JPH0684614B2 - Soft ground improvement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention aims to prevent liquefaction of sandy soft ground,
Gravel (gravel, crushed stone,
The present invention relates to a soft ground improvement device for burying piles (hereinafter referred to as gravel piles) made of gravel and slag.

(Prior art) While the gravel used for this type of construction is required to have sufficient water permeability for the ground sand, it should not cause clogging inside the gravel pile when it flows into the gravel pile. is necessary. However, conventional gravel piles that are generally formed have a completely random distribution when the grain composition of the gravel is viewed in the cross section of the pile,
There is a problem that the sand of the surrounding ground easily flows into the gravel pile together with water and is easily clogged inside the gravel pile, which hinders the water absorption function of the gravel pile and prevents sufficient drainage.

As a solution to this problem, as described in JP-A-61-246416, a coarse gravel having a large particle size is used in the central part and a fine gravel having a small particle size is used in the outer peripheral part. A gravel pile composed of the following is proposed. According to such a gravel pile, in the sandy soft ground, the sand in the original ground is filtered by the fine gravel layer on the outer periphery of the pile, that is, the filter layer, and only the soil particles having an extremely small particle diameter are water. With the rough gravel layer in the center of the pile,
That is, since it flows into the drain layer, it is difficult for the drain layer to be clogged, and therefore, the water permeability function and the drainage function of the gravel pile can be sufficiently exerted to effectively prevent the liquefaction of the ground.

By the way, in order to form a gravel pile having a double structure consisting of such a drain layer in the central portion and a filter layer in the outer peripheral portion, it has hitherto been done in the above-mentioned JP-A-61-246416 or JP-A-49-246416. A device as described in 98011 is used.

That is, the devices described in these publications are provided with an outer tube and an inner tube inserted into the outer tube, a fine gravel supply hopper is provided at the upper end of the outer tube, and a rough gravel is provided at the upper end of the inner tube. Each gravel supply hopper is provided, and both inner and outer pipes are penetrated into the ground to a predetermined depth, and then both pipes are pulled up to make a rough gravel from the lower end of the inner pipe and the gap between the inner and outer pipes. Eject each fine gravel from the section,
A double-layer gravel pile having a drain layer at the center and a filter layer at the outer periphery is formed in the ground.

(Problems to be Solved by the Invention) In the conventional device as described above, the gravel having a large particle size and the fine gravel having a small particle size are selected in advance, and these two types of gravel are selected. Gravel,
Since it is necessary to separately supply the hopper for supplying coarse gravel and the hopper for inputting fine gravel, it takes a lot of time and labor to select the gravel before construction of the gravel pile, and at the same time, both hoppers for the gravel during the construction can be removed. There is a problem that the individual supply work of gravel is very troublesome.

In view of the above-mentioned problems, the present invention automatically supplies a mixed gravel mixed with large and small particle sizes to a single hopper and automatically sifts it into a large particle size gravel and a small particle size gravel. The gravel with a large particle size is introduced into the outer pipe, and the gravel with a small particle size is introduced into the annular space between the outer and inner pipes, which simplifies the work and significantly improves the construction efficiency. Is provided.

(Means for Solving the Problem) In the soft ground improving apparatus according to the present invention, the inner pipe 9 is inserted and deployed in the fixed casing 8, and the large and small particle sizes are provided above the fixed casing 8 and the inner pipe 9. A hopper 10 is provided for supplying a gravel that is appropriately mixed with the gravel. Between the hopper 10 and the fixed casing 8 and the inner pipe 9, the gravel dropped from the hopper 10 is large and small. The gravel G ₁ having a large particle size is introduced into the inner tube 9, and the gravel G ₂ having a small particle size is introduced into the annular space 11 between the fixed casing 8 and the inner tube 9.
The sieving device 14 to be introduced into

(Operation) In this soft ground improvement device, by introducing a gravel in which a gravel having a large particle size and a gravel having a small particle size are mixed into the hopper 10, the mixed gravel is changed into a sieve device 14 The gravel having a large particle size and the gravel having a small particle size are sifted by the gravel, the large particle gravel G ₁ is introduced into the inner pipe 9, and the small particle gravel G ₂ is fixed casing 8 and the inner pipe 9. And is introduced into the annular space portion 11.

Then, after the fixed casing 8 and the inner pipe 9 are penetrated to a predetermined depth in the ground, the casing 8 and the inner pipe 9 are pulled out to push out the large particle gravel from the lower end of the inner pipe 9 and, at the same time, the annular space. A gravel of small particle size was extruded from the lower end of the part 11, and formed in the ground so as to surround the drain layer 19 of the large particle size gravel G ₁ and the outer periphery of the drain layer by the small particle size gravel G ₂ . Filter layer
A desired gravel pile P consisting of 20 is formed.

