JP7709635B2 - Wall strength estimation method, rock mass property evaluation method, and seismic wave exploration system - Google Patents

Description

The present invention relates to a method for estimating wall strength, a method for evaluating natural ground properties, and an elastic wave exploration system.

For example, in mountain tunnel construction, as disclosed in the prior art of Patent Document 1, a geological survey is conducted in advance using drilling work etc. to plan the support pattern, and then, as the tunnel construction progresses, various surveys such as in-situ surveys, indoor rock testing, and observation of the face are conducted to understand the characteristics of the ground and to determine the support pattern.

Laboratory rock tests include uniaxial compression tests using borehole cores taken from the face, and ultrasonic velocity tests of rocks using the pulse transmission method. In-situ investigations include tests using a rock testing hammer to qualitatively determine the softness or hardness of the ground, and Schmidt hammer tests to estimate the uniaxial compressive strength based on the degree of rebound when a Schmidt rock hammer is pressed against the face.

These in-situ surveys and laboratory rock tests are not only carried out in mountain tunnel construction, but also on rock slopes and other locations in construction projects involving rock masses, such as dams and roads, in order to understand the properties of the ground.

JP 2020-20208 A

In-situ surveys as well as laboratory rock tests involve tasks such as extracting rocks from the bedrock, which must be carried out by on-site workers on rock slopes and near the tunnel face. This type of work requires interruption of on-site construction work, but it can be time-consuming as it is cumbersome and time-consuming. Furthermore, work on rock slopes and near the tunnel face is prone to industrial accidents due to rockfall and falling rocks, creating challenges in ensuring work safety.

The present invention has been developed in consideration of these problems, and its main purpose is to quickly and safely estimate the uniaxial compressive strength of ground and evaluate ground properties.

In order to achieve this object, the wall strength estimation method of the present invention is a wall strength estimation method for estimating the uniaxial compressive strength of the natural ground near a survey target surface, and includes an estimation equation acquisition step of acquiring a strength estimation equation for estimating the uniaxial compressive strength of the natural ground based on a surface wave velocity, a velocity acquisition step of acquiring the surface wave velocity of a surface wave generated by applying an impact to the survey target surface, and a strength estimation step of estimating the uniaxial compressive strength based on the surface wave velocity and the strength estimation equation, wherein the estimation equation acquisition step separately acquires a strength estimation equation for estimating the uniaxial compressive strength of the natural ground based on a P-wave velocity, the velocity acquisition step attempts to acquire the P-wave velocity of a body wave generated together with the surface wave, and when the P-wave velocity has been acquired, the strength estimation step selects the P-wave velocity and estimates the uniaxial compressive strength based on the corresponding strength estimation equation.

According to the wall strength estimation method of the present invention, by remotely detecting surface waves using surface wave exploration technology, it is possible to obtain the surface wave velocity and estimate the uniaxial compressive strength of the ground. This makes it possible to omit tasks that have traditionally been performed by field workers near the surveyed surface, such as extracting cores for indoor rock testing from the surveyed surface, conducting tests with a Schmidt hammer on the surveyed surface, or conducting hammer tapping surveys. Therefore, regardless of the work environment in which the surveyed surface is located, it is possible to quickly evaluate the strength characteristics of the ground by remote operation while ensuring the safety of field workers.

In addition, because surface wave velocity is used, it is possible to evaluate the strength characteristics of the ground with high accuracy even when the surface being surveyed has deteriorated to such an extent that the unconfined compressive strength cannot be estimated using conventional survey methods.

According to the wall strength estimation method of the present invention, by applying an impact to the surface to be investigated, the body waves generated along with the surface waves are observed, and an attempt is made to obtain the P-wave velocity in addition to the surface wave velocity. This allows the P-wave velocity to be selected if it can be obtained, and the surface wave velocity to be selected if it cannot be obtained, making it possible to estimate the uniaxial compressive strength appropriate to the current state of the surface to be investigated and evaluate the strength characteristics of the natural ground.

The wall strength estimation method of the present invention is characterized by comprising a velocity acquisition process for providing a pair of receiving points on the surface to be surveyed and acquiring the surface wave velocity and/or P-wave velocity between the pair of receiving points.

The wall strength estimation method of the present invention further includes a shape acquisition process for acquiring three-dimensional shape data of the surface to be surveyed, and the velocity acquisition process is characterized in that it acquires the surface wave velocity and/or the P-wave velocity based on a propagation path estimated from the three-dimensional shape data.

According to the wall strength estimation method of the present invention, the surface wave velocity or P-wave velocity used to estimate the unconfined compressive strength can be calculated based on the propagation path estimated from the three-dimensional shape data. This makes it possible to estimate the unconfined compressive strength using a surface wave velocity appropriate for the current state of the surveyed surface.

The wall strength estimation method of the present invention is characterized in that the surface to be surveyed is a tunnel face.

The wall strength estimation method of the present invention makes it possible to eliminate the need for on-site workers to work near the tunnel face, where damage from surface collapse or falling rocks may occur, and to improve the safety of survey work related to tunnel construction work.

The method for evaluating ground properties of the present invention is a method for evaluating the extrusion properties during tunnel excavation using the ground strength ratio, and is characterized in that the uniaxial compressive strength estimated by the wall strength estimation method of the present invention is used to calculate the ground strength ratio.

The method for evaluating ground properties of the present invention is a method for evaluating ground properties that evaluates the extrusion properties during tunnel excavation using the ground strength ratio, and is characterized in that the ground strength ratio is calculated using the quasi-rock compressive strength, and the uniaxial compressive strength estimated by at least the wall strength estimation method of the present invention is used to calculate the quasi-rock compressive strength.

