Tunnel surrounding rock strength reserve monitoring device and evaluation method

Abstract

The application discloses a tunnel surrounding rock strength reserve monitoring device and an evaluation method, relates to the field of tunnel surrounding rock stress monitoring, and comprises a main stem, at least two three-way supports which are arranged at intervals along the axial direction of the main stem, and a data processing module; each three-way support is provided with a strain gauge corresponding to the axial direction, the radial direction and the ring direction of the tunnel; the data processing module is used for calculating the internal stress according to the external stress of the tunnel measured by the strain gauge. The application solves the problem that most of the existing monitoring technologies can only monitor the supporting structure, and can accurately evaluate the stability of the tunnel surrounding rock, and the cost is relatively low.

Description

Technical Field

[0001] This invention relates to the field of tunnel surrounding rock strength reserve monitoring, and in particular to a tunnel surrounding rock strength reserve monitoring device and evaluation method. Background Technology

[0002] Monitoring is a crucial means of assessing tunnel stability and ensuring smooth tunnel construction. It is essential for evaluating the rationality of design parameters and the feasibility of construction methods. There are many items that can be monitored in a tunnel. Generally, tunnel settlement and convergence displacement are mandatory items as stipulated by regulations. The stress on the support structure is usually an optional item, mainly including steel frame stress, concrete strain, and anchor bolt axial force. Sensors and supporting equipment such as rebar gauges, concrete strain gauges, and anchor bolt axial force gauges are typically used.

[0003] The strength reserve of the surrounding rock is a crucial indicator for determining the safety and stability of a tunnel. Obtaining this strength reserve requires understanding the stress state of the surrounding rock, but monitoring this stress presents significant challenges. While the aforementioned monitoring methods can address the deformation and stress monitoring of the support structure, they cannot effectively monitor and evaluate the stress state of the surrounding rock, especially its internal structure. Some technologies have attempted to monitor surrounding rock stress, such as a fiber optic grating-based method for monitoring internal strain in surrounding rock. This method monitors the internal stress of the supported rock by pre-embedding fiber optic grating sensors within the rock. However, optical fibers are relatively fragile and have stringent application requirements; on-site pre-embedding can easily lead to fiber breakage and failure, and the high cost makes widespread adoption difficult.

[0004] In summary, there are currently many methods for monitoring the stress on support structures such as anchor bolts, arch frames, shotcrete layers, and secondary linings, but there is a lack of effective methods for monitoring the stress of the surrounding rock, and consequently, a lack of evaluation methods for the strength reserve of the surrounding rock. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention adopts a novel technical approach, using stress and strain monitoring data of the support structure to estimate the stress and strength reserve of the surrounding rock. The aim is to provide a monitoring device and evaluation method for the strength reserve of tunnel surrounding rock, which solves the problem that existing monitoring technologies are unable to obtain the stress and strength reserve of the surrounding rock. At the same time, it is low in cost and easy to promote.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, embodiments of the present invention provide a tunnel surrounding rock strength reserve monitoring device, including a main trunk, at least two three-way supports are arranged at intervals along the axial direction of the main trunk, and each three-way support is equipped with strain gauges corresponding to the tunnel axial, radial and circumferential directions; it also includes a data processing module, which is used to calculate the internal stress based on the external forces measured by the strain gauges.

[0008] As a further implementation, the main trunk has an extension section to change the spacing between adjacent three-way supports; based on the spacing, a deformation coordination relationship between the concrete spraying layer and the surrounding rock is established.

[0009] As a further implementation, the three-way support includes three connecting parts, which are orthogonal to each other in pairs; the strain gauge is snapped into the corresponding connecting part.

[0010] As a further implementation, the three strain gauges mounted on each triaxial support are connected by wires arranged inside the main body.

[0011] As a further implementation, two three-way supports are set along the main trunk. When installed in the surrounding rock, one three-way support is close to the surrounding rock, and the other three-way support is far away from the surrounding rock.

[0012] Secondly, embodiments of the present invention also provide a method for evaluating the strength of tunnel surrounding rock, including:

[0013] Drill holes are made at the designated locations in the surrounding rock, and the anchoring end of the monitoring device is inserted into the drill holes so that the strain gauges of each three-dimensional support correspond to the tunnel axial, radial and circumferential directions respectively;

[0014] After securing the anchor end, the monitoring device is sprayed into the concrete spray layer.

