Fire extinguishing and cooling in spontaneous combustion coal gangue hill. Due to the combustion of spontaneous combustion coal gangue hill, the temperature of surface weathered materials is very high, so it is difficult for plants to grow at such high temperature, which is not conducive to the implementation of greening construction. Therefore, the primary task of site improvement in spontaneous combustion coal gangue hill is to extinguish fire and cool down; Attention should be paid to the fire prevention work of potential spontaneous combustion coal gangue hills.
The steep terrain of plastic soil preparation is easy to cause soil erosion. Due to the large slope, loose structure and some weathered fragments on the surface of coal gangue, wind erosion and water erosion are easy to occur under the condition of strong wind and heavy rain. In addition, in the process of vegetation restoration construction, due to human factors, gravity erosion such as collapse is easy to occur.
Improvement of weathered material on the surface of coal gangue hill. The physical properties of weathered materials on the surface of coal gangue are very poor, especially the water holding capacity is poor; At the same time, there are substances that restrict the growth of plants, including toxic elements such as acidity, salinity and heavy metals; Lack of nutrients such as nitrogen, phosphorus and potassium needed for plant growth and soil organisms (such as beneficial microorganisms such as earthworms and nematodes). Therefore, the improvement technology of plastic soil preparation and weathering matrix in coal gangue hill is directly related to the success or failure of vegetation restoration.
A, coal gangue hill plastic technology
1. the function and purpose of plastic soil preparation in coal gangue hill
The slope of coal gangue hill is steep. For example, the angle of repose of Yangquan coal gangue hill is generally around 40. The slope is large and the construction is difficult, which is not conducive to vegetation construction. The slope can be slowed down if possible. Moreover, steep slope is easy to cause soil erosion in coal gangue hill, so the terrain design is mainly to sort out the slope of coal gangue hill, reduce the slope, and properly prepare the soil for the project to increase the water and fertilizer conservation capacity of the sorted coal gangue hill.
In foreign countries, measures such as leveling the ground, gentle slope, covering soil and adding nutrients are usually adopted to improve the site conditions of coal gangue hills on a large scale. However, due to social and economic factors such as the shortage of land resources in China, it is difficult to achieve such a scale increase. At the same time, it is recognized that the process of gentle slope of spontaneous combustion coal gangue mountain will inevitably excavate the mountain and disturb the fire point. Unearthed mountain, due to years of weathering and deposition, the fire point is in a closed and compacted state, and the combustion is not intense. After excavation, the oxygen supply conditions improve and the fire may increase. Therefore, only small-scale plastic engineering, local soil preparation measures and less economic investment can achieve the goal of improving the site environment as much as possible. Moreover, it is very necessary to arrange the coal gangue hill before covering the soil, which is conducive to the next step of pushing the soil. Use excavators and manpower to level the slope and then roll it.
The main purposes and functions of shaping spontaneous combustion coal gangue hill are as follows:
1) slow down the slope, stabilize the surface structure and reduce soil erosion;
2) It is convenient for vegetation restoration and construction, and improves the afforestation quality;
3) improving pore conditions and soil water-holding capacity;
4) Find out the fire source and potential burning point, so as to prevent and extinguish the fire in time;
5) Increase the soil thickness in the planting area, improve the survival rate and preservation rate of planting, and promote plant growth.
2. Requirements for plastic soil preparation of spontaneous combustion coal gangue hill
The shaping of spontaneous combustion coal gangue hill generally includes slope cutting and shaping, fire prevention and extinguishing, terraced fields and soil and water conservation projects. The general requirements for plastic soil preparation are:
1) build a highway around the mountain to reach the top of the mountain, which is convenient for material transportation, soil preparation and tourists to climb to the top;
2) Leveling the top of the mountain and establishing pavilions and leisure places;
3) Combining landscape design and soil preparation and planting, the landform landscape is reconstructed by gentle slopes and terraces.
