JP2003194758A - Method of evaluating bedrock of tunnel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quantitatively and highly reliably evaluate the properties of the bedrock of a tunnel. <P>SOLUTION: A plurality of rock bolts E are driven into the bedrock of a tunnel A to be evaluated. The bolts E are composed of steel-made bar-like bodies and radially driven into the bedrock from the inside of the tunnel A, so that the bolts E may be arranged roughly on one cross section of the tunnel A and inclined toward the face B of the tunnel A. At the time of evaluating the properties of the bedrock on the face B, a plurality of rock bolts E are selected from among the driven rock bolts E as resistivity measuring electrodes. Of the selected resistivity measuring electrodes, the outside two are used as current electrodes and the inside two are used as voltage electrodes. Then the resistivity ρ of the bedrock is measured by measuring the voltage V across the voltage electrodes while a direct current I is made to flow between the current electrodes. In this case, the resistivity ρ is found as 2πaI/V (wherein, (a) denotes the distance between the voltage electrodes). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a rock mass of a tunnel, and in particular, the electrical characteristics of the rock mass, that is,
The present invention relates to a method for evaluating rock mass properties by measuring specific resistance.

[0002]

2. Description of the Related Art At the construction site of a mountain tunnel, it is extremely important to accurately grasp the nature of the ground in order to ensure the safety of the face during excavation during the tunnel construction.

In this case, for example, in the renewal (restoration) construction of an existing tunnel whose construction is increasing recently, elastic waves or electromagnetic waves are radiated from the wall surface of the tunnel to deteriorate the sprayed concrete and the rock mass. Techniques for diagnosing deterioration have been developed.

By the way, in a normal new tunnel construction, the condition of the bedrock (weathering, loosening, spring water, etc.) is generally considered.
For each item, the worker visually observes the ground condition, and together with sketch images and photographs of the face face, prepare a face face daily report that describes a 4 to 5 grade evaluation for each item divided into multiple items is doing.

However, such a conventional method for evaluating rock mass properties in tunnel rock has the following problems.

[0006]

That is, since the method for evaluating rock mass characteristics by the daily report of the face is based on the visual observation of the face of the face, the evaluation tends to vary due to the experience and knowledge of the worker, and the reliability of the evaluation is high. There was a problem of lack of sex.

As a solution to such a technical problem,
As disclosed in Japanese Patent Laid-Open No. 2000-346953, the present inventors install a plurality of electrodes on the face of a face,
We proposed a method of measuring the resistivity of the face rock and evaluating the properties of the face based on the obtained resistivity value.

According to such an evaluation method, since the properties of the face are evaluated based on the specific resistance value of the bedrock, it is possible to make a quantitative and highly reliable evaluation. However,
In the evaluation method proposed in this publication, it is necessary to install a plurality of electrodes on the face of the face, and this electrode also needs to be removed from the face of the face at the end of the measurement. The removal could have an impact on the progress of the tunnel construction.

The present invention has been made in view of the above conventional problems, and its purpose is to eliminate the need for installing and removing electrodes, and without affecting tunnel construction. It is to provide a method for evaluating a rock mass that can quantitatively and highly reliably evaluate mountain characteristics.

[0010]

In order to achieve the above object, the present invention is to measure the specific resistance between the rock bolts by using the rock bolts placed in the tunnel rock as electrodes.
Based on the obtained specific resistance value, the ground rock properties such as cracks, spring water, and rock mass strength of the tunnel rock mass were evaluated.

According to the tunnel rock mass evaluation method thus constructed, as an electrode for measuring the specific resistance of the rock mass,
Since the rock bolts placed in the tunnel rock are used, it is not necessary to install and remove the electrodes for measuring the specific resistance, and the installation and removal of the electrodes do not affect the progress of the tunnel construction.

[0012] In this case, cracks, spring water,
Since rock mass strength and other rock mass characteristics are evaluated based on the specific resistance value, quantitative evaluation can be performed regardless of the experience of the measurer, and highly reliable evaluation can be obtained.

The lock bolts are provided on substantially the same cross section of the tunnel cross section, and a plurality of lock bolts are driven in the upper half and side portions at predetermined intervals along the circumferential direction of the tunnel. It is possible to measure the specific resistance value by selecting any four bolts, using two outer electrodes as current electrodes, and two inner electrodes sandwiched between the current electrodes as voltage electrodes.

The evaluation can be based on the natural property of the face face near the driving position of the lock bolt selected as the specific resistance measuring electrode.

The specific resistance value can be obtained by sequentially shifting one by one along the circumferential direction of the tunnel, with four sets selected from the lock bolts as one set.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. 1 and 2 show one embodiment of a method for evaluating a tunnel rock mass according to the present invention.

