Soil deposits are affected by the mechanism of transport and deposition until their location. Soils that have not been transported but come from the parent rock that underlies them are called residual soils. Decomposed granite is a common example of residual soil. The most common transport mechanisms are the action of gravity, ice, wind and water. Aeolian processes include sand dunes and loess. Water transports particles depending on their size and the speed of the water, hence the granulometric distribution that appears in many rivers depending on the point where the sample is taken. Clay and silt generally accumulate in the slower areas of the river, or in lakes and swamps, while sand and gravel accumulate in the river beds. Glacial erosion is capable of moving large blocks of stone and breaking them on their way to the mouth. Gravity is also capable of transporting large amounts of materials from the tops of mountains to the valleys. These deposits formed on the slopes of the mountains are called colluvium (material deposited by small river currents). The transport mechanism also affects the shape of the particles, for example, particles in rivers are usually rounded and colluvia often have fresh fractures.

Soil mineralogy

Clays, silts, sands and gravels are classified by their size, but they can consist of a wide variety of minerals. Due to the stability of quartz relative to other mineral rocks, it is the most common constituent material of sand and silt. Mica and feldspar are other common minerals present in sands and silts. The minerals that make up gravel are usually very similar to those of the parent rock.

The most common minerals in clays are montmorillonite, smectite, illite and kaolinite. These minerals tend to form plate structures with a range between and and a thickness range between and , and have a relatively large specific surface area. The specific surface area is defined by the ratio of particle surface area to particle mass. Clay minerals have a specific surface area range of 10 to 1000 square meters per gram. This causes clays to have completely different chemical and electrostatic properties than other materials.

Soil minerals are predominantly made up of oxygen, silicon, hydrogen and aluminum atoms, organized in crystalline forms. These elements along with calcium, sodium, potassium, magnesium and carbon make up more than 99 percent of the Earth's solid mass.

Mass-soil ratio

There are a wide variety of parameters[2]​ used to describe the relative proportions of air, water and solids in a soil. This section defines these parameters and some of their interrelationships. The basic notation would be:

, , and represents the volume of air, water and solids in a soil mixture;.

, , and represents the weight of air, water and solids in a mixture of solids;.

, , and represents the mass of air, water and solids in the solids mixture;.

, , and represents the densities of the constituents (air, water and solids) in a soil mixture;.

Note that the weight, W, can be obtained by multiplying the mass, M, by the acceleration of gravity, g, e.g.,.

Specific gravity is the ratio between the density of the material and the density of pure water ().

Specific gravity of solids,.

Note that conventional units of weight can be obtained by multiplying the density by the acceleration due to gravity, .

Density or Wet density are the different names given to the density of the mixture, that is, the total of air, water and solids divided by the volume of water, air and solids. (air mass approaches zero for practical purposes):

Dry density, is the mass of solids divided by the total volume of air, water and solids:.

Buoyancy density, or Submerged density, is defined as the density of the mixture minus the density of water, which is useful in submerged soils:.

where is the density of water.

Water content or Humidity, is the ratio of the mass of water to the mass of solid. It is easy to measure since it is the ratio between the natural sample and the sample dried in the oven and weighed again. The procedure is standardized by ASTM.

Vacuum index, or void ratio, is the range of void volume times the volume of solids:.

Porosity, is the ratio between the volume of voids and the total volume, and is related to the void index:.

Degree of saturation, ratio between the volume of water and the volume of voids, thus a sample S=1 will be completely wet and will not admit more water:.

From the definitions above the following can be derived:.

Contenido

Para entender la mecánica de suelos es necesario entender cómo actúan las tensiones normales y efectivas entre las distintas fases. Ni la fase líquida ni la gaseosa aportan resistencia significativa a tensión cortante. La resistencia de cortante del suelo proviene de la fricción y el bloqueo interno de las partículas. La fricción depende de las tensiones de contacto entre las partículas sólidas. Por otro lado, las tensiones normales se distribuyen por todo el fluido y las partículas. Aunque los poros de aire son relativamente compresibles, pero los poros llenos de agua no por lo que en caso de esfuerzo normal las partículas se reordenarán distribuyendo toda la tensión por los fluidos, juntando aún más las partículas.

