Capillary resistance covering layer for soil dump in seasonal frozen region and preparation method and application thereof

Abstract

The application discloses a kind of seasonal frozen region dump capillary resistance coverings and preparation method and application thereof, belong to mine environmental protection and tailings processing technical field.The covering is sequentially arranged secondary impermeable layer, capillary resistance covering and ploughing soil layer from bottom to top.Secondary impermeable layer is clay layer with compaction degree ≥95%, and the thickness is 20-30cm;Capillary resistance covering includes coarse-grained drainage layer and water storage layer, and the coarse-grained drainage layer is slag with particle size 5-15mm, and the thickness is 20-30cm;Water storage layer is the mixture of clay and slag, and 2%-5% silicone is added, and the compaction degree is 85%-90%, and the thickness is 80-100cm;Ploughing soil layer is the mixture of clay and slag, and 1.0%-2.0% guar gum is added, and the compaction degree is 75%-80%, and the thickness is 30-40cm.The application effectively blocks capillary water rise by multilayer structure design and specific material proportioning, improves water storage capacity, and provides good environment for plant growth.

Description

Technical Field

[0001] This invention belongs to the field of mine environmental protection and tailings treatment technology, specifically relating to a capillary barrier covering layer for spoil heaps in seasonally frozen areas, its preparation method, and its application. Background Technology

[0002] With the continuous increase in mining activities, spoil heaps, as dumping grounds for solid waste from mines, are facing increasingly prominent environmental management and ecological restoration challenges. Spoil heap cover layers, as a key technical measure to prevent the spread of pollutants and promote ecological restoration, directly impact the effectiveness of mine environmental management through their design and construction quality. Especially in seasonally frozen soil areas, due to freeze-thaw cycles, traditional cover layers often face problems such as decreased impermeability and poor structural stability, making it difficult to meet the requirements for long-term stable operation.

[0003] Currently, research on spoil heap cover layers both domestically and internationally mainly focuses on seepage prevention, moisture control, and ecological restoration. In terms of seepage prevention technology, commonly used methods include compacted clay layers, geomembranes, and composite liners. Chinese invention patent CN115012455B discloses a capillary-retaining cover layer that promotes uniform distribution of interception drainage and landfill gas. This cover layer utilizes the capillary retraction effect formed at the interface between the fine-grained soil layer and the gravel layer to impede rainwater infiltration, allowing water to migrate along the interface to the gravel mound, reducing leachate production. Chinese invention patent CN109930611B proposes a capillary-retaining cover layer for slope protection. This cover layer includes a water-storage greening layer and a drainage layer arranged sequentially from the outside in. By reducing rainwater infiltration into the slope, it maintains a low moisture content in the slope, thereby preserving slope stability.

[0004] In terms of material selection, the resource utilization of industrial solid waste has become a research hotspot in recent years. Chinese invention patent CN116811374A discloses a self-healing cover layer primarily composed of tailings sand. This cover layer, from bottom to top, includes a coarse tailings salt-isolating layer, a fine tailings water-isolating layer, a coarse tailings capillary barrier layer, a fine tailings water-retaining layer, and a fine tailings nutrient soil layer, realizing the resource utilization of tailings sand while reducing the construction cost of the cover layer. Chinese invention patent CN111636443B proposes a shallow water-controlling cover system for expansive soil slopes based on capillary retardation mechanisms. This system, from top to bottom, consists of a vegetation layer, a fine-grained layer, a wicking layer, a coarse-grained layer, and a water-retaining fine-grained layer, effectively maintaining the stable water content of the slope. Chinese invention patent CN115012454B discloses a solid waste-based composite landfill cover barrier system. The system includes a capillary barrier layer, a seepage drainage layer and a water-blocking and air-tight layer stacked from the outside to the inside. It aims to solve engineering problems such as compacted clay shrinkage cracking and geomembrane bulging or tearing in existing cover barrier systems.

[0005] However, existing technologies for spoil heap cover layers still have the following problems: First, traditional compacted clay single cover layers are prone to hardening and have poor air permeability, leading to long-term accumulation of atmospheric precipitation in local layers of the cover layer during the rainy season, causing root rot due to lack of oxygen and affecting ecological restoration. Second, under freeze-thaw conditions, the pore structure of clay soil deteriorates significantly, reducing its impermeability and resulting in poor long-term stability. Third, impermeability methods relying on high-density polyethylene (HDPE) membranes are at risk of aging and damage, and seasonal freeze-thaw cycles will exacerbate this aging process, resulting in a limited service life and secondary pollution after disposal. Fourth, existing cover layer designs do not utilize the slag solid waste in spoil heaps, which is not conducive to the comprehensive utilization of spoil heap solid waste. Finally, in seasonally frozen soil areas, spoil heap cover layers must simultaneously meet technical requirements such as freeze-thaw stability, efficient moisture control, low cost and ecological compatibility, and no secondary pollution, which existing technologies cannot simultaneously meet. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a capillary barrier cover layer for spoil heaps in seasonally frozen areas, its preparation method and application, so as to solve the technical problems of poor seepage prevention performance, low freeze-thaw stability and insufficient ecological compatibility of traditional cover layers, and at the same time realize the resource utilization of mine solid waste.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] In a first aspect, the present invention provides a capillary barrier cover layer for spoil heaps in seasonally frozen areas, comprising a secondary impermeable layer, a capillary barrier cover layer and a topsoil layer arranged sequentially from bottom to top.

