Method for estimating strength of lining concrete before demolding and method for determining time of demolding lining concrete

Abstract

To more simply estimate the strength of lining concrete before demolding.SOLUTION: A method for estimating the strength of lining concrete before demolding comprises: placing lining concrete 3; hitting a hitting position 2H on the inner surface of an arch center 2 before demolding to vibrate the arch center 2 and the lining concrete 3; measuring vibration after the placing by a first vibration measurement device 11 separated by a first distance X from the hitting position 2H and a second vibration measurement device 12 separated by a second distance L rather than the first distance X from the hitting position 2H; calculating a difference between arrival times of elastic waves propagating from the hitting position 2H to the first and second vibration measurement devices 11 and 12 on the basis of the measured vibration after the placing when the second distance L is equal to or less than the first distance X; and calculating an elastic wave velocity on the basis of the difference and a difference between the path lengths of the elastic waves propagating from the hitting position 2H to the first and second vibration measurement devices 11 and 12 to estimate the compressive strength of the lining concrete 3 in a strength estimation area from the elastic wave velocity.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for estimating the strength of lining concrete before form stripping, and a method for determining the time to strip the lining concrete. [Background technology]

[0002] In the construction of lining concrete in mountain tunnel construction, ordinary concrete is poured in order from the side walls to the top, so the top, which is the last place to be poured, is the youngest. Therefore, at the top, where the concrete is at a young age, it is easy for the concrete to not develop its strength when it is removed from the form, and there is a concern that the concrete may peel off or fall off. Also, depending on the pouring conditions and environmental conditions, the concrete other than the top may not develop its strength easily. Furthermore, when high-flow (self-compacting) concrete is pumped in from a low position, the top is not necessarily the youngest.

[0003] For this reason, for example, a method has been proposed in which the accumulated temperature of the lining concrete before removal from the form is measured, and the compressive strength of the lining concrete is measured based on the correlation between this and the compressive strength (see Patent Document 1).

[0004] However, because this method directly measures the temperature of the concrete inside the center (steel formwork), it is necessary to either partially modify the center or to leave sensors or other equipment inside the hardened concrete. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-26734 A Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, the main object of the present invention is to provide a method for more easily estimating the strength of lining concrete before it is removed from the form. [Means for solving the problem]

[0007] The method for estimating the strength of lining concrete before removal from the form, which solves the above problems, is as follows. <First aspect> After pouring the lining concrete, and before removing the form, a striking position on the inner surface of the center is struck to vibrate the center and the lining concrete, and a first vibration measuring device is used to measure the post-pouring vibration at a first position on the inner surface of the center that is a first distance away from the striking position, and a second vibration measuring device is used to measure the post-pouring vibration at a second position on the inner surface of the center that is a second distance away from the striking position, the second distance being greater than the first distance; the second distance is less than or equal to the first distance, Based on the post-cast vibration measured by the first vibration measuring instrument and the post-cast vibration measured by the second vibration measuring instrument, a difference in arrival time of elastic waves propagating from the impact position to the first vibration measuring instrument and the second vibration measuring instrument is obtained, determining an elastic wave velocity based on a difference in arrival time of the elastic wave and a difference in path length of the elastic wave propagating from the impact position to the first vibration measuring device and the second vibration measuring device, respectively; A compressive strength of the lining concrete in a strength estimation region including the impact position, the first position, and the second position is estimated from the elastic wave velocity. A method for estimating the strength of lining concrete before removal from the form.

[0008] (Action and effect) According to this method for estimating the strength of lining concrete before form stripping, the strength of the lining concrete can be estimated at any location on the inner surface of the center as long as the impact and vibration measurement are possible, and there is no need to directly access the concrete. Furthermore, by striking the inner surface of the center as in this method, it is possible to reliably strike and measure vibration even on unhardened lining concrete without damaging it. Therefore, it is possible to estimate the strength of the lining concrete before form stripping more easily than in the past. Although a method for estimating the compressive strength of concrete by directly striking fully hardened concrete and measuring the elastic wave velocity based on the results of measurements made by a vibration measuring device in contact with the concrete was known, it was unclear whether a similar method would be effective when striking and measuring vibrations through a center on lining concrete whose degree of hardening is unknown. As a result of tests conducted by the inventor as described below, it was found to be effective, leading to the invention.

[0009] <Second aspect> The first vibration measuring device and the second vibration measuring device measure vibrations in a direction perpendicular to the center inner surface, By striking the inner surface of the center, vibrations in a direction perpendicular to the inner surface of the center are generated in the center and the lining concrete. A method for estimating the strength of lining concrete before removal from the form according to the first embodiment.

[0010] (Action and effect) The direction of vibration measured by the vibration measuring device is not particularly limited, but it is preferable that the direction is perpendicular to the inner surface of the center, since the amplitude is large and measurement is easy.

[0011] <Third aspect> a phase difference in the time domain determined by a phase-only correlation method between a first waveform measured by the first vibration measuring device and a second waveform measured by the second vibration measuring device; A phase difference at a specific frequency in the frequency domain obtained from the measurement result of the first vibration measuring device and the measurement result of the second vibration measuring device, or; a phase difference between a peak of a first waveform measured by the first vibration measuring device and a corresponding peak of a second waveform measured by the second vibration measuring device; is the difference in arrival time. A method for estimating the strength of lining concrete before removal from the form in the first or second aspect.

[0012] (Action and effect) The difference in arrival time between the elastic waves propagating from the impact position to the first vibration measuring device and the second vibration measuring device can be obtained by, for example, these methods. Note that the method using the phase-only correlation method is preferable to other methods in that the difference in arrival time can be obtained mechanically.

