Permeation-enhancing recharge construction method suitable for cohesive soil stratum

Abstract

The invention discloses a permeation-enhancing recharge construction method suitable for a viscous soil layer, and relates to the technical field of civil engineering. The method comprises a recharge well, a water filtering part is arranged on the lower portion of the recharge well, and the construction process comprises the following steps that firstly, at least one permeation increasing pipe with leakage holes is arranged on the stratum needing permeation increasing around the recharge well; 2, starting a pressurizing mechanism, pressurizing a pressurizing object, injecting the pressurizing object into the permeation increasing pipe, impacting the surrounding soil layer by the pressurizing object through a leakage hole in the permeation increasing pipe, and enabling the surrounding soil layer to generate cracks; 3, when the pressure of the permeation increasing pipe is suddenly reduced, the pressurization mechanism is closed; 4, muddy water in the recharge well is pumped through drainage equipment, and when the water level meets the design requirement, drainage of the recharge well is stopped; and 5, recharge water is injected into the recharge well. The seepage increasing well is arranged on the periphery of the recharge well, pressurized objects can be conveyed into the surrounding cohesive soil stratum, cracks are formed in the cohesive soil stratum, and the permeability of the surrounding soil stratum is improved.

Description

Technical Field

[0001] This invention relates to a method for enhancing permeability and recharge construction in cohesive soil layers, and pertains to the field of civil engineering technology. Background Technology

[0002] An excavation pit is a type of underground structure created by excavating soil from the ground surface to create underground space during the construction of underground works such as basements of high-rise buildings, subway stations, and sewage treatment systems.

[0003] During foundation pit excavation, artificial measures are needed to lower the groundwater level. This typically involves constructing drainage ditches around the pit to divert water to collection wells for pumping out. This ensures the construction surface remains dry, prevents foundation instability, and avoids problems such as slope collapse, quicksand, and piping caused by groundwater infiltration. It also improves the bearing capacity of the foundation. However, when groundwater is extracted, the drop in water level creates a cone of depression. Within this cone, the pore water pressure in the soil decreases, and the stress increases, leading to soil consolidation and settlement, which can affect surrounding buildings. Therefore, it is necessary to install recharge wells to inject water into the soil around the foundation pit, forming a seepage-resistant water curtain to prevent the spread of groundwater impact and maintain the stability of the original groundwater level for surrounding buildings.

[0004] When dewatering foundation pits in cohesive soil layers, the low permeability coefficient of these layers limits the effective recharge area of ​​the recharge wells, resulting in unsatisfactory recharge effects. Currently, some research has been conducted both domestically and internationally on improving the permeability of cohesive soil layers in soft soil foundation pits. Some scholars have proposed periodically pumping water back through recharge wells to clear seepage fissures in the cohesive soil, while others have suggested adding fine sand to the injection pipes to create drainage channels and thus increase permeability in the soft soil. However, cohesive soil layers have high water content and low bearing capacity, making it easy for fissures to close, hindering the achievement of the desired recharge effect. Furthermore, the injected fine sand often blocks the drainage channels of the cohesive soil layer. Summary of the Invention

[0005] The purpose of this invention is to design a permeability enhancement recharge construction method that can improve the recharge effect of cohesive soil layers.

[0006] This invention includes a recharge well, the lower part of which is equipped with a water filter section, and its construction process includes the following steps: Step 1: Install at least one permeation enhancement pipe with a seepage hole around the stratum that needs to be permeated around the reinjection well. The depth of the permeation enhancement pipe is less than the depth of the reinjection well. Install a sealing cap at the upper end of the permeation enhancement pipe. The outlet of the fluid-like pressurizing agent is located inside the permeation enhancement pipe. Install a seepage zone with a first seepage hole at the lower part of the permeation enhancement pipe. Step 2: Activate the pressurization mechanism to inject the pressurized material into the permeation pipe after pressurization. The pressurized material impacts the surrounding soil layer through the seepage holes in the permeation pipe, causing cracks in the surrounding soil layer. During this process, monitor the pressure in the permeation pipe. Step 3: When the pressure in the permeation intensifier tube suddenly decreases, shut off the pressurization mechanism; Step 4: Use drainage equipment to pump out the turbid water from the recharge well. Stop draining the recharge well when the water level reaches the design requirements. Step 5: Inject recharge water into the recharge well, allowing the recharge water to gradually seep into the ground.