El principio de tensión efectiva, introducida por Karl Terzaghi, determina que la tensión efectiva σ', es decir, la tensión media intergranular entre partículas sólidas puede ser calculada por una simple resta de la presión de los poros de la presión total:.

donde σ es la tensión total y u es la presión del poro. No es práctico medir σ' directamente, así que en la práctica la tensión vertical efectiva se calcula a partir de la presión de los poros y la tensión total vertical. La distinción entre los términos de presión y tensión es también importante. Por definición, la presión en un punto es igual en todas las direcciones pero la tensión de un punto puede ser distinta en diferentes direcciones. En mecánica de suelos, las tensiones y presiones de compresión se consideran positivas y las presiones de tensión se consideran negativas, a la inversa de la convención utilizada en mecánica de sólidos.

total pressure

For ground-level conditions, the total vertical pressure at a point, on average, is the weight of everything above that point per unit area. The vertical stress under a uniform surface layer with density , and thickness is for example:.

where is the acceleration due to gravity, and in the unit of mass of the top layer. If there are several layers on top of different densities or layers of water, the total value can be obtained by adding the product of all the layers. The total stress increases with increasing depth in proportion to the densities of the upper layers. To calculate the total horizontal stress you have to use other formulas, based on the vertical stress.

pore water pressure

If there were no water flow between the pores, the pore water pressure would be hydrostatic. The water table or phreatic level is located at the depth where the water pressure is equal to the atmospheric pressure. For hydrostatic conditions, water pressure increases linearly with depth below the water table.

where is the density of water, and is the depth below the water table.

Due to surface tension, water can rise through the small holes that occur in the ground. In this way the water can rise above the water table through the small pores between the soil particles. In fact the soil can become completely saturated above the water table. Above the capillary saturation height, the water content in the soil can decrease with elevation. If the water in the capillary zone is not moving, the water pressure forces the hydrostatic equation to balance, however it is negative above the water table. Therefore, the hydrostatic pressures of water above the water table are negative. The thickness of the capillary zone depends on the size of the soil particles, but generally, the heights can vary between centimeters (for a sandy soil) to tens of meters (for a clay or silty soil).

Los ingenieros geotécnicos clasifican los tipos de partículas del suelo en función de varios experimentos (secado, paso por tamizes y moldeado). Estos experimentos aportan la información necesaria sobre las características de los granos del suelo que los componen. Hay que decir que la clasificación de los tipos de granos presentes en el suelo no aporta información sobre la "estructura" o "fábrica" del suelo, condiciones que describen la compacidad de las partículas y el patrón en la disposición de las partículas en una zona de carga tanto como el tamaño del poro o la distribución de fluido en los poros. Los ingenieros geológicos también clasifican el suelo en función de su génesis o su historial de estratificación. La clasificación más común es la S.U.C.S.

Classification of soil grains

In the United States and other countries, the Unified Soil Classification System (Unified Soil Classification System or USCS) is used. In the United Kingdom, the British Standard BS5390 is used and the AASHTO soil classification is also well known. In Spain, the PG-3" classification is used for road works.[3]​.

In the USCS, gravels (with the symbol G) and sands (with the symbol S) are classified according to grain size and distribution. For the USCS, gravels can be classified by GW (well-graded gravel), GP (poorly graded gravel), GM (gravel with a large amount of silt), or GC (gravel with a significant amount of clay). Likewise, sands can be classified as SW, SP, SM or SC. Sands and gravels with a small but important amount of fines (between 5% and 12%) can have a double classification, such as SW-SC.

Clays and silts, sometimes called "fines soils", are classified based on their Atterberg limits; the most used are the Liquid Limit (denoted by LL o ), Plastic Limit (denoted by PL o ), and the shrinkage limit (denoted by SL). The shrinkage limit corresponds to the water content below which the soil will not shrink if it dries.

The liquid limit and the plastic limit are arbitrarily determined by tradition and conventions. The liquid limit is determined by measuring the water content of a closed spoon after 25 strokes in a standardized test.[4] It can also be determined by a cone drop test. The plastic limit is the water content below which it is not possible to mold cylinders smaller than 3 millimeters by hand. The soil tends to crack or fall apart if that humidity drops.

The plasticity index is the difference between the liquid limit and the plastic limit of the soil extract. It is an indicator of how much water the soil can absorb.

