JP2012097491A - Ground improvement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress displacement due to the total weight of a construction machine especially, by a simple configuration.SOLUTION: In a ground improvement method, the construction machine having an agitation shaft 6 and a supply mechanism for transferring a solidification material along the agitation shaft and discharging it into natural ground is used, and many improvement piles 15 to be produced by self-hardening fluid 15a for which the supply mechanism discharges the solidification material in the penetration process of the agitation shaft 6 or the like and mixes it with the soil of the natural ground are produced in order in crisscross directions while moving the construction machine in a target ground improvement area. In the method, when producing the improvement piles 15, a scaffold layer 16 integrated with the improvement piles to be produced is formed by using a part of the self-hardening fluid elevated to the surface and discharged as self-hardening sludge 15b in the process of forming the self-hardening fluid 15a in a depth direction, the construction machine is moved forward along the scaffold layer 16, and the total weight of the construction machine is dispersed and supported by the scaffold layer 16 and the produced improvement piles 15.

Description

  The present invention relates to a ground improvement method for creating a large number of improved piles in the vertical and horizontal directions while moving a construction machine in a target ground improvement region.

  The ground improvement method uses a construction machine with a stirring mechanism and a supply mechanism that transports solidified material such as cement slurry along the stirring axis and discharges it into the original ground, and moves the construction machine in the target ground improvement area. However, the improvement mechanism piled up by the self-hardening fluid mixed with the soil of the original ground by discharging the solidified material in the intrusion process of the stirring shaft or the intrusion and withdrawal process in the feed mechanism, in the vertical and horizontal directions May be created. This method is also called a deep mixing method, and usually has a stirring blade below the stirring shaft, and the solidified material discharged from the supply mechanism is mechanically mixed and stirred with the soil of the original ground.

  In the above construction method, in order to avoid the influence of the construction machine's total weight (several tens to hundreds of tons) as the pile placing order, the construction machine should not be placed on the constructed improved piles or pile rows. A moving down construction is preferred. In particular, in construction in areas close to existing structures (including rivers; the same applies hereinafter), a low-displacement type supply mechanism or a relatively light construction machine is selected as a method to minimize displacement effects. Falling construction that moves away from the structure is often used.

  In other words, when there is an existing structure near the ground improvement area, first, an improved pile is constructed along the side closest to the existing structure, and then another improvement is made toward the side away from the existing structure. Build piles in order. This is because the improved piles and pile rows that have been created function as protective walls, and the deformation of the ground caused by the improved piles that are created thereafter is prevented from affecting the existing structure. Another measure is to provide a displacement absorbing hole for absorbing expansion between the existing structure and the ground improvement region. Furthermore, the countermeasure of patent document 1 is N-1 row constructed | assembled at least just before it when constructing the improved pile row | line | column of N row by mixing a hardening retarder in a solidification material as FIG. 6 shows. It is the structure which makes the improvement pile row | line | column of an eye maintain an unhardened state, and makes the unhardened improvement pile row | line | column function as a displacement absorption hole.

Japanese Patent Laid-Open No. 10-60880

  However, the protection walls, displacement absorption holes, and countermeasures of Patent Document 1 described above are often not applicable to terrain conditions where one side is a river or an area very close to an existing structure, and solidified material in the original ground. Even if it was effective for the displacement due to the volume expansion of the ground due to the discharge, the displacement due to the total weight of the construction machine did not work. The same applies to the above-mentioned downfall construction. Before the improved pile or pile row is constructed, the surrounding ground or surrounding structure is displaced due to the total weight of the construction machine, and must be replaced with a light construction machine. There have also been cases that have not been reported.

  From the background as described above, the present inventors made changes in the volume of the ground during the construction of improved piles through actual construction where the ground improvement area was very soft or the total weight of the construction machine was restricted. As a result of studying a method for minimizing ground displacement due to the total weight of the construction machine before the improved pile construction, the present invention has been completed. That is, the objective of this invention is providing the ground improvement construction method which can suppress the displacement resulting from the total weight of a construction machine especially by simple structure.

