JP5173782B2 - Groundwater flow conservation method - Google Patents

Description

  The present invention relates to a groundwater flow maintenance method for securing groundwater flow by collecting and / or recharging groundwater blocked by a constructed retaining wall in a well structure provided on the retaining wall.

  Conventionally, for example, when constructing an underground structure 1 such as a subway or an underground road as shown in FIG. 8, a retaining wall 2 composed of a continuous underground wall or the like is constructed on both sides of the planned construction position and excavated between them. Thus, a so-called open-cut method for constructing the underground structure 1 is frequently used.

  On the other hand, the groundwater flow T (groundwater flow) of the aquifer 3 is blocked by the earth retaining wall 2, the groundwater level rises on the upstream side of the earth retaining wall 2, the groundwater level falls on the downstream side, and the well withers. And subsidence, or ecosystem changes and groundwater contamination.

  On the other hand, as shown in FIGS. 8 and 9, a device having a well structure is installed in the retaining wall 2, or the retaining wall 2 is partially broken using an abrasive jet to form a slit-like opening ( Proposal and implementation of groundwater collection and / or recharge through the opening 5a of the well structure 5 by providing a well structure 5), etc., and collecting groundwater blocked by the retaining wall 2 (For example, see Patent Document 1, Patent Document 2, and Patent Document 3).

And in such a groundwater flow maintenance construction method, as shown in FIG. 9, when determining the width | variety ( _Bw ) of the opening part 5a for collecting and / or recharging groundwater (designing the well structure 5) In general, the equivalent well radius (r _w ) calculated by Equation 1 is used instead of the equivalent well radius (r _w ) of a well having a peripheral length equivalent to the width (B _w ) of the opening. (See Non-Patent Document 1).

JP 2000-87385 A JP 2001-317045 A Japanese Patent Laid-Open No. 2004-232306 "Geotechnical engineering / practical series 19 Environmental impact assessment and countermeasures for groundwater flow conservation-from survey, design, construction to management", Geotechnical Society of Japan, October 15, 2004, p. 146

  However, since the applicability and validity of Formula 1 are not sufficiently confirmed, groundwater cannot be collected and / or recharged properly by the well structure 5 provided on the retaining wall 2. However, there was a risk that groundwater flow could not be secured. That is, there was a problem that the well structure 5 installed on the retaining wall 2 could not be properly designed.

On the other hand, the inventors of the present application have described the width (B _w ) of the opening of a well structure for collecting and / or recharging groundwater, and the equivalent well radius (r _w ) of a well having performance equivalent to this opening. ) Was derived as a relational expression, and after confirming its validity, it was found that the well structure provided on the retaining wall can be appropriately designed by using Expression 2.

ここで、ｒ_ｗ：井戸構造の開口部と等価な性能を有する井戸の等価井戸半径 [ｍ]
Ｂ_ｗ：井戸構造の開口部の幅 [ｍ]

Here, r _w : equivalent well radius of a well having performance equivalent to that of an opening of a well structure [m]
B _w : width of the opening of the well structure [m]

  However, Formula 2 assumes an ideal state in which the water permeability of the opening of the well structure is sufficiently secured. For this reason, the water collection performance and / or recharge performance of the well structure deteriorates when the opening is filled with a material with low water permeability. However, this situation should be evaluated and reflected in the design. However, the water collection performance and / or recharge performance of the well structure is appropriately evaluated and reflected in the design, or the construction management is performed after clarifying the design goal.

  In view of the above circumstances, the present invention can appropriately design the well structure by reflecting the water permeability of the opening of the well structure provided in the retaining wall, and can ensure a suitable groundwater flow. The purpose is to provide a possible groundwater flow protection method.

  In order to achieve the above object, the present invention provides the following means.

ここで、Q：井戸構造の実集水量又は実涵養量
ｓ_ｗ：開口部内の水位低下量又は水位上昇量
ｋ_１：地山の透水係数
ｋ_２：充填材の透水係数
D：開口部の長さ（＝帯水層の層厚）
Ｒ：影響圏半径
ｒ_ｗ：開口部の等価井戸半径
Ｂ_ｗ：開口部の幅
ｔ：開口部の奥行き（充填材の充填厚さ）
η：井戸効率（理想的な状態での集水量と実集水量の比、又は理想的な状態での涵養量と実涵養量の比）
Ｑ_０：理想的な状態での開口部の集水量又は涵養量 The groundwater flow maintenance method of the present invention is a groundwater that secures the flow of the groundwater by collecting and / or recharging groundwater blocked by the constructed retaining wall in a slit-like well structure provided on the retaining wall. In the fluidity maintenance method, the well efficiency of the well structure is set using the following equation.

