Association of Environmental and Engineering Geologists: Great Basin Section (AEG) Meeting Announcement – Thursday, April 21, 2016
TOPIC: Student Night Presentations
SPEAKERS: Mr. David Shaw, Mrs. Sara Jensen, Mr. Joseph Toth, Mr. Andrew Sadowski, and Mr. Loyd “Travis” West
Best Western Airport Plaza Court Restaurant
1981 Terminal Way, Reno, Nevada 89502
SOCIAL HOUR: 5:30 PM, DINNER: 6:30 PM
PRESENTATION: 7:00 PM
RSVP NO LATER THAN 5PM, TUESDAY April 19 BY 5:00: @ 775¬221¬1369 or firstname.lastname@example.org
Cost: Members: $25.00, non-members: $29.00
Mr. David Shaw, University of Nevada, Reno
“Ground Surface Observations in Evaluating Shallow Stress Fields in Granitic Rock Masses”
Observations and analyses of natural rock failures in the form of buckled granitic slabs (or “pop-ups”) in the northern Sierra Nevada range are explained by high compressive stresses acting along the longitudinal axis of the slabs producing failure. The presence of high near surface in-situ stresses have been invoked in explaining granite dome formation, exfoliation, and sheet jointed slabs in granitic rock masses. From a rock engineering perspective, high in-situ stress fields parallel to the ground surface can be problematic in man-made surface excavations (e.g. at open pit mine sites) or other areas where thin slabs of rock develop dip slope failures and the inclined slabs bend, buckle, and break. In near surface underground excavations, failures occur where slab-like instabilities develop in the wall, floor, or roof of the excavation.
Two main mechanisms have been developed to explain how high stress fields develop at shallow depths: a) plate-tectonics approaches and b) residual stress energy locked into the rocks as a result of past gravitational loading. Locating slab failures is time consuming and requires high resolution aerial photographs and numerous transects in likely geologic and topographic locations favoring slab instability. Field work has located numerous examples in the Sierras where slab failure depends on slab thickness, length, tensile and compressive rock strength, and magnitude of the in-situ stress field. Current work includes numerical modeling to quantify the in-situ stress field at different localities, spanning from Yosemite National Park to Desolation Wilderness. Several pop-ups were also identified and measured in a former granitic gneiss quarry outside of Atlanta, Georgia. Workers collected in-situ stress data with the overcoring method during the Georgia quarry operations and this data will be used to validate the modeling approach.
BIOGRAPHY: David Shaw obtained a bachelor’s degrees in geology and environmental studies from the University of North Carolina, Wilmington. After graduation, he was employed by Schnabel Engineering Consultants in Charlottesville, Virginia from 2007 to 2011. David was exposed to a variety of geotechnical and environmental consulting projects but was particularly interested in large-scale dam design projects, which eventually influenced him to return to school for a geological engineering master’s degree from the University of Nevada, Reno (UNR). His master’s thesis involved constructing a global slope stability model of Lassen Peak, California and he is currently researching in-situ stress fields within granitic rock masses while enrolled in the Geo-Engineering PhD program at UNR. When not studying rocks, David can typically be found at one of the local ski areas or paddling around Lake Tahoe.
Mrs. Sara Jensen, University of Nevada, Reno
Debris flows pose a significant threat to life and property in mountainous regions. Therefore, an accurate understanding of flow mechanics is necessary to recognize and mitigate the hazards they create. Using the Discrete Element Method (DEM), a grain-scale numeric modeling tool, our study will focus on simulating dry granular avalanches and their response to changes in flow path topography. We will study how flow velocity, runout distance, energy dissipation and impact force are influenced by linear, concave up and convex up slope profiles (all consisting of the same mean slope and total relief); as well as, how these flow properties are influenced by the number, size and spacing of closed-type check dams along the flow path. Results of our preliminary investigation suggest a path dependency for these systems. Due to this path dependency flow dynamics predicted from path-averaged properties should be done with care.
BIOGRAPHY: After completing her undergraduate degree in Geological Engineering at UNR, Sara spent several years in Industry. She then returned to UNR to pursue her Master’s Degree. Her thesis focuses on the engineering design of check dams in order to mitigate the dangers debris flows pose.
Mr. Joseph Toth, Graduate Teaching Assistant in Civil Engineering at University of Nevada, Reno
Post-disaster reconnaissance of areas affected by earthquakes has documented extensive damage to buildings with shallow foundations within liquefaction-prone areas. The 2010-2011 Canterbury earthquake sequence and the 2011 Great Tohoku earthquake are some of the most recent examples where large numbers of low-story structures sustained damage resulting from liquefaction-induced settlements. Until recently, estimation of liquefaction settlement was based on empirical correlations that evaluated settlement in the free-field. However, observations have shown that liquefaction settlement under buildings can be considerably greater.
