Liquefaction Evaluation Procedures Research Articles

8th Ishihara lecture: Holistic evaluation of liquefaction response

Soil liquefaction during earthquakes is a highly dynamic process involving rapid development of excess pore water pressures (EPWP), reduction in soil stiffness and strength, and diffusion of EPWPs through water flow. In addition, the liquefaction response is characterized by strong cross-layer interactions that significantly influence the severity of liquefaction and overall system response of liquefying deposits. To emphasize the importance of dynamic interactions and provide an in-depth understanding of the liquefaction response, a framework for a holistic evaluation of the liquefaction response is presented. Three key aspects of the response are required to be concurrently considered in the holistic evaluation of the liquefaction response: element (soil) response, cross-layer interactions (system response) and intensity of the input motion. The proposed approach is applied to a comprehensive series of nonlinear dynamic analyses (NDAs) of well-documented case history sites from Christchurch, New Zealand, to identify key interaction mechanisms and quantify effects of dynamic interactions on the liquefaction response. As state-of-practice simplified liquefaction evaluation procedures ignore interactions within the deposit, results from simplified analyses substantially differ from those observed in NDA and show significant anomalies in the evolution of the liquefaction response throughout the depth of liquefiable deposits. A systematic approach for an NDA-based improvement of simplified analysis is proposed to incorporate interaction mechanisms and system response effects in simplified liquefaction evaluation procedures.

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

System Response of an Interlayered Deposit with Spatially Preferential Liquefaction Manifestations

The Canterbury Earthquake Sequence produced a spatial pattern of liquefaction-induced surface ejecta at an open field along Palinurus Road in Christchurch, New Zealand, that would not be expected based on simplified liquefaction evaluation procedures. Half the site discharged sand boils and the other half did not. Two-dimensional fully-coupled nonlinear dynamic analyses (NDAs) were performed to examine why simplified one-dimensional liquefaction vulnerability indices (LVIs) overestimated liquefaction manifestations at this site for the 2010 Darfield and 2011 Christchurch earthquakes and did not distinguish between areas with and without surface ejecta. The NDAs use the PM4Sand and PM4Silt constitutive models for sand-like and clay-like portions of the subsurface, respectively, within the Fast Lagrangian Analysis of Continua (FLAC) finite-difference program. Material parameters are obtained from in situ geophysical and cone penetration test (CPT) data. A sensitivity study is performed to assess the influence of (1) representative soil property selections and the use of a CPT inverse filtering procedure to correct for thin-layer and transition zone effects, (2) ground motions developed by two distinct methods (i.e., recordings and physics-based simulations), and (3) model assumptions affecting diffusion during reconsolidation. Ground deformations and flow patterns during and after ground shaking are examined. The results provide insights on how stratigraphic details and other factors can affect the system response and dictate the degree and extent of liquefaction surface manifestations.

Experimental and numerical modeling on the liquefaction potential and ground settlement of silt-interlayered stratified sands

Recent seismic events indicate that the simplified liquefaction-evaluation procedures are incapable of depicting general trends in liquefaction damage for stratified sands interlayered with silts. The conditions and mechanisms affecting the liquefaction potential of stratified sands exist in the field and ground settlement after liquefaction remain poorly understood. This work aims to investigate the seismic response of nonhomogeneous soil deposits by large-scale model tests and numerical simulations using an advanced constitutive model. A comprehensive experimental program was undertaken in which a total of three shake-table tests were performed on uniform sand and two stratified-sand deposits interlayered with different thicknesses of silt to investigate the ground settlement and distribution and dissipation of excess pore pressure during and after shaking. The shake-table test results and the numerical simulations of the silt-interlayered stratified sands, first indicate that the thickness of the silt seam has a significant influence on the liquefaction resistance of stratified-sand deposits beneath the silt layer. The second conclusion of this study reveals that the thickness and coefficient of consolidation of the silt and the liquefied sand below the silt layer significantly alter the degree of dissipation after the shake, and this causes different deformation/settlement at the ground surface. Therefore, there will be probably inaccuracies in applying simplified liquefaction evaluation procedures to the actual soil profile characterized by various patterns of layering in the field.

