A method for suppressing frost heave deformation by reducing local saturation of soil layers

Abstract

The present invention discloses a method for suppressing frost heave deformation of a soil layer by reducing the local saturation of the soil layer, and relates to the technical field of geotechnical engineering construction. By reducing the water saturation and permeability of the soil modification zone, the migration of pore water is suppressed or even blocked, and the frost heave deformation of the stratum is reduced. Step 1, in the stratum to be frozen or at the interface with the non-frozen zone, several boreholes for soil modification are drilled at intervals; Step 2, first install coaxially docked special pipelines and flower pipes in the borehole; then install rubber sealing plugs and arrange pipelines; Step 3, fill the rubber sealing plugs with gas or hydraulic oil, and then shut off the pipeline; Step 4, press compressed air or foam slurry into the fine-grained soil layer around the flower pipe; Step 5, press expansive slurry into the soil layer to be modified. Compared with the comprehensive modification of soil using cement soil, the present invention can effectively control the frost heave deformation of soil with a relatively simpler process and more economical cost.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering construction, and in particular to a method for suppressing frost heave deformation of a soil layer by reducing the local saturation of the soil layer. Background Art

[0002] Existing technologies often use freezing methods to artificially freeze loose, unstable, water-bearing strata, creating a frozen soil structure that can seal out water and resist external water and soil pressure, thereby protecting underground excavation and masonry construction. In addition to its widespread application in mine shaft construction, freezing methods have also been widely used in municipal geotechnical engineering projects, such as the reinforcement of soil around subway access roads and shield tunnel entrances. However, freezing methods can also be accompanied by frost heave due to the expansion of frozen water in the soil. This frost heave, particularly in municipal engineering projects, poses a serious threat to the safety of the surrounding environment and facilities.

[0003] Currently, the main methods for controlling frost heave deformation in municipal geotechnical engineering freezing construction include: 1. Modifying the ground by adding materials such as cement and lime to reduce initial moisture content and increase soil strength, thereby reducing subsequent frost heave; 2. Setting pressure relief holes at appropriate locations in the frozen zone to release soil frost heave deformation; 3. Optimizing the layout of freezing holes, the freezing system startup sequence, and time intervals to accelerate drainage from coarse-grained soil to reduce frost heave; and 4. Using rapid freezing and intermittent freezing, reducing the migration of moisture in fine-grained soil toward the freezing front, thereby suppressing frost heave. However, these existing methods have their own advantages and disadvantages. For example, cement soil improvement requires comprehensive implementation in the frozen zone, the pressure relief holes have limited deformation buffering effect, and the optimization of freezing parameters is complex and affected by soil properties.

[0004] In addition, the frost heave of soil is not only related to soil properties and moisture content, but also closely related to water saturation. Saturated silt and silty clay below the groundwater level are prone to pore water infiltration and water migration, which in turn aggravates frost heave.

[0005] Based on this, in general, the existing technology lacks a method to effectively inhibit the frost heave deformation of soil. How to effectively inhibit the frost heave deformation of soil has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0006] In response to the above problems, the present invention proposes a method for inhibiting frost heave deformation by reducing the local saturation of the soil layer. By reducing the water saturation and permeability of the modified area of ​​the soil, the migration of pore water is inhibited or even blocked, thereby reducing the frost heave deformation of the formation.

[0007] The technical solution of the present invention is to carry out the following steps:

[0008] Step 1: Drilling a plurality of boreholes 2 for soil modification at intervals within the to-be-frozen stratum 1 or at its interface with the non-frozen zone, wherein the boreholes 2 are parallel to each other and distributed on the same plane, the same curved surface, or the same circumference;

[0009] Step 2: First, install a coaxially connected dedicated pipeline 3 and a flower tube 4 in the borehole 2. The side wall of the flower tube 4 has a plurality of through holes evenly distributed. Then, install a pneumatic or hydraulic expansion rubber sealing plug 5 between the outer wall of the dedicated pipeline 3 and the inner wall of the borehole 2. Arrange a pipeline 6 connected to an air pump or hydraulic pump, and arrange the other end of the pipeline 6 into the rubber sealing plug 5.

