Anti-collapse tunneling method for horizontal layered surrounding rock

Abstract

The application discloses a kind of horizontal layered surrounding rock tunnel collapse prevention excavation methods, specific steps are as follows: step one: in the tunnel excavation face two sides along design contour line, pre-splitting crack is blasted;Step two: between the pre-splitting crack of two sides, from bottom to top, the face is excavated layer by layer until arch crown protection layer;Step three: anchor rod is sequentially passed through the arch crown protection layer and arch crown deep stable rock stratum;Step four: the arch crown protection layer is blasted and excavated.The beneficial effects of the application are that the application can reduce the occurrence of overbreak and underbreak phenomenon by blasting pre-splitting crack along design contour line on the two sides of tunnel excavation face, and effectively control the excavation contour.The face is excavated layer by layer from bottom to top until arch crown protection layer, full-length bonded anchor rod is used to support arch crown protection layer and upper rock stratum of arch crown, which effectively prevents arch crown collapse during construction, and finally excavates arch crown protection layer and bends exposed anchor rod to ensure the stability of arch crown.

Description

Technical Field

[0001] This invention relates to a method for preventing collapse during the excavation of tunnels in horizontally layered surrounding rock, belonging to the field of tunnel construction technology. Background Technology

[0002] With the rapid development of my country's transportation infrastructure, mountain tunnels are playing an increasingly important role in highways and railways. Due to the widespread distribution of layered rock tunnels, the stability of layered rock is often encountered in tunnel design and construction. Layered rock generally has poor stability and self-stabilizing ability. Under its own weight and stress conditions, it is prone to sliding shear failure along the bedding plane. Furthermore, the arch is prone to rockfall, segregation, bending, and collapse, which seriously threatens the safety of tunnel construction. At the same time, the arch is prone to problems such as leveling, over-excavation and under-excavation, and difficulty in controlling the excavation profile, which affect the quality of subsequent construction and increase construction costs. Summary of the Invention

[0003] The purpose of this application is to provide a method for preventing collapse during excavation of horizontally layered rock tunnels, thereby solving the technical problems of easy collapse, over-excavation and under-excavation, and difficulty in controlling the excavation profile in existing technologies. To achieve the above objective, this invention proposes a method for preventing collapse during excavation of horizontally layered rock tunnels, the specific scheme of which is as follows:

[0004] A method for preventing collapse during excavation of horizontally layered surrounding rock tunnels, comprising the following specific steps:

[0005] Step 1: Pre-cracks are blasted along the design outline on both sides of the tunnel excavation face;

[0006] Step 2: Between the pre-cracks on both sides, excavate the working face layer by layer from bottom to top until the arch protective layer is reached;

[0007] Step 3: Pass the anchor bolts sequentially through the arch crown protective layer and the stable rock layer deep within the arch crown;

[0008] Step 4: Excavate the protective layer of the arch.

[0009] Preferably, before step two, a first area is excavated by blasting; the first area is an area extending from the pre-crack towards the center of the working face; the width of the first area is not less than 20cm.

[0010] Preferably, before step three, the method further includes drilling holes in the arch protective layer; the holes are perpendicular to the structural surface of the arch protective layer, and the drilling depth is greater than the length of the anchor bolt.

[0011] Alternatively, the anchor bolt is a full-length bonded anchor bolt.

[0012] Preferably, the bonding material filling the space between the anchor bolt and the borehole is concrete grout.

[0013] Preferably, after step four, the method further includes:

[0014] Step 5: Bend the exposed anchor bolts after excavating the arch protective layer.

[0015] The beneficial effects of this invention are that by blasting pre-cracks along the designed outline on both sides of the tunnel excavation face, over-excavation and under-excavation can be reduced, effectively controlling the excavation outline. The tunnel face is excavated layer by layer from bottom to top until the arch crown protective layer is reached. Full-length bonded anchor bolts are used to support the arch crown protective layer and the upper rock strata of the arch crown, effectively preventing arch crown collapse during construction. Finally, the arch crown protective layer is excavated, and the exposed anchor bolts are bent to ensure the stability of the arch crown. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the excavation face structure for preventing collapse of a horizontally layered surrounding rock tunnel according to an embodiment of the present invention;

[0017] In the diagram: 1. Pre-crack; 2. First region; 3. Second region; 4. Third region; 5. Arch protective layer; 6. Anchor bolt. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0020] Reference Figure 1 A method for preventing collapse during excavation of horizontally layered surrounding rock tunnels, the specific steps of which are as follows:

[0021] Step 1: Blasting pre-cracks 1 along the designed outline on both sides of the tunnel excavation face; When blasting to excavate a tunnel, it is required that the boundary of the blasting excavation conforms to the designed outline as much as possible to avoid over- or under-excavation, and at the same time, it is required that the rock mass on the excavation boundary can remain as intact and stable as possible. For the horizontal layered surrounding rock tunnel in this embodiment, the pre-splitting blasting technology is adopted. First, pre-cracks 1 of a certain width are blasted along the designed outline on both sides of the tunnel excavation face. The pre-cracks 1 can buffer and reflect the vibration waves of the excavation blasting, control the destructive impact of the main blasting on the preserved rock mass, and obtain a relatively flat excavation outline.

[0022] After obtaining the pre-crack 1, the first region 2 is excavated by blasting. Specifically, the first region 2 is located on both sides of the tunnel, and it extends from the pre-crack 1 towards the center of the tunnel face; the width of the first region 2 on one side is not less than 20cm. In this embodiment, the width of the first region 2 is 25cm.

