JP2010222805A - Method for evaluating stability of excavated surface against sump water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating stability of an excavated surface against sump water, which makes the stability of the excavated surface against the sump water rapidly and accurately evaluated in an excavation step. <P>SOLUTION: This method for evaluating the stability the excavated surface against the sump water includes: a measurement step of measuring bearing strength by a soil hardness meter on a cutting face (excavated surface); an estimation step of estimating a critical hydraulic gradient of natural ground of the cutting face by using the bearing strength measured by the soil hardness meter in the measurement step, and a uniformity coefficient of the natural ground, obtained by a soil survey before excavation; and an evaluation step of evaluating the stability of the cutting face against the sump water by comparing the critical hydraulic gradient, estimated in the estimation step, with a hydraulic gradient of surrounding ground of the cutting face. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for evaluating the stability of an excavated surface against spring water. More specifically, the present invention relates to a method for evaluating the stability of a drilling surface against spring water in a sandy mountain.

In underground excavation in unconsolidated sandy land, there have been many reports of collapse of the excavated surface due to spring water. Many methods have been proposed in the pre-planning stage before excavation as a method to evaluate the stability of the sandy mountain to spring water. These are based on, for example, the particle size of soil particles.
One of the stability indicators for spring water is the critical dynamic gradient. Non-Patent Document 1 describes that the value of the critical hydrodynamic gradient of a sample is obtained by a horizontal one-dimensional osmotic collapse model experiment. Further, Patent Document 1 discloses that a boring phenomenon is artificially generated by drilling a hole in a water-permeable ground to lower a water level in the drilling hole and increasing a hydraulic gradient, and the inside and outside of the drilling hole when the boiling occurs. A method for calculating a critical hydraulic gradient using a water level difference is described.

JP 2005-2711 A

Hideo Kitani, Hiroshi Oshima, Hideaki Enomoto “Classification of sandy ground for evaluation of face stability” Railway Research Institute, Vol. 5, no. 6, pp. 39-46.

  However, it is generally necessary to obtain stability indicators for spring water such as the critical hydrodynamic gradient by soil tests at the planning stage before excavation, and obtain similar indicators on the excavation surface during the excavation process. It is difficult. Moreover, the measurement method shown in Patent Document 1 also requires drilling in the ground during measurement, and is difficult to implement on the excavation surface during the excavation process. At present, no method has been established to evaluate the stability of the excavation surface against spring water during the excavation process, and the stability is evaluated mainly by visual observation.

  For this reason, there are cases where the evaluation of the stability of the natural ground against the spring at the planning stage and the stability of the excavation surface during the excavation with respect to the spring are different. In this case, for example, if the support selected based on the evaluation of the stability of the natural ground against the spring water at the planning stage is insufficient, there is a risk that the excavation surface during excavation will cause collapse due to the spring water.

  On the other hand, if there is a method for quickly and accurately evaluating the stability of the excavated surface against spring water, appropriate countermeasures can be implemented on the excavated surface during excavation according to the evaluation. Can be reduced. Establishing an evaluation method during the excavation process is necessary to examine the validity of the stability evaluation at the planning stage.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a method for evaluating the stability of an excavation surface against spring water, which quickly and accurately evaluates the stability of the excavation surface against spring water.

  The present invention for achieving the above-described object includes a measuring step for measuring a supporting strength by a soil hardness meter on an excavation surface, and a limit of a natural ground on the excavating surface by using the supporting strength by the soil hardness meter measured in the measuring step. The stability of the excavation surface against spring water is evaluated by comparing the estimation step for estimating the hydraulic gradient, the critical hydraulic gradient estimated in the estimation step, and the hydraulic gradient in the surrounding ground of the excavation surface. And a step of evaluating the stability of the excavated surface against spring water.

  With the above configuration, it becomes possible to evaluate the stability of the excavation surface against spring water. Further, since the stability of the excavated surface is quantitatively evaluated, it is advantageous in that accurate evaluation can be performed without requiring skill as compared with conventional visual evaluation, and anyone can perform it. In addition, it is possible to verify the stability evaluation of natural ground springs at the planning stage.

