A method for reinforcing frozen soil foundation by using a rotary drilling - precast membrane bag lightweight soil pile

Abstract

This patent relates to a method for reinforcing frozen ground foundations using rotary drilling and prefabricated film-bag lightweight soil piles. The method uses a rotary drilling rig to create holes, and lightweight soil is prepared using drill cuttings, a curing agent, and air bubble groups. At the construction site, molds and film bags are used to prefabricate piles for reinforcing frozen ground foundations. The lightweight soil mix ratio, by weight, is: 10-100 parts curing agent, 80-100 parts slag, 2-45 parts air bubble groups, and 20-400 parts water. The present invention adopts on-site ex-situ prefabricated lightweight soil piles to avoid the thermal melting of the frozen soil layer caused by the hydration heat of the in-situ pile formation, and also avoids the slurry leakage and slurry bubbling caused by in-situ mixing and grouting, with good construction quality and high efficiency; the thermal conductivity of the lightweight soil is small, and when the ground temperature rises, it can slow down the thermal melting of the frozen soil layer around the pile, effectively improving the stability and freeze-thaw resistance of the frozen soil foundation; and the lightweight soil pile body has a small dead weight, which in disguise improves the ability of the foundation to bear the overlying load; and the drilling slag can be reused, saving raw materials and processing costs, reducing construction costs, simplifying the process, and is of great significance to green, low-carbon and sustainable development.

Description

Technical Field

[0001] The invention belongs to the field of civil engineering, and in particular relates to a method for reinforcing a frozen soil foundation by using rotary drilling and prefabricated film bag lightweight soil piles. Background Art

[0002] my country's permafrost is primarily distributed in the Greater and Lesser Khingan Mountains in northeast China, the northern Songnen Plain, the high mountainous areas, and the Qinghai-Tibet Plateau. There are also scattered pockets of permafrost in some high mountainous areas within seasonally frozen regions, totaling approximately 2.15 million km², or 22.4% of China's total area. my country's development and planning call for the establishment of a transportation network that radiates across the country and even beyond its borders. These include the Beijing-Moscow high-speed railway, the planned China-Russia-US-Canada high-speed railway, and the Qinghai-Tibet high-speed railway. These railways, such as the Eurasian Corridor and the northeast, northwest, and Qinghai-Tibet regions of my country, largely encompass permafrost zones.

[0003] The physical and mechanical properties of permafrost are significantly affected by temperature. Under negative temperatures, the freezing and migration of water in the soil cause frost heave (frost heave). Under positive temperatures, the ice in the permafrost melts into water, causing the soil to shrink and thaw settlement (thaw settlement). This leads to a series of technical problems, such as road slurrying, slope and roadbed instability, and other issues. This poses significant challenges for transportation construction in cold regions. The thermal instability of permafrost, in addition to its susceptibility to the natural environment, is also affected by engineering thermal disturbances. In-situ pile types, such as cement-soil mixing piles and cast-in-place piles, generate hydration heat, disrupting the thermal balance of the permafrost layer and potentially causing permafrost degradation. This can lead to thawing of the permafrost foundation, uneven settlement, and a reduction in the bearing capacity of the pile foundation, resulting in a series of engineering problems.

[0004] Furthermore, the drilling and construction of rotary or cast-in-place piles generates large amounts of waste soil or mud. Improper disposal can cause devastating damage to the fragile ecological environment of frozen soil areas, significantly increasing costs and complicating the process. Furthermore, long-distance transportation is difficult in frozen soil areas, which undoubtedly increases the cost of using precast piles such as PHC pipe piles. Therefore, existing cement-soil mixing piles, cast-in-place piles, and precast piles from off-site locations are not adequate for pile foundation reinforcement in frozen soil.

