Large section loess tunnel primary support temporary steel arch and construction method

Abstract

The present application relates to the technical field of tunnel engineering, and especially relates to a large-section loess tunnel engineering excavation and support technology in the northwest region, a large-section loess tunnel primary support temporary steel arch, which comprises a left side arch foot profile steel, an arch top profile steel, a right side arch foot profile steel, a prefabricated cushion block, an arch foot side surface connecting steel plate, an inverted arch connecting steel plate, a fixing bolt, a first lock foot anchor rod, a second lock foot anchor rod, a left side inverted arch profile steel, a right side inverted arch profile steel, a lower temporary steel support, a lower connecting steel plate, an upper connecting steel plate, a side surface connecting steel plate, a temporary connecting steel plate, a connecting bolt one, a connecting bolt two, a support bottom plate, a movable clamping plate, a rotating shaft, a clamping hole, a plastic bag, a rod penetrating piece and a steel mesh. The present application is quick to install, has good stability of the support structure, is convenient to remove, and greatly plays the advantages of the assembly type technology.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology, and in particular to the excavation and support technology for large-section loess tunnels in Northwest China. Background Technology

[0002] During the construction of large-section loess tunnels, improper selection of construction technology or untimely excavation and support often leads to excessive deformation of shallow-buried tunnels, or even roof collapse. Summary of the Invention

[0003] The purpose of this invention is to solve the technical problem that excessive deformation or even roof collapse is prone to occur during the construction of large-section loess tunnels, and to propose a temporary steel arch frame for initial support and construction method for large-section loess tunnels.

[0004] The initial support temporary steel arch frame for a large-section loess tunnel includes: left arch foot steel, arch crown steel, right arch foot steel, precast pads, side connecting steel plates for the arch foot, connecting steel plates for the invert arch, fixing bolts, first locking anchor bolts, second locking anchor bolts, left invert arch steel, right invert arch steel, lower temporary steel support, lower connecting steel plate, upper connecting steel plate, side connecting steel plate, temporary connecting steel plate, connecting bolts, connecting bolts, support base plate, movable clamping plate, rotating shaft, clamping holes, plastic bags, through rods, and wire mesh;

[0005] The left arch foot steel is a section of I-beam bent into an arc shape. Near the bottom, it is fixed to the excavated loess tunnel cross-section using a first and second anchor rod. The outer side is tightly against the rock wall, and the inner side is welded with a steel plate connecting the arch foot. The bottom rests on a precast pad or the web of a longitudinal channel steel, and the top is welded with a lower connecting steel plate. The first anchor rod is a steel pipe of a certain diameter and wall thickness pressed into the rock wall, bent into an "L" shape, with its tail tightly against the inner side of the left arch foot steel and fixed by welding. Pressure grouting fills the holes in the rock wall inside the steel pipe. The second anchor rod is also a steel pipe of a certain diameter and wall thickness pressed into the rock wall, bent into an "L" shape, with its tail tightly against the inner side of the left arch foot steel and fixed by welding. The internal cavity is filled with pressure grouting; the side connecting steel plate of the arch foot is welded to the inner side of the left arch foot steel, and four bolt holes are reserved on the steel plate. The connecting steel plates of the invert arch can be connected together using fixing bolts; the precast pad is a precast concrete pad of a certain strength and thickness with a flat surface; the lower connecting steel plate has four round holes reserved, and its plane is perpendicular to the axis of the left arch foot steel. The upper connecting steel plate can be fixed together with the lower connecting steel plate using connecting bolts; the upper connecting steel plate is welded to the bottom of the arch crown steel, and its plane is perpendicular to the axis of the arch crown steel. The left arch foot steel and the arch crown steel can be connected into a whole using connecting bolts; the arch crown steel is a section of arc-shaped I-beam, with a piece welded near the center of the arch crown below. Side connecting steel plates are used, with an upper connecting steel plate welded to the bottom right side. The side connecting steel plates are welded to the bottom surface of the arch steel section, and temporary connecting steel plates are fixed together using connecting bolts. The temporary connecting steel plates are welded to the top of the lower temporary steel support. The lower temporary steel support consists of two sections of curved I-beams, with connecting bolts used to fix the curved steel section with connecting steel plates at both ends at the tunnel upper step excavation location. The bottom is fixed to the support base plate. The support base plate is welded to the right invert arch steel section, and movable clamping plates are fixed to both sides via rotating shafts. The right invert arch steel section is a curved I-beam of a certain specification, with one end connected to the invert arch connecting steel plate using fixing bolts, and the other end welded to the left invert arch steel section. The bottom flange steel plate is placed on the tunnel excavation invert arch. On the leveling layer; the movable plates are distributed on the front and rear sides of the right arch steel, and can be flipped up with the rotation axis. The movable plates are symmetrically reserved with through-rod holes, and the lower temporary steel support can be fixed by through-rods on both sides; the through-rods have threads at both ends, which can be fastened with screws; the upper connecting steel plate is connected to the lower connecting steel plate with connecting bolts, and the arch steel foot is fixed with the first locking foot anchor and the second locking foot anchor at this connection point; the lower connecting steel plate is a steel plate of a certain size with reserved bolt holes, which is welded to the top of the right arch foot steel; the right arch foot steel is a section of arc-shaped I-beam steel, the bottom of which rests on a prefabricated pad, and the arch foot side connecting steel plate is welded near the inner side of the foot, and the outer side is fixed with the first locking foot anchor and the second locking foot anchor;The side connecting steel plates of the arch foot are steel plates of a certain thickness and size, with four bolt holes pre-drilled for connecting the invert arch connecting steel plates using fixing bolts; the first locking anchor rod is an inverted "L" shape, with its tail welded to the steel section; the second locking anchor rod is an inverted "L" shape, with its tail welded to the steel section; steel wire mesh is tied and fixed between the lower temporary steel supports along the longitudinal section of the tunnel, and quick-setting concrete is sprayed on them; the side connecting steel plates and temporary connecting steel plates are fixed with connecting bolts and wrapped with plastic bags.

