A device and method for monitoring the pressure of roof fall at a tunnel excavation face

Abstract

The device for monitoring the pressure of tunnel arch collapse at the working face of this invention is characterized by comprising an anchor head, steel strands, a steel arch frame, and a pressure gauge. The anchor head is located at the front end of a hole drilled at the working face for installing a pre-guide pipe. The front end of the steel strand is fixedly connected to the anchor head, and the rear end of the steel strand passes through a steel pipe and is fixed to the pressure gauge. A bearing mechanism is provided on the steel strand between the anchor head and the steel pipe, and the anchor head is opened to be fixed in the hole. The monitoring method of this invention includes: a) drilling at the working face; b) inserting the monitoring device; c) opening and fixing the anchor head; d) connecting the steel strands; e) monitoring the rock mass condition; and f) acquiring the pressure in the bearing zone. The device and method for monitoring the pressure of tunnel arch collapse at the working face of this invention allow for the selection of different forms of overall support based on the pressure gauge reading. If the pressure gauge reading gradually increases, the overall support can be strengthened, such as by reducing the spacing of the steel arch frames and / or increasing the number of anchor bolts (cables).

Description

Technical Field

[0001] This invention relates to an apparatus and method for monitoring the pressure of a tunnel arch collapse, and more specifically, to an apparatus and method for monitoring the pressure of a tunnel arch collapse at the tunnel excavation face. Background Technology

[0002] During tunnel excavation, especially in layered rock masses, the disturbance caused by excavation can lead to stress concentration in the surrounding rock, potentially resulting in rockfalls and collapses at the tunnel arch. This poses a significant threat to subsequent tunnel construction and the safety of on-site workers. Currently, there are no relevant monitoring methods for this situation in tunnel construction, preventing on-site personnel from assessing the extent of damage to the tunnel arch rock after excavation. Consequently, appropriate protective measures cannot be taken in a timely manner, thus impacting the tunnel construction progress. For example, patent document CN112832818A discloses an invention patent entitled "A Tunnel Arch Top Risk Relief Device and Method After Blasting Construction". The technical solution it adopts is to inject concrete grout into the area of ​​the arch top where danger occurs in a timely manner after blasting construction at the working face to relieve the danger. It can only discover the danger while construction is underway and relieve the danger at the same time as it is discovered. It cannot monitor the risk of roof collapse in real time before the initial support, which can easily lead to unnecessary damage due to untimely detection. Another example is patent document CN108442946A, which discloses a "Tunnel Secondary Lining Arch Top and Sidewall Sealing and Curing Device and Method". It is an improvement solution proposed to address the quality problems of inadequate existing concrete curing measures, such as weak lining concrete, surface cracking, peeling and falling off. It also does not have the function of monitoring the risk of falling off or roof collapse in the tunnel arch.

[0003] Therefore, relevant monitoring methods are urgently needed during the tunnel surrounding rock excavation process to address the problem of arch collapse caused by tunnel excavation. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned technical problems, the present invention provides a device and method for monitoring the pressure of the arch collapse at the tunnel excavation face.

[0005] The device for monitoring the pressure of falling blocks on the tunnel arch face of the present invention is characterized by comprising an anchor head, a steel strand, a steel arch frame, and a pressure gauge. The steel arch frame is located inside the tunnel near the tunnel face, and a steel pipe with its front end extending into the tunnel face is fixed on the steel arch frame. The pressure gauge is fixed to the rear end of the steel pipe. The anchor head is located at the front end of a hole opened on the tunnel face for setting up a guide pipe. The front end of the steel strand is fixedly connected to the anchor head, and the rear end of the steel strand passes through the steel pipe and is fixed to the pressure gauge. A bearing mechanism is provided on the steel strand between the anchor head and the steel pipe. The bearing mechanism is used to support the falling blocks on the tunnel arch. The anchor head opens under the tension of the steel strand to be fixed in the hole opened on the tunnel face. The pressure gauge is used to detect the change in tension on the steel strand and output the change in tension signal through a signal line.