  In order to achieve the above object, the present invention uses a construction machine having a stirring shaft and a supply mechanism that transports the solidified material along the stirring shaft and discharges the solidified material into the original ground. While moving the machine, the supply mechanism discharges the solidified material in the intrusion process of the stirring shaft, etc. In the ground improvement method to be created, when the improved pile is created, in the process of forming the self-hardening fluid in the depth direction, the self-hardening fluid that rises to the ground surface and is discharged is self-hardening sludge. Forming a scaffold layer integrated with the improved pile constructed as the above, moving the construction machine forward along the scaffold layer, and the total weight of the construction machine by the scaffold layer and the constructed improved pile It is characterized by supporting dispersion.

  In the present invention described above, the “solidifying material” is cement slurry or the like. As a “supply mechanism”, in order to reduce the volume expansion or displacement of the original ground due to the penetration of the stirring shaft and the discharge of the solidified material during construction, the solidified material discharged to the original ground is mixed with the soil of the original ground and is self-hardening. It is a fluid that can be partially discharged to the surface. For example, the mechanism disclosed in Japanese Patent Publication No. 4-57805, Japanese Patent No. 3075449, and Japanese Patent No. 3125244 other than the mixed ejector discharge method specified in claim 4 is similar to them. Including mechanism.

The present invention as described above is more preferably embodied as in claims 2 to 4. That is,
(1) The self-hardening waste mud discharged to the ground surface has a composition that is substantially the same as that of the self-hardening fluid (Claim 2).
(2) The said scaffold layer is the structure provided in the breadth centering on the improvement pile built under it (Claim 3).

(3) The supply mechanism is provided in a lower part of the stirring shaft or a stirring blade attached to the stirring shaft, and the solidified material introduced from the solidified material supplying means is accompanied by compressed air introduced from the compressed air supplying means. And it is the structure which has the mixing ejector which discharges compressed air and a solidification material in mist form (Claim 4). For example, as disclosed in Japanese Patent No. 3622903, this mixed ejector discharges compressed air and a solidified material in the form of a mist, thereby reducing the bonding force between soil particles of the original ground, and the solidified material and the original material. Mixing and stirring with the soil of the ground is promoted so that a uniform self-hardening fluid can be obtained, and part of the self-hardening fluid is easily discharged to the ground due to the lift-up effect of compressed air.

  The invention of claim 1 forms a self-hardening fluid in the depth direction in which the solidified material discharged from the supply mechanism and the soil of the original ground are mixed in the depth direction in the process of creating the improved pile. The animal that is discharged to the surface of the animal is used as self-hardening mud to form a scaffold layer. As a construction procedure, the forward construction is reverse to the conventional downhill construction, that is, the construction machine is moved forward along the scaffold layer integrated with the improved pile to be constructed. For this reason, the present invention utilizes the self-hardening fluid that rises and discharges to the surface of the ground during the construction process of the improved pile as a material for the scaffold, and uses the scaffold layer integrated with the improved pile to be constructed, Displacement due to construction machine load can be easily reduced by supporting weight in a distributed manner. That is, the forward construction of the present invention is significant in that it is effective as a displacement reduction measure for preventing displacement due to the total weight of the construction machine. Of course, since the improved pile is integrated with the scaffold layer, it is also excellent in that it is difficult to be displaced even when a large load is applied.

  The invention of claim 2 is that the self-hardening sludge discharged to the ground surface is a part of the self-hardening fluid formed in the raw ground, and is used as a material for the scaffold layer as a high-quality self-hardening sludge. It has been identified for confirmation.

  In the invention of claim 3, since the scaffold layer is provided with a spread centered on the improved pile formed thereunder, the scaffold is efficiently reinforced by the improved pile formed, and is stable to the construction machine. Support force can be imparted.

