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.
At this location, bedrock was found to be at approximately 12 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:
- Determine depth to bedrock and rippability of rocks for housing developments, pipe line and other utility construction projects, power generating facilities, water treatment plants, water transmission facilities, commercial developments, roadway improvements, facility upgrades, bridge support evaluations, fill section evaluations, mining , and several other projects.
- Find depth to groundwater, in certain specific situations
- Generally characterize subsurface geology.
- Aid environmental contamination flow projects when used to evaluate locations of paleo stream channels or fault zones.
- Find buried bedrock valleys, which can be an important source of groundwater in unconfined aquifers.
- Record shear wave velocity profiles to help engineers calculate design parameters for potential earthquake hazards.
- Monitor ground vibration during construction to provide baseline data if there are concerns about the influence of construction activities on nearby existing structures.
- Certain specialized techniques can be used to approximately locate vertical joints or cracks, which can indicate subsidence features.