Efficient pre-compression processing method of deep layer soft ground using combination of gas lift and vacuum

Abstract

To provide an efficient pre-compression processing method of soft ground using combination of gas lift and vacuum, and a method for carrying out a construction work based on the same.SOLUTION: Gas with certain pressure and flow speed is introduced from a bottom of a drainage plate, so that gas with positive pressure flows upwards along a plate core of the drainage plate, and water in the plate core is carried upwards out of the drainage plate in the flowing process of the gas. After the water is emptied, a vacuum degree is only transmitted in a gas environment and can be transmitted to the bottom of the plate without attenuation. When a vacuum degree is stabilized between -80 kPa and -90 kPa, an air compressor is intermittently started to inject air, and the stored water in the drainage plate is emptied by using the gas lift principle, so that purposes of accelerating drainage and transferring the vacuum pressure to a deep part without attenuation are achieved.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to the technical field of geotechnical engineering, and in particular to an efficient method for pre-compressing deep soft soil by combining gas lift and vacuum, and a method for implementing construction work based on the method. [Background technology]

[0002] As an efficient and economical method for treating soft ground and sprayed super soft ground, vacuum pre-pressure technology has been widely applied in coastal areas. During construction, a plastic drainage plate is usually installed in the soil, and then a geomembrane is laid on the surface of the soil body to form a sealed space. Under the action of the vacuum pump, the vacuum pressure under the geomembrane (which can reach 85kPa in construction) is transmitted radially into the soil along the drainage plate to form a stable pressure field and promote the seepage fixation of the soft soil. After the water in the soil enters the drainage channel, it is discharged from the bottom to the top of the ground, finally achieving the effect of promoting the drainage fixation of the soil body and improving the strength of the soil body.

[0003] As can be seen from the above, the seepage consolidation process of soil is largely controlled by vacuum pressure, and its magnitude and distribution control the seepage consolidation rate and final reinforcement effect of soil. However, in previous research and construction, it was found that the vacuum has a significant damping effect along the drainage plate due to the existence of continuous flowing water in the drainage plate. (For example, the depth of the drainage plate is extended by 1 m, and the vacuum negative pressure is reduced by 5-10 kPa). This effect has a relatively limited adverse effect on shallow soft soil vacuum pre-compression treatment (treatment depth of 6 m or less), but when the treatment target is deep soft soil (treatment depth of 10 m or more), it has a significant effect on the treatment effect of the deep soil body. Therefore, a treatment method that can effectively improve the effect of deep soft soil vacuum pre-compression is required.

[0004] In mining and dredging works, gas lift is usually used to lift up solids and liquids (CN110630226A, CN105775752A). The method involves injecting compressed air into the bottom of the ascending passage to reduce the fluid density at the inlet, and then using the pressure difference to move the target (e.g., slag or sludge) vertically upward. The top outlet of the conventional gas lift passage is generally at atmospheric pressure, and only the high-pressure gas injected from the bottom of the gas lift passage forms a pressure difference to complete the lifting of a large amount of solid and liquid. In the vacuum pre-pressure process, the outlet at the top of the passage is at vacuum negative pressure, and the pressure difference between the top and bottom of the gas lift passage is larger, so the method of completely draining the water in the drainage plate by combining gas lift and vacuum is very different from the above conventional method. Also, the gas lift passages in the gas lift and vacuum combination are permeable vertical passages (e.g., precast drainage slabs or bagged sand wells; the side walls of which are permeable), which differs significantly from the sealed pipelines (e.g., steel pipes, flexible pipes, etc.) of conventional gas lift methods.

[0005] Considering the above-mentioned features of vacuum preloading and gas lifting comprehensively, when the vacuum negative pressure acts on the entire stroke of the top, the positive pressure gas flows upward along the plate core of the drainage plate, and in the process of flowing, it brings out the water in the plate core, and finally empties the drainage plate. At the moment when the gas lift is finished, the plate is in a gas-filled state, but the continuous suction of the vacuum pump at the top of the passage quickly sucks out the gas. Due to the permeability of the side wall of the passage, the surrounding liquid is re-accumulated in the passage, but this process is controlled by the low permeability of the soft soil and is slow enough. This allows the vacuum in the passage to be transmitted from the head of the plate to the bottom of the plate with almost no attenuation after the gas lift is finished. It is obvious that the combination of gas lift and vacuum can effectively improve the vacuum consolidation pressure within the entire depth range of the drainage plate, the drainage consolidation of the surrounding soil body is significant, and the vertical attenuation problem of the vacuum in the panel can be effectively solved. At present, there are no patents or papers related to the combination of gas lift and vacuum for soft ground preloading treatment.

