CPT-based Liquefaction Research Articles

Developing Liquefaction Prediction Equations for Gravels Based on DPT Blow Count and Shear Wave Velocity at Field Case History Sites

Gravelly soils have liquefied at multiple sites in at least 20 earthquakes over the past 130 years. These gravels typically contain more than 25% sand which lowers the permeability and makes them susceptible to liquefaction. In other cases, a low permeability layer at the surface impedes drainage and causes liquefaction. Typical SPT- or CPT-based liquefaction correlations can be affected by large gravel particles and lead to erroneous results. To deal with these problems, we have developed liquefaction triggering curves for gravelly soils based on (1) shear wave velocity (Vs) and (2) a 74-mm diameter dynamic cone penetrometer (DPT), that are less affected by gravel particles. These correlations are based on case histories where gravel did and did not liquefy in past earthquakes. The VS-based liquefaction triggering curves for gravels shift to the right relative to similar curves based on sands. Good agreement has been obtained with liquefaction resistance from the DPT and the CPT when these methods could all penetrate the gravel in Wellington New Zealand. Correlations are developed between Vs and blow count from the DPT.

Analysis of historical cases of liquefaction (sand boils) case study: Kelapa Gading Residence, Sigi Regency, Central Sulawesi Province

The Palu earthquake on September 28th, 2018, caused liquefaction in several locations in Central Sulawesi. According to The National Disaster Management Authority of Indonesia data, five prominent areas with massive impacts experienced liquefaction in flow liquefaction: Balaroa, Petobo, Jono Oge, Lolu, and Sibalaya. Meanwhile, the locations that experienced liquefaction in the form of sand boils needed to be recorded optimally. This research aims to see the parameters of soil layer behavior in areas that experience liquefaction in the form of sand boils. The study was conducted in Kelapa Gading housing, Sigi Regency, Central Sulawesi. Based on the initial survey, this location experienced sand boils in several areas. The research used the CPT-based liquefaction triggering procedure method and soil behavior index method. The result showed that the liquefaction potential was found at a depth of 2.5-3.3 meters for PGA 0.34 and -2.5-(-3.5) for PGA 0.68. When receiving cyclic load, the soil layer with an Ic value > 2.60 with a thickness of 1.6 m at the upper layer can withstand liquefaction with a thickness of 0.8 meters in the form of quicksand on the surface and only causes sand boils. Sand boils would not happen in the Kelapa Gading area if the excess pore water were redirected to discharge wells.

Groundwater level influence on liquefaction potential at Pombewe housing site, Sigi regency, Central Sulawesi

The September 28, 2018, earthquake in Palu, Central Sulawesi, caused liquefaction and destroyed at least 3,720 houses. Therefore, it is necessary to consider the potential of liquefaction in choosing a residential location, especially in liquefaction-prone zones. The parameters of soil type, seismicity, and the groundwater table as a determinant of the saturation level determine liquefaction potential. The research aims to see the influence of groundwater level parameters in increasing the liquefaction potential when other parameters are met. The study was conducted at the Pombewe permanent housing site, Sigi Regency, Central Sulawesi. This shelter is an official relocation area for victims of the 2018 earthquake. Preliminary data stated that the location is safe from liquefaction potential because it has a deep groundwater table. The study used the CPT-based liquefaction triggering procedure method by Boulanger and Idriss and assumed that the groundwater table at the site was shallow. The Liquefaction Potential Index determines the potential liquefaction level. The results show that the area under review will only experience liquefaction if the groundwater table is above 1.0-11.6 meters (LPI>0). If the water table rises above that depth, the LPI value increases to 1.6x10-9 – 0.44. Thus, the water table is a determining parameter in analyzing the liquefaction potential of an area.

Improved CPT-based Liquefaction Assessments with the I<sub>B</sub> Parameter: A Case Study in the San Francisco Bay Area

Improved CPT-based Liquefaction Assessments with the I<sub>B</sub> Parameter: A Case Study in the San Francisco Bay Area

Liquefaction potential analysis for Palu City based on CPT method

During the 28 September 2018 Palu-Donggala earthquake, liquefaction was also a prominent hazard causing significant damage to buildings and infrastructures in Palu City. To mitigate such a hazard in Palu City, knowledge of the depth of the liquified soil layer is necessary. This paper presents the results of CPT-based liquefaction potential analysis in some locations around the city where sand boiling and ground settlement occurred. The analysis shows that liquefaction occurs at various depths less than 15 m and may induce ground settlement up a few centimeters. In the Palu-Koro Fault zone, the liquified sand layer is likely thicker than in other locations. Consequently, the total ground settlement is higher than in other locations The results of this study suggest that the liquefaction potential should be accounted for in the development of Palu City to reduce future earthquake risk.