  According to the invention of claim 4, the supply mechanism has the above-mentioned mixed ejector, and the ejector discharge method reduces the bonding force between the soil particles of the original ground, and the self-mixing material is uniformly mixed with the solidified material and the soil of the original ground. It is possible to obtain a hard fluid, and a part of the self-hardening fluid is easily discharged to the ground by the lift-up effect of compressed air, so that the volume change of the ground due to the solidified material discharged into the original ground can be reduced. Be able to reduce.

(A), (b) is a schematic diagram for demonstrating the advance construction of this invention construction method. It is a block diagram which shows the mixing ejector etc. which comprise the supply mechanism used for this invention construction method. It is a schematic diagram which shows the 1st construction example by which this invention construction method was applied and the ground was improved. It is a graph which shows the displacement measurement result in the said 1st construction example. It is a schematic diagram which shows the 2nd example of construction improved by applying this invention construction method. It is a graph which shows the displacement measurement result in the said 2nd construction example. It is explanatory drawing which shows the falling construction currently disclosed by patent document 1. FIG.

  Embodiments of the present invention will be described with reference to the drawings. In this embodiment, as actual ground improvement, Example 1 applied in the ground improvement region shown in FIG. 3 and Example 2 applied in the ground improvement region shown in FIG. FIG.1 and FIG.2 is a schematic diagram which shows the principal part applied to the ground improvement construction method of each Example. In the following description, after clarifying the construction machine features and construction method features used in the ground improvement method employed in each example, Example 1 in FIG. 3 and Example 2 in FIG. 5 will be described in detail.

(Characteristics of construction machine) FIGS. 1 and 2 schematically show the main part of the ground improvement method applied in each embodiment. First, the construction machine used in the ground improvement method is a traveling base machine 1, a support leader 2 standing upright so as to be movable by the base machine 1, and a lifting mechanism that is moved up and down along one side of the support leader 2. 3, a rotation driving mechanism 4 and a swivel 5 held by the lifting mechanism 3, a stirring shaft 6 that is lifted and lowered by the lifting mechanism 3 and rotated by the rotation driving mechanism 4, and a lower side of the stirring shaft 6. And a supply mechanism for discharging the compressed air and the solidified material transferred along the stirring shaft 6 in the form of a mist into the original ground.

  At the time of construction, the stirring shaft 6 is supported so as to be movable up and down via the support leader 2 and the lifting mechanism 3, and penetrates or is pulled out under the ground. The rotation drive mechanism 4 rotates the stirring shaft 6 forward and backward via a motor, a reduction gear mechanism, and the like, and is moved up and down along the support leader 2 together with the stirring shaft 6. Reference numeral 9 is a protective cover for preventing dirt caused by the upwardly discharged jet air.

  The stirring shaft 6 has a single-shaft configuration as in the enlarged view of FIG. 1 in the first embodiment, and a two-shaft configuration as schematically illustrated in FIG. 2 in the second embodiment. It has become. Further, in the two-shaft configuration, the stirring blades 7 of each axis are disposed so as not to overlap with the rotation trajectory of each axis, and have a co-rotation prevention plate 17 interposed between the two stirring shafts 6. The co-rotation prevention plate 17 maintains the space between the stirring shafts 6 and makes it easy to prevent the movement of the soil accompanying the rotation of each stirring blade 7. A drilling blade (not shown) is attached to the lower end of the stirring shaft 6 according to the construction conditions.

  The supply mechanism includes piping paths 13 and 14 disposed along the vertical direction inside the stirring shaft 6, solid material supply means and compressed air supply means (not shown) provided on the ground surface side, and a stirring shaft. 6 and a mixing ejector 8 attached to the stirring blade 7. Among these, each upper end of the piping paths 13 and 14 is connected to the corresponding piping paths of the solidification material supply means and the compressed air supply means via the swivel 5 or the like. Each lower end is connected to the corresponding inlet side of the mixing ejector 8 either directly or through the connecting pipe and off the shaft.

