Stability, Erosion, and Morphology Considerations for Sustainable Slope Design

The construction of more natural and sustainable earth slopes requires the consideration of erosion and runoff characteristics as an integral part of the design. These effects not only result in high costs for removal of sediment, but also a profound damage to the ecosystem. In this dissertation, innovative techniques are developed such that more natural appearing slopes can be designed to minimize sediment delivery, while meeting mechanical equilibrium requirements. This was accomplished by: a) examining the fundamental failure modes of slopes built with minimum compaction (FRA) to enhance quick establishment of forest, b) investigating the geomechanical and erosion stability of concave slopes, and c) developing design equations for a new type of inclined-face retaining structure, the Piling Framed Retaining Wall (PFRW), which in the limit is a confined slope. The analysis of several potential failures via Limit Equilibrium (LEM) and Finite Element (FEM) suggested that the governing failure of FRA slopes is shallow and well represented by infinite slope conditions, and laboratory and field data suggests that seasonal increase of stability due to matric suction is possible, while instability may occur under local seismicity. The investigation of the mechanical and erosion stability of concave slopes began with a mathematical definition of critical concave slopes at limiting equilibrium. Based on this, a mechanism to design concave slopes for a selected Factor of Safety (FS) was proposed. Results indicated that concave slopes can yield 15-40% less sediment than planar slopes of equal FS, and the stability is not compromised by errors in the construction. Concave slopes satisfying mechanical equilibrium are not necessarily in erosion equilibrium as observed in many natural landscapes. It was shown that when these two equilibrium conditions are met, the slopes become sustainable and a set of equations describing sustainable concave slopes was proposed. Finally, rational design equations for the innovative PFRW were developed based on numerous FEM analyses for different soil and geometry conditions. The equations provided a good prediction of the soil stresses measured on a PFRW built in Knoxville, TN

Soil Arching as a Means to Resist Internal Erosion under High Seepage Gradients

Internal erosion is a common cause of dam failures and is a key consideration when designing tailing storage facilities (TSFs) and water retaining structures. Initiation of internal erosion is a complex phenomenon and can be difficult to characterize. Filters are often employed to prevent particle migration and can greatly reduce the risk of internal erosion. However, defects can occur in filter layers due to differential settlement, improper construction practices, seismic shaking, or other unforeseen factors. When a filter defect is present, initiation of internal erosion of base materials becomes more likely as concentrated seepage flow paths will force particle migration through the open defect. The ability of a soil medium to arch can be advantageous as arching can resist the effect of seepage drag forces by redistributing the stresses to the zones adjacent to the defect, providing resistance to initiation of internal erosion. However, if superior tractive seepage forces exist, arching can be overcome, the soil will lose its self-supporting ability, and internal erosion will be initiated. To explore this limiting stability condition, a series of finite-element stress-deformation simulations were performed. Varying material shear strengths, defect aperture sizes, and seepage gradients and their corresponding effects on the triggering of internal erosion were evaluated. This paper summarizes the methods and results of these analyses, including applicability to tailing dam design, with the aim of providing a screening tool for practitioners to use to quickly evaluate internal erosion resistance in the presence of a filter defect.Non UBCUnreviewedOthe

Connexin channels and hemichannels are modulated differently by charge reversal at residues forming the intracellular pocket

Background: Members of the β-subfamily of connexins contain an intracellular pocket surrounded by amino acid residues from the four transmembrane helices. The presence of this pocket has not previously been investigated in members of the α-, γ-, δ-, and ε-subfamilies. We studied connexin50 (Cx50) as a representative of the α-subfamily, because its structure has been determined and mutations of Cx50 are among the most common genetic causes of congenital cataracts. Methods: To investigate the presence and function of the intracellular pocket in Cx50 we used molecular dynamics simulation, site-directed mutagenesis, gap junction tracer intercellular transfer, and hemichannel activity detected by electrophysiology and by permeation of charged molecules. Results: Employing molecular dynamics, we determined the presence of the intracellular pocket in Cx50 hemichannels and identified the amino acids participating in its formation. We utilized site-directed mutagenesis to alter a salt-bridge interaction that supports the intracellular pocket and occurs between two residues highly conserved in the connexin family, R33 and E162. Substitution of opposite charges at either position decreased formation of gap junctional plaques and cell-cell communication and modestly reduced hemichannel currents. Simultaneous charge reversal at these positions produced plaque-forming non-functional gap junction channels with highly active hemichannels. Conclusions: These results show that interactions within the intracellular pocket influence both gap junction channel and hemichannel functions. Disruption of these interactions may be responsible for diseases associated with mutations at these positions.</p