Composite solidified soft soil roadbed filling structure and rainfall infiltration early warning method

Abstract

The application relates to the field of solid waste recycling, and discloses a composite solidified soft soil roadbed filling structure which comprises a bottom isolation adsorption layer, a core filling layer arranged above the bottom isolation adsorption layer and formed by a multi-source solid waste-based composite cementing material solidified soft soil, a shell layer barrier strip covering two side slopes and a top outer periphery of the core filling layer and composed of low-permeability modified clay or heavy metal adsorption material, and a top anti-seepage drainage layer covering the shell layer barrier strip and communicating with the shell layer barrier strip. The application starts from a roadbed macroscopic section instead of a single material ratio, simultaneously realizes core bearing, peripheral flow limiting and interface adsorption through a "core-shell" anti-seepage control structure, can significantly prolong a rainfall infiltration path, and reduces the pollution risk of surrounding soil.

Description

Technical Field

[0001] This invention relates to the field of solid waste recycling, and in particular to a composite solidified soft soil subgrade filling structure and a method for early warning of rainfall infiltration. Background Technology

[0002] With the increasing demand for the resource utilization of industrial solid wastes such as steel slag, red mud, fly ash, and desulfurization gypsum, the use of multi-source solid wastes, after composite cementing and solidification, for soft soil subgrade filling has become an important technical approach to reduce the pressure of solid waste storage, save on the consumption of natural fillers, and promote the construction of green transportation infrastructure. Especially in soft soil foundation treatment, subgrade transition section filling, and large-scale filling projects, multi-source solid waste materials have the characteristics of wide availability, large-scale utilization, and high engineering application potential.

[0003] However, solid wastes from multiple sources, such as steel slag and red mud, may contain heavy metals or metalloid components such as Cr, V, Pb, As, and Cd. If their solidification and utilization are only considered from the perspective of material ratio and strength formation, without taking into account the infiltration path, boundary barrier, and drainage control in the roadbed structure section for overall design, then under conditions such as heavy rainfall, continuous rainfall, and wet-dry cycles, rainwater is likely to form preferential infiltration channels along cracks, interlayer interfaces, shallow slope layers, and local weak areas, thereby inducing the dissolution, migration, and diffusion of heavy metal ions into the surrounding soil, affecting the environmental safety of the roadbed during long-term service.

[0004] In existing technologies, one type of approach mainly focuses on improving the strength, water resistance, or volume stability of solidified soil by adjusting the blending ratios of steel slag, red mud, fly ash, desulfurized gypsum, and admixtures. However, it often lacks sufficient disclosure regarding key physicochemical indicators such as the control of free calcium oxide content in steel slag, the moisture content and pH range of red mud, the fineness and loss on ignition of fly ash, as well as raw material pretreatment processes such as impurity removal, aging, grinding, and screening. This results in insufficient repeatability and unclear quality control boundaries in the implementation of these approaches. Another type of approach, while setting up impermeable layers, isolation layers, or drainage units around the roadbed, often lacks further refinement regarding the modification methods of low-permeability modified clay, the blending ratio of adsorbent materials, the layered filling and compaction process, and the methods for controlling the on-site permeability coefficient. This makes it difficult to stably form an external barrier system that balances low permeability, adsorption, and structural integrity.

[0005] Furthermore, existing assessment methods for the environmental risks of multi-source solid waste roadbeds mainly rely on static immersion tests, short-term infiltration tests, or general monitoring and analysis. There is a lack of unified explanation regarding the definition and value basis of key parameters such as effective seepage cross-sectional area, total monitoring depth, control concentration, and control migration flux. Specific operational methods for treatment steps such as background value correction and weighted toxicity response coefficients are also rarely clearly defined. At the same time, in field or model test monitoring, details such as the layout of monitoring sections, sensor installation locations, sampling point settings, and monitoring frequency are usually not systematically detailed, which affects the comparability, repeatability, and engineering applicability of evaluation results under different engineering or test conditions.

[0006] Therefore, it is still necessary to provide a technical solution that takes into account the high-volume resource utilization of multi-source solid waste, the improvement of the bearing capacity of soft soil subgrade, the inhibition of heavy metal leaching, and the dynamic assessment of rainfall infiltration, so as to achieve synergistic unity between structural resistance control design, construction implementation control, and service life process early warning. Summary of the Invention

[0007] To address the technical problems mentioned in the background section, this invention provides a composite solidified soft soil subgrade filling structure and a method for early warning of rainfall infiltration.

[0008] This invention is achieved using the following technical solution: a composite solidified soft soil subgrade filling structure, comprising:

[0009] Bottom isolation and adsorption layer;

[0010] The core filling layer, located above the bottom isolation and adsorption layer, is formed by solidifying soft soil with multi-source solid waste-based composite cementitious material;

[0011] The shell barrier zone, which covers the two sides of the core filling layer and the top outer perimeter, is composed of low-permeability modified clay or heavy metal adsorbent material.

