Method for inhibiting frost heaving deformation of soil layer by reducing local saturation of soil layer

Abstract

The invention discloses a method for inhibiting frost heaving deformation of a soil layer by reducing local saturation of the soil layer, and relates to the technical field of geotechnical engineering construction. By reducing the water saturation and permeability of a soil body modified area, migration of pore water is inhibited or even blocked, and the frost heaving deformation of a stratum is reduced. The method comprises the following steps: step 1, constructing and drilling a plurality of special drill holes for soil modification at intervals in a to-be-frozen stratum or an interface of the to-be-frozen stratum and a non-freezing area; 2, a special pipeline and a floral tube which are in coaxial butt joint are installed in the drill hole; then a rubber packing plug is installed, and a pipeline is arranged; 3, gas or hydraulic oil is filled into the rubber packing plug, and then the pipeline is closed; 4, compressed air or foam slurry is pressed into the fine particle soil layer around the floral tube; and step 5, pressing expansive slurry into the soil layer to be modified. Compared with comprehensive modification of the soil body by adopting cement soil, the method disclosed by the invention can effectively control the frost heaving deformation of the soil body by adopting a relatively simple and convenient process and a more economical manufacturing cost.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering construction, and particularly relates to a method for suppressing frost heaving deformation by reducing the local saturation of soil layers. Background Technique

[0002] In the prior art, the freezing method is commonly used to artificially freeze loose and unstable water-containing strata, so as to form a frozen soil structure that can seal water and resist external soil and water pressure to protect the excavation and lining construction of underground projects. In addition to being widely used in the construction of mine shafts, the freezing method has also been widely used in municipal geotechnical engineering such as subway connecting passages and soil reinforcement around the shield tunneling entrances and exits. However, the freezing method will also be accompanied by frost heaving due to the freezing and expansion of water in the soil. Especially in municipal engineering, the frost heaving of the strata will seriously threaten the safety of the surrounding environment and facilities.

[0003] At present, in the freezing construction of municipal geotechnical engineering, the methods for controlling the frost heaving deformation of the strata mainly include: First, modify the strata by adding materials such as cement and lime to reduce the initial moisture content and improve the soil strength to achieve the purpose of reducing the later frost heaving; Second, set pressure relief holes at appropriate positions in the freezing area to release the frost heaving deformation of the soil; Third, optimize the arrangement of freezing holes, the starting sequence and time interval of the freezing system, etc., to accelerate the drainage from coarse-grained soil to the outside to weaken the frost heaving; Fourth, by means of rapid freezing and intermittent freezing, reduce the migration of water in the fine-grained soil body to the freezing front, thereby suppressing the frost heaving. However, these existing methods have their own advantages and disadvantages. For example, the improvement of cement soil needs to be carried out comprehensively in the freezing area, the deformation buffer effect of the pressure relief hole is limited, the optimization of freezing parameters is relatively complex and the effect is affected by soil properties, etc.

[0004] In addition, the frost heaving property of the soil is not only related to the soil property and moisture content, but also closely related to the water saturation. And below the groundwater level, saturated silt, silty clay, etc. are prone to pore water penetration and water migration, which will further exacerbate the frost heaving.

[0005] Therefore, generally speaking, the prior art lacks an effective method for suppressing the frost heaving deformation of the soil, and how to effectively suppress the frost heaving deformation of the soil has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] In view of the above problems, the present invention proposes a method for suppressing frost heaving deformation by reducing the local saturation of soil layers, by reducing the water saturation and permeability of the soil modification area, suppressing or even blocking the migration of pore water, and reducing the frost heaving deformation amount of the strata.

