By Practica masa volumen del suelo gyjuancalzada «OR6pR 17, 2011 II pagos Objetivo Evaluar las características físicas del suelo y definir sus componentes principales con base a su masa y volumen, expresándolos en ecuaciones matemáticas, para aplicar los algoritmos para la obtención de componentes por medios indlrectos, en dos muestras dlferentes.
Introducción La evaluación de las características del suelo y la identificación se sus propiedades especificas que puedan servir como indicadores de su función presentan grandes variantes debido a muchos aspectos que definen a dicho sustrato y a los múltiples actores, físicos, químicos y biológicos que controlan los procesos biogeoquimicos y su variación en el tiempo, espacio e intensidad.
El estudio de las caracteristicas en relación a la masa volumen, se realizan con el fin de y así determinar sus tomar decisiones par eali con respecto a la acti ambiental o en el ra Marco Teórico PACE 1 ori 1 to View e forma estructural , y así discernir y nicas pertinentes, agronómica, Volume And Mass Relationship Of Soil Constituens We now consider the volume and mass relationships among the three soil phases and define some basic parameters that have een found useful in char- acterizing the composite soil physically.
Figure 1 is a schematic representa- tion of a hypothetic to nex: page hypothetical soil in which the three phases have been separated and stacked one atop the other for the purpose of showing their relative volumes and masses. (To do so in practice, we would need to compress the solid parti- cles into a Slngle poreless block, an obvious impossibility. But in the process of pedagogy, assuming the impossible is commonplace. In Fig. 1, the masses of the phases are indicated on the right- hand side: the mass of air Ma, which is negligible compared to he masses of solids and water; the mass of water Mw; the mass of solids M4 and the total mass M t. (These masses can also be represented in terms of their weights, being the product of each mass and the gravitational acceleration. The volumes of the same components are indicated on the left-hand side of the diagram: volume of air V-, volume of water Vw, volume of pares Vf = V— + Vw, volume of solids Vs, and the total volume of the representative sample Vt On the basis ofthis diagram, we can now define terms that are generally used to express the quantitative interrelations of the hree primary soil phases. Density Of Soil (Mean Particicle Density) Ps Ps=MS/VS In most mineral soils, the mean mass per unit volume of solids is about 2600-2700 kg/m 3.
This is close to the density of quartz, which is generally the most prevalent mineral in the coarsest fraction of the soil. Some of the miner- als composing the finest fractlon coarsest fraction ofthe soil. Some of the miner- als composing the finest fraction ofthe soil have a similar density. However, the presence ofiron oxides and ofvarious other «heavy» minerals (generally defined as those having a densiõy exceeding 2900 kg/ 3) increases the average value of ps, whereas the presence of Iow-density organic matter generally Iow- ers the mean density of the solids.
Sometimes the density is expressed in terms of the Gg, which is the ratio of the density of any material to that ofwater at 4 – C and at atmospheric pressure. The latter density is about 1000 kg/m 3, so the specific gravity of the solid phase in a typical mineral soil is about 2. 55, a value that is numerically (though not dimensionally) equal to the dens’ty expressed in the cgs system of units (g/cm3). Air Solids Mazo Water Ms Va VW Vt Volume Relations Mass Relations
Fig 1 Schematic diagram of the soils as a three-phase system Dry Bulk Density (Pb) Pb=MsVt-MsVs Va+Vw The dry bulk density expre of the mass of solids 30F11 to the total soil volume (s s together). Obviouslv, density to the density of water at standard conditions) of 1. 3-1. 35. The bulk specific gravity of Sandy soils with a relatively Iow volume of pores may be as high as 1. 6, whereas that of aggregated loams and Clay soils may be below 1 . 2. In contrast with the mean particle density, which is typically con- stant, the bulk density is highly labile.
It is affected by the structure of the oil, that is, its looseness or degree of compaction, as well as by its swelling and shrinkage characteristics. The latter depend both on Clay content and wáter content. Even in extremely compacted soils, however, the bulk density remains appreciably Iower than the density of the solid matter, because the particles can never interlock perfectly. Through the pore space can be greatly reduced by compaction, It can never be ellmlnated. Total (Wet) Bulk Density (Pt) Pt-MtVt—Ms+MwVs+Va+Vw This is an expression of the total mass of a moist soil per unit volume.
The wet bulk density depends even more strongly than he dry bulk density on the wet- ness or water content of the soil. Dry Specific Volume (Vb) Vb—VtMs- 1 Pb The volume of a unit mass of a dry soil (the reciprocal ofthe dry bulk density) serves as another useful index of the degree of looseness or compaction of a soil body. Porosity (f) Porosity is an index of the space in a soil. Its value index of the relative pore space in a soil. Its value generally ranges from 0. 3 to 0. 6 (30-60%).
Coarse-textured soils tend to be less porous than fine-textured soils, though the mean size of individual pores is greater in the former. In clayey solls, the orosity is highly variable as the soil alternately swells, shrinks, aggregates, disperses, compacts, and cracks. As generally defined, the term refers to the volume fraction of pores, and this value should be equal, on average, to the areal porosity (the fraction of pores in a presentative cross-sectional area) as well as to the average lineal poros- ity (the fractional length of pores along a straight line passing through the soil in any direction).
However, the total porosity reveals nothing about the sizes or shapes of the various pores in the soil. Void ratio (e) The void ratio is also an index of the fractional pore space, but t relates that space to the volume of solids rather than to the total volume of the soil. As such, it ranges between 0. 3 and 2. The advantage of this index over the pre- ceding one is that in the case of e any change in pore volume affects only the numerator of the defining equation, whereas in the case off such a change affects both the numerator and the denominator.
