Extra-large section tunnel anchor rod length design method for new Austrian method construction

Abstract

The invention discloses a method for designing the length of an anchor rod of an extra-large section tunnel constructed by a new Austrian method, which comprises the following steps of: entering equipment, and determining a specific position for measuring a surrounding rock loose circle; determining the depth of a surrounding rock loose circle according to a detection result, and determining the anchoring length and free length of an anchor rod according to engineering characteristics; constructing an anchor rod; measurement is conducted after construction of part of the anchor rods is completed, the depth of the loose circle of the surrounding rock after flexible supporting is determined, and the anchoring length and the free length of the follow-up anchor rods are further adjusted; closing of anchor rod construction is completed, other primary supports are constructed, final surrounding rock loose circle measurement is carried out, and then the anchoring length and the free length of the anchor rod are adjusted according to the depth of the surrounding rock loose circle in each anchor rod construction direction. Engineering materials can be effectively reduced, it is guaranteed that the anchor rod plays a full anchoring role, meanwhile, the self-bearing capacity of surrounding rock is fully utilized, and the problem of resource waste caused by unreasonable length design of the anchor rod in existing tunnel engineering is effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel engineering, and in particular to a method for designing anchor rod length of a large-section tunnel constructed by a new Austrian tunnelling method. Background Art

[0002] The New Austrian Tunneling Method (NATM) is a method for tunnel design and construction. According to the definition of the Underground Space Special Committee of the Austrian Civil Engineering Society: "The New Austrian Tunneling Method (NATM) is a construction method that aims to form a circular bearing structure in the rock (soil) around the underground space." China calls this method the secondary support method or the monitoring construction method, referred to as the New Austrian Tunneling Method (NATM). The New Austrian Tunneling Method (NATM) is an application of rock mechanics theory, based on the maintenance and utilization of the self-bearing capacity of the surrounding rock, using anchor rods and shotcrete as the main support means, timely support, control of the deformation and relaxation of the surrounding rock, making the surrounding rock an integral part of the support system, and guiding the methods and principles of tunnel construction and underground engineering design and construction through the measurement and monitoring of the surrounding rock and support.

[0003] For tunnels constructed by the New Austrian Tunneling Method (NATM), the construction process will affect the surrounding rock, causing damage and changes in its mechanical properties. In this case, the surrounding rock not only acts as an overburden load on the tunnel, but also has a certain self-bearing capacity to bear force together with the tunnel. In tunnel construction, anchor rods are often used to participate in initial support. Anchor rods can play roles such as suspension, composite beams, and masonry, so that the bearing capacity of the surrounding rock is fully improved. However, under normal circumstances, the geological conditions near the tunnel construction location and the load distribution above are not very uniform, resulting in uneven distribution of the surrounding rock loosening zone during excavation.

[0004] In traditional large-section tunnel construction, under the condition that the surrounding rock loosening zone is unevenly distributed along the tunnel cross section, the most unfavorable position, that is, the position where the surrounding rock is most disturbed, is often used as a reference to design the anchor length. Figure 1 As shown in the figure, this more conservative equal-length anchor support method can ensure the safety and stability of tunnel support. However, this equal-length anchor length design method will cause a considerable waste of engineering resources, and the basis for the anchor design length is contrary to the concept of making full use of the self-bearing capacity of the surrounding rock, resulting in uneven distribution of the safety factor of the cross-section ring, making it difficult to achieve the safety and economy of tunnel engineering design and construction. Summary of the invention

[0005] In order to overcome the shortcomings of the existing tunnel anchor rod length design method, which wastes engineering resources and is difficult to achieve the safety and economy of tunnel engineering design and construction, the present invention provides a method for designing the anchor rod length of a super-large section tunnel constructed by a New Austrian Tunneling Method.

