Liquefaction Resistance Of Sandy Soils Research Articles

Liquefaction resistance and small strain stiffness of silty sand: Effects of host sand gradation and fines content

In this paper, a well designed experimental study comprising undrained cyclic triaxial and bender element tests was carried out on five sand-silt mixtures with three grain size ratios (Rd) and three sand uniformity coefficients (Cus). The results reveal that at given fines content (FC) and void ratio, the liquefaction resistance (CRR) of the mixtures decreases as Rd increases from 9.7 to 27.8 or Cus from 1.50 to 4.46, and the CRR of the mixture at the highest Rd or Cus becomes as low as nearly 50% of that at the lowest Rd or Cus. The equivalent relative density (Dr*) based on the binary packing theory can be utilized to capture the coupled effects of host sand gradation and FC on the CRR of sand-silt mixtures. A novel finding is that a universal relationship exists between the liquefaction resistance and the shear modulus normalized by the minimum void ratio function of host sand (GN') for different FCs, initial effective confining pressures, sample preparation methods (SPMs), and host sand gradations. Based on the comprehensive laboratory test data, the empirical CRR15-GN' correlation is proposed and further adjusted for the field liquefaction triggering analysis based on the shear wave velocity (Vs). Soil can be considered non-liquefiable when its equivalent shear wave velocity exceeds 225 m/s or the applied cyclic stress ratio (CSR) is below 0.088. Comparisons with the previously established liquefaction triggering boundary curves validate the applicability of the proposed curve for initial evaluation of the liquefaction resistance of sandy soils, indicating laboratory studies can complement in-situ investigations for Vs-based liquefaction assessment.

Effects of prior non-liquefying undrained cyclic loading on sand liquefaction resistance via discrete element analysis

Earthquake cases demonstrate that prior earthquakes have critical impacts on the liquefaction resistance of sandy soils during subsequent earthquakes. Most previous studies focused on the influence of previous liquefaction events on soil reliquefaction resistance, while few have investigated the effects of prior non-liquefying undrained cyclic loading history on the liquefaction resistance. In this study, discrete element method (DEM) was employed to simulate the liquefaction behaviors of triaxial specimens reconsolidated from non-liquefying states during prior undrained cyclic tests with various cyclic stress ratios (CSRs). Results showed that prior non-liquefying loading could increase or decrease the sand liquefaction resistance, which significantly depended on the CSR of the prior loading and the excess pore pressure ratio (ru) caused during the prior loading. Specimens that were previously loaded under larger CSRs had stronger anisotropy and fewer interparticle contacts after reconsolidation and thereby exhibited lower liquefaction resistance, while specimens that were reconsolidated from prior tests with smaller CSRs had weaker anisotropy and more interparticle contacts and thus exhibited obviously higher liquefaction resistance. Sand liquefaction resistance after a prior non-liquefying loading was well correlated with initial anisotropic degree and mechanical average coordination number.

Hierarchical Bayesian Approach to Estimating Variability of Liquefaction Resistance of Sandy Soils Considering Individual Differences in Laboratory Tests

Hierarchical Bayesian Approach to Estimating Variability of Liquefaction Resistance of Sandy Soils Considering Individual Differences in Laboratory Tests

Unique relation between pore water pressure generated at the first loading cycle and liquefaction resistance

Accurate evaluation of excess pore water pressure (EPWP) generated in earthquake vibration is a key important factor in seismic engineering against liquefaction. Most previous studies were focused on the relation between cyclic resistance and EPWP developed in the entire liquefaction process. Only a few researchers pointed out that the maximum EPWP ratio accumulated at the first loading cycle, represented by (Δu/p0)max−N1, was intimately related to the liquefaction resistance of sand. Based on this viewpoint, liquefaction resistance of sandy soils can be improved significantly by repressing EPWP at the first cycle by engineering countermeasures. The relationship between (Δu/p0)max−N1 and liquefaction resistance or the cyclic number to liquefaction Nf, however, has not been established quantitatively yet. Moreover, whether this relationship is influenced by stress states such as liquefaction-induced anisotropy, structure or fabric of soils, and loading conditions, is not clear yet. Therefore, a series of undrained cyclic triaxial loading tests were conducted on Toyoura sand, a clean sand famous in Japan, to identify the above-mentioned uncertainties. Based on the test results, a unique empirical (Δu/p0)max−N1-Nf relation was proposed to evaluate the liquefaction resistance. Finally, three typical samples were given to display the application of (Δu/p0)max−N1-Nf relation.