FIG. 1 is a cross-sectional view of the tunnel A, in which a horseshoe-shaped portion is a facet B. A wire mesh C is installed on the excavated surface on the side of the tunnel A, and a sprayed concrete layer D is provided on the upper surface thereof.

The lock bolt E is a solid or hollow rod-shaped body made of metal such as steel or aluminum. A plurality of rock bolts E are laid radially from the inside of the tunnel A toward the ground F on the outside. There is. One end of each rock bolt E is exposed on the inner surface side of the sprayed concrete layer D.

Further, as shown in FIG. 2, the plurality of rock bolts E are arranged such that the driving positions are on substantially the same cross section of the tunnel cross section, and are driven so as to be orthogonal to the excavation well wall. Moreover, a total of 17 are provided at substantially equal intervals along the circumferential direction of the tunnel A.

The portion indicated by reference character G in FIG. 1 is the lining concrete formed on the inner surface of the sprayed concrete layer D. As described above, the construction mode of the tunnel A is exactly the same as the conventional tunnel construction method, but in the case of the present embodiment, especially the rock property of the rock face B of the face face, spring, rock strength, and other rock mass properties. The following special methods are used to evaluate

That is, when evaluating the ground characteristics of the facet B, a plurality of lock bolts E are selected as the specific resistance measuring electrodes. In the case of this embodiment,
A total of 11 lock bolts E shown by reference numerals 1 to 11 in FIG. 1 are selected.

In the case of this embodiment, only the lock bolt E arranged in the upper half of the tunnel A is selected as the electrode for measuring the specific resistance, but the selection is not limited to this. You may choose what is arrange | positioned at the side part.

Further, as the lock bolt E selected as the electrode, one which is driven near the face face B whose property is to be evaluated or in the vicinity thereof is selected.

When the specific resistance measuring electrode is selected, the outer two, for example, the lock bolts E of 1 and 4 are used as current electrodes, and the inner two, 2 and 3 of the locks sandwiched between the current electrodes. The voltage E is used as the voltage electrode, and the direct current I is applied between the current electrodes.
And then the voltage V between the voltage electrodes at that time is measured to measure the specific resistance ρ. The specific resistance ρ in this case is calculated as 2πaI / V, where a is the distance between the voltage electrodes.

In the measurement of such a specific resistance ρ, it is possible to measure the specific resistance by selecting four lock bolts E between the following 5 to 8 to measure the specific resistance. The rock bolts E and 5 are used as current electrodes, the lock bolts E and 3 and 4 are used as voltage electrodes, and the specific resistance ρ is measured. In addition, four sets of current and voltage electrodes are sequentially arranged along the circumferential direction. 1
It is also possible to measure the specific resistance while shifting each book.

When a plurality of specific resistance values are obtained as described above, the rock mass characteristics such as the fracture of the face B, the spring water, and the rock mass strength are evaluated based on the specific resistance values. .

According to the tunnel rock mass evaluation method thus constructed, as an electrode for measuring the specific resistance of the rock mass,
Since the rock bolt E placed in the tunnel rock is used, it is not necessary to install or remove the electrode for measuring the specific resistance, and the installation or removal of the electrode does not affect the progress of the tunnel construction.

In this case, cracks in the rock mass of the tunnel, spring water,
Since rock mass properties such as rock mass strength are determined based on the specific resistance value, quantitative evaluation is performed regardless of the experience of the measurer, and highly reliable evaluation is obtained.

In order to confirm the effectiveness of the present invention, the present inventors measured the specific resistance ρ at the actual tunnel construction site by the above-mentioned method, and confirmed the correlation with the conventional evaluation method by the face daily report. I observed.

Mac Ohm 21 (trade name) manufactured by Applied Geology Co., Ltd. was used to measure the specific resistance.
A 24 A lead acid battery was used. A cord with a crimp terminal was used to connect the ring to the lock bolt E, and the crimp terminal was crimped and fixed to the end of the lock bolt E.

The actual measurement is as shown in FIGS.
Adjacent two cross sections were set as one set, and a total of 1 to 10 cross sections were performed. In the measurement of the specific resistance in each cross section, as shown in FIG. 1, since the lock bolt E was arranged, 11 of the upper half portions were selected as the electrodes for measuring the specific resistance, and 4 of them were 1
The current and voltage electrodes of the group were measured one by one along the circumferential direction while shifting one by one, and the specific resistance was measured at eight locations in total for one cross section.