[0006] The technical solution of the present invention is as follows:

[0007] The present invention provides a method for designing anchor rod length of a large-section tunnel constructed by a new Austrian tunnelling method, comprising:

[0008] Step S1: The equipment enters the site and determines the specific location of the surrounding rock loosening zone measurement;

[0009] Step S2, determining the depth of the surrounding rock loosening zone according to the detection results, and determining the anchoring length and free length of the anchor rod according to the engineering characteristics;

[0010] Step S3, carrying out anchor rod construction;

[0011] Step S4: after completing the construction of some anchor bolts, measure to determine the depth of the loose zone of the surrounding rock after the flexible support, and further adjust the anchoring length and free length of the subsequent anchor bolts;

[0012] Step S5, complete the closure of the anchor bolt installation, implement the remaining initial support, and perform the final measurement of the surrounding rock loosening circle, and then adjust the anchor length and free length of the anchor bolt according to the depth of the surrounding rock loosening circle in the installation direction of each anchor bolt.

[0013] As a preferred solution of the present invention, the specific location of the surrounding rock loosening zone measurement includes the cross-section mileage and the coordinates of the measuring points and the detection angle along a ring of the tunnel.

[0014] As a preferred solution of the present invention, the engineering characteristics include anchor parameters and formation parameters.

[0015] As a preferred solution of the present invention, the anchoring length of the anchor rod is greater than the depth of the loosening zone of the surrounding rock, and the anchoring length of the anchor rod is less than the free length of the anchor rod.

[0016] As a preferred solution of the present invention, in step S2, the loosening conditions of the surrounding rocks in different anchoring directions are detected to determine the main distribution range of the loosening circle, and the size of the loosening circle of the surrounding rock is plotted according to the detection results of measuring points at different positions, and the depth of the loosening circle of the surrounding rock in the anchoring direction is listed.

[0017] As a preferred solution of the present invention, in step S3, during the anchor construction, the weak positions of the surrounding rock are firstly anchored, and then the stable positions of the surrounding rock are anchored.

[0018] As a preferred solution of the present invention, in step S4, after completing the construction of part of the anchor rods, the depth of the loosened zone of the surrounding rock after the flexible support is measured by ultrasonic detection, and the anchoring length and free length of the subsequent anchor rods are further adjusted according to the changes in the loosened zone of the surrounding rock.

[0019] As a preferred solution of the present invention, the calculation formula of the depth of the surrounding rock loose zone is:

[0020]

[0021] Among them, R p is the depth of the surrounding rock loosening zone, D is the radius of the tunnel lining, K is the surrounding rock coefficient, σ 0 is the confining pressure under burial depth conditions.

[0022] As a preferred solution of the present invention, the calculation formula of the anchoring length of the anchor rod is:

[0023]

[0024] Among them, L a is the anchorage length of the anchor rod, T is the design tensile strength of the anchor rod, σ t is the anchorage unit stress of the anchor rod, c is the anchorage performance coefficient;

[0025] The calculation formula of anchor unit stress of anchor bolt is:

[0026]

[0027] Among them, σ t is the anchoring unit stress of the anchor rod, d is the anchor rod diameter, and T is the design tensile strength of the anchor rod.

[0028] As a preferred embodiment of the present invention, it also includes:

[0029] Step S6: Perform a pull-out test on the anchor rod to determine the anchoring effect of the anchor rod.

[0030] The present invention according to the above scheme has the following beneficial effects:

[0031] 1. The present invention detects the loose zone of the surrounding rock around the tunnel during the construction process, comprehensively considers the complexity of the strata passed by the extra-large section tunnel and the periodicity and unevenness of the influence of the distributed construction of the extra-large section on the surrounding rock, and implements a reasonable anchor length, including free length and anchoring length, on the premise of considering the safety of anchor support, thereby saving engineering materials and improving the economy of tunnel engineering design and construction;

[0032] 2. Based on the characteristics of the New Austrian Tunneling Method (NATM) construction that fully utilizes the self-bearing capacity of the surrounding rock, the excessive difference in the safety factor of the surrounding rock along the first ring of the tunnel is reduced, the relative stability of the surrounding rock along the first ring of the tunnel is ensured, and the safety of the tunnel engineering design and construction is improved;

