Self-adjusting shear-resistant yielding anchor device and method of use thereof

Abstract

The self-adjusting anti-shearing pressure-relief anchor rod device and the use method thereof disclosed by the application belong to the field of underground engineering support such as roadway, tunnel and tunnel. The device comprises a sleeve, an anchor rod body and an anti-shearing device. The anti-shearing device is arranged on the anchor rod, the sleeve is arranged at the head of the anchor rod body, the anchor rod body comprises a first rod body arranged left and right along the axis for sequentially installing a tray and a nut, a second rod body for shearing deformation to adapt to the dislocation and sliding deformation of a rock stratum and a third rod body for pressure relief. The relative movement between the third rod body and the sleeve is realized by rotating the high-strength gear at the end of the third rod body, and then the constant resistance pressure relief effect of the anchor rod is realized. The shearing deformation is realized by the torsional bending of the second rod body and the anti-shearing device, and then the dislocation and sliding deformation of the rock stratum is adapted. The structure can realize the pressure relief effect, adapt to the dislocation and sliding deformation of the rock stratum, meet the requirement of large shearing lateral deformation, and has the advantages of multiple functions, reasonable structure, cost saving and economic applicability.

Description

TECHNICAL FIELD

[0001] The present application relates to a self-adjusting anti-shearing yielding anchor rod device and its use method, belonging to the field of underground engineering support such as roadway, tunnel and tunnel. BACKGROUND

[0002] With the increase of the depth of mineral exploitation, the engineering geological conditions faced by the mining industry are more complex, and the structure of deep roadway surrounding rock is also more complex. Due to the prominent contradiction between high in-situ stress and low strength of surrounding rock mass in deep surrounding pressure, the influence of engineering action and environmental conditions during excavation and the mining-induced stress formed during the process of mineral resource exploitation, the deep roadway surrounding rock is prone to large deformation and failure and anchor rod shear failure, which poses a great challenge to safe and efficient production, and is a hot and difficult problem that needs to be solved in deep mineral resource exploitation.

[0003] Anchor rod is a main support form widely and efficiently used in underground engineering support field. At present, in order to solve the support problem of large deformation of deep high stress surrounding rock, engineering requires that anchor rod not only can provide constant supporting force, but also can produce large elongation deformation to meet the requirement of large deformation of broken surrounding rock; in order to meet the above engineering requirements, yielding support technology is usually used to make anchor rod produce large tensile deformation without being pulled off. However, in actual engineering, it is found that anchor rod is often in the staggered zone of rock stratum, resulting in that many traditional anchor rods or yielding anchor rods are sheared off because they cannot bear large shear stress, leading to anchor rod support failure, and further affecting the normal use of roadway and endangering the safety of underground workers. In addition, because the anchor rod is deeply embedded in the surrounding rock, it belongs to concealed support, and after the anchor rod support is completed, the surrounding rock surface is usually sprayed with concrete to close it, which brings inconvenience to the discovery of anchor rod breakage and the replacement of anchor rod. Based on the above problems, it is urgent to develop an anchor rod device that can not only provide constant supporting force to effectively control the deformation of surrounding rock, but also produce large elongation deformation to meet the requirement of large deformation of surrounding rock, and automatically adjust the bending deformation of rod body to meet the lateral deformation and dislocation of surrounding rock, that is, an anchor rod device that integrates automatic adjustment, constant resistance, deformation yielding and anti-shearing functions to solve the existing engineering technical problems. SUMMARY

[0004] Technical problem: The purpose of the present application is to overcome the deficiencies in the prior art, and to provide a self-adjusting anti-shearing yielding anchor rod device and its use method, which can not only automatically adjust the bending deformation of rod body to meet the lateral deformation and dislocation of surrounding rock, but also provide constant supporting force and produce large elongation deformation to meet the requirement of large deformation of surrounding rock.

