A series of plate loading tests on clay has been conducted in the centrifuge. The aim of the tests is to create a data set, which is freely downloadable, to validate numerical tools that account for geometrical nonlinearities. The tests include two sources of geometrical non-linearities. The first source is the reducing clay layer thickness below the plate, which causes an increase in resistance. The second source is the backflow of the clay around the tip of the plate. The backflow has a reducing effect on the plate resistance. This paper outlines four tests: two involving a wide plate and two with a small plate. Each plate geometry is investigated under both smooth and rough side model boundaries. An material point method (MPM) schematization is used for numerical analysis. The schematization and parameter selection are initially validated by comparing the MPM results against CPTu data in each test. The numerical analysis examines the impact of a finite layer thickness by analyzing various layer thicknesses. Furthermore, the analysis shows the influence of the backflow on the plate resistance by analyzing different ratios of shaft to plate width. In this study, the pore pressures below the plate and vertical and horizontal displacement fields are considered in addition to the load displacement curves. The MPM simulations are in good agreement with the centrifuge data.

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Cone penetrometer tests (CPTs) are used to characterize soil for a variety of geotechnical engineering applications, including earthquake-induced liquefaction triggering assessment. Numerical modeling of CPTs is frequently used to better understand soil behavior, soil-penetrometer interaction, and engineering estimates made from CPT data. However, calibrating and validating numerical CPT simulations with experimental calibration chamber (CC) data can be challenging. Specifically, uncertainties in the interpretation of laboratory strength and compression data compound with uncertainties in the CC testing and the assumptions made when developing the numerical model. This article provides a comprehensive review of uncertainties in the calibration and validation of CPT numerical simulations performed in homogenous sand, homogenous clay, and layered sand-clay soil profiles, comparing numerical results with well-documented experimental calibration chamber tests performed at Deltares. In particular, the Material Point Method (MPM) is used to perform the numerical analyses. A framework is presented to assess how uncertainty in the numerical model output is attributed to each input parameter. It is demonstrated that uncertainties can be explored numerically. Finally, recommendations for future experimental and numerical studies of CPTs are provided.

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A full understanding of the interaction mechanisms among flow-like landslides and impacted protection structures is still an open issue. Although several approaches, from experimental to numerical, have been used so far, a thoroughly assessment of the hydromechanical behaviour of the landslide body is achievable only through a multiphase and large deformation approach. This paper firstly proposes a conceptual model for a specific type of protection structure, namely a Deformable Geosynthetics-Reinforced Barrier (DGRB), i.e., an embankment made of coarse-grained soil layers reinforced by geogrids. In such a case, the sliding of the barrier along its base, under the impulsive action of a flow-type landslide, is an important landslide energy dissipation mechanism, and a key issue for the design. Then, two different approaches are proposed: i) an advanced hydro-mechanical numerical model based on Material Point Method is tested in simulating the whole complex landslide-structure interaction mechanisms, ii) an analytical model is set up to deal with the landslide energy dissipation and the kinematics of both the landslide and barrier. The calibration of the proposed analytical model is pursued based on the numerical results. Finally, the analytical model is successfully validated to interpret a large dataset of landslide impact field evidence, for whose interpretation also five empirical methods available in the literature are tested.

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Cone penetration tests (CPTs) can quantitatively inform about the mechanical state of a sand. However, relating measured cone resistance values to sand state requires complex back-analysis of the processes occurring in the soil during the test. This paper provides new evidence of the value added in this area by modern large-deformation modelling based on the material point method (MPM). It is shown that accurate simulation of the relationship between cone resistance and sand state can be achieved, on condition that the constitutive behaviour of the soil - and especially its critical state features - is adequately modelled over a wide range of confining pressures. This study relies on the predictive capabilities of the critical state NorSand model, and shows how previous calibrations endeavours from the literature (based on triaxial test results) can support the MPM simulation of unrelated CPT results obtained through calibration chamber tests. MPM CPT simulations of ever-increasing quality will positively impact the state of the art of CPT interpretation procedures, to date still largely based on simplified cavity expansion theories.

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This paper describes an MPM formulation using linear quadrilateral elements suitable for soil-structure-interaction problems. The volumetric locking and stress-oscillations are mitigated using a reduced integration technique and the Gauss integration scheme, respectively. The formulation can be used with both structured and unstructured computational meshes. In addition, an improved calculation scheme is proposed to obtain accurate contact reaction forces, especially for contacts between non-porous structures and soils with high liquid pressures. The formulation is validated by simulating a wide range of applications such as a water dam break, 1D large-strain consolidation, and the bearing capacity of a strip footing. Finally, the installation of a cone penetrometer in a centrifuge is successfully simulated in soft soils and compared with the experimental data for the entire range of drainage conditions.

