JPH06220865A - Double cofferdam process - Google Patents

Abstract

PURPOSE:To economically design a double cofferdam without necessity of loading a residual hydraulic pressure upon designing, by embedding well points in sand filled between inner and outer steel sheet piles surrounding an underwater space so as to forcibly discharge water therefrom in order to hold the water at a low level. CONSTITUTION:Steel sheet piles 3, 4 are driven into the bottom 2 of a river around a bridge pier 1 with a predetermined space therebetween so as to define two chambers. Then, the steel sheet piles are fastened together by tie-rods 5 at positions near to the top ends thereof, and then cut beams 7 are laid in the space, and further, packing sand 8 is filled between the sheet piles 7. Then, well points 9 are driven into the sand 8 so as to forcibly discharge water from the packing sand 8 so that the level of the water in between the sheet piles 7 is lowered from a high level (HWL) equal to the water level on the river side, to a low level (LWL), and accordingly, the level (WL) of the water is held due to the balance between the remaining quantity of the water in the packing sand 8 and the displacement. Accordingly, it is only necessary for strength calculation for the outer sheet piles to count an active earth pressure and a passive earth pressure, thereby it is possible to economically construct a double cofferdam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double cut-off construction method which is carried out at the time of new construction or removal work of bridges such as coasts and rivers having different water levels due to the effects of the ebb and flow of tide.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a double deadline for removing bridge piers in a bridge removing work. The steel sheet piles 3 and 4 are struck on the riverbed 2 around the pier 1 with a required space between them. After the steel sheet piles 3 and 4 are connected near the top end with the tie rods 5 to double-enclose the underwater 6, the beam girder 7 is disposed inside.
Filling sand 8 between the steel sheet piles.

Further, when calculating the outer steel sheet pile 4 used therein, as shown in FIG. 4, in addition to the active earth pressure and the passive earth pressure, the water level difference due to the tide is considered in consideration of the high water level (HWL). ) And the low water level (LWL), the residual water pressure is to be loaded.

[0004]

However, since the inner and outer steel sheet piles 3 and 4 are only connected by the tie rods 5 near the top end, when the water depth becomes considerably deep, the residual water pressure comes into effect and the outer steel sheet is cut. The design span of the sheet pile 4 becomes long and the member size also becomes large, resulting in an uneconomical design.

The problem due to this residual water pressure is that the water level (WL) in the medium sand is still high (HWL) even though the water level on the river side has dropped from high water level (HWL) to low water level (LWL). It occurs when the water level (WL) in the stuffed sand is always lower than the high water level (HWL). Therefore, the water level (WL) in the stuffed sand is reduced to some low level by some means. If it is lowered to LWL), the problem is solved and the outer steel sheet pile 4 can be economically designed.

Therefore, the object of the present invention is to provide a new solution that can surely lower the water level in the filling sand and keep the water level (WL) at a low water level (LWL) to solve the problem due to the residual water pressure. It is to provide a double deadline construction method.

[0007]

Means for Solving the Problems The feature of the present invention according to the above-mentioned object is that the water in a river or the like is doubly surrounded by steel sheet piles inside and outside to fill the filling sand between the steel sheet piles, and the filling sand is a well. By embedding points, etc., the water level in the middle sand is lowered and maintained at a low water level on the river side by forced drainage, which enables economical design without the need to load residual water pressure during design. .

[0008]

1 and 2 show an embodiment of the present invention, in the same manner as in the conventional construction method, first, a steel sheet pile 3 is formed inside and outside the river bed 2 around the pier 1 with a required space. Place 4
Next, near the top ends of the steel sheet piles 3 and 4 are connected by a tie rod 5 to double-surround the underwater 6, and then a cross beam 7 is arranged inside to fill the filling sand 8 between the steel sheet piles. .

In addition, a well point 9 or the like used in a normal groundwater level lowering method is embedded in the upper layer of the filling sand 8 by driving. This well point 9 forcibly drains the water in the filling sand, lowers the water level (WL) in the filling sand that was at the high water level (HWL) on the river side to the low water level (LWL), and The water level (WL) is maintained from the balance between the residual water amount and the drainage amount.

In such a state, the water level (W
L) is always located at the low water level (LWL) on the river side without being affected by the water level difference on the river side caused by the ebb and flow of the tide. Therefore, the high water level (HWL) and the low water level (LWL) The residual water pressure at the time of calculation due to the water level difference is erased, and as shown in FIG. 2, when calculating the strength of the outer steel sheet pile 4, it is sufficient to consider only the active earth pressure and the passive earth pressure.

As a result, the following differences occurred for the outer steel sheet pile. Length (m) Insertion length (m) Type (FSP-VL type) According to the present invention 18.0m 7.1m Rigid is possible Conventional method 26.0m 15.2m Rigidity is not possible

Although the above-mentioned embodiment is directed to the deadline of rivers, the present invention is applicable to deadlines other than rivers, and is not particularly limited to the deadline construction method for rivers.

[0013]

As described above, according to the present invention, the water level in the filling sand is maintained at a low level on the river side by the forced drainage by the well point in the filling sand. Since the influence of residual water pressure has been solved, the depth of penetration of the outer steel sheet pile is shallower than before, and the steel sheet pile used there does not have to be highly rigid, so the sheet pile length and sheet pile size Since the tie rod and the like can be made small and the work of inserting the steel sheet pile becomes easy, the process and construction cost can be reduced.

Moreover, since the water level in the filled sand is maintained at a low level simply by performing forced drainage at a well point or the like, it is possible to use the conventional groundwater level lowering method as it is, and thus the deadline can be achieved. It is also possible to economically construct a double deadline for rivers with deep water, which was difficult with the construction method.

[Brief description of drawings]

FIG. 1 is an explanatory view of a double shutoff method according to the present invention.

FIG. 2 is a pressure distribution diagram for the outer steel sheet pile.

FIG. 3 is an explanatory diagram of a conventional double cutoff method.

FIG. 4 is a pressure distribution diagram for the outer steel sheet pile.

[Explanation of symbols]

 1 Bridge pier 2 Riverbed 3 Steel sheet pile on the inside 4 Steel sheet pile on the outside 5 Tie rod 6 Underwater in river 7 Cutting beam 8 Medium sand 9 Well point

Claims (1)

[Claims] 1. The water level in the inside filling sand is obtained by doubly surrounding the water of a river or the like with inner and outer steel sheet piles and filling the filling sand with the filling sand between the sheet piles. The double cutoff method is characterized in that the water is kept at a low water level on the river side by forced drainage.