JP2592362B2 - Liquefaction prevention method for sand ground - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Industrial applications] Saturated loose sandy ground is subjected to an earthquake. If the intensity of the vibration at this time exceeds a certain limit, the sandy ground liquefies and causes catastrophic damage to the structure. For this reason, the present invention is a ground improvement technology for preventing the occurrence of liquefaction by forming a columnar imlique liquefied ground while compacting the sand ground.
It is about .

[0002]

2. Description of the Related Art Conventional ground improvement techniques for preventing the occurrence of liquefaction include vibro flotation and compacted sand pile methods for increasing density by vibration compaction. is there. These compactions are mainly due to mechanical vibration. Drainage methods, such as gravel drain method and pipe drain method, are used as drainage methods to suppress the rise in pore water pressure in the sand layer during an earthquake.

[0003]

However, the conventional ground improvement techniques described above , such as the gravel drain method,
Pipe drain method is differential settlement of the ground of what is possible to prevent the liquefaction of sandy ground and have you at the time of the earthquake can not be avoided, will leave a negative impact on the structure. The vibro flotation method and compacted sand pile method are the most effective methods.However, when the ground is improved, the nearby structures may be adversely affected by mechanical vibration, and the improvement equipment will be large. Therefore, improvement costs tend to be very high. In order to further enhance the improvement effect, the compaction method alone would require enormous improvement costs. The most important of the construction management in soil improvement is the strength management at the time of improvement, which can be grasped in real time during the improvement, and flexibly responds to changes in soil properties, etc. to obtain the desired improvement strength. There is a need. However, conventional intensity management is at best unsatisfactory because it detects indirectly the improved intensity.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made in consideration of the above-mentioned problems. The problem is how to realize an improved construction method that can create a new construction and greatly reduce the cost of improvement.

[0005]

According to the method for improving a sand ground according to the present invention, a columnar non-liquefied ground is formed while compacting the sand ground to increase the density, thereby forming a composite ground resistant to liquefaction. Things. The method is improved by using a jacket outer casing improving device having a function of contracting and expanding a jacket and a function of pumping a non-liquefied ground material. To explain on the basis of an example of a mechanism of the jacket outer packaging improved apparatus, in the axial direction of the outer surface of the hollow rod as pumping tube not Liquefied Ground material which also serves as a penetration shaft force member, disconnect the tip and the head 33 A plurality of, preferably three, stiffening slats are fixed symmetrically in a sealed jacket between the combination rods of an airtight cylindrical jacket mounted so as to wrap the outer surface of the combination rod. The inner diameter when the sky expands to the limit as a column is preferably set to be substantially equal to the diameter of the circle inscribed at the tip of the stiffening blade. Then the method of ground improvement, work process is a vacuum as first preparation step jacket empty jacket outside packaging improved apparatus evacuated (wherein jacket sky
That the air is almost exhausted.
No. ) To bring the jacket into close contact with the combination rod. The subsequent step is to penetrate the jacket wrapping improvement device to a predetermined depth. The next step is to inflate the jacket by sending a highly pressurized fluid into the jacket.

[0006] Thereafter, the non-liquefied ground material is discharged from the leading end of the pressure-feeding pipe of the non-liquefied ground material by applying a pressure higher than the holding pressure in the inner space of the jacket, and simultaneously the discharge amount of the non-liquefied ground material is reduced. Discharge the highly pressurized fluid in the corresponding jacket inside the ground while balancing it, and press the jacket that has expanded upward from the tip of the jacket outer package improvement device against the combination rod to make it close to the liquefied ground material while closely contacting it. Replace them sequentially. In the next step, the trace space of the combination rod is backfilled with the immobilized ground material while lifting the jacket outer packaging improvement device. If necessary, the above-described steps are regarded as one cycle, and the predetermined ground is improved by repeating the cycle while moving the improvement place .

[0007]

