JP7683151B2 - Tunnel construction management method and construction management system - Google Patents

Description

The present invention relates to a tunnel construction management method and construction management system.

In the construction of mountain tunnels, it is common to carry out underground measurements to grasp the characteristics (or condition, behavior, etc.) of the ground, such as visually observing the tunnel face and measuring the deformation or stress state of the supports and the ground.
Control standards for underground displacement (or support displacement) are set in advance, and the measured values are compared with the control standards to determine whether the rigidity and strength of the current support is adequate and whether additional measures are necessary.
Here, the conventional method for setting control standard values is generally to use the direct strain method (or limit strain method). This method determines the limit strain based on the deformation modulus and uniaxial compressive strength of the natural ground, and sets the control standard value based on this limit strain. The limit strain is the strain that corresponds to the slope of the initial elastic modulus of the stress-strain curve obtained from the uniaxial compressive strength test of the rock core, and the uniaxial compressive strength. Therefore, the limit strain is defined as the strain that corresponds to the fracture stress of the natural ground, that is, the strain when the natural ground changes from a stable state to an unstable state. However, there are various issues with the method for setting control standard values using the direct strain method.

First, the relationship between the uniaxial compressive strength (deformation coefficient) of the rock core and the limit strain is obtained using a regression equation, but the properties of the rock core and the actual ground are not necessarily the same. Since the actual ground contains a number of discontinuous surfaces such as cracks and fissures, the properties of the rock core are significantly different, and the "limit strain of the rock core" and the "limit strain of the ground" are not equal.
Secondly, the uniaxial compressive strength and deformation coefficient of the natural ground cannot always be evaluated appropriately on-site. Currently, the limit strain is calculated based on the uniaxial compressive strength (deformation coefficient) recorded in the results of a prior geological survey, so there is a high possibility that the assumed uniaxial compressive strength (deformation coefficient) will differ from the actual natural ground, which may lead to a decrease in the reliability of the set management standard values.
Next, the control standard values set using the direct strain method are intended to ensure the stability of the ground based on limit strain, and are not intended to evaluate the soundness of the supports supporting the tunnel.
Next, the control standard values are generally set in three stages, control levels I to III, and the control standard value for control level III is set to the displacement equivalent to the limit strain (sometimes a predicted value from FEM (Finite Element Method) analysis, etc.), and the control standard values for levels I and II are often set to 50% and 75% of level III, respectively. However, in this management system, when the displacement exceeds the control standard value, countermeasures are taken according to each management level, making it necessary to take emergency measures. Therefore, in reality, construction is carried out while monitoring the increase in displacement, and emergency measures are taken when control level III is exceeded, and it is difficult to say that this is a construction management method that fully guarantees construction safety.

For these reasons, instead of construction management methods based on control standard values set by the direct strain method, a construction management method based on control standard values that can evaluate the soundness of the support structure is desirable.

Here, Patent Document 1 proposes a tunnel construction management method in which drilling surveys are carried out ahead of the excavation direction of the tunnel face to evaluate the ground in the area where supports are to be constructed, a support structure suitable for the surveyed section surveyed by drilling survey is set, and suitable supports are constructed. Specifically, the method includes a support structure setting process for setting a support structure according to the initial stress of the ground based on the natural ground elastic modulus corresponding to the drilling energy measured by performing a drilling survey of the ground ahead of the excavation direction of the tunnel face and the displacement after construction of the support constructed behind the tunnel face; a support construction process for constructing the support of the support structure set by the support structure setting process on the excavation wall surface of the ground excavated in the survey section where the drilling survey was performed; a judgment process for measuring the displacement of the support constructed by the support construction process, predicting the amount of displacement of the support over time based on the measurement results, and judging whether the support structure of the support was appropriate; and a support structure correction process for reviewing the correspondence between the drilling energy and the natural ground elastic modulus in the support structure setting process if the judgment process judges that the support structure was not appropriate.

JP 2011-52373 A

The tunnel construction management method described in Patent Document 1 is not a construction management method based on a management standard value that uses the presence or absence of deformation of the support structure as an indicator, but rather sets the support structure based on the results of drilling exploration of the natural ground, and is therefore not significantly different from conventional construction management methods based on management standard values set using the above-mentioned direct strain method.

The present invention aims to provide a tunnel construction management method and construction management system based on management standard values that can evaluate the soundness of support structures.

In order to achieve the above object, one aspect of the tunnel construction management method according to the present invention comprises:
A tunnel construction management method for performing construction management based on the displacement of a support structure when constructing a tunnel by repeatedly excavating the tunnel and installing a support structure, comprising:
Step A is to set the allowable strain when the support is damaged based on a number of tunnel construction cases in which damage to the support has been confirmed;
A process B of multiplying the allowable strain by the excavation radius of the tunnel to be managed to set a management reference value for the support;
A step C of measuring the displacement amount as the tunnel is excavated;
The method is characterized by having a step D of comparing the control standard value with the measured value to determine whether the support structure is suitable.

According to this aspect, the allowable strain when the shoring is damaged is set based on multiple tunnel construction cases in which damage to the shoring has been confirmed, and the control standard value for the shoring is set by multiplying the allowable strain by the excavation radius of the tunnel to be managed, thereby making it possible to set a control standard value that can evaluate the soundness of the shoring, reflecting the strain when the shoring is damaged and the size (excavation radius) of the tunnel to be managed.
The soundness of the support can be properly evaluated by comparing this control standard value with the measured value of the amount of displacement of the support associated with the excavation of the tunnel to determine whether the support is suitable or not.

