JP7666121B2 - Strain Measurement System - Google Patents

Description

The present invention relates to a strain measurement system that measures strain in steel supports installed inside a tunnel.

In mountain tunnel construction, when the soil cover is thin and the ground strength ratio is low, or when the ground is expansive, large earth pressure may be exerted on the steel supports, so strain measurements (stress measurements) of the steel supports may be carried out to confirm their stability and appropriateness (dimensions, pitch, etc.).

For example, technology is being considered for measuring internal displacement of structures such as tunnels and monitoring deformation of the structures (see, for example, Patent Document 1). In the technology disclosed in this document, one end of a beam that acts as an internal displacement sensor is fixed inside the structure, and a device capable of measuring strain is installed on the surface of the beam, and the vertical and horizontal displacement of the structure is calculated from the measured strain. Then, a strain measuring device acquires a signal from a strain detection device attached to the internal displacement sensor.

Measurement systems for understanding the behavior of tunnel linings during earthquakes in real time are also being considered (see, for example, Patent Document 2). In the tunnel lining behavior measurement system disclosed in this document, a sensor with a strain gauge is placed on the tunnel lining surface, and a wireless transmission device connected to this sensor. Information about the deformation of the tunnel lining surface from the wireless transmission device is received by a wireless receiving device outside the tunnel, and the deformation information of the lining surface is analyzed by a tunnel lining deformation information analysis device.

JP 2013-047629 A JP 2009-300323 A

However, with conventional technology, when measuring strain on steel supports, the strain gauges installed on the steel supports are connected to a data logger by wire. Therefore, in order to start strain measurement, it is necessary to temporarily stop excavation and run cables to the rear where they are not affected by the excavation, so strain measurement cannot start immediately after erecting the steel supports. In addition, because the cables are routed along the side walls, they also need to be protected, which is time-consuming and costly.

In addition, the measured strain data is collected in a data logger at the end of the cable. Therefore, if a large amount of strain occurs, there is a risk that the emergency evacuation command to the tunnel face may be delayed due to the distance between the data logger and the tunnel face.

Furthermore, conventional technology does not measure the distance between the strain measurement point and the tunnel face where excavation progresses day by day. As a result, it was not possible to predict ground behavior in real time.

The present invention was made in consideration of these circumstances, and aims to provide a strain measurement system that resolves the above-mentioned problems, can start measuring strain immediately after the steel support is erected, and can predict ground behavior in real time.

The strain measurement system of the present invention is a strain measurement system that measures strain in steel supports installed in a tunnel, and comprises a strain measuring device that is attached to the steel supports and wirelessly transmits measurement data including measured strain measurement values, and a monitoring device that is installed on a tunnel construction work vehicle working in front of the tunnel face and monitors the strain in the steel supports using the measurement data received from the strain measuring device . The monitoring device is characterized by comprising: a measurement distance estimation unit that estimates the measurement distance to the tunnel face at the time of measurement based on the radio wave intensity at the time the measurement data is received, an unknown quantity estimation unit that estimates the natural ground elastic modulus and initial stress as natural ground characteristics by an inverse analysis method using the strain measurement value and the measurement distance as measurement numbers, and a suitability determination unit that calculates internal displacement and shear stress distribution by forward analysis using the natural ground characteristics, and compares them with control values to confirm the suitability of the support .
Furthermore, in the strain measurement system of the present invention, the monitoring device is provided with a strain monitoring unit that, upon receiving the measurement data, compares it with past measurement data and issues a warning if the change in the strain measurement value exceeds a predetermined danger threshold .
Furthermore , in the strain measurement system of the present invention, the measurement distance estimation unit calculates the measurement distance based on the straight-line distance between the strain measurement device and the monitoring device estimated based on the radio wave intensity at the time the measurement data is received, the straight-line distance between the tunnel face on which the steel support to which the strain measurement device is attached is installed and the monitoring device, and the distance between the face and the monitoring device.

According to the present invention, since no cable wiring or protective work is required to install the strain measuring device, excavation does not need to be stopped in order to install the strain measuring device, and strain measurement and monitoring can be started near the face immediately after the steel support 1 is erected, which has the effect of enabling prediction of ground behavior in real time.

