JP7454526B2 - Method for estimating compressive strength of rock - Google Patents

Description

The present invention relates to a method for estimating the compressive strength of a rock, and particularly to a technique that is effective when applied to estimate the compressive strength of a rock in front of a face when excavating a tunnel or the like.

When excavating tunnels, etc., understanding the nature of the ground in front of the face is essential for safe and economical construction. Drill logging is a technique for exploring the properties of the ground in front of the face, such as hardness and softness. Furthermore, attempts have been made to predict the compressive strength of rock using this method.

This method uses a hydraulic rock drill mounted on a drill jumbo to perform non-core drilling (drilling without collecting a sample (core)) approximately 30 to 50 meters forward from the tunnel face, and the drilling speed is rock drilling machine impact pressure (the impact force generated on the shank rod by the rock jackhammer piston hitting the shank rod), rotational pressure (rotational force applied to the shank rod by the rotor), feed pressure (rock drilling machine This method predicts the properties of the ground at the drilling location from machine data such as the thrust force of the drill. Indices for evaluating the soil properties include the drilling speed determined from machine data during drilling and the drilling volume specific energy (also known as "drilling energy"), which is the amount of energy required for drilling per unit excavation volume. ).

However, the excavation volume specific energy changes not only depending on the rock properties, but also changes in operating pressures such as impact pressure, rotational pressure, and feed pressure, differences in the particle size of drilling shear, and the discharge state of drilling shear. Therefore, it is difficult to accurately grasp the properties of the ground.

In other words, if the drilling slag created by drilling is not sufficiently discharged from the hole, the secondary crushing of the drilling slag will result in drilling efficiency (ratio of energy consumed for drilling to energy generated by the rock drill). It is overestimated that the ground is more solid than it actually is. In addition, in weak ground such as cracked ground or fault fracture zones, drilling efficiency decreases due to hole wall collapse, resulting in an overestimation.

In addition, if the feed pressure is lower than the predetermined pressure and the bit does not reach enough rock, not only will the efficiency of energy transfer to the ground deteriorate, but the drilling speed itself will decrease, resulting in an increase in the excavation volume specific energy. However, the ground is perceived to be more solid than it actually is. Therefore, it is necessary to keep the feed pressure constant during excavation, but in order to perform stable drilling in extremely fragile ground, the feed pressure must be set low.

As described above, when excavation volume specific energy is used as an index, it is difficult to accurately grasp the degree of hardness and compressive strength of the ground.

Therefore, a technology has been proposed to investigate the compressive strength of the ground using damping pressure (hydraulic pressure) as an index. In a rock drill equipped with a damper device that absorbs the repulsive force received from the rock when a striking force is applied to the rock with a striking rod and bit, the damping pressure is used to determine the magnitude of the repulsive force (degree of repulsion). It is evaluated based on the impact reaction force transmitted from the ground to the damping piston. This is because the damping pressure is a direct reflection of the repulsive force from the rock at the tip of the bit, so it is thought to be more accurate than exploration, which uses excavation volume specific energy to evaluate the compressive strength of the rock. be.

Here, Patent Document 1 discloses a technique for investigating the compressive strength of a rock using the pulsating amplitude of damping pressure. Specifically, correlation data between the pulsation amplitude of the normalized damping pressure and the compressive strength of multiple test specimens with different compressive strengths was obtained in advance, and a striking force was applied to the ground using a rock drill. The compressive strength of the rock is estimated by dividing the measured pulsating amplitude of the damping pressure by the impact pressure, normalizing it, and referring to the correlation data.

Furthermore, Non-Patent Document 1 discloses a technique for investigating the compressive strength of a rock using damping pressure as an index. Specifically, since the relationship between damping pressure and feed pressure has a high correlation with the compressive strength of the rock, the compressive strength of the rock is estimated by measuring the values of damping pressure and feed pressure. It is something.

Japanese Patent Application Publication No. 2020-063639

Tunnel Engineering Research Papers and Reports Volume 6, November 1996 Report (7), "Face forward exploration method using damping pressure of hydraulic rock drill"

However, the techniques described in Patent Document 1 and Non-Patent Document 1 indirectly estimate the properties of the rock as the stress propagating through the shank rod and the striking rod as fluctuations in damping pressure (hydraulic pressure). Moreover, there was a possibility that the actual compressive strength could not be accurately estimated.

