Construction method for connecting channels in water-rich areas of ultra-deep, unconsolidated strata with sea-land interaction

Abstract

This invention provides a construction method for connecting tunnels in water-rich areas of ultra-deep, underconsolidated strata with sea-land interaction. The method is as follows: A closed rectangular or circular cement-soil mixing wall is constructed in the construction area of ​​the connecting tunnel to pre-reinforce the soil, forming a continuous, seamless, low-permeability rigid water-stopping curtain; after the reinforced strata reach the predetermined reinforcement strength, freezing pipes are drilled from the adjacent faces of the two tunnels towards the construction area of ​​the connecting tunnel, and freezing treatment is carried out on the construction area of ​​the connecting tunnel; once the soil freezing condition meets the excavation requirements, the excavation of the connecting tunnel begins. This invention follows a strict sequence of "seepage interception first, then freezing," with the pre-reinforcement process acting as the "vanguard," its primary task being to create low-permeability boundary conditions; the freezing process, as the "main force," efficiently forms a pressure-bearing structure in the optimized environment, solving the problems of high energy consumption and uncertain effects of freezing under unlimited recharge boundaries.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of connecting passages, and particularly relates to a construction method for a sea-land interaction super-deep under-consolidated water-rich connecting passage. BACKGROUND

[0002] With the development of society, shield method is used more and more for the construction of subway tunnels; in order to meet the requirements of drainage, emergency, fire prevention and the like in the section, a connecting passage needs to be arranged between the left and right lines of the section after the shield tunneling is completed. The so-called connecting passage is a passage arranged between two tunnels, and if a problem occurs in the whole tunnel, people can transfer to another tunnel through the connecting passage, and the safety factor of people will be greatly increased. The passage is an escape emergency contact passage.

[0003] The construction of the tunnel connecting passage is usually constructed by using the underground excavation method at present, but when the connecting passage is located in a water-rich soft soil area, such as a sea-land interaction area, there is a super-deep under-consolidated silt layer due to the long-term impact of seawater, and the silt layer has a large thickness and a high water-rich amount. The geological condition has the characteristics of strong permeability and sensitive and easy disturbance of the shallow stratum, and the excavation of the connecting passage will cause collapse and water seepage, which causes serious safety problems to the construction personnel and leads to the difficulty in the construction of the connecting passage. The freezing method is a special construction method for temporarily freezing the unstable water-bearing stratum by using artificial refrigeration technology to form a frozen soil wall to block underground water and maintain the stability of the stratum. The method sends low-temperature brine or liquid nitrogen to the stratum by using the freezing pipe, solidifies the soil by using the bonding effect of ice, forms a frozen soil curtain with high strength and water resistance, and is currently also applied to the construction of the connecting passage. However, the existing traditional single construction method is often difficult to simultaneously meet the dual requirements of deep bearing pressure and hydrological seepage control, and the frozen curtain formed by the simple freezing method in the complex stratum cannot guarantee the construction safety, that is, the compressive strength cannot meet the standard. SUMMARY

[0004] In view of the defects in the prior art, the application provides a construction method for a sea-land interaction super-deep under-consolidated water-rich connecting passage. The method proposes a "pre-reinforcement + local reinforcement freezing method" composite reinforcement system, which aims to realize reliable reinforcement in the high-permeability and under-consolidated stratum by using the staged control logic of "blocking water first and controlling pressure later". The application fully plays the advantages of pre-reinforcement in shallow seepage interception and stratum improvement, combines the role of the freezing method in deep bearing pressure and deformation control, forms a synergistic reinforcement mechanism, and establishes a double barrier with water resistance and structural stability in the super-deep complex stratum.

[0005] In order to achieve the above technical purpose, the application provides a construction method for a connecting passage in a water-rich area between two parallel tunnels in a sea-land interaction super-deep under-consolidated stratum. The specific steps are as follows:

[0006] S1. In the communication channel construction area, a closed rectangular or circular cement-soil mixing wall is constructed, the soil in the communication channel construction area is pre-reinforced, a continuous and seamless low-permeability rigid water-stop curtain is formed in the communication channel construction area, the pre-reinforcement treatment extends downward to at least 6m below the bottom of the communication channel, extends to at least 0.5m outward from the outside of the two tunnel side lines, and extends outward at least 3m in the plane direction from the outside of the communication channel structure side line; the cement-soil mixing wall uses a double-wheel stirring device to mill and crush the original stratum soil around the communication channel in situ, and simultaneously injects cement-based slurry through a grouting pipeline, so that the slurry and the soil are uniformly mixed under the action of mechanical stirring to form a cement-soil mixed wall;

[0007] S2. After the pre-reinforcement construction is completed, after the reinforced stratum reaches the predetermined reinforcement strength, freezing pipes are drilled and installed from the adjacent surfaces of the two tunnels towards the communication channel construction area, and the communication channel construction area is treated by freezing method to form a freezing wall that can withstand water and soil pressure and construction load around the tunnel; the freezing pipes are arranged in a plum blossom shape, and the hole spacing is controlled to be 0.6-1.0m;

[0008] S3. When the soil freezing condition meets the excavation requirements, the portal segment and the freezing pipe are removed, a protective door is constructed, and the communication channel excavation work is carried out.

[0009] The preferred technical solution of the application: the specification of the single-slot section wall of the cement-soil mixing wall in step S1 is 0.8m x 2.8m, the transverse engagement of adjacent slot section walls is not less than 150mm, and the longitudinal engagement is not less than 150mm.