[0009] The secondary impermeable layer is a clay layer with a compaction degree of ≥95%, a thickness of 20~30cm, and a saturated permeability coefficient of 1×10⁻⁶. -6 ~1×10 -7 m / s;

[0010] The capillary barrier covering layer includes a coarse-grained drainage layer and a water storage layer. The coarse-grained drainage layer is laid on the secondary seepage prevention layer. The material of the coarse-grained drainage layer is slag with a particle size of 5-15mm and a thickness of 20-30cm.

[0011] The water storage layer is laid on the coarse-grained drainage layer and is a soil-rock mixture composed of clay and slag, wherein 2% to 5% of the total mass of the soil-rock mixture is added. It is constructed by layered compaction, with each layer having a compaction thickness of 20 to 25 cm, compacted to 85% to 90% compaction degree, and a total thickness of 80 to 100 cm.

[0012] The topsoil layer is laid on top of the water storage layer and is a soil-rock mixture composed of clay and slag, wherein 1.0% to 2.0% of guar gum is added to the soil-rock mixture by mass, and then it is compacted to a compaction degree of 75% to 80% and a thickness of 30 to 40 cm.

[0013] A further improvement of the present invention is that the clay layer of the secondary impermeable layer is made of low plasticity clay with a liquid limit ≤40% and a plastic limit ≥15%.

[0014] A further improvement of the present invention is that the slag in the coarse-grained discharge layer is made from mine waste rock or tailings slag.

[0015] A further improvement of the present invention is that the particle size of the slag in the water storage layer is 5~15mm.

[0016] A further improvement of the present invention is that the mass ratio of clay to slag in the water storage layer is (1~2):1.

[0017] A further improvement of the present invention is that the mass ratio of clay to slag in the cultivated soil layer is 1:(1~4).

[0018] Secondly, the present invention also provides a method for preparing a capillary retaining cover layer for spoil heaps in seasonally frozen areas, comprising the following steps:

[0019] Step 1: Level and compact the surface of the mine spoil heap, lay clay and compact it in layers until the compaction degree is ≥95%, forming a secondary seepage prevention layer with a thickness of 20~30cm;

[0020] Step 2: Spread slag with a particle size of 5-15mm evenly on the secondary seepage barrier layer to form a coarse-grained drainage layer with a thickness of 20-30cm.

[0021] Step 3: Mix clay and slag according to the design ratio to form the first soil-rock mixture. Add 2% to 5% of organosilicon by mass to the first soil-rock mixture to obtain a modified filler. Spread and compact the modified filler in several layers on the coarse-grained drainage layer. The compaction thickness of each layer is 20 to 25 cm and the compaction degree is 85% to 90%, thereby forming a water storage layer with a total thickness of 80 to 100 cm.

[0022] Step 4: Mix clay and slag according to the design ratio to form a second soil-rock mixture. Add 1.0% to 2.0% of guar gum by weight to the second soil-rock mixture to obtain topsoil. Spread the topsoil on the water storage layer and then compact it to a compaction degree of 75% to 80% to form a topsoil layer with a thickness of 30 to 40 cm.

[0023] A further improvement of the present invention is that, in step 3, after adding organosilicon to the first soil-rock mixture, the mixture is stirred for 2 to 5 minutes until it is uniformly mixed.

[0024] A further improvement of the present invention is that, in step 3, when spreading and compacting each layer of the modified filler, the initial moisture content of the modified filler is controlled to be 12%~20%;

[0025] In step 4, when spreading the topsoil layer, the initial moisture content of the topsoil is controlled to be 12%~20%.