[0013] <Fourth aspect> When pouring lining concrete at the first center position in the tunnel extension direction, a test specimen is prepared using the lining concrete, and these specimens are placed in the same environment as the first center position while measuring the elastic wave velocities of the specimens at a plurality of test implementation ages to determine the relationship between the material age and the elastic wave velocity in the specimens. The lining concrete is subjected to a plurality of ages, and the difference in arrival time of the elastic wave is measured based on impact via the center and vibration measurement by the first vibration measuring device and the second vibration measuring device, From the path length of the elastic wave and the difference in arrival time of the elastic wave along each of a first path from the striking position, passing through the lining concrete, reflecting off the back surface of the lining concrete, and propagating to the first vibration measuring device and the second vibration measuring device, a second path from the striking position, passing through the lining concrete, reflecting off the back surface of the lining concrete, traveling toward the first vibration measuring device, and then reflecting off the outer surface of the center and the back surface of the lining concrete in order to propagate to the second vibration measuring device, a relationship between the age of the lining concrete and the velocity of the elastic wave is obtained for each of the first path, the second path, and the third path, Among the relationships between the age of the lining concrete and the velocity of the elastic wave in each of the first path, the second path, and the third path, a relationship similar to the relationship between the age of the concrete and the velocity of the elastic wave in the test specimen is selected, and the difference in the path length of the elastic wave is calculated based on the path of the selected relationship in the lining at the subsequent center position. A method for estimating strength of lining concrete before removal from the form according to any one of first to third aspects.

[0014] (Action and effect) In this way, the difference in the path length of the elastic waves used to calculate the elastic wave velocity can be calculated based on a preliminary experiment using a test specimen.

[0015] <Fifth aspect> When pouring lining concrete at the first center position in the tunnel extension direction, a test specimen is prepared using the lining concrete, and these specimens are placed in the same environment as the first center position while measuring the elastic wave velocities of the specimens at a plurality of test implementation ages to determine the relationship between the material age and the elastic wave velocity in the specimens. The lining concrete is subjected to a test at the same age as the test specimen, and the difference in arrival time of the elastic wave is measured based on impact via the center and vibration measurement by the first vibration measuring device and the second vibration measuring device, The number of test ages is k, and the difference in arrival time of the elastic wave propagating from the impact position to the first vibration measuring device and the second vibration measuring device in the kth measurement is Δtd k The elastic wave velocity measured for the specimen of the same age as the lining concrete of the kth measurement target is Vt k When the number of measurements is n>2 and Σ is the sum of k=1 to n in the formula in parentheses, the estimated path length difference R is calculated by the following formula (4). P Seeking R P =Σ(Vt k Δtd k ) / n …(4) In the subsequent lining at the center position, the estimated path length difference R Pis the difference in path length of the elastic wave; A method for estimating strength of lining concrete before removal from the form according to any one of first to third aspects.

[0016] (Action and effect) In this way, the difference in elastic wave path length used to calculate elastic wave velocity can be estimated based on a preliminary experiment using a test specimen.

[0017] <Sixth aspect> The thickness of the lining concrete is 200 to 800 mm. A method for estimating strength of lining concrete before removal from the form according to any one of first to fifth aspects.

[0018] (Action and effect) The above-mentioned method for estimating the strength of the lining concrete is particularly effective when the thickness of the lining concrete roll is within the range of this embodiment.

[0019] <Seventh aspect> After pouring the lining concrete, and before removing the form, a striking position on the inner surface of the center is struck to vibrate the center and the lining concrete, and a first vibration measuring device is used to measure the post-pouring vibration at a first position on the inner surface of the center that is a first distance away from the striking position, and a second vibration measuring device is used to measure the post-pouring vibration at a second position on the inner surface of the center that is a second distance away from the striking position, the second distance being greater than the first distance; the second distance is less than or equal to the first distance, Based on the post-cast vibration measured by the first vibration measuring instrument and the post-cast vibration measured by the second vibration measuring instrument, a difference in arrival time of elastic waves propagating from the impact position to the first vibration measuring instrument and the second vibration measuring instrument is obtained, determining an elastic wave velocity based on a difference in arrival time of the elastic wave and a difference in path length of the elastic wave propagating from the impact position to the first vibration measuring device and the second vibration measuring device, respectively; When the elastic wave velocity reaches a preset target value, it is determined that it is time to release the mold. A method for determining when to remove lining concrete before removal of the form, comprising:

[0020] (Action and effect) According to this method for determining when to remove the lining concrete before it is removed from the form, it is possible to determine when to remove the lining concrete from any location on the inner surface of the center as long as the impact and vibration measurement are possible, and there is no need to directly access the concrete. Furthermore, by striking the inner surface of the center as in this method, it is possible to reliably strike and measure vibration even in unhardened lining concrete without damaging it. Therefore, it is possible to determine when to remove the lining concrete before it is removed from the form more easily than in the past. Effect of the Invention

[0021] According to the present invention, advantages are provided such as making it easier to estimate the strength of the lining concrete before it is stripped of its form. [Brief description of the drawings]