The present invention was made from the above-mentioned technical background, and an object of the present invention is to provide a method for estimating the compressive strength of a rock that can estimate the compressive strength of a rock in front of a face with high accuracy.

In order to solve the above problems, the method for estimating the compressive strength of a rock according to the present invention according to claim 1 includes a shank rod that is struck by a piston, and a bit that is attached in series with the shank rod and fixed to the tip. A rock drill equipped with a striking rod that applies a striking force to a mountain, and a measuring means that measures reflected wave data that is reflected from the ground and propagates to the striking rod when the striking rod applies a striking force to the ground. Prepare a plurality of test specimens with different compressive strengths, apply impact force with the rock drill, obtain the reflected wave data for each test specimen, and calculate the maximum amplitude of the compressive stress of the reflected wave data. The reflected wave stress amplitude ratio coefficient, which is the ratio to the maximum amplitude of the tensile stress, is determined, and from the compressive strength in each test specimen and the reflected wave stress amplitude ratio coefficient determined for each test specimen, the compressive strength and the Find correlation data with the reflected wave stress amplitude ratio coefficient, and calculate the correlation data and the reflected wave stress amplitude ratio coefficient of the reflected wave data measured when the rock drilling machine applies a striking force to the ground to be excavated. It is characterized by estimating the compressive strength of the rock from the above.

The method for estimating the compressive strength of a rock according to the invention according to claim 2 is the method according to the invention according to claim 1, in which at least one of the reflected wave data of the respective test specimens and the reflected wave data of the rock is used. The data is characterized in that it is data of a reflected wave that is first reflected from the tip of the bit that comes into contact with the ground by applying a striking force and propagated to the striking rod.

The method for estimating the compressive strength of a rock according to the invention according to claim 3 is the invention according to claim 1 or 2, wherein the measuring means measures the center of the total length of the striking rod and the shank rod. It is characterized by being installed in the part.

The method for estimating the compressive strength of a ground according to the invention according to claim 4 is that in the invention according to claim 1 or 2, the measuring means is installed at a position where the input wave and the reflected wave do not interfere with each other. It is characterized by

The method for estimating the compressive strength of a rock according to the invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the measuring means is a strain gauge attached to the striking rod. , is characterized by.

The method for estimating the compressive strength of a rock according to the invention according to claim 6 is the invention according to any one of claims 1 to 5, in which the plurality of test specimens are formed by drilling a plurality of holes in a predetermined rock block. The method is characterized in that it is manufactured by filling the drilled holes with a cement-based solidifying material.

According to the present invention, impact force is applied to a plurality of test specimens having mutually different compressive strengths using a rock drill, reflected wave data for each test specimen is acquired by a measuring means, and the maximum amplitude of compressive stress in the reflected wave data is obtained. The reflected wave stress amplitude ratio coefficient, which is the ratio between the The compressive strength of the rock in front of the face can be estimated by estimating the compressive strength of the rock from the reflected wave stress amplitude ratio coefficient of the reflected wave data measured when the rock is hit by a rock drill. It becomes possible to estimate with high accuracy.