[0006] In the method for treating soft ground, Patent CN104895046A, Patent CN106677156A and Patent CN109653186A propose a method of disturbing soft soil using high-pressure gas or high-pressure aerosol. A specially made conduit is used to rotate and inject high-pressure stirring medium into the soil, forming a spiral or cone-shaped stirring surface / body in the soil under the action of pressure, increasing the horizontal drainage passage and improving the permeability coefficient of the soil body. The paper "Active Drainage Consolidation Method-Gas Lift Effect Model Test Research" (DOI:10.16285 / j.rsm.2020.1645) states that in the implementation of the above patents, after the high-pressure gas / aerosol exerts a cutting action in the soil body, it is discharged upward through the vertical drainage passage, and the water in it is rapidly carried to the ground, which is similar to the gas lift effect in mining and dredging works. Note that the air vent effect in the above paper is an additional effect that occurs during high-pressure disturbance. The above three patents and papers do not mainly use high-pressure media to cut turbulent soil and directly ventilate in the drainage passage, but do not pay attention to the effect of significantly improving the vacuum consolidation pressure after gas lift. The above three patents require a lot of equipment, and in addition to the conventional vacuum pre-pressure related equipment, high-pressure rotary injection equipment is required, and a medium pipe with a rotary injection hole is added to the treated area. The efficient pre-pressure treatment method for soft ground by combining gas lift and vacuum provided in the present invention directly injects positive pressure gas from the drainage passage to the bottom, and creates a high vacuum environment that does not decay from the top to the bottom after discharging the water in the passage at once, effectively improving the soil consolidation effect in the entire depth range of the drainage passage, which is significantly different from the above three patents (CN104895046A, CN106677156 A and CN109653186A).

[0007] The drainage plate itself is a vertical drainage passage with excellent flowability, and after being surrounded by a soft adhesive with poor permeability, high-pressure gas can be directly injected into the drainage plate to exert the effect of piping in gas lift, so that the gas lift method can be carried out. Based on this, the present invention provides an efficient pre-pressure treatment method for soft ground by combining gas lift and vacuum. In this method, gas with a specific pressure and flow rate is ventilated from the bottom of the drainage plate, and the water in the plate core is pushed up by the positive pressure of the gas at the bottom and pulled by the negative pressure of the vacuum at the top, so that the water in the plate core is quickly discharged over the entire length, and the effect of high-pressure gas is preferentially realized. When there is no flowing water in the drainage plate, the vacuum pump connected to the drainage plate head can continue to suck the plate core in the plate core, so that the vacuum degree can be transmitted from the plate head to the plate bottom with almost no attenuation, and the boundary condition of the fixed drainage is significantly improved. Compared with the existing patents, the main purpose of the present invention is to promote the transmission of vacuum pressure to the depth of the soil body. If it is desired to realize the gas lift effect by supplying air to the drainage plate, the drainage plate can be connected to the pneumatic duct. The drainage plate can transmit the vacuum pressure to the deeper part, so that the boundary conditions at the deeper part are improved even if the drainage depth is limited.

[0008] The present invention proves the above explanation by indoor model testing. The test results show that there is a difference in pressure between the top and bottom of the drainage plate before gas lift. After the water in the plate is exhausted and discharged all at once, the vacuum degree at the bottom rises sharply and is almost the same as the top. Under this condition, the maximum vacuum pressure at the top throughout the depth at the plate core. As the soil water continues to infiltrate into the plate core continuously, the vacuum degree in the plate recovers to the state before gas lift. In the process of collecting water after complete discharge, the infiltration rate in the soil is improved and increased with the pressure of high vacuum degree without attenuation, so that the soil infiltration fixation after air supply is significantly faster. The soil pore pressure obviously drops sharply. It shows that by completely discharging the water in the drainage plate by gas lift, the vacuum pressure can be transmitted to the bottom without attenuation, and the speed of infiltration fixation of soft soil can be accelerated.

[0009] Tests have proven that, according to the working principle of gas lift, by injecting an appropriate amount of compressed air into the drainage plate continuously, the water in the drainage plate can be completely discharged, and the purpose of promoting the efficient downward transmission of vacuum pressure can be realized, and the speed of consolidation settlement of soft ground can be effectively improved. The method of the present invention is simple to install, since it only requires adding a connector to connect an external air compressor to the bottom of the drainage plate. The air-supplied gas lift can be completed in an extremely short time, and is a construction method with low operating burden on machinery and equipment, low operating costs, high reliability, and construction benefits and economic effects. Summary of the Invention

