Overview of Soil Mechanics and Foundation Engineering

Geotechnical engineering is made up of three branches: soil mechanics, foundation engineering, and rock mechanics. Foundation engineering is the application of rock and soil mechanics. Soil mechanics describe the behavior of the soil, and rock mechanics describe the behavior of different types of rocks. Most individuals pursue a degree in geotechnical engineering. Under this degree, students learn about the three branches.

Soil Mechanics

Soil mechanics look at the physical properties of soil. Specifically, they are looking at how a soil’s properties may affect strength, drainage, and stability. This is the basis for all geotechnical engineering. These properties are important when it comes to foundations.

Most students pursuing a geotechnical engineering degree are required to take courses in soil mechanics. They may learn how to classify soil types, evaluate shear strength of soil mass, estimate seepage volume, and predict foundation settlement.

Rock Mechanics

It is important that engineers understand how the properties of rocks will function during various uses. As an engineer, one is likely to have to assess strengths and properties of rocks being used for foundations or structures. Rock mechanics help determine how a particular type of rock will react when used for roads, bridges, buildings, tunnels, and dams among other uses.

Students may learn to evaluate the bearing capacity of a rock’s surface. Furthermore, engineering students need to understand how the force applied to rock by structures may affect the rock at different depths. The point of such knowledge is to inform engineers of safety requirements necessary to ensure a stable foundation.

Foundation Engineering

Courses in foundation engineering use the knowledge gleaned from courses in soil and rock mechanics to inform foundation designs. Students may be introduced to a variety of foundation structures and systems. Courses usually encourage discussions about foundation solutions to a variety of types of soil and rock conditions.


Many graduates will find they are qualified to work in the field of geotechnical engineering or positions more specific to one of the three branches. Most engineering jobs require that individuals obtain an engineering license. Geotechnical engineers typically use the principles of engineering to ensure foundations and structures are secure and stable against natural events like mudslides and earthquakes. Their job is to analyze and plan the construction of these foundations and support structures.

Graduates may be able to find a job as a soil engineer specifically. In such a position, one may be expected to analyze soil structure for a proposed building site. They provide information about the soil and problems proposed and existing structures might face. Soil mechanics informs both the design of structures as well as the structure itself.

Most geotechnical engineers work for dedicated organizations. Some individuals can make a living as freelance consultants or on a contract basis. Freelance and contract workers provide a variety of engineering work, consultation, and research as self-employed individuals.

Geotechnical engineering deals with the foundations of a variety of buildings and structures. They make sure the soil and rock can withstand the demands manmade structures put on them.

What Causes Soil Liquefaction & How It Can Be Prevented

What Is Soil Liquefaction?

Soil liquefaction occurs when waterlogged soil behaves like a liquid. Some people refer to it as earthquake liquefaction. The vibrations of earthquake shockwaves in water-saturated soils trigger the phenomenon.

Earthquakes are a very common origin of soil liquefaction damage, but other vibration-creating events can be a factor. This includes construction activities, such as blasting, soil compaction, and similar tasks. Sometimes, people insert a vibrating probe into the ground to induce the effect intentionally. This process is vibroflotation.

Soil liquefaction occurs most frequently in sandy, silt-laden, gravel-based, loose or poorly drained soils. Quicksand is an example of this phenomenon. The water-saturated sandy soil cannot bear the weight of items, causing them to sink.


Why Is It a Problem?

During an earthquake or other vibration in the ground, the liquid consistency of the ground cannot support objects. Buildings, bridges, trees and other objects collapse or sink into the soil. In most countries, modern building codes require builders and architects to analyze the viscosity of the soil before developing the land.

Collapsed buildings are not the only problem that liquefaction causes. Since minor earthquakes, vibrations from construction and other incidents happen frequently; soil liquefaction happens often. Some of the other problems are:

  • Flotation of buried objects, such as pipelines, fuel tanks and more
  • Landslides
  • Lateral spreads, or landslides on gentle slopes
  • Quicksand
  • Sand boils, or sand volcano
  • Sinkholes

How can we prevent soil liquefaction?

Since the cost of the damage by liquefaction is so high, especially in the loss of human life, researchers are testing new ways to prevent it. One of the oldest methods is replacing the loose soil with denser soil and material. This is an inefficient method, in cost or effectiveness.

Often, builders set the footings of the foundation deeper than the layer of unstable soil. Wherever possible, builders try to set the footings onto bedrock. This is especially important for bridges, dams and other building sites near water. However, this is not always practical or possible.

A newer method is vibroflotation, which is proving to be an effective prevention. Technicians insert vibrating probes into the soil at deep levels, and the trembling shakes the loose soil. The compression of the loose soil particles lessens the number of air pockets where water can settle.

Another new method includes injecting the soil with stabilizing materials. Expert geologists and geotechnical engineers are studying the effectiveness of this process. If you would like more information on this technique, the City of Boston has an article describing the process in depth.


Soil liquefaction is a global problem. Expert geologists and geotechnical engineers are seeking environmentally safe ways to prevent loss of property and life when liquefaction occurs.