JP2003064657A - Construction method for improving soft ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a construction method for improving soft ground, which can prevent settlement of a superstructure, such as fill, constructed on the soft ground, the sliding rupture of the superstructure and the displacement of a neighboring area, and can avoid an influence exerted upon an environment by cut-off of underground water. SOLUTION: In the construction method for improving the soft ground, grouped columns, whose horizontal cross sections are formed annularly by making the columns overlap the ground, are vertically arranged at intervals; a superstructure supporting plate for supporting the superstructure is formed on upper parts of the grouped columns; and the superstructure is supported on the superstructure supporting plate.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is problematic when constructing an upper structure such as embankment or embankment on soft ground.
The present invention relates to a soft ground improvement method capable of preventing subsidence of an upper structure, sliding destruction of the upper structure, and displacement of a nearby ground, and avoiding the influence of groundwater interruption on the environment. [0002] When an embankment is formed as an upper structure on a soft ground, the embankment is settled because the soft layer is compressed, and the embankment is broken because the soft layer is sheared. At the time of earthquake liquefaction, a large earth pressure is generated due to the weight of the embankment, so that the earth and sand erupts, leading to destruction of the embankment. In order to prevent the settlement of the embankment on the soft layer and to make it stable, there are, for example, a block and grid improvement method or a composite ground improvement method. FIGS. 2A and 2B show a conventional block or lattice improvement method, in which FIG. 2A is a longitudinal sectional view and FIG. 2B is a horizontal sectional view. A pillar 1 is constructed in a block shape or a grid shape at an end of an embankment 2 and a ground improvement of a cross section which is stable against a large main earth pressure under embankment load and a soil water pressure during earthquake liquefaction. It builds the body. In this case, the ground improvement body is connected to a wall shape as shown in FIG. FIG. 3 shows a conventional composite ground method, in which (a)
Is a longitudinal sectional view, and (b) is a horizontal sectional view. [0007] A single pillar 1a is provided throughout the embankment, which is the upper structure.
Are to be evenly arranged on a plane to improve soft ground. [0008] The block or grid-like improvement method shown in FIG. 2 can stabilize against external forces, but the improved body is constructed in a wall shape in the extension direction of the embankment. Therefore, in recent years, the impact on the environment due to groundwater interruption has been a problem. In order to solve this problem, it is conceivable to provide slits for water passage in the continuous wall-shaped improvement body.In this case, the liquefied soil water pressure receiving the embankment load blows out from the slits, causing There is a concern that depression such as depression may occur. On the other hand, in the composite ground method shown in FIG. 3, the improved column strength qu is set by the vertical force of the embankment, and the stability of the embankment is determined by setting the composite ground average adhesive strength to qu / 2 × α (α: improvement ratio). It is considered by slip calculation and is not generally a countermeasure in the event of an earthquake. In addition, since a single column is weak against bending stress, it cannot be adopted in many cases when a horizontal force acts or when considering earthquake resistance. When constructing an earth structure such as a road embankment or embankment on a soft ground, there is a problem in that the embankment itself is always slid or destroyed during the earthquake, the embankment subsidence, and the influence of displacement on the surrounding ground. When designing and constructing in consideration of measures against these problems, it is necessary to avoid the influence on the environment such as groundwater shutoff. Accordingly, the present invention prevents the subsidence of an upper structure such as an embankment constructed on soft ground, the sliding destruction of the upper structure, and the displacement of a nearby ground, and the effect on the environment due to groundwater interruption. It is intended to provide a soft ground improvement method that can be avoided. A soft ground improvement method according to the present invention is characterized in that a plurality of columns having a horizontal cross section formed in an annular shape by overlapping a plurality of columns on the ground are vertically arranged at intervals. An upper structure support plate for supporting the upper structure is formed above the group pillar, and the upper structure is supported on the upper structure support plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plurality of group pillars having a stable shape at all times and during an earthquake and an upper structure supporting plate supported by the plurality of group pillars stabilize a load of an embankment as an upper structure. By supporting it, the increased stress is not applied to the soft ground.