Introduction and Application of a Simple Probabilistic Liquefaction Hazard Analysis Program: HAZ45PL Module

The 2016 Meinong Earthquake hit southern Taiwan and many shallow foundation structures were damaged due to soil liquefaction. In response, the government initiated an investigation project to construct liquefaction potential maps for metropolitans in Taiwan. These maps were used for the preliminary safety assessment of infrastructures or buildings. However, the constructed liquefaction potential map used the pseudo-probabilistic approach, which has inconsistent return period. To solve the inconsistency, the probabilistic liquefaction hazard analysis (PLHA) was introduced. However, due to its complicated calculation procedure, PLHA is not easy and convenient for engineers to use without a specialized program, such as in Taiwan. Therefore, PLHA is not a popular liquefaction evaluation procedure in practice. This study presents a simple PLHA program, HAZ45PL Module, customized for Taiwan. Sites in Tainan City and Yuanlin City are evaluated using the HAZ45PL Module to obtain the hazard curve and to construct the liquefaction probability map. The liquefaction probability map provides probabilities of different liquefaction potential levels for engineers or owners to assess the performance of an infrastructure or to design a mitigation plan.

Soil Liquefaction Assessment Using Soft Computing Approaches Based on Capacity Energy Concept

Soil liquefaction is one of the most complicated phenomena to assess in geotechnical earthquake engineering. The conventional procedures developed to determine the liquefaction potential of sandy soil deposits can be categorized into three main groups: Stress-based, strain-based, and energy-based procedures. The main advantage of the energy-based approach over the remaining two methods is the fact that it considers the effects of strain and stress concurrently unlike the stress or strain-based methods. Several liquefaction evaluation procedures and approaches have been developed relating the capacity energy to the initial soil parameters, such as the relative density, initial effective confining pressure, fine contents, and soil textural properties. In this study, based on the capacity energy database by Baziar et al. (2011), analyses have been carried out on a total of 405 previously published tests using soft computing approaches, including Ridge, Lasso & LassoCV, Random Forest, eXtreme Gradient Boost (XGBoost), and Multivariate Adaptive Regression Splines (MARS) approaches, to assess the capacity energy required to trigger liquefaction in sand and silty sands. The results clearly prove the capability of the proposed models and the capacity energy concept to assess liquefaction resistance of soils. It is also proposed that these approaches should be used as cross-validation against each other. The result shows that the capacity energy is most sensitive to the relative density.

Implementation and Use of a Mechanical Cone Penetration Test Database for Liquefaction Hazard Assessment of the Coastal Area of the Tuscany Region

This paper describes the implementation and use of a mechanical cone penetration test (CPTm) database for the evaluation of the liquefaction potential in some areas of Tuscany. More specifically, the database contains 4500 CPTm covering an area of 1787 square km and mainly concerns some coastal areas of Tuscany. Available simplified liquefaction evaluation procedures (LEPs) are mainly based on piezocone CPT (CPTu) test results and not on CPTm. An early interest on developing LEPs with reference to CPTm became quite soon obsolete because of the widespread use of piezocone. Unfortunately, in Italy, the use of CPTm is very popular. After the 2012 seismic sequence of Emilia-Romagna, the use of CPTm for liquefaction risk analysis has seen a renewed interest, even though such a topic should require further studies. This paper shows an empirical approach for liquefaction triggering assessment by CPTm using existing LEPs, thus making possible the use of the developed CPTm database for the preliminary screening of the study area.