[0026] Thirdly, the present invention also provides an application of a capillary barrier cover layer for mine spoil heaps in seasonally frozen areas in areas with ecological restoration needs.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention provides a capillary-retaining cover layer for spoil heaps in seasonally frozen areas. This cover layer, through a multi-level synergistic design, achieves a synergistic effect between solid waste resource utilization and ecological restoration. Its core structure, from bottom to top, includes: a secondary impermeable layer, a capillary-retaining cover layer, and a topsoil layer. The secondary impermeable layer is a clay layer with a compaction degree of not less than 95% and a thickness of 20-30 cm, with its saturated permeability coefficient controlled at 1×10⁻⁶. -6 ~1×10 -7The capillary retaining cap layer, designed to form a high-density bottom barrier, effectively prevents groundwater from migrating upwards or leachate from seeping downwards, providing a reliable seepage-proof foundation for the entire capping system. As the core functional layer, the capillary retaining cap layer sits above the secondary seepage-proof layer and consists of a coarse-grained drainage layer and a water-storage layer. The coarse-grained drainage layer uses slag with a particle size of 5-15 mm and a thickness of 20-30 cm. Its large porosity allows for rapid drainage of excess water during wet periods, preventing water accumulation. Under dry conditions, the significant particle size difference between the coarse-grained layer and the overlying material creates a capillary retaining effect, effectively hindering water infiltration and loss. The water storage layer is a soil-rock mixture composed of clay and slag, with 2%–5% organosilicon added. It is compacted in layers to 85%–90% compaction, with a total thickness of 80–100 cm. The addition of organosilicon enhances the material's hydrophobicity. Combined with appropriate compaction, this layer possesses good water-holding capacity even in an unsaturated state, storing the water needed for vegetation growth while avoiding excessively low permeability due to over-compaction. The uppermost topsoil layer is also a soil-rock mixture composed of clay and slag, with guar gum added to reduce surface permeability. Compaction is controlled at 75%–80%, with a thickness of 30–40 cm. The relatively low compaction creates favorable conditions for plant root growth. This layer also provides physical protection for the underlying water storage layer, helping to mitigate the negative impact of seasonal freeze-thaw cycles on the capillary-resistant cover structure's integrity and water storage function. The capping layer structure of this invention, through the optimized combination of coarse and fine particulate materials and the addition of organosilicon and guar gum, synergistically exerts the functions of capillary impingement, dynamic moisture regulation, and long-term seepage prevention. Its parameter settings ensure a more uniform moisture distribution field under the complex freeze-thaw cycles and alternating wet and dry climate conditions of seasonally frozen regions. This effectively prevents surface water accumulation that could lead to plant root rot, while also avoiding excessive moisture loss that could cause drought in the ecological layer. Ultimately, it achieves the dual goals of comprehensive utilization of mine solid waste and geological environmental protection.

[0029] The present invention also provides a method for preparing a capillary barrier cover layer for spoil heaps in seasonally frozen areas. This preparation method achieves efficient utilization of solid waste slag through layered implementation and material ratio control, and constructs a composite cover layer with seepage prevention, water conduction, water storage and ecological restoration functions. The preparation process is simple and can significantly improve the soil and water conservation capacity and adaptability of the cover layer to seasonally frozen environments. Attached Figure Description

[0030] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and do not specifically limit the shapes and proportions of the components of the invention.

[0031] Figure 1 This is a schematic diagram of the cover layer structure of the present invention;

[0032] Figure 2 The soil-water characteristic curves represent the enhanced effect of capillary resistance between the water storage layer and the coarse-grained drainage layer in this invention.

[0033] Figure 3 This is a plan view of the test site layout for the present invention;

[0034] Figure 4 These are the cumulative rainfall curves during the test periods of Examples 1 and 2 of the present invention;

[0035] Figure 5 The figures show the measured water storage capacity changes of the cover layer in each embodiment and the control group during the actual measurement period of this invention.

[0036] Figure 6(a) shows the soil-water characteristic curves and pore evolution characteristics of the reservoir with 50% stone content + 2% organosilicon + 1.5% guar gum after different freeze-thaw cycles according to the present invention.

[0037] Figure 6(b) shows the soil-water characteristic curves and pore evolution characteristics of the reservoir with 50% stone content after different freeze-thaw cycles according to the present invention.

[0038] Figure 7 Numerical modeling of the same overlay structure in Embodiment 3 of the present invention;

[0039] Figure 8(a) shows the curves of water potential at different depths of the reservoir after freeze-thaw cycles in Example 1 of the present invention as a function of rainfall time.

[0040] Figure 8(b) shows the curves of water potential at different depths of the reservoir after freeze-thaw cycles in Example 2 of the present invention as a function of rainfall time;

[0041] Figure 9(a) shows the comparison between the simulated and theoretical values ​​of the water storage capacity of the coating layer with 50% stone content + 2% organosilicon + 1.5% guar gum after 10 freeze-thaw cycles in Example 1 of the present invention.

[0042] Figure 9(b) shows the comparison between the simulated and theoretical values ​​of the water storage capacity of the cover layer with 50% stone content after 10 freeze-thaw cycles in Example 2 of the present invention.

[0043] The structure consists of: 1. Topsoil layer; 2. Water storage layer; 3. Coarse-grained drainage layer; 4. Secondary seepage prevention layer; 5. Waste dump pile. Detailed Implementation

[0044] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0045] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0046] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0047] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0048] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0049] This invention targets large-scale mine spoil heaps in seasonally frozen soil areas. Through indoor and field tests, it verifies the effects of organosilicon modification and layered design. It utilizes the difference in water-holding capacity between the mine tailings and fine-grained soil components in the spoil heap to create a capillary barrier effect. The freeze-thaw resistance of the mixed coarse and fine-grained components is adapted to seasonally frozen mining areas. Organosilicon enhances the barrier effect and freeze-thaw stability, providing a convenient and low-cost capping layer solution. While addressing the water retention and seepage prevention needs during mine ecological restoration, it also achieves more efficient utilization of mine solid waste.

