Rebound suppression method, rebound suppression structure and design method upon excavation

Abstract

To provide a rebound suppression method, a rebound suppression structure and a design method upon excavation, capable of carrying out rebound countermeasures in a low cost after starting underground work.SOLUTION: A rebound suppression method upon excavation of a ground at an excavation side of an earth retaining wall having impervious performance has: a step S1 of providing an impervious wall reaching a low-permeable layer in the ground with a predetermined distance from the earth retaining wall; and a step S2 of increasing effective stress in a region between the impervious wall and the earth retaining wall by pumping up underground water from the region.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for suppressing rebound during excavation, a rebound suppression structure, and a design method.

Background Art

[0002] Conventionally, it has been known that rebound (lifting) of the surrounding ground and existing structures occurs due to stress relief during excavation (see, for example, Patent Document 1). As shown in FIG. 6, when there is concern about the influence of the rebound of an existing structure due to adjacent construction (excavation work), it is confirmed in advance by numerical analysis (for example, FEM analysis) that the displacement of the existing structure is within the allowable value. If it is determined that the existing structure is adversely affected (for example, exceeding the management value, etc.), a radical review of the construction plan is required.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, it has been difficult to predict the deformation of the surrounding ground in advance by numerical analysis. In addition, there has been a problem that there is no low-cost and effective countermeasure work for the rebound of existing structures after the start of underground construction. For this reason, a technique that can perform a low-cost rebound countermeasure after the start of underground construction has been demanded.

[0005] The present invention has been made in view of the above, and an object thereof is to provide a method for suppressing rebound during excavation, a rebound suppression structure, and a design method that can perform a low-cost rebound countermeasure after the start of underground construction.

Means for Solving the Problems

[0006] In order to solve the above problems and achieve the object, a method for suppressing rebound during excavation according to the present invention is a method for suppressing rebound when excavating the ground on the excavation side of a water retaining wall having water impermeability, the method including: providing a water cutoff wall reaching a semi-permeable layer in the ground at a predetermined distance from the water retaining wall; and pumping groundwater from the region between the water cutoff wall and the water retaining wall to increase the effective stress in the region.

[0007] Further, a rebound suppression structure during excavation according to the present invention is a rebound suppression structure for suppressing rebound when excavating the ground on the excavation side of a water retaining wall having water impermeability, the structure including: a water cutoff wall reaching a semi-permeable layer in the ground and provided at a predetermined distance from the water retaining wall; and a pumping facility for pumping groundwater from the region between the water cutoff wall and the water retaining wall.

[0008] Further, a design method for a rebound suppression structure during excavation according to the present invention is a method for designing the above-described rebound suppression structure during excavation, the method including: setting an allowable displacement amount of an existing structure provided in the ground on the back side of the water retaining wall; calculating a rebound amount of the bedding surface of the ground on the excavation side; calculating a rebound amount of the ground on the back side based on the calculated rebound amount of the bedding surface; calculating a required settlement amount of the existing structure based on the calculated rebound amount of the ground and the set allowable displacement amount; calculating a required water level drop amount based on the calculated required settlement amount, a deformation coefficient of the ground, and the groundwater level; and designing a pumping facility capable of realizing the calculated required water level drop amount.

Advantages of the Invention

[0009] According to the method for suppressing rebound during excavation according to the present invention, it is a method for suppressing rebound when excavating the ground on the excavation side of a water retaining wall having water impermeability, the method comprising the steps of providing a water barrier reaching a semi-permeable layer in the ground at a predetermined distance from the water retaining wall, and pumping out groundwater from the area between the water barrier and the water retaining wall to increase the effective stress in the area. Therefore, it is possible to take countermeasures against rebound at low cost after the start of underground construction.

[0010] Further, according to the rebound suppression structure during excavation according to the present invention, it is a rebound suppression structure for suppressing rebound when excavating the ground on the excavation side of a water retaining wall having water impermeability, the structure comprising a water barrier reaching a semi-permeable layer in the ground and provided at a predetermined distance from the water retaining wall, and a pumping facility for pumping out groundwater from the area between the water barrier and the water retaining wall. Therefore, it is possible to take countermeasures against rebound at low cost after the start of underground construction.

[0011] Further, according to the design method of the rebound suppression structure during excavation according to the present invention, it is a method for designing the above-described rebound suppression structure during excavation, the method comprising the steps of setting an allowable displacement amount of an existing structure provided in the ground on the back side of the water retaining wall, calculating a rebound amount of the floor surface of the ground on the excavation side, calculating a rebound amount of the ground on the back side based on the calculated rebound amount of the floor surface, calculating a required settlement amount of the existing structure based on the calculated rebound amount of the ground and the set allowable displacement amount, calculating a required water level drop amount based on the calculated required settlement amount, the deformation coefficient of the ground, and the groundwater level, and designing a pumping facility capable of realizing the calculated required water level drop amount. Therefore, it is possible to efficiently design a rebound suppression structure.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of a rebound suppression method, a rebound suppression structure, and a design method during excavation according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by this embodiment.