[0006] Furthermore, in a standardized factory, following the design outline and considering deformation, the left arch foot steel, arch crown steel, right arch foot steel, left inverted arch steel, and right inverted arch steel are processed in sections. The stepped section on the working face is excavated, and the upper half of the arch crown steel and lower temporary steel supports are installed. Bolts or precast blocks are used for support at the joints. Tie bars and steel mesh are welded between the two arch crown steel sections, and wire mesh is tied between the lower temporary steel supports. Quick-setting concrete is then immediately sprayed. After excavating the upper step 3-5 meters ahead of schedule, the lower half of the left side is excavated, and the lower half of the left arch foot steel and lower temporary steel supports are installed. Precast blocks are used for temporary support at the bottom, and anchor bolts are used to fix the joints at the designed profile section. Simultaneously, the left inverted arch steel is excavated. For the arch, install the left inverted arch steel, and temporarily support the bottom of the lower temporary steel support again. After excavating the lower left half to 10m, excavate the lower right half, install the right arch foot steel, and use anchor bolts to lock the foot. Excavate the right inverted arch, install the right inverted arch steel, and place the lower temporary steel support on the support base plate on top of the right inverted arch steel for fixation. Along the same cross section, the left and right inverted arch steels are fixed by face-to-face welding to form a closed ring support. On the section where the complete ring support has been formed, remove the plastic bags, connecting bolts, and through rods, remove the middle lower temporary steel support, promptly pour the inverted arch lining concrete and construct the inverted arch filling, and then construct the drainage system and secondary lining to form a composite support.

[0007] Furthermore, before installing the arch steel, the upper step of the tunnel is excavated first to ensure that the joint between the lower connecting steel plate and the upper connecting steel plate is located at the foot of the upper step excavated at the tunnel face. The soil and rock at the arch foot of the left or right section are compacted, and a precast pad or channel steel is temporarily placed. After installing the upper half of the arch steel and the lower temporary steel support, the arch foot of each section of the steel arch frame is fixed with the first locking anchor rod and the second locking anchor rod. Then the soil and rock of the lower step are excavated.

[0008] Furthermore, before installing the left arch foot steel, the excavation face of the upper step is advanced by 3-5m before excavating the lower half of the left side. During excavation, the precast pad block at the left foot of the arch top steel is removed, and the left arch foot steel and the lower temporary steel support are installed so that the bottom rests on a solid and flat precast pad block and is fixed with the first and second locking anchor rods. Before installing the right arch foot steel, the excavation face of the upper step is advanced by 3-5m before excavating the lower half of the right side. During excavation, the precast pad block at the right foot of the arch top steel is removed, and the right arch foot steel is installed so that the bottom rests on a solid and flat precast pad block and is fixed with the first and second locking anchor rods.

