JP4423115B2 - An improved method for reducing land subsidence directly under existing embankments - Google Patents

Description

  The present invention relates to an improved method for reducing ground subsidence directly under an existing embankment for reducing or suppressing the settlement subsidence layer that forms the foundation ground with the embankment layer formed on the upper part due to the embankment load of the embankment layer.

  The embankment layer has been often built on top of the subsidence generation layer, which is a cohesive soil layer. For example, it forms behind the revetment of a quay using caisson, sheet pile, L-type block, etc. Such as the backfilled buried layer, and the embankment layer of the adjacent construction such as the abutment backfill formed on the back of the abutment such as the harborside bridge, etc. (These buried layers and the embankment layer are simply referred to as “filled layer”) )) Has been constructed frequently, and has been carried out frequently.

  By the way, in the ground having such an existing embankment layer, the settlement generation layer gradually subsides due to the embankment load of the embankment layer provided thereon, and there is a step between the surrounding ground. It has been observed that it causes problems such as failure to secure a predetermined ground height. For this reason, when creating a new embankment layer, a soil survey is usually conducted in advance, and when consolidation settlement is predicted in the settlement generation layer below it, consolidation settlement (ground settlement) in this settlement generation layer is expected. Various measures are taken to prevent).

  As a ground improvement construction method performed for such a purpose, for example, a method of replacing a part of the ground to be improved with a specific lightweight ground improvement material using a spiral screw auger (Japanese Patent Laid-Open No. 05-255,924), Drilling the ground to be improved to form a hole with a predetermined length, and filling this hole with soil cement obtained by mixing at least one of a material with low specific gravity or bubbles, earth and sand, cement, bentonite and water on the ground However, a substitution type deep layer improvement method (Japanese Patent Laid-Open No. 2001-241,035) for forming a soil cement column on the ground to be improved has been proposed.

  In addition, a plurality of columnar bodies are constructed on soft ground with a length that does not reach the support layer and with an improvement rate of 10 to 50%, and a reinforcing net is laid on the plurality of columnar bodies or installed. A road where a shallow improved soil layer (a layer obtained by mixing an additive and / or an additive in the earth and solidified material and solidified) is laid, and road pavement is applied on the shallow improved soil layer. Construction method (Japanese Patent Laid-Open No. 10-317,307, Japanese Patent Laid-Open No. 2003-239,276), and laying a bank of high quality earth and sand on soft ground, placing ready-made piles on this bank and soft ground, A solidified layer is formed on the ready-made pile, a pavement is built on the solidified layer, and the ready-made pile, embankment, solidified layer, and pavement are integrated, and the embankment, solidified layer, pavement, and other vehicles on the soft ground. And so on to the ground of the deep part of the soft ground and directly to the soft ground through the embankment. Reached method for (JP 2003-268,790) have also been proposed.

  Furthermore, in the embankment creation process of the embankment, a large number of hollow expansion members are embedded in the embankment deposit layer at appropriate intervals in the plane direction, and after the construction is completed, the structure on the embankment is transferred to the embankment In the case of tilting due to uneven settlement, a slurry-like solidifying agent is press-fitted into the expansion member directly below the settlement site and selectively expanded, and the embankment layer above it is raised to correct the uneven settlement. Kaihei 08-170,336) has also been proposed.

However, any of these methods is a construction method that is adopted when a new embankment layer is created, and cannot be applied as it is when an existing embankment layer that has already been constructed is used.
However, the ground that has been formed with the embankment layer on the subsidence generation layer has existed everywhere, and in recent years, the problem of subsidence due to the consolidation subsidence of the subsidence generation layer is becoming apparent.