  As shown in FIG. 2, the mixing ejector 8 includes an air supply unit 8a, a cement slurry (solidifying material) supply unit 8b, a mixing chamber 8c, a discharge port 8d, and the like. In this structure, the cement slurry introduced into the supply unit 8b is put on the compressed air introduced from the supply unit 8a, enters the mixing chamber 8c, and is then discharged from the discharge port 8d at a predetermined injection pressure. . For the solidified material supply means, compressed air supply means, and mixed ejector 9, refer to Japanese Patent No. 3416744 and Japanese Patent No. 3622903.

(Characteristics of construction method) In the ground improvement construction method, as shown in FIG. 1, a large number of improved piles 15 are created in order in the vertical and horizontal directions in the target improved ground region 10. In this case, the improved pile 15 is constructed in the order of pile rows L1, L2, L3, L4... As shown on the lower side of FIG. In this pile construction, a self-hardening fluid 15a obtained by stirring and mixing cement slurry, which is a solidifying material, with the soil of the original ground is formed in the depth direction. In this process, among the self-hardening fluid 15a, the one that rises to the ground surface and is discharged is used as the self-hardening sludge 15b, and the scaffold layer 16 integrated with the improved pile 15 to be formed is formed. As the pile placing order, the construction machine is moved forward along the scaffold layer 16, that is, forward construction.

  More specifically, during construction, the construction machine is moved to the construction site of the improved ground region 10 and positioned at the first pile creation planned portion. A recess 12 corresponding to the scaffold layer 16 is formed in the pile formation planned part prior to pile formation. The concave portion 12 may store the self-hardening mud 15b by excavating the ground on the ground surface side of the planned pile construction portion to a predetermined depth, a frame body or the like. The design of the recess 12 and the frame body is based on the construction conditions such as the ground properties of the construction site and the properties of the solidified material to be placed, and the discharge of the solidified material discharged from the ground to the ground surface in the process of creating the improved pile. The depth and area are set in consideration of the amount. Usually, the depth is, for example, about 30 cm to 150 cm, and the size is such that the upper portions of adjacent improved piles are connected to a single object by the scaffold layer 16. Moreover, it is preferable that the scaffolding layer 16 formed in the recessed part 12 or the recessed part 12 is provided in the breadth centering around the vertical hole 11 for piles according to the pile diameter of the improved pile 15 formed under it.

  In the construction, the stirring shaft 6 is rotated by the rotation drive mechanism 4 and penetrates to a predetermined depth. Agitation and mixing are performed in this penetration process, or in each process of penetration and extraction. In this operation, for example, the cement slurry that is a solidifying material is pumped to the supply unit 8b of the mixing ejector 8 through the pipe path 13, and the compressed air is pumped to the supply unit 8a of the mixing ejector 8 through the pipe path 14. Is done. In the mixing ejector 8, when the supply unit 8a reaches a predetermined pressure, a valve mechanism (not shown) is switched to an open state, compressed air is introduced from the supply unit 8a to the mixing chamber 8c, and the cement slurry in the supply unit 8b is compressed. After being put in the air and entering the mixing chamber 8c, the compressed air and the cement slurry are sprayed from the discharge port 8d in a mist toward the soil of the original ground. In this jetting mode, cement slurry is jetted in the form of mist accompanied by compressed air, and is sprayed forward, for example, in the rotational direction of the stirring blade 7 in the rotational direction of the stirring blade 7.

  In the above-mentioned air-entrained discharge mode, by controlling the jet pressure of compressed air and the supply amount of cement slurry, for example, the fluidity of soil and soil particles that have been crushed or subdivided into a lump of soil existing in front of the blade Efficiently enhance. As a result, in this construction, a uniform self-hardening fluid 15a for improved piles is obtained, and a part of the self-hardening fluid 15a rises along the stirring shaft 6 due to the lift-up effect of compressed air, It becomes easy to discharge to the concave portion 12 on the ground surface side as the self-hardening mud 15b. This discharge is considerably larger than other discharge methods. Usually, the amount is the same as the amount of cement slurry charged, the volume change in the ground is reduced, and the cement slurry is efficiently stored in the recess 12.

