Russell A. Westmann

Bio: Russell A. Westmann is an academic researcher from University of California, Los Angeles. The author has contributed to research in topics: Consolidation (soil) & Beam (structure). The author has an hindex of 4, co-authored 4 publications receiving 384 citations.

Dynamic Response of Circular Footings

Abstract: It is the purpose of the paper to present the dynamic compliances of a circular footing resting on an elastic half-space for a wide range of dimensionless frequency. Numerical results have been presented for the torsional, vertical, rocking and horizontal oscillations of a rigid disc placed on an elastic half-space, as well as for the coupling terms between the rocking and horizontal oscillations. The corresponding compliances, the stress distributions under the disc, and the Rayleigh wave part of the far-field displacements have been evaluated. It is hoped that these results will prove to be useful in the design of foundations for vibrating machinery and in the study of soil structure interaction.

Beam on tensionless foundation

Abstract: The problem of determining the response of a loaded beam on a bilinear Winkler foundation is solved. The problem of a tensionless foundation is then treated as a limiting case. The nonlinear integral equation formulation is solved numerically. Results for the beam deflections, moments, and shears are presented graphically.

Consolidation of porous media with non-darcy flow

Abstract: A nonlinear quasi-static theory of one-dimensional consolidation accounting for non-Darcy fluid flow is presented. A specific boundary value problem is examined with the physics being examined in detail. Using a similarity variable, an exact early-time solution is developed. An approximate long-time solution is obtained by assuming a trial solution and minimizing the residual error by the method of moments. The two solutions are then matched at intermediate values to give the settlements for all times. For one range of the nonlinearity parameter, the solution exhibits a wave type phenomenon. A finite consolidation time is demonstrated to exist for another range of the nonlinearity parameter.

Viscoelastic layered system subjected to moving loads

Abstract: A LAYERED SYSTEM COMPOSED OF A LINEAR VISCOELASTIC LAYER AND LINEAR ELASTIC SUPPORTING FOUNDATION IS CONSIDERED--THE LAYER BEING DESCRIBED BY A CLASSICAL THIN PLATE AND THE FOUNDATION AS A HOMOGENEOUS HALF SPACE. DISREGARDING INERTIAL EFFECTS, A FORMAL SOLUTION IS OBTAINED FOR ARBITRARY TIME-DEPENDENT SURFACE TRACTIONS. AS AN EXAMPLE, THE SPECIAL CASE OF A CONCENTRATED LOAD MOVING WITH CONSTANT VELOCITY IS EXAMINED. THE SOLUTION IS EXPRESSED IN TERMS OF KNOWN ELASTIC RESULTS PLUS TIME-DEPENDENT CORRECTION TERMS. BOUNDS OBTAINED FOR THESE CORRECTION TERMS INDICATE THEY ARE NEGLIGIBLE FOR LARGE VALUES OF THE DIMENSIONLESS VELOCITY, AS DEFINED BY THE WRITER. /ASCE/

Groundwater Flow in Low‐Permeability Environments

Abstract: Certain geologic media are known to have small permeability; subsurface environments composed of these media and lacking well developed secondary permeability have groundwater flow sytems with many distinctive characteristics. Moreover, groundwater flow in these environments appears to influence the evolution of certain hydrologic, geologic, and geochemical systems, may affect the accumulation of pertroleum and ores, and probably has a role in the structural evolution of parts of the crust. Such environments are also important in the context of waste disposal. This review attempts to synthesize the diverse contributions of various disciplines to the problem of flow in low-permeability environments. Problems hindering analysis are enumerated together with suggested approaches to overcoming them. A common thread running through the discussion is the significance of size- and time-scale limitations of the ability to directly observe flow behavior and make measurements of parameters. These limitations have resulted in rather distinct small- and large-scale approaches to the problem. The first part of the review considers experimental investigations of low-permeability flow, including in situ testing; these are generally conducted on temporal and spatial scales which are relatively small compared with those of interest. Results from this work have provided increasingly detailed information about many aspects of the flow but leave certain questions unanswered. Recent advances in laboratory and in situ testing techniques have permitted measurements of permeability and storage properties in progressively “tighter” media and investigation of transient flow under these conditions. However, very large hydraulic gradients are still required for the tests; an observational gap exists for typical in situ gradients. The applicability of Darcy's law in this range is therefore untested, although claims of observed non-Darcian behavior appear flawed. Two important nonhydraulic flow phenomena, osmosis and ultrafiltration, are experimentally well established in prepared clays but have been incompletely investigated, particularly in undisturbed geologic media. Small-scale experimental results form much of the basis for analyses of flow in low-permeability environments which occurs on scales of time and size too large to permit direct observation. Such large-scale flow behavior is the focus of the second part of the review. Extrapolation of small-scale experimental experience becomes an important and sometimes controversial problem in this context. In large flow systems under steady state conditions the regional permeability can sometimes be determined, but systems with transient flow are more difficult to analyze. The complexity of the problem is enhanced by the sensitivity of large-scale flow to the effects of slow geologic processes. One-dimensional studies have begun to elucidate how simple burial or exhumation can generate transient flow conditions by changing the state of stress and temperature and by burial metamorphism. Investigation of the more complex problem of the interaction of geologic processes and flow in two and three dimensions is just beginning. Because these transient flow analyses have largely been based on flow in experimental scale systems or in relatively permeable systems, deformation in response to effective stress changes is generally treated as linearly elastic; however, this treatment creates difficulties for the long periods of interest because viscoelastic deformation is probably significant. Also, large-scale flow simulations in argillaceous environments generally have neglected osmosis and ultrafiltration, in part because extrapolation of laboratory experience with coupled flow to large scales under in situ conditions is controversial. Nevertheless, the effects are potentially quite important because the coupled flow might cause ultra long lived transient conditions. The difficulties associated with analysis are matched by those of characterizing hydrologic conditions in tight environments; measurements of hydraulic head and sampling of pore fluids have been done only rarely because of the practical difficulties involved. These problems are also discussed in the second part of this paper.

Dynamics of building-soil interaction

Abstract: In this study of the dynamics of building-soil interaction, the soil is modeled by a linear elastic half-space, and the building structure by an n-degree-of-freedom oscillator. Both earthquake response and steady-state response to sinusoidal excitation are examined. By assuming that the interaction system possesses n + 2 significant resonant frequencies, the response of the system is reduced to the superposition of the responses of damped linear oscillators subjected to modified excitations. The results are valid even though the interaction systems do not possess classical normal modes. For the special cases of single-story systems and the first modes of n-story systems, simplified approximate formulas are developed for the modified natural frequency and damping ratio, and for the modified excitation. Example calculations are carried out by the approximate and more exact analysis for one-story, two-story and ten-story interaction systems. The results show that interaction tends to decrease all resonant frequencies, but that the effects are often significant only for the fundamental mode for many n-story structures and are more pronounced for rocking than for translation. If the fixed-base structure has damping, the effects of interaction on the earthquake responses are not always conservative, and an increase or decrease in the response can occur, depending on the parameters of the system.