Advanced steel chisel support and negative pressure guide grouting reinforcement treatment method for soft rock roof

Abstract

The invention discloses a treatment method for advanced steel chisel support and negative pressure guide grouting reinforcement of a soft rock roof, which belongs to the field of coal mining, and has the technical key points that the advanced steel chisel support and negative pressure guide grouting reinforcement are adopted during roadway tunneling, and the grouting effect of tiny cracks and deep cracks is improved by negative pressure guide grouting; the stability of the soft rock fracture roof is improved, and the integrity of the heading face roof is guaranteed. Due to the fact that negative pressure is adopted for guiding grouting, the distance range of the steel chisels can be enlarged.

Description

Technical Field

[0001] The invention relates to the field of coal mining, and in particular to a method for managing advanced steel drill support and negative pressure guided grouting reinforcement of a soft rock roof. Background Art

[0002] When excavating coal tunnels, the roof is made of soft rock layers such as coal powder and mudstone, and there are a lot of cracks in some areas of the roof, which have low strength and poor stability. It is easy to collapse during the excavation process, causing the phenomenon of collapse while excavating, which poses a great safety hazard to the workers and affects the excavation efficiency. Therefore, it is of great significance to find a method of direct advance support for the soft rock with cracks on the roof.

[0003] At present, the main methods for advanced support of soft rock roof are as follows:

[0004] (1) By carrying out advance small-duct grouting support on the roof during tunnel excavation, the roof is reinforced to prevent it from collapsing during excavation.

[0005] (2) By providing advance pipe-roof support to the roof during tunnel excavation, the pressure of the tunnel roof can be effectively borne, making the excavation process safer.

[0006] (3) Use TBM (full-section hard rock tunnel boring machine) to enable excavation and support operations to be carried out in parallel, thereby speeding up the excavation process.

[0007] (4) The soft rock roof can be effectively pre-supported through the traditional advance steel drill support device.

[0008] However, the current methods for preventing roof soft rock collapse have the following deficiencies and obvious defects:

[0009] (1) During tunnel excavation, the roof is supported by grouting with small pipes in advance. This method is highly feasible, but the cost of grouting the entire section is high, the support strength of the pipe itself is not high, and its support effect may not be ideal under extremely soft rock geological conditions.

[0010] (2) By providing advance pipe support to the roof during tunnel excavation, this method is effective but difficult to construct, has low excavation efficiency and high cost.

[0011] (3) Although TBM (full-section hard rock tunnel boring machine) can carry out excavation and support operations in parallel, due to insufficient prediction accuracy or failure to implement advance pretreatment in a timely manner, problems such as insufficient support strength and untimely support occur, which seriously affect the construction progress and cost.

[0012] (4) Although the traditional advance steel drill support device can effectively pre-support the soft rock of the roof, due to the small insertion angle, it is subject to greater roof pressure, which makes the roof easy to collapse. In addition, the roof conditions are not single and unchanging. For the more broken soft rock roof, additional reinforcement is required at a later stage.

[0013] To sum up, the existing advance support methods for soft rock roof have deficiencies and obvious defects, and cannot play a very effective role in solving the phenomenon of leakage while digging for soft rock roof. Based on the above problems, the present invention proposes a construction method of advance steel drill support and negative pressure guided grouting reinforcement, which adopts a cycle of grouting and negative pressure in sequence, guides the slurry to fill the cracks by applying negative pressure, improves the effect of slurry filling the cracks in the roof, thereby solving the phenomenon of tunnel roof collapse while digging and improving excavation efficiency. Summary of the invention

[0014] The invention provides a method for managing advanced steel drill support and negative pressure guided grouting reinforcement of a soft rock roof, aiming to solve the problems of the prior art.