[0006] The present invention relates to a device for monitoring the pressure of roof collapse at a tunnel excavation face. The anchor head consists of an inner cylinder, an annular outer sleeve, a barrier ring, and multiple anchor rods. The annular outer sleeve is fitted onto the inner cylinder and can move along the length of the inner cylinder. Multiple forward-inclined double-forked rods are uniformly fixed on the annular outer sleeve. The rear end of the inner cylinder is fixedly connected to the front end of a steel strand. Multiple fixed steel plates are fixed on the outer surface of the front end of the inner cylinder. The front end of the anchor rod is hinged to the fixed steel plates via a first hinge bolt. The anchor rod is hinged to the double-forked rods via a second hinge bolt near the first hinge bolt. The barrier ring is fixed to the outer periphery of the inner cylinder at the front end of the annular outer sleeve and is used to limit the maximum opening angle of the anchor rod.

[0007] The present invention relates to a device for monitoring the pressure of roof collapse at the tunnel excavation face. The bearing mechanism consists of two rear bearing rods, two front bearing rods, connecting steel plates, and several springs. The two rear bearing rods and two front bearing rods are located on both sides of a steel strand, and both rear and front bearing rods are connected to the steel strand via multiple springs. The ends of the two rear and front bearing rods are hinged together by a third hinge bolt passing through the two connecting steel plates. The two connecting steel plates hinged at the rear ends of the two rear bearing rods are fixed to the steel strand. The steel strand passes between the two connecting steel plates hinged at the front ends of the two front bearing rods, and the two connecting steel plates hinged at the front ends of the two front bearing rods can slide along the length of the steel strand.

[0008] The device for monitoring the pressure of the arch collapse at the tunnel excavation face of the present invention includes a retaining ring fitted around the two rear bearing rods. After the retaining ring is fitted around the two rear bearing rods, it is used to keep the two rear bearing rods and the two front bearing rods in a state of close contact with the steel strands.

[0009] The present invention relates to a device for monitoring the pressure of the arch collapse at the tunnel excavation face. A steel pad is fixed at the rear end of the steel pipe, a pressure gauge is located on the outer surface of the steel pad, and an anchor is fixed in the center of the pressure gauge. Multiple clamps are provided in the anchor, and a steel strand passes through the cavity formed between the multiple clamps. The multiple clamps clamp and fix the steel strand.

[0010] The monitoring method of the device for monitoring the pressure of the tunnel excavation face arch collapse according to the present invention is characterized by being implemented through the following steps:

[0011] a) Drilling holes at the tunnel face; Before excavation of the tunnel face, a certain number of holes are drilled on the steel arch frame through steel pipes according to the specific construction conditions of the tunnel site. The drilled holes are used to install advanced guide pipes. Among them, some holes near the tunnel arch are used to place the monitoring device of the present invention. The drilling direction of the holes for placing the monitoring device of the present invention is horizontal and forward to ensure that the monitoring device is exposed after the tunnel is excavated.

[0012] b) Insertion of monitoring device; Insert the anchor head and steel strand into the hole near the arch on the tunnel face through the steel pipe. At this time, the bearing mechanism is in a closed state under the restriction of the retaining ring, and the rear bearing rod, front bearing rod and spring are in a contracted state. When the bearing mechanism is basically in the hole, the retaining ring is slowly removed manually. At this time, since the tunnel face has not yet been excavated, the surrounding soil inside the hole is relatively compact, and the rear bearing rod, front bearing rod and spring are not fully opened.

[0013] c) Opening and fixing of the anchor head; continue to extend the steel strand into the hole. When the steel strand reaches the appropriate position in the hole, pull it outward. Due to the relatively narrow hole itself and the limitation of the surrounding rock, the anchor head opens as the steel strand is pulled, allowing the anchor rod to insert into the surrounding soil and gradually remain stable, thereby completely fixing the front end of the monitoring device.

[0014] d) Connection of steel strand to pressure gauge; weld a steel pad to the end of the steel pipe, and pass the steel strand through the through hole on the steel pad and the through hole on the pressure gauge. At this time, the pressure gauge is located on the outside of the steel pad; then, pass the anchor with multiple clips onto the steel strand, and then pass the anchor into the through hole of the pressure gauge, thus fixing the end of the entire monitoring device. This completes the fixing of both ends of the monitoring device.

