Rock stratum fracturing method and device for assisting mechanical tunneling of limestone roadway

Abstract

The invention discloses a rock stratum fracturing method and device for assisting mechanical tunneling of a limestone roadway, and aims to solve the problem that mechanical tunneling of the limestone roadway is difficult. According to the rock stratum fracturing method, firstly, a hole is drilled in a roadway tunneling working face, and then a fracture network is supported through segmented pulse acidizing fracturing and segmented proppant pumping injection, or the fracture network is supported through segmented pulse fracturing, whole-segment pressure maintaining acidizing and whole-segment proppant pumping injection. A dense crack network with a large opening degree is formed in the hard limestone in a mode of pulse fracturing, or segmented pulse fracturing, whole-section pump injection of a proppant to support a crack network and whole-section pressure maintaining acidification, so that the aim of fully transforming a rock mass structure is fulfilled. The hardness and integrity of the hard limestone can be reduced, the mechanical tunneling efficiency of the hard limestone roadway can be effectively improved, and the wear rate of the cutting pick is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of mining, and in particular relates to a rock stratum fracturing method and device for assisting mechanical excavation of limestone tunnels. Background Art

[0002] The shafts, parking lots, main tunnels, and other major roadways in underground mines are all constructed using rock tunnels. While rock tunnels offer greater stability and lower maintenance costs, they are significantly more challenging to excavate than coal tunnels, especially in hard limestone. Hard limestone, with a Proctor f coefficient exceeding 12, exhibits high strength and excellent integrity. Underground tunnels and mountain passages also contain a large amount of hard limestone, which is difficult to excavate.

[0003] Rock tunneling is typically driven solely by mechanical excavation, often resulting in problems such as inability to dig, low efficiency, severe pick wear, and high dust concentrations. This not only significantly impacts underground engineering schedules but also poses a health risk to the tunneling crew. Therefore, rock tunneling must overcome the challenges of the hardness and integrity of limestone. A common approach is to structurally modify the rock mass. This structural modification weakens the rock mass's integrity to facilitate mechanical rock breaking.

[0004] The current mainstream method for rock mass structural transformation is hydraulic fracturing, which artificially creates fractures within the rock mass to weaken its strength. Conventional hydraulic fracturing applies pressure to hard rock using high-pressure water, creating extended cracks within the rock mass. However, in the fracturing of dense limestone, the cracks are small in size and, due to the influence of geostress, tend to reclose after pumping stops, resulting in suboptimal rock mass structural transformation. Summary of the Invention

[0005] Purpose of the invention: The first purpose of the present invention is to provide a rock fracturing method for assisting mechanical excavation of limestone tunnels with good rock structure transformation effect, which helps to ensure the efficiency of mechanical excavation of rock tunnels; the second purpose of the present invention is to provide a rock fracturing device for assisting mechanical excavation of limestone tunnels.

[0006] Technical solution: The present invention provides a rock fracturing method for assisting mechanical excavation of limestone tunnels, comprising:

[0007] A hole is drilled on the tunnel excavation working face; a dense fracture network is fractured in a fractured area of the drilled hole by a pulse acid fracturing method, wherein the pulse acid fracturing method is to replace the working fluid of the pulse fracturing method with acid liquid; a proppant is injected into the dense fracture network of the fractured area by a proppant pumping method to form a dense large-opening fracture network, wherein the proppant is a solid hard material that does not react with the acid liquid; and pulse acid fracturing and proppant pumping are successively performed on the next fractured area in the same manner until all fractured areas have completed pulse acid fracturing and proppant pumping.

[0008] Furthermore, the acid solution is diluted hydrochloric acid with a concentration of 15% to 20%, and the proppant is quartz sand.

