JP6558685B2 - Ground improvement method - Google Patents

Description

  The present invention relates to a ground improvement method for consolidating a soft ground by placing a plurality of drain materials on the soft ground in construction of a reservoir and applying a negative pressure to the drain material.

  Conventionally, to improve soft ground, as shown in FIG. 6 (a), a plurality of drain materials 2, 2 ... are placed on the soft ground 1, and negative pressure is applied to each drain material 2, 2 ... A vacuum consolidation drain method is widely used in which the ground surface 3 is consolidated and submerged while draining pore water in the soft ground 1 to the ground (see, for example, Patent Document 1).

  At that time, as shown in FIG. 6 (a), each drain member 2, 2... Is fixed in the improvement target area 4 so that the entire improvement target area 4 of the soft ground 1 sinks evenly. It is common to place them evenly at intervals d. In addition, the code | symbol 4a in a figure is a boundary line with the non-improvement area | region 5 of the improvement object area | region 4 edge part.

  However, as shown by a two-dot chain line in FIG. 6A, the subsidence of the ground surface 3 at the actual site is a portion close to the non-improvement area 5 of the improvement target area 4, that is, the outer edge of the improvement target area 4. The resistance of the clay layer in the non-improvement area 5 that is in contact with the part inhibits the settlement compared to the central part of the improvement target area 4, so that the improvement target area 4 as a whole is not settled, that is, the improvement target area 4 There was a possibility that the ground surface 3 would not be uniformly submerged.

  In this case, if there is a part that has not reached the predetermined settlement due to uneven settlement, it will be necessary to move the earth and sand, and there is a risk that the construction period will be prolonged, etc. There was a risk of it occurring.

  Therefore, conventionally, as shown in FIG. 6 (b), the outside of the original area to be improved 4, that is, the range where the drain materials 2, 2. 6 is also considered to be a method of uniformly sinking the ground surface 3 of the original improvement target area 4 by carrying out consolidation settlement.

JP 2004-44168 A

  However, the conventional technique as described above widens the range in which the drain material is placed outside the original improvement target area, so that when the land acquisition is difficult, the widening portion cannot be provided, so the construction method In such a case, there are cases where other expensive construction methods such as construction of a solidified wall have to be adopted.

  Therefore, in view of such a conventional problem, the present invention aims to provide a ground improvement method that can uniformly improve soft ground by a vacuum consolidation drain method even when the range of land securing is limited. It was made as.

The feature of the invention according to claim 1 for solving the conventional problems as described above is that a large number of drain materials are placed in the improvement target area in the soft ground, and a negative pressure is applied to each drain material, In the ground improvement method for consolidation subsidence of the soft ground, the consolidation promoting portion having a larger number of drain materials placed per unit area inside the end portion of the improvement target region than in the central side portion of the improvement target region The drain material constituting the consolidation promoting part and the drain material in the other part of the improvement target area are connected to the same decompression means, and the decompression means is operated to simultaneously apply all the drain materials. In the ground improvement method, the negative pressure means is stopped after applying the negative pressure for a certain period of time to promote the consolidation of the consolidation promoting portion and consolidating the entire area to be improved.

The feature of the invention described in claim 2 is that, in addition to the configuration of claim 1, a combination of the consolidation promoting portion width and the drain material spacing in the consolidation promoting portion based on the set improvement depth and the normal drain material spacing It is to control the settlement of the consolidation promoting part by appropriately selecting.

  As described above, the ground improvement method according to the present invention is a ground in which a large number of drain materials are placed in an improvement target area in the soft ground, a negative pressure is applied to each drain material, and the soft ground is consolidated and settled. In the improvement method, a consolidation promoting portion having a larger number of drain materials to be placed per unit area than the center side portion of the improvement target region is formed inside the end portion of the improvement target region. By applying a negative pressure to the surface and promoting the consolidation of the consolidation promoting portion, the entire improvement target region is consolidated, thereby generating resistance between the end portion of the improvement target region and the non-improvement region. Even if the settlement at the end is inhibited, the consolidation settlement across the entire improvement target area can be made uniform.

  Further, in the present invention, the drain material constituting the consolidation promoting portion and the drain material in the other part of the improvement target area are connected to the same decompression means, and the decompression means is operated to operate all the drain materials. At the same time, after applying a negative pressure for a certain period of time, the pressure reducing means is stopped, so that a consolidation stress difference is generated between the consolidation promoting portion and the other portions, and consolidation settlement can be promoted in the consolidation promoting portion.

