Internal instability of a widely graded cohesionless soil refers to a phenomenon in which its finer particles migrate within the void network of its coarser particles, as a result of seepage flow. Onset of internal instability of a soil is governed by a combination of geometric and hydromechanical constraints. Much concern exists for embankment dams and levees built using soils with a potential for internal instability. Migration of finer particles to a boundary where they can exit, by washing out, may cause erosion or piping failure and, occasionally, induce collapse of these soil structures. There is a need, in professional practice, to better understand the phenomenon and to develop improved methods to evaluate the susceptibility of a soil. A series of permeameter tests was performed on six widely-graded cohesionless materials. The objectives are to assess the geometric indices proposed for evaluation of susceptibility, and examine hydromechanical factors influence the onset of internal instability. A modified slurry mixing technique, with discrete deposition, was found satisfactory for reconstitution of the homogeneous saturated test specimens. The onset of internal instability was founded to be triggered by a combination of effective stress and hydraulic gradient. The finding yields a hydromechanical envelope, unique for a particular gradation shape, at which internal instability initiated. Three commonly used geometric criteria were comprehensively evaluated with reference to these experimental data and also a database compiled from the literature. The relative conservatism of each criterion was examined and a modified semi-empirical geometric rule then proposed based on the capillary tube model. A theoretical framework for plotting the hydromechanical envelope was established based on an extension of the α concept of Skempton and Brogan, and subsequently verified by test data. Finally, a novel unified approach was proposed to assess the onset of internal instability, based on combining geometric and hydromechanical indices of a soil.

A new ‘transparent soil permeameter’ has been developed to study the mechanisms occurring during internal erosion in filter materials for embankment dams. Internal erosion or suffusion is the process where fine particles are removed from a matrix of coarse grains by seepage of water, and which ultimately leads to instabilities within the soil. The laboratory-based experiments in this thesis utilises a novel approach where up-scaled glass particles are used in place of soil particles, and optically matched oil is used in place of water. Rhodamine dye in the oil allows the fluid to fluoresce brightly when a sheet of laser light is shone through the sample, while the glass particles appear as dark shadows within the plane of the laser sheet. This technique is known as Planar Laser Induced Fluorescence (PLIF) and enables a two-dimensional "slice" or plane of particles and fluid to be viewed inside the permeameter, away from the permeameter walls. During a test, fluid is passed through the solid matrix in upward flow, with the flow rate (therefore hydraulic gradient) being increased in stages until internal erosion or bulk movement of the entire assembly develops and progresses. A high speed camera captures images of the two-dimensional plane over the duration of a test, which are then analysed using Image Pro and ImageJ processing software. Until now, the fundamental mechanisms that lead to internal erosion have been rather speculative, as there has been no way to physically observe the processes behind the initiation and continued movement of particles. This visualisation experiment allows internal erosion mechanisms to be studied away from permeameter walls where boundary effects do not occur. The technique was validated by confirming Darcy’s (1856) law of laminar flow, and Terzaghi’s (1925) theoretical critical hydraulic gradient for an upward flow through materials with no top stress. Results of replicated materials tested by Skempton and Brogan (1994) and Fannin and Moffat (2006) also confirm this methodology to be valid by way of material behaviour, permeability and the alpha factor (Skempton & Brogan 1994). An assessment to predict the stability of soils was carried out using the Kenney and Lau (1985), Kezdi (1979), Burenkova (1993), Wan and Fell (2008) and Istomina (1957) approaches, with the Kenny and Lau and Kezdi methods proving to be the most robust across the particle size distributions tested. In the tests, unstable materials showed a migration of fine grains under hydraulic gradients as low as ic = 0.25, while stable materials showed little movement of particles, and eventually failed by heave. Image processing using Image Pro and ImageJ were successful in producing quantitative results, however with further enhancements to the test equipment and methodology, these could be improved upon. The testing technique developed in this thesis has proven to be successful in the study of internal erosion of filter materials. The technique proves that optically matched glass and oil can behave similarly to soil and water materials as used in previous laboratory testing, and that the PLIF technique and image capturing has merit in understanding the mechanisms occurring during internal erosion processes.

Heat losses are an important problem in domestic hot water circulation systems. Therefore, toreduce these losses becomes an issue of utmost importance both economically andenvironmentally. Nevertheless, it has not been until recent years when these losses have beenstudied further. Commonly studies have focused on the heat space system operation or radiatorsystem. This study focuses on heat losses in the domestic hot water circulation through thepiping system in a building at a school located in Gävle (Sweden) using non-destructive flowand temperature reading devices. The heat used by the school is provided by the district heatingnetwork that feeds several heat exchangers. The heat losses, at the same time, will be comparedwith simulation and theoretical procedures to corroborate them. The domestic hot water pipingsystem of this study consists on more than 1200 meters of insulated copper pipes with differentdiameters and different insulation thickness. The system was measured for one week (April 26,2015 to May 3, 2015) when there are working days and nonworking days. A 5% of the annualdistrict heating consumption in the school was calculated as heat losses in the domestic hotwater circulation system in the building studied. Finally, improvements in insulation system andchanges in the domestic hot water temperature have been simulated and they demonstrate thatsavings of up to 35% of the heat losses can be achieved and produce significant energy savings.

Internal instability of a widely graded cohesionless soil refers to a phenomenon in which its finer particles migrate within the void network of its coarser particles, as a result of seepage flow. Onset of internal instability of a soil is governed by a combination of geometric and hydromechanical constraints. Much concern exists for embankment dams and levees built using soils with a potential for internal instability. Migration of finer particles to a boundary where they can exit, by washing out, may cause erosion or piping failure and, occasionally, induce collapse of these soil structures. There is a need, in professional practice, to better understand the phenomenon and to develop improved methods to evaluate the susceptibility of a soil. A series of permeameter tests was performed on six widely-graded cohesionless materials. The objectives are to assess the geometric indices proposed for evaluation of susceptibility, and examine hydromechanical factors influence the onset of internal instability. A modified slurry mixing technique, with discrete deposition, was found satisfactory for reconstitution of the homogeneous saturated test specimens. The onset of internal instability was founded to be triggered by a combination of effective stress and hydraulic gradient. The finding yields a hydromechanical envelope, unique for a particular gradation shape, at which internal instability initiated. Three commonly used geometric criteria were comprehensively evaluated with reference to these experimental data and also a database compiled from the literature. The relative conservatism of each criterion was examined and a modified semi-empirical geometric rule then proposed based on the capillary tube model. A theoretical framework for plotting the hydromechanical envelope was established based on an extension of the α concept of Skempton and Brogan, and subsequently verified by test data. Finally, a novel unified approach was proposed to assess the onset of internal instability, based on combining geometric and hydromechanical indices of a soil.

Thesis (M.S.)--Ohio University, June, 1999. / Title from PDF t.p.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Feb. 17, 2009). PDF text: x, 145 p. : ill. (some col.) ; 2 Mb. UMI publication number: AAT 3331439. Includes bibliographical references. Also available in microfilm and microfiche formats.

Seepage direction is crucial for understanding the critical state and development of piping erosion. A stress-controlled apparatus was designed to investigate the piping behavior of cohesionless soil under upward flow condition. The components of the new apparatus included a loading chamber, a vertical and confining loading system, an upstream water supply device, a soil-water separating system, and a water collecting system. The loading chamber provides space for a soil specimen setting and loading. The combination of a vertical and a confining loading system was designed to apply complex stresses to a soil specimen. Under the stresses, the specimen was then eroded by the gradually increasing hydraulic head supplied by the water supply system. The eroded particle and spilling water were collected and detected by the soil-water separating system and the water collecting system. A series of experiments were carried out using the new apparatus. Results demonstrated the repeatability experiments and usefulness of the apparatus. The new apparatus allowed us to investigate the piping behavior under different stress states and hydraulic gradients. With this new apparatus and experiments, we found that lower and high critical hydraulic gradients (CHGs) should be included as the criteria of piping development based on the relationship between the hydraulic gradient and the seepage response. In addition, the stress state on the CHG and the particle erosion rate played important roles in the piping development. The outer pressure on the specimen can retard the development of erosion. In contrast, the hydraulic gradient was found to be positively correlated to the erosion rate. Results also indicated that a specimen would collapse once the amount of eroded small particles exceeds the critical value of 46.5 % of the soil.

Internal instability of a widely graded cohesionless soil refers to a phenomenon in which its finer particles migrate within the void network of its coarser particles, as a result of seepage flow. Onset of internal instability of a soil is governed by a combination of geometric and hydromechanical constraints. Much concern exists for embankment dams and levees built using soils with a potential for internal instability. Migration of finer particles to a boundary where they can exit, by washing out, may cause erosion or piping failure and, occasionally, induce collapse of these soil structures. There is a need, in professional practice, to better understand the phenomenon and to develop improved methods to evaluate the susceptibility of a soil. A series of permeameter tests was performed on six widely-graded cohesionless materials. The objectives are to assess the geometric indices proposed for evaluation of susceptibility, and examine hydromechanical factors influence the onset of internal instability. A modified slurry mixing technique, with discrete deposition, was found satisfactory for reconstitution of the homogeneous saturated test specimens. The onset of internal instability was founded to be triggered by a combination of effective stress and hydraulic gradient. The finding yields a hydromechanical envelope, unique for a particular gradation shape, at which internal instability initiated. Three commonly used geometric criteria were comprehensively evaluated with reference to these experimental data and also a database compiled from the literature. The relative conservatism of each criterion was examined and a modified semi-empirical geometric rule then proposed based on the capillary tube model. A theoretical framework for plotting the hydromechanical envelope was established based on an extension of the α concept of Skempton and Brogan, and subsequently verified by test data. Finally, a novel unified approach was proposed to assess the onset of internal instability, based on combining geometric and hydromechanical indices of a soil. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

D.Ing. / This study is a numerical investigation into the behaviour of cracks in uPVC pipes under pressure. This study is a continuation of a Masters dissertation which showed that leakage exponents vary significantly from the theoretical orifice exponent of 0.5 for cracks in pipes for different materials. This study looks at the behaviour of cracks in more detail and specifically with regard to the parameters of the pipe and crack. Using Finite Element Analysis the relationship between the pressure head and the leak area in pipes with longitudinal, spiral and circumferential cracks was investigated. It was found that the longitudinal, spiral and circumferential crack areas increase linearly with pressure. The slope of this linear relationship depends on various parameters, including loading state, pipe dimensions and pipe material properties. The effect that the individual pipe parameters had on the pressure-area slope was investigated. These parameters included the material properties of the pipe (Young’s modulus, Poisson’s ratio and longitudinal stress), the geometry of the pipe (internal diameter and wall thickness) as well as the geometry of the crack (length of the crack and the width of the crack). Once the effect of the pressure-area slope m is known, the link between the conventional leakage exponent N1 and the pressure-area slope m was further investigated and the effect of each parameter on the leakage exponent N1 was found. Using various data techniques the above data was combined and processed to find mathematical relationships that give reasonable descriptions of the pressure-area slopes of longitudinal, spiral and circumferential cracks. Once these equations for the pressure-area slopes were determined it was possible to obtain three new relationships for leakage from longitudinal, spiral and circumferential cracks.

This diploma work is aimed at a proposal and an overall controll of the pipeline net. There is a preliminary calculation performed (by the analytical method) in this diploma work. There is also a comparison with the numerical computing to find out whether the pipe branch does or does not comply.