[0009] Furthermore, for the left inverted arch steel section, the excavation is carried out at least 40m ahead of the working face of the left lower step, excavating the left inverted arch portion, leveling the arc surface and pouring a cushion layer, and installing the left inverted arch steel section. The inverted arch connecting steel plate at one end of the left inverted arch steel section is fixed to the arch foot side connecting steel plate using fixing bolts. Each left inverted arch steel section is connected to the others using a staggered welded steel reinforcement to form an integral structure. For the right inverted arch steel section, the excavation is carried out at least 30m ahead of the working face of the right lower step, excavating the right inverted arch portion, leveling the arc surface and pouring a cushion layer, and installing the right inverted arch steel section. The inverted arch connecting steel plate at one end of the right inverted arch steel section is fixed to the arch foot side connecting steel plate using fixing bolts, and the other end is welded face-to-face to the already installed left inverted arch steel section. Each right inverted arch steel section is connected to the others using a staggered welded steel reinforcement to form tie rods.

[0010] Furthermore, when excavating the right inverted arch section, the lower half of the temporary steel support is to remove the bottom temporary precast pad block. After the excavation is completed, other pad blocks with higher cross sections or steel sections are used as temporary supports. After installing the right inverted arch steel sections one by one, the bottom of the temporary steel support is placed on the support base plate, and the movable clamping plate is rotated. The screws at both ends of the through rod are inserted into the clamping holes for fixation.

[0011] Furthermore, after the side connecting steel plate and the temporary connecting steel plate are connected, the connecting steel plate and the temporary connecting steel plate at the bottom of the arch steel are completely wrapped and fixed with hemp rope or tie wire.

[0012] Furthermore, the steel wire mesh tied between the lower temporary steel supports can prevent the shotcrete from falling and interlock with the shotcrete to form a stable plane.

[0013] Furthermore, the steel arch frame installed along the excavation section, when the left arch foot steel, arch top steel, right arch foot steel, left invert arch steel, and right invert arch steel of the same section are connected to form a ring, and the steel arch frames are welded with tie rods and steel mesh, and after the initial support is formed by spraying quick-setting concrete, the middle lower temporary steel support is removed, and the invert arch lining concrete is poured and the invert arch filling is carried out in a timely manner.

[0014] Compared with existing technologies, this invention is quick to install, has good support structure stability, and is easy to dismantle, thus giving full play to the advantages of prefabricated technology. Attached Figure Description

[0015] Figure 1 : A schematic diagram of the structure of an embodiment of the present invention;

[0016] Figure 2 : A temporary support structure diagram according to an embodiment of the present invention;

[0017] Figure 3 : A longitudinal section view of the temporary support in an embodiment of the present invention;

[0018] In the diagram: 1. Left arch foot steel; 2. Arch crown steel; 3. Right arch foot steel; 4. Precast pad block; 5. Side connecting steel plate of arch foot; 6. Invert arch connecting steel plate; 7. Fixing bolt; 8. First locking foot anchor rod; 9. Second locking foot anchor rod; 10. Left invert arch steel; 11. Right invert arch steel; 12. Lower temporary steel support; 13. Lower connecting steel plate; 14. Upper connecting steel plate; 15. Side connecting steel plate; 16. Temporary connecting steel plate; 17. Connecting bolt; 20. Connecting bolt; 24. Support base plate; 25. Movable clamping plate; 26. Rotating shaft; 27. Clamping hole; 34. Plastic bag; 35. Through rod; 36. Wire mesh. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0020] Example 1

[0021] The initial support temporary steel arch frame for a large-section loess tunnel includes: left arch foot steel 1, arch crown steel 2, right arch foot steel 3, precast pad block 4, arch foot side connecting steel plate 5, invert arch connecting steel plate 6, fixing bolt 7, first locking foot anchor rod 8, second locking foot anchor rod 9, left invert arch steel 10, right invert arch steel 11, lower temporary steel support 12, lower connecting steel plate 13, upper connecting steel plate 14, side connecting steel plate 15, temporary connecting steel plate 16, connecting bolt 17, connecting bolt 20, support base plate 24, movable clamping plate 25, rotating shaft 26, clamping hole 27, plastic bag 34, through rod 35, and wire mesh 36;

