Water-stopping method and structural foundation construction method

Abstract

This invention provides a simple and quick method for preventing the inflow of groundwater, as well as a method for constructing the foundation of a structure. [Solution] A method for stopping water flow into an excavation pit 1 into which groundwater flows, comprising: an installation step of assembling a steel formwork 10 having a steel plate 12 surrounding the inner perimeter of the wall surface 3 of the excavation pit 1 outside the excavation pit 1 and installing it inside the excavation pit 1 into which groundwater accumulates; a backfilling step of backfilling improved soil 20 between the steel plate 12 and the wall surface 3 of the excavation pit 1; and an underwater concrete pouring step of pouring underwater concrete C1 onto the bottom surface 5a of the excavation pit 1 surrounded by the steel formwork 10.

Description

Technical Field

[0001] The present invention relates to a water stop method for an excavation site, and particularly to a water stop method and a structure foundation construction method at an excavation site where spring water constantly flows in.

Background Art

[0002] Conventionally, when constructing underground structures such as structure foundations, a construction method is adopted in which a predetermined range of ground is excavated to form an excavation pit, the surrounding wall surfaces are retained, and then the underground structure is constructed inside the excavation pit. In addition, when the groundwater level around the excavation pit is high, a construction method is known in which deep wells or steel sheet piles are constructed on the wall surfaces and the bottom surface to prevent spring water from flowing in from the wall surfaces and the bottom surface. However, when the ground to be excavated is close to a water source such as the sea, or when the ground is soft in a reclaimed land or the like, a situation arises where a large amount of spring water constantly flows into the excavation pit. In addition, it is difficult to construct deep wells, steel sheet piles or the like in a situation where there are obstacles such as existing structures in the surroundings.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] The present invention has been made to solve the above problems, and provides a water stop method and a structure foundation construction method capable of preventing the inflow of spring water easily and in a short period of time even when spring water constantly flows into the excavation pit.

Means for Solving the Problem

[0005] As an embodiment of the present invention to solve the above problems, this invention provides a method for stopping water flow into an excavation pit, comprising: an installation step of assembling a steel formwork having steel plates surrounding the inner perimeter of the wall surface of the excavation pit outside the excavation pit and installing it inside the excavation pit where the water is accumulating; a backfilling step of backfilling improved soil between the steel plates and the wall surface of the excavation pit; and an underwater concrete pouring step of pouring underwater concrete into the bottom surface of the excavation pit surrounded by the steel formwork. According to this embodiment, it is possible to prevent groundwater from flowing into the excavation pit in a simple and short period of time. Furthermore, in a foundation construction method based on the above-mentioned water-stopping method, if the groundwater in the excavation pit is drained after the underwater concrete has hardened, leveling concrete is poured on top of the hardened underwater concrete, and the structural foundation is constructed on top of the leveling concrete after it has hardened, the time required to construct the structural foundation can be significantly shortened. [Brief explanation of the drawing]

[0006] [Figure 1] This is a schematic cross-sectional view showing the excavated ground. [Figure 2] This is a schematic perspective view showing a simple earth retaining frame. [Figure 3] This diagram shows the water-stopping process and the construction process for the structural foundation. [Modes for carrying out the invention]

[0007] The present invention will be described in detail below through embodiments of the invention. However, the following embodiments are not intended to limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the solution of the invention; rather, they include configurations that can be selectively adopted.

[0008] Figure 1 shows an excavation pit 1 constructed at the excavation site G, which is excavated in an inverted trapezoidal cross-section. Within the excavation pit 1, a structural foundation K, such as the underground structural part of a concrete structure or the foundation concrete of a bridge pier, is constructed. As shown in the figure, the groundwater level H around the excavation pit 1 in this example extends to near the center of the excavation height (e.g., 2.5 m), and it is assumed that groundwater is constantly flowing in from the wall surface 3 and the bottom surface 5.

