Construction method of underground continuous wall joint water stop

Abstract

The application provides a diaphragm wall joint water stop construction method, and relates to the technical field of underground engineering construction, which comprises the following steps: drilling a grouting hole to the bottom of the diaphragm wall on the inner side of the joint, injecting slurry into the joint gap to establish a first water stop barrier; before the initial setting of the slurry, the grouting hole is re-drilled and swept, and the re-drilled hole is reused as a temperature measuring hole; a freezing pipe hole is drilled in the soil on the outer side of the joint, the freezing pipe is installed and connected to a freezing system, the freezing system is started to freeze the soil on the outer side of the joint, and a second water stop barrier is formed; the freezing effect is monitored by using the temperature measuring hole, and the timing of foundation pit excavation and the operating parameters of the freezing system are controlled according to the monitoring data. The application constructs a double water stop guarantee by series connection of grouting and freezing inside and outside, and the water stop reliability is significantly improved. The freezing pipe is installed by using the post-drilling method, and the construction flexibility is greatly improved. The three-stage dynamic operation of the freezing system takes into account safety and economy.

Description

Technical Field

[0001] This invention relates to the field of underground engineering construction technology, specifically to a method for water-stopping construction of joints in underground continuous walls. Background Technology

[0002] Diaphragm walls are one of the most commonly used retaining structures in deep foundation pit engineering, widely applied in projects such as subway stations, large shafts, and underground utility tunnels. Because diaphragm walls require segmented construction, construction joints are unavoidable between adjacent segments. These joints are the weakest points in the waterproofing of the diaphragm wall, and leakage, even water and sand inrush, can easily occur here during foundation pit excavation, seriously threatening the safety of the foundation pit and the surrounding environment.

[0003] Currently, for the water-stopping treatment of diaphragm wall joints, engineering projects often use mixing piles or jet grouting piles to reinforce the soil outside the joint, or inject cement grout into the joint to fill the gaps. However, it is difficult to ensure a tight fit between the reinforced body and the diaphragm wall, which can easily form water-permeable channels; the diffusion range of the grout is affected by geological conditions, and the reliability of the water-stopping effect is limited.

[0004] Freezing has also been introduced into the field of joint sealing in diaphragm walls. In existing technologies, freezing pipes must be pre-embedded and tied to the reinforcing cage before the diaphragm wall is poured, and then lowered into place with the cage. Freezing is activated after the diaphragm wall reaches its design strength, forming a frozen soil water-stop curtain. This type of solution has the following common problems: the installation of freezing pipes is highly coupled with the main structure construction process, and the pipes are at risk of being squeezed, deformed, blocked, or displaced during concrete pouring; the pre-embedding scheme requires all joints to be arranged at once, making it impossible to differentiate treatment based on the actual leakage risk of each joint after completion, resulting in a large amount of ineffective investment, and the position and quantity of pipes cannot be adjusted after construction; as the only water-stopping method, freezing completely fails once the system malfunctions, lacking redundancy; the freezing system operates in a one-time, extensive mode of "starting up to meet standards," without dynamic control for different stages and risk levels throughout the entire excavation process, resulting in high energy consumption and insufficient emergency response capabilities.

[0005] Chinese patent document CN102409691A discloses a freezing method water-stopping device for pre-embedding freezing pipes at the opening of a diaphragm wall. It discloses a technical solution that pre-embedding annular freezing pipes in the diaphragm wall near the soil, and freezing the soil at the interface between the wall and the reinforced body below the freezing point through refrigerant circulation. This solution achieves the technical effect of sealing the water-permeable channel at the wall opening and ensuring the smooth progress of soil excavation. However, it still has problems such as the freezing pipes needing to be pre-embedded with the reinforcing cage, strong coupling with the main structure construction process, single water-stopping method with a lack of redundancy, and inability to differentiate treatment for the actual risks of the joints.

