Subsoils characteristics

The final composition of stream water is the product of the weathering reactions and related processes outlined above. However, the chemical processes are influenced and controlled by an intricate combination of environmental factors that are characteristic for each drainage system. Therefore, the composition of the bedrock in an area and the residual material left at the surface as soil and subsoil exert a strong influence on the chemical composition of mnoff from the area. The reactions of water with this material are the ultimate geological control and are the source of soluble weathering products. 

With regard to the last point, [62] rightly point out that the storage capacity of the soil and subsoil is not exhausted everywhere, even in the case of extreme precipitation It is therefore important to determine the limit beyond which a catchment is virtually incapable of storing any more water. However, steep mountainous catchments are only capable of storing low volumes of water and generally react rapidly. The authors [62] then use case studies to demonstrate that in many alpine catchments the response can also be slower, which ultimately results in major spatial variability in the flood characteristics of alpine catchments. 

The EXAFS spectra for the untreated and extracted subsoil samples are shown in Figure 8.8. For simplicity, only extraction steps 1 and 6 are shown, as there is little difference in the spectra between each step. The chi spectra (left panel) have a characteristic double beat at 3.5 and 4.2 A-1 in all three samples, which has been... 

The pollen of many plants can be classified by genus, and sometimes by species, on the basis of such characteristics as size, shape, and surface texture, hi contrast, most spores can only be classified by higher taxonomic levels, such as family or order. Both pollen and spores are well preserved in lake sediment, peat bog, and many archaeological sites. Fossil pollen has even been identified from the bodies of extinct animals, such as mammoths discovered frozen in arctic permafrost (permanently frozen subsoil). 

The high stress-strain characteristics and universal chemical resistance of concrete based on liquid rubber make possible to apply it in various chemically aggressive environments (subsoil waters, solutions of inorganic and mineral acids,... 

Since the spreading behaviour of organic substances in subsoil is very complicated depending on the site (subsoil structure) and material characteristics, at this point only a simplified description is given. For detailed information refer to the available technical literature [8,9]. 

Reference was made in Chapter 20 to some of the chief characteristics of the main types of soil horizons. For further information on the nature of the subsoil materials, reference should be made to the excellent discussion by Winters and Simonson (1951). They give much information on the physical properties, clay minerals and fertility levels of the B-horizons of podzols, latosols, chernozems, and desert soils. They also discuss pan layers. In many cases where these pan layers exist they play a major role in crop production and present problems in addition to those generally encountered in farming subsoils. 

Freshwater lakes often have well-defined catchments (or watersheds) and receive sediment from many sources, most of which have unique or well-defined magnetic characteristics (which must also be measured as part of a comprehensive magnetic study of lake-sediments). The majority of magnetic minerals found in lake-sediments are derived by catchment erosion and originate from bedrock, subsoil, and topsoil in the lake s drainage... 

The marine environment can have varying effects on different materials depending on the specific zones of exposure. Atmosphere, splash, time, immersion, and subsoil have very different characteristics and, therefore, have different influences on... 

It would however be difficult for us to evaluate the characteristics of the subsoil just by measuring the surface settlement only. But the compression of the various subsoil layers can also be measured with equipment such as the deep settlement probes or extensometer. When combined with measurements of pore water pressure, the in situ characteristics of the soil at various depths can be determined. 

The B horizon is commonly referred to as subsoil , consists of mineral layers which may contain concentrations of clay or minerals such as iron or aluminium oxides. This layer is also known as the zone of accumulation . Plant roots penetrate through this layer, but it has very little humus. It is usually brownish or red because of the clay and iron oxides washed down from A horizon. The B horizon may be divided into B1, B2 and B3 types. B1 is a transitional horizon to an A3 containing some A-horizon characteristics. B2 horizons have a concentration of clay, minerals, or organic debris. B3 horizons are transitional between the overlying B layers and materials of whether C or D horizons beneath it. This layer is little affected by soil forming processes. The C horizon may contain lumps or more likely large shelves of unweathered rock. The C horizon also contains parent material. 

The train starts at rest and then travels for a distance of 270 m before it encounters a change in the characteristics of the clay in the subsoil. The Young moduli are shifted from the values in Table 5 to those in Table 6 over a distance of 1.5 m. The transition is illustrated in Figure 4. 

On drainage the peat initially shrinks. Afterwards the organic matter breaks down very rapidly and the soil level can fall by as much as 2.5 cm per year this is called wastage . Eventually the mineral subsoil will come close to the topsoil and have a major effect on the characteristics and potential cropping of the soil. 

In both cases, it is strongly advised to preload the fill in order to control the stress history of the fill. The amount of preload should be related to the future design load of the subject area. When the soft subsoil has been pre-loaded and consolidated, the stiffness characteristics of the material can be predicted from laboratory testing. Where necessary, soil improvement techniques should be used to improve the consolidation rate of the soil (see Section 7). 

Resistance against liquefaction. This is determined by the density of the fill mass (and subsoil) and the characteristics of the dynamic shear load introduced by earthquakes. 

The electrical piezometer measures the actual value of the excess pore water pressures in (soft) cohesive subsoil. The results are used as input in geotechnical computer programmes to analyse the slope stability. Using excess pore pressures in a geotechnical analysis requires that sufficient information must be available on the drained shear strength characteristics c ) of the cohesive soil. Alternatively the undrained shear strength c can be used in the analysis but excess pore pressures are then not relevant. 

Ground improvement in case performance design requirements are not met then improve the soil characteristics increase soil strenght increase relative density (fill and/or subsoil) specify compaction moisture content = optimum moisture content +/-2 % generally not usefull this should not be a specifications, but a recommendation ... 

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