Assessment of Finite Element Softwares for Geotechnical Calculations

When building new constructions under ground level in cities it is important that the foundations of neighboring buildings are undisturbed. The regulations regarding soil deformations are hence very strict and conventional methods of predicting soil behavior is often too crude. Finite element calculations are therefore becoming an increasingly important tool used to predict soil behavior in and around a construction site. When modeling soil behavior today, specialized finite element softwares for analysis of soil and rock behavior are generally used. But as the need for numerical computations within geotechnical applications increase developers of more generalized finite element softwares enter the market. It is therefore of interest to compare how a generalized finite element software handles geotechnical problems compared to a specialized geotechnical finite element software. In this study an evaluation of how a general purpose finite element software, Comsol Multiphysics, performed in geotechnical simulations compared to two finite element softwares, Plaxis 2D and Z-soil, that where developed specially for modeling of soil and geotechnical calculations. As one important aspect to finite element calculations is the constitutive models used to capture the material behavior of the problem at hand. The two most widely used material models for simulating soil behavior are the Mohr-Coulomb criterion and the Drucker-Prager criterion, these material models have therefore been reviewed in this report. A simulation of a triaxial test has also been conducted to compare how these material models perform in the three softwares. In the work with this report a simulation has also been carried out to compare the functionality of the three softwares for a common geotechnical application. The simulation consisted of an idealized excavation problem with a tie back retaining wall. Modeling of a simple excavation project like the one in this report where the geometry and boundary conditions change over time is a bit more complicated and time consuming using Comsol Multiphysics compared to the two special purpose softwares. On the other hand, Comsol Multiphysics offers the user possibilities to take additional physical phenomena into account. Plaxis 2D was the software where a model could be established in the shortest time. However Plaxis 2D offers fewer options for the user than Comsol Multiphysics and Z-soil. Using Z-soil the user is given more complex alternatives to model constructions that in Plaxis 2D, but the software is on the other hand somewhat more difficult to learn. It also takes longer time to establish a model in Z-soil than in Plaxis 2D. From the calculations no major differences in soil deformation or forces in the ground anchoring could be identified from the three softwares, although some variations were observed

Comparing Apples & Oranges - A Life Cycle Perspective on Energy Requirements in Swedish & British Columbian Building Codes

“Comparing Apples & Oranges – A Life Cycle Perspective on the Energy Requirements in Swedish and British Columbian Building Codes” The requirements to decrease the energy use in a building vary in the building codes. “British Columbia Building Code” (BCBC) prescribes a nominal thermal resistance of insulation, while “Boverket’s Building Regulations” (BBR) requires an annual specific energy use for the whole building. A type-house of wood-frame construction complying with BCBC proved to have greater momentary heat losses and a greater average heat transfer coefficient than a type-house of wood frame construction complying with BBR. Further, energy simulations showed that the type-house complying with BCBC did not comply with specific energy use requirement in BBR. The life cycle primary energy use takes into account all stages and all upstream losses during a building’s life cycle. The life cycle perspective takes into account site conditions such as climate and infrastructure. The type-house complying with BCBC proved to use 31-38% more primary energy. The occupancy state proved to use 79-91% of the buildings’ total primary energy. The life cycle perspective can also take into account the greenhouse gas (GHG) emission caused by a building throughout its life cycle. The GHG emissions proved to be strongly dependent on primary energy use. The type-house complying with BCBC emitted 18-42% more GHG than the type-house complying with BBR. GHG emissions occurred predominantly during the occupancy state. BBR takes into account the functionality of the whole building, while BCBC is prescriptive regarding each building assembly. The comprehensive approach towards the building as a system in BBR is according to us a more effective way to decrease the energy use in a single family house

