Large-section deep-embedded soft rock tunnel combined support system and construction method

Abstract

The present application relates to a kind of large section deep soft rock tunnel combined support system and construction method, the present application is combined with elastic shell theory and equivalent section method, a steel arch frame-grating combined support mode suitable for deep large section soft rock tunnel is proposed, the support rigidity of simply using steel arch frame or grid steel frame is overcome or supported, the disadvantage of lower in long-term large deformation unfavorable surrounding rock stability and deformation control, solve the problem that the stress of existing support structure is larger, the self-bearing capacity of surrounding rock cannot be fully exerted, cause material waste is serious, the safety factor of support structure is low, difficult to guarantee the stability of tunnel, and provide a simple and practical construction method for tunnel excavation and support.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of tunnel support, and particularly relates to a large-section deep-embedded soft rock tunnel combined support system and a construction method. BACKGROUND

[0002] With the sustained development of China's economy, the comprehensive national strength is continuously enhanced, and high-tech is continuously developed. The application field and application depth of underground engineering will be continuously expanded. Meanwhile, the development of tunnels is the urgent need of China's economic development, the strategy of developing the west, and the strategy of opening to the sea. Traffic facilities and water and electricity supply are increasingly becoming the bottleneck of the economic development of a region. In the aspect of traffic tunnels, with the continuous improvement of China's highway trunk network, especially the continuous extension to the mountainous areas in the west of China, the extension of Hainan Island to the mainland, and the connection between the Liaodong Peninsula and the Jiaodong Peninsula, huge tunnel projects are needed to support. With the development of the west, the length and quantity records of China's railway tunnels and highway tunnels will be continuously broken. Tunnel projects are faced with more difficult construction environments and geological conditions, and the construction and operation technology of tunnel projects is unprecedentedly complex. For example, the Ga Longla Tunnel in Tibet, which is the largest slope highway tunnel in China at present, has a slope of 4.1%; the Yakexia Snow Mountain Tunnel in Sichuan, which is the highest highway tunnel in China at present, has an altitude of 4300m; the Changlasan Tunnel in Qinghai, which is the highest highway tunnel under construction in the world, has an exit altitude of 4493m; the Erlasan Tunnel in Qinghai, which is the longest highland permafrost double-hole highway tunnel under construction in the world; the Yangquan Tunnel and the Tangjiayuan Tunnel in Shaanxi are the longest and largest loess tunnels in the northwest of China at present, respectively.

[0003] Due to the limitation of geological exploration and the complexity and variability of geological conditions, sudden changes in geological conditions, unexpected situations (such as collapse, gushing water and rock burst, etc.) often occur during tunnel construction. The original construction plan, construction technical scheme, construction technical measures and construction schedule must be changed accordingly. Although rich experience in tunnel construction has been accumulated in the past engineering practice, there are still many deficiencies. Tunnel construction can be divided into main buildings and auxiliary buildings. The former is built to maintain the stability of the tunnel and ensure its normal use, consisting of the structure of the tunnel body and the portal. The latter refers to various auxiliary facilities required to ensure the normal use of the tunnel, such as mechanical ventilation facilities for strengthening air exchange inside and outside the long and large tunnel, and necessary fire-fighting and alarm devices, etc. After excavation, the tunnel generally needs to be supported and lined in order to maintain the stability of the surrounding rock. The main ways of support are: anchor rod, steel frame, steel mesh, concrete layer and other combinations. The main ways of lining are: monolithic concrete lining, assembled lining, concrete layer lining and composite lining, etc. It can be said that these ways, methods, types and their combinations can adapt to most surrounding rock geological conditions and engineering structural conditions, but this adaptation is not absolute in engineering practice. This inadaptation is caused by a variety of reasons: first, the surrounding rock properties are not accurately judged or the situation is not clear during construction design; second, the support type does not adapt to the actual requirements; third, the timing and method of support are not appropriate; and fourth, other unknown reasons. Due to the existence of the above reasons, abnormal phenomena such as adverse deformation and even relaxation collapse often occur during actual construction. SUMMARY

[0004] The purpose of the present application is to provide a large-section deep-buried soft rock tunnel combined support system and construction method to solve the problem that the existing support structure is not suitable for the technical construction requirements of large-section deep-buried soft rock tunnels. Another purpose of the present application is to provide a construction method for a large-section deep-buried soft rock tunnel combined support structure system.

[0005] To solve the above problems, the technical solution of the present application is:

[0006] The application discloses a combined support system for a large-section deep-buried soft rock tunnel, which comprises an advanced support structure, an initial support structure and a secondary lining structure, the advanced support structure is a horizontal rotary jetting pre-support, the horizontal rotary jetting pre-support is a pre-support arch shed structure formed by rotary jetting columns in a ring direction and longitudinally overlapped along an arch part of the tunnel; the initial support structure comprises flexible support and rigid support, the flexible support comprises anchor rods and a concrete layer, the anchor rods are inserted into the tunnel rock stratum through the horizontal rotary jetting pre-support, and the concrete layer is arranged at an inner periphery of the horizontal rotary jetting pre-support; the rigid support comprises a steel arch frame and a grid steel frame, the steel arch frame is fixed at an inner periphery of the concrete layer, and the grid steel frame is fixed at an inner periphery of the steel arch frame; a full-coverage waterproof layer is arranged between the initial support structure and the secondary lining structure; the secondary lining structure is a permanent support, and the permanent support structure comprises system anchor rods, a waterproof concrete layer and a backfill layer, the waterproof concrete layer is arranged at an inner periphery of the full-coverage waterproof layer, the system anchor rods are inserted into the rock stratum through the advanced support structure and the initial support structure, the system anchor rods are fixedly connected to edges of the waterproof concrete layer at tail ends, and the backfill layer is arranged in a foundation and covers end portions of the waterproof concrete layer.

[0007] Further, the steel arch frame is a profile steel, the shape of the steel arch frame is the same as the shape of the cross section of the tunnel, the steel arch frame is composed of two or more steel arch frame units, and an energy-absorbing buffer device is arranged between adjacent steel arch frame units.

[0008] Further, the energy-absorbing buffer device comprises connecting steel plates, lug plates, galvanized steel plates, rubber pads and energy-absorbing buffer steel pipes, the two ends of the connecting steel plates are fixedly connected to the lug plates through high-strength bolts, the lug plates are fixed to the upper and lower sides of the lock foot anchor rods of the steel arch frame, a group of oppositely arranged galvanized steel plates are fixedly clamped between the connecting steel plates on the upper and lower sides, rubber pads are arranged on the opposite sides of the galvanized steel plates, the opposite sides of the galvanized steel plates are respectively connected to the end portions of the corresponding lock foot anchor rods, and a plurality of energy-absorbing buffer steel pipes are fixedly arranged on the inner sides of the opposite rubber pads.

