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International audience; The main objective of this article is focus on the investigation methods to estimates two important geotechnical soil parameter that are modulus and shear wave velocity by using lightweight dynamic penetrometer called Panda 3®. Firstly, wave equation, decoupling and reconstruction implemented method are presented. Then, the approach to determine soil modulus as well as the soil shear velocity through shock polar curves in frequency domain will be presented. The obtained results are evaluated with other in-situ geotechnical tests. The analysis shows a good accuracy and quality of the measurements. In addition, due to the high resolution of the vertical measurements (around 200 measures/meter), the proposed device, Panda 3, could be a good tool in order to improve shallow soil characterization.

This paper presents algorithm improvements that reduce the numerical noise and increase the numerical stability of the material point method formulation. Because of the linear mapping required in each time step of the material point method algorithm, a possible mismatch between the number of material points and grid nodes leads to a loss of information. These null‐space related errors may accumulate and affect the numerical solution. To remove the null‐space errors, the presented algorithm utilizes a null‐space filter. The null‐space filter shown removes the null‐space errors, resulting from the rank deficient mapping and the difference between the number of material points and the number of nodes. The presented algorithm enhancements also include the use of the explicit generalized‐α integration method, which helps optimizing the numerical algorithmic dissipation. This paper demonstrates the performance of the improved algorithms in several numerical examples.

The paper shows a moving least squares reconstruction technique applied to the B-spline Material Point Method (B-spline MPM). It has been shown previously that B-spline MPM can reduce grid-crossing errors inherent in the original Material Point Method. However, in the large deformation regime where the gridcrossing occurs more frequently, the convergence rate of B-spline MPMis lower. In this paper, moving least squares reconstruction is employed to retrieve the expected convergence rate. The proposed improvement is examined in terms of the spatial convergence using the methods of manufactured solutions for large deformations.

In the field of in situ mechanical characterization of soils, penetration tests are commonly used. Penetration tests measure the properties of soils in the domain of large deformations. The tip resistances, deduced from pile driving theory, can be measured either in dynamic conditions (q d ) either in static conditions (q c ). Recently, the measurement technique in dynamic conditions has been improved and it is now possible to record the whole response of the soil during one impact in terms of tip force and penetration distance. The exploitation of this new curve provides information not only on dynamic tip resistance but also on additional mechanical parameters involved during the driving of the tip. The objective of this work is to develop a numerical model in 2D able to reproduce the penetrometric record obtained experimentally by static or dynamic penetration tests. This model is based on the discrete element method with a simple linear contact model. After the validation of the model, a parametric study was performed essentially on the loading type (static or dynamic), the penetration rate, the particle size of the granular material and the arrangement (density variation). Besides the influence of these parameters on the penetrometer signals and the tip resistance, a particular attention was focused on micromechanical analysis: energy dissipation in the medium, force chain evolution, contact orientation. This analysis requires the development of specific numerical tools to better understand the penetration mechanism and try to explain the macroscopic mechanical response obtained. The penetration rate influences significantly only in the dense flow regime on the static and dynamic penetration tests. There is no significant microscopic difference between static and dynamic penetration tests with similar penetration rates. Regarding the influence of the characteristics of the material, the numerical results obtained conform to the real results when the particle friction or the compactness of the medium