Undrained cyclic response of a dense saturated sand with various grain sizes and contents of nonplastic fines: Experimental analysis and constitutive modeling

The densification can increase the liquefaction resistance of sands. However, in most engineering practice, sands are not pure and contain a significant amount of fines with particle diameter smaller than 0.075 mm. Thus, it is necessary to quantitatively evaluate the influence of fines on the undrained cyclic behavior of dense sandy soils. In this study, a series of undrained cyclic triaxial tests were conducted on the dense saturated sand with various mean grain sizes and contents of nonplastic fines. A unified constitutive framework is modified to improve the capability of simulating the cyclic mobility behavior of sandy soils. The results indicate that the effect of the mean grain size on the cyclic stress ratio required to cause 5% double-amplitude axial strain for sandy soils depends on the amount of nonplastic fines added. Moreover, a good correlation between the cyclic resistance ratio and the initial value of the equivalent granular state parameter is obtained for various fines contents and mean grain sizes of nonplastic fines. The influence of the fines content and mean grain size of nonplastic fines on the liquefaction resistance of sandy soils can be reasonably characterized by the constitutive framework using a set of unique parameters. Additionally, the capability of the constitutive framework for describing the influence of the fines content on the cyclic instability behavior of sandy soils is also evaluated against the experimental data in the literature.

Evaluation of Thawing and Stress Restoration Method for Artificial Frozen Sandy Soils Using Sensors.

Undisturbed frozen samples can be efficiently obtained using the artificial ground freezing method. Thereafter, the restoration of in situ conditions, such as stress and density after thawing, is critical for laboratory testing. This study aims to experimentally explore the effects of thawing and the in situ stress restoration process on the geomechanical properties of sandy soils. Specimens were prepared at a relative density of 60% and frozen at −20 °C under the vertical stress of 100 kPa. After freezing, the specimens placed in the triaxial cell underwent thawing and consolidation phases with various drainage and confining stress conditions, followed by the shear phase. The elastic wave signals and axial deformation were measured during the entire protocol; the shear strength was evaluated from the triaxial compression test. Monotonic and cyclic simple shear tests were conducted to determine the packing density effect on liquefaction resistance. The results show that axial deformation, stiffness, and strength are minimized for a specimen undergoing drained thawing, restoring the initial stress during the consolidation phase, and that denser specimens are less susceptible to liquefaction. Results highlight that the thawing and stress restoration process should be considered to prevent the overestimation of stiffness, strength, and liquefaction resistance of sandy soils.

Liquefaction resistance of Christchurch sandy soils from direct simple shear tests

A series of cyclic direct simple shear tests are performed to investigate the liquefaction resistance of sandy soils from Christchurch, New Zealand. The study focuses on the combined effects of soil density and fines content on liquefaction resistance of sandy soils. Two sands, a non-plastic silt, and their mixtures prepared at different fines contents are tested at two sets of relative densities. Test specimens are reconstituted using a procedure for water sedimentation, yielding soil fabric and soil structure resembling those of fluvial soil deposits. Differences are observed between the two host sands in the sensitivity of the cyclic liquefaction resistance to changes in relative density. Differences are also seen in the effects of the addition of fines to the liquefaction resistances of the two sands. Monotonic undrained direct simple shear tests are employed to explore an interpretation of the liquefaction resistance of the tested soils within the critical state framework. The state-concept interpretation provides more consistent quantification of the effects of initial state on the liquefaction resistance; however, the relationship between the state parameter and liquefaction resistance is soil dependent. The results of cyclic direct simple shear tests for soils containing up to 30% fines show reasonably consistent liquefaction resistances relative to estimates from empirical CPT-based liquefaction triggering relationships.