[0022] [Figure 1] FIG. 2 is a schematic diagram showing the cross section of a tunnel when lining concrete is poured. [Diagram 2] FIG. 13 is a schematic cross-sectional view showing the measurement status of the top end portion. [Diagram 3] FIG. 1 is a schematic cross-sectional view showing a measurement situation in an experiment. [Figure 4] This is an example of the waveform measured 4.4 hours after pouring. [Diagram 5] This is an example of the waveform measured 19.1 hours after pouring. [Figure 6] (a) is the measured waveform in the X direction, (b) is the measured waveform in the Y direction, and (c) is the measured waveform in the Z direction when the material age is 22.5 hours and the first distance X1 = 50 cm. [Figure 7] (a) Measured waveform when the first distance X1 = 50 cm, (b) measured waveform when the first distance X2 = 100 cm, and (c) measured waveform when the first distance X3 = 150 cm at a material age of 6 hours. [Figure 8](a) Measured waveform when the first distance X1 = 50 cm, (b) measured waveform when the first distance X2 = 100 cm, and (c) measured waveform when the first distance X3 = 150 cm at a material age of 12 hours. [Figure 9] (a) Measured waveform when the first distance X1 = 50 cm, (b) measured waveform when the first distance X2 = 100 cm, and (c) measured waveform when the first distance X3 = 150 cm at a material age of 22.5 hours. [Figure 10] 1 is a graph showing the relationship between the difference in arrival time between elastic waves propagating from an impact position to a first vibration measuring device and a second vibration measuring device and the material age. [Figure 11] 1 is a graph showing the relationship between estimated elastic wave velocity and material age. [Figure 12] 1 is a graph showing the relationship between elastic wave velocity and compressive strength in a cylindrical specimen. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Figure 1 shows a cross section of a tunnel 1 with a center tunnel 2 installed, assuming a state after the pouring of the lining concrete 3 has been completed and before removal of the form. In the figure, reference numeral 1A denotes the top end, 1B the left shoulder, 1C the right shoulder, 1D the left spring line, and 1E the right spring line, respectively, and reference numeral 4 denotes the natural ground.

[0024] In order to estimate the compressive strength (uniaxial compressive strength) of the lining concrete 3 before demolding, as shown in FIG. 2, an impact position 2H is set on the inner surface of the center 2 in the strength estimation area, a first vibration measuring device 11 is installed at a first position that is a first distance X away from the impact position 2H, and a second vibration measuring device 12 is installed at a second position that is a sum of the first distance X and a second distance L that is equal to or less than the first distance X from the impact position 2H. Setting of the impact position 2H and installation of the first vibration measuring device 11 and the second vibration measuring device 12 can be performed after pouring of the lining concrete 3, not limited to before pouring, as long as it is before vibration measurement. The strength estimation area is an area where strength estimation is performed, and one or more locations can be selected from the top end 1A, left shoulder 1B, right shoulder 1C, left spring line 1D, and right spring line 1E, depending on pouring conditions and environmental conditions, or all locations can be selected. One or more impact positions 2H can be set in one strength estimation area. When there are multiple strength estimation areas, both the first vibration measuring device 11 and the second vibration measuring device 12 are installed at each area. As is well known, normal concrete is usually filled from the lap side to the gable side and from the spring line to the top end 1A, and the top end 1A (especially the gable), which is the final pouring area, is the youngest at the time of removal of the form, so the time of removal can be determined by estimating the compressive strength of the lining concrete 3 at least at the top end 1A. On the other hand, when high-flow (self-compacting) concrete is pressed in from a low position, the top end 1A is not necessarily the youngest, so the strength estimation area is set to multiple areas (for example, all areas of the top end 1A, left shoulder 1B, right shoulder 1C, left spring line 1D, and right spring line 1E), and the time of removal can be determined by estimating the compressive strength of the lining concrete 3 at each area. The striking position 2H and the installation positions of the first vibration measuring device 11 and the second vibration measuring device 12 may be appropriately determined as long as they are within the intensity estimation area, but it is preferable to set them as close to the center of the intensity estimation area as possible.

[0025] The first vibration measuring instrument 11 and the second vibration measuring instrument 12 may be an accelerometer, which is widely used in measuring impact elastic waves, or a speedometer, a displacement meter, a microphone, or the like. The performance of the first vibration measuring instrument 11 and the second vibration measuring instrument 12 is not particularly limited, but when an accelerometer is used, its sensitivity should be 1 to 20 mV / (m / s 2 ) and a frequency range of about ±3 dB: 3 Hz to 10 kHz, or a wider range than these can be suitably used. The direction of vibration measured by the first vibration measuring device 11 and the second vibration measuring device 12 is not particularly limited, but it is preferable that the direction is nearly perpendicular to the inner surface of the center 2, since the amplitude is large and measurement is easy. The sampling frequency of the first vibration measuring device 11 and the second vibration measuring device 12 is not limited, but it is preferable that it is, for example, 50 kHz or higher.

[0026] The second vibration measuring device 12 is preferably installed on a straight line extending from the impact position 2H through the first position (the first vibration measuring device 11) as shown in the figure, but is not limited thereto. The first distance X can be determined appropriately, but from the viewpoint of facilitating the path estimation of the elastic wave described later (reducing the influence of the reflected wave in the measured waveform), it is preferable that the first distance X is 3 times or less than the roll thickness T of the lining concrete 3, and more preferably 1 to 2 times the roll thickness T. The second distance L may be equal to or less than the first distance X, but for example, the second distance L may be 0.33 to 1 times the first distance X. In this case, the first vibration measuring device 11 and the second vibration measuring device 12 may be installed separately, but in order to keep the distance between the first position and the second position constant, the first vibration measuring device 11 and the second vibration measuring device 12 may be fixed to a single support, and the support may be held by an operator, who may press the first vibration measuring device 11 and the second vibration measuring device 12 against the inner surface of the center 2 in a desired strength estimation area to perform measurement.