Numerical modelling of geomaterials at failure

Geotechnical engineering is the science dealing with mechanics of soils and rocks and its engineering applications. Geotechnical engineering projects vary in a wide range, from evaluation of the stability of natural slopes and man-made soil deposits, to the design of earthworks and foundations. Traditional methods, using manual calculations or simplified computational methods, do not, as a rule, take into account the effects of soil-structure interaction, which can have a significant impact on the behaviour of the structure. The aim of the research presented in this dissertation is focussed on developing methods to analyse soil and rock behaviour. The research is in one part concerned with how soil-structure interaction can affect the design of foundations and geotechnical structures. The second part of the work is focussed on developing new methods to model geotechnical applications.When designing foundations it is a common practice that separate numerical models are used in the analysis of soil behaviour and of structural behaviour. A common procedure is that the geotechnical engineer establishes a model of the site conditions and performs a simulation of the behaviour of the ground using pre calculated load values received from the structural engineer. The resulting settlements can then in turn be used in the dimensioning of the structure. Using separate models can lead to unrealistic prediction of the behaviour of both structure and load, as the soil-structure interactions are disregarded. As the use of computational methods is increasing, both to simulate the response in soil and during the structural design. Paper A enlightens some of the risk that misuse of simplifications can lead to. The paper includes an evaluation of how using the modulus of subgrade reaction during the design of foundations can affect the dimensioning of the reinforcements in shallow foundations.Isogeometric analysis, is a numerical method that uses non-uniform rational B-splines (NURBS) as basis functions instead of the Lagrangian polynomials often used in the finite element method. These functions have a higher-order of continuity, making it possible to represent complex geometries exactly. The Higher-order continuity of the basis functions is also beneficial for problems that include frictional sliding and large displacements, overcoming the numerical instability caused by the C0-continuous basis functions often used in finite element formulations. A common problem in many geotechnical simulations. Paper B presents numerical simulations of soil plasticity using isogeometric analysis comparing the results to the solutions from conventional finite element method.The ability to predict rock behaviour using numerical models is pivotal to solve many rock-engineering problems. Numerical modelling can also be used to improve our understanding of the complicated failure process in rock. With models that better capture the fundamental failure mechanisms observed in laboratory, our ability to generate reliable large-scale models improves. Prediction of brittle fractures in rock and soil is a complex problem with a number of active research areas, ranging from landslides and fault mechanics to hydraulic fracturing.In this work a modified phase-field fracture model that can predict crack nucleation in porous rock and rock-like material is presented. In porous rock, the critical release rate for tensile cracks can be orders of magnitude smaller than the critical energy release rate for shear cracks and compressive stresses can lead to the formation of compaction driven cracks. Paper C and Paper D demonstrates the capability of the proposed phase-field model for simulating the evolution of mixed mode fractures and compressive driven fractures in porous artificial rocks and Neapolitan Fine Grained Tuff

Isogeometric Analysis of Soil Plasticity

In this paper we present numerical simulations of soil plasticity using isogeometric analysis comparing the results to the solutions from conventional finite element method. Isogeometric analysis is a numerical method that uses nonuniform rational B-splines (NURBS) as basis functions instead of the Lagrangian polynomials often used in the finite element method. These functions have a higher-order of continuity, making it possible to represent complex geometries exactly. After a brief outline of the theory behind the isogeometric concept, we give a presentation of the constitutive equations, used to simulate the soil behavior in this work. The paper concludes with numerical examples in two- and three-dimensions, which assess the accuracy of isogeometric analysis for simulations of soil behavior. The numerical examples presented show, that for drained soils, the results from isogeometric analysis are overall in good agreement with the conventional finite element method in two- and three-dimensions. Thus isogeometric analysis is a good alternative to conventional finite element analysis for simulations of soil behavior

A Modified Phase-Field Fracture Model for Simulation of Mixed Mode Brittle Fractures and Compressive Cracks in Porous Rock

In this work, we propose a modified phase-field model for simulating the evolution of mixed mode fractures and compressive driven fractures in porous artificial rocks. For the purpose of validation, the behaviour of artificial rock samples, with either a single or double saw cuts, under uniaxial plane strain compression has been numerically simulated. The simulated results are compared to experimental data, both qualitatively and quantitatively. It is shown that the proposed model is able to capture the commonly observed propagation pattern of wing cracks emergence followed by secondary cracks driven by compressive stresses. Additionally, the typical types of complex crack patterns observed in experimental tests are successfully reproduced, as well as the critical loads

