# Geotechnical Engineering Terms And Definitions

A lot of terms are used in geotechnical engineering like the Void Ratio, Water Content, Porosity, Degree Of Saturation, volume mass relationship, volume-weight relationship, etc.

Let’s dive into the Geotechnical Engineering Terms And Definitions that are related to the soil system-

**Geotechnical Engineering Terms And Definitions**

**Void Ratio**

The void ratio of the soil is defined as the ratio of the **volume of voids** to the** volume of solids**. The void ratio is denoted as **small e**.

Thus, the void ratio of the soil formula is **e= V _{v} / V_{s}**. Here the V

_{v }is the volume of voids, V

_{s}is the volume of solids, and e is the void ratio.

The value of the void ratio comes in decimals such as 0.6, 0.8, 0.4, etc. For some soil, the value of the void ratio may have greater than 1.

The void ratio is the dimensionless quantity.

**Porosity**

The porosity of the soil is defined as the ratio of the** volume of voids** to the **total volume of soil** and the porosity is denoted as small n.

Thus, the porosity of soil formula is **n= V _{v} / V**. Here

**V**is the volume of the void,

_{v}**V**is the total volume of soil, and

**n**is porosity.

The porosity is expressed in percentage and the porosity of the soil can not increase by 100%.

**Degree Of Saturation**

The degree of saturation of the soil is defined as the ratio of the **volume of water **to the **volume of voids**. And the degree of saturation is denoted as capital S.

Thus, the degree of saturation of the soil formula is **S= V _{w} / V_{v}**. Here S is the degree of saturation, V

_{w}is the volume of water, and V

_{v}is the volume of the voids.

The degree of saturation of soil is expressed in the percentage as like porosity of the soil.

The value of the degree of saturation is zero when the soil is absolutely dry and the value becomes 100% when the soil is fully saturated.

**Percentage Air Voids**

The percentage air voids of the soil are defined as the ratio of the **volume of air** to the **total volume **of soil and the percentage air void is denoted as** **n_{a}.

Thus, the percentage air voids of soil formula is **n _{a}= V_{a} / V**. Here V

_{a}is the volume of air, V is the total volume of soil and na is the percentage of air voids.

The percentage air voids of the soil are expressed in percentage as like porosity, and degree of saturation of the soil.

When the soil has saturated the value of the percentage air void of soil is zero.

**Air Content**

The air content of the soil is defined as the ratio of the **volume of air** to the **volume of voids** and the air content is denoted as **a _{c}**.

Thus, the air content of the soil formula is **a _{c}= V_{a} / V_{v}**. Here a

_{c }is the air content, V

_{a }is the volume of the air, and V

_{v}is the volume of void.

When the soil has saturated the value of the air content is zero like the percentage of air voids.

**Water Content**

The water content of the soil is defined as the ratio of the **mass of the water** to the **mass of solids**. The water content is denoted as small w.

Thus, the water content of the soil formula is w= Mw / Ms. Here w is the water content of the soil, Mw is the mass of the water, and Ms is the mass of the solid.

**Bulk Unit Weight**

The bulk unit weight of the soil is defined as the ratio of the **total weight** to the **total volume**.

Thus, the bulk unit weight of the soil formula is equal to **W / V**. Here W is the total weight and V is the total volume.

The bulk unit weight of the soil is also known as the **total unit weight** or **wet unit weight**.

**Dry Unit Weight**

The dry unit weight of the soil is defined as the ratio of the **weight of the solid** to the **total volume**.

Thus, the dry unit weight of the soil formula is equal to Ws / V. Here Ws is the weight of the solid and V is the total volume.

**Saturated Unit Weight**

The saturated unit weight of the soil is defined as the ratio of the **total weight** of the saturated soil to the **total volume**.

Thus, the saturated unit weight of the soil formula is equal to Wsat / V. Here Wsat is the total weight of the saturated soil and V is the total volume.

The saturated unit weight of the soil is the **bulk unit weight** when the soil is fully saturated.

**Submerged Unit Weight**

The submerged unit weight of the soil is defined as the ratio of the **submerged weight **of the soil to the **total volume**.

Thus, the submerged unit weight of soil formula is equal to **W _{sub} / V**. Here W

_{sub}is the submerged weight of soil and V is the total volume.

**Unit Weight Of Soil Solids**

The unit weight of soil solids is defined as the ratio of the **weight of the solids** to the **volume of solids**.

Thus, the unit weight of the soil solids formula is equal to Ws / Vs. Here Ws is the weight of the solid and Vs is the volume of the solid.

**Specific Gravity Of Solids**

The specific gravity of solids soil is defined as the ratio of the **mass of a given volume** of solids to the **mass of an equal volume of water** at 4 degrees centigrade.

