Freezing area development and frost heaving deformation control method based on boundary modification

Abstract

The invention discloses a boundary modification-based frozen area development and frost heaving deformation control method, and relates to the field of geotechnical engineering construction. By changing boundary moisture migration and heat exchange conditions, the development range of the frozen wall is controlled, and outward transfer of frost heaving deformation is inhibited. Before freezing engineering construction, the external boundary of a predetermined stratum freezing area is constructed according to the following steps: step 1, constructing and forming a plurality of grooves which are continuously arranged at the external boundary of the predetermined stratum freezing area; 2, by means of the under-slurry spraying technology, the slotted holes are located in the side wall of the fine-particle soil layer to form a surface waterproof covering layer, and mud cakes located on the side wall of the coarse-particle soil layer are removed on the premise that the stability of the slotted holes is guaranteed; and 3, each groove hole is filled with a heat insulation and deformation buffering material or provided with a heat insulation and deformation buffering device. The functional groove hole structure is arranged on the freezing boundary, and effective control over freezing area and frost heaving deformation is achieved.

Description

Technical Field

[0001] The present invention relates to the field of geotechnical engineering construction and is applicable to controlling the development of the frozen zone and frost heave deformation during the construction of the frozen method in geotechnical engineering, and protecting underground and surface buildings (structures) and other facilities around the frozen zone. Background Technique

[0002] The freezing method is a special construction method widely used in mine shafts and municipal geotechnical engineering construction. This method creates conditions for underground engineering construction by artificially freezing loose and unstable rock and soil layers to form a freezing wall (or called a frozen soil wall) with a certain thickness and strength. However, the frost heave and thaw settlement of the stratum often threaten the safety of surrounding buildings (structures). Therefore, it is often necessary to effectively control the development range of the freezing wall and eliminate the side effects of frost heave deformation.

[0003] In the existing freezing method construction, in order to prevent the influence of frost heave deformation on the safety of surrounding buildings, the following measures are usually taken: First, through the optimization of the freezing scheme, reduce the moisture migration and soil frost heave deformation during the freezing process of the stratum; Second, through the improvement of the soil properties of the stratum, such as reducing the initial water content and reducing the frost heave of the soil, thereby suppressing the amount of frost heave deformation induced by freezing; Third, construct pressure relief holes at appropriate positions in the frozen zone to play a role in buffering deformation and reduce the influence of stratum frost heave on surrounding facilities.

[0004] However, the existing measures actually do not have a good control effect on the development of the freezing wall, and multiple means need to be superimposed in construction to ensure the safety of buildings (structures) and equipment around the construction site to a certain extent. Not only is the construction period long, but also the construction cost is high and the economy is poor. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a method for controlling the development of the frozen zone and frost heave deformation based on boundary modification, which controls the development range of the freezing wall and inhibits the outward transmission of frost heave deformation by changing the boundary moisture migration and heat exchange conditions.

[0006] The technical solution of the present invention is as follows: Before the construction of the freezing project, first construct the outer boundary 2 of the predetermined stratum freezing zone 1 according to the following steps: Step 1: At the outer boundary 2 of the predetermined stratum freezing zone 1, construct a number of continuously arranged slot holes 3, the slot holes 3 pass through the coarse-grained soil layer 6 and the fine-grained soil layer 4 from top to bottom, and their depth is greater than the depth of the stratum freezing zone 1; Step 2: Using the mud-injection spraying technology, form a surface water-proof coating 5 on the side wall of the slot hole 3 in the fine-grained soil layer 4, and remove the mud cake on the side wall of the coarse-grained soil layer 6 in the slot hole 3 on the premise of ensuring the stability of the slot hole 3; Step 3: Fill the heat insulation and deformation buffer material 7 in each slot 3, or install the heat insulation and deformation buffer device 8, so as to form a soil modified area at the positions where a number of slots 3 are located. Thereby, the water permeability, heat transfer property and deformation control performance of the boundary surface of the freezing zone can be changed, the development of the freezing zone and frost heave deformation can be controlled, and the adverse effects of stratum frost heave can be reduced.

