Design method of yielding lining for high ground stress soft rock tunnel

Abstract

The application belongs to the field of underground engineering tunnel excavation and support, and discloses a design method of high ground stress soft rock tunnel yielding lining, which comprises the following steps: obtaining target extrusion large deformation tunnel lining parameters to obtain the mechanical parameters of the shotcrete lining and surrounding rock; judging whether the plastic zone of the surrounding rock is generated according to the mechanical parameters of the shotcrete lining and surrounding rock, and determining whether the maximum displacement of the tunnel matches the limit elastic displacement of the shotcrete; determining the design length, quantity, installation position and yield stress of the yielding element through the maximum displacement of the tunnel, the initial displacement after excavation and the limit elastic displacement of the shotcrete lining. The application comprehensively considers the tunnel design, geological conditions, calculated yielding displacement and yield stress results, and proposes a specific design scheme of the high ground stress soft rock large deformation tunnel yielding lining, which provides accurate data support for the large deformation tunnel yielding lining.

Description

Technical Field

[0001] This invention belongs to the field of underground engineering tunnel excavation and support, and relates to a design method for pressure-relief lining of soft rock tunnels with high ground stress. Background Technology

[0002] During tunnel construction under high ground stress conditions, if weak strata are encountered, the low rock strength can easily lead to large deformation of the surrounding rock due to compression, which in turn can cause engineering disasters such as failure of the support structure and instability of the tunnel.

[0003] Currently, the main approach to addressing the large deformation problem in tunnels located in squeezing-type weak surrounding rock is the traditional rigid support method based on the "strong roof and hard support" concept. This method primarily limits surrounding rock deformation by increasing support stiffness, resisting its development through extremely high support resistance. To increase the stiffness of the support structure, tunnel engineers often employ measures such as using larger I-beams, reducing the spacing between each steel arch frame, and increasing longitudinal bracing between arch frames. However, constructing tunnels in squeezing strata and strictly limiting surrounding rock deformation can lead to the support structure bearing excessive deformation pressure, undoubtedly increasing the risk of support failure.

[0004] In compression-type soft rock tunnels with large deformation, the approach of increasing the stiffness of the support structure to prevent the surrounding rock from converging and deforming is generally not feasible. The support structure should have a certain degree of compressibility and deformation capacity to release some of the deformation energy of the surrounding rock and reduce the surrounding rock pressure, which is the so-called "yielding lining". However, current research on yielding lining is still lacking. In most cases, tunnels using yielding lining are designed based on experience, requiring continuous adjustment and optimization of lining parameters during construction. This undoubtedly brings many uncertainties to the project and increases the economic cost of construction. Summary of the Invention

[0005] The purpose of this invention is to solve the problems in the prior art and provide a design method for pressure-bearing lining of soft rock tunnels with high ground stress, thereby solving the problem that there is a lack of accurate and effective calculation methods for pressure-bearing lining parameters of large deformation tunnels.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A design method for pressure-relief lining of a high-stress soft rock tunnel includes:

[0008] Obtain the target compression deformation tunnel lining parameters to obtain the mechanical parameters of the shotcrete lining and surrounding rock;

[0009] Based on the mechanical parameters of the shotcrete lining and the surrounding rock, determine whether the surrounding rock has a plastic zone and whether the maximum displacement of the tunnel matches the ultimate elastic displacement of the shotcrete.

[0010] The design length, quantity, installation location, and yield stress of the pressure relief element are determined by the maximum displacement of the tunnel, the initial displacement after excavation, and the ultimate elastic displacement of the shotcrete lining.

[0011] Furthermore, the mechanical parameters of the shotcrete lining include ultimate bearing capacity and ultimate elastic displacement, and the formula for calculating the ultimate bearing capacity is as follows:

[0012]

[0013] Among them, [P i [σ] represents the ultimate bearing capacity of the shotcrete lining. s [] represents the compressive strength of shotcrete, h s R0 represents the thickness of the shotcrete lining, and R0 represents the tunnel radius.

[0014] The formula for calculating the ultimate elastic displacement is:

[0015]

[0016] Where [u] represents the ultimate elastic displacement of the shotcrete lining, k s This indicates the stiffness of the concrete lining.

[0017] Furthermore, the stiffness of the concrete lining is calculated using the following formula:

[0018]

[0019] Among them, E s ν represents the elastic modulus of shotcrete. s This represents the Poisson's ratio of shotcrete.

[0020] Furthermore, the method for determining the mechanical parameters of the surrounding rock is as follows:

[0021] Hydraulic fracturing tests were conducted in sections of the tunnel engineering where there were significant large deformation problems to obtain the magnitude of the in-situ stress in the strata where the tunnel is located.

