A field carbonization construction method for reinforcing ground soil by using dry ice

Abstract

The application discloses a kind of field carbonization construction methods for reinforcing ground soil with dry ice, which comprises the following steps: site survey and unit division, construction preparation, insertion of processing device, solidifying agent spraying and stirring, gradient refrigeration, dry ice mixing, material bin displacement, soil layer compaction, cold storage bin removal and membrane laying maintenance and the like.The orderly combination between each step enables the method to replace carbon dioxide gas with dry ice, and to achieve the purpose of uniform carbonization and improvement and reinforcement of special soil.The specially designed gradient refrigeration step effectively reduces the volatilization of dry ice during mixing, so that each material is uniformly mixed.The cold storage bin, material bin and cover plate are connected through a latch plate, which improves the disassembly and assembly efficiency, realizes the compaction of mixed soil layer, and reduces the carbon dioxide escape through special isolation plate.The application can effectively solve the problems of difficult carbonization improvement and uneven carbonization of special soil, and efficiently utilize low-carbon solidifying agent and carbon dioxide resources, with the characteristics of efficient construction and excellent environmental protection benefits.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of special foundation soil treatment in geotechnical engineering, and particularly relates to a dry ice reinforced foundation soil on-site carbonization construction method. BACKGROUND

[0002] With the rapid development of infrastructure construction in China, various types of highways, railways, airports, ports and other projects will inevitably be constructed on special soils. These special soils include seasonal frozen soil and the like, which usually have undesirable properties such as high water content, high sensitivity, low strength, and are prone to swelling, thawing and mud boiling, etc., which greatly hinders the development of China's infrastructure. Therefore, it is necessary and urgent to carry out the reinforcement and treatment of special foundation soils.

[0003] The common foundation treatment method at present is the cement solidification method mainly based on the mixing pile technology. This method is widely used due to its high utilization rate of original soil, simple construction operation, small post-construction settlement and low cost. However, the cement reinforced soil has a long curing period and some problems have been exposed in practice, such as: 1) prone to dry shrinkage cracking, causing structural damage, and thus affecting the water stability and durability of the cement solidified soil; 2) in high latitude areas, seasonal freeze-thaw cycles can significantly affect the mechanical properties of cement soil; 3) in a salt-rich environment, especially in a sulfate-rich environment, cement soil is prone to significant deterioration; 4) cement production is accompanied by large carbon emissions and energy consumption, which has increased year by year, and has caused great challenges to global environmental protection and energy saving and emission reduction. It is urgent to develop a green, low-carbon and efficient new type of solidification material or an environmentally friendly construction method to replace the cement mixing pile method for foundation treatment.

[0004] In recent years, active MgO-CO2 carbonization solidification technology has gradually attracted attention in the industry. Studies have shown that active MgO carbonization solidification technology can achieve rapid growth of soil strength, and the soil strength after carbonization for several hours reaches the 28-day strength of cement solidified soil, with the significant advantages of short construction period and high efficiency. In addition, carbonization solidification technology also uses a large amount of greenhouse gas CO2, which has important practical significance for realizing China's "carbon neutralization" goal. At present, there are some technologies in the field of active MgO-CO2 carbonization solidification treatment of soil, such as "a vacuum drainage combined magnesium oxide carbonization shallow soft foundation solidification method" (201910839460.6), "a vacuum preloading guide pipe pile gas injection carbonization soft foundation reinforcement method" (201910839566.6), "a construction device for carbonization mixing pile-air permeable pipe pile composite foundation" (201710224418.4), "a shallow soft foundation in-situ carbonization solidification treatment method" (201510348797.9), etc. These technologies have the similar features and beneficial effects of mixing alkaline materials mainly containing active MgO with soil, inserting air pipes or drainage boards into the soil, and introducing CO2 for carbonization to achieve the purpose of reinforcing the foundation soil, with the advantages of fast reinforcement speed, high construction efficiency, and good environmental benefits. However, these technologies still have the following defects: 1) it is difficult to ensure uniform mixing of alkaline materials and soil in large-area site treatment; 2) the introduction of CO2 is significantly affected by soil moisture content and gas pressure, and when the soil moisture content is high, low-pressure CO2 infiltration, migration and diffusion into the soil are hindered, while high-pressure CO2 easily diffuses unevenly, causing soil splitting damage and leakage along the cracks; 3) although the use of plastic drainage boards improves the air permeability, the carbonization degree of the soil far from the plastic drainage boards significantly decreases, leading to uneven distribution of foundation soil strength and poor overall treatment effect. Therefore, based on the existing technology principles, the use of CO2 in the form of gas instead of air can effectively improve the uniformity of CO2 in the mixed soil.

