Centrifuge tests to assess seismic site response of partially saturated sand layers

Abstract

Seismic response of unsaturated soil layers may differ from that of saturated or dry soil deposits. A set of centrifuge experiments was conducted to study the influence of partial saturation on seismic response of sand layers under scaled Northridge earthquake motion. Steady state infiltration was implemented to control and provide uniform degrees of saturation profiles in depth. The amplification of peak ground acceleration at the soil surface was inversely proportional to the degree of saturation, especially in low period range. The cumulative intensity amplification of the motion was also higher in unsaturated soils with higher suctions. The lateral deformation and surface settlement of partially saturated sand with higher stiffness were generally lower than that in dry soil. Although neglecting the effect of partial saturation in sand layers might be conservative with respect to seismic deformations, it may result in underestimating the surface design spectra.

Cyclic Triaxial Test to Measure Strain-Dependent Shear Modulus of Unsaturated Sand

“…This is a result of the presence of interparticle suction forces that change the effective stresses in soils (Khalili et al 2004) and, in turn, the mechanical response. Thus, soils with different degrees of saturation differ in stiffness, and this consequently results in different dynamic response, seismic compression, and pore-water pressure generation and dissipation in geotechnical systems (Ghayoomi et al 2013;Ghayoomi and Mirshekari 2014;Mirshekari and Ghayoomi 2017;Cary and Zapata 2016). Experimental difficulties, such as direct measurement and control of matric suction, have hindered the investigation of the dynamic behavior of unsaturated soils.…”

Effect of Partial Drainage on Cyclic Strengths of Saturated Sands in Dynamic Centrifuge Tests

“…The comparison of volumetric strains due to partial drainage with volumetric strains in partially saturated samples is complicated by the influence of matric suction on the partially saturated samples. For example, pore water suction significantly affected seismic surface settlements of partially saturated sand models (degree of saturation ranging from 32 to 68%) in a series of dynamic centrifuge tests by Morteza and Ghayoomi (2017), with the observed effects reasonably attributed to the effects of suction on the sand properties and the subsequent dynamic response of the sand profile (e.g., Ghayoomi et al 2013). The studies referenced herein provide reasonably consistent trends between LRR and the εv due to either partial drainage or compression of partially saturated sands for degrees of saturation greater than about 70%, but the effects of pore water suction can be expected to be greater for greater suction magnitudes (e.g., finer sands with smaller pore sizes) and smaller confining stresses.…”

“…The effect of partial drainage on CRR is investigated with single element simulations of undrained direct simple shear (DSS) loading using the constitutive model PM4Sand (version 3) in the finitedifference code FLAC (version 8) (Itasca ( 2016)). PM4Sand is a stress-ratio controlled, critical state based, bounding surface plasticity model developed for earthquake engineering applications increase soil stiffness which can influence settlement and volumetric strain (Ghayoomi et al 2013, Morteza andGhayoomi 2017). The implications of neglecting matric suction are discussed later.…”

Variation of Pore Water Pressure in Tailing Sand under Dynamic Loading

“…In order to propose a new method for reliability analysis of dynamic slope stability with Shock and Vibration 5 [31] consider that Arias intensity combines more amplitude and duration and carries more vibration information than peak acceleration and peak velocity, so it was used to investigate the significant duration of seismic vibrations which is an indicator of seismic intensity. A well-known cumulative intensity characteristic (Arias intensity) and the equivalent loading cycles were are selected to represent the accumulated energy buildup during a shaking event as observed in papers by [32], Mirshekari and Ghayoomi (2017) [33], and Tombari et al (2017) [34]. Meanwhile, many factors can affect the strength of saturated soil liquefaction, including the characteristics of the soil itself (type, density, structure, grading, water permeability, etc.…”