Cyclic Liquefaction Research Articles

Liquefaction of a coal ash investigated by monotonic and cyclic triaxial tests

The critical state soil mechanics (CSSM) has been, recently, introduced as the major analytical framework for synthesising liquefaction behaviours of granular soils. However, liquefaction studies on coal ash have not been synthesised within the CSSM framework. Therefore, a series of monotonic and cyclic triaxial tests covering a range of initial states and testing conditions were conducted to evaluate static and cyclic liquefaction behaviours of coal ash. From the monotonic test results, a unique steady state line (SSL) was established for coal ash. Cyclic test results showed that cyclic liquefaction can be categorised into three distinct forms: cyclic instability, cyclic mobility and hybrid behaviour. Test results suggest that the occurrence of cyclic instability is related to static instability. Furthermore, the forms, if cyclic liquefaction occurred, were governed by the location of the initial state relative to the SSL.

Structural degradation of sands during cyclic liquefaction: Insight from DEM simulations

The macro stress–strain responses of sands are closely related to the evolution of the force transmission network. In this paper, variations of the mechanical stability and reversibility of the force transmission network during the cyclic liquefaction process are explored using discrete element method (DEM) simulations. It is shown that sands degrade gradually from hyperstatic states to isostatic states during cyclic loading and become hypostatic when approaching liquefaction. During this process, the number of excessive contacts decreases gradually and the sample becomes unjammed. An effective and resilient force transmission network should contain enough mechanically stable particles to spread throughout the entire sample. Structural degradation during cyclic loading towards liquefaction is associated with decreasing reversibility of the force transmission network that is characterized by increasing mean squared displacement, increasing fraction of broken contacts and decreasing size of the largest force transmission network. Flow deformation and the development of significant double-amplitude axial strain are attributed to the inability of a large proportion of the broken contacts to re-form post-liquefaction. The size of the largest force transmission network (SL) decays linearly with mean effective stress and there exists a critical value of SL below which liquefaction will occur.

Effects of fines on the cyclic liquefaction behaviour in unsaturated, well-graded materials

The liquefaction of cargoes of metallic ores during maritime transportation is believed to have caused a number of ships to capsize during the past 30 years. To minimise the risk of liquefaction, shipping standards specify a transportable moisture limit (TML), which is the maximum moisture content for ore cargoes to be loaded onto a ship. However, the mechanics leading to the liquefaction of these cargoes is not well understood. This study uses an unsaturated soil mechanics perspective to understand the cyclic liquefaction behaviour of partially saturated materials, similar in grading to iron ore fines, a metallic ore that is known to liquefy during shipping transportation. Iron ore fines are transported at relatively low densities and have variable gradings containing a wide range of particle sizes and fines contents. Therefore, the effects of the degree of saturation and the fines content on the cyclic liquefaction behaviour of well-graded materials have been investigated by performing unsaturated, compression-only cyclic triaxial tests on samples prepared with four different gradings containing particle sizes from 9.5 mm to 2 μm with fines (<75 μm) contents of 18%, 28%, 40% and 60%. The trends in the data are discussed and used to develop a simple method that can conservatively estimate the number of cycles that samples with different degrees of saturation and fines contents are able to resist. The use of this method to describe the liquefaction behaviour of cargoes containing iron ore fines, in practice, is discussed.

Shear wave velocity-based evaluation of liquefaction resistance for calcareous sands of different origin

This paper presents the results of an experimental research carried out in laboratory aimed at establishing a relationship between cyclic liquefaction resistance (CRRfield) and corrected shear wave velocity (VS1) of carbonate sands. Two carbonate skeletal sands, namely Quiou and Dubai, were investigated together with a carbonate non-skeletal sand from Kenya. The programme included also tests on two silica sands prepared and tested in similar conditions for comparison purposes. The research was based on undrained cyclic simple shear tests and bender element tests in triaxial cell performed on reconstituted specimens of sand at different initial density and stress states. The results obtained highlight that data points for carbonate sands are all located to the right of the currently used cyclic liquefaction resistance vs. shear wave velocity curves suggested for silica sands, implying that the latter curves should be considered non-conservative when applied to carbonate crushable sands. An insight into the effect of the initial effective vertical stress on liquefaction susceptibility of carbonate sands was presented and a stress normalization procedure was also proposed.