1 is a system configuration diagram showing a configuration of an embodiment of a strain measurement system according to the present invention. 2 is a block diagram showing the configuration of the strain measurement system shown in FIG. 1 . 3 is a diagram showing an analytical model of an unknown quantity estimation operation by the unknown quantity estimation unit shown in FIG. 2 . 3 is an explanatory diagram for explaining a measured distance estimation operation by a measured distance estimation unit shown in FIG. 2 . 3 is a flowchart showing an unknown quantity estimating operation and a compatibility determining operation by an unknown quantity estimating unit and a compatibility determining unit shown in FIG. 2 .

Next, a mode for carrying out the present invention (hereinafter simply referred to as an "embodiment") will be specifically described with reference to the drawings.
Referring to FIG. 1 , the strain measurement system of this embodiment includes a strain measurement device 10 attached to a steel support 1 and a monitoring device 20 installed in a drill jumbo 2 .

The steel support 1 is an arch-shaped steel material used in the New Austrian Tunneling Method (NATM) method for constructing tunnels. In the NATM method, the steel support 1 is erected into the tunnel wall near the tunnel face each time a tunnel is excavated, and the steel support 1 is installed at a preset interval L.

The strain measuring device 10 is attached to the steel support 1 before it is erected, and is installed inside the tunnel when the steel support 1 is erected. In this embodiment, the strain measuring device 10 is attached to three locations on the ceiling surface and both sides of the steel support 1, but there is no particular limit to the locations and number of the strain measuring devices 10 to be attached.

The drill jumbo 2 is a tunnel construction work vehicle that works in front of the tunnel face. Note that the monitoring device 20 may be installed in other tunnel construction work vehicles, such as an erector, instead of the drill jumbo 2.

Referring to FIG. 2, the strain measurement device 10 includes a strain gauge 11, a bridge 12, an amplifier 13, a strain measurement section 14, a measurement result storage section 15, a communication control unit 16, a wireless unit 17, and a battery 18.

The strain gauge 11 is attached to the surface of the steel support 1 and is a sensor whose physical property value (resistance value in this embodiment) changes depending on the stress (strain) applied to the steel support 1. In this embodiment, there are two strain gauges 11, but there is no particular limit to the number of strain gauges 11.

The bridge 12 is a circuit (e.g., a Wheatstone bridge) that uses the strain gauge 11 as a resistor to measure a resistance value corresponding to a change in strain and outputs the resistance value as a strain measurement signal. The strain measurement signal output from the bridge 12 is amplified by the amplifier 13 and input to the strain measurement unit 14.

The strain measurement unit 14 is an information processing unit that operates under program control. The strain measurement unit 14 measures the signal strength of the strain measurement signal input from the bridge 12 via the amplifier 13 as a strain measurement value. In this embodiment, the strain measurement unit 14 measures the strain measurement value at one-minute intervals for 24 hours after the start of the strain measurement device 10, and at ten-minute intervals after 24 hours.

The communication control unit 16 is a control unit that controls wireless communication with the monitoring device 20, and converts the measurement data output from the strain measurement unit 14 into a wireless signal. The wireless unit 17 then transmits a wireless signal of a preset strength via an antenna. In this embodiment, a communication distance of approximately 20 m is ensured by using a frequency in the 920 MHz band.

The strain measurement unit 14 determines whether the communication control unit 16 is in a state where wireless communication with the monitoring device 20 is possible, and if wireless communication with the monitoring device 20 is possible, transmits measurement data consisting of the measured strain measurement value and a unique device ID to the monitoring device 20 via the communication control unit 16 and the wireless unit 17.

When wireless communication with the monitoring device 20 is not possible, the strain measurement unit 14 stores the measured strain measurement value together with timing data indicating the timing of the measurement (time, measurement order, interval, etc.) in the measurement result storage unit 15 composed of a flash memory or the like. Then, when wireless communication with the monitoring device 20 becomes possible, the strain measurement unit 14 transmits measurement data consisting of the strain measurement value and timing data stored in the measurement result storage unit 15, and a unique device ID, to the monitoring device 20.

