Skip to content

PPI’s Geophysical Services History

PPI’s Geophysical Services Department was created in 2014 in response to a Client’s need to evaluate foundation bearing capacity at remote Project Sites with minimal site disturbance.  Since 2014, PPI has compiled a lengthy geophysical project resume using a combination of Ground Penetrating Radar (GPR), Near Surface Seismic methods, and Resistivity Testing methods. PPI has geophysical testing experience includes numerous karst studies, seismic site class ratings, sites with restricted excavation requirements, sites with slope failures, and sites with mine features.  PPI’s karst experience also includes studies of caves and sinkholes, including sinkhole rim determination studies.

What are Geophysical Services?

While not as common as performing subsurface borings/soundings, Geophysical Testing uses the physical properties of materials and their surrounding environments for qualitative analysis, allowing us to evaluate (or “scan”) the subsurface conditions through various methods without the use of borings/soundings.  In other words, geophysics can be used to get a glimpse of and evaluate the subsurface conditions or measure varying properties of the subsurface materials (such as soil electrical resistance for grounding grids). 

PPI commonly uses Geophysical Testing Methods for the following types of projects:
  • Sites with sinkhole and/or cave concerns;
  • Sites with shallow bedrock concerns;
  • Sites requiring a higher level of understanding of bedrock and subsurface conditions (dams, levees, water treatment and storage, horizontal drilling for utilities, large buildings, etc.);
  • Preliminary studies for developments;
  • Sites with variable undocumented fill depths;
  • Sites with historic mining features; 
  • Sites with slope failures; 
  • Non-invasive testing of existing site features and soils beneath existing site features; and
  • Pavement evaluations.

PPI’s Offered Geophysical Services 


Ground Penetrating Radar (GPR)

Click For More Information

Many people have heard of GPR from forensic TV shows, but PPI offers real GPR services for inspections and exploration.  GPR is generally the fastest and cheapest geophysical testing available but comes with some major drawbacks such as signal absorption in clay and saturated soils and limited site usage.  However, GPR testing can provide quick investigation for below ground oddities and geological features.  Additionally, GPR excels in quick investigation of pavement sections and on-grade slabs.  

PPI utilizes both a cart based GPR unit  and small wheeled based unit allowing for quick scanning of the subsurface which can be recorded and stored. Due to the cart and/or wheeled limitations, scan areas must be generally smooth and free of brush and debris.  GPR testing should not be performed in muddy conditions. Additionally, PPI can utilize our RTK GPS units with the GPR for added global positioning of GPR scans.  This allows us to record GPR scans and further review and analyze the data in the office while still being able to go back to the site to pinpoint features noted in review.

Below are some typical uses of GPR testing:

  • Locating structural reinforcement in concrete;
  • Estimating existing slab/pavement thicknesses;
  • Evaluating materials beneath existing slabs;
  • Identifying voids beneath slabs;
  • Pavement Analysis;
  • Looking for shallow geological features such as voids, caves, and bedrock; and
  • Identifying buried structures and mine shafts.
GPR With Rover - All Terrain View 2  Void

Seismic Refraction, MASW, and MAM/ReMI Testing

Click For More Information

 PPI offers Seismic Refraction Testing, MASW, and Passive Velocity MAM/ReMi testing.  Seismic Refraction provides P-wave information while MASW and MAM testing offers S-wave information.  MASW testing can be performed in 1D surveys as boring replacements and 2D cross-sections of the subsurface.  Seismic testing provides information relating to densities and seismic properties of the subsurface materials.  Below are typical uses of Seismic Testing:

  • Direct measurement for Seismic Site Class Rating, often improving the seismic site class provided;
  • 1D replacements for Borings for Subsurface strength properties in areas with restricted access and /or limitations on ground disturbance;
  • The combination of refraction and reflection can provide information needed for foundation design where vibrational conditions are a concern; and
  • 2D profiles of densities along testing locations.  This is commonly used in the following:
    • Karst evaluations including cave detection, sinkhole detection, and sinkhole rim estimation;
    • Historic subsurface mining feature detection;
    • Bedrock depth estimation; and
    • General geotechnical investigations for estimated N-values and densities beneath structures.
MASW of Open Void and Possible Cave

Electrical Resistivity Testing

Click For More Information

PPI offers 1D Vertical Electrical Sounding (VES) testing and 2D Electrical Resistivity Tomography (ERT) testing as well as Induced Polarization (IP) testing.  Generally, VES studies are used in electrical grounding applications where ground resistance is the primary focus; however, ERT and IP testing are more common in subsurface exploration uses as described below:

  • Karst evaluations including sinkhole evaluations, location of cave extents, and sinkhole rim location estimations;
  • Bedrock depth estimations; 
  • Slope failure analysis; and
  • General subsurface profiling.
ERT Sinkhole Scan


Mr. R. Todd Hercules, P.E. – Geotechnical Engineer – Ph.: (417) 864-6000, [Email]