Deep station underground excavation construction method based on freezing water stop technology

Abstract

The invention relates to a deep station underground excavation construction method based on a freezing water stop technology, which comprises the following steps of: detecting the distribution density of pebbles and the positions of super-large pores in a stratum, recording the particle size and the arrangement direction of the pebbles in the stratum, and establishing a three-dimensional pore model of the stratum; a main hole is constructed, and after construction of the main hole is completed, the micro directional drilling machine extends out of the main hole and conducts drilling according to the three-dimensional hole model so as to construct branch holes and micro holes; first refrigerants are introduced into the micro holes for preset duration until crack ice plugs are formed, and then second refrigerants are introduced into the main holes for refrigeration until a frozen soil curtain is formed; the stratum is excavated, a primary support is arranged after excavation is completed, and a self-adaptive expansion bag body is pre-buried between the primary support and the frozen soil curtain; and the frozen soil is naturally unfrozen, the stratum stability of the unfrozen area is monitored in real time, and when it is monitored that the pore water pressure of the unfrozen area is reduced to a preset triggering threshold value, cement paste of a preset type is slowly injected into the self-adaptive expansion bag body.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of excavation construction based on freezing water stopping technology, and particularly relates to a deep station excavation construction method based on freezing water stopping technology. BACKGROUND

[0002] As an important support means in urban underground engineering, freezing water stopping technology makes the ground water freeze to form a continuous frozen soil curtain through artificial refrigeration, effectively blocks the groundwater seepage and enhances the stability of the stratum, and creates a safe working environment for excavation construction. In various strata, high water content loose stratum is the main application object of this technology, and large particle size high permeability sand and gravel stratum becomes a difficult point of technology application due to its unique geological characteristics. This stratum takes pebbles (such as particle size of 200-800 mm) as the main skeleton particles, and sand particles are filled in the gap between pebbles to form a structure with extremely poor particle size distribution. The existence of super large pores (such as pore size of 50-200 mm) between pebbles leads to extremely fast groundwater seepage speed (such as permeability coefficient > 5 m / d). At the same time, although the pebble skeleton has high strength, it has poor self-stability, and the drilling construction is easily affected by the collision of large particle size pebbles to produce deflection; the low thermal conductivity of pebble skeleton makes the cold quantity transfer efficiency low, and it is difficult for the conventional freezing hole network to form a complete and continuous frozen soil curtain. In the process of excavation construction, the continuity and integrity of the frozen curtain are directly related to the construction safety, and the thawing settlement compensation after thawing is the key link to ensure the long-term stability of the stratum. Therefore, for the freezing water stopping technology of large particle size high permeability sand and gravel stratum, it is necessary to deeply understand the three-dimensional pore characteristics and freezing mechanism of the stratum, and to design a construction process that can adapt to the special geological conditions of the stratum to meet the dual needs of engineering safety and economy.

[0003] CN118008325A discloses a subway tunnel connecting passage expansion construction method based on freezing method, which comprises the following steps: S1: preparation before construction; S2: determining the freezing design parameters and calculating the thickness of the frozen curtain; S3: calculating the required cold quantity of the refrigeration freezing system design; S4: arranging the inner circle freezing hole and the outer circle freezing hole in a double circle mode; arranging the temperature measuring hole on the structural surface of the left line tunnel and the right line tunnel; arranging the pressure relief hole on both sides of the non-frozen area position in the frozen curtain; S5: assembling the refrigeration freezing system; S6: debugging and running the refrigeration freezing system; S7: entering the active freezing stage; S8: excavation determination and entering the maintenance freezing stage; S9: connecting passage excavation and primary support construction; S10: waterproof layer and secondary lining structure construction; S11: filling and grouting; S12: thawing and grouting; S13: hole sealing; S14: leaving the site; S15: whole process monitoring.

[0004] In the freezing water stop construction of large particle size high permeability sand and gravel stratum, the existing technology faces the core problems of difficult freezing curtain intersection and incomplete thawing settlement compensation. The encryption freezing hole technology causes large particle size gravel to lead to large drilling deflection rate, hole position deviation causes curtain gap, and cold energy cannot be accumulated at the super large pore, forming a continuous seepage channel, which leads to the difficulty of continuous closure of the freezing curtain. In the pre-embedded grouting pipe thawing settlement compensation technology, the slurry quickly flows along the gravel surface, cannot effectively fill the super large pore, and the small cracks (such as crack width of 1-5mm) are difficult to penetrate due to high slurry viscosity, and still have a settlement risk after thawing. The basin-shaped freezing technology only optimizes the plane layout of the hole network, and does not design a cold energy supplement path for the vertical super large pore, which leads to poor vertical continuity of the curtain. The root cause of these problems is that the existing technology does not consider the matching of the three-dimensional pore characteristics of the stratum and the cold energy transmission and slurry diffusion, but adopts a linear optimization idea, such as encryption of the hole network and reduction of the cold medium temperature, ignoring the matching of the pore shape and the cold energy transmission. At the same time, the existing technology lacks a cooperative mechanism for the freezing and grouting processes, the monitoring system and the control logic are independent of each other, and it is difficult to realize real-time response to the change of the stratum pore, which leads to the difficulty of freezing curtain intersection in high permeability sand and gravel stratum and the unsatisfactory effect of thawing settlement compensation, seriously restricting the safety and efficiency of the underground excavation construction of this type of stratum.

[0005] In addition, on the one hand, there are differences in the understanding of those skilled in the art; on the other hand, a large number of literatures and patents have been studied by the applicant when making the present application, but due to the limited space, all the details and contents have not been listed in detail, which does not mean that the present application does not have these characteristics of the prior art, on the contrary, the present application has all the characteristics of the prior art, and the applicant reserves the right to add related prior art in the background art. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a deep station underground excavation construction method based on freezing water stop technology to solve at least part of the above technical problems.

[0007] The present application discloses a deep station underground excavation construction method based on freezing water stop technology, characterized in that it comprises the following steps: S1, detecting the distribution density of gravel and the position of super large pore in the large particle size high permeability sand and gravel stratum, recording the particle size and arrangement direction of the gravel in the stratum, and establishing a three-dimensional pore model of the stratum based on the detection and recording results; S2, using the follow-up pipe drilling technology to construct the main hole, after the main hole construction is completed, a micro directional drilling machine is stretched out from the main hole and drilled into the super large pore area and the small crack area in the stratum according to the three-dimensional pore model to construct the branch hole and the micro hole; S3, the first refrigerant is introduced into the micro-hole for a preset time period until the temperature of the micro-fissure region reaches a preset freezing temperature to form a fissure ice plug through distributed optical fiber monitoring, and then the second refrigerant is introduced into the main hole for refrigeration until a frozen soil curtain with a thickness meeting the water stopping requirement is formed; S4, the stratum corresponding to the main structure of the station is excavated, and after the excavation is completed, initial support is arranged, and self-adapting expansion capsules are pre-buried at a preset interval between the initial support and the frozen soil curtain and connected with the ground grouting system through flexible connecting pipes; S5, the refrigeration operation of all freezing systems is stopped to allow the frozen soil to thaw naturally, and the stability of the stratum in the thawing area is monitored in real time through the pore water pressure sensor, and when the pore water pressure in the thawing area is detected to be reduced to a preset trigger threshold, the self-adapting expansion capsules are slowly injected with a preset type of cement slurry through the flexible connecting pipes.

