Particle characteristics (particle shape and size), along with relative density, significantly influence the frictional characteristics and liquefaction behavior of granular materials, particularly sand. While many studies have examined the individual effects of particle shape, gradation, and relative density on the frictional characteristics and liquefaction behavior of sand, they have often overlooked the combined effects of these soil parameters. In this study, the individual effect of these three soil parameters on the strength characteristics (angle of internal friction) and liquefaction resistance has been quantified by analyzing the data available in the literature. A novel dimensionless parameter, the 'packing index (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha $$\end{document}),' was developed to account for the bulk characteristics (relative density - RD) and grain properties (gradation, represented by the coefficient of uniformity (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$C_u$$\end{document}), and particle shape represented by the shape descriptor regularity (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\rho $$\end{document})) of the granular soils. Through statistical analysis, a power law-based equation was proposed and validated to relate the cyclic resistance ratio (CRR) and angle of internal friction (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi $$\end{document}) with the packing index. Finally, an approach to assess the liquefaction resistance was detailed considering the intrinsic soil parameters, aiming to bridge the gap between field observations and laboratory analysis to facilitate a comprehensive understanding of soil behavior under cyclic loading.
The present experimental study evaluates the overburden correction factor (K6) of different pond ash samples under earthquake loading for liquefaction analysis. A series of 54 stress-controlled cyclic simple shear tests was conducted on pond ash specimens at different overburden pressures and cyclic stress ratios. Cyclic resistance ratio (CRR) was evaluated for each pond ash sample at different overburden pressures using two criteria based on maximum excess pore water pressure and double amplitude shear strain to evaluate the K6. The K6 values obtained for the pond ash were compared with the K6 values for natural soils (clean sand and sand-silt mixtures). The cyclic resistance ratio (CRR) and K6 values were observed to decrease with an increase in overburden pressure from 50 kPa to 100 kPa, and a further increase in overburden pressure to 150 kPa led to an increase in CRR and K6 values for pond ash specimens with fine particles dominated matrix. However, an opposite trend was observed for pond ash specimens with coarse particles-dominated matrix. The unique response of K6 values for pond ash was found to be significantly different from the already available K6 response for natural cohesionless soil (clean sand and sand-silt mixtures) as it unavoidably included the effect of OCR and void ratio along with the vertical overburden pressure.
As a cost-effective and environmentally friendly technique for enhancing the liquefaction resistance of sandy soils, the air-injection method has attained widespread application in multiple soil improvement or desaturation strategies. This study reports undrained cyclic loading experiments on reconstituted, slightly desaturated sand specimens under either isotropic or anisotropic consolidation to examine the effects of the presence of injected air and initial stress anisotropy on the energy-based assessment of pore pressure and liquefaction resistance. The results exhibited three different cyclic response patterns for the saturated/desaturated specimens with distinct deformation mechanisms, revealing that the sand has a higher degree of stress anisotropy and lower degree of saturation typically being more dilative and less susceptible to cyclic liquefaction. The energy-based liquefaction potential evaluation indicates that the accumulative energy is mathematically correlated with the pore pressure, thus establishing a unified energy-pore pressure relationship for both saturated and desaturated sand. Furthermore, the energy capacity for triggering cyclic failure demonstrates a consistently rising trend with an increase in the consolidation stress ratio and a reduction in the degree of saturation, which seems closely linked to the cyclic liquefaction resistance. This result signifies the potential applicability of an energy-based approach to quantify the liquefaction susceptibility of desaturated in situ soils using strength data from conventional stress-based analyses.
Replacing soil with waste materials offers significant opportunities for advancing geoenvironmental practices in the construction of large-scale geostructures. The present study investigates the viability of utilizing sugarcane bagasse, a massively produced agricultural waste material, as a partial replacement for soil and its potential to control soil liquefaction. Utilization of bagasse in large geostructures not only aids in the management of a significant volume of bagasse but also facilitates the conservation of natural soil resources. Experimental investigations were conducted through a series of isotropically consolidated, stress-controlled, undrained cyclic triaxial tests. Various volumetric proportions of bagasse to sand, extending up to 50:50 (bagasse: sand), were examined to evaluate the performance of the mix under different cyclic loading conditions. The study evaluates the cyclic strength, stiffness degradation, cycle retaining index, etc., for different bagasse sand mixes across the expected cyclic stresses corresponding to Indian seismic zones 3, 4, and 5. Variation of these properties with relative density has also been studied. Results indicate that the bagasse can effectively be utilized as a geomaterial to partially replace the soil in large proportions ranging from 19 % to 41 % without compromising the initial cyclic strength of the natural soil. Notably, at an optimal content of 30 %, the bagasse sand mix exhibits higher resistance to the accumulation of excess pore water pressure, maximizing its liquefaction resistance. Furthermore, the utilization of bagasse as a partial replacement for soil increased the cyclic degradation index within the suggested range of bagasse content.