[0009] Further, the energy-absorbing buffer steel pipe in the energy-absorbing buffer device comprises a first high-strength spring steel sheet first damper, a circular steel pipe M and a circular steel pipe N, the first high-strength spring steel sheet is located in the circular steel pipe M, the first damper is located in the circular steel pipe N, one end of the circular steel pipe M and the circular steel pipe N is connected, the other end is respectively fixedly connected to the corresponding rubber pad, one end of the first high-strength spring steel sheet and the first damper is connected, and the other end of the first high-strength spring steel sheet and the first damper is respectively fixedly connected to the corresponding rubber pad.

[0010] Furthermore, the grating steel frame is composed of two or more grating steel frame units, and pressure-relief energy dissipation devices are provided between adjacent grating steel frame units. The pressure-relief energy dissipation device includes a second damper, a connecting box, and pressure-relief energy dissipation steel pipes X. One end of the second damper is fixedly connected to the vertical reinforcement of the horizontal grid structure of the grating steel frame, and the other end of the second damper is connected to the connecting box. Multiple pressure-relief energy dissipation steel pipes X are provided inside the connecting box, and the gap inside the connecting box is filled with first filling concrete.

[0011] A construction method for a combined support system for large-section, deep-buried soft rock tunnels includes the following steps:

[0012] Step 1: Based on hydrogeological conditions and stratigraphic parameters, determine the support structure parameters and design points for high-stress soft rock tunnels using a combined support mechanics analysis model, and determine the design scheme.

[0013] Step 2: Prefabricate steel profiles and grating frames according to the design scheme;

[0014] Step 3: Tunnel excavation must be carried out after the pre-support is completed. Construction shall be carried out in strict accordance with the principles of "short advance, short steps, strong support, early ring formation, and tight secondary lining". The arch of the tunnel shall be pre-supported first, and horizontal jet grouting pre-support shall be prepared.

[0015] Step 4: Install flexible support in the initial support of the upper half of the pilot tunnel in the preliminary tunnel. In the flexible support, the anchor rod passes through the horizontal jet grouting pre-support and is inserted into the rock strata of the upper half of the tunnel.

[0016] Step 5: Concrete layer construction. The concrete is mixed outside the tunnel using a forced mixing machine and transported by a concrete mixer truck. The concrete is sprayed using a wet spraying process on the inner circumference of the horizontal jet spraying pre-support, with the width of the concrete layer gradually increasing at both ends.

[0017] Step Six: Construction of the initial support steel arch frame for the tunnel. First, install the upper arch unit A and arch unit B, and place reinforced concrete pads at the arch foot. The arch unit A and arch unit B are fixedly connected using energy-absorbing buffer devices. The two side walls are excavated separately on the left and right sides, and the wall steel arch frame side wall units C and D are installed successively. The side wall units C and D are fixedly connected using energy-absorbing buffer devices. The installed steel arch frames are connected into one piece by longitudinal connecting bars, and the tail of the anchor rod is welded to the steel arch frame. The steel arch frame is tightly attached to the concrete layer.

[0018] Step seven, the inner perimeter of the steel arch is sprayed with concrete and leveled, and has sufficient protective layer, and the grid steel frame is installed; first, the arch part F unit and the arch part G unit are installed, the arch part F unit and the arch part G unit are fixedly connected by the pressure-allowing energy dissipation device, and the steel reinforced concrete pad is padded at the arch foot, the left and right side walls are excavated in staggered manner, the wall part H unit is installed in sequence, the wall part H unit and the arch part G unit are fixedly connected by the pressure-allowing energy dissipation device; the installed grid steel frame is connected into one body by the longitudinal connecting rib; the grid steel frame is tightly attached to the inner perimeter of the steel arch sprayed with concrete;

[0019] Step eight, a full waterproof layer is arranged between the initial support and the secondary lining of the tunnel, and construction joints and deformation joints are reserved in the construction of the initial support and the secondary lining, and water stop belts are arranged in the construction joints and the deformation joints;

[0020] Step nine, the inverted arch backfill layer is constructed, the inverted arch concrete is continuously poured and formed in sections, and no longitudinal construction joint is left to form the backfill layer;

[0021] Step ten, steps three to nine are repeated, and the pressure-allowing initial support is arranged in the axial direction of the tunnel according to the design parameters;

[0022] Step eleven, the permanent support structure is constructed;

[0023] Step twelve: steps three to eleven are repeated until the tunnel structure construction is completed.

[0024] Further, in the joint support mechanical analysis model in step one,

[0025] The support structure stiffness model K s and the maximum support force model P max,s are:

[0026]

[0027]

[0028] In the formula, R0 is the radius of the tunnel, E eq is the equivalent elastic modulus, v is the Poisson's ratio, t eq is the equivalent thickness, and σ s is the equivalent yield stress;

[0029] The equivalent yield stress model σ s is:

[0030]

[0031] In the formula, σ′ s is the yield stress of the shaped steel, A s is the cross-sectional area of the shaped steel, b is the spacing of the shaped steel support, and t eq is the equivalent thickness;

[0032] K - stiffness model of concrete c and P - maximum support force model max,c are respectively:

[0033]

[0034]

[0035] where R0 is the radius of the tunnel, v is the Poisson's ratio, E c is the elastic modulus of concrete, t c is the thickness of concrete layer, σ c is the ultimate compressive strength of the initial sprayed concrete layer;

[0036] The maximum allowable displacement model of the support structure is:

[0037]

[0038] where u el is the maximum elastic displacement of the combined support system, ε br is the failure strain of the support structure material, R0 is the radius of the tunnel, t c is the thickness of concrete layer, v is the Poisson's ratio, K c is the stiffness of concrete, P max,c is the maximum support force of concrete, σ c is the ultimate compressive strength of the initial sprayed concrete layer;

[0039] The initial displacement model of the surrounding rock is:

[0040]

[0041] where u r is the initial displacement; is the final displacement; x is the distance of the support from the face of the tunnel.

[0042] Further, in the stiffness model of the support structure and the maximum support force model:

[0043]

[0044]

[0045] where b is the width or support spacing, v is the Poisson's ratio, D1 and K1 are the compressive stiffness and flexural stiffness of the steel section respectively, and D2 and K2 are the compressive stiffness and flexural stiffness of the concrete layer respectively.

[0046] Further, the spacing and depth of the anchor rods in step four are:

[0047]

[0048] D—anchor spacing (m) ; d—anchor diameter (m) ; R a —design strength of anchor reinforcement (Pa) ; K—safety factor, preferably K = 1.5 ~ 2.0; P—gravity of dangerous rock or unstable mass (N), when there is unstable mass in side wall, P value is the sliding force minus the anti-sliding force; A—exposed area of dangerous rock or unstable mass (m 2 ) ;

[0049] The depth of anchor into stable rock mass is:

[0050]

[0051] L m —depth of anchor into stable rock mass (m) ; τ—bond strength of mortar (N / m 2 ) ;

[0052] The support stiffness of anchor in the flexible support is:

[0053]

[0054] Q is load deformation constant, S r and S l are longitudinal and circumferential spacing of anchor support respectively, L is anchor length, Φ is anchor diameter, E b is elastic modulus of anchor;

[0055] The maximum support force of anchor in the flexible support is:

[0056]

[0057] T max is the maximum yield of anchor;

[0058] The maximum allowable damage displacement of anchor in the flexible support is:

[0059]

[0060] u0 is initial displacement, L is anchor length, ε br is damage strain of anchor, T max is the maximum yield of anchor, Φ is anchor diameter, E b is elastic modulus of anchor.