[0022] The left arch foot steel 1 is a section of I-beam bent into an arc shape. Near the bottom end, it is fixed to the excavated loess tunnel cross-section using a first anchor rod 8 and a second anchor rod 9. The outer side is tightly against the rock wall, and the inner side is welded with an arch foot side connecting steel plate 5. The bottom rests on a precast pad 4 or the web of a longitudinal channel steel, and the top is welded with a lower connecting steel plate 13. The first anchor rod 8 is a steel pipe of a certain diameter and wall thickness pressed into the rock wall, bent into an "L" shape, with its tail tightly against the inner side of the left arch foot steel 1 and fixed by welding. Pressure grouting fills the holes in the rock wall inside the steel pipe. The second anchor rod 9 is a steel pipe of a certain diameter and wall thickness pressed into the rock wall, bent into an "L" shape, with its tail tightly against the inner side of the left arch foot steel 1 and fixed by welding. The steel pipe is filled with pressure grout to fill the holes in the rock wall; the side connecting steel plate 5 of the arch foot is welded to the inner side of the left arch foot steel 1, and four bolt holes are reserved on the steel plate. The fixing bolts 7 can be used to connect the invert arch connecting steel plate 6 together; the precast pad 4 is a precast concrete pad with a certain strength and thickness and a flat surface; the lower connecting steel plate 13 has four round holes reserved, and its plane is perpendicular to the axis of the left arch foot steel 1. The upper connecting steel plate 14 and the lower connecting steel plate 13 can be fixed together using connecting bolts 20; the upper connecting steel plate 14 is welded to the bottom end of the arch top steel 2, and its plane is perpendicular to the axis of the arch top steel 2. The connecting bolts 20 can be used to connect the left arch foot steel 1 and the arch top steel 2 into a whole; the arch top steel 2 is a A section of arc-shaped I-beam has a side connecting steel plate 15 welded to the lower center of the arch, and an upper connecting steel plate 14 welded to the bottom right side; the side connecting steel plate 15 is welded to the bottom surface of the arch steel 2, and a temporary connecting steel plate 16 can be fixed together using connecting bolts 17; the temporary connecting steel plate 16 is welded to the top of the lower temporary steel support 12; the lower temporary steel support 12 consists of two arc-shaped I-beams, with connecting bolts 20 used to fix the arc-shaped steel with connecting steel plates at both ends at the upper and lower steps of the tunnel excavation site, and the bottom is fixed to the support base plate 24; the support base plate 24 is welded to the right inverted arch steel 11, and movable clamping plates 25 are fixed to both sides by rotating shafts 26; the right inverted arch steel 11 is an arc-shaped I-beam of a certain specification, one The end of the steel plate 6 is connected to the invert arch using fixing bolts 7, and the other end is welded to the left invert arch steel 10. The bottom flange steel plate is placed on the leveling layer of the invert arch during tunnel excavation. The movable clamping plates 25 are distributed on the front and rear sides of the right invert arch steel 11 and can be flipped up with the rotating shaft 26. The movable clamping plates 25 have symmetrical holes for rods, and the lower temporary steel support 12 can be fixed by rods 35 on both sides. The rods 35 have threads at both ends and can be tightened with screws. The upper connecting steel plate 14 is connected to the lower connecting steel plate 13 using connecting bolts 20. The first locking foot anchor 8 and the second locking foot anchor 9 are used to fix the foot of the arch top steel 2 at this connection point. The lower connecting steel plate 13 is a steel plate of a certain size with pre-drilled bolt holes and is welded to the top of the right arch foot steel 3.The right arch foot steel 3 is an arc-shaped I-beam, resting on a precast pad 4 at the bottom. A side connecting steel plate 5 is welded to the inner side of the arch foot, and the outer side is fixed using a first locking anchor rod 8 and a second locking anchor rod 9. The side connecting steel plate 5 is a steel plate of a certain thickness and size, with four pre-drilled bolt holes for connecting the invert arch connecting steel plate 6 using fixing bolts 7. The first locking anchor rod 8 is an inverted "L" shape, with its tail welded to the steel section. The second locking anchor rod 9 is also an inverted "L" shape, with its tail welded to the steel section. Steel wire mesh 36 is tied and fixed between the lower temporary steel supports 12 along the tunnel longitudinal section, and quick-setting concrete is sprayed onto them. The side connecting steel plate 15 and the temporary connecting steel plate 16 are fixed using connecting bolts 17 and wrapped with plastic bags 34.