[Function] In the mechanism of the jacket outer casing improvement device, the eccentricity of the expansion of the jacket is prevented by further setting the diameter of the three symmetrical stiffening blades and the jacket, and the inside of the jacket is contracted to the utmost. Then, the circumference of the jacket becomes slightly larger than the surface of the combination rod, and the jacket can be brought into close contact with the combination rod without difficulty. Next, in the ground improvement method and work process, the interior of the jacket is evacuated in the preparatory process to bring the jacket into close contact with the combination rod. For this reason, the penetration resistance of the jacket outer casing improvement device is minimized, and the penetration process can be easily performed. Next, in the ground compaction step, the jacket is expanded into a column shape by the high pressurized fluid, so that the surrounding ground is compacted in the horizontal direction by the expansion pressure of the jacket. At this time, the compacting process can be quantitatively and statically and reliably performed by slowly increasing the pressure while checking the expansion pressure. Next, in the process of forming a columnar imliquefied ground, the operation is performed while balancing the discharge pressure of the immobilized ground material and the holding pressure inside the jacket, so that the compacted ground is not loosened and the ground subsidence The liquefied ground can be reliably created without causing stagnation.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 (A) is a cross-sectional view of a jacket outer casing improving device which is a main body of the improving machine according to the present invention. In the figure, reference numeral 1 denotes a hollow rod serving as a pressure-feeding pipe for a non-liquefied ground material also serving as a penetrating axial force material. 2 is a hollow rod 1 (pressure feeding
The nozzle at the center of the tip of the tube . Reference numeral 3 denotes discharge ports of the non-liquefied ground material provided at three places on the side surface of the distal end portion of the hollow rod 1. Reference numeral 4 denotes a stiffening blade plate which is attached and fixed symmetrically in the axial direction of the hollow rod 1 to form a combination rod together with the hollow rod 1. Reference numeral 5 denotes a cylindrical jacket that encloses the combination rod. Reference numeral 6 denotes the inside of a closed jacket between the combination rod and the jacket 5. Reference numeral 7 denotes a high water pressure pipe provided in the hollow rod 1 and connected to the nozzle 2. Reference numeral 8 denotes an air pressure control tube, which is connected to the inner space 6 of the jacket by a plurality of air pressure control holes. Reference numeral 9 denotes an air pressure adjusting hole. Reference numeral 10 denotes an air hole connected so that the inner space 6 of the jacket partitioned by the stiffening blades 4 always has the same pressure. Sign 1
1 is a fixed band of the jacket 5. In the figure, a pipe denoted by reference numeral A is a branch pipe of the air pressure control pipe 8 and is connected to a vacuum pump. The symbol C is also connected to the high pressure air pump. The pipe denoted by reference numeral B is an extension of the high water pressure pipe 7 and is connected to the high water pressure pump. The tube denoted by reference numeral 2 is connected to a grout pump by an extension tube of the hollow rod 1.

FIG . 1B is a cross-sectional view of the jacket outer packaging improvement device, showing a state in which the jacket 5 has contracted to the limit and is in intimate contact with the combination rod. FIG. 4C shows a state in which the jacket 5 has expanded to the limit. FIG. 2 is a conceptual diagram of construction. In the figure, reference numeral A denotes a jacket outer casing improving device, reference numeral B denotes a base machine, and reference numeral C denotes a ground surface. FIG. 2 shows the jacket outer casing improvement device inserted into a predetermined position. FIG. 3 is a diagram showing a construction process. In the figure, reference symbol D is a columnar imliquefied ground. FIG. 3 (a) shows a step of penetrating the jacket outer casing improving device A to a predetermined depth while injecting a high-pressure water stream from the nozzle 2 at the tip. FIG. 2B shows a process in which high-pressure air is sent by a high-pressure air pump through an air pressure control pipe 8 to expand the jacket 5 and compact the surrounding ground. Similarly, FIG. 3C shows that the non-liquefied ground material is pressure-fed through the hollow rod 1 and discharged from the discharge port 3 at a pressure higher than the holding pressure of the inner space 6 of the jacket, and the discharge amount of the non-liquefied ground material is reduced. The corresponding compressed air in the inner space 6 of the jacket is discharged through the air pressure regulating pipe 8 while balancing the air, and the non-liquefied ground material is sequentially replaced with the inner space 6 of the jacket upward from the front end of the jacket outer improvement device A. The steps are shown. Similarly (d) drawing shows a step of returning embedding traces space of the rod in a non Liquefied Ground material combination while hoisting a jacket outside packaging improved apparatus A.

The embodiment according to the present invention for the liquefaction countermeasure of the sand ground has been described above. When the construction method according to the present invention is applied to a viscous soil soft ground, a jacket outer layer improvement device to which a layered drain material on a jacket surface is adhered is used. This is inserted into the cohesive ground, the jacket is slowly expanded within the range where the cohesive soil does not plastically deform, the ground is forcibly compacted while draining pore water through drainage, and the trace space of the jacket external improvement device is fixed. The composite ground is formed by substituting the ground material.

[0011]

First, the energy and construction effects of the penetration of the jacket outer casing improvement device used in the present invention and the compaction of the surrounding ground thereby will be described.
When the jacket wrapping improvement device penetrates, the jacket is in close contact with the device, and the penetration resistance is in a minimum state. Generally, the cross-sectional area at this time is only about 10% of the cross-sectional area when the jacket expands to the maximum column shape. For this reason, the penetration of the improved device can be easily performed by the dead weight of the main body, the high pressure jet stream at the tip and the penetration auxiliary device, and can be performed statically with little energy without affecting the adjacent structures. Next, regarding the compaction of the surrounding ground, the jacket in the contracted state is expanded into a column shape with a highly pressurized fluid (highly compressed air or the like), and the surrounding ground is compacted directly in the horizontal direction. By slowly increasing while checking the inflation pressure during construction, compaction can be performed quantitatively and statically and reliably. For this reason, construction can be performed safely without causing land subsidence and for adjacent structures.
Also, unlike the compaction of the surrounding ground due to mechanical vibration energy in the vertical direction as in the compaction sand pile method, the energy efficiency is very good because the compaction is performed directly in the horizontal direction by fluid energy.