Assessment of state-of-practice use of field liquefaction charts at low and high overburden using centrifuge experiments

Practical application of the state of practice field liquefaction charts at low and high overburden is assessed with centrifuge testing. Available results of four centrifuge experiments of a 5 m-thick clean sand layer having free drainage at the top are used as case histories. The centrifuge tests include relative densities of 45% and 80% and overburden pressures of about 1 atm and 6 atm. The shear wave velocity (Vs) was measured in the centrifuge models using bender elements. The cone penetration testing (CPT) tip resistance was estimated with correlations from the literature. Vs-based and CPT-based liquefaction charts proposed by Andrus and Stokoe (2000) and Idriss and Boulanger (2008) were used. Both liquefaction charts worked well for the centrifuge tests having an effective overburden, σ'v0, of about 1 atm. This was expected as the charts were originally calibrated with field earthquake case histories having σ'v0 < 2 atm. Both liquefaction charts are too conservative for the centrifuge tests having an effective overburden, σ'v0 of about 6 atm. The agreement at 6 atm deteriorates even further when state-of-practice overburden correction factors, Kσ < 1 are applied, including a prediction of liquefaction when the measured maximum pore pressure ratio in the test was only 0.6. Values of Kσ > 1 were found to provide good agreement with the charts for the 6 atm tests.

Quantifying reliability of liquefaction severity map developed from sparse cone penetration tests

The liquefaction potential index (LPI) is widely used for evaluating the severity of liquefaction manifestation at the ground surface (e.g., settlement, lateral spreading, sand boils, and crack) and for developing liquefaction severity maps. Over the last two decades, several methods, such as cumulative probability distribution of LPI and geostatistics-based LPI mapping, have been proposed to develop a liquefaction severity map from in situ tests (e.g., cone penetration tests, CPT), which are often sparsely performed in sites. These methods are either based on an assumption of statistical homogeneity within each geologic unit or a stationary Gaussian model. However, subsurface soils frequently show significant spatial variability and LPI data obtained at different geological units usually exhibit non-stationary characteristics. More importantly, existing methods offer little insight into the reliability level of the obtained liquefaction severity map. To address these issues, this study proposes a non-parametric and data-driven method for CPT-based liquefaction severity mapping and, for the first time ever, quantification of the liquefaction severity maps’ reliability level using the probability of mis-predicting liquefaction severity from the map. Both synthetic and real-life data are used to demonstrate and validate the proposed method. The illustration examples indicate that the proposed method can properly deal with non-stationary LPI data from different geological units and quantify the mis-prediction probability of liquefaction severity at each point of the map.

Correction to: CPT-based liquefaction resistance of clean and silty sands: A drainage conditions based approach

Correction to: CPT-based liquefaction resistance of clean and silty sands: A drainage conditions based approach

CPT-based liquefaction resistance of clean and silty sands: a drainage conditions based approach

The cone penetration test-based simplified liquefaction triggering evaluations are largely based on linking liquefaction manifestations in the field to cone penetration resistance. These relationships are interpreted in such a way that for given penetration resistance, the liquefaction resistance increases as non-plastic fines content (FC) increases. However, several studies have indicated discrepancies in this relationship. Hence, there is a lag in rational scientific understanding of this observation. In this study, an experimental research program was undertaken to investigate the CPT-based liquefaction assessment by considering the effects of drainage conditions on the relationship between CPT resistance and liquefaction resistance. First, clean sand and silty sands having 5, 15, and 35% FC were tested at different relative densities by stress-controlled cyclic direct simple shear (CDSS) tests to investigate cyclic resistance of silty sand with varying amounts of non-plastic fines. Then, a set of tests involving piezocone penetration (CPTu), seismic CPTu (SCPTu), and direct push permeability (DPPT) were undertaken in a large-scale box filled with the same soils used in the CDSS tests. The large-scale test results quantified the effect of drainage conditions (coefficient of consolidation) on cone penetration resistance. Finally, by combining the CDSS and CPTu test results, an alternative CPT-based liquefaction resistance relationship was proposed by considering the effects of drainage conditions.

Mapping of the liquefaction index, case study

Abstract The present work uses a number of empirical models from geotechnical earthquake engineering (CPT-based liquefaction models) in combination with some geostatistics tools to assess the soil liquefaction potential over an extended area at the Airport of Algiers (Algeria), by the kriging approach. The SIG software program along with variograms and the kriging method were all applied together for the purpose of modeling the variation of the liquefaction potential (PL) against liquefaction in the region under study. This approach allowed determining the missing data in that region. This geostatistical method helped to draw maps at different soil depths. The results obtained revealed that the models developed were potentially capable of accurately estimating the needed data. This study made it possible to determine a number of parametric quantities that support the empirical correlation between the liquefaction potential index and liquefaction. The results show that the higher the standard deviation, the greater the uncertainty.

