Partitioned and segmented collaborative support construction method for open-type TBM (Tunnel Boring Machine) over-slowly-inclined soft rock stratum

Abstract

The invention discloses an open-type TBM over-slowly-inclined soft rock stratum zoning and sectioning collaborative supporting construction method. The method comprises the steps that S1, shield tail immediate supporting is conducted; s2, reinforcing and supporting the rear part of the supporting shoe; and S3, bottom arch anchor support closing regulation and control. According to the open-type TBM equipment structure characteristics and the slowly-inclined soft rock stratum deformation rule, a supporting area is divided into three operation sections including a near-shield-tail instant supporting area, a supporting shoe rear reinforcing supporting area and a bottom arch anchor supporting closed regulation and control area, differential supporting is implemented in a staged mode, space-time progressive construction of pre-stressed anchor cables and anchor rods is combined, and the supporting effect is greatly improved. Matching of supporting rigidity and stratum deformation is ensured through dynamic adjustment of prestress, a dynamic collaborative supporting system of instant supporting, reinforcement and closed-loop regulation and control is formed, and double improvement of supporting efficiency and safety is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel engineering, and in particular relates to a method for implementing zoning and segmented collaborative support of an open TBM in a gently inclined soft rock stratum. Background Art

[0002] Long and large tunnels inevitably pass through gently dipping soft rock formations (including mudstone, shale, phyllite, red bed soft rock and other soft rock formations), which brings great challenges to tunnel TBM construction. The surrounding rock of gently dipping soft rock formations is broken, has low strength, and has developed joints and bedding, and has significant anisotropy. The deformation of the surrounding rock is uneven within the section. The deformation rate of the top arch area where the normal line of the free surface intersects the layer at a large angle is fast, and the deformation rate of the side wall areas on both sides is relatively slow where the normal line of the free surface intersects the layer at a small angle. The support work of the soft rock tunnel section is large and difficult to implement. If handled improperly, it may lead to obstruction of TBM excavation or even collapse and instability of the surrounding rock as a whole, seriously threatening TBM excavation efficiency and construction safety. For open TBMs passing through gently dipping soft rock formations, traditional support schemes mainly have problems such as space limitations, inefficient processes, and poor coordination, which seriously restrict the advantages of TBM. The specific problems are as follows:

[0003] (1) The top arch of the gently dipping soft rock formation deforms quickly and the support timeliness is strong. However, the space behind the TBM shield is small. The traditional system support scheme concentrates construction in a single area at the shield tail, which easily leads to low construction efficiency.

[0004] (2) Support structures such as steel arches and anchors were not implemented in sections in accordance with the spatial characteristics of the TBM equipment, resulting in low efficiency. Simultaneous installation resulted in crowded working spaces, conflicting processes, and extended downtime.

[0005] (3) The working space behind the shield tail is limited, and full-section support cannot be completed efficiently. The support demand and its efficiency do not match the TBM excavation speed. The problem of TBM downtime waiting for support is prominent, which affects the continuous excavation of the TBM.

[0006] (4) Traditional support methods lack flexibility, support parameters are fixed, and there is a lack of dynamic control mechanisms based on real-time monitoring. Summary of the Invention

[0007] The present invention is proposed to solve the above-mentioned shortcomings, and its purpose is to provide a method for the coordinated support construction of an open TBM in gently inclined soft rock formations in zones and sections. Through spatial decomposition, time optimization, and dynamic regulation, this method systematically solves the problems of low TBM support efficiency and long downtime in gently inclined soft rock formations, realizes parallel operation of excavation and support, and provides an innovative path for efficient and safe TBM construction in soft rock formations.

[0008] In order to achieve the above purpose, the present invention adopts the following scheme:

