GEOTECHNICAL EXPLORATION


Geophysical techniques have many potential applications to geotechnical site characterization studies, including:


  • Establishing geological/geotechnical models based on parameters such
    as fill thickness, depth to bedrock, and depth to the water table
  • Estimating the in-situ deformation properties of soil and rock
  • Deriving the characteristics of soft ground under seismic loadings (liquefaction effects, amplification)
  • Characterizing karst terrain (locating buried sinkholes and voids)
  • Estimating the rippability of rock
  • Locating areas of seepage (in dams)
  • Providing parameters for cathodic protection design


DC Resistivity – This method is used to map electrical variations in the subsurface. Traditional archaeological application of this method has been to map lateral changes in resistance at shallow depths, but advances in computer processing capabilities have allowed mapping the variations of electrical properties as two- or three-dimensional profiles.

Electromagnetic (EM) methods – EM methods allow the rapid measurement of variations of soil electrical properties, as well as identification of metallic objects. EM techniques are commonly applied to industrial sites to locate underground tanks or pipes, but EM methods can also be very effective in mapping variations in shallow soil properties.

Ground Penetrating Radar (GPR) – GPR offers the highest resolution of any geophysical method when soil conditions are favorable. Typical applications that we have conducted with this technique include mapping of graves, middens (refuse piles), buried foundations, and industrial targets such as buried waste, tanks, pipelines and other utilities.

Magnetics – We routinely conduct total field and gradiometer surveys for mapping the distribution of buried materials. The sensitivity of this method allows for its application to mapping of subtle changes in soil conditions at archaeological sites.

GPR survey being conducted on the side wall of concrete arch culvert-tunnel.



Some representative geotechnical engineering projects where geophysical techniques have been utilized are provided below.


EXAMPLE PROJECTS


Geophysical Investigation of Casino Site in Pittsburgh

D’Appolonia conducted a geophysical survey at an 11-acre casino site in Pittsburgh, Pennsylvania. The survey was performed using a Geonics EM-61 metal detector capable of mapping metal and non-ferrous metallic objects to depths greater than 10 feet. The purpose of the survey was to identify potential obstructions that could interfere with the installation of auger-cast piles that were planned for the foundations of the casino complex. The survey data were contoured and plotted, and the results indicated the presence and location of buried foundations and other objects at the site.


Ground Penetrating Radar Evaluation of Arch-Culvert Tunnels

D’Appolonia was retained to evaluate the condition of two arch-culvert concrete tunnels using ground penetrating radar (GPR). The survey demonstrated that GPR is useful for relatively deep imaging of structural concrete and can aid the engineer in planning a program of sampling and testing.


Geotechnical Engineering for Light Rail Transit System

D’Appolonia conducted an extensive geotechnical exploration program associated with design and construction of underground construction for a Light Rail Transit system in Pittsburgh, Pennsylvania. Subsurface exploration included borehole camera surveys, borehole geophysical exploration, and seismic cross-hole testing to characterize rock mass behavior.


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