Within fractured reservoirs, such as tight gas reservoir, coupled processes between matrix deformation and fluid flow are very important for predicting reservoir behavior, pore pressure evolution and fracture closure. To study the coupling between gas desorption and rock matrix/fracture deformation, a poroelastic constitutive relation is developed and used for deformation of gas shale. Local continuity equation of dry gas model is developed by considering the mass conservation of gas, including both free and absorbed phases. The absorbed gas content and the sorption-induced volumetric strain are described through a Langmiur-type equation. A general porosity model that differs from other empirical correlations in the literature is developed and utilized in a finite element model to coupled gas diffusion and rock mass deformation. The dual permeability method (DPM) is implemented into the Finite Element Model (FEM) to investigate fracture deformation and closure and its impact on gas flow in naturally fractured reservoir. Within the framework of DPM, the fractured reservoir is treated as dual continuum. Two independent but overlapping meshes (or elements) are used to represent these kinds of reservoirs: one is the matrix elements used for deformation and fluid flow within matrix domain; while the other is the fracture element simulating the fluid flow only through the fractures. Both matrix and fractures are assumed to be permeable and can accomodate fluid transported. A quasi steady-state function is used to quantify the flow that is transferred between rock mass and fractures. By implementing the idea of equivalent fracture permeability and shape-factor within the transfer function into DPM, the fracture geometry and orientation are numerically considered and the complexity of the problem is well reduced. Both the normal deformation and shear dilation of fractures are considered and the stress-dependent fracture aperture can be updated in time. Further, a non-linear numerical model is constructed by implementing a poroviscoelastic model into the dual permeability (DPM)-finite element model (FEM) to investigate the coupled time-dependent viscoelastic deformation, fracture network evolution and compressible fluid flow in gas shale reservoir. The viscoelastic effect is addressed in both deviatoric and symmetric effective stresses to emphasize the effect of shear strain localization on fracture shear dilation. The new mechanical model is first verified with an analytical solution in a simple wellbore creep problem and then compared with the poroelastic solution in both wellbore and field cases.

The purpose of this thesis is to provide an overview of ETFE foil, as it applies to pneumatic cushion cladding, with a focus on creep behavior of the material. Characteristics of ETFE, including weight, optics, insulation, flexibility, environmental properties, fire performance, cushion span and other features are discussed, and, where possible, are compared to the characteristics of glass panels used in similar applications. Relevant chemical and mechanical properties of ETFE are given. Load carrying concepts of tension structures and inflated cushions are discussed, as well as structural design methods for ETFE cushions. Several prominent structures constructed using ETFE foil are introduced and benefits and design issues associated with these structures are reviewed. When used in cushion applications, ETFE films are placed in constant tension, and are therefore subject to creep. Quantifying this creep is desirable so that it can be predicted during the design phase. Therefore, this thesis summarizes the findings of other researchers in the area of creep of ETFE as well as the general mechanical behavior of the material, and presents the results of uniaxial creep tests done for the purpose of this study. These tests included 24 hour uniaxial creep tests done at four stress levels on both the transverse and longitudinal directions of three different brands of film. Two thicknesses of the third film were acquired and both were tested. The stress levels were chosen to coincide with typical design tensile stresses for ETFE film, and to be similar to the levels tested by other researchers. The effects of the different stresses, brands, directions and thicknesses are evaluated and discussed. Three seven day creep tests were also done on one of the films, each at a different stress level. Constitutive viscoelastic and viscoplastic models were developed to represent the 24-hour creep data. The viscoelastic models were based on a four-element Kelvin model and the viscoplastic models were based on a power-law model. The model parameters were determined from the data using linear least squares fitting. Models were also developed for the seven day creep data. Several of these models were based only upon the first 24 hours of data, and were used to determine the applicability of the 24-hour creep models to long-term behavior. It was found that while a viscoelastic model appears to fit long-term creep most closely, the 24-hour models are inadequate for modeling longer time frames. Another method is required for predicting long-term creep. Nonlinear fitting of the parameters is recommended as a possible alternative for creating more accurate models. Longer-term creep tests are also recommended. Tensile tests were also done on the films to confirm mechanical properties supplied by the film manufacturers. Good agreement to the given values was found in the test data.

