Wall strength estimation method, rock mass property evaluation method, and elastic wave exploration system

Abstract

To evaluate properties of a natural ground by estimating uniaxial compressive strength of the natural ground rapidly and safely.SOLUTION: A wall surface strength estimation method for estimating uniaxial compressive strength of a natural mountain near a surface to be investigated includes an estimation expression acquisition process of for acquiring a strength estimation expression for estimating uniaxial compressive strength of a natural mountain on the basis of a surface wave speed, a speed acquisition process for acquiring a surface wave speed of surface waves generated by applying shock to the surface to be investigated, and a strength estimation process for estimating the uniaxial compressive strength on the basis of the surface wave speed and the strength estimation expression.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for estimating wall strength, a method for evaluating the properties of natural ground, and an elastic wave exploration system.

Background Art

[0002] For example, in mountain tunnel construction, as disclosed in the prior art of Patent Document 1, after conducting geological surveys such as boring work in advance to plan the support pattern, while the tunnel construction is in progress, various surveys such as in-situ surveys, laboratory rock tests, and face observations are carried out to grasp the properties of the natural ground and determine the support pattern.

[0003] Examples of laboratory rock tests include uniaxial compression tests of rocks using core samples taken from the face and ultrasonic velocity tests of rocks by the pulse transmission method. Examples of in-situ surveys include tests for qualitatively determining the hardness of the natural ground using a rock hammer and Schmidt hammer tests for estimating the uniaxial compressive strength based on the degree of rebound when a Schmidt rock hammer is pressed against the face.

[0004] These in-situ surveys and laboratory rock tests are carried out using rock slopes and the like not only in mountain tunnel construction but also in construction projects targeting rock masses such as dams and roads to grasp the properties of the natural ground.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The original site survey, as well as indoor rock tests, includes operations that need to be carried out by field workers near the rock slope or tunnel face, such as collecting rocks from the rock mass. Such operations will interrupt the on-site construction, but due to the complexity and time-consuming nature of the operations, they may require a significant amount of time. In addition, operations near the rock slope or tunnel face are prone to labor accidents such as skin abrasions and rockfalls, posing challenges in ensuring work safety.

[0007] The present invention has been made in view of such problems, and its main object is to quickly and safely estimate the uniaxial compressive strength of the ground and evaluate the ground properties.

Means for Solving the Problems

[0008] To achieve such an object, the wall strength estimation method of the present invention is a wall strength estimation method for estimating the uniaxial compressive strength of the ground near the surface to be investigated, comprising an estimation formula acquisition step of obtaining an intensity estimation formula for estimating the uniaxial compressive strength of the ground based on the surface wave velocity, a velocity acquisition step of obtaining the surface wave velocity of the surface wave generated by applying an impact to the surface to be investigated, and an intensity estimation step of estimating the uniaxial compressive strength based on the surface wave velocity and the intensity estimation formula. In the estimated formula acquisition step, an intensity 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 the P-wave velocity of the body wave generated together with the surface wave. In the intensity estimation step, if the P-wave velocity can be acquired, the P-wave velocity is selected, and the uniaxial compressive strength is estimated based on the corresponding intensity estimation formula characterized in that

[0009] According to the wall strength estimation method of the present invention, by remotely detecting surface waves using surface wave exploration technology, the surface wave velocity can be obtained and the uniaxial compressive strength of the ground can be estimated. As a result, operations such as collecting cores for indoor rock tests from the surface to be investigated, conducting tests with a Schmidt hammer on the surface to be investigated, or conducting impact sound investigations with a hammer, which were conventionally carried out by field workers near the surface to be investigated, can be omitted. Therefore, regardless of the working environment of the surface to be investigated, it is possible to quickly evaluate the strength characteristics of the ground while ensuring the safety of field workers through remote operation.

[0010] In addition, since the surface wave velocity is adopted, it is possible to evaluate the strength characteristics of the natural ground with high accuracy even when the surface to be investigated is deteriorated to such an extent that the uniaxial compressive strength cannot be estimated by conventional investigation methods.

[0012] According to the wall strength estimation method of the present invention, by applying an impact to the surface to be investigated, the body wave generated together with the surface wave is observed, and an attempt is made to obtain the P-wave velocity in addition to the surface wave velocity. As a result, when the P-wave velocity can be obtained, the P-wave velocity can be selected, and when it cannot be obtained, the surface wave velocity can be selected, and it becomes possible to estimate the uniaxial compressive strength corresponding to the current state of the surface to be investigated and evaluate the strength characteristics of the natural ground.

[0013] The wall strength estimation method of the present invention is characterized by comprising a velocity acquisition step of providing a vibration receiving point paired with the surface to be investigated and acquiring the surface wave velocity and / or the P-wave velocity between the paired vibration receiving points.

[0014] Further, the wall strength estimation method of the present invention includes a shape acquisition step of acquiring three-dimensional shape data of the surface to be investigated, and the velocity acquisition step is characterized by acquiring the surface wave velocity and / or the P-wave velocity based on the propagation path estimated from the three-dimensional shape data.

[0015] According to the wall strength estimation method of the present invention, the surface wave velocity or the P-wave velocity used for estimating the uniaxial compressive strength can be calculated based on the propagation path estimated from the three-dimensional shape data. As a result, it becomes possible to estimate the uniaxial compressive strength by using the surface wave velocity corresponding to the current state of the surface to be investigated.

[0016] The wall strength estimation method of the present invention is characterized in that the surface to be investigated is a tunnel face.

