Soil mechanics: its content and place, main characteristics and what forces act

Soil properties are important in construction, especially how different types of soil behave under load and how the buildings themselves affect it. There is a special discipline that studies the strength and stability of soil masses and the conditions for their use as foundations for the construction of structures. Consider what is included in the concept of soil mechanics, how to correctly calculate soil parameters.

Soil density

Density is a soil property, which is determined by the ratio of specific gravity to volume. It depends on the mineralogical composition of the soil, as well as the degree of dispersion, which is why clay soils are denser than sandy ones, despite the fact that their mineral composition is the same.

Among the physical and mechanical properties of soils, density is considered one of the main ones. According to the characteristic density, one can judge their state. Determination of density is necessary in the construction of roads, foundations of buildings (to distribute stresses on the base), when laying communications, to calculate the resistance of slopes to landslides, settlements of constructed buildings, to determine the amount of earthworks.

Density affects soil water permeability. If it is damp or has good absorbency, then after the construction of the building it can sit down, in winter another problem arises - frost heaving. Knowing the density of the soil will help prevent the destruction or flooding of the building, choose the right materials for construction.

Particle density

This is a physical characteristic of the soil, it depends on the mineral composition, organomineral and organic substances.Particle density is the ratio of the mass of solid particles of completely dry (without moisture) soil to its volume with an undisturbed structure. Depends on the mineral composition, the density of particles is determined by structural bonds and structure, soil porosity. The more minerals the soil contains and the less porosity, the denser it is.

The value of particle density determines the values of strength and deformation characteristics, which evaluate the bearing capacity of soils and the possibility of their use for the construction of structures.

Soil moisture

Moisture is the ratio of the mass of liquid contained in the soil to its dry mass. The bearing capacity of the soil depends on this characteristic. In almost all soils, except for coarse-grained rocks and coarse sand, the bearing capacity decreases with increasing humidity. So, for a water-saturated one, it will be less than for a dry one.

Determine the humidity in the laboratory by compaction, that is, determine at what moisture content the soil will acquire the greatest density. The characteristic is expressed as a percentage, from 0 to 100%. The optimum humidity for sand is 8-14%, for sandy loam - 9-15%, loam - 12-18% and clay - 16-26%.

Grain size distribution

Granulometric or mechanical composition - the percentage of particles of different sizes in the soil or rock, regardless of its chemical and mineral composition. Soil particles are isolated remains of rocks, minerals, amorphous compounds, and other constituents of soil components that are in a chemical bond. Particles similar in size are combined into fractions. There are such types of soil mechanical elements: organomineral, organic and mineral.

Particle fractions are found in soils or rocks in different quantitative ratios and have different properties.As a result, soils also have unequal properties. All the variety of soils and rocks in terms of mechanical composition can be combined into groups that will be characterized by similar physical and chemical properties. The classification is based on the ratio of sand and clay. The sizes of the sand and clay fractions are determined by the diameter of the particles, which are larger or, respectively, smaller than 0.01 mm.

The agricultural properties of the earth depend on the mechanical composition, for example, the ability to pass and retain moisture and air, the processes of movement of substances, accumulation and transformation, structure, thermal and air modes. And, ultimately, it depends on how fertile the land will be, both with constant cultivation, watering, fertilization, and without them.

Density of dry soil

Defined as the ratio of the mass of absolutely dry soil (without moisture in the pores) to the volume, taking into account the volume of the pores. The characteristic is measured in g per cubic meter. see it can be determined if moisture and porosity are known. Calculations are carried out in laboratory conditions.

Porosity factor

The coefficient shows the presence of small voids in the soil. Calculated as a percentage ratio between void volume and total volume. Different methods are used to determine the value on different soils. On clay soils, due to cohesion, porosity is determined in accordance with the volumetric and specific gravity of the soil taken for the sample.

Determination of the porosity coefficient is necessary in preparation for construction, as there is a connection between it and other characteristics. The level of bearing capacity depends on the porosity index, it decreases with a decrease in porosity. Without information about porosity, it is impossible to learn about the degree of soil resistance, to determine the possible deformability of buildings.

Deformation of buildings occurs due to the movement and compressibility of soil particles, for example, due to the effects of precipitation. Minor and uniform do not reduce the stability of buildings, but a large amount of moisture can cause unwanted deformations. Uneven settlements are even more dangerous, they can cause displacements and tilts, leading to overstressing in load-bearing structures. If the compressibility of the soil under different parts of the foundation is not the same or the load on it is different, you can often encounter deformation of the building in the form of cracks and subsidence.

Degree of humidity

This is the ratio of natural soil moisture to moisture that corresponds to moisture in pores filled with water, in which no air bubbles remain. Soil is considered low-moisture with indicators from 0 to 0.5, wet - from 0.5 to 0.8 and water-saturated - from 0.8 to 1. Clay soils are often wetter, sandy, respectively, dry.

Calculator for calculating soil parameters

In the design of buildings, different calculation models are used, which are used for soils of varying complexity. For general tasks, the main assessment is the bearing capacity, which reveals the strength and deformation properties of the foundations. However, basic calculation models can help to calculate them for specific tasks.

To simplify calculations when creating a project, the Prandtl formula is used, which helps to calculate the bearing capacity of the soil. To determine the degree of stability and strength of the base and determine the possible deformation, it is necessary to determine the degree of stress. For this, equations can be applied that are based on a linear relationship between stress and strain, for example, Hooke's law. Thus, the load on the base should not be greater than the ultimate soil resistance.

The calculation is carried out according to the bearing capacity to determine the possible loss of stability of the building, the nature of the destruction, the degree of deformation and its type.It also calculates the state in which normal operation may be difficult, the durability of the building is reduced from the possibility of subsidence, inclinations, and so on.

Physical properties of soils are the defining characteristics by which it is possible to establish the state of the soil, the possibility of changing parameters under the influence of various physical and chemical factors.

To determine the type of soil and its behavior as a basis for construction, the properties necessary for design decisions, the determination of physical and mechanical characteristics by laboratory methods is a prerequisite.

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