A structure and method for regulating surrounding rock pressure in shallow-buried loess tunnels

Abstract

This invention discloses a structure and method for regulating surrounding rock pressure in shallow-buried loess tunnels, belonging to the technical field of shallow-buried loess tunnels. It solves the problem of reduced safety performance of existing shallow-buried loess tunnel support structures due to uneven load distribution. The invention includes a tunnel with initial support and secondary lining. Multiple load regulation layers are provided on the initial support, including two abutment load regulation layers and two arch foot load regulation layers. The two abutment load regulation layers are located at the abutments on both sides of the initial support, and the two arch foot load regulation layers are located at the arch feet on both sides of the initial support. The load regulation layers of this invention control uneven settlement of the strata in shallow-buried loess tunnels, curb the disorderly expansion of shear fracture surfaces, and improve the soil strength at the abutments and arch feet. This achieves uniform regulation of surrounding rock pressure, reducing the load on the support structure and improving its safety.

Description

Technical Field

[0001] This invention relates to the field of shallow-buried loess tunnel technology, specifically to a structure and method for regulating surrounding rock pressure in shallow-buried loess tunnels. Background Technology

[0002] Taking the construction of numerous loess tunnels as an opportunity, scholars at home and abroad have accumulated a wealth of monitoring data on the surrounding rock pressure of shallow-buried loess tunnels. Among them, the butterfly-shaped spatial distribution of the surrounding rock pressure in shallow-buried loess tunnels has been confirmed by a large amount of measured data. Specifically, the measurements show that stress concentration is common at the arch shoulders and arch feet of the tunnel, while the stress at the arch crown, arch waist, and invert center is relatively small. The surrounding rock pressure has a "cat ear" distribution pattern at the upper arch ring of the tunnel and a "tooth root" distribution pattern at the tunnel bottom.

[0003] The butterfly-shaped distribution of surrounding rock pressure in shallow-buried loess tunnels deviates significantly from existing design specifications. The stress concentration at the arch shoulders and arch feet greatly worsens the internal force state of the support structure, leading to widespread tunnel structural defects such as lining cracking and severe water leakage. However, current design and construction practices fail to adequately reflect the concept of uniform control of surrounding rock pressure. Some existing technologies, by simply increasing the strength and stiffness of the support structure, contradict the principles of safety, applicability, economic rationality, and environmental protection in tunnel construction. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a structure and method for regulating the surrounding rock pressure of shallow-buried loess tunnels, which solves the problem of reduced safety performance of existing support structures for shallow-buried loess tunnels due to uneven load distribution.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] Firstly, a structure for regulating the surrounding rock pressure of a shallow-buried loess tunnel is provided, including a tunnel with initial support and secondary lining. The tunnel has multiple load regulation layers on the initial support. The multiple load regulation layers include two load regulation layers for the arch shoulder and two load regulation layers for the arch foot. The two load regulation layers for the arch shoulder are located on the two sides of the arch shoulder on the initial support, and the two load regulation layers for the arch foot are located on the two sides of the arch foot on the initial support.

[0007] In this scheme, the load control layer controls the uneven settlement of the strata in the shallow-buried loess tunnel, curbs the disorderly expansion of the shear fracture surface, and improves the soil strength at the arch shoulder and arch foot. This achieves the regulation of the surrounding rock pressure from uneven to uniform, and has the advantages of reducing the load on the support structure and improving its safety. Compared with some existing technologies that simply increase the strength and stiffness of the support structure, the load control layer in this scheme has low construction cost and good effect, which is in line with the principles of safety, applicability, economic rationality, and environmental protection in tunnel construction.

[0008] Furthermore, the load control layer includes multiple grouting conduits for forming the grouting reinforcement layer. Each grouting conduit is welded to the steel arch frame of the initial support via L-beams, and each conduit has multiple grouting holes arranged in a quincunx pattern. The grouting reinforcement layer is a shear-resistant plate structure formed by grouting multiple conduits with cement grout. By welding grouting conduits to the steel arch frame and utilizing the grout to diffuse from the grouting holes into the surrounding soil to form a plate-like structure, a high-strength grouting reinforcement layer is formed without significantly damaging the surrounding soil. This grouting reinforcement layer indirectly controls the surrounding rock pressure by controlling uneven ground settlement, inhibiting the disorderly expansion of the ground shear fracture surface, and improving the soil strength at the arch shoulder and arch foot locations.

