A Day in the Life: Step Inside Princeton Hydro’s Geotechnical Laboratory

At Princeton Hydro, our Geosciences Team consists of Geotechnical Engineers and Geologists who are proficient in the behavior of earth materials and the application of soil and rock mechanics. Together, they assess the physical, mechanical, and chemical properties of soil and rock to design solutions, assess risks, and solve problems for a diverse array of projects, including infrastructure, stormwater management, and coastal restoration.

Supporting Princeton Hydro’s Geosciences team is our full service, in-house materials testing laboratory that provides soils, rock, and construction materials testing. Soils intended to support structures, roadways, or other infrastructure must be evaluated by geotechnical engineers to predict their behavior under applied forces and variable moisture conditions.

Our Soils Testing Laboratory, located in Sicklerville New Jersey, is certified by the American Association of State Highway and Transportation Officials (AASHTO) and validated by the United States Army Corps of Engineers (USACE) Materials Testing Center (MTC) to complete a full complement of tests. The AASHTO Accreditation Program is the largest accrediting body in the construction materials industry and most widely-accepted. The USACE MTC is the only agency authorized to validate commercial laboratories to work for the USACE. All of our laboratory testing is performed in accordance with applicable American Society for Testing and Materials (ASTM) standards.

For this edition of our “A Day in the Life” blog series, we opened the door to our geotechnical laboratory to walk you through “a day in the life” of our Staff Engineer and Soils Testing Lab expert Marissa Ciocco, PE.

Let’s roll up our sleeves and dig in the dirt!

Each day looks a little different for Marissa depending on what types of samples require testing and what tests need to be performed. Our testing capabilities include grain size analysis, soil classification, moisture content, liquid and plastic limits, permeability, organic content, moisture-density relationships (Proctor), soil strength tests (UC, UU, CU, CD), and many others.

For Marissa, first on the to-do list is the task of determining the liquid limit and plastic limit of a soil sample. Collectively, alongside the shrinkage limit, these tests are referred to as the Atterberg limits. This classification test determines the water content at which fine-grained soils transition between four states: solid, semi-solid, plastic, and liquid.

Soil exhibits significant differences in strength, consistency, and behavior depending on which state the soil is in. The Atterberg limits test determines when the physical changes occur, and provides valuable insights into soil strength, permeability, settlement values, and expansion potential, all of which are incredibly important in all aspects of planning, engineering design, and implementation.

First, Marissa prepares the soil sample. The Atterberg limits test is only performed on soil material that can pass through a 0.425mm sieve (an ASTM requirement).

Watch Marissa perform elements of the D4318 test is titled “Liquid Limit, Plastic Limit, and Plasticity Index of Soils.”

In the video, Marissa demonstrates the Liquid Limit test. She adds moisture to the test specimen by adding water and mixing with a spatula. She then spreads the sample into the brass bowl of the liquid limit device, uses a grooving tool and manual-crank, and (off camera) she proceeds to measure when the groove closes, which defines the soil’s liquid limit.

She also demonstrates the Plastic Limit test, which she does by rolling a small portion of the wet soil sample onto a glass plate, creating a thread of soil. In doing so, she determines the water content at which the soil thread crumbles before being completely rolled out. The plastic limit is defined at the water content where the soil thread breaks apart and cannot be re-rolled to a diameter of 3.2 mm. A soil is considered non-plastic if a thread cannot be rolled down to 3.2 mm at any level of moisture.

Next on Marissa’s to-do list is a soil compaction test referred to as a Modified Proctor test, which determines the relationship between a soil’s dry unit weight and water content. This test yields the optimal water content at which the soil sample will become most dense and achieve its maximum dry density.

Marissa first prepares the soil for testing by passing it through the appropriate sieve and mixing it with the appropriate amount of water as required by the testing parameters. The soil will be compacted into a specialized cylindrical mold, but first she weighs the empty mold to create a baseline.

The next step is to compact the moist soil into the mold. Soil is added in equal layers, and each layer is compacted by dropping a rammer of specific weight and length. The compacted soil specimen is then leveled, and the mass of the mold with compacted moist soil is measured. The compacted soil specimen is then extruded from the mold and the water content is measured. This process is repeated for multiple water contents and the results are charted to determine the optimum water content and maximum dry density.

Essentially, the test determines how much of the soil material can be compacted into the same volume at the various amounts of moisture. If soil is too dry, it cannot compress tightly due to particle friction. If the soil is too wet, it cannot compress tightly due to water absorbing the compactive effort. The compaction and Modified Proctor test help to indicate the stability of the soil and the load-bearing capacity of the soil, which is incredibly important for various types of engineering and construction projects.

A big thanks to Marissa for walking us through a portion of her day!

Marissa Ciocco, PE, is a graduate of Rowan University holding a B.S. in Civil Engineering with a Bantivoglio Honors Concentration. She worked in the Construction Materials Laboratory as part of the CREATE’s Fellowship program at Rowan University, and participated in clinic projects such as a green roof feasibility study, testing the effects of water quality on masonry mortar, and the sustainability of converting organic waste feedstock into liquid biocrude. Marissa is passionate about working towards creating a more sustainable environment.

Our team has provided sampling, testing, and qualification for a diverse array of projects and clients throughout the Northeast, including commercial, residential, and industrial applications. Our laboratory training, calibration, and quality control procedures ensure that testing is performed by competent, experienced personnel, like Marissa, utilizing properly calibrated equipment. And, our process ensures that the results are subjected to an exceptional quality control program.

Our Geosciences team, along with our in-house Soils Testing Laboratory, allows us to complete 100% of geotechnical site investigation, laboratory testing, analysis, engineering design, and reporting in-house. We can perform analyses for a multitude of geotechnical sub/specialized disciplines.

To read about a geotechnical investigation and soil borings analysis project we completed for the USACE New York District, click here. If you enjoyed this blog, check out another one from our “A Day in the Life” series, and stay tuned for more!

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