JP2008150902A - Long-term settlement prevention method of soft ground and long-term settlement determining method of soft ground - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a long-term settlement prevention method of the soft ground, capable of inexpensively and surely preventing settlement over a long period by simple construction. <P>SOLUTION: This long-term settlement prevention method of the soft ground is formed by laying banking 13 on the viscous ground 10 of developing a structure like natural sedimentation clay. Before laying the banking 13 on the viscous ground 10, a plurality of columnar vertical sand piles 11 are driven in the viscous ground 10, and the structure of the viscous ground 10 is positioned lower by forcibly pushing-in by compaction of sand when driving these respective sand piles 11, to approach to remolded soil 10'. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for suppressing long-term settlement of soft ground such as natural sedimentary clay ground and a method for determining occurrence of long-term settlement of soft ground.

  As a method for reducing settlement of this kind of soft ground, there is one shown in FIG. 8 (see, for example, Patent Document 1).

  In this method of reducing settlement of soft ground, first, as shown in FIG. 8A, high-quality earth and sand having a low possibility of sinking is laid on the soft ground 1 to a required thickness to form the embankment 2. Next, as shown in FIG. 8B, a predetermined number of ready-made piles 3 such as concrete piles are placed in the soft ground 1 to a required depth at a predetermined interval. At this time, the pile head 3 a of the ready-made pile 3 is installed so as to be buried at a predetermined depth in the embankment 2.

Next, as shown in FIG. 8 (c), a solidified material such as slurry cement is mixed into the embankment 2 around the pile head 3 a of the ready-made pile 3 and cured to form the solidified layer 4. Thereafter, as shown in FIG. 8 (d), the required pavement materials 5a, 5b and the like are laminated on the embankment 2 to form the pavement 5. As a result, the ready-made pile 3, the solidified layer 4, and the pavement 5 are integrated and constructed, so that the settlement of the soft ground 1 is reduced.
JP 2003-268790 A

  However, in the conventional settlement reduction method for the soft ground 1, a pre-made pile 3 such as a concrete pile is placed in the soft ground 1, and a solidified material is placed in the embankment 2 around the pile head 3 a of the pre-made pile 3. Since the solidified layer 4 mixed and cured is constructed, the construction is complicated and time-consuming, and the cost is high.

  In addition, in the case where the soft ground 1 is a naturally deposited soft clay ground, since the mechanism that causes long-term settlement (secondary consolidation) is not known, there is only an effective coping method such as increasing the number of existing piles 3 placed, Preliminary prediction and control measures for the long-term settlement have not been implemented.

  Therefore, the present invention has been made to solve the above-described problems, and provides a method for suppressing long-term settlement of soft ground that can reliably prevent ground settlement over a long period of time with simple construction and at low cost. It is another object of the present invention to provide a method for determining the occurrence of long-term subsidence in soft ground, which is capable of reliably predicting in advance a ground that may be subsidized (possible) over a long period of time.

  The invention of claim 1 is a method for suppressing long-term settlement of soft ground, which is constructed by laying embankment on a viscous ground having a structure developed like natural sedimentary clay, before laying embankment on the viscous ground, A plurality of columnar vertical granular piles are placed in the viscous ground, and the structure of the viscous ground is lowered by forced pushing by compaction of the granular bodies at the time of placing each granular pile. , It is characterized by approaching the reclaimed soil.

  The invention of claim 2 is the long-term settlement suppression method for soft ground according to claim 1, characterized in that the diameter of the pile of each granular material is 40 cm or more.

  The invention of claim 3 is a method for suppressing long-term settlement of soft ground by laying embankment on a viscous ground having a structure developed like natural sedimentary clay, before laying embankment on the viscous ground, When the compression index ratio is 1.5 or more, a plurality of columnar and vertical granular piles are placed in the viscous ground, and the granular bodies are compacted when the piles of each granular piece are placed. It is characterized by lowering the structure of the cohesive ground by forcibly pushing it closer to the ground soil.