[0005] Dry ice is a solid material formed by liquefying gaseous CO2 at 6200 kPa and rapidly solidifying under low pressure, with a boiling point of -78.5℃. Compared with CO2 gas, solid dry ice is easy to mix uniformly with soil and alkaline materials, achieving rapid carbonization of the internal foundation soil. Therefore, based on the trend of green and low-carbon development of geotechnical engineering, and in combination with the defects of the current active MgO-CO2 carbonization solidification technology, it is of important practical significance to develop a site construction method for reinforcing foundation soil using dry ice to improve the active MgO-CO2 carbonization solidification technology. SUMMARY

[0006] In view of the deficiencies in the above background art, in order to improve the uniformity of CO2 distribution in mixed soil layer and carbonization degree, solve the problem of uneven carbonization and difficulty in treating special permafrost in the prior art, the present application aims to provide a dry ice reinforced ground soil on-site carbonization construction method, that is, solid dry ice is mixed into the mixed soil layer for carbonization instead of gaseous CO2 injection into the soil layer, which has great practical significance for the application of MgO-CO2 carbonization technology in treating special ground soil.

[0007] In order to achieve the above-mentioned purpose, the present application discloses a dry ice reinforced ground soil on-site carbonization construction method, characterized in that the construction method comprises the following steps:

[0008] a. Site survey and unit division: survey the pretreatment site to determine the soil properties, boundaries, area, soil layer thickness, water content, organic matter content and salt content of the pretreatment site, the soil properties of the site are seasonal frozen soil or saline soil, the soil layer thickness of the pretreatment site is not more than 1.5m, and the organic matter content is not more than 6%; the pretreatment site is divided into a plurality of pretreatment units, the shape of the pretreatment unit is square or rectangular,

[0009] b. Construction preparation: connect the two ends of the steel cable to the winch and the lifting ring respectively; start the lifting press, move the treatment device to the predetermined starting position by adjusting the working arm, and align the edge of the plugboard with the boundary of the first treatment unit; open the wire reel and release the steel rope, open the bolt plate to integrate the cover plate with the material conveying bin and the freezing bin, and connect the connecting disc with the cover plate by extending the telescopic rod,

[0010] c. Treatment device insertion: start the working arm and the telescopic rod as well as the stirring plow A and the stirring plow B, and make the stirring plow A and the stirring plow B stir and press into the pretreatment unit at the same time, the plugboard, the freezing bin and the material conveying bin are also pressed into the pretreatment unit; after the treatment device is completely inserted into the pretreatment unit, the isolation plate is inserted into the pretreatment unit through the plugboard,

[0011] d. Solidified agent spraying and stirring: according to the solidified agent mixing amount of the preset soil layer, open the metering valve C, the pump and the rotating disc, adjust the flow of the metering valve C, the rotating speed of the rotating disc and the spraying time through the controller, and make the solidified agent in the storage tank enter into the hollow shaft of the stirring plow A through the metering valve C, the pump, the powder spraying pipe in the material conveying bin, the ball valve and the underground pipe A in sequence, and then sprayed into the soil layer through the spray hole of the stirring plow A, the stirring plow A and the stirring plow B rotate and stir independently at the same time, the solidified agent and the pretreatment soil are uniformly mixed while the pretreatment soil is crushed, and the metering valve C is closed when the spraying time is reached,

[0012] e. Gradient refrigeration: open the refrigeration device and metering valve A, pump liquid nitrogen in the liquid nitrogen tank into the circulating pipe in the refrigeration bin through metering valve A, liquid nitrogen pipe and pump, carry out gradient refrigeration of the pretreatment unit, the soil layer temperature of the pretreatment unit is gradually reduced, until the third level temperature is reached; the gradient refrigeration includes first level temperature 0℃ to -5℃, second level temperature -15℃ to -20℃ and third level temperature -30℃ to -35℃, after reaching each level temperature and maintaining for 5 to 10 minutes, it is lowered to the next level temperature, the speed of the gradient refrigeration is controlled by the flow rate of liquid nitrogen,