Where, Q: Actual water collection or recharge for well structure
s _w : Amount of decrease in water level or amount of increase in water level in the opening
k ₁ : Permeability coefficient of natural ground
k ₂ : permeability coefficient of filler
D: Length of opening (= layer thickness of aquifer)
R: radius of influence zone
r _w : equivalent well radius of the opening
_Bw : width of the opening
t: Depth of opening (filling thickness of filler)
η: well efficiency (ratio of the amount of water collected in the ideal state to the actual amount of water collected, or the ratio of the amount of recharge in the ideal state to the actual amount of recharge)
Q ₀ : Amount of water collected or recharged in an ideal state

  According to the groundwater flow maintenance method of the present invention, by using the above formula, the water permeability and / or recharge capacity of the well structure is accurately reflected by reflecting the water permeability of the opening of the well structure provided in the retaining wall. Therefore, the well structure can be appropriately designed. Moreover, since the management target value in the construction with respect to the water permeability of the filler to be filled in the opening is clarified, it is possible to perform the construction with high reliability. As a result, it is possible to reliably ensure a suitable groundwater flow.

  Hereinafter, a groundwater flow maintenance method according to an embodiment of the present invention will be described with reference to FIGS. 1 to 9. In this embodiment, for example, when constructing an underground structure such as a subway or an underground road, groundwater blocked by a retaining wall such as an underground continuous wall constructed on both sides of the planned construction position is used as the retaining wall. The present invention relates to a groundwater flow maintenance method that secures groundwater flow by collecting and / or recharging the well structure provided.

In the groundwater flow maintenance method of this embodiment, when designing the well structure 5 provided in the retaining wall 2 in order to ensure the flow of groundwater blocked by the constructed retaining wall 2, groundwater is collected and / or Using the above equation 2 as a relational expression between the width (B _w ) of the opening 5 a to be recharged and the equivalent well radius (r _w ) of the well having the performance equivalent to this opening 5 a, the opening of the well structure 5 A width (B _w ) of 5a is set (see FIGS. 8 and 9).

This equation 2 calculates the water collection capacity (and / or recharge capacity) of the well structure 5 installed on the retaining wall 2 using the osmotic flow analysis by the finite element method. Compared with the well theoretical formula for calculating the capacity (water collecting capacity and / or recharge capacity), as shown in FIG. 1, the width (B _w ) of the opening 5a of the well structure 5 and the opening 5a This is derived by obtaining the relationship with the equivalent well radius (r _w ) of a well having equivalent performance.

FIG. 2 shows an example in which the well structure 5 of the retaining wall 2 is designed by using this equation 2, and the width (B of the opening 5a of the well structure 5 when the radius of influence R of the groundwater is set to 100 m and 1000 m. _It shows a change in the installation interval of the openings 5a of the well structure 5 with respect to _w ). Then, referring to such a calculation result, rational design is possible by comparing designs under various conditions in which the width (B _w ) of the opening 5a and the installation interval of the openings 5a are changed. become.

  FIG. 3 shows the result of analyzing the amount of groundwater level fluctuation blocked by the retaining wall 2 using the finite element method when the well structure 5 is installed on the retaining wall 2 based on the formula 2. The results obtained by the design method based on Equation 2 are compared. Here, in FIG. 3, when the groundwater influence sphere radius R is 100 m and the groundwater dynamic gradient I is 0.046, the groundwater influence sphere radius R is 1000 m and the groundwater dynamic gradient I is 0.005. In this case, the results are shown in the case where the influence radius R of the groundwater is 100 m and the dynamic gradient I of the groundwater is 0.005.

As shown in FIG. 3, in all cases, the groundwater level fluctuation amount obtained by the finite element method and the groundwater level fluctuation amount obtained by the design method based on Equation 2 are substantially the same, and these results From Equation 2, the validity of the design method for setting the width (B _w ) of the opening 5a of the well structure 5 and the installation interval of the openings 5a is demonstrated. Equation 2 can be applied under various conditions such as the permeability of the ground and the radius of influence radius R.

  On the other hand, since this formula 2 assumes an ideal state in which the water permeability of the opening 5a of the well structure 5 is sufficiently ensured, the material having low water permeability in the opening 5a in an actual site. Cannot be reflected in the design by evaluating the situation where the water collection performance and / or the recharge performance of the well structure 5 is reduced.

  On the other hand, in this embodiment, the water collection performance and / or the recharge performance (well efficiency) of the well structure 5 are set using the following formulas 3 and 4.

Here, as shown in FIGS. 4 and 5, Q is the actual current water or actual recharge of the well structure ^{5 (m 3 / sec),} s w is drawdown or level rise amount in the opening 5a (m ), K ₁ is the permeability of the natural ground (m / sec), k ₂ is the permeability of the filler 6 (m / sec), D is the length of the opening 5a (= layer thickness of the aquifer 3) ( m), R is the radius of influence (m), r _w is the equivalent well radius (m) of the opening 5a obtained by Equation 2, B _w is the width (m) of the opening 5a, and t is the depth of the opening 5a. (= Filling thickness of the filler) (m), η is well efficiency (ratio of water collection amount to actual water collection amount in ideal state, or ratio of recharge amount to actual recharge amount in ideal state) ( -), Q ₀ is the water collection amount or recharge amount (m ³ / sec) of the opening 5a in an ideal state.