[0015] e) Monitoring of the rock mass condition at the arch crown after excavation; After the tunnel face is excavated, the integrity of the rock mass is damaged by the excavation process, and the rock mass around the hole becomes relatively loose. The rear bearing rod, front bearing rod, and spring are exposed on the free side of the surrounding rock, and the bearing mechanism gradually opens. The connecting steel plate near the anchor head slides on the steel strand, making the bearing mechanism form a rhomboid bearing monitoring area. If the rock mass at the tunnel arch crown moves slightly downward, it will put pressure on the bearing area, increasing the tension on the steel strand. The pressure value monitored by the pressure gauge will increase significantly. Based on the pressure gauge reading and the degree of deformation of the rock mass at the arch crown, different degrees of overall reinforcement support methods can be selected to support the arch crown. If the pressure gauge reading gradually increases, the overall support can be strengthened by reducing the spacing of the steel arch frames and / or increasing the number of anchor rods.

[0016] f) Obtaining the pressure in the bearing area: When a block falls from the roof onto the bearing mechanism, let the pressure exerted on the bearing area by the falling block be F1, and let the axial tension caused by the deformation of the steel strand be F2. Then, the tension value measured by the pressure gauge on the bearing mechanism is also F2. Calculate the pressure value σ1 on the bearing mechanism using the following formula:

[0017] The deformation of the steel strand can be expressed as:

[0018]

[0019] The angle between the steel strand and the horizontal direction is:

[0020]

[0021] The pressure caused by the collapse of the roof slab is:

[0022]

[0023] Therefore, the pressure value of the roof collapse is:

[0024]

[0025] in:

[0026] σ1 — Pressure caused by the collapse of the roof, in MPa;

[0027] F1 — Pressure caused by roof collapse, in N;

[0028] F2 — The tensile force on the steel strand, in N, measured by a pressure gauge.

[0029] k—Strength of the wire rope, in N / m;

[0030] Δl — Elongation of the steel strand at the load-bearing mechanism, in mm;

[0031] A – Area of ​​the bearing area, in m² 2 ;

[0032] α — The angle between the monitoring device and the horizontal direction, in degrees;

[0033] l — the length of the steel strand at the bearing mechanism, in mm.

[0034] The beneficial effects of this invention are as follows: The device and method for monitoring the pressure of the tunnel arch collapse at the working face of this invention are equipped with an anchor head, steel strand, steel arch frame, pressure gauge, and bearing mechanism. The front and rear ends of the steel strand are connected to the anchor head and the pressure gauge fixed on the steel arch frame, respectively. In use, the anchor head, steel strand, and bearing area are inserted into a hole opened on the working face near the arch. By pulling the steel strand backward, the anchor head is opened and fixed to the front end of the hole. Then, the rear end of the steel strand is fixedly connected to the pressure gauge. In this way, after the tunnel surrounding rock is excavated, the bearing area of ​​the device is opened. According to the pressure gauge reading and the degree of deformation observed, different forms of overall support can be selected. If the pressure gauge reading gradually increases, the overall support can be strengthened, such as by reducing the spacing of the steel arch frame and / or adding anchor rods (cables).

[0035] The device and method for monitoring the pressure of roof collapse at the tunnel excavation face of the present invention have the following advantages:

[0036] (1) Real-time monitoring. After the tunnel excavation is completed, the pressure gauge readings are observed in real time to determine whether the arch will collapse. Based on the pressure gauge readings and the deformation, different strengths of overall support are adopted to avoid unnecessary damage caused by the collapse of the arch after the tunnel excavation.

[0037] (2) Convenience. When using it, you only need to insert the anchor head and steel strand into the hole near the arch on the working face, then pull the steel strand to open the anchor head, and finally fix the entire monitoring device with the anchor and clamp. This can realize the prevention and monitoring of arch collapse. The operation steps are simple and it is very convenient to use.

