Tunneling method under soft surrounding rock conditions

Abstract

The application discloses a tunneling method under soft surrounding rock conditions, comprising the following steps: S1, performing advanced support construction outside a tunnel excavation contour; S2, dividing a working face into a center soil part, an arc part, a left wall part, a right wall part and an arch restraining part with an arch waist as a center line; S3, excavating the arc part and performing arc initial support construction; S4, excavating the center soil part and pouring temporary inverted arches corresponding to the arc initial support; S5, excavating the left wall part and then performing left wall initial support construction corresponding to the left wall part; S6, excavating the right wall part and then performing right wall initial support construction corresponding to the right wall part; S7, excavating the arch restraining part and then performing arch restraining part construction and concrete backfilling; S8, removing the temporary arch and performing secondary lining; and S9, circular tunneling to an end point. The application has the beneficial effects of controlling the deformation degree of surrounding rock, improving the self-stability of the surrounding rock, reducing the tangential stress of the surrounding rock, the stress of initial support, and the relaxation load borne by the initial support and the secondary lining.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology. More specifically, this invention relates to a tunnel excavation method under conditions of weak surrounding rock. Background Technology

[0002] Tunnels, as crucial elements in transportation, are increasingly being developed in terms of width and length. The addition of weak surrounding rock further exacerbates the risks of tunnel construction. Inappropriate construction methods or support measures can, at best, delay the project schedule, and at worst, cause significant loss of life and property. The definition of a large-section tunnel can refer to the standards recommended by the Japan Tunneling Association and the International Tunneling Association, namely, a cross-sectional area of ​​100–140 m². 2 The tunnel is a large-section tunnel. The difficulty in constructing a large-section tunnel under weak surrounding rock conditions lies in:

[0003] First, stress redistribution after tunnel excavation is detrimental to the stability of the surrounding rock. Studies have shown that in an ideal elastic medium, the maximum principal stress after tunnel excavation is twice the initial stress. When the stress in the surrounding rock exceeds its strength, plastic deformation will occur. For large-section tunnels, the flatness ratio is relatively small, and as the tunnel's height-to-width ratio decreases, the maximum principal stress of the surrounding rock and the bending moment at the arch increase rapidly after excavation. Therefore, large-section tunnels will generate a larger plastic zone and internal forces, which in turn places higher demands on the support structure.

[0004] Secondly, stress concentration is more pronounced at the arch foot, placing higher demands on the foundation's bearing capacity. Extensive numerical simulations and actual engineering monitoring data show that the stress in the surrounding rock of large-section tunnels is greatest on both side walls after excavation. Especially when the lateral pressure coefficient is low, the tangential stress in the surrounding rock gradually increases with the increase in excavation width, leading to a corresponding increase in the initial support stress and reducing the safety reserve of the initial support.

[0005] Third, instability phenomena such as rockfall at the arch crown intensify. The increase in tunnel excavation width leads to a gradual increase in tensile stress in the surrounding rock at the arch crown, which in turn causes instability phenomena such as rockfall at the arch crown.

[0006] Fourth, significant relaxation pressure. Research and engineering examples show that the wider the tunnel excavation section, the greater the required burial depth to achieve arching. If the excavation section is shallow and fails to reach the required depth for arching, significant relaxation pressure will be generated in the upper part of the excavation, and the initial support and secondary lining of the tunnel will bear greater relaxation loads.

[0007] Fifth, the initial support conditions are unfavorable. Large-section tunnels often have a flat profile, and flat arched support structures are not conducive to maximizing the performance of materials.

[0008] Therefore, determining the appropriate construction methods for building tunnels in weak surrounding rock and with large cross-sections to ensure safe construction is an important research direction at present. Summary of the Invention

[0009] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0010] To achieve these objectives and other advantages according to the present invention, a method for tunneling under weak surrounding rock conditions is provided, comprising the following steps:

[0011] S1. Conduct advance support construction outside the tunnel excavation outline;

[0012] S2. The tunnel face is divided into upper and lower layers with the arch waist as the center line. The upper layer is further divided into the central soil part and the arc-shaped part surrounding the central soil part. The lower layer, located above the invert arch, is further divided into the left wall part and the right wall part along the tunnel center line.

