Three basic physical properties of soil

The three basic physical properties of soil are soil density, soil particle density, and soil moisture content.

Extended knowledge: Density of soil (natural density): The density of soil refers to the ratio of the total mass of soil to the total volume, that is, the mass of the soil per unit volume, and its unit is g cm3, and the common value is shown in the table below).

In engineering practice, the density of soil is often converted to the gravity of soil ( ) The gravity is equal to the density multiplied by the acceleration of gravity.

g, the unit is kn m3, that is, the density of the soil is commonly used by the ring knife method.

Mensuration. Soil Particle Density (Soil Particle Specific Gravity) Soil particle density refers to the ratio of the mass of solid particles to their volume, that is, the mass of soil particles per unit volume, and its unit is g cm3. Soil particle density, also known as soil particle specific gravity (soil particle relative density), refers to the ratio of the mass of soil to the mass of the same volume of water at 4 o'clock, its value is the same as the soil particle density, but there is no unit, and it must be multiplied by the density value of water to balance the dimension when used as a three-phase index for soil.

The density of soil particles is determined by the mineral composition of soil particles, and has nothing to do with the pore size and water content of the soil.

The water content of the soil The ratio of the mass of the water contained in the soil to the mass of the solid particles, in percentages.

Representation, also known as the moisture content of the soil.

Water content is usually expressed as a percentage, and it is an important indicator to describe how dry and wet the soil is. The natural moisture content of the soil varies widely, from dry sand with a moisture content close to zero to montmorillonite.

The water content can reach several hundred percent.

The physical state indicators of soil are: particle composition, specific gravity (GS), wet density ( ) dry density ( ),Moisture content( ) Boundary moisture content (plastic limit moisture content p, liquid limit moisture content l),Porosityn, effective porosity ne,SaturationSR, inhomogeneity coefficient.

Significance of indicators in engineering:The compactness of sand has an important influence on its engineering properties. Dense sand soil has high strength and low compressibility, which is a good foundation for buildings; However, loose sand, especially saturated loose sand, not only has low strength, but also has poor water stability, and is prone to engineering accidents such as quicksand and liquefaction.

The main problem in the evaluation of sand is the correct division of its compactness.

Consistency status

The consistency state can be divided into fluid form: it has fluidity, and its consistency index is 》1;Plastic body: It has plastic properties, and its consistency index is 0-1;Solid:

It is solid or semi-solid, and its consistency index is <0. The transition boundary between the consistency states is called the consistency limit and is measured by the water content.

indicated, called the limit water content.

Due to the gradual increase of water content, the consistency state of soil transitions from solid to plastic and fluid. Among the boundaries of consistency, the upper limit of plasticity (referred to as the liquid limit WL) and the lower limit of plasticity (referred to as the plastic limit WP) are of the greatest practical significance, which are the specific boundaries that distinguish the three major consistency states.

Soil, like rock, is a product of natural history.

The nature of soil is determined by its geological origin, formation time, place, environment, and mode, as well as the conditions of metagenetic evolution and current production. Such as the formation of loess in arid areas, moist and hot.

The laterite formed in the area and the silt formed in the still water area are completely different in nature.

Nature of engineering. Engineering properties of loess.

Generally, it is divided into two categories: new loess and old loess, and their properties are also significantly different (see road construction and roadbed design in loess area).

Engineering properties of soft soils.

Soft soil generally refers to saturated clay soil with high compressibility and low strength, which is mostly distributed in rivers, rivers, ocean coasts, inland lakes, ponds, basins and rainy mountain depressions. The porosity ratio of soft soils.

Generally, the natural water content is often higher than its liquid limit, the shear strength of undrained water is very low, and the compressibility is very high, so it often needs to be reinforced.

Directly measurable items include moisture content, soil specific gravity, and soil sample density.

Since soil is composed of solid particles, liquid and gas, the proportional relationship of the content of each part directly affects the physical properties of soil and the state of soil. In soil mechanics, in order to further describe the physical and mechanical properties of soil, the proportional relationship of the three-phase composition of soil is quantified and expressed by some specific physical quantities, which are the physical and mechanical properties of soil.

The moisture content, density, and specific gravity of the soil particles of the soil.

Flow behavior of a fluid in the pores of a soil. It is one of the main mechanical properties of soil. Soil permeability is an important part of the study because: Civil engineering.

Many topics in the fields of hydrogeology, agriculture, water conservancy, and environmental protection are closely related to soil permeability. There is a close correlation between the three main mechanical properties of soil, namely deformation and permeability, so that the study of permeability is not limited to the seepage problem itself; The permeability of soil is the same as other physical properties of soil.

constants, which vary much more and are highly heterogeneous and anisotropic.