[0009] The present invention will be explained below with reference to Figures 2 and 3, following the flow of the watertight sealing process for the excavation pit 1 and the construction process for the structural foundation K. [Steel formwork assembly process] Figure 2 is a schematic perspective view of the steel formwork 10 assembled around the outside of the excavation pit 1. The steel formwork 10 comprises a plurality of steel plates 12 formed in a rectangular corrugated cross-section with uneven surfaces on both sides, and a plurality of angles 14 connecting the steel plates 12 to each other. The steel formwork 10 is assembled into a frame shape with openings at the top and bottom by connecting the plurality of steel plates 12 to each other.

[0010] The multiple angles 14 consist of an upper angle 14a extending along the extension direction of the upper edge of the multiple steel plates 12, a lower angle 14b extending along the extension direction of the lower edge of the multiple steel plates 12, and a vertical angle 14c extending along the extension direction of the side edge of the multiple steel plates 12. Each angle 14 and the multiple steel plates 12 are joined to each other at their contact surfaces, for example, by spot welding.

[0011] The width W and depth L of the steel formwork 10 are set to be slightly smaller than the width and depth (bottom area) of the bottom surface 5 of the excavation pit 1, so as to be sized to fit within the bottom surface 5. When the steel formwork 10 is installed in the excavation pit 1, each steel plate 12 of the steel formwork 10 faces the wall surface 3 of the excavation pit 1. In other words, the steel plates 12 of the steel formwork 10 surround the inner perimeter of the wall surface 3 of the excavation pit 1. Note that the planar shape of the steel formwork 10 and the number of steel plates 12 are not limited to those shown in the illustration and can be appropriately changed according to the shape and size of the excavation pit 1 in which it is to be installed.

[0012] The steel formwork 10 described above is filled with a waterproofing material 16 such as urethane foam. The waterproofing material 16 is a filling member that fills the small gaps that occur between each angle 14 and the steel plate 12. The waterproofing material 16 is provided along the extending direction of the lower angle 14b and along the lower half of the extending direction of the vertical angle 14c. The waterproofing material 16 provided on the lower angle 14b includes the area (corner) that comes into contact with the bottom surface 5 of the excavation pit 1. In addition, the filling range of the waterproofing material 16 on the vertical angle 14c is set so that the upper end of the waterproofing material 16 is higher than the groundwater level H.

[0013] [Steel formwork installation process] As shown in Figure 3(a), after the steel formwork 10 is created, the steel formwork 10 is installed in the excavation pit 1, which is filled with groundwater, using a lifting device such as a crane.

[0014] As shown in Figure 3(b), when the steel formwork 10 is installed in the excavation pit 1, the steel plates 12 of the steel formwork 10 face the wall surface 3, and a closed region R is formed around the inside of the wall surface 3, excluding the bottom surface 5 and the top of the excavation pit 1.

[0015] [Backfilling process] As shown in Figure 3(c), after the steel formwork 10 has been installed in the excavation pit 1, the space Q between the wall surface 3 of the excavation pit 1 and the steel plate 12 of the steel formwork 10 facing the inside of the wall surface 3 is backfilled with improved soil 20. The improved soil 20 may be soil generated when excavating the excavation pit 1, or treated soil with improved watertightness and compaction properties may be used.

[0016] The improved soil 20 is backfilled between the steel formwork 10 and the wall surface 3 and compacted, preventing excessive soil pressure from the wall surface 3 from causing deformation to the steel formwork 10. Furthermore, it provides watertightness against groundwater flowing in from the wall surface 3. The steel formwork 10 is then left permanently embedded in the excavation pit 1.

[0017] [Underwater concrete pouring process] As shown in Fig. 3(d), after backfilling the improved soil 20, underwater concrete C1 is placed. The underwater concrete C1 is placed on the bottom surface 5a within the region R surrounded by the steel formwork 10. By placing the underwater concrete C1 in the region R and allowing it to harden, a water stop layer conforming to the inner peripheral shape of the steel formwork 10 is formed on the bottom surface 5a in the region R.