[0008] The construction method of the present application guides the fractal freezing hole network design by establishing a three-dimensional pore model, adopts a collaborative control mechanism of phased freezing and adaptive grouting, and effectively solves the core problems of difficult freezing curtain closure and incomplete thawing compensation in large particle size and high permeability sand and gravel stratum. The accurate hole network design based on the three-dimensional pore model enables the arrangement of the main hole, the branch hole and the micro-hole to deeply adapt to the three-dimensional pore characteristics of the stratum, avoiding the poor curtain continuity caused by the plane layout in the conventional technology; the phased freezing strategy quickly forms a fissure ice plug by the micro-hole to block the micro-pore flow channel, creating a low-permeability environment for the formation of the main curtain, and then the collaborative action of the main hole salt water refrigeration and the branch hole phase change material cold compensation, targetedly supplements the cold quantity in the super-large pore area, ensures the thickness and continuity of the frozen soil curtain; the adaptive grouting in the thawing stage realizes accurate filling through the pressure sensor built-in capsule, avoiding the stratum uplift caused by slurry loss and excessive grouting. This whole-process collaborative control mechanism improves the efficiency of the freezing curtain formation and significantly improves the accuracy of the thawing compensation, providing a safe and reliable process guarantee for deep station excavation construction.

[0009] According to a preferred embodiment, in step S1, the stratum survey is carried out by combining geological radar detection, drilling camera observation and drilling core sampling to obtain detection and recording results, wherein the geological radar detection is performed along the longitudinal, transverse and oblique directions of the deep station excavation construction area; the drilling camera observation hole is arranged in the key area identified by the geological radar detection, and the characteristics of the pebbles, super-large pores and micro-fissures are recorded through the drilling camera probe; the drilling core sampling hole is arranged around the drilling camera observation hole to obtain complete stratum core samples and perform laboratory determination.

[0010] The present application realizes the accurate characterization of the three-dimensional pore structure of the large-diameter high-permeability sand-pebble stratum by the comprehensive exploration method combining the geological radar, the borehole camera observation and the borehole coring. The geological radar is arranged along multiple directions to detect the profile, which can effectively identify the pebble distribution density and the position of the super-large pore, and the resolution meets the accurate positioning demand of the 200-800mm pebble and the 50-200mm super-large pore. The borehole camera observation is arranged in the key area to record the pebble size, arrangement direction and the characteristics of the super-large pore and the micro crack through the high-resolution image, which makes up for the limitations of the indirect detection. The borehole coring obtains the complete stratum core sample and carries out the laboratory determination to accurately obtain the key physical and mechanical parameters such as the pebble thermal conductivity, density, uniaxial compressive strength and stratum permeability coefficient. The three-dimensional pore model constructed after the systematic integration of the data of the three provides the accurate geological basis for the fractal freezing pore network design, the refrigerant temperature determination and the grouting pressure setting, avoids the pore network design deviation caused by the misjudgment of the stratum characteristics, and ensures the depth adaptation of the subsequent construction steps and the stratum characteristics.

[0011] According to a preferred embodiment, in step S2, a directional geological drilling machine suitable for the space of the hidden excavation pilot tunnel is used in the construction of the main hole, the follow-up drilling technology adopts the mode of drilling the pilot hole and synchronously following up the casing, the micro while-drilling measurement system is built in the guide drill bit of the directional geological drilling machine, the micro while-drilling measurement system collects the drilling angle, azimuth angle and depth data of the borehole in real time, and synchronously feeds back to the ground control platform through the signal transmission device, when the ground control platform monitors that the borehole posture appears a deflection trend caused by the collision of the large-diameter pebble, the direction adjusting mechanism built in the guide drill bit is automatically triggered to correct the drilling trajectory.

[0012] The present application uses the directional geological drilling machine with the built-in micro while-drilling measurement system in the main hole construction, realizes the real-time monitoring and automatic correction of the drilling trajectory, and significantly improves the drilling accuracy in the large-diameter high-permeability sand-pebble stratum. The micro while-drilling measurement system collects the drilling angle, azimuth angle and depth data in real time, when the deflection trend of the borehole caused by the collision of the large-diameter pebble is monitored, the direction adjusting mechanism built in the guide drill bit is automatically triggered to correct the drilling trajectory, so as to control the hole deviation. This closed-loop control mechanism effectively solves the problem that the conventional drilling is easily affected by the collision of the large-diameter pebble to cause a large deflection rate, provides a stable hole environment for the subsequent branch hole construction, avoids the curtain gap caused by the hole deviation, and ensures the accurate implementation of the fractal freezing pore network.

[0013] According to a preferred embodiment, a composite wall protection fluid is continuously injected into the hole during the drilling process of the directional geological drilling machine, and the composite wall protection fluid can form a temporary reinforced shell on the hole wall and be broken by physical means such as high-pressure fluid during subsequent branch hole construction; during the whole main hole construction, the ground control platform compares the real-time drilling data with the formation parameters in the three-dimensional pore model, and when special formation conditions are encountered, the drilling is temporarily suspended and the drilling parameters are optimized, and after the parameters are adjusted to adapt to the formation characteristics, the construction is resumed.

[0014] The composite wall protection fluid continuously injected into the main hole can form a temporary reinforced shell on the hole wall, and can be broken by physical means such as high-pressure fluid during subsequent branch hole construction, effectively solving the problem of hole wall collapse caused by poor self-stability of large-diameter high-permeability sandy pebble stratum. The temporary reinforced layer formed by the wall protection fluid during drilling blocks the sandy pebble stratum and the hole space, providing a stable environment for drilling; its characteristic of being broken by high-pressure fluid ensures that the branch hole construction is not hindered. The ground control platform compares the real-time drilling data with the formation parameters in the three-dimensional pore model, and when special formation conditions such as dense pebble groups are encountered, the drilling is temporarily suspended and the parameters are optimized, further improving the drilling accuracy. The synergistic control mechanism of the wall protection fluid and the drilling parameters ensures that the main hole construction accuracy meets the positioning requirements of the subsequent branch holes, laying a foundation for the accurate implementation of the fractal frozen hole network.

[0015] According to a preferred embodiment, in step S2, the folded hydraulic branch device in a folded state is delivered to a preset branch position through the main hole drill rod, and the preset branch position is determined in combination with the main hole trajectory calibrated by the previous micro-while-drilling measurement system and the super-large pore distribution data in the three-dimensional pore model; after the folded hydraulic branch device reaches the target position, power is delivered to the folded hydraulic branch device through the ground hydraulic pump station to drive the movable arm to expand, so that the branch hole drill bit forms an angle with the main hole axis that is suitable for the design of the frozen curtain; during branch hole drilling, the rock breaking element on the drill bit cooperates with the high-pressure fluid, the high-pressure fluid pre-scatters loose sand particles on the drilling path, and the modified wall protection fluid with anti-dispersion components is injected into the hole while drilling; after the branch hole drilling is completed, the branch hole freezing pipe is immediately implanted into the branch hole through the preset channel of the folded hydraulic branch device.

[0016] The present application adopts a folding hydraulic branch device to realize accurate branch construction of the branch hole, solves the problem of accurately extending the branch hole to the super-large pore area in the limited space of the main hole. The folding hydraulic branch device is conveyed to the preset branch position (determined based on the three-dimensional pore model and the micro-while-drilling measurement system) through the main hole drill pipe, and after reaching the target position, the active arm is unfolded by the ground hydraulic pump station to make the branch hole drill bit form an angle with the main hole axis that matches the design of the frozen curtain. The rock breaking element on the drill bit cooperates with the high-pressure fluid to pre-disperse the loose sand particles on the drilling path, reducing the direct collision and wear of the drill bit by large-diameter pebbles. The modified wall protection fluid with anti-dispersion components is injected while drilling to avoid the rapid loss of the wall protection fluid due to high permeability of the formation. After the branch hole drilling is completed, the branch hole freezing pipe is immediately implanted through the preset channel to prevent the hole wall from collapsing without support. This branch construction technology effectively solves the deflection problem caused by directly penetrating pebbles in conventional branch hole construction, ensuring accurate pointing of the branch hole to the super-large pore area and providing a reliable carrier for phase change material cooling.

[0017] According to a preferred embodiment, in step S2, a hose type micro drill is used when constructing the micro hole, and the drill pipe of the hose type micro drill is made of flexible material. Before construction, a channel corresponding to the preset micro hole position is opened on the branch hole freezing pipe, and the hose type micro drill is slowly lowered to the preset drilling position in the branch hole through the channel. The front end of the hose type micro drill is equipped with an optical fiber attitude sensor and an electromagnetic guide head. The optical fiber 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 is coaxially arranged with the micro hole freezing pipe, and the micro hole freezing pipe follows the drill bit synchronously.