In the drawings shown in FIGS. 3 to 7, the measurement points are indicated by the numbers of the lock bolts E selected as the voltage electrodes. That is, the specific resistance values in the case where 1 to 4 shown in FIG. 1 are selected as the electrodes are represented as 2-3 in FIGS. 3 to 7, and one is displaced in the circumferential direction to 2 ~ 5
3 to 7 show a specific resistance value of 3-4 when the electrode is selected as the electrode. Similarly, when the specific resistance is measured, the specific resistance value of the lock bolt E selected as the voltage electrode is The measurement points are specified and displayed by numbers.

Further, in the construction of the tunnel for which this measurement was carried out, as shown in Table 1 below, three types of support work patterns C1, C2 and D1 were adopted and used in each of these patterns. Length of lock bolt E (3m
4m) was different from the driving interval (1.5m and 1.2m), the formula for calculating the specific resistance was also changed accordingly.

The support pattern C1 is an arrangement pattern adopted at a good portion of the bedrock, and the support pattern C1 is an arrangement pattern adopted at a fragile portion of the bedrock.
2 is an arrangement pattern adopted in the middle of these.

Table 1 shown below is a table in which the values of the specific resistances shown in FIGS.

[0036]

[Table 1] As is clear from the measurement results of the specific resistance value shown in Table 1,
In comparison with each cross section, both the cross section 7 and the cross section 8 show a large value of 800 Ωm at the maximum, and the cross sections 3 and 4 have a low value of less than 50 Ωm symmetrically. Of the measured values, the lowest specific resistance value is 0.2 Ωm.
So, there was a difference of 3 orders from the maximum value. In addition, 500
A resistivity value of up to 1000 Ωm corresponds to the value of crystalline medium-hard rock, and a value of several to 10 Ωm corresponds to the value of mudstone.

FIG. 8 to FIG. 12 are observation records of the cross-sectional face daily report whose specific resistance was measured. This observation record is shown in Figure 8.
This corresponds to the cross section 1 shown in FIG. 3, and the cross section 3 in FIG. 9 corresponds to odd cross sections.

Observing the tendency of each cross section, the specific resistance value is 2 in the cross sections 1 and 2 shown in FIG.
It is distributed in the range of 0.3 to 53.0 Ωm, and this value is relatively stable.

On the other hand, in the observation record of the cut face daily report shown in FIG. 8, the strength rank is 2 (easy with a hammer,
It is relatively good for small pieces or thinly cracked), but the rank of spring water is 4 (partially ejected), and it is considered that this effect appears in the specific resistance value.

Further, in the cross sections 3 and 4 shown in FIG. 4, the specific resistance values are distributed in the range of 1.0 to 48.8 Ωm, and large variations are recognized in the values.

On the other hand, in the observation record of the faceted daily report shown in FIG. 9, the strength rank is 3 (fragile with a hammer and easily cracks), and the spring rank is 4 (partially ejected).
In addition, there are records of rock properties such as difficulty in self-sustaining, weathering on the whole, oil marks at the opening, crush zones, etc. These properties are considered to be a cause of low resistivity, and the values vary. It is considered that the cause is the unevenness of the rock mass properties.

Further, in the cross-sections 5 and 6 shown in FIG. 5, in particular, in the cross-section 6, the specific resistance value exceeds 100 Ωm in two sections 5-6 and 7-8. It is considered that this is because the fixation of the No. 6 lock bolt E is unstable. However, since it was confirmed that no load was applied when connecting the cord, it does not affect the stability of the ground.

Excluding these, the specific resistance value is 0.2 to 6
It is distributed in 9.2 Ωm, and a very large variation is recognized in the value.

On the other hand, in the observation record of the cut face daily report shown in FIG. 10, the strength ranks are the same as those of the cross sections 3 and 4.
3 (brittle with a hammer and easy to break), 4 ranks of spring water (partially squirting), and rock characteristics such as difficulty in self-sustaining, weathering on the whole, oil marks at openings, crush zones, etc. There is.

The larger variation in the value of the specific resistance than in the cross sections 3 and 4 is considered to indicate that the difference in the degree of saturation is large.

Further, in the cross-sections 7 and 8 shown in FIG. 6, the specific resistance values are distributed in the range of 362 to 807 Ωm, which is very large and relatively stable.

On the other hand, in the observation record of the faceted daily report shown in FIG. 11, the strength rank is 1 (hammer bounces) to 2 and is good, and the spring rank is 2 (partially exudes). ) Is good, and white rocks showing thermal alteration have not been confirmed in the photograph of the face. It is considered that such properties are accurately reflected in the specific resistance value.

In the section 9 shown in FIG. 7, the specific resistance value is distributed in the range of 10.3 to 88.8 Ωm, and this value is
It is low and not stable.

