Novel supporting structure for layered soft rock tunnel

Abstract

The invention discloses a novel supporting structure for a layered soft rock tunnel, and relates to the field of tunnel supporting structures. The inner-layer primary support is arranged on the outer side of the secondary lining in a full-ring closed mode, and an arch wall full-section area is defined between the inner-layer primary support and the secondary lining; the buffer structure layer is arranged in the full-section area of the arch wall; the outer-layer primary support is arranged on the outer side of the inner-layer primary support, and an inverted arch of the outer-layer primary support is not capped. An inverted arch unclosed structure is adopted in the outer-layer primary support, and large extrusion deformation of surrounding rock can be effectively released on the premise that deformation is controllable. The inner-layer primary support is arranged on the outer side of the secondary lining in a full-ring closed mode, a plurality of compressible steel structure units are arranged in the inner-layer primary support, surrounding rock extrusion large deformation can be absorbed, and structural stress concentration is avoided. The concrete buffer structure layer arranged between the secondary lining and the inner-layer primary support can reduce the stress concentration coefficient of the secondary lining, and the long-term stability and durability of the tunnel and underground engineering lining structure are improved.

Description

Technical Field

[0001] The present invention relates to the field of tunnel support structures, in particular to a novel support structure suitable for tunnels with extruded rheological layered soft rocks. Background Art

[0002] Layered soft rock strata, due to their well-developed bedding, have transversely isotropic mechanical properties. These strata are susceptible to long-term creep deformation under high geostress conditions, causing tunnel support structures to bear asymmetric compressive loads. Traditional uniformly symmetrical support systems often employ a composite structure of primary support (anchor shotcrete + steel arch frame) and secondary lining, which presents the following problems:

[0003] (1) The support parameter design does not take into account the differences in bedding direction. The creep rates of the surrounding rock in the directions perpendicular to and parallel to the bedding are not matched, which can easily cause local cracking of the support structure and distortion of the steel arch frame.

[0004] (2) Premature closure of the inverted arch leads to insufficient release of surrounding rock compression deformation, which easily causes initial support stress concentration and a replacement rate of up to 40%-60%;

[0005] (3) There is a lack of buffer structure design between the secondary lining and the primary support, and the long-term creep pressure is directly transmitted to the lining, which can easily cause durability problems such as concrete spalling and steel corrosion.

[0006] In view of this, there is an urgent need for a new support structure that matches the creep characteristics of layered soft rock. Summary of the Invention

[0007] The purpose of the present invention is to provide a new type of support structure for layered soft rock tunnels to solve the problems existing in the prior art.

[0008] To achieve the above-mentioned object, the present invention provides a novel support structure for layered soft rock tunnels, comprising:

[0009] secondary lining;

[0010] The inner primary support is fully enclosed and arranged outside the secondary lining, and the arch wall full section area is defined between the inner primary support and the secondary lining;

[0011] A buffer structure layer is provided in the full cross-section area of the arch wall;

[0012] The outer layer initial support is arranged on the outside of the inner layer initial support, and its invert arch is not capped; the outer layer initial support is used to release the extrusion deformation of the surrounding rock, and the inner layer initial support is used to absorb the deformation displacement of the outer layer initial support.

[0013] Furthermore, the inner layer initial support includes:

[0014] an inner high compression concrete layer disposed on the outer side of the secondary lining;

[0015] A plurality of compressible steel structural units are composed of corrugated steel plates and rubber pads alternately stacked together. The compressible steel structural units are embedded in the inner high-compression concrete layer and are evenly arranged along the circumference of the tunnel at the vault, the waist and the side walls.

[0016] Furthermore, the inner high-compression concrete layer is made of porous lightweight aggregate concrete, has a thickness of 200-300 mm, and a compressive strength of 5-8 MPa; and the compressive deformation of the compressible steel structure unit is 15-25 mm.

[0017] Furthermore, the height of the corrugated steel plate is 20-30 mm, the wave pitch is 100-150 mm, and the Shore hardness of the rubber cushion layer is 40-60 HA.

[0018] Furthermore, it also includes:

[0019] A sliding steel arch frame is made of section steel and is arranged on the outside of the compressible steel structure unit. The sliding steel arch frame is slidably connected to the compressible steel structure unit, and a graphene composite lubricating coating is provided between the sliding steel arch frame and the compressible steel structure unit;

[0020] The sliding limit block has an integrally connected connecting plate and an extrusion plate, the extrusion plate is U-shaped and adapted to the groove shape of the sliding steel arch frame, and the connecting plate is arranged at both ends of the extrusion plate; the sliding limit block has two upper and lower grooves respectively arranged in the sliding steel arch frame, and the connecting plates of the two sliding limit blocks are connected by bolts, and at least one sliding limit block is welded to the outer initial support or compressible steel structure unit; the sliding limit block is used to adjust the sliding resistance between the sliding steel arch frame and the sliding limit block.