  As a method for improving the ground subsidence that occurs in the ground having such an existing embankment layer, for example, an embankment layer created as a backfill of the revetment will be described as shown in FIG. A number of holes c reaching from the upper part of the embankment layer a to the subsidence generation layer (viscous earth layer) b existing at the lower part of the embankment layer a are drilled and vertically supported by the subsidence generation layer b in each hole c Fig. 6 shows a method of reinforcing the ground improvement pile d for driving in the ground improvement piles d. The ground improvement piles d to reinforce the supporting force of the subsidence generation layer b which supports the embankment load of the embankment layer a by these ground improvement piles d. As shown in the figure, the existing embankment layer a created as the backfill of the revetment wall e is sequentially replaced with a light soil f such as bubble mixed soil while excavating the backfill layer a on the backside of the revetment wall e. A method etc. can be considered.

  However, in the former method of reinforcing with ground improvement piles, the subsidence generation layer b exists deep from the top of the embankment layer a, and when the construction depth becomes deep, a large construction machine is inevitably required. As a result, the construction work is difficult at the site where such a large construction machine cannot be carried in, and the backfilling work of the embankment material is also required for the blanking portion g formed when the hole c is drilled in the embankment layer a. There is a problem that the construction cost increases.

Further, in the latter replacement method with the light soil f, the construction period becomes relatively long because the light soil f is sequentially replaced while excavating the embankment layer a on the back side of the revetment wall e. Until the shore becomes stable, the strength of the revetment wall e itself will decrease, making it difficult to construct during periods when abnormal weather such as typhoons and heavy rains are likely to occur, and there will be restrictions on the choice of construction period. In recent weather situations where extreme weather conditions such as typhoons and heavy rains may occur, it is often difficult to adopt this method in practice.
JP-A-5-255,924 Japanese Patent Laid-Open No. 2001-241,035 Japanese Patent Laid-Open No. 10-317,307 JP2003-239,276 JP2003-268,790 Japanese Unexamined Patent Publication No. 08-170,336

Therefore, the inventors of the present invention can easily and reliably reduce or suppress the settlement generation layer that forms the foundation ground by forming the embankment layer on the upper part and the consolidation subsidence due to the embankment load of the embankment layer. As a result of earnestly examining the method for reducing and improving the subsidence directly under the ground, the maximum embankment load of the embankment layer required to make the subsidence generation layer normal or overconsolidated from the soil investigation results of the subsidence generation layer and the embankment layer, Based on the maximum embankment load and the specific gravity of the lightweight soil replacement pile to be used, the ratio of replacing the existing embankment material forming the embankment layer with the lightweight soil replacement pile is obtained, and based on the result, one of the existing embankment materials forming the embankment layer is determined. It was found that the purpose could be achieved by replacing the part with a lightweight soil replacement pile, and the present invention was completed.

  Accordingly, an object of the present invention is to provide an existing embankment that can easily and surely reduce or inhibit the settlement generation layer that forms the foundation ground by forming the embankment layer in the upper part and the consolidation settlement due to the embankment load of the embankment layer. The purpose is to provide an improved method of reducing land subsidence.

That is, the present invention is a subsidence reduction improved method for subsidence generating layer embankment layer is Construction at the top to constitute the foundation ground is reduced or suppressed to consolidation settlement by embankment load of embankment layers, subsidence occurs The maximum embankment load of the embankment layer necessary to bring the settlement generation layer into the normal consolidation state or overconsolidation state is obtained from the soil survey results of the layer and the embankment layer, and from this maximum embankment load and the specific gravity of the lightweight soil replacement pile to be used The ratio of replacing the existing embankment material forming the embankment layer with the lightweight soil replacement pile is obtained, and a predetermined number of holes are formed in the embankment layer based on the ratio of replacing the existing embankment material of the found embankment layer with the light soil replacement pile. This is an improved construction method for reducing ground subsidence directly under the existing embankment, characterized in that the existing embankment material to be drilled and removed is removed and a light soil replacement pile is provided in the predetermined number of holes .