  In the above ground improvement method, in the forward construction, as shown in the lower side of FIG. 1, as each improved pile 15 of the pile row L1 is finished as an improved pile 15, the construction machine is put on the pile row L1. It moves so that each improved pile 15 of the next pile row L2 is created. Subsequently, the construction machine is moved to ride on the pile row L2, and each improved pile 15 of the next pile row L3 is created. Subsequently, the construction machine is moved to ride on the pile row L3, and each improved pile 15 of the next pile row L4 is created. Subsequently, the construction machine is moved to ride on the pile row L4, and this is repeated until the final pile row. In this forward construction, since the total weight of the construction machine is distributed and supported by the scaffold layer 16 and the improved pile 15 that has been created, the displacement caused by the construction machine load can be greatly reduced even in soft ground.

(Embodiment 1) FIG. 3 shows a case 1 of forward construction employed in actual ground improvement. In this case 1 construction, prior to river improvement, the foundation ground of the revetment will be improved with a deep mixing treatment method to reduce settlement of the revetment and prevent slippage. The construction outline is shown below.
(1) The improved construction method is the CI-CMC construction method (the ejection method of the mixed ejector shown in FIG. 2 and 1600 mm × 2 axes)
(2) Recovery rate is ap = 46.8%
(3) Improved strength: quick = 200 KN / m ²
(4) The construction machine is a standard construction machine (SP110 manufactured by Hitachi Sumitomo Heavy Industries Construction Crane Co., Ltd.) (5) The total weight of the machine is 122.8 t.
(6) The mechanical ground pressure is 162 KN / m ²

  The ground in this ground improvement area is composed of soft alluvium (cohesive soil, organic soil) with a thickness of about 10-20m, and because it is an improvement along the river that tends to cause displacement, Construction requiring attention to displacement of ± 10 cm (displacement) was necessary.

During the ground improvement work, displacement piles were installed at 16 locations shown in Fig. 3 (locations indicated by black circles on one side of the river), and dynamic observations were carried out. Since the permissible displacement of the river revetment is 100 mm, the displacement management standards were set as follows. In this construction, the above-mentioned scaffold layer was laid on the improved pile so as to have a thickness of about 50 cm.
The primary management value is 50 mm (allowable value × 0.5). In construction, if the displacement exceeds the primary control value, report to the supervisor and discuss changes in construction methods (placement order, construction speed, etc.).
The secondary management value is 80 mm (allowable value × 0.8). In construction, if the displacement exceeds the secondary control value, the construction is temporarily suspended and measures are discussed.

  The displacement measurement result in FIG. 4 shows an example of the measurement result of the horizontal displacement when the above setting is performed. The horizontal axis is the construction date, and the vertical axis is the displacement (mm). In the construction work, the deep layer mixing process was originally planned to be carried out by using the CI-CMC construction method, which is a low displacement construction method, so construction was started from the front row on the river side. As a result, a displacement of 40 mm occurred in 4 days from the start of construction, and when construction was continued in the same manner, it was predicted that the allowable amount would be exceeded. Therefore, in order to investigate the cause of the displacement, the amount of mud generated during construction was measured and found to be about the same as the amount of slurry added. Therefore, considering that the cause of the displacement was the load on the construction machine, the placement order was changed from falling construction to forward construction. As a result, the displacement, which was on an increasing trend, stopped, and the displacement reduction effect by the forward construction was confirmed. This work was completed with a horizontal displacement of 50 mm or less.

(Embodiment 2) FIG. 5 shows a case 2 of forward construction employed in actual ground improvement. This construction in Case 2 is intended to prevent subsidence of the revetment foundation ground and secure its supporting capacity by improving the revetment revetment foundation with the deep mixed treatment method prior to river rehabilitation. The construction outline is shown below.
(1) The improved construction method is CI-CMC construction method (mixed ejector ejection system, 1300mm x single shaft)
(2) Recovery rate is ap = 78.5%
(3) Improved strength: quick = 150 KN / m ²
(4) The construction machine is a small construction machine (DHJ12 manufactured by Nippon Vehicle Manufacturing Co., Ltd.)
(5) Machine gross weight is 16.1t
(6) The mechanical ground pressure is 79 KN / m ²

The ground in this ground improvement area is composed of very soft high moisture specific humus (wn = 300% -1000%), and there is not enough scaffolding to make it difficult to run even with a small backhoe (0.4 m ³ ). It was in a stable state. Furthermore, because the construction site was close to the water-impervious wall (thin steel sheet pile: sheet wall) at the waste disposal site (minimum separation 1.0 m), as a countermeasure for stability and displacement reduction of the construction machine, forward construction with a small construction machine Was adopted.

