Seismic Design Chart for Anchored Bulkheads

Evaluation of numerous case histories reveals that the seismic performance of anchored sheet pile quaywalls depends primarily on the anchoring system. Current pseudo-static procedures often lead to deficient anchoring, whose excessive displacements or failure trigger excessive permanent seaward displacement at the top of the bulkhead, accompanied by cracking and settlement behind the anchor. The results of the case histories lead to a Seismic Design Chart to be used in conjunction with the pseudo static procedure. The Chart delineates between acceptable and unacceptable degrees of damage, depending on the values of two dimensionless parameters that are functions of the material and geometric characteristics of the bulkhead, and the intensity of seismic shaking. Soil softening/degradation due to development of pore water-pressures is indirectly accounted for in the proposed method; however, the engineer must ensure that no liquefaction-flow failure of cohesion less soils will occur in the backfill or the foundation

Aspects of Seismic Analysis and Design of Rockfill Dams

Theoretical methods for estimating the dynamic response and predicting the performance of modern rockfill dams subjected to strong earthquake shaking are reviewed. The focus is on methods accounting for nonlinear material behavior, for 3-Dimensional canyon geometry, and asynchronous base excitation. It is shown that both strong nonlinearities and lack of coherence in the seismic excitation tend to reduce the magnitude of the deleterious whip-lash effect computed for tall dams built in rigid-wall narrow canyons. Particular emphasis is accorded to Concrete-Faced Rockfill dams and a case study involving an actually designed dam in a narrow canyon points to some potential problems and suggests some desirable modifications. In the light of theoretical results the paper concludes with a discussion on design rules and defensive measures that would lead to robust design schemes of Earth-Core and Concrete Faced Rockfill dams

Behavior of Fine Sand Under Cyclic Rotation of Principal Stresses Using the Hollow Cylinder Apparatus

Results of an experimental investigation on a saturated fine Ottawa Silica Sand subjected to three different types of cyclic tests are presented in this paper. The effects of principal stress rotation at a constant deviator stress on the pore water pressure buildup and the deformation characteristics of sand are evaluated in comparison with results from cyclic triaxial and cyclic torsional simple shear using the hollow cylinder apparatus. The results presented and discussed in this article, representing a small part of the experimental program, suggest that the effects of rotational shear are more important than the effects of cyclic triaxial loading or cyclic torsional simple shear loading (of the same amplitude) in terms of the rate of pore water pressure buildup, the triggering of a liquefaction flow failure in contractive sand and the rate of accumulation of plastic deformation. Moreover, results from the monotonic test program on fine Ottawa Silica Sand under drained conditions were found in very good agreement with the failure surface incorporated in Lade\u27s constitutive model for frictional materials

Response of Earth Dams in Canyons Subjected to Asynchronous Base Excitation

A mathematical solution is presented for steady-state lateral response of earth and rock fill dams in canyons subjected to asynchronous excitation consisting of obliquely incident SH waves. The dam is idealized with a 2-dimensional shear wedge and the canyon is considered rectangular and consisting of flexible rock. A parametric study is undertaken to investigate the influence of (a) the angle of incidence, (b) the impedance ratio and (c) the canyon narrowness on the steady-state response, by considering in a simplifying way the effects of the dam-canyon interaction. The results demonstrate that the above factors may have a significant effect on the lateral response of the dam. For relatively flexible canyon rock, the effect of radiation damping is very important and, consequently, the assumption of rigid base may be very unrealistic. Due to interference phenomena, the response is not maximum for vertically propagating waves, but for waves incident at a certain angle. For obliquely incident waves travelling from left to the right, a gradual shift of the location of the peak response is observed from the mid-crest to the right side of the dam as the angle of incidence increases. Also, for very long dams subjected to high frequency obliquely incident waves, there is no amplification of the motion by the dam and, at a certain frequency of excitation; the presence of standing waves is indicated

Response of Earth Dams Subjected to Obliquely Incident P and SV Waves

A study of the effects of dam-foundation interaction on the response of earth dams to obliquely incident P and SV waves is presented. The numerical formulation combines the Finite Element Method and the Boundary Equation Method in a powerful hybrid technique. The FEM has been proven very efficient for finite size elastodynamics problems, but several previously suggested modifications for handling infinite domain dynamic problems seem to be either computationally expensive or have serious limitations on the geometry and excitation. The BEM is employed to solve the half space problem using exact Green\u27s functions to compute the half space stiffness, which is then incorporated in the FEM solution. This technique proved to be exceptionally powerful as it leads to accurate and very efficient solutions. A preliminary study is undertaken to investigate the response of dams subjected to obliquely incident P and SV waves, propagating across the dam width. The results of the present rigorous study extend the conclusions from earlier studies on the effects of the dam-foundation interaction and the special variability of the ground motion. Moreover, the proposed model provides an efficient tool for dynamic analysis of earth dams and is part of a broader study of 2D and 3D dams using the hybrid formulation in both the frequency and time domains, with final objective the incorporation, in the latter case, of soil nonlinearity

Modeling the surface and interior structure of comet nuclei using a multidisciplinary approach

The goal was to investigate the structural properties of the surface of comet nucleus and how the surface should change with time under effect of solar radiation. The basic model that was adopted was that the nucleus is an aggregate of frosty particles loosely bound together, so that it is essentially a soil. The nucleus must mostly be composed of dust particles. The observed mass ratios of dust to gas in the coma is never much greater than unity, but this ratio is probably a much lower limit than that of the nucleus because it is vastly easier to remove the gaseous component by sublimation than by carrying off the dust. Therefore the described models assumed that the particles in the soil were frost covered grains of submicron basic size, closely resembling the interstellar grains. The surface properties of such a nucleus under the effects of heating and cooling as the nucleus approaches and recedes from the Sun generally characterized