Geothermal-based self-compensating expansion shell rock bolt

Abstract

A geothermal-based self-compensating expansion shell rock bolt, includes a sleeve, a piston rod, a push member, and an expansion member, where the piston rod is slidably connected within the sleeve; the expansion member is connected to the sleeve; the push member is connected to the piston rod and configured to act on the expansion member; a push hole is defined in the sleeve for the push member to extend out therethrough; a cylinder is disposed within the sleeve; an end of the piston rod extends into the cylinder; the end of the piston rod that extends into the cylinder and an inner wall of the cylinder define an expansion cavity; and a phase change material is disposed within the expansion cavity. The phase change material within the expansion cavity is heated by high-geotemperature strata within rock mass.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Chinese Patent Application No. 202511233811 .0 with a filing date of Sep. 01, 2025. The content of the aforementioned application, including any intervening amendments thereto, is incorporated herein by reference.TECHNICAL FIELD

[0002] The present disclosure relates to the technical field of roadway surrounding rock support, and in particular, to a geothermal-based self-compensating expansion shell rock bolt.BACKGROUND

[0003] With the rapid development of deep-buried, long, and large mountain tunnel engineering, the number of tunnel projects traversing high-geotemperature strata is increasing. Thermal damage in tunnels leads to the deterioration of the mechanical properties of surrounding rock and changes in structural characteristics, posing a serious threat to surrounding rock stability.

[0004] Among the existing support technologies for high-geotemperature tunnels, expansion-shell prestressed rock bolts are widely used due to their minimal construction disturbance, high reliability, and high economic efficiency. However, when used as permanent support structures, such rock bolts experience significant prestress loss during tunnel service. Specifically, during the locking process by the rock bolts, prestress loss occurs due to the contraction of the anchor system itself, construction equipment, and construction techniques. During the working period of the rock bolt, additional prestress loss is caused by changes in ambient temperature and humidity, relaxation of its own steel material, concrete creep, as well as group anchor effects and rock mass creep, etc. If the prestress value falls below the design value by a certain level, the anchoring function may fail.

[0005] Therefore, there is an urgent need to develop a rock bolt device that can actively utilize high-geotemperature geothermal resources and achieve self-compensation of prestress for maintaining the long-term stability of the prestressed anchor system in high-geotemperature tunnels.SUMMARY OF PRESENT INVENTION

[0006] The present disclosure provides a geothermal-based self-compensating expansion shell rock bolt for solving the problem of easy prestress loss during the operation of the rock bolt in the prior art.

[0007] The present disclosure provides a geothermal-based self-compensating expansion shell rock bolt including a sleeve, a piston rod, a push member, and an expansion member, where the piston rod is slidably connected within the sleeve; the expansion member is connected to the sleeve; the push member is connected to the piston rod and configured to act on the expansion member; a push hole is defined in the sleeve for the push member to extend out therethrough; a cylinder is disposed within the sleeve; an end of the piston rod extends into the cylinder; the end of the piston rod that extends into the cylinder and an inner wall of the cylinder define an expansion cavity; and a phase change material is disposed within the expansion cavity; and when heated and vaporized, the phase change material pushes the piston rod to move, such that the piston rod slides through the push member and pushes the expansion member to expand outwards from inside the sleeve.

[0008] Further, an end of the expansion member is hinged to the sleeve; and the push member has one end hinged to the expansion member and another end hinged to the piston rod.

[0009] Further, the push member is fixedly connected to the piston rod; and an end of the push member close to the expansion member is provided with an inclined push surface that is in contact with a side of the expansion member close to the sleeve.

[0010] Further, the sleeve includes an inner barrel and an outer barrel that are arranged coaxially; the inner barrel is mounted within the outer barrel; the piston rod is slidably connected within the inner barrel; an end of the inner barrel extends out of the outer barrel; and the end of the inner barrel that extends out of the outer barrel is in threaded connection with an adjusting nut.

[0011] Further, a self-locking mechanism is disposed between the inner barrel and the outer barrel and comprises a ratchet bar, a pawl, and an elastic member; the ratchet bar is fixedly connected to an outer wall of the inner barrel; the elastic member is connected between the pawl and an inner wall of the outer barrel; and the pawl is pressed toward the ratchet bar to limit the inner barrel from moving back toward an inside of the outer barrel.