1 is a schematic diagram of a rock drill used in a method for estimating the compressive strength of a rock, which is an embodiment of the present invention. FIG. 2 is an explanatory diagram showing the generation of stress waves caused by the impact of the rock drill in FIG. 1, propagation of the impact rod, and the fracture mechanism of the ground; (a) shows the compressive stress generated in the shank rod and piston due to the impact of the piston; FIG. The figures, (b) to (d) are diagrams continuously showing the state in which the tip of the bit penetrates into the ground, and the relationship between the bit load and the penetration depth at that time. FIG. 3 is a schematic diagram showing the behavior of stress waves of a bit in a state of being pressed against a ground. FIG. 3 is an explanatory diagram showing the production of a test specimen using rock blocks. It is a figure showing the unconfined compressive strength of a test piece. FIG. 5 is an explanatory diagram showing how holes are drilled in the test specimen of FIG. 4; FIG. 2 is an explanatory diagram showing the measurement position of rod stress in the striking rod of the rock drill shown in FIG. 1; 8(a) is a diagram showing the measured waveform of rod stress during drilling of test specimen B; FIG. 8(a) is the stress waveform at measurement point 1, and FIG. 8(a) is the stress waveform at measurement point 2. 9A and 9B are enlarged views of the dashed-line frame in FIG. 8, where (a) is an enlarged view of the stress waveform at measurement point 1, and (b) is an enlarged view of the stress waveform at measurement point 2. FIG. 6 is a diagram showing stress waves incident on the bit due to the impact of the piston when holes are drilled in test specimens B, D, and E. 13 is a diagram showing the first reflected wave (first reflected wave) from the bit after the bit has applied an impact force to test specimens B, D, and E. FIG. FIG. 12 is a diagram illustrating an extracted first reflected wave from the bit after the bit has applied a striking force to the test object D in FIG. 11 . FIG. 6 is a diagram showing the drilling depth distribution of the stress amplitude ratio coefficient of the reflected wave obtained from the stress wave of the striking rod when drilling the test specimens A, B, C, D, and E. It is a graph showing the relationship between the stress amplitude ratio coefficient of reflected waves guided from test specimens A, B, C, D, and E and compressive strength.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment as an example of this invention will be described in detail based on drawing. In addition, in the drawings for explaining the embodiments, the same components are designated by the same reference numerals in principle, and repeated explanation thereof will be omitted.

FIG. 1 is a schematic diagram of a rock drill used in a method for estimating the compressive strength of a rock, which is an embodiment of the present invention.

The rock drilling machine 10 shown in FIG. 1 is a hydraulic rock drilling machine in which a striking mechanism and a rotating mechanism are driven by hydraulic pressure.The rock drilling machine 10 shown in FIG. A striking rod 15 is attached and has a bit 14 fixed to its tip. Further, the hydraulic drifter 11 includes a piston 16 that strikes the shank rod 13 and a rotor 17 (FIG. 7) that rotates the shank rod 13. Note that a tip 14a is embedded in the surface of the bit 14 facing the ground G (that is, the excavation side).

With such a rock drill 10, the piston 16 in the hydraulic drifter 11 is moved within a cylinder (not shown) by hydraulic oil and strikes the shank rod 13. The shank rod 13 transmits the striking force from the piston 16 as well as the rotational force R from the rotor 17 and the thrust (feed pressure) of the rock drill 10 to the striking rod 15 via the sleeve 12. and transmits the rotational force to the bit 14 at the tip. Then, the bit 14 applies striking force, rotational force, and thrust directly to the ground G, thereby crushing the ground G.

Here, the compressive stress wave (impact energy) generated when the piston 16 in the hydraulic drifter 11 hits the shank rod 13 propagates to the bit 14 at the tip and is consumed for crushing the ground, but some The stress wave returns to the hydraulic drifter 11 as a repulsive force. The repulsive force of this impact causes the rock drill 10 to move backward, and also deteriorates the rock landing property of the bit 14, which causes a decrease in excavation efficiency.

Therefore, a damper device is provided in order to alleviate the repulsive force from the ground and at the same time maintain the rock-landing property of the bit 14 regardless of the feed pressure.

As shown in the figure, this damper device is composed of a damping piston 18 that absorbs repulsive force from the earth, and a pushing piston 19 that is placed inside the damping piston 18 and applies a predetermined thrust to the striking rod 15. There is. The thrust from the pushing piston 19 to the striking rod 15 is applied by hydraulic pressure, and the repulsive force from the earth is absorbed by the hydraulic pressure of the damping piston 18, that is, the damping pressure. Note that a cylindrical bush 20 that serves as a bearing for the pushing piston 19 is installed on the pushing piston 19 side of the shank rod 13.

In the rock drill 10 of this embodiment, the piston 16 strikes the shank rod 13 2,800 to 4,500 times per minute. Furthermore, the excavated debris crushed by the impact is removed from the crushed position by flushing with water or the like, and is discharged out of the hole.

Here, the stress waves propagating through the striking rod 15 due to the impact of the rock drill 10 will be explained.