[0017] According to the wall strength estimation method of the present invention, it is possible to omit the work of on-site workers near the tunnel face where disasters such as spalling and rockfall may occur, and improve the safety of the investigation work related to tunnel construction work.

[0018] The method for evaluating the in-situ rock mass properties of the present invention is a method for evaluating the in-situ rock mass properties by evaluating the squeezing property during tunnel excavation based on the rock mass strength ratio, and is characterized in that the uniaxial compressive strength estimated by the wall surface strength estimation method of the present invention is adopted for calculating the rock mass strength ratio.

[0019] The method for evaluating the in-situ rock mass properties of the present invention is a method for evaluating the in-situ rock mass properties by evaluating the squeezing property during tunnel excavation based on the rock mass strength ratio. In calculating the rock mass strength ratio, the quasi-rock mass compressive strength is used, and at least the uniaxial compressive strength estimated by the wall surface strength estimation method of the present invention is adopted for calculating the quasi-rock mass compressive strength.

[0020] According to the method for evaluating the in-situ rock mass properties of the present invention, it is possible to quickly obtain the rock mass strength ratio by using the uniaxial compressive strength estimated by the wall surface strength estimation method, and to promptly carry out the design of the support pattern based on the rock mass strength ratio.

[0021] The elastic wave exploration system of the present invention is an elastic wave exploration system used in the wall surface strength estimation method of the present invention, and is characterized by comprising a vibration excitation device that applies an impact to the surface to be investigated, and a vibration measurement device that detects vibrations generated by the impact and acquires vibration information.

[0022] According to the elastic wave exploration system of the present invention, a series of operations from applying an impact to the surface to be investigated to estimating the uniaxial compressive strength can be continuously carried out, making it possible to achieve labor saving in the investigation work.

[0023] The elastic wave exploration system of the present invention is characterized in that the vibration measurement device is equipped with a laser Doppler vibrometer.

[0024] The elastic wave exploration system of the present invention is characterized in that the vibration measurement device is equipped with a vibration visualization radar.

[0025] The elastic wave exploration system of the present invention is characterized in that the vibration excitation device is equipped with a laser oscillator for vibration excitation.

[0026] The elastic wave exploration system of the present invention is characterized in that the vibration device is provided with a striking means for directly striking the surface to be investigated.

[0027] According to the elastic wave exploration system of the present invention, by providing a laser Doppler vibrometer or a vibration visualization radar in the vibration measurement device and a vibration laser oscillator in the vibration device, surface waves and body waves near the surface to be investigated can be detected safely and quickly from a distance. In addition, the separation distance between the vibration point and the receiving point can be freely set, and it can be set to about several centimeters, for example. Therefore, even in a tunnel face where the state of the rock mass is not uniform and various rocks appear, it is possible to easily measure the distribution of the rock mass strength in the face and contribute to the stability evaluation of the face.

Effect of the Invention

[0028] According to the present invention, regardless of the working environment of the surface to be investigated, the work carried out near the surface to be investigated can be greatly omitted, and it is possible to quickly evaluate the strength characteristics of the natural ground in-situ while ensuring the safety of on-site workers.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiment for Carrying Out the Invention

[0030] The present invention estimates the uniaxial compressive strength of the ground with high accuracy while ensuring the safety of on-site workers, and further, it is adopted for calculating a ground strength ratio used as a determination index for the extrusion property during tunnel excavation, and aims to grasp the ground properties near the face.

[0031] Hereinafter, with reference to FIGS. 1 to 9, the wall surface strength estimation method, the ground property evaluation method, and the elastic wave exploration system in the present invention will be described in detail. Note that the wall surface strength estimation method and the elastic wave exploration system used therefor can be adopted not only for the excavation work of mountain tunnels but also for various construction works such as dams and roads carried out in mountains or for the stability evaluation of rock slopes.

[0032] ≪≪Wall Surface Strength Estimation Method≫≫ As shown in FIG. 1(a), when an impact is applied to the excitation point P1 provided on the face 2 of the mountain tunnel 1, elastic waves are generated and propagate through the ground. In the wall surface strength estimation method, as shown in FIGS. 2(a) and (b), among the elastic waves, attention is paid to the surface wave 4 and the body wave 5, and the uniaxial compressive strength qu near the face is estimated.

[0033] Specifically, attempts are made to obtain the P-wave velocity PV and the surface-wave velocity Rv by observing both the body waves 5 and the surface waves 4 propagating in the ground at the face 2 surface. After that, 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 selected. Based on the selected velocity, the uniaxial compressive strength qu near the face 2 is estimated. For the estimation of the uniaxial compressive strength qu, a previously obtained strength estimation formula is adopted, and the P-wave velocity Pv or the surface-wave velocity Rv is substituted into the strength estimation formula.

[0034] The procedure of the wall strength estimation method will be described below along the flow shown in FIG. 3. Note that, among elastic waves, the surface wave 4 adopts the Rayleigh wave that propagates along the surface of the face 2, and the body wave 5 adopts the P-wave of the direct wave that propagates in the ground near the face 2.

[0035] ≪≪≪Estimation formula acquisition process≫≫≫ First, a strength estimation formula used for estimating the uniaxial compressive strength qu is obtained. The strength estimation formula includes the strength estimation formula (for P-wave) used when estimating the uniaxial compressive strength qu based on the P-wave velocity Pv and the strength estimation formula (for surface wave) used when estimating the uniaxial compressive strength qu based on the surface-wave velocity Rv.