[0012] Further, the end of the inner barrel that extends out of the outer barrel is sleeved with a supporting disk between the adjusting nut and the outer barrel.

[0013] Further, the cylinder includes a hydraulic cylinder and a driving cylinder that have inner cavities communicating with each other; the end of the piston rod extends into the hydraulic cylinder and is slidably connected to an inner wall of the hydraulic cylinder; a cross-sectional area of the inner wall of the hydraulic cylinder is larger than a cross-sectional area of an inner wall of the driving cylinder; a driving piston is slidably connected within the driving cylinder and fits against the inner wall of the driving cylinder; the expansion cavity includes a first cavity between the driving piston and the piston rod and a second cavity on a side of the driving piston away from the piston rod; the phase change material is arranged within the second cavity; and the first cavity is filled with a hydraulic oil.

[0014] Further, a one-way valve is mounted within the driving cylinder and located between the driving piston and the piston rod; and the one-way valve only allows the hydraulic oil to flow from the driving cylinder toward the hydraulic cylinder.

[0015] Further, the inner cavity of the driving cylinder is bottle-shaped and has a small-diameter end communicating with the hydraulic cylinder.

[0016] Further, the phase change material includes acetone.

[0017] The present disclosure has the following beneficial effects:

[0018] 1. The piston rod and the cylinder in slide fit with the piston rod are disposed within the rock bolt. The inner wall of the cylinder and the end of the piston rod define the expansion cavity. The phase change material is disposed within the expansion cavity. When the rock bolt is used, the end with the expansion cavity is inserted into the surrounding rock roadway wall of a high-geotemperature tunnel, and the phase change material within the expansion cavity is heated by high-geotemperature strata within rock mass. Under the action of the high geotemperature, the phase change material undergoes a phase change, resulting in a volume expansion which pushes the piston rod to slide within the sleeve. The piston rod slides through the push member and pushes the expansion member to expand outwards from inside the sleeve, thereby compressing the rock mass. This automatically compensates for prestress loss during the service life of the rock bolt, enhances the reinforcement effect of the prestressed rock bolt in high-geotemperature tunnels, and prolongs the service life of the rock bolt.

[0019] 2. The self-locking mechanism is disposed between the inner barrel and the outer barrel, and the elastic member is connected between the pawl and the inner wall of the outer barrel. The pawl is pressed toward the ratchet bar to limit the inner barrel from moving back toward the inside of the outer barrel, thereby reducing prestress loss during the locking process of the rock bolt and enhancing the reliability and firmness of the rock bolt during operation.

[0020] 3. The driving piston divides the expansion cavity into the second cavity filled with the phase change medium and the first cavity filled with the hydraulic oil. Utilizing the characteristic of the phase change material being prone to vaporization when heated, the geotemperature is converted into a pushing force. The pushing force is transmitted via the hydraulic oil to the piston rod, thereby pushing the piston rod to slide and driving the expansion member to expand outward from the outer wall of the outer barrel. This automatically compensates for prestress loss during the service life of the rock bolt. The cross-sectional area of the inner wall of the hydraulic cylinder is larger than that of the inner wall of the driving cylinder, such that the pushing force acting on the end of the piston rod is amplified, thereby improving the prestress compensation effect.

[0021] 4. The one-way valve between the driving piston and the piston rod is mounted within the driving cylinder, thereby avoiding the failure of prestress compensation due to backflow of the hydraulic oil into the driving cylinder when the geotemperature decreases, and improving the stability of the prestress.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a schematic structural diagram showing shell rock bolt a according to an embodiment of the present disclosure;

[0023] FIG. 2 is a schematic structural diagram showing a push member fixedly connected to a piston rod according to an embodiment of the present disclosure;

[0024] FIG. 3 is a schematic diagram showing a positional relationship of an expansion member under different conditions according to an embodiment of the present disclosure;

[0025] FIG. 4 is a schematic structural diagram showing a one-way valve according to an embodiment of the present disclosure; and