[0027] In estimating the compressive strength, after pouring the lining concrete 3, the striking position 2H on the inner surface of the center 2 in the strength estimation area is struck with a hammer 5 or the like before demolding to vibrate the center 2 and the lining concrete 3, and the post-casting vibration is measured with the first vibration measuring device 11 and the second vibration measuring device 12. Then, based on the post-casting vibration measured by the first vibration measuring device 11 and the post-casting vibration measured by the second vibration measuring device 12, the difference in arrival time of the elastic waves propagating from the striking position 2H to the first vibration measuring device 11 and the second vibration measuring device 12 is obtained, and the elastic wave velocity is obtained based on the difference in arrival time of the elastic waves and the difference in path length of the elastic waves propagating from the striking position 2H to the first vibration measuring device 11 and the second vibration measuring device 12, and the compressive strength of the lining concrete 3 in the strength estimation area is estimated from this elastic wave velocity. The time it takes for the elastic waves generated by striking to reach the first vibration measuring device 11 and the second vibration measuring device 12 varies depending on the rigidity of the vibration medium. Since the stiffness of the center 2 is constant and the stiffness of the lining concrete 3 increases with hardening, the wave propagation speed continues to change with the age of the material up to the target compressive strength (compressive strength that is a guideline for stripping in the actual construction). Therefore, even if the impact is on the inner surface of the center 2, the compressive strength can be estimated based on the correlation between the elastic wave speed and the compressive strength by using the measured elastic wave speed as an index. When recording the change in the elastic wave speed or compressive strength at each material age, or when the compressive strength does not reach the elastic wave speed or compressive strength required for stripping, it is possible to repeat the impact and vibration measurement at the same position at a predetermined time interval as necessary, or to perform the impact and vibration measurement at the same position again after a desired time has elapsed. In addition, in order to avoid the influence of measurement variations, it is also possible to perform the impact and vibration measurement multiple times at the same material age and the same position and obtain the compressive strength as the average value (including not only estimating the elastic wave speed based on the average value of the difference in arrival time, but also estimating the compressive strength based on the average value of the elastic wave speed and taking the average value of the compressive strength as the estimated value). In this case, it is preferable that the distance between the striking position 2H and the positions of the first vibration measuring device 11 and the second vibration measuring device 12 is constant.According to this estimation method, the strength of the lining concrete 3 can be estimated non-destructively at any location on the inner surface of the center 2 where the impact and vibration measurements can be performed, and there is no need to directly access the lining concrete 3. Therefore, the strength of the lining concrete 3 before stripping can be estimated more easily than before, and the time for stripping can also be determined.

[0028] Since the correlation between the compressive strength of the lining concrete 3 and the elastic wave velocity measured by impact, etc., varies depending on the conditions at the site, it is desirable to obtain the correlation by a prior experiment at the site or under the same conditions as at the site (e.g., temperature). That is, a required number of test specimens are prepared in advance at the site or under the same conditions as at the site (e.g., temperature) using the same mix of concrete as that used for the lining, and the elastic wave velocity and compressive strength of these test specimens are measured in sequence at a predetermined time interval (e.g., 1 hour), and a relational equation (e.g., an approximate straight line) between the elastic wave velocity and the compressive strength is obtained based on the measurement data at each material age, and the compressive strength of the lining concrete 3 during construction can be estimated by substituting the elastic wave velocity obtained based on the impact and vibration measurement of the center 2 into this relational equation during the actual construction. Also, the target strength for removal from the form (e.g., 2 N / mm 2 ) The elastic wave velocity at this time is calculated in advance, and when the elastic wave velocity calculated based on the impact and vibration measurement of center 2 during actual construction reaches the target vibration characteristic value, it can be determined that it is time to remove the formwork.

[0029] In the preliminary experiment for determining the relational expression between elastic wave velocity and compressive strength, the specifications of the specimen and the method of measuring the elastic wave velocity are not particularly limited. However, since the specimen is to be subjected to a compressive strength test, it is preferable to use a normal cylindrical specimen for compressive strength tests. In addition, considering the use of such a cylindrical specimen, the measurement of the elastic wave velocity in the preliminary experiment is preferably a transmission method in which an elastic wave (longitudinal wave) is transmitted from one of the upper and lower surfaces of the circle to the other, and the elastic wave is received by a sensor installed on the other side. In this case, the elastic wave can be ultrasonic or impact (axial impact), and the sensor can be an ultrasonic probe in the former case, and an accelerometer or the like in the latter case. Of course, when determining the elastic wave velocity of the shear wave in the specimen, the shear wave can be directly detected by a sensor capable of detecting vibration in the lateral direction to measure the elastic wave velocity of the shear wave, or the Poisson's ratio can be used to calculate the elastic wave velocity of the shear wave from the elastic wave velocity of the longitudinal wave.

[0030] The timing of the above-mentioned preliminary experiment is not particularly limited as long as it is performed before the estimation of the compressive strength or the determination of the time for removal of the form. In tunnel construction, lining is repeatedly performed while moving the center 2 in the tunnel extension direction. In one preferred example, when lining at any one or more centering positions in the tunnel extension direction (for example, the first centering position or the first centering position after the ground properties have changed, etc.), a test number of test specimens are prepared from the concrete to be used (or used) for the lining, and the above-mentioned preliminary experiment is performed while placing these test specimens in the same environment as the centering position (the internal environment of the center 2), and the results of the preliminary experiment are used when lining at the subsequent centering positions. It is preferable to prepare the test specimens so that they are approximately the same age as the lining concrete 3. In this case, it is also preferable to measure the elastic wave velocity at multiple material ages (preferably the same as the material age at which the test specimen is performed) based on the impact via the center 2 mentioned above and the vibration measurement by the first vibration measuring instrument 11 and the second vibration measuring instrument 12, and to confirm whether the relationship between material age and elastic wave velocity is similar to that of the preliminary experiment based on the specimen, and the propagation path of the elastic wave can be estimated using these results, as described below.

[0031] The winding thickness T of the lining concrete 3 is not particularly limited, but is particularly effective when it is 200 to 800 mm. In addition, the thickness S of the steel plate at the impact position 2H of the center 2 is also not particularly limited, but is preferably 6 to 9 mm.