[0050] like Figure 1 As shown, this invention provides a capillary barrier capillary cover layer for spoil heaps in seasonally frozen areas, comprising, from bottom to top, a secondary impermeable layer 4, a capillary barrier capillary cover layer, and a topsoil layer 1 disposed on the surface of the spoil heap body 5; the secondary impermeable layer 4 is a clay layer with a compaction degree ≥95%, a thickness of 20~30cm, and a saturated permeability coefficient of 1×10⁻⁶. -6 ~1×10 -7m / s; The capillary barrier capillary layer includes a coarse-grained drainage layer 3 and a water storage layer 2. The coarse-grained drainage layer 3 is laid on top of the secondary seepage barrier layer 4. The material of the coarse-grained drainage layer 3 is slag with a particle size of 5~15mm and a thickness of 20~30cm. The water storage layer 2 is laid on top of the coarse-grained drainage layer 3. It is a soil-rock mixture composed of clay and slag, with 2%~5% of organosilicon added to the total mass of the soil-rock mixture. It is constructed by layered compaction, with each layer compacted to a thickness of 20~25cm, compacted to 85%~90% of the compaction degree, and a total thickness of 80~100cm. The topsoil layer 1 is laid on top of the water storage layer 2. It is a soil-rock mixture composed of clay and slag, with 1.0%~2.0% of guar gum added to the total mass of the soil-rock mixture. It is then compacted to 75%~80% of the compaction degree and has a thickness of 30~40cm.

[0051] The coarse-grained drainage layer 3 and the water storage layer 2 together form the core functional unit of the capillary barrier capillary layer. These two layers of materials, through a specific particle size ratio, create a significant capillary barrier effect. The working principle is as follows: the capillary barrier band formed at the coarse-fine particle interface effectively blocks water infiltration, causing water to accumulate inside the water storage layer 2 above the coarse-grained drainage layer 3. Only when there is a short period of heavy rainfall exceeding the design capacity of the capillary barrier band will excess water penetrate the water storage layer 2 and enter the coarse-grained drainage layer 3, where it is quickly drained away through the water-conducting channels.

[0052] The secondary impermeable layer 4 serves as the foundational impermeable barrier of the cover system. Located at the deepest part of the structure, it is less directly affected by seasonal freeze-thaw cycles. Compared to traditional single-layer clay impermeable layers, this layer primarily acts as a reliable underlying layer for the upper coarse-grained drainage layer 3, providing final impermeability in the event of temporary capillary action due to extreme rainfall events causing minor leakage. This layer is constructed using low-plasticity clay with a liquid limit ≤40% and a plastic limit ≥15%, and is compacted to a high standard (compaction degree ≥95%) to form a continuous and dense water-resistant barrier. The selection of low-plasticity clay effectively reduces the material's frost heave sensitivity and enhances the long-term stability of this layer under seasonally frozen conditions.

[0053] The coarse-grained drainage layer 3 is made from solid waste such as mine waste rock or tailings slag through crushing and screening, and is a key layer for moisture control. This layer strictly controls the slag particle size within the range of 5-15 mm, with a thickness of 20-30 cm. Its core function is dual: firstly, as a component of the capillary repression system, its large porosity constitutes a low water-holding capacity layer, which, through the difference in particle size distribution with the upper water storage layer 2, forms and enhances the capillary repression effect; secondly, as an emergency drainage channel, it effectively drains seepage water after the water storage layer 2 becomes saturated, preventing water accumulation within the layer.

[0054] The water storage layer 2 is the core component of the overburden system for water retention. It is composed of clay and slag with a specific particle size range (5-15mm) mixed at a mass ratio of (1-2):1, with 2%-5% of an organosilicon amendment added to the total mass of the soil-rock mixture. It is constructed through layered compaction, with a total thickness of 80-100cm. Maintaining the slag particle size in water storage layer 2 is consistent with that of the underlying coarse-grained drainage layer 3 facilitates material preparation and construction quality control. The addition of organosilicon enhances the hydrophobicity of the mixture, and combined with 85%-90% layered compaction, this layer possesses excellent water-holding capacity even in an unsaturated state. Indoor tests have shown that... Figure 2 The soil-water characteristic curve shown indicates that the air suction difference between the water storage layer 2 and the coarse-grained drainage layer 3 under this mix ratio and compaction degree is consistently ≥0.7 kPa, ensuring the effectiveness of the capillary retardation interface. During construction, the mixture of water storage layer 2 must be thoroughly mixed to ensure uniformity, followed by layer-by-layer laying and compaction. The loose thickness of each layer is controlled at 25~30 cm, and the compacted thickness of a single layer is 20~25 cm. During the compaction process of each layer, the initial moisture content must be strictly controlled within the optimized range of 12%~20%, and the compaction degree must be ensured to meet the design requirement of 85%~90% through on-site testing. All layers are laid and compacted to a total thickness of 80~100 cm.

