Getting it perfect at OIINK: New direct-burial stations with Trillium broadband sensors
Getting it perfect at OIINK
Reposted from Iris Passcal Instrument Center
Gary Pavlis and Terry Stigall of Indiana University are proud of their geophysics students. The students were helping them to deploy some new direct-burial stations with Trillium broadband sensors for the OIINK project (a.k.a. SDYNAC, "Structure and Dynamics of the North American Craton"), and Terry directed them to get them perfectly level and lined up to north accurately. The students outdid themselves, and helped to make this a superb installation.
These students are from Gary Pavlis' Applied Geophysics class. They spent a weekend installing stations for the OIINK project.
Clockwise from upper right: Tyler Merrell, Steven Downey, Crystal Wespestad, and Brenden Fenerty.
Photographs courtesy Terry Stigall.
This research project, supported by the National Science Foundation, is playfully dubbed “OIINK” after its principal study area — the Ozarks, Illinois, Indiana, and Kentucky. The OIINK experiment includes a 3-D, broadband, passive seismic array centered over the depocenter of the Illinois Basin. The array was designed to provide enhanced station density of 3 to 1 relative to the Earthscope Transportable Array (TA). The design builds on the experience of the first major EarthScope Flexible Array (FA) experiment (SNEP, a.k.a. the Sierra Nevada EarthScope Project) that was set up in the southern Sierra Nevada.
Here, the students align the sensor to magnetic north. Terry Stigall writes "I love this photo. Gary's geophysics students were determined to align the Trillium perfectly to north. They really took me seriously to get them perfectly level and lined up to north, and they set the declination on the Brunton correctly!"
Terry's comment on the installation: "They got it spot on level! We used the blue house to protect the cable from shovel and rodents. We also wrapped the connector with Vulcan tape before putting on blue hose."
Here are the condensed instructions for the OIINK team regarding direct burial posthole installations.
Transport sensor in case or shipping box
Pick site with drainage and some relief
Auger hole so top of sensor is at least .5 meter from surface and there is at least 1.5 inches between wall and sensor for tamping
Use some type of flexible drainage hose split to protect cable sensor cable from shovel blades when removing later
Tamp bottom of hole to consolidate disturbed soil
Add 2-3 inches of mortar quality sand and tamp
Keep cable and sensor connectors clean and check for 2 O-rings, one in bottom of sensor connector and one on plug end of cable to sensor and hand tighten.
Connect cable to sensor before lowering in hole.
Place sensor, lowering in with hook, rotate and check for alignment
Push down on top of sensor to set feet and compress in to sand, check level with bubble level and remove before burying
Its best to use "local" material for filling in and tamping around sensor but this is in debate as some want to use sand. The problem I experienced is it become the preferred place for water drainage
Only tamp material to top of sensor, connect and try to relevel with DAS before completely burying sensor
After successfully testing sensor operation, finish burying sensor, push cable down into loose coil as burying but not tamping!
Top 2-3 inches of fill should be clay rich to discourage water draining through bore, mounding decreases diurnal thermal changes and sheds rain water, so not a bad thing!
Use standard PIC best practices for rest of station...
Here, Indiana University student Xiaotao Yang tests the Trilliums and other equipment on the isolated pier before deployment in Kentucky.
Here, students Brenden Fenerty (L) and Tyler Merrell (R) program the RefTek RT-130 with recording parameters for the sensor deployment.
With the increased interest in direct burial of posthole seismic sensors, the results of the OIINK project should prove both interesting and useful. PASSCAL wishes the project continued success.
Mar 6, 2014