JPH01125415A - Preventing work for liquefaction of ground by banded drain material - Google Patents

Abstract

PURPOSE:To prevent the liquefaction of the ground by a method in which a banded drain material formed by covering a water-passing material having may water paths connected in the longitudinal direction in parallel between its water-passing plates with a nonwoven fabric is driven into sandy ground. CONSTITUTION:The surface of a water-passing material 2 having mutually facing wide faces as water-passing plate faces 2A, with a nearly rectangular cross section, is covered with a nonwoven fabric 3 to make up a banded brain material 1. In the material 2, a number of water paths 2B connected in the longitudinal direction are formed in parallel dividedly by many ribs 2C, and many water holes 2E are formed in many grooves 2D formed in the plate face 2A. The drain material 1 is driven into sandy ground to discharge water in the ground and also to drain excess void water during earthquake.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for preventing liquefaction of soft ground using a belt-shaped drain material for preventing liquefaction of soft ground during an earthquake.

(Prior art) Due to repeated shearing forces caused by earthquakes, water-saturated, low-density sandy ground loses its effective stress due to the sudden increase in the pressure of pore water existing between soil particles, causing it to become as if it were a liquid. behave. This phenomenon is called ground liquefaction.

Conventionally, methods to prevent liquefaction of the ground include methods that increase the density of the ground to increase its strength (sand compaction method, vibrorod method, etc.), and methods that quickly dissipate pore water in the soil to prevent liquefaction. Drainage methods that prevent drainage (gravel drain method, drain pipe method) are mainly used.

In recent years, as the earthquake resistance of existing structures has been reviewed and ground reinforcement has been carried out around the structures, drainage methods are increasingly being used.

(Problems to be solved by the invention) However, the gravel lane construction method, which is a typical example of a drainage construction method, uses crushed stone, which requires a lot of effort to transport to the site, and the construction equipment is large, making it difficult to improve the area. There was a problem with being limited. Furthermore, in the gravel drain construction method, soil particles flow into the gaps between crushed stones due to fluctuations in groundwater.
There was a problem that clogging easily occurred, and it was difficult to say that liquefaction could be prevented for a long period of time.

An object of the present invention is to provide a method for preventing ground liquefaction using a strip-shaped drain material that is easy to transport, does not require large machinery, and is less likely to become clogged.

(Means for Solving the Problems) To explain in detail the present invention for achieving the above object, the method for preventing ground liquefaction using a belt-shaped drain material according to the present invention has a cross section that is approximately rectangular. A water-permeable material whose wide surfaces facing each other are water-permeable plate surfaces, and a nonwoven fabric covering the surface of the water-permeable material, and a water-permeable channel that continues in the longitudinal direction of the water-permeable material is provided between the two sides. The water passage plate surfaces are partitioned by a plurality of ribs connected at intervals in the width direction, and a plurality of ribs are arranged in parallel in the width direction, and both water passage plate surfaces have grooves along the width direction in the longitudinal direction. A belt-shaped drain material is used, in which a large number of holes are formed at intervals, and each of the valley grooves has a large number of water holes communicating with the water passage, and the belt-shaped drain material is driven into sandy ground. draining excess pore water in the sandy ground during an earthquake from the material, and penetrating the sandy ground into the ground where the sandy ground exists on unconsolidated soft ground with the belt-shaped drain material. It is characterized by being driven into soft geological formations to promote consolidation by draining water in the soft geological formations, as well as to drain excess pore water in sandy ground during earthquakes.

(Function) When such a strip-shaped drain material is used, a large number of grooves along the width direction are provided on both water-passing plate surfaces of the water-passing material at intervals in the longitudinal direction. It also becomes easier to roll up during transport, making it easier to transport to the site. In addition, by using such a strip-shaped drain material, it is possible to use a conventional paper tray driving machine that has traditionally been used to promote consolidation of soft ground, making it possible to perform construction even on relatively soft and rough roads. There is no problem as it is possible and the pouring method has been established. Since this strip-shaped drain material has a non-woven filter layer on its surface, clogging of each passageway inside the strip-shaped drain material can be prevented. In addition, excess pore water generated during earthquakes is
These drainage channels that do not clog can quickly drain water when it occurs, preventing liquefaction of sandy ground during earthquakes.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In the present invention, the strip-shaped drain material conventionally used for promoting consolidation of soft ground is improved and used. First, specific examples of the structure of the novel strip-shaped drain material 1 used in the present invention are shown in FIGS. This will be explained with reference to the figures.

