Day Four of First Strainmeter Installation: Putting the Pieces Together

Overview

June 20, 2005

Upon arriving at the site, we found good news: the concrete successfully blocked up the 6-inch casing, as the artesian water flowing out of the borehole now only comes out of the 2-inch PVC that holds the seismometer. From the opening of the borehole, crews measured 322 feet down to the top of the concrete. This area will be left open to allow the potential for other instruments to be installed in the future.

Next, the crew marked the ground with neon orange paint to indicate where a data cable hole and a trench needed to be carved out. The engineers gratefully accepted the landowner’s offer to use the fish hatchery’s 4-wheel drive backhoe to get the job done.

Meanwhile, Wade Johnson, “master electrician du jour,” took the road less traveled as he crept under the fish hatchery’s building to tie into the AC power. Wade had to crawl through shrews, spiders, and slugs to find the AC drop. Thanks for taking one for the team, Wade!

Once the backhoe completed the digging, the uppermost 250 feet of data cable and power cables were laid in the trench and covered with dirt. Then the crew installed a 6-inch wooden frame, slightly larger than the diameter of the enclosure, surrounding the pore pressure monitoring well and borehole and covering the buried data cable. Once that was leveled and in the right position, the crew filled the frame with 14 bags of cement to secure everything in place.

Next, the final instrument, a pore pressure monitor, was lowered into the 2-inch PVC that holds the seismometer. This instrument uses a quartz crystal to detect and measure changes in the pore pressure; because of the artesian surrounding, the monitor was lowered only 12 feet into the hole.

While the cement was still wet, the enclosure for the surface electronics was lowered into place. Large screws attached to the bottom of the enclosure were set into the cement to secure the enclosure in place once the cement dries. After the monitoring equipment and batteries were placed inside the enclosure and hooked up, another test was performed on the strainmeter indicating the instrument was working as expected. The crew continued to wrap up loose ends at the site, excited that the installation is very close to being completed!