JPH11352043A - Method for measuring degree of damage to base rock - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of speedily measuring the degree of damage to base rock by a simple device and operation without the need for a large number of devices, complicated facilities, a large amount of time, effort, or cost for installing them. SOLUTION: Acoustic emission which occurs at the time, when a core sample is collected from base rock and is uniaxially compressed is measured. Then a damage parameter x is obtained according to the equation χ=σAE×Sc/P<2> (where Sc is strength at sound state, σAE is a load when the occurrence of AE suddenly starts to increase at measurement, and P is a maximum load at measurement) to measure the degree of damage to the base rock in this method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for easily measuring the degree of damage to rock using acoustic emission (hereinafter abbreviated as AE).

[0002]

2. Description of the Related Art AE is a phenomenon in which, when a material to which a physical load is applied is deformed or a crack is generated therein, strain energy stored up to that time is released and propagated as sound. is there. By the way, when the rock is mechanically excavated or destroyed by blasting, the area around the area destroyed by the excavation or blasting is also damaged. However, it is important to know the damage quantitatively in the subsequent work plan. Therefore A
E-sensors are used to predict the collapse of the ground and to locate the collapse location.

[0003] For example, an AE sensor disposed in a ground or on a ground penetrating member, a counting circuit for an AE electric signal connected to the sensor, and count data of the counting circuit are inputted and analyzed to predict a ground collapse. Using a mountain landslide prediction device configured with a computer (Japanese Patent Laid-Open No. 2-24)
No. 521), a wave guide having AE sensors attached to both ends is buried in the ground where collapse is expected, and the AE phenomenon is detected by the two sensors, and the time difference between the two and the sound speed transmitted through the wave guide are determined. A method of locating a ground collapse by detecting a collapse position by measuring (JP-A-2-190520), capturing an AE sound generated due to an internal collapse behavior of a ground, converting the AE sound into an electric signal, and measuring. At the time of analysis, a method of grouping AE signals having different generation factors and estimating a destruction phenomenon inside the ground based on a change in the number of representative AE signals generated in each group (Japanese Patent Laid-Open No. 5-112923) ), Wave guides with AE sensors attached to both ends are installed on the ground over the expected slip surface to measure AE waves generated in the ground,
Data that has been located is selected from the data that has arrived at the AE sensors at both ends, and each A that has been located is selected.
A method of investigating the E waveform characteristics and locating the slope failure position using only the position locating results determined as AE waves from the same AE source as evaluation data (Japanese Patent Laid-Open No. 6-8874).
No. 4) has been proposed so far.

However, all of these methods are
A large number of AE sensors are placed on or around the rock where the collapse is expected, and the information obtained by them is analyzed.
Since it measures the degree of damage and detects the collapse position,
There are drawbacks in that a large number of devices and complicated equipment, a great deal of labor and cost for installing them, and a long time for analysis are required.

[0005]

SUMMARY OF THE INVENTION The present invention reduces the degree of rock damage quickly with a simple device and operation without requiring a large number of devices and complicated equipment and a great deal of labor and cost for installing them. It provides a method for measuring.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to develop a method for easily and quickly measuring the degree of rock damage utilizing the AE phenomenon. The present inventors have found that if a core sample is collected from a bedrock and a bedrock surrounding an area destroyed by excavation or blasting and is uniaxially compressed, data on the degree of damage can be easily obtained. Reached.

That is, according to the present invention, an acoustic core generated by collecting a core sample from rock and uniaxially compressing it.
Emission (Acoustic Emission)
And the equation 式 = σAE × Sc / P ² (where Sc is the strength at the time of soundness and σAE is the AE at the time of measurement.
(P is the maximum load at the time of measurement), and the damage parameter に 従 っ て is determined in accordance with the load at the time when the occurrence of abrupt increase starts to increase rapidly.

[0008]

Next, the method of the present invention will be described in more detail with reference to the accompanying drawings. Figure 1 shows core sample 1
Is sandwiched between the supports 2 and 3, and a load is applied from one or both of them to uniaxially compress, and the generated AE is measured by the sensor 4. When a load is applied to a rock or soil material, the material has the property that AE does not occur until the stress previously applied to the material.
This property is called the Kaiser effect.In the case of rocks and soil materials, if the time from when a core sample is collected to when it is used for measurement becomes long, the Kaiser effect becomes unclear, and the ground pressure is estimated. Becomes difficult.