[0010] In the first aspect of the present invention, there is provided an efficient method for pre-compression of soft ground by combining gas lift and vacuum, which is used for pre-compression of high water content fluidized mud, sludge ground, and deep soft ground, The pre-pressure treatment method includes the following steps: Step (1): Applying the gas lift principle to the vacuum preload, gas with a certain pressure and flow rate is introduced from the bottom of the drainage plate, so that the positive pressure gas flows upward along the core of the drainage plate, and in the process of flowing, the water in the core is carried upward and discharged from the drainage plate; Step (2): After the gas lift has drained all the water from the board core, it immediately stops, and the board core is now filled with gas. The gas in the board core is continuously sucked out by the vacuum pump connected to the head of the drainage board, so that the gas in the board core is quickly sucked out, and the vacuum can be transmitted from the head to the board bottom with almost no attenuation. Step (3): By realizing a high vacuum degree throughout the entire length of the drainage plate, the soil body within the driving depth range of the drainage plate can be under high vacuum consolidation pressure, which promotes the drainage consolidation of the deep soil body; Step (4): After the first gas lift is completed, under the vacuum pressure of the core of the board, the void water in the soil continues to collect in the core of the board through the filter membrane of the drainage plate, and the water level in the core of the board gradually rises until it is filled with water again. At this time, gas lift is performed again to drain all the water in the core of the board out of the drainage plate again, and thus a pre-pressure treatment method is provided in which high-vacuum drainage consolidation is resumed within the entire length of the drainage plate.

[0011] Furthermore, in step (1), when air is ventilated from the bottom of the drainage plate to perform gas lift, the gas is continuously sucked out by the vacuum pump connected to the drainage plate head, so that the water in the core of the plate is pushed up by the positive pressure of the gas at the bottom and pulled by the negative vacuum pressure at the top, and the water in the core of the plate can be quickly discharged over the entire length of the drainage plate.

[0012] Furthermore, in steps (3) and (4), after all the water has been drained, the vacuum is only transmitted in the gas environment, so it is transmitted to the bottom of the plate without attenuation. The boundary conditions for soil consolidation are improved by the efficient transmission of vacuum, and the pressure difference between the soil pore pressure and the pressure in the drainage plate is increased, thereby accelerating the infiltration flow rate of the soil water and improving the efficiency of the vacuum pre-compression treatment of soft soil.

[0013] In a second aspect of the present invention, there is provided a method for implementing construction based on an efficient pre-compression method for soft ground by combining gas lift and vacuum, comprising the steps of: Step 1: Modify the drainage board so that hand-shaped connectors are connected to both ends of the drainage board. Step 2: The pressure gas pipeline is connected to the bottom connector and driven into the soft ground together with the drainage plate, and the end of the pipeline is connected to the gas lift positive pressure pipeline at the ground level; Step 3: The vacuum line is connected to the drain plate by the top connector, and the end of the line is connected to the vacuum negative pressure line at the ground; Step 4: Lay and seal the geotextile and geomembrane. Step 5: Connect the pressure gas line and the vacuum line to the air compressor and the vacuum pump respectively; Step 6: The equipment is started and construction is carried out. When the vacuum level stabilizes at -80 to -90 kPa, a method for carrying out the construction is provided in which the air compressor is started intermittently to perform the air supply gas lift. Effect of the Invention

[0014] (1) A new pre-pressure processing method for vacuum pre-pressure is provided by utilizing the gas lift principle, which has the following beneficial effects in promoting soft soil consolidation: 1) Promoting drainage: By combining the upward pressure caused by the positive pressure gas at the bottom and the pulling force caused by the negative pressure at the top, the positive pressure gas flows upward along the core of the drainage plate, and in the process carries the water in the core and discharges it upward from the drainage plate, improving the water discharge speed. 2) Improved consolidation efficiency throughout the depth of the drainage plate: When the air pressure and flow rate reach a predetermined value, the water in the drainage plate can be completely drained within a relatively short time. Under conditions without flowing water, the vacuum can be transmitted to the depth along the drainage plate without attenuation, and the pressure difference between the soil pore pressure and the pressure inside the drainage plate is further increased. In addition, the deeper the drainage plate is cast, the more significant the consolidation promotion effect becomes, so the method of the present invention is particularly applicable to the consolidation treatment of deep and thick soft soil.

[0015] (2) Compared with the conventional vacuum preloading method, the present invention requires fewer changes to the drainage plate and is easily implemented. Since the added equipment is located outside the earth body, it is easy to install and maintain, which is favorable for promoting the practical implementation of the construction.

[0016] (3) The provided indoor test equipment can simulate the conditions of on-site construction and also provide a window for observing the flow pattern inside the plate, allowing the drainage consolidation efficiency to be analyzed qualitatively and quantitatively. It can be applied to the investigation of the drainage mechanism to obtain the optimal air supply flow rate, air supply pressure and air supply frequency, thereby optimizing the construction plan.