  A known soil hardness meter can be used. Generally, it is small and easy to carry, and it is only necessary to read the scale after inserting the cone at the tip into the face, so that the support strength by the soil hardness meter can be measured quickly. With the above configuration, it is not necessary to perform a test by collecting a sample at the time of excavation, and the stability of the excavated surface against spring water can be evaluated inexpensively and quickly. Since the evaluation is performed quickly, it is possible to evaluate the stability of the excavated surface against spring water during the excavation process.

In the estimation step, in addition to the support strength by the soil hardness meter measured in the measurement step, the natural hydrological gradient of the natural ground on the excavation surface is calculated using the physical property values of the natural ground obtained in the soil investigation before excavation. presume.
By the said structure, the precision of the stability evaluation with respect to spring water can be improved.

It is desirable that the physical property value is a uniformity coefficient of natural ground.
The uniformity coefficient of natural ground is advantageous in that it is an index with a large difference in value depending on natural ground, and is not related to the supporting strength by the soil hardness meter and does not cause a problem of collinearity.

  ADVANTAGE OF THE INVENTION By this invention, the stability evaluation method of the excavation surface with respect to the spring which evaluates the stability with respect to the spring of a excavation surface quickly and correctly can be provided.

Sectional view showing tunnel excavation process Flow chart showing the flow of the stability evaluation method of the excavation surface against the spring water of this embodiment The figure explaining the measurement of the support strength with the soil hardness meter The figure which shows the relationship between the support strength by the soil hardness meter and the critical hydrodynamic gradient Figure showing the relationship between the uniformity coefficient of natural ground, the support strength by the soil hardness tester, and the limit hydrodynamic gradient

Hereinafter, an embodiment of a method for evaluating the stability of an excavation surface against spring water according to the present invention will be described with reference to FIGS. 1, 2, and 3.
FIG. 1 is a cross-sectional view showing a tunnel excavation process.
FIG. 2 is a flowchart showing the flow of the method for evaluating the stability of the excavation surface against the spring water of the present embodiment.
FIG. 3 is a diagram for explaining the measurement of the support strength by the soil hardness meter.

The stability evaluation method of the excavation surface with respect to the spring water of this embodiment is based on the stability of the face of the tunnel 1 (excavation surface) against the spring water in the excavation process of the tunnel 1 as shown in FIG. Used when evaluating sex.
In FIG. 1, 3 a and 3 b are the faces of the tunnel 1. In this embodiment, the stability with respect to spring water is evaluated in the face 3a, 3b. 5a and 5b are boring holes. At the point where the tunnel 1 is scheduled to be excavated, the boreholes 5a, 5b,... Are excavated for soil investigation of the natural ground in the preliminary planning stage before excavation. 6a and 6b indicate groundwater levels observed in the boreholes 5a and 5b, respectively, in the soil survey. A broken line A is an example of the groundwater level of the natural ground before excavation of the tunnel 1, and a broken line B is an example of the groundwater level of the natural ground when the tunnel 1 is excavated to the face 3a.

  With reference to FIG. 2, the flow of the stability evaluation method of the excavation surface with respect to the spring water of this embodiment used in the excavation process of the tunnel 1 will be described.

  First, a soil survey of the target ground is conducted at a preliminary planning stage prior to excavation of the tunnel 1 (step 201).

  In the soil investigation in Step 201, the state of the formation is excavated from the ground surface at the point where the tunnel 1 is scheduled to be excavated, or the elastic wave exploration of the natural ground is performed by excavating the boreholes 5a, 5b,. Etc. are examined. Further, samples are taken from the boreholes 5a, 5b,..., And physical properties of the natural ground such as the uniaxial compressive strength, relative density, fine particle content, and uniformity coefficient of the sample are examined by various tests.

  Based on the soil investigation data in step 201, the natural ground classification is performed on the target natural ground (step 202). The natural ground classification classifies natural ground according to various characteristics that affect the stability of the tunnel. For example, the types of rocks that make up the natural ground and the type of earth and sand such as sandy soil, as well as the elastic wave velocity and natural ground strength ratio, etc. Natural mountains are classified according to their physical properties.