Equivalent number of uniform cycles versus earthquake magnitude relationships for fine-grained soils

In current geotechnical seismic design practice, the empirical correlation between equivalent number of uniform cycles (Neq) of shaking and earthquake magnitude (Mw) forms an integral part of liquefaction potential evaluation. This relationship, in turn, is used to derive the magnitude scaling factors that are commonly used in field-based liquefaction evaluation procedures. The Neqversus Mwrelationship for liquefaction assessment was examined for fine-grained soils using time-histories in the range 5 < Mw≤ 9, especially including strong ground motion time-histories from the latest subduction zone earthquakes with Mw> 8.0. The experimental database available from cyclic direct simple shear tests conducted on natural fine-grained soils retrieved from undisturbed soil sampling was used to obtain the cyclic shear resistance weighting curves for the study. The work presented herein has contributed to further improving the current models used to represent magnitude scaling factor (MSF) values for large earthquake magnitudes and the functional dependency of this parameter on soil type. The MSF–Mwcurve derived for low-plastic Fraser River Delta silt lies in-between the MSF curves derived for clean sand and clay, resonating with the inferences that have been made that the silt behavior can neither be considered sand-like nor clay-like.

Addressing limitations in existing ‘simplified’ liquefaction triggering evaluation procedures: application to induced seismicity in the Groningen gas field

The Groningen gas field is one of the largest in the world and has produced over 2000 billion m3 of natural gas since the start of production in 1963. The first earthquakes linked to gas production in the Groningen field occurred in 1991, with the largest event to date being a local magnitude (ML) 3.6. As a result, the field operator is leading an effort to quantify the seismic hazard and risk resulting from the gas production operations, including the assessment of liquefaction hazard. However, due to the unique characteristics of both the seismic hazard and the geological subsurface, particularly the unconsolidated sediments, direct application of existing liquefaction evaluation procedures is deemed inappropriate in Groningen. Specifically, the depth-stress reduction factor (rd) and the magnitude scaling factor relationships inherent to existing variants of the simplified liquefaction evaluation procedure are considered unsuitable for use. Accordingly, efforts have first focused on developing a framework for evaluating the liquefaction potential of the region for moment magnitudes (M) ranging from 3.5 to 7.0. The limitations of existing liquefaction procedures for use in Groningen and the path being followed to overcome these shortcomings are presented in detail herein.

Assessment of the cyclic strain approach for evaluating liquefaction triggering

The cyclic strain approach was proposed in the 1980s as a potential alternative to the stress-based simplified liquefaction evaluation procedure. However, despite its fundamental basis and many positive attributes, it has not been embraced by practice. One reason for this may be the need to perform cyclic laboratory tests on undisturbed/reconstituted samples to develop a relationship among excess pore water pressure, cyclic strain amplitude, and number of applied strain cycles. Herein an alternative implementation of the strain-based procedure is proposed that circumvents this requirement, using a strain-based pore pressure generation model in lieu of laboratory test data. To assess the efficacy of the alternative implementation, several hundred small strain shear wave velocity (Vs) and Standard Penetration Test (SPT) field liquefaction case histories are evaluated. The results are compared with both field observations and with predictions from the stress-based procedures. It was found that the stress-based approach yielded considerably more accurate predictions compared to the cyclic strain approach. One likely reason for this is the strain-based procedure's inherent and potentially fatal limitation of ignoring the decrease in soil stiffness due to excess pore pressure when representing the earthquake loading in terms of shear strain amplitude and number of equivalent cycles.

Depositional environment effects on observed liquefaction performance in silt swamps during the Canterbury earthquake sequence

Stratified silty soils deposited in back-swamp settings are shown through regional CPT-based analyses to have mitigating effects on the manifestation of liquefaction in Christchurch. Liquefaction triggering within these deposits is inadequately captured by simplified liquefaction assessment methodologies. Differing near-surface geology and depositional environments indicated in historical documents explain in part the limitations of current liquefaction evaluation procedures in southwest Christchurch. The historical swamp areas are shown through a regional CPT study to contain stratified silt/sand deposits or thick silt layers. Consideration of depositional environment distinguishes between liquefaction performances that are not able to be differentiated through the CPT-based liquefaction triggering assessment alone. CPT resolution is shown to be insufficient to capture the thin layering at these stratified sites, and the simplified liquefaction assessment methods do not take into account the effects of the stratification on pore water pressure movement within a soil profile. Instead, continuous sampling and careful logging of high-quality samples provide important insights on stratification at these silty soil swamp sites and in discerning differences in stratigraphy resulting from differences in depositional environment.

