JP3658296B2 - Ground improvement structure and construction method to control surrounding ground displacement - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ground improvement structure and method for improving hard ground by discharging water contained in soft ground, and more particularly to a method and structure for improving ground while controlling peripheral ground displacement.
[0002]
[Prior art]
A vacuum consolidation method is known as an economical method for improving soft and viscous ground. In this vacuum consolidation method, a plurality of drain materials are placed on the ground to be improved, the head is extended to the ground, and a water-permeable material such as a sand mat or drain material is laid so as to come into contact with the drain material head, A perforated pipe is placed under the water-permeable material and a vacuum pump is connected to it, and the drain material head, water-permeable material, and perforated pipe are covered in an airtight manner over the entire area of the ground to be improved. Lay the sheet material. Then, by operating the vacuum pump, a vacuum pressure acts on the ground covered with the sheet material, and this vacuum pressure is transmitted from the perforated pipe to the drain material via the water-permeable material and further transmitted into the ground. When the vacuum pressure acts in the ground in this way, the water in the ground is sucked by the vacuum pressure, flows from the drain material to the perforated tube through the water flow material, and is discharged to the ground.
[0003]
[Problems to be solved by the invention]
However, in the above conventional vacuum consolidation method, the subsidence of the surrounding ground progresses as the vacuum consolidation progresses, and the surrounding ground may cause horizontal displacement toward the center of the area to be improved. It is difficult to apply to areas subject to improvement where objects exist.
[0004]
The present invention focuses on the above-mentioned problems of the prior art and solves this problem. The problem is that the ground can suppress and control horizontal displacement and ground subsidence occurring in the surrounding ground in the improvement target area. It is to provide an improved construction method and structure.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, in the present invention, a plurality of drain materials are placed almost vertically in the ground to be improved, the head is extended to the ground surface, and water is passed through the heads of the plurality of drain materials. In the construction method of arranging a material and a perforated tube, hermetically covering the upper part with a sheet material , reducing the inside covered with the sheet material using a vacuum pump, and consolidating the improvement target ground, While measuring the horizontal displacement around the improvement target ground, it is controlled to suppress the displacement by loading a loading embankment on the sheet material in accordance with the increase or decrease of the displacement. A ground improvement method is provided. In the ground improvement method, the horizontal displacement measurement is preferably performed for each of a plurality of depths in the surrounding ground.
[0006]
In the present invention, and Da設in a substantially vertical improved target ground a plurality of drain material is extended the head to the ground surface, distribution of water flow material and perforated pipe to the head of the drain member of said plurality of Then, in the construction method in which the upper part is covered with a sheet material in an airtight manner , and the inside covered with the sheet material is decompressed using a vacuum pump and the improvement target ground is consolidated and improved , the surrounding ground of the improvement target ground together to build a wall or a groove along the drain material in, set the stations for measuring the horizontal displacement into the surrounding ground, while measuring the displacement of the measurement point, the from the drain over down member The water is guided and drained through the water- permeable material and the perforated pipe, and the loading is loaded on the sheet material according to the increase or decrease of the displacement, thereby controlling the displacement. Features ground improvement method
In the ground improvement method, the horizontal displacement measurement may be performed by measuring the horizontal displacement at one or more ground surfaces in the surrounding ground, and does not necessarily need to be measured for each of a plurality of depths in the ground.
[0007]
Further, in the present invention, to extend from the ground surface in the improved target region to the ground surface of the head by pouring a plurality of drain material substantially vertically into the ground, said plurality of water passing member and the head portion of the drain member of A ground improvement structure for arranging a perforated tube and hermetically covering the upper part with a sheet material, depressurizing the interior covered with the sheet material using a vacuum pump, and consolidating and improving the ground to be improved In the above, a wall body or a groove constructed along the drain material, a horizontal displacement measuring means provided for measuring a horizontal displacement in the surrounding ground of the area to be improved, and from the horizontal displacement measuring means There is provided a ground improvement structure comprising a loading embankment loaded on the sheet material so as to suppress and control the displacement according to displacement.
In the above ground improvement structure, the horizontal displacement measuring means may be installed on one or more ground surfaces in any one of the wall body, the groove or the surrounding ground, and does not necessarily need to be installed at a plurality of depths in the ground. .
[0008]
In the present invention, the drain material may be any material as long as it can guide moisture contained in the ground to the upper water flow material and the perforated pipe. For example, a cardboard drain material or a sand drain is used. However, the cardboard drain material is optimal because it is relatively easy to handle and place and is economical.
[0009]
In this invention, the said wall body and the said groove | channel suppress that the influence of subsidence or a horizontal displacement reaches the surrounding ground of an improvement object area. Here, the wall body can be a column wall formed by mixing cement and local soil by an SMW method or a deep mixing method, or an underground wall in which steel sheet piles are continuously provided. Considering that the ground in the target area is soft, it is preferable to apply a ground wall made of steel sheet piles that requires a minimum of large heavy machinery for construction.
