Freezing escape method

Abstract

The invention discloses a freezing escape method, which belongs to the technical field of tunnel construction, and comprises the following steps of: S1, forming a probe hole from a tunnel main hole to surrounding rock above a flat pilot tunnel, and detecting the position and the size of a cavity; s2, sand blowing and water backfilling are conducted on the cavity, and a drainage hole is formed for drainage; s3, a freezing hole is drilled from the tunnel main hole to the flat pilot tunnel, the freezing hole penetrates into surrounding rock of the flat pilot tunnel to form a freezing area, and a freezing pipe is installed in the freezing hole; s3, freezing liquid is injected into the freezing pipe, the rock mass in the freezing area is frozen, the freezing condition is observed, and the freezing pipe is pulled out after freezing reaches the standard; and S4, the tunnel boring machine performs normal tunneling in the flat pilot tunnel. The cavity of the subsidence area is detected through the exploring hole, sand blowing and backfilling are conducted on the cavity, the risk of re-collapse in the freezing process is reduced, then the subsidence area of the flat pilot tunnel is frozen through a freezing method, the stability of rock mass in the subsidence area is enhanced, it is guaranteed that the risk of secondary collapse does not occur in the subsequent construction process of the tunnel, and the construction efficiency is improved. And the deadline of difficult rework is helped to get rid of.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, in particular to a freezing escape method. Background Art

[0002] During tunnel construction, if the surrounding rock at the top of the horizontal pilot tunnel collapses, construction must be suspended to ensure the safety of construction workers and prevent further collapses, significantly delaying the construction schedule. Currently, there is no effective solution for effectively repairing the collapsed area of ​​the horizontal pilot tunnel to prevent further collapse and help resolve the impasse of resuming work. Therefore, a method is urgently needed to repair and reinforce the collapsed area after the horizontal pilot tunnel collapses to prevent secondary collapse. Summary of the Invention

[0003] The purpose of the present invention is to solve the above technical problems and provide a freezing escape method, which detects the cavity in the collapsed area through exploration holes and blows sand back to fill the cavity, thereby enhancing the stability of the rock mass in the collapsed area and reducing the risk of re-collapse during the freezing process. The collapsed area of ​​the flat pilot tunnel is then frozen by the freezing method to further enhance the stability of the rock mass in the collapsed area, ensuring that there is no risk of secondary collapse during the tunnel construction process, and helping the flat pilot tunnel to escape the deadlock of difficulty in resuming work.

[0004] To achieve the above object, the present invention provides the following solution: The present invention discloses a freezing escape method, comprising the following steps: S1. Drilling holes in the surrounding rock above the main tunnel toward the horizontal pilot tunnel to determine the location and size of the cavity in the collapsed area of ​​the fault segment, and then backfilling the cavity by blowing sand; S2. Blow sand and backfill the cavity in the collapsed area of ​​the fault segment with water, and set drainage holes at high positions in the cavity in the collapsed area of ​​the fault segment for drainage; S3, drilling freezing holes from the main tunnel to the horizontal pilot tunnel below the collapsed area of ​​the fault section, the freezing holes penetrating into the surrounding rock of the horizontal pilot tunnel to form a frozen zone, installing freezing pipes in the freezing holes, and sealing the freezing pipes at the ends away from the main tunnel; S3, circulating a freezing liquid into the freezing pipe to freeze the rock mass in the freezing area, observing the freezing condition during the freezing process, and pulling out the freezing pipe after the freezing condition is met; S4. The tunnel boring machine in the horizontal pilot tunnel is advancing normally.

[0005] Preferably, in step S1, during the process of drilling the exploratory hole, it is determined whether a cavity has been drilled according to the change in drilling speed within a preset drilling depth.

[0006] Preferably, in step S1, a horizontal drilling machine is used to drill holes from the main tunnel to the horizontal pilot tunnel at multiple angles for verification.

[0007] Preferably, in step S1, a panoramic borehole camera is inserted into the borehole to confirm the shape of the cavity in the collapsed area of ​​the fault segment.

[0008] Preferably, in step S3, the spacing between the freezing holes at both ends of the freezing zone along the extending direction of the flat guide hole is reduced.

[0009] Preferably, the freezing holes are arranged in a plum blossom shape.