[0013] S3. After the advanced support reaches the specified strength, the arc-shaped part is excavated along the tunnel excavation direction, and then the arc-shaped initial support construction corresponding to the arc-shaped part is carried out.

[0014] S4. After the initial arch support reaches the specified strength, excavate the central soil and pour the temporary invert arch corresponding to the initial arch support.

[0015] S5. After the temporary invert arch reaches the specified strength, the left wall is excavated, and then the corresponding initial support construction of the left wall is carried out.

[0016] S6. After the initial support of the left wall reaches the specified strength, the right wall is excavated, and then the corresponding initial support construction of the right wall is carried out.

[0017] S7. After the initial support of the right wall reaches the specified strength, excavate the arch-suppressing part and then backfill with concrete.

[0018] S8. After the arch support reaches the specified strength, the temporary arch support is removed and secondary lining is carried out.

[0019] S9. Repeat steps S1 to S8 until the tunnel excavation is completed.

[0020] Preferably, in step S1, the advanced support adopts multiple grouting pipes arranged along the circumferential spacing of the tunnel arch outside the tunnel excavation outline, and grouting fluid is injected along the grouting pipes. The grouting pipes are inclined upward along the tunnel excavation direction, and the length of the grouting pipes extending into the tunnel excavation direction is greater than the excavation distance of the arc section in the current construction cycle. The grouting pipes of two adjacent construction cycles overlap each other.

[0021] Preferably, the construction methods for the initial support of the arc-shaped wall, the initial support of the left wall, and the initial support of the right wall all adopt the following methods:

[0022] a. Shot concrete is sprayed along the tunnel excavation wall, and then steel mesh is laid;

[0023] b. Anchor bolts are arranged in a plum blossom pattern, and then shotcrete is applied. The anchor bolts located at the arch waist and arch foot are provided with connecting parts on the outside, and the connecting parts are arch-shaped.

[0024] c. Install the grating steel frame, fix the other end of the connecting part to the transverse reinforcement of the grating steel frame, and then spray concrete to the designed thickness.

[0025] Preferably, in step S7, an arch-suppressing steel reinforcement frame is placed inside the excavated arch-suppressing section, and connecting plates are stacked on both sides of the arch-suppressing steel reinforcement frame. The connecting plate includes a plate body, a pull plate set on the outer side of the bottom of the plate body, multiple support rods set on the inner side of the bottom of the plate body, and an abutment plate set on the top of the plate body. Multiple through holes are opened on the plate body. During installation, the support rods are passed through the arch-suppressing steel reinforcement frame and contact the bottom of the arch-suppressing section. The abutment plate abuts against the bottom side wall of the initial support. Then, concrete is poured until the specified strength is reached.

[0026] Preferably, the tunneling length for each construction cycle is less than 15m.

[0027] Preferably, the grouting overlap length of the grouting pipe between two adjacent construction cycles is 1-2m, and the thickness of the advance support is 40-60cm.

[0028] Preferably, the initial support thickness is 40–50 cm.

[0029] Preferably, the thickness of the secondary lining is 30–40 cm.

[0030] The present invention has at least the following beneficial effects:

[0031] First, by dividing the tunnel face into multiple sections and excavating and initially supporting them in stages—the arch section, the central soil section, the left wall section, the right wall section, and the invert section—the working conditions of weak self-stability of the surrounding rock in large-section tunnel construction can be adapted. This staged construction allows for moderate deformation of the surrounding rock, thereby leveraging its self-stabilizing capacity, releasing some stress, and reducing stress accumulation. Furthermore, the arched connections at the arch waist and arch foot prevent excessive deformation of the surrounding rock, thus improving its self-stabilizing capacity.