[0010] The preferred technical solution of the application: the plane reinforcement range of the cement-soil mixing wall in step S1 is 3m-5m outward from the communication channel structure side line, and the length extends to 0.5m-1m outward from the shield tunnel side line.

[0011] The preferred technical solution of the application: the pre-reinforced area is divided into a weak reinforcement area located 6m above the ground to the vault of the communication channel, and a strong reinforcement area located 6m above the vault to 6m below the vault; the cement content of the weak reinforcement area is 8%-16%, and the cement content of the strong reinforcement area is 50%-57%; and the unconfined compressive strength of the reinforced body after construction for 28d is not less than 2.0MPa in the strong reinforcement area and not less than 0.6MPa in the weak reinforcement area.

[0012] The preferred technical scheme of the present application: in the S2 step, for the key parts of the liaison passage opening and complex stress, local reinforcement freezing is carried out by encrypting the freezing hole arrangement and adjusting the freezing pipe circuit; when the water content is greater than 30%, it is determined as high water content, the hole spacing is adjusted to 0.6-0.8 m; when the water content is less than or equal to 30%, it is determined as low water content, the hole spacing is preferably adjusted to 0.8-1.0 m; generally, the hole spacing is 0.6-0.7 m when the saturated silt is high in water content, and the hole spacing is 0.7-0.8 m when the silt clay is high in water content; the low water content clay can be widened to 1.0 m.

[0013] The preferred technical scheme of the present application: the construction process of the freezing hole in the S2 step is as follows:

[0014] S201. After each freezing hole is positioned and opened, a hole opening pipe with a flange connecting disc is installed at the hole opening, and a hole opening device for preventing water and sand from gushing is installed; during the drilling process, the drill bit is inserted into the hole opening device for sealing, and then the drilling work is started; during the drilling process, the freezing pipe is used as a drill rod, the drilling is stopped when the freezing pipe reaches the designed depth, and then a one-way valve is matched with a plug to seal the hole bottom;

[0015] S202. After each freezing hole is drilled, grouting and hole sealing are carried out; if the sand output is large during the drilling process, compensation grouting should be carried out, and the ground settlement during the drilling construction is closely observed; the amount of compensation grouting is adjusted according to the sand output during the drilling and the settlement monitoring data; after grouting is completed, the pipe opening device is removed after observing that there is no leakage, and a ring-shaped steel plate is welded between the freezing pipe and the hole opening pipe for plugging;

[0016] S203. After all the freezing holes are drilled, the degree of deflection of the freezing holes is detected, the depth is re-measured, and the leakage test is monitored; the leakage test pressure of the freezing hole is controlled at 0.8-1.0 MPa;

[0017] S204. After the whole freezing system is installed and the trial operation is normal, the freezing machine is started to freeze the soil layer; during the freezing process, the salt water temperature of the inlet and return circuit dry pipe, the salt water temperature of the freezing device return circuit, the salt water tank liquid level change, and the cooling water temperature are detected every day, and whether the frost on the head of the freezing device has abnormal melting is observed.

[0018] The preferred technical scheme of the present application: in the S2 step, the settlement monitoring points are arranged on the ground before the drilling construction of the liaison passage, and the initial value is taken; during the drilling construction, the settlement value change of the ground is observed, and once the settlement exceeds the standard, compensation grouting is carried out on the ground layer, and the bypass valve on the hole opening pipe is used for compensation grouting on the ground layer.

[0019] The preferred technical solution of this invention is as follows: In step S3, the pilot tunnel is first excavated and temporary support is provided for the opening section of the connecting passage. The pilot tunnel is 2.0 to 2.5 meters wide and 2.0 to 2.5 meters high, with an advance of 1.0 to 1.2 meters. The standard section of the passage is excavated using short-section excavation and masonry techniques, with each excavation advance not exceeding 500 mm, consistent with the initial support steel arch spacing of 500 mm. After the earthwork excavation and shotcreting of the standard section of the passage and the opening section on the opposite side are completed in a single cycle, the remaining earthwork excavation and shotcreting of the opening section on the excavated side are completed.

[0020] The preferred technical solution of this invention is as follows: Data monitoring is conducted during the excavation process in step S3. If the monitoring data is abnormal, the construction method must be immediately adjusted to the step method. Four anchor bolts are installed at the connection between each steel arch frame. The freezing pipe in the horizontal direction at the center of the excavation face is protected during the excavation process. For each steel arch frame, one frame is immediately installed and fixed after excavation. Shotcrete is applied to every two steel arch frames; multiple frames cannot be shotcreted at once. When installing the steel arch frame, the connection between the steel arch frame and the support is reliable, and the first support frame is welded and fixed to the steel pipe segment.

[0021] The preferred technical solution of the present invention is as follows: In step S201, the orifice device includes an orifice pipe, a ball valve, and a sealing connection pipe. After the freezing hole is positioned and opened, the orifice pipe is installed. A flange connection plate is provided at the end of the orifice pipe, and a bypass ball valve is provided on the side wall of the orifice pipe. The ball valve is connected through the flange connection plate. Finally, the sealing connection pipe is installed at the end of the ball valve, and a sealing rubber ring is provided inside the sealing connection pipe.