[0015] Strain gauges monitor the strain values ​​in each direction at different locations on the three-dimensional support of the concrete spraying layer;

[0016] The surrounding rock strain is estimated based on the deformation compatibility relationship between concrete and surrounding rock, the spacing between adjacent groups of strain gauges, and the collected concrete spraying strain.

[0017] The stress increment after rock support is calculated based on the elastic modulus of the surrounding rock, Poisson's ratio and generalized Hooke's law, and then superimposed with the initial stress before rock support to obtain the total stress after rock support.

[0018] The strength reserve value of the surrounding rock is calculated based on the total stress after support and the strength criterion of the surrounding rock to quantitatively evaluate the stability of the tunnel surrounding rock.

[0019] As a further implementation, the surrounding rock strain is:

[0020]

[0021] Where, ε Ai ε represents the strain value at point A. Bi ε represents the strain value at point B. Ci d1 represents the strain value at point C, d2 represents the distance between the three-way support and the borehole on the side closest to the surrounding rock, and d2 represents the distance between adjacent three-way supports.

[0022] As a further implementation, the surrounding rock strength criterion is the MC criterion or the DP criterion.

[0023] As a further implementation method, the strength reserve value K of the surrounding rock after support is calculated based on the MC criterion as follows:

[0024]

[0025] The strength reserve value K of the surrounding rock after support is calculated based on the DP criterion:

[0026]

[0027] in,

[0028] α, c, k, I1, and J2 represent rock mechanics parameters, and σ1, σ2, and σ3 are the three principal stress values ​​of the surrounding rock at point C.

[0029] As a further implementation, the anchoring end is fixed inside the borehole using an anchoring agent.

[0030] The beneficial effects of this invention are as follows:

[0031] (1) The monitoring device of the present invention is equipped with multiple strain gauges. Each strain gauge can obtain the strain in three directions at the corresponding point in the concrete spray layer. Finally, the internal stress of the surrounding rock after support can be determined, which effectively solves the problem that most current monitoring technologies can only monitor the support structure and cannot monitor the mechanical information inside the surrounding rock. The strain gauge does not need to be pre-embedded in the surrounding rock, and the influence of the spray layer is reduced by the built-in wire, which effectively ensures the monitoring accuracy of the strain gauge.

[0032] (2) This invention obtains the internal stress value and strength reserve value of the surrounding rock through calculation, thereby quantitatively evaluating the stability of the tunnel surrounding rock and the support effect, so as to provide feedback to the design and guide the on-site construction, effectively solving the problems of high cost and low promotion of the monitoring device pre-embedded in the surrounding rock. Attached Figure Description

[0033] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0034] Figure 1 This is a schematic diagram showing the state of the monitoring device of the present invention installed in a concrete spray layer according to one or more embodiments;

[0035] Figure 2 This is a schematic diagram of the monitoring device structure according to one or more embodiments of the present invention;

[0036] Figure 3 This is a flowchart of the evaluation method according to one or more embodiments of the present invention.

[0037] Among them, 1. strain gauge, 2. connecting part, 3. elastic protrusion, 4. main body, 5. anchoring agent, 6. surrounding rock, 7. concrete spraying layer, 8. borehole, 9. monitoring device, 10. wire. Detailed Implementation

[0038] Example 1:

[0039] In a typical embodiment of the present invention, such as Figure 1 and Figure 2 As shown, a tunnel surrounding rock strength reserve monitoring device is presented.

[0040] Since most existing rock stress monitoring technologies can only monitor the mechanical state of the support structure, and a few monitoring technologies monitor the internal stress of the surrounding rock by pre-embedded sensors, they are prone to problems such as low sensor survival and high cost. Based on this, this embodiment provides a tunnel surrounding rock strength reserve monitoring device, which measures the external force through strain gauge 1 and calculates the internal stress, thus overcoming the problem that existing sensors cannot effectively measure the internal stress of the surrounding rock.

[0041] The monitoring device described above will now be explained in detail with reference to the accompanying drawings.

[0042] like Figure 2 As shown, the monitoring device 9 includes a main trunk 4, a three-way support, and a strain gauge 1. The main trunk 4 is a straight pipe, and the inside is used to lay the wires 10. At least two three-way supports are set at intervals along the axial direction of the main trunk 4.

