The self-potential method responds to the electrokinetic phenomenon of streaming potential and has been applied in hydrogeologic and engineering investigations to aid in the evaluation of subsurface hydraulic conditions. Of specific interest is the application of the method to embankment dam seepage monitoring and detection. This demands a quantitative interpretation of seepage conditions from the geophysical data. To enable the study of variably saturated flow problems of complicated geometry, a three-dimensional finite volume algorithm is developed to evaluate the self-potential distribution resulting from subsurface fluid flow. The algorithm explicitly calculates the distribution of streaming current sources and solves for the self-potential given a model of hydraulic head and prescribed distributions of the streaming current cross-coupling conductivity and electrical resistivity. A new laboratory apparatus is developed to measure the streaming potential coupling coefficient and resistivity in unconsolidated soil samples. Measuring both of these parameters on the same sample under the same conditions enables us to properly characterize the streaming current cross-coupling conductivity coefficient. I present the results of a laboratory investigation to study the influence of soil and fluid parameters on the cross-coupling coefficient, and characterize this property for representative well-graded embankment soils. The streaming potential signals associated with preferential seepage through the core of a synthetic embankment dam model are studied using the forward modelling algorithm and measured electrical properties to assess the sensitivity of the self-potential method in detecting internal erosion. Maximum self-potential anomalies are shown to be linked to large localized hydraulic gradients that develop in response to piping, prior to any detectable increase in seepage flow through the dam. A linear inversion algorithm is developed to evaluate the three-dimensional distribution of hydraulic head from self-potential data, given a known distribution of the cross-coupling coefficient and electrical resistivity. The inverse problem is solved by minimizing an objective function, which consists of a data misfit that accounts for measurement error and a model objective function that incorporates a priori information. The algorithm is suitable for saturated flow problems or where the position of the phreatic surface is known.

The mechanism of soil-reinforcement interaction for a reinforced embankment on soft clay has been explored by conducting a parametric study using a coupled non-linear elastoplastic finite element program. One of the major issues in the design of a reinforced embankment on soft clay is the magnitude of tension that can be mobilized in the geosynthetic reinforcement. Previous research using geotechnical centrifuge modelling and present research using finite element modelling has confirmed that the tension mobilized in the reinforcement is only of the order of active lateral thrust in the embankment. The parametric study has revealed that the soil-reinforcement interaction mechanism depends on the ratio of embankment height to the depth of the clay layer. The embankment behaves similar to a rigid footing in case of deep clay deposit. In this case, the failure mechanism is similar to a slip circle and there is very little contribution from the clay-reinforcement interface towards the mobilization of reinforcement tension. However, if the depth of clay deposit is small, the soil-reinforcement interaction mode is similar to direct shear failure and slip surface is located close to the clay-reinforcement interface. In this case, the contribution of clay-reinforcement interface towards the tension mobilized in the reinforcement is higher and therefore, the contribution of the reinforcement towards overall stability of the embankment is greater. Based on the results of the parametric study a novel serviceability criterion is proposed that aims to limit the lateral deformation of the clay foundation at the toe of the embankment by limiting the allowable mobilized tension in the reinforcement. A simple procedure for the evaluation of the efficiency of soil-reinforcement interface for reinforced embankments on soft clays is also proposed. The validity of the proposed serviceability criterion and the design charts was successfully tested using two field case studies. Sackville test embankment constructed to failure in 1989 and a levee test section that remained serviceable after construction in 1987 at Plaquemine, Louisiana were able to confirm the validity of the serviceability criterion proposed in the present study.

Ever since its founding, Rome has been vulnerable to the swelling waters of its Tiber River. This river was so important to the city that it was a defining character in Rome’s history for over two thousand years. However, this river-city relationship would be suddenly severed in the late 19th century as Rome was declared the Italian capital. And, with the creation of the capital, came the creation of the river walls. While this new infrastructure safeguarded the city from future flooding, it razed the relationship between the city and its river. It lost its use as a commercial trade route, transportation system and leisure landscape, and before long the Tiber was forgotten. This thesis proposes a design intervention at Rome’s historic river-city site, the Porto di Ripetta. Once the physical and symbolic gateway to the city, the Ripetta is presently the most disconnected site along the Tiber River. Not only does the proposed project aim to synergistically unite a series of complex archaeological layers from antiquity to present-day, it also aspires to reconnect the city to its historical relationship with its river, introduce another layer within Rome’s transportation network, and expand the city’s cultural agenda along its underutilized continuous corridor. The introduction of river-based programme is logical when created within a series of design solutions that both recognize and address the temporal nature of the riverscape. Through in-depth historical analysis, this thesis examines the complexities of the Tiber River’s existence and analyzes its sociological, physical and political importance to the Eternal City. This understanding of the Tiber River’s unique qualities reveals tangible opportunities for new public spaces connected the potential of the Tiber as part of an expanded network of new public transportation, leisure landscapes, and cultural institutions.

The mechanism of soil-reinforcement interaction for a reinforced embankment on soft clay has been explored by conducting a parametric study using a coupled non-linear elastoplastic finite element program. One of the major issues in the design of a reinforced embankment on soft clay is the magnitude of tension that can be mobilized in the geosynthetic reinforcement. Previous research using geotechnical centrifuge modelling and present research using finite element modelling has confirmed that the tension mobilized in the reinforcement is only of the order of active lateral thrust in the embankment. The parametric study has revealed that the soil-reinforcement interaction mechanism depends on the ratio of embankment height to the depth of the clay layer. The embankment behaves similar to a rigid footing in case of deep clay deposit. In this case, the failure mechanism is similar to a slip circle and there is very little contribution from the clay-reinforcement interface towards the mobilization of reinforcement tension. However, if the depth of clay deposit is small, the soil-reinforcement interaction mode is similar to direct shear failure and slip surface is located close to the clay-reinforcement interface. In this case, the contribution of clay-reinforcement interface towards the tension mobilized in the reinforcement is higher and therefore, the contribution of the reinforcement towards overall stability of the embankment is greater. Based on the results of the parametric study a novel serviceability criterion is proposed that aims to limit the lateral deformation of the clay foundation at the toe of the embankment by limiting the allowable mobilized tension in the reinforcement. A simple procedure for the evaluation of the efficiency of soil-reinforcement interface for reinforced embankments on soft clays is also proposed. The validity of the proposed serviceability criterion and the design charts was successfully tested using two field case studies. Sackville test embankment constructed to failure in 1989 and a levee test section that remained serviceable after construction in 1987 at Plaquemine, Louisiana were able to confirm the validity of the serviceability criterion proposed in the present study.

The self-potential method responds to the electrokinetic phenomenon of streaming potential and has been applied in hydrogeologic and engineering investigations to aid in the evaluation of subsurface hydraulic conditions. Of specific interest is the application of the method to embankment dam seepage monitoring and detection. This demands a quantitative interpretation of seepage conditions from the geophysical data. To enable the study of variably saturated flow problems of complicated geometry, a three-dimensional finite volume algorithm is developed to evaluate the self-potential distribution resulting from subsurface fluid flow. The algorithm explicitly calculates the distribution of streaming current sources and solves for the self-potential given a model of hydraulic head and prescribed distributions of the streaming current cross-coupling conductivity and electrical resistivity. A new laboratory apparatus is developed to measure the streaming potential coupling coefficient and resistivity in unconsolidated soil samples. Measuring both of these parameters on the same sample under the same conditions enables us to properly characterize the streaming current cross-coupling conductivity coefficient. I present the results of a laboratory investigation to study the influence of soil and fluid parameters on the cross-coupling coefficient, and characterize this property for representative well-graded embankment soils. The streaming potential signals associated with preferential seepage through the core of a synthetic embankment dam model are studied using the forward modelling algorithm and measured electrical properties to assess the sensitivity of the self-potential method in detecting internal erosion. Maximum self-potential anomalies are shown to be linked to large localized hydraulic gradients that develop in response to piping, prior to any detectable increase in seepage flow through the dam. A linear inversion algorithm is developed to evaluate the three-dimensional distribution of hydraulic head from self-potential data, given a known distribution of the cross-coupling coefficient and electrical resistivity. The inverse problem is solved by minimizing an objective function, which consists of a data misfit that accounts for measurement error and a model objective function that incorporates a priori information. The algorithm is suitable for saturated flow problems or where the position of the phreatic surface is known.