[0010] Preferably, a plurality of sections of the freezing pipe are installed section by section, and the end of the first freezing pipe extending into the freezing hole away from the main tunnel hole is sealed with a cover plate.

[0011] Preferably, the frozen zone includes the surrounding rock in front of the tunnel face of the horizontal pilot tunnel and a portion not less than 3m outside the surrounding rock.

[0012] Preferably, in step S3, a temperature measuring hole is drilled from the main tunnel to the freezing zone, and temperature monitoring is performed through the temperature measuring hole. When the temperature drops to a preset temperature, it indicates that the freezing standard has been met.

[0013] Preferably, in step S3, soil samples taken out from sampling holes are subjected to freezing tests every meter to observe the freezing effect. For soil samples with poor freezing effect due to insufficient moisture content, fresh water is injected to increase the freezing effect.

[0014] Compared with the prior art, the present invention has achieved the following technical effects: In the freezing escape method of the present invention, the cavity in the collapsed area is detected through exploration holes, and the cavity is backfilled by blowing sand, thereby enhancing the stability of the rock mass in the collapsed area and reducing the risk of re-collapse during the freezing process. The collapsed area of ​​the flat pilot tunnel is then frozen using the freezing method to further enhance the stability of the rock mass in the collapsed area, ensuring that there will be no risk of secondary collapse during the tunnel construction process, and helping the flat pilot tunnel to escape the deadlock of difficulty in resuming work. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the analysis of these drawings without paying any creative work.

[0016] Figure 1 This is a schematic diagram of the construction process of the freezing escape method in an embodiment of the present invention; Figure 2 A three-dimensional perspective diagram of the process of drilling a test hole to identify a cavity in an embodiment of the present invention; Figure 3Schematic diagram of the process of drilling a test hole to find a cavity in an embodiment of the present invention from a frontal perspective; Figure 4 Schematic diagram of the positional relationship among the TBM, cavity, and subsequent surrounding rock in an embodiment of the present invention; Figure 5 Schematic diagram of the sand blowing and backfilling process in a three-dimensional perspective according to an embodiment of the present invention; Figure 6 Schematic diagram of the sand blowing and backfilling process from a frontal perspective in an embodiment of the present invention; Figure 7 Schematic diagram of the positional relationship among the TBM, backfill area, and subsequent surrounding rock in an embodiment of the present invention; Figure 8 A schematic diagram of a three-dimensional perspective of the freezing pipe laying process according to an embodiment of the present invention; Figure 9 This is a schematic diagram of the freezing pipe arrangement structure in the longitudinal section of the middle of the freezing zone in an embodiment of the present invention; Figure 10 This is a schematic diagram of the three-dimensional structure of the freezing pipe arrangement in the middle of the freezing zone in an embodiment of the present invention; Figure 11 Schematic diagram of the arrangement structure of the freezing pipes in the longitudinal section at the end of the freezing zone in an embodiment of the present invention; Figure 12 This is a schematic diagram of the three-dimensional structure of the freezing pipe arrangement at the end of the freezing zone in an embodiment of the present invention; Figure 13 Schematic diagram of the arrangement of freezing pipes in a plum blossom shape in an embodiment of the present invention; Figure 14 Schematic diagram of the freezing process of the freezing pipe in an embodiment of the present invention; Figure 15 Schematic diagram of the positional relationship among the TBM, frozen zone, and subsequent surrounding rock in an embodiment of the present invention; Figure 16 Schematic diagram of the TBM excavation process in an embodiment of the present invention; Figure 17 Schematic diagram of the positional relationship between the freezing pipe and the injection pipe in an embodiment of the present invention.

[0017] Explanation of the accompanying symbols: 1. Tunnel main tunnel; 2. Pilot tunnel; 3. Working face; 4. Cavity; 5. Exploration hole; 6. Freezing pipe; 7. Freezing area; 8. Frozen surrounding rock area; 9. Frozen layer arch; 10. Injection pipe. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments analyzed and obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0019] The purpose of the present invention is to provide a freezing escape method to solve the problems existing in the prior art. The freezing escape method detects the cavity in the collapsed area through a probe hole and blows sand backfill into the cavity, thereby enhancing the stability of the rock mass in the collapsed area and reducing the risk of re-collapse during the freezing process. The freezing method is then used to freeze the collapsed area of ​​the flat pilot tunnel to further enhance the stability of the rock mass in the collapsed area, ensuring that there will be no risk of secondary collapse during the tunnel construction process, and helping the flat pilot tunnel to escape the deadlock of difficulty in resuming work.