According to the method for evaluating ground properties of the present invention, it is possible to quickly obtain the ground strength ratio using the uniaxial compressive strength estimated by the wall strength estimation method, and quickly design a support pattern based on the ground strength ratio.

The elastic wave exploration system of the present invention is an elastic wave exploration system used in the wall strength estimation method of the present invention, and is characterized by comprising a vibration device that applies an impact to the surface to be surveyed, and a vibration measuring device that detects vibrations generated by the impact and acquires vibration information.

The elastic wave exploration system of the present invention can carry out a series of operations in a continuous manner, from applying an impact to the surveyed surface to estimating the uniaxial compressive strength, making it possible to reduce the number of people required for the survey work.

The elastic wave exploration system of the present invention is characterized in that the vibration measurement device is equipped with a laser Doppler vibrometer.

The elastic wave exploration system of the present invention is characterized in that the vibration measurement device is equipped with a vibration visualization radar.

The elastic wave exploration system of the present invention is characterized in that the excitation device is equipped with an excitation laser oscillator.

The elastic wave exploration system of the present invention is characterized in that the excitation device is equipped with a striking means for directly striking the surface to be surveyed.

According to the elastic wave exploration system of the present invention, by equipping the vibration measuring device with a laser Doppler vibrometer or a vibration visualization radar, and the vibration excitation device with a laser oscillator for excitation, surface waves and body waves near the surface to be investigated can be detected safely and quickly from a remote location. In addition, the distance between the excitation point and the receiving point can be freely set, for example, to about a few centimeters. Therefore, even in the case of a tunnel face where the rock condition is not uniform and various rocks are exposed, it is possible to easily measure the distribution of rock strength within the face and contribute to the evaluation of the stability of the face.

According to the present invention, regardless of the working environment of the surface to be surveyed, the work carried out near the surface to be surveyed can be significantly reduced, and it becomes possible to quickly evaluate the strength characteristics of the ground in situ while ensuring the safety of on-site workers.

FIG. 1 is a diagram showing the state in which an elastic wave exploration system according to an embodiment of the present invention is installed. FIG. 2 is a diagram showing how surface wave velocity and P-wave velocity are acquired in an embodiment of the present invention. 4 is a diagram showing a procedure of a wall strength estimation method according to an embodiment of the present invention. FIG. FIG. 2 is a diagram illustrating a method for obtaining an intensity estimation equation based on a surface wave velocity in an embodiment of the present invention. FIG. 2 is a diagram showing how three-dimensional shape data of a face surface is acquired in an embodiment of the present invention. 1 is a diagram showing how a surface wave velocity is obtained based on a propagation path of a surface wave estimated from three-dimensional shape data according to an embodiment of the present invention. FIG. FIG. 2 is a diagram showing a procedure for calculating a ground strength ratio used in the method for evaluating ground properties in an embodiment of the present invention. FIG. 2 is a diagram showing how surface waves and body waves are detected in narrow and wide ranges set at a face in an embodiment of the present invention. 1 is a diagram showing an elastic wave exploration system equipped with a vibration visualization radar in an embodiment of the present invention.

The present invention aims to estimate the uniaxial compressive strength of the ground with high accuracy while ensuring the safety of on-site workers, and further to use the estimated uniaxial compressive strength of the ground to calculate the ground strength ratio, which is used as an indicator for determining extrusion properties during tunnel excavation, and to grasp the ground properties near the face.

The wall strength estimation method, natural ground property evaluation method, and elastic wave exploration system of the present invention will be described in detail below with reference to Figures 1 to 9. The wall strength estimation method and the elastic wave exploration system used therein can be used not only in mountain tunnel excavation work, but also in various construction works such as dams and roads carried out in mountains, or in the stability evaluation of rock slopes.

<<Wall strength estimation method>>
As shown in Fig. 1(a), when an impact is applied to an excitation point P1 provided at a face 2 of a mountain tunnel 1, elastic waves are generated and propagate through the natural ground. In the wall strength estimation method, as shown in Fig. 2(a) and (b), attention is paid to surface waves 4 and body waves 5 among the elastic waves, and the uniaxial compressive strength qu near the face is estimated.

Specifically, both the body waves 5 and surface waves 4 propagating through the ground are observed at the surface of the face 2 to attempt to obtain the P-wave velocity PV and the surface wave velocity Rv. After this, if the P-wave velocity PV can be obtained, the P-wave velocity Pv is selected, and if the P-wave velocity Pv cannot be obtained, the surface wave velocity Rv is selected. The unconfined compressive strength qu near the face 2 is estimated based on the selected velocity. To estimate the unconfined compressive strength qu, a strength estimation formula obtained in advance is used, and the P-wave velocity Pv or the surface wave velocity Rv is substituted into the strength estimation formula.

The procedure for the wall strength estimation method is explained below with reference to the flow shown in Figure 3. Note that the surface waves 4 are Rayleigh waves, which are elastic waves that propagate along the surface of the face 2, and the body waves 5 are P waves, which are direct waves that propagate through the ground near the face 2.

≪≪≪Estimated formula acquisition process≫≫≫
First, a strength estimation formula for estimating the unconfined compressive strength qu is obtained. The strength estimation formula includes a strength estimation formula (for P waves) used when estimating the unconfined compressive strength qu based on the P-wave velocity Pv, and a strength estimation formula (for surface waves) used when estimating the unconfined compressive strength qu based on the surface wave velocity Rv.