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 verified elasto-viscoplastic finite element model is used to develop a better understanding of the performance of embankments with geosynthetic reinforcement constructed over rate-sensitive soil. The interaction between reinforcement and prefabricated vertical drains (PVDs) and their effects on time-dependent behaviour of embankments are examined. For rate-sensitive soils, the generation of creep-induced pore pressures following the end of construction is evident along the potential slip surface. As a result, the minimum factor of safety with respect to embankment stability occurs after the end of construction. The combined use of reinforcement and PVDs are shown to provide an effective means of minimizing creep-induced excess pore pressure, increasing overall stability, and decreasing deformation of the embankments. The combined effects of the viscoelastic properties of geosynthetic reinforcement (polyester, polypropylene and polyethylene) and the rate-sensitive nature of foundation soils on the performance of embankments are examined. The effect of various factors, including reinforcement type (i.e., stiffness and viscosity), soil viscosity, construction rate and allowable long-term reinforcement strain, on the time-dependent behaviour of embankments are considered. The long-term performance of reinforced embankments is investigated for different maximum allowable long-term reinforcement strains. From a series of finite element analyses, the ideal allowable reinforcement strains to minimize embankment deformation while providing optimum long-term service height of the embankment, considering the effect of soil and reinforcement viscosity, are proposed for soils similar to those examined in this study. The currently proposed design methods for embankments with creep-susceptible reinforcement over rate-sensitive soils appear to be overly conservative. This study proposes a refined approach for establishing the allowable long-term reinforcement strains that are expected to provide adequate performance while reducing the level of conservativeness of reinforced embankment design. Finally, a previously developed elasto-viscoplastic constitutive model is modified to incorporate the effect of soil structure using a state-dependent fluidity parameter and damage law. The model was evaluated against data from a well-documented case study of a reinforced test embankment constructed on a sensitive Champlain clay deposit in Saint Alban, Quebec. The benefit of basal reinforcement and the effect of reinforcement viscosity are then discussed for these types of soil deposits. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2011-01-21 22:26:40.133

Levees are earth structures used for flood protection. Due to their easy availability and low permeability, clays are the most common material used for the construction of levees. Clays are susceptible to desiccation cracks when subjected to long dry spells during summers. There has been an increased interest in studying the occurrence of cracks in soil mass. In particular, many experimental investigations for soils have been undertaken to learn about the crack pattern in earth embankment. However, there is a dearth of work that focuses on the numerical modeling of desiccation cracks effects on levees. This study has been undertaken to analyze the effect of desiccation cracking on the hydraulic behavior of an earth embankment under flooding conditions. A numerical model was developed using the finite element package CODE_BRIGHT. The model was validated from the data obtained from a small scale embankment experiment under controlled environmental conditions. As the phenomenon of desiccation cracking is highly random, a simple random model was developed to capture the variability in crack geometry. The random crack geometry was then passed on to the finite element mesh, so that a probabilistic analysis can be carried out using a Monte Carlo approach, for assessing the embankment’s integrity. The results obtained from the analysis such as time to steady state saturation and steady state flow rate at the outward slope were very interesting to study and provided an insight on the effect of desiccation cracks on unsaturated earth embankments.

Ever since its founding, Rome has been vulnerable to the swelling waters of its Tiber River. This river was so important to the city that it was a defining character in Rome’s history for over two thousand years. However, this river-city relationship would be suddenly severed in the late 19th century as Rome was declared the Italian capital. And, with the creation of the capital, came the creation of the river walls. While this new infrastructure safeguarded the city from future flooding, it razed the relationship between the city and its river. It lost its use as a commercial trade route, transportation system and leisure landscape, and before long the Tiber was forgotten. This thesis proposes a design intervention at Rome’s historic river-city site, the Porto di Ripetta. Once the physical and symbolic gateway to the city, the Ripetta is presently the most disconnected site along the Tiber River. Not only does the proposed project aim to synergistically unite a series of complex archaeological layers from antiquity to present-day, it also aspires to reconnect the city to its historical relationship with its river, introduce another layer within Rome’s transportation network, and expand the city’s cultural agenda along its underutilized continuous corridor. The introduction of river-based programme is logical when created within a series of design solutions that both recognize and address the temporal nature of the riverscape. Through in-depth historical analysis, this thesis examines the complexities of the Tiber River’s existence and analyzes its sociological, physical and political importance to the Eternal City. This understanding of the Tiber River’s unique qualities reveals tangible opportunities for new public spaces connected the potential of the Tiber as part of an expanded network of new public transportation, leisure landscapes, and cultural institutions.

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.