First, the overburden profile model
Dalongliang Coal Gangue Mountain, No.3 Mine of Yangmei Group, is an old coal gangue mountain, with a total treatment area of about 395 mu, and the gangue discharge period has exceeded 20 years. Spontaneous combustion has spread to the whole coal gangue hill. If measures such as reducing stacking height and angle of repose or layered rolling are taken to prevent and extinguish fires, the investment cost will inevitably increase. Therefore, the control measures of "surface coverage, overall closure and comprehensive greening" have been adopted in this coal gangue hill. According to the local actual situation, in line with the principles of local materials, waste utilization, economic saving and so on. When selecting the covering material, consider adding fly ash in addition to the local loess. The greening treatment of spontaneous combustion coal gangue hill in this design finally covers a layer of structure, as shown in Figure 5- 16. The profile of the covering system is: vegetation layer, topsoil layer, effective covering layer and coal gangue from the surface to the inside.
Figure 5- 16 Profile Structure of Covering System in Spontaneous Combustion Coal Gangue Hill
Firstly, the gangue on the surface of coal gangue hill is rolled, with the purpose of reducing the porosity on the surface of coal gangue and helping to prevent seepage, on the other hand, improving the soft foundation and constructing an effective covering layer. The function of effective coating (coating for short) is to prevent oxygen and fire, and roll inert materials into a certain density, thus ensuring a certain air barrier. The main material is local loess, and other economical and effective materials such as fly ash can also be mixed. After experimental design and proportional mixing, the material is covered on the coal gangue hillside, and after rolling, it reaches a certain density (0.85), which makes it have a certain air isolation effect, thus preventing the external air from infiltrating into the coal gangue hill and preventing the spontaneous combustion of the coal gangue hill. Cover the effective cover with natural soil or nutrient soil (loam), select the thickness of topsoil (not less than 20cm) according to the specific situation, and plant vegetation on this basis. Topsoil with vegetation can effectively prevent the underlying overburden from cracking due to drying and dehydration, thus ensuring that it maintains a certain air barrier. In addition, the green vegetation layer can effectively prevent the erosion of the covering soil by wind and rain, and reduce the influence of external temperature on the coal gangue hill.
The main process flow chart is shown in figure 5- 17.
Fig. 5- 17 flow chart of implementation of test site scheme
Second, the construction method of effective oxygen barrier and anti-spontaneous combustion coating
According to the simulation test results, the local silt and silty clay in Yangquan mining area can be used as covering materials, and it is more economical to mix 30% fly ash. When silty soil and its mixture are used as covering material, the covering thickness should be above 60cm, and the method of layered soil spreading and layered rolling should be adopted when rolling, that is, the loose spreading thickness is 20 ~ 40 cm, and the rolling is carried out for 3 ~ 5 times, with two layers. When silty clay and its mixture are used as covering materials, the covering thickness can be about 20cm, so the loose laying thickness is 20 ~ 40 cm, and it can be rolled for 3 ~ 5 times, and one layer can work.
See fig. 5- 18 for the construction site.
Figure 5- 18 Construction Site