[0009] Optionally, a rock fracturing method for assisting mechanical excavation of a limestone tunnel according to the present invention comprises:

[0010] Drill holes on the tunnel excavation working face; use pulse fracturing to create a dense fracture network in a fractured area of the drilled hole, and use the same method to perform pulse fracturing on the next fractured area until all fractured areas have been pulse fractured; use pressure-maintaining acidification to inject acid into all fractured areas and maintain pressure for a period of time until the pressure is sufficient to open the fractures; use proppant pumping to inject proppant into the dense fracture network of all fractured areas to form a dense large-opening fracture network. The proppant is a solid, hard material that does not react with acid.

[0011] Furthermore, the acid solution is diluted hydrochloric acid with a concentration of 15% to 20%, and the proppant is quartz sand.

[0012] Furthermore, the holding pressure is 10-20 MPa, and the holding time is 10-20 min.

[0013] Optionally, a rock fracturing method for assisting mechanical excavation of a limestone tunnel according to the present invention comprises:

[0014] A hole is drilled on the tunnel excavation working face; a dense fracture network is fractured in a fractured area of the drilled hole by a pulse fracturing method; proppant is injected into the dense fracture network of the fractured area by a pumping proppant method to form a dense large-opening fracture network, wherein the proppant is a solid hard material that does not react with acid; pulse fracturing and proppant pumping are performed on the next fractured area in the same way until all fractured areas have completed pulse fracturing and proppant pumping; acid is injected into all fractured areas by a pressure-maintaining acidizing method and pressure is maintained for a period of time, and the pressure-maintaining pressure is sufficient to open the cracks.

[0015] Furthermore, the acid solution is diluted hydrochloric acid with a concentration of 15% to 20%, and the proppant is quartz sand.

[0016] Furthermore, the holding pressure is 10-20 MPa, and the holding time is 10-20 min.

[0017] Optionally, a rock fracturing method for assisting mechanical excavation of a limestone tunnel according to the present invention comprises:

[0018] For large-section tunnels, multiple holes are drilled on the tunnel excavation working face. The multiple holes are spaced apart and the following operations are performed simultaneously on each hole:

[0019] A dense fracture network is created in a fractured area of the drilled hole by pulse acid fracturing. The pulse acid fracturing method replaces water with acid as the working fluid in the pulse fracturing method. Proppant is injected into the dense fracture network of the fractured area by pumping proppant to form a dense large-aperture fracture network. The proppant is a solid, hard material that does not react with the acid. The next fractured area is pulse acid fracturing and proppant pumping are performed in the same manner until all fractured areas have been pulse acid fracturing and proppant pumping.

[0020] Alternatively, a dense fracture network is fractured in a fractured area of the drilled hole by pulse fracturing, and the next fractured area is pulse fractured in the same manner until all fractured areas are pulse fractured; an acid solution is injected into all fractured areas by pressure-maintaining acidification and pressure is maintained for a period of time until the pressure is sufficient to open the fractures; and a proppant is pumped into the dense fracture network of all fractured areas by proppant injection, where the proppant is a solid, hard material that does not react with the acid solution, to form a dense, large-opening fracture network;

[0021] Alternatively, a dense fracture network is fractured in a fractured area of the drilled hole by a pulse fracturing method; proppant is injected into the dense fracture network of the fractured area by a pumping proppant method to form a dense large-opening fracture network, wherein the proppant is a solid hard material that does not react with acid; pulse fracturing and proppant pumping are successively performed on the next fractured area in the same manner until all fractured areas have completed pulse fracturing and proppant pumping; acid is injected into all fractured areas by a pressure-maintaining acidizing method and pressure is maintained for a period of time, until the pressure is sufficient to open the fractures.

[0022] The present invention provides a rock fracturing device for assisting mechanical excavation of limestone tunnels, comprising a hydrochloric acid solution mixing box, a water tank, a pulse pump, a high-pressure hose, and a high-pressure sealed drill pipe connected in sequence. The high-pressure hose is equipped with a sand carrying tank, a hydraulic fracturing measurement and control instrument, and a pressure relief valve. A valve is installed on the pipeline between the hydrochloric acid solution mixing box and the water tank. The sand carrying tank is filled with quartz sand. When multiple high-pressure sealed drill pipes are provided, the multiple high-pressure sealed drill pipes are connected to the high-pressure hose via a multi-tube joint. The number of high-pressure sealed drill pipes is determined according to the number of holes to be drilled simultaneously.

