Underground seepage interception wall construction method and underground seepage interception wall

Abstract

The invention belongs to the technical field of underground cut-off walls, and particularly relates to an underground cut-off wall building method and an underground cut-off wall. According to the underground cut-off wall building method, grouting diffusion and migration rules under different medium conditions within the range of the cut-off wall are analyzed, based on the directional drilling technology, a drilling construction mode combining straight holes, directional inclined holes and bedding holes is combined, and the cut-off wall is built. Rapid construction of the loose aquifer long-distance seepage interception wall is achieved, the treatment cost is reduced, and the construction efficiency is improved; and closure of weak sections of the seepage interception wall is conducted through outer-injection and inner-guide grouting, top and bottom boundary faults are subjected to detour flow prevention plugging through bedding drilling, root taking and top contact of the seepage interception wall are achieved, and the flow interception effect of the seepage interception wall is improved.

Description

Technical Field

[0001] This invention belongs to the field of underground cutoff wall technology, specifically relating to a method for constructing an underground cutoff wall and the underground cutoff wall itself. Background Technology

[0002] Underground cutoff walls are commonly used structures in water conservancy projects to block underground runoff. They are constructed by drilling holes or excavating trenches in soft soil and pouring concrete into them to form continuous underground seepage barriers. They play a crucial role in ensuring the seepage stability of loose, permeable foundations and the safety of dams and sluices. They are not only used in dams, cofferdams, sluices, and dikes in water conservancy and hydropower projects, but also widely applied in large mine pits, various tailings dams, industrial waste dumps, and municipal engineering projects.

[0003] However, currently constructed underground cutoff walls in my country typically lack regulation capabilities, leading to long-term water quality deterioration upstream and impacting downstream ecological water use. Furthermore, the construction of underground cutoff walls in deeply buried, loosely porous, water-bearing soil layers or weathered bedrock fissures has consistently faced challenges such as low construction efficiency, faults at the top and bottom boundaries causing flow around the cutoff walls, and the presence of large amounts of water in the layers causing seepage at weak points during closure, resulting in poor closure performance.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for constructing an underground cutoff wall and an underground cutoff wall, so as to solve the technical problems mentioned in the background art.

[0006] To achieve one of the above objectives, the present invention provides the following technical solution:

[0007] A method for constructing an underground cutoff wall includes the following steps:

[0008] S100. Conduct hydrogeological surveys in the area where the underground cutoff wall is constructed, and analyze the parameters of porosity, fissures, and karst development in the injection layer of the lower cutoff wall.

[0009] S200. Based on the parameters, the design borehole density, grouting material, grout concentration, grouting section length and height, and final pressure standard are obtained through experiments. This forms the planar segmentation and sequential construction procedure for the lower cutoff wall. The root system skeleton of the underground cutoff wall is established through the grouting process.

[0010] S300, after drilling, the underground cutoff wall is filled, split, penetrated and consolidated in the root system of the underground cutoff wall through grouting process to form the water-proof cutoff wall closure.

[0011] Preferably, the method further includes the following steps:

[0012] After the S400 underground cutoff wall is fully connected, holes are drilled on the outside of the weak points of the wall, and the width of the closure section of the wall is increased by pressure-controlled water release and diversion grouting.

[0013] Preferably, in step S400:

[0014] Inner and outer electrodes are installed in the top and bottom rock strata along the entire underground cutoff wall. The weak areas and fault fracture zones of the cutoff wall are accurately detected by current density. The grouting position is calculated by the dichotomy method and the splitting reinforcement grouting is carried out to seal the bypass flow.

[0015] Preferably, the method also includes a step to test the blocking effect of the underground seepage interceptor wall:

[0016] The S500 system utilizes segmented and layered dynamic monitoring of groundwater levels to obtain real-time seepage parameters such as water level, water pressure, water quantity, and water quality. It is supplemented by high-density three-dimensional seismic fine exploration to monitor parameters such as the morphology, strength, stress deformation, and seepage interception stability of underground cutoff walls and sets early warning thresholds.

[0017] Preferably, in step S200:

[0018] The experimental process included scanning the underground borehole soil and core samples using X-ray and CT techniques to establish a three-dimensional model of the underground porous medium, and conducting indoor grouting tests, field grouting tests, and numerical simulation tests. In the numerical simulation, porosity was used to simplify the simulation of underground diffusion characteristics, and water content was used to replace the underground saturated and unsaturated zones, improving the traditional non-equilibrium interphase mass transfer model (eq 1), and identifying the multiphase diffusion rate and diffusion range during the grouting process.