FIG. 2 shows the generation of stress waves caused by the impact of the rock drill 10, the propagation of the impact rod 15, and the mechanism of fracture of the rock. Note that FIGS. 2(b) to 2(d) show the relationship between the bit load (load from the bit 14 to the ground G) and the penetration depth when the tip of the bit 14 penetrates the ground G (hereinafter referred to as " ``F-δ relationship'') is also written. Although the actual F-δ relationship is not a straight line but a curved line both during loading and unloading, it is simply shown as a straight line here. Moreover, in FIGS. 2(c) and 2(d), the compressive stress and the tensile stress are smaller as the dot density becomes sparser, and larger as the dot density becomes denser.

Now, when the piston 16 in the hydraulic drifter 11 hits the shank rod 13 and applies an impact force, a local compressive stress is generated in the hit area (FIG. 2(a)).

The local compressive stresses propagate as waves (stress waves) through the sleeve 12 and through the striking rod 15. The propagation speed of the stress wave propagating through the striking rod 15 is, for example, 5,080 m/s, and since the striking rod 15 is rod-shaped, it can be treated as a one-dimensional wave (FIG. 2(b)).

The stress wave propagates to the bit 14 and becomes an incident wave at the boundary with the ground G at the tip, and becomes a transmitted wave that transmits from the tip 14a embedded in the bit 14 into the ground G. Due to the difference in acoustic impedance between the ground and the rock G, it becomes a reflected wave of tensile stress at the boundary and returns to the rock drill 10 side. In the F-δ relationship, the bit enters a loading process in which the penetration depth increases as the bit load increases (Fig. 2(c)).

When the incidence of the stress wave ends, the bit 14 is repelled by the rigidity of the ground G, and the reflected wave changes from tensile stress to compressive stress. In the F-δ relationship, the bit enters an unloading process in which the amount of penetration decreases as the bit load decreases, reaching the final amount of penetration. The hatched area in FIG. 2(d) is the energy consumed in crushing the ground G (FIG. 2(d)).

Here, the behavior of stress waves of the bit 14 in a state of being pressed against the ground G is shown in FIG. If we assume that the bit side is elastic body 1 and the rock side is elastic body 2, and the two elastic bodies are in contact with each other on a plane, the incident wave will reach the boundary surface (the boundary between elastic body 1 and elastic body 2). It can be understood as a behavior that is divided into reflected waves and transmitted waves.

Next, a method for estimating the strength of a rock using such a rock drill 10 will be explained.

In the method for estimating the strength of a rock, first, using the aforementioned hydraulic rock drill 10, a hole is drilled into a test specimen S that simulates a rock whose compressive strength is known. Hole drilling was performed on a plurality of test specimens S having different compressive strengths.

In the compressive strength test, we created test specimens S that simulated rock formations with different compressive strengths by changing the type of cementitious solidifying material (non-separable grout) that was used. We measured rod stress, drilling speed, and mechanical data for each hydraulic pressure when drilling a hole by changing the working pressures of hydraulic pressure, rotational pressure, feed pressure, and damping pressure. The curing period of the solidifying material was the same.

To manufacture the test specimen S, a rock block E (100 cm x 100 cm x 100 cm) consisting of four granites (Inada granite mined in Kasama City, Ibaraki Prefecture) was used. Using a pneumatic crawler drill equipped with a φ127 mm bit with the surface to be drilled facing up in rock block E, holes were drilled vertically to a depth of 60 cm from 6 locations on one surface, as shown in Figure 4. Each of the four rock blocks E was filled with grout mortars A, B, C, and D of the same type to a thickness of 50 cm, and the top was filled with cap mortar P with a thickness of 10 cm to form the test specimen S. Manufactured.

The unconfined compressive strength (σ) of the test specimen S is shown in FIG. The unconfined compressive strength was measured by fabricating five test pieces (not shown) for each specimen S using grout mortars A, B, C, and D of the same type as the filled grout mortars A, B, C, and D. Then, a uniaxial compression test was conducted at the same time as the drilling experiment, and the average value was determined. In addition, the test specimen S was assumed to be a case in which a new hole was drilled from a position where a hole had not been drilled in a rock block E made of granite.