The battery 18 is a power supply unit that supplies power to each part of the strain measuring device 10, and in this embodiment, has a capacity that can ensure that the measurement and transmission operations of the strain measuring device 10 can continue for more than one month.

The monitoring device 20 includes a wireless unit 21, a communication control unit 22, and an analysis device 30. The wireless signal transmitted from the strain measuring device 10 is received by the wireless unit 21 of the monitoring device 20 via an antenna, and the communication control unit 22 demodulates the wireless signal received by the wireless unit 21 into measurement data. The communication control unit 22 then outputs the demodulated measurement data to the analysis device 30 together with the reception strength when the wireless unit 21 received the wireless signal from the strain measuring device 10.

The monitoring device 20 is installed on the drill jumbo 2 that travels through the mine. Therefore, when the drill jumbo 2 travels through the mine, the monitoring device 20 can receive comprehensive measurement data from the strain measuring device 10 installed in the mine.

The analysis device 30 is an information processing device such as a personal computer, and includes an input unit 31 such as a keyboard, a display unit 32 such as a liquid crystal display, an output unit 33 such as a speaker, a storage unit 34 such as a flash memory, and a control unit 40.

The control unit 40 is an information processing unit such as a microcomputer equipped with a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc. The ROM stores a control program for the analysis device 30 to execute jobs. The control unit 40 reads out the control program stored in the ROM and expands the control program into the RAM, thereby controlling the analysis device 30 and functioning as a measurement device registration acceptance unit 41, a measurement distance estimation unit 42, a strain monitoring unit 43, an unknown quantity estimation unit 44, and a compatibility determination unit 45.

The measuring device registration reception unit 41 receives the device ID of the strain measuring device 10 attached to the erected steel shoring 1, and stores the received device ID as measuring device information 341 that corresponds to the shoring ID of the steel shoring 1 and the installation position (ceiling surface, right side, left side).

When measurement data is input, the measurement distance estimation unit 42 refers to the measurement device information 341 based on the device ID to identify the installation position (ceiling surface, right side, left side) of the strain measurement device 10 that transmitted the measurement data, and estimates the measurement distance d to the face at the time of measurement based on the identified installation position (ceiling surface, right side, left side) and radio wave intensity.

When the measurement data is input, the strain monitoring unit 43 compares it with past measurement data at the installation position identified by the measurement distance estimation unit 42, and if the change in the strain measurement value exceeds a preset danger threshold, a warning is issued from the display unit 32 and output unit 33 to urge the worker to evacuate. This makes it possible to monitor strain in real time and issue a warning when strain increases.

The unknown quantity estimation unit 44 estimates the natural ground elastic modulus E _R and the initial stresses σ _x0 , σ _y0 , and τ _xy0 as natural ground properties by an inverse analysis method using the strain measurement value and the measurement distance d as measurement quantities. The inverse analysis method uses the two-dimensional elastic finite element method. First, using the analysis model shown in Figure 3, the initial stresses per unit σ _x0 , σ _y0 , and τ _xy0 and the natural ground elastic modulus E _R are provisionally set to calculate the strain (hereinafter referred to as unit strain) in advance.

Next, the unknown initial stresses σ _x0 , σ _y0 , τ _xy0 and the natural ground elastic modulus E _R are determined by calculating how many times the measured strain is larger than the previously calculated unit strain. In the analysis model shown in Figure 3, the natural ground is an isotropic elastic body, and the initial natural ground stresses σ _x0 , σ _y0 , τ _xy0 are constant throughout the analysis domain. The actual natural ground behaves inelastically and nonlinearly, but the analysis results are output as equivalent values including these.

The suitability determination unit 45 calculates the internal displacement and shear stress distribution by forward analysis using the natural ground properties estimated by the unknowns estimation unit 44, and checks the suitability of the support by comparing it with the control values.

Next, a method for estimating the measured distance d by the measured distance estimating unit 42 will be described in detail with reference to FIG.
In the measurement distance estimation unit 42, the distance A between the wireless unit 21 (antenna) and the tunnel face (e.g., 8 m when the wireless unit 21 is placed at the center of the tunnel cross section) and the distances C ₁ , C ₂ , C ₃ between the wireless unit 21 (antenna) and the ceiling surface, right side surface, and left side surface, respectively (e.g., tunnel diameter D/2) are set as fixed values.

