JP5541533B2 - Estimating method of water leakage position of earth retaining wall and ground excavation method - Google Patents

Description

  The present invention relates to a water-stopping retaining wall that is pre-constructed around the excavation area during ground excavation, and an estimation method for estimating in advance the presence / absence of water leakage and the leakage location after the start of excavation of the retaining wall, and The present invention relates to a ground excavation method using an estimation method.

  As is well known, in medium-scale or larger underground constructions for permeable ground, as a countermeasure against groundwater during excavation, a water-stopping retaining wall is preliminarily constructed so as to surround the excavation area, so that the outside of the retaining wall is moved from the inside to the inside. In general, excavation is performed while preventing leakage of groundwater, but even in such cases, water leakage that cannot be ignored during excavation may occur if the water retaining wall of the retaining wall is not sufficient. .

  When water leakage occurs during excavation, it is necessary to interrupt the excavation work and implement additional water stoppage measures such as a chemical injection method at the water leakage location. In some cases, it is not always possible to stop the water easily, and there is a concern that if the excessive injection pressure is applied to the outside (rear side) of the retaining wall, the retaining wall may be deformed to fall inside. It is usually a cumbersome work that requires caution, and usually requires a great deal of cost and construction time.

  In order to prevent a water leakage accident after the start of excavation as described above, the soundness of the retaining wall should be fully confirmed prior to excavation, and if it is assumed that water leakage will occur during excavation, before the excavation starts It is desirable to take appropriate measures to prevent water leakage in advance, but at present it is effective and appropriate to be able to confirm the soundness of the retaining wall before excavation and to estimate the risk of leakage and its location. However, such a proactive measure is not possible.

  Although not related to ground excavation, Patent Document 1 discloses that water leakage is detected by detecting damage to a water-impervious surface using an optical fiber in order to detect the presence and location of a water leakage location in a waste disposal site. A detection device has been proposed, and if it is installed around the retaining wall, it may be possible to estimate the presence and location of the leakage in advance, but it is intended for the retaining wall that is a temporary structure. As such, it is not practical in terms of workability and cost to apply such a complicated and advanced detection device.

JP 2004-45226 A

  In view of the above circumstances, the present invention targets a water-stopping retaining wall provided around the excavation area when excavating the ground, and accurately determines in advance whether or not there is a risk that the retaining wall will cause water leakage after the start of excavation and its position. An object of the present invention is to provide an effective and appropriate estimation method that enables estimation, and to provide an effective and appropriate ground excavation method that uses the estimation method.

  The invention according to claim 1 is directed to a retaining wall that is preliminarily constructed so as to surround the periphery thereof in order to prevent inflow of groundwater into the excavation area during ground excavation, from the outside of the retaining wall to the excavation area inside the retaining wall. Is an estimation method for estimating the presence or absence of water leakage and the location of water leakage before excavation, performing an initial pumping test on the surrounding ground of the excavation area, calculating a water permeability coefficient T and an affected area radius R, By installing at least three observation holes on the outside of the retaining wall and providing a pumping well on the inner side of the retaining wall and conducting a confirmation pumping test, the amount of pumped water Q and the amount of decrease in groundwater level at each observation hole s And calculate the distance r from each observation hole to the assumed spring point on the basis of the water permeability coefficient T, the radius of influence R, the pumping amount Q, and the groundwater level reduction amount s, and correspond to each observation hole. Based on the distance r to the assumed spring point Draw springs positions assumed circle around the each observation holes have, wherein the estimating the leakage point to earth retaining walls point of the intersection range or intersection range near each spring water position assumed circle.

The invention according to claim 2 is the method for estimating the leakage position of the retaining wall according to claim 1, wherein the distance r from each observation hole to the assumed spring point is expressed by the following equation based on Thiem's steady well theoretical formula: = R / exp (2πTs / Q)
It is characterized by calculating by.

  The invention according to claim 3 is a ground excavation method in which, when excavating the ground, the retaining wall is preliminarily constructed so as to surround the periphery of the retaining wall so as to prevent inflow of groundwater into the excavation area, and then the inside of the retaining wall is excavated. Then, prior to excavation of the inside of the retaining wall, a confirmation pumping test is performed to estimate the presence and location of water leakage from the outside of the retaining wall to the inner excavation area. According to the estimation method, the presence / absence of water leakage and the location of water leakage are estimated. When it is estimated that water leakage will occur, repair work is performed on the water leakage location and then the inside of the retaining wall is excavated.

