Method for reducing bias stress of tunnel surrounding rock

Abstract

This invention, entitled "A Method for Reducing Bias Stress in Tunnel Surrounding Rock," belongs to the field of tunnel engineering construction technology. The technical problem it aims to solve is that existing methods for addressing bias stress in tunnel surrounding rock primarily rely on reinforcement, which suffers from drawbacks such as high material consumption, significant construction difficulty, and long construction periods. These methods are ineffective in mitigating the problem of easily damaged tunnel support structures caused by unbalanced horizontal lateral pressure at tunnel entrances and exits. The key technical solution involves collecting engineering geological parameters and mechanical properties of the backfill concrete in the bias stress zone of the tunnel, calculating the total horizontal lateral pressure on the inside and outside of the tunnel, determining the bias stress risk, establishing a benchmark point, and peeling off the overburden layer and backfilling concrete on the outside of the tunnel. The peeling angle or concrete backfill elevation is iteratively adjusted until the difference in total horizontal lateral pressure between the inside and outside of the tunnel meets the engineering requirements.

Description

Technical Field

[0001] This invention belongs to the field of tunnel engineering construction technology, and specifically relates to a method for reducing the eccentric stress of the surrounding rock in a tunnel. Background Technology

[0002] In tunnel construction, the entrance and exit areas are generally characterized by large topographic relief and complex engineering geological conditions, making rock eccentricity a common engineering problem under such conditions. After tunnel excavation, the structure will be subjected to significant unbalanced forces formed by the horizontal lateral pressures on the inner and outer sides of the tunnel. Under the continuous influence of this unbalanced load, the tunnel support structure is highly susceptible to failure, which is a core safety management challenge in the construction of tunnel entrance and exit sections. Based on the calculation theory of horizontal lateral pressure of tunnel surrounding rock, the eccentric stress is mainly controlled by three core parameters: the unit weight of the surrounding rock, the height difference between the inner and outer sides of the tunnel arch and the ground, and the lateral pressure coefficient of the surrounding rock on the inner and outer sides of the tunnel. How to effectively alleviate the eccentric load in an eccentric engineering geological environment is a technical problem that engineers in this field urgently need to solve.

[0003] For tunnels under eccentric pressure conditions, existing conventional treatment methods mainly focus on reinforcement, which can be divided into three categories: The first category is slope side support and anchoring measures, which involves constructing anti-slide piles, retaining walls, prestressed anchor cables and other reinforcement structures on the outside of the tunnel; the second category is tunnel internal structure strengthening measures, which involves improving the structure's resistance to eccentric loads by strengthening the internal support of the tunnel and adding rigid support structures; the third category is a combined treatment scheme that uses the above two types of measures.

[0004] However, the existing measures mentioned above all have unavoidable inherent defects: the implementation of the project requires a large amount of main engineering materials, resulting in high material input costs; the working space in the tunnel entrance and exit areas is limited, the construction of the retaining structure and the reinforcement of the tunnel support are complex, and the on-site construction is difficult; at the same time, the reinforced structure must reach the design strength before the subsequent tunnel main work can be carried out, resulting in a long overall construction cycle and making it impossible to achieve efficient and low-cost treatment of the tunnel bias problem.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] In order to solve the above-mentioned technical problems in the prior art, the present invention provides a method for reducing the bias stress of the surrounding rock of tunnels. This method solves the problem that the existing treatment of bias stress in the surrounding rock of tunnels mainly relies on reinforcement, which has the disadvantages of high material consumption, high construction difficulty and long construction period. It cannot effectively alleviate the problem that the tunnel support structure is easily damaged due to unbalanced horizontal lateral pressure at the tunnel entrance and exit.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A method for reducing the eccentric stress in the surrounding rock of a tunnel includes: S1. Collect engineering geological parameters of the tunnel bias zone, as well as the physical and mechanical properties of the backfill concrete. S2. Based on the parameters collected in step S1, calculate the horizontal lateral pressure inside the tunnel and the horizontal lateral pressure outside the tunnel, and calculate the total horizontal lateral pressure inside the tunnel and the initial total horizontal lateral pressure outside the tunnel respectively. S3. Compare the total horizontal lateral pressure inside the tunnel with the initial total horizontal lateral pressure outside the tunnel. If the difference between the two exceeds the allowable range for engineering safety, proceed with the next steps. S4. Determine the benchmark point of the tunnel bias section. Using the benchmark point as a reference, peel off the overburden layer above the tunnel to the outside of the tunnel. After peeling, backfill the peeled area with concrete. S5. Calculate the total horizontal lateral pressure on the outside of the tunnel after backfilling with concrete. S6. Compare the total horizontal lateral pressure inside the tunnel with the total horizontal lateral pressure outside the tunnel after backfilling. Adjust the parameters of the stripping operation or the backfill elevation of the concrete. Repeat step S5 and the comparison operation until the difference between the two meets the set requirements.

