Recently, we were asked to conduct a seismic refraction survey to determine depth to bedrock and rippability of near surface materials along a proposed waterline alignment project in Scottsdale, Arizona. Seismic lines were conducted along the proposed alignment to compliment proposed geotechnical drill sites and to fill in the blanks, so to speak, in areas where drill rig access would require extensive permitting. No vehicle access was permitted, and therefore, equipment was packed in and survey lines were conducted as close to the alignment as possible without damaging plant life.  Relatively shallow bedrock was expected along portions of the alignment, based upon nearby outcrops of granitic bedrock at the ground surface.

Even though this site will eventually have custom homes, the biologists would not like you to drive a drill rig here.

At this location, bedrock was found to be at approximately 20 feet below ground surface.

This survey work was conducted despite nearby construction work involving grading of a new access road and residential construction pads. Our survey did not interfere with the access road work since we were able to initially collect useful data without needing access for a drill rig. Following construction grading, we were then able to access the site with a drill rig to conduct our ground truth soil borings.  In a few areas where drill rigs had access, seismic data was tied directly to drilling logs, in order to ground truth the geophysical findings. The geophysical data was found to correlate well with the boring logs.  Because we were able to offer a technique that can be done on foot without need for cutting extra access roads for a drill rig, the client was happy that he didn't have to obtain permits to transplant certain native plants prior to our survey. He was also happy that not cutting any extra access roads meant less soil erosion issues to deal with in a environmentally sensitive area.

Southwest Geophysics has used Seismic Refraction Surveys to: