Advanced support structure and method for loess tunnel construction

Abstract

The invention discloses a forepoling structure and method for loess tunnel construction in the technical field of tunnel construction, and the forepoling structure comprises a profile steel arch frame and supporting angle steel, a plurality of right-angle guide holes penetrating through the front side and the rear side of the profile steel arch frame are formed in the portion, corresponding to the tunnel vault area, of the profile steel arch frame at intervals in the extending direction of the profile steel arch frame, the shape of the right-angle guide holes is matched with the cross section of the supporting angle steel, and openings of the right-angle guide holes face upwards. The supporting angle steel penetrates through the right-angle guide hole and then is inserted into a soil body behind the tunnel face along the inclined upper portion. During supporting, a profile steel arch frame serves as a foundation, angle steel serves as a supporting body and is directly pressed into a soil body for advance supporting, drilling and grouting are not needed, disturbance of advance supporting to surrounding rock of a tunnel face can be reduced, the supporting force of the supporting structure to the surrounding rock in front of the tunnel face is enhanced, and compared with a traditional small guide pipe supporting structure, the supporting structure is more convenient to install and lower in cost. The construction speed is higher, the cost is lower, and the supporting structure is stable and reliable.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, and in particular to an advanced support structure and a support method for loess tunnel construction. Background Art

[0002] During the construction of collapsible loess tunnels, due to poor surrounding rock conditions and insufficient self-stabilizing capacity of the face, advance support is required during the excavation process to provide certain support and reinforcement to the rock around the tunnel and reduce the risk of collapse and block falling on the face. At present, small pipe grouting technology is generally used for advance support. For example, the patent document with publication number CN112855225A discloses a soft rock tunnel support construction method, which includes the construction of advance small pipes on the tunnel body. When the advance grouting small pipe is constructed, it passes through the reserved hole on the web of the arch steel arch frame, is pushed in by the top head, and the exposed end is supported on the steel arch frame to form an advance support system, and then high-pressure grouting is used to further reinforce the stratum. When constructing according to this method, due to the large cross-section of the small pipe, the penetration into the soil will cause certain disturbances to the rock around the tunnel. At the same time, the pressure and moisture generated by the small pipe grouting will cause a significant damage to the self-stabilizing capacity of the rock around the tunnel; on the other hand, the drilling and grouting technology takes up a lot of time, slowing down the progress of the closed ring and increasing the risk of block falling on the face. Summary of the invention

[0003] In order to overcome the above-mentioned deficiencies in the existing small-duct grouting support construction, the technical problem to be solved by the present invention is to provide an advanced support structure and a support method for loess tunnel construction which are convenient to construct and have little disturbance to the soil.

[0004] The technical solution adopted by the present invention to solve its technical problem is:

[0005] The advanced support structure used for loess tunnel construction comprises a steel arch frame arranged on the tunnel face along the inner wall of the tunnel, and supporting angle steels inserted on the steel arch frame. A plurality of right-angle guide holes penetrating the front and rear sides of the steel arch frame are arranged at intervals along the extension direction of the steel arch frame at the position corresponding to the tunnel vault area. The shape of the right-angle guide holes is adapted to the cross-section of the supporting angle steels, and the opening faces upward. After the supporting angle steel passes through the right-angle guide holes, it is inserted into the soil behind the tunnel face along an obliquely upward direction.

[0006] Furthermore, the steel arch frame is made of H-shaped steel, the right-angle guide hole is arranged on the web of the H-shaped steel, a guide block is provided on the side of the web away from the heading surface, the guide block is located in the opening of the right-angle guide hole, and the inner side of the supporting angle steel is inserted into the right-angle guide hole close to the guide block.

[0007] Furthermore, the included angle between the guide surface on the guide block that is in sliding contact with the supporting angle steel and the horizontal plane is 3 to 5 degrees.

[0008] Furthermore, the steel arch is divided into an arched section in the middle and support sections on both sides. The central angle corresponding to the arched section is 110-130°, and the right-angle guide holes are arranged at intervals in the arched section. The distance between two adjacent right-angle guide holes is 30-50 cm.