Effects of high-diluted colloidal silica grouting on the behaviour of a liquefiable sand

The effectiveness of colloidal silica (CS) treatment in increasing the liquefaction resistance of sandy soils is by now amply demonstrated. However, the best value of the CS content to achieve high performance, minimising economic cost and impact on buildings and the environment, has not yet been quantified. This paper presents the results of a laboratory study aimed to evaluate the influence of different CS contents on the behaviour of a liquefiable sand. The investigation included direct shear, cyclic triaxial, hydraulic conductivity and oedometer tests. CS contents 0, 2 and 5% (by weight) were used for all tests, except for direct shear tests (CS contents 0 and 2%) and oedometer tests (CS contents 0, 2, 3, 5, 10 and 13%). The test results showed that 2% CS content was enough to increase the soil strength under cyclic and monotonic loading conditions. The hydraulic conductivity of treated soil decreased significantly as CS content increased. Oedometer tests pointed out that the main disadvantage of CS treatment is the soil compressibility increase. On the basis of the obtained results, 2% CS content seems to be recommended because it shows effectiveness and capability to improve the liquefaction resistance of sand while minimising the soil compressibility increase.

Experimental Research on Effect of Fines Content on Liquefaction Properties of Sand

Liquefaction is a phenomenon mainly occurred in saturated fine grained soils under major earthquakes causes tremendous loss to infrastructure. From the literature it has been observed that liquefaction not only occurs in fine sands but also occurs in sands containing some amount of fines particles, which are of less than 75µ in size. Unfortunately there is no clear conclusions given as how effect the fines content on liquefaction resistance of sandy soils. In order to solve above mentioned problem this study was undertaken through stress-controlled cyclic triaxial tests to know the effect of fines content on liquefaction resistance of sandy soils. In this study the program of experimentation was done on base sand and sand mixed with four different combinations of fines like 10%, 20%, 30%, and 40% of fines with base sand by weight.. The main parameters changed in this work were percentage fines and shear stress ratio (CSR ), where the observed parameter was amount of pore water pressure and cycle of loading.. The result showed that, rate of pore water pressure generation during cyclic loading was largely affected by limiting silt content and density index. The trend observed as amount of pore water pressure is increased more than base sand with adding of fines content up to 20%, later the trend observed as reverse. And also noticed that more CSR value increases the pore water pressure generation and decreases the cyclic resistance

Liquefaction Resistance of Sandy Soils from Undrained Cyclic Triaxial Tests

Recent earthquakes frequently showed liquefaction of sandy soils. In these case one of the major challenges is the assessment of the residual strength of liquefied soil. Laboratory researches have clearly indicated that liquefaction susceptibility depend on many factors including soil grain size distribution, effective confining stresses and applied stress path in terms of cyclic shear stress amplitude. The complex cyclic shear stress path experienced by the soil during an earthquake can be reproduced in laboratory only by using sophisticated testing apparatuses. Cyclic triaxial tests have been widely used to asses soil liquefaction potential especially for coarse-grained soils, as in this study. In the framework of the design for the seismic retrofitting of the “Viadotto Ritiro” foundations along the A20 motorway connecting Messina with Palermo, a soil liquefaction study has been carried out. With this aim, a detailed geological and geotechnical characterization of the area has been performed by in situ and laboratory tests including the combined resonant column and torsional shear test and undrained cyclic triaxial tests (CTX). In particular, the paper presents the results of CTX, carried out on isotropically consolidated specimens carried out on specimens of a sandy soil to asses liquefaction strength. The results are plotted in terms of deviator stress q versus axial strain ea, cyclic stress ratio CSR and axial strain ea versus number of cycles Ncyc, effective mean stress p′ versus deviator stress q, cyclic stress ratio CSR and pore pressure ratio Ru versus number of cycles Ncyc. The results show that the cyclic resistance increases with the decrease in the initial confining stress and decreases as the silt content increases and confirme that the coarsest material has a lower tendency to liquefy.

Preshake: A Database for Centrifuge Modeling of the Effect of Seismic Preshaking History on the Liquefaction Resistance of Sands

Several researchers found that the behavior of natural preshaken soils can be very different from artificial recent fills. This paper presents an extensive database of two very long centrifuge experiments (CS-5-1-1 and CC-5-1-1) performed both on silty and clean sand at the geotechnical centrifuge testing facility at Rensselaer Polytechnic Institute (RPI). The two experiments test the effect of seismic preshaking history on the liquefaction resistance of sandy soils. The database described herein was generated using the NEEShub online DataStore tool under the name “PRESHAKE: Centrifuge modeling of the effect of seismic preshaking on the liquefaction resistance of sands” (DOI: http://dx.doi.org/10.4231/D38K74X78 ). The paper discusses the tools and materials used in the experiments along with an explanation of each item in the database. Sample analyses are also presented in the paper to give an insight on the capabilities of the database for numerical and analytical applications. The paper is concluded with some possible applications along with tips and limitations of the database.