[0009] Furthermore, one end of the arch shoulder load control layer is located at 40° of the initial support arch shoulder, and the other end of the arch shoulder load control layer is inclined upward at 8° and extends for more than 3.5m. The grouting reinforcement radius of the arch shoulder load control layer is greater than 0.3m, and the elastic modulus of the arch shoulder load control layer is greater than 400MPa. One end of the arch foot load control layer is located at the initial support arch foot, and the other end of the arch foot load control layer is inclined downward at 15° and extends for more than 4.0m. The grouting reinforcement radius of the arch foot load control layer is greater than 0.3m, and the elastic modulus of the arch foot load control layer is greater than 400MPa.

[0010] Secondly, a method for regulating the surrounding rock pressure of shallow-buried loess tunnels is provided, including the following steps:

[0011] S1. Determine the range of structural parameters for the load control layer. The structural parameters include length a, reinforcement radius b, tilt angle c, and elastic modulus d.

[0012] S2. Based on the structural parameter range of the load control layer, take representative parameters a, b, c, and d respectively, a1~a n b1~b n ,c1~c n d1~d n Orthogonal experimental design was conducted, and the optimal representative parameters of the abutment load control layer and the arch foot load control layer were obtained by solving the numerical calculation software FLAC 3D [a] s ,b s ,c s ,d s ] and [a′ s ,b′ s ,c′ s ,d′ s ], where n is a positive integer;

[0013] S3. Calculate the difference Δ between the vertical loads of the tunnel arch before and after the construction of the arch shoulder load control layer and the arch foot load control layer, and use the numerical calculation software FLAC 3D to calculate the distribution map of the plastic zone of the strata before and after the construction of the load control layer, and comprehensively verify the load control effect.

[0014] S4. When the tunnel is excavated to the upper bench and arch foot, according to [a] s ,b s ,c s ,d s ] and [a′ s ,b′ s ,c′ s ,d′ s The parameters are used to construct the arch shoulder load control layer and the arch foot load control layer simultaneously with the initial support of the tunnel.

[0015] In this scheme, the method can quickly determine the optimal load control layer structure parameters based on the tunnel cross-section size and surrounding rock conditions, thereby achieving good control of uneven loads acting on the tunnel structure.

[0016] Furthermore, the method for determining the range of structural parameters for the load control layer in S1 is as follows:

[0017] The range of values ​​for length 'a' should be:

[0018] a≥max{L1,L2}

[0019] In the formula, L1 is the minimum length of the load control layer, L1=N(1.5+W / 10), N is the surrounding rock influence coefficient, which is 1.1 for Class IV surrounding rock and 1.2 for Class V surrounding rock; W is the tunnel span; L2 is the minimum length of the load control layer that can penetrate the stratum fracture surface of the shallow buried loess tunnel, which is determined by combining the starting position of the load control layer.

[0020] The range of values ​​for the reinforcement radius b is:

[0021] {b|U1≥b≥U2}

[0022] In the formula, U1 is the maximum grouting radius that can be achieved by a single row of small guide pipes in the loess region; U2>S / 2, where S is the spacing between the small guide pipes.

[0023] The range of values ​​for the tilt angle c is:

[0024] {c|V1≥c≥V2}

[0025] In the formula, V1 is the load control layer installed vertically upwards from the horizontal plane, with an angle of 90° to the horizontal direction; V2 is the load control layer installed vertically downwards from the horizontal plane, with an angle of -90° to the horizontal direction.

[0026] The elastic modulus d takes the following values:

[0027] Where E1 and E2 are the elastic modulus of the soil and the elastic modulus of the grout, respectively; A1, A2 and A represent the cross-sectional areas of the original soil, the grout, and the solidified body after grouting, respectively.

