JPH0420045B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a groundwater drainage method using a deep well, which is one of the drainage methods used in civil engineering and construction work. The sandy soil layer (aquifer) that is the target of drainage when draining groundwater during underground construction work, etc.
Used when there are multiple.

(Prior art) For example, draining groundwater inside a mountain retaining wall such as an underground continuous wall is effective in eliminating spring water during ground excavation and making dry work possible. Prevent phenomena such as quick sand, boiling, and piping in the aquifer,
It is also extremely important in preventing phenomena such as heaving and blistering in cohesive soil layers (impermeable layers). In addition, draining groundwater outside the retaining wall reduces the water pressure applied to the back of the retaining wall, and prevents deformation and collapse of the retaining frame and underground outer wall, as well as abnormal subsidence of the surrounding ground due to these. This is very important for prevention.

By the way, when draining groundwater inside or outside or both inside and outside of a retaining wall using the deep well construction method, when there are multiple layers to be drained, the following two methods have conventionally been adopted.

The first method is to drain each layer simultaneously using one deep well. That is, as shown in FIG. 6, a vertical hole 1 is excavated to a planned depth across multiple aquifers A, B, and C, a strainer casing 2 is inserted into the vertical hole 1, and the strainer casing 2 and the hole wall are A filter material 3 is filled between the strainer casing 2 and the strainer casing 2, which has better water permeability than the original ground (aquifer) and is difficult for fine-grained soil in the original ground to pass through.
This is a method for draining water using a submersible pump 7 inserted into the interior of the tank. In the figure, a, b, and c are impermeable layers (cohesive soil layers).

This method has the advantage that the cost of installing a deep well is low because one deep well is used for drainage from each layer, and the installation depth of the submersible pump 7 can be adjusted depending on the progress of underground construction. Although it is possible to adjust the amount of drainage to a certain extent through adjustments, etc., when the construction work extends to deep layers, the groundwater of each layer A, B, and C will be drained at the same time, resulting in a huge amount of drainage.

In addition, with this method, when installing a deep well on the outside of the retaining wall to reduce the lateral pressure on the back of the retaining wall, if left without draining for a long time, the pressure water level in the lower layer will rise and Since this poses a danger to the retaining wall and the surrounding ground, it is a general rule to drain the water at all times during the installation period of the deep well.

In other words, in aquifer A that is in contact with the atmosphere, the groundwater level is the unpressurized (free) groundwater level P ₁ ,
In aquifers B and C located between impermeable layers a, b, and c,
As illustrated in the figure with pressure water levels P ₂ and P ₃ , each layer is often pressurized groundwater with its own water pressure. Therefore, different water pressures are originally applied to each layer A, B, and C on the back side of the retaining wall that spans these layers A, B, and C, but in the case of the above method, the upper and lower aquifers Since A, B, and C are connected through a single deep well, if left undisturbed for a long time, the water in the upper aquifers A and B will fall into the lower aquifer C, and this layer C will deteriorate. As the pressure water level increases,
Large water pressure is applied to the back of the retaining wall, creating a dangerous situation.

Therefore, this method requires draining a large amount of groundwater, and since the amount of drainage is large, it has a large impact on the surrounding ground, such as ground subsidence due to drainage.
The cost of discharging wastewater into a sewage system (sewage discharge charge) becomes enormous, and the operation and maintenance costs of the drainage equipment also increase, making these costs a fairly large portion of the overall construction cost.

The second method, as shown in Figure 7, is to install deep wells in each aquifer A, B, and C, and pump submersible pumps to the required layers at the necessary times as underground construction progresses. 7 is operated to drain water. 4' in the figure is a seal made of waterproof mortar or the like.

This method is very effective as a groundwater drainage method outside the retaining wall, but it requires a large number of deep wells, which requires a large installation cost, and the number of deep wells is limited. Due to the large number of holes, problems such as disturbance of the surrounding ground due to drilling, noise and vibration to the neighborhood due to deep well construction are likely to occur, and in addition, there is a large space for placing the deep well around the retaining wall. There are disadvantages such as the need for

In addition, in both of the above two methods, while the submersible pump 7 is in operation, the inside of the strainer casing 2 above the submersible pump 7 is a water-free space, so the noise and vibration of the submersible pump 7 is easily transmitted to the ground. , This has a considerable impact on the neighborhood.

