Freezing construction method and equipment for constructing structures in strata

Abstract

The present application discloses a freezing construction method and equipment for constructing a structure in a formation. The freezing construction method includes the following steps: pre-cooling the area of the freezing wall of the structure to be constructed with freezing equipment; draining water from the formation around the freezing wall with a vacuum drainage device during the pre-cooling stage; actively freezing the freezing wall with the freezing equipment after the pre-cooling stage; continuously draining water from the formation around the freezing wall with the vacuum drainage device during the active freezing stage; and constructing a structure in the freezing wall during the maintenance freezing stage of maintaining the temperature of the freezing wall after the active freezing stage; wherein the freezing equipment includes freezing pipes and a working medium supply device, and the vacuum drainage device includes a vacuum pump and a drainage channel. The freezing construction method and equipment of the present application can effectively control the frost heave deformation of the formation during freezing construction.

Description

Technical Field

[0001] The present application relates to the construction of structures in strata, and more particularly, to a freezing construction method and equipment for constructing structures in strata. Background Art

[0002] In modern society, it has become very common to construct structures in strata. For example, subways, underground transportation pipelines, underground cables and optical cables, and buildings in strata. Constructing structures in strata requires the stratum soil to have sufficient stability so that the project can be carried out while ensuring construction safety. Since not all strata where structures are to be constructed have suitable stability, engineers use various methods to reinforce the stratum soil before the project starts. The stratum freezing method is a widely used method for reinforcing stratum soil at present and is suitable for soil reinforcement in water-rich strata with abundant water content. In recent years, with the continuous deepening of underground structures and the increasingly complex construction environment, the application of the stratum freezing reinforcement method has become more and more extensive.

[0003] The stratum freezing method refers to a construction method in which, before constructing an underground structure, the water-bearing stratum around the structure to be constructed is frozen by an artificial refrigeration method to form a freezing wall with temporary load-bearing and water-blocking functions and meeting the safety requirements of engineering construction, and then the excavation and lining operation of the structure is carried out with the support and protection of the freezing wall. The stratum freezing method for reinforcing strata has the advantages of high reinforcement strength, good water-blocking property, strong adaptability, and no pollution. However, the stratum freezing method causes frost heave deformation of the freezing wall, resulting in deformation of the overlying stratum of the freezing wall, which may damage underground pipelines and road foundations. Therefore, it is very important to control frost heave deformation while using the freezing method for construction. Summary of the Invention

[0004] The purpose of the present application is to provide a freezing construction method and equipment for constructing structures in strata that can effectively control stratum frost heave deformation.

[0005] To achieve the above purpose, according to the first aspect of the present application, a freezing construction method for constructing a structure in strata is proposed, including the following steps:

[0006] a. Pre-cooling the area of the freezing wall of the structure to be constructed with a freezing device;

[0007] b. During the pre-cooling stage, draining water from the stratum around the freezing wall with a vacuum drainage device;

[0008] c. After the pre-cooling stage, actively freezing the freezing wall with a freezing device;

[0009] d. During the active freezing stage, continuing to drain water from the stratum around the freezing wall with a vacuum drainage device;

[0010] e. After the active freezing stage, during the maintenance freezing stage of maintaining the temperature of the frozen wall, construct a structure within the frozen wall;

[0011] Wherein, the freezing equipment includes: a plurality of freezing pipes arranged within the frozen wall, and a working fluid supply device fluidly connected to the freezing pipes, the working fluid supply device supplying a freezing working fluid to the freezing pipes and circulating the freezing working fluid within the freezing pipes; and

[0012] The vacuum drainage equipment includes: a vacuum pump arranged above the formation or within other structures already constructed within the formation; drainage channels arranged in the formation intersecting or parallel to each other, one end of the drainage channels leading to the vacuum pump, and the other end extending into the formation around the frozen wall.

[0013] Optionally, the temperature of the freezing working fluid is set to: 0 - 1 °C during the pre-cooling stage, - 30 - - 35 °C during the active freezing stage, and - 20 - - 25 °C during the maintenance freezing stage.

[0014] Optionally, monitor the frost heave deformation of the formation in real time. If the amount of frost heave deformation is within a predetermined threshold, set the working pressure of the vacuum pump to be above 80 kPa; if the amount of frost heave deformation exceeds the predetermined threshold, during the active freezing stage, increase the working pressure of the vacuum pump to 120 - 160 kPa, and / or during the maintenance freezing stage, start the vacuum pump to drain water from the frozen wall.

[0015] Optionally, the predetermined threshold for frost heave deformation is that the frost heave uplift speed is greater than 3 mm / day or the cumulative frost heave uplift is greater than 10 mm.

[0016] Optionally, the drainage channel includes a drainage pipe. At least the part of the drainage pipe extending into the formation around the frozen wall has through drainage holes arranged in a queue parallel to the longitudinal axis of the drainage pipe or at an angle relative to the longitudinal axis on the pipe wall of the drainage pipe, and the through area provided by the through drainage holes is not less than 40% of the total area of the pipe wall of the drainage pipe.

[0017] Optionally, a wire mesh made of metal wires is arranged on the inner wall around the through drainage holes, and the diameter of the metal wires is 1 - 3 mm.

[0018] Optionally, the drainage pipe is arranged in the formation around the frozen wall during the pre-freezing stage.

[0019] Optionally, the drainage pipe is arranged parallel to and / or vertically and / or obliquely relative to the surface of the formation.

[0020] Optionally, the structure already constructed in the formation is a subway tunnel, and the structure to be constructed is a connecting passage of the subway tunnel.

[0021] According to a second aspect of the present application, there is provided a freezing construction device for constructing a structure in a formation, comprising:

[0022] A freezing device, which includes a plurality of freezing pipes arranged in a freezing wall of an inner structure to be constructed, and a working medium supply device fluidly connected to both ends of the freezing pipes. The working medium supply device supplies a freezing working medium to the freezing pipes and circulates the freezing working medium in the freezing pipes. The temperature of the freezing working medium is selectively set for pre-cooling, active freezing, and maintenance freezing of the freezing wall;

[0023] A vacuum drainage device, which includes: a vacuum pump arranged above the formation or in other structures already constructed in the formation; drainage channels arranged crosswise or parallel to each other in the formation. One end of the drainage channel leads to the vacuum pump, and the other end extends to the formation around the freezing wall. The vacuum pump is started at least during the pre-cooling stage and the active freezing stage to drain water from the formation around the freezing wall.

[0024] The technical solutions provided by the embodiments of the present application may include the following beneficial effects: By pre-cooling the freezing wall, the freezing time can be reduced. By draining water from the freezing wall, the moisture migration during the frost heave process can be inhibited, and the frost heave deformation control during the freezing method construction can be achieved from the root cause. Moreover, the construction is simple and the process is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings forming a part of the present application are used to provide a further understanding of the present application, making other features, objectives, and advantages of the present application more obvious. The schematic embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0026] Figure 1 It is a schematic diagram of the internal condition of the formation after freezing by an existing freezing construction method;

[0027] Figure 2 It is an exemplary flowchart of a freezing construction method for constructing a structure in a formation according to an embodiment of the present invention;

[0028] Figure 3 It is an exemplary structural block diagram of a freezing construction device for constructing a structure in a formation according to an embodiment of the present invention;

[0029] Figure 4 It is a schematic diagram of a part of the freezing construction device arranged in the formation according to an embodiment of the present invention;

[0030] Figure 5 It is a schematic cross-sectional view of a formation frozen by a freezing construction method according to an embodiment of the present invention;

[0031] Figure 6Schematic diagram of the drain pipe of the freezing construction equipment according to an embodiment of the present invention;

[0032] Figure 7 Schematic diagram of the ground surface frost heave after freezing the stratum by the existing freezing construction method;

[0033] Figure 8 Schematic diagram of the ground surface frost heave after freezing the stratum by the freezing construction method according to an embodiment of the present invention;

[0034] Figure 9 Curve comparison diagram of the frost heave amounts of the existing freezing construction method and the freezing construction method according to an embodiment of the present invention. Specific embodiments

[0035] In order to enable those skilled in the art to better understand the solution of this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of this application.

[0036] It should be noted that the terms "first", "second", etc. in the description and claims of this application and the above-mentioned drawings are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances for the embodiments of this application described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0037] In this application, the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", etc. is based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe this application and its embodiments, and are not used to limit that the indicated devices, elements or components must have a specific orientation, or be constructed and operated in a specific orientation.

[0038] Moreover, in addition to being used to indicate orientation or positional relationship, some of the above terms may also be used to indicate other meanings. For example, the term "upper" may also be used to indicate a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to the specific circumstances.

[0039] In addition, the terms "install", "set", "provided with", "connect", "connected", "socketed" should be understood in a broad sense. For example, "connect" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or there can be internal communication between two devices, components or parts. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0040] Next, the implementation manner of this application will be described Figures 1-9 only by way of example.

[0041] Figure 1 The schematic diagram shows the internal condition of the formation after freezing the formation by the existing freezing construction method. Figure 1 It shows that the freezing construction method is used to build a connection passage for the already completed subway main tunnel, which is a common application of the freezing construction method.

[0042] After the construction of the subway main tunnel is completed, a connection passage needs to be built between two subway tunnels for evacuation, connection, drainage, fire prevention, etc. The connection passage is built entirely underground and has a relatively high risk, which is a difficult point in the construction of the interval tunnel. Usually, the soil body within the range of the connection passage needs to be reinforced before excavation construction, and the ground freezing method is currently the most common construction method for the connection passage. Figure 1 In [the figure], the formation is generally indicated by reference numeral 10. There is an already completed subway main tunnel 21 within the formation 10. The connection passage 22 to be built is between two subway main tunnels 21, and the periphery of the connection passage 21 is a frozen wall 11 formed by the freezing method.

[0043] The technical solution of the existing freezing method construction is: install freezing pipes ( Figure 1 not shown in [the figure]) in the area of the frozen wall 11. After the installation of the freezing pipes is completed, supply brine with a temperature of about -30 °C to the freezing pipes to start active freezing; after the strength of the frozen wall 11 reaches the construction requirements, supply brine with a temperature of about -25 °C to the freezing pipes and maintain the frozen wall 11 meeting the construction requirements for a period of time. This stage is the maintenance freezing stage; construct the structure during the maintenance freezing stage.