[0036] ≪Acquisition of the strength estimation formula (for P-wave)≫ Generally, it is known that there is a correlation between the uniaxial compressive strength of rocks sampled from bedrock and the elastic wave velocity of specimens obtained from the rocks, and approximate formulas are also widely used. Therefore, for the strength estimation formula (for P-wave) used when estimating the uniaxial compressive strength qu based on the P-wave velocity Pv, these approximate formulas can be appropriately adopted.

[0037] ≪Acquisition of the strength estimation formula (for surface wave)≫ On the other hand, the method for obtaining the strength estimation formula (for surface wave) for estimating the uniaxial compressive strength qu based on the surface-wave velocity Rv is as follows.

[0038] In view of the general finding 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 uniaxial compressive strength qu and the surface wave velocity Rv. Therefore, the following test was conducted to obtain the relational expression between the uniaxial compressive strength qu and the surface wave velocity Rv in the vicinity of the excavation face 2, and this was adopted as the strength estimation formula (for surface waves).

[0039] In the test, cores S were collected from each of a plurality of arbitrary rock masses, and uniaxial compression tests were performed on each of them to measure the uniaxial compressive strength qu. The uniaxial compression test was carried out based on JGS 2521 "Method for Uniaxial Compression Test of Rock". Also, as shown in Fig. 4(a), for each of the cores S used in the uniaxial compression test, elastic waves were artificially generated, and the surface wave velocity Rv of the surface wave 4 propagating on the surface of the core S was measured.

[0040] The means for measuring the surface wave velocity Rv is not restricted in any way, but in this embodiment, a laser was adopted for both the means for vibrating the core S and the means for receiving the surface wave 4. Specifically, the vibration laser beam L1 was irradiated toward the vibration point P1 provided on the side surface of the core S, and the measurement laser L2 was irradiated toward the measurement point P2 also provided on the side surface of the core S.

[0041] For the irradiation of the vibration laser beam L1, an Nd-YAG laser with a pulse interval of 8 ns was adopted as the vibration laser oscillator 201. The principle is that the surface of the core S instantaneously expands due to ablation or temperature rise by pulsed laser irradiation, generating elastic waves inside the core S. Also, for the irradiation of the measurement laser beam L2, a laser Doppler vibrometer 111 that can measure vibrations with high precision from a distance was adopted. The displacement resolution was set to 1 μm, the measurement distance was about 5 to 10 m, and the separation distance between the vibration point P1 and the measurement point P2 was set to about 40 to 80 mm.

[0042] The vibration laser oscillator 201 described above irradiated the vibration laser beam L1 toward the vibration point P1 of the core S to generate elastic waves. Further, the laser Doppler vibrometer 111 described above irradiated the measurement laser beam L2 toward the vibration receiving point P2 of the core S to perform vibration measurement and detect the surface wave 4. After that, based on the arrival time from the vibration point P1 to the vibration receiving point P2 and the separation distance between the two, the surface wave velocity Rv was measured.

[0043] As shown in Fig. 4(b), the measurement results were plotted on a graph with the uniaxial compressive strength qu on the vertical axis and the surface wave velocity Rv on the horizontal axis. The relational expression between the uniaxial compressive strength qu and the surface wave velocity Rv thus obtained was adopted as the strength estimation formula (for surface waves) for estimating the uniaxial compressive strength qu in the vicinity of the excavation face 2 based on the surface wave velocity Rv.

[0044] Looking at Fig. 4(b), the coefficient of determination R2 exceeds 0.8, and it can be seen that the relational expression fits the data obtained in the above test. In the above test, the side surface of the core S was polished to measure the surface wave velocity Rv.

[0045] ≪Installation of Elastic Wave Exploration System≫ As described above, simultaneously with or before and after the operation of obtaining the strength estimation formula, the elastic wave exploration system 100 was installed in the tunnel of the mountain tunnel 1 to vibrate the excavation face 2 and obtain the P-wave velocity Pv and the surface wave velocity Rv.

[0046] ≪Elastic Wave Exploration System 100≫ As shown in Fig. 1(a), the elastic wave exploration system 100 includes at least a vibration measurement device 10, a vibration device 20, and an information processing terminal 30.

[0047] The vibration measurement device 10 is a device that receives the vibration generated by vibration, 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.

[0048] The laser vibrometer 11 employs the laser Doppler vibrometer 111 used in the test for obtaining the intensity estimation formula (for surface waves) in the above-mentioned <<Preliminary Preparation>>. The laser Doppler vibrometer 111 irradiates the measurement laser L2 toward the vibration receiving point P2 provided on the face 2, detects the change in the frequency of the reflected laser light, and acquires vibration information.

[0049] Its performance (such as displacement resolution) can be appropriately controlled using the vibrometer controller 12. Based on the vibration information acquired by the laser vibrometer 11, the body wave 5 and the surface wave 4 can be detected.

[0050] The scanner 13 is used for the purpose of irradiating the measurement laser L2 pinpointedly onto the vibration receiving point P2, and employs a so-called galvanometer scanner. The galvanometer scanner includes a laser light reflecting mirror 131 and can be rotated to a desired angle by the scanner controller 14.

[0051] The vibration exciter 20 employs the laser oscillator 201 for excitation used in the test for obtaining the intensity estimation formula (for surface waves) in the above-mentioned <<Preliminary Preparation>>. The laser oscillator 201 for excitation ablates or raises the temperature of the surface of the face 2 by pulsed laser irradiation, and generates elastic waves inside the natural ground.

[0052] The information processing terminal 30 is connected wirelessly or by wire so as to enable data transmission and reception with the vibration measurement device 10 and the vibration exciter 20, and as shown in Fig. 1(b), includes an input device 31, an output device 32, a central processing unit 33, a file device 34, and a main memory 35.

