Deep station excavation construction method based on frozen water stop technology

Abstract

This invention relates to a method for deep underground railway station excavation based on freezing and water-stopping technology, comprising the following steps: detecting the distribution density of pebbles and the location of ultra-large pores in the stratum, recording the particle size and arrangement direction of the pebbles in the stratum, and establishing a three-dimensional pore model of the stratum; constructing the main borehole, and after the main borehole is completed, extending a micro-directional drilling rig from the main borehole and drilling according to the three-dimensional pore model to construct branch holes and micro-holes; introducing a first refrigerant into the micro-holes for a preset duration until ice plugs are formed in the cracks, and then introducing a second refrigerant into the main borehole for cooling until a frozen soil curtain is formed; excavating the stratum, and after the excavation is completed, setting initial support, and pre-embedding adaptive expansion bladders between the initial support and the frozen soil curtain; allowing the frozen soil to thaw naturally, monitoring the stratum stability in the thawing area in real time, and when the pore water pressure in the thawing area drops to a preset trigger threshold, slowly injecting a preset type of cement slurry into the adaptive expansion bladders.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology based on freezing and water-stopping technology, and more particularly to a method for deep station tunnel construction based on freezing and water-stopping technology. Background Technology

[0002] Freezing and water-stopping technology, as an important support method in urban underground engineering, uses artificial refrigeration to freeze groundwater, forming a continuous frozen soil curtain. This effectively blocks groundwater seepage and enhances ground stability, creating a safe working environment for tunneling operations. Among various geological formations, high-water-content loose strata are the primary application targets for this technology. However, large-particle-size, high-permeability gravel strata present a challenge due to their unique geological characteristics. These strata are characterized by gravel (e.g., 200-800mm in diameter) as the main framework particles, with sand filling the gaps between the gravel, resulting in a structure with extremely poor particle size distribution. The prevalent ultra-large pores (e.g., pore diameter 50-200mm) between the gravel particles lead to extremely rapid groundwater seepage (e.g., permeability coefficient > 5m / d). Furthermore, while the gravel framework has high strength, its self-stability is poor, making drilling operations susceptible to deviation due to collisions with large-particle-size gravel. The low thermal conductivity of gravel also results in low cold transfer efficiency, making it difficult for conventional freezing meshes to form a complete and continuous frozen soil curtain. During tunnel excavation, the continuity and integrity of the frozen curtain are directly related to construction safety, while thaw settlement compensation after thawing is a key factor in ensuring the long-term stability of the strata. Therefore, for freezing and water-stopping technology in large-particle-size, highly permeable sand and gravel strata, it is necessary to have a deep understanding of the three-dimensional porosity characteristics and freezing mechanism of the strata, and to design a construction process that can adapt to the special geological conditions of the strata, so as to meet the dual requirements of engineering safety and economy.

[0003] CN118008325A discloses a method for widening the excavation of a subway tunnel connecting passage based on freezing. The method includes the following steps: S1: Pre-construction preparation; S2: Determining freezing design parameters and calculating the thickness of the freezing curtain; S3: Calculating the required cooling capacity of the refrigeration freezing system; S4: Arranging inner and outer ring freezing holes in a double-ring manner; arranging temperature measuring holes on the structural surfaces of the left and right tunnels; arranging pressure relief holes on both sides of the non-freezing area within the freezing curtain; S5: Assembling the refrigeration freezing system; S6: Debugging and operating the refrigeration freezing system; S7: Entering the active freezing stage; S8: Excavation determination and entering the maintenance freezing stage; S9: Excavation and initial support construction of the connecting passage; S10: Construction of the waterproof layer and secondary lining structure; S11: Filling grouting; S12: Melting grouting; S13: Sealing the holes; S14: Site removal; S15: Monitoring throughout the construction process.

[0004] In freezing and sealing construction of large-diameter, highly permeable sand and gravel strata, existing technologies face core challenges such as difficulty in achieving complete freezing curtain closure and incomplete thawing settlement compensation. The denser freezing borehole technology suffers from excessive borehole deviation due to the large-diameter gravel, leading to gaps in the curtain due to borehole positional errors. Furthermore, the inability to accumulate cold energy in ultra-large pores creates continuous seepage channels, making continuous curtain closure difficult. In the pre-embedded grouting pipe thawing settlement compensation technology, grout rapidly flows along the gravel surface, failing to effectively fill ultra-large pores. Simultaneously, the high viscosity of the grout makes it difficult to penetrate micro-cracks (e.g., cracks 1-5 mm wide), posing a risk of settlement even after thawing. The basin-shaped freezing technology only optimizes the planar layout of the borehole network, neglecting to design cold energy replenishment paths for vertically large pores, resulting in poor vertical continuity of the curtain. The root cause of these problems lies in the fact that existing technologies fail to consider the compatibility between the three-dimensional porosity characteristics of the formation and the cold energy transfer and grout diffusion. Instead, they adopt a linear optimization approach, such as densifying the pore network and lowering the refrigerant temperature, neglecting the core contradiction of the compatibility between pore morphology and cold energy transfer. Furthermore, existing technologies lack a coordinated mechanism between freezing and grouting processes, and the monitoring system and control logic are independent, making it difficult to achieve real-time response to changes in formation porosity. This results in difficulties in forming a frozen curtain and unsatisfactory settlement compensation effects in highly permeable sandy and gravelly formations, severely restricting the safety and efficiency of underground excavation in such formations.

[0005] Furthermore, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the applicant studied a large number of documents and patents when making this invention, but due to space limitations, not all details and contents were listed in detail. However, this does not mean that the present invention does not possess the features of these prior art. On the contrary, the present invention already possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the present invention provides a method for deep station tunnel construction based on freezing and water-stopping technology to solve at least some of the above-mentioned technical problems.

[0007] This invention discloses a method for deep underground railway station excavation based on freezing and water-stopping technology, characterized by the following steps: S1. Detect the distribution density of pebbles and the location of ultra-large pores in large-particle-size, high-permeability sand and gravel strata, record the particle size and arrangement direction of pebbles in the strata, and establish a three-dimensional pore model of the strata based on the detection and recording results. S2. The main hole is constructed using casing drilling technology. After the main hole is completed, a micro directional drilling rig is extended from the main hole and drills into the ultra-large pore area and micro-fracture area in the formation according to the three-dimensional pore model to construct the branch hole and micro hole. S3. Introduce the first refrigerant into the micropores for a preset duration until the temperature of the micro-crack area is monitored by distributed optical fiber and reaches the preset freezing temperature to form a crack ice plug. Then, introduce the second refrigerant into the main hole for cooling until a frozen soil curtain with a thickness that meets the water-stopping requirements is formed. S4. Excavate the strata corresponding to the main structure of the station. After the excavation is completed, set up the initial support. Embed adaptive expansion bladders between the initial support and the frozen soil curtain at a preset interval and connect the adaptive expansion bladders to the ground grouting system through flexible connecting pipes. S5. Stop the refrigeration operation of all freezing systems to allow the frozen soil to thaw naturally. Monitor the stability of the strata in the thawing area in real time through a pore water pressure sensor. When the pore water pressure in the thawing area drops to a preset trigger threshold, slowly inject a preset type of cement slurry into the adaptive expansion bladder through a flexible connecting pipe.

[0008] The construction method of this invention, by establishing a three-dimensional pore model to guide the design of a fractal freezing perforation network, and employing a synergistic control mechanism of staged freezing and adaptive grouting, effectively solves the core problems of difficulty in forming a frozen curtain and incomplete thaw settlement compensation in large-particle-size, high-permeability gravel strata. The precise perforation network design based on the three-dimensional pore model allows the arrangement of main holes, branch holes, and micropores to deeply adapt to the three-dimensional pore characteristics of the strata, avoiding the poor curtain continuity caused by conventional techniques that only consider planar layout. The staged freezing strategy uses liquid nitrogen in micropores to rapidly form fracture ice plugs to block microscopic seepage channels, creating a low-permeability environment for the formation of the main curtain. Subsequently, the synergistic effect of brine cooling in the main holes and phase change material cooling in the branch holes specifically replenishes the cooling capacity of ultra-large pore areas, ensuring the thickness and continuity of the frozen soil curtain. The adaptive grouting during the thawing stage achieves precise filling through pressure sensors built into the bladder, avoiding grout loss and ground heave caused by excessive grouting. This full-process synergistic control mechanism improves the efficiency of frozen curtain formation and significantly enhances the accuracy of thaw settlement compensation, providing a safe and reliable technological guarantee for deep-level railway station excavation.