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Full understanding the interaction mechanisms between flow-like landslides and the impacted protection structures is an open issue. While several approaches, from experimental to numerical, have been used so far, it is clear that the adequate assessment of the hydromechanical behaviour of the landslide body requires both a multiphase and large deformation approach. This paper refers to a specific type of protection structure, namely a rigid barrier, fixed to the base ground. Firstly, a framework for the Landslide-Structure-Interaction (LSI) is outlined with special reference to the potential barrier overtopping (nil, moderate, large) depending on the features of both the flow and the barrier. Then, a novel empirical method is casted to estimate the impact force on the barrier and the time evolution of the flow kinetic energy. The new method is calibrated by using an advanced hydro-mechanical numerical model based on the Material Point Method. The validation of the empirical formulation is pursued referring to a large dataset of field evidence for the peak impact pressure. Both numerical and empirical methods can appropriately simulate the physical phenomena. The performance of the newly proposed empirical method is compared to the literature methods and its advantages are outlined.

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The study on impact mechanisms of flow-like landslides against structures is still an open issue in the scientific literature. Many researchers have so far employed either experiments or numerical methods, but the evaluation of the impact forces on mitigation obstacles remains difficult especially if the solid–fluid interaction within the flow is considered. This study shows how advanced numerical tools, such as material point method, may be used in simulating those complex processes. The simulations are carried out for two well-documented laboratory tests: a dry granular flow impacting a rigid wall under different geometries and testing conditions in a small-scaled flume and a saturated flow with complex propagation pattern in a centrifuge apparatus. The numerical modelling is validated against the observations and then used to explore the response of different flows impacting rigid structures in other conditions than in the experiments. The soil–fluid interaction influences the type of impact mechanism, the kinematics of the flow, and the space–time trend of the impact pressure against the structure.

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Numerical modelling, particularly fully-coupled hydro-mechanical large-deformation models, greatly helps in properly simulating the complex failure and post-failure mechanisms of rainfall-induced landslides. The affected soils, in fact, evolve from none or small deformation rates to large deformation rates during the initiation stage and vice-versa during deposition, with relevant interactions between the solid skeleton and interstitial water. The Material Point Method (MPM) has the potential to reproduce entirely those complex processes. However, a comparison with standard tools (e.g. FEM: Finite Element Method, LEM: Limit Equilibrium Method) may guide in the optimal choice (or in the combined use) of the various modelling approaches. A framework is here proposed based on a multi-tool approach consisting in the combination of: a) no-deformation LEM, b) small-deformation FEM, c) large-deformation MPM. The LEM slope stability analyses are performed for a realistic assessment of the major slip surface(s) and to back-analyse uncertain slope parameters. The FEM stress-strain analyses assess the progressive failure, the onset of initial velocity and the later acceleration of the landslide body, until large deformations occur in the slope and numerical convergence of FEM is lost. The MPM analyses are used to reproduce the whole landslide process, from the initiation to propagation and final deposition. Such an integrated framework is tested for an international landslide benchmark (the 1995 Fei Tsui Road landslide in Hong Kong). The results achieved through the different approaches are discussed in relation to the wide scientific literature available for the general topics and the specific case study. The paper highlights that the fully-coupled hydro-mechanical large-deformation model properly reproduces the complex failure and post-failure mechanisms of rainfall-induced landslides. However, no-deformation LEM analyses and small-deformation FEM analyses allow a reasonable understanding of both the pre-failure stage and the failure mechanism. These more traditional tools are confirmed as indispensable tools in the engineering practice and research.

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Cone penetration tests (CPTs) are widely used in geotechnical engineering for soil characterization and parameter determination. Throughout the years, experimental data have been used to determine correlations between CPT data and soil properties, such as stiffness or strength. Recent progress in advance numerical methods allows the simulation of the full CPT penetration by overcoming the limitations related to extreme deformations. The use of these numerical techniques provides new prospective to the soil characterization and determination of soil parameters, especially for the settings where limited (or no) experimental data is available and existing correlations are not accurate, or absent. This paper presents a numerical framework based on the Material Point Method (MPM) to simulate CPT in dry sand. First, it is proven that the calculation scheme is stable and accurate. Then, the model results are validated against chamber test data in terms of both cone resistance and displacement field during the penetration. Finally, some considerations about the formulation of the constitutive models of soils are presented, specifically oriented for CPT applications.

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The Harmonic Balance Method (HBM) is often used to determine the stationary response of nonlinear discrete systems to harmonic loading. The HBM has also been applied to nonlinear continuous systems, but in many cases the nonlinearity consists of discrete nonlinear elements. This chapter demonstrates the application of the HBM to dissipative continua with distributed nonlinearity by analysing three canonical problems: (a) 1-D layer with a free surface and rigid base (interfering upward and downward propagating shear waves), (b) 1-D half-space with a rigid base (vertically propagating shear waves), and (c) 2-D axially symmetric semiinfinite medium with a circular cavity (radially propagating compressional waves), all of them subject to harmonic excitation at a boundary. Results show that systems (a) and (c) exhibit softening behaviour and super-harmonic resonances, while only the former displays multiple response amplitudes for certain excitation frequencies; the unique frequency-amplitude relationship of system (c) is due to the strong damping (i.e., radiation damping and internal dissipation). Furthermore, although system (b) essentially does not resonate, the third-harmonic component exhibits a maximum caused by the interplay between the dissipative and nonlinear effects, a phenomenon that also occurs in system (c). Finally, the considered systems have applications in earthquake and geotechnical engineering, among others, but the presented methodology is generic.@en