[0044] The primary problem with the existing freezing method is that the stratum 10 (especially the water-rich stratum) above the freezing wall 11 has excessive frost heave deformation. Some literatures have proposed methods for controlling frost heave deformation in freezing construction, such as: drilling pressure relief holes near the freezing wall, adjusting freezing brine parameters in real time, grouting to improve the soil in the frozen area, and using thermal limit pipes for forced thawing. For example, see:

[0045] - Technical Specifications for Bypass Freezing Method, Shanghai Engineering Construction Specifications;

[0046] - Li Fangzheng et al., a comprehensive frost heave control method of temperature control, thermal limit and pressure relief in shallow soil freezing construction, invention patent;

[0047] -Yang Ping et al., a construction method for reinforcing frozen communication channels with grouting freezing pipes to inhibit frost heave and thaw settlement, invention patent;

[0048] -Yang Ping et al., a construction method for suppressing horizontal freezing, frost heaving, thawing and settlement by cement soil reinforcement, invention patent;

[0049] - Lu Lu et al., a method for controlling freezing, frost heave and thawing settlement of municipal engineering, invention patent;

[0050] -Liu Hua et al., a method and device for studying the frost heave and thaw sinking deformation mechanism of a large coastal shield tunnel based on deep learning, invention patent.

[0051] However, the above-mentioned frost heave deformation control method does not effectively control the frost heave deformation of the strata, especially the water-rich strata. At the same time, the above-mentioned frost heave deformation control method also has other disadvantages, including: the pressure relief hole technology is not effective in water-rich strata; the real-time adjustment of freezing parameters has a lag and cannot continuously ensure the strength of the frozen wall; the grouting improvement technology requires the injection of a large amount of slurry, which is complex to construct, has poor controllability, and pollutes groundwater; the use of thermal limit pipes for forced thawing requires the additional laying of thermal limit pipes and the preparation of thawing fluid, which is costly. In general, the inventors of this application believe that in the existing freezing method construction process, the freezing time is long, and there is a lack of moisture control technology. It is impossible to effectively control frost heave deformation under water-rich strata conditions, which is not conducive to maintaining the safety and stability of overlying pipelines, roads, and buildings in the freezing method construction area.

[0052] Existing research shows that frost heaving is a phenomenon in which, under low temperature and usually negative temperature conditions, the in-situ water in the soil and the water in the unfrozen zone above the frozen wall migrate to the frozen zone and freeze, causing volume expansion and soil expansion. The frost heaving caused by in-situ water is called in-situ frost heaving, and the frost heaving caused by water migration is called migration frost heaving. Among them, migration frost heaving is the main cause of frost heaving deformation, that is, water continuously migrates and accumulates from the unfrozen zone to the freezing front under a constant negative temperature gradient, resulting in the continuous development of frost heaving deformation. In water-rich strata, the soil water content is high, providing sufficient water supply for the development of frost heaving and exacerbating the frost heaving deformation problem in freezing method construction. Therefore, in freezing method construction, it is urgent to propose a new construction technology to reduce the migration amount of formation water to the frozen wall, which is very important for controlling the frost heaving amount and ensuring the safety of surface pipelines and roads.

[0053] The inventors of the present application believe that the existing frost heaving deformation control methods only control frost heaving deformation by controlling temperature factors and changing the formation, lacking water control measures. Moreover, in the existing freezing method technology, active freezing is directly carried out in the initial ground temperature environment, and the ground temperature is usually about 15 °C, which makes the frozen wall 11 develop slowly and the freezing time is long, providing sufficient migration time for formation water and exacerbating frost heaving deformation. The inventors believe that temperature is only the direct cause of formation frost heaving, and water migration is the root cause. The key to controlling water migration (migration frost heaving) is to reduce the water migration amount during the freezing process, which can be achieved through two key ways: First, reduce the negative temperature freezing duration; Second, reduce the water volume in the surrounding formation.

[0054] In response, the present application provides a freezing method construction method and equipment for constructing a connection passage in a formation, especially a water-rich formation, in which the "pre-cooling - drainage" method is used to control frost heaving deformation. According to the present application, a pre-cooling stage is added before the active freezing period of the traditional construction method to shorten the active freezing duration; water is drained from the formation throughout the freezing process. On the one hand, the formation water content is reduced in the pre-freezing stage without obvious frost heaving, and on the other hand, the water migration amount during the entire freezing process is reduced. By shortening the freezing duration, reducing the formation water content, and reducing the water migration amount, the technical solution of the present application can effectively control the frost heaving deformation of the formation above the frozen wall (especially the water-rich formation).