[0032] As long as the center 2 and the lining concrete 3 can be vibrated by striking, the striking means is not particularly limited, and may be a manual hammer 5 that a worker holds with the handle and strikes with arm strength, or a hammer device that strikes with a drive source such as a solenoid. The hammer 5 may be any hammer (with a built-in acceleration sensor) that is used for excitation in measuring impact elastic waves, but it is preferable to select a suitable hammer 5 through prior experiments or the like in order to reduce the influence of the material and weight of the hammer 5. The hammer 5 may be a hammer with a steel head whose striking surface is a sphere having a diameter of 30 to 70 mm.

[0033] The difference in arrival time can be obtained, for example, from the phase difference in the time domain obtained by the phase-only correlation method from the first waveform measured by the first vibration measuring device 11 and the second waveform measured by the second vibration measuring device 12. Figure 4 shows an example of the first waveform and the second waveform 4.4 hours after pouring, and Figure 5 shows an example of the waveform of the impact hammer (Model 086C04 manufactured by PCB Piezotronics, maximum applied force: 4484N) used for striking after 19.1 hours from pouring, in both cases where the winding thickness T is 400 mm, the first distance X is 100 cm, and the second distance L is 50 cm. As can be seen from these examples, the first waveform and the second waveform are very similar, so the phase difference (time difference Δtd) can be easily obtained by using the phase-only correlation method based on the measurement data of the first waveform and the second waveform.

[0034] The difference in arrival time can also be found from the phase difference at a specific frequency (for example, 1250 to 4000 Hz) in the frequency domain, which is found from the measurement results of the first vibration measuring device 11 and the measurement results of the second vibration measuring device 12.

[0035] Furthermore, the difference in arrival time can also be found from the time difference between the peak of the first waveform measured by the first vibration measuring instrument 11 and the corresponding peak of the second waveform measured by the second vibration measuring instrument 12. As can be seen from the waveform examples in Figures 4 and 5 described above, the first peak of the first waveform and the first peak of the second waveform have large amplitudes and are similar to each other, so that an operator can visually measure the phase difference (time difference Δtd) between these peaks.

[0036] The difference between the path length of the elastic wave propagating from the striking position 2H to the first vibration measuring device 11 and the path length of the elastic wave propagating from the striking position 2H to the second vibration measuring device 12 can be calculated by selecting the propagation path of the elastic wave. The propagation path of the compressional wave and the surface wave when the center 2 is hammered can be arbitrarily selected from three types, for example, as shown in Figure 2, which are: (1) a first path P1 that passes through the lining concrete from the striking position 2H, is reflected by the back surface of the lining concrete, and propagates to the first vibration measuring device 11 and the second vibration measuring device 12, (2) a second path P2 that propagates through the center 2 and propagates to the first vibration measuring device 11 and the second vibration measuring device 12, and (3) a third path P3 that passes through the lining concrete from the striking position 2H, is reflected by the back surface of the lining concrete, travels toward the first vibration measuring device 11, is reflected by the outer surface of the center 2 and the back surface of the lining concrete, and propagates to the second vibration measuring device 12. As an example, when considering a case where a vibration perpendicular to the inner surface of the center core 2 is generated in the center core 2 and the lining concrete 3 by striking the inner surface of the center core 2, when estimating the compressive strength based on the correlation between the shear wave or equivalent elastic wave velocity and the compressive strength, the second path P2 assumed as the path of the shear wave can be selected, and when estimating the compressive strength based on the correlation between the longitudinal wave or equivalent elastic wave velocity (in the case of the transmission method described above) and the compressive strength, the third path P3 assumed as the path of the longitudinal wave can be selected. Then, the elastic wave velocity can be calculated based on the difference in path length calculated based on this path selection and the difference in arrival time described above.

[0037] Furthermore, as mentioned above, when a pre-experiment is conducted at the time of lining at any one or more center positions in the tunnel extension direction, the elastic wave velocity of the specimen at multiple test ages is measured based on the pre-experiment, and the relationship between the age and elastic wave velocity of the specimen is determined. Also, for the lining concrete 3 at multiple ages (preferably the same as the test age), the difference in the arrival time of the elastic wave is measured based on impact via the center 2 and vibration measurement by the first vibration measuring device 11 and the second vibration measuring device 12. From the path length of the elastic wave and the difference in the arrival time of the elastic wave in each of the first path P1, the second path P2 and the third path P3, the relationship between the age and the elastic wave velocity in the lining concrete 3 is determined for each of the first path P1, the second path P2 and the third path P3, and a relationship similar to the former relationship is selected from the latter relationships. For the lining at subsequent center positions, the difference in the path length of the elastic wave can be calculated based on the path of the selected relationship. When there are multiple highly similar relationships, the one with the highest similarity can be selected, or a selection can be made based on a viewpoint other than the similarity. For example, when the similarity of the relationship in the case of the second path P2 is high, even if the similarity of the relationships of the other paths is equal to or higher than that, the second path P2 can be selected because it is less susceptible to the influence of the winding thickness T.

