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1. Harnessing Numerical Tools to Study the Limitations of CPTs for Characterizing Complex Soil Stratigraphies for Liquefaction Assessment

   Yost, K.M. (June 2022, Proc. 12th National Conf. on Earthquake Engineering (12NCEE))

   This paper describes the use of the Material Point Method (MPM) to simulate cone penetrometer testing (CPT) in complex soil profiles. CPT-based liquefaction evaluation procedures have been shown to be inaccurate in highly interlayered soil stratigraphies. One contributing factor to this inaccuracy is that CPT measurements at discrete depths reflect the properties of all soils that fall within a zone of influence around the cone tip, not just the properties of the soil at a particular depth. Consequently, the CPT loses resolution in soil profiles with many thin, interbedded soil layers (multiple thin-layer effects) and provides inaccurate input data to liquefaction analyses. While several procedures have been proposed to correct for multiple thin-layer effects, they tend to decrease in efficacy as the thickness of soil layers decreases. Results from the MPM analyses detailed in this paper highlight limitations of (1) the CPT in characterizing complex soil stratigraphies and (2) procedures proposed to correct for multiple thin-layer effects in CPT data. 

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2. A cone penetration test database for multiple thin-layer correction procedure development

   https://doi.org/10.1177/87552930231217002  

   Yost, Kaleigh_M; Yerro, Alba; Martin, Eileen_R; Green, Russell_A (January 2024, Earthquake Spectra)

   Cone penetration tests (CPTs) are a commonly used in situ method to characterize soil. The recorded data are used for various applications, including earthquake-induced liquefaction evaluation. However, data recorded at a given depth in a CPT sounding are influenced by the properties of all the soil that falls within the zone of influence around the cone tip rather than only the soil at that particular depth. This causes data to be blurred or averaged in layered zones, a phenomenon referred to as multiple thin-layer effects. Multiple thin-layer effects can result in the inaccurate characterization of the thickness and stiffness of thin, interbedded layers. Correction procedures have been proposed to adjust CPT tip resistance for multiple thin-layer effects, but many procedures become less effective as layer thickness decreases. To compare or improve these procedures and to develop new ones, it is critical to have pairs of measured tip resistance ( q^m) and true tip resistance ( q^t) data, where q^mis the tip resistance recorded by the CPT in a layered profile, and q^trepresents the tip resistance that would be measured in the profile absent of multiple thin-layer effects. Unfortunately, data sets containing q^mand q^tpairs are extremely rare. Accordingly, this article presents a unique database containing laboratory and numerically generated CPT data from 49 highly interlayered soil profiles. Both q^mand q^tare provided for each profile. An accompanying Jupyter notebook is provided to facilitate the use of the data and prepare them for future statistical learning (or other) applications to support multiple thin-layer correction procedure development. 

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3. Inverse filtering procedure to correct cone penetration data for thin-layer and transition effects

   Boulanger, Ross W.; DeJong, Jason T. (June 2018, Proc., Cone Penetration Testing 2018, Hicks, Pisano, and Peuchen, eds., Delft University of Technology, The Netherlands)

   This paper presents an inverse filtering procedure for developing estimates of "true" cone penetration tip re-sistance and sleeve friction values from measured cone penetration test data in interlayered soil profiles. Re-sults of prior studies of cone penetration in layered soil profiles are utilized for developing and evaluating the inverse filtering procedure. The inverse filtering procedure has three primary components: (1) a model for how the cone penetrometer acts as a low-pass spatial filter in sampling the true distribution of soil resistance versus depth, (2) a solution procedure for iteratively determining an estimate of the true cone penetration resistance profile from the measured profile given the cone penetration filter model, and (3) a procedure for identifying sharp transition interfaces and correcting the data at those interfaces. The details of the inverse filtering pro-cedure presented herein were developed with a focus on liquefaction problems, but the concepts and frame-work should be applicable to other problems. Example applications of the inverse filtering procedure are pre-sented for four CPT soundings illustrative of a range of soil profile characteristics. The proposed procedure provides an objective, repeatable, and automatable means for correcting cone penetration test data for thin-layer and transition zone effects. 

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4. 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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5. A new shared miniature cone penetrometer for centrifuge testing

   Carey, T. (July 2018, International Conference on Physical Modeling in Geotechnics)

   Cone penetrometers (CPTs) are commonly used for characterising the soil properties of centrifuge models; CPT data is useful for interpretation and quality control. This paper describes the development and design of a new robust CPT device for centrifuge testing. The new device consists of a 6mm cone, an outer sleeve, and an inner rod that transmits cone tip forces to a load cell above the ground surface. The design eliminates the need for a custom submerged strain gauge bridge near the tip, significantly reducing cost.A direct comparison was performed between this CPT device and another similar device developed at the University of Cambridge. CPT’s were manufactured using the new design and then shipped to eight different centrifuge facilities, for quality control of similar experiments performed for LEAP (Liquefaction Experiments and Analysis Projects). All the centrifuge tests simulated a 4 m deep deposit of soil, all consisting of Ottawa F-65 sand with relative densities ranging between about 45 to 80%. The results obtained have been extremely valuable as an independent assessment of the density calculated from mass and volume measurements at different laboratories. 

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