A soft foundation treatment method combining gas cavitation and charge neutralization

Abstract

The present invention discloses a soft foundation treatment method combining gas cavitation and charge neutralization. A plurality of vertical shafts are dug at intervals to the drainage depth at a predetermined location of the soft foundation, and a sealing trench is dug around the area where the vertical shafts are located. After the hole walls of the vertical shafts are stabilized, a pretreatment agent is put into the vertical shafts. A sand cushion layer is laid in the sealing trench and the area where the vertical shafts are located. A water collection channel on the ground surface is arranged above the sand cushion layer in the area where the vertical shafts are located. A sealing film is covered on the sand cushion layer and the water collection channel, and the sealing trench is backfilled and compacted. The sealing film forms a sealed space in the area where the vertical shafts are located. A gas circulation system is installed, and high-pressure dry air is filled into the sealed film to form a flowing air current, gathering the dry gas above the site to be treated, and taking out the moisture in the soil while compacting the soft foundation. The present invention can better discharge the pore water in the soft soil foundation with high water content, achieve the purpose of drainage consolidation, and has low construction risk and low cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering and relates to a soft foundation treatment method combining gas cavitation and charge neutralization. Background Art

[0002] Soft soil foundations generally mainly consist of clay particles, i.e., particles with a particle size less than 5 μm. Common soft soils in engineering include kaolin, montmorillonite, etc. Taking montmorillonite as an example, due to its extremely small particle size and extremely large specific surface area, isomorphic substitution can occur within the unit cell of the particle. High-valent silicon ions (Si 4+ ) and aluminum ions (Al 3+ ) can be partially or completely replaced by other low-valent cations, resulting in the unit cell of montmorillonite carrying a negative charge. Coupled with the hydroxyl hydrophilic groups carried by the unit cell, it can adsorb polar molecules such as water. Thus, when absorbing water during rainfall, the soft soil foundation can absorb a large amount of liquid water. These liquid waters are stored in the pores between soil particles, which will not only reduce the soil strength, reduce the shear and compressive resistance of the soil, and is prone to deformation when subjected to loads, but also, when drying and losing water, will cause the generation of cracks due to the loss of pore water, which not only damages the soil body but also is not conducive to bearing the upper load, and may even cause the settlement of the upper structure.

[0003] To reduce the water content of the soil and avoid the above problems, currently common methods in engineering include the vacuum preloading method. This method involves laying a sand cushion on the ground to be treated, setting up vertical wells, then laying a closed film on the working surface to isolate the ground from the atmosphere, and then using a vacuum pump to evacuate, creating a vacuum under the ground to increase the effective stress of the soil, thereby discharging groundwater. However, judging from the commonly used technical means in current construction production, the vacuum preloading technology is not satisfactory for the drainage consolidation effect of the shallow layer of the soft foundation, and its consolidation effect in the deep layer is even more unsatisfactory.

[0004] And because the soil particles carry a negative charge, a large number of water molecules are adsorbed around the soil particles, forming a strong bound water layer and a weak bound water layer. These bound waters are difficult to be stripped from the soil particles due to the action of the electric field force, resulting in that the vacuum densification method may not be able to completely remove the water in the soil. Therefore, it is of great significance for the improvement of the soft soil foundation to make the bound water around the soil particles easier to be discharged through pretreatment before vacuum densification.

[0005] Chinese Patent "In-situ Chemical Conditioning and Vacuum Preloading Reduction Method and Conditioning Device for Landfill Sludge" (CN103435245A) discloses an in-situ chemical conditioning and vacuum preloading reduction method and conditioning device for landfill sludge. This method uses Fe 3+Improve the drainage consolidation performance of the contaminated soil, and then use the vacuum compression method to carry out drainage consolidation on it. It is a method of treating soft foundation through the principle of electrochemistry, but this method ignores the differences in the acidity and alkalinity of soil in different regions and does not consider the problem that this treatment agent may fail in some regions.

[0006] In addition, the Chinese patent "Device and Method for Reinforcing Soft Soil Foundation by Combining Strong Drainage Preloading and Electroosmosis" (CN112962571A) discloses a device for reinforcing soft soil foundation by combining strong drainage preloading and electroosmosis and its treatment method. This method combines the vacuum preloading method and the electroosmotic drainage method, which is a strong drainage means. It is necessary to lay a film and evacuate on the site to be treated, and at the same time, it is necessary to set positive and negative electrodes in the site to make the pore water migrate to improve the drainage volume. Although the combination of these two drainage means can help each other to achieve a better drainage effect, it ignores the internal friction and loopholes in the system that may occur under the coupling conditions of multiple drainage elements. Not only may the final drainage effect not be good, but this treatment idea also does not conform to the concept of economy and practicality, consumes more resources, and is relatively complex in specific organization and implementation, and it is difficult to be a widely promoted method.