[0018] The present application uses a hose type micro drill during micro hole construction, which adapts to the space steering requirements in the branch hole through a flexible drill pipe, realizing accurate extension of the micro hole to the micro fracture area in a smaller space in the branch hole. The front end of the drill is equipped with an optical fiber attitude sensor and an electromagnetic guide head, which collects drilling angle and position data in real time and transmits them to the ground control platform. When it is monitored that the large-diameter pebbles will be contacted or the preset trajectory will be deviated, the guide head is adjusted by electromagnetic control to correct the drilling direction. During micro hole drilling, the micro drill bit is coaxially arranged with the disposable freezing pipe, and the disposable freezing pipe follows the drill bit synchronously during the drilling process, avoiding the hole wall collapse caused by secondary pipe lowering. This accurate directional drilling mechanism solves the difficulties caused by limited space and high drilling accuracy requirements in micro hole construction, ensuring that the micro hole can accurately reach the micro fracture area and providing a reliable guarantee for forming a fracture ice plug to block the micro seepage channel.

[0019] According to a preferred embodiment, in step S3, the staged freezing includes a first freezing stage with micro-holes as the core action unit and a second freezing stage with main holes and branch holes as the core action unit, wherein the first coolant for the first freezing stage is liquid nitrogen; the distributed optical fiber temperature measurement system arranged on the micro-hole pipe wall and the surrounding stratum collects temperature data of the micro-fissure area at preset intervals and transmits to the ground control platform, when the temperature is monitored to be below the preset freezing temperature and lasts for a preset time, the pore water pressure monitoring system detects the pore water pressure of the area; if the pore water pressure is stable in the preset low pressure range, it is determined that the first freezing stage achieves the expected effect and enters the second freezing stage; the second coolant for the second freezing stage is brine.

[0020] The staged freezing strategy quickly forms fissure ice plug through micro-holes with liquid nitrogen, effectively solving the problem of blocking micro-fissure seepage channel in large particle size and high permeability sand and gravel stratum. The low-temperature liquid nitrogen (-40°C or so) introduced in the first freezing stage quickly reduces the temperature of the micro-fissure area through the micro-holes, so that the fissure water is quickly frozen to form an "ice plug" to block the micro seepage channel; the distributed optical fiber temperature measurement system collects temperature data at preset intervals, when the temperature of the micro-fissure area is below the preset freezing temperature and remains, the seepage is verified by the pore water pressure monitoring system whether it has been blocked. This targeted fissure freezing strategy avoids the problem of not blocking micro-fissure seepage caused by low cold quantity transmission efficiency in conventional freezing technology, creates a low permeability environment for the formation of main curtain, and improves the efficiency and quality of subsequent main curtain formation.

[0021] According to a preferred embodiment, in the second freezing stage, the coolant circulation system of the main hole is equipped with a flow adjusting module, which adjusts the second coolant flow according to the temperature data fed back by the ground control platform; the distributed optical fiber temperature measurement system monitors the temperature change of the super-large pore area, when the temperature of the area is higher than the preset threshold, the phase change material cooling mechanism of the branch hole is triggered, the heating element in the branch hole is heated to make the phase change material release the stored cold energy; the pore water pressure monitoring system monitors the pore water pressure change of the frozen area, when the pore water pressure of a certain area abnormally rises, the problem area is located combined with the distributed optical fiber temperature data, if the problem area is located between the main hole and the branch hole coverage range, the second coolant flow of the main hole is adjusted or the cooling time of the phase change material of the branch hole is prolonged for optimization, if the problem area is a small local range, micro-holes are supplemented and low-temperature second coolant is injected to solve the freezing problem.

[0022] The closed-loop control mechanism of the second freezing stage solves the problem of discontinuity of the freezing curtain caused by the loss of cold energy in the super-large pore area through the synergistic effect of the main hole brine refrigeration and the branch hole phase change material cooling. The main hole refrigerant circulation system is equipped with a flow regulation module, which adjusts the brine flow in real time according to the temperature data fed back by the distributed optical fiber temperature measurement system, ensuring uniform temperature reduction of the surrounding stratum of the main hole; when the temperature of the super-large pore area is monitored to be higher than the preset threshold, the branch hole phase change material cooling mechanism is triggered, the phase change material (such as paraffin-graphite composite phase change material) is prompted to release the stored cold energy through the heating element, and the loss of cold energy is supplemented; the pore water pressure monitoring system synchronously monitors the pressure change of the frozen area, locates the problem area in combination with the temperature data when an abnormality is found, and takes targeted measures. This dynamic regulation mechanism precisely matches the cold energy supplement to the seepage characteristics of the stratum, effectively solves the curtain discontinuity problem caused by the delay of cold energy supplement in the conventional freezing technology, and ensures the integrity and continuity of the frozen soil curtain.

[0023] According to a preferred embodiment, in step S4, the sub-excavation method is used for the underground excavation construction, and is gradually advanced according to a preset cycle length. After completing the excavation operation of one cycle, the excavation face is temporarily protected. When the initial support is set, the excavation face is sprayed with a preset type of concrete to form an initial support structure. Before the self-adapting expansion capsule is embedded, the pre-embedded hole position is calibrated by a laser positioning device. The pre-embedded hole position is arranged according to the calibrated position in the previous three-dimensional pore model to match the super-large pore and the micro-fissure concentrated area. When the steel arch is erected, the steel arch is connected with the initial support structure, and a gap with a preset width is reserved between the steel arch and the self-adapting expansion capsule.

[0024] The sub-excavation method is used in the underground excavation construction to cooperate with the accurate arrangement of the self-adapting expansion capsule and the steel arch, solving the problem of the cooperation between the stratum stability and the thawing settlement compensation between the frozen curtain and the initial support. The sub-excavation method is gradually advanced according to a preset cycle length. After each cycle of excavation, temporary protection and initial support are immediately performed to ensure the stability of the excavation face. Before the self-adapting expansion capsule is embedded, the hole position is calibrated by a laser positioning device to accurately match the super-large pore and the micro-fissure concentrated area, providing targeted coverage for subsequent grouting compensation. The steel arch is reliably connected with the initial support, and a gap with a preset width is reserved between the steel arch and the capsule to avoid the capsule being squeezed and affecting its expansion and grouting function when the steel arch is installed or deformed under stress. This support system design forms a cooperative support system of the frozen curtain, the initial support, the steel arch and the self-adapting expansion capsule, ensuring the stratum stability during the whole underground excavation construction process, and providing a reliable capsule embedding environment for the thawing settlement compensation after thawing.

[0025] According to a preferred embodiment, in step S5, the natural thawing stage, the distributed optical fiber temperature measurement system continuously monitors the formation temperature change, and the pore water pressure monitoring system collects the pore water pressure data of the thawing area in real time. Both data are synchronously transmitted to the ground control platform, and the ground control platform analyzes the data in real time to determine the thawing progress and pore development of the formation. When the pore water pressure of the thawing area is monitored to be below the preset trigger threshold, it is determined that the formation has obvious pores and the adaptive grouting operation is started. When the adaptive grouting operation is started, 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 preferentially grouts the areas with large pore water pressure drop and high subsidence risk.