On the other hand, in the observation record of the faceted daily report shown in FIG. 12, the strength rank is 1 (hammer bounces), which is good, but the spring rank is 4 (partially ejects). And spring water was also confirmed in the photograph of the cutting face.
The specific resistance value is considered to be greatly affected by the presence of water.

FIG. 13 is a graph showing the correlation between the rock mass evaluation point and the specific resistance value obtained by the measurement. For the specific resistance value, the average value of each cross section shown in Table 1 is used, and the rock mass evaluation point is
The evaluation points set according to the stages shown in parentheses in FIG. 8 were totaled and used as the average score.

Correlation objects are bedrock, cracks, water, and total points.
For the rock mass, the average value of the evaluation points A to D (condition of face, condition of uncut surface, rock strength, weathered alteration) of the evaluation items shown in FIG. G (interval between cracks,
The average value of the evaluation points of the shape of the crack and the state of the crack) was used, and the water was the average value of the evaluation points of H and I (spring water, deterioration due to water).

As the total point, the rock mass of 4 items, the crack of 3 items, and the average value of 9 items in total of 2 items of water were used. The respective values are shown in Table 2 below.

[0053]

[Table 2] As is clear from the results shown in FIG. 13 and Table 2, the specific resistance value measured using the lock bolt E as an electrode is as follows, with respect to the evaluation points of the observation records described in the conventional Kirifuku daily report.
It can be seen that when the evaluation point is low, the specific resistance value is large, and when the evaluation point is high, the specific resistance value is small, and there is a good correlation between them.

In this case, in particular, the consistency between the total point and the specific resistance value is the best, followed by rock and cracks.
Regarding water, there is some discrepancy in consistency, but overall there is no contradiction. From the above results, it was confirmed that the tunnel rock mass evaluation method according to the present invention enables highly reliable evaluation.

[0055]

As described above in detail, according to the method for evaluating a tunnel bedrock according to the present invention, it is not necessary to install or remove electrodes, and the rock mass properties can be quantified without affecting the tunnel construction. And can be evaluated with high reliability.

[Brief description of drawings]

FIG. 1 is an explanatory view of a tunnel cross section to which a tunnel rock evaluation method according to the present invention is applied.

FIG. 2 is a side sectional view of FIG.

FIG. 3 is an explanatory diagram of a result of measurement of specific resistance, which was carried out in order to confirm the operation effect of the present invention in an excavated cross section of an actual tunnel construction.

FIG. 4 is an explanatory diagram of measurement results of specific resistance in an excavation cross section different from the excavation cross section shown in FIG. 3.

5 is an explanatory diagram of a measurement result of specific resistance in an excavation cross section different from the excavation cross section shown in FIG. 3;

6 is an explanatory diagram of a measurement result of a specific resistance in an excavation cross section different from the excavation cross section shown in FIG.

7 is an explanatory diagram of a measurement result of a specific resistance in an excavation cross section different from the excavation cross section shown in FIG.

FIG. 8 is a cutting face diary of a cutting face corresponding to the excavated cross section shown in FIG.

9 is a cutting face diary of a cutting face corresponding to the excavated cross section shown in FIG.

10 is a cutting face diary of a cutting face corresponding to the excavated cross section shown in FIG.

FIG. 11 is a cutting face diary of a cutting face corresponding to the excavated cross section shown in FIG.

FIG. 12 is a cutting face diary of a cutting face corresponding to the excavated cross section shown in FIG. 7.

FIG. 13 is a graph showing the relationship between rock mass evaluation points and specific resistance values.

[Explanation of symbols] A tunnel B face C wire mesh D Sprayed concrete layer E lock bolt

Claims (4)

[Claims] 1. A rock bolt, which is placed on a tunnel rock, is used as an electrode, and the specific resistance between the rock bolts is measured. Based on the obtained specific resistance value, cracks, springs, and rock strength of the tunnel rock are measured. A method for evaluating tunnel bedrock, which is characterized by evaluating the properties of natural ground. 2. A plurality of the lock bolts are provided on substantially the same cross section of the tunnel cross section, and a plurality of the lock bolts are driven in the upper half and side portions at predetermined intervals along the circumferential direction of the tunnel. Select any 4 of the lock bolts from
2. The method for evaluating a tunnel rock mass according to claim 1, wherein the outer two are used as current electrodes, and the inner two sandwiched between the current electrodes are used as voltage electrodes to measure the specific resistance value. 3. The method for evaluating a tunnel rock mass according to claim 2, wherein the evaluation is based on a ground property of a face face near a driving position of the lock bolt selected as a specific resistance measuring electrode. . 4. The specific resistance value is determined by sequentially shifting one by one along the circumferential direction of the tunnel, with four sets selected from the lock bolts as one set. The method for evaluating a tunnel bedrock according to any one of 3 above.