The vulnerability and movement behaviour of slow moving slides are investigated. The study focuses on slides moving at rates ranging from a few millimetres a year like extremely slow slides, to 13 meters per month, the upper velocity range of slow slides. An extensive review of the effect of pore pressure changes on movement reactivation of shallow and moderately thick slides is presented. The time dependent behaviour of fine geotechnical materials is also reviewed. Although the literature has reported many cases where the accumulation of slow movements led to a complete collapse of buildings, failure of embankment slopes carrying highways or railways and serviceability problems for dams and bridges, little attention has been paid to the vulnerability to slow moving slides. Hence, this thesis aims to provide more insight into the actual damage to facilities founded on slow moving slides. More than fifty cases of extremely slow, very slow and slow slides adversely affecting urban communities, highways, railways, bridges, dams and linear infrastructure are reviewed. The survey enables the development of new damage-extent scales that use the slide velocity to help assess the degree of damage to a facility founded on a landslide-prone area. Vulnerability is an important component of the specific risk. The other component is the hazard or the probability of occurrence of a certain damaging phenomenon like landslides. Defining the causal factors of the landslide movements and their contributions to the total movement is an important step towards the evaluation of the hazard. Hence, the geomechanical behaviour of two typical deep-seated and moderately thick slides, the Little Chief Slide and the Little Smoky Slide, respectively, are investigated. The objective is to determine all the triggers and causal factors of movement and to quantify their contribution to the total movement. The study involves groundwater flow modeling of one of the two slides, an extensive field monitoring of pore pressures and displacements and an investigation of the creep behaviour both in the field and in the laboratory. The outcome of the study shows that the total movement of each of the two slides can be separated into creep and seasonal movements. The contribution of each component is quantitatively defined. The quantification of the different causal factors aids in choosing the proper mitigation option in addition to predicting the future movement rates after the chosen remedial measures have been installed. / Geotechnical Engineering

abstract: The concept of Creep is a term used to define the tendency of stressed materials to develop an increasing strain through time under a sustained load, thus having an increase in deflection or having an elongation with time in relation to the short term strain. While the subject of compression creep of concrete is well developed, use of concrete under tension loads has been limited at best due to brittleness of concrete. However with the advent of using fiber reinforced concrete, more and more applications where concrete is expected to carry tensile loads due to incorporation of fibers is gaining popularity. While the creep behavior of concrete in tension is important, the main case of the study is what happened when the concrete that is cracked in service is subjected to sustained loads causing creep. The relationship of opening cracks under these conditions are of utmost importance especially when the serviceability criteria is addressed. Little work has been reported in literature on the long-term behavior of FRC under sustained flexural loadings. The main objective of this study is to investigate the Long Term Flexural Behavior of Pre-Cracked Fiber Reinforced Beams under Sustained Loads. The experimental reports document the effect of loading and temperature on the creep characteristics of concrete. A variety of study has been carried out for the different responses generated by the creep tests based on factors like effect of temperature and humidity, effect of fiber content, effect of fiber type, and effect of different loading levels. The Creep Testing Experimental Methodology is divided into three main parts which includes: (1) The Pre-cracking Partial Fracture Test; (2) Creep Test; (3) Post Creep Full Fracture Test. The magnitude of load applied to a specific specimen during creep testing was based on the results of average residual strength (ARS) tests, determined using EN14651. Specimens of the synthetic FRC mixture were creep tested at loads nominally equivalent to 30% and 50% of the FR1 value. The creep tests are usually continued until a steady Time versus CMOD response was obtained for the specimen signifying its presence in the secondary stage of creep. The creep recovery response is generated after unloading the specimen from the creep set up and later a full fracture test is carried out to obtain the complete post creep response of the beam under flexure. The behavior of the Creep Coefficient versus Time response has been studied using various existing models like the ACI 209-R 92 Model and the CEB-FIP Model. Basic and hybrid rheological viscoelastic models have also been used in order to generate the material behavior response. A study has been developed in order to understand the applicability of various viscoelastic models for obtaining the material response of real materials. An analytical model for predicting the Flexural Behavior of FRC under sustained creep loads is presented at the end. This model helps generate the stress strain and Moment Curvature response of FRC beams when subjected to creep loads post initial cracking / Dissertation/Thesis / Masters Thesis Civil Engineering 2017