[0009] According to a preferred embodiment, in step S1, a combination of ground-penetrating radar (GPR), borehole video surveillance, and core drilling is used to conduct geological exploration to obtain detection and recording results. Specifically, during GPR detection, detection profiles are set up longitudinally, laterally, and obliquely along the deep station excavation construction area; during borehole video surveillance, borehole video surveillance holes are arranged in key areas identified by GPR detection, and the characteristics of pebbles, as well as the characteristics of ultra-large pores and micro-fractures, are recorded through the borehole video probe; during core drilling, core drilling holes are arranged around the borehole video surveillance holes to obtain complete stratigraphic core samples for laboratory testing.

[0010] This invention utilizes a comprehensive exploration method combining ground-penetrating radar (GPR), borehole camera observation, and core drilling to achieve precise characterization of the three-dimensional pore structure of large-particle-size, highly permeable sand and gravel strata. GPR, with its multi-directional detection profiles, effectively identifies the distribution density of gravels and the location of super-large pores, achieving a resolution sufficient for precise positioning of 200-800mm gravels and 50-200mm super-large pores. Borehole camera observation, with observation holes deployed in key areas, records the characteristics of gravel particle size, arrangement direction, and super-large pores and micro-fractures through high-resolution images, overcoming the limitations of indirect detection. Core drilling obtains complete stratum core samples for laboratory testing, accurately acquiring key physical and mechanical parameters such as gravel thermal conductivity, density, uniaxial compressive strength, and stratum permeability. The integrated data from these three methods forms a three-dimensional pore model, providing precise geological basis for fractal freezing borehole network design, cold medium temperature determination, and grouting pressure setting. This avoids borehole network design deviations caused by misjudgment of stratum characteristics and ensures deep adaptation of subsequent construction steps to stratum properties.

[0011] According to a preferred embodiment, in step S2, when constructing the main hole, a directional geological drilling rig adapted to the space of the underground pilot tunnel is used. The casing drilling technology adopts a method of pilot hole drilling combined with casing synchronous follow-up. The directional geological drilling rig's guide drill bit has a built-in micro-drilling measurement system. The micro-drilling measurement system collects the drilling angle, azimuth angle and depth data of the borehole in real time, and synchronously feeds them back to the ground control platform through a signal transmission device. When the ground control platform detects that the borehole attitude is deviating due to the collision of large-diameter pebbles, the direction adjustment mechanism built into the guide drill bit is automatically triggered to correct the drilling trajectory.

[0012] This invention employs a directional geological drilling rig with a built-in micro-measuring-while-drilling system during main borehole construction. This enables real-time monitoring and automatic correction of the borehole trajectory, significantly improving drilling accuracy in large-diameter, high-permeability gravel formations. The micro-measuring-while-drilling system collects drilling angle, azimuth, and depth data in real time. When a borehole deviation trend caused by collisions with large-diameter pebbles is detected, the directional adjustment mechanism built into the guide bit automatically triggers a correction of the drilling trajectory to control borehole position deviation. This closed-loop control mechanism effectively solves the problem of conventional boreholes being easily affected by collisions with large-diameter pebbles, resulting in a large deviation rate. It provides a stable borehole environment for subsequent branch borehole construction, avoids curtain gaps caused by borehole position deviations, and ensures the accurate implementation of the fractal freezing borehole network.

[0013] According to a preferred embodiment, during the drilling process of the directional geological drilling rig, a composite wall-protecting fluid is continuously injected into the borehole. The composite wall-protecting fluid can form a temporary reinforced thin shell on the borehole wall, which can be broken by physical means such as high-pressure fluid during the subsequent branch hole construction. Throughout the main hole construction, the ground control platform compares the real-time drilling data with the formation parameters in the three-dimensional pore model. When encountering special formation conditions, drilling is paused and the drilling parameters are optimized. Construction is resumed after the parameters are adjusted to suit the formation characteristics.

[0014] This invention utilizes a composite wall-protecting fluid continuously injected into the main borehole to form a temporary reinforced thin shell on the borehole wall. This shell is simultaneously designed to be easily broken down by physical means such as high-pressure fluid during subsequent branch borehole construction, effectively solving the problem of borehole wall collapse caused by the poor self-stability of large-particle, high-permeability sand and gravel formations. During drilling, the wall-protecting fluid forms a temporary reinforced layer, isolating the sand and gravel formation from the borehole space and providing a stable environment for drilling. Its ability to be broken down by high-pressure fluid ensures that branch borehole construction is unimpeded. The ground control platform compares real-time drilling data with formation parameters in the three-dimensional pore model. When encountering special formation conditions such as dense gravel clusters, drilling is paused and parameters are optimized, further improving drilling accuracy. This collaborative control mechanism of the wall-protecting fluid and drilling parameters ensures that the main borehole construction accuracy meets the positioning requirements of subsequent branch boreholes, laying the foundation for the precise implementation of fractal frozen borehole networks.

[0015] According to a preferred embodiment, in step S2, the folded hydraulic branch unit in a folded state is transported to a preset branch position via the main borehole drill pipe. The preset branch position is determined by combining the main borehole trajectory calibrated by the micro-drilling measurement system and the ultra-large pore distribution data in the three-dimensional pore model. After the folded hydraulic branch unit reaches the target position, power is supplied to the folded hydraulic branch unit through the ground hydraulic pump station to drive its movable arm to unfold, so that the branch hole drill bit and the main borehole axis form an angle that matches the frozen curtain design. During branch hole drilling, the rock breaking element on the drill bit works in conjunction with the high-pressure fluid. The high-pressure fluid pre-disperses the loose sand particles on the drilling path, and a modified wall protection fluid with added anti-dispersion components is injected into the hole while drilling. After the branch hole drilling is completed, the branch hole freezing pipe is immediately inserted into the branch hole through the preset channel of the folded hydraulic branch unit.

[0016] This invention employs a folding hydraulic branching device to achieve precise branching construction of branch holes, solving the problem of accurately extending branch holes into ultra-large pore areas within the limited space of the main borehole. The folding hydraulic branching device is transported to the preset branching position (determined based on a three-dimensional pore model and a micro-drilling measurement system) via the main borehole drill rod. Upon reaching the target position, the movable arm is deployed via a ground hydraulic pump station, aligning the branch hole drill bit with the main borehole axis at an angle compatible with the frozen curtain design. The drill bit's built-in rock-breaking element, working in conjunction with high-pressure fluid, pre-disperses loose sand particles along the drilling path, reducing direct collisions and wear from large-diameter pebbles. Modified wall-protecting fluid with added anti-dispersion components is injected during drilling to prevent rapid loss of wall-protecting fluid due to high formation permeability. After the branch hole drilling is completed, a branch hole freezing pipe is immediately inserted through a preset channel to prevent the borehole wall from collapsing without support. This branching construction technology effectively solves the deviation problem caused by directly traversing pebbles in conventional branch hole construction, ensuring the branch hole accurately points to ultra-large pore areas and providing a reliable carrier for phase change material cooling.

[0017] According to a preferred embodiment, in step S2, a flexible hose-type micro-drill is used when constructing the micro-hole. The drill rod of the flexible hose-type micro-drill is made of flexible material. Before construction, a channel corresponding to the preset micro-hole position is opened on the support hole freezing pipe. The flexible hose-type micro-drill is slowly lowered into the preset drilling position in the support hole through the channel. The front end of the flexible hose-type micro-drill is equipped with a fiber optic attitude sensor and an electromagnetic guide head. The fiber optic attitude sensor collects drilling angle and position data in real time and transmits them to the ground control platform. During micro-hole drilling, the micro drill bit and the micro-hole freezing pipe are coaxially arranged, and the micro-hole freezing pipe follows the drill bit synchronously.

