An anti-seepage isolation wall of soil body modification and artificial freezing combination and a construction method thereof

Abstract

The application discloses a kind of soil modification and artificial freezing composite anti-seepage isolation wall and construction method, belong to environmental engineering and geotechnical engineering technical field.The modification material of specific function is injected to build a circle strip-shaped modification zone around pollution source, cut off large flow rate groundwater and carry out physical and chemical adsorption to pollution ion, then activate artificial freezing system in modification zone, make modified soil and ice crystal synergistic effect, form super-low permeability, high safety redundancy composite frozen soil wall curtain.The anti-seepage isolation wall includes the strip-shaped modification zone constructed in the periphery of underground pollution source, the modification material is injected in the strip-shaped modification zone;Multiple steel freezing pipes are also provided in the strip-shaped modification zone, and a composite frozen soil wall curtain is formed in the strip-shaped modification zone by providing cold to multiple steel freezing pipes.The isolation wall constructed by the application has the advantages of double anti-seepage, high flow rate scour resistance, ice point depression inhibition and green reversibility.

Description

Technical Field

[0001] This invention belongs to the field of environmental engineering and geotechnical engineering technology, and specifically relates to a seepage-proof isolation wall that combines soil modification and artificial freezing. Background Technology

[0002] Major environmental accidents such as nuclear waste leaks or the spread of high concentrations of toxic and hazardous chemicals are characterized by their suddenness and extreme harm. In emergency response to sudden environmental pollution incidents, the key to preventing further spread of pollution lies in how to quickly, efficiently, and safely construct a temporary, closed containment barrier underground to confine the pollution source to a specific area.

[0003] Currently, traditional underground physical waterproofing curtains (such as high-pressure jet grouting walls, diaphragm walls, and interlocking piles) have drawbacks in nuclear contamination emergency response, including long construction periods, the high risk of secondary contamination from large-scale mechanical excavation, and material degradation in highly radioactive or acidic / alkaline environments. Artificial ground freezing, on the other hand, utilizes artificial refrigeration technology to freeze water in the ground, transforming natural soil into a high-strength, impermeable frozen soil wall. This method offers unique advantages such as rapid response, in-situ construction without the need for soil removal, wide adaptability, and the ability to shut off the refrigeration system after the emergency response to allow natural thawing and restoration of the original state.

[0004] However, traditional artificially frozen impermeable walls exhibit significant common defects in complex geological formations: First, if the groundwater flow velocity at a suddenly contaminated site is too high (e.g., greater than 5 m / d), the heat from the groundwater will offset the cooling energy dissipated by the freezing pipes, preventing the frozen soil wall from closing completely and resulting in localized leaks. Second, nuclear-contaminated wastewater or toxic industrial wastewater typically contains high concentrations of acid, alkali, or salt ions. These dissolved substances significantly lower the freezing point of water (producing a freezing point depression effect), inhibiting ice crystal growth. This results in frozen soil walls with high unfrozen water content and a loose structure, with an overall permeability coefficient that can only be maintained at 1.0 × 10⁻⁶. -6 The flow rate is around cm / s, which cannot meet the absolute seepage prevention standard required for nuclear contamination containment. Summary of the Invention

[0005] To address the above problems, this invention proposes a seepage-proof barrier wall and construction method that combines soil modification and artificial freezing. By injecting modified materials with specific functions, a strip-shaped modification zone is constructed around the pollution source to cut off high-velocity groundwater and perform physicochemical adsorption of pollutant ions. Subsequently, an artificial freezing system is activated within the modification zone, allowing the modified soil and ice crystals to work synergistically to form a composite frozen soil wall curtain with ultra-low permeability and high safety redundancy.

[0006] The technical solution of the present invention is as follows: the seepage-proof isolation wall includes a strip-shaped modification zone constructed around the underground pollution source. The strip-shaped modification zone is a closed ring or a cofferdam in the horizontal projection, completely enclosing the underground pollution source 360 ​​degrees without dead angles. Modification materials for changing the soil pore structure, reducing soil sensitivity and optimizing thermal conductivity are injected into the strip-shaped modification zone to form a continuous closed strip-shaped modification zone.

