What We Do

Geophysical assessments -- to “see” what’s below the ground surface

Geophysical assessments measure, map and image various subsurface physical properties of the earth’s crust just as the medical profession uses a variety of diagnostic techniques to measure and image the interior of the human body.

Geophysics is defined as an interdisciplinary physical science dealing with the nature of the earth and its environment through the interpretation of contrasting physical properties of materials. SME's engineers use geophysical assessments to provide detailed characterizations of the subsurface in environmental, groundwater, natural resource, and geotechnical investigations and how they impact risk factors, design and construction costs for a wide range of projects. Preparing maps, cross sections and images of physical properties of the earth, we provide infrastructure, construction hazard and engineering design input including depth to bedrock, elastic properties, hazard discovery and site classification.

Geophysical Surveys

Seismic
Seismic refraction is used to assist in defining the geologic profile. Blast or impact induced stress waves from the ground surface are sent through the soil/rock, and the elapsed travel time of the waves is measured with geophones at known distances from the source of vibration. In denser soils and rocks, the sound waves travel much faster. These subtle differences in wave speeds can be detected, measured, evaluated, and analyzed to determine the geologic profile. Seismic cross-hole/down-hole tests uses the same methods but is performed below the surface in specially prepared boreholes. Specialized hammers or small-scale blasting is used to induce waves between the bore holes at specific depths. Travel times of various wave types are measured.

Electrical Resistivity
Electrical resistivity testing uses electrical current to define the geologic profile, evaluate corrosion potential, determine grounding requirements for electrical equipment, or to evaluate the extent of possible contamination. Typically, the resistivity test is performed with four steel pins placed in ground, the spacing of which is varied depending upon the site conditions and the type of test performed. During the four-pin analysis, an electrical current is forced to flow between the outside pins, and the potential voltage drop is measured across the inner pins to determine the electrical resistance of the soil.

Ground Penetrating Radar (GPR)
GPR uses electromagnetic radiation in the microwave band of the radio spectrum to detect the reflected signals from subsurface structures. GPR is useful in finding buried underground storage tanks, drums, and utility lines. It can also be used to define the geologic profile and to map contamination plumes.

Geodynamics

SME provides engineering services to monitor and evaluate existing (ambient) vibrations and vibrations from various man-made sources such as construction activities and machine foundations. Geodynamic engineers also use specialized seismic equipment to evaluate the potential response of subsoil and rock conditions during earthquake events and to provide design parameters for buildings to safely resist such seismic forces.

Vibration Monitoring
Demolition of existing structures, pile driving, vibratory compaction, deep dynamic compaction or other construction activities can generate vibrations which extend beyond the site boundaries. Special monitoring equipment is used to remotely collect, store and transmit data so engineers can assess the risk of damage to adjacent facilities and to provide recommendations to minimize possible damage.

Site Seismic
A proper identification of the seismic site classification used for structural design of buildings is a valued service. SME’s Multi-channel Analysis of Surface Waves (MASW) and Microtremor Array Method (MAM) equipment provide non-invasive seismic methods to develop a shear wave velocity profile to assist structural engineers with their building designs.