[0010] Step 3: Use an air pump or a hydraulic pump to fill the rubber sealing plug 5 with gas or hydraulic oil through the pipeline 6, so that the rubber sealing plug 5 expands and blocks the space between the dedicated pipeline 3 and the borehole 2, thereby blocking the passage between the formation to be modified and the upper formation along the borehole, and then shutting off the pipeline 6;

[0011] Step 4: Press compressed air 7 or foam slurry 8 into the fine-grained soil layer around the flower tube 4 through the dedicated pipeline 3 in the borehole 2 and the flower tube 4;

[0012] Step 5: Use the dedicated pipeline 3 to press the expansive slurry 9 into the soil layer to be modified. After it has initially solidified, the dedicated pipeline 3, the flower pipe 4, the rubber sealing plug 5, and the pipeline 6 are removed from the borehole 2. After curing to a predetermined age and forming a flat, curved or cylindrical soil modification area 10, freezing construction is carried out.

[0013] The stratum to be frozen 1 refers to the fine-grained soil layer below the groundwater level that requires freezing, such as saturated silt and clay, which is susceptible to water migration through the soil pores. The soil modification zone 10 refers to the flat, curved, or closed cylindrical soil modification zone formed using this technology within the intended freezing zone or at the interface between the intended freezing zone and the unfrozen zone. The direction of transfer of freezing cold should be perpendicular to the plate or cylindrical surface of the soil modification zone.

[0014] In this case, a certain volume of compressed air 7 or foam slurry 8 is first injected into the soil via a dedicated pipeline 3 and a floral pipe 4. Then, an expansive slurry 9 is used to seal the soil modification section of the drilled hole, forming a plate-like or cylindrical soil modification zone 10 of a certain thickness. By utilizing the modified soil zone, where water saturation and permeability are significantly reduced, pore water migration is inhibited or even blocked, reducing frost heave deformation of the stratum.

[0015] The spacing between adjacent boreholes 2 does not exceed twice the effective diffusion radius of the compressed air 7 or foam slurry 8 injected into step 4.

[0016] The pressure of the compressed air 7 or foam slurry 8 in step 4 is not less than the water pressure at the bottom of the borehole 2 and does not exceed the vertical ground pressure. The vertical ground pressure is the vertical ground pressure on the middle section of the soil modification area 10, which is the pressure formed by the deadweight of the soil.

[0017] When used in a rectangular cross-section vertical shaft freezing project, the borehole 2 is drilled vertically or obliquely downward from the ground into the to-be-frozen stratum 1, and is drilled on either side of the vertical shaft freezing zone to form a flat-plate soil modification zone 10; or drilled on both sides of the vertical shaft freezing zone to form two flat-plate soil modification zones 10; or drilled around the vertical shaft freezing zone to form four flat-plate soil modification zones 10, and the four flat-plate soil modification zones 10 are sequentially connected end to end to form a closed rectangle.

[0018] When used in a circular cross-section shaft freezing project, the borehole 2 is drilled vertically or obliquely downward from the ground into the stratum 1 to be frozen, and is constructed on the outer circle of the shaft freezing zone to form a circumferentially closed cylindrical soil modification zone 10; or the outer circle of the shaft freezing zone is partially constructed to form a curved plate-shaped soil modification zone 10;

[0019] When applied to the freezing project of a horizontal tunnel with a straight wall and a semicircular arch section, the drill hole 2 is arranged in a horizontal or inclined direction at the upper edge of the freezing zone of the tunnel arch, and constructed at the outer edge of the freezing zone of the horizontal tunnel arch to form a curved plate-shaped soil modification zone 10; or constructed in the freezing zone of the tunnel side and bottom plate to form multiple curved or flat plate-shaped soil modification zones 10; or constructed in all circumferential directions of the freezing zone around the tunnel to form a circumferentially closed soil modification zone 10.

[0020] The drill holes can be special drill holes used for soil modification, or they can be used as freezing holes, temperature measuring holes, hydrological observation holes or pressure relief holes, etc., for soil modification construction before the ground freezes.