In the drilling experiment, after solidifying the grout mortars A, B, C, and D filled in the rock block E, the test specimen S was turned over so that the filling surface was in the vertical direction as shown in Fig. 6, and then the grout mortars A, B were , C, and D were drilled in the horizontal direction to a depth of approximately 60 cm using a bit 14 having a diameter of 64 mm. In addition, in the drilling experiment, in order to stably drill holes in test specimens S having different compressive strengths, the impact pressure was set to 16 MPa, the feed pressure was 6 MPa, and the damping pressure was set to 9 MPa.

For measurements in the drilling experiment, a drilling logging device (not shown) that automatically measures drilling data such as oil pressure of the rock drill 10 and drilling length, and a general-purpose recording device that measures rod stress were used. . A hydraulic sensor installed in the hydraulic circuit of the rock drill 10 was used to measure impact pressure, rotation pressure, damping pressure, and feed pressure. In addition, in order to organize the rod stress measurement results with respect to the drilling depth, we used the drilling length data output from the drilling logging device.

In an experiment to measure the stress of the striking rod 15 using four rock blocks, a hexagonal hollow rod (opposite side: 35 mm, inner diameter: 9.5 mm) with a length of 3.70 m was used. Here, the measurement positions of rod stress are shown in FIG. The measurement position was 50 cm from the joint between the striking rod 15 and the shank rod 13 (measurement point 1), and a distance from measurement point 1 to the bit so that the centralizer CL and the measurement cable (not shown) would not interfere during drilling. There are two locations, one on the 14th side and a location 1.7m apart (measurement point 2). That is, for the striking rod 15 having a total length of 3.70 m, the measuring point 1 is on the opposite side of the center (1.85 m) from the bit 14, and the measuring point position is on the bit 14 side with respect to the center. Furthermore, a strain gauge (measuring means) M1 was installed at measuring point 1, and a strain gauge (measuring means) M2 was installed at measuring point 2. In order to cancel the influence of the bending stress of the striking rod 15, two strain gauges were attached to each location on opposite sides of the hexagonal cross section. Note that the measurement points are not limited to the positions shown in this embodiment, and the number of measurement points may be three or more.

Since the striking rod 15 rotates during drilling, the measurement cable is wound around the striking rod 15 about 30 times in the opposite direction of rotation in advance, and is unwound by the rotation of the striking rod 15, and then wound again about 30 times in the opposite direction. Approximately 25 seconds (rod rotation speed: 145 rpm) until winding was measured. The recording device synchronizes the rod stress data at two measurement points (measurement point 1 and measurement point 2) with the measurement data from a dedicated measurement device for drilling logging, and records data at a sampling frequency of 1 MHz (sampling time interval of 10 ^-6 seconds). ) was recorded.

FIG. 8 shows the measured waveform of rod stress during drilling of test specimen B. Here, FIG. 8(a) shows the stress waveform at measurement point 1, and FIG. 8(a) shows the stress waveform at measurement point 2. In FIG. 8, the measured strain is converted into stress with Young's modulus of 205.8 GPa, and tensile stress is shown as positive and tensile stress as negative.

FIG. 9 shows an enlarged view of the range from 0 ms to 5 ms (framed by broken lines) in which stress waves due to impact can be observed for measurement points 1 and 2. Here, FIG. 9(a) is an enlarged view of the stress waveform at measurement point 1, and FIG. 9(b) is an enlarged view of the stress waveform at measurement point 2. Since the elastic wave velocity of the striking rod 15 is 5,080 m/s, as shown in the figure, the stress wave caused by the impact of the rock drill 10 propagates through the striking rod 15 and reaches the measurement point 1 based on the time. Then (Fig. 9(a)), it reached the measurement point 2 located 1.7 m ahead with a delay of 0.335 ms (Fig. 9(b)). Time line RT where stress waves arrive, taking into consideration that the distance from measurement point 1 to the tip of bit 14 where reflection is expected is 3.25 m, and the distance to the end of shank rod 13 is 0.49 m. is also written in the figure. A solid travel line RTa indicates the travel time of the stress wave propagating from the hydraulic drifter 11 side to the bit 14 side, and a broken line travel line RTb represents the travel time of the stress wave propagating from the bit 14 side to the hydraulic drifter 11 side. It shows. To check the stress wave generated when the piston 16 hits the shank rod 13 and the wave that is incident on the bit 14 (incident wave) and the wave that is reflected from the bit 14 after applying the impact force to the test specimen (reflected wave). I can do it.