<Obtaining the intensity estimation formula (for P waves)>
In general, it is known that there is a correlation between the unconfined compressive strength of rocks taken from rock masses and the elastic wave velocity of specimens obtained from the rocks, and approximation formulas are widely used. Therefore, the strength estimation formula (for P waves) used when estimating the unconfined compressive strength qu based on the P-wave velocity Pv can be any of these approximation formulas.

<Obtaining the intensity estimation formula (for surface waves)>
On the other hand, the method of obtaining the strength estimation equation (for surface waves) for estimating the uniaxial compressive strength qu based on the surface wave velocity Rv is as follows.

Considering the general knowledge that there is a correlation between the surface wave velocity Rv and the P-wave velocity Pv, it can be said that there is also a correlation between the unconfined compressive strength qu and the surface wave velocity Rv. Therefore, the following test is carried out to obtain the relational equation between the unconfined compressive strength qu and the surface wave velocity Rv near the face 2, and this is adopted as the strength estimation equation (for surface waves).

For the test, cores S were taken from each of multiple random rock masses, and uniaxial compression tests were performed on each to measure the uniaxial compressive strength qu. The uniaxial compression tests were performed based on JGS 2521 "Method of uniaxial compression test of rocks." In addition, as shown in Figure 4 (a), elastic waves were artificially generated for each of the cores S used in the uniaxial compression tests, and the surface wave velocity Rv of the surface wave 4 propagating on the surface of the core S was measured.

There is no limitation on the means for measuring the surface wave velocity Rv, but in this embodiment, lasers are used for both the means for exciting the core S and the means for receiving the surface wave 4. Specifically, an exciting laser beam L1 is irradiated toward an exciting point P1 provided on the side surface of the core S, and a measurement laser beam L2 is irradiated toward an exciting point P2 also provided on the side surface of the core S.

For irradiation of the excitation laser light L1, an Nd-YAG laser with a pulse interval of 8 ns was used as the excitation laser oscillator 201. The principle is that the surface of the core S expands instantaneously due to ablation or temperature rise caused by pulsed laser irradiation, generating elastic waves inside the core S. For irradiation of the measurement laser light L2, a laser Doppler vibrometer 111 was used, which can measure vibrations remotely with high accuracy. The displacement resolution was set to 1 μm, the measurement distance to approximately 5 to 10 m, and the distance between the excitation point P1 and the receiving point P2 to approximately 40 to 80 mm.

The excitation laser oscillator 201 irradiated excitation laser light L1 toward the excitation point P1 of the core S to generate elastic waves. The laser Doppler vibrometer 111 irradiated measurement laser L2 toward the receiving point P2 of the core S to measure vibration and detect surface waves 4. After that, the surface wave velocity Rv was measured based on the arrival time from the excitation point P1 to the receiving point P2 and the distance between them.

The measurement results were plotted on a graph with the unconfined compressive strength qu on the vertical axis and the surface wave velocity Rv on the horizontal axis, as shown in Figure 4 (b). The relational equation between the unconfined compressive strength qu and the surface wave velocity Rv obtained in this way was adopted as the strength estimation equation (for surface waves) for estimating the unconfined compressive strength qu near the face 2 based on the surface wave velocity Rv.

As can be seen from Figure 4(b), the coefficient of determination R2 exceeds 0.8, and the relational equation fits the data obtained in the above test. In the above test, the side surface of the core S was polished and the surface wave velocity Rv was measured.

<Installation of the elastic wave exploration system>
As described above, simultaneously with or before or after the work of obtaining the strength estimation equation, an elastic wave exploration system 100 is installed inside the mountain tunnel 1 to vibrate the face 2 and obtain the P-wave velocity Pv and the surface wave velocity Rv.

<Elastic wave exploration system 100>
As shown in FIG. 1( a ), the elastic wave exploration system 100 includes at least a vibration measuring device 10 , a vibration excitation device 20 , and an information processing terminal 30 .

The vibration measuring device 10 is a device that receives vibrations generated by excitation, and includes a laser vibrometer 11 and a vibrometer controller 12 that controls the laser vibrometer 11. It also includes a scanner 13 and a scanner controller 14 that controls the scanner 13.

The laser vibrometer 11 is the laser Doppler vibrometer 111 used in the test to obtain the intensity estimation formula (for surface waves) in the above-mentioned <<Preparation>>. The laser Doppler vibrometer 111 irradiates a measurement laser L2 toward a receiving point P2 installed on the face 2, detects changes in the frequency of the reflected laser light, and obtains vibration information.

Its performance (displacement resolution, etc.) can be appropriately controlled using the vibrometer controller 12. Body waves 5 and surface waves 4 can be detected based on the vibration information acquired by the laser vibrometer 11.

The scanner 13 is used to pinpoint the measurement laser L2 at the receiving point P2, and employs a so-called galvanometer scanner. The galvanometer scanner is equipped with a laser light reflector 131 and can be rotated to a desired angle by the scanner controller 14.

The excitation device 20 employs the excitation laser oscillator 201 used in the test to obtain the intensity estimation formula (for surface waves) in the above-mentioned <<Preparation>>. The excitation laser oscillator 201 ablates or raises the temperature of the surface of the tunnel face 2 by irradiating it with a pulsed laser, generating elastic waves inside the natural ground.

The information processing terminal 30 is connected wirelessly or by wire to the vibration measuring device 10 and the vibration excitation device 20 so as to enable data transmission and reception therebetween, and is equipped with an input device 31, an output device 32, a central processing unit 33, a file device 34, and a main memory 35, as shown in FIG. 1(b).

The input device 31 is, for example, a keyboard, a scanner, a touch panel, etc., and the output device 32 is, for example, a display or a printer, etc. The central processing unit 33 is a computer having a CPU, a GPU, a ROM, a RAM, a hardware interface, etc.