[0032] Secondly, the stress concentration at the arch foot is significantly alleviated by the setting of the connecting plate. The connecting plate is used to connect the initial support and the invert arch and is integrated into the secondary lining. It can transfer stress among the three and, combined with the tie plate on the outside of the connecting plate extending into the surrounding rock, reduce the tangential stress in the surrounding rock, reduce the stress on the initial support, and reduce the relaxation load borne by the initial support and the secondary lining.

[0033] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the working face division according to one of the technical solutions of the present invention;

[0035] Figure 2 This is a diagram showing the arrangement of the connecting plate according to one of the technical solutions of the present invention;

[0036] Figure 3 This is a top view schematic diagram of the connecting plate according to one of the technical solutions of the present invention;

[0037] Figure 4 This is a diagram showing the arrangement of the connection portion in one of the technical solutions of the present invention. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0039] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the orientation or positional relationship indicated by the terms is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. It does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0040] like Figures 1-4 As shown, the present invention provides a tunnel excavation method under weak surrounding rock conditions, comprising the following steps:

[0041] S1. Use ground-penetrating radar for advanced geological forecasting to obtain engineering geological conditions, including strata lithology and thickness of each stratum, and classify them according to the main characteristics and basic indicators of the tunnel surrounding rock.

[0042] Based on the classification, it is proposed to adopt advanced support 100 construction to improve the stability of the surrounding rock.

[0043] The method for constructing 100mm of advance support outside the tunnel excavation outline is as follows:

[0044] Drill holes at the pre-designed locations along the circumference of the tunnel arch, then install grouting guide pipes and inject grouting fluid along them. The grouting fluid is usually a mixture of cement mortar and injected into the grouting guide pipes by a grouting machine. The grouting endpoint is determined by the grouting pressure, which is usually set at 2-3 MPa. Grouting is then stopped and the grouting fluid is allowed to solidify. The initial setting time of cement grout is generally 45-60 minutes. Therefore, after 50 minutes, a sample can be taken from the borehole to test whether the grout filling porosity reaches more than 80%. If it does, the grout filling is considered qualified, and the next construction step can proceed.

[0045] In order to improve the stability and safety of the connection between two adjacent construction cycles, the grouting pipes are inclined upward along the tunnel excavation direction, and the grouting pipes of two adjacent construction cycles overlap each other, with the overlap length being 1 to 2 meters. The thickness of the advance support 100 is 40 to 60 cm.

[0046] S2. Due to the weak surrounding rock in the location of the tunnel, and the cross-section being 100-140m... 2 Within this area, which is a large-section tunnel with extremely poor surrounding rock stability, sectional excavation and support are implemented to reduce safety risks. The specific method is as follows:

[0047] The tunnel face is divided into upper and lower layers with the arch waist as the center line. The upper layer is divided into the central soil part 2 and the arc-shaped part 1 surrounding the central soil part 2. The lower layer, located above the invert arch, is divided into the left wall part 3 and the right wall part 4 along the tunnel center line.

[0048] S3. After the pre-support 100 reaches the specified strength, that is, after the surrounding rock in the circumference of the excavation site has reached a certain stability and has the ability to cause disturbance to the surrounding rock caused by strain excavation, excavation shall be carried out according to the divided areas and sequence.

[0049] Excavate the arc-shaped section 1 along the tunnel excavation direction. The excavation depth must be less than the depth of the advance support 100mm. Then, promptly implement initial support 200mm at the excavation site. The specific construction method for the initial support 200mm includes:

[0050] a. The excavated tunnel wall is repaired and smoothed to make it flatter, and the slag is removed. Then, concrete is sprayed onto the wall to achieve a certain thickness, and then steel mesh is installed.

[0051] b. The anchor rods 21 are arranged in a plum blossom pattern, and then shotcrete is sprayed to fill the gaps in the steel mesh and wrap part of the anchor rods 21, thereby connecting the initial support 200 with the advanced support 100.