[0007] Furthermore, after step 1 and before step 2, a trial run of step 1.1 is performed. The method of step 1.1 is as follows: select a pressurizing material with an injection pressure in the range of 0.5MPa-2MPa as the initial injection pressure and inject the pressurizing material. Adjust the injection pressure according to the injection volume, with the criterion that no water seepage or air leakage occurs on the surrounding ground.

[0008] Furthermore, in step 1.1, the initial injection pressure range is 0.5MPa-1MPa. If there is no increase in gas pressure or the liquid level rises above the leakage zone of the permeation enhancement tube, the injection pressure is increased.

[0009] Furthermore, in step 5, when the reinjection rate slows down, reinjection is stopped, and then the infiltration well is opened. Steps 2, 3, 4, and 5 are executed again. Reinjection is stopped after the groundwater replenishment is completed.

[0010] Furthermore, the permeation-enhancing pipe is installed within the permeation-enhancing well. The upper part of the space between the permeation-enhancing well and the permeation-enhancing pipe is filled with a sealing material, while the lower part is filled with waterproof granules. This design prevents air and water leakage during the permeation process.

[0011] Furthermore, the feature is that: the infiltration well contains an isolation pipe fitted outside the infiltration pipe; large waterproof particles larger than the seepage holes are placed between the isolation pipe and the infiltration pipe; a second seepage hole is provided in the area corresponding to the seepage zone of the isolation pipe and the infiltration pipe; the second seepage hole is a funnel-shaped hole with a larger inner diameter and a smaller outer diameter. The second seepage hole designed as described above can increase the flow velocity of water from the hole, increase the spray intensity on cohesive soil layers, and accelerate the formation of fractures.

[0012] Furthermore, the pressurizing material delivery pipe is connected to the lower part of the permeation-enhancing pipe, and its outlet is located at or near its lower end. The pressurizing material flows back upward from the lower part of the permeation-enhancing pipe.

[0013] Furthermore, the pressurizing agent is a gas, a liquid, or a gas-liquid mixture.

[0014] Furthermore, the pressurizing agent is a liquid, and the permeation pipe is connected to an air compressor and a slurry pump respectively above ground via two branch pipes.

[0015] Furthermore, the slurry pump and air compressor maintain the same injection pressure. This design allows the pressurized material and compressed air to create turbulent flow within the permeation tube; this turbulent flow can then be injected through the permeation holes onto the cohesive soil layer to create fissures. This invention involves setting up an infiltration well in the cohesive soil layer surrounding the recharge well. The infiltration well can deliver pressurized material to the surrounding cohesive soil layer through the infiltration pipe in the infiltration well, forming fissures in the cohesive soil layer that extend towards the recharge well. This increases the permeability of the soil layer surrounding the recharge well and improves the recharge effect.

[0016] In this invention, multiple sets of leakage holes are provided on the permeation enhancement pipe and the isolation pipe, and the leakage holes of each set are all oriented toward the reinjection well in the corresponding direction, so that the gas-liquid mixture can be concentrated and output; the second leakage hole provided on the isolation pipe is in the shape of a bucket that gradually narrows outward, which increases the flow rate of the gas-liquid mixture and improves the formation rate of fractures. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the main structure of an embodiment of the present invention; Figure 2 for Figure 1 A magnified view of a section at point A in the middle; Figure 3 for Figure 1 Full sectional view of the central permeation infiltration pipe; Figure 4 for Figure 3 A magnified view of a section at point B in the middle; Figure 5 for Figure 3 A magnified view of a section at point C; Figure 6 for Figure 1 Schematic diagram of the middle isolation tube section; Among them: 1. Cohesive soil layer, 2. Recharge well, 3. Recharge well pipe, 4. Filter pipe, 5. Filter hole, 6. Cohesive soil filler layer, 7. Crushed stone filler layer, 8. Infiltration well, 9. Infiltration pipe, 10. First seepage hole, 11. Isolation pipe, 12. Second seepage hole, 13. Air compressor, 14. Slurry pump, 15. Branch pipe, 16. Sealing cap, 17. Delivery pipe, 18. Crack, 19. Water pump, 20. Water pumping pipe, 21. Check valve. Detailed Implementation

[0018] by Figure 1 Define the up, down, left, right, front, and back directions in this embodiment.