[0015] The specific scheme of this application is as follows:

[0016] A method for treating soft rock roof with advanced steel drill support and negative pressure guided grouting reinforcement comprises the following steps:

[0017] S1, before excavation, n steel drills are driven into the tunnel head, the steel drills play the role of leading anchor rods and form a supporting beam effect; n steel drills are arranged in a row, and n steel drills are hollow steel drills; n is a natural number greater than or equal to 2;

[0018] S2, n steel chisels are numbered 1, 2, 3, ..., n in sequence;

[0019] S2-1, the first steel drill is connected to the grouting system as a grouting hole, and the second steel drill is connected to the negative pressure system as a negative pressure hole; then, the grouting system is started, and the grout is pressed into the rock fracture through the first steel drill; then, after the grouting pressure reaches the first preset pressure, the negative pressure system is started to form a pressure difference between the grouting hole and the negative pressure hole; then, after slurry seeps out of the second steel drill, the negative pressure system stops working, the negative pressure system is disconnected from the second steel drill, and the port of the second steel drill is closed; then, after the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the first steel drill, and the port of the first steel drill is closed;

[0020] …

[0021] S2-m, the mth steel drill is connected to the grouting system as a grouting hole, and the m+1th steel drill is connected to the negative pressure system as a negative pressure hole; then, the grouting system is started, and the grout is pressed into the rock fracture through the mth steel drill; then, after the grouting pressure reaches the first preset pressure, the negative pressure system is started to form a pressure difference between the grouting hole and the negative pressure hole; then, after slurry seeps out of the m+1th steel drill, the negative pressure system stops working, the negative pressure system is disconnected from the m+1th steel drill, and the port of the m+1th steel drill is closed; then, after the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the mth steel drill, and the port of the mth steel drill is closed;

[0022] …

[0023] S2-n-1, the n-1th steel bar is connected to the grouting system as a grouting hole, and the nth steel bar is connected to the negative pressure system as a negative pressure hole; then, the grouting system is started, and the grout is pressed into the rock cracks through the n-1th steel bar; then, after the grouting pressure reaches the first preset pressure, the negative pressure system is started to form a pressure difference between the grouting hole and the negative pressure hole; then, after slurry seeps out of the nth steel bar, the negative pressure system stops working, the negative pressure system is disconnected from the nth steel bar and the port of the nth steel bar is closed; then, after the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the n-1th steel bar and the port of the n-1th steel bar is closed;

[0024] S2-n, the nth steel bar is connected to the grouting system as a grouting hole; then, the grouting system is started, and the grouting pressure is pressed into the rock cracks through the nth steel bar. After the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the nth steel bar and the port of the nth steel bar is closed.

[0025] Furthermore, step S1 further includes:

[0026] S1-1, collect engineering geological data of the excavation working face;

[0027] S1-2, design the length, spacing and external insertion angle of the steel chisel;

[0028] S1-3, before tunnel excavation, a number of steel drill holes are drilled in advance at a certain angle in front of the excavation working face using a drill rod, and the steel drills are driven into the corresponding steel drill holes. . .

[0029] Further, the method for determining the steel drill length L in S1-2 is as follows:

[0030]

[0031] Among them, λ is the mining influence coefficient, ranging from 1 to 3; K is the safety factor, which is 2; a is the half span of the tunnel (m); H is the buried depth of the tunnel (m); C is the cohesion (MPa); p is the steel drill strength (MPa); is the internal friction angle of rock; L s ——The length of the steel drill embedded in the stable surrounding rock is generally 0.5 to 1m.

[0032] Further, the method for determining the external insertion angle β of the steel drill in S1-2 is as follows:

[0033] β=arcsin(r / L)

[0034] Where r is the grouting radius (m).

[0035] Furthermore, the spacing of the steel chisels in step S1-2 ranges from 300 mm to 500 mm.

[0036] Furthermore, the engineering geological data of the excavation working face include: excavation working face design documents and geological survey reports.

[0037] Further, the method for sealing the port of the steel drill is to place a cork on the port of the steel drill.

[0038] The beneficial effects of this application are:

[0039] First, the basic concept of this application is that the present invention adopts "steel chisel + negative pressure guided grouting" for advance support during tunnel excavation. Negative pressure guided grouting improves the grouting effect of micro-cracks and deep cracks, improves the stability of the soft rock crack roof, and ensures the integrity of the excavation working face roof. Due to the use of negative pressure guided grouting, the spacing range of the steel chisel can also be increased from 200-300mm to (300mm-500mm).

[0040] Specifically, the following steps are taken:

[0041] S1. Before excavation, a steel drill is driven into the head of the tunnel. The drilled steel drill plays the role of an advance anchor and forms a supporting beam effect, so that the surrounding rock above the steel drill forms a whole, and the disturbance of the tunnel surrounding rock by mining stress is controlled to the minimum range.

