Liquefaction Strength Research Articles

Stress-strain behavior and liquefaction strength characteristics of Ottawa F65 sand

The stress-strain-strength response of soils is of significant interest to development and calibration of realistic constitutive models that can be used in numerical simulation of geotechnical engineering problems. An extensive characterization of Ottawa F65 sand along with various monotonic and cyclic tests conducted during the course of the Liquefaction Experiments and Analysis Projects (LEAP) are presented here. The specimens in these tests were prepared using a meticulous sample preparation technique to facilitate their consistency and repeatability. Monotonic drained and undrained triaxial tests shed light on the steady-state (critical state) of Ottawa sand, while stress-controlled and strain-controlled cyclic triaxial and direct simple shear tests provide key information on the cyclic stress-strain behavior and liquefaction strength of this soil. The triaxial tests identify the liquefaction strength of the soil at different densities, while the direct simple shear tests evaluate the effect of overburden pressure on the cyclic response. The results of these experiments are also compared to the experimental results available in the literature. The data obtained from the cyclic triaxial and direct simple shear tests were further analyzed by plotting the computed shear modulus degradation and damping curves. The results show how the soil stiffness degrades as cyclic shear stress is applied for soil at different densities and confining stresses. It can be seen that the rate of shear modulus degradation increases with the increase of confining stress and decreases with the increase of soil density. The damping curves consistently show an increasing in damping ratio until a shear strain of about 0.05%, followed by a plateau at about 20–25% damping ratio for shear strain between 0.05 and 0.5%, and ending with a decrease in damping until reaching a final damping ratio of about 10%.

Evaluation of liquefaction strength curve using cumulative dissipated energy

Evaluation of liquefaction strength curve using cumulative dissipated energy

The effects of base motion variability and soil heterogeneity on lateral spreading of mildly sloping ground

Centrifuge modeling has been used to observe some key characteristics of liquefiable soils during seismic motions. If carefully conducted, the results of centrifuge tests can be used for validation of constitutive models and numerical modeling tools. However, a thorough evaluation of numerical models requires knowledge of the soil properties and the uncertainties associated with these properties. Moreover, the base excitations achieved in centrifuge tests often vary from the target base excitation, and a fair evaluation of the quality of blind prediction of a centrifuge test requires an account of the uncertainties associated with the achieved base motion. This paper presents an analysis of the effects of the inherent variability present in the soil density and base motion on the lateral spreading of mildly sloping ground. The analysis combines fully-coupled non-linear finite element modeling with Monte Carlo simulation. The stochastic analysis is based on the variabilities observed in the density of the soil specimens and in the achieved base motions of the centrifuge tests conducted for the Liquefaction Experiments and Analysis Projects (LEAP): LEAP-GWU-2015 and LEAP-UCD-2017. The two-surface plasticity model for sand is used to model the soil response. The model is calibrated against element tests performed on Ottawa-F65 sand to determine its liquefaction strength. The finite element model is pre-validated through deterministic simulation of the centrifuge experiments conducted during the LEAP project. The sources of variability are identified and their magnitudes are quantified based on the results obtained from the LEAP centrifuge experiments. First, the effects of the soil spatial variability are presented. Then, the effects of the base motion variability are discussed. Finally the combined effects of the variability in the soil density and base motion are evaluated. The results obtained from the stochastic analysis are compared with the variability in the soil response observed in the centrifuge experiments. The results obtained from this study show that by carefully modeling the different sources of variability, the stochastic analysis was able to model the observed variability in the lateral displacement of the centrifuge experiments. The results obtained confirm the observation that the lateral displacement of liquefiable soil is more sensitive to the base excitation variability than the variability in the soil density.

Depth distribution of liquefaction strength characteristics at a site damaged by the Great East Japan Earthquake and predictions of liquefaction

Depth distribution of liquefaction strength characteristics at a site damaged by the Great East Japan Earthquake and predictions of liquefaction

Effects of gravel content on liquefaction resistance and its assessment considering deformation characteristics in gravel – mixed sand

Many reports describe overestimation of liquefaction resistance based on sounding data related to ground materials containing coarse particles such as gravel and cobbles. Better methods of liquefaction potential estimation must be developed using investigation data other than those from sounding. Gathering perfect and undisturbed samples is difficult, but using seismic methods such as PS logging might be effective for assessing liquefaction potential. For this study, bender element (BE) tests and local small strain (LSS) tests were conducted, respectively, to measure the dynamic and static shear moduli of gravel – mixed sand specimens. Subsequently, relations between liquefaction strength and secant shear moduli were examined to provide reliable estimation of liquefaction in gravel – mixed sand. Although the liquefaction resistance increased considerably with overconsolidation, the initial shear modulus exhibited only a slight change with the same overconsolidation. The experimentally obtained results elucidated that the important shear strain level, for which secant shear modulus has a strong relation with liquefaction strength, was not a linear elastic region of 0.001%: it was about 0.01%.

