Relations and Links Between Soil Mechanics, Porous Media Physics, Physiochemical Theory, and Effective Medium Theory

Modern soil mechanics (geotechnical engineering) was developed as a branch of civil engineering from the 1920's. While modern porous media physics was developed as a branch of physics and applied mathematics from roughly the same period of time. In soil mechanics the main concern is often on the deformations, resulting from mechanical, hydraulic, or thermal actions. In application of porous media physics the main concern is historically on the flow part, putting less emphasis on the mechanical part. However, deformation and flow are highly linked processes, especially in unconsolidated porous media (soil). This paper makes some links between concepts used in porous media physics, like the effective medium theory, and concepts in soil mechanics, like choice of stress measures. As an example, it shows that the use of Terzaghi effective stress is a matter of choice and can be consistently used also for cases where other effective stress measures are used in literature, like Biot effective stress. The requirement, to be consistent, is that the state variables considered, at the constitutive level, includes all relevant variables

Measurements of debris flow entrainment and dynamics

The mechanisms of debris flows and their interaction with mitigation structures are still not well understood. Among the research challenges, only few entrainment measurements are available in literature, as entrainment is often masked by deposition on top. In this paper, we present a simple, cheap, and effective method to measure the entrainment depths. Flume experiments have therefore been performed to assess the influence of the initial debris flow volume and of an upstream flexible barrier on entrainment. To better understand the debris flow dynamics, the flow basal stresses have been measured. A high degree of liquefaction at the base of the debris flow is observed. A mitigation measure to reduce entrainment has also been studied. A compact flexible barrier was installed in the upstream part of the channel and is observed to deflect the flow along a curvilinear path. High normal stresses are measured at the base of the overflow, which are caused by the additional centrifugal stresses from the overflow. The results from the flume tests suggest that the flow interaction with an upstream flexible barrier may significantly influence the debris flow dynamics both upstream and downstream of the barrier

Bidrar programmering i undervisningen til kompetanse?

Høsten 2020 ble de nye læreplanene i fagfornyelsen introdusert i skolen. I ny læreplan har programmering og algoritmisk tenking blitt tildelt større plass og fått sitt utsprang fra matematikkfaget. Kompetansene programmering og algoritmisk tenking knyttes opp mot begrepet «fremtidens kompetanser» og skal sikre elevene nødvendige kompetanse for et fremtidig samfunn og yrkesliv. Denne masteroppgaven har tatt utgangspunkt i problemstillingen «Hvordan opplever lærere at programmering bidrar til elevers kompetanse i matematikk». Videre ser oppgaven på hva som karakteriserer fremtidens kompetanser og hvordan en identifiserer algoritmisk tenking som en kompetanse hos elevene. For å svare på problemstillingen er det brukt kvalitative forskningsintervju med fem informanter. Informantene underviser alle i matematikkfaget i grunnskolen, er kjent med ny læreplan og bruker programmering i undervisningen. I litteraturoversikten er det gjort rede for tidligere forskning som er gjort på programmering i undervisningen og algoritmisk tenking som kompetanse. Det er også gjort rede for ideen om å knytte sammen kunnskap og læring i læreplanen i lys av Klafkis didaktiske teori. Det teoretiske grunnlaget i oppgaven er en kombinasjon av det sosiokulturelle læringsperspektivet, Lev Vygotskij og Wolfgang Klafkis danningsteori. Det er også brukt litteratur som omhandler programmering og algoritmisk tenking i undervisning. Analysen av datamaterialet viser at informantene opplever ulik grad av kompetanse i matematikkfaget ved bruk av programmering i undervisningen. Flere informanter opplever at elevene viser kompetanse i algoritmisk tenking og kan overføre strategier for problemløsning til andre fag. Andre opplever at elevene ikke umiddelbart ser en overføringsverdi, men legger dette ansvaret på pedagogen og hvilket fokus som tillegges overføring av strategi og kunnskap. Resultatene viser at lærere opplever økt motivasjon og mestring hos elevene ved bruk av programmering i undervisningen. Dette begrunnes med variasjonen programmering kan gi undervisningen og hvordan programmering «ufarliggjør» prøving og feiling hos elevene

Formulation of non-coaxial plastic dissipation and stress–dilatancy relations for geomaterials

Stress–dilatancy theories play a central role in the modeling of the plastic dissipation of geomaterials. There exist several mathematical frameworks for describing the stress–dilatancy behavior of soils. One of the limiting assumptions often introduced is coaxiality between principal directions of stresses and plastic strain increments. However, experimental evidences suggest that this assumption is generally invalid for the deformation behavior of granular materials. In this paper, non-coaxial stress–dilatancy framework is developed first in axis symmetric, plane strain and then for general stress–strain conditions. To facilitate the use of the stress–dilatancy framework for cyclic loading conditions, loading and unloading are explicitly considered in the development of the framework. Furthermore, a possible way of establishing the evolution of the degree of non-coaxiality in plane strain and axis symmetric cases is presented. Then the approach is applied to selected yield functions.publishedVersio

Effects of Drilling for Tieback Anchors on Surrounding Ground: Results from Field Tests