[0005] Lightweight soils offer advantages such as highly adjustable bulk density and strength, high fluidity, excellent thermal and acoustic insulation, and excellent freeze-thaw resistance. Consequently, they are used in projects such as bridge abutment backfill, road widening, steep embankments, landslide subgrades, and load reduction on soft soil subgrades. Leveraging their low thermal conductivity and excellent freeze-thaw resistance, we propose a prefabricated lightweight soil pile method for foundation reinforcement in frozen soil areas. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention designs a method for reinforcing frozen soil foundations by using rotary drilling and prefabricated film bag lightweight soil piles.

[0007] Technical solution: The present invention designs a method for reinforcing frozen soil foundations using rotary drilling and prefabricated film bag lightweight soil piles, which includes the following steps:

[0008] a. Use a rotary drilling rig to drill holes to the designed depth at the preset pile location to form pre-drilled holes, and collect the excavated drilling debris;

[0009] b. Press the sleeve into the pre-drilled hole and seal the hole with an insulation board;

[0010] c. Stirring the drill cuttings, curing agent and water in a stirring device to form a first mixture;

[0011] d. stirring the first mixture and the bubble group to form a second mixture;

[0012] e. Hoisting lightweight soil pile steel cage (16), put it into the film bag (13), the film bag (13) of the steel cage (16) is placed on the lower petal mold (5), covered with the upper petal mold (4), and the upper petal mold (4), the lower petal mold (5) is tightly connected;

[0013] An end plate (1) is fixed at one end of the mold near the bottom of the membrane bag (13), and the end plate (1) is connected and sealed with the upper lobe mold (4) and the lower lobe mold (5); an end plate (7) with a grouting hole (6) is put on and fixed at one end of the mold near the opening of the membrane bag (13), and a part of the membrane bag (13) is moved to the outside of the mold through the grouting hole (6);

[0014] f. Insert the grouting pipe into the film bag (13) through the grouting hole (6) into the mold, and seal the opening of the film bag (13); pour the second mixture into the film bag (13) through the grouting pipe until the film bag (13) in the mold is completely filled, pull out the grouting pipe, and tighten the opening of the film bag (13);

[0015] g. After the pile body hardens and reaches the designed strength to form a lightweight soil pile (15), lift the film bag lightweight soil pile (15) to the reserved sleeve in the rotary hole, send the pile to the designed depth, pull out the sleeve, and complete the construction of a pile;

[0016] h. Repeat steps a to g until all pile construction operations are completed.

[0017] Furthermore, the drilling waste is slag or mud.

[0018] Furthermore, the inner diameter of the sleeve is 20-100 mm larger than the designed diameter of the pile body, the length is consistent with the drilling depth, and the thickness is 5-15 mm.

[0019] Furthermore, the raw material composition of the lightweight soil pile (15) includes, by weight, 10-100 parts of a curing agent, 80-100 parts of drill slag, 2-45 parts of a bubble group, and 20-400 parts of water; wherein the curing agent is cement, including silicate cement, slag silicate cement, pozzolanic silicate cement, fly ash silicate cement, composite silicate cement, and other types of cementitious materials, including magnesium oxide, quicklime, and geopolymers, and the curing agent also includes various industrial waste materials that can be incorporated, including GGBS, fly ash, red mud, silica fume, and serpentine.

[0020] Furthermore, the bubble clusters are prepared by a foaming device using a pre-foaming method, mixing a foaming agent with water at a dilution ratio of 20-60 times to obtain a foaming liquid, and then using an air compressor to introduce high-pressure air to produce bubble clusters; the foaming agent used includes any one or more mixtures of rosin resins, synthetic surfactants, proteins, and composite foaming agents. When using rosin resins and synthetic surfactants, an appropriate amount of foam stabilizer is mixed according to the situation, including cellulose ether, lauryl alcohol, triethanolamine, and calcium stearate.

[0021] Furthermore, the steel cage (16) is used to bear the working load of the hanging pile and the pile top. The steel cage (16) of the lightweight soil pile is manufactured according to the design requirements. The steel cage includes main bars (8) and spiral stirrups (9). Four brackets (11) are set around the cross section every 2-5 m along the length direction of the steel cage (16) to assist the steel cage (16) to be located on the center line of the pile when pouring the second mixture. The minimum height of the bracket (11) is 30 mm.