Furthermore, since the above two methods are both gravity drainage methods, the water collection efficiency per deep well is naturally limited, and if for some reason it becomes necessary to increase the amount of drainage per unit time. , it is necessary to install additional deep wells, and it is not possible to respond quickly to emergencies.

(Objective of the Invention) In view of the above-mentioned conventional drawbacks, the present invention provides efficient drainage for geological strata in which there are multiple aquifers to be drained during underground construction, by installing a minimum number of deep wells, and providing drainage to nearby areas. This project proposes a groundwater drainage method using deep wells that has less impact and reduces the amount of drainage.

(Structure of the Invention) As a structure for achieving the above object, the present invention involves excavating a vertical hole spanning a plurality of aquifers, and placing a hole in the vertical hole at a position corresponding to each aquifer to be drained. A strainer casing with water holes formed therein is inserted, and filter material is filled between the strainer casing and the hole wall at positions corresponding to each of the aquifers, and at the same time, water is blocked at positions corresponding to the impermeable layers. An external packer is formed with mortar or the like, and a submersible pump is provided inside the strainer casing at a desired depth, and upper and lower belts are installed above the submersible pump and at a position corresponding to the external packer by operation from the ground. The system is characterized in that an internal packer is provided that can be switched between a state in which the water layer is blocked and a state in which it is communicated, and the aquifer to be drained is selected by blocking and communicating the upper and lower aquifers by the internal packer. .

In addition, in construction work, deep wells with the above configuration are installed inside or outside the retaining wall, or both inside and outside the retaining wall, depending on the purpose of drainage, but in civil engineering work, generally, retaining walls are not constructed. , Therefore, it will be installed regardless of the retaining wall.

(Example) As shown in FIG. 1A, a vertical hole 1 extending over a plurality of aquifers A, B, and C is formed by drilling to a planned depth. The diameter of the vertical hole 1 is usually about 1 m. In the figure, a, b, and c indicate an impermeable layer (cohesive soil layer), P ₁ indicates a free groundwater level, and P ₂ and P ₃ indicate a pressurized water level.

As shown in FIG. 1B, a strainer casing 2 of an appropriate diameter (usually about 0.2 to 0.6 m) is inserted into the vertical hole 1. Strainer casing 2
has water passage holes in the cylindrical wall at positions corresponding to aquifers A, B, and C that require drainage, and no water passage holes are provided in the other portions of the cylindrical wall.
Although not shown, a net is wrapped and fixed around the outer periphery to prevent the inflow of earth and sand.

After that, as shown in FIG. 1C, each aquifer A,
A filter material 3 is filled in the positions corresponding to B and C, and a water-blocking mortar is placed in the positions corresponding to the impermeable layers a and b to form an external packer 4. As the filter material 3, it is preferable to use gravel which has a particle size of several mm to more than ten mm, has a moderate distribution of particle sizes, and is well mixed. The water-shielding mortar can be replaced with concrete, but in any case, it is desirable to take measures to quickly obtain strength under water, such as adding a hardening accelerator or using early-strengthening cement. As the strainer casing 2, use one in which water passage holes made of slits etc. are bored throughout the cylindrical wall, and the water passage holes at positions corresponding to the impermeable layers a and b are made with water-shielding mortar etc. may be occluded.

Next, as shown in FIG. ), it can expand and contract, and when it expands, it comes into close contact with the inner surface of the strainer casing 2 and blocks the upper and lower aquifers A and B, and B and C (a state that can ensure upper and lower watertightness and airtightness) A state in which water and air are separated from the inner surface of the strainer casing 2 due to contraction and communicate with the upper and lower aquifers A and B, and B and C (a state in which water and air can freely flow up and down from the gap with the inner surface of the strainer casing). Internal police car 5 configured to be
... are provided, and a submersible pump 7 is installed at the lower end of the water pipe 6 which is provided by penetrating these internal packers 5...
will be established.

The internal packer 5 has a rubber hollow ring 8 that can expand and contract, and is configured to be held in position within the strainer casing 2 by the water pipe 6. . The hollow ring 8 may be made of neoprene rubber or the like, but in this embodiment, as shown in FIG. (Although tube tires are preferred.)
are using.

The specific configuration of the internal packer 5 is as follows.

