JP3963883B2 - Compaction method using low-strength injected solidified material. - Google Patents

Description

  The present invention relates to a compaction grouting method for injecting a low-strength injected solidified body and compacting a loose ground so that seismic waves do not propagate strongly to the ground.

  In recent years, urbanization has progressed rapidly, and the development of coastal areas in rivers, lakes and shallow coasts is underway. However, in these areas, the groundwater level is high and there are many loosely deposited sand grounds. For this reason, liquefaction is likely to occur when vibration caused by an earthquake acts. Therefore, there has been a risk of significant damage centering on buildings and various structures on the ground.

  As a typical method for improving these grounds, a ground improvement technique in which high-grade materials such as cement and cement milk are injected into the ground at a high pressure has been actively used. However, with this ground improvement technology, improvement materials such as cement and cement milk injected into the ground often run away and stray from a predetermined position where they have been pressed in soft ground such as sand ground. Non-uniformity was observed.

  For example, the ground 1 shown in FIG. 2 is composed of a surface layer 2 such as a thin soil layer, a liquefied layer 3 such as sandy soil, and a non-liquefied layer 4 such as a rock, and a building is formed on the surface layer 2. In the improvement of the ground 1 when it is constructed, a “deep mixing treatment method” is often employed in which the ground improvement material is forcibly conveyed to the liquefied layer 3 in the ground 1 and stirred and mixed.

  When such ground improvement work is performed, a large grid-like lump of concrete formed of cement, cement milk, or the like is formed in the liquefied layer 3 below the building, and the improved body 5 having higher strength than necessary is formed. Will form. In addition, the construction machine used for this construction is large, and therefore a large area is required for construction. Therefore, it is difficult to construct a facility under operation or directly under a narrow existing building.

  In addition, sand and crushed stones, such as sand compaction pile method and vibro flotation method, which dynamically inject sand and crushed stones, not only have problems such as noise and vibration, but also large construction machines. For this reason, there is a problem that it is not preferable for construction under a service facility or construction under a narrow existing structure.

In order to improve such problems as noise, vibration, and work space limitations, a ground improvement technique using “compaction grouting” that statically press-fits the ground improvement material and compacts the ground has been proposed (for example, (See Patent Document 1).
JP 2002-294684 A

  In the invention described in Patent Document 1, a small-diameter hole having a predetermined diameter is formed at a predetermined interval on the surface portion of the lower ground of an existing structure, and a non-fluid, self-curing low slump or the like (in practice) 2-5 cm, etc.), which is relatively hard, is press-fitted statically with a pump, and the consolidated ground 5A is formed in a layered shape to create a compression structure to compress and strengthen the surrounding ground (inter-pile ground). (Figure 3).

  The construction method using the injection material with the above-mentioned properties is to increase the strength and rigidity of the ground under the existing structure without the runaway and stray of the injection material in the ground, and the liquefaction phenomenon of the ground Can be prevented relatively easily. Therefore, the function of the existing structure on the improved ground 1 can be sufficiently maintained.

  Moreover, the injection material used for this is a low-slump, self-hardening material that is statically press-fitted into the ground, so it can be constructed without the occurrence of vibration or noise. It is. Moreover, since construction machines such as a boring machine and a special pump used for this construction are in-vehicle and compact equipment, construction is possible even in a narrow work space.

However, the strength of the laminated or dumpling-like consolidated body 5A formed after the ground injection by the conventional compaction grouting method is about 3000 kN / m ^2, which is the same strength as the deep layer processing method. Therefore, it is clear that the strength of the consolidated body by the compaction grouting method is considerably higher than the strength of the surrounding ground. In this way, the ground improvement material is press-fitted to continuously form a laminated solid body at a predetermined interval in the ground, so that a large number of strong columnar solid bodies are pressed into the ground. By this, it will be in the state which pushed away the ground 6 between the parts surrounded by this solidified body, and was compacted.

  Eventually, in the case of the conventional compaction grouting method as well, the solidified body 5A (FIG. 3) that is partially stronger than necessary is continuously formed as in the case of the deep-mixing method shown in FIG. Become.