This strip-shaped drain material 1 has a water-permeable material 2 whose cross section is approximately rectangular and whose opposing wide surfaces serve as water-permeable plate surfaces 2A.
and a nonwoven fabric 3 that covers the surface of the water permeable material 20. The water-permeable material 2 has a width W of 100 to 150 mm and a thickness T of 0.
It has a rectangular cross-sectional shape of about 15w. In the water passage material 2, there are a plurality of water passages 2B that are continuous in the longitudinal direction and partitioned by a plurality of ribs 2C that connect both water passage plate surfaces 2A at intervals in the width direction. They are installed in parallel.

There are 5 grooves 2D along the width direction on both water passage plate surfaces 2A.
They are formed in large number with a width of about fi and spaced apart from each other by about 5 lengths in the longitudinal direction. The grooves 2D are formed so as to exist in the longitudinal direction of both water passage plate surfaces 2A. Each groove 2
Inside D, a large number of rectangular water holes 2E communicating with the water passage 2B are formed along the longitudinal direction of the groove 2D. The water-permeable material 2 is made of a resin material such as vinyl chloride or polyethylene whose hardness and softness can be controlled by adjusting the composition.

Such a belt-shaped drain material 1 is formed by dividing the water passage 2B between both water flow plate surfaces 2A and the ribs 2C, and is designed not to be crushed by the restraining pressure in the ground. There is an advantage that the water permeability does not decrease even when confining pressure is applied, and the decrease in water permeability can be suppressed even when the length is increased. Furthermore, due to the material of the water passing material 2 and the presence of the grooves 2D on the surfaces of both water passing plate surfaces 2A, it is possible to follow the deformation of the ground, and it is also easy to wind up into a roll shape, making it easy to transport.

Figure 5 shows conventional strip-shaped drain materials A, B, and C, and the new strip-shaped drain material D used in this invention (width 100 fi during testing).
, the thickness is set to Low. ) shows the water flow rate when the lateral pressure during the test was increased step by step, taking into account the confining pressure in the soil. As a result, the new strip-shaped drain material used in this invention is different from the conventional strip-shaped drain materials A and B.
It was found that the water flow rate was about three times larger than that of , C, and it did not affect the lateral pressure.

Therefore, in the present invention, such a novel strip-shaped drain material 1
As shown in FIG. 6, the concrete is cast almost vertically into, for example, sandy ground 4 with a loose density. In Fig. 6, 5 is the groundwater level, 6 is a crushed stone mat provided on the surface of the sandy ground 4,
7 shows the seismic force, 8 shows the movement of pore water at that time, and 9 shows the movement of drainage from the belt-shaped drain material 1 at that time.

In this way, if the belt-shaped drain material l is cast in the sandy ground 4 using a pouring machine, when an earthquake cuff is applied, the saturated pore water in the sandy ground 4 will be spread out in the belt-like shape as shown by the arrow 8. It is collected in the drain material 1 and drained as shown by the arrow 9 to prevent liquefaction.

Next, the effect of the ground liquefaction prevention construction method using the belt-shaped drain material of the present invention will be explained using a comparative example with a conventional construction method based on an indoor experiment.

FIGS. 7(A) and 7(B) show an experimental facility that does not use the strip-shaped drain material 1 and the state of liquefaction of saturated sand with a loose density during vibration in this facility. That is, in FIG. 7(A), saturated sand 11 with a loose density is placed in a soil tank 10, and the saturated sand 1
A pore water pressure gauge 12 is set at point P in 1, and the saturated sand 11 is
An example of experimental equipment is shown in which no strip-shaped drain material is inserted. FIG. 7(B) shows the temporal change in the excess pore water pressure ratio at point P when a vibration experiment was conducted using the equipment shown in FIG. 7(^). Here, ΔU is excess pore water pressure, δV′
is the effective overburden pressure and ΔU/δV′ is the excess pore water pressure ratio.

In this case, ΔU/δV' in the sand is approximately 1, indicating that the ground has completely liquefied and behaves like water.

Figure 8 (A) (B) shows conventional gravel drain material 13
This figure shows the experimental equipment using this equipment and the state of liquefaction of loose saturated sand during vibration using this equipment. That is, Figure 8 (^
) is filled with saturated sand 11 having the same density as shown in FIG. This figure shows an example of experimental equipment in which pore water pressure gauges 5 are set at points 21, 22, and P3 out of 11, respectively. Figure 8 (B) shows 21 points when a vibration experiment was conducted using the equipment shown in Figure 8 (A).

This figure shows the temporal changes in the excess pore water pressure ratio at point 22 and point P3. This figure shows that even if a gravel drain is used, excess pore water pressure may increase in the saturated sand 11.