It can also be seen that the amplitude of the stress wave is attenuated as it is repeatedly reflected between the tip of the bit 14 and the end of the shank rod 13. That is, in FIG. 9, the incident wave and the reflected wave forming the stress wave are the first incident wave (first incident wave) and the reflected wave (first reflected wave) after the bit 14 applies a striking force to the specimen S. ) has the largest amplitude and becomes the next incident wave (second incident wave) and reflected wave (second reflected wave), and then the next incident wave (third incident wave) and reflected wave (third reflected wave). It can be seen that the amplitude decreases with time.

Furthermore, when comparing the waveform of FIG. 9(a) and the waveform of FIG. 9(b), it is found that the incident wave and the reflected wave measured by the strain gauge M1 installed at the measurement point 1 shown in FIG. 9(a) are The spacing (the spacing between the first incident wave and the first reflected wave, the spacing between the second incident wave and the second reflected wave, and the spacing between the third incident wave and the third reflected wave) is as shown in FIG. 9(b). It is larger than the interval between the incident wave and the reflected wave measured by the strain gauge M2 installed at measurement point 2 shown in . Therefore, it can be seen that the mutual interference between the incident wave and the reflected wave measured by the strain gauge M1 installed at the farthest measuring point 1 from the bit 14 is smaller than that of the measuring point 2 which is relatively closer to the bit 14.

In order to confirm changes in stress waveforms of incident waves and reflected waves due to differences in compressive strength (σ) of test specimens S (grout mortar A, B, C, D, rock block E), three types with large changes in compressive strength were examined. A comparison was made using test specimens B, D, and E. Figure 10 shows the results of comparing the stress waves caused by the impact of the piston 16 and the waves incident on the bit 14 when drilling holes in each of the test specimens B, D, and E. The results of comparing the first reflected waves (first reflected waves) from bit 14 after being applied are shown in FIG. 11, respectively. Note that the measurement point is measurement point 1 in both FIGS. 10 and 11.

The stress waves incident on the bit 14 have a large compressive stress that contributes to crushing the ground G, and a small tensile stress. As shown in Fig. 10, the maximum amplitude of the compressive stress of the incident stress wave in test specimens B, D, and E is 184.9 MPa, 222.8 MPa, and 210.0 MPa, and there is no large difference between them. It can be inferred that this was roughly constant. On the other hand, in the first reflected wave that propagates to the rock drill 10 side when the bit 14 crushes the test piece S, as shown in FIG. The maximum amplitude of the compressive stress becomes 27.6 MPa, 51.0 MPa, and 116.5 MPa. From these facts, it can be seen that as the compressive strength and rigidity of the test piece S increases, the difference in acoustic impedance between the bit 14 and the test piece S becomes smaller, and the tensile stress becomes smaller. When the reflected wave becomes a compressive stress, it can be inferred that the greater the rigidity of the test body S, the greater the repulsive force from the test body S, and the greater the compressive stress of the reflected wave.

The main stress of the incident wave is compressive stress, and the reflected wave becomes tensile stress since it enters the test specimen S with low impedance from the bit 14. The larger the compressive strength of the test specimen S, the smaller the tensile stress of the reflected wave, and the larger the compressive stress of the reflected wave. Therefore, as shown in FIG. 12, as an example, for test specimen D, a coefficient (hereinafter referred to as a reflection The wave stress amplitude ratio coefficient (referred to as wave stress amplitude ratio coefficient) is calculated from the following equation, and its relationship with compressive strength is examined.

α _R = (σ _C −σ _T )/(σ _C +σ _T )

Here, α _R is the stress amplitude ratio coefficient of the reflected wave, σ _C is the maximum compressive stress amplitude of the first reflected wave, and σ _T is the maximum tensile stress amplitude of the first reflected wave.

Note that the stress amplitude ratio coefficient of the reflected wave may be obtained from the second reflected wave or the third reflected wave. However, as described above, since the amplitude of the first reflected wave, which is the first reflected wave after the bit 14 applies a striking force to the test specimen S, is the largest, it is desirable to obtain it from the first reflected wave.