[0021] Furthermore, the sliding displacement of the sliding steel arch is 30-50 mm; a polytetrafluoroethylene wear-resistant coating is coated between the sliding limit block and the sliding steel arch, the friction coefficient is ≤0.08, and the ultimate sliding resistance is 100-150 kN.

[0022] Furthermore, the outer layer initial support is made of steel arch frame sprayed concrete, and the outer layer initial support is anchored with outer layer support anchor rods, and the outer layer support anchor rods extend along the directions of vertical bedding and horizontal bedding.

[0023] Furthermore, the spacing between adjacent steel arch frames is 0.8-1.2m, and the total unclosed length of the inverted arch of multiple steel arch frames accounts for 20%-30% of the total length of the tunnel; the length of the outer support anchor rods arranged along the vertical bedding is 1.2-1.5 times the length of the outer support anchor rods arranged along the horizontal bedding.

[0024] Furthermore, a deformation gap of 50-80 mm is reserved between the inner layer initial support and the outer layer initial support, and the deformation gap is filled with foam concrete with a density grade of A05-A07.

[0025] Furthermore, the buffer structure layer is made of concrete and has a thickness of 80-120 mm. A geotextile isolation layer is provided between the buffer structure layer and the secondary lining. A deformation monitoring optical fiber sensor is embedded in the buffer structure layer.

[0026] The present invention discloses the following technical effects:

[0027] 1. The outer initial support adopts an inverted arch non-closed structure, and the air-facing part has a large deformation release space, which can effectively release the large extrusion deformation of the surrounding rock of 20%-35% under the premise of controllable deformation.

[0028] 2. The inner primary support is fully enclosed and located outside the secondary lining. Multiple compressible steel structural units are incorporated within. These elastically absorb large extrusion deformations of the surrounding rock (15-25mm) while maintaining controllable deformation and avoiding extensive support removal and cross-section excavation, thus preventing structural stress concentration. To address varying surrounding rock conditions, sliding steel arches can be installed in addition to the inner primary support, with sliding limiters controlling the sliding displacement. This coupling of elastic and sliding absorption absorbs surrounding rock deformation.

[0029] 3. The primary support consists of the inner primary support and the outer primary support. The concrete buffer structure layer is set between the secondary lining and the inner primary support. The buffer structure layer can reduce the stress concentration factor of the secondary lining by more than 40%, and can effectively improve the long-term stress state of the secondary lining under the increasing extrusion deformation pressure during long-term operation, which is beneficial to improving the long-term stability and durability of the lining structure of tunnels and underground projects.

[0030] 4. Outer initial support anchors: The outer support anchors extend perpendicular to and horizontally along the bedding. The length of the outer support anchors arranged along the vertical bedding is 1.2-1.5 times that of the outer support anchors arranged along the horizontal bedding. The support parameter design fully accounts for the differences in bedding orientation. The outer support anchors adapt to the creep rates of the surrounding rock in directions perpendicular and parallel to the bedding, preventing local cracking in the support structure and distortion of the steel arch. This reduces the support replacement rate by over 60%, and keeps the deformation rate within 2 mm / year during the tunnel's operation.

[0031] 5. The buffer structure layer has built-in deformation monitoring fiber optic sensors to monitor deformation in real time. The sliding resistance between the sliding steel arch frame and the sliding limit block is adjusted through the sliding limit block, which reduces maintenance frequency and reduces the comprehensive operation and maintenance costs by 30%-40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0034] Figure 2 This is a schematic diagram of the inner layer initial support elevation;

[0035] Figure 3 This is the layout diagram of the corrugated steel plate inside the compressible steel structure;

[0036] Figure 4 This is the layout diagram of the outer support anchor rods;

[0037] Figure 5 It is a schematic diagram of the compressible steel structure unit;

[0038] Figure 6 This is a schematic diagram of the cooperation between the sliding steel arch and the sliding limit block;

[0039] Figure 7 This is a construction diagram;

[0040] Among them, 1. Advance support; 2. Outer support anchor rod; 3. Outer initial support; 4. Inner initial support; 5. Inner high-compression concrete layer; 6. Buffer structure layer; 7. Secondary lining; 8. Sliding steel arch frame; 9. Sliding limit block; 901. Connecting plate; 902. Extruded plate; 10. Surrounding rock; 11. Compressible steel structure unit; 12. Corrugated steel plate; 13. Connecting steel plate. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments 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.

