Post-liquefaction Settlement Research Articles

Post-liquefaction settlement analysis of shallow foundations: numerical modeling and effective parameters

ABSTRACT This paper evaluates the seismic performance of shallow foundations located on liquefiable soil during seismic shaking and post-liquefaction using numerical analyses. Numerical simulations are performed using the UBCSAND constitutive model in FLAC software with validation against prior centrifuge tests conducted by the last author. The numerical analyses carried out in this study emphasize the post-seismic-liquefaction settlement of foundations which has not been addressed adequately compared with the co-seismic settlements. The effect of the foundation surcharge type, embedment depth, relative density, compaction depth, and foundation width are studied by a series of numerical parametric studies. The results show that soil densification and embedment depth can significantly affect the post-liquefaction-induced settlement of shallow foundations compared to the other simulated mitigation strategies. The results indicate that simultaneously considering both the relative density and the compaction depth ratio can significantly contribute to reducing post-liquefaction foundation settlement.

Estimating of Post-liquefaction Settlement Based on SPT Data in Klaten Regency, Central Java

A strong earthquake with Mw 6.3 occurred in Yogyakarta on May 27, 2006, causes of damage to DI Yogyakarta Province and Central Java Province, including Klaten Regency. The geological stratigraphy consists of volcanic breccias, lava and tuff in this area and generally shallow groundwater levels, which can trigger liquefaction. The potential liquefaction analysis in this study uses Standard Penetration Test (SPT) data carried out in 3 districts, namely Delanggu, Polanharjo, and Karanganom District uses Idriss-Boulanger method. The peak ground acceleration was calculated by Next Generation Attenuation (NGA) method using data obtained from the Pacific Earthquake Engineering Research (PEER) Center database. The peak ground acceleration that causes liquefaction in this study is at least 0.29 g in bedrock. All areas indicated potential liquefaction with varying depths. Polanharjo District is the most susceptible to potential liquefaction. The method proposed by Zhang estimates post-liquefaction settlement in this study from 3.3 – 42.4 cm (light to extensive damage) in Klaten Regency. Based on the results, further mitigation studies are needed in Klaten Regency to minimize settlement that will occur due to liquefaction. This study is required in planning the construction of toll road in Klaten Regency.

Evaluation of post liquefaction settlement and treatment and reinforcement of the soil by stone columns

During earthquakes, the shear strength and bearing capacity of saturated sandy soils decreases; this is related to an increase in pore pressure. In the ultimate state, the pore pressure becomes equal to the initial effective stress, at which time the material loses all its resistance and liquefaction occurs. Thus, the prediction of the post-liquefaction settlement of the soil is an important step to reduce the seismic risk. Several methods have been developed for the prediction of Seismic-Induced Settlement, the most widely used is that based on the results of in-situ tests SPT, and Several soil reinforcement techniques can be considered, the choice depends mainly on the grain size of the soil to be treated. This article presents a comparative study of the methods for evaluating Seismic-Induced Settlement based on the experimental results of the in situ SPT tests, applied to an earthquake-prone area in northern Morocco which had specific soil formations characterized by the existence of layers of sand over several meters, which suggests the possibility of soil liquefaction and proposes a method of reducing the risk of liquefaction. The analysis of existing SPT data leads to interesting conclusions both in terms of the comparative analysis of methods for the prediction of the post-liquefaction settlement and the understanding of the effect of Soil treatments by Stone Columns to mitigate the risk of liquefaction.

Numerical study of the effect of Post-Liquefaction settlements on the response of infilled RC-frames