[0022] Then, within the large deformation range, representative original rock samples were selected for indoor triaxial shear tests to determine the values ​​of rock cohesion and internal friction angle.

[0023] Furthermore, the method for determining whether a plastic zone has formed in the surrounding rock is as follows:

[0024] Calculate the minimum support force σ required to prevent the formation of a plastic zone in the surrounding rock of the tunnel. rp :

[0025]

[0026] Wherein, P0 represents the magnitude of the in-situ stress in the stratum where the tunnel is located. The internal friction angle is represented by c, and the rock cohesion is represented by c.

[0027] Compared with the ultimate bearing capacity of shotcrete lining, if [p i Greater than σ rp This indicates that under the current lining conditions, the surrounding rock does not produce a plastic zone; if [p i Less than σ rp This indicates that under the current lining conditions, the surrounding rock will generate a plastic zone.

[0028] Furthermore, the method for calculating the maximum displacement of the tunnel is as follows:

[0029] If no plastic zone is generated, then the maximum displacement of the tunnel (u) max The following formula is used for calculation:

[0030]

[0031] When a plastic zone is formed, the maximum displacement of the tunnel is calculated using the following formula:

[0032]

[0033] Where Rp represents the radius of the tunnel in the plastic zone.

[0034] Furthermore, the method for calculating the radius of the plastic zone tunnel is as follows:

[0035]

[0036] Furthermore, the method for calculating the initial displacement after excavation is as follows:

[0037]

[0038] Furthermore, the design length of the pressure-relief element is:

[0039] 2πα(u max -u0-[u]) / nε lim

[0040] Where α represents the safety factor, n represents the number of pressure-relieving elements in the pressure-relieving lining, and ε lim This indicates the ultimate compressive strain of the pressure-reducing element.

[0041] Furthermore, the yield stress is 0.4 to 0.6 times the compressive strength of the shotcrete.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] This invention provides a design method for pressure-yielding linings in high-stress soft rock tunnels. By acquiring the mechanical parameters of the shotcrete lining and surrounding rock of the target tunnel with large deformation under compression, it determines whether the maximum displacement of the tunnel matches the ultimate elastic displacement of the shotcrete. By comparing the maximum displacement of the tunnel, the initial displacement after excavation, and the ultimate elastic displacement of the shotcrete lining, the circumferential compression of the pressure-yielding element can be obtained, thereby determining the design length of the pressure-yielding element, the optimal installation position of the pressure-yielding element in the lining, and the range of values ​​for the number of elements. Simultaneously, based on the age-hardening characteristics of shotcrete, a method for determining the yield stress of the pressure-yielding element is provided. This invention comprehensively considers tunnel design, geological conditions, and the calculated pressure-yielding displacement and yield stress results, proposing a specific design scheme for pressure-yielding linings in high-stress soft rock tunnels with large deformation, providing accurate data support for pressure-yielding linings in large deformation tunnels. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a flowchart illustrating the design method for pressure-relief lining of high-stress soft rock large deformation tunnels according to the present invention.

[0046] Figure 2 This is a schematic diagram of the pressure-relief lining of the present invention.

[0047] Wherein: 1-Shotcrete lining, 2-Pressure relief element. Detailed Implementation

[0048] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of this application, including various details to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0049] Obviously, the described embodiments are only some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0050] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0051] The present invention will now be described in further detail with reference to the accompanying drawings:

[0052] See Figure 1 This invention provides a design method for pressure-relief lining of high-stress soft rock tunnels, comprising the following steps:

[0053] S1: Obtain tunnel lining parameters and calculate the ultimate bearing capacity and ultimate elastic displacement of shotcrete lining 1 using the following formula:

[0054]

[0055]

[0056] Among them, [P] i [σ] represents the ultimate bearing capacity of the shotcrete lining. s [] represents the compressive strength of shotcrete, h s R0 represents the thickness of the shotcrete lining, [u] represents the tunnel radius, and [u] represents the ultimate elastic displacement of the shotcrete lining. s The stiffness of the concrete lining can be calculated using the following formula:

[0057]

[0058] Among them, E s ν represents the elastic modulus of shotcrete. s This represents the Poisson's ratio of shotcrete.

[0059] S2: Conduct in-situ tests to determine the magnitude of the ground stress in the target tunnel, and then take rock samples on-site for indoor rock mechanical property tests to determine the rock mechanical parameters.

[0060] Hydraulic fracturing tests were conducted in sections of the tunnel engineering project with significant large deformation problems to obtain the magnitude of the in-situ stress P0 of the strata where the tunnel is located. Then, in the field, triaxial shear tests were conducted on original rock samples from several representative locations within the large deformation range to determine the rock elastic modulus E. r Poisson's ratio r Cohesion c and internal friction angle The value of .