[0009] A method for implementing zoning and segmented collaborative support in gently dipping soft rock formations using an open TBM includes the following steps: S1: Shield tail instant support S101: Within the shield tail and the range of 0.5 to 0.8 m behind it, use the TBM arch assembler to quickly assemble the steel arch frame during the TBM advancement interval. The height of the steel arch frame is H1, and the distance between the steel arch frames is D1. S102: Spray concrete in the range of 240° to 270° on the top arch within the exposed shield range of 1.0 to 3.0 m. The thickness of the sprayed concrete is H2, H2 ≥ H1 + 2 cm; S103: The top arch prestressed anchor cable is applied within the range of 3.0 to 5.0 m above the exposed shield along the range of 100° to 120° at the top of the tunnel. The prestressed force of the top arch anchor cable is P s1 ; S2: Reinforcement support behind the shoe S201: Apply prestressed anchor cables on the side walls at 120° to 140° on both sides of the working platform behind the support shoe. The prestressed anchor cable pretension value is P s2 ; S202: Shotcrete the bottom arch at 90° to 120° behind the support shoe, with a thickness of H2. S3: Bottom arch anchor closure control When there is construction space behind the TBM head, self-drilling prestressed anchor rods are used to arrange long and short anchor rods in an circumferential manner within the 120° range of the bottom arch.

[0010] As a preferred embodiment, in step S1, the assembly of the steel arch frame is carried out synchronously with the TBM excavation, and the construction is completed within the range of 0.5 to 0.8 m behind the shield tail; the sprayed concrete for the side and top arches is immediately applied after the assembly of the steel arch frame, using the TBM emergency spray-mixing system; the prestressed anchor cables for the top arch are applied after the sprayed concrete for the side and top arches reaches 80% of the design strength.

[0011] As a preferred embodiment, in step S103, the spacing of the prestressed anchor cables is 1.0 to 2.0 m, the row spacing D2 = D1 to 2D1, D1 is the distance between the steel arch frames; the anchor cable length L s ≥L p1 +2, L s is the length of the anchor cable, L p1 It is the depth of the relaxation zone of the side-top arch surrounding rock, and the unit is m.

[0012] As a preferred embodiment, in step S103, the anchoring length of the prestressed anchor cable is calculated according to the following formula: L m1 =1.1×K×P s1 / π×D×C; Where, L m1 is the length of the anchoring section, K is the safety factor of the anchoring section, P s1 is the applied value of the pre-tensioning force of the top arch anchor cable, D is the diameter of the anchor cable, and C is the bonding strength between the cementing material and the hole wall; The anchorage length of the prestressed anchor cable is checked according to the following formula: L m1 =1.1×K×P s1 / π×d×C1; Where, L m1 is the length of the anchoring section, K is the safety factor of the anchoring section, P s1 is the applied value of the pre-tensioning force of the top arch anchor cable, d is the diameter of the prestressed steel strand, and C1 is the bond strength between the bonding material and the prestressed steel strand.

[0013] As a preferred embodiment, in step S2, the side wall prestressed anchor cables and the bottom arch shotcrete are applied behind the gripper shoes when the gripper shoes move to the next cycle position.

[0014] As a preferred embodiment, in step S201, the pre-tensioning force applied to the side wall anchor cable is P s2 Calculated according to the following formula: P s2 = P s1 +α1×E s ×A s ×δ1 / L f1 ; Where, P s1 is the applied value of the top arch anchor cable pre-tensioning force, α1 is the stiffness matching coefficient, E s is the elastic modulus of the anchor cable strand, A s is the cross-sectional area of the anchor cable strand, δ1 is the incremental deformation of the side wall surrounding rock during the time difference between the construction of the top arch and the side wall anchor cables, and L f1 is the free length of the prestressed steel strand, L f1 =L s -L m1 .

[0015] As a preferred embodiment, in step S3, the length of the short anchor rod is L g1 , L g1 ≈R, R is the TBM excavation radius, and the short anchor pre-tensioning force is P g1 ; The length of the long anchor rod is L g2 , L g2 ≥L p2 +2, L p2 is the depth of the bottom arch surrounding rock relaxation zone, in meters; the pre-tensioning force applied by the long anchor is P g2 .

[0016] As a preferred embodiment, in step S3, the pre-tensioning force values of the long and short anchor rods are adjusted according to the following formula: P g2 =P g1 +α1×E g ×A g ×δ2 / L f2 ; Where, P g1 is the pre-tensioning force applied to the short anchor rod, P g2 is the pre-tensioning force applied to the long anchor rod, E g is the elastic modulus of the anchor rod, A g is the cross-sectional area of the anchor, δ2 is the incremental deformation of the surrounding rock during the time difference between the long and short anchors, and L f2 is the free section length of the prestressed anchor rod, and α1 is the stiffness matching coefficient.

[0017] As a preferred embodiment, in step S3, the short anchor rod lags behind the side wall stress anchor cable by 1 to 2 excavation cycles.

