JP7483076B2 - Stress measurement method - Google Patents

Description

The present invention relates to a stress measurement method for measuring the stress in the sprayed concrete that is sprayed onto the inner wall surface of an excavation hole during tunnel construction.

In tunnel construction such as mountain tunnels, the ground (ground and bedrock in its natural state) is excavated to form a tunnel (excavated shaft), and then the supporting structure is constructed by erecting steel supports, applying a primary lining (support) using sprayed concrete, and driving in rock bolts, and then the tunnel is completed by applying a secondary lining using concrete.

Patent Document 1 discloses a technique for constructing support structures in tunnel construction, in which an underground displacement meter that measures underground displacement in the ground near the face is inserted from inside the excavation tunnel to check for changes and loosening of the ground caused by excavation, and the number of rock bolts to be installed is determined based on the results of the check.

Japanese Patent Application Laid-Open No. 8-14905

The above-mentioned sprayed concrete is sprayed onto the ground quickly after excavation, and is a material that reacts sensitively to the behavior of the ground around the tunnel. The inventors of the present application have realized that measuring the stress in the sprayed concrete during tunnel construction is an important construction management item for examining the stability of the tunnel and the suitability of the support structure.

Here, it is conceivable to insert the underground displacement meter described in Patent Document 1 into the sprayed concrete and measure the stress within the sprayed concrete from the measured displacement (strain), but this method can only measure the stress at the point where the underground displacement meter is inserted, and cannot measure the stress distribution in the sprayed concrete. Furthermore, when measuring the displacement of the sprayed concrete, that is, the strain, it is necessary to track the strain of the sprayed concrete, which reacts sensitively to the behavior of the ground, and to appropriately capture that strain.

Therefore, the present invention was made with attention to this situation, and aims to provide a stress measurement method that can measure the continuous stress distribution within sprayed concrete.

In response to the above problem, a stress measuring device is provided that measures the stress in the sprayed concrete sprayed on the wall surface of the excavation hole during tunnel construction. The stress measuring device includes an embedded cable embedded in the sprayed concrete, a strain measuring unit, and a stress measuring unit. The embedded cable is composed of an optical fiber cable and a protective member. The optical fiber cable extends along the wall surface and guides incident light. The protective member is a member that is provided along the optical fiber cable and protects the optical fiber cable. The strain measuring unit measures the distribution of strain in the optical fiber cable along the extension direction of the optical fiber cable based on the reflected light guided by the optical fiber cable. The stress measuring unit stores data indicating the relationship between stress and strain in the sprayed concrete in advance, and measures the distribution of stress in the sprayed concrete along the extension direction based on the measurement results by the strain measuring unit and the data. The embedded cable has convex portions on its surface intermittently in the extension direction of the buried cable.

In addition, in order to solve the above problem, a stress measurement method according to a reference embodiment of the present invention is a stress measurement method for measuring stress in sprayed concrete sprayed on a peripheral wall surface of an excavation hole in tunnel construction. The stress measurement method according to the reference embodiment includes: (1) extending a buried cable, which is composed of an optical fiber cable that guides incident light and a protective member that is provided along the optical fiber cable and protects the optical fiber cable, and has convex portions on its surface intermittently in the extension direction of the buried cable, along the peripheral wall surface; (2) spraying concrete on the peripheral wall surface so as to bury the buried cable; (3) measuring the distribution of strain of the optical fiber cable along the extension direction of the optical fiber cable based on the reflected light guided by the optical fiber cable; and (4) storing data indicating the relationship between stress and strain in the sprayed concrete in advance, and measuring the distribution of stress in the sprayed concrete along the extension direction based on the measurement result of the distribution of strain and the data.
A stress measurement method according to one aspect of the present invention is a method for measuring stress in concrete sprayed on a peripheral wall surface of an excavation hole in tunnel construction. The stress measurement method according to the one aspect includes: (1) extending an embedded cable, which includes an optical fiber cable for guiding incident light and a protective member for protecting the optical fiber cable, along the peripheral wall surface; (2) spraying concrete on the peripheral wall surface so as to bury the embedded cable; (3) timing the age of the concrete from the time when it was sprayed on the peripheral wall surface; (4) measuring the strain distribution of the optical fiber cable along the extension direction of the optical fiber cable; and (5) storing data showing the relationship between stress and strain for the concrete at multiple time points from a predetermined early age before the concrete develops its design strength, and measuring the stress distribution in the concrete along the extension direction after the predetermined early age based on the measurement results of the strain distribution and the data.

According to the stress measuring device and the stress measuring method of the reference embodiment, the buried cable, which is composed of the optical fiber cable and the protective member embedded in the sprayed concrete, has a convex portion on its surface, and therefore the adhesion between the sprayed concrete and the buried cable is improved. The convex portion is intermittently formed in the extending direction of the buried cable, so that when the sprayed concrete is distorted in the extending direction of the buried cable, the optical fiber cable can be distorted in the extending direction of the buried cable in response to the distortion. Therefore, by measuring the distortion of the optical fiber cable, the distortion of the sprayed concrete can be appropriately captured. Then, based on the reflected light guided by the optical fiber cable, the distribution of the distortion of the optical fiber cable along the extending direction of the optical fiber cable is measured, and based on the data showing the relationship between the stress and distortion of the sprayed concrete stored in advance and the measurement result of the distribution of the distortion, the distribution of the stress in the sprayed concrete can be continuously measured along the extending direction. Furthermore, the protective member can reliably prevent or suppress damage to the optical fiber cable when the concrete is sprayed.
Furthermore, the stress measurement method of the present invention makes it possible to reliably measure the stress distribution within the sprayed concrete from its early age onwards, starting immediately after spraying, enabling the stability of the tunnel and the adequacy of the support structure to be examined and analysed.

In this way, it is possible to provide a stress measuring device and a stress measuring method that can properly capture the distortion of the optical fiber cable by following the distortion of the sprayed concrete, and can measure the continuous stress distribution within the sprayed concrete.