[0006] Chinese patent document CN109505295A discloses a freezing construction process for water-stopping joints of underground continuous walls. It discloses a technical solution in which freezing pipes and temperature measuring pipes are simultaneously placed at the corners of the joint along with the reinforcing cage. The joint soil is frozen by circulating salt water, and the temperature is measured simultaneously. The freezing effect is judged according to quantitative parameters. This solution has the technical effect of expanding the water-stopping range and effectively controlling the water and sand inflow in the joint. However, it still has problems such as the high coupling between pipe installation and main structure construction, the lack of redundant protection due to the freezing method as the only water-stopping means, the freezing system adopting a one-time start-up mode and being unable to dynamically control the entire process of foundation pit excavation in stages, and the lack of rapid emergency response capability in the event of sudden leakage. Summary of the Invention

[0007] The purpose of this invention is to provide a construction method for sealing the joints of underground continuous walls that features high reliability in water sealing, flexible construction procedures, and dynamically adjustable refrigeration systems.

[0008] Terminology Explanation: Unless otherwise defined, all technical terms in this document have the same meanings as commonly understood by one of ordinary skill in the art to which the subject matter of the claims pertains. Unless otherwise stated, all patents, patent inventions, and publications cited in this document are incorporated herein by reference in their entirety. If multiple definitions exist for terms in this document, the definitions in this chapter shall prevail.

[0009] It should be understood that the above brief description and the following detailed description are exemplary and for illustrative purposes only, and do not limit the subject matter of the invention in any way. In this invention, the singular is used in conjunction with the plural unless otherwise specifically stated. It should also be noted that, unless otherwise stated, the use of “or” or “or” means “and / or”. Furthermore, the use of the term “comprising” and other forms such as “including,” “containing,” and “contains” are not limiting.

[0010] Unless specifically defined herein, the use of various commercially available products herein employs standard techniques, or is carried out in accordance with methods known in the art or the description of this invention. The techniques and methods described herein can generally be implemented according to conventional methods well known in the art, based on the descriptions in the various summary and more specific documents cited and discussed in this specification.

[0011] The term "joint" used in this article refers to the unavoidable construction interface between adjacent concrete sections during the construction of a diaphragm wall, which is the weakest link in the waterproofing of the diaphragm wall.

[0012] The term "second-order trench" used in this article refers to the trench section constructed later in the construction of a diaphragm wall, which is connected to the first-order trench constructed earlier by interlocking H-beam joints.

[0013] The term "I-beam joint" as used in this article refers to a steel connecting member with an I-shaped cross-section installed between adjacent trench sections to locate the joint position of adjacent trench sections and transfer shear force.

[0014] The term "first water-stopping barrier" used in this article refers to a permanent filling and sealing layer formed on the joint surface by injecting grout into the joint gaps, which prevents groundwater from entering the foundation pit from the outlet end of the leakage path.

[0015] The term "second water-stopping barrier" used in this article refers to a frozen soil water-stopping curtain formed by freezing pore water in the soil outside the joint through a freezing system, which then cements the water with the soil, thus cutting off the source of groundwater recharge from the inlet end of the seepage path.

[0016] The term "re-drilling and cleaning" used in this article refers to the construction operation of drilling along the original grouting hole channel again after grouting is completed and before the grout has initially set, in order to remove residual grout from the hole and keep the channel unobstructed.

[0017] The term "frost extension radius" used in this article refers to the maximum radius that the frozen area of ​​the soil can extend outward from a single freezing pipe within the designed freezing time. It depends on the temperature of the refrigerant, the thermophysical parameters of the soil, and the duration of freezing.

[0018] The term "safety overlap" used in this article refers to the thickness of the frozen soil overlap reserved to ensure the reliable closure of the frozen soil columns formed by adjacent freezing pipes, in order to offset the effects of construction deviations and the inhomogeneity of soil thermophysical parameters.

[0019] The term "maintenance mode" used in this article refers to the operating state in which the refrigeration system reduces its cooling output and maintains the stable existence of the frozen soil curtain with minimal energy consumption after the frozen soil curtain has reached its design requirements.

[0020] The term "enhanced freezing mode" used in this article refers to an emergency operating state in which, when a sudden leak occurs at a joint, the corresponding freezing pipeline in the leak area is subjected to maximum concentrated cold output to quickly form an ice plug in the leak channel.

