Cyclic Liquefaction Potential Research Articles

The influence of various end restraints and grain shape on the cyclic undrained behaviour of granular materials

ABSTRACT The paper describes the effect of the various ends restraints on the cyclic liquefaction potential of Karlsruhe fine sand and examines the influence of grain shape and gradation on the cyclic liquefaction susceptibility of granular materials. To assess the influence of grain shape and gradation, three materials with same mean size but two different gradations were considered. Different scenarios were considered including the influence of differing sizes of the porous discs at end platens, influence of sample size ratio at similar diameter and varying membrane thickness. Additionally, the influence of using end lubrication or filter papers is investigated. The results reflect a pronounced effect of the liquefaction resistance of KFS using porous discs with a larger diameter, where a significant increase in the number of cycles to initial liquefaction was noted. Furthermore, initial liquefaction resistance for angular/sub-angular materials reduced with increasing gradation. In contrast, it remained relatively unchanged for round materials.

CPTu-based approaches for cyclic liquefaction assessment of alluvial soil profiles

Over the years, methods to assess cyclic liquefaction potential based on piezocone penetration tests (CPTu) have been developed. This paper presents a comparative study between three CPTu-based methodologies, mainly in terms of the normalization procedures of overburden stresses, equivalent clean sand resistance, and magnitude scaling factor (MSF). Four CPTu profiles from a pilot site in southwest Portugal are thoroughly analysed with different methods, in terms of factor of safety against liquefaction, the Liquefaction Potential Index (LPI), and the Liquefaction Severity Number (LSN). The site presents very heterogeneous soil profiles, composed of alluvial deposits. Due to the presence of significant sand-silt–clay interbedded layers, the influence of transition zones and the use of different soil behaviour type index (Ic) cut-off values were also considered. From these analyses, a set of recommendations is presented for CPTu-based liquefaction assessment. Based on the extensive database of CPTu results in the pilot site area, a new classification relating LPI and LSN is proposed to assess liquefaction severity and damage.

Laboratory assessing of the liquefaction potential and strength properties of Sand soil treated with mixture of nanoclay and glass fiber under dynamic and static loading

This study evaluated an improvement method based on static and dynamic tests for dune sand soil on the coast of Bandar Anzali city. This soil has very poor and insufficient mechanical performance for many construction projects as well as the potential for liquefaction. Short glass fibers have been used in this improvement method to reinforce the soil modified with nanoclay. The effects of simultaneously adding glass fibers and modified nanoclay at optimal weight percentages on the sand specimen were evaluated through static triaxial tests at consolidated drained conditions. The results showed that the simultaneous addition of glass fibers and nanoclay at lower confining pressures had more significant effects and was more useful for soil modification. The results indicated increases of more than 31% and about 23% in the peak deviatoric stress of the modified sand specimen at the confining stresses of 50 and 100 kPa, respectively, compared to the pure sand specimen. Furthermore, the modified sand specimen had a 20% reduction and a 50% increase in failure axial strain, compared to the pure sand specimen, under the static triaxial test at the confining pressures of 50 and 200 kPa, respectively; however, its failure axial strain did not change at the confining pressure of 100 kPa compared to the pure sand specimen. The results of static triaxial tests showed that the simultaneous addition of glass fibers and nanoclay at the optimal weight percentages increased the cohesion of the sand specimen and did not change its internal friction angle. To investigate the effect of this improvement method on dune sand under dynamic loading, the cyclic liquefaction potential of pure and modified sand specimens was evaluated through cyclic triaxial tests under consolidated undrained conditions. The results showed a significant effect of sandy soil improvement on reducing its liquefaction potential. The number of loading cycles causing liquefaction was increased, by more than 5.5 times at the cyclic stress ratio of 0.27, by about 3 times at the cyclic stress ratio of 0.3, and finally, by more than 2 times at the cyclic stress ratio of 0.34 for the modified sand specimen compared to the pure sand specimen. By defining the cyclic stress ratio corresponding to liquefaction in the twentieth loading cycle as the specimen cyclic strength, the cyclic strength of the modified sand specimen was increased by more than 13% compared to the pure sand specimen. Based on the results of a series of different experiments conducted in this study, it was concluded that the simultaneous addition of glass fibers and modified nanoclay at their optimal weight percentages (0.5% and 1% by total dry weight of specimen, respectively) significantly improved many different resistance characteristics of dune sand soil from the Bandar Anzali coast, and using this composition can be considered as an effective and efficient way to improve this very special type of soil.