Here, "multiple tunnel construction examples" includes not only the past tunnel construction records held by construction companies, but also tunnel construction examples in which damage to supports has been confirmed and published by the Japan Tunnelling Association, the Japan Society of Civil Engineers, etc.
In addition, "shoring" includes sprayed concrete, steel shoring, rock bolts, etc., and "damage to shoring" includes cracks or spalling of sprayed concrete, deformation or buckling of steel shoring, deformation of rock bolt washers, and breakage of rock bolts.

In another aspect of the tunnel construction management method according to the present invention,
In the step A, the amount of displacement when the support is damaged is divided by the excavation radius of the tunnel, and then corrected by a predetermined safety factor to obtain the allowable strain.

According to this aspect, when setting the allowable strain that serves as the basis for the control standard value, the amount of displacement when the support is damaged is divided by the excavation radius of the tunnel to be managed, and then corrected with a specified safety factor to obtain the allowable strain, making it possible to set a safe control standard value.

In another aspect of the tunnel construction management method according to the present invention,
The process A is characterized in that the strain of the support when damaged is set to 2% or less.

According to this embodiment, by setting the strain when the shoring is damaged (displacement of the shoring (or tunnel wall)/tunnel excavation radius) to 2% or less, a highly accurate management standard value based on tunnel construction examples can be set. According to the inventors, as a result of examining many past tunnel construction examples, it has been determined that the strain when deformation occurs in the shoring is approximately 1 to 2%.
Based on the results of this verification, a dangerous control standard value based on tunnel construction examples can be set by setting the allowable strain at 2%, and a safe control standard value based on tunnel construction examples can be set by setting the allowable strain at 1%, and a safer control standard value can be set by taking into account a further safety factor for a strain of, for example, 1%. Here, the safety factor can be set to about 1.1 to 1.5, and for example, when a safety factor of 1.25 is taken into account for a strain of 1%, the allowable strain is set to 0.8%.

In another aspect of the tunnel construction management method according to the present invention,
In the step A, based on the tunnel construction examples, each initial displacement amount measured for each of a plurality of excavation stages from a reference position is set as the displacement amount, and based on the final displacement amount converged at the reference position as the tunnel is excavated and the initial displacement amount for each of the plurality of excavation stages, a relation coefficient between the final displacement amount and the initial displacement amount is set for each of the plurality of excavation stages;
In the step B, the allowable strain is multiplied by the excavation radius of the tunnel for each of a plurality of excavation stages, and then corrected by the relation coefficient to set the control reference value for each of a plurality of excavation stages;
In the C step, a measurement value related to the displacement is measured for each of a plurality of excavation stages,
The D step is characterized in that the control standard values and the measured values are compared for each of a plurality of excavation stages to determine whether the support is adequate.

According to this aspect, based on tunnel construction examples, a relationship coefficient is set between the initial displacement amount from the reference position for each of the multiple excavation stages and the final displacement amount at the reference position, and for each excavation stage, the value obtained by multiplying the allowable strain by the excavation radius of the tunnel is corrected with the relationship coefficient to set a control standard value for each of the multiple excavation stages, and construction management for each excavation stage is performed based on this control standard value, thereby making it possible to realize construction management with even higher construction safety.
Here, "correction using a relationship coefficient" includes a form of correction by multiplication by the relationship coefficient and a form of correction by division by the relationship coefficient.
In addition, "multiple excavation stages" include the first excavation of about 1 m (1 excavation), 0.5D excavation, 1D excavation, 2D excavation, etc., when the excavation diameter is D. In general, it is specified that the displacement of the tunnel wall surface (or the displacement of the support) at the reference position converges at about 2D excavation from the reference position, so it is good to set multiple excavation stages (excavation stages) up to about 2D excavation. In more detail, it is specified that at the stage when the face is constructed at the reference position, about 40% of the total stress is released at the reference position, and therefore, at the stage of excavation of about 2D from the reference position, a displacement equivalent to 60% of the total stress occurs.

In another aspect of the tunnel construction management method according to the present invention,
In the step A, the relationship coefficient is obtained by regression analysis.

According to this embodiment, by determining the relationship coefficient through regression analysis, it is possible to set the relationship coefficient based on multiple tunnel construction cases and the management standard value for each excavation stage based on this with high accuracy.

In addition, one aspect of the tunnel construction management system according to the present invention is
A tunnel construction management system that performs construction management based on the displacement of a support structure when constructing a tunnel by repeatedly excavating the tunnel and installing a support structure, comprising:
A setting evaluation device;
a measuring device that measures the amount of displacement as the tunnel is excavated to obtain a measurement value;
The setting evaluation device includes:
A storage unit that stores at least a plurality of tunnel construction examples in which damage to supports has been confirmed and a support table in which the plurality of supports are classified according to their rigidity;
an allowable strain setting unit that sets an allowable strain when the support is damaged based on a plurality of tunnel construction examples in the storage unit;
a control standard value setting unit that sets a control standard value of the support by multiplying the allowable strain by an excavation radius of a tunnel to be managed;
The present invention is characterized by having a support evaluation unit that compares the management standard value with the measurement value, extracts the currently set support from the support table, and determines whether the support is appropriate.