[0042] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] An embodiment of the present invention provides a novel support structure for a layered soft rock tunnel, comprising:

[0044] Secondary lining 7;

[0045] The inner primary support 4 is fully enclosed and arranged outside the secondary lining 7, and the arch wall full section area is defined between the inner primary support 4 and the secondary lining 7;

[0046] The buffer structure layer 6 is provided in the full section area of the arch wall;

[0047] The outer initial support 3 is arranged outside the inner initial support 4, and its invert arch is not capped; the outer initial support 3 is used to release the extrusion deformation of the surrounding rock 10, and the inner initial support 4 is used to absorb the deformation displacement of the outer initial support 3.

[0048] In this embodiment, the inner layer initial support 4 includes:

[0049] An inner high-compression concrete layer 5 is provided on the outside of the secondary lining 7;

[0050] Multiple compressible steel structure units 11 are composed of corrugated steel plates 12 and rubber pads alternately stacked. The compressible steel structure units 11 are embedded in the inner high-compression concrete layer 5 and are evenly arranged along the circumference of the tunnel at the arch crown, arch waist and side walls.

[0051] In this embodiment, the inner high-compression concrete layer 5 is made of porous lightweight aggregate concrete, has a thickness of 200-300 mm, and a compressive strength of 5-8 MPa; the compressive deformation of the compressible steel structure unit is 15-25 mm.

[0052] In this embodiment, the height of the corrugated steel plate 12 is 20-30 mm, the corrugation pitch is 100-150 mm, and the Shore hardness of the rubber cushion layer is 40-60 HA.

[0053] In this embodiment, it also includes:

[0054] A sliding steel arch 8 is made of section steel and is arranged on the outside of the compressible steel structure unit 11. The sliding steel arch 8 is slidably connected to the compressible steel structure unit 11. A graphene composite lubricating coating is provided between the sliding steel arch 8 and the compressible steel structure unit 11.

[0055] The sliding limit block 9 has an integrally connected connecting plate 901 and an extrusion plate 902. The extrusion plate 902 is U-shaped and adapted to the groove shape of the sliding steel arch frame 8. The connecting plate 901 is arranged at both ends of the extrusion plate 902; there are two sliding limit blocks 9 respectively arranged in the upper and lower grooves of the sliding steel arch frame 8, and the connecting plates 901 of the two sliding limit blocks 9 are connected by bolts. At least one sliding limit block 9 is welded to the outer initial support 3 or the compressible steel structure unit 11; the sliding limit block 9 is used to adjust the sliding resistance between the sliding steel arch frame 8 and the sliding limit block 9.

[0056] In this embodiment, the sliding displacement of the sliding steel arch frame 8 is 30-50 mm; a polytetrafluoroethylene wear-resistant coating is coated between the sliding limit block 9 and the sliding steel arch frame 8, the friction coefficient is ≤0.08, and the ultimate sliding resistance is 100-150 kN.

[0057] In this embodiment, the outer primary support 3 is made of steel arch frame sprayed concrete, and the outer primary support 3 anchors the outer support anchor rod 2, which extends in the direction perpendicular to the bedding and horizontal to the bedding.

[0058] In this embodiment, the spacing between adjacent steel arch frames is 0.8-1.2m, and the total unclosed length of the arch of multiple steel arch frames accounts for 20%-30% of the total length of the tunnel; the length of the outer support anchor rods 2 arranged along the vertical bedding is 1.2-1.5 times the length of the outer support anchor rods 2 arranged along the horizontal bedding.

[0059] In this embodiment, a deformation gap of 50-80 mm is reserved between the inner initial support 4 and the outer initial support 3, and the deformation gap is filled with foam concrete with a density grade of A05-A07.

[0060] In this embodiment, the buffer structure layer 6 is made of concrete and has a thickness of 80-120 mm. A geotextile isolation layer is provided between the buffer structure layer 6 and the secondary lining 7 . A deformation monitoring optical fiber sensor is embedded in the buffer structure layer 6 .

