Geotechnical Engineering: What on Earth to Do with Dirt

Geotechnical engineering is a very important, but sometimes overlooked parked of any construction project. Geotechnical engineering, AKA geotechnics, is a branch of civil engineering that deals with the behavior of different kinds of soils. It combines the principles of soil or rock mechanics to solve engineering problems. Geotechnical engineering also involves testing soils and foundational concrete in order to best suit a project's needs.

Geotechnical engineering is especially important when considering the design and construction of a foundation. The foundation engineering of any construction should be the first priority for anyone involved in the project.

The first topic to understand is the different kinds of soils. There are cohesive and cohesionless soils.

• Cohesive Soils

  • Include clays, silts, marl and muck

  • Can be compressed

  • Hard to control

  • Organic makeup

• Cohesionless Soils

  • Includes sands and limestones

  • Granular and don't compress

  • Easy to work with

There are also two foundation types, deep and shallow foundations. Both cohesive and cohesionless soils can require either type foundation based on several different factors (see below):

• Deep Foundations

  • For soils that can't support loads

  • Foundation loads exceed traditional footings

  • Building Settlement

  • Examples

    • Augercast pilings- a hole is drilled into the earth to a predetermined depth and then filled with grout to ground level.

      • Used when soil is weak & compressible

      • When there is water to transfer load from those weak soil strata to stronger, less compressible soil layers.

    • Precast concrete piling- displacement pile that comes in a variety of shapes that are hammered directly into the ground.

      • Used when weak soil is very deep

    • Steel H piling- square structural beams designed to reach deeper soil strata than other types of pilings.

      • Used for deep soil penetration that other piles can't reach

    • Cassions- watertight retaining structure used to work on foundations below water.

      • Used in construction of foundations for bridge piers or concrete dams

    • Micro piles-very small grouted pile with internal reinforcement.

    • Helical piles- consists of a round steel shaft and helical blades.

• Shallow Foundations

  • Economic Factors are important

  • Loading & soil types will permit

  • Soil treatments will work

  • Examples

    • Grade bearing- concrete foundation with rectangular cross section running around the perimeter of the house under exterior walls.

    • Used where the surface soil's load-bearing capacity is less then the expected design loads.

    • Isolated column pads- used to carry and spread concentrated loads

    • Common with columns or pillars

    • Continuous wall footings- supports more than two columns on a wall thus creating stability for the foundation.

However, the work of a geotechnical engineer does not stop at just determining what is to be built. They must also perform soil tests to see what the existing soil sample conditions on a site might be. Soil testing and construction materials testing is the second part of their job. Once work begins preparing the slab for the construction of the foundation, there are various soil tests that may be performed

• Proctors

• LBR (lime rock bearing ratio

• Densities.

After learning about soil testing and foundation construction, you can see why it's important to hire a geotechnical engineer you can trust.

Geotechnical engineering is sometimes overlooked. When it is overlooked, it can cause many delays on a construction project. At Specialty Engineering, we have learned the importance of advising a client of starting their project with a geotechnical site investigation. We have had to let a client know that they would have to stop their work because a geotechnical report was not followed.

The fate of your foundation rests completely on the condition of your soil. That being said, living in South Florida presents it's own challenges to geotechnical engineering because of our high water table and how sandy our soil is.

At SPEC we have been designing the foundations of South Florida since 1979. We have worked on projects from the I-595/I-75 interchange to several recently completed high rise structures in our metropolitan areas. Learn more about how Specialty Engineering can help you by exploring our services here: https://www.specsf.com/testing-geotechnical and find out if your project needs a geotechnical report.