Rebound, relaxation, and uplift
Rebound is defined as the expansive recovery of surficial crustal material, either instantaneous, or time dependent, or both, and is initiated by the removal or relaxation of superincumbent loads (Nichols, 1980). The displacements caused by rebound allow elastic and inelastic relaxation of the crustal masses to occur. The outward and upward movements associated with rebound are uplift displacements related to rebound processes. Rebound of geological materials is attributed to stress relief, but the process is poorly understood and the basis for predicting time-dependent rebound has not been clearly established. Not only are changes of stress important to the rebound process, but so are fabric, material properties, and anisotropy of the geologic materials, as well as external environmental factors such as moisture and temperature (Nichols, 1980). The problem of rebound is one with which design and construction engineers must deal, whenever the equilibrium of geologic materials is disturbed, especially in large excavations both surface and underground. In areas where rebound deformations can significantly affect engineering structures, it is desirable to understand rebound behavior, and to determine practical guidelines for prediction of the short- and long-term consequences of rebound.
The phenomenon of rebound undoubtedly has been observed by ancient as well as modern quarry operators, civil engineers, and applied geologists. In the United States and England, recorded accounts of rebound and actual measurements made to study the phenomenon appear in the mid-19th century (Nichols and Varnes, 1984) describing spontaneous and explosive expansion in a wide range of quarried rock types (sandstones, granites, vein rock).
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A review of milestones and changes in geological theory and practice from which modern engineering geology in North America has developed. Five chapters discuss historical events and the contributions of early scientists and engineers; nine chapters review the state of knowledge of dominant geologic processes, phenomena, and specialized principles critical to modern practice; and three chapters discuss geologic environs and the properties of construction materials. Four chapters are devoted to geoscience investigations and related techniques for: initial regional-areal evaluation of conceptual candidate sites (Phase I); selection of preferred-designated sites and design (Phase II); typical kinds of investigations used during project construction (Phase III); and as-built documentation and explorations of the operating or rehabilitation phases. Closing chapters focus on the geoscientist's responsibilities relative to engineering failures, errors of judgment that impact works, litigation, and forensic geoscience. The 34 contributors present extensive case histories applicable worldwide.