[0026] FIG. 5 is a structural schematic diagram showing a self-locking mechanism according to an embodiment of the present disclosure.List of Reference Numerals:

[0027] 1-sleeve; 11-inner barrel; 12-outer barrel; 13-push hole; 2-piston rod; 21-mounting base; 3-expansion member; 4-push member; 41-inclined push surface; 5-expansion cavity; 51-first cavity; 52-second cavity; 6-adjusting nut; 61-supporting disk; 7-self-locking mechanism; 71-ratchet bar; 72-pawl; 721-limiting protrusion; 73-elastic member; 74-connecting base; 741-connecting cavity; 742-limiting step; 8-cylinder; 81-hydraulic cylinder; 82-driving cylinder; 83-driving piston; 9-one-way valve; 91-valve body; 911-oil inlet cavity; 912-oil outlet cavity; 92-valve core; 93-push spring; 94-locking nut; and 941-oil outlet through hole.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] To make the objective, technical solutions, and advantages of the present disclosure clearer, the technical solutions in the present disclosure will be described clearly and completely below with reference to the accompanying drawings in the present disclosure. Apparently, the described embodiments are part of rather than all of the embodiments of the present disclosure. All other embodiments derived from the embodiments of the present disclosure by a person of ordinary skill in the art without creative efforts shall fall within the protection scope of the present disclosure.

[0029] Features defined with terms such as "first" and "second" in the specification of the present disclosure and the claims may explicitly or implicitly include one or more of such features. In the description of the present disclosure, unless otherwise specified, "a plurality of" means two or more. In addition, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates an "or" relationship between associated objects.

[0030] In the description of the present disclosure, the terms "central", ''longitudinal'', ''transverse'', ''long'', ''wide'', ''thick'', "upper", "lower", ''front'', ''back'', "left", "right", "vertical", "horizontal", ''top'', ''bottom'', "inner", "outer", ''clockwise'', ''anticlockwise'', ''axial'', ''radial'' and ''circumferential'' etc. are used to indicate orientations shown in the accompanying drawings. It should be noted that these terms are merely intended to facilitate a simple description of the present disclosure, rather than to indicate or imply that the mentioned apparatus or elements must have the specific orientation or be constructed and operated in the specific orientation. Therefore, these terms may not be construed as a limitation to the present disclosure.

[0031] A geothermal-based self-compensating expansion shell rock bolt of the present disclosure is described below with reference to FIG. 1 to FIG. 5, which includes a sleeve 1, a piston rod 2, a push member 4, and an expansion member 3. The piston rod 2 is slidably connected within the sleeve 1. The expansion member 3 is connected to the sleeve 1. The push member 4 is connected to the piston rod 2 and configured to act on the expansion member 3. A push hole 13 is defined in the sleeve for the push member 4 to extend out therethrough. A cylinder 8 is disposed within the sleeve 1. An end of the piston rod 2 extends into the cylinder 8. The end of the piston rod 2 that extends into the cylinder 8 and an inner wall of the cylinder 8 define an expansion cavity 5. A phase change material is disposed within the expansion cavity 5. When heated and vaporized, the phase change material pushes the piston rod 2 to move, such that the piston rod 2 slides through the push member 4 and pushes the expansion member 3 to expand outwards from inside the sleeve 1.

[0032] Specifically, as shown in FIG. 1, the piston rod 2 is slidably connected within the sleeve 1 and is capable of sliding axially along the sleeve 1. The expansion cavity 5 is located at the bottom of the piston rod 2. The expansion cavity 5 is filled with the phase change material which, when heated and vaporized, automatically pushes the piston rod 2 to slide toward the outside of the sleeve 1. The push member 4 is connected to the outer wall of the piston rod 2. The push member 4 extends out of the push hole 13 and slides together with the piston rod 2. The push hole 13 is a strip-shaped hole. An end of the push member 4 is in contact with the bottom of the expansion member 3. The expansion member 3 is connected to the sidewall of the sleeve 1 and is capable of expanding outwards. As the piston rod 2 slides axially, the push member 4 exerts a pushing force on the expansion member 3, thereby pushing the expansion member 3 to expand outwards. This achieves automatic compensation for prestress loss during the locking process of the rock bolt.