According to the Unified Soil Classification System, silts and clays are classified based on the values ​​of their plasticity index and liquid limit on a plasticity graph. Line A on the graph separates the clays (C) from the silts (M). The 50% liquid limit separates soils with high plasticity (the letter H is added) from those with low plasticity (the letter L is added). Other possible classifications of silts and clays are given by ML, CL and MH. If the Atterberg limits fall at a point on the graph close to the origin they can receive a dual 'CL-ML' classification.

Indices relating to soil resistance

The effects of water content on the resistance of saturated soils can be quantified by the use of the liquidity index or milk:.

The density of sands (cohesionless soils) is sometimes characterized by its relative density.

The terms rock and soil, in the meanings in which they are used by the civil engineer and unlike the geological concept that assumes rock to all the constituent elements of the Earth's crust, imply a clear difference between two types of materials.

Rock is considered a natural aggregate of mineral particles held together by great cohesive forces. And rock is called any material that has high resistance, and soil, on the contrary, is called any natural element composed of mineral corpuscles that can be separated by low-intensity mechanical means, such as agitation in water and pressure from the fingers of the hand.

To distinguish a soil from a rock, you can use a beaker with water in which the sample to be classified is placed and shaken. The disintegration of the material over time leads to the classification of soil, being considered rock in the case of opposite effects. Through compression a numerical boundary can be established; If the material breaks at less than 14 kg/cm², it is taken as soil, meaning that such limit is arbitrary and that, sometimes, samples that exceed the aforementioned stress in the laboratory are handled with soil criteria.

With the passage of time and due to weathering phenomena, the rock progressively loses its mechanical resistance and transforms into soil.

A soil mechanics study should lead us to obtain a set of data that allows us to have a better idea about the characteristics of the soil where we are going to build. Speaking of these characteristics, what a civil engineer or designer requires are the physical properties of the subsoil. For this, soil samples must be taken which will be taken to a laboratory where a person trained in the subject will report to us the data we need.

There are two types of polls: preliminary and final.

National University of Colombia. Soil Mechanics (2002) Archived November 4, 2018 at the Wayback Machine.

Soil deposits are affected by the mechanism of transport and deposition until their location. Soils that have not been transported but come from the parent rock that underlies them are called residual soils. Decomposed granite is a common example of residual soil. The most common transport mechanisms are the action of gravity, ice, wind and water. Aeolian processes include sand dunes and loess. Water transports particles depending on their size and the speed of the water, hence the granulometric distribution that appears in many rivers depending on the point where the sample is taken. Clay and silt generally accumulate in the slower areas of the river, or in lakes and swamps, while sand and gravel accumulate in the river beds. Glacial erosion is capable of moving large blocks of stone and breaking them on their way to the mouth. Gravity is also capable of transporting large amounts of materials from the tops of mountains to the valleys. These deposits formed on the slopes of the mountains are called colluvium (material deposited by small river currents). The transport mechanism also affects the shape of the particles, for example, particles in rivers are usually rounded and colluvia often have fresh fractures.

Soil mineralogy

Clays, silts, sands and gravels are classified by their size, but they can consist of a wide variety of minerals. Due to the stability of quartz relative to other mineral rocks, it is the most common constituent material of sand and silt. Mica and feldspar are other common minerals present in sands and silts. The minerals that make up gravel are usually very similar to those of the parent rock.

The most common minerals in clays are montmorillonite, smectite, illite and kaolinite. These minerals tend to form plate structures with a range between and and a thickness range between and , and have a relatively large specific surface area. The specific surface area is defined by the ratio of particle surface area to particle mass. Clay minerals have a specific surface area range of 10 to 1000 square meters per gram. This causes clays to have completely different chemical and electrostatic properties than other materials.

Soil minerals are predominantly made up of oxygen, silicon, hydrogen and aluminum atoms, organized in crystalline forms. These elements along with calcium, sodium, potassium, magnesium and carbon make up more than 99 percent of the Earth's solid mass.

Mass-soil ratio

There are a wide variety of parameters[2]​ used to describe the relative proportions of air, water and solids in a soil. This section defines these parameters and some of their interrelationships. The basic notation would be:

, , and represents the volume of air, water and solids in a soil mixture;.