That is, as shown in FIG. 2, metal plates 9 are provided on both sides of the hollow ring (automobile tire) 3 in the axial direction.
a, 9b, one metal plate 9a is supported on a seat 10 welded to the water pipe 6, and several bolts 11 passing through these three parts 10, 9a, 9b are screwed together. By adjusting the distance between both metal plates 9a, 9b with nuts 12..., the basic outer diameter (outer diameter when in a contracted state) of hollow ring 8 is adjusted, and both metal plates 9a, 9b and wheel 1 are adjusted.
3 to control the amount of expansion of the hollow ring 8 in the axial and radial directions. 14
16 is a pressure gauge, and 17 is a valve. In addition, the internal packer 5 includes a small diameter pipe 1 that passes through both metal plates 9a and 9b and is welded all around to the lower (or upper) metal plate 9a or 9b.
8 is provided. This small-diameter pipe 18 can be used for water level observation by inserting a liquid level switch (monitoring the pressurized water level in the aquifer during the period when no drainage is performed), or for forced suction by applying negative pressure to the area below the internal pump car 5. Strainer casing 2
It is used as a pressure reducing pipe to remove clogging (to rejuvenate wells).

According to the above configuration, when both the upper and lower internal packers 5, 5 are opened (contracted),
Three aquifers A, B, and C can be drained at the same time, and when the upper internal aquifer 5 is closed (inflated) and the lower internal aquifer 5 is open, the aquifers B, B, and C can be drained simultaneously.
C can be drained, and aquifer A is maintained at a constant water level. In addition, when both the upper and lower internal tankers 5 and 5 are closed, the water levels of aquifers A and B are maintained, only aquifer C is drained, and if the submersible pump 7 is stopped, the Since the pump 7 serves as a sealing material that cuts off communication between the upper and lower aquifers, the water levels of all the aquifers A, B, and C are maintained.

In addition, when drainage is performed with any of the internal gaskets 5 closed, gravity drainage occurs if the upper end of the small diameter pipe 8 is open, but if the upper end of the small diameter pipe 8 is closed airtight with a suitable plug. , submersible pump 7
As the water is pumped up, a negative pressure is generated below the internal packer 5, resulting in forced drainage and increasing water collection efficiency. Therefore, if it becomes necessary to increase the amount of water discharged per unit time for some reason, this can be done quickly.

In addition, when one of the internal packers 5 is closed and the aquifer below it is drained, the inside of the strainer casing 2 above the internal packer 5 is filled with water from the aquifer above. As a result, the noise and vibration of the submersible pump 7 are reduced.

FIG. 3 shows another embodiment of the invention. This embodiment is characterized in that the submersible pump 7 is provided between the upper and lower internal packers 5. Note that the upper internal packer 5 is attached to the water pipe 6 as in the previous embodiment, but the lower internal packer 5 is attached to a shaft body 6' that integrally extends downward from the submersible pump 7. ing. The other configurations are the same as in the previous embodiment.

According to this configuration, when both the upper and lower internal packers 5 are opened, the aquifers A and B can be drained, and the pressurized water level of the aquifer C is also lower than that of the submersible pump 7. If this is the case, water can be drained up to the water level of the submersible pump 7.

When the upper inner tanker 5 is closed and the lower inner tanker 5 is open, the water level of the aquifer A is maintained, the aquifer B is drained, and the aquifer C can be drained to a certain water level. . When the upper and lower internal packers 5 are closed, the aquifer A
The water level of the aquifer C is maintained, the aquifer B can be drained, and if the submersible pump 7 is stopped, the water level of the aquifer B is also maintained.

4 and 5 each show another embodiment of the invention.

In the embodiment shown in FIG. 4, submersible pumps 7 are arranged for each aquifer A, B, and C.
Both systems are characterized by the fact that they allow drainage to be carried out at any time and period. The structure of the internal packer 5 differs from the previous embodiments in that two water pipes 6 pass through the upper internal packer 5.

The embodiment shown in Fig. 5 utilizes the watertightness and airtightness of the internal packer 5 itself to create a clay layer (impermeable layer).
It is characterized by the fact that aquifers B and C, which are sandwiched between a, b, and c, are forcibly drained and water collection efficiency is increased by using a vacuum deep well (vacuum deep well construction method).

In conventional vacuum deep wells, in order to generate negative pressure inside the casing, a lid is welded to the top of the casing to provide airtightness, and the inside of the casing is suctioned with a vacuum pump to generate negative pressure. In this state, it was necessary to pump water with a submersible pump located at the bottom of the casing, but in the above example, the internal pump car and the water accumulated above it maintain complete airtightness, and the water is submerged in water. Since the volume reduction due to the pumping of groundwater by the pump 7 acts as negative pressure, a vacuum pump is not required, and there is no need to weld and fix a lid to the upper end of the strainer casing, so maintenance is easy.