[0028] Furthermore, the representative parameters a, b, c, and d in S2 were selected by combining the range of load control layer structural parameters determined in S1 with existing tunnel construction technical specifications. Since S1 has already determined a range of values ​​for a, b, c, and d, it is easier to eliminate unsuitable load control layer schemes and narrow down the selection range of representative parameters.

[0029] Furthermore, the method for calculating the difference in vertical load on the tunnel arch before and after the construction of the abutment load control layer and the foot load control layer in S3 is as follows:

[0030] Δ=q 浅 -q 浅 ′

[0031]

[0032]

[0033]

[0034]

[0035]

[0036] Where, q 浅 and q′ 浅 γ represents the vertical load on the arch before and after the application of the load control layer; H represents the soil weight and the thickness of the arch overburden; B represents the vertical load on the arch before and after the application of the load control layer. t For tunnel span, To calculate the friction angle, β is the angle between the stratum fracture surface and the tunnel horizontal plane, λ and λ′ are the correlation coefficients before and after the application of the load control layer, and θ and θ′ are the friction angles of the side of the arch-sinking soil column before and after the application of the load control layer.

[0037] This invention discloses a structure and method for regulating surrounding rock pressure in shallow-buried loess tunnels, the beneficial effects of which are:

[0038] To improve the load-bearing characteristics of the support structure, this invention does not simply increase the strength and stiffness of the support structure. Instead, it adopts the proposed load-regulating layer structure, which controls uneven settlement of the strata, curbs the disorderly expansion of the shear fracture surface of the strata, and improves the soil strength at the arch shoulder and arch foot. This achieves the regulation of the surrounding rock pressure from uneven to uniform, solving the problem of the significant reduction in the safety performance of the support structure in loess tunnels due to uneven loads. It has good economic benefits and social value. Attached Figure Description

[0039] Figure 1 A schematic diagram of a tunnel surrounding rock pressure regulation structure;

[0040] Figure 2 Axonometric drawing of the tunnel surrounding rock pressure control structure;

[0041] Figure 3 A three-dimensional schematic diagram showing the location of the load control layer and the initial support steel arch frame;

[0042] Figure 4 This is a schematic diagram showing the location of the load control layer and the initial support steel arch frame.

[0043] Figure 5 A schematic diagram of the load control layer and the position of the steel arch frame when the arch frame spacing is too large;

[0044] Figure 6 This is a map showing the distribution of the plastic zone in the surrounding rock after the construction of a conventional support structure.

[0045] Figure 7 This is a map showing the distribution of the plastic zone of the surrounding rock after the application of the load control layer.

[0046] Among them: 1. Arch shoulder load control layer; 2. Arch foot load control layer; 3. Grouting small pipe; 4. Grouting reinforcement layer; 5. Initial support; 6. Secondary lining; 7. Ground fracture surface of shallow buried loess tunnel. Detailed Implementation

[0047] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0048] According to one embodiment of this application, reference is made to... Figure 1A structure for regulating the surrounding rock pressure of a shallow-buried loess tunnel is provided, including a tunnel with an initial support 5 and a secondary lining 6. The tunnel has multiple load regulation layers on the initial support 5. The multiple load regulation layers include two arch shoulder load regulation layers 1 and two arch foot load regulation layers 2. The two arch shoulder load regulation layers 1 are located at the arch shoulder positions on both sides of the initial support 5, and the two arch foot load regulation layers 2 are located at the arch foot positions on both sides of the initial support 5.

[0049] In this embodiment, the load-regulating layer effectively controls uneven settlement of the strata in shallow-buried loess tunnels, curbs the disorderly expansion of shear fracture surfaces, and improves the soil strength at the arch shoulders and arch feet. This achieves the regulation of surrounding rock pressure from uneven to uniform, reducing the load on the support structure and improving its safety. Compared to some existing technologies that simply increase the strength and stiffness of the support structure, this load-regulating layer has low construction cost and good results, aligning with the principles of safety, applicability, economic rationality, and environmental protection in tunnel construction.

