Join us in learning from Mike Carpenter who retired from U.S. Geological Survey on his talk: Continuous Monitoring of an Earth Fissure in Chino, California—A Management Tool
About Mike Carpenter:
Mike Carpenter has bachelors and masters degrees in geology from Indiana University. In 1975 he logged holes and did geophysics on the Alaskan Pipeline. He then completed a PhD in hydrology from The University of Arizona. He joined the USGS Subsidence Research Project and was largely responsible for the Arizona work including the Invar-Wire horizontal extensometer and repeated precise surveys (Professional Paper 497-H). When that project ended, he worked on deformation of sandbars in Grand Canyon, eventually inventing the total-pressure-cell erosion and deposition sensor. After retiring from the USGS, Mike consulted with Richard Wilson for the Colorado River Indian Tribes (CRIT) and then returned to earth-fissure and subsidence work in Chino, California with the quartz-tube horizontal extensometers, liquid-level, and tilt-sensor instrumentation.
Presentation: Continuous Monitoring of an Earth Fissure in Chino, California—A Management Tool
Continuous measurements of deformation were made in Chino, California across an earth fissure and nearby unfissured soil during 2011-2013 in two buried, horizontal, 150 mm pipes, 51 m long, which were connected by sealed boxes enclosing vertical posts at 6 m intervals. Horizontal displacements and normal strain were measured in one line using nine end-to-end quartz tubes that were attached to posts and spanned fissured or unfissured soil. The free ends of the tubes were supported by slings and moved relative to the attachment post of the next quartz tube. Linear variable differential transformer (LVDT) sensors measured the relative movements. Five biaxial tilt sensors were also attached to selected posts in that line. Relative vertical movement was measured at nine locations along the line in the second pipe using low-level differential pressure sensors. The second pipe was half full of water giving a free water surface along its length. Data were recorded on a Campbell CR10 using multiplexers.
The quartz-tube horizontal extensometers exhibited more than 3 mm of predominantly elastic opening and closing in response to about 32 m of seasonal drawdown and recovery, respectively, in an observation well 0.8 km to the south. The nearest production well was 1.6 km to the west. The horizontal strain was 5.9 x 10-5 or 30 percent of the lowest estimate of strain-at-failure for alluvium. Maximum relative vertical movement was 4.8 mm. Maximum tilt in the fissure zone was 0.09 arc degrees (5.4 arc minutes) while tilt at a separate sensor 100 m to the east was 0.86 arc degrees, indicating a wider zone of deformation than is spanned by the instrumentation. High correlation of horizontal displacements during drawdown, and especially recovery, with change in effective stress supports differential compaction as the mechanism for earth-fissure movement.
Continuous measurements of horizontal strain coupled with water-level fluctuations and vertical borehole extensometry provide a real-time adaptive management tool for restricting pumping if strain approaches the lower limit of strain-at-failure or a stress-strain curve deviates from the previous mostly elastic regimen.
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