4) Set scattered stone steps in some places suitable for tourists to climb mountains;
5) Establish a drainage system. Because of the high height and steep slope of coal gangue hill, surface erosion is easy to occur after the surface is covered with soil, resulting in soil erosion. Therefore, a perfect drainage system should be designed at the same time as the transformation of coal gangue hill;
6) When reshaping the landform, if there is a high temperature area or a spontaneous combustion area, grouting should be carried out to extinguish the fire and soil should be covered for compaction, and fire prevention measures should be taken in the potential burning area.
Two, spontaneous combustion coal gangue hill land consolidation methods and technical specifications
1. Soil preparation method
There are two methods of soil preparation: comprehensive soil preparation and local soil preparation. According to the principle of saving labor and improving site quality as much as possible, and adhering to the principle of minimizing the exposure of oxygen to the fire source, we do not advocate the comprehensive soil preparation method for all coal gangue hills, but adopt the local soil preparation method. In the local land preparation methods, both strip land preparation methods and block land preparation methods can be adopted. Horizontal terrace and reverse slope terrace can be used as methods of strip soil preparation; Block soil preparation can adopt two methods: fish scale pit and hole shape.
In order to increase the thickness of the soil layer in the planting area, cover an appropriate amount of "exotic soil" in the whole tree planting belt or hole. "Exotic soil" can be soil from different places, and it can also be weathered material on the surface of coal gangue. Sludge mulching technology can be used when conditions permit, which can greatly improve the fertility level of coal gangue hill, improve the soil structure and reduce the cost.
2. Problems that should be paid attention to in soil preparation of spontaneous combustion coal gangue hill
In order to ensure the effect of soil preparation in spontaneous combustion coal gangue hill, which is beneficial to vegetation restoration, the factors such as soil preparation depth, platform width, section form, covering soil thickness, isolation layer and retaining wall should be considered during soil preparation.
(1) Soil preparation depth
The depth of soil preparation directly affects the development of plant roots and is an important index of soil preparation. The depth of soil preparation in coal gangue hill varies with different vegetation. Generally speaking, herbaceous plants are the lowest 15cm, low shrubs are 30cm, tall shrubs are 45cm, low trees are 60cm and tall trees are 90cm. Field experiments show that the survival rate of tall trees in Yangquan spontaneous combustion coal gangue mountain is very low, and the growth of tall trees needs a lot of soil. Therefore, we should construct a plant community structure with shrubs and herbs as the main components and trees as the auxiliary components.
(2) width of soil preparation
The basic principle of soil preparation width is to improve site conditions to the maximum extent and control soil erosion under the premise of natural and socio-economic conditions. Due to the steep slope of coal gangue, the width of soil preparation should not be too large. If the way of terrace is adopted, the width of soil preparation should be 2.0 ~1.0m. ..
(3) Section form
The cross-sectional form is a cross-sectional form composed of the soil surface after soil preparation and the original broken surface. In order to accumulate more rainfall, reduce evaporation and increase soil moisture, the slope of coal gangue hill is lower than the original slope and forms a certain angle with the original slope.
(4) Fire prevention measures such as isolation layer.
Before covering the coal gangue hill, cover it with inert materials (loess, lime, fly ash, clay, etc.). ) and rolled into an isolation layer. Select appropriate rolling tools and operating parameters for rolling, so that the bulk density of inert materials can reach 1.6 ~ 1.8g/cm3. Focus on rolling fire extinguishing areas and high temperature areas (increase the covering thickness and rolling strength of inert materials). In order to better inhibit the oxidation of pyrite in coal gangue, 2 ~ 3l thiobacillus ferrooxidans (sodium benzoate solution, concentration 0.3% ~ 0.4%) was sprayed on the surface of the formed coal gangue hill. Sulfate-reducing bacteria were inoculated on the surface of potential spontaneous combustion coal gangue hill, and the bacterial liquid was evenly sprayed on the coal gangue hill according to the inoculation amount of 500mL/m2.
