Method for reinforcing frozen soil foundation by rotary drilling-prefabricated membrane bag lightweight soil piles

Abstract

The present invention relates to a method for reinforcing a frozen soil foundation by rotary drilling-prefabricated membrane bag lightweight soil piles, comprising: employing a rotary drilling rig to drill holes; using drilling debris, a curing agent, and a bubble group as raw materials to prepare lightweight soil; and at a construction site, prefabricating piles by using molds and a membrane bag to reinforce a frozen soil foundation. The mixing ratio of the lightweight soil according to the parts by weight of the raw materials is: 10-100 parts of a curing agent, 80-100 parts of excavated soil, 2-45 parts of a bubble group, and 20-400 parts of water. According to the present invention, on-site ex-situ prefabrication of lightweight soil piles avoids thawing of frozen soil layers caused by heat of hydration from in-situ pile formation, and also avoids grout leaking and oozing out caused by in-situ mixing and grouting, such that the construction quality is good, and the efficiency is high; the heat conductivity coefficient of the lightweight soil is small, so that the thawing of the frozen soil layers around the piles can be slowed down when the ground temperature rises, thereby effectively improving the stability and freeze-thaw resistance of the frozen soil foundation; the self-weight of the lightweight soil piles is small, improving in disguise the ability of the foundation to bear the overlying load; and the reuse of the drilling debris saves the raw materials and processing costs, reduces construction costs, simplifies the process, and is of great significance for green, low-carbon, and sustainable development.

Description

A method for reinforcing frozen soil foundation using rotary drilling and prefabricated film bag lightweight soil piles 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 areas on some high mountain slopes in seasonally frozen areas, totaling approximately 2.15 million square kilometers, 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 temperature conditions, the freezing of water in the soil and the migration of water cause frost heave (frost heave); under positive temperature conditions, the ice in the permafrost melts into water, causing the soil to shrink and resulting in thaw settlement (thaw settlement), leading to a series of technical problems such as road slurrying, slope and roadbed instability. This poses significant challenges to transportation construction in cold regions. In addition to being susceptible to the natural environment, the thermal instability of permafrost 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, which disrupts the original thermal balance of the permafrost layer, easily causing permafrost degradation, melting of the permafrost foundation, uneven settlement, and a decrease in the bearing capacity of the pile foundation, leading to a series of engineering problems.

[0004] At the same time, the construction of rotary bored piles or cast-in-place piles generates a large amount of waste soil or mud. Improper handling can cause devastating damage to the fragile ecological environment of frozen soil areas. Its treatment also greatly increases costs and complicates the process. Furthermore, frozen soil areas also face the problem of long-distance transportation difficulties, which undoubtedly increases the application cost of off-site precast piles such as PHC pipe piles. Therefore, existing cement-soil mixing piles, cast-in-place piles, and off-site precast piles cannot fully meet the requirements of pile foundation reinforcement for frozen soil foundations.

[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.

[0006] Summary of the Invention

[0007] 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.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] The present invention provides a method for reinforcing frozen soil foundations by using rotary drilling and prefabricated film bag lightweight soil piles, which includes the following steps:

[0010] 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;

[0011] b. Press the sleeve into the pre-drilled hole and seal the hole with an insulation board;

[0012] c. Stirring the drill cuttings, curing agent and water in a stirring device to form a first mixture;

[0013] d. stirring the first mixture and the bubble group to form a second mixture;

[0014] e. Hoist the steel cage (16) of the lightweight soil pile and put it into the film bag (13), place the steel cage (16) with the film bag (13) on the lower lobe mold (5), cover the upper lobe mold (4), and tightly connect the upper lobe mold (4) and the lower lobe mold (5); fix the end plate (1) at one end of the mold near the bottom of the film bag (13), and the end plate (1) is connected and sealed with the upper lobe mold (4) and the lower lobe mold (5); put and fix the end plate (7) with the grouting hole (6) at one end of the mold near the opening of the film bag (13), and move part of the film bag (13) to the outside of the mold through the grouting hole (6);

[0015] f. Insert the grouting pipe into the film bag (13) through the grouting hole (6) into the interior of the mold, and seal the film bag (13) opening; 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 film bag (13) opening;

[0016] g. After the pile body is hardened to reach the design strength, a lightweight soil pile (15) is formed. The lightweight soil pile (15) is lifted from the membrane bag to the reserved sleeve for the rotary hole, and the pile is sent to the designed depth, the sleeve is pulled out, and the construction of a pile is completed;

[0017] h. Repeat steps a to g until all pile construction operations are completed.