FIG. 1 is a diagram for explaining a schematic configuration of a stress measuring device according to an embodiment of the present invention. 2 is a cross-sectional view taken along the line AA in FIG. 1. 2 is a cross-sectional view taken along the line B-B in FIG. 1, and is also a conceptual diagram for explaining the extension path of a buried cable buried in the shotcrete. FIG. 4 is a partially enlarged perspective view of part C shown in FIGS. 1 and 3 as viewed from inside the excavation hole. FIG. 2 is a schematic block diagram of the stress measuring device according to the embodiment. FIG. 2 is a diagram showing the appearance of the buried cable. FIG. 2 is a cross-sectional view of the buried cable. FIG. 2 is a conceptual diagram for explaining distortion of the sprayed concrete. 4 is a diagram for explaining an example of a change in elastic modulus with age of the sprayed concrete 6. FIG. FIG. 2 is a diagram showing the relationship between stress and strain in the sprayed concrete 6. This is a process diagram to explain the stress measurement method and tunnel construction method, and is a cross-section in the excavation direction at the top near the face. FIG. 12 is a process diagram continuing from FIG. FIG. 4 is another diagram for explaining the stress measuring method and the tunnel construction method. 11A and 11B are diagrams for explaining modified examples of the buried cable. FIG. 15 is a cross-sectional view of the buried cable shown in FIG. 14. FIG. 11 is a diagram for explaining another modified example of the buried cable. FIG. 17 is a cross-sectional view of the buried cable shown in FIG. 16.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Fig. 1 is a diagram showing a schematic configuration of a stress measuring device 100 according to an embodiment of the present invention, and shows a case where the device is applied to the construction of a support structure for a mountain tunnel. Fig. 1 is also a cross-sectional view of a tunnel viewed toward the face W. Fig. 2 is a cross-sectional view taken along the line A-A in Fig. 1, and Fig. 3 is a cross-sectional view taken along the line B-B in Fig. 1, and is also a conceptual diagram for explaining the extension path of a buried cable 10, which will be described later. Fig. 4 is a partially enlarged perspective view of part C shown in Figs. 1 and 3, as viewed from the inside of an excavation hole 1, which will be described later.

First, we will explain the tunnel constructed using the stress measuring device 100.

The tunnel in this embodiment is a mountain tunnel, and is constructed, for example, by the NATM method. The excavation hole 1, which is the main part of the tunnel, is formed by excavating the ground 2 using a breaker, a free-face excavator, blasting, etc.

As shown in FIG. 1, in this embodiment, the top of the excavation pit 1 is formed in an arch shape (approximately semicircular) in order to actively utilize the load-bearing capacity inherent to the surrounding ground. Also, as shown in FIGS. 2 to 4, steel supports (steel arch supports) 4 are provided at a predetermined interval S in the tunnel excavation direction along the top and left and right sides of the peripheral wall surface 3 of the excavation pit 1. The steel supports 4 are, for example, H-shaped steel, and are formed in a curved arch shape extending in the circumferential direction of the peripheral wall surface 3 in accordance with the cross-sectional shape (see FIG. 1) of the cross section of the excavation pit 1 perpendicular to the tunnel excavation direction. The interval S is determined according to the earth pressure of the ground 2, and is, for example, about 1 m. Also, as shown in FIG. 4, a wire mesh 5 is installed between the peripheral wall surface 3 and the steel supports 4 so as to be along the top and left and right sides of the peripheral wall surface 3. The wire mesh 5 is formed by arranging reinforcing bars in a mesh shape. In addition, in Figures 1 to 3, the wire mesh 5 is omitted from the illustration to simplify the drawings.

Concrete is sprayed onto the peripheral wall surface 3 of the excavation hole 1, and the peripheral wall surface 3 is primarily supported by the steel supports 4 and the shotcrete 6 sprayed onto the peripheral wall surface 3. The shotcrete 6 is sprayed over the entire circumference of the top and left and right sides of the peripheral wall surface 3 so as to fill the spaces between the adjacent steel supports 4, 4 and between the steel supports 4 and the peripheral wall surface 3. The concrete thickness t1 of the shotcrete 6 is determined in advance according to the earth pressure of the ground. When the shotcrete 6 is sprayed onto the peripheral wall surface 3, the inner surface of the shotcrete 6 is sprayed so as to be flush with the flange surface on the inside (opposite the peripheral wall surface 3) of the H-shaped steel as the steel support 4. Although not shown in the figure, a plurality of rock bolts are cast from the inside of the excavation hole 1 through the shotcrete 6 at positions spaced apart in the circumferential direction of the peripheral wall surface 3 between the adjacent steel supports 4, 4 so as to reach the ground. The number of rock bolts to be installed, their installation positions, and installation depth are determined according to the earth pressure of the ground 2. The construction of the support structure is repeated, with the primary lining (support) made of steel supports 4 and sprayed concrete 6, and then the rock bolts are installed. After that, although not shown in the figure, the tunnel is completed by applying a secondary lining of concrete from the inside of the sprayed concrete 6.

Next, the stress measuring device 100 will be described. Figure 5 is a schematic block diagram of the stress measuring device 100, Figure 6 is a partially enlarged view showing the appearance of the buried cable 10 described later, and Figure 7 is a cross-sectional view of the buried cable 10.

The stress measuring device 100 measures the stress σ in the sprayed concrete 6 sprayed onto the wall surface 3 of the excavation hole 1 during tunnel construction.

As shown in FIG. 5, the stress measuring device 100 is configured with a buried cable 10 that is buried in the sprayed concrete 6 and a device main body 20 that is connected to one end of the buried cable 10.

As shown in FIG. 6, the buried cable 10 extends along the top and left and right sides of the peripheral wall surface 3, and is a cable consisting of an optical fiber cable 11 and a protective member 12, and is a member that is buried in the sprayed concrete 6. The extension path of the buried cable 10 will be described in detail later.

In this embodiment, the buried cable 10 has an elastic modulus E' that is equal to or less than the elastic modulus E of the sprayed concrete 6 at a specified early age (E ≥ E'). Details of the elastic modulus E and the elastic modulus E' will be described later.

The optical fiber cable 11 extends along the top and left and right sides of the peripheral wall surface 3 and guides the incident light. The optical fiber cable 11 is formed with a core that serves as the optical path and a cladding that covers the core.

The protective member 12 is a member that is provided along the optical fiber cable 11 to protect the optical fiber cable 11.