The Low Viscosity Loess Liquefaction and its Microstructure Analysis

Low viscosity powder loess is widely distributed in loess plateau areas of northwest China. It has a high liquefaction potential. the mechanism of low viscosity loess water action is studied using CT scanning. CT scanning results showed that initially, water in loess will tend to rise as a whole. Then, cement salts around the loess grains melt and form large holes. Finally, deformation collapse and damage can occur. In this study, low viscosity loess is compared with sand loess and clayey loess obtained from Lanzhou, Guyuan, and Tongguan. Based on the results of dynamic triaxial torsion tests, the low viscous powder loess dynamic loading time was shorter and more easily liquefied than sandy loess and clayey loess. Electron microscope scanning of loess microstructures showed the chemical element ratios around the loess particles produced cemented material (such as Ca/Fe). The chemical elements around loess particles and the pore diameter/grain ratio were selected to evaluate liquefaction resistance in loess. In addition, loess particle size distribution and the pore/grain ratio also influenced the liquid level. It is an effective innovative method to judge the liquefaction strength of low viscosity silt based on microcosmic parameters.

Influence of initial conditions on the liquefaction strength of an earth structure

Liquefaction has been the major source of damage for structures and infrastructures in most recent earthquakes, as it induces loss of strength and stiffness in soils, resulting in settlement of buildings, landslides, and failure of pipelines and earth dams. Such a phenomenon is primarily associated with saturated cohesionless soils and strong-motion seismic events able to induce pore water pressure build-up. Even though the degree of soil saturation is strictly related to the oscillation of groundwater table and to the interaction flows (namely precipitation and evaporation) between the exposed surface and the atmosphere, the initial distribution of pore water pressure is commonly simplified in liquefaction potential analysis and the presence of unsaturated soil layers is almost always neglected. To try to fill this gap, this work investigates the effect of the initial distribution of pore water pressure on the liquefaction strength evaluation, considering the potential presence of unsaturated soil layers. The work uses as case-study a well-investigated inhabited levee damaged by the 2012 Emilia earthquake. The initial distribution of pore water pressure within the dyke is carried out by solving the Richards equation in steady-state and transient conditions, assuming as boundary conditions the evolution of potential flows recorded at the site in the time period including the earthquake event. The cyclic resistance of unsaturated soils is considered during the execution of dynamic analyses in effective stress conditions. Results of the analyses show that initial conditions influence the liquefaction strength of earth structure and that neglecting the cyclic resistance of unsaturated soils is not a conservative assumption.

모래의 입도분포와 세립분 함유량에 따른 액상화 저항특성 비교

The liquefaction phenomenon occurs when the groundwater is pumped up through the top of sediments as the pore pressure increases due to the earthquake. There have been many studies on the loose sandy soils and various samples through repeated triaxial compression tests and shaking table tests, but there have been few studies on the effects of particle size distributions and the fine contents of sand on the liquefaction of sand. In this study, the undrained repeated triaxial compression tests were performed on sands with different particle size distributions, confining pressures, relative densities, and deviatoric stresses. The results of analysis showed that, with increasing relative density, SW(Well-graded sand) samples had higher liquefaction strength than SP(Poor-graded sand) samples. This is due to the lower void ratio of sand in SW samples than in SP samples. It was also found that the liquefaction strength decreased with a high fine content due to he rapid destruction of the filling of fine particles between the soil particles, leading to lower liquefaction strength.

Pre-shaking effects on volumetric strain and cyclic strength of sand and comparison to unsaturated soils

Repeated small shaking events due to earthquakes significantly enhance liquefaction resistance of soils. Analyses of liquefaction case histories show that aged soils in seismically active zones tend to be less vulnerable to liquefaction despite having similar index parameters—such as standard penetration test N-values and shear wave velocities—as young soils. Significant efforts have been devoted to better understand the effects of the cyclic pre-shearing on liquefaction resistance and it was found that this effect depends on the number of cycles and cyclic stress ratio. However, none of these parameters quantify the improvement of liquefaction resistance due to pre-shaking. This study investigates the pre-shearing effects on liquefaction resistance through laboratory tests and centrifuge tests. An attempt was made to explain the effects quantitatively with a single index parameter of the volumetric strain caused by pre-shearing. It was confirmed from triaxial tests that the liquefaction resistance of pre-sheared sand uniquely increased with increasing volumetric strain regardless of the cyclic shear stress ratio and the number of cycles during the pre-shearing. To examine the pre-shaking effects on the liquefaction strength of sand under a level ground condition, centrifuge tests were conducted in this study. Sand models were subjected to small shaking events repeatedly, which were weak enough not to cause liquefaction. It was observed that changes in the index parameters of the models, including soil density (volumetric strain), shear wave velocity, and horizontal earth pressure during the pre-shaking events were very small. At the end of the test, the sand was subjected to a strong shaking event because models that had gone through pre-shaking need larger shaking acceleration to liquefy. Liquefaction resistance was derived from acceleration records with the aid of the cumulative damage theory. The relationship between liquefaction resistance ratio and volumetric strain that occurred in the pre-shaking events coincides with the relationship obtained from the triaxial tests. After the extensive liquefaction event, all index parameters except soil density—K0, Vs, liquefaction resistance—tended to return to their original values (before the pre-shaking).