Energy dissipation can macroscopically synthesize the evolutions in the microstructure of the marine clay during cyclic loading. Hence an energy-based method was employed to investigate the failure criterion and cyclic resistance of marine clay. A series of constant-volume cyclic direct simple shear tests was conducted on undisturbed saturated marine clay from the Yangtze Estuary considering the effects of the plasticity index (IP) and cyclic stress ratio (CSR). The results indicated that a threshold CSR (CSRth) exhibiting a power function relationship with IP exists in marine clay, which divides the cyclic response into non-failure and failure states. For failed specimens, the development of energy dissipation per cycle (Wi) with the number of cycles (N) exhibited an inflection point owing to the onset of serious damage to the soil structure. In this regard, the energy-based failure criterion was proposed by considering the inflection point as the failure point. Consequently, a model was proposed to quantify the relationships between failure energy dissipation per cycle (Wf) [or failure accumulative energy dissipation (Waf)], initial vertical effective stress, IP, and the number of cycles to failure (Nf,E). An evaluation model capturing the correlation among CSR, IP, and Nf,E was then established to predict the cyclic resistance, and its applicability was verified. Compared with the strain-based cyclic failure criterion, the energybased failure criterion provides a more robust and rational approach. Finally, a failure double-amplitude shear strain (gamma DA,f) evaluation method applicable to marine clay in different seas was presented for use in practical geotechnical engineering.
Seismic liquefaction is one of the most devastating natural hazards that can cause significant damage to structures and infrastructure. The liquefaction behaviour is simulated in the finite element code PLAXIS by the UBC3D-PLM constitutive model that is 3-D generalized formulation of the 2-D UBCSAND model developed at the University of British Colombia. The UBC3D-PLM model used in this work was successfully employed in many recent studies, e.g. to evaluate the liquefaction effects on the seismic soil-structure interaction, to assess the dynamic behaviour of earthen embankments built on liquefiable soil and to investigate the seismic performance of offshore foundations. Moreover, UBC3D-PLM model involves many input parameters to model the onset of the liquefaction phenomenon. Therefore, their determination becomes a crucial concern. Previous studies elaborated a specific formulation that requires the corrected Standard Penetration Test (SPT) blow counts as input. However, the Dilatometer Marchetti Test (DMT), compared to the SPT, is more sensitive to several factors that affect the liquefaction resistance such as aging, stress history, overconsolidation and horizontal earth pressure. For this reason, a new parameter selection procedure, which uses the horizontal stress index derived from DMT, was developed in this study. The new relationships were applied for determining the initial parameters of the UBC3D-PLM model to describe the behavior of several liquefiable deposits located in eastern Sicily (Italy) that experienced destructive earthquakes in the past. For each site, the model was calibrated to the DMT-based liquefaction triggering curve, developed by combining DMT correlations with the current method based on SPT test, by the simulation of cyclic direct simple shear tests (CDSS). Finally, CDSS tests were performed by means of the CDSS device at the Soil Dynamics and Geotechnical Engineering Laboratory of the University Kore of Enna (Italy). This allowed to validate the applicability of the proposed procedure in simulating the liquefaction behavior of sandy soils.
The effects of phase shift (delta) between compression and shear waves, and consolidation stress ratio (K-c) on the liquefaction resistance of sand under simultaneous compression and shear wave loading is investigated using a hollow cylinder torsional shear apparatus. The differences caused by prior stress history (assessed using drained versus undrained preshear) highlight the importance of test protocols in undertaking research to explore the effects of complex dynamic loading paths. The liquefaction resistance of sand was highly dependent on the loading path. However, it was not affected much by variations in delta, if the horizontal shear stress ratio (tau(z theta)/sigma(mc)') and the ratio between shear stress increment and normal stress increment (Delta S/Delta N) were held constant. In tests with constant cyclic stress ratio (CSR), an increase in delta decreases the cyclic resistance because the increase in delta causes a reduction in the rate of deviatoric stress increment per degree of principal stress rotation. At a given CSR, for delta not equal 0 cases, a change in Delta S/Delta N does not affect the liquefaction resistance of sand because the magnitude and pattern of rotation is not affected much by Delta S/Delta N (for the ratios explored in this research). Increasing K-c or static shear stress ratio (alpha(st)) increased the cyclic resistance of the tested sand for Delta S/Delta N<1. The rate of increase in cyclic resistance with increasing alpha(st) decreases with the increase in Delta S/Delta N and was essentially unchanged for Delta S/Delta N=1. This observation, that the rate of increase in cyclic resistance with alpha(st) decreases with increasing Delta S/Delta N, is consistent with the observation in the literature that the cyclic triaxial loading yields higher static shear stress correction factor (K-alpha) than cyclic simple shear in loose sand. (c) 2024 American Society of Civil Engineers.