[0018] By the backfilling of the improved soil 20 and the placement of the underwater concrete C1, the region R can be separated from the wall surface 3 and the bottom surface 5 of the excavation pit 1, and the water stop work for the excavation pit 1 is completed. Therefore, new spring water is prevented from flowing into the region R.

[0019] [Spring Water Discharge Step] As shown in Fig. 3(e), after the underwater concrete C1 hardens, the spring water accumulated in the region R is discharged. The discharge work may be performed, for example, by driving a pump P. By this discharge work, the region R inside the steel formwork 10 becomes a dry environment. Note that the installation of the pump P and the ladder S required for the discharge work can utilize the bench 22 formed by backfilling the improved soil 20.

[0020] [Leveling Concrete Placement Step] As shown in Fig. 3(f), after the spring water discharge work, leveling concrete C2 is placed. The leveling concrete C2 is concrete for flattening irregularities (unevenness) generated in the underwater concrete C1 placed in water.

[0021] [Structure Foundation Construction Step] As shown in Fig. 3(g), after placing and hardening the leveling concrete C2 in a dry environment, a structure foundation K such as a concrete structure can be constructed. For example, with the leveling concrete C2 as the bottom part, reinforced concrete is placed in a predetermined formwork. In addition, after the reinforced concrete hardens, the outer periphery is backfilled, so that the structure foundation K can be constructed in a state where a part thereof is embedded in the excavation pit 1.

[0022] According to the water-stopping method including the above steps, it is possible to prevent new groundwater from flowing into the area R of the steel formwork 10 by installing the steel formwork 10 in the excavation pit 1, backfilling with improved soil 20 using the steel formwork 10 as formwork, and pouring underwater concrete C1. Furthermore, by using the steel formwork 10 as formwork for the underwater concrete C1 and leveling concrete C2, it is possible to create a concrete bottom surface that corresponds to the inner circumference shape of the steel formwork 10. Furthermore, the assembly of the steel formwork 10 can be performed in a significantly shorter time compared to the waterproofing work (installation of impermeable layers and sheet piles) in the excavation pit 1 where groundwater constantly flows in. This allows for quick waterproofing of the excavation pit 1, resulting in a substantial reduction in the construction period until the structural foundation K is constructed. [Explanation of symbols]

[0023] 1 Excavation pit, 5 Bottom surface, 10 Steel formwork, 12 Steel plate, 14 Angle, 16 Waterproofing material, 20 Improved soil, C1 Underwater concrete, C2 Leveling concrete, H groundwater level, R area

Claims

1. A method for stopping water from seeping into an excavation pit, The installation process involves assembling a steel formwork having steel plates surrounding the inner perimeter of the wall surface of the excavation pit outside the aforementioned excavation pit, and then installing it inside the excavation pit where groundwater accumulates. A backfilling step in which improved soil is backfilled between the steel plate and the wall surface of the excavation pit, An underwater concrete pouring process in which underwater concrete is poured into the bottom surface of the excavation pit surrounded by the steel formwork, A method of stopping water flow, including a method of stopping water flow.

2. A method for constructing the foundation of a structure in an excavation pit into which groundwater flows, The installation process involves assembling a steel formwork having steel plates surrounding the inner perimeter of the wall surface of the excavation pit outside the aforementioned excavation pit, and then installing it inside the excavation pit where groundwater accumulates. A backfilling step in which improved soil is backfilled between the steel plate and the wall surface of the excavation pit, An underwater concrete pouring process in which underwater concrete is poured into the bottom surface of the excavation pit surrounded by the steel formwork, After the underwater concrete has hardened, a discharge step is performed to discharge the seepage water in the excavation pit, A leveling concrete pouring step in which leveling concrete is poured onto the hardened underwater concrete, A foundation construction process in which the foundation of the structure is constructed on the leveled concrete after the leveled concrete has hardened, A method for constructing the foundation of a structure, including [specific details omitted].

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