[0026] The adaptive grouting triggering mechanism in the thawing stage realizes the precise control of thawing compensation through the cooperative analysis of pore water pressure monitoring and distributed optical fiber temperature measurement. During the natural thawing process, the distributed optical fiber temperature measurement system continuously monitors the formation temperature change, and the pore water pressure monitoring system collects the pore water pressure data of the thawing area in real time. Both data are synchronously transmitted to the ground control platform for real-time analysis. When the pore water pressure is below the preset trigger threshold, it indicates that the formation has obvious pores, and the adaptive grouting operation can be started. 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 preferentially grouts the areas with large pore water pressure drop and high subsidence risk. This grouting triggering mechanism based on real-time monitoring data avoids the problems of slurry loss or excessive grouting caused by lack of real-time monitoring in traditional grouting technology, ensuring the precision and effectiveness of thawing compensation. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a step flow chart of a preferred embodiment of the tunneling construction method provided by the present application; Figure 2 is a construction execution schematic diagram of step S1 of a preferred embodiment provided by the present application; Figure 3 is a construction execution schematic diagram of step S2 of a preferred embodiment provided by the present application; Figure 4 is a construction execution schematic diagram of step S3 of a preferred embodiment provided by the present application; Figure 5 is a construction execution schematic diagram of step S4 of a preferred embodiment provided by the present application; Figure 6 is a construction execution schematic diagram of step S5 of a preferred embodiment provided by the present application. DETAILED DESCRIPTION

[0028] The following will be described in detail with reference to the accompanying drawings.

[0029] As Figure 1 shown, the application discloses a deep station underground excavation construction method based on frozen water stopping technology, which comprises the following steps: S1, detecting the distribution density of pebbles and the position of super-large pores in the large-diameter high-permeability sand-pebble stratum, recording the particle size and arrangement direction of the pebbles in the stratum, and establishing a three-dimensional pore model of the stratum based on the detection and recording results; S2, using the pipe following drilling technology to construct the main hole, and after the construction of the main hole is completed, extending the micro directional drilling machine from the main hole and drilling into the super-large pore area and the micro crack area in the stratum according to the three-dimensional pore model to construct the branch hole and the micro hole; S3, passing the first refrigerant into the micro hole and continuing for a preset time length, until the temperature of the micro crack area is monitored by the distributed optical fiber to reach a preset freezing temperature to form a crack ice plug, and then passing the second refrigerant into the main hole for refrigeration until a frozen soil curtain with a thickness meeting the water stopping requirement is formed; S4, excavating the stratum corresponding to the main structure of the station, setting the initial support after the excavation is completed, pre-burying the self-adapting expansion capsule between the initial support and the frozen soil curtain at a preset interval, and connecting the self-adapting expansion capsule with the ground grouting system through the flexible connecting pipe; S5, stopping the refrigeration operation of all the freezing systems to make the frozen soil naturally thaw, and monitoring the stability of the stratum in the thawing area in real time through the pore water pressure sensor, when the pore water pressure of the thawing area is monitored to be reduced to a preset trigger threshold, slowly injecting the cement slurry of a preset type into the self-adapting expansion capsule through the flexible connecting pipe.

[0030] In the application, the large-diameter high-permeability sand-pebble stratum refers to a high-water-content loose stratum, in which pebbles are the main skeleton particles, and sand particles fill the gaps between the pebbles, the particle size of the pebble particles is in a preset large size range (such as the preset size range is 200-800mm), and the overall permeability coefficient of the stratum meets the preset high permeability requirement (such as the permeability coefficient is greater than 5m / d); the stratum has the characteristics of poor particle size distribution, easy formation of large-size gaps between pebbles, fast seepage velocity of underground water, easy loss of cold energy by seepage water during freezing, and difficulty in forming a continuous curtain by a conventional freezing hole network.

[0031] In the application, the super-large pore refers to a gap with a pore size in a preset size range (such as the preset size range is 50-200mm) formed by irregular arrangement of large-diameter pebble particles in the large-diameter high-permeability sand-pebble stratum; the pore is the main channel for the seepage of underground water in the stratum, and the cold energy is easy to be lost at this place during freezing, resulting in a discontinuous area of the frozen curtain.

[0032] In the present application, the micro fissure refers to a fine crack with a preset size range (such as 1-5 mm) distributed in the sand particle aggregation area or the pebble particle surface in the large particle size high permeability sand and pebble stratum; the fissure is small in individual size, but when densely distributed, it is easy to form a through seepage channel, and it is difficult for conventional grouting to penetrate.

[0033] In the present application, the low-temperature liquid nitrogen refers to liquid nitrogen with a preset low-temperature range (such as about -40℃ to achieve rapid freezing of fissure water) after refrigeration treatment; it has the characteristics of low temperature and fast refrigeration speed. In the first freezing stage of the staged freezing of the present application, it is used to inject into the micro-pore, which can rapidly reduce the temperature of the micro-fissure area, freeze the fissure water to form an ice plug, thereby rapidly blocking the seepage channel of the micro-fissure, and creating a low-permeability environment for the subsequent main curtain formation.

[0034] In the present application, the low-temperature salt water refers to a salt water solution with a preset low-temperature range (such as about -35℃ to achieve large-scale stratum refrigeration and avoid excessive energy consumption) after refrigeration unit cooling treatment; it has the characteristics of good flowability and stable cold energy transfer. In the second freezing stage of the staged freezing of the present application, it is used to circulate into the main hole, and through the continuous release of cold energy, it realizes the refrigeration of the large-scale stratum around the station excavation contour, is the core refrigerant for building a macro-frozen soil curtain, and its temperature can be adjusted by the refrigeration unit to adapt to the stratum freezing demand.

[0035] In the present application, the low-viscosity ultra-fine cement slurry refers to a slurry prepared by mixing cement, water and necessary additives, wherein the cement particle size is in a preset ultra-fine range (such as a particle size <10 μm) and the slurry viscosity meets the preset low-viscosity requirement, so as to be easily exuded through the micro-pore of the self-adaptive inflatable capsule; it has the characteristics of strong permeability and good flowability. In step S5 of the present application, it is used to inject the self-adaptive inflatable capsule, which can slowly exude through the micro-pore on the surface of the capsule, at the same time, fill the ultra-large pores and micro-fissures in the large particle size high permeability sand and pebble stratum, and realize precise fusion sinking compensation.

[0036] Preferably, in order to accurately obtain the geological characteristic parameters of the large particle size high permeability sand and pebble stratum, to provide comprehensive and reliable basis for the subsequent fractal freezing hole network design, self-adaptive inflatable capsule pre-embedding and closed-loop control, and to ensure that the fractal phase change freezing and self-adaptive capsule grouting collaborative construction scheme can effectively solve the core problems of difficult freezing curtain closure and incomplete fusion sinking compensation in the stratum, the present application can perform fine stratum investigation on the deep station underground construction area and the stratum in the surrounding related range through the preliminary stratum investigation of step S1.

[0037] Preferably, as Figure 2As shown in step S1, the geological radar detection operation can be carried out. High-frequency geological radar with detection resolution adapted to the characteristics of large-diameter pebbles and super-large pore size can be selected to meet the accurate positioning requirements for large-diameter pebbles (particle size 200-800 mm) and super-large pores (50-200 mm). During the detection process, the detection profiles can be reasonably arranged along the longitudinal, transverse and oblique directions of the deep station underground construction area to ensure that the detection range can fully cover the construction area and the necessary range around it, and the detection depth needs to exceed the station floor design elevation by a certain distance to completely explore the distribution law and permeability of the pebbles in the lower stratum of the construction area. Through the reflection signal difference of the high-frequency electromagnetic wave emitted by the geological radar at the interface of different media (pebbles, sand particles, pore water), two-dimensional profile data of the stratum are obtained, and then the spatial distribution density of the pebbles, the position and approximate size of the super-large pores, and the development area and distribution characteristics of the micro cracks are identified and marked, which provides preliminary guidance for the subsequent arrangement of the borehole camera observation hole.

