Liquefaction Behaviour of Sand During Vibrations

Dynamic Response and Soil Properties, 2007

Under undrained cyclic loading, sand experiences decrease in effective stress, which can result in liquefaction. Test results show that large cyclic shear strain is generated at zero effective stress during undrained cyclic loading. This postliquefaction shear strain has been observed to progressively increase in amplitude with increasing number of loading cycles until it eventually stabilizes at a bounded value. However, there has been no clear explanation on why and how this cyclic shear strain is generated. The fabric mechanism behind this post-liquefaction shear strain phenomenon is briefly discussed in this study. 38.1 The Basic Phenomenon Under undrained cyclic loading, a sand sample experiences decrease in effective stress p, which can be large enough so that p approaches zero where the phenomenon of liquefaction takes place. The undrained stress path follows what is commonly known as the butterfly path shown in Fig. 38.1. Along with the reduction of p, some test results show that large cyclic shear strain is generated at a low but nontrivial shear stress values (Fig. 38.1a), but more recent evidence suggests that it is in fact generated at low enough shear stress values to be seen as zero (Fig. 38.1b, c).

Journal of Geotechnical and Geoenvironmental Engineering, 1997

ABSTRACT The state of knowledge with regard to static and cyclic liquefaction has progressed tremendously since the mid-1960s. In fact, it is generally accepted, based on the steady-state concepts of Casagrande, Castro, and Poulos that the end or steady-state condition of a liquefied loose sand is the same whether due to monotonic, cyclic, or dynamic undrained loading. Even so, a straightforward and fundamental explanation of the initiation and end-state liquefaction behavior is still needed. Toward that end, an effective stress approach that allows the assessment of the whole undrained stress-strain curve (including the peak and residual strength values) and the undrained effective stress path of a monotonic test from drained triaxial tests is presented. Results from three series of tests are shown to demonstrate the validity of the method. This method makes it possible for a geotechnical firm with the capability of performing the traditional drained test with volume change measurements to participate in static liquefaction and residual strength assessment. More importantly, it provides the conditions and logic for the development of complete versus limited liquefaction (and even dilative) response.

2017

Despite extensive amount of research on liquefaction analysis of sands, reliquefaction behavior and cyclic liquefaction resistance of cohesionless soils under a repeated cyclic load have not received the same amount of consideration. This is important as most soil deposits in high seismic areas have been subjected to repeated number of earthquakes. This paper presents series of laboratory cyclic simple shear tests on specimens of a local carbonate sand from London, Ontario. Sand specimens are reconstituted at relative densities of 25%, 45%, and 65% and subjected to effective vertical stresses of 50, 100, 200, 400, and 600 kPa. Reconstituted samples are subjected to two consecutive cyclic loads and sand behavior and liquefaction resistance are examined and compared following both cyclic loads. Reliquefaction is simulated by unloading the specimens after the first cyclic load and re-consolidating the specimen under the same initial vertical stress. A similar cyclic load is then re-app...

Mehran University Research Journal of Engineering and Technology, 2013

In this paper, the liquefaction potential of medium dense and dense sand layers was studied by performing constant volume (undrained) cyclic simple shear tests using cyclic simple shear apparatus. Strain-controlled approach was adopted. The liquefaction potential of two layers of a silty sand soil profile consisting of surface medium dense layer and underlying dense sand layers were studied. A medium dense sand surface layer exhibited flow type total liquefaction in cyclic loading in few cycles after initial liquefaction. An underlying dense sand base layer showed initial liquefaction in relatively more number of cycles and then cyclic mobility due to which pore pressure increases and decreases with cycles that is the characteristics of dense sand. The pore pressure increase and decrease is directly related to decrease and increase of effective stress.

1990

Liquefaction is a phenomenon during which saturated cohesionless soils lose a major portion of their shear strength. Liquefaction has been identified as the source of several major failures. In this study, a comprehensive program to investigate the in-situ and laboratory liquefaction potential of sandy soils was carried out. The in-situ testing program included friction cone, seismic cone, piezo-cone, and dual piezo-cone penetration tests. Several in-situ liquefaction procedures were reviewed. Four procedures were selected to evaluate the liquefaction potential of a number of sandy sublayers in two welldocumented sites in the southern Imperial Valley, California. The laboratory testing program included monotonic and cyclic liquefaction tests using two different testing equipment: triaxial and hollow cylinder cell. A new hollow cylinder cell equipment was designed, fabricated and calibrated. This new equipment allows performing monotonic or cyclic cavity expansion tests. Effect of th...

The assessment of earthquake-induced liquefaction of soils has been a major concern of Geo-technical earthquake engineering since the last century. The pioneering efforts were mostly focused on developing an understanding of the liquefaction response of clean sands. Recent field evidences of ground failure in sand with fines during strong earthquakes have highlighted the need of better understanding their behavior under saturated condition. This paper discusses the development of new criterion for assessment of liquefaction of sand with fines under earthquake forces on the foundation of analytical statistical technique Multi Criteria Decision Making (MCDM) tools such as Analytical Hierarchy Process (AHP) with Entropy method. The new criterion has positive results after assessed by the statistical technique, 'Design of Experiment'. Due to complexity of liquefaction phenomenon, a series of the static consolidated un-drained tri-axial shear test are performed on various proportions of kaolin clay in sand to confirm proposed liquefaction criterion. The results of this testing are in agreement with the previous work.