[0038] In addition, when the propagation path is the first path P1, the propagation velocity is V, the shortest distance of the first path P1 from the impact position 2H to the first vibration measuring device 11 is R1, the shortest distance of the first path P1 from the impact position 2H to the second vibration measuring device 12 is R2, the winding thickness is T, the difference in arrival time of the elastic waves propagating from the impact position 2H to the first vibration measuring device 11 and the second vibration measuring device 12 is Δtd, and the thickness of the center 2 is ignored (because the rigidity of the center 2 is constant and the effect of the path length is small; the same applies below), the difference in path length is R2-R1, and the propagation velocity V can be calculated by the following formula (1). R1 = 2·{T 2 +(X / 2) 2} 1 / 2 R2 = 2·{T 2 +((X+L) / 2) 2} 1 / 2 V = (R2-R1) / Δtd …(1)

[0039] Furthermore, when the propagation path is the second path P2, the propagation speed is V, the shortest distance of the second path P2 from the impact position 2H to the first vibration measuring device 11 is R1, the shortest distance of the second path P2 from the impact position 2H to the second vibration measuring device 12 is R2, the winding thickness is T, the difference in arrival time of the elastic waves propagating from the impact position 2H to the first vibration measuring device 11 and the second vibration measuring device 12 is Δtd, and if the thickness of the center 2 is ignored, the difference in path length is R2-R1 and the propagation speed V can be calculated by the following formula (2). The second path P2 is particularly preferable because it is not related to the winding thickness. R1 = X R2= X+L V = (R2-R1) / Δtd …(2)

[0040] Furthermore, when the propagation path is the third path P3, the distance between the first vibration measuring device 11 and the second vibration measuring device 12 is L, the roll thickness is T, the difference in arrival time between the elastic waves propagating from the impact position 2H to the first vibration measuring device 11 and the second vibration measuring device 12 is Δtd, and the thickness of the center 2 is ignored, the propagation velocity V can be calculated by the following formula (3). The difference in path length in this case is 2·((L / 2) 2 +T 2 ) 1 / 2 It is. V = 2 · ((L / 2) 2 +T 2 ) 1 / 2 / Δtd …(3)

[0041] On the other hand, as mentioned above, when a preliminary experiment is conducted for lining at one or more arbitrary center positions in the tunnel extension direction, the relationship between the age of the specimen and the elastic wave velocity is obtained by measuring the elastic wave velocity of the specimen at multiple test ages based on the preliminary experiment, and vibration measurements are performed on the lining concrete 3 at the same age as the test age of the specimen by impact via the center 2 and the first vibration measuring instrument 11 and the second vibration measuring instrument 12. Based on this, the age of the lining concrete 3 and the difference in the arrival time of the elastic wave propagating from the impact position 2H to the first vibration measuring instrument 11 and the second vibration measuring instrument 12 are measured by the above-mentioned method, and the estimated path length difference is calculated by the following method, and the elastic wave velocity can be calculated using the estimated path length difference for the lining at the subsequent center positions. In other words, the difference in the arrival time of the elastic wave propagating from the impact position 2H to the first vibration measuring instrument 11 and the second vibration measuring instrument 12 in the kth measurement is called Δtd k The elastic wave velocity measured for the specimen of the same age as the lining concrete being measured in the kth measurement is Vt k Let the number of measurements be n>2, and Σ be the sum of k=1 to n in the formula in parentheses. The estimated path length difference R P can be calculated using the following formula (4). R P =Σ(Vt k Δtd k ) / n …(4) This method is not a geometric calculation, but by calculating the product of the difference in arrival time measured at the construction target and the elastic wave velocity measured at a specimen of the same age for each measurement and taking the average value as the estimated path length difference, it is possible to estimate the path length difference with sufficient accuracy based on the measured data.

[0042] In addition, in the actual construction, the required number of cylindrical specimens (at least three or more required for at least one compressive strength test) are prepared using the concrete to be used for the lining or concrete of the same mix, and are cured in the on-site environment or in the same environment so that they will be the same age as the lining concrete 3 during construction. At the same time, the compressive strength of the lining concrete 3 during construction is estimated by measuring the elastic wave velocity based on impacts on the inner surface of the centre 2, and when this estimated result reaches the compressive strength required for removal from the form, a compressive strength test is conducted on the cylindrical specimens to actually measure the compressive strength, thereby making it possible to confirm whether the compressive strength of the lining concrete 3 during construction has reached the target value.

[0043] <Experiment to estimate compressive strength using elastic wave velocity as an index> (Experimental Method) A center tube to be used in the actual construction was prepared, and a simulated natural ground formwork was placed at a fixed interval (400mm roll thickness) around the outer periphery of the center tube to create a simulated environment, in which lining concrete was poured in the same way as in the actual construction. The concrete mix shown in Table 1 was used. In addition, cylindrical specimens measuring φ100 x height 200mm were prepared for the number of tests, using the same concrete as that poured in the simulated environment.

[0044] [Table 1]

[0045] As shown in FIG. 3, protrusions 6 (cubic magnets with sides each measuring 5 cm) were fixed to three impact positions aligned in a straight line, and a first vibration measuring device 11 and a second vibration measuring device 12 were also installed. The first vibration measuring device 11 and the second vibration measuring device 12 were accelerometers capable of measuring three axial directions and a maximum acceleration of 5.0 g (PCB Piezotronics Corporation triaxial accelerometer (Model 356B21), sensitivity: 1.02 mV / (m / s 2), Y-axis and Z-axis frequency range ±5%: 2 to 10,000 Hz, X-axis frequency range ±5%: 2 to 7,000 Hz) were used. The first distances X1, X2, and X3 (the distance between the impact position and the first vibration measuring device 11) were 50, 100, and 150 cm, and the second distance L (the distance between the first vibration measuring device 11 and the second vibration measuring device 12) L was 50 cm. 6, 7, 8, 9, 10, 12, 15, 17, 19, 21, and 22.5 hours after the casting of the lining concrete 3, each protrusion 6 was struck in the X direction, Y direction, and Z direction using an impact hammer (Model 086C04 manufactured by PCB Piezotronics, maximum applied force: 4484 N), and the vibration after casting was measured by the first vibration measuring device 11 and the second vibration measuring device 12, respectively.

