What are the three parts of soil?

It generally includes particle size composition, mineral composition and liquid phase composition.

① Particle size composition.

Soil particles are divided into particle groups according to the particle size and the similarity of their properties, and the particle size composition of soil is expressed by the percentage of each particle group in the total weight of soil.

② Mineral composition.

Coarse clastic particles in soil are mainly composed of primary minerals such as quartz, feldspar and mica. Primary minerals are weathered, and soluble substances are dissolved to form water-insoluble secondary minerals.

③ Liquid phase composition.

The liquid components in soil are usually not all free water. According to the activity of water molecules, they can be divided into capillary water, bound water and structured water. Bound water is the product of complex physical and chemical interaction between soil particles and water.

Atoms or ions with free electricity price are often distributed on the surface of soil particles, which can attract polar water molecules to form hydration films. The water in the hydration film that is in direct contact with soil particles and is firmly attracted is called adsorption bound water (strongly bound water). The water far away from the particle surface constitutes the concentration osmotic adsorption bound water (weak bound water).

Extended data:

I. Classification

There are many kinds of soil on the earth's crust. In order to facilitate research and practical application, they can be approximately classified according to their engineering properties, and the grain size composition has always been the basic basis for soil classification. The table lists the grain size limits of soils in several countries in the world.

Soil is divided into coarse-grained soil with a particle size greater than 0.074 mm and fine-grained soil with a particle size less than 0.074 mm according to particle size, and the standard for subdivision of coarse-grained soil is still particle size composition. Gravel soil with particle size greater than 2 mm accounts for more than 50%, otherwise it is sandy soil.

However, the relationship between the properties and particle size of fine-grained soil is not as close as that between fine-grained soil and water, so plastic index is widely used as the standard for dividing fine-grained soil all over the world. The classification method is to point the measured plastic index values on the plastic diagram and classify them according to their positions. In addition, there is a classification based on geological origin or mineral composition.

Second, the nature of water

The hydraulic properties of soil generally refer to the liquid limit and plastic limit of cohesive soil (measured in laboratory) and the liquid index and plastic index calculated from these two indexes. These indicators are also necessary in engineering. Saturated cohesive soil is also sensitive and thixotropic.

Cohesive soil can be divided into solid state, plastic state and flow state because of different water content, which is the consistency state of cohesive soil. The critical water content between different consistency states is called boundary water content, which varies greatly with clay content and mineral composition, and also reflects the significant difference of engineering geological properties.

Therefore, the boundary water content and the relationship between boundary water content and natural water content, that is, plasticity index and liquid index, are often used as important parameters for soil classification and foundation bearing capacity determination.

Clayey soil in natural state has a certain structure. When disturbed by external factors, the equilibrium system composed of cementing substances between soil particles and soil particles, ions and water molecules is destroyed, and the strength of soil decreases and the compressibility increases. This effect of soil structure on strength is usually reflected by sensitivity.

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