[0007] In addition, the Chinese patent "Method for Treating Soft Soil Foundation by Combining Chemical Solution Injection and Electroosmosis and Its Construction Method" (CN102162239A) also discloses a drainage method for treating soft foundation based on electrochemistry. The invention inserts metal electrodes into the site to be treated, injects solutions with different ions into them, and passes direct current. Under the action of the electric field, the water with positive charges and the cation solution will move towards the cathode, and the negatively charged ion solution will move towards the anode. At the same time, the precipitate generated by the chemical reaction will also play a certain role in cementing the soil particles. The main idea of this method is still to promote the movement of pore water through the electric field. According to its reinforcement mechanism, the electroosmotic drainage speed is largely affected by the electroosmotic coefficient of the soil. Different soils have different electroosmotic coefficients, so the application range of this method will be limited. In addition, since acid-base or salt solutions with ions will be used, as electroosmosis progresses, the electrodes will inevitably become heavier, greatly affecting the treatment effect. Considering the consumption of electric energy at the same time, this method has many limitations. Summary of the Invention

[0008] In order to solve the above problems, the present invention provides a soft foundation treatment method combining gas cavitation and charge neutralization, which can better drain the pore water of soft soil foundation with high water content, achieve the purpose of drainage consolidation, has low construction risk and low cost, and solves the problems existing in the prior art.

[0009] The technical solution adopted by the present invention is a soft foundation treatment method combining gas cavitation and charge neutralization, including the following steps:

[0010] S1, Site preparation;

[0011] S2, Dig a plurality of vertical shafts at intervals at a predetermined location in the soft foundation to the drainage depth, and dig a sealing trench around the area where the vertical shafts are located. The sealing trenches are connected to each other to enclose the area where the vertical shafts are located;

[0012] S3, After the hole wall of the vertical shaft is stabilized, put a pretreatment agent into the vertical shaft, and backfill and reinforce it in time after the placement is completed;

[0013] S4, Lay a sand cushion layer in the sealing trench and the area where the vertical shafts are located;

[0014] S5, Arrange a water collecting channel on the surface above the sand cushion layer in the area where the vertical shafts are located. The water collecting channel covers the area to be treated as much as possible. The water collecting channel has undulations. Condensate water is collected at the low places, and ventilation holes are opened at the high places for gas circulation;

[0015] S6, Cover a sealing film over the sand cushion layer and the water collecting channel, backfill and compact the sealing trench, and the sealing film forms a sealed space in the area where the vertical shafts are located;

[0016] S7, Install a gas circulation system, fill high-pressure dry air into the sealing film to form a flowing air current, gather the dry gas above the site to be treated, and compact the soft foundation while taking out the moisture in the soil.

[0017] Further, the water collecting channel is arranged in an overall inclined manner, and is arranged according to the principle that it is high at the air inlet and low at the exhaust outlet. The low places of the water collecting channel are connected to each other, and condensate water is collected through a water collecting trough at the lowest end and discharged out of the sealing film through a main drain pipe uniformly.

[0018] Further, the water collecting channels are overlapped with each other through drain pipes or are a complete shell. Ventilation holes are provided at the high places of the pipe body of the drain pipe; the complete shell is a plate with undulations. Condensate water is collected at the low places of the plate, and ventilation holes are opened at the high places.

[0019] Further, before adding the pretreatment agent, add 50 - 100 L of water to accelerate the diffusion of the pretreatment agent in the soil. After adding the pretreatment agent, add an appropriate amount of water again to make the pretreatment agent diffuse better and faster in the soil. The amount of water used is limited so that it does not overflow from the vertical shaft; when adding the pretreatment agent, conduct drainage through a drainage rod, move the drainage rod around the hole side wall of the vertical shaft, and try to make the pretreatment agent flow into the vertical shaft evenly along the side wall.

[0020] Further, the pretreatment agent is prone to ionization and can neutralize the hydrogen ions or hydroxide ions carried in the soil.

[0021] Further, for alkaline soil, the pretreatment agent is selected from sulfuric acid, hydrochloric acid or acetic acid. Based on the principle of chemical charge neutralization, the amount of anions required by the pretreatment agent is determined according to the number of soil cations, so as to determine the dosage of the pretreatment agent.

[0022] For neutral soil, the pretreatment agent is selected from sodium chloride or potassium chloride, and the dosage is 184h, where h represents the precipitation depth.

