A Loess Land Crack Tunnel Support Structure and Its Construction Method

Abstract

The present invention discloses a support structure for a loess soil fissure tunnel, comprising a pipe shed, an initial support layer, and a secondary lining layer. Several sections of lattice arches are provided between the initial support layer and the secondary lining layer, and adjacent lattice arches are connected by a connecting device. A raft is also provided at the bottom of the tunnel, and a crushed stone cushion layer and a sand layer are provided between the raft and the bottom of the tunnel from top to bottom. The secondary lining layer is provided with a deformation joint, and a waterstop assembly is installed in the deformation joint. The specific construction steps are: S1: perform construction preparation; S2: perform pipe shed construction; S3: adopt a three-step division method to perform tunnel excavation construction, and complete the construction process of the initial support layer and the lattice arch; S4: perform base processing; S5: perform secondary lining construction, and install a waterstop assembly for the deformation joint existing in the secondary lining. The present invention ensures that during the construction of the loess soil fissure tunnel, the deformation and internal force of the support structure are effectively controlled, thereby improving the safety and reliability of the tunnel support structure.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and specifically refers to a loess fissure tunnel support structure and a construction method thereof. Background Art

[0002] Existing ground fissure activity can adversely affect tunnel structures. The mechanism of disaster risk is sinking of the upper wall of the fissures, which causes uneven settlement, tensile cracking, and displacement. This in turn leads to cracking or collapse of buildings and underground caverns, as well as displacement and fracture of roadbeds and pipelines. In loess regions, surface water can also infiltrate and erode along the fissures, causing soil collapse and subsequent uneven settlement and deformation, resulting in secondary damage to buildings and structures and affecting the properties of the soil at the project site.

[0003] Currently, there's no comprehensive approach to ground fissure activity. Preventative measures primarily include: ① Avoiding ground fissures; ② Ground treatment, foundation reinforcement, and structural strengthening for buildings within the affected zone; ③ Using flexible joints to strengthen fracture resistance in underground pipelines; ④ Replacing ground fissures with flexible materials or spanning with simply supported bridges for surface road projects; ⑤ For subways crossing ground fissures, implementing segmented fissures, expanding the tunnel's cross-section, and implementing waterproofing measures; ⑥ Restricting or prohibiting groundwater extraction, especially confined water, while also implementing effective surface drainage measures. However, actively avoiding ground fissures can lead to significant waste of land resources. While limiting confined water extraction is relatively effective, it's difficult to implement, often leading to illegal groundwater extraction and difficult to effectively manage, making it less feasible.

[0004] An analysis of the fundamental causes of ground fissure activity in areas of land subsidence reveals that without ground subsidence, ground fissures will not experience significant activity; and without uneven ground subsidence at the locations of ground fissures, there will be no abnormal ground fissure activity. To control ground fissure activity in areas of land subsidence, it is necessary to control ground subsidence or prevent uneven ground subsidence. Prohibiting confined water extraction and completely controlling ground subsidence are fundamental measures for controlling ground fissure activity. However, controlling confined water extraction and abnormal fluctuations in confined water levels is difficult, making artificially controlled ground fissure activity countermeasures particularly effective. Therefore, a loess land fissure tunnel structure with a reliable structure, reasonable design, convenient construction, and effective practical results is needed. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a tunnel support structure that can effectively control the deformation and internal forces of the support structure during the construction of loess ground fissure tunnels, avoid uneven settlement, cracking and dislocation caused by the sinking of the upper wall of the ground fissures in the tunnel, and cause damage to the tunnel structure, thereby improving the safety and reliability of the tunnel.

[0006] Another object of the present invention is to provide a specific construction method for the above-mentioned loess fissure tunnel support structure.