[0014] (Rebound Suppression Method during Excavation) As shown in Fig. 1, the rebound suppression method during excavation according to the embodiment of the present invention is a method for suppressing rebound when excavating the ground on the excavation side of a retaining wall, and includes a step S1 of installing a water barrier near the excavation side of a retaining wall having water impermeability, a step S2 of pumping up the groundwater in the region surrounded by the water barrier and the retaining wall, and a step S3 of suppressing the rebound of an existing structure.

[0015] As shown in Figs. 2 and 3, the existing structure 10 is provided in the ground G1 on the back side of the retaining wall 12. In this embodiment, close construction is assumed in which the position of the existing structure 10 is such that the distance from the retaining wall 12 / excavation width < 0.5.

[0016] By arranging the water-blocking wall 14 in a U-shape when viewed from above, an area A surrounded by the water-blocking wall 14 and the retaining wall 12 is formed. When groundwater is partially pumped out from this area A by the pumping well 22 (partial area pumping), the groundwater level WL in this area A drops, and the effective stress in the area A increases. By implementing this partial area pumping during excavation, the in-situ stress acting near the retaining wall 12 is controlled and managed, and the rebound of the existing structure 10 on the back side of the retaining wall 12 is suppressed. According to this method, since it is only necessary to construct the water-blocking wall 14 near the excavation side of the retaining wall 12 and perform partial area pumping, after the start of the underground construction, countermeasures against rebound can be taken at low cost.

[0017] In addition, when the inventor applied the present invention to a certain site and lowered the groundwater level of the area by 1 m by partial area pumping, the vertical displacement of the existing structure located 10 m from the retaining wall was a rebound amount (settlement amount) of ±0.2 mm as measured value. From this measured value, it can be seen that the drop in the groundwater level WL can function effectively as a countermeasure against the rebound of the adjacent existing structure.

[0018] (Rebound suppression structure) As shown in FIGS. 2 and 3, the rebound suppression structure 100 during excavation according to the embodiment of the present invention is a rebound suppression structure for suppressing the rebound when excavating the ground G2 on the excavation side of the retaining wall 12, and includes the above-described water-blocking wall 14 and the pumping well 22 (pumping facility). According to this structure, as described above, after the start of the underground construction, countermeasures against rebound can be taken at low cost.

[0019] (Design method of rebound suppression structure) As shown in FIG. 4, the design method of the rebound suppression structure during excavation according to the embodiment of the present invention is a method for designing the above-described rebound suppression structure 100 during excavation, and is implemented by the following steps T1 to T7.

[0020] First, in step T1, the allowable displacement amount da of the existing structure 10 is set. The allowable displacement amount da of the existing structure 10 can be set, for example, according to the guidelines for adjacent construction determined by the operator who manages the existing structure 10.

[0021] In the next step T2, the rebound amount of the floor surface GL of the ground G2 on the excavation side is calculated. For the calculation of the rebound amount of the floor surface GL, for example, a simple theoretical solution (such as a multiple approximation solution using Steinbrenner's elastic solution) or the finite element method (FEM) can be used.

[0022] In the next step T3, based on the calculated rebound amount of the floor surface GL, the rebound amount d2 (see Fig. 6) of the back ground (the ground G1 on the back side) of the retaining wall 12 is calculated. The rebound amount d2 of the back ground of the retaining wall 12 can be calculated, for example, by the following empirical formula based on the measured data (see Fig. 5).

[0023]

Equation

[0024] Here, d1 is the maximum rebound amount of the floor surface GL (see Fig. 6), and α is the influence coefficient (0.2 - 0.5). When it is considered that the settlement of the back ground due to the collapse of the retaining wall 12 is small, d2 can be regarded as the rebound amount of the existing structure 10.

[0025] In the next step T4, based on the calculated rebound amount d2 of the back ground of the retaining wall 12 and the set allowable displacement amount da, the required settlement amount S of the existing structure 10 is calculated. The required settlement amount S can be calculated from the difference between the rebound amount d2 of the existing structure 10 and the allowable displacement amount da.

[0026] In the next step T5, the countermeasure range (the construction range of the water cutoff wall 14) of the area A where partial area pumping is performed is determined. The construction range of the water cutoff wall 14 can be determined, for example, based on the proximity extension W (see FIG. 2) of the existing structure 10 with respect to the retaining wall 12. In this case, as shown in FIG. 2, the horizontal length of the water cutoff wall 14 along the retaining wall 12 may be set to about W / 3, and the distance between the retaining wall 12 and the water cutoff wall 14 may be set to about W / 10 to W / 5. The retaining wall 12 and the water cutoff wall 14 are, in principle, embedded in the low-permeability layer 16, and a pumping well 22 (pumping facility) is provided in the area A surrounded by them.