As shown in FIG. 1 (enlarged view of the balloon portion in the figure), FIG. 6 and FIG. 7, in this embodiment, the protective member 12 is made of a plurality of twisted cords 12a. The plurality of twisted cords 12a are twisted in a spiral shape so as to surround the periphery of the core material, which is the optical fiber cable 11. In other words, the protective member 12 is formed by twisting a plurality of twisted cords 12a in a spiral shape, and the optical fiber cable 11 extends from the center of the spiral. The twisted cords 12a are made of, for example, a fiber material made of a predetermined synthetic resin. Although the twisted cords 12a are shown as being three in the figure, the number of twisted cords 12a is not limited to this, and any appropriate number can be adopted. Although each twisted cord 12a is the same, when it is necessary to distinguish between them for the sake of convenience, they are referred to as twisted cord 12a1, twisted cord 12a2, and twisted cord 12a3. In FIG. 7, the cross section of each twisted cord 12a is shown as a circular cross section for the sake of simplicity, but in reality, each twisted cord 12a has a flattened cross section according to the degree of twisting (spiral pitch), etc.

In this embodiment, the buried cable 10 has convex portions 13 on its surface intermittently in the extension direction of the buried cable 10. Specifically, in this embodiment, the convex portions 13 of the buried cable 10 are formed by the outer surface of the twisted strings 12a. In other words, when viewed in a cross section including the center line of the buried cable 10 (indicated by a dashed line in FIG. 6), the outer surface of the buried cable 10 is formed in an uneven shape, and the convex portions of this outer surface correspond to the convex portions 13.

Returning to Figures 3 and 4, the extension path of the buried cable 10 will be described. In this embodiment, the buried cable 10 extends continuously in a zigzag shape as a whole in a developed view of the peripheral wall surface 3 (see Figure 3) via a measurement path 10a for measurement that extends in a direction perpendicular to the excavation direction along the peripheral wall surface 3 at a plurality of cross-sectional positions spaced apart in the excavation direction of the excavation hole 1 (in other words, the circumferential direction of the peripheral wall surface 3) and a connection path 10b for connection that connects one of the left and right side parts of the peripheral wall surface 3 at adjacent cross-sectional positions or the other of the left and right side parts via a connector part 14. One end (connection end) of the buried cable 10 is connected to the device main body part 20 (more specifically, the strain measurement part 21 described later) in the excavation hole 1, and the other end of the buried cable 10 is located on the connection path 10b along the peripheral wall surface 3 at the lower ends of the left and right sides of the peripheral wall surface 3, for example. The one end of the buried cable 10 is extended along the bottom surface 7 of the excavation hole 1 via a wiring path 10c (see Figure 3), which is a path that extends between the flange surface on the peripheral wall surface 3 side of the H-shaped steel beam serving as the steel support 4 and the peripheral wall surface 3.

In the state shown in FIG. 3, the buried cable 10 extends via the measurement path 10a four times, passing through four mutually parallel cross-sectional positions spaced apart in the excavation direction of the excavation hole 1. The buried cable 10 also extends via the connection path 10b four times, alternating between the left and right. Each connection path 10b is, for example, formed by a gap between the flange surface on the peripheral wall surface 3 side of the H-beam as the steel support material 4 and the peripheral wall surface 3. A connector portion 14 is connected to the tip of the buried cable 10 in the connection path 10b closest to the face W (the upper left connection path 10b in FIG. 3) among the multiple connection paths 10b, for example, after the next excavation is completed, in order to extend the buried cable 10 for the next cross-sectional position.

The device main body 20 includes a strain measuring unit 21 and a stress measuring unit 22, and is arranged, for example, on the bottom surface 7 at the mouth side (opposite the face W) of the excavation hole 1.

The strain measuring unit 21 measures the distribution of strain ε of the optical fiber cable 11 along the extension direction of the optical fiber cable 11 based on the reflected light guided by the optical fiber cable 11, and has the function of acting as a light emitting unit that generates light, the function of receiving the reflected light, and the function of measuring the distribution of strain ε.

Here, as shown in FIG. 8, the shotcrete 6 having an arch-shaped cross-sectional shape following the peripheral wall surface 3 is loaded with stress σ due to the earth pressure P of the surrounding natural ground 2. In addition, this stress σ generally tends to gradually increase from the face W toward the mouth in the excavation direction, and to become approximately constant at a predetermined distance from the face W. Focusing on the magnitude of stress σ at a cross-sectional position perpendicular to the excavation direction, the magnitude of stress σ at this cross-sectional position changes with the excavation of the natural ground 2, and the shotcrete 6 reacts sensitively to the behavior of the natural ground 2 associated with excavation, etc. In detail, as the excavation of the natural ground 2 progresses and the distance from the face W at the cross-sectional position increases, the burden of supporting the natural ground 2 on the shotcrete 6 at the cross-sectional position increases, so the stress σ at the cross-sectional position becomes higher. In other words, the stress σ in the vicinity of the face W is relatively small. Then, when the excavation proceeds further and the one cross-sectional position is separated from the face W by the predetermined distance, the stress σ at the one cross-sectional position does not change substantially even if the excavation proceeds thereafter. In addition, in many cases, the excavation of the natural ground 2 is further proceeded in the vicinity of the already sprayed shotcrete 6 before it hardens. Therefore, the shotcrete 6 is compressed by the stress σ from an early age immediately after spraying, as shown in FIG. 8, and distorts in the direction toward the center of the excavation hole 1 and also in the circumferential direction of the peripheral wall surface 3. On the other hand, since the outer surface of the buried cable 10 has convex portions 13 intermittently provided in the extension direction of the buried cable 10, the portion of the optical fiber cable 11 buried in the shotcrete 6 on the measurement path 10a for measurement, which extends in the circumferential direction of the peripheral wall surface 3, distorts following the distortion ε' of the shotcrete 6 in the circumferential direction of the peripheral wall surface 3. The strain measuring unit 21 measures the circumferential strain ε of the peripheral wall surface 3 of the optical fiber cable 11, which follows the circumferential strain ε' of the peripheral wall surface 3 of the sprayed concrete 6. Therefore, the circumferential strain ε of the peripheral wall surface 3 of the optical fiber cable 11 is approximately equal to the circumferential strain ε' of the peripheral wall surface 3 of the sprayed concrete 6 (ε' ≒ ε).

