JPH06116935A - Liquefaction preventing method for sand ground - Google Patents

Abstract

PURPOSE:To create a columnar non-liquefying ground as a saturated loose sand ground is compacted under management of a quantitative strength without exercising an adverse influence on a proximity structure and to reduce a betterment cost. CONSTITUTION:By using a jacket outer cover bettering device A having a function to contract and expand a jacket 5 and a function to feed with a pressure a non-liquefying ground material, a jacket inner space 6 of the device A is forced into a vacuum and the jacket 5 is combined and brought into adhesion to a rod. The jacket outer cover bettering device A is penetrated down to a given depth. High pressure fluid is then fed in the jacket inner space 6 to expand the jacket. Simultaneous discharge of the non-liquefying ground material through the tip part of a forced feed pipe for the non-liquefying ground material with a pressure higher than the holding pressure of the jacket inner space 6, high pressure fluid in the jacket inner space 6 in an amount equivalent to the discharge amount thereof is discharged to a ground as a balance is kept, and orderly replacement with the non-liquefying ground material is carried out.

Description

[Detailed Description of the Invention] "Industrial application field" When saturated loose sand ground is subjected to an earthquake and the strength of vibration at this time exceeds a certain limit value, the sand ground is liquefied and the structure is devastating. Cause damage. Therefore, the present invention relates to a ground improvement method for preventing the occurrence of liquefaction by forming a columnar non-liquefied ground while compacting the sand ground. "Prior art" The conventional main ground improvement methods for preventing liquefaction are vibro flotation method and compacted sand pile method, which increase the density by vibration compaction. is there. These compactions are mainly due to mechanical vibrations. There are gravel drain method, pipe drain method, etc. as the drainage method for suppressing the increase of pore water pressure in the sand layer during an earthquake. "Problems to be solved by the invention" By the way, the conventional ground improvement method shown above, for example, the gravel drain method,
The pipe drain method can prevent liquefaction of the sand ground during an earthquake, but unequal subsidence of the ground is unavoidable, which will adversely affect the structure. The vibro flotation method and the compacted sand pile method are influential methods, but mechanical vibration may adversely affect neighboring structures during ground improvement, and improvement equipment will be large-scale. Therefore, the improvement cost tends to be very high. Further, in order to enhance the improvement effect, the compaction method alone would make the improvement cost enormous. In addition, strength management during improvement is particularly important in construction management for ground improvement, and it is possible to grasp in real time during improvement, and to flexibly respond to changes in the soil characteristics in order to obtain the desired improvement strength. There is a need. However, the conventional strength control is not satisfactory because it indirectly detects the improved strength at best. The present invention has been made in view of the above problems,
How to use an improved construction method that can create a columnar non-liquefied ground while compacting saturated loose sand ground under quantitative strength control without adversely affecting adjacent structures, and can significantly reduce improvement costs The question is whether or not it will be realized. "Means for Solving Problems" A method for improving sand ground according to the present invention is to form a columnar non-liquefied ground while compacting the sand ground to increase the density, thereby forming a composite ground resistant to liquefaction. It is a thing. The method is to improve by using a jacket envelope improving device having a function of contracting and expanding the jacket and a function of pumping the non-liquefied ground material. Explaining based on an example of the mechanism of the jacket envelope improving device, the tip and the head are removed symmetrically in the axial direction of the outer surface of the hollow rod as a pumping pipe for the non-liquefied ground material that also serves as the penetration axial force material. Three