The measurement distance estimation unit 42 identifies the installation position (ceiling surface, right side, left side) of the strain measurement device 10 that transmitted the measurement data by referring to the measurement device information 341 based on the device ID.

The measurement distance estimation unit 42 also estimates the linear distance r (linear distance r1 if the installation position is on the ceiling surface, linear distance _r2 if the installation position is on the right side surface, and linear distance r3 if the installation position is on the left side surface ₎ from the transmission source strain measurement device ₁₀ based on the reception strength. That is, the measurement distance estimation unit 42 estimates the linear distance r using the property of a wireless signal that attenuates in proportion to the square of the distance.

Then, the measurement distance estimation unit 42 estimates the measurement distance d to the face at the time of measurement using any one of the distances _C1 , _C2 , and _C3 corresponding to the identified installation position, the linear distance r, and the distance A. For example, when the installation position of the strain measurement device 10 is the ceiling surface,
The measured distance d to the face at the time of measurement is estimated by calculating d = √(r ₁ ² - _{C 1} ² ) + A.

Although the distance A between the wireless unit 21 (antenna) and the face and the distances _C1 , _C2 , and _C3 between the wireless unit 21 (antenna) and the ceiling surface, the right side surface, and the left side surface, respectively, are set to fixed values, these may also be measured values measured using a measuring device such as a laser rangefinder.

The estimated measurement distance d is the distance between the steel support 1 to which the strain measuring device 10 is attached and the face, and should be a value if the strain measuring device 10 is attached to the same steel support 1. Therefore, the accuracy can be improved by adjusting (for example, averaging) the measurement distances _d1 of the strain measuring devices _10a1 , _10a2 , and _10a3 attached to the same steel support _1a so that they are the same value.

Furthermore, when the distance L between adjacent steel supports 1 is known, the accuracy can be improved by adjusting (e.g., averaging) the difference between the measured distance _da of the strain measuring devices _10a1 , _10a2 , and _10a3 attached to the steel support _1a and the measured distance _db of the strain measuring devices _10b1 , _10b2 , and _10b3 attached to the steel support _1b so that it becomes distance L.

Next, the unknown quantity estimation method performed by the unknown quantity estimation unit 44 will be described in detail with reference to FIG.
First, the unknown quantity estimation unit 44 receives settings of the Poisson's ratio V _R of the natural ground, the Poisson's ratio V _L of the steel support 1, the vertical stress σ _y0 , and the support elastic modulus E _L of the steel support 1 as known quantities (step S101). The support elastic modulus E _L takes the permeable elastic modulus of the steel support 1 (H-beam) and the shotcrete as input values. The Poisson's ratio V _R of the natural ground is originally an unknown quantity, but a general value (e.g., 0.35) is input to simplify the analysis.

The unknown quantity estimating unit 44 also receives an input of the natural soil elastic modulus E _R , which is an unknown quantity (step S102). This natural soil elastic modulus E _R is used as an initial value for the iterations.

Then, the unknown quantity estimation unit 44 calculates the ratio of the elastic modulus of the natural ground to that of the support, R _i =E _L /E _R (step S103).

Furthermore, when the unknown quantity estimating unit 44 receives the strain measurement value ε _m ' and the measured distance d to the face at the time of measurement as input of the measurement values (step S104), it predicts the converged strain ε _m from the strain characteristic curve (step S105).

The measured strain value ε _m ' is a value based on the time when the steel support 1 was installed. The strain value after convergence ε _m is a value based on the time when excavation began. The strain characteristic curve represents the measured distance d to the face and the ratio of the current strain to the strain after convergence, and is determined from an empirical curve if no excavation data is available. If it is assumed that the stress-strain relationship is linear, the strain characteristic curve can be determined from the internal displacement and the amount of top settlement.

The ground also begins to deform before excavation begins. The strain characteristic curve for the area where the distance to the face is negative can also be determined from advance displacement measurements using advance settlement gauges, ground surface settlement, and three-dimensional analysis. Finally, the internal displacement and shear stress distribution are calculated using the determined ground properties, and the suitability of the support is confirmed based on the control values.

