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PublisherAmerican Rock Mechanics AssociationLanguageEnglish
Document ID 77-0298
Content TypeConference Paper
TitleSite Specific Study For Possible Ongoing Salt Dome Movement
AuthorsR. L. Thoms, T. A. Manning, L. K. Paille, R. M. Gehle, Louisiana State University
SourceThe 18th U.S. Symposium on Rock Mechanics (USRMS), June 22 - 24, 1977 , Golden, CO
Copyright1977. Colorado School of Mines Press. Permission to Distribute - American Rock Mechanics Association
PreviewABSTRACT

U.S. Gulf Coast salt domes, among other geologic structures, currently are being considered for storage of commercial radioactive wastes. A major concern with dome storage of long lived radioactive wastes lies with the possible tectonic movement of the host dome. Any ongoing movement of a salt dome can be monitored with a site specific complementary system of field instrumentation and finite element modelling. Field instrumentation and accompanying finite element analyses for a study dome in northwest Louisiana are described. Site specific data and early experience associated with tiltmeters over the dome are presented .Also, recommendations are made for modifications and extensions of the field instrumentation and finite element modelling appropriate to the specific site under study.

INTRODUCTION

Storage in U.S. Gulf Coast salt dome caverns currently is underway or is being studied for a number of materials, e.g., natural gas (1), crude oil (9), and radioactive wastes (13, 30, 31). For long lived radioactive waste storage, tectonic stability of the domes must be established prior to their selection as a possible disposal site (49). It is generally agreed that Gulf Coast salt domes were buoyancy driven from essentially horizontal salt beds into their present nearly vertical plug configurations (25, 26). A discussion of salt dome genesis is beyond the scope of this report, however it is obvious that any continuing vertical movement at a relatively rapid geologic rate eventually would expose a near surface dome to erosion. Erosion might result either from intercepted fresh water aquifers or surface effects (47, 50). It is also obvious that rapid erosion would be undesirable for a dome storage facility. Thus, current rates of site specific salt dome movement must be determined as baseline data for a potential storage dome. If the rate of dome movement is so small as to be immeasurable with current technology, then an upper bound on current rates of movement can be established. Ongoing movement of salt domes can be monitored with a surface or near surface system of field instrumentation and complementary finite element modelling (30, 31, 49, 51). A potential storage dome and adjoining geologic formations comprise a geomechanical system. Site specific geometrical configurations and in situ material properties of the geologic components of the geomechanical system must be reasonably well known prior to interpreting data from field instrumentation and prior also to relying heavily upon finite element modelling. Two domes in north Louisiana, among other domes, currently are being studied for possible storage of commercial radioactive wastes. These domes, Vacherie and Rayburn's, are located in the interior salt dome basin of the Gulf Coast region. The surface topography over both of these domes is characterized by a shallow valley over the central part of the dome with a rim of low hills encircling the approximate boundaries on flanks of the dome. This topography is well suited for a surface system of dome movement monitoring instruments. For if a dome is moving upward, then the surface manifestation of this movement will include (30, 51): (1) tilt (outward rotation from the dome center) of the encircling hills, (2) diametrical and circumferential increase of the hill "circle," and (3) vertical movement relative to a distant benchmark.
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