[0007] The technical solution of the present invention is as follows: It is carried out according to the following steps: Step 1. At the interface between the formation to be frozen 1 and the unfrozen area or within the formation to be frozen 1, a number of special drilling holes 2 for soil modification are drilled at intervals. The number of drilling holes 2 are distributed parallel to each other on the same plane, the same curved surface or the same circumference. Step 2. First, a special pipeline 3 and a perforated pipe 4 with coaxial docking are installed in the drilling hole 2. The side wall of the perforated pipe 4 is evenly provided with a number of through holes. Then, a pneumatically expandable or hydraulically expandable rubber packer 5 is installed between the outer wall of the special pipeline 3 and the inner wall of the drilling hole 2, and a pipeline 6 connecting an air pump or a hydraulic pump is arranged. The other end of the pipeline 6 penetrates into the rubber packer 5. Step 3. Using an air pump or a hydraulic pump, gas or hydraulic oil is filled into the rubber packer 5 through the pipeline 6, so that the rubber packer 5 expands to block the space between the special pipeline 3 and the drilling hole 2, blocking the channel along the drilling hole between the formation to be modified and the upper formation, and then the pipeline 6 is shut off. Step 4. Compressed air 7 or foam slurry 8 is pressed into the fine-grained soil layer around the perforated pipe 4 through the special pipeline 3 and the perforated pipe 4 in the drilling hole 2. Step 5. Using the special pipeline 3, an expansive slurry 9 is pressed into the soil layer to be modified. After its initial setting, the special pipeline 3, the perforated pipe 4, the rubber packer 5 and the pipeline 6 are all removed by pulling them out from the drilling hole 2. After curing to a predetermined age, a flat, curved or cylindrical soil modification area 10 is formed, and then freezing construction is carried out.

[0008] The formation to be frozen 1 refers to fine-grained soil layers such as saturated silt and clay that need to be frozen below the groundwater level and are prone to water migration through soil pores. The soil modification area 10 refers to a flat, curved or closed cylindrical soil modification area formed by this technology within the formation to be frozen or at the interface between the formation to be frozen and the unfrozen area. The direction of heat transfer of the formation freezing cold should be perpendicular to the plate surface or the cylindrical surface of the soil modification area.

[0009] In this case, a certain volume of compressed air 7 or foam slurry 8 is first pressed into the soil through the special pipeline 3 and the perforated pipe 4, and then the expansive slurry 9 is used to seal the soil modification section of the drilling hole, forming a plate-shaped or cylindrical soil modification area 10 with a certain thickness. The soil modification area with significantly reduced water saturation and permeability is used to inhibit or even block the migration of pore water and reduce the frost heave deformation of the formation.

[0010] The spacing between adjacent drilling holes 2 does not exceed 2 times the effective diffusion radius when compressed air 7 or foam slurry 8 is pressed into in Step 4.

[0011] The pressure of the compressed air 7 or foam slurry 8 pressed into in Step 4 is less than the water pressure at the bottom of the drilling hole 2 and does not exceed the vertical ground pressure, and the vertical ground pressure is the vertical ground pressure on the middle section of the soil modification area 10 and is the pressure formed by the self-weight of the soil.

[0012] When applied to the freezing project of a vertical shaft with a rectangular cross-section, the drill hole 2 is drilled vertically or obliquely downward from the ground into the formation 1 to be frozen, and is constructed on either side of the freezing area of the vertical shaft to form a flat soil modification area 10; or is constructed on both sides of the freezing area of the vertical shaft respectively to form two flat soil modification areas 10; or is constructed around the freezing area of the vertical shaft respectively to form four flat soil modification areas 10, and the four flat soil modification areas 10 are connected end to end in sequence to form a closed rectangle. When applied to the freezing project of a vertical shaft with a circular cross-section, the drill hole 2 is drilled vertically or obliquely downward from the ground into the formation 1 to be frozen, and is constructed on the outer circle of the freezing area of the vertical shaft to form a circumferentially closed cylindrical soil modification area 10; or is constructed on a partial circumference of the outer circle of the freezing area of the vertical shaft to form a curved plate-shaped soil modification area 10. When applied to the freezing project of a horizontal tunnel with a straight wall and semi-circular arch cross-section, the drill hole 2 is arranged along the horizontal or inclined direction at the upper edge of the freezing area of the tunnel arch crown, and is constructed on the outer edge of the freezing area at the top of the horizontal tunnel arch to form a curved plate-shaped soil modification area 10; or is constructed in the freezing areas of the side wall and bottom plate of the tunnel to form multiple curved or flat plate-shaped soil modification areas 10; or is constructed comprehensively in all circumferential directions of the freezing area around the tunnel to form a circumferentially closed soil modification area 10.

