Construction method of metro tunnel contact channel on karst development zone

Abstract

The invention relates to a construction method of a metro tunnel contact channel on a karst development zone. The construction method comprises the steps that the average temperature, the positive freezing time and the maintenance freezing time of a freezing wall are determined; determining the layout positions of a freezing hole, a temperature measuring hole and a pressure relief hole in a duct piece of the contact channel, drilling, and respectively arranging a temperature measuring instrument and a pressure monitoring instrument in the temperature measuring hole and the pressure relief hole; a freezing station is arranged at the position of the connection channel, the freezing station is started, the freezing holes are frozen according to the positive freezing time, the freezing maintenance stage is switched to after the set requirement is met, and the connection channel is excavated; and a support is arranged in the space formed by excavation, maintenance is carried out after the support is formed, a connection channel is formed, and maintenance and freezing are finished. The soil body is frozen and reinforced through the freezing holes in the distributed positions, so that the soil body on the periphery of the connecting channel and the periphery of the pump room is frozen, a freezing curtain high in strength and good in sealing performance is formed, the stability of a cavern is improved, the phenomena of mud overflowing and water bursting after pipe pieces are broken and removed are avoided, and the safety of the connecting channel is improved.

Description

Technical Field

[0001] The invention relates to the field of excavation construction of subway tunnel communication channels, and in particular to a construction method of subway tunnel communication channels in a karst development zone. Background Art

[0002] The subway tunnel communication channel (also pump room) is generally located at the lowest point of the interval tunnel. The communication channel (also pump room) not only connects the left and right lines of the tunnel and provides a passenger transfer channel; it also undertakes the functions of drainage, ventilation and fire prevention in the tunnel interval. The engineering geological and hydrogeological conditions of the communication channel (also pump room) are complex. When the tunnel surrounding rock grade is poor, it should be reinforced before excavation. Generally, the mining method (grouting and pipe shed) is used for reinforcement, but the communication channel (also pump room) is located in medium-weathered limestone, and the limestone karst development degree is medium. The thickness of the rock layer covering the top of the channel is about 1.5 to 2.0m. The surrounding rock types of the communication channel (also pump room) are mainly red clay, medium-weathered limestone, caves and fillings. In the karst development area, the overall groundwater storage conditions are excellent. The reinforcement effect of grouting on the irregular caves and fillings around the cavern is not ideal, and mud and water gushing occur after the pipe segments are broken. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a construction method for a subway tunnel communication channel in a karst development zone in view of the deficiencies of the above-mentioned prior art.

[0004] The technical solution of the present invention to solve the above technical problems is as follows: A construction method for a subway tunnel communication channel in a karst development zone comprises the following steps:

[0005] Determine the average freezing wall temperature according to the set minimum freezing curtain thickness of the communication channel, and determine the active freezing time and maintenance freezing time according to the frozen soil thickness and the average freezing wall temperature;

[0006] Determine the layout positions of freezing holes, temperature measuring holes and pressure relief holes on the pipe segments of the connecting channel, wherein the freezing holes are arranged on both sides of the left and right tunnels, the temperature measuring holes are arranged at the weak points of freezing in the connecting channel, and the pressure relief holes are arranged in the middle and lower part of the frozen soil layer of the connecting channel;

[0007] Drill holes at the locations where the freezing holes, temperature measuring holes and pressure relief holes are arranged, and form the freezing holes, temperature measuring holes and pressure relief holes respectively, and respectively set a temperature measuring instrument and a pressure monitoring instrument in the temperature measuring hole and the pressure relief hole;

[0008] A freezing station is arranged at the communication channel, and the freezing station at least comprises a refrigeration unit, a brine circulation pump, a clean water pump, a cooling tower, a power distribution control cabinet, and a freezing pipe extending into the freezing hole and connected to the brine circulation pump;

[0009] The freezing station is started to freeze the freezing hole according to the active freezing time, and the maintenance freezing stage is entered after the curtain thickness of the communication channel reaches the minimum curtain thickness, the temperature in the temperature measuring hole measured by the thermometer reaches the temperature setting value, and the pressure in the pressure relief hole measured by the pressure monitor reaches the setting value, the pipe segments are broken, and the communication channel is excavated according to the maintenance freezing time;

[0010] Reinforced concrete is used to set up supports in the space formed by excavation. After the supports are formed, they are maintained to form communication channels and end the maintenance freeze.