[0033] Further, in an optional embodiment, an end of the expansion member 3 is hinged to the sleeve 1. The push member 4 has one end hinged to the expansion member 3 and another end hinged to the piston rod 2.

[0034] Specifically, as shown in FIG. 1, there may be two expansion members 3 that are located on two sides of the sleeve 1, respectively. Of course, there may be a plurality of expansion members 3 that are uniformly distributed along the circumference of the sleeve 1. One end of the expansion member 3 is hinged to the sidewall of the sleeve 1 via a rotating shaft. A mounting base 21 is disposed to protrude from the outer wall of the piston rod 2. The push member 4 has one end hinged to the bottom of the expansion member 3 via a rotating shaft and another end hinged to the mounting base 21 of the piston rod 2 via a rotating shaft. The structure is simple and is convenient to mount. The phase change material, when heated and vaporized, automatically pushes the piston rod 2 to slide axially within the sleeve 1, and the push member 4 pushes the expansion member 3 to flip outwards, thereby increasing the anchoring force with the inner wall of the rock bolt mounting hole in the rock wall during the locking process of the rock bolt and compensating for the prestress loss of the rock bolt.

[0035] Specifically, as shown in FIG. 1, a plurality of barbs or anti-slip teeth are fixedly connected to the outer wall of the expansion member 3 to increase the friction between the expansion member 3 and the inner wall of the rock bolt mounting hole, thereby improving the mounting stability of the rock bolt.

[0036] Further, in another optional embodiment, the push member 4 is fixedly connected to the piston rod 2. An end of the push member 4 close to the expansion member 3 is provided with an inclined push surface 41 that is in contact with a side of the expansion member 3 close to the sleeve 1.

[0037] Specifically, as shown in FIG. 2, the push member 4 may be configured as a block-like structure fixedly connected to the outer wall of the piston rod 2. The side of the push member 4 close to the expansion member 3 is provided with the inclined push surface 41. The end of the expansion member 3 is hinged or fixedly connected to the sidewall of the sleeve 1, and is in contact with the bottom of the expansion member 3 via the inclined push surface 41. When the piston rod 2 moves upwards, it drives the push member 4 to move upwards synchronously. The push member 4 pushes the expansion member 3 to expand outwards via the inclined push surface 41. As the push member 4 gradually approaches the connection point between the expansion member 3 and the sleeve 1, the expansion angle of the expansion member 3 gradually increases, thereby increasing the anchoring force of the rock bolt with the inner wall of the rock bolt mounting hole in the rock wall during the locking process.

[0038] Further, the sleeve 1 includes an inner barrel 11 and an outer barrel 12 that are arranged coaxially. The inner barrel 11 is mounted within the outer barrel 12; the piston rod 2 is slidably connected within the inner barrel 11. An end of the inner barrel 11 extends out of the outer barrel 12. The end of the inner barrel 11 that extends out of the outer barrel 12 is in threaded connection with an adjusting nut 6.

[0039] Further, the end of the inner barrel 11 that extends out of the outer barrel 12 is sleeved with a supporting disk 61 between the adjusting nut 6 and the outer barrel 12.

[0040] Specifically, as shown in FIG. 1, the outer barrel 12 is sleeved over the outer wall of the inner barrel 11, and the inner barrel 11 is capable of sliding axially within the outer barrel 12. By rotating the adjusting nut 6, the adjusting nut 6 exerts an axial pulling force on the inner barrel 11, pulling the inner barrel 11 to slide upwards. The inner barrel 11, together with the piston rod 2, moves to the outside of the hole, thereby pushing the expansion member 3 to expand toward the outside of the outer barrel 12.

[0041] Specifically, when using the rock bolt of the present disclosure, a rock bolt hole is first drilled at a predetermined position in the surrounding rock wall of a high-geotemperature tunnel, with a hole diameter and a hole depth required by the design. After drilling is completed, the rock bolt hole is flushed 2 to 3 times to remove debris such as crushed stone and soil therein, ensuring that the rock bolt hole is clean and clear. The end of the rock bolt provided with the cylinder 8 is inserted into the rock bolt hole, with the end of the inner barrel 11 extending out of the rock bolt hole. A bonding agent is injected into the rock bolt hole to bond the outer barrel 12 to the surrounding rock mass. Subsequently, the supporting disk 61 and the adjusting nut 6 are sequentially mounted on the end of the inner barrel 11 extending out of the rock bolt hole.