[0061] Further, the thickness of concrete layer in step five should be controlled in:

[0062] h = (0.025 ~ 0.033) r0

[0063] In the formula, h is the thickness of the h-spray layer; r0 is a tunnel calculation radius, a non-circular tunnel, and the half of the circumscribed semicircle or span is approximately taken.

[0064] Compared with the current commonly used tunnel support bracket and its method, the present application has the following advantages:

[0065] 1. The present application combines the elastic thin shell theory and the equivalent section method, and proposes a steel arch support-grating combined support mode suitable for deep-buried large-section soft rock tunnels, which overcomes the shortcomings of low support stiffness of pure steel arch support or grating steel support, is not conducive to the stability and deformation control of long-term large deformation of surrounding rock, solves the problems of large stress of existing support structure, insufficient self-bearing capacity of surrounding rock, serious material waste, low safety factor of support structure, and difficulty in ensuring the stability of the tunnel, and provides a simple and practical construction method for tunnel excavation and support.

[0066] 2. By using the rigid support with pressure relief and energy dissipation device between the grating steel frame units and the rigid support with energy absorption and buffering device between the steel arch units, the impact energy of the long-term load or seismic load in the surrounding rock is buffered and absorbed, and the rapid bearing and common bearing of the two are realized, which can effectively utilize the bearing capacity of the surrounding rock, significantly improve the bearing capacity of the initial support, control the large deformation of the surrounding rock, more effectively cope with the large deformation of the deep-buried large-section soft rock tunnel, and ensure the construction safety and efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0067] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and other related drawings can also be obtained by those skilled in the art without creative labor.

[0068] Figure 1 It is a schematic diagram of the front view structure of the main body of the system;

[0069] Figure 2 It is a schematic diagram of the steel arch structure of the system;

[0070] Figure 3 It is a schematic diagram of the grating steel frame structure of the system;

[0071] Figure 4 It is a longitudinal sectional view of the system along the tunnel axis;

[0072] Figure 5 It is a large drawing of the energy absorption and buffering device of the system and the sectional view a-a corresponding to it; Figure 4

[0073] Figure 6 ​The general layout of the pressure relief energy dissipation device of the system and the corresponding Figure 4 sectional view b-b of the pressure relief energy dissipation device of the system;

[0074] Figure 7 The general layout of the pressure relief energy dissipation device of the system and the corresponding Figure 6 steel pipe (X) of the pressure relief energy dissipation device of the system;

[0075] Figure 8 The general layout of the pressure relief energy dissipation device of the system and the corresponding Figure 1 drainage device (P) of the system;

[0076] The figure is marked: 1-pre-support, 2-flexible support, 3-rigid support, 4-anchor rod, 5-concrete layer, 6-steel arch, 61-arch A unit, 62-arch B unit, 63-side wall C unit, 64-side wall D unit, 65-inverted arch E unit, 7-grid steel frame, 71-arch F unit, 72-arch G unit, 73-side wall H unit, 8-permanent support, 9-system anchor rod, 10-waterproof concrete, 11-full waterproof layer, 12-locking anchor rod, 13-energy absorption buffer device, 14-connection steel plate, 15-ear plate, 16-high-strength bolt, 17-galvanized steel plate, 18-rubber pad, 19-first high-strength spring steel sheet, 20-first damper, 21-energy absorption buffer steel pipe, 22-pressure relief energy dissipation device, 23-second damper, 24-first filling concrete, 25-second high-strength spring steel sheet, 26-second filling concrete, 27-geotextile layer, 28-cement mortar layer, 29-waterproof board layer; 30-vertical drainage pipe, 31-horizontal drainage pipe, 32-longitudinal drainage pipe, 33-backfill layer. DETAILED DESCRIPTION

[0077] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The present application will be described in further detail below in combination with the drawings and specific embodiments:

[0078] As Figure 1As shown, the present application relates to a large section deep soft rock tunnel combined support force system, which comprises an advanced support structure, an initial support structure and a secondary lining structure; the advanced support structure comprises a horizontal rotary jetting pre-support 1, which is a rotary jetting column body forming a pre-support arch shed structure with ring-shaped occlusion and longitudinal lap along the tunnel arch; the initial support structure comprises a flexible support 2 and a rigid support 3, the flexible support 2 comprises an anchor rod 4 and a concrete layer 5, the anchor rod 4 is inserted into the rock layer through the horizontal rotary jetting pre-support 1, and the concrete layer 5 is arranged on the inner periphery of the horizontal rotary jetting pre-support 1; the rigid support 3 comprises a steel arch 6 and a grid steel frame 7, the steel arch 6 is fixed on the inner periphery of the concrete layer 5, and the grid steel frame 7 is fixed on the inner periphery of the steel arch 6 by spraying concrete; a full waterproof layer 11 is arranged between the initial support structure and the secondary lining structure; the secondary lining structure is a permanent support 8, and the permanent support 8 structure comprises a system anchor rod 9, a waterproof concrete layer 10 and a backfill layer 33, the waterproof concrete layer 10 is arranged on the inner periphery of the full waterproof layer 11 by spraying concrete, the system anchor rod 9 is inserted into the rock layer through the advanced support structure and the initial support structure, the tail end of the system anchor rod 9 is fixedly connected with the edge of the waterproof concrete layer 10, and the backfill layer 33 is arranged in the upward supply foundation and covers the end of the waterproof concrete layer 10.

[0079] As shown in Figure 2 , 4 , the steel arch 6 is a profile steel, and the shape of the steel arch 6 is the same as the shape of the tunnel cross section. The steel arch 6 is composed of two or more steel arch units, and an energy-absorbing buffer device 13 is arranged between adjacent steel arch units. In this embodiment, the steel arch units include an arch A unit 61, an arch B unit 62, a side wall C unit 63, a side wall D unit 64 and an inverted arch E unit 65, and the steel arch units are connected by the connecting steel plates 14 of the energy-absorbing buffer device 13. The arch A unit 61 is fixed on the top of the tunnel arch, and the arch B unit 62, the side wall C unit 63, the side wall D unit 64 and the inverted arch E unit 65 are sequentially connected at both ends of the arch A unit 61. The inverted arch E unit 65 is a reverse arch structure arranged at the bottom of the tunnel, which is simply an upward arch.