[0007] Multiple steel freezing pipes are also installed within the strip-shaped modification zone. These steel freezing pipes are arranged vertically at equal intervals along the central axis of the strip-shaped modification zone. By providing cooling to the multiple steel freezing pipes, a composite frozen soil wall curtain is formed within the strip-shaped modification zone. The composite frozen soil wall curtain freezes the strip-shaped modification zone and part of the original soil on both sides together, forming a dense, zero-permeability composite seepage barrier.

[0008] Furthermore, the modified material is one or more of the following: bentonite-cement slurry, modified water glass slurry, sodium lignosulfonate solution, or environmentally friendly polyacrylamide solution.

[0009] Furthermore, the radial thickness of the strip-shaped modified region is 1.0m to 2.5m.

[0010] Furthermore, when the modified material is bentonite-cement slurry, the mass ratio of bentonite to cement is 1:3 to 1:1; when the modified material is modified water glass slurry, its gelation time is controlled to be 5 min to 30 min.

[0011] The seepage-proof isolation wall shall be constructed according to the following steps:

[0012] S1. Positioning and in-situ monitoring: Using a total station, determine the axis of the strip-shaped modification zone at a safe distance based on the diffusion boundary of the underground pollution source on site. Drill in-situ monitoring holes on the inner and outer sides of the axis respectively, and install temperature sensors, pore water pressure gauges and radiation dose monitors in in-situ monitoring hole 1 to obtain initial formation parameters.

[0013] S2. Construction of the strip-shaped modified zone: A high-pressure jet grouting machine is used to carry out grouting construction along the determined axis. Modified materials are injected into the strip-shaped modified zone using a segmented skip grouting process to form a continuous closed strip-shaped modified zone with a thickness of 1.0m to 2.5m underground.

[0014] S3. Quality Inspection and Drilling of Freezing Holes: After grouting is completed and cured for 3-7 days, the permeability coefficient of the strip-shaped modified zone is observed through in-situ monitoring holes until the permeability of the original soil begins to decrease. By reducing permeability, the local groundwater flow velocity is limited to below the critical scour velocity, providing the necessary static water environment for subsequent artificial freezing. Subsequently, freezing holes with a depth of 35m are drilled vertically along the central axis using a geological drilling rig.

[0015] S4. Install freezing pipes and perform combined freezing: Insert steel freezing pipes into the drilled multiple freezing holes, connect them to the ground freezing station using a distribution pipeline with an insulation layer, and circulate low-temperature calcium chloride brine at -30°C into the steel freezing pipes to officially activate the artificial freezing system, causing the soil and water in the strip-shaped modified zone to freeze, ultimately forming a continuous, interlocking composite frozen soil wall curtain.

[0016] Furthermore, the locations to be grouted by the high-pressure jet grouting machine are numbered sequentially, so that the resulting odd-numbered piles and even-numbered piles are distributed alternately. The segmented skip grouting process involves first constructing the odd-numbered piles at intervals, and then backfilling the even-numbered piles after they have initially set.

[0017] Furthermore, the grouting pressure in step S2 is strictly controlled at 1.2 to 1.5 times the hydrostatic pressure of the formation fractures.

[0018] This invention enables the constructed isolation wall to possess advantages such as dual impermeability, resistance to high-velocity erosion, suppression of freezing point depression, and green reversibility. It plays a crucial role in the temporary storage of nuclear contaminated waste and emergency environmental response. After the internal contaminants are treated, the wall is thawed without the need for subsequent refrigerant injection. Compared to existing technologies, this invention offers the following advantages:

[0019] I. Double-layered seepage prevention, high safety redundancy;

[0020] This invention uses a combination of "modification and freezing" to change the fragility of a single frozen soil wall. Even if a sudden power outage causes the artificial freezing system to fail temporarily, the solidified strip-shaped modified zone on the outside still has extremely low permeability and can continue to block pollutants, thus buying critical golden time for emergency repairs.