[0012] A top impermeable and drainage layer covers the shell barrier band and is in communication with the shell barrier band;

[0013] The bottom isolation and adsorption layer, the shell barrier strip, and the top seepage prevention and drainage layer together constitute the "core-shell" seepage prevention and control path for the core filling layer.

[0014] The slope toe of the roadbed filling structure is provided with side ditches, drainage blind ditches, and leachate collection tanks that are connected to the top seepage-proof drainage layer or the bottom isolation and adsorption layer.

[0015] Furthermore, the multi-source solid waste-based composite cementitious material includes at least two of steel slag, red mud, fly ash, and desulfurized gypsum, and may further include one or more of slag powder, lime, and alkaline activator; the multi-source solid waste-based composite cementitious material accounts for 12% to 35% of the dry mass of the soft soil to be solidified.

[0016] Furthermore, the shell barrier zone is composed of a modified clay matrix and one or more of bentonite, zeolite, biochar, sepiolite, attapulgite, and iron-based mineral powder dispersed in the modified clay matrix. The modified clay matrix is ​​sodium-modified using a sodium carbonate solution with a mass fraction of 1% to 3% and a curing time of 12h to 48h.

[0017] Furthermore, the thickness of the shell barrier band is 0.15m to 0.60m, and the permeability coefficient is not greater than 1×10⁻ 7 cm / s; the mass ratio of modified clay, bentonite, zeolite and biochar in the shell barrier material is 80:10:5:5. During construction, the moisture content of the mixture is controlled at 20% to 25%. It is formed by layered filling, with each layer having a loose thickness of no more than 20cm and a dry density of no less than 1.65g / cm³ after compaction.

[0018] Furthermore, the bottom isolation and adsorption layer is composed of a compacted clay cushion layer, a reactive adsorption layer, and a geotextile or bentonite waterproof blanket; the top seepage-proof drainage layer includes a sealing layer, a drainage layer, and a protective layer arranged sequentially from bottom to top, the cross slope or longitudinal slope of the drainage layer is 2% to 4%, and the protective layer is a vegetated soil layer, a graded crushed stone layer, or a combination of both.

[0019] Furthermore, a stepped or toothed interface interlocking structure is provided between the core filling layer and the shell barrier zone, and a geogrid, geotextile or fiber reinforcement layer is provided at the interface interlocking structure.

[0020] Furthermore, it also includes a monitoring unit, which includes a miniature earth pressure cell deployed in the easily expansive zone inside the core fill layer, a moisture meter deployed in the interface area between the core fill layer and the shell barrier zone, a sampling port and a pore water pressure meter deployed in the core fill layer, the outer side of the shell barrier zone or the surrounding soil, and a conductivity probe and a pH probe deployed in the drainage ditch and leachate collection tank.

[0021] This invention also proposes a method for early warning of rainfall infiltration in the above-mentioned composite solidified soft soil subgrade filling structure, comprising the following steps:

[0022] S1. Establish a monitoring section in the roadbed filling structure, and deploy monitoring sensors and sampling points inside the core filling layer, at the interface between the core filling layer and the shell layer barrier zone, and in the slope toe drainage area.

[0023] S2. Set at least one rainfall scenario and conduct rainfall simulation or on-site monitoring;

[0024] S3. Collect data according to time series, the data including seepage flow. Moisture content pore water pressure pH value Electrical conductivity The concentration of the i-th heavy metal collected in the slope toe drainage area. The concentration of the i-th heavy metal collected from the interface or internal sampling points And record the depth value of each sampling point relative to a unified depth reference. In the formula, Indicates the heavy metal type code. Indicates the sampling point number. Indicates the first The depth value of each sampling point relative to a unified depth reference;

[0025] S4. Calculate the comprehensive risk index based on the collected data. ,in:

[0026] Concentration risk item , The control concentration of the i-th heavy metal;

[0027] Migration flux risk item ,in = A is the effective seepage cross-sectional area. Let i be the controlled migration flux of the i-th heavy metal;

[0028] Migration depth risk items ,in H represents the total monitoring depth;

[0029] Overall Risk Index , where a, b, and c are weighting coefficients and a+b+c=1;

[0030] S5. The comprehensive risk index It is compared with at least one preset threshold, and a graded early warning result is output based on the comparison result.

[0031] Furthermore, the effective seepage cross-sectional area A mentioned in step S4 is defined as the cross-sectional area perpendicular to the water flow direction where seepage occurs; in indoor model tests, A is the product of the model box width and the effective seepage thickness of the core filling layer or the effective seepage thickness of the interface between the core filling layer and the shell barrier zone; in field monitoring, A is the cross-sectional area of ​​the potential seepage channels in the subgrade section per unit width; the total monitoring depth H is defined as the vertical distance from the top surface of the core filling layer to the bottom surface of the bottom isolation and adsorption layer.