[0021] The term "brine return loop" used in this article refers to: brine return path from the chiller unit outlet to the freezer inlet, and brine return loop from the freezer outlet back to the chiller unit.

[0022] To achieve the above objectives, the present invention provides the following technical solution: A method for constructing a waterproof joint in a diaphragm wall includes the following steps: S1: After the construction of the diaphragm wall is completed, grouting holes are drilled inside the joints to the bottom of the diaphragm wall. Grout is injected into the joint gaps through the grouting holes to establish the first water-stop barrier. S2: Before the grout initially sets, the grouting hole is re-drilled and cleaned to remove residual grout in the hole, and the re-drilled hole is reused as a temperature measuring hole. S3: Drill freezing pipe holes in the soil outside the joint, install freezing pipes in the freezing pipe holes, connect the freezing pipes to the freezing system, start the freezing system to freeze the soil outside the joint, and form a second water-stop barrier. S4: Use temperature measuring holes to monitor the freezing effect, and control the timing of foundation pit excavation and the operating parameters of the freezing system based on the monitoring data.

[0023] Furthermore: In S1, the grouting hole is located near the I-beam joint in the second-order trench, and the borehole diameter is 90-130mm; the grouting adopts a segmented grouting method, grouting is carried out segment by segment from the bottom of the hole to the opening, and the grouting pressure is 0.5-2.0MPa.

[0024] Furthermore: In S1, the grout is cement grout or cement-water glass two-component grout.

[0025] Furthermore: In S2, re-drilling is carried out within 2 to 6 hours after grouting is completed; during the re-drilling process, the drilling resistance at different depths is recorded, and when the drilling resistance at a certain depth is lower than the preset threshold, grouting is added to that depth.

[0026] Furthermore: In S3, the freezing pipe holes are located in the soil 0.3 to 0.8 m outside the outer wall of the continuous wall. The spacing L between adjacent freezing pipe holes along the joint direction satisfies: L≤2R-Δ, where R is the radius of frozen soil expansion of a single freezing pipe within the design freezing time, and Δ is the safe overlap amount, which is taken as 0.2 to 0.3 m.

[0027] Furthermore: In S3, the refrigeration system includes a refrigeration unit, a cooling tower, and a brine pump. The three are interconnected through pipelines to form a brine circulation loop. The refrigerant is brine. After being cooled by the refrigeration unit, the brine is driven by the brine pump to circulate through the freezing pipe, exchange heat with the surrounding soil, and then return to the refrigeration unit. The brine temperature is set to -28℃ to -30℃.

[0028] Furthermore, in S4, the refrigeration system operates in the following three stages: Before the excavation of the foundation pit, the refrigeration system operates at full power until the thickness of the frozen soil wall reaches the design value, the average temperature of the frozen soil body is ≤-10℃, the temperature difference between the brine return loop (the brine return loop is from the outlet of the refrigeration unit to the inlet of the freezing pipe, and the return loop is from the outlet of the freezing pipe back to the refrigeration unit) is ≤2℃ and the temperature of the temperature measuring hole is ≤-5℃; During the excavation of the foundation pit, the refrigeration system switches to maintenance mode, dynamically adjusting the refrigerant temperature and flow rate according to the actual temperature measured by the temperature measuring hole to maintain the stability of the frozen soil curtain (i.e., the second water-stop barrier) formed in S3; When the temperature of any temperature measuring hole rises by more than 3℃ within 24 hours, or rises to above -3℃, it is judged as an abnormal rise, and the freezing pipe in the corresponding area is switched to enhanced freezing mode, the refrigerant temperature is reduced to -28℃~-30℃, and the flow rate is increased to the maximum, and the maintenance mode is restored after the danger is controlled.

[0029] Furthermore: After the enhanced freezing mode ends, grouting is carried out on the leaking area under the freezing protection state. After the grouting is completed, the freezing system resumes operation in the maintenance mode.