[0050] As a further embodiment, refer to Figures 2-3 The load control layer includes multiple grouting conduits 3 for forming the grouting reinforcement layer 4. Each grouting conduit 3 is welded to the steel arch frame of the initial support via L-beams, and each grouting conduit 3 has multiple grouting holes arranged in a quincunx pattern. The grouting reinforcement layer 4 is a shear-resistant plate structure formed by the hardening of cement grout after grouting through multiple conduits. By welding the grouting conduits 3 to the steel arch frame and utilizing the grout to diffuse from the grouting holes into the surrounding soil to form a plate-like structure, a high-strength grouting reinforcement layer 4 is formed without significantly damaging the surrounding soil. This grouting reinforcement layer 4 indirectly controls the surrounding rock pressure by controlling uneven settlement of the strata, inhibiting the disorderly expansion of the strata shear fracture surface, and improving the soil strength at the arch shoulder and arch foot positions.

[0051] As a further embodiment, one end of the arch shoulder load control layer 1 is located at 40° of the initial support arch shoulder, and the other end of the arch shoulder load control layer 1 is inclined upward at 8° and extends for more than 3.5m. The grouting reinforcement radius of the arch shoulder load control layer 1 is greater than 0.3m, and the elastic modulus of the arch shoulder load control layer 1 is greater than 400MPa. One end of the arch foot load control layer 2 is located at the arch foot of the initial support 5, and the other end of the arch shoulder load control layer 1 is inclined downward at 15° and extends for more than 4.0m. The grouting reinforcement radius of the arch foot load control layer 2 is greater than 0.3m, and the elastic modulus of the arch foot load control layer 2 is greater than 400MPa.

[0052] In this embodiment, the distribution map of the formation plastic zone before and after the application of the load control layer was calculated using FLAC 3D numerical calculation software. (See attached image.) Figures 6-7The construction of the arch shoulder load control layer 1 prevented excessive damage to the soil near the arch shoulder and protected the soil in a small area below it. The construction of the arch foot load control layer 2 reduced the expansion range of the plastic zone at the arch foot. The reduction of the plastic zone range will reduce the load value acting on the initial support 5 structure and make the distribution pattern more uniform.

[0053] According to one embodiment of this application, a method for regulating the surrounding rock pressure of a shallow-buried loess tunnel is provided, comprising the following steps:

[0054] S1. Determine the range of structural parameters for the load control layer. The structural parameters include length a, reinforcement radius b, tilt angle c, and elastic modulus d.

[0055] S2. Based on the structural parameter range of the load control layer, take representative parameters a, b, c, and d respectively, a1~a n b1~b n ,c1~c n d1~d n Orthogonal experimental design was conducted, and the optimal representative parameters of the arch shoulder load control layer 1 and the arch foot load control layer 2 were obtained by solving the numerical calculation software FLAC 3D. S ,b S ,c S ,d S ] and [a′ s ,b′ s ,c′ s ,d′ S ], where n is a positive integer;

[0056] S3. Calculate the difference Δ between the vertical loads of the tunnel arch before and after the construction of the arch shoulder load control layer 1 and the arch foot load control layer 2, and use the numerical calculation software FLAC 3D to calculate the distribution map of the plastic zone of the strata before and after the construction of the load control layer, and comprehensively verify the load control effect.

[0057] Specifically, the method for calculating the difference in vertical load on the tunnel arch before and after the construction of the abutment load control layer 1 and the foot load control layer 2 in S3 is as follows:

[0058] Δ=q 浅 -q 浅 ′

[0059]

[0060]

[0061]

[0062]

[0063]

[0064] Where, q 浅 and q′ 浅 γ represents the vertical load on the arch before and after the application of the load control layer; H represents the soil weight and the thickness of the arch overburden; B represents the vertical load on the arch before and after the application of the load control layer. t For tunnel span, To calculate the friction angle, β is the angle between the stratum fracture surface and the tunnel horizontal plane, λ and λ′ are the correlation coefficients before and after the application of the load control layer, and θ and θ′ are the friction angles of the side of the arch-sinking soil column before and after the application of the load control layer.

