JP4463568B2 - Reinforcement method for soft ground - Google Patents

Description

  The present invention is a soft ground countermeasure construction method, especially a ground reinforcement construction method for preventing slip failure or uneven settlement, which may occur due to insufficient support capacity or compaction of the ground when building embankments on the soft ground. Further, the present invention relates to a method for promoting attenuation of traffic vibration generated by a vehicle or the like traveling on a structure such as embankment built on soft ground.

In Japan, the land area is small and there are few flat lands, and the flat terrain often forms soft ground, so the use of soft ground is unavoidable in new construction work. There are many.
Under these circumstances, various methods for improving soft ground have been studied and put into practical use. The soft ground improvement can be broadly divided into those for improving characteristics such as consolidation, drainage, compaction, or consolidation of soft ground, and reinforcement of soft ground by adding an external structure to the soft ground. It can be divided into those that aim to. Typical examples of the former include vertical drain methods such as sand drains, sand compaction pile methods, methods of injecting chemicals such as water glass, etc., and representative examples of the latter include surface coating methods that coat the surface with geotextiles, etc. There is a pile method that directly supports the superstructure with piles.
Edited by the Japan Geotechnical Society "Soft Ground Countermeasure Method"

The surface coating method that covers the surface with geotextile, which belongs to one of the above-mentioned soft ground countermeasure construction methods, is a soft ground improvement construction method that uses geotextiles recently developed as civil engineering materials. It is a construction method based on such an idea. As shown in Fig. 1, when the embankment 2 as a roadbed / roadbed is built on the soft ground 1, the soft ground below the embankment 2 slips due to lateral flow due to the uneven settlement of the center of the embankment 2 over time. It is well known that it causes the depression of the embankment 2 as a result.
As a measure to prevent such a phenomenon, a reinforcement method using geotextile was devised, and in this method, a reinforcing material 3 was arranged on the foundation of the embankment 2 itself as shown in FIG. By preventing the uneven settlement of the embankment 2, as a result, the lateral flow of the soft ground below the embankment 2 is prevented, and the reinforcing material 3 is disposed on the upper surface side of the soft ground 1 as shown in FIG. In some cases, lateral flow of the ground 1 is prevented. In either case, the basic idea is that a tensile axial force is generated in the geogrid, whose displacement is restricted by the frictional resistance with the ground, due to the vertical downward displacement that is maximum around the center of the geogrid. Thus, this axial force and the supporting force of the soft ground are intended to counter the loading load such as embankment (see FIG. 4).

By the way, in the type of reinforcement method as described above, in the former type in which the reinforcing material is arranged on the foundation of the embankment itself, the soft ground itself is not directly reinforced, so the softness of the soft ground When is large, the design is restricted by the relationship with the width of the embankment. That is, if the width of the embankment is narrow, lateral flow of the soft ground is unavoidable. Conversely, if the embankment width is large, multiple layers of reinforcing material are used to prevent uneven settlement across the entire width of the embankment. If not prepared, it will not be effective and will require time and cost for construction.
On the other hand, in the latter type in which the reinforcing material is arranged on the soft ground side, in order to effectively prevent the lateral flow of the ground, the laying width of the reinforcing material is sufficiently longer than the width of the embankment, and the soft ground It is necessary to be able to cope with the uneven settlement of the embankment, so that sufficient construction sites can be prepared on both sides of the soft ground where the embankment is made, and As a measure for increasing the frictional resistance with the soft ground, for example, the covering soil layer 4 as a pressing load as shown in FIG.

The first object of the present invention is to provide means for effectively preventing the lateral flow of the soft ground on the soft ground side, when embankment, covering soil, structures, etc. are constructed on the soft ground. And
The second object of the present invention is to provide a construction method that effectively prevents the lateral flow of the soft ground even when the width of the available soft ground is relatively small.
A third object of the present invention is to provide means for effectively attenuating vibrations transmitted to soft ground through embankment, covering soil, and other structures constructed on soft ground.

According to the first aspect of the present invention, on the soft ground, the intermediate portion is laid on the soft ground, and both sides continuous to the intermediate portion are singly from the surface of the laying without any other buried objects, and the soft ground. A soft ground reinforcement method is provided in which the geogrid is laid and fixed so as to be sufficiently inserted in the vertical lower direction of the ground.
This makes it possible to increase the tensile resistance of the geogrid even in a land where the usable width of the soft ground is narrow, so that the uneven settlement of the upper structure such as embankment can be effectively prevented.
Furthermore, the geogrid fully inserted in the lower direction of the soft ground works effectively as a reinforcing material against shear failure of the soft ground, and the side flow of the lower soft ground such as embankment is effective due to a synergistic effect with the above effect. Can be prevented.