[0021] II. Overcoming the challenges of freezing at high flow rates and high ion concentrations;

[0022] Modified materials pre-fill the large pores in the soil, reducing the groundwater flow rate to below the critical freezing velocity (5 m / d); at the same time, modifiers such as bentonite solidify some free pollutant ions through physical-chemical adsorption, weakening the freezing point depression effect of nuclear-contaminated wastewater, making the water extremely easy to freeze and form rings.

[0023] Third, a perfect combination of long-term and temporary effects;

[0024] After the emergency rescue is completed, the refrigeration system is shut down, and the core permafrost wall melts naturally, exhibiting environmental reversibility. Meanwhile, the environmentally friendly strip-shaped modified zone injected into the periphery can remain in the strata as a permanent auxiliary seepage barrier, achieving a seamless transition from "temporary emergency rescue" to "long-term protection". Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the construction sequence of stages S2 to S4 in this case.

[0026] Figure 2 This is a structural diagram of the composite frozen soil wall curtain formed in this case;

[0027] Figure 3 This is a construction step diagram for this case.

[0028] Explanation of reference numerals in the attached diagram: 1-In-situ monitoring well; 2-Strip modified zone; 3-Steel freezing pipe; 4-Composite frozen soil wall curtain; 5-Underground pollution source. Detailed Implementation

[0029] To clearly illustrate the technical features of the present invention, the present invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0030] The specific implementation structure of this case is as follows:

[0031] refer to Figure 1 and Figure 2 The overall structure of the seepage-proof isolation wall combining soil modification and artificial freezing in this invention is described. Figure 2 A schematic diagram of the structure after the formation of the composite frozen soil wall curtain is shown. The seepage-proof isolation wall is constructed around the underground pollution source 5, including in-situ monitoring holes 1, strip-shaped modification zones 2, and the composite frozen soil wall curtain 4 arranged from the inside out. The strip-shaped modification zones 2 form a closed ring or cofferdam shape in the horizontal projection, completely enclosing the underground pollution source 5 360 degrees without dead angles. The radial thickness of the strip-shaped modification zones 2 is 1.0m~2.5m.

[0032] Multiple steel freezing pipes 3 are installed vertically downwards along the geometric center axis of the strip-shaped modification zone 2. These steel freezing pipes 3 are made of low-carbon seamless steel, with diameters including, but not limited to, φ108mm × 6mm or φ159mm × 8mm. The spacing between adjacent steel freezing pipes 3 is 0.8m to 1.2m. Utilizing the low-temperature refrigerant circulating within the steel freezing pipes 3, a continuously looping composite frozen soil wall curtain 4 develops within the strip-shaped modification zone 2 and the surrounding undisturbed soil. The overall design thickness of the composite frozen soil wall curtain 4 is 2.0m to 4.5m, completely covering the entire modification zone and forming an ultra-thick ice-soil-modifier composite isolation barrier with extremely high shear strength and zero permeability.

[0033] The specific construction methods and material selections for this project are as follows:

[0034] refer to Figure 1 The construction method of the seepage-proof isolation wall combining soil modification and artificial freezing in this invention is described. This embodiment is based on a temporary emergency sealing project of a site suddenly contaminated by nuclear radiation. The specific steps are as follows: Figure 3 As shown:

[0035] S1. Positioning and In-situ Monitoring: Using a total station, determine the axis of the closed loop strip at a safe distance (e.g., 5 m outside the boundary) based on the diffusion boundary of the underground pollution source 5. Drill in-situ monitoring boreholes 1 inside and outside the axis, and install temperature sensors, pore water pressure gauges, and radiation dose monitors in the boreholes 1 to obtain initial formation parameters, such as... Figure 1 As shown.