[0065] S4. When the tunnel is excavated to the upper bench and arch foot, according to [a] s ,b s ,c s ,d s ] and [a′ s ,b′ s ,c′ s ,d′ s The parameters are as follows: while constructing the initial support 5 of the tunnel, the arch shoulder load control layer 1 and the arch foot load control layer 2 are constructed.

[0066] In this scheme, the method can quickly determine the optimal structural parameters of the load control layer based on the tunnel's cross-sectional size and surrounding rock conditions, thus achieving effective control over the loads acting on the tunnel structure. As a further aspect of this embodiment, the method for determining the range of structural parameters of the load control layer in S1 is as follows:

[0067] The range of values ​​for length 'a' should be:

[0068] a≥max{L1,L2}

[0069] In the formula, L1 is the minimum length of the load control layer, L1=N(1.5+W / 10), N is the surrounding rock influence coefficient, which is 1.1 for Class IV surrounding rock and 1.2 for Class V surrounding rock; W is the tunnel span; L2 is the minimum length of the load control layer that can penetrate the rupture surface 7 of the shallow buried loess tunnel stratum, which is determined by combining the starting position of the load control layer.

[0070] The range of values ​​for the reinforcement radius b is:

[0071] {b|U1≥b≥U2}

[0072] In the formula, U1 is the maximum grouting radius that can be achieved by a single row of small guide pipes in the loess area; U2>S / 2, where S is the spacing between the grouting small guide pipes.

[0073] The range of values ​​for the tilt angle c is:

[0074] {c|V1≥c≥V2}

[0075] In the formula, V1 is the load control layer installed vertically upwards from the horizontal plane, with an angle of 90° to the horizontal direction; V2 is the load control layer installed vertically downwards from the horizontal plane, with an angle of -90° to the horizontal direction.

[0076] The elastic modulus d takes the following values:

[0077] Where E1 and E2 are the elastic modulus of the soil and the elastic modulus of the grout, respectively; a1, A2 and A represent the cross-sectional areas of the original soil, the grout, and the solidified body after grouting, respectively.

[0078] As a further embodiment, the representative parameters of a, b, c, and d in S2 are selected by combining the range of load control layer structural parameters determined in S1 with existing tunnel construction technical specifications. Since S1 has already determined a range of values ​​for a, b, c, and d, it is easier to eliminate unsuitable load control layer schemes and narrow down the selection range of representative parameters.

[0079] Example 1

[0080] In this embodiment, the excavation span of a certain tunnel is 12.6m, the tunnel burial depth is 20.0m, and the unit weight of the surrounding rock is 17.2kN / m³. 3 The internal friction angle is 25.0°, and the cohesion is 32.0 kPa. In the above geological section, the range of values ​​for each parameter in the load control layer is obtained based on formula calculations and relevant test data, and satisfies the following:

[0081] The length 'a' of the load control layer is within the range of: a ≥ max{3.03m, 1.92m};

[0082] The value range of the reinforcement radius b of the load control layer is: {b|0.7m≥b≥0.3m};

[0083] The range of the inclination angle c of the load control layer is: {c|90°≥c≥-90°};

[0084] The range of the elastic modulus d of the load control layer is: {d|900MPa≥d≥200MPa};

[0085] Based on the determined range of parameters for each load-adjusting layer, representative parameters are selected. In this example, the starting construction positions of the arch shoulder load-adjusting layer 1 are 30°, 40°, and 50° of the arch shoulder, with lengths of 3.5m, 4.0m, and 4.5m, reinforcement radii of 0.3m, 0.4m, and 0.5m, inclination angles of 0°, 8°, and 16°, and elastic moduli of 400MPa, 600MPa, and 800MPa, respectively. The arch foot load-adjusting layer 2 has lengths of 3.5m, 4.0m, and 4.5m, reinforcement radii of 0.3m, 0.4m, and 0.5m, inclination angles of 0°, -15°, and -30°, and elastic moduli of 400MPa, 600MPa, and 800MPa, respectively.

[0086] It should be noted in this embodiment that the location for load control at the tunnel arch foot is fixed, so it is not necessary to select representative parameters for the initial construction location of the arch foot load control layer 2.