[0022] Furthermore, the membrane bag (13) is made of high-strength geotextile, has a tensile strength greater than 100 kN / m, and can block the second mixture fluid; the tensile strength of the membrane bag (13) joint is greater than 100 kN / m, and can block the second mixture fluid; the length of the membrane bag (13) is 1-2 m longer than the lightweight soil pile; and the diameter is 20-50 mm larger than the diameter of the designed pile body.

[0023] The present invention also discloses a mold for a method for reinforcing frozen soil foundations using rotary drilling and prefabricated film bag lightweight soil piles. The mold is a two-lobe mold, and the internal dimensions are consistent with the design dimensions of the prefabricated film bag lightweight soil piles. The mold is divided into an upper lobe mold (4) and a lower lobe mold (5) along the long axis of the pile. The upper lobe mold (4) and the lower lobe mold (5) are locked by a plurality of nuts (3) along the direction of the pile body. End plates are provided at both ends of the mold for sealing and fixing, and a grouting hole (6) is left on the end plate (7) at one end. Beneficial effects

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) Cement-soil mixing piles, cast-in-place piles, and rotary-drilled piles generate hydration heat, which can cause frozen soil foundations to melt, leading to uneven settlement and a decrease in pile foundation bearing capacity, thus causing a series of engineering problems. The membrane-bag lightweight soil piles of the present invention are prefabricated on-site, so the hydration heat is not transferred to the in-situ soil, thus avoiding these problems.

[0026] (2) When the frozen ground layer is heated, the lightweight soil prepared from waste slag or mud in the present invention has a low thermal conductivity and poor heat transfer capacity, so it will heat up more slowly than the surrounding soil, slowing down the thermal melting of the surrounding frozen ground layer and alleviating the settlement caused by thaw settlement.

[0027] (3) Improper treatment of the waste slag or mud produced by the drilling construction of rotary piles or cast-in-place piles will cause environmental pollution and have a huge impact on the fragile ecological environment in frozen areas. Its treatment also greatly increases the cost and complicates the process. The transportation of waste materials after the treatment of the slag or mud will also increase the cost, and improper treatment of waste materials will still cause environmental pollution. The membrane bag lightweight soil piles of the present invention use the waste slag or mud produced by rotary drilling construction as raw materials, eliminating the treatment and transportation process, which not only greatly saves costs and simplifies the process, but also has important significance for environmental protection, green and low-carbon sustainability, and meets the requirements of green and low-carbon transformation of my country's civil engineering and transportation industry.

[0028] (4) Compared with concrete piles, the lightweight soil piles used in the present invention use waste soil or mud generated by the drilling construction of rotary piles or cast-in-place piles as the main raw material, which saves materials and is environmentally friendly, and greatly reduces the project cost.

[0029] (5) Compared with traditional cement soil or concrete, the lightweight soil prepared with waste slag or mud in the present invention has a small bulk density. Its replacement of foundation soil greatly reduces the self-weight stress of the foundation, effectively unloads the underlying soft soil, and indirectly improves the foundation's ability to bear the overlying load, reducing foundation settlement and deformation.

[0030] (6) Compared with cement-soil mixing piles and cast-in-place piles, the membrane bag lightweight soil piles of the present invention are prefabricated, avoiding the slurry leakage and slurry leakage caused by in-situ mixing and grouting, and have better construction quality and high efficiency.

[0031] (7) Compared with prefabricated PHC pipe piles, the membrane bag lightweight soil piles of the present invention are prefabricated on-site, which is helpful to solve the problem of long-distance transportation difficulties in frozen soil areas and save transportation costs.

[0032] (8) The film bag used in the present invention can simplify the lightweight soil pile casting process, help improve the casting quality, facilitate the pile body molding, and facilitate the lifting of the pile body. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the mold for prefabricated film bag lightweight soil piles;

[0034] Figure 2 It is a schematic diagram of the supports around the steel cage;

[0035] Figure 3 This is a schematic diagram of prefabricated film bag lightweight soil piles and their pile formation.