In addition, in the underground wall where the steel sheet piles are arranged continuously, a sealing means for preventing the vacuum pressure applied to the improvement target area via the drain material from leaking out of the improvement target area from the joint portion of the steel sheet pile. It is necessary to provide it. Further, in the present invention, the groove is formed by filling the inside with a stabilizing liquid in order to prevent the collapse of the groove wall, and bentonite stabilizing liquid, mud water or fluidized soil can be used as the stabilizing liquid. .
For the construction of the groove, multi-axis agitating blade auger machine for soil cement wall construction, horizontal moving type soil cement wall construction machine, earth auger excavator, water jet type groove drilling machine, chain saw type groove drilling machine, etc. Can be used.
In principle, the depth of the wall body and the groove is the same as that of the drain material. However, it is difficult to uniquely define the depth because it varies depending on the degree of ground displacement to be reduced and ground conditions.
[0010]
In the present invention, the loading embankment described above may be provided only at a location where it is necessary to suppress and control the displacement in accordance with the horizontal displacement in the ground or the horizontal displacement on the ground surface. If it is close to, the loading embankment should be provided only on the sheet material in the proximity area.
[0011]
【Example】
Hereinafter, although an example is described based on an accompanying drawing, the present invention is not limited to this.
FIG. 1 is a sectional view showing one step of the ground improvement method.
In FIG. 1, the ground improvement structure 10 is in contact with a plurality of drain materials 16 placed at an interval of about 1 m in the vertical direction from the ground surface in the improvement target region 13 and the heads of these drain materials 16. A horizontal drainage material 12 comprising a water-permeable material (not shown) and a perforated pipe (not shown), and the horizontal drainage material 12 and the drain material 16 are laid on the ground surface so as to be airtightly covered. Improved to measure the horizontal horizontal displacement of the surrounding ground in the area to be improved, and the vacuum pump 15 communicated to the perforated pipe of the horizontal drainage material 12 through a connecting pipe (not shown). An inclinometer 18 extending deeper than the depth and a loading embankment 14 loaded on the sheet material 11 so as to control the displacement according to the increase or decrease of the horizontal horizontal displacement of the surrounding ground are provided.
[0012]
The inclinometer 18 performs boring deeper than the improved depth at the measurement site of the horizontal horizontal displacement in both the area to be improved 13 and the surrounding ground, and puts an inclinometer into each borehole to measure each depth. The inclination angle of 18a is measured, and the horizontal displacement is calculated from the inclination angle at each depth. A plurality of inclinometers 18 are arranged in a plurality of stages at a plurality of locations in the borehole, or a single inclinometer is moved up and down in the borehole each time it is measured and installed at each measurement point 18a. Can do. In either case, since the measurement deepest portion is assumed to be a fixed point and the horizontal displacement for each depth is calculated, the measurement deepest portion is made deeper than the improved depth.
In addition, a subsidence meter (not shown) is appropriately arranged on the improvement target area and the surrounding ground surface.
[0013]
For example, a cardboard drain material, a sand drain, or the like can be used as the drainage drain material 16, but the cardboard drain material is optimal in consideration of ease of handling, economy, and water collection effect. .
[0014]
The water-permeable material as the horizontal water-permeable material 12 is a belt-shaped material, and is laid at predetermined intervals so as to come into contact with the head of the drain material 16 protruding from the ground surface. Moreover, the perforated pipe | tube as the horizontal water-permeable material 12 uses what bored a some hole in pipe bodies, such as a vinyl chloride pipe, and is extended so that a some water-permeable material may be cross | intersected.
Further, the sheet material 11 is embedded in the sheet embedding groove 17 so that the outside air does not flow into the inside from these ends.
[0015]
Next, the ground improvement method and its operation will be described with reference to FIG.
First, a preparation step for vacuum-consolidating the improvement target area 13 and an inclinometer 18 for measuring the horizontal horizontal displacement around the improvement target area 13 are performed.
In the vacuum consolidation preparation step, a plurality of drain materials 16 are respectively placed almost vertically at an improvement target area 13 at intervals of about 1 m, and horizontal drainage materials 12 are laid so as to communicate with the heads of these drain materials 16. A plurality of drain members 16 and the horizontal drainage material 12 are hermetically covered with the sheet material 11, the end of the sheet material 11 is embedded in the sheet embedding groove 17, and the predetermined horizontal drainage material 12 is vacuumed via a connecting pipe. The pump 15 is connected.
Inclinometers 18 are arranged in multiple stages in the borehole, installed so that the deepest measurement part is deeper than the improved depth, and a settlement gauge is also installed.