[0061] The construction process is as follows:

[0062] In layered soft rock tunnel construction, the choice of advance support and excavation method is directly related to the stability of the surrounding rock and construction safety. Due to the compressive rheological properties of the strata, arch advance support or forward pre-reinforcement of the tunnel face is required in the initial construction phase:

[0063] The arch advance support 1 usually adopts grouting reinforcement of advance small pipes with a diameter of 42mm and a length of 4.5-6.0m (wall thickness of 3.5mm, circumferential spacing of 30-40cm). The grouting material is ordinary Portland cement slurry with a water-cement ratio of 1:1. The grouting pressure is controlled at 0.5-1.0MPa to form a reinforcement ring with a thickness of 1.2-1.5m. When the surrounding rock fragmentation index RQD 10 is less than 25%, pipe-roof support (Φ89×6mm seamless steel pipe, spacing of 20cm, external insertion angle of 3°-5°) is used instead, and C30 micro-expansive concrete is poured into the pipe-roof to enhance the integrity.

[0064] For positive pre-reinforcement of the tunnel face, 9-12m long fiberglass anchors (32mm diameter, tensile strength ≥600MPa) are mainly arranged in a plum blossom pattern with a spacing of 1.2×1.2m. The ends of the fiberglass anchors are connected by steel mesh to form a spatial truss structure. The preload force is applied to 80-100kN, which can control the extrusion deformation of the tunnel face within 5mm / d.

[0065] After the advanced support 1 is completed, the excavation method is selected according to the level of mechanized construction. When fully mechanized construction is adopted (such as Sandvik DT1131 anchor drilling rig, drilling speed 1.2m / min, positioning accuracy ±10mm; MeycoPotenza concrete spraying manipulator, spraying capacity 30m 3 / h, rebound rate ≤15%), full-section excavation is implemented, the excavation footage is strictly controlled at 1.0-1.2m / cycle, over-excavation and under-excavation are monitored in real time using a 3D laser scanner (error ±50mm), and local under-excavation areas are trimmed with a hydraulic breaker to ensure a smooth excavation contour; when restricted by site or equipment conditions, short-step excavation is adopted (step height 1.8-2.2m, step length 3-4m), the upper step is trimmed using a PC200 excavator with a manual jackhammer, and the lower step is excavated using a CAT336 hydraulic roadheader, with a step distance of 2.5-3.0D (D is the tunnel diameter), and a temporary invert (I18 I-beam, 1.0m spacing, sealed with sprayed C25 concrete) is immediately constructed after each excavation cycle to prevent bottom heave.

[0066] When using a pneumatic handheld anchor drill (Atlas Copco BBD 12T, working air pressure 0.6-0.8MPa, drilling diameter 42mm) to construct the outer support anchor 2, the anchors must be arranged with a spacing of 0.8m in the direction perpendicular to the bedding plane and 1.2m in the direction parallel to the bedding plane. The drilling depth error is ≤5%, and the grouting fullness is tested by ground penetrating radar (slurry filling rate ≥95%). When using a handheld concrete spray gun (Aliva-256 model, working pressure 0.4-0.6MPa) for spraying operations, the wet spraying process is adopted, and the concrete mix ratio is cement: sand: crushed stone: water = 1:2:2:0.45. 3% accelerator is added (initial setting time ≤5min). The spraying thickness is controlled by burying nails, and the thickness is controlled every 2m. 2A detection point is set, and the thickness tolerance is ±20mm. During full-section excavation, slag is removed using an LWL-120 crawler scraper in conjunction with a 20t dump truck. For the short-step method, a ZCY-60R side-dump loader and a short-arm excavator are used in conjunction to ensure that the slag removal time per cycle is ≤1.5h. Deformation monitoring is required during excavation. Convergence lines (accuracy 0.1mm) and multi-point displacement meters (range 0-150mm) are placed at the arch crown, arch haunch, and sidewalls. When the deformation rate exceeds 3mm / d, the emergency support plan is immediately activated. Deformation progression is controlled by adding locking anchors (Φ25 hollow grouting anchors, length 4.0m, four per steel frame) and installing temporary cross braces (I20a I-beams, spacing 0.8m). During this stage of construction, the focus should be on controlling the distance between the advance support 1 and the excavation face (maintaining 1.5-2.0D), as well as the connection time between mechanized equipment and manual processes, to ensure that the initial support closure is completed within the self-stabilization time of the surrounding rock 10 (usually 4-6 hours), thereby effectively suppressing the extrusion rheological effect of the layered soft rock.