[0038] Preferably, as Figure 2 As shown, borehole camera observation holes are arranged in the key areas (such as pebble dense areas, super-large pore development areas, and suspected micro crack areas) identified by the geological radar detection. The number of borehole camera observation holes can be reasonably determined according to the number of geological radar detection profiles, the distribution range of key areas, and the survey accuracy requirements. An environmental-resistant borehole camera probe capable of clearly obtaining image information of the stratum around the hole wall in a complex underground environment is selected. The probe is slowly lowered into the borehole camera observation hole through the drill rod at an appropriate speed to ensure that the probe can continuously and clearly shoot the image information of the stratum around the hole wall during movement. Through borehole camera observation, the actual particle size, arrangement direction, inter-particle contact state and surface characteristics of the pebbles at the hole wall are recorded in real time, and the specific position, cross-sectional size and extension direction of the super-large pores at the hole wall, as well as the opening width, length, trend and development degree of the micro cracks are determined. The shot image data is stored in segments according to the depth to provide intuitive and detailed image basis for the subsequent construction of the three-dimensional pore model, and to avoid misjudgment of the stratum characteristics caused by relying only on indirect detection data.

[0039] Preferably, as Figure 2The accuracy of the geological radar detection data and the drilling camera observation data is verified, and key physical and mechanical parameters of the large-diameter high-permeability sandy pebble stratum are obtained. A drilling core hole can be additionally arranged around the drilling camera observation hole. The number of the drilling core holes can be reasonably determined according to the number of the drilling camera observation holes and the data verification requirements. A professional core drilling machine capable of obtaining complete stratum core samples is used for drilling core sampling operation. The core sampling size needs to ensure that the obtained core samples can completely reflect the particle composition, particle size distribution and pore characteristics of the stratum, so as to avoid parameter measurement deviation caused by core sample damage. Core sampling operation is performed at reasonable intervals. Each section of the obtained core sample is uniformly numbered, sealed and packaged, and the core sample depth, actual length and integrity grade are recorded in detail. The correspondence between the core sample and the stratum depth is established. The packaged core sample is sent to a laboratory with corresponding qualifications for indoor testing to measure key physical and mechanical parameters such as thermal conductivity, density, uniaxial compressive strength of pebbles, particle size distribution, porosity of sand particles, and permeability coefficient of the entire stratum. These parameters will directly provide core data support for determining the refrigerant temperature in the fractal freezing hole network design, selecting and calculating the filling amount of the phase change material, and setting the grouting pressure and controlling the grouting amount of the self-adaptive expansion bladder, so as to ensure the scientificity and rationality of the subsequent construction parameter design.

[0040] Preferably, the two-dimensional profile data obtained by the geological radar detection, the image data obtained by the drilling camera observation and the physical and mechanical parameter data obtained by the drilling core sampling are systematically integrated, and then a three-dimensional pore model of the large-diameter high-permeability sandy pebble stratum is constructed by using a finite element analysis software. In the model construction process, the geological radar data can be converted into medium distribution information of the stratum to clearly define the distribution range of different media in the three-dimensional space. The drilling camera image data can be converted into spatial geometric information of pebbles and pores to accurately restore the arrangement form of the pebbles and the three-dimensional structure of the pores. The drilling core test data can be converted into physical and mechanical property information of the stratum to give the model with actual mechanical parameters. After the model construction is completed, the effectiveness of the three-dimensional pore model is verified. A certain number of verification drilling holes not involved in the model construction are selected. The actual investigation data (including stratum particle distribution, pore size, physical and mechanical parameters) at the verification drilling holes are compared and analyzed with the model prediction data to ensure that the prediction accuracy of the model on the pebble distribution, pore size and stratum parameters meets the subsequent construction design requirements. Through the verified three-dimensional pore model, the arrangement position and spacing of the main holes in the fractal freezing hole network, the extension angle and spacing of the branch holes to the super-large pore area, and the drilling position and number of the micro-holes to the micro-fissure area can be accurately determined. Meanwhile, detailed and accurate stratum basis is provided for the pre-embedding spacing, pre-embedding depth and grouting parameter design of the self-adaptive expansion bladder, so as to ensure that the subsequent construction steps can be deeply adapted to the characteristics of the large-diameter high-permeability sandy pebble stratum, and lay a solid foundation for the smooth implementation of the entire construction scheme.

[0041] Preferably, in order to achieve precise construction of the fractal freezing hole network in a large-grained high-permeability sand and gravel stratum, avoid the problem of hole deflection caused by large-grained pebble collision and poor self-stability of the stratum, and ensure that a continuous and complete freezing curtain can be formed during the subsequent freezing process, the three-dimensional pore model obtained from the preliminary stratum fine investigation is used as the basis for the construction process of the main hole, branch hole and micro-hole, and targeted technical measures are taken for each level of hole, through directional drilling control, real-time attitude monitoring and stratum adaptability adjustment, the construction accuracy and hole wall stability of each level of hole are ensured.

[0042] Preferably, during the construction of the main hole, the main hole, as the basic level of the fractal freezing hole network, bears the dual functions of branch carrier of the branch hole and main circuit of the freezing system, and its construction trajectory needs to strictly follow the path set along the station excavation contour in the three-dimensional pore model. A small directional geological drilling machine suitable for the space of the covered excavation pilot tunnel is used for construction. The drilling machine reduces the occupied space in the non-operation state through the folding design of the machine body, and realizes flexible turning and position adjustment in the narrow space with the caterpillar type mobile chassis, ensuring smooth deployment in the covered excavation pilot tunnel. As shown in Figure 3 , the drilling operation adopts the pipe following drilling technology of pilot hole drilling combined with casing synchronous following. The guide drill bit is equipped with a micro-measuring-while-drilling (MWD) system, which can collect drilling angle, azimuth angle and depth data of the hole in real time and synchronously feed back to the ground control platform through a signal transmission device. As shown in Figure 3 , when the ground control platform monitors that the hole attitude appears a deflection trend due to large-grained pebble collision, the direction adjustment mechanism built-in the guide drill bit is automatically triggered to correct the drilling trajectory by changing the cutting direction of the drill bit, ensuring that the pilot hole always extends along the preset route. During the pilot hole drilling process, the casing follows the pilot hole wall synchronously. The setting of the casing can effectively block the sand and gravel stratum and the space in the hole, avoiding the collapse of the hole wall caused by poor self-stability of the stratum, and providing a stable in-hole environment for the subsequent branch construction of the branch hole. At the same time of drilling, the composite wall protection liquid is continuously injected into the hole. The composite wall protection liquid can form a temporary reinforced shell on the hole wall, and needs to meet the characteristics that it can be broken by physical means (such as high-pressure fluid) during the subsequent branch construction of the branch hole, avoiding hindering the drilling of the branch hole. During the whole process of main hole construction, the ground control platform can compare the real-time drilling data with the stratum parameters (such as pebble distribution density and pore position) in the three-dimensional pore model. If special stratum conditions such as dense distribution of large-grained pebble groups are encountered, the drilling can be paused and the drilling parameters (such as drilling speed and cutting intensity) can be optimized. After the parameters are adjusted to adapt to the stratum characteristics, the construction is resumed, ensuring that the construction accuracy of the main hole meets the positioning requirements of the subsequent branch of the branch hole.