[0038] (3) Low cost. The anchor head, steel strand and bearing mechanism are all made of steel, which is inexpensive to manufacture, simple to assemble and install, and some parts of the monitoring device can be recycled and reused after the excavation and support of the working face where the monitoring device of the present invention is located are completed, so the cost of use is low. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the device for monitoring the pressure of the tunnel excavation face arch collapse according to the present invention;

[0040] Figure 2 This is a schematic diagram of the anchor head structure in this invention;

[0041] Figure 3 This is a schematic diagram of the load-bearing mechanism in this invention;

[0042] Figure 4 This is a schematic diagram of the structure of the bearing mechanism in the closed state in this invention;

[0043] Figure 5This is a schematic diagram of the fixed connection between the pressure gauge and the steel strand in this invention;

[0044] Figure 6 This is a diagram showing the usage status of the monitoring device in this invention;

[0045] Figure 7 This is a schematic diagram of the force distribution on the load-bearing mechanism in this invention.

[0046] In the diagram: 1 Anchor head, 2 Steel strand, 3 Steel arch, 4 Pressure gauge, 5 Steel pipe, 6 Bearing mechanism, 7 Signal line, 8 Steel pad, 9 Inner cylinder, 10 Anchor bolt, 11 Annular outer sleeve, 12 Barrier ring, 13 Double fork rod, 14 Fixing steel plate, 15 First hinge bolt, 16 Second hinge bolt, 17 Rear bearing rod, 18 Front bearing rod, 19 Spring, 20 Connecting steel plate, 21 Third hinge bolt, 22 Clamping ring, 23 Anchor, 24 Clamping plate. Detailed Implementation

[0047] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0048] like Figure 1 The diagram shows a schematic of the device for monitoring the pressure of the tunnel arch collapse at the working face, according to the present invention. It consists of an anchor head 1, steel strands 2, a steel arch frame 3, a pressure gauge 4, and a supporting mechanism 6. A steel pipe 5 is fixed to the steel arch frame 3, and the pressure gauge 4 is fixed to the rear end of the steel pipe 5. To ensure the pressure gauge 4 is firmly fixed to the steel pipe 5, a steel pad 8 is fixed to the rear end of the steel pipe 5, and the pressure gauge 4 is fixed to the steel pad 8. The front end of the steel strand 2 is fixed to the anchor head 1, and the rear end of the steel strand 2 passes through the steel pipe 5 and is fixed to the pressure gauge 4. The supporting mechanism 6 is located on the steel strand 2 between the anchor head 1 and the steel pipe 5. In use, the anchor head 1, steel strand 2, and supporting mechanism 6 are inserted into the holes opened at the tunnel face for installing the advance guide pipe.

[0049] When the anchor head 1, steel strand 2, and bearing mechanism 6 are inserted into the hole near the tunnel arch on the tunnel face, the steel strand 2 pulls the anchor head 1 backward to open it, and the opened anchor head 1 is firmly fixed to the front end in the hole. The rear end of the steel strand 2 is fixed to the pressure gauge 4. As the tunnel face is continuously excavated, the bearing mechanism 6 opens to form a bearing area. During the continuous excavation of the tunnel face, when there is a rockfall or collapse at the tunnel arch, the falling rockfall lands on the bearing area, causing the pressure signal value output by the pressure gauge 4 to change. The change in the output value of the pressure gauge 4 is then used to monitor the rockfall and collapse at the tunnel arch during the tunnel excavation process.

[0050] like Figure 2 As shown, a schematic diagram of the anchor head structure in this invention is provided. To enable the anchor head 1 to open under the pull of the steel strand 2, the following design is employed... Figure 2The anchor head 1 shown is composed of an inner cylinder 9, an annular outer sleeve 11, a barrier ring 12, and four anchor rods 10. The rear end of the inner cylinder 9 is fixedly connected to the front end of the steel strand 2, such as by welding. The annular outer sleeve 11 is fitted around the outer perimeter of the inner cylinder 9 and can slide along the length of the inner cylinder 9. Four forward-inclined double fork rods 13 are evenly fixed on the outer surface of the annular outer sleeve 11. Four pairs of fixing steel plates 14 are evenly fixed on the outer surface of the front end of the inner cylinder 9. The front ends of the four anchor rods 10 are respectively hinged to the four pairs of fixing steel plates 14 by first hinge bolts 15. The four anchor rods 10 are hinged to the four double fork rods 13 by second hinge bolts 16 at positions near the first hinge bolts 15.

