A mine electrical high-altitude detection device and use method

Abstract

The invention discloses a mine electrical high-altitude detection device and a use method, comprising a plurality of high-altitude detection rods, an on-site host, and a measuring cable. The top ends of the high-altitude detection rods are tightly pressed against electrical detection points on the side walls or roof of a tunnel. The high-altitude detection rods are connected to the on-site host through the measuring cables. The high-altitude detection rods comprise a detection end, a head end, a connecting rod, a tail end, and a conductive liquid filling mechanism. The detection end comprises a sponge sleeve and a copper electrode. The sponge sleeve is sleeved on the top end of the copper electrode. The end of the copper electrode is threadedly connected to the head end. The insides of the head end, the connecting rod, and the tail end are interconnected and fixed in turn through the matching connection of a lock buckle and a lock buckle hole. The number of connecting rods can be selected according to the height of the tunnel. The copper electrode is threadedly connected to a copper base through an inner screw hole, and the copper base is connected to the measuring cable. The invention can reduce the danger of high-altitude operations, improve the efficiency of exploration and construction, and at the same time ensure good coupling contact between the electrode and the rock mass, thereby ensuring high efficiency and accuracy of mine electrical high-altitude detection.

Description

Technical Field

[0001] The invention relates to the technical field of mine water hazard prevention and control, in particular to a mine electrical high-altitude detection device and a use method thereof. Background Art

[0002] Most coal mines in my country have complex hydrogeological conditions and frequent water disasters, and the situation of mine water disaster prevention and control is severe. In order to ensure the safe production of coal mines, the miners need to explore the water-bearing conditions of the coal and rock strata near the working face. After years of development, the existing hydrological detection technologies at home and abroad have mainly used mine electrical method and transient electromagnetic method for coal mine water disaster detection. Among them, mine electrical method has been widely used in two-dimensional exploration such as electrical depth sounding near mine tunnels due to its mature theory, flexible methods, simple instruments, strong anti-interference ability, and sensitivity to water, and has achieved good results.

[0003] However, at present, most of the electrical exploration in mines is limited to the detection of the bottom plate of the working face or tunnel, and there are many deficiencies in the high-altitude detection of the high side of the mine tunnel or the roof; 1. The rock mass at the high side of the tunnel or near the roof is generally hard and dry, and it is difficult to drive the electrode into the rock mass, making it difficult to arrange the electrode. The coupling contact between the electrode and the roof or side of the tunnel is poor, and it is difficult to ground. The collected data has large jumps, is extremely unstable, and has large deviations; 2. The detection point at the high side of the tunnel or near the roof is too high. The electrode arrangement requires construction personnel to use ladders and other tools to climb up to fix the electrode on the high side of the tunnel or the roof, and frequently go up and down the ladder as the measuring point moves. The construction is cumbersome and labor-intensive, which increases the danger of high-altitude operations and poses serious safety hazards. Summary of the invention

[0004] In order to overcome the above-mentioned shortcomings, the purpose of the present invention is to provide a mine electrical high-altitude detection device and a method of use.

[0005] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0006] A mine electrical high-altitude detection device is installed in a tunnel, comprising a plurality of high-altitude detection rods, an on-site host, and a measuring cable. The top of each high-altitude detection rod is pressed against an electrical detection point on a tunnel side or a tunnel roof. The plurality of high-altitude detection rods are connected to the on-site host through the measuring cable. The high-altitude detection rod comprises a detection end, a head end, a connecting rod, a tail end, and a conductive liquid filling mechanism. The detection end comprises a sponge sleeve and a copper electrode. The sponge sleeve is sleeved on the top of the copper electrode. The end of the copper electrode is threadedly connected to the head end. The head end, the connecting rod, and the tail end are internally connected and fixed in sequence by the matching connection of a lock buckle and a lock buckle hole. The number of connecting rods can be selected according to the height of the tunnel. A copper base is arranged in the head end, and an inner screw hole is arranged on the copper base. The copper electrode is threadedly connected to the copper base through the inner screw hole, and the copper base is connected to the measuring cable.