[0043] Preferably, after the main hole is completed, the hole wall stability and trajectory accuracy can be detected, and after confirming that it meets the requirements, the branch hole construction is turned on. The branch hole can extend from the main hole to the calibrated large pore area in the three-dimensional pore model. The core technical difficulty lies in realizing accurate branching in the limited space of the main hole and avoiding direct penetration of large-diameter pebbles causing deflection. Before construction, high-pressure fluid can be used to clean the inside of the main hole to remove residual sand and pebble particles and drilling debris inside the hole to ensure the smooth passage of the folding hydraulic branch device. Then the folding hydraulic branch device in the folded state is slowly transported to the preset branch position through the main hole drill pipe. The preset branch position can be determined in combination with the main hole trajectory calibrated by the early micro-while-drilling measurement system (MWD) and the large pore distribution data in the three-dimensional pore model. When the folding hydraulic branch device reaches the target position, power is delivered to the folding hydraulic branch device through the ground hydraulic pump station to drive the folding hydraulic branch device to unfold, so that the branch hole drill bit forms an angle with the main hole axis that matches the design of the frozen curtain, ensuring that the branch hole can accurately point to the large pore area. When the branch hole is drilled, the rock breaking elements on the drill bit and the high-pressure fluid work together. The high-pressure fluid can pre-disperse loose sand particles on the drilling path, reducing direct collision and wear of the drill bit by large-diameter pebbles and reducing the risk of drilling deviation. At the same time, modified wall protection fluid is injected into the hole while drilling. The modified wall protection fluid adds anti-dispersion components to prevent the rapid loss of wall protection fluid due to high formation permeability and ensure the stability of the hole wall. After the branch hole is drilled, the branch hole freezing pipe can be immediately implanted in the branch hole through the preset channel of the folding hydraulic branch device to realize the immediate connection of the pipe implantation after the hole is formed, preventing the hole wall from collapsing without support. During the implantation of the branch hole freezing pipe, the folding hydraulic branch device can be double calibrated by the angle sensor and the micro-while-drilling measurement system (MWD) 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 branch hole construction is completed and it is confirmed that the branch hole freezing pipe is installed stably, micro-hole construction is carried out. The micro-hole can extend from the branch hole to the micro-fissure area calibrated in the three-dimensional pore model. The construction difficulty lies in realizing directional drilling in the smaller space of the branch hole and accurately reaching the micro-fissure position. The construction adopts a soft tube type micro-drill. The drill rod of the drill is made of flexible material, which can adapt to the space turning requirement in the branch hole and facilitate the extension to the micro-fissure area. Before the construction, a channel corresponding to the preset micro-hole position is first opened on the branch hole freezing pipe to ensure that the soft tube type micro-drill can be smoothly lowered. Then, the soft tube type micro-drill is slowly lowered to the preset drilling position in the branch hole through the channel. The front end of the drill is equipped with an optical fiber type attitude sensor and an electromagnetic guide head. The optical fiber type 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 the remote control console. When it is monitored that the drill is about to contact the large-diameter pebbles or deviate from the preset trajectory, the electromagnetic control is used to adjust the guide head to deviate, so as to correct the drilling direction. During the micro-hole drilling, the micro-drill bit is coaxially arranged with the micro-hole freezing pipe. The micro-hole freezing pipe follows the bit synchronously during the drilling process. The drill advances forward while the micro-hole freezing pipe is installed, avoiding the hole wall collapse caused by the second pipe lowering. During the drilling process, the wall protection medium can be supplemented in time according to the permeability of the stratum to ensure the stability of the hole wall of the loose stratum around the micro-fissure. The drilling parameters are continuously adjusted through the data fed back by the optical fiber type attitude sensor during the whole micro-hole construction process, so as to ensure that the micro-hole can accurately reach the micro-fissure area and lay a foundation for the subsequent local strengthening freezing and plugging of the micro-pore leakage channel.

[0045] Preferably, in order to ensure the construction safety and efficiency, all drilling equipment can adopt pneumatic or hydraulic power mode to avoid the risk of electric leakage of electrical equipment in the high-water-content sand and pebble stratum. At the same time, an in-hole pressure monitor is provided to monitor the in-hole pressure changes of the freezing holes at all levels in real time. When an abnormal pressure is monitored (such as a sudden pressure drop indicating hole wall collapse or a sudden pressure rise indicating in-hole blockage), the drilling is immediately stopped and emergency measures (such as supplementing the wall protection liquid and cleaning the blockage) are taken. After the in-hole state is restored to stability, the construction is continued.

[0046] Preferably, in order to adapt to the seepage characteristics of the large-diameter high-permeability sand and pebble stratum and solve the core problem that the cold is easily taken away by the rapid seepage water in the stratum and the conventional freezing is difficult to form a continuous curtain, step S3 adopts a staged freezing strategy based on the construction results of the previous fractal freezing hole network (main hole, branch hole and micro-hole), uses a distributed optical fiber temperature measurement system and a pore water pressure monitoring system to realize real-time regulation and control of the freezing parameters, ensures that the freezing effect of each stage meets the design requirements, and finally forms a continuous, complete and sufficient strength freezing curtain. Figure 4 Preferably, in order to adapt to the seepage characteristics of the large-diameter high-permeability sand and pebble stratum and solve the core problem that the cold is easily taken away by the rapid seepage water in the stratum and the conventional freezing is difficult to form a continuous curtain, step S3 adopts a staged freezing strategy based on the construction results of the previous fractal freezing hole network (main hole, branch hole and micro-hole), uses a distributed optical fiber temperature measurement system and a pore water pressure monitoring system to realize real-time regulation and control of the freezing parameters, ensures that the freezing effect of each stage meets the design requirements, and finally forms a continuous, complete and sufficient strength freezing curtain.

[0047] Preferably, the staged freezing strategy can 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, as shown in Figure 4 The first freezing stage takes micropores as the core action unit, and the goal is to freeze the micro-crack water in the stratum and form crack ice plugs to block the micro seepage channels, thereby creating a low-permeability environment for subsequent main curtain formation. Before construction, the micropore freezing pipe can be connected with the ground coolant supply system to ensure that the connection part is sealed and reliable, and to avoid first coolant leakage leading to cold loss; at the same time, the delivery pipeline of the first coolant supply system is insulated to reduce the cold loss of the first coolant in the delivery process, and to ensure that the first coolant entering the micropore can maintain the preset low temperature, wherein the first coolant can be liquid nitrogen. After the connection is completed, the micropore is continuously injected with low-temperature first coolant, and the temperature change of the micro-crack region is monitored in real time by the distributed optical fiber temperature measurement system arranged on the micropore pipe wall and the surrounding stratum during the injection process. The distributed optical fiber temperature measurement system can collect temperature data at a preset interval, and transmit the data to the ground control platform. When the ground control platform monitors that the temperature of the micro-crack region drops below the preset freezing temperature, and the temperature state is maintained for a preset time, the change of the pore water pressure in the region is detected by the pore water pressure monitoring system, wherein, as shown in Figure 4 If the pore water pressure is stable in the preset low pressure range, it indicates that the seepage has been blocked, and it is determined that the first freezing stage achieves the expected effect, and the second freezing stage can be entered. If it is found by monitoring that the temperature of the local micro-crack region does not reach the preset value or the pore water pressure is still at a high level, it indicates that the seepage is not completely blocked, and the injection of the first coolant needs to be suspended to check the reasons (such as whether the micropore freezing pipe is blocked, whether the first coolant supply is stable), and after the problem is solved, the injection is restarted, and if necessary, micropores can be supplemented in the local region to supplement the injection of low-temperature first coolant, so as to ensure that all micro-cracks form effective ice plugs.

[0049] Preferably, as shown in Figure 4As shown, after the first freezing stage is completed and verified, the second freezing stage is entered, which takes the main hole and the branch hole as the core action unit, and the goal is to build a macroscopically continuous frozen curtain in the high-permeability sand-pebble stratum through the cooperation of large-scale refrigeration of the main hole and targeted cold compensation of the branch hole. During construction, the refrigerant circulation system of the main hole is started first, and low-temperature second refrigerant is continuously fed into the main hole. The refrigerant circulation system of the main hole can be equipped with a flow adjustment module to adjust the flow of the second refrigerant according to the temperature data fed back by the ground control platform, so as to ensure that the surrounding stratum of the main hole can be uniformly cooled, wherein the second refrigerant can be salt water. During the refrigeration process of the main hole, the distributed optical fiber temperature measurement system can focus on monitoring the temperature change of the super-large pore area, which is a key part where cold is easy to be lost and the curtain is easy to be discontinuous due to fast seepage velocity. When the ground control platform monitors that the temperature of the super-large pore area is higher than the preset threshold value, the phase change material cold compensation mechanism of the branch hole is triggered immediately, that is, the phase change material is heated by the pre-set heating element in the branch hole to make the phase change material release the stored cold and compensate for the cold loss of the super-large pore area caused by seepage, wherein the phase change material can be a paraffin-graphite composite phase change material. During the phase change material cold compensation process, the temperature change of the area can be continuously monitored by the distributed optical fiber temperature measurement system, and when the temperature drops below the preset threshold value and remains stable, the heating is stopped. If the temperature rises again, the cold compensation mechanism is triggered again until the temperature of the super-large pore area continuously meets the requirements. At the same time, the pore water pressure monitoring system can monitor the pore water pressure change of the frozen area throughout the process. If it is found that the pore water pressure of a certain area abnormally rises, it indicates that there may be an unfrozen seepage channel in the area. The problem area can be located in combination with the distributed optical fiber temperature data, and if the problem area is located between the coverage range of the main hole and the branch hole, the second refrigerant flow of the main hole or the phase change material cold compensation time of the branch hole can be adjusted for optimization, and if the problem area is a small local area, micro holes can be supplemented and low-temperature second refrigerant can be injected to solve the freezing problem of the area.

