JP2015030971A - Hole wall protection body of cast-in-place pile, and construction method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an existing structure from being affected by deformation of a foundation due to collapse of a hole wall when a cast-in-place pile is constructed, and to reduce a construction cost of a hole wall protection body.SOLUTION: In a hole wall protection body 10, a plurality of soil cement columns 12, 14 are arranged and connected to each other so as to surround a pile hole of a cast-in-place pile 1 in the vicinity of an existing structure 2. The soil cement columns 12 extending from their crowns to their bottom edges are constructed without forming gaps in a prescribed range 10B on the side of the existing structure 2. In a range 10C on a thinning-out side, the soil cement columns 12, 14 are constructed without forming gaps in an upper part 10A and the soil cement columns 12, 14 are constructed with gaps on a side below the upper part 10A.

Description

  The present invention relates to a hole wall protective body for a cast-in-place pile and a construction method thereof.

  When cast-in-place piles are constructed on a narrow site where existing structures exist in the vicinity, it is necessary to protect the hole walls because the collapse of the hole walls may affect the existing existing structures. Therefore, in the hole wall protection method described in Patent Document 1, a hole wall protection body in which a plurality of columnar improvements are connected in an annular shape is constructed so as to surround a pile hole of a cast-in-place pile, thereby protecting the hole wall. doing.

JP 2011-74675 A

  In order to reduce the construction cost of the hole wall protector described in Patent Document 1, the inventors of the present application have an interval between every other columnar improvement over the entire circumference of the hole wall protector. We examined the construction and conducted a centrifugal model experiment simulating the actual stress field, strain field and external force condition, and found that ground surface subsidence and deformation occurred between the hole wall guard and the existing structure. Deformation occurred.

  The present invention has been made in view of the above circumstances, and prevents the influence of the ground deformation due to the collapse of the hole wall during the construction of cast-in-place piles on the existing existing structures, The object is to reduce the construction cost.

  The cast-in-place pile wall protector according to the present invention is a cast-in-place pile, in which a plurality of columnar improvement bodies are arranged and connected so as to surround a pile hole of a cast-in-place pile constructed in the vicinity of an existing structure. In the predetermined range on the existing structure side, the columnar improvement body extending from the top end to the lower end is constructed without a gap, whereas in the predetermined range on the existing structure side, the hole length protector is constructed with a predetermined length from the top end except for the predetermined range. A columnar improvement body is constructed without gaps in the upper part of the frame, and a columnar improvement body is constructed with a gap between the lower side and the upper part.

  In the cast-in-place pile wall protective body, a columnar improvement body that suppresses expansion of the range of ground deformation may be constructed around the plurality of columnar improvement bodies.

  Moreover, the construction method of the hole wall protection body of the cast-in-place pile which concerns on this invention arrange | positions and connects a some columnar improvement body so that the pile hole of the cast-in-place pile constructed near the existing structure may be enclosed. Thus, a method for constructing a hole wall protector, wherein the predetermined range on the existing structure side of the hole wall protector constructs a columnar improvement body extending from the top end to the lower end of the hole wall protector without a gap. Except for the predetermined range of the hole wall protector, a columnar improvement body is constructed without a gap for an upper portion of a predetermined length from the top, and a columnar improvement body is constructed with an interval below the upper portion. It is characterized by that.

  In the method for constructing the hole wall protective body of the cast-in-place pile, a columnar improvement body that suppresses expansion of the ground deformation range may be constructed around the plurality of columnar improvement bodies.

  According to the present invention, it is possible to prevent the influence of the ground deformation due to the collapse of the hole wall during the construction of cast-in-place piles on the existing existing structures, and to reduce the construction cost of the hole wall protector. .

