JP3046540B2 - How to improve the ground - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for improving a ground, and more particularly, to a method for improving a ground by compacting a sandy ground.

[0002]

2. Description of the Related Art A plurality of drain columns are formed on the original ground using a drain material having a larger permeability than the soil of the original ground, and a pipe for water injection is arranged at a distance from the drain columns to pulsate water. Has been proposed (Japanese Patent Laid-Open No. 2-308007).

In the above compaction method, when pulsating water is injected into the ground from a water injection pipe, the pore water pressure increases and the effective stress acting between the soil particles decreases, so that the mutual movement of the soil particles is facilitated. become. In addition, the pulsation of the water flow is
Vibration is further applied to the soil particles that have become easier to move. As a result, the sandy ground is liquefied, pore water is drained from the drain column, and the sandy ground is compacted by utilizing downward osmotic pressure (page 2, upper right column, line 15 to lower left column, 3).
line).

[0004]

Incidentally, in addition to the compaction method described above, for example, the application of the present applicant separately (Japanese Patent Application No. Hei 6-277192), the flow of pressurized water to the ground and the In the method of compacting the ground by repeating the water absorption, the higher the pressure of the water flowing out to the ground, the more excellent the effect can be obtained. However, the pressure of water flowing out to the ground is determined by the capacity of pumps and other pressure sources installed on the ground, and since the piping and other pressure-resistant structures of the equipment are determined based on the capacity of this pressure source, the water flows out to the ground. Increasing the pressure of the water causes a rise in equipment costs. Primarily for this reason, increasing the pressure of the water to flow to the ground is limited.

[0005] The present invention provides a ground improvement method that can increase the pressure of water jetted to the ground by utilizing the water hammer action and can suppress the influence on the equipment cost.

[0006]

The ground improvement method according to the present invention comprises a water circulation passage, a shut-off valve disposed in the circulation passage, and a shut-off valve of the circulation passage when the shut-off valve is closed. A pipe provided with opening means for ejecting water to the outside is inserted into the ground. Next, water is circulated through the circulation passage, and the shutoff valve is closed instantaneously during the circulation of water to cause a water hammer action on the circulation passage. By this water hammer action, the opening means is opened, and water in the circulation passage is jetted to the ground.

When the shutoff valve in the circulation passage is closed instantaneously, a water hammer action occurs in which pressure increases rapidly in the circulation passage upstream of the shutoff valve. Since the opening means is opened by the increase in the pressure of the water hammer action, the water in the circulation passage blows out to the ground.
Thereby, compaction of the ground and other ground improvements are performed.

[0008] The water circulating in the circulation passage is pressurized and has a pressure, and the pressure may be large enough to cause an appropriate circulation of water in the circulation passage. The pressure is lower than. Therefore, the capacity of the pressure source connected to the circulation passage and the circulation passage and other pressure-resistant structures based on this capacity can be determined based on a low pressure except for the range where the effect of the water hammer is exerted. Since the method for improving the ground according to the present invention can be performed using a pipe having a simple structure including a valve, a shutoff valve, and an opening means, the equipment cost can be reduced. Also,
By changing the flow velocity of the water in the circulation passage, the water hammer generated by the water hammer action can be adjusted in a wide range, so that the pressure of the water to be jetted to the ground can be easily adjusted. In addition, since water having a high pressure that rises due to the water hammer action is only ejected for a short time, the effect of compacting the ground can be enhanced with a small amount of water.

[0009] In the case where groundwater flows in the ground, for example, it is considered that the water jetted to the ground is discharged by the groundwater. However, when there is no groundwater flow, it is necessary to absorb water from the ground. In such a ground, in a first aspect, the present invention provides a water circulation passage, a shutoff valve disposed in the circulation passage, and an opening for discharging water in the circulation passage to the outside when the shutoff valve is closed. This is performed by inserting a pipe having means and a water suction passage into the ground. In a second aspect, a first pipe including a water circulation passage, a shutoff valve disposed in the circulation passage, and an opening means for ejecting water in the circulation passage to the outside when the shutoff valve is closed is ground. And prior to or concurrently with the insertion of this first pipe, by inserting a second pipe with a water intake passage into the ground. In either embodiment,
Water is circulated through the circulation passage, and the shutoff valve is closed instantaneously during the circulation of water to cause a water hammer action. By this water hammer action, the opening means is opened, and the water in the circulation passage is jetted to the ground, while the water is sucked up from the ground through the water absorption passage.