Soils and Foundations, 2021

The estimation of strength deterioration with the increase in the undrained cyclic shear-induced strain in liquefiable soils is an important topic in geotechnical earthquake engineering that is still poorly understood and needs to be properly addressed. In this paper, in an attempt to provide new insights into this topic, the post-liquefaction undrained strength and deformation of Toyoura sand were investigated through a series of laboratory tests performed by using a large-strain torsional shear apparatus. In the tests, simple shear conditions were reproduced on a medium-size hollow cylindrical specimen to apply stress conditions that soil experiences in the field during earthquakes. Specimens prepared by the air-pluviation method were first liquefied by applying a constant amplitude undrained cyclic shearing to induce a target cyclic shear-induced damage strain (c D). The tests were terminated at different amplitudes of c D and subsequently loaded monotonically in undrained conditions to obtain stress-strain and excess pore water generation responses. The test results indicate that the post-liquefaction monotonic loading (ML) stress-strain behavior of sand can be divided into three regions, namely Region 1, 2 and 3. The sand behavior changes to strain-hardening from essentially zero strength and stiffness from Region 1 to 2. While Region 3 marks the beginning of strain-softening state in the sand. It is found that the strain localization is associated with the transition of sand behavior from strain-hardening to strain-softening state. It is proposed that the sand undrained strength in monotonic shearing is the true representation of specimen response until the state of uniform deformation is maintained, based on the sudden drop of the differential stress (r d = r 0 v-r 0 h). The test results also revealed that there is a progressive degradation in the shear strength with the increase in the amplitude of c D. A correlation depicting the degradation ratio (s d) with the increase in the c D is proposed. This correlation can be used to estimate the degree of degradation with the increase in the applied c D , and it is valid for different density states, confining stresses and cyclic stress ratios.

Liquefaction risk assessment is critical for the safety and economics of structures. As the soil strata of Ramsar area in north Iran is mostly composed of poorly graded clean sand and the ground water table is found at shallow depths, it is highly susceptible to liquefaction. In this study, a series of isotropic and anisotropic consolidated undrained triaxial tests are performed on reconstituted specimens of Ramsar sand to identify the liquefaction potential of the area. The specimens are consolidated isotropically to simulate the level ground condition, and anisotropically to simulate the soil condition on a slope and/ or under a structure. The various states of soil behavior are studied by preparing specimens at different initial relative densities and applying different levels of effective stress. The critical state soil mechanics approach for identifying the liquefaction susceptibility is adopted and the observed phenomena are further explained in relation to the micro-mechanica...

Periodica Polytechnica-civil Engineering, 2023

Structures located on sandy soils can be significantly damaged by earthquake-induced liquefaction. A series of stress-controlled cyclic triaxial tests under harmonic and irregular loading under various soil densities 30%, and 50%, was conducted to evaluate the effects of irregularities and relative densities on the liquefaction characteristics of saturated sand. The irregular actual ground motions time histories obtained from six stations of the 1999 Chi-Chi Earthquake and harmonic sinusoidal cyclic loading time histories were applied to Firoozkooh #161 sand specimens, and the results were compared in terms of the type waveforms loading and relative densities. Based on the stress and energy method, the Correction coefficient is calculated for a variety of densities and types of irregular loading. The present results reveal that it is not precise to assume a single correction coefficient for all records, regardless of the complicated time-domain characteristics of ground motions. Furthermore, the results indicate that the relative soil density and the type of irregular loading influenced sand's pore pressure generation and liquefaction potential.

2010

Determining the residual strength of liquefied sand is essential for estimating post-earthquake stability of vulnerable earth structures, or calculating runout of liquefaction flow slides. Current practice is to select values from a database of back-calculated residual strengths from failure case histories , which have been related to representative penetration test resistance numbers in the failed materials. Given the uncertainties involved, it is desirable to compare the field data with laboratory tests under controlled conditions. This paper describes residual strength measurements for a uniform fine sand using two recently-developed tests designed to impose large strains and strain rates: a modified triaxial test in which a metal coupon is dragged through the liquefied sample by an external dead weight, and a ring shear device which can impose constant rates of strain on the liquefied sand. In all cases, a stress-thinning behavior is observed; however, coupon movement through the liquefied sand is basically laminar, representing conditions in the interior of a flowing mass, while the rotating ring creates a well-defined contact shear band and higher resistance, which might be considered more representative of flow at the base of a sliding mass. Comparison with back-calculated field values shows that coupon residual strengths plot at the lower bound, and ring shear results at the upper bound, of backcalculated field values.