  Invention of Claim 4 is the ground excavation method of Claim 3, Comprising: After performing the repair work to a water leak location, the confirmation pumping test is performed again and the presence or absence of a water leak and a water leak location by the said estimation method By estimating again, when it is estimated that water leakage will occur, repair work will be repeated at the water leakage location, and excavation will be started after it is estimated that water leakage will not occur.

  According to the estimation method of the present invention, the water permeability coefficient T and the radius of influence radius R are calculated by the initial pumping test, the pumping test is performed before the excavation is started, and the pumping volume Q and the groundwater level drop at each observation hole are calculated. Only by measuring s, the location of water leakage can be accurately estimated from these data, for example, based on Thiem's steady well theory.

According to the ground excavation method of the present invention, when the excavation inside the retaining wall is started, the soundness of the retaining wall is confirmed based on the above estimation result, and water leakage is assumed to occur after the excavation starts. By starting excavation after identifying the location of the water leak and repairing it in advance, it is possible to prevent unpredictable pumping after the start of excavation. As described above, it is possible to avoid the situation where the excavation process is interrupted to repair the water leakage, and efficient excavation work is possible as a whole, which can contribute to the reduction of the construction cost and the construction cost.
Moreover, since the ground inside the retaining wall has not yet been excavated at the time of prior repair work, the amount of water leakage is much smaller than when similar repair work is performed after the excavation is started, so the repair work can be performed reliably and reliably. It is possible to carry out easily, and even if the injection pressure is excessive when the repair work is performed by chemical injection, the retaining wall is greatly deformed inward due to the reaction force from the inner ground. There is no such concern.
In addition, after the repair work is completed, a second test is performed to confirm whether the repair has been sufficiently performed. If the repair work is not sufficient, the leakage location is confirmed by the same procedure and the repair work is repeated. By doing this, it is possible to implement thorough water stoppage measures with the minimum amount of effort and cost before starting excavation.

The embodiment of the ground excavation method of this invention is shown, and is a figure which shows the outline | summary of the confirmation pumping test implemented before excavation, and the repair process to a water leak location. The embodiment of the estimation method of the present invention is shown, and is a diagram showing an outline of a water leak location estimation method. It is a figure which shows the outline | summary of a numerical analysis method similarly.

An embodiment of the present invention will be described with reference to FIGS.
First, an embodiment of the ground excavation method of the present invention will be described with reference to FIG. In the ground excavation method according to the present embodiment, a water-stopping retaining wall 1 is preliminarily constructed so as to surround the excavating area 2 when excavating the ground to the permeable ground, and the inside of the excavating area 2 is formed from the outside of the retaining wall 1. However, in this embodiment, a test for confirming the soundness of the retaining wall 1 is performed prior to excavation to ensure sufficient excavation. Evaluate whether or not the water stop performance can be exhibited, and if it is assumed that water leakage occurs, the water leakage position 5 is specified by the estimation method described later, and the water stoppage is secured for the water leakage position 5 The main purpose is to start excavation after ensuring the soundness of the retaining wall 1 by carrying out the repair work in advance.

Specifically, as shown in FIG. 1 (a), after the retaining wall 1 is constructed around the excavation area 2, one pumping well 3 is provided on the inner side, and the water level fluctuation is generated on the outer side of the retaining wall 1. A plurality of observation holes 4 for observation are installed.
In the case of the illustrated example, as shown in FIG. 2 (a), four retaining walls 1 are continuously provided around the excavation area 2 so as to surround the excavation area 2 as a whole, and at the substantially central position inside thereof. The pumping wells 3 are provided, and the observation holes 4 are installed at positions closest to the center of the outside of each retaining wall 1. In the present invention, the observation holes 4 may be installed at at least three locations. 3 and the position of each observation hole 4 are not particularly limited and are arbitrary.

Then, as shown in FIG. 1 (a), water is pumped from the pumping well 3 to reduce the water level inside the retaining wall 1, and the fluctuation of the groundwater level outside the retaining wall 1 is observed through each observation hole 4. .
As a result of this test, if the retaining wall 1 is healthy and there is no water leakage from the outside to the inside, the effect of pumping from the inside of the retaining wall 1 will not greatly affect the outside. The natural groundwater level is substantially maintained without significant fluctuation, and this can be detected from the water level observation for each observation hole 4. That is, in that case, it can be evaluated that the retaining wall 1 is healthy and there is no risk of water leakage after the start of excavation.

