Liquefaction Resistance Of Silty Sands Research Articles

Cyclic failure characteristics of silty sands with the presence of initial shear stress

Liquefaction of silty sands remains an outstanding issue since it continues to lead to catastrophic consequences in recent earthquake events. The cyclic characteristics, such as cyclic failure pattern and cyclic resistance, are the fundamental aspects of liquefaction analysis. The difficulty and uncertainty of characterization and evaluation of cyclic behavior and liquefaction resistance of silty sand mainly come from the complicated interactions of various influencing factors, such as packing density, confining pressure, initial shear stress, cyclic loading amplitude, soil properties, and soil fabric. This study presents a series of laboratory testing results to identify the cyclic failure patterns of silty sands considering different soil states, fines contents, initial static shear stress, etc. It is found that the failure patterns are related to the states of soils and the cyclic loading characteristics, i.e., the combination of initial shear stress and cyclic loading amplitude for silty sands with similar soil fabric, and that the cyclic resistance of silty sands is also a function of soil states and initial static shear stress for similar soil fabric. Critical state soil mechanics is implemented to characterize the cyclic failure patterns and cyclic resistance. Implications of the present study to the existing liquefaction assessment methods are also discussed.

Liquefaction assessment of silty sands: Experimental characterization and numerical calibration

The main goal of this paper is to assess the reliability of a nonlinear hysteretic model to capture the behavior of saturated silty sand mixtures under cyclic loading conditions. The parameters governing the liquefaction triggering are identified using the results of standard laboratory tests (monotonic and cyclic consolidated undrained triaxial tests as well as resonant column tests) undertaken for reconstituted soil samples. Consequently, the uncertainty related with collected samples is reduced. The numerical results, obtained after calibration of the constitutive model, are in good agreement with the experimental ones and they are analyzed through the effects of relative density, fine content, and confining pressure in the liquefaction resistance of silty sands.

Combined effect of fines content and uniformity coefficient on cyclic liquefaction resistance of silty sands

Cyclic liquefaction of silty sands remains to be very intriguing for both research and practice. Even though many factors are known to influence the liquefaction resistance of sands, the effect of fines content is perhaps one of the most studied yet still a controversial one. Effect of grain size distribution by means of uniformity coefficient is also studied in literature but not as much as fines content influence. Moreover, to date, no clear relationship has been established between the uniformity coefficient and cyclic liquefaction resistance of clean or silty sands. This study adopts a distinct methodology by considering the effects of fines content and uniformity coefficient together, which were typically considered separately as two isolated parameters in previous studies (i.e., typically, only one of them was considered or focused). A series of constant volume cyclic direct simple shear (CDSS) tests were performed on mixtures of two base sands and four non-plastic silts at different fines contents, which also enabled authors to observe the liquefaction response of silty sands with different gradations. Based on the analysis, a new equation was developed which predicts the cyclic liquefaction resistance of silty sand by considering the uniformity coefficients of the sand (CUsand) and silt (CUsilt) fractions forming the soil together with its fines content (FC). The proposed equation was also demonstrated to work very well on six distinct silty sands having different gradations and fines contents from literature. The level of the combined influence of fines content and uniformity coefficient on cyclic liquefaction resistance of silty sands is also shown to be considerably affected by the magnitude of relative density. Practical implications and limitations of the new equation are discussed as well.

Shaking table tests on wall-type gravel and rubber drains as a liquefaction countermeasure in silty sand

In this paper, the seismic performance of wall-type gravel and rubber drains as a liquefaction countermeasure in silty sand has been addressed using a series of 1 g shaking table tests. In these tests, the liquefaction resistance of silty sand was studied by changing soil relative density, silt content, number of walls, and materials of drainage walls. In order to evaluate shear wave propagation, the generation and dissipation of pore water pressure (PWP), and the ground surface settlement, various accelerometers, displacement and PWP transducers were placed. The obtained results indicated that an increase in the relative density and the number of wall-type gravel and rubber drains in liquefiable silty sand reduces the settlement, liquefaction-induced deformations, as well as the excess PWP and eventually improves the liquefaction resistance. Totally, it can be noted that the reinforced silty sand with wall-type gravel drains revealed less excess PWP and settlement than that with wall-type rubber drains.