[0013] The drill hole can be a special drill hole for soil modification, or can utilize freezing holes, temperature measuring holes, hydrographic observation holes, pressure relief holes, etc. for soil modification construction before formation freezing.

[0014] The special pipeline 3 refers to a sealed pipeline installed in the drill hole for transporting compressed air and foam slurry; the perforated pipe 4 refers to a section of pipeline connected to the end of the special pipeline and having several openings on the side wall for spraying and pressing compressed air, foam slurry, etc. into the soil layer; the perforated pipe can be specially processed, or can be formed by opening holes on the side wall of a section of the special pipeline located in the soil modification area; the rubber packer 5 refers to a pneumatic or hydraulic expandable rubber packer that is sleeved on the special pipeline and is close to the soil modification area and expands by the pressure of the pipeline 6, and is used to block the overflow of compressed air and foam slurry from the drill hole channel to the non-modified area; the pipeline is used to connect to a ground air pump or hydraulic pump.

[0015] The compressed air 7 is a pressurized gas output from a compressor or pressure vessel, supplied to the formation to be frozen through the special pipeline, and is non-toxic, harmless and has no risk of combustion and explosion. Usually, air or nitrogen is used.

[0016] The foam slurry 8 refers to a highly stable foam slurry generated by physical and chemical actions using water, foaming agent, compressed air or nitrogen, etc., transported to the formation through the pipeline, and then infiltrated into the formation through the bottom opening and side wall openings of the perforated pipe.

[0017] The expansive grout 9 refers to an expansive cement grout or a cement-bentonite grout that plugs the borehole section filled with the soil modification area and plays a plugging role after solidification. The special pipelines, perforated pipes, and sealing devices in the hole can be removed only after the initial setting of the grout.

[0018] By reducing the local saturation of the soil layer and blocking the seepage migration channels of pore water in the soil, the present invention can inhibit the frost heaving induced by water migration in the soil. It is mainly applicable to the local modification of frost-susceptible soil layers such as saturated silt and clay below the groundwater level before the freezing method is used in municipal engineering. By increasing the gas content in the local area of the formation to be frozen, reducing its water saturation and permeability, the migration of pore water can be inhibited or even blocked, thereby effectively controlling the frost heaving of the formation. Compared with the comprehensive modification of the soil with cement soil, the present invention can effectively control the frost heaving deformation of the soil with a relatively simpler process and more economical cost. Description of the Drawings

[0019] Figure 1 It is a three-dimensional schematic diagram of the flat soil modification area in the rectangular-section shaft freezing project in Example 1; Figure 2 It is a cross-sectional schematic diagram of the flat soil modification area in the rectangular-section shaft freezing project in Example 1; Figure 3 It is a longitudinal sectional view of the flat soil modification area in the rectangular-section shaft freezing project in Example 1; Figure 4 It is a three-dimensional schematic diagram of the cylindrical soil modification area in the circular-section shaft freezing project in Example 2; Figure 5 It is a cross-sectional schematic diagram of the cylindrical soil modification area in the circular-section shaft freezing project in Example 2; Figure 6 It is a longitudinal sectional view of the cylindrical soil modification area in the circular-section shaft freezing project in Example 2; Figure 7 It is a three-dimensional schematic diagram of the curved panel-shaped soil modification area at the arch crown during horizontal tunnel freezing in Example 3; Figure 8 It is a cross-sectional schematic diagram of the curved panel-shaped soil modification area at the arch crown during horizontal tunnel freezing in Example 3; Figure 9 It is a longitudinal sectional view of the curved panel-shaped soil modification area at the arch crown during horizontal tunnel freezing in Example 3; Figure 10 It is a longitudinal sectional view of the borehole and internal devices during soil modification (at this time, the borehole in the soil modification section is filled with compressed air or foam grout); Figure 11 It is a schematic diagram of the grouting plugging state in the borehole after soil modification (at this time, the borehole in the soil modification section is filled with expansive grout material).