[0042] Thereafter, prestress is applied to the inner wall of the rock bolt hole. The specific process is as follows: the adjusting nut 6 is tightened, gradually pulling the inner barrel 11 together with the piston rod 2 to move out of the rock bolt hole. The movement of the piston rod 2 drives the push member 4 to push the expansion member 3 to expand, thereby applying prestress to the inner wall of the rock bolt hole. After the application of prestress is completed, the anchor head is sealed. The adjusting nut 6 and the supporting disk 61 are sealed to protect the anchor head from external erosion.

[0043] Further, a self-locking mechanism 7 is disposed between the inner barrel 11 and the outer barrel 12 and includes a ratchet bar 71, a pawl 72, and an elastic member 73. The ratchet bar 71 is fixedly connected to an outer wall of the inner barrel 11. The elastic member 73 is connected between the pawl 72 and an inner wall of the outer barrel 12. The pawl 72 is pressed toward the ratchet bar 71 to limit the inner barrel 11 from moving back toward the inside of the outer barrel 12.

[0044] Specifically, as shown in FIG. 5, a ratchet bar 71 is fixedly connected to the outer wall of the inner barrel 11. The ratchet bar 71 is provided with a plurality of non-return teeth, and a side of each non-return tooth facing the adjusting nut 6 is configured as an inclined surface, and the inclined surface is inclined in a direction away from the adjusting nut 6. A side of each non-return tooth away from the adjusting nut 6 is configured as a flat surface perpendicular to the outer wall of the inner barrel 11. The elastic member 73 is configured as a spring. A connecting base 74 is fixedly connected to the inner wall of the outer barrel 12. An end of the pawl 72 extends into the connecting base 74 and is slidably connected to the connecting base 74. The connecting base 74 is provided with a connecting cavity 741 into which the pawl 72 is inserted. A limiting step 742 is fixedly connected at a port of the connecting cavity 741. A limiting protrusion 721 is fixedly connected to an end of the pawl 72 inserted into the connecting cavity 741, and the limiting protrusion 721 restricts the limiting step 742 from disengaging from the port of the connecting cavity 741. The elastic member 73 is disposed within the connecting cavity 741 and located between the pawl 72 and the inner wall of the outer barrel 12. The elastic member 73 is normally in a compressed state. The elastic member 73 pushes the pawl 72 toward the ratchet bar 71. When prestress is applied to the rock bolt hole, the adjusting nut 6 pulls the inner barrel 11 to move toward the rock bolt hole. The pawl 72 remains engaged with the ratchet bar 71, and the ratchet bar 71 pushes the pawl 72 to move into the connecting cavity 741 via the inclined surfaces. When the inner barrel 11 moves toward the interior of the outer barrel 12, the pawl 72 contacts the flat surfaces of the non-return teeth, thereby limiting the inner barrel 11 from moving back toward the inside of the outer barrel 12 and thus achieving one-way locking of the inner barrel 11.

[0045] Further, the cylinder 8 includes a hydraulic cylinder 81 and a driving cylinder 82 that have inner cavities communicating with each other. The end of the piston rod 2 extends into the hydraulic cylinder 81 and is slidably connected to an inner wall of the hydraulic cylinder 81. A cross-sectional area of the inner wall of the hydraulic cylinder 81 is larger than a cross-sectional area of an inner wall of the driving cylinder 82. A driving piston 83 is slidably connected within the driving cylinder 82 and fits against the inner wall of the driving cylinder 82. The expansion cavity 5 includes a first cavity 51 between the driving piston 83 and the piston rod 2 and a second cavity 52 on a side of the driving piston 83 away from the piston rod 2. The phase change material is arranged within the second cavity 52. The first cavity 51 is filled with a hydraulic oil.