[0023] The high-pressure sealed drill pipe is a multi-section structure with different sections connected by threads. The high-pressure sealed drill pipe is sequentially connected to a packer, an intermediate pipe, and another packer, and the connections between them are threaded. A one-way valve is installed on the circumferential surface of the intermediate pipe. The opening pressure of the one-way valve is greater than the expansion pressure of the packer.

[0024] The high-pressure sealed drill pipe is installed on a crawler drilling rig, which is used to deliver the high-pressure sealed drill pipe and two packers into the borehole; the pulse pump is used to deliver water or dilute hydrochloric acid in the water tank to the fracturing area to achieve pulse fracturing or pulse acid fracturing; the dilute hydrochloric acid is pre-mixed in the hydrochloric acid solution mixing box and then delivered to the water tank; when the sand carrying tank is opened, the quartz sand in the sand carrying tank is delivered to the fracturing area along with the water flow to achieve pumping of the proppant.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0026] (1) Pulse acid fracturing and proppant injection methods for treating hard limestone in tunnel excavation

[0027] On the one hand, a dense crack network is formed in the hard limestone through the pulse acid fracturing method. At the same time, during the crack expansion process, the acid dissolves the crack wall, increasing the crack opening, which can reduce the limestone strength of the borehole wall, thereby reducing the fracture pressure and crack expansion pressure when fracturing the hard limestone, and ultimately achieving the goal of reducing the construction pressure of hard limestone.

[0028] On the other hand, while the uneven crack walls formed by acid erosion have a certain degree of self-supporting strength, the rock blocks on both sides of the crack are still susceptible to interlocking due to the significant influence of ground stress during rock tunneling. Therefore, after the pulse acid fracturing operation, proppant is continuously pumped into the crack to expand and support the crack, ultimately achieving the goal of improving the limestone structure.

[0029] (2) Pulse fracturing, pressure-maintaining acidizing, and proppant injection methods for treating hard limestone in tunnel excavation

[0030] First, a dense network of fractures is formed in the hard limestone through pulse fracturing, achieving the first reduction in rock strength. Second, all fractured areas are acidified to weaken the borehole wall strength and expand the fracturing range. Due to the heterogeneity of the rock, the acid will erode irregular small pits on the surface of the fractures, which will increase the opening of the fractures to a certain extent and achieve the second reduction in rock strength. Finally, the pumped proppant plays a role in expanding and supporting the fractures, slowing down the bite effect of the fractures, thereby reducing construction pressure and ultimately achieving the purpose of improving the limestone structural transformation effect.

[0031] (3) Pulse fracturing, proppant injection, and pressure-maintaining acidizing methods for treating hard limestone in tunneling

[0032] The following considerations guide proppant injection early: After pulse fracturing, if pressure-maintained acidizing is performed on all fractured areas, the fractures may close prematurely before proppant injection. Therefore, injecting proppant after pulse fracturing to maintain fracture openness and then pressure-maintained acidizing on all fractured areas allows for better penetration of the acid into the fractures.

[0033] The invention is suitable for mechanical excavation of hard lanes (tunnels), especially for mechanical excavation of hard limestone lanes (tunnels), and is also suitable for excavation of large-section lanes when multi-hole fracturing is performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic structural diagram of a rock fracturing device for assisting mechanical excavation of a limestone tunnel provided by an embodiment of the present invention;

[0035] Figure 2 (a) is a schematic diagram of the tunnel cross section and pulse fracturing crack morphology in an embodiment of the present invention, Figure 2 (b) is a schematic diagram of a laneway in an embodiment of the present invention;

[0036] Figure 3 This is a comparison diagram of crack morphology before and after acidizing in an embodiment of the present invention;

[0037] Figure 4 This is a comparison diagram of the fracture morphology before and after proppant injection in an embodiment of the present invention;

[0038] Figure 5 (a) is a schematic diagram of a large-section roadway cross-section in an embodiment of the present invention, Figure 5 (b) is a schematic diagram of multi-hole fracturing in a large-section tunnel in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to the accompanying drawings.