[0018] As a preferred embodiment, in step S3, if the deformation rate of the bottom arch exceeds 5 mm / d and there is a risk of bottom arch uplift deformation, long anchor rods are immediately implemented; if the deformation rate of the bottom arch is less than 5 mm / d, long anchor rods can be implemented 30 to 35 m behind the TBM's gripper shoe.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] First, the present invention proposes a zoned and segmented collaborative support method that systematically solves the problems of inefficient processes and poor coordination exposed in the construction of open TBMs in soft rock formations through spatial decomposition, time optimization, dynamic control and other methods, providing an innovative path for the efficient and safe construction of TBMs in soft rock formations.

[0021] Secondly, based on the non-uniform deformation law of gently sloping soft rock formations, the present invention makes full use of the spatial characteristics of different parts of the TBM, decomposes the support process into the shield tail immediate support area, the support shoe rear reinforcement support area, the bottom arch anchor support closure control area, and the core idea of time and space coordination and dynamic adjustment, avoiding centralized operations, improving space utilization, and realizing parallel TBM excavation and support.

[0022] Third, the present invention implements differentiated support in stages, combines the temporal and spatial progressive construction and reinforcement of "prestressed anchor cables for top arches ~ prestressed anchor cables for side walls ~ prestressed anchor rods for the length and shortness of bottom arches", and ensures the matching of support stiffness and stratum deformation through dynamic adjustment of prestress, forming a temporal and spatial dynamic collaborative support system of "instant support - reinforcement and strengthening - closed-loop regulation", giving full play to the bearing capacity of the support structure, effectively suppressing the deformation of slowly dipping soft rocks, and achieving a dual improvement in support efficiency and safety.

[0023] Fourthly, the present invention improves the overall stiffness and bearing capacity of the arch frame through the combination of "steel arch frame + sprayed concrete + top arch prestressed anchor cable" in the "shield tail instant support area", and the difference between the thickness of the sprayed concrete and the height of the steel arch frame is not less than 2.0 cm, that is, a protective layer of more than 2.0 cm is left; the steel arch frame can effectively share the surrounding rock pressure to form an integral arch support structure; the sprayed concrete leaves enough protective layer, which is beneficial to corrosion and rust prevention, and can also provide a reliable working surface for subsequent anchor cables to cling to the concrete layer; using the TBM arch frame assembler and emergency spray-mixing system, the initial support can be completed in the shortest time and the surrounding rock relaxation can be controlled; thus, during the excavation process, the top arch and surrounding rock obtain timely and sufficient stiffness support, reducing the risk of deformation and collapse of the top arch surrounding rock.

[0024] Fifth, the present invention uses prestressed anchor cables at the top of the shield tail immediate support zone to provide active support. Prestressed anchor cables are placed in the arch to quickly apply a "reverse" restraining force to the surrounding rock, effectively suppressing early deformation of the layered soft rock at the top of the arch. Precise anchor length: Based on standard calculations and the actual depth of the relaxation zone, the anchor cables are fully anchored in the stable rock mass, ensuring safety and avoiding waste. High operability: Specific anchor cable parameters and length ranges are given, facilitating rapid on-site implementation and ensuring consistent and reliable support results. Therefore, by proactively and promptly controlling the surrounding rock at the top of the arch, the impact of deformation on subsequent construction can be significantly reduced, preventing TBM jams.

[0025] Sixth, for the prestressed anchor cables on both sides of the sidewalls in the reinforced support area behind the support shoe, this invention proposes a "dynamic correction of prestress based on incremental deformation of the sidewalls." This differentiates prestressing: Due to the timing mismatch between the construction of the sidewall and crown arch anchor cables, the sidewalls may have undergone some incremental deformation. Correction through the incremental term δ1 ensures coordinated support stiffness. The combined effect of sidewall reinforcement and crown arch reinforcement forms a complete and uniform support ring around the tunnel. Prestressing compensation for incremental deformation of the sidewalls helps control overall tunnel deformation and reduce the risk of late-stage lining settlement or bulging.