According to this aspect, the allowable strain setting unit sets the allowable strain when the shoring is damaged based on multiple tunnel construction cases, and the control reference value setting unit sets the control reference value for the shoring by multiplying the allowable strain by the excavation radius of the tunnel to be managed, thereby making it possible to set a control reference value that reflects the strain when the shoring is damaged and the scale of the tunnel to be managed and that can evaluate the soundness of the shoring.The soundness of the shoring can be properly evaluated by comparing this control reference value with the measured value related to the amount of displacement of the shoring associated with the excavation of the tunnel to determine whether the currently set shoring is appropriate.
Here, in the "support table classifying multiple supports according to their rigidity", support patterns such as B, CI, CII, DI, DII, etc. corresponding to the ground class are set, and for each support pattern, the thickness of the sprayed concrete, the specifications and erection intervals of the steel supports, the length and number of rock bolts, the circumferential spacing, the extension spacing, etc. are set.

In another aspect of the tunnel construction management system according to the present invention,
In the allowable strain setting unit, based on the tunnel construction examples, each initial displacement amount measured for each of a plurality of excavation stages from a reference position is set as the displacement amount, and based on the final displacement amount that converges at the reference position as the tunnel is excavated and the initial displacement amount for each of the plurality of excavation stages, a relation coefficient between the final displacement amount and the initial displacement amount is set for each of the plurality of excavation stages;
the control reference value setting unit sets the control reference value by correcting a value obtained by multiplying the allowable strain by the excavation radius of the tunnel with the relation coefficient for each of a plurality of excavation stages;
The storage unit stores the measurement values regarding the displacement amount for each of a plurality of excavation stages,
The support evaluation unit is characterized in that the control standard values and the measured values are compared for each of a plurality of excavation stages to determine whether the support is adequate.

According to this aspect, the allowable strain setting unit sets a relationship coefficient between the initial displacement amount from the reference position for each of multiple excavation stages and the final displacement amount at the reference position based on tunnel construction examples, the control standard value setting unit corrects the value obtained by multiplying the allowable strain by the tunnel excavation radius for each excavation stage using the relationship coefficient to set the control standard value for each of multiple excavation stages, and the support evaluation unit performs construction management for each excavation stage based on the control standard value for each excavation stage, thereby achieving construction management with even higher construction safety.

The tunnel construction management method and construction management system of the present invention allow the soundness of the support to be properly evaluated based on the management standard values that can evaluate the soundness of the support.

1 is an overall configuration diagram showing an example of a tunnel construction management system according to an embodiment. FIG. FIG. 2 is a diagram illustrating an example of a hardware configuration of a computer constituting a construction management system. FIG. 2 is a diagram illustrating an example of a functional configuration of a setting evaluation device constituting the construction management system. This is an example of a tunnel construction example, and is a table summarizing construction examples based on past construction results. 13 is another example of tunnel construction examples, which is a table summarizing construction examples described in publicly known documents. This is a frequency distribution diagram of strain related to the settlement of the tunnel top based on a tunnel construction example. This is a frequency distribution diagram of strain related to the internal displacement of a tunnel x 1/2, based on a tunnel construction example. FIG. 6C is a frequency distribution diagram of the average values of FIG. 6A and FIG. 6B. FIG. 1 is a distribution diagram showing the relationship between circumferential strain and tunnel radius based on tunnel construction examples. This is a distribution diagram showing the relationship between circumferential strain and sprayed concrete thickness based on a tunnel construction example. 7A and 7B, this is a distribution diagram showing the relationship between circumferential strain and the equivalent thickness of the shotcrete based on a tunnel radius of 5 m. This is a distribution diagram showing the relationship between circumferential strain and earth covering based on a tunnel construction example. This is a graph explaining a method for determining the support yield stress based on a ground characteristic curve using a circular hole theoretical solution and a support characteristic curve based on the support specifications at the time of deformation. FIG. 9 is a diagram showing an example of application of the graph shown in FIG. 8 to the No. 1 A tunnel in the table of FIG. 4 . 11 is a graph illustrating the relationship between the initial displacement and the final displacement at the reference position. FIG. 13 is a diagram showing regression lines determined by simple regression analysis from the relationship between initial strain and final strain for each of a number of excavation stages. FIG. 13 is an example of a control graph in which control reference values and measurement values set for multiple excavation stages are plotted, showing a case in which all measurement values are below the control reference values. FIG. 13 is an example of a control graph in which control reference values and measurement values set for multiple excavation stages are plotted, showing a case in which the measurement value exceeds the control reference value. 1 is a flowchart of an example of a tunnel construction management method according to an embodiment.

Below, the tunnel construction management system and construction management method according to the embodiment will be described with reference to the attached drawings. Note that in this specification and the drawings, substantially identical components may be designated by the same reference numerals to avoid redundant explanation.

[Embodiment]
<Tunnel construction management system>
First, an example of a tunnel construction management system according to an embodiment will be described with reference to Fig. 1 to Fig. 12. Fig. 1 is an overall configuration diagram showing an example of a tunnel construction management system according to an embodiment. Fig. 2 is a diagram showing an example of a hardware configuration of a computer constituting the construction management system, and Fig. 3 is a diagram showing an example of a functional configuration of a setting evaluation device constituting the construction management system.