[0022] This invention follows a strict sequence of "seepage interception first, then freezing." The pre-reinforcement process, acting as the "vanguard," primarily aims to create low-permeability boundary conditions. The freezing process, as the "main force," efficiently forms a pressure-bearing structure within the optimized environment, solving the problems of high energy consumption and uncertain effectiveness in freezing under unlimited recharge boundaries. The pre-reinforcement curtain effectively curbs soil disturbance and water migration that may be caused by the movement of the freezing front, reducing the risk of surface subsidence. Simultaneously, the robust frozen soil curtain provides internal support for the pre-reinforcement curtain, enhancing the stability of the overall composite structure. Ultimately, a composite load-bearing system of "rigid waterproof outer shell + high-strength frozen soil core" is formed. The pre-reinforcement curtain is the permanent and primary seepage barrier, while the freezing curtain is the temporary and primary pressure-bearing structure. The two complement each other, jointly ensuring the safe and controllable excavation and construction of the connecting passage under extremely complex geological conditions of ultra-deep, underconsolidated, and water-rich conditions.

[0023] This invention utilizes pre-reinforced mechanical milling and forced mixing to mill and break up the original soil in situ. Simultaneously, cement-based grout is injected through grouting pipelines, achieving forced and uniform mixing of the grout and soil under the action of pre-reinforced mechanical mixing. Through continuous and seamless construction, a continuous rigid water-stop curtain with low permeability is constructed. This curtain acts like a "waterproof box," physically isolating the highly permeable external water-rich strata from the planned frozen internal area. The hydration reaction of the cement-soil improves the strength and stiffness of the soil within the curtain area, providing a stable working surface for the precise construction of subsequent freezing holes. More importantly, this curtain effectively blocks the lateral recharge path of external water bodies, significantly reducing the hydrological load during the freezing construction and maintenance periods, reducing the water pressure that the freezing curtain needs to bear, and achieving "hydraulic unloading." Freezing construction is carried out in the closed, low-permeability environment formed by the pre-reinforced water-stop curtain. The principle is to use artificial refrigeration technology to freeze the pore water in the strata into ice, thereby cementing soil particles and forming a high-strength, high-integrity freezing curtain structure. Because the external water supply is cut off by the pre-reinforced water-stop curtain, the freezing system only needs to handle the limited water body within the curtain. This clearly defines the heat exchange range, significantly improving freezing efficiency, shortening the freezing cycle time, and ensuring the uniformity and reliability of the frozen curtain thickness. Under freezing conditions, the water in the soil transforms into ice, firmly binding loose soil particles and significantly increasing the compressive and shear strength of the frozen soil (several to tens of times higher than undisturbed soil). This forms the temporary load-bearing structure—the frozen wall—around the tunnel, capable of withstanding water and soil pressure and construction loads as designed. For critical areas such as tunnel openings and areas with complex stress, rapid freezing measures such as denser freezing hole layout and adjusted freezing pipe loops are used for localized enhanced freezing. This ensures that the frozen soil curtain in these stress concentration zones has sufficient thickness and strength, guaranteeing structural safety and stability during excavation.

[0024] The beneficial effects of this invention are:

[0025] (1) The core sample test results of the present invention show that the pre-reinforcement measures significantly improve the compressive strength and water-stopping performance of the soil, effectively improve the problem of loose and highly permeable soil, and provide a solid and reliable foundation for subsequent water interception operations, drilling construction and frozen soil formation;

[0026] (2) In view of the situation that the compressive strength of the solidified soil alone does not meet the construction requirements, the present invention carried out a special test on the solidified frozen soil. The field test data showed that after freezing treatment, the compressive strength of the soil before excavation reached 8.21 MPa and the flexural strength was 4.91 MPa, which fully met the relevant requirements of excavation technology and verified the key value of the synergistic effect of "pre-reinforcement + freezing".

[0027] (3) The practical results of this invention fully verify the scientific nature and feasibility of the pre-reinforcement + freezing construction process. By improving the soil foundation conditions through pre-reinforcement and then further enhancing the mechanical properties through freezing treatment, the problem of insufficient strength of the reinforced soil is solved, construction safety is ensured, and the overall quality of the project is improved simultaneously. This provides a reference for engineering construction under similar geological conditions. Through monitoring of the entire construction process, all monitoring data are in a stable and controlled state, with no abnormal fluctuations in the indicators, verifying the safety of this construction process, meeting the requirements for construction safety control, and ensuring the safe progress and stable operation of the entire construction process.

[0028] This invention utilizes a pre-reinforcement process to reconstruct hydrological boundaries and pre-control risks, followed by a freezing method to reliably construct the structural system within the reconstructed favorable boundaries. It represents a proactive, defensive, and precise control construction technique for specific high-risk geological conditions. This provides a reference for urban underground engineering construction under similar geological conditions in my country, helping to improve the risk resistance and overall construction level of deeply buried tunnels. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the reinforced structure formed in this invention;

[0030] Figure 2 yes Figure 1 Front view;

[0031] Figure 3 This is a schematic diagram of the reinforced area partitioning in this invention;

[0032] Figure 4 This is a schematic diagram of the structure of the cryogenic tube inlet in this invention;

[0033] Figure 5 This is a construction flowchart of an embodiment of the present invention;

[0034] Figure 6 This is a schematic diagram of settlement monitoring during the excavation of the connecting passage in the embodiment. Detailed Implementation

[0035] The present invention will now be described in detail with reference to specific embodiments.