Liquefaction Resistance of Silty Sand with Ground Rubber Additive

Abstract The contractive behavior and flow failure in saturated binary granular soils have been studied by many as functions of their physical properties [gradation, mean particle size, fines conte...

Liquefaction resistance improvement of silty sands using cyclic preloading

Liquefaction induced damages are plenty and cause various levels of destruction to civil engineering infrastructure. It is possible to prevent liquefaction-induced hazards by understanding the mechanism and adopting some improvement techniques or design the structure to resist the soil liquefaction. In the present study, the influence of cyclic preloading on the liquefaction resistance of sand-silt mixtures is analyzed by conducting undrained cyclic triaxial tests on the cylindrical samples reconstituted at medium dense conditions (Dr = 50%). All samples were tested at an effective confining pressure of 100 kPa by varying the cyclic stress ratios (CSR) in the range of 0.127 to 0.178 using a sinusoidal waveform of frequency 1 Hz. The results are presented in the forms of the pore pressure build-up, axial strain variation and liquefaction resistance curves. Test results indicate that the liquefaction resistance of silty sands is increased substantially with the application of preload under drained conditions.

Effect of particle rolling resistance on drained and undrained behaviour of silty sand

This paper explores the effect of particle rolling resistance on the mechanical behaviour of silty sand under various shearing conditions. The elastic–plastic spring–dashpot rolling resistance model was employed, and drained and undrained triaxial tests were conducted on silty sand with various fines contents and rolling resistance. It was found that the rolling resistance of fines contents had a strong impact on the critical state, peak state, phase transformation state as well as zero-dilatancy state of silty sands. Moreover, depending on the correlation between rolling resistance of coarse and fine particles, fines can positively or negatively contribute to the overall structure of silty sand. Increasing the rolling resistance of fines enhances the liquefaction resistance of silty sands. Thus, the presence of fines of high rolling resistance in the sand can result in a marked decrease in collapsibility or liquefaction susceptibility compared with the presence of fines of lower rolling resistance.

Characterizing the effects of fines on the liquefaction resistance of silty sands

Recent earthquakes in New Zealand and Japan indicate that evaluating the liquefaction potential of silty sands remains an area of difficulty and uncertainty in geotechnical engineering. This paper presents a comprehensive experimental study along with analysis and interpretation in the framework of critical state soil mechanics, with the aim to address the complicated effects of fines. Two series of sand-silt mixtures, formed by mixing two different base sands with the same type of non-plastic silt, were tested under a range of packing density, confining pressure and silt content, and a unified correlation was established between the cyclic resistance and the state parameter that collectively accounts for the effect of packing density and confining pressure. The proposed correlation is independent of packing density, confining pressure, fines content and base sand, and allows prediction of the cyclic resistance of silty sands under different states. Furthermore, the mechanism of the fines-content induced reduction of cyclic resistance and the mechanism of the base-sand effect observed from the tests are elaborated in the sound theoretical context. The present study suggests that the critical state soil mechanics is a rational and appealing framework for liquefaction analysis of both clean and silty sands.

Cyclic behavior and liquefaction resistance of silty sands with presence of initial static shear stress

The liquefaction resistance of silty sands and the potential effect of initial static shear stress are major concerns in seismic design of dams and embankments. This paper presents a systematic experimental study on non-plastic silty sands to address these concerns. It is shown that the concept of threshold α (αth) proposed by Yang and Sze (2011) to characterize the impact of α (representing the initial static shear stress level) on cyclic resistance (CRR) of clean sands is applicable to silty sands as well. When α < αth, CRR increases with increasing α, otherwise it decreases with increasing α. The threshold α is affected by the initial packing density, the initial effective confining pressure and the fines content. An improved state dependency of the threshold α, which is regardless of fines content, is proposed in the framework of critical state soil mechanics by using the state parameter (ψ). An analysis platform, known as CRR-ψ platform and developed based on clean sand data, is shown to have the capability of characterizing the state dependence of CRR for sands with varying fines contents. This platform in conjunction with the unified αth-ψ correlation provides a unified and consistent framework for understanding the complicated effects of initial static shear stress on soil liquefaction and for quantifying such effects for engineering practice.

Two Case Histories Demonstrating the Effect of Past Earthquakes on Liquefaction Resistance of Silty Sand

AbstractThe paper compares two liquefaction case histories in California: (1) the response of the Wildlife site in the Imperial Valley to the 2010 El-Mayor Cucapah earthquake (Mw=7.2, amax=0.15 g)...

Monotonic liquefaction resistance of silty sand reinforced with geotextile

Reinforcements can change the mechanical characteristics and liquefaction resistance of soils. The main purpose of this study is to realise the behaviour of static liquefaction of saturated silty sand reinforced by different arrangements of geotextile layers. Several series of undrained triaxial tests were conducted on reinforced and unreinforced saturated sand and sand mixed with varying amounts of silt (0–50%). Factors such as the silt content, arrangement and number of geotextile layers are discussed in this paper. The results indicate that by increasing the silt content up to about 35%, the static liquefaction resistance decreases in reinforced and unreinforced silty sand. With further increases in silt content from 35 to 50%, the liquefaction resistance increases. Also, it was found that geotextile inclusion increases the liquefaction resistance of saturated sand for all silt contents examined. The results of this study are limited to the use of sand and silty sand reinforced with one type of nonwoven geotextile.

The effects of surcharge on liquefaction resistance of silty sand

In the recent earthquakes, numerous cases of liquefaction occurred in sands containing both plastic and nonplastic fines that resulted in significant damage. Most previous research efforts have focused on clean sands regardless whether the sand contain fines or not made evident by widespread shallow foundation failures, numerous cases of settlement, and lateral displacement. Still, despite the amount of related research, results seem somewhat contradictory. This study directly demonstrates the beneficial or detrimental effect of uncertainty surcharges on seismic responses. Models were subjected to two destructive realistic events with similar PGA with various frequency contents and duration. In this paper, the dynamic analyses were conducted as fully non-linear elasto-plastic coupled stress-flow analyses with coupled liquefaction triggering which reasonably captured the actual behavior. The silty sand deposits underlying the surcharge are capable of liquefying and developing large shear deformations that can cause serious damage. Therefore, excess pore water pressure ratio cannot be enough by itself to evaluate liquefaction potential, so the deformations should be examined. Numerical results provide an estimate of the seismic performance liquefiable deposits underlying the surcharge; these results can be useful for a realistic practical engineering.

Influence of initial conditions on liquefaction resistance of silty sands

The influence of initial conditions, i.e. stress state and void ratio, on the liquefaction resistance of silty sands under two-way cyclic loading is investigated in this paper. Using a cyclic triaxial test device, a series of undrained stress-controlled cyclic triaxial tests was performed on reconstituted specimens of sand and sand mixed with 15, 30 and 50% non-plastic fines content (finer than 75 μm). The sand samples were prepared at different void ratios of 0.915, 0.855 and 0.795. Sand–silt mixtures were formed at 40% relative density. Specimens were consolidated at different pressures of 50, 100 and 200 kPa and then subjected to two-way cyclic loading with CSR values varying in the range 0.075–0.275. Test results indicated that the compressibility and cyclic resistance of soil mainly depends on initial conditions and type of soil. A correction factor (K σ) is considered to account for the influence of consolidation pressure on the liquefaction resistance of sand and sand–silt mixtures. The samples experience extensional strains in the case of low consolidation pressures and compression strains at high consolidation pressures. This behaviour is due to the increase in the contractive tendency of soil at high consolidation pressures.

Liquefaction Resistance of Silty Sands and Dynamic Properties of Cohesive Soils from Düzce, Turkey

This article presents results from a laboratory investigation into the cyclic and dynamic properties of soils from Düzce, Turkey, conducted after the destructive November 12, 1999 earthquake. The investigation was mainly conducted by means of monotonic and cyclic triaxial, as well as resonant-column tests. The triaxial tests allowed the determination of the liquefaction resistance of silty sands, as well as their critical state behavior, whereas the resonant-column tests allowed the determination of shear modulus and damping ratio of cohesive soils. The results are presented and then discussed together with their pertinence to soil behavior when subjected to earthquake loading.

