NSF Award
2420070
This award supports research to study the transient phase transition behavior of well-graded gravelly soil deposits to reveal the fundamental, coupled fluid-mechanical processes governing liquefaction of gravels. Earthquake-induced soil liquefaction, a phenomenon whereby stable two-phase (solid, liquid) materials transition into a transiently single-phase viscous liquid, can result in the loss of lives, property, and infrastructure. To date, scientists and engineers have relied on post-earthquake reconnaissance and case histories of gravelly soils to empirically bound subsurface conditions prone to liquefaction. Uncertainty in analyses and uncertain estimates of ground shaking intensity cloud the interpretation of liquefaction behavior of gravelly soils since liquefaction can significantly alter pre-earthquake soil fabric (i.e., soil structure) and thus the ability to investigate it. Through an original experimental technique to seismically test a gravelly soil deposit with controlled loading intensity, this award will aim to parameterize all aspects of the in-situ, dynamic constitutive degradation and liquefaction of gravelly soils and the resulting consequences in terms of deformations. Improved understanding of the dynamic and liquefaction responses of gravelly soils will serve to advance fundamental knowledge of these soils, help secure resilience of the nation’s civil infrastructure against earthquake hazards, and train the next generation of scientists and engineers. Specifically, this study will implement a coordinated outreach/education program to broaden participation of underrepresented students, integrate field research with an interdisciplinary experiential course learning activity that will improve the understanding of the local tectonic structure of a densely populated region, and develop comprehensive and unique datasets which will be disseminated to scientific and practitioner communities. Data from this project will be archived and publicly shared in the NSF-supported Natural Hazards Engineering Research Infrastructure (NHERI) Data Depot (https://www.DesignSafe-ci.org). This award will contribute to the NSF role in the National Earthquake Hazards Reduction Program (NEHRP). <br/><br/>There currently exists no direct, controlled, dynamic in-situ measurements of the dynamic properties, and coupled, fluid-mechanical responses and liquefaction, of gravelly soils. This work centers on experiments that target small to large shear strains, by implementing a newly validated controlled blasting experimental approach and coordinated laboratory testing program, allowing for an unprecedented dataset critical for the improving the understanding of the dynamic responses and liquefaction of gravels and uniting observations drawn from earthquake case histories and laboratory element tests. This work will specifically: (1) dynamically load a well-characterized and instrumented gravel deposit under existing and post-reconsolidation stresses and true drainage boundary conditions to provide the first direct observations of the seismic and post-seismic responses of gravels to multidirectional loadings under 1g stress states; (2) determine the fundamental, in-situ threshold shear strains to initiate nonlinearity, shear degradation/inelasticity, and liquefaction; (3) establish the variation of excess pore pressure and shear modulus with shear strain over the linear-elastic to nonlinear-inelastic regimes and for strains greater than 1%; (4) determine the in-situ variation of the cyclic resistance and excess pore pressure with the number of equivalent uniform shear stress cycles; (5) synthesize the field observations with previously-developed experimental data of reconstituted and intact gravelly soil specimens; and (6) provide an impactful and experiential educational component for a diverse, multidisciplinary student body.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