The liquefaction of soils is one of the most severe results of earthquakes. Indeed, post-liquefaction settlements are the main responsible for critical damages and collapse in shallow-founded buildings. The study of the behavior of buildings subjected to post-liquefaction settlements is rather complex since it requires to consider the interaction between the effects of ground shaking and the effects of liquefaction failure. In particular, large inelastic deformations occurring during severe earthquakes are responsible for residual permanent displacements which could particularly influence the response of structures with respect to post-liquefaction settlements. In this paper it is presented a simplified numerical approach finalized to assess the response of infilled reinforced concrete (RC) frames toward post-liquefaction settlements. Like to a previous approach presented by the Authors for bare RC-frames, the proposed approach is based on a procedure where the influence of seismic inelastic displacements on the effect of post-liquefaction settlements is evaluated throughout a set of static nonlinear analyses instead of more complex dynamic time-history analyses. Here, in addition, the Authors opportunely enrich the approach to account for the influence of the damage attained by the infill on both the seismic response and post-liquefaction settlements. After a preliminary discussion concerning some important aspects of the behavior of infilled RC-frames toward seismic events and post-liquefaction settlements, the proposed approach is presented in detail and applied to some cases of study deduced from literature. Additional numerical analyses are also performed in order to further underline the ability of the approach to account for the important role of infill panels on the seismic response and the subsequent activation of post-liquefaction settlements.

Evaluating the applicability of conventional CPT-based liquefaction assessment procedures to reclaimed gravelly soils

Gravelly soils are not well represented in current semi-empirical liquefaction procedures, which raises the question of whether state-of-the-practice liquefaction evaluation methods based on sands are applicable to gravelly soils. This paper investigates the applicability of Cone Penetration Test liquefaction triggering and settlement evaluation procedures to case histories of well-graded reclaimed gravelly soil at CentrePort, New Zealand. Sensitivity studies of the liquefaction triggering analysis show the uncertainty in the cyclic demand is larger than the uncertainty in the cyclic resistance within a critical layer. However, the modelling uncertainty over the entire depth of the fill is larger for the cyclic resistance, which can vary by over 50% due to a single material-characterization parameter, i.e., the fines content or soil behavior type index. Sand-based procedures for evaluation of liquefaction-induced settlement are found to be generally applicable to well-graded gravels that have a dominant silty sand fraction in the soil matrix, though they can overestimate the relative density and therefore underestimate post-liquefaction settlement of gravelly soils. The paper emphasizes the importance of soil composition, dominant soil fraction of the soil matrix, and its effects on the soil packing, penetration resistance, and liquefaction resistance in the context of current semi-empirical liquefaction evaluation procedures. • CPT-based liquefaction procedures are applicable to some gravel-sand-silt mixtures • Soil composition and dominating soil fractions are key to liquefaction assessment • FS L is more sensitive to uncertainties in PGA than FC or I c • Use of a constant FC throughout seemingly uniform fill could be problematic • Sand-based methods overestimate D R and underestimate settlement of gravelly soils

Simple approach to evaluate the influence of seismic residual displacements on post-liquefaction settlements of RC-frames

Residual permanent displacements generally characterize the status of structures at the end of severe earthquake events because of large inelastic deformations demand. When the structure is founded on soils susceptible to liquefaction phenomenon, this status could particularly influence the subsequent damages due to the occurrence of liquefaction induced vertical settlements. As a consequence, the correct prediction of the effects of earthquake induced liquefaction on the built environment must consider the residual displacements induced by the ground shaking. To this aim, the paper proposes a simplified approach to evaluate the seismic response of RC frames based on a four-steps procedure composed of a set of nonlinear static analyses reproducing a sequential process of a ground shaking followed by a liquefaction induced ground settlements. The novelty of the proposal is to carry out sequential nonlinear static analyses by preserving the status of the RC frame at the end of the seismic event in terms of residual displacements and then to directly consider their influence on the subsequent analysis simulating the occurrence of post-liquefaction vertical settlements.A parametric study has been developed by means of numerical analyses, referring to two RC frames derived from literature, in order to highlight the relevance of the seismic residual displacements on the damage induced by the subsequent vertical settlements due to soil liquefaction. The proposed simplified approach has then been validated through more sophisticated nonlinear dynamic time-history analyses. The results presented in the paper underline the efficacy of the proposed approach, the simplicity in implementing the four-steps procedure and the lower computational effort with respect to nonlinear dynamic time-history analyses.