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

Incorporating inherent uncertainties in seismic liquefaction assessments

Liquefaction assessments for tailings facilities have significant uncertainty, yet their results are typically presented as single-value deterministic factors of safety (FoSs) to compare against standard practice guidance. Some of the uncertainty is due to inherent material variability or measurement error associated with in situ testing techniques. There is also a considerable – and often ignored – contribution from the transformation models used to convert in situ measurements to design parameters. For seismic liquefaction assessments, the key sources of transformation model uncertainty are from the empirical relationships relating standard penetration testing or cone penetration testing (CPT) results to cyclic resistance and residual undrained strength. While the uncertainties associated with the material variability and measurement error will vary by site and can usually be reduced through additional investigation, the model uncertainties are constant and irreducible without further work. This paper shows how the transformation model uncertainties associated with CPT-based liquefaction assessments can be incorporated into design practice to estimate probabilities of failure and lead to very different outcomes than simply considering FoS alone.

Evaluation of a cone penetration test thin-layer correction procedure in the context of global liquefaction model performance

Engineering geologists routinely perform liquefaction hazard assessments using data from the cone penetration test (CPT). However, the volume of soil mobilized by the CPT acts as a low-pass filter on the true stratigraphy, potentially removing information such as the data defining a thin layer of soil or the interface between two dissimilar soils. The Boulanger and DeJong (2018) CPT inversion procedure, which aims to correct these effects, is herein evaluated in the context of CPT-based liquefaction model performance. Using over 15,000 case-histories from 24 earthquakes parsed into 2 datasets, 18 different liquefaction models are studied, resulting in 36 performance trials. In 1 of these trials, the CPT inversion procedure increases model efficiency to a statistically significant degree, but in 23 others it significantly decreases efficiency. This decline in performance tends to grow as profiles become more stratified. To explore remedies, a liquefaction triggering curve is rederived from inverted CPT data, such that its training and forward implementation are made consistent. Nonetheless, this exacerbates the decline in prediction efficiency. Ultimately, the results of this study are not a direct assessment of the pioneering Boulanger and DeJong (2018) procedure. However, the results do provide evidence that this procedure – when applied to existing CPT-based liquefaction models – may provide no demonstrable performance benefit.

CPT-based liquefaction case histories compiled from three earthquakes in Canterbury, New Zealand

Earthquakes occurring over the past decade in the Canterbury region of New Zealand have resulted in liquefaction case-history data of unprecedented quantity. This provides the profession with a unique opportunity to advance the prediction of liquefaction occurrence and consequences. Toward that end, this article presents a curated dataset containing ∼15,000 cone-penetration-test-based liquefaction case histories compiled from three earthquakes in Canterbury. The compiled, post-processed data are presented in a dense array structure, allowing researchers to easily access and analyze a wealth of information pertinent to free-field liquefaction response (i.e. triggering and surface manifestation). Research opportunities using these data include, but are not limited to, the training or testing of new and existing liquefaction-prediction models. The many methods used to obtain and process the case-history data are detailed herein, as is the structure of the compiled digital file. Finally, recommendations for analyzing the data are outlined, including nuances and limitations that users should carefully consider.

Assessment of the efficacies of correction procedures for multiple thin layer effects on Cone Penetration Tests

Multiple interbedded fine-grained layers in a sand deposit have a “smoothing” effect on the measured Cone Penetration Test (CPT) tip resistance (qc), resulting in a significant underestimation of the predicted liquefaction resistance of the sand layers. Trends identified by De Lange [14] through calibration chamber tests on stratified sand-clay profiles are used herein to develop a new thin-layer correction procedure for qc (the “Deltares” procedure). The efficacies of the Deltares and the independently-developed Boulanger and DeJong [6] procedures are both directly assessed using CPT data from calibration chamber tests and indirectly inferred from CPT-based liquefaction case histories in Christchurch, New Zealand. The results highlight limitations of the assessed thin-layer CPT qc correction procedures for layers less than 40 mm thick. Multiple, interbedded thin layers also influence the measured CPT sleeve friction (fs), but in a more complex way than they influence qc. To-date, no procedures have been proposed to address all the thin-layer-effects phenomena on the measured fs, with errors in properly characterizing the fs of a layer inherently influencing the accuracy of predicting the liquefaction susceptibility and potential of the layer. In totality, the thin-layer-effects correction procedures proposed to-date generally result in slightly less accurate predictions of the observed liquefaction severity for cases having highly stratified profiles, opposite of what would be expected and desired.

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.