Spatial variation of magnitude scaling factors during the 2010 Darfield and 2011 Christchurch, New Zealand, earthquakes

The combination of well-documented liquefaction response during the Darfield and Christchurch, New Zealand, earthquakes, densely-recorded ground motions for the events, and detailed subsurface characterization provides an unprecedented opportunity to investigate the significance of the spatial variation of magnitude scaling factors (MSF) on liquefaction triggering. Towards this end, MSF were computed at 15 SMS sites across Christchurch and its surroundings using two established approaches. Trends in the spatial variation of the MSF computed using number of equivalent cycles (neq) from both approaches were similar, with the spatial variation being more significant for the Christchurch earthquake than the Darfield earthquake. However, there was no consistent trend for regions with lower computed MSF having experienced more severe or widespread liquefaction. Additionally, there is a general correlation between MSF and amax, but because amax ranges more widely than MSF it has a greater influence on the resulting seismic demand imposed on the soil than MSF does. Nevertheless, the spatial variation of the MSF is deemed significant enough that it warrants being considered for incorporation into future variants of simplified liquefaction evaluation procedures.

The role of biomonitoring in chemical risk assessment: The contribution of the Scientific Committee of Occupational Toxicology of the International Commission on Occupational Health

The combination of well-documented liquefaction response during the Darfield and Christchurch, New Zealand, earthquakes, densely-recorded ground motions for the events, and detailed subsurface characterization provides an unprecedented opportunity to investigate the significance of the spatial variation of magnitude scaling factors (MSF) on liquefaction triggering. Towards this end, MSF were computed at 15 SMS sites across Christchurch and its surroundings using two established approaches. Trends in the spatial variation of the MSF computed using number of equivalent cycles (neq) from both approaches were similar, with the spatial variation being more significant for the Christchurch earthquake than the Darfield earthquake. However, there was no consistent trend for regions with lower computed MSF having experienced more severe or widespread liquefaction. Additionally, there is a general correlation between MSF and amax, but because amax ranges more widely than MSF it has a greater influence on the resulting seismic demand imposed on the soil than MSF does. Nevertheless, the spatial variation of the MSF is deemed significant enough that it warrants being considered for incorporation into future variants of simplified liquefaction evaluation procedures.

Deterministic and probabilistic liquefaction potential evaluation of Guwahati city

Northeastern region of India is one of the six most seismically active regions of the world. Guwahati, the major city in the region is growing rapidly in every aspect. The 1897 great Assam earthquake and the 1950 Assam earthquake both of magnitude 8.7 are two of the many great earthquakes that had occurred in this region. There have been reports of extensive liquefaction occurring during these two earthquakes. These instances of liquefaction necessitate the need to evaluate liquefaction potential of the area. In the present study, an attempt has been made to predict the liquefaction susceptibility of Guwahati city based on corrected SPT values using deterministic as well as probabilistic performance based approach. The deterministic and probabilistic version of Toprak et al., Youd et.al, Idriss and Boulanger and Cetin, standard penetration test (SPT)- based liquefaction triggering correlations have been used. The results obtained in the probabilistic approach are then compared with their deterministic approach. Standard Penetration Test (SPT) N values, engineering properties of the soils and depth of water table were taken from a data base of 200 boreholes upto 30 meter depth covering an area of 262 km2 in Guwahati city. Liquefaction susceptibility from the methods is presented as maps showing zones of levels of risk of liquefaction. Comparison of the three methods in the deterministic approach have shown that there is a difference in the factors of safety in the same depth and comparison in the probabilistic approach have also shown a difference in the values of probabilities in the same depth. The SPT- based liquefaction evaluation procedures have been found to yield significantly different predictions. This study feels that the issues and uncertainties regarding the use of both the deterministic and probabilistic liquefaction triggering relationships in practice must be resolved so as to arrive at a common consensus to determine the same.