[0020] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] like Figures 1 to 17 As shown, this embodiment provides a freezing escape method, comprising the following steps: S1, drill a exploratory hole 5 from the main tunnel 1 to the surrounding rock above the horizontal pilot tunnel 2 (refer to Figures 2 to 4 As shown), the position and size of the cavity 4 in the collapsed area of ​​the fault segment are ascertained. The position and size of the cavity 4 are mainly estimated based on the size of the entire range of the cavity 4 drilled by the exploration hole 5; S2. After obtaining the position and size of the cavity 4, the cavity 4 in the collapsed area of ​​the fault segment is backfilled by blowing sand and water (refer to Figures 5 to 7 As shown in the figure, water blowing helps the sand flow and ensures that the blown sand is full and dense. At least one drainage hole is set at a high position in the cavity of the fault segment collapse zone for drainage. If there is too much water, sand cannot be blown into the cavity. Therefore, water needs to be discharged in time from the drainage hole. When the high drainage hole continuously discharges sand, it proves that the cavity is full (when the drainage hole only discharges water, the sand is not full yet). At this time, stop blowing sand and water. After backfilling by blowing sand, the stability of the rock mass can be enhanced to prevent collapse again. S3. After the sand blowing backfill is completed, freezing holes are drilled from the main tunnel 1 to the horizontal pilot tunnel 2 below the fault segment collapse area. The freezing holes are drilled deep into the surrounding rock of the horizontal pilot tunnel 2 to form a freezing zone 7. Freezing pipes 6 are installed in the freezing holes. The end of the freezing pipe 6 away from the main tunnel 1 is closed, acting as a "freezing rod" to freeze the surrounding rock mass. S4, inject freezing liquid into the freezing pipe 6, and freeze the rock mass in the freezing area 7 (refer to Figures 8 to 15As shown), observe the freezing situation during the freezing process, and pull out the freezing pipe 6 after the freezing reaches the standard; wherein the freezing liquid is usually salt water, which is a low-temperature salt water that can cool the rock mass to -30°C. Of course, other suitable freezing liquids can also be used; S5, the tunnel boring machine (TBM) in the horizontal pilot tunnel 2 is excavating normally (refer to Figure 16 shown).

[0022] This cryo-rescue method uses a probe hole 5 to detect cavity 4 because the tunnel boring machine (TBM) construction space on site precludes the use of geological radar to detect the fault collapse cavity (cavity 4) from the horizontal pilot tunnel 2. However, if exploration were conducted parallel to the fault collapse cavity from the main tunnel 1, the straight-line distance between the main tunnel 1 and the horizontal pilot tunnel 2 is typically approximately 35 to 42 meters, while the geological radar detection range is approximately 30 meters, exceeding the detection range of geological radar. Furthermore, the signal attenuates more rapidly in loose areas (collapse cavities), rendering effective feedback ineffective. Low-frequency radar with a wider detection range can adequately cover the detection area, but its lower frequency yields lower resolution, making it even more difficult to distinguish loose collapse cavities. Therefore, after comprehensive considerations, it was decided to conduct advance drilling along the fault from the main tunnel 1 toward the horizontal pilot tunnel 2 to detect the collapse cavity area.

[0023] In one embodiment, in step S1, during the drilling of the exploratory hole 5, it is determined whether the cavity 4 has been drilled in accordance with the change in drilling speed within the preset drilling depth. If the rotation speed suddenly increases, it means that the rock mass has suddenly drilled into the cavity 4. Of course, the depth needs to be combined for judgment. If the rotation speed does not increase significantly after drilling into the preset depth, it means that there is no cavity 4 here.

[0024] In one embodiment, in step S1, a horizontal drilling machine is used to drill holes from the main tunnel 1 to the horizontal pilot tunnel 2 at multiple angles for verification.

[0025] In one embodiment, in step S1 , a panoramic borehole camera is inserted into the borehole if necessary, and the shape of the cavity 4 in the collapsed area of ​​the fault segment is confirmed by the in-hole scanning imaging function of the panoramic borehole camera.