It is a perspective view which shows the hole wall protective body which concerns on one Embodiment. It is a top view which shows the construction procedure of a hole wall protective body. It is a top view which shows the construction procedure of a hole wall protective body. It is a top view which shows the construction procedure of a hole wall protective body. It is a top view which shows the construction procedure of a hole wall protective body. It is an elevational view showing a model hole wall guard. It is a table | surface which shows the relationship between a real hole wall protector and a model hole wall protector. It is a top view which shows the whole plan of a centrifuge model experiment. It is an elevation which shows the whole plan of a centrifuge model experiment. It is a top view which shows the measurement position of the amount of settlement of the ground surface. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a photograph which shows the surface of the model ground after experiment implementation. It is a photograph which shows the surface of the model ground after experiment implementation.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a hole wall protector 10 according to an embodiment. As shown in this figure, the hole wall protector 10 is formed in an annular shape so as to surround the pile hole to be excavated when the cast-in-place pile 1 is constructed, to a depth that does not reach the lower end of the excavation hole from the ground to a depth below the groundwater level. Has been built.

  Here, in this embodiment, since the cast-in-place pile 1 is constructed in a narrow site where the existing structure 2 such as a railway exists in the vicinity, the hole wall collapses and the adjacent existing structure 2 is affected. It is necessary to prevent this. Therefore, the hole wall protector 10 is constructed to protect the hole wall.

  The hole wall protection body 10 is a soil cement column wall in which a plurality of columnar soil cement columns 12 and 14 are arranged in an annular shape and connected. The soil cement column 12 extends from the top end to the bottom end of the hole wall protection body 10, while the soil cement column 14 has a predetermined length L (for example, 2000 to 3000 mm or a pile length) downward from the top end. (Length of 1/3 to 1/5).

  Here, the hole wall protection body 10 has a half circumference range 10B on the existing structure 2 side (side facing the existing structure 2) and a half circumference on the opposite side (side not facing the existing structure 2). The configuration is different from the range 10C. In the range 10B on the existing structure 2 side, the soil cement columns 12 are continuously constructed, whereas in the range 10C on the opposite side, every other soil cement column 12 is constructed and adjacent to each other. A soil cement column 14 is constructed between the soil cement columns 12.

  In the range 10B on the existing structure 2 side, the distance between the centers of the adjacent soil cement columns 12 is shorter than these diameters, and the adjacent soil cement columns 12 are in a state where the side portions overlap each other. It is joined with. Further, in the range 10C opposite to the existing structure 2 side, the distance between the centers of the adjacent soil cement columns 12 and 14 is shorter than their diameter, and the adjacent soil cement columns 12 and 14 are adjacent to each other. Are joined with their side portions overlapping each other.

  In other words, if the hole wall does not collapse in the range 10B on the existing structure 2 side in the hole wall protector 10, even if the hole wall collapses in the range 10C on the opposite side, deformation of the surrounding ground or settlement of the ground surface The influence of ground deformation such as this does not reach the existing existing structures 2. Accordingly, in the range 10B on the existing structure 2 side in the hole wall protective body 10, the soil cement pillar 12 extending from the top end to the lower end of the hole wall protective body 10 is arranged without a gap, whereas the opposite side ( In the range 10C (hereinafter referred to as “thinning side”), the soil cement columns 12 and 14 are disposed without any gaps in the range of the predetermined length L (hereinafter referred to as the upper portion 10A) from the top to the bottom. In the range below the upper portion 10A, every other soil cement column 12 is arranged.

  Here, the strength of the upper part 10A of the hole wall protection body 10 is set to such an extent that it can resist the soil water pressure of the surrounding ground and can maintain an annular shape. This is because if the shape of the upper part 10A of the hole wall protective body 10 collapses, the hole wall may collapse near the ground surface and affect the existing existing structures 2. Moreover, about the head of the cast-in-place pile 1, it is necessary to carry out the turning work as a pile head process, and the placement work of post-cast concrete, and the work inside the upper part 10A of the hole wall protection body 10 is carried out. This is because it occurs. In addition, in the range 10B on the existing structure 2 side below the upper part 10A of the hole wall protection body 10, the strength can resist the soil water pressure of the surrounding ground and can maintain a semicircular shape. Is set to

  In addition, although it is desirable to set the waterstop of the hole wall protection body 10 high in order to suppress the inflow of groundwater to the upper part 10A and the outflow of the stable liquid from the excavation hole to the surrounding ground, this is not essential. .