[0019]

[0020] Using Sherwood number Sh m The flux ratio and rate ratio of convection and diffusion were calculated using Peclet number and other parameters (eq2, 3) respectively, to predict the spatiotemporal evolution of the slurry mass transfer coefficient and quantify the pollution diffusion state;

[0021]

[0022]

[0023] Preferably, in step S200:

[0024] Grouting processes include pulse grouting, multi-stage splitting grouting, and graded pressure and volume controlled grouting.

[0025] Preferably, in step S300:

[0026] Drilling methods include surface directional borehole drilling and in-seam borehole drilling.

[0027] To achieve the second objective mentioned above, the present invention provides the following technical solution:

[0028] An underground cutoff wall is constructed using the underground cutoff wall construction method described above.

[0029] Compared with existing technologies, the present invention provides a method for constructing an underground cutoff wall and an underground cutoff wall itself. By analyzing the diffusion and transport laws of grouting under different media conditions within the cutoff wall area, and based on directional drilling technology, it combines drilling construction methods of straight holes, directional inclined holes, and bedding boreholes to achieve rapid construction of long-distance cutoff walls in loose aquifers, reducing treatment costs and improving construction efficiency. The "external injection and internal diversion" grouting is used to close the weak sections of the cutoff wall, and bedding boreholes are used to prevent flow bypass at the top and bottom boundary faults, achieving "rooting and connection" of the cutoff wall and improving the cutoff wall's interception effect.

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a process flow diagram of an underground cutoff wall construction method provided in an embodiment of the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0034] Example 1: Vertical barriers in the remediation of a chlorinated hydrocarbon contaminated site at a chemical plant

[0035] (1) Refined hydrogeological investigation and grouting simulation

[0036] Drilling and sampling were conducted in the target area using a 20m×20m grid, and in-hole CT scanning technology was used to obtain the spatial distribution of soil porosity, fracture development, and permeability coefficient. Based on the exploration data, a three-dimensional heterogeneous porous media model was established. The improved non-equilibrium interphase mass transfer model of this invention was used to simulate grouting diffusion. By calculating the Peclet number (Pe) of different strata, the transport law of grout in silt layer (Pe≈15, convection-diffusion combined) and gravel layer (Pe>100, convection dominant) was predicted, and parameters such as grouting pressure and grout viscosity were optimized accordingly.

[0037] (2) Multi-process combined layered trenching construction

[0038] For 0-4m plain fill and miscellaneous fill layers, a 0.8m wide and 2.5m long hydraulic grab bucket is used to form trenches in three sections. For 4-10m fine sand layers (prone to borehole collapse), a twin-wheel trenching machine is used in conjunction with high-quality bentonite slurry (Marsh viscosity 32s, API filtration loss <15mL / 30min) for wall protection, with verticality controlled within 1 / 500. For 10-25m gravel layers and strongly weathered mudstone, a high-pressure rotary jet grouting system with a rated pressure of 35MPa is activated on the trenching machine to spray cement slurry with a water-cement ratio of 1:1, pre-crushing large-diameter gravel and softened rock mass to improve milling efficiency.

[0039] (3) Preparation and pouring of functional wall materials

[0040] The modified cement-bentonite curing mortar is mixed on-site according to the following weight ratio: 380 kg of ordinary Portland cement (PO 42.5), 80 kg of sodium-based bentonite (blue absorption >30 g / 100 g), 550 kg of water, 20 kg of 200 mesh activated carbon powder, and 5 kg of sodium hydroxide (to adjust the pH to 10-11). Underwater pouring is performed using a tremie pipe method, with the tremie pipe diameter being 250 mm. The depth of embedment in the concrete is maintained at 2-6 m, and pouring continues until the design elevation is reached.