[0009] Furthermore, the engineering geological parameters include the topographic slope of the tunnel bias zone, stratum lithology, overburden thickness, physical and mechanical properties of each rock stratum, and surrounding rock grade.

[0010] Furthermore, in step S2, the horizontal lateral pressure is calculated based on the unit weight of the surrounding rock, the distance from the calculation point to the ground, and the lateral pressure coefficient; The lateral pressure coefficient is determined based on the calculated friction angle of the surrounding rock, the ground slope angle, the friction angles on both sides of the top rock-soil column, and the rupture angle when the maximum thrust is generated on the inner and outer sides.

[0011] Furthermore, in step S4, the reference point is determined using any of the following methods: The reference point is the point where the line of symmetry of the vertical axis of the tunnel center contacts the ground surface above the tunnel. Starting from the ground boundary between the biased and non-biased sections of the tunnel, a perpendicular line is drawn longitudinally from the tunnel road, and the intersection of this perpendicular line and the tunnel axis is taken as the reference point.

[0012] Furthermore, in step S4, the initial operating parameters for stripping the overburden are as follows: with reference to the benchmark point, the initial angle for stripping the overburden outward from the tunnel is 45°, and the stripping range extends along the bedrock surface to a position one tunnel diameter away from the tunnel axis. Then, the remaining overburden is stripped by sloping outward from the tunnel at the initial angle.

[0013] Furthermore, in step S4, the concrete is backfilled to the elevation of the benchmark point, and the top surface of the concrete after backfilling is horizontal.

[0014] Furthermore, in step S6, when the total horizontal lateral pressure on the outside of the backfilled tunnel is greater than the total horizontal lateral pressure on the inside of the tunnel, the angle of peeling off the overburden layer to the outside of the tunnel is reduced, and step S5 and the comparison operation are repeated.

[0015] Furthermore, the angle of the stripped overburden was reduced to 30°, and the stripping range was maintained to extend along the bedrock surface to a position one tunnel diameter away from the tunnel axis.

[0016] Furthermore, in step S6, when the total horizontal lateral pressure on the outside of the tunnel after backfilling is less than the total horizontal lateral pressure on the inside of the tunnel, the backfill elevation of the concrete is raised according to the set gradient, and step S5 and the comparison operation are repeated.

[0017] Furthermore, in step S6, the setting requirement is that the total horizontal lateral pressure inside the tunnel is consistent with the total horizontal lateral pressure outside the tunnel after backfilling.

[0018] The beneficial effects of this invention are as follows: (1) To solve the problems of high material consumption, high construction difficulty and long cycle of existing tunnel bias reinforcement measures, by stripping the outer overburden layer and backfilling concrete, the horizontal pressure on the outer side is precisely controlled to achieve the balance of the inner and outer side pressure of the tunnel, eliminate the bias stress of the surrounding rock from the root, and ensure the safety of the tunnel structure. (2) Only open-air conventional operations such as stripping the overburden and backfilling concrete are required. The procedures are simple, avoiding the limitation of limited working space at the tunnel entrance and exit, and greatly reducing the difficulty of construction. At the same time, the input of main materials is reduced, the disposal cost is reduced, and there is no need to wait for the structure to reach the standard, which greatly shortens the construction cycle and achieves efficient and low-cost disposal of tunnel bias. (3) By iteratively adjusting the peeling angle of the overburden and the backfill elevation of the concrete, the horizontal pressure difference between the inside and outside of the tunnel is precisely controlled to ensure that the treatment effect meets the requirements set by the project. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of tunnel bias provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the stripped concrete backfill area provided in an embodiment of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0021] It should be noted that, unless otherwise specifically stated, the relative arrangement and numerical expressions of the components and steps described in these embodiments should not be construed as limiting the scope of the invention.