  Moreover, the hole wall protection body 10 includes a pair of cylindrical soil cement columns 16. The pair of soil cement columns 16 is formed on the outer peripheral side of the annular portion composed of the soil cement columns 12 and 14, and on the soil cement column 12 at the boundary between the range 10B on the existing structure 2 side and the range 10C on the thinning side. It arrange | positions so that it may adjoin and extends from the ceiling end of the hole wall protection body 10 to a lower end.

  2-5 is a top view which shows the construction procedure of the hole wall protective body 10. FIG. As shown in FIGS. 2 and 3, in the range 10 </ b> B on the existing structure 2 side, every other soil cement pillar 12 is constructed, and the soil cement pillar 12 is constructed between the constructed soil cement pillars 12. To do. On the other hand, as shown in FIGS. 4 and 5, in the range 10 </ b> C on the thinning-out side, every other soil cement pillar 12 is constructed, and the soil cement pillar 14 is constructed between the constructed soil cement pillars 12. . And although illustration is abbreviate | omitted, a pair of soil cement pillar 16 is made into the outer peripheral side of the annular part comprised by the soil cement pillars 12 and 14, and the range 10B on the existing structure 2 side and the range 10C on the thinning side It is constructed to be adjacent to the boundary soil cement pillar 12. The construction machine is a compact mechanical stirring type ground improvement machine that can be used for construction in a narrow and empty space, for example, a drilling stirring blade with a bit at the tip of a boring machine, and a discharge of cement milk. Use one with an outlet.

  Here, when the ground is drilled in order to construct the soil cement column 12 or the soil cement column 14 between the constructed soil cement columns 12, the soil cement already constructed by the drilling blades of the above example or the like. The side part of the column 12 is cut. Then, the cement milk 12 and 14 are constructed by stirring and mixing the cement milk and the excavated soil in the excavation hole, and the soil cement columns 12 and 14 are connected to the soil cement columns 12 on both sides thereof.

  In order to confirm the effect of the hole wall protection body 10 constructed as described above, a centrifugal model experiment simulating an actual stress field / strain field and external force conditions was performed, which will be described below.

  FIG. 6 is an elevational view showing the model hole wall protector 100, and FIG. 7 is a table showing the relationship between the actual hole wall protector 10 and the model hole wall protector 100. As shown in the elevation view of FIG. 6 and the table of FIG. 7, the inner diameter of the actual hole wall protection body 10, that is, the diameter of the permanent pile is 3000 mm, whereas the diameter of the permanent pile of the model is 120 mm. is there. Further, the length of the actual main pile is 10000 mm, whereas the length of the model main pile is 400 mm. The actual soil cement columns 12, 14, and 16 have a diameter of 600 mm, whereas the model soil cement columns 120, 140, and 160 have a diameter of 24 mm. Further, the wrap length (length between intersections) of the actual soil cement columns 12, 14, 16 is 130 mm, whereas the wrap length of the model soil cement columns 120, 140, 160 is 5.2 mm. . That is, the model hole wall protector 100 is 1/25 the size of the actual hole wall protector 10.

Here, the strength of the soil cement columns 120, 140, 160 was set to about 1.0 N / mm ² . For this reason, a model was prepared with the cement amount of the soil cement columns 120, 140, 160 being about 200 kg / m ³ . Further, the water cement ratio W / C of the soil cement columns 120, 140, 160 is set to about 100%.

  FIG. 8 is a plan view showing the overall plan of the centrifugal model experiment, and FIG. 9 is an elevation view showing the overall plan of the centrifugal model experiment. As shown in these figures, in this experiment, the hard earth basin 110 having a width of 1900 mm, a depth of 800 mm, and a depth of 700 mm is divided into four equal parts by dividing equally in the width direction and the depth direction. A model hole wall protector 100 was installed in the area 110A. The other region 110A was used in an experiment for a hole wall protector having another shape.

The model ground of the hard soil tank 110 was created by an air drop method using a sandy soil sample (G _s = 2.674) as the ground material. The upper part of this model ground was created with a relative density D _r = 40%, and the lower part of the model ground was created with a relative density D _r = 60% assuming that it would be the supporting ground for the hole wall protector 100. . Then, assuming that the groundwater level is high, the periphery of the hole wall protection body 100 was saturated to the surface of the model ground by passing water through the water pipe 102 from the lower part.