[0046] In addition, the cylindrical specimens were subjected to measurements of elastic wave velocity (longitudinal waves) using an ultrasonic transmission method at the same ages as those used for vibration measurements of the lining concrete 3 (i.e., 6, 7, 8, 9, 10, 12, 15, 17, 19, 21, and 22.5 hours), and compressive strength tests were also conducted. The compressive strength tests were performed with the cylindrical specimens' casting surfaces capped with plaster, and the loading rate was set to 0.01 N / mm 2 The experiment was carried out as / s.

[0047] (Experimental result 1: Influence of the measurement direction of the vibration measuring instrument) Figures 6(a)-(c) show the waveforms measured in the X, Y, and Z directions at a first distance X1 = 50 cm, measured 22.5 hours after the casting of the lining concrete 3 (material age 22.5 hours). Comparing these results, the amplitude of the waveform measured in the Z direction shown in Figure 6(c) was the largest. It was also found that the first two peaks of the waveform measured in the Z direction by the first vibration measuring device 11 corresponded to those of the waveform measured in the Z direction by the second vibration measuring device 12.

[0048] (Experimental result 2: Effects of impact position and changes due to material age) Figures 7(a)-(c) show waveforms measured in the Z direction when the first distances X1 = 50 cm, X2 = 100 cm, and X3 = 150 cm, respectively, measured 6 hours after pouring the lining concrete 3 (material age 6 hours). Similarly, Figures 8(a)-(c) and Figures 9(a)-(c) show waveforms measured in the Z direction when the material age is 12 hours and 22.5 hours. It can be seen that as the first distance becomes longer, the influence of the reflected wave becomes greater, making it difficult to visually distinguish the correspondence of the peaks. In this case, from the viewpoint of visual discrimination, it is preferable that the first distance is 100 cm or less.

[0049] Moreover, Figure 10 is a graph in which the difference in arrival time at each age of the lining concrete 3 is plotted for each impact position (50 cm, 100 cm, 150 cm). It can be seen that the difference in arrival time becomes smaller (i.e., the elastic wave velocity increases) as the age increases. The difference in arrival time was determined by visually distinguishing the first peak of the first waveform and the first peak of the second waveform, and from the phase difference between them.

[0050] FIG. 11(a) shows the measurement results of the elastic wave velocity at each age of the lining concrete 3 measured based on the first waveform and the second waveform (the average value of the elastic wave velocity when the first distance X1 = 50 cm, 100 cm, and 150 cm is calculated for each of the first to third paths P1 to P3 described above) and the measurement results of the elastic wave velocity (longitudinal wave) at each age of the cylindrical specimen. FIG. 11(b) shows the calculation results of the elastic wave velocity at each age of the lining concrete 3 measured based on the first waveform and the second waveform when the first distance X1 = 50 cm (the average value of the elastic wave velocity when the first distance X1 = 50 cm, 100 cm, and 150 cm is calculated for each of the first to third paths P1 to P3 described above) and the measurement results of the elastic wave velocity (longitudinal wave) at each age of the cylindrical specimen, which are set to 55% (equivalent to a transverse wave). Considering that the elastic wave velocity increases with age and that the stiffness of the center 2 is constant, it is believed that the change in stiffness of the concrete 3 due to hardening has affected the propagation time of the elastic wave. In addition, the elastic wave velocity obtained when the elastic wave propagation path is the aforementioned third path P3 almost coincides with the elastic wave velocity (longitudinal wave) measured in the cylindrical specimen, and the elastic wave velocity obtained when the elastic wave propagation path is the aforementioned second path P2 almost coincides with 55% (equivalent to transverse wave) of the elastic wave velocity (longitudinal wave) measured in the cylindrical specimen. Therefore, when calculating the difference in the path length of the elastic wave to estimate the compressive strength of the lining concrete 3, it is sufficient to select either the second path P2 or the third path P3 as the path of the elastic wave.

[0051] FIG. 12 is a graph plotting elastic wave velocity (longitudinal wave) and uniaxial compressive strength measured on a cylindrical specimen. It can be seen that the compressive strength of the lining concrete can be estimated from this result and the elastic wave velocity measured through the center of the lining concrete during construction. If the uniaxial compressive strength required for the center to be stripped is 2 MPa, in the case of this experiment, it can be seen that the elastic wave propagation path is the third path P3, and it can be determined that stripping is possible when the elastic wave velocity is 3000 m / s or more (material age 10 hours). It can also be seen that if the elastic wave propagation path is the second path P2, it can be determined that stripping is possible when the elastic wave velocity is converted to a shear wave equivalent (55%) and is 1650 m / s or more. [Industrial Applicability]

[0052] The present invention can be used to estimate the strength of the lining concrete before it is stripped, i.e., to determine when it is time to strip it. Even when estimating the compressive strength using the center strike method described above, it is also possible to use the conventional estimation of compressive strength based on the accumulated temperature of the lining concrete in combination, if necessary. [Explanation of symbols]

[0053] 1...tunnel, 1A...top end, 1B...left shoulder, 1C...right shoulder, 1D...left spring line section, 1E...right spring line section, 2...center, 3...lining concrete, 4...ground, 2H...impact position, T...winding thickness, 5...hammer, 6...projection, X...first distance, 11...first vibration measuring device, L...second distance, 12...second vibration measuring device, 21...steel plate, 22...formwork.

