JPH05132923A - Improving method for soft ground - Google Patents

Abstract

PURPOSE:To enable an improving effect to exhibited all over subject ground by a method in which soft ground is economically improved without raising the improving rate of the ground. CONSTITUTION:In an improving work for soft ground 1 where a building is to be constructed, the subject ground 1a is surrounded by a steel sheet pile wall 3 of a closed cross section, which is set to the bearing stratum 4. The inside ground layer is then improved by sand-compaction piles 8 and the upper part of the steel sheet piles is pulled inwards by a pressing means such as jack to give a prestress to the inside ground layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground improvement and seismic reinforcement construction method for constructing a building on soft ground such as a landfill.

[0002]

2. Description of the Related Art In the case of soft ground such as landfill, it is usual to improve the ground in the portion where the building is constructed in order to avoid the subsidence and the liquefaction phenomenon during an earthquake. As the improved construction methods, replacement method by dredging, excavation, etc., dehydration method typified by drain method, chemical or physical consolidation method such as mixing treatment method, compaction method such as sand compaction pile method or vibroflotation method Although the methods have been put into practical use, all of them can show sufficient improvement effects due to plastic flow of the ground, etc. unless the improvement work is done not only directly under the building but also in a wide area including the surrounding area. Absent. Similarly, since the main purpose is to physically increase the strength of the ground itself, it is necessary to take a large ground improvement rate (improved area ratio or improved volume ratio) to obtain a sufficient improvement effect, and the construction cost There is a problem that it becomes enormous.

On the other hand, in addition to the method of physically or chemically improving the ground itself as described above, it has also been studied to increase the earthquake resistance by constructing a pile-shaped body or a wall-shaped body in the ground. According to Japanese Patent Laid-Open No. 2-311613, let's improve in a liquefaction prevention method (ground improvement method) in which cement-based solidifying material is mixed and stirred in sand ground to chemically solidify the ground soil in situ. It has been proposed to construct a wall-shaped solid body around the ground, which surrounds the ground. An example of this method is shown in FIG. 1 is a sand ground (soft ground), 2 is a building, 3 is a solid body (wall-like body), 4 is a viscous ground bed (support layer), and 1a is an improvement target range of the sand ground.

Since the wall-shaped body 3 is constructed so as to surround the target ground in this manner, the shear deformation of the ground inside the wall-shaped body can be suppressed, and the ground improvement range is limited to the inside of the wall-shaped body. You can stay. Further, according to Japanese Patent Laid-Open No. 3-103534, in the ground surrounding the building to be built, an underground wall having a lower part embedded in a support layer is built, and the upper part of the underground wall and the building are integrated. Proposed to combine. An example of this method is shown in FIG. 1 is a soft ground layer, 2 is a building, 3 is an underground wall (wall-like body), 4 is a support layer, and 5 is a foundation pile. The wall-shaped body 3 here is formed of a steel pipe sheet pile. In this method as well, the existence of the wall-like body 3 divides and isolates the stratum inside and outside the building, so that the shear strain at the time of the earthquake on the outside ground and the effect of excess pore water pressure on the ground inside the underground wall Is suppressed.

[0005]

By the way, according to the methods described in Japanese Patent Application Laid-Open No. 2-311613 and Japanese Patent Application Laid-Open No. 3-103534, it is expected that the effect of suppressing the ground deformation will be exhibited in the vicinity of the wall-shaped body. However, the effect may be weakened as the distance from the wall-like body is reduced, and the wall-like body should be arranged quite densely with respect to the required ground improvement area.

It is an object of the present invention to provide a method for exerting a ground improvement effect on the entire wall-shaped body by adding a simple operation.

[0007]

SUMMARY OF THE INVENTION The present invention is a ground improvement method for constructing a structure on soft ground, which is made of steel having a closed cross section in which the range to be improved in the ground is rooted in the support layer. Enclosed with a sheet pile wall, after improving the ground in the inner formation surrounded by this steel sheet pile wall by any method, it was surrounded by the steel sheet pile wall by pulling the steel sheet pile wall upper part inward It is characterized by prestressing the inner strata.

[0008]

[Operation] Generally, when the ground is improved by a method that utilizes the volume change and the compaction effect, the ground tends to expand in the horizontal direction, and the horizontal displacement diminishes the density increase and the compaction effect, but is surrounded by a wall-shaped body. Since the expansion is restrained in the inside of the hollow, the loss due to the horizontal displacement is prevented. According to the present invention, the wall-shaped body is a steel sheet pile wall, and the ground is improved in a restrained state by the steel sheet pile wall,
After that, by further pulling the steel sheet pile wall inward, prestressing is applied to the inner strata surrounded by the steel sheet pile wall, so that the ground improvement effect is further promoted, and liquefaction phenomenon and ground subsidence due to earthquakes etc. It can be prevented almost completely. Also, when the formation surrounded by the sheet pile wall shows softening such as liquefaction, the balance between the elastic force and the ground pressure introduced into the sheet pile wall collapses, so the sheet pile wall deforms in the direction of tightening the ground. .. As a result, it is possible to suppress the softening of the ground and reduce the subsidence and the plastic flow.