[0009] Furthermore, the insertion end of the support angle steel is provided with a pointed head not less than 20 cm long. The depth of the support angle steel inserted into the heading face is 3-3.5 m, and the length outside the heading face is 0.5-1 m.

[0010] Furthermore, a steel mesh is provided inside the steel arch. The end of the support angle steel away from the heading face is fixed by the shotcrete between the steel mesh and the tunnel inner wall.

[0011] Furthermore, a steel arch and the support angle steel penetrating it form a support unit. Along the tunnel excavation direction, a support unit is arranged every 2-2.5 m. The support angle steels of two adjacent support units overlap 0.8-1 m in the vertical direction.

[0012] The advanced support method for loess tunnel construction uses the above-mentioned advanced support structure for loess tunnel construction, and includes the following construction steps:

[0013] Step 1: According to the cross-sectional size of the tunnel, fabricate the adapted steel arch and support angle steel in the factory, and process right-angle guide holes on the steel arch.

[0014] Step 2: Erector the steel arch at a position close to the heading face, and fix both sides to the tunnel inner wall through anchor bolts.

[0015] Step 3: Align the support angle steel with the right-angle guide holes on the steel arch, and use an air hammer to drive the support angle steel into the soil behind the heading face.

[0016] Step 4: Install a steel mesh inside the steel arch, and then spray concrete into the space between the steel mesh and the tunnel inner wall for support. Thus, the erection of one support unit is completed.

[0017] Step 5: After the shotcrete in Step 4 solidifies, excavate 2-2.5 m into the tunnel, and then erect the next support unit according to the content of Steps 2 to 4. Repeat this process until the entire tunnel construction is completed.

[0018] Furthermore, when inserting the support angle steel, insert it obliquely upward to ensure that the angle between the support angle steel and the horizontal plane is 3-5°. The depth of the support angle steel inserted into the heading face is 3-3.5 m, the length outside the heading face is 0.5-1 m, and it is completely wrapped by the shotcrete.

[0019] Further, when erecting the next support unit in Step 5, first excavate the inner wall of the tunnel circumferentially for a section to make its size the same as that of the inner wall of the tunnel corresponding to the previous support unit, then erect the steel arch, and finally when inserting the support angle steel, make the end of it lap with the front end of the support angle steel of the previous support unit by 0.8 - 1 m in the vertical direction.

[0020] The beneficial effects of the present invention are as follows: Using angle steel as the main body of the support, directly pressing it into the soil for advanced support without drilling and grouting can reduce the disturbance of the advanced support to the surrounding rock of the heading face, enhance the supporting force of the support structure to the surrounding rock in front of the heading face. Compared with the traditional small duct support structure, the present invention is more convenient to install, has a faster construction speed, lower cost, and the support structure is stable and reliable, and is particularly suitable for the advanced support construction of loess tunnels. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a sectional view of the support structure of the present invention;

[0022] Figure 2 is a front view of the steel arch of the present invention;

[0023] Figure 3 is Figure 2 an enlarged view of part A in

[0024] In the figure, the markings are: 1 - steel arch, 2 - support angle steel, 3 - heading face, 4 - steel mesh, 5 - shotcrete, 11 - right-angled guiding hole, 12 - guiding block, 13 - arched section, 14 - support section, 21 - pointed head. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present invention will be further described below with reference to the accompanying drawings.

[0026] It should be noted that if there are directional indication terms involved in the present invention, such as the direction and orientation terms of up, down, left, right, front, and back, they are for the description of the relative position relationship between components. They are not specific to the absolute position of the relevant components and the position relationship between components, but are only used to explain the relative position relationship and movement conditions between components in a certain specific posture. If this specific posture changes, then the directional indication also changes accordingly. If there are quantity terms involved in the present invention, such as "many", "multiple", "several", etc., it specifically refers to two or more.