[0030] Furthermore, prior to S1, a step of assessing the leakage risk of each joint is included. This risk assessment is determined based on a comprehensive analysis of the joint density obtained through ultrasonic testing, the permeability coefficient of the stratum where the joint is located, and the groundwater pressure. A high-risk condition is defined as any of the following: ultrasonic testing shows obvious voids or defects in the joint; or the permeability coefficient of the stratum is greater than 1×10⁻⁶. -4 The risk level is determined by the following criteria: m / s or groundwater head is more than 5m above the bottom of the diaphragm wall; otherwise, it is considered low risk. For joints assessed as high risk, all steps S1 to S4 are performed, while for joints assessed as low risk, only steps S1 and S2 are performed.

[0031] Furthermore: In S2, a temperature measuring tube is installed inside the temperature measuring hole. The temperature measuring tube consists of an outer tube and an internal temperature sensor. Clean water circulates inside the outer tube, and the temperature sensor collects the temperature data inside the hole in real time. The temperature measuring hole is located between the first and second water-stop barriers and is used to determine the closure status of the two barriers. In S3, S1 and S2 are completed before drilling the freezing pipe hole in the soil outside the joint. The grouting hole and the freezing pipe hole are arranged correspondingly inside and outside along the joint direction. The grouting hole is located inside the joint, and the freezing pipe hole is located outside the joint.

[0032] Compared with the prior art, the present invention has the following advantages: I. This invention employs a dual-barrier system, significantly improving the reliability of water-stopping. Grouting and freezing are independently implemented at the outlet and inlet ends of the joint leakage path, respectively, forming a series-connected dual-protection system. The two barriers are complementary rather than substitutive; if one barrier fails partially, the other can still maintain its water-stopping function. This effectively solves the reliability defects of existing technologies that rely solely on freezing as the only water-stopping method, resulting in complete system failure upon system malfunction. This is particularly advantageous under high water pressure and complex geological conditions.

[0033] Second, this invention adopts post-drilling installation, achieving decoupling of construction procedures. The frozen pipelines are independently installed via post-drilling after the main structure of the diaphragm wall is completed. The location, quantity, and depth of the pipelines can be flexibly determined based on the actual condition of each joint after completion, eliminating the risks of interference between pipelines and rebar cage binding construction in pre-embedded schemes, and the risk of pipeline damage during concrete pouring. Simultaneously, it allows for differentiated treatment of joints with different risk levels, avoiding the ineffective investment of "burying every joint."

[0034] Third, this invention adopts a three-stage operation control, balancing safety and economy. The refrigeration system operates differently in three stages: pre-freezing, maintaining freezing, and emergency response. It uses closed-loop feedback of temperature measurement data to adjust the cooling output, avoiding continuous full-power operation while maintaining the stability of the frozen soil curtain, thus reducing total energy consumption by approximately 40%. In the event of a sudden leak, the pre-installed freezing pipeline can immediately switch to enhanced freezing mode for emergency sealing, eliminating the need for temporary construction of new water-stopping facilities. This effectively solves the problems of extensive operation, lack of dynamic control throughout the entire process, and inadequate emergency response capabilities in existing refrigeration systems. Attached Figure Description

[0035] Figure 1 The flowchart of a method for constructing a water-stopping joint in a diaphragm wall provided by the present invention is shown. Detailed Implementation

[0036] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all instruments, devices, equipment, reagents, products, etc., used in the embodiments of the present invention are obtained through conventional commercial means.

[0038] Unless otherwise stated, conventional methods within the scope of the art shall be used.

[0039] Example 1 like Figure 1As shown: This invention provides a method for constructing a water-stopping system at the joint of a diaphragm wall. After the diaphragm wall is constructed in sections, grouting holes are first drilled inside the joint to the bottom of the diaphragm wall. Grout is injected under high pressure into the joint gaps through the grouting holes. After the grout solidifies, it forms a permanent filling layer on the joint surface, establishing the first water-stopping barrier. Before the grout initially sets, the grouting holes are re-drilled and cleaned to remove residual grout and keep the channels unobstructed. The re-drilled channels are then reused as temperature measuring holes. Freezing pipe holes are drilled separately in the soil outside the joint. Freezing pipes are installed in the holes and connected to a freezing system. After activation, the pore water in the soil outside the joint freezes into ice, forming a frozen soil water-stopping curtain, establishing the second water-stopping barrier. The freezing effect is continuously monitored using the temperature measuring holes. The timing of the foundation pit excavation is determined based on the monitoring data, and the operating parameters of the freezing system are dynamically adjusted.