According to the first aspect, a simple ground improvement method is provided since water can be ejected to the ground and water can be absorbed from the ground by a single pipe. On the other hand, according to the second aspect, since the second pipe can be inserted at an appropriate interval from the first pipe, water can be efficiently absorbed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The pipe is preferably formed in the form of a double tube, in which case the outer tube is used for protection and the inner tube is used as a circulation passage. The inner tube is bent at 180 ° at a portion corresponding to the lower end of the outer tube and formed to have a length substantially twice that of the outer tube. An electromagnetically actuated valve that takes two positions, open and closed, is attached to the inner tube to form a shutoff valve. An opening means consisting of an auxiliary pipe and a valve is mounted upstream of the shut-off valve and within a range where the water hammer can reach. The auxiliary pipe extends from the inner tube to the outer tube and connects the circulation passage to the ground. On the other hand, the valve can have the same structure as the safety valve. In other words, when the water is closed at the pressure circulating in the circulation passage, but when a water hammer occurs,
The pressure generated thereby opens and water is ejected from the circulation passage through the auxiliary pipe toward the ground. A plurality of combinations of shut-off valves and opening means are provided along the circulation passage.

When not only the jetting of water but also the absorption of water is performed by a pipe, the space between the inner tube and the outer tube of the double tube can be used as a water absorption passage. Further, the pipe is in the form of a triple tube, the innermost tube and the space between the inner tube and the intermediate tube are used as a circulation passage, and the space between the intermediate tube and the outer tube is used as a water absorption passage. Can be used as

The pipe is inserted into the ground to be improved by means of vibration, press-fitting or in a manner known per se. Then, one end of the circulation passage is immersed in the water tank, and the other end of the circulation passage is connected to the pump, and the pump is driven to circulate the water through the circulation passage. When the circulating water flow becomes steady,
For example, the electromagnetically actuated valve, which is the lowermost shutoff valve, is instantaneously closed to shut off the flow and cause a water hammer action. Then, since the pressure of the water in the circulation passage increases, the valve of the opening means associated with the shut-off valve opens, and the water in the circulation passage blows out to the ground under a high pressure state, thereby compacting the ground. If the water hammer action is canceled after a short time, the pressure of the water in the circulation passage becomes low, so that the valve of the opening means is closed, and the water in the circulation passage starts circulation again. When this circulation flow becomes steady,
The second shut-off valve from the bottom is closed instantaneously to cause water hammer. After that, the same operation is sequentially repeated for the shutoff valve on the upstream side of the circulation passage.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a method for improving ground according to the present invention, a special form of pipe 20 is used. In the embodiment of FIG. 2 showing a sectional state, the pipe 20 has a water circulation passage 22, a shutoff valve 24 disposed in the circulation passage 22, and the water in the circulation passage 22 ejected to the outside when the shutoff valve 24 is closed. Opening means 26;
And a protection tube 28.

In the illustrated embodiment, the circulation passage 22 is formed by bending a steel pipe at the center by 180 °. The steel pipe has two ends, as shown in FIG.
Has a length protruding upward from the ground 30 when inserted into the ground 30. The shutoff valve 24 is an electromagnetically actuated open / close type valve, and is normally kept open. When a current is applied when a water hammer action is to be caused, the circuit is closed and the circulation passage 22 is shut off.

On the other hand, the opening means 26 is provided in connection with the circulation passage 22 in a range where the water hammer action is exerted. In the illustrated embodiment, an auxiliary pipe 32 for communicating the circulation passage 22 with the ground 30 is provided. It comprises an automatically actuated open / close valve 34 arranged in a pipe 32. The valve 34 is normally in a closed state, and is opened when the pressure of water increases due to a water hammer action. That is, when water is circulating in the circulation passage 22, the valve 34 does not open due to the pressure of the circulating flow, but opens at a pressure which is much higher than the pressure of the circulating flow and rises due to the water hammer action. Shutoff valve 24 and opening means 2
6 is provided at a plurality of locations along the steel pipe which is the circulation passage 22.

The opening means 26 in the range where the water hammer action is exerted upstream of the shutoff valve 24 and the portion of the steel pipe serving as the circulation passage 22 are press-fitted with the reinforcing pipe 23 in order to secure sufficient strength. Reinforce the board by making it thicker than other parts.

