What are MASW & REMI?
MASW and ReMi are relatively new methods Geotechnology, Inc. uses to determine shear wave velocity profiles to a depth of approximately 100 feet (per International Building Code 2006 & 2009). These surveys utilize the dispersive property of surface waves and are conducted using a controlled sledgehammer source or by passively recording background surface wave “noise” such as the vibrations generated by passing vehicles, airplanes, and trains. The surface waves are recorded using a seismic system comprised of geophones, cables, and seismograph. Shear wave velocity profiles are constructed from this data.
MASW & REMI Benefits:
These data can provide valuable information to structural engineers for design of new and expanded structures in all seismic zones. The building code provides classifications based on seismic risk. These classifications can require expensive design and construction requirements. The shear wave assessment is considered more representative of seismic response. It can provide information that allows an owner to receive a less conservative seismic classification than an assessment from boring data alone, saving potentially hundreds of thousands of dollars in design and construction costs.
Because MASW and ReMi are non-invasive and nondestructive, and may be collected passively using ambient noise as a seismic source, surveys can be conducted in highly urbanized areas. The seismic lines can be deployed within road medians, at active construction sites or along highways, without disturbing work or traffic flow.
Shear Wave Velocity and IBC Classification
Structural designers following the International Building Code (IBC 2006 & 2009) must take into consideration the site classification for structure protection. The IBC site classification can be determined from site specific shear wave velocity measurements using methods such as MASW or ReMi, or estimated from a subsurface exploration using standard penetration tests (N) or soil undrained shear strength (su). This graph demonstrates how direct shear wave measurements often result in an improved IBC site classification when compared with a subsurface exploration. Thus MASW or ReMi surveying results can save the owner significant costs by requiring less conservative seismic designs and construction requirements.