(Example) An example will be described with reference to the drawings.

FIG. 1 shows an embodiment of a soft ground improving apparatus according to the present invention. In FIG. 1, reference numeral 1 is a machine frame suspended up and down by a leader (not shown) installed upright on a crawler crane or the like. At the lower part of the machine frame 1, a rotary casing 3 having a screw 2 on its outer peripheral surface is rotatably suspended.

The machine frame 1 is provided with a pair of drive motors 4, 4 on both sides, and small gears 5, 5 fixed to the output shafts of both motors 4, 4.
Is meshed with the large gear 6 fixed to the upper end of the rotary casing 3 from both sides thereof, and the rotary casing 3 is rotationally driven by starting each motor 4. A shoe (bottom lid) 7 is attached to the lower end of the rotary casing 3 so as to be openable and closable.

A fixed casing 8 is fitted in the rotary casing 3, and the fixed casing 8 has its upper end required portion fixed to the machine casing 1. And this fixed casing 8
The inner pipe 9 is inserted and deployed therein with a sufficient space maintained between the inner pipe 9 and the inner peripheral surface of the fixed casing 8, and an annular space 11 is provided between the inner pipe 9 and the fixed casing 8. It is formed. The lower end of the inner pipe 9 slightly projects from the lower end of the fixed casing 8.

Above the fixed casing 8 and the inner pipe 9, there is provided one hopper 10 for supplying a gravel in which a gravel having a large particle size and a gravel having a small particle size are appropriately mixed, and the hopper 10 and the fixed casing 8 are provided. A sieve device 14 having sieves 12, 13 arranged in a plurality of stages, for example, two stages, is interposed between the inner pipe 9 and the inner pipe 9. The sieving device 14 has a closed housing 16 formed in a cylindrical shape with a large diameter between the discharge port 15 of the hopper 10 and the upper end of the fixed casing 8, and the housing 16 has the two-stage sieving device. The gravel dropped from the discharge port 15 of the hopper 10 is screened into a large particle size and a small particle size, and a large particle size gravel is introduced into the inner pipe 9. The gravel having a small particle size is introduced into the annular space 11 between the fixed casing 8 and the inner pipe 9.

Therefore, when the hopper 10 is supplied with a gravel in which a gravel having a large particle diameter and a gravel having a small particle diameter are appropriately mixed, the gravel supplied to the hopper 10 has a relatively rough texture on the upper stage side. The gravel with a small particle size, which has been dropped onto the sieve 12 and passed through the mesh of the upper side sieve 12, is applied to the sieve 13 on the lower side, and the gravel with the large particle size remaining on the upper side sieve 12 is on the lower side sieve 13. Only the gravel with a large connecting diameter which flowed down to the lower stage sieve 13 and remained on the lower side sieve 13 was introduced into the inner pipe 9, and the gravel with a small particle size which passed through the mesh of the lower stage sieve 13 was fed to the inner pipe 9 and the fixed casing 8. It is introduced into the annular space 11 between them.

Then, after the fixed casing 8 and the inner pipe 9 are penetrated to a predetermined depth in the ground, the casing 8 and the inner pipe 9 are pulled out to push out the large particle gravel from the lower end of the inner pipe 9 and, at the same time, the annular space. A gravel having a small particle size is extruded from the lower end of the portion 11 and is composed of a drain layer having a large particle size gravel in the ground and a filter layer formed by the small particle size gravel so as to surround the drain layer. Gravel piles will be formed.

The discharge port 15 of the hopper 10 is provided with an opening / closing valve 17 for opening and closing the discharge port 15 and an air supply nozzle 18 as air supply means. This on-off valve 17
Is a well-known one, for example, it is always in the valve opening position as shown by the phantom line in FIG. 1 due to its own weight, and when the air is supplied by the air supply nozzle 18, it is shown by the solid line in FIG. It is designed to be closed.

Next, FIG. 2A shows a step of constructing a gravel pile in soft sand W having a sandy quality by using the apparatus having the above-mentioned configuration.
~ F will be described.

First, while the apparatus is suspended and supported from the top of a reader (not shown), the rotary casing 3 is driven to rotate as shown in FIG. At this time shoe 7
Will be closed. When the rotating casing 3 reaches a predetermined depth, its rotation is stopped, and a mixed gravel in which gravel having a large particle size and gravel having a small particle size are mixed is supplied to the hopper 10 as shown in FIG. The mixed gravel supplied to the hopper 10 is automatically sorted by the sieving device 14,
The gravel G _{1 with} a large particle size is in the inner tube 9, and the gravel G _{2 with} a small particle size is the annular space between the inner tube 9 and the fixed casing 8.
11 filled respectively. After the gravel G ₁ and G ₂ have been filled, as shown in FIG. 2C, the supply of pressure air from the air supply nozzle 18 is started, and at this time, the on-off valve is opened by the air injection pressure from the nozzle 18. Close each 17
The air pressure in each of the inner tube 9 and the annular space 11 is increased.