[0022] The following description of exemplary embodiments is merely illustrative and is not intended to limit the invention or its application or use in any way. Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail herein, but where applicable, such techniques, methods, and apparatus should be considered part of this specification.

[0023] Example The present invention proposes a method for reducing the bias stress in the surrounding rock of a tunnel, the specific steps of which may include: S1. Basic Parameter Acquisition: Collect engineering geological parameters of the tunnel's biased stress zone, as well as the physical and mechanical properties of the backfill concrete, to provide complete basic data support for subsequent biased stress calculation and construction parameter design. The engineering geological parameters of the tunnel bias zone include, but are not limited to, the topographic slope, lithology, overburden thickness, physical and mechanical properties of each rock layer, and surrounding rock grade of the tunnel bias zone; the physical and mechanical properties of the backfill concrete include, but are not limited to, the concrete's unit weight, strength, and other core mechanical parameters.

[0024] S2. Initial bias stress calculation: Based on the parameters collected in step S1, calculate the horizontal lateral pressure inside the tunnel and the horizontal lateral pressure outside the tunnel, and calculate the total horizontal lateral pressure inside the tunnel and the initial total horizontal lateral pressure outside the tunnel respectively. See Figure 1 The core parameters for calculating horizontal lateral pressure include the unit weight of the surrounding rock, the vertical distance from the calculation point to the ground, and the lateral pressure coefficient. The calculation formula is as follows: Horizontal lateral pressure inside the tunnel: ; Horizontal lateral pressure outside the tunnel:

[0025] in, The surrounding rock is heavily soiled; , These are arbitrary calculation points inside and outside the tunnel. Vertical distance from the ground; , These are the lateral pressure coefficients inside and outside the tunnel, respectively. The specific calculation formulas are as follows:

[0026]

[0027]

[0028]

[0029] in, The friction angle (°) between the two sides of the top rock-soil column; The slope angle is (°). ; Calculate the friction angle (°) for the surrounding rock; These are the fracture angles (°) at which the maximum thrust is generated on the inner and outer sides, respectively. The lateral pressure coefficient is determined based on the calculated friction angle of the surrounding rock, the slope angle of the ground, the friction angle on both sides of the roof rock-soil column, and the rupture angle when the maximum thrust is generated inside and outside the tunnel. The calculation of the rupture angle and the lateral pressure coefficient follows the relevant theoretical formulas for calculating the eccentric pressure of the surrounding rock in the tunnel.

[0030] S3. Determination of bias risk: Compare the total horizontal lateral pressure inside the tunnel with the initial total horizontal lateral pressure outside the tunnel. If the difference between the two exceeds the allowable range for engineering safety, proceed with the next steps. Specifically, by comparing the total horizontal lateral pressure inside the tunnel calculated in step S2 with the initial total horizontal lateral pressure outside the tunnel, it is determined whether the difference between the two exceeds the allowable range for engineering safety. S31. If the difference between the two values ​​is within the allowable range of engineering safety, it is determined that the bias stress is small and will not cause any risk to affect the construction of the project due to bias. The risk of bias in the tunnel is controllable and no subsequent bias treatment work is required. S32. If the difference between the two exceeds the allowable range for engineering safety, it is determined that the bias stress is too large and may affect engineering safety. The bias stress will have an adverse effect on the safety of the tunnel structure, and the subsequent steps shall be executed.

[0031] The permissible range of engineering safety is determined comprehensively based on tunnel design specifications, tunnel structural safety level, surrounding rock level, and engineering geological conditions.

[0032] S4. Overburden Removal and Concrete Backfilling: Based on the results of steps S1, S2, and S3, when the eccentric stress is large and may affect the safety of the project, the overburden of the eccentrically stressed tunnel will undergo overburden removal and concrete backfilling. Specifically, a reference point will be determined for the eccentrically stressed section of the tunnel. Using this reference point, the overburden above the tunnel will be removed outwards. After removal, concrete will be backfilled in the removed area. This includes: S41. Benchmark point determination, according to... Figure 2 This can be determined using any of the following methods: The first method: take the point of contact between the line of symmetry of the vertical axis of the tunnel center and the ground surface above the tunnel as the reference point; The second method: Take the ground boundary between the biased and non-biased parts of the tunnel as the starting point, draw a perpendicular line longitudinally to the tunnel road direction, and take the intersection of this perpendicular line and the tunnel axis as the reference point.