The file device 34 is a storage device consisting of a semiconductor memory or a hard disk drive. Details will be described later, but it stores a condition data file 341, an observation data file 342, a calculation data file 343, etc., used in the wall strength estimation method. For example, the condition data file 341 may store data such as a strength estimation formula required to calculate the P-wave velocity Pv and the surface wave velocity Rv.

In this embodiment, in consideration of the case where the information processing terminal 30 is also used for the method of evaluating natural ground properties, which will be described later, following the wall strength estimation method, the property evaluation file 344 and the like are stored in the filing device 34. Furthermore, in addition to these files, files recording information necessary for tunnel construction, such as position information of the tunnel face 2, geological information of the natural ground, or image data of the tunnel face 2, may be stored in the filing device 34.

The main memory 35 temporarily stores programs and data that can be executed by the central processing unit 33, and includes at least a speed calculation unit 351, a strength estimation unit 352, a strength ratio calculation unit 353 used in the evaluation method for natural ground properties, and a quasi-rock strength calculation unit 354, as will be described in detail later.

Using the above-mentioned elastic wave exploration system 100, a series of tasks from applying an impact to the face 2 to estimating the uniaxial compressive strength qu and calculating the ground strength ratio GN, which will be described later, can be performed continuously and quickly, thereby reducing the number of people required for the investigation work.

The elastic wave exploration system 100 is not limited to the above configuration, and for example, the information processing terminal 30 may be omitted. In the case where the information processing terminal 30 is omitted, another system or a mobile processing terminal having functions in place of the information processing terminal 30 may be separately prepared, and a wireless or wired connection may be made between the vibration measuring device 10 and the excitation device 20 so that data can be sent and received. Furthermore, the vibration measuring device 10 is not limited to one unit, and multiple units may be installed to obtain vibration information at multiple receiving points.

Furthermore, for the vibration measuring device 10 and the excitation device 20, any means or equipment may be used as long as a distance can be secured between the face 2 to ensure the safety of on-site workers. For example, as shown in FIG. 9, a giant breaker 202 may be used for the excitation device 20, and a vibration visualization radar 101 capable of detecting vibrations may be used for the vibration measuring device 10. As the vibration visualization radar 101, for example, a millimeter wave radar that senses by irradiating an object with millimeter waves (radio waves in the 30 to 300 GHz band with wavelengths in mm) may be used.

Millimeter-wave radar has an operating distance of several tens of meters, and a detection angle of approximately 100° for the transmission and reception of radio waves. Therefore, by detecting the surface of the face 2 with a millimeter-wave radar, the minute vibration behavior of the surface of the face 2 excited by the vibration device 20 can be detected simultaneously at multiple desired positions on the face 2. When using a millimeter-wave radar, measures are required to prevent objects that cannot transmit millimeter waves (e.g., construction equipment, on-site workers, etc.) from coming between the face and the millimeter-wave radar.

As described above, by adopting a laser Doppler vibrometer or vibration visualization radar 110 for the vibration measuring device 10 and an excitation laser oscillator for the excitation device 20, the distance between the excitation point P1 and the receiving point P2 can be freely set, for example to about a few centimeters, and it is also possible to detect body waves 5 and surface waves 4. Therefore, even if the rock mass near the face 2 is not uniform and various rock masses are present, it is possible to easily measure the distribution of rock mass strength within the face 2 and contribute to the evaluation of the stability of the face.

≪≪≪Speed acquisition process≫≫≫
Using the above-described elastic wave exploration system 100, the body waves 5 and surface waves 4 are observed, and an attempt is made to calculate the P-wave velocity Pv and the surface wave velocity Rv.

<<Example 1: Using excitation point P1 and receiving point P2>>
1(a), an excitation laser beam L1 is emitted from an excitation device 20 toward an excitation point P1 provided on the working face 2 to generate elastic waves and acquire the emission time. A measurement laser L2 is emitted from a vibration measuring device 10 toward a receiving point P2 provided on the working face 2 to measure vibrations, and surface waves 4 and body waves 5 are observed and the observation times are acquired.

The time of irradiation of the excitation laser light L1 toward the excitation point P1 and the observation time of each of the surface wave 4 and body wave 5 observed at the receiving point P2 are transmitted to the information processing terminal 30 and stored in the observation data file 342 of the file device 34. The central processing unit 33 then receives a command from the velocity calculation unit 351 and calculates the surface wave velocity Rv and the P-wave velocity Pv.

2A, the P-wave velocity Pv is calculated based on the time difference Δtp ₁ between the irradiation time at the excitation point P1 and the observation time of the body wave 5 at the receiving point P2, and the distance D1 between the excitation point P1 and the receiving point P2. On the other hand, the surface wave velocity Rv is calculated based on the time difference Δtr ₁ between the irradiation time at the excitation point P1 and the observation time of the surface wave 4 at the receiving point P2, and the distance D1 between the excitation point P1 and the receiving point P2.

<<Case 2: Using two receiving points P2 and P3>>
As shown in Fig. 2(b), the P-wave velocity Pv and the surface wave velocity Rv may be calculated using data observed at two receiving points P2 and P3 provided at the face 2. When a giant breaker 202 is used as the vibration device 20, it is advisable to arrange the two receiving points P2 and P3 and the vibration point P1 approximately on a straight line.

Specifically, the P-wave velocity Pv is calculated based on the arrival time difference _Δtp2 of the body wave 5 between the two receiving points P2 and P3 and the distance D2 between the two receiving points P2 and P3. On the other hand, the surface wave velocity Rv is calculated based on the arrival time difference _Δtr2 of the surface wave 4 between the two receiving points P2 and P3 and the distance D2 between the two receiving points P2 and P3.