[0040] Attachment Figures 1 to 5 The reference numerals in the figures are as follows:

[0041] 1. Pulse pump; 2. Water tank; 3. Hydraulic fracturing monitoring and control instrument; 4. Pressure relief valve; 5. High-pressure hose; 6. High-pressure sealed drill pipe; 7. Sand-carrying tank; 8. Crawler drill rig; 9. Packer; 10. One-way valve; 11. Hydrochloric acid solution mixing box; 12. Tunnel; 13 / 21. Borehole; 14. Dense fracture network; 15. Dilute hydrochloric acid; 16. Single fracture morphology after acidizing; 17. Single fracture morphology before acidizing; 18. Proppant-containing water flow; 19. Fracture morphology after proppant injection; 20. Proppant; 22. Large-section tunnel.

[0042] Example 1

[0043] like Figure 1 As shown, Example 1 provides a rock fracturing device for assisting mechanical excavation in limestone tunnels. The device comprises a hydrochloric acid solution mixing tank 11, a water tank 2, a pulse pump 1, a high-pressure hose 5, and a high-pressure sealed drill pipe 6, which are connected in sequence. The high-pressure hose 5 is equipped with a sand-carrying tank 7, a hydraulic fracturing control instrument 3, and a pressure relief valve 4. The hydraulic fracturing control instrument 3 and the pressure relief valve 4 are each connected to the high-pressure hose 5 via a tee. A valve is installed on the pipeline between the hydrochloric acid solution mixing tank 11 and the water tank 2. The sand-carrying tank 7 is filled with quartz sand, which serves as a proppant.

[0044] When multiple holes need to be drilled at the same time, a number of high-pressure sealed drill rods 6 equal to the number of holes need to be configured. Multiple high-pressure sealed drill rods 6 are connected to high-pressure rubber hoses 5 through a multi-tube joint. The multi-tube joint can be made by yourself or purchased from outside.

[0045] The high-pressure sealing drill pipe 6 is a multi-section structure, and different sections of the rod are threadedly connected, so that the high-pressure sealing drill pipe 6 can change the rod length according to the use requirements. Each high-pressure sealing drill pipe 6 is equipped with two packers 9. The front end of the high-pressure sealing drill pipe 6 is threadedly connected to a packer 9, and the two packers 9 are connected by a section of an intermediate pipe, and the connection method is a threaded connection. A one-way valve 10 is provided on the circumferential surface of the intermediate pipe. Preferably, the number of the one-way valves 10 is multiple and evenly arranged along the circumferential surface of the intermediate pipe. The opening pressure of the one-way valve 10 is greater than the expansion pressure of the packer 9, so that the packer 9 expands first, forming a sealed cavity between the two packers 9, and the one-way valve 10 opens later to communicate the sealed cavity.

[0046] The high-pressure sealed drill pipe 6 is installed on the crawler drilling rig 8. During construction, the crawler drilling rig 8 is used to deliver the high-pressure sealed drill pipe 6 and the two packers 9 to the borehole. The pulse pump 1 is used to deliver the water or dilute hydrochloric acid in the water tank 2 to the fracturing area to achieve pulse fracturing or pulse acid fracturing. The dilute hydrochloric acid is pre-prepared in the hydrochloric acid solution preparation box 11 and then transported to the water tank 2. When the sand carrying tank 7 is opened, the sand in the sand carrying tank 7 is delivered to the fracturing area along with the water flow to achieve the pumping of the proppant. After the construction is completed, the pressure is released by the pressure relief valve 4. After the packer 9 shrinks, the high-pressure sealed drill pipe 6 and the two packers 9 can be removed.

