Geological Research at the IGS
Evaluating geologic hazards at Bicycle Basin, Fort Irwin, California
||Sep 1, 2014
||Dec 31, 2015
Jill Densmore (USGS), Antonio Bobet (Purdue), Rodrigo Valente (Purdue)
U.S. Geological Survey (USGS) - - USGS - No Specific Program
||Land surface deformation at the U.S. Army Fort Irwin National Training Center (NTC) presents a significant geologic hazard and corresponding risk to the safe operation of aircraft. Land surface features including Earth fissures, sink-like depressions and giant desiccation cracks have been identified on the playa ephemeral lake bed that serves as an aircraft runway. At present it is unclear whether the emergence of these features is driven by natural or human-induced processes.
||The objective of this project is to determine the most likely driving mechanism for land surface deformation at Bicycle Basin playa. One hypothesis for surface crack/Earth fissure evolution is a tensile failure resulting from differential compaction of the aquifer system as depressurization occurs from groundwater pumping at nearby wells. Such a driving mechanism for Earth fissure development represents relatively deep-seeded stress and strain in the alluvial basin-fill units for which mitigation is likely to entail significant operations. In contrast, the observed presence of giant desiccation cracks in a network pattern across the playa suggests an alternative hypothesis is plausible in which surface cracks form from volume contraction with desiccation of clay-rich sediments. This potential mechanism for crack development represents a near-surface process for which mitigation is a relatively minor operation.
||Repeat geophysical surveys of the playa region and analysis of monitoring data such as first-order leveling surveys, tape extensometers and in-situ soil tension sensors will be conducted to elucidate the most plausible driving mechanism for the observed land surface deformation.
||Results will be published in two different arenas to maximize the impact and value of this work: 1) as a peer-reviewed technical report in the USGS publication series, and 2) as a peer-reviewed scientific journal article for broader exposure in the geoscience and geotechnical engineering communities.
||The results of this study will aid decision making at Fort Irwin with regard to the safe operation of aircraft and cost-effective mitigation strategies for ground-failure hazards. This study also benefits the Indiana Geological Survey in its continuous development of innovative techniques for addressing geologic hazards.