In both cases of Case 1 and Case 2, the calculated P-wave velocity Pv and surface wave velocity Rv are stored in the calculation data file 343 of the filing device 34. In addition, the distance D1 between the excitation point P1 and the receiving point P2, and the distance D2 between the two receiving points P2 and P3 should be the shortest distance between them, and should be stored in the condition data file 341.

<<Example 3: Using 3D shape data>>
When the surface shape of the face 2 is uneven, the surface waves 4 and the body waves 5 do not propagate linearly, and when the shortest distance D1 or D2 is used to calculate the surface wave velocity Rv and the P-wave velocity Pv as in Case 1 and Case 2, there is a risk that the velocities will be evaluated to be slower than the actual velocities. This is particularly noticeable when the surface shape of the face 2 has valleys.

Therefore, in Case 3, prior to calculating the surface wave velocity Rv and the P-wave velocity Pv, three-dimensional shape data is acquired to grasp the three-dimensional shape of the surface of the face 2. Then, based on the propagation path estimated from the acquired three-dimensional shape data, the shortest propagation distance D3 between the excitation point P1 and the receiving point P2 and the shortest propagation distance D4 between the two receiving points P2 and P3 are calculated.

The propagation distance D3 or D4 is used to calculate the surface wave velocity Rv and the P-wave velocity Pv. Below, we explain how to obtain the three-dimensional shape data of the face 2 surface, and how to calculate the propagation distance D3 and the propagation distance D4 based on the estimated propagation paths of the surface wave 4 and the body wave 5.

≪≪≪Shape acquisition process≫≫≫
<Acquisition of 3D shape data>
5A, the three-dimensional shape data of the surface of the working face 2 is acquired using a three-dimensional shape measuring device 40. The three-dimensional shape measuring device 40 is not limited in any way, but may be, for example, a 3D laser scanner or LiDAR.

3D laser scanners are widely used as a means of grasping the shape and measuring unevenness of the surface of a measurement object, and can obtain a point cloud model that expresses the surface shape of the measurement object as a point cloud on the xyz coordinate system as three-dimensional surface shape data. Therefore, if the face 2 is used as the measurement object, the three-dimensional shape of the face 2 surface can be obtained as a point cloud model. As a result, the dimensions and angles between two points set on the face 2 surface can be obtained from the position coordinates of the point cloud that forms the point cloud model, and by associating the point cloud model with three-dimensional CAD data, it is also possible to perform dimensional calculations on CAD.

<<Propagation distances D3 and D4 based on estimated propagation paths>>
For example, the shortest propagation distance D3 between the excitation point P1 and the receiving point P2 as shown in Fig. 5(b) can be calculated by the following procedure. In this embodiment, the shortest distance between two points located on the ridge line connecting the peak and valley on the surface of the face 2 is called the ridge line distance.

First, the shortest distance D31 between the valleys located adjacent to each of the excitation point P1 and the receiving point P2 is measured. Next, the ridgeline distance D32 from the excitation point P1 to the adjacent valley, and the ridgeline distance D33 from the receiving point P2 to the adjacent valley are measured. Then, by adding together these three calculation results, the shortest propagation distance D3 between the excitation point P1 and the receiving point P2 is calculated.

When the two receiving points P2 and P3 are located at positions such as those shown in Figures 6(a) to 6(c), the shortest propagation distance D4 between them can be calculated by the following procedure. Note that the procedure for calculating the propagation distance D4 can also be used to calculate the shortest propagation distance D4 between the excitation point P1 and the receiving point P2 described above.

Figure 6 (a) shows a method for calculating the shortest propagation distance D4 when the unevenness of the face 2 surface is small and gentle. First, the shortest distance D41 between the excitation point P1 and the receiving point P2, both of which are located in a valley, is measured. Next, the shortest distance D42 between the excitation points P1 and P3, both of which are also located in a valley, is measured, and the difference between the two is calculated as the propagation distance D4.

Figure 6 (b) shows a method for calculating the propagation distance D4 when the excitation point P1 and two receiving points P2, P3 are located in a recess on the surface of the face 2. First, the shortest distance D41 between the excitation point P1 located in a valley and the receiving point P2 located at the top is measured. The shortest distance D41 is calculated by adding up the straight-line distance between the excitation point P1 and the valley close to the receiving point P2, and the ridge distance between this valley and the receiving point P2. Next, the shortest distance D42 in the natural ground between the excitation point P1 located in the valley and the receiving point P3 also located in the valley is calculated. The difference between the shortest distance D42 and the shortest distance D41 is then calculated as the propagation distance D4.

Figure 6 (c) shows a method for calculating the propagation distance D4 when the excitation point P1 and two receiving points P2, P3 are located on the convex part of the face 2 surface. First, the shortest distance D41 between the excitation point P1 located on the ridgeline and the receiving point P2 located in the valley is calculated. The shortest distance D41 is calculated by adding up the ridgeline distance between the excitation point P1 and the nearby valley, and the straight-line distance between this valley and the receiving point P2. Next, the shortest distance D42 between the excitation point P1 located on the ridgeline and the receiving point P3 located in the valley is calculated. The shortest distance D42 is calculated by adding up the ridgeline distance between the excitation point P1 and the nearby valley, and the straight-line distance between this valley and the receiving point P3. Then, the difference between the shortest distance D42 and the shortest distance D41 is calculated as the propagation distance D4.