Cyclic Behaviors of Saturated Sand-Gravel Mixtures under Undrained Cyclic Triaxial Loading

ABSTRACT A few well-documented liquefaction case studies of gravelly soils during major earthquakes have increased concerns regarding the liquefaction susceptibility of gravelly sand soils. Understanding the failure mechanism of sand-gravel mixtures under undrained cyclic loading is important for better assessing their liquefaction susceptibility. The liquefaction mechanism and susceptibility of isotropically and anisotropically consolidated sand-gravel mixtures are investigated under undrained cyclic loading in a solid cylinder apparatus; and, the influences of the varying material properties, compactness states, and particle gradations are systematically studied. The authors introduce an index of the average flow coefficient (k a) that describes the fluidity of saturated sand-gravel mixtures, and then propose the elaboration of a new liquefaction mechanism of saturated sand-gravel mixtures. The specimens would experience cyclic liquefaction when the excess pore pressure ratio reaches 100% under undrained isotropic consolidation, whereas the cyclic mobility would be induced when the cumulative axial strain reaches 5% under undrained anisotropic consolidation. Particles with both sizes smaller than 0.25 mm and mass contents less than 30% in sand-gravel mixtures primarily play a role of the fillers of intergranular voids (fines in coarse). The skeleton void ratio (e sgk) is a unique physical state index to characterize the liquefaction susceptibility of saturated sand-gravel mixtures with the filler content less than 30%. The negative correlation between the cyclic resistance ratio (CRR) and e sgk can be expressed as the power function. Abbreviations: A cl: Closed-loop area of each loading cycle in Fig. 5; ACU: Anisotropically consolidated undrained; CRR: Cyclic resistance ratio; CRR 15: CRR in 15 cycle; CRR 25: CRR in 25 cycle; CSR: Cyclic stress ratio, Applied cyclic stress ratio in CTX test in the form of Equation (7); CTX: test Cyclic triaxial test; C u, C c: Coeffıcients of uniformity and curvature for the particle-size distribution curve; D, d: Size of coarse and small spherical particles in an idealized binary packing model; D 50: Median diameter of host coarse soils in binary mixtures; d 50: Median diameter; median diameter of host fine soils in binary mixtures; DA: Double-amplitude; D r: Relative density; initial relative density; D r0: Post-consolidation relative density; e: Global void ratio; initial void ratio; e 0: Post-consolidation void ratio; e min, e max: Minimum and maximum void ratios; e sgk: Skeleton void ratio; FC: Fines content for particles with the sizes less than 0.075 mm; FC th: Fines content threshold value; f f: Filler content by weight for particles with sizes less than 0.25 mm in the coarse-dominated grain contact sand-gravel mixtures; G c: Gravel content; G s: Specific gravityHCA Hollow cylinder apparatus; ICU: Isotropically consolidated undrained; k a: Index of the average flow coefficient; K c: Consolidation stress ratio, defined as the ratio of to m, n Fitting coefficients in Equations 11–13; N l: Number of cycles required to cause an r u = 100% for ICU CTX test or ε p = 5% for ACU CTX test; q: Deviatoric stress; q cyc: Peak cyclic deviatoric stress; q s: Initial static deviatoric stress; R: Roundness proposed by Power (1953); R d: Particle size disparity ratio in binary packing model; r u: Excess pore pressure ratio, defined as the ratio of Δ u to; Δu: Excess pore pressure change induced by the action of cyclic shear stressSA Single-amplitude; α d: Cyclic shear stress ratio of any plane in the specimen; β: Inclination angle to the horizontal axis in Mohr’s stress circle serve; : Shear strain rate; ,: Maximum and minimum shear strain rate of each loading cycle in Fig. 5; ε: Axial strain; ε p: Accumulated permanent axial strain; η: Apparent viscosity in fluid mechanics; ρ d: Dry densities; ,: Initial effective vertical and lateral consolidation stress; σ d: Applied sinusoidal cyclic axial stress amplitude; : Initial effective normal stress of any plane in the specimen; τ: Shear stress; τs : Initial shear stress of any plane in the specimen; τ d: Cyclic shear stress amplitudes of any cyclic shear effect plane; τ max, τ min: Maximum and minimum shear stress of each loading cycle in Fig. 5

