Cyclic Liquefaction Resistance of an Alluvial Natural Sand: A Comparison between Fully and Partially Saturated Conditions

Diana Cordeiro,António Viana Da Fonseca,Cristiana Ferreira,Sara Rios,Fausto Molina-Gómez

doi:10.3390/geotechnics2010001

Diana Cordeiro, António Viana Da Fonseca + Show 3 more

Open Access

https://doi.org/10.3390/geotechnics2010001

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Journal: Geotechnics	Publication Date: Jan 6, 2022
Citations: 5	License type: CC BY 4.0

Affiliation: University of Porto

Abstract

Earthquake-induced liquefaction is one of the major causes of building damage as it decreases the strength and stiffness of soil. The liquefaction resistance of soils increases significantly as the degree of saturation decreases, making soil desaturation an effective measure for the mitigation of this phenomenon. This paper presents a comparative analysis of liquefaction resistance of an alluvial sand from Aveiro (Portugal) under fully and partially saturated conditions. For this purpose, an in situ characterisation based on CPTu and a laboratory series of cyclic triaxial tests were carried out. The cyclic triaxial tests were conducted under undrained conditions on remoulded specimens with different degrees of saturation, including the full saturation. On the other hand, the triaxial apparatus was instrumented with Hall-effect transducers to accurately measure the strains during all testing phases. In addition, it was equipped with piezoelectric transducers to measure seismic waves velocities, namely P-wave velocity, for evaluation of the saturation level of the specimen in parallel with the Skempton’s B parameter. Hence, relations between the B-value, and P-wave velocity and cyclic strength resistance are presented. The number of cycles to trigger liquefaction, considering the pore pressure build-up criterion, is presented for the different degrees of saturation. Results confirmed the increase in liquefaction resistance for lower degrees of saturation in this soil.

Highlights

One of the most sensitive problems of buildings located in seismic zones and founded on granular soil deposits is liquefaction phenomena, which usually occur in saturated, cohesionless and contractive soils
An approach based on the normalised cyclic strength (NCS) and the P-wave velocity (V p), proposed by Ishihara & Tsukamoto [35], was implemented to analyse the increment of liquefaction resistance for different Sr
The NCS was estimated by computing the ratio between the cyclic resistance obtained in partially saturated and fully saturated conditions; where the cyclic resistance of partially saturated conditions is the cyclic stress ratios (CSR) applied during cyclic triaxial testing and the cyclic resistance of fully saturated conditions corresponds to the computation of Equation (3) for the number of cycles reported in partially saturated conditions

Summary

Introduction

One of the most sensitive problems of buildings located in seismic zones and founded on granular soil deposits is liquefaction phenomena, which usually occur in saturated, cohesionless and contractive soils. Several techniques to mitigate the phenomena have been developed to reduce or eliminate the liquefaction susceptibility and the associated structural damage [2,3]. Numerical simulations of liquefaction phenomenon showed that techniques, such as preloading, stone column installation, soil compaction or induced partial saturation, allow the pore pressure build-up and soil deformations to be reduced during seismic events [6,7]. It is of the utmost relevance to identify mitigation techniques able to tackle liquefaction susceptibility, while satisfying the requirements of design reliability, environmental impact, and cost-effectiveness [8,9]

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