[0036] Explanation of the accompanying reference numerals: 1—bottom end plate; 2—nut connecting the end plate and the upper and lower petal molds; 3—nut connecting the upper and lower petal molds; 4—upper petal mold; 5—lower petal mold; 6—grouting hole; 7—top end plate; 8—main reinforcement; 9—hoops; 10—protective layer; 11—bracket; 12—rope; 13—membrane bag; 14—ground; 15—lightweight soil pile body; 16—reinforcement cage. DETAILED DESCRIPTION

[0037] The technical solutions of the present invention are described in detail below in conjunction with the embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0038] This invention provides a method for reinforcing frozen ground foundations using rotary drilling and prefabricated film-bag lightweight soil piles. The method uses a rotary drilling rig to drill holes, and uses the excavated soil, a curing agent, air bubble groups, and water as raw materials to prepare lightweight soil. At the construction site, molds and film bags are used to prefabricate piles for frozen ground foundation reinforcement.

[0039] The method of reinforcing frozen soil foundation with rotary drilling and prefabricated film bag lightweight soil piles includes:

[0040] a. After cleaning and leveling the original ground in the construction area, use GPS to measure and lay out the lines and locate the pile positions;

[0041] b. Use a rotary drilling rig to drill holes at designated pile locations to the designed depth and collect the excavated soil;

[0042] c. Press a sleeve into the pre-drilled hole to maintain the hole diameter and prevent collapse, and seal the hole with an insulation board in time to prevent the frozen soil from melting;

[0043] d. Mix the slag, curing agent and water in a stirring device to form a first mixture. The amount of water added is determined according to the moisture content of the slag and the mix ratio of the lightweight soil.

[0044] e. Stirring the first mixture and the bubble group in a stirring device to ensure that the bubble group is evenly distributed and there is no sedimentation in the slurry to form a second mixture;

[0045] f. Prepare the mold for the film bag lightweight soil pile, hoist the steel cage 16 of the lightweight soil pile, put it into the film bag 13, place the steel cage with the film bag on the lower petal mold 5, cover the upper petal mold 4, and use nuts 3 to tightly connect the upper and lower petal molds; put the end plate 1 on one end of the mold at the bottom of the film bag, and the end plate and the upper and lower petal molds are connected and sealed by nuts 2; at one end of the mold at the opening of the film bag, put and fix the end plate 7 with the grouting hole 6, and pass the excess film bag through the grouting hole to the outside of the mold;

[0046] g. Insert the grouting pipe into the film bag 13 through the grouting hole 6 and 5 cm into the mold. Seal the opening of the film bag with wire or a fixing device. Pour the second mixture into the film bag through the grouting pipe until the film bag in the mold is completely filled. Pull out the grouting pipe and completely tighten the film bag opening.

[0047] h. After the pile has hardened and reached its designed strength, the film-bag lightweight soil pile 15 is hoisted into the reserved sleeve in the drilled hole, driven to the designed depth, and the sleeve removed, completing the construction of one pile. After the second mixture hardens, it forms lightweight soil. This lightweight soil is then used to form the lightweight soil pile 15 to reinforce the frozen ground foundation. The lightweight soil mix comprises, by weight, 10-100 parts curing agent, 80-100 parts slag, 2-45 parts air bubbles, and 20-400 parts water. The curing agent is typically cement, including but not limited to Portland cement, slag cement, pozzolanic cement, fly ash cement, composite Portland cement, and other types of cementitious materials. Other types of cementitious materials include but are not limited to magnesium oxide, quicklime, and geopolymers. The curing agent can also include various industrial waste materials, including but not limited to GGBS, fly ash, red mud, silica fume, and serpentine. According to preliminary tests, the lightweight soil mix ratio can be flexibly adjusted according to project requirements to prepare lightweight soils of different densities, which are generally between 300-1600 kg / m3.