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Tailings storage facilities (TSFs) and conventional water retaining dams are the largest manmade structures on Earth. Statistics show that TSFs are more likely to fail than water retaining dams.Recent catastrophic failures of TSFs have led to the loss of lives (Germano mine, Brazil), environmental damage (Mount Polley, Canada), contamination of drinking water (Baia Mare, Romania), and the destruction of property (Kingston Fossil Plant, USA). As the scale of mining increases, TSFs increase in height and volume, therefore increasing the consequence of failure. To help mitigate risk associated with large TSFs mining companies empanel expert groups to review operations of TSFs and conduct regular visual inspections. In the US the Mine Safety and Health Administration has regulatory responsibility for the safety of TSFs. As population centers expand nearer to existing and proposed TSFs, the public requires assurance of the integrity of these structures. A pro-active approach to public safety is more desirable than a post-mortem analysis after a major failure. We have examined both the regulatory practices, the industry practices, and public data on TSFs in Arizona. In this thesis paper we address inadequacies of the official government records on TSFs in the two largest publicly accessible databases of dams inthe US – the National Inventory of Dams (NID), and the National Performance of Dams Program (NPDP). Both databases contain numerous errors and omissions, including descriptions and geographic coordinates of TSFs that are inaccurate by many kilometers. Several large TSFs in Arizona are not included in either database.We address these shortcomings with a pilot project for Arizona that demonstrates recording accurate information in a database is neither expensive nor onerous, communicating best practices for operation can help alleviate community concerns, and continuous monitoring technology can resolve shortcomings with visual inspections.

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A comparison of the creep/duration of load (DOL) performance of a new structural wood composite material called Parallam® parallel strand lumber (PSL) to two grades of machine-stress-rated (HSR) Douglas-fir lumber is presented in this thesis. Evaluation of the creep/DOL performance was made on nominal 2x4 members under constant bending stress at three stress levels. A total of 306 test specimens were evaluated for a 15-1/2 month time period. The analysis suggests that the duration of load effect for Parallam PSL was consistent with the Madison curve for the time period studied while the MSR Douglas-fir lumber was consistent with recent duration of load models developed for structural lumber. The analysis also indicates that the current duration of load adjustment factors can be applied to develop working stresses for Parallam. The creep behaviour of the Parallam PSL was found to be equivalent or better than the two MSR lumber grades under dry-service conditions. Furthermore, evidence of linear viscoelastic behaviour was found for all test materials within the range of applied stresses evaluated. Two mathematical models of creep were fitted to the creep data and compared. A '4-parameter linear viscoelastic' model fitted the creep data better than an empirical 'power curve' model. The model parameters developed provide a basis for estimating the mean creep behaviour and variability in creep response for these materials under in-service load conditions for dry-service environments. / Forestry, Faculty of / Graduate

Bibliography: pages 92-98. / In this thesis a simplified analysis procedure is developed, in which creep laws are decoupled from damage laws, for the purposb of constructing methods of use in the early stages of high temperature design. The procedure is based on the creep and damage laws proposed by Kachanov and Rabotnov. The creep laws are normalised. with respect to a convenient normalising stress. As a consequence of this normalisation, the dependence of the creep law on the stress constant, the time and temperature functions, and the actual load level is removed. In addition, if the reference stress of the component is chosen as the normalising stress, the creep law becomes insensitive to the stress exponent. The non-dimensional creep laws are then implemented in a standard finite element scheme, from which the results of a stationary state creep analysis are then in non-dimensional form. In order to estimate rupture times, the maximum stationary stresses in a component are used together with the damage laws. Conservative failure criteria are derived from the creep and damage laws to extend the method to residual life assessment and damage monitoring. The procedure is illustrated and tested against simple examples and case studies.