Introduction to Geotechnical Engineering – The Engineer

1. Definition and Origin of Soil:

Soil is defined as the superficial layer of the Earth, composed of mineral particles, organic matter, water, and air. It results from the interaction of geological, climatic, and biological factors over millions of years. It forms through the decomposition of rocks by weathering and erosion processes, giving rise to different types of soils with specific characteristics.

2. Soil Structure and Mineralogy:

Soil structure refers to the arrangement and organization of its constituent particles. It can vary from a granular structure to a laminar or prismatic structure, depending on the formation conditions. Soil mineralogy relates to the types of minerals present in its composition, which may include quartz, feldspar, clays, and other minerals.

3. Soil Profile and Water Table:

The soil profile is a vertical section that displays the different layers or horizons of the soil at a specific site. Each horizon can have distinct characteristics in terms of composition, color, structure, and porosity. The water table is the depth at which groundwater is located in relation to the soil surface. It can influence soil stability and load-bearing capacity.

4. Tests for Soil Classification:

Various geotechnical tests allow the classification of soil based on its properties and characteristics. Some common tests include granulometric analysis, Atterberg limits test, in-situ density (Proctor test), permeability test, among others.

5. Moisture:

Soil moisture is the amount of water present relative to the dry weight of the material. Moisture content affects soil strength, compressibility, and load-bearing capacity.

6. Limits:

Atterberg limits are values that define the transitions of soil states between solid, plastic, and liquid. The main limits are the liquid limit (LL) and plastic limit (PL). From these values, the plasticity index (PI) can be determined.

7. Particle Size Distribution:

Particle size distribution is the analysis of the distribution of particle sizes in soil. It is carried out through a sieve analysis and helps classify soil into different granulometric fractions (sand, silt, clay, etc.), which influence its mechanical properties.

8. Physical Properties of Soil:

Physical properties of soil include density, porosity, permeability, compressibility, and load-bearing capacity. These properties determine soil behavior under different load and environmental conditions and can affect structure stability.

9. Index Properties:

Index properties of soil, such as Atterberg limits and plasticity index, are parameters used to classify and characterize soil in terms of its plasticity and ability to change state.

10. Soil Classification Methods:

There are several soil classification systems, with the most widely used being the Unified Soil Classification System (USCS) and the International Soil Classification System (ISSCS). These systems categorize soils into different classes based on their properties and characteristics.

11. Soil Phases:

Soil is composed of three phases: solid, liquid, and gas. The solid phase includes mineral and organic particles. The liquid phase corresponds to water in the soil, and the gas phase consists of air spaces between particles.

12. Soil Compaction:

Compaction is a process that increases the density of soil by applying forces to reduce voids and enhance its strength. This process is carried out during construction to improve load-bearing capacity.

13. Stresses in a Mass of Soil:

Stresses in a mass of soil are the forces applied to the soil, such as vertical loads or lateral forces. These stresses can affect soil stability and deformation.

14. Soil Shear Stresses:

Shear stresses are forces acting tangentially on the soil and can lead to sliding or failure. They are essential for the design of foundations and structures, as they affect soil stability under different load and environmental conditions.