, , and represents the weight of air, water and solids in a mixture of solids;.

, , and represents the mass of air, water and solids in the solids mixture;.

, , and represents the densities of the constituents (air, water and solids) in a soil mixture;.

Note that the weight, W, can be obtained by multiplying the mass, M, by the acceleration of gravity, g, e.g.,.

Specific gravity is the ratio between the density of the material and the density of pure water ().

Specific gravity of solids,.

Note that conventional units of weight can be obtained by multiplying the density by the acceleration due to gravity, .

Density or Wet density are the different names given to the density of the mixture, that is, the total of air, water and solids divided by the volume of water, air and solids. (air mass approaches zero for practical purposes):

Dry density, is the mass of solids divided by the total volume of air, water and solids:.

Buoyancy density, or Submerged density, is defined as the density of the mixture minus the density of water, which is useful in submerged soils:.

where is the density of water.

Water content or Humidity, is the ratio of the mass of water to the mass of solid. It is easy to measure since it is the ratio between the natural sample and the sample dried in the oven and weighed again. The procedure is standardized by ASTM.

Vacuum index, or void ratio, is the range of void volume times the volume of solids:.

Porosity, is the ratio between the volume of voids and the total volume, and is related to the void index:.

Degree of saturation, ratio between the volume of water and the volume of voids, thus a sample S=1 will be completely wet and will not admit more water:.

From the definitions above the following can be derived:.

Contenido

Para entender la mecánica de suelos es necesario entender cómo actúan las tensiones normales y efectivas entre las distintas fases. Ni la fase líquida ni la gaseosa aportan resistencia significativa a tensión cortante. La resistencia de cortante del suelo proviene de la fricción y el bloqueo interno de las partículas. La fricción depende de las tensiones de contacto entre las partículas sólidas. Por otro lado, las tensiones normales se distribuyen por todo el fluido y las partículas. Aunque los poros de aire son relativamente compresibles, pero los poros llenos de agua no por lo que en caso de esfuerzo normal las partículas se reordenarán distribuyendo toda la tensión por los fluidos, juntando aún más las partículas.

El principio de tensión efectiva, introducida por Karl Terzaghi, determina que la tensión efectiva σ', es decir, la tensión media intergranular entre partículas sólidas puede ser calculada por una simple resta de la presión de los poros de la presión total:.

donde σ es la tensión total y u es la presión del poro. No es práctico medir σ' directamente, así que en la práctica la tensión vertical efectiva se calcula a partir de la presión de los poros y la tensión total vertical. La distinción entre los términos de presión y tensión es también importante. Por definición, la presión en un punto es igual en todas las direcciones pero la tensión de un punto puede ser distinta en diferentes direcciones. En mecánica de suelos, las tensiones y presiones de compresión se consideran positivas y las presiones de tensión se consideran negativas, a la inversa de la convención utilizada en mecánica de sólidos.

total pressure

For ground-level conditions, the total vertical pressure at a point, on average, is the weight of everything above that point per unit area. The vertical stress under a uniform surface layer with density , and thickness is for example:.

where is the acceleration due to gravity, and in the unit of mass of the top layer. If there are several layers on top of different densities or layers of water, the total value can be obtained by adding the product of all the layers. The total stress increases with increasing depth in proportion to the densities of the upper layers. To calculate the total horizontal stress you have to use other formulas, based on the vertical stress.

pore water pressure

If there were no water flow between the pores, the pore water pressure would be hydrostatic. The water table or phreatic level is located at the depth where the water pressure is equal to the atmospheric pressure. For hydrostatic conditions, water pressure increases linearly with depth below the water table.

where is the density of water, and is the depth below the water table.

Due to surface tension, water can rise through the small holes that occur in the ground. In this way the water can rise above the water table through the small pores between the soil particles. In fact the soil can become completely saturated above the water table. Above the capillary saturation height, the water content in the soil can decrease with elevation. If the water in the capillary zone is not moving, the water pressure forces the hydrostatic equation to balance, however it is negative above the water table. Therefore, the hydrostatic pressures of water above the water table are negative. The thickness of the capillary zone depends on the size of the soil particles, but generally, the heights can vary between centimeters (for a sandy soil) to tens of meters (for a clay or silty soil).