Development of magnitude-bound relations for paleoliquefaction analyses: New Zealand case study

Magnitude-bound relations are often used to estimate paleoearthquake magnitudes from paleoliquefaction data. This study proposes New Zealand-based magnitude-bound curves that are developed using (a) liquefaction field observations and (b) a newly proposed back-calculation approach that combines the simplified liquefaction evaluation procedure with a regionally appropriate ground motion prediction equation. For (b) both deterministic and probabilistic frameworks are proposed. The magnitude bound curves back-calculated using either the deterministic or probabilistic frameworks are advantageous in that they can be used to predict the spatial distribution of liquefaction in regions where historical liquefaction field observations are limited or poorly documented, and because soil- and site-specific conditions can be incorporated into magnitude-bound analyses. Moreover, curves developed using the probabilistic framework allow for the range of possible causative earthquake magnitudes to be better understood and quantified. To demonstrate the use of the proposed relations, paleoliquefaction features discovered in eastern Christchurch (NZ) are analyzed. The 1869 ~Mw4.8 Christchurch earthquake and/or 1717 ~Mw8.1 Alpine Fault earthquake are found to be the most likely candidates amongst known historical and paleoearthquakes for triggering liquefaction over the permissible time range (ca. 1660 to 1905 A.D.). This study demonstrates the potential of the proposed magnitude-bound curves to provide insight in to past, present, and future hazards, proving their utility even in cases of limited evidence. The approach of developing and applying magnitude bound curves proposed herein is not limited to parts of New Zealand, but rather, can be applied worldwide.

Assessment of CPT-based methods for liquefaction evaluation in a liquefaction potential index framework

In practice, several competing liquefaction evaluation procedures (LEPs) are used to compute factors of safety against soil liquefaction, often for use within a liquefaction potential index (LPI) framework to assess liquefaction hazard. At present, the influence of the selected LEP on the accuracy of LPI hazard assessment is unknown, and the need for LEP-specific calibrations of the LPI hazard scale has never been thoroughly investigated. Therefore, the aim of this study is to assess the efficacy of three CPT-based LEPs from the literature, operating within the LPI framework, for predicting the severity of liquefaction manifestation. Utilising more than 7000 liquefaction case studies from the 2010–2011 Canterbury (NZ) earthquake sequence, this study found that: (a) the relationship between liquefaction manifestation severity and computed LPI values is LEP-specific; (b) using a calibrated, LEP-specific hazard scale, the performance of the LPI models is essentially equivalent; and (c) the existing LPI framework has inherent limitations, resulting in inconsistent severity predictions against field observations for certain soil profiles, regardless of which LEP is used. It is unlikely that revisions of the LEPs will completely resolve these erroneous assessments. Rather, a revised index which more adequately accounts for the mechanics of liquefaction manifestation is needed.

Assessment of liquefaction evaluation procedures and severity index frameworks at Christchurch strong motion stations

The objective of the study presented herein is to assess three commonly used CPT-based liquefaction evaluation procedures and three liquefaction severity index frameworks using data from the 2010–2011 Canterbury earthquake sequence. Specifically, post-event field observations, ground motion recordings, and results from a recently completed extensive geotechnical site investigation programme at selected strong motion stations (SMSs) in the city of Christchurch and surrounding towns are used herein. Unlike similar studies that used data from free-field sites, accelerogram characteristics at the SMS locations can be used to assess the performance of liquefaction evaluation procedures prior to their use in the computation of surficial manifestation severity indices. Results from this study indicate that for cases with evidence of liquefaction triggering in the accelerograms, the majority of liquefaction evaluation procedures yielded correct predictions, regardless of whether surficial manifestation of liquefaction was evident or not. For cases with no evidence of liquefaction in the accelerograms (and no observed surficial evidence of liquefaction triggering), the majority of liquefaction evaluation procedures predicted liquefaction was triggered. When all cases are used to assess the performance of liquefaction severity index frameworks, a poor correlation is shown between the observed severity of liquefaction surface manifestation and the calculated severity indices. However, only using those cases where the liquefaction evaluation procedures yielded correct predictions, there is an improvement in the correlation, with the Liquefaction Severity Number (LSN) being the best performing of the frameworks investigated herein. However scatter in the relationship between the observed and calculated surficial manifestation still remains for all liquefaction severity index frameworks.