Effect of flyash on liquefaction behaviour of sand-bentonite mixture

This manuscript analyses the effect of flyash (FA) on liquefaction behaviour of sand-bentonite (SB) mixture by conducting a series of undrained monotonic triaxial compression tests. The effect of adding 5% bentonite and three FA contents (i.e., 3, 5 and 7) at three relative densities (i.e., 10, 20, and 30%) on liquefaction behaviour of clean sandy soil were investigated. The analysis on shearing responses of the SB mixtures showed that the addition of bentonite reduced the ultimate deviatoric stress. Investigation on the effect of FA on shearing behaviour of SB specimens showed that the addition of FA caused a greater peak deviatoric stress and the formation of a non-flow behaviour. Furthermore, analysis of the effect of relative density showed that the peak deviatoric stress (qmax) is greater at a higher relative density in particular in FA treated specimens. The results showed that addition of FA into SB mixtures, caused more stability for the samples at peak state while the stress ratio value (q/p′) increased and the state parameter (Ψ) reduced. A similar behaviour observed for slope factor (Mcs) in stress-strain plane (q-p′), and for slope of critical state line (λcs), and intercept (Γcs) in compression plane (e-p′). Finally, investigation on the liquefaction behaviour of the specimens based on brittleness index (IB) showed that the untreated soil and SB specimens have a lower liquefaction strength than the FA treated specimens.

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.

Liquefaction resistance of fibre reinforced low-plasticity silt

This study sought to investigate the effect of bulk continuous filament (BCF) on the liquefaction resistance of low plasticity silt by performing a series of cyclic triaxial tests on the reference (unreinforced) and reinforced specimens. The effects of BCF contents and length (BL), relative density (Dr), and effective confining pressure (σ'3) on the liquefaction strength of the reinforced specimens were investigated and the results were compared with the reference tests. The results showed that increasing the BCF content improved the liquefaction resistance of the silt. Also, it was noted that increasing the fibre length from 5-mm, to 10-mm and 15-mm respectively, increased the liquefaction resistance of the specimens. The results in the next stage showed that by increasing the relative density (Dr), liquefaction resistance of a reinforced specimen is more pronounced than that of an unreinforced specimen. Finally, investigations on the effect of effective confining pressure (σ'3) on the liquefaction resistance of the reinforced specimens showed that increasing the effective confining pressure reduced the liquefaction resistance of the specimens due to suppression of the dilatancy.

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.

Liquefaction resistance of sand remediated with carbonate precipitation at different degrees of saturation during curing

In recent years, innovative soil improvement methods have provided more environmentally friendly and sustainable solutions for liquefaction countermeasure techniques. One such technology is enzymatically induced calcite precipitation (EICP), in which urease enzyme is used, instead of bacteria, as a promoter for the hydrolysis of urea. Utilizing the urease enzyme itself, which causes Ca2+ and CO32− to precipitate CaCO3 crystals in the void spaces and surface of grains, is more straightforward than using bacteria. In this study, the effects of the degree of saturation during the precipitation of calcite on the behavior of sand that has been lightly cemented using EICP were investigated through a series of undrained cyclic triaxial tests. Liquefaction strength curves correlating the cyclic stress ratio with the number of cycles needed to cause 5% double amplitude (DA) axial strain were compared for treated and untreated sand. It was found that the lower the degree of saturation during calcite precipitation and the higher the calcite content in the samples, the higher the liquefaction resistance of the EICP-treated sand. This can be clearly explained by the spatial distribution of the calcite in the sand. Microscopic observations by scanning electron microscopy (SEM) revealed that, in sand cured at a lower saturation degree, the precipitated calcite tended to be more concentrated at particle contacts than was the case in fully saturated sand. It was confirmed that only 1% of calcite precipitation at a lower degree of saturation (30%) can double the liquefaction resistance. However, excessive strain in the order of 1% degrades the bonding between sand particles.