  Invention of Claim 4 is the soft ground long-term settlement suppression method of Claim 3, Comprising: The diameter of the pile of each said granular material was 40 cm or more, It is characterized by the above-mentioned.

  The invention according to claim 5 is a method for suppressing long-term settlement of soft ground by laying embankment on a viscous ground having a structure developed like natural sedimentary clay, before laying embankment on the viscous ground, When the liquidity index is 0.7 or more, a plurality of columnar and vertical granular piles are placed in the viscous land, and by the compaction of the granular bodies at the time of placing these granular piles It is characterized by lowering the structure of the cohesive ground by forcibly pushing it closer to the ground soil.

  A sixth aspect of the present invention is the soft ground long-term settlement suppression method according to the fifth aspect, characterized in that the diameter of the pile of each granular material is 40 cm or more.

  The invention of claim 7 is a method for suppressing long-term settlement of soft ground, which is constructed by laying embankment on a viscous ground having a structure developed like natural sedimentary clay, before laying embankment on the viscous ground, When satisfying both the case where the compression index ratio is 1.5 or more and the case where the liquidity index is 0.7 or more, a plurality of columnar and vertical granular piles are placed in the viscous ground, It is characterized in that the structure of the cohesive land is lowered by forced pushing by compaction of the granular material at the time of placing the pile of each granular material, and it is brought closer to the ground soil.

  The invention according to claim 8 is the long-term settlement suppression method for soft ground according to claim 7, characterized in that the diameter of the pile of each granular material is 40 cm or more.

  The invention according to claim 9 is a method for determining the occurrence of long-term settlement of soft ground, in which embankment is laid on a viscous ground having a structure such as natural sedimentary clay. Occurs when the value is 1.5 or more.

  The invention according to claim 10 is the method of determining the occurrence of long-term settlement of soft ground, in which embankment is laid on a viscous ground having a structure such as natural sedimentary clay. It occurs when the value is 0.7 or more.

  The invention according to claim 11 is the method for determining the occurrence of long-term settlement of soft ground, in which embankment is laid on a viscous ground having a structure such as natural sedimentary clay. Occurs when both the case where the liquidity index is 1.5 or more and the case where the liquidity index is 0.7 or more are satisfied.

  As described above, according to the first aspect of the present invention, before laying the embankment on the viscous ground, a plurality of columnar and vertical granular piles are placed in the viscous ground, The structure of the viscous ground is lowered by forcing it by compaction of the granular material at the time of placing the piles of the body, and by making it close to the reclaimed soil, the long-term settlement of the viscous ground can be achieved with simple construction and low cost. It can be surely prevented.

  According to the invention of claim 3, before laying the embankment on the viscous ground, when the compression index ratio is 1.5 or more, a plurality of columnar and vertical granular piles are provided in the viscous ground. When the piles are laid and forced into the piles during the placement of the piles, the structure of the viscous ground is lowered and brought closer to the reclaimed soil. It is possible to improve the ground by predicting only the ground in advance, and it is possible to reliably prevent the settlement of the viscous ground for a long time with simple construction and low cost.

  According to the invention of claim 5, before laying the embankment on the viscous ground, when the liquidity index is 0.7 or more, a plurality of columnar and vertical granular piles are provided in the viscous ground. When the piles are laid and forced into the piles during the placement of the piles, the structure of the viscous ground is lowered and brought closer to the reclaimed soil. It is possible to improve the ground by predicting only the ground in advance, and it is possible to more reliably prevent long-term settlement of the viscous ground with simple construction and low cost.

  According to the invention of claim 7, before laying the embankment on the cohesive ground, when satisfying both the case where the compression index ratio is 1.5 or more and the case where the liquidity index is 0.7 or more A plurality of columnar and vertical granular piles are placed in the viscous ground, and the structure of the viscous ground is lowered by forced pushing by compaction of the granular bodies at the time of placing each granular pile. By moving closer to the reclaimed soil, it is possible to improve the ground by predicting only the viscous land that may be subsidized for a long time in advance, and more reliable long-term settlement of the viscous ground with simple construction and low cost. Can be prevented.