[0080] The energy-absorbing buffer device 13 is arranged in one set in every 1 to 5 steel arches 6. As shown in Figure 5As shown, the energy-absorbing buffer device 13 includes a connecting steel plate 14, an ear plate 15, a high-strength bolt 16, a galvanized steel plate 17, a rubber pad 18, and an energy-absorbing buffer steel pipe 21. The connecting steel plate 14 is fixedly connected to the ear plate 15 at both ends through the high-strength bolt 16, and the ear plate 15 is fixed to the upper and lower sides of the lock foot anchor rod 12 of the steel arch 6, that is, the energy-absorbing buffer device 13 is fixed to the lock foot anchor rod 12 of the steel arch 6. A set of oppositely arranged galvanized steel plates 17 are clamped between the connecting steel plates 14 on the upper and lower sides. The rubber pads 18 are arranged on the opposite sides of the galvanized steel plates 17. The opposite sides of the galvanized steel plates 17 are fixedly connected to the end portions of the lock foot anchor rods 12 of the corresponding steel arch units, respectively. The inner sides of the opposite rubber pads 18 are fixedly provided with a plurality of energy-absorbing buffer steel pipes 21. The energy-absorbing buffer device 13 bears the tunnel surrounding rock pressure together with the steel arch at the initial stage of construction, absorbs the energy released when the surrounding rock stress is redistributed, and resets the structure after the dynamic load, that is, the released energy, disappears. This effectively reduces the damage to the supporting structure caused by the dynamic load and prevents the connection of the steel arch from being damaged.

[0081] The energy-absorbing buffer steel pipe 21 in the energy-absorbing buffer device 13 includes a first high-strength spring steel sheet 19, a first damper 20, a circular steel pipe M, and a circular steel pipe N. The first high-strength spring steel sheet 19 is located inside the circular steel pipe M, and the first damper 20 is located inside the circular steel pipe N. One end of the circular steel pipe M is connected to the circular steel pipe N, and the other end is fixedly connected to the corresponding rubber pad 18. One end of the first high-strength spring steel sheet 19 is connected to the first damper 20, and the other end of the first high-strength spring steel sheet 19 is fixedly connected to the corresponding rubber pad 18. The outer diameter of the circular steel pipe N is equal to the inner diameter of the circular steel pipe M. The circular pipe M is inlaid in the circular pipe N, and the inner diameter is equal to the outer diameter, which reasonably utilizes the space and improves the synergistic effect.

[0082] The energy-absorbing buffer device 13 is a long rectangular structure with an arc, with a width of 10-20 cm, a circumferential length of 20-30 cm, and 2-6 energy-absorbing buffer steel pipes 21. The first high-strength spring steel sheet 19 in the energy-absorbing buffer steel pipe 21 is selected from 60CrMnBA high-strength spring steel sheets. The first damper 20 in the energy-absorbing buffer steel pipe 21 is selected from viscous dampers. The energy-absorbing buffer steel pipe 21 plays a role in absorbing energy when the surrounding rock stress is redistributed and energy is released. The high-strength spring steel sheet and the damper both have good energy-absorbing effects.

[0083] As Figure 3 , 4As shown, the grid steel frame 7 in the rigid support 3 is composed of two or more grid steel frame units, and a pressure-relief energy dissipation device 22 is arranged between adjacent grid steel frame units. The grid steel frame unit includes an arch portion F unit 71, an arch portion G unit 72, and a side wall H unit 73. Two arch portion F units 71 are symmetrically arranged at the top of the tunnel, and the two ends are symmetrically connected to the arch portion G unit 72 and the side wall H unit 73 in sequence. Adjacent grid steel frame units are connected by the pressure-relief energy dissipation device 22. The shape of the grid steel frame 7 in the rigid support 3 is the same as the shape of the cross section of the tunnel.

[0084] As shown in the drawings, Figure 6 The pressure-relief energy dissipation device 22 includes a second damper 23, a connecting box 34, and a pressure-relief energy dissipation steel pipe X. One end of the second damper 23 is fixedly connected to the horizontal web of the grid steel frame 7, and the other end of the second damper 23 is connected to the connecting box 34. The connecting box 34 includes 2-4 pressure-relief energy dissipation steel pipes X. The space in the connecting box 34 is filled with the first filling concrete 24. The pressure-relief energy dissipation steel pipe X is provided with a reserved hole, and the reserved hole is used to pour concrete into the steel pipe to improve the overall compression and bending resistance of the steel pipe. The second damper 23 in the pressure-relief energy dissipation device 22 is a viscous damping rod.

[0085] As shown in the drawings, Figure 7 The second high-strength spring steel sheet 25 is arranged in the inner periphery of the pressure-relief energy dissipation steel pipe X. The second high-strength spring steel sheet 25 has a ring structure, and the inner periphery of the second high-strength spring steel sheet 25 is filled with the second filling concrete 26. The second filling concrete 26 is tightly attached to the inner wall of the second high-strength spring steel sheet 25. The second high-strength spring steel sheet 25 is made of 60CrMnBA high-strength spring steel sheet.

[0086] As shown in the drawings, Figure 7 , 8 The full waterproof layer 11 includes a geotextile layer 27, a cement mortar layer 28, a water stop belt 35, a waterproof board layer 29, a vertical drainage pipe 30, a horizontal drainage pipe 31, and a longitudinal drainage pipe 32. The geotextile layer 27 is tightly attached to the outer concrete of the grid steel frame 7. The waterproof board layer 29 is located outside the permanent support 8. The cement mortar layer 28 is arranged between the geotextile layer 27 and the waterproof board layer 29. The water stop belt 35 is arranged in the deformation joint and the construction joint in the inner periphery of the waterproof board layer 29. The vertical drainage pipe 30 is located below the geotextile layer 27. The vertical drainage pipe 30 is communicated with the horizontal drainage pipe 31. The horizontal drainage pipe 31 is tightly attached to the vertical drainage pipe 30 and is communicated with the longitudinal drainage pipe 32 at the center line of the tunnel. The water in the surrounding rock penetrates into the geotextile layer 27 from the surrounding rock, flows into the vertical drainage pipe 30 from the geotextile layer 27, flows into the horizontal drainage pipe 31 from the vertical drainage pipe 30, and flows into the longitudinal drainage pipe 32 from the horizontal drainage pipe 31. The water in the longitudinal drainage pipe 32 is guided to a fixed location outside the tunnel.

[0087] The geotextile layer 27 in the full-encapsulated waterproof layer 11 is selected as a waterproof roll material or waterproof oil felt with a thickness of 1.5-5 mm. The waterproof board layer 29 in the full-encapsulated waterproof layer 11 is selected as a waterproof board with a thickness of 1.5-5 mm, and the lap joint is required to be in a scale-like shape to facilitate drainage. The vertical drainage pipe 30 in the full-encapsulated waterproof layer 11 and the hard polyvinyl chloride drainage pipe at the arch foot pass through the structure layer of the permanent support 8 and are discharged into the side ditch.

[0088] The system anchor rod 9 in the permanent support 8 structure is selected as a full-length bonded anchor rod. Part of fly ash is mixed into the waterproof concrete layer 10 in the permanent support 8 structure to improve the workability of the concrete. The fly ash in the waterproof concrete layer 10 adopts a first-level standard, and the mixing amount is not greater than 25%. The pump extrusion concrete construction technology is adopted when the vault concrete in the waterproof concrete layer 10 is poured. Two to four pouring holes are designed in the vault, and the pouring is performed from back to front. The grouting pipe is pre-buried close to the waterproof board surface at the highest position of the vault. The waterproof concrete layer 10 is a sprayed polypropylene fiber mesh concrete with a strength grade of C30-C60 and a thickness of 30-60 cm.