  In this experiment, after applying a predetermined centrifugal acceleration (25G) to the hard earth tank 110, the water level of the simulated stabilizing liquid (salt water, specific gravity 1.05) inside the hole wall protective body 100 was lowered. Also, 92 mm (2.3 m on the real scale as shown in FIG. 10) and 176 mm (4.4 m on the real scale as shown in FIG. 10) from the center of the hole wall protector 100 to the orbit side, opposite to the orbit. The amount of settlement on the ground surface at a position of 100 mm on the side (2.5 m on the actual scale as shown in FIG. 10) was measured with a laser displacement meter 104.

Here, in one region 110A, as shown in FIG. 10, an experiment was performed under the condition that an external force load (orbit load and train load = load corresponding to 34 kN / m ² ) was applied to the position of the track (this experiment was Case 2). Called). In the other region 110A, an experiment was performed without applying an external force load (this experiment is referred to as Case 1).

  11 to 14 are graphs showing experimental results. In this graph, the numerical value obtained by measuring the experimental model with a laser displacement meter is converted into an actual scale and displayed. Moreover, in FIG.11 and FIG.13, the result of the position of 2.3 m from the pile core to the track side is shown by a black line, and the result of the position of 4.4 m from the pile core to the track side is shown by a gray line. . Moreover, in FIG.12 and FIG.14, the result of the position of 2.5 m is shown from the pile core to the thinning side.

  As shown in FIG.11 and FIG.13, it turns out that the settlement of the ground surface has hardly arisen in both Case1 and Case2 by the track side. This is probably because the soil cement pillar 120 was arranged without being thinned and the adjacent soil cement pillars 120 were overlapped, so that the ground was not deformed.

  On the other hand, as shown in FIGS. 12 and 14, on the thinning-out side, it can be seen that there is almost no settlement of the ground surface immediately after the water level is lowered in both Case 1 and Case 2. However, it can be seen that after the water level drop amount is 2.3 to 2.7 m (down 0.3 to 0.7 m from the water level of the surrounding ground), the ground surface gradually subsides. The maximum value is about 50 to 60 cm.

  FIG. 15 is a photograph showing the model ground after the Case 1 experiment was conducted, and FIG. 16 is a photograph showing the model ground after the Case 2 experiment was conducted. From these photographs, the ground surface has subsided due to the water level drop on the thinning side, while the ground surface has subsided due to the water level drop on the track side. Was confirmed.

  In addition, it was confirmed that the ground surface subsidence occurred on the thinning side and the ground surface subsidence did not occur on the track side, with the soil cement column 160 at the boundary between the thinning side and the track side as a boundary. This indicates that the arrangement of the soil cement pillar 160 at the boundary between the thinning side and the track side is effective in preventing the range in which the deformation of the ground surface occurs from extending from the thinning side to the track side. ing.

  As described above, in the hole wall protection body 10 of the cast-in-place pile 1 according to the present embodiment, the pile hole of the cast-in-place pile 1 in which a plurality of soil cement columns 12 and 14 are constructed in the vicinity of the existing structure 2 is provided. It is arranged so as to surround it and connected. Here, in the predetermined range 10B on the existing structure 2 side of the hole wall protector 10, the soil cement pillar 12 extending from the top end to the lower end of the hole wall protector 10 is constructed without a gap, whereas thinning is performed. In the range 10C on the side, the soil cement pillars 12 and 14 are constructed without gaps for the upper part 10A, and the soil cement pillars 12 are constructed with a gap on the lower side of the upper part 10A.