[0032] Furthermore, in step S4, the comprehensive risk index is calculated. Previously, background values ​​were corrected for the concentrations of each monitored heavy metal ion: the background value correction concentration of the i-th heavy metal at the slope toe drainage area, drainage blind ditch, and leachate collection tank. ; Background correction concentration of the i-th heavy metal at the j-th sampling point ;in The background concentration of the i-th heavy metal is measured in unaffected soil or background water samples before the test or on-site monitoring.

[0033] In step S4, based on the background value correction, the toxicity response coefficient is further used. The toxicity response coefficient is weighted according to the concentration of each heavy metal; The parameters are: Hg=40, Cd=30, As=10, Pb=5, Cr=2, Zn=1; after background value correction and weighting by toxicity response coefficient, the concentration risk term, migration flux risk term, and migration depth risk term are calculated according to the following formulas:

[0034]

[0035]

[0036]

[0037]

[0038]

[0039] Wherein: the controlled concentration in step S4 The controlled migration flux is determined by referring to groundwater quality standards, surface water quality standards, or corresponding environmental quality control standards. Determined through preliminary soil column tests, small-scale model tests, environmental impact assessment limits, or calibration values ​​of similar projects.

[0040] The graded early warning results mentioned in step S5 include: a green warning when R(t) < 0.50, indicating that the seepage prevention and control status is good; a yellow warning when 0.50 ≤ R(t) < 0.80, indicating that local infiltration channels have begun to develop; an orange warning when 0.80 ≤ R(t) < 1.00, indicating that the risk of heavy metal migration has increased significantly; and a red warning when R(t) ≥ 1.00, indicating that seepage channels and escape paths have been formed and immediate action is required.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] This invention starts from the macroscopic cross-section of the roadbed rather than a single material ratio. Through the "core-shell" seepage prevention and control structure, it simultaneously achieves core bearing, peripheral flow restriction and interface adsorption, which can significantly extend the rainfall infiltration path and reduce the risk of pollution to the surrounding soil.

[0043] This invention, by clarifying the sodium modification method of the shell barrier zone, the ratio of adsorbent materials, and the process of layered filling and permeability coefficient control, is beneficial to the stable formation of a low-permeability outer barrier layer.

[0044] This invention enhances the engineering applicability and early warning reliability of the assessment method by refining the dimensions of the interlocking structure, the layout of sensors at the monitoring section, the monitoring frequency, the parameter definition, and the background value correction and toxicity weighting methods. Attached Figure Description

[0045] Figure 1 This is a schematic cross-sectional view of the composite solidified soft soil subgrade filling structure of the present invention.

[0046] Figure 2 This is a partially enlarged schematic diagram of the interlocking structure between the core filling layer and the shell barrier zone of this invention.

[0047] Figure 3 This is a schematic diagram of the sensor network layout for the rainfall model test or on-site standard monitoring section of the present invention.

[0048] Figure 4 This is a schematic diagram of the slope foot directional guide and liquid collection unit of the present invention.

[0049] Figure 5 This is a flowchart illustrating the rainfall infiltration assessment and early warning method of the present invention.

[0050] Explanation of key symbols:

[0051] 1. Foundation treatment transition layer; 2. Bottom isolation and adsorption layer; 3. Core filling layer; 4. Top seepage prevention and drainage layer; 5. Shell barrier zone; 6. Ecological protection layer; 7. Side ditch; 8. Drainage blind ditch; 9. Leachate collection tank; 10. Sampling port; 11. Miniature earth pressure cell; 12. Moisture meter; 13. Conductivity probe; 14. pH probe; 15. Pore water pressure gauge; 16. Interface reinforcement layer; 17. Rainfall simulator; 18. Model box. Detailed Implementation

[0052] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are only for explaining the present invention and should not be construed as limiting the scope of protection of the present invention. Equivalent substitutions or modifications made by those skilled in the art to the various technical features without departing from the concept of the present invention should all fall within the scope of protection of the present invention.

[0053] Example 1:

[0054] like Figure 1 and Figure 2 As shown in the figure, this embodiment provides a composite solidified soft soil subgrade filling structure. This structure is suitable for new construction or reconstruction projects on soft soil foundations, and can simultaneously address the resource utilization of large quantities of solid waste, improve the bearing capacity of the subgrade, and protect environmental safety.