The tunnel construction management system 100 is a construction management system that manages construction based on the amount of displacement of supports when constructing a tunnel by repeatedly excavating the tunnel and installing supports.

The construction management system 100 has a measuring device 10 and a setting evaluation device 20 that measure the amount of displacement of the support structure as the tunnel is excavated and obtains measurement values. The construction management system 100 shown in the figure is configured such that the measuring device 10 and the setting evaluation device 20 are connected via a network 30 so that they can send and receive measurement data. Here, the measuring device 10 and the setting evaluation device 20 may not be connected via the network 30 and may send and receive data via a wired connection.

Examples of the measuring device 10 include measuring instruments such as a three-dimensional laser measuring device and a total station, as well as a digital camera with a strobe. When using a digital camera, a digital photo measurement method is applied in which a reflector is attached to the side of the support structure and displacement is measured based on the captured image data.

The setting evaluation device 20 has various functions as shown in FIG. 3, which are described in detail below. Both the measurement device 10 and the setting evaluation device 20 are configured using computers, but the following explanation referring to FIG. 2 focuses on the setting evaluation device 20.

The personal computer constituting the setting evaluation device 20 includes a CPU (Central Processing Unit) 21, a main memory device 22, an auxiliary memory device 23, a communication IF 24, and an input/output IF (interface) 25, which are interconnected by a connection bus 26. The main memory device 22 and the auxiliary memory device 23 are computer-readable recording media. Note that each of the above components may be provided separately, or some of the components may not be provided.

The CPU 21 is also called an MPU (Microprocessor) or a processor, and may be a single processor or a multiprocessor. The CPU 21 is a central processing unit that performs overall control of the setting evaluation device 20. The CPU 21 provides functions that meet a specified purpose, for example, by expanding a program stored in the auxiliary storage device 23 in an executable manner in the working area of the main storage device 22, and controlling peripheral devices through the execution of the program.

The main memory device 22 stores the computer programs executed by the CPU 21, the data processed by the CPU 21, etc. The main memory device 22 includes, for example, a flash memory, a RAM (Random Access Memory), and a ROM (Read Only Memory). The auxiliary memory device 23 stores various programs and various data in a readable and writable recording medium, and is also called an external memory device. The auxiliary memory device 23 stores, for example, an OS (Operating System), various programs, various tables, etc. The OS includes, for example, a communication interface program that transfers data with external devices connected via the communication IF 24. External devices for the setting evaluation device 20 include the measurement device 10, a host computer in the department to which the measurer belongs, and smartphones and tablets carried by other measurers, etc.

The auxiliary storage device 23 is used, for example, as a storage area that supports the main storage device 22, and stores computer programs executed by the CPU 21, data processed by the CPU 21, etc. The auxiliary storage device 23 is a silicon disk including a non-volatile semiconductor memory (flash memory, EPROM (Erasable Programmable ROM)), a hard disk drive (HDD: Hard Disk Drive) device, a solid state drive device, etc. Examples of the auxiliary storage device 23 include drives for removable recording media such as CD drives, DVD drives, and BD drives, and examples of removable recording media include CDs, DVDs, BDs, USB (Universal Serial Bus) memories, and SD (Secure Digital) memory cards, etc.

The input/output IF 25 is an interface that inputs and outputs data between devices connected to the setting evaluation device 20. For example, input devices such as a keyboard, a pointing device such as a touch panel or a mouse, and a microphone are connected to the input/output IF 25. The setting evaluation device 20 receives operation instructions, etc. from an operator who operates the input device via the input/output IF 25.

The input/output IF 25 is also connected to display devices such as liquid crystal displays (LCDs) and organic electroluminescence (EL) panels, as well as output devices such as printers and speakers. The setting evaluation device 20 is configured to continually display the management reference values for each of the multiple excavation stages and the measured values relating to the displacement of the support structure.

The communication IF 24 is an interface with the network to which the setting evaluation device 20 is connected. The communication IF 24 receives the measurement value by the measurement device 10 via various networks such as a public network such as the Internet, a wireless network such as a mobile phone network, a dedicated network such as a VPN (Virtual Private Network), and a LAN (Local Area Network), and transmits management data indicating the management reference value and the measurement value to a host computer, etc. Here, an LPWA wireless communication module and a communication antenna, etc. may be connected to the communication IF 24. The LPWA wireless communication module is a device that realizes LPWA wireless communication (wireless transmission), and is, for example, an electronic component in which a wireless chip and a peripheral circuit are mounted on a small board. The main communication methods (communication protocols) of LPWA include Sigfox, LoRaWAN (Long Range Wide Area Network), NB-IoT, etc., but it is preferable to apply LoRaWAN, which does not require a license, can install a self-operated base station in a mine even in mountainous areas where mobile phone communication waves are difficult to reach, and can build a low-cost communication system. LoRaWAN is a communication method that uses the 920MHz ISM band and employs LoRa modulation, enabling long-distance communication even with low output of 13dBm or less.

