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1. 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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2. Plant Root Circumnutation-Inspired Penetration in Sand and Clay

   Anilkumar, Riya; Martinez, Alejandro (June 2024, Scipedia)

   Site investigation (SI) and subsurface exploration are vital for characterizing soil properties. However, a common challenge is the lack of sufficient reaction force to penetrate through stiff crusts or deep layers, leading to refusal. To address this issue, rigs typically have large sizes that can make mobility and accessibility challenging and increase the carbon footprint of SI activities. This paper experimentally investigates a plant root-inspired strategy called circumnutation-inspired motion (CIM) to reduce the vertical penetration forces (F_z) in comparison to quasi-static penetration used for example for Cone Penetration Testing (CPT). The CIM probes have a bent tip end and are rotated at a constant angular velocity (ω) while they are advanced at a constant vertical velocity (v) in uniform specimens of clay and sand. F_z for both soils decay exponentially by factors as high as 10 with increasing relative velocity, defined as the ratio of the tangential to the vertical velocity of the probe tip (ωR\/v). Torques for both soils increase with initial increases in ωR\/v which stabilize at higher velocities. While the cumulative total work, calculated for both clay and sand from the measured forces and torques, increases less than 25% for initial increases in ωR\/v between 0 and 0.3π, the F_z can be reduced by around 50%. Thus, CIM penetration can produce significant reductions in F_z in comparison to CPTs while limiting the additional energy consumed. CIM could be implemented to perform site investigation activities, such as obtaining samples or installing sensors, using smaller-sized, light-weight rigs. 

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3. A Consistent Correlation between Vs, SPT, and CPT Metrics for Use in Liquefaction Evaluation Procedures

   Ulmer, K.J. (February 2020, Geo-Congress 2020: Geotechnical Earthquake Engineering and Special Topics)

   J.P. Hambleton, R. Makhnenko (Ed.)

   The objective of this study is to develop a consistent relationship between small strain shear wave velocity (Vs), corrected cone penetration test (CPT) tip resistance (qc1Ncs), and corrected standard penetration test (SPT) blow count (N1,60cs) for liquefiable soils. In the absence of actual measurements of Vs in the field, it is common to use data from SPT or CPT testing to estimate Vs. However, empirical correlations between pairs of these in situ metrics can yield significantly different values of Vs. Using recent correlations between cyclic resistance ratio normalized to M7.5 (CRRM7.5) and Vs normalized to one atmosphere of overburden (Vs1), qc1Ncs, or N1,60cs, a consistent relationship is developed such that reasonably similar values of Vs can be obtained using either qc1Ncs or N1,60cs. In comparison to two published Vs correlations, the correlations given in this study provide an average Vs value when using N1,60cs as the dependent variable but a slightly lower prediction of Vs when using qc1Ncs as the dependent variable. 

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4. Experimental investigation of circumnutation-inspired penetration in sand

   https://doi.org/10.1088/1748-3190/ad8c89  

   Anilkumar, Riya; Martinez, Alejandro (November 2024, Bioinspiration & Biomimetics)

   Probes that penetrate soil are used in fields such as geotechnical engineering, agriculture, and ecology to classify soils and characterize their propertiesin situ. Conventional tools such as the Cone Penetration Test (CPT) often face challenges due to the lack of reaction force needed to penetrate stiff or dense soil layers, necessitating the use of large drill rigs. This paper investigates more efficient means of penetrating soil by taking inspiration from a plant-root motion known as circumnutation. Experimental penetration tests on sands are performed with circumnutation-inspired (CI) probes that advance at a constant vertical velocity ( $v$) while simultaneously rotating at a constant angular velocity ( $\omega$). These probes have bent tips with a given bent angle ( $\alpha$) and bent length ( $L_1$). The variation of the mobilized vertical force ( $F_z$), torque ( $T_z$.), and the mechanical work components with the ratio of tangential to vertical velocity (ωR/ν, whereRis the distance of the tip of the probe from the vertical axis of rotation) is investigated along with the effects of probe geometry, vertical velocity, and soil relative density ( $D_R$). The results show that the soil penetration resistance does not vary with $v$, but it increases as $\alpha$, $L_1$, and $D_R$are increased. $F_z$decays exponentially with increasing $\omega R/v$, $T_z$initially increases and then plateaus, while total work ( $W_T$) shows little magnitude changes initially but later increases monotonically. The mechanisms leading to these trends are identified as the changes in the probe projected areas and mobilized normal stresses due to differences in probe geometry and the effects of $\omega R/v$on the resultant force direction and soil disturbance. The results show that CI penetration within a specific range of $\omega R/v$leads to small increases in $W_T$(i.e., $\text{⩽}$25%), yet mobilizes $F_z$magnitudes that are 50%–80% lower than that mobilized during non-rotational penetration (i.e., CPT). This indicates that CI penetration can be adopted forin situcharacterization or sensor placement with smaller vertical forces, allowing for use of lighter rigs. 

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5. Effects of Tar on CPT and Shear Wave Velocity Correlations for the LA Metro Purple Line (D-Line)

   https://doi.org/10.1061/9780784484708.019  

   Chrysovergis, Taki; Lemnitzer, Anne; Star, Lisa M.; Rodriguez, Joseph; Hashash, Youssef; Sathialingam, Namasivayam; Cording, Edward; O’Rourke, Thomas D. (March 2023, ASCE Geo-Congress 2023)

   Rathje, E.; Montoya, B.; Wayne, M. (Ed.)

   The Los Angeles (LA) Metro Purple Line (D-Line) Extension project requires the design and construction of deep station excavations and tunnels for rail transit from downtown to west LA. The tunnel alignment for Reach 2 of the Westside Purple Line Extension 1 construction transects naturally-occurring tar-infused soils, which have been known to cause challenging construction conditions in southern California, as well as many other locations around the world. Two stations in similar geology but located within and outside tar soils were compared. The soil investigations of the tunnels and station excavations consisted of subsurface exploration including deep soil borings, Cone Penetration Testing (CPT), seismic velocity measurements, pressuremeter testing, and gas measurements, among others. The results of CPT and shear-wave velocity testing provide extensive data in tar soils unique to Southern California and an opportunity to increase our understanding of four-phase soil materials and the effects of tar on soil behavior interpretation and engineering properties. CPT correlations for conventional (non-tar-infused) soils were found to be inadequate for tar soils in the Los Angeles basin. The CPT based Soil Behavior Type Index (SBTn) determined in tar soils suggested the presence of much finer-grained material than determined from laboratory testing and field observations. Additionally, the presence of tar soils amplified the difference between CPT correlations for shear wave velocity (Vs) and direct Vs seismic CPT measurements. 

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