental results, and organized in the time factor _{Th = Ch · t / d e} 2, the relationship between the degree of consolidation U and time factor Th of FIG Shown in the figure.

The solid line shown in this figure is a U-Th curve obtained from Baron's equation, and from the left side, n = d _e / d _w = 2.
5, 10 and 30 are supported. Although there is no particular difference between the two at the beginning of the consolidation, as the consolidation progresses, the actual measurement value of the fly ash ground is shown on the right side. Corresponding to Th at n = 10.

Therefore, if only the experimental results are obtained, the diameter is 5.
As an equivalent sand drain diameter drainage effect of 1cm fly ash of _{d e / d w = 10,} d e = 30cm → d w = 3
cm is obtained. The relationship between the fly ash drain diameter d _w (f) at U = 90% obtained by this method and the equivalent sand drain diameter d _w (s) is shown by the relationship between the fly ash drain diameter and the equivalent sand drain diameter in FIG. This is shown in the relationship diagram.

Here, d _w (s) equivalent to d _w (f) = 3 cm → n = 10 shows an extremely small value. In order to use fly ash, n of a certain value or more is adopted. must also as d _w (f) = 5.1cm and d _w (f) = 7.7cm to an equivalent d _w (s), respectively 3.5cm and 5.5cm
The following values were obtained.

Accordingly, when the drainage effect of fly ash was evaluated as the drain diameter, it was confirmed that about 60% to 70% of the sand drain could be expected. From the above experiments, fly ash used as coal ash of the present invention has a self-hardening effect with the passage of time, and the composite ground of cohesive soil and fly ash columns has increased strength but decreased permeability. Since no was observed, it was confirmed that it could be used as a substitute for the sand drain material.

That is, the shear strength of the composite ground of fly ash and cohesive soil is inferior to that of the composite ground of sand and cohesive soil at the time of sand draining, considering the hardening effect of fly ash over time. In this case, no decrease in permeability is observed. On the other hand, the drainage effect of fly ash, when evaluated by drain diameter, is 60% of sand drain to 7%.
Although it is 0%, comparing the cost of drain material and the cost of fly ash can cover it sufficiently, and when fly ash pillars are erected, the diameter can be increased and the pitch and spacing of erected pillars can be increased. It was confirmed that sufficient coverage can be obtained by making the density higher.

On the other hand, as described above, coal ash is roughly classified into fly ash and clinker ash. It is natural that fly ash used in the present invention is a mixture of clinker ash having a larger diameter as fly ash. Good results will be obtained.

[0021]

According to the method for improving soft ground of the present invention,
Since coal ash such as fly ash and clinker ash generated in large quantities at thermal power plants is effectively used for the material of the sand drain column of the sand drain method for improving soft viscous ground that has been widely adopted conventionally, It is economical because it can greatly reduce the construction cost,
This is very effective as a solution to the problem of treating coal ash, which has conventionally required cost as an industrial waste.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a construction example in which ground improvement is performed by applying the soft ground improvement method of the present invention.

FIG. 2 is a particle size distribution diagram of fly ash in an experiment conducted by the present inventors regarding characteristics of fly ash used in the improved method of the present invention shown in FIG.

FIG. 3 is a diagram showing the relationship between the self-hardening effect and the elapse of time during the experiment of FIG. 2;

FIG. 4 is a diagram showing the relationship between the consolidation time and the hydraulic conductivity during the experiment of FIG. 2;

5 is a diagram showing the relationship between the pressure density and the time coefficient during the experiment of FIG. 2;

FIG. 6 is a diagram showing the relationship between the fly ash drain diameter and the equivalent sand drain diameter during the experiment of FIG. 2;

[Explanation of symbols]

 1 Cohesive ground 2 Piles of coal ash 4 Permeable material 5 Loading

Claims (6)

[Claims] 1. A method for improving soft ground in which pillars of coal ash are erected on soft viscous ground, the ground surface of which is covered with a water-permeable material, and then loaded. 2. A pillar of coal ash is erected on soft clay ground, the ground surface is covered with a water-permeable material and loaded, and moisture in the clay soil of the clay ground is removed through the pillar of coal ash. A method for improving soft ground in which a composite ground of cohesive soil and coal ash columns is formed by draining and hardening of coal ash columns. 3. The method for improving soft ground according to claim 1, wherein fly ash is used as the coal ash. 4. The method for improving soft ground according to claim 1, wherein fly ash is mixed with clinker ash as coal ash. 5. The method for improving soft ground according to claim 1, wherein the coal ash is used as a slurry with water. 6. The method according to claim 1, wherein the coal ash is packed in a bag and used.
The method for improving soft ground according to 2, 3, or 4.