[0017] (4) In the test device, the soft soil is sealed with a geomembrane, and the vacuum generation system is first started to draw water. After the water begins to be taken in the air-water separator, the gas pressure system is started, and the water in the drainage plate is quickly discharged with the compressed air according to the gas lift principle. After the liquid is discharged, the gas pressure system is turned off, and the vacuum pressure of the head can be efficiently transmitted downward. During the treatment process, the gas pressure system is intermittently started to improve the vacuum pressure range and magnitude of the deep soft soil, which can significantly improve the consolidation and drainage efficiency of the soft soil. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a structural schematic diagram of a testing device according to the present invention. [Diagram 2] FIG. 2 is a structural schematic diagram of a drainage plate and a hand-shaped structure in the testing device of the present invention. [Diagram 3] 1 is a flow chart of a testing method of the present invention. [Figure 4] FIG. 4 is a diagram showing the change in flow pattern in a drain plate when the present invention is implemented. [Diagram 5] FIG. 1 is a schematic diagram showing the change in water outflow amount when the present invention is carried out once. [Figure 6] FIG. 4 is a schematic diagram showing changes in water outflow when the present invention is implemented. [Figure 7] FIG. 2 is a schematic diagram showing the change in vacuum level and pore pressure in the soil when the present invention is implemented. [Figure 8] FIG. 1 is a schematic diagram of the overall structure of the on-site construction of the present invention.

[0019] 1, model box; 2, outlet; 3, air inlet; 4, drainage plate; 5, flange ring; 6, geomembrane; 7, through hole; 8, pore pressure sensor; 9, precision electronic scale; 10, air-water separator; 11, vacuum gauge; 12, vacuum pump; 13, check valve; 14, ball valve; 15, pressure gauge; 16, pressure regulating valve; 17, air compressor; 18, industrial camera; 19, drainage plate C-shaped inner structure; 20, drainage plate filtration membrane; 21, hand-shaped connector; 22, drainage plate; 23, connector; 24, air compressor; 25, pressure gas pipeline; 26, vacuum pump; 27, vacuum pipeline; 28, geotextile and geomembrane. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The technical means of the present invention will be described clearly and completely below with reference to the drawings. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and are not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts are all included in the protection scope of the present invention.

[0021] In the description of the present invention, the orientation or positional relationship indicated by terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., is based on the orientation or positional relationship shown in the drawings, and is for the purpose of simplifying the description of the present invention and the description, and does not indicate or imply that the devices or parts referred to have a particular orientation and must be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present invention. Also, the terms "first", "second", "third", etc. are for illustrative purposes only, and cannot be understood as indicating or implying relative importance.

[0022] In the description of the present invention, unless otherwise specified, the terms "attached", "coupled" and "connected" should be understood in a broad sense, for example, may be fixedly connected, detachably connected, integrally connected, mechanically connected, electrically connected, directly connected, indirectly connected via an intermediate medium, or internal communication between two elements. Those skilled in the art can specifically understand the specific meaning of the above terms in the present invention.

[0023] Example 1 The efficient pre-compression method for soft ground by combining gas lift and vacuum, which is used for drainage pre-compression of high water content fluid mud, sludge ground and deep soft ground, includes the following steps: Step (1): The gas lift principle is applied to the vacuum preload, and gas with a certain pressure and flow rate is ventilated from the bottom of the drainage plate, so that the gas with positive pressure flows upward along the core of the drainage plate, and in the process of flowing, it carries the water in the core and discharges it upward from the drainage plate. Step (2): After the gas lift has drained all the water from within the board core, it is immediately stopped, and the board core is now filled with gas. The gas in the board core is continuously sucked out by the vacuum pump connected to the head of the drainage plate, so that the gas in the board core is quickly sucked out, and the vacuum can be transmitted from the head to the bottom of the board with almost no attenuation. Step (3): By realizing a high vacuum degree throughout the entire length of the drainage plate, the soil body within the driving depth range of the drainage plate can all be under high vacuum consolidation pressure, which promotes the drainage consolidation of the deep soil body. Step (4): After the first gas lift is completed, under the vacuum pressure of the core of the board, the void water in the soil will continue to collect in the core of the board through the filter membrane of the drainage plate, so that the water level in the core of the board will gradually rise until it is filled with water again. At this time, gas lift is performed again to drain all the water in the core of the board out of the drainage plate again, and thus the high vacuum drainage consolidation within the entire length of the drainage plate is resumed.