[0042] S2-1, the first steel drill is connected to the grouting system as a grouting hole, and the second steel drill is connected to the negative pressure system as a negative pressure hole; then, the grouting system is started, and the grout is pressed into the rock fracture through the first steel drill; then, after the grouting pressure reaches the first preset pressure, the negative pressure system is started to form a pressure difference between the grouting hole and the negative pressure hole; then, after slurry seeps out of the second steel drill, the negative pressure system stops working, the negative pressure system is disconnected from the second steel drill, and the port of the second steel drill is closed; then, after the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the first steel drill, and the port of the first steel drill is closed;

[0043] …

[0044] S2-m, the mth steel drill is connected to the grouting system as a grouting hole, and the m+1th steel drill is connected to the negative pressure system as a negative pressure hole; then, the grouting system is started, and the grout is pressed into the rock fracture through the mth steel drill; then, after the grouting pressure reaches the first preset pressure, the negative pressure system is started to form a pressure difference between the grouting hole and the negative pressure hole; then, after slurry seeps out of the m+1th steel drill, the negative pressure system stops working, the negative pressure system is disconnected from the m+1th steel drill, and the port of the m+1th steel drill is closed; then, after the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the mth steel drill, and the port of the mth steel drill is closed;

[0045] …

[0046] S2-n-1, the n-1th steel bar is connected to the grouting system as a grouting hole, and the nth steel bar is connected to the negative pressure system as a negative pressure hole; then, the grouting system is started, and the grout is pressed into the rock cracks through the n-1th steel bar; then, after the grouting pressure reaches the first preset pressure, the negative pressure system is started to form a pressure difference between the grouting hole and the negative pressure hole; then, after slurry seeps out of the nth steel bar, the negative pressure system stops working, the negative pressure system is disconnected from the nth steel bar and the port of the nth steel bar is closed; then, after the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the n-1th steel bar and the port of the n-1th steel bar is closed;

[0047] S2-n, the nth steel bar is connected to the grouting system as a grouting hole; then, the grouting system is started, and the grouting pressure is pressed into the rock cracks through the nth steel bar. After the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the nth steel bar and the port of the nth steel bar is closed.

[0048] For any 2nd to nth steel bar, they are first used as negative pressure holes and then as grouting holes; therefore, it is appropriate to use corks to seal the ports of the steel bar, that is, when used as negative pressure holes, they are sealed with corks after the negative pressure ends; and then used as grouting holes, the corks are removed, which makes it convenient to connect with the grouting system, and they are sealed with corks after the grouting is completed.

[0049] Second, the present invention adopts steel chisels for advance pre-support. The steel chisels have high strength and rigidity. The support plays the role of advance anchor rods and support beams, improves the stability of the surrounding rock, and can adjust the steel chisel parameters according to the roof conditions to adapt to different roof conditions.

[0050] Third, this application breaks through the conventional steel chisel support and adopts hollow grouting steel chisel. The hollow grouting steel chisel is lighter than the solid one, easier to carry and install, and has low cost. Under the same dead weight, its bending stiffness may be greater, and it can better maintain the stability and integrity of its own structure.

[0051] Fourthly, the present application also proposes a calculation method for the steel chisel length and external insertion angle.

[0052] The steel chisel and external insertion angle are designed according to the roof collapse height, internal friction angle and other conditions. The steel chisel is made of high-strength round steel of not less than φ28mm, and the length can be 2 to 5m, with an exposed length of 200 to 300mm. The advanced steel chisel near the two sides is offset 4° outward along the tunnel excavation direction. The steel chisel is inserted into the roof of each section according to the conditions of the coal and the roof. After the construction of each face is completed, the excavation will continue. The excavation distance shall not exceed 2m, and then the steel chisel will continue to be inserted forward;

[0053] ⅠThe length of the steel drill is determined by the length of the excavation and the self-stabilizing capacity of the surrounding rock. The self-stabilizing capacity of the surrounding rock is determined by the internal friction angle of the rock mass. The length of the steel drill can be calculated by the following formula:

[0054]

[0055] Where: L——steel drill length (m);