[0018] Furthermore, the drilling waste is slag or mud.

[0019] 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.

[0020] 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 air bubble groups, 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.

[0021] 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, foam stabilizers can be mixed, including cellulose ether, lauryl alcohol, triethanolamine, and calcium stearate.

[0022] 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 2-5m 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 30mm.

[0023] Furthermore, the membrane bag (13) is made of high-strength geotextile, its tensile strength is greater than 100kN / m, and it can block the second mixture fluid; the tensile strength of the membrane bag (13) joint is greater than 100kN / m, and it can block the second mixture fluid; the length of the membrane bag (13) is 1-2m longer than the lightweight soil pile; and the diameter is 20-50mm larger than the diameter of the designed pile body.

[0024] The present invention also discloses a mold for a method of rotary drilling and prefabricated film bag lightweight soil pile reinforcement of frozen soil foundation. The mold adopts a two-lobe mold, and the internal size is consistent with the design size 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. Beneficial effects:

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (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.

[0027] (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.

[0028] (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.

[0029] (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.

[0030] (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.

[0031] (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.

[0032] (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.

[0033] (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

[0034] Figure 1 is a schematic diagram of a mold for a prefabricated film bag lightweight soil pile;

[0035] Figure 2 is a schematic diagram of the supports around the steel cage;

[0036] Figure 3 is a schematic diagram of a prefabricated film bag lightweight soil pile and its pile formation.

[0037] 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

[0038] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0039] 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.

[0040] 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.

[0041] The method of reinforcing frozen soil foundation with rotary drilling and prefabricated film bag lightweight soil piles includes:

[0042] 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;

[0043] b. Use a rotary drilling rig to drill holes at designated pile locations to the designed depth and collect the excavated soil;

[0044] 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;

[0045] 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.

[0046] 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;

[0047] 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, put the steel cage with the film bag on the lower petal mold 5, cover the upper petal mold 4, and use the nut 3 to tightly connect the upper and lower petals of the mold; 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 petals of the mold are connected and sealed by the nut 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;

[0048] g. Insert the grouting pipe into the film bag 13 through the grouting hole 6 and insert it 5 cm into the mold. Seal the film bag opening 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.

[0049] h. After the pile body hardens and reaches the designed strength, lift the film bag lightweight soil pile 15 into the sleeve reserved in the rotary drilling hole, send the pile to the designed depth, and pull out the sleeve to complete the construction of one pile.

[0050] After hardening, the second mixture forms lightweight soil. Lightweight soil piles 15 are formed from the lightweight soil to reinforce frozen ground foundations. The lightweight soil mix ratio, in terms of raw materials, includes, by weight, 10-100 parts of a curing agent, 80-100 parts of slag, 2-45 parts of air bubbles, and 20-400 parts of water. The curing agent is typically cement, including but not limited to Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement, composite Portland cement, and other types of cementitious materials, including but 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. Based on preliminary experiments, the lightweight soil mix ratio can be flexibly adjusted according to project requirements to produce lightweight soils of varying densities, typically ranging from 300 to 1600 kg / m³.

[0051] 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.

[0052] The inner diameter of the sleeve is slightly larger than the designed pile diameter by 20-100mm, the length is consistent with the drilling depth, and the thickness is generally 5-15mm. The sleeve has sufficient rigidity.