[0027] Such as Figures 1-3As shown, the present invention provides an advanced support structure for loess tunnel construction, including a steel arch frame 1 set against the tunnel face 3 along the inner wall of the tunnel, and a support angle steel 2 inserted in the steel arch frame 1. The portion of the steel arch frame 1 corresponding to the tunnel vault area is provided with a plurality of right-angle guide holes 11 passing through the front and rear sides of the steel arch frame 1 at intervals along its extension direction. The shape of the right-angle guide hole 11 is adapted to the cross-section of the support angle steel 2, and the opening faces upward. After passing through the right-angle guide hole 11, the support angle steel 2 is inserted into the soil behind the tunnel face 3 along the oblique upper side. The support angle steel 2 can be an equilateral angle steel with a side length of 40 to 60 mm and a thickness of 2 to 4 mm. After the support angle steel 2 is inserted into place, the support angle steel 2 can be welded to the steel arch frame 1 to ensure the stability of the support of the support angle steel 2. Compared with the traditional small-duct support structure, the present invention uses angle steel to support the soil. On the one hand, the cross-section of the support angle steel 2 is small, and it can be directly inserted into the collapsible loess with the help of air hammers and other equipment without drilling, thereby improving construction efficiency; on the other hand, the support angle steel 2 is inserted into the soil with the opening facing upward, which can provide a larger support area and better support effect on the soil above. At the same time, the support angle steel 2 is not easy to bend, which can ensure the support strength of the support structure. On this basis, there is no need to perform grouting operations on the soil, thereby reducing the disturbance to the surrounding rock and avoiding damage to the self-stabilizing ability of the surrounding rock.

[0028] The steel arch frame 1 can be a support frame welded by steel pipes or steel plates. In order to simplify the structure, the present invention preferably adopts H-shaped steel, and the specific model is selected according to the actual structural stress analysis on site. The upper and lower wing plates of the H-shaped steel serve as the inner and outer supporting surfaces of the steel arch frame 1, and the right-angle guide hole 11 is set on the web of the H-shaped steel. Since the web is thin, in order to improve the supporting effect of the H-shaped steel on the supporting angle steel 2, a guide block 12 is provided on the side of the web away from the face 3. The guide block 12 is located in the opening of the right-angle guide hole 11, and the inner side of the supporting angle steel 2 is inserted into the right-angle guide hole 11 close to the guide block 12. The guide block 12 can increase the supporting area of ​​the supporting angle steel 2 and the H-shaped steel, thereby better balancing the torque effect of the insertion end. In addition, the angle α between the guide surface on the guide block 12 that is in sliding contact with the supporting angle steel 2 and the horizontal plane is 3 to 5°, so that the guide block 12 can be used to control the insertion angle of the supporting angle steel 2, which is convenient and quick.

[0029] In order to facilitate the installation of the steel arch frame 1, the steel arch frame 1 can be divided into a central arch section 13 and supporting sections 14 on both sides. Figure 2As shown, the three-section structure is fabricated in the factory and then assembled and welded on site. The right-angle guide holes 11 are spaced within the arched section 13. The arched section 13 corresponds to the crown area of the tunnel, and its arc length and radian are selected according to the actual situation. Generally, the central angle of the arched section 13 can be controlled between 110° and 130°. According to theoretical calculation and analysis and multiple tests, the spacing between two adjacent right-angle guide holes 11 is controlled within 30 - 50 cm to ensure the support effect on the overlying soil mass.

[0030] For the support angle steel 2, in order to facilitate its insertion into the soil mass, a pointed head 21 not less than 20 cm long is provided at the insertion end of the support angle steel 2. Due to the limited length of the angle steel, considering the convenience of transportation and installation as well as the support strength, the support angle steel 2 can be set to a length of 4 m, with the depth inserted into the heading face 3 being 3 - 3.5 m and the length outside the heading face 3 being 0.5 - 1 m. Additionally, to increase the support strength of the support angle steel 2, a steel mesh 4 is provided inside the steel arch frame 1, and the end of the support angle steel 2 away from the heading face 3 is fixed by the shotcrete support 5 sprayed between the steel mesh 4 and the tunnel inner wall.