According to the invention of claim 2, in the invention of claim 1, the same geogrid is laid and fixed in multiple layers .
This provides a method for reinforcing a soft ground having a shape in which the effects of the present invention are superimposed.

According to the invention described in claim 3, in the invention described in claim 1, the central region of the geogrid is deformed into a cross-sectional groove shape and is laid and fixed.
This provides a soft ground reinforcement method in which the tensile strength of the geogrid is even greater.
In addition, since a tensile force can be effectively generated in the geogrid, it is easy to cause an elongation displacement in the geogrid, and this elongation displacement causes a displacement that tends to shift between the geogrid and the soft ground. Cause it to occur. Such both displacements can effectively damp vibrations such as vehicle traffic transmitted from a structure built on top of the geogrid.

According to the invention described in claim 4, it is provided that the geogrids adjacent in the longitudinal direction of the superstructure such as embankment to be constructed are laid and fixed so as to form a staggered arrangement with each other .
Thereby, even when the soft ground is meandering, an effective reinforcing method for the soft ground is provided.

According to the fifth aspect of the present invention, there is provided a soft ground reinforcement method for laying and fixing a geogrid on the soft ground so that the four sides are sufficiently inserted in the lower direction of the soft ground.
This provides an effective reinforcement method for forming an independent embankment or the like for an independent structure on soft ground.

As shown in FIG. 5, in the present invention, the intermediate portion or the main plane portion of the geogrid 3 is the same as the prior art in that it is laid on the soft ground 1 in the width direction of the embankment 2, for example. 3, both sides in the width direction are sufficiently inserted in the lower direction of the soft ground 1, and the geogrid is used three-dimensionally.
That is, the intermediate portion or the main plane portion of the geogrid 3 is laid on the soft ground 1 and covered with the thin soil covering layer 4 or not covered, or laid in the soft ground as in the conventional example. However, both sides in the width direction of the geogrid 3 are bent vertically downward from the intermediate portion or the main plane portion of the geogrid 3, and a sufficient length is inserted in the lower portion of the soft ground 1.

When the geogrid 3 is configured in this way, as shown in FIG. 6, the load of the embankment 2 loaded on the soft ground presses the intermediate portion or the main plane portion of the geogrid 3 downward. Such force is supported mainly by the supporting force of the ground 1 and, in addition, when the geogrid 3 is made of an elastic material, its elastic restoring force. That is, when the embankment 2 is large, the uneven settlement due to the embankment 2 causes the middle main plane portion of the geogrid 3 to be deformed downward and the geogrid 3 to be pulled out in the center direction. Since both sides are sufficiently deeply inserted into the soft ground, this pulling displacement is constrained by the frictional resistance between the ground 1 and the geogrid 3, and as a result, a sufficient tensile force is generated in the geogrid. A part of the embankment load is supported as an elastic restoring force. Further, the tensile force generated in the geogrid 3 restrained on both sides brings about the action of pulling the entire geogrid portion inserted into the soft ground in the center horizontal direction of the geogrid 3, and at the same time the soft ground 1 This restrains the displacement of the inner part of the geogrid to flow laterally in the outer direction.
Alternatively, when both sides of the geogrid are inserted into the soft ground at a sufficient depth, the insertion part of the geogrid is reinforced against slip failure formed in the soft ground around the lower part of the embankment 2 Also acts as a material to suppress lateral flow.
That is, according to the configuration of the present invention, since the deformation of the intermediate portion or the main plane portion of the geogrid 3 is effectively prevented, the lateral flow of the soft ground below the embankment is effectively prevented. It is.
In addition, even if a downward deformation occurs, in the present invention, unlike the conventional example (see FIG. 4) in which the embossment on both sides of the embankment is caused by lateral flow, the laying structure of the geogrid is constructed on both sides of the embankment. It is noted that the bulges can be relatively disturbed. When the embankment continues in the longitudinal direction, in the construction method according to the present invention, the unit-width geogrid is arranged in parallel in the longitudinal direction of the embankment, and adjacent portions of the intermediate portion or the main plane portion are sewn together, for example. Are installed side by side.

The geogrid used in the present invention is not particularly limited in its material and grid structure (for example, the shape of the grid and the distribution density of the grid), but may have the following characteristics with respect to the actual soft ground. It is considered necessary.
(1) The structure has a sufficiently large pulling resistance (friction resistance) against soft ground;
(2) It has a structure that does not block the relationship between embankment and soft ground in soft ground;
(3) The structure does not hinder drainage and consolidation;
(4) A material having elasticity is more preferable;
Considering the characteristics as described above, a plastic, for example, a geogrid made of polyethylene can be given as a representative example.
Appropriate geogrid (material, structure) suitability for each actual soft ground can be examined in the field test or in the laboratory based on the collected soil samples.