[0007] In order to achieve the above-mentioned purpose, the present invention is implemented through the following technical scheme: a loess fissure tunnel support structure, including a pipe roof, an initial support layer, and a secondary lining layer arranged on the inner wall of the tunnel from the outside to the inside, a plurality of sections of grid arch frames are arranged between the initial support layer and the secondary lining layer, and adjacent grid arch frames are connected by a connecting device that can reduce structural deformation and internal stress of the support structure; a raft plate is also provided at the bottom of the tunnel, and a crushed stone cushion layer and a sand layer are also provided between the raft plate and the bottom of the tunnel from top to bottom; the secondary lining layer is provided with a deformation joint, and a waterstop assembly is installed in the deformation joint.

[0008] In order to better realize the present invention, further, the initial support layer is composed of an outer thin concrete layer and an inner foam concrete layer.

[0009] In order to better implement the present invention, further, the grid arches are four in number, and the grid arches on the left and right sides are axially symmetrical with respect to the center line of the tunnel.

[0010] In order to better realize the present invention, the connecting device further includes a protective cover in the middle, and partitions are respectively installed at both ends of the protective cover. One end of the partition is placed in the protective cover, and the other end extends out of the protective cover and embedded in the side wall of the grid arch frame. Dampers are also connected between the partitions placed in the protective cover.

[0011] In order to better realize the present invention, further, the waterstop assembly mainly includes a back-stick waterstop compacted by a steel plate and fixed to the initial support layer by bolts, and two embedded waterstops arranged in the secondary lining layer. Fillers are provided between the back-stick waterstop and the embedded waterstop, as well as between the embedded waterstops. A waterproof board is provided in the middle of the two embedded waterstops, and a waterstop damper is provided between the waterproof boards.

[0012] The above-mentioned construction method of a loess crack tunnel support structure comprises the following steps:

[0013] S1: Carry out construction preparation, including site survey and leveling, selecting appropriate construction machinery and tools, and preparing a processing site and pipe shed workshop that meets construction requirements;

[0014] S2: Carry out pipe shed construction;

[0015] S3: Use the three-step method to carry out tunnel excavation and complete the construction process of the initial support layer and grid arch;

[0016] S4: perform substrate processing;

[0017] S5: Carry out the construction of the secondary lining layer and install the water stop assembly for the deformation joints existing in the secondary lining layer.

[0018] In order to better implement the method of the present invention, further, the specific process of the pipe roof construction in step S2 is as follows:

[0019] S21: According to the construction drawings, fix the drilling rig and level it with a spirit level;

[0020] S22: By combining manual labor with machinery, slowly push the steel pipe into the hole and grout until the slurry is relatively thick;

[0021] S23: After grouting is completed, the non-porous steel pipe is inserted and the grouting quality is checked;

[0022] S24: Repeat steps S22 to S23 until the designed section is fully covered, symmetrically from both sides toward the middle, to complete the pipe roof construction.

[0023] In order to better implement the method of the present invention, the specific process of the construction of step S3 is as follows:

[0024] S31: adopt the three-step construction method, which is divided into upper step, middle step and lower step;

[0025] S32: The construction process of the upper step is as follows:

[0026] S321: Circular excavation of the upper step, reserving core soil, with an advance of 0.5m per cycle;

[0027] S322: Excavate the upper step, and excavate the upper step in a circular direction along the tunnel excavation contour line;

[0028] S323: Immediately spray a thin layer of concrete (3-5 cm) on the excavated section to seal the excavation surface;

[0029] S324: Spraying foam concrete below thin concrete layer;

[0030] S325: In the processing yard outside the tunnel, according to the grid arch design drawings, conduct on-site layout at a 1:1 ratio, determine the cutting size of the main rods, make the arch processing workbench and make the processing mold according to the line shape, process the grid arch in units and check its size and welding quality;

[0031] S326: Erection of the grille arch frame of the upper step;

[0032] S327: Connect the lattice arches on the left and right sides of the upper step using a connecting device and install locking anchors. Adjacent lattice arches are fixed together using connecting steel bars arranged along the longitudinal direction of the tunnel.