[0046] Specifically, as shown in FIG. 1, the end of the piston rod 2 extends into the hydraulic cylinder 81. The end of the piston rod 2 extending into the hydraulic cylinder 81 has a T-shaped cross-section. The piston rod 2 is in clearance fit with the inner wall of the hydraulic cylinder 81, achieving a sliding connection of the piston rod 2 on the inner wall of the hydraulic cylinder 81. A sealing ring between the piston rod 2 and the inner wall of the hydraulic cylinder 81 is mounted on the piston rod 2. The portion of the piston rod 2 that is in clearance fit with the inner wall of the hydraulic cylinder 81 is sleeved with the sealing ring to improve the sealing effect between the piston rod 2 and the inner wall of the hydraulic cylinder 81. The driving piston 83 is slidably connected to the inner wall of the driving cylinder 82 and fits against the inner wall of the driving cylinder 82. The driving piston 83 divides the expansion cavity 5 into the first cavity 51 between the piston rod 2 and the driving piston 83 and the second cavity 52 on the side of the driving piston 83 away from the piston rod 2. The first cavity 51 is filled with the hydraulic oil, and the second cavity 52 is filled with the phase change material. When the phase change material is heated and vaporized, the pressure in the second cavity 52 increases, thereby pushing the driving piston 83 to move toward the piston rod 2. The driving piston 83 transmits the pressure to the end of the piston rod 2 through the hydraulic oil, thereby pushing the piston rod 2 to slide relative to the inner barrel 11. The cross-sectional area of the hydraulic cylinder 81 is set to be larger than that of the driving cylinder 82, thereby increasing the pushing force exerted by the hydraulic oil to the end of the piston rod 2.

[0047] Further, a one-way valve 9 is mounted within the driving cylinder 82 and located between the driving piston 83 and the piston rod 2. The one-way valve 9 only allows the hydraulic oil to flow from the driving cylinder 82 toward the hydraulic cylinder 81.

[0048] Further, the inner cavity of the driving cylinder 82 is bottle-shaped and has a small-diameter end communicating with the hydraulic cylinder 81.

[0049] Specifically, as shown in FIG. 1, the inner cavity of the driving cylinder 82 is configured as a bottle-shaped structure. The small-diameter end of the inner cavity of the driving cylinder 82 communicates with the hydraulic cylinder 81. The one-way valve 9 between the piston rod 2 and the driving piston 83 is mounted within the driving cylinder 82. The one-way valve 9 is configured to only allow the hydraulic oil to flow from the driving cylinder 82 toward the hydraulic cylinder 81, thereby avoiding the failure of prestress compensation due to backflow of the hydraulic oil into the driving cylinder 82 when the geotemperature decreases, and improving the stability of the prestress.

[0050] Specifically, as shown in FIG. 4, the one-way valve 9 includes a valve body 91, a valve core 92, a push spring 93, and a locking nut 94. The valve body 91 is provided with an oil passage extending therethrough in a front-rear direction. The oil passage includes an oil inlet cavity 911 and an oil outlet cavity 912 that communicate with each other. The valve core 92 is disposed within the oil outlet cavity 912. The diameter of the valve core 92 is larger than that of a port where the oil inlet cavity 911 communicates with the oil outlet cavity 912, and the valve core 92 covers the port of the oil inlet cavity 911. The push spring 93 and the locking nut 94 are mounted within the oil outlet cavity 912. The locking nut 94 is in threaded connection with the inner wall of the oil outlet cavity 912. The locking nut 94 is provided with an oil outlet through hole 941. The push spring 93 is located between the valve core 92 and the locking nut 94 and has one end in contact with the valve core 92 and another end in contact with the locking nut 94 for pushing the valve core 92 to cover the port of the oil inlet cavity 911. When mounting the one-way valve 9, the oil outlet cavity 912 is disposed opposite the piston rod 2. When the hydraulic oil flows from the driving cylinder 82 toward the hydraulic cylinder, it enters from the oil inlet cavity 911, pushing the valve core 92 to disengage from the port of the oil inlet cavity 911. The oil inlet cavity 911 communicates with the oil outlet cavity 912, and the hydraulic oil passes through the oil outlet through hole 941 of the locking nut 94 and then flows out from the oil outlet cavity 912 into the hydraulic cylinder 81. When the geotemperature decreases and the hydraulic oil cannot flow from the driving cylinder 82 toward the hydraulic cylinder, the hydraulic oil within the hydraulic cylinder 81 enters the oil passage from the oil outlet cavity 912. After passing through the oil outlet through hole 941 of the locking nut 94, it applies pressure together with the push spring 93 to the valve core 92, pressing the valve core 92 tightly against the port of the oil inlet cavity 911, thereby blocking the hydraulic oil from flowing from the oil outlet cavity 912 toward the oil inlet cavity 911 and thus only allowing the hydraulic oil to flow from the driving cylinder 82 toward the hydraulic cylinder 81.