[0007] Further, the conductive liquid filling mechanism includes a conductive liquid bottle, an air bag, a head end push rod, an intermediate push rod, a tail end push rod and an anti-slip grip, the conductive liquid bottle, the air bag and the head end push rod are arranged inside the head end, the intermediate push rod is arranged inside the connecting rod, the tail end push rod is arranged inside the tail end, the head end push rod, the intermediate push rod and the tail end push rod are connected in sequence through a clamping hole and a clamping column, the head end push rod, the intermediate push rod and the tail end push rod are all made of copper, the anti-slip grip is fixed on the outer wall of the tail end and is used to drive the tail end push rod to move, and the head end push rod is provided with a head end cable connected to the copper base;

[0008] Furthermore, the conductive liquid bottle is provided with a liquid outlet pipe, a liquid adding pipe and an air guide pipe connected to the conductive liquid bottle, the liquid outlet pipe is used to add conductive liquid to the sponge sleeve, the liquid adding pipe is connected to the liquid adding port on the head end shell, and the air guide pipe is connected to the air bag;

[0009] Furthermore, the head end push rod is provided with a flat ring, a first push rod fixing plate and a first spring, the flat ring abuts against the airbag and is used to squeeze the airbag, and the first spring is sleeved between the flat ring and the first push rod fixing plate;

[0010] Further, the interior of the head end is provided with a plurality of fixing rings to divide the interior of the head end into a liquid bottle fixing part, an airbag fixing part and a first spring moving part, the head end push rod is clamped at the center of the plurality of fixing rings, the conductive liquid bottle is arranged in the liquid bottle fixing part, the airbag is arranged in the airbag fixing part, the first spring and the first push rod fixing sheet are located in the first spring moving part, and the outer diameter of the first push rod fixing sheet is larger than the inner diameter of the central through hole of the fixing ring;

[0011] Furthermore, the intermediate push rod is provided with a second spring and a second push rod fixing sheet, a plurality of fixing rings are provided inside the connecting rod, the intermediate push rod is clamped at the center of the plurality of fixing rings, a second spring moving part is formed between adjacent fixing rings, the second spring and the second push rod fixing sheet are located inside the second spring moving part, and the outer diameter of the second push rod fixing sheet is greater than the inner diameter of the central through hole of the fixing ring;

[0012] Further, a third spring and a third push rod fixing plate are arranged on the tail end push rod, a plurality of fixing rings are arranged inside the tail end, the tail end push rod is clamped at the center of the plurality of fixing rings, a third spring moving part is formed between adjacent fixing rings, the third spring and the third push rod fixing plate are located inside the third spring moving part, and the outer diameter of the third push rod fixing plate is greater than the inner diameter of the central through hole of the fixing ring;

[0013] Further, the anti-slip handle comprises a gripping portion and a pushing portion, a symmetrical pin hole is provided on the outer wall of the tail end, the anti-slip handle is rotatably connected to the tail end through the pin shaft and the pin hole, the gripping portion is located inside the tail end, and the pushing portion is located inside the tail end and abuts against the end of the tail end push rod;

[0014] Furthermore, a cable hole is provided on the outer wall of the tail end, an extension cable is provided in the cable hole, one end of the extension cable is connected to the tail end push rod, and the other end is connected to the measuring cable;

[0015] A method for using a mine electrical high-altitude detection device comprises the following steps:

[0016] S1: Place the on-site host in the detection tunnel, calibrate the detection point position according to the high-altitude electrical detection method, hold the copper electrode at the detection end against the high electrical detection point on the tunnel side or roof by holding the high-altitude detection rod, and connect the high-altitude detection rod and the on-site host with a measuring cable to form an electrical high-altitude single-channel detection device;

[0017] S2: Before detection, press the non-slip handle to push the rear push rod forward. The movement of the rear push rod drives the middle push rod and the head push rod to move forward. The flat ring block of the head push rod squeezes the air bag. The air bag pressurizes the conductive liquid bottle through the air guide tube, so that the conductive liquid in the conductive liquid bottle flows out from the liquid outlet pipe to soak the sponge sleeve and the copper electrode, thereby improving the coupling contact between the copper electrode and the lane wall or top plate and weakening the excitation polarization effect of the copper electrode.