Further, in the present embodiment, in particular, the uniformity coefficient of the natural ground is obtained for the target natural ground by the soil investigation in Step 201 (Step 203).
The uniformity coefficient indicates the degree to which the particle diameters of the soil particles constituting the sample are uniform. Although it is a known index, the details are omitted, but the larger the value is, the more soil particles with various particle sizes are mixed. The uniformity coefficient is related to the value of the critical hydraulic gradient, which will be described later, and is used when evaluating the stability of the face against spring water described later.

  In addition, in the soil investigation in step 201, the groundwater level of the target ground is observed at the preliminary planning stage (step 204). In the boreholes 5a, 5b,... Excavated in the soil survey, groundwater levels 6a, 6b,.

  Based on the natural ground classification in step 202, support on the excavation surface during excavation of the tunnel 1 is planned (step 205). Appropriate support is selected for the tunnel 1 according to the ground classification, such as the number of rock bolts and the thickness of shotcrete. In some cases, measures to stabilize the face and lower the groundwater level, such as receiving work and drain holes, are planned.

  The tunnel 1 is excavated by the support planned in step 205 (step 206).

  When the tunnel 1 is excavated to a predetermined position in step 206, the stability evaluation for the spring shown below is performed for the face. Here, suppose that it excavated to the face 3a shown in FIG.

  First, in the face 3a, the support strength by the soil hardness meter is measured using the soil hardness meter (step 207). Examples of the soil hardness meter include a Yamanaka type soil hardness meter. Since the soil hardness meter is known, only a brief description will be given below.

  As shown in FIG. 3 (a), the (Yamanaka type) soil hardness meter 7 is a cylinder 9, a cone 11 located at the tip of the cylinder 9 and movable in the length direction of the cylinder 9, A spring (not shown) that is attached to the inside of the cylindrical body 9 and supports the bottom surface of the conical body 11 with an elastic force, and a floating index 13 that varies in the length direction of the cylindrical body 9 according to the amount of contraction of the spring. The cylindrical body 9 is provided with a support strength scale 15.

  As shown in FIG.3 (b), in this embodiment, the cone 11 of the soil hardness meter 7 is inserted perpendicularly with respect to the face 3a, and the front-end | tip of the cylinder 9 is used for the face 3a. At this time, the resistance force of the natural ground is obtained from the balance between the resistance force of the natural ground to the cone 11 and the elastic force due to the contraction of the spring supporting the cone 11, and is divided by the bottom area of the cone 11 to determine the soil hardness meter. Support strength by With the support strength scale 15, the support strength by the soil hardness meter can be seen at a glance from the position of the floating index 13.

  The soil hardness meter is generally small and easy to carry. Since the usage method only needs to read the scale after inserting the cone of the tip into the face, the support strength by the soil hardness meter is quickly measured.

  Here, it will be described with reference to FIG. 4 that the support strength obtained by the soil hardness meter is related to the limit hydrodynamic gradient.

  Fig. 4 shows a horizontal one-dimensional osmotic collapse model experiment (see Non-Patent Document 1) for a plurality of samples with little disturbance, and obtains the value of the critical hydrodynamic gradient, as well as the outcrop and tunnel face where each sample was collected (Yamanaka equation) ) It is a scatter diagram in which the support strength by a soil hardness meter is measured and the relationship is plotted.

The vertical axis in FIG. 4 is the critical hydraulic gradient and is the logarithmic axis. The horizontal axis is the support strength by the soil hardness meter. From FIG. 4, the coefficient of determination R ² has a strong association 0.75 or more and both the more critical hydraulic gradient support strength by soil hardness scale increases it can be seen that also increases.

  Next, the critical hydraulic gradient is estimated from the uniformity coefficient of the natural ground obtained in step 203 and the support strength by the soil hardness meter obtained in step 207 (step 208).