[0007] The freezing zone 1 refers to the area where artificial refrigeration is to be used to freeze the water-bearing stratum.

[0008] The outer boundary 2 of the freezing zone refers to the interface between the expected freezing zone and the non-freezing zone according to the freezing scheme; according to the sensitivity of the surrounding facilities to be protected to stratum frost heave, the outer boundary 2 can be the entire boundary of the freezing zone or only a part of it.

[0009] The slot 3 can be a rectangular-section slot constructed by a trenching machine or an interlocking slot constructed by a drilling rig; the depth (or length) of the slot should reach the designed freezing depth (or freezing length); the minimum width of the slot should meet the requirements for filling the heat insulation and deformation buffer material or installing the heat insulation and deformation buffer device.

[0010] The fine-grained soil layer section 4 refers to the silt and clay layer sections where the pore water in the soil migrates from the unfrozen zone to the freezing front during the freezing process.

[0011] The coarse-grained soil layer section 6 mainly refers to the sand and gravel soil layers where the pore water in the soil drains outwards from the freezing front during the freezing process. Part of the mud skin in this soil layer is removed to improve its water permeability and facilitate the drainage of the water in the freezing zone to the slots and the non-freezing zone.

[0012] The outer boundary 2 in Step 1 is the partial or entire boundary of the stratum freezing zone 1.

[0013] The surface water-proof covering layer 5 in Step 2 is a water-proof covering layer formed on the side wall of the slot 3 by continuously spraying a high-molecular-weight and high-viscosity cellulose solution with a spraying device, and is used to prevent the water in the slot and the non-freezing zone from migrating to the freezing front in the fine-grained soil layer.

[0014] The heat insulation and deformation buffer material 7 in Step 3 includes, but is not limited to, foamed cement, hollow microspheres or perlite particle foamed cement, polystyrene foamed material, polyurethane foamed material, and anti-freezing hydrogel doped with hollow microspheres or EPS particles; the heat insulation and deformation buffer material 7 is prepared on the ground and then filled, or is prepared in-situ after being injected into the slot.

[0015] The heat insulation and deformation buffer device 8 in Step 3 refers to a hollow capsule structure filled with antifreeze or gas in the cavity, and the capsule is connected to the pressure relief valve 9 through a pipeline. The pressure relief valve is used to open and discharge part of the liquid or gas when the pressure of the liquid or gas in the capsule exceeds the set value, playing a pressure relief role; the capsule can be made of impermeable and tough tensile materials such as rubber and nylon cloth.

[0016] In order to solve the problems of frozen area and frost heave deformation control faced in the construction of artificial ground freezing method, based on the concept of actively regulating the moisture migration or drainage conditions at the boundary of the frozen area in different property soil layers, as well as releasing the frost heave stress and deformation, this invention proposes an active transformation method for the hydraulic properties and thermophysical properties of the whole or part of the frozen area boundary, so as to effectively limit the development of the frozen area and the accumulation of frost heave deformation induced by moisture migration, and achieve the purpose of protecting the safety of surrounding facilities. This method can not only ensure the safety of buildings (structures) and equipment around the project site, but also significantly save freezing cooling capacity and improve economic efficiency.

[0017] Compared with the existing traditional methods for passive response to frost heave deformation, this invention effectively controls the frozen area and frost heave deformation by setting functional slot hole structures at the freezing boundary. This method is applicable to the construction scenario of artificial freezing method, especially in projects with high requirements for frost heave control such as the shield tunneling in and out of the subway tunnel and the freezing of underground passages, and has the following advantages: 1. Reduce the transfer of cooling capacity to the external non-frozen area and inhibit the development of ineffective frozen areas; 2. Respectively and specifically regulate the moisture migration direction during the freezing process of fine and coarse grained soils to inhibit the occurrence of frost heave deformation; 3. Actively release the frost heave stress and frost heave deformation of the formation to relieve the influence on external facilities in the frozen area; 4. Improve the safety and economic efficiency of artificial ground freezing construction, reduce the frost heave effect, and improve economic benefits. Description of the Drawings