[0020] Numbers and their meanings in the figure: 1 - Formation to be frozen; 2 - Borehole; 3 - Special pipeline; 4 - Slotted pipe; 5 - Rubber packer; 6 - Pipe; 7 - Compressed air; 8 - Foam slurry; 9 - Expansive slurry; 10 - Soil modification area Specific implementation manners

[0021] To clearly illustrate the technical features of the present invention, the present invention will be elaborated in detail below through specific implementation manners and in combination with its accompanying drawings.

[0022] Example 1: Example 1 is for the freezing project of a rectangular-section shaft of the present invention. Compressed air is injected into a specific area within the freezing zone to form a flat soil modification area, as shown in Figure 1 , 2 , 3, 10, 11.

[0023] Specific method: Step 1. First, in the proposed freezing area of the formation 1 to be frozen around the rectangular shaft, boreholes 2 dedicated to soil modification are constructed at a certain interval; the hole interval does not exceed 2 times the effective diffusion radius when injecting compressed air into the soil.

[0024] Step 2. Install the special pipeline 3 and the slotted pipe 4 in the borehole 2; and install a pneumatic or hydraulic expansion type rubber packer 5 and a pipe 6 at an appropriate position of the pipeline (generally at the upper boundary of the proposed modified soil layer).

[0025] Step 3. Use an air pump or a hydraulic pump to supply gas to the rubber packer 5 through the pipe 6, so that it expands to block the borehole space outside the pipe and block the channel along the borehole between the proposed modified formation and the upper formation, and then close the valve of this pipeline.

[0026] Step 4. Connect the air compressor pump with the special pipeline in the hole, and press the compressed air 7 into the fine-grained soil layer through the slotted pipe 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 should not exceed the vertical earth pressure.

[0027] Step 5. Use the special pipeline 3 to press the expansive slurry 9 (cement slurry or cement-bentonite slurry) into the soil modification section in the borehole. After its initial setting can effectively block the upward overflow of compressed air, the special pipeline 3, the slotted pipe 4, the rubber packer 5, etc. are all taken out and removed from the borehole; then cure for a certain age and carry out the freezing construction.

[0028] In Example 1, flat-shaped soil modification zones are formed on the left and right sides of the shaft freezing zone respectively, which are used to block the moisture migration across the soil modification zone, and inhibit the growth and transmission of frost heave deformation. According to the needs of protecting the surrounding environmental equipment, construction can also be carried out on either side of the freezing zone around the shaft only to form a flat-shaped soil modification zone; or construction can be carried out all around the outside of the freezing zone around the shaft to form a closed soil modification zone.

[0029] Example 2: Example 2 is the application of the present invention to the freezing project of a circular-section shaft. By injecting foam slurry into a specific area within the freezing zone, a closed cylindrical soil modification zone is formed, as shown in Figure 4 , 5 , 6, 10, and 11.

[0030] The main differences between Example 2 and Example 1 are as follows: on the one hand, the injected material into the formation is foam slurry; on the other hand, holes are arranged circumferentially along the proposed freezing zone to form a closed cylindrical soil modification zone, so as to comprehensively prevent the moisture outside the modification zone from penetrating through the modified soil and migrating towards the freezing front on its inner side, and comprehensively inhibit the growth of formation frost heave.

[0031] Specific method: The implementation steps of Example 2 are relatively similar to those of Example 1, and are briefly described below.

[0032] Step 1: First, in the proposed freezing zone of the formation 1 to be frozen around the circular shaft, special drilling holes 2 for soil modification are constructed at a certain spacing; the hole spacing does not exceed 2 times the effective diffusion radius when injecting foam slurry into the soil.

[0033] Step 2: Install special pipelines 3 and perforated pipes 4 in the drilling holes; and install a pneumatic or hydraulic expandable rubber packer and pipelines at the upper boundary of the soil layer to be modified.

[0034] Step 3: Use an air pump or a hydraulic pump to supply air to the rubber packer 5 through the pipeline, seal the drilling space outside the pipe, block the channel along the drilling hole between the proposed modified formation and the upper formation, and then close the valve of this pipeline.