There are many geotechnical applications involving dams, embankments and slopes where the presence of an initial static shear stress prior to the cyclic loadings plays an important role. The current paper presents the experimental results gathered from undrained cyclic simple shear tests carried out on non-plastic silty sand with fines content in the range 0-30% with the consideration of sustained static shear stress ratio (alpha). Two distinct parameters, namely the conventional state parameter Psi, and the equivalent state parameter Psi*, are introduced in the context of critical state soil mechanics (CSSM) framework to predict failure mode and undrained cyclic resistance (CRR) of investigated soils. It is proved that the failure patterns for silty sands are related to (a) the initial states of soils (Psi or Psi*) and (b) the combination of initial shear stress with respect to cyclic loading amplitude. At each alpha, the CRR-Psi (or Psi*) correlation can be well represented by an exponential trend which is practically unique for both clean sands and silty sands up to a threshold fines content (f thre congruent to 24.5%). Varying alpha from low to high levels simply brings about a clockwise rotation of the CRR-Psi (or Psi*) curves around a point. This CRR-Psi (or Psi*) platform thus provides an effective methodology for investigating the impact of initial shear stress on the cyclic strength of both clean sands and silty sands. The methodology for estimating Psi (or Psi*) state parameters from in-situ cone penetration tests in silty sands is also discussed.
Laboratory and field tests were performed on sandy soils from six Pleistocene-age sites in the South Carolina coastal region to investigate the age-related resistance to liquefaction. Stress-controlled cyclic triaxial tests were used to determine the cyclic strength of soils with geologic ages ranging from approximately 59,000 to 1,200,000 years. Three sites have evidence of liquefaction in the form of sand blows that are 467 to 4,185 years old as determined from C14 dating of embedded organic material. The other three sites show no indications of liquefaction. Cyclic stress ratios ranging from 0.095 to 0.225 were applied to undisturbed and reconstituted soil specimens that were consolidated to an effective stress equal to 100 kPa. Soil specimen liquefaction was defined to occur when the excess pore pressure was equal to the confining effective stress. Estimates of the at-rest earth pressure coefficient were determined using measurements from the flat plate dilatometer and the cone penetrometer and were applied to the laboratory cyclic stress ratio occurring at the 15th loading cycle to determine the laboratory-field equivalent cyclic resistance ratio. The age-dependent liquefaction resistance was determined using additional data from the inner coastal plain of South Carolina and assessing the cyclic resistance ratios and their associated KDR ratios relative to the base data and applying one of the more recently developed liquefaction triggering model. It was found that the development of the aging factor should be independent of the liquefaction triggering model. Subsequently, the aging factor is developed using an offset that is constrained at 20 years and a KDR=1.0, and was found to range from 1.00 at 20 years to 1.45 at 1.0 Ma for the original deposition ages of the soils and 1.00 at 20 years to 1.51 at 1.0 Ma for the data set consisting of the last disturbance and original deposition ages of the soils.
The stress-induced anisotropy of sand significantly affects the liquefaction susceptibility. This study systematically investigates the undrained behavior of saturated sand under both monotonic and cyclic loading through a series of torsional shear tests, considering the effects of initial anisotropic consolidation states, including extensional and compressional consolidation states. Special attention is paid to the evolution of effective stress paths, deformation pattern, pore water pressure generation, and the rotation of the principal stress direction during the torsional shear process. The experimental results show that specimens under different initial stress states and loading conditions exhibit two typical failure modes, i.e., residual strain accumulation and cyclic mobility. The evolutions of principal stress direction under both monotonic and cyclic loading are presented, which can provide useful insights into the underlying mechanism of the occurrence of different failure modes. Based on the experimental results, a new index, unified cyclic stress ratio (USR), is proposed by correlating the number of cycles required for failure (Nf) with the initial anisotropic stress state and the shear strength at the phase transformation point. The proposed index USR can serve as a unified criterion for the evaluation of liquefaction resistance of sand considering anisotropic consolidation conditions.