[0033] S328: Spray foam concrete on the steel mesh hanging below the grid arch;

[0034] S33: The construction process of the middle step is as follows:

[0035] S331: After the upper bench is constructed to the designed distance, the middle bench is excavated alternately on both sides, and the excavation advance is controlled within the distance between two grid arches per cycle;

[0036] S332: After one cycle, the excavated section is immediately sprayed with a thin layer of concrete of 3 to 5 cm to seal the excavation surface;

[0037] S333: spray foam concrete below thin concrete layer;

[0038] S334: In the processing yard outside the tunnel, according to the grid arch design drawings, conduct on-site layout at a 1:1 ratio, determine the cutting size of the main rods, make the grid arch processing workbench and make the processing mold according to the line shape, process the grid arch in units, and check its size and welding quality;

[0039] S335: Erect the grille arch frame of the middle step;

[0040] S336: Connect the lattice arch frame of the upper step and the lattice arch frame of the middle step using a connecting device and install locking anchor rods. The adjacent lattice arch frames are fixed together by connecting steel bars arranged along the longitudinal direction of the tunnel.

[0041] S337: Spray foam concrete on the steel mesh hanging below the grid arch;

[0042] S34: The construction process of the lower step is as follows:

[0043] S341: Locate and lay out the lines to determine the excavation location and make clear markings;

[0044] S342: Excavate the lower step down to the designed depth;

[0045] S343: Carry out raft slab construction, reinforcement tying and formwork installation;

[0046] S344: pouring concrete and curing;

[0047] S345: Backfill the sand layer above the raft slab to a predetermined thickness.

[0048] In order to better implement the method of the present invention, the specific process of the construction of step S4 is as follows:

[0049] S41: After the sand layer is backfilled, gravel is laid along the base in an arc shape and compacted manually to form a gravel cushion layer;

[0050] S42: Initial spraying of a thin layer of concrete 3~5cm;

[0051] S43: In the processing yard outside the tunnel, according to the grid arch design drawings, on-site layout is carried out at a 1:1 ratio to determine the cutting size of the main rods. A grid arch processing workbench is manufactured and a processing mold is made according to the linear shape. The grid arch is processed in units and its dimensions and welding quality are checked.

[0052] S44: Erect the lattice arch frame of the lower step;

[0053] S45: splicing the lattice arch frame of the middle step portion with the lattice arch frame of the lower step portion through a connecting device, and fixing the two adjacent lattice arch frames into one piece through connecting steel bars arranged along the longitudinal direction of the tunnel;

[0054] S46: pouring concrete.

[0055] In order to better implement the method of the present invention, the specific process of the construction of step S5 is as follows:

[0056] S51: Measure and lay out the lines to accurately locate the expansion joints;

[0057] S52: Make and install the steel frame, and leave appropriate gap width during the production to ensure that the water stop can be tightened;

[0058] S53: Install waterstop assembly in the expansion joint;

[0059] S54: Install the template and conduct preliminary inspection and acceptance after installation;

[0060] S55: pouring concrete;

[0061] S56: After removing the formwork on both sides of the expansion joint, clean the expansion joint. After cleaning, fill the bottom of the joint with caulking material, carry out caulking construction and apply a compatible base treatment agent.

[0062] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0063] (1) The tunnel support structure provided by the present invention has good adaptability to ground fissure activity. Flexible support is adopted in the structure, such as foam concrete and steel grid arch frame and deformation joints are set in the secondary lining. The steel grid has good adaptability to structural deformation.