[0048] The slag in this invention can also be slurry, depending on the rotary drilling process. For permafrost, the frozen soil surrounding the borehole generally does not thaw significantly, so the "dry soil extraction" method can be used, eliminating the need for slurry wall protection. In other situations, slurry wall protection is required. If unfavorable geological conditions cause the hole wall to become unstable during drilling, slurry should be added promptly to protect the wall.

[0049] The inner diameter of the sleeve is slightly larger than the designed pile diameter by 20-100 mm, its length is consistent with the drilling depth, and its thickness is generally 5-15 mm. The sleeve has sufficient rigidity.

[0050] The bubble clusters are produced in a foaming device using a pre-foaming method. A foaming agent and water are mixed at a dilution ratio of 20-60 times to produce a foaming liquid. High-pressure air is then introduced into the foam using an air compressor to produce the bubble clusters. The specific dilution ratio depends on the type of foaming agent and the target bubble cluster density. Generally, the bubble cluster density is approximately 48kg / m³-52kg / m³. Useful foaming agents include, but are not limited to, rosin resins (such as rosin soap foaming agents), synthetic surfactants (such as sodium lauryl alcohol ether sulfate and sodium dodecylbenzenesulfonate), proteins (such as plant and animal protein foaming agents), and composite foaming agents (such as plant-derived composite foaming agents). When using rosin resins and synthetic surfactants, an appropriate amount of foam stabilizer, including but not limited to cellulose ether, lauryl alcohol, triethanolamine, and calcium stearate, may be added.

[0051] The water is tap water, purified water or distilled water, including the water used for the bubble group.

[0052] The second mixture has a fluidity of about 160-200 mm for easy pouring.

[0053] The mold is a two-piece mold made of steel or other high-strength materials. Its internal dimensions (pile length and diameter) are consistent with the design dimensions of the prefabricated film-bag lightweight soil pile. The mold is divided into upper and lower halves 4 and 5 along the longitudinal axis of the pile, which can be locked together with several nuts 3 along the length of the pile. End plates 1 and 7 are installed at each end of the mold. After the film-bag-encased steel cage is placed inside, the ends are sealed with the end plates. Grouting holes 6 are provided on the end plate 7 at the mold end where the film bag opens. The end plates seal the pile end, facilitating the pouring of the secondary mix, thus completing the lightweight soil pile formation.

[0054] The reinforcement cage is used to support the working loads of the suspended pile and the pile top. The lightweight soil pile reinforcement cage 16 is manufactured according to design requirements. The cage consists of main reinforcement 8 and spiral stirrups 9, and the steel material selection should meet design requirements. Four brackets 11 are installed around the cross section every 2-5 meters along the length of the cage. These auxiliary reinforcement cages are positioned along the pile centerline during pouring of the secondary mix and maintain a certain protective layer thickness. The minimum height of the brackets 11 is 30 mm, and 50 mm is typical. For lightweight soil piles with smaller diameters (300 mm or less), a smaller bracket height is used.

[0055] The membrane bag 13 is typically made of high-strength geotextile or other suitable materials. Its tensile strength must be sufficient to support the weight of the pile, typically greater than 100 kN / m, and must also be able to block the flow of the secondary mixture. The same requirements must also be met at the joints of the membrane bag. The membrane bag should ideally be 1-2 meters longer than the lightweight soil pile to facilitate pile hanging, and its diameter should be slightly larger than the designed pile diameter by 20-50 mm. Example

[0056] The site's strata are primarily clayey with a moisture content of 20%-40%. The permafrost ranges from an upper limit of 2.1 m to a lower limit of 8.5 m. Thaw settlement is classified as II or III, and the average annual ground temperature is approximately -2.1°C, placing it within the low-temperature, essentially stable permafrost zone. The prefabricated lightweight soil piles used are 10.0 m long and 500 mm in diameter.