And FIG. 6 used the result (calculated value) which analyzed the water collection performance (or recharge performance) of the well structure 5 provided in the retaining wall 2 using the finite element method, and Formula 3 and Formula 4. The result (design formula) obtained by the design method is shown. Here, FIG. 6, the sphere of influence radius R is 100 m, the depth t of the opening 5a and 0.5 m, the water collecting performance (or recharge the performance of the well structure 5 when changing the width B _w of the opening 5a ) have the meanings indicated, and the horizontal axis represents the permeability k ₁ and the ratio of the permeability coefficient k ₂ of the filler 6 of natural ground, the vertical axis is the well efficiency eta. From this figure, the result analyzed using the finite element method and the result obtained by the design method using Equation 3 and Equation 4 are in agreement, and the validity of Equation 3 and Equation 4 is proved.

  Therefore, according to the groundwater flow maintenance method of the present embodiment, the water permeability of the opening 5a of the well structure 5 provided in the retaining wall 2 (reflecting the water permeability 9 of the filler 6) is reflected by using the equations 3 and 4. Thus, the water collecting capacity and / or the recharge capacity of the well structure 5 can be obtained with high accuracy, and the well structure 5 can be designed appropriately. Further, the water permeability of the filler 6 filling the opening 5a can be improved. Since the management target value for the construction is clarified, it is possible to perform the construction with high reliability, and it is possible to reliably secure a suitable groundwater flow.

Further, FIG. 7 is an example in which design the well structure 5 of earth retaining wall 2 using Equation 3 and Equation 4, by changing the permeability k ₁ and the ratio of the permeability coefficient k ₂ of the filler 6 of natural ground The change of the installation space | interval of the opening part 5a of the well structure 5 with respect to the width | variety ( _Bw ) of the opening part 5a of the well structure 5 is shown. Then, referring to such a calculation result, rational design is possible by comparing designs under various conditions in which the width (B _w ) of the opening 5a and the installation interval of the openings 5a are changed. become.

  As mentioned above, although one Embodiment of the groundwater flow maintenance construction method concerning this invention was described, this invention is not limited to said one Embodiment, In the range which does not deviate from the meaning, it can change suitably.

It is a figure which shows the relationship (relational expression) of the width of the opening part of a well structure, and the equivalent well radius of the well which has a performance equivalent to this opening part in the groundwater flow maintenance method which concerns on one Embodiment of this invention. In the groundwater flow maintenance method according to one embodiment of the present invention, the well structure of the retaining wall using the relational expression of the width of the opening of the well structure and the equivalent well radius of the well having the performance equivalent to this opening Is an example of designing. In the groundwater flow maintenance method according to an embodiment of the present invention, it is a diagram demonstrating the validity of the relational expression between the width of the opening of the well structure and the equivalent well radius of a well having a performance equivalent to this opening. . It is the figure which showed various conditions of Formula 3 and Formula 4 in the groundwater flow maintenance construction method which concerns on one Embodiment of this invention. It is the figure which showed various conditions of Formula 3 and Formula 4 in the groundwater flow maintenance construction method which concerns on one Embodiment of this invention. It is the figure which verified the validity of Formula 3 and Formula 4 in the groundwater flow maintenance construction method concerning one embodiment of the present invention. It is an example which designed the well structure of the retaining wall using Formula 3 and Formula 4 in the groundwater flow maintenance construction method concerning one embodiment of the present invention. It is a figure which shows the state which provided the well structure in the constructed earth retaining wall and ensured the flow of groundwater. When designing a well structure, it is the figure which showed replacing a well structure with the equivalent well radius of the well which has a performance equivalent to the opening part of this well structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Underground structure 2 Earth retaining wall 3 Aquifer 5 Well structure 5a Opening 6 Filling material T Groundwater flow

Claims (1)

A groundwater flow maintenance method that secures the flow of groundwater by collecting and / or recharging groundwater blocked by the constructed retaining wall with a slit-like well structure provided in the retaining wall,
A groundwater flow maintenance method, wherein the well efficiency of the well structure is set using the following equation.

Where, Q: Actual water collection or recharge for well structure
s _w : Amount of decrease in water level or amount of increase in water level in the opening
k ₁ : Permeability coefficient of natural ground
k ₂ : permeability coefficient of filler
D: Length of opening (= layer thickness of aquifer)
R: radius of influence zone
r _w : equivalent well radius of the opening
_Bw : width of the opening
t: Depth of opening (filling thickness of filler)
η: well efficiency (ratio of the amount of water collected in the ideal state to the actual amount of water collected, or the ratio of the amount of recharge in the ideal state to the actual amount of recharge)
Q ₀ : Amount of water collected or recharged in an ideal state

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