[0051] Thus, when the annular sleeve 11 moves to the rear end of the inner cylinder 9, it pulls the anchor rods 10 together. When the annular sleeve 11 moves to the front end of the inner cylinder 9, the four anchor rods are opened under the support of the double fork rods 13. To limit the opening angle of the anchor rods 10, the barrier ring 12 is fixed to the inner cylinder 9 in front of the annular sleeve 11. For example, the barrier ring 12 can limit the maximum opening angle of the anchor rods 10 to 45°. In use, when the anchor head 1 is inserted into the hole, the anchor rods 10 are in a converged state. When the inner cylinder 9 of the steel strand 2 is pulled, the anchor rods 10 open and insert into the soil or rock around the hole, thus achieving a firm fixation of the anchor head 1 in the hole.

[0052] like Figure 3 The diagram shows a schematic of the bearing mechanism in this invention. The bearing mechanism 6 consists of two rear bearing rods 17, two front bearing rods 18, several springs 19, retaining rings 22, and four sets of connecting steel plates 20. The two rear bearing rods 17 and two front bearing rods 18 are located on both sides of the steel strand 2, and are fixedly connected to the steel strand 2 by multiple springs 19. Each set of four connecting steel plates 20 consists of two parallel connecting steel plates arranged vertically. The two rear bearing rods 17 and two front bearing rods 18 are hinged end-to-end by a third hinge bolt 16 hinged to the connecting steel plates 20. The two connecting steel plates 20 hinged at the rear ends of the two rear bearing rods 17 (i.e., the end closest to the steel pipe 5) are welded to the steel strand 2. The steel strand 2 passes between the two connecting steel plates 20 hinged at the front ends of the two front bearing rods 18, allowing the two front bearing rods 18 to slide on the steel strand 2.

[0053] like Figure 5The diagram shows a fixed connection between the pressure gauge and the steel strand in this invention. A steel pad 8 is fixed to the rear end of the steel pipe 5. The pressure gauge 4 is located on the outer side of the steel pad 8. An anchor 23 is fixed in the center of the pressure gauge 4. Multiple clamping pieces 24 are provided in the anchor 23. The steel strand 2 passes through the cavity formed between the multiple clamping pieces 24. The multiple clamping pieces 24 clamp and fix the steel strand 2, thus achieving a fixed connection between the steel strand 2 and the pressure gauge 4, so that the pressure gauge 4 can measure the tensile force on the steel strand 2.

[0054] When the bearing mechanism 6 is in the closed position, the retaining ring 22 is fitted around the outer periphery of the rear ends of the two rear bearing rods 17. This facilitates the insertion of the bearing mechanism 6, the steel strand 2, and the anchor head 1 together into the hole near the arch on the working face. Figure 4 As shown, a structural schematic diagram of the bearing mechanism in the present invention when it is in the closed state is given, as follows. Figure 6 The diagram shows the usage state of the monitoring device in this invention. After being inserted into place, the retaining ring 22 is removed. As the excavation face further develops, the compressed spring 19 supports the two rear support rods 17 and the two front support rods 18, which gradually unfold outwards. The unfolded rear support rods 17 and the two front support rods 18 form a support area for supporting the falling blocks. When the lengths of the two rear support rods 17 and the two front support rods 18 are equal, the support area formed by the unfolded support mechanism 6 is rhomboid.

[0055] The monitoring method of the device for monitoring the pressure of the tunnel excavation face arch collapse according to the present invention is achieved through the following steps:

[0056] a) Drilling holes at the tunnel face; Before excavation of the tunnel face, a certain number of holes are drilled on the steel arch frame 3 through steel pipes 5 according to the specific construction conditions of the tunnel site. The drilled holes are used to install advanced guide pipes. Among them, some holes near the tunnel arch are used to place the monitoring device of the present invention. The drilling direction of the holes for placing the monitoring device of the present invention is horizontal and forward to ensure that the monitoring device is exposed after the tunnel is excavated.