Quality. The permeability of soil is generally based on the permeability coefficient of the soil.

Classification, as shown in Table 1.

Most of the objects involved in soil mechanics are applicable to: Coarse-grained materials, such as rockfill bodies, dense clays, or fine-grained soils that can flow freely, may exceed Darcy's law.

Scope of application. There are many methods for determining the permeability coefficient of soil (i.e., permeability index), which can be summarized into two categories: direct method and indirect method: direct method includes constant head method and variable head test, the former is suitable for soil with greater permeability, and the latter is suitable for soil with less permeability; The indirect method consists of calculations based on the results of consolidation tests, the former for cohesive soils and the latter for non-cohesive soils, and calculations based on particle size distributions.

The test methods can be divided into two categories: laboratory determination and on-site determination. The scope of application of the various test methods is shown in Table 2.

Factors influencing permeability The main factors affecting the permeability of sandy soil are the particle size, shape and gradation of permeable fluid and soil.

and density. The main influence of permeating fluids is viscosity, which in turn is affected by temperature. The higher the temperature, the lower the viscosity and the greater the seepage velocity.

The effect of soil particles is that the finer the particles, the lower the permeability; Well-graded soils reduce pore size due to fine particles filling the pores of large particles, thereby reducing permeability. As the density of the soil increases, the pores decrease, and the permeability decreases. The main factors influencing the permeability of cohesive soils are the mineral composition, shape and structure (pore size and distribution) of the particles, as well as the soil-water-electrolyte.

Interaction of systems. The shape of the clay particles is flattened and has a directional arrangement, so the permeability has a significant anisotropic property. The capillary model of permeability shows that the permeable flow rate is proportional to the square of the pore diameter, while the unit flow rate is proportional to the fourth power of the pore diameter.

PorosityThe permeability of the structure with the same cohesive soil, the large voids between the particles account for a high proportion, which is much greater than the permeability of the structure with uniform pore size, and the microstructure and macrostructure of the cohesive soil have a great influence on the permeability, so the measurement results in the real hazard room cannot reflect the actual soil situation. The permeability of layered clays in the horizontal direction tends to be much greater than in the vertical direction; In loess and loess-like soil, due to the development of vertical macropores, the permeability in the vertical direction is greater than that in the horizontal direction. Due to the presence of a fracture network, the permeability coefficient of fractured clay is close to that of coarse sand and has strict directionality. When studying the permeability of the actual soil, it is necessary to pay attention to its special laws.

The three basic physical indicators of soil are the density, moisture content and specific gravity of soil particles.

The density of soil (natural density) refers to the ratio of the total mass of soil to the total volume, that is, the mass of the soil per unit volume, and its unit g cm3, the common value is to see the table below). In engineering practice, the density of soil is often converted into the gravity of soil ( ) The gravity is equal to the density multiplied by gravity plus the ridge velocity g, and its unit is kn m3, that is, the density of soil is commonly determined by the ring knife method.

Soil Particle Density (Soil Particle Specific Gravity) Soil particle density refers to the ratio of the mass of solid particles to their volume, that is, the mass of soil particles per unit volume, and its unit is g cm3. Soil particle density, also known as soil particle specific gravity (soil particle relative density), refers to the ratio of the mass of soil to the mass of the same volume of water at 4 o'clock, and its value is the same as the soil particle density, but there is no unit, and it must be multiplied by the density value of water to balance the dimension when used as a three-phase index of soil.

Introduction to the density of soil:

The density of soil refers to the ratio of the total mass of the soil to the total volume, that is, the mass of the soil per unit volume, and its unit cherry blossom return is gram cubic centimeter. According to the different states of the soil, the density of the soil is divided into three types: natural density, dry density and saturated density. The mass of soil per unit volume in its natural state is called the natural density.

The magnitude of the natural density depends on the mineral composition of the soil, the confucius, and the water content: its value. The natural density is numerically smaller than the soil particle density.

It is a real continent index that can be measured directly indoors and in the field. It is an indispensable parameter in engineering geological calculation. The density of soil when there is no water at all in the pores is called the dry density of soil.

The commonly used physical property indexes of soil mainly include: particle composition, specific gravity, wet density, dry density, moisture content, boundary moisture content, porosity, effective porosity, saturation, inhomogeneity coefficient, etc.

1. Soil is a loose and soft accumulation that has not yet consolidated into rock. Rent tremor is mainly a product of the Quaternary period.

2. The fundamental difference between soil and rock is that soil does not have the connection of disadvantage and rigidity, the physical state is changeable, and the mechanical strength is low.

3. Soil is formed by weathering of various rocks. Soil is located on the surface of the earth's crust and is the main geological environment for human engineering and economic activities. Soil and rock together are the research objects of engineering geotechnicals.