[0057] The construction of prefabricated film bag lightweight soil piles follows the following steps:

[0058] 1) After cleaning and leveling the original ground in the construction area, use GPS to measure and lay out the lines and locate the pile positions;

[0059] 2) Use a rotary drilling rig to drill a hole to 10.0 m at the designated pile location and use the "rotary drilling dry soil method" to collect the excavated soil;

[0060] 3) Press a steel sleeve into the pre-drilled hole to maintain the hole diameter and prevent collapse, and seal the hole with an insulation board in time to prevent the frozen soil from melting;

[0061] 4) Mixing the slag, curing agent and water in a stirring device to form a first mixture;

[0062] 5) The first mixture and the gas bubbles were mixed in a stirring apparatus. The gas bubbles described in step 6) were prepared in a foaming apparatus using a pre-foaming method. A foaming liquid was prepared by mixing a foaming agent with water at a dilution ratio of 35 times. High-pressure air was then introduced using an air compressor to produce gas bubbles. The gas bubbles had a density of 50 kg / m³. The foaming agent used was sodium lauryl ether sulfate, mixed with an appropriate amount of lauryl alcohol as a foam stabilizer.

[0063] The water mentioned in step 6) is tap water, including the water used for the bubble group.

[0064] The fluidity of the second mixture described in step 6) is about 170 mm.

[0065] The mold described in step 7) is a two-piece mold made of steel or other high-strength materials. Its internal dimensions are consistent with the design dimensions of the prefabricated film-bag lightweight soil pile (pile length and diameter). The mold is divided into upper and lower halves 4 and 5 along the longitudinal axis of the pile, which can be locked together with several nuts along the pile shaft 3. End plates 1 and 7 are installed at each end of the mold. After the film-bag-encased steel cage is placed, the end plates are used to seal the ends. The end plate 7 at the mold end near the film bag opening is provided with a grouting hole 6. The end plates seal the pile end, facilitating the pouring of the second mixture and completing the lightweight soil pile formation.

[0066] The reinforcement cage mentioned in step 7) is manufactured according to design requirements to support the working loads of the suspended pile and the pile top. The lightweight soil pile reinforcement cage 16 is constructed from main reinforcement 8 and spiral stirrups 9. The steel material selection should meet design requirements. Four brackets 11 are installed around the cross section every 3 meters along the length of the reinforcement cage. The auxiliary reinforcement cage is positioned along the centerline of the pile during pouring of the second mix, maintaining a certain protective layer thickness. The brackets 11 are 50 mm high.

[0067] The membrane bag 13 described in step 7) is made of high-strength geotextile. Its tensile strength must be able to support the pile's deadweight, exceeding 100 kN / m, and be able to block the flow of the second mixture. The membrane bag's seams must also meet the same requirements. The membrane bag should be approximately 9 meters long to facilitate pile hanging and have a diameter of 830 mm.

[0068] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above examples. The above examples and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications are possible without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for reinforcing frozen soil foundations using rotary drilling and prefabricated film bag lightweight soil piles, characterized in that: The following steps are involved: a. Use a rotary drilling rig to drill holes to the designed depth at the preset pile location to form pre-drilled holes, and collect the excavated drilling debris; b. Press the sleeve into the pre-drilled hole and seal the hole with an insulation board; c. Stirring the drill cuttings, curing agent and water in a stirring device to form a first mixture; d. stirring the first mixture and the bubble group to form a second mixture; e. Hoisting lightweight soil pile steel cage (16), put it into the film bag (13), the film bag (13) of the steel cage (16) is placed on the lower petal mold (5), covered with the upper petal mold (4), and the upper petal mold (4), the lower petal mold (5) is tightly connected; An end plate (1) is fixed at one end of the mold near the bottom of the membrane bag (13), and the end plate (1) is connected and sealed with the upper lobe mold (4) and the lower lobe mold (5); an end plate (7) with a grouting hole (6) is put on and fixed at one end of the mold near the opening of the membrane bag (13), and a part of the membrane bag (13) is moved to the outside of the mold through the grouting hole (6); f. Insert the grouting pipe into the film bag (13) through the grouting hole (6) into the mold, and seal the opening of the film bag (13); pour the second mixture into the film bag (13) through the grouting pipe until the film bag (13) in the mold is completely filled, pull out the grouting pipe, and tighten the opening of the film bag (13); g. After the pile body hardens and reaches the designed strength to form a lightweight soil pile (15), lift the film bag lightweight soil pile (15) to the reserved sleeve in the rotary hole, send the pile to the designed depth, pull out the sleeve, and complete the construction of a pile; h. Repeat steps a to g until all pile construction operations are completed.