[0053] The input device 31 is, for example, a keyboard, a scanner, a touch panel, etc., and the output device 32 includes a display, a printer, etc. Also, the central processing unit 33 is a computer having a CPU, a GPU, a ROM, a RAM, and a hardware interface, etc.

[0054] The file device 34 is a storage device composed of a semiconductor memory, a hard disk drive, or the like. Although details will be described later, a condition data file 341, an observation data file 342, a calculation data file 343, etc., which are used in the wall strength estimation method, are stored therein. For example, the condition data file 341 may store data such as strength estimation formulas necessary for calculating the P-wave velocity Pv and the surface wave velocity Rv.

[0055] In addition, in the present embodiment, considering the case where the information processing terminal 30 is also used in the ground condition evaluation method described later following the wall strength estimation method, a property evaluation file 344 etc. are stored in the file device 34. Further, in addition to these files, a file recording information necessary for tunnel construction, such as the position information of the face 2, the geological information of the ground, or the image data of the face 2, may be stored in the file device 34.

[0056] The main memory 35 temporarily stores programs and data executable by the central processing unit 33. Although details will be described later, it at least includes a velocity calculation unit 351, a strength estimation unit 352, a strength ratio calculation unit 353 used in the ground condition evaluation method, and a quasi-rock mass strength calculation unit 354.

[0057] By using the elastic wave exploration system 100 described above, a series of operations from the operation of applying an impact to the face 2 to the estimation of the uniaxial compressive strength qu and further to the calculation of the ground strength ratio GN described later can be continuously and quickly performed, and labor saving related to the investigation work can be achieved.

[0058] Note that the elastic wave exploration system 100 is not limited to the above configuration. For example, the information processing terminal 30 may be omitted. When the information processing terminal 30 is omitted, another system or a portable processing terminal having a function replacing the information processing terminal 30 may be separately prepared and connected wirelessly or by wire so that data can be transmitted and received between the vibration measuring device 10 and the vibration exciter 20. Also, the vibration measuring device 10 is not limited to one unit, and a plurality of units may be equipped to acquire vibration information at a plurality of vibration receiving points.

[0059] Furthermore, regarding the vibration measuring device 10 and the vibration exciter 20, any means or equipment may be adopted as long as a distance that can ensure the safety of field workers can be secured between them and the face 2. For example, as shown in FIG. 9, a giant breaker 202 may be adopted for the vibration exciter 20, or a vibration visualization radar 101 capable of detecting vibration may be adopted for the vibration measuring device 10. As the vibration visualization radar 101, for example, the adoption of a millimeter-wave radar that irradiates an object with millimeter waves (radio waves in the 30 - 300 GHz band with a wavelength in the mm unit) for sensing may be considered.

[0060] The millimeter-wave radar has a performance with an operating distance of several tens of meters and a radio wave transmission and reception detection angle of about 100°. Therefore, by exploring the surface of the face 2 with the millimeter-wave radar, the fine vibration behavior of the surface of the face 2 vibrated by the vibration exciter 20 can be simultaneously detected at a plurality of desired positions on the face 2. When using a millimeter-wave radar, it is necessary to take measures to exclude the event that an object that does not transmit millimeter waves (for example, construction equipment or field workers, etc.) enters between the face and the millimeter-wave radar.

[0061] As described above, when a laser Doppler vibrometer or a vibration visualization radar 110 is adopted for the vibration measuring device 10 and a vibration laser oscillator is adopted for the vibration exciter 20, the separation distance between the vibration excitation point P1 and the vibration reception point P2 can be freely set, for example, set to about several centimeters, and it is also possible to detect the body wave 5 and the surface wave 4. Therefore, even when the rock mass near the face 2 is not uniform and various rock masses appear, it is possible to easily measure the distribution of the rock mass strength in the face 2 and contribute to the stability evaluation of the face.

[0062] ≪≪≪Velocity acquisition process≫≫≫ Using the elastic wave exploration system 100 described above, the body wave 5 and the surface wave 4 are observed, and an attempt is made to calculate the P-wave velocity Pv and the surface wave velocity Rv.

[0063] ≪Case 1: Utilizing the vibration excitation point P1 and the vibration reception point P2≫ First, as shown in Fig. 1(a), a laser beam L1 for vibration is irradiated from a vibration device 20 toward a vibration point P1 provided on the face 2 to generate an elastic wave, and the irradiation time is acquired. Further, a measurement laser L2 is irradiated from a vibration measurement device 10 toward a vibration reception point P2 provided on the face 2 to perform vibration measurement, and a surface wave 4 and a body wave 5 are observed, and the observation time is acquired.

[0064] The irradiation time of the laser beam L1 for vibration toward the vibration point P1 and the observation times of the surface wave 4 and the body wave 5 observed at the vibration reception point P2 are transmitted to an information processing terminal 30 and stored in an observation data file 342 of a file device 34. Then, a central processing unit 33 receives a command from a speed calculation unit 351 and calculates a surface wave speed Rv and a P-wave speed Pv.

[0065] As shown in Fig. 2(a), the P-wave speed Pv is calculated based on a time difference Δtp1, which is the difference between the irradiation time at the vibration point P1 and the observation time of the body wave 5 at the vibration reception point P2, and a separation distance D1 between the vibration point P1 and the vibration reception point P2. On the other hand, the surface wave speed Rv is calculated based on a time difference Δtr1, which is the difference between the irradiation time at the vibration point P1 and the observation time of the surface wave 4 at the vibration reception point P2, and the separation distance D1 between the vibration point P1 and the vibration reception point P2.