However, in the method of the present invention, the AE generation pattern obtained by repeatedly applying pressure to the core sample under uniaxial compressive stress shows that even if the Kaiser effect is not clear, the process of the subsequent repeated load application The increase in AE generation at the stress corresponding to the precedent stress is observed. Therefore, by utilizing this phenomenon, it has become possible to evaluate the degree of damage of rock mass even with a core sample that has been long time elapsed after collection, which has been considered difficult in the past.

In the method of the present invention, it is necessary to determine the damage parameter に よ っ て by the above formula. Sc in this equation is the strength of the rock mass at the time of soundness without any damage, which is obtained by taking a sample from a predetermined rock mass and measuring the strength before crushing by excavation or blasting. It can be obtained by: ΣAE is a load at which the occurrence of AE sharply increases when P is increased by a compression test and the corresponding AE is measured. This is the relationship between the applied load and AE. Can be easily known from the graph in which is plotted.

[0011] The damage parameter χ obtained in this way is the limit value of 50, at which the rock exhibits elastic behavior.
Since the% stress level is almost 1.0, this value indicates whether the rock mass is still in a range showing sound elastic behavior or is in a state showing plastic behavior in which cracks have increased beyond the elastic limit. Can be easily determined.

[0012]

Next, the present invention will be described in more detail with reference to examples.

Reference Example Sandstone specimen (diameter 4 cm, length 11 cm, compressive strength 40)
0 kgf / cm ² ), the compressive strength of which is 15 to 10
A load corresponding to 0% was applied to prepare a sample that had been damaged in advance. Next, a compression test was performed on each of the samples, and the AE at that time was measured. The results are shown as a graph in FIG. When the damage parameter was calculated from the AE measurement result and the relationship with the load level applied in advance was obtained, the damage parameter decreased as the load level, that is, the load increased, and the limit of 50, at which the rock exhibited elastic behavior. The% stress level was almost 1.0.

Example A core sample (4.5 cm in diameter and 10 cm in length) was taken by drilling around the area where a rock having a healthy compressive strength of 1600 kgf / cm ² was blasted and destroyed.
This core sample was allowed to stand for 24 hours after collection, and was subjected to a compression tester to calculate AE for each load, and this relationship is shown as a graph in FIG. ΣAE and P were obtained from this graph, and the damage parameter was calculated to be 1.28. From this, it was found that the rock mass from which this core sample was taken was within the elastic limit.

Comparative Example A core sample having the same dimensions was taken from a region different from that of the example, and the relationship between load and AE was examined in the same manner as in the example.
This result is shown in FIG. 4 as a graph. ΣAE and P were obtained based on this graph, and the damage parameter was calculated to be 0.816. From this, it was found that the rock mass from which this core sample was taken was in a state of showing plastic behavior due to cracks.

[0016]

According to the method of the present invention, a core sample obtained by boring a rock is attached to a compression tester, and while applying a load, the number of AEs generated while the load is increasing is measured. In addition, the degree of rock damage can be easily measured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a test method used in the method of the present invention.

FIG. 2 is a graph showing a relationship between a load and AE obtained in a reference example.

FIG. 3 is a graph showing a relationship between a load and AE obtained in an example.

FIG. 4 is a graph showing a relationship between a load and AE obtained in a comparative example.

[Explanation of symbols]

 1 core sample 2, 3 support 4 sensor

Claims (2)

[Claims] 1. Acoustic emission (Ac) generated by collecting a core sample from rock and uniaxially compressing the core sample.
and measuring a damage parameter に 従 っ て according to the following equation. χ = σAE × Sc / P ² where Sc is the strength at the time of soundness, σAE is the load at which the occurrence of AE starts to increase sharply at the time of measurement, and P is the maximum load at the time of measurement. 2. The method according to claim 1, wherein an elastic limit of the rock is detected.