Liquefaction Behavior Of Sand Research Articles

Liquefaction behavior of inherently anisotropic sand under cyclic simple shear: Insights from three-dimensional DEM simulations

Inherent fabric anisotropy has been widely recognized to have significant effects on the liquefaction behavior of sand. A discrete element method (DEM) study was conducted to investigate the liquefaction behavior of inherently anisotropic sand under cyclic simple shear conditions. In the DEM model, the under-compaction method was modified to generate uniform and inherently anisotropic specimens. A series of DEM simulations of undrained cyclic simple shear tests were performed to investigate the effects of bedding plane angles with a full spectrum ranging from −90° to +90°. The relative magnitudes of the three effective normal stress components were compared and analyzed. The internal structure evolution was quantified through a contact-normal-based fabric tensor that could describe the load-bearing structure of granular specimens. The simulation results show that the effect of bedding plane angle on the liquefaction resistance of anisotropic sand is not monotonic. For example, as the bedding plane angle of specimen increases from 0° to 90°, the liquefaction resistance first decreases and then increases, with the most detrimental scenario occurs at 45°. This could be explained by correlating the magnitudes of shear modulus with the discrepancy between the loading direction and the direction of fabric during each cycle.

Effect of Phase Difference on the Liquefaction Behavior of Sand in Multidirectional Simple Shear Tests

AbstractMultidirectional cyclic shearing induced by earthquakes involves variations not only in amplitude but also in direction. To investigate the undrained cyclic shear responses of sand under th...

Effect of non-plastic silt on liquefaction susceptibility of marine sand by transparent laminar shear box in shaking table

ABSTRACT There are some ambiguities in understanding of the effect of non-plastic fine content (silt) on the liquefaction behaviour of sand in the literature. Reviewing the results of field and laboratory studies suggests that increasing the amount of non-plastic fine content in sand can lead to improvement or deterioration of liquefaction resistance. In this study, the effect of non-plastic silt on liquefaction resistance of Anzali sand is investigated using shaking table tests. According to the results, for the relative density of 30%, liquefaction resistance was found to be initially decreasing by increasing the silt content until the limiting fine content (LFC) as 15% and increasing thereafter. However, for the relative density of 60%, liquefaction resistance showed a continuously decreasing trend by increasing the silt content. Finally, comparison of the result through the limiting bounds of pore pressure obtained in this study with that of other researchers showed an appropriate consistency.

Evaluation of the Liquefaction Potential of Sand under Random Loading Conditions: Equivalent Approach Versus Energy-Based Method

ABSTRACTThis paper presents a systematic experimental investigation into the liquefaction behavior of saturated sand subject to cyclic loadings with various types of random time histories. The triaxial test results indicate that the pore pressure generation and liquefaction resistance of sand are significantly influenced by the amplitude and sequence of stress pulses in the random loadings. The energy-based method using the energy density concept was applied in liquefaction assessment, which is found to be superior to the conventional equivalent approach that involving uniform stress cycles and can better capture the effect of loading randomness on the liquefaction behavior of sand.

Evaluation of Cyclic Stress–Strain and Liquefaction Behavior of Izmir Sand

This paper presents the results of a series of cyclic triaxial tests carried out on sands with different index properties. Samples from three grain-size distributions of Izmir (Turkey) sand were tested under consolidated-undrained conditions. The tests were performed under two different effective confining pressure values (100 and 200 kPa). The relative densities of the specimens were 30 and 50%. The results showed that the relative density plays a dominant role in the liquefaction behavior of the sand, whereas the confining pressure increase has greater effects on the stress–strain properties of the sand. It was observed that the relationship between the grain-size diameters and cyclic stress ratios of the sands would be more realistic. It was found that the pore water pressure generation curve falls outside the narrow band proposed by previous studies and a greater coefficient is required for the cycle ratio depending on the soil properties and test conditions. The shear moduli of the sands increased independently of the mean diameter with the relative density under a confining pressure of 100 kPa. Under a confining pressure of 200 kPa, the shear moduli increased with the uniformity coefficient of the sand. Increments in the relative density resulted in a slight increment of the shear moduli for the sands. The goal of the current study was to provide an understanding of the liquefaction and stress–strain behavior of Izmir sand, which represents the material of similar sites with loose alluvial sediments located in earthquake-prone areas found around the world.

