JPS6259727A - Water pressure-reducing construction work of sheathing wall and water drip tube - Google Patents

Abstract

PURPOSE:To reduce the pressure of water by a method in which a plurality of water drip holes are formed in a sheathing wall, the holes are closed to stop of outflow of groundwater to stabilize the back ground of the holes, and the holes are opened to allow groundwater in the back side of the holes of flow out through filters. CONSTITUTION:When a plurality of water drip holes 12 are drilled in a sheathing wall 10, groundwater in the back side of the wall 10 flows out through the holes 12. A plurality of water drip tubes 14 whose tips are closed are inserted into the holes 12 to prevent the outflow of groundwater from the holes 12. After the back ground of the holes 12 is stabilized, the covers 22 of the tubes 14 are removed, and groundwater in the back ground of the holes 12 is allowed to flow out through filters 26.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for reducing water pressure of retaining walls in construction work and a drainage pipe.

[Prior art]

During construction work, retaining walls are installed to prevent earth and sand from collapsing. The mountain retaining wall is formed to have a structure with excellent water-stopping properties so as to bear the water pressure of groundwater contained in the ground behind it. The mountain retaining wall is located on the back #! based on materials such as soil surveys.
The design assumes the groundwater level at the plate and calculates the water pressure acting on the retaining wall.However, the groundwater level is not constant and fluctuates due to temporary precipitation such as torrential rain. If the groundwater level rises, the water pressure acting on the retaining wall will increase, causing excessive water pressure to exceed the calculated water level. Then, it transformed into a retaining wall,
There is a risk of damage or collapse.

However, it is extremely difficult to accurately predict fluctuations in the groundwater level, and there are no methods available for dealing with excess water pressure when the groundwater level temporarily fluctuates. Taking into account the fluctuations,
Mountain retaining walls have traditionally been designed with a large safety factor. A mountain retaining wall designed in this way requires a large amount of extra materials and is not economical.

Also, 1'I where the groundwater level is high! ! When installing a mountain retaining wall by excavating deeply, large water pressure acts on the retaining wall. Because it is difficult to reduce the water pressure that occurs, retaining walls with large cross sections have traditionally been designed.

The following methods are known as construction methods for reducing the water pressure on the retaining wall by lowering the groundwater level behind the retaining wall.

(1) A deep well is drilled into the ground behind the retaining wall and water is pumped up through the deep well to lower the groundwater level at the back.

(2) A wellbore is drilled from the inner surface to the back of the mountain retaining wall to pump up water and lower the groundwater level at the back.

(3) By drilling a deep well in the ground inside the mountain retaining wall and pumping up the groundwater in the ground inside the mountain retaining wall, the groundwater on the back side of the mountain retaining wall is induced to be pumped up. lowering the groundwater level.

(4) A drain pipe is inserted into a drain hole drilled in the retaining wall, and water pressure causes the groundwater on the back of the retaining wall to flow out of the drain pipe, lowering the groundwater level.

[Problems with conventional technology]

However, the following problems have been pointed out with each of these construction methods.

Method (1) requires a space (site) to form a deep well at the back of the mountain retaining wall, and cannot be applied in places where there is not enough space. The groundwater level in the adjacent area is
However, it does not decrease as you move away from the deep well. Therefore, it is necessary to install a large number of deep wells with narrow intervals in order to uniformly lower the groundwater at the interface with the mountain retaining wall. Well drilling construction costs will increase.

In construction method (2), a large amount of construction cost is required because well points are expensive. In addition, this construction method uses a vacuum to forcibly draw groundwater, so
Groundwater is sucked in from the ground behind the retaining wall, and depending on geological conditions, there is a risk that extensive ground subsidence may occur behind the retaining wall.

Furthermore, method (3) is an indirect construction method that pumps up groundwater from the ground inside the retaining wall and expects the groundwater level behind the retaining wall to drop. In particular, if there is cohesive soil, the water level of groundwater located above the cohesive soil cannot be expected to decrease.