  In the present invention, the lightweight soil replacement pile used to replace a part of the existing embankment material forming the embankment layer needs to have a specific gravity at least smaller than that of the above existing embankment material, and a part of the existing embankment material However, after substituting this lightweight soil replacement pile, the subsidence generation layer below the embankment layer is reduced below the predetermined subsidence amount, and if necessary, it becomes a normal consolidated state, preferably an overconsolidated state, and the ground subsidence is completely completed. It is better to replace it so that it is suppressed.

The replacement of the existing embankment material and lightweight soil replacement piles in this embankment layer begins with the settlement of the construction site to be improved (a place where the embankment layer has been created on the upper part of the settlement subsidence layer and ground subsidence has begun). Conduct a soil survey of the generation layer and the embankment layer, and based on the results of this soil survey, the maximum of the embankment layer necessary to maintain the subsidence generation layer at least in a normal consolidated state, and preferably in an overconsolidated state Determine the fill load, and the specific gravity is smaller than the existing fill material that forms the fill layer, select the lightweight soil replacement pile to be used to replace this existing fill material, and select the maximum fill load determined here. Calculate the ratio of the existing embankment material that forms the embankment layer to the selected light soil replacement pile, and the result (replacement ratio). Based on the fill layer The existing embankment material to be replaced is removed by drilling a predetermined number of holes extending from the top of the ceiling toward the settlement generation layer at a fixed position, and then a lightweight soil replacement pile in the predetermined number of drilled holes By providing the , the embankment load of the embankment layer above the settlement generation layer is adjusted. The embankment load at this time is adjusted to a pressure density of 100, for example, when a certain amount of ground subsidence is allowed due to its function, such as a sewer pipe, and accuracy is not required to suppress land subsidence (zero subsidence). In some cases, it may be necessary to reduce the subsidence to an allowable level within a range of less than%, and when it is necessary to completely suppress subsidence, for example, when some subsidence is not permitted. Is adjusted to a normal consolidation state, preferably an overconsolidation state. And in adjusting this embankment load, it is good to control by any one or two or more elements chosen from the weight of the whole lightweight soil substitution pile to be replaced, pile length, and substitution rate.

In addition, when uneven settlement becomes a problem at the construction site to be improved, multiple soil surveys are conducted at multiple measurement points that traverse and / or cross the embankment layer, and the maximum embankment load is based on the results. As a distribution in the cross-sectional direction, and based on the maximum embankment load distribution in this embankment layer, the existing embankment material in the embankment layer may be replaced with lightweight soil replacement piles, whereby the embankment layer longitudinal and / or transverse direction It is possible to prevent the occurrence of the phenomenon of uneven settlement in advance. And even when replacing the existing embankment material with a lightweight soil replacement pile so as not to cause uneven settlement by obtaining this maximum embankment load distribution, the adjustment of the embankment load in the embankment layer is preferably a light soil replacement to be replaced It is good to control by any 1 or 2 or more elements chosen from the weight of the whole pile, the pile length, and the substitution rate.

  The lightweight soil replacement pile used for such purposes is not particularly limited, for example, cement solids such as cement, cement milk, limes and the like as disclosed in JP 05-255,924 A, clay, A lightweight ground improvement material obtained by mixing sand, silt or a viscous soil mixed with these and a bead-like synthetic resin foam made of polyethylene, polystyrene, propylene, ethylene copolymer, etc. in the presence of water, Formed by using curable lightweight soil such as soil cement obtained by mixing at least one of low specific gravity material or bubbles, earth and sand, cement, bentonite and water as disclosed in 2001-241,035 gazette Can be mentioned.

Then, the lightweight soil substitution piles, depending on the situation of the construction site to be improved target, curable lightweight soil specific gravity less than the existing embankment material forming at least the fill layer is prepared, also the fill layer Depending on the replacement ratio of the existing embankment material to the lightweight soil replacement pile, a predetermined length (corresponding to the pile length) and / or a predetermined number extending from the top to the subsidence generation layer in the predetermined position Are formed by filling the hole with the curable lightweight soil as described above and curing it in the hole.

