Geotechnical Engineering 101: Everything you need to know about this important niche of civil engineering

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Geotechnical Engineering | PredictSite

Geotechnical engineering is one of the most important disciplines within the broader civil engineering sector. Still, it’s one of the least well understood – by fellow civil engineers working on structures and roadways and the general public. Geotechnical engineers are most often found getting down and dirty out in the field. And while they may not have the glamorous job of constructing an eye-catching skyscraper or long-span bridge, don’t underestimate their importance.

Geotechnical engineers work hard studying and testing soil and rock to determine their engineering properties and how they can support foundations or retain tall walls of earth. Not only do geotechnical engineers design important components of buildings and bridges, they can also protect their communities from landslides and sinkholes by developing remediation strategies for problematic soils.

PredictSite aims to simplify geotechnical engineering’s ins and outs by offering quick and easy site and soil classifications and foundation estimates. PredictSite is making it easier to understand the complex discipline of geotechnical engineering, and we’ll also make an effort to answer some common questions about the field.


Let’s try and answer some of the most common questions about geotechnical engineering and soil properties and how the field relates to civil engineering at large.

Geotechnical Engineering & Civil Engineering

What is the meaning of geotechnical?
To get to the definition of “geotechnical,” one must break it down into its two main root words – geo and technical. Geo relates to the earth, or soil and rock. Technical relates to a scientific or engineering practice. Put it all together, and you come to the understanding that “geotechnical” means the scientific or engineering analysis of soil or rock. Geotechnical engineering is slightly different from geology because it does not touch on how rock formations came to be or their typology. That being said, geotechnical engineers benefit from studying geology because it will strengthen their understanding of rock mechanics.


What is meant by geotechnical engineering?
Geotechnical engineering is a discipline within the broader field of civil engineering that focuses on analysing and determining earth materials’ engineering properties like soil and rock. Geotechnical engineers rely on their understanding of soil mechanics, geotechnics and rock masses to design foundations that can carry the load from a building or bridge to the soil that supports it. Subsurface conditions can vary greatly, even on different sides of a construction site, so geotechnical engineering is a very important branch of civil engineering.
What is the role of a geotechnical engineer?
The role of a geotechnical engineer is to investigate and evaluate the engineering properties of soil and rock. Having completed the subsurface investigation, the geotechnical engineer determines fundamental engineering properties like soil strength, checks for the presence of chemicals and measures mechanical properties that can be predictive of problematic behaviour like settlement. The engineer then utilises the results of their investigation and testing to perform calculations and design for foundations, retaining walls, tunnels, landfills, wharves, levees and piers.
What does a geotechnical engineer do?
The job of a geotechnical engineer is to investigate subsurface conditions and determine the engineering properties of the soil and rock present on a construction site. Once this has been completed, the geotechnical engineer will work with structural engineers to design foundations, retaining walls, piers, tunnels or landfills based on their analysis and testing of soil and rock samples taken from the site. Geotechnical engineers write foundation reports, perform bearing strength and slope stability calculations, and develop strategies to improve problematic soil conditions.
Why is geotechnical engineering important?
Geotechnical engineering is an essential discipline within civil engineering because it works hand-in-hand with structural engineering and infrastructure engineering to design foundations capable of carrying building or bridge loads. Geotechnical engineers are an integral part of every construction project and help the rest of the engineering team understand how subsurface conditions will impact their design. In addition to working on buildings, bridges and highways, geotechnical engineers can also lend their expertise to ground improvement projects like sinkhole remediation or excessive settlement.
Geotechnical Drilling | PredictSite

Is Geotechnical Engineering right for me?

Is geotechnical engineering a good career?

A career as a geotechnical engineer can be incredibly rewarding and challenging. Geotechnical engineers work on projects that require them to design foundations, retaining walls, tunnels, embankments, dams and slopes. They work with soil and rock and evaluate subsurface conditions with engineering judgement. No two sites are the same because earth materials’ engineering properties can vary wildly, even on the same project location. Geotechnical engineers are given more freedom to use their own engineering judgment and develop creative design solutions than other disciplines, and many are very passionate about their work.

Is geotechnical engineering hard?
A land may be contaminated purposely, accidentally or naturally.


Service stations like dumping sites, are land contaminated on purpose. Of course, with a set of protocols and proper disposal activities, the land contamination levels are set to a minimum. Accidental land contamination happens by unintentional spillage of harmful chemicals to land surface like oil spills or gas spills. Natural land contamination is often due to decaying sediments or animals.