[0055] Compared with other frost heave control methods such as the pressure relief holes, soil-cement improvement, and active heating mentioned above, the method provided in this application also has the following advantages: The whole process of drainage during the freezing stage can actively block the migration path of groundwater in the formation, especially in water-rich formations, and control the recharge of water in the formation around the frozen wall from the source. Compared with other passive temperature control measures, it is more suitable for controlling the migration frost heave of water-rich formations with large water migration volume; Adding a pre-freezing stage can reduce the temperature of the freezing zone without causing frost heave, accelerate the speed of formal freezing (positive freezing), thereby shortening the positive freezing construction period and helping to reduce the amount of frost heave; In addition, the method of this application does not require injecting concrete slurry into the formation or laying special heating equipment, so the construction is simple, the process is environmentally friendly, and the economy is good.

[0056] Next, exemplary embodiments according to the present application will be described with reference to the accompanying drawings. Before describing the embodiments, a brief explanation of the technical terms in this field involved herein will be given.

[0057] Water-rich formation: A formation with high water content, high water pressure and large flow rate. Such a formation has a large amount of water recharge, and a large amount of frost heave will occur during the construction of the freezing method.

[0058] Connection passage: A short tunnel used to connect two or more main tunnels in the formation, such as subway tunnels, or a short tunnel used to install a tunnel pumping station. It is set between the main tunnels and plays roles such as evacuation, connection, drainage and fire prevention. It is usually carried out after the construction of the main tunnel is completed.

[0059] Stratum freezing method: Before constructing an underground structure, the water-bearing stratum around the structure is frozen by artificial refrigeration to form a frozen wall with temporary load-bearing and water-blocking functions and meeting the safety requirements of engineering construction. Then, the construction operation of the structure excavation and masonry is carried out under the protection of the frozen wall. It has the advantages of high reinforcement strength, good water-blocking property, strong adaptability, and no pollution.

[0060] Frozen wall: A continuous frozen rock and soil body with a certain thickness and strength formed in the stratum around the structure by refrigeration technology, also known as a frozen soil curtain or frozen soil wall.

[0061] Frozen wall thickness: The frozen wall is composed of frozen soil cylinders intersecting in pairs. The shortest distance between any point on the frozen wall surface and another wall surface is called the frozen wall thickness. Usually, the frozen wall needs to reach the designed thickness through artificial freezing before the connection passage can be excavated.

[0062] Positive freezing period: The time required from the start of stratum freezing to the formation of the frozen wall reaching the designed required thickness.

[0063] Maintenance freezing period: After the frozen wall is formed to meet the design requirements, in order to ensure the safety during the excavation and lining process of the structure, cold energy is continuously supplied to the freezing pipes to maintain the thickness of the frozen wall to meet the design requirements for a certain period of time.

[0064] Frost heave deformation: Under low temperature (negative temperature) conditions, due to the in-situ water in the soil (in-situ frost heave) and the water migrating from the unfrozen zone to the frozen zone (migratory frost heave) freezing and causing volume expansion, resulting in the phenomenon of soil expansion. Among them, migratory frost heave is the main cause of frost heave deformation.

[0065] Pre-cooling: According to the new link added in the present application before the existing active freezing period, the temperature of the freezing pipes is set to 0 - 1 °C, and without causing frost heave, the temperature field of the soil in the frozen wall area is reduced to about 1 °C. In this way, during the subsequent active freezing period, the formation speed of the frozen wall can be accelerated and the active freezing time can be shortened, thereby significantly reducing the frost heave amount.

[0066] Drainage: During the pre-cooling period, drainage holes are dug in the strata above the frozen wall and drainage pipe belts are installed, and the local drainage of the strata is carried out by the vacuum pumping method, which can fundamentally reduce the water migrating to the vicinity of the frozen wall during the active freezing period and control the frost heave amount.

[0067] Specifically, according to the exemplary implementation manner of the present application, a freezing construction method for constructing a structure in a stratum is provided, including the following steps:

[0068] a. Pre-cool the area of the frozen wall of the structure to be constructed with a freezing device;

[0069] b. During the pre-cooling stage, drain water from the frozen wall of the strata around the frozen wall with a vacuum drainage device;

[0070] c. After the pre-cooling stage, actively freeze the frozen wall with a freezing device;

[0071] d. During the active freezing stage, continue to drain water from the strata around the frozen wall with a vacuum drainage device;

[0072] e. After the active freezing stage, during the maintenance freezing stage of maintaining the temperature of the frozen wall, construct a structure in the frozen wall.

[0073] It should be noted that the above labels a - e do not limit the order of the steps. According to the principles of the present invention, the order of one or more of these steps can be changed, or they can be executed simultaneously or with overlap in time. For example, step a and step b can be carried out simultaneously, or step a can precede step b, or step b can precede step a; step c and step d can be carried out simultaneously, or step c can precede step d; or step d can precede step c. In the above cases, the drainage process is carried out continuously or in stages, but all can be considered as carrying out drainage during the whole process of formation freezing. In addition, in step e, the vacuum drainage equipment can be started or stopped according to the actual situation.

[0074] In the above freezing construction method according to the present application, the freezing operation and the drainage operation require the arrangement of corresponding freezing equipment and drainage equipment. According to an embodiment of the present application, the freezing equipment may include: a plurality of freezing pipes arranged in the formation where the freezing wall is to be formed, and a working medium supply device, for example, arranged above the formation or in other structures already built in the formation, which is in fluid communication with the freezing pipes, and the working medium supply device supplies the freezing working medium to the freezing pipes and circulates the freezing working medium in the freezing pipes. In addition, temperature measuring holes can be arranged in the area of the freezing wall to measure the formation temperature in real time. Conventionally, through steps such as measurement positioning, segment hole opening, drill rig tunneling, and inclination measurement and deviation correction, the freezing pipes are arranged at the designed position of the freezing wall, and the temperature measuring holes are arranged around the freezing wall.