[0067] In layered soft rock tunnel construction, the implementation of outer primary support (3) is crucial for controlling surrounding rock deformation and ensuring construction safety. After excavation and mucking are complete and cross-section trimming is complete, outer primary support (3) operations must begin immediately. Cross-section trimming utilizes a combination of manual pneumatic picks and hydraulic breakers, focusing on undercut areas (allowable overcut ≤50mm and undercut ≤30mm). After trimming, contour inspection is performed using a 3D laser scanner (such as the Trimble TX8, with a scanning accuracy of ±2mm) to ensure that the excavation surface deviates from the designed alignment within ±50mm. For short-bench excavation, the bottom closure of outer primary support (3) must be strictly controlled within a range of 1.0-1.5 times the tunnel diameter (D) from the tunnel face (e.g., for a 10m diameter tunnel, the closure distance is 10-15m). The surrounding rock (10) is generally exposed for no more than 6 hours to inhibit the development of rheological deformation.

[0068] The outer support anchor bolts 2 are Φ25mm hollow grouting anchor bolts (yield strength 400MPa), arranged in a 0.8m×0.8m plum blossom pattern perpendicular to the bedding direction (anchor bolt length 4.5m, external insertion angle 5°-10°), and the spacing parallel to the bedding direction is increased to 1.2m. Grouting uses cement slurry with a water-cement ratio of 0.45 (with 2% sodium-based bentonite added to improve fluidity), with a grouting pressure of 0.8-1.2MPa. The grouting fullness is tested by ground penetrating radar (main frequency 1GHz), and the slurry diffusion radius is required to be ≥0.6m.

[0069] The steel arch frame uses H175×175×7.5 hot-rolled H-shaped steel (yield strength 345MPa) with a spacing of 1.0m. Φ42mm locking foot anchor pipes (length 4.0m, inclination 30°) are installed at the arch foot. 8 longitudinal connecting reinforcements (Φ22mm, spacing 1.0m) are welded to each steel frame. The shotcrete is sprayed using the wet spraying process (Meyco Ultima sprayer) with a mix ratio of cement: sand: gravel: water = 1:2.1:1.9:0.43. 3% accelerator (initial setting ≤ 5min) and 0.5% polypropylene fiber (length 12mm) are added. The spraying thickness is 180mm (allowable deviation ±20mm), and the strength grade is C25. The construction quality is controlled by burying thickness marking nails (spacing 2m×2m). The design allows local plastic extrusion failure of the outer layer initial support 3 (the damage area accounts for ≤15%). By setting a deformable joint (such as a U29 steel retractable device with a compression amount of 50mm) and adjusting the support stiffness (the anchor rod pull-out force is designed to be 150kN, which is 80% of the conventional value), a controlled release of 40%-50% of the surrounding rock 10 extrusion deformation can be achieved.

[0070] During construction, real-time monitoring was performed using a JSS30A convergence meter (accuracy 0.01mm) and an MDS-10 multi-point displacement meter (range 200mm). Twelve monitoring sections (5m apart) were deployed in the vault, haunch, and sidewalls. When the deformation rate exceeded 3mm / d or the cumulative deformation reached 45% of the predicted value, a dynamic adjustment process was initiated: the outer support anchors were spaced 2 to 0.6m apart, I18 temporary cross braces were added (spacing 0.8m apart), or Marisan chemical grout (expansion ratio ≥30 times) was injected to reinforce the fractured area. This design enabled the outer primary support (3) to simultaneously perform its load-bearing function while forming a "flexible pressure relief zone," shifting the surrounding rock pressure from traditional passive resistance to active regulation. Measured data showed that when subjected to 120-150mm of extrusion deformation, the steel frame stress remained within 250MPa (below 72% of the yield strength), and the concrete crack width was ≤0.3mm, achieving a resilient support state of "crack without collapse." In terms of construction efficiency, fully mechanized operations can reduce the time for a single support cycle to 4.5 hours (1.5 hours for anchor drilling, 1.0 hours for steel frame installation, and 2.0 hours for shotcrete spraying), a 35% improvement over traditional methods. The rebound rate is also reduced to below 12% (compared to approximately 25% for traditional air-spraying). For quality control, BIM and 3D laser scanning technology are used for digital acceptance of support profiles (with a pass rate of ≥98%). Pre-embedded resistance strain gauges (model BX120-5AA) monitor the stress development of the steel frame to ensure that the support system is always in a controllable stage of elastic-plastic deformation.

