U.S.-Switzerland Cooperative Research on the Physics and Mechanics of Dehydration Embrittlement in Gypsum

点击翻译按钮获取中文摘要

This award supports Professor Teng-fong Wong and a graduate student and post-doctoral associate to collaborate in experi- mental and theoretical geophysics research with Professors Kenneth Hsu and David Olgaard of the Geological Institute of the ETH, Zurich, Switzerland. These investigators share an interest in the fundamental physics and mechanics of the process of dehydration embrittlement in gypsum. They propose to perform a systematic study of the dehydration rate, permeability and porosity change in gypsum under controlled conditions of temperature, pore pressure, stress and strain rate. They will quantitatively characterize the evolution of the decomposition reaction and pore structure using x-ray and electron microscopy techniques. Also, they will analyze theoretically the relation among the dehydration reaction, the porosity and the permeability. Ultimately, this experimental and theoretical work will enable them to compute numerically the degree of weakening and embrittle- ment at the bottom of an overthrust formation such as the Jura mountains in Switzerland. The results of such modelling will of course be compared with actual geological observations in the field. The collaborators bring complementary expertise and facilities to this work that guide the division of labor. The high temperature, high pressure deformation experiments and the x-ray analysis will be conducted at ETH. The microstructural observations will be done at ETH and SUNY at Stony Brook. The permeability measurements and theoretical analysis will be performed at Stony Brook. It has been recognized from field and laboratory observations that the deformation and metamorphism of rocks are closely linked. However, most of this work has been done on low porosity crystalline rocks for which the inelasticity and failure behavior are sensitively linked to temperature, pressure and strain rate. These factors are insufficient to explain the behavior of porous rocks, such as gypsum, or rocks that have undergone metamorphism. The decomposition or compaction of water-bearing (hydrous) phases during prograde metamorphism may lead to embrittlement and weakening. There are further differences in behavior as the porous rock is dehydrated. The proposed research will investigate these changes in both "drained" and "undrained" configurations of gypsum. The results will contribute substantially to understanding the tectonics of sedimentary rock formations.