[0026] In one embodiment, the borehole length must be no less than the sum of the reserved working length of the tunnel main tunnel 1 + the length of the rock mass between the tunnel main tunnel 1 and the horizontal pilot tunnel 2 + the thickness of the frozen layer arch 9. For example, if the distance between the tunnel main tunnel 1 and the horizontal pilot tunnel 2 is 28.5 meters, the length of the rock mass between the tunnel main tunnel 1 and the horizontal pilot tunnel 2 is 28.5 meters, so the borehole length is 2 meters (reserved working length) + 28.5 meters + 8.8 meters + 3 meters (thickness of the frozen layer arch 9).

[0027] In one embodiment, the sand blasting backfilling process in step S2 is as follows: sand blasting hole arrangement → sand material arrangement → sand blasting system assembly → graded backfilling → density testing → supplementary grouting and curing. The sand blasting equipment includes: an air compressor, a sand tank, a sand delivery pipe, and a sand injection head.

[0028] The arrangement of sand blowing holes: steel pipes are used as sand blowing pipes to form sand blowing holes. The steel pipes should extend into the boundary of cavity 4 at least 20cm deep. The density of sand injection pipes can be controlled at 10m per 10m. 2 A main sand injection pipe is arranged in the projected area of ​​cavity 4. A steel pipe with a diameter of φ108 can be used.

[0029] Sand material arrangement: Select a continuously graded sand material with a particle size of 0.15mm to 5mm and a mud content of ≤3% to prevent compaction. If water seepage occurs at the tunnel face 3 of the horizontal pilot tunnel 2, cement or polypropylene fiber may be added to the sand material to enhance its scour resistance. The water content of the sand material should be kept below 2% during mixing to prevent excessive water content from causing pipe blockage.

[0030] The sand blowing system assembly: the sand blowing equipment configuration includes: air compressor, sand tank, sand conveying pipe and sand injection head, etc.

[0031] The sandblasting process should be carried out from low to high, first around the perimeter and then in the center. The backfill thickness of a single sandblast should be no less than 1.5m. Pipeline cleanliness should be maintained during the sandblasting process, and the pipeline should be cleaned every 6 hours. The density of the sandblasted material should be monitored in real time, and secondary sandblasting should be performed promptly if it does not meet the requirements.

[0032] When water seepage within the fault section is high, sandblasting is suspended. Water glass slurry can be injected to seal the water according to design requirements before sandblasting is resumed. During sandblasting, it is preferred to close the connecting channel nodes in cavity 4 to reduce the connectivity of cavity 4. Sandblasting is continued until cavity 4 is completely backfilled.

[0033] In one embodiment, in step S3, a freezing pipe 6 with a diameter of not less than 1 m is selected, and the horizontal and vertical spacings of the freezing holes (i.e., the freezing pipes 6) are not greater than 2 m. Figure 9 and Figure 10 As shown, eight freezing pipes 6 are usually provided on the longitudinal section (ie, eight rows of freezing pipes 6 are provided along the longitudinal direction).

[0034] In one embodiment, the spacing between the freezing holes (i.e., freezing pipes 6) at both ends of the freezing zone 7 along the extension direction of the flat guide tunnel 2 is not greater than 1 m, so as to increase the density of the freezing holes (i.e., freezing pipes 6) at both ends of the freezing zone 7 and improve the freezing effect. Figure 11 and Figure 12As shown, 16 freezing pipes 6 are typically arranged on the longitudinal section (i.e., 16 rows of freezing pipes 6 are arranged longitudinally). The remaining freezing pipes 6 are located on both sides of the central area of ​​the freezing zone 7, resulting in a better freezing effect. However, the end areas of the freezing zone 7, especially the very end, only have the remaining freezing pipes 6 on the left or right side, with the other side being rock mass, which can easily lead to poor freezing effects. Therefore, the end areas are densified to improve the freezing effect. Typically, the densified area consists of two rows of freezing holes at the ends of the freezing zone 7. The number of rows at each end can be adjusted according to actual conditions, but generally cannot be less than two rows.

[0035] In one embodiment, the freezing holes (i.e., freezing pipes 6) are arranged in a plum blossom shape. Figure 8 and Figure 13 shown.