[0071] In the dynamic support system for layered soft rock tunnels, the timing of applying the inner primary support layer 4 is a key control point for coordinating the creep of the surrounding rock 10 with the support resistance. When tunnel excavation advances to a distance of 2.0-2.5 times the tunnel diameter from the working face (for example, for a 12m diameter tunnel, the application distance is 24-30m), the surrounding rock 10 enters a stage of accelerated rheology after experiencing stress release from the outer primary support layer 3. At this point, the inner primary support layer 4 must be applied promptly to establish a secondary load-bearing system.

[0072] The inner primary support 4 adopts the design concept of "combining rigidity and flexibility". Multiple compressible steel structure units 11, sliding steel arch frames 8 and sliding limit blocks 9 are installed at 6-8 key locations such as the arch waists (areas with sudden changes in curvature radius) on both sides where the stress is most unfavorable, side walls (horizontal stress concentration zones), arch feet (shear slip sensitive areas) and the bottom of the invert arch (areas with a high incidence of floor heave), forming a combined unit for directional deformation release. The inner high-compression concrete layer 5 adopts porous lightweight aggregate concrete (compressive strength 4-6MPa, elastic modulus 1.2-1.8GPa), the aggregate is sintered ceramsite with a particle size of 5-20mm (cylinder compressive strength 3.5MPa, porosity 38%-42%), and 12%-15% rubber particles (particle size 1-3mm) and 0.8% polypropylene fiber (length 12mm) are added to the cement matrix. By optimizing the gradation, the material produces uniformly distributed microcracks (crack width ≤0.2mm) when under pressure, achieving a plastic compression deformation of 30-35mm (equivalent to 6-8 times that of traditional C30 concrete). Its stress-strain curve shows a clear platform section, and it can still maintain more than 60% residual strength after the peak strength, ensuring ductile failure characteristics.

[0073] The sliding steel arch frame 8 is made of H175 steel, and the sliding node is provided with an Ω-shaped sliding limit block 9 (opening width 210mm, which is 1.2 times the height of the steel section). The sliding surface is coated with a 0.3mm thick graphene composite lubricating coating (friction coefficient ≤ 0.07), and is combined with Φ32mm high-strength bolts (preload force 80kN) to achieve graded sliding control: the initial sliding resistance is set to 120kN. When the pressure of the surrounding rock 10 exceeds this threshold, the sliding steel arch frame 8 slides at a rate of 0.5-1.2mm / d, with a maximum allowable displacement of 50mm. During the sliding process, the displacement is monitored in real time by a built-in LVDT displacement sensor (range ±60mm, accuracy 0.01mm). When the cumulative displacement reaches 45mm, the hydraulic locking device (locking force 300kN) is triggered to terminate the sliding.

[0074] The compressible steel structure unit 11 is made of corrugated steel plates 12 (wave height 25mm, wave distance 120mm) made of Q345 steel plates and chloroprene rubber cushions (thickness 20mm, Shore hardness 55HA) alternately stacked (4-6 layers). A pre-compressive stress of 15-20MPa is applied by connecting steel plates 13 and high-strength bolts. Under the pressure of the surrounding rock 10, a dual energy dissipation mechanism of interlayer slippage and material compression is generated. Actual measurements show that the unit can withstand 250-300kN / m 2 Under pressure, it can produce 25-30mm compression deformation, with an energy dissipation coefficient of 0.65-0.75. The compressible steel structure unit 11, the sliding steel arch frame 8, and the sliding limit block 9 form a combined unit with directional deformation release. The combined units are unevenly arranged along the tunnel circumference, with two groups set at the arch waist (spacing 1.2-1.5m), one or two groups each at the side walls and arch feet, and one group at the base of the inverted arch. The unit width is 1.0-1.2m, and adjacent units are connected by Φ22mm longitudinal connecting bars (spacing 0.6m) to form a continuous force system.

[0075] During the construction process, a phased grouting process of "soft first, hard later" was adopted: in the initial grouting, ultrafine cement slurry (particle size D50 = 8 μm, water-cement ratio 0.6) was used for penetration reinforcement (grouting pressure 0.3-0.5 MPa). After the deformation rate dropped to 1.0 mm / d, cement-water glass double liquid slurry (C:S = 1:0.6, gel time 45 s) was used for compensatory grouting (pressure 0.8-1.2 MPa) to ensure the coordinated deformation of the grouting body and the surrounding rock 10. Monitoring data show that this support system can orderly release 30%-40% of the large extrusion deformation of the surrounding rock 10 (about 80-120mm) through material compression, structural slippage and interface friction, reducing the residual load borne by the secondary lining 7 to 55%-60% of the traditional design, the maximum bending moment of the steel arch frame from 850kN·m to 520kN·m, and the tensile stress of the concrete within 1.5MPa (60% lower than the standard value of tensile strength).