[0057] b) Insertion of the monitoring device; the anchor head 1 and the steel strand 2 are inserted into the hole near the arch on the tunnel face through the steel pipe 5. At this time, the bearing mechanism 6 is in a closed state under the restriction of the retaining ring 22, and the rear bearing rod 17, the front bearing rod 18 and the spring 19 are in a contracted state. When the bearing mechanism 6 is basically in the hole, the retaining ring 22 is slowly removed manually. At this time, since the tunnel face has not yet been excavated, the surrounding soil inside the hole is relatively compact, and the rear bearing rod 17, the front bearing rod 18 and the spring 19 are not fully opened.

[0058] c) Opening and fixing of the anchor head; continue to extend the steel strand 2 into the hole. When the steel strand 2 is in the appropriate position in the hole, pull it outward. Due to the narrowness of the hole itself and the limitation of the surrounding rock, the anchor head 1 opens with the pulling of the steel strand 2, so that the anchor rod is inserted into the surrounding soil and gradually stabilized, thereby completely fixing the front end of the monitoring device.

[0059] d). Connection between steel strand and pressure gauge; weld steel pad 8 to the end of steel pipe 5, and pass steel strand (2) through the through hole on the steel pad and the through hole on pressure gauge 4. At this time, pressure gauge 4 is located outside the steel pad; then, insert anchor 23 with multiple clips 24 onto steel strand 2, and then insert the anchor into the through hole of pressure gauge, thus fixing the end of the entire monitoring device. This achieves the fixing of both ends of the monitoring device.

[0060] e) Monitoring of the rock mass condition at the arch crown after excavation; After the tunnel face is excavated, the integrity of the rock mass is damaged by the excavation process, and the rock mass around the hole becomes relatively loose. The rear bearing rod, front bearing rod, and spring are exposed on the free side of the surrounding rock, and the bearing mechanism gradually opens. The connecting steel plate near the anchor head slides on the steel strand, making the bearing mechanism form a rhomboid bearing monitoring area. If the rock mass at the tunnel arch crown moves slightly downward, it will put pressure on the bearing area, increasing the tension on the steel strand. The pressure value monitored by the pressure gauge will increase significantly. Based on the pressure gauge reading and the degree of deformation of the rock mass at the arch crown, different degrees of overall reinforcement support methods can be selected to support the arch crown. If the pressure gauge reading gradually increases, the overall support can be strengthened by reducing the spacing of the steel arch frames and / or increasing the number of anchor rods.

[0061] f) Obtaining the pressure in the bearing area: When a block falls from the roof onto the bearing mechanism, let the pressure exerted on the bearing area by the falling block be F1, and let the axial tensile force caused by the deformation of the steel strand be F2. Then, the tensile force measured by the pressure gauge on the bearing mechanism is also F2. Figure 7 The diagram shows the force distribution of the bearing mechanism in this invention. The pressure value σ1 on the bearing mechanism is calculated using the following formula:

[0062] The deformation of the steel strand can be expressed as:

[0063]

[0064] The angle between the steel strand and the horizontal direction is:

[0065]

[0066] The pressure caused by the collapse of the roof slab is:

[0067]

[0068] Therefore, the pressure value of the roof collapse is:

[0069]

[0070] in:

[0071] σ1 — Pressure caused by the collapse of the roof, in MPa;

[0072] F1 — Pressure caused by roof collapse, in N;

[0073] F2 — The tensile force on the steel strand, in N, measured by a pressure gauge.

[0074] k—Strength of the wire rope, in N / m;

[0075] Δl — Elongation of the steel strand at the load-bearing mechanism, in mm;

[0076] A – Area of ​​the bearing area, in m² 2 ;

[0077] α — The angle between the monitoring device and the horizontal direction, in degrees;

[0078] l — the length of the steel strand at the bearing mechanism, in mm.

[0079] As can be seen, the device for monitoring the pressure of tunnel arch collapse at the working face of the present invention has the following characteristics:

[0080] 1. The monitoring device proposed in this invention is easy to manufacture, and the connection method of the detailed structure of the monitoring device can all be welding, which is low in cost and simple to operate.