[0023] For acidic soil, the pretreatment agent is selected from sodium carbonate, caustic soda or ammonia water, and the dosage is 333h.

[0024] Further, the pretreatment agent adheres to the wellbore as much as possible, and is backfilled and reinforced in time after the placement is completed. The backfill soil is selected from sand and gravel or undisturbed soil; if there is still water in the shaft, the shaft is filled with gravelly soil; if there is less water in the shaft and the infiltration of the pretreatment agent solution is good, the undisturbed soil is directly backfilled; the shaft backfill does not require special compaction.

[0025] Further, the permeability coefficient of the soil layer of the sealing trench is less than 10-5mm / s.

[0026] Further, the gas circulation system includes an intake system and an exhaust system. The intake system is installed first, and then the exhaust system; the intake system includes an air compressor and an air dryer. The air outlet of the air compressor is connected to the air inlet of the sealing membrane, and the air outlet of the air dryer is connected to the air inlet of the air compressor. The air inlet of the sealing membrane is located at the higher end of the water collection channel; the exhaust system includes a blower, with a power matching that of the intake system, installed at the air outlet of the sealing membrane, located at the lower end of the water collection channel, and is used to discharge the moist air.

[0027] Further, the sealing membrane extends out of the sealing trench and folds around. During the process of filling high-pressure dry air into the sealing membrane, the airtightness of the sealing membrane, the operation of each machine in the air inflation system, and the change of the pressure inside the membrane should be checked, and the length of the sealing membrane reserved outside the sealing trench should be measured.

[0028] The beneficial effects of the present invention are as follows:

[0029] 1. Based on the water absorption ability of soft soil particles and through the gas cavitation effect, the soft foundation soil is drained and consolidated in the embodiments of the present invention, which can effectively weaken the water storage capacity of the soft soil, enable more pore water to be discharged during drainage consolidation, and bring the pore water out along the soil drainage channels through the cavitation effect of dry gas. It can be applied to engineering technical fields such as soft foundation treatment of soil with high water content, with low construction risk and low cost.

[0030] 2. The processing method of the embodiment of the present invention is economical, reasonable and has good effects. Most of the construction equipment used is relatively economical construction equipment, and all materials can be recycled after being used. For damaged materials, since the cost is low, new components can be directly replaced.

[0031] 3. The pretreatment agents used in the embodiments of the present invention are all inorganic materials, which cause little damage to the soil body and do not produce organic materials that are difficult to degrade, being environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 It is a schematic diagram of the excavation of the vertical shaft and the sealing trench in the embodiment of the present invention.

[0034] Figure 2 It is a schematic diagram of the arrangement of the vertical shafts in the embodiment of the present invention.

[0035] Figure 3 It is a spatial layout diagram (top view) of the vertical shaft and the sealing trench in the embodiment of the present invention.

[0036] Figure 4 It is a schematic diagram of the addition of the pretreatment agent in the embodiment of the present invention.

[0037] Figure 5 It is a schematic diagram of the backfilling of the vertical shaft in the embodiment of the present invention.

[0038] Figure 6 It is a schematic diagram of the laying of the sand cushion layer in the embodiment of the present invention.

[0039] Figure 7 It is a schematic diagram of the layout of the water collection channels on the ground surface in the embodiment of the present invention.

[0040] Figure 8 It is a schematic diagram of the laying of the closed film in the embodiment of the present invention.

[0041] Figure 9 It is a schematic diagram of the installation of the gas circulation system in the embodiment of the present invention.

[0042] Figure 10 It is a schematic diagram of the charge neutralization principle in the embodiment of the present invention.

[0043] Figure 11 It is a flowchart of the embodiment of the present invention.

[0044] In the figure, 1. vertical shaft, 2. sealing trench, 3. pretreatment agent, 4. sand cushion layer, 5. water collecting channel, 6. sealing film, 7. air intake system, 8. exhaust system, 9. soft soil particles, 10. negative charge, 11. strongly bound water molecules, 12. weakly bound water molecules, 13. strongly bound water layer, 14. weakly bound water layer, 15. positive ions of pretreatment agent, 16. combination, 17. released weakly bound water. Detailed implementation manner

[0045] The following will combine the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0046] Embodiment 1

[0047] A soft foundation treatment method combining gas cavitation and charge neutralization, as Figure 11 shown, includes the following steps:

[0048] S1, Site preparation; Before starting work, first carry out three connections and one leveling, remove the surface humus, remove the grass clippings, tree roots, etc. of the site to be treated, and remove underground obstacles, such as large stones or other buried objects. For an uneven site, site leveling is also required: calculate according to the data obtained from on-site measurement of the site, comprehensively weigh the excavation, filling, and earthwork transportation volume, determine the site leveling plan, divide the site into blocks, select a soil body with sufficient strength and stability for filling, and compact the filled ground to meet the relevant requirements. In addition, it also includes erecting temporary power supply facilities.