In method (4), the drainage pipe drains only groundwater,
It must be constructed to prevent the outflow of earth and sand, so a hollow drain pipe is used whose tip opening is covered with a filter. However, if the filter becomes clogged, groundwater flow is interrupted and the groundwater level cannot be lowered sufficiently.Clogged filters are thought to occur easily for the following reasons.

In other words, if a drainage hole is drilled in a retaining wall, groundwater will flow out forcefully due to the water pressure of the groundwater behind the drainage hole. And groundwater moves much faster than it can naturally seep into the ground. Therefore, the ground becomes in a state similar to a boiling state, and the shear resistance between soil particles decreases, making it easier to fluidize. The sediment, along with the groundwater, flows out of the drain hole with great force. Drain pipes are immediately inserted into the drain holes to prevent sediment from flowing out. However, because the ground is not stabilized, groundwater with sediment infiltrates the filter and flows through it, trapping fine soil particles and clogging the filter. especially,
The force of pushing the drainage pipe into the ground, which is easily fluidized, acts in the opposite direction to the water pressure of the groundwater, making the filter more likely to become clogged.

[Purpose of the invention]

This invention is an improvement of the above method (0), and aims to provide a water pressure reduction method for mountain retaining walls that prevents clogging of filters and lowers the water level of groundwater, and a drainage pipe that can be directly used in the method. There is.

[Summary of the invention]

In order to achieve this objective, in the method for reducing water pressure of a mountain retaining wall according to the present invention, a plurality of drain holes are bored in the mountain retaining wall, and then the drain holes are closed to stop the outflow of groundwater. and,
After the ground behind the drain hole becomes stable, the drain hole is opened and the groundwater behind the drain pipe flows out through the filter.

Further, the drain pipe of the present invention is configured to include a hollow outer pipe and a hollow inner pipe that is pushably housed within the outer pipe. The outer tube includes a lid that is removably attached and closes the tip. On the other hand.

The inner tube includes a slit formed in the wall and a filter covering the slit, and is housed in the outer tube in a pushable manner,
When pushed in, the lid is configured to separate from the tip of the outer tube and open the tip of the outer tube. [Example] Hereinafter, with reference to the drawings, a method for reducing water pressure of a retaining wall and a drain pipe of the present invention will be explained. Examples will be described in detail.

As shown in FIGS. 1 and 2, according to the present invention,
Multiple drainage holes 1 are made on the wall of the mountain retaining wall 1o by a rock drilling machine.
2 is drilled. The drain holes 12 have a diameter of 40 to 50 mm, for example, and are formed horizontally and vertically at a pitch of 1 to 4 m.

When the drain hole 12 is bored in the retaining wall 10, groundwater on the back side of the retaining wall flows out through the drain hole, accompanied by earth and sand, due to the water pressure on the back side. In order to prevent groundwater from flowing out, as can be clearly seen from Figures 1 and 3,
The drain pipe 14 is inserted into the drain hole 12 by an amount equivalent to the thickness of the retaining wall.

The water drain pipe 14 has a multi-pipe structure, and in the embodiment, as shown in FIG. It is constructed of double tubes. The outer tube 16 includes a packing 20 disposed on the outer periphery to fill the gap between the drain hole 12 and the drain hole 12 to prevent outflow of groundwater, and a lid 22 that closes the tip, thereby forming a guide tube. The lid 22 may have a flange or a tapered surface formed on the outer periphery of the outer tube 16 to prevent underground water from flowing out without providing the packing 20.
In an embodiment, it is removably attached to the tip of the outer tube 16, for example, by spot welding (see FIG. 5),
The lid 22 is formed into a plate shape, but if it is formed into a conical shape, as shown by the dashed line in FIG. 3, there is an advantage that the drain pipe 14 can be easily inserted into the drain hole 12. In addition, by spot welding and attaching a hinge to the tip of the outer tube, the inner tube 1
When 8 is pushed in, the lid 22 is.

The inner pipe does not move integrally with the end opening closed, so there is no risk of interfering with the flow of groundwater through the inner pipe opening.