Cyclic liquefaction screening of sand with non-plastic fines: Critical state approach

There have been significant advances in the application of critical state, CS, in liquefaction potential assessment. This was done by comparing state parameter, ψ with estimated characteristic cyclic stress ratio, CSR due to an earthquake. A cyclic resistance ratio, CRR curve, which can be determined from cyclic liquefaction tests, separates historical liquefied and non-liquefied data points (ψ, CSR). On the other hand, the concepts of equivalent granular state parameter, ψ*, which was developed for sands with fines, can be used in lieu ψ to provide a unifying framework for characterizing the undrained response of sands with non/low plasticity fines, irrespective of fines content (fc). The present work combines these two propositions, and by merely substituting ψ* for ψ into the aforementioned CS approach to capture the influence of fc. A series of static and cyclic triaxial tests were conducted, separately and independently of the concept of ψ*, for sand with up to fc of 30%. The clean sand was collected from Sabarmati river belt at Ahmedabad city in India which was severely affected during the Bhuj earthquake, 2001. The experimental data gave a single relation for CRR and ψ* which was then used to assess liquefaction potential for a SPT based case study, where fc varies along the depth. The prediction matched with the field observation.

Effects of fines on liquefaction behaviour in well-graded materials

This study uses a critical state soil mechanics perspective to understand the mechanics behind the liquefaction of metallic ores during transport by ship. These metallic ores are transported at relatively low densities and have variable gradings containing a wide range of particle sizes and fines contents. The effect of the fines content on the location of the critical state line (CSL) and the cyclic liquefaction behaviour of well-graded materials was investigated by performing saturated, standard drained and undrained monotonic and compression-only cyclic triaxial tests. Samples were prepared at four different gradings containing particle sizes from 9.5 mm to 2 μm with fines (&lt;75 μm) contents of 18%, 28%, 40%, and 60%. In the e versus log[Formula: see text] plane, where e is void ratio and [Formula: see text] is mean effective stress, the CSLs shifted upwards approximately parallel to one another as the fines content was increased. Transitional soil behaviour was observed in samples containing 28%, 40%, and 60% fines. A sample’s cyclic resistance to liquefaction depended on a combination of its density and state parameter, which were both related to the fines content. Samples with the same densities were more resistant to cyclic failure if they contained higher fines contents. The state parameter provided a useful prediction for general behavioural trends of all fines contents studied.

The Coupled Influence of Relative Density, CSR, Plasticity and Content of Fines on Cyclic Liquefaction Resistance of Sands

ABSTRACTIn this study, stress-controlled cyclic simple shear tests were performed on sand specimens with up to 10% silt or clay contents, and coupled effects of plasticity, fines content (FC), relative density (DR) and CSR (cyclic stress ratio) were investigated. The results demonstrated that for sands with low fines content, reasonable trends were obtained when the packing index control parameter was selected as DR. Also, clean sand specimens demonstrated highest liquefaction strength compared with that of sands with fines up to 10% FC. The effect of fines’ plasticity became apparent as the FC increases and CSR reduces in relatively denser specimens.

Evaluation of liquefaction potential in an intermountain Quaternary lacustrine basin (Fucino basin, central Italy)

In this study, we analyse the susceptibility to liquefaction of the Pozzone site, which is located on the northern side of the Fucino lacustrine basin in central Italy. In 1915, this region was struck by a M 7.0 earthquake, which produced widespread coseismic surface effects that were interpreted to be liquefaction-related. However, the interpretation of these phenomena at the Pozzone site is not straightforward. Furthermore, the site is characterized by an abundance of fine-grained sediments, which are not typically found in liquefiable soils. Therefore, in this study, we perform a number of detailed stratigraphic and geotechnical investigations (including continuous-coring borehole, CPTu, SDMT, SPT, and geotechnical laboratory tests) to better interpret these 1915 phenomena and to evaluate the liquefaction potential of a lacustrine environment dominated by fine-grained sedimentation. The upper 18.5 m of the stratigraphic succession comprises fine-grained sediments, including four strata of coarser sediments formed by interbedded layers of sand, silty sand and sandy silt. These strata, which are interpreted to represent the frontal lobes of an alluvial fan system within a lacustrine succession, are highly susceptible to liquefaction. We also find evidence of paleo-liquefaction, dated between 12.1–10.8 and 9.43–9.13 kyrs ago, occurring at depths of 2.1–2.3 m. These data, along with the aforementioned geotechnical analyses, indicate that this site would indeed be liquefiable in a 1915-like earthquake. Although we found a broad agreement among CPTu, DMT and shear wave velocity “simplified procedures” in detecting the liquefaction potential of the Pozzone soil, our results suggest that the use and comparison of different in situ techniques are highly recommended for reliable estimates of the cyclic liquefaction resistance in lacustrine sites characterized by high content of fine-grained soils. In geologic environments similar to the one analysed in this work, where it is difficult to detect liquefiable layers, one can identify sites that are susceptible to liquefaction only by using detailed stratigraphic reconstructions, in situ characterization, and laboratory analyses. This has implications for basic (Level 1) seismic microzonation mapping, which typically relies on the use of empirical evaluations based on geologic maps and pre-existing sub-surface data (i.e., age and type of deposits, prevailing grain size, with particular attention paid to clean sands, and depth of the water table).