[0041] (4) "External injection and internal introduction" precision reinforcement technology

[0042] After the wall was closed, stainless steel electrode pairs were installed at 10m intervals in the bedrock at the top and bottom of the wall. A constant current was passed through them, and by measuring the current density distribution inside and outside the wall (using resistivity imaging), two weak areas in the wall continuity caused by pebble lenses were accurately identified. Reinforcing inclined holes (60° inclination) were drilled 2m upstream of the weak areas. First, pressure-controlled water drainage was implemented. The drainage rate was controlled at 0.5 m³ / h using a regulating valve installed at the reinforcement hole opening, and drainage was continued for 4 hours, reducing the water head behind the wall by approximately 0.8m. Subsequently, grouting was performed using pure cement grout with a water-cement ratio of 0.8. The grouting pressure was controlled at 1.0-1.5 MPa, and the grouting volume was approximately 12m³.

[0043] Applications of contaminated site barrier engineering:

[0044] A 300m long, 25m deep, and 0.8m thick underground cutoff wall was constructed at a legacy chemical plant to block a chlorinated hydrocarbon pollution plume. The trench was divided into two 6m long sections, Phase I and Phase II, connected using a double-reverse-arc joint pipe method. Ultrasonic logging after trench completion showed that the verticality of the trench holes was ≤1 / 450. Core sampling 28 days after wall construction showed an unconfined compressive strength of 1.8 MPa and a permeability coefficient of 2.1×10⁻⁻⁻⁶. 8 cm / s. After testing with the electrode method and implementing "external injection and internal diversion" reinforcement, the stable head difference between the inside and outside of the wall reached 4.2m. The breakthrough curve test of the representative pollutant (vinyl chloride) showed that its breakthrough time was extended by 3 times, indicating that the wall has excellent impediment performance.

[0045] Example 2: A composite barrier system for controlling groundwater pollution at a municipal solid waste landfill

[0046] (1) Design of corrosion-resistant wall materials

[0047] To combat the strong corrosiveness of landfill leachate, sulfoaluminate cement (R·SAC 42.5) partially replaced ordinary silicate cement in the wall material, accounting for 30%. The bentonite content was increased to 15% (by weight) to enhance its self-healing ability. The basic grout mix ratio was: 114 kg sulfoaluminate cement, 266 kg ordinary silicate cement, 60 kg sodium-based bentonite, 550 kg water, and 25 kg activated carbon powder.

[0048] (2) Deep mixing and grouting combined construction method

[0049] In the upper part of the aquifer (0-12m), a continuous cement-soil wall is formed as a primary barrier using a quadriaxial deep mixing method (0.7m pile diameter, 0.2m overlap). In the lower part (12-28m), where it is difficult to mix dense sand layers and strongly weathered bedrock, the directional grouting process described in this invention is used to form a "root system" type grouting barrier that is reliably connected to the upper mixing wall.

[0050] (3) Deployment of online health monitoring system

[0051] Before the wall is poured, distributed fiber optic sensors (BOTDR technology) are pre-embedded in the reinforcing cage (if applicable) or at predetermined locations in representative trench sections, with one measuring point every meter along the wall depth direction, to monitor the strain distribution of the wall in real time. At the same time, piezometers are deployed inside and outside the wall to monitor the hydraulic gradient.

[0052] Applications of landfill barrier engineering:

[0053] A 500m long and 28m deep composite vertical barrier was constructed downstream of an informal municipal solid waste landfill. After 24 months of operation, monitoring data showed that the COD levels in the monitoring wells downstream of the barrier... a The concentration of pollutants decreased from 850 mg / L upstream to 85 mg / L, and ammonia nitrogen decreased from 120 mg / L to 18 mg / L, with removal rates reaching approximately 90%. Distributed fiber optic monitoring showed that the wall strain remained within the elastic micro-strain range (<150µε), with no obvious abnormal deformation observed. This composite barrier effectively prevented the pollution plume from spreading downstream.

[0054] Example 3: Suspended cutoff wall for controlling saline intrusion in a coastal area

[0055] (1) High-pressure jet grouting forms a suspended curtain.

[0056] In a narrow coastal area where fresh and brackish water meet, a suspended cutoff wall was constructed using a triple-pipe high-pressure jet grouting process, extending to the top of the relative impermeable layer (35m depth). The designed pile diameter is 1.2m, pile spacing is 0.9m, and overlap is 0.3m. Grouting pressure: water pressure 35MPa, air pressure 0.7MPa, grout pressure 2-5MPa. Lifting speed is 8cm / min, rotation speed is 10rpm.