[0066] <<Example 2: Using two vibration reception points P2 and P3>> As shown in Fig. 2(b), the P-wave speed Pv and the surface wave speed Rv may be calculated using data observed at two vibration reception points P2 and P3 provided on the face 2. When a giant breaker 202 is adopted as the vibration device 20, the two vibration reception points P2 and P3 and the vibration point P1 are preferably arranged substantially in a straight line.

[0067] Specifically, the P-wave speed Pv is calculated based on a time difference Δtp2 of the arrival times of the body wave 5 between the two vibration reception points P2 and P3 and a separation distance D2 between the two vibration reception points P2 and P3. On the other hand, the surface wave speed Rv is calculated based on a time difference Δtr2 of the arrival times of the surface wave 4 between the two vibration reception points P2 and P3 and the separation distance D2 between the two vibration reception points P2 and P3.

[0068] In both 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 file device 34. Also, the separation distance D1 between the excitation point P1 and the receiving point P2, and the separation distance D2 between the two receiving points P2 and P3 may each adopt the shortest distance and be stored in the condition data file 341.

[0069] <<Case 3: Using 3D Shape Data>> When there are irregularities on the surface shape of the face 2, neither the surface wave 4 nor the body wave 5 propagates linearly. If the shortest separation distance D1 or separation distance D2 is adopted for calculating the surface-wave velocity Rv and P-wave velocity Pv as in Case 1 and Case 2, there is a risk of being evaluated slower than the actual velocity. This is particularly significant when there is a valley on the surface shape of the face 2.

[0070] Therefore, in Case 3, prior to calculating the surface-wave velocity Rv and P-wave velocity Pv, 3D shape data is acquired to grasp the 3D shape of the face 2 surface. Then, based on the propagation path estimated from the acquired 3D 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.

[0071] This propagation distance D3 or propagation distance D4 is adopted to calculate the surface-wave velocity Rv and P-wave velocity Pv. Below, the method for acquiring the 3D shape data of the face 2 surface and the method for calculating the propagation distances D3 and D4 based on the estimated propagation paths of the surface wave 4 and body wave 5 will be described.

[0072] <<<Shape Acquisition Step>> >>> <<Acquisition of 3D Shape Data>> As shown in Fig. 5(a), the 3D shape data of the face 2 surface is acquired using a 3D shape measurement device 40. The 3D shape measurement device 40 is not limited in any way, but for example, a 3D laser scanner, LiDAR, etc. may be adopted.

[0073] 3D laser scanners are widely and commonly adopted as a means for grasping the shape and measuring the unevenness of the surface of an object to be measured, and a point cloud model representing the surface shape of the object to be measured as a point cloud on the xyz coordinates can be obtained as three-dimensional surface shape data. Therefore, if the face 2 is adopted as the object to be measured, the three-dimensional shape of the face 2 surface can be obtained as a point cloud model. Thereby, the dimensions and angles between two points set on the face 2 surface can be obtained from the position coordinates of the point cloud forming the point cloud model, and it is also possible to perform dimensional calculations on CAD by associating the point cloud model with the three-dimensional CAD data.

[0074] <<Propagation distances D3 and D4 based on the estimated propagation path>> For example, as shown in Fig. 5(b), the shortest propagation distance D3 between the excitation point P1 and the reception point P2 can be calculated by the following procedure. In the present embodiment, the shortest distance between two points located on the ridge line connecting the top and the valley on the face 2 surface is referred to as the ridge line distance.

[0075] First, the shortest distance D31 between the valleys located adjacent to each of the excitation point P1 and the reception point P2 is measured. Next, the ridge line distance D32 from the excitation point P1 to the adjacent valley and the ridge line distance D33 from the reception point P2 to the adjacent valley are measured respectively. Then, by adding up these three calculation results, the shortest propagation distance D3 between the excitation point P1 and the reception point P2 is calculated.

[0076] Also, when the two reception points P2 and P3 are located at positions as shown in Figs. 6(a) to (c) for example, the shortest propagation distance D4 between them can be calculated by the following procedure. Note that the calculation procedure for the propagation distance D4 can also be used for calculating the shortest propagation distance D4 between the excitation point P1 and the reception point P2 described above.

[0077] Fig. 6(a) shows a method for calculating the shortest propagation distance D4 in the case where the unevenness of the face 2 surface is small and smooth. First, the shortest distance D41 between the excitation point P1 and the reception point P2 both located in the valley is measured. Next, the shortest distance D42 between the excitation points P1 and P3 both also located in the valley is measured, and the difference between the two is calculated as the propagation distance D4.

[0078] Figure 6(b) shows a method for calculating the propagation distance D4 when the excitation point P1 and the two vibration receiving points P2 and P3 are located in the recesses on the surface of the heading face 2. First, the shortest distance D41 between the excitation point P1 located in the trough and the vibration receiving point P2 located at the peak is measured. The shortest distance D41 is obtained by adding the linear distance between the troughs adjacent to the excitation point P1 and the vibration receiving point P2 and the ridge line distance between this trough and the vibration receiving point P2. Next, the shortest distance D42 within the ground between the excitation point P1 located in the trough and the vibration receiving point P3 also located in the trough is calculated. Then, the difference between the shortest distance D42 and the shortest distance D41 is calculated as the propagation distance D4.