[0049] S2, Excavation of the vertical shaft 1 and the sealing trench 2;

[0050] After the site treatment and leveling are completed, immediately excavate the vertical shaft 1. The vertical shaft 1 is excavated by a small well drilling machine, and the excavation depth can be determined according to the depth range to be treated, and the vertical shaft 1 is excavated to the calculated drainage depth. Use a drilling machine with a diameter of 10 cm to form a hole. When forming the hole, attention should be paid to avoiding excessive sand and gravel falling into the hole. To avoid this situation, 5 - 10 cm more drilling can be considered as appropriate during actual drilling; the diameter of the vertical shaft 1 is 8 - 15 cm, and the interval between each vertical shaft is 0.8 - 1.2 m, as Figure 1-2 shown.

[0051] When the size of the vertical shaft 1 is too large, the workload may increase, and even collapse may occur, resulting in the pretreatment agent 3 sinking to the bottom and unable to play a good role; when the hole diameter is too small, the pretreatment agent 3 may not be able to infiltrate well and it is difficult to act on the deep soil.

[0052] The sealing trench 2 is excavated manually or in combination with a hydraulic backhoe excavator. The depth is 1.5 - 3 m and the width is 0.8 - 2 m. The soil layer with a permeability coefficient less than 10-5 mm / s is excavated. The poor water permeability can play a role in water isolation, avoiding water seepage to areas outside the drainage area during the compaction drainage process, resulting in the inability to achieve the expected drainage effect and even affecting the stability of the surrounding area; surround the drainage area according to the design to ensure the sealing effect, as Figure 3 shown.

[0053] The sealing trench 2 is not necessarily a regular rectangle or square, but the sealing trenches 2 should intersect with each other to form a closed area to enclose the area where the shaft 1 is located, so as to achieve the purpose of sealing the inner part of the sealing membrane and forming a vacuum area. If the width of the sealing trench 2 is too wide, the cost will increase, and if the width is too narrow, the tightness of the sealing trench 2 will be poor, which may cause air leakage during the treatment process and fail to achieve the treatment effect.

[0054] During the construction of the shaft 1 and the sealing trench 2, attention should be paid to avoiding excessive disturbance of the soft soil, resulting in the mixing of sand and mud or the collapse of the hole, etc., affecting the effect.

[0055] S3. Add the pretreatment agent 3; after the shaft 1 is dug and the hole wall is stable, the pretreatment agent 3 can be put into the shaft 1, as Figure 4 shown.

[0056] Before adding the pretreatment agent 3, an appropriate amount of water (50 - 100 L) can be added in combination with the working conditions and engineering experience to accelerate the diffusion of the pretreatment agent 3 in the soil, ensure the action range of the pretreatment agent 3, and ensure the effect of drainage consolidation. Then add the pretreatment agent 3 and add an appropriate amount of water again to make the pretreatment agent 3 spread better and faster in the soil. The amount of water used is limited by not overflowing from the shaft 1 and is determined in combination with the actual soil water content.

[0057] When adding the pretreatment agent 3, attention should be paid to using a wooden stick or a glass rod as a drainage rod for drainage. Move the drainage rod around the side wall to make the pretreatment agent 3 flow into the shaft 1 evenly along the side wall of the shaft 1 as much as possible.

[0058] For different soil types, the selection of the pretreatment agent 3 refers to Table 1, and the dosage per well is determined according to the formula in Table 2.

[0059] Table 1 Reference table for pretreatment agent selection

[0060] Soil type Type of pretreatment agent Alkaline soil Sulfuric acid with a mass fraction of 95% Neutral soil Industrial sodium chloride Acidic soil Sodium carbonate

[0061] Table 2 Calculation table for the dosage of pretreatment agent for a single shaft

[0062] Soil type Calculation formula (unit: g) Alkaline soil Neutral soil 184h (184 multiplied by precipitation depth h) Acidic soil 333h (333 multiplied by precipitation depth h)

[0063] For both neutral soil and acidic soil, the dosage of the pretreatment agent is controlled by a coefficient.

[0064] ω(%) represents the soil moisture content, ρ (kg / m 3 ) represents the soil density, h (m) represents the precipitation depth, and c OH - (kg / m 3 ) represents the concentration of hydroxide ions. 2.45×10 5 ωρhc OH- is based on the principle of chemical charge neutralization. By calculating the number of soil cations, the amount of anions that the pretreatment agent needs to provide is determined, thereby determining the dosage of the pretreatment agent.