[0018] This invention employs a flexible micro-drilling tool during micro-hole construction. The flexible drill rod adapts to the turning requirements within the support hole, enabling precise extension of the micro-hole into micro-fracture regions within a smaller space. The drill bit's front end is equipped with a fiber optic attitude sensor and an electromagnetic guide head, which collects drilling angle and position data in real time and transmits it to a ground control platform. When it detects impending contact with large-diameter pebbles or deviation from the preset trajectory, the guide head is adjusted via electromagnetic control to correct the drilling direction. During micro-hole drilling, the micro-drill bit and a disposable freezing tube are coaxially positioned. The disposable freezing tube advances synchronously with the drill bit during drilling, avoiding borehole wall collapse caused by secondary casing installation. This precise directional drilling mechanism solves the difficulties caused by space constraints and high drilling accuracy requirements in micro-hole construction, ensuring that the micro-hole accurately reaches micro-fracture regions and providing a reliable guarantee for the formation of ice plugs to block microscopic seepage channels.

[0019] According to a preferred embodiment, in step S3, the staged freezing includes a first freezing stage with micropores as the core working unit and a second freezing stage with main holes and branch holes as the core working units. In the first freezing stage, liquid nitrogen is introduced as the first refrigerant. A distributed fiber optic temperature measurement system deployed on the micropore wall and surrounding strata collects temperature data of the micro-fracture area at preset intervals and transmits it to a ground control platform. When the temperature drops below the preset freezing temperature and remains below it for a preset duration, the pore water pressure in the area is detected by a pore water pressure monitoring system. If the pore water pressure stabilizes within a preset low pressure range, the first freezing stage is deemed to have achieved the expected effect, and the process transitions to the second freezing stage. In the second freezing stage, brine is introduced as the second refrigerant.

[0020] A staged freezing strategy utilizes microporous liquid nitrogen to rapidly form ice plugs in fractures, effectively solving the problem of blocking micro-fracture seepage channels in large-particle, highly permeable sand and gravel formations. In the first freezing stage, cryogenic liquid nitrogen (around -40°C) is introduced through micropores to rapidly lower the temperature of the micro-fracture region, causing the fracture water to freeze quickly and form "ice plugs," blocking the microscopic seepage channels. A distributed fiber optic temperature monitoring system collects temperature data at preset intervals. When the temperature in the micro-fracture region drops below the preset freezing temperature and remains below it, a pore water pressure monitoring system verifies whether seepage has been blocked. This targeted fracture freezing strategy avoids the problem of unblocked micro-fracture seepage due to low cold transfer efficiency in conventional freezing techniques, creating a low-permeability environment for the formation of the main curtain and improving the efficiency and quality of subsequent main curtain formation.

[0021] According to a preferred embodiment, during the second freezing stage, the refrigerant circulation system of the main borehole is equipped with a flow regulation module to adjust the second refrigerant flow rate based on temperature data fed back from the ground control platform. A distributed fiber optic temperature measurement system monitors temperature changes in the ultra-large pore area. When the temperature in this area exceeds a preset threshold, a phase change material (PCM) cooling mechanism in the branch boreholes is triggered. Pre-set heating elements within the branch boreholes heat the PCM to release its stored cold energy. A pore water pressure monitoring system monitors pore water pressure changes in the frozen area. If an abnormal increase in pore water pressure is detected in a certain area, the problem area is located using the distributed fiber optic temperature measurement data. If the problem area is located between the coverage areas of the main borehole and the branch boreholes, optimization is achieved by adjusting the second refrigerant flow rate in the main borehole or extending the PCM cooling time in the branch boreholes. If the problem area is a small, localized area, micro-holes are drilled and low-temperature PCM is injected to resolve the insufficient freezing problem.

[0022] The closed-loop control mechanism of the second freezing stage solves the problem of discontinuous freezing curtain caused by cold loss in the ultra-large pore area through the synergistic effect of brine cooling in the main borehole and phase change material (PCM) replenishment in the branch boreholes. The main borehole refrigerant circulation system is equipped with a flow regulation module, which adjusts the brine flow in real time based on temperature data fed back by the distributed fiber optic temperature measurement system to ensure uniform cooling of the strata around the main borehole. When the temperature in the ultra-large pore area is detected to be higher than a preset threshold, the PCM replenishment mechanism in the branch boreholes is triggered. The heating element causes the PCM (such as paraffin-graphite composite PCM) to release the stored cold energy, specifically replenishing the cold loss. The pore water pressure monitoring system simultaneously monitors the pressure changes in the freezing area. When anomalies are detected, the problem area is located by combining the temperature data and targeted measures are taken. This dynamic regulation mechanism enables the cold replenishment to accurately match the stratum seepage characteristics, effectively solving the problem of discontinuous curtain caused by untimely cold replenishment in conventional freezing technology, and ensuring the integrity and continuity of the permafrost curtain.

[0023] According to a preferred embodiment, in step S4, the sectional excavation method is used for underground excavation, and the excavation is carried out step by step according to the preset cycle length. After each cycle of excavation is completed, the excavation face is temporarily protected. When setting the initial support, a preset type of concrete is sprayed onto the excavation face to form the initial support structure. Before pre-embedding the adaptive expansion bladder, the pre-embedded hole position is calibrated by a laser positioning device. The pre-embedded hole position is arranged according to the position marked in the previous three-dimensional pore model to match the concentrated areas of ultra-large pores and micro-cracks. When erecting the steel arch frame, the steel arch frame is connected to the initial support structure, and a gap of a preset width is reserved between the steel arch frame and the adaptive expansion bladder.

[0024] In the cut-and-cover excavation construction, a sectional excavation method combined with the pre-embedded adaptive expansion bladders and the precise arrangement of steel arches solved the coordination problem of ground stability and thaw settlement compensation between the frozen curtain and the initial support. The sectional excavation method proceeds step by step according to a preset cycle length. After each cycle, temporary protection and initial support are immediately implemented to ensure the stability of the excavation face. Before pre-embedding the adaptive expansion bladders, laser positioning equipment is used to calibrate the borehole positions, ensuring precise matching with areas of concentrated ultra-large pores and micro-cracks, providing targeted coverage for subsequent grouting compensation. The steel arches are reliably connected to the initial support, while a preset gap is reserved between the steel arches and the bladders to prevent the steel arches from squeezing the bladders during installation or under stress, thus affecting their expansion and grouting functions. This support system design creates a synergistic support system between the frozen curtain, initial support, steel arches, and adaptive expansion bladders, ensuring ground stability throughout the entire cut-and-cover construction process, while also providing a reliable environment for bladder pre-embedding for thaw settlement compensation after freezing.

[0025] According to a preferred embodiment, in step S5, during the natural thawing stage, the distributed optical fiber temperature measurement system continuously monitors the changes in formation temperature, and the pore water pressure monitoring system collects pore water pressure data of the thawing area in real time. Both data are transmitted synchronously to the ground control platform, which analyzes the data in real time to determine the thawing progress and pore development. When the pore water pressure in the thawing area drops below a preset trigger threshold, it is determined that obvious pores have appeared in the formation, and adaptive grouting operation is initiated. When the adaptive grouting operation is initiated, the ground control platform divides the grouting priority according to the pore water pressure data of each area and the previous three-dimensional pore model, and prioritizes grouting areas with large pore water pressure drops and high settlement risks.