[0013] f. Dry ice mixing: according to the preset dry ice amount of the soil layer, open metering valve B25, adjust the flow rate and delivery time of metering valve B25, deliver the dry ice in the dry ice tank to the hollow shaft of stirring plow B through metering valve B, pump, dry ice pipe in the material conveying bin, ball valve and dark pipe B, and spray it into the soil layer through the spray hole of stirring plow B, when the delivery time is reached, close metering valve B; stirring plow A, stirring plow B and the rotating disc continue to run for 2 to 5 minutes, then close the rotating disc, so that the curing agent, dry ice and soil in the pretreatment unit are mixed uniformly,

[0014] g. Material conveying bin displacement: through the controller, tighten the winch, so that the latch plate is separated from the material conveying bin and the refrigeration bin, and through the telescopic rod, separate the connecting disc from the cover plate; through the winch, tighten the steel cable, under the action of the working arm and the force transmission column, horizontally drag the material conveying bin, stirring plow A, stirring plow B and the rotating disc from the treated unit to the adjacent pretreatment unit, in the dragging process, stirring plow A and stirring plow B continue to stir and break the soil,

[0015] h. Soil layer compaction and refrigeration bin removal: adjust the steel cable to a free state, through the action of the working arm and the force transmission column, make the connecting disc return to the top of the adjacent treated unit, at the same time, adjust the telescopic rod to connect the connecting disc with the cover plate; press down the telescopic rod to compact the mixed soil layer, stop pressing down when the target compaction degree is reached; close metering valve A and the pump, loosen the winch and the steel cable, lift the telescopic rod to make the latch plate engage with the refrigeration bin, pull out the refrigeration bin and the latch plate from the soil layer, so that the isolation plate remains in the soil layer; move the refrigeration bin and the latch plate to the adjacent untreated unit, and place the isolation plate in the latch plate again,

[0016] i. Membrane laying and curing: lay a sealing layer on the upper part of the adjacent treated unit, and cure the compacted mixed soil layer, the dry ice in the mixed soil layer gradually changes into carbon dioxide gas, through the chemical reaction of carbon dioxide and the curing agent, carbonized cementation products are formed, which improves the mechanical strength of the soil layer, and the width of the sealing layer is greater than the distance between the two isolation plates.

[0017] As an improvement of the present application, the processing device is composed of a plug-in device, a freezing bin, a material conveying bin, a cover plate, a stirring plow A, a stirring plow B and a rotating disc; the plug-in device is arranged on the left and right sides of the processing device in the advancing direction, the two sides of the isolation plate are respectively provided with a clamping groove and a clamping buckle, the isolation plate is inserted into the plug-in device according to the sequence of the clamping groove and the clamping buckle, the clamping groove of the pre-inserted isolation plate is inserted into the clamping buckle of the soil layer, or the clamping buckle of the pre-inserted isolation plate is inserted into the clamping groove of the soil layer, so that the clamping buckle and the clamping groove of the adjacent isolation plates are tightly connected, and the underground continuous isolation wall is formed.

[0018] As another improvement of the present application, the curing agent is composed of 50-80 parts of magnesium oxide and 20-50 parts of quicklime, and the curing agent accounts for 5-15% of the mass of the pretreated soil layer; the dry ice is solid carbon dioxide, the shape of the dry ice particles is strip-shaped or spherical, the maximum size of the particles is not more than 10 mm, and the mixing mass of the dry ice is 0.8-1.0 times the mass of the curing agent.

[0019] As another improvement of the present application, the target compaction degree is 84-92%, the sealing layer is a geomembrane with a thickness of 3-5 mm or a clay layer with a thickness of 100-300 mm, and the curing time is determined according to the area and depth of the processing unit and is preset to be 24-72 h.

[0020] As another improvement of the present application, the size of the processing unit is consistent with the inner diameter of the processing device, and the thickness of the processed soil layer is not greater than the internal height of the processing device; the construction sequence of the processing device is performed in the "S" type direction, after the construction of an entire row or an entire column of processing units is completed, the processing device is adjusted and moved as a whole by using a lifting and pressing device, and is moved to the next row or the next column of the pretreated processing unit.

[0021] Compared with the prior art, the present application has the beneficial effects that:

[0022] 1) The present application mixes solid dry ice into the mixed soil containing the curing agent for carbonization and curing, replaces the traditional CO2 gas injection mode, realizes the uniform distribution of CO2 in the soil body, and achieves the purpose of good carbonization and processing effect, and solves the problems of large CO2 gas diffusion difficulty and poor uniformity and carbonization effect in the traditional injection mode.

[0023] 2) The present application adopts gradient refrigeration by liquid nitrogen circulation, the liquid nitrogen can be recycled, the environment is protected, and the construction cost and energy consumption are reduced.