[0075] The vacuum drainage equipment may include: a vacuum pump arranged above the formation or in other structures already built in the formation; and a drainage channel with one end leading to the vacuum pump and the other end extending to a part of the formation around the freezing wall, and the drainage channels are arranged cross -wise or parallel to each other. Further, a vacuum drainage pipe, such as a steel pipe, can be installed in the drainage channel, and the vacuum pump is used to drain the moisture in the formation through the drainage pipe into a water storage device, and the water storage device can be arranged, for example, on the formation surface or in the already built structure in the formation.

[0076] Meanwhile, according to the principles of the present application, an exemplary freezing construction equipment for constructing a structure in the formation is also provided, which includes the above - mentioned freezing equipment and vacuum drainage equipment. The temperature of the freezing working medium supplied by the working medium supply device of the freezing equipment is selectively set for pre - cooling, active freezing, and maintenance freezing of the freezing wall. The vacuum pump of the vacuum drainage equipment is started at least in the pre - cooling stage and the active freezing stage to drain water from the freezing wall, and is selectively started in the maintenance freezing stage.

[0077] Figure 2Specifically shown therein is an exemplary flowchart of a freezing construction method according to an embodiment of the present application. Generally, after the freezing equipment and drainage equipment are arranged, the freezing construction may include: pre-freezing - drainage, active freezing - drainage, and maintenance freezing stages. In addition, it may also include simultaneously performed temperature measurement steps, frost heave deformation monitoring steps, and ground settlement monitoring steps, which will be described later. Figure 2 For the equipment and devices mentioned therein, a part is arranged above the ground, and another part is arranged in the structures within the formation, which will be specifically described later.

[0078] As Figure 2 shown, following the indication of the arrow, after the freezing construction starts, first start the pre-freezing operation to prepare for forming the freezing wall. In this stage, the formation gradually cools down but no frost heave occurs. In the pre-freezing stage, the freezing medium can be set to, for example, 0 to 1 °C, so that the formation soil can be quickly consolidated in the subsequent active freezing stage, and at the same time, the water in the formation is allowed to be quickly drained. The freezing medium is, for example, brine, liquid nitrogen, and others. After starting for a period of time in the pre-freezing stage, start the vacuum pump to perform drainage operation on the formation above the freezing wall. According to the embodiment of the present application, maintaining the working pressure of the vacuum pump above 80 kPa can have a good drainage effect. Optionally, the drainage operation in the pre-freezing stage can be started simultaneously with the pre-freezing operation, as Figure 2 indicated by the dashed arrow in

[0079] Next, when the temperature of the freezing wall reaches about 0 to 1 °C and remains stable, start the active freezing operation. In this stage, the temperature of the freezing medium can be set to -30 °C to -35 °C to quickly form the freezing wall. The temperature of the freezing wall and the temperature in other areas of the formation can be measured in the temperature measurement step ( Figure 2 not shown therein), and the temperature of the freezing wall is obtained through the temperature measurement device ( Figure 3 shown therein). Optionally, the drainage operation in the active freezing stage can be started after the active freezing has been carried out for a period of time or can be started simultaneously with the active freezing (as Figure 2 indicated by the dashed arrow in

[0080] Thereafter, enter the maintenance freezing stage. In this stage, the temperature of the freezing wall is no longer lowered, but the temperature of the freezing medium is set to a relatively increased -20 to -25 °C or so, with the aim of maintaining the thickness of the freezing wall and meeting the design requirements of the freezing wall while not increasing the frost heave deformation. After starting the maintenance freezing, start to build structures, such as connection channels, within the freezing wall.

[0081] In the method according to the present application, at least during the active freezing stage and the maintenance freezing stage, the frost heave condition of the formation above the freezing wall is monitored in real time, and accordingly, the working pressure of the vacuum pump is adjusted. This monitoring is carried out in the frost heave deformation monitoring step. As Figure 2 shown, during the active freezing and drainage stage, if the frost heave deformation amount of the formation is within the predetermined threshold, the working pressure of the drainage vacuum pump is maintained at the set pressure. For example, it is maintained above 80 kPa. If it is monitored that the frost heave deformation of the formation exceeds the predetermined threshold, the working pressure of the vacuum pump is increased to, for example, 120 - 160 kPa to increase the drainage volume and inhibit the frost heave deformation. During the maintenance freezing stage, the freezing wall is no longer cooled further, and the freezing wall is maintained but not further expanded. Usually, the frost heave deformation will no longer increase or the growth rate is slow during this stage, and the vacuum pump can be turned off without carrying out the drainage operation. However, as Figure 2 shown, if the frost heave deformation monitored in real time during the maintenance freezing stage continues to increase and exceeds the predetermined threshold, the vacuum pump can be restarted for drainage. According to the present application, the working pressure of the vacuum pump during the pre-freezing stage and the maintenance freezing stage is maintained above 80 kPa, and the frost heave deformation can be optionally monitored during the pre-freezing stage.

