Your next project may be small or extensive, but it involves building something. Have you ever thought of the environmental impact of the project on the surrounding land? What if something goes wrong? You could end up losing hundreds of thousands – perhaps millions – of dollars. This is why geotechnical engineering is critical to your firm’s next project.
Geotechnical engineering deals with Earth materials, including soil, rock, and groundwater. Most projects are supported by ground, and geotechnical engineering interfaces with most aspects of nearly any major construction project. For example, geotechnical engineers design foundations for structures, sub-grades for roadways, embankments for water storage and flood control, and containment systems for hazardous materials.
Not only that, these engineers are absolutely essential in the design, construction, and operation of most civil engineering projects. Geotechnical engineers also deal with various geologic hazards impacting our society, such as landslides, soil erosion, and earthquakes.
A Review of the Project
The first step in the engineering process is to review the project site. Geotechnical engineers do this by physically surveying the site that will be worked on. The engineer defines the required material properties for the site. Then, he does an investigation of the soil, rock, fault distribution, and bedrock properties on and below where the construction project will take place.
The engineer needs to examine ground properties below the project site, and across a potentially wide area off-site, since underground activity near the site may affect the construction project long after it’s finished. A good job done here will prevent catastrophic failure of the project.
Some considerations for the initial examination include:
• Unit Weight: this is the total unit weight of the project. Cumulative weight of the solid particles, water, and air in the material per unit volume are included in this analysis.
• Shear Strength: this is the shear stress expected to cause structure failure, and needs to be analyzed to prevent catastrophic failure of the project.
• Void Ratio: this is the ratio of the volume of voids to the volume of solids in the soil. In other words, it’s the ratio of "empty space" to actual soil material in the ground.
• Porosity: this is the ratio of the volume of voids in the soil to the total volume of the soil. In other words, it’s the ratio of the "empty space" to the total volume consisting of soil and "empty space." This is related to void ratio, but includes the total volume of the soil and void instead of just the soil itself.
• Atterberg Limits: this is the "liquid limit," "plastic limit," and "shrinkage limit." This is how engineers measure and quantify what they are working with. It will tell them whether they will ultimately be building on top of silt or clay, for example. It can also distinguish between different types of clays, silts, and other ground material.
• Compressibility: this is the rate of change of volume with effective stress. If the pores of soil are filled with water, then the water has to be squeezed out of the pores to allow for volumetric compression. Called consolidation, this process will affect how a structure may be built on the land.
Ground Improvements Made
Many times, ground improvements need to be made. Ground improvements refer to engineering techniques that improve soil properties to be worked on. Usually, engineers must modify shear strength, permeability, and stiffness of the ground. These improvements have been developed into a complex and sophisticated tool to support foundations for a range of structures that otherwise simply could not be built in many areas. These improvements also save money and time, since proper preparation reduces the risk of project failure.
Laying the Foundation
Foundations built for above-ground structures may include both deep and shallow foundations, pavement subgrades, and earthworks. Foundations may support anything from high-rise buildings to parking lots to bridges and are necessary for the longevity of any project.
Liz Tyler is a full-time student working towards an advanced degree in engineering. She loves writing about various aspects of geological subjects that relate to "the real world" for a variety of websites. Click to learn more about Geotechnical Engineering.