[0047] Example 2

[0048] In a certain coal mine, the pit bottom parking lot was arranged in a rock tunnel. However, during the excavation process, hard limestone strata were encountered. The tunnel boring machine was unable to dig, had low efficiency, and suffered excessive tooth wear when cutting the hard rock. This had the adverse effects of slowing down the construction speed and increasing the construction cost.

[0049] To address the above issues, Example 2 provides a rock fracturing method for assisting mechanical excavation in limestone tunnels. The rock fracturing device described in Example 1 is used to transform the hard rock structure through segmented pulse acid fracturing and segmented proppant injection, thereby improving mechanical excavation efficiency. The specific steps are as follows:

[0050] Step S1: The crawler drill rig 8 constructs a 50m deep borehole 13 in the middle of the hard limestone in the excavation working face of the tunnel 12 (parking lot tunnel);

[0051] Step S2, assembling the high-pressure sealing drill pipe 6 and the two packers 9 and connecting the high-pressure hose 5;

[0052] Step S3: Use the crawler drill rig 8 to deliver the high pressure sealing drill pipe 6 and two packers 9 to the fracture area of the borehole 13. Figure 1 As shown;

[0053] Step S4: The diluted hydrochloric acid 15 with a concentration of 15% to 20% prepared in the hydrochloric acid solution preparation box 11 is transferred to the water tank 2, and the pulse pump 1 is turned on. When the hydraulic fracturing monitoring instrument 3 detects that the construction pressure is less than 5MPa or the fracturing time exceeds 60min, the pulse pump 1 pressure knob is slowly adjusted to zero, and the pulse pump 1 is turned off. A dense crack network 14 is formed in the tunnel 12. The internal morphology of the crack network after pulse acid fracturing is as follows: Figure 3 Open the sand tank 7, the quartz sand in the sand tank 7 flows into the layer with the water, and the internal fracture network is filled with proppant 20 after the proppant is pumped. Figure 4 As shown, Figure 4Where σ represents the in-situ stress in all directions. Close the sand-carrying tank 7, shorten the high-pressure sealed drill pipe 6, and retreat to the next fracturing zone. Repeat the pulse acid fracturing and proppant injection operations until all fracturing zones are completely completed.

[0054] Step S5: withdraw the high-pressure sealing drill pipe 6 and the two packers 9.

[0055] Example 3

[0056] In a certain coal mine, the completed mining area uphill needed to be extended forward. However, because the mining area uphill was arranged in a hard limestone stratum with high hardness and strong integrity, during the excavation process, the forward cutting speed of the tunnel boring machine was slow, affecting the normal mining and excavation continuity.

[0057] To address the above issues, Example 3 provides a rock fracturing method for assisting mechanical excavation in limestone tunnels. The rock fracturing device described in Example 1 is used to transform the hard rock structure through segmented pulse fracturing, whole-segment pressure-maintaining acidizing, and whole-segment proppant injection, thereby improving mechanical excavation efficiency. The specific steps are as follows:

[0058] Step S1: The crawler drill rig 8 constructs a 50m deep borehole 13 in the middle of the hard limestone in the tunneling working face of the tunnel 12 (uphill tunnel);

[0059] Step S2, assembling the high-pressure sealing drill pipe 6 and the two packers 9 and connecting the high-pressure hose 5;

[0060] Step S3: Use the crawler drill rig 8 to deliver the high pressure sealing drill pipe 6 and two packers 9 to the fracture area of the borehole 13. Figure 1 As shown;

