RESISTIVITY SURVEYS TO EVALUATE SOIL/BEDROCK PROPERTIES
The geophysical example shows the results of a dipole-dipole resistivity
survey conducted immediately adjacent to a bridge pier that was
encountering scour problems. The survey was conducted to determine the
competency and stability of rock or soil beneath the bridge pier. The
survey consisted of one resistivity array having a maximum length of 270
feet that yielded 230 data points within the depth interval of 0 to 50 feet.  
Low resistivity values of 20 to 200 ohm/meters recorded around the base
of the pier suggest the pier rests on a five-foot layer of soil and/or highly
fractured, broken or weathered rock and not on competent bedrock.
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Mark J. Denil, P.G.                                                 denilm@bellsouth.net                                                 Cell: (336) 339-839