  Considering a model of the strength distribution of a composite ground in which parts with different strengths are mixed, such as a high-strength consolidated body 5A after improvement and an inter-pile ground 6 after compaction, The hard bar-like improved body 5A is press-fitted into a flexible cushion corresponding to the intermediate ground 6.

  If the seismic wave W1 (vibration) is propagated as shown in FIG. 4 to the ground 1 including the improved body 5 with non-uniform strength as shown in FIG. The seismic wave W <b> 1 concentrates on the large improved body 5 and gives vibration to the whole including the improved body 5.

  Then, the seismic wave W1 is amplified inside the improved body 5 made of a large lump and becomes a large vibration W2. Along with this, a large shear force, that is, a ground that twists the improved body 5 is twisted. This will generate a deviation force.

  As a result, a large shearing force is also applied to the building K existing on the improved ground 1, and the building K may be seriously damaged.

  Further, if the seismic wave W1 as shown in FIG. 5 is transmitted to the ground 1 in which the columnar consolidated bodies 5A are dispersed and pushed in a staggered manner by the compaction grouting method as shown in FIG. In the solidified body 5A, the vibration W2 is amplified and propagated, but the vibration is propagated to the inter-pile ground 6B between the solidified bodies 5A as it is or slightly damped, and the surface layer 2 Vibration will be given to the building K supported above.

As a result, a large shearing force is also applied to the building k existing on the improved ground 1, and the building K may be seriously damaged.
In the conventional compaction grouting method, it is possible to adjust the strength of the solidified body 5A constituting the improved body 6 to a low strength by reducing the blending amount of a solidifying material such as cement. However, if the addition amount of the solidifying material is reduced, it becomes difficult to maintain the fluidity of the injecting material due to insufficient fine particles, and there is a possibility that the strength of the solidified body 5A varies.

  Thus, when the fluidity of the injection material decreases or the solidification strength inside the solidified body 5A varies, the ground between the piles 6B of the improved body 6A in which the solidified body 5A is dispersed is compacted. The effect will also vary, and parts that are liable to be liquefied by an earthquake will occur.

  From this knowledge, the present inventor considers the propagation state of seismic waves in the improved ground by the compaction grouting method, and when the ground 1 is improved, it is surrounded by the formed solid body 5A and the solid body 5A. If there is little difference in strength (rigidity) with the ground between piles 6B, that is, if the strength of the consolidated body 5A is comparable to that of the original ground (liquefied layer 3), the liquefied layer 3 Simultaneously with the compaction, it was found that it is necessary to develop a method in which seismic waves do not concentrate W1 on the consolidated body 5A as shown in FIG.

(Soil contamination problem)
By the way, ground improvement work using solidification materials such as blast furnace class B cement and ordinary Portland cement, which are generally used in civil engineering work, shows that the ground around the construction is highly alkaline due to the influence of the solidification material. It is also known that heavy metals such as valent chromium may be eluted and diffused.

  FIG. 7 shows that the large improvement body 5 shown in FIG. 2 is formed in the liquefied layer 3 portion of the ground 1 in a place where the water layer in the ground is in communication, such as a river, a lake, and a coastal area on a shallow coast. From the improved body 5 formed of this blast furnace type B cement or ordinary Portland cement, hexavalent chromium ions or hydroxyl ions are eluted in the water 7 as described above, or the improved body 5 is eluted in the sandy ground 3a at the bottom of the water where the water layer is continuous with the liquefied layer 3 in which the water 7 is formed, and this water 7 is further contaminated.

  By the way, sandy ground that easily liquefies with an earthquake is often scattered around watersides such as estuaries, coasts, and lakes. Moreover, in many cases, fisheries and ports for seafood are constructed on such watersides. Therefore, elution of heavy metals such as highly alkaline water and hexavalent chromium is allowed from the viewpoint of environmental protection. It is not done.