[0024] In step (1), when the gas is lifted by ventilating the bottom of the drainage plate, the vacuum pump connected to the drainage plate head continues to pump out the gas, so that the water in the core of the plate is pushed up by the positive pressure of the gas at the bottom and pulled by the negative vacuum pressure at the top, and the water in the core of the plate within the entire length of the drainage plate can be quickly discharged. In steps (3) and (4), after the water is completely discharged, the vacuum is only transmitted in the gas environment, so it can be transmitted to the bottom of the plate without attenuation. The boundary conditions of soil consolidation are significantly improved by the efficient transmission of vacuum, and the pressure difference between the soil pore pressure and the pressure in the drainage plate is increased, which increases the seepage flow rate of the soil water and effectively improves the efficiency of vacuum pre-pressure treatment of soft soil.

[0025] The method of the present invention applies the gas lift principle to the vacuum pre-pressure process. Gas with a certain pressure and flow rate is ventilated from the bottom of the drainage plate, and the gas with a positive pressure flows upward along the core of the drainage plate, and in the flow process, the water in the core is carried and discharged from the drainage plate in the direction of the drainage plate. After the water is completely discharged, the vacuum is only transmitted in the gas environment, so it can be transmitted to the bottom of the plate without attenuation. Indoor model tests show that after gas lift, the drainage speed is greatly improved, the water in the drainage plate can be completely discharged in a relatively short time, and the vacuum at the bottom of the plate is almost equal to the head. The boundary conditions of the soil body consolidation are significantly improved by the efficient transmission of the vacuum. The pressure difference between the soil pore pressure and the pressure in the drainage plate is increased, which increases the seepage flow rate of the soil water, and effectively improves the efficiency of the vacuum pre-pressure treatment of soft soil. When implementing the method of the present invention at a construction site, it is only necessary to simply improve the drainage plate of the conventional vacuum pre-pressure device system. A connector is connected to each of the top and bottom of the drainage plate, the upper end is connected to a vacuum pump through a vacuum line, and the lower end is connected to an air compressor through a pressure gas line. When the vacuum level is stable at -80~-90kPa, the air compressor is intermittently started to ventilate, and the water in the drainage plate is completely discharged according to the gas lift principle, thereby achieving the purpose of transmitting the vacuum pressure to the depths without attenuation while promoting drainage.

[0026] In addition, when the gas pressure and flow rate reach a certain value, the drainage speed of the water in the board core is greatly improved, and the water in the drain board can be completely drained in a relatively short time. Therefore, the air compressor for ventilation can be stopped every time the drainage is completed. The required energy consumption is relatively small. In addition, the length of the pressure gas passage is not limited by the ground depth, and the air compressor can be placed on the ground for operation and maintenance.

[0027] Example 2 As shown in Figures 1-2, this embodiment provides a measurement device based on the method described in Example 1. The device includes a transparent model box 1, a drainage plate 4, a vacuum generating system, and a pressurized gas system. Before using the method of the present invention, it is necessary to prepare the drainage plate 4. The H-shaped internal structure drainage plate used during construction, which takes in water from both sides, is simplified to a U-shaped internal structure which takes in water from one side. The U-shaped structure 19 of the drainage plate is made of transparent material, and the open surface is fixed to the filter membrane 20 of the drainage plate. The side of the drainage plate 4 covered with the filter membrane 20 is called the permeable side, and the side of the drainage plate 4 facing away from the filter membrane 20 is called the transparent side. The transparent side is glued to the inner wall of the model box by glass adhesive, providing a window for observing the fluid changes in the drainage plate 4. Both ends of the drainage plate 4 are connected to hand-shaped connectors 21. The hand-shaped connector 21 at the upper end is connected to a vacuum generation system, and the hand-shaped connector 21 at the lower end is connected to a pressure gas system. The internal size of the model box is 50 cm x 30 cm x 100 cm, and the transparent side of the drainage plate 4 is in close contact with the inner wall of the model box in the vertical direction to provide an observation window. The box is filled with the soft soil to be treated and then covered with a geomembrane 6. The geomembrane 6 is fixed to the top of the model box 1 via a flange ring 5. The flange ring 5 is bolted to the top of the model box 1 to provide a sealed environment.

[0028] The vacuum generation system includes a pore pressure sensor 8, an air-water separator 10, a vacuum gauge 11, and a vacuum pump 12. A water outlet 2 is provided on the upper wall of the model box 1. A hand-shaped connector 19 at the upper end of the drainage plate 4 is connected to a first steel wire water pipe. The first steel wire water pipe is connected to the water outlet 2 and a vacuum hose. The vacuum hose is connected to the upper part of the air-water separator 8. The pore pressure sensor 8 is placed on the soil body and the drainage plate from the through hole 7 on the model box 1 and is used to record pressure changes during the vacuum and gas injection cycles. A vacuum gauge 11 is provided on the top surface of the air-water separator 10. The top surface of the air-water separator 10 is connected to a vacuum pump 12 via a vacuum hose. The air-water separator 10 is placed on a precision electronic balance 9 and is used to record the time-dependent change in the consolidation drainage volume in the model box.