[0036] In one embodiment, multiple rows of freezing pipes 6 are arranged in the longitudinal direction, the middle row is horizontally arranged, and the inclination angle of the remaining rows increases by 1° with each additional row.

[0037] In one embodiment, the on-site hole spacing error must be controlled within ±20mm. Before the drilling equipment is deployed, the hole positions are precisely determined using instruments to improve positioning accuracy. Lighting inclination measurements are performed every 3 meters during drilling. If a hole is found to be tilted, the drilling angle and drilling parameters are promptly adjusted to correct the deviation. If the hole still deviates after correction, additional holes are required.

[0038] In one embodiment, multiple sections of freezing pipes 6 are installed section by section, and the end of the first freezing pipe 6 extending into the freezing hole away from the main tunnel hole 1 is sealed with a cover plate.

[0039] In one embodiment, the freezing pipe 6 is made of steel, with a single section diameter of 108 mm, a wall thickness of 4.5 mm, and a length of 1500 mm. During installation, each section is installed into the freezing hole one by one. Typically, the total length of the connected freezing pipe 6 is approximately 42 meters. This length will vary depending on the actual situation, and is provided here as a numerical value.

[0040] In one embodiment, the pipe sections of the freezing pipe 6 are connected by threaded connection and welding.

[0041] In one embodiment, an injection pipe 10 is inserted into the freezing pipe 6. This pipe is used to inject low-temperature brine (freezing fluid). The space between the freezing pipe 6 and the injection pipe 10 serves as a circulation space for circulating water. If the freezing pipe 6 is made of a 108 mm diameter steel pipe with a wall thickness of 4.5 mm, the freezing pipe 6 can be made of an 89 mm diameter steel pipe with a wall thickness of 4 mm.

[0042] In one embodiment, the freezing pipe 6 adopts a steel pipe. When taking out the pipe, depending on the freezing situation, warm water can be injected into the pipe to achieve the thawing effect with the frozen rock mass, which is convenient for taking out the pipe construction. Warm water can directly adopt the CaCl2 solution (salt water) after heating, and the CaCl2 solution after circulating the heating is injected to separate the freezing pipe 6 from the frozen rock mass. The freezing pipe is taken out in sections. The freezing pipe 6 also can be selected to be a reinforced plastic pipe that can be cut by TBM equipment, and the plastic freezing pipe does not need to be taken out. But the plastic freezing pipe structural strength is weaker than steel pipe, and is easily crushed and broken in rock mass interior, and the comprehensive cost is higher than steel freezing pipe, so the preferred suggestion is to select steel pipe.

[0043] In one embodiment, a pressure test is performed after the freezing pipe 6 is installed. The initial pressure must meet 0.8 MPa. A pressure drop of no more than 0.05 MPa over 30 minutes and a sustained pressure of 15 minutes is considered acceptable. If the test fails, the freezing pipe 6 must be re-drilled and reinstalled nearby. Otherwise, pressure leakage during the freezing process could easily cause personal injury.

[0044] In one embodiment, the freezing holes are drilled horizontally, using a tunnel active 1 to horizontally guide the tunnel 2 to drill the fan-shaped freezing holes. A TD200 horizontal directional drill rig with a drill diameter of 5 cm to 50 cm and a drilling range of 0 m to 200 m can be used for on-site drilling.

[0045] In one embodiment, frozen zone 7 includes the surrounding rock in front of the tunnel face 3 of the horizontal pilot tunnel 2 (here, the front refers to the front in the direction of subsequent construction) and a portion at least 3 meters outside the surrounding rock. After freezing, the surrounding rock forms a frozen surrounding rock zone 8. After freezing, the portion at least 3 meters outside the surrounding rock forms a frozen layer arch 9 (i.e., the thickness of frozen layer arch 9 is greater than or equal to 3 meters) surrounding the frozen surrounding rock zone 8.

[0046] In one embodiment, during the freezing process, a temperature measuring hole is drilled from the tunnel main hole 1 to the freezing zone 7, and temperature is monitored through the temperature measuring hole. When the temperature drops to a preset temperature, it indicates that the freezing standard has been met.