[0031] During the tunnel excavation process, advanced support needs to be continuously carried out. Therefore, a steel arch frame 1 and the support angle steel 2 passing through it form a support unit. Along the tunnel excavation direction, a support unit is set every 2 - 2.5 m, and the support angle steels 2 of two adjacent support units overlap by 0.8 - 1 m in the vertical direction. The front and rear support angle steels 2 do not need to be connected together, and only need to overlap in the vertical direction to ensure that there are continuous support angle steels 2 for support in the entire crown area of the tunnel.

[0032] The present invention also provides an advanced support method for loess tunnel construction. Using the above-mentioned advanced support structure for loess tunnel construction, it includes the following construction steps:

[0033] Step 1: According to the cross-sectional dimensions of the tunnel, fabricate the adapted steel arch frame 1 and support angle steel 2 in the factory, and process right-angle guide holes 11 on the steel arch frame 1.

[0034] Step 2: Erect the steel arch frame 1 at a position close to the heading face 3, and fix both sides to the tunnel inner wall through bolts.

[0035] Step 3: Align the support angle steel 2 with the right-angle guide holes 11 on the steel arch frame 1, and use an air hammer to drive the support angle steel 2 into the soil mass behind the heading face 3.

[0036] Step 4: Install the steel mesh 4 inside the steel arch frame 1, and then spray shotcrete support 5 into the space between the steel mesh 4 and the tunnel inner wall. Thus, the erection of one support unit is completed.

[0037] Step 5: After the supporting concrete 5 in Step 4 solidifies, tunnel 2 - 2.5 m into the tunnel, and then erect the next support unit according to the content of Steps 2 to 4, and so on until the entire tunnel construction is completed.

[0038] Among them, when inserting the support angle steel 2, it is inserted obliquely upward to ensure that the angle between the support angle steel 2 and the horizontal plane is 3 - 5°, the insertion depth of the support angle steel 2 into the heading face 3 is 3 - 3.5 m, the length outside the heading face 3 is 0.5 - 1 m, and it is completely wrapped by the supporting concrete 5. Since the tunnel is excavated along the inner side of the steel arch frame 1, when erecting the next support unit in Step 5, it is necessary to first excavate a section of the tunnel inner wall circumferentially to make its size the same as that of the tunnel inner wall corresponding to the previous support unit, then erect the steel arch frame 1, and finally, when inserting the support angle steel 2, make the end of it overlap with the front end of the support angle steel 2 of the previous support unit by 0.8 - 1 m in the vertical direction.

[0039] In summary, the present invention uses the support angle steel 2 as the supporting main body, directly presses it into the soil for advanced support, without drilling and grouting, which can reduce the disturbance of the advanced support to the surrounding rock of the heading face, enhance the supporting force of the supporting structure to the surrounding rock in front of the heading face. Compared with the traditional small - duct supporting structure, the present invention is more convenient to install, has a faster construction speed, lower cost, and the supporting structure is stable and reliable. It is especially suitable for the advanced support construction of loess tunnels and has good practicability and application prospects.

Claims

1. The advanced support structure used for loess tunnel construction is characterized by: The invention comprises a steel arch frame (1) arranged close to a tunnel face (3) along the inner wall of a tunnel, and a supporting angle steel (2) inserted through the steel arch frame (1). A portion of the steel arch frame (1) corresponding to the tunnel vault region is provided with a plurality of right-angle guide holes (11) passing through the front and rear sides of the steel arch frame (1) at intervals along its extension direction. The shape of the right-angle guide holes (11) is adapted to the cross section of the supporting angle steel (2) and the opening faces upward. After passing through the right-angle guide holes (11), the supporting angle steel (2) is inserted into the soil behind the tunnel face (3) along an obliquely upward direction.