Evaluation of cyclic shear strength of mixtures with sand and different types of fines

ABSTRACTSoils are classified as sandy soils and clayey soils in most soil classification systems, and appropriate equations are used for practical design, depending on soil type, to represent each soil behavior. Sand-clay mixtures, however, need a special standard to evaluate their specific behaviors since they are categorized as intermediate soils or transitional soils and typically show intermediate properties. In this article, a series of cyclic triaxial tests were conducted on specific sand-fines mixtures with three fine types and various fine contents. The behaviors of various soil mixtures (silica sand with Iwakuni natural clay, Tottori silt, and Kaolin clay) were investigated by considering a concept of granular void ratio expressed in terms of sand structure. The cyclic shear strengths of the soil mixtures were also evaluated by increasing the fine content but no more than the threshold fine content. In the results, the cyclic deviator stress ratio decreased in dense soils whereas it increased in loose soils by increasing the fine content. In addition, a simple equation was proposed to predict the liquefaction resistance of sandy soils by evaluating the cyclic deviator stress ratio with a concept of equivalent granular void ratio.

排水条件下の繰返しせん断履歴や高温環境での圧密によって年代効果を付与した砂質土試料の液状化特性

年代効果による液状化強度の上昇が土の微視的骨格構造の安定性向上の反映であるという観点に立ち，排水条件下の繰返しせん断履歴および高温環境下の圧密等による砂質土の液状化強度の上昇を検討するとともに年代効果の付与として評価した。その結果，上昇させられる液状化強度の範囲や再現性および異方性等が明らかになった。さらに両者による効果は繰返しせん断履歴で数千年分，高温圧密で実圧密時間の1000倍程度の年代効果に対応する可能性があることが明らかになった。

Liquefaction Resistance of Sands Containing Plastic Fines with Different Plasticity

Soils in the field or at reclaimed sites commonly contain some amount of silt or clay rather than clean sand only. The effect of a low fraction of plastic fines within sand matrix on liquefaction resistance is not clearly understood. In this study, clean sand was mixed with 10% plastic fines having different plasticity indexes (PIs), and the effect on liquefaction resistance was evaluated in terms of cyclic stress ratio. A series of undrained cyclic triaxial tests were carried out on loose, medium, and dense specimens that were reconstituted in the laboratory by the undercompaction method. The results showed that liquefaction resistance tended to decrease as the PI of 10% fines in the specimens increased. Liquefaction resistance of loose specimens was marginally influenced by the plasticity of fines. However, in the case of dense specimens, liquefaction resistance decreased up to 40% as the PI of 10% fines increased. It was shown that even though a low fraction of plastic fines was included within sand matrix, it still had a significant effect on the liquefaction resistance of sandy soils.

Preparation of fully saturated models for liquefaction study

The degree of saturation significantly influences the liquefaction resistance of sandy soils. In preparation of models for dynamic centrifuge tests and 1g shaking table tests, however, the degree of saturation has not been accurately controlled. A technique to prepare fully saturated model ground for liquefaction study is summarised in this paper, focusing on how vacuum pressure and centrifugal acceleration during the saturation process affect the degree of saturation. A method to evaluate degree of saturation of models accurately is developed first. Then, a total of ten experiments were conducted in which water was introduced to dry sand deposits at different atmospheric pressures at different centrifugal accelerations. It is confirmed that increased acceleration contributes to enhance degree of saturation and reduces time for the saturation process. Two dynamic centrifuge tests on models with different degrees of saturation, one almost fully saturated and the other slightly unsaturated, with the difference in degree of saturation between the two models being 1·5%, were conducted. Differences in excess pore pressure responses between the two models became more significant as the depth increased. It is concluded that a precise control of degree of saturation on the order of 0·1% is important in model tests related to liquefaction problems.