The inner tube 18 has a large number of water absorption slits 2 formed in the wall.
4, and a filter 2B disposed on the outer periphery and inside of the inner tube so as to cover the tip opening and the slit, constituting the drain tube main body (see FIG. 6), and the inner tube 14
is configured to be slidable so that when pushed in, the lid 22 is separated from the tip of the outer tube and the tip of the outer tube is released.

In the embodiment, the slit 24 extends in the axial direction from the tip of the inner tube, but it is sufficient that the slit 24 has a shape that allows underground water to pass therethrough, and can take various shapes such as a round hole. In addition, since the tip of the inner tube 18 is open, the filter 26 can be placed on the outer periphery and inside of the inner tube without increasing the thickness locally.
However, if a base is provided at the tip of the inner tube,
It is also possible to form a slit 26 in this base and cover it with a filter 28.
As the puffing material 20, a nonwoven fabric such as Tuffnel can be used, and as the puffing 20, a nonwoven fabric such as Tuffnel, or a rag or the like can be used.

As described above, the tip of the drain pipe 14 is closed by the lid 22, and the gap with the drain hole 12 is closed by the packing 20.
is filled in by Therefore, outflow of groundwater from the drain hole 12 is prevented by inserting the drain pipe 14 into the drain hole 12.

Immediately after drilling the drain hole 12 in the retaining wall 10, the ground behind the drain hole 12 decreases the shear resistance between soil particles and becomes fluid due to the rapid outflow of groundwater behind the drain type. It is in an unstable state. Therefore, after the drain pipe 14 is inserted into the drain hole 12 to stop the outflow of groundwater, it is left as it is until the ground is stabilized. The water pressure of the groundwater behind the drain hole 12 is
Although the lid 22 acts to pull out the drain pipe 14 from the drain hole 12, the resistance force generated by the puffing 20 prevents the drain pipe 14 from being pulled out. After the shear resistance between the soil particles on the back side of the drain hole 12 is restored and the ground is stabilized, the inner pipe 18 is pushed in. The lid 22 can be detached from the outer tube 16.
Since it is attached to the inner tube, when the inner tube is pushed in, it is pushed open and separated from the outer tube. The lid 22 is the outer tube 16
As shown in FIG. 7, the drain pipe 14 is opened and the groundwater on the back side of the drain hole 12 flows through the drain pipe.
Specifically, it tries to rapidly flow out through the opening at the tip of the inner tube 18 and the slit 24.

However, the distal opening of the inner tube 18 and the slit 24 are covered by a filter 28. Therefore, the flow of groundwater is restricted and a large amount of groundwater is not allowed to move, and only a small amount of groundwater that permeates through the filter 28 gradually flows out through the opening at the tip of the inner tube and the slit 24.

In this way, with the construction method in which groundwater does not flow out in large quantities but in small amounts, the flow rate pressure of groundwater is small. Therefore,
The shear resistance of the ground behind the drainage type has recovered, and
There is no decline, the fluidization of the ground is prevented, and a stable state is maintained. Therefore, the movement of sediment is prevented and clogging of the filter is prevented. In addition, because the flow pressure of groundwater is low, the groundwater level decreases less as it moves away from the ground behind the retaining wall, and the decrease in the groundwater level is greatest at the interface with the retaining wall. That is, as shown by the solid line 28 in FIG. 1, the groundwater level does not decrease much at first, but rapidly decreases behind the retaining wall 10. The water head height at the interface with the mountain retaining wall is the lowest, and the drop in water level at areas other than the interface with the retaining wall is small, so a stable state is maintained and ground subsidence does not occur. Since the water pressure acting on the mountain retaining wall is the water head height at the boundary surface, the water pressure acting on the mountain retaining wall is sufficiently reduced without causing the ground behind the mountain retaining wall to sink. According to experiments, the method of the present invention is particularly effective when the ground is a layer of fine sand or a layer of fine sand mixed with a small amount of silt. In addition, in the construction method using well points, the groundwater level gradually decreases over a relatively wide range, as shown by the dashed line 30 in FIG.