[0055] The uppermost topsoil layer 1 is made by mixing clay and slag in a mass ratio of 1:(1~4), and adding 1.0%~2.0% guar gum by mass of the total soil-rock mixture. Guar gum can effectively promote the formation of stable aggregates of soil particles, significantly enhancing the erosion resistance and water retention capacity of topsoil layer 1. This ratio is conducive to forming a soil structure suitable for plant root growth. The compaction degree of this layer is controlled at a low level of 75%~80%, providing a foundation for vegetation restoration.

[0056] This invention also provides a method for preparing a capillary retardant cover layer for seasonally frozen waste dumps based on solid waste slag and organosilicon materials, comprising the following steps:

[0057] Step 1: Level and compact the surface of the mine spoil heap, lay clay and compact it in layers until the compaction degree is ≥95%, forming a secondary seepage prevention layer 4 with a thickness of 20~30cm;

[0058] Step 2: Spread slag with a particle size of 5-15mm evenly on the secondary seepage barrier layer 4 to form a coarse-grained drainage layer 3 with a thickness of 20-30cm.

[0059] Step 3: Mix clay and slag according to the design ratio to form the first soil-rock mixture. Add 2% to 5% of organosilicon by mass to the first soil-rock mixture to obtain a modified filler. Spread and compact the modified filler in several layers on the coarse-grained drainage layer 3, wherein the compaction thickness of each layer is 20 to 25 cm and the compaction degree is 85% to 90%, thereby forming a water storage layer 2 with a total thickness of 80 to 100 cm.

[0060] Step 4: Mix clay and slag according to the design ratio to form a second soil-rock mixture. Add 1.0% to 2.0% of guar gum by weight to the second soil-rock mixture to obtain topsoil. Spread the topsoil on the water storage layer 2 and compact it to a compaction degree of 75% to 80% to form a topsoil layer 1 with a thickness of 30 to 40 cm. Sow drought-resistant herbaceous plants.

[0061] As a preferred embodiment, in step 3, after adding organosilicon to the first soil-rock mixture, a forced mixer is used for 2-5 minutes of mixing until the mixture is uniform. Through thorough mechanical mixing, the organosilicon is evenly coated on the surface of the soil and rock particles, forming a stable hydrophobic film.

[0062] As a preferred option, in step 3, when spreading and compacting each layer of modified filler, the initial moisture content is controlled at 12%~20%; in step 4, when spreading the topsoil layer 1, the initial moisture content of the topsoil is controlled at 12%~20%. By optimizing the moisture content, the soil-rock mixture reaches the optimal compaction state, forming an ideal pore structure.

[0063] This invention also provides an application of a capillary barrier cover layer for mine spoil heaps in seasonally frozen areas with ecological restoration needs. Through the comprehensive functions of the cover layer, it achieves synergistic effects of seepage prevention, water retention, and freeze-thaw resistance, providing technical support for the ecological restoration of spoil heaps.

[0064] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0065] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0066] This invention underwent systematic field tests at the Xinbeigou spoil heap of the Jindui molybdenum mine in Weinan City, Shaanxi Province (109°57′26″E, 34°19′43″N). The aim was to verify the effectiveness of the capillary-restricted cover layer by comparing the performance of different embodiments with that of a traditional HDPE film cover layer (control group). The tests focused on evaluating the capillary-restricted performance of the soil-rock mixture-gravel structure and the enhancing effect of organosilicon materials on moisture regulation. Simultaneously, using field conditions as a prototype, combined with indoor tests and numerical simulations (Example 3), the long-term stability of the cover layer under freeze-thaw conditions was further analyzed.

[0067] The test site was located in a typical seasonally frozen soil region, with a climate that is a transitional zone between subtropical and continental humid climates, and also exhibits characteristics of a high-altitude climate. For example... Figure 3 As shown, the site has a multi-year average temperature of 8.8℃, an average annual precipitation of 849.9mm, an average of 62 days of frozen soil per year, and a maximum frozen soil depth of 1.2m. The entire experimental area faces south, with a design range of 40m×40m, an overall slope of 6~7°, and a height difference of approximately 4.9m between the top and bottom of the slope, providing ideal conditions for simulating a real spoil heap environment.

[0068] The experimental area consisted of four core test zones, each a rectangular area of ​​26m × 6m, arranged from west to east: SY-1 (Example 1): a soil-rock mixture with 50% stone content, 2% organosilicon added to the water reservoir layer, and 1.5% guar gum added to the topsoil layer; SY-2 (Example 2): a soil-rock mixture with only 50% stone content, without additives; SY-3: not used in this invention; SY-4 (control group): a conventional compacted clay layer as a cover. The zone design, by comparing SY-1, SY-2, and SY-4, clarified the contributions of organosilicon and guar gum to the capillary repression effect.