[0051] Further, the phase change material includes acetone.

[0052] Specifically, the phase change material is selected to be chemically stable and have a relatively low boiling point. Acetone is preferred as the phase change material, with a boiling point of 56.5°C. Under the condition of the geotemperature above 60°C, acetone reaches its boiling point and expands in volume by approximately 400 times. Of course, other low-boiling-point substances may also be selected, such as one or more of dichloromethane, diethyl ether, methanol, perfluorohexanone, and n-pentane as the phase change material.

[0053] The use of the geothermal-based self-compensating expansion shell rock bolt of the present disclosure includes the following steps:

[0054] In step S1, hole drilling and cleaning are carried out.

[0055] Specifically, a rock bolt hole is drilled according to a hole diameter and a hole depth required by the design, and then the rock bolt hole is flushed 2 to 3 times to remove debris such as crushed stone and soil therein, ensuring that the rock bolt hole is clean and clear

[0056] In step S2, the geothermal-based self-compensating expansion shell rock bolt is inserted into the rock bolt hole and fixed with a bonding agent.

[0057] Specifically, the geothermal-based self-compensating expansion shell rock bolt is inserted into the rock bolt hole, with the second cavity 52 positioned in a high-geotemperature zone, and a high-temperature-resistant bonding agent is injected simultaneously.

[0058] In step S3, the supporting disk 61 and the adjusting nut 6 are sequentially mounted on the end of the outer barrel12 extending out of the rock bolt hole.

[0059] In step S4, initial tensioning is carried out.

[0060] Specifically, the adjusting nut 6 is tightened, gradually pulling the inner barrel 11 together with the piston rod 2 to move out of the rock bolt hole. Before tightening the adjusting nut 6, the state of the rock bolt is as shown in FIG. 3(a). After tightening the adjusting nut 6, the movement of the piston rod 2 drives the push member 4 to push the expansion member 3 to expand, as shown in FIG. 3(b), thereby applying prestress to the inner wall of the rock bolt hole. The elastic member 73 pushes the pawl 72 to remain engaged with the ratchet bar 71, thereby limiting the inner barrel 11 from moving back toward the inside of the outer barrel 12 and thus achieving one-way locking of the inner barrel 11. After the application of prestress is completed, the anchor head is sealed. The adjusting nut 6 and the supporting disk 61 are sealed to protect the anchor head from external erosion.

[0061] During the service life of the geothermal-based self-compensating expansion shell rock bolt of the present disclosure within the rock bolt hole, the rock bolt spontaneously performs prestress self-compensation. The specific process of prestress self-compensation is as follows: the phase change material disposed within the expansion cavity 5 undergoes a phase change under the action of the high geotemperature, resulting in a volume expansion which pushes the driving piston 83 to move toward the hydraulic cylinder 81. As shown in FIG. 3(c), the driving piston 83 pushes the hydraulic oil to flow into the hydraulic cylinder 81, thereby applying a pushing force via the hydraulic oil to the end of the piston rod 2 for pushing the piston rod 2 to move toward the port of the rock bolt hole. The movement of the piston rod 2 drives the push member 4 to move synchronously, and the push member 4 pushes the expansion member 3 to expand toward the outside of the outer barrel 12, thereby compensating for prestress loss during the locking process of the rock bolt and achieving prestress self-compensation. The one-way valve 9 disposed between the driving piston 83 and the piston rod 2 only allows the hydraulic oil to flow from the driving cylinder 82 toward the hydraulic cylinder 81, thereby avoiding the failure of prestress compensation due to backflow of the hydraulic oil into the driving cylinder 82 when the geotemperature decreases, and improving the stability of the prestress.