varies. Concerning the particle size, the dynamic signal variation and the dynamic tip force increases when the average particle diameter increases., Dans la pratique actuelle du génie géotechnique, les essais de pénétration tels que les CPT, SPT, Panda sont largement utilisés pour caractériser mécaniquement les sols, au travers notamment d’une caractéristique de rupture appelée résistance de pointe. Par ailleurs, les dernières évolutions technologiques apportées aux essais de pénétration dynamique (Panda 3) permettent d’obtenir pendant chaque impact une courbe charge–enfoncement donnant la charge en pointe en fonction de l’enfoncement à partir de la mesure et du découplage des ondes générées durant l’essai. L’exploitation de cette nouvelle courbe fournit des informations non seulement sur la résistance de pointe dynamique mais également sur des paramètres mécaniques complémentaires mis en jeu pendant l’enfoncement de la pointe. L’objectif de cette thèse est de développer un modèle numérique en 2D capable de reproduire les signaux pénétrométriques obtenus expérimentalement par essais de type statique ou dynamique. Ce modèle est basé sur la méthode des éléments discrets avec une loi de contact linéaire simple. Une fois le modèle validé, une étude paramétrique a été réalisée en jouant essentiellement sur les modes d’application de la sollicitation (vitesse d’impact ou de pénétration), la granulométrie du matériau ainsi que l’arrangement granulaire (variation de la densité). Outre l’influence de ces paramètres sur les signaux pénétrométriques et la résistance de pointe mesurée, une attention particulière est portée sur l’analyse micromécanique : dissipation d’énergie dans le milieu, évolution des chaines de force, orientations des contacts. Cette analyse nécessite de développer des outils numériques spécifiques afin de mieux comprendre le mécanisme de l’enfoncement et tenter d’expliquer la réponse mécanique macroscopique obtenue. L’effet de la vitesse n’influence significativement que sur les essais de pénétration statiques et dynamiques en régime d’écoulement dense. A vitesse d’enfoncement comparable, il n’y a aucune différence significative au niveau microscopique entre les deux modes de sollicitation statique et dynamique. En ce qui concerne l’influence des caractéristiques du matériau, les résultats obtenus par le modèle numérique conforment aux celui réel lors que le frottement entre particules ou la compacité du milieu varie. Concernant la granulométrie, la variation de la courbe charge-enfoncement et la force de pointe dynamique augmente lorsque le diamètre moyen augmente.

Den 30. desember 2020 gikk det et stort kvikkleireskred på Ask i Gjerdrum. Ti personer og et ufødt barn mistet livet, og skredet forårsaket store skader på bygninger og infrastruktur. For å forhindre slike skredhendelser er det opprettet kvikkleiresoner basert på mulig utstrekning til potensielle skred. Jo større utstrekning sonen defineres til å ha, desto større områder blir omfattet av restriksjoner på byggearbeider. Det er ønskelig å finne en balanse mellom kostnaden av en større sone sammenlignet med kostnadene ved å definere en mer presis mulig skredutbredelse. Denne oppgaven evaluerer empiriske og numeriske metoder for definere skredutbredelsen for skredet i Gjerdrum. Videre undersøker den hvordan ulik lagdeling og skjærstyrkeparametre påvirker retrogresjonslengden. Tre ulike detaljnivåer av lagdeling er benyttet for de empiriske kriteriene. Det første kriteriet tar kun hensyn til terrenget. Det andre kriteriet tar hensyn til terrenget og grunnfjellet. Til slutt tar det tredje kriteriet hensyn til terrenget, grunnfjellet og plassering og utbredelse av kvikkleirelaget. Skredutbredelsen definert av retrogresjonslengdene sammenlignes med utbredelsen av de simulerte 3D-skredene ved bruk av Material Point Method. For simuleringene er de to siste detaljnivåene av lagdelingen benyttet. I tillegg er det kjørt 2D analyser for å undersøke effekten av den omrørte udrenerte skjærstyrken, su,r, og skjærtøyning når styrken er 95 % redusert, γ95. 