[0079] Figure 6(c) shows a method for calculating the propagation distance D4 when the excitation point P1 and the two vibration receiving points P2 and P3 are located on the protrusions on the surface of the heading face 2. First, the shortest distance D41 from the excitation point P1 located on the ridge line to the vibration receiving point P2 located in the trough is calculated. The shortest distance D41 is obtained by adding the ridge line distance between the excitation point P1 and the adjacent trough and the linear distance between this trough and the vibration receiving point P2. Next, the shortest distance D42 from the excitation point P1 located on the ridge line to the vibration receiving point P3 located in the trough is calculated. The shortest distance D42 is obtained by adding the ridge line distance between the excitation point P1 and the adjacent trough and the linear distance between this trough and the vibration receiving point P3. Then, the difference between the shortest distance D42 and the shortest distance D41 is calculated as the propagation distance D4.

[0080] ≪≪≪Strength estimation step≫≫≫ When the calculated P-wave velocity Pv and surface-wave velocity Rv are stored in the calculation data file 343 of the file device 34, the central processing unit 33 receives a command from the strength estimation unit 352 and estimates the uniaxial compressive strength qu in the vicinity of the heading face 2 based on the surface-wave velocity Rv or the P-wave velocity Pv.

[0081] When calculating the uniaxial compressive strength qu, if the P-wave velocity Pv can be obtained, the P-wave velocity Pv is selected; if it cannot be obtained, the surface wave velocity Rv is adopted. When the P-wave velocity Pv is selected, the strength estimation formula (for P-wave) is adopted; when the surface wave velocity Rv is selected, the strength estimation formula (for surface wave) is adopted to calculate the uniaxial compressive strength qu. Both the strength estimation formulas (for P-wave and surface wave) are stored in the condition data file 341 of the file device 34. Also, the calculated uniaxial compressive strength qu is stored in the calculation data file 343 of the file device 34.

[0082] Since the body wave 5 has a smaller amplitude compared to the surface wave 4, for one strike on the excitation point P1, if the body wave 5 can be captured, 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 exciting force (such as when the giant breaker 202 is adopted in the excitation device 20), the probability of obtaining both the P-wave velocity Pv and the surface wave velocity Rv is high. In such a case, the P-wave velocity Pv is adopted.

[0083] On the other hand, in the case of a laser excitation with a small exciting force (such as when the laser oscillator 201 for excitation is adopted in the excitation device 20), the probability of not being able to obtain the P-wave velocity Pv is high. Thus, when the body wave 5 cannot be captured, the surface wave 4 is captured to obtain the surface wave velocity Rv and this is adopted.

[0084] As described above, according to the wall surface strength estimation method, the P-wave velocity Pv and the surface wave velocity Rv can be obtained by using the elastic wave exploration system 100, and the uniaxial compressive strength qu near the face 2 can be estimated. Thereby, operations such as collecting a core for an indoor rock test from the investigation target surface or conducting a test with a Schmidt hammer on the investigation target surface, which were conventionally carried out by on-site workers near the investigation target surface, can be omitted. Therefore, regardless of the working environment of the investigation target surface, it is possible to quickly evaluate the strength characteristics of the natural ground in-situ while ensuring the safety of on-site workers.

[0085] In addition, in order to estimate the uniaxial compressive strength by adopting the surface wave velocity Rv, it is possible to evaluate the strength characteristics of the natural ground even when the face 2 deteriorates to such an extent that it cannot be estimated by the conventional investigation method.

[0086] ≪≪Method for Evaluating Natural Ground Conditions≫≫ A procedure for calculating the natural ground strength ratio GN using the uniaxial compressive strength qu near the face 2 estimated by the above-described procedure will be described below with reference to FIG. 1(b) along the flow of FIG. 7. Note that, as an example, the case where the information processing terminal 30 of the elastic wave exploration system 100 performs the calculation will be described. Prior to these descriptions, the natural ground strength ratio GN and the quasi-rock mass compressive strength σC′ will be described.

[0087] ≪Natural Ground Strength Ratio≫ The natural ground strength ratio GN is a determination index for the squeezing property during tunnel excavation in soft rock natural ground, and is the ratio of the uniaxial compressive strength σc of the natural ground as shown in Equation (1) to the vertical overburden pressure. The vertical overburden pressure can be obtained 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 file device 34.

[0088] TIFF0007709635000001.tif28170

[0089] ≪Quasi-Rock Mass Compressive Strength≫ By the way, the natural ground strength ratio GN originally uses the uniaxial compressive strength σC of the natural ground including the crack 3 as shown in FIG. 1(a), but it takes a great deal of labor to measure the uniaxial compressive strength σC of the natural ground. Therefore, generally, the uniaxial compressive strength qu′ of a sample obtained from a boring core taken from a range not including the crack 3 of the face 2 is used.

[0090] However, it is known that when calculating the ground strength ratio GN from the uniaxial compressive strength qu' of the sample, it is likely to result in an evaluation on the dangerous side. Therefore, when evaluating the properties of the ground where the influence of crack 3 is significant, the quasi-rock mass compressive strength σc' is adopted as the uniaxial compressive strength σC of the ground required for calculating the ground strength ratio GN.

[0091] The quasi-rock mass compressive strength σC' can be obtained from the elastic wave velocity VP of the ground, the ultrasonic (elastic wave) velocity vP of the sample, and the uniaxial compressive strength qu' of the sample, as shown in the following equation (2).

[0092] TIFF0007709635000002.tif31170

[0093] Therefore, when calculating the ground strength ratio GN, it is necessary to select whether to adopt the quasi-rock mass compressive strength σC' in view of the above circumstances (Step1).

[0094] ≪Case where the quasi-rock mass compressive strength σC' is not adopted≫ When the quasi-rock mass compressive strength σC' is not adopted, first, the uniaxial compressive strength qu near the face 2 is estimated by the above-mentioned ground strength estimation method (Step2).