[0033] 3. Combining monitoring and measurement with dynamic construction concepts, the changes in the loose circle of the surrounding rock during the anchor construction process are fed back to the construction unit to adjust the reasonable anchor length, thereby improving the adaptability and effect of the support. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1It is a cross-sectional schematic diagram of traditional equal-length anchor support;

[0035] Figure 2 It is a flow chart of a method for designing anchor rod length of a tunnel with a large cross section constructed by the New Austrian Tunneling Method in one embodiment of the present invention;

[0036] Figure 3 A cross-sectional schematic diagram of unequal length anchor support in the present invention;

[0037] Figure 4 The figure is a flow chart of a method for designing anchor rod length for a tunnel with a particularly large cross section constructed by the New Austrian Tunneling Method in another embodiment of the present invention.

[0038] In the figure,

[0039] 1. Anchor rod; 2. Loose zone of surrounding rock. DETAILED DESCRIPTION

[0040] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device including a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products or devices.

[0042] Please refer to Figure 2 , Figure 3 This embodiment provides a method for designing anchor rod length for a large-section tunnel constructed using the New Austrian Tunneling Method, including:

[0043] Step S1, equipment enters the site, and determines the specific location of the surrounding rock loosening circle 2 measurement, including the section mileage and the coordinates of the measuring points along the tunnel ring, and the detection angle. By determining the specific location of the surrounding rock loosening circle 2 measurement, the loosening of the surrounding rock around the tunnel can be accurately understood, providing basic data for the subsequent design of the anchor length. The loosening of the surrounding rock around the tunnel can be accurately understood, providing basic data for the subsequent design of the anchor length.

[0044] Step S2: Determine the depth of the loose zone of the surrounding rock according to the detection results, and determine the anchoring length and free length of the anchor rod 1 according to the engineering characteristics, thereby determining the total length of the anchor rod 1 and forming an unequal length anchor rod support method. The engineering characteristics include anchor rod parameters and formation parameters, etc. The anchor rod parameters include anchor rod diameter, design tensile strength and cohesion, etc. The formation parameters include surrounding rock strength, deformation modulus, confining pressure, surrounding rock type, structural surface and other parameters.

[0045] When underground tunnels are located in uneven strata and close to existing buildings, such as existing tunnels and existing high-rise buildings on the surface, the loosening and crushing of the surrounding rock around the extra-large section tunnel are unevenly and asymmetrically distributed. The use of unequal length anchor support can ensure the safety of the support.

[0046] Specifically, for extra-large section tunnels or special-shaped section tunnels, they often pass through more rock layers, and the surrounding rock conditions and disturbance states are more complicated. The depth of the surrounding rock loosening zone 2 is non-uniformly distributed along the tunnel, and the depth extremes often differ greatly. Therefore, it is necessary to detect the surrounding rock loosening conditions in different anchor application directions by means of geophysical exploration, drilling or ultrasonic detection under the condition of NATM excavation to rough holes, determine the main distribution range of the loosening zone, and draw the size of the surrounding rock loosening zone 2 according to the detection results of measuring points at different positions, such as Figure 3 As shown, the depth of the loosened zone of the surrounding rock in the direction of the anchor bolt is listed. Among them, the ultrasonic detection method is suitable for the case where the type, strength and stability of the strata around the tunnel structure are unevenly distributed in space. It is preferred to use the ultrasonic detection method for detection, such as through acoustic wave field measurement geological radar.

[0047] When the strata around the tunnel are uneven, the depth of the loose zone caused by excavation is different, and the boundary of the loose zone on the weak surrounding rock side is deeper. In addition, the excavation methods are different according to different sections. Conventional tunnel construction methods such as full section construction, step method construction, CD method construction, CRD method construction, etc., due to the different excavation sequences of the sections, the development of the surrounding rock loose zone 2 is also different. Therefore, it is necessary to comprehensively analyze the uneven distribution of the strata and the excavation sequence of the sections, determine the disturbance of the strata by excavation, and reasonably design the length of the anchor 1.