[0018] S3: Specific measurement: Use single-channel electrical acquisition technology to power the power supply electrode at each sounding point or power supply point, and the corresponding measuring electrodes perform single-channel measurement in turn. When all the measuring points at this sounding point or power supply point are completed, similar observations are performed on the next sounding point or power supply point until all survey lines are detected;

[0019] S4: Extract the data collected by the on-site main engine electrical method, interpret the apparent resistivity detection results, and complete the exploration of the water-bearing properties of the coal and rock strata at the high side of the tunnel or near the roof.

[0020] Compared with the prior art, the mine electrical high-altitude detection device and the use method of the present invention have the following beneficial effects:

[0021] The high-altitude detection rod of the present invention is easy to operate. The operator does not need to work at heights, but only needs to stand in the tunnel to place the detection electrode on the designated detection point on the tunnel wall or roof through the high-altitude detection rod. The construction is flexible and convenient, which improves the construction efficiency while reducing the danger of high-altitude operations for personnel and eliminating safety hazards.

[0022] The sponge cover of the present invention is combined with a conductive liquid bottle. The conductive liquid is used to dip the sponge cover into the conductive liquid and wrap the front end of the copper electrode, thereby improving the coupling contact between the detection electrode and the rock mass, weakening the induced polarization effect of the copper electrode, and ensuring the stability and reliability of data collection during high-altitude electrical exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0024] Figure 1 It is a schematic diagram of the installation structure of the present invention;

[0025] Figure 2 It is a schematic diagram of the structure of the high-altitude detection rod of the present invention;

[0026] Figure 3 It is a schematic diagram of the three-dimensional structure of the detection end and the head end of the present invention;

[0027] Figure 4 is a cross-sectional view of the detection end and the head end of the present invention;

[0028] Figure 5 It is a schematic diagram of the three-dimensional structure of the connecting rod of the present invention;

[0029] Figure 6 is a cross-sectional view of a connecting rod of the present invention;

[0030] Figure 7 It is a schematic diagram of the three-dimensional structure of the tail end of the present invention;

[0031] Figure 8 is a cross-sectional view of the non-slip grip of the present invention in a normal state;

[0032] Fig. 9 is a cross-sectional view of the non-slip grip of the present invention in a holding state;

[0033] Fig.10 It is a flowchart of an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0035] like Figure 1-9A mine electrical high-altitude detection device shown is installed in a tunnel, including a plurality of high-altitude detection rods 5, a field host 7, and a measuring cable 6. The top of each high-altitude detection rod 5 is pressed against the electrical detection point of the tunnel side wall 2 or the tunnel roof 1. The plurality of high-altitude detection rods 5 are connected to the field host 7 through the measuring cable 6. The high-altitude detection rod 5 includes a detection end 8, a head end 9, a connecting rod 10, a tail end 11 and a conductive liquid filling mechanism. The detection end 8 includes a sponge sleeve 14 and a copper electrode 15. The sponge sleeve 14 is sleeved on the copper electrode The top of 15, the end of the copper electrode 15 is threadedly connected to the head end 9, the head end 9, the connecting rod 10, and the tail end 11 are internally connected, and are fixed in turn by pressing the lock buckle 29 and the lock buckle hole 12. The number of connecting rods 10 can be selected according to the height of the lane. A copper base 17 is provided in the head end 9, and an internal screw hole 171 is provided on the copper base 17. The copper electrode 15 is threadedly connected to the copper base 17 through the internal screw hole 171, and the copper base 17 is connected to the measuring cable 6.

[0036] refer to Figure 3-4 In this embodiment, the conductive liquid filling mechanism includes a conductive liquid bottle 19, an air bag 22, a head end push rod 25, an intermediate push rod 30, a tail end push rod 33 and an anti-slip grip 32. The conductive liquid bottle 19, the air bag 22 and the head end push rod 25 are arranged inside the head end 8, the intermediate push rod 30 is arranged inside the connecting rod 10, and the tail end push rod 33 is arranged inside the tail end 11. The head end push rod 25, the intermediate push rod 30 and the tail end push rod 33 are connected in sequence through the clamping hole 26 and the clamping column 31. The head end push rod 25, the intermediate push rod 30 and the tail end push rod 33 are all made of copper. The anti-slip grip 32 is fixed on the outer wall of the tail end 11 and is used to drive the tail end push rod 33 to move. The head end push rod 25 is provided with a head end cable 21 connected to the copper base 17.