[0036] This example uses a frozen construction project for a connecting passage in Guangzhou as a case study. It analyzes and explores the complex geological risks posed by the site's foundation, characterized by "ultra-deep (34.5m burial depth), under-consolidation (silt layer thickness greater than 15m), and abundant water." These geological conditions are characterized by high permeability and easily disturbed shallow strata, representing a rare high-risk tunnel engineering condition that poses a severe challenge to construction safety and technical reliability. Given the complex geological conditions of this project, traditional single-method approaches are often insufficient to simultaneously address the dual requirements of deep confined soil and hydrological seepage control. Furthermore, this project involves…

[0037] Currently, such complex geological formations are rare in ultra-deep connecting tunnel construction. Construction in these formations is high-risk and challenging, requiring the collection of undisturbed soil samples for permafrost testing. The permafrost test results of the undisturbed soil samples collected for this construction project show: compressive strength 1.467–2.01 MPa, flexural strength 1.15 MPa, and shear strength 1.26–1.77 MPa. All measured indicators are significantly lower than the standard permafrost strength (compressive strength ≥3.6 MPa, flexural strength ≥2.0 MPa, shear strength ≥1.5 MPa), indicating poor permafrost geological conditions in this area. Simply using freezing methods to reinforce the excavation area of ​​the connecting tunnel would not guarantee construction safety.

[0038] To address this issue, the inventors of this application propose a composite reinforcement system combining "pre-reinforcement + localized enhanced freezing," aiming to achieve reliable reinforcement in high-permeability, underconsolidated strata through a phased control logic of "first blocking water, then controlling pressure." This system fully leverages the advantages of pre-reinforcement in shallow seepage interception and strata improvement, combined with the role of freezing in deep pressure bearing and deformation control, forming a synergistic reinforcement mechanism to establish a dual barrier of seepage prevention and structural stability in ultra-deep, complex strata.

[0039] For the pre-reinforcement of the geological strata in this connecting passage (approximately 48m deep, with deep, high-velocity sand layers), the available technologies include triaxial mixing piles, intelligent shear mixing piles, CSM double-wheel mixing, TRD, and in-tunnel horizontal MJS; a comparative analysis of these three reinforcement methods is conducted:

[0040] ① Triaxial mixing piles: When the reinforcement depth exceeds 40m, the reinforcement effect decreases significantly and they are not suitable for use.

[0041] ② Intelligent shear mixing pile: In deep sand layers, it is difficult for the drill bit to stir, making it impossible to form piles effectively.

[0042] ③ Horizontal MJS inside the tunnel: Drilling in high-pressure, high-velocity sand layers poses an extremely high risk of gushing and has poor safety.

[0043] ④ CSM dual-wheel agitator and TRD: Both have advantages such as large reinforcement depth (meeting the 48m requirement), good mixing uniformity, high quality controllability, and safety and reliability, making them feasible choices. However, the cost of the TRD process is significantly higher than that of CSM.

[0044] Based on economic considerations, the CSM double-wheel mixing process is recommended for full-area reinforcement. The reinforced body formed by CSM in this location showed intact core samples, and the measured unconfined compressive strength reached 3.2-6.7 MPa, indicating that it can guarantee the required reinforcement effect for this project.

[0045] After determining the pre-reinforcement process, the communication channel in the embodiment was constructed according to the method in this invention. The specific construction process is as follows: Figure 5 As shown, the specific construction process is as follows:

[0046] S1. Construct closed rectangular or circular cement-soil mixing walls in the construction area of ​​the connecting passage to pre-reinforce the soil in the construction area, forming a continuous, seamless, low-permeability rigid water-stop curtain. The cement-soil mixing walls utilize a double-wheel mixing device to mill and break up the original soil around the connecting passage in situ. Simultaneously, cement-based grout is injected through grouting pipelines. Under mechanical mixing, the grout and soil are forcibly and uniformly mixed. Key technical parameters for pre-reinforcement: Single-slot wall specifications: 0.8m × 2.8m, with two interlocking dimensions of 200mm and 150mm to ensure tight wall connections and form a complete reinforcement system; Planar reinforcement range: Extending outwards by 3m from the structural edge line, with a length extending 0.5m beyond the shield tunnel edge line, covering the core construction area and surrounding influence range; The depth of the pre-reinforcement extends downwards to at least 6m to the bottom of the connecting passage, and the pre-reinforcement area extends from the ground to 6m above the arch of the connecting passage. The weak reinforcement zone is defined as the area from 6m above the arch crown to 6m below the arch bottom of the connecting passage, while the strong reinforcement zone is defined as 8% for the weak reinforcement zone and 57% for the strong reinforcement zone, as verified by pile testing. The pile testing report shows that core samples with 20%, 25%, and 40% admixture dosages were severely broken and could not meet the engineering requirements, while the core samples with 57% admixture dosage were intact and had stable mechanical properties. The 28-day unconfined compressive strength of the reinforced body is not less than 2.0MPa in the strong reinforcement zone and not less than 0.6MPa in the weak reinforcement zone, ensuring that the reinforced soil has the foundation bearing capacity. However, the compressive strength of the reinforced body alone still cannot directly meet the core mechanical requirements of subsequent excavation construction.