[0040] The core logic of the above scheme is as follows: grouting provides normal water-stopping function, sealing the outlet end of the leakage path; freezing provides emergency reinforcement function, cutting off groundwater recharge from the inlet end of the leakage path; the two barriers are connected in series spatially, so that if either barrier fails partially, the other barrier can still independently maintain water-stopping, making the system's reliability significantly better than a single water-stopping scheme. The frozen pipeline is installed independently after the diaphragm wall construction is completed, completely decoupled from the main structure construction process, eliminating the risk of pipeline deformation or displacement caused by compression in the pre-embedded scheme.

[0041] In one specific embodiment of this example, the grouting hole is located near the I-beam joint in the second-order trench. The borehole diameter is 90–130 mm. After the grouting pipe is lowered to the bottom of the hole, it is raised segment by segment from the bottom to the opening using a segmented grouting method. The grouting pressure is controlled between 0.5 and 2.0 MPa. Segmented grouting ensures that the grout is evenly distributed along the entire depth of the joint surface, avoiding localized leakage. The grouting pressure is determined based on the joint depth and groundwater pressure. The grouting is stopped when the grouting pressure reaches the design final pressure or the grouting volume reaches the design value.

[0042] In one specific embodiment of this example, the injected grout is either cement grout or cement-water glass two-component grout. The initial setting time of cement-water glass two-component grout is controllable, making it suitable for situations with strict requirements on setting time. Both can be flexibly selected based on geological conditions and site temperature.

[0043] In one specific embodiment of this example, re-drilling is performed within 2 to 6 hours after grouting is completed. Controlling this time window is crucial: re-drilling too early can lead to grout backflow and grouting failure; re-drilling too late will result in hardened grout, making the borehole unusable. During re-drilling, the drilling resistance at different depths is recorded. A significant increase in resistance indicates that the grouting in that section is densely filled; resistance similar to that during the original drilling indicates poor grouting performance, requiring additional grouting at that depth. This indirectly verifies the grouting quality.

[0044] In one specific embodiment of this example, the freezing pipe holes are located in the soil 0.3–0.8 m outside the outer wall of the continuous wall. The spacing L between adjacent freezing pipe holes along the joint direction satisfies L ≤ 2R - Δ, where R is the radius of frozen soil expansion of a single freezing pipe within the designed freezing time, and Δ is the safe overlap amount, taken as 0.2–0.3 m. By controlling the spacing according to this formula, it can be ensured that the frozen soil columns formed by adjacent freezing pipes interlock within the designed freezing time, forming a continuous and closed frozen soil curtain.

[0045] In one specific embodiment of this invention, the refrigeration system consists of a refrigeration unit, a cooling tower, and a brine pump. The refrigerant is brine, and the brine temperature is set to -28℃ to -30℃. After being cooled by the refrigeration unit, the brine is driven by the brine pump into the freezing pipe, where it exchanges heat with the surrounding soil before returning to the refrigeration unit for circulation.