[0023] This invention is quick to install, has a stable supporting structure, and is easy to dismantle, thus giving full play to the advantages of prefabricated technology.

[0024] Example 2

[0025] Construction method of temporary steel arch frame for initial support of large-section loess tunnel:

[0026] In a standardized factory, the left arch foot steel 1, arch top steel 2, right arch foot steel 3, left inverted arch steel 10, and right inverted arch steel 11 are processed in sections according to the design outline and taking into account the amount of deformation.

[0027] Excavate the stepped section on the working face, install the upper half of the arch steel 2 and the lower temporary steel support 12, use bolts or precast pads 4 for support at the joint, weld tie bars and steel mesh between the two arch steel 2 sections, tie wire mesh 36 between the lower temporary steel supports 12, and immediately spray quick-setting concrete.

[0028] After excavating the upper step 3-5m ahead, excavate the lower half of the left side, install the lower half of the left arch foot steel 1 and the lower temporary steel support 12, and use precast pad blocks 4 for temporary support at the bottom. Use locking anchor rods to fix the joint at the design profile section. At the same time, excavate the left inverted arch, install the left inverted arch steel 10, and temporarily support the bottom of the lower temporary steel support 12 again.

[0029] After excavating the lower left half for 10m, the lower right half is excavated, the right arch foot steel 3 is installed, the foot is locked with anchor bolts, the right invert arch is excavated, the right invert arch steel 11 is installed, and the lower temporary steel support 12 is placed on the support base plate 24 on top of the right invert arch steel 11 and fixed. Along the left invert arch steel 10 and the right invert arch steel 11 of the same section, they are fixed by face-to-face welding to form a closed ring support.

[0030] On the section where a complete ring support has been formed, remove the plastic bag 34, connecting bolt 17, and through rod 35, dismantle the middle lower temporary steel support 12, promptly pour the invert arch lining concrete and construct the invert arch filling, and then construct the drainage system and secondary lining to form a composite support.

[0031] Before installing the arch steel 2, the upper step of the tunnel is excavated first to ensure that the joint between the lower connecting steel plate 13 and the upper connecting steel plate 14 is located at the foot of the upper step excavated at the tunnel face. The soil and rock at the arch foot of the left or right section are compacted, and a precast pad block 4 is temporarily placed or a channel steel is laid. After installing the upper half of the arch steel 2 and the lower temporary steel support 12, the arch foot of each section of the steel arch frame is fixed with the first locking anchor rod 8 and the second locking anchor rod 9, and then the soil and rock of the lower step are excavated.

[0032] Before installing the left arch foot steel 1, the excavation face of the upper step is advanced by 3 to 5 meters before the lower half of the left side is excavated. During the excavation, the precast pad block 4 at the left foot of the arch top steel 2 is removed, and the left arch foot steel 1 and the lower temporary steel support 12 are installed so that the bottom rests on the solid and flat precast pad block 4 and is fixed with the first locking foot anchor rod 8 and the second locking foot anchor rod 9.

[0033] Before installing the right arch foot steel 3, the excavation face of the upper step is advanced by 3 to 5 meters before the lower half of the right side is excavated. During excavation, the precast pad block 4 at the right foot of the arch top steel 2 is removed, and the right arch foot steel 3 is installed so that the bottom rests on the solid and flat precast pad block 4, and is fixed with the first locking foot anchor rod 8 and the second locking foot anchor rod 9.

[0034] The left inverted arch steel 10 is excavated at a maximum of 40m ahead of the working face of the lower left step. The left inverted arch section is excavated, the arc surface is leveled and a cushion layer is poured, and the left inverted arch steel 10 is installed. The inverted arch connecting steel plate 6 at one end of the left inverted arch steel 10 is fixed to the arch foot side connecting steel plate 5 using fixing bolts 7. The left inverted arch steel 10s are connected by steel bars in a plum blossom pattern to form an integral structure.

[0035] The right inverted arch steel 11 is excavated at a maximum depth of 30m ahead of the working face of the lower right step. The right inverted arch section is excavated, the arc surface is leveled and a cushion layer is poured, and the right inverted arch steel 11 is installed. The inverted arch connecting steel plate 6 at one end of the right inverted arch steel 11 is fixed to the arch foot side connecting steel plate 5 using fixing bolts 7. The other end is welded to the already installed left inverted arch steel 10 face to face. The right inverted arch steel 11 is connected by reinforcing bars in a staggered pattern to form a tie.