[0064] (2) The present invention provides a four-section grid arch frame, each section of which is connected by a corresponding connecting device. The damper inside the connecting device can reduce the internal stress of the structure through a small range of deformation of the damper and the grid arch frame when ground fissures occur, thereby achieving overall safety and stability;

[0065] (3) The present invention provides a damper in the waterstop of the secondary lining deformation joint, which not only provides pressure to the waterstop and further allows the waterstop to fit closely to the structure surface, but also provides a certain deformation space for the secondary lining when ground fissures occur;

[0066] (4) The raft plate provided at the bottom of the tunnel of the present invention affects the friction between the sand layer and the bottom of the tunnel by the displacement of the raft plate caused by the activity of the ground fissures, and further reduces the influence of the activity of the ground fissures on the overall structure by the influence of the friction of the sand layer on the structure;

[0067] (5) The targeted construction method provided by the present invention ensures that the deformation and internal force of the support structure can be effectively controlled during the construction of the loess fissure tunnel, avoiding uneven settlement, cracking and dislocation caused by the sinking of the upper wall of the ground fissure in the tunnel, which may cause damage to the tunnel structure, thereby improving the safety and reliability of the tunnel support structure and being suitable for wide promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0069] Figure 1 It is a schematic diagram of the cross-sectional structure of the front side of the present invention;

[0070] Figure 2 Schematic diagram of the cross-sectional structure of the connecting device in the present invention;

[0071] Figure 3 This is a schematic diagram of the cross-sectional structure of the waterstop assembly installed at the expansion joint in the present invention.

[0072] Among them: 1-pipe roof, 2-initial support layer, 21-concrete thin layer, 22-foam concrete layer, 3-secondary lining layer, 4-grid arch, 5-connecting device, 51-protective cover, 52-partition, 53-damper, 6-gravel cushion, 7-sand layer, 8-raft, 9-extension joint, 10-waterstop assembly, 101-back-attached waterstop, 102-buried waterstop, 103-filler, 104-waterproof board, 105-waterstop damper. DETAILED DESCRIPTION

[0073] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0074] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "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 and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0075] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0076] Example 1:

[0077] This embodiment provides a loess soil crack tunnel support structure, such as Figure 1 As shown, it includes a pipe roof 1, an initial support layer 2, and a secondary lining layer 3 arranged on the inner wall of the tunnel from the outside to the inside, a plurality of sections of grid arch frames 4 are arranged between the initial support layer 2 and the secondary lining layer 3, and adjacent grid arch frames 4 are connected by a connecting device 5 that can reduce structural deformation and internal stress of the support structure; a raft 8 is also provided at the bottom of the tunnel, and a crushed stone cushion layer 6 and a sand layer 7 are also provided between the raft 8 and the bottom of the tunnel from top to bottom, and the secondary lining layer 3 is provided with a deformation joint 9, and a waterstop assembly 10 is installed in the deformation joint 9.

[0078] The specific construction method of the support structure includes the following steps:

[0079] S1: Carry out construction preparation, including site survey and leveling, selecting appropriate construction machinery and tools, and preparing a processing site and pipe shed workshop that meets construction requirements;

[0080] S2: Carry out pipe shed 1 construction;

[0081] S3: Using the three-step division method, tunnel excavation is carried out and the construction process of the initial support layer 2 and the grid arch 4 is completed;

[0082] S4: perform substrate processing;

[0083] S5: construct the secondary lining layer 3 and install the water stop strip assembly 10 for the deformation joint 9 existing in the secondary lining layer 3.

[0084] Example 2:

[0085] Based on the above embodiment, this embodiment further defines the structure of the initial support layer 2, such as Figure 1 As shown, the initial support layer 2 comprises an outer thin concrete layer 21 and an inner foamed concrete layer 22. The initial support layer 2 is sprayed sequentially with shotcrete 2 and a foamed concrete layer 3, which are applied along the tunnel cross-section. When ground fissures occur, the foamed concrete layer 3 can reduce structural deformation and internal forces, lowering the risk of damage. The remainder of this embodiment is identical to the previous embodiment and will not be further elaborated.