[0026] Seventh, in the same section behind the support shoe, the present invention sprays polypropylene coarse fiber concrete of the same thickness as the top arch on the bottom arch, forming a full-section closed loop together with the sprayed layers of the top arch and side walls. This forms a closed support system: the closure of the sprayed concrete loop can evenly distribute the surrounding rock stress to the arch top and both sides, reducing stress concentration; enhance the bottom's ability to resist deformation: the bottom arch sprayed concrete can suppress bottom heave, especially in weak strata, and can prevent water, soil, or rock strata from rising in advance; and cooperate with the upper arch frame: the support measures of the top arch and side walls are combined to construct a "circumferential" and "longitudinal" composite bearing system. The closed loop can improve the overall rigidity of the tunnel and reduce the risk of surrounding rock disturbance to the lining and equipment.

[0027] Eighth, the present invention uses self-drilling prestressed anchor rods in the bottom arch anchor support closure control area, with long and short anchor rods arranged circumferentially at intervals. A "combination of long and short" layered control method is adopted: short anchor rods can quickly reinforce shallow surrounding rock, while long anchor rods can strengthen control in deep plastic zones. Efficiency is improved: short anchor rods are easy to install and can be quickly deployed immediately behind the shield tail to control initial bottom arch deformation; long anchor rods can provide more targeted reinforcement in the later stages. Construction operability is improved: self-drilling anchor rods have the advantage of completing drilling and anchoring in soft rock in one go, saving operation time and reducing disturbance to the surrounding rock. This can not only timely suppress early bottom arch displacement, but also provide greater support when deep deformation becomes apparent in the later stages.

[0028] In summary, this invention proposes a zoning and segmenting support process for three major areas: the immediate shield tail support area, the rear support shoe reinforcement support area, and the bottom arch anchor support closure control area. This process also incorporates the core concepts of spatiotemporal coordination and dynamic adjustment. Tunnel support is broken down into different areas and time periods, and the most suitable support strategy is implemented based on the surrounding rock characteristics, exposure time, and construction conditions. The support process is coordinated with the TBM excavation process to minimize construction interference and downtime, thereby improving excavation efficiency. Through real-time monitoring and anchor cable (rod) prestressing control, the support stiffness is dynamically matched to the surrounding rock deformation development, avoiding over- or under-support. This comprehensive approach can effectively prevent excessive relaxation or large deformation of the surrounding rock during the initial excavation period, significantly improving construction safety and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the collaborative support construction of an open TBM in gently dipping soft rock formations using a zoning and segmenting method according to the present invention;

[0030] Figure 2 This is the cross-section diagram of the anchor cable's segmented and coordinated support;

[0031] Figure 3 It is a flow chart of the construction process of coordinated support in different zones and sections;

[0032] In the figure: 1-cutterhead, 2-shield, 3-shield tail, 4-TBM emergency spray-mix system, 5-gripper, 6-drilling rig, 7-excavation contour, 8-TBM body, 9-tunnel axis, 10-shield tail immediate support area, 11-gripper rear reinforcement support area, 12-bottom arch anchor support closure control area, 13-short anchor rod application area, 14-long anchor rod application area, 15-top arch prestressed anchor cable, 16-side wall prestressed anchor cable, 17-short anchor rod, 18-long anchor rod. DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] The method for implementing zoning and segmented collaborative support in a gently dipping soft rock formation using an open TBM according to the present invention comprises the following steps:

[0035] 1) Sectional support

[0036] (1) Shield tail immediate support area (within the shield tail and within 5m behind the shield tail)

[0037] Steel arch frame assembly: within the range of 0.5 to 0.8 m behind the shield tail 3, use the TBM arch frame assembler to quickly assemble the steel arch frame during the TBM advancement interval. The height of the steel arch frame is H1, and the distance between the steel arch frames is D1.

[0038] Spraying of polypropylene crude fiber concrete for the side and top arch: spraying of concrete in the range of 240° to 270° of the side and top arch is completed within the range of 1.0 to 3.0 m of the exposed shield 2. Considering that the steel arch frame requires a protective layer thickness of at least 2 cm, the sprayed concrete thickness H2 ≥ H1 + 2 cm, where H1 and H2 are in cm.

[0039] Top 100°~120° prestressed anchor cables: top arch prestressed anchor cables are arranged in the range of 3.0~5.0m along the top of the tunnel at 100°~120°, with a spacing of 1.0~2.0m and a row spacing of D2=D1~2D1; the anchor cable diameter is generally Φ21.8mm, and the anchor cable length is L s ≥L p1 +2, L s is the length of the anchor cable, L p1 The depth of the relaxation zone of the side arch surrounding rock is determined by theoretical analysis or acoustic wave testing. When the drilling capacity of the TBM airborne drilling rig is insufficient, a handheld pneumatic anchor drilling rig can be used to supplement the drilling. The pre-tensioning force applied to the arch anchor cable is P. s1 (Φ21.8mm anchor cable, P s1 250kN can be taken).