[0029] The pressure gas system includes a check valve 13, a ball valve 14, a pressure gauge 15, a pressure regulating valve 16, an air compressor 17, and an industrial camera 18. An air intake 3 is provided on the bottom of the model box 1. A hand-shaped connector 21 at the lower end of the drain plate 4 is connected to a second steel wire water pipe. The second steel wire water pipe passes through the air intake 3 and is connected to the check valve 13. The other end of the check valve 13 is connected to the ball valve 14, the pressure gauge 15, the pressure regulating valve 16, and the air compressor 17 in this order via a pneumatic duct. The pressure regulating valve 16 and the pressure gauge 15 control the pressure and flow rate of the output gas in the air compressor 17. The ball valve 14 and the check valve 13 control the input of gas and prevent backflow. The bottom of the industrial camera 18 is supported by a tripod. The industrial camera is placed directly facing the central axis of the transparent side of the drain plate 4 to observe and record the flow pattern change inside the plate during gas lift. The precision electronic scale that records the amount of water discharge and the industrial camera that records the fluid change are used to qualitatively and quantitatively analyze the gas lift vacuum pre-pressurization effect.

[0030] When in use, the vertical plastic drainage plate 4 is attached to the inner wall of the model box 1, the pressurized gas system and the vacuum generation system are connected, soil is filled in, the geomembrane 6 is laid, the model box is sealed, the vacuum generation system is started, and the pressurized gas system is started intermittently.

[0031] First, start the vacuum generating system, and after the drainage plate 4 is filled with water, turn on the ball valve 14 connected to the pressure gas system, start the air compressor 17, and inject the pressurized gas into the bottom of the drainage plate. The flow rate and pressure of the gas injection can be appropriately adjusted according to the pressure gauge 15 and the flow type in the drainage plate 4. After the water in the drainage plate 4 is completely drained, stop the pressure gas system, and in this case, the drainage plate 4 is at the maximum vacuum pressure throughout the entire depth. Under the action of pressure, the soil water quickly gathers in the drainage plate 4, and by intermittently starting the pressure gas system, the purpose of transmitting the vacuum pressure to the depth without attenuation while promoting drainage is achieved.

[0032] The air-water separator 10 in the vacuum system is placed on a high-precision electronic scale 9 to measure the drainage mass within a certain period of time. The pore pressure sensor 8 is inserted into the soil body and drainage plate 4 through the through hole 7 of the model box 1 and is used to record the pressure change during the vacuum and gas injection cycles. The effectiveness of the method of the present invention is judged according to the changes in pressure and water discharge caused by aeration, as well as the fluid changes photographed by an industrial camera, and the efficiency of the soft soil consolidation drainage in the box is further analyzed, and the test and qualitative and quantitative analysis of the method are realized.

[0033] Example 3 The soft ground treated by vacuum preloading is usually large in volume and has high cost, so the above construction operation procedure has not yet been implemented in actual construction. Therefore, an indoor test is designed to investigate the feasibility of this method. As shown in Figure 3, the measurement method based on the device described in Example 2 provided in this embodiment includes the following steps: Step 1: Before evacuation, adjust the pressure and flow rate of the air entering the system, and adjust the air pressure and flow rate output by the air compressor using the pressure regulating valve 16 and pressure gauge 15. Then, turn off the air compressor 17 and ball valve 14. Step 2: Turn on the vacuum pump to start drawing a vacuum, and observe that water continues to pass through the filter membrane 20 in the drainage plate 4. After the water starts to be pumped into the water-air separator 10, turn on the air compressor 17 and the ball valve 14 to discharge the water in the drainage plate 4 according to the gas lift principle. Step 3: After the water in the drain plate 4 is completely drained, the pressure gas system is stopped and the vacuum state is maintained. Step 4: Repeatedly start and stop the pressurized gas system intermittently until the soft soil consolidation reaches the desired state. During the entire process, the changes in pressure, water flow rate and flow pattern are recorded using a pore pressure sensor 8, a precision electronic scale 9 and an industrial camera 18.

[0034] It was observed that there was a gas-liquid two-phase flow in the drain plate 4, as shown in Figure 4. As the water was discharged, the gas content in the plate increased, and the flow pattern changed from a slug flow to an annular flow. Figure 5 shows the weight change in the water separator before and after one aeration, and it was observed that the water in the plate was quickly discharged and the discharge efficiency was effectively improved. After the water was completely discharged, the pressurized gas system was stopped, and the one-aeration process was completed.