[0082] According to the present application, the threshold value of the formation frost heave deformation can be set such that the uplift rate of the underground pipeline and / or the ground surface exceeds 3 mm / day, or the cumulative uplift deformation of the underground pipeline and / or the ground surface exceeds 10 mm. In addition, according to the present application, during the formation freezing process, the ground settlement should also be closely monitored. This monitoring is carried out in an optional ground settlement monitoring step ( Figure 2 not shown in the figure) as another reference value for adjusting the temperature of the freezing medium and the working pressure of the vacuum pump.

[0083] Figure 3 Specifically shows a block diagram of a freezing construction device for constructing a structure in a formation according to an exemplary embodiment of the present application. As Figure 3 shown, the freezing construction device generally includes a control device 100, a freezing device 200, a vacuum drainage device 300, a frost heave monitoring device 400, a water storage device 500, a temperature measuring device 600, and a ground settlement monitoring device 700. The freezing device 200 includes freezing pipes 210 extending into the freezing wall and a working medium supply device 220 for supplying a freezing medium to the freezing pipes 210. The vacuum drainage device 300 includes a vacuum pump 310 providing pumping pressure and a drainage pipe 320 extending into the formation above the freezing wall for drainage. The water in the formation above the freezing wall is drained away by the vacuum pump 310 through the drainage pipe 320. The vacuum pump 310 can be connected to the water storage device 500 to pump the formation water from the drainage pipe 320 to the water storage device 500 for storage. Both the freezing device 200 and the vacuum drainage device 300 are communicatively connected to the control device 100 and operate according to the control instructions of the control device 100. In addition, Figure 3The frost heave monitoring device 400, the temperature measuring device 500, and the ground settlement monitoring device 700 therein are all communicatively connected to the control device, and transmit the measured formation temperature, frost heave deformation amount, and ground settlement amount to the control device 100. The control device 100 controls the operations of the freezing equipment 200 and the vacuum drainage equipment 300 based on the above-mentioned measurement quantities. Figure 3 The working process of the freezing construction equipment can refer to Figure 2 .

[0084] According to the above freezing construction method and equipment of the present application, the frost heave deformation of the formation, especially the water-rich formation, during freezing construction can be effectively controlled. The specific advantages include: through the pre-cooling technology, without causing frost heave in the formation, the soil temperature field in the freezing wall area is reduced to about 1°C, thereby accelerating the formation speed of the freezing wall and shortening the active freezing duration; through the vacuum drainage technology, during the pre-cooling and formal freezing (active freezing) periods, drainage holes are drilled in the soil layer above the freezing wall and drain pipes are arranged to implement local drainage of the soil layer, so as to reduce the water migrating to the vicinity of the freezing wall during the active freezing period; the above two cooperate to effectively control the frost heave deformation caused by water migration.

[0085] In order to more clearly understand the composition of the freezing construction equipment of the present application, Figure 4 shows a schematic diagram of a part of the freezing construction equipment arranged in the formation according to an embodiment of the present invention, where establishing a connection between two subway tunnels is taken as an example for illustration. As Figure 4 shown, two subway tunnels 140 have been built in the formation 110, and the area between them is the area of the connection passage 130 (shown by a dotted line) to connect the two subway tunnels to be built. Above and below the connection passage 130 are the freezing walls 120 to be formed. Freezing pipes 210 are arranged in the area of the freezing walls 120. It can be seen that the freezing pipes 210 extend from the two already built subway tunnels 140 in a radiation manner to the area of the freezing walls 120 around the connection passage 130. Drain pipes 320 are arranged above the upper freezing wall 120. As Figure 4 shown in Figure 4 , the drain pipes 320 can be arranged parallel to each other along the frost heave direction of the formation indicated by the arrow A in Figure 4 (the cross-section of the drain pipe 320 is shown in

[0086] Figure 5FIG. shows a schematic view of a part of a freezing construction device arranged in a formation according to another embodiment of the present invention. Freezing pipes 210 are arranged within the area of the freezing wall 120 shown by the dashed line. In this embodiment, the freezing pipes 210 are arranged in a direction substantially vertical to the surface of the formation 110 and do not extend from the already constructed structure. The drain pipes 320 are arranged in a direction substantially parallel to the freezing pipes 210, that is, in a direction vertical to the ground surface. The free moisture 150 in the formation 110 enters the drain pipes 320 under the action of the vacuum pump 310 and is drained away. For example, the drain pipes 320 are uniformly arranged in multiple rows within the formation around the freezing wall 120 parallel to the freezing pipes 210. For example, 2 rows of drain pipes 320 are uniformly driven into the formation above and / or below the freezing wall 120, with a spacing of 1 - 2 m between each row, and the spacing between each drain pipe in each row can be 0.5 - 1 m. In addition, the drain pipes 320 can have an inner diameter of 50 - 100 mm and a pipe wall thickness of 5 mm.