Discrete-element method analysis of initial fabric effects on pre- and post-liquefaction behavior of sands

The initial fabric has great influence on the cyclic behaviours of sands. In this study, numerical simulations by the discrete-element method (DEM) were conducted to study the effects of the initial fabric of sands on their cyclic liquefaction resistance and post-liquefaction behaviour. Nine samples with different initial fabric but the same void ratio were prepared by the pre-shearing method, and then subjected to 47 cyclic simple shear tests. The DEM simulation demonstrated that samples with higher degrees of fabric anisotropy have much lower liquefaction resistance compared with an isotropic sample. By incorporating the initial fabric, a single equation can be used to characterise the liquefaction resistance of all the prepared samples. On the other hand, post-liquefaction deformation is not significantly influenced by the initial fabric such that all samples demonstrate similar cyclic behaviour after liquefaction.

Evolution of fabric anisotropy in cyclic liquefaction of sands

Cyclic liquefaction of sands is influenced by many factors including the initial fabric. Yet, it is difficult to quantify the soil fabric using laboratory technology. In this study, discrete element method (DEM) is used to numerically simulate the process of liquefaction under undrained cyclic loading. Samples with the same void ratio and varying degrees of fabric anisotropy are prepared by the pre-shearing method. Fabric evolution before and after cyclic liquefaction is quantified by the coordination number, angular distribution and the principal direction of inter-particle contacts. The DEM study demonstrated that the coordination number decreases and the fabric anisotropy increases gradually when the sand is cyclically sheared to approach the initial liquefaction. In this process, the principal direction of the anisotropic fabric tensor is not coaxial with the stress tensor. After initial liquefaction, all samples with different initial fabric evolve towards a same fabric, which is strongly anisotropic. The principal direction of the fabric aligns with the principal direction of the stress in the post-liquefaction stage.

Influence of Initial Conditions on Liquefaction Resistance of Sandy Soil from Chlef region in Northern Algeria

Two strong earthquakes occurred in the region of Chlef (north western part of Algeria) during the last century. From the geological context, there were several great masses of sandy soil ejections on the ground surface level and severe damages to civil and hydraulic structures. These damages were due to the soil liquefaction phenomenon. The objective of this paper is to study the resistance to static and cyclic liquefaction of Chlef sand through triaxial tests with focus on the effect of the initial state. For this purpose, a series of undrained monotonic and cyclic triaxial tests were carried out on saturated silty sand at two initial relative densities (Dr = 29 and 80 %). The initial confining pressure was kept at 200 kPa. Moist tamping and dry funnel Pluviation were used to prepare sand specimens. Test results indicated that the monotonic and cyclic resistance of soil mainly depends on initial conditions. Samples prepared by dry funnel Pluviation method have a greater resistance to liquefaction while those by moist tamping have been found to be potentially liquefiable. Further, liquefaction resistance increases with increase in initial relative density and confining pressure.