[0087] After determining the representative parameters of the load control layer, an orthogonal experimental design was carried out. The numerical calculation software FLAC 3D was used as the research tool, and the evaluation indexes were reduced surrounding rock pressure and improved support structure safety performance. The optimal design parameters of the arch shoulder load control layer 1 and the arch foot load control layer 2 were solved respectively.

[0088] The final results show that the starting position of the arch shoulder load control layer 1 is 40° at the arch shoulder, with a length greater than 3.5m, intersecting the horizontal line at an angle of 8° upwards, a grouting reinforcement radius greater than 0.3m, and an elastic modulus greater than 400MPa; the starting position of the arch foot load control layer 2 is located at the arch foot, with a length greater than 4.0m, intersecting the horizontal line at an angle of -15° downwards, a grouting reinforcement radius of 0.3m, and an elastic modulus greater than 400MPa.

[0089] The difference Δ in the vertical load of the tunnel arch before and after the construction of the abutment load control layer 1 and the foot load control layer 2 was calculated to further verify the load control effect.

[0090] Δ=q 浅 -q 浅 ′

[0091]

[0092]

[0093]

[0094]

[0095]

[0096] Where, q 浅and q′ 浅 γ represents the vertical load on the arch before and after the application of the load control layer; H represents the soil weight and the thickness of the arch overburden; B represents the vertical load on the arch before and after the application of the load control layer. t For tunnel span, To calculate the friction angle, β is the angle between the stratum fracture surface and the tunnel horizontal plane; λ and λ′ are the correlation coefficients before and after the application of the load control layer; θ and θ′ are the friction angles on the sides of the arch-sinking soil column before and after the application of the load control layer. In this geological condition, the surrounding rock level is IV. Without the load control layer, the friction angle of the vertical sliding surface of the arch-sinking soil is taken as the most unfavorable working condition. After the load-regulating layer is applied, the ground settlement tends to be uniform, and the resistance of the wedge-shaped soil on both sides to the subsiding soil in the middle is enhanced. At this time, the sliding friction angle is taken as... Substituting the above parameters into the vertical load calculation formula, the vertical loads on the arch before and after the application of the load control layer were obtained as 252.8 kPa and 189.4 kPa, respectively, with a load reduction of 63.4 kPa, demonstrating the good effect of the load control technology. Simultaneously, the distribution maps of the plastic zone of the strata before and after the application of the load control layer were calculated using FLAC 3D numerical calculation software, as shown in the figure. Figures 6-7 The study found that the range of the plastic failure zone of the strata was significantly reduced; the numerical calculation and theoretical calculation of the surrounding rock pressure at the crown were also very close; after the load adjustment, the concentrated load at the arch shoulder and arch foot positions decreased by about 20-30%, which shows the reliability of the load control technology.

[0097] The specific implementation method is as follows:

[0098] 1) Shallow-buried loess tunnels are generally excavated in stages. When excavation reaches the upper bench and arch foot, see... Figure 2 Construct 3 grouting pipes according to the above design parameters;

[0099] 2) The grouting guide pipe 3 is made of hot-rolled steel pipe with a diameter of 42mm and a wall thickness of 3.5mm. The pipe wall is drilled with 6mm grouting holes, and the hole spacing is 15cm, arranged in a quincunx pattern.

[0100] 3) The spacing of the grouting pipes 3 should, in principle, be consistent with the spacing of the steel arch frames in the initial support 5, see... Figure 4 On one side of the erected steel arch frame, determine the drilling position according to the design. The drilling position should not be too close to the steel arch frame to prevent the drill rod from affecting the grouting of the steel arch frame.

[0101] 4) Before the installation of the grouting pipe 3, a hole should be pre-drilled using a pneumatic drill. The diameter of the hole should be 50mm. When the design depth is reached, high-pressure air should be used to blow out the dust in the hole. The drilling depth should be measured using a tape measure. The diameter of the hole should be measured using a PVC pipe that is 10mm larger than the grouting pipe 3.