2. The advanced support structure for loess tunnel construction according to claim 1, characterized in that: The steel arch (1) is made of H-shaped steel, the right-angle guide hole (11) is arranged on the web of the H-shaped steel, a guide block (12) is arranged on the side of the web facing away from the tunnel face (3), the guide block (12) is located in the opening of the right-angle guide hole (11), and the inner side of the support angle steel (2) is closely attached to the guide block (12) and inserted into the right-angle guide hole (11).

3. The advanced support structure for loess tunnel construction according to claim 2, characterized in that: The included angle α between the guide surface on the guide block (12) that is in sliding contact with the supporting angle steel (2) and the horizontal plane is 3 to 5 degrees.

4. The advanced support structure for loess tunnel construction according to claim 1, characterized in that: The steel arch frame (1) is divided into an arch section (13) in the middle and support sections (14) on both sides, the central angle of the arch section (13) is 110-130°, the right-angle guide holes (11) are arranged at intervals in the arch section (13), and the distance between two adjacent right-angle guide holes (11) is 30-50 cm.

5. The advanced support structure for loess tunnel construction according to claim 1, characterized in that: The insertion end of the support angle steel (2) is provided with a pointed head (21) of not less than 20 cm. The support angle steel (2) is inserted into the tunnel face (3) to a depth of 3 to 3.5 m, and the length outside the tunnel face (3) is 0.5 to 1 m.

6. The advanced support structure for loess tunnel construction according to any one of claims 1 to 5, characterized in that: A steel mesh (4) is provided on the inner side of the steel arch (1), and the end of the support angle steel (2) away from the tunnel face (3) is fixed by spraying supporting concrete (5) between the steel mesh (4) and the inner wall of the tunnel.

7. The advanced support structure for loess tunnel construction according to claim 6, characterized in that: A steel arch frame (1) and a supporting angle steel (2) inserted thereon form a supporting unit. Along the tunnel excavation direction, a supporting unit is arranged at intervals of 2 to 2.5 m, and the supporting angle steels (2) of two adjacent supporting units overlap by 0.8 to 1 m in the vertical direction.

8. The advanced support method for loess tunnel construction is characterized by: The advanced support structure for loess tunnel construction as claimed in claim 7 comprises the following construction steps: Step 1: According to the cross-sectional dimensions of the tunnel, a suitable steel arch frame (1) and supporting angle steel (2) are manufactured in the factory, and a right-angle guide hole (11) is processed on the steel arch frame (1); Step 2: erecting a steel arch frame (1) close to the tunnel face (3), and fixing both sides of the steel arch frame to the inner wall of the tunnel by anchor rods; Step 3: align the support angle steel (2) with the right-angle guide hole (11) on the steel arch frame (1), and use an air hammer to drive the support angle steel (2) into the soil behind the tunnel face (3); Step 4: Install a steel mesh (4) on the inner side of the steel arch frame (1), and then spray support concrete (5) into the space between the steel mesh (4) and the inner wall of the tunnel, thus completing the erection of a support unit; Step 5: After the supporting concrete (5) in step 4 solidifies, excavate 2 to 2.5 m into the tunnel, and then erect the next supporting unit according to the contents of steps 2 to 4, and repeat this cycle until the entire tunnel construction is completed.

9. The advanced support method for loess tunnel construction according to claim 8, characterized in that: When inserting the support angle steel (2), it is inserted diagonally upward to ensure that the angle between the support angle steel (2) and the horizontal plane is 3 to 5 degrees. The support angle steel (2) is inserted into the tunnel face (3) to a depth of 3 to 3.5 meters, and the length outside the tunnel face (3) is 0.5 to 1 meter, and is completely wrapped by the supporting concrete (5).

10. The advanced support method for loess tunnel construction according to claim 8, characterized in that: When erecting the next support unit in step 5, first, a section of the tunnel inner wall is expanded along the circumferential direction to make it the same size as the tunnel inner wall corresponding to the previous support unit, and then the steel arch frame (1) is erected. Finally, when inserting the support angle steel (2), its end is overlapped with the front end of the support angle steel (2) of the previous support unit in the vertical direction by 0.8 to 1m.

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