  That is, if they flow into the water, death to aquatic organisms, especially seaweed and fish that are cultivated, will increase, and even if this death does not increase, the growth rate will be significantly inhibited.

  In addition, on the beach, there are cases where it is not only a fishing port and farm, but also a playground for children. Considering this, even if the ground improvement work is done, water pollution around the construction must be avoided.

  The present invention was obtained in order to solve the problems in the conventional ground improvement method, and the first object of the present invention is to inject in a method for improving loosely accumulated sand ground. The object of the present invention is to provide a ground compaction method with little difference in rigidity between the formed consolidated body and the ground between piles.

  The second purpose is that the ground around the reinforced ground does not show high alkalinity, and a heavy metal such as hexavalent chromium elutes from the reinforced ground, and aquatic organisms and aquaculture. The object of the present invention is to provide a compact sand ground compacting method that does not substantially increase the mortality and growth inhibition of seaweed and seafood.

  The sand ground compaction method according to the present invention for achieving the above object is configured as follows.

In the first invention, the ground consisting of loosely accumulated sandy soil, magnesium oxide 4 to 10% as a solidifying material, aggregate 65 to 72% having gravel, sand, silt and clay content, water 20 to 26% It is characterized by suppressing the propagation of seismic waves to the surrounding ground by statically injecting a low-fluidity self-hardening injection material prepared by stirring the above mixture to form a low-strength solidified body.

In the second invention, the ground around the construction communicates with the ground, and the ground is capable of eluting constituents from the injected self-hardening injecting material, 4-10% magnesium oxide as a solidifying material, gravel, sand, silt and clay By statically injecting a self-hardening injectable material prepared by stirring a mixture of 65-72% aggregate and 20-26% water, It is characterized by not inducing pollution .

The present invention is intended to reinforce and improve loosely accumulated sand ground such as rivers, estuaries, near estuaries, and shallow coasts, and ground having similar characteristics. By reducing the formation significantly, the mechanical influence of the sand ground is reduced .

Furthermore, considering the influence on aquatic organisms, magnesium oxide is particularly selected and used as the solidifying material used for the injection material.

  Magnesium oxide used in the invention is obtained by firing magnesite as a raw material at a temperature of about 700 ° C. to 1000 ° C., and has a purity of 90% or more.

  When the firing temperature of magnesite is less than 700 ° C., the activity of magnesium oxide is lowered and the injecting material does not solidify, so that it is unsuitable as a solidifying material. Moreover, since the thing baked at the temperature of 1000 degreeC or more does not show self-hardening, the magnesium oxide baked in the temperature range of about 700-1000 degreeC is suitable for a solidification material.

  The low-fluidity self-hardening injection material uses magnesium oxide as a solidifying material in an amount of 4 to 10% with respect to the injection material. If the mixed amount of magnesium oxide is less than this range, the consolidation strength becomes small, and it becomes impossible to compact the surrounding ground. Moreover, when magnesium oxide is made more than the said range, a solidified body intensity | strength will become larger than necessary and there exists a fault which promotes propagation of a seismic wave.

  Aggregate is a mixture of gravel, sand, silt and clay with 65-72% added to 20-26% water to adjust the self-hardening infused material and to improve the ground It is required to press-fit statically by the compaction grouting method.

  The compacting method according to the present invention is a method of improving by a compaction grouting method on a ground consisting of loosely accumulated sandy soil, by statically injecting a low-fluidity self-hardening injection material into the ground. It is characterized by continuously forming a low-strength solidified body and compressing and strengthening the surrounding ground.

  Therefore, the low-fluidity self-hardening injection material according to the present invention is adjusted so as to give the same strength as the inter-pile ground even when it is solidified, so that it can be used in the compacted improved body portion. As a result, unevenness in strength is prevented from occurring, and as a result, the influence of seismic waves on the improved ground can be prevented as much as possible.

  In addition, since self-hardening injecting material containing magnesium oxide is used, there is no pollution caused by elution of heavy metals such as hexavalent chromium in fish farms. Problems such as poor growth can be solved all at once.