[0065] The pretreatment agent 3 should adhere to the wellbore as much as possible and be backfilled and reinforced in a timely manner after placement. As Figure 5 shown, for the backfill soil, sand and gravel or the original soil remaining from the previous excavation steps can be considered. If there is still moisture in the shaft 1, the shaft 1 can be filled with gravelly soil; if there is less moisture in the shaft 1 and the infiltration of the pretreatment agent 3 solution is good, the original soil excavated during drilling can also be directly backfilled. In addition, the backfill of the shaft 1 can also be designed according to engineering experience. The backfill of the shaft 1 does not require special compaction.

[0066] The basic principle is as Figure 10 shown. The soft soil particles 9 carry negative charges 10, which enables the soil particles to have the function of adsorbing strongly bound water molecules 11 and weakly bound water molecules 12. The strongly bound water molecules 11 have a strong adsorption force with the soil particles and will form a strongly bound water layer 13 with relatively different physical properties. Therefore, the pretreatment agent 3 mainly treats the weakly bound water layer 14. The positive ions 15 of the pretreatment agent can combine with the negative charges 10 of the soft soil particles 9 to form a combination 16. By this method, the adsorption capacity of the soft soil particles 9 can be weakened, the weakly bound water layer 14 of the soft soil particles 9 can be thinned, and the weakly bound water is released, that is, Figure 10 the weakly bound water 17 released in

[0067] There are a wide variety of chemical agents for soft foundation treatment. However, considering economic rationality, environmental friendliness and other characteristics, in the embodiments of the present invention, the pretreatment agent 3 is selected as an agent that is easy to ionize in water and is easily available, so as to better achieve the purpose of enhancing the drainage performance. The pretreatment agent 3 is prone to ionize in water, neutralize the hydrogen ions or hydroxide ions carried in the soil, and is based on precipitating ions to absorb and control the charges in soil particles. For alkaline soil, in addition to sulfuric acid mentioned in Table 1, acids such as dilute hydrochloric acid and acetic acid that can ionize to produce hydrogen ions in water can also be used; for acidic soil, in addition to sodium carbonate mentioned in Table 1, alkaline substances such as caustic soda and ammonia water can also be selected; for neutral soil, in addition to industrial sodium chloride in Table 1, neutral salts such as potassium chloride or weak acid and weak base agents with very weak acidity and alkalinity can also be used.

[0068] S4, laying of the sand cushion layer 4; as Figure 6 shown, the sand cushion layer 4 is laid after the dosing of the pretreatment agent 3 is completed, covering the entire site. The mechanical stacking method can be used during paving. First, sand piles are stacked, and then mechanical paving is carried out.

[0069] The thickness range of the sand cushion layer 4 is preferably 20 - 30 cm. If the thickness of the sand cushion layer 4 is too large, it will affect the subsequent vacuum compression drainage effect, making it impossible for the dry gas to contact the soil to be treated well and affecting the treatment effect. If the thickness of the sand cushion layer 4 is too small, the influence is relatively small, but it may cause excessive stress on the vertical shaft 1, resulting in the treatment effect of the pretreatment agent being affected. The specific thickness of the sand cushion layer 4 can be adjusted as appropriate with reference to the engineering geological conditions.

[0070] The sand cushion layer 4 is selected from well-graded, larger-particle-size, hard-textured medium sand, coarse sand, pebbles, etc., and is evenly laid on the surface of the site to improve the bearing capacity of the shallow foundation and ensure the stability of the working site during equipment installation and drainage consolidation.

[0071] S5, layout of the surface water collection channel 5; since during the process of draining and consolidating the soil through gas cavitation, the water content of the gas in the sealing film 6 is relatively high, and at the same time, due to the difference in environmental temperature during operation, water vapor may condense to form liquid water flow. If drainage facilities are not used to collect and discharge it, it may affect the soil drainage consolidation effect. To prevent the condensed liquid water after gas cavitation from returning to the soil again, it is necessary to layout the water collection channel 5 above the sand cushion layer 4 on the surface, as Figure 7 shown; the function of the water collection channel 5 is to ensure the smooth entry of high-pressure dry air into the vertical shaft 1, while allowing the moisture in the air to condense and collect without re-flowing back into the soil to be treated, and discharging it from the high-pressure treatment area.

