JP2007217979A - Liquefaction prevention construction and its construction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquefaction prevention construction of the sandy soil capable of largely reducing construction expenses by reducing the amount of chemicals and its construction method. <P>SOLUTION: The liquefaction prevention construction 1 of the sandy soil is so constituted that solidifying bodies 3 of predetermined volume solidified by injecting chemicals 17 in the sandy soil 2 as an object of improvement are piled up in the vertical and horizontal directions and in the longitudinal direction to form the improved soil 4, non-improved sections 5 having the same volume as that of the solidifying bodies 3 are scattered in the improved soil 4 and that the vertical and horizontal directions and the longitudinal direction are surrounded by the solidifying bodies 3a, 3b, 3c, 3d, 3e and 3f without continuing two or more non-improved sections 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a structure for preventing liquefaction of sand ground and its construction method.

Conventionally, as one of the methods for preventing liquefaction of sand ground, there is a method of injecting and solidifying a solution-type chemical solution typified by an osmosis solidification treatment method into sand ground. In this construction method, as shown in FIG. 9, an injection tube 26 is inserted into the sand ground 25, and a solution-type chemical solution 27 is injected from its tip to form a solidified body 28 having a predetermined volume. The ground is improved in the left-right direction and the front-rear direction, and all of the improvement target sand ground 29 is improved. As another liquefaction prevention method, for example, the invention of Japanese Patent Application Laid-Open No. 2006-2529 is disclosed.
JP 2006-2529 A

  However, the above-described solution-type chemical solution injection method has a problem that the cost is high because the ratio of the chemical solution in the construction cost is very high.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a sand ground liquefaction prevention structure and its construction method capable of greatly reducing construction costs by reducing the amount of chemicals. It is to be.

  The liquefaction prevention structure of the sand ground to solve the above problems is the formation of the improved ground by solidifying the predetermined volume solidified by injecting the chemical into the sand ground to be improved and overlapping in the vertical and horizontal directions and the front and rear direction In the improved ground, unimproved portions having the same volume as the solidified body are scattered, and the unimproved portions are surrounded by the solidified body in the up, down, left, right, and front and rear directions without two or more continuous portions. . In addition, it includes that the solidified body and the unimproved portion are alternately formed in the vertical and horizontal directions and the longitudinal direction. In addition, the unimproved portion is not scattered near the ground surface of the improved ground, and all of them are improved by the solidified body.

  In addition, the liquefaction prevention method for sand ground is to form a solidified body of a predetermined volume by injecting a chemical solution from an injection pipe inserted into the sand ground to be improved, and superimpose this solidified body in the vertical and horizontal directions and the front-rear direction. In the process of forming a non-improved portion of the same volume as the solidified body in the improved ground without injecting a chemical solution from the injection tube, two or more unimproved portions are not continuously connected, and the upper, lower, left, right, front and rear Is surrounded by a solidified body. Moreover, it includes forming the solidified body and the unimproved portion alternately in the vertical and horizontal directions and the longitudinal direction.

  In the sand to be improved, a solidified body having a predetermined volume is overlapped in the vertical and horizontal directions and in the front-rear direction to form an improved ground, and unmodified parts having the same volume as the solidified body are scattered on the improved ground. Since the upper, lower, left, and right and front and back are surrounded by solidified bodies without being continuous two or more, efficient construction can be performed by injecting the chemical solution without waste, so that the construction cost can be greatly reduced. In addition, two or more unimproved portions do not continue, and the upper, lower, left, and right and front and rear are surrounded by solidified bodies, so that sufficient strength necessary for preventing liquefaction can be ensured.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a sand ground liquefaction prevention structure (hereinafter referred to as a liquefaction prevention structure) and a sand ground liquefaction prevention construction method (hereinafter referred to as a liquefaction prevention construction method) according to the present invention will be described below in detail with reference to the drawings. To do. First, the liquefaction prevention structure will be described, and then the liquefaction prevention method will be described. In each embodiment, the same components will be described with the same reference numerals, and only different configurations will be described with different reference numerals. . An object of the present invention is to provide a structure that prevents the occurrence of liquefaction by injecting a solution type chemical into the sand ground and improving the solidification by targeting a sand ground that is liable to be liquefied due to a large earthquake or the like.