Next, the unknown quantity estimation unit 44 uses the inverse analysis method to calculate the natural ground properties, ie, the natural ground elastic modulus E _R and the initial stresses σ _x0 , σ _y0 , and τ _xy0 , using the following equations (6) and (7), and updates the ratio of the inverse analysis elastic moduli (R _i+1 = E _L /E _R ) (step S106).

To analyze the deformation caused by tunnel excavation using the finite element method, it is necessary to calculate the excavation external force P acting on the inside of the steel support 1 using formula (1). The integral is the volume integral of the natural ground element. Since the initial stresses are all unknowns, the external force components P _i (i = 1 to 3) are calculated using formula (2) when the components σ _x0 , σ _y0 , τ _xy0 of the initial stress σ ₀ are used as units.

In addition, when the stiffness matrices when the natural ground elastic modulus _ER and the support elastic modulus _EL are both 1 are _KR and _KL , the overall stiffness matrix K is expressed by equation (3). In addition, when the elastic modulus ratio of the natural ground to the support is the parameter R = _EL / _ER , equation (3) becomes equation (4).

The finite element method finds the displacement u and strain ε by solving the stiffness equation P = k u. Similarly, the "unit strain" is found by solving K ^* and the external force component P _i . When the strain of the steel support 1 is measured at three points, the relationship with the unit strain at each measurement point is expressed by Equation (5).

The unknown matrix C is found by the least squares method using equation (6). Assuming that the vertical stress σ _y0 is equal to the overburden pressure, it is given by equation (7) from the overburden h and the average unit volume weight of the ground γ. Then, the remaining ground elastic modulus E _R and initial stresses σ _x0 and τ _xy0 are determined. By repeating the above process, the unknowns, the ground elastic modulus E _R and the initial stresses σ _x0 , σ _y0 , and τ _xy0 , converge.

Next, the unknown quantity estimation unit 44 determines whether (R _i+1 −R _i )/R _i is less than a preset allowable error (step S107).

If (R _i+1 -R _i )/R _i is equal to or greater than the allowable error in step S107, the process returns to step S103 and the ratio of the elastic modulus of the ground to the support, R _i =E _L /E _R, is recalculated using the natural ground elastic modulus E _R calculated in step S107.

If (R _i+1 -R _i )/R _i is less than the allowable error in step S107, the compatibility determination unit 45 calculates the inner displacement and shear stress distribution, etc. by direct analysis using the natural ground elastic modulus E _R calculated in step S106 and the initial stresses σ _x0 , σ _y0 , τ _xy0 (step S108).

Then, the suitability determination unit 45 checks the suitability of the support based on whether the calculated internal displacement and shear stress distribution are within the control values or exceed the control values (step S109).

If the internal displacement and shear stress distribution calculated in step S109 are within the control values, the support is confirmed to be suitable and the process ends.

If the internal displacement or shear stress distribution calculated in step S109 exceeds the control value, the support is found to be non-compliant, and the compatibility determination unit 45 issues a warning via the display unit 32 or output unit 33 to encourage the worker to review the support. This allows the worker to detect in advance the risk of a displacement exceeding the allowable value occurring in the future, and to consider installing additional rock bolts or upgrading the steel support 1.

In this way, because the measured strain value ε _m ' before convergence is used as the input value, the deformation behavior of the ground can be captured at a relatively early stage and reflected in the back analysis. Also, since there are no limitations to the analysis model if it is elastic, it is easy to devise measures such as increasing the number of known physical properties. Furthermore, accuracy can be improved by correcting the strain characteristic curve based on excavation results.

As described above, this embodiment is a strain measurement system that measures strain in a steel support 1 installed in a tunnel, and comprises a strain measuring device 10 that is attached to the steel support 1 and wirelessly transmits measurement data including the measured strain measurement value ε _m ', and a monitoring device 20 that is installed on a drill jumbo 2, a tunnel construction work vehicle that works in front of the tunnel face, and monitors the strain in the steel support 1 using the measurement data received from the strain measuring device 10.
With this configuration, no cable wiring or protective work is required to install the strain measuring device 10, so excavation does not need to be stopped in order to install the strain measuring device 10, and strain measurement and monitoring can be started near the face immediately after the steel support 1 is erected. The measurement data is then collected in real time by the monitoring device 20 installed in the drill jumbo 2. Since the system can be configured with only the strain measuring device 10 as a transmitter and the monitoring device 20 as a receiver, ground behavior can be predicted in real time without adding a new network inside the tunnel.