[0062] The above embodiments and the features of the embodiments herein may be combined with each other without conflict.

[0063] The above are merely preferred examples of the present disclosure, and are not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, and the like made within the spirit and principle of the present disclosure shall be all included in the protection scope of the present disclosure.

Claims

1. A geothermal-based self-compensating expansion shell rock bolt, comprising: a sleeve, a piston rod, a push member, and an expansion member, wherein the piston rod is slidably connected within the sleeve; the expansion member is connected to the sleeve; the push member is connected to the piston rod and configured to act on the expansion member; a push hole is defined in the sleeve for the push member to extend out therethrough; a cylinder is disposed within the sleeve; an end of the piston rod extends into the cylinder; the end of the piston rod that extends into the cylinder and an inner wall of the cylinder define an expansion cavity; and a phase change material is disposed within the expansion cavity; and when heated and vaporized, the phase change material pushes the piston rod to move, whereby the piston rod slides through the push member and pushes the expansion member to expand outwards from inside the sleeve.

2. The geothermal-based self-compensating expansion shell rock bolt according to claim 1, wherein an end of the expansion member is hinged to the sleeve; and the push member has one end hinged to the expansion member and an other end hinged to the piston rod.

3. The geothermal-based self-compensating expansion shell rock bolt according to claim 1, wherein the push member is fixedly connected to the piston rod; and an end of the push member close to the expansion member is provided with an inclined push surface that is in contact with a side of the expansion member close to the sleeve.

4. The geothermal-based self-compensating expansion shell rock bolt according to claim 1, wherein the sleeve comprises an inner barrel and an outer barrel that are arranged coaxially; the inner barrel is mounted within the outer barrel; the piston rod is slidably connected within the inner barrel; an end of the inner barrel extends out of the outer barrel; and the end of the inner barrel that extends out of the outer barrel is in threaded connection with an adjusting nut.

5. The geothermal-based self-compensating expansion shell rock bolt according to claim 4, wherein a self-locking mechanism is disposed between the inner barrel and the outer barrel and comprises a ratchet bar, a pawl, and an elastic member; the ratchet bar is fixedly connected to an outer wall of the inner barrel; the elastic member is connected between the pawl and an inner wall of the outer barrel; and the pawl is pressed toward the ratchet bar to limit the inner barrel from moving back toward an inside of the outer barrel.

6. The geothermal-based self-compensating expansion shell rock bolt according to claim 4, wherein the end of the inner barrel that extends out of the outer barrel is sleeved with a supporting disk between the adjusting nut and the outer barrel.

7. The geothermal-based self-compensating expansion shell rock bolt according to claim 1, wherein the cylinder comprises a hydraulic cylinder and a driving cylinder that have inner cavities communicating with each other; the end of the piston rod extends into the hydraulic cylinder and is slidably connected to an inner wall of the hydraulic cylinder; a cross-sectional area of the inner wall of the hydraulic cylinder is larger than a cross-sectional area of an inner wall of the driving cylinder; a driving piston is slidably connected within the driving cylinder and fits against the inner wall of the driving cylinder; the expansion cavity comprises a first cavity between the driving piston and the piston rod and a second cavity on a side of the driving piston away from the piston rod; the phase change material is arranged within the second cavity; and the first cavity is filled with a hydraulic oil.

8. The geothermal-based self-compensating expansion shell rock bolt according to claim 7, wherein a one-way valve is mounted within the driving cylinder and located between the driving piston and the piston rod; and the one-way valve only allows the hydraulic oil to flow from the driving cylinder toward the hydraulic cylinder.

9. The geothermal-based self-compensating expansion shell rock bolt according to claim 7, wherein the inner cavity of the driving cylinder is narrow-mouth bottle-shaped and has a small-diameter end communicating with the hydraulic cylinder.

10. The geothermal-based self-compensating expansion shell rock bolt according to claim 1, wherein the phase change material comprises acetone.

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