[0036] When excavating the right inverted arch section, the lower half of the temporary steel support 12 is removed from the bottom of the temporary precast pad 4. After the excavation is completed, other pads with higher cross sections or steel sections are used as temporary supports. After installing the right inverted arch steel sections 11 one by one, the bottom of the temporary steel support 12 is placed on the support base plate 24, and the movable clamping plate 25 is rotated. The screws at both ends of the through rod 35 are inserted into the clamping hole 27 for fixing.

[0037] After the side connecting steel plate 15 and the temporary connecting steel plate 16 are connected, the bottom connecting steel plate 15 and the temporary connecting steel plate 16 of the arch steel 2 are completely wrapped and fixed with hemp rope or tie wire.

[0038] The steel wire mesh 36 tied between the lower temporary steel supports 12 can prevent the sprayed concrete from falling and lock with the sprayed concrete to form a stable plane.

[0039] The steel arch frame installed along the excavation section, when the left arch foot steel 1, arch top steel 2, right arch foot steel 3, left invert arch steel 10, and right invert arch steel 11 of the same section are connected to form a ring, and the steel arch frames are welded with tie rods and steel mesh, and after the initial support is formed by spraying quick-setting concrete, the middle lower temporary steel support 12 is removed, and the invert arch lining concrete is poured and the invert arch filling is carried out in a timely manner.

Claims

1. A temporary steel arch frame for initial support of a large-section loess tunnel, characterized in that: Includes left arch foot steel (1), arch top steel (2), right arch foot steel (3), precast pad block (4), arch foot side connecting steel plate (5), invert arch connecting steel plate (6), fixing bolt (7), first locking foot anchor rod (8), second locking foot anchor rod (9), left invert arch steel (10), right invert arch steel (11), lower temporary steel support (12), lower connecting steel plate (13), upper connecting steel plate (14), side connecting steel plate (15), temporary connecting steel plate (16), connecting bolt one (17), connecting bolt two (20), support base plate (24), movable clamping plate (25), rotating shaft (26), clamping hole (27), plastic bag (34), through rod (35), wire mesh (36); The left arch foot steel (1) is a section of I-beam bent into an arc shape. Near the bottom end, it is fixed to the excavated loess tunnel section using the first locking foot anchor (8) and the second locking foot anchor (9). The outer side is close to the rock wall, and the inner side is welded with the arch foot side connecting steel plate (5). The bottom is placed on the precast pad (4) or the longitudinal channel steel web, and the top is welded with the lower connecting steel plate (13). The first locking foot anchor (8) is a steel pipe of a certain diameter and a certain wall thickness pressed into the rock wall, bent into an "L" shape, with the tail close to the inner side of the left arch foot steel (1) and fixed by welding. The rock wall holes are filled by pressure grouting. The second locking foot anchor (9) is a steel pipe of a certain diameter and a certain wall thickness. Pressed into the rock wall, bent into an "L" shape, with the tail end close to the inner side of the left arch foot steel (1) and fixed by welding. The rock wall holes are filled by pressure grouting inside the steel pipe. The arch foot side connecting steel plate (5) is welded to the inner side of the left arch foot steel (1), and four bolt holes are reserved on the arch foot side connecting steel plate (5). It can be connected to the invert arch connecting steel plate (6) by using fixing bolts (7). The precast pad (4) is a precast concrete pad with a certain strength and thickness and a flat surface. The lower connecting steel plate (13) has four round holes reserved, and its plane is perpendicular to the axis of the left arch foot steel (1). The upper connecting steel plate (14) can be connected by connecting bolt two (20). The upper connecting steel plate (14) is fixed together with the lower connecting steel plate (13); the upper connecting steel plate (14) is welded to the bottom end of the arch steel (2), and its plane is perpendicular to the axis of the arch steel (2). The left arch foot steel (1) and the arch steel (2) can be connected into a whole by connecting bolt two (20); the arch steel (2) is a section of arc-shaped I-beam, with a side connecting steel plate (15) welded near the center of the arch, and the upper connecting steel plate (14) welded to the bottom right end; the side connecting steel plate (15) is welded to the bottom surface of the arch steel (2), and can be fixed together with the temporary connecting steel plate (16) by connecting bolt one (17); the temporary connecting steel plate (16) is welded to the lower temporary steel. The top of the support (12); the lower temporary steel support (12) is two sections of arc-shaped I-beams, with connecting bolts two (20) used to fix the arc-shaped steel with connecting steel plates at both ends in the middle of the tunnel upper step excavation part, and the bottom is fixed on the support base plate (24); the support base plate (24) is welded to the right inverted arch steel (11), and the front and rear sides of the support base plate (24) are fixed with movable clamping plates (25) by rotating shafts (26); the right inverted arch steel (11) is an arc-shaped I-beam of a certain specification, one end is connected to the inverted arch connecting steel plate (6) with fixing bolts (7), and the other end is welded to the left inverted arch steel (10), and the bottom flange steel plate is placed on the tunnel excavation inverted arch leveling layer;The movable plates (25) are distributed on the front and rear sides of the right arch steel (11) and can be flipped up with the rotating shaft (26). The movable plates (25) are symmetrically reserved with through holes. Through rods (35) on both sides can be used to fix the lower temporary steel support (12). The through rods (35) have threads at both ends and can be tightened with screws. The upper connecting steel plate (14) is connected to the lower connecting steel plate (13) with connecting bolts (20). The first locking foot anchor (8) and the second locking foot anchor (9) are used to fix the foot of the arch steel (2) at this connection. The lower connecting steel plate (13) is a steel plate of a certain size with reserved bolt holes and is welded to the top of the right arch foot steel (3). The right arch foot steel (3) is a section of arc-shaped I-beam steel, with the bottom resting on the prefabricated pad (4) and close to the foot. The inner side of the arch foot side connecting steel plate (5) is welded, and the outer side is fixed with the first locking foot anchor rod (8) and the second locking foot anchor rod (9); the arch foot side connecting steel plate (5) is a steel plate of a certain thickness and size, and the steel plate has four bolt holes reserved, which can be used to connect the invert arch connecting steel plate (6) with fixing bolts (7); the first locking foot anchor rod (8) is an inverted "L" shape, and the tail is welded to the right arch foot steel (3); the second locking foot anchor rod (9) is an inverted "L" shape, and the tail is welded to the right arch foot steel (3); the lower temporary steel support (12) along the longitudinal section of the tunnel is tied and fixed with wire mesh (36), and sprayed with quick-setting concrete; the side connecting steel plate (15) and the temporary connecting steel plate (16) are fixed with connecting bolts (17) and wrapped with plastic bags (34).

