Effects Of Subsidence-Reclamation On Soil Physical Properties In Lime Concretion Black Soil Mining Area

With the acceleration of the urbanization process in modern China,the demand for coal is also increasing.Although the improvement of comprehensive national strength and changes in related policies in recent years have effectively reduced the current situation of coal mining overcapacity,but for many years,coal mining has brought The environmental problems in the future are difficult to eliminate.Among them,coal gangue accumulation mountains and coal mining subsidence problems are the most serious.Coal mining subsidence leads to serious waste of land resources.At the same time,the coal mining subsidence process is a process of ground deformation for several years.During the subsidence process,the physical properties of the soil will change due to the ground subsidence.After the ground is completely subsidenced,backfill the soil and rebuild the land.This process of resources will also lead to changes in the physical properties of the soil,and the study area is located in the Lime concretion black soil and the soil collapse will affect the Lime concretion black soil.Although Lime concretion black soil is called black soil,its organic matter content is not high compared with that of black soil in Northeast China.This is because although it is formed in the Quaternary shallow lake meadow area,it has a high degree of humus aromatization,which is basically extremely Stable humin exists and binds tightly with soil particles to form a complex that cannot be used by plants.Lime concretion black soil parent material developed in Quaternary river and lake sediments and shallow lake marsh sediments in low-lying areas,mainly calcareous parent material,clay minerals mainly montmorillonite,illite second,so the texture is heavy and dry The phenomenon of shrinkage and dampness is obvious.In the case of dry and wet reciprocation,large cracks are formed when dry,and the depth of the crack is equivalent to the black soil layer.The surface soil enters the lower layer through the crack.When wet,the soil absorbs water and expands rapidly.The crack closes,not only completely filling the soil,but also due to the upper soil Falling,causing the lower soil to be squeezed and move upward.In the process of subsidence-reclamation,this unique soil property will affect the changes of soil physical properties in subsidence-reclaimed areas.In this study,four types of subsidence-reclaimed soil types were measured in the control area,the unsteady set,the unsteady set two,and the reclamation group in the study area.The physical properties such as water rate,soil bulk density,soil moisture,soil particle composition,soil total nitrogen and organic matter content were measured.In addition,the pressure film method was used to determine the soil moisture characteristic curve to solve the equivalent pore distribution,and the data was analyzed to obtain the following conclusion :(1)After considering the time cost and accuracy of the measurement time of the saturated hydraulic conductivity of Lime concretion black soil,the recommended measurement time is one day.For the undisturbed soil and the disturbed soil under different bulk density conditions,the saturated hydraulic conductivity decreases with the increase of bulk density.The change trend of saturated hydraulic conductivity can be described by an exponential function,and the fitting level of undisturbed soil and soil with different bulk density can reach significantly related levels.(2)The effect of the degree of subsidence on the physical properties of the soil of Lime concretion black soil.The composition of the soil particles is that the greater the degree of subsidence is,the smaller the content of clay in the upper layer is;The lower the total nitrogen level and the organic matter content;the soil moisture is also affected by the degree of collapse,the greater the degree of collapse,the lower the lower soil moisture content;the soil bulk density and saturated hydraulic conductivity are less affected by the degree of collapse,and more affected by the sampling depth,The deeper the sampling depth,the larger the soil bulk density and the lower the saturated hydraulic conductivity.(3)On the whole,under the same water potential,the higher the clay content,the greater the soil water content,and the higher the bulk density,the smaller the soil water content.The impact of the degree of collapse on the soil moisture characteristic curve is that the greater the degree of collapse,the lower the water content of the deep soil under high water potential.The soil moisture characteristic curve of the reclamation group is weakened by the composition of the soil particles and increased by the bulk density.(4)For soil porosity,small pores with an equivalent pore size between one and thirty microns accounted for the highest percentage of total porosity,while the second largest pores with an equivalent pore size between thirty and one hundred microns accounted for the lowest,and The total porosity of the depth and the porosity of different equivalent pore diameters show a downward trend.In areas with greater collapse,the proportion of small porosity decreases,and the proportion of second largest porosity increases.(5)Through the statistical analysis of the soil physical properties and soil porosity of different soil layers of each group,it is found that the degree of collapse mainly affects the change of soil porosity by directly affecting the generation of soil cracks.The greater the degree of collapse,the smaller the number of small pores in the soil.;The degree of collapse indirectly affects the distribution of soil porosity by affecting the organic matter content and soil particle composition.The more organic matter content of the soil,the higher the proportion of small pores and sub-large pores,the higher the clay content,the higher the proportion of small porosity in the soil The higher.