[0040] The anchorage length of the prestressed anchor cable is calculated according to Formula ① and verified according to Formula ② in the "Design Code for Prestressed Anchorages for Hydraulic Engineering" SL / T 212-2020: ①L m1 =1.1×K×P s1 / π×D×C,②L m1 =1.1×K×P s1 / π×d×C1. In the formula, L m1is the length of the anchoring section, K is the safety factor of the anchoring section length, D is the diameter of the anchor hole, C is the bonding strength between the bonding material and the hole wall, C1 is the bond strength between the bonding material and the prestressed steel strand, and d is the diameter of the prestressed steel strand.

[0041] Prestressed anchor cables act as active support, rapidly compensating for stress in the gently dipping layered rock mass of the arch, creating a "combined arch" effect and suppressing premature deformation of the surrounding rock. Shotcrete and steel arch frames provide high-rigidity passive support, providing increased resistance and preventing further deformation of the surrounding rock.

[0042] (2) Reinforced support area behind the support shoe (within 3m from the support shoe to the rear of the support shoe)

[0043] Prestressed anchor cables in the range of 120° to 140° on the other two side walls: Prestressed anchor cables for the side walls are installed on the working platform behind the support shoe. The diameter, length and spacing of the anchor cables are the same as those of the top arch prestressed anchor cables. The pre-tensioning force of the side wall anchor cables is P s2 .

[0044] Bottom arch sprayed polypropylene fiber concrete: spray concrete in the range of 90° to 120° behind the support shoe. The thickness of the sprayed concrete is H2, which is the same as the thickness of the tunnel side arch. The sprayed concrete is closed into a ring.

[0045] (3) Bottom arch anchor support closure control area (within 3 to 35 m behind the support shoe)

[0046] The space beneath the TBM equipment is narrow, making anchor bolting (cable) installation difficult. For the bottom system anchors, a strategy of combining long and short anchors and implementing them at the right time is adopted. Due to the ballast load of the TBM head, the deformation rate and relaxation zone depth of the bottom arch are slower than those of the tunnel side arch. Therefore, bottom anchoring will be delayed slightly until space is available beneath the TBM equipment.

[0047] Self-drilling prestressed anchor rods are used in the 120° range of the bottom arch. Long and short anchor rods are arranged in an annular pattern. The diameter of the anchor rods is generally Φ25~Φ38. The length of the short anchor rod is L g1 , L g1 ≈R, R is the TBM excavation radius, which is convenient for early implementation and early play of the role. The short anchor pre-tensioning force value P g1 ; The length of the long anchor rod is L g2 , L g2 ≥L p2 +2, L p2is the depth of the loosened area of the bottom arch surrounding rock, determined by theoretical analysis or acoustic wave testing. The timing of long anchor bolting is determined by the deformation rate of the surrounding rock. For example, if the deformation rate of the bottom arch is large (deformation rate exceeds 5 mm / d) and there is a risk of bottom arch uplift deformation, long anchor bolting should be implemented immediately. If the deformation of the bottom arch is controllable (deformation rate is less than 5 mm / d), long anchor bolting can be implemented 30 to 35 m behind the TBM support shoe (L2 area). The pre-tensioning force applied to the long anchor bolt is P. g2 ,like Figure 1 As shown, the bottom arch anchor support closure control area 12 is located 3 to 35 meters behind the gripper, with a short anchor bolting area 13 and a long anchor bolting area 14 arranged therein. The TBM body 8 is positioned along the tunnel axis 9, within the excavation contour line 7, with drilling performed by a drilling rig 6.

[0048] 2) Spatiotemporal coordinated control method

[0049] Process connection: The installation of the steel arch frame is carried out simultaneously with the TBM excavation, and is completed within the range of 0.5 to 0.8 m behind the shield tail 3; the polypropylene coarse fiber concrete of the side and top arches is immediately applied after the steel arch frame is assembled, using the TBM emergency spraying system; the top anchor cable is applied after the sprayed concrete reaches 80% of the design strength; the prestressed anchor cables of the side walls on both sides and the sprayed concrete of the bottom arch are applied behind the support shoes when the support shoes move to the next cycle position; the short anchor rods of the bottom arch are completed after the side wall anchor cables 1 to 2 excavation cycles, and the long anchor rods are completed at an appropriate time according to the deformation rate of the bottom arch.