[0024] 3) The special low-temperature environment is used for the injection and stirring of solid dry ice, which not only reduces the volatilization amount in the dry ice mixing process, but also makes the frozen soil body have smaller adhesion and be easier to break into small particles, so that the curing agent and dry ice materials are fully and uniformly mixed with the soil body, and the uniformity of the later carbonization is improved.

[0025] 4) The curing agent used in the application is a mixture of active magnesium oxide and quicklime, which has the advantages of low carbon and environmental protection compared with traditional cement; the special curing agent composition and compaction degree range can meet the stronger cementation effect of CO2 carbonization.

[0026] 5) The application uses a latch plate to connect the freezing bin and the material conveying bin, and the connection method is simple and reliable, which optimizes the operation method of device assembly and disassembly during construction preparation, material conveying bin displacement and freezing bin removal, and improves the construction efficiency.

[0027] 6) The material conveying bin and the freezing bin are removed separately during construction, which ensures the continuity of operation, and the removal of the freezing bin can maintain the low temperature of the treatment unit, reducing the evaporation of dry ice caused by the removal of the material conveying bin and the rotation of the stirring plow; the isolation plate and the sealing film are specially designed to reduce CO2 loss and overflow caused by the removal of the freezing bin, and improve the utilization rate of CO2 dry ice and the carbonation rate.

[0028] 7) The application uses CO2 to carbonize and reinforce special soil, which has the significant advantages of low carbon and environmental protection. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a schematic diagram of the overall structure of a site carbonization treatment for reinforcing foundation soil by using dry ice;

[0030] Figure 2 It is a schematic diagram of the internal structure of a cover plate for a site carbonization treatment for reinforcing foundation soil by using dry ice;

[0031] Figure 3 It is a schematic diagram of the cover plate structure for a site carbonization treatment for reinforcing foundation soil by using dry ice;

[0032] Figure 4 It is a schematic diagram of the internal structure of a rotating disc for a site carbonization treatment for reinforcing foundation soil by using dry ice;

[0033] Figure 5 It is a schematic diagram of the internal structure of a freezing bin for a site carbonization treatment for reinforcing foundation soil by using dry ice;

[0034] Figure 6 It is a schematic diagram of the internal structure of a plug-in plate device for a site carbonization treatment for reinforcing foundation soil by using dry ice;

[0035] Figure 7 It is a schematic diagram of the structure of an isolation plate for a site carbonization treatment for reinforcing foundation soil by using dry ice;

[0036] Figure 8 It is a schematic diagram of the connection method of an isolation plate for a site carbonization treatment for reinforcing foundation soil by using dry ice;

[0037] Figure 9A schematic diagram of a construction progress sequence of a site carbonization treatment for reinforcing ground soil using dry ice.

[0038] In the figure: 11, a board inserting device, 12, a freezing bin, 13, a material conveying bin, 14, a cover plate, 15, a stirring plow A, 16, a stirring plow B, 17, a rotating disc, 18, a dry ice pipe, 19, a powder spraying pipe, 110, a liquid nitrogen pipe, 111, a board inserting shoe, 112, a controller, 113, a wire reel, 114, a steel rope, 115, a latch plate, 116, a rotor, 117, a ball valve, 118, a spray hole, 119, a buried pipe A, 120, a buried pipe B, 121, an isolation plate, 122, a spring sheet, 21, a material carrying vehicle, 22, a liquid nitrogen tank, 23, a metering valve A, 24, a dry ice tank, 25, a metering valve B, 26, a material storage tank, 27, a metering valve C, 28, a refrigeration device, 29, a pump, 31, a crane, 32, a rotating shaft, 33, a working arm, 34, a transmission wheel, 35, a hoist, 36, a lifting ring, 37, a steel cable, 38, a force transmission column, 39, a cross beam, 310, an extension rod, 311, a connecting disc, 41, a pretreatment site, 42, a pretreatment unit, 43, a treated unit. DETAILED DESCRIPTION

[0039] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application will be further described below in combination with the drawings.

