JP2001214452A - Ground-water level lowering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ground-water level lowering method without any restrictions on installing places with which water level lowering can be performed enough even in places where vertical wells are hard to install. SOLUTION: Lowering the ground-water level is designed by drilling a well horizontally from the inside of a shaft (3) which is installed under a construction work for a grade separation and draining water through a horizontal well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a countermeasure against groundwater using horizontal boring, and more particularly to a method for lowering a groundwater level by using a horizontal well.

[0002]

2. Description of the Related Art In a construction in which a track and a road are crossed in an overpass, if the groundwater level in the ground is high, the groundwater level in the surrounding ground must be lowered in order to facilitate construction prior to excavation work under the track. Is performed. As a technique for lowering the groundwater level, a deep well (deep well), a well point, and the like are conventionally known.

FIG. 3 is a view for explaining a conventional deep well construction method, and shows a cross section orthogonal to the line 1. A hole is drilled around the track 1 using a small-diameter steel pipe (casing) in the vertical direction from the ground surface, and then the casing is replaced with a screen (perforated pipe) 2 for draining only water without passing through the soil and forming a vertical well. Finishing is a method of collecting and pumping groundwater flowing out of the aquifer through the screen 2. Thus, the underground water level under the track is lowered, and the underground structure is constructed by excavating under the track through the adjacent shaft 3.

[0004]

FIG. 4 is a view for explaining a problem of the conventional method of lowering the groundwater level, and shows a cross section parallel to the railway track. Curve 4 in the figure shows the groundwater level. The water level drop is greatest in the area A near the well, the water level drop gradually decreases as the distance from the well increases, and in the construction section B, the distance between the wells is long. The groundwater cannot be lowered to the required water level.

As described above, in the method of lowering the groundwater level using a vertical well, when the vertical well cannot be installed due to the topography or obstacles, the water level may not be lowered to the groundwater level required for construction depending on the location. In addition, there is a problem in that the effective length of the screen (the length of a portion where water can be collected) is reduced as the groundwater level is reduced, so that the efficiency is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has an object to reduce the groundwater level sufficiently even in a place where it is difficult to install a vertical well without being restricted by an installation place. And

[0007]

For this purpose, the present invention is characterized in that a well is installed in a horizontal direction from inside a shaft installed in a grade separation work, and water is drained to lower the groundwater level. Since the horizontal well is constructed from inside the shaft, there is no restriction on the installation position such as a well which is conventionally installed vertically from the ground surface. Even if the water level drops, the catchment area (screen) is at the groundwater table and the catchment efficiency does not decrease. In addition, the vertical wells create an axisymmetric groundwater flow centered on the wells, while the horizontal wells create a flow parallel to the well axis at right angles to the wells, thus increasing the water collection efficiency. It has the characteristic of being good.

[0008]

Embodiments of the present invention will be described below. FIG. 1 is a view for explaining the groundwater level lowering method of the present invention, and shows a cross section orthogonal to the track 1. The construction method of the present invention is intended for a construction in which a shaft is installed in a grade separation work. Using a small-diameter steel pipe (casing) to protect the face from inside the shaft 3, drill the hole, insert the screen 10 when the drilling of a predetermined length is completed, and then gradually remove the casing to remove the casing. Swap the screen to make it a horizontal well. Due to the method of setting wells from inside the shaft, there is no possibility that they cannot be set due to topography and obstacles. If the ground is hard like sandstone, a screen may or may not be used. Depending on the distance between the shafts (the distance between the starting shaft and the reaching shaft), the installation of the horizontal well is performed as follows, for example. When the separation between the shafts is short, a hole from inside the shaft is penetrated to the opposite shaft, and the start shaft and the arrival shaft are penetrated by the well. When the separation between the shafts is long, drilling from inside the shaft is stopped in the ground, and wells are respectively installed from the starting shaft and the arrival shaft.

[0009] The water in the aquifer is collected and pumped through the horizontal wells thus set, and the water level is lowered. Conventionally, even if the water level drops, the entire surface area of the well installed horizontally in the aquifer becomes the catchment area compared to the wells installed vertically from the ground surface. The well produces an axisymmetric groundwater flow centered on the well, while the horizontal well produces a flow parallel to the well axis at right angles to the well.

FIG. 2 is a diagram for explaining the effect of lowering the groundwater level due to the horizontal well, showing a cross section parallel to the railway track, and a curve 11 showing the groundwater level. As shown in the figure, it can be seen that the water level can be effectively lowered by the horizontal well 12 installed below the installation location of the main body structure 5.

In some cases, there is a layer, such as a clay layer, which is difficult to pass water at a certain depth where the structure is installed. If such a layer is detected in advance by inspection, it is difficult to pass water. It is desirable to install a horizontal well also above the layer. When a vertical well is easily installed, the vertical well and the horizontal well may be used together to lower the water level.

[0012]

As described above, according to the present invention, a well is installed in a horizontal direction from the inside of a shaft to be installed in a grade separation work, and water is drained to lower the groundwater level. The groundwater level can be sufficiently lowered even in a place where it is difficult to install a vertical well due to topography and obstacles, without being restricted by the place. In addition, the effect of lowering groundwater continuously in the horizontal direction can be expected by installing a plurality of them.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for lowering a groundwater level using a horizontal well according to the present invention.

FIG. 2 is a diagram illustrating groundwater level drop according to the present invention.

FIG. 3 is a diagram illustrating a conventional deep well method.

FIG. 4 is a diagram illustrating a problem of a conventional groundwater level lowering method.

[Explanation of symbols]

1 ... track, 3 ... shaft, 5 ... structure, 10 ... screen,
11 ... groundwater level curve, 12 ... horizontal well,

Claims (4)

[Claims] 1. In an overpass construction where a shaft is installed,
A method of lowering the groundwater level, characterized by lowering the water level in the surrounding ground by draining water by installing wells laterally from the shaft. 2. The method according to claim 1, wherein the starting shaft and the reaching shaft are penetrated by wells. 3. The well according to claim 1, wherein wells are respectively installed from the starting shaft and the reaching shaft to the middle of the ground.
Groundwater level reduction method described. 4. In an overpass construction where a shaft is installed,
A groundwater level lowering method characterized by draining water by using a well installed horizontally from a shaft and a well installed vertically from the ground surface, and lowering the water level in the surrounding surrounding ground.