[0011] The beneficial effects of the present invention are as follows: the construction method of the subway tunnel connecting channel in the karst development zone of the present invention determines the average temperature of the frozen wall according to the minimum curtain thickness of the connecting channel freezing, and then determines the active freezing time and the maintenance freezing time, and freezes and reinforces the soil through freezing holes arranged on the pipe segments, so that the connecting channel and the soil outside the pump room are frozen to form a freezing curtain with high strength and good sealing, and the excavation and construction of the connecting channel and the pump room are carried out in the frozen soil. The stratum freezing and the excavation and construction are all carried out in the interval tunnel, which increases the stability of the cavern, avoids the occurrence of mud and water gushing after the pipe segments are broken, and improves the safety of the connecting channel.

[0012] On the basis of the above technical solution, the present invention can also be improved as follows:

[0013] Further: the method of determining the average temperature of the frozen wall according to the set minimum freezing curtain thickness of the communication channel, and determining the active freezing time and the maintenance freezing time according to the frozen soil thickness and the average freezing wall temperature specifically includes the following steps:

[0014] The average temperature of the freezing wall is determined according to the set minimum curtain thickness of the communication channel. The calculation formula is:

[0015]

[0016] Where t is the average temperature of the frozen wall, t b is the brine temperature, l is the freezing hole spacing, E is the frozen soil thickness, and tB is the excavation surface temperature;

[0017] The corresponding active freezing time is determined according to the thickness of frozen soil and the average temperature of frozen wall.

[0018] The beneficial effect of the above further scheme is that the average temperature of the frozen wall can be accurately calculated by setting the minimum curtain thickness and brine temperature, frozen soil thickness and excavation surface temperature, so that the active freezing time before construction and the maintenance freezing time during construction can be determined according to the average temperature of the frozen wall, ensuring that subsequent construction proceeds normally, reliably and smoothly.

[0019] Further: before excavating the communication channel, the following steps are also included:

[0020] The soil around the communication channel is pre-dug and drilled to form a probe hole, and the probe hole is used to confirm whether the curtain thickness of the communication channel reaches the minimum curtain thickness.

[0021] The beneficial effect of the above further scheme is: by pre-digging around the soil in the communication channel and drilling holes, exploration can be carried out before excavation, ensuring that the surrounding soil is completely frozen and stable before excavation, further ensuring construction safety.

[0022] Further: the use of reinforced concrete to set support in the space formed by excavation and perform maintenance to form a communication channel specifically includes the following steps:

[0023] Use steel frame and mesh sprayed concrete to pour to form initial support;

[0024] Use cast-in-place reinforced concrete for pouring to form permanent support;

[0025] The condensed water generated on the surface of the initial support and the permanent support located in the frozen soil is used to keep the surface of the initial support and the permanent support moist, thereby forming a maintenance for the initial support and the permanent support.

[0026] The beneficial effects of the above further scheme are: by pouring steel frame and mesh sprayed concrete, initial support is formed to effectively support the space formed by excavation and ensure the safety of subsequent construction; by pouring cast-in-place reinforced concrete, permanent support is formed to ensure the structural stability of the entire communication channel.

[0027] Further: the construction method of the subway tunnel communication channel in the karst development zone also includes the following steps:

[0028] A pump room is arranged at the communication channel, and after the construction of the pump room is completed, the freezing hole is poured and sealed with concrete.