[0055] The roadbed filling structure, from bottom to top, includes: a bottom isolation and adsorption layer 2, a core filling layer 3, a shell barrier zone 5, and a top seepage-proof drainage layer 4. The core filling layer 3, situated above the bottom isolation and adsorption layer 2, is formed by solidifying soft soil with a multi-source solid waste-based composite cementitious material, and bears the main load-bearing and solid waste disposal functions. The shell barrier zone 5 covers the two side slopes and the outer top perimeter of the core filling layer 3, and is composed of low-permeability modified clay or heavy metal adsorbent material, forming lateral and top-level encapsulation barriers. The top seepage-proof drainage layer 4 covers the shell barrier zone 5 and is connected to it, used to systematically drain shallow infiltration water. The bottom isolation and adsorption layer 2, the shell barrier zone 5, and the top seepage-proof drainage layer 4 together constitute a "core-shell" seepage control path for the core filling layer 3, thereby extending the rainfall infiltration channel and inhibiting the migration of heavy metal leachate into the surrounding soil.

[0056] In addition, at the toe of the roadbed filling structure, there are side ditches 7, drainage blind ditches 8 and leachate collection tanks 9 that are connected to the top seepage prevention and drainage layer 4 and the bottom isolation and adsorption layer 2, which are used to collect and discharge leachate to prevent leachate from accumulating inside the roadbed or spreading to the surrounding area.

[0057] It should be noted that although the foundation treatment transition layer 1 is not a necessary means to achieve the purpose of inhibiting heavy metal leaching in this invention, in actual engineering, the foundation treatment transition layer 1 is generally set on the undisturbed foundation. The foundation treatment transition layer 1 can be made of lime-modified soil, graded crushed stone cushion layer, or shallow cement-soil treatment structure, with a preferred thickness of 0.20m to 0.40m, used to reduce uneven settlement of the foundation and improve overall stability. In this embodiment, the foundation treatment transition layer 1 is set below the bottom isolation adsorption layer 2.

[0058] In this embodiment, the bottom isolation adsorption layer 2 is disposed above the foundation treatment transition layer 1 (if no foundation treatment transition layer is disposed, it is disposed directly on the undisturbed foundation). The bottom isolation adsorption layer 2 consists of a compacted clay cushion layer, a reactive adsorption layer, and a geotextile or bentonite waterproof blanket, with a total thickness of 0.10m to 0.50m. The reactive adsorption layer can be made of zeolite, biochar, iron-based mineral powder, or their composite materials, and is used to fix and re-adsorb potentially infiltrating heavy metal ions. The geotextile or bentonite waterproof blanket further reduces permeability and blocks infiltration channels.

[0059] In this embodiment, the core filling layer 3 is the main load-bearing and solid waste disposal unit of the present invention. The core filling layer 3 is formed by solidifying soft soil with a multi-source solid waste-based composite cementitious material. The multi-source solid waste-based composite cementitious material includes at least two of steel slag, red mud, fly ash, and desulfurization gypsum, and may further include one or more of slag powder, lime, and alkaline activators.

[0060] To ensure solidification effect and volume stability, each solid waste raw material needs to be pretreated:

[0061] Steel slag: After being crushed, magnetically separated to remove iron, and naturally aged or steam aged, it is then ground to a specific surface area of ​​350m² / kg to 450m² / kg, so that the free calcium oxide content f-CaO is no more than 5%, in order to reduce the risk of volume stability.

[0062] Red mud: After dehydration, sun drying or low-temperature drying, the moisture content is controlled at 10% to 25%, the pH value is 10 to 12.5, and it is preferably ground to a 0.075mm sieve with a passing rate of not less than 85%.

[0063] Fly ash: Class II fly ash with a 45μm sieve residue of no more than 25% and a loss on ignition of no more than 8% is preferred.

[0064] Desulfurized gypsum: preferably with a moisture content of no more than 10%, and agglomerated impurities are removed by sieving.

[0065] The multi-source solid waste-based composite cementitious material accounts for 12% to 35% of the dry weight of the soft soil to be solidified, preferably 18% to 28%. In a preferred formulation, the composite cementitious material comprises, by mass percentage, 40% to 55% steel slag, 15% to 30% red mud, 10% to 25% fly ash, and 5% to 15% desulfurized gypsum, and the sum of the mass percentages of the above four components is not greater than 100%. As the most preferred example, the mass ratio of steel slag, red mud, fly ash, and desulfurized gypsum is 50:25:15:10, and it is incorporated at 20% to 28% (e.g., 25%) of the dry weight of the soft soil to be solidified.

[0066] In this embodiment, the construction process of the core fill layer 3 is as follows: The natural moisture content and optimum moisture content of the soft soil are determined in advance, and the mixture is prepared using plant mixing or on-site mixing methods. During mixing, the moisture content of the mixture is controlled to be 95%–102% of the optimum moisture content. Water is added and mixed in two stages, with each mechanical mixing session lasting no less than 120 seconds (range: 120s–180s). After mixing, the mixture is loaded and transported, with the transportation time preferably not exceeding 2 hours. During paving, the loose thickness of each layer is no more than 25cm (range: 20cm–25cm). After leveling with a grader, it is compacted using a combination of a vibratory roller and a pneumatic tire roller to achieve a compaction degree of no less than 93%–95%. After molding, it is cured for 7–28 days (range: 14d–28d) using methods such as moisture-retaining covering, spraying water, or film sealing. The resulting solidified soil has an unconfined compressive strength of not less than 1.5 MPa after 28 days, preferably not less than 2.0 MPa; the toxicity leaching performance meets the preset environmental control standards (such as GB 5085.3 "Identification Standard for Hazardous Waste: Leaching Toxicity Identification" or the relevant limits of GB / T14848 "Groundwater Quality Standard").