[0033] S42. Overburden stripping operation: Using a determined benchmark as a reference, strip the loose overburden above the tunnel to the outside of the tunnel (the side of the mountain exposed to the air). The initial operating parameters are: the initial angle for stripping the overburden to the outside of the tunnel is 45°, and the stripping range extends along the bedrock surface to a position one tunnel diameter away from the tunnel axis. Then, slope outwards from the outside of the tunnel according to the initial stripping angle to complete the stripping of the overburden within the entire design range. During the stripping operation, avoid disturbing the surrounding rock and the underlying stable bedrock of the tunnel.

[0034] S43. Concrete backfilling operation: Concrete backfilling operation shall be carried out in the area where the stripping has been completed. The concrete shall be backfilled to the reference point elevation to ensure that the top surface of the concrete after backfilling is horizontal and forms a stable counterweight structure. The backfilling concrete shall be constructed by layering and vibrating to ensure the uniformity and stability of the backfill structure.

[0035] S5. Calculation of total horizontal lateral pressure on the outside of the tunnel after backfilling: Calculate the total horizontal lateral pressure on the outside of the tunnel after backfilling with concrete. Based on the basic parameters determined in step S1 and the backfilling results in step S4, the horizontal lateral pressure on the outside of the tunnel after backfilling concrete is calculated according to the above-mentioned formula for calculating the horizontal lateral pressure of the tunnel, and the total horizontal lateral pressure on the outside of the tunnel is calculated.

[0036] S6. Lateral Pressure Equilibrium Iterative Adjustment: Based on the total horizontal lateral pressure on the inside of the tunnel calculated in step S2 and the total horizontal lateral pressure on the outside of the tunnel calculated in step S5, compare and analyze the magnitudes of the two values, adjust the stripping operation parameters or the concrete backfill elevation, and repeat step S5 and the comparison operation until the difference between the two values ​​meets the set requirements; the specific iterative adjustment rules are as follows: S61. If the total horizontal lateral pressure inside the tunnel is basically the same as the total horizontal lateral pressure outside the tunnel after backfilling, it indicates that the bias problem of the biased tunnel has been eliminated and the treatment operation is completed. The setting requirement mentioned here is that the total horizontal lateral pressure inside the tunnel is basically the same as the total horizontal lateral pressure outside the tunnel after backfilling.

[0037] S62. If the total horizontal lateral pressure on the outside of the tunnel after backfilling is greater than that on the inside of the tunnel, it indicates that the thickness of the backfill concrete on the tunnel arch is too large. Adjust the angle of peeling the overburden layer to the outside of the tunnel. Change the parameter of peeling the overburden layer to the outside of the tunnel at a 45° angle in step S42 to peeling the overburden layer to the outside of the tunnel at a 30° angle. Keep the peeling range extending along the bedrock surface to a position one tunnel diameter away from the tunnel axis. After adjustment, recalculate the total horizontal lateral pressure on the outside of the tunnel according to step S5, and then compare and analyze it with the total horizontal lateral pressure on the inside of the tunnel. Repeat this operation by changing the peeling angle until the total horizontal lateral pressure on the inside of the tunnel is basically the same as that on the outside of the tunnel.

[0038] S63. If the total horizontal lateral pressure on the outside of the tunnel after backfilling is less than the total horizontal lateral pressure on the inside of the tunnel, it indicates that the thickness of the backfill concrete on the tunnel arch is insufficient. Raise the backfill elevation of the concrete according to the set gradient. The set gradient can be adjusted to 0.5m, 0.3m or 0.2m according to the engineering accuracy requirements. After raising the backfill elevation of the concrete according to the corresponding gradient, calculate the stress increment and compare the difference with the total horizontal lateral pressure on the inside of the tunnel. Repeat this operation until the total horizontal lateral pressure on the inside of the tunnel is basically consistent with the total horizontal lateral pressure on the outside of the tunnel.