Claims

1. After pouring the lining concrete, and before removing the form, a striking position on the inner surface of the center is struck to vibrate the center and the lining concrete, and a first vibration measuring device is used to measure the post-pouring vibration at a first position on the inner surface of the center that is a first distance away from the striking position, and a second vibration measuring device is used to measure the post-pouring vibration at a second position on the inner surface of the center that is a second distance away from the striking position, the second distance being greater than the first distance; The second distance is equal to or less than the first distance, Based on the post-cast vibration measured by the first vibration measuring instrument and the post-cast vibration measured by the second vibration measuring instrument, a difference in arrival time of elastic waves propagating from the impact position to the first vibration measuring instrument and the second vibration measuring instrument is calculated, determining an elastic wave velocity based on a difference in arrival time of the elastic wave and a difference in path length of the elastic wave propagating from the impact position to the first vibration measuring device and the second vibration measuring device, respectively; A compressive strength of the lining concrete in a strength estimation region including the impact position, the first position, and the second position is estimated from the elastic wave velocity. A method for estimating the strength of lining concrete before removal from the form.

2. The first vibration measuring device and the second vibration measuring device measure vibrations in a direction perpendicular to an inner surface of the center, By striking the inner surface of the center, vibrations in a direction perpendicular to the inner surface of the center are generated in the center and the lining concrete. A method for estimating strength of lining concrete before removal from the form as claimed in claim 1.

3. a phase difference in the time domain obtained by a phase-only correlation method between a first waveform measured by the first vibration measuring device and a second waveform measured by the second vibration measuring device; A phase difference of a specific frequency in the frequency domain obtained from the measurement result of the first vibration measuring device and the measurement result of the second vibration measuring device, or a phase difference between a peak of a first waveform measured by the first vibration measuring device and a corresponding peak of a second waveform measured by the second vibration measuring device; is the difference in arrival time. A method for estimating strength of lining concrete before removal from the form according to claim 1 or 2.

4. When pouring lining concrete at the first center position in the tunnel extension direction, a test specimen is prepared using the lining concrete, and these specimens are placed in the same environment as the first center position while measuring the elastic wave velocities of the specimens at a plurality of test implementation ages to determine the relationship between the material age and the elastic wave velocity in the specimens. The lining concrete is subjected to a plurality of ages, and the difference in arrival time of the elastic wave is measured based on impact via the center and vibration measurement by the first vibration measuring device and the second vibration measuring device, From the path length of the elastic wave and the difference in arrival time of the elastic wave along each of a first path in which the elastic wave passes from the striking position through the lining concrete, is reflected by the back surface of the lining concrete, and is propagated to the first vibration measuring device and the second vibration measuring device, respectively, a second path in which the elastic wave propagates through the center and is propagated to the first vibration measuring device and the second vibration measuring device, respectively, and a third path in which the elastic wave passes from the striking position through the lining concrete, is reflected by the back surface of the lining concrete, is propagated toward the first vibration measuring device, is reflected by the outer surface of the center and the back surface of the lining concrete in order, and is propagated to the second vibration measuring device, a relationship between the age of the lining concrete and the velocity of the elastic wave is obtained for each of the first path, the second path, and the third path. Among the relationships between the age of the lining concrete and the velocity of the elastic wave in each of the first path, the second path, and the third path, a relationship similar to the relationship between the age of the concrete and the velocity of the elastic wave in the test specimen is selected, and the difference in the path length of the elastic wave is calculated based on the path of the selected relationship in the lining at the subsequent center position. A method for estimating strength of lining concrete before removal from the form according to claim 1 or 2.

5. When pouring lining concrete at the first center position in the tunnel extension direction, a test specimen is prepared using the lining concrete, and these specimens are placed in the same environment as the first center position while measuring the elastic wave velocities of the specimens at a plurality of test implementation ages to determine the relationship between the material age and the elastic wave velocity in the specimens. The lining concrete is subjected to an impact via the center and a vibration measurement by the first vibration measuring device and the second vibration measuring device at the same material age as the test implementation material age of the specimen, and the difference in arrival time of the elastic wave is measured based on the impact via the center and the vibration measurement by the first vibration measuring device and the second vibration measuring device; The number of test ages is k, and the difference in arrival time of the elastic wave propagating from the impact position to the first vibration measuring device and the second vibration measuring device in the k-th measurement is Δtd ｋ The elastic wave velocity measured for the specimen of the same age as the lining concrete to be measured for the kth time is Vt ｋ When the number of measurements is n>2 and Σ is the sum of k=1 to n in the formula in parentheses, the estimated path length difference R is calculated by the following formula (4): Ｐ Seeking R Ｐ =Σ(Vt ｋ ・Δtd ｋ ) / n …(4) In the subsequent lining at the center position, the estimated path length difference R Ｐ is the difference in path length of the elastic wave; A method for estimating strength of lining concrete before removal from the form according to claim 1 or 2.

6. The thickness of the lining concrete is 200 to 800 mm. A method for estimating strength of lining concrete before removal from the form according to claim 1 or 2.

7. After pouring the lining concrete, and before removing the form, a striking position on the inner surface of the center is struck to vibrate the center and the lining concrete, and a first vibration measuring device is used to measure the post-pouring vibration at a first position on the inner surface of the center that is a first distance away from the striking position, and a second vibration measuring device is used to measure the post-pouring vibration at a second position on the inner surface of the center that is a second distance away from the striking position, the second distance being greater than the first distance; The second distance is equal to or less than the first distance, Based on the post-cast vibration measured by the first vibration measuring instrument and the post-cast vibration measured by the second vibration measuring instrument, a difference in arrival time of elastic waves propagating from the impact position to the first vibration measuring instrument and the second vibration measuring instrument is calculated, determining an elastic wave velocity based on a difference in arrival time of the elastic wave and a difference in path length of the elastic wave propagating from the impact position to the first vibration measuring device and the second vibration measuring device, respectively; When the elastic wave velocity reaches a preset target value, it is determined that it is time to release the mold. A method for determining when to remove lining concrete before removal of the form, comprising:

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