Specifically, the strain measurement unit 21 emits inspection light from the light emitting unit to the optical fiber cable 11 at the one end of the buried cable 10 and receives (detects) reflected light from the optical fiber cable 11. The strain measurement unit 21 then analyzes the detected reflected light to measure the distribution of strain ε of the optical fiber cable 11 along the extension direction of the optical fiber cable 11 (in other words, the circumferential direction or longitudinal direction of the peripheral wall surface 3). The measured data X of the distribution of strain ε is input to the stress measurement unit 22. As a method for measuring the distribution of strain ε in the strain measurement unit 21, a known method such as BOTDR (Brillouin Optical Time Domain Reflectometer) can be used. In this embodiment, for example, the BOTDR method is adopted. In this BOTDR method, the strain measurement unit 21 emits inspection light to the optical fiber cable 11 and detects Brillouin scattered light as reflected light, and analyzes its spectrum. The distortion measuring unit 21 identifies the location where the reflected light occurs based on the time delay between the incidence of the test light and the detection of the reflected light, and obtains the value of the distortion ε at the identified location from the frequency shift in the reflected light. In this way, the distortion measuring unit 21 is configured to continuously measure the distortion ε of the optical fiber cable 11 along the extension direction of the optical fiber cable 11 in the measurement path 10a, for example, by the BOTDR method, and to measure a continuous distribution along the extension direction. The distortion ε of the optical fiber cable 11 is approximately equal to the distortion ε' of the sprayed concrete 6 and is considered to be equivalent to the distortion ε', so the measurement result of the distortion measuring unit 21 can be considered to be the distribution of the distortion ε' along the circumferential direction of the peripheral wall surface 3 in the sprayed concrete 6 (i.e., the extension direction of the buried cable 10).

FIG. 9 is a diagram for explaining an example of change in the elastic modulus E (for example, tangent Young's modulus, i.e., tangent elastic modulus) of the shotcrete 6 with the progression of material age. In FIG. 9, the horizontal axis indicates the material age T (time) from the time when the concrete is sprayed onto the peripheral wall surface 3, and the vertical axis indicates the elastic modulus E of the shotcrete 6. As shown in FIG. 9, the longer the material age T of the shotcrete 6, the larger the elastic modulus E. In other words, the longer the material age T, the higher the rigidity (strength) of the shotcrete 6 becomes, and as the material age T becomes longer and the strength of the shotcrete 6 approaches a predetermined design strength, the amount of change in the elastic modulus E gradually decreases. Then, when the shotcrete 6 hardens and exhibits the design strength, the elastic modulus E becomes an approximately constant value (approximately 10,000 (N/mm ² ) in FIG. 9).

As described above, in this embodiment, the buried cable 10 has an elastic modulus E' equal to or less than the elastic modulus E of the shotcrete 6 at a predetermined early age (E≧E'). In this embodiment, the predetermined early age is, for example, 3 to 4 hours after spraying, and the elastic modulus E' of the buried cable 10 in this case is set to a predetermined value equal to or less than 1000 (N/mm ² ). In this way, the elastic modulus E' of the buried cable 10 including the optical fiber cable 11 is set to be relatively low. Therefore, the portion of the optical fiber cable 11 on the measurement path 10a for measurement extending in the circumferential direction of the peripheral wall surface 3 is distorted in a manner more reliably following the distortion of the shotcrete 6 in the circumferential direction of the peripheral wall surface 3 from a time shortly after the spraying of the shotcrete 6.

The stress measurement unit 22 prestores data D indicating the relationship between the stress σ and the strain ε' for the sprayed concrete 6, and measures the distribution of the stress σ in the sprayed concrete 6 along the extension direction of the optical fiber cable 11 based on the measurement results by the strain measurement unit 21 and the data D. The stress measurement unit 22 includes, for example, a memory unit 22a that stores the data D, and a calculation unit 22b that calculates the distribution of the stress σ in the sprayed concrete 6 and outputs the measurement result Z.

Here, in FIG. 10, an example of a σ-ε' curve showing the relationship between the stress σ generated in the sprayed concrete 6 due to the earth pressure P of the ground 2 and the strain ε' of the sprayed concrete 6 at that time is shown for each predetermined material age T. As shown in FIG. 10, the σ-ε' curve changes as the material age T progresses. For example, in the low-strain region (e.g., the region where ε'≦0.2), each σ-ε' curve shows a curve in which the stress σ increases relatively suddenly as the strain ε' increases, and then the increase in the stress σ gradually decreases as the strain ε' increases further, becoming approximately flat. And, as the material age T increases, the σ-ε' curve shows a steeper rise in the low-strain region, and for example, when the material age T is 48 hours or more, it shows a parabolic curve with an upward convex curve, and when the material age T exceeds a predetermined strain ε', the stress σ tends to decrease rapidly.

In this embodiment, the stress measurement unit 22 stores data D indicating the relationship between the stress σ and the strain ε' for the sprayed concrete 6 at multiple time points between the early age and the hardening time. Specifically, the memory unit 22a of the stress measurement unit 22 stores data D for the σ-ε' curve for each hour, for example, when the material age T is between 4 hours (early age) and 72 hours (hardening). The number of data D stored in the memory unit 22a (i.e., the number of tables in the data table indicating the correspondence between σ and ε') is not particularly limited and can be set as appropriate.

In detail, the stress measurement unit 22 is constantly input with data X of the measurement result of the distribution of strain ε from the strain measurement unit 21, for example. The stress measurement unit 22 is configured to detect, for example, that concrete has been sprayed on the measurement path 10a based on a change in the data X from the strain measurement unit 21, and to start timing the age T of the sprayed concrete 6 at the cross-sectional position where the measurement path 10a is located from the detection time. The stress measurement unit 22, for example, reads data D on the σ-ε' curve of the material age T closest to the timed material age T at the cross-sectional position from the storage unit 22a, and calculates the measurement result Z of the distribution of stress σ in the sprayed concrete 6 by identifying, from the read data D, the stress σ corresponding to each strain ε' that matches each strain ε in the distribution of strain ε along the extension direction in the input data X.

Next, the operation of the stress measuring device 100 will be briefly explained using an example of measurement at the cross-sectional position on the measurement path 10a closest to the face W side shown in Figure 3.