[0036] S2. Construction of the Strip-Shaped Modification Zone: A high-pressure jet grouting machine is used for grouting along the predetermined axis. To prevent excessive disturbance to the contaminated strata caused by high-pressure grouting, which could lead to fracturing and diffusion, this embodiment employs a "segmented skip-flow grouting process." This involves first constructing odd-numbered piles at intervals, and then backfilling even-numbered piles after initial setting. The grouting pressure is strictly controlled at 1.3 times the hydrostatic pressure of the strata fissures (specifically 0.8 MPa to 1.5 MPa). The modification material used in this embodiment is bentonite-cement grout, with a mass ratio of sodium-based bentonite to ordinary silicate cement of 1:2 and a water-cement ratio of 0.8. Adjacent jet-grouting modified piles interlock with an overlap length of no less than 200 mm, thus forming a continuous, closed strip-shaped modification zone 2 with a thickness of 1.5 m underground.

[0037] S3. Quality Inspection and Drilling of Freezing Holes: After grouting and curing for 3-7 days, in-situ monitoring test 1 showed that the permeability coefficient of the strip-shaped modified zone 2 had initially decreased from the permeability of the original soil. This stage of modification was not directly used for final nuclear contamination containment, but rather to successfully limit the local groundwater flow velocity below the critical scour velocity by reducing permeability, providing the necessary static water environment for subsequent artificial freezing. Simultaneously, the modified soil possessed initial consolidation strength, effectively preventing borehole narrowing or collapse during drilling. Subsequently, a geological drilling rig was used to drill freezing holes vertically along the central axis to a depth of 35m, with the verticality deviation strictly controlled within 0.3%.

[0038] S4. Install freezing pipes and perform combined freezing: Insert low-carbon seamless steel freezing pipes 3 with an outer diameter of φ108mm and a wall thickness of 6mm into the drilled freezing holes, and connect them to the ground freezing station using a manifold with an insulation layer. Circulate low-temperature calcium chloride brine at -30℃ into the steel freezing pipes 3 to officially activate the artificial freezing system. Cold energy diffuses evenly from the steel freezing pipes 3 to the surrounding area, initiating the synergistic physical and chemical action of the modified soil and artificial freezing.

[0039] The comparison of testing and application effects and the verification of the joint sealing mechanism in this case are as follows:

[0040] To further verify the ultra-high seepage prevention effect of the present invention after modification and freezing in the modified zone, this embodiment conducted systematic in-situ testing and mechanism analysis on the intrinsic permeability and storage performance of sodium lignosulfonate modified soil under negative temperature environment.

[0041] Combined freezing test scheme and data: In this embodiment, the strip-shaped modified zone 2 uses a sodium lignosulfonate solution with a mass percentage of 7% as the modifying material. When the artificial freezing system has been running continuously for 22 days and the core temperature of the strip-shaped modified zone 2 shows that it has stably reached the design temperature of -10℃, the permeability of the sodium lignosulfonate modified soil sample after combined freezing is tested using a high-pressure triaxial permeameter.

[0042] Test results show that, in the initial stage of combined freezing, the initial intrinsic permeability of the composite curtain reached 5.63 × 10⁻⁶. -17 m 2 As the frozen curtain continues to develop and microscopic ice crystals further compress and fill the pores, the minimum intrinsic permeability in the densest core region of the curtain reaches 1.02 × 10⁻⁶. -17 m 2 Even in the peripheral area near the boundary of unfrozen undisturbed soil, where the cold energy is relatively weak, the maximum intrinsic permeability is strictly controlled at 19.36 × 10⁻⁶. -17 m 2 .

[0043] At this point, the strip-shaped modified zone 2 is completely integrated with the ice curtain, and the overall internal permeability of the composite seepage-proof isolation wall reaches 10. -17 m 2 The order of magnitude fully meets the absolute seepage prevention and ultimate strength requirements for the long-term sealing of nuclear contaminated waste.