When a pair of stiffening vanes are fixed and the outer surface of this combination rod is wrapped around, the airtight cylindrical jacket and the inner space of the closed jacket between the combination rods are expanded to a column shape to the maximum extent. The inner diameter of is set equal to the diameter of the circle inscribed at the tip of the stiffening vane. Next, in the ground improvement method and work step, as a preparatory step, the inside of the jacket of the jacket outer package improving apparatus is evacuated to bring the jacket into close contact with the rod. In the subsequent step, the jacket envelope improving device is penetrated to a predetermined depth. In the next step, a highly pressurized fluid is sent to the inside of the jacket to expand the inside of the jacket. The next step is to discharge the non-liquefied ground material from the tip of the feed pipe of the non-liquefied ground material by applying a pressure higher than the holding pressure in the jacket, and at the same time, it corresponds to the discharge amount of the non-liquefied ground material. The highly pressurized fluid in the air inside the jacket is discharged to the ground while balancing, and the jacket that expands upward from the tip of the jacket envelopment improvement device is pressed against the combination rod and brought into close contact with the non-liquefied ground material in order. Replace it. In the next step, the vacant space of the combination rod is backfilled with the non-liquefied ground material while the jacket envelope improving device is being pulled up. The above steps are set as one cycle, and the predetermined ground is improved by repeating the cycle while moving to the improvement place. In the mechanism of the “work” jacket envelope improving device, 3
By setting the diameter of the symmetrical stiffening vanes and the jacket specially, the eccentricity of the expansion of the jacket is prevented, and when the inner space of the jacket is contracted to the maximum, the jacket circumference is the surface of the combination rod. It is slightly larger than the above, and the jacket can be easily attached to the combination rod. Next, in the ground improvement method and work step, the inside of the jacket is evacuated in the preparation step to bring the jacket into close contact with the rod. For this reason, the penetration resistance of the jacket envelope improving device is at a minimum state, and the penetration process can be easily performed. Next, in the step of compacting the ground, the jacket is expanded in a columnar shape by the high-pressure fluid, so that the peripheral ground is compacted in the horizontal direction by the expansion pressure of the jacket. At this time, the compaction process can be quantitatively and statically performed reliably by slowly increasing the expansion pressure while checking the expansion pressure. Next, in the process of constructing the columnar non-liquefied ground, the operation is performed while balancing the discharge pressure of the non-liquefied ground material and the holding pressure in the air inside the jacket, so that the compacted ground does not loosen and the ground subsidence occurs. The non-liquefied ground can be reliably created without causing [Examples] Examples of the present invention will be described below with reference to the drawings. FIG. 1 (A) is a sectional view of a jacket encasing improving device which is an improving machine main body according to the present invention. In the figure, reference numeral 1 is a hollow rod as a pumping pipe for the non-liquefied ground material which also serves as a penetrating axial force material. Reference numeral 2 is a hollow rod 1
Is the nozzle at the center of the tip of the. Reference numeral 3 is a discharge port for the non-liquefied ground material provided at three locations on the side surface of the distal end portion of the hollow rod 1. Reference numeral 4 is a stiffening vane, three of which are symmetrically attached and fixed in the axial direction of the hollow rod 1, and form a combined rod together with the hollow rod 1. Reference numeral 5 is a cylindrical jacket that encloses the combination rod. Reference numeral 6 is a closed inner space of the jacket between the combination rod and the jacket 5. Reference numeral 7 is a high water pressure pipe which is piped in the hollow rod 1 and is connected to the nozzle 2. Reference numeral 8 is also an air pressure control pipe, which is connected to the jacket inner space 6 by a plurality of air pressure control holes. Reference numeral 9 is an air pressure adjusting hole. Code 1
Reference numeral 0 denotes an air hole which is communicated so that the jacket inner space 6 partitioned by the stiffening vane plate 4 always has the same pressure. Reference numeral 11 is a fixed band of the jacket 5. In the drawing, the pipe denoted by reference numeral a is a branch pipe of the air pressure adjusting pipe 8 and is connected to the vacuum pump. Symbol C is also connected to the high-pressure air pump. The pipe denoted by B is an extension pipe of the high water pressure pipe 7 and is connected to the high water pressure pump. The pipe denoted by reference numeral 2 is an extension pipe of the hollow rod 1 and is connected to the grout pump. FIG. 1 (B) is a cross-sectional view of the jacket envelope improving device, showing a state in which the jacket 5 contracts to the limit and is in close contact with the combination rod.