The liquefaction potential of the upper quaternary sands of the Cape Flats, Western Cape, South Africa

Liquefaction of saturated cohesionless soils as a result of earthquake-induced ground shaking is a major concern for structures constructed within or on these soils. During an earthquake, shear waves propagate through the ground, generating shear stresses and strains that are cyclic in nature, causing the soil grains to rearrange into a denser state of packing. This process is too rapid for drainage to occur, which results in an increase in pore water pressure and a decrease in effective stress and shear resistance of the soil. The occurrence of a seismic event associated with the Milnerton Fault line extending below the Cape Flats, a low-lying sand-covered area connecting the Cape Peninsula with the southwestern Cape mainland of South Africa, can cause extensive damage to the largely inadequate infrastructure characterising the area. To evaluate the susceptibility of Cape Flats sand to undergo liquefaction during and after a seismic event, the empirical SPT-based method put forth by Idriss & Boulanger (2004) was used to assess the cyclic liquefaction potential of dense, dilative sands, whereas the CPT-based method published by Robertson (2016) was used to assess the volumetric response of the sands during undrained shear. Resistance of the Cape Flats sands to liquefy at probable earthquake moment magnitude and acceleration values of M = 6.0 and amax= 0.15 g respectively, was noted. Robertson's normalised Soil Behaviour Type (SBTn) chart revealed mostly dilative sands and silty sands susceptible to cyclic liquefaction. Loose, contractive sands prone to flow liquefaction are present, although limited in occurrence and extent.

CPT-BASED SIMPLIFIED LIQUEFACTION ASSESSMENT BY USING FUZZY-NEURAL NETWORK

Due to the difficulty and the cost of obtaining high quality undisturbed samples, simplified methods based on in-situ tests such as the standard penetration test (SPT) and the cone penetration test (CPT) are preferred by geotechnical engineers for evaluation of earthquake induced liquefaction potential of soils. Because of the increasing popularity worldwide of the CPT for site characterization, significant progress on the CPT-based methods has been made. In most existing CPT-based methods, empirically determined curves are used to predict liquefaction and non-liquefaction. These empirical curves are generally relied on engineering judgment and are essentially performance functions that were established based on field observations of soil performance during earthquakes at sites where in-situ CPT data are available. The performance functions can be referred to as the limit state functions and the empirical curves are generally limit state functions such that the curve are generally limit state curve. The limit state for liquefaction evaluation is defined by CRR being equal to CSR, in which CRR is liquefaction resistance of a soil that is generally expressed as cyclic resistance ratio, and CSR is the cyclic stress ratio, i.e., the seismic load that causes liquefaction. In this study, a fuzzy-neural network with 466 CPT field observations is developed first to evaluate liquefaction potential of soils. Then a search procedure is presented to locate data points on the limit state function. Finally, regression is used to determine a simple formula of limit state curve that can easily evaluate cyclic liquefaction potential of soils.

CPT-based liquefaction analysis, Part 1: Determination of limit state function

This paper is the first of a set of two papers that address the issue of earthquake-induced liquefaction potential. In this paper, a CPT-based limit state function for assessing the cyclic liquefaction resistance of sandy soils is presented. The liquefaction resistance of a soil is generally expressed as cyclic resistance ratio (CRR), while the seismic load that causes liquefaction is expressed as cyclic stress ratio (CSR). By definition, CRR is equal to the maximum CSR that a soil can sustain without the occurrence of cyclic liquefaction. In the present study, a new method to establish a limit state function for evaluating cyclic liquefaction resistance is developed. This new method is based on an artificial neural network (ANN) modelling and analysis of 225 field liquefaction performance records. First, an ANN model is developed to predict the occurrence of liquefaction based on historic field performance records. Second, a search procedure is developed to locate data points on the limit state surface. Third, another ANN model is created to approximate the multi-variable limit state function. The established approximate function, an ANN model, can be used to determine the CRR of a soil using CPT data. The developed CPT-based limit state function forms the basis for the development of a risk-based method for assessing cyclic liquefaction potential.

