JPH0229814B2 - YAMADOMEKABENOSUIATSUTEIGENKOHOOYOBIMIZUNUKIKAN - Google Patents

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. Mountain retaining walls are designed by estimating the groundwater level in the back ground based on materials such as soil surveys and calculating the water pressure that will act on the mountain retaining walls. 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, there is a risk that the retaining wall may be deformed, damaged, or collapsed.

However, it is extremely difficult to accurately predict changes in the groundwater level, and no construction method has been provided for dealing with excess water pressure when the groundwater level temporarily fluctuates. For this reason, mountain retaining walls have traditionally been designed with a large safety factor, taking into consideration small fluctuations in the groundwater level that may occur. A retaining wall designed in this way requires a large amount of extra material and is not economical.

Furthermore, when a retaining wall is installed by excavating deeply into the ground where the groundwater level is high, large water pressure acts on the retaining wall. However, because it is difficult to lower the groundwater level behind the mountain retaining wall and reduce the water pressure acting on the mountain retaining wall without inducing ground subsidence, mountain retaining walls with large cross sections have traditionally been designed. There is.

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 mountain retaining wall, and water is pumped up through the deep well to lower the groundwater level at the back.

(2) Well points will be drilled from the inner surface to the back of the 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. Lower the groundwater level behind the retaining wall.

(4) A drain pipe is inserted into the drain hole drilled in the retaining wall, and water pressure causes the groundwater behind 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 retaining wall, and cannot be applied in places where there is not enough space. In addition, when water is pumped using a deep well, the groundwater level in the area adjacent to the deep well is sufficiently lowered, but it does not drop further away from the deep well. Therefore, it is necessary to provide a large number of deep wells with narrow intervals in order to uniformly lower the groundwater at the interface with the retaining wall, which increases the cost of drilling the deep wells.

Method (2) requires a large amount of construction costs because well points are expensive. In addition, in this construction method, groundwater is forcibly sucked using a vacuum, so groundwater is sucked from the ground behind the retaining wall, and depending on geological conditions, it may spread over a wide area behind the retaining wall. There is a risk of causing significant ground subsidence.

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, so the groundwater level behind the retaining wall is reliably lowered. Does not decrease. In particular, if clayey soil is involved, a drop in the level of groundwater located above the clayey soil cannot be expected.

In method (4), the drainage pipe must be constructed to allow only groundwater to flow out and prevent soil from flowing out. Therefore, a drain pipe is used, which is a hollow drain pipe whose tip opening is covered with a filter. However, the filter becomes clogged and the outflow of groundwater is interrupted, making it impossible to lower the groundwater level sufficiently. It is thought that filter clogging is likely to occur for the following reasons.

In other words, if a drainage hole is drilled in the 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 carrying soil and sand permeates through the filters, trapping fine soil particles and clogging the filters. In particular, the force of pushing the drainage pipe into the ground that is easily fluidized acts in the opposite direction to the water pressure of the groundwater, so the filter can become clogged.
Even more likely to occur.

[Purpose of the invention]

This invention is an improvement of the above-mentioned method (4), and aims to provide a water pressure reduction method for mountain retaining walls that prevents clogging of filters and lowers the groundwater level, and a drainage pipe that can be directly used in the method. It is said that

[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. After the ground behind the drain hole is stabilized, the drain hole is opened and the water is passed through the filter.
Groundwater is being drained from the back of the drainage pipe.

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 that covers the slit, and is housed in the outer tube so that it can be pushed into the outer tube. It is composed of

[Embodiments] Hereinafter, embodiments of the water pressure reduction method for mountain retaining walls and drain pipes of the present invention will be described in detail with reference to the drawings.

As shown in FIGS. 1 and 2, according to the present invention, the wall surface of the mountain retaining wall 10 is drilled with a rock drilling machine.
A plurality of drainage holes 12 are drilled. The drain hole 12 is
For example, they have a diameter of 40 to 50 mm 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,
Due to the water pressure on the back side, the groundwater on the back side of the retaining wall flows out forcefully through the drain hole, accompanied by earth and sand. In order to prevent underground water from flowing out, as can be clearly seen from FIGS. 1 and 3, the drain pipe 14 is
An amount corresponding to the thickness of the retaining wall is inserted into the drain hole 12.

The drain pipe 14 has a multi-pipe structure, and in the embodiment, as shown in FIG. 4, a hollow outer pipe 16,
Hollow inner tube 18 that is pushably housed within the outer tube
It is composed of a double tube with and,
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, and constitutes a guide tube. Instead of providing the packing 20, a flange or a tapered surface may be formed on the outer periphery of the outer tube 16 to prevent outflow of groundwater. The lid 22 is removably attached to the tip of the outer tube 16.
For example, it is attached by spot welding (the fifth
(see figure). In the embodiment, the lid 22 is formed into a flat plate shape, but if it is formed into a conical shape, as shown by the dashed line in FIG. 3, the drain pipe 14 can be easily inserted into the drain hole 12. There is. In addition, if you do spot welding and attach a hinge to the tip of the outer tube,
When the inner tube 18 is pushed in, the lid 22 does not move integrally while closing the opening at the distal end of the inner tube. Therefore, there is no risk of interfering with the flow of groundwater through the opening at the tip of the inner pipe.