Thus, the specific gravity of solids soil formula **G=p _{s} / p_{w}**. Here p

_{s}is the

**mass density of the solid**and p

_{w}is the

**mass density of the water**.

The specific gravity of solids for **natural soils** varies from **2.65 to 2.8** and the smaller value for the **coarse-grained soil.**

The specific gravity of the **gravel and sand **varies from **2.65 to 2.68** and the specific gravity of the **silty sands** and the **silt **varies from **2.66 to 2.70**.

The specific gravity of the **inorganic clays **varies from 2.68 to 2.80. And the specific gravity of the **organic soils** varies below **2.0.**

**Mass Specific Gravity**

Mass-specific gravity of soil is defined as the ratio of the **mass density of soil** to the **mass density of water**.

Thus, the maas specific gravity of soil formula is **G _{m} = p / p_{w}**. Here p is the mass density of soil and p

_{w}is the mass density of water.

The mass-specific gravity is also called **apparent-specific gravity **or **bulk-specific gravity**.

**Absolute Specific Gravity**

The absolute specific gravity of soil is defined as the ratio of the **mass density of an absolute solid **to the **mass density of water**.

Thus, the absolute specific gravity of the soil formula is **G _{a} = (p_{s})_{a} / p_{w}**. Here (p

_{s})

_{a}is the mass density of absolute solid and p

_{w}is the mass density of water.

**Bulk Mass Density**

The bulk mass density of soil is defined as the ratio of **total mass** to **total volume.** The bulk mass density is also called the **wet mass density** or simply **bulk density**.

Thus, the bulk mass density of the soil formula is **p = M / V** . Here M is total mass and V is total volume.

**Dry Mass Density**

The dry mass density of the soil is defined as the ratio of the **mass of solids** to the **total volume**.

Thus, the dry mass density formula is **p _{d}= M_{s} / V**. Here M

_{s}is the mass of the solid, p

_{d}is dry mass density and V is the total volume.

The dry mass density is also known as the **dry density**.

The dry mass density is used to express the denseness of the soil. If the soil has a high dry mass density then it is in compact condition.

**Saturated Mass Density **

The saturated mass density of the soil is defined as the ratio of the **saturated mass of the **soil to the total volume or in other words the saturated mass density is the bulk mass density of the soil when the soil is fully saturated.

Thus, the saturated mass density of soil formula is **p _{sat} = M_{sat} / V**. Here M

_{sat}is the mass of saturated soil, p

_{sat}is saturated mass density and V is total volume.

**Submerged Mass Density**

The submerged mass density of soil is defined as the ratio of the **submerged mass **to the **total volume**.

Thus, the submerged mass density of the soil formula is **p’= M _{sub} / V**. Here M

_{sub}is the submerged mass, p’ is submerged mass density and V is the total volume.

The submerged mass density is also known as the **buoyant mass density**.

**Mass Density Of Solids**

The mass density of a solid is defined as the ratio of the mass of the **solid** to the **volume of the solids**.

Thus, the mass density of the solid formula is **p _{s} = M_{s }/ V_{s}**. Here M

_{s}is the mass of the solid and Vs is the volume of the solid.

More Read- **Scope of Soil Engineering | Definition Of Soil, Soil Mechanics, & Soil Engineering**

**Frequently Asked Questions(FAQ)**

**What are the void ratio and porosity of soil?**

The void ratio and porosity of soil are basically the looseness of the soil. When the soil becomes denser the value of the void ratio and the value of porosity decrease.

**Can the void ratio be less than 0?**

The void ratio is never less than 0 because the volume of the void is never going to be less than zero, it is always positive.

**What is the difference between void ratio and porosity?**

The main difference between void ratio and porosity is when the volume of a soil mass changes, in the void ratio only the volume of the void changes but in the porosity volume of the void and total volume changes.

**What is the relation between porosity and void ratio?**

The relation between porosity and the void ratio is porosity is equal to the void ratio divided by 1 plus the void ratio which is **n= e/1+e**. Here n is the porosity and e is the void ratio.

**How do you find the void ratio?**

For the calculation of void ratio, we first find the volume of the void and the volume of the solid, and after that, we divide the volume of the void by the volume of the solid, and after dividing we will get the value of the void ratio.

**Can the void ratio of soil be greater than 1?**

Yes, the void ratio of soil can be greater than 1 for some soils.

**Can the degree of saturation be greater than 1?**

No, the degree of saturation is never greater than 1. It only varies between 0 to 1.

**Porosity is also known as?**

The porosity is also known as the **percentage void**.

**What is the relation between the percentage of air void and air content?**

The relation between the percentage air void and air content is that the percentage air void is equal to the multiplication of porosity and air content that is **n _{a}= n a_{c}**.

**What is the difference between dry density and bulk density?**

The bulk density is the ratio of total mass to the total volume while the dry density is the ratio of the mass of soil to total volume.