[0037] In this embodiment, if Figure 3-4 As shown, the conductive liquid bottle 19 is provided with a liquid outlet pipe 16, a liquid adding pipe 18 and an air guide pipe 20 connected to the conductive liquid bottle 19, the liquid outlet pipe 16 is used to add conductive liquid to the sponge sleeve 14, the liquid adding pipe 18 is connected to the liquid adding port 13 on the head end 9, and the air guide pipe 20 is connected to the air bag 22.

[0038] like Figure 3-4 As shown, in this embodiment, a flat ring 251, a first push rod fixing plate 24 and a first spring 23 are provided on the head end push rod 25. The flat ring 251 is against the airbag 22 and is used to squeeze the airbag 22. The first spring 23 is sleeved between the flat ring 251 and the first push rod fixing plate 24.

[0039] like Figure 3-4As shown, in this embodiment, a plurality of fixing rings 27 are arranged inside the head end 9 to divide the inside of the head end 9 into a liquid bottle fixing part 91, an air bag fixing part 92 and a first spring moving part 93, the head end push rod 25 is clamped in the center of the plurality of fixing rings 27, the conductive liquid bottle 19 is arranged in the liquid bottle fixing part 91, the air bag 22 is arranged in the air bag fixing part 92, the first spring 23 and the first push rod fixing piece 24 are located in the first spring moving part 93, and the outer diameter of the first push rod fixing piece 24 is larger than the inner diameter of the central through hole of the fixing ring 27;

[0040] like Figure 5-6 As shown, in this embodiment, the intermediate push rod 30 is provided with a second spring 301 and a second push rod fixing plate 302, and a plurality of fixing rings 27 are provided inside the connecting rod 10. The intermediate push rod 30 is clamped in the center of the plurality of fixing rings 27, and a second spring moving part 94 is formed between adjacent fixing rings 27. The second spring 301 and the second push rod fixing plate 302 are located in the second spring moving part 94, and the outer diameter of the second push rod fixing plate 302 is larger than the inner diameter of the central through hole of the fixing ring 27.

[0041] like Figure 7-9 As shown, in this embodiment, a third spring 331 and a third push rod fixing plate 332 are provided on the tail end push rod 33, a plurality of fixing rings 27 are provided inside the tail end 11, the tail end push rod 33 is clamped in the center of the plurality of fixing rings 27, and a third spring moving part 95 is formed between adjacent fixing rings 27, the third spring 331 and the third push rod fixing plate 332 are located in the third spring moving part 95, and the outer diameter of the third push rod fixing plate 332 is larger than the inner diameter of the central through hole of the fixing ring 27.

[0042] like Figure 7-9 As shown, in this embodiment, the anti-slip handle 32 includes a gripping portion 321 and a pushing portion 322, and a symmetrical pin hole 323 is provided on the outer wall of the tail end 11. The anti-slip handle 32 is rotatably connected to the tail end 11 through the pin shaft and the pin hole 323. The gripping portion 321 is located outside the tail end 11, and the pushing portion 322 is located inside the tail end 11 and abuts against the end of the tail end push rod 33.

[0043] like Figure 7-9 As shown, in this embodiment, a cable hole 35 is provided on the outer wall of the tail end 11 , and an extension cable 36 is provided in the cable hole 35 . One end of the extension cable 36 is connected to the tail end push rod 33 , and the other end is connected to the measuring cable 6 .

[0044] Take a mine tunnel as an example. The tunnel section is arched, the tunnel height is about 4m, and the tunnel width is about 5m. There is a serious water outflow phenomenon at the arc dome near the roof of the working face tunnel. It is necessary to find out the water source and channel of the high water outflow point on the side of the tunnel, and carry out grouting and plugging operations in time. In order to find out the water-bearing property of the coal and rock strata near the high water outflow point on the tunnel side, the mine electrical method high-altitude detection device of the present invention is used for exploration. The construction layout structure is as follows: Figure 1 shown.