[0048] When setting the anchoring length and free length of the anchor rod 1, the anchoring length needs to be greater than the depth of the loose circle of the surrounding rock, so that the anchor rod 1 can play the role of suspension, composite beam, masonry, etc. Usually, the anchoring length will be less than the free length. This is because the anchoring length needs to ensure that the anchor rod can effectively combine with the surrounding rock or concrete, while the free length needs to provide enough space to transmit force and ensure structural stability.

[0049] Step S3, constructing the anchor rod 1.

[0050] Specifically, when anchor 1 is constructed using unequal length anchor support, considering that the surrounding rock continues to creep during the installation of anchor 1 and the creep on the weak side of the surrounding rock is more obvious, in order to ensure that the deformation of the overall surrounding rock is controllable, it is necessary to first anchor the weak position of the surrounding rock and then anchor the stable position of the surrounding rock.

[0051] Step S4: after completing the construction of some anchor bolts, measurement is performed to determine the depth of the loosening zone of the surrounding rock after the flexible support, and further adjust the anchoring length and free length of the subsequent anchor bolts 1.

[0052] Specifically, after completing the construction of some anchor bolts, the depth of the loosened zone of the surrounding rock after the flexible support is measured by ultrasonic detection, and the anchoring length and free length of the subsequent anchor bolt 1 are further adjusted according to the changes in the loosened zone 2 of the surrounding rock. If the loosened surrounding rock is serious, it is necessary to increase the anchoring length of the anchor bolt 1 to improve the support effect; if the surrounding rock is stable, the anchoring length of the anchor bolt 1 can be appropriately reduced to save costs. This anchor bolt support scheme that is dynamically adjusted according to the actual situation of the loosened zone 2 of the surrounding rock can improve the adaptability and effect of the support.

[0053] Step S5, complete the closure of the anchor bolt installation, implement the remaining initial support, and conduct the final measurement of the surrounding rock loosening circle 2, and then adjust the anchoring length and free length of the anchor bolt 1 according to the depth of the surrounding rock loosening circle in the direction of each anchor bolt installation, so as to ensure the integrity and effectiveness of the anchor bolt support and provide safety protection for the subsequent construction and use of the tunnel.

[0054] In one embodiment, a method for designing anchor bolt length for a large-section tunnel constructed using the New Austrian Tunneling Method (NATM) further includes:

[0055] Step S6: Perform a pull-out test on the anchor rod 1 to determine the anchoring effect of the anchor rod 1. The test can verify the strength and stability of the anchor rod 1 to ensure that it can play the expected supporting role in subsequent construction and use.

[0056] In one embodiment, the depth of the surrounding rock loosening zone is the distance between the tunnel and the elastic-plastic interface, which is often called the loosening zone radius in engineering, and its calculation formula is:

[0057]

[0058] Among them, R p is the depth of the surrounding rock loosening zone, D is the radius of the tunnel lining, K is the surrounding rock coefficient, which is related to the characteristics of the surrounding rock, σ 0 is the confining pressure under burial depth conditions.

[0059] The following is an analysis through specific cases:

[0060] In the construction of a large-section tunnel, the radius of the lining is 5m. For the third-level surrounding rock coefficient K≈0.1~0.3, the sixth-level surrounding rock coefficient K≈0.5~1.0, the confining pressure σ under the condition of burial depth of 3m 0 About 40kPa.

[0061] According to the calculation formula of the depth of the surrounding rock loose zone: It can be calculated that the depth of the loosening zone of the third-level surrounding rock is 4.17m, and that of the sixth-level surrounding rock is 9.17m.