The figure (C) also shows a state where the jacket 5 is expanded to the limit. FIG. 2 is a conceptual diagram of construction. In the figure, symbol A is a jacket envelope improving device, symbol B is a base machine, and symbol C is the ground surface. FIG. 2 shows the jacket envelope improving device inserted into a predetermined position.
FIG. 3 is a diagram showing a construction process. In the figure, reference numeral D is a columnar non-liquefied ground. FIG. 3 (a) shows a step of penetrating the jacket envelope improving device A to a predetermined depth while injecting a high-pressure water stream from the nozzle 2 at the tip. Similarly, FIG. 3B shows a process in which highly compressed air is sent by a high-pressure air pump through the air pressure control pipe 8 to expand the jacket 5 and compact the surrounding ground. Similarly (C)
The figure shows that the non-liquefied ground material is pressurized at a pressure higher than the holding pressure of the inner space 6 of the jacket, pressure-fed through the hollow rod 1 and discharged from the discharge port 3, and the inside of the jacket corresponds to the discharge amount of the non-liquefied ground material. A process of discharging compressed air in the air 6 through the air pressure control pipe 8 while balancing, and sequentially replacing the non-liquefied ground material upward from the tip of the jacket outer casing improving device A with the air 6 in the jacket. Shows. Similarly, FIG. 3D shows a step of backfilling the trace space of the combination rod with the non-liquefied ground material while pulling up the jacket outer casing improving device A. The embodiment according to the present invention as a countermeasure against liquefaction of sand ground has been described above. When the method according to the present invention is applied to soft soil-soft ground, a jacket outer casing improving device having a layered drain material adhered to the jacket surface is used. Insert this into the cohesive soil, slowly expand the jacket within the range where the cohesive soil does not plastically deform, drain the pore water to forcibly consolidate the soil, and solidify the trace space of the jacket envelope improvement device. The composite ground is formed by substituting the ground material. [Effects of the Invention] Penetration of the jacket envelope improving device and compaction of the surrounding ground according to the present invention will be described in terms of energy and construction. When the jacket envelope improving device penetrates, the jacket is in close contact with the device, and the penetration resistance is at a minimum. Generally, the cross-sectional area at this time is only about 10% of the cross-sectional area when the jacket is expanded in a columnar shape to the limit. For this reason, the penetration of the improved device can be easily performed by the weight of the main body, the high-pressure jet flow at the tip, and the penetration assist device, and can be statically performed with a small amount of energy without affecting adjacent structures. Next, regarding the compaction of the surrounding ground, the jacket in the contracted state is expanded into a columnar shape with a highly pressurized fluid (such as highly compressed air), and the surrounding ground is directly compacted in the horizontal direction. By confirming the expansion pressure during construction and slowly raising it, compaction can be performed quantitatively and reliably. For this reason, it is possible to perform construction safely on adjacent structures without causing subsidence. Further, unlike the compaction of the surrounding ground by mechanical vibration energy in the vertical direction as in the compaction sand pile method, direct energy compaction in the horizontal direction by fluid energy is very efficient. Next, the liquefaction prevention method will be described. The principle of the liquefaction prevention construction method of the present invention is that the columnar non-liquefaction ground is used as a core, and the surrounding ground is directly compacted in the horizontal direction to approach the critical void ratio of the sand layer, and the whole is constructed as a composite ground. . This is a ground that is much more resistant to liquefaction than the improved ground that is simply compacted with a sand layer. Next, the strength management method will be described. In the improved ground layer which one liquefied ground pile is responsible for, the reduction of the gap in the ground layer after compaction corresponds to the volume of the liquefied ground column, so it is compacted by measuring the expansion pressure of the jacket. The void ratio and relative density of the sand layer are obtained in real time. For this reason, the strength is quantitatively controlled, and when the strength of the initial plan cannot be obtained, the area covered by one liquefied ground column is reduced, and the construction plan is changed as necessary to secure the strength of the initial plan. be able to. Next, the ground improvement cost will be described. Compaction of the sand ground according to the invention,