[0061] Step S4, turn on the pulse pump 1. When the construction pressure monitored by the hydraulic fracturing monitoring instrument 3 is less than 5MPa or the fracturing time exceeds 60min, slowly adjust the pulse pump 1 pressure knob to zero, turn off the pulse pump 1, and form a dense crack network 14 in the hard limestone tunnel. The crack network morphology after pulse fracturing is as follows: Figure 2 As shown; shorten the high-pressure sealed drill pipe 6, retreat to the next fracturing area, and perform pulse fracturing again until all fracturing areas are fully completed by pulse fracturing; transport the diluted hydrochloric acid 15 with a concentration of 15% to 20% prepared in the hydrochloric acid solution box 11 to the water tank 2, and inject the diluted hydrochloric acid 15 into all fracturing areas at a pressure of 10 to 20 MPa. Maintain the pressure for 10 to 20 minutes to allow the diluted hydrochloric acid 15 to fully react with the limestone. The crack network morphology after pressure maintenance is as shown Figure 3 After the pressure is maintained, the sand tank 7 is opened and the pulse fracturing process is repeated to pump the proppant; the quartz sand in the sand tank 7 flows into the layer with the water, and the fracture network is filled with proppant 20 after the proppant is pumped. Figure 4Then close the sand carrying tank 7;

[0062] Step S5: After the proppant is pumped in, the high-pressure sealing drill pipe 6 and the two packers 9 are withdrawn.

[0063] Example 4

[0064] In a certain coal mine, the return air tunnel is arranged as a rock tunnel. However, the tunnel is set in a hard limestone stratum with high hardness and strong integrity, making it difficult for the tunnel boring machine to advance forward, seriously affecting the mine's safety engineering progress and production time.

[0065] To address the above issues, Example 4 provides a rock fracturing method for assisting mechanical excavation in limestone tunnels. The rock fracturing device described in Example 1 is used to improve mechanical excavation efficiency by transforming the hard rock structure through segmented pulse fracturing, whole-segment proppant injection, and whole-segment pressure-maintaining acidification. The specific steps are as follows:

[0066] Step S1: The crawler drill 8 constructs a 50m deep borehole 13 in the middle of the hard limestone on the working surface of the tunnel 12 (return air tunnel);

[0067] Step S2, assembling the high-pressure sealing drill pipe 6 and the two packers 9 and connecting the high-pressure hose 5;

[0068] Step S3: Use the crawler drill rig 8 to deliver the high pressure sealing drill pipe 6 and two packers 9 to the fracture area of the borehole 13. Figure 1 As shown;

[0069] Step S4, turn on the pulse pump 1. When the construction pressure monitored by the hydraulic fracturing monitoring instrument 3 is less than 5MPa or the fracturing time exceeds 60min, slowly adjust the pulse pump 1 pressure knob to zero, turn off the pulse pump 1, and form a dense crack network 14 in the hard limestone tunnel. The crack network morphology after pulse fracturing is as follows: Figure 2 Open the sand tank 7, repeat the pulse fracturing process, pumping the proppant; carrying sand tank 7 in the quartz sand with the water flow into the layer, after pumping the proppant inside the fracture network filled with proppant 20, as Figure 4 As shown; close the sand carrying tank 7, shorten the high-pressure sealed drill pipe 6, retreat to the next fracturing area, and perform pulse fracturing and proppant pumping operations again in sequence until all fracturing areas are completed with pulse fracturing and proppant pumping; transfer the diluted hydrochloric acid 15 with a concentration of 15% to 20% prepared in the hydrochloric acid solution equipment box 11 to the water tank 2, use a pressure of 10 to 20 MPa to inject the diluted hydrochloric acid 15 into all fracturing areas, maintain the pressure for 10 to 20 minutes, so that the diluted hydrochloric acid 15 fully reacts with the limestone, and the fracture network morphology after pressure maintenance is as shown Figure 3 As shown;

[0070] Step S5: After the pressure maintenance is completed, the high-pressure sealing drill pipe 6 and the two packers 9 are withdrawn.

[0071] Example 5

[0072] In a coal mine, during the excavation or extension of a large tunnel for infrastructure construction, a hard limestone stratum was encountered, making it difficult for the tunnel boring machine to advance. In addition, the high part of the tunnel section had strong integrity and was not likely to collapse with the excavation.