[0023] Step Two: Using blasting methods, the tunnel face is excavated layer by layer from bottom to top between the pre-cracks on both sides until the arch crown protective layer 5 is reached. After the horizontal layered surrounding rock tunnel is excavated, the rock mass is very likely to fall off along the crown stratum corneum, forming a flat top like a tabletop. This flat top causes the tunnel arch to support the weight of the overlying rock mass in the form of a "beam". When this span reaches the limit span of the rock "beam", the arch crown rock layer fractures. After fracture, the upper rock layer forms a "beam" structure. Under the action of the upper load, the tunnel arch rock layer continuously fractures and fails until the arch reaches stress equilibrium. Using a bottom-up approach to excavate the tunnel face in multiple zones can reduce the excavation volume and span, increase the stability of the surrounding rock during construction, and avoid rock layer fractures, collapses, or safety accidents.

[0024] In this embodiment, the blasting excavation face area is divided into a second area 3 and a third area 4. The second area 3 and the third area 4 are the main blasting areas, and blasting and excavation are carried out in sequence. When excavating to the third area 4, care should be taken not to damage the arch roof protective layer 5. The reserved arch roof protective layer 5 can prevent the direct impact of blasting on the arch roof, which may cause it to become loose, broken, collapsed, over-excavated, or even collapsed.

[0025] Step 3: Insert anchor bolts 6 sequentially through the arch crown protective layer 5 and the stable rock layer deep within the arch crown; anchor bolts 6 are used to support the arch crown protective layer 5. Since the horizontally layered surrounding rock is generally sedimentary rock, and sedimentary rocks generally undergo weathering, transportation, and sedimentation consolidation processes, the mechanical parameters such as compressive strength, tensile strength, and viscosity modulus of each rock layer in the surrounding rock are very different. Under the combined action of horizontal bedding, rock joints, and fissures, it is extremely unstable. Therefore, anchor bolts 6 are installed at the arch crown protective layer 5 for support, and the anchor bolts 6 sequentially pass through the arch crown protective layer 5 and the stable rock layer deep within the arch crown.

[0026] Drilling is performed on the protective layer 5 of the arch crown, with the borehole perpendicular to the structural surface of the protective layer 5. The borehole depth is greater than the length of the anchor bolt 6, and the length of the anchor bolt 6 is much greater than the thickness of the protective layer 5. Specifically, full-length bonded anchor bolts 6 are used for support. The anchor bolt 6 is inserted into the borehole, and cement mortar is injected into the borehole. Through the full-length injection of cement mortar into the borehole, the anchor bolt 6 is bonded to the rock mass along its entire length, allowing the anchor bolt 6 and the rock mass to share the load. The anchor bolt 6 passes through the loose zone to the elastic zone of the rock strata, achieving the anchoring and support function of the anchor bolt 6 for the rock strata. Full-length bonding ensures good force transmission while also guaranteeing the corrosion resistance of the anchor bolt 6. The axial force of the anchor bolt 6 clamps the rock strata of the arch crown, compressing them to enhance interlayer friction and improve interlayer shear strength. Unstable rock blocks that may collapse are fixed to stable rock masses deep within the surrounding rock mass using the anchor bolt 6, preventing the arch crown from collapsing.

[0027] Step 4: Blasting excavation of the arch crown protective layer 5. Blasting excavation of the arch crown protective layer 5 is carried out along the excavation outline to complete the excavation operation of the final excavation face, exposing the anchor bolts 6 in the area of ​​the arch crown protective layer 5.

[0028] Step 5: After blasting and excavating the protective layer 5 of the arch crown, the exposed anchor bolts 6 are treated by bending them from their roots towards the excavation face, making them fit tightly against the arch crown to further protect it and prevent collapse. Specifically, in this embodiment, after bending the anchor bolts 6, the tunnel surface is treated with shotcrete and wire mesh.

[0029] The beneficial effects of this invention are that by blasting pre-cracks along the designed outline on both sides of the tunnel excavation face, over-excavation and under-excavation can be reduced, effectively controlling the excavation outline. The tunnel face is excavated layer by layer from bottom to top until the arch crown protective layer is reached. Full-length bonded anchor bolts are used to support the arch crown protective layer and the upper rock strata of the arch crown, effectively preventing arch crown collapse during construction. Finally, the arch crown protective layer is excavated, and the exposed anchor bolts are bent to ensure the stability of the arch crown.

[0030] The above embodiments merely illustrate one real-time method of the present invention, and while the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for anti-collapse excavation of a horizontal layered surrounding rock tunnel, characterized by, The specific steps are as follows: Step one: blasting pre-cracks along the design contour line on both sides of the tunnel excavation face; Step two: excavating the face from bottom to top between the pre-cracks on both sides until the arch crown protection layer; Step three: sequentially passing the anchor rod through the arch crown protection layer and the deep stable rock layer of the arch crown; Step four: excavating the arch crown protection layer; Before the step three, further comprising drilling a hole in the arch crown protection layer; The hole is perpendicular to the structural plane of the arch crown protection layer, and the depth of the hole is greater than the length of the anchor rod.

2. A method of anti-collapse excavation of a tunnel in horizontal stratified surrounding rock according to claim 1, characterized in that, Before the step two, further comprising blasting to excavate a first area; The first area is an area extending from the pre-crack to the center of the face; The width of the first area is not less than 20 cm.

3. A method of preventing collapse of a tunnel in horizontal stratified surrounding rock according to claim 1, characterized in that, The anchor rod is a full-length bonded anchor rod.

4. A method of preventing collapse of a tunnel in horizontal stratified surrounding rock according to claim 3, characterized in that, The bonding material filled between the anchor rod and the hole is concrete slurry.

5. A method of collapse prevention excavation of a horizontal stratified surrounding rock tunnel according to any one of claims 1 to 4, characterized in that, After the step four, further comprising: Step five: bending the exposed anchor rod after excavating the arch crown protection layer.

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