GFA owns and operates state of the art geophysical equipment. This equipment is used in many of our geotechnical investigations by our geophysical experts. This equipment includes various Ground Penetrating Radar (GPR) units and Seismographs.

GPR Ground Penetrating Radar (GPR) is an electromagnetic geophysical method that detects interfaces between subsurface materials with differing dielectric constants. The GPR system consists of an antenna which houses the transmitter and receiver; a profiling recorder which processes the received signal and produces a graphic display of the data; and a video display unit which processes and transmits the output signal to a color video display and tape recorder.

The transmitter radiates repetitive short duration electromagnetic waves into the earth from an antenna moving across the ground surface. These radar waves are reflected back to the receiver by interfaces between materials with different dielectric constants. The intensity of the reflected signal is a function of the contrast in the dielectric constant between the materials, the conductivity of the material through which the wave is traveling, and the frequency of the signal. Subsurface features which commonly cause such reflections are: 1) natural geology such as changes in sediment composition, bedding and cementation horizons, voids, and water content; or 2) unnatural changes to the subsurface such as disturbed soils, soil backfill, buried debris, tanks, pipelines, and utilities.

Anomalous subsurface features, such as sinkholes, exhibit GPR reflectors which, in the area of the sinkhole or solution cavity, dip down toward the center of the feature. In the center of the sinkhole or solution cavity, the GPR reflectors associated with the suspected soil horizons either dip sharply downward or are discontinuous. Subsurface features such as water- or air-filled voids are typically characterized by: (1) a relatively high-amplitude reflection of the GPR signals, and (2) a hyperbolic shape of the GPR signals. Fractures are typically characterized by an abrupt increase in the depth of penetration of the GPR signal and the occurrence of relatively high angle reflectors near the boundaries of the suspected fracture.

GFA has been very successful at utilizing this technology to profile subsurface conditions in a broad manner at sites and detect subsurface anomalies that may otherwise be difficult to locate.

Seismographs

GFA specializes in the field of vibration monitoring. We utilize company owned and operated seismographs to monitor vibrations from construction related activities and document peak particle velocities and sound wave emissions. This service is a necessity where existing adjacent structures are very near earthwork proximity. GFA can document vibration levels to protect such structures and document against false damage claims.

GFA also is very experienced with blasting operations and has acted as blasting consultants for a variety of projects including the Everglades Construction Project where blasting of new canals was very near power transmission lines and structures.