2. The construction method for the initial support temporary steel arch frame of a large-section loess tunnel according to claim 1, characterized in that: In a standardized factory, the left arch foot steel (1), arch top steel (2), right arch foot steel (3), left inverted arch steel (10), and right inverted arch steel (11) are processed in sections according to the design outline and taking into account the amount of deformation. Excavate the stepped section on the working face, install the upper half of the arch steel (2) and the lower temporary steel support (12), use bolts or precast pads (4) to support the joint, weld the tie bars and steel mesh between the two arch steel (2), tie the wire mesh (36) between the lower temporary steel supports (12), and immediately spray quick-setting concrete. After the upper step is excavated 3-5m ahead, the lower half of the left side is excavated, and the lower half of the left arch foot steel (1) and the lower temporary steel support (12) are installed. The bottom is temporarily supported by precast pads (4). The joint at the design profile section is fixed with locking foot anchors. At the same time, the left invert arch is excavated, and the left invert arch steel (10) is installed. The bottom of the lower temporary steel support (12) is temporarily supported again. After the lower left half is excavated to 10m, the lower right half is excavated, the right arch foot steel (3) is installed, the foot is locked with anchor rods, the right invert arch is excavated, the right invert arch steel (11) is installed, and the lower temporary steel support (12) is placed on the support base plate (24) on the top of the right invert arch steel (11) and fixed. Along the left invert arch steel (10) and the right invert arch steel (11) of the same section, face-to-face welding is adopted to fix them and form a closed ring support form. On the section where a complete ring support has been formed, remove the plastic bag (34), connecting bolt (17), and through rod (35), dismantle the middle lower temporary steel support (12), promptly pour the invert arch lining concrete and construct the invert arch filling, and then construct the drainage system and secondary lining to form a composite support.

