Cycle of Soil Structure
(2013)
Our study deals with agricultural recultivation of open cast brown coal mining areas in Lusatia, Eastern Germany. In this region the largest brown coal (lignite) mining area of Germany is located. Lignite mining activities lead to major disturbances of the landscape. Recultivation efforts attempt to regenerate mining areas for agricultural land use options. The geological “parent” material is of saaleian origin, has a sandy texture and was excavated from several meters depths before mining and is now used for recultivating the excavated area. Consequently, it is free of recent soil organic carbon. The substrate itself is unstructured. The partly wet or dry substrate is subjected to strong mechanical stresses during the excavation, deposition, refilling and levelling processes throughout the year. This practice leads to more or less compacted soils/substrates which may result in small yields of agricultural crops. In this context we investigate the effect of different organic soil additives in combination with different recultivation crop rotations on the development of soil structure for improved agricultural land use. Our experimental site has been heaped up and levelled off in 2006 and 2007. On each of the 24 experimental sub areas undisturbed soil samples have been taken to characterise the substrates according to their mechanical and hydraulic parameters and to determine the scattering of these parameters on a site that is assumed to be recultivated as homogenously as possible. First results of our ongoing experimental study indicate that the soil physical properties such as texture, bulk density, precompression stress, air permeability and saturated hydraulic conductivity are not identical on each of the 24 subplots. The soil physical properties behave differently in relation to each other. E.g. we found a negative correlation between bulk density (∼1.35–∼1.90 g/cm3) and precompression stress (∼30–70 kPa) and no decisive interrelation between bulk density and air permeability or saturated hydraulic conductivity.
Grazing-induced alterations of soil hydraulic properties and functions in Inner Mongolia, PR China
(2009)
Natural shear forces due to gravity along inclined terrain surfaces are controlled by the inclination of the terrain, material composition and its mechanical properties, stratification and hydraulic stress states. Both shear forces and shear strength under a given inclination of the terrain surface strongly depend on the interaction between mechanical and hydraulic stresses. These internal conditions as well as the interactions between these various components are fundamentals in all nonplanar regions under arable, forest or grassland management and they dominate also under various geoscientific aims. Generally, soil creep is a slow soil movement downslope under gravity. It can occur even on gentle slopes when the shear forces exceed the shear strength of the soil. Deposited material on slopes is more sensitive to such movements than well-developed soils due to the absence of a pronounced soil structure, site and management dependent hydraulic properties and functions, which results in low soil strength. We applied the described measurements and the modelling approaches to investigate and to analyse the stability of an artificially constructed water catchment (Chicken Creek) in the mining district of Cottbus/Germany, where glacial sand was deposited above a clay layer with an inclination of about 3.5%. At the lower part of the catchment, an impermeable barrier (claywall)was positioned transversally to the main slope. Mechanical and hydraulic parameters of the soil layers were determined on soil samples taken from the field site. The measured values were inserted as input parameters for the finite element model (Plaxis 2D) to simulate soil movements and their effect on the stability of the catchment. The obtained results showed that the kind of construction negatively affected the physical low soil strength (low precompression stress) although the bulk density was very high (1.7–1.9 g/cm3 for the sandy material). Hydraulic conductivity revealed a significant anisotropy with higher hydraulic conductivity values in the horizontal direction. Furthermore, finite element results showed that the design of the newly formed landscape remains weak concerning mass movements too. The high water table in the sandy material in conjunction with low soil strength enhances the downslope movement and increases the shear stress near the clay wall at the lower end of the slope, which finally results in soil creep processes. These results also proof that such geotechnical and modelling approach is also suitable to validate or to predict mass movements and the internal processes responsible for these internal mass erosion.