  However, as shown in (a), in the case where there is a poor water-stopping location that becomes the water leakage location 5 on the mountain retaining wall 1, the water leakage location 5 moves inward as the groundwater level falls on the inside. As a result, a groundwater level drop that cannot be ignored even outside the retaining wall 1 occurs. In this case, the observation hole 4 closer to the water leakage point 5 has a groundwater level that appears earlier and more prominently. Therefore, it is qualitatively detected that water leakage has occurred due to groundwater level observation at each observation hole 4 and its approximate position. obtain.

Therefore, in the ground excavation method according to the present embodiment, the leak location 5 is specified with high accuracy by the estimation method of the present invention, which will be described later, and then repair work for closing the leak location 5 is performed.
As the repair work, additional water stoppage that covers the outside of the water leak point 5 as shown in (b) by implementing an additional water stoppage measure, for example, by a chemical injection method from directly above the water leak point 5 A wall 6 may be formed.
At this time, since the inner ground of the retaining wall 1 has not been excavated yet, the amount of water leakage is much smaller than in the case where the same repair work is performed after the start of excavation as usual, and therefore the repair work is surely performed. It is possible to carry out easily, and even if the injection pressure is excessive when the repair work is performed by injection of the chemical solution, the retaining wall 1 is greatly deformed inward due to the reaction force from the inner ground. There is no concern about this.

After repairing to the leaking point 5 as described above, the test is performed again as shown in (c). That is, as in (a), the presence or absence of water leakage is evaluated by pumping water from the pumping well 3 and further observing the water level fluctuation in each observation hole 4 associated therewith.
If the groundwater level drop in observation hole 4 is also observed in this second test, it is estimated that the effect of the repair work is not sufficient (the repair is not complete) or that new leaks have occurred elsewhere. Therefore, in that case, it is only necessary to start excavation after confirming that repair and testing are repeated by the same procedure, and finally water leakage can be prevented.

  As described above, in the ground excavation method according to the present embodiment, the soundness of the retaining wall 1 is confirmed before the start of excavation. Since excavation is started after repairs are made, it is possible to prevent unexpected water leakage after the start of excavation.Therefore, the excavation process is interrupted as if water leaks after the start of excavation. The situation where repair is performed can be avoided in advance, and efficient excavation work can be performed as a whole, which can contribute to reduction of construction cost and construction cost.

  In addition, in order to perform the above test under a condition where there are a plurality of aquifers, a plurality of pumping wells 3 and observation holes 4 corresponding to each aquifer are provided separately, and each aquifer is For example, the partial pumping test method disclosed in Japanese Patent No. 2788954 and the Japanese Patent No. 2847127 are shown after the tests are sequentially performed or the pumping well 3 and the observation hole 4 are provided so as to reach the lowermost aquifer. It is also possible to measure the water level of each aquifer individually by sequentially pumping water from each aquifer according to the multistage pore water pressure measurement method.

The above ground excavation method is based on the premise that the location to be repaired before the start of excavation, that is, the location 5 where water leakage is assumed to occur after the start of excavation can be accurately estimated in advance. In order to specify the location 5, it is necessary to use the estimation method of the present invention.
Hereinafter, an embodiment of the estimation method of the present invention will be described with reference to FIG.

In the estimation method of the present embodiment, an initial pumping test is performed on the excavation area 2 and its surrounding ground in advance to calculate the water permeability coefficient T and the influence area radius R.
The calculation can be easily obtained using a linear gradient method based on a known s-log (r) plot. In other words, the relationship between the distance from the pumping well 3 to each observation hole 4 and the water level drop at each observation hole 4 is plotted on a semilogarithmic graph and linearly approximated, and the permeability coefficient T and the influence radius are calculated from the slope and intercept. What is necessary is just to obtain | require R.

Moreover, the water permeability coefficient T and the influence radius R which are data obtained by the above-mentioned initial pumping test, the pumping volume Q which is the data obtained by the above-described pumping test, and the groundwater level lowering amount at each observation hole 4 From s, the distance r from each observation hole 4 to the assumed spring point is calculated based on a known theoretical formula.
That is, between each of the above data, it is known as Thiem's steady well theoretical formula
s = (Q / 2πT) ln (R / r)
Since there is a relationship, r = R / exp (2πTs / Q)
From this relational expression, the distance r from each observation hole to the assumed spring point can be obtained.