[0026] The adaptive grouting triggering mechanism during the thawing phase achieves precise control of melt-settlement compensation through the coordinated analysis of pore water pressure monitoring and distributed fiber optic temperature measurement. During natural thawing, the distributed fiber optic temperature measurement system continuously monitors changes in formation temperature, while the pore water pressure monitoring system collects pore water pressure data from the thawing area in real time. Both data are simultaneously transmitted to the ground control platform for real-time analysis. When the pore water pressure drops below a preset trigger threshold, it indicates that significant porosity has appeared in the formation, and adaptive grouting operations can be initiated. The ground control platform prioritizes grouting based on pore water pressure data for each area and the pre-existing three-dimensional pore model, prioritizing areas with large drops in pore water pressure and high risk of settlement. This grouting triggering mechanism based on real-time monitoring data avoids the problems of grout loss or over-grouting caused by the lack of real-time monitoring in traditional grouting techniques, ensuring the accuracy and effectiveness of melt-settlement compensation. Attached Figure Description

[0027] Figure 1 This is a flowchart of the steps of a preferred embodiment of the underground excavation method provided by the present invention; Figure 2 This is a schematic diagram illustrating the construction execution of step S1 in a preferred embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the construction execution of step S2 in a preferred embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the construction execution of step S3 in a preferred embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the construction execution of step S4 in a preferred embodiment of the present invention; Figure 6 This is a schematic diagram illustrating the construction execution of step S5 in a preferred embodiment of the present invention. Detailed Implementation

[0028] The following is a detailed explanation with reference to the accompanying drawings.

[0029] like Figure 1 As shown, this invention discloses a method for deep underground railway station excavation based on freezing and water-stopping technology, which includes the following steps: S1. Detect the distribution density of pebbles and the location of ultra-large pores in large-particle-size, high-permeability sand and gravel strata, record the particle size and arrangement direction of pebbles in the strata, and establish a three-dimensional pore model of the strata based on the detection and recording results. S2. The main hole is constructed using casing drilling technology. After the main hole is completed, a micro directional drilling rig is extended from the main hole and drills into the ultra-large pore area and micro-fracture area in the formation according to the three-dimensional pore model to construct the branch hole and micro hole. S3. Introduce the first refrigerant into the micropores for a preset duration until the temperature of the micro-crack area is monitored by distributed optical fiber and reaches the preset freezing temperature to form a crack ice plug. Then, introduce the second refrigerant into the main hole for cooling until a frozen soil curtain with a thickness that meets the water-stopping requirements is formed. S4. Excavate the strata corresponding to the main structure of the station. After the excavation is completed, set up the initial support. Embed adaptive expansion bladders between the initial support and the frozen soil curtain at a preset interval and connect the adaptive expansion bladders to the ground grouting system through flexible connecting pipes. S5. Stop the refrigeration operation of all freezing systems to allow the frozen soil to thaw naturally. Monitor the stability of the strata in the thawing area in real time through a pore water pressure sensor. When the pore water pressure in the thawing area drops to a preset trigger threshold, slowly inject a preset type of cement slurry into the adaptive expansion bladder through a flexible connecting pipe.

[0030] In this invention, the large-particle-size high-permeability sand and gravel stratum refers to a stratum that belongs to the category of loose strata with high water content, in which pebbles are the main skeleton particles and sand particles fill the gaps between pebbles. The particle size of the pebble particles is within a preset large size range (e.g., the preset size range is 200~800mm), and the overall permeability coefficient of the stratum meets the preset high permeability requirements (e.g., permeability coefficient > 5m / d). This stratum has the characteristics of extremely poor particle size distribution, easy formation of large gaps between pebbles, fast groundwater seepage velocity, easy removal of cold energy by seepage water during freezing, and difficulty in forming a continuous curtain with conventional freezing pore networks.

[0031] In this invention, ultra-large pores refer to gaps formed by the irregular arrangement of large-diameter gravel particles in a large-particle-size, highly permeable sand and gravel stratum, with pore sizes within a preset size range (e.g., the preset size range is 50~200mm). These pores are the main channels for groundwater seepage in the stratum, and during freezing, cold energy is easily lost here, resulting in discontinuous areas in the freezing curtain.

[0032] In this invention, micro-cracks refer to tiny fissures distributed in sand grain aggregation areas or on the surface of pebble particles in large-particle-size, highly permeable sand and gravel formations, with a crack width within a preset size range (e.g., 1-5 mm). Although the individual size of these cracks is small, when they are densely distributed, they can easily form through-flow channels, and conventional grouting is difficult to penetrate them.

[0033] In this invention, cryogenic liquid nitrogen refers to liquid nitrogen that has undergone refrigeration treatment and is at a preset low temperature range (e.g., around -40°C to achieve rapid freezing of fissure water); it has the characteristics of outstanding low-temperature properties and rapid cooling speed. In the first freezing stage of the phased freezing process of this invention, it is injected into the micropores, which can quickly reduce the temperature of the micro-fissure region, causing the fissure water to freeze and form ice plugs, thereby rapidly blocking the seepage channels of the micro-fissures and creating a low-permeability environment for the subsequent formation of the main curtain.

[0034] In this invention, low-temperature brine refers to a brine solution whose temperature is within a preset low-temperature range (e.g., around -35°C, to achieve large-scale ground cooling while avoiding excessive energy consumption) after being cooled by a refrigeration unit. It features good fluidity and stable cold energy transfer. In the second freezing stage of the phased freezing process of this invention, it is circulated into the main borehole to continuously release cold energy, thereby cooling a large area of ​​the ground around the station excavation outline. It is the core cooling medium for constructing the macroscopic permafrost curtain, and its temperature can be adjusted by the refrigeration unit to meet the ground freezing requirements.

[0035] In this invention, the low-viscosity ultrafine cement slurry refers to a slurry prepared by mixing cement, water, and necessary admixtures, wherein the cement particle size is within a preset ultrafine range (e.g., the preset ultrafine range is a particle size < 10 μm) and the slurry viscosity meets the preset low-viscosity requirement, so as to facilitate seepage through the micropores of the adaptive expansion bladder; it has the characteristics of strong permeability and good fluidity. In step S5 of this invention, it is used to inject the adaptive expansion bladder, which can slowly seep through the micropores on the surface of the bladder, while filling the ultra-large pores and micro-fractures in the large-particle-size, highly permeable sand and gravel strata, thereby achieving precise melting and settling compensation.

[0036] Preferably, in order to accurately obtain the geological characteristic parameters of large-particle-size, high-permeability sand and gravel strata, and to provide a comprehensive and reliable basis for subsequent fractal freezing hole network design, adaptive expansion bladder pre-embedding, and closed-loop control, and to ensure that the fractal phase change freezing and adaptive bladder grouting collaborative construction scheme can effectively solve the core problems of difficult freezing curtain intersection and incomplete melting settlement compensation in this stratum, the present invention can conduct a detailed exploration of the strata in the deep station underground excavation construction area and surrounding related areas through the preliminary detailed strata exploration in step S1.

[0037] Preferably, such as Figure 2As shown, in step S1, ground-penetrating radar (GPR) detection can be carried out. This operation utilizes a high-frequency GPR with a detection resolution adapted to the characteristics of large-diameter pebbles and ultra-large pore sizes, to meet the precise positioning requirements of large-diameter pebbles (200-800mm) and ultra-large pores (50-200mm). During the detection process, detection profiles can be reasonably set up longitudinally, laterally, and obliquely along the deep-level station excavation area to ensure that the detection range fully covers the construction area and its surrounding necessary areas. The detection depth must exceed the design elevation of the station floor slab by a certain distance to fully investigate the distribution pattern and permeability of pebbles in the underlying strata of the construction area. By utilizing the difference in reflection signals of high-frequency electromagnetic waves emitted by the GPR at the interfaces of different media (pebbles, sand, pore water), two-dimensional profile data of the strata are obtained. This allows for the identification and marking of the spatial distribution density of pebbles, the location and approximate size of ultra-large pores, and a preliminary assessment of the development area and distribution characteristics of micro-fractures, providing preliminary guidance for the subsequent layout of boreholes and video observation holes.