[0021] The dedicated pipeline 3 refers to a sealed pipeline installed in the borehole for conveying compressed air and foam slurry; the flower pipe 4 refers to a section of pipeline connected to the end of the dedicated pipeline, with several openings on the side wall, which is used to spray compressed air, foam slurry, etc. and press them into the soil layer; the flower pipe can be specially processed, or it can be formed by opening holes in the side wall of a section of the dedicated pipeline located in the soil modification area; the rubber sealing plug 5 refers to a pneumatic or hydraulic expansion rubber sealing plug that is sleeved on the dedicated pipeline and close to the soil modification area, and is pressurized and expanded by the pipeline 6, and is used to block the compressed air and foam slurry from overflowing through the borehole channel to the non-modified area; the pipeline is used to connect to a ground air pump or hydraulic pump.

[0022] The compressed air 7 is a non-toxic, harmless, and non-combustion and explosion-risk pressurized gas output from a compression pump or a pressure vessel and supplied to the stratum to be frozen via a dedicated pipeline. Air or nitrogen is usually used.

[0023] The foam slurry 8 refers to a high-stability foam slurry generated by physical and chemical foaming of water, foaming agent, compressed air or nitrogen, which is transported to the formation through a pipeline and then pressure-infiltrated into the formation through the bottom opening and side wall openings of the flower pipe.

[0024] The expansive slurry 9 refers to an expansive cement slurry or cement bentonite slurry that fills the drilled section of the soil modification area and performs a sealing effect after solidification; the dedicated pipelines, flower pipes and sealing devices in the hole can only be removed after the slurry has initially solidified.

[0025] The present invention reduces the local saturation of the soil layer and blocks the infiltration and migration channels of pore water within the soil, thereby inhibiting frost heaving caused by water migration. It is mainly suitable for local modification of frost-heaving soil layers such as saturated silt and clay below the groundwater level before construction using the freezing method in municipal engineering projects. By increasing the air content in the local area of ​​the stratum to be frozen, its water saturation and permeability are reduced, thereby inhibiting or even blocking the migration of pore water, thereby effectively controlling the frost heaving of the stratum. Compared with the comprehensive modification of soil using cement soil, the present invention can effectively control the frost heaving deformation of the soil with a relatively simpler process and more economical construction cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 3D schematic diagram of a flat-plate soil modification zone in a rectangular cross-section vertical shaft freezing project in Example 1;

[0027] Figure 2 Schematic diagram of the cross section of the flat-plate soil modification area in the rectangular cross-section shaft freezing project in Example 1;

[0028] Figure 3 This is a vertical cross-sectional view of a flat-plate soil modification area in the rectangular cross-section shaft freezing project in Example 1;

[0029] Figure 4 This is a three-dimensional schematic diagram of the cylindrical soil modification area in the circular cross-section vertical shaft freezing project in Example 2;

[0030] Figure 5 Schematic diagram of the cross section of the cylindrical soil modification area in the circular cross-section shaft freezing project in Example 2;

[0031] Figure 6 This is a vertical cross-sectional view of the cylindrical soil modification area in the circular cross-section shaft freezing project in Example 2;

[0032] Figure 7 is a three-dimensional schematic diagram of the soil modification zone in the shape of a curved plate of an arch when the horizontal tunnel is frozen in Example 3;

[0033] Figure 81 is a schematic cross-sectional view of the soil modification zone in the shape of a curved plate of an arch when the horizontal tunnel is frozen in Example 3;

[0034] Figure 9 is a vertical cross-sectional view of the soil modification zone in the form of a curved plate of an arch when the horizontal tunnel is frozen in Example 3;

[0035] Figure 10 It is a vertical cross-section of the drill hole and internal devices during the soil modification process (the soil modification section is filled with compressed air or foam slurry at this time);

[0036] Figure 11 It is a schematic diagram of the grouting and sealing state in the hole after soil modification (at this time, the hole in the soil modification section is filled with expansive slurry material).

[0037] Numbers and meanings in the figure:

[0038] 1- ground to be frozen; 2- borehole; 3- dedicated pipeline; 4- flower pipe; 5- rubber sealing plug; 6- pipeline;

[0039] 7- Compressed air; 8- Foam slurry; 9- Expansive slurry; 10- Soil modification area DETAILED DESCRIPTION

[0040] In order to clearly illustrate the technical features of the present invention, the present invention is described in detail below through specific implementation methods and in conjunction with the accompanying drawings.