[0057] (2) Preparation of high-density anti-erosion slurry

[0058] To enhance the stability and seawater corrosion resistance of the wall in coastal soft soil, 10% (by weight of cement) of finely ground slag powder (specific surface area > 600 m² / kg) and 5% (by weight of cement) of barite powder (BaSO4, density 4.3-4.5 g / cm³) were added to the conventional cement-bentonite slurry to increase the slurry density to above 1.6 g / cm³.

[0059] (3) Dynamic monitoring and regulation of the brackish water interface

[0060] A row of multi-layered monitoring wells is installed along the wall's orientation, both inside and outside (landside and seaside), to collect water samples at depths of 10m (shallow freshwater), 25m (freshwater-brine transition zone), and 35m (deep brackish water). Cl⁻ concentration, conductivity, and water level are monitored regularly, and dynamic changes at the freshwater-brine interface are plotted. When necessary, the hydraulic gradient inside and outside the wall is actively adjusted by regulating the opening of pre-set drainage valves within the wall to optimize the brackish water barrier effect.

[0061] Applications of saltwater intrusion control engineering:

[0062] A 1200m long and 35m deep suspended cutoff wall was constructed along the coast of an industrial zone. After one year of hydrological operation, monitoring data showed that the Cl⁻ concentration at a depth of 10m on the inland side of the wall decreased from 3500 mg / L before construction to 1400 mg / L, a reduction of 60%. The brackish water interface at a depth of 25m receded approximately 15m towards the sea. The overall continuity of the wall was confirmed by cross-hole radar, demonstrating its effectiveness in curbing the intrusion of brackish water.

[0063] Example 4: Directional grouting wall for blocking acidic groundwater in a metal mine spoil heap

[0064] (1) Directional inclined hole grouting forms a continuous barrier

[0065] In the downstream valley area of ​​the spoil heap, grouting holes were laid out at 1.5m intervals along the predetermined wall line. Directional drilling technology was used to extend the boreholes at a 30° angle in the highly permeable gravel layer at a depth of 15-30m, ensuring effective and continuous grouting overlap at this critical stratum. The borehole trajectory was monitored in real time using a measurement-while-drilling (MWD) system.

[0066] (2) Design of neutralization-adsorption functional slurry

[0067] The slurry is a composite system mainly composed of limestone powder (CaCO3>95%, 200 mesh, 30%), steel slag powder (specific surface area 450 m² / kg, 40%), fly ash (20%), and granular activated carbon (10%). This system can continuously neutralize acidity through the leaching of limestone and steel slag, and can also utilize activated carbon to adsorb heavy metal ions and organic pollutants.

[0068] (3) Ecological connection measures at the top of the wall

[0069] After the wall construction is completed, the top of the wall and the surrounding area will be repaired and covered with 30cm of topsoil. This will be seamlessly integrated with the overall slope ecological restoration project of the spoil heap (such as planting grass and shrubs) to form a three-dimensional pollution prevention and control system from underground to the surface.

[0070] Applications of mine spoil heap isolation engineering:

[0071] To prevent acidic groundwater from an iron ore dump, a directional grouting barrier wall, 800m long and 25m deep on average, was constructed. Long-term monitoring after the wall's completion showed that the pH of the groundwater downstream of the wall remained stable between 6.5 and 7.5, and the concentrations of iron (Fe) and manganese (Mn) decreased from 45 mg / L and 12 mg / L respectively before treatment to below 0.3 mg / L and 0.8 mg / L, meeting groundwater quality standards. The barrier wall's performance remained stable over time.

[0072] Example 5: Precise interception and remediation of pollution plumes from a historical industrial site

[0073] (1) Precise investigation and demarcation

[0074] By employing geophysical exploration techniques such as high-density resistivity method (ERT) and laser-induced fluorescence (LIF) profiling, combined with dense grid sampling analysis, the three-dimensional spatial distribution of non-aqueous liquid (NAPL) and dissolved contaminant plumes was accurately characterized, providing a scientific basis for the precise positioning of the barrier wall.

[0075] (2) Integrated “blocking-processing” system design

[0076] At the precisely determined downstream boundary of the pollution plume, a vertical barrier wall consisting of compacted clay and HDPE composite lining, extending to a depth of 18m to the waterproof layer, is first constructed using the method of this invention to completely block the lateral diffusion of the pollution plume. Adjacent to this barrier wall downstream (approximately 2m away), a 2.5m thick permeable reactive barrier (PRB) is constructed in parallel. The PRB is filled with a mixed reactive medium of zero-valent iron (ZVI) and activated carbon to deeply treat low-concentration pollutants that pass through the bottom of the barrier wall or flow around it.