Los ingenieros geotécnicos clasifican los tipos de partículas del suelo en función de varios experimentos (secado, paso por tamizes y moldeado). Estos experimentos aportan la información necesaria sobre las características de los granos del suelo que los componen. Hay que decir que la clasificación de los tipos de granos presentes en el suelo no aporta información sobre la "estructura" o "fábrica" del suelo, condiciones que describen la compacidad de las partículas y el patrón en la disposición de las partículas en una zona de carga tanto como el tamaño del poro o la distribución de fluido en los poros. Los ingenieros geológicos también clasifican el suelo en función de su génesis o su historial de estratificación. La clasificación más común es la S.U.C.S.

Classification of soil grains

In the United States and other countries, the Unified Soil Classification System (Unified Soil Classification System or USCS) is used. In the United Kingdom, the British Standard BS5390 is used and the AASHTO soil classification is also well known. In Spain, the PG-3" classification is used for road works.[3]​.

In the USCS, gravels (with the symbol G) and sands (with the symbol S) are classified according to grain size and distribution. For the USCS, gravels can be classified by GW (well-graded gravel), GP (poorly graded gravel), GM (gravel with a large amount of silt), or GC (gravel with a significant amount of clay). Likewise, sands can be classified as SW, SP, SM or SC. Sands and gravels with a small but important amount of fines (between 5% and 12%) can have a double classification, such as SW-SC.

Clays and silts, sometimes called "fines soils", are classified based on their Atterberg limits; the most used are the Liquid Limit (denoted by LL o ), Plastic Limit (denoted by PL o ), and the shrinkage limit (denoted by SL). The shrinkage limit corresponds to the water content below which the soil will not shrink if it dries.

The liquid limit and the plastic limit are arbitrarily determined by tradition and conventions. The liquid limit is determined by measuring the water content of a closed spoon after 25 strokes in a standardized test.[4] It can also be determined by a cone drop test. The plastic limit is the water content below which it is not possible to mold cylinders smaller than 3 millimeters by hand. The soil tends to crack or fall apart if that humidity drops.

The plasticity index is the difference between the liquid limit and the plastic limit of the soil extract. It is an indicator of how much water the soil can absorb.

According to the Unified Soil Classification System, silts and clays are classified based on the values ​​of their plasticity index and liquid limit on a plasticity graph. Line A on the graph separates the clays (C) from the silts (M). The 50% liquid limit separates soils with high plasticity (the letter H is added) from those with low plasticity (the letter L is added). Other possible classifications of silts and clays are given by ML, CL and MH. If the Atterberg limits fall at a point on the graph close to the origin they can receive a dual 'CL-ML' classification.

Indices relating to soil resistance

The effects of water content on the resistance of saturated soils can be quantified by the use of the liquidity index or milk:.

The density of sands (cohesionless soils) is sometimes characterized by its relative density.

The terms rock and soil, in the meanings in which they are used by the civil engineer and unlike the geological concept that assumes rock to all the constituent elements of the Earth's crust, imply a clear difference between two types of materials.

Rock is considered a natural aggregate of mineral particles held together by great cohesive forces. And rock is called any material that has high resistance, and soil, on the contrary, is called any natural element composed of mineral corpuscles that can be separated by low-intensity mechanical means, such as agitation in water and pressure from the fingers of the hand.

To distinguish a soil from a rock, you can use a beaker with water in which the sample to be classified is placed and shaken. The disintegration of the material over time leads to the classification of soil, being considered rock in the case of opposite effects. Through compression a numerical boundary can be established; If the material breaks at less than 14 kg/cm², it is taken as soil, meaning that such limit is arbitrary and that, sometimes, samples that exceed the aforementioned stress in the laboratory are handled with soil criteria.

With the passage of time and due to weathering phenomena, the rock progressively loses its mechanical resistance and transforms into soil.

A soil mechanics study should lead us to obtain a set of data that allows us to have a better idea about the characteristics of the soil where we are going to build. Speaking of these characteristics, what a civil engineer or designer requires are the physical properties of the subsoil. For this, soil samples must be taken which will be taken to a laboratory where a person trained in the subject will report to us the data we need.

There are two types of polls: preliminary and final.

National University of Colombia. Soil Mechanics (2002) Archived November 4, 2018 at the Wayback Machine.