[0018] Figure 1 It is a three-dimensional schematic diagram of the modification of the frozen area boundary of the circular cross-section shaft in Example 1; Figure 2 It is a cross-sectional view of the shaft of the modification of the frozen area boundary of the circular cross-section shaft in Example 1; Figure 3 It is a vertical sectional view of a partial modified area of the frozen area boundary of the circular cross-section shaft in Example 1; Figure 4 It is a three-dimensional schematic diagram of the modification of the frozen area boundary of the rectangular cross-section shaft in Example 2; Figure 5 It is a cross-sectional view of the shaft of the modification of the frozen area boundary of the rectangular cross-section shaft in Example 2; Figure 6Vertical sectional view of a partial boundary modification area of the frozen area for modifying the boundary of the rectangular-section shaft in Example 2; Figure 7 3D schematic diagram of the frozen area boundary modification of the horizontal tunnel with a circular cross-section in Example 3; Figure 8 Cross-sectional view of the tunnel of the frozen area boundary modification of the horizontal tunnel with a circular cross-section in Example 3; Figure 9 Vertical sectional view of a partial boundary modification area of the frozen area of the tunnel of the frozen area boundary modification of the horizontal tunnel with a circular cross-section in Example 3; Meanings of the numbers in the figure: 1 - Frozen area; 2 - Outer boundary; 3 - Slot hole; 4 - Fine-grained soil layer; 5 - Waterproof coating on the surface of the slot hole; 6 - Coarse-grained soil layer; 7 - Heat insulation and deformation buffer material; 8 - Heat insulation and deformation buffer device; 9 - Pressure relief valve; 10 - Area to be excavated; 11 - Freezing pipe. Specific implementation manners

[0019] To clearly illustrate the technical features of this patent, the following will elaborate on this patent in detail through specific implementation manners and in combination with its attached drawings. Example

[0020] Example 1 illustrates the schematic diagram of soil body modification for implementing the present invention in the frozen project of a vertical shaft with a circular cross-section, for the outer boundary 2 of the frozen area 1; the 3D schematic diagram, cross-sectional view, and partial vertical section of the soil body modification area are respectively as Figures 1-3 .

[0021] In Example 1, the entire outer boundary 2 of the frozen area 1 is modified. Continuous drilling is carried out to form slot holes 3. In the slot hole section located in the fine-grained soil layer 4, a waterproof coating 5 is sprayed on the wall surface, and the heat insulation and deformation buffer material 7 is filled in the slot holes.

[0022] The main construction steps are as follows: Step 1: Along the circumferential direction, continuous drilling is carried out at the expected outer boundary 2 of the frozen area (i.e., the frozen wall) of the vertical shaft with a circular cross-section to form continuous slot holes 3; the depth of the slot holes 3 should reach the designed freezing depth and meet the requirements for filling the heat insulation and deformation buffer material.

[0023] Step 2: After all the slot holes 3 are constructed, for the wall surface where the fine-grained soil layer 4 is located, spraying of high-viscosity CMC and other large-molecular-weight cellulose materials is carried out under the mud to form the waterproof coating 5 on the surface of the slot holes; at the same time, the mud cake on the side wall where the coarse-grained soil layer 6 is located in the slot holes 3 is appropriately removed to improve the ability of the water in the coarse-grained soil layer to drain into the slot holes without affecting the stability of the hole wall.

[0024] Step 3: Fill the slot holes 3 with hollow microsphere foamed cement slurry or cement slurry containing polystyrene foam particles, and cure in-situ to form a soil modification zone with heat insulation and deformation buffer material 7.

[0025] When fine-grained soil freezes, water is prone to migrate from the unfrozen zone to the freezing front; while when coarse-grained soil freezes, water is prone to drain from the frozen zone to the unfrozen zone. In the present invention, the water-proof coating on the surface of the slot holes in the fine-grained soil layer section can prevent water from migrating to the freezing front; the water permeability of the side walls of the slot holes in the coarse-grained soil layer section can promote outward drainage from the frozen zone, thereby reducing the accumulation of frost heave deformation in the two types of soil layers. The hollow microsphere foamed cement slurry or cement slurry containing polystyrene foam particles filled in the slot holes cures to form a lightweight porous material, which, on the one hand, has heat insulation performance and can reduce the conduction of freezing cold to the outside of the slot holes; on the other hand, has deformation buffer performance and can absorb the frost heave deformation outward from the frozen zone, reducing the adverse effects on the environment and facilities outside the boundary.