And the intersection of each spring position assumption circle | round | yen can be estimated as the water leak location 5 by drawing the spring position assumption circle | round | yen centering on each observation hole 4 by making said distance r into a radius.
For example, as shown in FIG. 2 (a), the water level drop amounts s at four observation holes 4 (shown as No. 1 to No. 4 in the figure) are s = 1.65m, 1.28m, 1.04m, When the distance r corresponding to each observation hole 4 is calculated as r = 10 m, 35 m, 70 m, and 40 m as shown in (b) from the above formula, Draw an assumed spring position circle whose radius is the value of the distance r.
Since the intersection of these four circles is unlikely to be one intersection, the intersection range of the four circles is estimated from the four intersections formed by the intersections of the two circles. If there is a mountain retaining wall within this intersection range, this mountain retaining wall location is estimated as a water leakage location 5, and if there is no mountain retaining wall within the intersection range, the mountain retaining wall location near the intersection range (closest location) is designated as the water leakage location 5. presume.

According to the estimation method described above, the initial pumping test is performed before the construction of the retaining wall 1 to calculate the water permeability coefficient T and the radius of influence radius R, and the pumping test confirmed before the start of excavation after the construction of the retaining wall 1 The leakage point 5 can be accurately estimated from these data only by measuring the pumping amount Q and the groundwater level drop s at each observation hole. It is sufficient to perform the additional water stop work only for the minimum necessary area around 5 of the leaked water location, and it becomes possible to carry out the prior water leak repair work reasonably and efficiently.
Of course, as described above, after the repair work is completed, a second test is performed to confirm whether the repair has been sufficiently performed. By repeating the repair work, it is possible to implement thorough water stoppage measures with the minimum amount of effort and cost before starting excavation.

In the present invention, it is also preferable to use a numerical analysis for specifying the water leakage location in combination with the estimation of the water leakage location by the above-mentioned confirmation pumping test. Will be described with reference to FIG.
In this case, preliminary analysis is performed in advance by temporarily setting a large number of water leakage points within a range where water leakage is expected to occur.
Specifically, for example, a preliminary analysis in the case shown in FIG. Three observation wells (No. 1 to No. 3) are installed in a straight line parallel to the one side of the rectangular retaining wall with a side of 150m in a rectangular view, and a pumping well is installed inside the retaining wall. This is an example of lowering the position. The observation well installation line is 10m away from the retaining wall. The No.2 observation well is the central position of the retaining wall, and the No.1 and No.3 observation wells are 150m away on both sides. The thickness of the aquifer is 8m and the hydraulic conductivity is k = 1.4 × 10 ⁻³ cm / s. And, when the groundwater level in the retaining wall is lowered by 3.9m, the amount of lowered water level at each observation well assumed when the leak point is temporarily set at 5m pitch on the one side of the retaining wall is calculated by the finite element method. A graph as shown in (b) is created by analyzing by plane two-dimensional osmotic flow analysis. Moreover, based on the graph, the ratio shown in (c) is created by determining the ratio of the water level drop at other observation wells with respect to the maximum water level drop.

Then, from the actual water level drop amount in each observation well 4 obtained by the pumping test by the pumping well inside the retaining wall, the ratio of the water level drop amount to the maximum water level drop amount is calculated, and the water leakage by the above graph (c) Assume a point.
Specifically, as shown in Fig. 3 (a), when the water level drop in the three observation wells is s ₁ = 0.65m, s ₂ = 0.91m, s ₃ = 0.57m, Since the drop amount s _max = s ₂ = 0.91 m and the water level drop amount ratio is s ₁ / s _max = 0.71 and s ₃ / s _max = 0.63, a plurality of observations can be made from these values by the graph (c). The position of y = -30m, which is the point where well data overlaps, can be obtained as the water leak location.