[0047] S2. After the pre-reinforcement construction is completed, the freezing pipe drilling operation will be initiated two months later (the operation will last approximately one month), meaning that the freezing construction will officially commence three months after the reinforcement is completed. The core advantage of this sequence is that, after a three-month curing period, the heat of hydration of the reinforced material has been fully released, minimizing the thermal interference to the subsequent freezing construction. Strict adherence to this plan will prevent delays in the construction period, achieving scientific coordination of procedures and controllability of the construction schedule. The dynamic freezing pipe drilling operation involves drilling holes from the adjacent faces of the two tunnels toward the construction area of ​​the connecting passage to install freezing pipes. The construction area of ​​the connecting passage will then be treated with freezing methods to form a frozen wall around the tunnel that can withstand water and soil pressure and construction loads. Before drilling the connecting passage, settlement monitoring points will be set up on the ground and initial values ​​will be recorded. During the drilling operation, close attention will be paid to changes in ground settlement. If the settlement exceeds the standard, compensating grouting will be carried out immediately. Based on the cross-sectional dimensions of the connecting passage, the water content of the formation, and the design thickness of the frozen wall (≥2.6m), the freezing pipes are arranged in a quincunx pattern, with the hole spacing strictly controlled between 0.6 and 1.0m. The staggered spacing between adjacent rows of freezing pipes is consistent with the spacing within the same row to ensure that the frozen wall overlaps tightly without gaps and to prevent the formation of freezing blind spots. For ultra-deep, under-consolidated, water-rich areas where the sea and land meet the water content requirements, the hole spacing can be adjusted to 0.6 to 0.8m when the water content is high to enhance the freezing effect and ensure that the frozen wall thickness meets the standards. When the water content is low, the spacing can be adjusted to 0.8 to 1.0m to balance construction efficiency and freezing quality.

[0048] After each freezing hole is positioned and drilled, a flanged pipe is installed at the hole opening, along with a device to prevent water and sand inrush. This device includes the pipe, a ball valve, and a sealing connection pipe. The pipe is installed after the freezing hole is positioned and drilled; a flange is located at the end of the pipe, and a bypass ball valve is located on the side wall of the pipe. The ball valve is connected via the flange, and finally, the sealing connection pipe is installed at the end of the ball valve. A sealing rubber ring (packing) is installed inside the sealing connection pipe. Figure 4 As shown, install the sealing connection pipe onto the ball valve with screws, ensuring the sealing gasket is properly installed. During drilling, insert the drill bit into the orifice device for sealing before starting drilling. Once the first hole is clear and there is no water or sand inflow, drilling can continue. However, the orifice device must still be installed for subsequent holes to prevent sudden water or sand inflow. If the water or sand inflow is severe, cement grout (or two-component grout) should be injected to stop the water. Drilling for connecting passages carries significant risks. To ensure construction safety, the freezing pipe connection method uses internal pipe clamps with threaded connections followed by welding with J422 welding rods. Use high-pressure, high-performance check valves during drilling to prevent water or sand inflow into the freezing pipe due to check valve failure. During drilling, strictly adhere to the requirements for installing the ball valve and sealing connection pipe. When installing the sealing connection pipe, use appropriately sized, high-quality packing to seal the orifice to prevent sandblasting and sand inflow during drilling.

[0049] The freezing drilling construction process in step S2 of the embodiment is as follows: positioning and drilling, and installation of the orifice pipe → installation of the orifice device → drilling → measurement → sealing the bottom of the hole → pressure testing for leaks. The specific steps are as follows:

[0050] (1) Use one horizontal drilling rig with a torque of not less than 3000 N·m and a thrust of not less than 25 KN. Select one grouting mud pump with a flow rate of not less than 160 L / min; the total power of a single drilling rig and mud pump is about 47 kW.

[0051] (2) Adjust the position of the drilling rig according to the construction orientation requirements of the freezing hole and fix it. Put the drill bit into the hole opening device and seal it with oil-immersed packing. First, use dry drilling. When drilling is difficult and the progress is not made, water drilling is carried out from the drilling rig. At the same time, open the bypass valve and observe the water and sand output. Use the bypass valve switch to control the slurry output to ensure the safety of the ground and prevent settlement.

[0052] (3) Use freezing pipes as drill rods. The freezing pipes are connected by internal pipe clamps and threads and welded to ensure concentricity and welding strength. To ensure borehole deviation, the centerline deviation of the left and right connecting channels should be calculated and verified by the shield tunneling measurement before drilling. Before drilling, a verification hole should be drilled according to the centerline deviation, and the borehole deviation value of the corresponding drilling face should be adjusted according to the verification hole. The opening section is crucial to ensure drilling accuracy. Before drilling, the direction of the freezing pipes should be repeatedly checked, the attitude and position of the drilling rig should be adjusted, and drilling can only continue after checking that there are no deviation problems.

[0053] (4) After the freezing pipe reaches the designed depth, drilling should be stopped. Then, the bottom of the hole should be sealed with a one-way valve and a threaded plug. The threaded plug is installed at the bottom of the freezing pipe using an extension rod. After each freezing hole is drilled, grouting should be performed to seal the hole. If the amount of sand produced during drilling is large, compensatory grouting should also be performed. Because the geology above the connecting passage is sensitive, the ground settlement should be closely monitored during drilling. The amount of compensatory grouting should be adjusted according to the amount of sand produced during drilling and the settlement monitoring data.