[0076] In the composite support system of layered soft rock tunnels, the coordinated construction of the drainage system and the buffer structure layer 6 is the core link to ensure the long-term durability of the tunnel. When the tunnel is excavated to a distance of 4.0-5.0 times the tunnel diameter (D) from the heading face (taking a 12m tunnel diameter as an example, the construction distance is 48-60m), the surrounding rock 10 enters the rheological stability stage after the stress adjustment of the early support system. At this time, the full-section construction of the drainage system and the high-compression lightweight concrete buffer structure layer 6 needs to be implemented simultaneously. The drainage system adopts the design concept of "divided interception and multi-channel defense": first, Φ50mm HDPE drainage blind pipes (permeable porosity ≥15%) are laid along the circumferential spacing of the tunnel at 8-10m, and the blind pipes are wrapped with 300g / m 2Non-woven geotextile is used as the filter layer; 1.5mm thick EVA waterproof board (elongation at break ≥ 600%) is laid on the arch wall, and the joints are welded by double-seams hot-melt welding (weld width ≥ 20mm, air tightness test pressure 0.2MPa maintained for 5 minutes without leakage); radial grouting (ultrafine cement-water glass double liquid slurry, gel time 30-60s) is implemented in the local water seepage section to form a 2.0m thick water-stop curtain, and the grouting holes are arranged in a 1.2×1.2m plum blossom shape, with a grouting pressure of 0.5-1.0MPa. The buffer structure layer 6 uses high-compression lightweight concrete (dry density ≤ 1600kg / m 3 ), whose thickness is dynamically adjusted according to the predicted value of large extrusion deformation: 25cm when the predicted deformation is ≤150mm, 28cm when 150-200mm, and 30cm when >200mm. Verified by finite element analysis, this thickness range can ensure that the compression modulus (0.5-0.8GPa) of the buffer structure layer 6 matches the creep stiffness (0.3-0.6GPa) of the surrounding rock 10, while meeting the self-stability requirements of the thin layer structure (slump control is 160±20mm). The concrete mix ratio is designed as follows: 42.5 grade ordinary Portland cement 280kg / m 3 , shale ceramsite with particle size of 5-10mm (cylinder pressure strength 3.2MPa) 650kg / m 3 , modified expanded perlite (bulk density 120kg / m 3 )80kg / m 3 , silica fume 40kg / m 3 , polycarboxylate water-reducing agent 1.2%, water-binder ratio 0.38; in areas with developed groundwater, adding 8%-12% penetrating crystalline waterproofing agent (the main components are active silica and calcium oxide, which react to form ettringite crystals to fill pores) can increase the concrete's impermeability grade from P6 to P10 and reduce the chloride ion diffusion coefficient to 1.5×10 -12 m 2 / s.

[0077] The construction adopts LSS-1200 hydraulic slipform paver (paving speed 1.2-1.8m / min) for full-section formwork construction. The formwork system is set with a 0.5% pre-camber to compensate for the later compression deformation. The concrete is poured in layers (each layer thickness ≤ 30cm). The inserted vibrator (frequency 12000r / min) and the attached vibrator (power 1.5kW / m 2) combined with vibration to ensure uniform distribution of aggregate (ceramsite floating rate ≤ 3%). After pouring, an automatic sprinkler system (water pressure 0.3MPa, interval 2h) is used for curing for 28 days, with humidity maintained at ≥90% and temperature controlled at 20±5℃ to prevent shrinkage cracks. The monitoring system integrates distributed fiber optic sensors (spacing 0.5m, strain measurement accuracy ±2με) and resistive piezometers (range 0-1MPa, accuracy 0.1%FS), and provides real-time feedback on the compressive strain of the buffer structure layer 6 (design allowable value 15mm) and groundwater pressure changes. When the monitoring data exceeds the threshold, an automatic warning is activated and the opening of the drainage blind pipe valve is adjusted. In a high-stress tunnel project in the southwest, a section with a 30cm thick buffer structure layer 6 was used. After three years of operation, tests showed that the average compression of the buffer structure layer 6 was 12mm (80% of the design value), the surface crack density of the secondary lining 7 was reduced from 0.8 / m in the traditional structure to 0.1 / m, the number of seepage points was reduced by 92%, and the maintenance cost over the entire life cycle was reduced by 40%, verifying the engineering effectiveness of the composite system.