[0077] (3) Intelligent grouting quality control

[0078] During grouting, an intelligent grouting recorder is used to collect and record the grouting pressure (MPa), flow rate (L / min), and grout density (g / cm³) of each grouting hole in real time. The data is wirelessly transmitted to the central control room, where software generates grouting process curves and a three-dimensional grout distribution model to ensure the uniformity and continuity of the wall quality.

[0079] Applications of precision remediation engineering for contaminated sites:

[0080] At a former pesticide factory site, an integrated "precision interception-infiltration treatment" project was implemented to address a trichloroethylene (TCE) contamination plume. Monitoring results after 36 months of system operation showed that the concentration of the contamination plume upstream of the interceptor wall remained stable, even slightly decreasing due to natural decay, with no significant downstream diffusion. The TCE concentration at the PRB effluent outlet remained consistently below 5 µg / L, achieving the remediation target. This combined system successfully achieved precise containment and effective purification of a high-risk contamination plume.

[0081] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0082] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0083] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

Claims

1. A method for constructing an underground cutoff wall, characterized in that, Includes the following steps: S100. Conduct hydrogeological surveys in the area where the underground cutoff wall is constructed, and analyze the parameters of porosity, fissures, and karst development in the injection layer of the lower cutoff wall. S200. Based on the parameters, the design borehole density, grouting material, grout concentration, grouting section length and height, and final pressure standard are obtained through experiments. This forms the planar segmentation and sequential construction procedure for the lower cutoff wall. The root system skeleton of the underground cutoff wall is established through the grouting process. S300, after drilling, the underground cutoff wall is filled, split, penetrated and consolidated in the root system of the underground cutoff wall through grouting process to form the water-proof cutoff wall closure.

2. The method for constructing an underground seepage interceptor wall according to claim 1, characterized in that, It also includes the following steps: After the S400 underground cutoff wall is fully connected, holes are drilled on the outside of the weak points of the wall, and the width of the closure section of the wall is increased by pressure-controlled water release and diversion grouting.

3. The method for constructing an underground seepage interceptor wall according to claim 1, characterized in that, In step S400: Inner and outer electrodes are installed in the top and bottom rock strata along the entire underground cutoff wall. The weak areas and fault fracture zones of the cutoff wall are accurately detected by current density. The grouting position is calculated by the dichotomy method and the splitting reinforcement grouting is carried out to seal the bypass flow.

4. The method for constructing an underground seepage interceptor wall according to claim 1, characterized in that, It also includes the steps for testing the effectiveness of underground cutoff walls: The S500 system utilizes segmented and layered dynamic monitoring of groundwater levels to obtain real-time seepage parameters such as water level, water pressure, water quantity, and water quality. It is supplemented by high-density three-dimensional seismic fine exploration to monitor parameters such as the morphology, strength, stress deformation, and seepage interception stability of underground cutoff walls and sets early warning thresholds.

5. A method for constructing an underground seepage interceptor wall according to claim 1, characterized in that, In step S200: The experimental process included scanning the underground borehole soil and core samples using X-ray and CT techniques to establish a three-dimensional model of the underground porous medium, and conducting indoor grouting tests, field grouting tests, and numerical simulation tests. In the numerical simulation, porosity was used to simplify the simulation of underground diffusion characteristics, and water content was used to replace the underground saturated and unsaturated zones, improving the traditional non-equilibrium interphase mass transfer model and identifying the multiphase diffusion rate and diffusion range during the grouting process. ； Using Sherwood number Sh m The flux ratio and rate ratio of convection and diffusion are calculated using the Peclet number (Pe) to predict the spatiotemporal evolution of the slurry mass transfer coefficient and quantify the pollution diffusion state. ； 。 6. A method for constructing an underground seepage interceptor wall according to claim 1, characterized in that, In step S200: Grouting processes include pulse grouting, multi-stage splitting grouting, and graded pressure and volume controlled grouting.

7. A method for constructing an underground seepage interceptor wall according to claim 1, characterized in that, In step S300: Drilling methods include surface directional borehole drilling and in-seam borehole drilling.

8. An underground seepage intercepting wall, characterized in that, It is constructed using the underground seepage interceptor wall construction method according to any one of claims 1-7.

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