Moreover, a typical Australian may not be aware that hazardous materials like asbestos were used in building construction in the past. If these buildings are demolished or renovated, asbestos present in the building is destroyed releasing asbestos fibers that cause health risks to repairmen and occupants, making the land accidentally contaminated.

How much does a geotechnical engineer earn?

Geotechnical engineers in Australia work hard and are well compensated for their efforts. According to Payscale, the median salary for a geotechnical engineer in Australia is roughly $77,000, with entry-level salaries in the range of $60,000. Senior geotechnical engineers can earn well over $125,000. Geotechnical engineers often have to make difficult judgement calls on the engineering properties of earth materials like soil and rock. If you are interested in becoming a geotechnical engineer, there are many top-notch civil engineering programs in Australia that can set you on the right path to becoming a professional engineer or engineering geologist.

Geotechnical Engineering | PredictSite

Soil Mechanics & Soil Engineering

What does a soil engineer do?
Soil engineers, sometimes referred to as ‘geotechnical engineers’ evaluate the engineering properties of soil by performing subsurface investigations to take samples. Laboratory tests, such as consolidation testing, soil classification and shear testing, are then performed on the samples to determine key characteristics like shear strength, friction angle, moisture content and bearing capacity. The soil engineer will use these test results, along with empirical data and research, to design foundation systems and retaining walls.


How do you become a soil engineer?
To become a soil engineer, you should seek out a civil engineering program at the university level that offers coursework in soils engineering or geotechnical engineering. Most civil engineering degree programs require students to take classes in soil mechanics and geotechnics where they will learn how to evaluate the engineering properties of different types of soil and rock and design basic foundations and retaining walls. If you find a passion for soil engineering, a good place to start is with an internship, which can set you up for a career in the field.
What is the difference between Soil Mechanics and Geotechnical Engineering?
Soil mechanics and geotechnical engineering are closely intertwined, but they are not precisely the same thing. Soil mechanics and rock mechanics relate to the study of soil and rock behaviour – how do they react to changes in water levels and saturation, how do they compress under load, how dense, etc. Geotechnical engineering is the real-world application of the soil properties typically measured in the field and lab. Geotechnical engineers need to have a strong understanding of soil mechanics and translate that into foundation design, retaining wall design or slope stability analysis.
What are the different types of engineering problems with soil?

Soil can be a difficult material for engineers to work with because its properties can vary greatly between different soil types. Some of the key problems a geotechnical engineer may face when dealing with soil include excessive settlement of soft or weak soil layers, poor bearing capacity, groundwater fluctuations and stability issues. Clay soils typically pose more problems for engineers, as they can be very expansive with fluctuations in water content. Clay also become extremely brittle when too dry.

If a soil's bearing capacity is too low, remedial measures may be required to increase capacity or deep foundations may be used to bridge the gap to a stronger bearing stratum. Soils that are prone to liquefaction may also lead to landslides, which can be very dangerous and cause significant damage to property.

What are some key soil engineering terms?
Let's break down a handful of key soil engineering terms that every geotechnical engineer needs to know:

  • Void ratio – the volume of voids in a soil to the volume of solids
  • Porosity – the ratio of volume of voids to the total volume
  • Saturation – the volume of water to the volume of voids. Saturation is at zero when soil is fully dry and 100% when soil is completely wetted.
  • Friction angle – angle whose tangent is the ratio of the maximum shear stress that resists slippage between two solid bodies at rest and the normal stress across the constant surface. A soil’s friction angle is determined through shear testing and is used in many of the empirical formulas for bearing strength.
  • Bearing capacity – the value of the contact pressure between the foundation and the soil which will produce shear failure in the soil. Safety factors are typically applied to reach an allowable bearing capacity.
  • Cohesion – Applies only to cohesive soils like clay and some silts. It is the shear resistance of a soil at zero normal stress. Physically, cohesion can be felt in a soil sample as a stickiness, or putty-like feeling.
  • Liquefaction – the sudden massive decrease in shear resistance of a cohesionless soil. The soil will essentially behave like a fluid and become very weak. This is how landslides occur.
Soil Engineering | Predictsite

Predictsite is proud of its status as one of the most valuable geotechnical resources for engineers and construction teams in Australia. Through our platform, we offer sophisticated site classification services to meet our clients’ needs. Our talented engineers are proud to serve the engineering and construction industry in Sydney, Melbourne, Brisbane and Adelaide.

Join the dozens of engineers and developers who have turned to PredictSite and Intrax to cut down on their geotechnical costs, provide faster, more accurate estimates, refine their slab designs and determine how best to address problematic soils. View our services here.

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