The stress measurement unit 22 is constantly receiving measurement result data X from the strain measurement unit 21 even before concrete is sprayed onto the peripheral wall surface 3. In this state, zero-level data indicating no strain ε (≒strain ε') is input at this cross-sectional position. Then, in the measurement path 10a closest to the face W side shown in FIG. 3, when concrete is sprayed onto the peripheral wall surface 3, immediately after that, stress σ due to the earth pressure P of the ground 2 is generated in the sprayed concrete 6, and the sprayed concrete 6 begins to distort in the circumferential direction of the peripheral wall surface 3. Meanwhile, the optical fiber cable 11 is distorted reliably following the strain ε' of the sprayed concrete 6, and the strain measurement unit 21 measures the distribution of the strain ε (≒strain ε') of this optical fiber cable 11 and inputs the measurement result data X to the stress measurement unit 22. This measurement is performed continuously at a predetermined sampling time interval, and the measurement result data X is constantly input to the stress measurement unit 22. Here, when concrete is sprayed onto the peripheral wall surface 3, the data X of the measurement result of the distribution of the strain ε input from the strain measuring unit 21 to the stress measuring unit 22 changes from the zero level. The stress measuring unit 22 detects that concrete has been sprayed on this measurement path 10a based on the change in the data X, and starts measuring the age T of the sprayed concrete 6 at this cross-sectional position. The stress measuring unit 22 reads out data D for the σ-ε' curve of the material age T closest to the measured material age T from the storage unit 22a, identifies stress σ corresponding to each strain ε' that coincides with each strain ε of the distribution of the strain ε along the extension direction in the input data X from the read out data D, and calculates it as the measurement result Z of the distribution of the stress σ in the sprayed concrete 6. This calculation may be performed when the measured material age T coincides with any of the material ages T stored in the storage unit 22a. In this case, the stress σ can be measured with higher accuracy. In addition, the measurement of the distribution of strain ε and the measurement of the distribution of stress σ are not limited to being performed for each measurement path 10a as described above, but may be performed for multiple measurement paths 10a at once. For example, when measuring the five measurement paths 10a shown in FIG. 3 at once, the buried cable 10 may be laid at once without using the connector portion 14.

Next, an example of a stress measurement method using the stress measurement device 100 according to this embodiment will be described together with a tunnel construction method with reference to Figures 11 to 13 and 4. Figures 11 and 12 show a cross section in the excavation direction at the top end near the tunnel face W. Figure 13 is a drawing for explaining the state in which the buried cable 10 is extended and laid after excavation. In Figure 13, the existing buried cable 10 is shown with a dashed line, and the extended buried cable 10 is shown with a solid line. In the following explanation, it is assumed that excavation and support structures have already been constructed up to the position shown in Figures 2 and 3, and excavation will proceed from this position. In this example, the NATM method is used as the tunnel construction method.

The stress measurement method in this embodiment is a method for measuring the stress in the shotcrete sprayed on the peripheral wall surface of the excavation hole during tunnel construction, and includes: (1) extending the buried cable 10 along the peripheral wall surface 3 (cable extension process); (2) spraying concrete on the peripheral wall surface 3 so as to bury the buried cable 10 (primary lining process); (3) measuring the distribution of strain ε of the optical fiber cable 11 along the extension direction of the optical fiber cable 11 based on the reflected light guided by the optical fiber cable 11 (strain measurement process); and (4) storing data D indicating the relationship between stress σ and strain ε' for the shotcrete 6 in advance, and measuring the distribution of stress σ in the shotcrete 6 along the extension direction of the optical fiber cable 11 based on the measurement result of the distribution of strain ε and the data D (stress measurement process).

In addition, in this embodiment, the buried cable 10 is configured to have an elastic modulus E' that is equal to or less than the elastic modulus E of the sprayed concrete 6 at a specified early age, and data D is pre-stored in the memory unit 22a of the stress measurement unit 22 for multiple time points between the early age and hardening.

In this embodiment, the stress measurement method further includes (5) installing a wire mesh 5 along the peripheral wall surface 3 (wire mesh installation process). The above (1) extending the buried cable 10 along the peripheral wall surface 3 (cable extension process) is performed by extending the buried cable 10 along the wire mesh 5 so that the buried cable 10 is movable relative to the wire mesh 5, thereby extending the buried cable 10 along the peripheral wall surface 3, and the above (2) spraying concrete onto the peripheral wall surface 3 (primary lining process) is performed by spraying concrete onto the peripheral wall surface 3 so as to bury the wire mesh 5 together with the buried cable 10.

Specifically, when constructing a tunnel, first, holes (not shown) for inserting explosives are drilled at the tunnel face W shown in FIG. 11(a) using a drill or the like, and then explosives such as dynamite are inserted into the holes and detonated, thereby digging the excavation shaft 1 from the tunnel face W to the tunnel face W' as shown in FIG. 11(b) (excavation process). At this point, the peripheral wall surface 3 of the excavation shaft 1 that has been dug is subjected to finish excavation using a tunnel excavation device or the like (not shown). Then, as shown in FIG. 11(c), steel supports (steel arch supports) 4 are erected at intervals S (steel support erection process).

Next, as the cable extension process, the buried cable 10 is extended as shown in FIG. 12(d) and FIG. 13. More specifically, as shown in FIG. 13, a connector portion 14 for extending the buried cable 10 for the next cross-sectional position is additionally connected to the tip of the buried cable 10 in the connection path 10b closest to the face W among the existing connection paths 10b. Then, as the wire mesh installation process, the wire mesh 5 shown in FIG. 4 is additionally installed along the peripheral wall surface 3. In the cable extension process, one end of the buried cable 10 to be extended is connected to the additionally connected connector portion 14, and the buried cable 10 is extended along the peripheral wall surface 3. At this time, the buried cable 10 is extended along the wire mesh 5 so as to be movable relative to the wire mesh 5, thereby extending the buried cable 10 along the peripheral wall surface 3. More specifically, as shown in FIG. 4, an S-shaped hook 15 is suspended on the wire mesh 5, and the buried cable 10 is extended movably relative to the wire mesh 5 via the hook 15. The extended buried cable 10 extends from the additionally connected connector portion 14 through the connection path 10b, then through the measurement path 10a at the next cross-sectional position, from the bottom end of one of the left and right sides of the peripheral wall surface 3 to the bottom end of the other of the left and right sides, and from the bottom end of the other of the left and right sides of the peripheral wall surface 3, it is further extended through the connection path 10b to the next cross-sectional position.

