What does Geotechnical Engineering deal with?

In this post, I will try to broadly classify what topics fall under Geotechnical Engineering, one of the 5 main branches of Civil Engineering.

We can first break Geotechnical Engineering into three main topics as:

Soil Mechanics

Foundation Engineering

Retaining Walls, Stabilized Slopes, Deep Excavations

Now, when I say break, it is only for grouping purposes. These three groups are always, and always thought together when designing any foundation or wall or slope. I mean, you do not just focus on foundation engineering topics and forget soil mechanics when designing foundations. To design foundations, you must apply soil mechanics principles.

Now that we explained that part, lets continue our classification. These two sub categories can further be classified as follows:

Soil Mechanics:

  • Phase Relationships : Soils are made of solid particles + water + air. Phase relationships deals with finding out the percentage of each, in a given soil, which has many implications in properties of soils. It can be considered as the most fundamental topic in soil mechanics and for this reason it is the first topic that is taught in universities to civil engineering students, when starting soil mechanics (and therefore geotechnical engineering).
  • Soil Classification: This topic deals with classifying the soils after measuring what they are made of. There are many different types of soils. Mainly they can be separated from smaller to larger grain size as: clays, silts, sands, gravels, boulders. A soil is rarely purely one of these, but a mix.
  • Soil Strength: This is the heart and the most complicated part of soil mechanics, where we calculate the stresses in soil, how it will settle based on its strength.
  • Subsurface Investigation: This subject deals with determining properties of subsurface soils, mostly with digging boreholes, but sometimes just by opening trenches.
  • Soil Testing and Measurement: To find out many soil properties, soils are tested and measured. These can be performed in the field or in laboratory, depending on the type of test.
  • Groundwater and Seepage: Water has so many implications in soil properties and foundations. The depth of water, and how it flows through soil, is of great importance.
  • Geotechnical Reports: These are very important documents that are generated when starting a project, in order to start the design of foundations for a given structure and its loads.

Now let’s move on to foundation engineering part of geotechnical engineering and classify that. Foundation engineering can be classified broadly as:

  • Shallow Foundations: When the loads are relatively low and the soil is strong enough, we only need shallow foundations.
  • Deep Foundations (Piles): When the loads are high and / or the foundation soil is not strong enough, we need deep foundations. They generate their strength through friction of their skin to soil on their side surfaces, plus the end bearing at the bottom.
  • Ground Improvement and Foundation Repair: Sometimes just excavating soil and installing shallow or deep foundations is not enough and the soil must be improved in the first place, made stronger. Ground improvement deals with these methods. Foundation repair is repairing existing foundations. These two subtopics can sometimes involve similar methods.

And finally, the last category is the retaining walls, slope stability and deep excavation category, which is as the name suggests. Soils exert lateral pressure and if not confined they will fail until they reach their natural angle which would allow them to stand on their own. Designing retaining walls and deep excavations deal with this topic. Slopes exist on many locations and to stabilize them against failure is also another major study area in geotechnical engineering.

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