[0019] As shown in the figure, a method for enhancing permeability and recharge in cohesive soil layers includes the following: This embodiment includes two recharge wells 2 located in a cohesive soil layer 1. Each well contains a recharge pipe 3. In practical applications, the number of recharge wells 2 can be adjusted according to site requirements. A filter pipe 4 with filter holes 5 is located at the lower part of the recharge pipe 3. The filter pipe 4 serves as the filter section of the recharge well 2, allowing recharge water to permeate into the cohesive soil layer 1. A gravel filler layer 7 is located between the filter pipe 4 and the inner wall of the recharge well 2. The gravel filler layer 7 is composed entirely of waterproof particles, each larger than the filter holes 5. In this embodiment, the waterproof particles at the lower part of the gravel filler layer 7 are larger than those at the upper part, reducing the loss of fine particles from the upper part and improving the service life of the filler layer. A cohesive soil filler layer 6 is set above the crushed stone filler layer. The cohesive soil filler layer 6 is compacted to a compaction degree of ≥93%, which can reduce fluid infiltration, form a reliable sealing layer, and prevent the backfill water from flowing out. During construction, concrete can be used to seal the cohesive soil filler layer 6 to increase its sealing performance.

[0020] After the above-mentioned reinjection wells are installed, proceed to step 1.

[0021] Step 1: Install permeability enhancement pipes around the reinjection well: First, an infiltration well 8 is installed on the cohesive soil layer 1 between the two recharge wells 2 where infiltration enhancement is required. In this embodiment, two infiltration wells 8 are installed side by side. In actual applications, 2-4 infiltration wells 8 can be installed according to site requirements. Each infiltration well 8 is equipped with an infiltration pipe 9, and the depth of the infiltration pipe 9 extending downward is less than the depth of the recharge well 2. A sealing cap 16 is installed at the upper end of each infiltration pipe 9, which is fixedly connected to the infiltration pipe 9 by bolts. Two delivery pipes 17 are fixedly welded to the sealing cap 16. The upper ends of the two delivery pipes 17 are located above the ground and are connected to the pressurization mechanism through branch pipes 15. The pressurization mechanism includes an air compressor 13 and a slurry pump 14. The slurry pump 14 delivers pressurizing material into the permeation pipe 9. A delivery pipe 17 connected to the slurry pump 14 extends to the lower part of the permeation pipe 9, with its outlet located at the lower end, allowing the output pressurizing material to flow back upwards from the lower part of the permeation pipe 9. The pressurizing material can be gas, liquid, or a gas-liquid mixture. In this embodiment, liquid is used, directly delivered to the permeation pipe 9 via the slurry pump 14. The slurry pump is a pressurized water pump, an existing device, and its specific structure will not be described in detail here. The air compressor 13 is connected to the left delivery pipe 17 via a branch pipe 15. The outlet end of the left delivery pipe 17 is located at the upper part of the permeation pipe 9, delivering compressed air into the permeation pipe 9 to promote the permeation of the pressurizing material into the cohesive soil layer 1. Both delivery pipes 17 are equipped with check valves 21 to prevent backflow of compressed air and pressurizing material into the permeation pipe 9.

[0022] Each permeation-enhancing pipe 9 has a leakage zone at its lower part, with multiple sets of first leakage holes 10. These first leakage holes 10 are staggered on the left and right sides of the permeation-enhancing pipe 9, allowing the pressurized material in the permeation-enhancing pipe 9 to be concentrated and output towards the reinjection wells 2 on the left and right sides. An isolation pipe 11 is installed at the lower part of the permeation-enhancing pipe 9, fitted around its outer periphery and fixed by welding. Multiple sets of second leakage holes 12 are installed on the isolation pipe 11, with each second leakage hole 12 corresponding to the first leakage hole 10. These second leakage holes are funnel-shaped, with a larger inner diameter and a smaller outer diameter, increasing the outflow velocity of the liquid in the permeation-enhancing pipe 9. Large waterproof particles are placed between the isolation pipe 11 and the permeation-enhancing pipe 9. These waterproof particles are larger than the first and second leakage holes, reducing the backflow of fine particles in the permeation wells 8 and preventing blockage of the permeation-enhancing pipe 9.