  According to the inventions of claims 2, 4, 6 and 8, by setting the diameter of each pile pile to 40 cm or more, it is possible to eliminate a small diameter construction method having a low effect of disturbing the viscous ground.

  According to the invention of claim 9, the settlement of the viscous ground is surely predicted beforehand in advance when the compression index ratio is 1.5 or more, so that the viscous ground that may sink for a long time is predicted. be able to.

  According to the invention of claim 10, the subsidence of the viscous ground is predicted when the liquidity index is 0.7 or more, so that the viscous land that may be subsidized for a long time is predicted in advance. be able to.

  According to the invention of claim 11, subsidence of the viscous ground is generated when the compression index ratio satisfies both the case where the compression index ratio is 1.5 or more and the case where the liquidity index is 0.7 or more. It is possible to predict in advance the viscous land that may sink for a long time.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of the ground constructed by the method for suppressing long-term settlement of soft ground according to the embodiment of the present invention, and FIGS. 2A to 2E illustrate the process of performing construction by the method for suppressing long-term settlement of the soft ground in order. It is explanatory drawing shown.

  As shown in FIG. 1, an embankment 13 made of high-quality earth and sand having a low risk of subsidence is laid on a naturally deposited clay ground (viscous ground) 10, which is a soft ground, with a sand 12. In addition, before laying the embankment 13 on the natural sedimentary clay ground 10, a columnar vertical sand pile (granular pile) having a diameter of about 40 cm is formed in the natural sedimentary clay ground 10 by the sand drain method shown in FIG. A plurality of 11 are provided. The sand pile 11 is placed when both the case where the compression index ratio of the naturally deposited clay ground 10 is 1.5 or more and the case where the liquidity index is 0.7 or more are satisfied. In addition, the numerical value obtained in advance by the method for determining the occurrence of long-term settlement of the soft ground described later is used as the numerical value of the compression index ratio 1.5 and the numerical value of the liquidity index 0.7.

  Next, construction of sand piles (sand drains) by the sand drain method will be described in order with reference to FIGS. 2 (a) to 2 (e).

  First, as shown in FIG. 2A, the casing pipe 20 is set at a predetermined position on the natural sediment clay ground 10. Next, as shown in FIG. 2B, the casing pipe 20 is driven into and penetrated into the natural sedimentary clay ground 10 while vibrating the casing 22 to vibrate the casing pipe 20. At this time, the tip of the casing pipe 20 is kept closed so that the soil of the surrounding ground does not enter. Next, as shown in FIG. 2 (c), sand (granular material) S is introduced into the casing pipe 20 from a hopper 21 provided at the top of the casing pipe 20.

  And as shown in FIG.2 (d), the sand S in the casing pipe 20 is discharged | emitted while drawing out the casing pipe 20, and it builds to the ground surface. When the casing pipe 20 is intruded (at the time of placing), the structure of the natural sedimentary clay ground 10 is lowered by forcing the casing pipe 20 by vibration and sand S compaction to bring it closer to the ground soil. The naturally deposited clay ground approaching this ground soil is indicated by reference numeral 10 'in FIGS. And finally, as shown in FIG.2 (e), creation of the sand pile 11 is completed by drawing the casing pipe 20 to the ground.

  FIG. 3 shows the relationship between the time (days) and the amount of settlement (cm) of the improved ground constructed by this sand drain method (a method for suppressing long-term settlement of soft ground) and the unmodified ground without construction. In addition, in FIG. 3, the graph of the subsidence amount of the improved ground which was constructed is shown by X, and the graph of the subsidence amount of the unmodified ground which is not constructed is shown by Y.