[0027] In the next step T6, based on the calculated required settlement amount S, the deformation coefficient of the ground in area A, and the groundwater level WL before pumping, the required water level drop amount s (see FIG. 3) is calculated. The required water level drop amount s can be calculated by transforming the relational expression of the immediate settlement under the one-dimensional compression condition as follows.

[0028]

Equation

[0029] Here, S: required settlement amount, Δσ: increment of effective stress caused by the drop of the groundwater level WL, E: deformation coefficient of the ground, H: distance from the groundwater level WL before pumping to the upper end of the low-permeability layer 16 (see FIG. 3), s: required water level drop amount, γ w : unit weight of water.

[0030] In the next step T7, a pumping well 22 (pumping facility) capable of realizing the calculated required water level drop amount s is designed. By doing so, the above-mentioned rebound suppression structure 100 can be designed efficiently.

[0031] As described above, according to the method for suppressing rebound during excavation according to the present invention, it is a method for suppressing rebound when excavating the ground on the excavation side of a water retaining wall having water impermeability, and includes the steps of providing a water cutoff wall reaching a semi-permeable layer in the ground at a predetermined distance from the water retaining wall, and pumping groundwater from the area between the water cutoff wall and the water retaining wall to increase the effective stress in the area. Therefore, it is possible to take rebound countermeasures at low cost after the start of underground construction.

[0032] Further, according to the rebound suppression structure during excavation according to the present invention, it is a rebound suppression structure for suppressing rebound when excavating the ground on the excavation side of a water retaining wall having water impermeability, and includes a water cutoff wall reaching a semi-permeable layer in the ground and provided at a predetermined distance from the water retaining wall, and a pumping facility for pumping groundwater from the area between the water cutoff wall and the water retaining wall. Therefore, it is possible to take rebound countermeasures at low cost after the start of underground construction.

[0033] Further, according to the design method of the rebound suppression structure during excavation according to the present invention, it is a method for designing the above-described rebound suppression structure during excavation, and includes the steps of setting the allowable displacement amount of an existing structure provided in the ground on the back side of the water retaining wall, calculating the rebound amount of the bedding surface of the ground on the excavation side, calculating the rebound amount of the ground on the back side based on the calculated rebound amount of the bedding surface, calculating the required settlement amount of the existing structure based on the calculated rebound amount of the ground and the set allowable displacement amount, calculating the required water level drop amount based on the calculated required settlement amount, the deformation coefficient of the ground, and the groundwater level, and designing a pumping facility capable of realizing the calculated required water level drop amount. Therefore, the rebound suppression structure can be designed efficiently.

[0034] Note that there are 17 international goals adopted at the United Nations Summit in September 2015, namely the "Sustainable Development Goals (SDGs)". The rebound suppression method, rebound suppression structure, and design method during excavation according to this embodiment of the present invention can contribute to the achievement of, for example, the goal of "12. The responsibility to produce and the responsibility to consume" among these 17 SDG goals.

Industrial Applicability

[0035] As described above, the rebound suppression method, rebound suppression structure, and design method during excavation according to the present invention are useful for countermeasures against the rebound of the surrounding ground and existing structures accompanying stress release during excavation. In particular, they are suitable for performing rebound countermeasures at low cost after the start of underground construction.

Explanation of Signs

[0036] 10 Existing structure 12 Retaining wall 14 Waterproof wall 16 Semi-permeable layer 22 Drain well (pumping equipment) 100 Rebound suppression structure during excavation Area A G1, G2 Ground GL Floor surface WL Groundwater level

Claims

1. A method for suppressing rebound when excavating the ground on the excavation side of a retaining wall having water shielding properties, comprising: providing a water shielding wall reaching a semi-permeable layer in the ground at a predetermined distance from the retaining wall; and pumping up groundwater from the area between the water shielding wall and the retaining wall to increase the effective stress in the area. A method for suppressing rebound during excavation, characterized by comprising these steps.

2. A rebound suppression structure for suppressing rebound when excavating the ground on the excavation side of a retaining wall having water shielding properties, comprising: a water shielding wall reaching a semi-permeable layer in the ground and provided at a predetermined distance from the retaining wall; and a pumping facility for pumping up groundwater from the area between the water shielding wall and the retaining wall. A rebound suppression structure during excavation, characterized by comprising these components.

3. A method for designing the rebound suppression structure during excavation according to Claim 2, comprising: setting an allowable displacement amount of an existing structure provided in the ground on the back side of the retaining wall; calculating a rebound amount of the floor surface of the ground on the excavation side; calculating a rebound amount of the ground on the back side based on the calculated rebound amount of the floor surface; calculating a required settlement amount of the existing structure based on the calculated rebound amount of the ground and the set allowable displacement amount; calculating a required water level drop amount based on the calculated required settlement amount, the deformation coefficient of the ground, and the groundwater level; and designing a pumping facility capable of achieving the calculated required water level drop amount. A method for designing a rebound suppression structure during excavation, characterized by comprising these steps.

Images