JP2001172955A - Method for using soil having high fine-grained fraction content - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for effectively using soil having a high fine- grained fraction content (higher than 15%) as a pile material for a sand pile soil improvement method. SOLUTION: When the moisture content is not more than 25% and a plasticity index is not more than 20%, soil having the high fine-grained fraction content is used as it is, and when it is not satisfied with conditions, it is satisfied with an appropriate measure (for the moisture content, one or both of sun-dry and addition of a dewatering material, and for the plasticity index, plasticity index, the adjustment of the particle size by addition of a coarse grain material) to use. When an available mode dose not consider pile strength in terms of design, it is used for the improvement of sandy soil at the low ratio of displacement, or it is used for the improvement of cohesive soil at the low ratio of displacement by using it together with a proper drainage material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for using soil having a high fine particle content.

[0002]

2. Description of the Related Art When soil having a large fine grain content (soil having a fine grain content of more than 15%) is used as a pile material in a sand pile-based soil improvement method, a casing of the material (pile for pile formation) is used. Sufficient consideration is needed from both the construction side regarding the introduction into the hollow tube, the movement in the casing, and the discharge of materials from the casing, and the design side regarding strength and drainage. There was no established guideline, and in each case, a lot of time and labor was required for preliminary examinations such as laboratory tests and field construction tests.

[0003]

SUMMARY OF THE INVENTION The problem to be solved by the present invention (object of the present invention) is that, in view of the above-mentioned circumstances, the conditions that can be used in construction and design are determined by relatively simple test results. It is an object of the present invention to provide a rational, efficient, and economical method for effectively using soil having a large fine particle content as a pile material in a sand pile-based ground improvement method.

[0004]

In order to solve the above problems, in the invention according to claim 1, the soil having a fine particle content of more than 15% has a water content of 25% or less and a plasticity index of 20 or less. In such a case, if the above condition is not satisfied, the condition is satisfied by an appropriate means, and the sand is used as a pile material in a sand pile ground improvement method.

[0005] In the invention according to claim 2 which is dependent on the invention of claim 1, when the water content of the soil is more than 25%, either one of the solar drying and / or the addition of the dewatering material is used. %, And in the invention according to claim 3 which is also dependent on the invention according to claim 1, when the plasticity index of the soil is larger than 20, the particle size is adjusted to be 20 or less by adding a coarse-grained material. I have to.

Next, in the case where soil having a fine grain content of more than 15%, a water content of 25% or less and a plasticity index of 20 or less is used as a pile material in a sand pile type soil improvement method, In the invention according to the present invention, when the pile strength is not taken into account in the design, it is used for improving the sand ground at a low replacement rate. In the invention according to claim 5, when the pile strength is not taken into account in the design, In the invention according to claim 6, when the pile strength is considered in the design but the drainage is not considered, the design pile strength is used. Is set lower than usual and is used for the improvement of cohesive ground at a medium / high replacement rate. In the invention according to claim 7, when the pile strength and drainage are taken into consideration in design, the design pile strength is Is set lower than usual, and with appropriate drainage material, It has been used to improve the viscosity of the land board.

The fine particle content, the water content and the plasticity index are determined from a prescribed particle size test, a water content test and a liquidity / plasticity limit test.

[0008] The water content is related to the difficulty of charging the soil into the casing and moving in the casing, and the plasticity index is related to the quality of the discharge (material removal) of the soil from the casing.
When the water content is 25% or less and the plasticity index is 20 or less, these points (injection into the casing, movement in the casing,
It has been experimentally confirmed by the present inventors that there is no problem in terms of discharge from the casing).

[0009] The plasticity index and the hydraulic conductivity are correlated, and when the plasticity index is 20 or more, a predetermined hydraulic conductivity is ensured, which ensures that the soil is well discharged from the casing. By securing the permeability, the permeability required for discharging the soil from the casing is secured.) In this case, the permeability of the soil is determined by the permeability required for draining the ground. Since it is smaller than the coefficient, when considering ground drainage in the design of ground improvement, appropriate drainage materials should be used together.

Also, the plasticity index and the shear strength are correlated,
When the plasticity index is 20 or less, a predetermined shear strength is secured. However, since this strength is smaller than the strength of soil having a normal fine grain content of 15% or less, the pile strength is reduced in the design of ground improvement. When considering, the design strength should be set lower than usual.

The criteria for the level of the replacement rate (the ratio of the area occupied by the piles to the improved ground) are not always clear, but are based on 0.3. The case of less than this can be called a low substitution rate.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In practicing the present invention, first, a soil grain size test is performed to check the grain size composition. The results are preferably plotted on triangular coordinates according to the Japan Unified Soil Classification Method.

FIG. 1 is a schematic view of the above-mentioned triangular coordinates. In the figure, A is a zone having a fine particle content of less than 15%, B is a zone having a fine particle content of more than 15% and a silt content. Zone where the ratio of clay to clay is 2 or more, and C has a fine particle content of 15
% And the ratio of silt to clay is less than 2.