  As shown in FIG. 3, in the improved ground where a plurality of sand piles 11 are placed in the natural sedimentary clay ground 10 to lower the structure of the natural sedimentary clay ground 10 and close to the ground soil (10 ′), Substantial subsidence (x) does not occur after service (after 1533 days), whereas it can be understood that continuous large subsidence (y) occurred after service on unmodified ground.

  FIG. 4 shows the relationship between the vertical load (vertical stress) and the density (gap ratio) of the improved ground constructed by the sand drain method (a method for suppressing the long-term settlement of soft ground) and the unmodified ground without construction.

  As shown in FIG. 4, there was a possibility of long-term settlement as indicated by the arrow in FIG. It can be seen that in the improved ground that has been placed to lower the structure of the natural sedimentary clay ground 10 and close to the ground clay (10 '), the possibility of long-term settlement is low.

  Thus, before laying the embankment 13 on the natural sedimentary clay ground 10, a plurality of pillar-shaped vertical sand piles 11 are placed in the natural sedimentary clay ground 10 by the construction of the sand drain construction method. By lowering the structure of the natural sedimentary clay ground 10 by the vibration of the casing pipe 20 and the forced pushing by compaction of the sand S at the time of laying, and bringing it closer to the ground clay (10 '), it can be done in a short time and at a low cost. It is possible to reliably prevent the natural sedimentation clay ground 10 from sinking for a long time.

  In particular, there is a risk of subsidence over a long period of time by performing the above construction when the compression index ratio of the natural sedimentary clay ground 10 is 1.5 or more and the liquidity index is 0.7 or more. It is possible to improve the ground by predicting only the natural sedimentation clay ground 10 in advance, and by simply constructing the sand pile 11 in the natural sedimentation clay ground 10, the long-term operation of the natural sedimentation clay ground 10 can be achieved at low cost. Can be prevented more reliably. In other words, the ready-made pile 3 such as a concrete pile is placed in the conventional soft ground 1 and the solidified layer 4 is mixed and hardened in the embankment 2 around the pile head 3 a of the ready-made pile 3. Compared to the construction, the construction period can be greatly shortened and the cost for the construction can be greatly reduced, and the natural sedimentation clay ground 10 can be subsidized for a long time at a low cost with simple construction. It can be surely prevented.

  In addition, if a highway or the like is constructed on the embankment 13 improved in this way, large subsidence will not occur even if several decades have passed since construction, so the asphalt pavement overlay and the surrounding area for securing the shoulder Costs such as repair costs can be greatly reduced.

  Furthermore, if the diameter of the columnar and vertical sand piles 11 placed in the natural sedimentary clay ground 10 by the sand drain method is 40 cm or more, a small diameter construction method with a low effect of disturbing the natural sedimentary clay ground 10 is eliminated. can do.

  Next, a method for determining the occurrence of long-term settlement of naturally deposited clay ground, which is soft ground, will be described with reference to FIGS. 5 and 6. FIG. 5 is an explanatory diagram showing the relationship between the natural water content ratio and the compression index ratio used in the method for determining the occurrence of long-term settlement in naturally deposited clay ground according to the embodiment of the present invention, and FIG. 6 is used in the method for determining the occurrence of long-term settlement in the soft ground. It is explanatory drawing which shows the relationship between a liquidity index and undrained shear strength.

  As a result of collecting and investigating soil data of A to D sites (Fig. 5) and E to Q sites (Fig. 6) where long-term subsidence was confirmed in natural sediment clay ground (viscous soil ground), natural sediment clay ground It has been found that subsidence over a long period of time occurs when both the compression index ratio (Cc / Ccr) is 1.5 or more and the liquidity index (IL) is 0.7 or more.

That is,
[Equation 1]
Compression index ratio Cc / Ccr> 1.5
Here, Cc: compression index (gradient of naturally deposited clay in FIG. 4), Ccr: compression index (gradient of ground soil in FIG. 4)
Also,
[Equation 2]
Liquidity index IL> 0.7
The liquidity index IL is expressed as IL = (wn−wp) / Ip, Ip = wl−wp.