2. The method for reinforcing frozen soil foundation by rotary drilling and prefabricated film bag lightweight soil piles according to claim 1, characterized in that: The drilling waste is slag or mud.

3. The method for reinforcing frozen soil foundation by rotary drilling and prefabricated film bag lightweight soil piles according to claim 1, characterized in that: The inner diameter of the sleeve is 20-100 mm larger than the diameter of the designed pile body, the length is consistent with the drilling depth, and the thickness is 5-15 mm.

4. The method for reinforcing frozen soil foundation by rotary drilling and prefabricated film bag lightweight soil piles according to claim 1, characterized in that: The lightweight soil pile (15) comprises the following raw materials in parts by weight: 10-100 parts of a curing agent, 80-100 parts of drill slag, 2-45 parts of a bubble group and 20-400 parts of water; wherein the curing agent is cement, including silicate cement, slag silicate cement, pozzolanic silicate cement, fly ash silicate cement, composite silicate cement and other types of cementitious materials, other types of cementitious materials include magnesium oxide, quicklime and geopolymer, and the curing agent also includes various industrial waste materials that can be added, including GGBS, fly ash, red mud, silica fume and serpentine.

5. The method for reinforcing frozen soil foundation by rotary drilling and prefabricated film bag lightweight soil piles according to claim 4, characterized in that: The bubble clusters are prepared by a foaming device using a pre-foaming method. A foaming agent is mixed with water at a dilution ratio of 20-60 times to obtain a foaming liquid, and high-pressure air is then introduced into the foaming liquid using an air compressor to produce the bubble clusters. The foaming agent used includes any one or more mixtures of rosin resins, synthetic surfactants, proteins, and composite foaming agents. When rosin resins and synthetic surfactants are used, an appropriate amount of foam stabilizer is added as needed, including cellulose ether, lauryl alcohol, triethanolamine, and calcium stearate.

6. The method for reinforcing frozen soil foundation by rotary drilling and prefabricated film bag lightweight soil piles according to claim 2, characterized in that: The mold is a two-lobe mold, and its internal dimensions are consistent with the design dimensions of the prefabricated film bag lightweight soil pile; the mold is divided into an upper lobe mold (4) and a lower lobe mold (5) along the long axis of the pile, and the upper lobe mold (4) and the lower lobe mold (5) are locked by a plurality of nuts (3) along the direction of the pile body. End plates are provided at both ends of the mold for sealing and fixing, and a grouting hole (6) is left on the end plate (7) at one end.

7. The method for reinforcing frozen soil foundation by rotary drilling and prefabricated film bag lightweight soil piles according to claim 1, characterized in that: The membrane bag (13) is made of high-strength geotextile, has a tensile strength greater than 100 kN / m, and can block the second mixture fluid; the tensile strength of the membrane bag (13) joint is greater than 100 kN / m, and can block the second mixture fluid; the length of the membrane bag (13) is 1-2 m longer than the lightweight soil pile; and the diameter is 20-50 mm larger than the diameter of the designed pile body.

8. The method for reinforcing frozen soil foundation by rotary drilling and prefabricated film bag lightweight soil piles according to claim 1, characterized in that: The steel cage (16) is used to bear the working load of the hanging pile and the pile top. The steel cage (16) of the lightweight soil pile is manufactured according to the design requirements. The steel cage includes main bars (8) and spiral stirrups (9). Four brackets (11) are set around the cross section every 2-5 m along the length direction of the steel cage (16) to assist the steel cage (16) to be located on the center line of the pile when pouring the second mixture. The minimum height of the bracket (11) is 30 mm.

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