The protection tube 28 is formed of a steel pipe, and a tapered excavation bit 29 is provided at the tip thereof. The protection tube 28 is provided with an auxiliary tube 32 of the opening means 26.
Is provided at a position corresponding to the auxiliary pipe 32, and the auxiliary pipe 32 penetrating the hole is welded. The steel pipe for the circulation passage 22 and the steel pipe for the protection tube 28 are:
A predetermined interval is maintained and fixed by a plurality of spacers 35 arranged at intervals in the axial direction.

At the place where the ground is to be improved, the pipe 20
Is inserted into the ground 30, one end of the circulation passage 22 is immersed in the water tank 36, and the other end of the circulation passage 22 is
Connect to When the pump 38 is driven, the pump 38 sucks the water in the water tank 36 and supplies it to the circulation passage 22, and the water entering the circulation passage 22 returns to the water tank 36. Thus, the water circulates in the circulation passage 22.

When the water is circulating in the circulation passage 22 in a steady flow as shown by the arrow A, as shown in FIG. 2B, when the shutoff valve 24 is closed instantaneously to shut off the circulation passage 22, A hammering action occurs, causing the water pressure to rise sharply. As a result, since the valve 34 of the opening means 26 is opened, the water in the circulation passage 22 is jetted under high pressure through the auxiliary pipe 32 to the ground 30 to compact the ground. Since the water hammer effect disappears spontaneously after a short time, the pressure of the water in the circulation passage 22 drops to the pressure at the time of circulation, and the valve 3 of the opening means 26
4 closes. Thereafter, when the shutoff valve 24 is opened, the water circulates through the circulation passage 22 again.

In the embodiment shown in FIG. 3, the pipe 40 has a water circulation passage 42 and a shutoff valve 44 disposed in the circulation passage 42.
And an opening means 46 for ejecting water in the circulation passage 42 to the outside when the shutoff valve 44 is closed, a water absorption passage 48, and a protection tube 50.

The pipe 40 is in the form of a triple tube,
The circulation passage 42 is formed by the thinnest tube 52 and a space between the tube 52 and a concentric tube 53 having a bottom portion. The shutoff valve 44 is an electromagnetically actuated open / close type valve disposed at the lower end of the tube 52. The auxiliary pipe 54 and the valve 56 of the opening means 46 have the same structure as the auxiliary pipe 32 and the valve 34 of the opening means 26 of the above embodiment. The auxiliary pipe 54 penetrates the tube 53 from the tube 52, further penetrates the protective tube 50, and connects the circulation passage 42 and the ground 30. In the embodiment shown, the two opening means 46 are provided radially at the same level position of the tube 52, so that the water is ejected radially as indicated by the arrow B.

The space between the tube 53 and the protective tube 50 having a concentric outer bit and a tapered bit 51 at the bottom constitutes a water absorption passage 48. The water suction passage 48 is connected to a vacuum pump (not shown) on the ground, and sucks water from the ground as indicated by an arrow C through a plurality of suction holes 60 provided in the protection tube 50.

After the pipe 40 is inserted into the ground, water is circulated through the circulation passage 42. When the shutoff valve 44 is closed instantaneously during the circulation of water to shut off the circulation passage 42, a water hammer action occurs. As a result, the valve 56 of the opening means 46 is opened, and the water in the circulation passage 42 blows out to the ground 30 through the auxiliary pipe 54 to compact the ground. After the water hammer disappears, the vacuum pump connected to the water suction passage 48 is operated to suck water from the ground 30. In this way, spouting the water onto the ground 30 and sucking up the water from the ground 30 are more convenient than simultaneously.
It is better to do it with a time lag.

A ground improvement method is carried out by using a pipe 20 shown in FIG. 2 and a water absorption pipe (not shown) which is a single water absorption pipe having a plurality of suction holes and having an internal water absorption passage. In this case, the pipe 20 and the water absorption pipe are inserted into the ground at an appropriate interval. Subsequent operations are substantially the same as described above.

The water hammer generated by the water hammer can be theoretically determined by the Zhukovsky's formula given by h = cV / g when the flow closing time is optimally controlled. Here, h is the water hammer pressure head, c is the pressure propagation velocity, V is the flow velocity of the steady flow, and g is the acceleration of gravity. The pressure propagation velocity is c ≒ 1000 for a normal penstock.
m / s. If the diameter of the circulation passage is 3 cm 2, and the water head obtained from the above equation is converted into the force per unit area as the water hammer, the water hammer and the flow velocity have the relationship shown in FIG. Therefore, if the flow velocity in the circulation passage is 10 m / s,
A water hammer of 140 kgf / cm ² , ie pressure, is obtained.