Furthermore, in this embodiment, the monitoring device 20 includes a strain monitoring unit 43 that, upon receiving measurement data, compares the received measurement data with past measurement data and issues a warning if the amount of change in the strain measurement value ε _m ′ exceeds a preset danger threshold.
With this configuration, if an increase in strain occurs, an emergency evacuation order can be quickly issued to face workers.

Furthermore, in this embodiment, the monitoring device 20 is equipped with a measurement distance estimation unit 42 that estimates the measurement distance d to the face at the time of measurement based on the radio wave intensity when the measurement data is received, an unknown quantity estimation unit 44 that estimates the ground elasticity coefficient E _R and initial stresses σ _x0 , σ _y0 , τ _xy0 as ground characteristics by an inverse analysis method using the strain measurement value _ε m ' and the measurement distance d as measurement numbers, and a suitability determination unit 45 that calculates internal displacement and shear stress distribution by forward analysis using the estimated ground characteristics and compares them with control values to confirm the suitability of the support.
This configuration makes it possible to capture the deformation behavior of the ground at a relatively early stage and reflect it in the back analysis.

Furthermore, in this embodiment, the measurement distance estimation unit 42 calculates the measurement distance d based on the linear distance r between the strain measuring device and the monitoring device 20, which is estimated based on the radio wave intensity when the measurement data is received, the linear distance C between the tunnel face (mounting position) on which the steel support 1 to which the strain measuring device 10 is attached is installed and the monitoring device 20, and the distance A between the face and the monitoring device 20.

The present invention has been described above based on an embodiment. This embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible in terms of the combination of each component, and that such modifications are also within the scope of the present invention.

REFERENCE SIGNS LIST 1 Steel support 2 Drill jumbo 10 Strain measurement device 11 Strain gauge 12 Bridge 13 Amplifier 14 Strain measurement section 15 Measurement result memory section 16 Communication control unit 17 Wireless unit 18 Battery 20 Monitoring device 21 Wireless unit 22 Communication control unit 30 Analysis device 31 Input section 32 Display section 33 Output section 34 Memory section 40 Control section 41 Measurement device registration reception section 42 Measurement distance estimation section 43 Strain monitoring section 44 Unknown quantity estimation section 45 Conformity determination section 341 Measurement device information

Claims (3)

A strain measurement system for measuring strain in a steel support structure installed in a tunnel,
A strain measuring device that is attached to the steel support and wirelessly transmits measurement data including a measured strain measurement value;
A monitoring device is installed on a tunnel construction vehicle working in front of the tunnel face and monitors the strain of the steel support structure using the measurement data received from the strain measuring device .
The monitoring device includes a measurement distance estimation unit that estimates a measurement distance to a face at the time of measurement based on radio wave intensity at the time of receiving the measurement data;
an unknown quantity estimation unit that estimates a natural ground elastic modulus and an initial stress as natural ground characteristics by an inverse analysis method using the strain measurement value and the measured distance as measurement quantities;
A strain measurement system characterized by comprising a suitability determination unit that calculates internal displacement and shear stress distribution by direct analysis using the ground characteristics and compares them with control values to confirm the suitability of the support structure . The strain measurement system according to claim 1, characterized in that the monitoring device is provided with a strain monitoring unit that, upon receiving the measurement data, compares the received measurement data with past measurement data and issues a warning if the amount of change in the strain measurement value exceeds a preset danger threshold. The strain measurement system described in claim 1, characterized in that the measurement distance estimation unit calculates the measurement distance based on the straight-line distance between the strain measuring device and the monitoring device estimated based on the radio wave intensity at the time the measurement data is received, the straight-line distance between the tunnel face on which the steel support to which the strain measuring device is attached is installed and the monitoring device, and the distance between the face and the monitoring device.

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