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1. ASSESSING LIQUEFACTION IN GRAVELLY SOILS BASED ON FIELD CASE HISTORIES [ASSESSING LIQUEFACTION IN GRAVELLY SOILS BASED ON FIELD CASE HISTORIES]

   https://doi.org/10.5592/CO/2CroCEE.2023.141  

   Rollins, Kyle; Roy, Jashod (March 2023, Proceedings of the 2nd Croatian Conference on Earthquake Engineering)

   Gravelly soils have liquefied at multiple sites in at least 27 earthquakes over the past 130 years. These gravels typically contain more than 25% sand which lowers the permeability and makes them susceptible to liquefaction. Developing a reliable, cost-effective liquefaction triggering procedure for gravelly soils has been a challenge for geotechnical engineers. Typical SPT- or CPT-based correlations can be affected by large-size gravel particles and can 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 large diameter cone penetrometer. With a cone diameter of 74 mm, the Chinese Dynamic Cone Penetration Test (DPT) is superior to smaller penetrometers and can be economically performed with conventional drilling equipment. Using logistic regression analysis, the DPT has been directly correlated to liquefaction resistance at sites where gravels did and did not liquefy in past earthquakes. Probabilistic liquefaction resistance curves were developed based on 137 data points from 10 different earthquakes in seven countries. Using a similar data set, probabilistic liquefaction triggering curves were also developed based on Vs measurements in gravelly soils. The Vs-based liquefaction triggering curves for gravels shift to the right relative to similar curves based on sands. New magnitude scaling factor (MSF) curves have also been developed specifically for gravel liquefaction which were found to be reasonably consistent with previous curves for sand. 

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2. Robust Identification and Characterization of Thin Soil Layers in Cone Penetration Data by Piecewise Layer Optimization

   https://doi.org/j.compgeo.2021.104404  

   Cooper, J. (January 2022, Computers and geotechnics)

   Cone penetration testing (CPT) is a preferred method for characterizing soil profiles for evaluating seismic liquefaction triggering potential. However, CPT has limitations in characterizing highly stratified profiles because the measured tip resistance (𝑞𝑐 ) of the cone penetrometer is influenced by the properties of the soils above and below the tip. This results in measured 𝑞𝑐 values that appear ‘‘blurred’’ at sediment layer boundaries, inhibiting our ability to characterize thinly layered strata that are potentially liquefiable. Removing this ‘‘blur’’ has been previously posed as a continuous optimization problem, but in some cases this methodology has been less efficacious than desired. Thus, we propose a new approach to determine the corrected 𝑞𝑐 values (i.e. values that would be measured in a stratum absent of thin-layer effects) from measured values. This new numerical optimization algorithm searches for soil profiles with a finite number of layers which can automatically be added or removed as needed. This algorithm is provided as open-source MATLAB software. It yields corrected 𝑞𝑐 values when applied to computer-simulated and calibration chamber CPT data. We compare two versions of the new algorithm that numerically optimize different functions, one of which uses a logarithm to refine fine-scale details, but which requires longer calculation times to yield improved corrected 𝑞𝑐 profiles. 

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3. Vs-based Evaluation of Select Liquefaction Case Histories from the 2010-2011 Canterbury Earthquake Sequence

   Wood, C.M. (January 2017, Journal of geotechnical and geoenvironmental engineering)