[0102] 5) Use a pneumatic drill to push in the grouting guide pipe 3, ensuring the drilling length is greater than 90% of the pipe length. The opening of the grouting guide pipe 3 should protrude 15cm from the sprayed concrete surface. Use L-shaped reinforcing bars to weld it to the steel arch frame. See [link / details]. Figure 4 ;

[0103] 6) Employing the fracturing grouting mechanism, grout is injected through the grouting conduit 3. The grout material is a 0.6–0.8:1 cement grout, and grouting is performed using a single-stage pressurization method. The grouting pressure is controlled between 0.5 and 1.0 MPa, and adjusted according to actual conditions during construction. After grouting, backfilling and sealing can be carried out using pressure grouting or mechanical grouting. The grouting effect should be tested according to relevant specifications.

[0104] This plan needs to emphasize that: (Refer to...) Figure 5 To ensure the effectiveness of use, if the spacing between adjacent grouting pipes 3 is too large, resulting in the inability to form an overlapping plate-like structure between the grouting units after grouting is completed, the grouting pipes 3 can be appropriately densified along the longitudinal direction of tunnel excavation.

[0105] Example 2

[0106] In this embodiment, the excavation span of a certain tunnel is 15.2m, the tunnel burial depth is 15.0m, and the unit weight of the surrounding rock is 16.5kN / m³. 3 The internal friction angle is 27.0°, and the cohesion is 24.0 kPa. Similar to Example 1, based on the determined range of values ​​for each parameter of the load control layer, representative parameters were selected for orthogonal experimental design. The optimal design parameters for the arch shoulder load control layer 1 and the arch foot load control layer 2 were obtained using the numerical calculation software FLAC 3D. This example calculated that the starting position of the arch shoulder load control layer 1 is 40° at the arch shoulder, with a length greater than 3.5m, intersecting the horizontal line at an 8° angle upwards, a grouting reinforcement radius greater than 0.3m, and an elastic modulus greater than 400 MPa; the starting point of the arch foot load control layer 2 is located at the arch foot, with a length greater than 4.0m, intersecting the horizontal line at a -15° angle downwards, a grouting reinforcement radius greater than 0.3m, and an elastic modulus greater than 400 MPa. In this type of geological condition, the surrounding rock grade is V. Without the load control layer, the friction angle of the vertical sliding surface of the subsided soil at the arch is taken as the most unfavorable condition. After the load-regulating layer is applied, the ground settlement tends to be uniform, and the resistance of the wedge-shaped soil on both sides to the subsiding soil in the middle is enhanced. At this time, the sliding friction angle is taken as... Substituting the above parameters into the vertical load calculation formula, the vertical loads of the arch before and after the application of the load adjustment layer were calculated to be 224.0 kPa and 208.3 kPa, respectively, with a load reduction of 15.7 kPa. At the same time, the range of the plastic failure zone of the stratum was calculated using FLAC 3D numerical calculation software. The distribution of the surrounding rock pressure values ​​at the arch crown obtained by theoretical calculation and numerical calculation was close. The concentrated loads at the arch shoulder and arch foot were weakened after the load adjustment, which mutually verified the reliability of the load adjustment technology.

[0107] The specific construction process is the same as that in Example 1.

[0108] Although specific embodiments of the invention have been described in detail with reference to the accompanying drawings, this should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by a person skilled in the art without inventive effort within the scope described in the claims still fall within the scope of protection of this patent.

