Page - 116 - in Book of Full Papers - Symposium Hydro Engineering

The drill rig geologist recorded drilling conditions such as rod drop, water loss and drill chatter, as well as sampling locations, material types, and any occurrences that might have proved informative to characterizing the subsurface conditions. Upon reaching total depth, all drill holes were geophysically logged using either acoustic or optical televiewer, or both, to ensure that the orientation of any discontinuity was documented. Although geophysical logging of nearly every borehole may seem excessive, the decision to geophysically log each boring proved invaluable, considering the time constraints and the need to develop a comprehensive geologic site model to support the range of OER design options being considered. Selected drill holes were additionally logged using suspension P- and S-wave velocity logging techniques to correlate with surficial geophysical results. Upon completion of each drill hole, the borehole was either completed as a VWP, open standpipe piezometer, inclinometer, or it was backfilled with cement- bentonite grout. The ultimate disposition of the borehole completions was developed using a collaborative process with the design team to confirm that the overall purpose of each borehole and the associated design objectives were being accomplished. Nearly all of the instrumentation (piezometers and inclinometers) was telemetered and viewable on an online dashboard in real time. Six locations within the FCO Spillway chute were completed as grouted VWPs with a data logger and wireless antenna; these data were retrieved manually, rather than through the online dashboard, and the instruments were installed prior to the last controlled spill through the FCO Spillway chute in May 2017. All drilling work within the FCO Spillway chute began by initially coring through the chute concrete using a 20.3 cm (8 in) diameter thin-walled coring bit. Once the coring reached the concrete-foundation rock interface, select locations were continued using rock-coring methods. Select rock core and hand samples were obtained for shear strength testing and petrographic analysis. Samples of shear gouge and compacted clayey fines from the foundation were analyzed for index properties testing, including mechanical sieve, hydrometer, and Atterberg limits. In addition, select samples were analyzed for clay mineralogy, using x-ray diffraction. 4.2. RESOURCES Execution of an exploration program of this magnitude is challenging under normal circumstances. In this case, there was very little time for the OER design team to assess the site conditions, review historic construction records, and develop the initial field exploration program. The demand on qualified personnel, including exploration subcontractors and testing laboratories, was unprecedented in magnitude and response. The execution of the initial exploration program, consisting of 60 borings and 16 P-wave surface refraction lines, along with the associated instrumentation, was needed within a very short time-frame to be incorporated into the spillway repair. The exploration program included test 116