[0040] As Figures 1-9 shown, the present application discloses a site carbonization construction method for reinforcing ground soil using dry ice, characterized in that the construction method comprises the following steps:

[0041] a. site survey and unit division: surveying the pretreatment site 41 to determine the soil property, boundary, area, soil layer thickness, water content, and organic matter content of the pretreatment site 41, wherein the soil property is seasonal frozen soil or saline soil, the soil layer thickness of the pretreatment site 41 is not more than 1.5 m, and the organic matter content is not more than 6%; dividing the pretreatment site 41 into a plurality of pretreatment units 42, wherein the shape of the pretreatment unit 42 is a square or a rectangle,

[0042] b. construction preparation: connecting the two ends of the steel cable 37 to the hoist 35 and the lifting ring 36, respectively; starting the crane 31, moving the treatment device to the predetermined starting position by adjusting the working arm 33, and aligning the edge of the board inserting device 11 with the boundary of the first treatment unit; opening the wire reel 113 and releasing the steel rope 114, opening the latch plate 115 to connect the cover plate 14, the material conveying bin 13, and the freezing bin 12 into one body, and connecting the connecting disc 311 to the cover plate 14 by extending the extension rod 310,

[0043] c. Treatment device insertion: Start the working arm 33 and telescopic rod 310, and the stirring plow A15 and stirring plow B16 in the treatment device, so that the stirring plow A15 and stirring plow B16 stir and press down into the soil layer, and the insertion boarder 11, refrigeration bin 12, and material conveying bin 13 are pressed into the pretreatment unit 42 together; after the treatment device is completely inserted, the isolation board 121 is inserted into the pretreatment unit 42 through the insertion boarder 11,

[0044] d. Solidifying agent spraying and stirring: According to the preset solidifying agent mixing amount of the soil layer, open the metering valve C27, the pump 29, and the rotating disc 17, adjust the flow of the metering valve C27, the rotating speed of the rotating disc 17, and the spraying time through the controller 112, and sequentially pass the solidifying agent in the storage tank 26 into the hollow shaft of the stirring plow A15 through the metering valve C27, the pump 29, the powder spraying pipe 19 in the material conveying bin 13, the ball valve 117, and the blind pipe A119, and spray the solidifying agent into the soil layer through the spray hole 118 of the stirring plow A15, so that the stirring plow A15 and the stirring plow B16 independently stir and rotate with the rotating disc 17 at the same time, break the pretreated soil, and uniformly mix the solidifying agent and the pretreated soil, and when the spraying time is reached, the metering valve C27 is closed,

[0045] e. Gradient refrigeration: Open the refrigeration device 28 and the metering valve A23, pump the liquid nitrogen in the liquid nitrogen tank 22 into the circulating pipe in the refrigeration bin 12 through the metering valve A23, the liquid nitrogen pipe 110, and the pump 29, perform gradient refrigeration of the pretreatment unit 42, and gradually reduce the temperature of the soil layer in the pretreatment unit 42 until the third-stage temperature is reached; the gradient refrigeration includes a first-stage temperature of 0℃ to -5℃, a second-stage temperature of -15℃ to -20℃, and a third-stage temperature of -30℃ to -35℃, and after reaching and maintaining each stage temperature for 5 to 10 minutes, the temperature is lowered to the next stage, and the gradient refrigeration is controlled by the flow of the liquid nitrogen,

[0046] f. Dry ice mixing: According to the preset dry ice usage of the soil layer, open and adjust the flow of the metering valve B25 and the conveying time, pass the dry ice in the dry ice tank 24 into the hollow shaft of the stirring plow B16 through the metering valve B25, the pump 29, the dry ice pipe 18 in the material conveying bin 13, the ball valve 117, and the blind pipe B120, and spray the dry ice into the soil layer through the spray hole 118 of the stirring plow B16, and when the conveying time is reached, the metering valve B25 is closed; the stirring plow A15, the stirring plow B16, and the rotating disc 17 continue to operate for 2 to 5 minutes to uniformly mix the solidifying agent, the dry ice, and the soil in the pretreatment unit 42, and the rotating disc 17 is closed,

[0047] g. The displacement of the material bin 13: through the controller 112, the winch 113 is tightened, the latch plate 115 is separated from the material bin 13 and the freezing bin 12, and through the telescopic rod 310, the connecting disc 311 is separated from the cover plate 14; through the winch 35, the steel cable 37 is tightened, under the action of the working arm 33 and the force column 38, the material bin 13, the stirring plow A 15, the stirring plow B 16 and the rotating disc 17 are horizontally dragged from the treated unit 43 to the adjacent pretreated unit 42, and in the process of dragging, the stirring plow A 15 and the stirring plow B 16 continue to stir the soil,