Furthermore, as described above, the reflected wave measured by the strain gauge M1 installed at the measurement point 1 relatively far from the bit 14 has less mutual interference with the input wave. Therefore, it is desirable that the measurement point be as far away as possible from the tip of the bit 14 (the side in contact with the earth) and the end of the shank rod 13 (the side in contact with the piston). It is better to use the measurement data of the strain gauge M1 installed at the measurement point 1, which is the central part of the total length of the striking rod 15 and the shank rod 13, than at the measurement point 2, which is closer to the measurement point 14.

However, the measurement point may be any position where the input wave and the reflected wave do not interfere, and does not necessarily have to be at the center of the total length of the striking rod 15 and the shank rod 13.

Now, regarding the stress amplitude ratio coefficient of the reflected wave, if the tip of the bit 14 is a free end, it can be considered that σ _C =0, and α _R = -1, whereas if it is a fixed end, σ _T =0. It can be considered that α _R =1. Therefore, as the compressive strength of the test specimen S increases, the value of the stress amplitude ratio coefficient of the reflected wave increases.

FIG. 13 shows the drilling depth distribution of the stress amplitude ratio coefficient of the reflected wave obtained from the stress wave of the striking rod 15 when drilling the test specimen S (grout mortar A, B, C, D, rock block E). . In addition, FIG. 13(a) is for specimen A, FIG. 13(b) is for specimen B, FIG. 13(c) is for specimen C, FIG. 13(d) is for specimen D, and FIG. 13(e) is for specimen A. ) is the drilling depth distribution of the stress amplitude ratio coefficient of the reflected wave in the specimen E.

In these drawings, the stress amplitude ratio coefficient of the reflected wave determined for each impact is indicated by a circle, and in order to see the trend in the drilling depth direction, the section average per 50 holes is indicated by a solid line. In addition, the average values of the coefficients in the drilling sections of test specimens A, B, C, D, and E are also shown. Note that the portion of the cap mortar P at the start of drilling was excluded from the evaluation of the stress amplitude ratio coefficient of the reflected wave, since this is a section where the working oil pressure rapidly increases.

From FIG. 13, the average values of the stress amplitude ratio coefficients of the reflected waves of test specimens A, B, C, D, and E are -0.66, -0.39, -0.35, -0.28, 0. 30, and it can be seen that the stress amplitude ratio coefficient of the reflected wave increases as the compressive strength increases. In addition, in test specimens A, B, C, and D, the stress amplitude ratio coefficient of the reflected wave suddenly increases at the position where the drilling depth changes to granite in test specimen E near 60 cm.

FIG. 14 shows the relationship between the stress amplitude ratio coefficient (α _R ) of the reflected wave and the compressive strength (f). In FIG. 14, since α _R =−1 and f=0 when the rock drill 10 is used for dry firing, the horizontal axis is arranged as α _R +1 so that the result of this condition becomes the origin. As shown in the figure, there is a relatively high correlation between the two. It is inferred that this is due to the use of an index (stress amplitude ratio coefficient) that takes into account the compressive stress of the reflected wave, which reflects the repulsive force from the test specimen S, which increases the correlation with the compressive strength.

When the relational expression between the stress amplitude ratio coefficient (α _R ) of the reflected wave and the compressive strength (f) is obtained by second-order polynomial approximation, it becomes the following expression.

f = 132.0 (α _R +1) ² +25.3 (α _R +1)

Here, f is the compressive strength (MPa), and α _R is the stress amplitude ratio coefficient of the reflected wave.

Further, the correlation coefficient (R ² ) is 0.94.

Note that in this embodiment, the relational expression between the stress amplitude ratio coefficient (α _R ) of the reflected wave and the compressive strength (f) was obtained using an approximate curve using the least squares method, but it may also be obtained using an approximate straight line.