Next, as the primary lining process, as shown in FIG. 12(e), additional concrete is sprayed onto the surrounding wall surface 3 so as to bury the wire mesh 5 together with the buried cable 10, thereby completing the primary lining. Here, the dashed lines shown in FIG. 11(a) to FIG. 12(f) indicate the surface of the sprayed concrete 6. After that, rock bolts (not shown) are installed.

Next, as the strain measurement process, the strain measurement unit 21 measures the distribution of strain ε of the optical fiber cable 11 at the cross-sectional position of the measurement path 10a of the extended buried cable 10.

Next, as the stress measurement process, the stress measurement unit 22 measures the distribution of stress σ in the sprayed concrete 6 at the cross-sectional position of the measurement path 10a of the extended buried cable 10. This completes the measurement of the stress distribution in the sprayed concrete 6 at this cross-sectional position. Here, for example, the construction manager monitors the measurement result Z of the distribution of stress σ, checks whether there is a location at this cross-sectional position where stress σ exceeds the allowable stress of the sprayed concrete 6 at the material age T at the time of measurement, and analyzes the stability of the tunnel and the validity of the support structure. If there is a location where the allowable stress is exceeded, for example, by adding a rock bolt at this cross-sectional position or by spraying more concrete to slightly thicken the concrete thickness t1 of the sprayed concrete 6 (analysis and correction process). The stress measurement unit 22 may be configured to be able to execute a judgment as to whether the measured stress σ exceeds the allowable stress. In this case, the allowable stress data may be stored in the memory unit 22a for each material age T, and the calculation unit 22b may execute the above judgment.

For example, the work of combining the excavation process, the steel support construction process, the wire mesh installation process, the cable extension process, the primary lining process (including driving rock bolts), the strain measurement process, the stress measurement process, and the analysis and correction process into one cycle (hereinafter referred to as the "first work") is carried out prior to the construction of the lining concrete 16, which will be described later. In the first work, construction is carried out for one span (for example, a 1 m-long tunnel) in one cycle, and for example, three to four cycles of construction are carried out in one day.

The second work is carried out at a location, for example, about 300 m behind the tunnel from the location where the first work is being carried out. This second work includes a secondary lining process. In this secondary lining process, as shown in FIG. 12(f), a lining concrete 16 is constructed on the surface of the sprayed concrete 6 to perform secondary lining. Here, the two-dot chain line shown in FIG. 12(f) is the surface of the lining concrete 16. The concrete thickness t2 of the lining concrete 16 is set according to the properties of the natural ground 2, etc. In addition, in the second work (secondary lining process), construction is carried out for one span (for example, a tunnel length of 10 m, i.e., 10 cycles of the first work) in one cycle, and one cycle of construction is carried out in, for example, three days. The tunnel is constructed through the above process. By separating the first work and the second work described above by about 300 m, it is possible to suppress the confusion of the work, and the work can be carried out efficiently.

The stress measuring device 100 constantly measures the strain ε of the optical fiber cable 11 and the stress σ in the sprayed concrete 6, and can constantly monitor the change in strain ε (≒ strain ε') and the change in stress σ associated with the progress of excavation at each cross-sectional position (measurement path 10a) as the material age T progresses. As the excavation of the excavation hole 1 progresses, the stress measuring device 100 gradually increases the number of cross-sectional positions measured at one time, and can obtain measurement results at multiple cross-sectional positions (measurement path 10a) at one time. As the excavation progresses, the stress σ loaded on the sprayed concrete 6 at each cross-sectional position gradually increases, and the allowable stress of the sprayed concrete 6 also increases as the material age T progresses. The construction manager continues the above-mentioned analysis and correction process for each cross-sectional position based on the stress σ at each cross-sectional position that changes as the excavation progresses and the allowable stress corresponding to the material age T at the time of measurement.

According to the stress measuring device 100 and the stress measuring method using the stress measuring device 100 of the present embodiment, the buried cable 10 buried in the shotcrete 6 has a convex portion 13 on its surface, so that the adhesion between the shotcrete 6 and the buried cable 10 is improved. Since the convex portion 13 is intermittently formed in the extending direction of the buried cable 10, when the shotcrete 6 is distorted in the extending direction of the buried cable 10, the optical fiber cable 11 can be distorted in the extending direction of the buried cable 10 following this distortion. Therefore, by measuring the distortion ε of the optical fiber cable 11, the distortion ε' of the shotcrete 6 can be appropriately captured. Then, based on the reflected light guided by the optical fiber cable 11, the distribution of the distortion ε of the optical fiber cable 11 along the extending direction of the optical fiber cable 11 is measured, and based on the data D showing the relationship between the stress σ and the distortion ε' for the shotcrete 6 stored in advance and the measurement result of the distribution of the distortion ε, the distribution of the stress σ in the shotcrete 6 can be continuously measured along the extending direction. Furthermore, the protective member 12 in the buried cable 10 can reliably prevent or suppress damage to the optical fiber cable 11 when the concrete is sprayed.
In this way, it is possible to provide a stress measuring device 100 and a stress measuring method that can appropriately capture the strain ε of the optical fiber cable 11 in accordance with the strain ε' of the shotcrete 6 and measure the distribution of continuous stress σ within the shotcrete 6.

In this embodiment, the buried cable 10 has an elastic modulus E' that is equal to or less than the elastic modulus E of the shotcrete 6 at a predetermined early age, and the stress measuring unit 22 is configured to store data D showing the relationship between the stress σ and the strain ε' of the shotcrete 6 at multiple time points between the early age and hardening. Therefore, the stress σ in the shotcrete 6 at or after the early age can be reliably measured immediately after spraying. Note that in this embodiment, 3 to 4 hours is used as an example of an early age, but this is not limiting, and for example, about 24 hours may also be acceptable. In this case, the elastic modulus E' of the buried cable 10 may be 7000 (N/mm ² ) or less.