[0087] Figure 6 FIG. specifically shows an example diagram of the drain pipe of the freezing construction device according to an embodiment of the present invention. The drain pipe 320 is arranged in a pre-constructed drainage channel (not shown). Figure 6 What is shown in FIG. can be the entire drain pipe 320 or a part of the drain pipe 320. According to the example, at least the part of the drain pipe 320 extending in the formation around the freezing wall 120 can be provided with a plurality of through-drainage holes 322 on the pipe wall 321 of the drain pipe 320. The through-drainage holes 322 can be circular, square, rectangular or other suitable shapes. For example, in Figure 6 the case of the circular drainage holes 322 shown in FIG., the inner diameter of the drainage holes 322 can be 10 mm, and the through area provided by the through-drainage holes 322 is not less than 40% of the total area of the pipe wall 321 of the drain pipe 320. Specifically, the through-drainage holes 322 can be arranged in a queue parallel to the longitudinal axis of the drain pipe 320 or at an angle relative to the longitudinal axis. Figure 6 FIG. shows that the through-drainage holes 322 are arranged in a direction parallel to the longitudinal axis A - A of the drain pipe 320.

[0088] Furthermore, in order to prevent soil particles and stone particles in the soil mass of the formation 110 from entering the drain pipe 320 through the through-drainage holes 322, a woven mesh 323 made of metal wire can be arranged around the inner wall of the through-drainage holes 322, where the diameter of the metal wire is, for example, 1 - 3 mm. In addition, as a convenient embodiment, a cylindrical metal mesh can be sleeved inside the drain pipe 320.

[0089] Figure 7 and Figure 8 FIGS. respectively show schematic views of the ground surface frost heave after freezing the formation by the existing freezing construction method and the ground surface frost heave after freezing the formation by the freezing construction method according to the embodiment of the present invention.

[0090] As Figure 7 shown, in the case where the drain pipe 320 is not arranged, the moisture in the formation 110 migrates from the area above the freezing wall 120 to the freezing wall 120 in the direction indicated by the arrow, causing the ground surface 170 to bulge upward to the position 171 due to the frost heaving deformation of the formation 110, and the heaving height is indicated by H1. In Figure 8 , a plurality of drain pipes 320 are arranged in the area of the formation 110 above the freezing wall 120, and the moisture in the formation 110 enters the drain pipes 320 in the direction of the arrow and enters the water storage device 500 arranged in the already constructed structure 140 (for example, a subway tunnel) through the drain pipes 320. In Figure 8 the case, the heaving height between the ground surface 170 and the position 171 it reaches after bulging is indicated by H2, and it can be clearly seen that the heaving height of the ground surface due to frost heaving is significantly reduced, that is, H2 is significantly smaller than H1.

[0091] Figure 9 Further shown is a comparison graph of the frost heaving amount curves of the existing freezing construction method and the freezing construction method according to the embodiments of the present invention. Figure 9 In, the curve indicating the change of the frost heaving amount of the formation with the freezing time in the existing freezing construction method is indicated by a dashed line, and the frost heaving curve of the freezing construction method according to the present invention is indicated by a solid line. From Figure 9 it can be clearly seen that the improvement of the frost heaving deformation includes three aspects: First, the existing freezing method has no pre-freezing stage, and the formation starts to show frost heaving deformation soon after the start of positive freezing before T1. The freezing method of the present application adds a pre-freezing stage before the positive freezing stage, and uses the starting part before T1 in the existing freezing method as the pre-freezing stage, and no frost heaving deformation occurs in this added pre-freezing stage; Second, in the positive freezing stage before T1, the frost heaving amount of the existing freezing method increases in direct proportion to the freezing time with a significant slope. In the freezing method of the present application, the growth slope of the frost heaving amount is significantly reduced; Third, in the maintenance freezing stage between T1 and T2, the frost heaving amount in the existing freezing method still increases significantly. In the freezing method according to the present application, the frost heaving amount only increases slightly or even no longer increases. The comparison of the curves clearly shows that the frost heaving amount of the formation is significantly reduced by using the freezing construction method of the present application.

[0092] The implementation manners and corresponding technical effects of the freezing construction method and equipment according to the present application described above by way of examples. Generally speaking, on the basis of the existing frost heave control technology, the present application aims at the problem of excessive frost heave in the freezing method construction of strata, especially water-rich strata. By adding a pre-cooling stage to shorten the active freezing period and increasing drainage operations to reduce the water content of the strata, the two work together to jointly control the frost heave deformation in the freezing method construction, and finally effectively control the frost heave deformation amount. The present invention breaks through the traditional single method of controlling frost heave by temperature, realizes controllable frost heave amount and pollution-free strata, reduces the influence of the freezing method construction of the connection passage on the overlying pipelines, roads and building foundations, and has good economic and social benefits.

[0093] In addition, although the implementation manners of the freezing construction method and equipment according to the present invention are described above by taking the construction of the main body of the subway tunnel and its connection passage as examples, the method and equipment of the present invention can be used for constructing any suitable strata structures, such as underground transportation pipelines, underground buildings, underground cables, and others. The construction details of these changed implementation manners may be different, but they will all be covered within the scope of the present invention.