  This will be described with reference to FIG. FIG. 5 is a diagram showing the relationship between the uniformity coefficient of natural ground, the support strength by the soil hardness meter, and the critical hydrodynamic gradient Ic. In the graph of FIG. 5, the vertical axis is the uniformity coefficient of the natural ground, and the horizontal axis is the support strength by the soil hardness meter, so that the critical hydraulic gradient Ic of the natural ground corresponding to each combination of values can be estimated. . These relationships have been obtained through prior experimental studies. In the preliminary study, using the samples collected from the outcrop around the tunnel planned site, the boring core, etc., the relationship between the critical hydrodynamic gradient and the support strength by the soil hardness tester is grasped, and the above-mentioned critical hydrodynamic gradient Ic is estimated. It is desirable to use it. Thereby, the estimation of the limit hydrodynamic gradient Ic and the evaluation of the stability of the face against the spring shown below can be made more suitable for the conditions at the site of the tunnel planned site.

For example, a point C in FIG. 5 represents a natural ground having an equality coefficient value of about 20 and a soil hardness meter supporting strength of about 2 (N / mm ² ), and the critical hydraulic gradient Ic is 20 ≦ Ic <50. It can be seen from FIG. Therefore, it is estimated that the range of values that can be taken by the limit hydrodynamic gradient Ic of the natural ground having the uniformity coefficient of about 20 and the soil strength meter support strength of about 2 (N / mm ² ) is 20 ≦ Ic <50. . As described above, the critical hydraulic gradient Ic is estimated from the uniformity coefficient of the natural ground and the support strength by the soil hardness meter.

The limit dynamic gradient in step 208 may be estimated as long as the limit hydraulic gradient value or value range is estimated directly or indirectly.
Therefore, in the graph of FIG. 5, it is only necessary to directly or indirectly represent the relationship between the uniformity coefficient of the natural ground, the support strength by the soil hardness meter, and the value or range of the limit hydrodynamic gradient Ic. Does not matter. For example, the lower limit value of the range that can be taken by the limit hydrodynamic gradient Ic according to the uniformity coefficient of the natural ground and the support strength by the soil hardness meter may be indicated. In addition, instead of the critical dynamic gradient Ic estimated from the uniformity coefficient of the natural ground and the support strength by the soil hardness meter, the dynamic water whose face is determined to be stable is compared with the critical dynamic gradient Ic in Step 210 described later. It is also possible to perform an expression in which the limit hydraulic gradient Ic is indirectly estimated, such as indicating a range of gradient values.

In addition, a hydrodynamic gradient in the ground around the face 3a is obtained (step 209).
This uses, for example, the result of groundwater level observation (groundwater level 6a) in the borehole 5a located in front of the face 3a performed in the preliminary planning stage (step 204). That is, the value of the hydrodynamic gradient is determined by the gradient formed by the groundwater level 6a and the position of the face 3a.

In practice, the groundwater level at the time of excavation of the tunnel 1 is generally the groundwater level at the time of prior planning (before tunnel excavation) as shown by the broken line A in FIG. In comparison, as shown by the broken line B in FIG. Therefore, when the hydraulic gradient is determined based on the groundwater level 6a observed in the preliminary planning stage as described above, generally, the evaluation is larger than the actual hydraulic gradient value when the tunnel 1 is excavated. This means that the hydrodynamic gradient is evaluated on the safe side in the stability evaluation of the face to be described later in the method for evaluating the stability of the excavated surface with respect to the spring water of the present embodiment.
In addition, although there is a difficulty that the evaluation cannot be performed quickly, it is possible to measure the hydrodynamic gradient by advanced boring from the face 3a.

  Next, the critical hydraulic gradient estimated in step 208 is compared with the hydraulic gradient obtained in step 209 (step 210). Thereby, the stability of the face against spring water is determined (evaluated) (step 211).

  That is, if the value of the hydraulic gradient is lower than the lower limit value of the estimated limit hydraulic gradient range, it is determined that the face 3a is stable with respect to the spring water. The branch of step 211 is Yes, and the tunnel is dug with a support planned in advance (step 212).

  On the other hand, if the hydrodynamic gradient is higher than the lower limit value of the range of the critical hydrodynamic gradient, it is determined that the face 3a is not stable with respect to the spring water, and the branch of step 211 becomes No. At this time, countermeasure work for stabilizing the spring water is performed on the face 3a (step 213). In some cases, change of countermeasure work or review of support. For example, the groundwater level is lowered by a drain hole or the face 3a is stabilized by injecting urethane into the face 3a. After implementing the countermeasure work, the process proceeds to step 212 and the tunnel 1 is dug.