Here, as described above, the stress σ of the shotcrete 6 in the vicinity of the face W is relatively small. Therefore, in some cases, the stress σ of the shotcrete 6 in the vicinity of the face W is lower than the allowable stress of the shotcrete 6 at an early age, and it may be easy to ensure this in advance without additional spraying. In this case, it is not necessary to measure the stress σ of the shotcrete 6 from an early age. Therefore, in such a case, the strain ε of the optical fiber cable 11 and the stress σ of the shotcrete 6 may be measured from the age T when the strength close to the design strength is expressed or at the time of hardening (for example, when the age T is 2 to 3 days). In this case, the elastic modulus E' of the buried cable 10 is not limited to be equal to or less than the elastic modulus E of the shotcrete at an early age, and the buried cable 10 may be equal to or less than the elastic modulus E of the shotcrete 6 at an age T of 2 to 3 days, specifically, 10,000 (N/mm ² ) or less.

In this embodiment, the protective member 12 is made of multiple twisted strings 12a, which are twisted in a spiral shape around the optical fiber cable 11 as a core material. This makes it easy to form the convex portion 13 of the buried cable 10, and also makes it easy to form a structure that protects the optical fiber cable 11. Furthermore, by using the twisted strings 12a, it is easy to form a buried cable 10 with low rigidity.

In this embodiment, the buried cable 10 is configured to extend continuously in a zigzag pattern as a whole when viewed from the expanded view of the peripheral wall surface 3. This allows the distribution of strain ε of the optical fiber cable 11 at multiple cross-sectional positions to be measured using a single device main body 20, eliminating the need to provide an expensive device main body 20 (particularly the strain measuring unit 21) for measuring each cross-sectional position, thereby reducing device and measurement costs.

In this embodiment, the buried cable 10 is movably extended along the wire mesh 5 using, for example, an S-shaped hook 15, so that the buried cable 10 is extended along the peripheral wall surface 3. This allows the buried cable 10 to be easily extended along the peripheral wall surface 3 without preventing the optical fiber cable 11 from distorting in response to the distortion ε' of the sprayed concrete 6.

The protective structure of the optical fiber cable 11 in the buried cable 10 is not limited to the structure shown in Figures 6 and 7. For example, the modified examples shown in Figures 14 and 15 (Variation 1) and Figures 16 and 17 (Variation 2) can also be used.

In detail, in the first modified example shown in Fig. 14 and Fig. 15, the protective member 12 is formed by twisting a plurality of twisted strings 12a in a spiral manner, as in Fig. 6 and Fig. 7, but the optical fiber cable 11 extends in a spiral manner along the twisted strings 12a in the region V between the adjacent twisted strings 12a. In other words, the optical fiber cable 11 extends in a spiral manner continuously along the V-groove-shaped region V on the buried cable outer surface side of two adjacent twisted strings (e.g., twisted strings 12a1 and 12a2) of the three twisted strings 12a1, 12a2, and 12a3. Note that in Fig. 7, the cross section of each twisted string 12a is shown as a circular cross section for the sake of simplicity of drawing, but in reality, each twisted string 12a has a flattened cross section according to the degree of twisting (spiral pitch), etc. In variant 1, the convex portion 13 of the buried cable 10 is also formed by the outer surface of the twisted string 12a.