[0052] During construction, it was found that significant settlement, exceeding the standard, often occurred at the arch waist and arch foot. Therefore, a connecting part 22 was welded to the outside of the anchor rod 21 located at the arch waist and arch foot. The connecting part 22 is arched and is formed by bending steel bars. A connecting block 24 is welded to the end of the connecting part 22. The bottom of the connecting block 24 has a groove, which is welded to the anchor rod 21. Then, the groove of another connecting block 24 is connected to the subsequent grid steel frame 23, so that the anchor rod 21 and the grid steel frame 23 are connected together, thereby significantly improving the stress transfer between the anchor rod 21 and the grid steel frame 23.

[0053] c. Install the grating frame 23, ensuring that the connecting block 24 aligns with and welds to the transverse ribs of the grating frame 23. During installation, ensure the base of the grating frame 23 is securely fixed to prevent displacement. Then, spray concrete to the designed thickness.

[0054] The total thickness of the initial support 200 (excluding the length of the anchor bolt 21) is usually 40-50 cm.

[0055] S4. After the initial arc-shaped support 200 reaches the specified strength, excavate the central soil part 2 and pour the temporary invert arch 5 corresponding to the initial arc-shaped support 200; all excavation is carried out using a cantilever excavator. An invert arch-shaped steel frame is used, and then concrete is poured to form the temporary invert arch 5.

[0056] S5. After the temporary invert arch 5 reaches the specified strength, the left wall 3 is excavated, and then the initial support 200 of the left wall corresponding to the left wall 3 is constructed.

[0057] S6. After the initial support 200 on the left wall reaches the specified strength, excavate the right wall 4, and then carry out the construction of the initial support 200 on the right wall corresponding to the right wall 4.

[0058] The initial support 200 in steps S5 and S6 is the same as in step S3, and will not be described again here.

[0059] The excavation sequence of the left wall 3 and the right wall 4 in steps S5 and S4 is determined according to the tunnel advance forecast, with the side with greater plasticity of the surrounding rock being preferred for excavation.

[0060] S7. After the initial support of the right wall reaches the specified strength, excavate the arch-suppressing section 6, and then carry out the construction of the arch-suppressing section 6 and concrete backfilling; the specific method is as follows:

[0061] An arch-suppressing steel frame 61 is placed inside the excavated arch-suppressing section 6. Connecting plates 400 are stacked on both sides of the arch-suppressing steel frame 61. The connecting plate 400 includes a plate body 41, a pull plate 42 set on the outer side of the bottom of the plate body 41, multiple support rods 43 set on the inner side of the bottom of the plate body 41, and an abutment plate 44 set on the top of the plate body 41. Multiple through holes 45 are opened on the plate body 41. During installation, the support rods 43 are passed through the arch-suppressing steel frame 61 and contact the bottom of the arch-suppressing section 6. The abutment plate 44 abuts against the bottom side wall of the initial support 200. Then, concrete is poured until the specified strength is reached.

[0062] As mentioned earlier, the arch foot is a stress concentration point, and under the condition of large-section tunnel construction, excessive settlement is particularly likely to occur. Therefore, during construction, connecting plates 400 are added to both sides of the invert arch steel reinforcement frame to transfer and release the stress at the foot, thereby reducing settlement.

[0063] S8. After the arch suppressor 6 reaches the specified strength, the temporary arch suppressor is removed, and secondary lining 300 is carried out. The timing of the secondary lining 300 is very important and is determined based on the measured settlement. Usually, the secondary lining 300 is carried out after the settlement of the tunnel surrounding rock has stabilized. The thickness of the secondary lining 300 should be 30-40cm.

[0064] S9. Repeat steps S1 to S8 until the tunnel excavation is completed. Note that the excavation length of each construction cycle should be less than 15m.

[0065] The changes brought about by the improvements in this paper are analyzed using a simulation method based on tunnel excavation data.

[0066] By welding connecting parts 22 to the outside of the anchor bolts 21 located at the arch waist and arch foot, and connecting the connecting parts 22 to the grid steel frame 23; and by stacking connecting plates 400 on both sides of the arch-suppressing steel frame 61, it is possible to:

[0067] 1. The maximum value of plastic deformation of the surrounding rock decreases.