A full-scale field test program was carried out to investigate the effects of drilling for tieback anchors on the surrounding ground. The test anchors were drilled from the ground surface through a soft clay deposit and into bedrock. Five different drilling methods were compared. All methods caused excess pore pressures in the surrounding clay, up to 70 kPa, extending several meters away from where drilling took place. This impact on pore pressures was for most drilling methods significantly larger than what has been observed for driven piles in clay. High penetration rate combined with water flushing during drilling through soft clay is the main reason for the effects on the pore pressure. Drilling with a down-the-hole hammer and air flushing through a layer of moraine and into bedrock in one of the test areas (Area B) caused significantly larger excess pore pressures and ground settlements than the other drilling methods. Approximately half of the maximum resulting settlements of 12 mm in Area B was most likely caused by reconsolidation of remolded clay around the casing tubes. Drilling with water-driven hammer in Area C had less effect on both pore pressures and ground settlements.publishedVersio

Physical modelling of pile drilling in sand

Drilling for foundation piles and tieback anchors through soils using a continuous casing to support the borehole is often referred to as "overburden drilling". Monitoring data from several case studies show that overburden drilling may cause considerable short-term ground settlements indicating a loss of soil volume around the casings. However, further insight is required to understand the mechanisms that govern overburden drilling. Novel physical model tests were carried out to investigate the effects of varying parameters such as flushing media (water or air), flow and penetration rate on the penetration force, pore pressure changes, soil displacements and drill cutting transport. Tests with water flushing indicate a clear relation between the flow and penetration rate and the resulting influence on the surrounding ground. Increasing flow rates caused larger excess pore pressures at greater radial distances and generated more excess drill cuttings compared to the theoretical casing volume. The obtained results were translated into a non-dimensional framework to estimate optimal flushing parameters in similar conditions. The air flushing tests were considerably limited by the modelling constraints. Notable reduction of pore pressures adjacent to the casing indicate an air-lift pump effect that can lead to extensive ground movements as observed in the field.publishedVersio

Implementation of non-newtonian rheology for granular flow simulation

Landslides of the debris flow type pose a serious natural hazard. These land-slides are often triggered by hydro-meteorological processes during extreme precipitationevents. Debris flows usually form a dense flow composed of water and poorly graded soilparticles. The propagation of these landslides greatly influences the consequences theyhave. The run-out of debris flows is usually simulated with depth-averaged models. Theseare fast to simulate due to the integration over the flow height, which reduces the problemfrom three to two dimensions. For the design of countermeasures resisting the pressurefrom the flow, it can be advantageous to use more advanced 3D numerical methods, suchas computational fluid dynamics (CFD). The particle phase of debris flows has here beenconsidered as a granular flow, and implemented as a non-Newtonian viscoplastic rheologyin the open-source CFD code REEF3D. In the numerical model, the Reynolds-Averaged Navier-Stokes (RANS) equations are discretized with the fifth-order accurate Weighted Essentially Non-Oscillatory (WENO) scheme in space and with a third-order Runge-Kuttabased fractional step scheme in time. The level set method used for representing the free surface handles the complex air-granular flow interface topology. The pressure gradient is modelled with Chorin’s projection method for incompressible flow. The granular flow rheology includes a Coulomb frictional yield stress, increasing with the normal stress, anda viscous term that is non-linear dependent on the shear rate. The implementation has been validated using results from laboratory dam break experiments with dry sands

Adaptive isogeometric finite element analysis of steady-state groundwater flow

Numerical challenges occur in the simulation of groundwater flow problems because of complex boundary conditions, varying material properties, presence of sources or sinks in the flow domain, or a combination of these. In this paper, we apply adaptive isogeometric finite element analysis using locally refined (LR) B-splines to address these types of problems. The fundamentals behind isogeometric analysis and LR B-splines are briefly presented. Galerkin's method is applied to the standard weak formulation of the governing equation to derive the linear system of equations. A posteriori error estimates are calculated to identify which B-splines should be locally refined. The error estimates are calculated based on recovery of the L2-projected solution. The adaptive analysis method is first illustrated by performing simulation of benchmark problems with analytical solutions. Numerical applications to two-dimensional groundwater flow problems are then presented. The problems studied are flow around an impervious corner, flow around a cutoff wall, and flow in a heterogeneous medium. The convergence rates obtained with adaptive analysis using local refinement were, in general, observed to be of optimal order in contrast to simulations with uniform refinement.acceptedVersio

Geotechnical characterization of Halsen-Stjørdal silt, Norway

The evaluation of geotechnical parameters for design problems in silty soils is complicated due to partially drained conditions and irregular soil structure, including small layers and pockets of both coarser and finer material. Many established methods to define soil parameters in clay and sand exist but little guidance is given to practicing engineers on how to interpret soil parameters for silty materials. This paper presents the results of an extensive laboratory and field test program which was carried out at a silt testing site Halsen-Stjø rdal in Norway. The main objective is to broaden the database of the engineering behaviour of silts and to gain a better understanding of the behaviour of these soils. Cone penetration tests (CPTU) were performed and shear wave velocity measurements close to the site were used to supplement the CPTU results, confirming the coarse, silty nature of the deposit. In addition, several samples were taken using thin walled 54 mm steel sample tubes and examined in the laboratory by means of index, oedometer and triaxial tests. Recently developed methods to determine sample quality in intermediate low plastic soils were adopted and showed promising results. The interpretation of the oedometer tests was challenging due to the shapes of the curves. The results did not identify the yield or preconsolidation stress clearly partly due to the nature of the silt and partly due to sample disturbance. Triaxial test results on the silt showed a strong dilative behaviour developing negative pore pressures with increasing axial strain. The shape of the stress paths revealed no unique undrained shear strength of the silt. Although many researchers doubt the use of undrained shear strength (su) for partially drained materials, this parameter is still frequently used. Several methods were applied to determine values of an apparent su in the silt in order to provide an overview over the range of strength values. The results from this study contribute to the existing database and increase the understanding of silty soils