[0050] Preferably, during the second freezing stage, the integrity of the frozen curtain can be detected periodically by applying pressure to the outside of the frozen curtain through a pre-set detection hole and observing the feedback data of the pore water pressure monitoring system. If there is no significant fluctuation in pore water pressure after pressure application, it indicates that the frozen curtain is continuous and has sufficient impermeability. If there is abnormal fluctuation in pore water pressure, the curtain defect position needs to be located and targeted repair measures (such as additional branch hole cold supplement or additional micro-hole freezing) need to be taken. After the second freezing stage continues for a pre-set period of time, and the distributed optical fiber temperature measurement system shows that the temperature of each region of the frozen curtain is stable below the pre-set freezing temperature, the pore water pressure monitoring system shows that the pore water pressure in the whole region is stable in the low pressure range, and the curtain integrity detection is qualified, it is determined that the main curtain meets the design requirements, and the second freezing stage can be stopped and the subsequent tunneling construction link can be entered. During the entire phased freezing process, the ground control platform can store and analyze all monitoring data in real time, form a freezing process data report, provide a reference for subsequent similar projects, and at the same time ensure that the entire freezing process is traceable and controllable, fully adapts to the seepage characteristics of the large-grained high-permeability sand and gravel stratum, and effectively solves the problem of difficult freezing curtain intersection in this stratum.

[0051] Preferably, in order to realize safe deep station tunneling operation in large-grained high-permeability sand and gravel stratum and preset adaptive expansion capsules for subsequent thawing and sinking compensation, step S4 takes the continuous frozen curtain formed by phased freezing as a safety barrier, adopts a technical route of coordinated division excavation and immediate support, precise capsule pre-burying and steel arch support adaptation, ensures stratum stability and frozen curtain integrity during excavation, and provides reliable pre-burying position and working environment for adaptive expansion capsules.

[0052] Preferably, as Figure 5As shown, the excavation construction can adopt the sub-excavation method, and gradually advance according to the preset cycle length. After completing the excavation operation of one cycle, the excavation face is immediately protected temporarily to prevent the collapse of the loose sand and pebble stratum; then the initial support construction is carried out, the concrete of the preset type is sprayed to the excavation face to form the initial support structure, and after the initial support construction is completed, the quality acceptance can be carried out to check the thickness, flatness and adhesion of the concrete to the stratum, so as to ensure that the initial support can effectively transmit the stratum pressure. After the acceptance, according to the calibrated position in the three-dimensional pore model, the pre-buried hole position of the self-adapting expansion capsule is arranged at a preset interval between the initial support and the frozen curtain. Before the arrangement, the hole position can be calibrated by the laser positioning equipment to ensure that the hole position accurately matches the large pore and micro-fissure concentrated area, and provides targeted coverage for subsequent grouting compensation. Further, the self-adapting expansion capsule is folded and implanted into the pre-buried hole position, and all self-adapting expansion capsules are connected with the ground grouting system through the flexible connecting pipe. After the connection is completed, the sealing test of the connecting pipeline can be carried out (such as filling the gas or liquid with a preset pressure, and observing whether there is leakage), so as to avoid the leakage of slurry in the subsequent grouting process. Finally, the steel arch is erected, which can be reliably connected with the initial support structure, and a gap with a preset width is reserved between the steel arch and the self-adapting expansion capsule to prevent the self-adapting expansion capsule from being squeezed by the steel arch during installation or stress deformation, thereby affecting the subsequent expansion and grouting functions. After the steel arch is installed, the perpendicularity and stress state thereof can be detected to ensure that the steel arch can effectively share the stratum pressure, and together with the frozen curtain, the initial support and the self-adapting expansion capsule, forms a collaborative support system to ensure the stratum stability during the whole excavation construction.

[0053] Preferably, to realize the safe thawing of the large-particle high-permeability sand and pebble stratum after freezing, and at the same time accurately fill the pores (including large pores and micro-fissures) generated during the thawing process through self-adapting grouting, and solve the problem of incomplete thawing compensation, step S5 takes the pore water pressure monitoring and distributed optical fiber temperature measurement system as the core monitoring means, and carries out the operation according to the process of natural thawing monitoring, self-adapting grouting triggering, grouting process control and local grouting optimization, so as to ensure the smoothness of the thawing process and the accuracy of the grouting compensation.

[0054] Preferably, as Figure 6As shown, after the thawing operation is started, all frozen systems (main hole second refrigerant circulation, branch hole phase change material cooling, and micro hole first refrigerant supply) are stopped, and the natural thawing stage is entered. During the natural thawing process, the distributed optical fiber temperature measurement system can continuously monitor the formation temperature change, and the pore water pressure monitoring system can collect pore water pressure data of the thawing area in real time. Both data are synchronously transmitted to the ground control platform, and the ground control platform analyzes the data in real time to determine the thawing progress and pore development of the formation. When the monitoring data shows that the pore water pressure of the thawing area drops below the preset trigger threshold, it indicates that the formation has obvious pores, and the adaptive grouting operation can be started. According to the pore water pressure data of each area and the previous three-dimensional pore model, the ground control platform can divide the grouting priority, and preferentially grout the areas with high pore water pressure drop amplitude and high subsidence risk (such as super-large pore concentration areas and areas around key structures of stations). During grouting, the preset type of cement slurry is slowly injected into the adaptive inflatable bladder in the corresponding area through the flexible connecting pipe, and the preset type of cement slurry can be selected as low-viscosity ultra-fine cement slurry. During the grouting process, the pressure in the bladder and the slurry flow can be synchronously monitored by the pressure sensor built-in the bladder. When the pressure in the bladder reaches the preset stop threshold (matching the bearing capacity of the sandy pebbly formation to avoid the uplift of the formation), or the slurry flow drops to the preset minimum threshold (indicating that the bladder has been fully inflated and the slurry has seeped out to fill the surrounding pores through the micro holes of the bladder), the grouting of the bladder is automatically stopped. If the grouting of a certain area is completed, and the distributed optical fiber temperature measurement system still monitors that the area has a subsidence trend or the pore water pressure is continuously abnormal, local slurry supplementing can be performed on the area. When supplementing the slurry, a slurry type with faster setting speed can be selected, and the slurry is injected through the reserved channel of the adaptive inflatable bladder to quickly fill the residual pores. After the grouting of each area is completed, the pore filling effect can be detected by drilling core or radar detection to ensure that the grouting compensation is complete and there are no obvious unfilled pores.

[0055] It should be noted that the above specific embodiments are exemplary, and those skilled in the art can think of various solutions under the inspiration of the disclosure of the present application, and these solutions also belong to the disclosed range of the present application and fall within the protection scope of the present application. Those skilled in the art should understand that the specification and drawings of the present application are illustrative and not constitute a limitation on the claims. The protection scope of the present application is defined by the claims and their equivalents. The specification of the present application contains multiple inventive concepts, such as "preferably", "according to a preferred embodiment", or "optionally", which all indicate that the corresponding paragraph discloses an independent concept, and the applicant reserves the right to file a divisional application according to each inventive concept.