Energy-based numerical models for assessment of soil liquefaction

This study presents promising variants of genetic programming (GP), namely linear genetic programming (LGP) and multi expression programming (MEP) to evaluate the liquefaction resistance of sandy soils. Generalized LGP and MEP-based relationships were developed between the strain energy density required to trigger liquefaction (capacity energy) and the factors affecting the liquefaction characteristics of sands. The correlations were established based on well established and widely dispersed experimental results obtained from the literature. To verify the applicability of the derived models, they were employed to estimate the capacity energy values of parts of the test results that were not included in the analysis. The external validation of the models was verified using statistical criteria recommended by researchers. Sensitivity and parametric analyses were performed for further verification of the correlations. The results indicate that the proposed correlations are effectively capable of capturing the liquefaction resistance of a number of sandy soils. The developed correlations provide a significantly better prediction performance than the models found in the literature. Furthermore, the best LGP and MEP models perform superior than the optimal traditional GP model. The verification phases confirm the efficiency of the derived correlations for their general application to the assessment of the strain energy at the onset of liquefaction.

Liquefaction Resistance of Sandy Soils under Partially Drained Condition

In order to simulate the effect of drainage on soils adjacent to gravel drains that are installed as countermeasure against liquefaction, several series of cyclic triaxial tests were performed on saturated sands under partially drained conditions. The condition of partial drainage under cyclic loading was simulated in the laboratory using triaxial testing equipment installed with a drainage control valve to precisely regulate the volume of water being drained from test specimens. Effects of both drainage conditions and loading frequencies on cyclic response were incorporated through the coefficient of drainage effect, α* . Experimental results showed that for sand exhibiting strain softening, the partially drained response was controlled by the critical effective stress ratio while for sand showing strain hardening behavior, the controlling factor was the phase transformation stress ratio. Moreover, test results indicated that the minimum liquefaction resistance under partially drained conditions can be u...

Laboratory Investigation on Assessing Liquefaction Resistance of Sandy Soils by Shear Wave Velocity

Shear wave velocity ( Vs ) offers engineers a promising alternative tool to evaluate liquefaction resistance of sandy soils, and the lack of sufficient in-situ databases makes controlled laboratory study very important. In this study, semitheoretical considerations were first given based on review of previous liquefaction studies, which predicted a possible relationship between laboratory cyclic resistance ratio ( CRRtx ) and Vs normalized with respect to the minimum void ratio, confining stress and exponent n of Hardin equation. Undrained cyclic triaxial tests were then performed on three reconstituted sands with Vs measured by bender elements, which verified this soil-type-dependent relationship. Further investigation on similar laboratory studies resulted in a database of 291 sets of data from 34 types of sandy soils, based on which the correlation between liquefaction resistance and Vs was established statistically and further converted to equivalent field conditions with well-defined parameters, reve...

Interpretation of Penetration Resistance for Back-analysis at Sites of Previous Liquefaction

Liquefaction and paleoliquefaction studies are being used increasingly to interpret ground motion parameters ( i.e. , acceleration distribution, earthquake magnitude, and epicentral location) in regions of the world that experience infrequent, but damaging, earthquakes. These studies are especially applicable when the most recent damaging earthquakes occurred prior to the development of ground-motion instrumentation. For example, Martin and Clough (1994) examined liquefaction features formed during the 1886 Charleston, South Carolina earthquake; Pond (1996) and Obermeier and Pond (1999) examined paleoliquefaction features formed during a number of paleoearthquakes in the Wabash Valley region along the Indiana–Illinois border; Dickenson and Obermeier (1998) and Obermeier and Dickenson (2000) examined paleoliquefaction features formed during the 1700 Cascadia earthquake of the Pacific Northwest; and Ellis and de Alba (1999) recently examined liquefaction features formed during the 1755 Cape Ann, Massachusetts earthquake. Many of these studies back-calculate seismic parameters using the results of penetration tests conducted long after the earthquake. The most common method to back-calculate a lower-bound peak ground surface acceleration is to use the lowest value of penetration resistance obtained at a historic or paleoliquefaction site in conjunction with a correlation for liquefaction resistance of sandy soils, e.g. , Seed et al. (1985) or Stark and Olson (1995). In some studies, the current value of penetration resistance is assumed to be the “representative” value for back-analysis ( e.g. , Pond, 1996), while in other studies corrections are made to the current value of penetration resistance prior to back-analysis ( e.g. , Ellis and de Alba, 1999). This paper examines some of the factors that affect the interpretation of a “representative” penetration resistance for back-analysis of seismic parameters. The interpretation of these factors is illustrated using an example historic liquefaction site. The back-calculated values of a max from the example case history show the sensitivity of the back-analysis …

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.