[0041] Example 1: Example 1 is the present invention used in a rectangular cross-section shaft freezing project, where compressed air is injected into a specific area within the freezing zone to form a flat soil modification zone, such as Figure 1 、 2 , 3, 10, and 11.

[0042] Specific methods:

[0043] Step 1: First, drill holes 2 for soil modification are constructed at a certain interval in the planned freezing area of ​​the to-be-frozen stratum 1 around the rectangular vertical shaft; the hole spacing does not exceed 2 times the effective diffusion radius when compressed air is pressed into the soil.

[0044] Step 2: Install a dedicated pipeline 3 and a flower pipe 4 in the borehole 2; and install an air pressure or hydraulic expansion rubber sealing plug 5 and a pipeline 6 at an appropriate position of the pipeline (generally at the upper boundary of the soil layer to be modified).

[0045] Step 3: Use an air pump or a hydraulic pump to supply air to the rubber sealing plug 5 through the pipeline 6, so that it expands and blocks the borehole space outside the pipe, blocking the channel along the borehole between the formation to be modified and the upper formation, and then close the pipeline valve.

[0046] Step 4: Connect the air compression pump to the dedicated pipeline in the hole, so that the compressed air 7 is pressed into the fine-grained soil layer through the flower tube 4 until the designed air pressure and volume are reached; the gas pressure should not be less than the water pressure at the bottom of the borehole and not exceed the vertical ground pressure.

[0047] Step 5: Use the dedicated pipeline 3 to press the expansive slurry 9 (cement slurry or cement bentonite slurry) into the soil modification section in the borehole. When it is initially solidified and can effectively block the overflow of compressed air, the dedicated pipeline 3, the flower pipe 4 and the rubber sealing plug 5 are removed from the borehole; then the soil is cured to a certain age and the freezing construction is carried out.

[0048] In Example 1, flat-plate soil modification zones are formed on the left and right sides of the frozen shaft. These zones block water migration across the modified zones and inhibit the growth and transmission of frost heave deformation. Depending on the need to protect surrounding equipment, construction can also be performed on either side of the frozen shaft to form a flat-plate soil modification zone, or on all sides of the frozen shaft to form a closed soil modification zone.

[0049] Example 2: Example 2 is an application of the present invention to a circular cross-section shaft freezing project. By pressing foam slurry into a specific area within the freezing zone, a closed cylindrical soil modification area is formed, such as Figure 4 、 5 , 6, 10, and 11.

[0050] The main difference between Example 2 and Example 1 is that, on the one hand, foam slurry is pressed into the stratum; on the other hand, holes are arranged around the circumference of the intended freezing area to form a closed cylindrical soil modification area, so as to completely prevent moisture outside the modification area from penetrating the modified soil and migrating to the freezing front inside it, thereby completely suppressing the growth of frost heave in the stratum.

[0051] Specific methods:

[0052] The implementation steps of Example 2 are similar to those of Example 1 and are briefly described below.

[0053] Step 1: First, in the planned freezing area of ​​the to-be-frozen stratum 1 around the circular vertical shaft, special soil modification holes 2 are constructed at a certain interval; the hole spacing does not exceed 2 times the effective diffusion radius when the foam slurry is injected into the soil.

[0054] Step 2: Install a dedicated pipeline 3 and a flower pipe 4 in the borehole; and install an air pressure or hydraulic expansion type rubber sealing plug and a pipeline at the upper boundary of the soil layer to be modified.

[0055] Step 3: Use an air pump or a hydraulic pump to supply air to the rubber sealing plug 5 through the pipeline to seal the borehole space outside the pipe, block the channel along the borehole between the formation to be modified and the upper formation, and then close the pipeline valve.

[0056] Step 4: Use water, chemical admixtures and compressed air to prepare a foam slurry 8 with good stability using a foaming agent at the construction site; connect the grouting pump with the dedicated pipeline in the hole, and press the foam slurry into the soil layer through the flower pipe 4 until the designed pressure and volume are reached; the grouting pressure should not be less than the water pressure at the bottom of the borehole and not exceed the vertical ground pressure.