[0094] It should be noted that the steps shown in the flowchart of the drawings can be executed in a computer system such as a set of computer-executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order from here.

[0095] Obviously, those skilled in the art should understand that the above-mentioned units or steps of the present application can be implemented by a general-purpose computing device. They can be concentrated on a single computing device or distributed on a network composed of multiple computing devices. Optionally, they can be implemented by program codes executable by the computing device, so that they can be stored in a storage device and executed by the computing device, or they can be separately made into individual integrated circuit modules, or multiple modules or steps among them can be made into a single integrated circuit module to be implemented. In this way, the present application is not limited to any specific combination of hardware and software.

[0096] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A freezing construction method for building a structure in a formation, comprising the following steps: a. Pre-cooling the area of the freezing wall of the structure to be built with a freezing device and keeping the freezing wall from frost heaving; b. During the pre-cooling stage, draining water from the formation around the freezing wall with a vacuum drainage device to control the migration of moisture in the formation towards the freezing wall; c. After the pre-cooling stage, actively freezing the freezing wall with the freezing device; d. During the active freezing stage, continuously draining water from the formation around the freezing wall with the vacuum drainage device; e. After the active freezing stage, during the maintenance freezing stage of maintaining the temperature of the freezing wall, building the structure inside the freezing wall; wherein, the freezing device includes: a plurality of freezing pipes arranged in the freezing wall, and a working medium supply device fluidly connected to the freezing pipes, the working medium supply device supplying a freezing working medium to the freezing pipes and circulating the freezing working medium in the freezing pipes; and the vacuum drainage device includes: a vacuum pump arranged above the formation or in other structures already built in the formation; drainage channels arranged in the formation intersecting or parallel to each other, one end of the drainage channel leading to the vacuum pump and the other end extending into the formation around the freezing wall; wherein, the vacuum pump is started at least during the pre-cooling stage and the active freezing stage to drain water from the freezing wall, the drainage channel includes a drainage pipe with through drainage holes, and the through area provided by the through drainage holes is not less than 40% of the total area of the pipe wall of the drainage pipe.

2. The freezing construction method for constructing a structure in a formation according to claim 1, characterized in that, The temperature of the freezing working medium is set to: 0 - 1 °C during the pre-cooling stage, -30 - -35 °C during the active freezing stage, and -20 - -25 °C during the maintenance freezing stage.

3. The freezing construction method for constructing a structure in a formation according to claim 1, characterized in that, The frost heaving deformation of the formation is monitored in real time. If the amount of frost heaving deformation is within a predetermined threshold, the working pressure of the vacuum pump is set to above 80 kPa; if the amount of frost heaving deformation exceeds the predetermined threshold, during the active freezing stage, the working pressure of the vacuum pump is increased to 120 - 160 kPa, and / or during the maintenance freezing stage, the vacuum pump is started to drain water from the freezing wall.

4. The freezing construction method for constructing a structure in a formation according to claim 3, characterized in that, The predetermined threshold of the frost heaving deformation is that the frost heaving uplift speed is greater than 3 mm / day or the cumulative frost heaving uplift is greater than 10 mm.

5. The freezing construction method for constructing a structure in a formation according to any one of claims 1 to 4, characterized in that, The drainage pipe is arranged parallel to and / or vertically and / or obliquely with respect to the surface of the formation, and at least a part of the drainage pipe extending in the formation around the freezing wall is provided with the through drainage holes arranged in a queue parallel to the longitudinal axis of the drainage pipe or at an angle with respect to the longitudinal axis.

6. The freezing construction method for constructing a structure in a formation according to claim 5, characterized in that, A wire mesh made of metal wires is arranged on the inner wall around the through drainage holes, and the diameter of the metal wires is 1 - 3 mm.

7. The freezing construction method for constructing a structure in a formation according to claim 5, characterized in that, The drainage pipe is arranged in the formation around the freezing wall during the pre-cooling stage or during the pre-cooling stage and the active freezing stage.

8. The freezing construction method for building structures in strata according to claim 5, characterized in that, The working fluid supply device and the vacuum pump are started simultaneously or successively, so that the pre-cooling stage and the active freezing stage are performed simultaneously with or prior to the drainage operation.

9. The freezing construction method for constructing a structure in a formation according to claim 1, characterized in that, The formation for constructing the structure is a water-rich formation.

10. A freezing construction device for the method according to any one of claims 1 to 9, comprising: A freezing device, which includes a plurality of freezing pipes arranged inside the freezing wall where the structure to be constructed is located, and a working fluid supply device that is fluidly connected to both ends of the freezing pipes. The working fluid supply device supplies a freezing working fluid to the freezing pipes and circulates the freezing working fluid in the freezing pipes. The temperature of the freezing working fluid is selectively set for pre-cooling, active freezing, and maintenance freezing of the freezing wall; A vacuum drainage device, which includes: a vacuum pump, which is arranged above the formation or in other structures already constructed in the formation; Drainage channels, which are arranged in the formation intersecting or parallel to each other. One end of the drainage channel leads to the vacuum pump, and the other end extends into the formation around the freezing wall. The vacuum pump is started at least during the pre-cooling stage and the active freezing stage to drain water from the formation around the freezing wall.

Images