[0016]
After the above preparation process and the installation of the inclinometer 18 are completed, the initial values before construction, which serve as a reference for horizontal displacement and subsidence, are measured in both the improvement target area and the surrounding ground, and then the vacuum pump 15 is operated to improve. The vacuum consolidation process of the target area 13 is started.
[0017]
When the horizontal displacement and the amount of settlement are measured at least once a day while performing the vacuum consolidation process, the subsidence proceeds in the improvement target area 13 as the vacuum consolidation progresses, and the surrounding ground is the center of the improvement target area 13. Displace horizontally to head toward.
That is, in the vacuum consolidation process, the ground contracts by reducing the pressure of the entire improvement target area 13 through the drain material 16 and the horizontal drainage material 12. As the ground contracts, ground subsidence and horizontal displacement of the ground toward the center of the area to be improved 13 occur. This horizontal displacement is usually the maximum near the ground surface and cracks occur in the surrounding ground. Is.
FIGS. 5 and 6 show examples of actual measurements of the amount of ground subsidence and horizontal displacement 35 days after the start of vacuum consolidation, and these figures also show the effects of subsidence and horizontal displacement occurring on the surrounding ground. I understand that there are not many.
[0018]
After starting the vacuum consolidation, the loading embankment is started when it is determined that the surface ground strength of the improvement target area 13 has increased to such an extent that a predetermined heavy machinery operation can be performed. Usually, loading embankment becomes possible in about one week after the start of vacuum consolidation. At this time, accompanying the embankment of the loading embankment 14, the ground is horizontally displaced from the improvement target area 13 toward the surrounding ground due to insufficient support force of the ground or sliding deformation. Since the maximum value of this horizontal displacement often occurs in the underground part, in the case of a loaded embankment, it is necessary to measure not only the ground surface displacement amount but also the underground horizontal displacement amount.
[0019]
FIG. 3 shows a comparison between the horizontal displacement generated by the loading embankment and the horizontal displacement generated by vacuum compaction. As shown in the figure, in the case of vacuum consolidation, in many cases, the amount of horizontal displacement is the maximum near the ground surface, and in the case of loaded embankments, the maximum amount of horizontal displacement often occurs in the ground. Acts to offset. Therefore, the horizontal displacement amount of the surrounding ground is within the allowable range if the embankment speed and height of the loaded embankment are adjusted within a range of about 10 to 30 cm / day while monitoring the direction and displacement amount of the underground horizontal displacement. It is also possible to control to be about ± 1 to 5 cm.
In addition, when the displacement toward the center of the improvement target area 13 is prominent, further embankment is performed. However, if there is a possibility that the influence on the surrounding area may be increased, a vacuum is temporarily used depending on the situation. An increase in displacement can be suppressed by stopping the pump 15.
Further, the area where the loading embankment is raised does not necessarily need to be performed in the entire area to be improved 13. For example, as shown in FIG. 7, the loading emphasis is placed on the end of the sheet material 11 facing the house 22. If the embankment is arranged, it is effective in terms of suppressing the influence on the house 22.
[0020]
FIG. 2 is a cross-sectional view showing one step of the ground improvement method different from FIG.
In the ground improvement structure of FIG. 2, as a configuration different from the embodiment of FIG. 1, a buffer groove 20 and a measuring device (not shown) for measuring the horizontal displacement of the ground surface in the improvement target region 13 and the surrounding ground 25. Inclinometer 18 as shown in FIG. 1 is not provided, and the configuration other than these is the same as that of FIG.
[0021]
Here, the buffer groove 20 is a groove formed between the improvement target region 13 and the surrounding ground 25 and filled with bentonite stabilizing liquid or the like. Reduce the transmission of displacement to the surrounding ground.
[0022]
In addition to the buffer groove 20, for example, a steel sheet pile may be connected to construct the underground wall, and FIG. 4 illustrates the displacement reduction effect during vacuum consolidation of the underground wall made of this steel sheet pile. From this example, it can be seen that by placing a steel sheet pile, the horizontal displacement of the ground surface could be reduced to about 15% of the case without the underground wall.
[0023]
By providing the buffer groove 20 or the underground wall of the steel sheet pile, the distribution of horizontal displacement in the ground during vacuum consolidation is averaged, and in many cases the ground surface displacement is maximized, so the ground surface displacement can be monitored. For example, the impact of subsidence on the surrounding ground and horizontal displacement during vacuum consolidation can be grasped. Therefore, in the embodiment of FIG. 2, the measurement of underground horizontal displacement is not a necessary condition.
In addition, the underground wall such as the buffer groove 20 or the steel sheet pile not only prevents the horizontal displacement from being transmitted but also serves as a water blocking wall. Therefore, there is a water permeable layer 21 in the improvement target area as shown in FIG. Even in this case, the vacuum consolidation method can be applied without hindrance.