[0069] To accurately monitor the performance of the overburden layer, multiple types of sensors were deployed at each measuring point. Soil thermo-hygrometers (model RS-WS-NO1-TR-1) and soil water potential meters (model CG36) were installed on the slope of each test area to collect real-time moisture and temperature data. Miniature earth pressure cells (model WY-ES050) were additionally installed at key locations at the top and bottom of the slope to monitor changes in overburden pressure. All sensor data cables were centrally deployed along the right side of the slope and ultimately connected to the DTU data acquisition unit via a bus, ensuring data continuity and reliability.

[0070] Example 1

[0071] This embodiment provides a method for preparing a capillary retaining capillary cover layer for spoil heaps in seasonally frozen areas based on solid waste slag and organosilicon, including the following steps:

[0072] Step 1: Level and compact the surface of the mine spoil heap, lay low-plasticity clay (liquid limit 40%, plastic limit 15%), and compact it in layers until the compaction degree is 95%, forming a 20cm thick layer with a saturated permeability coefficient of 1×10⁻⁶. -7 Secondary impermeable layer with a speed of m / s;

[0073] Step 2: Spread slag (from mine waste rock) with a particle size of 10mm evenly on the secondary seepage barrier layer to form a coarse-grained drainage layer;

[0074] Step 3: Mix clay and slag (50% stone content) at a mass ratio of 1:1, add 2% organosilicon by mass of the soil-stone mixture, and mix for 5 minutes using a forced mixer; lay the water storage layer in 4 layers, each layer is 25cm thick, compact to a thickness of 20cm and a compaction degree of 90%, control the initial moisture content to 16%±4%, and the total thickness is 80cm;

[0075] Step 4: Mix clay and slag at a mass ratio of 1:2, add 1.5% guar gum, compact to a compaction degree of 75% and a thickness of 30cm to form a cultivated soil layer. After compaction, the initial moisture content is tested to be 16%±4%, and drought-resistant herbaceous plants are sown.

[0076] Rainfall course during on-site monitoring as follows Figure 4 As shown, the cumulative rainfall was 183 mm. Changes in water storage are as follows: Figure 5 As shown in Table 1, Example 1 had the highest water storage capacity during rainfall events (e.g., 245.12 mm of water storage capacity when the cumulative rainfall was 154.7 mm) and no leakage, indicating that 2% organosilicon and 1.5% guar gum effectively enhanced the capillary resistance effect and water retention capacity.

[0077] Example 2

[0078] This embodiment provides a method for preparing a capillary retaining capillary cover layer for spoil heaps in seasonally frozen areas based on solid waste slag (without organosilicon and guar gum), including the following steps:

[0079] Step 1: Level and compact the surface of the mine spoil heap, lay low-plasticity clay (liquid limit 40%, plastic limit 15%), and compact it in layers until the compaction degree is 95%, forming a 20cm thick layer with a saturated permeability coefficient of 1×10⁻⁶. -7 Secondary impermeable layer with a speed of m / s;

[0080] Step 2: Spread slag (from mine waste rock) with a particle size of 10mm evenly on the secondary seepage barrier layer to form a coarse-grained drainage layer;

[0081] Step 3: Mix clay and slag (50% stone content) at a mass ratio of 1:1 and mix for 5 minutes using a forced mixer; lay the water storage layer in 4 layers, each layer is 25cm thick, compact to a thickness of 20cm and a compaction degree of 90%, control the initial moisture content to 16%±4%, and the total thickness is 80cm.

[0082] Step 4: Mix clay and slag at a mass ratio of 1:2, compact to a compaction degree of 75% and a thickness of 30cm to form a cultivated soil layer. After compaction, the initial moisture content is tested to be 16%±4%, and drought-resistant herbaceous plants are sown.

[0083] The location of this embodiment is adjacent to that of Embodiment 1, that is, the rainfall curve is the same.

[0084] The results are shown in Table 1 and Figure 5 As shown, the water storage capacity of Example 2 was significantly lower than that of Example 1 (e.g., water storage capacity was 207.76 mm when the cumulative rainfall was 154.7 mm), and slight leakage (0.03 mm) was observed, confirming the key role of organosilicon and guar gum in capillary retardation and impermeability. Despite the absence of additives, the 50% stone content structure still exhibited better water retention than the conventional clay layer (control group), indicating the effectiveness of the soil-rock mixture-gravel capillary retardant foundation design.