Observations and challenges in simulating post-liquefaction settlements from centrifuge and shake table tests

Liquefaction-induced reconsolidation settlements occur as excess pore pressures generated during shaking dissipate and can lead to significant damage to overlying infrastructure. Designing resilient infrastructure in areas affected by liquefaction requires methods to predict these settlements for different soil types and boundary conditions. Simplified empirical models are commonly utilized to evaluate settlements but they exhibit several limitations that might hinder the accuracy of settlement predictions, including effects of partial drainage, thin layers, non-liquefiable crusts, or soil fabric. Numerical models can capture these effects but require proper calibration and validation. This study uses a numerical approach to simulate centrifuge and shake table experiments with free-field level, ground conditions and five different sands for evaluating reconsolidation settlements. The numerical platform FLAC and constitutive relationship PM4Sand are utilized. The necessity of soil-specific calibration of post-liquefaction stiffness and an excess pore pressure ratio dependent hydraulic conductivity to accurately model the observed pore pressures and settlements is analyzed. A new relationship between the increase in hydraulic conductivity due to liquefaction and grain size diameter is proposed. The numerical simulations are able to capture the general trends, but the bias in the results appears to be correlated with the grain size distribution of the tested soil.

Potential Study of Liquefaction in the Downstream Area of Jono Oge-Paneki River, Central Sulawesi

Liquefaction during an earthquake is likely to occur in the quaternary geological layer of sediment. Based on the geological process, the mainland of Central Sulawesi was initially a sea lifted upward to become land Palu-Koro fault. Therefore, the land is basically of basic alluvium soil formation, sand deposits, and loose rock. The earthquake in Central Sulawesi in September 2018 was the cause of liquefaction, one of which was in the Jono Oge area, where most of the flow entered the Paneki river. This paper analyzed the potential for recurrent liquefaction by considering the soil structure and water level conditions. The authors focused on the downstream areas of the Paneki River, which passes through Langaleso and Kabobona Village. The data used is N-SPT data, followed by examining post-liquefaction settlement and lateral displacement. This study uses several variations of the earthquake magnitude and potential earthquakes that may occur. The results of observations indicate that the soil conditions of the study area are cohesionless soil. The liquefaction analysis shows that most of the research areas have liquefaction, land subsidence, and lateral displacement potential.

Seismic response of subsea structures on caissons and mudmats due to liquefaction

This paper presents a numerical study to investigate the seismic behavior of mudmat and caisson foundations supporting subsea structures, such as manifolds, in liquefiable sand. In seismic areas, substantial earthquake loads can be imparted to subsea structures during ground shaking, threatening their stability. In particular, soil liquefaction in sandy soil arising from strong ground motions could significantly influence the performance of subsea structures founded on liquefiable sand. The results of this study can provide a better understanding of the response of subsea manifolds in liquefiable soil during and after the earthquake. Three-dimensional, non-linear, dynamic analyses are performed using a finite difference scheme, and the ability of the model to reproduce the site response of a saturated sand deposit is assessed using the results of available centrifuge data. This study includes six computational models representing manifolds with different sizes and weights supported by caissons and mudmats in shallow and deep liquefiable sand subjected to moderate and strong earthquake shakings. The response is evaluated in terms of excess pore water pressure generated in the soil medium and displacements of the subsea foundation during and after the shaking. The results show that manifolds may experience considerable movement during liquefaction and post-liquefaction settlements. In addition, depending on the characteristics of the seismic motion and structural system, the manifold could also experience large tilting.

Probabilistic Seismic Loading Considerations for the Assessment of Liquefaction-Induced Volumetric Settlements in the Free Field

AbstractEngineers have long integrated predicted volumetric strains in liquefied soils to predict free-field, postliquefaction settlements. These free-field settlements have commonly been used to d...