[0047] In one embodiment, temperature measurement holes are arranged horizontally throughout the entire length of the tunnel, and can be fitted with thermocouples, thermal resistors, and thermometers. Measurements are taken twice daily. Based on the measured temperature data, the frozen soil curtain is judged to have reached its designed thickness. Once the thickness of the frozen arch 9 is confirmed to meet the design, exploratory drilling and trial excavation are performed. After confirming the absence of flowing water in the soil layer ahead of the tunnel face, the frozen pipes 6 are removed (if plastic pipes are used, removal is not necessary), and the TBM is started and excavation commences.

[0048] In one embodiment, in addition to measuring temperature through temperature holes, sampling holes are drilled to remove soil samples. Freezing tests are conducted every meter to observe the freezing effect. For soil layers with insufficient moisture content, which results in poor freezing, fresh water injection is used to improve freezing. For soil layers with water flow velocities exceeding 5 m / d, grouting is used to form a curtain to reduce the water flow and enhance the subsequent freezing effect.

[0049] In one embodiment, after the freezing pipe 6 is taken out, the freezing hole, the temperature measuring hole, and the exploration hole 5 are promptly sealed with insulation materials to prevent the frozen rock mass from heating up too quickly and affecting the freezing effect.

[0050] In one embodiment, in step S4, during the freezing construction process, the tunnel face 3 of the main tunnel 1 needs to be suspended. This is because, during the freezing construction process, the refrigeration unit and the freezing liquid circulation pipeline are arranged in the main tunnel, occupying the tunnel passage space, and the tunnel face 3 of the main tunnel 1 needs to be suspended. Generally speaking, the freezing efficiency is usually slow. The time from the injection of freezing liquid (low-temperature brine) into the freezing pipe 6 to the completion of the freezing of the soil is approximately 40 to 50 days. This period depends on the heat dissipation of the soil and may fluctuate, and its time cannot be accurately controlled. Taking into account the time for arranging and disassembling the refrigeration unit and the freezing liquid circulation pipeline, the time for suspending construction is approximately 72 to 82 days.

[0051] In one embodiment, the process of injecting the freezing liquid needs to determine the injection position and injection amount according to specific engineering conditions, and attention needs to be paid to the temperature and flow rate of the freezing liquid.

[0052] In one embodiment, a single freezer can theoretically drive the freezing operation of a freezing pipe of about 600m in length, so the number of freezers needs to be calculated based on the total length of the freezing pipe 6. For example: if the number of freezing pipes 6 is 216, and the length of a single freezing pipe 6 (composed of multiple sections of freezing pipes 6) is about 42m, then the total length of the freezing pipe 6 is 9072m. According to calculations, at least 16 freezers are required to meet the needs of on-site construction. The standard length of a single freezer is 3.5m, the width is 1.4m, and the height is 2.2m. Taking into account the flow rate, cooling loss, heat dissipation conditions and power load, the freezers are arranged horizontally in the tunnel. They are arranged along the length of the tunnel, with an installation spacing of 1m between each freezer. To ensure the normal operation of the refrigeration equipment and improve the refrigeration efficiency. The evaporator, low-temperature pipeline, water tank and main pipe of the refrigeration equipment are insulated with 5cm thick annular polyphenolic resin. The refrigeration equipment pipeline adopts DN125 pipe and is arranged horizontally along the tunnel.

[0053] Refrigerant filling and oiling of the refrigeration unit should be performed according to the equipment's instruction manual. First, perform a leak check and nitrogen flushing of the refrigeration system. Once the system is leak-free, refrigerant filling and oiling are performed. After the equipment is installed, commissioning and trial operation are performed. During the trial operation, various parameters such as pressure and temperature should be adjusted constantly to ensure that the unit operates within the technical parameters specified in the relevant process regulations and equipment requirements.

[0054] In one embodiment, the freezing fluid is prepared on-site using a low-temperature chloride (CaCl2) solution with a designed brine temperature of -28°C to -30°C and a concentration of 1.265. Solid CaCl2 is purchased on-site, transported to the construction site, and stored separately in a separate material warehouse at the entrance of the cave, away from sources of ignition and flammable materials. The storage temperature should be ≤25°C and the humidity ≤80%. The storage location should be out of direct sunlight.

