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The hydraulic gradient is the rate of change of total head with distance. The total head, at a point is defined as the height (measured relative to the datum) to which water would rise in a piezometer at that point. The total head is related to the excess water pressure by:
The first modern theoretical models for soil consolidation were proposed in the 1920s by Terzaghi and Fillunger, according to two substantially different approaches. [1] The former was based on diffusion equations in eulerian notation, whereas the latter considered the local Newton’s law for both liquid and solid phases, in which main variables, such as partial pressure, porosity, local ...
It is worth mentioning that Kuhnle et al. (2013) [34] applied the Wilcock and Kenworthy (2002) [33] formula to their experimental data and found out that predicted bed load rates of sand fraction were about 10 times greater than measured and approached 1 as the sand elevation became near the top of the gravel layer. [34]
The available volume for additional water in the soil depends on the porosity of the soil [7] and the rate at which previously infiltrated water can move away from the surface through the soil. The maximum rate at that water can enter soil in a given condition is the infiltration capacity.
The soil production rate due to weathering is approximately 1/10 mm per year. [5] New soils can also deepen from dust deposition. Gradually soil is able to support higher forms of plants and animals, starting with pioneer species and proceeding along ecological succession to more complex plant and animal communities. [6]
Soil temperature depends on the ratio of the energy absorbed to that lost. [68] Soil has a mean annual temperature from -10 to 26 °C according to biomes. [69] Soil temperature regulates seed germination, [70] breaking of seed dormancy, [71] [72] plant and root growth [73] and the availability of nutrients. [74]
Soil bulk density, when determined at standardized moisture conditions, is an estimate of soil compaction. [60] Soil porosity consists of the void part of the soil volume and is occupied by gases or water. Soil consistency is the ability of soil materials to stick together. Soil temperature and colour are self-defining.
The activity of soil is the ratio of the plasticity index to the clay size fraction. If activity is less than 0.75, the soil is inactive. If activity exceeds 1.4, then the soil is termed active. If activity lies within the above values, then the soil will be moderately active. [10]