LIQUEFACTION

Effects of permeability and compressibility on liquefaction assessment of silty soils using cone penetration resistance

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 Obiettivo del progetto (Objective)

'Several countries in Europe have paid a heavy price in terms of life loss and have suffered a serious damage to property and cultural heritage due to earthquakes in recent past. Failure of high hazards dams, earth structures, slopes and foundations have been attributed to the liquefaction of saturated silty soils. Therefore, numerous studies have been conducted to-date to understand the effects of silt on cyclic resistance of silty sands and its effect on liquefaction screening. However, the literature review points out that, there is no clear agreement on how silt content affects the liquefaction resistance and penetration resistances measured to diagnose it. The proposed project aims to revise the current liquefaction screening methods by taking into account the effects of consolidation characteristics on cone penetration resistance and liquefaction resistance. The data that will be obtained from Seismic Piezocone Penetration Tests (SCPTu) already in the database and possible future earthquake silty soil sites in Turkey will provide a perfect opportunity to further improve our understanding on effects of penetration velocity (v), cone diameter (d) and consolidation characteristics (ch) of silty sands on cone penetration resistance for different intergrain contact densities. Moreover, laboratory experiments will provide a clear perspective on effects of intergrain contact density of soils containing non-plastic fines on liquefaction resistance. As a result, the correlation between the liquefaction resistance, cone penetration resistance and normalized penetration rate T(vd/ch) will be presented and compared with the current CPT-based liquefaction screening methods. It is hoped that the majority of the inconsistencies in the literature will be resolved and engineers will have better understanding on the behavior of silty soils under seismic conditions at the end of this proposed project.'

Introduzione (Teaser)

Certain soils can liquefy during earthquakes. An EU project re-examined the main method for assessing such soils, based on field tests at sites in Izmir, Turkey, yielding new insights about liquefaction.

Descrizione progetto (Article)

Liquefaction means for water-saturated sediments or soils to suddenly lose strength and become a liquid, typically as a result of earthquake. The phenomenon came to scientific awareness in 1964, and has since been extensively studied, though uncertainties remain about the dominant screening method.

The method is the cone penetration test (CPT), which measures the penetration resistance and excess pore water pressure of the soils. The EU-funded LIQUEFACTION project aimed to evaluate the liquefaction screening by CPT, and detail the effects of low-plasticity fine sediments on cone penetration resistance and liquefaction resistance. The four-year investigation concluded at the end of 2013.

To obtain the needed field data, the project investigated 20 test locations in the Izmir Gulf, on Turkey's western coast. The sites were chosen by sediment type and propensity to liquefaction. Five tests were conducted at each location, establishing the drainage characteristics and strength of soil. Additionally, the study constructed a shake-box equipped with monitoring sensors, then filled the box with various kinds of soil that were experimentally shaken. The tests provided data valuable to the broader seismic research community.

Project activities included the training of graduate students, who will help to fill a skills shortage in Europe.

As a result of LIQUEFACTION, the currently used liquefaction assessment by CPT method is better understood. Hence, people and structures will be better protected from the destructive effects of earthquakes.