[0067] In this embodiment, the shell barrier 5 covers the two side slopes and the top outer perimeter of the core fill layer 3. The shell barrier 5 is composed of a modified clay matrix and one or more of bentonite, zeolite, biochar, sepiolite, attapulgite, and iron-based mineral powder dispersed in the modified clay matrix. The modified clay matrix is ​​modified by sodium carbonate solution, with a sodium carbonate solution mass fraction of 1% to 3%, and the curing time is 12h to 48h (range 24h).

[0068] In a preferred embodiment, the shell barrier strip 5 material comprises modified clay, bentonite, zeolite, and biochar in a mass ratio of 80:10:5:5. During construction, the moisture content of the mixture is controlled at 20%–25%, and a layered filling and compaction process is adopted. The loose thickness of each layer is no more than 20 cm, and the thickness of a single layer after compaction is 0.10 m–0.20 m, with a total thickness of 0.15 m–0.60 m (preferably 0.20 m–0.40 m). The dry density after compaction is no less than 1.65 g / cm³. The field permeability coefficient is controlled by ring sampling, indoor permeability testing, or on-site sealing testing methods, and is required to be no greater than 1 × 10⁻⁶. -7 cm / s.

[0069] In this embodiment, the top impermeable drainage layer 4 covers and communicates with the shell barrier zone 5. The top impermeable drainage layer 4 includes a sealing layer, a drainage layer, and a protective layer arranged sequentially from bottom to top. The sealing layer can be a fine-grained low-permeability soil layer or a geosynthetic composite layer; the drainage layer can be a graded crushed stone layer or a permeable board layer, with a cross slope or longitudinal slope of 2% to 4%; the protective layer can be a vegetated soil layer, a graded crushed stone layer, or a combination of both, or a turf slope protection or erosion control cover layer. The top impermeable drainage layer 4 is continuously connected to the shell barrier zone 5 and communicates with the slope toe ditch 7, the drainage blind ditch 8, and the leachate collection tank 9 to quickly drain shallow infiltrated water.

[0070] As an optional embodiment of the present invention, in order to improve the interface stability between the core filling layer 3 and the shell barrier zone 5 and weaken the preferential seepage at the interface, a stepped or toothed interface interlocking structure is provided between the core filling layer 3 and the shell barrier zone 5, and a geogrid, geotextile or fiber reinforcement layer 16 is provided at the interface interlocking structure.

[0071] Stepped interface interlocking structure: Each step has a width of 0.30m to 0.50m, a height of 0.20m to 0.30m, and a slope of 1:1.5 to 1:2.0.

[0072] Toothed interface interlocking structure: the toothed groove width is 0.08m~0.15m, the depth is 0.10m~0.20m, and the distance between adjacent toothed grooves is 0.15m~0.30m.

[0073] The aforementioned geometric dimensions can improve the interface's anti-slip and anti-cracking properties while extending the infiltration channel.

[0074] To monitor the performance of the roadbed during its service life, the roadbed filling structure of the present invention may further include a monitoring unit. The monitoring unit includes:

[0075] Miniature earth pressure cells 11 are installed in the easily expansive zone inside the core fill layer 3 to monitor local expansion stress;

[0076] Moisture meter 12 is installed at the interface between the core fill layer 3 and the shell barrier zone 5 to monitor changes in moisture content;

[0077] Sampling ports 10 and pore water pressure gauges 15 are installed in the core filling layer 3, the outer side of the shell barrier zone 5 or in the surrounding soil.

[0078] Conductivity probe 13 and pH probe 14 are installed at the drainage blind ditch 8 or leachate collection tank 9.

[0079] The specific location and number of monitoring units can be adjusted according to project requirements and cross-sectional dimensions, as detailed in Example 2.

[0080] Example 2:

[0081] This embodiment provides a rainfall infiltration early warning method applicable to the roadbed filling structure described in Embodiment 1. This method dynamically acquires "hydraulic-mechanical-chemical" indicators through indoor rainfall model tests or field monitoring test sections, establishes a tiered early warning judgment logic based on a comprehensive risk index, and achieves graded identification of rainfall infiltration, heavy metal migration, and environmental risks.

[0082] like Figure 3 and Figure 4 As shown, a monitoring section is established in the roadbed filling structure. With the centerline of the roadbed cross-section as x=0 and the longitudinal mileage direction of the roadbed as the y-axis, the monitoring section is selected at y=0, with the top surface of the core filling layer as z=0 and downwards as the positive direction. Taking a typical section as an example: the top width of the core filling layer is 6.0m, and the vertical distance H from the top surface of the core filling layer to the bottom surface of the bottom isolation and adsorption layer is 2.40m.