Further, such a lightweight soil replacement pile preferably has a plurality of regions having different unit volume weights along the pile length direction, and more preferably has a total average unit volume weight of 5 kN. / m ³ or more 13 kN / m ³ equal to or less than the unit volume weight of the water level surface or deeper in the specific weight of the water level surface shallower than the 5 kN / m ³ or more 10 kN / m ³ or less when it is substituted in the embankment layer is 10 kN / m ³ greater good that is formed such that. By constructing the lightweight soil replacement pile in this way, even if water accumulates in the hole drilled in the embankment layer, it can be constructed efficiently and the embankment load of the embankment layer can be adjusted efficiently and reliably. .

  According to the method of the present invention, in order to prevent consolidation subsidence in the subsidence generation layer directly under the existing embankment, a part of the existing embankment material is replaced with a lightweight soil replacement pile for the upper embankment layer of the subsidence generation layer. For example, it is possible to proceed with partial subsidence improvement work while leaving existing protective walls such as embankments as they are, and to improve the ground subsidence layer itself. The depth of construction will be significantly shallower than that of large-scale construction machines, and it will not be necessary to use large construction machines. In addition, it will not be necessary to backfill existing embankment materials for the embankment layer to be improved, resulting in a reduction in construction costs. In addition, since it is not necessary to excavate the embankment layer on the back side of the revetment wall, there is no influence on the strength of the revetment wall itself, and the construction period is not limited.

  Hereinafter, based on the Example shown to an accompanying drawing, suitable embodiment of the ground subsidence reduction improvement method directly under the existing embankment of this invention is described concretely.

  FIG. 1 shows an example in which the ground subsidence reduction improvement method according to Example 1 of the present invention is applied to a subsidence generation layer directly under an existing embankment having an embankment layer as a backfill for a revetment by an L-shaped block. ing.

  In Example 1, first, a soil investigation is performed on the settlement generation layer 1 made of a cohesive soil layer and the embankment layer 2 thereabove, and the settlement generation layer 1 becomes a normal consolidated state based on the result of the soil investigation. For calculating the maximum embankment load of the embankment layer 2 necessary for this, from the calculated maximum embankment load of the embankment layer 2, the results of the soil investigation of the embankment layer 2, and the specific gravity of the lightweight soil replacement pile 3 to be used, To what extent should the existing embankment material forming the embankment layer 2 be replaced with the lightweight soil replacement pile 3 in order to bring the settlement generation layer 1 into a normal consolidation state (preferably an overconsolidation state) (replacement) Information), and based on the replacement information, using a means such as a spiral screw auger, a predetermined number of holes 4 extending from the top of the embankment layer 2 toward the settlement generation layer 1 are drilled. A predetermined curable lightweight soil is poured into the hole 4 and the hole 4 In curing the curable lightweight soil is construction by a lightweight soil replacement pile 3. In FIG. 1, the revetment wall 5 composed of L-shaped blocks is supported by support piles 6 that reach the bedrock below the settlement generation layer 1.

  In the land subsidence reduction improvement method of the first embodiment, the curable lightweight soil filled in the hole 4 drilled by means such as a spiral screw auger is cured in the hole 4 to become a lightweight soil replacement pile 3. The embankment load of the embankment layer 2 is reduced according to the ratio of replacing the existing embankment material with this light-weight soil replacement pile 3 as a part of the existing embankment layer 2, and the settlement amount in the settlement occurrence layer 1 is reduced. Or deterred.

In Example 1, when a large number of holes 4 drilled in the existing embankment layer 2 are deep beyond the water level surface, for example, two mixers are prepared, and the unit deposition weight of these mixers is prepared. Prepare two different types of hardened light soil (for example, one with a unit volume weight of 0.7 kN / m ³ and one with a unit volume weight of 1.1 kN / m ³ ). Filled with curable lightweight soil with a volume weight of 1.1 kN / m ³ , and filled with curable lightweight soil with a unit volume weight of 0.7 kN / m ³ shallower than the water surface, preferably the average unit volume of the whole weight by adjusting such that the 5 kN / m ³ or more 13 kN / m ³ or less, efficiently Guests can construction can be carried out reliably and efficiently adjust the embankment load embankment layer.