[0005] Technical solution: To achieve the above technical purposes, the self-adjusting anti-shear yielding anchor rod device comprises an anchor rod body, the anchor rod body comprises a tail section, a middle section and a head end, wherein the tail section is used to apply tension, the middle section is used to adapt to the shear deformation caused by the rock layer dislocation slip deformation, and the head end is used to yield;

[0006] The tail section is a first rod body provided with threads, and the first rod body is provided with a tray and an anti-skid wire nut through threads;

[0007] The middle section is a plurality of anti-shear connecting rods connected at the head and tail, each anti-shear connecting rod comprises a second rod body, one end of the second rod body is movably connected with an anti-shear device through a high-strength bolt A and a high-strength nut A, and the other end of the second rod body is provided with a piston connection with another anti-shear device;

[0008] The head end comprises a third rod body, a sleeve is arranged on the outer side of the end of the third rod body, the tail of the third rod body extends out of the sleeve and is connected with an anti-shear device through a high-strength bolt B and a high-strength nut B, a high-strength gear is connected to the end of the third rod body through a high-strength bolt C, a plurality of annular plastic clamping teeth and annular rigid clamping teeth matched with the high-strength gear are arranged in the sleeve, the rotation of the high-strength gear at the end of the third rod body is used to realize the relative movement of the annular plastic clamping teeth and the annular rigid clamping teeth on the inner side of the sleeve, and then the constant resistance yielding effect is realized.

[0009] Further, the anti-shear device is a piston cylinder structure, one end of the second rod body is a piston structure, and the piston structure of the second rod body and the piston cylinder structure of the anti-shear device are matched and movably connected, so that there is a connection allowance between the second rod body and the anti-shear device; the bottom of the piston cylinder structure of the anti-shear device is provided with two parallel connection ears, the connection ears are provided with holes, and the non-piston end of the second rod body is movably connected through the high-strength bolt A and the high-strength nut A, so that the connection part can be bent.

[0010] Further, the anti-shear device and the first rod body or the second rod body form a piston structure, the anti-shear device is a piston cylinder structure, and the first rod body or the second rod body is a piston structure; a hollow annular cover disc is sleeved on the first rod body and the second rod body, the hollow annular cover disc is connected with the opening of the piston cylinder structure through a bolt, so as to prevent the piston structure at the end of the first rod body and the second rod body from sliding out of the piston cylinder structure of the anti-shear device; the piston structure of the first rod body and the second rod body is provided with a sliding steel ball around the piston rod to allow the first rod body and the second rod body to be twisted.

[0011] Further, the end of the first rod body and the end of the second rod body are both piston rod structures and are connected with the anti-shear device through the sliding steel ball; a plurality of second rod bodies are sequentially connected through the anti-shear device, and the number of the second rod bodies is adjusted according to actual needs.

[0012] Further, the sleeve is a hollow sleeve structure with a size smaller than the anchor hole, the annular plastic clamping teeth and the annular rigid clamping teeth arranged in the sleeve are matched with multiple layers, each layer is provided with a semicircular annular plastic clamping tooth and a semicircular annular rigid clamping tooth, the teeth of the high-strength gear are respectively engaged with the annular plastic clamping teeth and the annular rigid clamping teeth at both ends, the annular plastic clamping teeth have a certain plasticity and will be deformed and damaged under the cutting of the high-strength gear, when the surrounding rock is deformed greatly, the high-strength gear will rotate under the pulling of the anchor rod body, at this time, the annular plastic clamping teeth and the annular rigid clamping teeth jointly provide resistance to prevent the high-strength gear from rotating, and because the annular plastic clamping teeth will be plastically deformed and damaged under the cutting of the high-strength gear, thus realizing constant resistance and pressure relief; the front end of the sleeve is provided with a sealing disc for preventing dust and cement slurry from entering, the rear end of the sleeve is provided with a slurry stopping plug on the third rod body for preventing slurry backflow, the slurry stopping plug is matched with the anchor hole, the slurry stopping plug is connected with a grouting guide pipe extending out of the tray, and the outlet of the grouting guide pipe on the slurry stopping plug is located on the outside of the sleeve.