  FIG. 1 is a conceptual diagram of a shear force generated when a seismic wave propagates in an improved ground obtained by a ground compaction method according to an embodiment of the present invention.

  The ground 1 to which the present invention is applied is a ground made of loosely accumulated sandy soil formed near an estuary, a coast, or a lake, such as the Shinano River shore or Port Island.

  This sandy soil is characterized by its relatively high water level because it is a river, estuary or sandy coast. It is known that when earthquake vibrations act on such ground, there is a strong tendency to liquefy easily. Further, as described above, when the ground is improved by an improved body that is too strong as described above, the vibration of the earthquake is transmitted to the ground.

  As shown in FIG. 1, the present invention employs a compaction grouting method especially for a ground 1 made of loosely accumulated sandy soil such as a river or an estuary. The solid body 50 having a lower strength than the solid body obtained by the conventional construction method is continuously formed in a columnar shape, and the ground 51 between the piles between the solid bodies 50 is compacted. 52 is formed.

  The consolidated body 50 is formed with a diameter of 60 to 80 cm dispersed at a predetermined interval. A large number of consolidated bodies 50 are formed on the sand ground constituting the liquefied layer 3. It is in the state that pushed the columnar object.

  When the seismic wave W1 acts on the improved body 52 configured as described above, the seismic wave W1 is distributed and transmitted to the consolidated body 50 and the inter-pile ground 51, and is attenuated inside the consolidated body 50. It becomes the vibration W3, and the vibration W4 attenuated in the ground 51 between piles between the consolidated bodies 50. And in the surface layer 2, it is propagated as a damped vibration Ws and does not give a large vibration to the building K.

  As described above, according to the present invention, the improved body 52 includes the columnar solid body 50 formed by statically press-fitting a low-fluidity self-hardening injection material into the ground 1 at a predetermined interval d, and after compaction. Since it is comprised with the composite_body | complex which consists of the ground 51 between piles, there is no big difference in intensity between the surrounding ground.

Therefore, when the seismic wave W1 acts on the improved body 52, the seismic wave is attenuated and propagated to the building K on the ground surface as a gentle vibration W5, thereby minimizing damage to the building K. Can do it.
Example 1
Self-hardening by mixing a mixture of 8% magnesium oxide calcined at 800 ° C as a solidified material and 68% aggregate consisting of a mixture of gravel, sand, silt and clay, with water added to 24% The injection material was adjusted. The slump value of the injection material adjusted in this way was 4 cm.
Using the same type of compaction grouting apparatus as described in Patent Document 1, the self-hardening injection material adjusted as described above is statically applied to the ground to be improved, for example, at a maximum pressure of 6 Mpa. Press fit into.

The press-fitting depth varies depending on the ground to be constructed. For example, the depth H in FIG. 1 is in the range of GL-3 to GL-12 m, and the filling amount at one time is 2.6 to 3.8 m ³ . The number of steps required in consideration of the thickness of the liquefied layer, for example, 3 to 10 steps, is formed in the form of dumplings and columnar consolidated bodies 5 at intervals of 150 to 170 cm. Although it is estimated, the diameter D of the solidified body 50 formed in the ground 1 in the present invention is considered to be about 60 to 80 cm.
The improved body 52 in which the solidified bodies 50 formed in this way are assembled in a forested manner is a large-sized integrated body like the improved body 5 formed by the deep mixing treatment method as shown in FIG. It is not formed in a lump shape, but is formed as if a large number of large piles or pillars are erected, and the ground 51 between the piles is compacted by the press-fitting formation of the piles.

  The reason for this is that the self-hardening injection material is a low slump of 2 to 5 cm by using an injection material in which 4 to 10% magnesium oxide, 65 to 72% aggregate, and 20 to 26% water are stirred. Because it can be obtained. This low slump self-hardening injectable material is very close to the ground strength between piles after compaction.

  Therefore, even if such a self-hardening injection material is statically pressed into the soil, it does not spread in the lateral direction even in the softly accumulated sand ground, and it is relatively thin and has an independent pile or columnar shape. It has become.