With the air pressure thus increased, the large particle size gravel G ₁ in the inner tube 9 and the small particle size gravel G ₂ in the annular space 11 are pressurized from above, and the rotating casing 3 is reversed and the extraction is started. With this drawing operation, the large particle size gravel G ₁ in the inner tube 9 is pressed by the air pressure and pushed out from the lower end of the inner tube 9, and at the same time, the small particle size gravel G ₂ in the annular space 11 is The gravel pile P, which is pressed by the air pressure and is pushed out from the lower end of the annular space 11 and is composed of the cylindrical drain layer 19 and the annular filter layer 20 surrounding the drain layer 19, is continuous in the ground W. Is formed (see FIGS. 2D and E).

After burying the required number of gravel piles P in the ground W in this way, as shown in FIG. 2F, the gravel piles P are exposed on the surface of the ground W where the heads of these gravel piles P ... Are exposed.
The filter material 21 made of gravel having the same small particle size as that of the filter layer 20 is laid flat so as to come into contact with the head of each gravel pile P with a required thickness.
A gravel mat 22 made of gravel having a large grain size similar to that of the drain layer 19 of the gravel pile P is formed at a required height on the upper portion.

By embedding the gravel pile P in the soft ground W as described above and providing the gravel mat 22 on the surface of the ground W through the flat filter material 21, the water content in the soft ground W is reduced by the gravel. By passing through the filter layer 20 of the pile P, sand or the like having a relatively large particle size in water is prevented from entering the drain layer 19, and only the very small particle size flows into the drain layer 19. Then, it is sucked up to the surface side of the ground W through the drain layer 19. The water absorbed on the surface side of the ground W is filtered again by the flat filter material 21, sucked up by the gravel mat 22, and drained to a proper place through the gravel mat 22. In this case, the gravel mat 22 also absorbs water containing sand or the like on the upper surface of the ground W, but the presence of the filter material 21 causes the same filtering action as described above.

In the embodiment described above, on the outside of the fixed casing 8,
The rotary casing 3 with a screw that can be rotated is externally fitted, and the fixed casing 8 and the inner pipe 9 are driven while the rotary casing 3 is rotated, but such a rotary casing 3 is used. Instead, a vibrator is used, which allows the fixed casing 8
Driving can be performed by applying a vibration to. Therefore, the rotating casing 3 is not essential for the device of the present invention.

(Effect of the invention) According to the soft ground improvement device of the present invention, it is not necessary to separate the gravel of large particle size and the gravel of small particle size at the time of ground improvement work by using this device, It is possible to automatically sift by simply supplying the mixed gravel, which is a mixture of the small particle size and the small particle size, to a single hopper, and the large particle size gravel is used as the inner tube, and the small particle size gravel is used as the fixed casing. Since it can be introduced into each annular space between the pipe and the pipe, the work is very simple and easy, and the construction efficiency can be significantly improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a soft ground improvement device according to the present invention, FIGS. 2A to 2F are explanatory views showing a process of forming a gravel pile by using the same device, and FIG. 3 is a crossing of the gravel pile. FIG. 3 is an enlarged sectional view taken along the line III-III in FIG. 2D, which is a plan view. 3 ... Rotating casing, 4 ... Drive motor, 8 ... Fixed casing, 9 ... Inner tube, 10 ... Hopper, 11 ... Annular space between fixed casing and inner tube, 12 ... Upper stage side Screen, 13 ... lower screen, 14 ... screen device, 17 ... open / close valve, 18 ... air supply nozzle, G ₁ ...... large particle size gravel, G ₂ ...... small particle size gravel, P ... Gravel pile,
19 …… Gravel pile drain layer, 20 …… Gravel pile filter layer, 21 …… Planar filter material, 22 …… Gravel mat.

Claims (1)

[Claims] 1. An inner tube is inserted and arranged in a fixed casing, and a hopper is provided above the fixed casing and the inner tube to supply a gravel in which large particles and small particles are mixed appropriately. Between the hopper and the fixed casing and the inner tube, the gravel dropped from the hopper is screened into a large particle size and a small particle size, and a large particle size gravel is introduced into the inner tube. An apparatus for improving soft ground comprising a sieve device for introducing a small gravel into an annular space between a fixed casing and an inner pipe.