≪≪≪Strength estimation process≫≫≫
When the calculated P-wave velocity Pv and surface wave velocity Rv are stored in the calculation data file 343 of the filing device 34, the central processing unit 33 receives a command from the strength estimation unit 352 and estimates the uniaxial compressive strength qu near the face 2 based on the surface wave velocity Rv or the P-wave velocity Pv.

When calculating the uniaxial compressive strength qu, if the P-wave velocity Pv can be obtained, the P-wave velocity Pv is selected, and if it cannot be obtained, the surface wave velocity Rv is used. If the P-wave velocity Pv is selected, the strength estimation formula (for P waves) is used, and if the surface wave velocity Rv is selected, the strength estimation formula (for surface waves) is used to calculate the uniaxial compressive strength qu. Both strength estimation formulas (for P waves, for surface waves) are stored in the condition data file 341 of the filing device 34. The calculated uniaxial compressive strength qu is stored in the calculation data file 343 of the filing device 34.

Since the amplitude of the body wave 5 is smaller than that of the surface wave 4, if the body wave 5 can be captured for each impact on the excitation point P1, the surface wave 4 can also be captured, and both the P-wave velocity Pv and the surface wave velocity Rv can be obtained. For example, in the case of a breaker excitation with a large excitation force (such as when a giant breaker 202 is used for the excitation device 20), there is a high probability that both the P-wave velocity Pv and the surface wave velocity Rv can be obtained. In such a case, the P-wave velocity Pv is used.

On the other hand, in the case of laser excitation, which has a small excitation force (such as when an excitation laser oscillator 201 is used in the excitation device 20), there is a high probability that the P-wave velocity Pv cannot be obtained. In this way, when the body wave 5 cannot be captured, the surface wave 4 is captured to obtain the surface wave velocity Rv, and this is used.

As described above, according to the wall strength estimation method, the P-wave velocity Pv and the surface wave velocity Rv can be acquired using the elastic wave exploration system 100, and the uniaxial compressive strength qu near the face 2 can be estimated. This makes it possible to omit tasks that have traditionally been performed by field workers near the surveyed surface, such as extracting cores for indoor rock testing from the surveyed surface or conducting tests using a Schmidt hammer on the surveyed surface. Therefore, regardless of the work environment of the surveyed surface, it becomes possible to quickly evaluate the strength characteristics of the ground in situ while ensuring the safety of field workers.

In addition, because the surface wave velocity Rv is used to estimate the uniaxial compressive strength, it is possible to evaluate the strength characteristics of the ground even when the face 2 has deteriorated to a degree that cannot be estimated using conventional survey methods.

<<Evaluation method for ground properties>>
The procedure for calculating the natural ground strength ratio GN using the uniaxial compressive strength qu near the face 2 estimated by the above-mentioned procedure will be explained below with reference to Fig. 1(b) along the flow of Fig. 7. Note that the natural ground strength ratio GN is calculated by the information processing terminal 30 of the seismic wave exploration system 100 as an example. Prior to this explanation, the natural ground strength ratio GN and the quasi-rock compressive strength σC' will be explained.

<Natural mass strength ratio>
The natural ground strength ratio GN is an index for judging the extrusion property during tunnel excavation in soft rock natural ground, and is the ratio of the unconfined compressive strength σc of the natural ground to the vertical overburden pressure as shown in formula (1). The vertical overburden pressure can be calculated from the overburden thickness H and the unit volume weight γ of the rock. The overburden thickness H is known, and the unit volume weight γ can be the value of the same rock around the tunnel. Therefore, it is advisable to store the overburden thickness H and the unit volume weight γ in the condition data file 341 of the filing device 34.

<Quasi-rock compressive strength>
Incidentally, the natural ground strength ratio GN is originally calculated using the uniaxial compressive strength σC of the natural ground including the crack 3 as shown in Fig. 1(a), but measuring the uniaxial compressive strength σC of the natural ground is very time-consuming. Therefore, the uniaxial compressive strength qu' of a sample obtained from a boring core taken from an area of the face 2 not including the crack 3 is generally used.

However, it is known that calculating the ground strength ratio GN from the uniaxial compressive strength qu' of the sample tends to result in a dangerous assessment. For this reason, when evaluating the properties of ground that are significantly affected by crack 3, the quasi-rock compressive strength σc' is used for the uniaxial compressive strength σC of the ground, which is required to calculate the ground strength ratio GN.

The quasi-rock compressive strength σC' can be calculated from the elastic wave velocity VP of the natural ground, the ultrasonic (elastic wave) velocity vP of the sample, and the uniaxial compressive strength qu' of the sample, as shown in the following formula (2).

Therefore, when calculating the natural ground strength ratio GN, the decision as to whether or not to use the quasi-rock compressive strength σC' is made in consideration of the above circumstances (Step 1).

<When not using the quasi-rock compressive strength σC'>
When the quasi-rock compressive strength σC′ is not adopted, first, the uniaxial compressive strength qu in the vicinity of the face 2 is estimated by the above-mentioned ground strength estimation method (Step 2).

The uniaxial compressive strength qu may be estimated by the wall strength estimation method described above. In this case, when the surface wave 4 and the body wave 5 are detected only at the receiving point P2 as shown in FIG. 2(a), the crack 3 is included between the excitation point P1 and the receiving point P2. Similarly, when the surface wave 4 and the body wave 5 are detected at the two receiving points P2 and P3 as shown in FIG. 2(b), the crack 3 is included between the receiving points P2 and P3. Then, the P-wave velocity Pv and the surface wave velocity Rv are calculated. If the P-wave velocity Pv can be obtained, the P-wave velocity Pv is selected. If the P-wave velocity Pv cannot be obtained, the surface wave velocity Rv is adopted, and the uniaxial compressive strength qu near the face 2 is estimated. The estimated uniaxial compressive strength qu is stored in the calculation data file 343 of the filing device 34.