[0086] Example 3:

[0087] Based on the above embodiment, this embodiment further defines the number and position relationship of the grid arches 4, such as Figure 1 As shown, the grid arches 4 are four in number, and the grid arches 4 on the left and right sides are symmetrical about the center line of the tunnel. The other parts of this embodiment are the same as those of the above embodiment and will not be described in detail.

[0088] Example 4:

[0089] Based on the above embodiment, this embodiment further defines the structure of the connecting device 5, such as Figure 2 As shown, the connecting device 5 includes a protective sleeve 51 in the middle, with partitions 52 installed at both ends of the protective sleeve 51. One end of the partition 52 is placed in the protective sleeve 51, and the other end extends out of the protective sleeve 51 and is embedded in the side wall of the grid arch 4. A damper 53 is also connected between the partitions 52 placed in the protective sleeve 51. The two partitions 52 in the protective sleeve 51 extend out of the protective sleeve 51 at both ends and are embedded in the grid arch 4 at both ends, connecting adjacent grid arches 4. When local crack activity affects the structure and causes deformation, the internal damper 11 is used to offset or reduce the deformation of the structure and the internal force of the support structure to reduce the impact on the structure. The rest of this embodiment is the same as the above embodiment and will not be repeated.

[0090] Example 5:

[0091] Based on the above embodiment, this embodiment further defines the structure of the secondary lining layer 3, such as Figure 1 , Figure 3 As shown, other parts of this embodiment are the same as those of the above embodiment and will not be described again.

[0092] Example 6:

[0093] Based on the above embodiment, this embodiment further defines the structure of the water stop assembly 10, such as Figure 3As shown, the waterstop assembly 10 mainly includes a back-attached waterstop 101 which is compacted by a steel plate and fixed to the initial support layer 2 by bolts, and two embedded waterstops 102 arranged in the secondary lining layer 3. Fillers 103 are provided between the back-attached waterstop 101 and the embedded waterstop 102, as well as between the embedded waterstops 102. A waterproof plate 104 is provided in the middle of the two embedded waterstops 102, and a waterstop damper 105 is provided between the waterproof plates 104. The waterstop damper 105 provides pressure to the embedded waterstop 102 to make it in close contact with the secondary lining layer 3. At the same time, when the local crack activity causes the secondary lining layer 3 to deform, a certain deformation can occur to achieve the purpose of unloading and reduce the risk of damage. The other parts of this embodiment are the same as the above embodiment and will not be repeated.

[0094] Example 7:

[0095] This embodiment further defines the specific content of the construction method based on the above embodiment. The specific process of the pipe roof 1 construction in step S2 is as follows:

[0096] S21: According to the construction drawings, fix the drilling rig and level it with a spirit level;

[0097] S22: By combining manual labor with machinery, slowly push the steel pipe into the hole and grout until the slurry is relatively thick;

[0098] S23: After grouting is completed, the non-porous steel pipe is inserted and the grouting quality is checked;

[0099] S24: Repeat steps S22 to S23 until the designed section is fully covered, symmetrically from both sides to the middle, to complete the pipe-roof construction. The rest of this embodiment is the same as the above embodiment and will not be repeated here.

[0100] Example 8:

[0101] This embodiment further defines the specific content of the construction method based on the above embodiment. The specific process of the construction of step S3 is as follows:

[0102] S31: adopt the three-step construction method, which is divided into upper step, middle step and lower step;

[0103] S32: The construction process of the upper step is as follows:

[0104] S321: Circular excavation of the upper step, reserving core soil, with an advance of 0.5m per cycle;

[0105] S322: Excavate the upper step, and excavate the upper step in a circular direction along the tunnel excavation contour line;

[0106] S323: Immediately spray a thin layer of concrete (3-5 cm) on the excavated section to seal the excavation surface;

[0107] S324: Spraying foam concrete below thin concrete layer;

[0108] S325: In the processing yard outside the cave, according to the design drawing of the grid arch 4, on-site layout is carried out at a 1:1 ratio, the cutting size of the main rods is determined, the arch processing workbench is made and the processing mold is made according to the line shape, the grid arch 4 is processed in units and its size and welding quality are checked;

[0109] S326: Erecting the grille arch 4 of the upper step;

[0110] S327: Connect the lattice arches 4 on the left and right sides of the upper step using the connecting device 5, and install locking anchor rods. Adjacent lattice arches 4 are fixed together using connecting steel bars arranged along the longitudinal direction of the tunnel.