[0043] In this embodiment, two three-way supports are installed on the main trunk 4 to calculate the surrounding rock strain by measuring the strain values ​​at these two locations. The main trunk 4 has an expansion joint between the two three-way supports, and by adjusting the distance between them, a deformation coordination relationship between the concrete sprayed layer 7 and the surrounding rock 6 is established.

[0044] The telescopic section can be implemented in various ways. For example, the main trunk 4 can be set as a telescopic rod, or the main trunk 4 can be set as two sections that are nested together. One section has multiple sets of elastic protrusions 3 arranged along the axial direction, and the other section has a through hole. The length of the main trunk 4 can be adjusted by the elastic protrusions 3 at different positions being engaged in the through hole.

[0045] Each three-way support is equipped with three strain gauges 1, which correspond to the tunnel's axial, radial, and circumferential directions, respectively. The strain gauge 1 corresponding to the tunnel's axial direction is arranged parallel to the main trunk 4. For example... Figure 2 As shown, the three-way support consists of three connecting parts 2, which are orthogonal to each other. Each connecting part 2 is fixed with a strain gauge 1 through a slot, so that the three strain gauges 1 can measure the strain values ​​in three directions at the corresponding positions.

[0046] Three strain gauges 1 on the same three-dimensional support are connected by a conductor 10. The conductor 10 passes through the inside of the main trunk 4 and extends out from one end of the main trunk 4. The data processing module is connected through the conductor 10. The conductor 10 is arranged inside the main trunk 4 to reduce the impact of the concrete spraying layer 7 on the track. The data processing module is used to calculate the internal stress based on the external stress of the tunnel measured by the strain gauges 1.

[0047] like Figure 1 As shown, during the installation of the monitoring device 9, a borehole 8 of a certain depth is drilled in the surrounding rock 6, and the anchoring end is inserted into the borehole 8; the end of the main trunk 4 where the wire 10 does not protrude is the anchoring end. After the anchoring end is inserted into the borehole 8, the main trunk 4 faces the inside of the tunnel, and each strain gauge 1 is aligned with three different directions. For the monitoring device 9 at the apex position, the main trunk 4 is set vertically, with one three-way support close to the surrounding rock 6 and the other three-way support away from the surrounding rock 6.

[0048] In this embodiment, the strain in three directions at two points in the concrete sprayed layer 7 is obtained through the monitoring device 9, and the internal stress of the surrounding rock 6 after support can be determined. This effectively solves the problem that most current monitoring technologies can only monitor the support structure but cannot monitor the internal mechanical information of the surrounding rock 6. The strain gauge 1 does not need to be pre-embedded in the surrounding rock, and the influence of the sprayed layer is reduced by the built-in wire 10, which effectively ensures the monitoring accuracy of the strain gauge 1.

[0049] Example 2:

[0050] This embodiment provides a method for evaluating the strength of surrounding rock in tunnels, based on the monitoring device described in Embodiment 1, such as... Figure 1 As shown, the vertex of borehole 8 is point C, the position of the three-way support on the side closer to the surrounding rock 6 is point A, the position of the three-way support on the side farther from the surrounding rock 6 is point B, the depth of borehole 8 is x, the distance between the three-way support on the side closer to the surrounding rock 6 and the outer boundary of the surrounding rock is d1, and the distance between adjacent three-way supports is d2.

[0051] The specific process of the above evaluation method is as follows: Figure 3 As shown, the anchoring end of the main trunk 4 is inserted into the borehole 8, and the anchoring end is fixed to the borehole 8 using the anchoring agent 5. Then, the monitoring device 9 is sprayed onto the concrete spray layer 7. The strain at points A and B in three different directions is measured by the monitoring device 9 and used as the strain of the concrete to be treated.

[0052] The strain ε of the surrounding rock after support was calculated based on the spacing d1 and d2, and the deformation compatibility relationship between concrete and surrounding rock. Ci ,Right now:

[0053]

[0054] Where, εAi ε represents the strain value at point A. Bi ε represents the strain value at point B. Ci The value represents the strain at point C. The subscripts i = 1, 2, 3 represent the radial, circumferential, and axial directions, respectively.

[0055] Then, the surrounding rock strain is calculated as the stress increment σ of the surrounding rock after support using the surrounding rock elastic modulus E, Poisson's ratio u, and generalized Hooke's law. 增i(i＝1，2，3) The stress increment is superimposed with the initial stress σ of the surrounding rock before the 6th support. 初i (Generally based on numerical values) the total stress of the surrounding rock after support can be obtained, i.e., σ. 全i =σ 增i +σ 初i .