The inner tube 18 includes a large number of water absorption slits 24 formed in the wall, and a filter 26 disposed on the outer periphery and inside of the inner tube so as to cover the tip opening and the slits, and constitutes a drain tube body. (6th
(see figure). The inner tube 14 is configured to be slidable so that when pushed in, the lid 22 is removed from the outer tube tip, thereby releasing the outer tube tip.

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 other shapes such as a round hole. Moreover, since the tip of the inner tube 18 is open, the filter 26 can be uniformly disposed on the outer periphery and inside the inner tube without increasing the thickness locally. However, a base may be provided at the tip of the inner tube, the slit 26 may be formed in the base, and the base may be covered with the filter 26. Note that a non-woven fabric such as Toughnel can be used as the filter 26, and a non-woven fabric such as Toughnel or a waste cloth can be similarly used as the packing 20.

As described above, the tip of the drain pipe 14 is closed by the lid 22, and the gap between the drain hole 12 and the drain hole 12 is filled with the packing 20. Therefore, the outflow of groundwater from the drain hole 12 is limited to the drain pipe 1.
4 is inserted into the drain hole 12, this can be prevented.

Immediately after the drain hole 12 is drilled in the retaining wall 10, the ground behind the drain hole 12 has a lower shear resistance between soil particles due to the rapid outflow of groundwater behind the drain hole. 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 acts on the lid 22 to pull out the drain pipe 14 from the drain hole 12, but the resistance generated by the packing 20 prevents the drain pipe 14 from being pulled out. Ru.
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.
Since the lid 22 is removably attached to the outer tube 16, when the inner tube is pushed in, it is pushed open and removed from the outer tube. When the lid 22 is separated from the outer pipe 16, the drain pipe 14 is opened as shown in FIG. And through the slit 24, it tries to flow out rapidly.
However, the distal opening of the inner tube 18 and the slit 24
is covered by a filter 26. 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 26 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 drain hole, which has recovered, does not decrease again, the fluidization of the ground is prevented, and a stable state is maintained. Therefore, movement of earth and sand is prevented and clogging of the filter is prevented. In addition, since 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 retaining wall shows the lowest value. Because there is little drop in water level at areas other than the interface with the retaining wall, a stable state is maintained and ground subsidence does not occur. Further, since the water pressure acting on the mountain retaining wall is at 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. As a result, the groundwater level at the back of the retaining wall may drop due to heavy rain, etc.
Even if the water rises temporarily, 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 does not drop much at areas other than the interface with the retaining wall, a stable state is maintained and ground subsidence does not occur. Therefore, even during the mountain retaining construction period, water pressure fluctuations acting on the retaining wall can be controlled without causing ground subsidence, and construction can be carried out safely. Furthermore, this construction method does not require space at the back of the retaining wall, and compared to construction methods that use deep wells or well points,
It can be done cheaply.

Further, according to the drain pipe of the present invention, the earth and sand on the back side of the retaining wall are prevented from flowing out, so that the filter is not clogged. Therefore, the groundwater in the ground behind the mountain retaining wall is effectively drained, the water pressure acting on the mountain retaining wall can be controlled, and the mountain retaining wall can be designed with an economical cross section.

The above embodiments are for illustrating the present invention, and do not limit the present invention in any way, and all modifications and modifications within the technical scope of the present invention are also included in the present invention. Needless to say.

[Brief explanation of drawings]

Figures 1 and 2 are a cross-sectional view and a partial perspective view of the retaining wall, and Figure 3 is a longitudinal 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 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: Mountain retaining wall, 12: Drainage hole, 14: Drainage pipe,
16: Outer tube, 18: Inner tube, 20: Packing, 2
2: Lid, 24: Slit, 26: Filter.

Claims (1)

[Scope of Claims] 1. A plurality of drainage holes are drilled in a mountain retaining wall, and then the drainage holes are closed to stop the outflow of groundwater, and after the ground behind the drainage holes is stabilized, the drainage holes are opened. A water pressure reduction method for mountain retaining walls that drains groundwater from the back of the drain pipe through a filter. 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 remove the drain pipe through the filter. A water pressure reduction construction method for a mountain retaining wall according to claim 1, which drains groundwater from the back surface. 3. The water pressure reduction method for a mountain retaining wall according to claim 2, wherein 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 with a removably attached lid that closes the tip, a slit formed in the wall, and a filter that covers the slit, and is removably housed and pushed into the outer tube. and a hollow inner tube that opens the outer tube tip by removing the lid from the outer tube tip.