[0085] Control group (traditional compacted clay overburden)

[0086] This control group used a traditional compacted clay layer capping layer design to compare and evaluate the performance advantages of the capillary-retaining capping layer of this invention. The capping layer structure is a single compacted clay layer without layering, designed to simulate conventional mine spoil heap seepage prevention measures. The preparation method is as follows:

[0087] Step 1: Level and compact the surface of the mine spoil heap, remove surface debris, and ensure the base is flat;

[0088] Step 2: Lay low-plasticity clay (liquid limit 40%, plastic limit 15%), compact it in layers to a compaction degree of 95%, with each layer having a loose thickness of 30cm. After compaction, the thickness of each single layer is controlled at 25cm. Through multiple rolling processes, a single clay layer with a total thickness of approximately 150cm is formed (comparable to the total thickness in the example), with a saturated permeability coefficient of approximately 1×10⁻⁶. -7 m / s;

[0089] Step 3: During the compaction process, the initial moisture content is controlled at 16%±4%. After each layer is compacted, the density is tested to ensure overall uniformity.

[0090] Step 4: Simply rake the surface flat without adding any amendments or vegetation layers to maintain traditional construction characteristics.

[0091] During the on-site monitoring period, the rainfall course was the same as in Examples 1 and 2, with a cumulative rainfall of 183 mm. The rainfall distribution is as follows: Figure 4 As shown.

[0092] Water storage change data such as Figure 5 As shown in Table 1: when the cumulative rainfall was 154.7 mm, the water storage in the control group was 201.60 mm, and leakage occurred (leakage amount 0.11 mm); however, as the rainfall continued, the water storage fluctuated greatly, and the rate of water loss was significantly faster than in the example.

[0093] The results show that although traditional compacted clay overburden has basic seepage prevention capabilities, it lacks capillary retardant structures and amendments, resulting in poor water storage performance and a high risk of leakage. Under freeze-thaw cycles in seasonally frozen regions, its single structure is more prone to compaction or cracking, accelerating water infiltration, thus verifying the necessity of the layered design and material improvement of this invention.

[0094] Table 1. Statistics on water storage and leakage of the cover layer in Examples 1, 2 and the control group.

[0095]

[0096] Example 3

[0097] This embodiment aims to verify the impact of freeze-thaw cycles on the water storage performance of capillary-retaining capillary overburden through numerical simulation. The soil and rock parameters and construction process are completely consistent with Example 1 (2% organosilicon, 1.5% guar gum, 50% stone content). The difference lies in the use of a combination of indoor experiments and numerical modeling to focus on analyzing long-term stability under freeze-thaw conditions. The specific steps are as follows:

[0098] Step 1: Soil sampling and pretreatment

[0099] Soil samples from the reservoir layers of Example 1 (containing 2% organosilicon) and Example 2 (without organosilicon) were collected. The soil samples were 50% stone-containing mixtures of clay and slag at a mass ratio of 1:1, with a compaction degree controlled at 90%. After sampling, the samples were processed uniformly to ensure consistent initial conditions.

[0100] Step 2: Freeze-thaw cycle test and parameter determination

[0101] Soil samples were subjected to 0–10 freeze-thaw cycles using a freeze-thaw cycle chamber (each cycle consisting of freezing at -15°C for 12 hours and thawing at +5°C for 12 hours). Two key tests were conducted after each cycle:

[0102] Soil-water characteristic curve (SWCC) test: to measure soil-water characteristic parameters under unsaturated conditions and quantify changes in water-holding capacity.

[0103] Nuclear magnetic resonance (NMR) test: to analyze the pore size distribution inside the soil-rock mixture and to assess the impact of freeze-thaw cycles on the microstructure.

[0104] The SWCC curves of the water-holding layers in Examples 1 and 2 under different freeze-thaw cycles are shown in Figures 6(a) and 6(b). The results show that the soil sample with 2% organosilicon and 1.5% guar gum (Example 1) showed only a slight downward shift in its SWCC curve after 10 freeze-thaw cycles (water-holding capacity degradation rate <5%), while the soil sample without organosilicon and guar gum (Example 2) showed a degradation rate of approximately 10%. This indicates that organosilicon modification can significantly inhibit the decrease in water-holding capacity caused by freeze-thaw cycles and enhance the freeze-thaw stability of the cover layer.

[0105] Step 3: Numerical Model Construction

[0106] Based on the field test conditions, a two-dimensional numerical model of the cover layer was established, with the structure as follows: Figure 7 As shown. The model strictly follows the actual layered design (from bottom to top: secondary impermeable layer, coarse-grained drainage layer, water storage layer, topsoil layer), and imports the hydraulic parameters after freeze-thaw (such as permeability coefficient, soil-water characteristic curve) measured in step 2.

[0107] Step 4: Simulation Analysis and Result Verification

[0108] Input the same rainfall data as the field test (cumulative rainfall 183 mm, rainfall curve as shown) Figure 4 Figure 8(a) and Figure 8(b) show the simulation of the water infiltration process and water storage capacity of the cover layer after 0 to 10 freeze-thaw cycles. The water infiltration dynamics are shown in Figure 8(a) and Figure 8(b), and the water storage capacity is compared in Figure 9(a) and Figure 9(b).

[0109] Key data: After 10 freeze-thaw cycles, the simulated water content at a depth of 70cm (a critical location in the aquifer) shows:

[0110] Example 1 with added organosilicon had a moisture content of 34.4%, which was 1.88% higher than the field water holding capacity.