〔Effect of the invention〕

As described above, according to the water pressure reduction method for mountain retaining walls according to the present invention, the groundwater level at the interface with the mountain retaining wall is sufficiently lowered while minimizing the drop in the ground water level in the ground behind the mountain retaining wall. I'm letting you do it. Therefore, even if the groundwater level in the ground behind the retaining wall temporarily rises due to torrential rain or the like, the water pressure acting on the retaining wall is controlled and reduced. Therefore, a retaining wall with an economical cross section can be designed. In addition, because the water level decreases only at areas other than the interface with the retaining wall, a stable state is maintained, and j1
! ! No ground subsidence occurs. Therefore, even during the period of retaining work, there is no ground subsidence, and fluctuations in water pressure acting on the retaining walls can be controlled, allowing safe construction. Furthermore,
This construction method does not require any space at the back of the retaining wall,
Moreover, it is cheaper than construction methods that use deep wells or well points.

In addition, according to the drainage pipe of the present invention, since the earth and sand on the back side of the mountain retaining wall is prevented from flowing out, the filter is not clogged, and therefore, the ground water on the back side of the mountain retaining wall can be effectively drained. The water pressure acting on the retaining wall can be controlled, and the retaining wall can be designed with an economical cross section.

The above embodiments are for explaining this invention,
It goes without saying that this invention is not limited in any way, and that all modifications, modifications, etc. made within the technical scope of this invention are also included in this invention.

[Brief explanation of the drawing]

Figures 1 and 2 are a cross-sectional view and a partial perspective view of the retaining wall, and Figure 3 is a vertical cross-section of the drain pipe inserted into the drain hole of the retaining wall before the inner pipe is pushed in. Figure 4 is a vertical cross-sectional view of the drain pipe, Figure 5 is a vertical cross-sectional view of the outer pipe of the drain pipe, Figure 6 is a vertical cross-sectional view of the inner pipe of the drain pipe, and Figure 7 is a vertical cross-sectional view of the inner pipe of the drain pipe. It is a longitudinal cross-sectional view of the drain pipe inserted into the drain hole of the retaining wall after the inner pipe is pushed in. 10: Retaining wall, 12: Drain hole, 14: Drain pipe, 16: Outer pipe, 18: Inner pipe, 20: Packing, 22: Lid, 24:
Thrive, 26: Filter
−.

Claims (1)

[Claims] (1) A plurality of drainage holes are drilled in the mountain retaining wall, and then the drainage holes are closed to stop the outflow of groundwater. After the ground behind the drainage holes is stabilized, the drainage holes are opened. Release and filter through
A water pressure reduction method for mountain retaining walls that drains groundwater from the back of drainage pipes. (2) Insert the drain pipe with the tip blocked into the drain hole to prevent the flow of groundwater from the drain hole, and after the ground behind the drain hole is stabilized, open the drain pipe tip and pass it through the filter.
A water pressure reduction construction method for a mountain retaining wall according to claim 1, which drains groundwater from the back side of a drain pipe. (3) The water pressure reduction method for mountain retaining walls according to claim 2, in which the drainage pipe is composed of multiple pipes, and by pushing in the inner pipe, a cover at the tip of the outer pipe is released to allow groundwater to flow out. (4) A hollow outer tube equipped with a removably attached lid that closes the tip, a slit formed in the wall, and a filter that covers the slit, which is housed in the outer tube so that it can be pushed in, and which can be pushed into the outer tube. A drain pipe comprising: a hollow inner pipe whose lid is separated from the tip of the outer tube to open the tip of the outer tube when the water is drained; (5) The drainage pipe according to claim 4, wherein the inner pipe has an open end and is covered with a filter. (6) The drain pipe according to claim 4 or 5, wherein the packing is disposed around the outer pipe to prevent groundwater from flowing out from the gap between the drain hole and the drain hole. (7) The drain pipe according to claim 6, wherein the lid of the outer tube is attached to the tip of the outer tube by spot welding. The drain pipe according to claim 6, which is attached to the tip. (9) The drain pipe according to any one of claims 4 to 8, wherein the lid of the outer pipe is formed in a flat plate shape. (10) The drain pipe according to any one of claims 4 to 8, wherein the lid of the outer pipe is formed in a conical shape.