[0073] In response to the above problems, Example 5 provides a rock fracturing method to assist mechanical excavation of limestone tunnels. The rock fracturing device described in Example 1 is used to simultaneously fracture multiple pores to create a crack network in the hard limestone, transform the internal structure of the rock mass, ensure excavation efficiency, and prevent the high parts of the tunnel section from collapsing during excavation.

[0074] The crawler drill 8 constructs three 50m deep boreholes 21 in the hard limestone of the large cross-section tunnel 22. Figure 5 As shown; three high-pressure sealed drill pipes 6 are then prepared, and two packers 9 are assembled at the front end of each high-pressure sealed drill pipe 6. The three high-pressure sealed drill pipes 6 are then connected to a high-pressure hose 5 via a three-way pipe joint. Subsequently, a crawler drill rig 8 is used to simultaneously deliver the three high-pressure sealed drill pipes 6, connected to the two packers 9 at the front end, into the three boreholes 21, i.e., one high-pressure sealed drill pipe 6 is delivered to each borehole 2. The specific fracturing operation can be referred to the rock formation fracturing method described in any of Examples 2 to 4, and will not be described in detail here.

Claims

1. A rock fracturing method for assisting mechanical excavation of limestone tunnels, characterized in that: include: A hole is drilled on the tunnel excavation working face; a dense fracture network is fractured in a fractured area of the drilled hole by a pulse acid fracturing method, wherein the pulse acid fracturing method is to replace the working fluid of the pulse fracturing method with acid liquid; a proppant is injected into the dense fracture network of the fractured area by a proppant pumping method to form a dense large-opening fracture network, wherein the proppant is a solid hard material that does not react with the acid liquid; and pulse acid fracturing and proppant pumping are successively performed on the next fractured area in the same manner until all fractured areas have completed pulse acid fracturing and proppant pumping.

2. The rock fracturing method for assisting mechanical excavation of limestone tunnels according to claim 1, characterized in that: The acid solution is diluted hydrochloric acid with a concentration of 15% to 20%, and the proppant is quartz sand.

3. A rock fracturing method for assisting mechanical excavation of limestone tunnels, characterized in that: include: Drilling a hole on the tunnel excavation working face; using pulse fracturing to create a dense fracture network in a fractured area of the drilled hole, and then pulse fracturing the next fractured area using the same method until all fractured areas have been pulse fractured; Through the pressure-maintaining acidizing method, acid is injected into all fractured areas and the pressure is maintained for a period of time. The pressure maintenance pressure is sufficient to open the fractures. Through the pumping proppant method, proppant is injected into the dense fracture network of all fractured areas to form a dense large-opening fracture network. The proppant is a solid hard material that does not react with the acid.

4. The rock fracturing method for assisting mechanical excavation of limestone tunnels according to claim 3, characterized in that: The acid solution is diluted hydrochloric acid with a concentration of 15% to 20%, and the proppant is quartz sand.

5. The rock fracturing method for assisting mechanical excavation of limestone tunnels according to claim 3, characterized in that: The holding pressure is 10-20 MPa, and the holding time is 10-20 min.

6. A rock fracturing method for assisting mechanical excavation of limestone tunnels, characterized in that: include: Drilling holes on the tunnel excavation working face; fracturing a dense fracture network in a fracturing area of the drilled hole using a pulse fracturing method; The method of pumping proppant is to inject proppant into the dense fracture network of the first fracturing area to form a dense large-opening fracture network. The proppant is a solid hard material that does not react with acid. The next fracturing area is subjected to pulse fracturing and proppant pumping in the same way until all fracturing areas have completed pulse fracturing and proppant pumping. The method of pressure-maintaining acidizing is to inject acid into all fracturing areas and maintain pressure for a period of time. The pressure-maintaining pressure is sufficient to open the fractures.

7. The rock fracturing method for assisting mechanical excavation of limestone tunnels according to claim 6, characterized in that: The acid solution is diluted hydrochloric acid with a concentration of 15% to 20%, and the proppant is quartz sand.