[0046] In one specific embodiment of this example, the refrigeration system operates in three differentiated stages. Before excavation, a pre-freezing stage is implemented, during which the refrigeration system operates at full power. The comprehensive criteria for curtain closure are: temperature at the temperature measuring holes ≤ -5℃, average temperature of the frozen soil ≤ -10℃, temperature difference between the brine return path (from the refrigeration unit outlet to the freezing pipe inlet, and from the freezing pipe outlet back to the refrigeration unit) ≤ 2℃, and the frozen soil wall thickness reaching the design value. Excavation can only begin after these conditions are met. During excavation, the system switches to maintenance mode, dynamically adjusting the refrigerant temperature and flow rate based on measured data from the temperature measuring holes. As long as the temperature at each measuring point remains below the design limit and shows no upward trend, the current parameters are maintained; if the temperature slowly rises, the cooling output is appropriately increased. If the temperature at any temperature measuring hole rises by more than 3°C or above -3°C within 24 hours, it is considered an abnormal rise, indicating that the grouting body at that location may have partially failed. The corresponding area's freezing pipeline is immediately switched to enhanced freezing mode, with the refrigerant temperature lowered to -28°C to -30°C and the flow rate increased to maximum. This quickly forms an ice plug in the leakage channel, blocking the leakage flow. Once the situation is under control, the maintenance mode is restored. This three-stage operation strategy uses temperature measurement data as feedback, avoiding continuous full-power operation of the refrigeration system while ensuring safety, significantly reducing energy consumption and operating costs.

[0047] In one specific embodiment of this example, after the enhanced freezing mode controls the leakage, grouting is performed on the leaking area under frozen protection to repair local defects at the joint surface. After the grouting is completed, the freezing system resumes operation in maintenance mode. The frozen state provides a stable construction environment for the grouting, and the two work together to achieve permanent repair of sudden emergencies.

[0048] In one specific embodiment of this example, a leakage risk assessment is conducted on each joint before grouting. Joints assessed as high-risk undergo a complete process of grouting and sealing, re-drilling for temperature measurement, freezing, and full-process monitoring. Joints assessed as low-risk only undergo grouting and sealing and re-drilling for cleaning. This risk-based approach avoids indiscriminately applying the entire set of procedures to all joints, saving on project costs.

[0049] In one specific embodiment of this example, a temperature measuring tube is installed inside the temperature measuring hole. The temperature measuring tube consists of an outer tube and an internal temperature sensor. Clean water circulates inside the outer tube, and the temperature sensor collects the temperature data inside the hole in real time. The temperature measuring hole is a reused grouting hole, located in the boundary area between the first water-stopping barrier (grouting body) and the second water-stopping barrier (frozen soil curtain). It can directly reflect the closure status of the two barriers: if the temperature of the temperature measuring hole continues to drop and stabilizes, it indicates that the frozen soil has expanded to the joint surface and the double barrier is closed; if the temperature at a certain depth does not drop to the design value, it indicates that there are defects in the grouting body or frozen soil at that location, and reinforcement measures need to be taken; if the temperature suddenly rises during operation, it can serve as an early warning signal for groundwater penetration of the grouting layer. The same borehole successively serves three functions: grouting channel, grouting effect inspection channel, and temperature monitoring channel, reducing the total number of boreholes and minimizing disturbance to the continuous wall. Grouting holes and freezing pipes are arranged correspondingly inside and outside the joint, with the grouting holes located inside (on the pit side of the joint) and the freezing pipes outside (on the soil side of the joint). Both block the leakage path from both the outlet and inlet ends, forming a coordinated "inner grouting, outer freezing" protection pattern. The construction sequence involves completing the inner grouting and re-drilling first, followed by the construction of the outer freezing pipes. This is because grouting must be carried out at room temperature in the joint gaps to ensure the fluidity of the grout; if freezing occurs first, the frozen soil will hinder the penetration and diffusion of the grout.

[0050] Example 2 The following example, a deep foundation pit project for a subway station in a certain city, illustrates the specific implementation process of this invention. The foundation pit was excavated to a depth of 22m. A 1000mm thick, 35m deep underground continuous wall was used as the retaining structure. The project was divided into 28 sections with 27 joints, using I-beam joints. The groundwater level in the foundation pit area was high, and the pressure head was large, resulting in a high risk of leakage at the joints.

[0051] After the diaphragm wall construction was completed, ultrasonic testing and leakage risk assessment were conducted on 27 joints. Based on the joint density determined by ultrasonic testing, the permeability coefficient of the stratum where the joint is located, and the groundwater pressure, the results showed that 12 joints had obvious defects or were located in highly permeable strata with high groundwater head, and were therefore classified as high-risk; the remaining 15 joints did not reach the high-risk threshold in any of the indicators and were classified as low-risk. The 12 high-risk joints underwent a complete dual-protection treatment of grouting and freezing, while the 15 low-risk joints only underwent grouting treatment.

