Experimental Study On Reconstruction Of Multi-layered Soil Profiles By Using Coal Gangue For Reclamation Of Coal Mining Subsidence In Huainan City

As important overlapped areas of farmland and coal resources,large areas of cultivated land subsidence of the high submersible plain area due to coal mining every year in eastern China,forming a large area of stagnant water area,and the proportion of cultivated land reclamation is relatively low,so exacerbating the contradiction of more people and less land.Coal gangue,as the main solid waste in the process of coal mining,the comprehensive utilization ration is about 15%.The low utilization ratio of coal gangue not only leads to the idle waste of resources but also occupies a large amount of land,destroys the ecological balance.Some researches were focused on applying coal gangue directly to the reclamation of coal mining subsidence,due to its coarse particle size,poor water and fertilizer conservation,the traditional structure of the upper soil and lower gangue cannot effectively restrain soil water and fertilizer loss.Therefore,the reconstruction of soil profile which is beneficial to crop growth and saving soil has become an important research content of coal gangue filling coal mining subsidence.In this study,based on the principle of the reclaiming subsidence land with inter-layers of filling materials and the method of alternating multi-layer multiple filling soil reconstruction,combined with agronomy,soil science and other relative knowledge,adopted orthogonal test method to determine 10 different profiles.The maize growth,yield,and soil physical and chemical properties were compared and analyzed by indoor and filed maize planting experiments,the soil profile that was suitable for both maize growth and saving soil was summarized.To further elucidate the water factors affecting maize growth,according to different profiles of maize growth,the best profile of maize growth was selected from each group for indoor water infiltration and water holding tests.Quantitatively analyzing the cumulative infiltration,infiltration rate and water distribution characteristics of the infiltration tests of different profiles,and clarifing the infiltration characteristics of different profiles by using the Kostiavo infiltration model and the Philip equation model to simulate the water infiltration process of different profiles.The water holding capacity and water content distribution characteristics in different profiles were measured and analyzed by drainage test.The following conclusion were drawn from the above experimental studies:(1)The growth characteristics of maize in different profiles were preliminarily obtained by indoor planting experiments.There were no significant differences among control treatments and experimental treatments.By analyzing the physical and chemical indexes of the soil at different depths in different profiles,it was concluded that the water content,total nitrogen,total phosphorus,alkali-hydrolyzed nitrogen,available potassium and organic matter content,p H value,electrical conductivity,and total salt content of the surface soil in interlayered profiles were closed to that of in the control experiments.There were no significant differences of all the above indexes among interlayered profiles and control experiments.But the contents of total potassium and available phosphorus were significantly higher than those in the control experiments.The interlayer soil available phosphorus,p H value and total salt content in the interlayer profiles were significantly larger than those in the homogeneous soil at the same depth,and the contents of other physical and chemical indicators were not significantly different from those of the control group.(2)Through field planting experiments,CK2,that was the upper layer was soil and the lower layer was coal gangue profile,was the most suitable and economical profile for maize growth.The maize yield in the control experiments was significantly higher than that in the experimental treatments,but the differences of maize growth and yield in interlayered profile were not significant.The maize yields of CK1 and CK2 were 582.61kg acre^-1 and 549.31 kg acre^-1,respectively,the differences between them were not significant.Except for the p H value,electrical conductivity,and total salt content in the surface soil of the interlayer,which were greater than those of the control soil,the contents of other soil physical-chemical indicators were significantly smller than those of the control soil.The physical-chemical of soil at the interlayered was same as that of homogeneous soil at the same depth and there were no differences between interlayered profiles and control treatments.(3)The indoor water infiltration experiment showed that with the same soil thickness,the cumulative infiltration of the interlayered profiles was slightly larger than that of the upper soil and lower gangue profile,but the difference was not significant.The average infiltration rate and the stable infiltration rate of the interlayered profiles were smaller than those of homogeneous or layered profile with same thickness of the covering soil.The more the number of interlayers,the smaller the average infiltration rate and the stable infiltration rate.The average infiltration rate and stable infiltration rate of CK2 profile were larger than those of the other profiles.The influence of the interlayer profiles on the distribution of surface soil water content was not obvious.With the increase of depth,the difference between the water content of the interlayered profiles and the water content of the homogeneous soil becomes lager and lager,especially the water content of the interlayered position was significantly larger than that of the homogeneous soil at the same depth.Philip equation model and Kostiakov infiltration model were used to simulate the trend of cumulative infiltration.It was concluded that the Philip model could only simulate the homogeneous profile well,and was not suitable for the simulation of multi-layered profiles.The Kostiakov infiltration model could well simulate the water infiltration of homogeneous and multi-layered profiles,and the coefficient of determination was above 0.99.The Kostiakov infiltration model was used to simulate the water infiltration process.It was found that the initial infiltration capacity of the interlayered profiles was greater,but with the infiltration,the attenuation rate of the infiltration capacity of the interlayered profiles was greater than that of homogeneous profile and the upper and lower profile.(4)Through the drainage experiment,it was concluded that the change trends of water holding capacity in different profiles were similar,and they all showed power functions.When the thickness of the covering soil was the same,the water holding capacity of the interlayered profiles was larger than that of the upper and lower profile.The number of layers was positively related to the water holding capacity.With the extension of drainage time,the greater the number of interlayers,the smaller the water holding capacity reduction.During the drainage process,the soil water content of the interlayered profiles was higher than that of the homogeneous profile or the upper and lower profile.The water loss of gangue was larger than that of soil,and the drainage of the profile mainly came from the drainage of gangue layer.Although the lime concretion black soil interlayer could reduce the profile infiltration rate and increase water holding capacity,the lime concretion black soil interlayer is with heavy clay,poor aeration and permeability,and weak infiltration capacity,while the lime concretion black soil interlayer made the infiltration capacity and drainage performance become worse,the infiltration duration was longer,and it was more detrimental to the interlayered profiles infiltration and drainage.Therefore,when the filling material is the lime concretion black soil and coal gangue with the particle size of less than 2cm,the lime concretion black soil is not suitable to be as an interlayer.And the interlayer material must be different in texture from the filling material.The CK2 profile had strong infiltration capacity,good drainage,and the maize growth was obviously better than that of the interlayered profiles.Therefore,when the filling material is lime concretion black soil and coal gangue with a particle size of less than 2 cm,the CK2profile is the optimal reconstruction of soil structure.