[0057] Step 5: After the foam slurry is injected, the expansive slurry 9 (cement slurry or cement bentonite slurry) is pressed into the soil layer to be modified using a dedicated pipeline 3. After initial setting, the pipelines and devices in the hole are removed, and the ground is frozen after curing to a certain age.

[0058] In Example 2, a circumferentially closed cylindrical soil modification zone is formed outside the frozen zone of the circular shaft. This completely blocks the migration of moisture from the outer portion of the modification zone toward the freezing front within it, effectively suppressing frost heave caused by moisture migration. In fact, depending on the need to protect surrounding environmental facilities, the local modification zone outside the circular shaft can also be limited to a specific arc segment along the circumference, forming a non-enclosed soil modification zone, blocking moisture migration in a specific direction and suppressing frost heave deformation caused by it.

[0059] Example 3: Example 3 is the application of the present invention to a horizontal tunnel freezing project with a straight wall and a semicircular arch section. In a specific portion of the outer boundary of the arch freezing zone, a curved plate-shaped soil modification zone is formed by injecting foam slurry, such as Figure 7 、 8 , 9, 10, and 11.

[0060] The main difference between Example 3 and Examples 1 and 2 is that, on the one hand, the soil modification boreholes are only arranged at the upper edge of the tunnel vault freezing zone, forming only a curved plate-shaped soil modification zone; on the other hand, the soil modification is carried out along the full depth (length) of the borehole.

[0061] Specific methods:

[0062] The implementation steps of Example 3 are similar to those of Example 2 and are briefly described below.

[0063] Step 1: First, construct 2 special soil modification holes at a certain interval at the upper edge of the frozen zone of the tunnel vault (i.e., the interface between the frozen zone and the non-frozen zone); the hole spacing shall not exceed 2 times the effective diffusion radius when injecting foam slurry into the soil.

[0064] Step 2: Along the depth direction of the hole, a certain length of dedicated pipeline 3 is installed only at the hole mouth section, and flower pipes 4 are installed at the rest of the sections; a pneumatic or hydraulic expansion type rubber sealing plug 5 and a pipeline 6 are installed on the dedicated pipeline at the hole mouth section.

[0065] Step 3: Use an air pump or a hydraulic pump to supply air to the rubber sealing plug 5 through the pipeline to seal the annular space outside the pipe, block the path for the foam slurry to leak out of the formation to be modified along the borehole, and then close the pipeline valve.

[0066] Step 4: Use water, chemical admixtures and compressed air at the construction site, and use a foaming agent to prepare a foam slurry 8 with good stability; connect the grouting pump with the dedicated pipeline in the hole, and press the foam slurry 8 into the soil layer through the flower pipe 4 until the designed pressure and volume are reached; the grouting pressure should not be less than the bottom hole water pressure and not exceed the vertical ground pressure.

[0067] Step 5: After the foam slurry is injected, the expansive slurry 9 (cement slurry or cement bentonite slurry) is pressed into the soil modification section in the borehole through the dedicated pipeline 3. After the initial setting, the pipelines and devices in the hole are removed, and the ground is frozen after curing to a certain age.

[0068] In Example 3, a curved, plate-like soil modification zone is formed at the outer edge of the frozen zone at the crown of a horizontal tunnel. This prevents moisture from the unfrozen zone above from migrating to the frozen zone below, suppressing frost heave at the crown and protecting the safety of the upper facilities. In fact, as needed, local modification outside the frozen zone of a horizontal tunnel can be constructed in any orientation within the frozen zones of the tunnel roof, side walls, or floor, forming one or more curved or flat plate-like soil modification zones. Alternatively, the modification can be carried out in all directions around the frozen zone around the tunnel, forming a circumferentially enclosed soil modification zone.

[0069] There are many specific implementation ways of the present invention. The above is only the preferred implementation method of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be considered as the scope of protection of the present invention.