[0056] λ——mining influence coefficient, ranging from 1 to 3;

[0057] K——safety factor, take 2;

[0058] a——half span of the tunnel (m);

[0059] H——tunnel burial depth (m);

[0060] C——cohesion (MPa);

[0061] ——internal friction angle (°);

[0062] p——steel drill strength (MPa)

[0063] L s ——The length of the steel drill embedded in the stable surrounding rock is generally 0.5 to 1m;

[0064] If the length of the steel drill is too short, it will not provide effective support, and if it is too long, it will easily cause waste. Generally speaking, the length of the steel drill will be determined comprehensively based on the excavation conditions and surrounding rock conditions.

[0065] Ⅱ After the grouting radius is determined based on theoretical calculations and laboratory tests, the external insertion angle of the steel drill can be determined by the following formula:

[0066] β=arcsin(r / L)

[0067] Where: β——steel drill external insertion angle (°);

[0068] r——grouting radius (m);

[0069] L——Length of steel chisel (m). BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a front view of the first embodiment.

[0071] Figure 2 It is a side view of the first embodiment.

[0072] Figure 3 It is a top view of the first embodiment.

[0073] Figure 4 It is a front view of the second embodiment.

[0074] Figure 5 It is a side view of the second embodiment.

[0075] Figure 6 It is a top view of the second embodiment.

[0076] The following are the descriptions of the reference numerals:

[0077] Front through beam 1001, W steel belt 1002, steel pipe 1003;

[0078] Grouting device 100, negative pressure device 200, steel drill 300; DETAILED DESCRIPTION

[0079] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0080] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0081] Example 1: Excavation working face of lane 2-106 in a mine

[0082] like Figure 1-3 As shown, the present invention provides a method for the treatment of advanced steel drill support and negative pressure guided grouting reinforcement of soft rock roof, and the specific method is carried out according to the following steps:

[0083] Step Ⅰ: Go to the site to collect tunnel excavation operation procedures and support cross-section diagrams, mining engineering plan diagrams, surrounding drilling columnar diagrams, geological reports, preliminary mine design instructions, etc. According to the collected mine data, the No. 2 solid coal seam has an average thickness of 3.97 meters, with 0.3 meters of mudstone in the middle of the coal seam, the thickness of the upper mudstone coal seam is 2.17 meters, and the thickness of the lower mudstone coal seam is 0.74 meters. The basic roof of the No. 2 coal is mudstone with an average thickness of 0.7 meters, the direct roof is sandy mudstone with an average thickness of 5.2 meters, and the old roof is siltstone with medium stability and a thickness of 6.8 meters.

[0084] Step II: According to the cross-section excavation dimensions of 4.7m wide and 3.15m high, the internal friction angle of the roof is 31°, cohesion is 2.9MPa, burial depth is 100m, steel drill strength is 460MPa, mining influence coefficient is 3, L s Take 1m, take grouting radius as 0.8m, and calculate to use 2.5m steel chisel. According to the calculation, 15 steel chisels are used, the spacing is determined to be 300mm, and the steel chisels are driven in at an external insertion angle of 19°.

[0085] Step III: The leading steel drill uses a Φ33mm hollow steel drill with a length of 2.5m. First, 15 steel drill holes with a spacing of 300mm are drilled (and the site is inspected to determine whether grouting is required), and then the steel drill is driven into the steel drill hole with an exposed length of 200mm. The leading steel drills near the two sides are offset 4° outward along the tunnel direction.

[0086] Step IV: First, drill two steel pipe holes horizontally on the front scaffolding and the front side of the tunnel, and insert a 1-meter Φ90mm steel pipe and 0.8-meter one.

[0087] Step V: First, the first steel bar is used as a grouting steel bar for grouting, and the second steel bar is used as a negative pressure steel bar to provide negative pressure. First, slurry is injected into the grouting steel bar, and when the grouting pressure reaches the first grouting pressure, a pressure difference is created between the negative pressure steel bar and the grouting steel bar to guide the flow of slurry in the roof cracks.

[0088] Step VI: When slurry seeps out of the negative pressure steel drill, stop the negative pressure and seal the negative pressure steel drill with a cork to prevent the slurry from leaking out. Continue to inject slurry until the grouting pressure reaches the second preset pressure, stop grouting, and seal the first steel drill.