[0013] A use method of the self-adjusting anti-shearing pressure relief anchor rod device, the steps of which are as follows:

[0014] Drill the anchor hole at the pre-marked position of the surrounding rock, connect the parts of the anchor rod body, push the third part on the anchor rod body into the sleeve, and then fix the high-strength gear with the high-strength bolt C and the high-strength nut C; install the circular cover disc at the end of the sleeve to prevent dust and cement slurry from entering;

[0015] Place the slurry stopping plug close to the sleeve, then put the anchor rod body with the sleeve into the anchor hole, and then inject cement slurry into the space between the sleeve and the anchor hole separated by the slurry stopping plug through the grouting guide pipe in front of the slurry stopping plug to form a cement slurry setting body;

[0016] After the slurry solidifies, sequentially install the tray and the anti-slip wire nut on the exposed first rod body thread of the anchor hole, and provide pre-tightening force through the pre-tightening anti-slip wire nut along the thread rise angle;

[0017] When the surrounding rock is deformed greatly, the high-strength gear will rotate under the pulling of the anchor rod body, at this time, the annular plastic clamping teeth and the annular rigid clamping teeth jointly provide resistance to prevent the high-strength gear from rotating, and because the annular plastic clamping teeth will be plastically deformed and damaged under the cutting of the high-strength gear, thus realizing the mutual displacement between the third rod body and the sleeve, and further realizing the self-adjusting pressure relief effect to meet the requirement of the deformation of the surrounding rock;

[0018] When the rock stratum in the surrounding rock is dislocated and deformed, a shearing force will be applied to the anchor rod body. Since one end of the anti-shearing device is connected with the second rod body by rotating through the sliding steel ball, the two can be twisted along the stress direction to prevent damage. The other end of the anti-shearing device is connected with the second rod body by high-strength bolts and the matched high-strength nuts to ensure that the relative position of the two is bent under the action of the force. Since the anti-shearing device and the second rod body can rotate and bend, the anchor rod will not be sheared when any tangential deformation occurs, and the self-adjusting function can meet the requirement of the tangential deformation of the surrounding rock.

[0019] Beneficial effects: Since the above technical solutions are adopted, the anchor rod device has the functions of providing constant supporting force, producing large elongation deformation to meet the requirement of large deformation of the surrounding rock, and automatically adjusting the bending deformation of the rod body to meet the lateral deformation of the surrounding rock. The beneficial effects are self-evident: 1) large shear deformation can be produced to meet the lateral movement of the rock stratum; 2) large expansion deformation can be produced to meet the requirement of large deformation of the surrounding rock; 3) the anchor rod device can automatically adjust to the change of the surrounding rock, avoiding the inconvenience of secondary rework and saving a large amount of manpower and material resources. Meanwhile, the reasonable supporting structure ensures the stability of the surrounding rock roadway. The high-strength gear at the end of the third rod body rotates to realize the relative movement between the sleeve, and then the constant resistance and pressure release of the anchor rod are realized. The second rod body and the anti-shearing device are twisted and bent to produce shear deformation, and then adapt to the dislocation and sliding deformation of the rock stratum. The anchor rod device has multiple functions, solves the problem that the ordinary anchor rod cannot meet the large deformation of the surrounding rock, and solves the problem that the existing pressure release anchor rod is sheared under the lateral dislocation of the rock stratum. The anchor rod device has simple structure, low cost, stable function, can greatly improve the supporting benefit, and the deformation and pressure release function of the anchor rod can effectively reduce accidents and ensure the safety of workers. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a schematic diagram of the anchor hole in the embodiment of the present application;

[0021] Figure 2 It is a schematic diagram of the anchoring device in the embodiment of the present application;

[0022] Figure 3 It is a schematic diagram of the installation of the anchoring device in the embodiment of the present application;

[0023] Fig. 4(a) is a schematic diagram of the cross section where the high-strength bolt A is located in the embodiment of the present application;

[0024] Fig. 4(b) is a schematic diagram of the cross section where the sliding steel ball is located in the embodiment of the present application;

[0025] Fig. 5(a) is a schematic diagram of the cross section where the annular clamping tooth is located in the embodiment of the present application;

[0026] Figure 5(b) is a schematic diagram of the cross-section of the high-strength gear in an embodiment of the present invention;

[0027] Figure 6 This is an enlarged schematic diagram of the sleeve (pressure relief device) in an embodiment of the present invention;

[0028] Figure 7 This is an enlarged schematic diagram of the anti-shear device in an embodiment of the present invention;

[0029] Figure 8 This is a schematic diagram of the shear deformation of the anchor bolt body in an embodiment of the present invention.

