Morphology development evaluation of reclaimed soil in coal-mining subsidence areas with high groundwater levels

Soil morphological characteristics contain abundant environmental information. It is an important basis for environmental change and ecological reconstruction and can be used to infer the strength of soil development. Reclaimed soil is man-made new soil and its morphological characteristics are related to reclamation methods, which is significant for renovating reclamation technologies and improving reclaimed soils. This paper involved conducted research on soil morphological characteristics and its evaluation method of soil morphological development for reclaimed soils in coal-mining subsidence areas with high groundwater level, which were reclaimed by four-type reclamation methods. These methods included digging deep to fill shallow areas by excavators, digging deep to fill shallow areas by use of a hydraulic dredge pump, filling reclamation with exogenous soil and filling reclamation with fly ash or coal wastes. The quantitative evaluation of the morphology development of reclaimed soil in coal-mining subsidence areas with high groundwater level was done by a field investigation of 23 soil profiles and indoor analysis. The evaluation indicators and model were constructed based on the soil profile description standard of Chinese Soil Taxonomy (3rd edition, 2001). A soil morphology development evaluation index system was constructed to quantitatively measure the development degree of reclaimed soils. This evaluation index system combined features with six soil morphological properties based on morphological systematic observation and description for each layer soil. These six morphological properties are: color (hue, value and chroma), texture type, consistence (stickiness and plasticity), structure type, soil intrusions and horizon boundary (visibility and transition). On the basis of these indicators, the HI(horizon index) and WPDI (weighted profile development index) were developed preliminarily. The study then tried to research the reclaimed soil development status with a simple quantitative method.The results show that the horizon index (HI) and the weighted profile development index (WPDI) can reflect the difference of soil development degree between reclaimed soils and local original undisturbed soils. The HI and WPDI average values of reclaimed soil are 0.57, 0.56, and the values of local original undisturbed soil are 0.68, 0.69, which shows that the reclaimed soil formation development level is relatively weak. The HI shape of reclaimed soil significantly different from local original undisturbed soil, which indicates the different forming and developmental process between them, and the surface layer HI general higher than other soil layer, which indicates the reclaimed soil as still in a weaker development phase. The development degree sequence of reclaimed soil based on WPDI reveals that: filling reclamation with exogenous soil > digging deep to fill shallow by excavators > digging deep to fill shallow by hydraulic dredge pump > filling reclamation with fly ash or coal wastes. With the reclamation time extension, the soil morphology development degree presents a growth trend. The resulting soil morphology development evaluation system is probably a convenient and effective method to evaluate the pedologic development degree of reclaimed soil in the field of coal-mining subsidence areas with high groundwater levels.