  When the seismic wave W1 is transmitted to the improved body 52 (improved ground) formed as described above, the seismic wave W1 is transmitted upward while being attenuated within the solidified body 50 like the vibration wave W3. The transmitted vibration wave Ws is transmitted above the ground 1.

  An example of the amount of the injection material is shown in Table 1 below. In addition, when inject | pouring an injection material into the ground, in order to prevent the escape of the injection material in a ground, and a stray, the slump value of an injection material must be a fluid about 2-5 cm.

In addition, when the uniaxial compressive strength of the consolidated body formed of the injection material is less than 100 kN / m ² , the compaction effect on the ground between the piles is reduced, and when it is greater than 300 kN / m ² , seismic waves concentrate on the consolidated body. Therefore, the consolidated strength suitable for compacting the ground between piles without concentrating seismic waves is about 100 to 300 kN / m ² .

  No. 1 in Table 1 does not satisfy the standard values for slump value and strength because the mixing ratio of magnesium oxide, which is a solidifying material, and water is small. In addition, NO.4 also has a high mixing ratio of magnesium oxide, so the strength of the consolidated body has become larger than necessary.

  On the other hand, the range of the injection material shown in claim 1 is 4 to 10% magnesium oxide, 65 to 72% aggregate having gravel, sand, silt and clay and 20 to 26% water. NO.2 and NO.3 satisfy the standard values for both slump value and strength. Especially, when the injection material is mixed in the amount of NO.3, the compaction effect is the largest, so seismic waves Can be prevented from concentration.

(Example 2)
FIG. 6 shows the improvement work of the waterside section where the ground water of the ground 1 is communicated, particularly the liquefied layer 3 made of sandy ground. The solidified structure 50 formed in the ground by the compaction grouting method is shown in FIG. This shows a state in which valent chromium and hydroxide ions are not eluted in the water 7.

  The present invention uses an injection material in which 4 to 10% magnesium oxide, 65 to 72% aggregate, and 20 to 26% water are stirred as a self-hardening injection material.

  In addition, the present invention can suppress the rise in pH and elution of hexavalent chromium, etc. by statically press-fitting a low-fluidity self-hardening injection material by a compaction grouting method to improve the ground. Incentives for surrounding pollution can be prevented, and contamination of water quality at farms, harbors and beaches can be prevented.

  Further, in the present invention, since the injection material having a relatively small slump value is used, the building K on the ground 1 is not affected by the seismic wave as described with reference to FIG. Does not cause environmental degradation.

It is explanatory drawing of the improved ground which concerns on this invention. It is a perspective view which shows the conventional improvement body by a deep-layer mixing processing method. It is a perspective view which shows the conventional improvement body by a compaction grouting method. It is explanatory drawing of the propagation condition of the seismic wave of the improved body corresponding to FIG. It is explanatory drawing of the propagation condition of the seismic wave of the improved body corresponding to FIG. It is sectional drawing of the improved ground which applied this invention to the beach area. It is explanatory drawing of the contamination of the groundwater of the conventional ground improvement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ground 2 Surface layer 3 Liquefaction layer 4 Non-liquefaction layer 5, 52, 53 Improved body 5A, 50 Solidified body 6, 51 Ground between piles

Claims (2)

On the ground consisting of loosely deposited sandy soil, stir a mixture of magnesium oxide 4-10%, aggregate 65-72% with gravel, sand, silt and clay content and water 20-26% as solidification material A compacting method characterized by suppressing the propagation of seismic waves to the surrounding ground by statically injecting the adjusted low-fluidity self-hardening injection material to create a low-strength consolidated body. Aggregate 65 containing magnesium oxide 4-10% as solidification material, gravel, sand, silt and clay content on the ground where the construction area and groundwater communicate and the constituents can be eluted from the injected self-hardening injectable material By statically injecting a self-hardening injection material prepared by stirring a mixture of ~ 72% and water 20-26%, it will not induce contamination around the construction due to pH rise or elution of hexavalent chromium, etc. Characteristic compaction method .

Images