[0009]

【Example】

First Embodiment A first embodiment of the present invention will be described with reference to FIG. First, as shown in (a), a steel sheet pile wall 3 is placed by enclosing the improvement target range 1a of the soft ground 1 to be improved with a closed cross section such as a circle or a rectangle as necessary for constructing a building. .. The tip of the sheet pile is sufficiently rooted in a solid formation having supportive force, that is, the support layer 4. Next, as shown in (b), jack 6
The sheet pile wall 3 is pushed outward in the elastic range by a pressing means such as. In this state, as shown in (c), the ground is improved by any means such as forming the sand compaction pile 8 in the inner soft ground surrounded by the sheet pile wall 3,
After the completion, as shown in (d), by opening the jack 6 as described above, the sheet pile wall 3 is restored to the inside by its original elasticity and the inner strata is tightened, so that the prestress is given to the entire inside of the sheet pile wall 3. It becomes a state that suppresses the deterioration of the rigidity of the ground or reduces the subsidence of the ground.
Promote ground improvement effect.

Embodiment 2 FIG. 2 shows a second embodiment of the present invention. As in the case of (a), constructing the steel sheet pile wall 3 surrounding the improvement target range 1a of the soft ground 1 to be improved is similar to the first embodiment. Next, as shown in (b), the tie rods 7 are attached to the upper part of the sheet pile wall 3 by connecting the opposite sides. Continued (c)
As described above, the ground is improved by any means such as forming a sand compaction pile 8 in the inner soft ground surrounded by the sheet pile wall 3, and after the completion, the tie rod 7 attached to the blade as shown in (d) is tightened. Since the sheet pile wall 3 is deformed inward and tightens the inner formation, prestressing is applied to the entire interior of the sheet pile wall 3, suppressing deterioration of the rigidity of the ground or reducing the subsidence of the ground. Promote the effect. FIG. 3 is a plan view of the state (c) or (d) of FIG.

In the present embodiment, the timing of attaching the tie rods 7 is not limited to this example, and may be performed in parallel with the ground improvement or after the ground improvement. Compared with the first embodiment described above, in this embodiment, the internal formation is tightened by tightening the tie rods instead of opening the jack, so that the tightening force can be controlled arbitrarily and the follow-up can be performed for a long time while observing the progress. There are advantages such as being able to. Further, other pulling means such as a combination of a wire rope and a chain block may be used instead of the tie rod.

As is clear from the above description, since elastic deformation of the sheet pile is utilized in the present invention, it is necessary that the sheet pile to be used is made of steel. The type of sheet pile, steel pipe sheet pile, etc. is not particularly limited. In addition, the plane shape of the sheet pile wall is generally a closed cross section such as a circle or a rectangle, but when the building to be constructed has a straight line shape such as an embedded pipeline, the sheet pile wall is constructed in parallel parallel lines. Needless to say, the present invention can be carried out.

The ground improvement means may be any of the known construction methods described above.

[0014]

According to the present invention, prestress is introduced after the ground improvement, as compared with the case where the inside of the sheet pile wall having a closed cross section is simply improved. Therefore, the ground improvement effect extends to the entire inside of the sheet pile wall. Therefore, since the ground improvement rate can be set lower by that amount, the construction cost can be reduced, which is an economically excellent effect. Also,
When the internal ground shows softening such as liquefaction, the sheet pile wall is deformed in the direction of tightening the ground, so that softening or subsidence of the ground, plastic fluctuation, etc. can be suppressed.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a construction procedure of a first embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a construction procedure of a second embodiment of the present invention.

FIG. 3 is a plan view showing a second embodiment of the present invention.

FIG. 4 is a conceptual diagram showing a conventional technique.

FIG. 5 is a conceptual diagram showing another conventional technique.

[Explanation of symbols]

 1 Soft ground 1a Area to be improved 2 Buildings 3 Walls 4 Support layers 6 Jacks 7 Tie rods 8 Sand compaction piles

Claims (3)

[Claims] 1. A ground improvement method carried out when constructing a building or the like on soft ground, which is surrounded by a steel sheet pile wall having a closed cross section in which the target area of ground improvement is rooted in a support layer,
After improving the ground of the inner formation surrounded by the steel sheet pile wall by an arbitrary method, prestressing the inner formation surrounded by the steel sheet pile wall by pulling the upper part of the steel sheet pile wall inward. An improved construction method for soft ground, which is characterized by giving 2. The means for pulling the upper part of the steel sheet pile wall inward pushes the sheet pile wall after driving outward by a pressing means such as a jack, and thereafter improves the ground in the inner layer,
The method for improving soft ground according to claim 1, wherein the pressing means is subsequently opened. 3. The method for improving soft ground according to claim 1, wherein the means for pulling the upper part of the steel sheet pile wall inward is a tie rod or the like attached to the upper part of the sheet pile wall by connecting opposite sides.