  FIG. 1 shows a liquefaction prevention structure 1 according to the first embodiment. In this liquefaction prevention structure 1, an injection pipe is inserted into the sand ground 2 to be improved, and a silica-based aqueous chemical solution (hereinafter referred to as a chemical solution) is injected from the tip to obtain a height of 1.5 m, a width of 1.5 m, The solidified body 3 having a depth of 3 m is formed as an improved ground 4 by overlapping in the vertical direction and the horizontal direction, that is, in the vertical and horizontal directions and in the longitudinal direction.

  In this improved ground 4, unimproved portions 5 having the same volume as the solidified body 3 are scattered, and the unimproved portion 5 is surrounded by the solidified body 3 in the top, bottom, left, right, and front and back. It is supposed not to. The unimproved portion 5 is a portion into which no chemical solution is injected, and as shown in (2) and (3) of the figure, the six surfaces of the unimproved portion 5, that is, the front side 5a and the back side 5b, and the upper surface side 5c, bottom surface side 5d, and both side surfaces 5e, 5f are surrounded by solidified bodies 3a, 3b, 3c, 3d, 3e, 3f, so that there are two unmodified portions 5 in the six-face direction. It is not continuous.

  The unimproved portion 5 in such a state is scattered randomly in the improved ground 4 so that the improved portion 6 formed of the solidified body 3 has a ratio of 60% to 80% with respect to the sand ground 2 to be improved. An unimproved portion 5 is formed. That is, the unimproved portion 5 can be formed to less than 40% of the sand ground 2 to be improved. Therefore, even if the improvement target sand ground 2 is not improved by 100%, a predetermined strength can be secured and liquefaction can be prevented by an improvement of 60% to 80%.

  FIG. 2 shows the liquefaction prevention structure 7 of the second embodiment. This liquefaction prevention structure 7 includes a portion excluding the upper layer side 8 of the improved ground 4, that is, the solidified body 3 and the unimproved portion 5 on the lower layer 10 from the upper layer portion 8 alternately in the vertical and horizontal directions and the front and rear direction. Other than this, the configuration is the same as that of the liquefaction prevention structure 1 of the first embodiment. The lower layer portion 9 can be entirely improved in the same manner as the upper layer portion 8.

  This is because the solidified body 3 and the unimproved portion 5 are formed every other side in the up / down / left / right direction and the front / rear direction, and the unimproved portion 5 has six sides, that is, the front side 5a and the back side 5b, the top side 5c and the bottom side. Since the side 5d and the side surfaces 5e and 5f are surrounded by the solidified bodies 3a, 3b, 3c, 3d, 3e, and 3f, two or more unmodified portions 5 do not continue in six directions. .

  Moreover, although the unimproved portion 5 is formed at a location adjacent to the four corners of the unimproved portion 5, this is because the four corners of the solidified body 3 are overlapped with each other. Are not consecutive. Also in the improved ground 4, the improved portion 6 formed of the solidified body 3 is formed at a ratio of 60% to 80% with respect to the sand sand 2 to be improved, and the unreformed portion 5 is 40 to the sand sand 2 to be improved. %. Therefore, in this case as well, even if the improvement target sand ground 2 is not improved by 100%, liquefaction can be prevented while maintaining a predetermined strength with an improvement of 60% to 80%.

  FIG. 3 shows a liquefaction prevention structure 11 according to the third embodiment. This liquefaction prevention structure 11 improves the surface layer portion (single layer and double layer portion) 12 near the ground surface by 100%, and unmodified portions 5 are scattered randomly in the lower layer portion 13 below the surface layer portion, thereby solidifying the solidified body. 3 is formed at a ratio of 60% to 80% with respect to the sand ground 2 to be improved, and the other configuration is the same as the liquefaction prevention structure 1 of the first embodiment. It is. That is, the surface layer portion 12 of the liquefaction prevention structure 1 of the first embodiment is improved by 100%. When such an improvement is made, ground subsidence hardly occurs and a very stable ground is obtained. In this case as well, the lower layer part can all be improved in the same manner as the surface layer part 12.