Here, wn: natural water content ratio, wl: liquid limit, wp: plastic limit In this way, the subsidence of naturally deposited clay ground has a compression index ratio of 1.5 or more (Cc / Ccr> 1.5). It has been found that this occurs when both the case and the case where the liquidity index is 0.7 or more (IL> 0.7) are satisfied. As a result, it is possible to easily and surely predict a natural sedimentary clay ground that may sink for a long time.

  In addition, according to the said embodiment, when satisfy | filling both the case where the compression index ratio of a soft ground is 1.5 or more and the liquidity index is 0.7 or more, a plurality of sand piles are placed and the ground is improved. However, when the compression index ratio of the soft ground is 1.5 or more, or only when the liquidity index is 0.7 or more, a plurality of columnar and vertical sand piles are placed in the viscous ground, The structure of the viscous ground may be lowered by forcible pressing by sand compaction when each sand pile is placed, and the ground may be improved so as to approach the ground soil. Moreover, although the case where the natural sedimentation clay ground was used as a soft ground was demonstrated, of course, the said embodiment may be applied to viscous ground other than a natural sedimentation clay. Furthermore, although the case where the sand pile was created using sand as the pile material was described, it is needless to say that the above embodiment may be applied when creating the crushed stone pile etc. using crushed stone as the pile material. .

  Moreover, according to the said embodiment, although the case where the sand pile about 40 cm in diameter was laid by the sand drain construction method was demonstrated, you may lay a sand pile pillar about 70 cm in diameter by the sand compaction pile construction method.

  That is, sand pile construction by the sand compaction pile method will be described in order with reference to FIGS. 7A to 7F. First, as shown in FIG. It is set at a predetermined position on the ground 10. Next, as shown in FIG. 7B, the casing pipe 20 is driven into and penetrated into the natural sediment clay ground 10 while vibrating the casing 22 to vibrate the casing pipe 20. At this time, the tip of the casing pipe 20 is kept closed so that the soil of the surrounding ground does not enter. Next, as shown in FIG. 7C, sand S is introduced into the casing pipe 20 from a hopper 21 provided at the upper part of the casing pipe 20.

  Then, as shown in FIG. 7 (d), the sand S in the casing pipe 20 is discharged while the casing pipe 20 is pulled out, and as shown in FIG. Sand S is put into the pipe 20 and the casing pipe 20 is sequentially pulled out and inserted. When the casing pipe 20 is intruded (at the time of placing), the structure of the natural sedimentary clay ground 10 is lowered by forcing the casing pipe 20 by vibration and sand S compaction to bring it closer to the ground soil. The natural sedimentary clay ground approaching this ground soil is indicated by reference numeral 10 'in FIG. And finally, as shown in FIG.7 (f), creation of the large diameter sand pile 11 'is completed by extracting the casing pipe 20 to the ground.

It is sectional drawing of the ground constructed | assembled by the long-term settlement suppression method of the soft ground of embodiment of this invention. (A)-(e) is explanatory drawing which shows in order the process of constructing the said long-term settlement suppression method of the soft ground by the sand drain construction method. It is explanatory drawing which shows the relationship between the time of subsidence, and the time of the improvement ground which was constructed by the long-term settlement suppression method of the soft ground, and the non-improvement ground which is not constructed. It is explanatory drawing which shows the relationship between the vertical load (vertical stress) and density (gap ratio) of the improved ground which was constructed by the long-term settlement suppression method of the soft ground, and the unmodified ground which is not constructed. It is explanatory drawing which shows the relationship between the natural water content ratio and compression index ratio used for the long-term subsidence generation | occurrence | production determination method of the soft ground of embodiment of this invention. It is explanatory drawing which shows the relationship between the liquidity index used for the said long-term subsidence generation | occurrence | production determination method of the soft ground, and undrained shear strength. (A)-(f) is explanatory drawing which shows in order the process of constructing the said long-term settlement suppression method of the soft ground by the sand compaction pile construction method. (A)-(d) is explanatory drawing which shows in order the process of reducing the settlement of the conventional soft ground.