[0038] Preferably, such as Figure 2 As shown, boreholes with video cameras are deployed in key areas identified by ground-penetrating radar (GPR) (such as areas with dense gravel, areas with large pores, and areas suspected of having micro-fractures). The number of boreholes with video cameras can be reasonably determined based on the number of GPR profiles, the distribution range of key areas, and the required exploration accuracy. Environmentally resistant borehole camera probes capable of clearly acquiring images of the strata around the borehole wall in complex underground environments are selected. The probes are slowly lowered into the boreholes using the drill rod at an appropriate speed, ensuring continuous and clear image capture of the strata surrounding the borehole wall during the probe's movement. Through borehole video observation, the actual particle size, arrangement direction, interparticle contact state, and surface characteristics of the gravel at the borehole wall are recorded in real time. Simultaneously, the specific location, cross-sectional dimensions, and extension direction of large pores at the borehole wall, as well as the opening width, length, orientation, and development degree of micro-fractures, are clearly identified. The captured image data is stored in segments according to depth, providing intuitive and detailed image data for the subsequent construction of a three-dimensional porosity model, avoiding misjudgments of strata features caused by relying solely on indirect detection data.

[0039] Preferably, such as Figure 2As shown, to verify the accuracy of ground-penetrating radar and borehole camera observation data, and to obtain key physical and mechanical parameters of large-particle-size, high-permeability sand and gravel strata, additional core sampling holes can be arranged around the borehole camera observation holes. The number of core sampling holes can be reasonably determined based on the number of borehole camera observation holes and data verification requirements. A professional core drilling rig capable of obtaining complete stratigraphic core samples is used for core sampling. The core sample size must ensure that the obtained core sample fully reflects the grain composition, grain size distribution, and porosity characteristics of the strata, avoiding parameter measurement deviations due to core sample damage. Core sampling is performed at reasonable intervals. Each obtained core sample is uniformly numbered, sealed, and its acquisition depth, actual length, and integrity level are recorded in detail to establish a correspondence between the core sample and the stratigraphic depth. The encapsulated core samples were sent to a qualified laboratory for indoor testing to determine key physical and mechanical parameters such as the thermal conductivity, density, and uniaxial compressive strength of the pebbles, the particle size distribution and porosity of the sand, and the permeability of the entire formation. These parameters will provide core data support for determining the refrigerant temperature, selecting and calculating the filling amount of phase change materials in the design of fractal freezing perforated mesh, and setting the grouting pressure and controlling the grouting volume of the adaptive expansion bladder, ensuring the scientific and rational design of subsequent construction parameters.

[0040] Preferably, the two-dimensional profile data obtained from ground-penetrating radar (GPR), image data from borehole camera observations, and physical and mechanical parameter data obtained from borehole core sampling are systematically integrated. Then, a three-dimensional pore model of a large-particle-size, high-permeability sand and gravel stratum is constructed using finite element analysis software. During model construction, GPR data can be converted into stratum medium distribution information to clarify the distribution range of different media in three-dimensional space; borehole camera image data can be converted into spatial geometric information of pebbles and pores, accurately reconstructing the arrangement of pebbles and the three-dimensional structure of pores; and borehole core sampling data can be converted into stratum physical and mechanical property information, assigning the model realistic mechanical parameters. After model construction, the effectiveness of the three-dimensional pore model is verified. A certain number of verification boreholes not involved in model construction are selected, and the actual exploration data (including stratum particle distribution, pore size, and physical and mechanical parameters) at the verification boreholes are compared and analyzed with the model's predicted data to ensure that the model's prediction accuracy for pebble distribution, pore size, and stratum parameters meets the requirements of subsequent construction design. This validated three-dimensional pore model allows for the precise determination of the arrangement and spacing of main holes in the fractal freezing pore network, the extension angle and spacing of branch holes towards the ultra-large pore region, and the drilling location and number of micropores towards the micro-fracture region. Simultaneously, it provides detailed and accurate geological data for the design of the pre-embedded spacing, pre-embedded depth, and grouting parameters of the adaptive expansion bladder, ensuring that subsequent construction steps are deeply adapted to the characteristics of large-particle-size, highly permeable sand and gravel strata, thus laying a solid geological exploration foundation for the smooth implementation of the entire construction plan.

[0041] Preferably, in order to achieve precise construction of the fractal freezing hole network in large-diameter, high-permeability sand and gravel formations, avoid borehole deviation caused by collisions of large-diameter pebbles and poor formation self-stability, and ensure the formation of a continuous and complete freezing curtain during subsequent freezing processes, step S2 is based on the three-dimensional pore model obtained from the preliminary detailed formation survey. Targeted technical measures are adopted for the construction process of main holes, branch holes, and microholes, respectively. Through directional drilling control, real-time attitude monitoring, and formation adaptability adjustment, the construction accuracy and hole wall stability of each level of freezing holes are guaranteed.

[0042] Preferably, during the main borehole construction, the main borehole, as the foundational layer of the fractal freezing borehole network, serves the dual function of being a branch carrier for the branch boreholes and the main circuit of the freezing system. Its construction trajectory must strictly follow the path set along the station excavation contour in the three-dimensional pore model. The construction employs a miniaturized directional geological drilling rig adapted to the space of the underground pilot tunnel. This rig reduces its space occupation in non-operational states through a folding design, and its tracked mobile chassis enables flexible turning and position adjustment in confined spaces, ensuring smooth deployment within the underground pilot tunnel. For example... Figure 3 As shown, the drilling operation employs a pilot hole drilling combined with simultaneous casing drilling technology. The directional drill bit incorporates a built-in micro-measuring while drilling (MWD) system, which can collect real-time data on the drilling angle, azimuth, and depth of the borehole and synchronously feed this data back to the ground control platform via a signal transmission device. Figure 3 As shown, when the ground control platform detects a tendency for the borehole to deviate due to collisions with large-diameter pebbles, the directional adjustment mechanism built into the guide drill bit is automatically triggered. This corrects the drilling trajectory by changing the drill bit's cutting direction, ensuring the pilot hole always extends along the preset route. During pilot hole drilling, the casing advances synchronously along the borehole wall. The casing effectively isolates the sand and gravel strata from the borehole space, preventing borehole wall collapse due to poor formation stability and providing a stable borehole environment for subsequent branch hole construction. Simultaneously, a composite wall-protecting fluid is continuously injected into the borehole. This fluid forms a temporary reinforced thin shell on the borehole wall and must be able to be broken down by physical means (such as high-pressure fluid) during subsequent branch hole construction, thus avoiding obstruction to branch hole drilling. Throughout the main borehole construction, the ground control platform can compare real-time drilling data with formation parameters (such as pebble distribution density and pore location) in the three-dimensional pore model. If special formation conditions such as densely distributed large-diameter pebble groups are encountered, drilling can be paused and drilling parameters (such as drilling speed and cutting force) optimized. Construction can be resumed after the parameters are adjusted to suit the formation characteristics, ensuring that the main borehole construction accuracy meets the positioning requirements of subsequent branch boreholes.

[0043] Preferably, after the main hole is constructed, the stability of the hole wall and the accuracy of the trajectory can be tested. After confirming that they meet the requirements, the construction of the branch hole can begin. The branch hole can extend from the main hole to the ultra-large pore area marked in the three-dimensional pore model. The core technical difficulty lies in achieving precise branching within the limited space of the main hole to avoid deflection caused by directly passing through large-diameter pebbles. Before construction, high-pressure fluid can be used to clean the inside of the main borehole, removing residual sand, gravel, and drilling debris to ensure unobstructed transport channels for the folding hydraulic branch. The folded hydraulic branch is then slowly transported to the preset branch position via the main borehole drill pipe. This preset branch position can be determined by combining the main borehole trajectory calibrated by the micro-drilling measurement system (MWD) and the distribution data of ultra-large pores in the 3D pore model. Once the folding hydraulic branch reaches the target position, power is supplied to it via a ground hydraulic pump station, driving its movable arm to unfold. This allows the branch drill bit to form an angle with the main borehole axis that matches the frozen curtain design, ensuring the branch borehole accurately points towards the ultra-large pore area. During branch borehole drilling, the drill bit's built-in rock-breaking element and high-pressure fluid... The synergistic effect allows high-pressure fluid to pre-disperse loose sand particles on the drilling path, reducing direct collisions and wear of large-diameter pebbles on the drill bit and lowering the risk of borehole deviation. Simultaneously, modified wall-protecting fluid is injected into the borehole while drilling. This modified wall-protecting fluid contains anti-dispersion components, which can prevent rapid loss of wall-protecting fluid due to high formation permeability and ensure borehole stability. After the branch hole is drilled, the branch hole freezing pipe can be immediately inserted into the branch hole through the preset channel of the folding hydraulic branch, achieving immediate connection between hole completion and pipe insertion, preventing the borehole wall from collapsing without support. During the insertion of the branch hole freezing pipe, dual calibration can be performed through the angle sensor and the micro-drilling measurement system (MWD) on the folding hydraulic branch to ensure that the extension direction of the branch hole freezing pipe is consistent with the branch hole drilling trajectory, further ensuring the subsequent freezing effect.