2D simuleringene viste at γ95 påvirket retrogresjonslengden. Lengden var størst når γ95 var lik 1. γ95 lik 4 ga en lengre retrogresjonslengde enn γ95 lik 2, noe som var uventet. Retrogresjonslengden var lik for ulike verdier av su,r. Det er viktig å påpeke at utbredelsen av kvikkleirelaget så ut til å være den mest styrende faktoren for retrogresjonslengden. For Material Point Method-simuleringene ga den minst detaljerte lagdelingen det beste resultatet. Likevel ga den en utbredelse som var større enn skredet i Gjerdrum, og det kan derfor regnes som en konservativ tilnærming. Simuleringene som tok hensyn til kvikkleirelaget viste at initialskredet gikk ved Holmen, slik som for skredet i Gjerdrum. Skredet i simuleringen utviklet seg ikke til et retrogressivt skred fordi skredmassene hadde av mobilitet. Videre analyser for å undersøke om en endring i sensitivitetsparametrene eller en annen numerisk geometri av kvikkleirelaget gir en annen skredutbredelse er anbefalt. For de empiriske kriteriene ga den mest detaljerte lagdelingen det beste resultatet. Dette kriteriet viste en svært god tilnærming til utbredelsen av skredet i Gjerdrum. Det andre kriteriet som tok hensyn til terreng og grunnfjell hadde en utbredelse som samsvarte godt resultatet fra den tilsvarende simuleringen. Det mest konservative empiriske kriteriet overestimerer utbredelsen av skredet. Tatt i betraktning ressursbruken som kreves for å kjøre Material Point Method-simuleringer fremstår de empiriske kriteriene som bedre egnet for å definere skredutbredelsen i Gjerdrum. A large sensitive clay landslide occurred on the 30th of December 2020 in Ask in Gjerdrum. Ten people and an unborn child lost their lives, and the slide caused extensive damage to buildings and infrastructure. As a measure to prevent sensitive clay slides, quick clay hazard zones are defined based on the estimated retrogression of potential slides. The larger area of the retrogression extent is defined to be, the larger area will be subjected to restrictions on the construction of buildings and other measures. Therefore, it is desirable to find a balance between the cost of a conservative retrogression extent and the cost to define a more precise retrogression extent. This thesis evaluates empirical and numerical methods to determine the retrogression of the Gjerdrum slide. Furthermore, it determines how the level of detail in the soil layering and the shear strength degradation parameters in the material model affect the retrogression. Three different levels of detail in soil layering have been used for the empirical criteria. The first one only takes the terrain into account. The second one takes the terrain and bedrock into account. Lastly, the third criterion takes the terrain, bedrock, and sensitive clay layer into account. The Material Point Method is the chosen numerical method because it is suitable for large deformations. The areas defined by the retrogression distances from the empirical criteria are compared to the extent of the slides from the 3D Material Point Method simulations. Two different levels of detail in soil layering were used for the simulations. In addition, 2D Material Point Method simulations were run to investigate the effect of the remolded undrained shear strength, su,r, and the shear strain at 95 % reduced shear strength, γ95. The 2D simulations showed that γ95 affected the retrogression distance. The retrogression was largest for γ95 equal to 1. However, γ95 equal to 4 gave a longer retrogression distance compared to γ95 equal to 2. The retrogression distance was constant for different values of su,r. It should be noted that the retrogression distance mainly appeared controlled by the extent of the sensitive clay layer. For the 3D simulations, the least detailed soil layering gave the best results. However, the slide extent was larger than in Gjerdrum, and it is considered a conservative approach. The simulations that took the sensitive clay layer into account, showed an initial failure in the slope west of Holmen where the initial slide is believed to have occurred. The simulated slide did not develop into a retrogressive slide because the slide masses had low mobility. Further investigations are recommended to examine if a change in sensitivity parameters or the numerical geometry of the sensitive clay layer gives a different extent of the slide. For the empirical criteria, the most detailed soil layering gave the best results. This criterion corresponded almost precisely to the extent of the Gjerdrum slide. The criterion that took terrain and bedrock into account, corresponded quite well with the equivalent 3D simulation. The most conservative empirical criterion overestimated the retrogression of the Gjerdrum slide. Taking into consideration the necessary resources to perform a Material Point Method simulation, the empirical criteria appear to be the most favorable way to determine the retrogression extent of the Gjerdrum slide.