In addition, in the second modified example shown in Figs. 16 and 17, the protective member 12 may be provided so as to cover the outer periphery of the optical fiber cable 11, and may have aggregate 17 inside. Specifically, the protective member 12 may be formed by applying an adhesive containing sand or the like as aggregate 17 to the outer periphery of the optical fiber cable 11. In this case, the convex portion 13 of the buried cable 10 is formed by a portion of the protective member 12 that corresponds to the aggregate 17. In addition, the protective member 12 may be formed by applying a paint capable of obtaining a rough (rough) surface to the outer periphery of the optical fiber cable 11.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and changes are possible based on the technical concept of the present invention.
The claims of Patent Application No. 2018-168121 at the time of filing and immediately prior to the division were as follows.
At the time of application
[Claim 1]
In a stress measuring device for measuring the stress in the shotcrete sprayed on the wall surface of a tunnel excavation,
a buried cable to be buried in the sprayed concrete, the buried cable including an optical fiber cable extending along the peripheral wall surface and guiding incident light, and a protective member provided along the optical fiber cable for protecting the optical fiber cable;
a distortion measuring unit that measures a distribution of distortion of the optical fiber cable along an extension direction of the optical fiber cable based on reflected light guided by the optical fiber cable;
A stress measuring unit that stores data indicating a relationship between stress and strain in the sprayed concrete in advance and measures a distribution of stress in the sprayed concrete along the extension direction based on the measurement results by the strain measuring unit and the data;
Including,
The buried cable has convex portions intermittently on its surface in the extending direction of the buried cable.
[Claim 2]
The buried cable has an elastic modulus equal to or less than the elastic modulus of the sprayed concrete at a predetermined early age,
2. The stress measuring device according to claim 1, wherein the stress measuring unit pre-stores data indicating a relationship between stress and strain in the sprayed concrete for each of a plurality of time points from the early age to the hardening time.
[Claim 3]
The protective member is made of a plurality of twisted cords,
The plurality of twisted cords are twisted together in a spiral shape around a core material of the optical fiber cable,
3. The stress measuring device according to claim 1, wherein the convex portion is formed by an outer surface of the twisted cord.
[Claim 4]
The protective member is formed by twisting a plurality of twisted cords together in a spiral shape,
the fiber optic cable extends helically along the strands in areas between adjacent strands;
3. The stress measuring device according to claim 1, wherein the convex portion is formed by an outer surface of the twisted cord.
[Claim 5]
The protective member is provided so as to cover an outer periphery of the optical fiber cable and has an aggregate therein,
3. The stress measuring device according to claim 1, wherein the convex portion is formed by a portion of the protective member that corresponds to the aggregate.
[Claim 6]
The buried cable extends continuously in a zigzag pattern as a whole in a developed view of the peripheral wall surface, via a measurement path for measurement that extends in a direction perpendicular to the excavation direction along the peripheral wall surface at a plurality of cross-sectional positions spaced apart in the excavation direction of the excavation hole, and a connection path for connecting one of the left and right side portions at adjacent cross-sectional positions or the other of the left and right side portions via a connector portion. A stress measuring device as described in any one of claims 1 to 5.
[Claim 7]
A stress measurement method for measuring stress in sprayed concrete sprayed on the peripheral wall surface of an excavation hole in tunnel construction, comprising:
a buried cable including an optical fiber cable for guiding incident light and a protective member for protecting the optical fiber cable, the buried cable having convex portions intermittently on a surface thereof in an extending direction of the buried cable, extending along the peripheral wall surface;
spraying concrete on the peripheral wall surface so as to bury the buried cable;
measuring a distribution of strain of the optical fiber cable along an extension direction of the optical fiber cable based on reflected light guided by the optical fiber cable;
storing data indicating a relationship between stress and strain for the sprayed concrete in advance, and measuring a stress distribution in the sprayed concrete along the extension direction based on the measurement results of the strain distribution and the data;
A method for measuring stress, comprising:
[Claim 8]
The buried cable has an elastic modulus equal to or less than the elastic modulus of the sprayed concrete at a predetermined early age,
8. The stress measuring method according to claim 7, wherein the data indicating the relationship between the strain and the stress in the sprayed concrete is stored in advance for each of a plurality of time points from the early age to the hardening time.
[Claim 9]
Further comprising installing a wire mesh along the peripheral wall surface;
The extending of the buried cable along the peripheral wall surface includes extending the buried cable along the wire mesh so as to be movable relative to the wire mesh, thereby extending the buried cable along the peripheral wall surface,
9. The stress measuring method according to claim 7, wherein the step of spraying concrete onto the peripheral wall surface comprises spraying concrete onto the peripheral wall surface so as to bury the wire mesh together with the buried cable.
Just before split
[Claim 1]
A stress measurement method for measuring stress in shotcrete sprayed on a peripheral wall surface of an excavation hole in tunnel construction, comprising:
erecting a plurality of supports along the peripheral wall surface at positions spaced apart in the excavation direction of the excavation hole;
a buried cable comprising an optical fiber cable for guiding incident light and a protective member provided along the optical fiber cable to protect the optical fiber cable, the buried cable having an elastic modulus equal to or lower than the elastic modulus of the sprayed concrete at a predetermined early age before the sprayed concrete exhibits its design strength, the buried cable being extended from one of the left and right sides of the peripheral wall surface between adjacent supports to the other of the left and right sides, and being extended continuously from the other of the left and right sides so as to exceed the face-side support of the adjacent supports to the face side;
burying most of the buried cable by spraying concrete onto the peripheral wall surface so as to fill spaces between the adjacent supports and spaces between the supports and the peripheral wall surface and expose the tip of the buried cable on the face side;
connecting a connector portion for extending the buried cable to the tip portion of the buried cable;
measuring a distribution of strain of the optical fiber cable along an extension direction of the optical fiber cable based on reflected light guided by the optical fiber cable;
storing data indicating a relationship between stress and strain for the sprayed concrete in advance, and measuring a stress distribution in the sprayed concrete along the extension direction based on the measurement results of the strain distribution and the data;
A stress measurement method comprising:
[Claim 2]
The method further includes timing the age of the sprayed concrete.
Measuring the distribution of strain in the optical fiber cable includes measuring the distribution of strain in the optical fiber cable from the predetermined early age,
Measuring the distribution of stress in the sprayed concrete includes storing data showing the relationship between stress and strain in the sprayed concrete at multiple time points from the early age, and measuring the distribution of stress in the sprayed concrete along the extension direction from the early age onwards based on the measurement results of the strain distribution and the data.
The stress measuring method according to claim 1 .
[Claim 3]
Further comprising installing a wire mesh along the peripheral wall surface;
The extending of the buried cable includes extending the buried cable along the wire mesh so as to be movable relative to the wire mesh, thereby extending the buried cable along the peripheral wall surface;
3. The stress measuring method according to claim 1, wherein the spraying of concrete onto the peripheral wall surface comprises spraying concrete onto the peripheral wall surface so as to bury the wire mesh together with the buried cable.
[Claim 4]
The excavation of the excavation hole and the spraying of the sprayed concrete are carried out for each predetermined tunnel length,
4. The stress measuring method according to claim 1, wherein the connector portion is embedded in concrete sprayed onto the peripheral wall surface after the next excavation.

Reference Signs List 1...Excavation hole 3...Peripheral wall surface 5...Wire mesh 6...Sprayed concrete 10...Buried cable 10a...Measurement path 10b...Connection path 11...Optical fiber cable 12...Protective member 12a...Twisted string 13...Convex portion 21...Strain measurement section 22...Stress measurement section 100...Stress measurement device

Claims (4)

A method for measuring stress in a tunnel constructed by excavating natural ground, spraying concrete onto a peripheral wall surface of a hole formed therein, and constructing a lining concrete on the inside of the sprayed concrete, comprising the steps of:
a buried cable including an optical fiber cable for guiding incident light and a protective member for protecting the optical fiber cable, the buried cable being extended along the peripheral wall surface;
spraying the sprayed concrete onto the peripheral wall surface so as to bury the buried cable;
Further excavating the natural ground in the vicinity of the sprayed concrete sprayed on the peripheral wall surface;
Measuring the age of the sprayed concrete from the time it was sprayed onto the peripheral wall surface;
Measuring a distribution of strain in the optical fiber cable along an extension direction of the optical fiber cable;
data showing the relationship between stress and strain for the sprayed concrete is stored in advance for each of a plurality of time points from a predetermined early age before the sprayed concrete exhibits its design strength, and a stress distribution in the sprayed concrete sprayed on the peripheral wall surface along the extension direction from the predetermined early age onward is measured based on the strain distribution measurement results and the data;
A stress measurement method comprising: The method further includes erecting a plurality of supports along the peripheral wall surface at positions spaced apart in the excavation direction of the excavation hole before the buried cable is extended;
The extending of the buried cable includes extending the buried cable from one of the left and right side portions of the peripheral wall surface between the adjacent supports to the other of the left and right side portions, and extending the buried cable continuously from the other of the left and right side portions to exceed the face-side support of the adjacent supports to the face side,
The sprayed concrete is sprayed onto the peripheral wall surface to fill the spaces between the adjacent supports and between the supports and the peripheral wall surface, and to expose the tip of the buried cable on the face side, thereby burying most of the buried cable.
The stress measuring method according to claim 1 . The timing of the material age includes detecting that the sprayed concrete has been sprayed onto the peripheral wall surface based on a change in the measurement result of the strain distribution of the optical fiber cable, and starting the timing of the material age from the time of the detection.
The stress measuring method according to claim 1 or 2. The stress measuring method according to claim 1 , wherein the further excavation of the natural ground is performed before the sprayed concrete develops the design strength.