[0072] The water collecting channel 5 is overlapped with each other through drain pipes or is a complete shell. There are ventilation holes provided at the higher part of the pipe body of the drain pipe. The ventilation holes are round holes with a diameter of 1 cm, and the distance between holes is 20 - 30 cm. The ventilation holes should be arranged in rows at the higher part of the pipe body of the drain pipe to ensure that the gas flow is not blocked and the cavitation is not hindered. At the same time, the collected water flow will not flow out of the pipe body.

[0073] The complete shell is a plate with undulations. From the side view, it is a zigzag plate. Condensate water is collected at the lower part of the plate, and ventilation holes are opened at the higher part to provide a channel for gas flow.

[0074] The liquid water formed by the condensation of water vapor in the sealing film 6 will condense when it reaches the relatively lower temperature area near the upper part inside the film, and then naturally fall into the water collecting channel 5. The water collecting channel 5 is preferably able to completely cover the treatment area, and should be arranged obliquely as a whole, with the high part at the air inlet and the low part at the exhaust port. The lower parts of the water collecting channel 5 are interconnected, and the condensate water is collected through a water collecting trough at the lowest end and discharged out of the sealing film 6 uniformly by the main drain pipe.

[0075] In some embodiments, the cross-section of the water collecting channel 5 can be trapezoidal or arc-shaped, etc., but it should not affect the contact between the filled gas and the soil surface. The drain pipes of the water collecting channel 5 can be made of common PVC material pipes.

[0076] S6, the laying of the sealing film 6; After the water collecting channel 5 is completed, the sealing film 6 is laid, covering the sand cushion layer 4 and the water collecting channel 5. When laying, care should be taken to avoid damaging the surface of the sealing film 6. After the sealing film 6 is laid, the sealing trench 2 is backfilled and compacted with clay or silt, etc. The sealing film 6 is laid in two layers in total. The sealing trench 2 is filled with soil, and the film should extend out of the sealing trench and be folded around to achieve sufficient sealing effect, as Figure 8 shown.

[0077] The sealing film 6 should be formed in one piece at the factory. During processing, the total ventilation volume should be calculated according to the drainage volume, and the part buried in the sealing trench 2 should be considered to leave enough length. It should be noted that there should be no sharp objects in the site before laying to prevent the sealing film 6 from being scratched. The laying of the sealing film 6 is generally carried out manually, and it is laid in two layers during a period of no wind or light wind. According to the junction of the partitions, the reinforcement area is laid first, leaving enough long film joints. It should also be noted that about 10 cm of folding is reserved every 10 m during laying to avoid pulling the sealing film 6 damaged during pressurization. To ensure the inflation effect, after the sealing film 6 is arranged, the sealing trench 2 should be fully filled and pressed with clay or silt to ensure that the sealing film 6 can work stably and will not be pulled out of the sealing trench due to the high pressure inside the film, so as to achieve the purpose of peripheral sealing.

[0078] S7. Installation of the gas circulation system and consolidation by air inflation and drainage: After the sealing membrane 6 is laid, the gas circulation system can be installed. High-pressure dry air is filled into the sealing membrane 6 to form a flowing air current, gathering the dry gas above the site to be treated and forming a certain air pressure (3 - 4 atmospheres), which can carry out compaction on the soft foundation while taking out the moisture in the soil to assist in drainage consolidation.

[0079] When the air pressure inside the membrane is too low, it may not provide sufficient pressure for the site due to insufficient air pressure, resulting in an unsatisfactory compression effect. When the air pressure inside the membrane is too high, the impact is relatively small, but there may be a risk of damaging the sealing membrane 6, presenting certain potential safety hazards. Specifically, the maximum value should be determined according to the specific model of the sealing membrane 6 used.

[0080] The installation of the gas circulation system includes the installation of the air intake system 7 and the exhaust system 8. First, install the air intake system 7, and then install the exhaust system 8. The air intake system 7 is installed at the air intake, and the exhaust system 8 is installed at the exhaust. The cooperation of the two systems can form a flowing air current and a high-pressure environment inside the sealing membrane 6, taking out the moisture in the soil while compacting the soft foundation, as Figure 9 shown.

[0081] The air intake system 7 includes an air compressor and an air dryer. The selection of the machine power and air storage capacity should refer to the area of the site to be treated, the depth of water drainage and the designed air pressure inside the membrane. During installation, connect the air outlet of the air compressor to the air intake of the sealing membrane 6, and install the air outlet of the air dryer at the air intake of the air compressor. At the same time, it should be noted that the air intake should be at the higher section of the water collection channel 5, and the connection line between the air intake and the air outlet should be parallel to the flow direction of the water collection channel 5. The exhaust system 8 includes a blower, and the machine power should match that of the air intake system 7. It is installed at the exhaust of the sealing membrane 6, at the lower end of the water collection channel 5, to discharge the moist air.