This research is based on a series of 1-g shake table experiments using a transparent soil box to reproduce liquefaction-induced building settlement. Building settlements were evaluated using a scaled model of a building foundation representing a 1-2 story home. Comprehensive parametric study was carried out to establish the effects of several parameters on free-field and building settlements such as building width and thickness of liquefiable soil layer.
Results of the experimental evaluation have provided measurements of liquefaction-induced settlement for both free-field and building conditions. The experiments utilized LVDT, accelerometers and pore water pressure sensors to monitor the rate of settlement, ground accelerations and build up of pore water pressures in both the free-field and model building footprint. Results of these experiments are compared to available centrifuge tests and field observations and conclusions are drawn with respect to the potential scaling effects.
The feasibility of installing helical piles as a mitigation strategy to reduce the building settlements will be discussed by presenting some of the exploratory experimental data obtained from a series of 1-g shake table tests.
BIOGRAPHY: Joseph Toth is a Graduate Teaching Assistant in Civil Engineering at the University of Nevada Reno. His research is currently focused on mitigation of liquefaction induced settlement. In addition he is also assisting with research in alternative applications of activated sludge for geotechnical purposes and subsurface characterization using ReMi.
Mr. Andrew Sadowski, Masters in Geology at University of Nevada, Reno (2016)
The Black Warrior geothermal system lies 20 km east of the southern end of Pyramid Lake in the Truckee Range of northwestern Nevada on the Washoe-Churchill county line. It is an amagmatic blind geothermal system, as the region lacks recent (<5 Ma) volcanism and the system lacks hydrothermal surface manifestations (no fumaroles, hot springs, sinter deposits, or high temperature alteration). The system was discovered by shallow temperature gradient drilling (100-600 m, max temp: 128°C) by Phillips Petroleum Company in the 1980s.
The thermal anomaly resides in a structurally complex zone that has not been previously characterized. Detailed geologic mapping in the area has identified faults and stratigraphic relationships between successive and interfingering Tertiary volcanic sequences that nonconformably overlie Mesozoic plutonic and metamorphic basement. The structural framework is characterized by north-northeast-striking, moderately to steeply west-dipping normal faults that terminate and step in the vicinity of the thermal anomaly. This suggests two possible favorable structural settings: (1) a fault termination of the southeastern rangefront fault with accompanying horse-tail splaying producing an area with abundant closely spaced faults and high fracture permeability; and/or (2) a fault step-over in a broad left-step of the major normal faults, whereby many closely-spaced minor faults provide hard linkage and a zone of high fracture permeability. In either case, the study area lies in a favorable structural setting for geothermal activity and may host a robust geothermal system at depth.
BIOGRAPHY: Born and raised on the east coast in south Florida, Andrew began pursuing geology during his undergraduate time at Cornell University in upstate New York. After graduation, he worked in water resources and the environmental sector in New Hampshire, before returning to graduate school to study the structural geology of geothermal systems. Basically, turning his focus from cold springs to hot springs. He attended field camp across the western US as well as western Argentina, and TA’d UNR’s field camp. He has toured Iceland with fellow NBMG/UNR folks to further his understanding of geothermal systems, and has had geothermal industry internships at Ormat Nevada and Calpine’s The Geysers. He is completing his masters in geology from the University of Nevada, Reno this semester, and is looking for employment opportunities.
Mr. Loyd “Travis” West, University of Nevada, Reno
Mr. West is a Nevada native, born and raised in Las Vegas. Upon returning home from active duty in the US Army he earned my Bachelor of Science in Geology at UNLV. Loyd began his career as a geotechnical consultant for a prominent geotechnical firm in San Diego, California where his duties involved all aspects of the field investigation process for both preliminary and forensic soils investigations. Upon moving back to Las Vegas, he continued to work as a geotechnical consultant, and began gaining experience in advanced near-surface seismic studies using Refraction Microtremor (ReMi) and refraction. Loyd utilized both passive and active source methods for various engineering applications, including site classification, fault characterization, fissure and void studies, determining rippability, and depth to bedrock.
In 2007, Loyd joined the Reno-based geophysical consulting firm Optim SDS, as the general manager of their Las Vegas field office. From Las Vegas he oversaw the data-collection of over 10,700 ReMi measurements throughout Clark County for the multiyear Clark County Parcel Vs30 Microzonation Project. This dataset has become an integral part of his research efforts towards his Master of Science in Geophysics under Prof. John Louie, here at the University of Nevada, Reno. In addition to his research and TA responsibilities at UNR, he continues to work for Optim SDS guiding data-collection efforts for ReMi, Deep ReMi, refraction, and reflection based projects. Loyd’s research interests currently include earthquake site-characterization, geo-hazards, seismic microzonation, and earthquake mitigation.