JP2711203B2 - Ground improvement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a freezing method for improving soft ground, in which the frozen soil expands due to moisture in the ground, thereby acting as an expansion pressure on existing structures in the vicinity, resulting in destruction and displacement. It relates to a construction method for preventing such adverse effects.

[0002]

2. Description of the Related Art Conventionally, various methods have been used as methods for improving soft ground. Among them, the freezing method for waterproofing and strengthening soft ground has a certainty of improvement. It has been evaluated for its low pollution and low noise, and is gradually being adopted in large-scale sites such as the Tokyo Bay Crossing Road. Such a freezing method generally involves burying freeze pipes at intervals of 0.5 to 1 m from the vertical or horizontal direction of the target ground, and using a refrigerator installed on the ground surface or in a tunnel at a temperature of −20 to −20.
By producing brine at −25 ° C., circulating the brine in the freezing tube to gradually lower the temperature of the surrounding ground by heat transfer, and finally completing freezing at around −10 to −20 ° C. The purpose is to stop water and strengthen the ground.

However, when freezing spreads from the ground surrounding the freezing pipe, expansion stress is generated due to freezing and expansion of water in the ground, particularly in clay ground and viscous ground. Expansion stress soil generated at this time varies depending on the magnitude of the freezing range of moisture content and ground, for example, several 10ton / m ² if improvements width of 20m in the clay soil, in the case of the more extensive freeze about It is expected to reach 50 tons / m ² . Therefore, when existing structures such as foundation piles, subways, and power transmission pipes are laid around such frozen ground, deformation damage of these structures due to expansion stress generated during freezing becomes a problem. ing.

[0004]

Means for Solving the Problems In order to solve the above problems, the present inventors laid a continuous wall-shaped groove in the ground near the existing structure in the freezing zone, It has been found that, by filling a predetermined medicine material into the medicine material, the expansion stress generated at the time of freezing can be favorably released into the medicine material. According to the present invention based on this finding, in the ground freezing method, a continuous wall-shaped groove is provided in a part of the ground to be frozen and solidified in opposition to the existing structure, and the compressive strength at the time of freezing is set in the groove. A ground improvement method characterized by filling a drug material having a compressive strength smaller than the compressive strength of the ground.

[0005] The continuous wall-shaped groove in the ground to be frozen and solidified according to the present invention may be provided at a predetermined distance facing the periphery of the existing structure within a range that does not damage the structure when excavating the ground.
Also, the shape of the groove may have a width capable of releasing the expansion stress generated at the time of freezing of the ground, and is not particularly limited.
The width, length, and depth may be appropriately determined according to the shape, position, and the like of the existing structure.

[0006] The drug material suitably used in the present invention includes:
If the unconfined compression strength at the time of freezing is lower than the freezing strength of the original ground, it can be used without particular limitation. More preferably, the temperature at the time of the start of freezing is 0 ° C. or less, the liquid specific gravity is 1.05 or more, the liquid is easy to handle before construction, and the viscosity increases after a certain period of time after construction. Those which form colloid can be preferably used. That is, in constructing the continuous wall-shaped groove in the ground before freezing, a stable liquid (specific gravity: 1.
2005), it is necessary to fill the drug material while replacing the stabilizing liquid in the ground, and therefore, a drug material having a specific gravity of 1.05 or more is preferable. Also, from the viewpoint of the simplest method of workability in the filling operation, the drug material is in a solution state at the time of being transferred into the continuous wall-shaped groove, and is replaced with a stable solution, and gradually increases after a certain period of time. Preference is given to substances which are viscous and have a suitable amount of oncotic and which completely stabilize the digging wall.

The action of thickening and gelatinization as a preferred drug material of the present invention is achieved, for example, by the chemical action of a sodium silicate solution and a reactant. That is, sodium silicate solutions have the property of being very slowly or rapidly gelatinized by certain concentrations of reactants. As the sodium silicate used here, a general commercial product can be used without any particular limitation. In general, the molar ratio of SiO ₂ / Na ₂ O is 2 to 4 and the liquid specific gravity is 1.
Those having a density of 3 to 1.4 can be used after being diluted with water as needed.

[0008] Examples of the reactant include bicarbonates, carbonates, alkaline earth metal salts, aldehydes, and the like.
It is selected from esters, chlorides, etc., and particularly preferably selected from sodium hydrogen carbonate, potassium hydrogen carbonate, sodium acid sulfate, sodium carbonate, sodium chloride, potassium chloride, calcium chloride, glyoxal, ethylene carbonate, and acetates. You can
If necessary, cement, slag, lime, gypsum, etc. can be mixed.

As the water for dissolving these salts and sodium silicate, seawater as well as fresh water can be used.

As a means for dissolving or mixing such agents, a high-speed stirring mixer or the like can be suitably used in addition to a stirrer used for ordinary civil engineering work.