  In this construction, eight observation points (measurement points 1 to 8 indicated by black circles in FIG. 5) and two inclinometers (two underground points indicated by squares) installed at the top of the impermeable wall. Dynamic observation was carried out using an inclinometer. Moreover, since the allowable displacement of the adjacent impermeable walls was 50 mm, the construction was performed with the primary management value set to 15 mm (allowable value × 0.3) and the secondary management value set to 30 mm (allowable value × 0.6). In this construction as well, the above-mentioned scaffold layer was laid on the improved pile so that the thickness was about 50 cm.

  6 (a) and 6 (b) show the displacement measurement results of the top of the impermeable wall at the position closest to the disposal site, that is, the measurement points 5 to 8 among the displacement measurement results when performed with the above settings. The results are shown. The horizontal axis is the construction date, and the vertical axis is the amount of displacement (mm) in the X or Y direction. Also in this case 2, it can be seen that by adopting the CI-CMC method and the forward construction, ultra-low displacement construction with a maximum displacement of about 9 mm could be realized. As described above, in each of Examples 1 and 2, ultra-low displacement construction was realized under ground conditions where displacement is likely to occur, and it can be determined that forward construction was effective as a displacement reduction measure.

  The construction method of the present invention only needs to have the configuration specified in the claims, and the details can be changed or developed with reference to the above embodiment. As an example, the supply mechanism is not limited to the discharge method of the mixed ejector, but may be another method that can discharge the equivalent of the solidified material (cement slurry) into the ground surface during pile construction.

DESCRIPTION OF SYMBOLS 1 ... Base machine 2 ... Support leader 3 ... Elevating mechanism 4 ... Rotation drive mechanism 5 ... Swivel 6 ... Agitation shaft 7 ... Agitation blade 8 ... Mixing ejector 10. ..Ground improvement area (11 is vertical hole for pile, 12 is concave)
13, 14 ... piping route 15 ... improved pile (15a is self-hardening fluid, 15b is self-hardening mud)
16 ... scaffolding layer L1-L5 ... pile row

Claims (4)

Using the construction machine having a stirring mechanism and a supply mechanism that transports the solidified material along the stirring shaft and discharges it into the original ground, the supply mechanism is moved while moving the construction machine in the target ground improvement region. In the ground improvement construction method in which a large number of improved piles are formed in order in the vertical and horizontal directions by discharging the solidified material in the process of penetration of the stirring shaft and mixing with the self-hardening fluid mixed with the soil of the original ground,
In the process of forming the self-hardening fluid in the depth direction when forming the improved pile, the self-hardening fluid is improved using the one that rises to the surface and is discharged as self-hardening sludge. Form a scaffold layer integrated with the pile,
A ground improvement construction method characterized in that the construction machine is moved forward along the scaffold layer, and the total weight of the construction machine is distributed and supported by the scaffold layer and the constructed improved pile.   The ground improvement construction method according to claim 1, wherein the self-hardening waste mud discharged to the ground surface has substantially the same composition as the self-hardening fluid.   The ground improvement construction method according to claim 1 or 2, wherein the scaffold layer is provided so as to have an extension centered on an improved pile formed thereunder.   The supply mechanism is provided in a lower part of the stirring shaft or a stirring blade attached to the stirring shaft, and is accompanied by the solidified material introduced from the solidified material supply means by the compressed air introduced from the compressed air supply means, The ground improvement method according to any one of claims 1 to 3, further comprising a mixed ejector for discharging the compressed air and the solidified material in a mist form.

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