Classification of soils - the system of dividing the set of subordinated units (classes, species, varieties, etc.) of the object "soil" used to establish relationships between them, necessary to achieve the goal.
The problem of soil classification in engineering geology is one of the key problems, since without the dismemberment of the studied area of the lithosphere on a variety of soils having different, certain types of behavior during interactions, it is impossible to imagine the engineering-geological conditions of the construction of the structure. Most engineering-geological tasks and operations require the assignment of soils to a certain class, species, variety. The quality of the general and particular classifications of the object in engineering geology reflects the level of its development as a scientific direction.
The level of quality of classification necessary and sufficient for achieving the goal and solving theoretical and practical problems is ensured by the optimal number and composition of units of the classified set and grounds, compliance with the classification of taxonomic analysis rules. The general classification of soils must encompass a complete set of private representatives (models, objects).
Each class of the analyzed set is represented by a necessary and sufficient number of particular elements. For classification, clear taxonomic rules for dividing the set into taxa and the values of the parameters according to which the private representative will be assigned, for example a soil sample to a certain soil class, will be specified.
The choice of the classification structure, the ranges of possible changes in indicators of different qualities within the classes and the composition of the characteristics within the class of the set remains with the geologist engineer. He is guided by the existing ideas about the object and the tasks that follow from the goal.
Types of soil classification in engineering geology
The construction of classifications is based on the use of direct and indirect (diagnostic) grounds. The former are directly related to the tasks being solved, the second is closely corroded with direct attributes and can be used to assign objects to a particular class. In the simplest cases, the classification of soils can be built on one set of indicator indicators (for example, for sands by the granulometric composition), in complex (with the allocation of several co-ordinated levels) on several sets of characteristics, and at each level one can be used (the matrix system ) and different feature sets (tree-like system). Formal attributes-bases used in the construction of classifications are determined in their majority by theoretical, statistical and experimental field or laboratory methods. Both types of classifications can be combined in one form or another.
By appointment all the indicators can be divided into two types: classification and calculated.
Estimates are the indicators used in engineering design, as well as in engineering and geological work, in particular in calculating the values of the indices of some properties of the soil according to its characteristics composition or other properties. As a design, a wide range of parameters of composition (granulometric composition, humidity, etc.) and properties (first of all, strength, deformation, water permeability) of soils can be used.
Classification indicators are any indicators describing the features of the composition, structure, condition and properties of soils, on the basis of which their various categories are distinguished in their sample (classes, types , species, etc.). It is the classification indicators used in the compilation of soil classifications by their various characteristics (mineral and granulometric composition, swelling value, etc.).
In terms of representativeness the parameters used to characterize the soils are divided into particular (individual) and generalized (normative and calculated.
Particular indicators characterize any feature of the composition, structure, condition or property of the soil at a particular point.
The generalized characteristics describe the same soil characteristics, but applied to a specific sample obtained by examining one soil sample at different points or different samples of the same soil selected for that or other system of testing in the thickness. The categories refer to the so-called normative and calculated indicators. The normative values of soil characteristics (X ") are defined as the arithmetic mean of the partial results of the definitions for each element or layer selected on the construction site.
The calculated values of soil characteristics are determined by the formula X = X "/ y gt where X" is the normative the value of this characteristic; y g - the coefficient of reliability on the ground ensuring the safety of calculation. The coefficient of reliability in calculating the calculated values of strength and physical characteristics (specific adhesion, the angle of the internal view of non-subsurface soils, co-generation, and specific gravity) is determined depending on their variability, the number of definitions and the confidence probability value (for base calculations, , 95, and for deformations - 0.85). For other characteristics it is allowed to take y x = 1.
In the practice of engineering and geological research, two types of classifications are used: genetic and formal-logical.
Genetic classifications are based on the definition of genesis and soil formation conditions, which are established on the basis of general geological considerations and a set of diagnostic features. These operations are only amenable to limited formalization, which is their significant drawback. However, the allocated genetic types contain rich information about the physical, mechanical and other properties of soils and can serve as a reliable basis for predicting their predisposition to various natural and anthropogenic processes, behavior when interacting with engineering structures.
Formal-logical classifications are based on the rules of formal logic, taxonomic analysis. They can be subdivided into private , industry, regional , and general.
Private classifications are logical constructions that subdivide a multitude of soils along one or several concrete, as a rule, quantitative, morphological for the composition and properties of soils. Their examples are the classification of soils by the granulometric composition, the classification of clay soils by the consistency index, the classification of soils by the size of the swelling deformation or swelling pressure.