2 and 3 show an example in which the ground subsidence reduction improvement method according to Example 2 of the present invention is applied to the subsidence generation layer 1 just under the existing embankment similar to Example 1 described above.
In the second embodiment, unlike the first embodiment, a plurality of measurement points 7a, 7b, and a plurality of measurement points 7a, 7b, along the direction (cross-sectional direction) crossing the embankment layer 2 on the back side from the revetment wall 5 at a substantially right angle. In 7c, ..., multiple soil investigations are performed on the settlement generation layer 1 and the embankment layer 2 above it, and the embankment necessary for the subsidence generation layer 1 to be in a normal consolidated state based on the results of the plurality of soil investigations The maximum embankment load distribution of the layer 2 is obtained, and the subsidence generation layer 1 is determined from the obtained maximum embankment load distribution of the embankment layer 2, the result of the soil investigation of the embankment layer 2, and the specific gravity of the lightweight soil replacement pile 3 to be used. To replace the existing embankment material forming the embankment layer 2 with the light-weight soil replacement pile 3 in which part in order to make the normal consolidated state (preferably an overconsolidated state) (replacement information) ) The maximum embankment load distribution of the embankment layer 2 obtained here is obtained as a subsidence curve 8a of uneven settlement that occurs along a direction away from the revetment wall 5 at a substantially right angle.

  Next, based on the replacement information for bringing the settlement generation layer 1 obtained above into a normal consolidated state (preferably an overconsolidated state), a means such as a spiral screw auger is used, and the top of the embankment layer 2 is applied to the top of the embankment layer 2. A predetermined number of holes 4a, 4b, 4c,... That extend toward the subsidence generation layer 1 at a predetermined interval and a predetermined depth are sequentially drilled, and cured in these holes 4a, 4b, 4c,. Filled with a lightweight soil and hardened in each hole 4a, 4b, 4c, ... to form the required number and length of lightweight soil replacement piles 3a, 3b, 3c, ..., thereby the embankment layer 2 Part of the existing embankment material is replaced with lightweight soil replacement piles 3a, 3b, 3c,.

In this Example 2, lightweight soil replacement piles 3a, 3b, 3c,... That are replaced with the existing embankment material of the embankment layer 2, total weight , pile length, and replacement rate (along the cross-sectional direction of the embankment layer 2) The filling load of the improved embankment layer 2 is adjusted by the light-weight soil replacement piles 3a, 3b, 3c,... , 3c,... Can be used to bring the subsidence generation layer 1 into a normal compaction state, and the subsidence curve 8a shown in FIG. 2 is changed to the subsidence curve 8b shown in FIG. It is corrected and can prevent the phenomenon of uneven settlement.

FIG. 4 shows an example in which the ground subsidence reduction improvement method according to Example 3 of the present invention is applied to the subsidence generation layer 1 just below the existing embankment similar to Examples 1 and 2.
In this Example 3, unlike the said Example 1 and 2, the existing embankment material of the surface part of the embankment layer 2 is removed, and ground improvement is performed similarly to the said Example 1 or 2 about the remaining part of the embankment layer 2. At the same time, a lightweight soil 9 corresponding to the removed existing embankment material may be laid on the upper portion of the remaining portion of the improved embankment layer 2, and all of the existing embankment materials forming the embankment layer 2 thereby. The land subsidence reduction and improvement immediately below the embankment layer 2 can be performed without removing.

  According to the ground subsidence reduction improvement method of the present invention, the embankment layer is formed in the upper part, and consolidation settlement begins due to the embankment load of this existing embankment layer, or, for the subsidence generation layer concerned, the consolidation of the subsidence generation layer Settlement can be prevented easily and reliably, and it can be easily constructed even on existing embankments that are difficult to use with large construction machines, and the excavation layer on the back side of the revetment wall is greatly excavated. It is not necessary and the construction period is not limited, and it is extremely useful industrially.

