1539
Dynamic Properties and Liquefaction Potential of a Sandy Soil Containing Silt
Propriétés dynamiques et potentiel de liquéfaction d’un sol sablonneux contenant de la vase
Mominul H.M., Alam M.J., Ansary M.A., Karim M.E.
Department of Civil Engineering, BUET, Dhaka, Bangladesh
ABSTRACT: The most common cause of ground failure during earthquakes is the liquefaction phenomen which has produced severe
damage all over the world. Shear modulus and damping of soil are important parameters. Appropriate evaluation of liquefaction
potential, shear modulus and damping characteristics of soil subjected to dynamic loading is the key to accurate dynamic response
analysis and soil modeling programs. This paper summarizes the behavior of dynamic properties as well as potential for liquefaction
of a sandy soil deposit in Bangladesh. A fine sand sample was collected from a site close to Piyain river of Jaflong, Sylhet,
Bangladesh. Another fine sand sample and nonplastic-silt sample was collected from Padma Bridge site. A series of cyclic triaxial
tests was performed using fine sands and mixing silt content. Shear modulus decreased with increasing shear strain and damping ratio
increased with increasing shear strain. Most interesting finding is that upto 30% silt, liquefaction resistance of sand decreased with
increasing silt content. Above 30% silt, liquefaction resistance of soil had insignificant variation with silt content.
RÉSUMÉ : La cause la plus commune d'échec de terre pendant des tremblements de terre est le phénomène de liquéfaction qui a
produit des dégâts sévères dans le monde entier. Module de cisaillement et l'amortissement de sol sont des paramètres importants.
L'évaluation appropriée de potentiel de liquéfaction, module de cisaillement et les caractéristiques d'amortissement de sol soumis au
chargement dynamique sont la clé de l'analyse de réponse dynamique précise et les programmes de modélisation de sol. Ce papier
récapitule le comportement de propriétés dynamiques aussi bien que le potentiel pour la liquéfaction d'un dépôt de sol sablonneux au
Bangladesh. Un échantillon de sable fin a été rassemblé d'un site près de la rivière Piyain de Jaflong, Sylhet, le Bangladesh. Un autre
échantillon de sable fin et l'échantillon de non-plastique-vase ont été rassemblés du site de Pont de Padma. Une série des tests
triaxiaux cycliques a été exécutée utilisant des sables fins et mélangeant le contenu de vase. Module de cisaillement a diminué avec
l'augmentation de la tension cisaillement et le ratio d'amortissement a augmenté avec l'augmentation de la tension cisaillement. La
découverte la plus intéressante est que jusqu’à 30% de vase, la résistance de liquéfaction de sable a diminué avec l’augmentation du
contenu de vase. Au-dessus de 30% de vase, la résistance de liquéfaction de sol n'avait aucune variation avec le contenu de vase.
KEYWORDS: Shear Modulus, Damping, Liquefaction, Nonplastic Silt, Cyclic Triaxial Test.
1 INTRODUCTION
Because of geographical, topographical and meteorological
conditions of Bangladesh, the country is subject to frequent
natural disasters. The country is situated in the moderate seismic
zone in world seismic map. Information on earthquakes in and
around Bangladesh is available for the last 250 years. The
earthquake record suggests that since 1900 more than 100
moderate to large earthquakes occurred in Bangladesh, out of
which more than 65 events occurred after 1960. During the last
ten years, the occurrence and damage caused by some
earthquakes (magnitude between 4 and 6) inside the country and
near the country's border, has raised the concern about the effect
of earthquake. Most of the land area in Bangladesh has been
built up of alluvial deposits brought down by some major rivers.
The soil condition is loose silty sand deposit and most of it
remains in saturated condition round the year, thereby
vulnerable to liquefaction in case of strong ground motions.
The catastrophic landslide caused by the Chili earthquake in
1960 (Duke and Leeds, 1963), Alaska earthquake in 1964 as
well as the subsidence and foundation failures due to
liquefaction during Niigata Earthquake in 1964 (Seed and Idris,
1967) has strongly established the need for a better
understanding of the behavior of soil under dynamic loading
conditions. Due to these events, liquefaction and the shear
behavior has been extensively studied in the field and
laboratory. In recent years evaluation of dynamic properties of
soil is a great concern to design geotechnical related problems
that are involved with dynamic loading.
The measurement of dynamic soil properties is a critical task
in the solution of geotechnical earthquake engineering problem.
A wide variety of field and laboratory techniques are available
each with different advantages and limitations with respect to
different problems. Many are oriented toward measurement of
low-strain properties and many other towards properties
mobilized at large strains. The cyclic triaxial test has been the
most commonly used test for measurement of dynamic soil
properties at large strain levels. No research has so far been
undertaken to assess the liquefaction susceptibility and dynamic
properties of local sands using cyclic triaxial test. This paper
presents the liquefaction potential and dynamic properties of a
sandy soil using cyclic triaxial test at large strain levels. Effect
of nonplastic silt content on liquefaction was also investigated.
2 REVIEWS OF PREVIOUS STUDIES
Previously many researchers extensively studied dynamic
properties and liquefaction resistance of soils in the field and
laboratory. Cyclic triaxial test results indicate that, higher the
void ratio, lower the confining pressure and greater the cyclic
stress and the number of cycles, easier the development of
liquefaction (Seed and Lee, 1966). Liquefaction resistance of
soil increases with increase in density, frequency and confining
pressure (Choudhary et al, 2010). Cyclic triaxial test results
show that when the degree of saturation reduced, the number of
cycles required for liquefaction increased by 1.5 to 2.5 times to
that observed in fully saturated sand (Raghunandan and Ashish,
2011). Liquefaction resistance of sands increases with a
decreasing degree of saturation (Sherif et al, 1977; Ishihara et
al, 2001; Okamura and Soga, 2006). Reduction in the degree of
saturation from 100 to 97.8% led to greater than 30% increase
in liquefaction strength (Xia and Hu, 1991).
Lowest resistance against liquefaction in uniformly graded
loose sand with fines content between 25% and 30% (Koester,
1994). Fines content increasing from 0 to 44 % the liquefaction
resistance of mixture with constant global void ratio decrease
compared to that of the clean sand, whereas this trend reversed