[0035] The soft soil is vacuum pre-pressurized under the condition of repeatedly starting and stopping the air supply. The change in the amount of water discharged is shown in Figure 6. As can be seen from Figure 6, the water in the plate can be smoothly discharged every time the air supply is stopped, and after the air supply is stopped, it takes a certain amount of time for the soil water to enter the plate core and fill it with water again. Figure 7 shows the change in the vacuum degree in the plate and the soil pore water pressure. After the vacuum is started, the vacuum value at the top is maintained at around -70 kPa, and the vacuum value at the bottom is about -65 kPa, indicating that there is a pressure difference at both ends of the drainage plate. After the air supply is used to discharge the water, the vacuum degree at the bottom increases rapidly and almost matches the top. Under this condition, the maximum vacuum pressure at the top is at the plate core throughout the depth. As the soil water continues to be newly injected into the plate, the vacuum degree in the plate recovers to the state before the air supply. In the process of collecting new water after the complete discharge, the seepage flow rate in the soil increases due to the improvement of the boundary conditions, so the soil pore pressure drops significantly and rapidly after the air supply. This shows that by completely discharging the water in the drainage plate by gas lift, the vacuum pressure can be transmitted downward to the bottom without attenuation, and the rate of soft soil seepage consolidation can be increased. Compared with the conventional vacuum preloading in which the vacuum pressure in the plate is attenuated, the method of the present invention greatly improves the boundary conditions of deep soil consolidation and greatly improves the consolidation drainage efficiency.

[0036] As can be seen from the above implementation procedure, the present invention has achieved an ideal effect by properly applying the gas lift principle to the model test in the vacuum pre-compression chamber. Therefore, a new on-site construction method was developed by modifying the on-site construction equipment with a similar design to the above. In addition, the on-site construction can be realized by using the pressure gas system and connection method similar to Figure 1, and the power and operating time of each equipment need to be adjusted according to the actual situation.

[0037] Example 4 The operation efficiency of the gas lift method is affected by the air supply pressure, the air supply flow rate and the flow pattern of the two-phase flow formed. In order to realize the indoor test and investigate its mechanism and operation details, the present invention provides an efficient processing device for deep soft soil vacuum pre-compression based on the conditions of field construction. Based on the test method described in Example 3, i.e., the operation process of the above indoor test, the present invention designs an operation method for field construction.

[0038] The overall structure of the site construction is as shown in Figure 8, and the operation process includes the following steps: Step 1: Modify the drainage board so that a hand-shaped connector is attached to each end of the board. Step 2: The pressure gas pipeline is connected to the bottom connector and driven into the soft ground together with a drainage plate, and the end of the pipeline is connected to become the gas lift positive pressure pipeline at ground level. Step 3: The vacuum line is connected to the drain plate by the top connector and the end of the line is connected to the vacuum line at ground level. Step 4: Lay and seal the geotextile and geomembrane. Step 5: Connect the pressure gas line and the vacuum line to the air compressor and vacuum pump respectively. Step 6: Start the equipment and carry out construction. When the vacuum level stabilizes at -80 to -90 kPa, start the air compressor intermittently to perform air supply gas lift.

[0039] The pressure gas system is composed of an air compressor and a pneumatic duct, and the pneumatic duct can connect the bottom connection port of the drain plate to the air compressor to form a gas lift positive pressure gas passage.

[0040] The bottom connection of the drainage plate and the pneumatic duct are already connected before the drainage plate is inserted, so that the injected gas passage is maintained both before and after the drainage plate is inserted into the soft soil.

[0041] In the process of the vacuum pre-pressure construction, the gas lift system can be used multiple times to perform gas lift operations to promote the drainage of water at the core of the drainage plate. The interval between gas lift operations is 6 hours to 48 hours, and the selection of the time interval between gas lift operations is related to the rate of rise of the water level in the drainage plate after the previous gas lift, the rate of formation of a vacuum gradient at the top and bottom of the drainage plate, and the change in the pore water pressure of the soil around the drainage plate.

[0042] In addition, when the gas pressure and flow rate reach a predetermined value, the drainage speed is greatly improved, and the water in the drainage plate can be completely drained in a relatively short time. Therefore, the air compressor that supplies air can be stopped every time the drainage is completed, which requires less energy consumption. In addition, the length of the gas passage of the pressurized gas is not limited by the depth of the soft soil, and the air compressor can be placed on the ground for operation and maintenance.