[0052] During the grouting construction phase, grouting holes with a diameter of 110mm and a depth of 35m to the bottom of the diaphragm wall were drilled near the I-beams in the secondary trenches of each treatment joint. Cement-water glass dual-liquid grout was used for segmented grouting at a pressure of 0.8–1.5 MPa. Within 3 hours after grouting (the initial setting time of the dual-liquid grout is approximately 4 hours), the holes were re-drilled using a 100mm drill bit to clean them. The drilling resistance at each depth was recorded, and sections with abnormally low resistance were supplemented with grout. After re-drilling, a temperature sensor was installed inside the hole to convert the grouting hole into a temperature measuring hole.

[0053] For 12 high-risk joints, freezing pipe holes with a diameter of 130mm and a depth of 35m were drilled in the soil outside each joint, 0.5m from the outer wall of the continuous wall. One hole was drilled every 1.0m along the joint direction, with 3-5 holes drilled per joint. Freezing pipes were installed inside the holes and led to the ground for connection to the freezing unit. During the pre-freezing phase, the freezing system operated at full power for 15 days. The brine temperature reached -28℃, and the temperature at each temperature measuring hole dropped below -8℃. The estimated thickness of the frozen soil wall reached 2.2m, indicating curtain closure and readiness for excavation. Compared to the pure freezing scheme (designed frozen soil wall thickness 2.6m, pre-freezing time 35 days), the freezing design parameters were reduced and the pre-freezing period was shortened because the grouting body already served as the first barrier.

[0054] During the excavation of the foundation pit, the brine temperature was adjusted to -22℃, and the flow rate was reduced to 60% of the pre-freezing stage. The temperature of each temperature measuring hole was stabilized between -6℃ and -10℃. When the excavation reached -18m, the temperature of a temperature measuring hole at a certain joint abnormally rose from -7℃ to -2℃. At the same time, water seepage appeared on the inner wall of the foundation pit at this location. The enhanced freezing mode for the corresponding three freezing pipes was immediately activated, the brine temperature was reduced to -30℃, and the flow rate was increased to 100%. After 12 hours of enhanced freezing, the seepage stopped, and the temperature of the temperature measuring hole dropped back below -6℃. Subsequently, grouting was performed to repair the area under freeze protection. After the repair was completed, the maintenance mode was restored.

[0055] During the entire excavation of the foundation pit, only one of the 27 joints experienced leakage, which was promptly controlled, demonstrating significantly better water-stopping reliability than similar projects. The phased operation of the freezing system reduced the total energy consumption by approximately 40% compared to the full-power operation scheme.

[0056] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for constructing a water-stopping joint in a diaphragm wall, characterized in that, Includes the following steps: S1: After the construction of the diaphragm wall is completed, grouting holes are drilled inside the joint to the bottom of the diaphragm wall. Grout is injected into the joint gap through the grouting holes to establish the first water-stop barrier. S2: Before the grout initially sets, the grouting hole is re-drilled and cleaned to remove residual grout in the hole, and the re-drilled hole is reused as a temperature measuring hole. S3: Drill freezing pipe holes in the soil outside the joint, install freezing pipes in the freezing pipe holes, connect the freezing pipes to the freezing system, start the freezing system to freeze the soil outside the joint, and form a second water-stop barrier. S4: Use temperature measuring holes to monitor the freezing effect, and control the timing of foundation pit excavation and the operating parameters of the freezing system based on the monitoring data.

2. The method for constructing a water-stopping joint in a diaphragm wall according to claim 1, characterized in that: In S1, the grouting hole is located near the I-beam joint in the second-order trench, and the hole diameter is 90-130mm. The grouting adopts a segmented grouting method, and the grouting is carried out segment by segment from the bottom of the hole to the opening of the hole. The grouting pressure is 0.5-2.0MPa.

3. The method for constructing a water-stopping joint in a diaphragm wall according to claim 1, characterized in that: In S1, the slurry is cement slurry or cement-water glass two-component slurry.