8. The rock fracturing method for assisting mechanical excavation of limestone tunnels according to claim 6, characterized in that: The holding pressure is 10-20 MPa, and the holding time is 10-20 min.

9. A rock fracturing method for assisting mechanical excavation of limestone tunnels, characterized in that: include: For large-section tunnels, multiple holes are drilled on the tunnel excavation working face. The multiple holes are spaced apart and the following operations are performed simultaneously on each hole: A dense fracture network is created in a fractured area of the drilled hole by pulse acid fracturing. The pulse acid fracturing method replaces water with acid as the working fluid in the pulse fracturing method. Proppant is injected into the dense fracture network of the fractured area by pumping proppant to form a dense large-aperture fracture network. The proppant is a solid, hard material that does not react with the acid. The next fractured area is pulse acid fracturing and proppant pumping are performed in the same manner until all fractured areas have been pulse acid fracturing and proppant pumping. Alternatively, a dense fracture network is fractured in a fracturing area of the drilled hole by pulse fracturing, and the next fracturing area is pulse fractured using the same method until all fracturing areas are pulse fractured. Acid is injected into all fractured areas through pressure-maintaining acidification and maintained for a period of time until the pressure is sufficient to open the fractures. Proppants are then pumped into the dense fracture network of all fractured areas to form a dense, wide-opening fracture network. Proppants are solid, hard materials that do not react with acid. Alternatively, a dense fracture network is fractured in a fractured area of the drilled hole by a pulse fracturing method; proppant is injected into the dense fracture network of the fractured area by a pumping proppant method to form a dense large-opening fracture network, wherein the proppant is a solid hard material that does not react with acid; pulse fracturing and proppant pumping are successively performed on the next fractured area in the same manner until all fractured areas have completed pulse fracturing and proppant pumping; acid is injected into all fractured areas by a pressure-maintaining acidizing method and pressure is maintained for a period of time, until the pressure is sufficient to open the fractures.

10. A rock fracturing device for assisting mechanical excavation of limestone tunnels, characterized in that: The invention comprises a hydrochloric acid solution mixing box (11), a water tank (2), a pulse pump (1), a high-pressure rubber hose (5) and a high-pressure sealing drill pipe (6) which are connected in sequence. The high-pressure rubber hose (5) is equipped with a sand carrying tank (7), a hydraulic fracturing measuring and controlling instrument (3) and a pressure relief valve (4); a valve is installed on the pipeline between the hydrochloric acid solution mixing box (11) and the water tank (2); the sand carrying tank (7) is filled with quartz sand; when there are multiple high-pressure sealing drill pipes (6), the multiple high-pressure sealing drill pipes (6) are connected to the high-pressure rubber hose (5) through a multi-tube joint; the number of high-pressure sealing drill pipes (6) is determined according to the number of drill holes to be constructed simultaneously; The high-pressure sealing drill pipe (6) is a multi-section structure, and different sections are connected by threads; the high-pressure sealing drill pipe (6) is sequentially connected to a packer (9), an intermediate pipe and another packer (9), and the connection between them is threaded; a one-way valve (10) is provided on the circumferential surface of the intermediate pipe, and the opening pressure of the one-way valve (10) is greater than the expansion pressure of the packer (9); A high-pressure sealed drill pipe (6) is installed on a crawler drill rig (8), and the crawler drill rig (8) is used to deliver the high-pressure sealed drill pipe (6) and two packers (9) to the borehole; a pulse pump (1) is used to deliver water or dilute hydrochloric acid in a water tank (2) to a fracturing area, thereby realizing pulse fracturing or pulse acid fracturing; dilute hydrochloric acid is pre-prepared in a hydrochloric acid solution preparation box (11) and then delivered to the water tank (2); when a sand carrying tank (7) is opened, quartz sand in the sand carrying tank (7) is delivered to the fracturing area along with the water flow, thereby realizing pump injection of a proppant.

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