[0111] S328: Spray foam concrete on the steel mesh below the grid arch 4;

[0112] S33: The construction process of the middle step is as follows:

[0113] S331: After the upper step is constructed to the designed distance, the middle step is excavated alternately on both sides, and the excavation progress is controlled at 4 spacings between two grid arches per cycle;

[0114] S332: After one cycle, the excavated section is immediately sprayed with a thin layer of concrete of 3 to 5 cm to seal the excavation surface;

[0115] S333: spray foam concrete below thin concrete layer;

[0116] S334: In the processing yard outside the tunnel, according to the grid arch design drawings, conduct on-site layout at a 1:1 ratio, determine the cutting size of the main rods, make the grid arch processing workbench and make the processing mold according to the line shape, process the grid arch in units, and check its size and welding quality;

[0117] S335: Erecting the grille arch 4 of the middle step;

[0118] S336: Splice the lattice arch frame 4 of the upper step and the lattice arch frame 4 of the middle step using the connecting device 5 and apply locking anchor rods. The adjacent lattice arch frames 4 are fixed together by connecting steel bars arranged along the longitudinal direction of the tunnel.

[0119] S337: Spray foam concrete on the steel mesh below the grid arch 4;

[0120] S34: The construction process of the lower step is as follows:

[0121] S341: Locate and lay out the lines to determine the excavation location and make clear markings;

[0122] S342: Excavate the lower step down to the designed depth;

[0123] S343: Carry out raft 8 cushion construction, steel bar binding and formwork installation;

[0124] S344: pouring concrete and curing;

[0125] S345: Backfill the sand layer 7 above the raft 8 to a predetermined thickness.

[0126] Example 9:

[0127] This embodiment further defines the specific content of the construction method based on the above embodiment. The specific process of the construction of step S4 is as follows:

[0128] S41: After the sand layer 7 is backfilled, gravel is laid along the base in an arc shape and manually compacted to form a gravel cushion layer 6;

[0129] S42: Initial spraying of a thin layer of concrete 3~5cm;

[0130] S43: In the processing yard outside the tunnel, according to the design drawing of the grid arch 4, on-site layout is carried out at a 1:1 ratio, the cutting size of the main rods is determined, a processing table for the grid arch 4 is manufactured, and a processing mold is made according to the line shape. The grid arch 4 is processed in units and its size and welding quality are checked;

[0131] S44: Erecting the grid arch 4 of the lower step;

[0132] S45: splicing the grid arch frame 4 of the middle step portion with the grid arch frame 4 of the lower step portion through the connecting device 5, and fixing the adjacent grid arch frames 4 into one piece through connecting steel bars arranged along the longitudinal direction of the tunnel;

[0133] S46: pouring concrete. The rest of this embodiment is the same as the above embodiment and will not be described in detail.

[0134] Example 10:

[0135] This embodiment further defines the specific content of the construction method based on the above embodiment. The specific process of the construction of step S5 is as follows:

[0136] S51: Measure and lay out the lines to accurately locate the position of the expansion joint 9;

[0137] S52: Make and install the steel frame, and leave appropriate gap width during the production to ensure that the water stop can be tightened;

[0138] S53: Install waterstop assembly in the expansion joint;

[0139] S54: Install the template and conduct preliminary inspection and acceptance after installation;

[0140] S55: pouring concrete;

[0141] S56: After removing the molds on both sides of the expansion joint 9, clean the expansion joint 9, and after cleaning, fill the bottom of the joint with caulking material, perform caulking construction, and apply a compatible base treatment agent. The rest of this embodiment is the same as the above embodiment and will not be repeated.