[0023] A filler layer is provided between each infiltration pipe 9 and the infiltration well 8. This filler layer is the same as the filler layer of the recharge well 2. The unperforated part of the upper infiltration pipe 9 is filled with compacted cohesive soil filler, which has a certain sealing effect and prevents water seepage or air leakage. Waterproof granules are filled below the cohesive soil filler, and the volume of the lower waterproof granules is larger than that of the upper waterproof granules, which can reduce the loss of fine particles from the upper part.

[0024] Step 1.1: After the infiltration pipe 9 is set up, select the initial injection pressure according to the actual project site. Select the pressurizing material with an injection pressure in the range of 0.5MPa-1MPa as the initial injection pressure and inject the pressurizing material. Test run the infiltration pipe 9. During the injection process, the injection pressure can be adjusted according to the injection volume, with the criterion that no water seepage or air leakage occurs on the surrounding ground.

[0025] During the injection process, the air compressor 13 and the slurry pump 14 maintain the same injection pressure to create turbulent flow within the infiltration pipe 9; and the turbulent flow can be sprayed into the cohesive soil layer 1 through the second seepage hole 12 of the isolation pipe 11, forming cracks 18 in the cohesive soil layer 1.

[0026] If no increase in air pressure or rise in liquid level above the leakage zone of the permeation infiltration pipe 9 occurs, the injection pressure is increased to 2MPa. In this embodiment, pressure sensors are installed at the outlets of both the air compressor 13 and the slurry pump 14 to detect the pressure output from the pressurizing mechanism to the permeation infiltration pipe 9.

[0027] After the trial operation of the permeation enhancement pipe 9 is completed, proceed to step 2.

[0028] Step 2: Start the pressurization mechanism to keep the air compressor 13 and the slurry pump 14 at the same injection pressure, pressurize the pressurized material and inject it into the permeation pipe 9. The pressurized material impacts the surrounding soil layer through the seepage holes in the permeation pipe 9 and causes cracks 18 in the surrounding soil layer. During this process, the pressure in the permeation pipe 9 is monitored. In this embodiment, the slurry pump 14 delivers the pressurized material to the lower part of the permeation-enhancing pipe 9 via the right-side delivery pipe 17, and then flows back upward from the lower part of the permeation-enhancing pipe 9. After passing through the first seepage hole 10, it is discharged through the second seepage hole 12, concentrating on impacting the cohesive soil layer 1 on the left and right sides, causing the fractures 18 to extend toward the two injection wells. At the same time, the air compressor 13 delivers compressed air to the upper part of the permeation-enhancing pipe 9 via the left-side delivery pipe 17, forming a turbulent flow in the permeation-enhancing pipe 9, which promotes the pressurized material to flow out from each seepage hole, strengthens the impact intensity of the pressurized material on the cohesive soil layer 1, and increases the formation rate of the fractures 18.

[0029] Step 3: When the pressure in the permeation enhancement pipe 9 suddenly decreases, shut down the pressurization mechanism. At this time, the fracture 18 has extended to the inner wall of the reinjection well 2, connecting the permeation enhancement pipe 9 with the reinjection well 2. The pressurizing material and compressed air in the permeation enhancement pipe 9 rush into the reinjection well 2, resulting in a sudden decrease in pressure.

[0030] Step 4: Use drainage equipment to pump out the turbid water in the reinjection well 2. When the water level reaches the design requirement, stop the drainage of the reinjection well 2. In this embodiment, the drainage mechanism includes a water pump 19. A water pumping pipe 20 is provided at the inlet of the water pump 19. The water pumping pipe 20 extends to a position about 1 meter below the bottom of the reinjection well to avoid attracting sediment at the bottom of the well and clogging the drainage mechanism during pumping. Drainage can be stopped when the turbid water level in the reinjection well is pumped out to below the water pumping pipe 20.

[0031] Step 5: Inject recharge water into recharge well 2. The recharge water gradually seeps into the groundwater through the cohesive soil layer 1. In this embodiment, the fissure 18 created by the infiltration enhancement pipe 9 can increase the infiltration area of ​​the recharge water and improve the infiltration rate of the recharge water.

[0032] If, during step 5, the recharge rate of recharge well 2 slows down and the single-well recharge capacity decreases by 20%-30%, recharge is stopped. At this point, fissure 18 shows signs of closure, leading to a decrease in recharge capacity. It is necessary to wait for the water in recharge well 2 to drain before opening infiltration well 8 and repeating steps 2, 3, 4, and 5 to complete the infiltration process and allow fissure 18 to form. During the recharge process, changes in the groundwater level are monitored through a water level monitoring well. Recharge is stopped once groundwater replenishment is complete. In this embodiment, the water level monitoring well, its supporting equipment, and the groundwater monitoring method are all existing technologies and will not be elaborated upon further.