[0035] Step 4: At the construction site, use water, chemical admixtures and compressed air to prepare foam slurry 8 with good stability by using a foaming agent; connect the grouting pump with the special pipeline in the hole, and press the foam slurry into the soil layer through the perforated 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 drilling hole and should not exceed the vertical earth pressure.

[0036] Step 5: After the injection of the foam slurry is completed, inject expansive slurry 9 (cement slurry or cement-bentonite slurry) into the proposed modified soil layer through the special pipeline 3. After initial setting, remove the pipelines and devices in the hole, and carry out formation freezing after curing to a certain age.

[0037] In Example 2, a circumferentially closed cylindrical soil modification zone was formed outside the frozen zone of the circular shaft, which could completely block the migration of moisture from the outside of the modification zone to its internal freezing front, effectively inhibiting the frost heave induced by moisture migration. In fact, according to the needs of protecting surrounding environmental facilities, etc., the local modification zone outside the circular shaft could also be carried out only within a certain arc segment along the circumferential direction to form an unclosed soil modification zone, blocking the moisture migration in a specific direction and inhibiting the frost heave deformation induced by it.

[0038] Example 3: Example 3 is the application of the present invention to the freezing project of a horizontal tunnel with a straight wall and semi-circular arch section. At specific positions on the outer boundary of the frozen zone at the crown of the tunnel, a curved panel-shaped soil modification zone is formed by injecting foam slurry, as shown in Figure 7 、 8 、9, 10, 11.

[0039] The main differences between Example 3 and Examples 1 and 2 are as follows: On the one hand, the soil modification drilling holes are only arranged at the upper edge of the frozen zone at the crown of the tunnel, and only a curved panel-shaped soil modification zone is formed; on the other hand, the soil modification is carried out along the entire depth (length) of the drilling holes.

[0040] Specific method: The implementation steps of Example 3 are relatively similar to those of Example 2, and are briefly described below.

[0041] Step 1. First, at the upper edge of the frozen zone at the crown of the tunnel (i.e., the interface between the frozen zone and the non-frozen zone), construct special drilling holes 2 for soil modification at a certain spacing; the hole spacing does not exceed 2 times the effective diffusion radius when injecting foam slurry into the soil.

[0042] Step 2. Along the hole depth direction, only a certain length of special pipeline 3 is installed at the hole mouth section, and slotted pipes 4 are installed in the remaining parts; a pneumatic or hydraulic expansion-type rubber packer 5 and a pipeline 6 are installed on the special pipeline at the hole mouth section.

[0043] Step 3. Use an air pump or a hydraulic pump to supply air to the rubber packer 5 through the pipeline to block the annular space outside the pipe, block the channel for the foam slurry to leak out of the formation to be modified along the drilling hole, and then close the valve of this pipeline.

[0044] Step 4. At the construction site, use water, chemical admixtures and compressed air to prepare foam slurry 8 with good stability by using a foaming agent; connect the grouting pump with the special pipeline in the hole, and press the foam slurry 8 into the soil layer through the slotted 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 hole and should not exceed the vertical earth pressure.

[0045] Step 5. After the foam slurry injection is completed, inject expansive slurry 9 (cement slurry or cement bentonite slurry) into the soil modification section in the drilling hole through the special pipeline 3. After initial setting, remove the pipelines and devices in the hole, and carry out formation freezing after curing to a certain age.

[0046] Example 3: A curved panel-shaped soil modification area is formed at the outer edge of the frozen area at the crown of the horizontal tunnel, preventing the moisture in the unfrozen area above from migrating to the frozen area below and inhibiting the frost heave of the strata at the crown to protect the safety of the upper facilities. In fact, as needed, local modification outside the frozen area of the horizontal tunnel can be carried out at any position of the frozen areas of the tunnel roof, sidewalls, and floor to form one or more curved or flat panel-shaped soil modification areas, or construction can be carried out comprehensively in all circumferential directions of the frozen area around the tunnel to form a circumferentially closed soil modification area.