Figures 9 (A) and 9 (B) show experimental equipment using the belt-shaped drain material 1 of the present invention and loose saturated sand 11 during vibration in this equipment.
This shows the behavior of That is, in FIG. 9(A), saturated sand 11 having the same density as that in FIG.
This shows an example of experimental equipment in which a pore water pressure gauge 5 is installed at the PI point, P2 point, and PJ point in the strip-shaped drain material 1 and the saturated sand 11. .

FIG. 9(B) shows temporal changes in the excess pore water pressure ratio at points P1, P2, and P3 when a vibration experiment was conducted using the equipment shown in FIG. 9(A). As is clear from the figure, according to the present invention, no liquefaction phenomenon occurs in the saturated sand 11, and it has become clear that it can be used as a countermeasure against liquefaction.

FIG. 10 shows an example in which the construction method of the present invention can be implemented even in the vicinity of an existing structure 14. In the figure, 15 is soft ground on the surface of the sandy ground 4 with a loose density, and 16 is a belt-shaped drain material casting machine.

As described above, this invention only uses a strip-shaped drain material (for example, width 100n, thickness 10mm) which is thicker than the conventional strip-shaped drain material (eg, width 100n, thickness 3mm). It is possible to use a pouring machine, and it is also possible to perform construction even on soft ground, making it possible to take measures to prevent liquefaction even in places where conventional large machines could not handle it.

FIG. 11 shows an example in which the present invention is applied to a composite ground in which the surface layer is sandy ground 4 and there is unconsolidated soft ground 17 underneath. That is, in the present invention, in this case, the belt-shaped drain material 1 is cast across both the ground 4 and 17, and crushed stone is provided on the surface of the ground 4.

FIG. 12 shows the function of the strip-shaped drain material 1 during consolidation when constructed as shown in FIG. 11. Note that parts corresponding to those in FIG. 6 are designated by the same reference numerals. That is, in this case, consolidation settlement shown by arrow 18 occurs in the unconsolidated soft ground 17, and as a result, pore water in the ground 17 flows as shown by arrow 8.
The water is collected in a belt-shaped drain material 1 as shown by , and drained as shown by an arrow 9 . As the consolidation of ground 17 progresses,
The strip-shaped drain material 1 in the ground 17 is curved in a meandering manner as shown in the figure to accommodate this.

FIG. 13 shows the action of the band-shaped train material 1 when the earthquake cuff acts after the ground 17 has been consolidated as shown in FIG. 12. In this case, saturated pore water in the sandy ground 4 is collected in the belt-shaped drain material 1 as shown by arrow 8 and drained as shown by arrow 9 to prevent liquefaction.

That is, if the construction shown in FIG. 11 is carried out, two effects can be expected: promotion of consolidation of the lower soft ground 17 and prevention of liquefaction of the upper sandy ground 4.

Figure 14 (8) (B) (C) (D) shows soft ground 1
7 is a schematic diagram of the construction process of the conventional belt-shaped drain construction method for promoting consolidation in the case where measures to prevent liquefaction are taken on the upper mold sand. That is, Fig. 14 (A) shows an unconstructed state, and Fig. 14 (B) shows a conventional type belt-shaped drain material (for example, 100 mm wide and 3 m thick) with sand 19 laid on soft ground 17.
Fig. 14 (C) shows the state in which molding sand 21 is placed on top of the sand 19 and consolidation is performed, and Fig. 14 (D
) shows the state in which the mold sand 21 is being compacted. That is, in conventional construction, measures to prevent liquefaction of the upper mold sand 21 are taken after the consolidation of the lower soft ground 17 is completed.

FIGS. 15(A), 15(B), and 15(C) are schematic diagrams of the process in which the construction method of the present invention is applied to promote consolidation of the soft ground 17, and in which measures are taken to prevent liquefaction of the upper mold sand. That is, FIG. 15(A) shows the unconstructed state, FIG. 15(B) shows the state where the molding sand 21 is placed on the soft ground 17, and FIG. This figure shows the state in which the belt-shaped drain material 1 has been cast using the construction method described above, and crushed stone matsutoro has been placed on top of the molding sand 21. That is, when the construction method of the present invention is used, consolidation of the lower soft ground 17 is promoted and the upper mold sand 21 is
The same strip-shaped drain material 1 can prevent liquefaction of the drain material 1, and the process can be shortened.