[0095] The uniaxial compressive strength qu can be estimated by the above-mentioned wall surface strength estimation method. At this time, when detecting the surface wave 4 and the body wave 5 only at the vibration receiving point P2 as shown in Fig. 2(a), crack 3 is included between the vibration exciting point P1 and the vibration receiving point P2. Similarly, when detecting at two vibration receiving points P2 and P3 as shown in Fig. 2(b), crack 3 is also included between the vibration receiving points P2 and P3. Then, an attempt is made to calculate the P-wave velocity Pv and the surface wave velocity Rv. When the P-wave velocity Pv can be obtained, the P-wave velocity Pv is selected; when it cannot be obtained, the surface wave velocity Rv is adopted to estimate the uniaxial compressive strength qu near the face 2. The estimated uniaxial compressive strength qu is stored in the calculation data file 343 of the file device 34.

[0096] Then, the central processing unit 33 receives the command from the strength ratio calculation unit 353, regards the uniaxial compressive strength qu near the face 2 stored in the calculation data file 343 as the uniaxial compressive strength σc of the rock mass required for the calculation of the rock mass strength ratio GN, and substitutes it into the above formula (1). At the same time, the soil cover thickness H and the unit volume weight γ stored in the condition data file 341 of the file device 34 are substituted into the above formula (1) to calculate the rock mass strength ratio GN (Step3, Step4).

[0097] ≪When adopting the quasi-rock mass compressive strength σC′≫ On the other hand, when adopting the quasi-rock mass compressive strength σC′, first, a narrow range not including the crack 3 and a wide range including the crack 3 are respectively set as the target ranges, and the uniaxial compressive strength qu near the face 2 is estimated by the above-mentioned ground strength estimation method.

[0098] ≪Estimate the uniaxial compressive strength qu in a narrow range≫ As shown in Fig. 8(a), set the separation distance between the vibration receiving points P2 and P3 in a narrow range of several centimeters to about 10 cm that does not include the crack 3. It is advisable to adopt the vibration laser oscillator 201 for the vibration device 20. When 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 adopted. When the P-wave velocity Pv cannot be obtained, the surface wave velocity Rv is adopted to estimate the uniaxial compressive strength qu near the face 2.

[0099] At this time, for the calculation of the P-wave velocity Pv and the surface wave velocity Rv, the separation distance between the vibration receiving points P2 and P3 may be adopted, or the propagation distance D4 estimated from the three-dimensional shape data as shown in Figs. 6(a) to (c) may be adopted. The calculation results are stored in the calculation data file 343 of the file device 34 (Step5).

[0100] Then, the central processing unit 33 receives a command from the quasi-rock strength calculation unit 354, 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 for calculating the quasi-rock compressive strength σC', and substitutes it into the above formula (2). When 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 for calculating the quasi-rock compressive strength σC', and substituted into the above formula (2).

[0101] On the other hand, when the surface wave velocity Rv is used to estimate the uniaxial compressive strength qu near the face 2, based on the correlation formula between the surface wave velocity Rv and the P-wave velocity Pv, the converted P-wave velocity is calculated from the surface wave velocity Rv, and this converted P-wave velocity is regarded as the ultrasonic (elastic wave) velocity vP of the sample required for calculating the quasi-rock compressive strength σC', and substituted into the above formula (2) (Step6).

[0102] ≪Obtain the P-wave velocity Pv and the surface wave velocity Rv in a wide range≫ As shown in Fig. 8(b), the separation distance between the receiving points P2 and P3 is set in a wide range that is sufficiently larger than the narrow range including the crack 3 and ahead. Considering avoiding the influence of the relaxation of the rock mass, it is advisable to set between two points as far apart as possible within the face 2. In addition, it is advisable to adopt the giant breaker 202 for the vibration exciter 20. When the giant breaker 202 is adopted, the probability of obtaining the P-wave velocity Pv is high. Here, the process of estimating the uniaxial compressive strength qu near the face 2 is omitted (Step7).

[0103] Also in this case, for calculating the P-wave velocity Pv and the surface wave velocity Rv, the separation distance between the receiving points P2 and P3 may be adopted, or the propagation distance D4 estimated from the three-dimensional shape data as shown in Figs. 6(a) to (c) may be adopted. The calculation results are stored in the calculation data file 343 of the file device 34. Then, when the central processing unit 33 receives a command from the quasi-rock strength calculation unit 354 and 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 rock mass required for calculating the quasi-rock compressive strength σC', and substituted into formula (2) (Step8).

[0104] On the other hand, when 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 formula 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 ground required for calculating the quasi-rock mass compressive strength σC′ and substituted into equation (2) (Step 8).

[0105] The quasi-rock mass compressive strength σC′ is calculated by the above procedure, and the calculation result is stored in the calculation data file 343 of the file device 34 (Step 9). Then, the central processing unit 33 receives a command from the strength ratio calculation unit 353, regards the quasi-rock mass compressive strength σC′ stored in the calculation data file 343 as the uniaxial compressive strength σc for obtaining the ground strength ratio GN, and substitutes it into the above equation (1). At the same time, the soil cover thickness H and the unit volume weight γ stored in the condition data file 341 of the file device 34 are substituted into the above equation (1) to calculate the ground strength ratio GN (Steps 3 and 4).

[0106] As described above, according to the ground property evaluation method, the ground strength ratio GN can be quickly obtained by using the uniaxial compressive strength qu near the face 2 estimated by the face strength estimation method, and the design of the support pattern based on the ground strength ratio GN can be promptly implemented.