[0068] 2. The displacement of the tunnel body is reduced.

[0069] 3. The circumferential stress of the tunnel is reduced.

[0070] 4. The radial stress values ​​at the tunnel arch and bottom decrease.

[0071] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for tunnel excavation under weak surrounding rock conditions, characterized in that, Includes the following steps: S1. Conduct advance support construction outside the tunnel excavation outline; S2. The tunnel face is divided into upper and lower layers with the arch waist as the center line. The upper layer is divided into the central soil part and the arc-shaped part surrounding the central soil part. The lower layer, located above the invert arch, is divided into the left wall part and the right wall part along the tunnel center line. S3. After the advanced support reaches the specified strength, the arc-shaped part is excavated along the tunnel excavation direction, and then the arc-shaped initial support construction corresponding to the arc-shaped part is carried out. S4. After the initial arch support reaches the specified strength, excavate the central soil and pour the temporary invert arch corresponding to the initial arch support. S5. After the temporary invert arch reaches the specified strength, excavate the left wall and then carry out the corresponding initial support construction of the left wall. S6. After the initial support of the left wall reaches the specified strength, the right wall is excavated, and then the corresponding initial support construction of the right wall is carried out. S7. After the initial support of the right wall reaches the specified strength, the arch suppression part is excavated, and then the arch suppression part is constructed and the concrete is backfilled. S8. After the arch has reached the specified strength, the temporary arch is removed and secondary lining is carried out. S9. Repeat steps S1 to S8 until the tunnel excavation is completed; In step S7, an arch-suppressing steel reinforcement frame is placed inside the excavated arch-suppressing section. Connecting plates are stacked on both sides of the arch-suppressing steel reinforcement frame. Each connecting plate includes a plate body, a pull plate located on the outer side of the bottom of the plate body, multiple support rods located on the inner side of the bottom of the plate body, and an abutment plate located on the top of the plate body. Multiple through holes are opened on the plate body. During installation, the support rods are passed through the arch-suppressing steel reinforcement frame and contact the bottom of the arch-suppressing section. The abutment plate abuts against the bottom side wall of the initial support. Then, concrete is poured until the specified strength is reached.

2. The tunnel excavation method under weak surrounding rock conditions as described in claim 1, characterized in that, In step S1, the advanced support adopts multiple grouting pipes arranged along the circumferential spacing of the tunnel arch outside the tunnel excavation outline. Grouting fluid is injected along the grouting pipes. The grouting pipes are inclined upward along the tunnel excavation direction, and the length of the grouting pipes extending into the tunnel excavation direction is greater than the excavation distance of the arc section in the current construction cycle. The grouting pipes of two adjacent construction cycles overlap each other.

3. The tunnel excavation method under weak surrounding rock conditions as described in claim 1, characterized in that, The construction methods for the initial support of the arc-shaped wall, the initial support of the left wall, and the initial support of the right wall are all as follows: a. Shot concrete is sprayed along the tunnel excavation wall, and then steel mesh is laid; b. Anchor bolts are arranged in a plum blossom pattern, and then shotcrete is applied. The anchor bolts located at the arch waist and arch foot are provided with connecting parts on the outside, and the connecting parts are arch-shaped. c. Install the grating steel frame, fix the other end of the connecting part to the transverse reinforcement of the grating steel frame, and then spray concrete to the designed thickness.

4. The tunnel excavation method under weak surrounding rock conditions as described in claim 1, characterized in that, Each construction cycle involves tunneling for less than 15 m.

5. The tunnel excavation method under weak surrounding rock conditions as described in claim 1, characterized in that, The grouting overlap length of the grouting pipe between two adjacent construction cycles is 1~2 m, and the thickness of the advance support is 40~60 cm.

6. The tunnel excavation method under weak surrounding rock conditions as described in claim 1, characterized in that, The initial support thickness is 40-50 cm.

7. The tunnel excavation method under weak surrounding rock conditions as described in claim 1, characterized in that, The thickness of the secondary lining is 30-40 cm.

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