[0083] In this scheme, the monitoring sensors and sampling points are deployed as follows:

[0084] Miniature earth pressure cells 11 are installed in the easily expandable zone inside the core fill layer 3, with preferred locations at (0, 0, 0.80m) and (±1.50m, 0, 1.40m).

[0085] Moisture meters 12 are installed at the interface between the core filling layer 3 and the shell barrier zone 5, with preferred locations being (±2.70m, 0, 0.20m), (±2.90m, 0, 0.80m) and (±3.10m, 0, 1.60m).

[0086] Sampling ports 10 and pore water pressure gauges 15 are installed in the soil outside the core filling layer 3 and the shell barrier zone 5 or in the surrounding soil. For example, pore water pressure gauges 15 are added near (±2.50m, 0, 1.20m).

[0087] Conductivity probe 13 and pH probe 14 are installed at the drainage ditch 8 and leachate collection tank 9 at the toe of the slope, preferably at a location near (±4.20m, 0, 2.55m).

[0088] The above-mentioned point layout method can be used for on-site monitoring sections, or scaled down for model box 18 according to the principle of geometric similarity (e.g., Figure 3 (As shown).

[0089] In practical implementation, at least one rainfall scenario should be set up for rainfall simulation (indoor model test) or on-site monitoring (natural rainfall or artificially simulated rainfall). The rainfall scenario should include at least regular rainfall, continuous rainfall, and extreme rainfall after experiencing a preset wet-dry cycle. The rainfall intensity is preferably 20 mm / h to 150 mm / h, and the rainfall duration is preferably 0.5 h to 24 h. The number of wet-dry cycles can be set from 1 to 30 times according to project needs.

[0090] 3. The specific steps for collecting data by time series are as follows:

[0091] The following data were collected in time series format:

[0092] seepage flow (Unit: L / s or m³ / s);

[0093] Moisture content (unit:%);

[0094] Pore ​​water pressure u(t) (unit: kPa);

[0095] pH value pH(t);

[0096] Electrical conductivity EC(t) (unit: μS / cm);

[0097] The concentration of the i-th heavy metal was collected at the slope toe drainage area, drainage blind ditch and leachate collection tank. Unit: mg / L)

[0098] The concentration of the i-th heavy metal collected from the interface or internal sampling points (Unit: mg / kg or mg / L), where i represents the heavy metal type number (such as Cr, Pb, As, Cd, etc.), and j represents the sampling point number;

[0099] Simultaneously, the depth value of each sampling point relative to a unified depth benchmark (with the top surface of the core fill layer as z=0) is recorded. (Unit: m).

[0100] The monitoring frequency will be implemented according to the following strategy:

[0101] For the first 2 hours after rainfall begins: record data every 15 minutes;

[0102] Within 2 hours to 12 hours: Record data once every hour;

[0103] From 12 hours later until 48 hours after the rainfall stops: record data every 6 hours;

[0104] During the drying phase of the wet-dry cycle test: data was recorded every 12 hours.

[0105] 4. Calculate the comprehensive risk index R(t)

[0106] Based on the collected data, the key parameters are first defined:

[0107] Effective seepage cross-sectional area A: defined as the cross-sectional area perpendicular to the direction of water flow where seepage occurs. In indoor model tests, A is the product of the model box width and the effective seepage thickness of the core fill layer or the effective seepage thickness at the interface between the core fill layer and the shell barrier zone; in field monitoring, A is the cross-sectional area of ​​potential seepage channels in a unit width of roadbed section.

[0108] Total monitoring depth H: defined as the vertical distance from the top surface of the core filling layer to the bottom surface of the bottom isolation and adsorption layer.

[0109] Control concentration The standard is determined with reference to the "Groundwater Quality Standard" (GB / T 14848), the "Surface Water Environmental Quality Standard" (GB 3838), or the corresponding environmental quality control standards.

[0110] Controlling migration flux The value is determined through preliminary soil column tests, small-scale model tests, environmental impact assessment limits, or calibration values ​​of similar projects.

[0111] Then calculate each risk item using the following formula:

[0112] Concentration risk item , The control concentration of the i-th heavy metal;

[0113] Migration flux risk item ,in = A is the effective seepage cross-sectional area. Let i be the controlled migration flux of the i-th heavy metal;

[0114] Migration depth risk items ,in H represents the total monitoring depth;

[0115] Overall Risk Index , where a, b, and c are weighting coefficients and a+b+c=1.

[0116] Where a, b, and c are weighting coefficients, and a + b + c = 1. The weighting coefficients can be determined based on the importance of the project and the sensitivity of the environment, for example, a = 0.4, b = 0.3, and c = 0.3.