[0142] It is understandable that the working principles and working processes of the tunnel support structure according to an embodiment of the present invention, such as the pipe roof 1, the damper 53 and other components, are prior art and are well known to those skilled in the art, and will not be described in detail here.

[0143] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A loess fissure tunnel support structure, characterized in that: The invention comprises a pipe shed (1), an initial support layer (2), and a secondary lining layer (3) which are sequentially arranged on the inner wall of a tunnel from outside to inside, a plurality of grid arches (4) are arranged between the initial support layer (2) and the secondary lining layer (3), and adjacent grid arches (4) are connected by a connection device (5) capable of reducing structural deformation and internal stress of the support structure; a raft (8) is also arranged at the bottom of the tunnel, and a crushed stone cushion layer (6) and a sand layer (7) are also arranged between the raft (8) and the bottom of the tunnel from top to bottom; the secondary lining layer (3) is provided with a deformation joint (9), and a water stop assembly (10) is installed in the deformation joint (9); the initial support layer (2) is composed of an outer concrete thin layer (21) and an inner foam concrete layer (22); the connection device (5) includes a protective sleeve (51) in the middle, and the protective sleeve (51) ) are respectively provided with partitions (52), one end of the partition (52) is placed in the protective sleeve (51), and the other end extends out of the protective sleeve (51) and is embedded in the side wall of the grid arch (4), and a damper (53) is also connected between the partitions (52) placed in the protective sleeve (51); the water stop assembly (10) mainly includes a back-attached water stop (101) compacted by a steel plate and fixed to the initial support layer (2) by bolts, and two embedded water stop belts (102) arranged in the secondary lining layer (3), fillers (103) are provided between the back-attached water stop (101) and the embedded water stop belt (102), and between the embedded water stop belts (102), waterproof boards (104) are provided in the middle of the two embedded water stop belts (102), and a water stop damper (105) is provided between the waterproof boards (104).

2. The loess soil fissure tunnel support structure according to claim 1, characterized in that: The grid arches (4) are four in number, and the grid arches (4) on the left and right sides are axially symmetrical about the center line of the tunnel.

3. The construction method of a loess fissure tunnel support structure according to claim 1 or 2, characterized in that: The following steps are involved: S1: Carry out construction preparation, including site survey and leveling, selecting appropriate construction machinery and tools, and preparing a processing site and pipe shed workshop that meets construction requirements; S2: Carry out pipe shed (1) construction; S3: Using the three-step division method, the tunnel excavation construction is carried out and the construction process of the initial support layer (2) and the grid arch (4) is completed; S4: perform substrate processing; S5: The secondary lining layer (3) is constructed, and a water stop assembly (10) is installed at the deformation joint (9) existing in the secondary lining layer (3).

4. The construction method of a loess fissure tunnel support structure according to claim 3, characterized in that: The specific process of the pipe shed (1) construction in step S2 is as follows: S21: According to the construction drawings, fix the drilling rig and level it with a spirit level; S22: By combining manual labor with machinery, slowly push the steel pipe into the hole and grout until the slurry is relatively thick; S23: After grouting is completed, the non-porous steel pipe is inserted and the grouting quality is checked; S24: Repeat steps S22 to S23 until the designed section is fully covered, symmetrically from both sides toward the middle, to complete the pipe roof construction.