[0082] Aeration and drainage consolidation includes trial gas charging and formal drainage consolidation. During the trial gas charging process, first open the air inlet and close the air outlet, start the air dryer and air compressor of the air inlet system 7 to prepare gas. After reaching the predetermined amount, start to charge the gas into the sealing film 6. During this period, pay attention to continuously checking the airtightness of the sealing film 6, the operation of each machine in the gas charging system, and the change of the pressure inside the film. After the pressure inside the film reaches the predetermined value, close the air inlet and let the air inlet system 7 continue to prepare gas for 6 hours. During this period, pay attention to continuously monitoring the air pressure inside the film and measuring the length of the sealing film 6 reserved outside the sealing trench every hour. Then open the air inlet and air outlet of the sealing film 6, start the air inlet system 7 and the exhaust system 8, and start the gas circulation. Pay attention to regularly opening the drainage outlet to drain the accumulated water, and check the length of the sealing film 6 reserved outside the sealing trench 2 every half day. During this period, pay attention to monitoring the air pressure condition inside the film, checking the motor condition, and replenishing water and cooling in time. If all components operate normally and no abnormal conditions occur after 25 - 30 days of trial gas charging, formal drainage consolidation can begin. During the formal drainage consolidation stage, the groundwater drained from the drainage outlet should be drained away through a special pipeline.

[0083] In the practical application of the embodiments of the present invention, first, it is necessary to analyze the on-site engineering geology and hydrogeological data, carry out the construction organization design of soft foundation treatment, and complete safety disclosure and technical disclosure, etc. At the same time, according to the highway grade and measurement accuracy requirements, select a measurement method to carry out construction measurement on the site.

[0084] The machinery and equipment include: construction equipment for the sand cushion layer 4: loaders, transport vehicles, small trolleys; excavation equipment: excavators, electric shovels, drilling machines (10 cm); air charging and discharging equipment: air compressors, air dryers, blowers; power supply equipment: power supply lines, ammeters, knife switches, distribution boxes; measurement equipment: levels, total stations, steel tapes; other equipment: handheld sewing machines, plastic welders. Material preparation includes: crushed stones, plastic drainage pipes, sealing films, etc.

[0085] It is found through experiments that when dry gas is filled above the soil with high water content, after several hours, most of the water in the soil can be discharged by the cavitation effect of the dry gas, achieving the purpose of drainage consolidation. The cavitation effect here refers to that due to the large water content difference between the soil and the dry gas above, under the action of the concentration gradient, the liquid water in the pores will spontaneously migrate from the high water content medium to the low water content medium, making the whole system move towards the direction of achieving the concentration balance of each phase medium. The embodiments of the present invention enclose the gas through the sealing film 6, fully utilize the cavitation characteristics of the gas, and at the same time provide air flow through the air compressor to control the flow of the gas, and then manipulate the gas to play its role.

[0086] Embodiments of the present invention are directed to soft foundations with high water content, that is, the water content of the soil is more than 5% higher than the optimal water content of the soil; when the water content of the soft foundation is relatively high, the project cost of common soft foundation treatment methods of drainage consolidation will increase significantly, and there are also greater construction risks. Embodiments of the present invention select the type of pretreatment agent 3 according to the soil type, determine the dosage calculation formula of the pretreatment agent per unit of soil, and release the weakly bound water layer 14 of the soft soil particles 9; at the same time, high-pressure dry air is introduced into the area where the vertical shaft 1 is located, and the dry gas can carry out the water in the water-containing soil through cavitation to achieve the purpose of drainage; the high-pressure gas can provide power for the flow of the dry gas above the soil, and the high-pressure gas itself will also exert pressure on the soil to play a role in compression drainage. Thus, the drainage consolidation of the high-water-content foundation can be carried out more economically, without generating greater production risks, with a relatively high construction error tolerance, and the construction method is relatively safer.