[0026] The soil modification in Example 1 is implemented circumferentially along the outer boundary of the frozen zone; in fact, it can be implemented only on some arc segments according to needs, or at the inner boundary of the frozen zone (located outside the excavation area). Example

[0027] Example 2 illustrates a schematic diagram of implementing soil modification on the outer boundary 2 of the frozen zone 1 in a rectangular-section shaft freezing project; the three-dimensional schematic diagram, cross-sectional view, and partial vertical section of the soil modification zone are respectively as Figures 4-6 .

[0028] In Example 2, the entire outer boundary 2 of the frozen zone 1 is modified. A slot hole 3 is formed by using a trenching machine. In the slot hole section of the fine-grained soil layer 4, a water-proof coating 5 is sprayed on the side wall surface. An insulation and deformation buffer device 8 (filled with antifreeze) is installed in the slot hole and is connected to a pressure relief valve 9 to implement pressure relief according to needs.

[0029] Main construction steps: Step 1: Continuously excavate with a trenching machine at the designed or expected outer boundary 2 position of the frozen zone around the rectangular-section shaft to form continuous slot holes 3; the depth of the slot holes 3 covers the freezing depth, and the width should meet the installation requirements of the insulation and deformation buffer device.

[0030] After all the slot holes 3 are constructed, for the wall surface of the slot holes where the fine-grained soil layer 4 is located, spray a high-viscosity CMC and other large-molecular-weight cellulose materials under the mud to form a water-proof coating 5 on the surface of the slot holes; at the same time, remove the mud skin on the side walls of the slot holes where the coarse-grained soil layer 6 is located, and improve the ability of water in the coarse-grained soil layer to drain into the slot holes without affecting the stability of the hole wall.

[0031] Step 3: Install a heat insulation and deformation buffer device 8 in the slot hole. A hollow capsule filled with antifreeze (such as brine, antifreeze hydraulic oil) or dry gas (such as air, nitrogen) can be used and connected to a pressure relief valve through a pipeline to achieve stress control and release functions. The capsule is made of materials such as rubber and nylon cloth with high tensile strength and low temperature resistance to ensure working performance, especially sealing and compressive resistance.

[0032] Similar to Example 1, the water-proof coating on the surface of the slot hole can prevent the migration of moisture in the fine-grained soil layer section towards the freezing front, and the removal of part of the mud skin in the slot hole can promote the drainage of moisture in the coarse-grained soil layer towards the slot hole and the non-freezing area, comprehensively reducing frost heave deformation. The capsule installed in the slot hole has certain heat insulation performance (especially better heat insulation performance when filled with gas), and through the control of air pressure or hydraulic pressure and overpressure release, it has a regulation performance for the frost heave deformation of the formation, and finally realizes the control of the development of the freezing area and frost heave deformation, reducing the adverse effects of frost heave deformation on the environment and facilities outside the boundary.

[0033] In Example 2, the soil modification area is implemented comprehensively in four directions along the outer boundary of the freezing area. In fact, it can also be implemented only in a certain area in any direction according to needs, or implemented at the inner boundary of the freezing area (outside the excavation area). Example

[0034] Example 3 illustrates a schematic diagram of implementing soil modification on a part of the outer boundary 2 of the freezing area 1 of the vault in the horizontal tunnel freezing project. The three-dimensional schematic diagram, cross-sectional view, and partial vertical section of the soil modification area are respectively as Figures 7-9 .

[0035] In Example 3, only the local outer boundary 2 of the freezing area 1 of the tunnel vault is modified. A slot hole 3 is formed by drilling and overlapping construction, and a surface water-proof coating 5 is formed on the wall surface of the slot hole by spraying. An insulation and deformation buffer capsule 8 (filled with antifreeze) is installed in the slot hole and is connected to a pressure relief valve 9 to implement pressure relief according to needs.