Intergrain contact density indices for granular mixes—II: Liquefaction resistance

Whether the presence of non-plastic silt in a granular mix soil impact its liquefaction potential and how to evaluate liquefaction resistance of sand containing different amounts of silt contents are both controversial issues. This paper presents the results of an experimental evaluation to address these issues. Two parameters, namely, equivalent intergranular void ratio (e c)eq and equivalent interfine void ratio (e f)eq, proposed in a companion paper (Thevanayagam, 2007) as indices of active grain contacts in a granular mix, are used to characterize liquefaction resistance of sands and silty sands. Results indicate that, at the same global void ratio (e), liquefaction resistance of silty sand decreases with an increase in fines content (C F) up to a threshold value (C Fth). This is due to a reduction in intergrain contact density between the coarse grains. Beyond C Fth, with further addition of fines, the interfine contacts become significant while the inter-coarse grain contacts diminish and coarse grains become dispersed. At the same e, the liquefaction resistance increases and the soil becomes stronger with a further increase in silt content. Beyond a limiting fines content (C FL), the liquefaction resistance is controlled by interfine contacts only. When C F C Fth, at the same (e f)eq, the cyclic strength of a sandy silt is comparable to the host silt at a void ratio equal to (e f)eq.

Influence of Nonplastic Fines on Shear Wave Velocity-Based Assessment of Liquefaction

Many false positives (no liquefaction detected when the normalized shear wave velocity-cyclic stress ratio ( Vs1 -CSR) combination indicated that it should have been) are observed in the database used in the simplified liquefaction assessment procedure based on shear wave velocity. Two possible reasons for false positives are the presence of a thick surface layer of nonliquefiable soil and the effects of fines on cyclic shear resistance (CRR) and Vs1 . About 67% of the false positives that could not have been caused by an overlying thick surface layer are associated with silty sands with less than 35% fines. The effects of fines on the liquefaction resistance of silty sands and on the shear wave velocity are analyzed. Theoretical CRRfield versus Vs1 curves for silty sands containing 0 to 15% nonplastic fines are established. They show that the theoretical CRR- Vs1 correlations for silty sands with 5 to 15% nonplastic fines are all located to the far left of the semi-empirical curves that separate liquefac...

A critical state interpretation for the cyclic liquefaction resistance of silty sands

Contrary to many laboratory investigations, common empirical correlations from in situ tests consider that the increase in the percentage of fines leads to an increase of the cyclic liquefaction resistance of sands. This paper draws upon the integrated Critical State Soil Mechanics framework in order to study this seemingly not univocal effect. Firstly the effect of fines on the Critical State Line (CSL) is studied through a statistical analysis of a large data set of published monotonic triaxial tests. The results show that increasing the content of non-plastic fines practically leads to a clockwise rotation of the CSL in ( e–ln p) space. The implication of this effect on cyclic liquefaction resistance is subsequently evaluated with the aid of a properly calibrated critical state elasto-plastic constitutive model, as well as a large number of published experimental results and in situ empirical correlations. Both sets of data show clearly that a fines content, less than about 30% by weight, may prove beneficial at relatively small effective stresses ( p 0<50–70 kPa), such as the in situ stresses prevailing in most liquefaction case studies, and detrimental at larger confining stresses, i.e. the stresses usually considered in laboratory tests. To the extent of these findings, a correction factor is proposed for the practical evaluation of liquefaction resistance in terms of the fines content and the mean effective confining stress.

Liquefaction resistance of silty sand based on in situ frozen samples : Y. Yoshimi & S. Goto, Geotechnique, 46(1), 1996, pp 153–156

Liquefaction resistance of silty sand based on in situ frozen samples : Y. Yoshimi & S. Goto, Geotechnique, 46(1), 1996, pp 153–156

Liquefaction resistance of silty sand based on in situ frozen samples

Liquefaction resistance of silty sand based on in situ frozen samples

Evaluation of Liquefaction Potential Using Field Performance Data

The evolution of a simplified procedure for evaluating the liquefaction potential of sand deposits using data obtained from standard penetration tests is reviewed. Field data for sites which are known to have liquefied or not liquefied during earthquakes in the United States, Japan, China, Guatemala, Argentina, and other countries are presented to establish a criterion for evaluating the liquefaction potential of sands in Magnitude 7‐1/2 earthquakes. The results of this study are then extended to other magnitude earthquakes using a combination of laboratory and field data. Available information on the liquefaction resistance of silty sands is also reviewed and a simple procedure for considering the influence of silt content is proposed. A method is presented for using the field data to evaluate the possible magnitude of pore water pressure generation in sands and silty sands which remain stable during earthquake shaking. Finally, the applicability of other in situ field tests, such as the static cone pene...