Effect of frequency of cyclic loading on liquefaction and dynamic properties of saturated sand

The effect of frequency of cyclic loading on liquefaction and post-liquefaction resistance of original Ahmedabad sand has been presented in this technical paper. Saturated and consolidated specimens prepared to a particular relative density were subjected to varied frequencies at a constant cyclic stress ratio under undrained conditions. Specimens were cyclically loaded till liquefaction. It was observed that the rate of generation of excess pore water pressure increases with increase in frequency of cyclic loading as a result the cyclic liquefaction resistance decreases with increase in the loading frequency. From the study on dynamic properties, it is found that the shear modulus decreases and damping ratio increases with increase in frequency. The frequency of cyclic loading has no influence on the shear modulus at a particular shear strain. It is also seen that the shear modulus decreases and damping ratio increases with increase in shear strain.

Cyclic resistance and liquefaction behavior of silt and sandy silt soils

The liquefaction behavior and cyclic resistance ratio (CRR) of reconstituted samples of non-plastic silt and sandy silts with 50% and 75% silt content are examined using constant-volume cyclic and monotonic ring shear tests along with bender element shear wave velocity (Vs) measurements. Liquefaction occurred at excess pore water pressure ratios (ru) between 0.6 and 0.7 associated with cumulative cyclic shear strains (γ) of 4% to 7%, after which cyclic liquefaction ensued with very large shear strains and excess pore water pressure ratio (ru>0.8). The cyclic ring shear tests demonstrate that cyclic resistance ratio of silt and sandy silts decreases with increasing void ratio, or with decreasing silt content at a certain void ratio. The results also show good agreement with those from cyclic direct simple shear tests on silts and sandy silts. A unique correlation is developed for estimating CRR of silts and sandy silts (with more than 50% silt content) from stress-normalized shear wave velocity measurements (Vs1) with negligible effect of silt content. The results indicate that the existing CRR–Vs1 correlations would underestimate the liquefaction resistance of silts and sandy silt soils.

Density Index for Estimating the Postliquefaction Volumetric Strain of Silty Soils

AbstractThis study examined the liquefaction-induced ground settlement of silty sand ground, in which many nonplastic fines are contained. Investigation determined that if fines were included in the specimen, the minimum void ratio shrank more under water-immersion than dry conditions. In addition, the cyclic minimum void ratio was examined, which was obtained by cyclic liquefaction and drainage testing conducted by assuming earthquake excitation. The results illustrated that the difference between the estimated dry and cyclic minimum void ratios uniquely correlated with fines content. A new density index, the normalized margin of void ratio, was proposed for postliquefaction volumetric strain based on examination of the minimum void ratio of soils containing nonplastic fines. The test results confirmed that maximum and accumulated shear strains are satisfactory indices of loading history. Furthermore, the normalized margin of void ratio performed well as a density index for estimating postliquefaction se...

Liquefaction potential of soils around circular double tunnels

The aim of this paper is to investigate the effect of underground circular tunnels on cyclic behavior and liquefaction potential of soils surrounding them. For this purpose, an intensive numerical analyses scheme which includes three-dimensional, finite difference based total stress analyses on generic soil, tunnel and earthquake combinations has been performed. The effect of tunnel diameters, depth of tunnel center and the strength of soils on the maximum ground accelerations and liquefaction potential have been discussed in detail. The liquefaction potential is discussed in terms of both the factor of safety (FSliq) and liquefaction potential index. It is concluded that changing the diameter and support thickness of the tunnels does not make a remarkable change on peak ground accelerations. Similarly, the liquefaction potential of the soils considered does not depend on the diameter of the tunnel. However, it was shown that the most important parameters which are effective in peak ground acceleration and liquefaction potential are the depth of the tunnel and the rigidity of the soil in which the tunnel is constructed. The analyses showed that, the maximum ground acceleration values are observed in the middle of the two tunnels. Moreover, the peak ground acceleration value increases with increasing shear wave velocity and accordingly increases the resistance to liquefaction potential as expected. This study showed that, if a tunnel is to be built in a liquefaction prone zone, it should be constructed as deep as possible to reduce the probable risk of liquefaction.

