Sensitivity of the “bed-structure” system

Abstract

Sensitivity, Adaptation, Risk ManagementThese concepts are widely used in describing the behavior of systems in various fields (power generation, telecommunication, medicine, ecology, etc.). The sensitivity of many systems is such that they can function where feedback, which includes monitoring, adaptation, and risk management, exists. In geotechnics, feedback is, in large part, monitoring, and only when necessary, adaptation, which is not previously specified in the plans, despite the risk associated with the indeterminacy of geologic-engineering data, the approximate nature of geotechnical calculations, and the conditionality of theoretical assumptions and hypotheses. Reliability of the BFS system is ensured only by safety factors introduced in the design stage.The observational method represents a more flexible approach to reliability assurance of an BFS system. The design is adapted in the construction process using data derived from on-going monitoring. This approach was first used by K. Terzaghi, and developed later on by Peck and Powderham [2].Unplanned situations also arise, however, during service. In Santos (Brazil) [3], therefore, tens of high-rise buildings had sustained significant settlements and tilts by the time their construction had been completed. The tilts could have been corrected had there been special devices specified by design [4] in these buildings.It is simpler to manage risks, if the sensitivity of the BFS system is assessed, i.e., its behavior as a function of variations in initial data. Monitoring data are insufficient for these assessments; it is possible, however, to compensate for this deficiency by numerical experiments using standards -simplified design schemes, which reflect existing behavioral characteristics of the BFS system. Standards permit use of highspeed computer programs, which are based on exact mathematical solutions free of the error-generated "noise" of numerical methods, and make it possible to obtain both expert, and also statistical assessments of the sensitivity of the BFS system (Monte Carlo method).As early as the 1980s, we had conducted a numerical analysis of the sensitivity of the BFS system [5,6,7]. This analysis is required in selecting design solutions, in developing regulatory documents, and for optimization of experiments, interpretation of monitoring data, calibration and verification of theoretical models, and development of practical intuition and adaptive measures.Mathematical modeling with the use of exact solutions [1] has made it possible to ascertain a number of qualitative characteristics features of the behavior of the "bed/foundationslab/structure" system (BFS) over the entire practical range of initial data.

Consideration of soil-failure zones beneath foundation edges in analyzing a “bed-foundation-structure” system

“…Nevertheless, it is possible to use any other CM with an upper Winkler layer, since when cut-off, and the stiffness of the superstructure are considered, the forces in the foundation slab will be virtually independent of the form of the CM, and variation in its parameters [7,8].…”

“…For a CM CC, it is a biharmonic equation, the solution of which yields concentrated loads beneath the edge of the foundation due to disregard of cut-off, and hence instability of the numerical solution. For a CM CCC, it is a triharmonic equation with consideration given to cut-off, the curve of contact pressures does not possess singularities, and the numerical solutions are stable to variations in the initial data [7,8].…”

“…According to Eurocode [7,9]: "... knowledge of the soil conditions will depend on the volume and quality of geomechanical surveys. This knowledge and monitoring of work production is usually more critical for fulfillment of fundamental requirements than the accuracy of computational models and particular coefficients."…”

“…In Section 12.5.5 of [2], it is stated: "It is recommended to select the most unfavorable values of the stiffness parameters of the bed, and model of the bed ...." This principle is written in greater detail in [9], but the selection of (un)favorable values of the parameters and models, and the exposure of significant factors is not always obvious [10], and physical experiments are usually not conducted. A reliable tool remains − virtual simulation using models-standards, which provide reliable qualitative information on the sensitivity and vulnerability of BFSS [7,8]. Significant factors are frequently disregarded in methods of analysis, while insignificant factors are considered with excessive accuracy.…”

“…The critique of [7,8] "is incorrect, since the authors of [12] did not take note of the fact that this "connection" is made through compressible supports, just as in nature. References to the works of L. A. Galin and M. I. Gorbunov-Posadov, who had investigated the bending of a narrow beam over its length, are also incorrect, since plane deformations are considered in [7,8]. Bezvolev and Shulyat'ev [12] use the PLAXIS 2D program, which is compiled for plane deformation, determining the coefficient of subgrade reaction.…”