[0050] Dynamic adjustment of prestressing force: Based on the surrounding rock monitoring data (such as convergence deformation, anchor cable axial force, etc.), the prestressing force value of the anchor cable and anchor rod is adjusted through intelligent tensioning equipment to ensure that the support stiffness matches the formation deformation.

[0051] Considering that the timing of the installation of the side wall anchor cables is relatively delayed, compared with the top arch anchor cables, the side walls have undergone incremental deformation before the anchor cables are installed. In order to ensure that the support stiffness in the section matches the stratum deformation, the pre-tensioning force of the side wall anchor cables is appropriately increased according to the incremental deformation. The pre-tensioning force applied to the side wall anchor cables is P s2 = P s1 +α1×E s ×A s ×δ1 / L f1 , where P s1 is the pre-tensioning force applied to the top arch anchor cable, E s is the elastic modulus of the anchor cable strand, A s is the cross-sectional area of the anchor cable strand, δ1 is the incremental deformation of the side wall surrounding rock during the time difference between the construction of the top arch and the side wall anchor cables, and L f1 is the free section length of the prestressed steel strand, and α1 is the stiffness matching coefficient introduced to take into account the possible incomplete coordination between the deformation of the anchor cable and the surrounding rock, with a value of 0.5~1.0.

[0052] The bottom anchor rods are of different lengths and the long anchor rods are installed later. The pre-tensioning force value also needs to be adjusted dynamically: P g2 =P g1 +α1×E g ×A g ×δ2 / L f2 , where P g1 is the pre-tensioning force applied to the short anchor rod, E g is the elastic modulus of the anchor rod, A g is the cross-sectional area of the anchor, δ2 is the incremental deformation of the surrounding rock during the time difference between the long and short anchors, and L f2 is the free section length of the prestressed anchor rod, α1 is the stiffness matching coefficient, and its value ranges from 0.5 to 1.0.

[0053] Example:

[0054] The following is an example of a deep, long water diversion tunnel using an open TBM through soft rock formations, with accompanying drawings and an actual construction process. In this example, an open TBM was used for the tunnel, with a cutterhead diameter of 9.83m. Other projects can adjust the cutterhead diameter based on actual conditions.

[0055] The method for implementing zoning and segmented collaborative support in gently dipping soft rock formations using an open TBM in this embodiment includes the following steps:

[0056] S1: Shield tail immediate support area (from the shield tail to the 5m range behind the shield tail)

[0057] like Figure 1 As shown, the shield tail immediate support area 10 is within the range of 0.5 to 0.8 m behind the shield tail 3. During the TBM advancement interval, the TBM arch frame assembler is used to quickly assemble and install the H175 steel arch frame with a frame spacing of 55 cm, and half-section I20 I-beams are used for longitudinal connection to enhance the stability and bearing capacity of the support structure.

[0058] When the surrounding rock gradually emerges from the range of 1.0~3.0m of shield 2, the open TBM emergency spraying system is activated. TBM emergency spraying system 4 immediately sprays polypropylene crude fiber concrete within 240° of the side top arch with a thickness of 20cm (protective layer thickness of 2.5cm) to ensure the thickness and quality of the sprayed concrete.

[0059] At 5m from the shield tail (when the sprayed early strength concrete reaches 80% of the design strength), 6 arch prestressed anchor cables 15 are arranged along the 110° range of the tunnel top. The anchor cable body is made of 1×19S steel strand with a nominal diameter of 21.8mm, a tensile strength of 1860MPa, and a designed pull-out resistance of 350kN. The prestressed force applied to the arch anchor cable is P s1 Take it as 250kN. The length of the anchor section of the anchor cable is calculated according to formula ① and verified by formula ②: ①L m1 =1.1×K×P s1 / π×D×C,②L m1 =1.1×K×P s1 / π×d×C1. K is 2.2, D is 42mm, the anchoring section uses resin anchoring agent, C is 1.6MPa according to the recommended value of the specification, C1 is 12.0MPa, and d is 21.8mm. By calculation, the anchoring section length L is obtained m1 For safety reasons, the anchoring length L is 2.865m. m1 Take 3.0m. The annular spacing of prestressed anchor cables is 1.5m, and the row spacing is 1.1m. The depth of the loosened area of the arch surrounding rock in this soft rock cave section is measured by drilling acoustic waves. p1 About 7.5m, anchor cable length L s ≥L p1 +2=9.5m, L s Take 10.0m.