[0039] The above specific embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for reducing the eccentric stress in the surrounding rock of a tunnel, characterized in that, include: S1. Collect engineering geological parameters of the tunnel bias zone, as well as the physical and mechanical properties of the backfill concrete. S2. Based on the parameters collected in step S1, calculate the horizontal lateral pressure inside the tunnel and the horizontal lateral pressure outside the tunnel, and calculate the total horizontal lateral pressure inside the tunnel and the initial total horizontal lateral pressure outside the tunnel respectively. S3. Compare the total horizontal lateral pressure inside the tunnel with the initial total horizontal lateral pressure outside the tunnel. If the difference between the two exceeds the allowable range for engineering safety, proceed with the next steps. S4. Determine the benchmark point of the tunnel bias section. Using the benchmark point as a reference, peel off the overburden layer above the tunnel to the outside of the tunnel. After peeling, backfill the peeled area with concrete. S5. Calculate the total horizontal lateral pressure on the outside of the tunnel after backfilling with concrete. S6. Compare the total horizontal lateral pressure inside the tunnel with the total horizontal lateral pressure outside the tunnel after backfilling. Adjust the parameters of the stripping operation or the backfill elevation of the concrete. Repeat step S5 and the comparison operation until the difference between the two meets the set requirements.

2. The method for reducing the eccentric stress in the surrounding rock of a tunnel according to claim 1, characterized in that, In step S1, the engineering geological parameters include the topographic slope of the tunnel bias zone, the lithology of the strata, the thickness of the overburden layer, the physical and mechanical properties of each rock layer, and the surrounding rock grade.

3. The method for reducing the eccentric stress in the surrounding rock of a tunnel according to claim 1, characterized in that, In step S2, the horizontal lateral pressure is calculated based on the unit weight of the surrounding rock, the distance from the calculation point to the ground, and the lateral pressure coefficient. The lateral pressure coefficient is determined based on the calculated friction angle of the surrounding rock, the ground slope angle, the friction angles on both sides of the top rock-soil column, and the rupture angle when the maximum thrust is generated on the inner and outer sides.

4. The method for reducing the eccentric stress in the surrounding rock of a tunnel according to claim 1, characterized in that, In step S4, the reference point is determined using any of the following methods: The reference point is the point where the line of symmetry of the vertical axis of the tunnel center contacts the ground surface above the tunnel. Starting from the ground boundary between the biased and non-biased sections of the tunnel, a perpendicular line is drawn longitudinally from the tunnel road, and the intersection of this perpendicular line and the tunnel axis is taken as the reference point.

5. The method for reducing the eccentric stress in the surrounding rock of a tunnel according to claim 1, characterized in that, In step S4, the initial operating parameters for stripping the overburden are as follows: with the reference point as the reference, the initial angle for stripping the overburden outward from the tunnel is 45°, and the stripping range extends along the bedrock surface to a position one tunnel diameter away from the tunnel axis. Then, the remaining overburden is stripped by sloping outward from the tunnel at the initial angle.

6. The method for reducing the eccentric stress in the surrounding rock of a tunnel according to claim 1, characterized in that, In step S4, the concrete is backfilled to the reference point elevation, and the top surface of the concrete after backfilling is horizontal.

7. The method for reducing the eccentric stress in the surrounding rock of a tunnel according to claim 1, characterized in that, In step S6, when the total horizontal lateral pressure on the outside of the backfilled tunnel is greater than the total horizontal lateral pressure on the inside of the tunnel, the angle of peeling off the overburden layer to the outside of the tunnel is reduced, and step S5 and the comparison operation are repeated.

8. The method for reducing the eccentric stress in the surrounding rock of a tunnel according to claim 7, characterized in that, The angle of the stripped overburden is reduced to 30°, and the stripping range extends along the bedrock surface to a position one tunnel diameter away from the tunnel axis.

9. The method for reducing the eccentric stress in the surrounding rock of a tunnel according to claim 1, characterized in that, In step S6, when the total horizontal lateral pressure on the outside of the tunnel after backfilling is less than the total horizontal lateral pressure on the inside of the tunnel, the backfill elevation of the concrete is raised according to the set gradient, and step S5 and the comparison operation are repeated.

10. The method for reducing the eccentric stress in the surrounding rock of a tunnel according to claim 1, characterized in that, In step S6, the setting requirement is that the total horizontal lateral pressure inside the tunnel is the same as the total horizontal lateral pressure outside the tunnel after backfilling.

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