[0062] In one embodiment, the calculation formula of the anchoring length of the anchor rod 1 is:

[0063]

[0064] Among them, L a is the anchorage length of anchor 1, T is the design tensile strength of anchor 1, σ t is the anchoring unit stress of anchor bolt 1, c is the anchoring performance coefficient, which is related to the anchoring method, anchor bolt type, etc.;

[0065] The calculation formula of the anchoring unit stress of anchor bolt 1 is:

[0066]

[0067] Among them, σ t is the anchoring unit stress of anchor rod 1, d is the anchor rod diameter, and T is the design tensile strength of anchor rod 1.

[0068] The following is an analysis through specific cases:

[0069] Assuming that the diameter of the anchor rod is d = 0.02m, the design tensile strength is T = 50kN, and the cohesion is 25kPa, which is determined by the rod body and the anchoring agent. The tensile strength of the third-level surrounding rock and the sixth-level surrounding rock is 0.1MPa and 0.05MPa. In the design, it is necessary to control the anchoring strength of the anchor rod to be lower than the tensile strength of the formation to ensure the rationality of the anchoring.

[0070] First, according to the calculation formula of the anchor unit stress of anchor rod 1: The anchoring unit stress σ of anchor bolt 1 can be calculated t It is 159.15Kpa. Under the third-level surrounding rock, the anchor unit stress is lower than the tensile strength of the formation, which is reasonable. Under the sixth-level surrounding rock, the anchor unit stress is higher than the tensile strength of the surrounding rock, which is unreasonable and the design length of anchor rod 1 needs to be lengthened. t =0.05MPa, calculate the anchorage length.

[0071] Then according to the calculation formula of the anchoring length of anchor rod 1: It can be calculated that the anchoring length of the anchor rod 1 under the third-level surrounding rock is about 625mm, and the anchoring length of the anchor rod 1 under the sixth-level surrounding rock is about 1500mm. And according to the sum of the free section length and the anchoring section length, the total length of the anchor rod 1 is L = L 1 +L 2 (L is the total length of anchor rod 1, L 1 is the free length of anchor 1, L 2 is the anchoring length of the anchor rod 1), and the free length is determined. Since the anchoring length is generally less than the free length, it proves that the traditional equal-length anchor rod length design method under the sixth-level surrounding rock is unreasonable. It is precisely because of this unreasonableness that the unequal-length anchor rod length design method of the present invention needs to be adopted. At the same time, when the formation conditions are poor, the loosening zone depth of the formation is large. In order to extend the anchoring section beyond the loosening zone, a longer anchor rod 1 is required for formation support.

[0072] The method for designing anchor rod length for extra-large-section tunnels constructed by the new Austrian tunneling method provided in this embodiment detects the loose zone of the surrounding rock around the tunnel during the construction process, comprehensively considers the complexity of the formation traversed by the extra-large-section tunnel and the periodicity and unevenness of the influence of the distributed construction of the extra-large section on the surrounding rock, and, under the premise of considering the safety of anchor rod support, implements a reasonable anchor rod length, including free length and anchoring length, thereby saving engineering materials; the method for designing unequal anchor rod lengths reduces the excessive difference in the safety factor of the surrounding rock along a ring of the tunnel according to the characteristics of the new Austrian tunneling method construction that fully utilizes the self-bearing capacity of the surrounding rock, and ensures the relative stability of the surrounding rock along a ring of the tunnel; in addition, the method for designing anchor rod length combines monitoring and measurement with the concept of dynamic construction, and feeds back the changes of the loose zone 2 of the surrounding rock during the anchor rod construction process to the construction unit for reasonable adjustment of the anchor rod length.

[0073] In addition, although the operations of the method of the present invention are described in a specific order in the drawings, this does not require or imply that the operations must be performed in this specific order, or that all the operations shown must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps.