[0087] The above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A soft foundation treatment method combining gas cavitation and charge neutralization, characterized in that It includes the following steps: S1, Site preparation; S2, Dig a plurality of vertical shafts (1) at intervals to the drainage depth at predetermined locations of the soft foundation, and dig a sealing trench (2) around the periphery of the area where the vertical shafts (1) are located to enclose the area where the vertical shafts (1) are located; S3, After the hole wall of the vertical shaft (1) is stable, put a pretreatment agent (3) into the vertical shaft (1), and backfill and reinforce it in time after the placement is completed; S4, Lay a sand cushion layer (4) in the sealing trench (2) and the area where the vertical shafts (1) are located; S5, Arrange a surface water collection channel (5) above the sand cushion layer (4) in the area where the vertical shafts (1) are located. The water collection channel (5) covers the area to be treated. The water collection channel (5) is undulating, with condensate water collected at the low places and ventilation holes opened at the high places for gas circulation; S6, Cover the sand cushion layer (4) and the water collection channel (5) with a sealing film (6), backfill and compact the sealing trench (2), and the sealing film (6) forms a sealed space in the area where the vertical shafts (1) are located; S7, Install a gas circulation system, fill high-pressure dry air into the sealing film (6) to form a flowing air current, gather the dry gas above the site to be treated, and compact the soft foundation while taking out the moisture in the soil; The water collection channel (5) is arranged in an overall inclined manner, and is arranged according to the principle of being high at the air inlet and low at the exhaust outlet. The low places of the water collection channel (5) are interconnected, and condensate water is collected through a water collection trough at the lowest end and discharged out of the sealing film (6) uniformly by a main drain pipe; Before adding the pretreatment agent (3), add 50 - 100 L of water to accelerate the diffusion of the pretreatment agent (3) in the soil. After adding the pretreatment agent (3), add an appropriate amount of water again to make the pretreatment agent (3) diffuse better and faster in the soil. The amount of water used is limited to not overflowing from the vertical shaft (1); When adding the pretreatment agent (3), use a drainage rod for drainage, move the drainage rod around the hole side wall of the vertical shaft (1), and try to make the pretreatment agent (3) flow into the vertical shaft (1) evenly along the side wall; The pretreatment agent (3) is prone to ionization and can neutralize the hydrogen ions or hydroxide ions carried in the soil.

2. The soft foundation treatment method combining gas cavitation and charge neutralization according to claim 1, wherein The water collection channel (5) is mutually overlapped through drain pipes or is a complete shell. Ventilation holes are provided at the high places of the pipe body of the drain pipe; The complete shell is a plate with undulations. Condensate water is collected at the low places of the plate, and ventilation holes are opened at the high places.

3. The soft foundation treatment method combining gas cavitation and charge neutralization according to claim 1, characterized in that, For alkaline soil, the pretreatment agent (3) is selected from sulfuric acid, hydrochloric acid or acetic acid. Based on the principle of chemical charge neutralization, the amount of anions that the pretreatment agent (3) needs to provide is determined by the number of soil cations, so as to determine the dosage of the pretreatment agent (3); For neutral soil, the pretreatment agent (3) is selected from sodium chloride or potassium chloride, and the dosage is 184 h , h representing the precipitation depth; For acidic soil, the pretreatment agent (3) is selected from sodium carbonate, caustic soda or ammonia water, and the dosage is 333 h .

4. A soft foundation treatment method combining gas cavitation and charge neutralization according to claim 1, characterized in that The pretreatment agent (3) adheres to the well wall as much as possible, and is backfilled and reinforced in time after the placement is completed. The backfill soil is selected from sand and gravel or undisturbed soil; If there is still moisture in the vertical shaft (1), fill the vertical shaft (1) with gravelly soil; If the moisture in the vertical shaft (1) is less and the infiltration of the pretreatment agent (3) solution is good, directly backfill with undisturbed soil; The backfill of the vertical shaft (1) does not require special compaction.

5. A soft foundation treatment method combining gas cavitation and charge neutralization according to claim 1, characterized in that, The permeability coefficient of the soil layer of the sealing trench (2) is less than 10 -5 mm / s.

6. The soft foundation treatment method combining gas cavitation and charge neutralization according to claim 1, characterized in that, The gas circulation system includes an intake system (7) and an exhaust system (8). The intake system (7) is installed first, and then the exhaust system (8). The intake system (7) includes an air compressor and an air dryer. The outlet of the air compressor is connected to the intake of the sealing film (6), and the outlet of the air dryer is connected to the inlet of the air compressor. The intake of the sealing film (6) is located at the higher end of the water collecting channel (5). The exhaust system (8) includes a blower with a power matching that of the intake system (7). It is installed at the exhaust outlet of the sealing film (6) and is located at the lower end of the water collecting channel (5) for discharging the moist air.

7. A soft foundation treatment method combining gas cavitation and charge neutralization according to claim 1, characterized in that The sealing film (6) extends out of the sealing groove (2) and folds around it. During the filling of high-pressure dry air into the sealing film (6), the airtightness of the sealing film (6), the operation of each machine in the air filling system, and the change of the pressure inside the film should be checked, and the length of the sealing film (6) reserved outside the sealing groove (2) should be measured.

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