[0060] S2: Reinforced support area behind the gripper (within 3m of the gripper to the rear of the gripper)

[0061] In the reinforcement support area 11 behind the shoe, 8 prestressed anchor cables 16 are installed on both sides of the side wall within a 130° range within 3m behind the shoe 5. The anchor cable diameter is Φ21.8mm, the circumferential spacing is 1.5m, and the row spacing is 1.1m. Considering that the incremental deformation of the side wall surrounding rock is about 0.5-1.0cm during the time difference between the top arch and the side wall anchor cable installation, in order to ensure that the support stiffness in the section matches the stratum deformation, the prestressed force applied to the side wall anchor cable is Ps2 = Ps1 + α1 × Es × As × δ1 / L f1 , where P s1 The value is 250kN, Es is 195GPa, and As is 313mm 2 , δ1 is 10mm, L f1 The value of α1 is 0.5 and the pre-tensioning force applied to the side wall anchor cable Ps2 is 290 kN.

[0062] Polypropylene coarse fiber concrete is sprayed behind the gripper shoe 5 in a 120° range of the bottom arch with a thickness of 20 cm, and the sprayed concrete is closed into a ring.

[0063] S3: Bottom arch anchor support closure control area (within 3~35m behind the support shoe)

[0064] The bottom arch anchor support closed control area 12 adopts a "long and short combination" scheme for the bottom system anchor rods. The anchor rods are all Φ25 self-drilling prestressed anchor rods. The long anchor rods 18 and the short anchor rods 17 are arranged in an annular manner. The length of the short anchor rod is L g1The anchor cable is 4.5m long and is completed after 1-2 excavation cycles behind the support shoe 5. The pre-tensioning force is 90kN, so as to achieve the effect of early implementation and early performance. The long anchor rod is completed at the right time according to the deformation rate of the bottom arch. In this embodiment, the deformation rate of the bottom arch in the soft rock cave section is controllable, about 0.5~1.0mm / d. The long anchor rod 18 is implemented in the L2 area of the TBM (30~35m behind the support shoe). The depth of the loose rock area of the bottom arch is L p2 About 6.0m, long anchor length L g2 The incremental deformation of the surrounding rock during the time difference between the long and short anchor bolts is generally 0.5cm~1.0cm, and the pre-tensioning force applied to the long anchor bolt is 120kN.

[0065] The sectional and segmented collaborative support method significantly reduces process conflicts and downtime through staggered construction in time and space, increasing daily excavation efficiency by 25%-30%. Furthermore, the combination of staggered layout and dynamic adjustment (anchor cable and bolt pre-tensioning forces are dynamically adjusted based on ground deformation) better matches the mechanical behavior of gently dipping soft rock, achieving "dynamic reinforcement" and improving the collaborative bearing capacity of the support.

[0066] The above embodiments are merely illustrative of the technical solutions of the present invention. The present invention is not limited to the contents described in the above embodiments, but is subject to the scope defined by the claims. Any modifications, supplements, or equivalent substitutions made by those skilled in the art based on these embodiments are within the scope of protection claimed in the claims of the present invention.

Claims

1. A method for implementing zoning and segmented collaborative support in gently dipping soft rock formations using an open TBM, characterized by: The steps include: S1: Shield tail instant support S101: Within the shield tail and the range of 0.5 to 0.8 m behind it, use the TBM arch assembler to quickly assemble the steel arch frame during the TBM advancement interval. The height of the steel arch frame is H1, and the distance between the steel arch frames is D1. S102: Spray concrete in the range of 240° to 270° on the top arch within the exposed shield range of 1.0 to 3.0 m. The thickness of the sprayed concrete is H2, H2 ≥ H1 + 2 cm; S103: The top arch prestressed anchor cable is applied within the range of 3.0 to 5.0 m above the exposed shield along the range of 100° to 120° at the top of the tunnel. The prestressed force of the top arch anchor cable is P s1 ; S2: Reinforcement support behind the shoe S201: Apply prestressed anchor cables on the side walls at 120° to 140° on both sides of the working platform behind the support shoe. The prestressed anchor cable pretension value is P s2 ; S202: Shotcrete the bottom arch at 90° to 120° behind the support shoe, with a thickness of H2. S3: Bottom arch anchor closure control When there is construction space behind the TBM head, self-drilling prestressed anchor rods are used to arrange long and short anchor rods in an circumferential manner within the 120° range of the bottom arch.