[0029] The beneficial effect of the above further scheme is that by using concrete to cast and seal the freezing hole, the stability of the soil structure around the tunnel can be ensured, and the probability of mud and water gushing in the later stage can be reduced.

[0030] Further: after the connecting channel is formed, the pre-buried grouting pipe is used to perform melting and settling compensation grouting on the stratum around the connecting channel.

[0031] The beneficial effect of the above further scheme is: by performing melt-settlement compensating grouting on the strata around the connecting channel, the strata around the connecting channel can be reinforced, reducing the risk of subsequent settlement and further ensuring the structural stability of the entire connecting channel.

[0032] Further: when drilling holes at the locations where the freezing holes are arranged, sealing treatment is performed on the pipe segments at the locations where the freezing holes are arranged.

[0033] The beneficial effect of the above further scheme is: since the stratum where the communication channel (also serving as the pump room) is located has poor stability and is rich in water, sealing treatment is performed on the pipe segments at the layout position of the freezing holes, thereby avoiding water and mud gushing during the drilling process.

[0034] Further: after starting the freezing station, the freezing hole is gradually cooled and frozen according to the active freezing time.

[0035] The beneficial effect of the above further scheme is that by gradually cooling and freezing the freezing hole, cracking of the freezing pipe caused by temperature stress can be prevented, and the brine flow and uniformity can be easily controlled to ensure reliable support of the freezing curtain. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a schematic diagram of the process flow of a method for constructing a subway tunnel communication channel in a karst development zone according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0038] like Figure 1 As shown, a construction method for a subway tunnel communication channel in a karst development zone includes the following steps:

[0039] S102: determining the average temperature of the freezing wall according to the set minimum freezing curtain thickness of the communication channel, and determining the active freezing time and the maintenance freezing time according to the frozen soil thickness and the average temperature of the freezing wall;

[0040] S104: Determine the layout positions of freezing holes, temperature measuring holes and pressure relief holes on the pipe segments of the connecting channel, wherein the freezing holes are arranged on both sides of the left and right tunnels, the temperature measuring holes are arranged at the weak points of freezing in the connecting channel, and the pressure relief holes are arranged in the middle and lower part of the frozen soil layer of the connecting channel;

[0041] S106: drilling holes at the locations where the freezing holes, temperature measuring holes and pressure relief holes are arranged, and forming the freezing holes, temperature measuring holes and pressure relief holes respectively, and setting a temperature measuring instrument and a pressure monitoring instrument in the temperature measuring hole and the pressure relief hole respectively;

[0042] S108: Setting a freezing station at the communication channel, the freezing station at least comprising a refrigeration unit, a brine circulation pump, a clean water pump, a cooling tower, a power distribution control cabinet, and a freezing pipe extending into the freezing hole and connected to the brine circulation pump;

[0043] S110: starting the freezing station, freezing the freezing hole according to the active freezing time, and entering the maintenance freezing stage after the curtain thickness of the communication channel reaches the minimum curtain thickness, the temperature in the temperature measuring hole measured by the thermometer reaches the temperature setting value, and the pressure in the pressure relief hole measured by the pressure monitor reaches the setting value (which may be within the set safety range value), breaking the pipe segment and excavating the communication channel according to the maintenance freezing time;

[0044] S112: Use reinforced concrete to set up supports in the space formed by excavation. After the supports are formed, they are maintained to form communication channels and end the maintenance freeze.

[0045] The construction method of the subway tunnel connecting channel in the karst development zone of the present invention determines the average temperature of the frozen wall according to the minimum curtain thickness of the connecting channel, and then determines the active freezing time and the maintenance freezing time. By setting a freezing station and freezing holes arranged on the pipe segment to freeze and reinforce the soil, the connecting channel and the soil outside the pump room are frozen to form a freezing curtain with high strength and good sealing performance. The excavation and construction of the connecting channel and the pump room are carried out in the frozen soil. The ground freezing and excavation and construction are all carried out in the interval tunnel, which increases the stability of the cavern, avoids mud and water gushing after the pipe segment is broken, and improves the safety of the connecting channel.