3. The construction method of the temporary steel arch frame for the initial support of a large-section loess tunnel according to claim 2, characterized in that, Before installing the arch steel (2), the upper step of the tunnel is excavated first to ensure that the joint between the lower connecting steel plate (13) and the upper connecting steel plate (14) of the connecting bolt two (20) is located at the foot of the upper step excavated at the tunnel face. The soil and rock at the arch foot of the left or right section are compacted, and a precast pad block (4) is temporarily placed or a channel steel is laid. After installing the upper half of the arch steel (2) and the lower temporary steel support (12), the arch foot of each section of the steel arch frame is fixed with the first locking foot anchor rod (8) and the second locking foot anchor rod (9), and then the soil and rock of the lower step are excavated.

4. The construction method of the temporary steel arch frame for the initial support of a large-section loess tunnel according to claim 2, characterized in that, Before installing the left arch foot steel (1), the excavation face of the upper step is advanced by 3 to 5 m before the lower half of the left side is excavated. During the excavation, the precast pad block (4) at the left foot of the arch top steel (2) is removed, and the left arch foot steel (1) and the lower temporary steel support (12) are installed so that the bottom rests on the solid and flat precast pad block (4) and is fixed with the first locking foot anchor rod (8) and the second locking foot anchor rod (9). Before installing the right arch foot steel (3), the excavation face of the upper step is advanced by 3 to 5 meters before the lower half of the right side is excavated. During the excavation, the precast pad (4) at the right foot of the arch top steel (2) is removed, and the right arch foot steel (3) is installed so that the bottom rests on the solid and flat precast pad (4) and is fixed with the first locking foot anchor (8) and the second locking foot anchor (9).

5. The construction method of the temporary steel arch frame for the initial support of a large-section loess tunnel according to claim 2, characterized in that, The left inverted arch steel (10) is excavated at a maximum of 40m ahead of the working face of the lower step on the left side. The left inverted arch part is excavated, the arc surface is leveled and the cushion layer is poured. The left inverted arch steel (10) is installed. The inverted arch connecting steel plate (6) at one end of the left inverted arch steel (10) is fixed to the arch foot side connecting steel plate (5) using fixing bolts (7). The left inverted arch steel (10) of each frame is welded together with steel bars in a plum blossom shape to form an integral structure. The right inverted arch steel (11) is excavated at a maximum depth of 30m ahead of the right lower step face, the right inverted arch part is excavated, the arc surface is leveled and the cushion layer is poured, the right inverted arch steel (11) is installed, and the inverted arch connecting steel plate (6) at one end of the right inverted arch steel (11) is fixed to the arch foot side connecting steel plate (5) by fixing bolts (7), and the other end is welded to the installed left inverted arch steel (10) face to face. The right inverted arch steel (11) of each frame is connected by steel reinforcement in a plum blossom pattern to form a tie.

6. The construction method of the temporary steel arch frame for the initial support of a large-section loess tunnel according to claim 2, characterized in that, When excavating the right inverted arch section, the lower half of the temporary steel support (12) is removed by removing the bottom temporary precast pad (4). After excavation, other pads or temporary steel supports with higher cross sections are used. After installing the right inverted arch steel (11) one by one, the bottom of the temporary steel support (12) is placed on the support base plate (24), and the movable card plate (25) is rotated. The screws at both ends of the through rod (35) are inserted into the card hole (27) for fixing.

7. The construction method of the temporary steel arch frame for the initial support of a large-section loess tunnel according to claim 2, characterized in that, After the side connecting steel plate (15) and the temporary connecting steel plate (16) are connected, the connecting steel plate (15) and the temporary connecting steel plate (16) at the bottom of the arch steel (2) are completely wrapped and fixed with hemp rope or binding wire.

8. The construction method of the initial support temporary steel arch frame for large-section loess tunnels according to claim 2, characterized in that: The wire mesh (36) tied between the lower temporary steel supports (12) can prevent the sprayed concrete from falling and lock with the sprayed concrete to form a stable plane.

9. The construction method of the initial support temporary steel arch frame for large-section loess tunnels according to claim 2, characterized in that: The steel arch frame installed along the excavation section, when the left arch foot steel (1), arch top steel (2), right arch foot steel (3), left inverted arch steel (10), and right inverted arch steel (11) of the same section are connected to form a ring, and the steel arch frames are welded with tie rods and steel mesh, and after the initial support is formed by spraying quick-setting concrete, the middle lower temporary steel support (12) is removed, and the inverted arch lining concrete is poured and the inverted arch filling is carried out in a timely manner.

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