[0053] The bubble group is prepared by a foaming device using a pre-foaming method. The foaming agent is mixed with water at a dilution ratio of 20-60 times to obtain a foaming liquid, and then high-pressure air is introduced into the air compressor to produce the bubble group. The specific dilution ratio needs to be determined according to the type of foaming agent and the target bubble group density. Under normal circumstances, the density of the bubble group is about 48kg / m3-52kg / m3. The foaming agents used include but are not limited to any one or more mixtures of rosin resins (rosin soap foaming agents, etc.), synthetic surfactants (sodium lauryl alcohol ether sulfate, sodium dodecylbenzenesulfonate, etc.), proteins (plant protein and animal protein foaming agents), composite foaming agents (plant-derived composite foaming agents, etc.). When using rosin resins and synthetic surfactants, an appropriate amount of foam stabilizer can be mixed according to the situation, including but not limited to cellulose ether, lauryl alcohol, triethanolamine, calcium stearate, etc.

[0054] The water is tap water, purified water or distilled water, including the water used for the bubble group.

[0055] The fluidity of the second mixture is about 160-200mm for easy pouring.

[0056] The mold 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 two halves 4 and 5 along the longitudinal axis of the pile, and can be locked with a number of nuts 3 along the pile body. End plates 1 and 7 are provided at both ends of the mold. After the film-bag-encased steel cage is placed, the ends are sealed with the end plates. The end plate 7 at one end of the mold at the film bag opening has a grouting hole 6. The end plate is used to seal the pile end, thereby facilitating the pouring of the second mixture and forming the lightweight soil pile.

[0057] The steel cage 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 made according to the design requirements. The steel cage is composed of main reinforcement 8 and spiral stirrups 9. The selection of steel should meet the design requirements. Four brackets 11 are set around the cross section every 2-5m along the length of the steel cage. The auxiliary steel cage is on the center line of the pile when the second mixture is poured, and a certain thickness of the protective layer is maintained. The minimum height of the bracket 11 is 30mm, generally 50mm. When the diameter of the lightweight soil pile is small (300mm and below), a smaller bracket height is used.

[0058] 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.

[0059] Example 1

[0060] The site's strata are primarily clayey with a moisture content of 20%-40%. The permafrost ranges from an upper limit of 2.1m to a lower limit of 8.5m. Thaw settlement is classified as Class 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 film-bag lightweight soil piles used are 10.0m long and 500mm in diameter.

[0061] The construction of prefabricated film bag lightweight soil piles follows the following steps:

[0062] 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;

[0063] 2) Use a rotary drilling rig to drill a hole to a depth of 10.0m at the designated pile location and use the "rotary drilling dry soil method" to collect the excavated soil;

[0064] 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;

[0065] 4) Mixing the slag, curing agent and water in a stirring device to form a first mixture;

[0066] 5) Stirring the first mixture and the bubble clusters in a stirring device to ensure that the bubble clusters are evenly distributed and there is no sedimentation in the slurry, thereby forming a second mixture. The second mixture has the following proportions: 100 parts of Portland cement, 100 parts of slag, 10 parts of bubble clusters, and 140 parts of water;

[0067] 6) Prepare the mold for the film bag lightweight soil pile (as shown in Figure 1), 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 tightly connect the upper and lower petal molds with nuts 3; 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; also put and fix the end plate 7 with grouting holes 6 on one end of the mold at the opening of the film bag, and pass the excess film bag through the grouting holes to the outside of the mold;

[0068] 7) Insert the grouting pipe into the film bag 13 through the grouting hole 6 and insert it 5 cm into the mold. Seal the film bag opening 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.

[0069] 8) After the pile body hardens and reaches the designed strength, the membrane bag lightweight soil pile 15 is hoisted into the sleeve reserved in the rotary drilling hole, the pile is sent to the designed depth, and the sleeve is pulled out to complete the construction of one pile (as shown in Figure 3).

[0070] The steel sleeve described in step 4) has an inner diameter of 550 mm, a length of 10.0 m, and a thickness of 10 mm.

[0071] The bubble clusters described in step 6) are prepared in a foaming apparatus using a pre-foaming method. A foaming agent is mixed with water at a dilution ratio of 40 to produce a foaming liquid. High-pressure air is then introduced into the liquid using an air compressor to produce the bubble clusters. The bubble clusters have a density of 48 kg / m³. The foaming agent used is a composite foaming agent.