As a means for inserting both sides of the geogrid sufficiently deep into the soft ground, it is conceivable to use an apparatus itself known as a plastic board drain placing machine or an improved apparatus. That is, there is a plastic board drain method as one of the methods currently known as vertical drain methods. As such a plastic board placing machine, a wire type, a vibro type, a friction wheel type, a chain drive type, a rack Gear type, hydraulic jack type and other devices are known, and these devices are used, or these devices are considered to be limited in the width of the plastic board inserted into the ground. It is conceivable to use an improved type utilizing the technical idea of the device. Alternatively, even in such a device, when the insertion width is further limited, one piece is used for the middle part or the main plane part of the geogrid, but both sides thereof are in the longitudinal direction of the embankment (if it is a road) It is also possible to make a cut in the direction of the road) and make each side multiple pieces and insert them one by one into the ground.
In this way, even when using the one with both sides of the geogrid cut in the longitudinal direction of the embankment, it is considered that there is not much difference in tensile resistance etc., and the basic technical idea of the present invention is impaired is not.

The present invention can be implemented in various forms in addition to the embodiment shown in FIG. 5 as described above.
FIG. 7 shows an example in which the geogrid 3 is laid in multiple layers.
In this case, a structure in which the intermediate portion or the central plane portion of each geogrid 3 is overlapped and only both sides are separated from each other can be considered.

  In the embodiment shown in FIG. 8, the intermediate portion or the main plane portion of the geogrid 3 is laid and fixed by bending the cross section into a groove shape. In such an embodiment, since a geogrid portion is formed along the non-settlement direction on both sides of the middle portion or the main plane portion of the geogrid 3, it is easy to introduce a tensile force into the geogrid, and the laying area As a result of the expansion, a greater pulling resistance is expected, and the ground uplift on both sides of the embankment due to the lateral flow is more effectively prevented.

  In the embodiment shown in FIG. 9, the geogrids 3 adjacent in the longitudinal direction of the embankment (for example, the road direction) are arranged in a staggered manner. This is considered to be an effective laying structure when soft ground meanders in the longitudinal direction of the planned embankment.

  The embodiment shown in FIG. 10 shows an example in which the geogrid 3 is inserted sufficiently deep into the soft ground from each of the four sides of the middle part of the geogrid 3 or the main plane part, and such soft ground reinforcement is shown. The construction method is considered to be suitable for supporting the embankment 2 and the like having independent shapes on the four sides.

  According to the invention of the present application, since both sides of the geogrid are sufficiently deeply inserted into the soft ground on the soft ground below the planned structure such as embankment or the like, the pullout resistance of the geogrid is large, and the soft ground below the embankment In addition to effectively preventing lateral flow, it is possible to prevent as much as possible the uplift of the ground on both sides of the embankment that could not be hindered by the conventional planar geogrid laying method.

It is typical sectional drawing which shows the side flow of the soft ground of the embankment lower part. It is sectional drawing of the prior art example which laid the planar geogrid in the foundation part of the embankment. It is sectional drawing of the prior art example which laid the planar geogrid on the soft ground. It is typical sectional drawing which shows the effect | action of the geogrid resisting the uneven settlement of embankment in the construction method of the prior art example of FIG. It is sectional drawing which shows the laying form of the geogrid by this invention. It is typical sectional drawing which shows the effect | action of the geogrid resisting the uneven settlement of the embankment in the construction method of FIG. It is sectional drawing of the example which laid the multilayer geogrid. It is sectional drawing of the example which made the groove | channel type the intermediate part or main plane part of the geogrid. It is a perspective view of the example which has arranged geogrid in a zigzag form. It is a perspective view of the example which inserted the 4th circumference of the geogrid in the soft ground.

Explanation of symbols

  1 ... Soft ground, 2 ... Filling, 3 ... Reinforcement material (Geogrid)

Claims (5)

On the soft ground, the middle part is laid on the soft ground, and both sides continuous to the middle part are laid on the soft ground H in the vertical lower direction of the soft ground alone without any other buried objects. Reinforcement method for soft ground, characterized by laying and fixing the geogrid so that it can be fully inserted.   The reinforcing method according to claim 1, wherein the geogrid is laid and fixed in multiple layers.   The reinforcing method according to claim 1, wherein the center region of the geogrid is deformed and fixed in a cross-sectional groove shape.   The reinforcing method according to claim 1, wherein the geogrids adjacent to each other in the longitudinal direction of the superstructure such as embankment to be constructed are laid and fixed so as to form a staggered arrangement with each other.   2. The reinforcing method according to claim 1, wherein a geogrid is laid and fixed on the soft ground so that all four sides are sufficiently inserted in a lower direction of the soft ground.

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