Explanation of symbols

10 Naturally deposited clay ground (viscous ground)
10 'Crushing soil 11 Sand pile (granular pile)
11 'Sand pile (granular pile)
13 Filling 20 Casing pipe S Sand (granular)

Claims (11)

In the long-term settlement suppression method for soft ground, which is constructed by laying embankment on viscous ground with a structure like natural sedimentary clay,
Before laying the embankment on the viscous ground, a plurality of columnar and vertical granular piles are placed in the viscous ground, and by the compaction of the granular materials at the time of placing each granular pile A method for suppressing long-term settlement of soft ground, characterized in that the structure of the viscous ground is lowered by forcible pushing and is brought closer to the ground soil. A method for suppressing long-term settlement of soft ground according to claim 1,
The diameter of the pile of each said granular material was 40 cm or more, The long-term settlement suppression method of the soft ground characterized by the above-mentioned. In the long-term settlement suppression method for soft ground, which is constructed by laying embankment on viscous ground with a structure like natural sedimentary clay,
Before laying the embankment on the viscous ground, when the compression index ratio is 1.5 or more, a plurality of columnar vertical granular piles are placed in the viscous ground, A method for suppressing long-term settlement of soft ground, characterized in that the structure of the viscous ground is lowered by forcible pushing by compaction of the granular material at the time of placing the pile of the pile, and the structure is brought closer to the ground soil. A method for suppressing long-term settlement of soft ground according to claim 3,
The diameter of the pile of each said granular material was 40 cm or more, The long-term settlement suppression method of the soft ground characterized by the above-mentioned. In the long-term settlement suppression method for soft ground, which is constructed by laying embankment on viscous ground with a structure like natural sedimentary clay,
Before laying the embankment on the viscous ground, when the liquidity index is 0.7 or more, a plurality of columnar vertical granular piles are placed in the viscous ground, A method for suppressing long-term settlement of soft ground, characterized in that the structure of the viscous ground is lowered by forcible pushing by compaction of the granular material at the time of placing the pile of the pile, and the structure is brought closer to the ground soil. The method for suppressing long-term settlement of soft ground according to claim 5,
The diameter of the pile of each said granular material was 40 cm or more, The long-term settlement suppression method of the soft ground characterized by the above-mentioned. In the long-term settlement suppression method for soft ground, which is constructed by laying embankment on viscous ground with a structure like natural sedimentary clay,
Before laying the embankment on the viscous ground, when both the compression index ratio is 1.5 or more and the liquidity index is 0.7 or more, a columnar shape is formed in the viscous ground. A plurality of vertical granular piles are laid down, and the structure of the cohesive ground is lowered by forcible pressing by compaction of the granular bodies at the time of placing each of the granular piles so as to be close to the ground soil. A long-term settlement control method for soft ground. The method for suppressing long-term settlement of soft ground according to claim 7,
The diameter of the pile of each said granular material was 40 cm or more, The long-term settlement suppression method of the soft ground characterized by the above-mentioned. In the method of judging the occurrence of long-term settlement of soft ground, which is constructed by laying embankment on viscous ground with a structure like natural sedimentary clay,
The subsidence of the viscous ground is generated when the compression index ratio is 1.5 or more. In the method of judging the occurrence of long-term settlement of soft ground, which is constructed by laying embankment on viscous ground with a structure like natural sedimentary clay,
The subsidence of the viscous ground is generated when the liquidity index is 0.7 or more. In the method of judging the occurrence of long-term settlement of soft ground, which is constructed by laying embankment on viscous ground with a structure like natural sedimentary clay,
The subsidence of the viscous ground occurs when both the compression index ratio is 1.5 or more and the liquidity index is 0.7 or more. Judgment method.

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