[0055] During the freezing construction trial operation, the brine temperature, brine flow rate and frozen soil curtain expansion are regularly monitored and the freezing system operating parameters are adjusted if necessary. After the freezing system is operating normally, the active freezing phase begins. During the active freezing phase, the brine flow rate in a single freezing pipe is approximately 0.25m / s = 900m / h. The brine flow rate per hole per hour is calculated as: 3.14*(0.089-0.004) / 2) 2 =0.0057m 2 , 0.0057*900=5.13m 3 .

[0056] The volume of freezing liquid in a single freezing pipe is: 0.0066m 2 *42=0.2772m 3 Taking 216 main freezing pipes + 20 spare pipes as an example, the volume of freezing liquid in freezing pipe 6 is 0.2772*236=65m 3 .

[0057] The freezing circulation pipeline uses DN125 pipe. The length of the circulation pipeline of a single refrigeration unit is about 24m. The volume of the refrigerant in the circulation pipeline is: 3.14*((0.14-0.008) / 2) 2 *24=0.33m 3 The volume of refrigerant in all refrigeration units is 0.33*16=1.98m 3 The theoretical amount of refrigerant is 65+1.98=66.98m3 3 .

[0058] In one embodiment, in step S5, the TBM excavation process requires careful attention to excavation length and advance rate control. The advance rate should be kept to a minimum, and steel segments should be installed promptly during excavation to prevent prolonged exposure of frozen rock mass, which could lead to accelerated thawing and collapse. During excavation, advanced geological forecasts should be used to accurately assess the surrounding rock at the transition between frozen and unfrozen sections. Steady progress is essential, and reckless advances are strictly prohibited.

[0059] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A freezing escape method, characterized in that: The following steps are involved: S1. Drill holes in the surrounding rock above the main tunnel toward the horizontal pilot tunnel to determine the location and size of the cavity in the collapsed area of ​​the fault segment. S2. Blow sand and backfill the cavity in the collapsed area of ​​the fault segment with water, and set drainage holes at high positions in the cavity in the collapsed area of ​​the fault segment for drainage; S3, drilling freezing holes from the main tunnel to the horizontal pilot tunnel below the collapsed area of ​​the fault section, the freezing holes penetrating into the surrounding rock of the horizontal pilot tunnel to form a frozen zone, installing freezing pipes in the freezing holes, and sealing the freezing pipes at the ends away from the main tunnel; S4, circulating a freezing liquid into the freezing pipe to freeze the rock mass in the freezing area, observing the freezing condition during the freezing process, and pulling out the freezing pipe after the freezing condition is met; S5. The tunnel boring machine in the horizontal pilot tunnel is advancing normally.

2. The freeze escape method according to claim 1, wherein: In step S1, during the process of drilling the exploratory hole, it is determined whether a cavity has been drilled according to the change in drilling speed within a preset drilling depth.

3. The freeze escape method according to claim 1, wherein: In step S1, a horizontal drilling machine is used to drill holes from the main tunnel to the horizontal pilot tunnel at multiple angles for verification.

4. The freeze escape method according to any one of claims 1 to 3, characterized in that: In step S1 , a panoramic borehole camera is inserted into the borehole to confirm the shape of the cavity in the collapsed area of ​​the fault segment.

5. The freeze escape method according to claim 1, wherein: In step S3, the spacing between the freezing holes at both ends of the freezing zone along the extending direction of the flat guide hole is reduced.

6. The freeze escape method according to claim 1 or 5, characterized in that: The freezing holes are arranged in a plum blossom shape.

7. The freeze escape method according to claim 6, wherein: The freezing pipes are installed section by section, and the end of the first freezing pipe extending into the freezing hole away from the main tunnel hole is sealed with a cover plate.

8. The freeze escape method according to claim 1, wherein: The freezing zone includes the surrounding rock in front of the tunnel face of the horizontal pilot tunnel and a portion not less than 3m outside the surrounding rock.

9. The freeze escape method according to claim 1, wherein: In step S3, a temperature measuring hole is drilled from the main tunnel to the freezing zone, and temperature is monitored through the temperature measuring hole. When the temperature drops to a preset temperature, it indicates that the freezing standard has been met.

10. The freeze escape method according to claim 9, characterized in that: In step S3, soil samples taken from sampling holes are subjected to freezing tests every meter to observe the freezing effect. For soil samples with poor freezing effect due to insufficient moisture content, fresh water is injected to increase the freezing effect.

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