[0074] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

[0075] The above is an exemplary description of the present invention in conjunction with the accompanying drawings. It is obvious that the implementation of the present invention is not limited to the above-mentioned method. As long as various improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for designing anchor bolt length for a large-section tunnel constructed using the New Austrian Tunneling Method, characterized in that: include: Step S1: The equipment enters the site and determines the specific location of the surrounding rock loosening zone measurement; Step S2, determining the depth of the surrounding rock loosening zone according to the detection results, and determining the anchoring length and free length of the anchor rod according to the engineering characteristics; Step S3, carrying out anchor rod construction; Step S4: after completing the construction of some anchor bolts, measure to determine the depth of the loose zone of the surrounding rock after the flexible support, and further adjust the anchoring length and free length of the subsequent anchor bolts; Step S5, complete the closure of the anchor bolt installation, implement the remaining initial support, and perform the final measurement of the surrounding rock loosening circle, and then adjust the anchor length and free length of the anchor bolt according to the depth of the surrounding rock loosening circle in the installation direction of each anchor bolt.

2. The method for designing anchor bolt length for a large-section tunnel constructed by the New Austrian Tunneling Method according to claim 1 is characterized in that: The specific location of the surrounding rock loosening zone measurement includes the section mileage, measuring point coordinates and detection angles along one ring of the tunnel.

3. The method for designing anchor bolt length for a large-section tunnel constructed by the New Austrian Tunneling Method according to claim 1 is characterized in that: Engineering properties include anchor parameters and formation parameters.

4. The method for designing anchor bolt length for a large-section tunnel constructed by the New Austrian Tunneling Method according to claim 1 is characterized in that: The anchoring length of the anchor rod is greater than the depth of the loose zone of the surrounding rock, and the anchoring length of the anchor rod is less than the free length of the anchor rod.

5. The method for designing anchor bolt length for extra-large cross-section tunnels constructed by NATM according to claim 1 is characterized in that: In step S2, the loosening conditions of the surrounding rocks in different anchor bolting directions are detected to determine the main distribution range of the loosening circle, and the size of the loosening circle of the surrounding rock is plotted according to the detection results of measuring points at different positions, and the depth of the loosening circle of the surrounding rock in the anchor bolting direction is listed.

6. The method for designing anchor bolt length for a large-section tunnel constructed by the New Austrian Tunneling Method according to claim 1 is characterized in that: In step S3, during the anchor construction, the weak positions of the surrounding rock are firstly anchored, and then the stable positions of the surrounding rock are anchored.

7. The method for designing anchor bolt length for a large-section tunnel constructed by the New Austrian Tunneling Method according to claim 1 is characterized in that: In step S4, after completing the construction of some anchors, the depth of the loose zone of the surrounding rock after the flexible support is measured by ultrasonic detection, and the anchoring length and free length of the subsequent anchors are further adjusted according to the changes in the loose zone of the surrounding rock.

8. The method for designing anchor bolt length for a large-section tunnel constructed by the New Austrian Tunneling Method according to claim 1 is characterized in that: The calculation formula of surrounding rock loosening zone is: Among them, R p is the surrounding rock loosening zone, D is the tunnel lining radius, K is the surrounding rock coefficient, which is related to the characteristics of the stratum material, and σ0 is the confining pressure under the burial depth condition.

9. The method for designing anchor bolt length for a large-section tunnel constructed by the New Austrian Tunneling Method according to claim 1 is characterized in that: The calculation formula of the anchor length of the anchor rod is: Among them, L a is the anchorage length of the anchor rod, T is the design tensile strength of the anchor rod, σ t is the anchorage unit stress of the anchor rod, c is the anchorage performance coefficient; The calculation formula of anchor unit stress of anchor bolt is: Among them, σ t is the anchoring unit stress of the anchor rod, d is the anchor rod diameter, and T is the design tensile strength of the anchor rod.

10. The method for designing anchor bolt length for a large-section tunnel constructed by the New Austrian Tunneling Method according to claim 1, characterized in that: Also includes: Step S6: Perform a pull-out test on the anchor rod to determine the anchoring effect of the anchor rod.

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