Private classifications, reflecting the interaction of indicators of mechanical and physical properties, it is advisable to build according to the following scheme. The first stage reflects the characteristics that ultimately determine the name of the soil, the second stage - the composition indicators, the third - the indicators of the state (physical properties), the fourth - the characteristics of the mechanical properties. Therefore, the main task arising in the development of a private classification is the identification of composition indicators, physical and mechanical properties that would correlate satisfactorily with each other. In a private classification, the values of mechanical characteristics can be given, while the varieties are selected in such a way that the parameters of the mechanical properties vary within a narrow predetermined range.
Industry classifications are usually private soil classifications developed with respect to the tasks and requirements of a particular, specific type of human construction activity. Such classifications were developed in relation to the requirements of road, hydraulic engineering and other types of construction. Of the sectoral special classifications, the following are most common.
Classification of soils by their stability in slopes. The measure of this stability is the angle of the natural slope, ie, the maximum, the greatest slope angle of the slope surface, where the ureuses are still in a stable state. Classification is applicable for the design and construction of canals, low embankments, depressions, dams and other earthworks.
Classification according to the carrying capacity of soils, determined by the greatest load, which does not cause dangerous deformations of structures, sediment, disturbance of their stability. Classification is widely used in the design and construction of structures, calculations of patency of technology.
Classification by the method and difficulty of mining of rocks. In this construction classification, rocks are categorized according to the type of tool they are developed: with percussion instruments, with partial application of blasting operations or only explosive way. Widely used in the performance of excavation, as a category of rocks determines their value.
Classification of rock strength , characterized by their resistance to destructive forces. Strength of rocks depends on many physical and mechanical properties: hardness, viscosity, fracturing, brittleness and elasticity. In mining, the scale of the rock fortress, proposed by M.M. Protodyakonov, according to which all the rocks, depending on the strength of the fortress, are divided into ten categories. The strongest rocks (quartzites, basalts, etc.), having the coefficient of strength Uph = 20, are classified in the I category, and the least strong (quicksand, liquefied soils), having Ukr 0.3, to the X category. The construction normative documents adopted a reverse scale in which the strongest rocks (sUf = 20) are assigned to the highest, XI, group for the complexity of development, and the least strong - to the I group.
Classification by degree of water permeability or water absorption. The water permeability of rocks, and for rock and semi-rock rocks also their fractures, are the filtration coefficient and specific water absorption. The coefficient of filtration characterizes the velocity of water in the rock with a pressure gradient equal to unity. By specific water absorption is meant the flow of water absorbed by the rocks, opened by the well, at the head and the length of the interval equal to 1 m. The coefficient of filtration is an absolute characteristic of the rock, and the specific water absorption is relative, comparative. Both these indicators are often used to solve various construction problems.
The regional classifications systematizes knowledge of soils developed in one or another, but a certain territory. At their construction not only quantitative and qualitative, but also genetic and age indices are taken into account. In the form of regional, private classifications, tied to chemical-mineral features of soils of a certain territory. At the initial stages of design, regional typifications are widely used, which are developed taking into account the regionalization of the territory of the region by natural conditions. The zoning is also performed according to certain logical principles :
• objectivity, according to which the allocated areas are objectively existing in nature reality;
• the genetic relationship and the interdependence of natural conditions;
• multifacetedness, expressed in the possibility of wide practical application of regionalization;
• the conventions of boundaries, which in reality are represented not by lines but by zones of transition of quantitative characteristics to a new qualitative state;
• a general contour that does not allow the existence of non-ionized sections and the crossing of boundaries of sections of the same rank;
• Monologue - the leading principle that determines the unity of criteria for the allocation of territories of one hierarchical rank.
Zoning is carried out on the basis of the classification characteristics chosen by the researcher, the most important of which are the characteristics characterizing the distribution of rock complexes, which have the same structure, composition, state and engineering-geological properties. When establishing the importance and sequence of characteristics in the case of using multistage zoning schemes, the first steps should always give preference to those features that are associated with the greatest number of individual components of engineering-geological conditions. Usually when zoning the territory is divided:
• on the regions - according to the structural-tectonic character;
• on the field - by geomorphological conditions and features of the relief;
• to areas - but to geological and genetic rock complexes;
• on the sites - according to one of the factors characteristic for the given territory.
General classification is designed to consider the complete, global diversity (a full set) of soils and systematize them into a certain, logically consistent hierarchical system. When it is compiled, the logical operation of dividing the concept of "soil" is performed. according to the classification criteria selected by the researchers, which can be used as genetic age and morphological indicators. Each of these groups of indicators should be used at certain stages of classification, but they can not be confused at one stage. The general classification of soils is used to solve many problems: the systematization of multiple soils into a logically consistent hierarchical system, obtaining a "measure of the theoretical maturity of soil science" or "tool for the further development of the theory", finding the basis for constructing private classifications used in the practice of a geological engineer.
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