[0056] Specifically, the generalized Hooke's Law is as follows:

[0057]

[0058]

[0059]

[0060] Among them, μ and E represent rock mechanics parameters, which can be obtained from laboratory tests.

[0061] σ 初i The data is obtained through two methods: first, by pre-embedding a small number of surrounding rock stress monitoring sensors; and second, through numerical calculations.

[0062] The strength reserve value K of the tunnel surrounding rock is calculated based on the total stress after surrounding rock support and the surrounding rock strength criterion to quantitatively evaluate the stability of the tunnel surrounding rock.

[0063] The surrounding rock strength criterion is either the MC criterion or the DP criterion. Based on the MC criterion, the strength reserve value K of the surrounding rock after support is calculated as follows:

[0064]

[0065] The strength reserve value K of the surrounding rock after support is calculated based on the DP criterion:

[0066]

[0067] Among them, α, c, k, I1, J2, etc., represent rock mechanics parameters, which are calculated by the following formula:

[0068]

[0069]

[0070] I1=σ1+σ2+σ3

[0071]

[0072] σ1, σ2, and σ3 are the three principal stress values ​​of the surrounding rock at point C, derived from σ 增i(i＝1，2，3) The result is obtained through conversion.

[0073] The evaluation method in this embodiment does not require pre-embedded sensors in the surrounding rock. Instead, it obtains the internal stress value and strength reserve value K of the surrounding rock through calculation, quantitatively evaluates the stability of the tunnel surrounding rock and the support effect, provides feedback to the design, and guides on-site construction. This effectively solves the problems of high cost and low scalability of pre-embedded monitoring devices in the surrounding rock.

[0074] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for evaluating the strength of surrounding rock in tunnels, characterized in that, The tunnel surrounding rock strength reserve monitoring device used in this evaluation method includes a main trunk, with at least two three-way supports spaced apart along the main trunk axis. Each three-way support is equipped with strain gauges corresponding to the tunnel's axial, radial, and circumferential directions. It also includes a data processing module, which is used to calculate the internal stress based on the external forces measured by the strain gauges. The main trunk has a telescopic section to change the spacing between adjacent three-way supports. Based on the aforementioned spacing, a deformation coordination relationship between the sprayed concrete layer and the surrounding rock is established; the three-way support includes three connecting parts, which are orthogonal to each other; the strain gauges are snapped into the corresponding connecting parts; the three strain gauges installed on each three-way support are connected by wires, which are arranged inside the main body; Two three-way supports are installed along the main trunk. When installed in the surrounding rock, one three-way support is close to the surrounding rock and the other three-way support is far away from the surrounding rock. The evaluation methods include: Drill holes are made at the designated locations in the surrounding rock, and the anchoring end of the monitoring device is inserted into the drill holes so that the strain gauges of each three-dimensional support correspond to the tunnel axial, radial and circumferential directions respectively; After securing the anchor end, the monitoring device is sprayed into the concrete spray layer. Strain gauges monitor the strain values ​​in each direction at different locations on the three-dimensional support of the concrete spraying layer; The surrounding rock strain is estimated based on the deformation compatibility relationship between concrete and surrounding rock, the spacing between adjacent groups of strain gauges, and the collected concrete spraying strain. The stress increment after rock support is calculated based on the elastic modulus of the surrounding rock, Poisson's ratio and generalized Hooke's law, and then superimposed with the initial stress before rock support to obtain the total stress after rock support. The strength reserve value of the surrounding rock is calculated based on the total stress after support and the strength criterion of the surrounding rock to quantitatively evaluate the stability of the tunnel surrounding rock.

2. The method for evaluating the strength of tunnel surrounding rock according to claim 1, characterized in that, The strain of the surrounding rock is: ； in, ε Ai This represents the strain value at point A. ε Bi This represents the strain value at point B. ε Ci This represents the strain value at point C. d 1 indicates the distance between the three-way support and the borehole on the side closest to the surrounding rock. d 2 indicates the spacing between adjacent three-way supports.

3. The method for evaluating the strength of tunnel surrounding rock according to claim 1, characterized in that, The anchoring end is fixed inside the borehole using an anchoring agent.

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