[0054] (5) After grouting is completed, the ball valve and clamping device can be removed only after observing that there is no leakage at the bypass valve and the orifice flange. The observation time shall not be less than 12 hours. A ring steel plate shall be welded between the freezing pipe and the orifice pipe for sealing. The ring steel plate shall overlap with the flange and shall not cover the flange hole. The ring steel plate shall be welded to the outer wall of the freezing pipe and the orifice flange. At this point, the drilling of the single-hole freezing hole is completed.

[0055] (6) After all the freezing holes are drilled, the degree of deviation is detected by the theodolite light inclination method. The depth of the freezing holes is re-measured by tape measure + aluminum-plastic pipe. The freezing holes are tested for leaks. The test pressure of the freezing holes is controlled at 0.8-1.0 MPa. The pressure is stable for 30 minutes without change or the pressure drop is <0.05 MPa in the first 30 minutes and does not drop in the last 15 minutes. The test is considered qualified.

[0056] (7) For the three types of non-compliance—excessive deviation of the freezing hole, freezing hole depth less than the design depth, and freezing hole leak test failure preventing casing from being lowered—a specific analysis should be conducted based on the cause of the non-compliance, and a new freezing hole should be drilled at the defective location. The new freezing hole must be re-inspected for deviation, depth, and leak test. For cases where the freezing hole leak test fails but the casing can be lowered, the casing should be lowered. The casing specifications are Φ57mm, and the internal liquid supply pipe is Φ32mm. The freezing hole for lowering the casing must be connected in series with a separate set of cooling capacity for freezing. Drilling sequence: ① First, drill 1-2 through holes for verification orientation. ② Next, drill the bottom horizontal row of freezing holes and temperature measurement holes. If the bottom freezing holes are close to each other, a skip drilling method or M-shaped drilling method can be used (i.e., select the nearest hole, drill 1 hole in the first row, then move to the second row of holes closest to the hole, drill 1 hole in the second row, then move to the third row of holes closest to the hole, and so on). There are a total of 2 rows at the bottom of the main freezing surface and a total of 3 rows at the bottom of the secondary freezing surface (including temperature measurement holes).

[0057] S3. After the entire refrigeration system is installed, first conduct a trial run of the brine system. The clean water system should not be involved in the operation, and the chiller should be run for 12 hours with the chiller off, observing the liquid level. Only if the liquid level remains unchanged can it be confirmed that the refrigeration system is sealed and leak-free. After the brine system leak test is completed, check and confirm that the parameters of the refrigeration circuit system and cooling water circulation system are normal before starting the chiller. Run the chiller idle for 1-3 hours initially, observing for any abnormalities. During the trial run, gradually adjust various state parameters such as energy, pressure, temperature, and motor load to ensure the unit operates under the technical parameters required by the relevant equipment regulations and operating procedures. Under normal operation, the brine temperature should drop below -18℃ after 7 days; under active freezing, the brine temperature should drop below -24℃ after 15 days. After freezing begins, regularly check the freezers for any breaks or leaks. If any brine leakage is found, immediately close the valve and take remedial measures according to the extent of the leakage.

[0058] During the freezing process, the brine temperatures in the outgoing and return mains, the brine temperature in the freezer circuit, the brine tank level, and the cooling water temperature are monitored daily. The frost on the freezer head is also observed for abnormal melting. In the initial stage of freezing operation, the brine flow rate of each freezer is checked. If the flow rate is found to be lower than the design requirements, the control valves are adjusted, or the brine pump flow rate is increased to meet the design requirements. The freezing process must be inspected daily, and the temperature at the temperature measuring holes is monitored daily. Based on the temperature data, the expansion rate and thickness of the frozen wall are analyzed, and the time it takes for the frozen wall to reach the design thickness is estimated.

[0059] Refrigeration unit cooling temperature monitoring: Key parameters such as refrigeration unit cooling temperature, suction pressure, discharge pressure, discharge temperature, and clean water temperature should be recorded every two hours. After the refrigeration unit starts normal operation, the values ​​of cooling temperature, suction pressure, and discharge pressure should gradually decrease. The cooling temperature should drop to -18℃ on the 7th day of freezing, to -24℃ on the 15th day, and to -28℃ before excavation, with the temperature difference between the outflow and inflow narrowing to within 2℃. The maximum warning value for the refrigeration unit discharge pressure is 1.8 MPa, and the minimum warning value for the refrigeration unit suction pressure is 0.02 MPa. If any abnormalities occur during monitoring, the team leader should be notified immediately for parameter adjustments or extension of the active freezing time.

[0060] Temperature monitoring at the temperature measuring holes: The temperature at the measuring points is monitored by an information-based temperature monitoring system every 6 hours to dynamically track the cooling of the soil. The average soil temperature must be reduced to below -15℃ before excavation.