[0107] In addition, for the adjustment of the separation distance between the vibration receiving points P2 and P3 as shown in FIGS. 8(a) and 8(b), for example, the vibration measuring device 10 that irradiates the measuring laser beam L2 toward the vibration receiving point P3 may be appropriately operated. That is, as shown in FIGS. 1(a) and 8(b), the laser beam reflector 131 provided on the scanner 13 is rotated to a desired angle by the scanner controller 14. In this way, the position of the vibration receiving point P3 that irradiates the measuring laser beam L2 can be easily changed.

[0108] Therefore, in order to estimate the uniaxial compressive strength qu in a narrow range, after installing the vibration measuring device 10 in the mountain tunnel 1, it is possible to perform the operation of acquiring the P-wave velocity Pv and the surface wave velocity Rv in a wide range without moving the installation position, and it is possible to significantly improve the work efficiency.

[0109] The method for estimating the wall strength and the method for evaluating the ground properties of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0110] For example, in the present embodiment, the method for estimating the wall strength is implemented using the elastic wave exploration system 100, but it is not necessarily limited to this. An elastic wave exploration technique generally adopted in ground surveys may be adopted to acquire the P-wave velocity PV or the surface wave velocity Rv.

[0111] Furthermore, in the present embodiment, 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 the quasi-ground strength σC' in the method for evaluating the ground properties is cited as an example. However, it is not necessarily limited to this. For example, a processing terminal used for calculating the ground strength ratio GN and the quasi-ground strength σC' in the method for evaluating the ground properties may be separately prepared and configured to be connected wirelessly or wired so that data can be transmitted and received between the elastic wave exploration system 100.

Explanation of Reference Numerals

[0112] 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 exciter 201 Vibration excitation 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 Calculated data file 344 Property evaluation file 35 Main memory 351 Speed calculation unit 352 Strength estimation unit 353 Strength ratio calculation unit 40 3D shape measurement device 1 Tunnel 2 Face (investigation target surface) 3 Crack 4 Surface wave 5 Body wave Rv Surface wave velocity Pv P-wave velocity S Core P1 Vibration point P2 Receiving point P3 Receiving point L1 Laser light for vibration L2 Laser light for measurement

Claims

1. A method for estimating the uniaxial compressive strength of the natural ground near the surface to be surveyed, comprising: an estimation formula acquisition step of obtaining an estimation formula for estimating the uniaxial compressive strength of the natural ground based on the surface wave velocity; a velocity acquisition step of obtaining the surface wave velocity of the surface wave generated by applying an impact to the surface to be surveyed; a strength estimation step of estimating the uniaxial compressive strength based on the surface wave velocity and the strength estimation formula, wherein in the estimation formula acquisition step, an estimation formula for estimating the uniaxial compressive strength of the natural ground based on the P-wave velocity is separately obtained; in the velocity acquisition step, an attempt is made to obtain the P-wave velocity of the body wave generated together with the surface wave; in the strength estimation step, when the P-wave velocity can be obtained, the P-wave velocity is selected, and the uniaxial compressive strength is estimated based on the corresponding strength estimation formula. A method for estimating wall strength is characterized by this.

2. In the method for estimating wall strength according to Claim 1, a velocity acquisition step of providing a vibration receiving point opposite to the surface to be surveyed and obtaining the surface wave velocity and / or P-wave velocity between the vibration receiving points forming a pair; A method for estimating wall strength is characterized by comprising this.

3. In the method for estimating wall strength according to Claim 1 or 2, a shape acquisition step of obtaining three-dimensional shape data of the surface to be surveyed is provided, wherein the velocity acquisition step obtains the surface wave velocity and / or the P-wave velocity based on the propagation path estimated from the three-dimensional shape data. A method for estimating wall strength is characterized by this.

4. In the method for estimating wall strength according to any one of Claims 1 to 3, the surface to be surveyed is a tunnel face. A method for estimating wall strength is characterized by this.

5. A method for evaluating the ground properties by evaluating the extrudability during tunnel excavation based on the ground strength ratio, wherein the uniaxial compressive strength estimated by the method for estimating wall strength according to Claim 4 is adopted for calculating the ground strength ratio. A method for evaluating ground properties is characterized by this.

6. A method for evaluating the ground properties by evaluating the extrudability during tunnel excavation based on the ground strength ratio, wherein the quasi-rock mass compressive strength is used for calculating the ground strength ratio, and at least the uniaxial compressive strength estimated by the method for estimating wall strength according to Claim 4 is adopted for calculating the quasi-rock mass compressive strength. A method for evaluating ground properties is characterized by this.

7. An elastic wave exploration system used for the method for estimating wall strength according to any one of Claims 1 to 4, a vibration exciter for applying an impact to the surface to be surveyed; A vibration measuring device that detects vibrations generated by an impact and acquires vibration information, An elastic wave exploration system characterized by comprising the same. **Claim 8** In the elastic wave exploration system according to Claim 7, The elastic wave exploration system characterized in that the vibration measuring device is equipped with a laser Doppler vibrometer. **Claim 9** In the elastic wave exploration system according to Claim 7 or 8, The elastic wave exploration system characterized in that the vibration measuring device is equipped with a vibration visualization radar. **Claim 10** In the elastic wave exploration system according to any one of Claims 7 to 9, The elastic wave exploration system characterized in that the vibration exciter is equipped with a laser oscillator for vibration excitation. **Claim 11** In the elastic wave exploration system according to any one of Claims 7 to 9, The elastic wave exploration system characterized in that the vibration exciter is equipped with a striking means for directly striking the surface to be investigated.

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