Critical State Soil Mechanics for Cyclic Liquefaction and Postliquefaction Behavior: DEM study

Discrete-element method (DEM) simulations of three-dimensional (3D) assemblies of ellipsoid particles were used to evaluate the critical state (CS) for both drained and undrained (constant volume) conditions. A series of conventional triaxial cyclic liquefaction tests with symmetrical cyclic deviatoric stress (σd) with initial q=0 kPa were simulated to develop a relationship between the cyclic stress ratio (CSR=σd/2σ0′) and the number of cycles required for initial liquefaction (NL), where σ0′ is the mean effective normal stress at the end of consolidation. Both cyclic mobility and instability type behaviors were observed depending on the initial void ratio (e0) and σ0′. The micromechanics quantities, i.e., the coordination number (CN), von Mises fabric (FvM), fabric anisotropy intensity (αc), and stress-strain behavior, suggested that cyclic mobility and instability may depend on the phase transformation and instability state, respectively. The cyclic resistance ratio (CRR15), i.e., CSR at NL=15, showed a unique relation with the initial state parameter (ψ0), irrespective of e0 and σ0′. Two series of postliquefaction monotonic simulations with and without reconsolidation exhibited a unique CS, which perfectly matched with the original CS line. The FvM also reached a unique, narrow range at the CS. The postliquefaction settlement during reconsolidation also showed a linear relation with ψ0.

Centrifuge modeling of hybrid foundation to mitigate liquefaction-induced effects on shallow foundation resting on liquefiable ground

A hybrid foundation is developed in this study to mitigate the liquefaction-induced effects on shallow foundations. The proposed hybrid foundation is a combination of a gravel drainage system and friction steel piles with spiral blades, framed under the footing. The motivation behind having a gravel drainage system, as an integral part of the hybrid foundation, is its ability to improve the liquefaction resistance of the ground in the most economical way. However, case histories and the development of recent research have highlighted that gravel drainage systems have exhibited poor performances and could not prevent ground liquefaction during strong ground motion. To counteract these shortcomings, friction steel piles are provided which are supposed to yield frictional resistance during earthquakes and are presumed to minimize the rocking/tilting behavior of the foundation-structure system even if the ground undergoes liquefaction. The evolution of excess pore water pressure, specifically in the vicinity of the foundation-structure system, dominatingly influences the settlement mechanism of shallow foundations. Centrifuge test results show that the presence of gravel drainage can minimize the post-liquefaction settlement of shallow foundations through the rapid dissipation of excess pore water pressure. Moreover, friction piles are able to minimize the tilting/differential settlement of shallow foundations. It is found that the proposed hybrid foundation provides the desired function of reducing the overall liquefaction-induced effects on shallow foundations resting on liquefiable grounds.

Cyclic undrained behavior and post liquefaction settlement of a nonplastic silt

This study presents an investigation into liquefaction and post-liquefaction behavior of a nonplastic silt under cyclic loading. A systematic approach was adopted for assessment of above-mentioned behavior by performing cyclic triaxial tests on saturated specimens in terms of pore water pressure build-up characteristics, effective stress, number of cycles and double amplitude axial strain. The specimens, consolidated under an effective confining pressure of 100 kPa, were prepared at relative densities ranging among 30–80%. The results revealed that the axial strains of specimens of lower relative densities were increased at higher CSR levels. For prediction of pre- and post-liquefaction behavior, a family of curves for establishing relationships among factor of safety to liquefaction, post-liquefaction volumetric strain and relative density were established. These curves, along with the calculation of post-liquefaction volumetric strain, may be useful in estimation of settlements of silt after being subjected to cyclic loading.

Overestimation of liquefaction hazard in areas of low to moderate seismicity due to improper characterization of probabilistic seismic loading

This study evaluates the impact of characterizing probabilistic ground motions for liquefaction hazard analysis (defined and quantified in this paper as liquefaction triggering and free-field post-liquefaction settlements) in areas of low to moderate seismicity. Both pseudo-probabilistic and probabilistic (i.e., performance-based) methods are assessed and compared. Results of the comparative study suggest that pseudo-probabilistic methods can significantly overestimate liquefaction hazards in areas of low seismicity. Performance-based probabilistic methods are shown to predict between 5.2 cm and 16.5 cm (approximately 36–47%) less post-liquefaction free-field settlement on average than pseudo-probabilistic methods in areas of low seismicity at a return period of 2475 years, and to predict 9 cm to 19.7cm (approximately 96%) less post-liquefaction free-field settlement on average than pseudo-probabilistic methods at a return period of 475 years. Soil site classification is shown to have substantial impact on the estimated liquefaction hazards in areas of low seismicity due to soil amplification, potentially increasing design accelerations by up to 56%. Consequences of inconsistencies regarding design ground motions in current seismic design provisions are also discussed. To avoid potential for overpredicting liquefaction hazards, engineers should apply a performance-based approach when assessing liquefaction triggering and its effects in areas of low to moderate seismicity.