2. The method according to claim 1, wherein: In step S1, the assembly of the steel arch frame is carried out synchronously with the TBM excavation, and the construction is completed within the range of 0.5 to 0.8 meters behind the shield tail; the shotcrete of the side top arch is immediately applied after the assembly of the steel arch frame, using the TBM emergency shotcrete system; the prestressed anchor cable of the top arch is applied after the shotcrete of the side top arch reaches 80% of the design strength.

3. The method according to claim 2, wherein: In step S103, the spacing of the prestressed anchor cables is 1.0 to 2.0 m, the row spacing D2 = D1 to 2D1, where D1 is the distance between the steel arch frames; the anchor cable length L s ≥L p1 +2, L s is the length of the anchor cable, L p1 It is the depth of the relaxation zone of the side-top arch surrounding rock, and the unit is m.

4. The method according to claim 3, wherein: In step S103, the anchoring length of the prestressed anchor cable is calculated according to the following formula: L m1 =1.1×K×P s1 / π×D×C; Where, L m1 is the length of the anchoring section, K is the safety factor of the anchoring section, P s1 is the applied value of the pre-tensioning force of the top arch anchor cable, D is the diameter of the anchor cable, and C is the bonding strength between the cementing material and the hole wall; The anchorage length of the prestressed anchor cable is checked according to the following formula: L m1 =1.1×K×P s1 / π×d×C1; Where, L m1 is the length of the anchoring section, K is the safety factor of the anchoring section, P s1 is the applied value of the pre-tensioning force of the top arch anchor cable, d is the diameter of the prestressed steel strand, and C1 is the bond strength between the bonding material and the prestressed steel strand.

5. The method according to any one of claims 1 to 4, characterized in that: In step S2, the side wall prestressed anchor cables and the bottom arch shotcrete are applied behind the gripper shoes when the gripper shoes move to the next cycle position.

6. The method according to claim 5, characterized in that: In step S201, the pre-tensioning force applied to the side wall anchor cable is P s2 Calculated according to the following formula: P s2 = P s1 +α1×E s ×A s ×δ1 / L f1 ; Where, P s1 is the applied value of the top arch anchor cable pre-tensioning force, α1 is the stiffness matching coefficient, E s is the elastic modulus of the anchor cable strand, A s is the cross-sectional area of the anchor cable strand, δ1 is the incremental deformation of the side wall surrounding rock during the time difference between the construction of the top arch and the side wall anchor cables, and L f1 is the free section length of the prestressed steel strand.

7. The method according to any one of claims 1 to 4, characterized in that: In step S3, the length of the long anchor rod is L g2 , L g2 ≥L p2 +2, L p2 is the depth of the relaxation zone of the bottom arch surrounding rock, and the unit is m.

8. The method according to claim 7, wherein: In step S3, the pre-tensioning force values of the long and short anchor rods are adjusted according to the following formula: P g2 =P g1 +α1×E g ×A g ×δ2 / L f2 ; Where, P g1 is the pre-tensioning force applied to the short anchor rod, P g2 is the pre-tensioning force applied to the long anchor rod, E g is the elastic modulus of the anchor rod, A g is the cross-sectional area of the anchor, δ2 is the incremental deformation of the surrounding rock during the time difference between the long and short anchors, and L f2 is the free section length of the prestressed anchor rod, and α1 is the stiffness matching coefficient.

9. The method according to claim 8, characterized in that: In step S3, the short anchor rod lags behind the side wall stress anchor cable by 1 to 2 excavation cycles.

10. The method according to claim 9, characterized in that: In step S3, if the bottom arch deformation rate exceeds 5 mm / d and there is a risk of bottom arch uplift deformation, long anchor bolts are immediately implemented; if the bottom arch deformation rate is less than 5 mm / d, long anchor bolts can be implemented 30 to 35 m behind the TBM gripper shoe.

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