[0046] In one or more embodiments of the present invention, the steps of determining the average temperature of the frozen wall according to the set minimum curtain thickness of the communication channel, and determining the active freezing time and the maintenance freezing time according to the frozen soil thickness and the average temperature of the frozen wall specifically include the following steps:

[0047] S1021: Determine the average temperature of the freezing wall according to the set minimum freezing curtain thickness of the communication channel. The calculation formula is:

[0048]

[0049] Wherein, t is the average temperature of the frozen wall; l is the spacing between the frozen holes, which is 1.1 m in this embodiment; E is the thickness of the frozen soil, which is 2.5 m in this embodiment; tB is the excavation surface temperature, which is -5 °C in this embodiment; t b is the brine temperature, which is -28°C in this embodiment, corresponding to an average freezing wall temperature of -10.03°C.

[0050] S1022: Determine the corresponding active freezing time according to the thickness of the frozen soil and the average temperature of the frozen wall.

[0051] Here, the comparison table of brine temperature and active freezing time is as follows: the brine temperature drops to below -18°C after 7 days of active freezing; the brine temperature drops to below -24°C after 15 days of active freezing, and the brine temperature drops to -28°C to -30°C during excavation.

[0052] In addition, in order to ensure that the design requirements are met, the temperature difference between the outgoing and return brine should not exceed 2°C; if the brine temperature and brine flow rate do not meet the design requirements, the active freezing time should be extended to ensure that the designed freezing wall thickness and temperature are reached. After the temperature measurement determines that the freezing curtain is in a circle and reaches the designed thickness and is completely bonded to the tunnel, the maintenance freezing stage can be entered.

[0053] The average temperature of the frozen wall can be accurately calculated by setting the minimum curtain thickness and brine temperature, frozen soil thickness and excavation surface temperature. In this way, the active freezing time before construction and the maintenance freezing time during construction can be determined according to the average temperature of the frozen wall to ensure that subsequent construction proceeds normally, reliably and smoothly.

[0054] In one or more embodiments of the present invention, in S104, the layout positions of the freezing holes, the temperature measuring holes and the pressure relief holes are determined on the pipe segments of the communication channel, and the corresponding quantities are determined, as shown in Table 1 below;

[0055] Table 1

[0056]

[0057] In particular, in the embodiments of the present invention, it is necessary to strictly control the opening position of the freezing hole, control the deflection rate and deviation value of the freezing hole, ensure that the final hole spacing of the freezing hole is within the design range, and ensure the accuracy of the freezing hole position. The hole spacing error is controlled within ±20mm, and the drilling and positioning work should be completed before the drilling equipment is in place to improve the positioning accuracy. Every 2 to 3 freezing holes are connected in series to supply liquid, and the brine flow and uniformity of the freezer are monitored according to the flow rate and the temperature difference of the return circuit to ensure the reliability of the freezing curtain support.

[0058] In practice, the average temperature of the frozen wall of each section is calculated based on the temperature of the monitored temperature measuring holes, and the brine flow rate is adjusted to control the areas with higher temperatures.

[0059] In one or more embodiments of the present invention, in S104, the temperature measuring hole is set at the freezing weak point of the communication channel, where the weak point specifically includes the following situations:

[0060] (1) The freezing curtain develops unevenly due to the unbalanced cooling of the freezing pipe series branches, which leads to weak points of the freezing curtain;

[0061] (2) Since concrete and steel pipe segments can easily dissipate heat relative to the soil layer, the freezing speed of the soil layer near the tunnel segments will be seriously affected, resulting in poor bonding between the freezing curtain and the segments, and weak points will appear.

[0062] (3) During the freezing process, salt water leaks into the reinforced soil due to pipe breakage, making the soil less likely to freeze, reducing its strength and creating weak points.