[0045] A method for using a mine electrical high-altitude detection device comprises the following steps:

[0046] S1: Figure 1 As shown; in the detection tunnel, a field host is placed, and multiple measuring lines are arranged in parallel along the tunnel direction near the water outlet point at the high part of the tunnel inner wall. In this embodiment, five measuring lines are used. The electrical method construction of each measuring line adopts a symmetrical quadrupole device with the most accurate abnormality positioning in the mine electrical method. The detection point position is calibrated according to the form of the symmetrical quadrupole device. Four construction workers hold a high-altitude detection rod and press the copper electrode at the detection end against the high electrical detection point of the tunnel inner wall. The high-altitude detection rod is connected to the field host with a measuring cable to form an electrical method high-altitude single-channel detection device;

[0047] S2: Figure 2-8 As shown; before detection, press the non-slip handle to push the rear push rod forward. The movement of the rear push rod drives the middle push rod and the head push rod to move forward. The flat ring block of the head push rod squeezes the air bag. The air bag pressurizes the conductive liquid bottle through the air guide tube, so that the conductive liquid in the conductive liquid bottle flows out from the liquid outlet pipe to soak the sponge sleeve and the copper electrode, thereby improving the coupling contact between the copper electrode and the rock mass on the side of the lane and weakening the induced polarization effect of the copper electrode.

[0048] S3: Figure 1 As shown; Specific measurement: Each survey line uses single-channel electrical acquisition technology, based on the symmetrical quadrupole AMONB device, O is the midpoint of MN and corresponds to the detection recording point position, AB is the power supply electrode, and MN is the measurement electrode. Power is supplied to the power supply electrode at each sounding point or power supply point, and the corresponding measurement electrode performs single-channel measurement in turn. When all measurement points at this sounding point or power supply point are completed, similar observations are performed on the next sounding point or power supply point until the high-altitude electrical detection of all survey lines is completed;

[0049] S4: Fig.10 As shown; the high-altitude electrical data of each survey line are extracted, and the apparent resistivity detection results of multiple survey lines are interpreted. Through comprehensive comparative analysis of the detection results of multiple survey lines, the water-bearing properties of the coal and rock strata near the water outlet point of the tunnel are found out, the water source and channel of the water outlet point at the high point of the tunnel inner wall are determined, and the grouting and plugging operation of the tunnel is guided.

[0050] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A mine electrical high-altitude detection device, installed in a tunnel, characterized in that: It includes a number of high-altitude detection rods, an on-site host, and measuring cables. The top of each high-altitude detection rod is pressed against the electrical detection point of the side wall or the top plate of the tunnel. The high-altitude detection rods are connected to the on-site host through the measuring cables. The high-altitude detection rod includes a detection end, a head end, a connecting rod, a tail end, and a conductive liquid filling mechanism. The detection end includes a sponge sleeve and a copper electrode. The sponge sleeve is sleeved on the top of the copper electrode. The end of the copper electrode is threadedly connected to the head end. The head end, the connecting rod, and the tail end are internally connected and fixed in turn by the matching connection of the lock and the lock hole. A copper base is arranged in the head end, and an internal screw hole is arranged on the copper base. The copper electrode is threadedly connected to the copper base through the internal screw hole, and the copper base is connected to the measuring cable. The conductive liquid filling mechanism comprises a conductive liquid bottle, an air bag, a head end push rod, an intermediate push rod, a tail end push rod and an anti-slip grip, wherein the conductive liquid bottle, the air bag and the head end push rod are arranged inside the head end, the intermediate push rod is arranged inside the connecting rod, and the tail end push rod is arranged inside the tail end, the head end push rod, the intermediate push rod and the tail end push rod are connected in sequence through a clamping hole and a clamping column, the head end push rod, the intermediate push rod and the tail end push rod are all made of copper, the anti-slip grip is fixed on the outer wall of the tail end and is used to drive the tail end push rod to move, and the head end push rod is provided with a head end cable connected to the copper base; The conductive liquid bottle is provided with a liquid outlet pipe, a liquid adding pipe and an air guide pipe connected to the conductive liquid bottle. The liquid outlet pipe is used to add conductive liquid to the sponge sleeve, the liquid adding pipe is connected to the liquid adding port on the head end, and the air guide pipe is connected to the air bag.