[0044] There are many specific ways to implement this invention. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A seepage-proof isolation wall of soil body modification and artificial freezing combination, characterized in that, The seepage-proof isolation wall includes a strip-shaped modification zone (2) constructed around the underground pollution source (5). The strip-shaped modification zone (2) is a closed ring or a cofferdam that surrounds the underground pollution source (5) in a horizontal projection. Modification materials for changing the soil pore structure, reducing soil sensitivity and optimizing thermal conductivity are injected into the strip-shaped modification zone (2) to form a continuous closed strip-shaped modification zone (2). Multiple steel freezing pipes (3) are also provided in the strip-shaped modification zone (2). The multiple steel freezing pipes (3) are arranged at equal intervals along the central axis of the strip-shaped modification zone (2). By providing cold energy to the multiple steel freezing pipes (3), a composite frozen soil wall curtain (4) is formed in the strip-shaped modification zone (2). The composite frozen soil wall curtain (4) freezes the strip-shaped modification zone (2) and the original soil on both sides together, forming a dense zero-permeability composite seepage barrier.

2. The seepage-proof isolation wall composed of soil modification and artificial freezing as described in claim 1, characterized in that, The modified material is one or more of the following: bentonite-cement slurry, modified water glass slurry, sodium lignosulfonate solution, or environmentally friendly polyacrylamide solution.

3. The seepage-proof isolation wall composed of soil modification and artificial freezing as described in claim 1, characterized in that, The radial thickness of the strip-shaped modified region (2) is 1.0m to 2.5m.

4. The seepage-proof isolation wall composed of soil modification and artificial freezing as described in claim 2, characterized in that, When the modified material is bentonite-cement slurry, the mass ratio of bentonite to cement is 1:3 to 1:1; when the modified material is modified water glass slurry, its gelation time is controlled to be 5 min to 30 min.

5. A construction method for a seepage-proof isolation wall combining soil modification and artificial freezing as described in claim 1, characterized in that, The seepage-proof isolation wall shall be constructed according to the following steps: S1. Positioning and in-situ monitoring: Using a total station, the axis of the strip-shaped modification zone (2) is determined at a safe distance based on the diffusion boundary of the underground pollution source (5) on site. In-situ monitoring holes (1) are drilled on the inner and outer sides of the axis, and temperature sensors, pore water pressure gauges and radiation dose monitors are installed in the in-situ monitoring holes (1) to obtain the initial formation parameters. S2. Construction of the strip-shaped modified zone: High-pressure jet grouting machine is used to carry out grouting construction along the determined axis. Modified materials are injected into the strip-shaped modified zone (2) using segmented jumping grouting technology to form a continuous closed strip-shaped modified zone (2) with a thickness of 1.0m~2.5m underground. S3. Quality inspection and drilling of freezing holes: After grouting is completed and cured for 3 to 7 days, the permeability coefficient of the strip-shaped modified zone (2) is tested and observed through the in-situ monitoring hole (1) until the permeability of the original soil begins to decrease. By reducing the permeability, the local groundwater flow velocity is limited to below the critical scouring velocity, providing the necessary static water environment for subsequent artificial freezing. Then, freezing holes are drilled vertically along the central axis using a geological drilling rig. S4. Install freezing pipes and freeze together: Insert steel freezing pipes (3) into the drilled multiple freezing holes and connect them to the ground freezing station using a distribution pipeline with insulation layer; then circulate low-temperature calcium chloride brine at -30℃ into the steel freezing pipes (3) to officially activate the artificial freezing system, so that the soil and water in the strip-shaped modified zone (2) are frozen, and finally form a continuous ring-shaped composite frozen soil wall curtain (4).

6. The construction method of a seepage-proof isolation wall combining soil modification and artificial freezing according to claim 5, characterized in that, The locations to be grouted by the high-pressure jet grouting machine are numbered sequentially so that the odd-numbered piles and even-numbered piles are distributed alternately. The segmented grouting process involves first constructing the odd-numbered piles at intervals, and then backfilling the even-numbered piles after they have initially set.

7. The construction method of a seepage-proof isolation wall combining soil modification and artificial freezing according to claim 5, characterized in that, In step S2, the grouting pressure is controlled at 1.2 to 1.5 times the hydrostatic pressure of the formation fractures.

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