  Furthermore, in the present invention, based on the set improvement depth and the normal drain material interval, the combination of the consolidation facilitating portion can be reduced by appropriately selecting a combination of the consolidation facilitating portion width and the drain material interval in the consolidation facilitating portion. By controlling, the consolidation settlement of the entire improvement target area can be made uniform with high accuracy.

(A) is a top view which shows the embodiment of the ground improvement construction method based on this invention, (b) is the longitudinal cross-sectional view. It is a flowchart which shows the process of setting the consolidation promotion part width | variety in this invention method. It is an analysis mesh figure which shows an example of the two-dimensional FEM analysis model used at the process in FIG. It is a graph which shows the effect of the ground improvement construction method concerning the present invention. It is sectional drawing which shows the other Example which concerns on the ground improvement construction method which concerns on this invention. (A) is a longitudinal cross-sectional view which shows an example of the ground improvement by the conventional vacuum consolidation drain method, (b) is a longitudinal cross-sectional view which shows the state which expanded the placement range of the drain material.

  Next, an embodiment of the ground improvement method according to the present invention will be described based on the examples shown in the drawings. It should be noted that the same components as those in the above-described conventional example will be described with the same reference numerals. A boundary line with the non-improvement area 5 at the end, 7 is a central point of the improvement object area 4.

FIG. 1 shows a state when the ground improvement method according to the present invention is carried out, and a plurality of drain materials 2, 2... end inner, i.e., the portion having a constant width W _E of the inner boundary line 4a of the unmodified region 5, drain material 2, which is pouring per unit area than the other portions of the modified target area 4, The consolidation promoting part 10 having a large number of 2 ... is formed, and the entire improvement target area 4 is consolidated and settled while promoting the settlement of the consolidation promoting part 10.

  Each drain material 2, 2... Is formed to have the same length, for example, plastic board drain is used. Although not particularly shown, both surfaces of the core material having a corrugated cross section are permeable coating such as nonwoven fabric. It is covered with a material, and the inside and outside of each drain material 2, 2 ... communicate with each other in a state in which the inflow of earth and sand is prevented. The drain materials 2, 2... Are not limited to plastic board drains. For example, chemical drains made of a synthetic resin fiber porous material may be used.

  The upper ends of the drain materials 2, 2... Are connected to the water flow hose 12 through the impermeable connection cap 11, and the other end of each water flow hose 12 is decompressed by the vacuum pump 14 and the like through the water collection pipe 13. Connected to the means. Moreover, each drain material 2, 2 ... embeds the upper end part (cap part) from the ground surface of the soft ground 1 to a desired depth, whereby the surface layer part of the improvement target area 4 forms an airtight seal layer, A pressure difference is preferably generated between the drain materials 2, 2.

As shown in FIGS. 1 (a) and 1 (b), the consolidation facilitating portion 10 has an interval between drain materials 2, 2... _E )) is set narrowly, and the number of drain materials 2, 2 ... per unit area based on the ground surface 3 is larger than the central 7 side portion of the improvement target area 4, and the drain material accordingly. When the negative pressure is applied to 2, 2..., The consolidation stress increases, and the consolidation is promoted from the center 7 side of the improvement target area 4.

The consolidation promoting unit 10 determines an improved depth D (drain material 2, 2... Length) and a normal drain material interval d on the basis of the results of prior soil investigation and consolidation test, and adjusts accordingly. Thus, a suitable combination of the consolidation promoting portion width W _E and the promoting portion drain material interval d _E is appropriately selected, and thereby the settlement of the consolidation promoting portion 10 is controlled.

The combination of the consolidation promoting portion width W _E and the promoting portion drain material interval d _E is, for example, when the improved depth D = 15 m and the normal drain material interval d = 1.0 m, the promoting portion drain material interval d _E = 0. When it is 0.5 m (1/2 of d), the consolidation promoting portion width W _E = 3 m (1/5 of D), and when the promoting portion drain material interval d _{E is} 0.7 m, the consolidation promoting portion width WE And W _E = 5.0 (1/3 of D).

Incidentally, consolidation promoting region width W _E is based on the FEM (finite element method) deformation analysis of soft ground 1 by compaction analysis result, considering the extent of influence of resistance by unmodified region 5, the ratio of the improved depth D It is desirable to select within a range not exceeding 1.

  Below, the concrete construction procedure of this invention method is demonstrated. In addition, the code | symbol b in a figure is the width | variety of the improvement object area 4, and the code | symbol H is a clay layer thickness.