Influence of Bentonite Content on the Static Liquefaction Behavior of Sand

The landslide with static liquefaction often occurs in loose fill slopes with silty sand for the rainfall, causing lots of casualties and property loss. This study performed a series of static CU triaxial tests to investigate the influence of Bentonite content on the static liquefaction behavior of sand. The results indicate that there exists a critical value, below what increasing the Bentonite content reduces the resistance to static liquefaction. However, above the value the resistance to static liquefaction is increased with the rise of Bentonite content. This conclusion can be applied to manage the disaster triggered by the landslide with static liquefaction.

Influence of silt size and content on liquefaction behavior of sands

This study investigates the fines content influence on liquefaction potential of a single base sand mixed with three different essentially nonplastic silts through strain-controlled monotonic undrained triaxial compression tests. Confining stress (30 kPa) and deposition method (dry funnel deposition) were kept the same, while fines content was varied, to solely focus on how different silts and their contents influence the undrained response of the sand under comparable conditions. It was found that if the mean grain diameter ratio (D50-sand/d50-silt) of the sand grains to silt grains is sufficiently small, the liquefaction potential of the sand increases steadily with increasing fines content for the studied range (0%–20%). As D50-sand/d50-silt increases, the liquefaction potential of the silty sand might actually be less than the liquefaction potential of the clean sand. Test results also revealed that commonly used comparison bases (i.e., void ratio, intergranular void ratio, relative density) are not sufficient for assessing the influence of fines on liquefaction potential of silty sands. Finally, relative size of the silt grains should also be considered in geotechnical engineering practice in addition to content and plasticity of fines to characterize the influence of silt on liquefaction potential of sands.

Initial Static Shear Effect on Cyclic Liquefaction Behaviour of Sand

Evaluation of soil liquefaction potential plays a key role in geotechnical earthquake engineering design since liquefaction is a major cause of earthquake-induced damages. While the evaluation procedure works well for free-field level ground conditions, the existence of initial static driving shear stress under earth dams or buildings complicates the issue. To address the insufficiency in current understanding, this paper presents an experimental study of the initial shear effect on the liquefaction resistance of sand, focusing mainly on the dependence of the effect on the initial state and sand type. A large number of cyclic triaxial tests have been conducted on two standard silica sands under a wide range of initial shear stress, density and confining pressure. Three distinct cyclic responses are identified to be dependent on the initial state and degree of stress reversal. The test results indicate that while the initial shear effect on loose sand can be beneficial or detrimental, that on dense sand is...

An Effective Stress Understanding of Liquefaction Behavior

The state of knowledge with regard to the static and cyclic liquefaction behavior of sands (sands according to the Unified Soil Classification System) has progressed tremendously in the last twenty years (National Research Council, 1985). In fact, based upon the so-called steady state concepts of Casagrande (1975), Castro (1975) and Poulos (1981), it is generally accepted that the end or steady state condition of a liquefied loose sand is the same whether due to static, dynamic, or cyclic undrained loading. Even so, there is still much work to be done, particularly in regard to the post peak (or strain softening) response that follows the initiation of liquefaction. It is necessary that the post-earthquake stability of earth embankments, in which there is such liquefiable material, be assessed based on the residual strength of that type of material. At present, the two approaches to the evaluation of residual strength are less than adequate for the task. One approach is based on an empirical relationship as derived from a limited number of field case studies involving the failure of embankment slopes via liquefaction. Alternatively, a laboratory approach for evaluating residual strength involves running static consolidated-undrained triaxial tests on both reconstituted and undisturbed samples. Such testing requires a degree of sophistication and experience that is beyond the capability of the great majority of geotechnical firms. It is shown here, however, that the laboratory determined undrained steady state (or residual) strength and the associated critical confining pressure can be assessed in a straightforward manner from drained triaxial tests with volume change measurements based upon a proposed effective stress interpretation of such undrained behavior. Accordingly, it should be possible for all geotechnical firms with the standard capability to perform drained triaxial tests on sands (with associated volume change measurements) to accurately assess the residual strength of such liquefying material. The same procedure also allows the prediction of the whole undrained stress-strain curve and the corresponding effective stress path. (A)

Significance of formation factor in sand structure characterization

The formation factor F, obtained by electrical conductivity measurements of saturated sand samples, has been recently correlated with the liquefaction behavior of sands (2). The significance of F as a parameter obtained by nondestructive technique is discussed here, showing its capability to characterize the structure of anisotropic sand aggregates.