Fully Metal-Coated Scanning Near-Field Optical Microscopy Probes with Spiral Corrugations for Superfocusing under Arbitrarily Oriented Linearly Polarised Excitation

We study the effect of a spiral corrugation on the outer surface of a fully metal-coated scanning near-field optical microscopy (SNOM) probe using the finite element method. The introduction of a novel form of asymmetry, devoid of any preferential spatial direction and covering the whole angular range of the originally axisymmetric tip, allows attaining strong field localization for a linearly polarised mode with arbitrary orientation. Compared to previously proposed asymmetric structures which require linearly polarised excitation properly oriented with respect to the asymmetry, such a configuration enables significant simplification in mode injection. In fact, not only is the need for the delicate procedure to generate radially polarised beams overcome, but also the relative alignment between the linearly polarised beam and the tip modification is no longer critical

Seismic Earth Pressures on Deep Stiff Walls

Experimental and numerical studies of the seismic response of a deep, stiff basement structure were motivated by the fact that the current seismic design methodologies based on previous works predict very large dynamic forces in areas of high seismicity. The experimental program consisted of a geotechnical centrifuge model with a basement structure embedded in cohesionless backfill. The numerical analyses sought to replicate the results of the centrifuge experiment and to validate the use of numerical analyses for the prediction of expected behavior. Overall, the results of this study show that the Mononobe-Okabe method of analysis provides a reasonable estimate of the expected response of stiff basement structures provided depth-Averaged design accelerations are considered

Comparison of Pseudo-Static Limit Equilibrium and Elastic Wave Equation Analyses of Dynamic Earth Pressures on Retaining Structures

The seismic earth pressure increment is typically computed using either pseudo-static limit equilibrium methods or elastic wave equation analyses of the interaction between a retaining structure and backfill material, yet current interpretations of the two methods provide conflicting recommendations. The focus of this study is to compare the seismic earth pressure increment computed using the two methods. This approach is demonstrated by subjecting an initially uniform prototype site selected from standard site classifications to harmonic excitation in one-dimensional equivalent linear analyses. Then, the seismic earth pressure resultant for a rigid wall is computed using the two methods. The limit equilibrium approach utilizes the acceleration records from the equivalent linear analysis to compute a seismic coefficient, whereas the elastic solution incorporates the reduced modulus and damping from the final iteration of the analysis, as well as the relative displacement records. The results presented herein corroborate the findings of recent centrifuge experiments and associated analyses

Soil Structure Interactions of Retaining Walls

Structural stiffness of a retaining wall, properties of the foundation soils, and the construction sequence, including order of placement of fill in front and back of the wall, affect movements and hence the development of active and passive earth pressures. Retaining walls considered in this paper are the traditional reinforced concrete type usually constructed along highways and dam spillway structures-the highway wall is a simple cantilever and the spillway wall in an earth dam is a counterfort. Another type of earth retaining structure considered is an unconventional type, which was used during construction of a second large-diameter reinforced concrete siphon alongside an existing siphon of similar proportions for water conveyance on a hydro project. Results of numerical modeling for the highway retaining wall are compared with measured data. For the spillway and the siphon structures, only numerical analyses are included, as these structures were not instrumented. Practical significance of the information included in the paper are: (a) both the structure and the soil on which it is founded form an integrated system that needs to be analyzed as such for meaningful results; (b) interfaces between the soil and structure, where separation and slip can occur, should be included in numerical modeling; and (c) sequence of construction starting with the initial excavation, and construction sequence including placement of the fill in lifts, should be simulated