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Achieving stable stress solutions at large strains using the Material Point Method (MPM) is challenging due to the accumulation of errors associated with geometry discretization, cell-crossing noise, and volumetric locking. Several simplified attempts exist in the literature to mitigate these errors, including higher-order frameworks. However, the stability of the MPM solution in such frameworks has been limited to simple geometries and the single-phase formulation (i.e., neglecting pore fluid). Although never explored, multipatch isogeometric analysis offers desirable qualities to simulate complex geometries while mitigating errors in the MPM. The degree of required high-order spatial integration has also never been investigated to infer a minimum limit for the stability of the stress solution in MPM. This paper presents a general-purpose numerical framework for simulating stable stresses in porous media, capturing both near incompressibility and multiphase interactions. First, the numerical framework is presented considering Non-Uniform Rational B-splines (NURBS) to perform isogeometric analysis (IGA) in MPM. Additionally, a volumetric strain smoothing algorithm is used to alleviate errors associated with volumetric locking. Second, the manifestation of cell-crossing errors is assessed via a series of problems with orders ranging from linear to cubic interpolation functions. Third, the use of NURBS is investigated and verified for problems with circular geometries. Finally, multipatch analysis is deployed to simulate plane strain and 3D penetration in soils, considering nearly incompressible elastoplastic (total stress) analysis and fully-coupled hydro-mechanical (effective stress) analysis. The stability of the solution is also analyzed for different constitutive models. From the results, it can be concluded that the framework using cubic interpolation functions with strain smoothing is the most convenient, presenting stable stress solutions for a broad range of multiphase geotechnical applications. 

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. 

Impact penetration into soils is one of the most challenging phenomena to model using numerical techniques due to the very rapid large-deformations and water-soil-structure interaction problems involved in the process. In this work, portable free fall penetration testing (FFP) in dry and saturated sands is modeled using the material point method (MPM). MPM is a powerful tool for large-deformation applications in history-dependent materials. A parametric analysis is performed to understand the influence of the soil stiffness and the water excess pore pressures produced during the impact. The effect of the sand stiffness is studied by modifying its Young’s modulus, and the effect of the water is considered by comparing a fully dry model with a fully coupled hydro-mechanical model. The results indicate that the stiffness of the sand strongly controls the appearance of a general bearing capacity failure, which produces deceleration responses with more than one peak, dissimilar to physical tests. In the case of fully saturated sand, the penetration depth is lower than for dry sand with the same properties and the kinematical response of the FFP is consistent with experiments. The results are promising and encourage further development of the simulations.