[0030] In the diagram: 1-surrounding rock, 2-anchor bolt body, 3-anti-slip threaded nut, 4-pallet, 5-anchor hole, 6-first rod body, 7-anti-shear device, 8-second rod body, 9-third rod body, 10-sleeve, 11-ring plastic tooth, 12-ring rigid tooth, 13-high-strength gear, 14-high-strength bolt C, 15-sealing disc, 16-cement grout solidification, 17-grout stop plug, 18-sliding steel ball, 19-high-strength bolt B, 20-high-strength nut B, 21-high-strength bolt A, 22-grouting conduit, 23-high-strength nut C, 24-high-strength nut A, 25-bolt, 26-hollow annular cover plate. Detailed Implementation

[0031] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings:

[0032] like Figure 1 and Figure 2 As shown, a self-adjusting anti-shear pressure relief anchor bolt device of the present invention includes an anchor bolt body 2, which comprises three parts: a tail section, a middle section, and a head end. The tail section is used to apply tensile force, the middle section is used to adapt to shear deformation caused by rock slippage and deformation, and the head end is used to relieve pressure. The tail section is a threaded first rod body 6, which is threaded with a tray 4 and an anti-slip nut 3. The middle section consists of multiple anti-shear connecting rods connected end to end. Each anti-shear connecting rod includes a second rod body 8. One end of the second rod body 8 is movably connected to an anti-shear device 7 via a high-strength bolt A21 and a high-strength nut A24. The other end of the second rod body 8 is provided with a connection to another... The anti-shear device 7 is connected to a piston; the head end includes a third rod 9, and a sleeve 10 is provided on the outer side of the end of the third rod 9. The sleeve 10 extends from the tail of the third rod 9 and is connected to an anti-shear device 7 through a high-strength bolt B19 and a high-strength nut B20. A high-strength gear 13 is connected to the end of the third rod 9 through a high-strength bolt C14. The sleeve 10 is provided with multiple annular plastic teeth 11 and annular rigid teeth 12 that match the high-strength gear 13. The rotation of the high-strength gear 13 at the end of the third rod enables relative movement with the annular plastic teeth 11 and annular rigid teeth 12 on the inner side of the sleeve 10, thereby achieving constant resistance and pressure relief.

[0033] As shown in Figure 3 the sleeve 10 is provided with a stop plug 17 near one side of the third rod body 9, which can prevent the backflow of grout during grouting. The other end is provided with a sealing disc 15, which can prevent dust and cement grout from entering.

[0034] The space between the sleeve 10 and the anchor hole 5 is isolated and grouted through the grouting pipe 22 and the stop plug 17. After the cement grout is solidified, the tray 4 and the anti-skid wire nut 3 are successively sleeved on the first rod body 6 exposed outside the anchor hole. The pre-tightening force is provided by the pre-tightening of the anti-skid wire nut 3 along the thread rise angle.

[0035] As shown in FIG. 4(a), FIG. 4(b) and Figure 7 The anti-shearing device 7 is a piston-cylinder structure, one end of the second rod body 8 is a piston structure, and the piston structure of the second rod body 8 and the piston-cylinder structure of the anti-shearing device 7 are matched and movably connected, so that there is a connection allowance between the second rod body 8 and the anti-shearing device 7; the cylinder bottom of the piston-cylinder structure of the anti-shearing device 7 is provided with two parallel connection ears, and the connection ears are provided with holes, and are movably connected with the non-piston end of the second rod body 8 through high-strength bolts A21 and high-strength nuts A24, so that the connection part can be bent.

[0036] As shown in FIG. 5(a), FIG. 5(b) and Figure 6 The sleeve 10 is a hollow sleeve structure with a size smaller than that of the anchor hole 5, and the annular plastic clamping teeth 11 and the annular rigid clamping teeth 12 arranged in the sleeve 10 are matched and provided with multiple layers, each layer is provided with a semicircular annular plastic clamping tooth 11 and a semicircular annular rigid clamping tooth 12, the teeth of the high-strength gear 13 are respectively engaged with the annular plastic clamping teeth 11 and the annular rigid clamping teeth 12 at both ends, the annular plastic clamping teeth 11 have a certain plasticity and will be damaged and deformed under the cutting of the high-strength gear 13, when the surrounding rock 1 deforms greatly, the high-strength gear 13 will rotate under the pulling of the anchor rod body 2, at this time, the annular plastic clamping teeth 11 and the annular rigid clamping teeth 12 jointly provide resistance to prevent the high-strength gear 13 from rotating, and because the annular plastic clamping teeth 11 will be damaged and deformed plastically under the cutting of the high-strength gear 13, thus realizing constant resistance and pressure relief; the sleeve 10 is provided with a sealing disc 15 at the front end to prevent dust and cement grout from entering, and the sleeve is provided with a stop plug 17 on the third rod body 9 at the rear end to prevent the backflow of grout, the stop plug 17 is matched with the anchor hole 5, the stop plug 17 is connected with the grouting pipe 22 extending out of the tray 4, and the outlet of the grouting pipe 22 on the stop plug 17 is located outside the sleeve 10.