Characterization of soil deformation due to blast-induced liquefaction by UAV-based photogrammetry and terrestrial laser scanning

ABSTRACTSoil liquefaction due to an earthquake can lead to permanent soil deformation and reduction of load-bearing capacity that in turn could act on building stability. Since a quantitative evaluation of post-liquefaction settlements is often very difficult, field scale liquefaction tests, carried out under controlled conditions, such as blast tests, are used to perform a correct quantitative analysis of the liquefaction phenomena. Among the significant parameters related to a blast test, there are the geometric ones, i.e. the extension of the area affected by the blast-induced liquefaction and the corresponding vertical displacements. This article shows the results of a blast test carried out at a trial site located in Mirabello (Ferrara, Italy) from a remote-sensing perspective. Data provided by aerial Structure-from-Motion photogrammetry, supported by terrestrial laser scanning measurements, were used to evaluate the soil deformation that, in the specific case study, aided a geological/geotechnical interpretation of the blast test results. In general, the proposed method can be used to characterize areas affected by blast-induced liquefaction, including those cases where blasting is used as ground improvement technique aimed at mitigating the seismic hazard.

The first Italian blast-induced liquefaction test (Mirabello, Emilia-Romagna, Italy): description of the experiment and preliminary results

Soil liquefaction can result in significant settlement and reduction of load-bearing capacity. Moreover, the increase and the accumulation of pore pressure during an earthquake and its post-seismic dissipation can generate permanent deformations and settlements. The quantitative evaluation of post-liquefaction settlements is of extreme importance for engineering purposes, i.e. for earthquake-resistant design of new buildings and safety evaluation of existing ones. Quantifying the extent of these phenomena is, however, rather difficult. Uncertainties arise from the stochastic nature of the earthquake loading, from the simplifications of soil models, and from the difficulty in establishing correlations between the pre-earthquake soil state and the post-seismic deformations. Field scale liquefaction tests, under controlled conditions, are therefore important for a correct quantification of these phenomena. Recent experiences (e.g. New Zealand, United States) show that liquefaction can be induced and monitored with field scale blast tests to study the related effects on soil geotechnical properties. Within this framework this paper introduces the preliminary results obtained from a research project on blast-induced liquefaction at the field scale; tests were performed at a trial site located in Mirabello (Ferrara, Italy), a village strongly affected by liquefaction phenomena during the 2012 Emilia Romagna earthquake. Invasive tests, such as piezocone, seismic dilatometer and down-hole tests, and non-invasive tests were carried out before and after the execution of two blast test sequences to study the variation in physical properties of the soils. Pore pressure transducers, settlement profilometers, accelerometers and an instrumented micropile were installed with the objective of measuring, during and after the detonations, the generation and subsequent dissipation of the pore pressure, the vertical deformations, and the blast-induced ground motions respectively. Variations in load distribution on deep foundations due to soil liquefaction were also evaluated on a test micropile instrumented with a strain gauge chain. Topographical surveys were carried out to measure ground surface settlements. Laboratory tests and trenches also provided increase understanding of the site characteristics.

Evaluation of liquefaction potential and post-liquefaction settlements in a coastal region in Atakum