[0061] S3: The minimum support force σ required to prevent the formation of a plastic zone in the tunnel surrounding rock is calculated using the following formula. rpAnd compare its magnitude with the ultimate bearing capacity of the shotcrete lining.

[0062]

[0063] If [p] i Greater than σ rp This indicates that under the current lining conditions, the surrounding rock does not produce a plastic zone; if [p i Less than σ rp This indicates that under the current lining conditions, the surrounding rock will generate a plastic zone.

[0064] S4: If no plastic zone is generated, the maximum displacement of the tunnel (u) max The following formula can be used for calculation:

[0065]

[0066] If a plastic zone is formed, the maximum displacement of the tunnel can be calculated using the following formula:

[0067]

[0068] Where Rp represents the radius of the tunnel in the plastic zone, which can be calculated using the following formula:

[0069]

[0070] S5: Calculate the initial displacement u0 after tunnel excavation using the following formula. If the surrounding rock does not produce a plastic zone, then R in the following formula... p It equals R0.

[0071]

[0072] S6: Compare [u] and u max The value of -u0 indicates that if the former is large, it means that the existing lining design parameters can ensure the safety of the tunnel under the given conditions; if the latter is large, it means that the deformation of the surrounding rock is still too large, the lining will fail, and a pressure-relief lining is required.

[0073] S7: When using a pressure-relief lining, the tunnel displacement released by the pressure-relief element 2 needs to be u. max -u0-[u]. Therefore, the design length of each pressure-relieving element is:

[0074] 2πα(u max -u0-[u]) / nε lim .

[0075] Where α represents the safety factor, which ranges from 1.1 to 1.2, n represents the number of pressure-relieving elements in the pressure-relieving lining, and ε limThis indicates the ultimate compressive strain of the pressure-bearing element; this value should not be less than 50%.

[0076] Considering the actual stress conditions of the lining and the efficiency of tunnel construction, for the pressure-relief lining, the number n of the pressure-relief elements 2 should not be too small or too large. The value should be between 4 and 6, and they should be symmetrically installed at the arch shoulder, arch waist or arch bottom.

[0077] S8: Based on the age-hardening characteristics of shotcrete, in order to prevent the yield pressure of the pressure lining from being too small, and the situation where the shotcrete has been damaged but the pressure lining element 2 has not yet yielded, the yield stress of the pressure lining element 2 should be 0.4 to 0.6 times the compressive strength of the shotcrete.

[0078] This application provides a design method for pressure-relief lining of soft rock tunnels with high ground stress. It is used to provide specific structural schemes for pressure-relief lining of large deformation tunnels, taking into account yield stress and pressure-relief displacement, and to provide accurate and effective calculation methods for the design of tunnel pressure-relief elements.

[0079] The present invention will be further described in detail below with reference to specific embodiments:

[0080] Example 1:

[0081] Xinhua Tunnel is a key section of the Dali-Lincang Railway in Yunnan Province, China. With a radius of 6.2 meters, the tunnel has poor geological conditions and is highly susceptible to large deformation and failure. Therefore, it is necessary to determine whether pressure-relief lining should be used in Xinhua Tunnel.

[0082] S1: Based on the parameters of the shotcrete lining (elastic modulus E) s =25000MPa, compressive strength [σ s =25MPa, Poisson's ratio ν s =0.2, thickness h s =240mm), its ultimate bearing capacity and ultimate elastic displacement can be calculated as follows:

[0083]

[0084]

[0085]

[0086] S2: Based on in-situ testing, the geostress magnitude of the stratum where the tunnel is located is determined to be P0 = 15 MPa, the rock cohesion c = 0.85 MPa, and the internal friction angle is... Elastic modulus E r =1000MPa, Poisson's ratio ν r =0.36.

[0087] S3: Calculate the minimum support force σ required to prevent the formation of a plastic zone in the tunnel surrounding rock. rp equal:

[0088] σ rp =15·(1-sin28°)-0.85·cos28°=7.207MPa

[0089] It can be observed that this value is much greater than the ultimate bearing capacity of the shotcrete lining, which means that with the current support parameters, the surrounding rock of the tunnel will generate a plastic zone.

[0090] S4: When the tunnel develops a plastic zone, the maximum displacement of the tunnel is:

[0091]

[0092] Wherein, the tunnel radius Rp in the plastic zone is equal to:

[0093]

[0094] S5: Calculate the initial displacement u0 after tunnel excavation.

[0095]

[0096] S6: Compare [u] = 5.783 mm and u max The value of -u0 = 0.477m indicates that the deformation of the surrounding rock is too large, thus requiring the use of pressure-reducing lining.