Claims

1. A method for suppressing frost heave deformation of a soil layer by reducing its local saturation, characterized in that: Follow these steps: Step 1: Drilling a plurality of boreholes (2) for soil modification at intervals within the to-be-frozen stratum (1) or at its interface with the non-frozen zone, wherein the plurality of boreholes (2) are parallel to each other and distributed on the same plane, the same curved surface or the same circumference; Step 2: First, a dedicated pipe (3) and a flower pipe (4) are coaxially connected and installed in the borehole (2), and a plurality of through holes are evenly arranged on the side wall of the flower pipe (4); then, a pneumatic expansion type or hydraulic expansion type rubber sealing plug (5) is installed between the outer wall of the dedicated pipe (3) and the inner wall of the borehole (2), and a pipe (6) connected to an air pump or a hydraulic pump is arranged, and the other end of the pipe (6) is inserted into the rubber sealing plug (5); Step 3: using an air pump or a hydraulic pump, filling the rubber sealing plug (5) with gas or hydraulic oil through the pipeline (6), so that the rubber sealing plug (5) expands and blocks the space between the dedicated pipeline (3) and the borehole (2), thereby blocking the passage between the formation to be modified and the upper formation along the borehole, and then shutting off the pipeline (6); Step 4: Press compressed air (7) or foam slurry (8) into the fine-grained soil layer around the flower tube (4) through the dedicated pipeline (3) in the borehole (2) and the flower tube (4); In step 4, the pressure of the compressed air (7) or foam slurry (8) is not less than the water pressure at the bottom of the borehole (2) and does not exceed the vertical ground pressure, which is the vertical ground pressure on the middle section of the soil modification area (10); Step 5: Use a dedicated pipeline (3) to press the expansive slurry (9) into the soil layer to be modified. After the slurry is initially solidified, the dedicated pipeline (3), the flower pipe (4), the rubber sealing plug (5), and the pipeline (6) are removed from the borehole (2). After the soil modification area (10) is formed into a flat plate, curved plate, or cylindrical shape after curing to a predetermined age, freezing construction is carried out.

2. The method of suppressing frost heave deformation of a soil layer by reducing the local saturation of the soil layer according to claim 1, characterized in that: The spacing between adjacent drill holes (2) does not exceed twice the effective diffusion radius of the compressed air (7) or foam slurry (8) injected into step 4.

3. The method of suppressing frost heave deformation of a soil layer by reducing the local saturation of the soil layer according to claim 1, characterized in that: When applied to a rectangular cross-section vertical shaft freezing project, the borehole (2) is drilled vertically or obliquely downward from the ground into the to-be-frozen stratum (1), and is constructed on either side of the vertical shaft freezing zone to form a flat-plate-shaped soil modification zone (10); or is constructed on both sides of the vertical shaft freezing zone to form two flat-plate-shaped soil modification zones (10); or is constructed around the vertical shaft freezing zone to form four flat-plate-shaped soil modification zones (10), and the four flat-plate-shaped soil modification zones (10) are sequentially connected end to end to form a closed rectangle.

4. The method of suppressing frost heave deformation of a soil layer by reducing the local saturation of the soil layer according to claim 1, characterized in that: When applied to a circular cross-section shaft freezing project, the borehole (2) is drilled vertically or obliquely downward from the ground into the to-be-frozen stratum (1), and is constructed on the outer circle of the shaft freezing zone to form a circumferentially closed cylindrical soil modification zone (10); or a local circumference of the outer circle of the shaft freezing zone is constructed to form a curved plate-shaped soil modification zone (10).

5. The method of suppressing frost heave deformation of a soil layer by reducing the local saturation of the soil layer according to claim 1, characterized in that: When applied to a horizontal tunnel freezing project with a straight wall and a semicircular arch section, the borehole (2) is arranged in a horizontal or inclined direction at the upper edge of the tunnel arch freezing zone, and is constructed at the outer edge of the horizontal tunnel arch freezing zone to form a curved plate-shaped soil modification zone (10); or is constructed in the tunnel side wall and bottom plate freezing zone to form multiple curved or flat plate-shaped soil modification zones (10); or is constructed in all directions around the freezing zone around the tunnel to form a circumferentially closed soil modification zone (10).

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