As shown in FIG. 3, the setting evaluation device 20 provides various functions, at least a communication unit 202, an allowable strain setting unit 204, a management reference value setting unit 206, a support evaluation unit 208, a display unit 210, and a storage unit 212, by executing a program by a CPU 21. Here, at least a part of the above processing functions may be provided by a DSP (Digital Signal Processor), a GPU (Graphics Processing Unit), etc., and similarly, at least a part of the above processing functions may be a dedicated LSI (large scale integration) such as an FPGA (Field-Programmable Gate Array), a numerical calculation processor, an image processing processor, or other digital circuit, etc.

The communication unit 202 receives the displacement measurement data (measurement values) of the support structure sent from the measuring device 10 at any time and stores it in the storage unit 212 at any time.

Storage section 212 stores multiple tunnel construction cases in which damage to shoring has been confirmed. Storage section 212 also stores a shoring table that classifies multiple shoring according to their rigidity.

Here, Figures 4 and 5 show examples of tunnel construction examples. More specifically, Figure 4 is a table summarizing construction examples based on past construction results, and Figure 5 is a table summarizing construction examples described in publicly known documents.

Figure 4 shows the soil cover, geology, deformation position of support members (shoring), face separation, tunnel conversion radius (for example, the radius when a horseshoe-shaped tunnel is simulated as a circle), support pattern (shoring pattern) at the time of deformation, and measured displacement for 26 cases from A tunnel to Z tunnel, and the "circumferential strain" in the right column is calculated from the tunnel conversion radius and measured displacement. In this specification, "circumferential strain" refers to the radial strain at multiple points around the circumference of the tunnel (top, inner space, wall surface). There are other construction examples based on construction performance compiled by the inventors other than the example shown in Figure 4, but Figure 4 shows one example.

The method for calculating the circumferential strain: εt (%) is to divide the measured displacement of the tunnel (radial displacement): Ur (m) by the tunnel excavation radius (or converted radius, in m): R, and multiply it by 100.

On the other hand, Figure 5 shows 15 examples from the Japan Tunneling Association's Tunnels and Underground, January 2000 issue to December 2017 issue (total 216 volumes) as literature, and in principle shows the same information as Figure 4 (information other than circumferential strain). Here, in addition to the examples shown in Figure 5, construction examples described in publicly available literature compiled by the inventors include those described in the Japan Society of Civil Engineers: Tunnel Engineering Research Presentations, Papers and Reports, 1991 to 2020 (total 20 volumes), Japan Tunneling Association: Construction Experience Presentations, 2000 to 2019 (total 20 volumes), etc.

The inventors have determined the frequency distribution of strain related to the amount of displacement of the tunnel support, including the construction examples shown in Figures 4 and 5 and other construction examples not shown, and the results are shown in Figures 6A to 6C. Here, Figure 6A is a frequency distribution diagram of strain related to the amount of settlement of the top of the tunnel based on the tunnel construction examples, Figure 6B is a frequency distribution diagram of strain related to the amount of internal displacement of the tunnel x 1/2, and Figure 6C is a frequency distribution diagram of the average value of Figures 6A and 6B.

The percentages in each figure indicate the frequency of each strain range relative to the total number of surveys. As shown in Figures 6A and 6B, strains due to crown settlement or internal displacement x 1/2 are mostly distributed in the range of 2.0% or less, accounting for 87.5% of the total number of surveys in the former and 91.1% in the latter. Therefore, regardless of differences in deformation mode, such as when crown settlement or internal displacement is predominant, it is presumed that deformation occurs in the support at a strain level of 2% or less. In addition, since the average values of strains in the range of 2% or less in Figures 6A to 6C are 0.81%, 1.02%, and 0.97%, respectively, it can be evaluated that deformation occurs in the support at a strain of approximately 1%.

Next, the analysis results of the relationship between the strain when deformation of the support occurs and three items: (1) tunnel radius, (2) thickness of the shotcrete, and (3) earth covering are shown in Figures 7A to 7D. Here, Figure 7A is a distribution diagram showing the relationship between circumferential strain and tunnel radius based on a tunnel construction example, Figure 7B is a distribution diagram showing the relationship between circumferential strain and thickness of the shotcrete, and Figure 7C is a distribution diagram showing the relationship between circumferential strain and the equivalent thickness of the shotcrete based on a tunnel radius of 5 m based on Figures 7A and 7B. Also, Figure 7D is a distribution diagram showing the relationship between circumferential strain and earth covering based on a tunnel construction example.

Figure 7A shows that for any tunnel radius, the strain caused by deformation of the support is mostly distributed in the range of around 1% to 2%.

Figure 7B also shows that the thickness of the sprayed concrete is in the range of 100 mm to 300 mm, and that the strain caused by deformation of the support is mostly distributed in the range of around 1% to 2%, regardless of the thickness of the sprayed concrete.

Here, since the results of FIG. 7B also include the effect of the tunnel radius, this effect is removed by the following method, and the relationship between the shotcrete thickness and the strain is rearranged. Specifically, the shotcrete thickness of all deformation cases is obtained as a converted thickness based on a tunnel radius of 5 m. The ring stiffness Kc (MPa) of the shotcrete can theoretically be expressed as Kc = Ectc / (1 - νc ² ) / R (Ec: elastic modulus of the shotcrete (MPa), tc: thickness of the shotcrete (m), νc: Poisson's ratio of the shotcrete, R: tunnel excavation radius (m)), where Kc is proportional to the shotcrete thickness and inversely proportional to the tunnel radius. The shotcrete thickness tc of all deformation cases is divided by the tunnel radius R and further multiplied by the radius of 5 m to obtain the converted thickness based on a tunnel radius of 5 m. FIG. 7C shows the relationship between the strain and this converted thickness.