[0063] In one or more embodiments of the present invention, in S108, when setting up a freezing station at the communication channel, the model of the refrigeration unit is selected according to the freezing required cooling capacity. In this embodiment, two refrigeration units are selected (one for standby). Two brine circulation pumps, flow rate 200m 3 / h, 2 cooling water circulation pumps, flow rate 138m 3 / h. It should be noted that when installing the freezing station, it is decided to install the freezing station on the construction platform in the right tunnel of the tunnel according to the on-site construction environment. Here, the screw refrigeration unit with no pollution, high efficiency, small size, light weight, large cooling capacity, convenient installation and transportation is preferred as the main unit of the refrigeration system to meet the needs of small subway construction sites and tight construction periods. At the same time, in order to increase the flow of brine in the freezing pipe, a series-parallel circulation method is adopted to speed up the heat exchange of the freezing pipe; freezing plates can also be added in the opposite tunnel, and foam insulation materials can be set outside the freezing plate pipes to ensure the intact freezing state at the junction of the opposite tunnel. In the process of active freezing, strengthen the monitoring and supervision of the frozen wall, stratum and support structure, and adjust the strength and deformation of the frozen wall according to the monitoring situation.

[0064] In addition, the freezing pipe adopts φ63×4mm seamless steel pipe, the steel pipes are threadedly connected and welded, and the pipe ends are sealed with bottom cover plates and bottom cones. After the freezing pipe is installed, a water pressure leak test is performed, with an initial pressure of 0.8MPa. After 30 minutes of observation, the pressure drop is less than or equal to 0.05MPa, and the pressure is not reduced for another 15 minutes, which is qualified. In the embodiment of the present invention, the freezing pipe adopts threaded connection and welding, which can greatly improve the joint strength and enhance the anti-breaking ability. In case of pipe breaking, remedial measures must be taken.

[0065] After the installation of the refrigeration station is completed, leak testing and vacuuming must be carried out in accordance with relevant specifications to ensure that the installation quality meets the design requirements.

[0066] In an embodiment of the present invention, in S110, excavation begins after the curtain thickness of the communication channel reaches the minimum curtain thickness of 2.5m, the temperature in the temperature measuring hole measured by the thermometer reaches the temperature setting value (refer to the brine temperature and active freezing time comparison table), and the pressure in the pressure relief hole measured by the pressure monitor reaches the setting value (the pressure rises to twice the original pressure or is greater than the original pressure of 0.15Mpa).

[0067] In particular, the pressure relief hole is arranged in the unfrozen area inside the freezing curtain. When the pressure relief hole is installed, the pressure relief hole should be opened to check whether it is unobstructed and record the initial data of the pressure gauge. After the pressure starts to rise, the pressure of the pressure relief hole should be monitored in real time.

[0068] In one or more embodiments of the present invention, before excavating the communication channel, the following steps are also included:

[0069] S111: Pre-dig around the soil in the communication channel and drill holes to form exploration holes, and confirm through the exploration holes whether the curtain thickness of the communication channel reaches the minimum curtain thickness.

[0070] By pre-digging around the soil in the communication channel and drilling holes, it is possible to explore before excavation, and then excavate after the surrounding soil is completely frozen and stable, further ensuring construction safety. In this embodiment, the minimum freezing curtain thickness is 2.5m. After reaching the minimum freezing curtain thickness, the mining method can be used for dark excavation construction.

[0071] In one or more embodiments of the present invention, the use of reinforced concrete to set support in the space formed by excavation and perform maintenance to form a communication channel specifically includes the following steps:

[0072] S1121: Use steel frame and mesh sprayed concrete to pour and form initial support;

[0073] S1122: 400mm cast-in-place reinforced concrete is used for pouring to form permanent support;

[0074] S1123: Condensation water generated on the surface of the initial support and permanent support located in the frozen soil is used to keep the surface of the initial support and permanent support moist, thereby forming maintenance for the initial support and permanent support.