[0037] As shown in Figure 8As shown, when the rock stratum in the surrounding rock 1 is dislocated and deformed, a shearing force will be applied to the anchor rod body 2. Since the anti-shearing device 7 is connected to each rod body at one end through the sliding steel ball 18, it can ensure that the two can be twisted; the other end is connected to each rod body through a high-strength bolt and its matching high-strength nut, which can ensure that the two can be bent. Based on the principle that the anti-shearing device 7 and each rod body can be bent and twisted, the device can also produce a certain tangential deformation without being sheared off, and self-adjusting to meet the requirements of the tangential deformation of the surrounding rock 1.

Claims

1. A self-adjusting shear-resistant yielding anchor device, characterized by: The anchor rod body (2) comprises a tail section, a middle section and a head end, wherein the tail section is used to apply tension, the middle section is used to adapt to the shear deformation of the rock stratum dislocation slip deformation, and the head end is used to yield; The tail section is a first rod body (6) provided with threads, and the first rod body (6) is provided with a tray (4) and an anti-skid wire nut (3) through threads; The middle section is a plurality of anti-shear connecting rods connected at the head and tail, each anti-shear connecting rod comprises a second rod body (8), one end of the second rod body (8) is movably connected with an anti-shear device (7) through a high-strength bolt A (21) and a high-strength nut A (24), and the other end of the second rod body (8) is movably connected with another anti-shear device (7); The head end comprises a third rod body (9), the outer side of the end of the third rod body (9) is provided with a sleeve (10), the tail of the third rod body (9) extends out of the sleeve (10) and is connected with an anti-shear device (7) through a high-strength bolt B (19) and a high-strength nut B (20), the end of the third rod body (9) is connected with a high-strength gear (13) through a high-strength bolt C (14), the inside of the sleeve (10) is provided with a plurality of annular plastic clamping teeth (11) and annular rigid clamping teeth (12) matched with the high-strength gear (13), the rotation of the high-strength gear (13) at the end of the third rod body is used to realize the relative movement of the annular plastic clamping teeth (11) and the annular rigid clamping teeth (12) on the inside of the sleeve (10), thereby realizing the constant resistance yield effect; The sleeve (10) is a hollow sleeve structure with a size smaller than that of the anchor hole (5), the annular plastic clamping teeth (11) and the annular rigid clamping teeth (12) arranged in the sleeve (10) are matched with multiple layers, each layer is provided with a half-ring annular plastic clamping tooth (11) and a half-ring annular rigid clamping tooth (12), the teeth of the high-strength gear (13) are respectively engaged with the annular plastic clamping teeth (11) and the annular rigid clamping teeth (12), the annular plastic clamping teeth (11) have a certain plasticity and will be deformed and damaged under the cutting of the high-strength gear (13), when the surrounding rock (1) is deformed greatly, the high-strength gear (13) will rotate under the pulling of the anchor rod body (2), at this time, the annular plastic clamping teeth (11) and the annular rigid clamping teeth (12) jointly provide resistance to prevent the rotation of the high-strength gear (13), and because the annular plastic clamping teeth (11) will be plastically deformed and damaged under the cutting of the high-strength gear (13), the constant resistance yield is realized.

2. A self-adjusting shear-resistant yielding anchor rod device according to claim 1, characterized in that: The anti-shear device (7) is a piston-cylinder structure, one end of the second rod body (8) is a piston structure, the piston structure of the second rod body (8) and the piston-cylinder structure of the anti-shear device (7) are matched and movably connected, so as to allow a connection allowance between the second rod body (8) and the anti-shear device (7); the cylinder bottom of the piston-cylinder structure of the anti-shear device (7) is provided with two parallel connection ears, the connection ears are provided with holes, and the non-piston end of the second rod body (8) is movably connected with the connection ears through the high-strength bolt A (21) and the high-strength nut A (24), so as to allow the connection to be bent.