[0033] In this embodiment, each waterproof particle can be filled with gravel, which can ensure the supporting strength while reducing water accumulation.

Claims

1. A method for enhancing permeability and recharge construction in cohesive soil strata, comprising a recharge well, wherein a filter section is provided at the bottom of the recharge well, characterized in that: Its construction process includes the following steps: Step 1: Install at least one permeation enhancement pipe with a seepage hole around the stratum that needs to be permeated around the reinjection well. The depth of the permeation enhancement pipe is less than the depth of the reinjection well. Install a sealing cap at the upper end of the permeation enhancement pipe. The outlet of the fluid-like pressurizing agent is located inside the permeation enhancement pipe. Install a seepage zone with a first seepage hole at the lower part of the permeation enhancement pipe. Step 2: Activate the pressurization mechanism to inject the pressurized material into the permeation pipe after pressurization. The pressurized material impacts the surrounding soil layer through the seepage holes in the permeation pipe, causing cracks in the surrounding soil layer. During this process, monitor the pressure in the permeation pipe. Step 3: When the pressure in the permeation intensifier tube suddenly decreases, shut off the pressurization mechanism; Step 4: Use drainage equipment to pump out the turbid water from the recharge well. Stop draining the recharge well when the water level reaches the design requirements. Step 5: Inject recharge water into the recharge well, allowing the recharge water to gradually seep into the ground.

2. The method for enhancing permeability and recharge in cohesive soil layers according to claim 1, characterized in that: After step 1 is completed and before step 2 is run, a trial run of step 1.1 is performed. The method of step 1.1 is as follows: select a pressurizing material with an injection pressure in the range of 0.5MPa-2MPa as the initial injection pressure and inject the pressurizing material. Adjust the injection pressure according to the injection volume, so that there is no water seepage or air leakage on the surrounding ground.

3. The method for enhancing permeability and recharge in cohesive soil layers according to claim 2, characterized in that: in In step 1.1, the initial injection pressure range is 0.5MPa-1MPa. If there is no increase in gas pressure or the liquid level rises above the leakage zone of the permeation enhancement tube, the injection pressure is increased.

4. The infiltration enhancement and recharge construction method applicable to cohesive soil layers according to claim 2, characterized in that: in In step 5, when the reinjection rate slows down, stop the reinjection, then open the infiltration well and repeat steps 2, 3, 4, and 5. Stop the reinjection after the groundwater replenishment is complete.

5. The method for enhancing permeability and recharge in cohesive soil layers according to claim 1, 2, or 3, characterized in that: The infiltration enhancement pipe is installed in the infiltration enhancement well. The upper part of the space between the infiltration enhancement well and the infiltration enhancement pipe is filled with a sealing material, and the lower part is filled with waterproof granules.

6. The method for enhancing permeability and recharge in cohesive soil layers according to claim 5, characterized in that: The infiltration well contains an isolation pipe fitted outside the infiltration pipe. Large waterproof particles larger than the leakage holes are placed between the isolation pipe and the infiltration pipe. A second leakage hole is set in the area corresponding to the leakage area of ​​the isolation pipe and the infiltration pipe. The second leakage hole is a funnel-shaped hole with a larger inner diameter and a smaller outer diameter.

7. The method for enhancing permeability and recharge in cohesive soil layers according to claim 1, 2, or 3, characterized in that: The pressurizing material is delivered through the lower part of the permeation tube, and its outlet is located at or near the lower end of the tube. The pressurizing material flows back upward from the lower part of the permeation tube.

8. The method for enhancing permeability and recharge in cohesive soil layers according to claim 1, 2, or 3, characterized in that: The pressurizing agent is a gas, a liquid, or a gas-liquid mixture.

9. The method for enhancing permeability and recharge in cohesive soil layers according to claim 8, characterized in that: The pressurizing agent is a liquid, and the infiltration pipe is connected to an air compressor and a slurry pump respectively above ground via two branch pipes.

10. The method for enhancing permeability and recharge in cohesive soil layers according to claim 9, characterized in that: The slurry pump maintains the same injection pressure as the air compressor.

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