[0089] A construction method of a large-section deep-buried soft rock tunnel combined support mechanical analysis model, comprising the following steps:

[0090] Step one, determining the support structure parameters and design points of the high ground stress soft rock tunnel according to the hydrogeological conditions and stratum parameters, and determining the design scheme;

[0091] Step two, precasting the steel and grid frames according to the design scheme;

[0092] Step three, the tunnel excavation must be performed after the completion of the advanced support, and the construction is strictly performed according to the principles of "short footage, short steps, strong support, early ring formation, and tight secondary lining". The advanced support is first performed on the arch part of the tunnel, and the horizontal rotary jetting pre-support 1 is prepared;

[0093] The horizontal rotary jetting pre-support 1 in the advanced support has the following construction steps:

[0094] 1. Drilling machine positioning;

[0095] 2. Drilling the rotary jetting hole to the required depth;

[0096] 3. Jetting the slurry from the bottom of the hole, rotating while jetting, and retreating while jetting to form a consolidated body;

[0097] 4. After jetting, pulling out the jetting head, and inserting the wooden plug into the hole to stop the outflow of the slurry;

[0098] 5. If necessary, a reinforcing bar or a steel pipe can be inserted to improve the bending resistance of the consolidated body.

[0099] The horizontal rotary jet pre-supporting is suitable for soft rock stratum such as clay and sandy soil, and a pre-supporting arch shed is formed by the rotary jet column along the arch of the tunnel, which is ring-shaped and longitudinally overlapped, and can effectively control collapse and stratum deformation in loose and unstable stratum tunnel.

[0100] Step four, installing the flexible support 2 in the initial support of the upper half section of the pilot hole, and the anchor rod 4 in the flexible support 2 is inserted into the rock stratum of the upper half section of the pilot hole through the horizontal rotary jet pre-supporting 1;

[0101] The flexible support 2 in the initial support of the upper half section of the pilot hole is installed, and the anchor rod 4 in the flexible support 2 is selected as an early strength cement mortar anchor rod, which has the advantages of high early strength, fast bearing, convenient installation and the like, and the anchor rod 4 is pre-processed according to the design requirements in the steel bar processing plant. The drilling position and hole depth of the anchor rod 4 must be accurate during construction, and the anchor rod 4 must be free of oil, rust and impurities. According to the design requirements, the anchor rod hole is drilled, and after reaching the standard, the hole is cleaned by high-pressure air, and then the hole is filled with anchoring agent. Then, the processed rod body is inserted into the hole.

[0102] The anchor rod 4 in the flexible support 2 is selected as an early strength cement mortar anchor rod 4. The support stiffness, maximum support force and maximum allowable damage displacement of the anchor rod 4 in the flexible support 2 can be designed according to engineering needs.

[0103] The anchor rod 4 in the flexible support 2 is locally arranged at the vault when the tunnel surrounding rock is fissured surrounding rock, and is arranged in a radial plum blossom shape in the tunnel, with a ring angle of 90-150°, for key reinforcement of unstable blocks. The tensile failure zone of the tunnel vault is the key reinforcement area. The fixing condition of the anchor rod 4 is used to ensure the effective connection of the unstable blocks and the stable rock mass. The spacing and depth of the anchor rod 4 are:

[0104]

[0105] In the formula, D is the anchor rod spacing (m); d is the anchor rod diameter (m); R is the radius of the tunnel vault (m); P is the gravity of the dangerous rock or unstable block (N); A is the exposed area of the dangerous rock or unstable block (m a ). 2

[0106] The depth of the anchor rod 4 into the stable rock mass is:

[0107]

[0108] In the formula, L m is the depth of anchoring into the stable rock mass (which should not be less than 30-40 times the diameter of the rod body) (m); τ is the bonding strength of the mortar (N / m 2 ).​

[0109] The anchor rod 4 in the flexible support 2 is arranged vertically to the tunnel peripheral contour on the tunnel section when the tunnel surrounding rock is broken and weak surrounding rock. For horizontally layered rock, the anchor rod 4 is arranged vertically to the layer or is arranged obliquely to the layer as far as possible. For inclined layered rock, the anchor rod 4 is arranged obliquely to the layer. The anchor rod 4 plays a whole reinforcing role to the surrounding rock. The "inclined layered rock" is mainly caused by layer sliding. The advantage is to prevent the layer from sliding.

[0110] The support rigidity of the anchor rod 4 in the flexible support 2 is:

[0111]

[0112] In the formula, Q is the load deformation constant, S r and S l are the longitudinal and circumferential spacing of the anchor rod support respectively, L is the length of the anchor rod, Φ is the diameter of the anchor rod, E b is the elastic modulus of the anchor rod;

[0113] The maximum support force of the anchor rod 4 in the flexible support 2 is:

[0114]

[0115] In the formula, T max is the maximum yield of the anchor rod.

[0116] The maximum allowable damage displacement of the anchor rod 4 in the flexible support 2 is:

[0117]

[0118] Step five, the concrete layer 5 is constructed. The concrete is mixed by a forced mixer outside the hole, the concrete is transported by a concrete mixing and transporting vehicle, and the concrete is constructed according to a wet spraying process. The concrete is sprayed on the inner wall of the horizontal rotary spraying pre-support 1. The width of the two ends of the concrete layer 5 is gradually increased.

[0119] The shotcrete 5 is constructed, and the polypropylene fiber concrete with good flexibility and enough resistance is selected, wherein the polypropylene fiber is selected as the net fiber to enhance the dispersion performance in the concrete. The preparation before construction: the floating dust and debris on the sprayed surface can be washed by the high-pressure water, when the rock surface is easily deliquesced and mudified, the high-pressure air is used to blow the rock surface, so as to ensure the firm adhesion between the shotcrete 5 and the sprayed rock surface, and ensure the good common stress between the shotcrete and the stratum. The wet shotcrete machine is used to spray the concrete 5, the concrete 5 is mixed by the forced mixer, the concrete mixing and transporting vehicle is used to transport the material, and the wet shotcrete process is constructed. The initial spraying is performed immediately after the excavation (or the partial excavation) is completed, so as to close the exposed excavation surface as soon as possible, and prevent the surface weathering and peeling. The re-spraying concrete 5 is performed after the system anchor 9 and the steel arch 6 are installed and constructed, the fast closed support is stressed as a whole, so as to restrain the deformation of the surrounding rock. The concrete 5 is used to re-spray and smooth between the steel arch 6 and the grid steel frame 7, and the enough protection layer is provided.

[0120] The concrete layer 5 in the flexible support 2 is selected as the polypropylene net fiber concrete, the function of the concrete layer 5 is changed from the bearing component to the construction and leveling layer, and the spraying thickness of the concrete layer 5 should be controlled as follows:

[0121] h = (0.025-0.033) r0

[0122] In the formula, h is the spraying thickness, r0 is the calculation radius of the tunnel, and for the non-circular tunnel, the half of the circumscribed semicircle or span is approximately taken. The thickness can meet the better flexibility and enough resistance.