  FIG. 4 shows a liquefaction prevention structure 14 according to the fourth embodiment. This liquefaction prevention structure 14 improves the surface layer portion (single layer and double layer portion) 12 near the ground surface by 100%, and alternately forms the solidified body 3 and the unimproved portion 5 in the lower layer portion 13 below the surface portion. And the improvement part 6 formed with the solidified body 3 is formed in a ratio of 60% to 80% with respect to the sand ground 2 to be improved, and the liquefaction prevention structure of the second embodiment other than this is provided. 7 is the same configuration. Similarly to the above, the surface layer portion 12 of the liquefaction prevention structure 7 of the second embodiment is improved by 100%, and as in the above, no ground subsidence occurs and a very stable ground is obtained. .

  Note that the solidified body 3 is not limited to a height of 1.5 m, a width of 1.5 m, and a depth of 3 m as described above, and may be smaller or larger.

  Next, the liquefaction prevention method will be described based on the liquefaction prevention structure of the first embodiment. First, as shown in FIG. 5, an injection tube 16 is inserted to a predetermined location of the sand ground 15 to be improved to a predetermined depth, and a chemical solution 17 is injected from the tip of the injection tube 16 to a height of 1.5 m, a width of 1. A first solidified body 18 having a depth of 5 m and a depth of 3 m is formed.

  Next, after forming the first solidified body 18, the injection tube 16 is pulled up and the chemical solution 17 is injected into the upper part of the first solidified body 18 to form a second solidified body 19 having the same size. Then, it will be in the state where these overlapped up and down.

  Then, after the second solidified body 19 is formed, the injection tube 16 is pulled up to the upper part of the second solidified body 19, that is, the portion 20 where the third solidified body is to be formed. Instead, the injection tube 16 is pulled up to the point 20 where the fourth solidified body is formed. And if the 3rd solidified body 21 is formed by inject | pouring the chemical | medical solution 17 here by the same method as the above, the solidified body unit 23 with the unimproved part 22 will be formed.

  Next, the solidified unit 23 is sequentially formed in the horizontal direction (left-right direction) by the same method as described above. At this time, the other unimproved portions 22 are not formed adjacent to the six sides of the portion where the unimproved portions 22 are formed so that two or more unmodified portions 22 do not continue. Then, after the formation of the solidified body unit 23 in the lateral direction (left-right direction) is completed, when the solidified body unit 23 is sequentially formed in the front-rear direction (depth direction) by the same method as described above, unimproved surrounded by the solidified body 3 The liquefaction prevention structure 1 of the first embodiment in which the parts 5 are scattered is formed. In addition, it is decided before inject | pouring a chemical | medical solution where the improvement part (ratio of the solidified body formed with respect to the improvement object sand ground) is made where it is formed.

  The above liquefaction prevention method has been described based on the liquefaction prevention structure 1 of the first embodiment, but this also forms the liquefaction prevention structures of the second to fourth embodiments by the same method. .

Next, experimental examples replacing the embodiment of the present invention will be described with reference to FIGS. FIG. 6 shows the model soil layer 24 used in this experiment. The ground is divided into 4 rows × 5 columns, and the various ground elements are defined as Line 1 to Line 5 in order from the left column. The size of each board element was 150 mm in height, 150 mm in width, and 150 mm in depth, and the experiment was conducted with a 1/10 scale model of the actual ground. In addition, in order to express the ground with variation, the model was simplified to two elements, a liquefied element and a non-liquefied element. For the element to be liquefied, No. 5 silica sand (D ₅₀ = 0.63) was used, and the relative density was adjusted to 60% by the underwater dropping method. For the elements that do not liquefy, osmotic solidification treatment was performed, the chemical concentration was 6%, and the curing period was 7 days.