[0078] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0079] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A new support structure for layered soft rock tunnels, characterized by: include: Secondary lining (7); The inner layer initial support (4) is fully enclosed and arranged outside the secondary lining (7), and the arch wall full section area is defined between the inner layer initial support (4) and the secondary lining (7); A buffer structure layer (6) is provided in the full cross-section area of the arch wall; The outer layer initial support (3) is arranged outside the inner layer initial support (4), and its inverted arch is not capped; the outer layer initial support (3) is used to release the extrusion deformation of the surrounding rock (10), and the inner layer initial support (4) is used to absorb the deformation displacement of the outer layer initial support (3).

2. A novel support structure for layered soft rock tunnels according to claim 1, characterized in that: The inner layer initial support (4) comprises: An inner high-compression concrete layer (5) is arranged on the outer side of the secondary lining (7); A plurality of compressible steel structure units (11) are composed of corrugated steel plates (12) and rubber pads alternately stacked, wherein the compressible steel structure units (11) are embedded in the inner high-compression concrete layer (5) and are evenly arranged at the arch crown, arch waist and side walls along the tunnel circumference.

3. The novel support structure for layered soft rock tunnel according to claim 2 is characterized in that: The inner high-compression concrete layer (5) is made of porous lightweight aggregate concrete, has a thickness of 200-300 mm, and a compressive strength of 5-8 MPa; the compressible steel structure unit has a compression deformation of 15-25 mm.

4. The novel support structure for layered soft rock tunnel according to claim 3 is characterized in that: The height of the corrugated steel plate (12) is 20-30 mm, the wave pitch is 100-150 mm, and the Shore hardness of the rubber cushion layer is 40-60 HA.

5. The novel support structure for layered soft rock tunnel according to claim 3 is characterized in that: Also includes: A sliding steel arch (8) is made of section steel and is arranged outside the compressible steel structure unit (11); the sliding steel arch (8) is slidably connected to the compressible steel structure unit (11); and a graphene composite lubricating coating is provided between the sliding steel arch (8) and the compressible steel structure unit (11); A sliding limit block (9) comprises an integrally connected connecting plate (901) and an extrusion plate (902), wherein the extrusion plate (902) is U-shaped and adapted to the groove shape of the sliding steel arch frame (8), and the connecting plate (901) is arranged at both ends of the extrusion plate (902); the sliding limit block (9) has two connecting plates (901) arranged in the upper and lower grooves of the sliding steel arch frame (8), respectively, and the two connecting plates (901) of the sliding limit blocks (9) are connected by bolts, and at least one of the sliding limit blocks (9) is welded to the outer initial support (3) or the compressible steel structure unit (11); the sliding limit block (9) is used to adjust the sliding resistance between the sliding steel arch frame (8) and the sliding limit block (9).

6. The novel support structure for layered soft rock tunnel according to claim 5, characterized in that: The sliding displacement of the sliding steel arch frame (8) is 30-50 mm; a polytetrafluoroethylene wear-resistant coating is coated between the sliding limit block (9) and the sliding steel arch frame (8), the friction coefficient is ≤0.08, and the ultimate sliding resistance is 100-150 kN.

7. The novel support structure for layered soft rock tunnel according to claim 1, characterized in that: The outer layer initial support (3) is made of steel arch frame sprayed concrete, and the outer layer initial support (3) anchors the outer layer support anchor rod (2), and the outer layer support anchor rod (2) extends in the direction of vertical bedding and horizontal bedding.

8. The novel support structure for layered soft rock tunnel according to claim 7, characterized in that: The spacing between adjacent steel arch frames is 0.8-1.2m, and the total unclosed length of the inverted arch of the multiple steel arch frames accounts for 20%-30% of the total length of the tunnel; the length of the outer layer support anchor rods (2) arranged along the vertical bedding is 1.2-1.5 times the length of the outer layer support anchor rods (2) arranged along the horizontal bedding.

9. The novel support structure for layered soft rock tunnel according to claim 1, characterized in that: A deformation gap of 50-80 mm is reserved between the inner layer initial support (4) and the outer layer initial support (3), and the deformation gap is filled with foam concrete with a density grade of A05-A07.

10. The novel support structure for layered soft rock tunnel according to claim 1, characterized in that: The buffer structure layer (6) is made of concrete and has a thickness of 80-120 mm. A geotextile isolation layer is provided between the buffer structure layer (6) and the secondary lining (7). A deformation monitoring optical fiber sensor is pre-embedded in the buffer structure layer (6).

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