[0036] The main construction steps are as follows: Step 1: At the designed outer boundary part of the freezing area of the horizontal tunnel vault (i.e., the roof freezing wall), form a continuous slot hole with a certain width through continuous overlapping drilling. The depth of the slot hole should reach the designed freezing length and meet the filling requirements of the heat insulation and deformation buffer device.

[0037] Step 2: After all the slot holes are constructed, spray high-viscosity CMC and other large molecular weight cellulose materials on the wall surface of the fine-grained soil layer section to form a surface water-proof coating.

[0038] In Step 3, a device with heat insulation and deformation buffering functions is installed in the slot hole. A hollow capsule filled with antifreeze (such as brine, antifreeze hydraulic oil) or dry gas (such as air, nitrogen) can be used and connected to a pressure relief valve through a pipeline to achieve stress control and release functions.

[0039] Similar to Embodiments 1 and 2, by controlling the moisture migration or drainage in different soil property strata, the frost heave deformation of the soil body is reduced; by utilizing the heat insulation performance and pressure regulation performance of the capsule in the slot hole, the development of the frozen zone at the vault part and the frost heave deformation are controlled, and the adverse effects of the frost heave deformation on the external environment and facilities in a specific area and direction are reduced.

[0040] In Embodiment 3, the soil body modification area is only locally implemented at the outer boundary of the frozen zone at the tunnel vault part; in fact, it can also be implemented in any direction and area of the frozen area around the tunnel according to needs, or at the inner boundary of the frozen zone (the outside of the tunnel excavation area).

[0041] There are many specific implementation ways of the present invention. The above are only the preferred implementation manners of the present invention. It should be pointed out that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements can still be made, and these improvements should also be regarded as the protection scope of the present invention.

Claims

1. A method for the development of a freezing zone and the control of frost heave deformation based on boundary modification, characterized in that, Before the freezing project construction, first construct the outer boundary (2) of the predetermined formation freezing zone (1) according to the following steps: Step 1: At the outer boundary (2) of the predetermined formation freezing zone (1), construct a number of continuously arranged slot holes (3). The slot holes (3) penetrate the coarse-grained soil layer (6) and the fine-grained soil layer (4) from top to bottom, and their depth is greater than the depth of the formation freezing zone (1). Step 2: Using the under-mud spraying technique, form a surface water-proof coating (5) on the side wall of the slot hole (3) in the fine-grained soil layer (4), and remove the mud skin on the side wall of the coarse-grained soil layer (6) in the slot hole (3) on the premise of ensuring the stability of the slot hole (3). Step 3: Fill the heat insulation and deformation buffer material (7) in each slot hole (3), or install the heat insulation and deformation buffer device (8), so as to form a soil modification area at the position where a number of slot holes (3) are located.

2. A method for controlling the development of a frozen zone and frost heaving deformation based on boundary modification according to claim 1, characterized in that The outer boundary (2) in Step 1 is a partial or total boundary of the formation freezing zone (1).

3. A method for the development of a freezing zone and the control of frost heave deformation based on boundary modification according to claim 1, characterized in that The surface water-proof coating (5) in Step 2 is a water-proof coating formed on the hole wall surface by continuously spraying a high molecular weight and high viscosity cellulose solution to the side wall of the slot hole (3) using a spraying device.

4. A method for the development of a freezing zone and the control of frost heave deformation based on boundary modification according to claim 1, characterized in that The heat insulation and deformation buffer material (7) in Step 3 includes, but is not limited to, foamed cement, hollow microspheres or perlite particle foamed cement, polystyrene foamed material, polyurethane foamed material, and anti-freezing hydrogel doped with hollow microspheres or EPS particles; the heat insulation and deformation buffer material (7) is prepared on the ground and then filled, or prepared in situ after being injected into the slot hole.

5. A method for the development of a freezing zone and the control of frost heave deformation based on boundary modification according to claim 1, characterized in that The heat insulation and deformation buffer device (8) in Step 3 refers to a hollow capsule structure with an antifreeze or gas filled in the cavity, and the capsule is connected to a pressure relief valve (9) through a pipeline.

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