Soil liquefaction is one of the most momentous causes of damages induced by earthquakes. It can be described as a sudden decrease in the strength of saturated, cohesionless soil layers, remaining effectual for a length of time under transient and cyclic loading due to excess pore water pressure generation. Consequently, the most appropriate and typical soil condition which brings the potential out to liquefy is loose sand with a groundwater table close to ground surface. This study is pertinent to determine the liquefaction potential in a coastal region in Atakum County of Samsun Province, Turkey. Therefore, empirical equations were used to determine the peak ground accelerations for three scenario earthquakes with the magnitudes of 6.5, 7.0, and 7.2 in order to consider in the simplified procedure context proposed by Seed and Idriss (J. Soil Mech. Found. Div. ASCE 97:1249–1273 1971). Liquefaction potential evaluations were performed using standard penetration test blow counts for four boreholes for sandy portions of the soil profile which exist in the first 20 m below ground surface. In addition to analytical evaluations, two-dimensional nonlinear analyses were ran with Towhata-Iai constitutive model suitable for liquefaction analysis available in DIANA finite element software to clarify excess pore pressure generation that leads to liquefaction. It is also well-known that sands tend to densify when subjected to seismic shaking. Densification of undersoil causes settlement at the ground surface. Liquefaction induced settlements usually cause damages on both superstructures and infrastructures. On the basis of this fact, the method proposed by Ishihara and Yoshimine (Soils Found. 32:173–188 1992) was used to determine the settlements for scenario earthquakes.

Optimization of Shear Wave Velocity (Vs) from a Post-Liquefaction Settlement Using a Genetic Algorithm Multi-Objective NSGA II

Several studies applied heuristic methods such as neuronal networks (ANN), genetic algorithms (GA) and particle swarm optimization (PSO) to predict and optimize soil parameters. Therefore, the aim of the present paper is to optimize shear wave velocity of soil. In this direction, the genetic algorithm NSGA II was used to find the optimum values of shear wave velocity of soil that give an actual value of 0.3m settlement post-liquefaction. The results show that our genetic algorithm has been successfully employed to optimize the shear wave velocity (vs) with acceptable test errors of (R2=0.9999, RMSE=4.029). Moreover, this algorithm can be easily used for prediction and optimization of other geotechnical systems. The genetic algorithm can solve other problems in this field than the presented in this study.

Vertical ground motion and its effects on liquefaction resistance of fully saturated sand deposits.

Soil liquefaction has been extensively investigated over the years with the aim to understand its fundamental mechanism and successfully remediate it. Despite the multi-directional nature of earthquakes, the vertical seismic component is largely neglected, as it is traditionally considered to be of much lower amplitude than the components in the horizontal plane. The 2010–2011 Canterbury earthquake sequence in New Zealand is a prime example that vertical accelerations can be of significant magnitude, with peak amplitudes well exceeding their horizontal counterparts. As research on this topic is very limited, there is an emerging need for a more thorough investigation of the vertical motion and its effect on soil liquefaction. As such, throughout this study, uni- and bidirectional finite-element analyses are carried out focusing on the influence of the input vertical motion on sand liquefaction. The effects of the frequency content of the input motion, of the depth of the deposit and of the hydraulic regime, using variable permeability, are investigated and exhaustively discussed. The results indicate that the usual assumption of linear elastic response when compressional waves propagate in a fully saturated sand deposit does not always hold true. Most importantly post-liquefaction settlements appear to be increased when the vertical component is included in the analysis.

Post-liquefaction settlement analyses based on the volume change characteristics of undisturbed and reconstituted samples

Available data on post-liquefaction volumetric strain were collected from the results of tests conducted in several laboratories on both undisturbed samples and reconstituted samples. The volume change characteristics were found to depend significantly on the degree of disturbance during the undrained cyclic loading preceding the drainage. Its effect was shown to be expressed quantitatively by way of the maximum shear strain, γmax, as an index parameter. Charts were prepared for the volumetric strain as a function of the ranges in relative density and void ratio considering two levels of disturbance, as expressed by γmax=4.13% and 10%. These charts were provided for each post-liquefaction volumetric strain in association with the reconstituted and undisturbed samples. By postulating the former to represent the performance of recent man-made fills and the latter to represent that of alluvial or diluvial deposits, simple analyses were conducted to estimate the settlements of the ground surface at five sites which were affected by liquefaction during the 2011 East Japan Earthquake. A comparison of these estimated values with those actually observed indicated a reasonable level of agreement. Four sites where compaction piles had been installed were also chosen for similar analyses. Both the observed and the estimated settlements were small, namely, in the order of a few centimetres, which also indicates mutual coincidence as a whole.