  That is, the soil cement pillar 12 is constructed without thinning out so that the shape is maintained in the upper part 10A of the hole wall protective body 10 and the predetermined range 10B on the existing structure 2 side below it. On the other hand, every other soil cement column 12 is thinned out in a predetermined range 10C on the thinning side below the upper portion 10A. Thereby, the deformation of the ground such as the deformation of the ground surface and subsidence between the cast-in-place pile 1 and the existing structure 2 can be suppressed, and the existing existing structure 2 can be prevented from being affected. Further, by preventing the shape of the upper portion 10A from collapsing, it is possible to safely carry out the turning work as a pile head treatment, the placing work of post-cast concrete, and the like inside the upper portion 10A. Furthermore, in the predetermined range 10C below the upper portion 10A and on the thinning side, the construction cost can be reduced by reducing the number of soil cement columns to be constructed.

  Further, the range of ground deformation is enlarged adjacent to the soil cement pillar 12 located at the boundary between the predetermined range 10B on the existing structure 2 side of the hole wall protection body 10 and other than the range 10B (range 10C). By constructing the soil cement pillar 16 that suppresses the above, it is possible to prevent the influence of the ground deformation generated on the thinning side from reaching the existing structure 2.

  In addition, the above-mentioned embodiment is for making an understanding of this invention easy, and does not limit this invention. It goes without saying that the present invention can be changed and improved without departing from the gist thereof, and that the present invention includes equivalents thereof. For example, in the above-described embodiment, the half circumference on the existing structure 2 side of the hole wall protector 10 is set as a predetermined range to be constructed without thinning out the soil cement column 12, and the half circumference outside the predetermined range is set as the soil cement column 12. Although the thinning range is used, the predetermined range may be determined as appropriate according to the soil quality at the original position, the groundwater pressure, the distance between the cast-in-place pile 1 and the existing structure 2, and the like. Further, on the thinning side of the hole wall protector 10, the soil cement pillars 12 are thinned out every other line. For example, a plurality of soil cement pillars 12 are constructed in succession, or one soil cement pillar 12 is thinned out. This may be thinned out continuously.

  In addition, as an example of the construction machine, a drilling machine with a drilling stirrer blade with a bit at the tip of the boring machine and a discharge port for cement milk was mentioned. Just choose. In addition, the blending of cement milk in the experiment is an example, and may be determined as appropriate according to the in situ soil quality, groundwater pressure, and the like.

  Furthermore, in the above-described embodiment, it is assumed that the improved body is lapped, but the same effect can be obtained even when the adjacent improved bodies are in contact with each other at points.

DESCRIPTION OF SYMBOLS 1 Cast-in-place pile, 2 Existing structure, 10 Hole wall guard, 10A upper part, 10B range, 10C range, 12, 14, 16 Soil cement pillar, 100 Hole wall guard, 102 Water pipe, 104 Laser displacement meter, 110 Hard soil tank, 110A area, 120, 140, 160 soil cement pillar

Claims (4)

A plurality of columnar improvement bodies are cast-in-place pile wall protective bodies arranged and connected so as to surround a pile hole of a cast-in-place pile constructed in the vicinity of an existing structure,
In the predetermined range on the existing structure side, the columnar improvement body extending from the top end to the lower end is constructed without a gap, whereas in the case other than the predetermined range, the columnar improvement body is provided on the upper portion of the predetermined length from the top end. Is constructed without gaps, and the pillar-shaped improvement body is constructed with a space between the upper part and the lower part of the upper part, so that the hole wall protective body for cast-in-place piles is provided.   2. The cast-in-place pile hole wall protector according to claim 1, wherein a columnar improvement body is constructed around the plurality of columnar improvement bodies to suppress expansion of a range of ground deformation. A method of constructing a hole wall protective body by arranging and connecting a plurality of columnar improvements so as to surround a pile hole of a cast-in-place pile constructed in the vicinity of an existing structure,
The predetermined range on the existing structure side of the hole wall protector is a columnar improvement body that extends from the top to the bottom of the hole wall protector without any gaps,
Except for the predetermined range of the hole wall protective body, a columnar improvement body is constructed without a gap for the upper part of the predetermined length from the top, and a columnar improvement body is constructed with a gap for the lower side from the upper part. A method for constructing a hole wall protective body for a cast-in-place pile.   4. The method for constructing a hole protection body for a cast-in-place pile according to claim 3, wherein a pillar-shaped improvement body that suppresses expansion of a range of ground deformation is constructed around the plurality of columnar improvement bodies.