Claims

1. A structure for regulating surrounding rock pressure in a shallow-buried loess tunnel, comprising a tunnel with initial support (5) and secondary lining (6), characterized in that: The tunnel is provided with multiple load control layers on the initial support (5). The multiple load control layers include two shoulder load control layers (1) and two foot load control layers (2). The two shoulder load control layers (1) are located on the two sides of the initial support (5), and the two foot load control layers (2) are located on the two sides of the initial support (5). The load control layer includes multiple grouting conduits (3) for forming the grouting reinforcement layer (4). Each grouting conduit (3) is welded to the steel arch frame of the initial support (5) by L-beams, and each grouting conduit (3) has multiple grouting holes arranged in a quincunx pattern. The grouting reinforcement layer (4) is a shear plate structure formed by grouting multiple grouting conduits (3) with cement grout. One end of the shoulder load control layer (1) is located at 40° of the shoulder of the initial support (5), and the other end of the shoulder load control layer (1) is inclined upward at 8° and extended for a length greater than 3.5m. The reinforcement radius of the grouting reinforcement layer (4) of the shoulder load control layer (1) is greater than 0.3m, and the elastic modulus of the shoulder load control layer (1) is greater than 400MPa. One end of the arch foot load control layer (2) is located at the arch foot of the initial support (5), and the other end of the arch foot load control layer (2) is inclined downward at 15° and extended for a length greater than 4.0m. The reinforcement radius of the grouting reinforcement layer (4) of the arch foot load control layer (2) is greater than 0.3m, and the elastic modulus of the arch foot load control layer (2) is greater than 400MPa.

2. The method for regulating the surrounding rock pressure of a shallow-buried loess tunnel according to claim 1, characterized in that: Includes the following steps: S1. Determine the range of structural parameters for the load control layer. The structural parameters include length a, reinforcement radius b, tilt angle c, and elastic modulus d. S2. Based on the structural parameter range of the load control layer, select representative parameters a, b, c, and d respectively. , , , Orthogonal experimental design was conducted, and the optimal representative parameters of the arch shoulder load control layer (1) and arch foot load control layer (2) were obtained by solving the numerical calculation software FLAC 3D. and where n is a positive integer; S3 The difference in vertical load on the tunnel arch before and after the construction of the abutment load control layer (1) and the foot load control layer (2) was calculated. The distribution map of the plastic zone of the strata before and after the application of the load control layer was obtained by numerical calculation software FLAC 3D, and the load control effect was comprehensively verified. S4. When the tunnel is excavated to the upper bench and arch foot, according to and The parameters are as follows: while constructing the initial support (5) of the tunnel, the load control layer (1) of the arch shoulder and the load control layer (2) of the arch foot are constructed.

3. The method for regulating the surrounding rock pressure of a shallow-buried loess tunnel according to claim 2, characterized in that: The method for determining the range of structural parameters for the load control layer in S1 is as follows: The range of values ​​for length 'a' is: In the formula, To determine the minimum length of the load control layer, , The influence coefficient of the surrounding rock is 1.1 for Class IV surrounding rock and 1.2 for Class V surrounding rock. The minimum length that the load control layer can penetrate the rupture surface (7) of the shallow buried loess tunnel is determined by combining the starting construction position of the load control layer; The range of values ​​for the reinforcement radius b is: In the formula, This represents the maximum grouting radius achievable with a single row of small guide pipes in the loess region. , The spacing of the grouting guide pipes (3); The range of values ​​for the tilt angle c is: In the formula, The load control layer is installed perpendicular to the horizontal plane and at an angle of 90° to the horizontal direction. The load control layer is installed perpendicular to the horizontal plane and downwards, at an angle of -90° to the horizontal direction; The elastic modulus d takes the following values: ,in , These are the elastic modulus of soil and the elastic modulus of grout, respectively. , and These represent the cross-sectional areas of the original soil, the grouting body, and the solidified body after grouting, respectively.

4. The method for regulating the surrounding rock pressure of a shallow-buried loess tunnel according to claim 2, characterized in that: The representative parameters of a, b, c, and d in S2 were selected by combining the range of load control layer structural parameters determined in S1 with existing tunnel construction technical specifications.

5. The method for regulating the surrounding rock pressure of a shallow-buried loess tunnel according to claim 2, characterized in that: The method for calculating the difference in vertical load on the tunnel arch before and after the construction of the abutment load control layer and the foot load control layer in S3 is as follows: 、 ； ； in, and These are the vertical loads on the arch before and after the application of the load control layer; For soil weight, The thickness of the soil covering the arch; For tunnel span, To calculate the friction angle, The angle between the stratum fracture surface and the tunnel horizontal plane. and These are the correlation coefficients before and after the application of the load control layer. These are the friction angles of the sides of the arched subsidence columns before and after the application of the load control layer.

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