Assessment of soil liquefaction based on capacity energy concept and multivariate adaptive regression splines

Soil liquefaction is one of the most complicated phenomena to assess in geotechnical earthquake engineering. The procedures that have been developed to determine the liquefaction potential of sandy soil deposits can be categorized into three main groups: stress-based, strain-based, and energy-based procedures. The main advantage of the energy-based approach over the other two methods is the fact that it considers the effects of strain and stress concurrently unlike the stress or strain-based methods. Several liquefaction evaluation procedures have been developed, relating the capacity energy to initial soil parameters such as the relative density, initial effective confining pressure, fine contents and soil textural properties. Analyses have been carried out on a total of 302 previously published tests using a nonparametric regression procedure known as multivariate adaptive regression splines (MARS), to assess the capacity energy required to trigger liquefaction in sand and silty sands. The capacity energies estimated by this proposed model compare favorably with the centrifuge test data sets used for validation purpose.

Fines-content effects on liquefaction hazard evaluation for infrastructure in Christchurch, New Zealand

To assess soil liquefaction hazards for civil infrastructure, several competing liquefaction evaluation procedures (LEPs) are used to estimate the potential for liquefaction triggering, often for use in a liquefaction potential index (LPI) framework. However, due to the relatively uncertain effects of fines-content (FC) on liquefaction behavior, LPI hazard assessments may be less accurate at sites with high FC. Accordingly, this study investigates “fines-content effects” on the accuracy of LPI hazard assessment during the 2010–2011 Canterbury Earthquake Sequence (CES). These effects are resolved into: (1) criteria based on the soil-behavior-type index (Ic) for identifying liquefaction-susceptible soils; (2) FC-corrections inherent to each LEP, used to adjust liquefaction resistance for the presence of fines; and (3) the potential for non-liquefied, high-FC soils to inhibit liquefaction manifestation. This investigation is performed using 7000 liquefaction case studies from the CES, wherein LPI hazard assessments computed with the Robertson and Wride [50], Moss et al. [41], and Idriss and Boulanger [30] LEPs are compared to field observations. For the assessed dataset, LPI hazard assessments were significantly and uniformly less accurate at sites with silty and clayey soil mixtures. For these sites, the existing LPI framework has inherent limitations, such that all LEPs produce erroneous hazard assessments. In particular, the capacity of plastic soils to inhibit liquefaction manifestation by affecting pore pressure development and redistribution should be further evaluated.

Select Liquefaction Case Histories from the 2010–2011 Canterbury Earthquake Sequence

The 2010–2011 Canterbury earthquake sequence began with the 4 September 2010, Mw7.1 Darfield earthquake and includes up to ten events that induced liquefaction. Most notably, widespread liquefaction was induced by the Darfield and Mw6.2 Christchurch earthquakes. The combination of well-documented liquefaction response during multiple events, densely recorded ground motions for the events, and detailed subsurface characterization provides an unprecedented opportunity to add well-documented case histories to the liquefaction database. This paper presents and applies 50 high-quality cone penetration test (CPT) liquefaction case histories to evaluate three commonly used, deterministic, CPT-based simplified liquefaction evaluation procedures. While all the procedures predicted the majority of the cases correctly, the procedure proposed by Idriss and Boulanger (2008) results in the lowest error index for the case histories analyzed, thus indicating better predictions of the observed liquefaction response.