Claims

1. A deep station excavation construction method based on a frozen water stop technology, characterized in that, It comprises the following steps: S1, detecting the distribution density of pebbles and the location of super-large pores in the large-diameter high-permeability sand-pebble stratum, recording the particle size and arrangement direction of the pebbles in the stratum, and establishing a three-dimensional pore model of the stratum based on the detection and recording results; S2, using the follow-up pipe drilling technology to construct the main hole, extending the micro directional drilling machine from the main hole after the construction of the main hole is completed, and drilling into the super-large pore area and the micro crack area in the stratum respectively according to the three-dimensional pore model to construct the branch hole and the micro hole; S3, passing the first refrigerant into the micro hole for a predetermined time, until the temperature of the micro crack area is monitored by the distributed optical fiber to reach the preset freezing temperature to form a crack ice plug, and then passing the second refrigerant into the main hole for refrigeration until a frozen soil curtain with a thickness meeting the water stopping requirement is formed; S4, excavating the stratum corresponding to the main structure of the station, setting up the initial support after the excavation is completed, pre-burying the self-adapting expansion capsule between the initial support and the frozen soil curtain at a predetermined interval, and connecting the self-adapting expansion capsule with the ground grouting system through the flexible connecting pipe; S5, stopping the refrigeration operation of all freezing systems to make the frozen soil thaw naturally, and monitoring the stability of the stratum in the thawing area in real time through the pore water pressure sensor, when the pore water pressure in the thawing area is monitored to be reduced to a preset trigger threshold, slowly injecting the cement slurry of a predetermined type into the self-adapting expansion capsule through the flexible connecting pipe.

2. The construction method according to claim 1, characterized in that, In step S1, geological radar detection, borehole camera observation and borehole coring are combined to carry out stratum investigation to obtain the detection and recording results. During the geological radar detection, detection profiles are arranged along the longitudinal, transverse and oblique directions of the deep station underground excavation construction area. During the borehole camera observation, borehole camera observation holes are arranged in the key areas identified by the geological radar detection, and the characteristics of the pebbles, super-large pores and micro cracks are recorded by the borehole camera probe. During the borehole coring, borehole coring holes are arranged around the borehole camera observation holes to obtain complete stratum core samples for laboratory determination.

3. The construction method according to claim 1 or 2, characterized in that, In step S2, a directional geological drill adapted to the space of the underground excavation pilot hole is used to drill the main hole, and the follow-up pipe drilling technology uses the combination of pilot hole drilling and synchronous follow-up of the casing. The micro while-drilling measurement system is built-in the directional drill bit of the directional geological drill, which collects drilling angle, azimuth angle and depth data in real time and synchronously feeds back to the ground control platform through the signal transmission device. When the ground control platform monitors that the drilling posture appears a deflection trend due to the collision of large-diameter pebbles, the direction adjusting mechanism built-in the directional drill bit is automatically triggered to correct the drilling trajectory.

4. The construction method according to any one of claims 1 to 3, characterized in that, The composite wall protection liquid is continuously injected into the hole during the drilling process of the directional geological drill, which can form a temporary reinforced shell on the hole wall and be broken by physical means such as high-pressure fluid during subsequent branch hole branch construction. During the whole process of main hole construction, the ground control platform compares the real-time drilling data with the stratum parameters in the three-dimensional pore model, and when special stratum conditions are encountered, the drilling is temporarily stopped and the drilling parameters are optimized, and then the construction is resumed after the parameters are adjusted to adapt to the stratum characteristics.

5. The construction method according to any one of claims 1 to 4, characterized in that, In step S2, the folded hydraulic branch device in the folded state is conveyed to the preset branch position through the main hole drill pipe, the preset branch position is determined in combination with the main hole track calibrated by the previous micro-while-drilling system and the super-large pore distribution data in the three-dimensional pore model, after the folded hydraulic branch device reaches the target position, power is transmitted to the folded hydraulic branch device through the ground hydraulic pump station to drive the movable arm to unfold, so that the branch hole drill bit forms an angle with the main hole axis that matches the design of the frozen curtain, during branch hole drilling, the rock breaking element carried by the drill bit cooperates with the high-pressure fluid, the high-pressure fluid pre-scatters the loose sand particles on the drilling path, and the modified 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 implanted into the branch hole through the preset channel of the folded hydraulic branch device.

6. The construction method according to any one of claims 1 to 5, characterized in that, In step S2, a hose type micro drill is used when constructing the micro hole, the drill pipe of the hose type micro drill is made of flexible material; before construction, a channel corresponding to the preset micro hole position is opened on the branch hole freezing pipe, the hose type micro drill is slowly lowered to the preset drilling position in the branch hole through the channel, the front end of the hose type micro drill is equipped with an optical fiber type attitude sensor and an electromagnetic guide head, the optical fiber type 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 is coaxially arranged with the micro hole freezing pipe, and the micro hole freezing pipe follows the drill bit synchronously.

7. The construction method according to any one of claims 1 to 6, characterized in that, In step S3, the phased freezing includes a first freezing phase taking the micro hole as the core action unit and a second freezing phase taking the main hole and the branch hole as the core action units, wherein the first coolant for the first freezing phase is liquid nitrogen; the distributed optical fiber temperature measurement system arranged on the micro hole pipe wall and the surrounding stratum collects temperature data of the micro fissure area at preset intervals and transmits them to the ground control platform, when it is monitored that the temperature drops below the preset freezing temperature and lasts for a preset time length, the pore water pressure of the area is detected by the pore water pressure monitoring system; if the pore water pressure stabilizes in the preset low pressure range, it is determined that the first freezing phase achieves the expected effect and the second freezing phase is entered; the second coolant for the second freezing phase is salt water.

8. The construction method according to any one of claims 1 to 7, characterized in that, In the second freezing phase, the coolant circulation system of the main hole is equipped with a flow adjustment module, the second coolant flow is adjusted according to the temperature data fed back by the ground control platform; the temperature change of the super-large pore area is monitored by the distributed optical fiber temperature measurement system, when the temperature of the area is higher than the preset threshold, the phase change material cooling supplement mechanism of the branch hole is triggered, the preset heating element in the branch hole is heated to make the phase change material release the stored cold energy; the pore water pressure change of the frozen area is monitored by the pore water pressure monitoring system, when the pore water pressure of a certain area abnormally rises, the problem area is located in combination with the distributed optical fiber temperature data, if the problem area is located between the coverage ranges of the main hole and the branch hole, the main hole second coolant flow is adjusted or the branch hole phase change material cooling time is prolonged for optimization, if the problem area is a small local range, a micro hole is additionally drilled and low-temperature second coolant is injected to solve the freezing deficiency problem.

9. The construction method according to any one of claims 1 to 8, characterized in that, In step S4, the sub-excavation method is used for the underground excavation construction, and the excavation is gradually pushed forward according to the preset cycle length. After the excavation of one cycle is completed, the excavation face is temporarily protected. When the initial support is set, the concrete of a preset type is sprayed to the excavation face to form the initial support structure. Before the self-adapting expansion capsule is embedded, the laser positioning equipment is used to calibrate the embedded hole position, and the embedded hole position is arranged according to the calibrated position in the three-dimensional pore model to match the super-large pore and the micro-fissure concentrated area. When the steel arch is erected, the steel arch is connected with the initial support structure, and a gap with a preset width is reserved between the steel arch and the self-adapting expansion capsule.

10. The construction method according to any one of claims 1 to 9, characterized in that, In step S5, in the natural thawing stage, the distributed optical fiber temperature measurement system continuously monitors the change of the stratum temperature, the pore water pressure monitoring system collects the pore water pressure data of the thawing area in real time, and the data of the two is synchronously transmitted to the ground control platform. The ground control platform analyzes the data in real time to determine the thawing progress and the pore development of the stratum. When it is monitored that the pore water pressure of the thawing area is below the preset trigger threshold, it is determined that the stratum has obvious pores, and the self-adapting grouting operation is started. When the self-adapting grouting operation is started, the ground control platform divides the grouting priority according to the pore water pressure data of each area and the three-dimensional pore model, and grouting is preferentially performed on the area with a large pore water pressure drop and a high subsidence risk.

Images