[0123] Step six, the steel arch 6 of the initial support of the tunnel is constructed, the arch A unit 61 and the arch B unit 62 of the upper part are installed, the steel reinforced concrete pad is used at the arch foot, the arch A unit 61 and the arch B unit 62 are fixedly connected by the energy absorbing buffer device 13; the left and right side walls are excavated in the left and right sides, the wall C unit 63 and the wall D unit 64 of the wall of the steel arch 6 are installed in sequence, the wall C unit 63 and the wall D unit 64 are fixedly connected by the energy absorbing buffer device 13; the installed steel arch 6 is connected into a whole by the longitudinal connecting rib, the tail of the anchor 4 is welded on the steel arch 6, and the steel arch 6 is tightly attached to the concrete layer 5;

[0124] The tunnel initial support steel arch 6 is constructed, uniformly concentrated processing, the steel arch 6 is set up only in the steel reinforcement assembly field, the steel arch 6 is formed in the design by using a special mold in the hole processing shed, and the connecting plate is welded on both ends of each section. The well-processed steel arch 6 is tested and assembled on the flat site, the plane warping degree is controlled within the allowable range. Whether the welding point meets the specification requirements, whether the welding is omitted, and whether the welding is double-sided welding are checked; the number is numbered to avoid mixing. According to the excavation method, the arch part A unit 61 and the arch part B unit 62 of the upper part are installed first, the steel reinforced concrete cushion is padded at the arch foot, which is convenient for installation and lower connection, and the energy-absorbing buffer device 13 is used for fixed connection between the arch part A unit 61 and the arch part B unit 62. The left and right side walls are excavated in staggered left and right sides, and the wall part steel arch side wall C unit 63 and the wall part steel arch side wall D unit 64 are installed in sequence, and the energy-absorbing buffer device 13 is used for fixed connection between the wall part steel arch side wall C unit 63 and the wall part steel arch side wall D unit 64. The installed steel arch 6 is connected into a whole by longitudinal connecting bars, and the tail of the anchor rod is welded on the arch. The steel arch 6 and the initial sprayed concrete 5 are as close as possible, if there is a concave-convex gap due to excavation, a concrete pad or a steel plate is arranged, and wood and stone are strictly prohibited to be filled, and the protection layer thickness is not less than 2 cm. According to the design, the lock foot anchor rod 12 is arranged for each arch, the lock foot anchor rod 12 can also be a lock foot anchor pipe, which is selected according to the actual situation, the eye hole is punched by using a pneumatic rock drill, the lock foot anchor rod 12 is inserted, and the threaded steel "U" connecting bar is used to weld and connect the two lock foot anchor rods 12 and the steel arch 6 together.

[0125] Step seven, the inner wall of the steel arch 6 is sprayed with concrete, and the protection layer is sufficient, and the grid steel frame 7 is installed; the arch part F unit and the arch part G unit of the upper part are installed first, the pressure-releasing energy-consuming device 22 is used for fixed connection between the arch part F unit and the arch part G unit, the steel reinforced concrete cushion is padded at the arch foot, the left and right side walls are excavated in staggered left and right sides, the wall part side wall H unit is installed in sequence, and the pressure-releasing energy-consuming device 22 is used for fixed connection between the wall part side wall H unit and the arch part G unit; the installed grid steel frame 7 is connected into a whole by longitudinal connecting bars; the grid steel frame 7 is closely attached to the inner wall of the steel arch 6 sprayed with concrete;

[0126] In this embodiment, after the steel arch 6 is constructed, the concrete is sprayed, the inner circumference of the steel arch 6 is sprayed and flattened with concrete, and there is a sufficient protective layer. The grid steel frame 7 is installed on the concrete layer. The entire grid steel frame 7 is finally an integral annular structure, and the whole ring is closed. The preparation before installation and the steel arch 6 are the same. First, the arch portion F unit 71 and the arch portion G unit 72 of the upper portion are installed. The arch portion F unit 71 and the arch portion G unit 72 are fixedly connected by the pressure-relieving energy dissipation device 22. During installation, a 35 cm × 25 cm × 20 cm reinforced concrete cushion is placed at the arch foot to facilitate installation and lower connection. The two side walls are excavated in a left-right staggered manner, and the wall portion side wall H unit 73 is installed in succession. The wall portion side wall H unit 73 and the arch portion G unit 72 are fixedly connected by the pressure-relieving energy dissipation device 22, which also serves to connect the various units. The installed grid steel frame 7 is connected into a whole by longitudinal connecting ribs. The tail of the anchor rod is welded to the arch. The grid steel frame 7 is as close as possible to the sprayed concrete 5. If there is a large gap due to excavation, a concrete pad or a steel plate is arranged. It is strictly forbidden to use stone and wood to fill in. The thickness of the protective layer is not less than 2 cm.

[0127] The rigid support 3 composed of the steel arch 6 and the grid steel frame 7 is designed according to the engineering needs, with the support structure stiffness, the maximum support force, and the maximum allowable displacement of the support structure. The elastic shell theory is used to establish a joint support mechanical analysis model. The mechanical properties of the joint support structure are analyzed, and the equivalent section method is used to calculate the equivalent support stiffness of the joint support mechanical analysis model.

[0128] The joint support mechanical analysis model can be equivalent to a homogeneous rectangular material, and the equivalent elastic modulus E of the joint support mechanical analysis model is: eq and the thickness t eq is:

[0129]

[0130]

[0131] In the formula, b is the width or the support spacing, v is the Poisson's ratio, D1 and K1 are the compressive stiffness and bending stiffness of the steel, respectively, and D2 and K2 are the compressive stiffness and bending stiffness of the concrete layer, respectively.

[0132] The support structure stiffness model and the maximum support force model of the equivalent joint support mechanical analysis model are:

[0133]

[0134]

[0135] For the steel support, the equivalent yield stress model of the equivalent rectangular section of the joint support mechanical analysis model is:

[0136]

[0137] wherein σ' is the yield stress of the section steel, A is the section area of the section steel, b is the support spacing of the section steel, t is the equivalent thickness. s s eq

[0138] The stiffness model K of the concrete and the maximum support force model P are respectively: c max,c

[0139]

[0140]

[0141] wherein R0 is the radius of the tunnel, t is the thickness of the concrete layer, σ is the limit value of the compressive strength of the initial sprayed concrete layer. c c

[0142] The maximum allowable displacement model of the support structure in the combined support mechanical analysis model is:

[0143]

[0144] The initial displacement of the surrounding rock in the combined support mechanical analysis model is calculated by the field measured data and the empirical formula proposed by Hoek:

[0145]

[0146] wherein u is the initial displacement; u is the final displacement; and x is the distance from the support to the tunnel face. r

[0147] Step eight, a full waterproof layer 11 is arranged between the initial support and the secondary lining of the tunnel, and construction joints and deformation joints are reserved in the construction of the initial support and the secondary lining, and a water stop belt 35 is arranged in the construction joints and the deformation joints;

[0148] A full waterproof layer 11 is arranged between the initial support and the secondary lining of the tunnel, and construction joints and deformation joints are reserved in the construction of the initial support and the secondary lining, and a water stop belt 35 is arranged in the construction joints and the deformation joints; the construction joints and the deformation joints adopt a middle-buried rubber water stop belt or other water stop measures; the water stop belt and the like arranged at the construction joints is arranged at 1 / 2 of the thickness of the structure; the deformation joint is about 20-30 mm wide, and if the water stop belt 35 is adopted, the steel rubber water stop belt is embedded in the middle of the structure, and the both sides of the water stop belt are filled with polystyrene foam boards.