Next, the effect of preventing liquefaction will be described. The principle of the liquefaction prevention method of the present invention is that the columnar imliquefied ground is used as a core, the surrounding ground is directly compacted in the horizontal direction, and the sand layer is close to the limit gap, and the whole is configured as a composite ground. . This is a ground that is much more resistant to liquefaction than an improved ground that only compacts the sand layer.

[0013] Next will be explained in terms of the strength of management. In the improved soil layer served by one non-liquefied ground pile, the decrease in the gap of the ground layer after compaction corresponds to the volume of the non-liquefied ground column, so the compacted soil is measured by measuring the expansion pressure of the jacket. The gap ratio and relative density of the sand layer are obtained in real time. For this reason, strength management is performed quantitatively, and if the strength of the initial plan is not obtained, the range of one immobilized ground pillar is reduced, and the construction plan is changed as needed to secure the strength of the initial plan. be able to.

[0014] Next will be explained in terms of the ground improvement costs.
The compaction of sand ground and the formation of non-liquefied ground columns according to the present invention utilize fluid energy. Because of the easy control of fluid energy, these facilities are becoming smaller and more agile. In addition, since the non-liquid ground material is made by mixing a small amount of an admixture for improving fluidity and a cement or other consolidation material into the cohesive soil in or near the site, it is extremely inexpensive. It's becoming As a result, ground improvement costs have been significantly reduced. As described above, the construction method of the present invention does not cause land subsidence under quantitative construction management, does not adversely affect adjacent structures, and uses immiscible ground columns using inexpensive materials. This is to economically create a composite ground that is resistant to liquefaction.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a jacket outer packaging improving device according to the present invention .

FIG. 2 is a conceptual diagram of construction according to the present invention .

FIG. 3 is a construction sequence diagram of the present invention .

[Explanation of symbols]

 Reference Signs List A Jacket outer package improvement device B Base machine C Ground surface D Column-shaped non-liquefied ground 1 Hollow rod 2 Nozzle 3 Discharge port 4 Stiffening vane plate 5 Jacket 6 Inside of jacket 7 High water pressure pipe 8 Air pressure control pipe 9 Air pressure control hole 10 air hole 11 jacket fixing band

Claims (3)

(57) [Claims] 1. A method of improving a saturated loose sand ground, wherein the method also serves as a penetrating axial force member for penetrating into the sand ground.
From the pumping pipe of the non-liquefied ground material and the outer surface of the pumping pipe
The tip and the head of the combination rod including a plurality of projecting stiffening blades are removed, and an airtight cylindrical jacket is attached so as to wrap the outer surface of the combination rod, Prepare a jacket outer packaging improvement device that seals the inside of the jacket between the combination rod and the jacket, and evacuate the inside of the jacket to combine the jacket with the rod.
So as to be brought into close contact with the preparation process and, penetrating to penetrate the jacket outer packaging improved device to a predetermined depth in the sand ground
And a compacting step of expanding the inside of the jacket by sending a high-pressure fluid to the inside of the jacket and compacting the surrounding sand by the jacket expansion pressure.
Liquefaction prevention method. After wherein said compaction step, the non-liquefaction soil material under pressure higher than the holding pressure in an empty jacket, while the discharge from the tip of the pumping tube not liquefied soil material, the non the jacket air corresponding to the discharge amount of the liquefied soil material of high pressurized fluid discharged into the ground while achieving a balance, push rod combination of jacket expanded upward from the front end of the jacket outer packaging improved apparatus It is a special feature to carry out a process of sequentially replacing with liquefied ground material
The method for preventing liquefaction of sand ground according to claim 1, wherein 3. A combination b of the jacket outer package improving device.
The pressure pipes are spaced at equal intervals in the outer circumferential direction of the
Protruding from the outer surface of the feed pipe and along the axial direction of the feed pipe
Three stiffening blades extending, and
The jacket to be wrapped around the outer surface is cylindrical.
I, Ho as the diameter of a circle inscribed inside diameter when closed jacket blank between the rods in combination with the cylindrical jacket is expanded to the limit in a columnar shape on the tip of the respective stiffening vane plates
By setting them to be almost equal, eccentricity when the jacket expands to the limit in a columnar shape is prevented, and when the inside of the jacket is contracted to the limit, the jacket circumference is slightly larger than the circumference of the combination rod surface. The method for preventing liquefaction of sand ground according to claim 1 or 2 , wherein the jacket is brought into close contact with the combination rod without difficulty .