[0048] h. The compaction of the soil layer and the removal of the freezing bin 12: the steel cable 37 is adjusted to the free state, the connecting disc 311 is returned to the upper side of the adjacent treated unit 43 through the action of the working arm 33 and the force column 38, and the telescopic rod 310 is adjusted to connect the connecting disc 311 with the cover plate 14; the telescopic rod 310 is pressed to compact the mixed soil layer of the cover plate 14, and the pressing is stopped after the target compaction degree is reached; the metering valve A 23 and the pump 29 are closed, the winch 113 and the steel cable 114 are loosened, the telescopic rod 310 is lifted to make the latch plate 115 buckle with the freezing bin 12, the freezing bin 12 and the plug plate device 11 are pulled out of the soil layer, the isolation plate 121 is left in the soil layer, and the freezing bin 12 and the plug plate device 11 are moved to the adjacent untreated unit 42, and the isolation plate 121 is placed in the plug plate device 11 again,

[0049] i. Membrane laying and curing: a sealing layer is laid on the upper part of the adjacent treated unit 43 to cure the compacted mixed soil layer, the dry ice in the mixed soil layer is gradually converted into carbon dioxide gas, the carbon dioxide gas reacts with the curing agent to form carbonized cementation products, and the mechanical strength of the soil layer is improved, and the width of the sealing layer is greater than the distance between the two isolation plates 121.

[0050] Preferably, the treatment device is composed of the plug plate device 11, the freezing bin 12, the material bin 13, the cover plate 14, the stirring plow A 15, the stirring plow B 16 and the rotating disc 17; the plug plate device 11 is arranged on the left and right sides of the treatment device in the advancing direction, the two sides of the isolation plate 121 are respectively provided with a clamping groove and a buckle, the isolation plate 121 is inserted into the plug plate device 11 in the order of the clamping groove and the buckle, the pre-inserted isolation plate 121 is inserted into the clamping groove of the isolation plate 121 in the soil layer, or the pre-inserted isolation plate 121 is inserted into the buckle of the isolation plate 121 in the soil layer, so that the buckle and the clamping groove of the adjacent isolation plate 121 are closely connected, and an underground continuous isolation wall is formed.

[0051] Preferably, the curing agent is composed of 50-80 parts of magnesium oxide and 20-50 parts of quicklime, and the curing agent accounts for 5%-15% of the mass of the pretreated soil layer; the dry ice is solid carbon dioxide, the shape of the dry ice particles is strip-shaped or spherical, the maximum size of the particles is not more than 10 mm, and the mixing mass of the dry ice is 0.8-1.0 times the mass of the curing agent.

[0052] Preferably, the target compaction degree is 84% to 92%; the sealing layer is a geomembrane with a thickness of 3 to 5 mm or a clay layer with a thickness of 100 to 300 mm; and the curing time is determined according to the area and depth of the treatment unit and is preset to be 24 to 72 hours.

[0053] Further preferably, the size of the treatment unit is consistent with the inner diameter of the treatment device, and the thickness of the treated soil layer is not greater than the internal height of the treatment device; the construction sequence of the treatment device is performed in an "S" type direction, and after the construction of an entire row or an entire column of treatment units is completed, the treatment device is adjusted and moved away as a whole by using the lifting and pressing device and is moved to the next row or the next column of the pretreated units 42.

[0054] The application will be described in more detail below with reference to the accompanying drawings and specific embodiments.

[0055] Embodiment 1:

[0056] The pretreatment site 41 has an area of about 200 m 2 The soil is seasonal frozen soil, the soil layer thickness is 1 m, the average water content of the soil body is 35%, and the organic matter content is 0%. The pretreatment site 41 is divided into a plurality of 1 m x 1 m x 1 m (length x width x height) square treatment units. A treatment device with an inner diameter of 1 m x 1 m x 1 m and a size of 1 m x 0.05 m x 1.2 m is selected. In the solidification agent spraying and stirring process, the solidification agent dosage is set to 5% of the mass of the soil body of the treatment unit, the solidification agent ratio is 50 parts of magnesium oxide and 50 parts of quicklime, the rotating disc 17 rotates at a speed of 40 r / min, the flow rate of the metering valve C27 is 6 kg / min, and the powder spraying time is 15 min. In the dry ice mixing process, the dry ice is a strip-shaped particle with a length of 8 mm, the dry ice is mixed in an amount of 0.8 times the mass of the solidification agent, the flow rate of the metering valve B25 is 7 kg / min, and the conveying time is 10 min. In the film laying and curing process, the sealing layer is a geomembrane with a thickness of 3 mm, and the natural curing time is 24 hours.