(Effects of the Invention) As explained above, the ground liquefaction prevention method of the present invention aims to prevent liquefaction by using a belt-shaped drain material that is an improved version of the conventional belt-shaped drain material. Therefore, it is possible to perform construction even on relatively soft and rough roads, and the casting method has been established, so there are no problems in construction. And also,
The strip-shaped drain material used in the present invention has grooves along the width direction at intervals in the longitudinal direction on the double-channel water plate surface of the water-permeable material, so it is easy to roll up during transportation, and therefore it can be easily rolled up at the site. It is easy to transport to the ground, and it has the advantage of being curved to accommodate the consolidation of the ground. Furthermore, this strip-shaped drain material has a double-channel water plate surface and a plurality of ribs between them to ensure that the necessary cross-sectional area of the water passageway will not be crushed.Moreover, there is a filter made of non-woven fabric on the surface to prevent the water passageway from being crushed. Since it is designed to prevent clogging, it can prevent deterioration in drainage performance, allow for early drainage of excess pore water that occurs during earthquakes, and has the advantage of excellent liquefaction prevention performance. .

[Brief explanation of the drawing]

FIG. 1 is a plan view of an example of the belt-shaped drain material used in the present invention with a portion of the nonwoven fabric removed, FIG. 2 is a side view of the same, and FIG.
The figure is a vertical side view of the same, Figure 4 is a cross-sectional view taken along the line IV-TV in Figure 3, Figure 5 is a comparison diagram of the change in water flow rate with respect to lateral pressure of the present invention and the conventional belt-shaped drain material, and Figure 6 is Vertical cross-sectional views of the ground showing an example of the construction state of the present invention, Fig. 7 (A), Fig. 8 (A), and Fig. 9 (A) show the case where no measures are taken in saturated sand, and the case where no measures are taken in saturated sand, and The vertical cross-sectional views of the experimental equipment when the drain material is installed and when the belt-shaped drain material of the present invention is installed, FIG. 7 (B), FIG. 8 (B), and FIG. 9 (B) are the above-mentioned Excess pore water pressure ratio characteristic diagram showing changes in excess pore water pressure ratio during foreshock in experimental equipment;
Figure 1 is a longitudinal cross-sectional view showing the construction state of the present invention on a layered ground consisting of unconsolidated soft ground and loose sandy ground;
Figures 12 and 13 are explanatory diagrams showing the operation during consolidation and earthquake in the construction state shown in Figure 11, and Figures 14 (8) to (8)
D) is a process diagram for promoting consolidation of soft ground and preventing liquefaction using the conventional method, and Figures 15 (A) to (C) are process diagrams for promoting consolidation of soft ground and preventing liquefaction using the construction method of the present invention. It is a process diagram. 1... Belt-shaped drain material, 2... Water-permeable material, 2A...
Water flow plate surface, 2B... Water flow path, 2C... Rib, 2D.
...Groove, 2E...Water hole, 3...Nonwoven fabric, 4...
Sandy ground, 6... crushed〕φ:) (E) lip) It yield, -1. Go, [11 7△-9/rlV ward 7△≠V kuto, △≠V ku■ faction

Claims (2)

[Claims] (1) A water-permeable material having a substantially rectangular cross section and opposite wide surfaces serving as water-permeable plate surfaces, and a nonwoven fabric covering the surface of the water-permeable material; has a plurality of water passages that are continuous in the longitudinal direction and are partitioned by a plurality of ribs that connect the two water passage plate surfaces at intervals in the width direction, and are arranged in parallel in the width direction; uses a band-shaped drain material in which a large number of grooves are formed along the width direction at intervals in the longitudinal direction, and each groove has a large number of water holes communicating with the water passage, A method for preventing ground liquefaction using a strip-shaped drain material, characterized in that a drain material is driven into sandy ground, and excess pore water in the sandy ground is drained from the strip-shaped drain material during an earthquake. (2) A water-permeable material having a substantially rectangular cross section and opposite wide surfaces serving as water-permeable plate surfaces, and a nonwoven fabric covering the surface of the water-permeable material; has a plurality of water passages that are continuous in the longitudinal direction and are partitioned by a plurality of ribs that connect the two water passage plate surfaces at intervals in the width direction, and are arranged in parallel in the width direction; uses a band-shaped drain material in which a large number of grooves are formed along the width direction at intervals in the longitudinal direction, and each groove has a large number of water holes communicating with the water passage, A drain material is driven into the soft ground where sandy ground exists on unconsolidated soft ground, penetrating the sandy ground and driving it into the soft ground to drain water in the soft ground to promote consolidation and to prevent earthquakes. A construction method for preventing ground liquefaction using a belt-shaped drain material, which is characterized by draining excess pore water in sandy ground.