Cyclic liquefaction of loose gassy sand

Gas can be found in many soils, but none more common than in seabed soils. Gas-charged sediments are known to be widely distributed throughout the world's oceans. Numerous research programs have studied saturated soil response to cyclic loading; however, little is known about the behavior of gassy soils subjected to cyclic loading. The response of loose gassy specimens subjected to cyclic loading was studied in a laboratory program. Triaxial tests were performed on specimens of reconstituted Ottawa sand prepared to various gas contents and densities. The specimens were consolidated and then sheared under undrained cyclic loading. Gas content was measured at the beginning and end of each test using time domain reflectometry. The response of the gassy specimens has been shown to be influenced by the soil state and grain characteristics and the intensity, duration, and frequency of the cyclic loading. The propensity of a soil to liquefy is represented by a cyclic resistance ratio, defined as the cyclic stress ratio to cause liquefaction, or to cause a specified amount of strain. The results of this laboratory program show that the cyclic resistance ratio increases as gas content and density increase. The laboratory study demonstrates that the cyclic liquefaction potential of a soil is reduced by the addition of gas; however, soils containing some gas may still experience cyclic liquefaction provided they are sufficiently loose.Key words: triaxial testing, cyclic liquefaction, Ottawa sand, gassy, unsaturated.

Evaluating cyclic liquefaction potential using the cone penetration test: Reply

Evaluating cyclic liquefaction potential using the cone penetration test: Reply

Evaluating cyclic liquefaction potential using the cone penetration test: Discussion

The authors have presented an update on the use of the cone penetration test (CPT) for assessment of liquefaction potential. The writers consider some of the information presented to be potentially misleading. In particular, the proposed method appears to confuse the soil-identification or stratigraphic-logging phase of site exploration with the assessment of stress–strain behaviour of the soil under particular loading conditions. This may result in a short-circuiting of the design process. The writers wish to address three specific issues: (1) apparent errors in the text, (2) the link between the liquefaction definitions and the CPT screening method, and (3) the concept of “apparent fines content.”

Evaluating cyclic liquefaction potential using the cone penetration test: Reply

Evaluating cyclic liquefaction potential using the cone penetration test: Reply

Evaluating cyclic liquefaction potential using the cone penetration test: Discussion

Evaluating cyclic liquefaction potential using the cone penetration test: Discussion

Evaluating cyclic liquefaction potential using the cone penetration test

Soil liquefaction is a major concern for structures constructed with or on sandy soils. This paper describes the phenomena of soil liquefaction, reviews suitable definitions, and provides an update on methods to evaluate cyclic liquefaction using the cone penetration test (CPT). A method is described to estimate grain characteristics directly from the CPT and to incorporate this into one of the methods for evaluating resistance to cyclic loading. A worked example is also provided, illustrating how the continuous nature of the CPT can provide a good evaluation of cyclic liquefaction potential, on an overall profile basis. This paper forms part of the final submission by the authors to the proceedings of the 1996 National Center for Earthquake Engineering Research workshop on evaluation of liquefaction resistance of soils.Key words: cyclic liquefaction, sandy soils, cone penetration test

Evaluating cyclic liquefaction potential using the cone penetration test

Evaluating cyclic liquefaction potential using the cone penetration test

Static and cyclic liquefaction potential of Fraser Delta sand in simple shear and triaxial tests

The potential for static and cyclic liquefaction of the sand that underlies the highly seismic Fraser Delta is assessed under simple shear test conditions, typical of an earthquake shaking. A comparison of liquefaction potential is also made between simple shear and conventional triaxial stress conditions. It is shown that the liquefaction potential of sand is profoundly influenced by the stress path. The reduction factors currently applied to the cyclic triaxial resistance for representing simple shear response may involve a large degree of conservatism in design. A direct measurement of soil behaviour under stress conditions typical of earthquake loading may thus have large economic benefits. Key words: sand, liquefaction, static, cyclic, triaxial, simple shear.