Radoslaw L. Michalowski

Bio: Radoslaw L. Michalowski is an academic researcher from University of Michigan. The author has contributed to research in topics: Limit analysis & Bearing capacity. The author has an hindex of 34, co-authored 130 publications receiving 4384 citations. Previous affiliations of Radoslaw L. Michalowski include University of Minnesota & Johns Hopkins University.

Coefficient of Earth Pressure at Rest

Abstract: The widely used Jaky coefficient of earth pressure at rest, K0 , is revisited. It is demonstrated that this coefficient was derived from an analysis of the stress state in a sand prism that yields an unrealistic stress field. It is also surprising that the at rest stress state is represented as a function of the limit state parameter (internal friction angle). Consequently, one arrives at the conclusion that reasonable predictions made by classical K0 are somewhat coincidental. Jaky’s solution to K0 is discussed in view of more recent research on the stress fields in prismatic mounds of sand.

Triaxial Compression of Sand Reinforced with Fibers

Abstract: Results from drained triaxial compression tests on specimens of fiber-reinforced sand are reported. It is evident that the addition of a small amount of synthetic fibers increases the failure stress of the composite. This effect, however, is associated with a drop in initial stiffness and an increase in strain to failure. Steel fibers did not reduce initial stiffness of the composite. The increase in failure stress can be as much as 70% at a fiber concentration of 2% (by volume) and an aspect ratio of 85. The reinforcement benefit increases with an increase in fiber concentration and aspect ratio, but it also depends on the relative size of the grains and fiber length. A larger reinforcement effect in terms of the peak shear stress was found in fine sand, compared to coarse sand, when the fiber concentration was small (0.5%). This trend was reversed for a larger fiber concentration (1.5%). A model for prediction of the failure stress in triaxial compression was developed. The failure envelope has two segments: a linear part associated with fiber slip, and a nonlinear one related to yielding of the fiber material. The analysis indicates that yielding of fibers occurs well beyond the stress range encountered in practice. The concept of a macroscopic internal friction angle was introduced to describe the failure criterion of a fiber-reinforced sand. This concept is a straightforward way to include fiber reinforcement in stability analyses of earth structures.

Slope stability analysis: a kinematical approach

Abstract: A stability analysis of slopes based on a translational mechanism of failure is presented. The collapse mechanism is assumed to be in the form of rigid blocks analogous to slices in traditional slice methods. The proposed analysis, although based on the kinematical approach of limit analysis, always satisfies the equilibrium of forces acting on all blocks in the selected mechanism. All slope stability analyses based on the limit equilibrium of slices can be interpreted in the context of their implicitly assumed collapse mechanisms. The static assumptions made are equivalent to assuming an arbitrary strength of the soil on interfaces between slices. Solutions to stability factor &ammaH/cfrom all analyses based on the limit equilibrium of slices fall into a relatively narrow range bounded by the solutions using the proposed analysis for two extreme assumptions of soil strength between the blocks. Solutions beyond this range obtained by any method of slices indicate unreasonable consequences when interpreted...

Three-Dimensional Stability of Slopes and Excavations

Abstract: Three-dimensional (3D) limit analysis of stability of slopes is presented. Such analyses are not common, because of the difficulties in constructing three-dimensional mechanisms of failure in frictional soils. A class of admissible rotational mechanisms is considered in this paper. The failure surface has the shape of a curvilinear cone (‘horn'), with upper and lower contours defined by log-spirals; all radial cross-sections of the surface are circular. In the special case of cohesive soils (undrained behaviour), the shape of the failure surface reduces to a torus. An alternative failure surface is generated when the axis of rotation intersects the circle that generates the surface. The 3D mechanism is further modified with a plane-strain central insert to ensure the transition to a plane-strain mechanism if no restraint is placed on the slope width. Also, the spherical failure surface considered in the literature is re-examined. The critical height of slopes with finite width is determined, and the resul...

State of the Art: Limit Equilibrium and Finite-Element Analysis of Slopes

Abstract: In the past 25 years great strides have been made in the area of static stability and deformation analysis. The widespread availability of microcomputers has brought about considerable change in the computational aspects of slope stability analysis. Analyses can be done much more thoroughly, and, from the point of view of mechanics, more accurately than was possible without computers. Still, engineers performing slope stability analyses must have more than a computer program. They must have a thorough mastery of soil mechanics and soil strength, a solid understanding of the computer programs they use, and the ability and patience to test and judge the results of their analyses to avoid mistakes and misuse. Realistic analyses of deformations of slopes and embankments were not possible until about 25 years ago. They are possible now mainly because the finite-element method has been developed and adapted to these applications. The principal requirement for achieving reasonably accurate and useful results fro...

Slope stability analysis by strength reduction

Abstract: INTRODUCTION For slopes, the factor of safety F is traditionally de®ned as the ratio of the actual soil shear strength to the minimum shear strength required to prevent failure (Bishop, 1955). As Duncan (1996) points out, F is the factor by which the soil shear strength must be divided to bring the slope to the verge of failure. Since it is de®ned as a shear strength reduction factor, an obvious way of computing F with a ®nite element or ®nite difference program is simply to reduce the soil shear strength until collapse occurs. The resulting factor of safety is the ratio of the soil's actual shear strength to the reduced shear strength at failure. This `shear strength reduction technique' was used as early as 1975 by Zienkiewicz et al. (1975), and has since been applied by Naylor (1982), Donald & Giam (1988), Matsui & San (1992), Ugai (1989), Ugai & Leshchinsky (1995) and others. The shear strength reduction technique has a number of advantages over the method of slices for slope stability analysis. Most importantly, the critical failure surface is found automatically. Application of the technique has been limited in the past due to the long computer run times required. But with the increasing speed of desktop computers, the technique is becoming a reasonable alternative to the method of slices, and is being used increasingly in engineering practice. However, there has been little investigation of the accuracy of the technique. In this paper, factors of safety obtained with the shear strength reduction technique are compared to limit analysis solutions for a homogeneous embankment.

Models and Computational Methods for Dynamic Friction Phenomena. 1. Physical Aspects of Dynamic Friction. 2. Continuum Models and Variational Principles for Dynamic Friction. 3. Finite Element Models and Numerical Analysis

Abstract: : This work addresses the general problems of formulating continuum models of a large class of dynamic frictional phenomena and of developing computation methods for analyzing these phenomena. Of particular interest are theories which can adequately predict stick slip motion, frictional damping in structural dynamics, and sliding resistance. This work id divided into three principal parts. In Part I, a large body of experimental and theoretical literature on friction is critically reviewed and interpreted as a basis for models of dynamic friction phenomena. In part II, continuum models of interfaces are developed which simulate key interface properties identified in Part I. Variational principles for a class of dynamic friction problems are also established. In Part III, finite element models and numerical algorithms for analyzing dynamic friction are presented. Also, a dynamic stability analysis is presented in which it is established that stick slip motion can be associated with dynamic instability of the governing nonlinear system for certain ranges of slip velocity and coefficient of friction. Numerical results suggest that the new models derived here can satisfactorily depict a large and important class of dynamic friction effects. Keywords: Friction damping; Sliding friction models; Finite element methods; and Structural dynamic.