[0047] 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 of this technology, 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 suppressing frost heaving deformation of soil layers by reducing the local saturation degree of the soil layers, characterized in that, Proceed as follows: Step 1: At the interface between the formation to be frozen (1) and the unfrozen area or within the formation to be frozen (1), construct a number of special drilling holes (2) for soil modification at intervals. The number of drilling holes (2) are distributed parallel to each other on the same plane, the same curved surface or the same circumference; Step 2: First, install a special pipeline (3) and a perforated pipe (4) with coaxial docking in the drilling hole (2). The side wall of the perforated pipe (4) is evenly provided with a number of through holes; then install a pneumatic expansion type or hydraulic expansion type rubber packer (5) between the outer wall of the special pipeline (3) and the inner wall of the drilling hole (2), and arrange a pipeline (6) connecting an air pump or a hydraulic pump. The other end of the pipeline (6) penetrates into the rubber packer (5); Step 3: Use an air pump or a hydraulic pump to fill the rubber packer (5) with gas or hydraulic oil through the pipeline (6), so that the rubber packer (5) expands to block the space between the special pipeline (3) and the drilling hole (2), blocking the channel along the drilling hole between the formation to be modified and the upper formation, and then shut off the pipeline (6); Step 4: Press compressed air (7) or foam slurry (8) into the fine-grained soil layer around the perforated pipe (4) through the special pipeline (3) and the perforated pipe (4) in the drilling hole (2); Step 5: Press the expansive slurry (9) into the soil layer to be modified through the special pipeline (3). After its initial setting, lift out and remove the special pipeline (3), the perforated pipe (4), the rubber packer (5) and the pipeline (6) from the drilling hole (2) together; after curing to the predetermined age, when a flat plate-shaped, curved plate-shaped or cylindrical soil modification area (10) is formed, carry out freezing construction.

2. A method for suppressing frost heaving deformation by reducing the local saturation of soil layers according to claim 1, characterized in that, The spacing between adjacent drilling holes (2) does not exceed 2 times the effective diffusion radius when pressing compressed air (7) or foam slurry (8) in Step 4.

3. A method for suppressing frost heaving deformation by reducing the local saturation of soil layers according to claim 1, characterized in that The pressure of pressing compressed air (7) or foam slurry (8) in Step 4 is less than the water pressure at the bottom of the drilling hole (2) and does not exceed the vertical earth pressure, and the vertical earth pressure is the vertical earth pressure on the middle section of the soil modification area (10).

4. A method for suppressing frost heaving deformation by reducing the local saturation of soil layers according to claim 1, characterized in that, When applied to the freezing project of a rectangular-section shaft, the drilling holes (2) are drilled vertically or obliquely downward from the ground into the formation to be frozen (1), and are constructed on any side of the freezing area of the shaft to form a flat plate-shaped soil modification area (10); or are constructed on both sides of the freezing area of the shaft respectively to form two flat plate-shaped soil modification areas (10); or are constructed on the four sides of the freezing area of the shaft respectively to form four flat plate-shaped soil modification areas (10), and the four flat plate-shaped soil modification areas (10) are connected end to end in sequence to form a closed rectangle.

5. A method for suppressing frost heaving deformation by reducing the local saturation of soil layers according to claim 1, characterized in that When applied to the freezing project of a circular-section shaft, the drilling holes (2) are drilled vertically or obliquely downward from the ground into the formation to be frozen (1), and are constructed on the outer circle of the freezing area of the shaft to form a circumferentially closed cylindrical soil modification area (10); or are constructed on a partial circumference of the outer circle of the freezing area of the shaft to form a curved plate-shaped soil modification area (10).

6. A method for suppressing frost heaving deformation by reducing the local saturation of soil layers according to claim 1, characterized in that When applied to the horizontal tunnel freezing project with a straight wall semi-circular arch section, the boreholes (2) are arranged along the horizontal or inclined direction at the upper edge of the freezing zone at the tunnel crown, and construction is carried out at the outer edge of the freezing zone at the top of the horizontal tunnel arch to form a curved panel-shaped soil modification zone (10); or construction is carried out in the freezing zones on the sidewalls and the floor of the tunnel to form multiple curved or flat panel-shaped soil modification zones (10); or construction is carried out comprehensively in all circumferential directions of the freezing zone around the tunnel to form a circumferentially closed soil modification zone (10).

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