[0117] Preferably, before calculating the comprehensive risk index, the concentrations of each monitored heavy metal ion are corrected for background values:

[0118] Before the test or on-site monitoring, the background concentration of the i-th heavy metal was measured in unaffected soil or background water samples in the surrounding area. .

[0119] Background correction concentration at the slope toe drainage area:

[0120]

[0121] Background value correction concentration at sampling point:

[0122]

[0123] Furthermore, based on background value correction, a toxicity response coefficient is used. The concentrations of each heavy metal were weighted. The toxicity response coefficients were determined using the Hakanson potential ecological risk index method: Hg=40, Cd=30, As=10, Pb=5, Cr=2, Zn=1. After background value correction and weighting by the toxicity response coefficients, each risk item was calculated using the following formula:

[0124]

[0125]

[0126]

[0127]

[0128]

[0129] 5. Tiered early warning

[0130] The comprehensive risk index R(t) is compared with at least one preset threshold, and a graded early warning result and corresponding handling suggestions are output based on the comparison result. This embodiment adopts a four-level early warning determination method:

[0131] Green alert: When R(t) < 0.50, it indicates that the overall seepage prevention and control status of the structure is good, and only routine inspection is required.

[0132] Yellow alert: When 0.50 ≤ R(t) < 0.80, it indicates that local infiltration channels have begun to develop. The integrity of the surface layer of the side ditch 7, drainage blind ditch 8 and shell barrier zone 5 should be checked, and local dredging, repair and surface compaction should be carried out.

[0133] Orange alert: When 0.80 ≤ R(t) < 1.00, it indicates a significant increase in the risk of heavy metal migration. Local adsorption and barrier materials should be added, slope toe interception and drainage should be strengthened, and load control should be implemented as appropriate.

[0134] Red alert: When R(t) ≥ 1.00, emergency interception, rapid sealing, and local replacement or grouting repair should be implemented immediately to block the seepage channels and escape paths.

[0135] The composite solidification soft soil subgrade filling structure and rainfall infiltration assessment method for inhibiting heavy metal leaching from multi-source solid waste provided by this invention can be widely applied to new or expanded soft soil subgrade projects. Through the "core-shell" seepage control structure design, the large-scale resource utilization of multi-source solid waste and the environmental safety protection of the subgrade are synergistically unified. The dynamic early warning method enables the graded identification of rainfall infiltration, heavy metal migration, and environmental risks, providing a scientific basis for the safe operation and maintenance of the subgrade during its service life.

[0136] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various modifications and refinements without departing from the concept of the present invention, and all such modifications and refinements should fall within the protection scope of the present invention.

Claims

1. A composite solidified soft soil subgrade filling structure, characterized in that, include: Bottom isolation and adsorption layer; The core filling layer, located above the bottom isolation and adsorption layer, is formed by solidifying soft soil with multi-source solid waste-based composite cementitious material; The shell barrier zone, which covers the two sides of the core filling layer and the top outer perimeter, is composed of low-permeability modified clay or heavy metal adsorbent material. A top impermeable and drainage layer covers the shell barrier band and is in communication with the shell barrier band; The bottom isolation and adsorption layer, the shell barrier strip, and the top seepage prevention and drainage layer together constitute the "core-shell" seepage prevention and control path for the core filling layer. The slope toe of the roadbed filling structure is provided with side ditches, drainage blind ditches, and leachate collection tanks that are connected to the top seepage-proof drainage layer or the bottom isolation and adsorption layer.

2. The composite solidified soft soil subgrade filling structure according to claim 1, characterized in that, The multi-source solid waste-based composite cementitious material includes at least two of steel slag, red mud, fly ash, and desulfurized gypsum, and may further include one or more of slag powder, lime, and alkaline activator; the multi-source solid waste-based composite cementitious material accounts for 12% to 35% of the dry mass of the soft soil to be solidified.

3. The composite solidified soft soil subgrade filling structure according to claim 1, characterized in that, The shell barrier zone is composed of a modified clay matrix and one or more of bentonite, zeolite, biochar, sepiolite, attapulgite and iron-based mineral powder dispersed in the modified clay matrix. The modified clay matrix is ​​modified by sodium carbonate solution, the mass fraction of which is 1% to 3%, and the curing time is 12h to 48h.

4. The composite solidified soft soil subgrade filling structure according to claim 3, characterized in that, The thickness of the shell barrier is 0.15m to 0.60m, and the permeability coefficient is no greater than 1×10⁻ 7 cm / s; the mass ratio of modified clay, bentonite, zeolite and biochar in the shell barrier material is 80:10:5:

5. During construction, the moisture content of the mixture is controlled at 20% to 25%. It is formed by layered filling, with each layer having a loose thickness of no more than 20cm and a dry density of no less than 1.65g / cm³ after compaction.