As a result, the embankment load does not act on the soft layer, so the settlement of the embankment, arc-slide destruction, and the influence of displacement to the nearby ground do not occur. The problem of land subsidence can be solved. 1A and 1B are explanatory views of the soft ground improvement method of the present invention, wherein FIG. 1A is a longitudinal sectional view and FIG. 1B is a horizontal sectional view. A group pillar 1 is formed in the soft ground, and an upper structure support plate 3 for supporting an upper structure 2 such as an embankment or a dike is formed above the group pillar 1 to reduce the load of the upper structure 2. It is supported by the group pillar 1 and the upper structure support plate 3. The group pillars are formed by overlapping a single pillar 1a with each other, and forming a horizontal section in a ring shape such as a rectangular, circular, or polygonal shape to form one group pillar 1, and a plurality of group pillars 1 are formed. Place at intervals. The group pillar can be formed by a known method. For example, a powder injection stirring method and a slurry mechanical stirring method can be used. In the powder injection stirring method, a cement-based or lime-based powder is injected and supplied into soft ground, and is stirred and mixed with the soil at the current position by a stirring blade to form a group pillar. Further, in the slurry mechanical stirring method, a slurry-type cement-based solidifying material is supplied into soft ground, and is stirred and mixed with the soil at the present position to be consolidated to form a group pillar.
The construction top of the group pillar shall be deeper than the improved part. The size, strength and arrangement of the group columns are determined so as to be stable to the vertical force and the horizontal force due to the superstructure at all times and during an earthquake. Since the group pillars need to stably support the embankment load, they have the strength to support the vertical force of the embankment, are stable against overturning and sliding when horizontal force or liquefaction is applied, and have a section where no tensile stress is applied. The size is such that the coefficient can be obtained. After the group pillar 1 is constructed, the cement or lime-based solidification material and the soil at the current position or the loaded soil are mixed above the group pillar with a stabilizer, a backhoe, a plant, or the like, and solidified in a plate shape on the surface layer at the site. Thus, the upper structure support plate 3 is formed. The upper structure supporting plate has a thickness capable of transmitting the embankment load borne by the group columns by a vertical force, and is set to be at least 1/2 of the maximum distance between adjacent group columns. The strength of the structure support plate is pushed out to give a compressive strength that is stable against shearing force. As a result, the excess pore water pressure generated during seismic liquefaction is not affected by the large embankment load, and is only equivalent to the depth of the overburden below the upper structure support plate, and the embankment supported by the group columns stabilized under this condition subsidence,
No destruction. In addition, as a countermeasure against deformation of the nearby ground, there is no influence because no stress due to the soil structure is generated on the soft ground. Further, in order to arrange the group columns in the groundwater environment at intervals such that the upper structure support plate does not bend and break,
The effect of groundwater interruption can be avoided. The basic concept of the design of the construction method according to the present invention is as follows. 1. A group pillar is formed in the soft ground, and an embankment support plate is constructed above the group pillar to support the embankment load with the embankment support plate and the group column. As a result, (1) no vertical increase stress due to embankment is applied to the soft layer (consolidation settlement does not occur). (2) No shearing force due to embankment is applied to the soft layer (the arc-slip failure does not occur). (3) The earth pressure acting on the improved group pillar at all times is:
This is due to the earth covering below the embankment support plate. (4) The earth pressure acting on the group columns at the time of the earthquake is the soil water pressure at the time of liquefaction below the embankment support plate and the earth pressure at the time of the study of the inertial force. 2. The embankment load borne by one group column is to the center between each group column. 3. It is assumed that the earth pressure and the soil pressure during one earthquake that act on one group column affect the width of each group column, both active and passive. 4. The horizontal force acting on the columns by the embankment is borne by the columns. (1) It is assumed that the normal main earth pressure inside the embankment acts as a horizontal force and a moment on the group column head via the embankment support plate. (2) The inertia force of the embankment during an earthquake acts on the head of the group column as a horizontal force via the embankment support plate. At this time, if a seismic design ground surface due to liquefaction is set, consider it as a column protruding from this surface. According to the present invention, a group pillar having a shape that is stable at all times and during an earthquake and an upper structure support plate supported by the group pillar stably support the load of an upper structure such as an embankment. It is possible to prevent the settlement of the embankment on the soft ground, the sliding destruction of the embankment, and the displacement of the nearby ground, and to avoid the influence on the environment due to groundwater interruption.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of a soft ground improvement method of the present invention, wherein (a)
Is a longitudinal sectional view, and (b) is a horizontal sectional view. 2A and 2B show a conventional block or grid-like improvement method, in which FIG. 2A is a longitudinal sectional view, and FIG. 2B is a horizontal sectional view. 3A and 3B show a conventional composite ground method, in which FIG. 3A is a longitudinal sectional view and FIG. 3B is a horizontal sectional view. [Description of Signs] 1: Group pillar 1a: Single pillar 2: Upper structure (embankment etc.) 3: Upper structure support plate

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Claims (1)

Claims 1. A plurality of pillars, each having a plurality of pillars overlapped on the ground and having a horizontal cross section formed in an annular shape, are vertically arranged at intervals, and an upper structure is provided above the pillars. A soft ground improvement method comprising: forming an upper structure support plate for supporting; and supporting the upper structure on the upper structure support plate.