[0149] ​​​​​​​​​Step nine, the inverted arch backfill layer 33 is constructed, the inverted arch concrete should be poured continuously in sections, one-time forming, no longitudinal construction joint is left to form the backfill layer 33;

[0150] The inverted arch backfill layer 33 is constructed, after the inverted arch foundation is excavated, water, sundries, virtual slag and the like are cleaned immediately, the base is strictly prohibited from being soaked in water. The measurement and the line laying and the inverted arch excavation process control are strengthened, the inverted arch base excavation size is ensured to meet the design requirements, excavation is strictly prohibited, overexcavation is controlled, the overexcavation part is poured with the concrete with the same mark number as the inverted arch, and the virtual soil and the virtual slag are strictly prohibited from backfilling. The inverted arch concrete selects C35 concrete, and vibration must be paid attention to, especially for the concrete at the arch foot, the concrete is fully tamped, the inverted arch is poured in sections, and the head template must be arranged. The inverted arch filling concrete must be poured 12 hours after the inverted arch concrete construction is completed, and the C35 inverted arch concrete and the C15 inverted arch filling concrete are strictly prohibited from one-time construction. The inverted arch concrete should be poured continuously in sections, one-time forming, and no longitudinal construction joint is left.

[0151] Step ten, steps three to nine are repeated, and the pressure-relief initial support is arranged in the tunnel axial direction according to the design parameters;

[0152] Step eleven, the pressure-relief energy storage layer, that is, the permanent support 8 structure is constructed;

[0153] Step twelve: steps three to eleven are repeated until the tunnel structure construction is completed.

[0154] The present application is only described by taking a tunnel support as an example, but is also applicable to the support of the subway, the mine roadway, the karst cavity, the hidden hole and some special underground engineering.

[0155] The present application combines the elastic thin shell theory and the equivalent section method, and proposes a steel arch frame-grating combined support mode suitable for the deep-buried large-section soft rock tunnel, overcomes the shortcomings that the support rigidity is low when the steel arch frame or the grating steel frame is simply used for supporting, is not conducive to the stability and deformation control of the long-term large deformation of the surrounding rock, solves the problems that the existing support structure is under great stress, the self-bearing capacity of the surrounding rock cannot be fully utilized, the material is seriously wasted, the safety factor of the support structure is low, and the stability of the tunnel cannot be ensured, and provides a simple and practical construction method for the tunnel excavation and support. Through the rigid support with the pressure-relief energy consumption device between the grating steel frame units and the energy-absorbing buffer device between the steel arch frame units, the impact energy of the long-term load or the seismic load in the surrounding rock is buffered and absorbed, and the rapid bearing and common bearing of the two are realized, the bearing capacity of the surrounding rock can be effectively utilized, the bearing capacity of the initial support is significantly improved, the large deformation of the surrounding rock is controlled, the large deformation of the deep-buried large-section soft rock tunnel is more effectively coped with, and the construction safety and the construction efficiency are ensured.

[0156] It is apparent that the application can be carried out by other embodiments that do not depart from the spirit or essential characteristics thereof. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the foregoing description, and all changes coming within the meaning and equivalency range of the claims are intended to be embraced therein.

Claims

1. A large cross-section deep-embedded soft rock tunnel combined support system, characterized in that: The system comprises a pre-support structure, an initial support structure and a secondary lining structure, the pre-support structure is a horizontal rotary jet pre-support (1), the horizontal rotary jet pre-support (1) is a pre-support arch shed structure formed by rotary jet columns along the arch of the tunnel in a ring direction and longitudinally overlapped; the initial support structure comprises a flexible support (2) and a rigid support (3), the flexible support (2) comprises an anchor rod (4) and a concrete layer (5), the anchor rod (4) is inserted into the tunnel rock stratum through the horizontal rotary jet pre-support (1), and the inner periphery of the horizontal rotary jet pre-support (1) is provided with the concrete layer (5); the rigid support (3) comprises a steel arch (6) and a grid steel frame (7), the steel arch (6) is fixed to the inner periphery of the concrete layer (5), and the grid steel frame (7) is fixed to the inner periphery of the steel arch (6); a full waterproof layer (11) is arranged between the initial support structure and the secondary lining structure; the secondary lining structure is a permanent support (8), the permanent support (8) comprises system anchor rods (9), a waterproof concrete layer (10) and a backfill layer (33), the waterproof concrete layer (10) is arranged on the inner periphery of the full waterproof layer (11), the system anchor rods (9) are inserted into the rock stratum through the pre-support structure and the initial support structure, the tail ends of the system anchor rods (9) are fixedly connected to the edge of the waterproof concrete layer (10), and the backfill layer (33) is arranged in the upward supply foundation and covers the end of the waterproof concrete layer (10); The steel arch (6) is a profile steel, the shape of the steel arch (6) is the same as that of the cross section of the tunnel, the steel arch (6) is composed of two or more steel arch units, and an energy-absorbing buffer device (13) is arranged between adjacent steel arch units; The energy-absorbing buffer device (13) comprises connecting steel plates (14), ear plates (15), galvanized steel plates (17), rubber pads (18) and energy-absorbing buffer steel pipes (21), the two ends of the connecting steel plate (14) are fixedly connected to the ear plate (15) through high-strength bolts (16), the ear plate (15) is fixed to the upper and lower sides of the locking foot anchor rod (12) of the steel arch (6), a pair of oppositely arranged galvanized steel plates (17) are fixedly clamped between the connecting steel plates (14) on the upper and lower sides, the rubber pads (18) are arranged on the opposite sides of the galvanized steel plates (17), the opposite sides of the galvanized steel plates (17) are respectively connected to the end portions of the corresponding locking foot anchor rods (12), and a plurality of energy-absorbing buffer steel pipes (21) are fixedly arranged on the inner sides of the opposite rubber pads (18); The energy-absorbing buffer steel pipe (21) in the energy-absorbing buffer device (13) comprises a first high-strength spring steel sheet (19), a first damper (20), a circular steel pipe (M) and a circular steel pipe (N), wherein the first high-strength spring steel sheet (19) is located in the circular steel pipe (M), the first damper (20) is located in the circular steel pipe (N), one end of the circular steel pipe (M) and the circular steel pipe (N) is connected, the other end is respectively fixedly connected to the corresponding rubber pad (18), one end of the first high-strength spring steel sheet (19) and the first damper (20) is connected, and the other end of the first high-strength spring steel sheet (19) and the first damper (20) is respectively fixedly connected to the corresponding rubber pad (18).