[0024]
In addition, also when providing underground walls, such as the buffer groove | channel 20 or a steel sheet pile like FIG. 2, ground improvement is made | formed by the process similar to the ground improvement construction method of FIG.
That is, in the ground improvement method shown in FIG. 2, a device for measuring the horizontal displacement of the ground surface is installed in place of the inclinometer 18, and the horizontal displacement of the ground surface due to vacuum compaction and loading embankment is monitored by this device. However, the horizontal displacement amount of the surrounding ground is within the allowable range by adjusting the embankment speed and height of the loading embankment and stopping / resuming the vacuum pump 15 so that the horizontal displacement amount by the both cancels out. It is controlled to be about ± 1 to 5 cm.
[0025]
【The invention's effect】
In the present invention, the horizontal displacement of the surrounding ground can be greatly reduced by performing the loading embankment based on the measurement data of the horizontal displacement of the surrounding ground while performing vacuum consolidation. Even in places where houses are densely packed around, the vacuum consolidation method can be applied.
[0026]
Further, in the present invention, since a device for measuring the horizontal displacement in the ground is used, even when the ground is complicated, the embankment speed and height of the loading embankment and the stop / vacuum operation of the vacuum operation are based on the accurate horizontal displacement in the ground. The restart can be controlled reliably.
In the present invention, since the wall body and the buffer groove are provided, the horizontal displacement of the surrounding ground can be further reduced by the blocking effect and the displacement absorbing effect. In addition, due to the water-stopping effect of the walls and buffer grooves, it is possible to prevent or block the groundwater drop in the surrounding ground, so that the settlement of the surrounding ground can be greatly reduced. Furthermore, when there is a water-permeable ground in the area to be improved, it was difficult to apply the vacuum consolidation method due to air leakage, but it was possible to prevent air leakage by providing walls and buffer grooves, Application of vacuum consolidation method became possible. Moreover, since the ground horizontal displacement is averaged by providing the wall, displacement control based on the ground surface displacement can be performed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing one step of a ground improvement method according to the present invention.
FIG. 2 is a cross-sectional view showing one step of a ground improvement method different from FIG.
FIG. 3 is a diagram for comparing and explaining underground displacement due to vacuum consolidation and loaded embankment.
FIG. 4 is a view for explaining an effect of reducing horizontal displacement by a wall made of steel sheet piles.
FIG. 5 is a diagram showing a shape of ground subsidence caused by vacuum consolidation.
FIG. 6 is a diagram showing horizontal displacement of the ground due to vacuum consolidation.
FIG. 7 is a cross-sectional view showing the arrangement of the loading embankment in the improvement target area.
[Explanation of symbols]
10 Ground improvement structure 11 Sheet material 12 Horizontal drainage material (water flow material and perforated pipe)
13 Improvement target ground 14 Loading embankment 15 Vacuum pump 16 Drain material 18 Inclinometer

Claims (3)

A plurality of drain materials are placed almost vertically in the ground to be improved, the head is extended to the ground surface, a water-permeable material and a perforated pipe are arranged on the heads of the plurality of drain materials, In the construction method of airtightly covering with the sheet material, reducing the inside covered with the sheet material by using a vacuum pump and consolidating the improvement target ground,
While measuring the horizontal displacement around the improvement target ground, it is controlled to suppress the displacement by loading a loading embankment on the sheet material in accordance with the increase or decrease of the displacement. Ground improvement method. A plurality of drain materials are placed almost vertically in the ground to be improved, the head is extended to the ground surface , a water-permeable material and a perforated pipe are arranged on the heads of the plurality of drain materials, In the construction method of airtightly covering with the sheet material, reducing the inside covered with the sheet material by using a vacuum pump and consolidating the improvement target ground,
While constructing a wall or a groove along the drain material in the surrounding ground of the improvement target ground, setting a measuring point for measuring the horizontal displacement in the surrounding ground, while measuring the displacement at the measuring point , by the from drain over emission material via the water passage material and the perforated tube to drain leading the water, loading the loading embankment on the sheet material in accordance with the increase or decrease of the displacement, suppressing the displacement The ground improvement construction method characterized by controlling to do. By pouring a plurality of drain material substantially vertically into the ground from the ground surface in the improved target range by extending the head to the ground surface, distribution of water flow material and perforated tube head portion of the drain member of said plurality of In the ground improvement structure for airtightly covering the upper portion with a sheet material, depressurizing the interior covered with the sheet material using a vacuum pump, and consolidating and improving the improvement target ground,
A wall or a groove built along the drain member, and a horizontal displacement measurement means provided for measuring the horizontal displacement of the surrounding ground of the improvement target zone, the displacement from the horizontal displacement measuring means A ground improvement structure comprising a loading embankment loaded on the sheet material so as to suppress and control this accordingly.

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