FIG. 1 is an explanatory cross-sectional view showing an example in which the land subsidence reduction and improvement method according to Example 1 of the present invention is applied to a subsidence generation layer directly under an existing embankment as backfilling of a revetment by an L-shaped block. . FIG. 2 is a cross-sectional explanatory view showing a subsidence generation layer having an existing embankment layer as backfill of a revetment by an L-shaped block to which the ground subsidence reduction improvement method is applied.

FIG. 3 is a cross-sectional explanatory view similar to FIG. 1 showing an example in which the ground settlement reduction improving method according to Example 2 of the present invention is applied to the embankment layer of FIG. FIG. 4 is a cross-sectional explanatory view similar to FIG. 1 showing an example in which the ground settlement reduction improvement method according to Example 3 of the present invention is applied.

FIG. 5 is a cross-sectional explanatory view similar to FIG. 1 showing an example in which a conventional ground settlement reduction improvement method is applied to a settlement generation layer having an existing embankment layer. FIG. 6 is a cross-sectional explanatory view similar to FIG. 1 showing an example in which another conventional subsidence reduction improvement method is applied to a subsidence generation layer having an existing embankment layer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Subsidence generation layer (viscous soil layer), 2 ... Embankment layer, 3,3a, 3b, 3c, Lightweight soil substitution pile, 4,4a, 4b, 4c, ... Hole, 5 ... Revetment wall, 6 ... Support pile 7a, 7b, 7c, ... measurement points, 8a ... subsidence curve (non-uniform subsidence), 8b ... subsidence curve (equal subsidence), 9 ... lightweight soil.

Claims (5)

This is an improved subsidence reduction method to reduce or prevent the subsidence generation layer that forms the foundation ground by forming a subsidence layer above the consolidation subsidence due to the embankment load of the embankment layer, and the soil quality of the subsidence generation layer and the embankment layer Based on the survey results, obtain the maximum embankment load of the embankment layer necessary to bring the subsidence generation layer into a normal or overconsolidated state, and form the embankment layer from the maximum embankment load and the specific gravity of the lightweight soil replacement pile to be used. Obtain the ratio of replacing the embankment material with the lightweight soil replacement pile, and drill and replace the predetermined number of holes in the embankment layer based on the ratio of replacing the existing embankment material of the found embankment layer with the lightweight soil replacement pile. A method for reducing ground subsidence directly under an existing embankment, characterized in that the existing embankment material is removed and lightweight soil replacement piles are provided in the predetermined number of holes . Maximum embankment load embankment layers, based on a plurality of soil investigation that is conducted in a plurality of measurement points of the embankment layers, obtained as the maximum embankment load distribution, existing embankment embankment layer in accordance with the maximum fill load distribution subsidence reduction improved method of directly under existing embankment according to claim 1 or 2 Ru determined the rate of replacing a wood lightweight soil replacement piles. Embankment load after improvements in fill layer, the weight of the total weight soil replacement piles to be replaced to claim 1 or 2 is controlled by any one or two or more elements selected from the pile length and substitution rate An improved construction method to reduce land subsidence directly under the existing embankment. Lightweight earth substitution piles, the average specific weight of the total is not more 5 kN / m ³ or more 13 kN / m ³ or less, the unit volume weight of water surface shallower when substituted the embankment layer 5 kN / m ³ or more 10kN / m ³ or less, subsidence reduction improved method of directly under existing embankment according to any one of claims 1 to 3 in which the unit volume weight of the water level surface or deeper are formed so as to be 10 kN / m ³ greater. Lightweight earth substitution pile to replace some of the existing embankment material embankment layer, a curable lightweight soil was filled in a hole formed in the embankment layer, according to claim 1-4 which is formed by curing in the hole The ground subsidence reduction improvement method just under the existing embankment as described in any one of.

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