[0081] 2. In order to ensure the safety of the tunnel excavation process, it is necessary to install advance guide pipes (small guide pipes) on the tunnel face in advance, which provides convenience for the installation of the monitoring device designed in this invention.

[0082] 3. The present invention fixes the front end of the device with an anchor head and the end of the device with an anchor and a clamp, which makes the monitoring device more stable and the disturbance generated during the excavation process is less likely to damage the device.

[0083] 4. By using the pressure sensor readings and the above-described derivation formula, this invention can accurately calculate the stress of the collapse block on the bearing mechanism, providing a basis for selecting the overall support strength.

Claims

1. A device for monitoring the pressure of roof collapse at a tunnel excavation face, characterized in that: The system includes an anchor head (1), a steel strand (2), a steel arch frame (3), and a pressure gauge (4). The steel arch frame is located inside the tunnel near the tunnel face. A steel pipe (5) with its front end extending into the tunnel face is fixed on the steel arch frame. The pressure gauge is fixed to the rear end of the steel pipe. The anchor head is located at the front end of a hole on the tunnel face where a pre-conduit pipe is installed. The front end of the steel strand is fixedly connected to the anchor head. The rear end of the steel strand passes through the steel pipe (5) and is fixed to the pressure gauge. A bearing mechanism (6) is installed on the steel strand between the anchor head and the steel pipe. The bearing mechanism is used to support the falling blocks on the tunnel arch. The anchor head opens under the tension of the steel strand to be fixed in the hole on the tunnel face. The pressure gauge is used to detect the change in tension on the steel strand and output the change in tension signal through the signal line (7). The anchor head (1) is composed of an inner cylinder (9), an annular outer sleeve (11), a barrier ring (12) and multiple anchor rods (10). The annular outer sleeve (11) is fitted onto the inner cylinder and can move along the length of the inner cylinder. Multiple forward-inclined double fork rods (13) are evenly fixed on the annular outer sleeve. The rear end of the inner cylinder is fixedly connected to the front end of the steel strand. Multiple fixed steel plates (14) are fixed on the outer surface of the front end of the inner cylinder. The front end of the anchor rod is hinged to the fixed steel plate by a first hinge bolt (15). The anchor rod is hinged to the double fork rod (13) by a second hinge bolt near the position of the first hinge bolt. The barrier ring is fixed to the outer periphery of the inner cylinder at the front end of the annular outer sleeve. The barrier ring is used to limit the maximum opening angle of the anchor rod. The bearing mechanism (6) consists of two rear bearing rods (17), two front bearing rods (18), connecting steel plates (20), and several springs (19). The two rear bearing rods and two front bearing rods are located on both sides of the steel strand (2). The two rear bearing rods and two front bearing rods are connected to the steel strand through multiple springs. The ends of the two rear bearing rods and two front bearing rods are hinged together by a third hinge bolt (21) that passes through the two connecting steel plates. The two connecting steel plates hinged at the rear ends of the two rear bearing rods are fixed to the steel strand. The steel strand passes between the two connecting steel plates hinged at the front ends of the two front bearing rods (18), and the two connecting steel plates hinged at the front ends of the two front bearing rods can slide along the length of the steel strand.

2. The device for monitoring the pressure of roof collapse at the tunnel excavation face according to claim 1, characterized in that: Includes a retaining ring (22) that is fitted around the two rear bearing rods (17). After the retaining ring is fitted around the two rear bearing rods, it is used to keep the two rear bearing rods and the two front bearing rods in a state close to the steel strand (2).

3. The device for monitoring the pressure of tunnel arch collapse according to claim 1 or 2, characterized in that: The steel pipe (5) is fixed with a steel pad (8) at its rear end. The pressure gauge is located on the outer side of the steel pad. An anchor (23) is fixed in the center of the pressure gauge (4). Multiple clamps (24) are provided in the anchor. The steel strand (2) passes through the cavity formed between the multiple clamps. The multiple clamps clamp and fix the steel strand.