(5) The multi-layer structure is covered by soil.
The infiltration rate of coal gangue hill compacted by vibration is small, and the permeability is lower after loess covering compaction, which is beneficial to fire prevention and extinguishing. The compactness is inversely proportional to the air fluidity, and the compactness is directly proportional to the fire extinguishing effect. However, over-compacted soil is not conducive to plant growth, which seriously affects rainfall infiltration and plant root development. In order to prevent spontaneous combustion of coal gangue hill, the density of coal gangue hill should be compacted to above 0.75; In order to control the burned coal gangue piles, it is necessary to compact the density of coal gangue piles above 0.82.
In view of the contradiction between fire fighting and planting, combined with the requirements of covering soil compaction and the needs of plants for soil conditions, the method of compacting the lower soil and maintaining the normal density of the upper soil is studied to facilitate water storage and plant growth, which can take into account the requirements of fire fighting and planting.
(6) Drainage ditch
In order to reduce the erosion of surface runoff on the topsoil of coal gangue hill and maintain the soil and water of coal gangue hill; At the same time, because the exposed gangue will produce a higher temperature, once exposed to the air, it will soon rekindle, making plants short of water. In order to protect the covering sealing effect, the drainage of terraces, platforms (roads) and longitudinal slopes of coal gangue hills (top-down drains) should be done well. Rainwater from terraces and platforms flows into the drainage ditch on the longitudinal slope of the coal gangue hill through the drainage ditch, and then is discharged to the bottom of the coal gangue hill, which avoids the concentration of surface runoff on the ground and the increase of velocity, and reduces the soil erosion on the surface. When building drainage ditches and reservoirs, an isolation layer is added between buildings and coal gangue to reduce the infiltration of oxygen (Figure 6-5).
(7) Retaining wall
In view of the "stack effect" in the coal gangue hill, the isolation design should be carried out for the retaining wall at the toe of the slope, that is, isolation layers should be added to the lower and inner sides of the retaining wall. The isolation layer is connected with the covering soil layer on the slope to form a complete oxygen isolation layer of alkaline substances such as lime, so as to ensure that air does not enter from the bottom, block the entrance passage of the stack effect of the coal gangue hill, and restrict the air from entering, thus preventing or cutting off the oxygen required for the spontaneous combustion of coal gangue.
3. Soil preparation season and construction method
The soil preparation of coal gangue hill should be carried out according to the principle of at least one rainy season in advance, that is, if it is spring afforestation, it is best to carry out soil preparation before the rainy season one year before afforestation; If it is afforestation in autumn, it is best to prepare the soil before the rainy season of that year. This is beneficial to water storage and moisture conservation, and increases the nutrient content of organic matter and so on in the tree planting belt.
Figure 6-5 Drainage System of Coal Gangue Mountain
In the construction of land preparation, the construction is generally carried out from top to bottom, which can not only facilitate the construction with the help of gravity, but also ensure that the construction of the next terrace will not affect the previously constructed terrace.
Three, spontaneous combustion coal gangue hill matrix improvement technology
1. Acidity improvement
(1) Loess
Loess has a good neutralization effect on the acid in coal gangue, which can buffer the acidity of coal gangue hill. Located in Yangquan and other places on the loess plateau, the local loess is used to improve the soil pH of coal gangue hill. After the spontaneous combustion coal gangue hill is covered with loess, the acidity is greatly reduced. Generally, adding 10% loess or covering soil with coal gangue can satisfy the growth of most plants.
(2) bicarbonate and lime, limestone, etc.
Because bicarbonate, lime and limestone are very alkaline, they can be used to neutralize acidic substances in coal gangue. The treatment effect of these substances is good, but if the coal gangue mountain is treated in a large area, the cost is higher.