[0044] Preferably, after the support borehole construction is completed and the support borehole freezing pipe is confirmed to be securely installed, micro-hole construction is carried out. Micro-holes extend from the support borehole to the micro-fracture region marked in the three-dimensional pore model. The difficulty lies in achieving directional drilling within the smaller space of the support borehole and precisely reaching the micro-fracture location. A flexible hose-type micro-drilling tool is used. The drill rod of this tool is made of flexible material, which can adapt to the spatial turning requirements within the support borehole, facilitating extension to the micro-fracture region. Before construction, a channel corresponding to the preset micro-hole position is opened on the support borehole freezing pipe to ensure a clear path for the flexible hose-type micro-drilling tool. Then, the flexible hose-type micro-drilling tool is slowly lowered through this channel to the preset drilling position within the support borehole. The front end of the drill is equipped with a fiber optic attitude sensor and an electromagnetic guide head. The fiber optic attitude sensor can collect drilling angle and position data in real time and transmit the data to the ground control platform. The operator monitors the drill attitude through a remote control console. When the drill is detected to be about to contact large-diameter pebbles or deviate from the preset trajectory, the guide head is adjusted via electromagnetic control. Correct the drilling direction; during micro-hole drilling, the micro drill bit and the micro-hole freezing tube are set coaxially. During the drilling process, the micro-hole freezing tube follows the drill bit synchronously. The installation of the micro-hole freezing tube is completed while the drill bit moves forward, avoiding the collapse of the hole wall caused by secondary casing installation; during the drilling process, the wall protection medium can be added in a timely manner according to the permeability of the formation to ensure the stability of the hole wall of the loose formation around the micro-fractures; throughout the micro-hole construction process, the drilling parameters need to be continuously adjusted through the data feedback from the fiber optic attitude sensor to ensure that the micro-hole can accurately reach the micro-fracture area, laying the foundation for subsequent local enhanced freezing and sealing of micro-leaking channels.

[0045] Preferably, to ensure construction safety and efficiency, all drilling equipment can be pneumatic or hydraulically powered to avoid the risk of electrical leakage in high-water-content sandy and gravelly strata. Simultaneously, a borehole pressure monitoring instrument is installed to monitor real-time pressure changes in each level of freezing borehole. When an abnormal pressure is detected (e.g., a sudden drop in pressure indicating borehole wall collapse, or a sudden increase in pressure indicating borehole blockage), drilling is immediately stopped and emergency measures are taken (e.g., replenishing wall-protecting fluid, clearing blockages). Construction resumes only after the borehole condition stabilizes. Through the aforementioned hierarchical construction techniques and supporting measures for main holes, branch holes, and microholes, the construction accuracy and stability of the fractal freezing borehole network can be ensured, providing a reliable borehole network foundation for subsequent phased freezing processes.

[0046] Preferably, to adapt to the seepage characteristics of large-particle-size, high-permeability sand and gravel formations and address the core issues of the formation's cold energy being easily carried away by rapidly flowing water and the difficulty of forming a continuous curtain through conventional freezing, step S3, based on the previous construction results of the fractal freezing perforation network (main holes, branch holes, and micropores), adopts the following... Figure 4 The staged freezing strategy shown uses the coordinated application of a distributed fiber optic temperature measurement system and a pore water pressure monitoring system to adjust freezing parameters in real time, ensuring that the freezing effect at each stage meets the design requirements, and ultimately forming a continuous, complete freezing curtain with sufficient strength.

[0047] Preferably, the phased freezing strategy may include a first freezing stage and a second freezing stage, wherein the first freezing stage is crack freezing and the second freezing stage is main curtain formation.

[0048] Preferably, such as Figure 4 As shown, the first freezing stage uses micropores as the core unit, aiming to freeze the micro-fracture water in the formation, forming ice plugs to block microscopic seepage channels and create a low-permeability environment for the subsequent formation of the main curtain. Before construction, the micropore freezing pipe can be connected to the ground refrigerant supply system, ensuring a reliable seal at the connection point to prevent refrigerant leakage and subsequent cooling loss. Simultaneously, the refrigerant supply system's pipeline is insulated to reduce cooling loss during transport, ensuring the refrigerant entering the micropores maintains a preset low temperature. Liquid nitrogen can be selected as the first refrigerant. After connection, low-temperature refrigerant is continuously injected into the micropores. During injection, a distributed fiber optic temperature measurement system deployed on the micropore pipe wall and surrounding strata monitors the temperature changes in the micro-fracture area in real time. The distributed fiber optic temperature measurement system collects temperature data at preset intervals and transmits the data to the ground control platform. When the ground control platform detects that the temperature in the micro-fracture area has dropped below the preset freezing temperature and remains at this temperature for a preset duration, the pore water pressure monitoring system detects the pore water pressure changes in that area. Figure 4 As shown, if the pore water pressure is stable within the preset low pressure range, it indicates that the seepage has been blocked, and the first freezing stage is considered to have achieved the expected effect, and the second freezing stage can be started. If monitoring finds that the temperature in a local micro-crack area has not reached the preset value or the pore water pressure is still at a high level, it indicates that the seepage has not been completely blocked, and the injection of the first refrigerant needs to be suspended to investigate the cause (such as whether the micro-hole freezing pipe is blocked or whether the supply of the first refrigerant is stable). After the problem is solved, the injection is restarted. If necessary, micro-holes can be drilled in the local area to inject low-temperature first refrigerant to ensure that all micro-cracks form effective ice plugs.

[0049] Preferably, such as Figure 4As shown, after the first freezing stage is completed and verified, the second freezing stage begins. This stage uses the main borehole and branch boreholes as the core functional units, aiming to construct a macroscopically continuous freezing curtain in large-particle-size, high-permeability sand and gravel formations through the synergistic effect of large-scale cooling in the main borehole and targeted cooling in the branch boreholes. During construction, the refrigerant circulation system of the main borehole is first activated, continuously introducing a low-temperature secondary refrigerant into the main borehole. The main borehole's refrigerant circulation system can be equipped with a flow regulation module to adjust the secondary refrigerant flow rate based on temperature data fed back from the ground control platform, ensuring uniform cooling of the formation around the main borehole. The secondary refrigerant can be brine. During the main borehole cooling process, a distributed fiber optic temperature measurement system can focus on monitoring temperature changes in the ultra-large pore area, a critical area where cold energy is easily lost and the curtain is prone to discontinuity due to rapid seepage. When the ground control platform detects that the temperature in the ultra-large pore area exceeds a preset threshold, it immediately triggers the phase change material (PCM) cooling mechanism in the support pores. This involves heating the PCM through pre-installed heating elements within the support pores, causing it to release its stored cold energy to compensate for the cold loss caused by seepage in the ultra-large pore area. The PCM can be a paraffin-graphite composite PCM. During the PCM cooling process, the temperature change in this area is continuously monitored by a distributed fiber optic temperature measurement system. Heating stops when the temperature drops below the preset threshold and remains stable. If the temperature rises again, the cooling mechanism is triggered repeatedly until the temperature in the ultra-large pore area consistently meets the requirements. Meanwhile, the pore water pressure monitoring system can monitor the changes in pore water pressure in the frozen area throughout the process. If an abnormal increase in pore water pressure is found in a certain area, it indicates that there may be unfrozen seepage channels in that area. The problem area can be located by combining distributed fiber optic temperature measurement data. If the problem area is located between the coverage of the main hole and the branch hole, it can be optimized by adjusting the flow rate of the second refrigerant in the main hole or extending the cooling time of the phase change material in the branch hole. If the problem area is a small local area, micro-holes can be drilled and low-temperature second refrigerant can be injected to specifically solve the problem of insufficient freezing in that area.

