Most natural soils exhibit a certain degree of soil structure which, in general, leads to increased strength and stiffness properties. However, the mechanical characterization of these soils based on conventional laboratory testing proves difficult in many cases due to sample disturbance. The present work aims to characterize the microstructure of a postglacial, normally consolidated, fine-grained deposit in Seekirchen, Austria, adopting in situ testing, laboratory testing on high-quality samples, and numerical analysis. The latter involves recalculating in situ piezocone penetration tests (CPTu) using an advanced constitutive model for structured soil. In contrast to existing in situ interpretation methods, the results of the numerical study, the mineralogical and hydrochemical testing, as well as the oedometer and bender element testing on undisturbed and reconstituted samples suggest that the soil is characterized by a significant amount of structure. It is demonstrated that the difference in shear wave velocity measured in situ and through bender element testing on reconstituted samples can be used as an indicator for soil structure. Ignoring the effects of structure may lead to inaccurate parameter determination for advanced constitutive models, which are subsequently employed to solve complex boundary value problems in geotechnical practice. As a consequence, the prediction of expected displacement may not be reliable.

The Smoothed Particle Finite Element Method (SPFEM) has gained popularity as an effective numerical method for modelling geotechnical problems involving large deformations. To promote the research and application of SPFEM in geotechnical engineering, we present ESPFEM2D, an open-source two-dimensional SPFEM solver developed using MATLAB. ESPFEM2D discretizes the problem domain into computable particle clouds and generates the finite element mesh using Delaunay triangulation and the alpha\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \alpha $$\end{document}-shape technique to resolve mesh distortion issues. Additionally, it incorporates a nodal integration technique based on strain smoothing, effectively eliminating defects associated with the state variable mapping after remeshing. Furthermore, the solver adopts a simple yet robust approach to prevent the rank-deficiency problem due to under-integration by using only nodes as integration points. The Drucker-Prager model is adopted to describe the soil's constitutive behavior as a demonstration. Implemented in MATLAB, this open-source solver ensures easy accessibility and readability for researchers interested in utilizing SPFEM. ESPFEM2D can be easily extended and effectively coupled with other existing codes, enabling its application to simulate a wide range of large geomechanical deformation problems. Through rigorous validation using four numerical examples, namely the oscillation of an elastic cantilever beam, non-cohesive soil collapse, cohesive soil collapse, and slope stability analysis, the accuracy, effectiveness and stability of this open-source solver have been thoroughly confirmed.