From the above, it can be seen that the stress amplitude ratio coefficient (α _R ) of the reflected wave obtained from the amplitude of the reflected waveform during drilling is an effective index for estimating the compressive strength (f) of the rock. Therefore, a plurality of test specimens S (in this embodiment, test specimens A, B, C, D, and E) having mutually different compressive strengths (f) are hit with a rock drill 10, and each test specimen S is The reflected wave data was acquired with strain gauge M1, and the reflected wave stress amplitude ratio coefficient (α _R ), which is the ratio between the maximum amplitude of compressive stress and the maximum amplitude of tensile stress in the reflected wave data, was determined, and the compressive strength of each specimen was determined. Correlation data between the compressive strength (f) and the reflected wave stress amplitude ratio coefficient (α _R ) is obtained in advance using an approximate curve or an approximate straight line derived from (f) and the reflected wave stress amplitude ratio coefficient (α _R ). put. Then, from the obtained correlation data and the reflected wave stress amplitude ratio coefficient (α _R ) of the reflected wave data measured when the rock jack 10 applied impact force to the ground to be excavated, the ground in front of the face is determined. By estimating the compressive strength (f), it becomes possible to estimate the compressive strength of the rock with high accuracy.

Although the invention made by the present inventor has been specifically explained based on the embodiments above, the embodiments disclosed in this specification are illustrative in all respects, and are limited to the disclosed technology. isn't it. In other words, the technical scope of the present invention should not be construed in a limited manner based on the description of the embodiments described above, but should be construed solely in accordance with the description of the claims, and the scope of the claims This invention includes techniques equivalent to the techniques described in , and all changes without departing from the gist of the claims.

For example, in this embodiment, electric strain gauges M1 and M2 are used as measuring means for measuring the strain on the striking rod 15 due to the impact of the piston 16, but FBG (fiber Bragg grating) technology An optical fiber strain sensor may also be used.

As described above, the method for estimating the compressive strength of a rock according to the present invention is effective when applied to estimate the strength of a rock in front of a face when excavating a tunnel or the like into the rock.

10 rock drill 11 hydraulic drifter 12 sleeve 13 shank rod 14 bit 14a tip 15 striking rod 16 piston 17 rotor 18 damping piston 19 pushing piston 20 bush test specimen A, B, C, D, E, S
CL Centralizer G Ground M1, M2 Strain gauge (measurement means)
P Mortar for cap

Claims (6)

A shank rod that is struck by a piston, a striking rod that is attached in series with the shank rod and applies striking force to the ground with a bit fixed at its tip, and a striking rod that applies striking force to the ground when the striking force is applied to the ground with the striking rod. Prepare a rock drill equipped with a measuring means for measuring reflected wave data reflected from the mountain and propagated to the striking rod,
A striking force is applied by the rock drill to a plurality of specimens having different compressive strengths, and the reflected wave data for each specimen is obtained, and the maximum amplitude of compressive stress and the maximum amplitude of tensile stress of the reflected wave data are determined. Find the reflected wave stress amplitude ratio coefficient, which is the ratio to the amplitude,
Determining correlation data between the compressive strength and the reflected wave stress amplitude ratio coefficient from the compressive strength in each of the test specimens and the reflected wave stress amplitude ratio coefficient determined for each of the test specimens,
Estimating the compressive strength of the rock from the correlation data and the reflected wave stress amplitude ratio coefficient of the reflected wave data measured when the rock drill applies impact force to the rock to be excavated;
A method for estimating the compressive strength of a rock, characterized by the following. The reflected wave data of at least one of the reflected wave data of each test piece and the reflected wave data of the rock is the reflected wave that was first reflected from the tip of the bit that came into contact with the rock by hitting and propagated to the striking rod. is data,
The method for estimating the compressive strength of a rock according to claim 1. The measuring means is installed at a central portion of the total length of the striking rod and the shank rod,
3. The method for estimating the compressive strength of a rock according to claim 1 or 2. The measuring means is installed at a position where the input wave and the reflected wave do not interfere,
3. The method for estimating the compressive strength of a rock according to claim 1 or 2. The measuring means is a strain gauge attached to the striking rod,
The method for estimating the compressive strength of a rock according to any one of claims 1 to 4. The plurality of test specimens are manufactured by drilling a plurality of holes in a predetermined rock block and filling the drilled holes with a cement-based solidifying material.
The method for estimating the compressive strength of a rock according to any one of claims 1 to 5.

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