On the other hand, when the closing time T of the flow satisfies T ≦ 2L / c, the closing time is optimally controlled. Here, L is the distance from the pressure source to the location where the water hammer occurs. For example, when a water hammer action is caused 10 m below the ground, the optimal closing time T is less than 0.02 s. Since the response time of the electromagnetically operated on-off valve is shorter than several ms, the use of the electromagnetically operated on-off valve as in the above-described embodiment can cause a sufficient water hammer action.

As can be seen from FIG. 4, the water hammer force is proportional to the flow velocity. Therefore, as shown in FIG. 5, a reducing portion 63 is provided upstream of a portion 64 of the circulation passage 62 where the water hammer action is generated, and the flow speed downstream of the reducing portion 63 is increased. While keeping the pressure low, the pressure of the water squirting into the ground can be increased. Downstream of the point 64 where the water hammer occurs, the circulation passage can be enlarged.

A preliminary experiment was conducted in a laboratory to confirm the effect of the method for improving the ground according to the present invention. As an experimental apparatus, an earth tank 70, a water injection pipe 72, and a water absorption pipe 74 shown in FIG. 6 were used. In this experiment, the water pressure applied to the water injection pipe 72 was 3.0 to 5.0 kgf / cm ² , the water injection time was 1.2 to 0.1 s, the water was injected for about 1 minute, and the water absorption time was changed from 0.5 s to pulling.
Each point indicated by a circle in FIG. 6B is 10 cm in the depth direction.
Cone penetration resistance was measured at intervals. This revealed the following effects. The higher the injection pressure, the higher the effect. The cycle between water injection and water absorption is the most effective when the cycle of water injection is 0.1 seconds and water absorption is repeated 0.5 seconds. It is considered that this is because the same action as compaction by the vibrating rod is performed by the impact force of water caused by applying instantaneous water pressure. This is important for estimating the effect of the present invention. As for water absorption, it is slightly better to intermittently absorb water than to continuously absorb water. Even if the initial ground is somewhat compacted, it can be further compacted without loosening the ground. There is substantially no difference in effect depending on the measurement position.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a method for improving a ground according to the present invention.

FIGS. 2A and 2B show two parts of FIG. 1, wherein FIG. 2A is an enlarged sectional view, and FIG. 2B is a schematic view showing a state in which circulating water is shut off.

FIG. 3 is a schematic view of another embodiment, similar to the two parts in FIG. 1;

FIG. 4 is a graph showing the relationship between water hammer and flow velocity.

FIG. 5 is a schematic diagram showing a method of increasing a flow velocity.

6A and 6B show an apparatus used in a preliminary experiment, in which FIG. 6A is a side view, and FIG. 6B is a plan view showing a measurement position.

[Explanation of symbols]

 20, 40 Pipe 22, 42 Circulation passage 24, 44 Shutoff valve 26, 46 Opening means 32, 54 Auxiliary pipe 34, 56 Valve 48 Water absorption passage

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) E02D 3/00-3/12

Claims (3)

(57) [Claims] 1. A pipe having a water circulation passage, a shutoff valve disposed in the circulation passage, and an opening means for jetting water in the circulation passage to the outside when the shutoff valve is closed, is inserted into the ground. Circulating water in the circulation passage, instantaneously closing the shut-off valve to cause a water hammer action in the circulation passage, opening the opening means by the water hammer action, and discharging water in the circulation passage into the ground. A method of improving the ground, including squirting into the ground. 2. A pipe comprising a water circulation passage, a shutoff valve disposed in the circulation passage, an opening means for ejecting water in the circulation passage to the outside when the shutoff valve is closed, and a water absorption passage. Circulating water in the circulation passage, instantaneously closing the shut-off valve to cause a water hammer action in the circulation passage, opening the opening means by the water hammer action, A method for improving the ground, comprising: spouting water onto the ground; and sucking water from the ground via the water absorption passage. 3. A ground pipe comprising a water circulation passage, a shutoff valve disposed in the circulation passage, and an opening means for jetting water in the circulation passage to the outside when the shutoff valve is closed. Inserting a second pipe having a water suction passage into the ground, circulating water in the circulation passage, instantaneously closing the shutoff valve to cause a water hammer action in the circulation passage, A method for improving the ground, comprising: opening the opening means by a hammer action to cause water in the circulation passage to jet to the ground; and sucking water from the ground through the water absorption passage.