Then, the central processing unit 33 receives a command from the strength ratio calculation unit 353, and substitutes the uniaxial compressive strength qu near the face 2 stored in the calculation data file 343 into the above formula (1), regarding it as the uniaxial compressive strength σc of the ground required to calculate the ground strength ratio GN. In addition, the soil overburden thickness H and unit volume weight γ stored in the condition data file 341 of the filing device 34 are substituted into the above formula (1) to calculate the ground strength ratio GN (Step 3, Step 4).

<When using quasi-rock compressive strength σC'>
On the other hand, when adopting the quasi-rock compressive strength σC', first, the narrow range not including crack 3 and the wide range including crack 3 are taken as the target ranges, and the uniaxial compressive strength qu near the face 2 is estimated using the above-mentioned ground strength estimation method.

<Estimating uniaxial compressive strength q in a narrow range>
8(a), the distance between the receiving points P2 and P3 is set to a narrow range of several centimeters to 10 cm that does not include the crack 3. A laser oscillator 201 for excitation is preferably used for the excitation device 20. If the P-wave velocity Pv can be obtained in such a narrow range that does not include the crack 3, the P-wave velocity Pv is used, and if not, the surface wave velocity Rv is used to estimate the uniaxial compressive strength qu in the vicinity of the face 2.

At this time, the P-wave velocity Pv and the surface wave velocity Rv may be calculated using the distance between the receiving points P2 and P3, or the propagation distance D4 estimated from the three-dimensional shape data as shown in Figures 6(a) to (c). The calculation results are stored in the calculation data file 343 of the filing device 34 (Step 5).

Then, the central processing unit 33 receives a command from the quasi-rock strength calculation unit 354, and regards the uniaxial compressive strength qu near the face 2 stored in the calculation data file 343 as the uniaxial compressive strength qu' of the sample required to calculate the quasi-rock compressive strength σC', and substitutes it into the above formula (2). Also, if the P-wave velocity Pv is used to estimate the uniaxial compressive strength qu near the face 2, the P-wave velocity Pv is regarded as the ultrasonic (elastic wave) velocity vP of the sample required to calculate the quasi-rock compressive strength σC', and substitutes it into the above formula (2).

On the other hand, when the surface wave velocity Rv is used to estimate the uniaxial compressive strength qu near the face 2, the converted P-wave velocity is calculated from the surface wave velocity Rv based on the correlation equation between the surface wave velocity Rv and the P-wave velocity Pv, and this converted P-wave velocity is regarded as the ultrasonic (elastic wave) velocity vP of the sample required to calculate the quasi-rock compressive strength σC', and is substituted into the above equation (2) (Step 6).

≪Obtaining P-wave velocity Pv and surface wave velocity Rv over a wide area≫
As shown in Fig. 8(b), the separation distance between receiving points P2 and P3 is set to a wide range that includes the crack 3 and is sufficiently larger than the previous narrow range. The wide range should be set between two points as far apart as possible within the face 2, taking into consideration the effect of loosening of the ground. In addition, it is preferable to use a giant breaker 202 for the vibration device 20. When the giant breaker 202 is used, there is a high probability that the P-wave velocity Pv can be obtained. Here, the process of estimating the uniaxial compressive strength qu near the face 2 is omitted (Step 7).

In this case, the P-wave velocity Pv and the surface wave velocity Rv may be calculated using the distance between the receiving points P2 and P3, or the propagation distance D4 estimated from the three-dimensional shape data as shown in Figures 6(a) to (c). The calculation results are stored in the calculation data file 343 of the file device 34. Then, the central processing unit 33 receives a command from the quasi-rock strength calculation unit 354, and when the P-wave velocity Pv and the surface wave velocity Rv are stored in the calculation data file 343, the P-wave velocity Pv is regarded as the elastic wave velocity VP of the ground required to calculate the quasi-rock compressive strength σC' and is substituted into equation (2) (Step 8).

On the other hand, if the P-wave velocity Pv cannot be obtained and only the surface wave velocity Rv is stored in the calculation data file 343, the converted P-wave velocity is calculated from the surface wave velocity Rv based on the correlation equation between the surface wave velocity Rv and the P-wave velocity Pv. This converted P-wave velocity is regarded as the elastic wave velocity VP of the natural ground required to calculate the quasi-rock compressive strength σC', and is substituted into equation (2) (Step 8).

The quasi-rock compressive strength σC' is calculated by the above procedure, and the calculation result is stored in the calculation data file 343 of the filing device 34 (Step 9). Then, the central processing unit 33 receives a command from the strength ratio calculation unit 353, and substitutes the quasi-rock compressive strength σC' stored in the calculation data file 343 into the above formula (1), regarding it as the uniaxial compressive strength σc for calculating the natural ground strength ratio GN. In addition, the soil overburden thickness H and unit volume weight γ stored in the condition data file 341 of the filing device 34 are substituted into the above formula (1) to calculate the natural ground strength ratio GN (Steps 3 and 4).

As described above, the method for evaluating ground properties makes it possible to quickly obtain the ground strength ratio GN by using the uniaxial compressive strength qu near the face 2 estimated by the wall strength estimation method, and to quickly design a support pattern based on the ground strength ratio GN.