[0089] Step VII: Use the second negative pressure steel bar as the grouting steel bar, and the third steel bar as the negative pressure steel bar, take out the cork, and repeat the above operation. In this way, the grouting and negative pressure operations are performed alternately until the last steel bar completes the grouting.

[0090] Step VIII: By drilling holes on the tunnel roof after excavation, it was found that the cracks had been effectively filled, the roof was stable during excavation, and the excavation speed increased by 25% compared to no measures taken.

[0091] Example 2: Excavation working face of 1201 lane in a mine

[0092] As shown in the figure, the present invention provides a method for the treatment of advanced steel drill support and negative pressure guided grouting reinforcement of soft rock roof, and the specific method is carried out according to the following steps:

[0093] Step Ⅰ: Go to the site to collect tunnel excavation operation procedures and support cross-section diagrams, mining engineering plan, surrounding drilling column diagrams, geological reports, preliminary mine design instructions, etc. According to the collected mine data, it can be seen that the roof is mostly mudstone and sandy mudstone, the coal seam thickness is 0 to 13.04m, with an average of 4.41m, the bottom plate is mudstone, the coal seam contains 0 to 4 layers of interbedded gangue, and the structure is simple.

[0094] Step II: According to the cross-section excavation dimensions of 4.7m wide and 3.55m high, the internal friction angle of the roof is 38°, cohesion is 9.29MPa, burial depth is 450m, steel drill strength is 460MPa, mining influence coefficient is 2, L s Take 0.6m, take grouting radius as 0.8m, and calculate to use 3.4m steel chisel. According to the calculation, 10 steel chisels are used, the spacing is determined to be 500mm, and the steel chisels are driven in at an external insertion angle of 14°.

[0095] Step III: The leading steel drill uses a Φ33mm hollow steel drill with a length of 3.4m. First, 10 steel drill holes with a spacing of 500mm are drilled (and the site is inspected to determine whether grouting is required), and then the steel drill is driven into the steel drill hole with an exposed length of 200mm. The leading steel drills near the two gangs are offset 4° outward along the tunnel direction.

[0096] Step IV: First, drill two horizontal holes for steel pipes on the front scaffolding and one side of the tunnel, and insert a 1-meter Φ90mm steel pipe and a 0.8-meter one.

[0097] Step V: First, the first steel bar is used as a grouting steel bar for grouting, and the second steel bar is used as a negative pressure steel bar to provide negative pressure. First, slurry is injected into the grouting steel bar, and when the grouting pressure reaches the first grouting pressure, a pressure difference is created between the negative pressure steel bar and the grouting steel bar to guide the flow of slurry in the roof cracks.

[0098] Step VI: When slurry seeps out of the negative pressure steel drill, stop the negative pressure and seal the negative pressure steel drill with a cork to prevent the slurry from leaking out. Continue to inject slurry until the grouting pressure reaches the second preset pressure, stop grouting, and seal the first steel drill.

[0099] Step VII: Use the second negative pressure steel bar as the grouting steel bar, and the third steel bar as the negative pressure steel bar, take out the cork, and repeat the above operation. In this way, the grouting and negative pressure operations are performed alternately until the last steel bar completes the grouting.

[0100] Step VIII: By drilling holes on the tunnel roof after excavation, it was found that the cracks had been effectively filled, the roof was stable during excavation, and the excavation speed increased by 28% compared to no measures taken.

[0101] The above embodiments are preferred implementation modes of the present invention and are only used to facilitate the description of the present invention. They are not intended to limit the present invention in any form. Any person with ordinary knowledge in the relevant technical field, if they do not depart from the scope of the technical features of the present invention, can make equivalent embodiments by partial changes or modifications to the technical contents disclosed in the present invention, and they still fall within the scope of the technical features of the present invention without departing from the technical features of the present invention.