  As described above, the method of estimating the location of water leakage from the intersection range of circles (assumed spring water circles) drawn at the distance r from each observation hole to the assumed spring water point based on the steady well theoretical formula (referred to as the intersection point method), Method of estimating leakage location by applying the actual water level drop of each observation well outside the retaining wall due to pumping inside the wall to a modified osmotic flow analysis graph based on the assumed groundwater level drop (called analysis method) Explained. However, if the water level drop curve cannot be expressed by a simple well theory formula (Thiem formula), the intersection method cannot be used, and if the installation length of the retaining wall is relatively long in plan view, the analysis method can be applied. The method is basically used properly depending on the shape of the retaining wall, the soil condition of the construction site, etc., but if the intersection method can be applied in cases where the analysis method can be applied, it is more appropriate to apply both estimation methods. The estimation accuracy can be increased.

  In the estimation method of the present invention, the planar position of the water leakage location 5 can be estimated with high accuracy, but in the case where there are a plurality of aquifers, the water leakage position in the depth direction cannot always be estimated with high accuracy. However, in that case, it can be considered that water leakage has occurred at the location of the aquifer where the water level drop has occurred remarkably, so it is usually sufficient to repair around the depth of the aquifer. It is.

  Also, when there are multiple aquifers and the specific aquifer is thick and it is necessary to identify the leak location in the aquifer, the leak location is determined in the same way as the numerical analysis method shown in FIG. Preliminary analysis in the case of a large number of temporary settings in the vertical direction can be performed in advance, so that the location of water leakage in the vertical direction can be accurately identified by matching the analysis results with the observation results at the observation hole. .

The embodiments of the estimation method and the ground excavation method of the present invention have been described above. However, the above embodiments are merely preferred examples, and the present invention is not limited to the above embodiments, and departs from the gist of the present invention. Appropriate design changes and applications can be made without departing from the scope.
For example, in the above embodiment, the distance r from each observation hole to the hypothetical spring point is expressed in Thiem's steady well theoretical formula based on the data of the water permeability coefficient T, the radius of influence R, the pumping amount Q, and the groundwater level drop s. Although it is not necessarily based on Thiem's steady well theoretical formula, it can be estimated based on other theoretical formulas as long as the distance r can be obtained from the relationship between these elements, It does not preclude obtaining an interrelation between these elements experimentally in advance and performing the estimation by contrast with the relationship.

1 Mountain retaining wall 2 Excavation area 3 Pumping well 4 Observation hole 5 Leakage location 6 Additional retaining wall

Claims (4)

In order to prevent the inflow of groundwater to the excavation area when excavating the ground, the presence of leakage from the outside of the retaining wall to the inner excavation area and the location of the leakage are determined. An estimation method for estimating before excavation,
An initial pumping test is conducted on the ground around the excavation area to calculate the permeability coefficient T and the radius of influence radius R,
At least three observation holes are installed outside the retaining wall, and a pumping well is provided inside the retaining wall, and a confirmed pumping test is performed, whereby the pumping amount Q and the groundwater level drop s at each observation hole are measured. And measure
Calculate the distance r from each observation hole to the assumed spring point based on the water permeability coefficient T, the radius of influence radius R, the pumping amount Q, and the groundwater level drop amount s.
Based on the distance r to the assumed spring point corresponding to each observation hole, draw an assumed spring position circle around each observation hole,
A method for estimating a water leakage position of a mountain retaining wall, wherein a mountain retaining wall location within or near the intersection range of each of the estimated spring position circles is estimated as a water leakage location. A method for estimating a leakage position of a retaining wall according to claim 1,
The distance r from each observation hole to the assumed spring point is expressed by the following equation based on Thiem's steady well theoretical formula: r = R / exp (2πTs / Q)
The leakage position estimation method of a mountain retaining wall characterized by calculating by this. A ground excavation method for excavating the inside of the retaining wall after pre-constructing the retaining wall so as to surround the surrounding area in order to prevent the inflow of groundwater to the excavation area when excavating the ground,
The estimation according to claim 1 or 2, wherein prior to excavation of the inside of the retaining wall, a confirmation pumping test is performed to estimate the presence or absence of water leakage from the outside of the retaining wall to the inner excavation area and the location of the leakage. The ground excavation method is characterized by estimating the presence and location of water leakage and the location of leakage by the method, and excavating the inside of the retaining wall after carrying out repair work to the leakage location when water leakage is estimated to occur. . The ground excavation method according to claim 3,
After carrying out repair work to the leak location, perform the confirmation pumping test again and re-estimate the presence of the leak and the leak location using the estimation method. A ground excavation method characterized in that excavation is started after it is estimated that no water leakage will occur after repeated repair work.

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