[0072] The water described in step 6) is tap water, including the water used for the bubble groups.

[0073] The fluidity of the second mixture in step 6) is about 180 mm.

[0074] The mold described in step 7): The mold adopts a two-piece mold, and the material is selected from steel or other high-strength materials. The internal dimensions are consistent with the design dimensions of the prefabricated film bag lightweight soil pile (pile length and pile diameter). The mold is divided into upper and lower halves 4, 5 along the longitudinal axis of the pile, and can be locked 3 by several nuts along the direction of the pile body. End plates 1, 7 are provided at both ends of the mold. After the steel cage with the film bag is placed, the two ends are sealed with end plates, and the end plate 7 at one end of the mold at the opening of the film bag is provided with a grouting hole 6. The end plate is used to seal the pile end, thereby facilitating the pouring of the second mixture, so that the lightweight soil pile is formed.

[0075] The reinforcement cage described in step 7) is manufactured according to the design requirements to support the working loads of the suspended pile and the pile top. The reinforcement cage 16 is composed of main bars 8 and spiral stirrups 9, and the steel material selected should meet the design requirements. Four brackets 11 are installed every 3 meters along the length of the reinforcement cage around the cross section (as shown in Figure 2). The auxiliary reinforcement cage is positioned on the pile centerline during the pouring of the second mixture and maintains a certain protective layer thickness. The brackets 11 are 50 mm high.

[0076] The membrane bag 13 described in step 7) is made of high-strength geotextile fabric. Its tensile strength must be greater than 100 kN / m, capable of supporting the pile's deadweight, and must also 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 12 meters long to facilitate pile hanging and have a diameter of 530 mm.

[0077] Example 2

[0078] The site's strata are primarily gravelly sand, primarily composed of schist, with a moisture content of 20%-40%. The strata are permafrost, with an upper permafrost depth of 1.5 meters and a thaw settlement rating of III. The average annual ground temperature is approximately -1.6°C, placing the site in a generally stable zone. The prefabricated film-bag lightweight soil piles used are 8.0 meters long and 800 mm in diameter.

[0079] The construction of prefabricated film bag lightweight soil piles follows the following steps:

[0080] 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;

[0081] 2) Use a rotary drilling rig to drill a hole to a depth of 8.0m at the designated pile location and use the "rotary drilling dry soil method" to collect the excavated soil;

[0082] 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;

[0083] 4) Mixing the slag, curing agent and water in a stirring device to form a first mixture;

[0084] 5) The first mixture and the bubble clusters are stirred in a stirring device to ensure that the bubble clusters are evenly distributed and there is no sedimentation in the slurry, thereby forming a second mixture. The second mixture has the following proportions: 60 parts of Portland cement, 40 parts of fly ash, 100 parts of slag, 20 parts of bubble clusters, and 130 parts of water;

[0085] 6) 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 tightly connect the upper and lower petal molds with nuts 3; 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; also put and fix the end plate 7 with grouting holes 6 on one end of the mold at the opening of the film bag, and pass the excess film bag through the grouting holes to the outside of the mold;

[0086] 7) Insert the grouting pipe into the film bag 13 through the grouting hole 6 and insert it 5 cm into the mold. Seal the film bag opening 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.

[0087] 8) After the pile body hardens and reaches the designed strength, lift the film bag lightweight soil pile 15 into the sleeve reserved in the rotary drilling hole, send the pile to the designed depth, and pull out the sleeve to complete the construction of one pile.

[0088] The steel sleeve described in step 4) has an inner diameter of 850 mm, a length of 8.0 m, and a thickness of 10 mm.

[0089] The bubble clusters described in step 6) are prepared in a foaming apparatus using a pre-foaming method. A foaming agent is mixed with water at a dilution factor of 35 to produce a foaming solution. High-pressure air is then introduced into the solution using an air compressor to produce the bubble clusters. The bubble cluster density is 50 kg / m³. The foaming agent used is sodium lauryl ether sulfate, mixed with an appropriate amount of lauryl alcohol as a foam stabilizer.

[0090] The water described in step 6) is tap water, including the water used for the bubble groups.