[0057] Embodiment 2:

[0058] The pretreatment site 41 has an area of about 400 m 2The pretreatment site 41 is divided into several square treatment units of 2m x 2m x 1.2m (length x width x height). A treatment device with an inner diameter of 2m x 2m x 1.2m is selected, and a partition plate with a size of 2m x 0.05m x 1.4m is selected. In the solidification agent spraying and stirring, the solidification agent mixing amount is set to 10% of the mass of the soil in the treatment unit, the solidification agent ratio is 70 parts of magnesium oxide and 30 parts of lime, the rotating disc 17 rotates at a speed of 30r / min, the flow of the metering valve C27 is 35kg / min, and the powder spraying time is 25min. In the dry ice mixing, the dry ice is a strip-shaped particle with a length of 10mm, the dry ice mixing amount is 0.9 times the mass of the solidification agent, the flow of the metering valve B25 is 39kg / min, and the conveying time is 20min. In the film laying and curing, the sealing layer is a geomembrane with a thickness of 5mm, and the natural curing time is 48h.

[0059] Example 3:

[0060] The pretreatment site 41 has an area of about 600m 2 The pretreatment site 41 is divided into several rectangular treatment units of 3m x 2m x 1.5m (length x width x height). A treatment device with an inner diameter of 3m x 2m x 1.5m is selected, and a partition plate with a size of 3m x 0.05m x 1.7m is selected. In the solidification agent spraying and stirring, the solidification agent mixing amount is set to 15% of the mass of the soil in the treatment unit, the solidification agent ratio is 80 parts of magnesium oxide and 20 parts of lime, the rotating disc 17 rotates at a speed of 20r / min, the flow of the metering valve C27 is 60kg / min, and the powder spraying time is 40min. In the dry ice mixing, the dry ice is a spherical particle with a diameter of 9mm, the dry ice mixing amount is 1 times the mass of the solidification agent, the flow of the metering valve B25 is 81kg / min, and the conveying time is 30min. In the film laying and curing, the sealing layer is a clay layer with a thickness of 500mm, and the natural curing time is 72h.

[0061] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A field carbonation construction method for reinforcing ground soil with dry ice, characterized by, The construction method comprises the following steps: a. site survey and unit division: survey the pretreatment site, determine the soil properties, boundaries, area, soil thickness, moisture content, organic matter content and salt content of the pretreatment site, the soil properties of the site are seasonal frozen soil or saline soil, the soil thickness of the pretreatment site is not more than 1.5 m, and the organic matter content is not more than 6%; the pretreatment site is divided into several pretreatment units, the shape of the pretreatment unit is square or rectangular, b. construction preparation: connect the two ends of the steel cable to the winch and the lifting ring respectively; start the lifting pressure machine, move the treatment device to the predetermined starting position by adjusting the working arm, and align the edge of the plugboard with the boundary of the first treatment unit; open the winding device and release the steel rope, open the bolt plate to integrate the cover plate with the material conveying bin and the freezing bin, and extend the telescopic rod to connect the connecting disc with the cover plate, c. treatment device insertion: start the working arm, telescopic rod, stirring plow A and stirring plow B, and make stirring plow A and stirring plow B stir and press into the pretreatment unit, and the plugboard, freezing bin and material conveying bin are also pressed into the pretreatment unit; after the treatment device is completely inserted into the pretreatment unit, the isolation plate is inserted into the pretreatment unit through the plugboard, d. solidifying agent spraying and stirring: according to the preset solidifying agent mixing amount of the soil layer, open the metering valve C, the pump and the rotating disc, adjust the flow of the metering valve C, the rotating speed of the rotating disc and the spraying time through the controller, and make the solidifying agent in the storage tank enter into the hollow shaft of stirring plow A through the metering valve C, the pump, the powder spraying pipe in the material conveying bin, the ball valve and the underground pipe A in sequence, and then is sprayed into the soil layer through the spraying hole of stirring plow A, and stirring plow A and stirring plow B rotate and stir independently while rotating with the rotating disc, so that the solidifying agent and the pretreatment soil are uniformly mixed while the pretreatment soil is crushed, and the metering valve C is closed when the spraying time is reached, e. gradient refrigeration: open the refrigeration device and the metering valve A, pump the liquid nitrogen in the liquid nitrogen tank into the circulating pipe in the freezing bin through the metering valve A, the liquid nitrogen pipe and the pump, and perform gradient refrigeration on the pretreatment unit, and the temperature of the soil layer of the pretreatment unit is gradually reduced until the third level temperature is reached; the gradient refrigeration comprises a first level temperature of 0℃ to -5℃, a second level temperature of -15℃ to -20℃ and a third level temperature of -30℃ to -35℃, and after reaching each level temperature and maintaining for 5-10 min, it is lowered to the next level temperature, and the speed of the gradient refrigeration is controlled by the flow of the liquid nitrogen, f. dry ice uniform mixing: according to the preset dry ice amount of the soil layer, open the metering valve B, adjust the flow of the metering valve B and the conveying time, and make the dry ice in the dry ice tank enter into the hollow shaft of stirring plow B through the metering valve B, the pump, the dry ice pipe in the material conveying bin, the ball valve and the underground pipe B, and then is sprayed into the soil layer through the spraying hole of stirring plow B, and the metering valve B is closed when the conveying time is reached; the stirring plow A, the stirring plow B and the rotating disc continue to operate for 2-5 min, and then the rotating disc is closed, so that the solidifying agent, the dry ice and the soil in the pretreatment unit are uniformly mixed, g. The material bin is displaced: the controller tightens the winch, the latch plate is separated from the material bin and the freezing bin, and the connecting disc is separated from the cover plate through the telescopic rod; the steel cable is tightened by the winch, and under the action of the working arm and the force transmission column, the material bin is horizontally dragged from the treated unit to the adjacent pretreated unit with the stirring plow A, the stirring plow B and the rotating disc, and in the process of dragging, the stirring plow A and the stirring plow B continue to stir and break the soil, h. The soil layer is compacted and the freezing bin is removed: the steel cable is loosened to a free state, the connecting disc is returned to the top of the adjacent treated unit through the action of the working arm and the force transmission column, and the connecting disc is connected with the cover plate by adjusting the telescopic rod; the cover plate is compacted by lowering the telescopic rod, and the process is stopped after the target compaction degree is reached; the metering valve A and the pump are closed, the winch and the steel cable are loosened, the connecting disc is buckled with the freezing bin by lifting the telescopic rod, and the freezing bin and the plug-in device are pulled out of the soil layer, so that the isolation plate remains in the soil layer; the freezing bin and the plug-in device are moved to the adjacent untreated unit, and the isolation plate is placed in the plug-in device again, i. Membrane laying and curing: a sealing layer is laid on the upper part of the adjacent treated unit to cure the compacted mixed soil layer, the dry ice in the mixed soil layer gradually changes into carbon dioxide gas, and the carbonized cementation product is formed through the chemical reaction of carbon dioxide and the curing agent, which improves the mechanical strength of the soil layer, and the width of the sealing layer is greater than the distance between the two isolation plates.