4. The method for constructing a water-stopping joint in a diaphragm wall according to claim 1, characterized in that: In S2, re-drilling is carried out within 2 to 6 hours after grouting is completed; during the re-drilling process, the drilling resistance at different depths is recorded, and when the drilling resistance at a certain depth is lower than a preset threshold, grouting is added to that depth.

5. The method for constructing a water-stopping joint in a diaphragm wall according to claim 1, characterized in that: In S3, the freezing pipe hole is located in the soil 0.3 to 0.8m outside the outer wall of the continuous wall. The spacing L between adjacent freezing pipe holes along the joint direction satisfies: L≤2R-Δ, where R is the radius of frozen soil expansion of a single freezing pipe within the designed freezing time, and Δ is the safe overlap amount, which is 0.2 to 0.3m.

6. The method for constructing a water-stopping joint in a diaphragm wall according to claim 1, characterized in that: In S3, the refrigeration system includes a refrigeration unit, a cooling tower, and a brine pump. The three are interconnected through pipelines to form a brine circulation loop. The refrigerant is brine. After being cooled by the refrigeration unit, the brine is driven by the brine pump to circulate through the freezing pipe, exchange heat with the surrounding soil, and then return to the refrigeration unit. The brine temperature is set to -28℃ to -30℃.

7. The method for constructing a water-stopping joint in a diaphragm wall according to claim 1, characterized in that: In S4, the refrigeration system operates in the following three stages: Before the foundation pit is excavated, the refrigeration system runs at full power until the thickness of the frozen soil wall reaches the design value, the average temperature of the frozen soil body is ≤-10℃, the temperature difference between the brine and the return loop is ≤2℃ and the temperature of the temperature measuring hole is ≤-5℃. During the excavation of the foundation pit, the refrigeration system was switched to maintenance mode, and the refrigerant temperature and flow rate were dynamically adjusted according to the actual temperature measured by the temperature measuring hole to maintain the stability of the second water-stop barrier formed in S3. If the temperature of any temperature measuring hole rises by more than 3°C or rises above -3°C within 24 hours, it is determined to be an abnormal rise. The freezing pipeline in the corresponding area will be switched to enhanced freezing mode, the refrigerant temperature will be reduced to -28°C to -30°C, and the flow rate will be increased to the maximum. After the emergency is under control, the maintenance mode will be restored.

8. A method for constructing a water-stopping joint in a diaphragm wall according to claim 7, characterized in that: After the enhanced freezing mode ends, grouting is performed on the leaking area under the freezing protection state. After the grouting is completed, the freezing system resumes operation in the maintenance mode.

9. A method for constructing a water-stopping joint in a diaphragm wall according to claim 1, characterized in that: Before S1, there is also a step of assessing the leakage risk of each joint, which is determined based on the ultrasonic testing of the joint density, the permeability coefficient of the stratum where the joint is located, and the groundwater pressure. The following conditions are considered high-risk: ultrasonic testing shows obvious voids or defects in the joint; or the permeability coefficient of the stratum is greater than 1×10⁻⁶. -4 The risk level is determined by the following criteria: m / s or groundwater head is more than 5m above the bottom of the diaphragm wall; otherwise, it is considered low risk. For joints assessed as high risk, all steps S1 to S4 are performed, while for joints assessed as low risk, only steps S1 and S2 are performed.

10. A method for constructing a water-stopping joint in a diaphragm wall according to claim 1, characterized in that: In S2, a temperature measuring tube is installed inside the temperature measuring hole. The temperature measuring tube consists of an outer tube and an internal temperature sensor. Clean water circulates inside the outer tube, and the temperature sensor collects the temperature data inside the hole in real time. The temperature measuring hole is located between the first water-stop barrier and the second water-stop barrier and is used to determine the closure status of the two barriers. In S3, before drilling freezing pipe holes in the soil outside the joint, S1 and S2 are completed first; the grouting holes and freezing pipe holes are arranged correspondingly inside and outside along the joint direction, with the grouting holes located inside the joint and the freezing pipe holes located outside the joint.

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