[0091] The fluidity of the second mixture in step 6) is about 170 mm.

[0092] The mold described in step 7): The mold adopts a two-piece mold, and the material is selected from steel or other high-strength materials. The internal dimensions are consistent with the design dimensions of the prefabricated film bag lightweight soil pile (pile length and pile diameter). The mold is divided into upper and lower halves 4, 5 along the longitudinal axis of the pile, and can be locked 3 by several nuts along the direction of the pile body. End plates 1, 7 are provided at both ends of the mold. After the steel cage with the film bag is placed, the two ends are sealed with end plates, and the end plate 7 at one end of the mold at the opening of the film bag is provided with a grouting hole 6. The end plate is used to seal the pile end, thereby facilitating the pouring of the second mixture, so that the lightweight soil pile is formed.

[0093] The reinforcement cage described in step 7) is manufactured according to design requirements to support the working loads of the suspended pile and the pile top. The cage consists of main bars 8 and spiral stirrups 9, and the steel material selected should meet design requirements. Four brackets 11 are installed around the cross section every 3 meters along the length of the cage. This auxiliary cage is positioned along the centerline of the pile during pouring of the second mixture, maintaining a certain protective layer thickness. The brackets 11 are 50 mm high.

[0094] The membrane bag 13 described in step 7) is made of high-strength geotextile fabric. Its tensile strength must be greater than 100 kN / m, capable of supporting the pile's deadweight, and must also 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.

[0095] 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 foundation by 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 at the preset pile position to the designed depth to form pre-drilled holes, and collect the excavated drilling slag; b. Press the sleeve into the pre-drilled hole and seal the hole with an insulation board; c. Mix 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. hoist the steel cage (16) of the lightweight soil pile, put it into the film bag (13), put the steel cage (16) with the film bag (13) on the lower lobe mold (5), cover it with the upper lobe mold (4), and tightly connect the upper lobe mold (4) and the lower lobe mold (5); fix the end plate (1) at one end of the mold near the bottom of the film bag (13), and the end plate (1) is connected and sealed with the upper lobe mold (4) and the lower lobe mold (5); put and fix the end plate (7) with the grouting hole (6) at one end of the mold near the opening of the film bag (13), and move part of the film bag (13) 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. When the pile body is hardened to reach the designed strength, a lightweight soil pile (15) is formed. The lightweight soil pile (15) is hoisted into the reserved sleeve of the rotary hole, the pile is sent to the designed depth, the sleeve is pulled out, and the construction of a pile is completed; 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 is 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 is characterized in that: 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.

4. The method for reinforcing frozen soil foundation by rotary drilling and prefabricated film bag lightweight soil piles according to claim 1 is characterized in that: The lightweight soil pile (15) comprises, 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 is characterized in that: The bubble group is 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 prepare the bubble group; the foaming agent used includes any one or more mixtures of rosin resin, synthetic surfactant, protein, and composite foaming agents. When using rosin resin and synthetic surfactant foaming agents, foam stabilizers can be mixed, including cellulose ether, lauryl alcohol, triethanolamine, and calcium stearate.

6. The technology of rotary drilling and prefabricated film bag lightweight soil piles for reinforcing frozen soil foundation according to claim 2 is characterized in that: The mold is a two-piece 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 mold piece (4) and a lower mold piece (5) along the long axis of the pile, and the upper mold piece (4) and the lower mold piece (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 reserved at one end of the end plate (7). According to the method of reinforcing frozen soil foundation by rotary drilling and prefabricated membrane bag lightweight soil piles as described in claim 1, it is characterized in that the steel cage (16) is used to bear the working load of the hanging pile and the pile top, and 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) along the length direction of the steel cage (16) every 2-5m, and four brackets (11) are arranged around the cross section to assist the steel cage (16) to be located on the center line of the pile when pouring the second mixture, and the minimum height of the bracket (11) is 30mm.

7. The method for reinforcing frozen soil foundation by rotary drilling and prefabricated film bag lightweight soil piles according to claim 1 is 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 light soil pile, and the diameter is 20-50 mm larger than the designed diameter of the pile body.

Images