Fluid energy is used to create non-liquefied ground columns. Fluid energy is easy to control, so its equipment is small and agile. In addition, non-liquid ground material is a very inexpensive material because it is made by mixing a small amount of admixture for improving fluidization and solidifying material such as cement into cohesive soil in the local soil or in the vicinity of the site. It is getting worse. Therefore, the ground improvement cost has been reduced significantly. As described above, the construction method of the present invention does not cause ground subsidence under quantitative construction management, does not adversely affect adjacent structures, and also uses an inexpensive material for a non-liquefied ground column. It is an economical construction of a complex ground that is strong against liquefaction and that is used as a core.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 (A) is a sectional view of a jacket envelope improving device according to the present invention. FIG. 1 (B) is a transverse sectional view of FIG. 1 (A), showing a state where the jacket is contracted to the limit. Similarly, FIG. 7C shows a state in which the jacket is expanded in a columnar shape to the limit. FIG. 2 is a conceptual diagram of construction. FIG. 3 is a construction sequence diagram. A ... Jacket envelope improving device, B ... Base machine, C
... ground surface, D ... columnar non-liquefied ground, 1 ... hollow rod,
2 ... Nozzle, 3 ... Discharge port, 4 ... Stiffening vane plate, 5 ... Jacket, 6 ... Jacket inner air, 7 ... High water pressure pipe, 8 ... Air pressure control pipe, 9 ... Air pressure control hole, 10 ... Air hole, 11 ... Jacket fixing band,

Claims (1)

(1) In the method for improving saturated loose sand ground, the tip and the head of a combination rod in which a penetrating axial force material, a non-liquefied ground material pressure feed pipe, a stiffening vane plate, etc. are combined. , A tubular jacket having airtightness is attached so as to wrap the outer surface of the combination rod, and a jacket outer envelope improving device in which a jacket inner space between the combination rod and the jacket is sealed is prepared, Following the preparatory step of evacuating the inner space of the jacket to bring the jacket into close contact with the rod, the step of penetrating the jacket outer packaging improving device to a predetermined depth, and then the highly pressurized fluid in the inner space of the jacket. To inflate the inner space of the jacket and expand the jacket sand to densify the surrounding sand ground to increase the density, and then to hold the non-liquefied ground material in the inner space of the jacket. With a higher pressure than that, it is discharged from the tip of the liquefied ground material pumping pipe, and at the same time, the highly pressurized fluid inside the jacket, which is equivalent to the discharge amount of the liquefied ground material, is discharged to the ground while balancing. Then, without loosening the compacted ground, a step of sequentially replacing the non-liquefied ground material while pressing the jacket expanded toward the upper part of the jacket outer casing improving device against the combination rod while closely contacting it, Repeating the above-mentioned cycle while moving the improvement location through the step of backfilling the trace space of the combination rod with the non-liquefied ground material while pulling up the jacket encapsulation improvement device With this, the specified ground is strongly compacted directly by surrounding the ground by expanding the jacket, and the trace space of the jacket envelope improvement device is maintained without loosening the compacted ground. Improved method of Sand that was replaced by liquefied soil material and forming a composite ground. (2) In the structure of the jacket envelope improving device, three pieces are symmetrically arranged in the axial direction of the outer surface of the hollow rod as a pressure-feeding pipe for the non-liquefied ground material that also serves as the penetrating axial force material, with the tip and the head removed. The stiffening vane is fixed and the outer surface of this combination rod is wrapped around the outer surface of the cylindrical jacket and the closed jacket between the combination rod. By setting the inner diameter equal to the diameter of the circle that inscribes the tip of the stiffening blade, eccentricity is prevented when the jacket is expanded to the limit in a columnar shape, and the jacket circumference is shortened when the inner space of the jacket is contracted to the limit. Is slightly larger than the perimeter of the surface of the combination rod, so that the jacket is reasonably brought into close contact with the combination rod. Apparatus.