[0043] In this invention, a new vacuum pre-pressurization method is developed based on the gas lift principle. Until now, there has been no process that combines the two to reinforce weak ground. The device of the present invention provides a means to observe the flow pattern in the drainage plate and control the air supply pressure and air supply flow rate, which allows the effect of this method to be better analyzed.

[0044] The contents described in the examples of this specification are merely examples of embodiments of the concept of the invention, and the scope of protection of the present invention is not limited to the specific forms shown in the examples. The scope of protection of the present invention also includes equivalent technical means that a person skilled in the art can conceive based on the concept of the present invention.

Claims

1. An efficient method for pre-compression of soft ground by combining gas lift and vacuum, which is used for pre-compression of high water content fluidized mud, sludge ground and deep soft ground, The pre-pressure treatment method includes the following steps: Step (1): Applying the gas lift principle to the vacuum preload, gas with a certain pressure and flow rate is introduced from the bottom of the drainage plate, so that the positive pressure gas flows upward along the core of the drainage plate, and in the process of flowing, the water in the core is carried upward and discharged from the drainage plate; Step (2): After the gas lift has completely drained the water in the board core, it immediately stops, and the board core is filled with gas. The gas in the board core is continuously sucked out by the vacuum pump connected to the head of the drainage plate, so that the gas in the board core is quickly sucked out, and the vacuum can be transmitted from the head to the board bottom with almost no attenuation; Step (3): By realizing a high vacuum degree in the full length range of the drainage plate, the soil body within the driving depth range of the drainage plate can be under high vacuum consolidation pressure, and the drainage consolidation of the deep soil body is promoted; Step (4): After the first gas lift is completed, under the vacuum pressure of the core of the board, the gap water in the soil continues to collect in the core of the board through the filter membrane of the drainage plate, so that the water level in the core of the board gradually rises until it is filled with water again. At this time, gas lift is performed again to drain all the water in the core of the board out of the drainage plate again, and thus high vacuum drainage consolidation within the entire length of the drainage plate is resumed. This is the pre-pressure treatment method.

2. The pre-pressure treatment method of claim 1, characterized in that in step (1), when air is ventilated from the bottom of the drainage plate to perform gas lift, the gas is continuously sucked out by a vacuum pump connected to the drainage plate head, so that the water in the plate core is pushed up by the positive pressure of the gas at the bottom and pulled by the negative vacuum pressure at the top, and the water in the plate core is quickly discharged over the entire length of the drainage plate.

3. The pre-pressure treatment method of claim 1, characterized in that in steps (3) and (4), after all the water is drained, the vacuum is only transmitted in a gas environment, so that it is transmitted to the bottom of the plate without attenuation, the boundary conditions of the soil body consolidation are improved by the efficient transmission of vacuum, and the pressure difference between the soil pore pressure and the pressure in the drainage plate is increased, thereby accelerating the seepage flow rate of the soil water and improving the efficiency of the vacuum pre-pressure treatment of soft soil.

4. A method for implementing construction based on the pre-pressure treatment method according to claim 1, comprising the steps of: Step 1: Modify the drainage board so that hand-shaped connectors can be connected to both ends of the board. Step 2: The pressure gas pipeline is connected to the bottom connector and driven into the soft ground together with the drainage plate, and the end of the pipeline is connected to the gas lift positive pressure pipeline at the ground level; Step 3: The vacuum line is connected to the drain plate by the top connector, and the end of the line is connected to the vacuum negative pressure line at the ground; Step 4: Lay and seal the geotextile and geomembrane. Step 5: Connect the pressure gas line and the vacuum line to the air compressor and the vacuum pump, respectively; Step 6: A method of carrying out construction work by starting up the equipment, and when the degree of vacuum stabilizes at -80 to -90 kPa, starting the air compressor intermittently to carry out an air supply gas lift.

5. The construction method according to claim 4, characterized in that the bottom connection port of the drainage plate is connected to the air compressor by a pneumatic duct to form a gas lift positive pressure gas passage.

6. The method for carrying out the construction work described in claim 5, characterized in that the bottom connection port of the drainage plate and the pneumatic duct are already connected before the drainage plate is inserted, thereby maintaining the injected gas passage both before and after the drainage plate is inserted into the soft soil.

7. The method for realizing the construction work described in claim 5, characterized in that the gas lift operation can be performed multiple times using the gas lift positive pressure gas passage to promote the discharge of water at the core of the drainage plate, the interval between gas lift operations is 6 hours to 48 hours, and the selection of the time interval between gas lifts is related to the rate of rise of the water level in the drainage plate after the previous gas lift, the rate of formation of a vacuum gradient at the top and bottom of the drainage plate, and the change in the gap water pressure of the soil around the drainage plate.

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