2. The mine electrical high-altitude detection device according to claim 1 is characterized in that: The head end push rod is provided with a flat ring, a first push rod fixing plate and a first spring. The flat ring abuts against the airbag and is used to squeeze the airbag. The first spring is sleeved between the flat ring and the first push rod fixing plate.

3. The mine electrical high-altitude detection device according to claim 1 is characterized in that: Several fixing rings are arranged inside the head end to divide the inside of the head end into a liquid bottle fixing part, an airbag fixing part and a first spring moving part. The head end push rod is clamped in the center of the several fixing rings, the conductive liquid bottle is arranged in the liquid bottle fixing part, the airbag is arranged in the airbag fixing part, the first spring and the first push rod fixing plate are located in the first spring moving part, and the outer diameter of the first push rod fixing plate is larger than the inner diameter of the central through hole of the fixing ring.

4. The mine electrical high-altitude detection device according to claim 1 is characterized in that: The intermediate push rod is provided with a second spring and a second push rod fixing plate, and a plurality of fixing rings are provided inside the connecting rod. The intermediate push rod is clamped in the center of the plurality of fixing rings, and a second spring moving part is formed between adjacent fixing rings. The second spring and the second push rod fixing plate are located in the second spring moving part, and the outer diameter of the second push rod fixing plate is larger than the inner diameter of the central through hole of the fixing ring.

5. The mine electrical high-altitude detection device according to claim 1 is characterized in that: A third spring and a third push rod fixing plate are arranged on the push rod at the tail end, a plurality of fixing rings are arranged inside the tail end, the push rod at the tail end is clamped in the center of the plurality of fixing rings, a third spring moving part is formed between adjacent fixing rings, the third spring and the third push rod fixing plate are located in the third spring moving part, and an outer diameter of the third push rod fixing plate is larger than an inner diameter of a central through hole of the fixing ring.

6. The mine electrical high-altitude detection device according to any one of claims 1 to 5, characterized in that: The anti-slip handle includes a gripping portion and a pushing portion. Symmetrical pin holes are provided on the outer wall of the tail end. The anti-slip handle is rotatably connected to the tail end through the pin shaft and the pin hole. The gripping portion is located inside the tail end, and the pushing portion is located inside the tail end and abuts against the end of the tail end push rod.

7. The mine electrical high-altitude detection device according to claim 6, characterized in that: A cable hole is arranged on the outer wall of the tail end, an extension cable is arranged in the cable hole, one end of the extension cable is connected to the tail end push rod, and the other end of the extension cable is connected to the measuring cable.

8. A method for using the mine electrical high-altitude detection device as claimed in claim 7, characterized in that: The following steps are involved: S1: Place the on-site host in the detection tunnel, calibrate the detection point position according to the high-altitude electrical detection method, hold the copper electrode at the detection end against the high electrical detection point on the tunnel side or roof by holding the high-altitude detection rod, and connect the high-altitude detection rod and the on-site host with a measuring cable to form an electrical high-altitude single-channel detection device; S2: Before detection, press the non-slip handle to push the rear push rod forward. The movement of the rear push rod drives the middle push rod and the head push rod to move forward. The flat ring block of the head push rod squeezes the air bag. The air bag pressurizes the conductive liquid bottle through the air guide tube, so that the conductive liquid in the conductive liquid bottle flows out from the liquid outlet pipe to soak the sponge sleeve and the copper electrode, thereby improving the coupling contact between the copper electrode and the lane wall or top plate and weakening the excitation polarization effect of the copper electrode. S3: Specific measurement: Use single-channel electrical acquisition technology to power the power supply electrode at each sounding point or power supply point, and the corresponding measuring electrodes perform single-channel measurement in turn. When all the measuring points at this sounding point or power supply point are completed, similar observations are performed on the next sounding point or power supply point until all survey lines are detected; S4: Extract the data collected by the on-site main engine electrical method, interpret the apparent resistivity detection results, and complete the exploration of the water-bearing properties of the coal and rock strata at the high side of the tunnel or near the roof.

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