[0111] Example 2, without additives, had a moisture content of 30.5%, which was 6.94% higher than the field water holding capacity.

[0112] This embodiment demonstrates through numerical simulation that even after 10 freeze-thaw cycles, the capillary repression effect of the soil-rock mixture-gravel effectively maintains the water storage function of the caprock layer. Furthermore, the addition of organosilicon further mitigates freeze-thaw degradation and enhances the long-term applicability in seasonally frozen regions. This method provides a theoretical basis for the engineering design of caprock layers in seasonally frozen soil regions.

[0113] This invention, verified through field trials, is applicable to ecological restoration projects of spoil heaps in metal mines and coal mines, and is particularly suitable for seasonally frozen soil areas with an annual rainfall of 300-800 mm. Construction costs are reduced by 30%-40% compared to traditional HDPE membrane coverings, demonstrating significant environmental and economic benefits.

[0114] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A capillary retardant cover layer for spoil heaps in seasonally frozen areas, characterized in that, It includes a secondary impermeable layer (4), a capillary barrier cover layer and a topsoil layer (1) arranged sequentially from bottom to top. The secondary impermeable layer (4) is a clay layer with a compaction degree ≥95%, a thickness of 20~30cm, and a saturated permeability coefficient of 1×10⁻⁶. -6 ~1×10 -7 m / s; the clay layer is made of low-plasticity clay with a liquid limit ≤40% and a plastic limit ≥15%; The capillary barrier covering layer includes a coarse particle drainage layer (3) and a water storage layer (2). The coarse particle drainage layer (3) is laid on the secondary seepage prevention layer (4). The material of the coarse particle drainage layer (3) is slag with a particle size of 5~15mm and a thickness of 20~30cm. The water storage layer (2) is laid on the coarse-grained drainage layer (3). It is a soil-rock mixture composed of clay and slag in a mass ratio of (1~2):1, with 2%~5% organic silicon added to the total mass of the soil-rock mixture. It is constructed by layered compaction, with each layer having a compaction thickness of 20~25cm, compacted to 85%~90% compaction degree, and a total thickness of 80~100cm. The cultivated soil layer (1) is laid on the water storage layer (2) and is a soil-rock mixture composed of clay and slag in a mass ratio of 1:(1~4). Guar gum accounting for 1.0%~2.0% of the total mass of the soil-rock mixture is added, and then it is compacted to a compaction degree of 75%~80% and a thickness of 30~40cm.

2. The capillary retardant cover layer for spoil heaps in seasonally frozen areas according to claim 1, characterized in that, The slag in the coarse-grained drainage layer (3) is made from mine waste rock or tailings.

3. The capillary retardant cover layer for spoil heaps in seasonally frozen areas according to claim 1, characterized in that, The slag in the water storage layer (2) has a particle size of 5~15mm.

4. A method for preparing a capillary retardant cover layer for spoil heaps in seasonally frozen areas as described in any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Level and compact the surface of the mine spoil heap, lay clay and compact it in layers until the compaction degree is ≥95%, forming a secondary seepage prevention layer with a thickness of 20~30cm (4). Step 2: Spread slag with a particle size of 5-15mm evenly on the secondary seepage barrier layer (4) to form a coarse-grained drainage layer (3) with a thickness of 20-30cm. Step 3: Mix clay and slag according to the design ratio to form the first soil-rock mixture. Add 2% to 5% of organosilicon by mass to the first soil-rock mixture to obtain modified filler. Spread and compact the modified filler in several layers on the coarse-grained drainage layer (3). The compaction thickness of each layer is 20 to 25 cm and the compaction degree is 85% to 90%, thereby forming a water storage layer (2) with a total thickness of 80 to 100 cm. Step 4: Mix clay and slag according to the design ratio to form a second soil-rock mixture. Add 1.0% to 2.0% of guar gum by mass to the second soil-rock mixture to obtain topsoil. Spread the topsoil on the water storage layer (2) and compact it to a compaction degree of 75% to 80% to form a topsoil layer (1) with a thickness of 30 to 40 cm.

5. The method for preparing a capillary retardant cover layer for a spoil heap in a seasonally frozen area according to claim 4, characterized in that, In step 3, after adding organosilicon to the first soil-rock mixture, the mixture is stirred for 2-5 minutes until it is uniformly mixed.

6. The method for preparing a capillary retardant cover layer for a spoil heap in a seasonally frozen area according to claim 4, characterized in that, In step 3, when spreading and compacting each layer of the modified filler, the initial moisture content of the modified filler is controlled to be 12%~20%; In step 4, when spreading the topsoil layer (1), the initial moisture content of the topsoil is controlled to be 12%~20%.

7. The application of a capillary retardant cover layer for a seasonally frozen waste dump according to any one of claims 1-3 in a mine waste dump with ecological restoration requirements.

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