3. A self-adjusting shear resistant yielding anchor device according to claim 2, wherein: The anti-shear device (7) forms a piston structure with the first rod (6) or the second rod (8). The anti-shear device (7) is a piston cylinder structure, and the first rod (6) or the second rod (8) is a piston structure. A hollow annular cover plate (26) is fitted on the first rod (6) and the second rod (8). The hollow annular cover plate (26) is connected to the opening of the piston cylinder structure by bolts (25), thereby preventing the piston structure at the end of the first rod (6) and the second rod (8) from sliding out of the piston cylinder structure of the anti-shear device (7). A sliding steel ball (18) is provided between the piston structure of the first rod (6) and the second rod (8) and the hollow annular cover plate (26) to allow the first rod (6) and the second rod (8) to twist around the piston rod.

4. A self-adjusting shear-resistant yielding anchor rod apparatus according to claim 3, wherein: The end of the first rod (6) and the end of the second rod (8) have the same structure, both being piston rod structures, and are connected to the anti-shear device (7) via a sliding steel ball (18); multiple second rods (8) are connected sequentially via the anti-shear device (7), and the number of second rods (8) is adjusted according to actual needs.

5. A self-adjusting shear-resistant yielding anchor rod apparatus as defined in claim 1, wherein: The sleeve (10) has a sealing disc (15) at the front end to prevent dust and cement slurry from entering. The sleeve has a grout stop plug (17) on the third rod (9) at the rear end to prevent grout backflow. The grout stop plug (17) matches the anchor hole (5). A grouting conduit (22) extending out of the tray (4) is connected to the grout stop plug (17). The outlet of the grouting conduit (22) on the grout stop plug (17) is located outside the sleeve (10).

6. A method of using a self-adjusting shear-resistant yielding anchor device according to any one of claims 1-5, characterized in that The steps are as follows: Drill anchor holes (5) at the pre-marked position in the surrounding rock (1), connect the various parts of the anchor body (2), push the third rod (9) on the anchor body (2) into the sleeve (10), and then fix the high-strength gear (13) with high-strength bolt C (14) and high-strength nut C (23); install the sealing plate (15) at the end of the sleeve (10) to prevent dust and cement slurry from entering; The grout stop plug (17) is placed tightly against the sleeve (10). Then, the anchor rod body (2) along with the sleeve (10) is placed into the anchor hole (5). Grouting is performed on the outside of the sleeve (10) in front of the grout stop plug (17) through the grouting pipe (22). The cement grout is injected to fill the space between the sleeve (10) and the anchor hole (5) separated by the grout stop plug (17) to form a cement grout solid (16). After the grout has cured, a tray (4) and an anti-slip nut (3) are sequentially fitted onto the thread of the first exposed rod (6) outside the anchor hole. The pre-tightening force is provided along the thread helix angle by pre-tightening the anti-slip nut (3). When the surrounding rock (1) undergoes large deformation, the high-strength gear (13) will rotate under the pull of the anchor body (2). At this time, the annular plastic tooth (11) and the annular rigid tooth (12) together provide resistance to prevent the high-strength gear (13) from rotating. Also, because the annular plastic tooth (11) will undergo plastic deformation and failure due to being cut by the high-strength gear (13), the mutual misalignment between the third rod (9) and the sleeve (10) is realized, thereby achieving the self-adjusting pressure relief effect to meet the requirements of large deformation of the surrounding rock (1). When the rock strata in the surrounding rock (1) undergo displacement deformation, shear force will be applied to the anchor body (2). Since one end of the anti-shear device (7) is rotatably connected to the second rod (8) through the sliding steel ball (18), it can be ensured that the two can be twisted in the direction of the force to prevent damage. The other end of the anti-shear device (7) is connected to the second rod (8) through the high-strength bolt and its matching high-strength nut to ensure that the relative position of the two is bent under the action of the inside. Since the anti-shear device (7) and each second rod (8) can rotate, bend and twist, they will not be sheared when any tangential deformation occurs. The self-adjustment type meets the requirements of the tangential deformation of the surrounding rock (1).

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