[0061] S4. Once the soil freezing condition meets the excavation requirements, remove the tunnel lining segments and freezing pipes at the tunnel entrance, install protective doors, and commence the excavation of the connecting tunnel. Based on the engineering structure and the characteristics of the freezing method, the connecting tunnel will be excavated in sections. First, excavate the pilot tunnel on the excavation side, then excavate the standard section of the tunnel and the opposite side's pilot tunnel sequentially, and finally excavate the remaining soil in the opening section on the excavation side. Due to the limited space in the opening section, steel supports cannot be transported to the working face for installation; therefore, the pilot tunnel will be excavated first and temporary support will be provided. The pilot tunnel dimensions are 2.0–2.5 meters wide and 2.0–2.5 meters high, with an advance of 1.0–1.2 meters. The standard section of the tunnel will be excavated using short-section excavation and masonry techniques, with each excavation advance not exceeding 500mm, consistent with the initial 500mm spacing of the steel arch supports. After the excavation and shotcreting of the standard section and the opposite opening section are completed in a single cycle, the remaining soil excavation and shotcreting of the opening section on the excavation side will be completed. Data monitoring is conducted during excavation. If any abnormal data is detected, the construction method must be immediately adjusted to the bench method. Four anchor bolts are installed at the connection points between each steel arch frame. For each steel arch frame, one frame is installed and fixed immediately after excavation. Shotcrete is applied to every two steel arch frames; multiple frames should not be shotcreted at once. During excavation, care must be taken to protect the frozen pipes in the horizontal direction at the center of the excavation face. When installing the steel arch frames, ensure reliable connection to the supports, strictly control the welding and fixing between the first support frame and the steel segments to ensure support stability. Due to the high strength and toughness of frozen soil, pneumatic drills are required for excavation. During excavation, the excavation step distance and support strength are adjusted promptly based on the reinforcement effect of the exposed soil and construction monitoring information to ensure safe construction.

[0062] The inventors of this application verified the effectiveness of the pre-reinforcement and frozen soil tests in the embodiments:

[0063] Pre-reinforcement effect: Core sample test results show that the pre-reinforcement measures significantly improved the compressive strength and water-stopping performance of the soil, effectively improved the problems of loose and highly permeable original soil, and provided a solid and reliable foundation for subsequent water interception operations, drilling construction and frozen soil formation;

[0064] Core verification of frozen soil test: In response to the situation where the compressive strength of the solidified soil alone does not meet the construction requirements, a special test of the solidified frozen soil was carried out. The field test data showed that after freezing treatment, the compressive strength of the soil before excavation reached 8.21 MPa and the flexural strength was 4.91 MPa, which fully met the relevant requirements of excavation technology, and verified the key value of the synergistic effect of "pre-reinforcement + freezing".

[0065] The successful implementation of this project fully validates the scientific validity and feasibility of the pre-reinforcement + freezing construction process. Pre-reinforcement improves the soil foundation conditions, and subsequent freezing further enhances mechanical properties. This approach not only solves the problem of insufficient strength from simple reinforcement but also ensures construction safety and simultaneously improves the overall quality of the project, providing a reference for construction projects under similar geological conditions. Monitoring throughout the entire construction process yielded the following results: Figure 6 As shown, all monitoring data are in a stable and controlled state, with no abnormal fluctuations in the indicators, which verifies the safety of this construction process, meets the construction safety control requirements, and can ensure the safe progress and stable operation of the entire construction process.

Claims

1. A method for constructing a connecting passage between two parallel tunnels in a water-rich area of ​​ultra-deep, underconsolidated strata with sea-land interaction, characterized in that: The specific steps are as follows: S1. Construct a closed rectangular or circular cement-soil mixing wall in the construction area of ​​the connecting passage to pre-reinforce the soil in the construction area of ​​the connecting passage, forming a continuous, seamless, low-permeability rigid water-stop curtain in the construction area of ​​the connecting passage. The depth of the pre-reinforcement extends downward to the bottom of the connecting passage by at least 6m, and the length extends outward from the outer edge of the two tunnels by at least 0.5m, and in the plane direction, it extends outward from the edge of the connecting passage structure by at least 3m. The cement-soil mixing wall uses a double-wheel mixing device to mill and break the original soil around the connecting passage in situ. At the same time, cement-based grout is injected synchronously through grouting pipelines. Under the action of mechanical mixing, the grout and soil are forcibly and uniformly mixed to form the wall. S2. After the pre-reinforcement construction is completed, once the reinforced stratum reaches the predetermined reinforcement strength, holes are drilled from the adjacent faces of the two tunnels toward the construction area of ​​the connecting passage to install freezing pipes, and the construction area of ​​the connecting passage is treated by freezing method to form a frozen wall around the tunnel that can withstand water and soil pressure and construction load; the freezing pipes are arranged in a quincunx pattern, and the hole spacing is controlled between 0.6 and 1.0 m. S3. Once the soil freezing condition meets the excavation requirements, the tunnel segment and freezing pipe are removed, a protective door is installed, and the excavation of the connecting tunnel begins. The connecting tunnel is excavated in sections. First, the funnel-shaped guide hole on the excavation side is excavated, then the standard section of the tunnel and the funnel on the opposite side are excavated in sequence, and finally the remaining soil in the opening section on the excavation side is excavated.

2. The construction method for a connecting channel in a water-rich area of ​​ultra-deep, underconsolidated strata with sea-land interaction, as described in claim 1, is characterized in that: In step S1, the specifications of a single trench section of the cement-soil mixing wall are 0.8m × 2.8m, and the transverse interlocking of adjacent trench sections is not less than 150mm, and the longitudinal interlocking is not less than 150mm.

3. The construction method for a connecting channel in a water-rich area of ​​ultra-deep, underconsolidated strata with sea-land interaction, as described in claim 1, is characterized in that: The planar reinforcement range of the cement-soil mixing wall in step S1 is 3m to 5m outward from the edge of the connecting passage structure, and the length extends 0.5m to 1m outward from the edge of the shield tunnel.

