Geophysics

Geophysics is the science of investigating subsurface conditions by measuring, analyzing, and interpreting how energy travels through the ground. Geophysics can provide a generalized view of subsurface conditions, fill gaps between test borings, and/or identify zones of interest to be targeted with intrusive methods.

At Schnabel, our geophysicists focus on the “shallow” subsurface—the depths of which affect, or are affected by, civil engineering projects. Our team specializes in non-invasive visualization of the subsurface. They assist with the development of comprehensive subsurface models by combining geophysical results with other relevant site information. The models this team creates help designers and owners understand the impact of subsurface conditions on project design and enable them to make evidence-based decisions that can reduce risk and costs.

Our geophysical services team takes a holistic approach to each project, working closely with clients to provide meaningful and clear results. Specific methods used in geophysics depend on the geologic setting, project objectives, and other site-related considerations. Schnabel’s geophysicists are licensed professionals with a broad range of experience applying and interpreting geologic and geophysical results for engineering and environmental projects.

Typical Geophysical Methods

• Seismic refraction tomography (SRT)
• Active and passive multi-channel analysis of surface waves (MASW)
• Horizontal to vertical spectral ratio (HVSR, H/V)
• Downhole, crosshole, and parallel seismic
• Electrical resistivity imaging (ERI)
• Induced polarization (IP)
• Self-potential (SP)
• Magnetics
• Time and frequency domain electromagnetics (TDEM/FDEM)
• Ground penetrating radar (GPR), pulse, and step-frequency
• Microgravity
• Bathymetry and sub-bottom profiling
• Non-destructive testing/evaluation (NDT/NDE)
• Impact echo/impulse response (IE/IR)
• Spectral analysis of surface waves (SASW)
• Ultrasonic

Typical Geophysical Applications

Dams and water

• Soil and rock evaluation for aquifer characterization
• Target water well siting
• New dam site evaluations
• Identify seepage through dams and levees
• Depth to rock (rippability) for remediation and erosion analysis

Environmental

• Map contamination plumes and preferential pathway
• Locate underground sources of contamination such as USTs, drums, and pipes
• Delineate landfill and buried debris boundaries

Geotechnical

• Depth to disintegrated or partially weathered rock, and rock
• Soil and rock properties (VS and VP), site-specific response input
• Extrapolate information from boreholes to a wider area and/or to focus a drilling program

Transportation

• Depth to and rippability of rock along alignment
• Soil stiffness and variability
• Subsidence evaluation
• Pavement and bridge-deck and unknown foundation evaluations
• Power and energy soil resistivity for grounding design
• Site-wide evaluation for depth to rock or karst risk

Tunneling

• Evaluate rock rippability
• Map variable rock conditions and depths

Archaeological or Cultural Resource

• Map locations of buried historical assets such as foundations
• Locate burial sites

Geohazards

• Karst evaluation
• Sinkhole, void, and subsidence evaluation
• Risk assessment for site development landslides and slope stability
• In-situ shear wave velocity measurement
• Abandoned mine evaluations
• Depth to rock for scour analysis