  First, a soil survey (s1) and a consolidation test (s2) of the target soft ground 1 are performed, and an improvement target area width b, an improvement depth D, and a normal drain material placement interval d are set based on the results. (S3).

Next, a combination of an arbitrary consolidation promoting portion width W _E and a promoting portion drain material placement interval d _E is appropriately selected (s4).

The improved depth D is set, drain material hitting set distance d, based on the consolidation promoting region width W _E and the accelerator unit drain member hitting set distance d _E creating an analysis mesh, two-dimensional FEM (Finite Element Method) Consolidation An analysis is performed, and a settlement amount S at the center 7 of the improvement target area and a settlement amount S _E at the end portion 4a of the improvement target area are calculated from the result (s5).

FIG. 3 shows an example of a two-dimensional FEM consolidation analysis model. For example, clay is set as an elastoplastic body, and the drainage boundary is set at a distance d except for the consolidation promoting section 10 and at a distance d _E at the consolidation promoting section 10. Then, an analysis mesh is created, and calculation is performed under a condition that a negative pressure of −65 kN / m ² acts on the drainage boundary. An example of the ground constant used for the analysis is presented below.

When the calculated subsidence ratio S _E / S is outside a predetermined range (S _E /S<0.9), the selected consolidation promoting portion width W _E and the promoting portion drain material placement interval d The combination with _E is made non-conforming, a combination of an arbitrary consolidation promoting portion width W _E and a promoting portion drain material placement interval d _E is selected again, and steps s4 to s6 in FIG. 2 are repeated.

On the other hand, when the calculated subsidence amount ratio S _E / S is within a predetermined range (S _E /S≧0.9), the selected consolidation promoting portion width W _E and the promoting portion drain material placement interval d _E The combination is adopted.

Then, the determined improvement target zone width b, improved depth D, normal drain material hitting set distance d, the drain on the basis of the consolidation promoting region width W _E and the accelerator unit drain member hitting set distance d _E material 2,2. Are placed in the improvement target area 4 and the consolidation promoting portion 10 is formed, and all the drain materials 2, 2... Are connected to the vacuum pump 14 through the water hose 12 and the water collecting pipe 13.

  Then, the pressure reducing means such as the vacuum pump 14 is operated, and the negative pressure is simultaneously applied to all the drain materials 2, 2.

  In the settlement of the ground surface 3, the consolidation stress acting on the consolidation promoting portion 10 is larger than the central 7 side portion. Therefore, as shown by the solid line in FIG. 4, the consolidation promoting portion 10 is not provided (dotted line in FIG. 4). ), The consolidation of the consolidation promoting portion 10 is promoted, and even if shear resistance occurs due to consolidation settlement with the non-improved area 5, the difference in settlement with the central 7 side portion is minimized, and the object of improvement The consolidation settlement of the entire area 4 is made uniform.

  Then, after operating for a certain period of time, the decompression means such as the vacuum pump 14 is stopped, and the vacuum pump 14 and the like are removed as necessary to complete the improvement work.

  In addition, the embodiment of the present invention is not limited to the above-described embodiment, and can be applied to a construction method using a loading embankment 20 as shown in FIG. The same components as those in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the above-described embodiment, the example in which all the drain materials are connected to the pressure reducing means such as one vacuum pump 14 has been described. However, the drain materials 2, 2. You may connect to decompression means, such as a pump.

DESCRIPTION OF SYMBOLS 1 Soft ground 2 Drain material 3 Ground surface 4 Improvement object area 5 Non-improvement area 10 Consolidation promotion part 11 Connection cap 12 Water flow hose 13 Water collecting pipe 14 Vacuum pump

Claims (2)

In the ground improvement method of placing a large number of drain materials in the improvement target area in the soft ground, applying a negative pressure to each drain material, and consolidating the soft ground,
A consolidation promoting portion is formed inside the end portion of the improvement target area, the consolidation promoting portion having a larger number of drain materials per unit area than the central side portion of the improvement targeted area, and constituting the consolidation promoting portion. The material and the drain material in the other part of the improvement target area are connected to the same pressure reducing means, and the pressure reducing means is operated to apply a negative pressure to all the drain materials simultaneously for a certain period of time. A ground improvement construction method characterized by stopping the pressure-reducing means after consolidating the entire area to be improved while promoting compaction. Based on the improved depth set and the normal drain material spacing in claim 1 for controlling subsidence of the consolidation promoting portion by appropriately selecting the combination of the distance between the drain material in the compaction promoting region width and the consolidation promoting portion The ground improvement method described.

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