A STUDY ON GROUND IMPROVEMENT TECNIQUE WITH IN-SITU MICROOGANISMS ISOLATED FROM JAPAN

Damage by a liquefaction phenomenon was a problem in recent years, and the Great East Japan Earthquake occurred on March 11, 2011 in Japan, and liquefaction damage occurred frequently. There is also more adoption of Paris agreement in COP21 of the end of last year, and correspondence to a global warming problem is also desired reduction in greenhouse effect gas amount of emission in the construction field. Therefore considered ground improvement technology is necessary for the environment in Japan an earthquake-ridden country. So we considered for practical use ground improvement techniques based microorganism. That is watched as new liquefaction countermeasure technology for reduction in cost and the point of view by which material and construction waste are reduction. In that ground improvement techniques, it is difficult to using specific microbes. So we aimed at Microbial carbonate precipitation using in-situ microorganism as the method to solve this problem. We made solidify sand using isolated microorganisms in japan and Bacillus pasteurii the solidification ability becomes clear. We measured to urease activity values of each microorganism. And we making of the test pieces, undrained cyclic triaxial test and acid decomposition for using CaCO3(0.5mol/L). And we compared results. We understood two things from examination results. 1) The difference occurs to liquefaction strength by urease activity value. 2) The improvement effect of the liquefaction strength was admitted in Microbial carbonate precipitation using insitu microorganisms in the spots selected by this research.

Experimental study on effect of fly ash on liquefaction resistance of sand

A series of cyclic triaxial tests were performed to determine the liquefaction resistance of sand stabilised with fly ash (FA). In order to understand the cyclic behaviour of the FA stabilised sand, the effect of relative density (Dr), FA content, confining pressure (CP) and curing time liquefaction resistance were considered. In the first stage of the laboratory tests, specimens of sand mixed with 2% FA under 50 kPa CP and 0.2 CSR with relative density of 20%, 40%, 60%, and 80%, were tested and compared with untreated soil. The results indicated that mixtures of sand-FA in all relative densities have more resistance to liquefaction failure in comparison with untreated soil, and mixture of sand-FA for relative density of 80% has the greatest resistance value. In the second stage, two types of sand-FA mixture (i.e., 4% and 6% FA) with a relative density of 20% under three ranges of confining pressure, namely 50, 70 and 90 kPa, were tested. The results in this stage suggested that the addition of 6% FA to the sand led to an increase in the cyclic response of the soil to the liquefaction in comparison with the specimens of sand mixed with 4% FA in all tested confining pressures. In the last part of the study, variation of the CSR with the number of cycles to liquefaction for a mixture of sand and 2% FA with 20% relative density under 50, 70 and 90 kPa confining pressure were presented and results indicated that the specimens under greater CP liquefied at earlier cycle numbers and vice versa. In continuing to investigate the effect of curing time, the specimens containing 2% FA were cured for 14 and 28 days and tested under 50 kPa CP and 20% relative density. The result showed that an increase in curing time led to an increase in the liquefaction strength of the sand containing FA.

Variation of Liquefaction Strength Induced by Monotonic and Cyclic Loading Histories

AbstractOnce loose sand has liquefied, it becomes denser along with water drainage after liquefaction. Therefore, liquefied sand is regarded as more robust against liquefaction. Such sand after liq...

A study on the improvements of geotechnical properties of in-situ soils by grouting

This paper discusses improvements of compressibility, permeability, static and liquefaction strengths of in-situ soils by grouting. Both field testing and laboratory evaluation of the on-site samples were conducted. The improvement of soils was influenced by two main factors, i.e., the grout materials and the injection mechanisms introduced by the field grouting. On-site grout mapping revealed the major mechanism was fracturing accompanied with some permeation at deeper zones of sandy soils, where long-gel time suspension grout and solution grout were applied. The study found the compressibility and swelling potential of CL soils at a 0.5 m distance to grout hole could be reduced by 25% and 50%, respectively, due to the grouting. The effect on hydraulic conductivity of the CL soils appeared insignificant. The grouting slightly improved the cohesion of the CL soils by 10~15 kPa, and the friction angle appeared unaffected. The grouting had also improved the cohesion of the on-site SM soils by 10~90 kPa, while influences on the friction angle of soils were uncertain. Liquefaction resistances could be enhanced for the sandy soils within a 2~3 m extent to the grout hole. Average improvements of 40% and 20% on the liquefaction resistance were achievable for the sandy soils for earthquake magnitudes of 6 and ≥ 7.5, respectively, by the grouting.

液状化強度曲線の類型化と経験式の提案

液状化強度曲線の類型化と経験式の提案

酵素活性の異なる各種微生物を用いた固化処理砂の液状化特性改善効果に関する検討

酵素活性の異なる各種微生物を用いた固化処理砂の液状化特性改善効果に関する検討