ReMi Shear Wave Velocity Testing — Part 2

As part of our ongoing geotechnical investigation at St. Joseph’s Medical Facility, our team performed non-invasive shear wave velocity testing using the Refraction Microtremor (ReMi) method. This testing was performed to better understand the stiffness of the subsurface materials and to help determine the site’s seismic classification. 

The process involved placing a series of geophones on the ground. These sensitive instruments detect vibrations from both passive sources—such as vehicles driving by or people walking nearby—and active sources. For the active testing, we generated vibrations by striking a Teflon plate with a 10-pound sledgehammer, creating energy waves that traveled through the soil and were captured by the geophones. 

By recording how these vibrations moved through the subsurface, we were able to measure shear wave velocities across different soil layers. Once data was accumulated to depths of approximately 100 feet, we used it to establish a site classification in accordance with ASCE 7-16 or ASCE 7-22, depending on the governing building code for the proposed structure.  Since site classification is based on soil properties in the upper 100 feet of the soil profile, use of this method eliminates the need for a deeper borehole, thus saving time and money to the project. In the new code cycle (2025 CBC), projects will be required to utilize measured shear-wave velocity to determine Site Class, and this non-invasive geophysical method complies with the updated code requirements.

This ReMi testing provided essential information about the stiffness of the site, complementing the soil sampling and borings performed in Part 1. Together, these investigations form components for designing a safe and code compliant foundation system. 

Stay tuned for Part 3, where we’ll highlight the laboratory testing phase and how it validates the data collected in the field.

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