   The 2010–2011 Canterbury earthquake sequence included a number of events that triggered recurrent soil liquefaction at many locations in Christchurch, New Zealand. However, the most severe liquefaction was induced by the Mw7.1 September 4, 2010, Darfield and Mw6.2 February 22, 2011, Christchurch earthquakes. The combination of well-documented liquefaction surface manifestations during multiple events, densely recorded ground motions during these events, and detailed subsurface characterization information at the selected sites provides an unprecedented opportunity to add quality case histories to the empirical soil liquefaction database. The authors have already documented and published 50 high-quality liquefaction case histories from these earthquakes using cone penetration test (CPT) data. This paper examines 46 of these case histories using shear-wave velocity (Vs) profiles derived from surface wave (SW) methods and a Christchurch-specific Vs correlation based on CPT tip resistance. The Vs profiles have been used to evaluate the two most commonly used Vs-based simplified liquefaction evaluation procedures (i.e., Andrus and Stokoe and Kayen et al.). An error index (EI ) has been used to quantify the overall performance of these two procedures in relation to liquefaction observations. Although the two procedures are essentially equivalent for sites with normalized Vs (i.e., Vs1) <180 m=s, the Kayen et al. procedure, with 15% probability of liquefaction, provides better predictions of liquefaction triggering for sites with Vs1 greater than 180 m=s. Additionally, total EI values obtained using Vs profiles from surface wave testing in conjunction with the Kayen et al. procedure are lower than two other CPT-based triggering procedures but higher than the total EI value obtained using the Idriss and Boulanger CPT-based procedure. 

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4. Evaluation of dynamic cone penetration test for liquefaction assessment of gravels from case histories in Italy

   Rollins, K.M. and (July 2019, Earthquake Geotechnical Engineering for Protection and Development of Environment and Constructions, Procs. 7th Intl. Conf. on Earthquake Geotechnical Engineering)

   In North American practice, the Becker Penetration Test (BPT) has become the primary field test used to evaluate liquefaction resistance of gravelly soils. However, this test is expensive and uncertainties exist regarding correlations and corrections. As an alternative, the 74 mm diameter dynamic cone penetration test (DPT) developed in China has recently been correlated with liquefaction resistance based on field performance data from the Mw7.9 Wenchuan earth-quake. In this study, liquefaction resistance was evaluated using DPT soundings with two hammer energies at two sites in Avasinis, Italy where gravelly soil liquefied in the 1976 Friuli, Italy earthquake. Gravel content ranged from 20 to 40% based on the 4.75mm criteria and The DPT liquefaction correlation correctly predicted liquefaction in all cases where liquefaction features were observed. These results indicate that the DPT can provide accurate liquefaction hazard evaluations for gravelly soils more economically than alternative procedures. Standard SPT energy corrections were found to be reasonable for the DPT. 

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5. Axial Load Capacity Predictions of Drilled Displacement Piles With SPT- and CPT-based Direct Methods

   https://doi.org/10.37308/DFIJnl.20220512.262  

   Figueroa, Genesis (November 2022, DFI Journal The Journal of the Deep Foundations Institute)

   Drilled Displacement Piles (DDP) provide an ideal foundation solution that combines the benefits of ground improvement with traditional advantages of piling systems. This paper offers insights gathered from 55 construction projects in which nearly 130 DDPs were installed and tested axially. High quality site exploration data (e.g., Cone Penetration Test (CPT) and Standard Penetration Test (SPT)) were evaluated to derive geotechnical analysis parameters. The test sites consisted of mostly mixed soil types with strongly stratified layers of sand, silt, and clay. Pile diameters ranged between 35 and 61 cm (14 to 24 inches). Prior to analyzing the axial performance of DDPs, a variety of failure interpretation methods were assessed to confidently extrapolate failure loads when field testing was terminated prior to pile failure. Results of this study suggested the Van der Veen’s (1953) method to most closely estimate the load that triggers pile plunging behavior specific to DDPs, followed by the Butler & Hoy (1977) and L1-L2 methods (Hirany and Kulhawy, 1989). Hereafter, in-situ axial load test results were compared with a wide range of analytical methods, including those developed specifically for DDPs. Predictive accuracy was assessed in terms of total pile capacity and pile settlement and separated based on pile diameter, stiffness, and soil type. Most examined analytical methods underpredict the in-situ pile capacities for both, CPT and SPT -based analysis. It was also found that the difference between the experimentally determined and predicted capacities is related to the level of improvement in the surrounding soil following pile installation. A general comparison between predictive axial accuracy and the observed level of ground improvement is also discussed for sandy and mixed type of soils. 

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