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).