[0097] S7: When using a pressure-relief lining, the tunnel displacement released by pressure-relief element 2 needs to be 0.471m. If the safety factor α = 1.1, the number of pressure-relief elements n = 6, ε lim =0.8, then the design length of each pressure relief element 2 is 0.626m.

[0098] S8: Based on the age-hardening characteristics of shotcrete, in order to prevent the yield pressure of the pressure lining from being too low, and the situation where the shotcrete has been damaged but the pressure lining element 2 has not yet yielded, the yield stress of the pressure lining element 2 needs to be 10MPa.

[0099] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A design method for pressure-relief lining of a high-stress soft rock tunnel, characterized in that, include: Obtain the target compression large deformation tunnel lining parameters to obtain the mechanical parameters of the shotcrete lining and surrounding rock; Based on the mechanical parameters of the shotcrete lining and the surrounding rock, determine whether the surrounding rock has a plastic zone and whether the maximum displacement of the tunnel matches the ultimate elastic displacement of the shotcrete. The design length, quantity, and yield stress of the pressure relief element are determined by the maximum displacement of the tunnel, the initial displacement after excavation, and the ultimate elastic displacement of the shotcrete lining. The target parameters for large-deformation tunnel linings include elastic modulus, compressive strength, Poisson's ratio, and thickness. The mechanical parameters of shotcrete lining include ultimate bearing capacity and ultimate elastic displacement. The method for determining whether a plastic zone has formed in the surrounding rock is as follows: Calculate the minimum support force required to prevent the formation of a plastic zone in the surrounding rock of the tunnel. : in, This indicates the magnitude of the ground stress in the stratum where the tunnel is located. Indicates the angle of internal friction. Indicates rock cohesion; Compare the magnitude with the ultimate bearing capacity of the shotcrete lining; if the ultimate bearing capacity... Greater than This indicates that under the current lining conditions, the surrounding rock does not produce a plastic zone; if the ultimate bearing capacity... Less than This indicates that under the current lining conditions, the surrounding rock will generate a plastic zone; The design length of the pressure relief element is: 2pa( - - ) / n lim Where α represents the safety factor, n represents the number of pressure-relieving elements in the pressure-relieving lining, and ε lim This indicates the ultimate compressive strain of the compression element. This indicates the maximum displacement of the tunnel. This represents the ultimate elastic displacement of the shotcrete lining. This indicates the initial displacement after tunnel excavation.

2. The design method for pressure-relief lining of a high-stress soft rock tunnel according to claim 1, characterized in that, The formula for calculating the ultimate bearing capacity is: in, This indicates the ultimate bearing capacity of the shotcrete lining. This indicates the compressive strength of the shotcrete. Indicates the thickness of the shotcrete lining. Indicates the tunnel radius; The formula for calculating the ultimate elastic displacement is: in, This represents the ultimate elastic displacement of the shotcrete lining. This indicates the stiffness of the concrete lining.

3. The design method for pressure-relief lining of a high-stress soft rock tunnel according to claim 2, characterized in that, The stiffness of the concrete lining is calculated using the following formula: in, This indicates the elastic modulus of shotcrete. This represents the Poisson's ratio of shotcrete.

4. The design method for pressure-relief lining of a high-stress soft rock tunnel according to claim 1, characterized in that, The method for determining the mechanical parameters of the surrounding rock is as follows: Hydraulic fracturing tests were conducted in sections of the tunnel engineering where there were significant large deformation problems to obtain the magnitude of the in-situ stress in the strata where the tunnel is located. Then, within the large deformation range, representative original rock samples were selected for indoor triaxial shear tests to determine the values ​​of rock cohesion and internal friction angle.

5. The design method for pressure-relief lining of a high-stress soft rock tunnel according to claim 1, characterized in that, The method for calculating the maximum displacement of the tunnel is as follows: If no plastic zone is generated, then the maximum displacement of the tunnel ( The following formula is used for calculation: When a plastic zone is formed, the maximum displacement of the tunnel is calculated using the following formula: in, Indicates the radius of the tunnel in the plastic zone. Poisson's ratio represents the ratio of rocks. This represents the elastic modulus of rock. This indicates the ultimate bearing capacity of the shotcrete lining. Indicates the tunnel radius.

6. The design method for pressure-relief lining of a high-stress soft rock tunnel according to claim 5, characterized in that, The method for calculating the radius of the tunnel in the plastic zone is as follows: 。 7. The design method for pressure-relief lining of a high-stress soft rock tunnel according to claim 1, characterized in that, The method for calculating the initial displacement after excavation is as follows: in, Indicates the radius of the tunnel in the plastic zone. Indicates the tunnel radius.

8. The design method for pressure-relief lining of a high-stress soft rock tunnel according to claim 1, characterized in that, The yield stress is 0.4 to 0.6 times the compressive strength of the shotcrete.

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