[0075] Initial support is formed by pouring steel frame and mesh sprayed concrete, which effectively supports the space formed by excavation and ensures the safety of subsequent construction. Permanent support is formed by pouring cast-in-place reinforced concrete to ensure the structural stability of the entire communication channel.

[0076] In one or more embodiments of the present invention, the construction method of the subway tunnel communication channel in the karst development zone further includes the following steps:

[0077] S114: a pump room is set up at the communication channel, and after the construction of the pump room is completed, the freezing hole is cast and sealed with concrete.

[0078] By pouring and sealing the freezing hole with concrete, the stability of the soil structure around the tunnel can be ensured, and the probability of mud and water gushing in the later period can be reduced.

[0079] Here, freezing can be stopped 2 to 3 days after the construction of the pump room structure. After freezing is stopped, the orifice pipes and frozen pipes on the tunnel segments should be cut off. The order of cutting and sealing the holes should be stop one group and cut one group. A row of holes needs to be cut from the liquid distribution ring. Use a hacksaw to saw off the rubber tubes, and be sure to clean up the cement and other debris around the frozen holes. First cut off the pipe heads outside the segment, pull out the liquid supply pipes in the pipe, and then cut off the orifice pipes in the segment.

[0080] In one or more embodiments of the present invention, after forming the communication channel, the following steps are further included:

[0081] S116: Using the pre-buried grouting pipe, grouting is performed on the stratum around the connecting channel for compensation of melting and settling.

[0082] By performing melt-settlement compensating grouting on the strata around the communication channel, the strata around the communication channel can be reinforced, reducing the risk of subsequent settlement, and further ensuring the structural stability of the entire communication channel.

[0083] It should be noted that here, the melting settlement compensation grouting starts 5 to 7 days after the filling and pouring is completed, and the grouting frequency is adjusted in combination with the ground settlement monitoring situation. The melting settlement compensation grouting is carried out using the grouting pipes pre-buried during the structural construction. If necessary, the grouting holes of the tunnel segments on both sides of the communication channel and the pump room can also be used for grouting. When the settlement of the communication channel and the pump room is greater than 0.5mm in one day, or the cumulative settlement of the communication channel and the pump room is greater than 1.0mm, the melting settlement compensation grouting should be carried out; when the communication channel and the pump room are uplifted by 2.0mm, the grouting should be suspended. The melting settlement compensation grouting follows the principle of small amount, multiple times and uniformity. When the daily ground settlement is kept within 0.5mm every half a month for a month, and the ground deformation remains basically stable, the melting settlement grouting can be ended.

[0084] In one or more embodiments of the present invention, in S106, when drilling holes at the locations where the freezing holes are arranged, sealing treatment is performed on the pipe segments at the locations where the freezing holes are arranged.

[0085] Since the stratum where the communication channel (also serving as the pump room) is located has poor stability and is rich in water, sealing treatment is performed on the pipe segments at the locations where the freezing holes are arranged, thereby preventing water and mud gushing during the drilling process.

[0086] In one or more embodiments of the present invention, in S110, after the freezing station is started, the freezing hole is gradually cooled and frozen according to the active freezing time.

[0087] By gradually cooling and freezing the freezing hole, cracking of the freezing pipe caused by temperature stress can be prevented, and the brine flow and uniformity can be easily controlled to ensure reliable support of the freezing curtain.