[0011] The filling of the drug in the present invention is carried out by using a single pipe or a multi-tube installed in a continuous wall-shaped groove, or a homogeneous mixture prepared in advance from the above-mentioned sodium silicate solution and the reactant, or a mixture thereof. This is achieved by feeding separately while displacing the stabilizing solution into the groove by transferring separately. Then, according to the present invention, the freezing method may be applied to a predetermined ground after the drug material filled in the groove has undergone appropriate thickening and gelatinization. As the freezing method, a conventionally known technique is employed without any particular limitation. Generally, a freezing tube is erected at a predetermined interval in a predetermined freezing / solidification scheduled ground, and brine cooled by a refrigerator is circulated through the freezing tube, or Freeze and solidify the ground by releasing gas from a nitrogen cylinder into a freezing tube.

[0012]

According to the present invention, there is provided a medicine material having a small volume expansion rate at the time of freezing and a uniaxial compressive strength at the time of freezing smaller than the compressive strength of the surrounding ground around the existing structure in the frozen ground. This is achieved by forming an underground continuous wall-like stress relief zone.

That is, the expansion stress generated inside the ground is transmitted to the release zone, but the expansion stress transmitted due to the low strength of the drug material filled in the zone is released by destroying the drug material itself. The existing structure can be protected.

Therefore, according to the present invention, the expansive stress generated in the ground particularly at a large-scale freezing method site can be effectively released in the drug material. As a result, the freezing method can proceed without giving any adverse effect such as deformation to the existing buried object in the vicinity, which is extremely useful.

[0015]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited to these examples.

Example 1 In a sandy clayey ground, a width of 0.8 m and a length of 30 m
A continuous wall-shaped groove having a depth of m and a depth (GL) of -20 m was excavated and filled with a drug material. The drug material is sodium silicate solution (Si
O ₂ / Na ₂ O molar ratio = 3.14, specific gravity 1.39) 100
Volume and pre-concentrated calcium chloride solution 100
The two liquids were mixed with a high-speed mixer to obtain a uniform drug material. The filling was performed while replacing the stabilizing solution (specific gravity: 1.06) through a single tube installed in a continuous wall-shaped groove. When all the filling was completed, the single tube was removed.

The filled drug material becomes colloidal in two and a half hours after preparation, and has a uniaxial compressive strength of 0.1 to 0.2 kgf / h.
cm ² (room temperature). The freezing zone is 35 m wide and 30 m long across a continuous wall filled with drug material.
The depth (GL) was −5 m to −20 m, and the calculated expansion stress was 50 ton / m ² . 10m from filled continuous wall
The H-section steel with five earth pressure gauges attached was installed at a depth (GL) of -20 m in front of the existing basement at the position of, and the increase in earth pressure during freezing was measured. The amount of increase in earth pressure measured with the progress of the ground freezing was 5 to 8 ton / m ² , and there was no trouble in construction.

The freezing point of the drug is -2 ° C.
The uniaxial compressive strength when frozen alone is 18 kgf / at -15 ° C.
It was cm ^2.

Example 2 In the same construction place and conditions as in Example 1, a two-pack type chemical was used. 57 parts by weight of sodium silicate and seawater 4
A liquid obtained by uniformly mixing 3 parts by weight with a high-speed mixer and B liquid obtained by uniformly mixing 95 parts by weight of sodium bicarbonate, 12 parts by weight of a mixed salt composed of 5 parts by weight of sodium salts, and 88 parts by weight of seawater. The solution A and the solution B were separately prepared and separately supplied from the inner tube and the outer tube of the double tube installed in the groove on the continuous wall, and the two solutions were separated at the tip of the double tube. Merged and filled. The filling was performed while pulling up the double tube to the upper part with the replacement of the stabilizing solution.

This drug material becomes gelatinous within 2 minutes after merging,
Homogeru strength 0.2~0.3kgf / cm ^2, freezing point -2
℃, the unconfined compression strength at the time of freezing is 23 kgf / cm ² at -15 ℃
Met.

The freezing zone was the same as in Example 1, and the result of the same measurement of the amount of increase in earth pressure was 6 to 9 ton / m ² .

Comparative Example 1 A freezing work was performed under the same working place and conditions as in Example 1 without using the stress release method.

When the ground temperature around the freezing pipe reached -2 to -7 ° C, the increase in earth pressure exceeded 20 ton / m ^2, which affected the existing underground wall and confirmed the necessity of stress release.

Claims (1)

(57) [Claims] In the ground freezing method, a continuous wall-shaped groove is provided in a part of a ground to be frozen and solidified in opposition to an existing structure, and the compressive strength during freezing in the groove is the compressive strength of the surrounding frozen ground. A ground improvement method characterized by filling a smaller drug material.