2. Fertilizer improvement
(1) chemical fertilizer
Coal gangue hill is short of nutrients needed for plant growth, so it is necessary to improve soil fertility. The application of nitrogen, phosphorus and potassium fertilizer can generally achieve rapid and remarkable results. Due to the loose structure and high porosity of coal gangue, chemical fertilizer is easy to be lost, so a small amount of chemical fertilizer should be applied more.
(2) Organic fertilizer
Traditional fertilization and farmyard manure are traditional ways to improve soil fertility rapidly, which have the characteristics of quick effect and simple process, and can effectively improve the physical structure and poor performance of coal gangue.
③ Biological nitrogen fixation
Planting interspecific nitrogen-fixing plants on the coal gangue hill absorbs nitrogen through the nitrogen-fixing function of plants, and releases nitrogen into the soil after plant decomposition, thus improving the coal gangue matrix.
(4) Microbial fertilization technology
Microbial fertilization mainly refers to the process of improving and improving soil fertility by relying on microbial activities. It mainly uses specific microorganisms, root exudates, mycorrhiza and soil animals in the soil to improve soil activity and productivity.
In the process of controlling coal gangue hill, the role of microorganisms has been paid more and more attention, and special attention has been paid to promoting the proliferation and increase of microorganisms in soil or specific microorganisms from outside. As a mutually beneficial combination of mycorrhizal fungi in soil and vegetative roots of higher plants, mycorrhiza has attracted much attention because of its high adaptability to environmental stress (Figure 6-6). Studies on endomycorrhizal plants show that plants inoculated with mycorrhizal fungi can absorb more nutrients and inhibit the accumulation of excessive harmful elements compared with non-mycorrhizal plants. For example, arbuscular mycorrhiza can not only promote the absorption of a large number of nutrients (N, P, K) by crops, but also promote the absorption of medium and trace elements. This is because the combination of mycorrhiza and plants increases the contact surface area between plant roots and soil, and the nutrients that were originally ineffective in space become effective nutrients. This is mainly because the growth of mycorrhiza reduces the diffusion distance of ions to the root surface and increases the absorption efficiency of the root system. At the same time, the growth of mycelium outside the root increases the contact position between plant roots and soil, and shortens the diffusion distance of ions to the root system. At the same time, mycorrhiza has a strong complexing ability to heavy metals. Mucus secreted by fungal cell wall and polyphosphoric acid and organic acid in fungal tissue can complex heavy metals, thus reducing the transport of heavy metals to the upper part of soil and avoiding or alleviating the toxicity of heavy metals to plants. In addition, arbuscular mycorrhiza can also improve plant water metabolism; Improve the resistance and disease resistance of plants.
Figure 6-6 Mycorrhiza
Therefore, through the research, it is found that different endophytic/ectomycorrhizal fungi and different plants can improve the nutrition of soil matrix in coal gangue hill, the adaptability of mycorrhizal fungi to salinization, acidification and high temperature of coal gangue matrix, and the resistance to excessive heavy metals and organic pollutants in matrix, screening out the combination of microorganisms and plants that adapt to spontaneous combustion after fire extinguishing in coal gangue hill, and establishing microbial technology to improve soil structure and function in spontaneous combustion coal gangue hill are important development directions of microbial fertilization technology in the future.
3. Salt water hazard treatment
In the coal gangue hill in arid and semi-arid areas, the annual precipitation is less, and the evaporation is greater than the precipitation. The soil in coal gangue hill is often in a state of drought and dehumidification, and the soil salt leaching is weak, and it is in a state of salt accumulation almost all the year round, lasting for many years.
Through observation and research, it is found that salt is produced at high temperature, so once the coal gangue hill is put out, the harm of salt is reduced. If you can't put out the fire, high salt still restricts the construction of high-temperature vegetation, so you must put out the fire before removing salt. It is difficult for plants to survive at high temperature, and the premise of vegetation construction in spontaneous combustion coal gangue hill is to extinguish fire. After the coal gangue fire is put out, the salt stress will be reduced accordingly. Therefore, the salt problem of coal gangue hill will be solved with the solution of high temperature problem.