Decoded: Engineering Properties Terminology (Part 3 of 5 in the Decoded Terminology Series)

The successful outcome of any construction effort is driven by rapid-fire collaboration among specialists with different areas of expertise—from contractors in the field to civil, structural, and geotechnical engineers overseeing design and performance.

While these professionals speak a common industry language shaped by real-world situations and challenges, each discipline also brings its own technical vocabulary to the mix, including terminology that may not appear in standard references.

To help teams align on definitions and avoid misunderstandings that can slow progress—especially when working with accelerated schedules—the following overview provides clarity around essential terms and acronyms related to engineering properties.

Engineering Properties Terms

Besides knowing what types of soils are on your site, you’ll also need to know their engineering properties, and how they’ll behave when they’re excavated, compacted, and subjected to loads. Obtaining this information requires sampling site soils and testing them in situ (in place on site, without removing them) or in a geotechnical lab.

Here are some of the most widely used terms related to this work: 

• Shear Strength: 
  The shear strength of a soil refers to the maximum force (or shear stress) it can withstand under any given conditions. For example, if a wheel rolling over soil creates a rut in the soil, this indicates that the force applied is greater than the shear strength of the soil. 
  
  
• Pore Pressure/Pore Water Pressure: 
  These terms refer to the pressure of water held in the voids of a soil mass. The higher the pore pressure, the weaker the soil strength. 
  
  
• Waterbed Effect: 
  In soil, the waterbed effect occurs when soil is highly saturated and the pore pressure rises, which causes the loads to be carried by the water instead of the soil particles. This creates very unstable conditions where the soil becomes “spongy” or “bouncy,” and loses strength. 
  
  
• Maximum Dry Density (MDD): 
  MDD refers to the highest density that any given soil can achieve under a given compaction effort. It’s important to measure the MDD, to determine whether a soil is properly compacted. 
  
  
• Standard Penetration Test (SPT): 
  SPT is a standardized test that measures the strength of soils in the field. A sampler (called a split-spoon) is driven into the ground using a specific procedure, and the strength of the soil being measured is determined by the number of blows (known as the N-value) required to reach 12” of penetration. The higher the N-value, the stronger the soil. 
  
  
• California Bearing Ratio (CBR): CBR is an empirical penetration test used to evaluate the strength of a subgrade soil and base materials for road construction, expressed as a percentage of a standard high-quality crushed rock. 
  
  
• Dynamic Cone Penetrometer (DCP): 
  A DCP is an instrument used to collect and test subgrade soil strength data. 
  
  
• Compaction: 
  In soil mechanics, compaction means making soil denser by applying mechanical energy through the use of rollers, tampers, and/or vibration. Properly compacted soils are stronger, experience less settlement under load, and have higher bearing capacities than poorly compacted soils. 
  
  
• Consolidation: 
  Consolidation refers to the slow reduction in the volume of saturated, low-permeability soils, like clays, when a load is applied over time. It occurs when water is pushed out of the soil voids, effectively “squeezing” the soil particles together. 
  
  
• Settlement: 
  Settlement refers to the downward movement of the ground under an applied load—like a building or other structure. Differential settlement happens when settlement is uneven across a structure, while total settlement is the total vertical movement. Settlement can happen for many reasons, and can cause a building to tilt or crack—like the Leaning Tower of Pisa, for example.
  
  

Want to learn more?

We cover more geotechnical terms and abbreviations in our Beneath the Build series on YouTube! Click here to the first episode and learn more.

This blog is part of a 5-part Decoded Terminology Series, click here to read part 2.