From Figure 7C, it can be seen that the strain caused by deformation of the support is mostly distributed in the range of 100mm to 250mm equivalent thickness, and is around 1% to 2% regardless of the equivalent thickness. Since a sprayed concrete thickness of 100mm to 250mm corresponds to the thickness generally set as the standard support pattern, it is inferred that some kind of deformation will occur in the support member when a strain of around 1% to 2% occurs, regardless of the rank of the standard support pattern (or the size of the sprayed concrete thickness). Therefore, a strain value of around 1% to 2% can be used as a suitable index range for evaluating the stability of the support structure.

Finally, Figure 7D shows that the strain caused by deformation of the support is mostly distributed in the range of about 1% to 2%, with no bias in distribution due to the amount of soil cover. Therefore, regardless of the amount of soil cover, if the strain occurs at about 1% to 2%, it can be inferred that some kind of deformation will occur in the support member.

Here, we will look at examples of support deformation using theoretical calculations, with reference to Figure 8. Figure 8 is a graph that explains how to determine the support yield stress based on the natural ground characteristic curve using the circular hole theoretical solution and the support characteristic curve based on the support specifications at the time the deformation occurred.

Factors that affect tunnel deformation include soil overburden (initial ground pressure) and the physical properties of the ground related to the geology and ground characteristics (deformation coefficient, strength constant, etc.), but as discussed with reference to Figure 7D, in past construction records, deformations have been observed in support components regardless of the amount of soil overburden. Therefore, focusing on the deformation coefficient, one of the physical properties of the ground, we estimate the stress generated in the supports based on a circular hole theoretical solution that represents tunnel excavation for tunnels where examples of support deformation have been investigated.

The deformation coefficient of the ground is set to an arbitrary value, and the ground characteristic curve is drawn using the circular hole theory solution. Here, the ground characteristic curve is determined by the following parameters. In other words, these parameters include the tunnel excavation radius, soil cover, unit volume weight of the ground, deformation coefficient, and Poisson's ratio.

Next, a support characteristic curve is drawn based on the specifications of the support components at the time the deformation occurred. The slope of the support characteristic curve and the stress value at yield are determined by the following parameters. That is, these parameters include: shotcrete: tunnel excavation radius, elastic modulus, thickness, design strength; steel support: tunnel excavation radius, elastic modulus, cross-sectional area, pitch, yield strength. Rock bolts are not taken into consideration as they do not contribute to deformation suppression more than shotcrete and steel support.

Next, since the amount of displacement that occurs from when the support characteristic curve is drawn until it intersects with the ground characteristic curve (the point where the "stress and displacement" of the "ground and support" are balanced) corresponds to the amount of measured displacement, the ground deformation coefficient (ground characteristic curve) is repeatedly changed until this amount of displacement becomes equal to the amount of displacement when the deformation occurred, thereby estimating the ground deformation coefficient.

Next, the intersection point (the balance point of stress and displacement) between the natural ground characteristic curve and the support characteristic curve is found, and the stress generated in the support at the balance point is compared with the strength of the support structure.

Figure 9 shows the results of verifying examples of support deformation using theoretical calculations for tunnel No. 1 A in the table in Figure 4.

From Figure 9, it can be confirmed that the stress generated in the sprayed concrete and the steel support exceeded the design standard strength or yield strength, respectively, and that a stress equivalent to or greater than the stress that would cause deformation in the support had occurred. Although not shown, the inventors performed a similar verification in the other tunnels shown in Figure 4, and obtained similar results. Therefore, the post-verification using the theoretical solution provides evidence that deformation had occurred in the support, as in the case of the investigation. It was also confirmed that the estimated deformation coefficient of the ground varied from tunnel to tunnel. From this, it can be inferred that, regardless of the magnitude of the deformation coefficient, when a strain of around 1% to 2% occurs, some kind of deformation will occur in the support members.

Returning to FIG. 3, based on the various considerations described above, the allowable strain setting unit 204 sets the allowable strain when the support is damaged in the range of 1% to 2%. Here, by setting the allowable strain to 2%, a dangerous management standard value based on tunnel construction examples can be set, and by setting the allowable strain to 1%, a safe management standard value based on tunnel construction examples can be set. The allowable strain setting unit 204 may automatically set an appropriate allowable strain for the tunnel to be managed in the range of about 1% to 2%, or the allowable strain set by the construction manager or the like in the range of about 1% to 2% may be input to the allowable strain setting unit 204.

It is also possible to allow for a safety factor of, for example, 1% strain, and by allowing for a safety factor, a safer control standard value can be set. Here, the safety factor can be set to approximately 1.1 to 1.5, and for example, if a safety factor of 1.25 is allowed for 1% strain, the allowable strain is set to 0.8%.

The management standard value setting unit 206 sets the management standard value for the support by multiplying the allowable strain set in the allowable strain setting unit 204 by the excavation radius of the tunnel to be managed.