Moreover, the chemical | medical solution used for preparation of an improved ground is permanent water glass (ecosilica), the initial stage ph of a chemical | medical solution is set to 3, and the uniaxial compressive strength of the test piece at the time of experiment is 38 KN / m < ² >. The shaking table was subjected to step loading in which a 3 Hz sine wave was increased by 10 waves in increments of 100 Gal from 100 Gal to 400 Gal. A water pressure gauge was installed in the model soil tank, and the amount of ground subsidence was measured in Line 1 to Line 5.

  Here, Line 1 in (1) in FIG. 6 is not improved, Line 2 in (2) is improved by 40%, Line 3 in (3) is improved by 60%, and Line 4 in (4) is improved by 80%. It shows the ratio of improved ground to sand ground.

  FIG. 7 shows the relationship between the improvement rate and the amount of ground subsidence. According to this, the subsidence amount of the unimproved ground is about 3 cm, which is about 30 cm when converted to the actual ground. On the other hand, the subsidence amount of the ground with an improvement rate of 60% is an average of 5 mm, which is about 5 cm when converted to the actual ground. In many cases, the allowable amount of settlement during liquefaction of a general civil engineering structure is 10 cm or less in order to prevent an extreme step. From this, it was possible to confirm that the sand subsidence had sufficient strength to prevent liquefaction even when the improvement rate was 60%.

(1) is a perspective view showing the liquefaction prevention structure of the first embodiment, (2) is a perspective view of a solidified body surrounding an unmodified, and (3) is an exploded perspective view thereof. It is a perspective view which shows the liquefaction prevention structure of 2nd Embodiment. It is a perspective view which shows the liquefaction prevention structure of 3rd Embodiment. It is a perspective view which shows the liquefaction prevention structure of 4th Embodiment. It is sectional drawing of a liquefaction prevention construction method. It is sectional drawing of a model soil tank. (1)-(4) is sectional drawing of a model soil tank. It is a graph which shows the relationship between an improvement rate and the amount of ground subsidence. It is sectional drawing of the conventional liquefaction prevention construction method.

Explanation of symbols

1, 7, 11, 14 Liquefaction prevention structure 2, 15, 29 Improvement target ground 3, 18, 19, 21, 28 Solidified body 4 Improved ground 5, 22 Unimproved part 6 Improved part 8 Upper part 9 Lower part 10 Lower Side layer 12 Surface layer portion 13 Lower layer portion 16, 26 Injection pipe 17, 27 Chemical solution 20 Location where solidified body is formed 23 Solidified body unit 24 Model soil tank 25 Sand ground

Claims (5)

A solidified body of a predetermined volume, which is solidified by injecting a chemical solution into the improvement target sand ground, is overlapped in the vertical and horizontal directions and the front-rear direction to form an improved ground, and the improved ground has an unreformed portion having the same volume as the solidified body. A structure for preventing liquefaction of sandy ground, characterized in that it is scattered, and two or more unimproved portions are not continuous but are surrounded by solidified bodies in the upper, lower, left, and right sides. The structure for preventing liquefaction of sand ground according to claim 1, wherein the solidified body and the unimproved portion are alternately formed in the vertical and horizontal directions and the longitudinal direction. The structure for preventing liquefaction of sand ground according to claim 1 or 2, wherein unimproved portions are not scattered in the vicinity of the ground surface of the improved ground, and all are improved by a solidified body. In the step of forming a solidified body having a predetermined volume by injecting a chemical solution from an injection pipe inserted into the sand ground to be improved, and forming the improved ground by overlapping this solidified body in the vertical and horizontal directions and the front-rear direction, from the injection pipe It is characterized in that an unmodified part having the same volume as the solidified body is formed in the improved ground without injecting a chemical solution, and two or more unimproved parts are not continuously connected, and the solidified body is surrounded by the solidified body in the upper, lower, left and right sides. Liquefaction prevention method for sand ground. The method for preventing liquefaction of sand ground according to claim 4, wherein the solidified body and the unimproved portion are alternately formed in the vertical and horizontal directions and the longitudinal direction.

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