  The stability of the face against the spring water can be evaluated appropriately according to the excavation length of the tunnel 1, the positional relationship with the boreholes 5a, 5b,.

  When the tunnel 1 is dug in Step 212 and the point where the stability of the face is to be evaluated (face 3b in FIG. 1) is reached, the uniformity coefficient obtained in the soil investigation and the support by the soil hardness meter measured by the face 3b The limit hydrodynamic gradient of the ground of the face 3b is estimated from the strength, and the stability evaluation of the face 3b against the spring water is performed again in comparison with the hydrodynamic gradient in the surrounding ground of the face 3b.

  In addition, in this embodiment, in the stability evaluation of the face with respect to spring water, in addition to the support strength by a soil hardness meter, it evaluated using the uniformity coefficient of a natural mountain. This is to improve the accuracy of evaluation. However, it is also possible to evaluate the stability of the face using only the supporting strength by the soil hardness meter. This is because, for example, based on the relationship between the support strength by the soil hardness meter and the critical hydrodynamic gradient as shown in FIG. This can be done by estimating the possible range.

  Further, the uniformity coefficient of the natural ground may be changed to a physical property value of other natural ground related to the critical hydrodynamic gradient of the natural ground such as the fine particle content rate of the soil particles. However, the use of the uniformity coefficient of natural ground is advantageous in that it is an index with a large difference in values depending on natural ground, and that the correlation with the support strength by the soil hardness meter is low and the problem of collinearity does not occur. In addition, it is possible to roughly estimate the uniformity coefficient during the excavation process by taking a correspondence between the uniformity coefficient and the result of the naked eye observation in advance.

  As described above, according to the method for evaluating the stability of the excavated surface with respect to the spring water according to the present embodiment, the stability evaluation of the excavated surface with respect to the spring water is performed using the support strength by the soil hardness meter and the uniformity coefficient of the natural ground. . The uniformity coefficient is a value obtained from a soil survey at the preliminary planning stage, and the support strength by the soil hardness meter is measured at the face during excavation. For this reason, it is not necessary to perform a test by collecting a sample, and the stability evaluation of the face against spring water can be performed inexpensively and promptly. Therefore, stability evaluation can be performed in the excavation process. Further, since the stability evaluation is quantitatively performed, anyone can perform an accurate evaluation without requiring skill as compared with the conventional visual evaluation. In addition, it is possible to improve the accuracy by verifying the validity of the initial ground classification and the details of the evaluation method such as the index. In addition, since a pure mechanical index is used, it is not affected by the locality of the natural ground and is advantageous in that it has versatility.

  As mentioned above, although embodiment of the stability evaluation method of the excavation surface with respect to the spring which concerns on this invention was described, referring an accompanying drawing, this invention is not limited to this example. It will be apparent to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea disclosed in the present application, and these naturally belong to the technical scope of the present invention. Understood.

1 ......... Tunnels 3a, 3b ......... Faces 5a, 5b ......... Boring holes 6a, 6b ......... Ground water level 7 ......... (Yamanaka type) soil hardness meter

Claims (3)

A measurement process for measuring the support strength by a soil hardness meter on the excavation surface;
An estimation step for estimating a limit hydrodynamic gradient of a natural ground on the excavation surface using a support strength by a soil hardness meter measured in the measurement step;
An evaluation step for evaluating the stability of the excavation surface against spring water by comparing the critical hydraulic gradient estimated in the estimation step with the hydraulic gradient in the surrounding ground of the excavation surface;
The stability evaluation method of the excavation surface with respect to the spring water characterized by comprising.   In the estimation step, in addition to the support strength by the soil hardness meter measured in the measurement step, the natural hydrological gradient of the natural ground on the excavation surface is calculated using the physical property values of the natural ground obtained in the soil investigation before excavation. The method for evaluating stability of an excavation surface against spring water according to claim 1, wherein the estimation is performed.   The method for evaluating stability of an excavated surface against spring water according to claim 2, wherein the physical property value is a uniformity coefficient of natural ground.

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