Phase-field fracture modelling of crack nucleation and propagation in porous rock

In this work, we suggest a modified phase-field model for simulating the evolution of mixed mode fractures and compressive driven fractures in porous artificial rocks and Neapolitan Fine Grained Tuff. The numerical model has been calibrated using experimental observations of rock samples with a single saw cut under uniaxial plane strain compression. For the purpose of validation, results from the numerical model are compared to Meuwissen samples with different angles of rock bridge inclination subjected to uni-axial compression. The simulated results are compared to experimental data, both qualitatively and quantitatively. It is shown that the proposed model is able to capture the emergence of shear cracks between the notches observed in the Neapolitan Fine Grained Tuff samples as well as the propagation pattern of cracks driven by compressive stresses observed in the artificial rock samples. Additionally, the typical types of complex crack patterns observed in experimental tests are successfully reproduced, as well as the critical loads

The impact of the nursing hours per patient day (NHPPD) staffing method on patient outcomes: A retrospective analysis of patient and staffing data

In March 2002 the Australian Industrial Relations Commission ordered the introduction of a new staffing method – nursing hours per patient day (NHPPD) – for implementation in Western Australia public hospitals. This method used a ‘‘bottom up’’ approach to classify each hospital ward into one of seven categories using characteristics such as patient complexity, intervention levels, the presence of high dependency beds, the emergency/elective patient mix and patient turnover. Once classified, NHPPD were allocated for each ward. The objective of this study was to determine the impact of implementing the NHPPD staffing method on 14 nursing-sensitive outcomes: central nervous system complications, wound infections, pulmonary failure, urinary tract infection, pressure ulcer, pneumonia, deep vein thrombosis, ulcer/gastritis/upper gastrointestinal bleed, sepsis, physiologic/metabolic derangement, shock/cardiac arrest, mortality, failure to rescue and length of stay. The research design was an interrupted time series using retrospective analysis of patient and staffing administrative data from three adult tertiary hospitals in metropolitan Perth over a 4-year period. All patient records (N = 236,454) and nurse staffing records (N = 150,925) from NHPPD wards were included. The study found significant decreases in the rates of nine nursing-sensitive outcomes when examining hospital-level data following implementation of NHPPD; mortality, central nervous system complications, pressure ulcers, deep vein thrombosis, sepsis, ulcer/gastritis/upper gastrointestinal bleed shock/cardiac arrest, pneumonia and average length of stay. At the ward level, significant decreases in the rates of five nursingsensitive outcomes; mortality, shock/cardiac arrest, ulcer/gastritis/upper gastrointestinal bleed, length of stay and urinary tract infections occurred. Conclusions: The findings provide evidence to support the continuation of the NHPPD staffing method. They also add to evidence about the importance of nurse staffing to patient safety; evidence that must influence policy.This study is one of the first to empirically review a specific nurse staffing method, based on an individual assessment of each ward to determine staffing requirements, rather than a ‘‘one-size-fits-all’’ approach

Age-dependent regulation of SARS-CoV-2 cell entry genes and cell death programs correlates with COVID-19 severity.

Novel coronavirus disease 2019 (COVID-19) severity is highly variable, with pediatric patients typically experiencing less severe infection than adults and especially the elderly. The basis for this difference is unclear. We find that mRNA and protein expression of angiotensin-converting enzyme 2 (ACE2), the cell entry receptor for the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes COVID-19, increases with advancing age in distal lung epithelial cells. However, in humans, ACE2 expression exhibits high levels of intra- and interindividual heterogeneity. Further, cells infected with SARS-CoV-2 experience endoplasmic reticulum stress, triggering an unfolded protein response and caspase-mediated apoptosis, a natural host defense system that halts virion production. Apoptosis of infected cells can be selectively induced by treatment with apoptosis-modulating BH3 mimetic drugs. Notably, epithelial cells within young lungs and airways are more primed to undergo apoptosis than those in adults, which may naturally hinder virion production and support milder COVID-19 severity