4. A monitoring method based on the device for monitoring the pressure of roof collapse at a tunnel excavation face as described in claim 1, characterized in that, This can be achieved through the following steps: a). Drilling holes at the tunnel face; Before the tunnel face is excavated, a certain number of holes are drilled on the steel arch frame (3) through steel pipe (5) according to the specific construction conditions of the tunnel site. The holes are used to set up the advanced guide pipe. Among them, some holes near the tunnel arch are used to place the monitoring device of the present invention. The drilling direction of the holes for placing the monitoring device of the present invention is horizontal and forward to ensure that the monitoring device is exposed after the tunnel is excavated. b). Insertion of monitoring device; Insert the anchor head (1) and steel strand (2) into the hole near the arch on the tunnel face through the steel pipe (5). At this time, the bearing mechanism (6) is in a closed state under the restriction of the retaining ring (22), and the rear bearing rod (17), the front bearing rod (18) and the spring (19) are in a contracted state. When the bearing mechanism (6) is basically in the hole, the retaining ring (22) is slowly removed manually. At this time, since the tunnel face has not yet been excavated, the surrounding soil inside the hole is relatively compact, and the rear bearing rod (17), the front bearing rod (18) and the spring (19) are not fully opened. c). Opening and fixing of the anchor head; continue to extend the steel strand (2) into the hole. When the steel strand (2) is in the appropriate position in the hole, pull it outward. Due to the narrowness of the hole itself and the limitation of the surrounding rock, the anchor head (1) opens with the pulling of the steel strand (2) so that the anchor rod is inserted into the surrounding soil and gradually stabilized, thereby completely fixing the front end of the monitoring device. d). Connection between steel strand and pressure gauge; weld steel pad (8) to the end of steel pipe (5), pass steel strand (2) through the through hole on steel pad and through the through hole on pressure gauge (4), at which time pressure gauge (4) is located outside steel pad; then, pass anchor (23) with multiple clips (24) onto steel strand, then pass anchor into through hole of pressure gauge, and finally firmly anchor steel strand on steel strand, that is, fix the end of the entire monitoring device, thus realizing the fixation of both ends of monitoring device; e) Monitoring of the rock mass condition at the arch crown after excavation; After the tunnel face is excavated, the integrity of the rock mass is damaged by the excavation process, and the rock mass around the hole becomes relatively loose. The rear bearing rod, front bearing rod, and spring are exposed on the free side of the surrounding rock, and the bearing mechanism gradually opens. The connecting steel plate near the anchor head slides on the steel strand, making the bearing mechanism form a rhomboid bearing monitoring area. If the rock mass at the tunnel arch crown moves slightly downward, it will put pressure on the bearing area, increasing the tension on the steel strand. The pressure value monitored by the pressure gauge will increase significantly. Based on the pressure gauge reading and the degree of deformation of the rock mass at the arch crown, different degrees of overall reinforcement support methods can be selected to support the arch crown. If the pressure gauge reading gradually increases, the overall support can be strengthened by reducing the spacing of the steel arch frames and / or increasing the number of anchor rods. f) Obtaining the pressure in the bearing area: When a block falls from the roof onto the bearing mechanism, let the pressure exerted on the bearing area by the falling block be F1, and let the axial tension caused by the deformation of the steel strand be F2. Then, the tension value measured by the pressure gauge on the bearing mechanism is also F2. Calculate the pressure value on the bearing mechanism using the following formula. : The deformation of the steel strand can be expressed as: The deformation of the steel strand can be expressed as: ; The angle between the steel strand and the horizontal direction is: ; The pressure caused by the collapse of the roof slab is: ; Therefore, the pressure value of the roof collapse is: ; in: —Pressure caused by roof collapse, in MPa; F1 — Pressure caused by roof collapse, in N; F2 — The tensile force on the steel strand, in N, measured by a pressure gauge. k—Strength of the wire rope, in N / m; —Elongation of the steel strand at the load-bearing mechanism, in mm; A – Area of ​​the bearing area, in m² 2 ; —The angle between the monitoring device and the horizontal direction, in degrees; — This refers to the length of the steel strand at the load-bearing mechanism, in mm.

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