Claims

1. A method for the treatment of advanced steel drill support and negative pressure guided grouting reinforcement of soft rock roof, characterized in that: The steps include: S1, before excavation, n steel drills are driven into the tunnel head, the steel drills play the role of leading anchor rods and form a supporting beam effect; n steel drills are arranged in a row, and n steel drills are hollow steel drills; n is a natural number greater than or equal to 2; S2, n steel chisels are numbered 1, 2, 3, ..., n in sequence; S2-1, the first steel drill is used as a grouting hole connected to the grouting system, and the second steel drill is used as a negative pressure hole connected to the negative pressure system; then, the grouting system is started, and the grout is pressed into the rock mass fractures through the first steel drill; Then, after the grouting pressure reaches the first preset pressure, the negative pressure system is started to form a pressure difference between the grouting hole and the negative pressure hole; then, after slurry seeps out of the second steel drill, the negative pressure system stops working, the negative pressure system is disconnected from the second steel drill and the port of the second steel drill is closed; then, after the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the first steel drill and the port of the first steel drill is closed; …… S2-m, the mth steel drill is used as a grouting hole connected to the grouting system, and the m+1th steel drill is used as a negative pressure hole connected to the negative pressure system; then, the grouting system is started, and the grout is pressed into the rock mass fractures through the mth steel drill; Then, after the grouting pressure reaches the first preset pressure, the negative pressure system is started to form a pressure difference between the grouting hole and the negative pressure hole; then, after slurry seeps out of the m+1th steel drill, the negative pressure system stops working, the negative pressure system is disconnected from the m+1th steel drill, and the port of the m+1th steel drill is closed; then, after the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the mth steel drill, and the port of the mth steel drill is closed; …… S2-n-1, the n-1th steel drill is used as a grouting hole connected to the grouting system, and the nth steel drill is used as a negative pressure hole connected to the negative pressure system; then, the grouting system is started, and the grout is pressed into the rock mass fractures through the n-1th steel drill; Then, after the grouting pressure reaches the first preset pressure, the negative pressure system is started to form a pressure difference between the grouting hole and the negative pressure hole; then, after slurry seeps out of the nth steel drill, the negative pressure system stops working, the negative pressure system is disconnected from the nth steel drill and the port of the nth steel drill is closed; then, after the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the n-1th steel drill and the port of the n-1th steel drill is closed; S2-n, the nth steel bar is connected to the grouting system as a grouting hole; then, the grouting system is started, and the grouting pressure is pressed into the rock cracks through the nth steel bar. After the grouting pressure reaches the second preset pressure, the grouting pressure stops working, the grouting system is disconnected from the nth steel bar and the port of the nth steel bar is closed.

2. The method for treating soft rock roof with advanced steel drill support and negative pressure guided grouting reinforcement according to claim 1 is characterized in that: Step S1 also includes: S1-1, collect engineering geological data of the excavation working face; S1-2, design the length, spacing and external insertion angle of the steel chisel; S1-3, before tunnel excavation, a number of steel drill holes are drilled in advance in front of the excavation working face along a certain angle using a drill rod, and the steel drills are driven into the corresponding steel drill holes.

3. The method for treating soft rock roof with advanced steel drill support and negative pressure guided grouting reinforcement according to claim 2 is characterized in that: The method for determining the steel drill length L in S1-2 is as follows: Among them, λ is the mining influence coefficient, ranging from 1 to 3; K is the safety factor, which is 2; a is the half span of the tunnel; H is the tunnel burial depth; C is the cohesion; p is the steel drill strength; is the internal friction angle of rock; L s Indicates the length of the steel drill embedded in the stable surrounding rock.

4. The method for treating soft rock roof with advanced steel drill support and negative pressure guided grouting reinforcement according to claim 3 is characterized in that: The method for determining the external insertion angle β of the steel drill in S1-2 is as follows: β=arcsin(r / L) Where r is the grouting radius.

5. The method for treating soft rock roof with advanced steel drill support and negative pressure guided grouting reinforcement according to claim 3 is characterized in that: The spacing of the steel chisels in step S1-2 ranges from 300 mm to 500 mm.

6. The method for treating soft rock roof with advanced steel drill support and negative pressure guided grouting reinforcement according to claim 2 is characterized in that: The engineering geological data of the excavation working face include: excavation working face design documents and geological survey reports.

7. The method for treating soft rock roof with advanced steel drill support and negative pressure guided grouting reinforcement according to claim 2 is characterized in that: The method for sealing the end of the steel chisel is to place a cork at the end of the steel chisel.

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