[0050] Preferably, during the second freezing stage, the integrity of the freezing curtain can be periodically checked. The check method is to apply pressure to the outside of the freezing curtain through preset detection holes and observe the feedback data from the pore water pressure monitoring system. If there is no significant fluctuation in pore water pressure after the pressure is applied, it indicates that the freezing curtain is continuous and has sufficient anti-seepage capacity. If abnormal fluctuations in pore water pressure occur, the location of the curtain defect needs to be located and targeted repair measures should be taken (such as supplementing the cooling through the branch holes or drilling micro-holes for freezing). After the second freezing stage has lasted for the preset duration, and the distributed fiber optic temperature measurement system shows that the temperature in each area of ​​the freezing curtain is stable below the preset freezing temperature, the pore water pressure monitoring system shows that the pore water pressure in the entire area is stable in the low pressure range, and the curtain integrity check is qualified, it is determined that the formation of the main curtain meets the design requirements, the second freezing stage can be stopped, and the subsequent tunneling construction can begin. Throughout the phased freezing process, the ground control platform can store and analyze all monitoring data in real time, generating a freezing process data report to provide a reference for subsequent similar projects. At the same time, it ensures that the entire freezing process is traceable and controllable, fully adapts to the seepage characteristics of large-particle-size, high-permeability sand and gravel strata, and effectively solves the problem of the freezing curtain being difficult to form in this stratum.

[0051] Preferably, in order to achieve safe deep station excavation operations in large-particle-size, high-permeability sand and gravel strata, and to pre-set adaptive expansion bladders for subsequent settlement compensation, step S4 uses a continuous frozen curtain formed by staged freezing as a safety barrier. It adopts a technical approach of coordinated excavation and immediate support, precise pre-embedding of bladders and adaptation of steel arches to ensure stratum stability and prevent damage to the frozen curtain during excavation, while providing a reliable pre-embedding location and working environment for the adaptive expansion bladders.

[0052] Preferably, such as Figure 5As shown, the tunneling construction can adopt a sectional excavation method, advancing step by step according to the preset cycle length. After each cycle of excavation is completed, temporary protection is immediately applied to the excavation face to prevent the collapse of loose sand and gravel strata. Subsequently, initial support construction is carried out, spraying a preset type of concrete onto the excavation face to form the initial support structure. After the initial support construction is completed, quality acceptance can be carried out to check the thickness, flatness, and adhesion to the strata of the concrete, ensuring that the initial support can effectively transmit strata pressure. After acceptance, based on the positions marked in the previous three-dimensional pore model, the pre-embedded holes of the adaptive expansion bladder are arranged at preset intervals between the initial support and the freezing curtain. Before placement, the hole positions can be calibrated using laser positioning equipment to ensure that the hole positions accurately match the concentrated areas of ultra-large pores and micro-cracks, providing targeted coverage for subsequent grouting compensation. Furthermore, the adaptive expansion bladders are folded and implanted into pre-buried holes. All adaptive expansion bladders are then connected to the ground grouting system via flexible connecting pipes. After connection, a sealing test can be performed on the connecting pipes (e.g., introducing gas or liquid at a preset pressure to observe for leaks) to prevent grout leakage during subsequent grouting. Finally, a steel arch frame is erected. The steel arch frame can reliably connect to the initial support structure, and a preset width gap is reserved between the steel arch frame and the adaptive expansion bladders to prevent the adaptive expansion bladders from being squeezed during installation or deformation under stress, thus affecting their subsequent expansion and grouting functions. After the steel arch frame is installed, its verticality and stress state can be checked to ensure that the steel arch frame can effectively share the ground pressure and, together with the freezing curtain, initial support, and adaptive expansion bladders, form a collaborative support system to ensure ground stability throughout the entire tunneling construction process.

[0053] Preferably, in order to achieve safe thawing of large-particle-size, high-permeability sand and gravel strata after freezing, and to solve the problem of incomplete thawing settlement compensation by accurately filling the pores (including ultra-large pores and micro-cracks) generated during the thawing process through adaptive grouting, step S5 uses pore water pressure monitoring and a distributed fiber optic temperature measurement system as the core monitoring means, and carries out the operation according to the process of natural thawing monitoring, adaptive grouting triggering, grouting process control, and local grouting optimization, to ensure a stable thawing process and accurate grouting compensation.

[0054] Preferably, such as Figure 6As shown, after the thawing operation is initiated, all freezing systems (main borehole second refrigerant circulation, branch borehole phase change material recooling, and micropore first refrigerant supply) are stopped, and the natural thawing stage begins. During natural thawing, the distributed fiber optic temperature measurement system continuously monitors changes in formation temperature, and the pore water pressure monitoring system collects pore water pressure data in the thawing area in real time. Both data are transmitted synchronously to the ground control platform, which analyzes the data in real time to determine the thawing progress and porosity development. When the monitoring data shows that the pore water pressure in the thawing area drops below the preset trigger threshold, it indicates that significant porosity has appeared in the formation, and adaptive grouting can be initiated. The ground control platform can prioritize grouting based on the pore water pressure data of each area and the previous three-dimensional pore model, prioritizing areas with large pore water pressure drops and high settlement risks (such as areas with concentrated ultra-large pores and areas surrounding key station structures). During grouting, a preset type of cement slurry is slowly injected into the adaptive expansion bladder of the corresponding area through a flexible connecting pipe. The preset type of cement slurry can be selected as low-viscosity ultrafine cement slurry. During grouting, the pressure and grout flow rate inside the grout capsule are monitored synchronously by a pressure sensor built into the capsule. Grouting automatically stops when the pressure inside the capsule reaches a preset stop threshold (matching the bearing capacity of the gravel strata to prevent ground uplift), or when the grout flow rate drops to a preset minimum threshold (indicating that the capsule has fully expanded and the grout has seeped through the capsule's micropores to fill the surrounding pores). If, after grouting in a certain area, the distributed fiber optic temperature monitoring system still detects a settlement trend or persistently abnormal pore water pressure, local grouting can be performed in that area. For grouting, a faster-setting grout type can be selected and injected through the pre-reserved channels of the adaptive expansion capsule to quickly fill the remaining pores. After grouting in each area is completed, the pore filling effect can be detected by core drilling or radar detection to ensure thorough grouting compensation and no obvious unfilled pores.

[0055] It should be noted that the specific embodiments described above are exemplary. Those skilled in the art can devise various solutions inspired by the disclosure of this invention, and these solutions all fall within the scope of this invention and its protection. Those skilled in the art should understand that this specification and its accompanying drawings are illustrative and not intended to limit the scope of the claims. The scope of protection of this invention is defined by the claims and their equivalents. This specification contains multiple inventive concepts; terms such as "preferredly," "according to a preferred embodiment," or "optionally" indicate that the corresponding paragraph discloses an independent concept. The applicant reserves the right to file divisional applications based on each inventive concept.