Cyclic liquefaction behaviour of a moderately cemented grouted sand under repeated loading

The aim of this paper is to provide an insight into the effects of a previous cyclic history “triggering” full liquefaction on the subsequent undrained cyclic behaviour of a moderately cemented grouted sand in terms of strength, deformability and pore pressure response. The research was conducted on sand specimens stabilized by a commercial mineral based chemical grout (“Silacsol”), capable of imparting unconfined compression strength (UCS) values ranging between 500kPa and 700kPa. Monotonic shear strength parameters of treated specimens were preliminary assessed through a series of isotropically consolidated drained triaxial tests (TX-CID). Afterwards, stress-controlled undrained cyclic simple shear (SS) tests were conducted on both treated and untreated sand specimens in order to evaluate the improvement provided by the grout on the liquefaction resistance of the sand. A significant beneficial effect of the grout was observed, regardless of the initial density of the pure sand. Finally the influence of a cyclic large preshearing on the undrained cyclic behaviour of the grouted sand was investigated by subjecting the specimens to a sequence of two cyclic loadings with the same stress ratio (CSR). After the first loading in which specimens were brought to full liquefaction, they were allowed to reconsolidate in approximately K0 conditions and then subjected to the second loading. An increase in liquefaction resistance induced by cyclic history was clearly apparent on treated specimens.Excess pore pressures build-up during the first cyclic loading on treated specimens followed a different trend compared to that observed on untreated ones. A significant difference was also observed on the excess pore pressure trends developed in the second loading compared to that developed in the primary loading. A simple model for the prediction of pore water pressure build-up of grouted sands during cyclic loading is proposed.

Influence of consolidation properties on the cyclic re-liquefaction potential of sands

The relative density can be used as the main indicator to assess the liquefaction resistance of clean sands. As relative density of the sand deposit increases significantly following the initial liquefaction, one should expect that the soil can improve its liquefaction resistance. However, earthquake records indicate that densified sand can be liquefied again (re-liquefied) at smaller cycles by the similar seismic loadings. This work aims to clarify the counterintuitive finding that, after the first liquefaction, the resulting significant increase in relative density (induced by settlements and variation of the water level) do not necessarily imply an increase in the number of loading cycles for re-liquefaction. In this paper, we present a series of experimental results concerning the cyclic liquefaction and the following re-liquefaction of clean sand deposits. The experimental setup is performed by a shaking table, transmitting one-degree of freedom transversal motion to the soil within the 1.5 m high laminar shear box. At four different seismic demands, the input excitation was imposed three times to examine the influence of the initial distributions of the relative density and the consolidation characteristics on the liquefaction potential of the sand. The re-liquefaction cycles of the sand, which previously experienced liquefaction under the same seismic loadings, show that post-liquefaction reconsolidation of the sand deposits affects the re-liquefaction resistance.

Investigation of Cyclic Liquefaction with Discrete Element Simulations

A discrete-element method (DEM) assembly of virtual particles is calibrated to approximate the behavior of a natural sand in undrained loading. The particles are octahedral, bumpy clusters of spheres that are compacted into assemblies of different densities. The contact model is a Jäger generalization of the Hertz contact, which yields a small-strain shear modulus that is proportional to the square root of confining stress. Simulations made of triaxial extension and compression loading conditions and of simple shear produce behaviors that are similar to sand. Undrained cyclic shearing simulations are performed with nonuniform amplitudes of shearing pulses and with 24 irregular seismic shearing sequences. A methodology is proposed for quantifying the severities of such irregular shearing records, allowing the 24 sequences to be ranked in severity. The relative severities of the 24 seismic sequences show an anomalous dependence on sampling density. Four scalar measures are proposed for predicting the severity of a particular loading sequence. A stress-based scalar measure shows superior efficiency in predicting initial liquefaction and pore pressure rise.

Prediction of Undrained Monotonic and Cyclic Liquefaction Behavior of Sand with Fines Based on the Equivalent Granular State Parameter

AbstractThe undrained behavior of sand with fines under both monotonic and cyclic loading was investigated experimentally by triaxial testing. The testing program covers fines content ranging from 0 to 30%, and a wide range of initial void ratios and confining stresses. The spectrum of cyclic loading includes one- and two-way cyclic loading, and in the latter case, the cyclic loading may be symmetrical or nonsymmetrical. The influence of fines content can be captured by using the equivalent granular void ratio, e∗, in lieu of the void ratio, e. All steady-state data points can be described by a single relationship referred to as the equivalent granular steady-state line. This study proposes the concept of the equivalent granular state parameter, ψ∗, for capturing the combined effects of the stress state, density state, and fines content. The observed behavior can then be related to e∗ and/or ψ∗. Irrespective of fines contents, the behavior under monotonic loading can be classified into three types, and ψ∗...