4. The construction method for a connecting channel in a water-rich area of ​​ultra-deep, underconsolidated strata with sea-land interaction, as described in claim 1, is characterized in that: The pre-reinforced area is a weakly reinforced zone located 6m above the arch of the connecting passage from the ground level, and a strongly reinforced zone located 6m above the arch of the connecting passage to 6m below the arch base. The cement content in the weakly reinforced zone is 8%–16%, and the cement content in the strongly reinforced zone is 50%–57%. Furthermore, the unconfined compressive strength of the reinforced body after 28 days is not less than 2.0 MPa in the strongly reinforced zone and not less than 0.6 MPa in the weakly reinforced zone.

5. A construction method for a connecting channel in a water-rich area of ​​ultra-deep, underconsolidated strata with sea-land interaction, as described in claim 1, characterized in that: In step S2, for key parts with complex stress and openings in the connecting channel, local enhanced freezing is carried out by increasing the density of freezing holes and adjusting the freezing pipe circuit; when the moisture content is >30%, it is judged as high moisture content, and the hole spacing is reduced to 0.6-0.8m; when the moisture content is ≤30%, it is judged as low moisture content, and the hole spacing should be increased to 0.8-1.0m.

6. A construction method for a connecting channel in a water-rich area of ​​ultra-deep, underconsolidated strata with sea-land interaction, as described in claim 1, characterized in that... The construction process of the freezing holes in step S2 is as follows: S201. After each freezing hole is positioned and opened, a pipe with a flange connection is installed at the hole opening, and a hole opening device to prevent water and sand from flowing in is installed. During the drilling process, the drill bit is inserted into the hole opening device for sealing before drilling begins. During the drilling process, the freezing pipe is used as the drill rod. Drilling stops after the freezing pipe reaches the designed depth, and then the bottom of the hole is sealed with a one-way valve and a matching plug. S202. After each freezing hole is drilled, grouting is performed to seal the hole. If the amount of sand produced during drilling is large, compensatory grouting should be performed. The ground settlement should be closely monitored during drilling. The amount of compensatory grouting should be adjusted according to the amount of sand produced during drilling and the settlement monitoring data. After grouting is completed, the pipe opening device should be removed after observing that there is no leakage at the pipe opening. A ring steel plate should be welded between the freezing pipe and the hole opening pipe to seal the hole. S203. After all the freezing holes have been drilled, the deviation degree, depth re-measurement and leak monitoring processes are carried out on the freezing holes in sequence. The leak test pressure of the freezing holes is controlled at 0.8 to 1.0 MPa. S204. After the entire refrigeration system is installed and tested normally, turn on the refrigeration unit to freeze the soil. During the freezing process, check the brine temperature of the inlet and outlet main pipes, the brine temperature of the freezer circuit, the brine tank level change, and the cooling water temperature every day. Observe whether there is any abnormal melting of the frost on the freezer head.

7. A construction method for a connecting channel in a water-rich area of ​​ultra-deep, underconsolidated strata with sea-land interaction, as described in claim 1, characterized in that: Before drilling the connecting passage in step S2, settlement monitoring points are set up on the ground and initial values ​​are taken. During the drilling, the changes in ground settlement are monitored. If the settlement exceeds the standard, the stratum is immediately compensated by grouting. The bypass valve on the borehole pipe is used to compensate the stratum by grouting.

8. A construction method for a connecting channel in a water-rich area of ​​ultra-deep, underconsolidated strata with sea-land interaction, as described in claim 1, characterized in that: In step S3, the pilot tunnel for the opening section of the connecting passage is first excavated and temporarily supported. The pilot tunnel is 2.0-2.5 meters wide and 2.0-2.5 meters high, with an advance of 1.0-1.2 meters. The standard section of the passage is excavated using short-section excavation and masonry techniques, with each excavation advance not exceeding 500mm, consistent with the initial support steel arch spacing of 500mm. After the earthwork excavation and shotcreting of the standard section of the passage and the opening section on the opposite side are completed in a single cycle, the remaining earthwork excavation and shotcreting work of the opening section on the excavated side is completed.

9. A construction method for a connecting channel in a water-rich area of ​​ultra-deep, underconsolidated strata with sea-land interaction, as described in claim 1, characterized in that: In step S3, data monitoring is conducted during the excavation process. If the monitoring data is abnormal, the construction method must be adjusted immediately to the step method. Four anchor bolts are installed at the connection between each steel arch frame. During the excavation process, the freezing pipe in the horizontal direction of the center of the excavation face is protected. After each steel arch frame is excavated, one frame is immediately installed and fixed. Shotcrete is applied to every two steel arch frames. It is strictly forbidden to apply shotcrete to multiple frames at once. When installing the steel arch frame, the connection between the steel arch frame and the support is reliable. The first support frame is welded and fixed to the steel pipe segment.

10. A construction method for a connecting channel in a water-rich area of ​​ultra-deep, underconsolidated strata with sea-land interaction, as described in claim 6, characterized in that: In step S201, the orifice device includes an orifice pipe, a ball valve, and a sealing connection pipe. After the freezing hole is positioned and opened, the orifice pipe is installed. A flange connection plate is provided at the end of the orifice pipe, and a bypass ball valve is provided on the side wall of the orifice pipe. The ball valve is connected through the flange connection plate. Finally, the sealing connection pipe is installed at the end of the ball valve, and a sealing rubber ring is provided inside the sealing connection pipe.

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