In the list of geodetic works, you can sometimes find such a service as determining the composition of the soil. This procedure is performed in order to obtain information about the content of particles in the soil in a particular area. In construction work, the determination of such a composition is required infrequently, but in agriculture and geological exploration activities it is indispensable. In this case, the granulometric composition can be determined by different methods. The choice of one of them depends on many factors and conditions.
General information about particle size distribution
Under the granulometric composition is understood the presence of mechanical elements in the soil. Moreover, in this case, the soil can be considered as a general designation of the soil, which can also be artificial. As for the particles, they can have different characteristics and origins. There are also different types of compositions in concentration. For example, the particle size distribution of sand will be more or less homogeneous, even in terms of the content of particles of a certain fraction. Experts note that the minimum size of elements that are able to identify the practiced techniques of this analysis,is only 0.001mm.
In accordance with GOST, six types of fractions are distinguished - these are the same sand particles, blocky, gravel, clay, etc. Each fraction has not only its own range of standard sizes, but also a biological origin. At the same time, one should not think that only the content of small particles characterizes the granulometric composition. GOST under the number 12536-79 also notes that the maximum size of the fraction, which is taken into account as an integral part of the soil, reaches 200 mm. These are mainly boulder elements, which can be large. The smallest fraction is clay, although sand particles can compete with it in this indicator.
Grain Size Classifications
Besides the fractional gradation of soils, there are other principles of classification. One of them provides for separation based on the content of clay particles. In this case, the nature of soil formation is also taken into account and the dominant fraction is revealed. An alternative classification is to determine the type of composition through the presence of elements of sand, dust and the same clay. That is, in some way, such a particle size distribution will be determined by a combined principle with a comprehensive presentation of information about the elements included in it. It is important to note that due to the similarity between the two approaches to the classification of compounds, it is quite difficult to distinguish between them in practice.
Direct methods for determining composition
There are two fundamentally different groups of ways to determine the mechanical composition of the soil. One of them is indirect and designed to identify the patterns of soil formation in a particular area, and the other represents a segment of direct methods based on technical means of analysis. In particular, the group of direct methods can use special devices, devices and fixtures that make it possible to determine the parameters of particles with a high degree of accuracy. In particular, electron and optical microscopes can be used that realize micrometric examination. The direct method allows you to more accurately determine the granulometric composition of the soil, however, due to the complexity of the technical organization of the process and the high cost, it is used extremely rarely.
Indirect methods for determining composition
This group of methods for determining the composition usually includes methods that are based on the use of different patterns in the structure of the mixture under study. In particular, dependencies between the array elements themselves can be identified, but most often a complex analysis is assumed. That is, other characteristics of the soil are also taken into account in the comparison process, including moisture, suspension properties, sedimentation dynamics, etc. Indirect methods for determining particle size distribution also involve optical and hydrometric methods of recording physical qualities. In addition, the latest technologies allow the use of natural sedimentation modeling. If we compare this line of analysis with direct methods,then its disadvantages include low accuracy. Therefore, if it is required to carry out a one-time study on a specific site, then the direct method will still be preferable. But in large-scale and regular work, only indirect methods are economically justified.
Areometric method
This is a highly specialized, albeit popular, technique that is based on the principles of displaced fluid. Actually, this is how the hydrometer used in the analysis process works. The principle itself operates according to the rule according to which the volume of the displaced liquid will be equivalent to the mass replaced by a new body. Only in the case of the practice of using hydrometric techniques, the granulometric composition of the soil is determined through the collected suspension. In particular, the person skilled in the art also checks for deviations from previously obtained data by immersing the particles in water. Typically, such an analysis is performed serially, and in each case, work is carried out to determine one characteristic - density. Again, based on the relationship of particles and the conditions of their stay in the soil, in this way it is possible to determine the fractional and mechanical composition.
Pipet method
In this case, a liquid medium is also used, which makes it possible to distinguish between individual particles according to their characteristics. The sample taken is immersed in water, after which the rate of fall of the elements of the composition is recorded. After a certain period of time, the analysis is completed, and the settled particles are removed. The sample is then dried, measured and shapedtest report. As a rule, the determination of particle size distribution by this method is used in the analysis of clay soils. This is due precisely to the fact that the particles in such soil have a fine fraction, which can be analyzed by the rate of fall in liquid media.
Rutkowski method
Like all indirect methods of composition analysis, this technique is not very accurate and gives only a general idea of the elements contained in the studied mass. The very principle of determining the characteristics of particles by the Rutkowski method is based on two parameters. First of all, this is the same speed of falling of an element in a liquid medium. But in this case, the relationship is traced not between the speed and the origin of the particle, but in relation to the dynamics of immersion to size. And the second parameter, which makes it possible to determine the granulometric composition of the soil using this technique, is based on the ability of the particles to swell in the same aqueous medium. This part of the analysis reveals both the physical and, in some ways, the chemical qualities of the mass.
Sieve method
This is one of the oldest and most common methods for determining soil composition. It is based on the use of special sets of sieves that let through fractions of the same size, and do not let particles with larger parameters pass. The method is simple and affordable to use, so it is often used in the construction industry, where it is not possible to organize complex methods of indirect analysis. However, it is impossible to check the composition through a sieve withcan be confidently attributed to direct methods. Nevertheless, such an analysis will not allow one to determine, for example, the granulometric composition of rocks with the same degree of accuracy as a micrometric study will do. True, the accuracy will largely depend on the analysis tool - that is, a set of sieves. There are two categories of these devices. One of them focuses on working with sifting without washing. In this case, the cells have a size of 0.5 to 10 mm. Another group represents sieves having a passage fraction from 0.1 to 10 mm.
How does particle size distribution affect plants?
Both the fraction and the representation of different minerals affect the agro-technical properties of the soil. In particular, the composition can determine the water-air environment of the soil, its tendency to erosion processes, aggregation, density, biological and chemical qualities. For example, sandy and clay soils cause the environment to be weak in terms of air and moisture exchange. This is detrimental to most plants - especially those grown within agricultural land, where the fertile layer is also affected by the nature of cultivation. But the granulometric composition is important for vegetation, not so much in terms of structure and density, but in terms of the content of useful elements. Sometimes the presence of magnesium, phosphorus and s alts in itself provides an optimal layer of nutrient base, eliminating the need for additional fertilizers.
Conclusion
An example of technological approaches to the analysis of soil in terms of granulometric composition shows how the latest measuring instruments are not competitive in front of research methods using elementary physical rules and patterns. Of course, it cannot be said that the determination of the granulometric composition of the soil through micrometric analysis loses to indirect methods in terms of quality performance. But in terms of practicality, it is the second group that is more effective. At the same time, the very concept of using high-precision technical means is not canceled at all. The most promising methods just involve combining the two principles of research.