Claims

1. A deep station excavation construction method based on a frozen water stop technology, characterized in that, It includes the following steps: S1. Detect the distribution density of pebbles and the location of ultra-large pores in large-particle-size, high-permeability sand and gravel strata, record the particle size and arrangement direction of pebbles in the strata, and establish a three-dimensional pore model of the strata based on the detection and recording results. S2. The main hole is constructed using casing drilling technology. After the main hole is completed, a micro directional drilling rig is extended from the main hole and drills into the ultra-large pore area and micro-fracture area in the formation according to the three-dimensional pore model to construct the support hole and micro hole. S3. Staged freezing includes a first freezing stage with micropores as the core working unit and a second freezing stage with main holes and branch holes as the core working units. A first refrigerant is introduced into the micropores for a preset duration until the temperature of the micro-crack area is monitored by distributed optical fibers and reaches the preset freezing temperature to form crack ice plugs. Then, a second refrigerant is introduced into the main hole for cooling until a frozen soil curtain with a thickness that meets the water-stopping requirements is formed. The main hole's large-scale cooling and the branch holes' targeted cooling work together. S4. Excavate the strata corresponding to the main structure of the station. After the excavation is completed, set up the initial support. Embed adaptive expansion bladders between the initial support and the frozen soil curtain at a preset interval and connect the adaptive expansion bladders to the ground grouting system through flexible connecting pipes. S5. Stop the refrigeration operation of all freezing systems to allow the frozen soil to thaw naturally. Monitor the stability of the strata in the thawing area in real time through a pore water pressure sensor. When the pore water pressure in the thawing area drops to a preset trigger threshold, slowly inject a preset type of cement slurry into the adaptive expansion bladder through a flexible connecting pipe.

2. The construction method according to claim 1, characterized in that, In step S1, a combination of ground-penetrating radar (GPR), borehole video surveillance, and core drilling is used to conduct geological exploration to obtain the detection and recording results. Specifically, during GPR detection, detection profiles are set up longitudinally, laterally, and obliquely along the deep station excavation area. During borehole video surveillance, borehole video surveillance holes are arranged in key areas identified by GPR detection, and the characteristics of pebbles, as well as the characteristics of ultra-large pores and micro-fractures, are recorded through the borehole video surveillance probe. During core drilling, core sampling holes are arranged around the borehole video surveillance holes to obtain complete stratigraphic core samples for laboratory analysis.

3. The construction method according to claim 1 or 2, characterized in that, In step S2, a directional geological drilling rig adapted to the space of the underground pilot tunnel is used when constructing the main hole. The casing drilling technology adopts a method of pilot hole drilling combined with synchronous casing advance. The directional geological drilling rig's guide drill bit has a built-in micro-drilling measurement system. The micro-drilling measurement system collects the drilling angle, azimuth angle and depth data of the borehole in real time, and synchronously feeds them back to the ground control platform through a signal transmission device. When the ground control platform detects that the borehole attitude is deviating due to the collision of large-diameter pebbles, the direction adjustment mechanism built into the guide drill bit is automatically triggered to correct the drilling trajectory.

4. The construction method according to claim 3, characterized in that, During the drilling process of the directional geological drilling rig, a composite wall-protecting fluid is continuously injected into the borehole. The composite wall-protecting fluid can form a temporary reinforced thin shell on the borehole wall, which can be broken by physical means such as high-pressure fluid during the subsequent branch hole construction. Throughout the main hole construction, the ground control platform compares the real-time drilling data with the formation parameters in the three-dimensional pore model. When encountering special formation conditions, drilling is paused and the drilling parameters are optimized. Construction is resumed after the parameters are adjusted to suit the formation characteristics.

5. The construction method according to claim 3, characterized in that, In step S2, the folded hydraulic branch unit, which is in a folded state, is transported to the preset branch position through the main hole drill pipe. The preset branch position is determined by combining the main hole trajectory calibrated by the micro-drilling measurement system in the early stage and the ultra-large pore distribution data in the three-dimensional pore model. After the folded hydraulic branch unit reaches the target position, power is supplied to the folded hydraulic branch unit through the ground hydraulic pump station to drive its movable arm to unfold, so that the branch hole drill bit and the main hole axis form an angle that matches the frozen curtain design. When drilling the branch hole, the rock breaking element on the drill bit works together with the high-pressure fluid. The high-pressure fluid pre-disperses the loose sand particles on the drilling path, and a modified wall protection fluid with added anti-dispersion components is injected into the hole while drilling. After the branch hole is drilled, the branch hole freezing pipe is immediately inserted into the branch hole through the preset channel of the folding hydraulic branch device.

6. The construction method according to claim 5, characterized in that, In step S2, a flexible hose-type micro-drill is used when constructing the micro-hole. The drill rod of the flexible hose-type micro-drill is made of flexible material. Before construction, a channel corresponding to the preset micro-hole position is opened on the support hole freezing pipe. The flexible hose-type micro-drill is slowly lowered into the preset drilling position in the support hole through the channel. The front end of the flexible hose-type micro-drill is equipped with a fiber optic attitude sensor and an electromagnetic guide head. The fiber optic attitude sensor collects drilling angle and position data in real time and transmits them to the ground control platform. During micro-hole drilling, the micro drill bit and the micro-hole freezing pipe are coaxially set, and the micro-hole freezing pipe follows the drill bit synchronously.

7. The construction method according to claim 3, characterized in that, In step S3, the first refrigerant introduced in the first freezing stage is liquid nitrogen; temperature data of the micro-crack area is collected at preset intervals by a distributed optical fiber temperature measurement system deployed on the microporous tube wall and the surrounding stratum and transmitted to the ground control platform; when the temperature is detected to drop below the preset freezing temperature and remain below the preset freezing temperature for a preset duration, the pore water pressure in the area is detected by a pore water pressure monitoring system; if the pore water pressure is stable within the preset low pressure range, it is determined that the first freezing stage has achieved the expected effect and the process proceeds to the second freezing stage; the second refrigerant introduced in the second freezing stage is brine.

8. The construction method according to claim 7, characterized in that, During the second freezing stage, the refrigerant circulation system of the main borehole is equipped with a flow regulation module to adjust the second refrigerant flow rate based on temperature data fed back from the ground control platform. A distributed fiber optic temperature measurement system monitors temperature changes in the ultra-large pore area. When the temperature in this area exceeds a preset threshold, the phase change material (PCM) cooling mechanism of the branch boreholes is triggered. Pre-set heating elements within the branch boreholes heat the PCM to release its stored cold energy. A pore water pressure monitoring system monitors pore water pressure changes in the frozen area. If an abnormal increase in pore water pressure is detected in a certain area, the problem area is located using distributed fiber optic temperature measurement data. If the problem area is located between the coverage of the main borehole and the branch boreholes, optimization is achieved by adjusting the second refrigerant flow rate in the main borehole or extending the PCM cooling time in the branch boreholes. If the problem area is a small, localized area, micro-holes are drilled and low-temperature PCM is injected to resolve the insufficient freezing issue.

9. The construction method according to claim 1 or 2, characterized by, In step S4, the sectional excavation method is used for underground excavation, and the excavation is carried out step by step according to the preset cycle length. After each cycle of excavation is completed, the excavation face is temporarily protected. When setting the initial support, a preset type of concrete is sprayed onto the excavation face to form the initial support structure. Before pre-embedding the adaptive expansion bladder, the pre-embedded hole positions are calibrated by laser positioning equipment. The pre-embedded hole positions are arranged according to the positions marked in the previous three-dimensional pore model to match the concentrated areas of ultra-large pores and micro-cracks. When erecting the steel arch frame, the steel arch frame is connected to the initial support structure, and a gap of a preset width is reserved between the steel arch frame and the adaptive expansion bladder.

10. The construction method according to claim 7, characterized in that, In step S5, during the natural thawing stage, the distributed fiber optic temperature measurement system continuously monitors changes in formation temperature, and the pore water pressure monitoring system collects pore water pressure data of the thawing area in real time. Both data are transmitted synchronously to the ground control platform, which analyzes the data in real time to determine the thawing progress and pore development. When the pore water pressure in the thawing area drops below the preset trigger threshold, it is determined that obvious pores have appeared in the formation, and adaptive grouting operation is initiated. When adaptive grouting operation is initiated, the ground control platform divides the grouting priority according to the pore water pressure data of each area and the previous three-dimensional pore model, and prioritizes grouting areas with large drops in pore water pressure and high risk of settlement.

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