5. The construction method of a loess fissure tunnel support structure according to claim 3 or 4, characterized in that: The specific process of the construction of step S3 is as follows: S31: adopt the three-step construction method, which is divided into upper step, middle step and lower step; S32: The construction process of the upper step is as follows: S321: Circular excavation of the upper step, reserving core soil, with an advance of 0.5m per cycle; S322: Excavate the upper step, and excavate the upper step in a circular direction along the tunnel excavation contour line; S323: Immediately spray a thin layer of concrete (3-5 cm) on the excavated section to seal the excavation surface; S324: Spraying foam concrete below thin concrete layer; S325: In the processing yard outside the cave, according to the design drawing of the grid arch frame (4), the field layout is carried out in a 1:1 ratio, the cutting size of the main rods is determined, the arch frame processing workbench is made and the processing mold is made according to the line shape, the grid arch frame (4) is processed in units and its size and welding quality are checked; S326: Erecting the grille arch frame (4) of the upper step; S327: splicing the grid arches (4) on the left and right sides of the upper step portion through the connecting device (5), and applying locking anchor rods, and fixing the adjacent grid arches (4) into one piece through connecting steel bars arranged along the longitudinal direction of the tunnel; S328: spray foam concrete on the steel mesh hanging below the grid arch (4); S33: The construction process of the middle step is as follows: S331: After the upper step is constructed to the designed distance, the middle step is excavated alternately on both sides, and the excavation progress is controlled within the spacing of two grid arches (4) per cycle; S332: After one cycle, the excavated section is immediately sprayed with a thin layer of concrete of 3 to 5 cm to seal the excavation surface; S333: spray foam concrete below thin concrete layer; S334: In the processing yard outside the tunnel, according to the grid arch design drawings, conduct on-site layout at a 1:1 ratio, determine the cutting size of the main rods, make the grid arch processing workbench and make the processing mold according to the line shape, process the grid arch in units, and check its size and welding quality; S335: Erection of the grille arch frame (4) at the middle step; S336: splicing the grid arch frame (4) of the upper step portion and the grid arch frame (4) of the middle step portion through the connecting device (5) and applying a locking anchor rod, and fixing the adjacent grid arch frames (4) into one piece through connecting steel bars arranged along the longitudinal direction of the tunnel; S337: spray foam concrete on the steel mesh below the grid arch (4); S34: The construction process of the lower step is as follows: S341: Locate and lay out the lines to determine the excavation location and make clear markings; S342: Excavate the lower step down to the designed depth; S343: Carry out raft slab (8) cushion construction, reinforcement tying and formwork installation; S344: pouring concrete and curing; S345: Backfill the sand layer (7) above the raft (8) to a predetermined thickness.

6. The construction method of a loess fissure tunnel support structure according to claim 5, characterized in that: The specific process of the construction of step S4 is as follows: S41: After the sand layer (7) is backfilled, gravel is laid along the base in an arc shape and compacted manually to form a gravel cushion layer (6); S42: Initial spraying of a thin layer of concrete 3~5cm; S43: In the processing yard outside the tunnel, according to the design drawing of the grid arch frame (4), the field layout is carried out at a ratio of 1:1, the cutting size of the main rods is determined, the processing table of the grid arch frame (4) is manufactured and the processing mold is manufactured according to the line shape, the grid arch frame (4) is processed in units and its size and welding quality are checked; S44: Erection of the grid arch frame (4) of the lower step; S45: splicing the grid arch frame (4) of the middle step portion and the grid arch frame (4) of the lower step portion through the connecting device (5), and fixing the two adjacent grid arch frames (4) into one body through connecting steel bars arranged along the longitudinal direction of the tunnel; S46: pouring concrete.

7. The construction method of a loess fissure tunnel support structure according to claim 6, characterized in that: The specific process of the construction of step S5 is as follows: S51: Measure and lay out the lines to accurately locate the position of the expansion joint (9); S52: Make and install the steel frame, and leave appropriate gap width during the production to ensure that the water stop can be tightened; S53: Install waterstop assembly in the expansion joint; S54: Install the template and conduct preliminary inspection and acceptance after installation; S55: pouring concrete; S56: After removing the molds on both sides of the expansion joint (9), clean the expansion joint (9). After cleaning, fill the bottom of the joint with caulking material, perform caulking construction and apply a compatible base treatment agent.

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