Here, regarding the setting of the control standard values for the shoring, setting control standard values for each of the multiple excavation stages can lead to an even more reliable evaluation of the soundness of the shoring. Here, referring to Figures 10 and 11, we will consider the displacement of the ground at the shoring (or tunnel wall) according to the excavation stage. Figure 10 is a graph explaining the relationship between the initial displacement and the final displacement at the reference position, and is a conceptual diagram showing the displacement occurrence state during the tunnel excavation process. Also, Figure 11 is a diagram showing the regression line identified by simple regression analysis from the relationship between the initial strain and the final strain for each of the multiple excavation stages.

When predicting the final displacement (amount) from the initial displacement (amount) at any reference position according to the tunnel excavation, the relationship between the initial displacement and the final displacement is estimated by regression analysis. Here, "initial displacement (amount)" is defined as the displacement (amount) that occurs from when the initial measurement value is obtained until the face advances to approximately 2D (D is the excavation diameter of the tunnel), and "final displacement (amount)" is defined as the displacement (amount) at the point when the tunnel deformation converges.

The displacement from when the initial measurement value is obtained at the face until 1D of excavation (approximately 1m of excavation), 0.5D of excavation, 1D of excavation, and 2D of excavation are defined as the initial displacement, and then a regression analysis is performed on the relationship between the measurement data and the final displacement. Here, the strain based on the initial displacement is referred to as the initial strain, and the strain based on the final displacement is referred to as the final strain.

The inventors performed regression analysis on 950 tunnels from past construction records (construction examples). To determine the relationship between initial strain and final strain, final strain/initial strain (= relationship coefficient A) was calculated using simple regression analysis. An example of the results is shown in Figure 11.

Figure 11 shows that the later the initial strain is obtained (the longer the face separation), the closer the relationship coefficient A is to 1, and the higher the correlation between the initial strain and the final strain (the reliability of the relationship coefficient A). Figure 11 also shows that the final strain is generally about 3 to 3.4 times, 1.5 to 1.7 times, 1.2 to 1.4 times, and 1.1 to 1.2 times the initial strain at 1D excavation, 0.5D excavation, 1D excavation, and 2D excavation, respectively, after the initial measurement value is obtained.

As an example, the allowable strain is set to 0.8%, and the control standard values for each excavation stage are set as shown in Table 1 below.

The display unit 210 displays the control standard values for each excavation stage and the measurement values related to the displacement of the support structure during the excavation stage. Here, Fig. 12A and Fig. 12B show an example of a control graph in which the control standard values and measurement values set for multiple excavation stages are plotted. More specifically, Fig. 12A shows a case in which all measurement values are below the control standard values, and Fig. 12B shows a case in which the measurement values exceed the control standard values.

Returning to FIG. 3, the shoring evaluation unit 208 compares the management standard values and the measured values for each excavation stage. It then extracts the currently set shoring from the shoring table stored in the storage unit 212 and judges whether the shoring is appropriate.

Here, the support table is not shown in the figure, but support patterns such as B, CI, CII, DI, DII, etc. are set according to the ground grade, and for each support pattern, the thickness of the sprayed concrete, the specifications and erection intervals of the steel support, the length and number of rock bolts, the circumferential interval, the extension interval, etc. are set.

In Figure 12B, the measurement value exceeds the control standard value at 0.5D of excavation, and the subsequent measurement values also exceed the control standard value, eventually causing a deformation in the support structure. The illustrated example shows that some kind of countermeasure work needs to be implemented early at 0.5D of excavation, but by managing the construction based on the control standard values for each excavation stage, early countermeasure work can be planned and implemented, resulting in tunnel construction with high construction safety.

According to the construction management system 100, the allowable strain setting unit 204 sets the allowable strain when the shoring is damaged based on multiple tunnel construction cases, and the control standard value setting unit 206 sets the control standard value for the shoring by multiplying the allowable strain by the excavation radius of the tunnel to be managed, making it possible to set a control standard value that can evaluate the soundness of the shoring, reflecting the strain when the shoring is damaged and the scale of the tunnel to be managed.

Then, by comparing this control standard value with the measured value of the displacement of the support caused by the tunnel excavation to determine whether the currently set support is adequate, the soundness of the support can be properly evaluated.

Furthermore, by managing construction based on the control standard values for each excavation stage, early countermeasure work can be planned and implemented, resulting in tunnel construction with high construction safety.

<Tunnel construction management method>
Next, an example of a tunnel construction management method according to the embodiment will be described with reference to Fig. 13. Here, Fig. 13 is a flowchart of an example of a tunnel construction management method according to the embodiment.

This construction management method involves repeatedly excavating the tunnel and installing supports to construct the tunnel, and manages the construction based on the amount of displacement of the supports.

First, the allowable strain when the support is damaged is set based on multiple tunnel construction examples where damage to the support has been confirmed. Here, an example of multiple tunnel construction examples is explained with reference to Figures 4 and 5.

The allowable strain should be set in the range of about 1% to 2%, and if a greater safety factor is required, a safer allowable strain is set (step S10, process A).

Next, the support management standard value is set by multiplying the allowable strain by the excavation radius of the tunnel to be managed.

When setting these control standards, setting control standards for each of the multiple excavation stages leads to early planning and implementation of countermeasures, leading to the realization of tunnel construction with high construction safety (step S12, process B).

