Visiting Scholar: Majid Ghayoomi, Ph.D.
Assistant Professor
University of New Hampshire

Tues., March 13
10:00 a.m.
Milner Exec. Boardroom (0560 MEK)

Abstract: Seismic waves generated by earthquakes often travel through soils with different mechanical and hydraulic properties. This transition affects the earthquake motion characteristics as it travels from the bedrock to the soil surface. Site response analysis is typically performed in practice to evaluate this process, which is a crucial step toward seismic design of soil-structure systems. Among different soil properties, soil’s water content or the degree of water saturation could influence the surface motion, which received less attention in comparison with other effective factors.

The seismic response of partially saturated soils differs from that of dry or water saturated soil deposits. Yet, the available site response analysis methods ignore the influence of partial saturation in the soil. Inter-particle suction stresses in partially saturated soils increase the dynamic properties of soils including stiffness, damping, wave velocity, and seismic compression. As a result, the distribution of suction with depth is expected to affect the propagation of seismic waves and the resulting ground accelerations. This, in turn, influences the seismic demand imposed on the soil and surface structures. The seasonal fluctuation of the water table and its impact on degree of saturation may alter the site response. The current state of practice commonly relies on procedures that include dynamic material properties of either water saturated or dry soils as the most conservative scenarios. This might be an appropriate assumption for problems dealing with soils’ strength and deformation. However, stiffer partially saturated soils can result in a higher intensity motion at the soil surface.

The outcome of recent investigations on unsaturated soil dynamics ranging from dynamic soil characterization, site response analysis, and seismic compression, obtained from a series of element-level, centrifuge physical model, numerical simulations, will be discussed and presented.

Bio: Dr. Ghayoomi is currently an Assistant Professor at the University of New Hampshire. He received his PhD from the University of Colorado, Boulder in 2011. He also obtained his BSc and MSc degrees from the University of Tehran and Sharif University of Technology. He has extensive experience in centrifuge physical modeling of geotechnical systems. Dr. Ghayoomi has expertise in the areas of unsaturated soil mechanics, dynamic material characterization, and seismic soil-structure interaction. He is a member of ASCE unsaturated soil and geotechnical earthquake engineering committees.