The distance between the receiving points P2 and P3 as shown in Figures 8(a) and (b) can be adjusted, for example, by appropriately operating the vibration measuring device 10 that irradiates the measurement laser light L2 toward the receiving point P3. That is, as shown in Figures 1(a) and 8(b), the laser light reflector 131 provided on the scanner 13 is rotated to the desired angle by the scanner controller 14. In this way, it is possible to easily change the position of the receiving point P3 to which the measurement laser light L2 is irradiated.

Therefore, after installing the vibration measuring device 10 inside the mountain tunnel 1 to estimate the uniaxial compressive strength qu in a narrow range, the P-wave velocity Pv and surface wave velocity Rv can be obtained over a wide range without moving the installation location, making it possible to significantly improve work efficiency.

The wall strength estimation method and ground property evaluation method of the present invention are not limited to the above-mentioned embodiment, and various modifications are possible without departing from the spirit of the present invention.

For example, in this embodiment, the wall strength estimation method is carried out using the elastic wave exploration system 100, but this is not necessarily limited to this, and the P-wave velocity PV or surface wave velocity Rv may be obtained by adopting an elastic wave exploration technique that is generally used in ground investigations.

Furthermore, in this embodiment, an example is given of the case where the information processing terminal 30 of the elastic wave exploration system 100 is used to calculate the ground strength ratio GN and quasi-ground strength σC' in the ground property evaluation method. However, this is not necessarily limited to this. For example, a processing terminal used to calculate the ground strength ratio GN and quasi-ground strength σC' in the ground property evaluation method may be prepared separately, and connected wirelessly or by wire to the elastic wave exploration system 100 so that data can be sent and received.

100 Elastic wave exploration system 10 Vibration measuring device 11 Laser vibrometer 111 Laser Doppler vibrometer 12 Vibration meter controller 13 Scanner 14 Scanner controller 101 Vibration visualization radar 20 Vibration device 201 Vibration laser oscillator 202 Giant breaker 30 Information processing terminal 31 Input device 32 Output device 33 Central processing unit 34 File device 341 Condition data file 342 Observation data file 343 Calculation data file 344 Property evaluation file 35 Main memory 351 Speed calculation unit 352 Strength estimation unit 353 Strength ratio calculation unit 40 Three-dimensional shape measurement device 1 Tunnel 2 Face (survey target surface)
3 Crack 4 Surface wave 5 Body wave Rv Surface wave velocity Pv P wave velocity S Core P1 Excitation point P2 Receiving point P3 Receiving point L1 Excitation laser light L2 Measurement laser light

Claims (11)

A wall strength estimation method for estimating the uniaxial compressive strength of a ground near a survey target surface, comprising:
An estimation equation acquisition step of acquiring a strength estimation equation for estimating the uniaxial compressive strength of natural ground based on the surface wave velocity;
a velocity acquisition step of acquiring a surface wave velocity of a surface wave generated by applying an impact to the surface to be inspected;
A strength estimation step of estimating the uniaxial compressive strength based on the surface wave velocity and the strength estimation formula,
In the estimation formula acquisition step, a strength estimation formula for estimating the uniaxial compressive strength of the ground based on the P-wave velocity is separately acquired,
In the velocity acquisition step, an attempt is made to acquire a P-wave velocity of a body wave generated together with the surface wave;
A wall strength estimation method characterized in that, in the strength estimation process, if the P-wave velocity can be obtained, the P-wave velocity is selected and the uniaxial compressive strength is estimated based on a corresponding strength estimation equation . The wall strength estimation method according to claim 1 ,
a velocity acquisition step of providing a pair of receiving points on the survey target surface and acquiring the surface wave velocity and/or P-wave velocity between the pair of receiving points;
A wall strength estimation method comprising: The wall strength estimation method according to claim 1 or 2 ,
A shape acquisition step of acquiring three-dimensional shape data of the survey target surface,
A wall strength estimation method characterized in that the velocity acquisition process acquires the surface wave velocity and/or the P-wave velocity based on a propagation path estimated from the three-dimensional shape data. The wall strength estimation method according to any one of claims 1 to 3 ,
A method for estimating wall strength, characterized in that the surface to be investigated is a tunnel face. A method for evaluating rock mass properties in which pushability during tunnel excavation is evaluated based on rock mass strength ratio, comprising the steps of:
A method for evaluating ground properties, comprising the step of employing the uniaxial compressive strength estimated by the wall strength estimation method according to claim 4 in calculating the ground strength ratio. A method for evaluating natural ground properties, which evaluates pushability during tunnel excavation based on natural ground strength ratio, comprising:
The rock mass strength ratio is calculated using the quasi-rock compressive strength,
A method for evaluating natural ground properties, comprising the steps of: calculating the quasi-rock compressive strength by using at least the uniaxial compressive strength estimated by the wall strength estimation method according to claim 4 . A seismic exploration system for use in the wall strength estimation method according to any one of claims 1 to 4 ,
A vibration device that applies an impact to the surface to be inspected;
A vibration measuring device that detects vibrations caused by impacts and acquires vibration information;
An elastic wave exploration system comprising: The elastic wave exploration system according to claim 7 ,
An elastic wave exploration system, characterized in that the vibration measuring device is equipped with a laser Doppler vibrometer. The elastic wave exploration system according to claim 7 or 8 ,
An elastic wave exploration system characterized in that the vibration measuring device is equipped with a vibration visualization radar. The elastic wave exploration system according to any one of claims 7 to 9 ,
An elastic wave exploration system characterized in that the vibration device is equipped with a vibration laser oscillator. The elastic wave exploration system according to any one of claims 7 to 9 ,
An elastic wave exploration system characterized in that the vibration device is equipped with a striking means for directly striking the surface to be surveyed.