Geotechnical characterization and liquefaction evaluation of gravelly reclamations and hydraulic fills (Port of Wellington, New Zealand)

In the 2016 Mw7.8 Kaikōura earthquake, widespread liquefaction occurred in the reclamations at CentrePort, Wellington (New Zealand), while less intense shaking during two earthquakes in 2013 produced only some liquefaction manifestation over isolated areas of the port. The two types of reclamations, comprised of end-dumped gravelly fills and hydraulically placed silty-sandy fills, are not well represented in current empirical simplified liquefaction procedures. Comprehensive CPT investigations are presented and used to characterize the fills, and then perform CPT-based liquefaction evaluation for the three earthquakes that affected the port in 2013 and 2016. The results of the analyses are compared to observations of liquefaction performance and are examined in relation to the soil and deposit characteristics of the fills. The CPT-based liquefaction assessment was generally consistent with observations, though clear shortcomings and limitations of these procedures were also evident. The paper scrutinizes conventional engineering procedures for liquefaction assessment when applied to non-conventional or problematic soils for such assessment, with reference to a well-documented case history.

Effect of Micropiles on Clean Sand Liquefaction Risk Based on CPT and SPT

Liquefaction is a hazardous seismic-based phenomenon, which causes an abrupt decrease in soil strength properties and can result in the massive destruction of the built environment. This research presents a novel approach to reduce the risk of soil liquefaction using jet-grouted micropiles in clean sands. The saturated soil profile of the study project mainly contains clean sands, which are suitable to more reliably employ simplified soil liquefaction analyses. The grouting is conducted using 420 micropiles to increase the existing soil properties. The effect of jet grouting on reducing the potential of liquefaction is assessed using the results of the cone penetration test (CPT) and the standard penetration test (SPT), which were conducted before and after jet grouting by implementing micropiles in the project sites. According to three CPT-based liquefaction analyses, the Juang method predicts the most effective improvement range of the factor of safety in the clean sand. The Boulanger and Idriss, and Eurocode methods show comparable evaluations. Results of the SPT-based analyses show the most considerable increase of the factor of safety following the Boulanger and Idriss, and NCEER approaches in the SP soil. CPT- and SPT-based analyses confirm the effectiveness of jet grouting by micropiles on enhancing soil properties and reducing the risk of liquefaction.

LIQUEFACTION ASSESSMENT OF RECLAIMED LAND AT CENTREPORT, WELLINGTON

Observations of liquefaction-induced damage at the port of Wellington (CentrePort) provide an opportunity to evaluate the applicability of state-of-the-practice liquefaction evaluation methodologies on reclaimed land. This study focuses on the application of widely used simplified liquefaction assessment methods on the end-dumped gravelly fills and hydraulically-placed silty and sandy fills at CentrePort for the 2013 Cook Strait, 2013 Lake Grassmere, and 2016 Kaikōura earthquakes. Liquefaction assessment of the gravel reclamation poses several challenges due to its large percentage of gravel-sized particles making it difficult to obtain high-quality in situ data. The hydraulic fills at CentrePort are also of significant interest as they relate to a range of issues in the simplified engineering assessment around effects of fines and their plasticity on the liquefaction resistance. Following the 2016 Kaikōura earthquake, subsurface explorations were performed which included 121 Cone Penetration Tests (CPTs). Results of CPT-based liquefaction triggering and post-liquefaction reconsolidation settlement assessments using state-of-the-practice procedures are discussed and compared with observed liquefaction manifestation and settlements.

Liquefaction case histories from the 1987 Edgecumbe earthquake, New Zealand – Insights from an extensive CPT dataset and paleo-liquefaction trenching

The 1987 ML 6.3 Edgecumbe earthquake triggered localized liquefaction and associated lateral spreading in the township of Whakatane in the North Island of New Zealand. Subsequent simplified CPT-based liquefaction assessments undertaken using modelled Peak Ground Accelerations (PGA) and depth to ground-water for the Edgecumbe earthquake predicts moderate-to-severe liquefaction for much of Whakatane. Variations between the predicted and observed liquefaction severities highlights areas of inconsistent prediction. Potential reasoning for the inconsistencies are subsequently examined through trenching and comparison of CPT traces at selected sites where liquefaction was predicted and was observed during the Edgecumbe earthquake, and sites where liquefaction was predicted yet not observed. Variations in depositional age, stratigraphy including thin-scale interlayering of sands, silts, and pumice, and/or sediment composition are shown to be potential contributing factors. Sites where liquefaction was observed are shown to contain thick potentially liquefiable deposits of recently deposited sand and silt, while sites where liquefaction was predicted yet not observed contain thinner and/or inter-layered liquefiable deposits of older sands and silts. The results highlight the benefit of cross-examining predicted liquefaction severities with historical case histories and outline local site conditions that may result in inconsistent liquefaction assessments.