5. The composite solidified soft soil subgrade filling structure according to claim 1, characterized in that, The bottom isolation and adsorption layer consists of a compacted clay cushion layer, a reactive adsorption layer, and a geotextile or bentonite waterproof blanket; the top seepage-proof drainage layer includes a sealing layer, a drainage layer, and a protective layer arranged sequentially from bottom to top. The cross slope or longitudinal slope of the drainage layer is 2% to 4%, and the protective layer is a vegetated soil layer, a graded crushed stone layer, or a combination of both.

6. The composite solidified soft soil subgrade filling structure according to claim 1, characterized in that, A stepped or toothed interface interlocking structure is provided between the core filling layer and the shell barrier zone, and a geogrid, geotextile or fiber reinforcement layer is provided at the interface interlocking structure.

7. The composite solidified soft soil subgrade filling structure according to claim 1, characterized in that, It also includes a monitoring unit, which includes a miniature earth pressure cell deployed in the easily expansive zone inside the core fill layer, a moisture meter deployed in the interface area between the core fill layer and the shell barrier zone, a sampling port and a pore water pressure meter deployed in the core fill layer, the outer side of the shell barrier zone or the surrounding soil, and a conductivity probe and a pH probe deployed in the drainage ditch and leachate collection tank.

8. A method for early warning of rainfall infiltration in composite solidified soft soil subgrade filling structures according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Establish a monitoring section in the roadbed filling structure, and deploy monitoring sensors and sampling points inside the core filling layer, at the interface between the core filling layer and the shell layer barrier zone, and in the slope toe drainage area. S2. Set at least one rainfall scenario and conduct rainfall simulation or on-site monitoring; S3. Collect data according to time series, the data including seepage flow. Moisture content pore water pressure pH value Electrical conductivity The concentration of the i-th heavy metal collected in the slope toe drainage area. The concentration of the i-th heavy metal collected from the interface or internal sampling points And record the depth value of each sampling point relative to a unified depth reference. In the formula, Indicates the heavy metal type code. Indicates the sampling point number. Indicates the first The depth value of each sampling point relative to a unified depth reference; S4. Calculate the comprehensive risk index based on the collected data. ,in: Concentration risk item , The control concentration of the i-th heavy metal; Migration flux risk item ,in = A is the effective seepage cross-sectional area. Let i be the controlled migration flux of the i-th heavy metal; Migration depth risk items ,in H represents the total monitoring depth; Overall Risk Index , where a, b, and c are weighting coefficients and a+b+c=1; S5. The comprehensive risk index It is compared with at least one preset threshold, and a graded early warning result is output based on the comparison result.

9. The rainfall infiltration early warning method according to claim 8, characterized in that, The effective seepage cross-sectional area A mentioned in step S4 is defined as the cross-sectional area perpendicular to the water flow direction where seepage occurs; in the indoor model test, A is the product of the model box width and the effective seepage thickness of the core filling layer or the effective seepage thickness of the interface between the core filling layer and the shell barrier zone. In on-site monitoring, A is taken as the cross-sectional area of ​​potential seepage channels in a unit width roadbed section; the total monitoring depth H is defined as the vertical distance from the top surface of the core filling layer to the bottom surface of the bottom isolation and adsorption layer.

10. The rainfall infiltration early warning method according to claim 8, characterized in that, In step S4, the comprehensive risk index is calculated. Previously, background values ​​were corrected for the concentrations of each monitored heavy metal ion: the background value correction concentration of the i-th heavy metal at the slope toe drainage area, drainage blind ditch, and leachate collection tank. ; Background correction concentration of the i-th heavy metal at the j-th sampling point ;in The background concentration of the i-th heavy metal is measured in unaffected soil or background water samples before the test or on-site monitoring. In step S4, based on the background value correction, the toxicity response coefficient is further used. The toxicity response coefficient is weighted according to the concentration of each heavy metal; The parameters are: Hg=40, Cd=30, As=10, Pb=5, Cr=2, Zn=1; after background value correction and weighting by toxicity response coefficient, the concentration risk term, migration flux risk term, and migration depth risk term are calculated according to the following formulas: ； ； ； ； ； Wherein: the controlled concentration in step S4 The controlled migration flux is determined by referring to groundwater quality standards, surface water quality standards, or corresponding environmental quality control standards. Determined through preliminary soil column tests, small-scale model tests, environmental impact assessment limits, or calibration values ​​of similar projects; The graded early warning results mentioned in step S5 include: a green warning when R(t) < 0.50, indicating that the seepage prevention and control status is good; a yellow warning when 0.50 ≤ R(t) < 0.80, indicating that local infiltration channels have begun to develop; an orange warning when 0.80 ≤ R(t) < 1.00, indicating that the risk of heavy metal migration has increased significantly; and a red warning when R(t) ≥ 1.00, indicating that seepage channels and escape paths have been formed and immediate action is required.

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