The zones B and C are classified based on the compaction characteristics of the soil. The soil belonging to the zone B has good compaction characteristics, and the soil belonging to the zone C has poor compaction characteristics.

In the present invention, when the content of fine particles is 15% or more as a result of the soil particle size test, a water content test and a liquidity / plastic limit test are performed to determine whether or not the water content is 25% or less. And whether the plasticity index is 20 or less.

In this case, since the present inventors have confirmed based on experiments and the like that the plasticity index of the soil belonging to zone B in the case of zone division as described above is 20 or less, The liquid / plastic limit test of the soil plotted in (1) can be omitted.

The soil plotted in zone B is
If the water content is 25% or less, it can be used as it is as a pile material in the sand pile ground improvement method. If the water content is more than 25%, it can be used as a pile material by lowering the water content by solar drying. To

In the case of the soil plotted in the zone C, first, the plasticity index is obtained, and if it is 20 or less, the moisture content is obtained. If this is 25% or less, the pile index of the sand pile ground improvement method is directly used. If it is larger than 25%, it is used as a pile material by adding a dehydrated material such as quicklime or cement, or by drying in the sun to lower the water content.

On the other hand, when the plasticity index is larger than 20,
Add coarse-grained materials such as sand, gravel and crushed stone to adjust the particle size,
Again, it is used as a pile material in the above procedure, and if there is no suitable material for adjusting the particle size, another use is searched.

Next, when the above-mentioned soil having a fine particle content of 15% or more, a water content of 25% or less, and a plasticity index of 20 or less is used as a pile material in a sand pile type soil improvement method,
When the pile strength is not considered in the design, it can be used for improvement of sandy ground and cohesive ground at a low replacement rate (for example, 0.05 to 0.3). In this case, it is used for improvement of cohesive ground. In this case, an appropriate drainage material (for example, a plastic board) should be used together.

When considering the pile strength and drainage in the design, the above-mentioned soil can be used in combination with an appropriate drainage material to improve the viscous ground at a low replacement rate. The pile strength should be set lower than usual (for example, the strength corresponding to an internal friction angle of 28 °).

The above-mentioned soil can be used for improvement of cohesive ground at a medium / high replacement rate (for example, larger than 0.3) when the pile strength is considered in design but drainage is not considered. In this case, the design strength of the pile should be set in the same manner as described above.

It is convenient to carry out the present invention if the above-described embodiment is displayed in a flowchart separately for the construction side and the design side.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of triangular coordinates used for implementing the present invention.

[Explanation of symbols]

 A: zone, B: zone, C: zone.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomohiro Isoda 2-15-102 Ninoki, Asahigaoka-cho, Hanamigawa-ku, Chiba-shi, Chiba Prefecture (Park Town 3rd Avenue 8-301) (72) Inventor Hideki Ishida 2479-2 Wakakusa-cho, Nakakoma-gun, Yamanashi F-term (reference) 2D043 CA06 DA05 EA01

Claims (7)

[Claims] 1. When the water content of the soil having a fine particle content of more than 15% is 25% or less and the plasticity index is 20 or less, the condition is satisfied as it is. A method of using soil with a high fine-grain content as a pile material in pile-based ground improvement methods. 2. When the water content of the soil is greater than 25%,
2. The method of claim 1, wherein the content of fine soil is large by 25% or less by one or both of solar drying and addition of a dewatering material. 3. When the plasticity index of the soil is greater than 20,
2. The method according to claim 1, wherein the grain size is adjusted to 20 or less by adding a coarse-grained material. 4. When using soil having a fine particle content of more than 15%, a water content of 25% or less and a plasticity index of 20 or less as a pile material in a sand pile-based soil improvement method,
A method of using soil with a high subdivision rate that is used to improve sand ground at a low replacement rate when pile strength is not considered in design. 5. Use of soil having a fine particle content of more than 15%, a water content of 25% or less and a plasticity index of 20 or less as a pile material in a sand pile-based soil improvement method.
A method of using soil with a large subdivision rate that is used for the improvement of viscous soil with a low replacement rate by using appropriate drainage materials when pile strength is not considered in design. 6. In the case where soil having a fine particle content of more than 15%, a water content of 25% or less and a plasticity index of 20 or less is used as a pile material in a sand pile type soil improvement method,
When the pile strength is considered in the design but drainage is not considered, the design pile strength is set lower than usual, and the content of fine particles used for improving the viscous ground with a medium / high replacement rate is large. How to use the soil. 7. In the case where soil having a fine particle content of more than 15%, a water content of 25% or less, and a plasticity index of 20 or less is used as a pile material in a sand pile type soil improvement method,
When considering the pile strength and drainage in the design, set the design pile strength lower than usual, and use appropriate drainage materials in combination with the fine-grained fraction used to improve the viscous ground with a low replacement rate. How to use soil with high content.