2. The method according to claim 1, wherein the method is characterized by, The treatment device is composed of a plug-in device, a freezing bin, a material bin, a cover plate, a stirring plow A, a stirring plow B and a rotating disc; the plug-in device is arranged on the left and right sides of the treatment device in the advancing direction, the two sides of the isolation plate are respectively provided with a clamping groove and a clamping buckle, the isolation plate is inserted into the plug-in device in the order of the clamping groove and the clamping buckle, the clamping groove of the pre-inserted isolation plate is inserted into the clamping buckle of the isolation plate in the soil layer, or the clamping buckle of the pre-inserted isolation plate is inserted into the clamping groove of the isolation plate in the soil layer, so that the clamping buckle and the clamping groove of the adjacent isolation plate are closely connected to form an underground continuous isolation wall.

3. The method of claim 1, wherein the method further comprises: The curing agent is composed of 50-80 parts of magnesium oxide and 20-50 parts of quicklime, and the curing agent accounts for 5%-15% of the mass of the pretreated soil layer; the dry ice is solid carbon dioxide, the shape of the dry ice particles is strip-shaped or spherical, the maximum size of the particles is not more than 10 mm, and the mixing mass of the dry ice is 0.8-1.0 times the mass of the curing agent.

4. The method of claim 1, wherein the method further comprises: The target compaction degree is 84%-92%, the sealing layer is a geotextile with a thickness of 3-5 mm or a clay layer with a thickness of 100-300 mm, and the curing time is determined according to the area and depth of the treatment unit and is preset to be 24-72 h.

5. The method of claim 1, wherein the method further comprises: The size of the treatment unit is consistent with the inner diameter of the treatment device, and the thickness of the treated soil layer is not greater than the internal height of the treatment device; the construction sequence of the treatment device is in the "S" type direction, and after the construction of a whole row or a whole column of treatment units is completed, the treatment device is adjusted and moved as a whole by using a lifting and pressing device to the next row or the next column of pretreated units.

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