[0088] Here, in the process of gradual cooling and freezing, the temperature of the frozen brine should be kept stable as required by the design. The temperature of the well wall should be measured in time after the frozen wall is exposed. The temperature error of the well wall measured at all directions at the same level should be less than 3°C.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A construction method for a subway tunnel communication channel in a karst development zone, characterized in that: The steps include: Determine the average freezing wall temperature according to the set minimum freezing curtain thickness of the communication channel, and determine the active freezing time and maintenance freezing time according to the frozen soil thickness and the average freezing wall temperature; Determine the layout positions of freezing holes, temperature measuring holes and pressure relief holes on the pipe segments on both sides of the left and right tunnels of the connecting channel, wherein the freezing holes are arranged on both sides of the left and right tunnels, the temperature measuring holes are arranged at the weak points of freezing in the connecting channel, and the pressure relief holes are arranged in the middle and lower part of the frozen soil layer of the connecting channel; Drill holes at the locations where the freezing holes, temperature measuring holes and pressure relief holes are arranged, and form the freezing holes, temperature measuring holes and pressure relief holes respectively, and respectively set a temperature measuring instrument and a pressure monitoring instrument in the temperature measuring hole and the pressure relief hole; A freezing station is arranged at the communication channel, and the freezing station at least comprises a refrigeration unit, a brine circulation pump, a clean water pump, a cooling tower, a power distribution control cabinet, and a freezing pipe extending into the freezing hole and connected to the brine circulation pump; The freezing station is started to freeze the freezing hole according to the active freezing time, and the maintenance freezing stage is entered after the curtain thickness of the communication channel reaches the minimum curtain thickness, the temperature in the temperature measuring hole measured by the thermometer reaches the temperature setting value, and the pressure in the pressure relief hole measured by the pressure monitor reaches the setting value, the pipe segments are broken, and the communication channel is excavated according to the maintenance freezing time; Reinforced concrete is used to set up supports in the space formed by excavation. After the supports are formed, they are maintained to form communication channels and end the maintenance freeze.

2. The construction method of a subway tunnel communication channel in a karst development zone according to claim 1, characterized in that: The method of determining the average temperature of the frozen wall according to the set minimum freezing curtain thickness of the communication channel, and determining the active freezing time and the maintenance freezing time according to the frozen soil thickness and the average temperature of the frozen wall specifically includes the following steps: The average temperature of the freezing wall is determined according to the set minimum curtain thickness of the communication channel. The calculation formula is: Where t is the average temperature of the frozen wall, t b is the brine temperature, l is the freezing hole spacing, E is the frozen soil thickness, and tB is the excavation surface temperature; The corresponding active freezing time is determined according to the thickness of frozen soil and the average temperature of frozen wall.

3. The construction method of a subway tunnel communication channel in a karst development zone according to claim 1, characterized in that: Before excavating the communication channel, the following steps are also included: The soil around the communication channel is pre-dug and drilled to form a probe hole, and the probe hole is used to confirm whether the curtain thickness of the communication channel reaches the minimum curtain thickness.

4. The construction method of a subway tunnel communication channel in a karst development zone according to claim 1, characterized in that: The method of using reinforced concrete to support and maintain the space formed by excavation to form a communication channel specifically includes the following steps: Use steel frame and mesh sprayed concrete to pour to form initial support; Use cast-in-place reinforced concrete for pouring to form permanent support; The condensed water generated on the surface of the initial support and the permanent support located in the frozen soil is used to keep the surface of the initial support and the permanent support moist, thereby forming a maintenance for the initial support and the permanent support.

5. The construction method of a subway tunnel communication channel in a karst development zone according to claim 1, characterized in that: The following steps are also included: A pump room is arranged at the communication channel, and after the construction of the pump room is completed, the freezing hole is poured and sealed with concrete.

6. The construction method of a subway tunnel communication channel in a karst development zone according to claim 1, characterized in that: After the communication channel is formed, the following steps are also included: The pre-buried grouting pipe is used to carry out melting settlement compensation grouting on the stratum around the communication channel.

7. The construction method of a subway tunnel communication channel in a karst development zone according to any one of claims 1 to 6, characterized in that: When drilling holes at the locations where the freezing holes are arranged, sealing treatment is performed on the pipe segments at the locations where the freezing holes are arranged.

8. The construction method of a subway tunnel communication channel in a karst development zone according to any one of claims 1 to 6, characterized in that: After the freezing station is started, the freezing holes are gradually cooled and frozen according to the active freezing time.

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