Void ratio is the index gener- ally preferred by soil engineers, whereas porosity is more frequently used by ecologists and agronomists. Soil Wet engineers, whereas porosity is more frequently used by ecologists nd agronomists. Soll Wetness (water Content) The water content of a soil can be expressed in various ways: relative to the mass of solids, or to the total mass, or to the volume of solids, or to the total volumet or to the volume of pores. The various indexes are defined as follows: Mass Wetness (w) w=Mw/Ms This is the mass of water relative to the mass of dry soil particles.
The stan- dard definition of refers to a mass of soil dried to equilibrium (in practice, over a 24-hour period) in an oven at 105— though a clayey soil may Still contain an appreciable amount of water at that state. Mass wetness is sometimes expressed as a decimal fraction but more often as a percentage. A sample of soil dried in «ordinary» air at ambient temperature (rather than in an oven) Will generally retain several percent more water than if dried in the oven.
Similarly, an oven-dry soil exposed to «ordinarya air Will gradually gain appreciable moisture. This phenomenon results from the tendency of the soilis Clay fraction to adsorb moisture from the air, a property known as HYGROSCOPOSITY. The amount thus adsorbed depends on the type and content of Clay in the soil, as well as on the humidity of the ambient tmosphere. The water content at saturation with all pores filled with water, is also higher in clayey than in Sandy soils.
In different soils, w2 can range with water, is also higher in clayey than in Sandy soils. In different soils, w2 can range between 25 and 60%, depending on bulk density. In the special case of organic soils, such as peat or muck soils, the saturation water content on the mass basis may exceed 100%. Volume Wetness (B) a —VwVt-VwVs+Vf The volume wetness (often termed is generally com- puted as a percentage of the total volume of the soil. At saturation, herefore, it is equal to the porosity.
In Sandy soils, Os at saturatlon is on the arder of 40%, in medum-textured soils, it is approximately 50%; and in clayey soils it can approach 60%. In the latter, the volume of water at saturation may even exceed the porosity of the dry soil, since clayey soils swell on wetting. The use of O rather than w to express water content is often more convenient because it is directly applicable to the computation of fluxes and water volumes added to soil by rain or irrigation and to quantities extracted from the soil by evapora- tion, transpiration, and drainage.
The volume ratio 0 is also equivalent to the depth rato of soil watm, that is, the depth of water per unit depth of Water Volume Ratio (vw) For swelling soils, in which the porosity changes markedly with wetness, it may be preferable to refer the volume of water present in a sample to the invariant volume of particles rather than to the changing total volume. At sat- uratlon, v w is equal 1 invariant volume of particles rather than to the changing total volume. At sat- uration, v w is equal to the void ratio e. Degree of saturation (s) This index expresses the water volume present in the soil relative o the pore volume.
Index s ranges from zero in a completely dry soil to unity (100%) in a completely saturated soil. Complete saturation, however, is hardly ever attain- able in field conditions, because some air is nearly always present. In a rela- tively dry soil, the air phase occupies a continuous space, whereas in a very wet soll air may be occluded or encapsulated in the form of discontinuous bubbles. Air-Filled Porosity (Fractional Air Content) (fa) fa=VaVt=VaVs+Va+Vw This is a measure of the relative content of air in the soil, and as such an important criterion of soil aeration.
It is related negatively to the degree of sat- uration s (i. e. , — = f- s). The relative volume of air in the soil may also be expressed as a fraction, a, of the pore volume- Thus, Additional relationships From the basic definitions given one may derive the relations of vanous parameters to one another. Relation between Porosity and Void Ratio e-fl-f Density Pb=l-fps Relation between Mass Wetness and Volume Wetness 9=wPbPw vv=epwpb Here pw is density ofwater (1000 kg/m 3 at standard temperature and pres- sure).
The ratio of bulk density to water density is the bulk specific gravo’. In mineral soils, bulk density is generally greater than water density, so volume wetness exceeds mass wetness—the more so in compact soils of higher bulk density. Relation among Volume Wetness, Air Content, and Degree of Saturation Several of these relationships are derived at the end of this chapter, and the proof of the others is left as a useful exercise for students.
Of the parameters defined, the most commonly used are porosity, bulk density, volume wetness, and mass wetness. Metodología para llevar a esta práctica se realizaron los siguientes pasos: De dos parcelas definidas, tomar tres muestras a una rofundidad aproximada al principio, a la mitad V a iferentes puntos, uestra debe pesar quedar agregados mayores, se procedió a desintegrar de forma mecánica para posteriormente tamizar de nuevo y homogeneizar la muestra.
Ya con la muestra homogeneizada se prosiguió a llenar un cilindro de PVC, con dimensiones de 15 cm de altura y 10 cm de diámetro. Y se tomaron los pesos del cilindro (Pc) y el peso del cilindro más el peso del suelo seco al aire (Pssa). Antes de esto se tomaron dos porciones de igual magnitud de la muestra de un kilogramo, de las cuales una se secó al aire y otra se procedió secar en el horno a una temperatura de 1050C hasta alcanzar un peso constante.
Se tomaron los pesos de dichas muestras, el peso de suelo seco al aire (Pssa) y el peso del suelo seco al horno (Pssh). Con estos datos se procedió determinar el porcentaje de humedad Hum), con la siguiente formula: Y asi mismo determinar la densidad aparente del suelo (Pb), a través del uso de las siguientes formulas y deducciones Pb=MssVol Donde: Pb=Densidad Aparente Mss=Masa del Suelo Vol= Volumen n-3. 1416 r= radio altura 1–;urn100 Paz peso de agua Pssa= peso suelo seco al a