2. The large cross-section deep-buried soft rock tunnel combined support system according to claim 1, characterized in that: The grid steel frame (7) is composed of two or more grid steel frame units, and a pressure-relief energy dissipation device (22) is arranged between adjacent grid steel frame units, the pressure-relief energy dissipation device (22) comprising a second damper (23), a connecting box (34) and a pressure-relief energy dissipation steel pipe (X), wherein one end of the second damper (23) is fixedly connected with a horizontal web frame stand of the grid steel frame (7), the other end of the second damper (23) is connected with the connecting box (34), a plurality of pressure-relief energy dissipation steel pipes (X) are arranged in the connecting box (34), and the space in the connecting box (34) is filled with the first filling concrete (24).

3. The construction method of the combined support system for large cross-section deep-lying soft rock tunnel according to claim 1, characterized in that: The method comprises the following steps: Step one, determine the high ground stress soft rock tunnel support structure parameters and design points according to the hydrogeological conditions and stratum parameters through the combined support mechanical analysis model, and determine the design scheme; Step two, according to the design scheme, prefabricate the steel and grid steel frame; Step three, the tunnel excavation must be carried out after the advance support is completed, and the construction is strictly carried out according to the principle of "short footage, short steps, strong support, early ring forming, and tight secondary lining"; the advance support is first carried out on the arch part of the pilot tunnel, and the horizontal rotary jetting pre-support (1) is prepared; Step four, install the flexible support (2) in the initial support of the upper half section of the pilot tunnel guide hole, and the anchor rod (4) in the flexible support (2) penetrates through the horizontal rotary jetting pre-support (1) and is inserted into the rock layer of the upper half section of the hole; Step five, carry out the concrete layer (5) construction, mix the concrete with a forced mixer, transport the concrete with a concrete mixing and transporting vehicle, and construct according to the wet spraying process, so that the concrete is sprayed on the inner wall of the horizontal rotary jetting pre-support (1), and the width of the two end portions of the concrete layer (5) gradually increases; Step six, carry out the tunnel initial support steel arch frame (6) construction, first install the arch part A unit (61) and the arch part B unit (62) of the upper portion, place a reinforced concrete pad at the arch foot, and fixedly connect the arch part A unit (61) and the arch part B unit (62) with the energy absorption buffer device (13); the two side walls are excavated in a left-right staggered manner, and the wall part steel arch frame (6) wall C unit (63) and wall D unit (64) are successively installed, the wall C unit (63) and the wall D unit (64) are fixedly connected with the energy absorption buffer device (13); the installed steel arch frame (6) is connected into a whole by a longitudinal connecting rib, the tail portion of the anchor rod (4) is welded on the steel arch frame (6), and the steel arch frame (6) is tightly attached to the concrete layer (5); Step seven, the inner wall of the steel arch frame (6) is sprayed with concrete and has a sufficient protective layer, and the grid steel frame (7) is installed; first install the arch part F unit and the arch part G unit of the upper portion, fixedly connect the arch part F unit and the arch part G unit with the pressure-relief energy dissipation device (22), place a reinforced concrete pad at the arch foot, excavate the two side walls in a left-right staggered manner, successively install the wall part wall H unit, and fixedly connect the wall H unit and the arch part G unit with the pressure-relief energy dissipation device (22); the installed grid steel frame (7) is connected into a whole by a longitudinal connecting rib; and the grid steel frame (7) is tightly attached to the inner wall of the steel arch frame (6) sprayed with concrete; Step eight, set full package waterproof layer (11) between the initial support and secondary lining, and pre-reserve construction joints and deformation joints in the initial support and secondary lining construction, and set water stop belt (35) in the construction joints and deformation joints; Step nine, construction of inverted arch backfill layer (33), inverted arch concrete should be poured continuously in sections, once forming, without longitudinal construction joints to form backfill layer (33); Step ten, repeat steps three to nine to set pressure initial support in the axial direction of the tunnel according to the design parameters; Step eleven, construction of permanent support (8) structure; Step twelve: repeat steps three to eleven until the tunnel structure construction is completed.

4. The construction method of the combined support system for large cross-section deep-buried soft rock tunnel according to claim 3, characterized in that: In the joint support mechanical analysis model in step one, Support structure stiffness model and maximum support force model is: ； ； wherein is the tunnel radius, is the equivalent elastic modulus, is the Poisson's ratio, is the equivalent thickness, is the equivalent yield stress; Equivalent yield stress model is: ； wherein is the yield stress of the section steel, is the cross-sectional area of the section steel, is the support spacing of the section steel, is the equivalent thickness; Stiffness model of concrete and maximum support force model respectively: ； ； wherein is the tunnel radius, is the Poisson's ratio, is the concrete elastic modulus, is the concrete layer thickness, is the initial sprayed concrete layer compressive strength limit value; The maximum allowable displacement model of the support structure is: ； wherein, is the maximum elastic displacement of the combined support system, is the failure strain of the support structure material, is the radius of the tunnel, is the thickness of the concrete layer, is the Poisson's ratio, is the concrete stiffness, is the maximum support force of the concrete, is the ultimate compressive strength of the initial shotcrete layer; The initial displacement model of the surrounding rock is: ； wherein - initial displacement; - final displacement; - distance of the support applied from the face.

5. The construction method of the large cross-section deep-embedded soft rock tunnel combined support mechanical analysis model according to claim 4, characterized in that: In the support structure stiffness model and the maximum support force model: ； ； wherein is the width or support spacing, is the Poisson's ratio, and are the compressive and flexural rigidity of the shape steel, respectively, and are the compressive and flexural rigidity of the concrete layer, respectively.

6. The construction method of the combined support system for large cross-section deep-buried soft rock tunnel according to claim 3, characterized in that: The spacing and depth of the anchor rod (4) in step four are: ； wherein, — anchor rod spacing (m); — anchor rod diameter (m); — design strength of anchor rod reinforcement (Pa); — safety factor, preferably ; — gravity of dangerous rock or unstable mass (N), when a side wall has an unstable mass, value is the sliding force minus the anti-sliding force; — exposed area of dangerous rock or unstable mass (m2); ); The depth of the anchor rod (4) into the stable rock mass is: ; In the formula, — Depth of anchoring in stable rock mass (m); — Bond strength of the mortar (N / m 2 ); The support stiffness of the anchor rod (4) in the flexible support (2) is: ； wherein is the load deformation constant, and are the longitudinal and circumferential spacing of the anchor supports, respectively, is the anchor length, is the anchor diameter, is the anchor elastic modulus; The maximum support force of the anchor rod (4) in the flexible support (2) is: ； In the formula, is the maximum yield of the anchor rod; The maximum allowable failure displacement of the anchor rod (4) in the flexible support (2) is: ； wherein is the initial displacement, is the length of the anchor, is the failure strain of the anchor, is the maximum yield of the anchor, is the diameter of the anchor (4), is the elastic modulus of the anchor (4).

7. The construction method of the combined support system for large cross-section deep-buried soft rock tunnel according to claim 3, characterized in that: The thickness of the concrete layer (5) in step five should be controlled within: ； In the formula, - the thickness of the sprayed layer; - the tunnel calculation radius, for non-circular tunnels, approximately half the circumscribed semicircle or span.

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