Next, measurements are taken of the displacement of the support structure as the tunnel advances.

In construction management based on control standard values for multiple excavation stages, measurement values are taken for each excavation stage (step S14, process C).

Next, the control standard values are compared with the measured values to determine whether the support structure is suitable.

In construction management based on control criteria for multiple excavation stages, the suitability of support work is judged for each excavation stage (step S16, process D).

If the support is judged to be inappropriate in this suitability assessment, countermeasures will be considered and implemented (step S18).

According to the tunnel construction management method of the embodiment, the allowable strain when the shoring is damaged is set from multiple tunnel construction cases where damage to the shoring has been confirmed, and the allowable strain is multiplied by the excavation radius of the tunnel to be managed to set the management standard value for the shoring, thereby making it possible to set a management standard value that reflects the strain when the shoring is damaged and the scale of the tunnel to be managed and that can evaluate the soundness of the shoring. The soundness of the shoring can be properly evaluated by comparing this management standard value with the measured value of the displacement of the shoring associated with the excavation of the tunnel to determine whether the shoring is suitable or not. Furthermore, by performing construction management based on the management standard value for each excavation stage, early countermeasure work can be planned and implemented, and tunnel construction with high construction safety can be realized.

Note that the configurations described in the above embodiments may be combined with other components, and the present invention is not limited to the configurations shown here. In this regard, changes can be made without departing from the spirit of the present invention, and can be determined appropriately according to the application form.

10: Measuring device 20: Setting evaluation device 30: Network 100: Tunnel construction management system (construction management system)
202: Communication unit 204: Allowable strain setting unit 206: Control standard value setting unit 208: Support evaluation unit 210: Display unit 212: Storage unit

Claims (7)

A tunnel construction management method for performing construction management based on the displacement of a support structure when constructing a tunnel by repeatedly excavating the tunnel and installing a support structure, comprising:
Step A is to set the allowable strain when the support is damaged based on a number of tunnel construction cases in which damage to the support has been confirmed;
A process B of multiplying the allowable strain by the excavation radius of the tunnel to be managed to set a management reference value for the support;
A step C of measuring the displacement amount as the tunnel is excavated;
A tunnel construction management method, comprising a step D of comparing the management standard value with the measured value to determine whether the support work is suitable. The tunnel construction management method according to claim 1, characterized in that in step A, the amount of displacement when the support is damaged is divided by the excavation radius of the tunnel, and then corrected by a predetermined safety factor to obtain the allowable strain. The tunnel construction management method according to claim 1 or 2, characterized in that in step A, the strain of the support structure when damaged is set to 2% or less. In the step A, based on the tunnel construction examples, each initial displacement amount measured for each of a plurality of excavation stages from a reference position is set as the displacement amount, and based on the final displacement amount converged at the reference position as the tunnel is excavated and the initial displacement amount for each of the plurality of excavation stages, a relation coefficient between the final displacement amount and the initial displacement amount is set for each of the plurality of excavation stages;
In the step B, the allowable strain is multiplied by the excavation radius of the tunnel for each of a plurality of excavation stages, and then corrected by the relation coefficient to set the control reference value for each of a plurality of excavation stages;
In the C step, a measurement value related to the displacement is measured for each of a plurality of excavation stages,
4. A tunnel construction management method according to claim 1, wherein in step D, the management standard value is compared with the measured value for each of a plurality of excavation stages to determine whether the support work is appropriate. The tunnel construction management method according to claim 4, characterized in that in step A, the relationship coefficient is determined by regression analysis. A tunnel construction management system that performs construction management based on the displacement of a support structure when constructing a tunnel by repeatedly excavating the tunnel and installing a support structure, comprising:
A setting evaluation device;
a measuring device that measures the amount of displacement as the tunnel is excavated to obtain a measurement value;
The setting evaluation device includes:
A storage unit that stores at least a plurality of tunnel construction examples in which damage to supports has been confirmed and a support table in which the plurality of supports are classified according to their rigidity;
an allowable strain setting unit that sets an allowable strain when the support is damaged based on a plurality of tunnel construction examples in the storage unit;
a control standard value setting unit that sets a control standard value of the support by multiplying the allowable strain by an excavation radius of a tunnel to be managed;
A tunnel construction management system characterized by having a support evaluation unit that compares the management standard value with the measured value, extracts the currently set support from the support table, and determines whether the support is appropriate. In the allowable strain setting unit, based on the tunnel construction examples, each initial displacement amount measured for each of a plurality of excavation stages from a reference position is set as the displacement amount, and based on the final displacement amount that converges at the reference position as the tunnel is excavated and the initial displacement amount for each of the plurality of excavation stages, a relation coefficient between the final displacement amount and the initial displacement amount is set for each of the plurality of excavation stages;
In the control standard value setting unit, the control standard value is set by correcting a value obtained by multiplying the allowable strain by the excavation radius of the tunnel for each of a plurality of excavation stages using the relation coefficient;
The storage unit stores the measurement values regarding the displacement amount for each of a plurality of excavation stages,
The tunnel construction management system according to claim 6, characterized in that in the support evaluation unit, the control standard value and the measured value are compared for each of a plurality of excavation stages to determine whether the support is appropriate.

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