The submersible pumps 7 were placed in the aquifers B and C, but the combinations of the positions of the submersible pumps 7 and the aquifers to be drained were shown in the above-mentioned Figures 1A, 3, and 4. But that's fine.

In each of the above embodiments, the case where the aquifers A, B, and C to be drained are three layers is explained as an example, but the method of the present invention can be applied to any case where the aquifers have two or more layers. It can be implemented as appropriate.

In addition, by installing a deep well with the above configuration inside a pile retaining wall such as an underground continuous wall, it is possible to perform dry work during underground excavation, and to prevent boiling, piping, plate blistering, etc. A deep well with the above configuration can be installed either inside or outside the retaining wall, as described above to reduce the lateral pressure on the back of the retaining wall and prevent heaving. , may be installed both inside and outside.

(Effects of the Invention) The present invention has the above-mentioned configuration, and since multiple aquifers can be drained with one deep well, the number of deep wells and installation cost can be reduced, and the internal tank By operating the submersible pump, only the lower aquifer can be drained without draining the upper aquifer, eliminating the need to drain unnecessary aquifers above the submersible pump. Therefore, by reducing the amount of drainage water, it is possible to prevent subsidence of the surrounding ground due to drainage water and to reduce the cost of discharging water into the sewage system.

In particular, when draining the lower aquifer with the internal aquifer blocking the upper and lower aquifers, the strainer casing above the internal aquifer is filled with water from the upper aquifer. In this state, water is drained using a submersible pump, so
Noise and vibration from submersible pumps are less likely to be transmitted to the ground,
It is possible to reduce the noise and vibration of submersible pumps that affect the surrounding area.

Moreover, when draining the lower aquifer with the internal tanker blocking the upper and lower aquifers, the airtightness and watertightness of the internal tanker are used to generate negative pressure as water is pumped by the submersible pump. This makes it possible to demonstrate the effectiveness of the vacuum deep well construction method, increase water collection efficiency, and reduce the number of deep wells installed.

In addition, as in the above-mentioned embodiment, by installing a small diameter pipe for water level observation etc. and opening the lower part of the inner tanker to the atmosphere, a deep well can be created using the gravity drainage method, but the small diameter pipe can be airtight. By blocking it, the vacuum deep well construction method is effective, and forced drainage can increase water collection efficiency, so if it becomes necessary to increase the amount of drainage for some reason, it can be done immediately. can be countered.

In addition, if a deep well with the above configuration is installed outside the retaining wall, by blocking the upper and lower aquifers with an internal tanker, even if the water is left without draining for a long time, the upper layer will still be drained. It is not necessary to constantly drain the water, as this prevents the water from falling and causing the pressure water level at the lowest level to rise, creating a dangerous situation when excessive pressure is applied to the back of the retaining wall.

Furthermore, since the minimum number of deep wells is required, it can be applied even when there is little space for deep wells around the retaining wall. The impact on the surrounding neighborhood can be minimized.

[Brief explanation of drawings]

Figure 1 A, B, C, and D are schematic sectional views showing one embodiment of the present invention, and Figure 2 is a configuration diagram of an internal packer.
3 to 5 are schematic cross-sectional views showing other embodiments of the present invention. FIGS. 6 and 7 are explanatory diagrams of conventional examples. A, B, C...aquifer, a, b, c...impermeable layer,
1... Vertical hole, 2... Strainer casing, 3... Filter material, 4... External filter, 5... Internal filter, 7... Submersible pump.

Claims (1)

[Claims] 1. A vertical hole spanning multiple aquifers is excavated, a strainer casing with water holes formed at positions corresponding to each aquifer to be drained is inserted into the vertical hole, and the strainer casing and the hole wall are connected. In between,
A filter material is filled in the positions corresponding to each of the aquifers, and an external packer made of impermeable mortar is formed in the position corresponding to the impermeable layer, and a submersible pump is installed at a desired depth inside the strainer casing. At the same time, an internal packer is provided above the submersible pump and at a position corresponding to the external packer, which can be switched between a state in which the upper and lower aquifers are cut off and a state in which the upper and lower aquifers are communicated by operation from the ground. A groundwater drainage method using a deep well, characterized in that an aquifer to be drained is selected by blocking and communicating upper and lower aquifers.